characterization and application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1699 77 original research article study on the absorption characteristics and refractive index sensitivity characteristics of the periodic structure of double nanorods fengying yang college of science and technology, guizhou university, guiyang 550025, guizhou, china. e-mail: yfy748@163.com abstract metamaterial perfect absorber is very important in the study of refractive index sensor. the time domain finite difference method is used to simulate the surface plasmon structure. the double nanorod periodic structure is designed, and the parameters of the top layer structure are optimized according to the impedance matching principle, and the absorption rate of the structure to the light wave reaches 99.6% when the wavelength is about 12 mm. the absorption spectroscopy of the structure is studied with the change of the refractive index of the spatial medium around the structure, and the sensitivity of the double nanorod structure is 4,008 nm/riu, which can be used to measure the refractive index of the gas. keywords: surface plasmon; sensor; nanorod; absorption spectrum; sensitivity article info received: 16 july 2022 accepted: 5 september 2022 available online: 21 september 2022 copyright copyright © 2022 fengying yang. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction electromagnetic metamaterials are light-manipulated artificial composites. by changing the parameters of the surface nanostructure units or the arrangement of the structural units, the effective dielectric constant and effective permeability of the metamaterial can be adjusted, so that electromagnetic devices with extraordinary properties can be obtained, such as polarization converters, stealth cloaks, superlenses and absorbers[1–4]. in 2008, landy et al. designed the first metamaterial perfect absorber, and researchers began a research boom on metamaterial absorbers. according to the bandwidth of the absorption band, the absorber is mainly divided into two types of absorbers. one is the broadband absorber, which is mainly used in solar cells[6,7]; the other is the narrowband absorber, which is mainly used in the field of photoelectric detection and sensors. high-sensitivity sensors have broad application prospects in chemical, biological, and medical fields[8]. metamaterial structures based on narrow bandwidth, high absorption and high-quality factors have received great attention for the study of highly sensitive refractive index sensors, and scholars have proposed nanostructures of various shapes, such as nano-rings, nano-disks, nano-rectangles, butterfly-shaped and other mixed arrangement structures[9–13]. in 2013, tuongs designed a concentric double-ring structure to implement a dual-band absorber. in 2015, lu et al. proposed a nanorod absorber with an absorption rate of more than 95%[15]. although the absorption coefficient of these study structures is high, the morphology and structure of the surface plasmon nanostructures are more complex. 78 at present, the research of metamaterials is mainly in the theoretical and experimental stages, and the production cost and efficiency of metamaterials with complex structures are high and inefficient, which is not conducive to the future large-scale production of metamaterials. in this paper, a metal-dielectric-metal surface plasma nanostructure is proposed, the structure of which is mainly composed of three layers, the top layer is a periodic double nanorod, the middle layer is the substrate, and the bottom layer is the metal reflective layer. firstly, the time domain finite difference method is used to excite the surface plasmon resonance according to the impedance matching principle, and the peak of the absorption spectrum of the sensor is increased by optimizing the structural parameters. secondly, the sensitivity and quality factor of the sensor are calculated by changing the refractive index of the medium around the structure. compared with other narrow-band absorbers, the periodic structure of the absorber designed herein is a square nanorod, which has the characteristics of simple preparation under the characteristics of high absorption, creating conditions for the large-scale and large-volume production of metamaterials in the future and shortening its production cycle. 2. simulation structure and calculation method the absorber designed herein is based on a thickness of t1 = 30 nm of silica as a substrate, and a metal reflective layer is provided under the substrate, the thickness of which is t2 = 50 nm, the material is gold, and the upper surface of the substrate is plated with a periodic two-line structure, as shown in figure 1a. the two-line structure period is px = 700 nm and py = 1 mm, as shown in figure 1b. the array cell consists of two rectangular nanorods, w = 80 nm wide and t = 100 nm in the z direction, where the length of the nanowires is l and the spacing between the two nanowires is g. the plane wave with a wavelength of 0.2–3 mm of the incident light wave is polarized along the y direction and propagates in the negative direction of the z-axis to the two-line structure structure. simulation space settings: the x and y directions set periodic boundary conditions, while the z direction is set to perfectly match the layer. during the calculation, the refractive index of the gold model was modeled jc and sio2 adopts palick model. figure 1. (a) three-dimensional illustration of the double nanorods perfect absorber; (b) top view of unit cell. based on maxwell’s equations, the absorption spectral characteristics and refractive index sensitivity characteristics of the sensor are simulated by using the time domain finite difference method. according to the energy conservation of light waves, the absorption rate of the structure is a = 1-r-t, where r is the reflectivity of light and t is the transmittance of light. in order to improve the absorption rate of the structure to a certain range of light waves, it mainly starts from the following two points. first of all, reduce the reflectivity of the structure; according to the principle of impedance matching, adjust the parameters of the top structure of the sensor, so that the resistance of the sensor is approximately equal to the resistance in free space, so that the reflectivity of the sensor is close to 0. secondly, the transmittance of the structure is reduced t, and a metal layer is added as a reflective layer under the medium, thereby reducing the transmittance coefficient of light waves passing 79 through the sensor s12. (1) (2) (3) where s11 represents the reflection coefficient of the structure, z1 represents the equivalent impedance of the structure, z0 represents the impedance of a free space. reflectance r = s12, in order to obtain a small enough reflectivity, adjust the parameters of the metamaterial structure, so that the equivalent impedance of the structure and the free space impedance z0. approximately equal, so that s11 tends to zero. among them, 𝜀𝜀1, 𝜀𝜀0 represents the equivalent dielectric constant of the structure and the dielectric constant in vacuum, respectively. the equivalent permeability and vacuum permeability of the structure are represented, respectively. based on the above two adjustments, when l = 600 nm, g = 140 nm, w = 80 nm, the two-line structure produces a local surface plasmon resonance at wavelengths of 12 μm and 23 μm, the near field is enhanced, and the absorption rate is up to 99.96%, so that the absorption coefficient of the structure gets the optimal value. as shown in figure 2a, the absorption rate of a single nanowire structure is lower than that of a double nanowire structure. from figure 2b and figure 2c, it is found that the absorption spectrum has two peaks, and absorption enhancement is achieved at both wavelength positions. among them, the larger peak is at 12 mm, which is the resonance mode of the oscillation excitation of the electric dipole oscillation in the local area of the structure, because the direction of the electric field strength of the left and right nanorods is consistently reinforced, and the sub-peak is the near-field coupling between the two nanorods, resulting in a larger absorption rate at the wavelength of 23 mm. figure 2. (a) absorption spectrogram; (b) electric field diagram of absorption spectrum peak in x-y plane; (c) electric field diagram with absorption spectrum peak in y-z plane. 3. effect of structural parameters on absorption spectral characteristics the effect of vertical nanorod length l on the absorption spectral characteristic curve of the sensor was investigated. the distance between two vertical nanorods is g2 = 140 nm, change the length of the vertical nanorods, and investigate their effect on the sensor absorption spectrum, as shown in figure 3. 23 μm corresponds to absorptivity of 99.6% and 40%. as l continues to increase from 600 to 800, the two peaks of the absorption spectrum are redshifted, and the larger peak value decreases to 93%. it can be seen that when l = 600 nm, w = 80 nm, and g = 140 nm, the absorption rate value of the double nanorod structure is the largest. 80 figure 3. influence of nanorods length on absorption spectrum. figure 4. influence of the distance between nanorods on absorption spectra. the effect of the spacing g between double nanorods on the absorption spectral characteristic curve of the sensor was investigated. the length of the vertical nanorod l = 600 nm, the distance between the two vertical nanorods g = 50 nm, change the spacing of the double nanorods, and investigate its effect on the sensor absorption spectrum, as shown in figure 3. when g increases from 50 nm to 140 nm, the wavelength corresponding to the two peaks in the absorption spectrum changes blue, and the corresponding absorption rate of the larger peak increases from 85% to 99.6%. when g continues to increase from 140 nm to 200 nm, the wavelength corresponding to the two peaks in the absorption spectrum is redshifted, and the corresponding absorption rate of the larger peak decreases from 99.6% to 84.5%. it can be seen that when l = 600 nm, g = 140 nm, and w = 80 nm, the absorption rate value of the structure is the largest, reaching 99.6%. 4. the influence of the spatial medium on the refractive index sensitivity characteristics of the sensor when the oscillation frequency of the free electrons on the surface of the metal nanostructure is consistent with the frequency of the incident wave, the surface plasmon resonance phenomenon will be generated, and the near field of the metal nanostructure will be significantly enhanced. as the refractive index of the space medium occurs, the wavelength corresponding to the surface plasmon resonance moves. therefore, this principle can be used as a refractive index sensor to detect changes in the refractive index of an object, as shown in figure 5. figure 5. (a) influence of refractive index n on absorption spectrum; (b) relationship between the change of refractive index n in the external environment and the change of large peak wavelength of absorbed light wave. keep the structural parameters l = 600 nm, g = 140 nm unchanged, change the refractive index of the spatial medium around the sensor, and investigate the influence of the spatial medium on the refractive index sensitivity characteristics of the sensor the external refractive index n = 1.0, 1.1, 1.2, 1.3, 1.4, the wavelength corresponding to the larger peak in the absorption spectrum of the structure is shown in the figure. as shown in figure 5a, the resonant wavelength is redshifted as the refractive index value increases. in figure 5b, the change of the external refractive index is the abscissa, and the change of the wavelength corresponding to the peak of the absorption spectrum is plotted on the ordinate. through data fitting, the sensitivity s of the sensor 81 at the corresponding wavelength is obtained as 4,008 nm/riu. when the wavelength measurement resolution is 0.1 nm, the theoretical resolution of the sensor is 2.5 × 10−5 riu. as the surrounding refractive index increases, the peak wavelength of the absorption rate is redshifted, indicating that high-sensitivity gas detection can be achieved using this design. 5. conclusions in this paper, a two-nanowire structure metamaterial perfect absorber is designed, and the spectral characteristics of the absorber, the electric field distribution at the formant of resonance and its refractive index sensing characteristics are studied by the time domain finite difference method, and the influence of structural parameters on the absorption spectrum and sensing characteristics is analyzed. the absorber designed in this paper has a high absorption rate, mainly for the following three reasons. first, when the incident light is illuminated vertically onto the surface of the absorber, the interaction between the two nanowires of the structural layer makes the local electric field enhanced. second, a local plasma resonance is generated between the structural layer and the dielectric layer, which makes the electric field enhanced. finally, the basal layer of the absorber can reflect the incident light, and the light local is localized between the media layer and the substrate, which greatly improves the absorption rate of the absorber. by changing the structural parameters can adjust the absorption rate of the absorber, the peak position and its sensing characteristics, the absorber designed herein has two absorption peaks, at the wavelength of 12 mm and 23 mm, the absorption rate reaches 99.6% and 60%, respectively, where the sensitivity near the wavelength of 12 mm reaches 4,008 nm/riu. therefore, the double nanowire metamaterial structure perfect absorber designed in this paper can achieve a measurement resolution of 10−5 magnitudes, which provides a certain foundation and support for the plasmon hypersurface structure in terms of refractive index sensor. conflict of interest the authors declared no conflict of interest. acknowledgement this work was supported by the engineering research project of the ministry of education on semiconductor power device reliability (ercmekfjj2019-(03), the higher education research project of guizhou university in 2019 (gdgigy2019006). references 1. pendry jb, negative refraction makes a perfect lens. physical review letters 2000; 85(18): 3966–3969. 2. fang n, lee h, sun c, et al. sub-diffraction-limited optical imaging with a silver superlens. science 2005; 308(5721): 534–537. 3. schurig d, mock jj, justice bj, et al. metamaterial electromagnetic cloak at microwave frequencies. science 2006; 314(5801): 977–980. 4. iwaszczuk k, strikwerda ac, fan kb, et al. flexible metamaterial absorbers for stealth applications at terahertz frequencies. optics express 2012; 20(1): 635–643. 5. landy ni, sajuyigbe s, mock jj, et al. perfect metamaterial absorber. physical review letters 2008; 100(20): 207402. 6. pan w, yu x, zhang j, et al. absorption characteristics analysis of terahertz metamaterial absorber based on double-open square sheet. applied laser 2016; 36(3): 346–350. 7. mo m, wen q, chen z, et al. ultra-wideband polarization insensitive terahertz absorber based on truncated cone structure. chinese journal of physics 2013; 62(23): 237801. 8. liu n, mesch m, weiss t, et al. infrared perfect absorber and its application asplasmonic sensor. nano letters 2010; 10(7): 2342–2348. 9. lou w, shen t, liu h, et al. fiber optic transverse pressure sensor based on long-cycle fiber grating and butterfly cone. optoelectronics & lasers 2016; 27(11): 1145–1148. 10. xu h, hu l, lu y, et al. dual-band metamaterial absorbers in the visible and near-infrared regions. journal of physical chemistry c 2019; 123(15): 10028–10033. 11. wang s, sun x, ding m, et al. the investigation of an lspr refractive index sensor-based on periodic gold nanoringsarray. journal of physics d: applied physics 2018; 51(4): 045101. 12. xu j, zhao z, yu h, et al. design of triple-band metamaterial absorbers with refractive index sensitivity at infrared frequencies references and links. optics express 2016; 24(22): 25742–25751. 13. wang b, koschny t, soukoulis cm. wide-angle and 82 polarization-independent chiral metamaterial absorber. physical review b 2009; 80(3): 033108. 14. tuong pv, park jw, rhee jy, et al. polarization-insensitive and polarization-controlled dual-band absorption in metamaterials. applied physics letters 2013; 102(8): 081122. 15. lu x, zhang l, zhang t. nanoslit-microcavity-based narrow band absorber forsensingapplications. optics express 2015; 23(16): 20715–20720. characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.1953 1 original research article is creating materials with a desired refraction coefficient practically possible? alexander g. ramm department of mathematics, kansas state university, manhattan, ks 66506-2602, usa. e-mail: ramm@ksu.edu abstract a theory of many-body wave scattering is developed under the assumption a << d << λ, where a is the characteristic size of the small body, d is the distance between neighboring bodies and λ is the wave-length in the medium in which the bodies are embedded. the multiple scattering is essential under these assumptions. the author’s theory is used for creating materials with a desired refraction coefficient. this theory can be used in practice. a recipe for creating materials with a desired refraction coefficient is formulated. materials with a desired radiation pattern, for example, wave-focusing materials, can be created. pacs: 02.30.rz; 02.30.mv; 41.20.jb msc: 35q60; 78a40; 78a45; 78a48 keywords: wave scattering by many small bodies; smart materials article info received: 8 february 2023 accepted: 2 march 2023 available online: 16 march 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction the aim of this paper is to give an affirmative answer to the question in the title of this paper. this brings potentially many possibilities for progress in technology. there is a large literature on wave scattering by small bodies, starting from rayleigh’s work (1871)[1–3]. if the scatterer is small then the scattered field can be calculated analytically for bodies of arbitrary shapes, see reference [4]. the many-body wave scattering problem was discussed in the literature mostly numerically, if the number of scatterers was small, or under the assumption that the influence of the waves, scattered by other particles on a particular particle is negligible[5]. this corresponds to the case when the distance d between neighbouring particles is much larger than the wavelength λ, and the characteristic size a of a small body (particle) is much smaller than λ. theoretically and practically the assumptions a << λ, d >> λ, (1) are the simplest ones which allow one to neglect multiple scattering. by k = 2𝜋𝜋 𝜆𝜆 , the wave number is denoted. in the author’s theory, the basic assumptions are a << d << λ, (2) and the multiple scattering is of basic importance under these assumptions[4,6–35]. it is clear that assumption (2) can be practically realized. its https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ 2 importance comes from the fact that the author gave a rigorous asymptotically exact solution of the manybody scattering problem under assumption (2) when a → 0. this solution can be well approximated numerically by the particles of the size a > 30 nm. practically the size of a can be found by comparison of the solution for some a and for 𝑎𝑎 2 . if these solutions are practically close, then one considers this a as suitable. the aim of this paper is to show that our theory can be used practically. in reference [36], for the first time the author’s theory was used for solving the scattering problem for 10 billion small particles. this problem was solved numerically and numerical results were presented. let us formulate the wave scattering problems we deal with. let d be a bounded domain in ℝ3 with a sufficiently smooth boundary. the scattering problem consists of finding the solution to the problem: (∇2 + 𝑘𝑘2)𝑢𝑢 = 0 in g’ := ℝ3\𝐺𝐺, g := 𝑈𝑈𝑚𝑚=1 𝑀𝑀 𝐷𝐷𝑚𝑚, k = const > 0, (3) where dm = b(xm, a) is an impedance ball, centered at xm and of small radius a, u = u0 + v, u0 = eikα·x, α ∈ s2, (4) s2 is the unit sphere in ℝ3, u0 is the incident field, v is the scattered field satisfying the radiation condition vr – ikv = o(1 𝑟𝑟 ), r := |𝑥𝑥| → ∞, vr := 𝜕𝜕𝜕𝜕 ∂r , (5) and u satisfies the impedance boundary condition (bc) on the boundary of g: un – ζmu = 0, on sm, imζm ≤ 0, (6) where ζm is a constant, n is the unit normal to s := 𝑈𝑈𝑚𝑚=1 𝑀𝑀 𝑆𝑆𝑚𝑚, pointing out of g := 𝑈𝑈𝑚𝑚=1 𝑀𝑀 𝐷𝐷𝑚𝑚, and sm is the surface of dm = b(xm, a). by refraction coefficient n(x) the coefficient in the equation (∇2 + 𝑘𝑘2𝑛𝑛2(𝑥𝑥))𝑢𝑢 = (∇2 + 𝑘𝑘2 − 𝑞𝑞(𝑥𝑥))𝑢𝑢 = 0 (7) is understood, where q(x) := k2(n2(x) – 1). let g(x, y) = 𝑒𝑒𝑖𝑖𝑖𝑖|𝑥𝑥−𝑦𝑦| 4π|𝑥𝑥−𝑦𝑦| . then (∇2 + k2)g(x, y) = – δ(x – y), where δ(x) is the delta function. let us distribute small impedance particles dm = b(xm, a) in d so that ℕ(∆) = aκ–2|∆|[1 + o(1)], a → 0, (8) where ∆ ⸦ d is an arbitrary connected open subset of d, |∆| is its volume, κ ∈ (0, 1) is a number the experimenter may choose arbitrarily and ℕ(∆) is the number of particles in ∆. throughout this paper the important assumptions a << d << λ and (8) are satisfied. as a → 0, the number of small particles ℕ(∆) in (8) tends to infinity since κ – 2 < 0. we assume in this paper (for simplicity only) that the small particles are distributed in the domain d and the refraction coefficient in d equals to 1. in the monograph [31], it is assumed that d is filled with the material whose refraction coefficient n0(x) is known and we wanted to create in d the material with the desired refraction coefficient n(x). the boundary impedances ζm are chosen by the formula ζm = a–κh(xm), (9) where h(x) is a continuous function in d, imh ≤ 0. it will be clear from section 3 that the function h(x) can be determined by choosing a suitable boundary impedance ζ(x). when a → 0, the ζm and h(xm) can be considered as continuous functions ζ(x) and h(x). 2. solution of many-body scattering problem we look for the solution of the form (10) where σm(s) are unknown, qm := ∫ 𝜎𝜎𝑚𝑚(𝑠𝑠)𝑑𝑑𝑠𝑠𝑆𝑆𝑚𝑚 . one may think about σm as of charge densities on sm and 3 of qm as of total charge on the surface sm. we prove that 𝐽𝐽 ≔ � � [𝑔𝑔(𝑥𝑥, 𝑠𝑠) − 𝑔𝑔(𝑥𝑥, 𝑥𝑥𝑚𝑚)]𝜎𝜎𝑚𝑚(𝑠𝑠)𝑑𝑑𝑠𝑠 𝑆𝑆𝑚𝑚 𝑀𝑀 𝑚𝑚=1 (11) is negligible compared to (12) so j << i as a → 0. (13) we prove that the field u satisfies the following integral equation as a → 0: u(x) = u0(x) – 4π∫ 𝑔𝑔(𝑥𝑥,𝑦𝑦)ℎ(𝑦𝑦)𝑢𝑢(𝑦𝑦)𝑑𝑑𝑦𝑦𝐷𝐷 , (14) where h(xm) = 𝜁𝜁𝑚𝑚 𝑎𝑎𝜅𝜅 , and, since there are sufficiently many points xm ∈ d, the function h(x) is uniquely determined in d if the boundary impedances are known. apply the operator to ∇2 + k2 to both sides of equation (14) and get �∇2 + 𝑘𝑘2 − 4𝜋𝜋ℎ(𝑥𝑥)�𝑢𝑢(𝑥𝑥) ∶= �∇2 + 𝑘𝑘2𝑛𝑛2(𝑥𝑥)�𝑢𝑢(𝑥𝑥) = 0 (15) therefore, n2(x) = 1 – 4πk–2h(x). (16) we omit details since they can be found in the author’s publications listed in the references, in particular, in monograph [31]. if originally in d were material with the known refraction coefficient n0(x), then formula (16) were n2(x) = 𝑛𝑛02(𝑥𝑥) – 4πh(x)n(x)k–2, where n(x) is the distribution density for the small particles, see reference [31]. in this paper, we assume (for simplicity only) that n(x) = 1, see formula (8). 3. recipe for creating materials with a desired refraction coefficient let us formulate a recipe for creating materials with a desired refraction coefficient. formula (16) shows that if h(x) is chosen properly, then any n(x) can be obtained in d. recipe for creating materials with a desired refraction coefficient: a) calculate by formula (16) the function h(x); b) distribute small impedance balls in the domain d by the distribution law (8). the boundary impedances of these balls are defined by the function h(x). theorem 1. the refraction coefficient of the resulting medium tends to the desired coefficient n(x) as a → 0. let us show that practically negative refraction coefficient n(x) can be obtained by the above recipe. denote b := 4πk–2 > 0 and write equation (16) as n(x) = (1 – bh(x))1/2 = |1 − 𝑏𝑏ℎ(𝑥𝑥)|1/2𝑒𝑒𝜙𝜙/2, (17) where ϕ is the argument of 1 – bh(x). since the operator in (14) is of fredholm type, it remains fredholm type under small perturbations. therefore one can take h – i𝜖𝜖, where 𝜖𝜖 > 0 is sufficiently small, and equation (14) will still have a unique solution. by choosing h so that re(1 – bh) > 0 and im(1 – bh) < 0 and small, one gets the argument ϕ = 2π – δ, where δ > 0 is arbitrarily small if 𝜖𝜖 is sufficiently small. then n(x) will be nearly negative: its argument will be π – δ/2. 4. creating materials with a desired radiation pattern let us define what we mean by the radiation pattern. consider the scattering problem for the equation: ∇2𝑢𝑢 + 𝑘𝑘2𝑢𝑢 − 𝑞𝑞(𝑥𝑥)𝑢𝑢 = 0, 𝑢𝑢 = 𝑒𝑒𝑖𝑖𝑖𝑖𝑎𝑎·𝑥𝑥 + 𝑣𝑣, (18) where v satisfies the radiation condition. assume that k > 0 and α ∈ s2 are fixed. then the scattering amplitude a(β, α, k) = a(β), where the dependence on k, α is dropped since k and α are fixed. the formula for the scattering amplitude is known, see, e.g., reference [35]: a(β): = aq(β) = − 1 4𝜋𝜋 ∫ 𝑒𝑒 −𝑖𝑖𝑖𝑖𝑖𝑖·𝑦𝑦𝑞𝑞(𝑦𝑦)𝑢𝑢(𝑦𝑦)𝑑𝑑𝑦𝑦. (19) we call a(β) the radiation pattern. consider an inverse problem (ip): given an arbitrary f(β) ∈ l2(s2) and an arbitrary small 𝜖𝜖 > 0, can one find a q ∈ l2(d) such that �𝑓𝑓(𝛽𝛽) − 𝐴𝐴𝑞𝑞(𝛽𝛽)� 𝐿𝐿2(𝑆𝑆2) < 𝜖𝜖. (20) 4 this inverse problem was not formulated and was not studied in the works of other authors, to our knowledge. our result is stated in theorem 2. theorem 2. for any f(β) ∈ l2(s2) and an arbitrary small 𝜖𝜖 > 0 there is a q ∈ l2(d) such that (20) holds. since small perturbations of q result in small perturbations of a(β), there are infinitely many potentials q for which inequality (20) holds. the conclusion of theorem 2 follows from lemmas 3 and 4. lemma 3. the set �∫ 𝑒𝑒−𝑖𝑖𝑖𝑖𝑖𝑖·𝑥𝑥ℎ(𝑥𝑥)𝑑𝑑𝑥𝑥𝐷𝐷 � ∀ℎ∈𝐿𝐿2(𝐷𝐷) is dense in l2(s2). corollary 1. given f ∈ l2(s2) and 𝜖𝜖 > 0, one can find h ∈ l2(d) such that �𝑓𝑓(𝛽𝛽) + 1 4𝜋𝜋 ∫ 𝑒𝑒−𝑖𝑖𝑖𝑖𝑖𝑖·𝑥𝑥ℎ(𝑥𝑥)𝑑𝑑𝑥𝑥𝐷𝐷 � < 𝜖𝜖. lemma 4. the set {𝑞𝑞(𝑥𝑥)𝑢𝑢(𝑥𝑥,𝛼𝛼)}∀𝑞𝑞∈𝐿𝐿2(𝐷𝐷) is dense in l2(d). corollary 2. given h ∈ l2(d) and 𝜖𝜖 > 0, one can find q ∈ l2(d) such that ‖ℎ(𝑥𝑥) − 𝑞𝑞(𝑥𝑥)𝑢𝑢(𝑥𝑥,𝛼𝛼)‖𝐿𝐿2(𝐷𝐷) < 𝜖𝜖. since the scattering amplitude a(β) = − 1 4𝜋𝜋 ∫ 𝑒𝑒−𝑖𝑖𝑖𝑖𝑖𝑖·𝑥𝑥ℎ(𝑥𝑥)𝑑𝑑𝑥𝑥𝐷𝐷 depends continuously on h, the inverse problem ip is solved by lemmas 3 and 4. proofs are omitted. they can be found in reference [31]. 5. discussion how is the theory, outlined in the previous sections, can be used practically? to create a material with a desired refraction coefficient, or a material with a refraction coefficient close to the desired, is practically very important. to my knowledge, there were no general methods for creating material with a desired refraction coefficient. to use the theory, outlined in this paper and in the monographs[31–33], one has to solve a technological problem: how to prepare a small particle, say, a ball of radius a, with the prescribed boundary impedance ζ. this problem should be solvable, see reference [33] for arguments supporting this conclusions. if this technological problem is solved, then the recipe outlined in this paper (and in the author’s monographs[31–33] can be immediately used in practice. the problem of creating materials with a desired radiation pattern, the wave focusing materials, for example, was not investigated earlier. this problem is of great practical interest. the usual bodies scatter waves mostly backwards, somewhat sidewise and a little forwards. if one creates a body which scatters waves, for example, in a given solid angle, this would be of great practical interest. such a body can be created as follows from the theory outlined in the previous section. the author wrote this paper in an attempt to draw attention of the specialists in material sciences to the theory he has developed for creating materials with the desired refraction coefficient. the author is not aware of the experimental results based on his theory. such results are very desirable. there are numerical results, based on his theory, see references [37] and [38]. conflict of interest author declares no conflict of interest. references 1. rayleigh j. scientific papers. cambridge: cambridge university press; 1992. 2. van de hulst hc. light scattering by small particles. new york: dover publications; 1961. 3. landau l, lifschitz l. electrodynamics of continuous media. oxford: pergamon press; 1984. 4. ramm ag. wave scattering by small bodies of arbitrary shapes. singapore: world scientific publishing co. pte. ltd.; 2005. 5. martin p. multiple scattering. cambridge: cambridge university press; 2006. 6. ramm ag. scattering by obstacles. dordrecht: d. reidel; 1986. 7. ramm ag. scattering by many small bodies and applications to condensed matter physics. europhysics letters 2007; 80(4): 44001. doi: 10.1209/0295-5075/80/44001. 8. ramm ag. many-body wave scattering by small bodies and applications. journal of mathematical physics 2007; 48: 103511. doi: 10.1063/1.2799258. 9. ramm ag. wave scattering by small particles in a medium. physics letters a 2007; 367(1-2): 156– 161. doi: 10.1016/j.physleta.2007.02.076. 10. ramm ag. wave scattering by small impedance particles in a medium. physics letters a 2007; 368(1-2): 164–172. doi: 10.1016/j.physleta.2007.04.061. 5 11. ramm ag. distribution of particles which produces a desired radiation pattern. communications in nonlinear science and numerical simulation 2007; 12(7): 1115–1119. doi: 10.1016/j.cnsns.2005.11.001. 12. ramm ag. distribution of particles which produces a “smart” material. journal of statistical physics 2007; 127: 915–934. doi: 10.1007/s10955-007-9303-3. 13. ramm ag. distribution of particles which produces a desired radiation pattern. physica b: condensed matter 2007; 394(2): 253–255. doi: 10.1016/j.physb.2006.12.019. 14. ramm ag. creating wave-focusing materials. latin american journal of solids and structures 2008; 5(2): 119–127. 15. ramm ag. electromagnetic wave scattering by small bodies. physics letters a 2008; 372(23): 4298–4306. doi: 10.1016/j.physleta.2008.03.010. 16. ramm ag. wave scattering by many small particles embedded in a medium. physics letters a 2008; 372(17): 3064–3070. doi: 10.1016/j.physleta.2008.01.006. 17. ramm ag. preparing materials with a desired refraction coefficient and applications. in: skiadas c, dimotikalis i, skiadas c (editors). topics on chaotic systems: selected papers from chaos 2008 international conference. singapore: world scientific publishing co. pte. ltd.; 2009. p. 265–273. 18. ramm ag. preparing materials with a desired refraction coefficient. nonlinear analysis: theory, methods & applications 2009; 71(12): e186–e190. doi: 10.1016/j.na.2008.10.011. 19. ramm ag. creating desired potentials by embedding small inhomogeneities. journal of mathematical physics 2009; 50: 123525. doi: 10.1063/1.3267887. 20. ramm ag. a method for creating materials with a desired refraction coefficient. international journal of modern physics b 2010; 24(27): 5261–5268. doi: 10.1142/s0217979210056074. 21. ramm ag. materials with a desired refraction coefficient can be created by embedding small particles into a given material. international journal of structural changes in solids 2010; 2(2): 17–23. 22. ramm ag. wave scattering by many small bodies and creating materials with a desired refraction coefficient. afrika matematika 2011; 22: 33–55. doi: 10.1007/s13370-011-0004-3. 23. ramm ag. scattering by many small inhomogeneities and applications. in: skiadas c, dimotikalis i, skiadas c (editors). topics on chaotic systems: selected papers from chaos 2010 international conference. singapore: world scientific publishing co. pte. ltd.; 2011. p. 41–52. 24. ramm ag. collocation method for solving some integral equations of estimation theory. international journal of pure and applied mathematics 2010; 62(1): 57–65. doi: 10.1504/ijcsm.2009.027874. 25. ramm ag. electromagnetic wave scattering by a small impedance particle of arbitrary shape. optics communications 2011; 284(16-17): 3872–3877. doi: 10.1016/j.optcom.2011.04.035. 26. ramm ag. scattering of scalar waves by many small particles. aip advances 2011; 1(2): 022135. doi: 10.1063/1.3600704. 27. ramm ag. scattering of electromagnetic waves by many thin cylinders. results in physics 2011; 1(1): 13–16. doi: 10.1016/j.rinp.2011.05.002. 28. ramm ag. electromagnetic wave scattering by many small perfectly conducting particles of an arbitrary shape. optics communications 2012; 285(18): 3679–3683. doi: 10.1016/j.optcom.2012.05.010. 29. ramm ag. electromagnetic wave scattering by small impedance particles of an arbitrary shape. journal of applied mathematics and computing 2013; 43(1): 427–444. doi: 10.1007/s12190-013-0671-3. 30. ramm ag. many-body wave scattering problems in the case of small scatterers. journal of applied mathematics and computing 2013; 41(1): 473–500. doi: 10.1007/s12190-012-0609-1 31. ramm ag. scattering of acoustic and electromagnetic waves by small bodies of arbitrary shapes. applications to creating new engineered materials. new york: momentum press; 2013. p. 260. 32. ramm ag. creating materials with a desired refraction coefficient. doi: 10.1088/978-1-6817-4708-8. san rafael, california: iop concise physics, morgan & claypool publishers; 2017. 33. ramm ag. creating 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theory and computational modeling, optics communications 2012; 285(20): 4019–4026. doi: 10.1016/j.optcom.2012.06.017. 8 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1331 original research article electrospun li3v2(po4)3/carbon nanofiber as cathode materials for the high-performance lithium-ion batteries mengxi zhao1, zhongpei lu1, lin chen2, xuefan jiang3, fan yin1,2, gang yang1,2* 1 school of chemistry and material engineering, changshu institute of technology, changshu 215500, jiangsu, china. e-mail: gyang@cslg.cn 2 school of chemistry and chemical engineering, jiangsu university, zhenjiang 212013, jiangsu, china 3 school of physics and electronic engineering, changshu institute of technology, changshu 215500, jiangsu, china abstract in this paper, a series of li3v2(po4)3/c composite nanofibers is prepared by a facile and environmentally friendly electrospinning method and calcined under different temperatures. the lvp nanofiber calcined under 900 oc exhibits the best electrochemical performance. the bicontinuous morphologies of lvp/cnf are the fibers shrunk and the lvp crystals simultaneously grown. at the range of 3.0–4.3 v, lvp/cnf obtained under 900 oc delivers the initial capacity of 135 mah/g, close to the theoretical capacity of lvp. even at high current density, the sample of lvp/cnf still presents good electrochemical performance. keywords: lithium-ion batteries; cathode material; graphene; nanocomposite; electrochemical performance article info received: 1 april 2021 accepted: 20 may 2021 available online: 28 may 2021 copyright copyright © 2021 mengxi zhao, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction lithium battery has the advantages of high specific energy, high battery voltage, wide working temperature range and long storage life. it has been widely used in small electrical appliances, such as portable computers, cameras, electric tools, etc. in recent years, with the increasing shortage of non-renewable resources, such as oil and coal and the urgent needs of environmental protection, energy conservation and emission reduction, countries all over the world such as the united states, japan germany and france actively carry out the research on electric vehicle (ev) and hybrid electric vehicle (hev), and put the development and application of lithium power battery on the important agenda. because lithium battery has no pollution to the environment, it is more suitable to be used as the power supply of electric vehicle and large power reserve, so it has a very broad application prospect[1]. in recent years, great progress has been made in the research of positive and negative active materials for lithium batteries. at present, the most widely studied positive materials include layered lithium cobalt oxide licoo2, spinel oxide limn2o4, phosphate limpo4 (m = mn, fe, co, etc.) and li3v2(po4)3, but these materials have their own shortcomings, it is difficult to meet the increasing requirements for lithium batteries[2–4]. therefore, the existing electrode materials and search methods are improved. finding new high-energy electrode materials 9 is the top priority of research work, especially new cathode materials, which have become the key factor restricting the further improvement of the overall performance of lithium batteries. monoclinic li3v2(po4)3 (lvp), as the cathode material of lithium-ion battery, has gradually attracted extensive attention because of its high theoretical capacity and energy density. the stable frame structure of lvp provides a three-dimensional channel for the insertion/removal of li+, and its theoretical capacity is as high as 197 mah/g in the voltage range of 3.0–4.8 v[5–7]. however, the electronic conductivity of lvp is very poor. it affects the electrochemical performance of lvp and limits its commercial application. researchers have proposed many methods to overcome the problem of electronic conductivity of lvp. in addition to effective carbon coating and metal ion doping, reducing the particle size or embedding lvp particles into carbon nanonetworks can also effectively improve the electronic conductivity of lvp[8,9]. as we all know, the migration rate of ions and electrons in lvp plays a key role in improving its electrochemical properties. therefore, it is a very effective method to improve both ionic conductivity and electronic conductivity, because nanostructured lvp is conducive to the movement and intercalation/ de-intercalation of li+ in active electrode materials. it can improve the ionic conductivity of lvp. conductive carbon materials can effectively improve the electronic conductivity of lvp. nanostructured lvp/c materials can meet the requirements of high electronic and ionic conductivity at the same time. in recent years, lvp nanocomposites with different morphologies, such as spherical particles, nanorods, nanobelts, nanoplates and films, have attracted more and more attention. it is proved that it is beneficial to improve the electrochemical properties of lvp. the preparation of nanofiber materials by electrospinning technology is a hot spot in the field of material science and technology in the world in recent ten years. electrospinning has become the main way to effectively prepare nanofiber materials because of its simple manufacturing device, low spinning cost, wide variety of spinnable materials and controllable process. electrospinning technology is a simple and low-cost method for preparing nanofibers, which has been widely used to prepare materials with one-dimensional nanostructures. with long length and porous structure, nanofibers obtained by electrospinning generally have a large specific surface volume ratio. many nanofibers are randomly dispersed to form a multi space dense 3d structure. in recent years, the research on the preparation of olivine structure limpo4 (m = mn, fe, co, etc.) nanofibers by electrospinning is increasing, and the obtained limpo4 fibers show good electrochemical properties[11–13]. however, there are few reports on the preparation of nasicon structure li3v2(po4)3. considering that nanofibers are conducive to improvement. in this paper, li3v2(po4)3 with nanofiber structure was prepared by electrospinning, which improved the conductivity and electrochemical properties of li3v2(po4)3 as electrode material. 2. experimental part firstly, electrospinning precursor was synthesized, an appropriate amount of citric acid was dissolved in deionized water, nh4vo3 and stoichiometric nh4h2po3 and ch3cooli·2h2o were added, and the reaction was stirred in oil bath for 4 h to obtain uniform mixed sol a. polyvinylpyrrolidone (pvp) was added to an appropriate amount of h2o and stirred for 4 h to obtain transparent viscous liquid b. drop sol solution a into solution b and stir for 4 h to obtain uniform solution c. the precursor film is prepared by electrospinning method. the obtained white film is raised to 350 oc at a heating rate of 5 oc/min in nitrogen atmosphere and kept at a constant temperature for 4 h to decompose the mixture and release gas. then it is cooled to room temperature with the furnace. after full grinding, it is burned in a high-temperature tubular furnace. in this process, pvp is carbonized. at the same time, lithium vanadium phosphate (lvp) is generated under high temperature. in order to study the optimal calcination temperature, the effects of heat treatment at four temperatures of 600 oc, 700 oc, 800 oc and 900 oc on the morphology and electrochemical properties of lvp/carbon nanofibers were tried. the samples were analyzed by x-ray diffraction 10 (xrd) using d/max-2200/pc x-ray diffractometer of rigaku (science) company in japan. the test conditions were cu target, tube pressure 40 kv. the tube current is 100 ma, the continuous scanning speed is 4°/min, and the step width is 0.02°. the sample surface morphology is analyzed by jsm6700f scanning electron microscope produced by jeol (japan electronics) co., ltd., the tube voltage is 10 kv and 15 kv, and the tube current is 10 μa. the electrochemical performance test process of the sample is as follows: weigh the synthesized cathode material, conductive carbon black and polytetrafluoroethylene (ptfe) binder according to the mass percentage of 80:15:5, fully mix, and roll the material into 40 by manual membrane rolling machine μm thin film, cut into a square positive electrode sheet with a side length of 6 mm. the negative electrode adopts high-purity metal lithium sheet with a purity of 99.9%, a thickness of 0.4 mm and a diameter of 10 mm. in order to reduce the impact of humidity on the battery performance, the positive electrode sheet needs to be vacuum dried at 120 oc for 12 h before simulating the battery assembly. the battery assembly is carried out in a glove box filled with high-purity argon. the diaphragm used is celgard 2500 microporous film, and the battery shell is 2016 button type. place the positive shell, positive plate, diaphragm, negative plate and negative shell in order from top to bottom, and inject an appropriate amount of electrolyte. the solvent in the electrolyte is a 1:1:1 mixture of vinyl carbonate, diethyl carbonate and dimethyl carbonate, and the solute is lipf6. the charge discharge performance test of the assembled button battery with a concentration of 1 mol/l was carried out on the land ct2001a battery performance test system produced by wuhan lantian electronics co., ltd. 3. results and discussion figure 1 shows the surface morphology of the precursor of lvp/c composite nanofibers after drying in a 60 oc oven. it can be seen from figure 1(a) that the fibers obtained by electrospinning are distributed continuously, and each fiber is interwoven vertically and horizontally to form a dense nanofiber film. however, it can be seen that the diameter distribution of the fibers is uneven. the fiber with larger diameter may be caused by the superposition of several fibers. figure 1(b) shows the specific characteristics of the fiber more intuitively: the diameter is about 500 nm and the fiber surface is smooth. figure 1. sem image of the nanofiber precursors obtained from electrospinning. the lvp nanofiber film obtained by electrospinning was treated at high temperature in a nitrogen atmosphere tubular furnace for 4 h. as shown in figure 2, the sem images after heat treatment at different temperatures. it can be seen from the figure that after high temperature treatment, the fibrous morphology of the precursor was not damaged, but different changes occurred on the basis of fiber dimension. however, temperature has a great influence on the morphology of the material. as shown in figure 2(a) and 2(b), after calcination at 600 oc for 4 h, the fiber breaks, the diameter is about 600 nm, and small holes are formed on the fiber surface. combined with xrd data analysis, we know that after calcination at 600 oc, no lvp phase is formed. therefore, it can be judged that the fiber with rough surface shown in figures 2(a) and 2(b) is the carbon fiber obtained by pvp carbonization. after increasing the calcination temperature to 700 oc, the fiber surface changes significantly. as shown in figures 2(c) and 2(d), the fiber does not break and the diameter becomes smaller at 600 oc, with improved continuity. in addition to similar pores, needle and block particles also appear on the fiber surface. it can be seen from the above analysis that the fiber is the carbide of pvp. combined with the xrd analysis results, it can be inferred that the needle and block formed on the fiber surface should be the particles of lvp phase. when the temperature continues to rise to 800 oc, as shown in figure 2(e) and 2(f), the diameter of the nanofibers obtained at 700 oc is close to that of 11 the nanofibers, but the needles disappear, the number of massive particles gradually increases, distributed on the surface of the nanofibers, and the particle surface is smooth, which indicates that the lvp phase formed gradually increases with the increase of the calcination temperature. figure 2(g) and 2(h) are the sem images after calcination for 4 h when the temperature rises to 900 oc, which can be clearly seen from the figure. the diameter of nanofibers is about 100 nm, and the lvp particles grow gradually. at this time, the pvp transformed carbon fibers still exist continuously and play a supporting role, and the lvp particles are distributed on its surface. it can be seen that the sintering temperature has an effect on the formation of lvp phase, and the heat treatment temperature affects the change of morphology in the treatment of electrospinning precursors. figure 2. sem profile of lvp at different calcination temperatures. after high temperature treatment at different temperatures, the xrd diffraction patterns of each sample are shown in figure 3. it can be seen from the figure that the xrd of the obtained lvp is obviously different. after high temperature treatment at 600 oc at the same heat treatment time, as shown in figure 3(a), there is no diffraction peak of lvp, showing amorphous characteristics. it shows that it is not enough to react at 600 oc to form lvp phase. when the heat treatment temperature rises to 700 oc, it can be clearly seen from figure 3(b), the xrd spectrum of the sample shows the characteristic diffraction peak of lvp, but the diffraction peaks of (002) and (111) crystal planes around 15° do not appear, indicating that the temperature still needs to be increased. when the temperature rises to 800 oc, as shown in figure 3(c). as shown in figure 3(d), in addition to the enhancement of the diffraction peak intensity, the diffraction peaks of (002) and (111) crystal planes also began to appear. figure 3(d) shows the xrd diffraction peaks of lvp samples obtained after calcination for 4 h after the temperature increased to 900 oc, with monoclinic structure, belonging to p21/n space group, which corresponds to the standard spectral peaks one by one. from the analysis of xrd results, at the same time, heat treatment temperature plays an important role in the formation of lvp phase. figure 3. the xrd spectrogram of the lvp at the different calcination temperatures. after high temperature heat treatment at 700 oc, 800 oc, 900 oc, the obtained lvp nanofibers were ground and prepared into electrode sheets, and then assembled into batteries. the electrochemical properties were tested respectively in the voltage range of 3.0–4.3 v and 3.0–4.8 v. figure 4 shows the constant magnification (0.1 c, 1 c = 133 mah/ g) of lvp samples in the voltage range of 3.0–4.3 v. it can be seen from the charging curve that there are three platforms at 3.59, 3.68 and 4.09 v, but these three platforms are not obvious for the lvp samples calcined at 700 oc and 800 oc, which is consistent with the xrd data because the crystallinity of lvp 12 phase in the samples is not high. with the increase of temperature, the crystallinity of lvp phase gradually increases. the characteristic platform of lvp in the charge discharge curve is also gradually obvious. the cycle performance of each sample after 50 charge discharge cycles at a constant magnification of 0.1 c is shown in figure 4(b). it can be seen from the figure that with the increase of calcination temperature, the discharge specific capacity of lvp samples gradually increases, and the cycle stability also improves. after 50 cycles, specific discharge capacity of lvp at 900 oc, 800 oc, 700 oc retains 132 mah/g, 119 mah/g, and 92 mah/g respectively, which are 90%, 91% and 76% of the initial discharge specific capacity respectively. according to the charge discharge test results at small magnification (0.1 c), the lvp samples treated at 700 oc have shown poor capacity and cycle stability. in order to further study the effect of 800 oc and 900 oc on the performance of lvp, the variable rate charge and discharge performance at high voltage was tested. figure 4. first circle charge and discharge curve and cycle performance diagram of the lvp in the 3.0–4.3 v voltage range obtained at different calcination temperatures, and the charge and discharge ratio is 0.1 c. figure 5 is the first charge discharge curve and cycle performance diagram of each electrode material under the charge discharge ratio of 0.1 c and 50 cycles in the voltage range of 3.0–4.8 v. when the battery is charged to 4.8 v, three li+ are completely separated from the lvp, with two-phase electrochemical platforms of 3.59, 3.68, 4.09 and 4.56 v respectively. the platforms of lvp charge curve obtained by calcination at 700 oc are not obvious, and in the discharge curve, the platforms of the three samples at about 4.0 v are inclined because of the irreversibility of the reaction. two platforms can be seen in the discharge process, and the three discharge platforms are lvp electrodes. according to the cycle performance diagram in figure 5(b), the capacity of each sample decreases because the electrode material may dissolve in the electrolyte under high voltage, resulting in the instability of the lvp frame structure. after 50 cycles, the discharge specific capacities of the three samples are 114.2 mah/g, 134.7 mah/g, 151.6 mah/g respectively, 74%, 73% and 77% of the specific discharge capacity of the first cycle are retained. figure 5. first cycle charge discharge curve and cycle performance diagram of lvp obtained at different calcination temperatures in the voltage range of 3.0–4.8 v. the charge discharge ratio is 0.1 c. similarly, we studied the variable rate performance of lvp samples calcined at 800 and 900 oc. as shown in figure 6, the two samples were charged at constant current rate of 0.1 c and discharged at different discharge rates of 0.1 c, 1 c, 2 c, 5 c, 10 c and 20 c. it can be seen that with the increase of discharge ratio, the platform of charge discharge curve decreases gradually, and the first discharge specific capacity at each ratio decreases. lvp electrode calcined at 900 oc. under the variable rate performance test, although the coulomb efficiency is less than 800 oc, the material shows good electrochemical performance. even at higher rates, such as 10 c and 20 c, its specific discharge capacity can still maintain 88 mah/g and 50 mah/g. lvp nanoparticles are attached to carbon nanofibers with excellent conductivity. the composite structure effectively improves the electrochemical properties of lvp particles. 4. conclusion lvp nanofibers were prepared by a simple and feasible electrospinning method. lvp nanofibers with different morphologies were obtained after treatment at different calcination temperatures for 13 4 h. lvp particles can be embedded on the surface of nanofibers at higher temperatures. the sintering temperature plays an important role in the phase formation of lvp. the higher the temperature, the more lvp phase is formed, through the test of electrochemical properties, the lvp calcined at 900 oc has good cycle performance and rate performance. therefore, the lvp phase with high electrochemical activity is the most at this temperature. lvp nanoparticles are embedded on polymer fibers, and the particles are connected through fibers. through comparison, the optimal sintering temperature is 900 oc. the first discharge capacities of lvp samples calcined at 800 oc and 900 oc are 134 mah/g and 135 mah/ g in the voltage range of 3.0–4.3 v, reaching the theoretical capacity of li3v2(po4)3, which is 133 mah/ g. at high magnification, the lvp/c fiber composite sample still has excellent electrochemical properties. conflict of interest the authors declare that they have no conflict of interest. acknowledgements this work was supported by the jiangsu natural science foundation “synthesis and electrochemical properties of cathode material lithium nickel manganite of high performance lithium batteries” (bk20141229). references 1. huang k, wang z, liu s. principle and key technology of lithium batteries (in chinese). beijing: chemical industry press; 2007. p. 12. 2. yang g, liu h, ji h, et al. temperature-controlled microwave solid-state synthesis of li3v2(po4)3 as at cathode materials for lithium batteries. journal of power sources 2010; 195: 5374–5378. 3. zhang x, wang k, wei x, et al. carbon-coated v2o5 nanocrystals as high performance cathode materials for lithium ion batteries. chemistry of materials 2011; 23: 5290–5292. 4. son j, kim g, kim m, et al. carbon coated nasicon type li3v2–xmx(po4)3 (m=mn, fe and al) materials with enhanced cyclability for li-ion batteries. journal of the electrochemical society 2013; 160: a87–a92. 5. sun c, rajasekhara s, dong y, et al. hydrothermal synthesis and electrochemical properties of li3v2(po4)3/c-based composites for lithium 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et al. improved lithium storage properties of electrospun tio2 with tunable morphology: from porous anatase to necklace rutile. nanoscale 2013; 5: 10267–10274. 11. hagen rv, lorrmann h, moller kc, et al. electrospun life1–ymnypo4/c nanofiber composites as self-supporting cathodes in li-ion batteries. advanced energy materials 2012; 2: 553–559. 12. damen l, giorgio f d, monaco s, et al. synthesis and characterization of carbon-coated limnpo4 and limn1–xfexpo4 (x=0.2, 0.3) materials for lithium-ion batteries. journal of power sources 2012; 218: 250–253. 15 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1332 original research article synthesis and application of nano-mh/mpb as intumescent flame retardant (ifr) aiming zhao, yanmao dong, qiuyang ni, zhiyu bao* school of chemistry and bioengineering, suzhou university of science and technology, suzhou 215009, jiangsu, china. e-mail: bzy1952@126.com abstract magnesium hydroxide/melamine phosphate borate (nano mh/mpb), a novel nano-composition intumescent flame retardant, was synthesized with the in-situ reaction method from mgcl2·6h2o sodium hydroxide (naoh) and melamine phosphate borate (mpb) in the absence of h2o. the structure of the product was confirmed by edax ir and xrd. the effects of reaction temperature and time on the dimension of magnesium hydroxide were observed. the effects of mass ratio of magnesium hydroxide to mpb on the flame retardancy of nano-mh/mpb/ep were examined with the limiting oxygen test. the results show that the optimal condition of synthesis of mh/mpb is mmh/mmpb = 0.25, reacting under 75 oc for 30 minutes. finally, the mechanism for flame retardancy of nano-mh/mpb/ep was pilot studied by means of ir of char layer and tg of mh/mpb. keywords: intumescent flame retardant; magnesium hydroxide; nano-composition; melamine phosphate borate; synergistic agents article info received: 23 april 2021 accepted: 16 june 2021 available online: 23 june 2021 copyright copyright © 2021 aiming zhao, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction in recent years, intumescent flame-retarded (ifr) has become a research hotspot because of its high thermal stability and environmental friendliness[1]. ifr is mainly composed of carbon source (such as pentaerythritol), acid source (such as ammonium polyphosphate) and gas source (such as melamine), which can be divided into mixed type and simple type. among them, hybrid ifr has some disadvantages, such as easy moisture absorption, poor thermal stability, low flame-retarded efficiency and difficult compatibility with polymers[2]. simple ifr can effectively solve the above problems, but it also has the disadvantages of single element composition and high cost. in order to improve the above problems, ifr and nanoparticles can be used as flame-retarded polymers. nanoparticles have the characteristics of high surface atomic ratio, large specific surface area and good dispersion, showing a unique volume effect and surface effect[3], which can improve the mechanical properties and flame-retarded properties of materials. it is reported that clay[4,5], nano magnesium hydroxide (mh) [6], nano aluminum hydroxide[7], nano sio2 [8], nano zinc oxide (zno)[9,10], nano tio2 can be used as synergistic agents of ifr to flame-retarded pp, pe, pa66, etc.[11] however, the current research mainly focuses on intumescent clay nanocomposite flame-retarded pp and pa66[12]. 16 magnesium hydroxide (mh) decomposes at 340–490 oc, and the initial decomposition temperature is 100 oc higher than that of al(oh)3; the heat absorption capacity of 1.37kj·g–1 is higher than that of al(oh)3 (1.17kj·g–1), and the heat capacity is also 17%, which is helpful to improve the flame-retarded efficiency[13,14]; in addition, magnesium hydroxide is a good smoke suppressant[15]. nano mh was introduced into ifr system to flame-retarded ep for the first time to improve the disadvantages of ifr, such as low flame-retarded efficiency and incompatibility with materials. nano mh/mpb intumescent nanocomposite flame-retarded was prepared by in-situ generation method. the flame-retarded synergistic effect of mh and mpb in ep was studied. 2. experiment 2.1 main raw materials melamine phosphate borate (mpb), self-made (as shown in figure 1)[16]; mgcl2·6h2o, analytical reagent, produced by shanghai tongya chemical technology development co., ltd; ethylenediamine, analytical pure, produced by shanghai qiangshun chemical co., ltd; e-44 epoxy resin (ep), produced by zhenjiang danbao resin co., ltd. figure 1. sketch pattern of mpb and mh/mpb. 2.2 synthesis of mh/mpb mpb, mgcl2·6h2o and water are added into a three-mouth bottle in a certain proportion, heated and stirred, and completely dissolved by ultrasonic oscillation. then, slowly drop the prepared precipitant naoh solution into the aqueous solution of mpb and mgcl2·6h2o, gradually appear white turbidity, ultrasonic oscillation, stirring and holding for a period of time. cool, filter, wash with water and absolute ethanol until there is no cl (agno3 detection), dry at 60 °c and weigh. 2.3 preparation of flame-retarded epoxy resin samples of mh/mpb ethylenediamine was used as curing agent, 10 g epoxy resin and 1 g ethylenediamine were mixed at room temperature, stirred evenly, and a certain amount of mh/mpb flame-retarded was added. after stirring evenly, it is injected into a self-made aluminum mold with specific size, cured at room temperature for 24 hours, and then cured at 80 oc for 2 hours. after complete curing, it shall be trimmed into the required spline for testing. 2.4 testing and characterization 1) the products were detected by prostar lc240 infrared spectrometer (kbr tablet pressing method). 2) the x-ray powder diffraction test is continuously scanned on the german bruker d8 x-ray diffractometer for xrd test. the test conditions are: cu target, rear monochrome tube, 45 kv of tube pressure, 20 ma of tube flow, scanning ranging 10° ≤ 2θ ≤ 80°, 4°·min-1 of scanning speed. 3) the elemental composition of the product was detected by s-570 scanning electron microscope (sem) (equipped with edaxpv9900 energy spectrometer). 4) the oxygen index test (loi) adopts hc9002 oxygen index tester according to gb/t 2406-93, and the flame-retarded epoxy resin spline size is 110 mm × 6 mm × 3.5 mm; limiting oxygen index test is conducted. 5) american pekin elmer tga7 thermogravimetric analyzer is used for thermogravimetric analysis. 3. results and discussion 3.1 theory mpb molecules contain -nh2, -oh, p=o and other groups. these groups can form hydrogen bonds with -oh of nano mh (as shown in figure 1). at the same time, nanoparticles have high activity and are easy to combine with macromolecules. in this way, nano mh/mpb intumescent nanocomposite 17 flame-retarded was prepared by combining mh and mpb through chemical and physical effects. 3.2 infrared spectrum analysis the infrared spectra of mh, mpb and mh/ mpb are shown in figure 2. infrared spectrum analysis is as follows[17]: in figure 2a, 3,698 cm–1 is o-h stretching absorption peak in the mh crystal structure, 1,467 cm–1 is the bending vibration absorption peak of -oh, and the wide absorption peak near 1,643 cm–1 and 3,413 cm–1 should be the absorption peak of h2o in mh crystal. this result is consistent with the mh results reported in literature[18]. figure 2c is obviously different from figures 2a and 2b. in figure 2c, there are not only the o-h stretching absorption peak 3,702 cm–1 in mh structure, but also the overlapping 3,339 cm–1 and 3,132 cm–1 of n-h stretching vibration absorption peaks in -nh3+, -oh and -nh2 in mpb structure, p=o stretching vibration absorption peak 1,265 cm–1, c=n stretching vibration absorption peak 1,656 cm–1. this shows that mh/mpb composite flame-retarded was prepared. figure 2. infrared spectrum of mh/mpb and mh/mpb. 3.3 elemental analysis the energy spectrum of mhmpb (mmh/ mmpb = 0.25) is shown in figure 3. it can be seen from figure 3 that the product mainly contains c, n, o, p, mg and other elements, which further confirms the preparation of mh/mpb composite flame-retarded. figure 3. energy spectrum of mh/mpb (mmh/mmpb). 3.4 xrd analysis of mh, mpb and mh/mpb the xrd spectra of mh, mpb and mh/mpb are shown in figure 4. it can be seen from the comparison of the diffraction peak positions of figure 4c with figure 4a and figure 4b that in figure 4c, mpb and mg(oh)2 diffraction peaks exist. thus, the preparation of mh/mpb complex was further confirmed. the diffraction peak position of crystal plane of mh’s (001), (100), (101) in figure 4c is obvious and widened, indicating that the particle size is small[19]. the grain size can be determined by xrd using scherrer formula. the peak is calculated to obtain, and the calculation results are shown in table 1[20]. the calculated results show that mg(oh)2 in the prepared mh/mpb composite has reached nano level. figure 4. xrd spectra of mh, mpb and mh/mpb (a: mpb; b: mh; c: mh/mpb). 18 table 1. grain size of mh/mpb 2θ/° crystal plane/hkl half peak width/° grain size/nm 17.72 31.70 38.24 59.34 001 100 101 110 0.33 0.19 0.15 0.40 24.12 43.03 55.51 20.12 3.5 effect of reaction temperature on grain size of mh/mpb using single factor experimental analysis, keep other influencing factors unchanged, change the reaction temperature to 35 oc, 45 oc, 55 oc, 65 oc and 75 oc, and compare the effect of mh/mpb xrd spectrum (figure 5), and the grain size is calculated and compared by scherrer formula (table 2). figure 5. xrd patterns of mh/mpb at different reaction temperatures (a: 35 °c; b: 45 °c; c: 55 °c; d: 65 °c; e: 75 °c). figure 5 shows that when the temperature is too high, the diffraction peak is obviously refined, indicating that the grain size becomes larger, and the change of (201) crystal plane is obvious. in addition, it can be concluded from table 2 that when the stress temperature is lower than 75 oc, the grain size of mh/mpb decreases slightly with the increase of temperature; when the reaction temperature reaches 75 oc, the grain size of mh/mpb increases sharply. this is because the reaction temperature has an effect on the formation and growth of nuclei[21]. the nucleation rate in low temperature region is higher than that in crystal. the growth rate is fast, that is, low temperature is conducive to the formation of crystal nucleus, which is not conducive to the growth of crystal nucleus. generally, fine crystals are obtained; as the temperature increases, the solubility decreases. the viscosity of the liquid increases the mass transfer coefficient and greatly improves the crystal growth rate, so as to increase the crystal nucleus. when the temperature exceeds 75 oc, the crystal nuclei agglomerate and the grain size increases sharply. 3.6 effect of reaction time on grain size of mh/mpb keep other influencing factors unchanged, change the reaction time to 10, 20, 30, 40 and 50 minutes, and compare the xrd spectra of mh/mpb (figure 6). the grain size is calculated and compared by scherrer formula (table 3). as shown in figure 6, when the reaction time is less than 30 min, the diffraction peak broadening is obvious, indicating that the grain size is small; more than 30 minutes, the diffraction peak is obviously refined, indicating table 2. grain size of mh/mpb at different reaction temperatures temperature /℃ crystal plane / hkl 2θ/° half peak width /° grain size / nm average size /nm temperature /℃ crystal plane / hkl 2θ/° half peak width /° grain size /nm average size /nm 35 001 17.86 0.40 19.91 26.50 65 001 17.76 0.50 15.92 21.93100 31.76 0.25 32.71 100 31.74 0.37 22.10 101 38.48 0.31 26.88 101 38.34 0.30 22.76 45 001 17.86 0.26 30.61 27.53 75 001 17.94 0.13 61.23 51.39100 31.72 0.41 19.94 100 31.74 0.20 40.89 101 38.46 0.26 32.04 101 38.32 0.16 52.05 55 001 18 0.28 28.44 23.80100 31.84 0.40 20.45 101 38.46 0.37 22.52 19 that the grain size becomes larger; (101) and (110) crystal planes change significantly. this moment the image is confirmed by table 3. when the reaction time is 30 minutes, the grain size of mh/mpb is the smallest, close to 19 nm. the reaction speed between magnesium chloride and sodium hydroxide is very fast, and the whole reaction can be completed in an instant. at the initial stage of the reaction, fine mh is easy to agglomerate and form larger mh; but with the extension of time, the energy and activity of mh crystal increase, and the smaller mh can be removed from the larger mh crystal separated to form mh particles with small particle size[22]. if the reaction time is too long, mh particles will agglomerate again. so it’s not easy to react too short or too long and the optimum reaction time is 30 minutes. figure 6. xrd pattern of mh / mpb at different reaction times. table 3. grain size of mh/mpb at different reaction temperatures table 4. effect of mmh/mmpb on loi of epoxy resin order 1 2 3 4 5 6 7 8 9 fire retardant mpb mh/mpb (0.05:1)* mh/mpb (0.15:1)* mh/mpb (0.25:1)* mh/mpb (0.35:1)* mh/mpb (0.5:1)* mh/mpb (0.5:1)* mh/mpb (0.75:1)* loi/% 18 25 27 27 28 26 25 24 (self-extinguish) 24 note: (*) is mmh/mmpb. 3.7 effect of mmh/mmpb on loi of mh/ mpb flame-retarded epoxy resin table 4 is the limiting oxygen index of mh/ mpb with different mmh/mmpb ratio when adding 20% (mass fraction) to epoxy resin. it can be seen from table 4 that mh and mpb have good flame-retarded synergistic effect. when mmh/mmpb is 0.05, the loi of ep increases from 25% to 27%, and when mmh/mmpb is 0.25, the loi of ep reaches the highest point of 28%. with the increase of mmh/ mmpb, the amount of mgo produced by hydrolysis is more, which leads to the increase of flame-retarded effect of flame-retarded composites in the combustion process of the flame-retarded composite increased. however, when the mmh/mmpb value exceeds 0.25, the loi of ep decreased significantly, even lower than that of mpb/ep. the reason may be that there is too much mh, which leads to the relatemperature /℃ crystal plane / hkl 2θ/° half peak width /° grain size /nm average size /nm temperature /℃ crystal plane / hkl 2θ/° half peak width /° grain size /nm average size /nm 10 001 17.74 0.14 58.86 37.86 40 001 17.82 0.16 49.76 48.94101 37.66 0.24 34.63 101 37.92 0.14 59.41 110 59.32 0.45 20.11 110 58.96 0.24 37.65 20 001 17.72 0.33 24.12 34.08 50 001 17.7 0.13 61.24 90.48101 38.24 0.15 55.50 101 39.12 0.08 104.35 110 59.34 0.4 22.63 110 59.3 0.06 105.85 30 001 17.7 0.3 26.5 19.05101 38.26 0.47 17.71 110 59.46 0.7 12.94 20 tive reduction of mpb and the impact on its flame retardancy. therefore, 0.25 mmh/mmpb is the best ratio. 3.8 mh/mpb thermogravimetric analysis according to the tg analysis of mh/mpb (figure 7), mh/mpb is mainly decomposed at 200–300 oc; after 300 oc, mh/mpb is decomposed very little; at 700 oc, there is still a high carbon residue rate, up to 39%, which shows that mh/mpb has better flame retardancy. the dtg diagram (figure 8) shows that, mh/mpb has three main thermogravimetric rate peaks 106.2 oc, 261.3 oc and 303.7 oc. small molecular water contained in mh/mpb shall be at 106.2 oc, 261.3 oc and 303.7 oc are the thermal weight loss rate peaks of mh/mpb. the main peaks of dta (figure 9) are 266.9 oc and 317 oc, which is basically consistent with the dtg peak. figure 7. tg pattern of mh/mpb. figure 8. dtg pattern of mh/mpb. figure 9. dta pattern of mh/mpb. table 5. effect of addition amount of mh/mpb (0.25:1)* on loi order 1 2 3 4 5 addition amount /% 0 10 20 30 40 loi /% 18 25 28 29 (self-extinguish) 30 note: (*) is mmh/mmpb = 0.25:1. 3.9 preliminary study on the mechanism of mh/mpb flame-retarded epoxy resin it can be seen from table 5 that the loi of mh/ mpb/ep is significantly higher than that of ep without mh/mpb (0.25:1)* (loi is 18%), and the loi of ep gradually increases with the increase of mh/ mpb addition. when the addition amount reaches 40%, the loi of epoxy resin reaches 31%. when the addition of mpb was 20%, the loi of epoxy resin increased significantly, and then tended to be flat. it can be seen that the best addition amount of mh/ mpb is 20%, loi reached 28%. xrd analysis of carbon residue (figure10) shows that the addition of mh makes the peak of carbon residue tend to be flat, and the carbon residue tends to amorphous carbon. so mh changed the morphology of carbon residue. the carbon slag produced by ep, ep/mpb and ep/mh/mpb in the oxygen index test experiment shall be tested by infrared to understand the carbon layer structure, as shown in figure 11. by analyzing figure 11, the infrared spectrum of carbon residue of ep/mh/mpb is obviously different from the other two, and the position of absorption peak changes. 21 figure 10. xrd pattern of carbon slag. figure 11. infrared spectra of ep, ep/mpb and ep/mh/mpb carbon residues (a: ep; b: ep/mh/mpb; c: ep/mpb). in figure 11b, the peak at 424 cm–1 is the stretching vibration absorption peak of mg-o bond, 1,317 cm–1 is the stretching vibration absorption peak of b-o, 959 cm–1 is the stretching vibration absorption peak of p-o-p, 1,652 cm–1 is the stretching vibration peak of c=c double bond, and 620 cm–1 is the characteristic peak of aromatic ring[17,23]. this shows that the combustion carbon residue contains mg-o bond, b-o bond, p-o-p bond and c=c double bond. in figure 11c, the bi-peaks at 2,955 cm–1 as c=o characteristic peaks disappeared in figure 6b. it is seen that the addition of mh affects the structure and composition of ep combustion carbon slag and the ep combustion thermal decomposition process. during thermal degradation or combustion processes, mh/mpb produces phosphate-polyphosphate-polydephosphate, and forms a nonvolatile phosphate layer (p-o-p bond) protective layer. polydephosphate has dehydration, so it can form the carbonized layer[24]; mh/mpb produces boric anhydride or boric acid during combustion. boric acid can form a glass-like melt (b-o bond) during thermal cracking, which is covered on the material; the combustion carbon residue contains mg-o bond, b-o bond, p-o-p bond and c=c double bond. in figure 11c, the double peak at 2,955 cm–1 is c=o, and the characteristic peak disappeared in figure 6b. it can be seen that the addition of mh affects the structure and composition of ep combustion carbon slag and the thermal decomposition process of ep combustion. during thermal degradation or combustion or the burning process, mh/mpb produces phosphoric acid–metaphosphoric acid–polymetaphosphoric acid to form a non-volatile phosphoric acid layer (p-o-p bond) protective layer. polymetaphosphoric acid has dehydration and it can form a carbonization layer[24]; during the combustion of mh/mpb, boric anhydride or boric acid is produced. boric acid can form a glass like molten metal during thermal cracking. the melt (b-o bond) is covered on the material; the high temperature decomposition of mh in mh/ mpb produces mgo, which can interact with the pyrolysis products of ep and mpb. it can be transformed into a more stable carbon layer containing mg, p, b, c and other elements, promote the direct oxidation of the material into carbon dioxide and reduce the combustible gas carbon monoxide. the generation of stable carbon layer can isolate the air and prevent the outward diffusion of combustible gas, so as to achieve the purpose of flame-retarded. in addition, mh/mpb contains nitrogen, which can release refractory gas nh3 when heated, diluting the concentration of oxygen in the air. high temperature mh contained in mh/mpb decomposition endothermic has cooling effect and flame-retarded effect. it can be seen that the flame-retarded ep of mh/mpb has flame-retarded mechanisms such as condensed phase, gas phase and synergy. it can’t be explained by one mechanism. it contains nitrogen, which can release refractory gas nh3 when heated, diluting the concentration of oxygen in the air. 22 4. conclusion (1) mh/mpb nanocomposite flame-retarded was prepared by in-situ formation method. through single factor experimental analysis, it is concluded that the grain size of mh/mpb synthesized is small when the reaction temperature is lower than 75 oc and the reaction time is 30 min. it can be seen that mh reaches nano level through scherrer formula. (2) when mmh/mmpb is 0.25, mh and mpb have the best synergistic effect and the best flame-retarded performance; when the addition amount of epoxy resin (ep) is 20%, the limiting oxygen index (loi) of epoxy resin reaches 28%. (3) the thermogravimetric analysis of mh/mpb shows that mh/mpb has a high decomposition temperature, and the remaining carbon rate is still 39% at 700 oc. 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63(3): 100–125. microsoft word can-6046 characterization and application of nanomaterials2024, 7(2), 6046. https://doi.org/10.24294/can.v7i2.6046 1 article mechanical properties of spinel (mgcr2o4) phase containing aluminosilicate glass-ceramic mrinmoy garai1,*, arianit a. reka2, shibayan roy1 1 materials science center, indian institute of technology (iit), kharagpur 600036, india 2 department of chemistry, faculty of natural sciences and mathematics, university of tetova, tetovo 1200, north macedonia * corresponding author: mrinmoy garai, mrinmoygarai@iitkgp.ac.in abstract: this research study explores the addition of chromium (cr6+) ions as a nucleating agent in the alumino-silicate-glass (asg) system (i.e., al2o3-sio2-mgo-b2o3-k2o-f). the important feature of this study is the induction of nucleation/crystallization in the base glass matrix on addition of cr6+ content under annealing heat treatment (600 ± 10 °c) only. the melt-quenched glass is found to be amorphous, which in the presence of cr6+ ions became crystalline with a predominant crystalline phase, spinel (mgcr2o4). microstructural experiment revealed the development of 200–500 nm crystallite particles in cr6+-doped glassceramic matrix, and such type microstructure governed the mechanical properties. the machinability of the cr-doped glass-ceramic was thereby higher compared to base aluminosilicate glass (asg). from the nano-indentation experiment, the young’s modulus was estimated 25(±10) gpa for base glass and increased to 894(±21) gpa for cr-doped glass ceramics. similarly, the microhardness for the base glass was 0.6(±0.5) gpa (nano-indentation measurements) and 3.63(±0.18) gpa (micro-indentation measurements). and that found increased to 8.4(±2.3) (nano-indentation measurements) and 3.94(±0.20) gpa (microindentation measurements) for cr-containing glass ceramic. keywords: alumino-silicate glass; nucleation; microstructure; microhardness 1. introduction al2o3-sio2-mgo-b2o3-k2o-f (alumino-silicate-glass) is converted into corresponding glass-ceramic/glass-ceramic composite with typical microstructuredriven mechanical properties [1–3]. in practice, a heat-treatment schedule is followed for converting such silicate-based glass into corresponding glass-ceramic [4,5]. however, the heat treatment requires specified time and electrical energy. it is thus desired to get the glass crystallized with the least energy, i.e., without performing any heat treatment [4,6]. for this purpose, self-nucleation during the glass melting or annealing is desired. k2o-mgo-b2o3-sio2-f systems have the ability to incorporate active ions (like chromium, aluminum, lanthanoids, etc.) at various concentrations, making it easier to provide bulk samples compared to crystalline materials. in order to add chromium ions in silicate (sio2)-based glasses, it can possess variable oxidation states, viz. +2, +3, +6, etc. cr3+ serves as a modifier, whereas cr6+ (i.e., cro4 2− structural units) can act as the glass network former [3,4]. since chromium ions have multi-oxidation states crn+(n = 2–6), the mechanical properties depend on its structural units (i.e., properties of the former and modifier). as the glasses possess no long-range order, the position of cr-ions can vary depending on the ligand’s locations as well as the coordination number and the average distance of the central ion-ligand [6–8]. it is reported that the higher valent chromium ion (i.e., cr6+) is effective for the citation garai m, reka aa, roy s. mechanical properties of spinel (mgcr2o4) phase containing alumino-silicate glass-ceramic. characterization and application of nanomaterials. 2024; 7(2): 6046. https://doi.org/10.24294/can.v7i2.6046 article info received: 26 april 2024 accepted: 9 july 2024 available online: 1 august 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials2024, 7(2), 6046. 2 crystallization as well as microstructure in boro-silicate/alumino-silicate glass [7–9]. if nucleation in al2o3-sio2-mgo-b2o3-k2o-f glass occurs during melting or annealing temperature, glass-ceramic composite-type material is obtained instead of getting superior glass phase [6–8]. in the study on sio2-b2o3-based glass systems, aktas et al. [8] demonstrated that 0–1 wt% cr2o3-containing glass is completely amorphous, but cr2o3 contents >1 wt% make those glasses crystalline, i.e., glassceramic. however, the effectiveness of such a technique comes from creating a finely structured crystalline phase with random orientation, typically free from pits, dents, voids, micro-cracks, or porosity [7,10]. and such a fine grain type of microstructure can generate the desired mechanical properties in final glass ceramics. in this report, the substitution of al3+ ions by cr6+ ions in alumino-silicate glass (asg), i.e., al2o3-sio2-mgo-b2o3-k2o-f system, is studied. due to the cr6+ addition in such glass, the relevant variation of the crystallization features (xrd, fesem) is interrelated with mechanical properties (microhardness, youngs modulus, contact depth) [4]. 2. experimental figure 1. differential scanning calorimetric (dsc) thermogram of al2o3-sio2mgo-b2o3-k2o-f glass containing. (a) 0 mol%; (c) 2 mol% chromium content (inset of figure 1a,c shows the photograph of corresponding glasses) and xrd pattern (b) 0 mol%; (d) 2 mol% cr-doped glasses [4]. two alumino-silicate-glass (asg) of composition (mol%) (i) asg-0cr (7k2o20mgo-10b2o3-44sio2-12mgf2-7al2o3) and (ii) asg-2cr (7k2o-20mgo-10b2o344sio2-12mgf2-5al2o3-2k2cr2o7) were synthesized by melt-casting using pure characterization and application of nanomaterials2024, 7(2), 6046. 3 chemicals, i.e., sio2, al(oh)3, mg(oh)2, h3bo3,k2co3, mgf2, and k2cr2o7. the details/purity of reagents are described in a previous report on a similar glass system [4]. the glasses were melted in a platinum (pt) crucible in an electrically heated furnace at 1570(±10) °c for 2 h, followed by casting in graphite mold and thereafter annealing at 600(±10) °c (2 h). the photographs of the annealed glasses are exhibited in the inset of figure 1 that clearly demonstrates the opaque nature [4]. annealed glass was characterized for microstructural and mechanical properties using the techniques of differential scanning calorimetry (dsc), x-ray diffraction (xrd), field emission scanning electron microscopy (fesem), energy dispersive x-ray spectroscopy (edx), nanoindentation, and vickers microindentation [11–15]. finely powdered (particle size < 60 µm) asg samples were subjected to differential scanning calorimetry (dsc setaramlabsys, setaram instrumentation, france) at a heating rate of 10 °c/min to obtain the phase transformation temperature. xrd analysis was recorded using an xpertpro mpd diffractometer (panalytical, netherlands) operating with ni-filtered cukα = 1.5406 å radiation as the x-ray source. the morphology of the glasses (chemically etched by 2 vol.% aqueous hf solution for 10 min) was examined using a fesem (model s430i, leo, cea, usa). to dictate the elements present in the synthesized glass, qualitative elemental composition analysis was performed using the energy dispersive x-ray spectroscopy (edx) detector attached to the fesem microscope [11,12]. nano-indentation was taken using polished glass samples by the berkovich indenter tip (radius = 100 nm & angle = 142.3°) hystron, model no. tin 50 triboindenter, usa. the indentation was carried out with an applied force of 5 mn under a dwell time of 10 s followed by constant unloading. the indentations were obtained from various locations within the specimen surface. for measurement, a total of 20 indentations were taken at any given location following a 4 × 5 square matrix pattern. standard indentation p-h curves were generated from the load (p) controlled nano-indentation tests and the corresponding measurements of indentation depth (h). the microhardness (h) and young’s modulus (e) were determined from the p-h curves based on the oliver-pharr method [16]. the vickers microhardness (microindentation) of the glasses was also estimated (measurement error ± 5%) using a micro-indentation hardness testing instrument (uhl vmht, walter uhltm). for each sample, ten (10) micro-indentions were taken with a constant spacing of 10 μm under identical loading conditions (=500 g) under a 10 s dwell time [4]. the diagonal of different indents was carefully measured using an optical microscope attached to the instrument, and consequently the microhardness values were calculated using the standard equation (1) for the vickers geometry. 𝐻𝑉 = 1.854𝑃 𝑑 (1) where hv is the vickers hardness number (vhn) in kg/mm2. p is the normal load in g, d is the average diagonal length of the indentation in mm. here, the hv value obtained/100.1 = vickers hardness in gpa. 3. results and discussion in order to ensure the nucleation of chromium (cr6+) with respect to phase characterization and application of nanomaterials2024, 7(2), 6046. 4 transformation phenomena in al2o3-sio2-mgo-b2o3-k2o-f system, a nonisothermal differential scanning calorimetric (dsc) study was conducted, and the representative thermograms are shown in figure 1 [4]. the dsc pattern of asg-0cr glass exhibited in figure 1a is very different compared to the chromium-doped one, i.e., the asg-2cr system (exhibited in figure 1c). as seen from figure 1a, the characteristic endothermic hump corresponding to the glass transition region is initiated at 580–590 °c and ended towards the minimum at 625–627 ℃. from the onset of that endothermic hump, the glass transition temperature (tg) is estimated at 610 ± 2 ℃ for asg-0cr glass. in the case of the chromium-doped system, the appearance of the glass transition hump (dsc) presented in figure 1c is very different compared to asg-0cr. the hump for asg-2cr in figure 1c is insignificant to define those as amorphous material; however, the minor endothermic hump that appeared is the indication of residual al2o3-sio2-mgo-b2o3-k2o-f glassy phase [1,2]. as mentioned in the experimental section, after melting, the as-quenched glass was annealing heat-treated. after annealing, asg-2cr found crystallized. in the present system, the asg-0cr glass is not crystallized upon annealing temperature. it is a wellestablished fact that nucleation is the process by which atoms or molecules come together to form a new phase or structure, and such a process is the initial stage in the formation of a crystal and involves the formation of a small cluster of atoms or molecules, i.e., a nucleus. hence, it can be elucidated that asg-0cr is practically glass, but asg-2cr is not glass; it can be a glass-ceramic composite [8,9], and the pattern of exothermic peak broadening in figure 1c is due to a minor residual glass phase. in a similar study on boro-silicate systems, aktas et al. [8] argued that 0–1 wt% cr2o3 containing silicate glass is completely amorphous, but cr2o3 contents >1 wt% make those glass crystalline. for asg-0cr glass, the exothermic maximum (peak) is estimated at 768 ± 2 ℃, which is corresponding to crystallization temperature [9]. lin et al. [3] similarly studied dsc on cr-doped alumino-silicate glass and argued that the incorporation of cr-ion, as a modifier, can break the glass network and finally result in the decreased glass phase (i.e., si-o-si) stability. thus, from dsc it is pointed out that the asg-0cr is glass but the asg-2cr contains crystallinity [4]. the nucleation phenomena of chromium (cr6+) doped al2o3-sio2-mgo-b2o3k2o-f glass predicted from the dsc study were further confirmed from the x-ray diffraction (xrd) study [17]. xrd analysis revealed the formation of spinel phases at nucleation temperatures. as is evident from figure 1b (i.e., asg-0cr glass), the broad hump that appeared at (2θ) 20°–35° signifies the amorphous nature. in view of the dsc experiment (figure 1), it is pointed out that the catalyzed nucleation for initiating the crystallization process occurred in chromium-containing glass. thus, crystalline nature is demonstrated by asg-2cr, as depicted in figure 1d. as evident from figure 1d, the crystalline peaks that appeared at (2θ) 18°, 30°, 36°, 37°, 44°, 58° and 63° are attributed to the crystalline planes (111), (220), (311), (222), (400), (511) and (531) of the spinel phase, mgcr2o4; jcpds-pdf file number = 82–1529, fcc lattice [5]. the characteristic peaks appeared at (2θ) 18°, 30°, 36°, and 53° and are attributed to the formation of crystalline planes (101), (200), (202), and (312) of k3crf6; jcpds-pdf file number = 27–1354, tetragonal bcc lattice. asg-2cr is hence a glass-ceramic or glass-ceramic composite of multi-crystalline nature [4]. during the annealing at 600(±10) °c, mgf2 crystals are precipitated as primary characterization and application of nanomaterials2024, 7(2), 6046. 5 crystalline phase, and the characteristic peaks (2θ) 36°, 40°, 44°, 53°, and 63° are ascribed to the (101), (111), (210), (211), and (310) crystalline planes of mgf2, jcpds-pdf file number = 72–2231. another aland si-enriched crystalline phase is also developed in these glasses during annealing at 600(±10) °c. the crystalline peaks formed at (2θ) 23°, 26°, 30°, 33°, 37°, 40° and 58° correspond to the crystalline planes (200), (120), (001), (220), (130), (121) and (041) of mullite (3al2o3∙2sio2), jcpdspdf file number = 82–0037 [4]. for the asg-2cr system, the crystalline peak that appeared at (2θ) 36° is associated with the highest intensity, and that peak is ascribed to the development of the spinel phase (mgcr2o4) [4,16]. thus, from xrd, it can be clarified that through the annealing heat treatment in such al2o3-sio2-mgo-b2o3k2o-f system, the spinel phase, i.e., mgcr2o4 can be predominately obtained when using cr6+ as a nucleation agent [6–9]. the cr-controlled nucleation at annealing temperature was caused by chromium ions in the asg-2cr system, and thus the microstructures (fesem) developed in such chromium-doped glass ceramic were studied. figure 2 presents the results of experimental investigation on microstructure (size and morphology of crystalline phases) [4]. as observed in figure 2a, the randomly distributed crystallite particles throughout the matrix gathered to develop a colony-like arrangement. under higher magnification, i.e., from figure 2b, it is seen that rock-like 200-500 nm-sized crystalline particles are dispersed throughout the asg system and further lead to a compact microstructure. from the edx pattern (inset of figure 2b), the elements present in the asg-2cr matrix are made out as k, o, cr, mg, al, and si, and it confirms the development of the predominant spinel phase (mgcr2o4), as already pointed out from xrd. such fine-grained compact microstructure developed in the asg-2cr system significantly controls the mechanical parameters (microhardness, young’s mudulus, etc.) as analyzed from nanoindentation and microindentation studies [17,18]. figure 2. fesem photomicrograph of al2o3-sio2-mgo-b2o3-k2o-f glass-ceramic (asg-2cr) in (a) 10 μm; (b) 500 nm scale (inset of figure 2b presents the edx pattern of asg-2cr system) [4]. characterization and application of nanomaterials2024, 7(2), 6046. 6 the load-displacement curves and loading-unloading p-h curves from the nanoindentation tests on the studied glasses are presented in figures 3 and 4, respectively. as pointed out from xrd and fesem observations, the base al2o3-sio2-mgo-b2o3k2o-f glass (cr-0) is an amorphous system, which, on addition of chromium, was converted into the glass-ceramic, and such a similar observation is further evidenced from the load-displacement study exhibited in figure 3. figure 3. load-displacement curves exhibiting asg-0cr as glass and csg-2cr as glass-ceramic. figure 4. p-h curves from nano-indentation tests using berkovich indenter tip from al2o3-sio2-mgo-b2o3-k2o-f glasses i.e., (a) asg-0cr; (c) asg-2cr. photograph of vickers microhardness indentation impression on; (b) asg-0cr; (d) asg-2cr glasses showing the increasing crystallinity with chromium content [4]. characterization and application of nanomaterials2024, 7(2), 6046. 7 figure 4a thus represents loading-unloading p-h curve characteristics for asg0cr glass with a much higher depth of penetration for the constant load of 5 mn [4]. the low depth of penetration for asg-2cr glass-ceramics (figure 4c), on the other hand, suggests higher strength due to correspondingly higher crystallinity and compactness of the microstructures [4]. the load-displacement curve also demonstrates the trend of increasing elastic modulus. the contact depth is the depth of indenter in contact with the asg glass samples under used load p (constant load of 5 mn). when under the same load (p), a higher contact depth occurs, which means the sample is not so hard (comparatively), i.e., lower microhardness is observed [16,18]. for the asg-0cr system (glass), the depth of penetration reached to ~950 nm, whereas for asg-2cr glass-ceramics, it is ~200–250 nm. interestingly, young’s modulus and microhardness both found to increase when cr-ion was added to the base asg glass (table 1), and that is ascribed to the change in morphology of the crystal phases. table 1. depth of penetration (h), young’s modulus and microhardness measured from the nano-indentation tests on al2o3-sio2-mgo-b2o3-k2o-f glasses with and without k2cr2o7 [4]. sample contact depth (nm) young’s modulus (gpa) microhardness (gpa) asg-0cr 619 ± 195 25 ± 10 0.6 ± 0.5 asgr-2cr 139 ± 16 94 ± 21 8.4 ± 2.3 microhardness microhardness of glass/glass-ceramic materials is largely dependent on strength, crystallinity, as well as residual glass phase in the microstructure [17]. vicker’s microhardness indentation impression for the studied glasses is presented in figures 4b,d. for asg-0cr glass, the microhardness is estimated at 3.63 (±0.18) gpa, and for chromium-containing systems, it is higher due to the crystalline nature [18]. the asg-2cr matrix (figure 2) is composed of 200– 500 nm-sized crystals dispersed randomly, and such arrangements are the reason for the microhardness value of 3.94 (±0.20) gpa [12,16]. thus, the addition of cr-ion caused self-nucleation and, moreover, a significant change in the microstructure and hence the mechanical properties, i.e., contact depth, modulus, and hardness value, of the asg-2cr system [18–20]. the residual glass phase in asg-2cr is directly related to the mechanical properties of such al2o3-sio2mgo-b2o3-k2o-f glass ceramics [17,20]. this fact led to the suitability of asg-2cr glasses as a machinable glass-ceramic (macor) due to their specific microstructuredriven mechanical properties, including a microhardness of 3.94 ± 0.20 gpa [15–18]. 4. conclusions in presence of chromium ion (cr6+), self-nucleation of al2o3-sio2-mgo-b2o3k2o-f glass occurred at annealing heating 600 ± 10 ℃ only. from the xrd pattern, it is confirmed that the base glass is amorphous, whereas chromium-doped glass is crystalline with predominant phases of spinel (mgcr2o4). dense and compact microstructure containing 200–500 nm crystallites is obtained in chromium-doped al2o3-sio2-mgo-b2o3-k2o-f glass ceramic. from nano-indentation, the hardness characterization and application of nanomaterials2024, 7(2), 6046. 8 and young’s modulus for base glass were estimated 0.6(±0.5) and 25(±10) gpa, respectively, which increased in the case of chromium-doped glass ceramics. vicker’s microhardness for the base glass was 3.63(±0.18) gpa which was also increased to 3.94(±0.20) gpa for chromium-containing glass ceramic. in brief, the hexavalent chromium ion (cr6+) doping in alumino-silicate glass al2o3-sio2-mgo-b2o3-k2o-f imposed nucleation at annealing temperature and was thereby effective for improving the machinability. author contributions: conceptualization, mg; methodology, mg; data curation, mg and aar; writing—original draft preparation, mg and aar; writing—review and editing, sr. all authors have read and agreed to the published version of the manuscript. funding: the author is thankful to b. karmakar, former head, gsts, csir-central glass and ceramic research institute, kolkata for his guidance (phd thesis) to carry out this work. mg thankfully acknowledges dst-serb for financial support under the national post doctoral fellowship (n-pdf) scheme (ref no: pdf/2016/003799) at indian institute of technology (iit), kharagpur. aar is thankful for the partial support form university of tetova. conflict of interest: the authors declare no conflict of interest. references 1. zarabi golkhatmi s, asghar mi, lund pd. a review on solid oxide fuel cell durability: latest progress, mechanisms, and study tools. renewable and sustainable energy reviews. 2022; 161: 112339. doi: 10.1016/j.rser.2022.112339 2. beall gh. milestones in glass‐ceramics: a personal perspective. international journal of applied glass science. 2014; 5(2): 93-103. doi: 10.1111/ijag.12063 3. lin c, liu j, han l, et al. study on the structure, thermal and optical properties in cr2o3-incorporated mgo-al2o3-sio2b2o3 glass. journal of non-crystalline solids. 2018; 500: 235-242. 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doi:10.24294/can.v4i1.1326 original research article synthesis of zno nanometer powders doped with ce4+ ions and the photocatalytic degradation of dying wastewater guishan gu, yuanyuan zhang, chi huang, li sun, xueying wang* school of chemistry and material engineering, changshu institute of technology, changshu 215500, china. e-mail: wxy62@cslg.edu.cn abstract ce4+-doped nanometer zno powder was synthesized by sol-gel method. the microstructures and properties of the samples were characterized through xrd, uv-vis and ftir. the results indicated that the ce4+ was successfully incorporated into zno, and the diameter of the nanometer was about 10.7 nm. it induced the redshifting in the uv-vis spectra. the photocatalytic activity of the samples was investigated using methylene blue (mb) as the model reaction under irradiation with ultraviolet light. the results showed that the doping of ce4+ could increase the photocatalytic activities of zno nanopowders and that the best molar ratio of ce4+ was n(ce)/n(zn) = 0.05, that the surfactant was sodium dodecyl sulfate, and that the nanometer zno was calcinated at 550 ℃ for 3 hours. meanwhile, it inspected the effect of photocatalytic efficiency through the ph of mb, the amount of catalyst, and illumination time. the experimental results revealed that the initial mass concentration of mb was 10 mg/l, that the ph value was 7–8, that the dosage of ce4+/zno photo-catalyst was 5 g/l, that the uv-irradiation time was 2 h, and that the removal rate of mb reached above 85%. under the optimized conditions, the degradation rate of real dye wastewater was up to 87.67% and the removal efficiency of cod was 63.5%. keywords: ce4+-doped nanometer zno powder; photocatalytic degradation; methylene blue article info received: 28 december 2020 accepted: 14 february 2021 available online: 23 february 2021 copyright copyright © 2021 guishan gu, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction in recent years, with the increasing abundance of textile products, the substances that are difficult to biodegrade in printing and dyeing wastewater are increasing, resulting in the poor treatment effect of the simple biochemical process on printing and dyeing wastewater, which has become one of the important factors threatening the safety of water environment in china. azo compounds and organic compounds in printing and dyeing wastewater, the discharge of phenols and amines in wastewater seriously pollute the water environment and endanger human health[1–4]. at present, the treatment methods of dyeing wastewater mainly include adsorption, coagulation, oxidation, reduction, electrolysis, biodegradation, etc.[5] however, above methods have the disadvantages of secondary pollution and high cost. photocatalytic oxidation of organic pollutants is a new technology developed in recent years. nano zno has become the most active research direction for the elimination and degradation of organic contaminants due to many outstanding characters, such as high catalytic activity, complete degradation, carried out at room temperature and pressure, wide application range, and other advantages[6,7]. nano zno is one of the highly active photocatalysts with great application prospects because of its high effi48 ciency and non-toxic characteristics. in recent years, its preparation and performance studies have become a hot topic in the field of catalysis research[8–10]. it can be of extensive application. in this paper, zinc acetate is the raw material, ammonium ceric nitrate is dopant. then, hydrolytic and condensation reaction in organic medium so that the solution is soldered and gelatinized, and the gel is dried and burned into powder. the samples were characterized through x-ray diffraction (xrd), ultraviolet-visible spectroscopy (uv-vis), and ftir (ir). the decolorization and degradation of mb were for the model reaction. it investigated the effects of cerium doping amount, calcination temperature, and calcination time on catalytic performance. at the same time, it also studied the influence of the initial ph value of the solution, reaction time, and catalyst addition on the catalytic effect. the results show that the synthesized cerium doped nano zinc oxide powder could effectively under uv light. this experiment has the advantages of low raw material cost, easy synthesis of catalytic materials, simple operation, low requirements for equipment, and environmental protection. 2. experimental section 2.1 main reagents and instruments main instrument: tu-1901 dual-beam uv-visible spectrophotometer (beijing general instrument co., ltd.); x-ray powder diffractor (d/max-2200/ pc, rigaku corporation, japan); uv-visible spectrophotometer (shimin manufacturing institute); the fourier infrared spectral analyzer (nico-let380, shimjin manufacturing institute); nano ce/zno ggz-125 uv hp mercury lamp (200–670 nm, 125 w, shanghai yaming co., ltd.); lg10-2.4 a highspeed centrifuge (beijing leibel centrifuge co., ltd.). the reagents used were analyzed pure, cerium ammonium nitrate, zinc acetate, triethanolamine, sodium dodecyl phenyl sulfonate (sds), polyethylene glycol-400, sodium dodecyl sulfate (sdbs), sodium stearate, oxalic acid (ar, jiangsu strong chemical co., ltd.); methylene blue (ar, shanghai maikun chemical co., ltd.). 2.2 preparation of nano ce/zno dissolve 11.34 g of oxalic acid into 100 ml of absolute ethanol, then it obtains solution a. dissolve 7.859 g of zinc acetate (zn(ac)2•2h2o) into 50 ml of distilled water, then add an appropriate amount of surfactant and ceric ammonium nitrate solution to obtain solution b. then, slowly drop solution b into an under vigorous stirring, react for about 1.5 h, and keep it in a constant temperature (80 ℃) water bath for 0.5 h. it obtains the sol. the sol was washed twice with distilled water and ethanol, dried in an 80 ℃ drying oven for 2 h, calcined in a muffle furnace for a certain time, cooled and ground, and finally prepared the sample. except that ceric ammonium nitrate solution should not be added, the nano zno was prepared according to the above steps. 2.3 characterization of nano ce/zno the crystal phase of the product was analyzed by xrd and scherrer formula [d(hkl) = kλ/βcosθ]. the average grain size of the sample was calculated, the uv absorption spectrum of nanomaterials was measured by uv-vis spectrophotometer, and the infrared spectrum of ce/zno crystal was measured by fourier infrared spectrum analysis. 2.4 determination of the photocatalytic degradation efficiency of 1.4 nano ce/zno weigh some amount of photocatalyst, add it to mb solution of 20 ml 10 mg/l, stir and degrade it for some time under uv irradiation, take a certain volume of solution and centrifuge it in a centrifuge tube at high speed for 5 min, take the supernatant, analyze and measure it with uv-1901 uv-v is spectrophotometer. during measurement, take distilled water as blank and measure the absorbance at 665 nm, that is, the absorbance of the liquid sample a at this time. set the absorbance of mb solution without catalyst at 665 nm as a0, and calculate the degradation rate according to the following formula. d% = (a0-a)/a0 × 100% 49 3. experimental results and discussion 3.1 characterization of nano ce/zno 3.1.1 xrd analyses figure 1 shows the xrd spectra of pure nanoscale zno prepared with doped cerium nanosize znon(ce): n(zn) = 0.05 under optimal conditions. as shown from figure 1, all diffraction peaks are sharp, indicating that the well crystalline generated under this condition[11]. compared to the standard map, it should be hexagonal, and the peaks became slightly wider after doping, but no cerium oxide peak was observed, indicating the incorporation of ce into zno. the particle size of ce/zno was approximately 10.7 nm, while undoped nano zno was about 17 nm. figure 1. xrd patterns of nano zno and ce/zno. 3.1.2 ultraviolet analysis figure 2 shows the uv absorption spectra of pure zno and cerium-doped zinc oxide prepared under optimal conditions. as shown from figure 2, the absorption intensity of the nano zinc oxide doped uv region is much higher than the undoped nano zinc oxide with a small redshift in the uv peak, indicating successful incorporation of rare earth ce ions into the zno lattice and a better crystal mass[12,13]. figure 2. uv spectra of ce4+/zno and zno. 3.1.3 infrared spectrum analysis it can be seen from the infrared spectrum of figure 3 that there is a strong absorption peak around 430 cm–1, which is the skeleton peak of zno, indicating that it got zno after calcination[14]. there is a wide absorption peak at 3380–3600 cm–1, and it is caused by the stretching vibration of -oh group that forms intermolecular hydrogen bond, indicating that there is strong adsorbed water on the surface of small-size ce/zno nanoparticles. the adsorption activity is high, which is conducive to improving the photocatalytic properties of ce/zno. figure 3. infrared spectro spectra (ft-ir) plots of nano zinc oxide doped with cerium. 3.2 optimization of the preparation conditions for the nanoscale ce/zno 3.2.1 effect of the different doping ratios on the photocatalytic properties weigh 0.1000 g of zno (n(ce):n(zn) = 0, 0.01, 50 0.05, 0.10, 0.20) respectively, use sodium dodecyl sulfonate as surfactant, add the catalyst with calcination temperature of 550 ℃ and calcination time of 3 h to 20 ml of 10 mg/l mb solution, and irradiate it under uv lamp for 2 h. then centrifuge the reaction solution at high speed and take the supernatant. the absorption spectrum and absorbance were measured with an ultraviolet spectrometer. the absorbance at 665 nm was measured with distilled water as blank. the experimental results are shown in figure 4. as can be seen from figure 4, when n(ce): n(zn) = 0.05, the effect of nano zinc oxide on mb reached the maximum degradation, and the degradation rate of mb was about 26.27%, higher than that of pure zinc oxide. the possible reason is that some ce4+ ions enter the zno lattice during heat treatment, which result in local lattice defects and charges imbalance. to achieve charge balance, some ohwill be adsorbed on the surface of the catalyst, which can combine with holes generated under uv irradiation to form •oh, which can react with the adsorbed substances on the surface. in addition, some ce4+ ions cover the surface of zno grains in the form of small clusters of ceo2, while ce4+ ions can generate electron-hole pairs under uv excitation, which may play the synergism with the generation of electron-hole pairs by photocatalysts[16]. the doped photocatalyst also has a strong adsorption capacity for photons, promotes the migration of photons to the catalyst surface, prevents the simple recombination of electron-hole pairs, and improves photocatalytic efficiency. however, when the content of ce4+ further increases, ceo2 covers part of the surface of zinc oxide nanoparticles, affecting the light absorption of zinc oxide[17]. therefore, the optimal doping degree of cerium is n(ce): n(zn) = 0.05. figure 4. effect of cerium doping on the catalytic properties of zinc oxide nanomaterials. 3.2.2 effect of different calcination temperatures on the photocatalytic degradation effects figure 5 shows the photocatalytic activity of cerium doped zinc oxide nanoparticles obtained at different calcination temperatures (450–650 ℃) under ultraviolet light. it can be seen from the figure that the catalytic activity of cerium doped zinc oxide nanoparticles obtained at 550 ℃ under ultraviolet light is the highest, and the degradation rate of mb is the highest at 2 h. the calcination temperature affects the photocatalytic performance of nano zinc oxide. in the temperature range of 500–600 ℃, the catalyst has a good degradation effect on mb, but 550 ℃ is the highest, and the degradation rate decreases rapidly when it exceeds 600 ℃. it may be that the nano zinc oxide crystal obtained at 550 ℃ develops best, and with the further increase of temperature, the growth rate of the zno crystal nucleus is accelerated, resulting in the bigger particle size and agglomeration in some parts[15]. the particle increases while the specific surface area decreases, resulting in the decline of photocatalytic performance. therefore, the calcination temperature is 550 ℃. figure 5. effect of the calcination temperature on the photocatalytic activity of the cerium-doped nanoscale zno. 3.2.3 effect of different calcination times on the photocatalytic properties figure 6 shows the photocatalytic activity of cerium doped zinc oxide nanoparticles under ultraviolet light when n(ce): n(zn) = 0.05, the surfactant is sds, the calcination temperature is 550 ℃, and 51 calcination time is different. it shows from the figure that the calcination time is in the range of 3–3.5 h, and the degradation rate of mb reaches about 85%. because the longer the calcination time, the more small grains will be formed by the precursor. if burning time is too short, the precursor can not sufficiently decompose. thus, the particle size of the product is coarse. therefore, when the time is 3.0 h, the precursor can sufficiently decompose, and there are not too large grains, so the photocatalytic degradation efficiency is the highest. 3.2.4 the effect of different surfactants taking n(ce): n(zn) = 0.05, calcination temperature 550 ℃, calcination time 3.0 h, adding a small amount of different surfactants, the prepared catalyst is 0.1 g, and adding 20 ml 10 mg/l mb for catalytic degradation for 2 h. the experimental results show that the catalyst prepared by adding a small amount of triethanolamine and sodium dodecyl sulfonate has a good effect on the degradation of mb. it can effectively reduce the agglomeration of nano zinc oxide, but considering the impact on the environment, the selected surfactant is sodium dodecyl sulfonate[18]. in summary, the doping degree of ce is n(ce) : n(zn) = 0.05, the burning temperature is 550 ℃, the burning time is 3.0 h, and the surfactant is sodium dodecyl sulfonate, is the optimum conditions for the synthesis of the photocatalyst. figure 6. effect of burning time on the photocatalytic properties of nano ce/zno. 3.3 optimization of mb degradation conditions 3.3.1 effect of the initial ph values of the dye solution on the catalytic degradation take 8 parts of 20 ml and 10 mg/l mb solution, adjust the ph values of the solution to 3, 4, 5, 6, 7, 8, 9 and 10 with 1 mol/l hcl and naoh individually, add 0.1000 g catalyst, and carry out photocatalytic degradation for 2 h. the experimental results are as in figure 7. it shows from figure 7 that cerium doped zno has a high degradation rate of mb under neutral and alkaline conditions, but a low degradation rate under acidic conditions. however, when ph = 4, the degradation rate suddenly increases and then decreases. it may be due to that the change of catalyst surface charge caused by the change of ph value and affecting the adsorption behavior on the catalyst surface[19,20]. mb (c16h18n3s +) is a cationic dye. under acidic conditions, mb molecules cannot be effectively adsorbed on the catalyst surface, resulting in low photocatalytic capacity. under alkaline conditions, ohcan trap holes, and the generated ▪oh harms photocatalytic degradation. solution plays a vital role. with the increase of ph value, the oh content in the solution increases, and the adsorption ability of mb enhances. the combined action of the two makes mb have a high photocatalytic degradation rate under alkaline conditions[21]. excessive acidity and alkalinity may cause changes in the structure of nano zno, which is not conducive to photocatalytic degradation. therefore, the ph value of photocatalytic degradation of mb is 7. figure 7. effect of initial ph on mb degradation rate. 52 3.3.2 effect of the catalyst dosage on the photocatalytic degradation of mb under the conditions of mb solution concentration of 10 mg/l, ph = 7 and photocatalyst dosage of 1 g/l, 2 g/l, 3 g/l, 5 g/l, 7 g/l and 10 g/l individually, it studied the effect of catalyst dosage on the degradation rate of mb solution. it shows from figure 8 that the photocatalytic degradation efficiency of mb increased rapidly with the increase of catalyst dosage in the range of 1–5 g/l. when the dosage exceeds 5 g/l, the increase decreases. if the dosage of nanocatalyst continues to increase, the photocatalytic degradation efficiency of mb decreases. the reason is that when the dose of catalyst is small, it cannot utilize the light energy adequately, and the carrier produces less. with the increase of the dose of catalyzer, it means more electron-hole pairs form, which accelerates the photocatalytic reaction when the amount of catalyst reaches. at 7 g/l, the degradation rate reaches the maximum. however, when the number of catalyzers increases to a certain extent, the excessive catalyzers will cause light scattering, coupled with the shielding effect between catalyst particles, so that photons cannot be used effectively, resulting in the decline of photocatalytic degradation rate[22]. considering the cost and environmental effects, the amount of catalyst is 5 g/l. figure 8. effect of the catalyst dosage on the photocatalytic degradation of methylene blue. 3.3.3 effect of light time on the photocatalytic degradation of mb weigh 6 parts of 0.1000 g catalyst, add 20 ml of 10 mg/l mb solution with a ph value of 7 respectively, and stir with the magnetic force for 20 min, 40 min, 60 min, 90 min, 120 min, and 150 min under the irradiation of uv light to investigate the influence of illumination time on the catalytic effect. the results show in figure 9. it shows that in the initial stage of photocatalysis, the catalyst degradation rate of mb increases rapidly. when the photocatalytic time exceeds 60 min, the increased degradation rate slows down. it is mainly due to the strong adsorption capacity of nano materials for mb in the initial stage and more active sites on the catalyst surface, so the photocatalytic efficiency increases rapidly. with the extension of photocatalytic time, the oxygen molecules in water constantly capture electrons, and the final generation with the amount of highly active superoxide anion (o2-) and hydroxyl radical (oh) also increased. therefore, the degradation rate increased with the extension of illumination time, but the adsorption of nanomaterials gradually became saturated during the reaction. some intermediates accumulated in nanomaterials and occupied some active sites, resulting in the reduction of photocatalytic efficiency of photocatalysts. therefore, the increase of degradation rate slows down, that is the cause the degradation time is 2 h. in conclusion, the optimum conditions for photocatalytic degradation are as follows: ph is neutral or weakly alkaline, catalyst mass is 5 g/l, and illumination time is about 2 h. figure 9. effect of light time on ce/zno photocatalytic methylene blue. 53 3.4 practical application of the photocatalyst it measured the actual dye wastewater in the experiment. the dye wastewater from a printing and dyeing enterprise was taken, and the decolorization rate and codcr removal rate were measured by photocatalytic degradation method and national standard method separately. put 100 ml of the diluted wastewater into a beaker, add 0.5000 g of self-made ce/ zno catalyst, adjust the ph value to 7, and stir the reaction under uv light for 2 hours. measure the decolorization rate and codcr removal rate separately. the decolorization rate was 87.67%, the codcr removal rate was 63.5%. after 2 hours of light degradation, the dye wastewater is almost colorless, but the cod value is still high. it speculates that the organic dye molecules may not completely convert into small molecule inorganic substances in the process of light degradation. how to improve the removal efficiency of cod by photocatalyst needs further research. 4. conclusion a. characterized by xrd, uv-vis and ftir, the particle size of ce/zno nanopowder prepared in this experiment is smaller than that of pure nano zno. the absorption ability in the uv-vis region is stronger and moves to the visible region. the broad absorption peak at 3380–3600 cm–1 shows that there is strong adsorbed water on the surface of ce/zno nanoparticles and high adsorption activity. these properties will help to improve the photocatalytic ability of ce doped nano zno. b. taking mb as the photocatalytic model, the effects of cerium doping, calcination temperature and calcination time on photocatalytic performance were studied. the results showed that the degradation of mb by nano zno reached the maximum when n(ce): n(zn) = 0.05, calcination temperature 550 ℃, calcination time 3.0 h and surfactant sds. c. it studied the effects of ph value, photocatalyst dosage, and photocatalytic time on the photocatalytic degradation of mb by ce/zno nanoparticles. the results showed that the initial ph value of mb had more influence on the degradation rate, and the degradation efficiency was higher under neutral and weak alkaline conditions. however, the hydrolysis rate is lower in strong acids. the dosage of catalyst also affects the degradation. when the dosage of catalyzers reaches 5 g/l, the catalytic efficiency is higher. the light application time also has an impact on the degradation. the changing trend shows more growth rate in the initial stage, and the increase slows down after 1 h of reaction. the longer the time is, the higher the degradation rate is. in view of the cost, the time should be 2 h after the reaction starts. d. the composition of the actual dye wastewater is complex. the decolorization rate is 87.67% and the codcr removal rate is 63.5% when it is catalyzed by ce/zno nano photocatalyst under ultraviolet light for 2 h. conflict 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bis(crown ether)s and cbpqt4+ salt: ion-controlled switchable processes and changeable role of the cbpqt4+ in host-guest systems. journal of organic chemistry 2011; 76(6): 1644– 1652. review article on polymeric nanoparticle final work 20240304 characterization and application of nanomaterials 2025, 8(1), 10219. https://doi.org/10.24294/can10219 1 article enzymatic electrochemical biosensor for detection of l-cysteine based on reduced graphene oxide modified glassy carbon electrode neeta ukirade pratibha college of commerce and computer studies, pune 411019, india; nitugatkal@gmail.com abstract: cysteine is one of the body’s essential amino acids to build proteins. for the early diagnosis of a number of diseases and biological issues, l-cysteine (l-cys) is essential. our study presents an electrochemical sensor that detects l-cysteine by immobilizing the horseradish peroxidase (hrp) enzyme on a reduced graphene oxide (gce) modified glassy carbon electrode. the morphologies and chemical compositions of synthesized materials were examined using fourier transform infrared spectroscopy (ftir) and field-emission scanning electron microscopy (fesem). the modified electrode’s electrochemical behavior was investigated using cyclic voltammetry (cv). cyclic voltammetry demonstrated hrp/rgo/gce has better electrocatalytic activity than bare gce in the oxidation of lcysteine oxidation in a solution of acetate buffer. the electrochemical sensor had a broad linear range of 0 µm to 1 mm, a 0.32 µm detection limit, and a sensitivity of 6.08 μa μm−1 cm−2. the developed sensor was successfully used for the l-cysteine detection in a real blood sample with good results. keywords: l-cysteine; enzyme; graphene oxide; electrochemical sensor; cyclic voltammetry 1. introduction the human body is composed of numerous biomolecules that are essential for various physiological functions. biomolecules such as nucleic acids, carbohydrates, proteins, and amino acids are substances produced by living organisms and cells that perform a wide range of functions. detection of the biomarkers associated with the diseases should be known and is possible by using biosensors. cysteine (cys) is an important amino acid used in the body and can also be taken as a supplement in the form of n-acetyl-l-cysteine. the detection of cysteine in biological samples has been the focus of numerous research efforts, as it plays an important role in many physiological processes [1]. cys is often found in blood plasma in concentrations ranging from 53 to 300 mm, and it can be used as a key marker of health and disease risk. cys insufficiency also causes skin lesions, hair depigmentation, edema, liver damage, muscle and fat loss, fatigue, and tiredness in addition to slower body growth. as a result, neurological pathogeneses, cystinosis, parkinson’s and alzheimer’s illnesses, and metabolic problems have all been linked to aberrant cys accumulation and production. therefore, developing rapid, low-cost, dependable, and sensitive analytical techniques to detect cys would be crucial for protein quantification as well as for the early detection and prevention of neurological conditions, including parkinson’s and alzheimer’s illnesses as well as motor neuron disease [2]. to detect cysteine, various methods can be used, such as capillary electrophoresis (ce) [3], high-performance liquid chromatography (hplc) [4], chemiluminescence [5], fluorescent probes [6], colorimetric [7], and electrochemical methods [8–10]. these citation ukirade n. enzymatic electrochemical biosensor for detection of l-cysteine based on reduced graphene oxide modified glassy carbon electrode. characterization and application of nanomaterials. 2025; 8(1): 10219. https://doi.org/10.24294/can10219 article info received: 23 december 2024 accepted: 25 january 2025 available online: 10 march 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 10219. 2 techniques allow for the sensitive as well as accurate detection of cysteine in biological samples. however, the aforementioned recognized methods are almost solely used in a rigorous lab environment, which is time demanding and requires a professional operator and expensive equipment [11,12]. electrochemical techniques were recently thought to be the most practical because of their low cost, fast responsiveness, low detection limit, and great sensitivity [13,14]. many studies on the electrochemical determination of cys in various modified electrodes have been undertaken, for example, carbon-based electrodes [15–17], metal modified electrodes [18–20], polymer-modified electrodes [21,22]. several electrochemical methods have been used to detect cys. the electrochemical techniques used to detect cys in an aqueous solution have been categorized based on the many electrical signals that cys produces in the solution. voltammetric techniques such as cyclic voltammetry (cv), differential pulse voltammetry (dpv), square wave voltammetry (swv), linear sweep voltammetry (lsv), and others are highly suitable due to their high sensitivity, short analysis times, low level of detection (lod), and low cost of equipment [23–25]. furthermore, materials with enhanced surface conductivity were integrated into the sensor design to improve sensitivity and selectivity. nanomaterial based electrochemical signal amplifications have enormous promise to improve both sensitivity and selectivity for electrochemical sensors and biosensors, with notable advancements in nanotechnology and nanoscience. in addition to metal nanoparticles, carbon-based materials (such as carbon nanotubes and graphene and its derivatives) have also gained a lot of attention in the development of electrochemical sensing platforms. this is primarily because of their advantageous properties, which include high surface area, excellent electrical conductivity, high mechanical strength, excellent performance and thermal stability [26,27]. enzymes are large, intricate macromolecules that catalyze the rapid conversion of substrates into products; they are primarily composed of proteins. enzyme-based electrochemical biosensors find extensive use in various fields such as healthcare, food safety, environmental monitoring. an enzyme-based biosensor uses the enzyme as the recognition element; to preserve enzyme activity, the enzyme is immobilized on or within the transducer surface’s support matrix. immobilized enzymes act as electrocatalysts, facilitating electron transfer between the electrode and the substrate molecule, leading to signal amplification and improved detection limits. designing the biorecognition component of enzymatic biosensors requires careful consideration of the immobilization of enzymes. numerous studies on enzyme immobilization methods, including entrapment, covalence, adsorption, affinity, and cross-linking, have been published [28–30]. in this study, we used an enzyme electrochemical biosensor based on horseradish peroxidase to investigate electrochemical properties cys. firstly, we have synthesized rgo which was electrodeposited onto the bare gce’s surface. and horseradish peroxidase enzyme was then immobilized on the electrode surface using a gelatin membrane that was then cross-linked with glutaraldehyde. for the measurement of l-cysteine, the suggested sensor demonstrated great sensitivity, good biocompatibility, and a low detection limit. graphene’s huge specific surface area makes it an excellent substrate for providing a large number of catalytic active characterization and application of nanomaterials 2025, 8(1), 10219. 3 sites. the designed electrode (horseradish peroxidase/rgo/gce) showed high selectivity for determination of cys. 2. materials and methods 2.1. chemicals and apparatus l-cysteine, l-ascorbic acid, hydrochloride, dopamine, nafion solution, uric acid and palladium (ii) nitrate dihydrate phosphate buffer (pb) solution, horseradish peroxidase, gluteraldehyde were purchased from sigma-aldrich (usa). graphite powder potassium permanganate sulfuric acid (99.99%), hydrochloric acid, sodium nitrate, were purchased from merck company (germany). all other compounds were analytical reagent grade and all solutions were made with double distilled water. the electrolyte used as the backdrop was phosphate buffer solution of 0.1 m (pbs, ph 7). a potentiostat (chi-1205b) was used for all of the cyclic voltammetry (cv) experiments. the frequency response analysis (fra) module of a potentiostat was used to perform the electrochemical impedance spectroscopy (eis) measurements. for the electrochemical measurements, a standard threeelectrode cell assembly made up of a pt wire counter electrode and an ag/agcl reference electrode was used. the working electrode was modified gce. 2.2. electrode preparation the bare gc electrode was polished using alumina slurry at a thickness of 1, 0.3, and 0.05 μm respectively followed by washing with di water, isopropanol, and finally sonication in di water. graphene oxide (go) was synthesized by modified hummer’s method [31]. furthermore, the synthesized go reduced by annealing at 200, 300 and 400 ℃. after being thermally treated to become rgo powder, the dark brown powder turned to black [32]. then 1 mg/ml of prepared rgo was dissolved in deionized water using an ultrasonicator. subsequently, 5 μl rgo of the suspension was applied using the drop casting technique to the gce surface, and it was allowed to dry for one hour at room temperature to produce the rgo modified gce. in the next step, horseradish peroxidase was immobilized onto rgo/gce. this was accomplished by diluting 1 mg of horseradish peroxidase in 1 ml of phosphate buffer solution (ph 7.0). they then combined 12 mg of gelatin and 4 u of horseradish peroxidase in 100 µl of potassium phosphate buffer (ph 7.0) at 38 ℃ the modified electrode surface was then covered with 0.25µl of the mixed solution, which was let to dry for one hour at 4 ℃. lastly, it was submerged for 5 min in a phosphate buffer (50 mm, ph 7.0) containing 2.5% glutaraldehyde to facilitate cross-linking. the films were further used to study electrochemical characteristics by voltammetry (cv). 3. results and discussion 3.1. characterization of hrp/rgo nanocomposite 3.1.1. morphological studies characterization and application of nanomaterials 2025, 8(1), 10219. 4 surface morphology of the samples was observed by using field emission scanning electron microscopy (fesem). figure 1 shows fesem of figure 1a rgo nanosheet and figure 1b hrp/rgo surface. the result revealed that rgo exhibits a translucent, wrinkled-type, ultrathin, and flexible, sheet-like morphology. however, in case of rgo/gce, a spherical like beads is spread over the surface as shown in figure 1b. the result revealed that rgo proved to be an excellent carrier support for hrp immobilization. (a) characterization and application of nanomaterials 2025, 8(1), 10219. 5 (b) figure 1. fesem images of (a) rgo; (b) hrp/rgo. 3.1.2. fourier transform infrared spectroscopy (ftir) fourier-transform infrared spectroscopy (ftir) is a potent analytical method which is commonly used to study the chemical composition and bonding of materials. figure 2 shows the ftir spectra in the range from 4000 to 800 cm−1). in the case of reduced graphene oxide (rgo), ftir can provide information on the functional groups present on the rgo surface. the peaks visible at 3454 cm−1, 1591 cm−1, 1220 cm−1 corresponding to the o-h stretching, o-h stretching, c = o stretching, and c-o stretching vibration suggesting that the graphene was oxidised and the product rgo could be successfully dispersed in water. the alkyl (-ch2) chains’ o-h vibration modes are responsible for the observed spectrum areas at 3380 cm−1 and 2920 cm−1. peaks at 1651 cm−1 assigned to the amide i, while aliphatic amines (c–n stretching vibration) assign at the region 1045 cm−1. the ftir spectrum of rgo-hrp showed that hrp was successfully immobilized onto rgo due to presence of characteristic peaks of hrp and the rgo. characterization and application of nanomaterials 2025, 8(1), 10219. 6 figure 2. fourier transform infrared spectroscopy (ftir) spectra of rgo and hrp/rgo. 3.2. electrochemical characterization of modified electrode the electrochemical behavior of the various electrodes was examined by using cv at 40 mv scan rate in a 5 mm [fe (cn)6]3−/4− solution made in 0.1 m kcl solution. the chosen scanning speed for the cyclic voltammetry (cv) measurements was 40 mv/s. this value was selected based on a balance between achieving good signal resolution and maintaining reasonable experimental time. cyclic voltammograms (cvs) of bare gce and modified gce are shown in figure 3a the cv of the bare gce initially showed a 1:1 ratio between the anodic and cathodic peak currents and well-defined redox peaks showed related to the reversible redox behavior of [fe (cn)6]3−/4−. after the modification of gce with rgo, redox peak currents increase potentially as a result of semiconducting elements present. additionally, compared to rgo/gce electrode, the modified hrp/ rgo/gce electrode showed significantly higher peak current, due to presence of hrp enzyme. electrochemical impedance spectroscopy (eis) was used to examine the electron transfer properties of these electrodes. the electrode/electrolyte’s electrontransfer resistance rct is represented by the diameter of the semicircle in the eis nyquist plot. figure 3b shows eis of a) gce, b) rgo/gce, c) hrp/rgo/gce in in 0.1 m kcl with 5 mm [fe (cn)6]3−/4−. the bare gce exhibited a ret of (310.5 ω). a noticeable drop in resistance (267.6 ω) was seen when the rgo was modified in the gce. this was caused by the faster electron transport of fe[(cn)6]3−/4− from the rgo to the electrode surface. however, the the modified electrode hrp/rgo/gce had a lowest ret of 89.2 ω and hence it shows the highest conductivity. characterization and application of nanomaterials 2025, 8(1), 10219. 7 (a) (b) figure 3. (a) a cyclic voltammetry of modified electrodes in 0.1 m kcl containing 5 mm [fe (cn)6]3−/4− at a scan rate 40 mv/s; (b) nyquist plots for various modified electrodes in 0.1 m kcl with 5 mm [fe (cn)6]3−/4−. frequency range: 0.1 hz to 10 hz. 3.3. effect of scan rate to assess the behavior of l-cys electrocatalytic oxidation on the hrp/rgo/gce modified electrode, cvs were obtained at various scan rates using 0.1 m pb solution containing 200 μm l-cys. the peak current density rises as the scan rate is increased from 10 to 100 mv.s−1. as shown in figure 4. there is a linear connection between the square root of the scan rate and the peak current density with r2 = 0.9958. this suggests that the electrocatalytic oxidation of l-cys is a diffusion-controlled electron transfer process on the modified electrode. (a) (b) figure 4. (a) cv of the hrp/rgo/gce under different scan rates (10 to 100 mvs−1) in 0.5 mm cys; (b) relation between scan rate and peak current. characterization and application of nanomaterials 2025, 8(1), 10219. 8 3.4. electrocatalytic oxidation of l-cysteine to assess the catalytic response of the hrp/rgo/gce modified electrode to the oxidation of l-cys, as shown in figure 5a. a series of cv were recorded for various l-cys concentrations. the results reveled that as the l-cys concentration increases; current density also increases, providing more evidence of the electrode’s electrocatalytic activity toward the oxidation of l-cys. as seen in figure 5b, the sensor shows high linearity in the concentration range of 0 μm to 1 mm with a correlation coefficient (r2) of 0.9992. there is a linear relationship between the concentration of l-cys and the current density of l-cys. the sensor achieved a sensitivity of 6.08 μa.μm−1cm−2 with a lod of 0.32 μm and quick response time demonstrates the hrp/rgo/gce’s promising catalytic activity toward l-cys. for comparison, the detecting parameters based on different reported-nanomaterials with the proposed sensor in this study were listed in table 1. (a) (b) figure 5. (a) cv of a modified electrode scanning at a rate of 40 mvs−1 in a phosphate buffer with varying l-cys concentrations; (b) peak current against l-cys concentration calibration plot 3.5. 3.5. interference study the applied voltage has a significant impact on the selectivity and sensitivity of the electrochemical sensors. figure 6 shows the electrochemical oxidation of 100 μm of various species aa, ua, da, glucose and l-cysteine of 10 μm individually at ph 7.0 with a scan rate of 40 mvs−1 at different applied potentials by cv. the anodic peak is evidently the primary difference, since the catalytic current of lcysteine oxidation peaked at the applied potential v, indicating that the applied voltage affects the sensor’s selectivity. almost no interference was observed in the presence of these foreign species. these findings indicated that aa, ua, da, glucose did not significantly interfere with l-cysteine determination, and that this electrode has the potential to be employed for l-cysteine sensing in the presence of aa, ua, da, glucose. these findings thus imply that the sensor electrode has outstanding selectivity for l-cys detection. the reproducibility of the sensor was examined using four identical hrp/go/gce sensors. the cv responses to 10μm characterization and application of nanomaterials 2025, 8(1), 10219. 9 l-cys indicated no obvious current change among the four electrodes. the sensor’s strong repeatability was confirmed by the 1.5% rsd value. cv from five successive measurements on a single electrode was used to assess repeatability, and the results were compared to the original value. after five iterations of measurements, the sensor maintains 94.2% of the original value. the electrode demonstrated 90% recovery with an rsd of 4.03% for lcys detection after 8 days, indicating the sensor’s strong stability. figure 6. the electrochemical oxidation of 100 μm of some species (aa, ua, da, glucose and l-cysteine) at ph 7.0 with scan rate 40 mv/s by cv technique. table 1. comparison of the analytical performance of hrp/go/gce sensor with some carbon-based earlier sensors for the detection of cys. sr. no modified electrodes linear range (μm) limit of detection (μm) references 1 cufe2o4/rgo–au 50–200; 0–15,000 0.383; 0.598 [33] 2 20%pd@ti3c2tx/gce 0.5–10 0.14 [34] 3 pt-fe3o4-rgo/gce 100–1000 10.1 [35] 4 cohcf/gce 6–1000 1.5–200 4 [36] 5 rgo-nafion@pd6/gce 0.5–10 0.15 [37] 6 aunr/mwcnt/gce 5–200 0.008 [38] 7 hrp /rgo/gce 0–1000 0.32 this work 4. conclusions the electroanalytical measurement of cysteine was carried out using horseradish peroxidase (hrp) enzyme immobilized on a modified glassy carbon electrode (gce) using graphene oxide where electrocatalytic oxidation was observed to occur at a lower overpotential when compared to bare gce. this sensor apparatus offered a quick response, a good lod, and great selectivity. in addition, the sensor demonstrated good reproducibility, repeatability, and stability. lastly, the characterization 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conformational switch by secm. sensors and actuators b: chemical. 2023; 393: 134193. doi: 10.1016/j.snb.2023.134193 characterization and application of nanomaterials 2025, 8(2), 11021. https://doi.org/10.24294/can11021 1 article tracking the thermostimulated transformations of silicon suboxide film through absorption edge characterization mykola sopinskyy*, ivan indutnyi, katerina michailovska, volodymyr yukhymchuk v. lashkaryov institute of semiconductor physics, national academy of sciences of ukraine, kyiv 03028, ukraine * corresponding author: mykola sopinskyy, sopinskyy@ua.fm, sopinsky@isp.kiev.ua abstract: in this work, the structural transformations of a suboxide vacuum-deposited film of sio1.3 composition annealed in an inert atmosphere in a wide temperature range of 100 °c– 1100 °c were characterized by the reflection-transmission spectroscopy technique. the experimental spectroscopic data were used to obtain the spectra of the absorption coefficient α(hν) in the absorption edge region of the film. based on their processing, the dependences of urbach energy eu and optical (tauc) bandgap eo on the annealing temperature were obtained. an assessment of the electronic band gap (mobility gap) eg was also carried out. analysis of these dependences allowed us to trace dynamics of thermally stimulated disproportionation of the suboxide film and the features of the formation of nanocomposites consisting of amorphous and/or crystalline silicon nanoparticles in an oxide matrix. keywords: non-stoichiometric silicon oxide; siox; nanocomposite; silicon nanoparticles; absorption edge; optical band gap; electronic band gap; mobility gap; urbach energy 1. introduction silicon suboxide (siox, x < 2) films have been the subject of intensive research for several decades. at an early stage, these studies were mainly driven by the widespread use of such films as passive, insulating, and anti-reflective coatings [1,2]. in recent years, non-stoichiometric silicon oxides, both amorphous and crystalline, have attracted increasing attention for both scientific and technological reasons [3–5]. one of these reasons is that high-temperature phase separation of non-stoichiometric siox films is a key method for the formation of composite structures consisting of nanoscale silicon inclusions (amorphous or crystalline) embedded in a silicon oxide matrix [4–9]. the interest in structures with nanoparticles is due to the unique properties of these structures, which can be radically different from the properties of massive homogeneous materials. and silicon nanostructures are one of the three most convenient building blocks of nanotechnology, along with gold and carbon nanostructures [10]. silicon oxide—nanosilicon composites are of particular interest [11–16] because of their promising use in modern photonic, optoelectronic, and photovoltaic devices; flash memory devices; as field emission cathodes; etc. that are compatible with the mainstream microelectronics technology. furthermore, non-stoichiometric siox films show great potential for applications in nonvolatile resistive random access memory (rram, reram) [17,18]. these advanced devices operate by switching between high and low resistance states when a voltage is applied to a metal-insulator-metal (m-i-m) memory cell. the development of rram devices based on siox films could potentially lead to the low-cost integration of such cells into chips fabricated using silicon-based complementary citation sopinskyy m, indutnyi i, michailovska k, yukhymchuk v. tracking the thermostimulated transformations of silicon suboxide film through absorption edge characterization. characterization and application of nanomaterials. 2025; 8(2): 11021. https://doi.org/10.24294/can11021 article info received: 23 december 2024 accepted: 18 march 2025 available online: 6 may 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 11021. 2 metal-oxide-semiconductor (cmos) technology. the possibility of using rram devices based on siox films as electronic synapses in neuromorphic computing has also been demonstrated [19]. large variations in the structural topology of siox films with low-energy topological defects provide the structural complexity necessary for the implementation of a new, relatively simple, and reliable method for information encryption, storage, and user identification. this method uses a physical key known as the ‘physical unclonable function’ [20]. the results of theoretical calculations performed in [20] indicate that siox films with a stoichiometry index of x ~ 1.3–1.5 are the most promising in this regard. a review of the above works allows us to conclude that understanding the structure and properties of silicon suboxide is, on the one hand, a scientific problem of some complexity and, on the other hand, of great practical importance. in this work, the near-edge absorption spectra of vacuum-deposited films of sio1.3 composition, both as-deposited and annealed at temperatures from 100 c to 1100 c, are studied in more detail using the reflection-transmission technique and analytical processing of the experimental results. we chose the specific temperature range for annealing the samples because structural transformations occur in non-stoichiometric siox films at these temperatures. specifically, detailed studies using xrd, hrtem, raman, ir, and esr spectral techniques [21−24] have shown that during low-temperature annealing, the broken bonds of silicon and oxygen are healed, and the film becomes compacted. when the annealing temperature exceeds 500 c−600 °c, amorphous si nanoinclusions are formed and then enlarged, with subsequent crystallization occurring at temperatures above 1000 °c. these structural transformations in the siox layers lead to the observed changes in their optical properties, which are studied in detail in this paper. 2. materials and methods siox films with a ~0.5 m thickness were simultaneously deposited at a rate of 8 nm/s on ten 10  10  1 mm polished fused quartz substrates heated to td = 100 c by thermal evaporation of 99.9% pure silicon monoxide sio powder (cerac inc., milwaukee, wi, usa) in vacuum at a residual pressure of (1–2) × 10−5 torr. the deposition rate and thickness of the deposited films were controlled using a quartzcrystal microbalance thickness gauge (kit-1) calibrated with an mii-4 microinterferometer. the films were annealed for 15 min in a nitrogen atmosphere at temperatures tan = 100 °c–1100 °c. the thicknesses of the resulting films were measured with an accuracy of 5 nm using a lef-3-m1 laser ellipsometer. the details of the used methodology can be found in the works [6,25]. the transmission t and reflection r spectra of these samples before and after annealing were measured in the wavelength range  = 400–750 nm (photon energy hν = 1.65–3.10 ev) using an apparatus based on the mdr-23 diffraction monochromator. the stoichiometry index x of the deposited films was evaluated using infrared spectroscopy performed on films deposited in the same vacuum cycle on doublepolished silicon wafers. the method for determining x using ir spectral measurements is described in [26]; for our samples, the value x = 1.3 was obtained. characterization and application of nanomaterials 2025, 8(2), 11021. 3 3. results and discussion figure 1 illustrates the spectral evolution of the absorptance, a = (1 − r − t), both prior to and following the annealing. there is an increase in a from 0.014−0.12 at the long-wave edge of the measuring range to 0.84−0.92 at its short-wave edge. the difference between a and 1 at the short-wave edge of the range is almost entirely due to the value of r, i.e., there is almost no transmission here. figure 1 also shows that the growth of tan in the range 300 °c–500 °c gradually shifts the absorption edge to shorter wavelengths. however, annealing at 600 °c changes the direction of the absorption edge shift to the opposite. the long-wavelength shift in the absorption edge is augmented by annealing at 770 °c and is further enhanced by annealing at 910 °c. annealing at 1010 °c shifts the absorption edge of the film to the short-wavelength side compared to annealing at 910 °c. further increase in the annealing temperature to 1100 °c results in a shift of the absorption edge to a position that is in close proximity to that of the as-deposited film. such a non-monotonic excursion of the absorption band edge indicates the complex nature of the structural changes undergone by the film during annealing. this is also evident in the shape of the absorption curves, which differs significantly for different annealing temperatures. figure 1. absorptance spectra of a = 1 − r − t of the as-deposited siox film (1) and after 15-minute annealing at 300 (2), 500 (3), 600 (4), 770 (5), 910 (6), 1010 (7), and 1100 °c (8). the absorption coefficient α of the films was determined by the formula [27]: 𝛼 = 1 𝑑 ln 𝑇s(1 − 𝑅) 𝑇 (1) where ts is the transmittance of the substrate without film. in amorphous, disordered, heterogeneous, nanostructured semiconductor and dielectric materials, there are usually regions of the spectra described by the urbach dependence [28]: 𝛼(ℎ𝑣) = 𝐴 ∙ exp⁡(ℎ𝑣/𝐸u) (2) 1.8 2.1 2.4 2.7 3.0 0.0 0.2 0.4 0.6 0.8 photon energy h, ev a b so r p ta n c e a = 1 -r -t 1 2 3 4 5 6 7 8 characterization and application of nanomaterials 2025, 8(2), 11021. 4 the absorption in the region described by equation (2) is caused by the superposition of transitions from localized states in the valence band tail to nonlocalized states in the conduction band and transitions from non-localized states in the valence band to localized states in the conduction band tail. in equation (2), a is a numerical constant and eu (urbach energy) characterizes the width of the exponential absorption tail. it correlates with the widths of the tails of the localized valence band states γv and conduction band states γc and is mainly determined by the larger of the two, i.e., eu ~ max(γc, γv) [29]. figure 2. spectra of the absorption coefficient α of the as-deposited siox film (1) and after 15-minute annealing at 300 (2), 500 (3), 600 (4), 770 (5), 910 (6), 1010 (7), and 1100 °c (8), plotted in semi-logarithmic coordinates. figure 2 presents the absorption coefficient spectra plotted in semi-logarithmic coordinates. the relative error of the α values is 2%, which is only slightly greater than the thickness of the lines in the figure. as can be seen, the exponential dependence of the absorption coefficient on the photon energy in the as-deposited film and in the one annealed at 300 c and 400 c is quite well fulfilled in a significant part of the measured spectral range, including its high-energy edge. that is, this dependence is still observed at α values up to 8.46 × 104 cm−1 for the as-deposited film, 7.05 × 104 cm−1 after annealing at 300 c. the corresponding еu values were 0.42, 0.35 ev. after annealing at 500 c and 600 °c, the urbach region extends to 2.8 ev, with α ≤ 3.3 × 104 and 5 × 104 cm−1, respectively. eu continues to decrease, reaching 0.26 and 0.23 ev, respectively. after annealing at 770 c the corridor of fulfillment of the urbach dependence narrows much more significantly both in terms of photon energy (to 2.1 ev) and absorption coefficient (α ≤ 1.0 × 104 cm−1), however, no further decrease in еu is observed (еu = 0.245 ev). the value of еu after annealing at 910 c is almost the same as that after annealing at 770 c, but the straight-line section in semilogarithmic coordinates extends to 2.4 ev (α ≤ 4.3 × 104 cm−1). the spectral range of the urbach dependence and the value of the urbach energy after annealing at 1010 c are similar: hν ≤ 2.48 ev, α ≤ 3.7 × 104 cm−1, еu = 0.22 ev. after annealing at 1100 1.8 2.1 2.4 2.7 3.0 10 3 10 4 10 5 photon energy h, ev a b so rp ti o n c o ef fi c ie n t   c m -1 1 3 4 2 5 7 6 8 characterization and application of nanomaterials 2025, 8(2), 11021. 5 c, the region of fulfillment of the urbach dependence extends to 2.7 ev, with α ≤ 3.4 × 104 cm−1, еu = 0.36 ev. thus, the absorption behavior in this deposited film, which is an alloy of silicon with oxygen, differs significantly from the behavior of amorphous homogeneous stoichiometric materials. first, in such materials, the urbach dependence is observed at α  104 cm−1. secondly, the urbach energy values themselves are much smaller. for example, in high-quality amorphous silicon films еu = 0.042 ev [28], and in pure silica glass еu = 0.075 ev [30]. for amorphous and composite materials, whose energy structure is characterized by the presence of localized states in the band gap (and, accordingly, the “blurring” of the valence band top and the conduction band bottom), several methods for determining the band gap width are used in the literature. for siox, the formula proposed by tauc et al. [31] is most widely used: 𝛼(𝐸) = 𝐵 ∙ (ℎ𝑣 − 𝐸𝑜) 2/ℎ𝑣 (3) in equation (3), b is a numerical constant, and eo is the tauc optical band gap. equation (3) describes the absorption due to indirect allowed transitions from nonlocalized states in the valence band to non-localized states in the conduction band. this postulates a quadratic dispersion law in both bands and the independence of the matrix element of optical transitions from the photon energy. figure 3 shows the absorption coefficient spectra plotted in the tauc coordinates hν − (αhν)1/2. the tauc optical bandgap eo has been defined as the intersection of the linear approximation of the values of (αhν)1/2 in the high energy part of the spectrum with the abscissa. comparing figures 2 and 3, it is easy to see that the less the exponential dependence region extends into the high energy region, the further the observed tauc dependence region extends into the low energy region. although the urbach energy еu is almost halved by annealing, it is still at least three times higher than the urbach energy in perfect sio2. this indicates a much greater structural disorder (which may also imply nanoheterogeneity) of these films both before and after annealing compared to the structure of amorphous silica in glassy form. such large еu values and the length of the exponential region up to α  104 cm−1 indicate that the urbachian edge and interband transitions of different (nano)regions may overlap in these samples. in general, for a heterogeneous medium, the еu and eo values should be considered effective, since the heterogeneous medium differs in its structure from the “classical” amorphous medium. characterization and application of nanomaterials 2025, 8(2), 11021. 6 figure 3. spectra of the absorption coefficient α of the as-deposited siox film (1) and after annealing for 15 min at 300 (2), 500 (3), 600 (4), 770 (5), 910 (6), 1010 (7), and 1100 °c (8), plotted in tauc coordinates hν − (αhν)1/2. given the uncertainty involved in determining eo, tauc et al. [31] considered eo to be an empirical quantity. in view of this, an alternative empirical measure of the optical band gap for amorphous semiconductors has been proposed: the isoabsorption band gap eα. it corresponds to the photon energy at which the absorption coefficient α is equal to a specific value [32,33]. by analyzing the absorption spectra of a-sihx films with different degrees of disorder achieved by different degrees of hydrogenation, cody et al. [34] found a linear anticorrelation between the optical band gap eo and eu in amorphous silicon: 𝐸o = 𝐸g − 𝐶o ∙ 𝐸u (4) where eg is the optical band gap limit at zero width of the tails of localized states (mobility gap). from the approximation equation (4), a value of eg ~ 2.1 ev was obtained with a constant co of 6.2. thus, for defect-free amorphous silicon, the mobility gap is about 1 ev larger than for pure crystalline silicon. grein and johnn [35] found that the linear anticorrelation between eo and eu also occurs for a-as2s3 and a-as2se3. a linear anticorrelation between eα and eu was observed for amorphous ge in [33]. in this case, the approximation used to estimate the mobility band gap eg was: 𝐸𝛼 = 𝐸g − 𝐶𝛼 ∙ 𝐸u (5) it is expected that linear anticorrelations of the type equations (4) and (5) will be fulfilled for a wide range of amorphous and disordered semiconductors. 1.8 2.1 2.4 2.7 3.0 0 150 300 450 600 photon energy h, ev ( h  )1 /2 , cm -1 /2 .e v 1 /2 ) 1 2 3 4 5 6 7 8 characterization and application of nanomaterials 2025, 8(2), 11021. 7 figure 4. dependence of the urbach energy eu, tauc optical band gap eo, and e04— the isoabsorption band gap at α = 104 cm−1—on the annealing temperature of the sio1.3 film in a nitrogen atmosphere for 15 min. figure 4 shows the temperature dependence of e04, eo, and eu for the investigated samples. the isoabsorption band gap e04 corresponds to the photon energy at which α = 104 cm−1. the error in determining the obtained values of eu, eo and e04 in our case was ±0.01 ev. different temperature regions can be distinguished in these dependences. first, there is a clear anti-correlation between the value of eu, on the one hand, and the values of e04 and eo, on the other hand, at annealing temperatures tan ≤ 500 °c. by analogy with the results of the above works, it is logical to assume that changes in the parameters e04, eo, and eu in the range of annealing temperatures up to 500 °c are due to a decrease in the degree of structural disorder of the film with increasing tan. the linear approximation of the e04(еu) dependence in this annealing temperature range gave the eg = e04(еu = 0) = 3.00 ± 0.16 ev, and the linear approximation of the eo(еu) dependence gave the value eg = eo(еu = 0) = 2.63 ± 0.13 ev. based on these results, the mobility gap eg of amorphous sio1.3 can be estimated to be eg = 2.50–3.16 ev. in [36], the value of eg for siox alloys in the bulk glassy state was calculated using density functional theory. these calculations gave a value of eg = 2.5 ev for x = 1.3. although this value, as the authors point out, is an underestimate due to the peculiarities of the method, it correlates better with the eg value obtained using the tauc optical band gap. with an increase in tan from 500 °c to 600 °c and further to 910 °c a significant decrease in the values of e04 and eo is observed compared to their values at tan = 500 °c. this takes place against the background of a slight decrease in the value of the еu. this shows that, at these annealing temperatures, the prevailing processes are fundamentally different from the processes of structural ordering of the sio1.3 film that take place at tan ≤ 500 °c. it is known that, at high annealing temperatures, siox films undergo disproportionation with the formation of amorphous [21,37–40], and, at ta ≥ 800 °c−900 °c, amorphous, amorphous-crystalline, and crystalline silicon nanoinclusions [37–40] in the matrix of the sioy (y > x) composition. in suboxide siox 0.20 0.25 0.30 0.35 0.40 0 300 600 900 1200 1.8 2.0 2.2 2.4 2.6 e u e o ( e v ), e 0 4 ( e v ) annealing temperature t an , o c e 04 e o e u , e v characterization and application of nanomaterials 2025, 8(2), 11021. 8 films with stoichiometry indices x ≤ 1.5, the optical band gap eo grows very rapidly with increasing x [3]. thus, the main contribution to the absorption of the nanocomposite ‘si nanoinclusions—sioy’ after annealing at 600 °c ≤ tan ≤ 800 °c−900 °c should be attributed to the amorphous silicon nanoparticles. as can be seen from the graph, they already begin to play a noticeable role at tan = 600 °c. the decrease in the values of the empirical parameters e04 and eo with further growth of tan can, obviously, be interpreted as a manifestation of the size effect in amorphous silicon nanoparticles. the еu values for annealing temperatures of 600 °c–910 °c do not demonstrate any pronounced trend depending on the sizes of amorphous inclusions: the еu almost does not change, remaining at the level of values slightly lower than after annealing at 500 °c. this distinguishes the behavior of the ‘а-si nanoinclusions—sioy’ (y > 1.3) nanocomposites from the behavior of the ‘c-si nanoinclusions—sio2’ nanocomposites. the latter are characterized by the growth of the еu with decreasing nanocrystallite size due to the increasing influence of the c-si/sio2 interface [41]. the values of еu = 0.23–0.246 ev obtained by us in this range of annealing temperatures are very close to the values of еu obtained in [42] for non-hydrogenated a-si films with thicknesses of 769–1174 nm, grain sizes of 20–30 nm, and porosities of 0.14– 0.24 (i.e., with natural oxide-coated grains). the еu values in these films were 0.230– 0.258 ev, and the eo values were 1.32–1.38 ev. almost identical еu values and higher eo values for the nanocomposite films ‘а-si nanoinclusions—sioy’ obtained by annealing sio1.3 films at temperatures of 600 °c−910 °c compared to the nonhydrogenated a-si films can be explained by the size effect. it causes an increase in the band gap of amorphous silicon inclusions with decreasing size. if we assume that for the non-hydrogenated partially porous oxidized a-si films there is the anticorrelation (equation 4) with the same coefficient co = 6.2, then we obtain a mobility gap еg ~ 2.8 ev. assuming the validity of equation (4) with co = 6.2 for the sio1.3 films annealed at 600 °c−910 °c, we obtain estimates of the mobility gap еg ≈ 3.4–3.75 ev. if we assume that еg for non-hydrogenated partially porous oxidized a-si films is the same as for hydrogenated films, i.e., 2.1 ev, and that for them equation (4) is fulfilled, then the coefficient of such an anticorrelation is co = 3.0. if we accept this coefficient for the films obtained by annealing sio1.3 films at 600 °c−910 °c, we obtain an estimate of the mobility gap еg ≈ 2.61−2.98 ev. in [43], the values of eo were determined for non-hydrogenated a-si nanoparticles (nanodots) in a solution of highly purified ethanol. unfortunately, the authors did not determine the value of еu in their samples. therefore, the obtained values of the optical band gap eo, which increased from 2.58 ev for particles with an average diameter of 5.15 nm to 3.22 ev for particles with an average diameter of 1.15 nm, are lower estimates of eg. as can be seen, these estimates of eg for nanoparticles in ethanol are still in better agreement with the estimates of eg for nanoparticles in our suboxide matrix at a value of the coefficient co = 3.0 in equation (4), which is not surprising. the application of annealing at 1010 °c in comparison to annealing at 910 °c has been observed to result in an increase in e04 and eo, while eu exhibited a decrease from 0.24 to 0.22 ev. in works [44,45] the nucleation of crystalline inclusions in amorphous a-si:н films was studied using the tauc-lorentz parametric model. it was characterization and application of nanomaterials 2025, 8(2), 11021. 9 determined that this results in an increase in the optical (tauc) band gap eo and a decrease in the parameter γ (half-width of the lorentz oscillator function), which serves as a measure of the film disorder. these results provide a rationale for associating the observed increase in eo and decrease in eu following annealing at 1010 °c with an increase in the ordering of the amorphous nanoparticles’ structure, including the formation of a quasi-crystalline core. annealing at 1100 °c maintains the tendency of increasing e04, eo. the value of eo = 2.11 ev is very close to the value of eo = 2.1 ev for the sio1.3 film obtained by molecular beam deposition after its annealing at 1100 °c [46]. after such annealing, the film contains both crystalline and amorphous nanoparticles, and eo should be considered as the effective (averaged) optical band gap. following annealing at 1100 °c, a pronounced increase in eu for our film is observed, which is indicative of the presence of silicon nanoparticles exhibiting diverse structural and size characteristics. in their investigation of ‘silicon nanocrystallites—sio2’ superlattices, the authors [41] identified a direct correlation between the concentration of so-called pb centers—dangling bonds of silicon atoms at the si/sio2 boundary—and the urbach energy, eu. given that the appearance of pb centers was recorded following annealing of the films with a similar composition to ours at 1100 °c [37], it is reasonable to conclude that the formation of these centers also contributes to the observed increase in еu. 4. conclusion non-stoichiometric siox (x ≈ 1.3) films exhibit significant variations in the behavior of the fundamental absorption edge as a function of the annealing temperature. at annealing temperatures ta ≤ 500 с, a short-wavelength shift of the absorption edge occurs, which is then replaced by a long-wavelength shift in the range 600 с ≤ ta ≤ 900 с. the short-wavelength shift is accompanied by an increase in the optical band gap eo and a decrease in the urbach energy eu, indicating structural ordering of the film. in this case, defect annealing, healing of broken silicon and oxygen bonds, film densification, and a corresponding decrease in defect absorption take place. the long-wavelength shift is due to film disproportionation and the formation of amorphous silicon inclusions, which exhibit significant indirect interband absorption. eo decreases with increasing amorphous silicon nanoparticle size and their volume fraction in the annealed film, while eu remains almost unchanged. by further increasing the annealing temperature of the siox film, the absorption edge shifts to shorter wavelengths again, and both eo and eu increase. the increase in eo in this case is due to the increasing fraction of the crystalline silicon phase (c-si nanocrystals have a larger band gap) and a decrease in the fraction of amorphous silicon, while the increase in eu is attributed to the corresponding increase in the area of the c-si/sio2 interface, where interface centers (pb centers) form. author contributions: conceptualization, ms and ii; methodology, ms, ii and vy; validation, ii and km; investigation, ii, vy and ms; writing—original draft preparation, ms and km; writing—review and editing, ms, ii, km and vy; characterization and application of nanomaterials 2025, 8(2), 11021. 10 visualization, km; supervision, ii. all authors have read and agreed to the published version of the manuscript. acknowledgments: the authors would like to thank jeffrey monastyrsky (usa) for his help with the english edition of this article. institutional review board statement: not applicable. informed consent statement: not applicable. dedication: this article is dedicated to the memory of our colleague and friend, dr petro shepeliavyi, who recently passed away. he was a prolific author of many sophisticated technological developments that significantly advanced both fundamental research and the creation of specific devices. among his notable contributions are developments utilizing siox films and structures based on them. these include the development of technologies for manufacturing solid and porous light-emitting silicon–silicon oxide nanocomposites, light-sensitive sio-as2(s,se)3 nano multilayers, gradient light-absorbing siox/me coatings for display panels, thin film siox<ti>, siox<fe> nanocomposites combining functions of ir-absorption and formation of an electric signal for the thermosensitive detectors 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cross-linked polymer nanocomposite networks coated nano sand light-weight proppants for hydraulic fracturing applications mohan raj krishnan1,*, wengang li2,*, edreese housni alsharaeh1,* 1 college of science and general studies, alfaisal university, po box 50927, riyadh, 11533, saudi arabia. 2 expec advanced research center, saudi aramco, po box 5000, dhahran, 31311, saudi arabia. * corresponding authors: mohan raj krishnan, mkrishnan@alfaisal.edu; wengang li, wengag.li@aramco.com; edreese housni alsharaeh, ealsaraeh@alfaisal.edu abstract three-dimensionally cross-linked polymer nanocomposite networks coated nano sand light-weight proppants (lwps) were successfully prepared via ball-milling the macro sand and subsequently modifying the resultant nano sand with sequential polymer nanocomposite coating. the modified nano sand proppants had good sphericity and roundness. thermal analyses showed that the samples can withstand up to 411 ℃. moreover, the proppant samples’ specific gravity (s.g.) was 1.02–1.10 g/cm3 with excellent water dispersibility. therefore, cross-linked polymer nanocomposite networks coated nano sand particles can act as potential candidates as water-carrying proppants for hydraulic fracturing operations. keywords: proppants; nano sand; polymer; nanocomposites; graphene; hydraulic fracturing article info received: 16 november 2023 accepted: 22 november 2023 available online: 29 november 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction in general, proppants are millior micrometer-sized solid particles with specific crush resistance employed to keep open the cracks and enhance oil production from a wellbore[1–5]. since the proppants are used in downhole a few kilometers deep, they must be stable at harsh conditions of high temperature and high pressure (ht-hp), high temperature-high salinity (ht-hs) coming from either groundwater in deep wells or the strong acid mixtures (hydrofluoric and hydrochloric acids) that are pumped into wellbore to clear blockages, and corrosion from the fracturing fluid itself[1,6–22]. therefore, the nature and quality of the proppant are vital to a successful hydraulic fracturing operation and subsequent oil production. frac sand and modified frac sands are widely employed as proppants[23–26]. even though the frac is abundantly available and has a low cost due to its high density, low crush resistance (6000 psi), and relatively decreased sphericity and roundness, it often causes poor fracture permeability[2,27,28]. conversely, although the ceramic proppants have very high crush resistance (up to 20,000 psi) and thermal stability, the settling rate in fracturing fluid is high, which is ascribed to their high specific gravity values (3 g/cm3)[2,28–33]. hence, various conventional hydraulic fracturing operations exploit large volumes of water-based hydraulic fluid to enhance the well permeability, potentially producing large amounts of wastewater as flow back and pose severe environmental threats[33–39]. therefore, water-based fracturing technology has recently attracted the attention of scientists, and it 2 requires the development of ultra-lightweight proppant[40–44]. at the same time, the ultra-lightweight proppants should possess excellent crush resistance, thermal stability, acid resistance, and higher roundness and sphericity. polymeric composite microspheres have been recently employed as low-density proppants for water-based hydraulic fracturing operations[4,42,44–47]. for instance, chen et al.[48] reported polymethylmethacrylate (pmma)/graphite composite microspheres with sg of 1.055–1.135 g/cm3 and can withstand crushing stress up to 69 mpa. they have also reported polystyrene (ps)/graphite microspheres with sg of 1.025–1.185 g/cm3 with a crush resistance of 68 mpa[49]. the primary preparation methods of the polymeric microspheres are emulsion polymerization, suspension polymerization, dispersion polymerization, and so on[50–52]. however, this method involves multi-step syntheses with yield limitations and is most often not scalable to meet the growing industrial demands[53–64]. therefore, we conceived the idea of making nano sand particles by ball-milling the abundant and low-cost frac sand and suitably modifying them to withstand high temperature-high pressure-high salinity (ht-hp-hs) downhole conditions[17]. incorporating nanofillers like graphene can potentially increase the final material’s thermal and mechanical properties[65,66]. to our knowledge, no publications exist on nano sand particles as lightweight proppants in hydraulic fracturing applications. we have recently reported different surface modification techniques using various polymers, resins, and their combinations to improve the crush resistance of frac sand. the existing modification techniques are majorly of one-layer coating, and there is still space for improvement in thermo-mechanical and structural integrities in the coated sand proppants[45,67]. our group has recently introduced a two-layer coating approach for the surface modification of frac sand using sequential coating polymer nanocomposites with graphene or boron nitride nanosheets. interestingly, the two-layer coating sand proppants exhibited a crush resistance to a maximum of 10,000-14,000 psi[2,28,33,68–70]. however, practical applications of these proppants are limited due to their high specific gravity values and poor dispersibility in water-based fracturing fluid. also, pumping the high-density proppants into formations may result in discontinuous structures that may have an adverse impact on oil production. therefore, the proppants with ultra-low density, good water dispersibility (low-settling rate), and enhanced thermal properties are highly preferred. in this study, we aimed to fabricate cross-linked polymer nanocomposite networks modified nano sand particles as a potential proppant candidate for successful hydraulic fracturing. in addition, the present study also reports the successful co-polymerization of styrene (s), methyl methacrylate (mma), and divinylbenzene (dvb) into a cross-linked nanonetwork onto the nano sand particles. the first-layer modified nano sand particles were further subjected to another modification using an epoxy-cg (commercial graphene) composite layer. in contrast to the conventional resin coating approaches, this method applies a direct co-polymerization onto the nano sand surfaces and subsequent second-layer modification. in an alternative approach, nano sand particles were pre-modified with zirconia nanoparticles (zro2) as an attempt to enhance the inter-layer interaction of an inorganic component (nano sand surface) to a polymer layer (organic component). the nano sand-based lightweight proppants with reinforced thermo-mechanical properties and high crush resistance can be potential water-carrying fracturing proppants. the novelty of the work is the utilization of nano sand derived from the abundant natural source of macro sand through ball-milling and its successful surface modification with a two-layer polymer composite layer. 2. experimental 2.1. chemicals the monomers styrene with a purity of >99% (s), methyl methacrylate with a purity of 99% (mma), and divinylbenzene with a purity of >99% (mma) were purchased from sigma aldrich. the monomers were used as received. azoisobutyronitrile (aibn) was obtained from aldrich and recrystallized using methanol. saudi aramco provided us with sand samples, epoxy resin, and the curing agent. the commercial graphene (cg) 3 was procured from xg sciences. zro2 samples were prepared in our laboratory[15]. 2.2. preparation of nano sand and zro2 modified nano sand nano sand samples were prepared by ball milling the frac sand particles for 12 h. to prepare the zro2modified nano sand, the nano sand sample is mixed with a specific amount of zro2 nanoparticles and ballmilled for another hour. the experimental preparation for zro2 can be found elsewhere[14,15]. 2.3. preparation of dual-coated nano sand proppants a sequential coating of cross-linked ps-pmma/dvb nanonetworks (layer 1) and epoxy-cg composite (layer 2) onto the nano sand surface was used to prepare lightweight nano sand proppants. the cross-linked ps-pmma/dvb nanonetworks onto nano sand particle surfaces were prepared by carrying out an in-situ cross-linking and one-step copolymerization of s and mma monomers (1:1 wt%), with dvb (10 wt% to s: mma mixture) as a cross-linker with aibn as an initiator (0.01 wt% to the monomer and cross-linker mixture). to carry out the surface polymerization, the monomer, cross-linker, and initiator mixture (5 wt% to the nano sand weight) is well-mixed with nano sand samples and heated to 70 ℃. cross-linked co-polymer networks’ modified nano sand was mixed with 4:1 wt% of epoxy resin, curing agent, and cg (0.001 wt% to epoxy resin) and treated at 150 ℃ for curing of the epoxy. the curing reaction is optimized to be 5 min. the ps-pmma coating on the nano sand was carried out using the same procedure but without adding the dvb. 2.4. characterizations 2.4.1. x-ray diffraction (xrd) the rigaku miniflex 600 instrument was used to record the xrd patterns for the samples. the diffraction measurements were recorded in the range of 5°–80°. 2.4.2. thermal analysis thermogravimetric analyses (tga, hitachi sta7200) evaluated the samples’ degradation temperatures (tdeg). the measurements were conducted from 30 ℃ to 500 ℃ at a heating rate of 10 ℃/min under a constant inert gas (n2) flow. 3. results and discussion 3.1. preparation of cross-linked ps-pmma/dvb nanonetworks and epoxy-cg nanocomposite modified nano sand particles figure 1 shows a sequential two-layer coating of cross-linked ps-pmma/dvb layer followed by an epoxy-cg layer onto nano sand surfaces. the first layer of cross-linked ps-pmma/dvb nanonetworks onto the surface of nano sand was prepared by polymerizing monomers mixture of s and mma, cross-linker dvb, with the aid of aibn at 70 ℃. the detailed formation and the mechanistic pathway for the cross-linked pspmma/dvb nanonetworks can be found in our previous reports[2,28,33,68,70]. at 70 ℃, the aibn produces free radicals, and the monomers are converted into free radicals instantaneously. then, the monomer radicals reacted randomly with other monomers, and the polymeric chain propagated. at the same time, the growing polymer chains also randomly reacted with the dvb molecules, resulting in the cross-linking of polymer chains[2,39,71]. therefore, a cross-linked ps-pmma/dvb nanonetwork is formed on the surface of the nano sand. the second layer of epoxy-cg was prepared using an epoxy resin, curing agent, and cg that was cured at 150 ℃ for 5 min. 4 figure 1. sequential two-layer coating of cross-linked ps-pmma/dvb layer followed by epoxy-cg layer onto nano sand surfaces. 3.2. xrd figure 2 shows the xrd of micro sand (100 mesh) and nano sand samples that were prepared by ballmilling for various times ranging from 1 to 12 h. the peaks detected at 21°, 26.5°, 42°, 44°, 51°, 58°, 68°, 77° are assigned to sio2 (quartz phase). as for the micro sand, two major peaks were observed: one is at 21° (100), and the other is at 26.5°. when the micro sand is subjected to ball-milling for 1 h, the intensities of 100 and 101 peaks are slightly reduced. the decrease in the peak intensities is more evident when the ball-milling time is increased, for instance, from 2 h to 12 h. the reduction in the intensities of the characteristic peaks of frac sand can directly be related to the particle size of the resultant ball-milled nano sand particles. using debyescherer’s equation, the particle sizes can be calculated for each hour of ball-milling. the nano sand’s average particle size was 9 nm for the sample ball-milled for 12 h. figure 3 shows the xrd for the nano sand (ball-milled for 12 h), epoxy-cg (commercial graphene) composite coating layer, and modified nano sand with oneor two-layer polymer composite coating layers with and without zro2 cross-linker modification of the nano sand. as for the nano sand, the characteristic peaks detected at 21°, 26.5°, 42°, 44°, 51°, 58°, 68°, and 77° correspond to the quartz phase of sio2. for the epoxy-cg, peaks were detected at 15°, 18°, and 26° and attributed to cg; for the samples of ns-(epoxy-cg), ns-(ps-pmma-cg-zro2)-(epoxy-cg), ns-(ps-pmma-zro2-cg)-(epoxy-cg), ns-zro2-(ps-pmma)(epoxy-cg), ns-zro2-(ps-pmma-cg-zro2)-(epoxy-cg), and ns-zro2-(ps-pmma)-(epoxy-cg), the characteristic peak position and their relative intensities of the nano sand were not altered. this indicates that the relative weight ratio of the coating layers to nano sand particles is low enough as the peak position or the intensities are unchanged. figure 4 shows the xrd patterns for the nano sand modified with epoxy-cg, ns-(ps-pmma)-(epoxycg), ns-(ps-pmma-cg)-(epoxy-cg), ns-(ps-pmma/dvb)-(epoxy-cg), and ns-(ps-pmma/dvbcg)-(epoxy-cg). as evident from the unaltered the characteristic peak position and intensities of the nano sand weight ratio of the nano sand to coating layers particles are much lower. 5 figure 2. xrd of ball-milled sand samples for 0–12 h. (a) 0–4 h, (b) 5–8 h, and (c) 9–12 h. figure 3. xrd patterns of coated nano sand proppants with zro2 as a cross-linker in comparison to neat nano sand and epoxy-cg. 6 figure 4. xrd patterns of coated nano sand proppants with dvb as a cross-linker. 3.3. thermal stability analyses thermal degradation temperatures (tdeg) of the modified nano sand proppant samples were evaluated using their respective tga curves. figure 5 shows the tga of neat-nano sand, epoxy-cg, nano sand-(zro2)(epoxy-cg), nano sand-(zro2)-(ps-pmma)-(epoxy-cg), nano sand-(zro2)-(ps-pmma-zro2)-(epoxycg), nano sand-(zro2)-(ps-pmma-cg)-(epoxy-cg), nano sand-(zro2)-(ps-pmma-cg-zro2)-(epoxycg), and nano sand-(ps-pmma-cg-zro2)-(epoxy-cg). the tdeg was calculated using a differential thermal curve for the samples with clear degradation steps. however, for the samples with no clear degradation patterns, the temperature at which half of the weight loss was observed was considered to be their tdeg [72]. the nano sand lost weight at 500 ℃, while the epoxy-cg layer had a degradation peak at 362 ℃. when the zro2modified nano sand is coated with an epoxy-cg layer, the tdeg is increased to 365 ℃, and this thermal stability enhancement is a clear indication of cross-linking of zro2 to the epoxy layer. for the samples of nano sand(zro2)-(ps-pmma)-(epoxy-cg), nano sand-(zro2)-(ps-pmma-zro2)-(epoxy-cg), nano sand-(zro2) figure 5. tga of coated nano sand proppants with zro2 as a cross-linker compared to neat nano sand and epoxy-cg. inset: magnified plot. 7 (ps-pmma-cg)-(epoxy-cg), nano sand-(zro2)-(ps-pmma-cg-zro2)-(epoxy-cg), tdeg values are 368 ℃, 369 ℃, 371 ℃, and 371 ℃, respectively. from these results, it can be noted that polymer and polymer composite coating of ps-pmma and ps-pmma-cg, in addition to the epoxy-cg coating onto the zro2modified nano sand, would further enhance the stabilities of the respective proppant samples. interestingly, for the sample of nano sand-(ps-pmma-cgzro2)-(epoxy-cg), the tdeg value is 375 ℃. this can be attributed to the higher cross-linking ability of zro2 between ps-pmma-cg and epoxy-cg layers. therefore, it is more desirable to have cross-linked dual-coating of copolymer-2d nanofiller composite and cured resin composite onto nano sand particles for the successful hydraulic fracture operation with modified nano sand as proppants. figure 6 shows the tgs curves for nano sand-(ps-pmma)-(epoxy-cg), nano sand-(ps-pmma-cg)(epoxy-cg), nano sand-(ps-pmma/dvb)-(epoxy-cg), and nano sand-(ps-pmma/dvb-cg)-(epoxy-cg) in comparison to nano sand-(epoxy-cg) and neat-nano sand. table 1 summarizes all the degradation temperatures of the samples. as shown in figure 6, the tdeg values are found to be 372 ℃, 375 ℃, 396 ℃, and 411 ℃ for nano sand-(ps-pmma)-(epoxy-cg), nano sand-(ps-pmma-cg)-(epoxy-cg), nano sand(ps-pmma/dvb)-(epoxy-cg), and nano sand-(ps-pmma/dvb-cg)-(epoxy-cg) respectively. this increase can be explained by forming 3dnanonetworks of ps-pmma/dvb. this can be credited to the higher thermal stability of the epoxy-cg composite layer. interestingly, a synergistic increase in the degradation temperature values for the samples with a two-layer coating of cross-linked ps-pmma/dvb followed by epoxy-cg coating was observed. therefore, these proppant samples would be highly suitable for hightemperature wells. figure 6. compared to neat nano sand and epoxy-cg, tga curves for coated nano sand proppants with dvb as a cross-linker. table 1. summary of thermal properties of the nano sand-based proppants. sample tdeg (℃) sg (g/cm3) nano sand 1.02 epoxy-cg 362 nano sand-(zro2)-(epoxy-cg) 365 1.05 nano sand-(zro2)-(ps-pmma)-(epoxy-cg) 368 1.07 nano sand-(zro2)-(ps-pmma-zro2)-(epoxy-cg) 369 1.09 nano sand-(zro2)-(ps-pmma-cg)-(epoxy-cg) 371 1.08 nano sand-(zro2)-(ps-pmma-cg-zro2)-(epoxy-cg) 372 1.10 nano sand-(ps-pmma-cg-zro2)-(epoxy-cg) 375 1.08 nano sand-(epoxy-cg) 336 1.04 nano sand-(ps-pmma)-(epoxy-cg) 372 1.06 nano sand-(ps-pmma-cg)-(epoxy-cg) 375 1.07 nano sand-(ps-pmma/dvb)-(epoxy-cg) 396 1.07 nano sand-(ps-pmma/dvb-cg)-(epoxy-cg) 411 1.09 8 3.4. specific gravity (sg) and water suspension analyses the specific gravity of the nano sand proppant samples was summarized in table 1. the neat-nano sand has an sg value as low as 1.02. at the same time, the sg values for nano sand-(zro2)-(epoxy-cg), nano sand(zro2)-(ps-pmma)-(epoxy-cg), nano sand-(zro2)-(ps-pmma-zro2)-(epoxy-cg), nano sand-(zro2)-(pspmma-cg)-(epoxy-cg), nano sand-(zro2)-(ps-pmma-cg-zro2)-(epoxy-cg), nano sand-(ps-pmmacgzro2)-(epoxy-cg), and nano sand-(ps-pmma-cg-zro2)-(epoxy-cg) are 1.05, 1.07, 1.09, 1.08, 1.08 and 1.10. the values indicate that the sg values also increase when we increase the coating layer and materials. similarly, for the samples of nano sand-(ps-pmma)-(epoxy-cg), nano sand-(ps-pmma-cg)-(epoxy-cg), nano sand-(ps-pmma/dvb)-(epoxy-cg), and nano sand-(ps-pmma/dvb-cg)-(epoxy-cg), the s.g values are found to be 1.06, 1.07, 1.07, and 1.09. the values indicate that the sg values also increase when we increase the coating layer and the coating materials. figure 7 shows the suspension of the nano sand proppant samples of nano sand-(ps-pmma/dvb)(epoxy-cg) and nano sand-(ps-pmma-zro2)-(epoxy-cg) in gulf sea water after 1 h of dispersion in comparison neat-nano sand and correspondingly modified macro sand sample. it can be seen that the macro sand proppant particles are instantaneously settled in the water, whereas the neat nano sand remains suspended because of its low sg value of 1.02. for the modified nano sand proppant samples, the one with (ps-pmma/dvb)-(epoxy-cg) suspended in the seawater for a longer time in comparison to the one with (ps-pmma-zro2)-(epoxy-cg). this observation is consistent with their corresponding sg values. figure 7. suspension of coated nano sand lightweight proppants compared to coated macro sand proppants after 1 h of dispersion in gulf sea water. (a) coated macro sand[2,28], (b) neat-nano sand, (c) nano sand-(ps-pmma/dvb)-(epoxy-cg), and (d) nano sand(ps-pmma-zro2)-(epoxy-cg). besides, the s.g. of the nano sand-(ps-pmma/dvb)-(epoxy-cg) proppant is determined to be only 1.09 g/cm3 while that of resin-coated sand proppant counterparts is 1.40g/cm3. the decrease in bulk density of the developed nano sand-(ps-pmma/dvb)-(epoxy-cg) proppants is an obvious indication of successful dual coating of cross-linked polymer nanonetworks and epoxy-graphene composite layer while not compromising the permeability of the fractures. 4. conclusion two-layer coated nano sand particles were successfully prepared via ball-milling the macro sand and subsequently modifying the resultant nano sand with polymer nanocomposites with different surface modifications. the first layer of cross-linked ps-pmma/dvb was prepared using s and mma monomers, crosslinker (dvb) at 70 ℃. the second layer of epoxy-cg was prepared using a mixture of epoxy resin, a 9 curing agent, and cg that was cured at 150 ℃ for 5 min. xrd and tga studies confirmed successful surface coatings onto the nano sand particles. the dual-coating layer of (ps-pmma/dvb)-(epoxy-cg) exhibited thermal stability up to 411 ℃. nevertheless, specific gravity (sg) analysis illustrated that the density of the proppants was about 1.02–1.10 g/cm3 with good dispersion in water. thermal studies showed that the samples can withstand up to 411 ℃. therefore, the polymer nanocomposite-modified nano sand proppant samples can act as potential candidates as water-carrying proppants in oil and gas industries. the thermally enhanced polymer nanocomposites modified nano sand proppant samples with low s.g. values and excellent water dispersibility characteristics would be highly useful for the current oil and gas industries. author contributions conceptualization, mrk, wl, and eha; methodology, mrk; validation, wl and eha; formal analysis, wl; investigation, mrk; resources, wl; data curation, mrk and 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ceramer coatings: part 1-inert atmosphere parameters. polymer degradation and stability 2009; 94(10): 1754–1771. doi: 10.1016/j.polymdegradstab.2009.06.010 review article on polymeric nanoparticle final work 20240304 characterization and application of nanomaterials 2025, 8(1), 10521. https://doi.org/10.24294/can10521 1 article tuning dielectric properties in metal-doped nio nanoparticles muhammad fasih aamir1,2,3,*,†, ahmar ali3,4,†, kashif nadeem3 1 international center for materials nanoarchitectonics (mana), national institute for materials science (nims), 1-1 namiki, tsukuba 3050044, japan 2 graduate school of science and technology, university of tsukuba, 1-1-1 tennodai, tsukuba ibaraki 305-8577, japan 3 department of physics, faculty of basic and applied sciences (fbas), international islamic university (iiu), islamabad 44000, pakistan 4 king fahd university of petroleum and minerals (kfupm), academic belt road, dhahran 31261, saudi arabia * corresponding authors: muhammad fasih aamir, aamir.muhammadfasih@nims.go.jp † these authors contributed equally to this work abstract: nickel oxide (nio) nanoparticles (nps), doped with manganese (mn) and cobalt (co) at concentrations up to 8%, were synthesized using the composite hydroxide method (chm). x-ray diffraction (xrd) analysis confirmed the formation of a cubic nio structure, with no additional peaks detected, indicating successful doping. the average crystallite size was determined to range from 15 to 17.8 nm, depending on the dopant concentration. scanning electron microscopy (sem) images revealed mostly spherical, agglomerated particles, likely due to magnetic interactions. fourier transform infrared spectroscopy (ftir) confirmed the incorporation of mn and co into the nio lattice, consistent with the xrd results. the dielectric properties exhibited a high dielectric constant at low frequencies, which can be attributed to ion jump orientation and space charge effects. the imaginary part of the dielectric constant decreased with increasing frequency, as it became harder for electrons to align with the alternating field at higher frequencies. both the real and imaginary dielectric constants showed behavior consistent with koop’s theory, increasing at low frequencies and decreasing at higher frequencies. dielectric loss was primarily attributed to dipole flipping and charge migration. ac conductivity increased with frequency, and exhibited higher conductivity at high frequencies due to small polaron hopping. these co-doped nps show potential for applications in solid oxide fuel cells. keywords: dielectrics; ac conductivity; koop’s theory; space charge effect; metal doped nanoparticles 1. introduction transition metal oxide nanoparticles, including materials such as nickel oxide (nio), manganese oxide (mno), iron oxide (feo), and cobalt oxide (coo), have garnered substantial interest due to their remarkable characteristics at the nanoscale [1–4]. these materials exhibit distinctive properties that diverge significantly from their bulk counterparts, influenced by factors such as particle size, surface effects, and electrical behavior [5–8]. among them, nio emerges as a particularly promising candidate, recognized for its role as a p-type semiconductor [9,10]. it exhibits a high exciton binding energy and a bandgap in the range of 3.6 to 4.0 ev, offering unique advantages over other metal oxides. nio’s antiferromagnetic nature, combined with its electrically insulating behavior and rock-salt cubic structure, further enhances its appeal [11]. these characteristics, alongside its chemical stability and suitability for diverse technological applications, have positioned nio at the forefront of research in materials science [12,13]. citation aamir mf, ali a, nadeem k. tuning dielectric properties in metal-doped nio nanoparticles. characterization and application of nanomaterials. 2025; 8(1): 10521. https://doi.org/10.24294/can10521 article info received: 15 november 2024 accepted: 23 december 2024 available online: 15 january 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 10521. 2 despite its many benefits, nio’s low conductivity at room temperature, with resistance on the order of 1013 ω-cm, poses challenges for certain applications [14]. this behavior is linked to charge carrier hopping facilitated by ni2 + vacancies, which limits its electrical performance. modifying the material through doping offers a viable solution to this problem [15]. for instance, introducing monovalent elements like lithium generates ni3 + ions, which effectively reduces resistivity [16]. however, while bulk and single-crystal forms of nio have been widely studied, the dielectric behavior of nio nanoparticles, particularly co-doped variants, remains underexplored [17]. this knowledge gap underscores the need for further investigation into how innovative doping strategies can unlock the full potential of nio in practical applications [18,19]. the structural and compositional properties of nio are intrinsically linked to its nanoscale behavior [20]. nio adopts a rock-salt lattice configuration, with octahedral coordination of ni2 + and o2 − ions [21]. its appearance is influenced by stoichiometry, transitioning from black in stoichiometric compositions to greenish hues when nonstoichiometric [22]. these optical and structural changes highlight the importance of controlling stoichiometry to optimize performance [23]. additionally, factors such as synthesis method, particle size, annealing time, and doping significantly influence the properties of nio at the nanoscale [24]. managing structural and compositional defects, which are often intrinsic to nanostructured materials, is a critical challenge [25]. addressing these defects is essential for enhancing the performance and reliability of nio-based devices [26]. defects within nanostructured materials play a pivotal role in shaping their electrical and dielectric properties [27,28]. for example, magnetic nanoparticles often experience strong interparticle interactions that lead to agglomeration, which can negatively impact material performance [29]. single-doping strategies, while effective in introducing new functionalities, often result in clustering of the dopant within the host lattice, creating inhomogeneities. co-doping presents a more sophisticated approach, addressing these limitations by introducing two dopant elements simultaneously [30]. this technique not only prevents dopant clustering but also enables fine-tuning of the material’s electronic, magnetic, and dielectric properties. co-doping has proven effective in enhancing conductivity, improving magnetic interactions, and achieving more uniform defect distributions [31]. the dielectric properties of nio nanoparticles have been the focus of several studies. for instance, different studies demonstrated the potential of nio nanoparticles synthesized through wet chemical precipitation, reporting a large dielectric constant [32]. similarly, some authors investigated nio nanoparticles prepared via the sol-gel method and found that dielectric loss decreases with increasing frequency, attributed to the inability of ions to respond to alternating fields at higher frequencies [33,34]. these findings underscore the importance of dielectric studies in understanding and optimizing nio for practical applications. however, there remains a significant gap in research on the frequency-dependent dielectric properties of co-doped nio nanoparticles, providing a clear motivation for further exploration [35,36]. to address these challenges, this study investigates the effects of co-doping nio nanoparticles with manganese (mn) and cobalt (co). these elements were chosen for characterization and application of nanomaterials 2025, 8(1), 10521. 3 their ability to enhance both dielectric and magnetic properties while maintaining structural stability [37]. co-doping introduces new energy states into the nio lattice, facilitating charge carrier hopping and improving conductivity. furthermore, the combination of mn and co ensures a more even distribution of dopant ions within the host matrix, minimizing the clustering observed in single-doped systems. this approach not only optimizes the dielectric response but also enhances the overall performance of the material. the frequency-dependent dielectric behavior of nio is particularly noteworthy. dielectric properties, such as real and imaginary dielectric constants, exhibit distinct frequency-dependent trends [38]. at low frequencies, the dielectric constant is influenced by space charge effects and ion jump orientation, aligning with koop’s theory [39]. at higher frequencies, these effects diminish, resulting in a decrease in the dielectric constant as charge carriers are unable to keep pace with the alternating field [40]. by leveraging co-doping, this study aims to refine these properties, creating materials with tailored electrical and dielectric behavior for advanced applications [41,42]. the study also sheds light on the magnetic properties of co-doped nio nanoparticles [43]. mn and co co-doping enhances magnetic interactions, reducing agglomeration caused by interparticle forces and improving the uniformity of particle dispersion [44]. these magnetic improvements, combined with enhanced dielectric performance, have significant implications for the use of co-doped nio in applications such as solid oxide fuel cells [45–47]. the increased ac conductivity observed in co-doped nio nanoparticles, particularly at higher frequencies, can be attributed to small polaron hopping, which further underscores their potential in energy-related technologies [48–50]. this research addresses critical challenges in the design of nanostructured materials, focusing on defect control and achieving optimal dopant distribution. by employing a co-doping strategy, the study demonstrates how the structural, electrical, and dielectric properties of materials can be simultaneously enhanced, offering a pathway to tailor these properties for specific functional requirements. investigating the synthesis and frequency-dependent dielectric properties of both undoped and mnco co-doped nio nanoparticles, the research emphasizes their potential for superior performance. the novelty of this work lies in using the composite hydroxide method (chm), a simple and cost-effective approach that allows precise control over dopant concentration. by overcoming the challenges of defect management and dopant clustering in single-doped systems, this study contributes to creating materials with refined characteristics suitable for practical applications. the insights gained into the role of mn and co co-doping in enhancing dielectric performance, conductivity, and ion mobility in nio nanoparticles pave the way for innovative applications in cuttingedge technologies, including renewable energy systems, high-performance electronics, solid oxide fuel cells, capacitors, and advanced sensors, offering new opportunities for technological advancements. 2. experimental details composite hydroxide method (chm) is a low-temperature method for characterization and application of nanomaterials 2025, 8(1), 10521. 4 synthesizing single-phase nanoparticles (nps). in this process, composite hydroxides are used as a solvent. it is a one-step process where all raw materials are mixed with hydroxides and placed in a beaker. the beaker is then placed in an oven at 200 ℃ for 24 h, allowing the nps to form. after 24 h, the heating is stopped, and the sample is washed with distilled water to remove impurities. to form nio nps and mn-co codoped nio nps, a specified number of mixed hydroxides (koh, naoh) is added to the beaker. nickel nitrate is then combined with the hydroxides, and the mixture is placed in an oven at 200 ℃ for 24 h. afterward, the sample is allowed to cool to room temperature. finally, the sample is washed several times with distilled water to remove impurities, resulting in the desired nio and co-doped nio nps. a flow chart illustrating the composite hydroxide-mediated method for preparing nio and mn-codoped nio nanoparticles is shown in. 3. results and discussions 3.1. x-ray diffraction figure 1a presents the xrd patterns of nio and mn-co co-doped nio nanoparticles with varying concentrations. the samples are labeled as s1 = undoped nio, s2 = 2% mn-6% co doped nio, s3 = 4% mn-4% co doped nio, and s4 = 6% mn-2% co doped nio. the diffraction peaks observed at 2θ = 37.30°, 43.30°, 62.90°, 75.30°, and 80.0° correspond to the (111), (200), (220), (311), and (222) crystal planes, respectively. these peaks align with jcpds, no. 04-0835 data for nio, confirming the formation of a cubic structure. the absence of additional peaks indicates high purity and successful doping, with no secondary phases detected. (a) (b) figure 1. (a) xrd pattern of nio pure and co-doped nio nanoparticles with jcpds data; (b) macrostrain vs crystalline size of nio nanoparticles. the crystallite size and lattice distortions varied with the dopant concentrations, as reflected by slight shifts in the diffraction peaks, which are attributed to differences in the ionic radii of mn and co. furthermore, macrostrain was calculated for each crystal plane using the fwhm values and bragg angles with the relation as: characterization and application of nanomaterials 2025, 8(1), 10521. 5 ε = 𝛽 4𝑡𝑎𝑛𝛿 where 휀 is the dielectric constant, 𝛽 is the full width at half maximum (fwhm) and 𝛿 is bragg angle [51]. the calculated macrostrain values were: (111) = 0.00660, (200) = 0.00561, (220) = 0.00367, (311) = 0.00253, and (222) = 0.00233. these results confirm the uniform incorporation of mn and co into the nio lattice, with macrostrain progressively decreasing from the (111) to the (222) planes, further highlighting the influence of doping on the structural properties. macrostrain and crystallite effects in mn-co doped nio figure 1b illustrates the relationship between macrostrain and crystallite size, revealing the influence of mn-co doping concentrations on structural and dielectric properties of nio. macrostrain, calculated for different crystal planes using the fwhm values and bragg angles, shows a progressive decrease from the (111) to the (222) planes, highlighting the uniform incorporation of dopants into the nio lattice. this decreasing trend indicates reduced lattice distortions, which directly correlates with changes in crystallite size. the observed variations in macrostrain and crystallite effects are significant for optimizing the dielectric properties of nio. higher macrostrain in the (111) and (200) planes correspond to greater lattice distortions, which can enhance polarization effects, improving the dielectric constant. conversely, reduced macrostrain in the (220), (311), and (222) planes align with improved structural stability, facilitating the reduction of dielectric losses. this interplay between macrostrain and crystallite size demonstrates the potential of mn-co doping to tailor the dielectric properties of nio, making it suitable for advanced electronic and energy storage applications. the optimization of doping concentrations is critical to achieving the desired balance between dielectric constant and loss, as reflected in the graph. 3.2. fourier transform infrared spectroscopy figure 2 presents the fourier transform infrared spectroscopy (ftir) spectra of both undoped and co-doped nio nanoparticles, with varying concentrations of mn and co, within the wavenumber range of 350 to 1000 cm−1. the prominent bands between 400 and 600 cm−1 are attributed to the stretching vibration mode of nio, confirming the presence of nio in all samples. this specific range is characteristic of ni-o bond vibrations, indicating the formation of the nio lattice structure. an absorption peak around 620 cm−1 further validates the presence of nio, which is a typical feature in the ftir spectra of nickel oxide. additionally, a band observed at 870 cm−1 corresponds to the stretching and bending vibrations of c-o species, which are commonly present due to environmental exposure, such as carbon dioxide and moisture absorption from the air during synthesis and handling. this peak suggests that the nanoparticles may have adsorbed atmospheric contaminants or surface-bound species, which is typical in nanoparticle synthesis under ambient conditions. importantly, no additional peaks appear in the ftir spectra of the mn-co codoped nio nanoparticles compared to the undoped nio. this lack of extra peaks characterization and application of nanomaterials 2025, 8(1), 10521. 6 indicates that the dopants (mn and co) are successfully integrated into the nio lattice without forming separate phases or clusters. the absence of distinct peaks corresponding to mn or co oxides suggests that these dopants are likely dispersed or substituted within the nio crystal structure, ensuring uniform doping. this behavior confirms a successful doping process where the metal ions (mn2+ and co2+) replace ni2+ ions in the lattice without causing significant structural disturbances. the findings highlight the effectiveness of the co-doping strategy in modifying nio properties while maintaining its structural integrity, which is essential for applications in electronics, catalysis, and energy storage devices. figure 2. ftir spectra of pure and co-doped nio nanoparticles. 3.3. scanning electron microscopy figure 3 displays the sem (scanning electron microscope) micrographs of undoped and mn-co co-doped nio nanoparticles at a magnification of 30,000x. the images reveal that the synthesized nanoparticles predominantly exhibit a spherical morphology. however, the particles appear highly agglomerated, likely due to the magnetic interactions between the mn and co dopants within the nio matrix. such agglomeration is a common phenomenon in magnetic nanoparticles, as magnetic forces cause particle clustering, which can influence the material’s properties. despite this, the overall shape and distribution of the particles provide valuable insights into the effects of mn-co doping on the morphology of nio nanoparticles. table 1. structural parameters of nio pure and co-doped nio nanoparticles. samples planes (hkl) 2 theta fwhm (radians) lattice constant (𝑨𝟎) average crystalline size d (nm) dislocation density 𝜹 = 𝟏/𝑫𝟐 𝟏/𝒏𝒎𝟐 un-doped nio 200 43.27 0.5106 0.208 17.2 0.0029 s2 200 43.29 0.5139 0.207 15.7 0.0029 s3 200 43.55 0.4481 0.207 17.8 0.0022 s4 200 43.30 0.4488 0.208 17.6 0.0022 characterization and application of nanomaterials 2025, 8(1), 10521. 7 (a) (b) figure 3. sem images of co-doped nio nanoparticles (a) undoped nio; (b) doped nio. 3.4. dielectric properties the dielectric properties of nanoparticles are influenced by various factors, including the synthesis method, grain size, annealing temperature, and ac conductivity. in the case of nio and its mn, co co-doped derivatives, the crystallite size plays a crucial role in shaping the dielectric behavior as shown in table 1. smaller crystallites typically result in higher dielectric constants at low frequencies, as the material exhibits enhanced ion jump orientation and space charge effects. as the crystallite size increases, the material’s ac conductivity tends to improve, which in turn influences the dielectric loss and behavior at higher frequencies. these observations highlight that crystallite size is a key parameter in tailoring the dielectric properties of nio-based materials for applications in electronic devices and energy storage systems. in this study, dielectric measurements were conducted on pure nio and mn, co co-doped nio samples, exploring their frequency-dependent dielectric constants and loss over a range of dopant concentrations and frequencies from 1 khz to 2 mhz. 3.4.1. frequency vs real part the dielectric constant is calculated by using the relation [52], 휀𝑟 = 𝐶𝑑 휀0𝐴 where; εr is the relative permittivity (dielectric constant) of the material, c is the measured capacitance of the material, d is the thickness of the material, ε0 is the vacuum permittivity (approximately 8.854 × 10−12 f/m), a is the area of the electrodes. figure 4a shows that at low frequencies, the dielectric constant increases, and at higher frequencies, it decreases. the higher value of the dielectric constant at low frequency may be attributed to the increased ion jump orientation effect and the enhanced space charge effect exhibited by the nanoparticles. in nanocrystalline materials, most of the atoms reside at the grain boundaries, where they become characterization and application of nanomaterials 2025, 8(1), 10521. 8 electrically active due to charge trapping. the changes in the electric field can be easily followed by the dipole moment at low frequencies. as a result, space charge polarization and rotational polarization occur at the interfaces, enhancing the dielectric constant at low frequencies. these findings align with koop’s theory, which suggests that the grains are conductive, while the grain boundaries act as insulators. at higher frequencies, it becomes more difficult for electrons to align with the alternating electric field, causing the dielectric constant to decrease. nio nanoparticles with co-doping of mn and co show a higher dielectric constant at low frequencies compared to pure nio, due to the larger polarization in the co-doped nanoparticles. (a) (b) figure 4. (a) dielectric constant of nio nanoparticles; (b) imaginary part of nio nanoparticles. 3.4.2. frequency vs imaginary part figure 4b represents the frequency dependence of the imaginary part of the dielectric constant. the imaginary part of the dielectric constant reflects the energy loss within the material when it is subjected to an alternating electric field. it indicates the resistance offered by the material to the applied electric field and provides insights into the material’s ability to store and dissipate energy. for an ideal, pure dielectric material, the imaginary part of the dielectric constant would be zero, as there would be no energy dissipation. however, in practical materials, the imaginary part is nonzero and varies with frequency. this part is calculated using the formula [53]; ɛ′′ = 휀′𝑡𝑎𝑛 𝛿 where; ɛ′′ is the imaginary part of the dielectric constant, which corresponds to the energy loss in the material. ɛ′ is the real part of the dielectric constant, which represents the energy stored in the material. tan δ is the loss tangent, a measure of the energy dissipation in the material when it is exposed to an alternating electric field. it is defined as the ratio of the imaginary part to the real part of the dielectric constant. as the frequency increases, the imaginary part of the dielectric constant typically characterization and application of nanomaterials 2025, 8(1), 10521. 9 decreases. this occurs because, at higher frequencies, the electrons within the material struggle to keep up with the rapidly alternating field, making it harder for them to align with the field direction. as a result, the energy loss due to electron alignment decreases with increasing frequency, causing the imaginary part of the dielectric constant to reduce. this frequency-dependent behavior is essential in understanding how the material performs under different operating conditions, particularly in applications like capacitors, sensors, and energy storage devices. 3.4.3. frequency vs tangent loss figure 5 shows the frequency dependence of the tangent loss for nio, also known as the dissipation factor. mathematically, it can be expressed as [54]: tan δ = ε"/ε′ the dielectric loss tangent is higher at low frequencies and exhibits a decreasing trend at higher frequencies. this decrease in the dissipation factor follows koop’s model. dielectric loss primarily results from the flipping of dipoles and the migration of charge carriers from the grains to the grain boundaries. at low frequencies, the grain boundaries are more dominant and provide more resistance to the flow of electrons, resulting in a higher tangent loss in this region. undoped nio has a larger tangent loss compared to co-doped nanomaterials, likely due to the larger imaginary part of undoped nio at low frequencies, which may be attributed to its smaller particle size compared to other samples. figure 5. frequency dependence for tangent loss for nio nanoparticles. 3.4.4. frequency vs ac conductivity ac conductivity illustrates about the conduction mechanism. we calculated it by using formula [55]; σac = 휀׳𝑡𝑎𝑛(𝛿)𝜔휀0 where ac is the ac conductivity, which measures how well a material conducts electricity when subjected to an alternating electric field and ω: the angular frequency of the applied alternating field, defined as ω = 2πf, where f is the frequency. characterization and application of nanomaterials 2025, 8(1), 10521. 10 figure 6 shows the frequency dependence of ac conductivity at room temperature for different concentrations of mn and co doped in nio nps. it is evident from the figure that all the samples exhibit an increase in conductivity with an increase in frequency. at low frequencies, the grain boundaries contribute significantly, making it difficult for electrons to overcome the barrier, leading to a minimum in ac conductivity. however, at higher frequencies, the role of the grains becomes more dominant, allowing electrons to move more easily, which results in a slight increase in ac conductivity compared to low frequencies. the conductivity of sample s4 is greater than that of the others, which may be due to the larger size of these co-doped nps compared to s1, s2, and s3 samples. additionally, the stronger small polaron hopping conduction mechanism in sample s4 may also contribute to this higher conductivity. these results suggest that the dielectric properties of co-doped nio nanoparticles are strongly influenced by the nature of the dopants, their concentrations, and the average crystallite size of the nps. these properties make them suitable for applications in energy conversion devices, such as solid oxide fuel cells. figure 6. ac conductivity of pure and co-doped nio nanoparticles. 4. conclusions nio nanoparticles doped with varying concentrations of mn and co were successfully synthesized using the composite hydroxide method (chm). x-ray diffraction analysis confirmed the formation of a cubic crystal structure, consistent with the expected phase. scanning electron microscopy (sem) images revealed agglomeration of nanoparticles, likely caused by the magnetic interactions between the mn and co dopants within the nio matrix. fourier transform infrared spectroscopy (ftir) analysis further validated the successful co-doping of mn and co into the nio structure. the observed high dielectric constant at low frequencies is attributed to enhanced ion jump orientation and space charge effects, while the imaginary dielectric constant decreased at higher frequencies, suggesting a difficulty in electron alignment with the alternating field. ac conductivity measurements revealed an increase in conductivity with frequency, influenced by both the grains and grain boundaries. notably, s4 = 6% mn-2% co doped nio exhibited the highest conductivity at higher frequencies, potentially due to the small polaron hopping characterization and application of nanomaterials 2025, 8(1), 10521. 11 conduction mechanism and the increased 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to its unique combination of properties and ease of processing. pmma, also known as acrylic or plexiglass, is a transparent thermoplastic with exceptional optical clarity, high-impact resistance, and excellent weatherability. this scholarly article endeavors to offer an exhaustive examination of the composition, characteristics, and broad utilization of poly(methyl methacrylate) (pmma). this study aims to conduct an in-depth analysis of the molecular composition and chemical attributes inherent to pmma. furthermore, it intends to examine the mechanical and physical attributes exhibited by pmma meticulously. additionally, an exploration of varied methodologies employed in the processing and fabrication of pmma will be undertaken. the extensive array of applications of pmma spanning multiple industries will be underscored, followed by a comprehensive discourse on its merits, constraints, contemporary advancements, and prospective avenues. understanding the properties and applications of pmma is crucial for engineers, scientists, and professionals working in fields such as automotive, aerospace, medical, and signage, where pmma finds extensive use. keywords: poly(methyl methacrylate); structure; properties; application; polymer 1. introduction 1.1 poly(methyl methacrylate) (pmma) the discovery of poly(methyl methacrylate) (pmma) was attributed to two british chemists, both rowland hill and john crawford, in the 1930s. however, its maiden implementation was in 1934 by german chemist otto rohm[1]. pmma, commonly referred to as acrylic resin, is typically produced through the radical polymerization of methyl methacrylate (mma), although anionic and coordination polymerization methods are also viable alternatives. pmma is a transparent thermoplastic material that exhibits desirable properties such as impact resistance, weather resistance, and chemical resistance. it is often utilized as a substitute for inorganic glass due to its optical clarity and durability[2]. pmma is recognized for its exceptional optical properties, rendering it an excellent polymer for optical applications. it exhibits a remarkable visible light transmittance of 92%, surpassing that of glass. additionally, pmma possesses the ability to withstand ultraviolet (uv) radiation and harsh outdoor conditions, making it an ideal glass substitute (see figure 1). pmma further demonstrates advantageous attributes as a low-cost, non-toxic, environmentally friendly, recyclable, and highly biocompatible polymer. these remarkable characteristics have propelled pmma’s extensive utilization in article info received: 9 march 2023 accepted: 24 april 2023 available online: 6 may 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 diverse fields such as aviation, construction, automotive, advertising, medicine, and the electronics industry[3]. high tensile strength and roughness, high resistance to chemicals, and low-cost production as a result of its properties [r6]. pmma, also known as plexi-glass or acrylic glass, is a polymer whose monomer structures are demonstrated in figures 1 and 2, respectively[4,5]. figure 1. the chemical structures of pmma and its monomer mma. figure 2. pmma crystalline fashion. 1.2 distinct structural forms of pmma: isotactic, syndiotactic, and atactic in an academic context, polymer tacticity refers to the spatial arrangement of neighboring chiral centers within a polymer, with particular emphasis on vinyl polymers. the physical characteristics and properties of a polymer are significantly influenced by the composition of its monomer and its overall molecular structure[6]. the isotactic state occurs upon the addition of adjacent monomer groups in a meso diad mode, with the ester groups located on the successive asymmetrical carbons on the same side of the polymeric chain[7]. in contrast, the syndiotactic state occurs when the addition of the monomer groups is in a racemic diad mode and the ester groups on successive asymmetric carbons are projected in a regular alternation method on both sides of the plane of a polymeric chain. similarly, the atactic state represents another racemic diad mode, but it differs in the distribution of the ester groups located on the successive asymmetrical carbons, which are showcased in a random method on either of the plane sides of a polymeric chain, as illustrated in figure 3[8,9]. through the employment of radical polymerization (control/living), anionic polymerization, and reversible addition-fragmentation chain transfer techniques, pmma can be synthesized in its pure form, exhibiting isotactic, syndiotactic, and atactic configurations, contingent upon the specific initiator, monomer feed, and solvent utilized[8,10]. figure 3. the different tacticities of pmma[11]. 55c ̊ isotac�c 120c ̊ atactic 130c ̊ syndiotactic tg 3 1.3 lifetime and degradation science: applicability to polymers in the pursuit of understanding the degradation mechanisms arising from weathering of pmma, data-driven techniques from the interdisciplinary area of data science were employed. specifically, lifetime and degradation science (l & ds) were utilized, employing a stressor, mechanism, and response framework, to quantify the correlation between environmental stresses and the resulting degradation accumulation caused by distinct degradation mechanisms during the weathering process (figure 4). the weathering data encompassed the monitoring of physical and chemical alterations in pmma under varying exposure conditions, such as irradiation, temperature, and moisture. to gauge the physical and chemical degradation of pmma, nondestructive measurements like fourier-transform infrared spectroscopy (ftir), colorimetry, and uvvis spectroscopy were employed[11]. figure 4. weathering process. depolymerization reaction of paam the transformative procedure of depolymerization involves disassembling a polymer into constituent monomers or smaller molecular units[12]. the depolymerization phenomenon concerning pmma holds considerable research interest, primarily due to its extensive spectrum of industrial applications and the potential it harbors for chemical recycling endeavors[13]. pmma embodies a polymer characterized by an aliphatic foundational structure, contributing to its robust chemical and thermal stability[14]. the deliberate disintegration of pmma can be instigated through thermal or chemical methodologies[13]. thermal pathways for pmma depolymerization encompass diverse postulations[15]. one articulated mechanism, as proposed by kashiwagi et al.[16], involves cleavages occurring within the principal pmma chain. another theoretical framework put forth by manring contemplates homolytic cleavages of adjoining methoxycarbonyl groups nestled within the pmma structure[17]. notably, the rate constants and activation energies associated with the thermal deterioration of pmma exhibit variance, thereby engendering distinctions in the effectiveness of the depolymerization process[18]. nonetheless, consensus aligns with the notion that pmma’s thermal decomposition transpires via a biphasic sequence[19]. in the primary stage, there emerges a stochastic degradation of polymer chains, culminating in the generation of diminutive fragments[12]. subsequently, the secondary stage heralds depolymerization, wherein both the initial chains and the fragments undergo rupture, culminating in the formation of monomers[12]. the trajectory of pmma’s depolymerization is intrinsically molded by an amalgamation of factors, encompassing temperature, bond cleavage proclivities, and the presence of inhibitory agents[19]. 1.4 applications of pmma pmma found its initial significant application during world war ii, where it was employed as aircraft windows and bubble canopies for gun turrets[20]. the suitability of pmma for these applications hinged on achieving the appropriate weight, composition, and thickness tailored to its intended purposes. some other studies highlight the essential characteristics of pmma, with the representative values corresponding to new and unexposed material. furthermore, figure 5 illustrates the various applications contributing to the global demand for pmma[21,22]. figure 5. some application of glass replacement. 4 figure 6 shows the applications for global pmma demand. figure 6. applications for global pmma demand since 2014– 2024. 1.4.1 applications of solar technology in the quest for developing a quasi-solid-state dye-sensitized solar cell (dssc) with a high-conductivity polymer gel electrolyte, the selection of a suitable polymeric material as a host matrix within the composite was crucial[23]. consequently, pmma emerged as a favorable and compatible choice for this application[24]. this selection was attributed to pmma’s advantageous mechanical strength, compatibility, and optical clarity properties[23]. recently, shen et al.[22] presented a pioneering study reporting the hydrothermal synthesis of europium ion (eu+3)doped sodium gadolinium fluoride (nagdf4: eu) nanocrystals (ncs). for the first time, a down-conversion (dc) layer comprising pmma doped with luminescent nagdf4: eu was prepared and affixed to the rear of tio2 anodes to enhance the efficiency of dye-sensitized solar cells (dsscs)[23]. the evaluation of the impact of doped and undoped nagdf4 nanocrystal layers on the photovoltaic device, with incident-photon-to-current efficiency (ipce) as the parameter of comparison, revealed that the dssc incorporating a doped nagdf4: eu dc-pmma layer exhibited an improved photoelectric conversion efficiency by 4.5%[23]. in another study, yan et al.[25] conducted successful preparations of a polymer gel electrolyte employing a blend of pmma, ethylene carbonate, 1,2-propanediol carbonate, dimethyl carbonate, and sodium iodide/iodine as the source of i/i-3[26]. this specific polymer electrolyte, denoted as pmma-ec/pc/dmc-nai/i2, exhibited a remarkable ionic conductivity of 6.89 ms cm–1. the researchers further utilized this high-conductivity electrolyte to fabricate a quasi-solid-state dye-sensitized solar cell (dssc), which displayed impressive longterm stability and achieved a notable light-to-electrical energy conversion efficiency of 4.78%[27]. moreover, hammam et al.[24] fabricated a fluorescent pmma film incorporating a commercial coumarin dyestuff (macrolex fluorescent red g) via a flow-spin coating technique. the dye concentration within the film was adjusted to achieve the maximum intensity, and its emission characteristics were optimized to align with the absorption bands of chlorophyll (650–680 nm) for greenhouse applications[28]. remarkably weather-resistant, this fluorescent film proves suitable for deployment in growing rooms dedicated to commercial plant cultivation[29]. 1.4.2 applications in optics optical science plays a vital role across various disciplines, including engineering, medicine, pure science, and astronomy[29]. its practical applications encompass a wide range of technologies, such as lenses, microscopes, lasers, fibers, and polymers[30]. in particular, the optical activity of materials is an outcome observed when they interact with light, and this activity can be quantified through the refractive index[31]. in the case of pmma, its optical applications are primarily attributed to its favorable refractive index, excellent resistance to uv light, chemical durability, and commendable mechanical properties[32]. moreover, organic polymers offer advantages like cost-effectiveness, lightweight nature, and ease of processing, rendering them well-suited for immobilizing semiconductors in heterogeneous photocatalytic applications[33]. recently, camara et al.[34] conducted an investigation involving eleven synthetic polymers capable of being coated with tio2. these coated polymers were exposed to solar radiation for 150 days, both with and without the tio2 layer, to study the weathering effects[28]. such studies contribute to a better understanding of how polymers respond to environmental exposure and play a crucial role in advancing practical applications and innovations in the field of optical materials[31]. upon careful observation, it was found that among the studied materials, only pmma exhibited excellent retention of both the optical and mechanical properties of titania after undergoing natural weathering[32]. consequently, pmma emerges as the 5 most promising candidate for effectively immobilizing tio2 in applications related to photocatalytic treatment[33]. 1.4.3 application in dentistry thermoplastic resins have a long-standing history of utilization in dentistry, characterized by their ability to undergo multiple cycles of softening through heating and hardening via cooling without undergoing chemical alterations[35]. these resins consist of polymer chains, composed of diverse lengths and molecular weights, organized into bundles. four broad classifications of thermoplastic resins include thermoplastic acetal, thermoplastic polycarbonates, thermoplastic acrylic, and thermoplastic nylon[36]. in particular, thermoplastic acetal exists in both homo-polymer and copolymer forms, with the latter exhibiting superior long-term stability compared to its homopolymer counterpart[37]. its resistance to occlusal wear makes it highly suitable for preserving the vertical dimension during provisional restorative therapy[37]. however, when compared to thermoplastic acrylic and polycarbonate, thermoplastic acetal lacks the natural translucency and vitality, making it more suitable for short-term temporary restorations[38]. thermoplastic polycarbonates, composed of bisphenol-a carbonate polymer chains, find ideal applications in provisional crowns and bridges, yet are not well-suited for partial denture frameworks[39]. however, dentists have long been using thermoplastic acrylic, which is shown in figure 7, for temporary crowns and as a base plate material for partial and complete dentures[39]. nevertheless, thermally polymerized pmma does exhibit certain drawbacks, such as high porosity, water absorption, volumetric changes, and residual monomer[40]. figure 7. temporary crowns. due to their limited impact resistance, tensile strength, and flexural strength in various applications, the use of traditional thermoplastic resins faces challenges[41]. consequently, for specific circumstances that demand enhanced flexibility, improved resistance to flexural fatigue, and superior impact strength, the adoption of improvised thermoplastic nylon can present a valuable alternative to polymethylmethacrylate[42]. 1.4.4 applications of the viscosity in the realm of fluid dynamics, viscosity represents the extent of a fluid’s resistance to flow when subjected to applied shear stress[43]. when considering polymeric melts or solutions, they exhibit nonnewtonian behavior, meaning that the shear stress is not directly proportional to the shear rate[44]. however, polymers possess an intrinsic viscosity, serving as an indicator of their capacity to enhance the viscosity of another fluid[45]. as a result, a high-molecular-weight polymer can effectively modify or influence the viscosity of low molecular weight polymers. pmma, due to its compatibility and ease of processing, proves valuable for developing viscosifier copolymers in conjunction with natural polymers[46]. in a study conducted by mishra and sen, the grafting of pmma onto guar gum was accomplished using a microwave-initiated method. the investigation focused on the correlation between the percentage of grafting and the intrinsic viscosity of the resulting product. the findings demonstrated that the modified product could serve as a superior viscosifier compared to guar gum in its pristine form[47]. 1.4.5 nanotechnology applications the interplay between polymers and nanomaterials has revolutionized the field of nanotechnology, leading to the development of polymer nanocomposites[48]. these composites exhibit significant enhancements in material properties despite incorporating only minute amounts of nanoparticles. the improvements encompass a wide range of characteristics, including mechanical strength, solubility, electrical conductivity, optical properties, scratch resistance, thermal stability, and flame retardation, among others. the extensive application potential of nanocomposites in nanotechnology has attracted considerable research attention towards their fabrication and diverse applications[49]. perween et al.[31] explored the utilization of 6 pmma and graphite in the production of plastic chip electrodes (pces) using a straightforward solution casting technique. the resulting electrodes were cost-effective, versatile, and dispensable for various applications. microscopy (sem and afm), thermal properties (tga), and mechanical and electrical analyses were conducted to characterize the fabricated electrode. in a novel approach for preparing nanocomposites involving nanoparticles, the combination of covalent and noncovalent interactions was found to be highly beneficial. wang et al.[32] investigated the effect of sio2 nanoparticles on sio2/pmma composites. the fabrication involved a two-step process: noncovalent modification of sio2 nanoparticles with tetraoctylammonium bromide to facilitate their dispersion in the solvent, and covalent process through radical suspension polymerization with mma monomer, leading to the formation of silicon oxide/pmma nanocomposite. this method aimed at enhancing the mechanical properties of pmma for broader applications. the study revealed remarkable improvements in tensile strength and flexural strength, with enhancements of up to 80.6% and 127.3% compared to pure pmma, respectively. surface functionalization of nanoparticles through polymer grafting holds significant importance in the design of both organic and inorganic nanocomposites. atom transfer radical polymerization (atrp) has emerged as a leading method due to its superior control over molecular weight and low polydispersity. the surface-initiated atrp technique is widely adopted for grafting homopolymers, diblock copolymers, graft copolymers, star polymers, and branched polymers from various nanoparticles, such as nanotubes, nanowires, and nanoclays[26]. pmma has been successfully grafted into carbon nanotubes (cnts) to improve the solubility and processability of cnts. this is significant considering the exceptionally low density, mechanical, electrical, and thermal properties of cnts, which are hindered by limited solubility due to π-π bond interactions. 1.4.6 applying thick pmma layers onto conductive metal substrates three distinct methods are available for the application of thick pmma layers onto a conducting metal substrate: multilayer coating, casting, and sheet adhesion. among these, casting and commercial sheet adhesion are the most frequently employed techniques[50]. 1.4.7 application of pmma in the construction of microanalytical separation apparatus pmma possesses several advantageous characteristics that render it a suitable substrate for the fabrication of microanalytical separation devices. its ease of machinability using various methods, such as laser ablation, injection molding, imprinting, and hot embossing, allows for efficient device production. additionally, molds produced through the liga process, which is a german acronym for lithography, electroplating, and moulding (lithographie, galvanik und abformung), have been effectively employed to create pmma microanalytical separation devices. the material’s optical properties enable analyte detection using fluorescence and visible spectroscopies[46]. furthermore, pmma demonstrates the ability to withstand high electric fields and effectively dissipate heat, making it a desirable choice for applications in the microanalytical separation device industry. with a glass transition temperature (tg) of –100 ℃ in commercially available pmma sheets, microdevices fabricated from pmma can be thermally sealed using a pmma top plate via thermal bonding procedures. notably, pmma exhibits solubility in various organic solvents while remaining insoluble in polar solvents like water and alcohols, which are commonly employed in conventional ce and cec solvent systems. likewise, it remains insoluble in nonpolar solvents such as hexanes and cyclohexane[42,43]. 1.4.8 pmma as a significant resist material in microelectronic applications pmma has garnered considerable significance as a pivotal resist material within the realm of microelectronic applications. its prominence arises from its capability to form ultra-thin, coherent films and its susceptibility to etching processes in lithographic operations due to its notable depolymerization proficiency[28–35]. notably, pmma demonstrates a distinct characteristic in facilitating controlled solvent mobility over its polymeric matrices, owing to the facile 7 manipulability of its dissolution kinetics. this attribute has enabled the achievement of highly defined edges with desired slopes in the imagery of the resist material when employing a pmma matrix[28,36]. the rate of pmma dissolution during photoresist development is notably contingent upon parameters such as molecular weight and molecular weight distribution, both of which significantly impact the fabrication of diverse optical elements[45]. consequently, pmma serves as a benchmark against which the efficacy of resistive materials can be measured. while numerous alternative polymers have been unveiled, many surpass pmma in terms of sensitivity. nonetheless, the amalgamation of attributes encompassing stability, sensitivity, contrast, adhesion, and solubility has perpetuated pmma’s preeminence[28,47–49]. consequently, renewed interest has arisen in the innovative synthesis of pmma. photoresists founded on photoinduced free-radical chemistry have garnered escalating attention within the sphere of microelectronic applications[50]. researchers have successfully used the solution casting technique to synthesize pmma and rhodamine-b fluorescent dyedoped pmma[51]. the researchers meticulously recorded the uv-visible spectra of these films[52]. they then utilized the spectral data to derive various optical properties, including band gap, refractive index, and metallization criterion[52]. notably, the investigation revealed that while the band gap generally diminishes with increasing dopant concentration, the direct band gap exhibited a gradual reduction, whereas the indirect band gap displayed an initial moderate decline that transitioned into a more pronounced reduction beyond a dopant concentration of 10 wt%[51]. this discernment underscores the potential for precise modulation of pmma’s optical characteristics through judicious doping with rhodamine b dye[53]. 1.5 further positive sides of pmma the commendable attributes of poly(methyl methacrylate) (pmma) find significant relevance within diverse academic and industrial spheres, substantiated by empirical evidence: 1) exceptional transparency: pmma’s exceptional transparency, allowing the transmission of up to 92% of visible light, is well documented[54]. this unique property positions pmma as a preferred choice for applications necessitating unimpeded clarity and visibility, such as optical lenses, display panels, and windows[54]. 2) resilience to weather elements: pmma’s remarkable resistance to uv radiation is extensively recognized[55]. this characteristic endows pmma with suitability for outdoor deployment, as it resists yellowing or degradation under prolonged sunlight exposure, thereby maintaining optical integrity over time[55]. 3) vigorous impact endurance: studies affirm pmma’s superior impact resistance compared to glass[56]. this intrinsic property fosters its adoption in scenarios demanding shatterproof or impact-resistant attributes, ensuring safety in contexts predisposed to high winds or unintended collisions[57]. 4) featherweight composition: the lightweight nature of pmma has been acknowledged in both academic and industrial realms[58]. this feature enhances its handling ease, transportation convenience, and capacity to contribute to weight reduction in diverse structures, thereby exemplifying its pertinence in industries like automotive and aerospace[58]. 5) adaptability and dexterity: pmma’s adaptability, facilitated shaping, and facile fabrication processes are well-documented[59]. this versatility translates into various forms, including sheets, rods, and intricate designs, thereby spanning applications in architecture, medical equipment, and consumer goods[59]. 6) chemical endurance: extensive research underscores pmma’s commendable chemical resistance to acids, alkalis, and solvents[60]. this property positions it favorably in settings involving chemical exposure, such as laboratory equipment and chemical storage containers[60]. 7) simplicity in upkeep: scholarly work corroborates the ease of maintenance of pmma[57]. its potential for polishing to mitigate surface imperfections and reduced susceptibility to staining compared to other materials support its longevity and cost-effectiveness[60]. the confluence of these positive attributes underscores pmma’s indispensability within a myriad 8 of industries and applications. a dynamic equilibrium between optical performance, resilience, and adaptability substantiates pmma’s continued prominence. 2. conclusions in conclusion, poly(methyl methacrylate) (pmma) is a remarkable polymer with a wide range of applications and unique properties. its transparent nature, excellent mechanical strength, and ease of processing make it highly valuable in industries such as automotive, aerospace, medical, and signage. while pmma offers numerous advantages, it also has certain limitations that need to be considered in specific applications. ongoing research and development efforts continue to explore new manufacturing processes and expand the potential applications of pmma. further research should focus on enhancing its properties, improving its sustainability, and exploring novel applications in emerging fields. with its versatility and promising future prospects, pmma remains an important material in the polymer industry. author contributions conceptualization, ss and ey; methodology, ss; software, ss; validation, ss, ey and kz; formal analysis, ss; investigation, ss; resources, ss; data curation, ey; writing—original draft preparation, ss and kz; writing—review and editing, kz; visualization, ey and kz; supervision, ey; project administration, ss and ey. all authors have read and agreed to the published version of the manuscript. conflict of interest the authors declare no conflict of 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decades is undeniable. responsible for this interest in nanomaterials are mainly the nanostructured forms of carbon, since historically they were the ones that inaugurated the study of nanomaterials with the discovery of fullerenes in 1985 and carbon nanotubes in 1991. although a variety of techniques exist to produce these materials, chemical vapor deposition (cvd) is particularly valuable as it allows the production of a wide variety of carbon nanostructures, is versatile, scalable, easy to implement and relatively low cost. this review article highlights the importance of cvd and details its principles, operating conditions and parameters, as well as its main variants. a description of the technique used to produce fullerenes, nano-ceramics, carbon nanotubes, nanospheres, graphene and others is made, emphasizing the specific parameters for each synthesis. keywords: chemical vapor deposition, carbon nanostructures, synthesis article info received: 2 march 2022 accepted: 4 april 2022 available online: 12 april 2022 copyright copyright © 2022 ali roberto ruiz hernández, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction the discovery of c60 (buckminsterfullerene) in 1985[1], triggered a wave of research on allotropic nano-sized forms of carbon. this event triggered the discovery of other nanostructured forms of carbon such as: singleand multi-walled nanotubes[2,3], nano-onions[4], nanolistones[5], nano-horns, nano-diamond, carbon dots[6], nanospheres[7]) and recently graphene[8]. various nanofabrication methods are involved in the synthesis of these nanostructures such as: laser ablation, arc discharge, chemical vapor deposition and more recently hydrothermal or wet chemical methods such as sol-gel. of particular importance is the chemical vapor deposition (cvd) method due to its versatility, ease of implementation, low cost, scalability, among other advantages. figure 1 illustrates models of carbon nanostructures that can be produced by the cvd technique, most of these materials are made of carbon atoms with sp2 hybridization. fullerenes are a family of spherical molecules that can contain 60 atoms or more (even numbers), achieving giant fullerene structures of up to hundreds of atoms. structurally, the fullerene or c60 is a spherical cage (similar to a soccer ball) made up of exactly 60 carbon atoms, in this structure are the carbons with sp2 hybridization, each attached to 3 neighboring atoms, the introduction of pentagons is essential to form the curvature needed to close[1]. related to fullerenes are nano-onions, which consist of concentric fullerenes inside each other, generating an onion-like structure. graphene is a sheet of carbon atoms with sp2 80 hybridization configured in a hexagonal arrangement, it is a two-dimensional nanomaterial, graphite is formed by stacking graphene sheets one on top of the other. starting from a graphene sheet, by rolling it up, carbon nanotubes can be obtained[2,3]. these nanostructures motivated further research in the 1990s and the first decade of the 2000s, their amazing mechanical and electrical properties have led to technological applications in the market and in development. undoubtedly, the nanostructure that receives more attention is graphene, for its isolation was awarded the nobel prize in physics to novoselov and geim in 2010[9]; increasing the number of research and technological innovation projects in order to enhance the amazing properties of this material. the aforementioned nanostructures, and others, are produced by the cvd method. this review article aims to introduce the reader to the principles, parameters and variants of cvd for the synthesis of carbon nanostructures, in addition to listing the most common carbon nanomaterials that are produced by this technique and their synthesis conditions. 2. cvd technique 2.1 generalities the chemical vapor deposition technique consists of promoting chemical reactions in the gaseous state from precursors, which trigger the formation of nanomaterials of interest. these chemical reactions generally take place inside a reaction chamber and are activated by high temperatures. the reaction precursors can be in liquid, solid or gaseous state and are brought into the reaction chamber where their decomposition is promoted by the high temperatures involved in the process, generally temperatures for the synthesis of carbon nanomaterials range between 800 ℃ and 1,000 ℃. the reaction chamber must have an evacuation route for the gases that did not participate in the reaction or the vapors containing the products that have not been deposited. normally at the exit of the reaction chamber a gas washing or evacuation system is located by means of mechanical systems (vacuum pumps)[10,11]. a cvd setup can be presented in horizontal or vertical configuration, the most common configuration being horizontal at the research laboratory level, however, on the industrial scale there are equipment in vertical format. for the reaction chamber a material is required that resists exposure to high temperatures, which at the same time is inert and does not participate in the reactions of the process; the most common is to use quartz or alumina. figure 1. models of the most representative carbon nanostructures[12–16]. although there are various configurations, the most used is to place a quartz tube inside an electric tubular furnace, as exemplified in figure 2. the region of the quartz tube inside the furnace is considered the reaction chamber, and at the ends of the tube, at the inlet and outlet, borosilicate glass gaskets are placed to allow the coupling of the pipes for the delivery of the precursors through the flow of a carrier gas[17]. the obvious choice of carrier gas is argon gas, as it is inert and easily accessible, although some groups choose nitrogen (n2) as the gas in the system; hydrogen (h2), which is important in the decomposition of precursors, is also used in some processes. substrates with specific properties can be introduced into the reaction chamber and promote the deposition of the nanomaterials on its 81 surface, although generally, the quartz tube walls themselves serve as substrates for the deposition of the reaction products, except in cases where the synthesis requires a catalyst and this is not present among the precursors, as will be detailed later[18]. the most common precursors for the synthesis of carbon nanostructures are hydrocarbons, although it has been shown that thermal decomposition of any carbon source can be successful in the production of carbon nanostructures. specifically for graphene, its synthesis using cvd from insects or cookies has been demonstrated[19]. figure 2. detailed diagrams of the different cvd variants. apcvd: atmospheric pressure cvd, aacvd: aerosol assisted cvd[21], lpcvd: low pressure cvd[22] and pecvd: plasma enhanced cvd[23,24]. the synthesis of some carbon nanostructures, such as nanotubes, requires the presence of catalysts. the catalysts normally used are metals such as iron, cobalt or nickel. a successful way to provide such elements to the system is by organometallic molecules (ferrocene, cobaltocene, nickelocene) that are mixed with the carbon precursor. there are two ways of providing the catalysts to the system, the first is called “floating catalyst” and the second “seeded catalyst” (floating catalyst and seeded catalyst, respectively), illustrated in figure 3. the floating catalyst process is characterized by the use of gaseous or solution catalysts mixed with the carbon precursor, which “float” into the reaction chamber. these catalysts are used to favor the decomposition reactions of the precursor, lowering the temperature required for the process. in this technique in particular, as the catalyst is floating, it interacts favorably with the precursor gas, favoring easier and faster decomposition[25]. in the seeded catalyst mode, solid catalysts “seeded” or attached to the substrate where the nanomaterials will be deposited, serve as nucleation points and the substrate is placed inside the reaction chamber. as the precursor decomposes into individual particles or atoms, they will be placed around or on the catalysts to form the final carbon nanostructure. this procedure is widely used in the synthesis of carbon nanotubes since from this “seed” the tubes can be elongated vertically[26]; it also allows the growth of nanotubes on the substrates, obeying specific patterns, since in areas without a seeded catalyst growth is not favored. 2.2 variants there are variants in the cvd process, some of them are: atmospheric pressure chemical vapor deposition (apcvd), low pressure chemical vapor deposition (lpcvd), aerosol assisted chemical va 82 por deposition (aacvd), plasma activated chemical vapor deposition (pecvd) and microwave assisted chemical vapor deposition and plasma activation (mw-pecvd), described in the following lines and illustrated in figure 2. 2.3 ambient pressure chemical vapor deposition (apcvd) this is the most common form, described above, and is operated at a pressure of 1 atm (ambient pressure). a vacuum pump is not used to regulate the pressure. the precursor is usually a liquid or a dissolved solid, so it is heated to sufficiently high temperatures so that it begins to evaporate and a vapor cloud is generated. the carrier gas is responsible for pushing the precursor vapor into the tube and through the furnace (reaction chamber) to the outlet[27]. 2.4 low pressure chemical vapor deposition (lpcvd) it consists of a cvd process using a vacuum pump connected to the tube outlet that regulates the internal pressure of the equipment to pressures close to vacuum (approximately 10−1 to 10−2 torr). for this process, a fully gaseous precursor is used, which travels through the tube to the outlet along with the carrier gas. due to the low pressures, the decomposed atoms are better dispersed in the substrate[27]. figure 3. schematic representation of the types of catalysts used in a cvd process for the synthesis of carbon nanotubes. on the left, floating catalyst, which is introduced into the reaction chamber along with the precursor; on the right, seeded catalyst, which is deposited on a substrate inside the reaction chamber and is activated when the precursor is introduced. personal elaboration. 2.5 aerosol-assisted chemical vapor deposition (aacvd) in this method, a liquid precursor is used for the synthesis, which is transported to the reaction chamber in the form of an aerosol. usually an ultrasonic bath is used, which generates ultrasound that propagates throughout the precursor to agitate its particles until aerosol droplets appear. the carrier gas transports the aerosol through the system to react and deposit on the substrate[28]. 2.6 plasma activated chemical vapor deposition (pecvd) this method is classified as a variant of lpcvd, very low pressures are used for the decomposition of the precursor, however, in this method much lower temperatures are used due to the use of a plasma, which “activates” the precursor, facilitating its decomposition. the plasma is a gaseous state where reactive radicals coexist in the form of electrons, ions, neutral atoms and other highly energetic particles. this plasma is produced through the acceleration of electrons in an electric field, generated by means of two electrodes connected to a voltage source[29]. in this method, gaseous precursors are used, which with the help of a carrier gas pass through the plasma zone, where the decomposition and deposition reaction takes place on the substrate. 2.7 microwave assisted chemical vapor deposition and plasma activation (mw-pecvd) this methodology is a sub-variant of pecvd, 83 a plasma is also produced for the decomposition of the precursor, but this is produced by microwave action, which is a low energy electromagnetic radiation. a source of approximately 2.45 ghz is introduced through a dielectric window, which will excite the gases producing the characteristic luminescent plasma that will carry out the decomposition reaction. it is characterized by being able to operate at higher pressures than pecvd[30]. 3. carbon nanostructures produced by cvd 3.1 fullerenes as mentioned, in 1985, the synthesis of c60 fullerene was reported for the first time by the laser ablation method, a technique used to date to obtain the nanomaterial, where the vaporization of graphite is carried out by laser irradiation[1]. since then, other methods such as chemical vapor deposition, pyrolytic routes[31], arc discharge, and combustion processes have been employed in search of better yields. combustion processes are emerging as the most favorable for the industrial production of fullerenes due to the high efficiencies reported[32]. regarding chemical vapor deposition for the synthesis of c60 and c70, it should be noted that the technique has been less prominent due to the low yields obtained; however, the formation of these fullerenes as by-products of diamond synthesis by the hot filament chemical vapor deposition method and microwave-assisted chemical vapor deposition has been reported[33]. the microwave-assisted chemical vapor deposition used for the synthesis of diamond and fullerenes consists of a quartz tube as a reaction chamber, inside which an excitation source from a generator (100 w, 2.45 ghz) is incident[34], responsible for the generation of the plasma precursor of the nanostructure. the gases used in this method are argon, hydrogen and acetylene, the latter being the carbon source. the process is subjected to pressures between 1 and 10 torr, but experiments with pressures above 25 torr and below 10 torr are also reported[34]. with regard to hot filament chemical vapor deposition[34], it consists of a stainless steel chamber, inside which is a tungsten filament, hanging vertically, with one of its terminals fixed and the other connected to a braided copper wire to avoid tension on the filament. generally, the filament has a diameter of 0.75 mm and a length of 8 cm. the gases used for the synthesis are methane as a carbon source (0.4 sccm) and hydrogen (99.6 sccm). likewise, a stainless-steel substrate support is used for the deposition of the diamond film and, consequently, for obtaining c60 and c70 fullerenes. generally, the filament currents are between 50 and 60 a, and filament temperatures are 2,000 to 2,200 ℃. typical substrate temperatures are between 950 and 1,000 ℃. 3.2 nano-onions other nanostructures belonging to the family of fullerenes are known as nano-onions. nano-onions were discovered in 1992 and are multiple layers of carbon that form encapsulated structures[35]. their first synthesis method was by irradiation of an electron beam to a carbon nanotube sample, however, other methods such as nanodiamond heat treatment, arc discharge, chemical vapor deposition or implantation of carbon ions into metal particles[33]. with respect to chemical vapor deposition, some synthesis routes are based on the use of catalysts or plasma handling as an upgrading method. the catalysts employed are generally iron-containing alloys or compounds and the resulting nanostructures possess a core of this catalyst[36]. an example is using methane as a carbon source and stainless steel as a substrate at 800 ℃[37] or the use of a nickel-iron alloy as a catalyst at 850 ℃[38]. plasma assisted chemical vapor deposition is a process generally carried out at pressures ranging from millitorr to a few torr. inside the chamber there are two electrodes subjected to a small discharge, which generates a plasma from the gases between them, the plasma is generally produced by radiofrequency or direct current. when this process is carried out by radiofrequency, the gases most frequently handled are methane, as a 84 carbon source, and hydrogen. this synthesis method is very favorable due to the formation of pentagonal carbon rings, which are indispensable for the formation of the concentric spheres[39]. unlike other methods, nanoonions produced by radiofrequency plasma-assisted chemical vapor deposition do not generate other types of products, such as carbon nanotubes[39]. structures up to 50 nm in diameter with wave-like behavior in the layers due to the formation of pentagonal, hexagonal and heptagonal carbon rings have been reported[39]. in addition to not obtaining carbon nanotubes by this synthesis, the nano-beads present a unique behavior because during the growth mechanism they do not encapsulate the catalyst used as had been reported in other synthesis methods[39] and the result is a product with fewer impurities. 3.3 nanotubes the field of research on carbon nanotubes began in 1991, when they were experimentally observed by transmission electron microscopy (tem), and the conditions for the synthesis of large quantities of nanotubes were subsequently reported, early work was carried out on multi-wall carbon nanotubes (mwcnts), which later led to the discovery of smaller diameter single-wall carbon nanotubes (swcnts) in 1993[40]. the synthesis of nanotubes can be carried out by different methods that have been reported in recent years, however, the most important is chemical vapor deposition (cvd), with which mwcnts can be obtained, with the presence of a floating catalyst, by carrying out a pyrolytic decomposition of a feed solution (benzene-ferrocene, for example) in a furnace, by flowing argon through a reaction chamber, with temperatures of about 750 ℃ in the growth zone and 120 ℃ at the feedstock injection point[41]. the latter is placed in an alumina crucible and vaporized so that the argon flow transports the vapor to the growth zone and the carbon nanotubes are deposited on the substrate. the aacvd variant has also been used for the synthesis of carbon nanotubes. the same technique can be carried out at atmospheric pressure using metal nanoparticles (nps) on a substrate as a seeded catalyst, obtaining swcnt. by heating the catalyst to elevated temperatures, the nps become liquid or semi-liquid and hydrocarbon decomposition occurs on the surface of these metal droplets, producing carbon. carbon precipitates on the outer layer of the catalysts upon reaching its required saturation level, starting to precipitate on its outer layer, forming tubular carbon solids with sp2 structure, resulting in the growth of carbon nanotubes[42]. 3.4 graphene graphene is a two-dimensional (2d) material composed of a layer of carbon atoms densely packed in a hexagonal arrangement of sp2 carbons bonded in a benzene ring structure[43,44]. the term “graphene”, first used in 1987 by sylvie mouras, refers to a single atom-thick layer of carbon[45]). graphene films were first isolated by the method of mechanical exfoliation of a piece of highly oriented pyrolytic graphite[8]. in this method, graphene sheets stacked on graphite, weakly bound by van der waals forces, are separated using adhesive tape, obtaining small films of varying thickness[43]. unfortunately, apart from variations in thickness, they have irregular shapes and there is no control in their orientation[10]. because of this, the most commonly used synthesis method today is chemical vapor deposition, which consists of the decomposition of a frequently gaseous hydrocarbon (solid and liquid precursors are also possible), usually by means of high temperatures (~1,000 ℃), and its deposition on a copper surface[10]. carbon atoms are provided by the precursor hydrocarbon, deposited on the nucleation sites of the metal substrate and dispersed on its surface aided by low pressures (~10−3–10−4 atm) forming graphene layers. this technique allows producing continuous graphene films of high purity over large areas[8]. in recent years this material has been extensively studied, due to the belief that graphene could replace many of the existing materials on the market, since it possesses unique properties such as: high mechanical strength and elasticity, high elec 85 trical and thermal conductivity, transparency and impermeability. for the reader who wishes to delve into the study of graphene, it is recommended to consult the review by soldano and collaborators on its production and properties[46]. 3.5 nanospheres for the synthesis of carbon nanospheres by the ambient pressure chemical vapor deposition (apcvd) method, solid, liquid and gaseous carbon precursors are used. for liquid precursors, various delivery systems are applied such as the use of bubblers[47], injection pumps or syringes (direct liquid injection)[47], capillary tubes, as well as aerosol assisted pyrolysis mechanisms [48] from the precursor solution (toluene, naphthalene, etc.). for gaseous precursors different types of gas injectors are generally used[49] to regulate the amount of precursor that will enter the system. finally, for solid precursors, sublimation methods[50] or bubblers[51] are applied. these systems transport the precursors to a previously heated oven where the temperature range varies between 800 ℃ and 1,100 ℃[52], the synthesis time is variable, at the end of the reaction the oven is programmed to return to room temperature. subsequently, the product is recovered for analysis. it should be noted that the temperature of the synthesis plays an important role in the particle size obtained, the higher the temperature the smaller the diameter[52], and depending on the size, these structures can have a larger or smaller surface area. due to this property, it is also believed that they can be used as adsorbents[53], or additives for different nanocomposites[54] with a wide range of applications. as the nanostructure is carbon in nature, it is likely to avoid damage to the environment and the human body; moreover, due to its low toxicity, it is considered for use in the biomedical area[55,56]. 3.6 nanolistones another carbon nanostructure that has been produced by cvd is the graphitic nanoliston. nanolistons are one-dimensional structures with lengths in the millimeter range, widths of 100200 nm and thicknesses of ~20 nm[5]. the synthesis is carried out in an aacvd system, pyrolyzing at 950 ℃ a precursor solution containing ethanol (ch3ch2 oh), ferrocene (fecp2) and a small concentration of thiophene (c4h4s). these nanolayers are made up of graphene layers stacked along the ribbon axis. the structure has been confirmed by x-ray diffraction and tem. the morphology of the nanolayers guarantees a large surface area and the edges of the graphene sheets represent potential sites for binding molecules that will allow them to have varied applications. it has been studied that when subjected to high temperatures, the contiguous layers of graphene in the nanolayers tend to join together, forming bonds, to reduce the action of the highly reactive edges[5]. 3.7 other nanostructures on the other hand, the cvd technique is not limited to the individual synthesis of nanomaterials, but can also be used as a means to obtain complex structures. using a two-step procedure, a hybrid carbon nanostructure consisting of double-walled carbon nanotubes (dwcnts) with graphene nanosheets has been synthesized by this technique. the first step consists of the synthesis of the dwcnts by cvd with a floating catalyst. the process starts with the flow of argon into the system (500 sccm) until reaching 1,300 ℃, at which time the flow of h2 as carrier gas (1,000 sccm) is started and a solution of ferrocene and thiophene dissolved in ethanol (0.04 ml/min for 20 min) is pumped at ambient pressure. after being purified, the obtained dwcnts are introduced into the reaction zone to produce the graphene nanosheets by cvd. a flow of argon (500 sccm) is initiated until reaching 1,300 ℃ and effecting the injection of ethanol (0.04 ml/min) as carbon source, employing h2 as carrier gas (1,000 sccm). the result of the process is the growth of structures with sharp edges, resembling petals, along the walls of dwcnts but maintaining the one-dimensional nanotube structure[58]. another type of nanostructures that are synthesized by the chemical deposition method are nanowalls (nw’s), where the plasma-assisted method (pecvd) is used. these are anchored to the surface of a substrate as elemental silicon wafers, without the need for metal catalysts, the structures 86 are grown by using a copper or tantalum cube located in the center of the substrate holder and a power of 500 w is applied to the system, two plasma treatments are made: one of hydrogen and the other of a combination of ammonia-acetylene. the degree of graphitization and growth rate depend mainly on the amount of ammonia used and the wall thickness depends on the anchorage to the substrate[59]. the utility of this nanostructure would be in electrochemical applications such as batteries and fuel cells, research has also been conducted for its use as a backlighting material for liquid crystal displays[60]. finally, another nanostructure obtained by cvd is graphene quantum dots (graphene quantum dots, gqd’s). these structures are obtained when the growth rate of graphene in the initial stage is suppressed well below the nucleation rate[61]. these conditions are obtained with a low precursor flow rate (2 ml/min) and at a relatively low temperature (1,000 ℃), the product is deposited on copper substrates[61]. these structures possess a large number of vents such as biocompatability, low toxicity, good solubility and large surface area[62], so they can have a wide range of applications. 4. conclusions the chemical vapor deposition technique is a widely used bottom-up nanofabrication method for the synthesis of nanomaterials. its versatility and easy implementation make it a highly popular technique for the production of carbon nanostructures. the 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devices. energy and environmental science 2012; 8(1): 31–54. doi: 10.1039/c4ee02594f. can v3i1 2020.pdf characterization and application of nanomaterials (2020) volume 3 issue 1 original research article nesmeyanov institute of organoelement compounds, russian academy of sciences, 28 vavilov st., moscow 119991, russia. e-mail: naumkin@ineos.ac.ru keywords: et al. e.g. etc etc i.e. viz e e e e e e e e e e e e e e e e e e e e e e e note: e e e e e e e e e e e e et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. can v2i2 2019.pdf characterization and application of nanomaterials (2019) volume 2 issue 2 original research article institute of automation and control processes, far east branch, russian academy of sciences, vladivostok 690041, russia. e-mail: plusnin@dvo.ru keywords: et al et al et al et al et al et al can v3i1 2020.pdf characterization and application of nanomaterials (2020) volume 3 issue 1 review article 1department of mechanical engineering, national institute of technology, srinagar 190006, india. e-mail: sajad_08ph d12@nitsri.net 2p.g department of physics, special center for nanosciences, national institute of technology, srinagar (j&k) 191131, india. keywords: et al et al. et al et al. et al. et al. et al et al. et al et al et al et al. et al et al et al et al et al et al. et al et al et al et al et al et al. et al et al et al et al et al et al et al et al et al et al et al et al characterization and application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1688 68 original research article comparative analysis of mechanical properties of geopolymers incorporating sic nanowhiskers and tio2 nanoparticles madeleing taborda-barraza1*, nagilla huerb de azevedo1, philippe jean paul gleize1, natalia prieto-jimenez2 1 departamento de ingeniería civil, universidad federal de santa catarina, florianópolis, brazil. e-mail: madelatb@hotmail.com 2 grupo de investigación en energía y medio ambiente (giema), universidad industrial de santander, colombia. abstract a metakaolin-based geopolymer was fabricated with 5 ratios of two different nanomaterials. on the one hand, silicon carbide nanowhiskers and, on the other hand, titanium dioxide nanoparticles. both were placed in water and received ultrasonic energy to be dispersed. the effects on mechanical properties and reaction kinetics were analyzed. compared to the reference matrix, the results showed a tendency to increase the flexural strength. probably due to the geometry of the sic nanowhiskers and the pore refinement by the nano-tio2 particles. the calorimetry curves showed that incorporating tio2 nanoparticles resulted in a 92% reduction in total heat, while sic nanowhiskers produced a 25% reduction in total heat. keywords: geopolymers; nanomaterials; mechanical strength article info received: 10 july 2022 accepted: 30 august 2022 available online: 12 september 2022 copyright copyright © 2022 madeleing taborda-barraza, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction 1.1 geopolymers “geopolymer” can be considered a generic term to define an alternative binder to portland cement paste. structured as an inorganic polymer and with similar or higher mechanical strength than a portland cement cementitious material[1–3], it offers environmental advantages during its manufacture such as: the use of industrial waste[4], reduction of the calcination temperature in clay materials, which positively affects the emission of co2 into the atmosphere[1], encapsulation of toxic elements[5–7], resistance to acid attack and other types of attacks[2,3]. however, as a ceramic material, it has certain limitations that continue to be investigated, such as: easy propagation of cracks that can compromise mechanical strength[8,9], flexural strength lower than compressive strength[10,11] and the appearance of efflorescence[12]. many ceramic and polymeric materials have mechanical limitations that can be reduced by using reinforcement elements in different scales such as steel, metallic fibers, vegetable fibers[13], polypropylene microfibers[14]. in this way, the geopolymers become a matrix and the additive element acts as a reinforcement against the weaknesses of the main matrix. 1.2 nanomaterials in geopolymeric and cementitious matrices nanomaterials, in the form of fibers or particles, can also contribute to the modification of the microstructure of cementitious matrices, 69 attributing their properties and improving their mechanical response. adding nanomaterials in geopolymeric matrices has been a trend in recent years. the results show: increases in compressive strength when materials such as nano-clay, carbon nanotubes (cnt) and nano-sio2 are added[15–18], densification of the microstructure, reduction of the initial setting time, reduction of shrinkage[19,20], increase of ductility with the use of carbon nanofibers (nfcs), alumina nanofibers (nfas), silicon carbide whiskers (wsc)[10], and even ntc, which are the most commonly used[20–22]. sic is widely used in mechanical engineering for its high abrasion and wear resistance, high hardness record, thermal stability, flexural strength and others[23]. sic can be found in the form of fibers, nanoparticles of sic (npsc) or nanofibers, called nanowhiskers of sic (nwsc). these are usually incorporated in epoxy-type resin and alumina matrices[24,25]. for chemistry, tio2 is considered the best photocatalyst, chemically stable and low cost[26], which enables the degradation of organic pollutants in aqueous media[27]. it is normally used for water treatment, paint pigmentation and sun protection. over time, it was considered to introduce this property in ceramic materials with the use of titanium dioxide nanoparticles (nt) and thus, they would be transformed into materials with photocatalytic properties and consequently, more durable materials[28–30]. in several studies[31,32], it was indicated that nt would not be producing relevant changes on geopolymeric matrices. despite this[33–35], they were able to record increases in compressive strength when nt was added to geopolymers based on blast furnace slag or fly ash. increases in compressive strength, up to 51% over the reference matrix, when 5% nt was used in the early ages. in the nanomaterial form[36] incorporated sic nanowhiskers in portland cement matrices and obtained relevant changes in compressive and flexural strength when they added 0.25% and 1.00% nwsc in relation to the cement mass, respectively. similarly[37], added sic nanowhiskers in a geopolymeric matrix, registering an increase of up to 192% in the flexural strength of the reference matrix when 0.2% was added in relation to the mass of metakaolin. 1.2.1 implications of the use of nanomaterials the difficulty of nanomaterials lies in the fact that, due to their small size and high specific surface area, they tend to agglomerate. van der waals forces become more intense under these size conditions, making it difficult to disperse them in the dry state and even within water. ntc are an example of this[22]. therefore, dispersion techniques are commonly used to alter the surface of nanomaterials and/or cause particle separation by using chemical surface treatment with acid, surfactants, applying ultrasonic energy or altering the ph of the medium to obtain homogeneous compounds. this study focuses on understanding the effects of the incorporation of titanium dioxide and silicon carbide based nanomaterials, individually and together, on a geopolymer matrix. the fraction used for nwsc was 0.10% and 0.20%, while for nt it was 0.50% and 1.50%, on the weight of metakaolin. in view of having favorable results during additions by other authors, the influence of these nanomaterials on the compressive strength, flexural strength and reaction kinetics measured by isothermal conduction calorimetry is analyzed. 2. materials and methods the aluminosilicate source, metakaolin (mk), was granted by the company metacaulim do brasil, são paulo, brazil, its granulometric distribution is shown in figure 1. its chemical composition is recorded in table 1. the activating solution was constituted by sodium hydroxide (naoh) in bead format (>98% purity) and a sodium silicate solution (sio2/na2o = 2.5), both sigma aldrich brand. the water used was distilled. the sic nanowhiskers (nwsc) were obtained from nanostructured & amorphous materials inc., texas, usa; their main characteristics are shown in table 2 and the geometry of one of these is shown in figure 2. the tio2 nanoparticles (nt) were obtained from the aldrich company and their characteristics are recorded in table 3. similarly, figure 3 shows the geometry of the nanoparticles. 70 figure 1. granulometric distribution of metakaolin. figure 2. transmission electron microscope (tem) image of nwscs. figure 3. met image of nt[38]. table 1. chemical composition of metakaolin oxide sio2 al2o3 fe2o3 cao tio2 % 57.0 34.0 0.10 0.10 1.50 source: metacaulim do brasil[2]. table 2. characteristics of the nwsc free carbon <0.05 type of glass beta diameter 0.1–2.5 μm length >2.0–50 μm hardness (mohs) 9.5 density 3.216 g/cm3 table 3. characteristics of titanium oxide nanoparticles (nt) diameter 21 nm surface area 35–65 m2/g the activating solution (12 m naoh) was prepared by slowly dissolving naoh in sodium silicate. since this combination is strongly exothermic, it was necessary to let the solution stand until it reached room temperature 23 ℃ ± 2 ℃. on the other hand, the nanomaterial was added in distilled water, slightly stirred and the solution was separated to receive the ultrasonic energy applied by a vibra-cell 750 w sonicator with vcx series ultrasonic processor—20 khz frequency. the total duration of the ultrasonic energy cycle was 10 minutes, in times of 20 seconds applied and then 20 seconds stopped (until the end of the 10 minutes, in order to avoid heating the solution), this cycle was chosen based on tests carried out in the laboratory of the work team. once the sonication cycle was finished and the activating solution reached stable temperature, a single solution was formed from the two previous solutions (±140 ml), which was manually and con 71 trolled and added to the metakaolin (145.3 g). the whole paste was mixed homogeneously in a mechanical stirrer for 5 minutes. finally, the paste was poured into molds and placed in the oven at 65 ℃ for 24 hours. the samples were named based on the content of nwsc or nt incorporated. the results were subjected to statistical analysis using past version 2.17 software. 2.1 tests 2.1.1 isothermal conduction calorimetry the heat flow recording was done by means of the thermometric ab of tam air (ta instruments). the samples were prepared with mixers incorporated to the device, being able to record the heat flow after the contact of the solid material with the activating solution. in this way, the reactions were monitored in four mixtures: the reference (r) (without nanomaterial), with nwsc (r + 0.20% sic), with nt (r + 0.50% nt) and with joint nanomaterials (r + 0.20% sic + 0.40% nt), at the same temperature of 65 ℃ for 24 hours (1,140 minutes). however, after 150 minutes from the start of the test, stability in the heat flux was recorded and based on this time the graph was cut for thermal analysis. 2.1.2 compressive strength for the resistance test, an instron press model 5,569 was used, with a speed rate of 5,000 n/min. for the compression test, the samples had a cylindrical format of 20 × 40 mm. three samples per age were manufactured. 2.1.3 bending strength for the strength test, an instron press model 5,569 was used, with a speed rate of 5,000 n/min, applied in the center of the specimen, which was supported at two points spaced at 6 cm. for the flexural test the format was prismatic 20 × 20 × 100 mm. three specimens per age were manufactured. 2.1.4 density and young’s modulus to determine young’s modulus, the impulse natural frequency technique was applied, using the actp sonelastic version 2.8 equipment. based on the same equipment, the bulk density of the samples could be estimated. the samples were used for flexural testing, 3 samples per age. 3. results and discussion 3.1 isothermal conduction calorimetry the reactions associated with geopolymerization are characterized by being partially exothermic and there are many factors that affect it: concentrations of si, al and na in the precursor materials and in the activating solution; the presence of water; the presence of additives and additions or even the cure temperature, as indicated by rodriguez et al.[3], abbasi et al.[15], bigno et al.[39], and ma et al.[40]. figure 4 shows the behavior for all the samples. a figure 4. evolution of the heat flux of the different pastes. 72 pronounced exothermic peak associated with the initial dissolution of metakaolin (along the vertical axis) was observed, which was not recorded for all samples. a subsequent short endothermic period was associated with the need for the system to enter into equilibrium with the environment created inside the calorimeter. in this way, the sample is forced to absorb the heat until it begins to emit a heat typical of geopolymerization reactions. subsequently, a third peak with variations in amplitude and length, specific to each sample, but exothermic in nature. finally, the samples stabilize in an estimated time of 110 minutes. for the paste containing sic the highest peak of heat flux occurs at the same time as the reference, however, the form of energy emission is slightly different for these samples. on the other hand, the behavior of the emission rate of this energy is completely different when we refer to the pastes incorporating nt. the behavior of the heat flow modifies their intensities and durations. this would indicate that the incorporation of nt in geopolymeric matrices, with thermal cure, stimulates the dissipation of the heat generated by the reactions of geopolymerization and the environment, as shown in figure 5. this phenomenon may enter into discussion with that indicated by ma and collaborators[41], who with the addition of nt recorded the acceleration of the reaction process of alkaline activated materials, when 1% by mass was added. further comments on this subject are made below. studies analyzing this parameter in geopolymeric matrices are scarce. however, this behavior is also representative in cementitious matrices: the presence of titanium nanoparticles results in the acceleration of hydration reactions and increase of total heat[42–44]. for this study, a reduction of up to 95.87% was obtained in the first 3 hours, when 0.50% of nt is incorporated in the sample. in the system incorporating nwsc this development is not accentuated, but a reduction of up to 24.24% can be obtained for the first 3 hours, compared to the reference. even with the total heat differences in the samples, no hardening process was observed during their preparation. figure 5. total heat behavior of the different pastes. 3.2 mechanical resistors in general, when sic nanowhiskers are added, the compressive strength has a tendency to increase, as can be seen in figure 6. the statistical analysis identified that, after 14 days, only the addition of sic produces a significant difference in the matrix, generating the greatest increase of 28.80% in resistance when compared to 73 figure 6. results of the compressive strength of the different pastes. figure 7. results of the flexural strength of the different pastes. figure 8. young’s modulus of the samples. the reference. as reported by yuan et al.[45], the addition of sic in the form of fibers up to 2% by volume contributes to a 36.70% increase in compressive strength. however, in the form of whiskers[46] records decrease in strength when they are incorpo 74 rated more than 5% by mass. both using metakaolin-based geopolymeric matrix this last author indicates that, in the form of particles, sic helps in the filling effect, registering better packing than whiskers and, therefore, contribute considerably to the compressive strength, with an increase of up to 102% in the matrix. in view of this confusion about the effects of incorporating sic in geopolymeric matrices, it is indicated that, for the case of portland cement-based matrices[36,47] the presence of sic in the nanomaterial form contributes positively to the compressive strength. the amount and format will define the contribution to the type of strength. nt particles, on the contrary, produced a reduction of up to 7.43% in compressive strength or no difference with the reference matrix. the higher percentage of nt in this study fails to produce a significant difference with the reference matrix, however, higher percentages (5%) of nt used by zhang et al.[43] produced relevant increases from early ages (±22%). this probably indicates that the use of higher percentages will contribute to the increase of this property. in the case of the flexural strength results shown in figure 7, an increase in strength is recorded for any amount of added nanomaterial, except when 1.50% of nt is added. the increases are between 80.02% (with addition of 0.10% sic) and 100.49% (with addition of 0.20% sic), in the first 3 days. the highest resistance with the addition of 0.50% nt results in 62.71% increase in the same time. but all of them decrease after 14 days. from the above, it can be inferred that the addition of sic nanowhiskers contributes simultaneously to the improvement of compressive and flexural strength. whereas, the addition of nt does not contribute significantly to the simultaneous improvement of the strengths. the additions cause a large differential at late ages when it comes to compressive strength[48]. interrelating the calorimetry and resistance profiles, it can be stated that nwscs would not be modifying the geopolymerization process, by virtue of their shape, they would be acting as nanofibers that allow the transmission of stresses. however, nts in the alkaline environment and thermal cure conditions, rapidly interact with the oh group that dissolves the precursor material[49], slowing down this polymeric reorganization process. this would lead to the formation of fewer polymeric chains compared to the reference. considering that the calorimetry was performed during the first 24 hours and the first resistance evaluation took place after 3 days, a stability of chain formation could actually be reached after 24 hours, showing stability or slight reduction. figure 8 shows the density and young’s modulus results for the different samples. statistically, the density values do not represent significant differences for any nanomaterial addition, however, the higher nanomaterial additions cause a significant difference in the young’s modulus of the reference matrix. confirming the indication of chen et al.[44], nts eventually produce a filling effect within the cementitious matrix. such a possibility would induce to use higher proportions to evaluate their incidence on the mechanical strength and still contribute with the photocatalytic effect on cementitious and geopolymeric matrices[33]. 4. conclusions the influence of adding tio2 nanoparticles and sic nanowhiskers was recorded by different experimental tests and it could be concluded that: these nanomaterials are able to modify the reaction kinetics, the mechanical performance of the reference matrix and some physical properties. regarding the reaction kinetics, the additions modified the heat emission rate, in what seems to be retarding and dissipative effect specified for nts. when it comes to mechanical performance, sic nanowhiskers simultaneously increase the compressive and flexural strength of the geopolymer matrix. 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hollow spheres are gaining attention due to their exceptional properties and potential applications in various fields. this study investigates the impact of different zinc precursors zinc chloride (zncl2), zinc nitrate [zn(no3)2], and zinc acetate [zn(ch3coo)2] on the hydrothermal synthesis of zno hollow spheres. a comprehensive set of characterization techniques, including field emission scanning electron microscopy (fesem), x-ray diffraction (xrd), thermogravimetric analysis (tga), and brunauer-emmettteller (bet) analysis, was utilized to assess the structural and morphological features of the synthesized materials. our findings demonstrate that all samples exhibit a high degree of crystallinity with a wurtzite structure, and crystallite sizes range between 34 to 91 nm. among the different precursors, zno derived from zinc nitrate showed markedly higher porosity and a well-defined mesoporous structure than those obtained from zinc acetate and zinc chloride. this research underscores the significance of precursor selection in optimizing the properties of zno hollow spheres, ultimately contributing to advancements in the design and application of zno-based nanomaterials. keywords: zinc oxide; hollow spheres; hydrothermal synthesis; precursors; morphology 1. introduction zinc oxide (zno) stands out as a versatile material with applications in diverse fields like photocatalysis and sensors due to its unique properties [1]. among various zno nanostructures, hollow spheres hold particular promise for these applications. their high surface area, tunable pore structure, and enhanced light harvesting capabilities make them ideal candidates [2,3]. the hydrothermal method offers a simple and cost-effective approach for synthesizing zno hollow spheres with controlled morphologies [4]. however, a crucial factor influencing the final product is the choice of zinc precursor. the precursor significantly impacts the formation process, ultimately affecting the structure and properties of the resulting zno hollow spheres [5]. despite extensive research on zno nanostructures, a systematic understanding of how different precursors influence the synthesis of zno hollow spheres via hydrothermal methods remains limited. while the relationship between morphology and performance is established, the precise mechanisms governing zno nanostructure growth and their correlation with morphology require further investigation, particularly for hydrothermal synthesis using different precursors [6]. to investigate this further, our research explores the effects of various zinc precursors (acetate, chloride, and nitrate) on the structural and morphological characteristics of hydrothermally synthesized zinc oxide hollow spheres. by elucidating the role of precursors, we aim citation khanali o, nekouee k, naderisamani h. comparative analysis of zinc precursors in the hydrothermal synthesis of zinc oxide hollow spheres. characterization and application of nanomaterials. 2025; 8(1): 10286. https://doi.org/10.24294/can10286 article info received: 13 november 2024 accepted: 13 december 2024 available online: 17 february 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 10286. 2 to contribute to the advancement of zno-based nanomaterial design and its targeted application development [7,8]. 2. experimental section 2.1. materials all solvents and reagents were used as received from commercial suppliers without any further purification. zinc nitrate anhydrous (zn(no3)2, 99.99% purity, (mr = 189.36 g/mol) sigma aldrich), zinc acetate anhydrous (znac2, zn(c2h3o2)2, 99.98%, (mr = 183.48 g/mol), sigma aldrich), zinc chloride (zncl2, > 99%, (mr = 136.28 g/mol) alfa aesar, germany), d-glucose (c6h12o6, 99.95% sigma aldrich), ethanol (etoh, 100%, molar chemicals, hungary) and ultrapure water was used to prepare aqueous solutions for the chemical synthesis and all the experiments. 2.2. synthesis of zno hollow spheres this study employed a hydrothermal method to synthesize zno hollow spheres using various zinc precursors. zinc chloride (zc), zinc nitrate (zn), and zinc acetate (za) served as the zinc source, while glucose (c6h12o6·h2o, 99.5%) acted as the carbonaceous source. table 1 details the specific quantities of materials used for each precursor combination [9]. the ratio of zinc precursors to glucose was considered as 1/2. a typical synthesis involved dissolving a specified amount of the chosen zinc precursor in deionized water under stirring to create a clear solution. subsequently, glucose was introduced dropwise to initiate the hydrothermal reaction. the synthesized mixture was subsequently transferred to a 100 ml teflon-lined stainless-steel autoclave and heated in a muffle furnace at 180 ℃ for 20 h. upon cooling to ambient temperature, the product was collected. the resulting black precipitate was subjected to a thorough washing process using both distilled water and ethanol. following synthesis, the black precipitate was dried in a vacuum oven at 80 ℃ for 5 h and finally calcined at 550 ℃ for 2 h. the detailed steps for preparing the zno hollow spheres are illustrated in the scheme of figure 1 [5,10,11]. table 1. raw materials and conditions for the hydrothermal synthesis of zno nanostructures. code of material chemical formula zinc salt precursors d-glucose deionized water zc (zinc chloride) zncl2 0.1 mol (13.62 g) 40 g (0.2 mol) 60 zn (zinc nitrate) zn(no3)2 0.1 mol (18.94 g) 40 g (0.2 mol) 60 za (zinc acetate) zn(ch3co2)2 0.1 mol (18.34 g) 40 g (0.2 mol) 60 characterization and application of nanomaterials 2025, 8(1), 10286. 3 figure 1. schematic of progresses for the preparation of hollow sphere zno. 2.3. characterization the crystalline phases of the synthesized zno hollow spheres were identified using x-ray diffraction (xrd) analysis with fe-kα radiation source (λ = 0.1937 nm) operated at 40 kv and 150 ma at a scanning step of 0.05 in the 2θ range 20–80_. the surface morphology and sizes of the hollow zno microspheres were observed by fieldemission scanning electron microscopy (fe-sem, mira3tescan-xmu with an accelerating voltage of 20 kv) with energy-dispersive spectra. this technique provides high-resolution images, allowing for detailed observation of the surface features and particle size distribution of the zno hollow spheres. to understand the thermal decomposition behavior and crystallization process of the as-prepared powders, thermogravimetric analysis (tga) and differential thermogravimetric analysis (dtg) were performed using a thermogravimetric analyzer (sdt 2960, ta instruments, new castle, de) under atmospheric air. the analysis was conducted over a temperature range of 40 to 600 ℃ with a heating rate of 10 ℃/min. typically, a sample weight 10 mg was used for the tests to ensure measurable changes, while the analysis utilized ceramic crucibles due to their high-temperature stability and inertness. this technique provides information about the weight loss associated with the decomposition of organic residues and the formation of the final zno phase. functional groups present in the zno hollow spheres were identified through fourier transform infrared (ft-ir) spectroscopy jasco model 4100_japan ft-ir spectra of zno . was recorded between 400 and 4000 cm−1 using a resolution of 4 cm−1. this technique provides valuable information about the chemical composition and bonding environment within the material. finally, the pore size distribution and specific surface area of the synthesized zno hollow spheres were determined using nitrogen gas adsorption-desorption isotherms measured with a micromeritics asap 2020 brunauer-emmett-teller (bet) characterization and application of nanomaterials 2025, 8(1), 10286. 4 surface area analyzer. this analysis enables the characterization of the material’s porosity, a crucial factor in various applications such as catalysis and adsorption. 3. results and discussion 3.1. ft-ir spectroscopy ft-ir spectroscopy was employed in the range of 400–4000 cm−1 to investigate the presence of organic residues and their influence on the properties of the zno hollow spheres. figure 2 presents the ft-ir spectra of samples prepared using different precursors (zc, zn, za) and calcined at 550 ℃. the broad peak observed between 3250 and 3650 cm−1 in all samples is attributed to the o–h stretching vibration of adsorbed water molecules on the surface of the zno hollow spheres. these peaks indicate the presence of surface hydroxyl groups and adsorbed water molecules, which are commonly observed in metal oxide materials. additionally, the peak at around 1650 cm−1 can be assigned to the bending vibration of co-o bonds. the characteristic peaks for zno are observed at 400 cm−1 and 570 cm−1. these strong absorption bands correspond to the stretching vibrations of the zn-o bond in the wurtzite hexagonal structure of zno. the presence of these peaks confirms the successful formation of the zno phase in the synthesized hollow spheres [10]. figure 2. ft-ir spectra of zno hollow spheres synthesis with different precursors. 3.2. x-ray diffraction (xrd) the crystal structures of the synthesized zno hollow spheres were investigated using x-ray diffraction (xrd) analysis. figure 3 presents the xrd patterns of the samples prepared using different precursors (zc, zn, za). these sharp diffraction peaks, in good agreement with the standard zno reference pattern, indicate the high purity and good crystallinity of the zno phase in all samples. all samples exhibited diffraction peaks at 40°, 43°, 45°, 61°, 74°, 82°, 89° and 91°, which can be readily indexed to the (100), (002), (101), (102), (110), (103), characterization and application of nanomaterials 2025, 8(1), 10286. 5 and (112) crystal planes of the hexagonal wurtzite structure of zno (reference code: 01-076-0704) [12]. figure 3. xrd pattern of the zno thin film prepared by different precursor materials. the crystallite size of the zno hollow spheres was estimated using scherrer’s equation. based on the full width at half maximum (fwhm) of the (101) peak in the xrd patterns. the calculated crystallite sizes are summarized in table 2. the results indicate that the choice of precursor influences the crystallite size of the zno hollow spheres, with values ranging from 39 to 91 nm [13]. table 2. crystal size, lattice parameters of the samples with different precursors. zinc precursors pos. [°2th.] fwhm left [°2th.] crystallite size (nm) lattice parameter c/a a c zinc chloride (zc) 46.051450 0.669120 48 3.2660 5.1988 1.5917 zinc nitrate (zn) 45.820390 0.944640 34 3.2562 5.1969 1.5960 zinc acetate (za) 45.986160 0.354240 91 3.2548 5.2139 1.6019 furthermore, the lattice parameters (a, c) and the c/a ratio were determined for each sample and are presented in table 2, further confirming the successful formation of the desired crystalline phase [14]. 3.3. thermal behavior the thermal decomposition behavior of the zno precursor powders (zc, zn, and za) was investigated using thermogravimetric analysis (tga) and differential thermogravimetric analysis (dtg). these analyses were employed to determine the material’s thermal stability and guide the selection of the calcination temperature. figure 4 presents the tg and dtg curves for the different precursors. the tg curve indicates a gradual weight loss for all samples in the temperature range of 40–600 ℃. the residual weight percentages at 600 ℃ were approximately, 20%, 20%, and 38% for zinc chloride, zinc nitrate, and zinc acetate, respectively. the quantitative reduction in mass during decomposition is presented in table 3 [15]. the high characterization and application of nanomaterials 2025, 8(1), 10286. 6 percentage of precipitation of zinc oxide particles in the zinc acetate precursor is related to the growth of irregularly shaped crystals that did not form a hallow sphere and grew as a single crystal. also, in the fe-sem images of figure 5, these particles can be identified as see clearly. table 3. thermal analysis corresponding to the tga, tg and dtg curves. zinc precursors exothermic region (℃) maximum temperature peak (℃) weight loss % zinc chloride (zc) 200–460 458 80 zinc nitrate (zn) 200–450 436 80 zinc acetate (za) 200–440 413 65 (a) (b) figure 4. (a) tg; (b) dtg analysis of zno hollow sphere that synthesis by different precursors. characterization and application of nanomaterials 2025, 8(1), 10286. 7 figure 5. fe-sem and eds images of zno hollow sphere that synthesis by different precursors. two prominent peaks are observed in the dtg curves, located around 300 ℃ and 440 ℃. the first peak can be attributed to the desorption of water molecules physically adsorbed on the precursor surfaces. the second, more significant peak at around 440 ℃ corresponds to the decomposition of residual carbon species that might be physically or chemically bound to the precursor materials. a significant weight loss is observed in the temperature range of 320–460 ℃, coinciding with the dtg peak at 440 ℃. this suggests the decomposition of organic moieties present in the precursors. the tg curve plateaus above 460 ℃, indicating minimal further weight loss. this implies that at this temperature, the residual organic components from the precursors are nearly completely decomposed. these findings suggest that a calcination temperature above 460 ℃ is necessary to ensure the complete removal of organic residues and achieve the desired final product composition [16]. 5µm 200 nm 5µm 5µm 200 nm zn zn zc zc za za zn zn zc za 200 nm zinc nitrate zinc chloride zinc acetate characterization and application of nanomaterials 2025, 8(1), 10286. 8 3.4. morphological analysis figure 5 shows fe-sem images of distinct morphologies of zno hollow spheres synthesized using different precursors. zno samples derived from zinc chloride and zinc nitrate exhibited well-defined hollow spherical structures with smooth surfaces. in contrast, zno synthesized from zinc acetate displayed irregular morphologies with partial aggregation and the presence of smaller nanoparticles. also, we can see nanoparticles that have not turned into hallow spheres and they have grown in the form of rods. this has led to the amount of weight percentage produced in zinc acetate precursor being higher than others. it can also be seen in figure 5 that the diameter of zno hallow spheres synthesized for zinc nitrate precursor is in the range of 500 nm, while the diameter of hallow spheres synthesized for zinc chloride and zinc acetate precursors is in the range of 700 nm. eds analysis for all three types of precursors shows that zinc oxide is well synthesized and does not contain any impurities. 3.5. surface properties the specific surface area, pore size distribution, and specific pore volume of the calcined zno hollow spheres prepared from different precursors were determined using nitrogen adsorption-desorption isotherms measured with a brunauer-emmettteller (bet) surface area analyzer. figure 6 presents the nitrogen adsorption and desorption isotherms, along with the pore size distribution of zno hollow structures synthesized from different precursors. the nitrogen adsorption shows a type iii isotherm with a hysteresis loop, indicating the presence of mesopores (2–50 nm) and macropores (> 50 nm). adsorption for zno synthesized from zinc nitrate is approximately ten times higher than from zinc acetate and five times higher than from zinc chloride, suggesting more mesopores in the zinc nitrate sample, as corroborated by fe-sem images. the bjh plot reveals a bimodal pore size distribution, with zinc acetate showing peaks at 2–4 nm (micropores), while zinc chloride shows a pore size distribution graph with two prominent peaks in the range of 8 to 10, indicating the presence of mesoporous. the zinc nitrate sample demonstrates a wide distribution from 1 to 100 nm, with peaks at 15 and 24 nm, indicating a well-developed porous structure and significantly larger pore volumes compared to the other precursors [15,17]. table 4 summarizes the physical parameters of the synthesized samples, showing that zinc nitrate and zinc chloride samples have higher specific surface areas and more uniform structures than those from zinc acetate. the increased porosity of zno hollow spheres primarily stems from their hollow morphology and the effective removal of template species during hydrothermal synthesis. samples derived from zinc chloride and zinc nitrate exhibited a higher specific surface area and well-defined mesoporous structure compared to those synthesized from zinc acetate. the superior porosity of zno hollow spheres obtained from zinc chloride and zinc nitrate precursor can be attributed to the well-defined hollow morphology and efficient removal of template species during hydrothermal synthesis [18,19]. characterization and application of nanomaterials 2025, 8(1), 10286. 9 figure 6. nitrogen adsorption isotherm and pore size distribution curve (inset) of the samples synthesis by different precursors characterized by bet & bjh techniques. table 4. specific surface area, mean pore diameter, pore volume of the sample’s synthesis with different precursors. material specific surface area (m2∙g−1) mean pore diameter [nm] pore volume (cm3∙g−1) zinc chloride (zc) 48.829 161.75 1.445 zinc nitrate (zn) 35.722 72.69 0.333 zinc acetate (za) 18.271 12.1 0.1477 4. conclusion hydrothermal synthesis successfully produced zno hollow spheres using all three precursors (zinc nitrate, zinc acetate, and zinc chloride).  field-emission scanning electron microscopy (fe-sem) images revealed greater uniformity in hollow spheres synthesized with zinc chloride and zinc nitrate compared to zinc acetate.  thermogravimetric analysis (tga) analysis indicated a higher production efficiency of zno using the zinc acetate precursor. however, this method resulted in irregular and rod-shaped particles with incomplete conversion to hollow spheres.  the thermogravimetric analysis (tga) curve displayed two exothermic peaks around 300 ℃ and 440 ℃. these peaks likely correspond to the evaporation of z in c n it r a te ( z n ) z in c c h lo r id e ( z c ) z in c a ce ta te ( z a ) characterization and application of nanomaterials 2025, 8(1), 10286. 10 adsorbed water molecules from the zno surface, the removal of organic content and impurities from the lattice, and the conversion of zn(oh)2 to zno.  the specific surface area, average diameter, and void volume of the hollow spheres decreased in the order of zinc chloride, zinc nitrate, and zinc acetate precursors.  notably, zinc nitrate and zinc chloride precursors yielded well-defined hollow spheres with high surface area and porosity. this makes them promising candidates for various applications requiring tailored nanostructured zno materials. author contributions: conceptualization, ok, kn and hns; investigation, ok; writing—review and editing, ok, kn and hns; writing—original draft, ok; project administration, kn and hns; funding acquisition, kn and hns; discussion on results, kn and hns; writing the results, kn and hns; visualization, kn and hns; resources, kn and hns; data-curation, kn and hns. all authors have read and agreed to the published version of the 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enhanced photocatalytic performance. journal of porous materials. 2009; 17(1): 79–84. doi: 10.1007/s10934-009-9266-7 microsoft word can-2539-pb-online characterization and application of nanomaterials 2024, 7(2), 2539. https://doi.org/10.24294/can.v7i2.2539 1 review nanorobots in drug delivery systems and treatment of cancer mudavath hanuma naik1,*, jala satyanarayana2, raj kumar kudari3 1 department of pharmaceutics, st mary’s college of pharmacy, guntur 522212, andhra pradesh, india 2 department of pharmacology, st mary’s college of pharmacy, guntur 522212, andhra pradesh, india 3 principal & professor department of pharmaceutical analysis, st mary’s college of pharmacy, guntur 522212, andhra pradesh, india * corresponding author: mudavath hanuma naik, m.hanumanaik7@gmail.com abstract: cancer is the 3rd leading cause of death globally, and the countries with low-tomiddle income account for most cancer cases. the current diagnostic tools, including imaging, molecular detection, and immune histochemistry (ihc), have intrinsic limitations, such as poor accuracy. however, researchers have been working to improve anti-cancer treatment using different drug delivery systems (dds) to target tumor cells more precisely. current advances, however, are enough to meet the growing call for more efficient drug delivery systems, but the adverse effects of these systems are a major problem. nanorobots are typically controlled devices made up of nanometric component assemblies that can interact with and even diffuse the cellular membrane due to their small size, offering a direct channel to the cellular level. the nanorobots improve treatment efficiency by performing advanced biomedical therapies using minimally invasive operations. chemotherapy’s harsh side effects and untargeted drug distribution necessitate new cancer treatment trials. the nanorobots are currently designed to recognize 12 different types of cancer cells. nanorobots are an emerging field of nanotechnology with nanoscale dimensions and are predictable to work at an atomic, molecular, and cellular level. nanorobots to date are under the line of investigation, but some primary molecular models of these medically programmable machines have been tested. this review on nanorobots presents the various aspects allied, i.e., introduction, history, ideal characteristics, approaches in nanorobots, basis for the development, tool kit recognition and retrieval from the body, and application considering diagnosis and treatment. keywords: nanorobots; atherosclerosis; cancer; nano sensors; nanoscale 1. introduction cancer is the 3rd leading cause of death globally, as almost every six deaths is caused by it. by 2030, it’s expected to be 26 million new cases of cancer, with almost 17 million deaths per year. the countries with low-to-middle income account for most cancer cases that are expected to be 61% by 2050. in 1965, the international agency for research on cancer (iarc) was established with the mission of conducting multidisciplinary investigations into the causes of human cancers. after conducting several studies, particularly on the structure of genes, experts have concluded that changes in human lifestyle, diet, and environmental factors have resulted in an increased number of cancer cases. the current diagnostic tools, including imaging, molecular detection, and immune histochemistry (ihc), have intrinsic limitations, such as poor accuracy. however, researchers have been working to improve anticancer medication delivery systems so that they can target tumor cells more precisely and create fewer adverse effects than chemotherapy. current advances, however, will not be enough to meet the growing demand for more efficient drug delivery systems. citation naik mh, satyanarayana j, kudari rk. nanorobots in drug delivery systems and treatment of cancer. characterization and application of nanomaterials. 2024; 7(2): 2539. https://doi.org/10.24294/can.v7i2.2539 article info received: 22 april 2024 accepted: 16 june 2024 available online: 28 august 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 2539. 2 nanorobots, an emerging technology, are nano-devices developed to perform specific tasks with precision at the nanoscale (1–100 nm). to perform these specific tasks, nanorobots are designed to work at cellular levels in medical fields. these are machines with nanoscale intelligence and information that can sense, signal, respond, and process. for the synthesis of nanorobots, the mainly used element is carbon due to its inertness, high thermal conductivity, and strength. moreover, the externally passive diamond coating is performed to elude host immune system attack. recent advancement in this field leads to the development of nanorobotic drug delivery systems, including surgical and cellular repair nanorobots. first of all, in 1986, eric drexler presented the idea of inserting medical nanorobots into the human body. in these nanorobots, artificial mechanical rbcs (respirocytes), wbcs (microbivores), and platelets (clottocytes) were used. a group of scientists in korea led by designed a nanorobot that can diffuse a cancer cell’s outer surface and then destroy the cell from the inside. these machine nanoparticles are gold-made and frequently fold and unfold to destroy a cell without any anti-cancer drug. dna-based cancer-fighting nanobots are being utilized to cure tumors. similarly, in another study, a new cancer treatment idea is proposed in which nanorobots formed from fragments of dna (deoxyribonucleic acid) can not only eradicate cancer cells in the body but also kill them. nanorobots, however, have certain drawbacks, including expensive design and development, high complexity, and invisibility. it becomes harder for drugloaded nanorobots to travel through blood arteries due to the high blood viscosity; however, researchers are working to address this issue. the use of nanodevices with higher complexity and possible uses in cancer treatment is the most current challenge in nanotechnology. these nanorobots can support or improve treatment efficiency by performing advanced biomedical therapies using minimally invasive operations. chemotherapy’s harsh side effects and untargeted drug distribution necessitate new cancer treatment trials. the nanorobots are currently designed to recognize 12 different types of cancer cells. furthermore, the molecular motors in this equipment can alter their response to uv light and pass through cellular layers to cause necrosis and medications to target specific areas. the nanorobots, or nanoparticles, are made with a mixture of a polymer and a protein called transferring, which has the capacity of detecting tumor cells because of its molecular particularities. once they are in the cells, the chemical sensor gives the order to dissolve, and when nanoparticles are dissolved, they let loose some substances that act on the rna of each cell, disabling the gene responsible for the cancer. specifically, what the nanoparticles deactivate is the ribonucleic redacts, the protein associated with the cancer growth that is fabricated by the disabled gene. cancer can be successfully treated with current stages of medical technologies and therapy tools. however, a decisive factor to determine the chances for a patient with cancer to survive is: how earlier it was diagnosed; what means, if possible, a cancer should be detected at least before the metastasis has begun. another important aspect of achieving a successful treatment for patients is the development of efficient targeted drug delivery to decrease the side effects from chemotherapy. considering the properties of nanorobots to navigate as bloodborne devices, they can help on such extremely important aspects of cancer therapy. nanorobots with embedded chemical biosensors can be used to perform detection of tumor cells in early stages of characterization and application of nanomaterials 2024, 7(2), 2539. 3 development inside the patient’s body. integrated nano sensors can be utilized for such a task in order to find the intensity of e-adhering signals. therefore, a hardware architecture based on nano-bioelectronics is described for the application of nanorobots for cancer therapy [1–4]. 2. history of nanorobots 1980’s by nobel prize laureate richard smalley. smalley has extended his vision to carbon nanotubes, discovered by sumio iijima, which he envisions as the next super interconnection for ultra-small electronics. the term nanotechnology has evolved to mean the manipulation of the elements to create unique and hopefully useful structures [4]. beginnings: 1981: gerd binnig and heinrich rohrer of ibm zürich invented the scanning tunneling microscope (stm). used for imaging surfaces at the atomic level and identifying some properties (i.e., energy). 1985: discovery of fullerenes (molecules composed entirely of carbon). they have many applications in materials science, electronics, and nanotechnology. 1991: discovering carbon nanotubes (cylindrical fullerenes) as a direct result of the fullerenes. exhibit high tensile strength, unique electrical properties, and efficient thermal conductivity. their electrical properties make them ideal circuit components (i.e., transistors or sand ultracapacitors). recently, research in chemical and biomedical engineering has used carbon nanotubes as a vessel for delivering drugs into the body [5]. contents: 1991: invention of the atomic force microscope (afm). one of the foremost tools for imaging, measuring, and manipulating matter at the nanoscale. it performs sit functions by feeling the surface with a mechanical probe. since it allows for precision interaction with materials on the nanoscale, it is considered a nanorobot. 2000: the united states national nanotechnology initiative is founded to coordinate federal research and development in nanotechnology. marks the start of a serious effort in nanotechnology research. 2000: the company nano factory collaboration is founded. developing a research agenda for building a nano factory capable of building nanorobots for medical purposes. currently, dna machines (nucleic acid robots) are being developed. performs mechanical-like movements, such as switching, in response to certain stimuli (inputs). molecular-sized robots and machines paved the way for nanotechnology by creating smaller and smaller machines and robots. 3. ideal characteristics it will communicate with the doctor by encoding messages to acoustic signals at carrier wave frequencies of 1–100 mhz. it might produce multiple copies of it to replace worn-out units, a process called self-replication. after the completion of the task, it can be retrieved by allowing it to excuse itself via the usual human excretory channel, so it can also be removed by active scavenger systems. nanorobots must have a size between 0.5 and 3 microns large with 1–100 nm parts. it will prevent itself from being attacked by the immune system by having a passive, diamond exterior [6]. characterization and application of nanomaterials 2024, 7(2), 2539. 4 3.1. advantages of nanorobots nanotechnology enables us to create functional materials, devices, and systems by controlling matter at the atomic and molecular scales, and exploiting novel properties and phenomena.  cost benefit ration is great.  environmentally friendly.  little pollution from production.  no wasted materials.  very durable.  can complete work faster than larger robots.  nanorobots can be programmed to self‐replicate.  as the nanorobot does not generate any harmful activities there is no side effect. it operates at specific sites only.  it has no side effect. 3.2. disadvantages of nanorobots  the initial design cost is very high [7].  the design of the nanorobot is a very complicated one.  electrical systems can create stray fields, which may activate bioelectric-based molecular recognition systems in biology.  electrical nanorobots are susceptible to electrical interference from external sources such as rf or electric fields, emp pulses, and stray fields from other in vivo electrical devices.  hard to interface, customize, and design; complex.  nanorobots can cause a brutal risk in the field of terrorism. terrorism and antigroups can make use of nanorobots as a new form of torturing the communities, as nanotechnology also has the capability of destructing the human body at the molecular level.  privacy is the other potential risk involved with nanorobots. as nanorobots deal with the design of compact and minute devices, there are chances for more eavesdropping than that already exists in nanorobots.  the nanorobot should be very accurate; otherwise, harmful effects may occur. 4. nanorobots and drug delivery systems predictions about the use of nanorobots considered applications in the central nervous system (cns), cancer treatment, body surveillance, delicate surgeries, and endoscopy, among others. challenges such as limitations of nanotechnology and few studies focused on the fundamental understanding of behavior in the nanoworld, difficult handling, and construction of these nanomachines. in nanomedicine, it has been explored in dds, which acts directly on target points of the human body. researchers develop systems able to deliver drugs in specific locations, also controlling the dosage and frequency of this release. drug delivery systems can be applied in the treatment of articular diseases, dental, diabetes, cancer, and others. diseases such as neoplasms, hepatitis, diabetes, pulmonary, dentistry, and cancer can be used nanorobot technology as a means of implementing the dds. one of the characterization and application of nanomaterials 2024, 7(2), 2539. 5 advantages of this technology is the diagnosis and treatment of diseases with minimum prejudice to the healthy cells, lowering the risk of unfavorable effects, and directing healing and reconstructive treatment at the cellular and subcellular levels [8–21]. 5. technology applied in nanorobots for use as dds recent improvements in drug delivery turn up higher quality in targeted drug delivery that identifies the specific cells with the self of nano sensors and regulates the discharge by use of smart drugs. some researchers classify nanorobots in drug delivery and therapeutics according to their application, which is described below: pharmacy: classified as medical nanorobots with a size of 1–2 μm able to carry up to 1 μm3 of a given drug in the tanks. they are controlled using mechanical systems for sorting pumps. depending on the situation, the weight is discharged into the extracellular fluid or cytosol (the aqueous component of the cytoplasm of a cell). they are provided with molecular markers or chemotactic sensors that guarantee full targeting accuracy. glucose and oxygen extracted from the local environment, such as blood, intestinal fluid, and cytosol, are the onboard power supplies. after the nanorobot completes tasks, they can be removed or recovered by centrifuge nan apheresis [22–28]. diagnosis and imaging: the authors cite microchips that are overlaid with human molecules. the chip is projected to send an electrical signal when the molecules detect disease. gives an example of special sensor nanorobots that can be introduced into the blood under the skin, where they verify blood contents and notify of any possible diseases. they can also be used to monitor the sugar level in the blood. the advantages are the low price to produce and ease of manipulation [26–32]. reciprocates: it’s about an artificial red blood cell, which is a blood-borne spherical 1 μm diamondoid 1000 atmosphere pressure vessel with reversible molecules and selective pumps. the power is obtained by endogenous serum glucose. this artificial cell can give 236 times more oxygen to the tissues per unit volume than rbcs (red blood cells) and to administer acidity. the nanomachine is constructed with 18 billion atoms justly organized in a diamondoid pressure tank that is pumped full of up to 3 billion oxygen (o2) and carbon dioxide (co2) molecules. it is impossible to release these gases from the tank. gas concentration sensors on the outside will signal when it is time to discharge o2 and unload co2 [26,27]. clottocytes: this nanorobot is classified with a unique biological capability: “instant” hemostasis using clottocytes, or artificial mechanical platelets. it is known that platelets are roughly spheroidal nucleus-free blood cells measuring approximately 2 μm in diameter. platelets join at a place of bleeding. there they are activated, becoming tacky and lumping together to form a tampon that aids in stamping the blood vessel and stopping the bleeding. they also deliver substances that help promote coagulation. another interesting feature is its ability to perform phagocytosis of foreign particles and killing of microfilariae larval parasites. a complete functional design is elaborate, but the work of freitas focuses on the purely mechanical aspects of the hemostatic function of platelets and reports the function in a small in vivo population of medical nanorobotic devices [33]. microbivores: it is an oblate spheroidal device for biomedical applications with 3.4 μm in diameter along its major axis and 2.0 μm in diameter along its minor axis. characterization and application of nanomaterials 2024, 7(2), 2539. 6 composed precisely organized of 610 billion atoms in a 12.1 μm 3 geometric volume. the nanobot can continuously consume up to 200 pw. this power is used to digest trapped microbes. microbivores have different characteristics of natural or antibioticassisted biological phagocytic defenses, acting approximately up to 1000 times faster. another distinctive feature is related to the ability to phagocyte approximately 80 times more efficiently than macrophage agents in terms of volume/sec digested per unit volume of phagocytic agent. thus, according to the existing technological proposals, nanorobots are an efficient and innovative way for applications in nanomedicine, including dds and therapeutics (diagnostic and therapeutic) [34]. searching keywords “drug delivery systems” in the database periodic capes, it was obtained 176,511 publications. only 0.21% is related to nanorobots, and in this amount of work, only 8% have a relationship between “drug delivery systems and nanorobots”. another database searched was web of science [35,36]. the results were 113,896 publications with the keyword “drug delivery” and 201 for nanorobots. the survey also showed that only 0.02% was published with the correlation “drug delivery and nanorobots”. before the number of published papers, it is noted that much more should be done so that nanomedicine can grow apace with the help of nanorobots in treating diseases, in particular cancer. 6. drug delivery systems for anticancer drugs the therapeutic index of most anticancer drugs is narrow, causing toxicity to normal stem cells, hematological adverse effects, and gastrointestinal effects, among others. doxorubicin is used in several types of cancer, such as hd (hodgkin’s disease), in which treatment is administered in combination with other antineoplastic agents in order to reduce their toxicity [37]. paclitaxel is administered by intravenous infusion and plays a role in the treatment of breast cancer. among the adverse effects encountered, some serious, are bone marrow suppression and cumulative neurotoxicity [38]. cisplatin is an alkylating agent that causes intra-dna-binding filaments. some of its side effects are nausea and severe vomiting, as well as being nephrotoxic. camptothecin is used in the treatment of neoplasias due to the inhibition of type i topoisomerases, an essential enzyme for the cellular replication of genetic material. several efforts have been implemented to use nanotechnology to develop dds that can minimize the harmful effects of conventional therapies. clinical trials are studies in humans to measure the parameters of safety and efficacy of new drugs; they are essential for the arrival of new therapeutic alternatives in the market [39]. anyway, just a few dds reached more advanced stages of clinical evaluation, such as those consisting of doxorubicin, paclitaxel, camptothecin, and platinum complexes [40]. doxorubicin was stacked on the surface of single-walled carbon nanotubes (swnts) [41]. doxorubicin was employed as a polymer prodrug/collagen hybrid in metastatic tumor cells. the use of polymeric prodrug nanotechnology applied to the treatment of neoplasia shows up as a new development in this area boundary [42]. super paramagnetic nanoparticles of iron oxide (spions) loaded with doxorubicin were coated with modified inulin and evaluated for potential use in anti-neoplastic therapy [43]. characterization and application of nanomaterials 2024, 7(2), 2539. 7 this arch for biocompatible materials that can serve as a drug delivery system is always the focus of nanotechnology. nanoparticles ha (hydroxyapatite)—a major constituent of bone and teeth—were used to carry paclitaxel (tax), an antineoplastic agent, and the results suggest good expectations with treatment starting from hydrophobic drugs [44]. searching carbon materials, nanoscale graphene oxide was tested as a drug carrier of anti-cancer [45]. another possible application area of the drug delivery system is especially important in the intrathecal route of administration for the relief of pain related to certain types of cancer. the application drug delivery system intrathecal may be useful in refractory pain to others of administration or even in cases of persistent pain [46]. again, observing the research with the themes “drug delivery systems and cancer” found a total of 31,134 publications. as noted in recent years, the interest increases in dds have been directly associated with the need for alternative conventional chemotherapeutics, which possess some serious side effects for the patient [47]. 6.1. limitations of chemotherapy conventional chemotherapeutic agents work by destroying rapidly dividing cells, which is the main property of neoplastic cells. this is why chemotherapy also damages normal healthy cells that divide rapidly, such as cells in the bone marrow, macrophages, digestive tract, and hair follicles [48]. conventional chemotherapy is that it cannot give selective action only to the cancerous cells. this results in common side effects of most chemotherapeutic agents, which include myelosuppression (decreased production of white blood cells causing immunosuppression), mucositis (inflammation of the lining of the digestive tract), alopecia (hair loss), organ dysfunction, and even anemia or thrombocytopenia. these side effects sometimes impose dose reduction, treatment delay, or discontinuance of the given therapy [49]. furthermore, chemotherapeutic agents often cannot penetrate and reach the core of solid tumors, failing to kill the cancerous cells [50]. traditional chemotherapeutic agents often get washed out from the circulation being engulfed by macrophages. thus, they remain in circulation for a very short time and cannot interact with the cancerous cells, making the chemotherapy completely ineffective. the poor solubility of the drugs is also a major problem in conventional chemotherapy, making them unable to penetrate the biological membranes [51]. another problem is associated with p-glycoprotein, a multidrug resistance protein that is overexpressed on the surface of cancerous cells, which prevents drug accumulation inside the tumor, acts as the efflux pump, and often mediates the development of resistance to anticancer drugs. thus, the administered drugs remain unsuccessful or cannot bring the desired output [52–60]. 6.2. drug delivery and nanorobots in cancer treatment the clinical use of nanorobots for diagnosis, therapeutic, and surgical purposes should be done with intravenous injection. therefore, the nanorobots can be released directly into the patient’s bloodstream. the major cancer treatment cycle for chemotherapy pharmacokinetics includes absorption and metabolism, plus a break for the body’s re-establishment before the next chemotherapy session. patients are normally treated in cycles of every 2 weeks for small tumors. as an initial time characterization and application of nanomaterials 2024, 7(2), 2539. 8 threshold for medical purposes, nanorobots should be able to analyze and provide a body diagnosis within one week through the use of proteomic-based sensors. the uptake kinetics of a low molecular weight using a magnetic resonance contrast agent can predict the delivery of protein drugs to solid tumors. hence, a similar approach is useful to verify in vivo nanorobot biosensor activation through targeted detection. the test and diagnosis are an important part of the research on nanorobots. it enables rapid testing and diagnosis at the first visit, so without the need for a followup visit after the lab test, and the detection of diseases at an earlier stage. the limitation in vivo use of nanorobots is the need for energy for propulsion. higher levels of energy are required since “low inertia and high viscous forces are coupled with low efficiency and low convective motion”. the fuels of chemically powered nanomotors were toxic. the availability of alternative sources of energy, such as sound waves and light, has led to an increase in the research on in vivo use of nanorobots, which resulted in more patent applications. one study of nanomotors is the acoustic propulsion of nanorod motors inside living cells” [61–67]. which was a result of the development of ultrasonic-wave-powered minerals, which are safe for living systems. 65 reported an in vivo model of artificial micromotors in a living organism. the model examines the distribution, retention, cargo delivery, and acute toxicity role of synthetic motors in mouse stomachs via oral administration. this work is anticipated to significantly advance the emerging field of nano/micromotors and to open the door to in vivo evaluation and clinical applications of these synthetic motors. this development may be an important step for the possibility of in vivo applications of drug delivery for cancer treatment with decreasing the side effects of chemotherapy. juul et al. published a paper on their research into nanorobots that contain medicine that can be opened and closed based on the surrounding temperatures. recently, reported bacteria-based microrobots (bacteriology) as a new type of active drug delivery system. in the study, genetically modified non-toxic salmonella typhi-murium (flagellar bacteria), which is attracted to chemicals released by cancer cells, is used. perault and shih from the wyss institute for biologically inspired engineering at harvard university introduced virus-inspired enveloped dna nanostructures as a design strategy for biomedical applications. recent studies revealed that nanotechnology, dna engineering of molecular-scale devices with superb control over geometry, and site-specific functionalization promise fascinating advantages in advancing nanomedicine. however, instability in biological environments and innate immune activation remain obstacles for in vivo application. after nanorobots cross cellular membranes for targeted delivery, drug retention in the tumor will determine the therapeutic efficiency. the chemotherapy is influenced by drug transfer processes from plasma to tissue in achieving more effective tumor chemotherapy based on its composition. thus, the major advantage of nanorobots for cancer drug delivery is to minimize chemotherapy side effects. as the best approach, the nanorobot architecture incorporates cnt (carbon nanotubes) and dna, which are recent candidates for new forms of nanoelectronics. acmos (complementary metal oxide semiconductor) for constructing circuits with features in the tens of nanometers as a hybrid biosensor with single-chain antigenbinding proteins. this process uses activation based on proteomics and bioelectronics characterization and application of nanomaterials 2024, 7(2), 2539. 9 signals for formation release. therefore, each time the nanorobot detects predefined changes in protein gradients, nanoactuators are activated to manipulate drug delivery. changes to chemical and thermal signals are applicable conditions directly related to major medical target identification. some examples of changing protein concentrations inside the body near a medical target under pathological circumstances are nos (nitric oxide synthase), e-cadherin, and bcl-2 [68,69]. 7. approaches in nanorobots biochip: the joint use of nanoelectronics, photolithography, and new biomaterials provides a possible approach to manufacturing nanorobots for common medical applications, such as surgical instrumentation, diagnosis, and drug delivery [69]. biochips not only consist of immobilized molecules spatially addressed on planar surfaces but also contain biomolecules fixed in microchannels or microcells or on an array of beads or sensors. nanotechnology has made biochips more applicable for commercialization purposes where biochips could be implanted inside the body to dynamically transmit information and monitor any biological changes in vivo [70]. nubot: nubot is an abbreviation for “nucleic acid robot”. they are organic molecular machines [71]. dna structure can provide means to assemble 2d and 3d nanomechanical devices. dna-based machines can be activated using small molecules, proteins, and other molecules of dna [72]. nubots have dna structures used for targeting drug delivery as a carrier. bacteria-based: this approach proposes the use of biological microorganisms, like the bacterium escherichia coli. thus, the model uses a flagellum for propulsion purposes. electromagnetic fields normally control the motion of this kind of biologically integrated device. open technology: a document with a proposal for nanobiotech development using open technology approaches has been addressed to the united nations general assembly. according to the document sent to the un, in the same way that open source has in recent years accelerated the development of computer systems, a similar approach should benefit society at large and accelerate nanorobots development. nanobearing and nanogears: to establish the feasibility of molecular manufacturing, it is first necessary to create and analyze possible designs for nanoscale mechanical parts that could, in principle, be manufactured [73]. “ability to model molecular machines (systems and devices) of specific kinds, designed in part for ease of modeling, has far out run our ability to make them. design calculations and computational experiments enable the theoretical studies of these devices, independent of the technologies needed to implement them.” the simple structure and operation of molecular bearings make it the most convenient class of components to be designed. oneofthesimplestexamplesisdrexler’soverlap-repulsionbearingdesign. medical nanorobot architecture: the main parameters used for the medical nanorobot architecture and its control activation, as well as the required technological background that may lead to manufacturing hardware for molecular machines, are described next. manufacturing technology: the ability to manufacture nanorobots may result from current trends and new methodologies in fabrication, computation, transducers, characterization and application of nanomaterials 2024, 7(2), 2539. 10 and manipulation. depending on the case, different gradients on temperature, the concentration of chemicals in the bloodstream, and electromagnetic signature are some of the relevant parameters for diagnostic purposes [74]. cmos vlsi (very large scale integration) systems designed using deep ultraviolet lithography provide high precision and a commercial way of manufacturing early nanodevices and nanoelectronics systems. the cmos industry may successfully drive the pathway for the assembly processes needed to manufacture nanorobots, where the joint use of nano photonics and nanotubes may even accelerate further the actual levels of resolution ranging from 248 nm to 157 nm devices [75]. to validate designs and achieve a successful implementation, the use of vhdl (verification hardware description language) has become the most common methodology utilized in the integrated circuit manufacturing industry [76]. chemical sensor: manufacturing silicon-based chemicaland motion-sensor arrays using a two-level system architecture hierarchy has been successfully conducted in the last 15 years. applications range from the automotive and chemical industry with detection of air to water element pattern recognition through embedded software programming to biomedical uses. through the use of nanowires, the existing significant costs of energy demand for data transfer and circuit operation can be decreased by up to 60%. cmos-based biosensors using nanowires as materials for circuit assembly can achieve maximal efficiency for applications regarding chemical changes, enabling new medical treatments [77]. chemical nano sensors can be embedded in the nanorobot to monitor e-cadherin gradients. thus, nanorobots programmed for such tasks can make a detailed screening of the patient’s whole body. in our medical nanorobotic architecture, the mobile phone is applied to retrieve information about the patient’s conditions [78,79]. for that, it uses electromagnetic waves to command and detect the current status of nanorobots inside the patient. new materials, such as strained channels with relaxed si gelayer scan, reduce self-heating and improve performance. recent developments in 3d circuits and finfet doublegates have achieved astonishing results, and according to the semiconductor roadmap, they should improve even more [80]. to further advance manufacturing techniques, silicon-on-insulator (soi) technology has been used to assemble high-performance logic sub90nm circuits. circuit design approaches to solve problems with bipolar effects and hysteretic variations based on soi structure have been demonstrated successfully [81]. thus, already-feasible 90nm and 45nm cmos devices represent breakthrough technology devices that are already being utilized in products. power supply: the use of cmos for active telemetry and power supply is the most effective and secure way to ensure energy as long as necessary to keep the nanorobot in operation. the same technique is also appropriate for other purposes, like digital bit-encoded data transfer from inside a human body [82]. thus, nanocircuits with resonant electric properties can operate as a chip, providing electro-magnetic energy supplying 1.7 ma at 3.3 v for power, allowing the operation of many tasks with few or no significant losses during transmission [83]. radio frequency-based telemetry procedures have demonstrated good results in patient monitoring and power transmission with the use of inductive coupling [84] using well-established techniques already widely used in commercial applications of rfid (radio frequency identification device). the energy received can also be saved in ranges of 1 μw while characterization and application of nanomaterials 2024, 7(2), 2539. 11 the nanorobot stays in inactive modes, just becoming active when signal patterns require it to do so. some typical nanorobotic tasks may require the device only to spend low power amounts once it has been strategically activated. for communication, sending rf signals 1 mw is required. a practical way to achieve easy implementation of this architecture will obtain both energy and data transfer capabilities for nanorobots by employing mobile phones in such a process [85]. the mobile phone should be uploaded with the control software that includes the communication and energy transfer protocols. data transmission: the application of devices and sensors implanted inside the human body to transmit data about the health of patients can provide great advantages in continuous medical monitoring [86]. most recently, the use of rfid for in vivo data collection and transmission was successfully tested for electroencephalograms. for communication in liquid workspaces, depending on the application, acoustic, light, rf, and chemical signals may be considered as possible choices for communication and data transmission. chemical signaling is quite useful for nearby communication among nanorobots for some teamwork coordination [87]. work with rfid has been developed as an integrated circuit device for medicine [88,89]. using integrated sensors for data transfer is the better answer to reading and writing data in implanted devices. teams of nanorobots may be equipped with single-chip rfid cmos-based sensors. cmos with a submicron system-on-chip design could be used for extremely low power and longer distances through acoustic sensors. for the nanorobot, active sonar communication frequencies may reach up to 20 μw @ 8 hz at resonance rates with a 3v supply [90]. in our molecular machine architecture, to successfully set an embedded antenna with a 200 nm size for the nanorobot rf communication, a small loop planar device is adopted as an electromagnetic pick-up having a good matching on low noise amplifier; it is based on gold nanocrystal with 1.4 nm, cmos, and nano electronic circuit technologies [91]. frequencies ranging from 1 to 20 mhz can be successfully used for biomedical applications without any damage. targets it and their communication with the machines [92]: the nanorobot design includes integrated nano electronics which involves the use of mobile phones. it uses an rfid (cmos transponder system) for in vivo positioning, using a wellestablished communication protocol that allows tracking information about its positioning. there are three approaches to recognizing the target site: first, as a point of comparison, the scientists use nanorobots with small brownian motions to find the target by random search. in a second method, it monitors for chemical concentration significantly above the background level. after detecting the signal, it estimates the concentration gradient and moves toward higher concentrations until it reaches the target. in the third approach, nanorobots at the target release another chemical, which others use as an additional guiding signal to the target. with these signal concentrations, only it passes within a few microns of the target is likely to detect the signal. most recently, the use of rfid for in vivo data collection and transmission was successfully tested for electroencephalograms. for communication in liquid workspaces, depending on the application, acoustic, light, rf, and chemical signals may be considered as possible choices for communication and data transmission. one of the simplest ways to send broadcast-type messages into the body, to be received by in vivo nanorobots, is aural characterization and application of nanomaterials 2024, 7(2), 2539. 12 messaging. a device similar to an ultrasound probe would encode messages on aural carrier waves at frequencies between 1–10 mhz. thus, the supervising physician can easily send new commands or parameters to nanorobots already at work inside the body. each nanorobot has its own power supply, computer, and sensorium; thus, it can receive the physician’s messages via aural sensors, then compute and implement the appropriate response. the other half of the process is getting messages back out of the body, from the working nanodevices out to the physician [93]. applications-diagnosis and treatment [92–94]: medical nanorobots can perform a vast array of diagnostic, testing, and monitoring functions, both in tissues and in the blood stream. these devices could continuously record and report all vital signs, including temperature, pressure, chemical composition, and immune system activity, from all different parts of the body. cancer therapy: nanorobots with embedded chemical biosensors can be used to perform the detection of tumor cells in the early stages of development inside the patient’s body. these nanorobots would search out and identify the cancer-affected cells using certain molecules as they could be introduced into the bloodstream. medical nanorobots would then destroy these cells. nanorobots with chemical nano biosensors can be programmed to detect different levels of e-cadherin and beta-catenin as medical targets in primary and metastatic phases, helping target identification and drug delivery. integrated nano sensors can be utilized for such a job to find the intensity of e-cadherin signals. nanorobots could also carry the chemicals used in chemotherapy to treat cancer directly at the site. diabetes: the protein sodium-dependent glucose co-transporter system has an important influence in maintaining proper gastrointestinal cholinergic nerve and skeletal muscle function activities, regulating extracellular glucose concentration. the hsglt3 molecule can serve to define glucose levels and serves as a sensor to identify glucose for diabetes patients. for glucose monitoring, the nanorobot uses an embedded chemo sensor that involves the modulation of hsglt3 protein glucose sensor activity. through its onboard chemical sensor, the nanorobot can thus effectively determine if the patient needs to inject insulin or take any further action, such as any medication clinically prescribed. they flow with the rbcs through the blood stream, detecting the glucose levels. in the medical nanorobot architecture, the significant measured data can be then transferred automatically through the rf signals to the mobile phone carried by the patient. at any time, if the glucose achieves critical levels, the nanorobot emits an alarm through the mobile phone. 8. surgery surgical nanorobots could be introduced into the body through the vascular system or at the ends of catheters into various vessels and other cavities in the human body. a surgical nanorobot, programmed or guided by a human surgeon, could act as a semiautonomous on-site surgeon inside the human body. it performs various functions, such as searching for pathology and then diagnosing and correcting lesions by nanomanipulation, coordinated by an onboard computer while maintaining contact with the supervising surgeon via coded ultrasound signals. the earliest forms of cellular nano surgery are already being explored today. characterization and application of nanomaterials 2024, 7(2), 2539. 13 8.1. as an artificial oxygen carrier the artificial mechanical red cell, the respirocyte, is an imaginary nanorobot that floats all along in the bloodstream. the respirocyte is a tiny pressure tank that can be pumped full of oxygen (o2) and carbon dioxide (co2) molecules. these gases can be released from the tiny tank in a controlled manner. when the nanorobot passes through the lung capillaries, o2 partial pressure is high and co2 partial pressure is low, so the onboard computer tells the sorting rotors to load the tanks with oxygen and dump the co2. when the device later finds itself in the oxygen-starved peripheral tissues, the sensor readings are reversed. co2 partial pressure is relatively high and o2 partial pressure is relatively low, so the onboard computer commands the sorting rotors to release o2 and absorb co2. respirocytes mimic the action of the natural hemoglobinfilled red blood cells and can deliver 236 times more oxygen per unit than a natural red cell. 8.2. as artificial phagocyte(microbivore) microbivore is an artificial mechanical phagocyte of microscopic size whose primary function is to destroy microbiological pathogens found in the human bloodstream using the “digest and discharge” protocol. the chief function of microbes is to wipe out microbiological pathogens found in the human bloodstream using the “digest and discharge” procedure. microbivores, upon given intravenously (i.v.), would achieve complete clearance of the most severe septicemic infections in hours or less, far better than the weeks or months needed for antibiotic-assisted natural phagocytic defenses. the nanorobots do not boost the risk of sepsis or septic shock because the pathogens are completely digested into harmless simple sugars, monoresidue amino acids, mononucleotides, free fatty acids, and glycerol, which are the biologically inactive effluents from the nanorobot. 8.3. as artificial neurons nanorobots can be employed in replacing every neuron in one’s brain with a nanorobot that is designed to function just like normal, natural neurons. the nanotech neurons are functionally equivalent. they connect to the same synapse of the original neuron, and they perform the same functional roles. atherosclerosis: medical nanorobots can locate atherosclerotic lesions in blood vessels, mainly in the coronary circulation, and treat them either mechanically, chemically, or pharmacologically. cell repair and lysis: an interesting utilization of nanorobots may be their attachment to transmigrating inflammatory cells or white blood cells to reach swollen tissues and assist in their healing process. mobile cell-repair nanorobot is capable of limited vascular surface travel into the capillary bed of the targeted tissue or organ, followed by extravasations, histation, cyto-penetration, and complete chromatin replacement in the nucleus of one target cell, and ending with a return to the bloodstream and subsequent extraction of the device from the body, completing the cell repair mission. hemophilia: one particular kind of nanorobot is the choanocyte or artificial platelet. the choanocyte carries a small mesh net that dissolves into a sticky membrane characterization and application of nanomaterials 2024, 7(2), 2539. 14 upon contact with blood plasma. according to freitas ra, the man who designed the choanocyte, clotting could be up to 1000 times faster than the body’s natural clotting mechanism. gout: gout is a situation where the kidneys lose the ability to remove waste from the breakdown of fats from the bloodstream. this waste sometimes crystallizes at points near joints like the knees and ankles. a nanorobot could break up the crystalline structures at the joints, providing relief from the symptoms, though it wouldn’t be able to reverse the state permanently. kidney stones: kidney stones can be intensely painful; the larger the stone, the more difficult it is to pass. an nanorobot could break up kidney stones using a small laser. cleaning wounds: nanorobots could help remove debris from wounds, decreasing the likelihood of infection. they would be particularly useful in cases of puncture wounds, which can be difficult to treat using more conventional methods. gene therapy: medical nanorobots can readily treat genetic diseases by comparing the molecular structures of both dna and proteins found in the cell to known or desired reference structures. any irregularities can then be corrected, or desired modifications can be edited in place. in some cases, chromosomal replacement therapy is more efficient than cyto repair. conflict of interest: the authors declare no conflict of interest. references 1. who. cancer. available online: https://www.who.int/news-room/fact-sheets/detail/cancer (accessed on 3 february 2022). 2. thun mj, de lancey jo, center mm, et al. the global burden of cancer: priorities for prevention. carcinogenesis. 2010; 31(1): 100-110. doi: 10.1093/carcin/bgp263 3. bray f, møller b. predicting the future burden of cancer. nature reviews cancer. 2006; 6(1): 63-74. doi: 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review nanoreinforcement effects in multifunctional polyurethane foams— scientific status hitherto and future ayesha kausar* national center for physics, quaid-i-azam university campus, islamabad 45320, pakistan * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract: polyurethane is a multipurpose polymer with valuable mechanical, thermal, and chemical stability, and countless other physical features. polyurethanes can be processed as foam, elastomer, or fibers. this innovative overview is designed to uncover the present state and opportunities in the field of polyurethanes and their nanocomposite sponges. special emphasis has been given to fundamentals of polyurethanes and foam materials, related nanocomposite categories, and associated properties and applications. according to literature so far, adding carbon nanoparticles such as graphene and carbon nanotube influenced cell structure, overall microstructure, electrical/thermal conductivity, mechanical/heat stability, of the resulting polyurethane nanocomposite foams. such progressions enabled high tech applications in the fields such as electromagnetic interference shielding, shape memory, and biomedical materials, underscoring the need of integrating these macromolecular sponges on industrial level environmentally friendly designs. future research must be intended to resolve key challenges related to manufacturing and applicability of polyurethane nanocomposite foams. in particular, material design optimization, invention of low price processing methods, appropriate choice of nanofiller type/contents, understanding and control of interfacial and structure-property interplay must be determined. keywords: polyurethane; nanocomposite; foam; manufacturing; properties; radiation shielding; shape memory; biomedical 1. introduction polyurethane forms an important contribution to the thermosetting, thermoplastics, or elastomeric type of polymers due to the range of intrinsic physical features and advanced utilizations [1]. these polymers have flexibility of backbone variations by altering soft or hard units and probable hydrogen bonding between the segments [2]. worth mentioning application areas of polyurethanes (as coatings, fibers, sponges) expand from defense and devices to medical sectors [3]. moreover, advancements in the field of polyurethane materials can be seen in the form of nanocomposites with inorganic or carbon nanoadditives [4,5]. abundant literature reports have been noted on preparation, physical aspects, and technical significance of polyurethane sponges or foams [6]. similarly, polyurethane foams filled with different types of nanofillers have also been investigated for designs and applied attributes [7]. in this regard, most important types of nanofillers have been noted as graphene and carbon nanotube [8‒10]. these hybrid foams have been manufactured by using variety of self foaming, free rising, foaming agent, freeze drying, in situ, solution, and chemical methods [11]. consequently, nanocomposite foams own low density, flexibility, mechanical/compression strength, thermal features, other high tech features [12]. the high performance nanocellular polyurethane citation kausar a. (2025). nanoreinforcement effects in multifunctional polyurethane foams—scientific status hitherto and future. characterization and application of nanomaterials. 8(3): 11881. https://doi.org/10.24294/can11881 article info received: 27 august 2025 accepted: 31 october 2025 available online: 24 november 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(3), 11881. 2 architectures have been applied for important applications concerned to radiation shielding, stimuli responsiveness, and biomedical sectors [13]. this up-to-the-minute review is planned to cover almost every physical and practical facet of polyurethane nanocomposite foams, for first time in the literature so far. in this concern, basics, synthesis, categories of polyurethane hybrid sponges (polyurethane/graphene nanocomposite foams, polyurethane/carbon nanotubes nanocomposite foams), and applications (radiation shields, shape memory, tissue scaffolds) have been conversed. as per reported knowledge, future of polyurethane nanocomposite foams simply relies upon overcoming field challenges of facile processing, design and property optimization, ecofriendliness, and large scale processing. 2. polyurethane and polyurethane foams polyurethane is a versatile polymer with thermoplastic, thermosetting, or elastomeric backbone structure [14]. basically, a polyurethane main chain consists of carbamate or urethane links [15]. in the case of segmented polyurethanes, prepolymers with isocyanate functionalities have been developed to further react with diamine, dihydroxyl, or similar short chain bifunctional compound [16]. consequently, segmented polyurethanes have two types of segmental units, i.e., isocyanate based hard segments and polyol based soft segments [17]. it is important to mention that secondary interactions or crosslinking may exist between polyurethane chains due to the presence of amine (-n-h) and carbonyl (-c=o) functionalities in the main chain [18]. notable features of polyurethanes can be listed as mechanical strength, thermal stability, thermal conductivity, electrical conductivity, nonflammability, anticorrosion, chemical resistant, and so on [19]. subsequently, applications of these remarkable macromolecules have been reported for thermal insulating materials, foams, gaskets/seals, packaging, building, electronics, and transportation to name a few [20]. one of the outstanding behaviors of polyurethanes have been noted as the formation of polymeric sponges or foams [21]. polyurethane foams may have close or open cell microstructures [22]. these polymeric foams usually have the elasticity, low density, heat stability, heat conductivity, and nonflammability characters [23]. practical uses of polyurethane foams have been observed for aerospace automobile interiors, industrial packaging, insulating materials, furnishing, and other areas [24‒ 26]. for synthesizing polyurethane foams, numerous facile routes have been practiced, as per literature reports so far. usually, the synthesis of polyurethane foam may involve reactions of isocyanate and polyols, as shown in figure 1. an initial attempt by saint-michel et. al. [27] reported the polyurethane foam fabrication using 4,4'diphenylmethanediisocyanate and polypropylene triol in the presence of dibutyltin dilaurate (as catalyst). in this process, in situ produced carbon dioxide from polyisocyanate caused self foaming process [28]. the microstructural analysis revealed close shell cell nanostructures. consequently, fine electrical conductivity and mechanical properties were observed form these polymeric sponges. advancements in the field of polyurethane foams led to the development of nanoparticle reinforced hybrid materials [29,30]. figure 1 shows most probable reactions of isocyanate functionalities involved in the formation of polyurethane foams [31]. herein, in situ characterization and application of nanomaterials 2025, 8(3), 11881. 3 production of carbon dioxide (key agent for self foaming) can be seen as a result of reactions between isocyanate groups and water [32]. figure 2a shows scanning electron microscopy images of polyurethane foam having varying isocyanate index (0.88‒1.1). with increasing values of isocyanate index, strength/integrity of cell walls seemed to be enhanced and porosity was decreased due to increasing viscosity, crosslinking, and foam reactions of the system. figure 2b depicts relationships of tensile strength with isocyanate index and compressive strength vs. isocyanate index at 50% deformation and 20% deformation of foamed samples. according to these results, the linear relationships between the properties were observed due to enhancements in integrity of the cellular foam structure with rising isocyanate index. figure 2c illustrates glass transition temperature vs. isocyanate index of polyurethane foam. hither, glass transition temperature was found linearly dependent upon the isocyanate index of polyurethane foams, which may also affect their mechanical properties. it can be suggested that optimal temperature around ~23 ° must be used to attain desirable mechanical properties of these sponges. figure 1. common reactions involved in polyurethane foam manufacturing via isocyanate reactions [31]. reproduced with permission from mdpi. characterization and application of nanomaterials 2025, 8(3), 11881. 4 besides, waterborne polyurethanes have been considered as an environmentally friendly type of polymers with solvent-borne backbone units [33,34]. these polymers have been studied for valuable thermal, mechanical, anticorrosion/antichemical, barrier, permeability, and other characteristics [35‒37]. consequently, waterborne polyurethanes have developed in the form of nanocomposites, foams, nanofibers, and other industrially viable materials been and their foams have been reported for advanced applications [38‒40]. figure 2. (a) scanning electron microscopy images of polyurethane foam having varying isocyanate index; (b) tensile strength vs. isocyanate index (blue circles) and compressive strength vs. isocyanate index at 50% deformation (red squares) and 20% deformation (brown squares) of foamed samples; (c) glass transition temperature vs. isocyanate index of polyurethane foam [31]. reproduced with permission from mdpi. characterization and application of nanomaterials 2025, 8(3), 11881. 5 3. polyurethane foams with carbonaceous nanoreinforcements 3.1. graphene nanoreinforced polyurethane nanocomposite foam name of graphene appears first among the most remarkable nanocarbon discoveries [41]. graphene occurs as a nanosheet of hexagonally organised sp2 hybrid carbon atoms [42]. according to structural specifications, graphene is believed as a single layer out of a stacked graphite structure [43]. since discovery, countless bottom up or top down strategies have been adopted to form two dimensional graphene nanostructure, including exfoliation, hydrothermal, vapor deposition, plasma/laser, and chemical or electrochemical routes [44]. subsequently, scientific explorations on graphene unveiled a range of notable attributes, such as superior surface area, young's modulus (~i tpa), thermal transport (~2000-5000 w/mk), electrical conduction (~200,000 cm2v-1s-1), and other valued characteristics [45]. amid high-tech applications, worth of graphene has been noted in the fields of space/defense, energy devices (solar cells, fuel cells, capacitors, batteries), electronics (sensors, diodes), civil engineering, textile, environmental remediation, and medical areas [46,47]. technical implications of graphene have been further enhanced in the form of polymeric hybrids using varying matrices [48]. in this regard, polyurethanes have also been applied as valuable matrices for graphene and derivative nanofillers [49]. several high performance polyurethane/graphene nanocomposites have been designed and examined for physical properties and advanced industrial uses from energy and environment to biomedical devices [50]. similar to polyurethanes, hybrid foams or sponges have been prepared with graphene reinforcements [51,52]. among early attempts, hodlur et. al. [53] reported coating method for graphene deposition on polyurethane foam. the hierarchical sponges depicted fine percolation and electron conduction behavior under low applied pressures, e.g., ~0.5 atmospheres. chen et. al. [54] used curing method for the formation of polyurethane/graphene nanocomposite foam. adding 5‒20 phr graphene contents to polyurethane foam matrix exhibited significantly higher electrical conductivity (1.5 × 10-3 to 1.3 s cm-1), than the unfilled foams (1.0 × 10-11 s cm-1). these superior conductivity properties of hybrid foams seemed to be due to the formation of consistent three dimensional networks in these materials. kim et. al. [55] preferred catalyst foaming strategy to form polyurethane/graphene nanocomposite foam. these spongy nanomaterials revealed notable sound absorption properties. herein, including 0.5 phr graphene nanofiller to polyurethane foam caused 7 times higher sound absorption coefficient than the unfilled foams. patole et. al. [56] prepared a system based on polyurethane/poly(dimethyl siloxane)/graphene foams. figure 3a shows a facile resin infiltration technique for the formation of hybrid foams. in this regard, initially polyurethane/graphene foam was formed using carbonization process. later, poly(dimethyl siloxane) was impregnated on the nanocomposite foam to form polyurethane/poly(dimethyl siloxane)/graphene foam hybrids. figure 3b illustrates scanning electron microscopy micrograph of the hybrid foam, where graphene can be observed with a defect free lattice structure. such morphology confirmed the effectiveness of synthesis techniques characterization and application of nanomaterials 2025, 8(3), 11881. 6 applied to form these polymeric sponges. moreover, the hybrid foam had electrical conductivity of ~2.9 s m-1, due to the presence of three dimensional graphene architecture. figure 3c shows functioning and resistance vs. time plot of a pressure sensor based on polyurethane/poly(dimethyl siloxane)/graphene foam. pressure was applied using fingertip and resistance variations were measured with a multimeter. the resistance behavior was found directly related to the applied pressure over repeated cyclic process. such pressure or strain sensors based on polyurethane foams can be useful for future soft robotics applications. zhong et. al. [57] fabricated polyurethane/graphene oxide and polyurethane/reduced graphene oxide nanocomposite foams. for this purpose, a commercial polyurethane foam (40 × 40 × 30 mm3) was coated with graphene oxide through continuous solution dipping plus squeezing processes (figure 4a). the as prepared polyurethane/graphene oxide hybrid foam was treated with hydrazine hydrate (reducing agent) to form polyurethane/reduced graphene oxide nanocomposite sponge. figure 3. (a) step wise fabrication of polyurethane/poly(dimethyl siloxane)/graphene foam; (b) scanning electron microscopy image of hybrid foam, inset: atomic-resolution image of the same with graphene crystal lattice; (c) resistance vs. time plot for polyurethane/poly(dimethyl siloxane)/graphene foam, inset: experimental setup for hybrid characterization and application of nanomaterials 2025, 8(3), 11881. 7 based pressure sensor with fingertip for applying pressure [56]. pu = polyurethane; pdms = /poly(dimethyl siloxane); gf = graphene foam; gf-pdms = graphene foam-poly(dimethyl siloxane); gc-pu = graphene crystal-polyurethane. reproduced with permission from acs. figure 4. (a) schematic of the formation of polyurethane and reduced graphene oxide based foam and derived pressure or piezo-resistive sensor; (b) scanning electron microscopy images of (a) pristine polyurethane foam; (b, c) reduced graphene oxide based polyurethane foam with different magnifications; (c) current vs. real time scan of polyurethane and reduced graphene oxide based nanocomposite foam under different applied pressures [57]. go = characterization and application of nanomaterials 2025, 8(3), 11881. 8 graphene oxide; pu = polyurethane; go/pu = graphene oxide/polyurethane; rgo/pu = reduced graphene oxide/polyurethane. reproduced with permission from mdpi. figure 4b a-c present scanning electron microscopy micrographs of pristine polyurethane foam and reduced graphene oxide filled polyurethane foam. in the case of pristine foam, uniform porosity and surface roughness was observed. this surface roughness was found beneficial for the adsorption of graphene oxide in the foam architecture. consequently, polyurethane/reduced graphene oxide nanocomposite foam revealed typical graphene like wrinkled surfaces. furthermore, figure 4c shows a relationship between current and real time for polyurethane/reduced graphene oxide hybrid foam, with increasing applied pressures (0.62-10.4 kpa). it was observed that increasing pressure on the hybrid foam caused continuous rise in current stages due to signal-to-noise ratio and recyclability of the piezoresistive sensor. 3.2. carbon nanotube filled polyurethane nanocomposite foam carbon nanotube is one of the most remarkable discovery (1991) in the field of nanocarbon nanoallotropes [58]. it is a one dimensional hollow cylinder shaped carbon nanotecture which is composed of sp2 hybrid atoms [59]. this cylindrical nanostructure may exist as single walled or possess overlapping cylinders to form double walled, or multi walled carbon nanotubes [60]. the diameter of carbon nanotube can be as small as few nm, whereas length has been reported in the range of 100 nm to few µm [61]. among common synthesis tactics, arc discharge, chemical vapor deposition, laser ablation, catalytic, and chemical approaches have been applied to form carbon nanotube [62]. the precisely designed nanocarbon nanostructures have superior aspect ratio, chirality, optical, electronic, electrical, magnetic, and thermal attributes [63,64]. subsequently, an endless potential of carbon nanotube can be noted for defense/space, energy/electronics, coatings, construction, textile, sports, and biomedical areas [65‒67]. besides, carbon nanotube can form the most valuable type of nanocomposites with different polymeric matrices [68]. in this concern, notable scientific attempts can be seen regarding polyurethane and carbon nanotube derived nanocomposites [69]. consequently, carbon nanotube reinforced thermosetting, thermoplastics, or biobased polyurethanes exhibited countless structural, thermal, mechanical, and tribological features; therefore leading to high end commercial acceptance [70]. along the similar lines, carbon nanotube has also been reinforced in polyurethane foams to form high performance next level industrial hybrids. as compared to polyurethane/carbon nanotube nanocomposites, the derived hybrid foam revealed exceptional advantages of strength-to-weight ratio, mechanical firmness, flexibility, electrical percolation, thermal transport/stability, and other beneficial properties [71]. therefore, polyurethane/carbon nanotube foams have been found promising for numerous industrial applications, where polyurethane nanocomposites were found least efficient [72]. among initial scientific attempts, you et. al. [73] used free rise foaming technique (cyclopentane as foaming agent) to form polyurethane/carbon nanotube hybrid foams. the resulting spongy nanomaterials developed efficient matrixnanofiller links and percolation effects leading to reasonable electrical conductivity of about 0.2 scm-1. later, zhai et. al. [74] adopted facile water blowing practice to form characterization and application of nanomaterials 2025, 8(3), 11881. 9 carbon nanotube filled polyurethane foam. these hybrid foams revealed valuable compression based stress-strain features due to load transfer effects of increasing carbon nanotube contents. espadas-escalante et. al. [75] applied blowing agent based free foam rising practice to design polyurethane/carbon nanotube foams. these spongy hybrids were tested for compressibility, heat conduction, and flame resistance attributes. accordingly, adding carbon nanotube contents (0.1‒2 wt.%) to polyurethane foams enhanced the flame stability by reducing the flame propagation speed. huang et. al. [76] adopted an innovative direction dependent freezing process for the formation of carbon nanotube reinforced thermoplastic polyurethane foams. figure 5a a-c show complete steps, equipment, and mechanism for ice crystal growth involved in the freezing process applied for the formation of thermoplastic polyurethane/carbon nanotube foams. herein, use of direction dependent freezing led to the formation of aligned hybrid foam architecture. figure 5b a-c depict scanning electron microscopy micrographs for pristine thermoplastic polyurethane sponges and thermoplastic polyurethane/carbon nanotube hybrid foams. these nanocomposite sponges revealed unique consistently aligned architectures due to the effectiveness of the manufacturing technique used. hence, polyurethane/carbon nanotube hybrid foams formed unidirectional stairs like nanoarchitectures. besides, figure 5c displays a reversible compression behaviour of aligned (freezing method) and irregularly grown nanocomposite foams. as expected, aligned polyurethane/carbon nanotube hybrid foams revealed superior shape reattaining behavior after compression due to structural integrity and synthesis technique used. on the other hand, irregularly grown hybrid foam was suggested to have distorted cell structure and meagre shape recovery on compression cycles. guo et. al. [77] formed pristine thermoplastic polyurethane and thermoplastic polyurethane/carbon nanotube nanocomposite foams using fused filament fabrication based three dimensional printing technique. figure 6a demonstrates scanning electron microscopy micrographs of pristine thermoplastic polyurethane and thermoplastic polyurethane/carbon nanotube nanocomposite foams with 1 and 4 wt.% loading level. relative to the unfilled foam, adding nanofiller contents reduced the cell sizes and enhance the number of cells in the hybrid foams. this effect was observed due to heterogeneous nucleation caused by the nanocarbon nanoparticles in the polyurethane spongy matrix. figure 6b displays actual compression loading and release processes applied on the hybrid foam at varying compression rates. accordingly, figure 6c present relative current vs. time scan of 4 wt.% carbon nanotube filled thermoplastic polyurethane foam. herein, a constant current changes over different applied compression rates were observed. similarly, figure 6d a shows a polyurethane/carbon nanotube nanocomposite foam based wearable sensor for gait recognition (linked to a multimeter). the changes in current were found directly linked to the variations in human gait. characterization and application of nanomaterials 2025, 8(3), 11881. 10 characterization and application of nanomaterials 2025, 8(3), 11881. 11 figure 5. (a) (a) manufacturing of thermoplastic polyurethane/carbon nanotube hybrid foam by freezing technique; (b) freezing equipment used; (c) a schematic of process showing directional freezing and growth of ice crystals; (b) scanning electron microscopy images of (a1-3) unfilled thermoplastic polyurethane foams; and (b1-3) thermoplastic polyurethane/carbon nanotube foams; (c-e) as prepared samples of conducting thermoplastic polyurethane/carbon nanotube foams; (c) comparative models showing reversibility processes for aligned and disordered thermoplastic polyurethane/carbon nanotube nanocomposite foams [76]. cnts = carbon nanotubes; tpu = thermoplastic polyurethane. reproduced with permission from acs. figure 6. (a) scanning electron microscopy images of pristine tpu foam and tpu/mwcnts nanocomposite foam (1 & 4 wt.%), left to right, respectively; (b) compression loading and releasing stages of the hybrid foam; (c) relative current vs. time plot of tpu/mwcnts at varying compression rates; (d) tpu/mwcnts nanocomposite foam based plantar wearable sensor for gait recognition [77]. tpu = thermoplastic polyurethane; tpu/mwcnts = thermoplastic polyurethane/multiwalled carbon nanotubes. reproduced with permission from mdpi. characterization and application of nanomaterials 2025, 8(3), 11881. 12 4. technical significance of polyurethane/carbonaceous nanocomposite foams 4.1. radiation shielding hazardous effects of continuously rising radiation pollution generated by functional electronics and other devices have been observed for the entire ecosystem (human beings, animals, vegetation, electronic systems) [78,79]. to cope the damaging influences of electromagnetic radiations, several solutions have been proposed, including the use of high performance materials/nanomaterials shields [80,81]. in this regard, polymers as well as derived nanocomposites have gained enormous worth to design high tech radiation shields [82]. for polymeric nanocomposites, carbonaceous nanoreinforcements like graphene or carbon nanotubes have attained scientific curiosity to deal with the environmentally interfering radiations [83,84]. furthermore, polyurethane has been studied as an important matrix material to deal with the challenges of electromagnetic, gamma, or nuclear rays [85]. particularly, polyurethane foams and derived nanocomposite foams have been noted for low weight, flexibility, facile synthesis, and valuable electrical conductivity and dielectric properties [86]. however, emi shielding competency of polyurethane nanocomposite foams seemed to be reliant upon polymer backbone, nanoadditive type/content, dispersion, matrix-nanofiller links, and manufacturing route applied [87]. as per literature reports so far, nanocarbons such as graphene, graphene derivatives, carbon nanotubes, carbon nanofibers, carbon black, etc., have been recurrently applied as nanoreinforcements for polyurethane foams [88]. li et. al. [89] designed polyurethane filled foams with carbon nanotube nanofillers using latex approach. these polyurethane/carbon nanotube sponges exhibited fairly high electrical conductivity (>360 sm-1) and radiation shielding efficiency (~25 db). the radiation shielding performance was suggested to be because of the formation of percolation network supporting electron transfer and radiation shielding performance of the hybrids. jiang et. al. [90] used reduced graphene oxide as nanofiller and co2 foaming process for polyurethane foams. these nanomaterials revealed lower conductivity (2.5×10-1) than carbon nanotube filled foams, however had reasonable emi shielding effectiveness (22 db). in this concern, gavgani et. al. [91] reported on a outperforming polyurethane and reduced graphene oxide derived foams by adding foaming agents (voranol/tin). these nanocomposite foams had electrical conductivity of ~4 sm-1 and enormously high radiation shielding efficiency (>253 db). such performance of polyurethane/reduced graphene oxide foams seemed to be because of the effectiveness of synthesis method used for developing hierarchical and inerfacially connected three dimensional porous nanostructures. oraby et. al. [92] manufactured polyurethane/iron(ii,iii) oxide/reduced graphene oxide based nanocomposite foams using facile solution sonication and curing routes. these hybrid sponges were investigated for microstructural, mechanical, and radiation absorption properties. accordingly, figure 7a a-c show transmission electron microscopy micrographs of iron(ii,iii) oxide/iron(iii) oxide nanoparticles, pristine reduced graphene oxide nanosheet, and iron(ii,iii) oxide/reduced graphene oxide hybrid nanoparticles, respectively. characterization and application of nanomaterials 2025, 8(3), 11881. 13 figure 7. (a) transmission electron microscopy images of: (a) iron(ii,iii) oxide/iron(iii) oxide (fe3o4/fe2o3) nanoparticles, inset: particle size distributions; (b) reduced graphene oxide (rgo) nanosheets; (c) iron(ii,iii) oxide/reduced graphene oxide (fe3o4/rgo) hybrids; (b) mechanical properties vs. shielding effectiveness (se) and polyurethane foam with filler loading [92]. reproduced with permission from mdpi. the iron(ii,iii) oxide/reduced graphene oxide hybrid had fine dispersion of tiny nanoparticle (~70 nm) over thin transparent graphene surface. in addition, figure 7b illustrates the effect of increasing iron(ii,iii) oxide/reduced graphene oxide nanofiller contents as well as compression strength and modulus on shielding effectiveness of the nanocomposite foams. as per results, adding nanoparticle contents (up to 35%) caused notable shielding effectiveness of ~33 db. this effect was attributed to the formation of continuous percolation network of reduced graphene oxide and iron nanoparticles in the polyurethane foams, so leading to valuable electrical conductivity and radiation absorption properties. similarly, reasonably high compressive strength and modulus of around 15.6 and 5.3 mpa, respectively, were attained for the hybrid foams. superior mechanical properties of polyurethane foams reinforced with iron(ii,iii) oxide/reduced graphene oxide hybrid nanoparticles were visibly linked to the integrity of three dimensional nanoarchitectures due to mutual interfacial compatibility. into the bargain, polyurethane foams and polyurethane nanocomposite foams (whether open cell or close cell) have been employed in space sector owing to their capabilities towards efficiently attenuating fast moving neutron, γ-rays, and characterization and application of nanomaterials 2025, 8(3), 11881. 14 electromagnetic interfering radiations [93]. in addition, these foams have low densities and nonflammability properties to be employed as promising radiation shields for electronics, energy devices, communication equipment, and defense system of aerospace industry [94]. hence, using high performance polyurethane foam based radiation shields may open invaluable ways for deployments in advanced future space architectures. for a better literature analysis, table 1 shows some significant polyurethane nanocomposite foams applied for electromagnetic interference shielding purposes. table 1. electromagnetic interference shielding (emi) shielding effectiveness of polyurethane nanocomposite foams. foam matrix nanofiller fabrication electrical conductivity (scm-1) emi shielding effectiveness (db) ref waterborne polyurethane carbon nanotube latex technology 362 25 db [89] polyurethane reduced graphene oxide supercritical co2 foaming 2.5×10-1 3.17 vol.%; 22 db [90] polyurethane reduced graphene oxide tin catalyst and voranol foaming agent 4.0 253 db [91] polyurethane fe3o4 functional reduced graphene oxide sonication; curing 25 wt.%; 23 db [92] polyurethane graphene oxide solution, heating, casting 3.0 20 wt.%; 17-24 db [95] polyurethane/polydopamine graphene dip coating; ultrasonic; compression heating ~ 60 db [96] polyurethane graphene nanoplatelets supercritical co2 foaming 1 wt.%; 16-18 db [97] polyurethane graphene catalyst; foaming agent acoustic performance [98] 4.2. shape memory applications shape memory (stimuli active) polymers own intrinsic ability to change their shape reversibly, when exposed to light, heat, electricity, or any environmental effect [99]. innumerable shape memory polymers (thermoplastics, thermosets, rubbers, etc.) have been reported in the literature to date [100]. in this concern, polyurethanes have been studied for proficient shape reversibility behaviour [101]. accordingly, stimuli responsive polyurethane may display one-/two-/or multi-way shape changing phenomenon [102]. as per literature, uses of shape memory polyurethanes can be seen in smart coatings, textiles, and medical appliances [103]. in nanocomposite form, polyurethanes filled with carbon nanoparticles have been investigated for shape memory effects [104]. mostly studies reported on the thermoresponsive stimuli responsive effects of polyurethane/nanocarbon nanocomposites [105]. consequently, these smart polyurethane hybrids revealed notable potential for engineering materials, electronics, defense, and medical areas [106]. for example, graphene has been used as an efficient nanofiller to support the stimuli sensitive behavior of polyurethanes [107]. zarghami dehaghani et. al. [108] used solution condensation method to form polyurethane from poly(tetramethylene ether) glycol, α,ω-dihydroxy(ethylenebutylene adipate), 1,4-butanediol, and methylene diphenyl diisocyanate. adding characterization and application of nanomaterials 2025, 8(3), 11881. 15 0.25 wt.% graphene resulted in >92 % enhancement in thermos responsive shape memory effects. wu et. al. [109] filled carbon nanotube in a commercially available thermoplastic polyurethane using solution method. these nanocomposites depicted water sensitive shape recovery in ~120 s. similarly, few other reports available for nanocarbon filled shape memory polyurethanes [110]. as per literature reports, polyurethane foam materials have stimuli sensitivity towards photo, thermal, current, ph, and water effects [111]. an earlier effort by singhal et. al. [112] mentioned the formation of polyurethane via condensation of 2,2',2"-nitrilotriethanol, n,n,n',n'-tetrakis(2-hydroxypropyl)ethylenediamine, and 1,6-diisocyanatohexane. later, foaming agent method was applied to form polyurethane foams having glass transition temperature up to ~50-70 ºc. moreover, thermomechanical shape retrieval of 97-98 % was attained. moreover, in an earlier attempt, kang et. al. [113] also applied blowing agent technique to form polyurethane foams of polypropylene glycol and 2,4/2,6-toluene diisocyanate with carbon nanotube additives. these nanocomposite foams were tested for thermomechanical shape memory effects. according to results, adding 5 wt.% carbon nanotubes in polyurethan foam caused up to 85% shape recovery properties. later, kim et. al. [114] preferred microwave heating technique to form stimuli responsive polyurethane/carbon nanotube foams. these thermoresponsive spongy nanomaterials revealed shape fixity and shape recovery ratio of ~95% and 84%, respectively. kumar et. al. [115] performed pressure sensitivity studies on shape memory polyurethane foams. in this regard, figure 8a presents schematic of probable volume changes in shape fixity/recovery of shape memory polyurethane foams. such changes usually occur around glass transition temperature of the polymer and external pressure was applied in this study. figure 8b shows tekscan f scan pressure system used to analyze the effect of applied pressure (male heel) on the shape memory polyurethane foams. characterization and application of nanomaterials 2025, 8(3), 11881. 16 figure 8. (a) schematic of volume changes in shape fixity and shape recovery processes of shape memory polyurethane at glass transition temperature (tg) with strain; (b) tekscan f scan pressure analysis using male heel; (c) areal pressure distribution of shape memory polyurethane foams under varying surface temperatures and applied force [115]. reproduced with permission from acs. consequently, figure 8c depicts areal pressure distribution under variable surface temperatures for shape memory polyurethane foam (static force). it was observed that increasing temperature up to 20 °c effectively distributed the applied force and had low modulus due to polymer backbone softening. contrarily, lower temperatures (10-15 °c) did not efficiently distribute the pressure (concentrated red pressure peaks in figure 8c) due to rigidity of polyurethane foam. it can be suggested that temperature changes along with the applied pressure play important role in shape memory behavior of polyurethane foams. 4.3. in biomedical sector polyurethanes have been noted as significant macromolecules for biomedical purposes [116]. in this concern, polyurethanes have countless valuable attributes including optimum physiological features, biodegradability, biocompatibility, prolonged in vivo stability, nontoxicity, and so on [117]. looking at the medical applications of polyurethanes, a myriad of uses has been reported for tissue scaffolds, bioimplants, drug delivery, coatings, wound healing, smart devices, etc. [118‒120]. polyurethane foams have been designed and tested for in vitro and in vivo conditions for biomedical uses [121]. consequently, these spongy materials depicted fine biocompatibility and long term biosustainability during desirable applications in living systems [122]. among earliest attempts on biocompatible polyurethane foams, guelcher et. al. [123] performed condensation of poly(ε-caprolactone-coglycolide)triol, lysine methyl ester diisocyanate, and tertiary amine. the resulting polyurethane foams were applied as injectable tissue scaffolds [124]. later, schreader et. al. [125] explored polyurethane foams reinforced with hydroxyapatite nanoparticles for biocompatibility and bone tissue engineering. furthermore, an olden attempt by zawadza et. al. [126] disclosed the use of electrophoretic deposition to coat polyurethane foam with carbon nanotube nanofiller. the resulting polyurethane/carbon nanotube hybrid foams were tested for bone tissue engineering. in this concern, growth, compatibility, noncytoxicity, and hydroxyapatite growth have been studies for the nanocomposite foams. besides, shin et. al. [127] formed polyurethane nanocomposite foams with graphene and graphene oxide and studied for skeletal tissue rejuvenation due to biomimetic effects. these polyurethane/graphene nanocomposite foams had minimum cytotoxicity and optimum porosity (~300 μm), which were suitable skeletal cell growth. hence, both the polyurethane/carbon nanotube and polyurethane/graphene hybrid sponges have been studied for biocompatibility/non cytotoxicity effects towards biomimetic injectable scaffolds or hydroxyapatite growth for bone or skeletal tissue engineering. future studies must focus on more design combination, long term in vivo stability, and other biomedical uses like drug delivery, bioimaging, etc. characterization and application of nanomaterials 2025, 8(3), 11881. 17 5. conclusive remarks and future opportunities in summary, polyurethane, being a multiuse polymer, has been studied for variety of physical and practical probabilities. among well practiced forms of polyurethanes, spongy materials have been manufactured for strategic features and applications. in the form of foam materials, polyurethanes own specific cell sizes, distribution, and open/close structures, so contributing to valuable characteristics. as compared to pristine polyurethanes, development of nanocomposite foams using valued nanocarbons, graphene and carbon nanotube, revealed notable surface area, cellular nanostructures, nanoparticle dispersion, electron and heat transportation, flexibility retaining integrity, barrier, noncytoxicity, biocompatibility, and other beneficial attributes towards high end uses. according to research efforts to date, application areas discovered for polyurethane nanocomposite foams include electromagnetic radiation shielding, stimuli responsiveness, and medical related uses (figure 9). in polyurethane/graphene nanocomposite foams, polyurethane/carbon nanotube nanocomposite foams, and all the applied fields, adding nanoparticles type, contents, scattering, and interfacial specifications directly influence the materials properties and applied contours. moreover, feasibility and effectiveness of processing techniques may affect the implication of ultimate spongy architecture. figure 9. prospects of multifunctional polyurethane foams. looking at the valuable properties of polyurethane nanocomposite foams, we can suggest several future applications of these spongy materials. especially due to thermal conductivity properties, polyurethane hybrid foams can be used to substitute commercial panels and interiors in aerospace and automotive vehicle structures. characterization and application of nanomaterials 2025, 8(3), 11881. 18 similarly, such materials can be practiced for advanced construction and civil engineering utilizations. another side of these nanocarbon filled hybrid sponges not discovered yet seemed to be the smart wearable devices and e-electronics. in addition to radiation absorption, these nanocomposite sponges can be used for encounter sound and acoustic effects in relevant fields. due to limited research so far on medical sides, comprehensive efforts may reveal application of polyurethane nanocomposite foams in smart drug/gene delivery and smart tissues and artificial muscles. concisely, further applied breakthroughs of polyurethane hybrid aerogels can be protracted by explorations of key mechanisms for ultimate cellular structure and interfacial relationships. in addition, scalable manufacturing of polyurethane nanocomposite foams by achieving global sustainability and environmental demands seem indispensable for future commercial modules in high tech industries, from energy to medical. conflict of interest: the authors declare no conflict of interest. references 1. zarmehr sp, kazemi m, madasu nga, et al. application of bio-based polyurethanes in construction: a state-of-the-art review. resources, conservation and recycling. 2025; 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covid-19; polymeric nanoparticle; drug delivery 1. introduction nanotechnology is the study and creation of devices and structures at the nanoscale. because of their ability to increase drug stability, prolong the therapeutic effect of the drug, decrease metabolism of the drug, and reduce cellular uptake, nanoparticles have been the subject of extensive research in the biomedical and biotechnological fields. this is especially true when it comes to drug delivery systems [1]. the rapid evolution of humanity has led to the development of technology that can help us overcome daily struggles. while some advances may not be essential for survival, others are crucial. one such necessary development is the field of vaccine development and delivery. for many years, humans have faced numerous infectious diseases, some of which have proven to be deadly on a global scale, such as the plague, cholera, and various types of coronaviruses. throughout history, countless pandemics have been caused by viruses, including the spanish flu. (h1n1) in 1918 [2], ebola in 1976, aids (hiv) in 1981, avian flu (h5n1) in 1996, sars (sarscov) in 2002, mers (mers-cov) in 2012, and covid-19 (sars-cov-2) in 2019 [3,4]. these outbreaks have taught us valuable lessons about citation adu e, patel sa, catino aj, medhi r. polymeric nanoparticles (pnps) as drug delivery systems for sarscov-2. characterization and application of nanomaterials. 2024; 7(1): 4959. https://doi.org/10.24294/can.v7i1.4959 article info received: 5 march 2024 accepted: 9 april 2024 available online: 30 may 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 4959. 2 the importance of novel technologies for testing, tracing, and developing vaccines to effectively respond to pandemics in the future [5,6]. respiratory tract infections are a major cause of disease and a significant public health concern globally. lower respiratory tract infections (lrti) and pneumonia have been reported to be responsible for over four million deaths each year, which is more than the combined deaths caused by hiv, malaria, and tuberculosis. respiratory viruses are the cause of more than 80% of these infections [7]. an outbreak of the lung illness coronavirus disease 2019 (covid-19) began in december 2019 in the chinese city of wuhan due to a new coronavirus known as severe acute respiratory syndrome coronavirus 2 (sars-cov-2) [8,9]. fever, severe respiratory disease, pneumonia, and dyspnea are the main signs and symptoms of covid-19 [10,11]. the morphology of sars-cov-2 is shown in figure 1. we must prioritize the development of rapid diagnostic testing, drug repurposing, and biomarkers of disease severity, as well as new platforms for vaccine production [12,13]. (a) (b) figure 1. sars-cov-2 morphology. (a) representation of the viral structure is illustrated with its structural viral proteins; (b) transmission electron microscope image of sars-cov-2 spherical viral particles in a cell. the virus is colorized in blue (adapted from the us centers for disease control) permission from udugama et al. [22]. one of the most crucial considerations in vaccine development is the availability of platforms that can deliver the vaccine to specific sites in the human body without interfering with other functions [14]. in recent decades, nanoparticles have been developed to address the limitations of free drug molecules and overcome biological barriers at both systemic and cellular levels [15]. this has resulted in the development of new therapeutics to treat a variety of diseases [16]. various types of nanoparticles are currently in use for different applications [17], but this paper only focuses on polymeric nanoparticles (pnps). pnps are particles that range in size from 1 to 1000 nm [18] and can be loaded with active compounds that travel through our body to deliver the active compound to the targeted location [19]. pnps can be divided into two categories: natural and synthetic. both offer excellent medicinal applicability due to their non-toxicity and biodegradability [20]. pnps can be modified to control drug release based on receptor proteins, temperature, and ph [21]. this review article discusses various pnps platforms that have been developed to fight against the most recent pandemic, sars-cov-2. the article focuses on the polymeric material, size, design, cytotoxicity, and release mechanism of each np. it characterization and application of nanomaterials 2024, 7(1), 4959. 3 also covers some of the nps that have been used against other viral outbreaks but exhibit potential for use against sars-cov-2. common polymers covered in this paper include poly (lactic-co-glycolic acid) (plga), poly (ethyleneglycol) (peg), poly(n-isopropylacrylamide) (pnipam), and poly (3,4-ethylene dioxythiophene) (pedot). 2. polymer nanoparticles (pnps) the term “polymeric nanoparticle” refers to solid nanospheres or nanocapsules that either adsorb molecules on their surface or encapsulate them within a polymeric matrix, as shown in figure 2 [19,23,24]. biodegradable polymeric nanoparticles are the most promising drug delivery strategy for pulmonary/respiratory applications [25,26]. pnps can be used instead of liposomes. they have similar size and shape properties as liposomes but offer additional benefits such as improved stability in vitro and in vivo, high cargo capacity, and targeting. their ability to efficiently deliver therapeutics to specific targets makes them ideal drug carriers [27]. a wide range of products and application fields, such as electronics, photonics, paints, adhesives, food technology, cosmetics, catalysis, analytical assays, sensors, purifications, and drug administration, have shown interest in polymer particles [28]. various polymeric structures have been developed for vaccine delivery systems, including solid polymeric nanoparticles, micelles, nanogels, polymersomes, and coreshell nanoparticles [29]. biocompatible and biodegradable lipids that remain solid at room temperature and body temperature make up solid lipid nanoparticles (slns), which are submicron-sized drug carriers [30]. for controlled and targeted delivery, solid lipid nanoparticles (slns) are becoming a more viable option than colloidal systems as carriers and amalgamate the benefits of various colloidal carriers, such as emulsions and liposomes, which are physiologically acceptable and can be expected to release drugs from the lipid matrix in a controlled manner, much like polymeric nanoparticles [31,32]. in recent years, the polymeric micelles (pm) system has garnered increasing scientific attention as an effective drug carrier due to its unique properties such as solubilization, selective targeting, inhibition of p-glycoprotein, altered drug internalization route, and subcellular localization [33,34]. delivering drugs to their targets with micellar solutions of amphiphiles is an efficient method. owing to the hydrophobic environment present in the core of micelles, drugs that are insoluble in water can be readily dissolved and subsequently transported to the desired locations [35]. additionally, polymer chains that are cross-linked form threedimensional networks known as nanogels [36,37]. to improve a wide range of therapies and diagnostic tests for various human diseases, nanogels are widely acknowledged as highly versatile drug delivery systems. significant volumes of water or biological fluid can be absorbed by these hydrophilic cross-linked polymers that are three-dimensional [38]. a class of artificial vesicles called polymersomes (ps) is created from synthetic amphiphilic block copolymers. typical ps are hollow spheres with a bi-layer membrane enclosing an aqueous solution within [39]. additionally, ps have many advantages over liposomes in the delivery of drugs because of their high levels of stability, control over their architecture, adaptability to surface modifications, and high drug loading efficiencies [40]. understanding how core/shell particles form characterization and application of nanomaterials 2024, 7(1), 4959. 4 has been the subject of several studies, and creating core/shell particles as a practical way to encapsulate a wide range of materials, from organic molecules to biological macromolecules, has drawn a lot of attention [41]. because bare nanoparticles are toxic, host tissues may be harmed or troubled. core-shell nanoparticles exhibit better characteristics than bare nanoparticles, including reduced cytotoxicity, high dispersible nature biocompatibility, improved conjugation with drugs and biomolecules because of improved surface properties, and improved chemical and thermal stability [42,43]. figure 2. schematic representation of the structure of nanocapsules and nanospheres. the arrow indicates the presence of drug or bioactive within the nanoparticles. reproduced with permission from zielińska et al. [19]. 2.1. synthesis of pnps pnps are created using biodegradable polymers such as polyesters (such as poly(lactideco-glycolide) (plga) and poly-caprolactone (pcl), polyamides (such as gelatin and albumin), polyanhydrides, polyurethanes, and polyphosphazenes. these polymers are utilized to produce pnps [2,44]. several preparation techniques have been developed; these can be categorized into two groups: those that rely on the polymerization of monomers and those that utilize preformed polymers. these techniques can be further divided into two groups: one-step procedures where the formation of nanoparticles does not require emulsification and two-step procedures that involve the preparation of an emulsification system followed by the formation of nanoparticles in the second step of the process [20]. 2.1.1. emulsification/solvent diffusion (esd) this is an altered form of the solvent evaporation technique [45]. to maintain the initial thermodynamic equilibrium of both liquids, the encapsulating polymer is dissolved in a solvent that is partially soluble in water, such as propylene carbonate, and then saturated with water. when the organic solvent is partially miscible with characterization and application of nanomaterials 2024, 7(1), 4959. 5 water, it is necessary to dilute it with excess water to promote the diffusion of the solvent of the dispersed phase; in the opposite case, it is necessary to dilute it with another organic solvent to produce the precipitation of the polymer and the subsequent formation of nanoparticles. the solvent phase that is saturated with polymer and water is then emulsified in an aqueous solution that contains a stabilizer. this process causes the solvent to diffuse to the exterior phase and, depending on the oil-to-polymer ratio, forms nanospheres or nano capsules. ultimately, the solvent is removed through either filtering or evaporation based on its boiling point. figure 3 illustrates the process. various emulsion types can be employed, but oil/water emulsions are noteworthy due to their use of water as a nonsolvent. this reduces the need for recycling, facilitates the washing step, and minimizes agglomeration, all of which simplifies and enhances process economics [46]. numerous benefits come with this method, including high encapsulation efficiency (usually >70%), simplicity, ease of scale-up, high batch-to-batch consistency, and narrow size distribution. it also doesn’t require homogenization. the large amounts of water that must be removed from the suspension and the watersoluble medication that leaks into the saturated-aqueous exterior phase during emulsification, decreasing the effectiveness of encapsulation, are drawbacks [1,46]. like a few others, this method works well for encasing lipophilic medications. the esd method produced several drug-loaded nanoparticles, including meso-tetra (3hydroxyphenyl) porphine (mthpp)-loaded plga nanoparticles, polylactic acid (pla) nanoparticles [47,48] loaded with plasmid deoxyribonucleic acid (dna) [49], plga nanoparticles loaded with doxorubicin, pla nanoparticles loaded with coumarin [46], indocyanine, cyclosporine (cya)-laden gelatin, and sodium glycolate nanoparticles loaded with cyclosporin (cy-a) [46,50]. figure 3. schematic representation of the emulsification/solvent diffusion technique. reproduced with permission from nagavarma et al. [50]. 2.1.2. polymerization of monomers the previously mentioned technique did not require any polymerization operations; instead, pnps were produced from premade polymers. during the polymerization of monomers, appropriate polymer nanoparticles can be developed to achieve the required qualities for a certain application. the article discusses methods characterization and application of nanomaterials 2024, 7(1), 4959. 6 for producing pnps by polymerizing monomers, with a primary focus on three main techniques: mini-, micro-, and emulsion polymerization [51]. emulsion polymerization remains the most widely utilized and well-proven technique as of 2013. when an aqueous and an organic phase are mixed, spontaneous emulsification takes place in the production of nano-emulsions. whereas the organic phase is a homogenous mixture of lipophilic surfactant, oil, and water-miscible solvent, the aqueous phase is composed of hydrophilic surfactant and water [52]. pnps with very small droplets (50–100 nm) will form at the end of the reaction [53]. it is well known that this process raises costs and complicates purification since it needs a lot of surfactants or co-surfactants to create tiny nps [54]. thus, nakabayashi and colleagues [55] used ‘acoustic emulsification,’ one of the effective methods for producing emulsions quickly and sustainably, to produce poly(methyl methacrylate) (pmma) nps with regulated size as shown in figure 4. by employing consecutive ultrasonic irradiation, they created a new synthesis technique for size-controlled pnps in surfactant-free environments [52]. in figure 4, the original mma solution in an aqueous solution mixture is shown (a) after 20 khz for 8 min; (c) 20 khz for 8 min → 500 khz; (d) 20 khz for 8 min → 500 khz, 10 min → 1.6 mhz, 10 min; and (e) 20 khz for 8 min → 500 khz, 10 min → 1.6 mhz, 10 min → 2.4 mhz, 10 min. figure 4. photographic documentation of mma in aqueous solution using tandem acoustic emulsification. reproduced with permission from nakabayashi et al. [55]. 2.2. characteristics of pnps in the fields of nanotechnology and nanomedicine, a wide range of nanomaterials are utilized to deliver drugs with various beneficial properties such as enhanced solubility, extended formulation action, different degrees of lipophilicity or hydrophilicity, and reduced toxicity. nanoparticle drug delivery systems possess unique physicochemical characteristics including surface properties, shape, size (figure 5a), treatment efficacy, drug release, and loading, among others. the surface properties of nanoparticles can significantly impact the biocompatibility, biodistribution, and pharmacokinetics of the drug molecules [26,56]. 2.2.1. infrared spectroscopy fourier transformed infrared spectroscopy (ftir) is a spectroscopic technique based on the measurement of vibrational transitions between different excitation states of molecules [57]. tulbah and lee employed ftir analysis to investigate potential peak shifts or modifications in the favipiravir solid lipid nanoparticles (fpv-sln) formulation resulting from the usage of chemicals like tween 80 and compritol 888 in the nanoparticle manufacturing process. the ftir of unprocessed favipiravir characterization and application of nanomaterials 2024, 7(1), 4959. 7 (fpv), measured between 400 and 4000 cm−1, is shown in figure 5c. the c=o, c–f, and c–oh stretching were characterized by stretching peaks at 1659.17, 1259.51, and 1178.64 cm−1, respectively [58]. figure 5. (a–b) characterization of plga-peg-plga nps loaded with 5fu@chrysin; (c) ftir spectra of (i) unprocessed (fpv); (ii) compritol 888; (iii) tween 80; and (iv) fpv-slns; (d) afm analysis of peg-g-pla pnps’ surface morphology; (e–f) tem photographs of bare and hydrogenated spherical ps/pbd core-shell nps, respectively. reproduced with permission from mostafavi et al. [13], khaledi et al. [59], tulbah and lee [58], and wang et al. [60], respectively. 2.2.2. scanning electron microscopy before being placed on a sample holder and coated with a conductive metal, such as gold, using a sputter coater, the nanoparticle solution needs to be dried out for sem characterization. after that, a finely focused electron beam is utilized to scan the sample. the secondary electrons that are released from the sample surface provide information about their surface properties. the polymer may be harmed by the electron beam, and the nanoparticles need to be able to endure a vacuum. the sem mean size and the dynamic light scattering mean size are similar [53]. figure 5a,b shows the particle size distribution and sem of the size and shape of plga-peg-plga loaded with 5fu@chrysin. 2.2.3. atomic force microscopy atomic force microscopy (afm) is an additional sophisticated microscopic method for characterizing nanoparticles. this is a novel method for imaging the particles’ natural, unaltered form and surface characteristics. this method achieves a spatial resolution of up to 0.01 nm due to the force operating between the probing tip and the surface. it is not necessary for the samples to be conductive, and sample preparation is straightforward. as a result, it permits the examination of samples that are solventand hydrate-containing compounds [31,53]. it is used to calculate the force that exists between the sample’s particle surface and the probing tip. the technique offers good resolution, easy sample preparation, and quick picture capture. afm does not require a vacuum, nor does it require a conducting sample [30]. afm (a) (b) (c) (d) (e) (f)(i) (ii) (iii) (iv) (a) (b) (e) (c) (d) (f) characterization and application of nanomaterials 2024, 7(1), 4959. 8 analysis of peg-g-pla pnps’ surface morphology with x-axis scale of 0.200 μm/div is shown in figure 5d. 2.2.4. transmission electron microscope (tem) nanostructures are small, making it impossible to measure their physical properties with conventional methods, which makes them challenging to examine experimentally. imaging, diffraction, and spectroscopic data of the specimen can be obtained using transmission electron microscopy techniques with an atomic or subnanometer spatial resolution, either concurrently or individually [61]. a microscopy method called tem involves “transmitting” an electron beam through an extremely thin material. the electrons’ interaction effects with the sample produce a picture with a resolution of up to 0.08 nm [62]. figure 5e,f show tem of ps/pbd core-shell and hydrogenated ps/pbd nanoparticles. 3. pnps for antiviral drug delivery systems across the world, there are thousands of committed drug delivery scientists who are working tirelessly to develop vaccines that are safer and more effective against the new variants of sars-cov-2. they are also focused on creating new carriers and drug delivery strategies to fight against any future viral pathogens that may emerge [63]. a well-designed delivery system can significantly improve the bioavailability of viral antigens by enhancing cellular uptake, providing metabolic stability, and targeting relevant tissues [64]. the efficacy of antiviral drugs can be enhanced using polymeric nanoparticles that facilitate prolonged drug release and target the virus. ivermectin, a sars-cov-2 inhibitor, has been successfully administered utilizing plga-b-peg-mal polymeric nanoparticles [16]. one of the main elements influencing drug release is the molecular weight of the polymer. the polymer’s chain length can be determined by its molecular weight, where a higher molecular weight corresponds to a longer chain [65]. in addition, the hydrophilicity/lipophilicity of the polymer is reflected in the chain length. longer chains have a higher lipophilicity and a slower rate of polymer breakdown. therefore, the drug release kinetics and polymer breakdown rate can be adjusted by adjusting the molecular weight [65,66]. physical stability, cellular absorption, biodistribution, and drug release are all strongly impacted by particle size, making it a crucial parameter. nanoparticle performance often improves with decreasing particle size [65]. some of the effects of nanoparticle grain size are:  decrease drug resistance [66].  enhance the rate of dissolution [67].  increase surface area [68].  enhance solubility [69]  enhance oral bioavailability [70].  decrease toxicity [71].  increase the stability of the drug and formulation [68].  increase drug-targeting ability [69]. characterization and application of nanomaterials 2024, 7(1), 4959. 9 3.1. plga plga is a popular polymer used in the creation of micelles, which are used as drug delivery systems. one of the reasons for its widespread use is its high level of biocompatibility and biodegradability. the fda approved its clinical use in 1989 [72]. in a recent study, researchers aimed to develop a biodegradable drug delivery system that targets specific receptor-binding sites for controlled drug release. they used the commonly used pnp, plga, and loaded it with oseltamivir phosphate (op), a well-known antiviral drug [73]. the plga nanoparticles were modified to bind specifically to spike binding peptide-1 (sbp1) of sars-cov-2. the size of the oploaded nps and the op-loaded nps targeted with sbp1 peptide were reported as 162.0 ± 11.0 and 226.9 ± 21.4 nm, respectively. the drug release study was conducted at a ph of 7.4 and a temperature of 37 ℃, and it showed a long and effective release of op. the release rate was fast for the first 30 days and then steady at about 72 days. there was no burst release of op, indicating a successful development of the drug delivery system as indicated in figure 6 [74]. figure 6. in-vitro stability evaluation and release profile of op-loaded nps. (a) size stored at 5 ℃ for four weeks. (b) release profile of the op from the nps targeted with sbp1 peptide or not. reproduced with permission from ucar et al. [74] in another study, plga was utilized to administer fingolimod (fty720). the nps were fabricated through a single emulsion solvent evaporation technique, resulting in a positively charged system with reported sizes of approximately 400 and 190 nm for empty nps and fty720-np, respectively. the system demonstrated a notable drug entrapment rate of 90%, with drug release being contingent upon ph [75]. the study found that drug release required an acidic environment, which the developed nps can access through caveolin-mediated endocytosis and micropinocytosis pathways. once inside lysosomes, the required acidic environment becomes available to the nps. the drug release rate at ph 5 was 10%, 80%, and 100% after 2, 8, and 24 h, respectively. however, at ph 7.4, a lower drug release rate of 10%, 10%, and 20% was observed for the same time spans as shown in figure 7. the size of the system remained relatively unchanged over 90 days, and the use of nps allowed for 70 times higher inhibition of viral infection compared to free drugs. cytotoxicity studies on human and veroccl81 cell lines at 24, 48, and 72 h intervals showed that the characterization and application of nanomaterials 2024, 7(1), 4959. 10 fty720-np system was less toxic than the free drug. overall, the drug delivery system has great potential as it helps preserve the drug until it reaches a specific ph [59]. similar works were done by lui and colleagues in 2024 [3], and struzek and scherließ in 2023 reported on the preparation of ovalbumin (ova)-loaded plga np with a size of 700 nm for pulmonary delivery of antigens. they were successfully produced using several principles of quality by design [76]. also in the work of chandan and coworkers in 2010, porous pla and plga nanoparticles were tested for pulmonary delivery of the hepatitis b vaccine [77]. similar work was also done by claudia and colleagues on the topic “characterization of polymeric nanoparticles for intravenous delivery: focus on stability” [78]. figure 7. fty720 release from the nanostructure system. fty720 release profile from np@fty720 in a phosphate buffer with ph 7.4 and an acetate medium with ph 5.0. data show the average of three independent measurements (n = 3) ± standard deviation (sd). obtained from mirinda et al. [75]. 3.2. poly (n-isopropyl acrylamide) (pnipam) xu and his colleagues developed a drug delivery system that releases drugs in response to specific temperatures. they loaded the fpv drug into silica nanocapsules (sncs) and functionalized the ncs with block polymers [79,80]. the poly (nisopropyl acrylamide)-block-poly (n, n-dimethylamino ethyl methacrylate) (pnipam-b-pdmaema)-modified sncs were embedded in multilayer films to extend release time. the system can release as low as 50% of the drug over 80 days at 37 and 40 ℃. a morphological stability study showed that the system was unharmed for 80 days, promising an effective drug release for a longer period as indicated in figure 8 [79]. figure 8c shows the schematic representation of “on-demand” temperature-triggered film swelling and drug release from multilayer films. characterization and application of nanomaterials 2024, 7(1), 4959. 11 figure 8. release kinetics of fpv from [snc-g-pnipam-b-pdmaema/pmaa]3 (squares) and [snc-g-pnipam-b-q100m/pmaa]3 (circles) films at (a) 25 and (b) 37 ℃; (c) schematic representation of mechanism. reproduced with permission from xu et al. [79]. in a study also conducted by xu and colleagues, they coated silica nanocapsules (sncs) with block polymers and loaded molnupiravir into the system [81]. molnupiravir is a drug that was approved for the treatment of sars-cov-2 from its early days. the block copolymer was quaternized to a certain degree to control the steric hindrance around the charged groups of the polymer blocks in the capsule. the entire snc-block polymer nanoparticle system was then embedded in well-defined films with polystyrene sulfonate (pss) homopolymers by layer-by-layer self-assembly via electrostatic interaction. the polymer that the study group coated on sncs was pnipam-bpdmaema, which is sensitive to temperature change. therefore, the drug release was dependent on the temperature [81]. speaking of how molnupiravir operates, it introduces copying errors during viral rna replication. the average thickness of various combinations of the system, namely [snc-g-pnipam-bpdmaema/pss], [snc-g-pnipam-b-q20m/pss], [snc-g-pnipambq40m/pss], and [snc-g-pnipam-b-q100m/pss] films, were reported as 125 ± 16, 135 ± 19, 170 ± 25, and 205 ± 28 nm, respectively, at 37 ℃. the drug release was found to be around 81, 76, 62, and 45 % from [snc-g-pnipam-b-pdmaema/pss]3, [snc-g-pnipam-b-q20m/pss]3, [snc-g-pnipam-b-q40m/pss]3, and [snc-gpnipam-b-q100m/pss]3 films after 80 days, respectively [81] as shown in figure 9. like the previous study, the drug release was found to be faster as the temperature was decreased, and the reason behind this could be the temperature-induced hydration of pnipam moieties in lbl films, as per the researchers [81]. the transition of the delivery system in terms of its thickness was found to be reversible even after going through so many temperature-manipulating cycles, suggesting the system to be robust [81]. the overall design of this drug delivery system, where steric hindrance in the amino group of qpdmaema moieties was enhanced and the quaternization degree, the thickness of the film layer, and molecular diffusion distance were increased, allowed a reduction in the drug release from the nanoparticle system [81]. characterization and application of nanomaterials 2024, 7(1), 4959. 12 figure 9. reversible temperature-triggered swelling/deswelling of [snc-gpnipam-b-pdmaema/pss]3 (squares), [snc-g-pnipam-b-q20m/pss]3 (circles), [snc-g-pnipam-bq40m/pss]3 (triangles), and [snc-g-pnipam-bq100m/pss]3 (pentagons) films at 25 and 37 ℃, respectively. reproduced with permission from xu et al. [81]. 3.3. peg/plga-b peg moving on, the next system was developed using plga-b-peg-mal nanoparticles in which the ivermectin drug (ivm) was loaded, and this can be delivered orally [82]. the reported size of nanoparticles was 70-80 nm with a 20% feed capability of ivm [82]. the goal of the researchers was to develop a system that can decrease the expression of viral spike protein present on sars-cov-2 as well as down-regulate its receptor protein (ace2), and therefore they attached an fc immunoglobulin fragment forming t-fc-ivm-nps (igg fc antibody-treated ivmnps) [82]. the mechanism of action of this np system has been reported by the researchers in the paper, but for now, it is important to know that the results of western blotting showed a significantly lower spike protein and ace2 in the hek293t and hela cells when t-fc-ivm-nps were administered, but not by free ivm [82]. the cytotoxic results reported suggest that the free ivm decreases basal and maximum [82] respiration and severely impacts atp production inside the mitochondria of cells; however, no such side effects were observed when nt-ivm-np (not treated ivmnps) and t-fc-ivm-np were administered to the cells [82]. this result shows a great possibility of decreasing the spread of any virus from the sars family, including sars-cov-2, as the system targets the spike proteins present on the surface of each member of this family [82]. up next, we found another study that used ivermectin (ivm), which was loaded in synthetic nanoparticles: poly (l-lactide-co-glycolide)-block-poly (ethylene glycol)amide (plga-b-peg-nh2); plga-b-peg-mal.; poly (l-lactide-co-glycolide)block-poly (ethylene glycol)-hydroxide (plga-b-peg-oh), against zika virus [16,83]. the goal of this group was to develop a platform that allows the delivery of ivm at a higher concentration without affecting other cellular functions inside our body. they created a system whose size was found to be 60 nm at ivm fed of 10% characterization and application of nanomaterials 2024, 7(1), 4959. 13 and 140 nm at ivm fed of 50%; however, they also reported the np system was only stable up to 30% fed [82]. they reported that the targeted t-fc-ivm-nps were successfully able to cross the intestinal epithelial barrier model and enter the bloodstream in comparison to non-targeted nt-oh-ivm-mps. specifically, 65% of injected targeted np was distributed in the blood after 24 h, and the rest (24%) was still in different parts of the intestine [83]. a comparison study with free ivm showed that most of the drug was stuck in intestinal tissue, indicating that the nps are needed to cross that intestinal barrier [83]. the study also reported that the free ivm was easily able to cross the placental membrane in comparison to that of t-fc-ivm-nps; however, the free ivm completely disrupts the cellular respirations of the cell that forms the placental barrier, but this is not the case for t-fc-ivm-nps [83]. the overall cytotoxic study showed that the toxicity of ivm is significantly reduced when loaded with polymeric nps, as indicated in figures 10 and 11 [83]. specifically, figures 10 a,b show the western blot decreasing expression of ace2 in a549 adenocarcinoma alveolar basal epithelial cells transfected with a plasmid expressing spike protein with the treatment of ivm, nt-ivm-nps, or t-fc-ivm-, while figure 10c shows the ace2 expression in hela malignant epithelial cells. immunofluorescence staining in figure 10d confirms the same trend in a549 cells. additionally, the researchers also reported that t-fc-ivm-np can reduce ns1 protein, suggesting its usage could be beneficial against the zika virus and other viral infections [83]. taking their word as it is, one can tweak this np system to target the spike proteins present in sars-cov2. figure 10. expression of ace2 with the treatment of ivm, nt-ivm-nps, or t-fc-ivm-nps. reproduced with permission from surnar et al. [83]. characterization and application of nanomaterials 2024, 7(1), 4959. 14 figure 11. ns1 expression level in hek293t cells after treatment with nps by (a) western blotting and (b) immunofluorescence. cells were treated with ivm, nt-oh-ivm-np, or t-fc-ivm-np at a concentration of 10 μm concerning ivm for 6 h—scale bar: 10 μm. reproduced with permission from surnar et al. [83]. 3.4. pedot we found a new study that used a unique system that responds to electricity. the researchers used curcumin (cur), an antiviral and anticancer drug, and combined it with electrospun poly(ε-caprolactone) (pcl) microfibers (mfs) loaded with poly (3,4ethylene dioxythiophene) nanoparticles (pedot nps). the pedot nps, which are polymeric nanoparticles, have a diameter of 99 ± 21 nm and are located inside the pcl mfs [84]. the study reported that when external stimuli were applied after embedding pedot nps in the electro-fiber, the release of cur was promoted [84]. although the release of cur by simple diffusion was very low, a linear increase in drug release was observed with the increased number of potential pulses. notably, this increase in the release was not observed when pedot was excluded from the system, indicating that their presence is crucial for responding to electrical stimuli in the form of potential pulses in a pbs + tween 20 electrolyte medium, mimicking a physiological environment. the study found that the specific increases with the number of pulses for pcl/pedot/cur mfs were 8.1% ± 4.3%, 18.4% ± 7.2%, and 30.2% ± 10.2% after 1, 3, and 5 potential pulses, respectively [84]. the increase is based on the voltametric response of pedot nps, which results in volume variations and structural changes [84]. the drug system’s cytotoxic study revealed that cell growth decreases only when pedot is not used, indicating that the presence of pedot also reduces the toxicity of cur, as shown in figure 12 [84]. in conclusion, this study shows the potential for using pcl/pedot/cur mfs to control drug release in response to electrical stimulation within our bodies, regardless of the virus we are dealing with. characterization and application of nanomaterials 2024, 7(1), 4959. 15 figure 12. cur release from pcl/cur and pcl/pedot/cur mfs. (a,c) cur release profiles in pbs-etoh, and after electrostimulation by applying 1, 3, and 5 consecutive potential pulses, respectively; (b,d) scheme representing the diffusion mechanism for cur release in the absence/presence of electrostimulation, respectively; (e) sem micrographs of pcl/pedot/cur fibers after electrostimulation. reproduced with permission from puiggali-jou et al. [84]. 4. conclusion according to the findings, the utilization of pnps presents numerous therapeutic benefits in combating the sars-cov-2 virus. pnps provide a means of effectively delivering drugs to targeted locations for a prolonged period, thereby saving considerable costs associated with repeated drug administration due to quick elimination from the body. table 1 shows a list of selected pnps used for anti-viral drug delivery strategies. table 1. list of selected pnps used for anti-viral drug delivery strategies. polymer conjugate properties application ref plga plga-b-peg-nh2 ova-plga water-insoluble, biocompatibility, and biodegradability drug delivery of hydrophilic as well as hydrophobic actives, diabetic retinopathy, neovascular age-related macular degeneration (ocular neovascularization) [76], [85– 87] pedot pcl/pedot/cur electrical conductivity, electrochemical activity, thermoelectric behavior, and high specific capacitance. facilitating cell spreading and enhancing cell proliferation [84], [88– 90] pnipam pnipam-bpdmaema temperature-triggered hydration−dehydration transition, high surface areas, and irregular structures temperature-modulated drug delivery systems [81], [91], [92] peg t-fc-ivm biocompatibility, protein repellent ability, immunodeficiency disease, bioconjugation, and drug delivery [93], [94] characterization and application of nanomaterials 2024, 7(1), 4959. 16 table 1. (continued). polymer conjugate properties application ref remdesivir remdesivir-gs5734 the heterocyclic part analogous to adenine, allowing hydrogen bonding, contains c-nucleoside, the presence of a 1′-cn group, the ribosyl moiety ensuing inhibition of rna (instead of dna) synthesis, and the presence of a phosphoramidate group, contributing to its tissue targeting activity against ebolavirus, filo-, pneumo and paramyxoviruses [95] pcl peo-pcl excellent biocompatibility, high hydrophobicity, and neutral biodegradation end products used as emulsifying agents, solubilizing agents, surfactants, wetting agents, and treating hiv/aids [96] pva pva-tpu-ag antibacterial and antiviral properties wound dressings, medical device coatings, treatment of covid-19 [97] pla pla-ag high mechanical strength, biocompatibility and non-toxicity biomedical packaging, food packaging, and 3d printing technology. [98] pniipam pnipam high stability, biocompatibility, treat hiv-1 infection [99] additionally, various studies have shown that pnps significantly reduce the cytotoxicity of many drugs on vital cells within the body. given their biodegradability, pnps are promising contenders for replacing current drug delivery systems with polymeric nanoparticle-based systems for covid-19. some peg-based nanoparticle systems have already been applied in clinical trials for covid-related treatment [100]. additionally, peg-plga systems have been widely applied in clinical trials for anticancer treatment [101,102] and hence one can expect these platforms to be approved for coronavirus-related trials as well in the near future. the number of nanoparticles in clinical approvals has gone up each year since 1992 and saw a total of 32 approvals in 2020, a part of which were for covid-19 vaccines [103]. further, the number of human clinical trials peaked in 2021 for various nanoparticle systems, which only provides a bright prospect for the upcoming future. acknowledgments: we thank the university of scranton for generously supporting this research. conflict of interest: the authors declare no conflict of interest. abbreviations afm atomic force microscopy cur curcumin cy-a cyclosporin dna deoxyribonucleic acid esd emulsification/solvent diffusion ftir fourier transformed infrared spectroscopy fpv favipiravir fpv-sln favipiravir solid lipid nanoparticles fty720 fingolimod h1n1 spanish flu, lower respiratory tract infections characterization and application of nanomaterials 2024, 7(1), 4959. 17 ivm ivermectin drug mal maleimide mfs microfibers mthpp meso-tetra (3-hydroxyphenyl) porphine nh2 amide op oseltamivir phosphate ova ovalbumin pbd polybutadiene pcl poly-caprolactone pbs polybutylene succinate pedot poly (3,4-ethylene dioxythiophene) pla polylactic acid plga poly (lactic-co-glycolic acid) pm polymeric micelles pmma poly (methyl methacrylate) pnipam-b-pdmaema poly (n-isopropyl acrylamide)-block-poly (n, n-dimethylamino ethyl methacrylate) pnipam poly (n-isopropyl acrylamide) peg poly (ethylene glycol) pnp polymeric nanoparticle ps polystyrene ps polymersomes pss polystyrene sulfonate sars‑cov‑2 covid 19 severe acute respiratory syndrome coronavirus 2 sbp1 spike binding peptide sem scanning electron microscopy sd standard deviation slns solid lipid nanoparticles sncs silica nanocapsules tem transmission electron microscope who world health organization references 1. bohrey s, chourasiya v, pandey a. polymeric nanoparticles containing diazepam: preparation, optimization, characterization, in-vitro drug release and release kinetic study. nano convergence. 2016; 3(1). doi: 10.1186/s40580-0160061-2 2. ftouh m, kalboussi n, abid n, et al. contribution of nanotechnologies to vaccine development and drug delivery against respiratory viruses. ppar research. 2021; 2021: 1-28. doi: 10.1155/2021/6741290 3. liu s, hu m, liu x, et al. nanoparticles and antiviral vaccines. 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tehran 14515/775, iran. abstract according to the world health organization (who), breast cancer is among the most common cancers worldwide. most of the anticancer agents have been showing a variety of side effects. recently, bacterial proteins have been investigated as promising anticancer agents. azurin is a bacterial cupredoxin protein secreted from pseudomonas aeruginosa and has been reported as a potent multi-targeting anticancer agent, which makes it an appropriate candidate for drug delivery. azurin may be delivered to cancer cells using different carriers like polymeric micro and nanoparticles. in the present study, azurin was extracted from the bacterial host and loaded into chitosan particles. then its effect on mcf-7 cell line was investigated. chitosan-azurin particles were made using the ion gelation method. results showed that chitosan-azurin particles are about 200 nm, and the loading of the protein in particles did not affect its integrity. the mtt assay showed a significant reduction in cell viability in azurin and chitosan-azurin-treated cells. the toxicity level after 5 days was 63.78% and 82.53% for free azurin and chitosan-azurin-treated cells, respectively. it seems using an appropriate carrier system for anticancer proteins like azurin is a promising tool for developing low side effect anticancer agents. keywords: chitosan nanoparticles; azurin; anticancer activity; breast cancer; bacterial protein 1. introduction cancer is the overproduction and malfunction of the body’s cells that could invade different tissues. cells become cancerous because of the buildup of defects or mutations of their dna. inherited genetic defects, infections, environmental elements like air pollutants, and unhealthy lifestyle alternatives, along with smoking and heavy alcohol use, also can harm dna and result in cancer. according to the world health organization (who), cancer is a leading cause of death worldwide, accounting for an estimated 9.6 million deaths in 2018. the most common cancers are lung (2.09 million cases), breast (2.09 million cases), colorectal (1.80 million cases), prostate (1.28 million cases), skin cancer (1.04 million cases), and stomach (1.03 million cases). today, the main challenge in cancer therapy is the secondary effects caused by standard treatments like ionizing radiation, chemotherapy, immunotherapy, and tumor cell resistance. therefore, new therapeutics and novel strategies for drug delivery with fewer side effects are essential. it has been proved that some bacterial-purified products, especially those that target and article info received: 28 april 2023 accepted: 24 may 2023 available online: 27 june 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4. 0/ 2 specifically kill cancerous cells, can be used as anticancer agents[1]. pseudomonas aeruginosa is a gram-negative opportunistic pathogenic bacterium. depending on its culture medium, it secrets different pigments, such as pyocyanin, pyoverdine, and pyorubin[2]. azurin (az) is a member of the cupredoxin protein family, secreted by several bacteria, especially p. aeruginosa. az is a small blue-colored protein that consists of 128 amino acids with a molecular weight of about 14 kda. it comprises one α-helix and two β-sheets, creating a β-barrel motif[3]. az is effective in the electron transfer cycle of the bacterial respiration system. this small protein is one of the bacterial derivatives efficient as an anticancer factor against different cancerous cell lines like breast cancer cell line mcf-7; also, its antiparasitic and anti-hiv properties have been proven[4]. az has been used in various kinds of research because of its anticancer abilities. the first intention for investigating az anticancer properties on mcf-7 cell line showed it can block proliferation and induce apoptosis significantly in vitro and in vivo[5]. az can enter human melanoma (uiso-mei-2) in nude mice and make significant regression in this cancerous cell line[6]. the record has shown it also induces apoptosis in human osteosarcoma u2os[7]. az and its peptide, laz, effectively treat leukemia k562 and hl60 cells[8]. also, laz was useful in attacking brain tumors and disrupting the entry barrier of this highly protected organ[9]. azurin’s strong anticancer effect was exhibited in the human colon carcinoma cell line (hct116)[10] and simultaneously with anticancer drugs in oral squamous carcinoma cells (yd-9)[11]. lastly, the p28 amino acid of az was quite effective in treating advanced solid tumors at a clinical trial level[12]. it seems that az forms a compound with p53 and raises its intracellular level, leading the increased p53 to provoke apoptosis in cells through amplifying bax formation and releasing mitochondrial cytochrome c in the cytosol[13]. az is reportedly the first bacterial protein to make a compound with the protein p53. az easily enters human cancerous cells, whereas it is insufficient in entering normal cells. the p28 amino acid of this protein is the main factor for preferential entry to cancerous cells[14]. chitosan (cs) is a polymer obtained from the deacetylation of chitin. it is one of the popular drug carriers because of its unique characteristics, such as biocompatibility, biodegradability and antibacterial properties. this polymer also has a stunning affinity to some proteins[15]. based on previous studies on azurin’s anticancer and apoptosis induction proficiency, it is predictable to use nanotechnology targeting and delivery systems to eliminate cancerous cells using az. by using convenient nanoparticles (nps) for carrying az, we might be able to terminate cancer cells effectively. amongst different nanocarriers for drug delivery, polymeric nps are the most efficient[16]. nano drug delivery system offers many advantages like increasing absorption, reducing the dose and side effects. it also increases the drug concentration at the treatment site[17,18]. cs was the subject of many studies, used to deliver gene, protein and anticancer chemical drugs. in 1994 cs nps were used for delivering 5-fluorouracil (an anticancer drug) for the first time[19], later it was used for delivering other anticancer agents such as doxorubicin[20] and paclitaxel[21]. this polymer was efficient in delivering a variety of proteins in treating cancers. it was used to encapsulate anti-β-catenin sirna against colon cancer cells to reduce β-catenin and thereby minimize tumor progression[22]. furthermore, recombinant neutrophil-activating protein derived from helicobacter pylori, encapsulated with cs, effectively treated breast cancer[23]. moreover, in a study, curcumin was encapsulated in alginate-cs-pluronic composite nps against hela cells, where inhibition was more efficient in encapsulated curcumin than the free curcumin[24]. cs nps can be prepared in different ways, such as emulsion cross-linking, reverse micellar method, ionic gelation[25], precipitation[26], microfluidics[27] and spray drying[28]. in the present work, cs-az nps were prepared and characterized. then particles’ toxic effect on the breast cancer cell line was investigated. 3 2. material and methods 2.1 materials p. aeruginosa atcc 27853 was prepared by the microorganism’s bank of i.a.u science and research branch university, iran. cs was purchased from sigma aldrich, lysogenia broth (lb) medium, ammonium sulfate, coomassie brilliant blue, penta-sodium triphosphate, phosphoric acid, sodium dodecyl sulfate (sds), mtt, trypan blue, and 2-mercaptoethanol were all ordered from merck. mcf-7 cell line, dmem, fbs, and phosphate buffered saline (pbs) were purchased from gibco. 2.2 azrin extraction and characterization p. aeruginosa was cultured in lb medium at 37 ℃ for 21 h[29]. copper sulfate (1 μg/ml–5 μg/ml) and potassium nitrate (5 μg/l–20 μg/l) were introduced both together and separately to the medium. after centrifugation at 13,200 g for 15–20 min, the bacterial suspension’s pellet was suspended in 0.02 m, ph 7.0 potassium phosphate buffer, sonicated, and then centrifuged at 10,000 g for 20 min. the resulting supernatant was collected, treated with 45% ammonium sulfate, and left overnight at 4 ℃. subsequent centrifugation at 20,000 g and 23,000 g concentrated the supernatant containing az, dissolved in 0.02 m, ph 7.0 potassium phosphate buffer[2,30]. the molecular weight of the extracted az was determined using sds-page following established procedures[2]. gel preparation used deionized water, tris, ammonium persulfate, sds, acrylamide, and temed. extracted az and bromophenol blue were applied to the gel and subjected to electrophoresis at 100 v for 100 min. coomassie brilliant blue staining, destaining, and lamp-based examination followed[2,31,32]. protein concentration was evaluated using the bradford assay. the bradford reagent was formulated by mixing 100% ethanol with coomassie brilliant blue g-250, adding 85% phosphoric acid, and adjusting the volume with di water. this mixture was filtered, and a standard curve was created using serial dilutions of 1 mg/ml bsa in pbs buffer. various amounts of extracted az were mixed with the bradford reagent incubated in darkness for 5 min, and their absorbance was measured at 595 nm using a spectrophotometer. 2.3 cs-az nanoparticle synthesis the ion gelation technique was used for the preparation of cs-az nps. cs solution (solution 1) was prepared by adding 3% w/v of medium molecular weight cs to di containing 1% w/v acetic acid under stir mood. the ph of solution 1 was adjusted to 5.5, and a 0.45 µm filter filtered the solution to discard unsolved components. another solution (solution 2) that contains 3% w/v of penta-sodium triphosphate was prepared, and its ph was adjusted to 9.5[33,34]. az was added to solution 2 in the desired concentration. 1 ml of solution 2 was added dropwise to 3 ml of solution 1 under stirring in an ice bucket at 1,000 rpm for 30 min. the slight turbidity of the final solution was considered as particle formation. 2.4 cs-az particles characterization 2.4.1 sem and sds-page cs-az particles morphology, size and dispersity were investigated by particle size analyzer (malvern, u.k.) and scanning electron microscopy (leo 440i, u.k.)[35]. the particles were used without any filtration and dilution for size analysis. 2.4.2 encapsulation efficiency the amount of encapsulated az in cs nps was measured by spectrophotometry (pg instruments). prepared nps were centrifuged at 10,000 g for 20 min. after mixing crude with coomassie brilliant blue reagent, it was left for 5 min and measured at 595 nm wavelength, and efficiency was calculated due to the standard curve. 2.4.3 protein integrity sds-pag assay (bio-rad) was used to ensure the encapsulation of az protein. prepared cs-az nps was centrifuged at 10,000 g for 20 min, and the crude mixed with bromophenol was loaded in lanes with 100 w for 100 min for profiling integrity. 2.5 cs-az particles anticancer effect assay 2.5.1 mcf-7 cell culturing mcf-7 cell line was cultured in the medium 4 which contains commercial dmem with 10% fbs and 1% penicillin/streptomycin and incubated at 37 ℃ under 5% co2 [13,36,37]. after 24 h, cells were counted using a hemocytometer and trypan blue and cell numbers were calculated by equation (1). here df is the dilution factor. cell number = number of cell in 1 mm2 × 10,000 × df (1) 2.5.2 mtt assay mcf-7 cells were seeded in 96-well microplates at a density of 104 cells and incubated overnight at 37 ℃ in 5% co2 [38]. then the supernatant was discarded, and 100 µl of samples, i.e., extracted az and cs-az nps, were added to each well. after 24 h and 72 h, the solution was replaced with 100 µl of mtt reagent and incubated for 3 h at 37 ℃. finally, 100 µl of dmso was added to each well for dissolving formazan crystals, and samples od were measured at 570 nm by a microplate reader (elx808, bio tek, u.s.). untreated cells were considered as control during the mtt assay[14,39]. 3. results 3.1 extracted protein analysis for az extraction, the optical density of grown bacteria (figure 1) was measured at 265 nm and adjusted according to clinical and laboratory standards 2018 (1.5 × 108 cfu/ml). figure 1. gram staining assay, the red color of bacteria and rod shape morphology unique gram-negative p. aeruginosa. all samples, i.e., the az extracted with sonication with different doses of cuso4 and kno3 in their culture, were all characterized using sds-page where results showed extracted substances contain 14 kd az protein (figure 2). the az was further purified with dialysis in its buffer to discard extra salt and smaller proteins. extracted protein concentrations were assayed using bradford assay (table 1). as shown in the table concentration of extracted az by sonication in the absence of cuso4, and kno3 was about 10.73 µg/ml. az concentration in the simultaneous addition of cuso4 and kno3 in the culture medium was 2.35 µg/ml. besides, in addition to kno3 and cuso4 separately, the concentration was about 6.97 and 5.24 µg/ml, respectively. figure 2. molecular weight determination of extracted protein. the protein that extracted by sonication, showing 14 kda bond of az. (a) protein ladder.; (b) and (c1) az in absence of cuso4 and kno3 in the culture medium; (d1) az in presence of cuso4 and kno3 in the culture medium; (e1) az in presence of kno3 in the culture medium; (f1) az in presence of cuso4 in the culture medium. table 1. concentration and optical density of extracted proteins at 595 nm. samples b c1 d1 e1 f1 od 0.17 0.18 0.03 0.11 0.08 concentration (µg/ml) 10.44 11.02 2.35 6.97 5.24 3.2 cs-az nps characterization as mentioned, az was encapsulated in cs using the ionic gelation method. the particle size and zeta potential were assayed using sem and dls (figure 3). sem result (figure 3a) showed that the particles have a spherical shape and their size is about 200 nm. cs-az particles’ hydrodynamic size, pdi, and zeta potential were about 265 nm, 0.26 and +27 mv, respectively (figure 3b,c). 5 figure 3. (a) sem of cs-az nps in two different scales; (b) nps hydrodynamic size, pdi; and (c) zeta potential. 3.3 encapsulated protein analysis 3.3.1 concentration and integrity protein concentration was calculated by its absorbance at 595 nm using the standard curve. the results showed 1.48 µg az was loaded in each ml of nps. the integrity of the protein that led in nps was assayed by sds-page. as detailed in figure 4, the free and encapsulated az band was seen in an acrylamide gel. figure 4. analysis of integrity and presence of az in nps profiled by sds-page. (a) protein ladder; (b) cs-az nps; (c) free az; (b1) and (c1) are repeat of previous specimens respectively. 3.3.2 anticancer efficiency mtt assay was used to monitor the anticancer effect of cs-az nps on the mcf-7 cell line. mcf-7 cells were treated with free az and cs-az nps in 1, 3 and 5 days, considering untreated cells as control. in comparison, after 24 h, free az had more inhibition effect than nps. further outcomes from mtt assay after 72 h define cs-az nps had better toxic efficiency than free az. obtained information from the free protein treatment clarifies 74% toxicity in one day and 67% after 5 days. for cs-az nps, it was 63% and 82% after one day and five days, respectively. mann-whitney u test showed during 5 days, the efficiency of cs-az nps was increased significantly (p value < 0.05) while the free az partially lost its efficiency (figure 5). figure 5. toxicity (%) of free az, and cs-az nps on mcf-7 cells. * p ˂ 0.05 using mann-whitney u test. 6 4. discussion the present study evaluated the anticancer effect of az combined with cs nanocarriers on the mcf-7 cell line. cupredoxin protein az was extracted from p. aeruginosa (atcc 27853), while the production of this protein by this microorganism was promised[2,29]. az was extracted using sonication. visualized bonds confirmed the presence of 14 kd az[2,30,31] in sds-page and the concentration was calculated using a spectrophotometer. ramachandran reported that cuso4 and kno3 in a culture medium can increase the amount of az[2,30]. at the same time, this wasn’t clarified in this intention, and another research by sutherland declared the amount of az increased in a small range by adding cuso4 to the medium yet failed to rise more by adding more copper (up to 10–17 µg/ml)[40]. still, the comparison between sds-page bonds shows that they might be effective in the purity of producing az and reducing the unnecessary secreted proteins. amongst different bacterial derivatives, there was much attention on az derived from p. aeruginosa because of its anticancer details and multi-targeting ability. it can enter cancerous cells without any toxic effect on normal cells. its anticancer effect and the inhibitory property have been proved on various cancerous cell lines such as melanoma[6], bone[7], leukemia[8], malignant brain tumor[9], and in vivo apoptosis properties of az on mcf-7 cell line were reported by punj et al.[5]. in this study, cs-az nanoparticle was produced using the ion gelation method. cs polymer was used considering its remarkable characteristics and beneficial advantages in drug delivery, like reducing the possibility of embolism and easy injection properties[41]. this polymer has good stability and less toxicity, making it a good choice for making nps[42]. cs can improve the stability of nps in biological solutions, blood circulation, and while entering tissues and cells[43,44]. various reagents and conditions, such as heat, organic compounds and ph changes, can cause protein denaturation. the ion gelation method is one of the easiest and most common ways of drug delivery; it does not require heat and organic solvent, which makes it a suitable technique for encapsulating proteins[26]. the process accomplishes through inter and intramolecular cross-linkage, cooperating with anionic molecules. the size characterization and zeta potential of cs-az nps were measured by dynamic light scattering. the assessment showed hydrodynamic size, pdi and zeta potential were about 265 nm, 0.26 mv and 27 mv, respectively, and nps were stable[25]. cs nps were used in combination with the az gene and mammaglobin agencies. 98.8% of these nps had a size of 111.7 nm. the size difference of nps can be related to production procedures or differences in encapsulated drugs[26]. based on results from the mtt assay, free az and cs-az nps were both functional and showed extraordinary anticancer effects. cs-az nps showed decisive inhibitory action over time in comparison to free protein. this change demonstrates that encapsulation of az with cs has made it more stable, so protein structure remains sustained during the time and as exposed to the environment. based on the results of punj et al.[5], after 72 h of treating mcf-7 cells with 53 µm pure az, cell viability was 29%. in another study, osman et al.[31] reported near 34% cell viability for mcf-7 cells treated with az 5 µg/ml. comparing these results, cs-az nps showed better inhibition results. toxicity results also define 74%, and 66% toxicity after treatment on the first day with free and nps loaded az, respectively. still, after five days, the toxicity of cs-az nps increased to 82%, whereas for free az, it decreased to 63%. high toxicity is critical in producing anticancer drugs; although toxicity results in this research were satisfying, it takes much effort to put these valuable results into use at clinical levels. encapsulating az with cs can protect it from the attack of the immune system and can help to pass through main drug-resistant mechanisms[1,45,46]; in addition, it helps az to remain in the targeted areas longer than free protein and extends drug releasing time. one of the problems we face in common cancer treatments is that in treatments like chemotherapy, there is no border in attacking healthy and cancerous cells, but by using nanocarriers, we can reduce the harmful attacks on healthy cells. also, the need for more injections makes financial difficulties for patients while slow drug re7 lease of cs-az nps can decrease numerous injections, so considering the ability of cs-az nps, this can be an inflection point in breast cancer treatment with fewer side effects and lower price. 5. conclusion overall properties of az in former studies prove its apoptotic qualification on mcf-7 human breast adenocarcinoma cell line. based on this and cs characteristics in drug delivery, we analyzed the anticancer efficiency of cs-az nps, successfully synthesized by ionic gelation method on the mcf-7 cell line. results from the mtt assay imply significant inhibition of cells treated with our nps compared with ones treated with free az. as the size of nps can be effective in their capability to enter cells, different studies can focus on cs-az nps with different sizes and dosages. lastly, regarding azurin’s potential to inhibit diverse cancers, cs-az nps can be tested on other cell lines. also, further investigations can be done on cs-az nps in vivo levels. author contributions conceptualization, hb and pm; methodology, sb; software, hb; validation, sb, hb and pm; formal analysis, sb; investigation, sb; resources, sb; data curation, hb; writing—original draft preparation, sb; writing—review and editing, hb; visualization, pm; supervision, hb; project administration, pm; funding acquisition, sb. all authors have read and agreed to the published version of the manuscript. acknowledgments the authors wish to acknowledge islamic azad university, science and research branch 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nanotube macroscopic materials, carbon nanotube film not only retains the microscopic properties of carbon nanotube, but also has good mechanical properties and stable chemical properties. the preparation and application of carbon nanotubes (cnts) have attracted extensive attention from scholars at home and abroad. in this paper, the research on carbon nanotube films in recent years is reviewed. based on the preparation of carbon nanotube films, chemical vapor deposition, lb (langmuir-blodgett) film and electrostatic layer-by-layer self-assembly techniques are briefly described. in addition, the applications of carbon nanotubes in biological field, photoelectric nano devices, water treatment, seawater desalination and other fields are also described. keywords: carbon nanotubes; carbon nanotube film; preparation method; application progress article info received: 1 august 2022 accepted: 19 october 2022 available online: 27 october 2022 copyright copyright © 2022 yaxian wu, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. research background since carbon nanotubes were discovered by iijima[1] in 1991, a research upsurge has been set off worldwide. carbon nanotubes have been widely used in molecular sieve, drug transport, particle exchange, seawater desalination and other aspects due to their unique mechanical, electrical and optical properties, as well as their good performance at the nanoscale[2–5]. in 2001, hummer[6] studied the transportation behavior of water molecules in carbon nanotubes by means of computer simulation, and selected the radius of carbon nanotubes at 0.8 nm, the one-dimensional distribution of water molecules in the carbon nanotubes was observed. it was also found that when the molecular interaction potential between water molecules and the pipe changed to a small degree, the pipe would change from empty state to filled state. holt[7] found through experiments that the inner surface of carbon nanotubes with a diameter of 1 to 2 nm has a long slip length. under the same external pressure, water flow can reach about one thousand times that predicted by macroscopic (no slip) theory. carbon nanotube thin film is a two-dimensional carbon nanotube network structure formed by filling freely arranged carbon nanotube arrays through physical or chemical methods[8]. since the carbon nanotube arrays suitable for filling are perpendicular to and parallel to the substrate orientation respectively[9,10], the carbon nanotube films can be divided into horizontally aligned carbon nanotube films, vertically 129 aligned carbon nanotube films and hybrid aligned carbon nanotube films. carbon nanotube films retain the original microscopic properties of carbon nanotubes, and have the advantages of low operating pressure, large flux, high retention rate and low cost, so they are widely used in many fields. in this paper, the preparation methods of carbon nanotubes are reviewed, and their applications in biology, nano devices, water treatment and other fields are reviewed. 2. preparation of carbon nanotube films at present, there are many preparation methods for carbon nanotube films, such as spin coating[11], electrophoresis[12], vacuum filtration[13–16], spraying[17–20] and chemical vapor deposition method, lb (langmuir-blodgett) membrane method, electrostatic layer-by-layer self-assembly technology, etc. the last three methods of preparing carbon nanotube films are briefly described below. 2.1 chemical vapor deposition chemical vapor deposition (cvd) is a method for preparing carbon nanotube films. this method is characterized by convenient operation, low cost and high productivity. the pore size of carbon nanotube films can be controlled by separating fluid or gas[21], which is suitable for large-scale production and widely used by researchers. holt[22] used chemical vapor deposition method to fill gaps in multi-walled carbon nanotube arrays with si3n4 to synthesize carbon nanotube films, which have high water flux. yu[23] prepared high-density vertical array carbon nanotube films by chemical vapor deposition in order to solve the problems of low porosity and low permeability efficiency. in order to significantly improve the growth efficiency of single-walled carbon nanotubes, hata [24] add appropriate oxidants in the preparation process by chemical vapor deposition, and it was found in the experiment that single-walled carbon nanotubes arrays with consistent aperture, high density and high purity could be grown in 10 min. haque[25], through chemical vapor deposition, uses pulse laser to melt diamond and form composite carbon nanotube film, which is applied in such aspects as wear-resistant coating, thermal management of integrated circuits, electrochemistry, field emission equipment and electric field shielding in mems. 2.2 langmuir-blodgett (lb) membrane method lb film technology is one of the traditional film making technologies. the method is to transfer monolayer molecules to the surface of solid matrix to form a film. if multilayer films preparations are wanted, layer by layer transfer is required[26,27]. at present, lb film technology has been widely used, but its mechanical stability and thermal stability are problematic. therefore, researchers have adopted various physical or chemical methods to improve the mechanical carrying capacity of lb film and improve its stability. lb film technology requires specific film forming equipment and strict operation, which makes it difficult to produce large area films. the stability of lb films depends on the film van der waals forces and hydrogen bond energies on the surface of medium and substrate, molecules within and between layers. venet[28] used lb film method to prepare films containing single-walled carbon nanotubes (swcnts), and studied the morphology of the films by atomic force microscopy. under low applied voltage, pure swcnts layers showed relatively high ohmic conductivity, while mixed lb films showed nonlinear current-voltage behavior. song[29] prepared orderly and organized carbon nanotube composite films by lb film method at room temperature, which has potential application prospect in many fields. figure 1 is the process of preparing carbon nanotube film by kim et al.[30] using lb film method. figure 1(a) is the induced orientation obtained by barrier compression, figure 1(b) is the horizontally deposited film, and figure 1(c) is the vertically deposited film. by using this method, kim et al. prepared carbon nanotube films with good spreading performance, and the latter had a higher degree of tube orientation than the former[30]. 130 figure 1. preparation of carbon nanotubes by lb film method. 2.3 electrostatic layer-by-layer self-assembly technology electrostatic layer-by-layer self-assembly is a polyelectrolyte with an opposite charge that can be used in an aqueous solution to prepare multiple layers on a deposited substrate thin film technology. compared with lb technology, this method has the advantages of simple operation, fast film forming speed, no special equipment is required, and the film made is stable. at present, the driving force of self-assembly has changed greatly from electrostatic force diffusion to hydrogen bond and charge interaction, which provides experimental conditions for the preparation of composite carbon nanotube films such as nanoparticles and carbon nanotubes. figure 2. preparation of carbon nanotube films by electrostatic layer-by-layer self-assembly method. the method of preparing carbon nanotube film by electrostatic self-assembly technology[31] is shown in figure 2. it is continuously adsorbed alternately on the substrate surface with positive and negative charges, so as to obtain carbon nanotube film of appropriate thickness. lee[32] used the layer-by-layer self-assembly technology to prepare the surface functionalized multi-walled carbon nanotube films with positive and negative charges. the thickness and morphology were controlled by ph value, which showed higher conductivity compared with single-walled carbon nanotube composites. rivadulla[33] first used the coating technology to wrap the carbon nanotubes dispersed in water before film formation, which was convenient to control the transmission characteristics independent of the substrate. then, the electrostatic layer-by-layer self-assembly technology was used to prepare the carbon nanotubes film, which could improve the conductivity and thermoelectric power. the above three methods of preparing carbon nanotube films are commonly used by researchers in the experimental process, which can prepare carbon nanotube films with stable performance. 3. application of carbon nanotube films the carbon nanotube membrane retains the original excellent properties, while obtaining many outstanding properties, which can potentially improve the fouling resistance, hydrophilicity and permeability of the membrane. membrane separation technology can have important applications in such situations as harmful diffusion of methanol in fuel cells, retention of valuable proteins in biopharmaceutical processing, rejection of organics and microorganisms in water treatment, and salt penetration in desalination processes. therefore, carbon nanotube membrane has become a research hotspot at home and abroad, and is widely used in biology, medicine, water treatment and other fields. 3.1 biological field in 2001, de groot[34] found that the flow of water molecules in biological systems is one-dimensional, similar to the flow of water mol 131 ecules in carbon nanotubes discovered by hummer[6] (figure 3). since then, researchers have inclined to use carbon nanotubes to mimic alternative biological channel proteins, which are simpler and easier to study. in nature, most biological macromolecules are electrically charged, so carbon nanotube membranes with better biological activity, conductivity and catalytic properties can be prepared with carbon nanotube membranes or nanoparticles modified by biological macromolecules. figure 3. flow of water molecules in carbon nanotubes. yang[35] used the layer-by-layer self-assembly method to prepare ultra-thin carbon nanotube films with positive and negative charges, which can detect hydrogen peroxide h2o2 at low potential. moreover, such nanotube films have high sensitivity. cholesterol enzyme is added on the surface of the film, and the original biological activity can be maintained on the surface of the film, which can be used for cholesterol detection. du[36] uses electrostatic self-assembly technology to assemble carbon nanotubes and dna aptamers into a film (figure 3), which is characterized by high sensitivity, good stability and high molecular selective permeability, and can be used to detect targeted substances thrombin and dissolved alcohol. the application of carbon nanotube film as a biosensor is also a mainstream direction at present. biosensors use enzymes, antibodies, receptors or catalysis as biosensitive materials as recognition elements, convert their concentration into electrical signals, and use carbon nanotubes as modified materials for detection instruments[37]. the carbon nanotube-polymer composite prepared by adding cyclodextrin is insoluble in water, and the stability and electrical conductivity of carbon nanotubes are greatly improved due to the presence of cyclodextrin, and it has catalytic activity; and the addition of ethyl phthalate cholinesterase can obtain carbon nanotube composite films with high sensitivity for biosensors[38]. wee[39] added dispersed carbon nanotubes into enzyme solution to prepare phenol biosensor, which greatly improved its analysis and detection ability and sensitivity in water environment. 3.2 field of optoelectronic nano devices carbon nanotubes have been widely welcomed in the field of optoelectronic nanodevices due to their low preparation cost, good electrical conductivity, good chemical stability and large specific surface area. as a new type of energy storage device, supercapacitors (or electrochemical capacitors) have long cycle life, high power density and high energy density. it fills the gap in energy and power of traditional capacitors and batteries. wu[40] made use of the excellent performance of carbon nanotube array and put carbon nanotube array with weak mechanical strength into neutral gel electrolyte to prepare flexible composite carbon nanotube film and obtain flexible solid supercapacitor. kaempgen[41] used single-wall carbon nanotube films to prepare high-performance supercapacitors, as shown in figure 4(a), which can be used as electrodes and charge collection devices, greatly improving the performance of printed electronic devices. carbon nanotube films can be used as electrodes in transparent scalable capacitor arrays and as pressure and strain sensors[42]. as shown in figure 4(b), dharap[43] developed a carbon nanotube 132 film for strain sensor by using the characteristic that carbon nanotubes change their electrical properties when subjected to strain, and attached the insulated carbon nanotube film to brass to measure its strain. wan[44] made a flexible nanogenerator with p (vdf trfe) nanofiber and pdms /mwcnt composite film. as shown in figure 4(c), the film can work under the hybrid mechanism of triboelectric and piezoelectric. when the pressure is 5 n, the output peak voltage can reach 25 v, the power is 98.56 μ w and the power density is 1.98 mw·cm−3. the films prepared by chen[45] with superaligned carbon nanotube arrays can be used to prepare transparent conductive films, as shown in figure 4(d), which are comparable to the sheet resistance and conductivity values of indium tin oxide (ito) films. the carbon nanotube film prepared by liu[46] is applied to the infrared sensor. as shown in figure 4(e), working in voltage mode can not only reduce the low-frequency noise, but also improve the signal-to-noise ratio of the detector. figure 4. practical application in the field of optoelectronic nano devices. 3.3 water treatment field 3.3.1 drinking water treatment due to the rapid increase of population, environmental pollution is becoming more and more serious, leading to a series of natural disasters such as greenhouse effect and sea level rise. it is a difficult problem for people in many areas to drink safe and healthy drinking water. unhealthy drinking water can cause physical diseases, and even people may lose their lives. therefore, researchers are committed to studying how to effectively remove pollutants in water and ensure the health of drinking water. membrane water treatment is expected to play an increasingly important role in drinking water treatment, brackish water and seawater desalination, wastewater treatment and reuse, etc. water softening[47], desalination[48], removal of organic matter in water and so on are common drinking water treatment methods, all of which need the help of carbon nanotube film. ion exchange is often used in water softening treatment to reduce the hardness of water. in order to achieve water softening, other polyvalent ions in water need to be replaced by na+. however, this method has the disadvantage that ion exchange has no effect on na+. chemical method is often used for desalting treatment. in this process, new reaction substances need to be added, but products harmful to human body will be produced in the reaction process. biodegradation is a method to remove organic matter from water, but this method not only has no obvious removal effect, but also has high requirements on the type and tolerance of microorganisms. for the removal of metal ions in drinking water, dipankar[49] reported that water rich in sodium ions can be separated with charged polyamide 133 membrane. the results show that when the ph of the solution is reasonably acidic or alkaline, the flux decreases and the rejection rate increases. when the ionic strength remains constant, the flux and rejection rate decrease with the increase of ph, which is suitable for tap water treatment. ahmad[50] prepared two types of carbon nanotube membranes, and analyzed and compared the performance of nanofiltration membranes in nacl and mgso4 aqueous solution under the operating pressure of 500 kpa and 1,000 kpa and the temperature of 25 ℃, and drew the following conclusions. (1) asymmetric polyethersulfone (pes) carbon nanotube membranes were prepared by the method of phase inversion induced by immersion deposition technology, and two different non-solvents were selected, and it was found that the performance of the membrane containing water mixture as the non-solvent was better than that of pure water as the non-solvent. (2) the composite polyamide carbon nanotube film was prepared by interfacial polymerization of 1,3-phe nylenediamine (pda) and tmc, and it was found that the film had high water softening ability. carbon nanotube film removes metal ions from water by adsorption. the carbon nanotube film prepared by liu[51] has a strong adsorption capacity for cu2+, and the maximum adsorption capacity is 4.14 mg·g−1. figure 5(a) shows the process of electro-adsorption and electro-desorption of carbon nanotube film. wang[52] studied the adsorption capacity of carbon nanotube film for pb2+. the concentration of pb2+ in the original solution was 3 μg·ml-1, and the concentration after adsorption was 0.31 μg·ml-1, the removal rate could reach 89%. the mno2/cnt composite membrane prepared by zeng[53] can remove 97.73% of antimony when the ph value of the solution is 2.00 and the temperature is 298 k. yu[54] also prepared fe2o3/cnt composite membrane. when the ph value is 7.00 and the temperature is 298 k, the antimony removal rate can reach 99.97%. the comparison shows that fe2o3/cnt membrane is superior to mno2/cnt membrane in antimony removal performance. drinking water is polluted not only by metal ions, but also by endocrine disrupting chemicals (edcs), pesticide residues and chemical residues. the increase of pollutants will increase the risk of cancer, and the quality of drinking water is very important to human health. therefore, it is urgent to remove pollutants from drinking water. gu[55] prepared superhydrophobic polymer/carbon nanotube hybrid membrane with polystyrene hydrophobic polymer and carbon nanotubes, which can remove organic solvents in water, and the separation efficiency of water-in-oil emulsion is 99.94%, and the flux is high, which can reach 0.05 l·m−2·h−1·pa−1. figure 5(b) is a photo of the separation of water and toluene emulsion by carbon nanotube hybrid membrane. majewska[56] studied the transport and separation performance of ds-ge composite polysulfone/polyamide membrane for atrazine. when the concentration was 20 g·m −3, the highest rejection rate could reach 80%. rgo-cnt hybrid membrane prepared by vacuum filtration method is used to purify drinking water, which has good interception, contamination resistance and permeability[57]. perfluorooctane sulfonate (pfos) is a persistent pollutant in water environment, and pfos in drinking water can be removed by using hybrid carbon nanotube membrane[58]. similarly, there are some hormone pollutants in the water source. carbon nanotube membrane was used to separate several hormones and antibiotics in the solution, and its adsorption rate for hormones and antibiotics was studied. it was found that the membrane had a good adsorption capacity for tetracycline, and its adsorption rate could reach 80%[59]. 3.3.2 wastewater treatment in order to save costs and reduce the links of wastewater treatment, many factories directly discharge sewage containing pollutants into clean rivers, resulting in serious river water pollution treatment and bad environment, thus threatening human health. traditional wastewater treatment methods may not meet the standard of clean water quality, and membrane water separation technology can easily solve this problem. water separation technology can effectively treat industrial wastewater, which can replace traditional wastewater treatment methods. carbon nanotube membrane is considered as one of the best choices to remove polluted wastewater[60]. akban[61] used carbon nanotube membrane to treat dye 134 figure 5. removing impurities in drinking water. figure 6. separation of dye wastewater by carbon nanotube membrane. wastewater, and studied the effects of concentration, ph value and salt on the flux and rejection rate. it was found that the rejection rate of cationic dyes by concentration and ph value exceeded 95%, but the flux would be reduced with the increase of salt concentration. rahdi[62] used carbon nanotube membrane to filter refractory dye wastewater in textile industry. under the working condition of 500 kpa, the rejection rates of green and blue dyes were 95.2% and 93.8%, respectively. han[63] prepared high-flux carbon nanotube films from graphene and multi-walled carbon nanotubes, with water flux of 1.13 × 10−4 l·m−2·h−1·pa−1, high dye rejection rate (direct yellow is greater than 99%, methyl orange is greater than 96%), and salt ion rejection rate in na2so4 solution is 83.5% and in nacl is 51.4%. the antifouling performance of sodium alginate (sa) and humic acid (ha) is strong. figure 6(a) is a digital photo of g-cntm film, and figure 6(b) is a comparison before and after removal of dye by methyl orange solution. oil industry will inevitably produce oily wastewater, which is discharged into nature, causing a series of ecological problems. oil-water separation is to separate the oil phase from the water figure 7. separation of water-in-oil emulsion by independent ultra-thin swcnt membrane. phase by using the hydrophobic, oleophobic and hydrophilic properties of carbon nanotubes. ahmad[64] studied the permeation efficiency of several carbon nanotube membranes in oily wastewater and the efficiency of wastewater treatment, and found that the permeation flux would increase with the increase of applied pressure and temperature. shi[65] used carbon nanotube membranes to separate five nano-scale water-in-oil, and the flux was 2 to 3 orders of magnitude higher than that of commercial nanofiltration membranes, and the oil purity after separation could reach 99.9%. figure 7 is a schematic diagram of the separation of water-in-oil 135 emulsion by single-walled carbon nanotube film, in which oil can selectively penetrate into the single-walled carbon nanotube film. selby[66] uses carbon nanotubes/polysulfone/ polyvinyl alcohol composite membrane to separate oily wastewater. experiments show that when the oil concentration is less than 10 mg·l−1, the oil retention rate can reach 95%. 3.3.3 desalination of seawater carbon nanotube film can allow water to flow, adsorb chemical and biological pollutants and separate particles in seawater. carbon nanotube film can not only filter na+ and clbut also filter water, which can remove bacteria from water and heavy hydrocarbons from petroleum. the properties of carbon nanotube film and its preparation technology play a decisive role in seawater desalination[67]. in order to get the best permeation effect of seawater desalination, reverse osmosis technology and electroosmosis technology are the best choices. amt[68] used md simulation to study the molecular transport of water through the nanopores of carbon nanotubes. the water flow in these simulations is driven by the permeation gradient between two self-assembled carbon nanotube membranes, as shown in figure 8(a), this membrane separates water from saline solution and can be used for seawater desalination. in figure 8(b), the cation -π binds na+ at the entrance of the (6,6) nanotube, and the upper left corner of figure 8(b) can also block na+ at the (8,8) carbon nanotube channel, the upper right corner of figure 8(b), indicating that cation -π plays a decisive role in seawater filtration[69]. farzadeh[70] studied the effect of functional nano-porous boron nitride nanosheets (bnns) membrane on separating salt from seawater by molecular dynamics simulation. when the membrane was placed in aqueous solution containing na+ and cl−, salt could be separated out. when the pressure is 30–100 mpa, the permeability and rejection of the membrane are extremely high. tofiguhy[71] used carbon nanotube membrane to desalinate seawater, the experiment found that after 6 days, the desalination rejection rate was still 1,320 mg·g−1, which indicated that using carbon nanotube membrane to desalinate seawater was economically feasible. takizawa[72] used multi-walled carbon nanotubes (mwcnts)polyamide (pa) nanocomposite membrane technology to desalt seawater. because of the smooth surface of mwcnts-pa membrane and the formation of water layer at the interface, the scale inhibition performance of the membrane is very good, which is beneficial to water treatment. single-layer transverse flow carbon nanotube film (tfcm) is used as an alternative material for effective desalination. for seawater desalination, harmful algae are in a suspended state, preventing water circulation and blocking the filter. wang[73] used low-pollution carbon nanocomposite membrane to separate algae from seawater, under low pressure, the average permeation efficiency can reach 99%, and the rejection rate and anti-pollution rate are also very good. figure 8. application of carbon nanotube film in seawater desalination. 4. conclusion and prospect nanotechnology is the core technology in the 21st century. with the deepening of research, the preparation and application of carbon nanotube film has become an important aspect of nanotechnology. the particularity of carbon nanotube film 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engineering, zhengzhou, henan 450007, china. e-mail: zijieyb@163.com abstract electrospinning nanofiber membrane has the advantages of wide raw materials, large specific surface area, and high porosity. it is an ideal separator material for lithium-ion batteries. this paper first introduces two common electrospinning nanofiber diaphragms: polymer, polymer, and inorganic composite, and then focuses on the modification methods of composite modification, blending modification, and inorganic modification, as well as the methods of electrospinning nano modified polyolefin diaphragm. finally, the development direction of the electrospinning lithium-ion battery separator has prospected. keywords: electrospinning nanofibers; lithium-ion battery; modification; polyolefin; separator article info received: 7 december 2021 accepted: 16 january 2022 available online: 10 february 2022 copyright copyright © 2022 yan zhang, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4 .0/ 1. introduction lithium-ion batteries have the advantages of high specific capacity and long service life. they are widely used in portable electronic equipment, new energy vehicles, energy storage of large power grids, and other fields[1]. as the main component of the lithium-ion battery, the separator can effectively prevent the bad condition of short circuit between the positive and negative electrodes due to direct contact, and allow the lithium-ion battery to move rapidly between the positive and negative electrodes, so as to achieve the purpose of charging and discharging[2]. nowadays, most commercial separators are polyolefin microporous separators. although they have certain advantages in cost and processing technology, there are still many deficiencies in liquid retention, thermal stability, electrolyte wetting and ion permeability[3]. in order to improve the above shortcomings, researchers have done a lot of work in the preparation of nanofiber porous lithium-ion battery separators by electrospinning technology. electrospinning technology is one of the most effective methods to prepare nanofibers at present. its products have the advantages of wide raw materials, large specific surface area, and high porosity. it has been widely used in the fields of battery diaphragm, filtration and adsorption, medical supplies, and fashion[4–6]. at present, polyimide (pi), polyacrylonitrile (pan), polyethylene terephthalate (pet), polyvinylidene fluoride (pvdf), polymethylmethacrylate (pmma), polyvinylidene fluoride hexafluoropropylene (pvdf-hfp), and other materials are often used to prepare electrospinning nanofiber lithium battery separator[7–8]. this paper mainly introduces the research progress of 47 electrospun lithium-ion battery membrane from three aspects: electrospinning nanofiber membrane material, electrospinning membrane modification and polyolefin membrane modification by electrospinning. 2. electrospinning nanofiber separator 2.1 polymer nanofiber separator priya et al.[9] prepared pan porous nanofiber separator by optimizing the electrospinning process parameters as lithium-ion battery diaphragm. the fiber diameter distribution is 880 ~ 1260 nm. the obtained pan nanofiber membrane has good mechanical properties and high porosity, and the ionic conductivity is much higher than that of celgard diaphragm. xu caidi et al.[10] dissolved heated pvdf in dmf through electrospinning method to prepare spinning stock solution and pvdf nanofiber separator. according to relevant tests, it can be concluded that when the concentration of pvdf is 12%, the spinning rate is better; when the voltage is 14 kv, the diameter of pvdf nanofiber diaphragm spun under electrospinning is better, the spindle is less and evenly distributed, which meets the relevant standards. although common organic polymer nanofiber materials show good electrochemical properties, their heat resistance is relatively poor. high temperature resistant polymers can be used to make up for this deficiency. ye et al.[11] dissolves peek with two chloroacetic acid (dca) at 180 degrees celsius. after coating the peek solution in the nanofiber shell of the spinnable polymer pbs by coaxial electrospinning, the shell core structure nanofibers are obtained, and then the core shell fibers are treated at low temperature to convert peek solution into gel state. peek nanofibers were obtained by removing the shell. after heat treatment at different temperatures for 2 hours, it was found that peek separator could maintain a good shape even at a high temperature of 370 ℃, and the shrinkage rates along h and t directions were 3.1% and 2.8% respectively. xiao ke[12] used the advantages of aramid nanofibers such as high melting point, good thermal stability and good affinity for electrolyte to obtain pmia based nanofiber films with good multiple properties by using meta aramid (pmia) and polyurethane (pu). the results show that electrospinning nanofiber membrane has high porosity. pmia pu blend membrane with high tensile strength (>15.79 mpa) is produced by introducing pu and nano cobweb structure, and its ionic conductivity can be as high as 1.38 ms/cm; the introduction of pmia makes the blend membrane have excellent thermal stability, flame retardancy and excellent electrolyte wettability, which improves the safety performance of lithium battery to a certain extent. 2.2 polymer and inorganic composite nanofiber separator a common method for preparing polymer and inorganic composite nanofiber separators is to dope inorganic nanoparticles[13]. peng shujing et al.[14] added sio2 nanoparticles into pvdf solution to make composite membrane. for pvdf separator and cel-gard 2400 separator, the composite separator has better charge discharge performance and battery cycle performance. through relevant tests, it can be seen that its performance is the best when 5% sio2 is added. zhang zhixiong[15] prepared pva-sio2 nanofiber composite separator by electrospinning technology. the separator has a unique three-dimensional network pore structure, and the porosity is as high as 73%; the porous structure and surface polar functional groups make the composite membrane have better electrolyte wettability. its liquid absorption rate is as high as 405%, which is more than 3 times that of pp separator. its ionic conductivity is as high as 1.81 ms/cm. after heat treatment at 170 ℃ for 0.5 h, the composite separator has no obvious thermal shrinkage and shows good thermal dimensional stability. ding jun[16] prepared pi and tio2 composite nanofiber films by electrospinning. the addition of tio2 reduces the average fiber separator, increases the porosity and improves the electrochemical performance of the composite nanofiber separator, which makes its battery performance better than that of pi nanofiber separator. li lin et al.[17] used 48 electrospinning technology to blend pvdf and nano-tio2, and nano-tio2 particles played an auxiliary role in the process of pore formation. according to the relevant experiments, when the mass ratio of pvdf to tio2 is 22:3, the porosity of the composite separator is improved; the liquid absorption rate is 20 times higher than that of commercial pp separator, with excellent performance and obvious improvement effect after compounding. the prepared composite membrane has good porosity and provides more and better channels for the passage of li+. due to its superior battery performance, the charge and discharge performance of lithium-ion batteries with pvdf and tio2 composite membrane can be tested. compared with the doping process, the inorganic nanoparticles produced by the electrostatic spraying method can be directly attached to the positive and negative electrodes of the polymer, and the inorganic composite separator can be directly attached to the surface of the polymer and inorganic composite separator, so as to further optimize the separator performance[18]. jiao xiaoning et al.[19] made a sandwich structure of polymer and inorganic composite separator by spraying electrostatic spraying technology between two layers of nanofibers. the test results show that the composite separator has an excellent liquid absorption rate, thermal dimensional stability, and electrochemical stability. 3. modification of electrospinning nanofiber separator although electrospinning nanofiber diaphragm has certain advantages, it also has some problems, such as low strength and electrochemical performance to be further improved. therefore, researchers at home and abroad have done a lot of research on the modification of electrospinning nanofiber separator in order to obtain separator materials with better performance[20]. 3.1 composite modification zhao jianmeng[21] prepared pvdf, pmma and pvdf multilayer composite separators by electrospinning technology. compared with single-layer separators, the tensile strength of multilayer separators was improved, and the electrochemical potential was stable at 5.2 v, meeting the needs of lithium-ion batteries. chen et al.[22] prepared interleaved and disordered polyimide (pi) and polyvinylidene fluoride hexafluoride (pvdf-hfp) composite fiber separators by cross spinning process. the separator not only combines the advantages of the two materials but also melts part of pvdf-hfp through a special hot rolling treatment to realize the adhesion between fibers and improve the strength of the separator. although the multi-layer composite modified electrospinning separator optimizes the strength and electrochemical properties of the separator to some extent, there is no strong interaction between the composite separator layers, and the battery performance may be affected by the separation of swelling and other effects after the separator absorbs the electrolyte[23]. 3.2 blending modification gopalan et al.[24] mixed pvdf and pan by electrospinning to prepare lithium-ion battery separator. it was found that compared with pure pvdf separator, the affinity of mixed polymer membrane to electrolyte was better. when the mass fraction of pan reached 25.0%, the membrane had higher liquid absorption rate, and the ionic conductivity at room temperature was as high as 7.80 ms/cm. when the mass fraction of pan is 0.5%, the average diameter of the prepared separator fiber is different from that of pvdf separator fiber. at the same time, the fibers in the separator are entangled and knotted, which is very helpful to improve the electrochemical performance of polymer electrolyte. yang et al.[25] the preparation of pan@pvdf-hfp composite fiber separator with core-shell structure is carried out by coaxial electrospinning technology. pvdf-hfp and pan were used as shell and core materials respectively to study the structure, surface morphology, porosity and thermal properties of core-shell fiber separator. compared with the traditional commercial porous pe separator, pan@pvdf-hfp fiber composite 49 separator has better porosity, thermal stability and electrochemical performance. blending modification uses the complementary effect of polymer properties to optimize the performance of electrospinning separator in some aspects. however, due to the large property differences between complementary polymers, it is still a difficult problem to select the appropriate solvent for the preparation of blended polymer solution, and this research still has certain development possibility. 3.3 inorganic modification in the polymer doped with inorganic particles, not only polymer and inorganic composite nanofiber separator can be prepared, but also electrospinning nanofiber separator can be modified. inorganic nanoparticles have good thermodynamic stability. the composite nanofiber separator prepared by doping inorganic particles into polymer can effectively improve the thermal size and electrochemical properties of the separator. in order to disperse nano-sio2 particles, wang yuan et al.[26] used pvdf-hfp as the basic material to prepare sio2 and pvdf-hfp composite lithium-ion battery separator by electrospinning. it is found that the addition of sio2 significantly improves the liquid absorption rate and electrochemical performance of the separator. the fibers obtained by electrospinning are not only small in diameter, but also loosely and irregularly stacked. therefore, the porosity of the fiber separator can reach 87%, the liquid absorption rate of the prepared composite separator can reach 620%, and the ionic conductivity at room temperature can reach 2.92 ms/cm. the discharge specific capacity of the button battery assembled by the composite separator is 175 mah/g, and the battery capacity retention rate is 92% after 100 cycles, showing excellent cycle performance. wang zhenyu[27] formed a sio2 inorganic layer on the surface of pei nanofibers by in-situ growth method on the basis of the prepared polyetherimide (pei) nanofiber film. the introduction of sio2 ensures the three-dimensional storage space of the electrolyte, which provides more space for the internal storage of sio2 groups, and it is found that the introduction of sio2 has a good affinity for the electrolyte. compared with commercial separator, pei-sio2 separator has better electrolyte affinity and heat resistance. the composite nanofiber separator prepared by mixing inorganic metal materials and polymers can not only make the composite separator material take into account the advantages of metal materials and polymers, but also improve the mechanical properties and thermal stability of the membrane. wang ya et al.[28] made films with pi and ag composite nanofibers. the test shows that the dielectric constant of the composite film is 6 times that of the pure pi film. the relevant experiments show that the pi nanofiber separator modified by nano ag has excellent mechanical properties, thermal stability and better dielectric constant. the modified pi lithium battery separator also has other advantages. 4. electrospinning modified polyolefin separator due to the limitation of its processing technology, the liquid absorption rate and liquid retention performance of commercial polyolefin separator are poor, while electrospinning nanofiber membrane has a unique three-dimensional network structure. electrospinning nanofibers can be deposited on one or both sides of polyolefin separator to prepare composite diaphragm, so as to improve the thermal stability, wettability and liquid retention of diaphragm, and to improve the electrochemical performance of the battery[29]. lee et al.[30] deposited polyvinylidene fluoride, chlorotrifluoroethylene and aluminum oxide composite nanofibers on both sides of polyolefin separator to prepare three-layer composite separator. the results show that the prepared three-layer composite separator has good thermal dimensional stability and good battery cycle performance. in order to improve the adhesion between polyolefin separator and polyvinylidene fluoride nanofibers, liang yinzheng[31] treated the surface of polyolefin separator under the condition of argon atmospheric pressure plasma, which improved the adhesion between nanofibers and polyolefin separator and reduced the delamination of composite separator. wang yuan[32] analyzed the wettability, 50 thermal stability, mechanical properties and electrochemical properties of pvdf modified polyethylene lithium ion battery separator. the results showed that pvdf modified pe separator showed better mechanical properties, the tensile strength and elongation at break of the separator were improved accordingly, and the modified separator also showed excellent ion conductivity battery charge discharge cycle and rate performance. 5. expectation to sum up, the development of lithium ion spinning equipment should focus on reducing the production efficiency of lithium-ion separator; second, continuously improve the mechanical and electrochemical properties of existing separator materials through modification technology; third, continuously develop new materials to meet the needs of lithium-ion battery separator, such as high temperature resistant and low-cost power lithium-ion battery separator materials. 6. conclusion with the continuous development of portable electronic equipment, new energy vehicles and other industries, it not only brings high-speed development opportunities to the lithium-ion battery separator industry, but also brings demand challenges in terms of high performance and low cost. electrospinning nanofiber separator as lithium-ion battery separator has many advantages, but also has some shortcomings. it still needs long-term discussion and research in the future. acknowledgement 2020 henan provincial colleges and universities national college students innovation and entrepreneurship training program project (202011517012). conflict of interest the authors declare 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2011. 32. wang y. study on the properties of the modified polyethylene membrane for lithium-ion battery. nanchang: nanchang university; 2020. characterization and application of nanomaterials 2024, 7(2), 6414. https://doi.org/10.24294/can.v7i2.6414 1 article micro/nanoscaled cellulose from coffee pods do not impact ht-29 cells while improving viability and endosomal compartment after c. jejuni cdt intoxication daniele lopez1,2, giovanna panza1, pietro gobbi1, michele guescini1, laura valentini1, stefano papa1, vieri fusi2, eleonora macedi2, daniele paderni2, mariele montanari1, barbara canonico1,* 1 department of biomolecular sciences, university of urbino carlo bo, 61029 urbino, italy 2 department of pure and applied sciences (dispea), university of urbino carlo bo, 61029 urbino, italy * corresponding author: canonico barbara, barbara.canonico@uniurb.it abstract: the food industry progressively requires innovative and environmentally safe packaging materials with increased physical, mechanical, and barrier properties. due to its unique properties, cellulose has several potential applications in the food industry as a packaging material, stabilizing agent, and functional food ingredient. a coffee pod is a filter of cellulosic, non-rigid, ready-made material containing ground portions and pressed coffee prepared in dedicated machines. in our study, we obtained, with homogenization and sonication, cellulose micro/nanoparticles from three different coffee pods. it is known that nanoparticulate systems can enter live cells and, if ingested, could exert alterations in gastrointestinal tract cells. our work aims to investigate the response of ht-29 cells to cellulose nanoparticles from coffee pods. in particular, the subcellular effects between coffee-embedded nanocellulose (cenc) and cellulose nanoparticles (nc) were compared. finally, we analysed the pathologic condition (cytolethal distending toxin (cdt) from campylobacter jejuni) on the same cells conditioned by nc and cenc. we evidenced that, for the cellular functional features analysed, nc and cenc pre-treatments do not worsen cell response to the c. jejuni cdt, also pointing out an improvement of the autophagic flux, particularly for cenc preconditioning. keywords: coffee embedded nanocellulose; nanocellulose; c. jejuni cdt; ht-29 intestinal cells; vacuolar compartment; biological improving responses; mitochondrial damage 1. introduction cellulose materials are “generally regarded as safe” (gras) as binders and thickeners in food products. however, nanocellulose materials have unique properties that can improve food quality and safety and have not received us food and drug administration (fda) approval as food ingredients. because of their unique properties, nanoscale fibrillated cellulose and crystals have additional potential applications in the food industry as 1) packaging materials, 2) stabilizing agents, and 3) functional food ingredients [1–3]. moreover, several studies have been published regarding the use of the material to produce edible films, act as a stabilizer, and be used as an emulsifying agent, among others [4–12]. in vitro and in vivo toxicological studies of ingested nanocellulose revealed minimal cytotoxicity and no subacute in vivo toxicity. however, ingested materials may modulate gut microbial populations or alter aspects of intestinal function not elucidated by toxicity testing, which could have significant health implications [3]. citation lopez d, panza g, gobbi p, et al. micro/nanoscaled cellulose from coffee pods do not impact ht-29 cells while improving viability and endosomal compartment after c. jejuni cdt intoxication. characterization and application of nanomaterials. 2024; 7(2): 6414. https://doi.org/10.24294/can.v7i2.6414 article info received: 15 may 2024 accepted: 28 june 2024 available online: 1 august 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 6414. 2 nanocellulose may have applications in modulating digestion and the absorption of nutrients and other ingested substances. nanocellulose materials are also potentially applicable as a non-caloric fibre source to reduce the energy density of foods like chocolate, hamburgers, and dough-based products [13,14]. in addition, some studies have suggested that using nanocellulose as a source of dietary fibres may offer a range of health benefits and assist in reducing the risk of chronic diseases [2,14]. although cellulose, widely used as a thickener and filler in foods and drugs, has been designated as gras [15], as cited, nanocellulose (nc) has yet to be designated as gras. several researchers found that ingested nc has slightly acute toxicity and is likely non-hazardous after small quantities of ingestion [16]. from a toxicological point of view, cellulose-based ingredients have shown excellent biocompatibility, particularly nc, which exhibits minimal cytotoxicity in a wide range of human and animal cells. cellulose nanocrystals are employed as drug carriers in medicine [17], and their cellular uptake was demonstrated. a coffee pod is a filter of cellulosic, nonrigid, ready-made material containing portions of ground and pressed coffee prepared in dedicated machines through boiling water under pressure. coffee is the most widely known and popular beverage globally, with more than 500 billion cups consumed annually [18]. the function of the paper filter is to store the coffee powder and allow for coffee brewing. commercially available paper filters have characteristics corresponding to the preferences and needs of the consumer, such as size, which enables the preparation of larger or smaller volumes of coffee. the coffee pods contain a precise amount of coffee between two cellulose layers. the international coffee pod market has shown rapid growth due to consumers' inclinations towards innovation, convenience, and lifestyle changes, which have, in turn, driven the global adoption of coffee pod machines (figure 1a) [19]. even with homemade coffee pods, you can get a cup of coffee with a good yield, just like with professional espresso machines. recently published studies [20–23] tested how many nano plastics (np) are released when coffee cups (or other plastic disposables) are exposed to hot water. indeed, hernandez and co-workers found recently that plastic teabags release billions of microparticles and nanoparticles into tea [21]. although cellulose is a renewable, sustainable, inexpensive, eco-friendly, and safely employable polymer compared to plastics, it was recently reported that water swelling has a negative impact on cellulosic material applications in packaging [24,25] and as composite additives [26]. indeed, this cellulose response may be temperature dependent [25] and could induce some nanoparticle release, impacting the behaviour of nc along the gastrointestinal tract and its influence on food digestion and nutrient absorption [27]. generally, the uptake of nanoparticles by the cellular system occurs through a process known as endocytosis. it is influenced by the physicochemical characteristics of nanoparticles, such as size, shape, surface chemistry, and the employed experimental conditions [28]. nanoparticulate systems can enter live cells, often through several endocytic pathways. considering that passive penetration of the plasma membrane may occur as an alternative route, in that case, the internalized nanomaterials are directly transferred into the cytoplasm [28,29]. characterization and application of nanomaterials 2024, 7(2), 6414. 3 figure 1. (a) scheme of the path of coffee from producer to the consumer up to the disposal of the pods and highlight the relative percentages for each type (created in biorender.com); (b) photos illustrating the different coffee pods we used, i1, k2, and l3; (c) table explaining the characteristics of paper filters, such as the color and weight of the individual waffle containing and not containing coffee. intestinal mucus is the first barrier for ingested nanoparticles (nps) [30,31]. small nps penetrate more quickly than large ones [31]. recently, cao and co-workers [14] analysed the effects of cellulose nanocrystals (cnc) in different food models. they measured the volume-weighted particle size distributions in food models and oral, gastric, and small intestinal phases of digestion, exposing a tricultured small intestinal epithelium to this obtained nanoparticulate matter. they demonstrated that cnc is relatively non-cytotoxic in a triculture of human intestinal epithelium under the tested experimental conditions. moreover, cnc in the employed food models had little impact on the triculture proteome. therefore, several authors agree that nanocellulose's applications in the food industry need future investigations to determine its potential implications for human health. foodborne pathogens (bacteria, parasites, etc.) are biological agents that cause food poisoning [32], and foodborne disease is divided into two categories: infection and intoxication. foodborne infection is associated with a prolonged incubation period; therefore, the onset of symptoms in foodborne intoxication is shorter than in characterization and application of nanomaterials 2024, 7(2), 6414. 4 foodborne infection [33]. gram-negative campylobacter jejuni is a major cause of foodborne gastroenteritis in humans worldwide. the cytotoxic effects of campylobacter have been mainly ascribed to the actions of the cytolethal distending toxin (cdt) [34]. cdt is a tripartite genotoxin composed of cdta, cdtb, and cdtc subunits [35–37]. among them, cdtb has deoxyribonuclease activity and induces double-strand breaks (dsbs). dsb stimulates spontaneous activation of dna damage responses, leading to cell cycle arrest. cdtb has been shown to arrest the cell cycle in the g2/m phase [37]. indeed, we previously demonstrated [38] that cdt-treated hela cells increase their endolysosomal compartment because of toxin internalization, in addition to simultaneous and partial lysosomal destabilization. indeed, in humanisolated monocytes, we found that mitochondria and lysosomes were targeted differently by cdts from different c. jejuni strains [39]. we investigated the response of ht-29 cells, representing a model of goblet intestinal cells, to cellulose nanoparticles from three different typologies of coffee pods. besides evaluating possible cytotoxic effects, we detailed the mitochondrial network and vacuolar compartment (endosome-lysosomes). indeed, since we are investigating effects induced by cellulose from coffee pods, we treated ht-29 cells with homogenates obtained without coffee brewing (eliminating coffee powder) and homogenates of pods after coffee brewing to consider the peculiar impact of coffee embedding. the comparison of the subcellular effects between cellulose nanoparticles (nc) and coffee-embedded nanoparticles (cenc) was performed, mixing the three pod typologies, for a better interpretation of the data. finally, we analysed the impact (on the same endosomal-lysosomal routes) of c. jejuni cdt on ht-29 intestinal cells conditioned by micro/nanoscaled cellulose from coffee pods. this step enables us to verify possible differences between cenc and nc treatments in physiological conditions (w/o cdt exposure) and pathological conditions (during cdt exposure). our work highlights that micro/nanoscaled cellulose from coffee pods does not significantly impact the viability and functions of ht-29 cells but even improves cell status/condition and endosomal compartment after c. jejuni cdt intoxication. 2. materials and methods 2.1. nanocellulose obtainment from coffee pods: i1, k2 and l3 we selected three coffee pods of the most famous brands of coffee present in italy, to which we have assigned the acronyms i1, k2, and l3. coffee embedded nano cellulose (cenc): coffee was prepared, taking care to recover the waffles, deprived of their coffee content prior to the homogenization of cellulose. for nano cellulose (nc) we used the coffee pod border (not brewing coffee). for the extraction of microand nanoparticles of cellulose, we used the homogenization technique through medimachine ii (ctsv, torino) and serial filtration (figure s1). for sonication, we took 7 ml of homogenate containing micro and nanoparticles of cellulose and sonicated at 30 khz with 100 w power for 1 h and 30 min with a up200s hielscher ultrasonic technology (teltow, germany) in an ice/water bath. characterization and application of nanomaterials 2024, 7(2), 6414. 5 2.2. growth conditions of bacterial strains and cell lysate preparation jejuni atcc 33291 were grown at 37 ℃ in a microaerobic chamber (don whitley scientific, shipley, united kingdom) containing 85% n2, 10% co2, and 5% o2, either on blood agar (ba) plates containing columbia agar base (oxoid, basingstoke, united kingdom) supplemented with 7% (v/v) horse blood (tcs microbiology, united kingdom) and campylobacter selective supplement (oxoid) or in brucella broth (oxoid) with shaking at 75 rpm. c. jejuni strain was grown on ba plates for 24 h prior to use in all assays, unless otherwise stated. c. jejuni strain was grown in 50 ml brucella broth (oxoid) at 37 ℃ in a shaking incubator under microaerophilic conditions for 48 h. the bacterial suspensions were centrifuged at 4000 rpm for 10 min and the pellets were resuspended in 20 ml of dulbecco’s modified eagle medium (d-mem) (sigma-aldrich, st louis, mo, usa). then, bacterial suspensions were adjusted spectrophotometrically to approximately 108 bacteria/ml and lysed by sonication (2 × 30 s bursts with 30 s intervals between each burst) by using a sonicator (sonifier 450, branson, danbury, ct, usa). cell debris and unlisted bacterial cells were then removed by centrifugation at 4000 rpm for 10 min. aliquots of each lysate were sterilised by a 0.22-µm membrane filter (millipore, milano, italy) and stored at −20 ℃ before use [40]. 2.3. esem -eds characterisation morphological characterisation of the microand nanoparticles was carried out using an environmental scanning electron microscope-energy dispersive spectrometer (esem-eds). a fei quanta 200 microscope (fei, hillsboro, or, usa), equipped with an energy dispersive x-ray spectrometer (edax inc., mahwah, nj, usa), was used to evaluate the elemental composition of the sample. observations were made on samples prepared in non-demineralized distilled water without any subsequent treatment after air drying at low vacuum (0.2−1.2 torr) at a working distance of 10 mm using secondary and back-diffused electrons with a variable acceleration voltage of 12 to 25 kv. for elemental mapping, a real-time count of 100 s was used with spot mode—focused beam on discrete points of the sample, repeating the analysis 3–5 times per measurement. 2.4. nta characterisation for nanosight tracking analysis (nta), the homogenate underwent an additional 0.22 µm filtration to discriminate nanoparticles from micro particles. nta measurements were performed with a nanosight lm10 (nanosight, malvern instruments ltd., uk), equipped with a sampling chamber with a 640 nm laser and a viton o-ring fluoroelastomer. the samples were injected into the sample chamber with sterile syringes until the liquid reached the tip of the nozzle. all measurements were made at room temperature (rt). 2.5. in vitro acute exposure of ht-29 cells the ht-29 cell line is a human colorectal adenocarcinoma cell line and was cultured in rpmi 1640 medium (sigma-aldrich, st louis, mo, usa) supplemented with 10% heat-inactivated foetal bovine serum (fbs; gibco; thermo fisher characterization and application of nanomaterials 2024, 7(2), 6414. 6 scientific, inc., waltham, ma, usa), 1% l-glutamine (sigma-aldrich, st louis, mo, usa), and 1% penicillin/streptomycin (sigma-aldrich, st louis, mo, usa) at 37 ℃ in humidified air with 5% co2. regarding experimental assays, cells were seeded in 6-well plates at a density of 1.5 × 105 cells per well. cenc and nc were added to the medium at a dilution of 1:10 for i1 and k2, and 1:9 for l3 samples, and incubated for 24 h, 48 h, 72 h and 96 h. for the negative control, the cells were incubated with medium only. 2.6. treatment of ht-29 cells with c. jejuni lysates ht-29 cells after pre-treatment with cenc and nc were incubated with 2 ml of media enriched with c. jejuni cell lysates (1:50 dilution) from atcc 33291 strains previously prepared for 24 h and 72 h. treated cells were analysed by means of flow cytometry and confocal microscopy to evaluate different cellular parameters. for the negative control, cells were incubated with media only. 2.7. flow cytometric analyses cytometric experiments were performed with a facscanto ii (bd) flow cytometer equipped with an argon laser (blue, ex 488 nm), a helium neon laser (red, ex 633 nm), and a solid-state diode laser (violet, ex 405 nm). the analyses were performed with the facsdiva tm (bd) software. at least 10,000 cellular events were acquired for each sample. cell viability was assessed by means of propidium iodide (pi; sigma-aldrich, st louis, mo, usa) or 7-aad staining. the cells were incubated for 10 min in the dark with pi 1 mg/ml or with 7-aad (beckman coulter, usa). we detected the percentage of pi or 7-aad-positive events. mitochondrial characteristics were investigated through tmre staining. tetra-methylrodamine ethyl ester perchlorate (tmre) (sigma-aldrich, st. louis, mo, usa) is a cationic dye that can penetrate the mitochondria, generating a red-orange fluorescence as intense as the mitochondrial membrane potential. tmre 40 nm was added to the sample 15 min before the acquisition time. the samples were analysed by flow cytometry using the appropriate fluorescence channel [41]. lysotracker green or deep red (ltg/ltdr) dye (thermo fisher scientific, usa) was used to mark and trace the lysosomes. the lysotracker is an acidotropic and fluorescent probe that serves to monitor acidic organelles in living cells. the amount of fluorescence obtained by lysotracker staining is directly proportional to the volume of lysosomes in the cell. lysotracker 100 nm was used to mark the lysosomes, and after 30 min of incubation, the green or red lysosomal fluorescence was detected by flow cytometry and confocal microscopy [42]. to study the autophagic machinery, the cells were incubated with 50 μm monodansylcadaverine mdc (sigma-aldrich, st. louis, mo, usa) in order to evaluate the autophagolysosomes (autophagic vacuoles). the generation of reactive oxygen species was determined by the cytometric analysis of cells labelled with cmh2dcfda (thermo fisher scientific, usa), which can detect the generation of intracellular h2o2. the 5-(e-6)-chloromethyl-2,7-dichlorodihydrofluorescein diacetate acetyl ester (cm-h2dcfda) fluorescent probe is a membrane-permeable compound that is converted into a fluorescent, impermeable compound, h2dcf, by characterization and application of nanomaterials 2024, 7(2), 6414. 7 intracellular esterases. dcf (dichlorofluorescein) is a highly fluorescent compound produced by the oxidation of h2dcf by hydrogen peroxide. the amount of peroxide produced affects the intensity of dcf fluorescence inside the cells. cm-h2dcfda was solubilized in dimethyl sulfoxide (dmso) (sigma-aldrich, usa) and then diluted in phosphate-buffered saline (pbs) and used at a final concentration of 5 μm for 30 min at 37 ℃ [43,44]. a new fluorescent probe for vesicular trafficking, the 1,7bis-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-4,10-dimethyl-1,4,7,10tetraazacyclododecane, called aj2nbd [45], was used. aj2nbd was dissolved in dmso at the final concentration of 15 mm. cells were incubated at 37 ℃ with 500 nm (f.c.) of aj2nbd for 20 min [46]. in order to quantify the vesicular trafficking in treated cells, ht-29 cells were incubated in complete culture medium and stained at different time points from 0 to 1 day with the specific probe aj2nbd (500 nm for 20 min). 2.8. confocal microscopy to evaluate the behaviour of different probes, the cells were grown on mattek glass bottom chambers (mattek corporation) and then stained with fluorescent probes. to evaluate the vesicular trafficking in treated cells, ht-29 cells were incubated in complete culture medium with the specific probe aj2nbd (500 nm for 20 min), and the vesicular compartment was studied by confocal microscopy at different time points from t0 (after incubation of aj2nbd) up to 1 day. to evaluate the lysosomal formation, the cells were stained with lysotracker deep red (ltdr) at 100 nm. the images were acquired by a leica tcs sp5 ii confocal microscope (leica microsystem, germany) with 488, 543, and 633 nm illumination and oilimmersed objectives and averaged in real time using a line average to reduce random noise. the images were further processed and analysed in imagej software (national institutes of health, bethesda, md, usa). 2.9. statistical analyses data are shown as the mean (or percentage, as indicated) ± standard deviation (sd) of at least three independent experiments. the means of two groups were compared using a t test. the p values less than 0.05 were considered statistically significant. analysis of variance (anova) approaches were used to compare values among more than two different experimental groups for data that met the normality assumption. one-way anova or two-way anova were followed by a bonferroni post-hoc test. the p values less than 0.05 were considered statistically significant. bonferroni’s multiple comparison test revealed statistical significance: * = p < 0.05, ** = p < 0.01, *** = p < 0.001, **** = p < 0.0001. all statistical analyses were performed using graphpad prism 9.0.0 (graphpad software, san diego, ca, usa). 3. results 3.1. nanocellulose evaluation by esem and nanosight characterisation we selected three types of coffee pods (i1, k2, l3). a first evaluation of the pods was made macroscopically based on the physical and morphological characteristics of characterization and application of nanomaterials 2024, 7(2), 6414. 8 the coffee waffle, in particular the size (weight) and the colour (figure 1c). as reported in the materials and methods section, we obtained two types of nanocellulose: coffee embedded nano cellulose (cenc) and nano cellulose (nc). we characterized 1) the presence of microand cellulose nanoparticles, and then 2) we evaluated whether the use of sonication improved the yield of nanoparticles. esem data show the best morphological uniformity in the homogenate samples than in the homogenization + sonication procedure (figure 2a). consequently, we continue the analyses on the nanoparticles obtained by the unique homogenization step. we evaluated the size and morphology of cellulose nanoparticles by nta (figure 2b). from nta and esem, the average size of the nanoparticles obtained by the homogenization technique is 80 nm (figures 2a and 2b). the esem-eds elemental analysis peaks showed the presence of sulfur (s) (figure 2c). hydrochloric and sulfuric acids have been extensively used to obtain cellulose from wood [47]. sulfuric acid hydrolysis of native cellulose fibres causes the breakdown of the fibres into rodlike fragments [48]. during the hydrolysis by sulfuric acid, negatively charged sulfate groups will be introduced on the cellulose chain through the esterification of hydroxyls [47]. for this reason, the presence of sulphur must be considered normal based on wood treatment to obtain cellulose. we evaluated each homogenate's dry weight (figure 2d) to gain further knowledge of the concentration of our homogenates. the results obtained (figure 2e) were assessed as a value of μg/ml. however, besides such quantitative assessment, we performed the nanoparticle counts employing nta (figure 2f), obtaining the particle concentration/ml that we equally administered to ht-29 cells. characterization and application of nanomaterials 2024, 7(2), 6414. 9 figure 2. (a) esem analysis of microparticles and nanoparticles obtained by homogenization and by homogenization and sonication. histograms reveal the size of microparticles and nanoparticles with the t-test assessments (p value to two tails); (b) nta of the size distribution of the different types of pods (i1, k2, l3); (c) eds spectra for homogenates i1, k2, l3 and histogram evaluating the percentage of sulphur present in homogenates. one-way anova with bonferroni’s multiple comparison tests revealed a significant difference: ** = p < 0.01; (d) photos of the homogenates of microand nanoparticles/fibrils in petri dishes following complete evaporation of the liquid medium (fore dry weight of microand nanoparticles/fibrils); (e) table reporting the concentration in μg/ml for each type of micro and nanoparticles/fibrils analyzed by the dry weight; (f) table reporting the number of particles per ml by nanosight. 3.2. intestinal cell response to nanosized cellulose (nc) and to coffee embedded nanosized cellulose (cenc) the most important factors influencing recognition, uptake, and cellular response include nanocellulose size, length of fibres, shape, surface area and charge, degree of characterization and application of nanomaterials 2024, 7(2), 6414. 10 agglomeration in biological media, source, and type of nanocellulose [49]. in our model, all these features are identical for cenc and nc samples, varying only for the presence of the imbibition of the cellulose by coffee brewing. cell viability although nanocellulose is largely considered non-toxic in its bulk form, different authors reported that chronic cell exposure to high concentrations of nanocellulose may result in an apoptotic cellular response [50]; moreover, coffee has the ability to trigger apoptosis by modulating multiple components of the apoptotic response [51,52]. cell death was assessed using supravital propidium iodide (supravital pi). we did not detect any relevant cell death induction or significant differences in cenc and nc-treated cells with respect to control (figure 3a,c), (figure 3b,d) for the investigated time points. in detail, after 24 h of exposure, cenc-treated cells (i1, k2, l3) appear to maintain viable conditions as in the control. the analyses showed that, compared with control cells, the treatment with cenc and nc did not cause any significant increase in the percentage of pi-positive cells. indeed, cenc-treated ht29 cells revealed, after 24 h and 72 h, lower pi positivity than control samples (figure 3b). figure 3. (a) contour plot ssc vs pi from ht-29 control cells, i1 cenc ht-29 treated cells, k2 cenc ht-29 treated cells, l3 cenc ht-29 treated cells at 48 h. the rectangular region identifies events with high pi uptake (cell death); (b) percentages of pi-positive ht-29 cells for each cenc experimental condition from 24 h to 72 h; (c) contour plot ssc vs. pi from ht-29 control cells, i1 nc ht-29 treated cells, k2 nc ht-29 treated cells, and l3 nc ht-29 treated cells at 48 h. high pi uptake reveals cell death; (d) percentages of pi-positive ht-29 cells for each nc experimental condition from 24 h to 72 h. 3.3. mitochondrial oxidative stress and autophagolysosome modulation in cells treated by the tree different cenc and nc types of pods mitochondrial membrane potential was investigated through tmre staining, a cationic dye able to penetrate the mitochondria and generate a red-orange fluorescence characterization and application of nanomaterials 2024, 7(2), 6414. 11 as intense as the mitochondrial membrane potential (mmp). figure 4 highlights a comparison between ht-29 cell mmp after administration of the three typologies of nanosized cellulose (nc) and coffee embedded nanosized cellulose (cenc). we did not observe relevant and significant differences between exposure to nc and cenc, except for l3 at the longest times (72 h and 96 h, figure 4a,d, respectively), revealing a significant increase in mitochondria hyperpolarization in nc samples. figure 4. fold change of: (a) tmre intensity relative to untreated ht-29 cells (ctrl) for l3 cenc-treated ht-29 cells and l3 nc-treated ht-29 cells at 72 h; (b) dcf intensity relative to untreated ht-29 cells for l3 cenc-treated ht-29 cells and l3 nc-treated ht-29 cells at 72 h; (c) dcf intensity relative to untreated ht-29 cells for k2 cenc-treated ht-29 cells and k2 nc-treated ht-29 cells at 72 h; (d) tmre intensity relative to untreated ht-29 cells for l3 cenc-treated ht-29 cells and l3 nc-treated ht-29 cells at 96 h; (e) dcf intensity relative to untreated ht-29 cells for i1 cenc-treated ht-29 cells and i1 nc-treated ht-29 cells at 96 h; (f) dcf intensity relative to untreated ht-29 cells for k2 cenc-treated ht-29 cells and k2 nc-treated ht-29 cells at 96 h. fold change of autophagic-like vacuoles (mdc) intensity relative to untreated ht-29 cells (ctrl) for cenc-treated ht-29 cells; (g) nc-treated ht-29 cells (h) 48 h to 96 h. t-test and one-way anova with bonferroni’s multiple comparison tests revealed significant differences * = p < 0.05, ** = p < 0.01. characterization and application of nanomaterials 2024, 7(2), 6414. 12 to evaluate changes in the amount of intracellular reactive oxygen species (ros), h2o2 was targeted by means of cm-h2dcfda (dcf). these evaluations are further coupled with data on mmp, in agreement with the findings of several researchers [53–56]. histograms b and c in figure 4 show higher hydrogen peroxide concentrations in specific nc samples, lacking in cenc samples, in agreement with the antioxidant activity of coffee. higher ros amounts were registered for l3 and k2 nc-treated cells after 72 h (figure 4b,c), whereas after 96 h, h2o2 increased significantly in i1 nc-treated cells. the two major cellular sites of ros production are the electron transport chain in mitochondria and endosomes via the nox2-oxidase enzyme [57]. therefore, to verify possible modulations of autophagic-like vacuoles, we investigated the intracellular presence of autophagosomes with monodansylcadaverine (mdc). our data show that cenc and nc-treated cells show a progressive increase of autophagiclike vacuoles at 72 h (figure 4g,h). of note, at 96 h, both cenc and nc-treated cells show a decrease in mdc fluorescence, suggesting that cells were able to clear the excess of autophagosomes. we did not detect any significant differences in time trends of cenc and nc samples, revealing that autophagic vacuole increase is mainly primed by nanocellulose internalisation and the modulation is essentially dependent on time and not coffee. autophagy is a lysosome-mediated intracellular biological degradation process [58]. for this reason, we also investigated lysosome networks. indeed, the cellular uptake of cenc and nc particles in ht-29 cells may lead to direct lysosome damage. to assess lysosome integrity, we used a lysosomotropic dye (lysotracker deep red, ltdr), analysed by flow cytometry and confocal microscopy (figure 5). moreover, we coupled these analyses to aj2nbd (figure 5c), useful in intracellular vesicular organelle detection [46]. aj2nbd is a new dye containing the 7nitrobenzo[1,2,5]oxadiazole-4-yl (nbd) fluorophore [59] synthesised (and patented) by fusi and co-workers [45]. flow cytometry highlights a not-significantly lower mfi (mean fluorescence intensity) registered for k2 and l3-treated samples in respect to controls, whereas confocal images illustrate in detail aj2nbd and ltdr co-staining. characterization and application of nanomaterials 2024, 7(2), 6414. 13 figure 5. (a) fold change of: ltdr intensity relative to untreated ht-29 cells (ctrl) for k2 cenc-treated ht-29 cells and k2 nc-treated ht-29 cells at 72 h; (b) ltdr intensity relative to untreated ht-29 cells (ctrl) for l3 cenc-treated ht-29 cells and l3 nc-treated ht-29 cells at 72 h; (c) confocal images of aj2nbd (green) and lysotracker deep red (ltdr, red) fluorescence from ht-29 control cells (ctrl), k2 cenc-treated ht-29 cells and k2 nc-treated ht-29 cells, after 72 h of treatments. scale bar: 15 µm; (d) confocal images of aj2nbd (green) and lysotracker deep red (ltdr, red) fluorescence from ht-29 control cells (ctrl), l3 cenc-treated ht-29 cells and l3 nc-treated ht-29 cells, after 72 h of treatments. scale bar: 15 µm. 3.4. evaluation of dna content and cell cycle profiles in cells treated by cenc and nc preparations finally, we evaluated the dna content of samples treated with the three different coffee pod types (figure 6). the statistical evaluation of s and g2/m phases at 72 h for both cenc and nc treatments did not highlight significant differences, except for characterization and application of nanomaterials 2024, 7(2), 6414. 14 k2 treatments. in detail, after k2-cenc treatment, ht-29 cells revealed a mild but significant increase in s phase events, whereas after k2-nc treatment, g2/m phase events appeared to have mildly increased. this finding could arise from the highest sulphur content detected in these specific coffee pods, as shown in figure 2c. in fact, different authors [60] published on the biologic effects of sulphur compounds that can inhibit or delay the cell cycle progression [61]. the overall data suggest that ingested nc has negligible toxicity, even at the massive concentrations used in our study. moreover, coffee embedding demonstrates that it can further modulate the nc effects, even improving the baseline condition of the control, as demonstrated by the pi data as well as by other studies on coffee biologic effects [62]. coffee includes a wide array of components that can have potential implications for health. in particular, the vast array of components included in the brewed product and the varied effects of each compound drastically limit the understanding of its physiological effects. a scheme of the most represented compounds is shown in figure s2. nevertheless, we want to underline that in our model, coffee is present in scarce amounts, derived from cellulose embedding. figure 6. (a) statistical histogram of the cell cycle phases was calculated by fc via pi staining at 72 h for ht-29 control cells and i1, k2, and l3 cenc ht-29 treated cells; (b) fc histograms representing the ht-29 cell population in the s and g2/m phases of the cell cycle after 72 h of i1, k2, l3 cenc administration; two-way anova with a bonferroni’s multiple comparison test revealed a significant difference (**p < 0.01); (c) statistical histogram of the cell cycle phases at 72 h for ht-29 control cells, i1/k2/l3 nc ht-29 treated cells; two-way anova with a bonferroni’s multiple comparison test revealed a significant difference (*p < 0.05); (d) fc markers represent the ht29 cell population in the s and g2/m cell cycle phases after 72 h of i1, k2, and l3 nc administration. 3.5. cell response to cdt in mixed ncand cenc-treated intestinal cells 3.5.1. evaluation of cell viability during the time course in this step of the study, we considered the exposure of intestinal cells to c. jejuni cdt-containing lysate. we mixed the homogenates from the three different coffee characterization and application of nanomaterials 2024, 7(2), 6414. 15 pods in a unique formulation to correlate only two main groups (nc and cenc). this mixing is also justified by the lack of striking differences between the three different coffee pods (i1, k2, l3). our data did not reveal any significant cytotoxic effects of the nc and cenc treatments; indeed, positive pi events after 24 h of nc administration were even lower than in control cells (figure 7a). at 72 h the cells treated with cenc and nc show a slight increase in dead cells but are still not significant (figure 7b). as observed in other cell lines [34,38,39,63], the atcc lysate did not induce in ht-29 cells an important necrotic/apoptotic effect after 24 h (figure 7); however, previous conditioning with cenc treatment showed a reduction in cell death percentages (figure 7c). after 72 h, we found a mild, although significant, increase in cell death after atcc cdt lysate administration (figure 7d), observing a decrease in dead cells in nc and cenc pretreated samples. in agreement with our previous research [34,38,39,63] and literature [64–67], the type and timing of cdt-induced cell death depend on the cell type, requiring at least 24 h to be observed. figure 7. in the green square, % dead cells in physiological condition: (a) statistical histogram at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, nc; (b) statistical histogram at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, nc. in the red square, % dead cells in pathological condition: (c) statistical histogram at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc + cenc, and atcc + nc; (d) statistical histogram at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc + cenc, and atcc + nc; one-way anova with bonferroni’s multiple comparison test revealed significant differences (*p < 0.05, **p < 0.01, ***p < 0.001). characterization and application of nanomaterials 2024, 7(2), 6414. 16 3.5.2. short term analyses of subcellular effects: 24 h we evaluated intracellular ros levels, mainly hydrogen peroxide, as shown in figure 8a,c. since mitochondria are one of the main producers of ros, we contemporary assessed the mmp (figure 8b). ht-29 intestinal cells slightly decrease mmp to a similar extent after nc and cenc treatment, in both groups, i.e., with and without cdt-containing lysate exposure (figure 8,d). cellulose conditioning slightly decreases mmp, to a similar extent for control and cdt-poisoned cells (figure 8b,d) [68]. indeed, the possible impact of nanocellulose on mmp has been reported by ventura et al. [69], describing the entry of nanoparticles and nanofibers into the mitochondrial outer membrane, causing an initial disturbance in mitochondrial activity [70]. figure 8. in the green square, the status of mmp and ros levels in physiological conditions: (a) statistical histogram of ros levels at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc; expressed as fold of change of treated cells/ctrl cells of dcf mfi; (b) statistical histogram of mmp levels at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc.; expressed as fold of change of treated cells/ctrl cells of tmre mfi in the red square, the status of mmp and ros levels in pathological conditions; in the red square, the status of mmp and ros levels in pathological condition: (c) statistical histogram of ros levels at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc+cenc, and atcc+nc; (d) statistical histogram of mmp levels at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc+cenc, and atcc+nc. one-way anova with bonferroni’s multiple comparison tests revealed significant differences (*p < 0.05, **p < 0.01, ***p < 0.001). characterization and application of nanomaterials 2024, 7(2), 6414. 17 finally, autophagic-like vesicles, labelled by means of an mdc probe, did not show any relevant modifications among cenc, nc, and the untreated cells during short-term analyses (figure 9a). to evaluate the autophagic features, we coupled lysosomal network detection to intracellular vesicle determination by means of ltdr and aj2nbd (a new patented dye), respectively, in both nc and cenc-treated cells, with and without cdt infection (figure 9). cytometric data report conditions similar to control cells in nc and cenctreated cells, both for autophagosomes (figure 9a) and lysosomes (figure 9b). in figure 9c, the aj2nbd labelling highlights only a slight but significant decrease in atcc-treated ht-29 cells. contemporary findings showed that the atcc cdt lysate induced an accumulation of autophagic-like vacuoles (figure 9a,d). in pathological conditions, treatment with nc appears to weakly and significantly counteract the effects of cdt. statistical histograms revealed that the lysosomal compartment decreased after atcc cdt administration; on the contrary, nc conditioning limited this phenomenon (figure 9e). vesicular trafficking does not appear altered in nc and cenc samples (figure 9f). confocal images of aj2nbd and ltdr co-labelling show a similar distribution of green vesicles in untreated cells and cells treated by cenc and nc (figure 9g, upper). after atcc conditioning, clustered and perinuclear green vesicles are visible, and ltdr red fluorescence almost disappears; indeed, no colocalization is appreciable (figure 9g). of note, as quantified by flow cytometry, cenc and nc pretreatment rescue cells from lysosome acidity loss, and yellow fluorescence (merging green and red organelles) suggests a priming of the ajnbd+ vesicles towards lysosomal features. characterization and application of nanomaterials 2024, 7(2), 6414. 18 figure 9. in the green square, the status of lysosomal and vesicular compartment in physiological conditions: (a) statistical histogram of autophagic-like vacuole at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc; expressed as fold of change of treated cells/ctrl cells of mdc mfi; (b) statistical histogram of the lysosomal compartment at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc; expressed as fold of change of treated cells/ctrl cells of ltdr mfi; (c) statistical histogram of vesicular compartments at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc.; expressed as fold of change of treated cells/ctrl cells of aj2nbd mfi; in the red square, the status of lysosomal and vesicular compartment in pathological conditions: (d) statistical histogram of autophagic-like vacuole at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc; (e) statistical histogram of the lysosomal compartment at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc; (f) statistical histogram of vesicular compartments at 24 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc + cenc, and atcc + nc. one-way anova with bonferroni’s multiple comparison tests revealed significant differences (*p < 0.05, **p < 0.01, ***p < 0.001); (g) confocal images of aj2nbd (green) and lysotracker deep red (ltdr, red) fluorescence on ht-29 untreated cells (ctrl), cells in physiological condition treated with cenc, nc, atcc, and cells in pathological condition atcc + cenc and atcc + nc after 24 h of treatments. characterization and application of nanomaterials 2024, 7(2), 6414. 19 3.5.3. long term analyses of subcellular effects: 72 h after 72 h, ros levels demonstrated a significant reduction between untreated, control, and atcc-cdt-infected cells. unexpectedly, cenc-atcc samples (figure 10) revealed ros rising at 72 h, whereas no increase in ros was detected in nc-atcc-infected ht-29 cells. this finding propelled us to consider the properties of coffee [71,72]. it is known that coffee exhibits antioxidant and pro-oxidant properties [73]. coffee varieties also influence the antioxidant/pro-oxidant capacities. several bioactive molecules are present in coffee; among these, caffeine displays significant antioxidant activity, protecting membranes from oxidative damage [74] at millimolar concentrations, whereas there is no antioxidant activity present in caffeine at micromolar concentrations [75]. furthermore, it is important to consider that the coffee traces act directly on intestinal cells without the insertion of an oral phase (as normally happens in the case of regular coffee consumption). our data appear in agreement with [76], describing the prooxidative action of regular coffee samples during the intestinal phase. figure 10. in the green square, ros levels and mmp in physiological conditions: (a) statistical histogram of ros levels at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc and nc; expressed as fold of change of treated cells/ctrl cells of dcf mfi; (b) statistical histogram of mmp levels at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc, and nc; expressed as fold of change of treated cells/ctrl cells of tmre mfi. in the red square, ros levels and mmp in pathological conditions: (c) statistical histogram of ros levels at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc + cenc, and atcc + nc; (d) statistical histogram of mmp levels at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc + cenc, and atcc + nc. oneway anova with bonferroni’s multiple comparison tests revealed significant differences (*p < 0.05, **p < 0.01, ***p < 0.001). characterization and application of nanomaterials 2024, 7(2), 6414. 20 mmp highlighted a different response after cenc and nc administration in physiological conditions: a decrease and an increase, respectively (figure 10). the pathologic condition panel highlights cenc and nc being able to lower the mmp rise induced by atcc: the decrease is mild and not significant in cenc samples and more relevant and significant in nc samples. autophagic-like vesicles, actors of the autophagic process strictly linked to mitochondrial functions and ros production [77], are traced by mdc labelling and quantified by flow cytometry. our data did not point out any significant difference between the control, cenc, and nc samples; of note, the mfi increase observable in atcc cdt-treated cells is reduced by both cenc and nc conditioning, reaching values like controls (figure 11a,d). figure 11. in the green square, the status of lysosomal and vesicular compartment in physiological conditions: (a) statistical histogram of autophagic-like vacuole at 72 h on ht-29 untreated cells (ctrl), atcc treated cells cenc and nc; expressed as fold of change of treated cells/ctrl cells of mdc mfi; (b) statistical histogram of the lysosomal compartment at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc and nc; expressed as fold of change of treated cells/ctrl cells of ltdr mfi; (c) statistical histogram of vesicular compartments at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc and nc; expressed as fold of change of treated cells/ctrl cells of aj2nbd mfi; in the red square, the status of lysosomal and vesicular compartment in pathological conditions; (d) statistical histogram of autophagic-like vacuole at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc and nc; (e) statistical histogram of the lysosomal compartment at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, cenc and nc; (f) statistical histogram of vesicular compartments at 72 h on ht-29 untreated cells (ctrl), atcc treated cells, atcc + cenc, and atcc + nc. one-way anova with bonferroni’s multiple comparison tests revealed significant differences (*p < 0.05, **p < 0.01, ***p < 0.001). characterization and application of nanomaterials 2024, 7(2), 6414. 21 we found significant differences for nc and cenc treatments in physiological conditions for lysosomes (ltdr mfi): both nanocellulose conditioning induced a relevant decrease compared to control and atcc cdt-treated samples (figure 11b,e). given the high interconnectivity of endosomal, lysosomal, and autophagosomal pathways, dysfunctions in one of these systems may trigger alterations in another [78]. briefly, the more acidic vacuoles, such as lysosomes, progressively decreased, from 24 h to 72 h in each atcc cdt-treated sample, whereas after cenc treatments we observed an initial lysosome number/function increase (at 24 h), followed by a subsequent decrease (at 72 h). this finding is in agreement with other researchers [79,80] at least for the bioactive compound caffeine. regarding non-acidic vacuoles targeted by aj2nbd, a drop was detected after the 72 h treatment with atcc, whereas cenc and nc seem to contribute, at any time points, to restoring the vesicle compartment (and trafficking) altered by atcc cdt (figure 11c,f). the following scenario emerges from the data: i) after 24 h, nc and cenc treatments did not produce any relevant and significant modification; ii) atcc-treated cells, as expected, revealed perturbations in the autophagic flux (increased autophagolysosomes and decreased acidic, mature lysosomes); iii) cenc and nc preconditioning restored autophagic vacuoles to the values of control cells, revealing a partial improvement of the perturbed autophagic flux. 4. discussion and conclusion nanocellulose in food packaging applications, like any other food contact material, raises potential safety concerns [81]. several review studies on nc have shown that toxicity studies remain scarce and knowledge gaps remain. studies of nanocellulose exposure in various in vitro cell lines and animal models are limited, and no evidence of significant toxicity has been found [82], but certain studies have shown diverging results [83]. our study is then useful to identify the properties of coffee-embedded nanocellulose and nanocellulose from coffee pods in an in vitro model represented by ht-29 intestinal cells. the in vitro toxicological endpoints evaluated in this study consider cell death, ros production (often an early precursor of cytotoxicity), mitochondria membrane potential, lysosomes, and autophagosomes. these approaches allowed to detect: i) mitochondrial damage, a crucial event in particulate matter (pm)-induced cytotoxicity [84]; ii) lysosomal network impairment; and iii) endosome and autophagosome alteration. in fact, endocytosis and autophagy are two major pathways for cellular homeostasis, and although endosomal and autophagy are discrete pathways, there is extensive crosstalk between these vesicular compartments. the initial response to pm is a decrease in mitochondrial membrane potential and increased oxygen radical production, followed by inner mitochondrial membrane damage [85]. our data reveal a mild decrease in mmp of cenc-treated cells after 72, but with cdt administration, mmp restores to the control level. these findings confirm that, also in our model and at the massive concentrations employed, both cenc and nc are non-cytotoxic. furthermore, the three different interrelated intracellular vacuole/vesicle compartments analysed highlight the improvement of the characterization and application of nanomaterials 2024, 7(2), 6414. 22 autophagic flux due to cenc and nc conditioning, suggesting the increase of nonacidic vacuoles (i.e., endosomes). in conclusion, the micro/nanoscaled cellulose in both cenc and nc formats from coffee pods does not significantly impact the viability and functions of ht-29 intestinal cells but does indeed improve the viable status and endosomal compartment after c. jejuni cdt intoxication. however, results obtained from in vitro studies cannot often be used directly to predict the biological responses of organisms to chemical exposure in vivo. therefore, further studies are needed, including chronic in vivo feeding studies and assessments of other potential endpoints. supplementary materials: figures s1 and s2 can be downloaded at supplementary material. author contributions: conceptualization, bc, mm and dl; methodology, dl, mm, bc, gp, mg, pg, lv, em and dp; validation, dl, gp, mm and bc; formal analysis, dl, bc and mm; investigation, dl, bc, gp, em and mm; resources, vf, sp and bc; data curation, dl, gp, mm, bc, lv and mg; writing—original draft preparation, dl, mm, bc and gp; writing—review and editing, dl, pg, mg, vl, em, bc and mm; visualization, bc and dl; supervision, bc, dl and mm; project administration, bc and dl; funding acquisition, vf, sp and bc. all authors have read and agreed to the published version of the manuscript. acknowledgments: we want to thank ctsv for providing us the newly developed medimachineii, medicons, foodcons and filcons and to have supplied foodcons by their early days of marketing. we want to acknowledge doctor caterina ciacci for her excellent assistance for confocal microscope analysis. conflict of interest: the authors declare no conflict of interest. references 1. athinarayanan j, periasamy vs, alsaif ma, et al. presence of nanosilica (e551) in commercial food products: tnfmediated oxidative stress and altered cell cycle progression in human lung fibroblast cells. cell biology and toxicology. 2014; 30(2): 89-100. doi: 10.1007/s10565-014-9271-8 2. gómez hc, serpa a, velásquez-cock j, et al. vegetable nanocellulose in food science: a review. food hydrocolloids. 2016; 57: 178-186. doi: 10.1016/j.foodhyd.2016.01.023 3. khare s, deloid gm, molina rm, et al. effects of ingested nanocellulose on intestinal microbiota and homeostasis in wistar han rats. nanoimpact. 2020; 18: 100216. doi: 10.1016/j.impact.2020.100216 4. onyango c, unbehend g, lindhauer mg. effect of cellulose-derivatives and emulsifiers on 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toxicity of silver nanoparticles in vitro: a mitochondrial perspective. toxicology in vitro. 2011; 25(3): 664-670. doi: 10.1016/j.tiv.2011.01.004 microsoft word can-4898 online characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.4898 1 editorial editorial for characterization and application of nanomaterials (volume 6 issue 1) amir hatamie1,2,† 1 department of chemistry, institute for advanced studies in basic sciences, zanjan 999067, iran. e-mail: amir.hatami@iasbs.ac.ir 2 department of chemistry and molecular biology, university of gothenburg, 40530 gothenburg, sweden. † editor of characterization and application of nanomaterials nanomaterials stand as transformative elements across diverse domains, ranging from biotechnology, aircraft, aviation, and space exploration to medicine, health, environmental preservation, resources, energy, and aerospace[1]. this issue, comprising nine original research articles and two insightful reviews, we embark on a journey to unravel the multifaceted uses of nanomaterials, with a special emphasis on their contributions to environmental protection and medicine. delving into the unique traits of various nanomaterials, our aim is to provide readers with a comprehensive understanding that transcends conventional boundaries, fostering a deeper appreciation for the impact of nanomaterials. nowadays, the relentless growth of industries has inadvertently ushered in a surge of pollutants into the environment, sparking a range of environmental issues, from air and water pollution to soil contamination[2]. the consequences are dire for both human health and the delicate balance of the natural environment. responding to this urgent need, nanomaterials have emerged as pivotal players in the remediation of environmental pollutants, capitalizing on the advancements in nanotechnology[2]. their superiority lies in the abundance of active sites and a vast specific surface area, setting them apart from standard materials and positioning them as potent tools in the fight against pollution[2]. notably, in this collection, bellucci[3] showcased the prowess of graphene nanoplatelets in cleansing surface water, offering a glimpse into the potential of nanomaterials for environmental sustainability. furthermore, shanmugam et al.[4] shed light on the remarkable sustainability of cnf, attributing it to its potential in the circular economy, presenting an ecofriendly alternative to synthetic plastics. their insights pave the way for replacing synthetic packaging materials with cnf, marking a significant stride towards sustainable practices. in the realm of medicine, bahramifar et al.[5] underscore the substantial promise of nanomaterials in creating efficient and low-impact anticancer drugs. their exploration of suitable carrier systems for anticancer proteins, such as azurin, opens avenues for developing treatments with minimal side effects. these findings accentuate the potential of nanomaterials in revolutionizing healthcare. diving deep into the workings, one paper meticulously examines article info received: 6 june 2023 available online: 30 june 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterial is published by en-press publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 the structure and properties of the nanomaterial pmma, offering invaluable insights for researchers in related fields. despite the widespread use of nanomaterials and their exceptional capacity to address diverse issues, the realm of nanomaterial research remains an ever-evolving landscape, brimming with possibilities and discoveries. in conclusion, we extend our warm appreciation to all the authors who have graciously permitted us to share their invaluable research achievements. together, let us continue to explore the uncharted territories of nanomaterials, where innovation converges with sustainability, shaping a future of endless possibilities. conflict of interest the author declares no conflict of interest. references 1. chinese academy of sciences. definition, characteristics, and application prospects of nanomaterials (chinese) [internet]. beijing: chinese academic of science [cited 2023 dec 20]. available from: https://www.cas.cn/zt/kjzt/kpf/xcl/200307/t20030 704_1711355.shtml. 2. the application of nanomaterials in environmental governance (chinese) [internet]. beijing: sohu.com [updated 2019 dec 4; cited 2023 dec 20]. available from: https://www.sohu.com/a/358244731_229957. 3. bellucci s. decontamination of surface water from organic pollutants using graphene membranes. characterization and application of nanomaterials 2023; 6(1): 2033. doi: 10.24294/can.v6i1.2033. 4. shanmugam k, chandrasekar n, balaji r. water vapor permeability of smooth cellulose nanofiber film prepared via spraying. characterization and application of nanomaterials 2023; 6(1): 2068. doi: 10.24294/can.v6i1.2068. 5. bahramifar s, baharifar h, maghami p. enhancement of anticancer effect of azurin using polymeric nanoparticles. characterization and application of nanomaterials 2023; 6(1): 2306. doi: 10.24294/can.v6i1.2306. characterization and application of nanomaterials (2018) volume 1 doi:10.24294/can.v1i2.495 1 nanotransformations in the blanket of materials at the combined processing by untied granules v. p. smolentsev1, a. v. kuzovkin2 1 voronezh state technical university, 14, moskovsky avenue, voronezh, 394026, russia e-mail: vsmolen@inbox.ru abstract summary: nanotransformations of a blanket at the fair dimensional combined processing with imposing of electric field the tool in the form of untied metal granules are considered. an object of researches are the figurine details applied in aviation, the missile and space equipment and in the oil and gas industry: driving wheels and a flowing part of cases of turbo-pump units, screws, krylchatka where there are sites of variable curvature with limited access of the tool in a processing zone. it is shown that the combination in the combined process of two-component technological environments of current carrying granules and the electroconductive liquid environment given with a high speed to a processing zone allows to receive the required quality of a blanket; action of electric field from a source with the increased tension allows to create at fair dimensional processing the required peening from blows of firm granules. it gives the chance to raise a resource and durability of responsible knots of the aerospace equipment and oil and gas equipment, to expand the field of use of the combined processing with untied granules on a detail with the sites not available to processing by a profile electrode. keywords: the combined processing; untied granules; the two-component environment; the mechanism of management 1. introduction in aviation and the missile and space equipment is available details spoluzakryty cavities which are difficult for processing the profile tool. in cavities it is necessary to develop the modes and ways for obtaining the required quality of a blanket [1, 2], the providing directed nanotransformations of properties of materal of details in the course of the combined processing. for this purpose follows at fair processing in a blanket of material to carry out the nanotransformations providing a surface roughness within ra=0,32-0,63 of a micrometer and squeezing internal residual tension in detail material. mechanism of formation of microroughnesses the combined processing with a filler, irrespective of the used scheme, is intended for finishing operations of formation of a blanket of a detail, i.e. at that stage of technological process when there is a formation of characteristics of quality of the processed surface of a detail including on a nanolevel. the firm granules which are a part of a liquid component of the technological environment are the tool which, having considerable energy, makes decrease in microroughnesses of a surface and creation of internal microtension. these factors considerably define operational indicators of a detail. the blanket is characterized by two key parameters: a roughness of a surface and physicomechanical properties which have significant effect on wear resistance, durability, resistance to fatigue and sign-variable loadings and other similar factors. 2. technique of researches the research of a condition of a blanket was made by a standard technique and consisted in a research of samples by means of production of cross mikroshlif of the processed surfaces. mikroshlifa were exposed to special chemical processing and etching for identification of structure of material and to their further studying on optical and electronic microscopes. besides, on samples, in the location of a near-surface layer with the changed structure and copyright © 2018 v. p. smolentsev et al. doi: 10.24294/can.v1i2.495 enpress publisher llc.this work is licensed under the creative commonsattribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 hardness the measurement of microhardness by introduction of indentor on slanting cuts was made. the condition of a blanket of a detail in case of influence of all technology factors was originally determined (the combined processing by the scheme with anode dissolution of a surface of a detail and its plastic deformation of a firm component of a working environment): anode dissolution of material of preparation and removal of a hereditary layer and simultaneous hardening of a surface of a firm component of a working environment. the surface condition after processing can be estimated by several characteristics: the size of microhardness and depth of its bedding, character of residual tension, a roughness of a surface and structure of material in a near-surface layer, i.e. in that layer which perceives the main electrochemical and mechanical influences of a two-component working environment. 3. discussion of results of researches researches showed that the greatest influence on process of formation on a nanolevel of a blanket of a detail is played by parameters of the movement of a filler and its physicomechanical properties. metalgraphic researches revealed at the changed layer from 4 to 12 microns in depth with the maximum peening directly at the upper bound of this layer is model. photos of mikroshlif of the studied samples before processing are presented in fig. 1. various materials having a different hereditary blanket were subjected to processing. besides, conditions and the modes of processing varied. the sample from steel 40xh2ma (fig. 1, a and b) was received by draft milling and will subject to elektrokhimikomekhanichesky processing (ehmp) at more "rigid" modes: granules of a filler were made of steel 45 by the size d = 5 mm; concentration in mep 25 30%; electrolyte 15% nacl solution; the scheme of giving of granules told them high kinetic energy – about 10 m/s (calculated value); working tension on electrodes 75 v; the general distance from a hydraulic element to a detail surface 50 mm; processing time, as well as in the previous case made 40 seconds. in photos of mikroshlif (fig. 1) on a nanolevel the uniform changed superficial microlayer of metal of which more dense arrangement of grains of material is characteristic is clearly visible. measurement of microhardness showed its increase due to mechanical influence of a filler up to hrce value 43.5 that above than at preparation where this indicator makes 35.5 hrce. change of microhardness of a blanket of a detail proves formation in it internal, and as by us it was established – the squeezing microtension. at boundary, greatest possible at the used schemes of processing and the equipment, the processing modes (the photo on rice 1; 2, a, b), the size of a peening made un  of 22,5% at the general depth of hn of 10 microns. the maximum of a peening is observed at its upper bound. the sample presented in fig. 1 c and d, was made of steel 38h2mya, and fair milling was the previous operation of machining. at its processing "the soft modes" were used: diameter of the granules of a filler made of the most widespread steel 45, equaled 5 mm; their concentration in a total amount of a working environment 25 30%; as electrolyte fifteen percentage solution of chloride of nacl sodium were used; granules moved to the processed surface with the rated speed of 5 m/s; working tension on electrodes 50 v; size mep 50 mm; time of processing of the area of a detail equal to an effective spot made 40 seconds. mikroshlify of this sample reflect existence of the strengthened layer with depth of hn ≈ 4,5 microns and un  13,5%. on a surface of a detail there are no microcracks and a mikrorastravlivaniye on borders of grains in the strengthened layer. it demonstrates presence of the squeezing residual tension which increases the fatigue durability of a detail. the performed measurement of microhardness, showed that unlike not changed state (34.5 hrce) it increased due to processing up to the size of 39.5 hrce. a b 3 c d figure 1: results of a research of a blanket of the detail subjected to elektrokhimikomekhanichesky processing with use of a filler and imposing of electric field: a steel 40xh2ma before processing (increase by 200 times); b steel 40xh2ma after processing (increase by 200 times); c, d steel 38h2mya after processing (increase in 200 and 320 times) the research of an external surface of the samples characterized earlier at various sizes of an interelectrode interval (mep) was made for visual assessment of results of the combined processing with use of a firm conducting filler. photos of an external surface of samples from steel 38h2myua are presented in fig. 2. the appearance of a surface of samples from steel 40xh2ma received at change of size mep from 40 to 70 mm is given in fig. 3, other technological modes of processing when carrying out an experiment did not change. the analysis of these surfaces allows to draw a conclusion that when processing with a filler there is no rastravlivaniye on borders of grains of material of a detail. some decrease in size of a roughness of a surface of a detail at increase in mep can be explained with decrease in amount of total energy of the working environment participating in a shaping. similar experiments were made for other processed materials. figure 2: shlif is exemplary from steel 38h2myaafter ehmp at various sizes mep: a – size mep is 35 – 40 mm; b – size mep – 70 – 75 mm (increase in 300 times) figure 3: shlifa of samples from steel 40xh2ma after ehmo at various sizes mep: a – size mep is 40 42 mm; b – size mep – 70 71 mm (increase in 300 times) 4. conclusion to the main scientific results, the received authors, it is necessary to carry: elements of the theory of nanotransformations and the method of a dimensional shaping based by complex influence on a nanolevel of the electric field providing electrochemical dissolution of nanolayers of an allowance, and untied granules of the tool; а а 4 justification of influence of the dimensional combined processing with a filler on change of nanostructure of a blanket of a detail that provides high-quality preparation of a surface under anode removal of an allowance at achievement of the set characteristics of quality of a blanket providing increase in operational properties of products; the practical value of researches consists in: 1. creation of process of the dimensional shaping of details of conducting materials which allowed to expand the field of technological use of electrochemical processing with a firm conducting filler on a dimensional shaping of surfaces of various profile, remote for the tool. 2. implementation dimensional a shaping of details of difficult geometry with obtaining the required characteristics of quality of a blanket that gives the chance to raise operational characteristics of products. 3. creation of technological processes of a dimensional shaping of the surfaces, remote for the integral tool, which allowed the technologist to the mechanician to expand the knowledge base on ehmo with a firm conducting filler. 4. implementation of the technology solution of a problem of dimensional processing of surfaces of the details located under a negative corner to an axis of symmetry of a stream of a working environment (the patent of russia[1]) and thin-walled details (the patent of russia[2]). references 1. patent of russia no. 2166417. the device for the combined electroprocessing /смоленцев вп, kuzovkin av, boldyrev ai, smolentsev gp//byul.izobr., 2001, no. 13. 2. patent of russia no. 2072281. a filler granule for the combined electroprocessing /смоленцев вп, boldyrev ai, kuzovkin av//byul.izobr., 1997, no. 3. characterization and application of nanomaterials (2019) volume 2 issue 1 doi:10.24294/can.v2i1.552 1 a study on the oxygen percent and the crystalline structure of silver nanoparticles obtained by electrochemical method s. s. parhizgar, s. sibouyeh plasma physics research center, science and research branch, islamic azad university p.o. box p. o. box: 14665-678, tehran, iran abstract in this paper silver nanoparticles (nps) which are synthesized by a simple plasma arc discharge method, that is a kind of electrochemical methods, are examined. the method is very simple and silver nps are obtained very fast by means of two polished silver plates and electrochemical cell. the effects of changing some terms of the experiment including using hydrogen peroxide (h2o2), temperature and the medium of experiment on oxygen percent and crystalline structure of silver nps have been studied by transmission electron microscopy, uv-visible spectrophotometery, and x-ray diffraction. water medium gets larger nanoparticles with less oxygen content compare to air medium. the size of synthesized nanoparticles become smaller and they also become more spherical by using h2o2in air medium. in water medium, the size and concentration of the silver crystallite increase by temperature growth and adding h2o2 respectively. keywords:silver; nanoparticles; h2o2; electrochemical method. 1. introduction metal nanoparticles have often been studied and used in the different areas of nanotechnology[1, 2]. nanoparticles (nps) have a larger surface area than macro sized materialstherefore they have distinct properties in comparison with the bulk form of the same materials. nps are being used in the field of biosensors, biomedicine and also diagnosis, drug delivery and treatment for many diseases[3]. a lot of studies carried out in the last three decades show that silver nps have valuable properties namely unique optical properties associated with the surface plasmon resonance (spr), well developed surfaces, catalytic activity, high electrical double layer capacitance, etc. in particular, silver nps are being used in the development of new generation of electronic, optical and sensor devices[4]. it should be noted that the colloidal silver has attracted more attention because of different properties such as good conductivity, chemical stability, catalytic and antibacterial activity. moreover, it has been shown that the growing small particles of silver are more effective catalysts than stable colloidal particles[5]. the reduction rate catalyzed by them could be noticeably faster than the stable and larger silver nps which are the final products of growing particles. overall, it can be said that the catalytic activity of silver nps is dependent on their size[5]. furthermore silver nps are used for purification and quality management of air, coating for solar energy absorption, imaging, intercalation material for electrical batteries, as optical receptors, for bio labeling[6] and cancer treatment[7]. a lot of methods have been tried to obtain silver nps with various shapes and sizes, like photochemical method[8,3], electron irradiation[9], laser ablation[10], microwave-assisted[11], electrochemical and etc. in most of these methods, the size of particles obtained cannot be controlled easily and because the process demands stabilizing agents and also lots of materials, is not simple. particles obtained by the electrochemical methods have high purity and their size can be controlled easily without using expensive equipment. among these methods, the copyright © 2019 s. s. parhizgar et al. doi: 10.24294/can.v2i1.552 enpress publisher llc.this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 one that the current search is based on it[1], results in long-lived silver particles without using stabilizing agents in the process of electrochemical. the method is very simple and there are not a lot of terms to adjust, so the effect of some terms of the experiment including i: using hydrogen peroxide (h2o2), ii: temperature and iii: reaction in water medium or in air medium on results were analyzed. 2. experimental 2.1 materials and set up the simple set up for the arc plasma method was used for producing silver nps. the system was made up of two electrodes in two electrochemical cell medium (distilled water or air). the anode and the cathode were two polished silver plates (80mm ×10mm ×1mm) and they were vertically placed face to face, 10mm apart. it should be mentioned that the electrolysis performed at a constant voltage. in water medium, a magnetic stirrer was used for intensive stirring during the process of electrolysis to prevent the precipitates. 2.2 methods and analysis the products were analyzed after each experiment to check the effect of changing conditions on the products, as follow: (1) at first experiment, the electrochemical cell was without water, the voltage was 22v which was turned off after 30 minutes. after that, the electrochemical cell was filled with 50ml distilled water. the solution was filtered by means of a 3μm filter paper (sample 1a) and then 3 drops of h2o2 was added to the solution (sample 1b). before adding h2o2, a gray solution obtained and after adding h2o2, the solution became so lucid and large particles in solution disappeared. (2) in the second experiment, electrolysis was performed with 50ml distilled water in the temperature range 70-80 °c at the constant voltage of 22v. the polarity of the direct current was constant and the process continued for 30 minutes. after filtering (sample 2a) 3 drops of h2o2 was added to the solution (sample 2b). (3) the third experiment was done with 50ml distilled water in the room temperature at a constant voltage of 22v. in this sample h2o2 was not used (sample3). finally the absorbance spectrum of the samples was measured by a varian cary-500 spectrophotometer at room temperature. the nps crystal structure was measured by x-ray diffraction (xrd) (a stoe with cu-kα radiation). transmission electron microscopy (tem) (leo-912-ab) with resolution 700kx and philipsem 208(100 kv) with resolution 200 kx analysis was used to estimate the size and shape of the nps in solution. 3. results and discussion the effect of temperature, using h2o2 and some other terms on the size of silver nps were studied in previous work[1]. in this paper, the main concern was to examine the effect of h2o2, temperature and experimental medium on the oxygen percent and crystallites of obtained silver nps. after the first experiment a very dark solution (sample 1a) which was containing a lot of microand nano-particles obtained. so it had to be filtered. after filtering, 3 drops of h2o2 was added to the solution and the color of that changed to yellow immediately (sample 1b). figure 1 shows the tem images of nanoparticles of sample 1a and 1b .the size of nps in sample 1a is about 230 nm and in sample 1b is about 25nm. it is obvious that in sample 1b by adding h2o2 particles became smaller and spherical. 3 figure 1.tem image of sample 1a (left) and sample 1b (right). the optical density was measured immediately after the experiment and also one week later. sample 1 doesn't showplasmonpeak which indicates it doesn't behave as metal. according to optical density results of sample 1, nanoparticles have more absorbance on the day of doing the experiment, because they were distributed in all over the solution.after one week, the nanoparticles stick to each other and deposit. figure 2. xrd analyze of sample 1a (up) and sample 1b (down). figure 2 shows xrd patterns of sample 1a and 1b. in this figure, ag2o(111) peak is clear[12, 13]. the average size of nanocrystals was estimated by the scherrer equation. the average size of crystallitebefore adding h2o2 have been calculated 30.6nm and after that 23nm. so xrd analysis results show that by adding h2o2 the size of crystallitedecreases. before adding h2o2, the average size estimated by xrd patterns was smaller than what tem images showed, but after adding h2o2, xrd results are in common with tem images. these results show that by adding h2o2, nanoparticles nearly reduction to single crystallite.increasing xrd peakintensity of sample 1b indicatesthe crystallite concentration increases in this sample. according to the tem analyze the average size of nanoparticles in sample 2b was about 102nm (fig. 3). blackcore and gray shell seen in this image indicate twocompounds in the nanoparticles with twodensities.ag and agxo makethe core and the shell of this nanocomposite respectively. 4 figure 3. tem image of sample 2b. the optical density of sample 2a and 2b are presented in figure 4 as it is shown in these curves, sample 2b plasmon peak is narrower and stronger than sample 2a, because the particles were sticking to each other and did not exist in all over the solution before adding h2o2, and adding h2o2 caused smaller particles with uniform distribution. the plasmon peak of these samples appears at 450nm; peak position could be changed by increasing size, increasing geometrical anisotropy, decreasing the metallic character of nanoparticle[14];thenpeak position of sample 2 influenced bywith hexagonal shape of diameter 100nm and oxide shell. figure 4. optical density of sample 2a (left) and 2b (right). figure 5 presents the xrd patterns of samples 2a and 2b, respectively. this fig. shows ag(111) diffraction peak. more intensity ofag(111) peak after adding h2o2 deduces ag crystallite concentration increase in solution which is indicated by increasing absorption by adding h2o2in fig. 4. due to scherrer equation, the size of crystallite calculated is about 25.8 nm. 5 figure 5. xrd analyze sample2a (up) and 2b (down). sample 3 was a colloidal solution. it is obvious in fig.6, that this solution has the least absorbance among all, because after synthesis, most of nanoparticles are aggregate and deposited. figure 6. optical density of sample 3. figure7 presents xrd pattern of sample 3. this figure shows ag(111) diffraction peak. the size of suspend nanoparticles, according to scherrer equation was about 11.7nm. in sample 3, by decreasing the synthesis temperature, the ag(111) diffraction peak width increased that confirms crystallite of silver decline, in every nanoparticle. 6 figure 7. xrd analyze of sample 3. the difference between oxygen stoichiometry can be resulted by changing in cell medium. plasma arc in water medium prevents more oxidation in sample 2&3 compare to sample 1, that plasma arc was done in air medium. additionally increase of the plasmon peak intensity in sample 2b compare to sample 2a shows monodispersity of nanoparticles in sample 1b that caused by adding h2o2. 4. conclusions in this work silver nps obtained by plasma arc method. the main goal of this paper was to observe the effect of changing the experimental medium, using h2o2 and temperature on the crystalline structure and oxygen percent of silver nps. synthesis of nanoparticles at water medium in comparison with the air medium leads to less oxygen content in ag nanoparticles. by adding h2o2 to nanoparticle solution theaverage size of particles decrease and get monodispersed solution. after adding h2o2 to solutions that were prepared in water medium, nanoparticles cannot have spherical shape like nanoparticles that prepared in air medium. adding h2o2 also increased thenanoparticle concentration withmore crystallite. the average crystalline size that resulted from xrd smaller in comparison with the average size that was measured by tem, clear the resulted nanoparticle are not single crystallite. besides xrd analysis demonstrates that in higher temperature the silver crystallites are bigger. references 1. khaydarovra, khaydarovrr, gapurovao, et al. 2009; 11, 1193. 2. sudeeppk, kamatpv, chem. mater. 2005; 17, 5404. 3. h.yin hsu, nnin reu research accomplishments, 2004; 68. 4. prikhozhdenkoes, lengertaev, parakhonskiybv, et al. acta physica polonicaa. 2016; 129,247. 5. asheb, thesismsc.national institute of technologyrourkela, india, (2011). 6. hengleinchema. mater.1998; 10, 444. 7. manshianbb, advanced healthcare materials 2017;6, 1601099. 8. lihx, linmz, houjg,journal ofcrystalgrowth.2012;212, 222. 9. hettiarachchima ,wickramarachchipasr,scij. univ.kelaniya.2011;6, 65. 10. the binhn, thi lyd,thi huen, et al.vnu journal of science. 2008;mathematics – physics 24. 11. wangb, zhuangx, dengw, et al.engineering.2010; 2, 384. 12. polvg, srivastavadn, palchiko, et al.langmuir.2002;18, 3352. 13. hong-liangf, xiao-yongg, zeng-yuan z. et al. journal of the korean physical society.2010;56, 1176. 14. amendolav, osman m, bakr f. stellacci, plasmonics.2010; 5, 85. characterization and application of nanomaterials 2025, 8(2), 10951. https://doi.org/10.24294/can10951 1 article sers characterization of rhodamine 6g dye molecule response using thin gold film covalently immobilized with gold nanourchins mohammad e. khosroshahi1,2,3,*, yesha patel1,4, christine gaoiran1, vithurshan umashanker1,5 1 nanobiophotonics & biomedical research laboratory, m.i.s. electronics inc., richmond hill on l4b 1b4, canada 2 institute for advanced non-destructive and non-invasive diagnostic technologies (iandit), university of toronto, toronto on m5s 3g8, canada 3 department of mechanical and industrial engineering, university of toronto, toronto on m5s 3g8, canada 4 department of biochemical engineering, university of waterloo, waterloo on n2l 3g1, canada 5 department of electrical and computer engineering, university of waterloo, waterloo on n2l 3g1, canada * corresponding author: mohammad e. khosroshahi, m.khosro@miselectronics.com, me.khosroshahi@gmail.com abstract: we report on the measurement of the response of rhodamine 6g (r6g) dye to enhanced local surface plasmon resonance (lspr) using a plasmonic-active nanostructured thin gold film (pantf) sensor. this sensor features an active area of approximately ≈ 2.5 × 1013 nm2 and is immobilized with gold nanourchins (gnu) on a thin gold film substrate (tgfs). the hexane-functionalized tgfs was immobilized with a 90 nm diameter gnu via the strong sulfhydryl group (sh) thiol bond and excited by a 637 nm raman probe. to collect both raman and sers spectra, 10 μl of r6g was used at concentrations of 1 μm (6 × 1012 molecules) and 10 mm (600 × 1014 molecules), respectively. ft-nir showed a higher reflectivity of pantf than tgfs. sers was performed three times at three different laser powers for tgfs and pantf with r6g. two pantf substrates were prepared at different gnu incubation times of 10 and 60 min for the purpose of comparison. the code for processing the data was written in python. the data was filtered using the filtfilt filter from scipy.signals, and baseline corrected using the improved asymmetric least squares (isals) function from the pybaselines.whittaker library. the results were then normalized using the minmax_scale function from sklearn.preprocessing. atomic force microscopy (afm) was used to capture the topography of the substrates. signals exhibited a stochastic fluctuation in intensity and shape. an average corresponding enhancement factor (ef) of 0.3 × 105 and 0.14 × 105 was determined for pantf incubated at 10 and 60 min, respectively. keywords: thin film; gold nanourchins; r6g molecule; sers; ft-nir; enhancement factor 1. introduction there has been a great interest in recent years in the potential applications of nanostructured materials in analytical chemistry, molecular biology, and biochemical analysis [1–3]. in contrast to rayleigh scattering, raman scattering is an inelastic process where photons undergo scattering, and the energy of molecular transitions is detected by measuring the change in wavelength or frequency shift of the scattered photons, typically analyzed using raman spectroscopy (rs). as a result, a chemical fingerprint of the sample is achieved for identification and quantitation. to be ramanactive, the molecular vibrations induced by an external electric field, such as a laser, should be able to induce a change in the polarizability of molecules within the sample, which gives rise to raman scattering. the intensity of scattered light varies with the change in the molecular polarization. raman shift is an intrinsic property of a molecule. by measuring the intensity of the scattered light as a function of frequency citation khosroshahi me, patel y, gaoiran c, umashanker v. sers characterization of rhodamine 6g dye molecule response using thin gold film covalently immobilized with gold nanourchins. characterization and application of nanomaterials. 2025; 8(2): 10951. https://doi.org/10.24294/can10951 article info received: 17 december 2024 accepted: 28 february 2025 available online: 3 april 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 10951. 2 shift in cm−1, one can obtain insights into molecular vibration. thus, it makes rs a powerful label-free and non-destructive analytical tool to distinguish biological constituents and conformation through their molecular vibrational modes. unfortunately, in the spontaneous raman, the stokes and anti-stokes scattering are so weak and inefficient that only about 1 in 107 photons can be detected, with a crosssection of ≈ 10−30 cm−2 . however, the efficiency can be improved using surfaceenhanced raman scattering (sers), which is an ultrasensitive, non-destructive optical technique that has been utilized for biosensing of analytes at very low concentrations in solutions or deposited as a monolayer on nanostructured metal substrates [4–7]. there has been increasing interest in developing advanced sers-based non-invasive point-of-care devices for clinical applications, particularly in the early diagnosis of cancer. this is because the advances in ultrasensitive instrumentation for sers and nanostructure-enhanced sers studies provide more accurate detection and identification of the analyte and vibrational spectrum of high information content for molecules in room-temperature colloids [1,8–11] and solid surfaces [12–16]. plasmonics is the study of how light interacts with charged particles, particularly electrons in metals. it primarily involves the excitation of electromagnetic modes when these particles are influenced by an external electric field 𝐸0 , leading to a collective oscillation of the conduction band electrons within the metal. in the case of thin metal film, the electronic charge density is delocalized called surface plasmon polaritons (spp), which are confined near the metal-dielectric interface, propagating over relatively large distance, for example, about 5–10 μm for gold. however, in the case of nps with subwavelength sizes, the oscillations are localized, called localized surface plasmon (lsp). gold, as a noble and the most non-reactive of all metals, has excellent corrosion resistance in moist air, resistance to oxidation, and catalytic characteristics, and is widely used in optical sensor applications. the optical properties of plasmonic nanoparticles (pnps) offer significant advantages, including considerable optical attenuation due to absorption and scattering associated with localized surface plasmon resonance (lspr) [17,18], nonlinear optical properties, surface-enhanced scattering, tunable resonance in the visible-nir range, low oxidation, time-dependent absorption, and biocompatibility. these properties are determined by nanoparticle size, shape, refractive index, and density of the surrounding environment [19–23]. normally, sers can be accounted for by two main mechanisms: (a) lsprinduced electromagnetic (em) field enhancement at the molecular positions due to coupling of enhanced local electric field 𝐸(𝜔𝑙) at frequency 𝜔 at the surface of the pnp caused by the induced dipole of plasmon oscillation to the incident field 𝐸0. the enhancement depends on the topology of the metallic film, the size and shape of the nps, and the strong light absorption and scattering that occur at the spr frequency; and (b) charge transfer (ct), i.e., a molecular chemisorption during which the electrons are transferred from the analyte molecules into the vacant levels on the metal surface. as a result, a new band forms in the electronic spectrum of the molecule due to the electronic excitation of the coupled molecule-metal surface. it is noteworthy that ct is limited to molecules adsorbed directly on the metal surface, whereas em effects can act as a nanoantenna to transfer the spr radiation over a certain distance from the characterization and application of nanomaterials 2025, 8(2), 10951. 3 origin. the enhancement is usually expressed as|𝐸(𝜔𝑙)|4/|𝐸0|4, but in more precise evaluations, the dipole reradiation term 𝐸(𝜔𝑟𝑒) specifically the raman emitted frequency is also included |𝐸(𝜔𝑙)|2|𝐸(𝜔𝑟𝑒)|2/|𝐸0|4 [24]. the resonant frequency of a pnp is dependent on its size, shape, material properties, and surrounding medium [15–24]. the sers intensity depends on several factors, including a) the type of substrate, as they react differently to sers; b) the type, shape, and the size of nanostructure as each plays a key role and responds differently; c) the type of analyte, as various molecules have different raman scattering, i.e., the greater the cross-section, the more intense the raman scattering; and d) an optical setup with a higher numerical aperture objective improves raman collection efficiency. uniformly distributed and self-assembled pnps can enhance raman scattering when introduced into a sample by increasing the number of hot spots or nanogaps, which effectively amplifies the electric field, leading to enhanced raman signal. among the various nanostructures with different geometrical shapes, gnu is an anisotropic three-dimensional nanocrystal that possesses unique optical properties compared to spherical gold nanoparticles of the same core diameter. this distinction arises from its uneven, spiky surface, which causes a redshift in the spr peak and creates a greater enhancement of the 𝐸(𝜔𝑙) at the tips of the gnu. this enhancement is confined to a smaller and more localized area [25]. the larger aspect ratio of the branches and plasmon hybridization between the spike core and tips enhances the polarization sensitivity of gnu by inducing different dipole moments [26,27]. gnu enhances the electric field due to hot spots, high core-tip aspect ratio, and off-resonant excitation at 637 nm of the raman probe compared to the plasmon absorption band of 90 nm gnu at 652 nm. previously, we reported the sers detection of cancer biomarkers using a thin gold film substrate [28] where the planar nanometer-thin film was used as a twodimensional plasmonic-active nanostructure; however, it was not considered as pantf, i.e., a nanostructure possessing the properties of both thin films and individual nanoparticles. the importance of pantf is due to reproducible hotspots between thin film-pns and its rich plasmonic properties caused by the hybridization between the lspr of nps and propagating surface plasmon polaritons (spp) of the metallic film. the physicochemical properties, including electrical, thermal, mechanical, and optical properties, of thin films can be significantly influenced by the roughness of the substrate. recent studies have examined the optical properties of noble-metal nps in proximity to a metal film [29,30]. these studies have demonstrated that the localization and field strength in the plasmonic gap are significantly influenced by factors such as nanoparticle composition, the film characteristics, nanoparticle size and shape, and the distance of the plasmonic gap [29,31]. therefore, choosing rough metallic substrates plays a key role in achieving sers since the enhancement is heavily influenced by the shape, size, morphology, distribution of nps, and ef of the substrate [32–40]. the goals of the present work are to a) fabricate gnu-based pantf; and b) characterize and compare the interaction of the r6g dye with tgfs and pantf using ft-nir and sers. the goal of this ongoing research is to develop a multiplexed pantf-based nanobiosensor for the active detection of cancer biomarkers in serum. characterization and application of nanomaterials 2025, 8(2), 10951. 4 2. materials and methods for assembly of the gnu-gold film substrate, deionized (di) water (6442-85), reagent alcohol (277649), 1,6-hexanedithiol (h12005), ultrapure water (6b7133), and 95% rhodamine 6g (r4127) were purchased from sigma-aldrich. 70% ethanol (bp820) was purchased from thermo fisher. citric acid-stabilized gnu with a 90 nm diameter and 8.92 × 10−12 molar concentration was purchased from cytodiagnostics (gu-90-20). phosphate buffered saline, ph 7.4 (10010031), was purchased from gibco. commercially available sealed gold thin film substrates (spr-1000-050) with 10 nm gold thickness prepared by conventional electron beam evaporation were purchased from platypus technologies. low retention 1.5 ml microcentrifuge tubes (3451pk, biolynx) were used as reaction tubes. equipment used in the reaction process was a microcentrifuge (of-17710-11), a centrifugal filter (ufc503096, millipore sigma), an ultrasonic bath (elmasonic), an orbital shaker (rk-51700-13), and a vortex shaker (rk-04729-07) purchased from cole-palmer, canada; a combo ph meter (blu2300e, canada), an analytical balance (sartorius, usa); as well as micropipettes and micropipette tips (eppendorf, 2231302001). for the investigation of the enhancement factor using r6g as a probe molecule, a raman concentration of 10 mm and an sers concentration of 1 μm were used. the sers concentration accounts for the increased surface area as a result of the gnu presence on the substrate [41–43]. for each raman and sers reading, 10 μl of the respective r6g concentration was added to the substrate. spectra were collected at 637 nm at varying laser powers (2, 4, and 8 mw). 3. substrate preparation the preparation procedure of the gnu-immobilized tgfs for the sers experiment is schematically shown in figure 1. figure 1. schematic representation of gnu-immobilized tgfs. 3.1. cleaning of gold substrate a previously cut 1 × 1 cm piece of the tgfs was placed in its own respective plastic circular container as a functionalization chamber. a total of 500 μl of 70% ethanol was added to the container to completely submerge the substrates. the container was sealed and sonicated at 60 khz and 60% power for 10 min. the substrate was rinsed twice with fresh ethanol to remove any remaining debris. the substrate was left to air dry and stored in an airtight container until further use. characterization and application of nanomaterials 2025, 8(2), 10951. 5 3.2. preparation of 15 pm concentrated gnu in a class ii a2 biosafety cabinet (labgard, usa), 1.12 ml, 1.12 ml, and 1.13 ml of 90 nm gnu were added to three separate microcentrifuge tubes. to maintain balance, 1.13 ml of water was added to a fourth tube. the tubes were then placed in a microcentrifuge and spun at 3200 rpm for 30 min. after centrifugation, the supernatant was discarded, leaving 25 μl of gnu pellet in each tube. the gnu pellets were then resuspended by adding 560 μl of ultrapure water to the tube that contained 1.12 ml of gnu and 565 μl of ultrapure water to the tube containing 1.13 ml of gnu. the three resuspended gnu solutions were combined in a 20 ml scintillation vial, resulting in a total volume of 1.685 ml resuspended gnu. to achieve a final volume of 2.013 ml at a concentration of 15 pm, 350 μl of ultrapure water was added to this vial. 3.3. preparation of ethanolic hexane (hdt) solution the concentrated gnu was immobilized on a tgfs via gold-thiol bonds. in the biosafety cabinet, 1999 μl of pure ethanol reagent alcohol was mixed with 1 μl of 1,6-hexanedithiol in a 20 ml glass scintillation vial, which was then immediately capped. the vial was vortexed at 1800 rpm to prepare a 2 ml solution of 3 mm hdt. 3.4. preparation of 10 mm r6g 9.60 mg of r6g dye was accurately weighed using an analytical balance and then added to a scintillation vial containing 2 ml of ultrapure water. the solution was vortexed at 1800 rpm to create a 10 mm r6g stock solution. 3.5. preparation of 1 μm r6g 0.5 μl of the prepared 10 mm r6g stock solution was added to a scintillation vial containing 4999.5 μl of ultrapure water. the resulting mixture was vortexed until homogeneous to obtain 5 ml of 1 μm r6g solution. 3.6. functionalization of tgfs with hdt and gnu the cleaned gold chip was immersed in a vial containing 2 ml of 3 mm hdt and then sonicated at 60 khz and 60% power for 2 min to functionalize the tgfs with hdt molecules. after sonication, the substrate was rinsed twice with 70% ethanol followed by ultrapure water to remove any unbound hdt molecules. immediately following the rinsing, 200 μl of prepared 15 pm gnu was pipetted onto the gold surface. the container was sealed and placed on the orbital shaker for 10 min at 150 rpm to allow gnu to bind to the free thiol end of hdt. the substrate was rinsed then with ultrapure water and air-dried in the biosafety cabinet before characterization using raman spectroscopy. 4. characterization 10 μl each of 10 mm and 1 μm r6g samples were pipetted separately onto the gnu-functionalized substrate. the substrate was analyzed using raman spectroscopy as outlined in this section. the remaining volumes of 10 mm and 1 μm r6g samples were transferred to their respective cuvettes. these solutions were analyzed using uvcharacterization and application of nanomaterials 2025, 8(2), 10951. 6 vis, fluorescence, ft-nir, and raman spectroscopy as described. the absorbance of the two r6g solutions was measured using the jenway 7205 uv-vis spectrometer with a wavelength range of 200–800 nm (cole-palmer). fluorescence spectra of the identical solutions were recorded using a 532 nm laser with a power output of 50 mw. the fluorescence emission was transmitted by a 500 μm core diameter optical fiber to the flame-t-xr1-es spectrometer (ocean optics). the spectrometer was equipped with a 2048-pixel (14 μm × 200 μm) linear silicon ccd array. the device had a detection range spanning from 200 nm to 1050 nm and an optical resolution of 1.5 nm full-width half maximum (fwhm). ft-nir spectra were recorded using a tungsten halogen light source, with a wavelength range between 360 and 2500 nm, and an output power of 8.8 mw. the light was transmitted through a 400 μm core diameter optical fiber (nanoq-fiber-400-vis-nir) and detected by the nanoquest 2.5 spectrometer (ocean insight) with the transmission scan time being 5 s with an 8 nm resolution. the sers spectra were obtained using a benchtop 637 nm laser with a tunable output power of up to 10 mw (s1fc637, thorlabs, usa) connected to a 638 nm raman probe (rip-rpb-638-fc-apc-sma, ocean insight, usa). the raman parameters on the oceanview software were set to an integration time of 5 s, a number of scans of 3 to average, and a boxcar width of 5. nonlinearity correction and clean peaks options were applied, and a background spectrum was acquired with the raman probe shutter closed. the raman probe contains a fiber bundle, which directs excitation light from the laser to the sample and collects the raman scattered light within a spectral range between 300–3900 cm−1. the working distance of the probe was 1.8 cm perpendicular to the substrate, creating a 3 mm laser diameter comparable to the sample drop size. the beam was centered in the middle of the droplet without directly interacting with the surface of the substrate before sers spectrum was obtained. the experiment was performed using the laser at 2, 4, and 8 mw, respectively. while conducting measurements, the light at the laser’s wavelength (known as rayleigh scattering) was blocked along the path to the spectrometer (hdxvis-nir, ocean insight, usa) using a dichroic filter that has a spectral sensitivity range of 150–3400 cm−1 to avoid saturating the detector. 5. results and discussion the absorbance of 90 nm gnus is shown in figure 2 with a bandwidth between 500 and 800 nm and a single broad lspr peak at about 652 nm. the inset shows the morphology of a single gnu with short and long branches, which play a key role in the field enhancement. characterization and application of nanomaterials 2025, 8(2), 10951. 7 figure 2. uv-vis absorbance of gnu with a maximum spr peak at 652 nm. figure 3a illustrates a scanning electron microscope (sem) image of a single, multi-branched gnu morphology with each tip having an axial size of ≈ 12 nm. an example of clustered gnu is shown in figure 3b, where it causes an increase in size and the height of the nanostructure, which in turn red-shifts the spr. the coupling between clusters of metal nps becomes important and can influence the sers results. the clustering or aggregation of nps increases with the incubation time. unlike the densely packed single gnu layer in a 2-d plane, clusters tend to form at the top layer and in overlapping areas due to the spatial overlap of double-layer clusters. the randomly distributed nanogaps between the individual gnus or aggregates can excite the gap plasmon modes [44]. the larger gnus exhibit a lspr peak at longer wavelengths because the branches facilitate more extended longitudinal plasmon resonance [45]. a two-dimensional afm image of a single gnu is shown in figure 3c. in our study, we maintain a constant diameter for the gnus (neglecting the clustering); the ratio of center-to-center distance (𝐷) between gnus to the radius 𝑅𝑝 of the gnu (𝐷/𝑅𝑝) decreases as (𝐷) decreases or the particle size increases. as a result, we anticipate a stronger plasmon resonance coupling, which could lead to a greater positive shift in the lspr wavelength when the interparticle distance decreases. previous work suggests that the coupling, hence the resonance shift, becomes negligible at 𝐷 ≥ 2.5 times the nanoparticle size [46]. in addition, since most of the gnus are well separated with a narrow size range of 80–90 nm in diameter, it indicates a strong correlation between the particle size and enhancement efficiency. figure 3. sem of (a) single gnu showing the branched surface topology, (b) clustered gnus, and (c) 2d afm of gnu. characterization and application of nanomaterials 2025, 8(2), 10951. 8 prior to the experiments of r6g interaction with the substrate, uv-vis, fluorescence spectroscopy, and the raman scattering of pure r6g molecules in solution were performed at 1 μm and 10 mm. r6g is a cationic dye, and the molecule contains 12 aromatic bonds, 5 double bonds, 36 non-h bonds, 17 multiple bonds, and 7 rotatable bonds, 4 six-membered rings, i.e., benzene, which has 6 carbons, 2 tenmembered rings, 1 aromatic ester, 1 aliphatic imine, 1 aromatic secondary amine, and 1 aromatic ether. to avoid saturation during uv-vis spectroscopy at 10 mm, 9 μl of r6g stock solution was diluted in a cuvette containing 2991 μl ultrapure water to obtain 0.03 mm r6g. figure 4a illustrates the molecular structure of r6g with the corresponding uv-vis spectrum of 1 μl of r6g in ultrapure water shown in figure 4b with a main peak at around 530 nm relating to a transition moment due to π ∗-π transition, and less intense peaks at 257 and 350 nm, respectively, corresponding to transitions to higher singlet excited states. since there is a linear dependence between the initial concentration of r6g at their maximum absorption, at the higher concentration of 0.03 mm, the main peak at 530 nm and the secondary peaks become stronger (figure 4c). solvent molecules can interact with the molecules of absorbing species of ground or excited state(s) through intermolecular bonding, resulting in a change in the wavelength of absorption due to a decrease or increase in the energies of the ground or excited states. it is noteworthy that the position of the band may vary with solvent, which is usually attributed to solvent parameters such as polarity and refractive index; however, the intensity or the amplitude of response, i.e., the population of excited molecules, is directly related to laser intensity as well as the concentration and path length. the fluorescence emission spectrum of r6g is shown in figure 5a with a maximum peak at 571 nm. figure 5b indicates the comparison of fluorescence emission of two different concentrations at 1 μm and 0.03 mm, where the higher concentration exhibits a higher emission intensity. the samples prepared at 1 μm, 0.03 mm, and 10 mm are shown in figure 5c–e, with the corresponding images of fluorescence emission illustrated in figure 5f–h, respectively. it is noted that as expected at higher concentrations, the emission becomes stronger, but at 10 mm no result was obtained due to total optical attenuation. the brightness of the fluorescence emission is defined as 𝐵 = 𝑄𝑦/𝜀, where 𝑄𝑦 = 𝑘𝑟 𝑘𝑟+𝑘𝑛𝑟 , 𝑘𝑛𝑟 and 𝑘𝑟 are non-radiative and radiative decay rates, respectively, and the molar absorption coefficient 𝜀 (m−1 cm−1) is directly proportional to quantum yield. using the beer’s law in a dilute solution, the intensity of measured fluorescence emission is given by 𝐼𝑓 = 𝑄𝑦𝑃0(1 − 10−𝜀𝑐𝑙) ≈ 𝑄𝑦𝑃0𝜀𝑐𝑙 where 𝑃0 is the laser power, 𝑐 is the concentration of analyte, and 𝑙 is the optical path length, respectively, i.e., the higher the value of b, the higher it will be 𝐼𝑓. characterization and application of nanomaterials 2025, 8(2), 10951. 9 figure 4. (a) molecular structure and uv-vis spectra of r6g at (b) 1 μl and at (c) 0.03 mm. figure 5. (a) fluorescence emission of r6g at 571 nm excited by 532 nm laser, images of the sample prepared at different concentrations of (b) 1 μm, (c) 0.03 mm, and (d) 10 mm with corresponding fluorescence emission shown in (e), (f), and (g) respectively, and (h) shows the corresponding fluorescence emission of 1 μm and 0.03 mm, respectively. characterization and application of nanomaterials 2025, 8(2), 10951. 10 figure 6 illustrates the raman spectra of dilute r6g solution at various concentrations of 0.03 mm and 10 mm, where each result is the average of three trials. the intensity of the lines in the case of 10 mm is higher than those at 0.03 mm, and two peaks at 1386 and 2757 cm−1 corresponding to aromatic c-c and ester(s) stretching modes are closely overlapped. previous work has reported that the intensity of active modes is sensitive to the 𝜋-electron configuration of r6g located at the nitrogen atoms of the ethylamine external groups through the xanthene ring [47]. the amount of scattered light is directly proportional to the product of the weight-average molar mass, the solute concentration, and the polarizability of the molecule. the polarizability, in turn, is influenced by the molecular size and weight. therefore, larger particle polarizability results in a greater magnitude of induced polarization and higher signal intensity. figure 6. averaged raman spectrum for pure r6g using 0.03and 10-mm solutions. the raman spectra are superimposed for comparison. the peak at 653 cm−1 corresponds to c-c ring in-plane bending, 824 and 1097 cm−1 are related to c-h outof-plane bending, and the peak at 1289 cm−1 likely corresponds to n-h in-plane bend mode. most significant peaks between 1300 and 1700 cm−1 indicate aromatic esters. therefore, the overlapped peaks probably correspond to aromatic c-c and n-h stretching modes. this can be due to over-masking at the higher concentration. in addition, the raman lines at higher concentrations between 500 and 1500 cm−1 are blueshifted compared to the lower concentration. the most dominant lines start from the bottom of table 1, moving upwards in the order of decreasing intensity, i.e., the highest lines belong to n-h stretching modes and the least to c-c ring in-plane bending in xanthene/phenyl. the corresponding raman lines are shown in table 1 [47–52]. figure 7a shows an example of tgfs prior to adding r6g. the optical picture of the tgfs is shown in figure 7b and the 2-d afm images of the initial substrate as supplied are shown in figure 7c,d, respectively, before and after magnification. figure 7e indicates an enlarged portion of figure 7d with the corresponding histogram of the surface. the 3-d image is shown in figure 7f, where the surface appears to have some micro-level size scratches, irregularities, and impurities shown as bright spikes despite our initial thorough cleaning of the substrate with ethanol prior to imaging. characterization and application of nanomaterials 2025, 8(2), 10951. 11 table 1. assignments corresponding to the raman shifts observed for pure r6g [47–52]. raman shift (cm−1) assignment reference 613 c-c-c ring in-plane vibration mode [45] 772 c-h out-of-plane bend mode 1126, 1185 c-h in-plane bend mode 1312, 1575 n-h in-plane bend modes 1362, 1510, 1648 c-c stretching modes 780 aromatic c-h bending mode [46] 1199 c-o-c stretching mode 1375, 1511, 1545, 1580, 1650 c-c stretching mode 772, 1187 c-h out-of-plane bending vibration [47] 1313, 1366, 1513, 1652 aromatic c-c stretching 608 in-plane bending vibration [48] 772 c-h out-of-plane bending vibration 1184, 1309, 1362, 1495, 1567, 1646 in-plane c-c stretching vibrations 614 c-c-c ring [49] 779 out-of-plane bending of c-h 1183 c-h stretching 1312 in-plane bending of c-o-c 1364, 1511, 1576, 1652 c-c stretching of the aromatic ring [50] 612 c-c ring in-plane bending in xanthene/phenyl ring 772 c-h out-of-plane bending 797 hybrid mode xanthene/phenyl rings 1127 c-h in-plane bending in xanthene/phenyl rings 1187 c-h in-plane bending in xanthene ring 1204 hybrid mode (xanthene/phenyl rings) 1275 c-o-c stretching cooc2h5 group on phenyl ring 1312 hybrid mode (xanthene/phenyl rings & nhc2h5 group) 1363 c-c stretching in xanthene ring 1449 c-n stretching nhc2h5 1509 c-c stretching in xanthene ring 1575 c-c stretching in phenyl ring hybrid mode (phenyl ring with cooc2h5 1651 c-c stretching in xanthene ring 1700–2800 ester(s) aromatic > 2800 nh stretching modes characterization and application of nanomaterials 2025, 8(2), 10951. 12 figure 7. (a) schematic diagram of tgfs; (b) optical and 2d afm images of tgfs; (c) before; (d) after magnification; (e) enlarged portion of (d) with the corresponding histogram; and (f) 3d image showing some rough morphology. in diffuse reflectance measurement, a reference reflector such as gold acts as a reference for background measurement and exhibits extremely high reflectance in the nir region. the corresponding ft-nir reflectivity of tgfs in figure 8a shows the dominant strong signals in the 4500–5200 cm−1 (2.2–1.92 μm) region. normally, a gold-coated surface shows an increasing reflectivity of 65%–90% between 500 and 1000 nm and more than 90% at longer ir wavelengths. figure 8b illustrates the nonlinear response of raman line intensity of the substrate without r6g with the probe power, where the intense lines occur between ≈ 500–1500 cm−1. all materials generate a raman spectrum, except for pure metals, which are highly reflective because of the free electrons on their surface. if a crystal is centrosymmetric, ir bands will not show up in the raman spectrum and vice versa. an essential condition to obtain raman spectra of samples is a change in polarizability during molecular vibration, and the metals do not show the polarizability change. as a result, metallic elements with the face-centered cubic (fcc) structure, such as gold, have no raman-active vibrations. therefore, the peaks shown in figure 8b are considered the background spectral profile partly because of the presence of some impurities in the substrate. characterization and application of nanomaterials 2025, 8(2), 10951. 13 figure 8. (a) ft-nir reflectivity of the tgfs where most reflection occurs between 4000 and 5200 cm−1, i.e., at shorter ir wavelengths, and (b) indicates the averaged raman intensity at various laser powers. figure 9a shows the schematic representation of r6g dye added to the substrate, and figure 9b illustrates the experimental setup where the beam travels through the sample droplet placed on the substrate. figure 9c displays the sers results of 10 mm r6g on tgfs at different power levels, showing significant fluctuations in the relative intensities of certain vibrational bands. it is noticed as expected that the intensity of the r6g raman lines is enhanced compared to those in figure 6. a common feature of molecular spectra is the variation of the temporal spectrum, which is mainly associated with a deviation from the ensemble average [53–55]. the fluctuation occurs due to varying charge transfer contributions caused by dynamic changes in the molecular environment, such as random movement of the molecule on the metallic surface during the adsorption [45]. the spectral fluctuations can be influenced by various physical and chemical properties of molecules and substrates, including diffusion, reorientation, adsorption, and desorption of the molecules. indeed, it has been demonstrated that diffusive processes on the surface can cause molecules to experience continuously varying interaction forces that may result in the modulation of emission and control of the vibrational modes [56,57]. additionally, environmental factors such as light and temperature, optical parameters like light intensity, and chemical factors including charge transfer have been shown to influence spectral fluctuations [58,59]. as shown characterization and application of nanomaterials 2025, 8(2), 10951. 14 in figure 5, the intensity of the scattered raman lines, i.e., the population of vibrationally excited molecules, varies almost linearly with the laser power and is more intense at lower wavenumber, particularly between 500 and 1500 cm−1, i.e., lower energy corresponding to aromatic modes of xanthene/phenyl rings, c-c rings [60], aromatic c-h bending, nh in-plane modes, and c-c stretching modes [56,61]. the overall stochastic behavior of such spectral fluctuation has been observed previously [62,63], which is attributed to changes in the dynamic molecular environment or thermally activated diffusion of individual molecules [64]. the coupling between the vibrational modes and electronic states of r6g molecules and small changes in the position of adsorbed molecules on the tgfs and nps can create a temporal modulation of these states, leading to the enhancement of the intensity of the analyte molecules. it has been suggested that in high-concentration analyte ensembles, these changes are normally masked by ensemble averages and therefore cannot be detected [55]. figure 9. (a) schematic representation of r6g dye sers; (b) the experimental setup; (c) averaged sers intensity of r6g at 10 mm. the optical properties of gold thin films, along with the connection between the metallic thin films and the intrinsic characteristics of a plasmonic device, can be studied through the optical absorption of metal inter-band and intra-band electron transitions, as outlined by drude’s theory. for polycrystalline metal films, the electron scattering at surfaces and grain boundaries plays a great role in losses [65] and affects the complex dielectric constant of the metallic materials 𝜀𝑚 [66]. 𝜀𝑚 = 𝜀𝑟 + 𝑗𝜀𝑖 = 𝜀∞ − 𝜔𝑝 2 𝜔2 − 𝑖𝛾𝜔 (1) characterization and application of nanomaterials 2025, 8(2), 10951. 15 𝜀𝑚 = 𝜀∞ − 𝜔𝑝 2 𝜔2 + 𝛾2 + 𝛾𝜔𝑝 2 𝜔(𝜔2 + 𝛾2) (2) where the real part 𝜀𝑟 = (𝑛𝑠 2 − 𝑘𝑒 2) indicates the polarization of the metal in response to an applied external electric field, the imaginary part 𝑗𝜀𝑖 = 2𝑛𝑠𝑘𝑒 = 𝛾𝜔𝑝 2/𝜔(𝜔2 + 𝛾2) represents the optical absorption in metal, quantifying the relative phase shift of the induced polarization with respect to the external field, which includes losses such as ohmic loss as heat, 𝜀∞ is the infinite-frequency dielectric constant (i.e., the net electric field inside the metal is zero), 𝛾 is the damping factor, 𝑛𝑠 is the refractive index of metal, and 𝜔𝑝 is the plasmon frequency defined as: 𝜔𝑝 2 = 𝑛𝑒𝑒2 𝑚𝑒𝑓𝑓𝜀0 (3) where 𝑛𝑒 is the density of electrons, 𝑒 is the electron charge, 𝜀0 is the vacuum dielectric constant permittivity, and 𝑚𝑒𝑓𝑓 is the electron effective mass, respectively. since the total field at the metal surface is 𝐸𝑇 = 𝐸0(𝜔) + 𝐸𝑠(𝜔) where 𝐸𝑠(𝜔) in the dipolar mode, is given by [67]. 𝐸𝑠 = (1 + 𝐾)𝜀𝑒 (𝜀𝑚 + 𝐾𝜀𝑒) 𝐸0(𝜔) (4) where 𝐾 is the shape factor and 𝜀𝑒 is the dielectric constant of the surrounding environment. when a molecule is placed close to a surface, its scattering cross-section is significantly enhanced. a key aspect related to the origin of sers is that the oscillating dipole moment 𝜇𝑑 of a plasmonic molecule re-radiates some of its energy at the same frequency as 𝐸0. after interacting with the laser, the molecule’s associated field 𝐸𝜇𝑑 interacts with the incident light, causing it to scatter elastically. this scattering produces an isotropic intensity distribution because the wavelets emitted by the oscillating charges are approximately in phase with one another [68]. 𝜇𝑑 = 4𝜋𝜀𝑚𝑅𝑚𝑜 3 ( 𝜀𝑚𝑜 − 𝜀𝑒𝑛 𝜀𝑚𝑜 + 2𝜀𝑒𝑛 ) �̄�0𝑒𝑖𝜔𝑡 (5) where 𝜀𝑚𝑜 and 𝜀𝑒𝑛 are the molecule and the medium dielectric constants, respectively, 𝑅𝑚𝑜 is the molecule radius, and 𝜔 is the field angular frequency. the intensity of the scattered light, 𝐼𝑠 directly depends on the polarizability, 𝛼𝑝, which in turn depends on the molecular weight and on the particle size. therefore, the higher a particle 𝛼𝑝, the greater will be the magnitude of induced 𝜇𝑑 and 𝐼𝑠 . since 𝐸𝜇𝑑 in the molecule is proportional to its volume 𝑉𝑚𝑜 , and 𝐼𝑠 is proportional to 𝑉𝑚𝑜 2 , it follows that the intensity of reradiated light 𝐼𝑟 = |𝐸𝜇𝑑 | 2 is proportional to 𝑉𝑚𝑜 2 as well. therefore, the scattered intensity will be stronger than at lower molecular weight or volume. therefore, when a raman scattering molecule is subject to an intense electric field generated near metal surfaces, the strong electric field intensity enhances the polarization on the molecule, leading to a higher induced 𝜇𝑑 [69,70]. figure 10a is a schematic representation of hexane-functionalized tgfs immobilized by gnu via a simple covalent thiol bond, i.e., the pantf structure. figure 10b compares the characterization and application of nanomaterials 2025, 8(2), 10951. 16 reflectivity of tgfs before and after gnu immobilization; the reflectivity significantly increases when gnu is added with the dominant lines of 1443, 1511, 1685, 1702, 2044, 2125, 2200, and 2397 nm (i.e., ≈ 4172–6930 cm−1). figure 10. (a) schematic of gnu immobilized on the hexane functionalized tgfs (i.e., pantf) and (b) ft-nir of pantf. figure 11a shows the sers of the tgfs due to its plasmonic properties, with the dominant raman scattering observed at 2333 cm−1 corresponding to approximately ≈ 4.2 μm. it is known that metals do not produce strong raman signals due to a lack of vibrational modes that can be excited by incident light. what is observed in figure 11a is not the raman signal but the enhancement of signals from molecules in close proximity. homonuclear diatomic molecules are raman active because the stretching and contraction of the bonds alter the interactions between the nuclei and electrons, causing a change in the molecule’s polarizability. thus, it is expected that au(i), i.e., aurous ion, which is the most common oxidation state with soft ligands such as thioethers, thiolates, and organophosphines, may produce the above result. figure 11b presents the sers spectrum of gnu colloids, highlighting prominent peaks at 1475, 2314, 2590, 2696, and 2981 cm−1, which are associated with citrate. citrate acts as an intermediate in the citric acid cycle and plays a role in reducing gold ions into atoms, which helps stabilize the colloidal aunps formed from these aggregated atoms. generally, aunps are plasmonically active in the nir region, making them suitable for biomedical applications because they exhibit minimal autofluorescence from biological samples. the primary factor contributing to the sers enhancement is the increased intensity of inelastically scattered raman signal due to the presence of nanostructured metal systems in the sample. moreover, these particles enhance the morphological interaction with the incident laser, leading to more intense spectroscopic signals. the effect of probe power on the sers lines of the pantf is shown in figure 11c, where the intensity is relatively enhanced due to the immobilization of gnu compared to those in figure 8b of tgfs as background. the increase in the size of the gnu is attributed to conjugation via thiol bonds, which results in raman vibrational scattering at higher frequencies. the sers bands of hexane thiol are at 780 cm−1, which is associated with ch2 vibration; 935 cm−1 corresponds to the ch3 rocking vibration, 1032 cm−1 and 1209 cm−1 indicate c-c cm−1 stretching vibration, while the bands at 1301 cm−1 and 1448 cm−1 are likely due to the ch2 wagging vibration [71]. characterization and application of nanomaterials 2025, 8(2), 10951. 17 figure 11. sers of (a) tgfs, (b) gnu solution, and (c) pantf at various probe power. the gnu layer serves as hotspots within the adjacent irregular morphology of tgfs, enhancing the plasmon resonance effect for the detection of r6g through the lspr mechanism. when the size of the nps is much smaller than the incident wavelengths, the elastic scattering cross-section of the np increases significantly, which leads to a strong enhancement of the local electromagnetic fields. theoretical studies [56] have demonstrated that in a single np-film system, the wavelength of surface plasmon polariton (spp) remains unchanged. this is because the perturbation of the delocalized spps supported by an infinitely thin film is negligible, unlike in systems with a larger number of nanoparticles. in our sers experiment, it is assumed that the laser directly excites the lspr of gnus but does not directly couple to the spp of tgfs. this is due to a mismatch between the in-plane wavevectors of these mods and those of the incident photons that propagate through the air gap between the probe and the tgfs [72,73]. the gnu provides an indirect way to excite the spps of the tgfs across all wavelengths. this implies that gnu does not interact preferentially with any specific spp; instead, it couples with the entire range of spp modes. therefore, the lsp scattering of gnus transmits both into far-field, acting as a nano antenna, and into the non-resonant continuum of spp modes within the tgfs, which further enhances the sers signal and induces a polarization to the single nanoparticle light scattering [74]. figure 12 illustrates sem images of pantf where the surface morphology exhibits a clustering feature, figure 12a, where each cluster consists of a number of nanoparticles aggregated together. the clusters demonstrate various shapes and sizes, characterization and application of nanomaterials 2025, 8(2), 10951. 18 which in turn will affect the sers signal; some scratches and artifacts are also observed. at much higher magnification shown in figure 12b, the clusters do not show the same smooth curve but instead an irregular and spiky shape similar to the geometrical shape of gnu is formed. figure 12. sem images of pantf at (a) low and (b) high magnification. the inset shows an example of a gnu particle that could not be seen in (a). the surface topography and roughness of pantf were also investigated by afm in non-contact scanning mode for a number of scans. the images were taken from the center of the chip at a 10 × 10 μm resolution, and a 3-d profile is associated. figure 13a,b illustrate the 2-d surface morphology of pantf, where the gnus are aggregated together due to surface-attractive interactions to generate a larger cluster and have created an irregular topological feature on the surface. this effectively affects the surface roughness, which in turn affects the sers signal because of a change in the surface plasmon probing depth between the analyte molecule and the substrate base. the brighter regions in the image are caused by the laser beam used to detect deflections of the cantilever either towards or away from the surface. when an incident beam reflects off the flat top of the cantilever, any deflection will cause small changes in the direction of the reflected beam. when the incident beam reflects off the flat top of the cantilever, any deflection will cause small changes in the direction of the reflected beam. the corresponding 3-d images are illustrated in figure 13c,d. in these images, the previous spikes have nearly vanished due to coverage by gnus. characterization and application of nanomaterials 2025, 8(2), 10951. 19 figure 13. (a) and (b) 2d afm images of pantf where gnus are partly aggregated and distributed on the surface; (c) and (d) are 3d images showing the irregular feature of the surface. the final step was to study the sers of r6g using pantf as illustrated in figure 14a, where the initial enhanced hexane raman probe signal is coupled to that of the r6g to produce the final sers signal. this is because gnu particles act as hotspots that amplify the plasmon resonance effect in r6g detection. this amplification is due to the increased light scattering cross-section when exposed to laser excitation [75]. the differential spectra indicate that r6g can be effectively used for sers sensing. it is well known that sers signals arise from a strong interaction between a molecule and its substrate. furthermore, the spatial arrangement of these components significantly influences the electromagnetic and chemical enhancements observed in the raman signal. the variations in the recorded sers signal are likely due to different charge transfer effects, which are probably caused by dynamic changes in the molecular environment. this includes the random movement of the molecule onto the metallic surface during the adsorption process [45]. interactions of molecules and substrates, including adsorption, desorption, surface diffusion, and molecular reorientation, can influence fluctuations. furthermore, the analyte molecules are likely located on the surface of the substrate rather than in between gnu hotspots. this placement impacts the reproducibility of sers because the number of gnus can vary from one position to another. as a result of this non-homogeneous distribution, signals are produced with varying intensities and levels of enhancement. the variation of averaged sers intensity (a total of three readings for each sample) of r6g using the 10 min incubated substrate with laser power is shown in figure 14b–d, whereby increasing the power, the relative intensity increases, particularly at 8 mw. certain lines, including 583, 641, 786, 799, 923 cm−1 in the low characterization and application of nanomaterials 2025, 8(2), 10951. 20 wavenumbers range, as well as 2757, 2766, and 3254 cm−1 in the high wavenumbers range, are significantly enhanced by pantf substrate. in the range between 1500 and 2500 cm−1, the intensity of both cases remains relatively low or unchanged, and a few lines, such as 1220, 1363, 1698, 2398, and 2933 cm−1 mainly corresponding to secondary and nh3 + amines, remained higher in the case of tgfs. it was noted that the nh3 + amine peak showed an increase in intensity when gnu was present, compared to when it was absent. however, the other r6g peaks associated with the benzoic ester and secondary amine functional groups did not exhibit the same level of enhancement. it is proposed that the nh3 + functional group underwent a notable enhancement as a result of the electrostatic interaction between its positive charge and the naturally occurring negative charge on gnu. since the enhancement in sers enhancement is dependent on distance, nh3 + showed the strongest enhancement due to its direct interaction with gnu. it was also noted that higher laser power resulted in a stronger intensity of both raman and sers peaks. some slight shifts in the raman lines were noted, particularly those associated with aromatic c-c stretching. these shifts may result from interactions between the substrates and the probe molecules. the molecules of r6g contain conjugated aromatic rings, which predispose 𝜋 − 𝜋 to stack with gnu [76,77]. figure 14. (a) schematic diagram of enhanced sers of r6g using pantf after 10 min of incubation via thiol covalent bond, the corresponding raman and sers spectra of tgfs and pantf are presented at (b) 2 mw, (c) 4 mw, and (d) 8 mw, respectively. characterization and application of nanomaterials 2025, 8(2), 10951. 21 when using a 60 min pantf, the results at 2 mw shown in figure 15a are slightly worse compared to those in figure 14a. in figure 14a, the line intensity remains predominantly low across the spectrum except for two significant peaks at 2998 cm−1 and 3156 cm−1. as the power increases, the raman lines show a noticeable improvement across the spectrum, especially at 8 mw. one of the primary reasons for the varying profile patterns and reproducibility of sers is a lack of surface stability in most enhancing material surfaces. figure 15. schematic diagram of the enhanced sers of r6g using pantf after 60 min of gnu incubation through thiol covalent bond. the corresponding raman and sers spectra of tgfs and pantf are presented at (a) 2 mw, (b) 4 mw, and (c) 8 mw, respectively. figure 16a shows the overlapped results related to the pantf incubated for 10 min at various power levels, and similarly, the results for the 60 min incubation are shown in figure 16b. it is noteworthy that as the power increases, the intensity behaves non-linearly at different spectral positions with increasing overall profiles. the positions at which the intensity of overlapped peaks increases linearly, such as 647 and 3258 cm−1 in figure 16a and 923, 1232, and 3156 cm−1 in figure 16b, the sensor can be utilized for monitoring the detection of analyte, in our case r6g. characterization and application of nanomaterials 2025, 8(2), 10951. 22 figure 16. comparison of overlapped peaks of pantf for (a) 10 min and (b) 60 min incubation time. figure 9a illustrates the addition of 10 μl of a 10 mm solution of r6g, a ramanactive probe molecule, to the tfgs. the calculation is performed using 𝑁 = 𝑛𝑁𝐴 where 𝑛 = 𝐶𝑉 is the number of moles, 𝐶 is the concentration, and 𝑉 is the volume of the solution; 𝑁 is the number of molecules, and 𝑁𝐴 = 6.0224 × 1023 mol−1 is avogadro’s number. the corresponding values are n = 100 × 10−9 mol and 𝑁 = 600 × 1014 r6g molecules, respectively. for pantf, 10 μl of a 1 μm r6g solution was applied to the surface to accommodate the larger surface area of the gnu during the sers measurements [35]. similarly, we found corresponding values of n = 10 × 10−12 mol and 𝑁 = 6 × 1012 molecules for sers. the enhancement of line intensity due to lspr is utilized to determine the ef at a specific power, as illustrated in figures 13 and 14 and calculated using equation (6), which is summarized in tables 2 and 3. 𝐸𝐹 = 𝐼𝑆𝐸𝑅𝑆 𝐼𝑅𝑎𝑚𝑎𝑛 × 𝐶𝑅𝑎𝑚𝑎𝑛 𝐶𝑆𝐸𝑅𝑆 (6) where 𝐼𝑅𝑎𝑚𝑎𝑛 is the intensity of the bare substrate with r6g at concentration 𝐶𝑅𝑎𝑚𝑎𝑛 = 10 mm, 𝐼𝑆𝐸𝑅𝑆 is the intensity of the gnu-immobilized substrate with r6g at concentration 𝐶𝑆𝐸𝑅𝑆 = 1 μm, so 𝐶𝑅𝑎𝑚𝑎𝑛 𝐶𝑆𝐸𝑅𝑆 = 104. substituting the above values given in table 2 in equation (6), we obtain 𝐸𝐹 = 3 × 104 for all three 10 min incubation pantf substrates at various powers, and similarly, using the corresponding values of intensity for rs and sers in table 3, it yields corresponding average values of 0.9 × 104, 2.1 × 104, and 1.1 × 104 for 60 min pantf substrates, respectively. table 2. peaks used to determine the average value of ef for 10 min incubation pantaf at the various power levels based on figure 13. common peaks (cm−1) rs intensity sers intensity ef value 573 40.69 80.73 1 × 104 923 30.41 230.32 6 × 104 1220 240.82 30.51 1 × 103 2757 60.68 320.62 4 × 104 average ef, figure 13a 3 × 104 characterization and application of nanomaterials 2025, 8(2), 10951. 23 table 2. (continued). common peaks (cm−1) rs intensity sers intensity ef value 583 30.63 220.14 6 × 104 786 170.62 400.07 2 × 104 2398 280.84 40.55 1 × 103 2766 30.21 270.28 8 × 104 2993 230.40 60.68 2 × 103 average ef, figure 13b 3 × 104 641 390.51 340.44 8 × 103 799 130.54 280.14 2 × 104 1375 210.96 90.71 4 × 103 2757 20.14 240.81 1 × 105 3254 120.47 350.62 2 × 104 average ef, figure 13c 3 × 104 table 3. peaks used to determine the average value of ef for 60 min incubation pantf at the various power levels based on figure 14. common peaks (cm−1) rs intensity sers intensity ef value 628 40.32 7046 2 × 104 1220 240.82 60.11 2 × 104 2328 140.26 80.17 6 × 104 2722 150.96 200.10 1 × 104 2998 100.92 160.46 2 × 104 average ef, figure 14a 0.9 × 104 641 90.70 120.63 1.3 × 104 2328 90.06 390.52 4.4 × 104 3003 220.72 100.49 0.5 × 104 average ef, figure 14b 2.1 × 104 653 380.07 100.89 3 × 104 1238 160.47 180.98 1.1 × 104 2621 70.65 140.10 2 × 104 average ef, figure 14c 1.1 × 104 a single nanoparticle (np) typically does not provide sufficient ef for smsers, and only the gaps between nanoparticles are active. it has been demonstrated that only the aggregation of multiple nanoparticles can provide enough ef for smsers [78–80]. each nanostructured tgfs has a different morphology with a certain number of nps of various sizes acting as dipoles and multipoles under an applied field, and shapes, both of which depend on the thickness of the thin films [81]. in the case of the thinner film, there is more unoccupied space by nps with no or very little scattering, and as the film thickness increases, the empty space becomes more occupied by nps. this in turn increases the np-np interaction in the films due to a decrease in the inter-particle separation, thus causing the higher scattering, i.e., increased intensity of sers, thus ef. the inter-particle distance, i.e., hot spots, can characterization and application of nanomaterials 2025, 8(2), 10951. 24 vary either due to an increase in number density or an increase in the size of aunps, which contributes to the variation of sers intensity [73]. when the analyte molecule is positioned in the gap between the nps, the raman scattering is significantly enhanced. research has demonstrated that the enhancement is most significant when the interparticle gap is less than 15 nm [82]. the relatively low ef may be attributed to several reasons, including variation in the spatial distribution of enhancements at hot spots and issues related to photobleaching. this is a photophysical phenomenon wherein a dye or a fluorophore molecule undergoes permanent chemical damage caused by prolonged laser (or non-laser) excitation, hence cleaving covalent bonds or non-specific reactions between the fluorophore and surrounding molecules. as a result, the dye loses its functionality. it is well-established that as temperature rises, the diffusion and randomness of molecules also increase. the solution to the 1-d random walk is expressed as the average of the square of the displacement 𝑥2 = 2𝐷𝑡, where d represents the fick’s diffusion coefficient (m2/s). this coefficient is defined by the stokes-einstein equation, which indicates that a larger 𝑥2 corresponds to greater diffusion. as a result, raising the temperature due to the increase in power increases the molecular fluctuations within the medium. as a result, the temperature gradient can drive the analyte molecules out of confined spaces, leading to microscale movement driven by thermal diffusion and convection. the overall effect impacts the molecular distribution, resulting in varying concentrations at different positions, which in turn generates the corresponding sers signal. the signal is stronger when the combined forces are balanced, causing the laser to irradiate areas with higher particle concentration. it weakens when the particles are dispersed or depleted from the hotspot, where the localized coupled plasmon resonance occurs between two or more pnp [83,84]. some molecules on the substrate are also susceptible to photodecomposition at high laser power, creating so-called dynamic species change over time [14]. the microscopic temperature gradient and radiation pressure can propel the analyte molecules and the nps out of the confined regions, resulting in microscale movement driven by the photo-thermophoresis force. this movement can redistribute their concentrations on the surface, ultimately influencing the final sers results [85–87]. the heating effect can cause the degradation of the hot spot, trigger molecular desorption, or initiate pyrolysis. these outcomes may lead to a reduction in the sers signal and its instability. the difference in the sers spectra could be attributed to variations in scattered light at different power levels, affecting the intensity, 𝐼 = |�̄�|2. additionally, the heating effect on the molecules at the microscale, such as thermally induced fluctuation or diffusion of dynamical changes in the microenvironment, may play a role. according to quasi-classical thermodynamics, these effects could be stochastic in nature. another interesting reason is related to the np-film distance, where the spectral response interplay between lsp and spp, for short separations (0– 50 nm), the coupling between them can create significant enhancement, and at larger distances, lsp and spp resonances overlap [72]. the concentrated raman signal stems from the tips or junctions of gnu, where field enhancement is most significant, and possibly from the interstitial sites between characterization and application of nanomaterials 2025, 8(2), 10951. 25 the core and tips of the gnu [88,89]. at certain binding sites, a red shift may occur due to the increasing size of the nanocomplex. this leads to greater retardation of multi-scattering and dispersion, which are influenced by the r6g molecular coating and the varying sizes of the gnu [90]. therefore, the clustering of gnu leads to mie scattering, causing the scattered light to shift to a longer wavelength and lower energy. indeed, 𝐼𝑆𝐸𝑅𝑆 depends on the number of molecules within the vicinity of 0.1–1 nm to metallic nanostructures in the position of the laser excitation spot. it has been suggested that one evidence for sm behavior is the spectral changes during the observation and that the photochemical and photobleaching is significantly decreased. this is due to the rapidly quenched excited electronic state by the metal surface, thus preventing excited state reactions. it was noticed during the experiment that some of the observed sers signals vanished or changed after irradiation for a longer time. there are several factors that contribute to the varying intensities observed in sers, one of which is the presence of hot spots, which occur at the junctions or close interactions between two or more nps. therefore, when gnus are chemisorbed onto a substrate with a lower 𝐷/𝑅𝑝 ratio, they should display stronger resonance coupling. this is due to plasmonic interactions between nps at high surface densities, which leads to the formation of more pronounced hot spots and, as a result, an enhancement of sers signals [46,91,92]. agglomerates can have hot spots, with characteristics depending on the shape and size of the built unit. increasing the separation between the gnu cores decouples the corresponding spr, thereby decreasing the ef. the overall sers intensity 𝐼(𝜔𝑅) can be expressed as [3]. 𝐼(𝜔𝑅) = 𝜂𝐸𝑖𝑛𝑑|𝛼𝑅(𝜔𝑅 , 𝜔0)|2𝐼0(𝑟, 𝜔0) (7) where the collection efficiency of the device is 𝜂 = [ 𝐸𝑙(𝑟, 𝜔0) 𝐸0(𝑟, 𝜔0) ] 2 [ 𝐸𝑙(𝑟, 𝜔𝑅) 𝐸0(𝑟, 𝜔𝑅) ] 2 (8) 𝐸𝑖𝑛𝑑 is the electromagnetic-induced enhancement, 𝜔0 is the frequency of excitation photons, 𝜔𝑅 is the frequency of raman photons, 𝛼𝑅(𝜔𝑅 , 𝜔0) is the raman polarizability of the molecule, and 𝐼0(𝑟, 𝜔0) is the intensity of the excitation light. polarizability can impact dispersion forces, the weakest type of intermolecular force, in several ways, including enhancing the polarizability and being influenced by the shape of the molecule. elongated molecules have electrons that move easily, which increases their polarizability and strengthens the dispersion forces. additionally, gnu is sensitive to polarization because its branches create different dipole moments. the spatial charge distribution in each branch can produce individual dipoles pointing in various directions on the gnu [93,94], and alter could change the spatial thermal distribution when heated [14]. the scattering response of a single gnu is strongly polarized when excited at spr wavelength. the polarization dependence of the scattering intensity, which suggests that surface plasmon resonance behaves like a single dipole scatterer, can have a significant impact on the results of sers [95]. thus, the sers signals from different substrates differ with wavenumber, which corresponds to the wavelength of the emitted radiation. this variation represents the molecular rotational and vibrational energy of specific chemical bonds, as well as the overall chemical composition. characterization and application of nanomaterials 2025, 8(2), 10951. 26 6. conclusions the preliminary study demonstrated a higher intensity of r6g raman lines for tgfs compared to the r6g solution alone. the surface morphology of the gnuimmobilized tgfs was analyzed using sem and afm. it was shown that pantf can relatively improve the sers results compared to tgfs due to lspr contribution. the results showed a stronger raman response for r6g at higher concentrations, and tgfs and pantf indicated an enhanced signal compared to r6g alone. the pantf incubated with gnu at 10 min exhibited moderately better sers results than tgfs, particularly at low wavenumbers such as the overlapped single peak at 647 cm−1 corresponding to c-c-c ring in-plane bending in xanthene/phenyl. however, the results deteriorated when incubated for a longer time (60 min) and became comparable to tgfs results. the ef for 10 min was higher than 60 min incubation. two key features were consistently observed throughout the experiments. first, there was a variation in the raman shift signal, which indicated changes in molecular vibrations. secondly, the signal exhibited a non-linear response to the probe power. lastly, the sensitivity of the pantf sensor can be enhanced by further optimizing the film thickness, gnu size, concentration, and incubation time. author contributions: supervision, 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characterization and application of nanomaterials (2021) volume 4 issue 1 doi:10.24294/can.v4i1.1330 original research article liquid deposition modification of nano-zsm-5 zeolite and catalytic performance in aromatization of hexene-1 yujun fang1,2,3, xiaofang su1,2,3, wei wang1,2,3, wei wu1,2,3* 1 national center for international research on catalytic technology, heilongjiang university, harbin 150080, china. e-mail: wuwei@hlju.edu.cn 2 functional inorganic materials chemistry ministry of education, heilongjiang university, harbin 150080, china 3 school of chemical and materials science, heilongjiang university, harbin 150080, china abstract the olefin aromatization is an important method for the upgrade of catalytic cracking (fcc) gasoline and production of fuel oil with high octane number. the nano-zsm-5 zeolite was synthesized via a seed-induced method, a series of modified nano-zsm-5 zeolite samples with different ga deposition amount were prepared by ga liquid deposition method. the xrd, n2 physical adsorption, sem, tem, xps, h2-tpr and py-ir measurements were used to characterize the morphology, textural properties and acidity of the modified zsm-5 zeolites. the catalytic performance of the hexene-1 aromatization was evaluated on a fixed-bed microreactor. the effects of ga modification on the physicochemical and catalytic performance of nano-zsm-5 zeolites were investigated. the ga species in the modified nano-zsm-5 zeolites mainly exist as the form of ga2o3 and gao+, which provide strong lewis acid sites. the aromatics selectivity over ga modified nano-zsm-5 zeolite in the hexene-1 aromatization was significantly increased, which could be attributed to the improvement of the dehydrogenation activity. the selectivity for aromatics over the ga4.2/nz5 catalyst with suitable ga deposition amount reached 55.4%. keywords: nanosized zsm-5 zeolite; ga modification; liquid deposition; hexene-1; aromatization article info received: 10 february 2021 accepted: 29 march 2021 available online: 7 april 2021 copyright copyright © 2021 yujun fang, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction with the rapid development of china’s automobile industry, the demand for fuel oil such as gasoline is increasing day by day. at present, catalytic cracking (fcc) gasoline is still the main vehicle fuel oil used all over the world, especially in china, the proportion of fcc gasoline is as high as about 80%. due to the high olefin content in fcc gasoline, insufficient combustion will lead to a series of environmental pollution problems such as high pm2.5 content in automobile exhaust and photochemical smoke[1]. therefore, reducing the olefin content in fcc gasoline to improve fuel quality has become an urgent problem to be solved. aromatics are not only gasoline blending components with high octane number, but also important basic chemical raw materials. therefore, converting olefins in fcc gasoline into high value-added aromatics through aromatization reaction can not only reduce the olefin content in gasoline and maintain or improve the octane number of gasoline, but also provide an effective channel for the production of aromatics. the research and development of high-efficiency catalyst is the technical core of this process. 88 zsm-5 zeolite is widely used in petrochemical and other fields as an efficient catalyst because of its unique three-dimensional cross pore structure, rich active centers and good hydrothermal stability[2,3]. however, zsm-5 zeolite with micron scale and single micro-porous structure will limit the formation and diffusion of transition intermediates and products in the pores in the acid catalytic reaction, resulting in the rapid deactivation of the zeolite due to coking and carbon deposition. the strong brønsted acid center of aluminosilicate zeolite is easy to lead to side reactions such as cracking of longchain olefin intermediates generated in the process of olefin aromatization, so as to reduce the selectivity of aromatics. the pore characteristics and acidity of zsm-5 zeolite can be adjusted by reducing the particle size of zeolite and adopting the modification method of secondary synthesis[4–6]. the existing template method for synthesizing nano zsm-5 still has many environmental problems such as large amount of organic template, high cost and large amount of nitrogen-containing wastewater. therefore, it is necessary to establish a new green and efficient method for the synthesis of nano zsm-5 zeolite. methods for adjusting the acidity of zeolite include ion exchange method, isomorphic replacement method and liquid deposition method[7–11]. although acid dealumination modification will remove some skeleton aluminum atoms of zeolite and reduce strong acid sites, it will destroy the skeleton stability of zeolite and produce a large amount of acid wastewater. the introduction of metal species by ion exchange method is limited, and the acid regulation of the catalyst and the improvement of catalytic reaction performance are small. the isomorphic substitution modification reduces the acid strength of zeolite by introducing heteroatoms into the zeolite skeleton, and forms skeleton defect sites to a certain extent. introducing ga species into zeolite by liquid phase deposition is the simplest and effective modification method to adjust its acid strength, brosted and lewis acid site density and the ratio of two active sites[12]. in the process of liquid phase deposition, ga species will cover some strong acid sites of zeolite, and form active ga species providing strong l acid, promote the dehydrogenation rate control step in the aromatization reaction process, and effectively improve its catalytic aromatization performance. in this paper, nano zsm-5 zeolite synthesized by prefabricated seed method was modified by ga liquid deposition, and the effects of ga modification on the pore characteristics, acidity and catalytic aromatization of hexene-1 of nano zsm-5 zeolite were studied. 2. experiment 2.1 synthesis of nano zsm⁃5 zeolite the mixture of four propyl ammonium hydroxide, aluminum isopropyl alcohol, tetraethyl orthosilicate and deionized water were mixed according to the ratio of 35.7 tpaoh:100 sio2:al2o3:1,083 h2o (mole ratio). after mixing at room temperature, the mixed gel was prepared and then transferred into the crystallization reactor to heat the 30 min by microwave radiation. obtain the preformed crystal seed for use. a uniform gel was prepared by mixing sodium aluminate, silica sol, sodium hydroxide and two deionized water, adding the preformed seed and then crystallizing 6 h at 180 ℃. the crystallization product is centrifuged, dried, roasted, ion exchanged with nh4no3 solution, dried and roasted to obtain h-type zsm-5 zeolite, which is recorded as nz5. 2.2 preparation of ga modified nano zsm-5 zeolite a certain amount of h-type nano zsm-5 zeolite sample (nz5) prepared according to the method described in 2.1 is added to a certain concentration of ga(no3)3 solution, stirred at room temperature for 2 h, dried overnight, and calcined at 550 degrees celsius for 3 h. the prepared ga modified nano zsm-5 zeolite is recorded as gax/nz5, x is the mass percentage of ga in the modified zeolite. 2.3 evaluation of catalytic reaction performance a fixed bed micro reactor was used to evaluate the catalytic performance of zeolite before and after modification for the aromatization of hexene-1. 89 weigh 1.0 g of 20–40 mesh catalyst, place it in the constant temperature zone of the reactor, and fill both ends with quartz sand. the reaction temperature was 480 degrees celsius, the pressure was 0.5 mpa, the mass space velocity was 2.0 h–1, and the flow rate of carrier gas (nitrogen) was 75 ml∙min–1. the reaction product was cooled in a low-temperature constant temperature bath, and the time when the first drop of liquid phase product appeared was recorded as zero time, and then the product was collected every 2 h. the composition of the reaction product was analyzed by gc⁃7900 installed with fid detector and pona capillary column (50.0 m × 200 μm × 0.5 μm). 3. experimental results and discussion 3.1structural characterization and analysis of ga modified nano zsm-5 zeolite nano zsm-5 zeoli te (sample nz5) and ga4.2⁃nz5 (ga content of 4.2 wt.%) modified by ga liquid deposition were characterized by sem and tem, as shown in figure 1. gallium oxide nano-clusters with a uniform size of about 2 nm can be observed on the surface of the modified sample ga4.2⁃nz5. the nano zsm-5 zeolite before and after liquid deposition modification with different ga content were characterized by xrd. the xrd spectrum and relative crystallinity are shown in table 1 and figure 2. figure 1. sem and ten images of nanosized zsm-5 zeolit (a, b) and tem image of ga4.2-nz5 sample modified by ga-impregnation (c). table 1. relative crystallinity, textural properties and chemical composition of zsm-5 zeolite samples modified by ga-impregnation sample relative crystallinitya /% chemical composition ga /(wt%) surface area /(m2∙g–1) si/alb si/gac si(me)d betf microporeg hnz5 100 48 — 48 0 386 74 ga1.5/nz5 96 48 77 30 2.5 358 70 ga2.1/nz5 96 48 58 26 3.3 352 69 ga4.2/nz5 96 48 27 17 5.1 336 55 note: arelative crystallinity (rc) calculated from xrd patterns; bobtained by xrf method; cdetermined from icp; dme corresponds to the al and ga; emass percent content of ga on the surface determined from xps; fbet method; gt-plot method. it can be seen from figure 2 that the xrd spectrum of the modified zeolite still has only the characteristic diffraction peak of mfi topology, and there is no spectral peak of ga2o3, indicating that ga species are highly dispersed in zsm-5 zeolite. it can be seen from table 1 that the relative crystallinity of zsm-5 zeolite modified by ga decreases slightly, and its specific surface area decreases with the increase of ga deposition, because gallium species block some pores of the zeolite. in addition, the ga content on the outer surface of ga modified zeolite was analyzed by x-ray photoelectron spectroscopy (xps), and compared with the ga content of zeolite measured by icp method, it was found that the ga content on the outer surface of zeolite was higher, indicating that ga species were mainly distributed on the outer surface of zeolite. ga modification can not only form ga2o3 nano clusters on the surface of zeolite, but also form gao+ species with dehydrogenation activity[13]. in order to 90 prove the existence of gao+ active species in the zeolite modified by ga liquid phase deposition, the samples were characterized by h2⁃tpr and xps. the results are shown in figure 3, figure 4 and table 2 respectively. figure 2. xrd patterns of nanosized zsm-5 zeolite samples modified by ga-impregnation. figure 3. h2⁃tpr profiles of nanosized zsm-5 zeolite samples modified by ga-impregnation. figure 4. ga 2p3/2 xps spectra of nanosized zsm-5 zeolite samples modified by ga-impregnation. it can be seen from figure 3 and table 2 that in the h2-tpr curve of modified gax/nz5 series samples, there are reduction peaks corresponding to ga2o3 and active gao+ species with strong interaction with the negative charge of zeolite skeleton at 350–600 ℃ and 500–800 ℃ respectively. with the increase of ga deposition, the amount of hydrogen consumed when ga2o3 and gao+ species are restored increases. the reduction temperature of ga2o3 increases slightly with the increase of ga deposition amount, from 486 ℃ to 501 ℃, which may be due to the increase of the size of ga2o3 nano clusters formed when the deposition amount of ga increases, and thus it may be more difficult to be restored. when the deposition amount of ga increases from 1.5% to 4.2%, the reduction temperature of corresponding gao+ species in gax/nz5 series modified samples increases significantly from 602 ℃ to 693 ℃, which is due to the enhanced interaction between gao+ species and the negative charge of zeolite skeltable 2. h2⁃tpr data of nanosized zsm-5 zeolite samples modified by ga-impregnation sample temperature/℃ consumption of h2/(× 10–5 mol∙g–1) l.t. h.t. ga2o3→ga2o gao+→ga+ total ga1.5/nz5 486 602 8.71 3.29 12.00 ga2.1/nz5 489 636 12.11 7.89 20.00 ga4.2/nz5 501 693 15.82 15.52 31.34 eton[14]. it can be seen from figure 4 that with the increase of ga deposition in the sample, the electron binding energy of gax/nz5 series modified samples increases from 1117.5 ev to 1117.8 ev, which can be attributed to the strong interaction between more gao+ species and the negative charge of zeolite skeleton. it is consistent with the characterization results of h2-tpr. 91 3.2 characterization and analysis of acidity of ga modified nano zsm-5 zeolite in order to study the effect of ga liquid deposition modification on the acidity of nano zsm⁃5 zeolite, the samples before and after modification were characterized by pyridine adsorption infrared spectroscopy (py⁃ir). the results are shown in figure 5. it can be seen from figure 5(a) that the py⁃ir spectrum of the modified series of samples gax/nz5 corresponds to the absorption peaks of acid sites of brθsted near 1,545 cm–1 move towards low wave number, indicating that the acid intensity decreases. as can be seen from figure 5(b), the acid content of brθsted of ga modified zeolite decreased significantly. due to partial brθsted acid site is covered by the deposited ga species, or the acid site of brθsted in the pore cannot be detected due to blocking part of the pore of zeolite. the acid content of brθsted of ga modified gax/nz5 series modified samples did not change significantly. however, with the increase of ga deposition, the lewis acid content and total acid content of the modified samples increased due to the formation of more ga2o3 and active gao+ species. figure 5. py-ir spectra (a) and acid amount (b) of the nano-sized zsm-5 zeolite samples modified by a. hnz5, b. ga1.5/nz5, c. ga2.1/nz5, d. ga4.2/nz5. 3.3 catalytic performance of ga modified nano zsm-5 zeolite for aromatization of hexene-1 in order to explore the corresponding relationship between the structure and acidity of ga modified nano zsm-5 zeolite and its catalytic aromatization reaction performance, the catalytic performance of ga liquid-phase deposition modified nano zsm5 was studied with hexene-1 as a model compound. the results are shown in figure 6. it can be seen from figure 6(a) that the modified zeolite ga4.2/nz5 catalyst has better catalytic stability than the unmodified zsm-5 zeolite (hnz5), and the conversion of hexene-1 is still close to 100% at 35 h, which is due to the reduction of strong acid content and milder acidity of ga modified molecular sieve, the deactivation of molecular sieve due to carbon deposition is inhibited. it can be seen from figure 6(b) that when gax/ figure 6. catalytic performance in hexene-1 aromatization over the nanosized zsm-5 zeolite samples modified by ga-impregnated. 92 nz5 series modified zeolite are used as catalysts, the total aromatics selectivity of hexene-1 aromatization reaction is improved to varying degrees. when the deposition amount of ga on zsm-5 zeolite is 1.5% and 2.1% respectively, the corresponding catalysts ga1.5/nz5 and ga2.1/nz5 can greatly improve the selectivity of aromatics in the reaction products. when the deposition amount of ga increases to 4.2%, the selectivity of ga4.2/nz5 catalyst for aromatics reached the maximum, up to 55.4%, which is that the active gao+ species with more strong l acid sites in ga4.2/nz5 catalyst promoted the dehydrogenation reaction. 4. conclusion the preformed seed method can not only greatly reduce the amount of organic template, but also synthesize nano zsm-5 zeolite with regular morphology and high crystallinity. liquid deposition modification is a simple and easy method to adjust the acidity of molecules. because the liquid deposition modified gazsm-5 not only weakens the strength of the acid site of brθsted and inhibits the cracking reaction, but also forms an active gao+ species with strong lewis acid site, improves the dehydrogenation activity of the zeolite catalyst, and therefore significantly improves the aromatics selectivity of the aromatization reaction of hexene-1. this research work provides a useful idea for the improvement of acidity regulation and catalytic performance of zeolites. conflict of interest the authors declare that they have no conflict of interest. acknowledgements this article was supported by the general program of national natural science foundation of china (21276067, 21676074). references 1. long h, jin f, xiong g, et al. effect of lanthanum and phosphorus on the aromatization activity of zn/ zsm-5 in fcc gasoline upgrading. microporous and mesoporous materials 2014; 198(1): 29–34. 2. chevella d, macharla ak, banothu r, et al. synthesis of non-symmetrical alkyl carbonates from alcohols and dmc over nanocrystalline zsm-5 zeolite. green chemistry 2019; 21(11): 2938–2945. 3. lok cm, van doorn j, almansa ga. promoted zsm-5 catalysts for the production of bio-aromatics, a review. renewable and sustainable energy reviews 2019; 113: 109248. 4. peng p, stosic d, liu xm, et al. strategy towards enhanced performance of zeolite catalysts: raising effective diffusion coefficient versus reducing diffusion length. chemical engineering journal 2020; 385: 123800. 5. milina m, mitchell s, crivelli p, et al. mesopore quality determines the lifetime of hierarchically structured zeolite catalysts. nature communications 2014; 5: 1–10. 6. zhang y, wu s, xu x, et al. ethane aromatization and evolution of carbon deposits over nanosized and microsized zn/zsm-5 catalysts. catalysis science & technology 2020; 10(3): 835–845. 7. raad m, astafan a, hamieh s, et al. catalytic properties of ga-containing mfi-type zeolite in cyclohexane dehydrogenation and propane aromatization. journal of catalysis 2018; 365: 376–390. 8. su x, fang y, bai x, et al. synergic effect of gao+/ brønsted acid in hierarchical ga/al-zsm-5 bifunctional catalysts for 1-hexene aromatization. industrial & engineering chemistry research 2019; 58(45): 20543–20552. 9. zhang p, guo x, guo h, et al. study of the performance of modified nano-scale zsm-5 zeolite on olefins reduction in fcc gasoline. journal of molecular catalysis a: chemical 2007; 261(2): 139–146. 10. su x, fang y, gao p, et al. in-situ microwave synthesis of nano-gazsm-5 bifunctional catalysts with controllable location of active gao+ species for olefins aromatization. microporous and mesoporous materials 2020; 306: 110388. 11. jiang yc, du yy, he zf, et al. preparation of mesoporous carbon nanospheres from resorcinol/melamine resins and performances of supercapacitors. journal of engineering of heilongjiang university 2021; 12(1): 31–36. 93 12. ausavasukhi a, sooknoi t. tunable activity of [ga] hzsm-5 with h2 treatment: ethane dehydrogenation. catalysis communications 2014; 45: 63–68. 13. fang y, su x, bai x, et al. aromatization over nanosized ga-containing zsm-5 zeolites prepared by different methods: effect of acidity of active ga species on the catalytic performance. journal of energy chemistry 2017; 26 (4): 768–775. 14. varela-gandía fj, berenguer-murcia á, lozano-castelló d, et al. total oxidation of naphthalene using palladium nanoparticles supported on beta, zsm5, sapo-5 and alumina powders. applied catalysis b: environmental 2013; 129: 98–105. microsoft word can-6240 characterization and application of nanomaterials 2024, 7(2), 6240. https://doi.org/10.24294/can.v7i2.6240 1 article the potency of agno3 nanoparticles combined with sweet potato (ipomea batatas) starch as a sensor for mercury detection in cosmetic products esa ghanim fadhallah*, vera pertiwi, duwinda, sugaluh yulianti, umi adila tsani, yunita rachmawati department of agricultural product technology, faculty of agriculture, universitas lampung, bandar lampung 35145, indonesia * corresponding author: esa ghanim fadhallah, esa.ghanim@fp.unila.ac.id abstract: fraudulence in cosmetic ingredients is becoming increasingly prevalent, alongside the rising demand and utilization of cosmetics within the populace. one of the whitening agents still utilized in cosmetics is mercury, present in forms such as mercury chloramide (hgnh2cl2) and mercury chloride (hgcl2). prolonged mercury exposure can have adverse health effects. to address this issue, alternative mercury analysis methods in samples have been developed, including the utilization of silver nanoparticles amalgamated with sweet potato starch as a stabilizing agent. this paper aims to delve into the roles of silver nanoparticle agno3 and sweet potato starch (as a stabilizer) as a sensor for mercury detection, which can be applied in cosmetic products. detection of mercury utilizing nanoparticles is based on the surface plasmon resonance phenomenon, which endows a high level of selectivity and sensitivity toward the presence of mercury metal ions. when interaction occurs between mercury metal and silver nanoparticles, the liquid undergoes a color change from yellowish-brown to transparent. this phenomenon arises from the oxidation of ago (yellow) to ag+ ions (transparent) by the mercury metal. consequently, a silver nanoparticle sensor utilizing sweet potato starch as a stabilizing agent exhibits the potential to detect mercury metal within a substance with high efficacy. keywords: cosmetic; mercury detection; stabilizer; sweet potato starch 1. introduction commercial whitening creams are widely available and easy to use, at affordable prices. in indonesia, many cosmetic producers engage in fraudulent practices due to the increasing demand and consumption of cosmetics, driven by the high enthusiasm of the indonesian population for cosmetics. consequently, cosmetic producers compete to create products that can quickly brighten and whiten skin at affordable prices, leading to fraudulent practices in cosmetics production. according to the central statistics agency, online transactions increased by 480% during the sevenmonth pandemic period. unscrupulous e-commerce sellers exploit this trend to distribute unauthorized (tie) or illegal and hazardous cosmetic products in various markets. data on crime vulnerability reported by the center for drug and food control (pom) from 1 january 2018, to 15 september 2020, revealed several cosmetic products containing harmful whitening agents circulating in indonesia. mercury is a commonly used whitening agent in cosmetics, present in forms such as mercury chloride (hgcl2) and mercury amino chloride (hgnh2cl2). prolonged mercury exposure can cause skin discoloration, black spots, allergies, skin irritation, and permanent damage to the nervous system, brain, kidneys, and fetal development. therefore, there is a need for mercury content analysis in various cosmetics available on the market. citation fadhallah eg, pertiwi v, duwinda, et al. the potency of agno3 nanoparticles combined with sweet potato (ipomea batatas) starch as a sensor for mercury detection in cosmetic products. characterization and application of nanomaterials. 2024; 7(2): 6240. https://doi.org/10.24294/can.v7i2.6240 article info received: 6 may 2024 accepted: 29 may 2024 available online: 5 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 6240. 2 according to azhar [1], there are several methods for measuring mercury metal concentrations in samples, such as inductive coupled plasma mass spectrometry (icpms) and atomic absorption spectroscopy (aas). however, the equipment costs for these methods are relatively high, necessitating alternative mercury analysis methods, including the use of silver nanoparticles mixed with starch as a stabilizing agent. previous studies have utilized starch as a new nanocomposite material containing zinc sulfide quantum dots coated with l-cysteine. nanocomposites were prepared in the form of potato starch gel and foil embedded with spherical quantum dots sized at 1020 nm. pb2+ and cu2+ ions reduced emission intensity in the photoluminescence spectral band. the described quantum dots were obtained using a simple, safe, and inexpensive method. due to these properties, alternative sensors for pb2+ and cu2+ can be used in biotechnology and food technology. sweet potato is a nutritious tuber, containing fiber 6.33%–9.51%, protein 2.14%– 2.86%, and b-carotene 18.83 mg/100 g [2]. however, it is still containing antinutrients such as phytate, oxalate, and tannin [2,3]. additionally, its starch is widely used for thickening or stabilizing, as it contains 95.26%–96.73% of starch with 18.17%– 18.56% of amylose [4]. the native starch from sweet potatoes has previously been reported to have a stable viscosity, with a peak viscosity of 3421.5 cp and a final viscosity of 3447.0 cp [5], making it a potential candidate for use as a stabilizer in mercury detection sensors. innovation in the utilization of sweet potato starch potentially makes sweet potatoes more widely utilized. furthermore, with sweet potato starch used as a mercury (hg) detection sensor, which is more affordable and readily available, it can reduce operational costs in the production of mercury (hg) detection sensors. with affordable prices and ease of use, it is hoped that many cosmetic producers will be more conscientious in their cosmetic selections, as they can easily utilize these mercury (hg) detection sensors. the innovation of sweet potato starch as a stabilizer in the mixing of silver nanoparticles can be beneficial in reducing the production and distribution of cosmetics containing mercury. this concept is also useful in creating a cheap, fast, and effective tool for detecting mercury. the development of sweet potato starch can also increase the productivity of sweet potatoes. the paper aimed to explore the potency of agno3 nanoparticles and sweet potato starch (as stabilizers) as a sensor for mercury detection in cosmetic products. 2. methods the method used is an effective literature review following the topic. the method of discussion is based on the research results found by previous researchers, which are then integrated with other researchers to get strong results and conclusions. 3. results and discussion 3.1. mercury as heavy metals heavy metal ions have become a widely discussed environmental pollution issue. apart from polluting the environment, these metals pose significant risks to human health. one such example of heavy metal is mercury, which is commonly encountered. characterization and application of nanomaterials 2024, 7(2), 6240. 3 mercury is identified as a hazardous pollutant due to its high toxicity and strong bioaccumulation potential, capable of causing damage to vital organs and tissues in the human body even at low concentrations [6]. mercury metal sensors are technologies used to detect the presence of mercury in a substance. these sensors are fabricated using agno3 nanoparticles stabilized with sweet potato starch. the detection of mercury metal using these nanoparticles is based on the surface plasmon resonance (spr) effect, wherein the agno3 nanoparticles exhibit high selectivity and sensitivity towards the presence of mercury metal ions (hg) [1]. according to wahyudi [7], the production of silver nanoparticles requires a stabilizing agent to prevent the colloidal particles from agglomerating. agglomeration refers to the formation of particle clusters in a solution, leading to colloidal instability in nanoparticles. starch derived from sweet potatoes is employed as the stabilizing agent in this sensor due to its environmentally friendly nature and non-hazardous properties. typically, the preparation of materials for synthesizing silver nanoparticles involves hazardous chemicals, high energy consumption, and complex purification processes [8]. innovations in nanoparticle synthesis using starch as a stabilizer offer a non-toxic and environmentally friendly chemical development solution, requiring minimal costs for silver nanoparticle synthesis. this is attributed to the abundance of sweet potatoes in indonesia and their affordable prices. according to data from the agricultural data and information center of the ministry of agriculture in 2022, sweet potato production in indonesia showed a slight increase of 4.02% from 2020 to 2022. this rise in sweet potato production presents an opportunity for expanding the utilization of sweet potatoes, particularly in non-food applications. detection of mercury metal in cosmetics can be conducted on a laboratory scale or implemented by cosmetic resellers to ascertain whether the products being sold are free from mercury. this testing involves mixing the mercury metal sensor solution with the cosmetics under examination, followed by analyzing their absorbance using a uv-vis spectrophotometer. during this process, a change in the solution’s color occurs, enabling the determination of absorbance values. 3.2. previous study previous research studies related to mercury metal sensors using nanoparticles include the research by winiari and kurniawan [9], which focused on mercury detection using direct solutions of gold nanoparticles. the results of this study indicated that the sensor activity was demonstrated by a shift in the wavelength towards higher values with increasing concentrations of mercury and gold nanoparticles without modification, which can be utilized for simple, rapid, and practical mercury detection. another study relevant to mercury metal sensors utilizing nanoparticles is by vasileva [10], which explored the application of silver nanoparticles stabilized with starch as a colorimetric sensor for mercury (ii) in 0.005 mol/l nitric acid. this study highlighted that the presence of 0.005 mol/l nitric acid utilizing starch-coated agnps as an optical sensor based on lspr (localized surface plasmon resonance) is effective in mercury detection. the procedures conducted were practical, fast, and characterization and application of nanomaterials 2024, 7(2), 6240. 4 cost-effective. the mercury metal sensor using nanoparticles in this optical sensor based on lspr can be applied for drinking water and wastewater. in the study by vasileva [8], it was reported that they successfully synthesized silver nanoparticles using environmentally friendly starch as a stabilizing agent. the research revealed that the nanoparticle sensor developed to test hydrogen peroxide exhibited excellent sensitivity and a high response to the presence of hydrogen peroxide in the sample. 3.3. mercury detection the detection of mercury has been extensively developed using various methods such as cold vapor atomic absorption spectroscopy (cv-aas), inductively coupled plasma optical emission spectroscopy (icp-oes), gas chromatography, and others. according to wang [11], these methods exhibit excellent performance in detecting metals; however, their application requires expensive and sophisticated instruments, complex sample processing, and high analysis costs, hindering their routine application in mercury detection. the increasing mercury metal pollution, particularly in cosmetic products, necessitates routine testing of these products. to reduce the operational costs of mercury detection, cheaper, practical, easy-toimplement, and environmentally friendly technologies are needed. mercury metal sensors using agno3 nanoparticles with sweet potato starch as a stabilizing agent represent an innovative heavy metal detection technology. in previous research conducted by wahyudi [7], polyacrylic acid (paa) was used as the stabilizing agent in the production of silver nanoparticles, while in the study by khachatryan and khachatryan [12], potato starch was utilized as the stabilizer in nanocomposites. in this mercury metal sensor, we employ sweet potato starch as an innovation in the use of agno3 nanoparticle stabilizers (silver). this innovation is based on the research by vasileva [10] on the application of nanoparticle particles stabilized with starch for mercury metal detection. figure 1 illustrates the reaction that occurs between agno3 nanoparticles when reacted with mercury metal (hg). figure 1. schematic representation of the interaction mechanism between sweet potato starch-stabilized agno3 nanoparticles and mercury. source: vasileva [10]. the interaction between hg2+ and nanoparticles involves electrostatic attraction between negatively charged silver nanoparticles and positively charged hg2+. this leads to a reduction in the distance between nanoparticles, resulting in aggregation. hg2+ is adsorbed on the surface of agnps and reduced to hg by surface ag atoms, while simultaneous diffusion of ag+ into the solution occurs. the reaction leads to the formation of new mercury atoms combined with surface ag atoms. this interaction characterization and application of nanomaterials 2024, 7(2), 6240. 5 may alter the surface charge of nanoparticles, leading to destabilization and agglomeration. 3.4. role of agno3 nanoparticles with sweet potato starch the mercury metal sensor is formulated in liquid form, allowing direct application to cosmetics suspected of containing mercury. the production of nanoparticles entails the reduction of agno using d-glucose as the reducing agent. a starch solution serves as the capping and stabilizing agent, with the addition of naoh as a catalyst in the reaction to produce an aqueous dispersion of silver nanoparticles. the schematic diagram of the silver nanoparticle synthesis process with sweet potato starch as the stabilizing agent is illustrated in figure 2. figure 2. schematic diagram of the silver nanoparticle synthesis process with sweet potato starch as the stabilizing agent. the molar ratio of metal to reducer is 1:3, ensuring the complete reduction of ag+ ions in the solution into silver metal nanoparticles [10]. as depicted in figure 2, the synthesis process involves stirring a starch solution (0.2% w/v) in a sonication bath for 15 minutes, followed by the addition of 16 ml of 0.0001 mol/l agno3 solution. the mixture is stirred for 10 minutes to facilitate the diffusion of metal ions into the starch capping/stabilizing agent. subsequently, the reducing solution containing dglucose (0.01 m) is injected under sonication, followed by the addition of 2.4 ml of naoh solution at 30 ℃ temperature maintained constant in an ultrasound bath. the reaction is completed within 60 minutes after the color change occurs. the mercury metal sensor, in the form of silver nanoparticle liquid with starch stabilizer, will react with the tested cosmetic samples. the kinetics of interaction between sweet potato starch-stabilized silver nanoparticles and mercury metal (hg) are reflected in the color change. according to research by azhar [1], silver nanoparticles extracted from starfruit are selectively reactive towards mercury metal, indicated by a color change from yellowish-brown to clear. this occurs because mercury metal oxidizes ago in the yellowish-brown silver nanoparticles to form clear ag+ ions. further characterization of the sensor solution involves measuring the absorbance of the solution via uv-vis spectrophotometer to determine the effect of mercury on sweet potato starch-stabilized silver nanoparticles. the predicted uv-vis absorbance graph and color change of the sweet potato starch-stabilized silver nanoparticle liquid with added mercury are illustrated in figures 4 and 3, respectively. characterization and application of nanomaterials 2024, 7(2), 6240. 6 figure 3. prediction of mercury metal sensor results using silver nanoparticles with sweet potato starch as the stabilizing agent. numbers indicated the concentration of mercury. figure 4. predicted schematic of uv-vis absorbance graph for mercury metal sensor using nanoparticles with sweet potato starch as the stabilizing agent. source: vasileva [6]. 4. conclusion in conclusion, the silver nanoparticle sensor with sweet potato starch as the stabilizing agent shows potential for detecting mercury metal in a substance. this sensor is formulated in liquid form, allowing direct testing on samples suspected of containing mercury, with a color change from yellowish-brown to clear indicating the presence of mercury. the utilization of sweet potato starch for mercury sensor production is expected to enhance the productivity and utilization of sweet potatoes in indonesia. author contributions: conceptualization, vp, d, sy and uat; writing the draft in bahasa, vp, d, sy and uat; editing to manuscript layout, yr; reviewing the manuscript, egf; translating article to english, egf; original draft preparation, egf; supervision, egf. all authors have read and agreed to the published version of the manuscript. characterization and application of nanomaterials 2024, 7(2), 6240. 7 conflict of interest: the authors declare no conflict of interest. references 1. azhar ff. utilization of silver nanoparticles of star fruit extract as colorimetric indicator of mercury metal (indonesian). jurnal ipteks terapan. 2019; 13(1): 34. doi: 10.22216/jit.2019.v13i1.3614 2. oloniyo ro, omoba os, awolu oo. biochemical and antioxidant properties of cream and orange-fleshed sweet potato. heliyon. 2021; 7(3): e06533. doi: 10.1016/j.heliyon.2021.e06533 3. gouveia cs, ganança jf, lebot v, et al. changes in oxalate composition and other nutritive traits in root tubers and shoots of sweet potato (ipomoea batatas l. [lam.]) under water stress. journal of the science of food and agriculture. 2019; 100(4): 1702-1710. doi: 10.1002/jsfa.10185 4. babu as, parimalavalli r. effect of starch isolation method on properties of sweet potato starch. food technology. 2014; 38(1): 48-63. 5. babu as, parimalavalli r, jagannadham k, et al. chemical and structural properties of sweet potato starch treated with organic and inorganic acid. journal of food science and technology. 2014; 52(9): 5745-5753. doi: 10.1007/s13197-0141650-x 6. zhang s, zhang d, zhang x, et al. ultratrace naked-eye colorimetric detection of hg2+ in wastewater and serum utilizing mercury-stimulated peroxidase mimetic activity of reduced graphene oxide-pei-pd nanohybrids. analytical chemistry. 2017; 89(6): 3538-3544. doi: 10.1021/acs.analchem.6b04805 7. wahyudi t, sugiyana d, helmy q. synthesis of silver nanoparticles and their activity test against bacteria e. coli and s. aureus (indonesian). arena tekstil. 2011; 26(1). doi: 10.31266/at.v26i1.1442 8. vasileva p, donkova b, karadjova i, et al. synthesis of starch-stabilized silver nanoparticles and their application as a surface plasmon resonance-based sensor of hydrogen peroxide. colloids and surfaces a: physicochemical and engineering aspects. 2011; 382(1-3): 203-210. doi: 10.1016/j.colsurfa.2010.11.060 9. winiari a, kurniawan f. direct detection of mercury using gold nanoparticle solution (indonesian). jurnal sains dan seni pomits. 2013; 2(1): 1-3. 10. vasileva p, alexandrova t, karadjova i. application of starch-stabilized silver nanoparticles as a colorimetric sensor for mercury(ii) in 0.005 mol/l nitric acid. journal of chemistry. 2017; 2017: 1-9. doi: 10.1155/2017/6897960 11. wang w, zhang y, yang q, et al. fluorescent and colorimetric magnetic microspheres as nanosensors for hg2+ in aqueous solution prepared by a sol–gel grafting reaction and host–guest interaction. nanoscale. 2013; 5(11): 4958. doi: 10.1039/c3nr00580a 12. khachatryan gc, khachatryan k. starch based nanocomposites as sensors for heavy metals – detection of cu2+ and pb2+ ions. international agrophysics. 2019; 33: 121-126. doi: 10.31545/intagr/104414 microsoft word can-3573 pb online characterization and application of nanomaterials (2023) volume 6 issue 2 doi:10.24294/can.v6i2.3573 1 original research article photocatalytic degradation of organic dyes using transition metal based mixed metal oxide nanocomposite under different illumination r. biju department of physics, tkm college of arts and science (affiliated to university of kerala), karicode, kollam 691005, kerala, india; bijur4u@gmail.com abstract nowadays, copper and zinc nanoparticles are widely employed in a variety of applications. with nanoscale particle sizes, copper oxide/zinc oxide composite is easily synthesized using a variety of techniques, including hydrothermal, microwave, precipitation, etc. in the current work, chemical precipitation is used to create a copper oxide/zinc oxide nanocomposite. xrd analysis was used to determine the nanocomposite’s structural characteristics. through sem analysis, the surface morphological properties are investigated. edax is used to study the chemical composition of produced materials, while uv/visible spectroscopy is used to determine their optical properties. the assessment of the copper oxide/zinc oxide nanocomposite’s degrading property on dyes like methyl red and methyl orange under uv and visible light are the main objectives of the current work. keywords: nanocomposite; metal oxide; photocatalysis; methyl orange; methyl red article info received: 8 november 2023 accepted: 10 december 2023 available online: 26 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction materials that contain multiple naturally occurring materials, one of which is in the nano form, are called nanocomposite materials. the three main types of nanocomposite materials are ceramic matrix, metal matrix, and polymer matrix. each form of nanocomposite material consists of a continuous component known as the matrix portion and a dispersed part. one of the technologies that is frequently employed for a variety of purposes is nanotechnology. people are typically drawn to items that are colorful. many sectors consider coloring agents to be essential because of their demand. the plastics, cosmetics, paper, leather, pharmaceutical, and printing industries are among those that use dyes or coloring chemicals extensively. the textile industry has around 80% of utilization of various type of dye materials. in the present study we are selected methyl orange (mo) and methyl red (mr) as dye materials for photocatalytic degradation various studies conducted by different scientists reported that methyl orange is highly susceptible for development of cancer, development of tumour and genetic disorder moreover it is a very toxic azo dye [1]. the common source of discharging methyl orange to environment is occurred by industries such as fabric manufacturing, medicine. the use of mo as a ph indicator in research laboratories and industries also discharge huge amount into water resources. some of the potential hazards property of mo include stability, great solubility, bright color, and low biodegradability[2,3]. whereas mr 2 is also an azo dye with some potential health risks; largely used in microbiological application such as “methyl red test”. mr is considered as an acute toxic material. over dose of mr may be leads to irritation in skin and eye, it also responsible for breathing problems. recent research shows that different synthetic dye coloring ingredients have severely contaminated the world’s primary water resources. because of its extreme solubility these kinds of contaminants are not amenable to the traditional ways of purifying water. water use and recycling are always kept under check by nature. nature recycles water in a variety of ways. numerous industries have developed as a result of the industrial revolution. a necessary component of most enterprises is water. the current state of affairs surpasses the ability of natural processes to supply clean water. numerous studies demonstrate that almost all naturally occurring sources of drinking water are found to be unclean and contaminated with a variety of contaminants, hazardous chemicals, and pathogenic organisms. using catalytic nanocomposite materials, the very hazardous compounds can break down during photocatalysis. in photocatalysis, ultraviolet light activates a semiconductor surface, which readily produces free radicals. through the process of photocatalysis, we may convert extremely poisonous industrial colors into innocuous material by using capable nanoscale catalytic material. these methods are among the best candidates for treating water because of their environmentally beneficial qualities. studies on the topic of copper-based nanocomposites have revealed a wide range of applications. for example, copper oxide nanoparticles are utilized to make gas sensors[4]. catalytic actions are employed to remove organic pollutants like dyes. according to certain research, copper oxide may find application as a semiconductor[5]. the shortage of fresh water is one of the major threats to humankind. numerous organic contaminants have severely contaminated the majority of the water resources. these kinds of contaminants cannot be removed from water using the traditional methods of water filtration. the extremely hazardous substance can be broken down into co2 and water using photocatalysis using nanocomposite materials. one of the most effective and environmentally beneficial methods of treating water is photocatalysis. wastewater treatment basically involves three key techniques. these techniques include chemical, biological, and physical ones. biological treatment techniques often require extensive spaces and operational protocols due to their intricate architecture. one drawback of chemical treatments is sludge formation. in addition, the sludge itself produces fresh trash. there are many different kinds of chemicals needed for the process. adsorption techniques and membrane filtration technologies are two popular physical methods. the membrane filtration techniques have a limited lifespan. it is discovered that the adsorption method is costly because activated carbon is used in it. photocatalysis process in which two stages, as a liquid and a solid. molecules may be photo excited by uv rays during this process. in this process, hydroxyl radicals or free holes are the oxidizing species produced is termed as heterogeneous photocatalysis[6]. the process of heterogeneous photocatalysis commences when a photocatalyst absorbs light radiation. consequently, the semiconductor experiences the generation of photoinduced electron-hole pairs. holes are created in the valence band when a photon is absorbed by the semiconductor and excites the valence band electrons to move into the conduction band. an electron acceptor, such as oxygen in the solution, is reduced by the photoinduced electron. in a similar manner, an electron produced by a donor species can join with a hole that has moved to the surface. oxygen serves as an electron acceptor in semiconductor photocatalysts. it is understood that the electron generated by photoreaction can reduce oxygen molecules into oxygen radicals o2 –. these radicals undergo several succeeding processes and harvest various types of reactive species such as ho2 , ho2 –, h2o2 and possibly ho radicals. the organic electron donor may oxidize as a result of the presence of activated oxygen species. similarly, holes created when a photon is absorbed can oxidize the electron donor and result in the production of ho. when the two reactions mentioned above work together, organic contaminants are broken down into mineral acids, carbon dioxide, and water. the process of heterogeneous photocatalysis involves several steps. there are two primary processes that 3 produce the hydroxyl radicals. during the first stage, the catalyst absorbs light radiation, creating valance band holes. when the generated holes interact with water molecules, a water molecule splits into a proton and a hydroxyl-free radical. in the alternative mechanism, hydroxyl free radicals can be created when the valance band holes react with hydroxyl groups (oh-)[7]. 2. materials and methods well-known chemical method co-precipitation process was used for the preparation of copper oxide/zinc oxide (cuo/zno) nanocomposites. precursors for the preparation include copper nitrate, zinc nitrate, ethylene diamine tetra acetic acid (edta) and sodium hydroxide. the precursors were purchased from local laboratory chemical supplier all chemicals are ar grade with purity 99.4% manufactured by loba chemie pvt ltd. mumbai, maharashtra, india. 3. preparation of cuo/zno nanocomposite preparation begins with making of 20 ml solutions of 0.15 m copper nitrate, 0.15 m zinc nitrate, and 0.0254 m edta are used in the preparation process. they were all placed in a conical flask and thoroughly mixed. a 250 ml solution of 2 m sodium hydroxide was placed in a burette and the aforesaid solution was allowed to gradually fall at a steady pace. a thick copper hydroxide/zinc hydroxide precipitate formed after five hours of continuous stirring using a magnetic stirrer at an rpm of 2000. in the reaction described above, edta functions as a capping agent to stop the agglomeration and as a stabilizer. the precipitate that was formed above is extracted by filtering it with ultra-filter paper. afterwards, it undergoes many washings using triple-distilled water, ethanol, and acetone to eliminate any leftover contaminants. after the obtained powder was dried in a hot air oven set at 60 ℃ for 12 h, the dried powder is heated for six hours at 500 ℃ in a muffle furnace. final product is cuo/zno (cz5) with a black color was obtained. 4. results and discussions 4.1. analysis of xrd pattern x-ray diffraction (xrd) is used to assess the crystalline clarity and structural purities. figure 1 displays the xrd pattern for the nanocomposites. it is abundantly obvious that the xrd patterns shows prominent peaks, which occur during the creation of nanocomposites, are indicative of the nanocomposite's crystalline character. the scherrer equation, d = 0.9/cos[8], was utilized to calculate the particle sizes of the synthesized nanocomposite. the fwhm (full width at half maximum) of the xrd lines is represented by , whereas  = 1.54060 å. the samples that were annealed at 500 ℃ had average crystallite sizes of 31 nm. the xrd pattern of cz5 nanocomposite individually matched with icdd standard diffraction data of copper oxide and zinc oxide. the obtained xrd pattern for cuo was found to match well with icdd pattern number 801916 with monoclinic phase and edge centered geometry. similarly, zno was in well agreement with icdd pattern number 750576 with primitive geometry and wurtzite (hexagonal) phase[9]. figure 1. xrd pattern of cz5 nanocomposite annealed 500 ℃. 20 30 40 50 60 70 80 0 300 600 900 1200 1500 1800 (2 02 )z no (2 03 )c uo (0 04 )z no (2 01 )z no (2 00 )z no (1 03 )c u o (1 12 )z n o (̀ 11 3) c u o (2 02 )c u o (1 10 )z n o (̀ 2 02 ) c u o (0 20 )c u o(1 02 )z n o (1 11 )c uo (1 01 )z n o (̀ 1 11 ) c u o (1 10 )c uo (1 00 )z no (0 02 )z no in te n si ty ( c ou n ts ) angle (2) cz5 4 4.2. uv spectral studies with the aid of a uv/visible spectrophotometer with a 1 nm resolution, the uv spectrum of a cuo/zno nanocomposite sintered at 500 ℃ was conducted in the wavelength range of 200 to 900 nm, as illustrated in figure 2. uv spectra provide amazing details regarding the material’s optical bandgaps. by using tauc formula, α αhυ = a(hυ – eg)n, where a is a constant, hυ is the photon energy (υ = c/), eg is the bandgap, and n = 1/2 for an allowed direct transition, the material’s energy band and the absorption coefficient α are connected. the tacu plot[10] is used to compute the direct optical bandgap, which is shown in figure 3. cuo/zno nanocomposite annealed at 500 ℃ has a direct optical bandgap of 2 ev and 3.78 ev. presence of multiple band gap is the clear-cut representation of nanocomposite formation. figure 2. uv-visible spectrum of cz5. figure 3. tauc plot of cz5. figure 4. sem image of cz5. 200 300 400 500 600 700 800 900 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 a b so rb an ce (a .u ) wavelength(nm) cz5 1 2 3 4 5 6 0 5 10 15 20 25 30 ( h ) 2 energy (ev) cz5 3.78 ev2.00ev 5 figure 5. edax spectrum of cz5. figures 4 displays the sem image of the cz5 nanocomposite. the particles have a substantially agglomerated appearance and are roughly uniform in shape. figure 5 displays the nanocomposite’s edax pattern. the presence of oxygen, zinc, and copper in the nanocomposite was confirmed by the edax results. the mass percentage of different elements in the sample obtained from edax analysis are oxygen 26.96%, copper 34.38% and zinc 38.66%, which confirms the formation of nanocomposite. 5. photocatalytic studies photocatalytic degradation ability of cz5 was studied using methyl orange and methyl red under uv and visible radiation. in the present study, the parameters such as dose rate of photocatalyst is fixed at 0.1 gm. the amount of catalyst load increased the number of active sites on the photocatalytic surface which increase the photocatlatitic efficiency[11]. the entire reaction was carried out in a constant temperature. using the uv-vis spectroscope, the initial absorbance of the blank solution was recoded. thereafter at each half an hour 10 ml dye solution was collected from the cell and absorbance were recorded. the variations in absorbance with wavelength at a time ranging from 0.5 to 3 h in an interval of half an hour are shown in the figures 6 and 7. the mechanism proposed for the degradation of organic dyes methyl orange and methyl red by cz5 is relatively due to the high band gap in the synthesized cz5 nanocomposite the presence of two different transition metal oxide is helped to prevent the recombination of photo generated electron and holes this will leads to the production of more and more reactive species such as oh● and o2 ●− involved in the degradation process. additionally, the enhanced surface area of mixed metal oxide nanocomposite also enhances the photocatalytic activity of the morphology and surface sites of nanocomposite increases the adsorption process of dye molecules on the surface of the catalyst. as the adsorption of dye molecule on the surface of the photocatalyst increases the more photocatalyst sites. are available and the degradation processes get enhanced. both studies revealed that the photocatalytic is higher at uv illumination as compared with visible radiation. the surface morphological parameters of the material are also playing a vital role in the case of catalytic activity the sem image of the cz5 shows the spherical homogeneous structure of the material. as the means that a crystal is arranged and structured will decide the performance of the atoms that represent the crystal and catalytic activity depends upon the surface structure of a crystal. the previous studies suggested that copper oxides with dominant (111) facet have higher photocatalytic activity compared with those don’t have it[12]. 6 (a) (b) figure 6. (a) degradation of methyl orange under visible radiation; (b) degradation of methyl orange under uv radiation. (a) (b) figure 7. (a) degradation of methyl red under visible radiation; (b) degradation of methyl red under uv radiation. from experimental results shows that the illumination radiation has dominant significance to degradation efficiency. the degradation of organic dye may arise from the high surface areas of the nanocomposite and the multiple band gap produced due to the composite formation. another reason behind the photocatalytic degradation of organic dyes may be due to the oxidation and reduction. the relatively high band gap in the synthesized cz5 nanocomposite material is probable to avoid the recombination of photo generated free electron and holes, which are liable for the creation of reactive free radicals such as oh● and o2 ●−. they are responsible for the degradation of organic dyes into carbon dioxide and water[13–15]. the nanocomposite of cz5 with spherical morphology was found to have high band gap values and hence its higher activity can be accounted. further, its high surface area and spherical morphology might have contributed to its efficiency. figure 8 represents the mechanism of photocatalytic degradation of dyes under uv or visible radiation using cz5 as photo catalyst. in the case of both dye materials maximum photocatalytic degradation efficiency was obtained for uv illumination. 200 300 400 500 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 wavelength (nm) a b so rb an ce ( a. u ) mo 50 ppm rf 0.5 hr 1 hr 1.5 hr 2 hr 2.5 hr 3 hr 200 300 400 500 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 wavelength (nm) a b so rb an ce ( a. u ) mo 50 ppm rf 0.5 hr 1 hr 1.5 hr 2 hr 2.5 hr 3 hr 200 300 400 500 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 wavelength (nm) a bs or b an ce ( a. u) mr 50 ppm rf 0.5 hr 1 hr 1.5 hr 2 hr 2.5 hr 3 hr 200 300 400 500 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 a b so rb an ce ( a. u) wavelength (nm) mr 50 ppm rf 0.5 hr 1 hr 1.5 hr 2 hr 2.5 hr 3 hr 7 figure 8. proposed photocatalytic mechanism of cz5 nanocomposite. cz5 + hν → cz5 (e– cb + h+ vb) h+ vb + h2o → oh● + h+ h+ vb + oh– → oh● oxygen can react with conduction band electrons formed from semiconductors and thereby convert them into superoxide ions (o2 ●–). these superoxide ions can react with hydrogen ions forming ho2 ●. e– cb+ o2→ o2 ●– o2 ●– + h+ → ho2 ● three distinct processes can be used to describe how h2o2 produces hydroxyl radicals. it directly absorbs light energy and transforms it into hydroxyl free radicals in the first process. hydrogen peroxide absorbs super oxide ions to create hydroxyl free radicals in the following process. finally, h2o2 absorbs electrons and instantly transforms into hydroxyl free radicals[16–18]. h2o2 + e– cb → oh● + ho– according to the theoretical principle, one hydroxyl radical can only be produced with three electrons. however, one prerequisite for the production of hydroxyl free radicals is the presence of holes. it is evident from that hole reactions generate the majority of hydroxyl free radicals. one crucial element needed to keep the reaction going is the presence of the oxygen that absorbs electrons. superoxide radicals and the prevention of electron-hole recombination both require oxygen to exist[19–21]. organic dye + cz5/hν → co2 + h2o 6. conclusion nanocomposite of copper oxide/zinc was synthesized by co-precipitation method and was annealed at 500 ℃. xrd patterns of the sample can be considered as an express suggestion of its nanocrystalline nature. the particle sizes of the nanocomposite 31 nms. the direct optical bandgaps of the samples were calculated using tauc relation and were found to be 2.00 ev and 3.78 ev. surface morphological studies are carried out using sem images. edax pattern confirms the chemical composition of nanocomposite. the photocatalytic studies reveal that copper zin oxide nanocomposite have better degradation power in methyl red and methyl orange under uv irradiation. conflict of interest the author declares no conflict of interest. 8 references 1. ali i, irina b, evgeny g, et al. high-speed and high-capacity removal of methyl orange and malachite green in water using newly developed mesoporous carbon: kinetic and isotherm studies. acs omega 2019; 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mxene; mb-ssdna; freeze thawing; physical crosslinking 1. introduction freeze thawing is a critical process used extensively in the fields of medicine and healthcare. this technique involves freezing a substance, followed by thawing at a later stage [1]. this cycle is repeated multiple times, allowing for the preservation and utilization of various medical components such as proteins, cells, tissues, and organs [2]. the freeze–thaw technique has been employed to develop hydrogels for medical materials. the advantages of this freeze-thaw technique compared to the conventional technique are that it does not require a high temperature or any extra chemicals as crosslinking agents that may cause toxicity [3,4]. on the hand, one of the important challenges in using gene delivery is protecting dna during the delivery process, optimal control of dna release from carriers, and proper cellular uptake of dna. this technique allows for the enhanced delivery, protection, controlled release, and cellular uptake of dna [5,6]. dna hydrogels are three-dimensional networks formed by selfassembling dna strands. these materials exhibit exceptional biocompatibility, biodegradability, and programmability, making them an ideal choice for various biomedical applications. however, to fully harness their potential, it is essential to optimize their structure and properties. this is where the freeze-thaw method comes into play. in this article, we will explore the significance of freeze-thawing pva –mbssdna –mxene in the medical field. zhao et al. prepared a flame-retardant citation ghazizadeh e, aghayani s. pva/mb-ssdna/mxene hydrogel synthesized by freeze thawing process with the effect of mbssdna. characterization and application of nanomaterials. 2024; 7(2): 4682. https://doi.org/10.24294/can.v7i2.4682 article info received: 19 february 2024 accepted: 4 march 2024 available online: 22 october 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 4682. 2 pva/pa/mxene hydrogel coating via a freeze–thaw cycle [7]. this coating showed excellent self-healing properties and high water retention (water content  ≥  90%) owing to the increased number of hydrogen bonds with the introduction of mxene. many studies have been conducted on pva-based hydrogels using the freeze-thaw process in the medical industry. waresindo et al. showed that a polyvinyl alcohol (pva) hydrogel loaded with guava leaf extract (gle) could be fabricated by freeze– thaw (f-t) method as a wound dressing with good antibacterial activity [8]. in 2008, the effect of dna on the mechanical properties of nanofiber hydrogels was demonstrated. pva nanofiber gels incorporating double-stranded deoxyribonucleic acid dna were fabricated without the aid of cross-linkers using electrospinning. unlike the weak connection between dna and pva, the elastic modulus of the dna/pva gels was higher than that of the pva gel [9]. in this study, we synthesized a pva –mb-ssdna –mxene hydrogel using the freeze-thawing method, which can be used as an effective hydrogel approaches carrier in gene delivery research using single-stranded dna (ss-dna). so, we investigated pva –mb-ssdna –mxene synthesis using the f-t method to study the structural, morphological, and thermal properties of this hydrogel compared to the synthesis hydrogel of pva –mb-ssdna –mxene without f-t method. due to the fact that biological cross-linking as mbssdna is used in both methods, we have tried to investigate the effect of freeze-thaw cycles on the structure and increasing the tensile strength of the hydrogel. the results show that the samples were successfully prepared during different f-t processes (1, 3, and 5 cycles). the pva –mb-ssdna –mxene hydrogel synthesized by the f-t method was also stronger than pva –mb-ssdna –mxene without f-t methods the. our study also showed the effect of mb-ssdna on the increasing the tensile strength and reducing the swelling properties of pva –mb-ssdna –mxene hydrogel structure synthesized by freeze-thawing method. as a result, we introduced the novel synthesis of pva –mb-ssdna –mxene hydrogel structure by the f-t method, which was influenced of biological (mb-ssdna) and physical cross-linking which can be used as a future reliable gene carrier based hydrogel in medical purposes. 2. experimental 2.1. chemicals and reagents lithium fluoride (lif), ti3alc2 (powder, 200 mesh), tris buffer, poly (vinyl alcohol), and borax (sodium tetraborate decahydrate, purity > 99.5%, na2b4o7, 10h2o, mw = 381.37 g/mol) ammonia water were purchased from sigma-aldrich. all the chemicals were used directly without further purification. single-strand dna such as mb-ssdna; 5'atto mb2-tca aca tca gtc tga taa gct a –(oh) 3’ was synthesized from metabion (german). 2.2. methods 2.2.1. preparation of ti3c2tx mxene nanosheets ti3c2tx mxene nanosheets were prepared by modified hydrofluoric acid etching. in brief, 2 g ti3alc2 powder and 2 g lif were dissolved in 20 ml hcl solution (9 m), injected with nitrogen for deoxygenation, and sealed in an oven at 200 ℃ for 24 h. characterization and application of nanomaterials 2024, 7(2), 4682. 3 the resulting suspension was collected and washed again. ti3c2 was collected by centrifugal washing. finally, the supernatant was freeze-dried to obtain mxene (ti3c2) nanosheets. 2.2.2. preparation of pva –mb-ssdna –mxene nanocomposite hydrogel the synthesized was modified by pva–mxeneborax protocol [10]. after completely dissolved 0.6 g pva (10%w/v) at 90 ℃ for about 4 h, 6 mg/ml of ss-mbdna were dissolved in 16 ml distilled water and stirred continuously at 30 ℃ until dna was completely dissolved without denaturation. subsequently, a certain amount of mxene was added to the solution and stirred for 5 h. the mixture was cast onto a petri dish, followed by freezing at −20 ℃ for 18 h, and thawed at room temperature for 6 h. the experiment was conducted for 1, 3 and 5 consecutive cycles, respectively (figure 1). the hydrogel was stored in a desiccator to prevent moisture adsorption. in parallel, we synthesized non f-t pva –mb-ssdna –mxene hydrogel as described above but without the consecutive cycles. figure 1. step-wise preparation of pva –mb-ssdna –mxene hydrogel using the freeze thaw process. 2.2.3. swelling behavior to investigate the swelling behavior of the synthesized of pva –mb-ssdna – mxene with freeze thawing method, the samples were cut into 1 cm2 × 1 cm2 pieces with the same weight (wd) and immersed in deionized water (di) for 24 h. samples were removed from the solution, dried with filter paper to remove excess water, and characterization and application of nanomaterials 2024, 7(2), 4682. 4 weighed (ww). the samples were then investigated using the following equation, and the data were reported as the statistical average and standard deviation. 𝑆𝑤𝑒𝑙𝑙𝑖𝑛𝑔 (%) = 𝑊𝑤 − 𝑊𝑑 wd ⨯ 100 where ww is the weight of the swollen sample and wd is the initial weight of the hydrogel. 2.2.4. fourier transform infrared (f-tir) characterization of the samples a fourier-transform infrared spectrometer (spectrum one, perkin elmer, usa) was used to determine the chemical structure. the sample was scanned from 400 cm−1 to 4000 cm−1 at room temperature in air mode at a resolution of 4 cm−1. 2.2.5. scanning electron microscope (sem) the morphology was determined by scanning electron microscopy. in detail, the micromorphology of pva –mb-ssdna-mxene hydrogel by freeze thawing processes and non-freeze thawing process composite hydrogel was analyzed by fei inspect f50 scanning electron microscope (sem, quanta 250 microscope, japan). hydrogels were treated with liquid nitrogen to expose the inner structure. then, hydrogel samples were rapidly dropped onto a gold-coated high purity copper block cooled in liquid nitrogen due to entering the rapid freezing to minimize compression of the hydrogel samples. in the following, we used as the airlock transfer adapter to remove the hydrogel sample from liquid nitrogen immersion and transferred to the sample preparation airlock precooled to −175 ℃. 2.2.6. differential scanning calorimetry (dsc) thermal behavior of pva –mb-ssdna –mxene hydrogel was determined using dsc (netzsch dsc 204 f1 phoenix, germany). the samples were placed in aluminum pans at a flow rate of 40 ml⋅min−1. the temperature was fixed at 30 ℃ to 350 ℃ at a flow rate of 10 ℃⋅min−1. the data are presented as the glass transition temperature, melting temperature, and specific heat capacity. by passing a nitrogen gas stream from 0–600 ℃ at a heating rate of 20 ℃/min, samples were scanned and thermograms were collected. 2.2.7. tensile testing the samples (1 mm thickness) for the tensile tests were cut with a dumbbell cutter (analyzer texture xt2i, iran). the speed of the test was 10 mm/min to obtain the tensile stress (r)–strain (dl/l0) curve, where r was calculated using the cross-sectional area of the unreformed gel. dl and l0 indicate the deformation of the gel and initial length before deformation, respectively. 3. results and discussion pva –mb-ssdna –mxene hydrogel was successfully prepared using the freezethaw technique. it exhibits a reformable shape. figure 2 illustrates the f-tir spectra of the pva –mb-ssdna –mxene hydrogel prepared by the freeze-thaw technique. no significant changes in the functional groups of the hydrogels were observed based on the variation of consecutive cycles in the freeze-thaw process. the functional groups of the hydrogels were similar for all compositions of hydrogel pva –mbssdna –mxene without the f-t process based on the f-tir analysis that was used to characterization and application of nanomaterials 2024, 7(2), 4682. 5 qualitatively analyze the presence of functional groups in the hydrogels. in figure 2, the characteristic peak at 3445 cm−1was observed. this indicates the presence of an oh-stretching group (hydroxyl group). it refers to the presence of polyvinyl alcohol, mxene, and mb-dna. this was in agreement with our work for synthesizing mxene-pva hydrogel without f-t processes. it also clearly showed the major peaks related to freeze-thawed pva (10). another peak was attributed to the c–h stretching vibrations at 1410 cm−1 and 2911 cm−1. f-tir peaks at 2225 cm−1 and 1600 cm−1 were observed sequentially for the c–n stretching and c=o stretching groups. this can be created by the adsorption of mb on mxene and pva. this is in agreement with a previous study by zhang on mb adsorption on mxene based on electrostatic forces [11]. another peak at 1579 cm−1 and the c–h bond can imply the bond between mb and pva or mxene. in this study, the f-tir peaks at 500 cm−1 and 1350 cm−1and 1575 cm−1 were related to c–o, c–n, and n–h bonds of dna. generally, our results showed that there is no significant change on functional group of hydrogels during on variation of consecutive cycle in f-t process. as f-tir analysis indicated the qualitatively analyze the existence of functional group of hydrogels, it can be concluded that functional group of hydrogels was still similar for all compositions of hydrogel. on the hand, f-t hydrogel results were also similar to the non f-t mxenepva/mb-ssdna hydrogel, with the difference in the shifting of the c-c and ch2 at 800 cm−1and 900 cm−1. on the hand, results indicated f-tir peaks at 1220 cm−1at the c-o-c bond between the intramolecular pva chains with the highlighting of the new peaks at 1141 cm−1 and 2882 cm−1, which indicate the intra-or intermolecular bonds of pva. these results showed that the existence of a physical process besides crosslinking (mb-ssdna) can lead to the formation of more intraand intermolecular pva networks., in comparison with the conventional hydrogel methods of mxenepva/mb-ssdna. figure 2. f-tir spectra of pva –mb-ssdna –mxene hydrogel prepared with/out f-t process. characterization and application of nanomaterials 2024, 7(2), 4682. 6 figure 3 shows the morphological properties of the pva –mb-ssdna –mxene hydrogel could prepared using also the freeze-thaw technique. our results revealed a porous structure. it was remarkable to note that all microstructural images presented the porous structure about forming of hydrogel by f-t methods similar non f-t method. the pores are interconnected and regularly distributed. the pores were mostly caused by the f-t process which can show the existence of more obvious pores than non f-t method. moreover, it seems that with three and five consecutive cycles, the number of pores was less than that with one consecutive cycle. the surface became homogenous when compared to that of the control. this implies that the hydrogel was well packed. with a high number of consecutive cycles of freeze thawing, the crosslinking reaction between dna and mxene or pva was successfully prepared. our results may provide a reliable method for synthesizing dna hydrogel carriers. also, our results show that the presence of porous and dense structures of pva –mbssdna –mxene using without freeze-thaw technique is more than the consecutive cycles of freeze-thaw technique. this is in agreement with a study by sornkamnerd et al. on synthesize the tough and porous hydrogels by simple lyophilization of lc gels [12]. figure 3. morphological properties of pva –mb-ssdna –mxene hydrogels. (a) pva –mb-ssdna –mxene hydrogels synthesized without f-t methods; (b–c) pva –mb-ssdna –mxene hydrogels synthesized with f-t processes. characterization and application of nanomaterials 2024, 7(2), 4682. 7 differential scanning calorimetry was performed to detect the presence of water molecules in the hydrogel network owing to the large amount of water in the hydrogel. these results showed the water state change in the mxene and pva-based hydrogel networks in previous studies. figure 4 showed the dsc measurements of dna, polyvinyl alcohol, and the mxene hydrogel prepared by the freeze–thaw technique. various compositions of dna, pva, and mxene were evaluated based on 1, 3, and 5 consecutive freeze-thaw cycles. all curves were reported in a similar form. the dsc thermogram of of mxene-pva/mb-ssdna hydrogel showed a small peak at 70 ℃ and then two large endothermic at approximately 180 ℃ and 300 ℃. dsc characterization confirmed the formation of the new hydrogel. crosslinked matrices of pva –mb-ssdna –mxene revealed higher thermal stability than mb-dna. the dsc peaks at 70 ℃ indicate the water loss from the matrices, which was followed by decomposition at approximately 180 ℃ and 300 ℃. clearly, our hydrogel fabrication method yields thermally stable cross-linked matrices of mb-dna. dsc results also slightly shifted to 330 ℃ for three and five consecutive cycles. the presence of more pva-pva network may enhance the compactness of the hydrogel by the freeze–thaw process. these findings are in good agreement with the f-tir results. figure 4. thermal properties of pva –mb-ssdna –mxene hydrogel composite prepared by freeze thaw process. figure 5 showed the swelling characteristics of the pva –mb-ssdna –mxene hydrogel composite. the swelling ratio of the hydrogel structure was observed within 200 min. subsequently, the swelling ratio remained constant. the swelling behavior can be explained by the hydrophilicity of pva located inside the hydrogel network. they can adsorb water molecules from the system. these results are consistent with those of a study by asy-syifa [13]. as mb-ssdna contains methylene blue, it can affect the swelling behavior of the pva –mb-ssdna –mxene hydrogel. martinez et al. showed the swelling and adsorption of mb in a poly (n, n-dimethylacrylamide-co2-hydroxyethyl methacrylate) hydrogel [14]. mb-ssdna, as a crosslinker, can reduce the swelling ratio. our results showed that, as the concentration of mb-ssdna increased, the swelling rate of the pva –mb-ssdna –mxene hydrogel decreased (figure 6). characterization and application of nanomaterials 2024, 7(2), 4682. 8 figure 5. swelling behavior of pva –mb-ssdna –mxene hydrogel composite prepared by freeze thaw process compare to non f-t process. figure 6. swelling behavior of pva –mb-ssdna –mxene hydrogel prepared by freeze thaw process with the effecting of mb-ssdna. generally, the swelling behavior is associated with the interconnected porous structure in the hydrogel network, as suggested by yu et al. [15]. our results agree with those of the sem analysis. in addition, the swelling (%) increased as the number of cycles increased to five. at a higher number of cycles (five), the swelling (%) rapidly increased within 30 min and reached equilibrium in approximately 50 min. the blockage of active sites on pva chains results in a decrease in hydrophilic groups [16]. on the one hand, the swelling ratio of the hydrogel synthesized by non f-t process was lower than the nonporous hydrogels prepared by freeze–thawing of the original hydrogels. this is also in agreement with a study by sornkamnerd [12]. analysis of the mechanical properties of hydrogels for medical use is very important. figure 7 showed the tensile strength of the pva –mb-ssdna –mxene hydrogel composite. our measurements were tested, and the data were reported. a uniform structure of pva –mb-ssdna –mxene was prepared by f-t processes, as shown in figure 2. we tested the four measurements and the datas were also evaluated by statistical average and standard deviation. characterization and application of nanomaterials 2024, 7(2), 4682. 9 figure 7. tensile strength of mb-ssdna hydrogel prepared by freeze thaw process with the effecting of mb-ssdna. here, the level of tensile strength for all hydrogels by the f-t process in three cycles was in the region of 2.1 mpa to 2.5 mpa. this indicates that the pva –mbssdna –mxene hydrogel can be prepared using the f-t technique. based on our parallel study, it has been shown that mb-dna can act as a biological cross-linkage which it could increase the tensile strength. as a result of the current study, the f-t process was also influenced by mb-dna. this indicated that the hydrogel structure with the f-t method was stronger than that without the f-t method. on the hand, the tensile stress can be affected by an increase in the mb-ssdna concentration, indicating that mb-ssdna plays a significant role in the enhancement of mechanical strength. in fact, the pva –mb-ssdna –mxene gel was robust, for example, 2 µl mxene-pva / mb-ssdna (figure 8). figure 8. tensile strength of mb-ssdna hydrogel prepared by freeze thaw process. 4. conclusions the freeze-thawing method is a versatile and straightforward technique for synthesizing hydrogels. this method offers flexibility in terms of tailoring the properties of the hydrogel according to specific requirements, making it highly suitable for various biomedical applications [17,18]. dna hydrogels are threedimensional structures composed of crosslinked dna molecules. these materials possess unique properties such as high water content, biocompatibility, and the ability characterization and application of nanomaterials 2024, 7(2), 4682. 10 to respond to external stimuli like temperature variations. however, obtaining hydrogels with precise characteristics and performance remains a challenge. this is where the freeze-thawing method comes into play [19]. in this report, we successfully synthesized the pva –mb-ssdna –mxene hydrogel using the freeze-thaw technique in addition to the effect of mb-ssdna. five consecutive freeze-thaw cycles were optimal for hydrogel formation compared to the conventional methods. fourier transform infrared spectroscopy confirmed that hydrogen bonding resulted in a new inter-and intramolecular network of pva-pva throughout the hydrogel network by the oh group affected by mb-ssdna. scanning electron microscopy revealed the microstructure of the hydrogel. it presented as a porous network with an increase in dna concentration, the swelling rate decreased, whereas relatively increase the tensile stress behavior occurred. also, we showed that freeze-thaw processes can form stronger hydrogels of pva –mb-ssdna –mxene with less swelling behavior compare the non f-t processes. generally, the pva –mb-ssdna –mxene hydrogel prepared with f-t method exhibited extraordinary properties for use as a medical material. authors contributions: provide draft and methodology, eg; provide some of methodology and editing, sa. all authors have read and agreed to the published version of the manuscript. acknowledgments: the authors acknowledge the support of the alexander von humboldt foundation for elham ghazizadeh via the post-doctoral research fellowship conflict of interest: the authors declare no conflict interest. references 1. bernal-chávez sa, romero-montero a, hernández-parra h, et al. enhancing chemical and physical stability of pharmaceuticals using freeze-thaw method: challenges and opportunities for process optimization through quality by design approach. journal of biological engineering. 2023; 17(1). doi: 10.1186/s13036-023-00353-9 2. oyama t. cross-linked polymer synthesis. in: encyclopedia of polymeric nanomaterials. berlin, heidelberg: springer berlin heidelberg; 2014. pp. 1-11. 3. figueroa-pizano md, vélaz i, peñas fj, et al. effect of freeze-thawing conditions for preparation of chitosan-poly (vinyl alcohol) hydrogels and drug release studies. carbohydrate polymers. 2018; 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10(2): 024003. doi: 10.1088/20531591/acb98e 19. adelnia h, ensandoost r, shebbrin moonshi s, et al. freeze/thawed polyvinyl alcohol hydrogels: present, past and future. european polymer journal. 2022; 164: 110974. doi: 10.1016/j.eurpolymj.2021.110974 characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.2562 1 original research article nanoscale water flows in networks against a total fail sungsook ahn ivy tech community college, 200 daniels way, bloomington, in 47404, usa. e-mail: sungsookahn@yahoo.com abstract a failsafe network design recovering from the stressed condition against a massive supply disruption is generally useful for various applications. water flow in plants under a tension is inherently vulnerable to an embolism, a water supply cut off, causing a death. however, the function of the network structures of leaf veins and xylem stems effectively reduces the embolism-induced failure. in this study, water transport in plants under the pressurized conditions compared to the normal physiological conditions is observed by x-ray imaing. by examining embolism-induced water supply limits in the architecturally diverse leaf and stem networks, a progressive hydraulic rule has been found: the limited flows in the selected parts of the network structures against a total fail. for a scientific explanation on nanoscale water flow dynamics occurring in plants, temporal meniscus development in the nanomembrane model system is investigated. the pressuredriven hydrodynamic transport phenomena can be explained to follow network dynamics of the modified imbibition typically occuring in nanostrutcures. this study contributes to a variety of design technologies of networked materials against the spread of flow damages under the stressed conditions. keywords: water flow; network; xylem; leaf venation; imbibition 1. introduction the network performance in broad physical[1,2], biological[3] and ecological[4] systems relies largely on the dynamic connection patterns[5,6]. in complex dynamic networks such as power outage[5,7], traffic congestion[8,9], extinction cascade[10,11] and genetic disease[12,13], a local perturbation propagates through a network and reaches a systemspecific equilibrium, resulting in a total network failure. nonetheless, majority of live networks including brain[14] and cellular networks[15] has been reported to generate few catastrophic failures by stable correlations[16–18]. a characteristic of live networks is an evolutionary dynamics to reach an optimum performance. paradoxically, a compensatory perturbation can direct a network to a desirable state[19]. well-known examples are a knockdown of a specific gene to recover the strain growth against genetic defects[20], a targeted suppression against extinction of multiple species[19], an appropriate power trimming to reduce subsequent blackouts caused by equipment or operational errors[21,22]. the influences of hydraulic design have been reviewed in terms of the movement of water from roots to leaves of trees[23]. the hydraulic architecture of trees can limit their water relations, gas exchange throughout the crown of trees, the distribution of trees over different habitats and the maximum height that a particular species can achieve. parameters of particular importance include: (1) the vulnerability of stems to drought-induced cavitation events because cavitation reduces article info received: 11 april 2023 accepted: 20 may 2023 available online: 28 may 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4. 0/ 2 the hydraulic conductance of stems; (2) the leaf specific conductivity of stems because it determines the pressure gradients and most negative water potentials needed to sustain evaporation from leaves; (3) the water storage capacity of tissues because this might determine the ability of trees to survive long drought periods. all of these determining parameters are determined by the optimized structure and function of anatomical components of trees. the dynamic perturbation of network has been observed in the flow systems of plants. water flows through xylem conduits at a negative pressure by which water is in a metastable state at a risk of cavitation[24,25], resulting in a subsequent loss of xylem function[26]. the hydraulic constraint enables the plant to sacrifice lesser important organs and to save more critical parts for long-term survival and propagation[27]. the susceptibility to an embolism is higher for expendable organs (e.g., leaves) compared with more permanent parts[28]. however, the mechanism and conditional factors of flow limitation against total fail occurring in plants have not yet been clearly understood. water ascent through the xylem is driven by the hydrodynamic flow not by the controlled diffusion[29]. capillary force generated by an evaporation at leaves pulls up water generating a negative pressure[24] by which conduits can cavitate[30]. further negative pressure in the xylem is promoted by water supply limit such as soil drying. the embolism propagates through the interconnected network by traversing pit membranes between the xylem conduits[31,32]. this droughtinduced cavitation occurs via air seeding[26] and is promoted by the pressure difference between gasfilled and water-filled conduits[33]. this cavitation mechanism is more likely than homogeneous nucleation occurring in the bulk phase[34]. on the other hand, refilling process of xylem is more puzzling. it occurs during the daylight thus under a negative tension[35,36]. this result is an apparent paradox against typical understanding where a positive pressure would need to increase the gas solubility restoring back into the sap fluid or pushing out of the conduit[37]. refilling occurs over a timescale of hours in some species[27,38], but the mechanism is still controversial. the volumetric flow rate is proportional to the fourth power of the xylem size by hagen–poiseuille relation[28], thus long and large conduits are advantageous for water flow[28,39,40]. nonetheless, the water flow in a stem has not been considered as a network dynamics working by cooperative adoption of conduits in a bundle. leaf network has been naturally evolved for a long history to maximize flow efficiency against embolism[41–43]. however, little is known about the dynamic adoption of leaf networks and refilling after the embolism to avoid the catastrophic failure. high hydraulic tension in xylem is prone to exogenous embolism during the manipulation thus typical intrusive measurements unable the studies on the water supply initiation and embolism propagation in plants under the increased stress[37]. however, in-situ imaging techniques such as x-ray, magnetic resonance and neutron have provided new insights[31,44–49]. air seeding has been directly visualized by synchrotron x-ray imaging in this point[44,48]. the limited resolution and possible damage by ionizing radiation have been overcome in microand nano-imaging technologies[46–49]. effectively utilizing gold nanoparticle (aunp), isotope chemical tracer or water-air interface as an imaging contrast, water transport in plants has been successfully traced with minimum sample damage. here, water movement in plants is observed by synchrotron x-ray imaging and the suggested physical phenomena is reenacted by nanomembrane model systems. an explanation has been developed first to our knowledge for the water flow network dynamics under the stressed condition and refilling mechanism. the resultant knowledge is important for the understanding the plant mortality over a drought which is the results of natural selection[41] and for the providing useful engineering solutions for failsafe network designs[50] in diverse applications such as effective fluid delivery[51], energy distribution[52], and data communication[53]. 2. results water movement in the xylem vessels of a stem. water flows in the xylem and phloem bundles of 3 a b c d e figure 1. (a) x-ray image of the arabidopsis stem cut. cross-sectional images are obtained by x-ray computed tomography (x-ray ct). (b) the projected images of stem cut arabidopsis obtained by x-ray microscopy (xm) [i] and axially accumulated into 3d images [ii]. the image of the bundle marked by a white rectangle in [ii] is magnified in [iii]. water moves up naturally by the physiological self-action of the plant under the normal condition where a cut is dipped in the aunp containing aqueous culture medium. (c) water moves up by the additionally introduced negative pressure in an arabidopsis stem cut. (d) water uptake of arabidopsis grown in long day (ld) and short day (sd) condition is evaluated in terms of the stained volume by the aunp. the samples grown in ld condition display higher water uptake than those of sd condition. but each system shows linear relation of water uptake with stained volume. (e) total number of active xylem vessels in an arabidopsis stem is similar regardless of total stained volume for both normal pressure (p) and additionally introduced pressure (p + pa) conditions. the total number of active vessels has no strong relation with the total water uptake. however the number of active vessels used under the additionally introduced negative pressure (p + pa) shows less number than normal pressure condition (p). 4 arabidopsis are experimentally observed (figure 1a) for which x-ray imaging is employed using gold nanoparticle (aunp) tracer[46–49]. xylem vessels are divided into three types according to the water uptake efficiency: the xylem vessels filled with stationary water, embolized vessels due to low water uptake and aunp-stained vessels induced by active water uptake. the water uptake efficiency occurring in a plant is in strong relation with the structural pathways of the water movement. in this point, the interconnected microstructural networks in a bundle are investigated[54] for which the location of the active xylems of high water uptake is determined by the aunp-stained vessels[46,47] (figure 1b,c). water movement in a stem is investigated by crosssectional 2d images [i] which are axially accumulated into 3d images [ii]. a representative bundle marked by a white dotted rectangle in [ii] is magnified in [iii]. first, water moves up in a stem cut by a physiological self-action under the typical pressure (p) natural in a plant (figure 1b). stained by aunps, many short tracks are dispersed in an axial direction in addition to the vertical water flow tracks. the water movement pathway in natural physiological condition (p) is spatially broad across the vessels. second, additional negative pressure is introduced (p + pa where both p & pa < 0) at a rate of 0.002 l/min to a stem cut (methods) and modified water flow pattern is investigated (figure 1c). when an additional negative pressure is applied the water moves in straight long lines in fewer number vessels (point-selection) compared with the normal pressure condition in figure 1b. especially, the number of active vessels in a bundle decreases. it is noticeable that the increased pressure is related with the flow pattern change into straight long lines limited in the selected active points. the water movements in arabidopsis stems are graphically analyzed by the x-ray images. the total volume of active xylem vessels evaluated by aunp stain is in strong relation with total water uptake (figure 1d). the total volume of water uptake is determined by the remaining solution in the vials at 10 min intervals. all water uptake experiments are carried out in the chamber in which plants were grown at two growth conditions: long day (ld) and short day (sd). the total stained volume is linearly proportional to the total water uptake for each growth condition. overall, the ld condition generates high water uptake over the sd condition with similar stained volume, indicating faster flow rate. on the other hand, the total number of active vessels (aunp-stained vessels) of both ld and sd condition is independent of total stained volume (figure 1e). under the normal physiological pressure condition (p), both ld and sd show total number of active vessels between 70 to 90. meanwhile, the total number of active vessels counted under the additional negative pressure condition (p + pa) is between 40 to 60. the total stained volume under the additional pressure condition (p + pa) is slightly larger than normal pressure condition (p), thus less number of vessels transport more water. in summary, under the pressurized condition, the water flow in a stem is limited in some points. this is one survival strategy of plant segmentation as a compensatory perturbation of network dynamics. the flow pattern generates more straight lines with less meandering, thus it is more advantageous for more effective water delivery in a short time duration. water movement in the xylem vessels of a leaf. as a systematically designed network structure, leaves with different venations are investigated. the vein structure typically possesses a hierarchy of vein orders[55,56]. the lower-order veins are major veins, thus one or more 1st order veins run from the petiole to the leaf apex. meanwhile, 2nd order veins branch at intervals and 3rd order veins branch between. from lower to higher vein orders, cross-sectional areas of the xylems and phloems typically decrease[57–59]. a hierarchy of vein orders typically forms a reticulate mesh[56,60]. this is determined by the looping where the end points of higher order veins link back to the lower order ones. in this study, three different venation structures are investigated (figure 2): 1st order veins are colored in black lines, 2nd order veins in red lines and 3rd order veins in blue lines both in the schemes at the left and in the graphs at the right. privet has a reticulate venation with 3rd order hierarchy (figure 2a), rhapis excelsa a reticulate 5 a b figure 2. (continued). 6 c figure 2. the leaves with different venation structures observed by the optical microscopy and x-ray microscopy (xm) images for (a) reticulate venation (privet) with 3rd order hierarchy. (b) reticulate venation (rhapis excelsa) with 2nd order hierarchy. (c) nonreticulate venation (ficus lutea) with 3rd order hierarchy. the scale bar in the optical microscopy image [i] is 1 cm. timedependent xm images are captured consecutively and representative images at two interval t1 and t2 are displayed in [ii] & [iii]. the newly introduced iopamidol aqueous solution is traced against the water already existing in the veins under normal pressure condition at water-water interface [ii] and under increased negative pressure by dried condition at water-air interface [iii]. timedependent water filling into the veins is graphically analyzed under the corresponding xn image according to the hierarchy of the vein structure. venation with 2nd order hierarchy (figure 2b), and ficus lutea a nonreticulate (open) venation with 3rd order hierarchy (figure 2c). to clarify the anatomical morphology of the venation, optical microscopy images [i] are arranged together. the contrast in the x-ray image can be generated by water-air interface, iopamidol or aunp aqueous solution[46–49]. in this study iopamidol aqueous solution shows the best result for leaf venation observation. by combining small patches captured in different regions, a whole picture of the microscale x-ray image is obtained at two different time interval t1 [ii] and t2 [iii]. the newly introduced iopamidol aqueous solution is traced against already existing water in the leaf veins under the normal physiological condition (p) generating water-water interface [ii]. in addition to the normal pressure condition, additional negative pressure is introduced (p + pa) inside the veins by drying the samples [iii] (methods). filling the xylems by air reduces water transport and further increases xylem tension[61]. matric potential (ψm) is the amount of water bound to the matrix of a plant via hydrogen bonds and is always negative to zero. in a dried plant it can be as low as −2 mpa while it is as high as zero in a watersaturated state[61]. the water movement in dried leaves is traced at the water-air interface by which the water filling in the highest order veins is displayed as white lines. temporal water movement of reticulate venation with 3rd order hierarchy (privet) (figure 2a) shows that iopamidol aqueous solution fills the 1st order main vein at the center, and spreads to the 2nd and 3rd order veins. the temporal vein filling is graphically investigated for each xm image. it is expressed by the % of whole veins at a hierarchy 7 order for which the % of the vein is determined by total vein length estomated by optical microscopy. at the water-saturated normal condition [ii], the veins close to the petiole and the higher order veins are filled together without fully filling the entire lower order veins. on the other hand, the iopamidol solution fills the veins of the dried samples in different ways [iii]. with additionally applied negative pressure generated by drying (p + pa) and by making water-air interface, iopamidol aq. solution fully fills the lower order main veins first and then moves to the higher order veins. fluid traced images of rhapis excelsa a reticulate venation with 2nd order hierarchy with multiple 1st order veins, also display time-dependent water filling through hierarchically ordered veins (figure 2b). in the fully watered samples [ii] the veins close the petiole are first filled rather than filling entire 1st order main veins. meanwhile, in the dried sample [iii], the lower order main veins are first filled significantly. ficus lutea a nonreticulate thus open venation with 3rd order hierarchy (figure 2c) also shows more effective main vein filling under the dried state. regardless of the venation structure, hierarchical water filling of the lower order main veins preferentially occurs under the high pressure condition (p + pa), while distance from the water source is important for the vein filling at normal pressure condition (p). in terms of venation-specific water flow difference, rhapis excelsa with 2nd order hierarchy with multiple 1st order veins can be more advantageous for effective water filling under a stressed condition. nonetheless, the number of orders and the degree of reticulation seems not the determining factors to decide the water flow tracks. the water flow in a leaf under the pressurized condition is limited preferably for the main veins according to the hierarchy. this also can be considered as one of the plant segmentation phenomena as a compensatory perturbation of network dynamics. nanoscale water movement model system. water movement in model systems is investigated by cellulose acetate nanomembranes (surface free energy, γs = 52.6 mj/m2)[62] (chmlab co., barcelona, spain) with 200 nm (i) and 800 nm (ii) pore size (provided by chmlab co.). the structure is visualized and the average pore size is confirmed by x-ray nanoimaging (figure 3a)[63,64]. rhodamine b aqueous solution of low concentration (1 ppm) clearly visualizes the flow tracks in red, which continuously moves filling the nanopores. moving distance of this clear-cut meniscus vs. time is measured to obtain the flow rate by taking movie clips (10 fps speed). to trace the regionally diversified meniscus location as a sharp point, membranes are linearly folded (0.2 cm in span). flows through the membranes are evaluated in three arrangement (figure 3b): first, water flow from the bottom to the top of the membrane against the gravity (−pg, pg is the pressure induced by the gravity) generates the typical spontaneous imbibition [i]. a part of the membrane is still dipped in the rhodamine b aqueous solution, so that water is continuously provided without any level change of the container. second, the membrane is horizontally placed where the gravity effect on the meniscus movement in the membrane is minimized [ii]. the meniscus change is analyzed from the line where horizontal water movement starts. in the third position, water flows from the top to the bottom thus it is accelerated by the gravity (+pg) [iii]. the meniscus movement is analyzed from the line where the vertical water movement starts. for each case in figure 3b, representative meniscus movements in a membrane traced by red color are displayed as an inset. for safe meniscus recording, the data is collected from 30 sec after the dipping so that rapid invasion of water into the pores is not considered. in addition, by the unavoidable rhodamine b mass transfer even at very low concentration and natural water evaporation from the membranes surface, the final meniscus becomes a dark red line because of the rhodamine b accumulation by the marangoni effect[64]. but this is hardly observed when the flow moves dynamically thus the time-dependent meniscus movement is recorded before this phenomena becomes serious. 8 a b figure 3. (continued). 9 c figure 3. (a) x-ray nanoscopy (xn) image of the cellulose acetate nanomembranes with average pore size of 200 (i) and 800 nm (ii). rhodamine b aqueous solution is used for visualization of newly introduced flow against already existing fluid. (b) flow through the membrane is evaluated in three position: [i] the water flows from the bottom to the top against the gravity (pg). [ii] the membrane is horizontally placed so that gravity effect is minimized. [iii] water flows from the top to the bottom thus accelerated by the gravity (+pg). for each case representative meniscus movement in a membrane is displayed on which the dotted baseline represents the minimum position of the meniscus while the fastest point marked by an arrow represents the maximum distance from the baseline. the flows through the two membranes (mem 1 and mem 2) are graphically investigated at the right of each flow type. lines represent the baseline of the minimum meniscus while symbols indicate the fastest point. (c) time-dependent meniscus position, h(t) follows power law dependency by h(t) = atn + b. based on this relation, the results in fig 3b are fitted by least squares fitting method (r2 > 0.99). the fitting parameters are summarized in a table and graphical comparison of a and b values are displayed at the left. for the quantitative flow analysis at the right graphs, the degree of meniscus development is considered in this study rather than average meniscus position. two time-dependent tracking points are focused in this aspect: one is the time-dependent base line (lines in the membrane at the left and in the graph at the right) representing the minimum position of the meniscus. from this line, each flow point of the membrane is diversified by the local flow rate difference. the other is the fastest moving point (arrows in the membrane and solid symbols in the graph). running faster from the base line it represents the maximum position of the meniscus. flows through the two membranes of different pore size are graphically summarized. the pore size of the membrane i (mem 1) is four times smaller than that of membrane ii (mem 2). this is accompanied by three suggested flow types from [i] to [iii]. the penetration length, h(t) during a time is considered by the spontaneous imbibition of water into hydrophilic porous structures. the absolute h(t) value significantly increases from flow [i] to [iii], and time-dependent flow rate (slope of the graph) is also prominently increases in that order. especially large pore size mem 2 shows higher values than those of smaller pore size mem 1 in every case. power-law dependency on the time. the h(t) by the spontaneous imbibition follows the scaling law of lucas-washburn[64,65], h(t) = (trlv cos/2)1/2 (1) : dynamic viscosity, r: effective pore size, lv: liquid-vapor surface tension, : contact angle. although both capillarity and gravity forces exist in spontaneous imbibition, gravity is not included in lucas-washburn relation, which causes a deviation from the half-power dependency on the time[66–68]. in addition, there are intermediate stages before and after the typical lucas-washburn regime, where the half-power time dependency is not 10 effective any more[69–71]. at the very beginning of water contact with a membrane, the water invades to the porous media in a radical manner, by which the meniscus moves in linear relation with the elapsed time, h(t) ~ t. meanwhile, at the very late period of spontaneous imbibition, gravitational force significantly overcomes the capillary dynamics, h(t) < t1/2. for the flows arranged in figure 3b, timedependent meniscus position from the water source, h(t) follows power law dependency on the time which is generalized as h(t) = atn + b (2) n reflects the power law-dependent flow mechanism. a is the multiplication factor diversified by the structure and compatibility of the media and viscosity of the moving fluid. meanwhile, b is the addition factor considering added forces such as forced diffusion, gravity and the like. in all three membrane arrangement, large pore size mem 2 shows high h(t) values both for the minimum baseline (lines) and the maximum fastest point (solid symbols). based on the general power law relation, the results are demonstrated by least squares fitting within a reasonable error range (r2 > 0.99) (figure 3c). the fitting parameters are arranged in a table. the a and b values are graphically compared at the left, which are same for flow [i] and [ii] while those of flow [iii] increases significantly. the a and b values obtained by the flow [i] through the mem 1 at the baseline position are used as calibration factor (1 and 0, respectively, bold characters in the table). therefore, the values for other conditions are normalized in the table by these two multiplication and addition factors. in a typical imbibition against gravity in flow [i], fitting by n = 0.5 is applied. compared with baseline, the fastest point shows slightly increased a values both for mem 1 (1.1/1.0) and mem 2 (2.2/2.0). in terms of the pore size effect, the a values reflect 2 times faster movement in mem 2 than mem 1 based on both minimum (2.0/1.0) and maximum (2.2/1.1) position of the meniscus. this corresponds to the expected value by the relation of h(t) ~ (r)1/2. in this condition, the b values for fastest point increases to 0.15 and 0.2 for mem 1 and mem 2, respectively, while the b values for the base lines are all zero. this indicates that no additional force is employed for the baseline movement. however, additional force is generated to the fastest point movement and this is pore size-dependent. this makes the difference (even though it is slight) between the fastest point and the baseline in spontaneous imbibition. in a horizontal movement with minimized gravity [ii], n = 1 is effective. this indicates different mechanism of the flow [ii] with minimized gravity compared with the flow [i] against gravity. however, the a and the b values are same with those of the flow [i], indicating no additional modification or added force to the flow when the membrane is posed in horizontal direction. on the other hand, in a vertical movement accelerated by the gravity in [iii], n = 1.3 is properly fitted. compared with flow [i], a values for baseline increases 1.2 times (1.2/1.0) for mem 1 and 1.7 times (3.6/2.0) for mem 2. meanwhile, for the fastest point, a values increases 1.4 times (1.5/1.1) for mem 1 and more than 2 times (4.5/2.2) for mem 2. therefore, flow increase is more prominent for the fastest point than the baseline. in terms of the pore size effect, the a values of mem 2 are three times larger than those of mem 1 both for baseline (3.6/1.2) and fastest point (4.5/1.5), satisfying the relation, h(t) ~ (r)4/5 > (r)1/2. therefore, the pore size dependency becomes more significant for flow [iii] than the flow [i] and [ii]. compared with zero values for the flow [i] and [ii], the b values of flow [iii] increases to 0.2 (mem 1) and 0.4 (mem 2) for baseline, indicating size-dependent additional force generation by the vertical flow. this becomes 1.5 times larger for fastest points as 0.3 (mem 1) and 0.4 (mem 2) respectively. therefore, added gravity significantly affects additional force generation which is more prominent for fastest point than baseline. and this becomes more prominent for larger pore size. in any flow type occurring in a complex network, there is a meniscus development making minimum and maximum position. this might depend on the local geometry difference: there is a more advantageous point for the flow in the media such as large pore and direct shortcut flow path etc., which can make stronger connection in a network. this difference becomes more significant with large 11 pore size and additional force introduction. in a spontaneous imbibition, the arrangement of flow direction multiplies the flow rate. this is affected by the pore size of the media, flow mechanism and additionally added pressures. prominently, the flow at the fastest point away from the baseline increases significantly by an additionally added pressure (+pg). this can be one supporting information where some selected points in a network takes faster flow. 3. discussion new insights for the imbibition. spontaneous imbibition is important not only for its fundamental aspects but also for its special applications in liquid penetration into nano materials[67], ink penetration in paper or coating on paper[72], oil recovery where gas/oil is displaced by a different liquid[73], and the like. in the spontaneous imbibition the mean advancing front is known to follow lucaswashburn’s law[74,75]. for this the behavior of h ~ t1/2 is followed, which also has been reported with other similar models[66,67]. nonetheless, the one-half power scaling law is not always effective with other factors affected by property of fluids and media[67,68,73]. the effect of gravity on spontaneous imbibition in porous media investigated both theoretically and experimentally[77], shows that the spontaneous imbibition can be governed by the hydraulic conductivity (permeability) of the porous media. in addition, few study has focused on the scientific explanation of the local meniscus development rather than using mean values. by the aforementioned water movement mechanisms occurring in nanomembrane models, the fluid flows in a complex nanoporous network structure are observed to follow the power dependency on the time, h(t) = atn + b. depending on the timedependent mechanism, power dependency n as well as magnitude a and additive b values are modified. it is experimentally observed that for a spontaneous imbibition n = 0.5 is satisfied however when gravity effect is minimized n = 1 is effective. in addition, with added gravity, n > 1 is satisfied. therefore, halfpower time dependency is not the criteria to explain the imbibition mechanism in which water fills the nano-scale structures spontaneously. in addition, multiplication and addition factors are observed to strongly depend on the membrane pore size and added forces. the way of water movement by spontaneous imbibition is also sensitively modified by the geometry of the porous media. imbibition is a dynamic procedure limited in the situation where water moves by forming an air-water interface. the variation of mass (m) during the time (t) by the spontaneous imbibition of water into hydrophilic porous structures follows the lucas-washburn scaling law[64,65], m(t) = ct, c = a(r lv cos/2) (3) : density of the fluid : dynamic viscosity a: cross-sectional area of the sample : pore volume fraction r: effective pore radius lv: liquid-vapor surface tension : contact angle : tortuosity the main structural contribution,  describes the connectivity and meandering of the pores[78]. the meandering of the pores increases the length of the flow path hence increases . therefore, by locally differentiated thus smaller , water flows with minimized meandering and effective transportability. the water permeation under a pressure gradient contains a filtration constant, elastic modulus of the media, and osmotic concentration. when a pressure is applied to a vessel channel, the free energy of water is isothermally raised by vp, where v is the volume of water in the sample and p is the pressure increase necessary to establish an equilibrium between water in and out of the system. in the water movement by capilarity, the water flows through smooth walled capillaries, where the volumetric flow rate (dv/dt) is proportional to the applied pressure gradient by the distance l (dp/dl) mediated by the hydraulic conductivity (kcapillary), dv/dt = −kcapillary(dp/dl), (the minus sign indicates the water flow from high to low pressure). the kcapillary is then proportional to the fourth power of the capillary size : kcapillary = r4/8, where  is the dynamic viscosity of fluid (pa.s). this pressure-induced hagen12 poiseuille based capillarity relation displays strong media size-dependency of water movement through pipe-like channels. therefore, when a pressure is further loaded over the normal condition (addition factor b value increase) hagen-poiseuille based capillarity become significant. this condition is more sensitively affected by the pore size (~r4). other spontaneous movement of water is diffusion (even though water flow in a plant is not considered in this category) which follows the fick’s law[79–81]. water enters the free space of a medium, surrounds and diffuses into each subunit overcoming the diffusion barriers. the kinetics of this diffusion follows fick’s first law, ci/t = da(c0  ci)/vh, (ci: concentration of moving molecules in the media; c0: external concentration, d: the diffusion coefficient of in the media; v: the volume of the media; a: the area through which the diffusion is taking place; h: the distance of the diffusion). on the other hand, water enters and diffuses continuously through uniformly distributed resistance. such diffusion into a sheet would follow fick's second law, yielding a time course relation of ci/t = d(2ci/h2)[82]. inhirently diffusion is not driven by the forced action but a result of the random movement of molecules. however, considering the concentration difference of the water molecules, water-air interface is more advantageous for fast movement than water-water condition in any of diffusion condition. point-selection and faster movement. in the time-dependent h(t) value change for two mem 1 and mem 2 tracked in red in the membrane, the flow of a specific point is far faster than baseline movement (figure 4a). the time-dependent difference between the minimum baseline and the maximum fastest point is indicated by h(t) for three flow types [i] to [iii]. this quantifies a specific point movement faster than other local fluid body tracks even though it also follows same power law dependency with baseline track. overall, the absolute value of h(t) is large in the order of flow [i] < flow [ii] < flow [iii], indicating effective acceleration by additionally introduced forces such as gravity. in addition, large pore size mem 2 shows higher h(t). for every case, time-dependent change, dh(t)/dt strongly depends on the flow type in the order of flow [i] < flow [ii] < flow [iii]. from the graphical investigation of three flow types, mem 2 generates higher h(t) value in flow [iii] prominently. survival strategy of the live systems. in a graphical summary at the right (re-graphed from figure 2a), for the dried samples (p + pa, solid symbol lines) the lower order veins are more effectively filled out in a fast way than those under the normal physiological pressure (p, empty symbol lines) (figure 4b). this is explained by additionally added pressure (p + pa) loaded on the water flow mechanism which is more sensitive for pointselected faster movement. the phenomena are also observed in membrane model system where the spontaneous imbibition is modified as summarized in figure 4a. a figure 4. (continued). 13 b figure 4. (a) the time-dependent difference between the minimum baseline and the maximum fastest point expressed by h(t) for three flow types [i] to [iii] with two mem 1 (solid lines) and mem 2(dotted lines). (b) water uptake profile of a selected venation structure is arranged by x-ray image at the left and analyzed graph are the right. at normal pressure condition (p, empty symbol lines) and additional pressure condition (p + pa, solid symbol lines). 4. conclusion as an important survival strategy the important main veins of a plant is filled out first under the water deficient stressed condition. by this way, water can be provided for more urgent parts first. the way of transport phenomena adopted by the live system is one of the naturally adopted strategies for a long evolution history. in this study, compensatory perturbations of network dynamics and the concept of plant segmentation are discussed as a related apparent phenomenon. the science behind is water flow mechanism affected by many conditional factors. water movements observed in plant systems are explained in conjunction with model systems. as a result, it is confirmed that specific structures enhances the water flow and this is favorably performed by the appropriate physical factors such as pressure vs. flow in the structure. 5. methods synchrotron x-ray micro imaging (xm). xm images of plants were obtained at the 6c biomedical imaging beamline at the pohang ligh source ii (pls ii, pohang, south korea). for the x-ray computed tomography (x-ray ct) scanning, the plants were rotated in the x-ray white beam from 0 to 180° by the increments of 0.5° yielding two-dimensionally projected images which are accumulated into 3d images. each projection was magnified through an objective lens and relayed onto a 4,008 × 2,600 pixel ccd camera (vieworks). these raw 2d tomographic projections were reconstructed into 1340 tif image slices using octopus 8.3 software (institute for nuclear science). these images were analysed in amira 5.2 software. first, the white beam allows x-ray image acquisition with high spatial and temporal resolutions. to reduce potential damages to live samples, additional 1 mm-thick aluminium plates were used to remove most x-rays below 10 kev. a ccd camera (vieworks, vm2m35) with 1,600 × 1,200 pixels provides magnified images by a 5 × objective lens (field-of-view (fov) = 2,083 × 1,563 m2) or a 10 × objective lens (fov = 1,013 × 759 m2). x-ray images were consecutively captured at 10 to 20 frames per second (fps), with an exposure time of 60 to 100 ms. a safe time limit of 20 s was set for continuous imaging of a given experimental set-up to avoid possible damage to the live tissues. generally, the objective lens with low magnification (5×) was used for the long-distance tracking of the water/air menisci through the vessel elements. the 10× objective lens was used to precisely visualize the anatomical structure. second, the monochromatic beam (10 kev x-ray) was used to trace sap movement for an extended period (longer than 5 min for total exposure) as well as to minimize potential damage to the live samples. a 1,024 × 1,024 pixel ccd camera (redlake, megaplusii es2001) was used to capture 14 x-ray images at 24 fps, with an exposure time of 30 ms (fov=735 × 735 m2 with a 10 × objective lens or fov = 2,219 × 2,219 m2 with a 4 objective lens). synchrotron x-ray nanoscopy (xn). experiments were carried out at the 7c beamline at pls ii. the x-ray source of 1011 photons/m2/sec consists of undulator with 20 mm period and 70 poles. the beam size is about 100 m  100 m at 7 kev. the x-ray source was radiated from a 3 gev bending magnet and then monochromatized using a ge (111) dcm. to achieve focused images, monochromatic x-ray beam was focused on the sample using a condenser zone-plate (czp, 1 mm dia. beryllium refractive compound lenses) with innermost and outermost diameters of 4 nm and 100 nm, respectively. the primary x-ray image was magnified 50 times with an objective zone plate lens (140 m innermost and 50 nm outermost diameter, w). it was then converted into a visible image on a thin scintillator crystal (tb: lso, 20 m thickness). the visible image was further magnified ×20, using an optical microscope. this provides a total ×1,000 magnification of image on a cooled ccd camera (princeton instrument versarray 1300b cooled ccd) of 1,340 × 1,300 pixels, which corresponds to an equivalent fov of 21 × 21 µm2 with 30 nm resolution. plant sample preparation. arabidopsis seeds were germinated in an incubator at 30 ℃. after 3 days, the germinated seeds were transferred to a hydroponic culture system and grown in a greenhouse (16/8 hr photoperiod at 300 mol m−2 s−1, 27/22 ℃ day/night, 50%–60% humidity) up to the flag leaf stage (approximately 7 weeks). the culture solution (ph 6) contains (mm): kh2po4 = 0.21, k2hpo4 = 0.06, kno3 = 1.98, ca(no3)2 = 2.96, mgso4 = 0.61, (nh4)2so4 = 0.53, mnso4 = 2.9 × 10−3, znso4 = 2.5 × 10−3, kcl = 0.1, (nh4)2moo4 = 6 × 10−5, cuso4 = 6.3 × 10−2, h3bo3 = 7.4 × 10−3, and edta-fe=0.206. all the plant samples prepared for x-ray observation were collected from wellwatered plants early in the morning to ensure low levels of native embolism. branches were collected in the morning half an hour before the experiment. to prevent an invasion of air from the cut edge of the plant, vessel lengths were measured by air-injection, and branches were cut more than two times longer than the longest vessel. all measurements were performed on the leaves at the distal ends of these cut branches. plants of different leaf venation, privet, ficus lutea and rhapis excelsa were purchased[83] in a soil pot and used without further treatment. the leaves attached to a sprig were used. the samples were cut and dipped in an iopamidol solution (0.1% m/m) to keep water-water interaction. after xm observation, the same samples were dipped in the media solution for 12 hr for stabilization. and then the samples were taken out of the media and left for 12 hr to generate water-air interface in the veins. these dried samples were dipped in the iopamidol solution during the xm observation. during the venation observation, due to limited fov, small patches were put together to complete one whole image of a large size. for this, an exposure time was limited no longer than 3 sec at a time and focus region was carefully controlled without unnecessary exposure of samples to the beam. negative pressure generation. artificial negative pressure was applied using a syringe pump (remote infuse/withdraw phd ultra 4400 programmable syringe pumps, harvard apparatus, usa). the upper cut end of stem sections or branches were connected to the syringe via a silicon tube and the negative pressure was monitored using a cell pressure probe. the pressure value, i.e. the gauge pressure, was maintained at approximately −0.1 mpa throughout the experiments. for negative pressure generated onto a stem cut, an air-tight plastic tube was tightly connected. after link to the syringe pump, negative pressure was controlled by withdrawing mode at a −0.002 l/min speed. pressure probe technique (der werkzeugmacher) was adopted to control water suction mode in a plant. negative pressure in the leaves with three different venations was generated by drying each sample for 12 hrs. the dried state was confirmed by using imagej to detect the embolism events from the previous water-saturated x-ray image sequence. to increase the difference between noise and the embolized region, a smoothing filter was applied. next, threshold was applied to the image sequence, 15 that maximizes the embolized region and minimizes the noise. water movement in xylem vessels in a stem. water movement in a stem occurs in a complex structure. arabidopsis thaliana is employed with two different genotypes (ler and clv3) and growth conditions (long-day, ld and short-day, sd) as a live model system. gold nanoparticle (aunp) aqueous solution is employed to trace sap fluid movement in a stem and observed by x-ray microscopy (xm) computed tomography (figure a1)[46,47]. xylems and phloems in bundles are investigated by rendering the cross-sectional 2d images into 3d images (figure 1a). in terms of the total number of xylem vessels, the genotype clv3 has more vessels over ler (figure a2). however, active vessels (aunp-stained vessels) are not much differentiated by the genotypes, while the growth condition (ld and sd) generates noticeable difference. therefore, arabidopsis (ler) of ld and sd conditions are selected in this study for water flow observation. in addition to typical axial flow, radial flow is generated by the interconnection of pores among the adjacent xylems within a bundle (figure a3). for this process a stem cut is dipped in an aqueous culture medium containing concentration-controlledaunp (~20 nm diameter, 2.4 × 1021 aunp/m3). acknowledgments the authors are grateful for the valuable help in the experiments performed at the pohang light source ii (pls-ii, pohang, south korea) utilizing xray micro imaging (xm) at 6c beamline and x-ray nanoimaging (xn) at 7c beamline. conflict of interest the author 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(b) gold nanoparticle stained x-ray microscopy (xm) computed tomography 2d images (left) which are accumulated into 3d image (right). figure a2. xylem vessel types of arabidopsis are evaluated. total number of xylem vessels, aunp-stained xylem vessels and number of xylem vessels per bundle are counted for each genotypes and growth condition. 20 a b figure a3. morphology of vascular bundles obtained by sem. (a) xylems are in the form of bundles across the cross section. the vessels are interconnected through which water flows in the networked structures. (b) the longitudinally sectioned xylems. in addition to the typical axial flow, radial water flows are promoted by the interconnection among the adjacent xylems within a bundle. the radial flows are possible by the holes on the vessel walls through which water is transported. characterization and application of nanomaterials (2022) volume 5 issue 1 doi:10.24294/can.v5i1.1416 39 original research article the comparable study of isoelectronic-bodies of single-walled b/n nanotubes hua zhao1,2, chunchua tian1, suna wang1, dezhi sun1, chong zhang1* 1 school of chemistry and chemical engineering, liaocheng university, liaocheng 252059, china. e-mail: zhangchong@lcu.edu.cn 2chemistry group, wei shan no.1 senior middle school, jining 277600, china article info received: 28 november 2021 accepted: 5 january 2022 available online: 18 january 2022 copyright © 2022 hua zhao et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ abstract the structure, thermodynamic stability, ionization potential (ip) and electron affinity (ea) energy level difference (eg) and tension of lowest unoccupied orbit (lumo) and highest occupied orbit (homo) of armchair single wall carbon nanotubes (c-nts), bn hybrid carbon nanotubes (bc2n-nts) and all bn nanotubes (bn-nts) were systematically studied with am1 method in this paper. calculation results show that when n value is constant, (n, n) c-nts (n = 3, 4, 5, 6) has the largest diameter and bn-nts has the smallest diameter; (n, n) the values of eg (homolumo) and n of c-nts and bc2n-nts are related; poav analysis shows that different hybrid atoms have different contributions to the hybrid mode of nanotube atoms and the tension of nanotubes. keywords: carbon nanotubes; bn nanotubes; energy gaps (ehomo-elomo); hybrid tension 1. introduction since the discovery of carbon nanotubes[1], especially singlewalled carbon nanotubes[2,3] were found, carbon nanotubes have had potential applications in many aspects due to their unique mechanical, optical and electronic properties[4-6]. scientists have not stopped their research. in addition to the body, many substitution products of carbon nanotubes have been synthesized, and bn hybrid carbon nanotubes are one of them. up to now, bn hybrid carbon nanotubes (bxcynz) [7,8] with various components have been synthesized, including isoelectronic isomers of carbon nanotubes, namely nanotubes composed of bc2n and all boron nitrogen bn nanotubes[9,10]. all bn nanotube is a semiconductor material with an energy gap close to 5.8 ev, which is similar to the electronic properties of a large number of hexagonal bn network structures, and the size of the energy gap is independent of the diameter, helicity and the interaction between tubes and tubes of bn nanotube[11]. this electronic property of bxcynz nanotube is obviously different from that of carbon nanotube, because the size, diameter, length and helicity of the electron energy level band gap (egap) of carbon nanotubes are related[11]. taking three kinds of isoelectronic nanotubes (n, n) c-nts, bc2nnts and bn-nts (n = 3, 4, 5 , 6) as research objects, we systematically studied the relationship between their geometric structure, thermodynamic stability, ionization potential, electron affinity and copyright 40 tension with diameter by using semi empirical am1 calculation method, having revealed the diameter effect and hybrid effect of boron nitrogen heteroatomized carbon nanotubes, which provides a theoretical method for relevant research law and theoretical basis[12,13]. 2. the way of calculation in this paper, the full optimization of the molecular geometry of nanotube (n, n) c-nts, bc2n-nts and bn-nts (n = 3, 4, 5, 6) is based on the am1 method in the gaussian 98 package[14]. in order to ensure that all the optimized geometries are the minimum points of the geometric potential energy surface, based on the same method, all the optimization results are frequency analyzed, and no virtual frequency is found. in addition, the tension calculation (strains,) of these optimized configurations are done in the program poav[15] provided by professor haddon. it is reported that all bn nanotubes bnnts can have many structures, and the most thermodynamically stable structure is shown in figure 1c [this paper takes (3, 3) bn-nt as an example]. in figure 1c, all b atoms are separated by an equal number of n atoms. similarly, all n atoms are also separated by an equal number of b atoms. for bc2n-nts, although there are many different composition structures, both experiments[16,17] and theory[18,19] have confirmed that figure 1b is the most stable structure; in figure 1b, the number of carbon strips and bn strips reaches the maximum. for the convenience of research, the pure c nanotube (3, 3) c-nt is also listed in figure 1a. it should be noted that in figure 1a, b and c, for each sawtooth nanotube, there are only two kinds of bonds, namely vertical bond (v, the abbreviation of vertical) and oblique bond (s, the abbreviation of sloppy). the vertical bond (v) is the bond between atoms at positions 1 and 2, and the oblique bond (s) is the bond between atoms at positions 2 and 3. in order to save computer time and accuracy, the nanotube (n, n) c-nts, bc2n-nts and bn-nts (n = 3, 4, 5, 6) models in this paper contain 8 layers of atoms, and the suspended bonds at both ends are saturated with h atoms (as shown in figure 1). the molecular formulas of bc2n-nts and c-nts are expressed as b8nn8nh4n, b4nc8nn4nh4n and c16nh4n, respectively. 3. the result and discussion (a) carbon nanotube of (3,3); (b) bc2n nanotube of (3,3); (c) bn nanotube of (3,3) “v” and “s” represent vertical keys and diagonal keys respectively figure 1. schematic diagram of three isoelectronic nanotubes. 3.1 geometry based on the am1 method, the geometric structures and millikan charges of nanotubes (n, n) c-nts, bc2n-nts and bn-nts (n = 3, 4, 5, 6) are calculated. the calculated nanotube diameter and corresponding key bond length are listed in table 1, and the millikan charges carried by each key atom are listed in table 2. it can be seen from table 1 that for nanotubes c-nts, bc2n-nts and bn-nts (n = 3 or 4 or 5 or 6) with the same n value, the diameter increases slightly from the former to the latter. taking nanotubes (3, 3) c-nt, bc2n-nt and bn-nt as examples, the diameter calculated by am1 is 4.110 respectively, 4.241 and 4.321 å, gradually increase, and the diameters of other (n, n) nanotubes c-nt, bc2n-nt and bn-nt also show a similar trend. this shows that bn substitution reaction can increase the diameter of carbon nanotubes, and the more the number of bn bonds, the more obvious the diameter increase. it can be seen from table 1, the oblique bond lengths of nanotubes (3, 3) c-nt and bc2nnt are 1.453 (c2-c3) and 1.427 (average bond lengths of c2-c3 and n1-b4), respectively. the latter is 0.022 å longer than the former. the bond lengths of the two vertical bonds are 1.428 (c1-c2) and 1.427 å (n1-c2) respectively, which is almost the same, indicating that the oblique bond contributes more to the increase of nanotube diameter than 41 the vertical bond. in the process of c-c bond being further replaced by b-n bond and finally becoming fully substituted bn nanotube, both vertical and oblique bonds contribute to the increase of diameter. taking (3, 3) tube as an example, it can be seen from table 1 that the bond lengths of vertical and oblique bonds of (3, 3) bn-nt are 1.508 and 1.504 å respectively. the bond lengths of (n, n) bc2n-nt are longer than those of (n, n) bn-nt. therefore, from the fact that the bond lengths of c-nt, bc2nnt and bn-nts increase gradually, it can be seen that the stability of nanotubes decreases gradually due to the progress of bn substitution. it can also be seen from table 1 that on the basis of am1 calculation, the diameters of (3, 3), (4, 4), (5, 5) and (6, 6) c-nts are 4.110, 5.487 ‘6.776 and 8.147 å respectively, gradually increasing; the corresponding vertical bond (c1-c2) bond lengths are 1.428, 1.413, 1.407 and 1.404 å, respectively, and the corresponding oblique bond (c2-c3) bond lengths are 1.453, 1.446, 1.443 and 1.441 å, respectively. the vertical and oblique bonds of bc2n-nt and bn-nt tubes also gradually decrease with the increase of diameter. this shows that for c-nts, bc2n-nt and bn-nt tubes, the vertical and oblique bonds become more and more stable with the increase of diameter. accordingly, the thermodynamic stability of the corresponding nanotubes becomes stronger and stronger. table 2 lists the values of mulliken charges carried by the key atoms of (n, n) (n = 3, 4, 5, 6) c-nts, bc2n-nts and bn-nts based on am1. it is obvious that for any n value, whether c-nts, bc2nnts or bn-nts, there is no obvious relationship between the charge on its atom and its diameter, which is almost constant. for example, the charges on n1, c2, c3 and b4 atoms on (3, 3) bc2n-nt tubes are −0.3342, 0.2246, −0.2724 and 0.3563 e respectively, which are almost equal to the charges on the corresponding atoms on the (4, 4), (5, 5) and (6, 6) bc2n-nt tube. it can also be seen from table 2 that for the same kind of nanotube, even for the same atom, the charges on it are very different, which is particularly obvious for bc2n-nts tubes, although c2 and c3 atoms in bc2n-nts tubes are carbon atoms. however, the average charges are 0.2246 and −0.2724 e respectively, which is very different because the two c atoms are in different chemical environments. specifically, c2 atom is connected table 1. diameters and key bond lengths of (n n) (n = 3, 4, 5, 6) c-nts, bc2n-nts and bn-nts nanotubes calculated by am1 method/å (n, n) c-nts bc2n-nts bn-nts diameters bond length diameters bond length diameters bond length c1-c2 c2-c3 n1-c2 c2-c3 n1-b4 n1-b2 b2-n3 (3, 3) 4.110 1.428 1.453 4.214 1.427 1.479 1.479 4.321 1.508 1.504 (4, 4) 5.487 1.413 1.446 5.645 1.412 1.473 1.461 5.754 1.493 1.494 (5, 5) 6.776 1.407 1.443 6.986 1.407 1.471 1.453 7.099 1.487 1.490 (6, 6) 8.147 1.404 1.441 8.389 1.405 1.470 1.450 8.530 1.483 1.487 table 2. mulliken charge/e calculated by am1 of carbon nanotube (n n) (n = 3, 4, 5, 6) c-nts, bc2n-nts and bn-nts c-nts bc2n-nts bn-nts c1 c2 c3 n1 c2 c3 b4 n1 b2 n3 (3, 3) −0.007 −0.007 -0.007 −0.335 5 0.226 9 −0.295 5 0.367 8 −0.362 2 0.349 8 −0.362 2 (4, 4) −0.005 −0.005 −0.005 −0.336 8 0.227 0 −0.273 4 0.357 7 −0.372 9 0.363 8 −0.372 9 (5, 5) −0.005 −0.005 −0.005 −0.333 3 0223 5 −0.263 0 0.351 6 −0.379 3 0.371 8 −0.379 3 (6, 6) −0.004 −0.004 −0.004 −0.331 1 0.220 9 −0.257 5 0.348 0 −0.383 5 0.376 7 −0.383 5 average −0.005 −0.005 −0.005 −0.334 2 0.224 6 −0.272 4 0.356 3 −0.374 5 0.365 5 −0.374 5 −0.000 0.69 0.74 42 with one n atom and two c atoms, while c3 atom is connected with one b atom and two other c protons (as shown in figure 1b). as we all know, the electronegativity of n atom is much greater than that of b atom, so the electrons on c2 atom connected to n atom will be attracted by n atom, so c2 will be positively charged, while c3 atom connected to b atom with less electronegativity will attract the charges on b atom, so it will be negatively charged. in addition, it can be seen from table 2 that the average charge difference between adjacent c atoms in c-nt tube is approximately zero, the average charge difference between adjacent b and n atoms in bc2n-nt tube is 0.69 e, and the average charge difference between adjacent b and n atoms in bnnt tube is 0.74 e. among the three nanotubes, the electron delocalization degree of c-nt tube is the largest, followed by bc2n-nt tube, and bnnt tube is the smallest, that is, the bond strength between adjacent atoms in c-nt tube is the largest, followed by bc2n-nt, bn-nt is the smallest, which further proves the previous conclusion on the stability order of the three nanotubes: c-nt > bc2n-nt > bn-nt. 3.2 atomic energy (hat) to further explore the relative thermodynamic stability of nanotubes (n, n) c-nts, bc2n-nts and bn-nts (n = 3,4,5,6), these three nanotubes are also evaluated from the perspective of atomization energy. the definition of atomization energy can be expressed as: hat(bxcynz) = hf(bxcynz)–xhf(b)– yhf (c)–zhf (n). here, hf(x) represents the heat of formation of atom (molecule) x. it is obvious that the greater the negativity of atomization energy hat, the better the stability of the tube, figure 2 shows the atomization energy of the above nanotubes. it can be seen from figure 2 that bn heteroatomization reaction increases the number of corresponding nanotubes, indicating that the thermodynamic stability is reduced, which is similar to the previous conclusion and the bn heteroatomization conclusion of fullerenes[20]. it can also be seen from figure 2 that whether (n, n) c-nt, bc2n-nt or bn-nt, hf(x) gradually decreases with the increase of n, indicating that their thermodynamic stability gradually increases with the increase of diameter. this conclusion is also consistent with the consensus on the thermal stability law of nanotubes generally accepted by the scientific community at present: that is, the larger the diameter of nanotubes, the stronger the thermodynamic stability. figure 2. isoelectronic nanotube (n, n) (n = 3, 4, 5, 6) c-nt, atomization energy based on am1 method of bc2n-nt and bn-nt. 3.3 ionization potential (ip), electron affinity potential (ea) and lowest unoccupied orbital (lumo) ionization potential (ip) and electron affinity (ea) are two important concepts related to chemical reaction. according to koopmans’ theoretical viewpoint: ip = –ehomo, ea = –elumo. in this paper, the ionization potential (ip) and electron affinity (ea) of (n, n) c-nts, bc2n-nts and bn-nts (n = 3, 4, 5, 6) calculated by am1 method are listed in table 3. as can be seen from table 3, firstly, the effects of bn substitution on ip, ea and eg between the highest occupied orbit and the lowest occupied orbit of c-nts are very obvious. for example, when (3, 3) c-nt is replaced by bn to form (3, 3) bc2nnt, ip becomes smaller, ea increases. when bn substitution continues to occur and pure (3,3) bnnt is finally generated, ip becomes smaller and ea becomes larger. therefore, eg of (3, 3) bn-nt is the largest (13.64 ev), followed by (3,3) bc2nnt, which is 7.39 ev, and the energy level c-nt is the smallest, which is 5.42 ev. this shows that bn hybridization not only reduces the ability of obtaining electrons, but also the ability of losing electrons, that is, bn heteroatomization of c-nts 43 can effectively reduce its oxygen. from table 3, it can also be seen that eg increases by 2.09 ev from (3, 3) to (6, 6) c-nts, and from (3, 3) to (6, 6) bc2n-nts. eg increased by 0.11 ev, but from (3, 3) to (6, 6) bn-nts, eg increased by only 0.02 ev, which is almost negligible. this shows that compared with c-nts and bc2n-nts, eg of bnnts has almost nothing to do with the diameter. this characteristic of bn-nts has also been confirmed by relevant experiments: according to the report in literature[21], regardless of the number, diameter and helicity of bn-nts tubes, they have a stable electron gap (energy gap, ~ 5 ev). therefore, pure bn-nts is a very suitable insulating or semiconductor material. 3.4 rehybridizations and strains similar to spherical fullerenes, carbon nanotubes and their derivatives will produce nonparallel π orbitals due to curved surfaces, so the electron delocalization phenomenon on the surface will be reduced and the conjugation will be destroyed to a certain extent. because the nanotubes bc2n-nts and bn-nts can be regarded that they are formed by the c-c bond in c-nts through bn substitution reaction. therefore, these bn heteroatoms will also affect the π bond on carbon nanotubes. to explore this effect, the rehybridizations and strains of molecular orbitals of nanotubes (n, n) c-nts, bc2n-nts and bn-nts (n = 3, 4, 5, 6) are calculated by poav program, and the calculation results are listed in table 4, where sap represents the rehybridization of π orbitals and spb represents σ orbital rehybrid, p 2i represents the square of the table 3. ip, ea and eg of (n n) (n = 3, 4, 5, 6) c-nts, bc2n-nts and bn-nts in am1 method c-nts bc2n-nts bn-nts ip ea eg ip ea eg ip ea eg (3,3) −5.29 0.14 5.42 −6.57 0.82 7.39 −10.12 3.52 13.64 (4,4) −5.56 0.40 5.96 −6.50 0.93 7.43 −10.04 3.65 13.69 (5,5) −5.47 0.23 -5.70 −6.32 1.02 7.35 −9.97 3.72 13.69 (6,6) −5.22 -1.90 3.33 −6.25 10.3 7.28 −9.88 −3.77 13.66 table 4. poav analysis results of nanotube (n n) (n = 3, 4, 5, 6) c-nts, bc2n-nts and bn-nts nanotubes sap spb p 2i c b n c b n c b n (3, 3) bn-nt 0.085 3 0.068 3 2.256 1 2.204 9 0.033 9 0.027 5 (4, 4) bn-nt 0.033 2 0.047 0 2.099 5 2.140 7 0.014 8 0.020 7 (5, 5) bn-nt 0.024 8 0.022 9 2.074 2 2.068 8 0.011 5 0.010 6 (6, 6) bn-nt 0.016 2 0.015 3 2.048 7 2.046 1 0.007 7 0.007 3 (3, 3) bc2n-nt 0.046 9 0.055 1 0.108 8 2.139 9 2.165 3 2.326 2 0.020 3 0.023 4 0.044 0 (4, 4) bc2n-nt 0.026 9 0.039 6 0.027 3 2.080 7 2.118 8 2.081 8 0.012 6 0.018 2 0.012 8 (5, 5) bc2n-nt 0.015 4 0.020 8 0.018 4 2.046 1 2.065 5 2.055 1 0.007 4 0.010 5 0.008 8 (6, 6) bc2n-nt 0.010 4 0.011 9 0.013 5 2.031 2 2.035 8 2.040 4 0.005 1 0.005 8 0.006 6 (3, 3) c-nt 0.046 8 2.140 3 0.021 5 (4, 4) c-nt 0.024 9 2.074 8 0.011 9 (5,5) c-nt 0.015 1 2.045 5 0.007 4 (6,6) c-nt 0.010 0 2.029 8 0.004 9 note: a and b are the re hybridization of s orbital component and p orbital component in hybrid atom respectively, and p 2i is the calculated tension of the corresponding carbon nanotube. 44 pyramid angle between adjacent p orbitals, which can qualitatively describe the change of nanotube tension caused by bn hybridization. it can be seen from table 4 that because nanotubes bc2n-nts and bn-nts have different element compositions (c or b or n), each element has its own contribution to the rehybrid and tension of molecular orbitals. this paper takes (3, 3) bnnt as an example to illustrate this problem. the analysis results of poav show that the sap values of element b and element n of (3, 3) bn-nt are 0.0853 and 0.0683 respectively, the spb values are 22,561 and 2.2049 respectively, and the values are 0.0339 and 0.0275 respectively. this shows that compared with element b, the n element in (3, 3) bn-nts is closer to hybridization, so its contribution to nanotube tension is smaller. however, when the diameters of bc2n-nts and bn nts gradually increase, the contribution of different elements to the rehybridization and tension of molecular orbitals becomes smaller and smaller. for example, the difference of element b and element n’s a, b and of nanotube (3, 3) bn-nt are 0.0170, 0.0512 and 0.0064 respectively; however, the difference of element b and element n’s a, b and of nanotube (6, 6) bn-nt decrease to 0.0009, 0.0026 and 0.0004 respectively. although n atom has a pair of lone pair electrons and its electronegativity is greater than that of b atom and c atom, with the increase of tube diameter, the π π conjugation on the tube wall also gradually increases, and n atom makes these absorbed excess electrons return to the original c atom or b atom through the π π conjugation system, thus, the electrons of the whole system tend to average among atoms. we can also see from table 4 that with the increase of diameter, the s component (a) of π orbital rehybridization (sap) of nanotube c-nts, bc2n-nts and bn-nts, and the p component (n) of σ orbital rehybrid (spb) decrease gradually with the increase of diameter, which indicates that the increase of diameter will make the c atom or b atom or n atom on the tube gradually close to the classical plane hybrid mode of sp2. in addition, with the increase of diameter, the c atom in c-nts, bc2n-nts and bnnts, b atom or n atom, the value of also decreases gradually, which indicates that the larger the diameter of the meter tube, the smaller the tension, so that the system is more stable. 4. conclusion based on the am1 method, the equilibrium geometry, hat, ip and ea, e g between the highest occupied orbital (homo) and the lowest unoccupied orbital (lumo), and plane tension, etc. of nanotubes (n, n) (n = 3, 4, 5, 6) c-nts, bc2nnts and bn-nts are systematically studied. the results show that the diameter of nanotubes increases slightly and the stability decreases due to the bn substitution reaction, which is consistent with the calculation results of atomic energy. the results of poav analysis show that, although b atom, n atom and c atom have different contributions to molecular orbital rehybridization and tube tension in bc2n-nts and bn-nts nanotubes, the difference of rehybridization and tension contribution between these different atoms becomes smaller and smaller with the increase of tube diameter. and the result also show that eg between the highest occupied orbital (homo) and the lowest unoccupied orbital (lumo) of bn-nts tubes is not 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muhammed furkan yaşar1, samet bozkurt1, sude naz bahar1, furkan bayram çoşkun2, serap yalcin azarkan3* 1 department of medicine, faculty of medicine, kırsehir ahi evran university, kırsehir 40100, turkey 2 department of medical biology, graduate school of health sciences, kırsehir ahi evran university, kırsehir 40100, turkey 3 department of pharmacology, faculty of medicine, kırsehir ahi evran university, kırsehir 40100, turkey * corresponding author: serap yalcin azarkan, syalcin @ahievran.edu.tr abstract:the mda-mb-231 cell line is derived from triple-negative breast cancer (tnbc), representing one of the most aggressive forms of breast cancer. innovative therapeutic strategies, including s targeted therapies using nanocarriers, hold significant promise, particularly for difficult-to-treat cancers such as tnbc. nanoparticles have transformed the medical field by serving as advanced drug delivery systems for cancer treatment. they play a critical role in overcoming the drug resistance often associated with cancer therapies. when utilized as drug delivery vehicles, nanoparticles can specifically target cancer cells and effectively reduce or eliminate multidrug resistance. among them, chitosan-coated magnetic nanoparticles (mnps) have been widely explored for the loading and controlled release of various anticancer agents. in this study, we evaluated the effects of dexamethasone-loaded chitosan-coated mnps on mda-mb-231 cell lines. fourier transform infrared spectroscopy and scanning electron microscopy were employed to verify the successful loading of dexamethasone onto the nanoparticles. to assess cytotoxicity, empty nanoparticles, free drug, and drug-loaded nanoparticles were tested on the cells. the results indicated that empty nanoparticles exhibited no toxic effects. the ic50 value of the free drug was 123 µg/ml, while the ic50 value of the drug-loaded nanoparticles was significantly lower, at 63 µg/ml. these findings confirmed the successful conjugation of dexamethasone to the chitosan-coated mnps, demonstrating substantial cytotoxic effects on breast cancer cells. although dexamethasone has been reported to exhibit both tumor-suppressive and pro-metastatic effects, its specific impact on tnbc warrants further investigation in future studies. keywords: nanoparticles; dexamethasone; breast cancer; cytotoxicity 1. introduction breast cancer is the most commonly diagnosed cancer among women worldwide and is treatable when detected at an early stage. however, advanced-stage breast cancer is considered incurable by current treatment methods [1,2,3]. breast cancer is known to be a molecularly heterogeneous disease. the key molecular characteristics include the human epidermal growth factor receptor 2 (her2), hormone receptors (estrogen and progesterone receptors), and brca mutations [1,3,4]. these molecular subtypes determine treatment strategies and significantly impact disease management [2]. treatments of breast cancer encompass local (surgery and radiotherapy) and systemic (endocrine therapy, chemotherapy, anti-her2 therapy, and immunotherapy) citation polat ds, atar d, doğan da et al. (2025). investigation of the effect of dexamethasone-loaded magnetic nanoparticles on mda-mb-231 cell lines. characterization and application of nanomaterials. 8(3): 11500. https://doi.org/10.24294/can11500 article info received: 11 february 2025 accepted: 3 march 2025 available online: 20 november 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(3), 11500. 2 approaches. neo-adjuvant therapy is a widely used practice in her2-positive breast cancer and triple-negative breast cancer (tnbc) [1,3,5]. in metastatic breast cancer, the treatment goals are to prolong survival and maintain quality of life [2,3]. genetic predisposition, particularly brca1 and brca2 gene mutations, has been reported to play a significant role in the development of breast cancer. additionally, environmental and lifestyle factors may also influence the risk [4,6,7]. mda-mb-231 is recognized as a tnbc cell line, and these cells are reported to represent one of the most aggressive forms of breast cancer. they exhibit increased resistance to antitumor compounds, and this resistance has been reported to become more pronounced in 3d spheroid models [8]. novel treatment methods, such as immunotherapy and targeted therapies (nanocarriers), hold significant promise, particularly for challenging cancers such as tnbc [4,9]. nanoparticles have revolutionized the field of medicine by being utilized in next-generation drug delivery systems for cancer treatment. they have demonstrated experimental success as drug delivery agents, fundamentally transforming the cancer treatment landscape by enabling more accurate detection methods, diagnosis, and targeted drug delivery to eradicate tumors [10]. nanocarriers accumulate in tumors through the enhanced permeability and retention effect, along with other complementary mechanisms, such as vascular transcytosis. because cell membrane transporters cannot remove nanoparticles that accumulate in tumors, lower doses achieve effective results [11]. nanoparticles play a crucial role in overcoming drug resistance associated with cancer. when used as drug delivery systems, these particles can target and reduce or eliminate multidrug resistance [12,13]. by leveraging the unique pathophysiology of tumors, nanoparticles can actively deliver drugs to cancer cells through increased permeability and retention effects, providing a more effective treatment in cases where traditional therapies are ineffective [12]. chitosan-coated magnetic nanoparticles (mnps) have been utilized for the loading and controlled release of various anticancer drugs. researchers have successfully incorporated drugs such as 5-fluorouracil and gemcitabine into these nanoparticles, demonstrating improved efficacy in target cells [14]. chitosan-coated mnps can be directed to the target site using a magnetic field, allowing for the specific delivery of drugs to cancer cells. this approach shows that cancer cells can be targeted while minimizing damage to healthy tissues [15]. chitosan-coated mnps exhibit high biocompatibility and a low toxicity profile, suggesting that these nanoparticles can be safely used in cancer treatment [16,17]. dexamethasone is a synthetic glucocorticoid that presents as an odorless, white crystalline powder with a mildly bitter taste (figure 1). it is a fluorinated steroid, specifically a 9-fluoro-pregna-1,4-diene, characterized by hydroxyl groups at the 11, 17, and 21 positions, a methyl group at the 16 position, and oxo groups at the 3 and 20 positions. renowned for its anti-inflammatory, immunosuppressive, and painrelieving properties, dexamethasone is widely used to manage conditions such as postoperative nausea and vomiting, autoimmune disorders, and allergic reactions [19]. characterization and application of nanomaterials 2025, 8(3), 11500. 3 figure 1. chemical structure of dexamethasone. reprinted from national center for biotechnology information [18]. this study investigates the impact of dexamethasone-loaded chitosan-coated mnps on tnbc (mda-mb-231) cell lines. 2. materials and methods 2.1. synthesis and characterization of magnetic nanoparticles and drug loading analyses the mnps (fe3o4) were synthesized using the co-precipitation method. the surface of the synthesized mnps was designed according to the properties of the drug and polymer to be loaded onto them. to optimize the synthesis of mnps, parameters such as mixing speed, reagent ratios, and temperature were studied to determine the optimal conditions. the crystal structures of the mnps were determined using x-ray diffraction (xrd). the shape and size of the mnps were examined at each stage of synthesis using transmission electron microscopy (tem). changes in the functional groups of the mnps after synthesis were identified using fourier transform infrared spectroscopy (ftir). at each stage of synthesis, properties such as size distribution (dls), zeta potential, vibrating sample magnetometry (vsm), thermogravimetric analysis (tga), x-ray photoelectron spectroscopy (xps), and electrical and magnetic characteristics were determined [19]. specifically, chitosan-coated magnetic iron oxide nanoparticles were prepared by co-precipitating fe(ii) and fe(iii) salts in a 1:2 molar ratio in the presence of chitosan and tripolyphosphate (tpp) using a five-neck glass flask [20]. during the formation of fe3o4 nuclei, chitosan molecules surround these anionic nuclei, and tpp acts as a cross-linker, binding the chitosan molecules around the fe3o4 core. the synthesized chitosan-coated mnps were characterized using techniques including xrd, xps, ftir, tem, dls, tga, vsm, and zeta potential analysis [20]. dexamethasone was then loaded onto the nanoparticles, followed by stability and release studies [20]. the synthesis and characterization of chitosan-coated mnps loaded with various anticancer agents are standard procedures in our laboratory, and the results have been and continue to be published in scientific journals. the drugs and characterization and application of nanomaterials 2025, 8(3), 11500. 4 mnps were mixed in a potassium buffer and rotated at 500 rpm for 24 h at room temperature (figure 2). drug-loaded mnps were isolated from unbound drug using neodymium magnets. the drug loading efficiency was determined by measuring absorbance at 240 nm using a uv spectrophotometer (multiskan go, thermo scientific, united states [us]). ftir and scanning electron microscopy (sem), conducted at kırşehir ahi evran university, were employed to confirm the successful loading of dexamethasone onto the mnps. figure 2. drug loading analyses. the drug was loaded onto free magnetic nanoparticles by stirring at room temperature for 24 h using a rotator machine. 2.2. drug release analyses the in vitro drug release study of mnps, free nanoparticles, and dexamethasone-loaded mnps was conducted in a sodium phosphate buffer solution (pbs, ph 7.4). at predetermined time intervals, a 10 μl aliquot was withdrawn from the pbs stock solution containing dexamethasone-loaded mnps. the samples were analyzed at 242 nm using a uv spectrophotometer (shimadzu uv-1800, shimadzu corporation, japan). 2.3. cancer cell cultivation the mda-mb-231 cancer cell line was cultured in 75-cm2 flasks using rpmi1640 medium supplemented with 10% (v/v) fetal bovine serum and 1% (v/v) gentamicin. the cells were maintained in a 5% co2 incubator at 37 °c. 2.4. cytotoxicity analysis in 2d cell cultures the cytotoxicity of dexamethasone was assessed in 2d cell cultures using an xtt (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2h-tetrazolium-5-carboxanilide)based cytotoxicity assay kit. viable cells convert the tetrazolium salt xtt into a colored formazan dye through mitochondrial enzymes. the amount of viable cells was determined by colorimetric measurement of this dye. cells were seeded in 96-well plates at a density of 5,000 cells per well. one column of the plate was reserved as a medium control, and no cells were added to these wells. after seeding, the cells were characterization and application of nanomaterials 2025, 8(3), 11500. 5 treated with serial dilutions of the drug and incubated for 24 to 96 h. activated xtt solution was then added to each well, and the plates were incubated at 37 °c for 2 to 5 h. the formazan dye in each well was quantified using a microplate reader. cell growth in wells without drug-loaded mnps was assumed to be 100%, and the growth in treated wells was calculated relative to this control. the ic50 (concentration required to kill 50% of the cells) was determined. each experiment was performed in triplicate. 2.5. migration assay the migration assay was conducted using the method outlined by liang et al. [21] cells were seeded at a density of 1.5 × 105 cells per well in six-well plates, with three wells serving as controls and three wells treated with the drug. the plates were incubated for 24 h. once the well surface was 80% confluent, a straight scratch was made through the cell monolayer using a pipette tip. microscopic images were taken immediately after creating the scratch (0 h) and at 6-h intervals until wound closure. the images were analyzed using the imagej software (national institutes of health, us) to evaluate cell migration. 2.6. cellular internalization of nanoparticles to determine the cellular uptake of nanoparticles, both neutral and charged nanoparticles were treated with cells. subsequently, the internalization status of the nanoparticles into the cells was examined under a microscope (bab-ters, bab, turkey) at 1, 2, 4, 6, 8, and 12-h intervals. 3. results and discussion the system consists of fe3o4 mnps at its core, enveloped by chitosan polymers that serve as drug carriers on the nanoparticle surface. as depicted in figure 3, dexamethasone molecules (marked by blue circles) were bound to the polymer via covalent or electrostatic interactions. this structure was designed to facilitate controlled drug release, enhance biocompatibility, and support targeted therapy. to verify the successful loading of dexamethasone onto the nanoparticles, ftir and sem analyses were conducted. analysis of the sem images revealed distinct morphological features. in figure 4, the surface displayed a rough and irregular texture, a characteristic commonly associated with chitosan-coated nanoparticles. this irregularity arises from the uneven coating of the chitosan polymer, which creates a porous and granular structure. such a structure is likely to enhance drug loading capacity, thereby improving bioavailability. the sem images confirmed the successful synthesis of chitosancoated fe3o4 mnps. in figure 5, the loading of dexamethasone was observed to increase the density of the nanoparticles and form an adhesive structure. the presence of 13.7% carbon content further supported the successful coating of chitosan and the loading of dexamethasone. these findings collectively demonstrate that fe3o4 mnps were effectively coated with chitosan and subsequently loaded with dexamethasone. characterization and application of nanomaterials 2025, 8(3), 11500. 6 (a) (b) figure 3. fourier transform infrared spectroscopy analysis results. (a) pure dexamethasone. (b) dexamethasoneloaded nanoparticles. characterization and application of nanomaterials 2025, 8(3), 11500. 7 figure 4. scanning electron microscopy analysis results of the chitosan-coated magnetic nanoparticles. scale bar: 50 µm; magnification: 1200×. figure 5. scanning electron microscopy analysis results of the dexamethasone-loaded chitosan-coated magnetic nanoparticles. scale bar: 3 µm; magnification: 10×. figure 6 displays the in vitro release profiles of dexmethasone from mnps in pbs solution. the dexamethasone-loaded mnps exhibited an initial burst release of 56% within the first 72 h. then, the drug reached a stable state. characterization and application of nanomaterials 2025, 8(3), 11500. 8 figure 6. the release of dexamethasone from magnetic nanoparticles across various time points. figure 7. image of the control mda-mb-231 cell line. scale bar: 100 µm; magnification: 10×. it was observed that chitosan-coated mnps were internalized by mda-mb-231 cells. these nanoparticles were expected to be utilized for controlled drug release. the findings revealed a disruption in cellular structural integrity and a decrease in cell density compared to the control group (figures 7–9). dexamethasone-loaded nanoparticles were shown to enhance the localized effect of dexamethasone while minimizing peripheral toxicity. in the red-marked areas in figure 8, dexamethasoneloaded nanoparticles were observed to be localized either along the cell membrane or dispersed within the cytoplasm. characterization and application of nanomaterials 2025, 8(3), 11500. 9 figure 8. image of dexamethasone-loaded chitosan-coated magnetic nanoparticles in and around mda-mb-231 cells post-transfection. scale bar: 100 µm; magnification: 100×. figure 9. cell internalization analyses. (a) microscopic image showing cell death following nanoparticle entry. scale bar: 100 µm; magnification: 10×. (b) time-dependent increase in nanoparticle internalization in cells. (c) 3d surface (surface/density) mapping(x: pixel, y: pixel, z: intensity) characterization and application of nanomaterials 2025, 8(3), 11500. 10 previous studies have demonstrated that chitosan nanoparticles exhibit varying transfection efficiencies depending on their formulation and the cell type. for example, chitosan–dna nanoparticles have displayed cell type-dependent transfection efficiency, with higher efficiency observed in hek293 cells compared to other cell types, such as mg63 and mesenchymal stem cells [22,23]. the use of lipochitoplexes—liposome-encapsulated chitosan nanoparticles—has been shown to increase transfection efficiency at least twofold under physiological conditions [24]. in the mda-mb-231 cell line, as illustrated in figure 9, the transfer of nanoparticles to the cell membrane and interior was confirmed. cytotoxicity analysis was conducted using the xtt assay kit. the xtt assay operates on the principle that the yellow tetrazolium salt is cleaved by the metabolic activity of living cells, producing an orange color change. chitosan-coated mnps, dexamethasone alone, and dexamethasone-loaded mnps were administered in diluted form. after 72 h, readings were taken using the elisa reader (elx808, biotek, us), and the results were analyzed to determine the ic50 doses. the xtt cytotoxicity analysis revealed that chitosan-coated mnps exhibited no toxic effects on cell viability. in contrast, dexamethasone alone was found to reduce cell proliferation by approximately 60%. importantly, when dexamethasone was loaded onto the nanoparticles, its effectiveness increased, potentially due to the controlled release mechanism that more efficiently inhibits cell proliferation. these findings suggest that chitosan-coated mnps are non-toxic and, when combined with dexamethasone, can act as a more potent therapeutic agent for targeting cancer cells compared to free dexamethasone (figure 10). the free nanoparticles, free drug, and drug-loaded nanoparticles were applied to the cells, and cytotoxicity analysis was performed. according to the obtained results, empty nanoparticles did not show any toxic effect. while the ic50 value of the free drug was 123 µg/ml, the ic50 value of the drug-loaded nanoparticles was 63 µg/ml. characterization and application of nanomaterials 2025, 8(3), 11500. 11 figure 10. cytotoxicity analysis of control, free nanoparticles, dexamethasone, and dexamethasone-loaded nanoparticles. note: *p<0.05, **p<0.01. the migration assay showed that dexamethasone-loaded mnp treatment significantly suppressed cell migration (p<0.05; figure 11). figure 11. the results of the migration assay. note: *p<0.05. abbreviation: dex-mnps: dexamethasone-loaded magnetic nanoparticles. characterization and application of nanomaterials 2025, 8(3), 11500. 12 dexamethasone is known to influence the tumor microenvironment by regulating blood vessels and the extracellular matrix. these regulations reduce interstitial fluid pressure, tissue stiffness, and solid stress, thereby enhancing the penetration of nanocarriers into tumors. this characteristic indicates that dexamethasone could improve the effectiveness of metastatic breast cancer treatment [25]. however, its use in brain tumors, such as glioblastoma, has been linked to poor outcomes, as high doses may cause more side effects without improving clinical results [26,27]. furthermore, dexamethasone has been shown to promote metastatic behavior in certain breast cancer cell lines, particularly estrogen receptor-negative cells, by increasing cell count, invasiveness, and migration [28]. it has also been found to promote lung metastasis [29,30]. in this study, dexamethasone was successfully attached to chitosan-coated mnps, and the mnps demonstrated significant cytotoxic effects on breast cancer cells (figure 9). these results highlight the effectiveness of mnps as a delivery system and their potential to amplify the biological impact of dexamethasone on target cells. the findings suggest that further optimization of the surface modification and drug-loading capacity of mnps is possible. the chitosan coating created a biocompatible environment for controlled drug release, enabling efficient delivery of dexamethasone to target cells (figure 7). moreover, the magnetic properties of the nanoparticles provide a promising method for targeted drug delivery using external magnetic fields. however, this study is preliminary, and additional validation of the data is necessary. key factors such as drug-loading capacity, release kinetics, bioavailability, and targeting efficiency need to be thoroughly examined. in vivo studies are also essential to draw more definitive conclusions about the safety and efficacy of this system. future research should focus on assessing the biological safety and pharmacokinetic properties of the system, as well as testing its effectiveness across various cancer types and larger cell populations. such data are crucial for evaluating the clinical potential of nanoparticle-based drug delivery systems. 4. conclusion in conclusion, the dexamethasone-loaded mnp system developed in this study represents an innovative approach to drug delivery and targeting, with the potential to become a patentable technology in the future. author contributions: conceptualization, dsp, da, dad, ea, fb, gy, heb, mao, mb, mfy, sb, snb, fbc, sya; formal analysis, sya; investigation, dsp, da, dad, ea, fb, gy, heb, mao, mb, mfy, sb, snb, fbc, sya; methodology, sya; visualization, fbc; writing–original draft, sya; writing–review and editing, fbc, sya. all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. data availability statement: the data that support the findings of this study are available from the corresponding author upon reasonable request. characterization and application of nanomaterials 2025, 8(3), 11500. 13 references 1. harbeck n, 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10.1016/j.biopha.2014.07.003 characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.1852 1 original research article construction of semiclassical interatomic b–b pair potential to characterize all-boron nanomaterials levan chkhartishvili engineering physics department, georgian technical university, tbilisi 0160, georgia. e-mail: levanchkhartishvili@gtu.ge abstract the semiclassical boron–boron interatomic pair potential is constructed in an integral form allowing its converting into the analytical one. it is an ab initio b–b potential free of any semiempirical adjusting parameters, which would serve as an effective tool for the theoretical characterization of all-boron and boron-rich nanomaterials. keywords: interatomic potential; semiclassical approach; ground state parameters; nanomaterial; boron 1. introduction currently, the prospective wide technological applications of borophenes and boron-rich nanomaterials in general are of special research interests due to their variable interatomic bonding mechanism and related unique complex of physical and chemical properties (see some of recent reviews[1–6]). among them, the small all-boron clusters bn (containing 푛 < 20 atoms) preferring (quasi) planar structures play an important role in characterization of borophenes and other 2d boron nanomaterials as can serve for their building blocks[7]. boron nanoclusters’ ground state parameters—bond lengths, specific (per atom) binding energy, atomic vibration frequencies, etc.—can be estimated on the basis of interatomic b–b pair potentials depended on a few rigorously chosen semiempirical parameters—see the paper and also the review of chkhartishvili[8,9] which summarize results of similar attempts. same approach has been found useful for the characterization of the relative stability of small (quasi) planar boron clusters, including the most abundant species b11, b12, and b13 in different charge states[10,11]. as is known, to study molecular properties quantitatively, e.g., determining the spectroscopic data or performing the collision calculations, potential curves of diatomic molecules are useful in analytical form. analytical pair interatomic potential curves are also needed to deduce the polyatomic molecular curves. in view of this, in the present work, we demonstrate how it is possible based on semiclassical approach to construct the b–b interatomic pair potential in an integral form, which is reducible to the analytical one. paper is organized as follows. after this introduction, there is given a short review on interatomic potentials in general. then charge density and potential distributions in boron atom are described semiclassically. they are used to construct the b–b interaction potential energy curve in an integral form. and finally, based on discussion of obtained results some conclusions are drawn. article info received: 10 december 2022 accepted: 6 february 2023 available online: 17 february 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses /by-nc/4.0/ 2 2. interatomic potentials when developing the numerical physical model of a material, the ab initio approaches, such as the dft (density functional theory) or qc (quantum chemistry), providing the best accuracy on its electronic properties is limited to fragments up to thousands of atoms. to larger systems, it should be employed the computations by classical md (molecular dynamics), mc (monte carlo) or fe (finite element) methods, which are much faster but less accurate and assume that constituent atoms are solid spheres influenced by interactions and in a good approximation follow the classical equations of motion. then behavior of materials in the elastic, electric or magnetic force fields depends on type and energy of interatomic bonding and the general understanding of their properties can be based on interaction potentials between atoms or ions[12]. the (long-range) interatomic forces, i.e., gradients of interatomic potentials prescribed as functions of atomic coordinates, play key role in capillarity and wetting phenomena as well[13]. the choice of forms or these potentials depends on the particular problem features. recent special issue of the journal molecules: “intermolecular forces: from atoms and molecules to nanostructures”[14] has been devoted the relationship between forces acting between the atomic system particles and its properties across different scales: from molecules, simple aggregates or small clusters to nanostructures and other types of condensed matter at the mesoscale. the parameters of introduced types of interatomic potentials can be derived both from experiments or quantum mechanics. to understand molecules chemical properties and also for their force fields high-quality empirical parameterization, the obtaining of accurate conformational energetics is of significance. molecule conformational energy includes strain energy coming from bond distortions, valence angles, torsion strains, etc., and enables to describe deviations of actual molecular geometry from the ideal one. as for intermolecular forces, they control most of the properties of the materials, such as their existence in solid, liquid or gaseous states, relative stability and chemical reactivity. the ab initio potentials are found in dft or electron gas approximations, in which various contributions in the multi-atomic system energy— coulomb, kinetic, exchange, correlation, etc.—are additively taken into account. in this case, in calculating the interaction potentials for heteroatomic systems, it is more correct to use a separate combination of these types of contributions. recent alternative to both empirical and ab initio interatomic potentials are ml (machine learning) potentials. ml is becoming a method of choice for modeling complex chemical processes and materials providing a surrogate model trained on a reference dataset that can be used to establish a relationship between molecular structure and chemical properties. ml trained on quantum mechanical calculations is a powerful tool for modeling the pes (potential energy surface). a critical factor for the automated discovery of robust interatomic potentials by ml is the quality and diversity of the training dataset. the course to atomistic simulations[15] provides classification of popular interatomic potentials; their characterization in terms of accuracy, transferability and computational speed; potential cut-off procedures; short review of potentials used in md and mc methods; derivation of the force from pair potential and force fields in materials; relationship between pair potential and elastic constants; limitations of pair potentials; and description of pair potentials versus many-atomic potentials. the nist’s (national institute of standards and technology) ipr (interatomic potentials repository)[16] serves for a source of interatomic potentials and force fields, in which there are presented all the possible classes of potentials and materials (metals, semiconductors, oxides and carbon-containing systems). interatomic and also fictional potentials are provided both for elementary and non-elementary (alloys and compounds) materials. it is specially noted that: (i) multicomponent potentials may not be applicable to the full composition range; (ii) coarse-grained poten3 tials reduce the simulation complexity by representing molecular or alloy compositions with a single particle type; and (iii) fictional potentials purposefully fitted to target properties are not able to represent real materials accurately. 2.1 empirical potentials interactions between atoms can be modeled using different twoor many-atomic potentials. the total interaction potential can be written as a series of terms depending on the position of one, two, three, … atoms at a definite moment of time: 푈�����(푟⃗�, 푟⃗�, 푟⃗�, … ) = ∑ 푈�(푟⃗�)� + ∑ 푈�(푟⃗�, 푟⃗�)�� + ∑ 푈�(푟⃗�, 푟⃗�, 푟⃗�)��� + ⋯. here 푟⃗�, 푟⃗�, 푟⃗�, … are the radius-vectors of atoms and 푈�, 푈�, 푈�, …—one-, two-, three-atomic, … potentials, respectively. the term 푈� is an atom’s potential in selfconsistent or external force field. as for the term 푈� , in the simplest ionic bonding model, it is expressed by the potential energy of coulomb or electrostatic interaction between a pair of oppositely charged ions: 푈�(푟) = − 퐴 푟⁄ , where 퐴 > 0 is the constant dependent on effective point charges of interacting atomic ions and 푟 = |푟⃗� − 푟⃗�| is the distance separating them. the madelung or electrostatic energy of an ionic crystal is the sum of potential energies of interaction between constituent ions. a negative overall energy implies attraction and then system’s stability. electrostatic attraction between cations and anions increases as they approach each other, until at some distance their electron clouds begin to overlap leading to repulsion. these two forces of opposite signs are balanced at equilibrium separation. the repulsive energy typically is formulated as 푈�(푟) = 퐵 푟�⁄ , where 퐵 > 0 and 푛 > 0 are the empirical constants. bond length and binding energy can be determined by minimizing the total potential energy: 푈(푟) = 푈�(푟) + 푈�(푟) = 퐵 푟�⁄ − 퐴 푟⁄ . alternatively, the repulsion can be expressed by the born–mayer potential: 푈���(푟) = 퐶 exp(− 푟 푎⁄ ) with 퐶 > 0 and 푎 > 0 for constants. usually, the interatomic potentials obtained empirically are approximated by model potentials without separation of terms with clear physical sense. these are lennard–jones 푈��(푟) = 퐵 푟��⁄ − 퐴 푟�⁄ , morse 푈�(푟) = 퐷(exp(−2훼(푟 − 푎) − exp(−훼(푟 − 푎)) , buckingham 푈�(푟) = 퐶 exp(− 푟 푎⁄ ) − 퐴 푟�⁄ , … potentials including two more positive parameters: 퐷 and 훼. sometimes, the lennard–jones potential, which is frequently used for modeling rare gas crystals bounded by van der waals forces, is presented as 푈��(푟) = 4퐷((푟� 푟⁄ )�� − (푟� 푟⁄ )�) , where 푟�, called as van der waals diameter, is the value of 푟, when 푈��(푟) function is zero, and 퐷 is the potential well depth. the origin of such interatomic interaction can be imagined as interplay between van der waals attraction and pauli repulsion related to zero point fluctuations of electrons leading to induced dipole forces and their shortrange interaction due to exclusion principle, respectively. an important special form of 푈��(푟) is the mie–lennard–jones potential: 푈����(푟) = (퐷 (푏 − 푎)⁄ )�푎(푟��� 푟⁄ )� − 푏(푟��� 푟⁄ )�� , where 퐷 and 푟��� denote depth and coordinate of the potential minimum, 푎 and 푏 are the numerical parameters, 1 < 푎 < 푏, characterizing long-range action and rigidity of the potential. to construct adequate theoretical model for a material, it is necessary to use the empirical potentials that correctly take into account all the available types of interactions in a wide range of interatomic distances. in the simplest case, the pair interatomic potential can be chosen in the form of 푈(푟) = 퐷(푋(푟)� − 2푋(푟)), where 푋(푟) is some function of distance 푟 . the first term takes into account the repulsion, while the second—the attraction of atoms. the expediency of choosing this approximation is due to following reasons. it, firstly, quite adequately describes the pair interaction energy dependence on the interatomic distance and, secondly, allows one to obtain the widely used analytical formulas for interaction potential energies and forces between systems of atoms, in particular, above mentioned lennard– jones and morse potentials. the use of the lennard–jones potential leads to simple and easy-tocalculate explicit relations that describe the physical properties, such as the potential energy of sol4 id structure, liquid surface tension and solid surface energies, and heat of sublimation. its disadvantage is the power-law dependence of the repulsion energy, which gives too fast fall as the distance increases. morse potential, which takes into account the repulsive forces “softness”, is deprived of this shortcoming and preferable to be used in modeling interactions in nanosystems, as well as quantum mechanical calculations since it allows one to obtain schrodinger equation solutions in an explicit form. in the vicinity of minimum, any pair interaction potential is represented as a parabolic dependence 푈(푟) = −퐷 + 푘(푟 − 푟���)� 2⁄ , where 푘 is the bond stiffness factor. in various solid state physics applications, it turns out to be useful the mie–lennard–jones potential, whose parameters for most of elements of the periodic table were estimated by magomedov[17]. the potential well depth 퐷 and equilibrium distance 푟��� values were calculated from heat of sublimation and the lattice constant or molar volume. to estimate the pair interaction potential of different atoms, it can be used the lorentz– berthelot empirical combination rules: 푈��� → 푈�� = �푈�푈� and 푟��� → 푟�� = (푟� + 푟�) 2⁄ , where indices a and b denote the interacting atoms. three-atomic term 푈� frequently is expressed by the tersoff potential: 푈�(푟⃗�, 푟⃗�, 푟⃗�) = (1 2⁄ ) � 푓��푟��� ��� �푎��푓��푟��� + 푏��푓��푟���� where 푟�� = |푟⃗� − 푟⃗�| is the distance separating 푖 and 푗 atoms, 푓�(푟) = −훼 exp(−휆�푟) is the attractive three-atomic potential and 푓�(푟) = 휌 exp(−휆�푟) is the repulsive two-atomic term (here parameters 훼, 휆� , 휌 and 휆� are the positive constants), while 푓�(푟) is a smooth cutoff function. the three-atomic contributions arise due to the bond-order parameters 푎�� dependent on bonds length and angle between them. the parameters 푏�� limiting the repulsive interactions range can be chosen as functions only of bonds length. the most recent comprehensive review of empirical interatomic potentials designed to reproduce materials elastic properties, defect energies, bond formation and breaking, redox reactions, etc., has been done in the study of muser et al.[18]. there are described the most popular twoatomic potentials such as: embedded-atom model potential for metals, bond-order potential for covalently bonded semiconductors, polarizable potentials including ionic systems of atoms, and quantum-drude oscillator model potential mimicking multi-atomic dispersion. emphasis is laid on the constraints ensue from the functional form of a potential. the review highlights potentials with simple functional forms allowing the analytical treatment. below, some of interesting examples of practical applications of the empirical potentials are given. periodic table’s carbon subgroup elements—c, si, ge, sn and pb—are of interests because of occurring of the covalent-to-metallic bond-type transition. the available experimental data were used[19] to obtain the parameters of their pair interatomic potentials represented in the mie– lennard–jones form. all the different approaches suggested for the self-consistent determination have same disadvantage: it is unclear whether it is correct or not to use the parameters obtained for a free atoms pair for double covalent bond in a crystal. to answer this question, it was investigated the evolution of the potential depth 퐷 value experimentally determined from the crystal properties during the covalent-to-metallic bond-type transition and demonstrated that 퐷 of a covalent bond determined from the bulk modulus is approximately twice the value which follows from the crystal atomization energy. a conclusion was drawn about the covalent bonding nature: such bond between in a crystal is double and these two bonds differ in potential depth value. each of the generalized valence electrons realizes strong and weak bonds with own and alien ions, respectively. a double covalent bond under elastic, i.e., reversible, deformation of the crystal is about twice stronger than in the case of its sublimation, i.e., its destruction, because two valence electrons cannot depart from each other without breaking the weaker one. bonds of both types are active at elastic deformation, but only weak bonds break at 5 plastic one, i.e., irreversible deformation. this explains the covalent crystals high brittleness along with their high strength. recently, based on paired covalent bond model, it has been determined[20] that the causes of both the appearance of surface cracks on a semiconductor crystal at temperature 푇 below its brittle-to-plastic transition point 푇��� , 푇 < 푇��� , and such transition at 푇 > 푇���. at small deformations of a covalent crystal, it is energetically preferable to create a surface by irreversible rupture, than by reversible stretching. the brittle–plastic transition in elemental covalent crystals would accompanied by the surface covalent bonds metallization. it is shown that the transition temperature under static loads has an upper limit: 푇��� 푇�⁄ < 0.45 , where 푇� is the melting temperature. thus, an analytical (i.e., without computer simulation) method was suggested for calculating the brittle–plastic transition temperature for elemental covalent crystals. to overcome some drawbacks of previous determinations of four parameters characterizing the mie–lennard–jones potential as applied to crystals, a different parameterization method was introduced by magomedov[21]. it is based on the best agreement of the crystal thermoelastic properties calculated values from experimental data such as: crystal sublimation energy at zero temperature, thermal expansion coefficient and isothermal elasticity modulus at room temperature, and pressure–volume dependence according to the equation of state’s room temperature isotherm curve. method verification for iron fe and gold au showed good results, as well as its application for accurate calculation of some refractory metals (such as niobium nb, tantalum ta, molybdenum mo and tungsten w) debye temperature and sublimation and surface energies. disordered au–fe substitution alloys were studied by magomedov[22]. namely, based on mie–lennard–jones-type interatomic potential parameters, au and fe fcc (facecentered cubic) and bcc (body-centered cubic) structures were analytically determined, and the composition dependences of the au–fe alloys properties at the fcc–bcc structural phase transition were found. then, the key parameters of activation processes were calculated[23] in various structures of iron. these are: gibbs energy, enthalpy, entropy, and volume both for processes of formation of electrically neutral vacancies and self-diffusion of atoms. a beryllium–tungsten be–w interatomic potential was derived[24] using a formalism originated from the pauling bond order concept. it found to be suitable for simulation of plasma–wall interactions (be surface with w atom and vice versa) taking place in fusion reactor. obtained interaction energies are qualitatively similar to that from ab initio, namely, dft calculations showing that diffusion of be into bulk w is not energetically favorable and the opposite is true for the reversed system. this be–w potential can reasonably describe bexwy molecules with 푥, 푦 = 1, 2, 3, 4 and intermetallic phases be2w and be12w as well. a correlation between binding energy of an individual atom in metal lattice and its macroscopic parameters like debye temperature, young’s modulus and sound speed was considered in the study of erokhin and kalashnikov[25]. based on the lennard–jones potential, the anharmonic zero-point oscillations of a crystal were analyzed[26] within the framework of the diatomic model. it is shown that their amplitude cannot exceed the limiting value which is a certain part of the equilibrium interatomic distance. the compression of a crystal decreases the zero oscillations amplitude, while the tension increases it. it was found that crystal melting point depends on the de boer parameter. the processes of melting and solidification of gold nanoclusters consisting of 43–1,055 atoms were studied[27] using the mc method and the gupta multiatomic potential. it was shown that the temperature-dependences of the specific internal energy potential part and average first coordination number have pronounced hysteresis. the work previously carried out in the context of quantitative crystal engineering involving the analysis of intermolecular interactions such as carbon (tetrel), pnicogen, chalcogen, and halogen bonding using experimental charge density methodology has been reviewed by thomas et al.[28]. the focus was to extract electron density distribution in the intermolecular space and to obtain 6 guidelines to evaluate the strength and directionality of such interactions towards the design of molecular crystals with desired properties. in this formalism, the atomic electron density is divided into three terms: spherical core and spherical and asperical valence electron densities. it was demonstrated power and limits of x-ray diffraction experimental analysis using the cdmm (charge density multipole modeling) approach. using the continuum approximation for interacting atoms and the mie–grüneisen theory, a simple equation of state for a monatomic crystal was constructed[29], which describes the phase diagram even in the vicinity of the critical point. the use of the lennard–jones formula for a pair potential made it possible to analytically find expressions for the critical volume, pressure, and temperature. based on investigation[30] of interactions of a rigid sphere with another rigid sphere and halfspace using the lennard–jones potential, by their integrating over the surfaces and volumes, respectively, the analytical forms of surface tractions and total force between two rigid spheres were obtained. first of them can be used for the description of adhesive contact between rigid and elastic bodies. the fvt (free volume theory) extended to explicitly include the hard-sphere character of colloidal depletants into the free volume fraction expression was used[31] as a basis for comprehensive calculations performed to predict the phase behavior of large spherical colloids mixed with small spherical ones acting as depletant. the parameters of the mie–lennard–jones pair potential for nearest bond-forming fullerenes or interfullerene interaction in fcc-fullerites were determined[32] from the data on correlation revealed between fullerene mass and corresponding fullerite properties. the experimentally observed fact that under the same conditions c70 fullerite is more stable than c60 was explained[33] by calculation equilibrium bond energy between c60–c60 and c70–c70 fullerene pairs using the potential energy curve for interaction between two identical hollow spherical molecules, which is given with formula including the lennard–jones potential parameters. it has been emphasized[34] that pair-wise interatomic potentials presentable in analytical form serve for powerful theoretical tools to model various nanosystems: nanoparticles, nanotubes, fullerenes, afm (atomic force microscope) probes, etc. in particular, using so-called equilibrium md simulations the effect of electrostatic interactions influence on heat transfer mechanism and interfacial properties was investigated[35] for the hexagonal boron nitride−water system kapitza resistance in nanoscale planar (nanosheet) and cylindrical (nanotube) geometries. a water molecule was imaged by the simple point charge model due to its reliability, precision, and relatively low computational cost. an optimized tersoff potential was used to model the h-bn sheet–tube interactions. and the pairwise interactions between atoms or ions were described by adding coulomb and lennard–jones potentials. the optimum structure of some materials at the nanoscale, including boron-based clusters, was modeled[36] by employing standard and ab initio md simulations. the used instantaneous forces on atoms were calculated from lennard–jones, van der waals, coulomb, etc. potentials. 2.2 ab initio potentials the zrpm (zero-range potential model) treats[37,38] the atomic and molecular potentials as short-range potential-wells with a shallow energy level near the continuum spectrum boundary. it is a schematic description of these potentials for cases (e.g., negative atomic ion), in which the internal structure details are not too significant. the basic idea of the approach is to replace the wave equation solution inside the well by a boundary condition at its center. the single potential well model useful for atoms can be directly generalized for the case of molecules, when there are several potential wells. dolgonosov[39] has proposed an atomic electron gas model together with the generalized charges theory and the subsequent development of the interatomic interactions theory for the ab initio description of covalent bonding and van der 7 waals forces, as well as complex molecules adsorption on homogeneous surfaces. in the studies of shukla and eliasson[40–42], it was pointed out a short-range attractive force between two ions screened by degenerate electron gas in an unmagnetized plasma. at quantum scale, due to that force it can arise ordered ion structures such as ion clusters or coulomb ion lattices, as well as the phase separations in dense quantum plasmas, e.g., from solid to liquid–vapor. corresponding electric potential is attributed to the quantum statistical pressure and the quantum bohm potential, as well as the electron exchange and electron correlations due to electron-1/2 spin. bonding in the excited alkali dimers involving resonant ionic, covalent and steric interactions was studied[43] by ab initio calculation for case of second, third, fourth and fifth 1σu +-states of lithium diatomic molecule li2. in particular, the corresponding potential energy curves were obtained and applied for high resolution laser spectroscopy. usually, conformational profiles are obtained with dft methods, using of which is timeconsuming when the molecules are relatively large or there are many molecules of interest. wang et al.[44] compared several possible alternatives to this traditional approach, including a neural network potential. it was found that a sequential geometry optimization with the semiempirical method and single-point energy high-level dft calculation can provide satisfactory conformational energy profiles hundreds of times faster. the concept of electronegativity 휒 reformulated within dft has acquired a central place in chemical reactivity due to its special relationship with the chemical potential 휇:휇 = −휒, and definition of so-called local electronegativity viewed as the functional variation of the system energy with respect to the electronic density in a given potential environment. on the one hand, the chemical hardness concept realization within the conceptual dft is approached with perspective of electronegativity and hardness equalization of atoms in molecules. on the other hand, the maximum hardness principle presents a relation with the chemical stability of the hardness concept. in light of these concepts and inverse relation between hardness and polarizability, the minimum polarizability principle has been proposed by kaya and putz[45]. additionally, this review includes applications of the chemical hardness concept. elucidating the quantum nature of the chemical bond is fundamental to establishing the directed chemical synthesis of new compounds with predefined properties and reactivity aiming at specific interactions. the structures, intermolecular interactions, and energy of some energetic materials crystal models were comparatively predicted based on md quantum chemical simulations[46]. detecting the intermolecular interactions would provide fundamental insights for the energetic materials crystal engineering. electronic structure of charged defects in crystals often is calculated in the supercell models, which include the jellium counter charges to maintain system’s overall neutrality. however, the correction related to these artificially charges becomes paramount for low-dimensional crystals, where they may induce the spurious vacuum states. a corresponding self-consistent potential correction scheme was presented in the study of silva et al.[47]. a problem of identification of parameters of the mie–lennard–jonesand morsetype pairwise interatomic potentials from the interaction between metal atom and graphene layer was considered by rekhviashvili et al.[48] using the continuum approximation. the potential parameters were calculated by the dft method from the equilibrium adsorption energy and distances in the adatom–graphene system. the advantage of this method is that the empirical combining rules are not used. the mie–lennard–jones potential was found to be the most suitable for describing such interaction. the problem with the morse potential is that the exponential function cannot equally correctly describe the attractive and repulsive forces. 2.3 machine learning potentials in ml schemes, the potentials of interaction between constituent atoms 푖 and 푗 and crystal molar energy can be represented in forms of 푈���푟��� = ∑ 퐴� 푟�� �⁄� and 푢 = ∑ ∑ ∑ 퐴� 푟�� �⁄���� , respectively. here 퐴� is the constant, summation 8 is done over unit cells number l = 0, 1, 2, … and index 푖 is assumed to refer to the atom in the cell with l = 0. in these lattice sums, the terms with indices k = 0, 1, 2 describe so-called long-range interactions, because corresponding volume integrals over whole space diverge. one has to calculate them only inside a finite sphere. the wellknown ewald method developed for the coulomb part, k = 1, can be generalized to terms with k = 0, 1, 2, 3 as well. below, a few recent examples of ml potentials development are given. a machine learning scheme[49] for an unbiased and accurate representation of interatomic potentials is a combination of an artificial neural network and a simple approach for reconstruction of pair interatomic (e.g., al–al, he–he and xe– xe) potentials in elementary crystals providing accuracy comparable with ab initio ones, but at a small computational cost. this method can be applied to structures of real systems of atoms by md simulations. a highly automated approach to dataset construction and then building a potential for elementary aluminum, called as ani-al, was presented in the research of smith et al.[50]. in this active scheme, the ml potential under development is used to drive non-equilibrium md simulations with time-varying applied temperatures. whenever a configuration is reached for which the ml uncertainty is large, new qc data is collected. the ml model is periodically retrained on all the available qc data. the final ani-al potential makes accurate predictions of radial distribution function in melt, liquid-solid coexistence curve, and crystal properties such as defect energies and barriers. it was performed a 1.3 × 106 atom shock simulation and shown that corresponding force predictions agree well with dft calculations. in the study of mortazavi et al.[51], it was shown that ml interatomic potentials trained over short ab initio md trajectories enable ab initio multiscale modeling, in which dft is hierarchically bridged to efficiently simulate macroscopic structures. it was demonstrated that such approach can efficiently predict the lattice thermal conductivity of graphene and borophene pristine phases, as well as graphene–borophene interfaces. thus, ml interatomic potentials enable ab initio multiscale modeling via hierarchical employment of dft/md/fe simulations for computational design of novel nanostructures. the structural properties of amorphous boron nitride a-bn doped with varying amount of carbon c were modeled[52] by generating versatile force fields using ab initio and designing realistic disordered bn:c ml simulations. the recent review[53] highlights developments in the use of ml to evaluate chemical properties such as partial atomic charges, dipole moments, spin and electron densities, and chemical bonding, as well as to obtain a reduced qc description. there is overviewed several neural network architectures, their predictive capabilities, generality and transferability, and illustrated their applicability to various chemical properties. it is emphasized that ml molecular representations resemble qc analogues demonstrating the ability of the models to capture the underlying physics. it is also discussed how ml models can describe non-local quantum effects. the observed trends demonstrate that this field is evolving towards physics-based models augmented by ml. 3. charge density and potential distributions in boron atom atom is a bounded system of electrically interacting electric charges—positive nucleus and negative electrons. so, to calculate potential energy of interaction between two atoms in fully theoretical manner, one needs their detailed electronic structure, including the explicit expressions for electric charge density and electric field potential distributions in interacting atoms. recently, it has been demonstrated[54,55] that electronic structure of any bounded system of atoms—molecules, clusters or even condensed matter—with a good accuracy can be calculated within the semiclassical approximation expressing electric scf (self consistent field) affecting atomic electrons by coulomb-like (pseudo) potentials. based on electric charge density and electric field potential radial distributions in constituent atoms obtained in this way, one can construct semiclassical interatomic pair potentials needed 9 for calculating the important physical characteristics of any bounded system of atoms. in such type semiclassical approximation, for ground-state electronic configuration 1s22s22p1, the radial wave functions 푅�(푞�(푟)) of five electrons, k = 1, 2, 3, 4, 5 (1) of an isolated electrically neutral boron b atom with nuclei centered at the origin, 푟⃗ = 0, are 푅��푞�(푟)� = �� 푍� 푟� � � 2exp �− 푞�(푟) 2 � (2) 푅��푞�(푟)� = �� 푍� 푟� � � 2 exp �− 푞�(푟) 2 � (3) 푅��푞�(푟)� = �� 푍� 푟� � � 1 2√2 �2 − 푞�(푟)� exp �− 푞�(푟) 2 � (4) 푅��푞�(푟)� = �� 푍� 푟� � � 1 2√2 �2 − 푞�(푟)� exp �− 푞�(푟) 2 � (5) and 푅��푞�(푟)� = �� 푍� 푟� � � 1 2√6 푞�(푟) exp �− 푞�(푟) 2 � (6) here the variables 푞�(푟) = 2푍� 푛� 푟 푟� (7) stand for radial wave functions’ arguments. the constant 푟� = ℏ� 푒�푚 ≈ 0.53 å (8) is the bohr radius, 푛� = 푛� = 1 (9) 푛� = 푛� = 2 (10) and 푛� = 2 (11) are the electron orbitals’ principal quantum numbers, while the parameters 푍� equal to 푍�� ≡ 푍� = 푍� ≈ 4.69 (12) 푍�� ≡ 푍� = 푍� ≈ 2.76 (13) and 푍� ≈ 1.48 (14) respectively. these are the nucleus effective charge numbers, respectively, for 1s2, 2s2, and 2p1 electrons bounded in boron atom. they could be considered for known numerical quantities. on the one hand, in the coulomb-like intraatomic field the classical orbit radii 푟� of electrons or their characteristic displacements from the nucleus could be found from the relations: 푟� 푟� = 푛� � 푍� (15) on the other hand, the nuclear charge radii of boron stable isotopes 10b and 11b with charge number of 푍 = 5 approximately equal to[56] 푅� ≈ 2.4 × 10�� å (16) 푅� 푟� ≈ 2.2 × 10�� (17) and, consequently, in the boron atom the nucleus electric charge radius is negligible in comparison with electrons’ characteristic displacements from it: 푅� 푟� ≪ 1 (18) these relations meet a key assumption of the semiclassical method used that atomic nucleus could be considered as point electric charge. the squared semiclassical radial wave functions, 푅�� � (푟) ≡ 푅� �(푟) = 푅� �(푟) = 4푍�� � 푟� � exp �− 2푍��푟 푟� � 10 (19) 푅�� � (푟) ≡ 푅� �(푟) = 푅� �(푟) = 푍�� � 8푟� � �2 − 푍��푟 푟� � � exp �− 푍��푟 푟� � = � 푍�� � 2푟� � − 푍�� � 푟 2푟� � + 푍�� � 푟� 8푟� � � exp �− 푍��푟 푟� � (20) and 푅� �(푟) = 푍� � 24푟� � � 푍�푟 푟� � � exp �− 푍�푟 푟� � = 푍� �푟� 24푟� � exp �− 푍�푟 푟� � (21) determine the semiclassical electrical charge density distribution in the isolated boron atom: 휌�(푟⃗) = 5푒훿(푟⃗) − 푒 4휋 � 푅� �(|푟⃗|) ��� ��� = 푒 �5훿(푟⃗) − 2푅�� � (푟) + 2푅�� � (푟) + 푅� �(푟) 4휋 � (22) here, the first term containing dirac deltafunction 훿(푟⃗) stands for positive charge density of point-like nucleus with charge number of 푍 = 5 and the second term is negative charge density of electron cloud. from the corresponding semiclassical electrical charge density radial distribution. 휌�(푟⃗) = 푒 �5훿(푟⃗) − 2푍�� � 휋푟� � exp �− 2푍�푟 푟� � − � 푍�� � 4휋푟� � − 푍�� � 푟 4휋푟� � + 푍�� � 푟� 16휋푟� �� exp �− 푍��푟 푟� � − 푍� �푟� 96휋푟� � exp �− 푍�푟 푟� �� (23) the poisson’s equation determines that of the electrical field potential, 휑�(푟) = 푒 �� 2 푟 + 2푍�� 푟� � exp �− 2푍��푟 푟� � + � 2 푟 + 3푍�� 2푟� + 푍�� � 푟 2푟� � + 푍�� � 푟� 4푟� � � exp �− 푍��푟 푟� � + � 1 푟 + 3푍� 4푟� + 푍� �푟 4푟� � + 푍� �푟� 24푟� �� exp �− 푍�푟 푟� �� (24) in the boron atom centered at the origin: 푟⃗ = 0. 4. potential energy of b–b interaction in general, an atom electrically interacting with another one affects its electric charge density and, consequently, electric field potential distributions. however, in the vicinity of interatomic chemical bond equilibrium length such redistributions are relatively small: both in finite and infinite bounded systems of atoms electric charge density and electric field potential distributions can be approximated by the simple superposition of corresponding distributions in constituent atoms in their isolated states, when they are localized in structure sites. assuming electric charge density and related electric field potential redistributions in electrically interacting pair of boron atoms displaced at vector 푎⃗ (figure 1) to be negligible, the semiclassical potential energy of such interaction can be found as volume integral: 푈���(푎) = � 푑�푟⃗ 휑�(푟)휌�(푟⃗ − 푎⃗) (25) figure 1. to calculation of b–b pair potential. 11 the trivial integration over the polar angle 0 ≤ 휙 ≤ 2휋 yields the following result: 푈���(푎) = 5푒� �� 2 푎 + 2푍�� 푟� � exp �− 2푍��푎 푟� � + � 2 푎 + 3푍�� 2푟� + 푍�� � 푎 2푟� � + 푍�� � 푎� 4푟� � � exp �− 푍��푎 푟� � + � 1 푎 + 3푍� 4푟� + 푍� �푎 4푟� � + 푍� �푎� 24푟� �� exp �− 푍�푎 푟� �� − 푒� � 푑푟 푟� ∞ � �� 2 푟 + 2푍�� 푟� � exp �− 2푍��푟 푟� � + � 2 푟 + 3푍�� 2푟� + 푍�� � 푟 2푟� � + 푍�� � 푟� 4푟� � � exp �− 푍��푟 푟� � + � 1 푟 + 3푍� 4푟� + 푍� �푟 4푟� � + 푍� �푟� 24푟� �� exp �− 푍�푟 푟� �� × � 푑휃 sin 휃 � 4푍�� � 푟� � exp �− 2푍�√푟� − 2푎푟 cos 휃 + 푎� 푟� � � � + � 푍�� � 2푟� � − 푍�� � √푟� − 2푎푟 cos 휃 + 푎� 2푟� � + 푍�� � (푟� − 2푎푟 cos 휃 + 푎�) 8푟� � � exp �− 푍��√푟� − 2푎푟 cos 휃 + 푎� 푟� � + 푍� �(푟� − 2푎푟 cos 휃 + 푎�) 48푟� � exp �− 푍�√푟� − 2푎푟 cos 휃 + 푎� 푟� �� (26) as for integration over the azimuthal angle 0 ≤ 휃 ≤ 휋 , it can be conducted via two successive transformations into new integration variables 푥 and 푡: cos 휃 = 푥 (27) and 푟� − 2푎푟푥 + 푎� = 푡� (28) finally leading to the form 푈���(푎) = 5푒� �� 2 푎 + 2푍�� 푟� � exp �− 2푍��푎 푟� � + � 2 푎 + 3푍�� 2푟� + 푍�� � 푎 2푟� � + 푍�� � 푎� 4푟� � � exp �− 푍��푎 푟� � + � 1 푎 + 3푍� 4푟� + 푍� �푎 4푟� � + 푍� �푎� 24푟� �� exp �− 푍�푎 푟� �� − 푒� 푟�푎 � 푑푟 푟 ∞ � �� 2 푟 + 2푍�� 푟� � exp �− 2푍��푟 푟� � + � 2 푟 + 3푍�� 2푟� + 푍�� � 푟 2푟� � + 푍�� � 푟� 4푟� � � exp �− 푍��푟 푟� � + � 1 푟 + 3푍� 4푟� + 푍� �푟 4푟� � + 푍� �푟� 24푟� �� exp �− 푍�푟 푟� �� × �퐽��(푟) + 퐽��(푟) + 퐽�(푟)� (29) where 퐽��(푟) = 4푍�� � 푟� � � 푑푡 푡 exp �− 2푍��푡 푟� � ��� |���| = 푍�� ��1 + 2푍��|푟 − 푎| 푟� � exp �− 2푍��|푟 − 푎| 푟� � − �1 + 2푍��(푟 + 푎) 푟� � exp �− 2푍��(푟 + 푎) 푟� �� (30) 12 퐽��(푟) = � 푑푡 푡 � 푍�� � 2푟� � − 푍�� � 푡 2푟� � + 푍�� � 푡� 8푟� � � exp �− 푍��푡 푟� � = ��� |���| = 푍�� 4 ��1 + 푍��|푟 − 푎| 푟� − 푍�� � |푟 − 푎|� 2푟� � + 푍�� � |푟 − 푎|� 2푟� � � exp �− 푍��|푟 − 푎| 푟� � − �1 + 푍��(푟 + 푎) 푟� − 푍�� � (푟 + 푎)� 2푟� � + 푍�� � (푟 + 푎)� 2푟� � � exp �− 푍��(푟 + 푎) 푟� �� (31) and 퐽�(푟) = 푍� �푡� 48푟� � � 푑푡 푡 exp �− 푍�푡 푟� � ��� |���| = 푍� 8 ��1 + 푍�|푟 − 푎| 푟� + 푍� �|푟 − 푎|� 2푟� � + 푍� �|푟 − 푎|� 6푟� � � exp �− 푍�|푟 − 푎| 푟� � − �1 + 푍�(푟 + 푎) 푟� + 푍� �(푟 + 푎)� 2푟� � + 푍� �(푟 + 푎)� 6푟� � � exp �− 푍�(푟 + 푎) 푟� �� (32) are the definite radial, 0 ≤ 푟 ≤ ∞, integrals. thus, semiclassical approximation has allowed us to express the boron–boron pair potential 푈��� = 푈���(푎) (33) in dependence on interatomic distance 푎 by a radial integral. schematic view of an interatomic pair potential 푈 as a function of the interatomic distance 푟 is shown in figure 2. here 푟� is the equilibrium interatomic distance, i.e., bond length in corresponding diatomic molecule, and 푈� is its binding energy (not corrected for relative atomic vibrations zero-point energy). figure 2. schematic of interatomic pair potential. the integration over the radius is possible to conduct in elementary functions, although it will give the result in a cumbersome analytical form. therefore, it seems that for the practical applications of the constructed b–b potential often it will be necessary to convert it in a numerical form. it is clear that the same goal can be achieved by the direct numerical integration. 5. discussion and conclusion further work aims to convert the obtained in integral form semiclassical b–b potential function into analytical and/or numerical forms, which will allow to determine the b–b bond’s parameters such as bond length, dissociation energy, frequency of relative atomic vibrations, etc. they should be compared with currently available data given below. to the best our knowledge for the first time the fully theoretical pair potential energy curves for low-lying energy states of diboron molecule b2 were constructed[57] by so-called completeactive-space scf method at the multi-reference ci (configuration interaction) level of theory. the potential curves of ground and some of low-lying excited electronic states of b2 neutral molecule and b2 + positive ion were also obtained[58] by using another ci approach. the b2 + cation ground state showed a rather shallow potential curve with a bond length of 2.13 å and vibration quantum of 0.052 ev, when compared with b2 neutral ground state with that of 1.59 å and 0.131 ev, respectively. in result of bonding electron loss, the b2 + molecular ion ground-state dissociation energy of 1.94 ev was found to be significantly smaller than that of b2: 3.06 ev. later, same authors by extensive multi-reference ci calculations were constructed[59] b2 and b2 + potential curves yielding 13 the following sets of parameters 1.59 å, 2.75 ev, 0.131 ev and 2.12 å, 1.90 ev, 0.052 ev, respectively. and according to the one more multireference ci study[60], the ground-state curve parameters of b2 such as bond length, dissociation energy and two atoms relative vibration quantum are of 1.60–1.61 å, 2.70–2.78 ev and 0.128– 0.129 ev, respectively. first principles quadratic ci method was used[61] to calculate the equilibrium potential energy curves of ground and lowlying excited electronic states of b2 and b2 +. the corresponding analytical potentials were constructed by the fitting calculation results to the murrell–sorbie potential energy function. curve parameters obtained for b2 and b2 + were, respectively, 1.62 å, 3.14 ev, 0.125 ev and 2.18 å, 1.69 ev, 0.052 ev. a non-scf dft based construction of nonorthogonal tb (tight-binding) matrix elements for b–b, n–n, b–n, b–h and n–h systems within the framework of the lcao (linear combination of atomic orbitals) formalism was presented[62] using the lda (local density approximation). despite the simplicity of the scheme considering only two-center hamiltonian integrals and overlap matrix elements, the method has been proven to be sufficiently accurate and transferable to all scale b–b(n,h) structures from small clusters and molecules to crystalline solids and solid surfaces. the calculation of forces from these tb potentials is straightforward and allows an application of the method to md simulations of structure formation in complex bnh systems. for the b2 molecule ground-state interatomic potential, the energy curve was also constructed[63,64] within a quasi-classical approach. the obtained in such way curve’s parameters are as follows: equilibrium bond length of 1.78 å, dissociation energy of 2.80 ev, and vibration quantum of 0.130 ev. most of nist’s ipr potentials are presented in efficient “universal” shifted lennard–jones model for all kim api supported species developed by elliott and akerson in 2015[65]. cohesive energy graphs generated for each elemental crystals supported by the model show the cohesive energy versus volume-per-atom for four monoatomic cubic phases: sc (simple cubic), bcc, fcc, and diamond-like. the curve with the lowest minimum is the ground state of the crystal, if stable. point is that the crystal structure is enforced in these calculations, so the phase may not be stable. in particular, cohesive energy graphs are available for elemental boron, i.e., b–b, and some boroncontaining systems: b–n, b–hf, b–zr and b–c– n. the local nature of different types of boron– boron bonds—b∙b, b–b, b=b and b≡b—from the topological analysis of elf (electron localization function) perspective was investigated[66] in number of boron-containing molecules. as for the experimental parameters of b–b pair interatomic potential curve, they are available in the reference book[67]: 1.59 å, 3.09 ev, 0.130 ev. currently, for neutral diboron b2 molecule in ground state configuration (σ1s)2(σ*1s)2(σ2s)2 (σ*2s)2(π2p)2 bond length and bond energy are estimated[68] as 0.159 nm and 3.00 ev, respectively. in similar way, one can construct different semiclassical interatomic pair potentials to characterize the nanomaterials containing not only boron, but some other chemical elements as well. for example, results obtained on the basis of semiclassical boron–nitrogen, i.e., b–n, potential for pristine and doped hexagonal boron nitride h-bn nanotubes prospective for toxic gas sensors can be compared with dft ones on their electrical sensitivity toward ethyl benzene c8h10 and phosphine ph3 molecules[69,70]. in summary, introduced in this work semiclassical boron–boron potential integral function allowing presentation both analytically or 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engineering, liaocheng university of technology, shandong, china abstract fe3+-doped nano-tio2 powders were prepared by sol-gel method. the photocatalytic activity of fe3+-doped tio2 nanoparticles was studied by using uv lamp as light source and methylene blue as degradation target. the photocatalytic activity of fe3+-doped tio2 was studied by degradation of 4l methylene blue solution with initial concentration of 10mg · l 1. the results show that the photocatalytic activity of tio2 can be improved by the addition of fe3+. when the molar ratio of fe3+ is 0.5-1%, the calcination temperature is 500 ℃. the photocatalytic degradation of methylene blue is the best. keywords: sol gel method; doped iron nanometer; tio2 methylene blue 1. introduction with the development of global industrialization process, energy crisis and environmental pollution is becoming increasingly serious, industrial waste gas, waste water, agricultural pesticides and other pollutants surge, how to solve the energy and environmental problems has become a hot topic of social concern. due to the excellent photocatalytic performance, the semiconductor photocatalyst has a wide development and application prospect in sewage treatment, air purifi cation, cleaning and sterilization. tio2 photocatalyst has become the most promising photocatalytic material because of its stable chemical properties, strong oxidation and reducibility, non-toxic and low cost. it can convert many organic or inorganic pollutants degradation into h2o, co2 and salts and other substances, to achieve harmless purifi cation of the environment [1]. the photocatalytic properties of nano-tio2 are used to degrade toxic and harmful substances in the environment in order to optimize the environment. it is an important aspect of nano-tio2 application. tio2 as a photodegradation catalyst has the following advantages [2]: (1) the use of natural light without additional energy, energy conservation, to avoid the energy regeneration process caused by environmental problems; (2) tio2 nano-catalyst purifi cation effi ciency, wide range of applications, from water treatment to air purifi cation, are very applicable; (3) tio2 itself stable nature can be long-term use, the human body non-toxic harmless with the development of photocatalytic materials and properties of tio2, the preparation of photocatalytic materials and the research of photocatalytic environmental protection devices have been paid more and more attention [3]. 1.1. what is a nanomaterial? nanometer (nm) is the length of the unit, 1 nanometer is 10-9 meters (one billionth of a meter), the macro substance, the nano is a small unit, as the diameter of the hair is generally 70008000nm, the diameter of human erythrocytes is generally 3000-5000nm, the general diameter of the virus is also tens to hundreds of nanometer size, the metal grain size is generally in the order of microns; for microscopic substances such as atoms, molecules and other previously used to show , 1 angstrom corresponds to the diameter of one hydrogen atom, 1 nanometer is 10 angstroms [2]. it is generally believed that nanomaterials should include two basic conditions: one is the characteristic size of the material between 1-100nm and the other is that the material has some special physical and chemical properties that distinguish the conventional size material at this time. preparation and catalytic performance of fe3+ doped nano-materials 2 1.2. application of tio2 in wastewater treatment 1.2.1 treatment of organic wastewater nano-powder technology is the hotspot of materials science research, and has been widely used in industrial production and daily life. at present, the semiconductor used for photocatalytic oxidation of organic semiconductors are mostly semiconducting semiconductor materials, such as tio2, zno2, wo3, sno2 and so on. because tio2 itself has high photocatalytic activity, high chemical stability, low cost, safe to use. as a new generation of environmental purifi cation materials, it has been widely used. tio2 photocatalyst can degrade water, most of the organic matter in the air, inorganic, and has the ability to antibacterial, deodorant and clean air [1]. 1.2.1.1 organophosphorus pesticide wastewater treatment the results of the degradation of organic phosphorus showed that the photocatalytic oxidation of phosphorus in the suspension of tio2 could be completely inorganic and could produce po quantitatively. similarly, sulfur-containing organic matter is photocatalytic oxidation of tio2; a similar result can be obtained in which sulfur is oxidized to so2 quantitatively. chen shifu's research on dichlorvos and monocrotophos pesticides showed that the photolysis rate of tio2 glass fi ber was more than 90% for 50 min. 1.2.1.2 chlorinated organic wastewater treatment japan's tokyo university noguchi real use of nano-tio2 photocatalyst and ozone combined treatment of waste water in the 3-chlorophenol, with 3-chlorophenol completely removed; with the surface coated nano-tio2 photocatalyst ceramic tube treatment of trichlorethylene aqueous solution, trichlorethylene is also completely decomposed soon. british london and ontario nuclear technology environment company developed a new room temperature photocatalytic technology using artifi cial lighting and nano-tio2 to completely decompose pcbs from industrial waste and contaminated groundwater into co, ho and hci [ 2]. 1.2.1.3 oily wastewater treatment oily wastewater containing aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, organic acids and phenols., it is difficult to degradation. using nano-tio2 photocatalytic oxidation technology, can quickly degrade these organic matter. the eff ects of sunlight and nano-tio2 powder on the aqueous solution of phenol and aqueous sodium dodecylbenzene sulfonate were tested by the chinese academy of sciences. the results showed that the concentration of phenol was 0.5mmol / l in the cloudy and cloudy days has been completely degraded, the concentration of 1mol / l of sodium dodecyl benzene sulfonate is also basically completed degradation, high clarity and no secondary pollution, zhao wenkuan et al. prepared a tio2 powder carrying a fl oating type photocatalyst. in the ultraviolet light irradiation, can eff ectively degrade the surface of the oil pollutants and inhibit the crude oil in the natural oxidation process of the formation of harmful copolymer [2]. 1.2.1.4 wastewater treatment with surfactant household or industrial surfactants are one of the main sources of pollution of water, which is prone to odor and foam. surfactants mainly contain sodium dodecyl sulfonate, which are diffi cult to naturally or biodegradably, have a long residence time, and sometimes produce toxic or insoluble intermediates. the use of nano-tio2 photocatalytic decomposition of surfactants has made some progress. the mechanism, reaction kinetics and influencing factors of photocatalytic degradation of sodium dodecyl sulfonate by tio2 were studied [1-2]. 1.2.1.5 wool dyeing and fi nishing wastewater treatment the glass fi ller fi lled with nano-tio2 fi lm is fi lled in the glass reactor. the waste water is circulated in the reactor for photocatalytic oxidation. the organic matter in the wastewater can decompose into h2o and co2 quickly, and the catalyst can be used continuously without separation recovery, with high effi ciency, energy saving, no secondary pollution and other characteristics, to facilitate industrial applications [2]. 1.2.2 treatment of inorganic wastewater the inorganic pollutants in water are mainly heavy metal ions, such as hg, cr, pb and so on. the photocatalytic degradation of nano-tio2 can also solve the pollution problem of metal ions such as mercury, chromium and lead. mercury is the main heavy metal pollutants in the water body, great harm to the human brain system. chromium is a serious carcinogen, can cause local sarcoma, the incidence of cancer increased. lead is easy to cause poisoning, may also lead to respiratory cancer. hydrogenation of nano-tio2 in the presence of citrate ions, hg2+ from the oxygen solution was e-reduced to hg deposition on the surface of tio2, this method also applies to lead. dai et al. investigated the eff ect of znogi 'io2 ultrafi ne powder on the reduction of hexavalent chromium in aqueous solution under diff erent reaction conditions, and discussed the feasibility of this method. skubal modifi ed the surface jianhui chen, et al 3 of tio2 with arginine, and then adsorption and reduction effi ciency of the photocatalytic reduction rig was increased to 99.9%. serpone et al. reported the process of reducing au from au (cn) 4-1 by tio2 photocatalysis while oxidizing cn to nh3 and co2, and pointed out that treatment of electroplating industrial wastewater can not only restore the precious metal in the bath, but also eliminate the cyanide pollution in the bath. it is a practical method to deal with it. it can be seen that the application of tio2 photocatalyst in the treatment of inorganic wastewater has a good eff ect and great application potential. 1.3. the use of nano-tio2 can prevent the production of sewage light nano – tio2, at its interface, macroscopically exhibits hydrophilic and lipophilic amphiphilic. nano-tio2 will be applied to the production of chemical fi ber, so that the surface of the fi ber contains a certain amount of tio2, chemical fi ber also has an amphipathic performance. the use of the chemical fi ber production of military, agricultural tents can play a role in self-cleaning. such as the chemical fiber made of people clothes, curtains and other daily necessities, due to amphipathic, self-cleaning degree is very large, the clothes are not easy to dirty, even dirty clothes, wash with water can be easy to wash, without chemical detergent, both reduced waste water discharge and the formation of pollution, but also save the water, electricity, detergents, reduce the burden on people's lives, but also reduce the people's manual labor. 1.4. application of nanometer tio2 in tap water treatment many tap water is taken from the surface water, the conventional purifi cation can remove suspended solids and other toxic substances, but for some easy to dissolve impurities and bacteria and other commonly used fungicides ag, cu can make cells lose their activity, but the bacteria were killed after the resulting endotoxin cannot be eliminated. endotoxin is a deadly substance that can cause typhoid fever, cholera and other diseases, so that water quality standards are not high, aff ecting people's health. university of tokyo, japan, department of engineering, professor teng daozhao and other experiments have proved that nano-titanium dioxide on pseudomonas, escherichia coli, staphylococcus aureus and other strong kill ability. therefore, nano-titanium dioxide will be a good treatment of water treatment. in 1998, tongji university li tian and others using fi xed titanium dioxide on the glass fi ber network to form a catalytic fi lm, the depth of purifi cation of drinking water, the results show: the total amount of organic matter in tap water removal rate of 60%, 19 kinds of priority pollutants, completely removed, the other 21 kinds of harmful organic matter has 10 kinds of concentrations below the detection limit. at the same time, the total number of bacteria is also signifi cantly reduced, a comprehensive increase in water quality, to achieve direct and safe drinking requirements [4]. 1.5. crystal structure of tio2 and its relationship with photocatalytic activity tio2 is an important n-type semiconductor, according to its crystal form, can be divided into plate titanium, rutile and anatase three phase. figure 1 for the anatase tio2 two crystal structure. anatase and rutile crystals can be represented by interconnected tio6 octahedrons (figure 1), the diff erence between the octahedral distortion and the octahedral connection is usually considered anatase is the highest activity of a crystal form, followed by rutile type, while the plate titanium and amorphous tio2 did not have obvious photocatalytic activity. however, it is simple to think that anatase is more stringent than rutile activity, and their activity is aff ected by some factors in its crystallization process. the results showed that the activity of tio2 was related to the preparation method and the calcination temperature. the rutile tio2 exhibited high photocatalytic activity under certain conditions [2]. the photocatalytic activity of tio2 was better than that of rutile tio2. fig.1 two crystal structure of nano-tio2 [2] preparation and catalytic performance of fe3+ doped nano-materials 4 it can be seen that both anatase and rutile tio2, they may have a high activity, and the level of activity is mainly depends on the grain surface properties and size and other factors. recent studies have shown that mixed crystals composed of anatase and rutile in an appropriate proportion are generally higher than single crystal activity. the mixed crystals exhibit higher activity because the formation of thin rutile layers in the anatase during the crystallization process can eff ectively improve the electron-hole separation effi ciency (called the mixed crystal eff ect) in the anatase crystal form through the rutile layer, 100% anatase was not as high as 100% rutile activity, while that of the two mixtures showed higher activity than pure anatase or rutile, especially 30% gold redstone and 70% anatase composed of the highest mixed crystal activity, we can see that the two crystal forms do have a certain synergistic eff ect [2]. 2. catalytic principles of fe3+ doped tio2 the photocatalytic technology utilizes the photocatalytic activity of the semiconductor material to excite the electrons and holes in the light to participate in the photochemical reaction to complete the degradation of the microbial organism of the organic gas. anatase tio2 semiconductor, for example, the band structure is filled with electronic low energy band (valence bandvb) and empty high-energy conduction band (conducti on band, cb), between the price band and conduction band gap (forbidden band, fb), conduction band and valence band gap between the 3.2ev, wavelength λ <385nm light can overcome the bandgap energy. as shown in fig. 2, when the tio2 semiconductor is irradiated with light at a wavelength of λ <385 nm, the electrons on the valence band are excited to transition to the conduction band, holes (h +) are generated on the valence band, and electrons are generated on the conduction band (e -), the photogenerated hole has a strong oxidizing property, can be adsorbed on the surface of the semiconductor particles of substances oxidized into high-priced substances, and electrons are reducible, can be absorbed on the semiconductor surface of the electronic receptor reduction. photogenerated electrons and holes in addition to participate in the redox reaction, part of the composite directly in the semiconductor, and the release of energy, the size of the semiconductor photocatalytic activity and electron hole recombination probability is directly related. in general, the smaller the size of the semiconductor particles, the smaller the time of electrons and holes migrating to the surface, the smaller the probability of recombination. at the same time, the smaller the particle size, the larger the specifi c surface area, the more favorable the adsorption of the reactants. this is the use of nano-tio2 material instead of bulk semiconductor materials for the reasons, the use of nano-particles as a catalyst for photocatalytic technology is often referred to as nano-photocatalytic technology. figure 2 schematic diagram of photocatalytic reaction however, because tio2 is a kind of wide band gap semiconductor, only the use of ultraviolet excitation, the utilization of sunlight is low, and the excited state of electrons and holes easy to complex, resulting in further reduction of photon quantum effi ciency, seriously aff ected its application. the in order to promote the practical application of tio2 photocatalytic materials, some means must be used to improve its catalytic activity. doping is one of the most commonly used methods to improve the catalytic performance of tio2. since the crystal is only perfect at an approximate absolute zero, so that each crystal has a diff erent degree of lattice defects, when other substances into the crystal, the lattice defects may be replaced, the replacement of the defect can make electronic cavities effectively separate and inhibit their recombination, resulting in improved catalyst performance. fe3+ can be used as the acceptor of electrons. when the doping concentration is low, the capture electrons and holes cannot be eff ectively separated, and the number of capture centers for electrons or holes is not enough to improve the catalytic activity with the increase of the doping amount, the capture space also increases, the surface space charge layer becomes narrower, and the photo-generated electrons and holes can be eff ectively separated by the photoexcitation. the lifetime of the photogenerator is prolonged. when the doping concentration is high, the transition metal may become a composite center of holes and electrons, increasing the recombination probability of electrons and holes, resulting in an increase in the surface photogenerated recombination centers, thereby reducing the photocatalytic activity. tio2 + hv → h + + e(1 1) o2 + e→ o2(1 2) h + + h2o → h + + · oh (1 3) jianhui chen, et al 5 2e + o2 + h + → oh (1 4) o 2 + e + 2h + → h2o2 (1 5) the reason and method of preparing fe3+ doped tio2 however, because tio2 is a kind of wide band gap semiconductor, only the use of ultraviolet excitation, the utilization of sunlight is low, and the excited state of electrons and holes easy to complex, resulting in further reduction of photon quantum effi ciency, seriously aff ected its application. the in order to promote the practical application of tio2 photocatalytic materials, some means must be used to improve its catalytic activity. ion doping is undoubtedly an important means to improve its photocatalytic activity. the transition metal ions such as fe3+, cr6 +, v4 + and other research is more extensive. and there are many reports on the photocatalysis of fe3+ doped in tio2 phase. therefore, fe3+ ion doped tio2 was used to improve the catalytic activity of tio2. at present, the preparation methods of tio2 mainly include sol-gel method, coprecipitation, dipping method, ion implantation method and magnetron sputtering method. in this experiment, fe3+ doped tio2 powder was prepared by sol-gel method. 3. the purpose and content of this study the purpose of this experiment is to prepare fe3+ -doped tio2 powder to explore the eff ect of diff erent doping amount and different calcination time on the degradation rate of methylene blue on tio2 powder. the optimum conditions for the preparation of tio2 powder and the optimum conditions for degradation of methylene blue were studied. the study includes the following aspects: (1) sol gel synthesis of fe3+-doped tio2 photocatalyst (2) performance test of photocatalyst 4. preparation of 4 fe3+-doped tio2 photocatalyst 4.1. experimental materials and methods 4.1.1 experimental materials and instruments table 1 shows the main experimental equipment. table 1 main experimental equipment instrument name model manufacturer use constant temperature magnetic stirrer 85-2 jintan medical equipment factory mixing electric thermostatic blast oven 101-3-s s h a n g h a i yu e j i n m e d i c a l equipment factory dry and dry electronic balance weighing elebox-type resistance furnace shanghai bairide industrial co., ltd. roasting k series temperature controller zhejiang province 02810218 yuyao jin point instrument co., ltd. adjust the temperature uv spectrophotometer uv photocatalytic reactor kl-1 wuhan kel in envi ronmental protection technology co., ltd. photocatalytic reactor centrifugal separator centrifugal separation preparation and catalytic performance of fe3+ doped nano-materials 6 table 2 shows the main reagents. table 2 major reagents drug name chemical grade grade manufacturer anhydrous ethanol ch3ch2oh ar tianjin tianchen chemical reagent factory titanium tetrachlorate ti(oc4h9)4 br tianjin beilian fine chemicals development co., ltd. iron nitrate fe(no3).9h2o3 ar tianjin beilian fine chemicals development co., ltd nitrate hno3 ar tianjin north union fine chemicals development co., ltd glacial acetic acid ch3cooh ar tianjin tianchen chemical reagent factory methylene blue (mb) c16h18cln3s3h2o ar tianjin branch of the european chemical reagents development center the preparation of diff erent concentrations of fe (no3) 39h2o solution was prepared according to table 3. table 3 preparation of fe (no3) solution miscellaneous 0.5% 1% 5% 20% fe(no3)39h2o(g) 0.4000 0.3000 15.6000 74.2000 distilled water (ml) 100 100 100 100 density (mg/l) 0.0080 0.0300 0.1560 0.7420 as long as the addition of 2ml of table 3 of diff erent fe (no3) 39h2o solution to get diff erent fe3+ doped tio2 powder. the photocatalysts with diff erent doping amounts and calcined at diff erent temperatures are labeled as an (n is the mole percent of fe3+ dopant, 0.5, 1, 5, 20) refers to the sample obtained by calcination, bn, cn, dn, respectively, at 400,500 and 600 ℃ under the calcined sample. 4.1.2 test methods 4.1.2.1 synthesis of fe3+ -doped tio2 photocatalyst by sol-gel method [6] proceed as follows: (1) 5 ml of tetrabutyl titanate was dissolved in 34 ml of absolute ethanol and stirred well. (2) adding 2 ml of glacial acetic acid to form a complex with ti to inhibit the hydrolysis of tetrabutyl titanate. (3) and then slowly add 2ml dissolved in a certain amount of iron nitrate deionized water, with 1ml / l nitric acid to adjust the ph value ≈ 2.0, stirring overnight can be fe3+ doped tio2 photocatalyst precursor. (4) it was fi nally dried in an electric thermostatic blast oven at 70 ° c until it became a powder and calcined at a diff erent temperature (300 ° c to 600 ° c) for 2 h with a box-type resistance furnace. the following is a picture of the cn roasting 500 ° c group: figure 3 doping amount of 0.5% of the powder c1 figure 4 doping content of 1% powder c2 jianhui chen, et al 7 figure 5 doping amount of 5% powder c3 figure 6 doping amount of 20% powder c4 4.1.2.2 performance test of photocatalyst the photocatalytic activity of the catalyst is evaluated by photocatalytic degradation of methylene blue (mb), which is a kind of non-degradable colored compound. the azo and formula structure under acidic and alkaline conditions is the main structure of the dye compound. therefore, it has a certain representation as a dye compound model. the photocatalytic activity of fe3+ doped tio2 powder was tested by kl-1 uv photocatalytic reactor with 10 mg / l mb solution as standard. the test procedure was as follows: 0.3 g of the catalyst powder was dispersed in an aqueous solution of 4 l mb (10 mg / l-1), and the solution was passed through a cylindrical photocatalytic reactor using a low pressure mercury lamp as a line light source. the reaction was allowed to proceed for 30 minutes and centrifuged at 15 min. the mb concentration in the middle of the night was measured at 690 nm using a uv-vis spectrophotometer. the lighting time is 3 hours. calculate the degradation rate (η%) with absorbance instead of concentration: 0 0 % 100% ta a a ( 2 ) where a0 is the initial absorbance value of the methylene blue solution; at is the absorbance value of the methylene blue solution after photocatalytic degradation. figure 7-1 kl-1 type uv photocatalytic reactor preparation and catalytic performance of fe3+ doped nano-materials 8 figure 7-2 kl-1 type uv photocatalytic reactor diagram figure 8 ultraviolet-visible absorption spectra of methylene blue 5. experimental results and discussion 5.1. experimental results 5.1.1 xrd characterization analysis the xd-3 x-ray diff ractometer was used to analyze the crystal form of the powder by x-ray diff raction spectrometer. according to the half-width of the diff raction peak, the grain size was calculated by scherrer equation (3). cos k d = (3) fig. 9 shows the xrd patterns of dn samples. it can be seen from the fi gure that the content of rutile increases with the increase of fe3+ doping amount, which indicates that fe3+ can promote the conversion of tio2 from anatase phase to rutile phase. there is no obvious fe2o3 crystal phase in the fi gure, and fe2o3 may exist in small clusters. or fe3+ into the tio2 lattice, the formation of ti-o-ti structure, from d0.5 to d20, a (101) surface diff raction angle gradually shifted to high angle, which is due to the formation of ti-o-ti structure of the lattice constant is less than the anatase caused by the lattice constant. the absorption intensity of fe3+ modifi ed tio2 was higher than that of pure tio2, and the pure tio2 was only strongly absorbed in the ultraviolet region, and the spectrum of the fe3+ modifi ed tio2 catalyst had a certain degree of red shift in the visible region. the results show that fe3+ can improve the absorptive capacity of tio2 on the visible light. fe3+ modifi ed anatase tio2 crystal, the tio2 valence band position to move up, while the conduction band position unchanged, the forbidden band becomes smaller, tio2 forbidden band formed in the impurity level, so that the absorption wavelength range extended to the visible area [13]. with the increase of the amount of fe(no3)3, the amount of fe3+ added to the surface of tio2 was increased, and the absorption of visible light was enhanced by the catalyst [6]. jianhui chen, et al 9 figure 9 x-ray diff raction patterns of group d samples using the xrd pattern, four groups of diff erent doping amounts of rutile content can be calculated according to the commonly used formula (4): 0.886 r r a r i w i i (4) the ia and ir are the diff raction intensities of the diff raction peaks of the (101) plane of the anatase phase and the diff raction peaks of the (110) plane of the rutile. the rutile content and grain size of all samples are listed in table 4. it can be seen from the data in the table that the amount of fe3+ (0.5-5.0at%) doping can inhibit the growth of tio2 grains, with the doping amount continues to increase, rutile content increased rapidly, and at the same temperature the growth rate of rutile is greater than that of anatase. the temperature of the immersion of the pure tio2 from the anatase phase (a) to the rutile crystal phase (r) is generally 600-700 ℃, while the transition temperature of the rutile in fe3+ doped tio2 is about 400 ℃ the fe3+ doping reduces the transition temperature of tio2 from a-r. there may be two reasons: on the one hand, the melting point of ferric nitrate is only 47 ℃, 100 ℃ can begin to break down, molten iron salt can play similar to the alumina system observed in the role of liquid sintering additives, liquid phase sintering is favorable for the decrease of ar phase transition temperature. on the other hand, part of the decomposed fe2o3 exists in the form of small clusters, which is distributed in tio2 and is likely to be the center of r phase nucleation. table 4 rutile content and grain size of diff erent samples sample ia ir rutile content /% grain size /nm da dr a0.5 908.4 0 1.23 a1 808.4 0 1.22 a5 536.58 0.92 a20 234.3 0.86 b0.5 1196 0 1.48 b1 1249 0 1.50 b5 813.9 1.17 b20 270.9 91.0 0.27 1.03 0.61 c0.5 1639 0 2.01 c1 1806 0 2.47 c5 1023 69.23 7.10 1.23 0.58 c20 402.8 112.43 23.96 1.06 1.95 d0.5 2830 42.25 1.66 3.52 0.47 d1 3100 64.3 2.29 3.70 1.02 d5 2000 234.2 11.67 2.47 2.83 d20 226.3 361.2 64.30 1.51 3.44 preparation and catalytic performance of fe3+ doped nano-materials 10 5.1.2 fe3+ doping amount on the catalytic activity of nano-tio2 the catalytic activity of photodegradation of mb after calcination at diff erent temperatures is shown in fig. 10-13. it can be seen from the test results that the appropriate amount of fe3+ (0.5-5.0at %) greatly improved the photocatalytic activity of tio2, mb degradation rate increased from 68.124% to 95.008% but excessive fe3+ but negative for photocatalytic reaction. because fe3+ over doping will make a large number of fe2o3 clusters on the surface of tio2, reducing the contact area of tio2 with the degradation of the substrate, thereby reducing the activity of the catalyst [6]. table 5 degradation rates of tio2 at diff erent roasting temperatures with diff erent doping values η% component light time / min 15 30 45 60 75 90 105 120 a1 13.078 18.309 29.547 40.527 55.318 63.187 63.876 68.124 a2 11.309 18.902 31.257 48.314 59.867 66.758 70.248 71.025 a3 9.098 12.307 32.047 41.067 54.78 69.317 71.254 72.314 a4 8.965 11.305 23.619 40.357 52.39 58.342 60.327 61.058 b1 10.547 17.354 26.958 48.389 61.524 68.024 74.03 76.024 b2 14.503 20.354 35.68 54.025 74.324 80.657 84.125 85.694 b3 15.367 25.068 41.302 61.038 80.124 82.036 84.219 85.312 b4 8.157 15.034 24.961 44.324 56.368 61.328 63.589 69.315 c1 15.361 34.258 58.764 70.124 80.367 82.567 83.104 83.547 c2 19.023 40.124 70.214 84.025 92.316 92.415 92.963 93.064 c3 20.461 47.314 76.325 90.001 94.123 94.861 95.036 95.008 c4 9.258 14.201 26.058 45.012 57.146 60.159 63.14 67.124 d1 16.06 22.397 33.257 55.681 68.741 79.04 83.047 86.015 d2 14.367 20.751 30.569 52.605 65.3 74.398 83.128 85.347 d3 12.036 18.069 30.285 51.304 60.247 67.524 73.025 75.21 d4 10.067 14.364 20.478 30.154 48.387 64.014 68.159 73.058 6. conclusions the photocatalyst precursor was prepared by sol gel method using tetrabutyl titanate and fe (no3) 3 · 9h2o as raw materials. fe-doped nano-tio2 with diff erent disperse particle size and anatase phase was prepared at diff erent doping amount and diff erent calcination temperature. the composite doping of fe3+ reduced the transition temperature of anatase crystal to rutile phase. the photocatalytic performance of nano tio2 with fe3+-doped calcination temperature of 500 ℃ has excellent photocatalytic performance. under the acidic condition, the degradation rate of the degradation of methine blue by fe3+ -doped nano-tio2 was close to 92% after 120 min irradiation with low pressure mercury lamp. main problems and application prospects of 7 nanometer materials tio2 photocatalytic oxidation is a promising water treatment technology, has been a large number of studies have shown that it has low energy consumption, easy operation, no secondary pollution and other advantages, and the ozone is diffi cult to oxidize some organic matter such as trichloride methane, carbon tetrachloride, hexachlorobenzene and hexachlorobenzene can eff ectively degrade and become a frontier and research hotspot in environmental management, but it is still in the experimental research stage and has not yet matured in the actual wastewater treatment project available processes. in this paper, the modification method of tio2 photocatalyst is discussed. with the rapid development of tio2 photocatalytic oxidation method, the catalyst is prepared by high efficiency and the proper carrier is used to realize solidifi cation and practical photocatalytic reactor. in the industrial, agricultural, environmental protection and other fi elds play an increasingly important role [15]. the current use of tio2 catalyst because of its bandgap width of 3.2 ev, can only use the wavelength of less than 388 × 10-9 range of ultraviolet light, so the absorption spectrum of solar spectrum accounted for a small part of the solar energy cannot take full advantage of only artifi cial energy mercury lamp and uv lamp, so not only energy consumption, but also limits the further development of photocatalytic technology and practical application. in foreign countries, has developed a gpg method, it can well absorb the sun spectrum, is an economical and eff ective way to degrade organic pollutants in sewage. in addition, the photon fl ux of tio2 also needs to be improved [16]. in the aspect of nano functional and structural materials, high-tech new products such as abnormal optical properties, electrical properties, magnetic properties, mechanical properties, sensitive properties, catalysis and chemical properties jianhui chen, et al 11 of nanomaterials, and the modifi cation of traditional materials focusing on breakthroughs in various types of nanofunctional and structural materials, the industrialization of key technologies, detection technology and characterization technology. multi-functional nano-composite materials, high-performance nano-carbide for chemical, and building materials, light industry, metallurgical and other industries by leaps and bounds to provide a wide range of opportunities. it is expected that during the 15th period, the industrialization of various kinds of nanomaterials may form a large number of large enterprises or enterprise groups, which will have an 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nano-medicine and bio-nanotechnology, 4681. https://doi.org/10.24294/can.v7i1.4681 1 review carbon and graphene based nanocomposites for gas sensors—current state and advances ayesha kausar1,2,*, ishaq ahmad1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, china 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract: after the discovery of carbon nanoforms, carbon nanotube (one dimensional) and tube like nanostructure and graphene (two dimensional) nanosheets have gained immense research curiosity. further nanotechnological developments have moved towards the formation of carbon nanotube nanocomposites and graphene nanocomposites. for the purpose, various matrices including thermoplastic polymers and conjugated polymers have been used. methodology is the systematic gathering of the literature and development of a novel review outline, theme, and discussions regarding the discussed topics. hence, varying conjugated polymers such as polyaniline, polythiophene, poly(3,4-ethylenedioxythiophene), and nonconjugated nylon, poly(ethylene glycol), etc. have been processed using techniques like in situ, solution, electropolymerization, spin coating, etc. in sensors, the nanocomposites need to develop fine nanoparticle dispersion, network formation, and interfacial interactions ultimately supporting the electron or charge transfer in these nanomaterials desirable for the recognition of the gaseous species. moreover, interactions of the nanocomposite with the analyte molecules define the sensing capabilities of the nanomaterials. consequently, nanocarbon nanocomposite based gas sensors have been analyzed for conductivity, change in resistance, sensitivity, selectivity, response time, detection limit, and other desirable properties. for future designs, it is recommended to develop high-tech combinations of conjugated polymers like polythiophene derivatives using functional forms of graphene and carbon nanotube. in addition, use of advanced manufacturing techniques like 3d/4d printing and spin coating must be applied to form efficient sensors. in conclusions, this manuscript presents not only comprehensive but also comparative analysis on different gas analysis parameters such as detection limit, concentration, response time, etc. for various nanocomposite sensors. lastly, the encounters in preparing and applying graphene/carbon nanotube sensors, associated utilizations, and possible future prospects have been discussed. keywords: carbon nanotube; graphene; polymer; nanocomposite; conductivity; gas sensing 1. introduction in the field of sensors, efficient carbon nanomaterials have gained interest [1]. accordingly, the advanced sensing features have been observed for the nanocomposites [2]. different types of matrices including conducting and nonconducting matrices have been applied in gas sensors [3–5]. non-conductive matrices include polyamides and olefinic polymers to form the sensing nanocomposites [6]. conjugated polymers for gas sensors include polyaniline, polypyrrole, polythiophene, and related polymers [7]. forming nanocomposites of carbon nanoparticles with these matrices have been found to upsurge the electron conduction through formation of citation kausar a, ahmad i. carbon and graphene based nanocomposites for gas sensors—current state and advances. characterization and application of nanomaterials. 2024; special issue: nanoscience, nanomedicine and bio-nanotechnology: 4681. https://doi.org/10.24294/can.v7i1.468 1 article info received: 19 february 2024 accepted: 26 february 2024 available online: 9 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 2 percolating and interconnected network nanostructures [8,9]. carbon nanoparticles like graphene, carbon nanotube, carbon nanofibers, etc., in nanocomposite form have revealed fine sensing features towards gases, ions, and chemical species [10]. these nanomaterials have been designed through facile techniques like electropolymerization, in situ, solution, coating, etc. [11,12]. such nanocarbon nanocomposite designs have been reported for better molecular recognition, detection, and rapid responses for the desired analytes in addition to fine electrical, dielectric, electrochemical, and other structural properties [13,14]. for enhanced sensing properties, carbon nanostructures have known to develop the charge transfer complex due to interactions and so revealed better microstructure, charge transport, and specific interactions for analytes causing high responsiveness and detection limit [15]. this state-of-the-art article covers gas sensing designs and features of the systems based on carbon nanotube nanocomposites and graphene nanocomposites. the multifunctional nanocarbon nanocomposites in gas sensing revealed high sensitivity, selectivity, and response time values. this overview portrays the progress in the field of two important nanocarbon nanostructures for gas sensing applications. here, the nanocarbon nanofillers have been used in combination with important polymer matrices and sensing behavior has been analyzed for various gaseous species. hence, this comprehensive review reports on the fundamentals to advanced potential of carbon nanocomposite sensors. methodology of this review involves systematic gathering of scientific information collected from the reported literature on graphene and carbon nanotube nanocomposites. consequently, the applications of these nanocomposite systems have been observed for the gas sensing application. during this review development, novelty is particularly considered in terms of the literature discussed, outlined topics, and variation of nanocomposite types, and polymers used for the formation of nanocomposite sensors. hence, purpose is to report a radical and up-to-date article on nanocomposite gas sensors portraying indispensable features from fabrication—to—advanced potential. need of developing this review has been analyzed due to the lack of comprehensive recent review articles in the field of carbon and graphene filler nanocomposite for gas sensing purposes. although research reports can be seen in literature, however an all-inclusive article throwing light on the past, current, and predicted future developments need to be developed to benefit the interested field experts. future progress in this field is not possible for the researchers before getting prior knowledge of the gathered literature on these nanomaterials. hence, current state, advancements, future, and challenges in the field of nanocarbon based gas sensors have been comprehensively deliberated. this article is definitely beneficial for the field researchers and scientists striving to investigate better sensing designs in the field of nanocarbon sensors. 2. gas sensing potential of carbon nanotube nanocomposites carbon nanotube was initially discovered in 1991 [16]. since that time, carbon nanotube has been applied in significant industrial arenas [17]. carbon nanotube is a hollow one dimensional nanotube like nanocarbon nanostructure consisting of sp2 hybridization [18,19]. carbon nanotube can be categorized as single walled, double walled, as well as multi walled nanostructures [20,21]. a single walled carbon characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 3 nanotube has 1 nm diameter and around 100 nm length with chiral features [22]. cabon nanotube has been analyzed for outstanding optical, electrical, mechanical, and physical properties [23]. synthesis of carbon nanotube has been performed using variety of techniques like chemical vapor deposition, physical vapor deposition, laser techniques, and chemical methods [24]. wide ranging applications of carbon nanotube has been observed in the field ranging from energy and electronics to automotive and space sectors [25–27]. carbon nanotube has been used as a remarkable nanofiller to form the polymeric nanocomposites [28]. these nanomaterials have been recognized for number of superior structural/physical characteristics [29]. small amounts of carbon nanotube have resulted in imperative properties of the nanocomposites. furthermore, increasing nanofiller amounts have been found to increase the nanocomposite characters. to improve the effectiveness of carbon nanotube, functional nanofiller has been often included in the matrices. difference between nanoparticles and nanocomposites can be seen as nanoparticles possess tens/hundreds of atoms of various shape/chemistry, whereas nanocomposite have nanolattices as part a part of the bulk matrix material. electron conduction and ionic conduction have been observed due to high aspect ratio of the nanotube and alignment in the matrices [30]. carbon nanotube has been recognized for the formation of interconnecting network in the matrices leading to tunneling effect and so the effective electrical conductivity [31]. owing to conductivity properties, carbon nanotube nanocomposites have been found functional for electrostatic/conductive coatings, electronic devices, textiles, transportation, engineering structures, and so on [32–34]. another important application of carbon nanotube has been observed for sensing or detection of gaseous molecules, ions, and chemical species [35]. consequently, carbon nanotube based nanomaterials have been employed for environmental relevance [36]. it has been observed that the sensing properties of carbon nanotube depend upon the charge or electron transport features [37–39]. selectivity, sensitivity, and response times of carbon nanotube derived nanomaterials have studied for the carbon nanotube based sensors [40]. for sensors based on carbon nanotube nanocomposites, uniform dispersion of nanotube inn matrices, interface formation and choice of facile processing technique have been found indispensable. among fabrication tactics, in situ, electropolymerization, coating, dipping, and solution methods have been mostly adopted for the formation of sensors [41–44]. for the analyte sensing, molecular interactions with the nanocomposite surface and interfaces, adsorption, and binding interactions have been investigated [45–47]. for carbon nanotube nanocomposite designs for sensors, conjugated polymers as well as nonconductive polymers like polyamide and olefinic polymers have been applied [48,49]. the resulting nanocomposites have effectively sensed the noxious gases and vapors. akbari et al. [50] developed the carbon nanotube based field effect transistor as sensor for the ammonia analysis. gas sensing mechanism was explained using a simple model and conductivity was analyzed through the current-voltage measurements. figure 1 shows the cylindrical tube like nanostructure of single walled carbon nanotube with hexagonally connected atoms. characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 4 figure 1. (a) single walled carbon nanotube structures; and (b) field effect transistor (fet)-based structure for a gas sensor with carbon nanotube channel [50]. reproduced with permission from mdpi. the length of nanotube has been found larger than the diameter to form a cylinder like nanostructure. the field effect transistor based gas sensor with carbon nanotube has also been presented. conductivity responses of single walled carbon nanotube towards analyte gas molecules have been credited to the semiconducting nature of carbon nanotube. like metal based field effect transistors, carbon nanotube have been observed to form conductive channels for the passage of electrons and detection of gaseous species. for the formation of carbon nanotube conducting channels, silicon and silica based layered dielectric substrate has been used. upon the interaction of ammonia molecules with the field effect transistor, electron flow was observed in the external circuit for gas sensing analysis. chiou et al. [51] designed the chemi-resistive gas sensor based on the poly(ethylene glycol)/multi walled carbon nanotube nanocomposite. the gas sensor was used to sense the acetone vapors at moderate temperature without using heat treatments. the sensing mechanism of the nanomaterial was also analyzed. figure 2 designates the testing apparatus used for the gas sensor. here, mass flow controller was used to pass the acetone vapors over the sensors under controlled temperature and concentration. multi steps were involved in the repeated test cycles during gas sensing. according to scanning electron microscopy, nanocomposite sensor had thickness of 217.6 nm (figure 3). the nanotubes were observed enfolded with the polymer. the sensor response was also studied as a function temperature in the acetone concentration of 300–1000 ppm. the linear correlation coefficient was found around 0.98 at room temperature, as per fitting curves of sensing responses. a b characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 5 figure 2. test instrument of poly(ethylene glycol)/multi-walled carbon nanotube (peg/mwcnt) gas sensor [51]. reproduced with permission from mdpi. figure 3. scanning electron microscopy images of (a) close view of the interface between electrode and poly(ethylene glycol)/multi-walled carbon nanotube (peg/mwcnt) nanocomposite film; (b) close view of peg/mwcnt nanocomposite film; and (c) the fitting curves of sensor response at different operating temperature as a function of acetone concentration (300–1000 ppm) [51]. reproduced with permission from mdpi. characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 6 lapointe et al. [52] fabricated the carbon nanotube filled nylon 69 based nanomaterial for gas sensor. according to scanning electron microscopy micrograph, carbon nanotubes were found to be uniformly dispersed in the matrix (figure 4). the fine dispersion and network formation led to the development of interfaces for gas interaction and analysis. on the field effect transistor, carbon nanotube was seemed to be dispersed and due to high surface area and interfaces, gaseous species were interacted and sensed. figure 4. a percolation network of carbon nanotubes: (a) scanning electron microscopy of single walled carbon nanotubes on nylon 69; and (b) schematic illustration of the air solid interfaces where analytes may interact with the carbon nanotube network field effect transistors as highlighted by the arrows [52]. reproduced with permission from acs. figure 5 shows the scheme of carbon nanotube based field effect transistor having silica dielectric gate i.e., 1000 nm thick. the measurement of transfer characters of sensor revealed superior gas selectivity due to high aspect ratio of carbon nanotube. using the trans-conductivity and threshold voltage, superior sensitivity and selectivity have been observed towards alcohol and organic molecules. characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 7 figure 5. (a) carbon nanotube network field effect transistor (cnn-fet) in bottom gate; and configuration as used in this work; (b) transfer characteristics of a cnnfet with silica sio2 gate dielectric at normalized relative humidity of 60% rh; and (c,d) rh dependence of cnn-fet threshold voltage and transconductance determined from linear fit of transfer curves using the −6 v to −4 v range. red and orange symbols correspond to forward (fwd) and reverse (rev) sweep directions, respectively, and black symbols show hysteresis between reverse and forward sweeps [52]. reproduced with permission from acs. among conjugated polymers, polyaniline, polypyrrole, and polythiophene have been applied for gas sensing [53]. the gaseous molecules of no2, so2, co2, methane, halogens, and other organic vapors have been sensed using the conjugated polymers [54–56]. srivastava and co-workers [57] formed the single walled and multi walled carbon nanotube filled polyaniline nanocomposites through solution casting and spin coating. change in resistance was used to assess the sensor response for hydrogen gas. high sensitivity was observed due to high surface area of carbon nanotube. karmakar and colleagues [58] used polyaniline and carbon nanotube derived the sensing nanomaterial for sensing the no2 and co2 molecules. miah and researchers [59] proposed a gas sensor based on polypyrrole/carbon nanotube nanocomposite for sensing nox molecules. the nanocomposite was formed using the in situ method. vijeth and workers [60] established the polythiophene and carbon nanotube derived nanocomposite using in situ oxidative method. the polythiophene/carbon nanotube characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 8 based gas sensor was applied for hydrazine gas. the sensor had detection limit of 0.18 μm and sensitivity of 0.285 μa μm−1cm−2. badhulika and co-workers [61] formed the single walled carbon nanotube filled poly(3,4-ethylenedioxythiophene):polystyrene nanomaterial for sensing of vapors like ethanol, methanol, and methyl ethyl ketone. electropolymerization was used to form the nanocomposite. the resulting sensor response was recorded through the change in resistance values with enhancing vapor concentrations from 2.5% to 5%. sensing mechanism was also studied using electrostatic effects. sharma and researchers [62] developed the multi walled carbon nanotube filled poly(3,4-ethylenedioxythiophene):polystyrene nanocomposite sensor using solution method. the sensor was applied for sensing the ammonia gas. the sensitivity of 16% was attained with the response time of 15 min. the sensitivity of 5.59% was observed. in this manner, effective gas sensors have been fabricated using the carbon nanotube derived nanocomposites. table 1 demonstrates various convenient designs of carbon nanotube nanocomposites for gas sensing. table 1. essential polymer/carbon nanotube nanocomposite in gas sensing. polymer/conjugated polymer nanofiller processing property/application ref. nylon 69 carbon nanotube solution method field effect transistor; solid interfaces; lock-and-key sensing mechanism; alcohol/organic solvent vapor sensing [52] polyaniline carbon nanotube, zinc oxide nanorods in situ oxidative polymerization technique nox and cox molecules; chemiresistive response 70 % at 120 ppm; recovery time <120 s [58] polyaniline single walled carbon nanotube solution method h2 gas sensing response rg/r0 1.83 [57] polyaniline multi walled carbon nanotube solution method h2 gas sensing response rg/r0 2.30 [57] polyaniline carbon nanotube interfacial technique ammonia sensing [63] polypyrrole carbon nanotube spin coating ammonia sensing [64] polypyrrole carbon nanotube in situ; spin coating methods ammonia sensor [65] poly(3,4ethylenedioxythiophene): polystyrene multi walled carbon nanotube solution casting technique nh3 gas sensing; response time < 15 min; sensitivity 16% [62] poly(3,4ethylenedioxythiophene): polystyrene single walled carbon nanotube electropolymerization volatile organic vapors methanol, ethanol, methyl ethyl ketone; ethanol and methyl ethyl ketone vapor detection; detection limit 5.95% and 3%, respectively [61] 3. graphene nanomaterials for gas sensing graphene has been categorized as an exclusive carbon nanomaterials having one atom thick nanosheet of carbon atoms [66]. initially, graphene was discovered in 2010 [67]. sp2 hybridization and delocalization have been observed in the carbon atoms. specific graphene nanostructure has led to the advanced structural and physical characteristic of this unique carbon nanomaterial. most importantly, graphene has characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 9 verry high young’s modulus of about i tpa, electron mobility of 200,000 cm2v−1s−1, and thermal conductivity of 3000–5000 w/mk [68]. graphene has been further modified in various forms to attain further high structural features. effective methods for graphene formation involve graphite liquid or mechanical exfoliation, chemical vapor deposition, plasma and laser techniques, and organic synthesis approaches [69,70]. essential modified forms of graphene have been recognized as graphene oxide (oxidized graphene nanosheet), reduced graphene oxide, graphene nanosheet with functional groups, and nanoparticle functional graphene nanosheets [71]. among these, graphene oxide has been the most widely used functional form of graphene, commonly prepared through facile hummer’s method [72]. applications of graphene has been found wide ranging from the electronics and engineering sectors to biomedical fields [73]. in environmental gas sensing application, carbon nanomaterials have gained increasing research curiosity owing to fine electrical conductivity and ionic or molecular sensitivity features. graphene, with delocalized nanostructure, may form conjugated system with the conducting matrices to further enhance the conduction properties and resulting applications. such systems have been studied for superior selectivity and sensitivity towards various gaseous species such as the oxides of nitrogen, sulfur, carbon, and other vapors. consequently, conductive polymeric matrices have been used for gas sensing, however, several non-conjugated matrices or polymers have also been applied to for the effective gas sensors [74]. noticeable conjugated polymers may include the polyaniline, polypyrrole, and polythiophene derivatives for gaseous detection. these polymers with graphene nanocarbon have been applied for the sensing of the gases like methane, halogen gases, and various noxious oxides of sulfur, nitrogen, or carbon [75]. for example, polyaniline and polypyrrole nanomaterials have been used to sense the no2 and co2 gaseous species [76,77]. polythiophene and derivatives have been found to detect the hydrazine and toxic gases [78]. pristine graphene has been applied as an important material for gas sensing [79,80]. with conjugated polymers, graphene has revealed further improved sensing behavior [81–83]. graphene based sensors depicted visible change in resistance upon coming in contact with the analyte molecules [84]. for ion and gas sensing, combinations of polyaniline and graphene have exposed superior performance [85– 87]. wei et al. [88] reported on the long-period fiber grating based on graphene and formed surface plasmon resonance. figure 6 shows the design of graphene long period fiber grating/surface plasmon resonance and interaction with methane molecules. using the co2 laser, nanomaterial was coated on the fiber core and then graphene long period fiber grating/surface plasmon resonance was coated on the silver film on silica substrate. afterwards, graphene was deposited using the chemical vapor deposition method to form the final sensor design. figure 7 demonstrates that the sensor had resonance wavelength at 1541.3 nm, as per signal collected every 5 s. the response time was observed as 50 s. the 90% methane sensitivity was attained within 65 s. with the methane gas exposure, the resonance wavelength revealed increase/decrease behaviors. it was observed that the resonant wavelength observed was 0.05 nm for graphene long period fiber grating/surface plasmon resonance. characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 10 figure 6. schematic of graphene-based lpfg spr sensor [88]. lpfg/spr = longperiod fiber grating/surface plasmon resonance. reproduced with permission from mdpi. figure 7. (a) repeatability response curve of graphene-based lpfg spr sensor to 3.5% methane gas sample; and (b) reusability of graphene-based lpfg spr sensor to methane gas sample with different concentrations [88]. lpfg/spr = long-period fiber grating/surface plasmon resonance. reproduced with permission from mdpi. wu et al. [89] fabricated the nanocomposite of polypropylene, polyaniline, and graphene based gas sensor. the nanomaterials have been formed using the in situ method and dip coating process. the resulting polypropylene/graphene/polyaniline nanocomposite derived gas sensor was used for ammonia gas sensing. the nanocomposite has fine interconnected hierarchical nanostructure for fine molecular analysis. figure 8 shows the sensing mechanism of the nanocomposite depending upon the doping and de-doping processes and charge transportation occurring at interfacial areas [90]. the gas senor was used for noxious gases sensing in exhaled human breath. characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 11 figure 8. sensing mechanism of pp/g/pani hybrid sensors [89]. pp = polypropylene; pani = polyaniline; g = graphene; pp/g/pani = polypropylene/graphene/polyaniline. reproduced with permission from acs. consequently, volatile sulfur compound like h2s gas (2%) and ammonia gas (100 ppb in 114 s) were effectively sensed in the exhaled human breath (figure 9). as compared with the pristine polyaniline, the polypropylene/graphene/polyaniline nanocomposite sensor had 250% superior sensing performance [91]. figure 9. photograph of pp/g/pani sensor for volatile sulfur compounds in human breath and pure h2s [89]. pp/g/pani = polypropylene/graphene/polyaniline; reproduced with permission from acs. tange et al. [92] fabricated the polyaniline and graphene oxide derived nanocomposites through in situ polymerization. the microstructure, electrochemical, and electrical conductivity properties have been studied for the nanocomposites. the nanocomposites have fine nanofiller dispersion and interactions between the matrix and nanofiller. for structural analysis, x ray diffraction patterns of polyaniline, characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 12 graphene oxide, polyaniline/graphene oxide, polyaniline/modified graphene oxide were scanned (figure 10). neat polyaniline had crystalline peaks appeared at 2θ of 19.4° and 25.4°, while graphene oxide depicted peak at 2θ of 10.12° due to (001). in modified graphene oxide, the shift in diffraction peak was observed to 9.90° due to change in interlayer spacing. in the formation of nanocomposites with polyaniline, the diffraction pattern had amorphous nature and there was decrease in the crystalline order. consequently, the electrochemical characters of the nanocomposites were enhanced. in addition, electrical conductivity of the nanocomposite was increased to 508 sm−1 was attained. figure 10. x-ray diffraction patterns of pani, go, m-go, pani/go, and pani/mgo nanocomposite [92]. pani = polyaniline; go = graphene oxide; pani/go = polyaniline/graphene oxide; pani/m-go = polyaniline/modified graphene oxide. reproduced with permission from mdpi. similarly, effective combinations of conjugated polymers with graphene, graphene oxide, or reduced graphene oxide have been developed for the sensing of gaseous species like methane, methanol, hydrogen, ammonia, and so on [93,94]. table 2 illustrates the gas sensitivity behavior of various combinations of conjugated polymers and graphene nanofillers. in such systems, polymers and graphene nanofillers have been found to develop a charge transfer complex and electron donoracceptor nanostructures for sensing of analyte gases. by comparing the nanocarbon based gas sensors with inorganic nanoparticles filled sensors, the efficiency can be analyzed. for example, bonyani et al. [95] reported on the gold decorated zinc oxide nanoparticle based polyaniline nanocomposite sensors. the 9 nm zinc oxide nanoparticles were prepared and filled in 10–50 wt.% in the polyaniline matrix and gas sensing response was analyzed. fine gas sensor response was analyzed at 300 ℃ for no2 gas. the ∆r/r0 sensor response was found comparable to the polyaniline/graphene nanocomposite sensor. bairi et al. [96] formed tanninsulfonic acid doped polyaniline and titania nanocomposites for ammonia gas sensor using in situ and spin coating. the gas sensor was tested in the ammonia concentration range of 20–60 ppm. the sensor had revealed 90% change in resistivity, which is higher than the sensitivity of polyaniline/graphene nanocomposite characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 13 observed [97]. the comparative analysis revealed that the inorganic nanoparticles filled conjugated polymer sensors may have higher performance than the graphene or carbon nanotube based sensors, depending upon the material design. it has been observed that the crystal size or grain size of the nanofiller particles in polymeric nanocomposite played important role for gas sensing performance. by reducing the crystal or particle sizes, the sensitivity as well as response speed of the sensors were considerably enhanced [98]. decrease in sizes usually causes increase in surface area of the nanoparticles, which is used to enhance the vacancies by decreasing the free electrons concentration. consequently, the adsorption of gas molecules is improved, in turn enhancing the gas sensing response. table 2. provisions of polymer/graphene nanocomposites in gas sensing. conjugated polymer nanofiller processing property/application ref long-period fiber grating graphene coating plasmon resonance sensor; sensitivity ch4 1%–3% [88] polypropylene/polyaniline graphene in situ polymerization; dip coating h2s gas; detection limit 100 ppb; nh3 gas sensing; response time 114 s [89] polyaniline graphene interfacial technique h2o2 sensing [99] polyaniline graphene oxide in situ method methanol sensitivity; electrical conductivity 241 sm−1 [100] polyaniline graphene layer-by-layer technique π-π conjugation; high methane sensitivity [101] polythiophene reduced graphene oxide in situ method humidity sensor [102] polyaniline/palladium reduced graphene oxide deposition technique h2 gas; ∆r/r0 = 25%; response time 20 s [103] polyaniline reduced graphene oxide in situ method nh3 sensing; response 59.2% at 50 ppm; response time 20 s [97] polyaniline graphene in situ method ∆r/r0 = 30%; [104] polypyrene graphene oxide electrochemical codeposition linear reversible response; sensitivity 9.87 × 10−4 [105] poly(methyl methacrylate) graphene solution method octanoic acid detection; current response per power law with exponent in the range 0.4–0.8 [106] 4. prospects and future scenarios fabrication of the gas sensing nanocomposites with graphene or carbon nanotube has been mostly carried out using the solution and in situ route. the solution mixing method has been most commonly applied for the formation of nanocarbon nanocomposites owing to low price and facile parameters [107]. this technique includes the simple mixing of polymer and nanoparticles in a suitable solvent and then the material casting through solvent evaporation. the technique has been found practicable for variety of thermoplastic and conjugated matrices [108]. in the presence of a suitable solvent, the polymers or monomers are adsorbed on the nanocarbon characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 14 nanoparticles to enhance the interactions and dispersion [109,110]. consequently, the solution formed nanocomposites have revealed desired physical and technical features [111]. in situ polymerization has also been extensively used to form the carbon nanocomposites for sensors. in this technique, first the monomer molecules are dispersed in a solvent and then subsequently polymerized with the pre dispersed nanoparticles [112]. monomers are finely adsorbed on the nanocarbon nanoparticles for better dispersion and nanocomposite production [113]. both the solution casting and in situ technique possess advantages of using non-toxic solvents and environmental friendliness. these methods have been known for well-matched interface formation and compatibility of the nanocomposites [114]. consequently, high-tech carbon nanotube nanocomposites and graphene nanocomposites have been reported to be utilized in the gas sensing applications. nanoparticle type, contents, interaction with matrices, dispersion, and interfacial effects influence the sensor performance [115]. consequently, carbon nanoparticles like carbon nanotube or graphene may form interconnecting network in the matrices for electron conduction, percolation effects, and development of charge transfer complex or π-π interactions leading to fine sensing performance [116]. in addition, nanocarbon nanocomposites have advantages of robustness, functioning reliability, and environmental stability features [117]. better nanoparticle dispersion has been analyzed as an important feature to enhance the electrical conduction and sensing performance [118]. conversely, nanoparticle aggregation or self-association may deteriorate the sensing and conductivity performance of the nanocomposites. besides the nanoparticle nanofiller, type of polymer or matrix has been found important to define the sensing behavior of nanocomposite. various nanocarbon based designs have been formed and utilized for sensing the gaseous molecules like hydrogen, hydrocarbon, ammonia, carbon dioxide, halogens, and range of toxic oxides. bulk of literature is available on the conjugated polymer with carbon nanoparticles for sensing designs, however non-conjugated systems have been less explored for gas sensing applications. despite of the research so far, there is need of new sensing designs to be explored for future high performance nanomaterials [119]. there is need of focused research labors to find out the real sensing mechanism for the gas detection and possibilities for the development of next-generation sensors [120]. facile methods like in situ, solution, and coating have been applied to form the gas sensors, still there is need of applying sophisticated techniques like three or four dimensional printing to form more precise nanomaterial designs [121]. printing techniques can be beneficial for not only designing the sensors with optimized structure and conditions but also the superior sensitivity, selectivity, and responsiveness of the nanomaterials due to better compatibility, material interactions, and synergistic effects. further exertions on the fabrication of modified nanocarbon based sensors may lead to marvelous high performance sensor designs. 5. conclusions concisely, this overview hearsays competent carbon nanotube and graphene based nanocomposite designs utilized for gas sensors. consequently, the nanomaterials have been investigated for microstructure, and structural as well as characterization and application of nanomaterials 2024, special issue: nanoscience, nano-medicine and bio-nanotechnology, 4681. 15 physical properties. specific features regarding the gas sensing such as conductivity, change in resistance, nanomaterial sensitivity, selectivity, detection limit, response time, etc. have been explored to analyze the sensor performance. it has been observed that the carbon nanostructures like graphene and carbon nanotube have been efficiently adopted for gas sensor designs. the nanocarbon nanostructures have been mostly used in the nanocomposite form with polymer matrices. thermoplastic and conductive polymers have been filled with the nanocarbon nanoparticles to form the desired sensing nanomaterials. among these sensors, polyaniline and nanocarbon based gas sensors may have response time of 20–100 s. these sensors can have response of up to 60% and ∆r/r0 was detected in the range of 20%–30%. fine dispersion of nanocarbon nanoparticles and network formation in matrices have led to superior electron conduction and so the sensing properties of the nanocomposites. the resulting gas sensors have been found to analyze various noxious gas species like oxides of nitrogen, carbon, or sulfur, halogens, hydrocarbon or organic vapors, and others. although, significant literature has been found in this regard, nevertheless there is need of further research efforts in this direction for better nanomaterial design and property optimization and exploration of the sensing mechanisms involved. though, research up till now has anticipated abundant designs for gas sensors, as per studies development of new graphene and carbon nanotube based sensors may disclose technical fields due to advantageous performance. using functional carbon nanotube and graphene based sensors may reveal low price, high electrical conductivity, electrochemical performance, stability, sensitivity, and reproducibility. new gas sensing designs can be advantageous for potential environment, energy, beverages, and medical industries. the desired gas molecules can be easily detected for uses in these sectors. conflict of interest: the authors declare 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10.1016/j.cej.2022.140655 56 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1336 original research article spin thermoelectric effects on aluminum or phosphorus doped zigzag silicene nanoribbons jiali song1, xue zhang1, xuefeng wang2, jinfu feng1,3, yushen liu1,3* 1 school of physics and electronic engineering, changshu institute of technology, changshu 215500, china 2 jiangsu laboratory of advanced functional materials, changshu 215500, china 3 school of physical science and technology, soochow university, suzhou 215006, china. e-mail: ysliu@cslg.cn abstract based on the density-functional theory (dft) combined with nonequilibrium green’s function (ngf), this paper investigates the effects of either single aluminum (al) or single phosphorus (p) atom substitutions at different edge positions of zigzag-edged silicene nanoribbons (zgnrs) in the ferromagnetic state on the spin-dependent transport properties and spin thermoelectric effects. it has been found that the spin polarization at the fermi level can reach 100% or –100% in the doped zsinrs. meanwhile, the spin-up seebeck effect (for –100% case) and spin-down seebeck effect (for 100% case) are also enhanced. moreover, the spin seebeck coefficient is much larger than the corresponding charge seebeck coefficient at a special doping position and electron energy. therefore, the study shows that the al or p doped zsinrs can be used to prepare the ideal thermospin devices. keywords: silicene nanoribbons; doping; spin seebeck coefficients article info received: 10 august 2021 accepted: 4 october 2021 available online: 9 october 2021 copyright copyright © 2021 jiali song, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction since graphene was successfully prepared by mechanical method for the first time in 2004, people have become more and more interested in other two-dimensional honeycomb structural materials[1]. among them, silicone material is such a structure-silicon atoms of two-dimensional hexagonal lattice. unlike graphene with planar structure, because the distance between silicon atoms is farther than that between carbon atoms, therefore, silene has a low degree of fold structure, and the distance between its two silicon atoms is about 0.44 å[2]. its unique geometry brings many interesting properties, such as quantum hall effect[3], large spin orbit interaction[4] and mechanically adjustable energy gap[5]. similar to graphene, in the fermi level and zero band gap structure, silene has a semi metallic low energy state. although spin orbit coupling can open an energy gap at the dirac energy point, its value is only 1.5 mev[3]. however, from the perspective of application, we need to open a relatively large energy gap. silene nanoribbons provide a feasible method. recent experimental studies have confirmed that one-dimensional silene nanostructures can be prepared[6]. similar to graphene ribbons, silene nanoribbons also have two types of edges, namely serrated silene ribbons (zsinrs) and armrest silene ribbons (asinrs). hydrogen saturated armrest nano ribbons can behave as semiconductors and metals according to the change of their length. however, the 57 ground state of hydrogen saturated sawtooth silene nano ribbons is the boundary antiferromagnetically coupled semiconductor state[6]. under the action of the transverse electric field, for boundary doping with phosphorus or nitrogen atoms in the serrated silene nanoband, its magnetic semiconductor state can be converted into a semimetallic state[7]. recently, molecular dynamics studies have shown that the boundary hydrogen saturated silene nanoribbons have very good stability, and their geometry even exists under 800 k temperature[8]. this shows that hydrogen saturated silene nanoribbons can be used to prepare very stable thermoelectric devices. based on the first principle method, zberecki et al. found that due to a conductivity gap on the fermi surface, its conductivity is extremely suppressed. due to the inverse relationship between seebeck coefficient and conductivity in the low temperature region, it leads to the great increase of its thermoelectric coefficient[9]. in addition, with the maturity of spin detection technology, people can detect spin current through spin hall effect. in 2008, the phenomenon that a spin flow can arise when a temperature gradient is applied at both ends of the magnetic metal ni81fe19 connected to the pt line was found by uchida et al[10]. similar to the traditional charge thermoelectric effect, this effect is called “spin seebeck effect” or “thermal spin effect”. this pioneering experiment has stimulated a large number of relevant theoretical and experimental studies[11–17]. when the silene nanoribbons are in the boundary ferromagnetic coupling state, they exhibit spin degenerate metal behavior at the fermi plane. because the boundary antiferromagnetic state shows semiconductor behavior, such a large magnetoresistance behavior can be found[18]. in this paper, the spin thermoelectric effect of single aluminum (al) or phosphorus (p) atomic boundary instead of doped zsinrs double probe structure will be studied in the first principle (see figure 1). this device consists of the left electrode part, the intermediate scattering region, and the right electrode part. the width of zsinrs is 6. we consider four different boundary doping positions and find that for al atom doping, the spin polarization at the fermi plane is close to –100% at the second and third positions, but it is just the opposite for p atom doping. the results show that for phosphorus atom doping, at position 3, the spin polarizability at the fermi surface reaches 100%. the main reason is that there are transmission nodes at the fermi surface. at the same time, the spin thermoelectric coefficient at the fermi is also significantly strengthened by adjusting the electron energy, the spin thermoelectric coefficient of doped zsinrs can be similar to or even greater than the charge thermoelectric coefficient. 2. model establishment bilateral monohydrogenated zsinrs are used as the original package of the nano system, and the bandwidth is generally taken as 6. using vasp software package, we first optimized the fm state single package structure of hydrogenated zsinrs, and the cut-off energy is taken as 360 ev[19]. the exchange correlation function adopts generalized gradient approximation (ggapbe). the maximum force per atom does not exceed 0.01 eva–1. after geometric optimization, based on the original package structure, this paper designed a nano double probe system as shown in figure 1. the boundary si atoms are saturated with h atoms. the si atoms with middle marks 1–4 in the middle scattering region are replaced with other atoms respectively (i.e. only one si atom is replaced for each doping). the atoms replaced in this paper include al and p. here, for simplicity, al doped silene nanoribbons are referred to as al-zsinrs; p-doped silene nanoribbons are abbreviated as p-zsinrs. figure 1. a spin device structure composed of 6-zsinrs. the box on the left represents the left electrode and the box on the right represents the right electrode. 1–4 in the figure represents different doping positions in the scattering region. the large ball represents si atom and the small ball represents h atom. 58 in this paper, a software package atomistix toolkit (atk) based on nonequilibrium green’s function and density functional theory is used to complete the calculation and simulation of the electron transport process of the system. the system optimization adopts newton optimization. the exchange correlation function adopts generalized gradient approximation (gga), and the basis vector adopts dzp (double zeta polarized). the size of the contracted brillouin area is set to (1, 1, 100). in order to avoid the interaction between images, the vacuum layer is taken as 15 å and the energy truncation radius is taken as 150 ry. the electron transmission coefficient of the eigenenergy of e is: (1) here γl/r(e) is the wire width function of the central center coupled to the left/right wire, σ is the spin exponential index and e is the energy. gr/a(e) is the delayed and advance green function of the central scattering region and can be calculated by equations and . i is the unit matrix and h is the hamiltonian of the central scattering region. the spin polarizability at the fermi plane can be defined as: (2) in order to study the spin thermoelectric effect, we give the expression of spin dependent seebeck coefficient in the linear region: (3) where, , fl(r) is the fermi dirac distribution function. spin seebeck coefficient is expressed as ss = (s↑ – s↓)/2, and the corresponding charge seebeck coefficient is sc = (s↑ + s↓)/2 [20]. 3. results and discussion formula (3) can be reduced at low temperatures to: (4) the formula (4) shows that the spin-dependent seebeck coefficient and transmission odds are proportional to the slope of the energy, and inversely proportional to its size. figure 2(a) shows the transmission spectrum of pure zsinrs in the energy range [–2 ev, 2 ev]. it can be seen from figure 2(a) that the complete zsinrs shows typical metal behavior, that is, the transmission function value near the fermi level (e = ef = 0), τσ(e) = 1 is a constant. the upper and lower spin channels are almost degenerate. for the spin-up channel, a peak is generated in the energy e – ef ≈ –0.2 ev region, and its transmission function value is τσ(e) ≈ 3. for the spin-down channel, a peak is generated near the energy e – ef ≈ 0.1 ev, and its transmission function value is τσ(e) ≈ 3. figure 2(b) shows the relationship between the spin-dependent thermoelectric coefficient sσ and the chemical potential μ for the pure zsinrs. here the figure 2. the transmission spectrum and thermal power coefficients of the full zsinrs at zero bias. (a) for the t0-energy relation diagram, (b) and (c) for the absolute value of the spin-correlation thermoelectric coefficient sσ and the spin (charge) seebeck coefficient for the pure zsinrs |ss|(|sc|). 59 temperature is taken as 300 k. we find that with the change of chemical potential μ, the spin-associated thermoelectric coefficient sσ of the full zsinrs (fm state) is significantly enhanced at the position where the transport function has mutations. the spin polarizability at the fermi surface is close to zero and its seebeck coefficient is very weak. the main reason is that the slope of the transmission probability at the fermi surface is almost zero. figure 3 shows the spin dependent transmission spectra of zsinrs with different doping types and doping positions. from the figure, we can see that when zsinrs is doped, the upper and lower spin electron transport characteristics appear non-degenerate phenomenon, and the non-degenerate phenomenon shows different behavior with different doping positions (position 1 turns to 4 in turn). there are some conductivity troughs on both sides of fermi level (also known as local quantum state). the transmission spectrum of doped zsinrs is related not only to the spin direction, but also to the type and position of doping. as shown in figures 3(a) and (b), when the edge of pure zsinrs along si atom (figure 1, position 1) is replaced by al or p atoms, the metal behavior near the fermi level remains almost unchanged, and the spin degeneracy phenomenon is still obvious. for spin-up electrons both doping causes a conductance trough at energy slightly below ef and for spin-down electrons a similar narrow decrease at energy slightly above ef, there was a more pronounced decrease near the |e – ef| ≈ 0.5 ev, with a decrease in the transmission function of both the upper and lower spins. when the doping position is moved to position 2 in figure 1, the transmission spectrum of al-zsinrs in figure 3(c) changes more obviously, and its spin degeneracy is destroyed. at the fermi level (e – ef = 0), the upper spin transmission function of al doped zsinrs is obviously suppressed, while the lower spin transmission function remains unchanged. figure 3(d) shows that the transmission function of p-zsinrs is just the opposite here. compared with the change of the transmission spectrum of doped zsinrs at position 1, the spin dependent local quantum state of p-zsinrs near e – ef ≈ –0.5 ev disappears; while the spin dependent local quantum state of al-zsinrs near e – ef ≈ 0.5 ev disappears, and there are more narrow falling states near e – ef ≈ –0.5 ev. when the doping position moves to position 3, the spin degeneracy of the transmission spectra of al-zsinrs or p-zsinrs in figures 3(e) and (f) is further destroyed, and the former is more obvious. interestingly, at the fermi level (e – ef = 0) nearby, the inhibition of the upper-spin transmission function of al-zsinrs intensifies, τ↑ = 0, that is, the spin upward behavior of zsinrs changes from metallicity to insulation, while the lower-spin transmission function remains unchanged; its spin polarizability even reaches –100%. the case of p-zsinrs transmission function is just the opposite. its spin polarizability can be close to 100%. similarly, the transmission function of alzsinrs at e – ef ≈ 0.5 ev also has a trough, while the trough of p-zsinrs appears at e – ef ≈ 0.5 ev. when the doping is further to position 4, for the two spin channels, the transmission function of doped zsinrs shows cash properties near the fermi level, and the metal behavior of the system is restored. figure 3. transmission spectrum of the ferromagnetic state zsinrs doped with al (left) and p (right) at zero bias. black and red lines are represented, upper spin and lower spin electrons, respectively. the left and right columns represent the zsinrs transmission spectra at different doping positions of al and p, respectively. 60 figure 4 and figure 5 show the relationship between the spin-dependent thermoelectric coefficient sσ and the spin (charge) seebeck coefficient ss(sc) and the chemical potential μ of the zsinrs for different doping positions and types, respectively. here, the temperature t = 300 k. for each spin channel of the pure silene band, the transmission spectrum is spin-degenerate. since and τ'(ef) = 0, sσ = 0, near the transmission probability node, the corresponding spin thermoelectric effect is significantly strengthened. for example, when the doping position is 1, both the spin-dependent thermoelectric coefficient sσ of figure 4(a) at μ ≈ 0.2 ev and (b) p-zsinrs at μ ≈ –0.5 ev, zsinrs is enhanced. only the positions of the positive maximum and negative maximum of s↑ and s↓ are slightly different, which leads to the obvious strengthening of the spin thermoelectric effect, which is comparable to the corresponding charges (as shown in figures 5(a) and (b)). however, the thermoelectric effect at the fermi plane is relatively weak. with the doping position moving to position 2, the s↑ corresponding to the μ = 0 of al-zsinrs is significantly strengthened, but s↓ maintains a relatively weak value. the main reason is that there is a node in the spin upward transmission probability at about 0.05 ev on the fermi plane. since the slope of τ↑ at the fermi plane is positive, according to the formula (4), its value should be negative, which is in good agreement with our numerical results (as shown in figure 4(c)). while 4(d) p-zsinrs shows that the spin dependent thermoelectric effect is relatively weak at μ = 0. figure 5. ferromagnetic zsinrs (n = 6) doped with al (left column) and p (right column) at zero bias with respect to chemical potential μ. the spin (charge) thermoelectric coefficient function |ss|(|sc|). the black line and red line represent |ss| and |sc|. the left and right columns represent |ss|(|sc|) of zsinrs at different doping positions of al (left) and p (right) respectively. however, when the doping position is moved from position 2 to position 3, it can be seen from figures 4(e) and (f) that in the al-zsinrs (p-zsinrs) system μ = 0, s↑(s↓) is greatly enhanced, but s↓(s↑) is almost zero, resulting in |ss| ≈ |sc| (as shown in figures 5(e) and (f)). when the doping position is moved to position 4, the spin related thermoelectric effect becomes relatively weak because the semi metallic property at the fermi plane is transformed into metal property. looking at figure 5(g), we find that for al-zsinrs, at energy μ ≈ –0.3 ev, there is a high spin thermoelectric effect, while the corresponding charge thermoelectric coefficient is very small, alfigure 4. spin-dependent thermoelectric coefficient function sσ of chemical potential μ for the ferro zsinrs of al (left) and p (right) at zero bias. black and red lines represent upper spin and lower spin electrons, respectively. the left and right columns represent zsinrs at different doping positions of al (left) and p (right), respectively. 61 most zero. therefore, we fix the chemical potential μ = –0.3 ev, and calculated the al-zsinrs relation of sσ and |ss|(|sc|) with temperature τ. the temperature range is taken as [0, 400 k] (as shown in figure 6). as the temperature t changes from 0 to 400 k, the signs of s↑ and s↓ are opposite, and |sc| changes little in the whole temperature range, and its value is almost zero. therefore, for the nano equipment based on zsinrs, we can obtain an almost ideal pure selfswirl generation device by doping al atoms in specific parts. 4. conclusion we propose a spin thermoelectric device composed of doped silene nanoribbons (zsinrs). here, the doping method of zsinrs is to replace the si atom at the edge with al and p atoms. we find that due to al(p) doping, some spin up (down) quantum states appear near the fermi level, which leads to the spin polarizability close to –100% (aluminum atom doping) and 100% (phosphorus atom doping). in addition, the thermoelectric coefficient of doped zsinrs, including spin dependent thermoelectric coefficient and spin (charge) thermoelectric coefficient, has been significantly strengthened. while al atom doping at a specific position can obtain an ideal pure self-swirling thermoelectric device. conflict of interest the authors declare that they have no conflict of interest. acknowledgements this paper was supported by national natural science foundation of china “research on theory and application of molecular thermoelectric devices” (11247028). references 1. novoselov ks, geim ak, morozov sv, et al. electric field effect in atomically thin carbon films. science 2004; 306: 666–669. 2. morishita t, nishio k, mikami m. formation of singleand double-layer silicon in slit pores. physical review b, condensed matter 2008; 77: 081401(r). 3. liu c, feng w, yao y. quantum spin hall effect in silicene and two-dimensional germanium. physical review letters 2011; 107(7): 6802. 4. liu c, jiang h, yao y. low-energy effective hamiltonian involving spin-orbit 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characterization and application of nanomaterials 2024, 7(2), 6348. https://doi.org/10.24294/can.v7i2.6348 1 review synthesis, technological prospects and applications of mxene in biomedicine, supercapacitors and sensors: a review nujud badawi m. 1,* , m. bhuyan 2,* , namrata agrawal 3 , yogesh kumar 4 1 university of hafr al-batin college of science, hafer al-batin 39921, saudi arabia 2 institute of physics, sachivalaya marg, bhubaneswar 751005, india 3 department of physics, swami shraddhanand college, university of delhi, new delhi 110036, india 4 department of physics, arsd college, university of delhi, delhi 110021, india * corresponding authors: nujud badawi m., nujuds@uhb.edu.sa; m. bhuyan, bunuphy@um.edu.my abstract: mxenes are one of the most important classes of materials discussed worldwide by many researchers of diverse fields for diverse applications in recent years. it is a nanomaterial with a wide range of applications due to its multiple forms and structures with fascinating properties, for example, high surface area and porosity, biocompatibility, ease of fictionalizing with various active chemical moieties, benefit of high metallic conductivity, activated metallic hydroxide sites, and sensitivity to moisture. mxenes have great chances for potential applications in environmental issues, water purification, biological applications, and energy storage devices and sensors. mxenes show great selectivity towards the absorption of heavy metals and a good capability to reduce chemical and biological pollutants present in the water. the present review article critically analyzed advancements in water purification using the adsorption and reduction abilities of mxenes and their composites. the mechanism of various procedures, important challenges, and associated problems using mxene and their composites are discussed in detail. the future research directions can be extracted from this article efficiently and comprehensively. the energy storage issues of rechargeable lithium-ion batteries, batteries other than lithium-ion batteries, and electrochemical capacitors are also discussed in detail. keywords: 2d materials; mxene; energy storage; batteries; capacitors 1. introduction in 2011, a new type of two-dimensional substance called mxene was discovered for the first time. the mxene family sparked intense interest in research across many disciplines due to its diverse chemical composition and excellent physical and chemical properties, particularly in the areas of energy storage, the environment, catalysis, and biomedical applications, the latter of which, in particular, is experiencing rapid growth. since graphene’s exfoliation [1,2], a lot of attention has been paid to other 2d layered materials [3,4] because of their exceptional electrical, mechanical, and optical capabilities. most studied examples of 2d materials other than graphene include transition metal dichalcogenides [4,5], phosphorene [6,7], and their derivatives. in recent years [6], a family of 2d-layered compounds known as “mxenes” has attracted a great deal of interest from the scientific community due to their unusual structural and electrical properties, which make them applicable to a wide range of fields. mxenes are compounds produced by the chemical delamination of ternary (or quaternary) layered carbides or nitrides. the unique properties of the mxene family citation badawi m. n, bhuyan m, agrawal n, kumar y. synthesis, technological prospects and applications of mxene in biomedicine, supercapacitors and sensors: a review. characterization and application of nanomaterials. 2024; 7(2): 6348. https://doi.org/10.24294/can.v7i2.6348 article info received: 11 may 2024 accepted: 27 may 2024 available online:14 september 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 6348. 2 are due to their electrical structures, atomic stacking, synthetic methods, surface terminal groups, and peculiar bonding, which consists of metallic and covalent connections. despite mxenes rising star power, there is a dearth of comprehensive information on them. many sensors [2–4], as well as portable and wearable electronic devices [5–7], have emerged to sense and interact with physical worlds to foster the development of a smarter life with the vigorous rise of the internet of things (iot) and the great improvement of the reliability of wireless communication protocols [1]. despite this, a reliable power supply [8–10] requires the successful integration of on-chip energystorage units with novel electronic devices due to the intermittent nature of renewable resources (wind [11], solar [12], tidal [13], and geothermal energy [14]). conventional micro-batteries have a high energy density [15] and can keep devices running for a while, but they are unable to meet the requirement of rapid power delivery in applications where battery replacement is impractical [16]. microsupercapacitors (mscs) have gained widespread interest as a micro-battery substitute because of their fascinating long lifetime, high power density, and fast charging rate [17]. however, their progress in microelectronics is hampered by their low power and energy density [18]. with the rapid development of biomedicine and the attractive physiochemical properties of two-dimensional materials, many researchers have focused on the biomedical applications of two-dimensional materials, such as hexagonal boron nitrides (h-bn), graphene and its derivatives, transition metal oxides (tmos), layered double hydroxides (ldhs), and mxenes. mxenes have more functional groups on their surface, allowing for greater versatility in modification than most other 2d materials. mxenes are useful for biomedical applications due to their hydrophilicity, compositional versatility, and the presence of full metal atomic layers. another advantage is that mxenes can be mass-produced at low cost. bioimaging, antimicrobials, biosensors, drug delivery, tissue engineering, and a wide range of therapeutics are just some of the ways mxenes have been put to use in the medical field so far (figure 1a) [19]. because of their high near-infrared light absorption and conversion efficiency, mxenes have found applications in photothermal therapy for tumour ablation. this form of treatment is highly effective in targeting cancer cells while causing minimal collateral damage to healthy tissue. in addition, bioimaging can be used in real-time to track the tumour’s location as contrast chemicals are administered during cancer treatment. in addition, the modified mxenes can also carry anticancer medications and release pharmaceuticals in a specific manner. photothermal therapy, chemotherapy, and real-time bioimaging monitoring have considerably increased the success rate of cancer treatment thus far. as a bonus, mxenes are proving to be promising raw materials for developing biocompatible tools for easy, rapid detection of biological events [19]. characterization and application of nanomaterials 2024, 7(2), 6348. 3 figure 1. (a) properties and biomedical applications of mxenes [19]; (b) mxenes in a wide range of applications [20]. the purpose of this study was to analyze and remark on the most important basic and technological aspects of mxenes about their structure, electronics, properties, applications, and devices (see figure 1b) [20]. the history of mxenes’ creation is presented first, followed by examples of mxene production, structure, and characteristics, surface modification schemes, biomedical applications, cytotoxicity, and biocompatibility. we have examined the key features and properties of mxenes. the present status, trends and future possibilities in various fields, such as energy, electronics, biomedicine, etc., have been critically examined. finally, current challenges and future potential applications of mxene have been discussed. 2. logic of mxene new 2d transition metal carbides, nitrides, and carbonitrides called mxenes (pronounced “machines”) were first fabricated by wind [11], solar [12], tidal [13], and geothermal energy [14]. hydrofluoric acid (hf) was used at room temperature to selectively etch the “a” (al atoms) in layered hexagonal ternary carbide, ti3alc2, to produce the first mxene made of 2d titanium carbide (ti3c2). from the precursor max phase (mn+1axn), mxenes can be constructed with the general formula mn+1xntx (n = 1–3), where m is an early transition metal, x is carbon and/or nitrogen, a is an element from groups 12 to 16, t is the surface termination groups like fluorine (–f), oxygen (=o), chlorine (–cl), and hydroxyl (–oh), and x is the number of surface functionalities [21]. there is a strong m-x bond and a comparatively weak m-a bond in the max phase, where an a layer is sandwiched by octahedral mn+1xn [22]. elements that produce max phases (mn+1axn) are denoted in bold in figure 2 [23]. depending on the n value in mxenes (mn+1xntx), the interlayer spacing can be anywhere from 0.1 to 1.0 nm [8]. characterization and application of nanomaterials 2024, 7(2), 6348. 4 figure 2. elements in the periodic table that are known to form mn+1axnphases. reprinted with the permission from ref [23]. 3. synthesis methodologies of mxene: procedures and structures about 30 different compositions of mxenes have been described in the literature, all of which have been synthesized from max phase precursors, with the addition of two or more transition metals to the m layers as the primary route to do so [20]. in particular, mxenes based on titanium, such as ti3c2tx and ti2ctx, are widely used for ecological purposes [1,17]. other mxene structures, such as those including nitride and carbonitride, have also found use outside of the realm of carbides [23]. mxenes’ distinct layered structures and 2d morphology make them an ideal candidate for use in composites, which can be utilized to improve the properties of other materials [8]. preparing a sample for synthesis involves taking a few parameters into account, like safety, cost, procedures, instruments (such as monitors and gauges), and control systems. etching, exfoliation, and chemical vapour deposition (cvd) are the three most common approaches to mxene production. etching and exfoliation are examples of top-down processes, while chemical vapour deposition, the template method, and plasma-enhanced pulsed laser deposition are examples of bottom-up techniques. the most popular method for synthesizing 2d mxenes is the top-down etching of ‘a’ from max phases (mn+1axn), where m is an early transition metal; a is one of numerous elements (al, si, p, s, ga, ge, as, cd, in, sn, tl, or pb); x is c, n or both; and n is 1–4. metallic bonds are typical between m and a, but covalent, ionic, or metallic bonds can exist between m and x [19]. as a result, it is difficult to break the m-a connection using mechanical shearing or direct exfoliation. etchants, such as hf, can, however, etch it selectively. two processes are required in the synthesis of mxenes [20,24] (figure 3) [25]: first, selective etching of the a element from a precursor (max phases or other layered ceramics); second, delamination to obtain a single-layer mxene. however, the manufacturing of mxenes for energy storage applications has not been thoroughly addressed using these methods. the processes of mxene manufacturing are explained in greater detail below. each mxene has a mother mx phase from which it is created, where “m” represents an early transition metal, “a” represents a group 13 or 14 element, “x” represents carbon or nitrogen, and “n” ranges from 1 to 3 [21]. characterization and application of nanomaterials 2024, 7(2), 6348. 5 figure 3. synthesis of mxene—selective etching of max and non-max phases to form multilayered mxenes, followed by delamination (chemical/mechanical) to produce a colloidal suspensionof single-layered mxene [25]. mxenes. in the top-down process, mxenes were synthesized from the bulk by a two-stage procedure: chemical etching and delamination [8,26]. to remove the interleaved layers of ‘a’ atoms from the bulk ceramic, an etchant is utilized to cleave the m-a metallic connection. the aggregated nanosheets are then delaminated via liquid-phase exfoliation [8], tetrapropylammonium hydroxide (tpaoh) intercalation [27,28], or ultrasonication [26]. in figure 4a [29], a schematic depicting the steps involved in creating mxene is given. to prevent the dangers of fluorine-based etchants, fluorine-free techniques are also used [30]. bottom-up methods often employ cvd technology, which works upwards from the atomic or molecular level [31]. both top-down synthesis and bottom-up approaches can be used to create characterization and application of nanomaterials 2024, 7(2), 6348. 6 figure 4. (a) fabrication of 2d ultrathin ti3c2 nanosheets by etching, delamination, and surface modification along with its crystal structure [29]; (b) different structures of mxenes [27]. 4. simulation-based studies on mxene structures to complement experimental studies and get a more in-depth understanding of mxene structures, computer simulations are frequently used. mxenes typically end with surface groups, including –f, –oh, and –o, following exfoliation from the max phase. the usefulness of such structures is determined by the relationships among their features and characteristics [26]. there are three possible configurations of mxenes, all of which correspond to the parent max phases and have a single characterization and application of nanomaterials 2024, 7(2), 6348. 7 metal in the m site: m2c, m3c2, and m4c3, where m is an early transition metal, a is a particular element from groups 13 or 14, x is carbon or nitrogen, and n is a number from one to four. the a element must be carefully removed from a max phase or other stacked precursor (such as mo2ga2c). in max phases, x atoms fill octahedral sites in an otherwise hexagonally stacked m layer with p63/mmc symmetry. as a result, the a and m elements form metallic bonds. mn+1xn layers and mxenes containing ordered double-transition metals, like (cr2v) c2 and (mo2ti2) c3, are interwoven throughout the “a” element [29]. computer modelling has helped disclose the structures of mxenes and has also aided in the discovery of new, stable mxenes. there are six distinct mxene structures: (1) nb4c3 and ti2c are examples of mono-m components; (2) (cr, v)3c2 and (ti, v)3c2 are examples of solid solutions; (3) ordered out-of-plane two-fold m components have one transition metal (typically cr and mo) filling the outer layers and the other the focus layers (ta and nb); (4) ordered in-plane two-fold m components have the distinguishing m components arranged in the basal plane, such as in [22,27,29–32]. structures of different mxenes are shown in figure 4b. the surface terminations (–f, –oh, and –o) group linked to m atoms give mxene its chemical formula, mn+1xntz (1 n 3). figure 5a [22] depicts the steps required to prepare mxene. a typical schematic diagram is depicted in figure 5b [33], representing the process of synthesizing mxenes from max phases. characterization and application of nanomaterials 2024, 7(2), 6348. 8 figure 5. (a) mxenes, derived from the parent layered solids max phases [22]; (b) the schematic diagram represents the process of synthesizing mxenes from max phases. reproduced with permission from [33]. 5. applications 5.1. prospects of mxenes in biological applications the promising results of mxenes in stem cell-based tissue treatments and the material sciences make it reasonable to expect future multi-tasking biomedical therapies to be based on their unique properties [33]. titanium carbide (ti3c2) mxene nanofibers were used to create smart biomaterials for tissue engineering and cell culture in one study. fabrication of hydrophilic composite nanofibers via electrospinning and doping was carried out by chen et al. [34]. the mxene nanofiber composites’ surface functional groups were considered to foster healthy characterization and application of nanomaterials 2024, 7(2), 6348. 9 cellular environments. bone marrow-derived mesenchymal stem cells (bmscs) were used to analyse the biochemically representative characteristics, and the resulting mxene composite nanofibers showed good biocompatibility and significantly improved cellular activity, as well as boosting bmsc differentiation to osteoblasts. smart biomaterials, which have many desirable biological characteristics, are very useful in tissue engineering and repair procedures [35]. because of their immunomodulatory properties, which selectively reduced the activation of human cd4+ifn-+ t-lymphocytes while stimulating the expansion of immunosuppressive cd4+cd25+foxp3+regulatory t-cells in a stimulated lymphocyte population, twodimensional structures with bmsc biocompatibility could stimulate fibroblasts derived from bone marrow-derived stem cells (bmscs) for post-injury tissue repair. [35,36]. the incorporation of ti3c2mxene qds (quantum dots (mqds) sensor) into a chitosan hydrogel resulted in the creation of a 3d platform with enhanced physicochemical characteristics, which can facilitate stem cell trafficking and tissue restoration. the resultant composite hydrogel was both injectable and thermossensitive, and it showed excellent conductivity [37]. in a similar line, biocompatible ti3c2tz-enhanced poly (lactic acid) nanocomposite membranes were created by mediating the interface between the hydrophobic poly (lactic acid) matrix and the ti3c2tz nanosheets. these membranes achieved an optimized tensile strength of 72 mpa, which is approximately 33% greater than a pure poly (lactic acid) membrane [37,38]. therefore, ti3c2tz insertion into the membrane might improve its biological characteristics, including osteogenic differentiation, proliferation, and in vitro adhesion of mc3t3-e1 murine preosteoblasts. mxenes’ exceptional properties, which include hydrophilicity, high electronic conductivity, and adsorptive, reductive, and antibacterial properties, make them well-suited for a wide range of ecological uses. the adaptability of mxenes makes them desirable for a wide range of uses. their chemical stability, ion intercalation, and adjustable bang gaps suggest catalysis and energy storage applications like fuel cells, hydrogen storage, and lithium-ion batteries (libs), while their high young’s modulus, good electrical conductivity, and surface chemistry alteration are appealing for the creation of composites. 5.2. mxenes for environmental and water treatment applications 5.2.1. h2o2 oxidation activated by mxene-based materials hydrogen peroxide (h2o2) oxidation has attracted much attention in the removal of pollutants [36], where fe2+ can act as a catalyst to form free radicals [36,39]. 2d mxene has a layered structure and surface electronegativity. metal particles can be loaded onto the surface and layered surfaces of 2d mxene [24,40]. in addition, 2d mxene can also degrade metal nanoparticles and inhibit the aggregation of metal nanoparticles [41]. interestingly, metal particle-loaded 2d mxene has a larger surface area and better pore structure than pure 2d mxene. the pores in the composite can serve as microreactors for h2o2 activation. magnetic nanoscale zero-valent iron particles (nzvi)@ti3c2 nanosheets could remove 91.1% of ranitidine in 30 min [42]. therefore, 2d mxene-supported metal particles can be characterization and application of nanomaterials 2024, 7(2), 6348. 10 considered a good catalyst to activate h2o2 to degrade organic pollutants. wu et al. [43] developed a nanoplatform based on multimodal tmo connecting ultrathin ti3c2 nanosheets to self-assembled mnfe2o4 nanoparticles using chitosan as a chemical cross-linking agent to form an interfacial schottky junction, ti3c2@chitosan-mnfe2o4(tc@ch-mfo). this led to an improvement in reactive oxygen species (ros) production and optimization of biocompatibility. this heterojunction could control the catalysis of h2o2 to produce o2 and deplete excess glutathione levels in the hypoxic tumor microenvironment, so that under nearinfrared stimulation, the cyclization was completed by the fenton reaction. tc@chmfo also provided a multifunctional nanoplatform for photothermal therapy by introducing an effective photothermal agent, ti3c2. additionally, it integrated visualization with t1and t2-weighted magnetic resonance imaging simultaneously (see figure 6a) [43]. as the toxicity of tc@chmfo to normal tissues is negligible, this platform might provide new insights into the development of multimodal synergistic nanoplatforms for biological applications. figure 6. (a) mxene-based schottky junctions self-assembled transition metal oxides for near-infrared radiation to modify the tumor microenvironment and enhance cdt/ptt/mri activation [43]; (b) oxidized mxene co-wrinkled multi scale porous structure [44]. lee et al. [44] proposed a new method to produce mxene oxidative wrinkled multiscale porous structures through a sequential process involving partial oxidation with h2o2 as agglomeration in acid (see figure 6b). these processes lead to the characterization and application of nanomaterials 2024, 7(2), 6348. 11 simultaneous formation of mesopores caused by oxidation and macropores due to shrinkage patterns. the specific surface area of oxidatively co-degraded mxene (72 m2/g) was found to be five times that of pure mxene. the efficiency of the performance (307 f/g at 20 mv/s in 1 m h2so4) and the capacity of the scan (225 f/g at 100 mv/s) were also found to be better than in pure mxene. additionally, 87.6% of capacity was retained after 6000 cycles. this was due to the structure of porous, oxidized, folded mxene. here, the diffusion of ions through mesopores was promoted, while folded macropores prevented restacking. the performance and mechanism of ti3c2 mxene-modified fe3+/hydrogen peroxide system in dark light and visible light were compared in detail, and a new standard for coating fe3+ reactions and reductions of mxene was proposed by xu et al. [45]. taking bisphenol a (bpa) as the target pollutant, the degradation effect of bpa in the fe3+/h2o2 system was improved after adding mxene in the dark. the degradation of bpa in 12.5 min under visible light was ≥95%, which was 6 times higher than in the dark. fe2+ was identified as a useful element for the activation of h2o2 to form oh. it was found that mxene formed a complex with fe3+. mxene reacted with fe3+, breaking the tic bond and activating the fe3+/fe2+ cycle. mxene used photogenerated electrons to promote chemical reactions under light. oh and o2 were found to be the main reactive oxygen species in light, while oh was the main reactive oxygen species in light (see figure 7a). thus, mxene could utilize o2 to produce o2 and promote the fe3+/fe2+ cycle in light. this work provided a theoretical basis for the combination of visible light catalysis and the higher oxidation process of ti3c2 mxene. characterization and application of nanomaterials 2024, 7(2), 6348. 12 figure 7. (a) ti3c2 mxene promotes fe3+/h2o2 fenton oxidation: comparison of the process under dark light and visible light [45]; (b) the fabrication process of the cu/cu2o/tio2-x electrode [46]. to detect h2o2, li et al. [46] used in-situ produced tio2-x nanoparticles to modify cu/cu2o nanoparticles on ti3c2 mxene to form heterojunctions via a singlestep hydrothermal process. the produced cu/cu2o/tio2-x/ti3c2(cu/cu2o/tt) was found to have a linear range of 28.328 mm, a sensitivity of 312 μa mm−1 cm−2 and detection limit of 0.42 μm. the synergistic effect of cu/cu2o nanoparticles and tio2-x/ti3c2 heterojunction not only improved the electron transfer and electrocatalytic activity but also increased the strength of the target molecules of the catalyst due to the abundance of extended catalytic sites. therefore, compared to tio2x/ti3c2, the detection limit of cu/cu2o/tt was low, its reaction faster, and its sensitivity five times higher. also, cu/cu2o/tt exhibited excellent photoelectrochemical sensing performance in detecting h2o2 with a low detection limit, long-term stability, repeatability, and selectivity. the fabrication process of the cu/cu2o/tt electrode followed by li et al. [46] is shown in figure 7b. iron particles deposited on the 2d mxene surface may exhibit multiple reaction zones. 2d mxene can facilitate the electrical transfer of magnetic materials. in addition, there are many hydrophilic functional groups (such as oh, cooh, and characterization and application of nanomaterials 2024, 7(2), 6348. 13 cho) on the surface of mxene/nanoscale zero-valent iron particle nanosheets, designed to promote h2o2 activation [43]. zhu et al. [47] used ti3c2tx to develop a sensitive and enzyme-free electrochemical sensing interface to detect h2o2 simply and practically. prussian blue (pb) was electrochemically deposited on the surface of the glassy carbon electrode (gce). chitosan (cs) and mxene were degraded on the pb modified gce surface. simple mx/cs/pb/gce detection interface demonstrated good electrochemical detection performance and good selection for h2o2 with a low limit (4 nm) and a wide linear range from 50 nm to 667 μm. the light-driven magnetic mxene microrobot (mxebot) was developed as a moveable stage for the removal and degradation of bisphenol a (bpa) by dekanovsky et al. [48]. a second control motor composed of embedded fe2o3 nanoparticles (nps) for magnetic push assisted the mxebot. grafted bismuth nanoparticles acted as co-catalysts. it was investigated how bpa concentration and the chemical composition of the swimming environment affected the stability and reusability of mxebots. maxbot could remove/degrade approximately 60% of bpa in just 10 minutes and approximately 100% in 1 hour. more than 86% of bpa mineralized within 1 h. using bi/fe/mxebots for the photocatalytic degradation of bpa demonstrated a significant advantage in converting bpa into co2 and h2o [49]. 5.2.2. other advanced water remediation applications of mxenes mxene and its compounds have also proven effective in other environmental applications such as membranes, capacitive deionization, and anti-bacterial agents. mxene is a promising product for water filtration due to its hydrophilicity, high surface area, and excellent electrical properties [48]. molecules can be separated based on the size of the surface layer and the interaction with the mxene layer. in recent years, mxenes have been used in a variety of environmental applications for the treatment of contaminated groundwater and municipal wastewater, including desalination, outperforming the most widely used material in all regions [50]. mxene composites can adsorb a variety of organic and inorganic compounds and can undergo faradaic capacitive deionization (cdi) when used in electrochemical applications. this method overcomes the concentration polarization limit of conventional cdi electrodes, greatly reducing the energy required and providing a solution for low-energy desalination of brackish water. researchers provide an updated review of mxene and mxene mixtures for water purification and desalination applications. kinetics and isotherms were examined, and the effects of water composition and activity discussed. based on the literature review, the application of mxene in cdi, pervaporation desalination, and photothermal desalination have been studied. the impact of water composition and performance on recovery efficiency and long-term use has also been highlighted (see figure 8a) [51]. characterization and application of nanomaterials 2024, 7(2), 6348. 14 figure 8. (a) use of mxenes in water purification and energy-saving desalination [51]; (b) mxenes (2d metal carbides) as nanomaterials for water purification [49]. there is an interest in using mxene and its derivatives in water purification due to their unique properties. mxene has high electrical conductivity and hydrophilicity, as well as outstanding adsorption, reduction, and disinfection properties. in particular, ti3c2tx and its compounds are widely used in water purification to remove various contaminants such as dyes, radionuclides, and heavy metals. ihsanullah [49] evaluated the effectiveness of mxene and mxene-based mixtures in removing various pollutants from water, focusing on heavy metals, dyes, and radionuclides. the role of the mxene structure in the contaminant elimination process and the regeneration were reviewed and analyzed (see figure 8b). the properties of mxene, such as high electricity, hydrophilicity, and catalytic activity, have attracted increasing research attention in environmental remediation and water purification applications [50]. reports are available on recent advances in the synthesis and use of mxenes as adsorbents, desalination membranes, electrochemical deionization electrodes, and catalysts or antimicrobial agents for water purification and other environmental treatment. the challenges and opportunities have also been highlighted for advanced 2d materials by discussing experimental efforts to investigate mxenes for water use, biocompatibility, and environmental impact. due to their unique mechanical, chemical, and electrical characterization and application of nanomaterials 2024, 7(2), 6348. 15 properties, many successful experiments have been carried out on the use of mxenes in water purification and environmental remediation applications. however, more efforts are needed to solve the stability, biocompatibility, and reusability issues of mxenes in aqueous environments. mxenes are reported to be used for pollutant adsorption/remediation, photodegradation, membrane separation, etc. the increase in pollutants such as air pollution, organic dyes, chemicals, and pesticides released into the water due to population and the global economy has become the most important health problem in the world [51]. magnetic mxene nanocomposites have many attractive and successful applications due to their unique properties, ease of production, cost-effective preparation, and excellent capability to degrade water and wastewater pollutants. these compounds offer exciting new opportunities for many applications, such as biosensors, cancer therapy, measurement systems, and especially water purification. researchers are studying magnetic mxene nanocomposites to remove contaminants from ambient water. the use of magnetic nanomaterials for water treatment, the applications and implications of mxene in degrading water and wastewater pollutants, and the role of magneticmxene nanocomposites in water treatment have been studied and discussed (figure 9a) [52]. characterization and application of nanomaterials 2024, 7(2), 6348. 16 figure 9. (a) magnetic-mxene-based nanocomposites for water and wastewater treatment [52]; (b) advanced applications of mxenes in cdi, solar desalination, ion sieving and pervaporation [53]. the advantages of mxene, such as high surface area, high metal conductivity, easy functionalization, biocompatibility, active metal hydroxide surface, and hydrophilicity, make it a good candidate for energy storage, catalysis, sensors, electronics, and environmental application. due to their good physical and chemical properties and wide range of chemical properties, mxenes have attracted attention in water purification and desalination applications in recent years. ihsanullah studied the advances in the synthesis of mxenes and mxene-based compounds for seawater desalination. the desalination potential of mxenes was described in detail, focusing on ion screen membranes, capacitive deionization, and solar desalination. the ion removal process and the recycling potential of mxene were also documented to provide insight into the process [53]. mxene has also emerged as a strong candidate for oil/water separation and photocatalytic environmental remediation applications (see figure 9b) [53]. the ability to reduce organic molecules and some cations is a unique property that makes characterization and application of nanomaterials 2024, 7(2), 6348. 17 mxene the best choice for future water purification applications [12]. due to its hydrophilicity, high conductivity, high adsorption capacity for anions and cations, and tunable surface, mxene can also be used as a new electrode material for cdi applications [54]. the solar and evaporative desalination properties of mxene have also been investigated in various studies [55]. the rapid development of the economy causes serious water pollution and poses a threat to the environment. currently, heterogeneous fenton oxidation has attracted widespread attention due to its high efficiency and simple operation. hydrogen peroxide and persulfate are two oxidants used in fenton-like processes. 5.3. mxene-based battery significant efforts have been devoted to the development of electronic devices with excellent electrical properties and high energy density for energy storage and conversion. 2d materials show great potential in energy storage due to their unique properties. mxenes have excellent properties when used as electrodes for lithiumbased batteries. tang et al. have discussed the developments in mxene and mxenebased composites in terms of synthesis strategies, morphology engineering, physical/chemical attributes, and their use in lithium-ion batteries and lithium-sulfur batteries [56]. 5.3.1. mxeneforlithiumbatteries lithium batteries are one of the most common types of batteries because they are the engines of modern electronic devices. lithium batteries are currently used in mobile phones, computers, small cars, airplanes, and home appliances. lithium’s high electropositivity and flexibility make it better than hydrogen [57]. lithiumbased cathodes have problems such as short life, low charge, toxicity, unstable electrolyte, high cost, high self-discharge, and poor specific energy. anodes made of materials such as graphite, lithium, soft carbon, and tin have problems such as dendrites, low energy density, cracking/dissolution, and voltage fluctuations [58]. therefore, it is necessary and urgent to produce good electrodes for these batteries. mxene is considered an effective material due to its large surface area, electrical conductivity, tunable thermal conductivity, and chemical stability. rechargeable lithium-ion batteries (libs) have provided much-needed applications in electric vehicles and consumer electronics due to their high energy density and reduced storage capacity. in particular, research on libs focuses on their applications in small electronic devices by increasing energy density and reducing the footprint during fast charging [56]. mxene can not only produce lithium-ion batteries but also can produce lighter fuel than lithium ion. deng tested mxene as a lib anode material and found it good due to its high specific surface area, weak interlayer strength, open structure, and surface functional groups [59]. since mxene consists of functional groups m (when the substituted metal is), x (c and/or n), and t (functional groups o, oh, and f), it is possible to use many substituents for the treatment. goods. for example, the specific potential of different mxenes follows the order ti2c < nb2c < v2c, with both nb2c and v2c exhibiting higher activity [1]. in addition, the difference between different mxenes is also different. this shows the difference between mxenes for anodes or cathodes. characterization and application of nanomaterials 2024, 7(2), 6348. 18 additionally, work groups often have different characteristics; for example, bare mxene is magnetic, while active mxene is a semiconductor material. they may also interfere with lithium absorption and transport [54]. nonnatural functional groups (e.g., chlorine) may be beneficial to mxene by hardening the surface and reducing the interaction of natural oh and f functional groups [55]. even if the “m” stoichiometry is the same type and prepared by the manufacturing process, the capacity of the lithium-ion battery will be directly affected due to the difference in surface properties. generally speaking, ti2ctx has a higher surface energy than ti3c2tx, which tends to reduce the lattice parameter k and thus inhibit the addition of lithium ions [59]. lithium-ion mxene/metal electrodes: the electrode material must have excellent electrical conductivity and be able to withstand high temperatures without cracking or breaking. nowadays, metal electrodes such as titanium, aluminum, magnesium, copper, silver, zinc, and platinum face many problems. corrosion, cracking, and low energy density are associated with intrinsic metallic electrodes. due to the excellent properties of mxene, some researchers have mixed metal electrodes with mxene to improve its electrochemical behavior. mxene has a significant problem that affects its performance, such as the aggregation problem of mxene flakes [60]. a simple and effective way to solve this problem is to provide mxene hybrid composites produced with suitable materials such as silicon, tin, different nanocarbon fillers, metal oxides, phosphorus, metal sulfides, and double-layer oxides. the mxene surface is modified in many aspects, including decoration with siliconand tin-based nanoparticles, bonding the network with carbon nanofillers, and creating heterostructures between graphene and mxene layers. these hybrid materials have high ion energy, high lithium-ion emissivity, and conductivity, in addition to extraordinary capacity. according to the current situation, lithium-ion battery electrode materials should help in improving the electrical properties of batteries, making them more efficient than before. mxenebased hybrid nanostructured materials provide insight into future challenges and guide in finding new materials to be used in future energy applications. since the discovery and development of graphene [60], 2d materials and the study of their properties have attracted widespread attention in materials science [34]. in recent years, 2d transition metal carbides, nitrides, and carbonitrides (mxenes for short) have been rapidly developed since the discovery of ti3c2 in 2011 [35]. mxene is prepared by selectively etching individual atomic layers (called max phases) in a precursor layer [60]. the general structure of the max phase is mn+1axn (n = 1, 2, 3), where m represents the early transition metal (m = ti, sr, v, cr, ta, nb, zr, mo, or hf), and a represents group sp elements (iiia or iva only), x represents c or n, and both [39,61]. the max phase can be said to be a symbiotic structure in which tightly packed planar atom layers and hexagonal mx layers are stacked alternately. figure 10 shows the classical configuration of the max system (using ti2alc as an example) [62]. in this structure, mx bonds are mostly ionic/covalent bonds, and all ma bonds are metal bonds [38]. therefore, the mx bond is stronger than the ma bond and enables the removal of the a layer from the lamellar layer. however, characterization and application of nanomaterials 2024, 7(2), 6348. 19 unlike the weak van der waals interlayer interactions between graphite and transition metal dichalcogenides, the ma bond is very strong, resulting in detachment of the mx layer from the max strength; this is not easily achieved by direct cleavage or ultrasonication techniques. due to the different properties and strengths of m-x and ma bonds, it is possible to select the appropriate chemical in the process. this leaves a stable chemical structure of the volume near mn+1xntx (t, f, oh, o, etc.), representing the functional group on the surface, near mxene (figure 10a) [62]. the interactions between mxene layers are mainly hydrogen bonds and van der waals bonds. water, cations, dmso, tbaoh, etc. are added to different parts of mxene. after sonication, the mxene layer becomes a suspension. figure 10. schematic illustration for the formation of ti2ctx mxene from ti2alc phase. (a) reproduced with permission [61]; (b) plate-to-layer bi2moo6/mxeneheterostructured anode for lithium-ion batteries [62]. due to the low electrical conductivity of bi2moo6 and the large volume expansion/contraction during charging and discharging, appropriate modification is essential to solve these problems. to overcome the issues, zhang et al. [62] prepared the plate-to-layer bi2moo6/ti3c2tx (mxene) heterostructure by electrostatically assembling positively charged bi2moo6 nanosheets onto negatively charged mxene nanosheets. mxene nanosheets in heterostructure provided a highly conductive substrate to support and anchor bi2moo6 nanosheets, thereby increasing electrical conductivity and structure stability (see figure 10b). when the mass fraction of characterization and application of nanomaterials 2024, 7(2), 6348. 20 mxene was optimized to 30%, the bi2moo6/mxene heterostructure exhibited a specific capacity of 692 mah g−1 at 100 ma g−1 after 200 cycles. a 99.6% coulomb efficiency was achieved with 545.1 mahg-1 at 1 ag−1 after 1000 cycles. the research resulted not only in providing high-performance lithium materials but also presented an idea to create heterostructures by modifying various metal oxides of mxene nanosheets and using them as lithium-ion batteries [62]. zou et al. [63] synthesized a mxene/ag composite product (ti3c2(oh)0.8f1.2) by directly reducing agno3 aqueous solution in the presence of mxene. the results demonstrated that the reduction of ag in mxene solutions was associated with the presence of low-valence ti. the recovery capacity at 1 ℃ was 310 mahg−1, at 10 ℃ it was 260 mahg−1 and the recovery capacity at 50 ℃ was 150 mahg−1. moreover, the composite could withstand more than 5000 cycles at 1 to 50 ℃ without decay (see figure 11a). figure 11. (a) synthesis of mxene/ag composites for high-speed lithium storage with ultra-long cycle life [63]; (b) schematic diagram of the preparation process of mxene@sinps@nc foam composites [64]. metal-based anode materials such as sb, sn, and bi have received great attention in battery applications due to their high electrical conductivity and high energy density. however, the large volume expansion during the alloying process makes the work very fast. tian et al. synthesized sb, sn, and bi on mxene sheets via a simple one-step electrodeposition process in a green ethylene glycol system. a strong, flexible, self-contained, and binder-free anode for potassium-ion batteries was prepared. the coating ensured a short diffusion for potassium ions and provided a buffer for the volume change during potassiumization/depotassiumization. characterization and application of nanomaterials 2024, 7(2), 6348. 21 efficient and flexible mxene materials could then be used as current generators, providing wide electrical paths to facilitate the transport of electricity while cycling and adapting to changing volumes. mxene@sb resulted in a high reversible capacity of 516.8 mahg−1, a peak value of 270 mahg−1 at 500 ma g−1, with the fading of only 0.042% per cycle [64]. lithium-ion mxene/silicon electrode. organo-silicon electrodes are one of the best energy storage electrodes due to their unique capacity, non-toxicity, and raw materials. however, silicon expands in volume during cycling, resulting in poor electrochemical cycling performance [65]. the volume expansion that occurs during lithiation/delithiation is the cause of cracking and breakage in the electrode. the combination of silicon and mxene can be used to produce excellent electrochemical electrodes for lithium-ion batteries. the improved cycling performance of silicon/mxene electrodes can be attributed to the excellent thermal stability of mxene. titanium-based mxene (ti3c2tx) nanosheets have become useful materials for low-voltage electronics (si) due to their unique charge (lithium) storage capacity and rich abundance of silicon (si). si/ti3c2tx composite material has been shown to have a wide and stable cycle time, good performance, and high economic value. to better understand and improve the electrochemical performance of composites, a review by jiang et al. focused on the electrochemical processes occurring in si/mxene composites [65]. silicon (si) is one of the most promising materials for lithium-ion batteries (lib) due to its unique properties. however, low transmission efficiency and large voltage fluctuations block the development of silicon-based anodes. zhang et al. [66] created a 3d structure containing silicon nanoparticles (sinps) anchored on nitrogen-doped carbon (nc) foam and coated with an mxene layer (mxene@sinps@nc foam) (see figure 11b), which could act as a self-standing si-based anode for highperformance libs. the design of the nc foam was based on the conductivity principle, and the mxene-based layer provided the advantage of electrons/ion diffusion while allowing the anode to adapt to large changes in si volume during lithiation/desalination. the independent mxene@sinps@nc foam electrode had a capacity (1658 mahg−1 after 100 cycles at 0.1 ℃) and a residual capacity (857 mahg−1 after 500 cycles at 0.5 ℃). moreover, the battery developed entirely using mxene@sinps@nc foam //ncm111 exhibited a high gravimetric energy density (433 wh kg−1). this mxene@sinps@nc foam anode demonstrated good electrical properties. silicon (si) is considered one of the candidates that can replace graphite in anodes. lithium-ion batteries store greater energy and, therefore, improve returns. however, the high mechanical stress caused by its high volumetric variation during charge and discharge cycles, added to its low electrical conductivity, has impeded its wide use. for this reason, silicon-based composites are studied to find out their commercial viability. mxene ti3c2 is a two-dimensional material whose good mechanical resistance and conductivity can contribute to solving the problems of si anodes. the results revealed that the addition of ti3c2 particles to electrodes could reach 80% and 89% of their theoretical capacity when ti3c2 represents 20% and 40% of the mass of the active electrode material, respectively, compared to the 56% achieved by the pure si electrode. this improvement is explained by a reduction in characterization and application of nanomaterials 2024, 7(2), 6348. 22 the resistance to charge transfer observed in the eis results. finally, the electrode with 20% by weight of ti3c2 (640 mahg−1) obtained the best specific capacity after 100 charge and discharge cycles than obtained by the pure si electrode (572 mahg−1) [67]. flexible pressure sensors are one of the most important sensors in electronic skin (e-skin), robotics, and medicine. however, sensors are still complex and expensive due to power consumption, unreliable operation, and manufacturing processes. ti3c2tx is the most studied mxene in the field of pressure sensing, with good mechanical and electrical properties, excellent hydrophilicity, and flexibility. it increases the sensitivity of pressure sensors and the efficiency of the electrode process and continues to use pressure measurements in various areas, such as electrical skin elasticity. the mxene can be used in pressure sensors, which include piezoresistive, capacitive, piezoelectric, triboelectric, and potentiometric switching technologies. integration of various devices is also possible [68]. 5.3.2. mxene promoting beyond lithium battery the lithium-based battery is undoubtedly the most studied and analyzed battery in scientific literature. however, lithium is not abundant in the earth’s crust and will soon suffer the same fate as the overconsumption of fossil fuels, forcing us to look beyond lithium. fortunately, research on other metal-ion batteries (sodium, potassium, aluminum, magnesium, zinc, etc.) has rapidly increased, and much has been borrowed from research on lithium-ion batteries. although their theoretical capacity is lower than that of lithium [69], they can reduce the cost of lithium resources by serving as another energy store. the lithium-ion battery has been a leader in the electronics industry and research and development for nearly two decades. due to concerns about the cost and future availability of lithium, sodiumion batteries (sibs) and other new technologies are emerging as candidates for sustainable energy. research in this technology is increasing, with a focus on developing new cathode and anode materials that can improve cycle stability, operating costs, and energy. 2d materials are promising in many energy-related applications, especially energy storage, due to their ability to transport ions between layers and over large areas, enhanced ion adsorption, and rapid surface redox reactions [70]. tang et al.’s [70] potassium metal batteries are considered attractive alternatives to lithium-ion batteries. however, uncontrollable dendrite growth of potassium metal anodes limits their practical applications. functionalization of the potassium anode has been reported to be achieved by encapsulating the metal in a titanium-free, nitrogen-containing mxene/carbon nanotube freestanding scaffold. high and fast electrical conduction in the scaffold helps reduce density and current flow during coating/stripping. additionally, theoretical calculations and experimental studies confirmed that the “potassium-loving” form of mxene can cause potassium nucleation and add potassium during exposure to stabilize the products. as a result, the produced potassium metal anode exhibits dendrite-free morphology, high coulomb efficiency, and a long lifetime during the plating/stripping process. such anodes also improve the electrochemical performance of potassium-sulfur batteries compared to bare metal anodes. the potential of ti2n monolayers and their ti2nt2 derivatives (t = o, f, and oh) as characterization and application of nanomaterials 2024, 7(2), 6348. 23 anode materials for lithium-ion and ultra-lithium-ion batteries were investigated by first-principle calculations. the single layer exposed and removed is a very good metal material. the diffusion barriers of the bare ti2n monolayer were approximately li+ 21.5 mev, na+ 14.0 mev, k+ 7.0 mev, mg2+ 75.9 mev, and ca2+ 38.0 mev. the 2d functional groups of ti2nt2 increased the conduction effect by approximately 1-fold. the calculated capacity of single cations of ti2n and ti2nt2 was close to conventional graphite anodes in lithium-ion batteries. in comparison, the mg2+ capacity of ti2n and ti2nt2 exceeded 2000 mahg-1 due to the twoelectron reaction and multilayer adsorption of mg2+. a comparison of the electrical properties of ti2n and ti2c showed that ti2n is a better material than ti2c due to its sensitivity to various cations [24] (see figure 12a). the heavy reliance on libs has led to growing concerns about the sustainability of lithium and alternative metals and ethical issues in mining. developing alternative energy storage technologies beyond lithium has become an important part of the world’s energy research portfolio [71]. other technologies, from electric transportation to renewable energy to large-scale energy storage, play an important role in developing energy storage for the future. considering their chemical and economic benefits, potassium ion batteries (pibs) are promising and are becoming strong competitors to libs and sibs in many forms. however, many people do not understand the process by which potassium is deposited in materials and how it differs from lithium and sodium, and the material liquid interface chemistry in pibs is also not fully understood. therefore, there are still some important problems in the commercialization of pib technology. 5.4. supercapacitor supercapacitors have attracted significant attention as promising successors to traditional energy storage devices due to several key advantages like higher power density, faster charge-discharge cycles, and greater energy density over batteries and conventional dielectric capacitors [1,22]. there are two main types of supercapacitors based on their working principles: electrochemical double-layer capacitors (edlc), pseudocapacitors, and hybrid capacitors. edlcs store energy by the adsorption/desorption of ions on the surface through the electrical double layer, whereas pseudocapacitors store energy through surface redox reactions [4]. the energy density (e) of supercapacitors is governed by the formula e = cv2/2, where c is capacitance and v is voltage. therefore, enhancing capacitance and voltage window results in higher energy density supercapacitors. voltage remains relatively constant for a specific electrolyte, so increasing capacitance is crucial for overall capacitor performance improvement [2,22]. as a result, there is significant research interest in enhancing capacitance to improve supercapacitor performance. mxene exhibits significant potential as an electrode material for batteries and supercapacitors, due to its remarkable electrochemical properties resulting from the presence of transition metal carbide/nitride components and its high electrical conductivity [28]. mxenes typically originate from the max phase, which follows the general formula mn+1axn. here, m represents an early transition metal, a is a group of 13 or 14 elements, and x consists of c and/or n; n is generally 1–3. mxene characterization and application of nanomaterials 2024, 7(2), 6348. 24 formation occurs through the chemical etching of the a layer within the max phase using fluoride ion-containing solutions such as hydrofluoric acid (hf) [11]. following the etching process, the configuration of mxene may exhibit significant variations, depending on the specific post-treatment method employed. after selectively etching the a layer with hf, the resultant powder manifests a multilayered mxene structure [72]. in this structure, the atoms of the a layer, predominantly al or si, are substituted by terminal groups such as –o, –oh, and/or –f, leading to a phase denoted as mn+1xntx. otherwise, when intercalants like li+ ions are used instead of etchants, sonication yields a colloidal phase comprising fewlayered or monolayer-exfoliated mxene nanosheets. these exfoliated mxene nanosheets reveal a significantly expanded surface area due to the removal of the a layer spacing. generally, the use of alkali metal ions as intercalants results in an enlargement of the surface area by at least a factor of two compared to that of the multilayered mxene [33,34,73]. upon the exfoliation of mxene nanosheets, stacked layers will probably form in mxene films, driven by impromptu attractive interactions such as van der waals forces and hydrogen bonding [36]. mxene films offer the benefits of flexibility, large conductivity, and surface hydrophilicity, making them favorable for enhanced electrochemical processes. consequently, freestanding films based on mxene have been widely employed as active materials in supercapacitors and various electrochemical electrodes [37–38,74]. while mxene films possess numerous advantages, their applications are limited due to the lack of regulated film-forming processes [75]. while monolayer mxene nanosheets allow for the optimization of theoretical surface area and electrochemical surface activity, processes primarily involving layer-stacking film formation compromise the intrinsic properties anticipated from monolayers, thus affecting the performance of electrochemical applications [22,76]. couly et al. proposed a simple approach to fabricate asymmetric microsupercapacitors using mxene. these micro-supercapacitors are modifiable, free of binder, and current-collector-free. the method involved employing a customized mask and an expandable spray coating technique on a flexible and transparent substrate [77]. the electrode comprised titanium carbide mxene (ti3c2tx) and reduced graphene oxide, both possessing a 2d layered structure that facilitated rapid ion diffusion within the interdigitated electrode framework. this asymmetric microsupercapacitor operated within a 1 v voltage window and retained 97% of its initial capacitance after ten thousand cycles. furthermore, it demonstrated an energy density of 8.6 mw hcm−3 at a power density of 0.2 w cm−3. moreover, these microsupercapacitors exhibited remarkable flexibility under mechanical bending. by leveraging the capacity of ti3c2tx—mxene electrodes to operate at negative potentials in aqueous electrolytes, it was demonstrated that employing ti3c2tx as a negative electrode and reduced graphene oxide as a positive electrode in asymmetric configurations represented a viable approach to enhance both the energy and power densities of micro-supercapacitors. rakhi et al. [78] developed 2d ti2ctx mxene nanosheets by selectively etching the al layer from the ti2alc max phase, utilizing hf. the hexagonal symmetry of the parent ti2alc max phase was preserved in the mxene sheets. an extensive investigation was conducted to evaluate the influence of various post-etch characterization and application of nanomaterials 2024, 7(2), 6348. 25 annealing atmospheres, including argon (ar), nitrogen (n2), a combination of nitrogen and hydrogen (n2/h2), and air, on both the structure and electrochemical characteristics of the mxene nanosheets. it was found that the mxene sheets displayed changes in structure, morphology, and electrochemical behavior following annealing in air compared to the hf-treated max phase. in contrast, samples subjected to annealing in ar, n2, and n2/h2 atmospheres maintained their initial morphology. a substantial enhancement was observed in the supercapacitor performance of the annealed samples, particularly in those annealed in ar, n2, and n2/h2 atmospheres. in a symmetric two-electrode setup, the mxene sample annealed in an n2/h2 atmosphere exhibited superior capacitive performance, boasting a specific capacitance of 51 fg−1 at 1 ag−1 and an impressive rate performance of 86%. this notable enhancement in electrochemical performance post-annealing was attributed to several factors, including the increased carbon content, decreased fluorine content on the surface, and the preservation of the original two-dimensional layered morphology, ensuring optimal access of the aqueous electrolyte to the electrodes. wen et al. [79] introduced a novel electrode material for supercapacitors, nitrogen-doped two-dimensional mxene (n-ti3c2tx), through annealing of ti3c2tx in ammonia post-etching. through precise control of annealing temperatures within the range of 200 ℃ to 700 ℃, the concentrations of nitrogen in n-ti3c2tx materials were made ranging from 1.7% to 20.7%. the incorporation of nitrogen as a heteroatom into the ti3c2tx structure led to an expansion of the c-lattice parameter in mxene sheets, from 1.92 nm in ti3c2tx to 2.46 nm in n-doped counterparts after treatment with ammonia at 200 ℃. the resultant doped mxene materials exhibited significantly enhanced electrochemical capacitance of 192 f/g in 1 m h2so4 and 82 f/g in 1 m mgso4 electrolyte, under optimized conditions. these values represented a substantial rise in the capacitances, as observed for undoped ti3c2tx materials, which recorded 34 f/g in 1 m h2so4 and 52 f/g in 1 m mgso4 (see figure 12b). characterization and application of nanomaterials 2024, 7(2), 6348. 26 figure 12. (a) first calculations of ti2n and ti2nt2 (t=o, f, oh) monolayers as anode materials for lithium-ion batteries and other batteries [24]; (b) nitrogen-doped ti3c2tx mxene electrodes for high-performance supercapacitors [79]. 5.5. biomedical applications levitt et al. [80] fabricated free-standing ti3c2tx mxene/carbon nanofiber electrodes by electrospinning to combine ti3c2tx mxene flakes with polyacrylonitrile (pan), followed by carbonization. through this approach, delaminated mxene flakes could be incorporated within carbon nanofibers, resulting in fiber mats that could be employed as electrodes. notably, these composite electrodes exhibited superior sturdiness compared to their coated counterparts. in the spinning dope, mxene flakes were introduced into pan solutions at a weight ratio of 2:1, resulting in fiber mats containing mxene up to 35 wt%. the resulting composite electrodes demonstrated an impressive areal capacitance of up to 205 mf cm−2 at 50 mv s−1, nearly three times higher than that of pure carbonized pan nanofibers, which registered at 70 mf cm−2 under the same conditions. furthermore, in comparison to electrospun nanofibers spray-coated with ti3c2tx, these composite fibers exhibited a twofold increase in areal capacitance at 10 mv s−1 (refer to figure 13a). this versatile technique holds promise beyond energy storage applications, as it can be extended to generate mxene composite fibers using a variety of polymers. such applications may include filtration, adsorption, and electrocatalysis, where fibers with high aspect ratios, accessible surface areas, and porosity are highly desirable. 5.6. mxene as gas sensors kim et al. [81] introduced chemical sensors with exceptional gas-sensing characterization and application of nanomaterials 2024, 7(2), 6348. 27 characteristics through the synthesis of ti3c2tx (see figure 13b). these sensors exhibited remarkable selectivity towards hydrogen-bonding gases compared to acidic gases. also, an empirical limit of detection (lod) of 50 ppb was achieved and a theoretical lod reaching the sub-ppb level for volatile organic compounds (voc), making the lowest detection limits among gas sensors utilizing 2d materials and functioning at room temperature without any pretreatment. furthermore, the signalto-noise ratio (snr) of ti3c2tx sensors surpassed that of all other 2d materials by up to two orders of magnitude. the remarkable sensitivity of ti3c2tx sensors could be attributed to both the metallic conductivity of the core channels and the robust adsorption energy of the surface functional groups (figure 13b) [82]. figure 13. (a) electrospun mxene/carbon nanofibers as supercapacitor electrodes [81]; (b)schematic representation of ti3c2tx films [82]. 5.7. sensors in biomedical applications the distinctive 2d layered structure and remarkable array of physical and chemical attributes exhibited by mxenes, such as hydrophilic nature, biocompatibility, adeptness in light-to-heat conversion, and mechanical resilience, make them promising candidates across diverse biomedical domains. these applications encompass sensor technologies, bioimaging modalities, tissue engineering approaches, and advanced drug delivery systems. biosensors upon their discovery, mxenes swiftly ascended as a profoundly promising category of 2d materials. their notable characteristics, including a substantial specific surface area, elevated conductivity, near-infrared absorption, and ease of functionalization, make them exceptionally well-suited for biomedical and characterization and application of nanomaterials 2024, 7(2), 6348. 28 environmental applications (tables 1 and 2) [83]. in in-vitro experiments, mxenes exhibit toxicity against bacterial and animal cells, primarily due to mechanisms such as oxidative stress and the mechanical damage inflicted on cell membranes by the sharp edges of the nanosheets (figure 14a). figure 14. (a) schematic representation of cytotoxic effects of mxene on bacterial cells [83]; (b) schematic representation of (a) in vivo computed tomography imaging of the ta4c3 mxene composite (b) disintegration of mnox components from mnox/ta4c3 under a specific tumor microenvironment for contrast-enhanced t1-weighted magnetic resonance imaging (c) in vivo photoacoustic imaging [84]. table 1. biosensors for medicinal use [83]. sensor composition detectable analyte sensor type sensor efficiency mxene-ti3c2 hemoglobin electrochemical biosensors detection limit of 20 nm mxene-ti3c2 hemoglobin electrochemical biosensor linear range of 0.5–11,800 μm, detection limit of 0.12 μm gox/au/ti3c2txmxene/nafion/gce glucose electrochemical biosensor (amperometric) detection limit of 5.9 μm ti3c2-mxene functionalized with aminosilane carcinoembryonic antigen (cea) electrochemical biosensor linear detection range of 0.0001–2000 ng ml−1 with sensitivity of 37.9 µa ng−1ml cm−2 per decade ti3c2 human papillomavirus (hpv) optical biosensor detection limit of 100 pm ti3c2tx mxene and phosphomolybdic acid embedded with polypyrrole osteopontin aptamer biosensor 0.98 μg/l ti3c2tx/ptnp modified gce ascorbic acid, dopamine, uric acid, acetaminophen electrochemical biosensor nm level oh-terminated ti3c2 label-free singlenucleotide in human urine electrochemiluminescence biosensor detection limit of 5 nm characterization and application of nanomaterials 2024, 7(2), 6348. 29 table 1. (continued). table 2. biosensors for environmental use [83]. sensor composition detectable analyte sensor type sensor efficiency mo2ti2alc3/mwcnt bisphenol a electrochemical biosensor (amperometric) 0.01–8.50 μm mxene-ti3c2 tyrosinase electrochemical biosensor linear range from 0.05 to 15.5 μm l−1, detection limit of 12 nm l−1 mxene-ti3c2 ag+and mn2+ optical sensors range of 0.1–40 μm for ag+, detection limits of 9.7 nm; 0.5–60 μm for mn2+ions, ti3c2tx (mxene)-modified glassy carbon electrode bro3− electrochemical biosensor linear response from 50 nm to 5 μm, detection limit of 41 nm hydroxyl terminated alkti3c2 modified gce cd(ii), pb(ii), cu(ii) and hg(ii) electrochemical biosensor detection limit of 0.098, 0.041, 0.032 and 0.130 μm for cd(ii), pb(ii), cu(ii) and hg(ii), respectively ache-chit/ti3c2-mxene/au nps/mno2/mn3o4/gce organophosphorus pesticides electrochemical biosensor concentration range (10−12–10−6m), limit of detection (1.34 × 10−13m) ache/cs-ti3c2tx/gce organophosphorous pesticides (malathion) electrochemical biosensor concentration range of 10−14–10−8m, limit of detection 0.3 × 10−14m ache/ag@ti3c2tx organophosphorous pesticides (malathion) electrochemical biosensor concentration range of 10−14–10−8 m ti3c2tx carbamate pesticides (methiocarb and diethofencarb) electrochemical biosensor detection limits were 0.19 μg ml−1 and 0.46 μg ml−1 for methiocarb and diethofencarb respectively cds/mxene-nh2/znsno3 cd2+, perfluorohexane photoelectrochemical biosensor linear range of 0.008–100 nm, detection limit of 4.21 pm mnmoo4-mxene-gce hydroquinone, catechol electrochemical biosensor linear response from 5 nm to 65 nm, detection limit of 0.26 nm for hydroquinone and 0.30 nm for catechol sensor composition detectable analyte sensor type sensor efficiency ti3c2tx/prussian blue glucose and lactate in sweat electrochemical biosensor (amperometric) sensitivities of 35.3 µa mm−1cm−2 for glucose and 11.4 µa mm−1cm−2 for lactate mxene-ti3c2tx incorporated with a dialysis microfluidic chip urea, uric acid, and creatinine electrochemical biosensor mxene-ti3c2tx modified screen-printed electrode acetaminophen (acop), isoniazid (inz) electrochemical biosensor linear ranges from 0.25 to 2000 μm for acop and 0.1–4.6 mm for inz. the detection limits of acop and inz were 0.048 μm and 0.064 mm ti3c2tx/zif-8 hiv-1 protein electrochemical biosensor detection limit 0.3 fm au/ti3c2t/hb5 her2-positive cancer cells electrochemical cytosensor linear range of 102–106 cells/ml, detection limit of 47 cells/ml chit/chox/ti3c2tx cholesterol electrochemical biosensor concentration of cholesterol ranging from 0.3 to 4.5 nm, detection limit of 0.11 nm, sensitivity of 132.66 μa nm−1cm−2 ti3c2tx mxene/lbg/pdms cortisol electrochemical impedimetric immunosensor linearity 0.01–100 nm, detection limit 88 pm pei-ru@ti3c2@aunps sars-cov-2 rdrp gene electrochemiluminescent biosensor detection limit of 12.8 am zno/ti3c2 glucose electrochemical enzymatic biosensor sensitivity 29 μa mm−1cm−2, limit of detection ≈ 17 μm, linear detection range 0.05–0.7 mm) characterization and application of nanomaterials 2024, 7(2), 6348. 30 the interest in early detection of cancer has grown in the context of bioimaging and biosensing, owing to their capacity to unveil intricate cellular processes and a diverse array of diagnostic indicators. ti3c2 is the most extensively researched mxene nanostructure in applications related to bioimaging and biosensing, while ta4c3 mxene is commonly employed for multimodal imaging. the presence of tantalum (ta) in the ta4c3 mxene, characterized by a high atomic number and a notable x-ray attenuation coefficient, enables its utilization in ct imaging without requiring supplementary contrast agents. this streamlines the setting up of multimodal imaging. regarding biosensing, platforms utilizing mxenes have been developed for various techniques, including electrochemistry, fluorescence, surface plasmon resonance, surface-enhanced raman scattering, and colorimetric and chemiluminescence-based biosensing [84] (see figure 14b). surface modification and functionalization are pivotal in augmenting the characteristics of materials based on mxene. following surface modification, mxene-based materials have been propelled into the spotlight and have found widespread application in various fields, such as biomedicine, energy, and the environment. specifically, this includes biosensing, drug delivery systems, bioimaging, photothermal therapy, antibacterial agents, and theragnostic nanoplatforms within the realm of biomedical applications [85]. 5.8. flexible pressure sensor mxenes have found application in different sensing scenarios because of their adjustable surface functionalities. sensors based on mxenes have proven effective in detecting a range of pollutants, exhibiting a lower detection limit and impressive selectivity/sensitivity [85,86]. the domains of electronic skin, human-machine interaction, and health monitoring demand pressure sensors that are both flexible and highly sensitive. however, most microstructure designs employed for creating pressure sensors with high performance involve intricate preparation processes. yin et al. [87] obtained a 3d porous structure of mxene/polyaniline (pani) foam through the application of a steam-induced foaming method. utilizing this structure, a flexible piezoresistive sensor was manufactured. it demonstrated remarkable characteristics, including high sensitivity (690.91 kpa−1 quick response and recovery time of 106/95 ms, and excellent fatigue resistance (10,000 cycles). the pressure sensor, derived from mxene/pani foam, could rapidly perceive subtle pressure changes. it was found suitable for applications in human activity and supervision of health [86,87]. as composite materials find extensive use in aeronautic structures, research on composite material repair methods is becoming increasingly comprehensive. however, owing to the unique nature of the composite materials, the visual efficacy of repairs and the service condition of the composite repaired structure is challenging, necessitating highly sensitive piezoresistive strain sensors. wang et al. [88] introduced an innovative mxene film sensor technology capable of real-time and in-situ health monitoring of composite structures. the proposed method enabled the creation of mxene thin films with exceptional properties. mxene sensors were produced and organized into arrays and integrated into the composite repair structure to monitor strain across various points. the piezoresistive reaction of the mxene characterization and application of nanomaterials 2024, 7(2), 6348. 31 sensor was acquired, and the primary operational mechanism was elucidated. the strategic arrangement of mxene sensors in the repaired structure enhanced the monitoring process, offering a more thorough understanding of the failure mechanism. this monitoring approach, utilizing mxene sensors, can be used for investigating the health status of composite repair structures under both tensile and compression conditions [88] (see figure 15). figure 15. monitoring of repaired composite structure [88]. sen mechanism of mxene sensor and sensor array arrangement of composite material repair structure. despite possessing notable properties such as a large surface area, biocompatibility, metallic conductivity, hydrophilicity and tunable size, the application of mxene in biomedical settings is constrained by its limited stability in physiological environments, absence of sustained and controlled drug release, and low biodegradability. these challenges have prompted consideration for the adoption of mxene/polymer nanocomposites. the presence of functional groups on the mxene surface allows for polymer functionalization. hence, these mxene nanocomposites functionalized with polymers showcase notable features such as high photothermal conversion efficiency, selectivity, responsiveness to stimuli, electron sensitivity, enhanced antibacterial properties, and more. these characteristics make them suitable for use in biomedical applications, including photothermal therapy, drug delivery, diagnostic imaging, biosensing, bone regeneration, and antibacterial activities [89] (see figure 16). characterization and application of nanomaterials 2024, 7(2), 6348. 32 figure 16. mxene-polymer composites in biomedical applications [89]. 5.9. drug delivery system the healing of chronic wounds is a fundamental and significant concern in medical and healthcare domains, and in recent times, hydrogel systems have emerged as promising carriers for drug delivery in the context of wound management, which is responsive to stimuli. yang et al. [90] introduced a hydrogel system based on 2d mxene, designed for effective drug delivery with photoand magnetic-responsive capabilities, specifically tailored for the treatment of deep chronic wounds. the smart and responsive drug delivery system using mxene consisted of magnetic colloids enveloped by mxene and dual-network hydrogels made from poly (n-isopropyl acrylamide) and alginate. it exhibited versatile responsiveness and precise drug release mechanisms, effectively mitigating the toxic side effects of drugs and enhancing the wound healing process. the real-world efficacy of the mxene-based hydrogel drug delivery system was validated through its application in treating full-thickness cutaneous wounds and subcutaneous infected wounds in a rat model, highlighting its substantial potential in clinical wound healing management and other relevant biomedical domains. 5.10. mxene in cancer treatment typical approaches to cancer treatment encompass surgical procedures, chemotherapy, and radiotherapy involving the use of anti-cancer medications. recently, mxenes have generated considerable attention for their potential use as drug carriers. this is attributed to their planar structure, abundant surface functional groups, biocompatibility, and negatively charged surface. even though nanosized ti3c2, the pioneering mxene for drug delivery vehicles, exhibits an enhanced permeability and retention effect that allows it to accumulate at the tumor site, surface modification is essential. this is because it tends to restack under physiological conditions. the tumor microenvironment, which typically has a lower ph compared to normal tissues, offers an opportunity for controlled drug release, as the presence of h+ ions can disrupt the electrostatic interaction between the drug and mxene. additionally, controlled drug release can be achieved through near-infrared radiation stimulation [91]. characterization and application of nanomaterials 2024, 7(2), 6348. 33 microand nanosystems incorporating mxene can be utilized for precise administration of anticancer drugs or therapeutic agents, offering the benefits of minimal toxicity and excellent biocompatibility. confirming the effective uptake of therapeutic chemicals from the bloodstream to the intended site presents a significant challenge in systemic disposition. the vascular endothelial cell, serving as a barrier between organs and blood, emerges as a crucial focal point in this regard. by incorporating mxene into composites and subsequently functionalizing or modifying them with appropriate functional groups or agents, their loading capacity, biocompatibility, and bioavailability can be enhanced [92]. mxene-based microand nanosystems, following surface functionalization or modification with bioactive or biocompatible agents, have been employed for targeted delivery of anticancer drugs or therapeutic agents in cancer therapy (figure 17) [92]. figure 17. mxene with potential biomedical applications [92]. liu et al. [93] described the creation of a drug delivery platform for the efficient loading of the chemotherapeutic doxorubicin (dox) (see figure 18). this platform exhibited dual drug release modes, responding to both near-infrared laser stimulation and variations in ph. due to the surface modification involving thiol polyethene glycol aldehyde chains (sh-peg-cho) linked to the mxene through gold nanoparticles, the mxene@au-peg-dox system exhibited favorable photothermal stability, biocompatibility, and tissue compatibility. furthermore, using the effective photothermal conversion capabilities of both gold particles and mxene, it demonstrated a synergistic approach to combine photothermal ablation with chemotherapy to treat tumors. the enhancement of mxene through surface modification involving au and peg served not only to enhance the photothermal characterization and application of nanomaterials 2024, 7(2), 6348. 34 stability of the drug delivery system and the biocompatibility of the nanocomposites but also to regulate drug release through the formation of schiff base bonds. consequently, this, in turn, led to improved targeted therapeutic effects. figure 18. (a) illustrative diagram of fabrication of mxene and mxene@au nanosheets; (b) modification of mxene@au surface using thiol polyethylene glycol aldehyde chains (sh-peg-cho), and dox loading; (c) illustrative representation of mxene-based drug delivery system for near-infrared laser-triggered and phresponsive drug release in tumor tissue [93]. a drug carrier with targeting capabilities for folate receptors was developed by liu et al. [93], leveraging the plentiful surface functional groups and outstanding biocompatibility of mxenes. the drug carrier exhibited a drug-loading capacity of up to 69.9%, along with an extended drug release duration of up to 48 h. the findings indicated a substantial release of dox in a ph 4.5 pbs solution. in comparison to the free drug, mxenes-fa-sp@dox demonstrated increased cell inhibition and prolonged drug efficacy at lower concentrations (below 10 μg mg−1). this drug delivery system can be used for the treatment of malignant tumors. dong et al. [94] synthesized drug-loaded mxene/agarose hydrogel (mxene@hydrogel). initially, superior photothermal conversion efficiency and stability were achieved by preparing two-dimensional mxene nanosheets. subsequently, these mxene nanosheets, along with the therapeutic drug, were integrated into a low-melting-point agarose hydrogel network to form the drug-loaded mxene/agarose hydrogel (mxene@hydrogel). incorporating a low concentration of mxene (20 ppm) facilitated rapid heating of the mxene@hydrogel to 60 ℃ under near-infrared (nir) irradiation, prompting its melting and subsequent release of encapsulated drugs. control over drug release kinetics and on/off functionality could be easily characterization and application of nanomaterials 2024, 7(2), 6348. 35 modulated by adjusting agarose concentration, mxene concentration, light intensity, and exposure duration. moreover, doxorubicin, an anticancer drug, maintained its efficacy upon release from the mxene@hydrogel network under nir irradiation. with its outstanding biocompatibility, this nir-responsive mxene@hydrogel represents a promising strategy for developing a smart hydrogel-based drug delivery system tailored for localized cancer therapy. a nanoparticle system (mxene-tk-dox@pda) sensitive to reactive oxygen species (ros) was engineered for efficient drug delivery in chemotherapy and applications in antibacterial therapy by zhang et al. [95] (see figure 19). the surface of (3-aminopropyl) triethoxysilane (aptes)-functionalized mxene served as a platform for conjugating dox via a ros-cleavable diacetyl thioketal (tk) linkage. following this, the mxene nanosheets were coated with ph-responsive polydopamine (pda) to serve as a gatekeeper. this incorporation of pda enhanced the biocompatibility and stability of the mxene-tk-dox@pda nanoparticles. the ultrathin planar structure of mxene-tk-dox@pda nanoparticles, with a compact lateral size of around 180 nm, showcased exceptional photothermal conversion efficiency, superior stability in photothermal applications, and a notable extinction coefficient of 23.3 lg−1cm−1 at 808 nm. the synthesized nanoparticles demonstrated effective release of dox, responsive to both ros and ph, attributed to the cleavage of the thioketal linker in mxene-tk-dox@pda. furthermore, the mxene-tkdox@pda nanoparticles exhibited potent antibacterial effects against both gramnegative escherichia coli (e. coli) and gram-positive bacillus subtilis (b. subtilis) within a 5-hour timeframe. figure 19. mxene-based nanoparticles as drug delivery carriers [95]. using a layer-by-layer approach, a drug delivery system with ph/near-infrared responsiveness was created by wu et al. [96]. this system is comprised of hollow hydroxyapatite (hap), chitosan (cs)/hyaluronic acid (ha) multilayers, gold nanorods (aunrs), and mxene. multilayers of chitosan/hyaluronic acid were applied to the hollow hydroxyapatite (hap) surface to mitigate the abrupt release of dox during the initial delivery phase. integration of mxenes and gold nanorods characterization and application of nanomaterials 2024, 7(2), 6348. 36 (aunrs) into the hybrid matrix notably enhanced the photothermal conversion efficiency of the microcapsules. the exceptional ph-/nir-responsive drug delivery properties of hap/cs/ha/mxene/aunrs microcapsules were demonstrated through the disruption of electrostatic forces among chitosan/hyaluronic acid multilayers, the dissolution of hap under acidic conditions, and the synergistically enhanced photothermal effect between mxene and aunrs. liu et al. [97] developed a novel catalyst heterostructure (mxene/conws) activated by nir radiation, comprising 2d mxene and 1d cobalt nanowires (conws), for combating bacteria without the use of drugs (see figure 20). the incorporated conws swiftly captured photogenerated electrons from ti3c2 mxene nanosheets, thus mitigating the recombination of electron-hole pairs and enhancing carrier transfer under 808 nm nir illumination, leading to increased reactive oxygen species (ros) production. moreover, the 2d/1d heterostructure exhibited a significantly amplified photothermal effect due to synergistic interactions between plasmonic conws and the mxene semiconductor. coatings of this heterostructure on orthopaedic implants demonstrated antibacterial efficacy exceeding 90% against both gram-positive and gram-negative bacteria within a mere 20-minute exposure period. additionally, in vitro assessments indicated acceptable cytocompatibility of mxene/conws heterojunctions. figure 20. schematic representation of mxene/cowns activation and action on bacteria [97]. 5.11. recent advanced progress in biomedical applications of mxenes owing to the captivating physicochemical attributes of mxenes, these materials and their blends have been engineered for diverse biomedical applications. ti3c2tx was the first mxene to be identified, and it soon emerged as the most extensively researched mxenes. it demonstrated outstanding catalytic characteristics in the field characterization and application of nanomaterials 2024, 7(2), 6348. 37 of photocatalytic hydrogen evolution reaction. nevertheless, the characteristics of ti3c2tx were significantly influenced by its surface functional groups and associated materials. in particular, ti3c2tx terminated with oxygen displayed the most optimal catalytic activity. its efficacy could also be enhanced by combining it with other photoactive materials like tio2, zno, mos2, ws2, cds, and graphitic carbon nitride. these composite materials not only enhanced light absorption but also improved charge separation and active sites, thereby enhancing the overall performance of ti3c2tx under uv-visible light irradiation [98] (see figure 21). koyappayil et al. [99] modified ti3c2tx mxene nanosheets by incorporating β-hydroxybutyrate dehydrogenase to create a biosensor for amperometric detection of βhydroxybutyrate. mxene demonstrated its excellence as an immobilization matrix, exhibiting strong compatibility with the enzyme β-hydroxybutyrate dehydrogenase. the biosensor utilizing mxene, working optimally at a potential of −0.35 v (vs. ag/agcl), exhibited a broad linear detection range (0.36 to 17.9 mm), a sensitivity of 0.480 μa mm−1 cm−2, and a low detection limit (45 μm). successful application of this biosensor was demonstrated in accurately determining β-hydroxybutyrate levels in real serum samples, even when spiked with additional compounds. figure 21. titanium carbide mxene in hydrogen production [98]. 5.12. cytocompatibility and cytotoxicity evaluations of mxenes in contemporary biomedical research, mxene materials are increasingly employed. zhang et al. [100] conducted experiments to assess the osteogenic potential of ti3c2tx films, crucial for bone tissue engineering. results from cellular studies revealed strong compatibility with cells and a propensity to stimulate osteogenic differentiation in vitro. furthermore, the implantation of mxene films into rat subcutaneous and calvarial defect sites showcased remarkable biocompatibility, osteoinductive properties, and the ability to facilitate in vivo bone regeneration. examining the potential risks associated with ti3c2tx mxene exposure to the circulatory system, huang et al. [101] investigated its cytocompatibility with red blood cells (rbcs) and human umbilical vein endothelial cells (huvecs). results indicated excellent compatibility even at high concentrations, with minimal hemolysis observed. even at a high concentration of 200 μg/ml, ti3c2tx induced minimal hemolysis at 0.8%, whereas go at the same treatment concentration resulted in a considerably higher hemolysis rate of 50.8%. the structures of rbcs were left undisturbed. the presence of fully covered surface-terminating –o and – oh groups in ti3c2tx resulted in a highly hydrophilic surface, impeding its influx characterization and application of nanomaterials 2024, 7(2), 6348. 38 into the inherently hydrophobic interior of the cell membrane (figure 22). the remarkable compatibility of ti3c2tx nanosheets with cell membranes and their minimal capacity to induce excessive reactive oxygen species (ros) generation make them compatible with huvecs. figure 22. cytocompatibility of ti3c2tx mxene with red blood cells and human umbilical vein endothelial cells and the underlying mechanisms [101]. in the realm of flexible electronics and biomedical devices, mxene fibers hold promise due to their superior conductivity. usman et al. [102] investigated the incorporation of silk fibroin biopolymer into mxene formulations to enhance fiber properties. the addition of silk fibroin led to improved durability, with fibres enduring up to 1 hour of high-frequency sonication. also, fibers containing approximately 5 wt% silk fibroin demonstrated intriguing characteristics, such as high conductivity (approximately 3700 s cm−1), elevated volumetric capacitance (approximately 910 f cm−3), and non-cytotoxicity towards thp−1 monocytic cells. for the development of bioimaging tools, neubertova et al. [103] suggested covalent functionalization of ti3c2t flakes using the chelating agent diethylenetriaminepentaacetic acid (dtpa), followed by complexation with gd3+ ions. this established functionalization technique endowed the inherently diamagnetic ti3c2t flakes with a paramagnetic response, facilitating their utilization in t1-weighted magnetic resonance (mr) imaging. additionally, a noticeable relationship between magnetic relaxation time and flake concentration was observed, enabling the estimation of the distribution of flakes in space. the covalent decoration approach applied to mxene resulted in safeguarding its surface against oxidation in phosphate buffered saline and blood serum while enhancing cytocompatibility simultaneously. furthermore, the chelation of gd3+ ions demonstrated superior prevention of leakage compared to electrostatic chemisorption. a high photothermal conversion efficiency of mxene-gd was demonstrated, suggesting potential applications in photothermal therapy. yang et al. [104] highlighted the emergence of phototherapy as a promising strategy for combating bacterial infections without the associated risk of antibiotic resistance. however, the presence of endogenous antioxidative glutathione (gsh) in bacteria poses a challenge, as it hampers the desired antibacterial effects of externally generated reactive oxygen species (ros) during phototherapy. a quadcharacterization and application of nanomaterials 2024, 7(2), 6348. 39 channel synergistic antibacterial nanoplatform composed of ti3c2 mxene/mos2 (mm) 2d bio-heterojunctions (2d bio-hjs) was fabricated. this platform exhibited photothermal, photodynamic, peroxidase-like (pod-like), and glutathione oxidaselike properties. upon exposure to nir laser, the 2d bio-hjs induced localized heating and elevated extracellular ros levels, resulting in bacterial inactivation. also, the mo4+ ions released from the platform penetrated the bacterial membrane, triggering intracellular ros generation and depletion of intracellular gsh, further contributing to bacterial eradication. the 2d bio-hjs produced localized heating and elevated extracellular ros levels upon nir laser irradiation, leading to bacterial deactivation. simultaneously, mo4+ ions easily penetrated the ruptured bacterial membrane, triggering intracellular ros and depleting intracellular gsh. in the “ros hurricane”, bacteria faced substantial destruction from internal and external sources. however, when supplemented with fibroblast growth factor-21 (fgf21), 2d bio-hybrid junctions (bio-hjs) demonstrated favorable compatibility with cells and enhanced cell movement in vitro. scheibe et al. [105] emphasized the necessity of conducting an in vitro examination to assess the impact of various types of mxenes and their precursors on human cell lines within the framework of nanomaterial safety. to this end, a range of multi-layered, few-layered, and singlelayered ti3c2tx, alongside tic, ti2alc, and ti3alc2, were synthesized. following the trends in nanomaterial safety assessment, thorough characterization encompassing morphology, size purity, and surface charge was conducted (figure 23). subsequently, various biological responses (including cytotoxicity, membrane permeability, reactive oxygen species generation, and mechanical stress) induced by mxenes, tic, and parental max phases were investigated and compared using human fibroblasts (msu1.1) and cervical cancer cells (hela) as model systems, reflecting differing tumorigenic properties. the findings indicated that exposure to elevated concentrations (≥400 μg/ml) of tic, ti2alc, and ti3alc2 particles, sized < 44 μm, could pose significant harm, eliciting pronounced cytotoxic effects through oxidative and mechanical stress mechanisms. conversely, all forms of ti3c2tx were deemed safe for msu1.1 cells, exhibiting only minor cytotoxic tendencies at the highest concentration levels. furthermore, the observed cytotoxic behaviors were contingent upon cell type, with greater susceptibilities observed in cancer-derived cells. figure 23. cytotoxicity assessment of ti-al-c based max phases and ti3c2tx mxenes on human fibroblasts and cervical cancer cells [105]. characterization and application of nanomaterials 2024, 7(2), 6348. 40 5.13. mxene-based materials for tissue engineering 2d mxenes are being used in the fields of tissue engineering and regenerative medicine. also, because of their good electrical behavior, mxenes are used for neural tissue regeneration. establishing artificial conduits to facilitate the growth of regenerating nerves and guide them through damaged areas is imperative for neuronal restoration. despite the historical use of various natural and synthetic polymers in neural tissue engineering, certain drawbacks persist [106]. for instance, while poly (3,4-ethylene dioxythiophene) exhibits commendable biocompatibility and sufficient electrical and chemical stability, its proclivity towards chronic inflammation and limited degradability render it an unsuitable candidate. presently, mxenes are being incorporated as additives into polymeric nanofibers, fostering the growth of supportive cells and endowing them with sustained neurotrophic properties [107]. to validate the efficacy of mxene-modified polylactic acid nanofibers in facilitating nerve-guiding path formation, an experimental study was conducted. integration of mxenes notably augmented the electrical conductivity of the material. the resultant current flow in the modified nanofiber membrane remained below 150 ma under an applied voltage of 5.5 v, although higher potentials induced dielectric behavior in the fabricated nanofibers. these findings underscore the potential of mxenes in conferring electroconductivity to polymer membranes for neural tissue engineering applications. notably, the presence of polylactic acid membranes containing immobilized mxenes did not exhibit adverse effects on cellular viability, as evidenced by resazurin reduction assays. however, the outcomes were partially satisfactory due to challenges associated with mxene immobilization and handling during cell culture. furthermore, the composite material demonstrated promising anti-adhesive properties against bacterial colonization, potentially disrupting cellular morphology and membrane integrity. 6. challenges and future prospects the numerous studies on mxenes and scientific reports, conferences, and articles are growing day by day, and the research in the right direction may address all challenges and issues. the possible right direction to the current state-of-art can open up new opportunities for innovations and developments of mxene-based devices. the current cutting-edge research on water-related issues can address the real problems, and the remarkable properties can make these efforts successful [3,9– 13,73]. mxenes are mostly designed using the top-down approach, while very few reports on the bottom-up approaches are available in the literature [11,72]. serious efforts are needed to explore the hidden potential in the bottom-up approaches to the synthesis of mxenes, to improve the characteristic properties of the mxenes, and to obtain desirable forms and structures of mxenes. after almost a decade of discovery of mxenes, this remarkable progress has been observed in the many fields and aspects related to mxenes, for example, synthesis, structural patterns, more applicability, and the discovery of new mxene compounds. but still, there are challenges left. the major challenges remain for mxenes and the application of mxene-based materials. very few max phases have been experimentally exfoliated characterization and application of nanomaterials 2024, 7(2), 6348. 41 to date, while a few dozen possibilities are predicted. theoretically, the mxenes can be the best possible cathode for high energy density 3458 wh kg−1 li-air batteries, but there is no successful report regarding this aspect [108,109]. recently, zn-air batteries have been successfully reported with promising performance, which proves the potential of mxenes [106,107]. most of the reports are about coin-cell-based devices; it is just to see the actual potential of the material, while the pouch-type or large assembly of cells is needed to be tested for futuristic flexible, printable, or wearable applications of mxene-based batteries and supercapacitors. the performance of mxene-based devices with solid electrolytes needs to be tested to confirm the possibility of flexible and wearable mxene-based devices [61,110]. mxenes are proposed to be the future materials for absorption of toxic pollutants, but they need to be exploited fully [111]. for example, one of the promising mxene kxmeo2-based electrodes for batteries is under investigation, while the existing report shows lower operating potential and lower energy density in comparison to graphite/limn2o4-based libs [112] (figure 24). figure 24. (a) average operating potential versus gravimetric capacity plot for selected layered tmos for pibs; (b) typical charge/discharge curve for p2-type kxcoo2xu [112]. the operating potential and capacity values reported for the various battery cells are derived from the potentiated state in half cells. while calculating the energy densities of full cells, graphite (with a capacity of 279 mahg−1 at 0.25 v vs. k/k+) is characterization and application of nanomaterials 2024, 7(2), 6348. 42 employed as the negative electrode material in conjunction with various positive electrode materials. the key latest developments in mxene and mxene-based materials and devices are presented. some key challenges and issues related to mxene-based materials for various applications need to be taken up [112]. 7. conclusion mxene and mxene-based materials can be synthesized through various approaches and methodologies tailored to meet some specific properties and structural specification requirements. the exponential growth in the research articles and expansion of research groups around the world suggests expected tremendous improvement in the synthesis techniques soon. the specific properties of mxenes and mxene-based materials, e.g., specific surface area, chemical stability, hydrophilicity, thermal conductivity, and environmental compatibility, can be modified and customized according to the needs of applications. water purification, absorption of impurities, metal removal, and degradation of impurities can be successfully done using mxenes-based materials in a better way. mxenes exhibit promising potential in diverse realms, including environmental remediation, biomedical applications, batteries, supercapacitors, and other advanced engineering fields. mxenes demonstrate excellent biocompatibility in biomedical applications. nonetheless, there exist several challenges and unexplored research avenues that demand immediate attention to fully capitalize on the remarkable 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and application of nanomaterials 2024, 7(2), 7007. https://doi.org/10.24294/can.v7i2.7007 1 article ajwa date seed mediated green synthesis of alginate-silver nanocomposite beads and films for antibacterial and catalytic degradation applications naba almukharraq†, marwa almarzooqi†, hasan ruyan†, fatima alhannan, praveen kumar, fryad henari, g. roshan deen* materials for medicine research group, school of medicine, royal college of surgeons in ireland (rcsi), medical university of bahrain, busaiteen 228, kingdom of bahrain * corresponding author: g. roshan deen, rdeen@rcsi.com † equal contribution to this work and share first author status. abstract: alginate-silver nanocomposites in the form of spherical beads and films were prepared using a green approach by using the aqueous extract of ajwa date seeds. the nanocomposites were fabricated by in situ reduction and gelation by ionotropic crosslinking using calcium ions in solution. the rich phytochemicals of the date seed extract played a dual role as a reducing and stabilizing agent in the synthesis of silver nanoparticles. the formation of silver nanoparticles was studied using uv-vis absorption spectroscopy, and a distinct surface plasmon resonance peak at 421 nm characteristic of silver nanoparticles confirmed the green synthesis of silver nanoparticles. the morphology of the nanocomposite beads and film was compact, with an even distribution of silver nanoclusters. the catalytic property of the nanocomposite beads was evaluated for the degradation of 2-nitrophenol in the presence of sodium borohydride. the degradation followed pseudo-first-order kinetics with a rate constant of 1.40 × 10−3 s−1 at 23 ℃ and an activation energy of 18.45 kj mol−1. the thermodynamic parameters, such as changes in enthalpy and entropy, were evaluated to be 15.22 kj mol−1 and −197.50 j mol−1 k−1, respectively. the nanocomposite exhibited properties against three clinically important pathogens (gram-positive and gram-negative bacteria). keywords: ajwa dates seed; silver nanoparticles; green synthesis; alginate beads; degradation; 2-nitrophenol; antibacterial activities 1. introduction water contamination from toxic organic chemical waste from pharmaceutical, textile, and electrochemical industries and their adverse effects on human and aquatic life have received tremendous attention in recent years. exposure to chemicals above the threshold limits leads to skin discoloration, damage to the nervous system and organs, and developmental effects [1]. the toxic chemicals include nitrophenols, azo dyes, and heavy metals, and water containing these needs to be treated before it is safely discharged into waterbodies or land. various approaches have been employed in the removal of harmful pollutants, such as adsorption, ion exchange, solvent extraction, photochemical reactions, etc. [2], and among these techniques, adsorption using activated carbon is widely used as the process is economical and effective in the removal of various pollutants. however, this method allows for the adsorption of pollutants but not their degradation to nontoxic substances. in recent years, photocatalysis or photodegradation methods using metallic and metal oxide nanoparticles such as silver, gold, platinum, palladium, copper, nickel, citation almukharraq n, almarzooqi m, ruyan h, et al. ajwa date seed mediated green synthesis of alginatesilver nanocomposite beads and films for antibacterial and catalytic degradation applications. characterization and application of nanomaterials. 2024; 7(2): 7007. https://doi.org/10.24294/can.v7i2.7007 article info received: 11 june 2024 accepted: 3 july 2024 available online: 1 august 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 7007. 2 cobalt, iron, zinc oxide (zno), and titanium dioxide (tio2) have gained much research attention for the complete reduction of toxic chemical waste to non-toxic substances in water [3–7]. nanoparticles on solid polymer supports such as polysulfone, polypropylene, poly(vinylidene fluoride), polyamide, cellulose acetate, and sodium alginate offer improved catalytic properties along with material sustainability, as these materials can be used repeatedly [7–9]. silver nanoparticles supported on various inorganic and organic substrates such as zeolite, silica or fiber glass, carbon materials, natural macro-porous materials, and polymers have been recognized as effective photocatalysts and antimicrobial agents. nanocomposite beads based on the natural polymers sodium alginate and silver nanoparticles offer extended physical and chemical properties and are currently being considered for point-of-use drinking water disinfection [8–10]. sodium alginate is a linear polysaccharide found in marine brown algae and is composed of irregular blocks of b-d-mannuronic acid (m) and a-l-guluronic residues (g). due to their non-toxicity, degradability, and bio-compatibility alginatebased gels have attracted numerous biomedical applications, such as drug and protein delivery, wound dressing, 3d bioprinting for tissue engineering, scaffolds for cell growth and organoid morphogenesis, and flexible electronics for health monitoring [11–15]. silver nanoparticles synthesized by green chemistry using the extracts of plants or plant products have been used in the fabrication or engineering of alginatenanocomposite beads. the phytochemicals present in the extract act both as reducing agents for the reduction of silver salt to silver nanoparticles and as stabilizing the resulting nanoparticles against aggregation [16,17]. date palm, commonly known as phoenix dactylifera, is one of the oldest cultivated varieties of date palm trees with nutritional, economic, and environmental benefits. there are about 5000 varieties of date palm that are grown in different regions of the world, and the nutritional and phytochemical values vary among the dates. among these, ajwa dates are widely cultivated in the al madinah and surrounding regions of saudi arabia. this type of date has high sugar (34.5% glucose, 25.6% fructose, and 0.5% sucrose) and mineral (3%) content compared to other varieties of dates [18,19]. these date seeds are a rich source of polyphenols, flavonoids, glycosides, phenolic acids, proteins, and carbohydrates and demonstrate antioxidant, anti-inflammatory, antimicrobial, and anti-tumor properties. the extract of the ajwa date seed in methanol and acetone exhibits reasonable antibacterial properties against gram-positive and gram-negative bacteria [19,20]. in this study, we have developed reusable alginate-based silver nanocomposite beads by in situ chemical reduction and gelation methods for the quick reduction of 2-nitrophenol. the silver nanoparticles were first synthesized by green chemistry using the extract of ajwa date seeds as an efficient source for reduction and stabilization, and then incorporated into alginate beads by ionotropic crosslinking using calcium ions. to the best of our knowledge, this is the first study on the fabrication of alginate-silver nanocomposite beads using the extracts of ajwa date seed. characterization and application of nanomaterials 2024, 7(2), 7007. 3 2. experimental 2.1. materials ajwa date (phoenix dactylifera) seed powder was purchased from a grocery store in hoora, bahrain. silver nitrate (agno3), sodium alginate (nac6h7o6), sodium hydroxide (naoh), sodium borohydride (nabh4), 2-nitrophenol (2-np), congo red (cr), and calcium chloride (cacl2) were purchased from sigma and used as received. deionized water collected from a millipore system (elix technology, germany) with a conductivity of 18.2 mw cm−1 was used for all aqueous sample preparations. the antibacterial properties of the synthesized nanoparticles, nanocomposite beads, and films were evaluated against three different types of bacteria: staphylococcus aureus (s. aureus), escherichia coli (e. coli), and salmonella typhimurium (s. typhimurium). the bacteria were obtained from the ministry of health, kingdom of bahrain (moh, bahrain, microbiologiscs, france). 2.2. preparation of date seeds extract about 1.00 g of the date seed powder was added to 100 ml of water in a beaker and boiled for 30 min under magnetic stirring. the mixture was air-cooled and centrifuged for 10 min at an rpm of 4200 to remove any suspended materials. the clear extract was used fresh in the synthesis of silver nanoparticles. 2.3. green synthesis of silver nanoparticles silver nanoparticles were synthesized by reducing the silver nitrate in the freshly prepared date seed extract as follows: agno3 (1 mm, 5 ml) was placed in a screw-capped glass vial and stirred gently using a magnetic stirring bar. freshly prepared date seed extract (1 ml) was added dropwise into the vial with continuous stirring. after about 5 min, naoh (0.5 m, 50 ml) was added dropwise, and the mixture was stirred overnight for the completion of the reaction. upon addition of naoh, the color of the solution turned pale yellow and finally to brown (after 24 h). the observed color changes are an indication of the formation of nanoparticles. the solution containing the nanoparticle was centrifuged (rpm 10,000) for 10 min, and the sedimented nanoparticles were washed repeatedly with water and dried in an oven at 70 ℃. 2.4. synthesis of alginate-silver nanocomposite beads alginate beads containing silver nanoparticles were prepared by the sequential chemical reduction and gelation method as described as follows: in this method, silver nanoparticles were first synthesized using the date seed extract and then incorporated into the alginate beads during the gelation. a silver nitrate solution of concentration 1 mm was first prepared by dissolving 0.0175 g of the salt in 100 ml of water. to this solution, 20 ml of fresh date seed extract was added under magnetic stirring, followed by the addition of 1 ml of 0.5 m naoh. upon addition of sodium hydroxide, the solution turned pale gray and then pale brown, indicating the onset of the formation of silver nanoparticles. the solution was continuously stirred for an additional 24 h for the completion of the reaction, followed by the characterization and application of nanomaterials 2024, 7(2), 7007. 4 addition of 2.20 g of sodium alginate. the solution was heated to 60 ℃ and continuously stirred for another 24 h for the complete dissolution of sodium alginate, resulting in a homogenous mixture. the solution was air-cooled and then stored in the refrigerator to remove any air bubbles. the prepared alginate-silver nanoparticle solution was injected into 200 ml of a 5 wt% calcium chloride solution using a plastic syringe of 20 ml capacity at a rate of 20 drops per minute. the resulting black-colored beads were washed thoroughly with water and dried at 70 ℃ until a constant weight was maintained. 2.5. synthesis of peelable alginate-silver nanocomposite films peelable alginate-silver nanocomposite film was prepared by a mist spray gelation method as described as follows: a 10 ml alginate-silver nanoparticle solution described in the previous section was placed in a clean glass petri dish and mist sprayed with cacl2 solution (5 wt%). the petri dish was covered and left overnight at room temperature for the completion of gelation. the dark brown film was carefully peeled off from the petri dish, washed repeatedly with water, and dried at 50 ℃ until a constant weight was maintained. 2.6. uv-vis absorption spectroscopy the formation of silver nanoparticles was confirmed by measuring the absorbance of the silver nanoparticle solution using a double-beam shimadzu uv1800 spectrophotometer. the solution (3 ml) was placed in a quartz cuvette (helma) of 1 cm path length, and the absorption spectrum was recorded in the wavelength range 250–1000 nm with a resolution of 1 mm. water was used as the blank reference for all measurements. 2.7. scanning electron microscopy (sem) the size and morphology of the alginate-silver nanocomposite beads were characterized using a scanning electron microscope operating at a voltage of 10 kv (inovenso, iem-11). the samples were sputtered with gold for 15 s using an inovenso spt-20 coater. 2.8. catalytic degradation studies of 2-nitrophenol (2-np) the catalytic degradation of 2-np by the alginate-silver nanocomposite beads was followed using a uv-vis spectrophotometer. a solution of 2-np (0.13 mm, 2.5 ml) was placed in a quartz cuvette of 1 cm path length, and the absorbance was recorded. after this, 0.5 ml of freshly prepared nabh4 (0.1 m) was added to the solution, and the absorbance was recorded again. about 10 nanocomposite beads were then added to the solution, and the change in absorbance was recorded at intervals of 3 min for a period of 15 min. the percentage degradation of 2-np was calculated using the following equation, degradation (%) = 𝐴0 − 𝐴𝑡 𝐴0 × 100 (1) where, a0 and at are the absorbance at time zero and absorbance at time t, respectively. characterization and application of nanomaterials 2024, 7(2), 7007. 5 2.9. antibacterial activity the antibacterial activity of the synthesized silver nanoparticles against different types of gram-positive and gram-negative bacteria, such as s. aureus, e. coli, and s. typhimurium, was carried out using the kirby-bauer disk diffusion susceptibility test method. the bacteria strains were spread on a nutrient agar (lb agar) medium using a sterile spreader in all directions. the filter paper discs were loaded with silver nanoparticles with aseptic precautions, and then the agar plate was incubated at 37 ℃ for 24 h. the zone of inhibition was observed and measured after 24 h of incubation. 3. results and discussion 3.1. ajwa date seeds mediated green synthesis of silver nanoparticles plant extract-mediated synthesis of metallic nanoparticles is a desired method as it is environmentally friendly and toxic reagents are not used in the process. the formation of silver nanoparticles using the aqueous extract of ajwa date seeds was studied by visual observation and spectrophotometry. upon the addition of the date seed extract to the silver nitrate solution, a color change to pale brown was observed, which indicates the in situ chemical reduction of silver ions (ag+) to silver nanoparticles (ag0). the formation of silver nanoparticles was quantified using uvvis absorption spectroscopy, and a distinct surface plasmon resonance (spr) peak centered at 421 nm confirmed the presence of silver nanoparticles in the solution, as shown in figure 1. figure 1. uv-vis absorption spectra of colloidal silver nanoparticles synthesized using ajwa dates seeds (insert: digital image of colloidal silver nanoparticles). this peak arises due to collective oscillations of conduction electrons in the electromagnetic field of the incident light [16,17]. the ajwa date seeds are rich in phytochemicals such as polyphenols, flavonoids including rutin, catechins, isoflavonoids, and lignans [18–20]. these phytochemicals present in the extract of ajwa date seeds are responsible for the chemical reduction and subsequent characterization and application of nanomaterials 2024, 7(2), 7007. 6 stabilization of the resulting silver nanoparticles. the peak at 276 nm for the date seeds is attributed to the active phytochemicals that are responsible for the chemical reduction. the absence of this peak in the spectrum of the silver nanoparticles correlates to the reaction and the reduction in concentration of the active phytochemical. the nanoparticles were stable against aggregation for more than a month, with no obvious change in the position (401 nm) and intensity of the spr peak observed in the absorption spectrum. 3.2. formation and morphology of alginate beads and film silver particles encapsulated in alginate beads were prepared by ionotropic crosslinking with divalent cations such as calcium ions (ca2+). the divalent cations bind to the guluronate blocks of the sodium alginate chains, as the blocks allow a high degree of coordination with the cations. the guluronate blocks of one polymer then form physical junctions (crosslink points) with the guluronate blocks of adjacent polymer chains. this type of crosslinking and formation of a gel is termed the egg-box model of crosslinking [21]. the alginate beads containing silver particles prepared in this study were pale brown in color in their hydrated state and black when completely dry, as shown in figure 2a,b. the dry beads were close to spherical in shape, with an average size of 1.2 mm, as shown by the sem micrograph in figure 2c. the surface of the nanocomposite beads was compact, with dense particulate clusters of silver in the form of plates (figure 2d). to verify the presence of silver nanoparticles, the alginate beads were soaked in a phosphate buffer solution and dissociated. figure 2. images of alginate beads; (a) wet alginate beads; (b) dry alginate-silver nanocomposite beads; (c) sem image of nanocomposite bead; (d) high magnification sem image of nanocomposite bead; (e) sem image of nanocomposite film. the dissociation causes chelation of ca2+ by po4 − and hpo4 2− ligands, releasing the alginate and silver nanoparticles in solution. the resulting viscous solution was analyzed by uv-vis absorption spectroscopy. a strong spr peak around 420 nm characterization and application of nanomaterials 2024, 7(2), 7007. 7 confirmed the presence of silver nanoparticles in the alginate-nanocomposite beads. the nanocomposite film does not show any significant morphology, and the silver nanoparticles were evenly distributed on the surface of the film, as observed in figure 2e. 3.3. catalytic degradation of 2-nitrophenol (2-np) effluents from the dye and pesticide industries contain 2-np, which is an environmental hazard and is known to cause methemoglobinemia. the reduced product of 2-np is 2-amino phenol (2-ap), which is a non-toxic product. the catalytic activity of the alginate-silver nanocomposite beads in the degradation of 2np in the presence of nabh4 was studied using uv-vis absorption spectroscopy. the time-dependent change in absorbance during the degradation of 2-np is shown in figure 3a. the absorption peak at 351 nm corresponds to 2-np, and this shifts to 416 nm due to the formation of a 2-nitrophenolate ion (due to deprotonation of the −oh group) upon the addition of nabh4 as observed in figure 3a. the reduction in the absorption of the 2-nitrophenolaote ion corresponds to the formation of 2-ap; however, this reaction has a large kinetic barrier due to the large potential difference between the reducing agent (nabh4) and 2-np [22]. as a result, a catalyst is required to overcome the large energy barrier associated with this reduction process at room temperature. (a) (b) figure 3. degradation of 2-np in the presence of alginate-silver nanocomposite beads in the presence of nabh4; (a) uv-vis absorption spectra showing the degradation; (b) plot of percent degradation as function of reaction time. upon addition of the nanocomposite beads (10 beads) into the solution, the initial absorption (0.30) at 416 nm decreased significantly, reaching 0.05 in 15 min. this decrease corresponds to about 83% of the of the degradation of 2-np. at the same time, the intensity of the absorption peak at 300 nm increased, which indicates the formation of 2-ap and the reaction being accelerated by the silver nanoparticles present in the nanocomposite. the degradation kinetics are shown in figure 3b, and a degradation of 83% is observed in just 15 min of the reaction. characterization and application of nanomaterials 2024, 7(2), 7007. 8 the rate of reaction could be shortened by improving the surface morphology of the nanocomposite beads by making them more porous, which would allow higher diffusion of the 2-nitrophenolate ion into the beads for a faster reaction with the active proton species, or by increasing the number of beads. in the absence of the nanocomposite beads, the degradation reaction was extremely slow (more than 3 days), confirming the major catalytic role of the silver nanoparticles. the degradation reaction mechanism [21–23] in the presence of the nanocomposite takes place in four steps, such as: (i) adsorption of 2-np onto the nanocomposite bead; (ii) diffusion of 2-np to the active site; (iii) reaction of 2-np to form the adsorbed product; and (iv) desorption of the product from the nanocomposite. a schematic representing the degradation of 2-np in the presence of the strong reducing agent, nabh4, is shown in figure 4, according to literature reports [22,23]. figure 4. mechanism of degradation of 2-np in the presence of alginate-silver nanocomposite beads and nabh4. the rate constant (k) of the degradation was determined from the linear plot of ln(at/a0) versus reaction time (t) in min (figure 5) according to the following linear equation, ln 𝐶𝑡 𝐶0 = ln 𝐴𝑡 𝐴0 = −𝑘𝑡 (2) where ct and c0 are the concentration of 2-np, and at and a0 are the absorbances at time t, and t = 0, respectively, k (min−1) is the rate constant of the reaction. figure 5. plot of ln(at/a0) versus time for the reduction of 2-np in the presence of nabh4 at 23 ℃. the degradation reaction follows a pseudo-first order reaction kinetics with characterization and application of nanomaterials 2024, 7(2), 7007. 9 respect to the alginate-silver nanocomposite beads because the concentration of nabh4 (10 mm) was much higher than that of 2-np (1 mm). the rate constant for the degradation reaction was determined to be 1.40  10−3 s−1. the reaction kinetics and the rate constant obtained agree with reported values for catalytic reduction of nitrophenol compounds by green synthesized silver and gold nanoparticles and polymer nanocomposites [21,23–25]. 3.4. catalytic performance of alginate-silver nanocomposite beads the activation energy (ea) for the degradation process was determined from the gradient of a plot of ln(k) versus 1/t according to arrhenius equation as [26], ln(𝑘) = ( 𝐸𝑎 𝑅 ) 1 𝑇 + ln(𝐴) where a = frequency factor or arrhenius constant, r = 8.314 j k−1 mol−1, t = absolute temperature in kelvin, and k = rate constant. from a linear plot of ln(k) versus 1/t, the ea and a were determined from the gradient and intercept as 18.45 kj mol−1 and 5.19 s−1, respectively (figure 6). figure 6. effect of temperature on the pseudo-first order rate constant and determination of activation energy. an activation energy of 17 kj mol−1 has been reported for the degradation of 2np using calcium alginate beads containing iron-silver bimetallic nanoparticles [5]. our results agree with this, confirming the excellent catalytic properties of the nanocomposite beads. the results indicate that the catalytic reduction has a low potential barrier and that the catalytic reduction reactions occur via surface catalysis. in comparison to 4-np (ea = 10.51 kj mol−1), the obtained activation energy for 2np is higher by a factor of about 1.5, and this increase is attributed to the steric hinderance of 2-np. the thermodynamic parameters of degradation reaction, such as enthalpy change, (h), and entropy change (s) were determined using the eyring equation as [5,27], ln 𝑘 𝑇 = ln 𝑘𝐵 ℎ + ∆𝑆 𝑅 − ∆𝐻 𝑅 ( 1 𝑇 ) (3) characterization and application of nanomaterials 2024, 7(2), 7007. 10 where kb is the boltzmann constant (1.381  10−23 jk−1), h is the planck’s constant (6.626  10−34 j∙s), r is the ideal gas constant, and t is the absolute temperature in kelvin. from a linear plot of ln(k/t) versus 1/t (figure 7), the enthalpy (h) and entropy (s) changes for the degradation of 2-np were determined to be 15.22 kj mol−1 and −197.50 j mol−1 k−1, respectively. these values agree with reported values of h = 12.77 kj mol−1 and s = −198.42 j mol−1 k−1 for the degradation of 2-np using alginate nanocomposite beads containing iron and silver nanoparticles [5]. the negative entropy values indicate that the randomness on the interface between the nanocomposite bead and 2-np decreases during the degradation process. the kinetic and thermodynamic parameters for the catalytic reduction of 2-np by the alginatesilver nanocomposite beads are summarized in table 1. table 1. kinetic and thermodynamic parameters for catalytic degradation of 2-np by the alginate-silver nanocomposite beads. temperature (k) k (s−1) ea (kj mol−1) h (kj mol−1) s (j mol−1 k−1) 296 1.400  10−3 18.45 12.77 −198.42 303 3.528  10−3 308 4.101  10−3 318 5.650  10−3 figure 7. eyring plot to determine the thermodynamic parameters for the degradation reaction. the conversion efficiency of the alginate-silver nanocomposite beads was also evaluated for five successive cycles, and the results are shown in figure 8. after the first cycle of 2-np degradation, the beads were removed from the solution, washed repeatedly with water, and then placed into a fresh solution containing 2-np and nabh4. the conversion efficiency of the nanocomposite beads was constant within the range of 80%–83% up to five successive cycles, which indicates good catalytic efficiency on repeated usage. during this process, no leaching of silver nanoparticles from the beads was observed. characterization and application of nanomaterials 2024, 7(2), 7007. 11 figure 8. plot showing the degradation efficiency of the alginate-silver nanocomposite beads for 5 reaction cycles. 3.5. antibacterial properties the silver nanoparticles (no. 7), alginate-silver nanocomposite beads (no. 3), and alginate-silver nanocomposite film (no. 2) exhibited weak to good antibacterial properties against e. coli, s. aureus, and s. typhimurium. the bacterial agar plates with the zone of inhibition for a concentration of 10 mm agno3 are shown in figure 9. the ajwa seed extract (no. 5) showed a very weak antibacterial effect against all three types of bacteria, and interestingly, the neat alginate beads (no. 4) showed a comparable effect. the silver nanoparticles (no. 2) were effective against all three types of bacteria, and the antibacterial effect of silver nanoparticles is well known. however, a higher susceptibility was observed for s. typhimurium. the alginate-silver nanocomposite beads exhibited a larger zone of inhibition relative to the neat alginate beads, which indicates the synergistic antibacterial effect of the nanocomposites. similar synergistic effects have been observed for many greensynthesised silver nanocomposites [28]. figure 9. the antibacterial activity of silver nanoparticles, alginate-silver nanocomposite films and alginate-silver nanocomposite beads on different pathogenic bacteria. the mechanism of interaction of silver nanoparticles with bacteria is mainly ionic. the silver nanoparticles and silver ions (released from the nanoparticles) can accumulate in the pits of the cell wall, which leads to denaturation of the cell membrane [29]. in addition, the silver nanoparticles could penetrate the cell membrane, leading to denaturation and rupture of organelles, resulting in lysis. 1 2 3 4 5 0 10 20 30 40 50 60 70 80 number of cycle d e g ra d a ti o n ( % ) characterization and application of nanomaterials 2024, 7(2), 7007. 12 further, the silver nanoparticles can disrupt bacterial signal transduction, leading to cell apoptosis and the termination of bacterial cell multiplication. 4. conclusion and future perspectives alginate-silver nanocomposites in the form of spherical beads and thin films were successfully fabricated using silver nanoparticles synthesized using the extract of ajwa date seed. the nanocomposite beads were effective in the catalytic degradation of 2-nitrophenol, and 80% degradation was achieved in 15 min. the beads showed good reusability, with no appreciable decrease in their degradation capacity even after five successive cycles of operation. the degradation followed pseudo-first-order reaction kinetics. the nanocomposite exhibited antibacterial effects against three clinically important pathogens, with a higher susceptibility to s. typhimurium. overall, this study has laid the foundation for a new, effective strategy as an alternative to high-cost commercial catalysis for the detoxification of organic pollutants. the new material developed through the eco-friendly green approach, in addition to its catalytic properties, has the potential to treat hospital wastewater in the future. author contributions: conceptualization, rd; methodology, rd, na, ma and hr; software, rd; validation, rd and fh; formal analysis, rd, na and hr; investigation, rd, na, ma, hr, fa and pk; resources, fa; data curation, rd; writing—original draft preparation, rd; writing—review and editing, rd, na, ma and hr; supervision, rd and fh; project administration, rd; funding acquisition, rd. all authors have read and agreed to the 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antimicrobial, mosquitocidal and photocatalytic activities. scientific reports. 2021; 11(1): 1032-1046. doi: 10.1038/s41598-020-80327-9 microsoft word 7509-37762-2-le characterization and application of nanomaterials 2025, 8(1), 7509. https://doi.org/10.24294/can7509 1 review a review on antimicrobial properties of nano-ferrites: biomedical applications g. m. shweta1,*, lalsingh naik2, sushant kakati3, rangappa pujar4, shridhar mathad3,*, deepak shirgaonkar5 1 department of physics, k.r.pete krishna government engineering college, krishnarajapete, karnataka 571426, india 2 department of physics, karnatak university, dharwad, karnataka 580001, india 3 department of engineering physics, k.l.e.institute of technology, hubli, karnataka 58027, india 4 department of physics, p.c. jabin college, hubli, karnataka 580020, india 5 department of physics, anandibai raorane arts, commerce and science college, vaibhavwadi, dist sindhudurg, maharashtra 416810, india * corresponding authors: g. m. shweta, shwetagm01@gmail.com; shridhar mathad, physicssiddu@kleit.ac.in abstract: this review focuses on ferrites, which are gaining popularity with their unique properties like high electrical resistivity, thermal stability, and chemical stability, making them suitable for versatile applications both in industry and in biomedicine. this review is highly indicative of the importance of synthesis technique in order to control ferrite properties and, consequently, their specific applications. while synthesizing the materials with consideration of certain properties that help in certain methods of preparation using polyol route, green synthesis, sol-gel combustion, or other wise to tailor make certain properties shown by ferrites, this study also covers biomedical applications of ferrites, including magnetic resonance imaging (mri), drug delivery systems, cancer hyperthermia therapy, and antimicrobial agents. this was able to inhibit the growth of all tested gramnegative and positive bacteria as compared with pure ferrite nanoparticles without co, mn or zn doping. in addition, ferrites possess the ability to be used in environmental remediation; such as treatment of wastewater which makes them useful for high-surface-area and adsorption capacity due heavy metals and organic pollutants. a critical analysis of functionalization strategies and possible applications are presented in this work to emphasize the capability of nanoferrites as an aid for the advancement both biomedical technology and environmental sustainability due to their versatile properties combined with a simple, cost effective synthetic methodology. keywords: nano-ferrites; ferrites; dopants; biomedical 1. introduction human development is the epicenter of all study through the use of resources and the creation of new chemicals that benefit society. in particular, magnetic materials have grown in significance, and now, these are widely employed in many different sectors because of their unique properties; these properties are used in many fields, such as the chemical industry, the medical field, and electronics [1]. when pure metals are compared with ferrite materials, which are known as magnetic materials due to their special properties, this includes low cost, high resistance, and simple production processes. in ferrites, ferric oxides are the main components, which are a mixture of other metal oxides; these ferrites can be synthesized by using hematite (fe2o3) or magnetite (fe3o4) and are typically non-conducting [2]. the characteristics of structural, electrical and magnetic are greatly improved by substituting tiny quantities of dopants, which makes ferrites appropriate for many citation shweta gm, naik l, kakati s, et al. a review on antimicrobial properties of nano-ferrites: biomedical applications. characterization and application of nanomaterials. 2025; 8(1): 7509. https://doi.org/10.24294/can7509 article info received: 27 june 2024 accepted: 29 october 2024 available online: 22 november 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 7509. 2 technological applications [3]. the production of nanoferrites has received great interest which is due to their improved magnetic and electrical characteristics and this is easy comparable bulk counterparts [4,5]. these ferrites useful for different field due their improved magnetic characteristics which is in nanoscale in size, and also contain lager surface to volume ratio and quantum confinement effect [6]. this result indicates that nanoferrites is a essential materials for industry and technology, propelling breakthroughs in electronics, telecommunications, and healthcare. high magnetic permeability, chemical and thermal stability, high electrical resistivity, and gentle magnetic behavior are just a few of the remarkable qualities that ferrites have. these characteristics make them extremely adaptable for a different application, which includes choke coils, ferrites are utilized across a range of applications due to their unique properties. in microwave frequency devices, they exhibit high permeability (μ > 1000) and low loss tangents (tan δ < 0.1), facilitating efficient signal transmission. in computer memory core elements, magnetic saturation (50–80 emu/g) and moderate coercivity (hc~20–300 oe) ensure reliable data storage and retrieval. for biomedical applications, surface-coated ferrites (peg or silica) with particle sizes of 10–100 nm enhance biocompatibility and cellular uptake. they also show promise in hyperthermia treatments with a specific absorption rate (> 100 w/g) and smaller particle sizes (10–50 nm) for effective heat generation. in drug delivery, ferrites allow for targeted therapy through magnetic saturation (50–80 emu/g) while maintaining biocompatibility. their antibacterial and antifungal efficacy is supported by small particle sizes (10–50 nm) and functionalization with antimicrobial agents, ensuring chemical stability across various ph ranges. lastly, in water treatment, nano-sized ferrites (10–200 nm) with magnetic saturation (50–70 emu/g) and a surface area of 50–150 m2/g enable efficient, transformer cores, antenna rods, gas sensors, recording heads, electrodes telecommunication systems, and biomedical applications like drug delivery, magnetic hyperthermia, and magnetic resonance imaging [7–9]. the electrical and magnetic characteristics work together to provide substantial performance and efficiency gains, making them widely used in contemporary electronics and healthcare systems [10–12]. this review article starts a discussion of different synthesis methods for ferrites, their antibacterial characteristics, and their prospective uses in biomedicine. in specific condition the dopants to the improvement of their characteristics are discussed, along with the difficulties and prospects associated with the switch from bulk to nano-ferrites for next-generation technological advancements. 2. synthesis of ferrites the synthesis methods of ferrites are critically important because the properties and applications of ferrites are highly dependent on their synthesis techniques. the choice of synthesis method influences the size, shape, purity, crystallinity, magnetic properties, and surface characteristics of the ferrite nano-particles. these factors, in turn, determine the material’s suitability for specific applications, such as in electronics, catalysis, medical devices, and environmental remediation. many synthesis techniques is shown in figure 1 like ball milling, solid state reaction method, coprecipitation method, hydrothermal, micro-emulsion techniques are used characterization and application of nanomaterials 2025, 8(1), 7509. 3 to synthesize ferrite materials [13–16]. different approaches like polyol technique, green synthesis technique, sol gel method, sol gel auto-combustion fast firing method (pramanik method) etc., are employed to prepare ferrites [15–23]. figure 1. synthesis techniques of ferrites. table 1. different synthesis methods of ferrites. method description key features typical conditions solid-state reaction mixing metal oxides or carbonates followed by high-temperature sintering. simple, cost-effective, suitable for bulk synthesis high temperatures (1000–1400 ℃), long sintering times (4–8 h) sol-gel method using metal alkoxides or nitrates to form a gel, followed by drying and calcination. high purity, fine particle size, homogeneity low to moderate temperatures (400– 800 ℃), controlled atmosphere co-precipitation precipitating metal hydroxides from a solution, followed by drying and calcination. uniform particle size, suitable for nanoparticles moderate temperatures (300–700 ℃), ph control during precipitation hydrothermal synthesis reacting metal precursors in a sealed vessel at high pressure and temperature. controlled particle size, high crystallinity high pressures (autoclave), moderate to high temperatures (150–300 ℃) microwave-assisted synthesis using microwave radiation to heat precursors rapidly, leading to faster reaction times. fast processing, energy efficient, fine particles rapid heating, moderate to high temperatures (100–200 ℃) mechanical milling ball milling metal oxides or carbonates to achieve fine particle sizes before sintering. simple, scalable, cost-effective room temperature for milling, high temperatures for sintering spray pyrolysis spraying a solution of metal salts into a hot furnace to form fine particles through pyrolysis. fine, spherical particles, continuous process high temperatures (800–1200 ℃), controlled spray conditions combustion synthesis using a fuel and oxidizer mixture to ignite a self-sustaining combustion reaction. rapid, energy efficient, can produce high-purity products exothermic reaction, moderate temperatures (300–600 ℃) chemical vapor deposition (cvd) decomposing metal precursors in vapor phase onto a substrate to form ferrites. high purity, controlled composition, and thickness high temperatures (500–1000 ℃), vacuum or controlled atmosphere electrochemical deposition electroplating metal ions onto a substrate to form ferrite films. precise thickness control, suitable for thin films room to moderate temperatures (25– 100 ℃), controlled current/voltage table 1 depicts different synthesis methods, description of techniques, key features of synthesis methods and requirement of typical conditions for synthesis of ferrites [17,24]. the synthesis of ferrites is critically important because it dictates the material's final properties, and including yield which can improve by optimizing key factors such as temperature, reaction time, ph level, precursor concentration, and stirring speed. considering choice of the solvent and fuel to oxidant ratio in methods like sol-gel or auto-combustion plays a significant role, controlling reaction cooling characterization and application of nanomaterials 2025, 8(1), 7509. 4 rates enhance product quality and yield, sometime crucial for their performance in various applications. by choosing and optimizing the synthesis method, researchers and engineers can tailor ferrites for specific uses, ensuring they meet the necessary requirements in fields ranging from electronics to medicine. 3. biomedical applications of ferrites nanoferrites have obtained a significant attention due to their applications in different fields ranging from industry to biomedicine (figure 2) [25]. one of the applications is magnetic resonance imaging (mri), the most common use of nanoferrites in biomedicine field as a contrast agent. this mri is a noninvasive diagnostic technique that helps to get detailed picture of the body tissues. mri modifying the relaxation duration (t1 and t2) by adjacent water protons, iron oxides like magnetite helps find the difference between normal and diseased tissue by making the tissues harboring these nanoparticles seem brighter or darker in the mri images. similarly, manganese ferrite (mnfe2o4) and cobalt ferrite (cofe2o4) used to get sharper, higher-resolution pictures [23–29]. the magnetic hyperthermia is a method where nanoferrites also used to treat cancer, magnetic nanoparticles are subjected to an alternating magnetic field, this technique utilized the particle’s temperature. this heated particle injected in to the diseased tissues causes the tumor cells to heat up to a point where all cancer cells die, but leaving the surrounding healthy tissues unaffected [30–33]. cobalt ferrites is a an important to treat the magnetic hypothermia-based cancer treatment using cobalt ferrites which is a magnetic hyperthermia-based cancer therapy because of their high coercivity and magnetic saturation [34–36]. for magnetic refrigeration, key parameters include high magnetic anisotropy (k: 104 to 106 j/m3), significant adiabatic temperature change (δtad: 2–4 k at 2–5 tesla), and a transition temperature near room temperature (tc: 290–310k). common materials include gadolinium (gd), with a transition temperature of 293 k and δtad of~3–4 k, and gd-alloys like gd-si-ge, which enhance refrigeration properties [37]. the main reason to study for the targeted drug delivery methods represents a notable’s applications in biomedicine. delivering medicines to targeted locations like tumor or particular organ these systems are intended to increase the effectiveness of medicine while lowering the amount of the drug that comes into contact with heathy tissues, to avoid adverse effects. the infected cells or organ medication is delivered in a regulated manner once it reaches the target, guaranteeing minimum systemic toxicity and high therapeutic concentrations at the illness site. once the targeted organ treated very well need to make sure the health of the cells needs to monitor with the help of biosensors which is based on nano-ferrites which is also became very essential tool in diagnostics and healthcare. these biosensors designed to detect biological entities such as proteins, dna, or pathogens. the combination of nano-ferrites with bio-molecules that bind to specific target analytes, these particles can provide highly sensitive detection of disease markers, toxins, or infectious agents. for example: cobalt ferrite (cofe2o4) and zinc ferrite (znfe2o4) ferrites used in biosensors due to their stability and large surface area, which improves ability of sensors and also its very important to detect early diagnosis, enabling more timely treatment and patient outcomes [36,37]. the characterization and application of nanomaterials 2025, 8(1), 7509. 5 nanoferrites can also exabits strong antimicrobial properties that makes suitable for many applications in health care segment where infection control is critical, some nanoferrites, particularly those doped with other metals like zinc, copper and silver are known as disrupt the cell membranes of bacteria and fungi, leading to their destruction. this quality used in antimicrobial ferrites can be incorporated into medical device coatings, wound dressings, or even hospital textiles, where they act as barriers to microbial growth. this kind of feature is very important to prevent hospital acquired infections, which are major cause of complications and healthcare system [38–48]. in addition to this nano-ferrites are being explored for different use in this section medical field being explored for use in tissue engineering and regenerative medicine. when combined with biodegradable scaffolds, magnetic nanoparticles can be used to guide cell growth and tissue regranulation scaffolds, magnetic nanoparticles can be used to guide cell growth and tissue regeneration through the application of magnetic fields. this approach has been particularly promising in regeneration of bones and nerves, where magnetic fields can help to align bio cells in a way that mimics tissue natural growth, accelerating the healing process. ferrites, ndfeb magnets, and samarium cobalt (smco) magnets exhibit distinct magnetic properties, making them suitable for various applications. ferrites typically have a coercivity (hc) ranging from 400 to 450 ka/m, a curie temperature (tc) between 300 and 450 ℃, and an energy product (bhmax) of 1 to 5 mgoe (8 to 40 kj/m3). in contrast, ndfeb magnets possess higher coercivity values, ranging from 800 to 2000 ka/m, with a curie temperature of 310 to 400℃ (which can be elevated with doping), and an impressive energy product of 30 to 55 mgoe (240 to 440 kj/m3). samarium cobalt magnets also demonstrate significant coercivity, ranging from 600 to 2000 ka/m, with a higher curie temperature of 720 to 820 ℃ and an energy product between 16 to 30 mgoe (128 to 240 kj/m3) [23,49–54]. figure 2. schematic diagram of biological applications of ferrites. 3.1. diagnosis and mri imaging medical imaging being used an important tool by using ferrite nanoparticles which is very actively and effective in diagnosing cancer. actually, these nanoparticles are very useful and have protentional to high to provide high quality characterization and application of nanomaterials 2025, 8(1), 7509. 6 interior picture of human body. magnetic resonance imaging (mri) is the most widely used therapeutic instruments [55,57]. diagnosing cancer or ill cell is not only that much important but finding exact locations, dimensions and distinction from healthy tissues. nano ferrites such as cofe2o4 and fega2o4 also one of the best examples for diagnostic applications because of their advantageous qualities, such as magnetic features that make them appropriate for improving contrast in mri scans. fe3o4and γ-fe2o3iron oxides nano-particles is studied for long time and being used as contrasting agents, beyond these improved imaging capabilities, manganese and zinc doped zinc ferrite nano-particles, as well as mn–znfe2o4 are also emerging as viable possibilities [41,50]. mnfe2o4 ferrites are the nano particles are new mri contrast agents that provide better performance than conventional ferrites like fe3o4, γ-fe2o3, cofe2o4, and nife2o4 best for magnetic characteristics including their reduced toxicity and biocompatibility. using mnfe2o4 nano-particles in mri and developing new ferrites nanoparticles to open new possibilities for better early diagnosis and management of a range of illnesses [35,41]. 3.2. hyperthermia magnetic hyperthermia is important and cutting-edge technical tool to cure cancer, in this method heat applies to tumor location in order to kill cancerous cells. the process of heating at exact location is possible by only using ferrite-based nanoparticles have a special capacity to absorb energy when exposed to an external alternating magnetic field [32,34,35]. the successful elimination of malignant cells while protecting healthy ones, a condition known as hyperthermia [54,55]. this treatment technique is very sensitive technique to eliminate malignancy at exact location resulting in classifications of localized, regional, whole-body hyperthermia [54]. timer cells are intrinsically more heat-sensitive than normal cells because of their atypical blood arteries, these arteries works differently so this is very week and more sensitive towards heat. the fe3o4 applied for tumor treatment are proficiently studied, these nanoparticles uses néel and brownian relaxation to collect energy from the magnetic field and transform it into heat [55]. cofe2o4nanoferrite has immense capacity of self-heating and therefore is the most encouraging nanoferrite for application of hyperthermia [57]. these nanoparticles magnetic nature, size and shape of a particle, including intensity and frequency of the applied magnetic field, all these depends on how much heat they produce. the fe2o4 nanoferrite or co fe3o4are able to absorbing magnetic energy and releasing it as heat (42–45 ℃) due to this is used in hyperthermia treatments. this type of treatment helps to kill directly or make very week towards the treatment like radiation and chemotherapy. this technological development provides focused, non-invasive approach to cancer treatment which has great protentional to improve the efficacy of currently available medicines and lessons the adverse effects of old traditional approaches. 3.3. drug delivery and release ferrite nanoparticles show significant advantages such as treating cancer, delivery of drug and its release and safe excretion from the human body. for instance, characterization and application of nanomaterials 2025, 8(1), 7509. 7 the test carried on synthesized cofe2o4 nanoparticles disclosed all the abovementioned benefits [58]. in comparison with conventional drug use, the utilization of nanoferrites has helped to minimize the requirement of drug needed and related side effects [59,60]. in treating cancer by this system, the nanoferrites act as core whereas various biocompatible organic moieties act as shell. ferrite nanoparticles are capable of carrying drugs and circulating them without dripping. they also effortlessly travelto the site of target tumor with the help of an external magnetic field. they support in lending effective treatment by bypassing normal cells [61]. after delivering the drugs, either they get removed from the human body or get biodegradable [62]. the method of targeted drug delivery is having variousbenefit’s like depletion of wastage of drug, minimizing the drug administration frequency, lowering side-effects, increasing efficacy of treatment, being safe and reliable [32] etc. manganese (ii) complexes is a high catalytic activity which has a potential benefit in medical applications, for drug synthesis or therapeutic applications which is helpful medication manufacturing and treatment procedures [63]. zirconium oxide (zro2) synthesized material which has high optical characteristics and cubic structure with size of the grain zro2 is 10–30 nm due to this which suitable to get improved by surfactants like polyethylene glycol (peg) have great potential which is used for drug delivery [64]. copper (ii) hexaaza macrocyclic complexes is new content which is synthesized by using situ one-pot template synthesis (iopts) ultimately a good for drug delivery [65]. ferrites are valuable in various applications, including drug delivery, antibacterial/antifungal treatments, and water treatment, due to their unique properties. for drug delivery, key parameters such as particle size (10–100 nm), magnetic saturation (50–80 emu/g), biocompatibility (surface-coated with peg, silica, dextran), and zeta potential (−30 to +30 mv) enhance cellular uptake and ensure effective targeting and stability. in antibacterial and antifungal applications, small particle size (10–50 nm), appropriate magnetic saturation (40–70 emu/g), surface functionalization with antimicrobial agents, and chemical stability in various environments are crucial for maximizing antimicrobial efficacy. for water treatment, ferrites should exhibit a particle size of 10–200 nm, magnetic saturation of 50–70 emu/g, high chemical stability across ph ranges, and a large surface area (50– 150 m2/g) to optimize pollutant removal and ensure durability in treatment processes [54,66–68]. 3.4. antibacterial and antifungal studies nano ferrites exhibit antibacterial and antifungal properties due to several key factors related to their unique chemical composition, surface characteristics, and magnetic properties. nano ferrites possess a high surface-to-volume ratio, which increases the interaction between the nanoparticles and microbial cells. this enhanced contact can lead to more efficient microbial killing. the surface of nano ferrites can generate reactive oxygen species (ros) when exposed to environmental conditions. ros, such as hydroxyl radicals, superoxide anions, and hydrogen peroxide, can damage microbial cell membranes, proteins, and dna, leading to cell death. magnetic nanoparticles are significantly used as antibacterial and antifungals. the preparation and verification are done for nanoferrites for their extensive usage in characterization and application of nanomaterials 2025, 8(1), 7509. 8 medicinal field [69,70]. as antifungals are toxic, less efficient and resistant, there is a need for developing novel antifungal drugs that are safe and efficient. therefore, taking into account these aspects, new antifungal substances have evolved [71]. cobalt ferrite nanoparticles have been shown to exhibit significant antibacterial activity. the mechanism involves the generation of ros and the release of cobalt ions, which can penetrate bacterial cells and cause oxidative damage. zinc ferrite nanoparticles are known for their antifungal activity. zinc ions can interfere with fungal cell wall synthesis and membrane integrity, while the ferrite structure helps in the generation of ros, leading to fungal cell death. thus nano ferrites show antibacterial and antifungal properties due to their high surface area, magnetic properties, metal ion release, and ability to generate reactive oxygen species. these properties make them effective in disrupting microbial cells and killing bacteria and fungi. the kirby–bauer also called agar diffusion test is an antibiotic susceptibility test that makes use of discs of antibiotics to examine the extent of bacteria and fungi [72]. zinc copper ferrites were studied for antibacterial activity where it was noticed that activity was dependent of zinc concentration [53]. the zinc substituted cobalt ferrite and manganese substituted cobalt ferrite were utilized for antibacterial and antibiofilm activities towards bacteria that commonly diffused on the surfaces of medical operating room walls [73]. the mg substituted mn-zn ferrites act as outstanding antimicrobial potentials [42]. also, the cobalt doped manganese ferrites are proposed as a candidate material for industries manufacturing antifungal products [74]. ag doped ni co nanoferrites show an exceptional antifungal action [75]. figure 3 is a schematic representation of biological applications of ferrites whereas table 2 provides information about different biological applications of ferrites along with the description. thenanoferrite sample ni0.45zn0.45cu0.1fe2o4 exhibited the highest antibacterial activity against bacillus cereus, with inhibition zones measuring 21, 23, 23, and 23 mm for concentrations of 25, 50, 100, and 250 μg/ml, respectively (table 3). figure 4 and figure 5 illustrate the antibacterial studies of nickel zinc ferrites and copper-doped nickel zinc ferrites. in contrast, the other nanoferrite samples demonstrated negligible antibacterial activity. the antifungal activity was evaluated for cobaltdoped nickel zinc ferrites, with ni0.45zn0.35co0.2fe2o4 showing the highest inhibition zones of 25, 27, 30, and 30 mm for 25, 50, 100, and 250 μg/ml concentrations against aspergillus niger (table 4) [56]. figures 6 and 7 present the antifungal studies of nickel zinc ferrites and cobalt-doped nickel zinc ferrites. the results highlight the importance of compositional variations in enhancing the antimicrobial properties of nanoferrites, paving the way for their potential use in biomedical applications. characterization and application of nanomaterials 2025, 8(1), 7509. 9 table 2. biological applications of ferrites with description. biological application description reference mri contrast agents ferrite nanoparticles enhance mri contrast by affecting the relaxation times of hydrogen nuclei in tissues. 71 drug delivery magnetic ferrite nanoparticles can be directed to specific locations in the body using an external magnetic field, allowing for controlled drug release. 72 hyperthermia treatment magnetic ferrite nanoparticles generate heat when exposed to an alternating magnetic field, which can be used to kill cancer cells selectively. 73 biosensors ferrite nanoparticles enhance the sensitivity and specificity of biosensors used to detect various biological molecules. 38 cell separation cells can be tagged with magnetic ferrite nanoparticles and separated from a mixture using a magnetic field. 74 antifungal applications ferrite nanoparticles exhibit antifungal properties, inhibiting the growth of various fungal species. 42 antimicrobial applications ferrite nanoparticles have antimicrobial properties effective against a wide range of bacterial strains. 43 antibacterial coatings ferrite nanoparticles can be used in coatings to prevent bacterial colonization on medical devices. 44 antimicrobial textiles ferrite nanoparticles are incorporated into textiles to provide long-lasting antimicrobial properties. 45 water purification ferrite nanoparticles can be used to remove microbial contaminants from water, providing an effective purification method. 46 figure 3. schematic diagram of biological applications of ferrites. table 3. antibacterial activity of copper doped nickel zinc nano ferrites against bacillus cerus. sample zone of inhibition(mm) 25μg/ml 50μg/ml 100 μg/ml 250 μg/ml ni0.45 zn0.55fe2o4 1 1 2 1 ni0.45 zn0.45cu0.1fe2o4 21 23 23 23 ni0.45 zn0.35cu0.2fe2o4 1 1 2 1 ni0.45 zn0.25cu0.3fe2o4 1 1 2 1 characterization and application of nanomaterials 2025, 8(1), 7509. 10 figure 4. antibacterial activity of nickel zinc nanoferrites (ni0.45zn0.55fe2o4) against bacilluscerus. figure 5. antibacterial activity of copper doped nickel zinc nanoferrites (ni0.45 zn0.45cu0.1fe2o4)againstbacillus cerus. table 4. antifungal activity of cobalt doped nickel zinc nanoferrites against aspergillus niger. sample zone of inhibition(mm) 25μg/ml 50μg/ml 100 μg/ml 250 μg/ml ni0.45 zn0.55fe2o4 1 2 2 1 ni0.45 zn0.45co0.1fe2o4 1 2 2 1 ni0.45 zn0.35co0.2fe2o4 25 27 30 30 ni0.45 zn0.25co0.3fe2o4 1 2 2 2 characterization and application of nanomaterials 2025, 8(1), 7509. 11 figure 6. antifungal activity of nickel zinc nanoferrites (ni0.45 zn0.55fe2o4) against aspergillus niger. figure 7. antifungal activity of cobalt doped nickel zinc nanoferrites (ni0.45 zn0.35co0.2fe2o4) against aspergillus niger. thus unique magnetic properties and biocompatibility of ferrites (table 5) make them invaluable in various biological and medical applications, shown in figure 8. research continues to expand their potential uses, offering promising advancements in diagnostics, treatment, and research methodologies in the life sciences. ferrites exhibit notable antibacterial and antifungal properties, with particle sizes typically ranging from 10–50 nm for fe3o4 (magnetite), effective against e. coli and s. aureus, and 20–60 nm for cofe2o4 (cobalt ferrite), demonstrating antibacterial activity against e. coli. their magnetic saturation (ms) values are 40–60 emu/g for magnetite, enhancing drug targeting, and 25–35 emu/g for znfe2o4 (zinc ferrite), which still shows moderate antibacterial activity. zeta potential for magnetite ranges from −10 to −20 mv, ensuring stability in colloidal suspension. minimum inhibitory concentrations (mic) for fe3o4 nanoparticles are 50–100 µg/ml for e. coli and s. aureus. cofe2o4 achieves 80%–90% antibacterial efficiency against e. coli, while nife2o4 (nickel ferrite) shows 70%–85% antifungal efficiency against c. albicans. functionalizing ferrites, such as with silver, further enhances antibacterial activity. ferrites are biocompatible, with cytotoxicity showing ≥80% cell viability at ≤100 µg/ml [68,76–80]. characterization and application of nanomaterials 2025, 8(1), 7509. 12 table 5. applications, key parameters, and their importance. application important parameters reasons for importance microwave frequency devices permeability, loss tangent (high (μ> 1000, low (tan δ < 0.1)) high permeability ensures efficient signal transmission, while low loss tangents minimize energy loss. frequency response affects device performance at various microwave frequencies. computer memory core elements magnetic saturation (50–80 emu/g), coercivity(hc~20– 300 oe) (hc~20–300 oe) (hc~20–300 oe) high saturation magnetization allows for reliable data storage and retrieval; moderate coercivity ensures stability. thermal stability essential for maintaining performance under operating conditions. biomedical applications biocompatibility, particle size biocompatibility is crucial for safety; smaller particles enhance cellular uptake and interaction with tissues. particle size10–100 nm enhances cellular uptake and improves interactions with biological systems. surface functionalization modifications improve interactions with biological systems, reducing toxicity. diagnosis magnetic susceptibility, high susceptibility enhances imaging quality; biocompatible coatings improve safety in medical applications. surface coating sensitivity and resolution crucial for improving diagnostic accuracy in imaging techniques. hyperthermia specific absorption rate high sar values indicate efficient heat generation, while smaller sizes improve localization in tumors. particle size (10–50nm) magnetic properties essential for effective induction heating in targeted cancer therapy. drug delivery magnetic saturation (ms), enables targeted delivery through external magnetic fields; biocompatibility ensures safety. biocompatibility release profile important for controlling drug release rates in therapeutic applications. antibacterial and antifungal particle size (10–50 nm) smaller sizes enhance interaction with microbes; functionalization improves antimicrobial efficacy. surface functionalization, chemical stability efficacy in biological environments chemical stability ensures prolonged activity in diverse conditions. water treatment particle size (10–200 nm) nano-sized particles provide high surface area for adsorption; magnetic properties enable easy recovery. magnetic saturation (ms), (50–70 emu/g) surface area (50–150 m2/g) chemical stability ensures durability and effectiveness during treatment processes across various ph levels. characterization and application of nanomaterials 2025, 8(1), 7509. 13 figure 8. various biological applications of nano ferrites. 3.5. waste water treatment water sources are at high risk of pollution. they get polluted because of discharging wastes into the water bodies such as plastic, glass, chemicals, etc. the common pollutants in waste water are metal ions, aromatic compounds, anions, phenols, dyes, pesticides, detergents, etc. because of the presence of such contaminants in waste water, it makes the water unfit for drinking and also becomes poisonous to aquatic life. ferrites, especially those with high surface areas, are effective adsorbents for removing heavy metals like lead (pb2⁺), cadmium (cd2⁺), chromium (cr6⁺), and arsenic (as3⁺) from wastewater due to unique properties of ferrites (figure 9). the metal ions are adsorbed onto the surface of the ferrite particles through electrostatic interactions and chemical bonding. ferrites can adsorb organic pollutants, such as dyes, from wastewater due to their surface properties and ability to be modified with functional groups that enhance adsorption. all over the world, there is demand for clean and safe water. hence, the purification of water is of utmost priority. new methods of purification of water are to be developed that are cost effective. magnetic nanoparticles because of their adsorption and high surface area to volume ratio have become significant candidates for treating waste water. therefore, nanoferrites are checked for removing contaminants and purifying water. they have proved to be promising candidates in this aspect. the process of adsorption or degradation is responsible for the removal of contaminants in water [47,81–84]. the waste water of the industries is treated to remove dyes and phenols, toxic metals by using nanoferrites [75–82]. magnetite (fe3o4), cobalt ferrite (cofe2o4), nickel ferrite (nife2o4), zinc ferrite (znfe2o4), copper ferrite (cufe2o4), manganese ferrite (mnfe2o4), and barium ferrite (bafe12o19)—is used in wastewater treatment for specific applications based on their magnetic properties, ability to adsorb contaminants, and catalytic capabilities. nanoferrites are good adsorbents that are of low cost, efficient, can be recovered with ease and reused. by literature review, it is clear that trend of using nanoferrites in waste water treatment has increased. the fe3o4 is a popular candidate for this. this might be because of non-toxicity, ease of availability of precursors required in its synthesis [32,85]. dy2o3-sio2 nanocomposite is best and effective in photocatalysis which break down the pollutants like erythrosine so it’s best for sanitation and environmental cleanup similarly reduced graphene oxide (rgo) from graphite oxide using urea also used as non-toxic reducing agent [70,86]. cspbi3 perovskite nanostructures is capable characterization and application of nanomaterials 2025, 8(1), 7509. 14 enough fight against the pseudomonas aeruginosa, escherichia coli, and streptococcus pyogenes which is good to addressing pollution [86]. ferrites with a large surface area (50–150 m2/g) demonstrate high adsorption capacities, making them effective for removing heavy metals and dyes in water treatment applications. their high magnetic saturation (ms) values, particularly in magnetite (50–60 emu/g), facilitate easy magnetic separation, which is beneficial for magnetic filtration systems. the adsorption capacity of ferrites is quantified in mg of pollutant per gram of ferrite, with magnetite nanoparticles exhibiting significant adsorption capabilities for heavy metals like pb2+, cr6+, and as3+. ferrites also show remarkable removal efficiencies, achieving 90%–95% removal rates for pollutants such as pb2+, as3+, and cr6+. additionally, ferrites like fe3o4 maintain good stability across a wide ph range (4–9), enhancing their versatility for various wastewater treatment scenarios. some ferrites, such as nife2o4, possess antimicrobial properties, allowing them to function as disinfectants in water treatment systems. [36,66,87–90] figure 9. advantages of nano ferrites in using them for waste and waste water treatment as compared to conventional techniques. 4. conclusions in conclusion, ferrite synthesis techniques are essential for determining their magnetic, chemical, and physical characteristics; all synthesis techniques are widely and effectively synthesized and utilized. sol-gel, co-precipitation, hydrothermal, and green synthesis methods are used to get the desired particle size, shape, and magnetic properties, depending on the application synthesis method utilized. using the best synthesis method, prepared ferrites provide flexibility in health care, demonstrated by their biomedical applications, mainly in medication administration, magnetic hyperthermia, biosensing, and magnetic resonance imaging (mri). cofe3o4and mnfe3o4 are essential for mri to get strong magnetic characteristics and biocompatibility, which helps mri to contrast agents and cancer therapies. various methods of synthesis of ferrites are discussed to get information related to antimicrobial properties and biological applications of ferrites, such as the biomedical field comprising cancer diagnosis, mri, hyperthermia, drug delivery and release, antimicrobial properties, and wastewater treatment. compared with conventional drug use, the utilization of nano-ferrites has helped minimize the amount of drug needed and avoid side effects. in wastewater treatment, nano-ferrites are cost-effective and efficient compared to conventional methods. also, nano-ferrites are promising candidates for antimicrobial and biomedical applications. the optimization of feature synthesis techniques is characterization and application of nanomaterials 2025, 8(1), 7509. 15 necessary to improve the biocompatibility, stability, and magnetic properties of ferrites for specific biomedical applications by considering green synthesis methods to avoid or minimize environmental impact while maintaining the exact costeffectiveness and 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journal of water process engineering. 2020; 33: 101038. doi: 10.1016/j.jwpe.2019.101038 microsoft word can 3587 pb online characterization and application of nanomaterials 2024, 7(1), 3587. https://doi.org/10.24294/can.v7i1.3587 1 article mo-doped titanate nanofibers from hydrothermal syntheses for improving bone scaffold yang tian1,2,†, lu zhang3,†, yiting xiao4,†, trenton collins5, abdussamad akhter5, yan huang6, z. ryan tian1,2,3,5,* 1 department of materials science and engineering, university of arkansas, fayetteville, ar 72701, usa. 2 institute for nanoscience and engineering, university of arkansas, fayetteville, ar 72701, usa. 3 department of cell and molecular biology, university of arkansas, fayetteville, ar 72701, usa. 4 department of biological and agricultural engineering, university of arkansas, fayetteville, ar 72701, usa. 5 department of chemistry and biochemistry, university of arkansas, fayetteville, ar 72701, usa. 6 department of animal science, university of arkansas, fayetteville, ar 72701, usa. * corresponding author: z. ryan tian, rtian@uark.edu †these authors contributed equally to this work. abstract: a longstanding interest in bone tissue engineering is the development of new bioscaffolds that can be manufactured on a large scale with high throughput at low cost. here, we report a low-cost and systematically optimized hydrothermal synthesis for producing modoped potassium titanate nanofibers with high structural purity. this new nanosynthesis is based on bone tissue growth on an undoped titanate nanowires-entangled scaffold, as previously reported by our team. the morphological and structural characterization data suggest that the crystal structure of mo-doped titanate nanofibers closely resembles that of the undoped ones. this resemblance is potentially valuable for assessing the role of mo dopants in engineering bone tissue. keywords: nanosynthesis; titanate nanofiber; bone scaffold; molybdenum dopant 1. introduction exploiting new methods for synthesizing biocompatible nanowires with novel structures and surface properties is critical to the development of new tissue engineering scaffolds. the nanowires-entangled scaffolds with well-tuned surface chemistry (e.g., the surface energy, protein adsorption, and pore structure) can facilitate a programmable release of growth hormones, drugs, and nutrients to promote the osteoblast cells adhesion, proliferation, and differentiation, thus-upgrading the bioscaffolds versatilities [1]. further, doping valve metal atoms in the nanowire structure or on the nanowire surface can enhance the scaffold’s radio-opacity to boost the orthopedic x-ray imaging’s contrast, i.e., resolution [2–6]. under these inspirations, this work has successfully doped and optimized the nanowire analogs of natural bone scaffold, in a series of systematic syntheses for doping the scaffold nanowire rationally using different valve metals in different doping ratios. thus, varied properties of the nanowires, such as aspect ratio, surface chemistry, and the chemical environment of the doping atoms, are anticipated to provide new insights into the role of valve metals in bone implants [1]. titanium dioxide (tio2) has been attracting enormous interest in both nanomaterial chemistry and orthopedic nanomedicine. the tio2-based nanosyntheses have typically resulted in a clay-like layered titanate structure in the nanowire [7] or citation tian y, zhang l, xiao y, et al. modoped titanate nanofibers from hydrothermal syntheses for improving bone scaffold. characterization and application of nanomaterials. 2024; 7(1): 3587. https://doi.org/10.24294/can.v7i1.358 7 article info received: 9 december 2023 accepted: 9 january 2024 available online: 18 january 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 3587. 2 nanotube [8] morphologies, with the edge-sharing [tio6] octahedra in the negatively charged layer and the cations intercalating in between the layers, which can promote the hydroxyapatite nucleation and formation on the nanowire surface quickly in a simulated body fluid (sbf) [9]. in a hydrothermal treatment, the tio2 powders (regardless of the rutile or anatase phase) originally suspended in an aqueous koh solution can quickly start to form the k-titanate of one-dimensional (1d) nanowires [10]. the resultant layered 1d-nanostructure can act like a cation “reservoir”, facilitating the ion-exchange of k+ with other cations in the body fluids. this allows for an autonomous, real-time balance of cations in situ, on which the bone tissue growth can be promoted. here, the k-titanate, in a hypotonic condition with respect to the plenty of calcium (ca2+) ions nearby, can prompt the ion-exchange of k+ ions with the ca2+ in sbf. subsequently, the phosphate anions in the body fluid, including (po4)3⁻, (hpo4)2⁻, and (h2po4)⁻, can support the interactions with the ca2+ ions on the titanate surface. this interaction results in the formation of hydrated calcium phosphate, commonly referred to as hydroxyapatite, which is a vital component of natural bone and essential for establishing an osteogenic/osteoconductive environment [9]. in addition, nanomaterials containing valve metals such as molybdenum (mo), zirconium (zr), niobium (nb), or tantalum (ta) can help improve the osteointegration [10–16]. here, the mo ions can promote the immunomodulation and facilitate bone repair by comodulating the balance between bone formation and resorption, showing a good potential to help regenerate bones [12]. further, the mobased nanomaterials syntheses in literature should be optimized to meet the need for large-scale productions. moreover, doping the relatively expensive valve metals on or in the low-cost titanate scaffold nanowire can reduce the cost and the valve metals cytotoxicity to the bone tissue. in this work, we systematically conducted nanosynthesis to produce long and pristine mo-doped titanate nanofibers with the good feasibility for mass-production of the new orthopedic implants. the doping ratio was optimized using the structural, morphological, and chemical characterizations data from the scanning electron microscopy with an energy-dispersive elemental analyzer (sem-edx), x-ray diffraction (xrd), and x-ray photoelectron spectroscopy (xps). 2. materials and methods 2.1. nanowire synthesis the mo-doped potassium titanate nanowires were prepared following a protocol in literature [10,17–20] with some modifications. briefly, in a teflon cup containing 50 ml water solution of 10m koh, 500 mg of tio2 powder (aeroxide p25) was added in and stirred for about 5 min with a teflon-coated magnetic stirring bar on an electrical stirrer. thereafter, molybdenum oxide powder (from alfa aesar) was mixed into the teflon cup to form a mixture upon stirring. here, the weight ratio of modopant to titanate was in the range of 1%–4%. next, the mixture containing teflon cup was sealed in an autoclave container, heated in an oven at 240 ℃ for 72 h and then cooled down in air. the white powdery product was collected, water-washed to ph = 7, and oven-dried at 60 ℃ for the characterization and application of nanomaterials 2024, 7(1), 3587. 3 characterizations. to keep the nanowire lattice intact, it is important to do the waterwashing step carefully, as detailed separately below. 2.2. characterizations the sem-edx analysis was done on the fei nova nanolab 200 to check the nanowires morphology and chemical composition. typically, a nanowire sample was placed on an aluminum holder to let the sample dry in air, then surface-coated with au in a plasma sputtering coater. the xrd analysis was performed on the rigaku miniflex ii desktop x-ray diffractometer using monochromatized cu-kα (λ = 1.5406 å) at 30 kv and 15 ma, in the range of 2θ from 5o to 60o at a speed of 1o/min. the xps characterization was conducted on the phi versaprobe scanning xps system to study the chemical environment of mo. 3. results and discussions 3.1. evidence of the novel mo-doping the mo-doped potassium titanate nanowires underwent a self-assembly process, resulting in the formation of a bio-scaffold, as illustrated in figure 1. this selfassembled nanofibrous scaffold has pores in the size of tens of microns (figure 1(a)) to support the effective adhesion of osteoblast cells into the pores, while the pore wall (of self-entangled nanowires) is also highly porous (figure 1(b)) to allow the osteoblast cells’ nutrients and metabolites to diffuse quickly across. figure 1. sem micrographs of mo-doped potassium titanate. upon examination at a higher magnification (figure 2(a)), the clean and wellcrystallized long nanowires in self-entangled form can be clearly seen, which is a characteristic of the mo-doped potassium titanate nanowires. the nanofibers length extends into tens of microns, while retaining their width below 100 nm. in addition, figure 2(a) shows the relatively smooth surface of the high length-to-width ratio (or aspect ratio) nanofibers, suggesting the optimal control over the nanowires’ nucleation and 1d-growth in nanoscale, which is crucial for the mo-dopant’s good distribution throughout the crystal lattice of all the nanowires from the “one-pot” nanosynthesis. in the energy-dispersive x-ray (edx) spectroscopy mapping (figure 2(b)), the mo dopants exhibit a uniform distribution in the nanofibers. this uniformity in distribution suggests the dopant well-dispersed in the mo-doped potassium titanate nanowires, which is indicative of a quite precisely controlled nano-synthesis process. in theory, the [moo6] octahedron in the nanowire lattice is larger than the [tio6] characterization and application of nanomaterials 2024, 7(1), 3587. 4 octahedra [21]. however, this size difference-induced structural distortions were welltolerated without compromising the overall lattice continuity, as suggested by the edx mapping in figure 2. intuitively, the good dispersion of mo allows each [moo6] octahedron to integrate into the lattice without disrupting the structural integrity, thus keeping the framework intact everywhere. in other words, the high dispersion of mo dopant in the nanofiber structure suggests the optimal doping conditions that support the figure 1. figure 2. the edx mapping of the mo-doped potassium titanate nanofibers. (a) the high-resolution sem of mo-doped potassium with the yellow box for edx mapping. (b) the edx mapping showed that the mo, k, ti, and o are evenly distributed on the titanate nanowires. the nanofiber crystal structure was further characterized using the xrd patterns (figure 3). all the xrd peaks of (200), (110), (310), (312), (404), and (020) can be assigned to the layered k2ti6o13 titanate lattice (jcpds no. 40-0403). the xrd patterns of titanate nanofibers with various doping ratios were identical and no residual impurity was detected, as evidenced by no extra peaks in the xrd pattern with respect to the xrd detection limit, which again indicates that the larger [moo6] octahedron was evenly doped in the titanate crystal structure to maintain the lattice integrity and nanowire structure. figure 3. x-ray diffraction of mo-doped potassium titanate nanofibers with doping percentage. comparing the xrd patterns with and without the mo-dopants (figure 4(a)), the large mo-dopant increases the d-space between adjacent titanate sheets by shifting the xrd peak to d(200) = 8.0919 å (or a lower 2-theta angle at 2θ = 11.03o). this is in contrast with the undoped nanowire’s smaller d-space of d(200) = 7.7415 å at a higher 2-theta angle (2θ = 11.43o). this interlayer spacing expansion is indicative of mo substitutional doping within the titanate lattice. more specifically, the ionic radius of mo5+ (75 pm) and mo6+ (73 pm) is larger than that of ti4+ (53 pm) which leads to interlayer spacing expansion with mo5+/6+ replacing ti4+ while without destroying the original lattice structure [21]. equivalently, the mo dopant’s higher content can shift characterization and application of nanomaterials 2024, 7(1), 3587. 5 the d(200) peak to a lower diffraction angle. the same shift happened to (110), (310), (312), and (020), as shown in figure a1. moreover, the doped samples xrd patterns show no structural impurity. apparently, all the xrd peaks are in the same width and can be indexed to that of potassium titanate, matching what our lab reported in literature before [10,17,18]. figure 4. (a) xrd analysis of mo-doped potassium titanate nanowires with (b) d-space. (c) and (d) the schematics for illustrating the mo-dopant impact on the titanate crystal structure. the xps characterization investigated the chemical environment of the mo dopant. the mo 3d3/2 and 3d5/2 peaks of the 4% mo‐doped k-titanate nanofibers are presented in figure 5. the peaks observed at 232.5 and 235.7 ev came from the mo 3d5/2 and mo 3d3/2 of mo6+, while the peaks at 231.9 and 235.0 ev came from the mo 3d5/2 and mo 3d3/2 of mo5+ [22]. these characteristic peaks are attributed to mo-o bonds, indicating the successful integration of mo into the k-titanate lattice. obtaining from the ratio of peak area, the atomic percentage of mo6+ is 67.5% while that of mo5+ is 32.5%, showing that mo6+ is the main dopant form in the k-titanate nanofiber crystal lattice. figure 5. xps spectroscopy of 4% mo-doped potassium titanate nanofibers. characterization and application of nanomaterials 2024, 7(1), 3587. 6 3.2. lessons from the mo-doping evidently, within the k-titanate nanofiber’s clay-like layered crystal structure, the ti4+-based [tio6] octahedra were partially substituted by the mo-based [moo6] octahedra, confirming the sterically challenging doping of mo. naturally, the larger [moo6] compared to [tio6] would position itself more easily on the nanofiber surface to reduce perturbations in the [tio6]-dominated nanowire crystal lattice. such surfaceexposed [moo6] units can be recognized by the osteoblast cell surface to facilitate the bone-tissue adhesion, as supported by the previous studies [12,13]. in this logic, the interlayer k+ cations near the [moo6] could be rapidly substituted by the nearby ca2+ cations in the body fluids. the ca2+ cations’ rapid exchange can in turn accelerate the formation of hydrated calcium phosphates, or hydroxyapatite, on the nanowire surface, matching the findings from other research groups using sbf [9,23], which supports this project’s logic in the rational design. on this basis, the hydroxyapatite layer on the underlying titanate nanofiber should in turn support the sustained bone tissue adhesion on the hydroxyapatite-supported nanofiber, crafting an optimal osteogenic/osteoconductive milieu [9], which is under an ongoing verification using the slow and tedious in vitro cell-culture experiments. the doping-modified titanate nanofibers surface characteristics has demonstrated a simple approach to existing methodologies in literature, for potentially improving the osteoconductivity of bonescaffolds [10,12,15,18,24]. fundamentally, this work found a new and manufacturingviable route to incorporating mo into the titanate nanowire matrix, which could be generally applicable to other subfields of the orthopedic nanomedicine. 4. conclusions potassium titanate nanofibers doped with mo have been successfully fabricated through a simple hydrothermal process, which to the best of our knowledge is quite new, especially in orthopedic nanomedicine. the doping process has been wellcontrolled to keep the nanowire’s morphology, structure, and chemical composition intact. these are indicative of the successful development of an efficient and wellcontrolled doping method for varying the mo dopant concentrations while preserving the nanowires lattice. this is critical for further optimizing the nanowires other properties for different applications. to evaluate the influence of this material in the field of bone tissue engineering, nanofibers with different concentrations of modopant have been investigating in vitro to determine their biocompatibility and osteogenic capabilities. currently, a critical and logical phase of the follow-up research is in progress, concentrating on the analysis of these nanofibers with systematically varied concentrations of mo dopants, for specifically assessing these new nanowires biocompatibility and osteogenic potential. the investigation into the interactions between these mo-doped nanofibers and bone cells is pivotal for acquiring a deeper understanding of their suitability as potential materials for bone implants. the thorough evaluation of the biocompatibility is pivotal to determining these materials viability in for medical applications, especially in the bone tissue regeneration. a forward-thinking strategy to expand upon this research entails the doping of titanate nanowires with, for example, dual oxide dopants. such a new methodology could pave characterization and application of nanomaterials 2024, 7(1), 3587. 7 the way for exploring a broader spectrum of bone implants of new types with the potentially greater physiological adaptability. comprehending the biocompatible transition metals’ doping impact on the physical and chemical properties of these nanowire-based bone implants is crucial and fruitful. this understanding is pivotal for the tailored customization of biomaterials to suit each unique application, ensuring their optimal performance and compatibility. finally, developing a diverse and novel family of doped titanate nanofibers, each characterized by distinct compositions and properties, constitutes a strategic approach for enabling researchers to systematically explore how variations in doping influence the material's characteristics and performance. gathering such data is imperative for the precise optimization of these materials, tailoring them for specific uses in bone tissue engineering or other relevant fields. author contributions: investigation, yt, yx, tc, and aa; writing—original draft preparation, yt, lz, zrt; writing—review and editing, yt, lz, yh, and zrt. all authors have read and agreed to the published version of the manuscript. funding: this work was partially supported from the nsf (grant #2230853) and nist (grant #70nanb22h010). conflict of interest: the authors declare no conflict of interest. the funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. 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doi:10.24294/can.v1i2.529 1 efficiency beta batteries with direct energy conversion sergey v. bulyarskiy1, ivan e. abanin2, alexander v. lakalin1 1 institute of nanotechnology of microelectronics of the russian academy of sciences, moscow, russia 2 scientific-manufacturing complex «technological centre» moscow, russia e-mail: bulyar2954@mail.ru abstract the properties of the beta batteries are compared, which are made on the basis of the different β-isotopes with beta decay. tritium and ni-63 make it possible to make β-sources of high activity, without harmful associated emissions, with low self-absorption, emitting high-energy β-electrons that penetrate deep into the semiconductor and generate a large number of electron-hole pairs. the efficiency of beta batteries needs to be analyzed based on the real energy distribution of β-electrons. it makes possible to obtain the real value of the energy absorbed inside the β-source, correctly estimate the amount of self-absorption of the β-electrons and part of the β-electrons there is a penetrate into the semiconductor, the number of electrons and holes that are generated in the semiconductor, and the magnitude of the idling voltage. formulas for these quantities are calculated in this paper. keywords: isotopes; tritium; nickel-63; sources of beta radiation; self-absorption; surface activity; β-electrons; reflection coefficient; secondary electrons; idling voltage. 1. introduction the sources of β-decay radiation contained a high specific energy density in the unit mass or volume of the substance[1]. beta batteries with direct energy conversion attract scientists more often than other devices. the isotopes used in power supply units (β-batteries) are: ni-63, tritium, sr-90 and pm-147. they have a stock of energies from 3105 to 2107 w·h/kg. therefore, it is reasonable to use them to fabricate batteries for long-term periods of use. for example, beta batteries can be developed with a service life more than 30 years based on the ni-63 isotope[2,3]. batteries based on direct energy conversion have an efficiency of about 1%. in this case, β-electrons generate electron-hole pairs in a semiconductor, which are separated by the electric field of a p–n-junction or a metal-semiconductor contact[4-6]. the nickel ni-63 isotope has a half-life of 100 years. the low average energy of β-electrons (17.6 kev) does not create problems concerning radiation protection and is quite a lot lower than the semiconductor radiation-damage threshold, thus completely excluding p–n-junction degradation. therefore, this isotope, despite its high cost, is rather widely used to fabricate β-batteries[2,3,7,8]. a disadvantage of structures based on this isotope is the low efficiency (not exceeding 1%) of β-batteries. this is a significant problem, which limits the use of beta batteries. an analysis of the scientific literature[1-8] shows that the structures with isotopes with shorter half-lives have an advantage. in this case, the number of decays per unit time (isotope activity) is larger and the current value proportional to the activity is higher. however, the efficiency of direct conversion of all the devices is rather low. it is evident that numerous factors affect the battery efficiency. firstly, the source of emission: activity, energy of the emitted electrons, and their energy distribution. secondly, design parameters: thickness of the isotope active layer, effects of self-absorption, structure and morphology of the layer, and the design features of the p–n-junction. these factors are rather weakly elucidated in the scientific literature. this work is aimed at comparing the efficiency of the power supplies produced based on various sources of β-radiation and revealing the factors that reduce the efficiency of a device copyright © 2018 sergey v. bulyarskiy et al. doi: 10.24294/can.v1i2.529 enpress publisher llc.this work is licensed under the creative commonsattribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 2. samples for studies the power supplies that were studied in this work were composed of the source of β-radiation and specially prepared semiconductor convertor based on pin-structure. two types of beta sources were used. the first type of source was made of titanium foil, on the one of surfaces of which was located a layer of titanium ditrite tit2. the second type of source was made from a nickel foil, which contained 20% of the ni-63 isotope. the β-source sizes corresponded to the pin-diode working surface. when the source was superimposed onto the diode, it contacted to the surface tightly enough practically without passing diffused light. a small air gap existed between the diode surface and the source, which did not play any significant role. the set of radiation sources of different activities was used by measurements. the properties of isotopes of beta radiation are given in table 1. isotopes half-life 5.0t , years average energy of the β-electrons (еm), kev density (ρ), g/sm3 power emitted by a β-source with activity 1 ci (pk), µw/ci isotope content in the material β-source, % the activity on the surface of the β-source (as), mci sm-2 film of the tit2. 12.5 5.7 4.1 34 6 1.2-2.2 foil of the ni-63 100 17.8 8.9 100 17-20 5-27 table 1. properties of the isotopes we used pin-diodes with a 0.6 cm2 working surface as convertors. the substrates of high quality monocrystalline silicon of the 100 kef-4400 (111) brand (n-type silicon doped with phosphorous) were used as the initial material for the creation of pin-diodes. silicon ingots with a specific resistance of 1000 ω·cm were grown using a floating zone remelting method. the density of stacking faults is not more than 5102 cm–2, the density of the dislocations is less than 1102 cm–2 according to the technical specifications for the wafers of this bran. surface activity (as) was measured by a beta spectrometer directly on the finished samples. it is known that the coefficient of converting β-radiation into the electrical current increases with a decrease in the reverse currents. two technological operations were introduced in the pin-diode technology, namely, an internal gettering and the creation of a guarding ring. the gettering was implemented by forming a strongly doped region with electron conductivity on the back side of a silicon wafer. this region was covered by layers of polysilicon and silicon nitride. then, a gettering annealing was carried out at temperatures ranging from 700 to 1000°c. the reverse currents in the dark at 295 k and at a reverse bias voltage of 40 v was to 0.1-0.2 na. a small reverse current took place thanks to the choice of high-quality silicon as the initial material and the introduction of the operations that were mentioned made it possible to reduce the current. 3. experimental results the dark current–voltage (i–v) characteristics at direct and reverse biases were measured for all the diodes by the standard method. further, the sources of β-radiation of different activities were superimposed onto the diodes and the measurements of the i–v characteristics were repeated. in this case, the open-circuit voltage and short-circuit current were determined. the short-circuit current of the beta battery is shown in figure 1. parameters of beta batteries are shown in table 2. 3 figure 1: dependence of the shot-circuit current from surface activity of the isotope, mci: 1 – ni-63; 2 – tritium. изотоп as,mci pav,nw ics, na uxx, mv p, nw η,% h-3 1.2 43 5.8 58 0.22 0.53 1.8 64 9.6 69 0.44 0.70 2.2 79 11.2 72 0.54 0.65 ni-63 5 535 40 105 2.81 0.53 10 1070 57 112 4.3 0.4 16 1170 62 117 4.94 0.29 22 2350 64 119 5.1 0.22 27 2780 67 120 5.8 0.21 table 2. parameters of beta batteries. note: as surface activity of the β-source; pav power of the β-radiation of the β-source; ics short-circuit current; uxx open-circuit voltage; p the electrical power in the circuit is allocated to the load resistance of the optimum value; η beta battery efficiency. power of the β-radiation of the β-source is calculated by formula: skav app  ,(1) where pk power emitted by a substance with activity 1 ci. the electrical power in the circuit is allocated to the load resistance of the optimum value ( optp ) and is calculated by means of the load current-voltage characteristic, which is shown in figure 2 by formula [9]: maxmaxuipopt  ,(2) maxu voltage of the pin-diode with the optimum load resistance of the electrical circuit. maxi the diode current at the optimum load resistance of the electrical circuit. the load characteristic (figure 2, curve 2) was used to determine maxu and maxi . the voltage maxu corresponds to the maximum of the load characteristic. 4 figure 2: electrical characteristics of the beta battery based on ni-63. 1 – i–vcharacteristic; 2 – the power, which is released on the load resistance, on the electrical voltage. the current-voltage characteristic (i–vcharacteristic) (figure 2) makes it possible to calculate the fill factor ( eff ) of a semiconductor converter eq. (2) [9]: xxsc ef ui uif maxmax .(3) this value varied from 0.62 to 0.66 for the pin-diodes used in this work. the beta battery efficiency is calculated by formula: av opt p p  .(4) the open-circuit voltage was achieved maximum (120 mv) for the isotope ni-63, while the short-circuit current was 67 na. it’s power achieved 5.8 nw (see table 2). the isotope has undoubted advantages in comparison with tritium. our result exceeds the achieved values by a factor of 1.5. the experimental data for the beta battery with tritium and ni-63 isotopes differ significantly. the experimental data for power sources with isotopes of tritium and ni-63 differ significantly. the power of the ni-63 isotope power sources exceeds the power of the same device with the tritium isotope by a factor of 3, with the same particle flux emitted from the source surface unit per unit time (surface activity as = 1 mci). in addition, with increasing activity of the β-source, the power of the instrument with the isotope ni-63 grows faster. this fenomen is associated with the fact that the ni-63 isotope is characterized by a higher average energy of an electron emitted in β-decay. it is equal to eav = 17.6 kev, while for tritium it is 5 kev. in order to form an electron-hole pair, an energy of is required in the case of silicon (eg is the bandgap width of the semiconductor). the greater the energy of an electron emitted in β-decay the larger the number of electron-hole pairs it forms and the larger its quantum yield. the table 2 shows a comparison between the quantum yields for ni-63 and tritium isotopes. 4. discussion of experimental results 4.1 beta battery efficiency the total efficiency of the beta battery is controlled by four main processes: self-absorption; the collection efficiency of electrons and holes which are generated in the space-charge region of the semiconductor part of the converter; secondary x-ray radiation, which occurs when electrons interact with matte and the semiconductor-structure efficiency [1,9]: 5 sheс    ,(5) where  is the fraction of β-electrons which reach the semiconductor converter surface; с is the fraction of β-electrons which arrive at the space-charge region and can contribute to the electric current; he is fraction of β-electrons that cause electron-hole pairs, s is the total efficiency of the diode which provides conversion. 4.2 self-absorption of the β-source in this section, we consider the first term of the eq. (5)  . the efficiency of beta batteries is related to the maximum flow that the source radioactive substance can emit from its surface (as). this quantity will be called surface activity. it is equal to the number of β-electrons that are emitted per unit time from a unit surface. it must be distinguished from the volumetric activity, which is declared in the passport of the β-radiation source. volumetric activity is equal to the number of decays occurring in the entire volume of matter per unit time. this value can be determined on the basis of the parameters of the law of radioactive decay:  tnn  exp0 , (6) where n0 is the number of radionuclide atoms at the initial time (t = 0);  is the decay constant, which is a property of the radionuclide. the decay constant is related to the half-life ( 5.0т ), which is defined as the time interval during which half of the atoms of the radionuclide material there are decay /2ln5.0 т . this value is a reference and is known for all isotopes of radionuclides. activity is a physical quantity that is equal to the number of decays per unit of time. it characterizes the decay rate, i.e. the number of decays per unit time in the entire volume of the source. 5.00 /2ln/ tndtdnа  (7) in isotopes, the self-absorption phenomenon is pronounced, which means that far from all electrons are incident on the active-layer surface. therefore, isotope-layer growth does not mean an increase in its surface activity. let the initial activity of 1 cm3 of a material be a0v. this activity is calculated by the formula: vaаv /0  , (8) where v is the volume of the β-source;  is a fraction of the atoms of the radioactive isotope in the β-source substance. electrons emitted during β-decay have energies of tens of kev. they lose their energy when they are scattered by a solid lattice. there are several scattering mechanisms among which of primary interest to us is scattering with the emission of secondary electrons which further contribute to the electric current of the power supply unit. for practical purposes, it is convenient to use a formula approximating the mentioned calculations performed by the monte-carlo method [10]: 32 23.504.1221.660.0)(  h , )(er z  ,(9) where z is the average depth of electron penetration into a material and r(e) is the maximum path length along the trajectory of an electron with energy e in a material with density ρ. to estimate this value, we use the formula [11]: 75.10398.0)( eer   (10) function (10) means the probability of the detecting a particle with energy e at a certain depth. the efficiency of beta batteries is related to the maximum flow that the source radioactive substance can emit from its surface. then the activity of a material layer of thickness dz at the depth z from the surface is az = a0vsdz. this quantity is proportional to the number of electrons of any energy, which are generated in this layer. the active-layer parameters are calculated as a rule using the average energies of β-electrons. such an approach is 6 not sufficiently accurate. in the present study, we perform numerical calculations using the experimental distributions of electrons emitted during the decay [12]. the electron energy during β-decay is known with a certain probability wc(e). we calculate this value by normalizing the experimental distribution to unity, )()(;1)( max 0 efaewdeefa zс e z  , (11) where wc(e) means the probability of detecting a β-electron in the energy range from e to e + de. this value is shown in figure 3 for ni-63 isotopes. figure 3: the probability of detecting a β-electron in the energy range from e to e + de for the isotopes ni-63 by eq. (11). the probability that an electron with energy e, generated at depth z will reach the surface is given by:      )(/ erzhewew ccs  . (12) this formula takes into account that half of all electrons have momentum directed toward the surface; however, two semiconductor converters are used. the structure is shaped as a sandwich with an emitter between the converters. the probability that an electron of any energy, generated at depth z will reach the surface is given by     max 0 )(/ e ccs deerzheww . (13) then the expression for the surface activity takes the form      d e ccvs deerzhewdzsaa 0 0 0 max )(/ . (14) the total activity of the β-source (a) increases in proportion to its thickness d: a = a0vsd. the ratio of the surface activity eq. (9) to the total activity is equal to the β-source efficiency factor  :      d e cc deerzhewdzd 0 0 1 max )(/ (15) power emitted by the β-source has a maximum at a certain thickness dopt which is the optimal β-source thickness. figure 4 shows the calculated ni-63 and c-14 isotopes power emitted by the β-source of the isotope-layer thickness. the dependence, which is shown in figure 4, is nonlinear. therefore, the β-electrons are absorbed and at the optimum source thickness. so, efficiency factor  there is less than one at optimum thickness. it can be calculated using ed. (15). the results of the calculation for all isotopes are shown in table 3. 7 figure 4: radiation power of the β-sources based on isotopes ni-63. β source material titanium ditrite ni-63 optimal thickness dopt, µm 0.35 1.5 maximum surface activity, maxsa , mci·sm-2 18 24 the maximum power emitted by the β-source, pavmax, µw 0.61 2.7 efficiency factor  at optimum source thickness, % 70 75 table 3. optimal thickness of the β source. the optimal isotope ni-63 layer thickness estimated in this study is on the order of 1.5 µm 4.3 fraction of β-electrons which arrive at the space-charge region a β-radiation source and a semiconductor converter of β-electron energy into electrical energy (pin-diode) exist in close contact without a significant air gap. the physical boundary is between them, so the β-electrons emitted by the β-source are reflected from the outer boundary. the reflection coefficient ( сr ) increases monotonically with increasing ordinal number of the target material. this coefficient can be estimated from the formula [13]: z с zr /92)(  ,(16) where: z is the ordinal number of the element. this formula is applied when the energy of the β-electron is e > 30 kev. if the inequality is not satisfied, then an additional error arises for β-electrons. the average electron energy of ni-63 is 17.6 kev. calculation by formula (16) contains an error. the coefficient of reflection of electrons with an energy of 5 kev (tritium) сr = 0.22, and 17.6 kev (ni-63) is сr =0.2. thus, for tritium, the error of the reflection coefficient is 10%, and for nickel the result 0.2 is accurate and it can be used in calculations. now fraction of β-electrons which arrive at the space-charge region (ηc) is equal to ηc =1сr =0.8. losses on the reflection of the β-electrons, that have average energies and there is a move normally to the surface, do not determine the real losses with the required accuracy. the β-electrons exist from the β-source not only normally to the surface, but at any arbitrary angle. this dependence was calculated for an aluminum foil in [15] by the monte carlo method. the density of silicon is close to the density of aluminum, so these results can be used to analyze the reflection of the β-electrons from the surface of silicon. the results, which are shown in figure 5 are approximated by the formula: 36253 1020.11018.51048.2121.0)(   r .(17) 8 figure 5: the coefficient of reflection of electrons from the surface of the pin-structure at various angles of incidence. the reflection coefficient was calculated by the mean value theorem by integrating ed. (17) in the range from 0 to 90°. it is equal to 0.31 for silicon. the part of electrons that have passed through the surface of the silicon is 69%. 4.4 fraction of β-electrons that cause the generation of electron-hole pairs in the pin-structure eh we calculated the fraction of β-electrons that penetrate the semiconductor in points b and c. these electrons have a lot of energy and create different phenomena in a solid state, when they lose their energy. for a systemization, the interactions are classified into two different types, namely elastic and inelastic interactions. elastic interactions is the case, then, no energy is transferred from the electron to the sample. as a result, the electron leaving the sample still has its original energy e0. such electrons contribute to the direct beam which contains the electrons that passes the sample in direction of the incident beam. beta batteries have a thick semiconductor layer and these losses can be ignored. elasticlу scattered electrons will take part in the processes of inelastic interaction sooner or later. therefore, the total cross section is the sum of the elastic (σel) and inelastic (σinel) cross sections. the ratio of these sections is determined by the empirical law [16,17]: zel inel 18    this law shows that the inelastic scattering cross-section for the silicon is larger than the elastic cross section. electrons are scattered inelastically in 70% of cases. the processes of inelastic scattered of electrons with matter lead to the following phenomena: 1. the energy of electrons is consumed by the electron-impact ionization of the atoms of matter into which the particle is introduced. this phenomenon produces electron-hole pairs that create a beta-voltaic effect. 2. the β-electrons in the field of the lattice nuclei of a substance results in the appearance of the different signals such plasmons, phonons, uv quanta or cathodoluminescence secondary x-ray radiation, which also reduces the energy of the particles. 3. the energy of electrons is consumed to form lattice defects of matter. the electron energy of the isotopes used has a value from 2 to 150 kev. this value is small to form defects in the silicon of which the pin-diode is made. therefore, phenomenon 3 does not occur in our case. the energy of the β-electrons is small for the formation of any defects. phenomenon 1 is useful, since it leads to the formation of electron-hole pairs and the appearance of a beta voltaic effect. phenomenon 2 leads to energy loss, which is not desirable for the operation of beta batteries. 9 the loss of the energy of any β-electrons by inelastic scattering is determined by the energy of the β-electron and by the mechanism of these losses. the total value of these losses is determined by the bethe-bloch theory. in this value, the greatest contribution is made by the mechanisms that are associated with the formation of secondary electrons, plasmons, and x-rays. the calculations performed in [18] show that in the β-electron energy region up to 100 ev 70% of their energy is expended on the formation of secondary electrons and 30% on the formation plasmons. at energies above 1 kev, the excitation energy of the inner shells of atoms predominates and exceeds the loss of plasmon formation by a factor of 4-6. calculation of losses associated with secondary x-ray radiation is done in [19]. the coefficient of this losses r is only ηλ = 0.2%. the results of [20-22] show that the excitation of the l-series will swell less than 10% of the energy. leamy h.j. [23] believes that the main electron energy losses are due to the formation of secondary electron-hole pairs, and the other losses are 8%. one may assume that 60-80% of the electron energy is expended on the formation of secondary electrons. 4.5 efficiency of the diode is provided conversion high energy electrons are generated the electrons and holes in the i-region of the pin-diode, which causes the current diffusion towards the surface. at diffusion, the electrons and holes recombine by non-radiative recombination centers in the bulk material. we will solve the continuity equation to obtain the theoretical value of the open circuit voltage under the assumptions [9]: 1. because of the high doping level of the pand n-regions, as compared to the i-base, the hole current flows through p-i-junction, and electronic current through n-i-junction. this assumption means that because the excess minor carriers do not penetrate the pand n-regions, the recombination of electron-hole pairs can be neglected; 2. high level of carrier injection is realized in the i-region, then n » ni, p » ni. the voltage across the resistances of the pand n-regions due to heavy doping is negligible. full voltage across the p-i-n-diode is composed of the voltage drops across p-i-transition, n-i-transition and in i-region; 3 at high injection level, the lifetime of charge carriers in the i-region τ = τ∞ and does not depend on the charge carrier concentration (τ∞ is the lifetime at high excitation level of the semiconductor). this assumption is valid for recombination of the charge carriers through the recombination centers; 4. in the i-region, the condition of the quasineutrality is true (n(x) = p(x)). under these assumptions, the equations for the current densities of electrons jn and holes jp and the continuity equation of i-region can be written as [9]: dx dpedpeej ppp   dx dpedpeej nnn   (18) 0)(1    xgnp dx dj e ip  0)(1    xgnp dx dj e in  where e is elementary charge; μn is mobility of the electrons; μp is mobility of holes; p is concentration of holes; f is electric field strength in i-region; dp is diffusion coefficient of the holes; dn is diffusion coefficient of the electrons; ni is the intrinsic carrier concentration; g(x) is distribution function of the generated electrons and holes by i-region. high-energy electrons, flying out of the isotope layer penetrate the semiconductor and generate secondary electrons, which cause the current. each β-electron with energy (e) there are generates not one but multiple electron-hole pairs in interaction with the semiconductor material. therefore, it is necessary to introduce the ratio β-electron energy to the energy of formation of electron-hole pairs in the material into a generation formula. the semiconductor layer parameters should be used for distribution of the generation function along space-charge region. the generation rate of secondary electrons at a depth x is determined by the electrons of all energies that are emitted from the β-source, so: 10 de er xh e eewaxg e efi cs           max 0 )( **)(*)( ,(19) where kevevee gi 00362.062.3714.0596.2  is energy of the formation of electron-hole pairs in silicon. the density of silicon substituted into eq. (10), which determines r(e). the eq. (19) defines the number of electrons generated per second at a depth x (fig.6). dependency g(x) can be described by the empirical function in general    n i ii xkagxg 1 1 )exp()( ,(20) where g1 is generation rate of electron-hole pairs by β-electrons; ai and ki are approximation constants of the generation rate determined by the eq. (19). figure 6: distribution of high-energy electrons in the space-charge region of the pin-diodes. points is calculation by the eq. (19); line is the approximation of calculation by three exponential terms by eq. (20). to calculate the open-circuit voltage it is necessary to solve the continuity equation eq. (18). it is possible to formulate the problem in our case:                       ; 2 ; 2 ; ;0)exp()( 0 1 1 22 2 nwx px n i ii aa ii ed j dx dp ed j dx dp pn xka d g l np dx npd (21) where )( 2 np npb a e tk d     is ambipolar diffusion coefficient; e is the elementary charge; kb is the boltzmann constant; )()( np b np e tkd  is diffusion coefficient; aa dl 2 is ambipolar diffusion length; w is thickness of the i-region. a solution of eq. (21) is a relationship: 11                                                                     n i ia ii a a aa a a p a n a a a i kl xka d lg l xwch l xch l wsh l d l xwch d l xch l wshe jlnxp 1 22 2 1 1 )exp( 2 )(  (22) here we use the notations:                  ; 1 )exp( ; 1 1 22 2 1 1 22 2 1 n i ia iii a a n i ia ii a a kl wkak d lg kl ak d lg                   ; 1 )exp(~ ; 1 ~ 1 22 2 1 1 22 2 1 n i ia ii a a n i ia i a a kl wka d lg kl a d lg   (23) we can calculate the idling voltage from the ed. (22) and (23) it follows that:                                                                                                                                                   ~ ~ ln ~~1ln 2 a a a i a a a i np pn a a a i a a a i i b xx l wch l wsh ln l wch l wsh ln dd l wch l wsh ln l wch l wsh ln ne tku (24) we can calculate the current of the pin-structure only by numerical methods. we cat to get s after that by equation: xxscefs uif .(25) however, if we do not know anything about the processes of generation and recombination in the pin-diode, the properties of the recombination centers in it, the lifetimes of electrons and holes, we can’t to calculate the efficiency of a semiconductor converter. 5. conclusions the efficiency of the beta battery is dependent on a number of factors and is determined by the ed. (4). the fraction of β-electrons, which reach the semiconductor converter surface  , is about 0.4. this is due to the fact that at the optimal thickness 80% of β-electrons pass into the radiation and half of them go back to the source. some of the electrons are reflected from the surface of the semiconductor. this fraction which arrive the space-charge region and can contribute to the electric current is 0.7. the fraction of β-electrons that cause electron-hole pairs ( he ) is 0.6-0.8. the efficiency of the diode which provides conversion ( s ) is 0.66 in our case. the total efficiency is 0.12-0.16. the experimental value of the efficiency is 0.01. these values differ from each other and this is due to two factors: 1 recombination in the active region of the diode; 2 excess return current, which is not described by the classical shockley-read theory. 12 the number of secondary electrons that are generated by one β-electron and it can take part in the creation of an electric current is determined by the energy of the β-electron and the width of the forbidden band of the semiconductor. 5.08.2   g midl e en a great advantage of the isotope ni-63 is the high energy of the electrons and the absence of harmful spurious emissions, such as gamma quants. therefore, this isotope exceeds tritium and pm-147. this β-source allows you to get the best electrical parameters of the batteries even with less activity of the source. loss of energy in beta batteries should be analyzed and understand ways to increase the efficiency references 1. bower ke, barbanel ya, shreter yg, et al. polymers, phosphors, and voltaics for radioisotope microbatteries. crc press, boca raton, london, new york, washington. 2002; 472 p. 2. reznev aa, pustovalov aa, maksimov em, et al. perspektivy sozdaniya miniatyurnogo istochnika toka na beta-voltaicheskom effekte s ispolzovaniem v kachestve aktivnogo elementa izotopa ni-63. nanomikrosist. tekh. 2009; 3 (104): 14-16. 3. chandrashekhar mvs, thomas chi, li h, et al. demonstration of a 4h sic betavoltaic cell. appl. phys. lett. 2006; 88: 033506-3. 4. eiting cj, krishnamoorthy v, romero e, et al. proceedings of the 42nd power source conference, philadelphia, pa, june 12–15, 2006; 601-606. 5. andreev vm, kavetsky ag, khvostikov vs, et al. tritium-powered betacells based on alxga1-xas. proceedings of the 28th ieee photovoltaic specialists conference, anchorage, 2000; 1253-1256. 6. rybicki gc. silicon carbide radioisotope batteries. nasa/cp-2001-210747/rev1, 2001; 199-233. 7. guo h, lal a. nanopower betavoltaic microbatteries. transducers, solid-state sensors, actuators and microsystems, 12th international conference, boston, 2003; 36-39. 8. sun w, kherani np, et al. a three-dimensional porous silicon p-n diode for betavoltaics and photovoltaics. adv. mater. 2005; 17: 1230-1233. 9. sze sm. physics of semiconductor devices. john wiley and sons (wie), new york, chichester, brisbar, toronto, singapore, 1981; 868 p. 10. everhart te, hoff p.h. determination of kilovolt electron energy dissipation versus penetration distance in solid materials. j. appl. phys. 1971; 42: 5837-5846. 11. ong vks, phua pc. junction depth determination by reconstruction of the charge collection probability in a semiconductor device. semicond. sci. technol. 2001; 16: 691-698. 12. kolobashkin vm, rubtsov pm, aleksankin vg, ruzhanskiy pabeta-izluchenie produktov deleniya: spravochnik. atomizdat, moscow, 1978; 472 p. (beta-radiation of fission products: handbook) 13. arnal h, verdier p, vincensini p. coefficient de retrodiffussion dans de gas d’electrons monocinetiques arrivant sur la cible sous une incindence oblique. compt. rend. acad. sci. 1969; 386: 1526-1536. 14. remier l, tollkamp c. measuring the backscattering coefficient and secondary electron yield inside a sem. scanning. 1980; 3: 35-39. 15. seltzer sm transmission of electrons through foils. national bureau of standards. washington, d.c. 20234. 1974. 16. reimer l. transmission electron microscopy, physics of image formation, and microanalysis. springer, berlin. 1989; 547 p. 17. egerton rf. electron energy-loss spectroscopy in the electron microscope. plenum press, new york. 1996; 485 p. 18. tung cj, ritchie rh, ashley jc et al. inelastic interactions of swift electrons in solids. port royal hoad, springfield, virginia. 1976; 118 p. 19. pucherov nn, romanovsky sv, chesnokova nd et al. tablicy massovoy tormoznoy sposobnosti i probegov zaryazhennyh chastic s energiey 1-100 mev. kiev: "naukova dumka". 1975. 345 p. (tables of the mass stopping power and ranges of charged particles with an energy of 1-100 mev) 20. egerton rf. electron energy-loss spectroscopy in the electron microscope, appendix b. plenum press, new york. 1986; 410 p. 21. bartlett pl, stelbovics at. calculation of electron-impact total-ionization cross sections. phys. rev. a 2002; 66: 012707-10. 22. gryzinski m. classical theory of atomic collisions. i. theory of inelastic collisions. phys. rev. 1965; 138: a336-a358. 23. leamy hj. charge collection scanning electron microscopy j. appl. phys. 1982; 53: r51-r80. characterization and application of nanomaterials (2020) volume 3 issue 2 doi:10.24294/can.v3i2.551 87 review article a review on metal-organic framework: synthesis, properties and application sanju soni 1 , parmendra kumar bajpai 2 , charu arora 1 1 department of chemistry, guru ghasidas vishwavidyalaya, bilaspur, c.g. 495009, india e-mail: charuarora77@gmail.com 2 department of pure and applied physics, guru ghasidas vishwavidyalaya, bilaspur, c.g. 495009, india abstract metal organic framework is a class of hybrid network of supramolecular solid materials comprised of a large number of inorganic and organic linkers all bounded to metal ions in a well-organized fashion. this type of compounds possess a greater surface area with an advantage of changing pore sizes, diversified and beautiful structure which withdrew an intense interest in this field. in the present review articles, the structural aspects, classification, methods of synthesis, various factors affecting the synthesis and stability, properties and applications have been discussed. recent advances in the field and new directions to explore the future scope and applications of mofs have been incorporated in this article to provide current status of the field. keywords: metal organic framework; nanoporous material; drug delivery; gas sensor; secondary building unit article info article history: received 5 august 2020 received in revised form 4 september 2020 accepted 7 september 2020 available online 20 september 2020 copyright copyright © 2020 sanju soni et al. doi: 10.24294/can.v3i2.551 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/by/4.0/ framework of this paper framework of this paper http://creativecommons.org/licenses/by/4.0/ 88 1. introduction metal-organic framework (mof) is a promising class of materials composed of metal centres or clusters and organic linkers. these are porous crystalline materials in which metal is locked into a position to produce rigid and porous geometry and connected through different organic groups. due to structural flexibility, large surface area and tailorable pore size, mofs have wide applications in field of gas adsorption and storage, separation, catalysis, sensing, molecular recognition, drug delivery, non linear optics, luminescence etc. [1-12] . due to three di mensional tuneable porous channels, mofs are useful materials for storage, separation or conversion of molecules on the basis of dimension. generally, mofs are related to the general class of co-ordination polymers. however, mofs are more specific than co-ordination polymers for 2d or 3d crystallized networks with porous structure. thus these are also termed as porous coordination polymer (pcp) [13,14] . although, several review articles on metal-organic frameworks have been published previously, however, recent advances including the contributions of some indian research groups, such as banerjee et al., ghosh et al., and kumar etc. necessitates further review on this topic. the present paper comprehensively reviewed the methods of synthesis, properties and applications of mofs bas ed on reported literature. recent advances and new foundations, direction for further exploring mofs for their applications as well as critical analysis of the research have been incorporated in this paper so as to provide the current status of the field. figure 1. some linkers used in synthesis of mofs. 2. structural aspects 2.1 primary building units the metal ions (connectors) connecting the organic polymers which are linkers are basic primary units that result in porous three dimension structure mofs. thus, the metal ions and organic compounds used in the formation of metal-organic frameworks are the ―primary building units‖. commonly, metal ions of first row transition series such as cr 3+ , fe 3+ , co 2+ , zn 2+ are used as connectors in the formation of mofs [15-17] . some alkali metal ions [18,19] , alkaline-earth metal ions [20-22] and rare earth metal ions [23-27] are also used as a metal connector in the synthesis of mofs. nitrate, acetate, sulphate, chloride and oxide of metals are used as precursor for preparing mofs in most of the synthesis routes. however, in electrochemical synthesis 89 of mofs metal rods are used. organic linkers, through which the metal ions or nodes are connected, generally contain functional groups that are capable of forming coordination bonds such as carboxylate, phosphate, sulfonate, amine, nitrile etc. some examples of organic linkers are shown in figure 1. 2.2 secondary building units (sbus) in mofs, organic linkers are connected throu gh metal-oxygen-carbon clusters, instead of metal ions alone. these metal-oxygen-carbon clusters are referred as ―secondary building units‖ (sbus). sbus have intrinsic geometric properties, which facilitate mof’s topology [28] . some sbus are shown in figure 2. figure 2. some secondary building units (sbus). 2.3 classification of metal-organic frameworks on the basis of structural features, mofs have been classified [29] in following groups. (a) rigid frameworks: these are stable and robust porous frameworks and retain their porous framework on adsorption or desorption of guest molecules. these mofs are applicable in molecular sieving [30] . (b) flexible/dynamic frameworks: flexible fra meworks show an utmost change in shape on insertion or removal of guest particles and also affected by external factors such as pressure, temperature. dynamic mofs show a change in framework on removal of solvent molecules but retain their porous structure on adsorption of gas molecules at high pressure [4] . mil-5 [31,32] , mil-8 [33] and snu-m10 [34] are some mofs that exhibit breathing effect during adsorption and desorption. in breathing mofs [35] , there is a severe change in unit cell volume (pore volume) on adsorption/desorption of guest molecules. different types of flexibility modes are identified and reviewed as shown in figure 3. figure 3. classification of different flexibility modes of mofs. (c) open metal site: performance of mofs can be enhanced by the presence of open metal site. presence of water in open metal site mofs enhances the co2 capture ability of the mofs. for example, hkust-1 [(cu)3(btc)2] which has an open metal site structure and consists of paddlewheel units cu2(coo ) connected through btc 3 ligands, exhibits a significant increase in co2 adsorption when it contains 4 wt.% water [36] . (d) surface functionalized framework: adsorption ability of mofs can be enhanced by grafting functional groups onto the surface of the mofs. functional groups with a high affinity for co2 (e.g. arylamine [37] , alkylamine [38] , hydroxyl [39] ) have been reported to enhance the capacity and selectivity of mofs for co2 adsorption when these functional groups are grafted onto the surface of the porous framework through either ligand modification or coordination to unsaturated metal centre. 3. synthesis of mofs as discussed earlier, mofs consists of two major components, metal ion and organic linkers 90 or bridging ligands. conventionally, mofs are prepared by combining metal ions and organic linkers under mild conditions in order to get a crystalline and porous network. this is termed as ―modular synthesis‖ [40] . during the last two decades, different synthesis methods have been developed and applied to synthesize these materials. in general, these can be classified as conventional solvothermal method and unconventional method. 3.1 conventional solvothermal/hydrotherm al and non-solvothermal method in conventional solvothermal synthesis, a mix ture of metal ions and organic linkers in solvent is heated in glass vials (for lower temperature) or in teflon lined autoclaves or bomb reactor (for temperature higher than ≈400 k) [41] . if water is used as solvent, this method is termed as hydrothermal method. the synthesis parameters that are controlled for specific structure are pressure, temperature, solvent composition, reagent concentration etc. temperature of reaction mixture is an important parameter in the synthesis of mofs. when the temperature of the reaction is higher than the boiling point of solvent, then the reaction is referred as solvothermal reaction and when the temperature is lower than the boiling point of solvent, it is referred as nonisothermal reaction. some mofs, such as mof-5, mof-74, mof-177, hkust-1 zif-8, have been reported to synthesize at ambient condition [42-44] . this method is also known as direct precipitation reaction. morphology of the crystals produced is highly affected by the reaction temperature [45] . 3.2 unconventional methods a mixture of metal salt and organic linker is grinded in a mortar pestle or in a ball mill without using solvent after grinding the mixture is heated gently to evaporate water or other volatile molecules which are formed as by products in the reaction mixture [46] . this method is termed as mechanochemical method. in this method, breaking of intramolecular bonds by mechanical force takes place followed by a chemical transformation. the method is known to be environmentally friendly because of no use of any solvent and can give high yield of products [47,48] . quantitative yields of small mof particles can be obtained in short reactions times, normally in the range of 10-60 min. in many cases, metal oxides were preferred over metal salts as starting material, which results in water as the only byproduct [49] . synthesis of porous framework using mechanochemical method is first reported by pichon et al. [50] in 2006. comparative stu dy of a bipyridene-based covalent organic framewo rk (cof) has been reported using solvothermal and mechanochemical methods and it is revealed that proton conducting property [51] is revealed by mechanochemically synthesized cof only. when solvent is added in a small amount, the mechanochemical process is termed as liquid-assisted grinding (lag). addition of small amount of solvents in reaction mixture accelerates the mechanochemical reactions by increasing the mobility of the reactants [52] . 3.3 alternative synthesis methods alternative routes have also been attempted in addition to these methods. alternative routes can lead to different crystallization rate, particle size, size distribution and adsorption properties as well as morphologies that can have an influence on the properties of material. for example, diffusion of guest molecules in porous materials with different particle size can exhibit a direct effect on catalytic activity, adsorption and separation capacity of molecules. important alternate routes can be categorised as: 3.3.1 microwave-assisted synthesis in this method, energy for reaction is provided in the form of microwave (mw) radiation. it is generally used in organic syntheses, but it has wide application in rapid synthesis of nanoporous materials. apart from fast crystallization, phase selectivity [53,54] , narrow particle size distribution [55] and morphological controls [56,57] are some of the advantages of this method. several mofs containing metal ions + organic linkers mof 91 fe 3+ , al 3+ , cr 3+ , v 3+ , ce 3+ have been synthesised using mw assisted method. cr-mil-100 [58] is the first mof which has been synthesized via mw method. formation of mofs has been reported to carry out under mw radiation at a temperature over 100˚c with reaction time exceeding 1 hour. generally, mofs can be formed quickly via mw irradiation with respect to conventional electrical heating process. by applying mw synthesis route two mofs, named irmof-1 and hkust-1, are studied widely. irmof-1 reveals crystals of higher quality and better co2 adsorption when it is synthesized via mw assisted route [59] . highly pure and micropore with high volume (0.79 cm 2 gm -1 ) hkust-1 is pre pared by mw synthesis in a short time of 30 minutes [60] . 3.3.2 electrochemical synthesis researchers at basf first reported the synthesis of mof using electrochemical route [61] . they developed new synthesis procedures for some mofs using zn, cu, mg, co as cathode material and 1,3,5-h3btc and 1,2,3-h3btc, h2bdc and h2bdc-(oh)2 as linkers. electrochemical synthesis of mof uses metal ions continuously supplied through anodic dissolution as a metal source instead of metals salts, which react with the dissolved linker molecules and a conducting salt in the reaction medium. protic solvents are used to avoid deposition of metal on cathode, but h2 is generated in this process [62] . the electrochemical route is also possible to run normal batch reactions [49] . mofs containing ionic liquids as linker e.g. [zn(mim)2] and [zn(bim)2] are also synthesized via electrochemical route [63] . schlesinger et al. [60] synthesized hkust-1 using solvothermal, ambient pressure and electrochemical routes and compared the effect of synthesis procedures on its properties. it has been pointed out that the product obtained via electrochemical route reveals inferior quality due to incorporation of linker molecules and/or conducting salt in the pores during crystallization. 3.3.3 sonochemical synthesis this is a rapid and environmental-friendly method in which ultra-sonic radiation (20 khz-10 mhz) is used for mofs synthesis. this method, via homogenous and accelerated nucleation, can also achieve a reduction in crystallization time and significantly smaller particles size than those by the conventional solvothermal synthesis [64,65] . when hi gh energy ultrasound interacts with liquid, cavitation (process of bubble formation, growth and collapse under altering pressure) takes place and provides energy with high temperature of ≈5000k and pressure of ≈1000 bar [66] . in case of solids, microjets are formed as a result of cavitation process and these microjets clean, erode or activate the surface. dispersion of agglomerated smaller particles takes place. a chemical reaction can take place when ultrasonic radiation is applied to homogenous liquid. qiu et al. [67] were the first who reported a mof [zn3(btc)2] synthesized sonochemically in ethanol which reveals selective sensing towards organoamine. effect of reaction time on particle size is also investigated in sonochemical synthesis of mofs. partial decom position of crystals at long reaction time is obtained in the sonochemical synthesis of hkust-1 [68] . 3.3.4 layer by layer synthesis layer by layer method is used for the preparation of mof thin films. the method is based on surface chemistry in which functionalized organic surface is immersed sequentially into the solutions of metal ion and organic linker. it was observed that orientation of thin film depends on that sequence through which the reactants are added [69] . the kinetics for stepwise formation in this method has been studied using surface plasmon resonance (spr) spectroscopy. metal source and surface termination are the two major factors that affect the rate of growth mof film [70,71] . highly oriented growth was observed for substrates functionalized with different functional groups such as cooh, oh [72] . besides these synthesis routes, other routes such as chemical solution deposition [73-75] (for the preparation of thin film mofs), post syntheis modi 92 fication [49] (when functional groups cannot be incorporated during mof synthesis), and ionothermal method [76, 77] (ionic liquids are used as solvent) have also been implemented for mof synthesis. banerj ee and coworkers have reported fe-based mof which is prepared by fe-metallogels via gel degradation [78] . however, other mof has not been reported by this method so far. 4. factors affecting the synthesis of mofs 4.1 solvents solvent system plays an important role in mof synthesis as well as in deciding the morphology of mofs. solvents may coordinate with metal ion and or may act as space filling molecules [79,80] . instead, they also act as a structure directing agent [49] . solvents used in mof synthesis should have high boiling point and polar nature. usually, dimethyl formamide (dmf), diethyl formamide (def), dimethyl sulphoxide (dmso), dimethyl acetamie (dma), alcohols, acetone, acetonitrile etc. are used as solvent as is shown in figure 4. sometimes a mixture of solvents is also used, which depends on the solubility of starting materials. mof synthesis process is affected by the reaction medium because of polarity of solvent used and solubility and protolysis property of organic linker. it is also reported that different solvent systems in same reaction condition provide mof of different morphology. this may happen because of difference in degree of deprotonation of organic linker in different solvent system. banerjee et al. [81] reported mofs containing magnesium and pdc (3, 5–pyrid ine dicarboxylic acid) have different crystal structure prepared under same condition using different solvent system (figure 5). they found that coordination ability of solvent with metal determines the dimensionality of mof network. among dmf, h2o, etoh and meoh, h2o has the highest affinity towards mg while etoh and meoh do not having any affinity to coordinate with metal centres when dmf/meoh and etoh/h2o are used as solvent. figure 4. solvents used in synthesis of mofs. figure 5. effect of solvent systems on morphology of mof. 93 in addition to structure, different solvent systems result in synthesis of mofs having difference in pore size. mofs of cobalt and 4,4’-((5-carboxy 1,3-phenylene bis(oxy)) dibenzoic acid (h3cpbda) were synthesized using three different solvents viz. dmp, dma and dmf under the similar conditions resulting into pore sizes of 76.84 å, 74.37 å and 72.76 å respectively. the change in pore size due to different solvents has been correlated with the size of the solvent molecule. among the three solvents used the size of the molecules varies as dmp > dma > dmf. the pore size also reduces in the same order [82] . similar correlations are reported by other researchers [83] . 4.2 effect of temperature and ph on synthesis of mofs temperature and ph of reaction medium have remarkable influence on synthesis of mofs. different coordination modes can be adopted by linkers at different ph ranges [84] . further, the degree of deprotonation of linker increases on increasing the ph value. for example, al 3+ ion is coordinated with four, six and eight carboxyl o-atoms with increasing ph resulting into mil-121 (ph = 1.4), mil-118 (ph = 2) and mil-120 (ph = 12.2) respectively [85] . interpenetrated network has been reported to be formed at higher ph value and uninterpenetrated at lower ph [86] . colour of mof compounds also depend on ph of reaction medium. luo et al [87] , through their experimental work, explored three co-mof complexes, viz. [co2(l)(hb-tc)2(μ2 h2o)(h2o)2].3h2o (1), [co3(l)2(btc)2].4h2o (2), [co2(l)(btc)(μ2-oh)(h2o)2].2h2o (3), (l = 3,3’, 5,5’-tetra(1h-imidazol-1-yl)1,1’-biphenyl and btc = 1,3,5-benzenetricarboxylate) exhibit different str ucture and colour, by altering the ph value. along with structure and colour, these three mofs exhibited different adsorption capability. it is also revealed that compounds of higher dimension are formed at higher ph [88] . the effect of ph on various properties of mofs is summarized in table 1 as reported in the study of chu et al. [88] table 1. effect of ph on mofs s. no. properties of co-mofs complex-1 complex-2 complex-3 1 chemical formula [co2(l)(hbtc)2(μ2-h2o)(h2o)2].3h2o [co3(l)2(btc)2].4h2o [co2(l)(btc)(μ2-oh)(h2o)2].2h2o 2 morphology monoclinic monoclinic orthorhombic 3 space group p2/c c2/c pccn 4 ph 5 7 9 5 colour pink purple brown temperature of the reaction is another important factor which affects the properties of synthesized mofs. high temperature favours higher crystallization due to high solubility of reactants and results in formation of large crystals of high quality [89-91] . nucleation and crystal growth rates were affected by temperature of reaction mixture. morphology of synthesized mofs can also be altered by varying the temperature of reaction medium. mofs of tm-succinate [92] , are synthesized at different temperatures with same empirical formula but different morphology i.e. monoclinic and triclinic. bernini et al. prepared two ho-succinate mofs and reported that the mofs prepared via hydrothermal method at higher temperature is ther mally more stable as compared to the other prepared at room temperature [93] . along with thermal stability, hydrothermal methods also provide denser, less hydrated and higher dimensional solids [94] . 5. factors affecting the stability of mofs 5.1 surface engineering crystal growth of mofs can be altered via ―coordination modulation‖ [95] which involves introduction of monodentate ligands known as ―modulators‖ with same functional group as to the existing multidentate organic ligand. modulators can increase or decrease the crystal growth by control 94 ling the nucleation leading to the formation of mofs crystals of different size. when modulators decrease the crystal growth they can be used as ―capping agents‖. sodium acetate [96-99] , sodium formate [99-101] , acetic acid [102-104] , benzoic acid [103] , n-dodecanoic acid [105] , trifluoroacetic acid (tfa) [106] , pyridine [104] , n-butyl amine [101] , 1-methyl imidazole [101] , polymers such as pvp [107] , peg [108] , chitosan [108] have been used as modulators/capping agents in synthesis of mof. it is also reported that the concentration of modulator can influence the crystal size and morphology of mof crystals. in microwave synthesis [109] of hkust-1, when lauric acid is used as modulator, the crystal sizes change from nano to micro scale range. however, when capping agent is used in large amount formation of a new phase is induced [99] . stability and specific properties of mof crystals such as molecule sensing [107,110] , drug delivery [108] etc. can be enhanced by using modulators. mof [111] coated with liposomes lipid has been explored for imaging and anticancer property. effect of some modulators or capping agents on the properties of mofs has been summarized in the table 2. table 2. effect of capping agents/modulators on mof properties s. no. modulator/caping agent mof change in mof’s property ref 1 sodium formate hkust-1 reduction in crystal size, phase change 100 2 sodium acetate mil-68(in) decrease in length and diameter of hexagonal nanorods 97 3 n-dodecanoic acid hkust-1 change in morphology 105 4 acetic acid nh2-mil-53 (al) selective capping of crystal faces 102 5 benzoic acid, acetic acid uio-66, uio-66(nh2), uio-67, uio-68 improve crystallinity, formation of single crystal 103 6 tfa uio-66 induce defects 106 7 sodium acetate [ln(1,3,5-btc)(h2o)]n (ln = dy3+, tb3+) 2d nano sheet 98 8 pvp/silica [mn(1,4-bdc)(h2o)]n selective uptake in human cancer cell, enhance imaging 110 9 peg mil-88, mil-100 improve aggregation, neutral zeta potential 108 mofs are also modified via exchanging a terminal ligand by a bridging ligand of different functionality (figure 6). research group of kitagava successfully exchanged the surface ligands of zn-based mofs [zn2(1,4-ndc)2 (dabco)]n and [zn2(1,4-bdc)2(dabco)]n with a fluorescent dye boron dipyromethene (bodipy). in these mofs, only surface carboxylate ligands were exchanged and surface dabco ligands remained unmodified. furth er, due to bulkier nature of bodipy in comparison to original carboxylate ligand, it gets attached to surface only [112] . liu et al. [113] demonstrated the effect of surface modification on properties of zif–8. it shows greater stability towards hydrolysis when its surface ligand 2-methylim-idazole has been exchanged with more hydrophobic ligand 5, 6-dimeth ylbenzimidazol (dmbim). figure 6. effect of ph control and crystal capping during coordination modulation. 95 unlike linker ligand exchange, it has been difficult to control metal cation exchange in mofs, as it can lead to the formation of core-shell structure [114] . kitagawa and group reported the core shell hybrid of cu-mof [cu2(1,4-ndc)2(dabco)]n synthesized on zn analogous [zn2(1,4-ndc)2(dabco)]n by adding zn crystals to the solution of cuso4.5h2o, 1,4-ndc and dabco. formation of green crystals confirms the formation of cu-mof on zn framework surface [115] . 6. major applications of mofs in mofs, there is a simultaneous appearance of three characteristics, viz. crystallinity, porosity and existence of strong metal-ligand interaction. the unique combination of these properties makes mofs a very special class of materials [116] . mofs show application in catalysis, drug delivery, gas storage, nanoparticle precursor, luminescence, electrochemistry and as sensor in technology. 6.1 gas storage and separation there are several methods for storing gas effectively but these require high pressure tank and multistage compressor. these methods are highly expensive for practical uses and there is a need of simpler and cheaper solution. to overcome these issues and to find safer storage methods, several materials, like zeolite or activated porous carbons, have been studied for gas storage. in this context, mofs have provided edge over other materials. this is due to easy preparative methods, high surface area, wide opportunities for functionalization and tuneable pore structure which makes mofs preferable compared to other porous materials. more than 300 mofs have been tested for h2 storage. one of the promising mofs for this purpose is mof-177 which consists of [zn4o] clusters and 4,4’,4’’-benzene-1,3,5–triyltribenzoate (btb) to form (6,3) net [117] . due to its high surface area (~5000 m 2 g -1 ) and large pore volume, it shows a gravimetric h2 uptake of 7.5 wt.% at 70 bar and 77 k. mof-5 (irmof-1), which is constructed from [zn(oac)2] and terepthalic acid, possesses a bet surface area of 3800 m 2 g -1 and takes up 7.1 wt.% at 40 bar and 77 k. apart from these two, mof-210, mil-101, hkust-1, nu-100, pcn-12, nott-102 and mof-205 are also known for h2 storage [118-121] . generally mofs with open metal sites provide high surface area facilitating stronger interaction between the metal ion and h2 molecule. this is the principal reason behind the high h2 uptake in mofs. nu-100 [120] has the highest excess h2 storage capacity i.e., 99.5 mgg -1 at 56 bar and 77 k. mof 210 [121] has been reported as highest total h2 storage capacity of value 176 mgg -1 at 80 bar and 77 k. in addition experimentally, it is reported that doping mofs with metal ions could enhance the h2 uptake capacity [46,122] . as compared to other h2 storage systems such as transition metal hydrides, mofs require little energy to release adsorbed hydrogen. this released hydrogen can be used in automobile and fuel cell industries [123] . mofs are reported to be useful for reducing co2 level in atmosphere. for example, mof-210 is the highest surface area (10450 m 2 g -1 ) mof known to date, synthesized from 4,4’,4’’-[benzene-1,3,5 triyl-tris(ethyne-2,1-diyl)] tribenzoate (h3bte), bi phenyl-4,4’-dicarboxylat (h2bpdc), and zinc (ii) nitrate hexahydrate [121] and has an uptake of co2 2400 mg g -1 (74.2 wt.%, 50 bar at 298 k) which exceeds that of any other porous material. mof-200 has a similar co2 uptake as mof-210 under similar experimental conditions [121] . other well-known mofs, such as nu-100 (69.8 wt.%, 40 bar at 298 k), mg-mof-74 (68.9 wt.%, 36 bar at 278 k), mof-5 (58 wt.%, 10 bar at 273 k), and hkust-1 (19.8 wt.%, 1 bar at 298 k) also show considerable co2 uptake. it has also been proved experimentally and theoretically that the presence of polar groups such as — nh2 or free n containing organic heterocyclic residues on the pores is helpful for high co2 uptake compared with unfunctionalized analogues. one of the best examples, biomof-11, exhibited the effects of an n-heterocycle and its co2 uptake of 15.2 wt.% (at 1 bar and 298 k) exceeds any other mof in the same category [124] . noro et al. studied the first methane sorption 96 study on mofs [125] . zhou and co-workers showed methane uptake of 16 wt.% (35 bar) in pcn-14 [cu2(adip), adip = 5,5’-(9,10-anthracenediyl)di isophthalate] mof, having bet surface area 1753 m2 g-1[126]. other mofs such as hkust-1 (15.7 wt.% at 150 bar), mil-101 (14.2 wt.% at 125 bar), irmof-1 [228 cm3 (stp) g-1 at 298 k and ~36 bar], and mof-210 (264 mg g -1 ) [121] also show considerably high methane uptake capacity. in the case of ni-mof-74 [190 cm 3 (stp) g -1 (298 k, 35 bar)], open metal sites are the dominating factor responsible for the high methane capacity [15] . other important hydrocarbons like benzene, toluene, xylene and linear hydrocarbons have also been effectively separated from liquid mixtures by trapping inside mofs. hazardous gases like co and no can also be separated from gas mixtures by using mofs. though separation of co in mofs could not be achieved experimentally, it is believed that interaction between co dipole and open metal sites in mofs are the dominating factor for the sorption performance. on the other hand, mofs have been used for capturing no gas, e. g. cu-sip-3 [127] and zn (tcnq-tcnq) (bpy) [tcnq = 7,7,8,8-tetracya -no-p-quino dimethane, bpy = 4,4’-bipyridyl] [128] . usually these two mofs are nonporous in nature and they do not absorb gases like ar, n2, co2 etc., however, these are reported for uptake of no gas (~9 molecules per formula unit at 1 bar) above gate–opening pressure. reducing the pressure, the desorption path is not like adsorption. in 2010, allen and co-workers reported the reason for this performance of the above two mofs. the strong coordination to coordinatively unsaturated metal sites (cums) in case of cu-sip-3, while for [zn (tcnq-tcnq)(bpy)], charge transfer plays a crucial role for high no capture [127] . niand co-mof-74 also exhibited very high no uptake (~7.0 mmol no per g of activated material) at room temperature [129] . in 2014, yan et al. synthesized and characterized a new organic linker 1,2,4,5-tetrakis(3-carbox yphenyl)-benzene (m-h4tcpb) and its first metal-organic framework cu-m-tcpb. this compound can uptake 24.4 cm 3 g -1 h2 and 2.3 cm 3 g -1 n2 at 77k and 1 atm. it has been reported to possess uptake capacity 23.3 cm 3 g -1 acetylene, 23.0 cm 3 g -1 co2 and 7.3 cm 3 g -1 at 273 k and 1 atm [130] . instead of gaseous molecule uptake, some mofs have also been prepared which are capable of adsorption of water molecule. in this direction, r. banerjee and his research group demonstrated the water adsorption ability of chemically stable keto-enamine cofs [131] . 6.2 magnetism and its application metal organic framework materials show magnetism when paramagnetic 3d transition metal nodes are used along with suitable diamagnetic organic linkers and mofs with magnetic properties are named as magnetic metal organic frameworks (mmofs). the mofs consist of first-row transition metals (v, cr, mn, fe, co, ni and cu) have contributed significantly to develop porous molecular magnets [132-137] . close-shell ligands [138] such as oxo, cyano, azido bridges and polycarboxylic ligands, which give weak magnetic interaction, are good candidates for this purpose. another reason for magnetic behaviour of mofs is the framework structure, which may involve layered geometry with a shorter conjugated distance between metal clusters. organic linkers have also been used for synthesis of mmofs, where radicals present in organic linker are responsible for magnetic properties. this metal-radical combined approach has also been used for synthesizing a variety of mmofs [139-141] . a ni-glutarate based mof [ni20(h2o)8(c5h6 o4)20.40h2o] [142] showed ferromagnetic behaviour with a curie temperature of 4k due to weak ferromagnetic interactions of ni-o-ni angle. hkust-1 is antiferromagnetic at high temperature and below 65k shows weak ferromagnetism [143] . mil-9 [144] [co5(oh)2(c4h4o4)4] is reported to possess ferrimagnetic properties. jain et al. [145] reported four mofs of general formula [(ch3)2nh2] m(hcoo)3 (m = mn, fe, co, ni) as multiferroics. instead of 3d transition metals, lanthanides also produce magnetic metal-organic frameworks. two magnetic lanthanide-organic frameworks [146] 97 (lnof), having formula [dy2(bpa)2(h2o)3] and [er4(bpa)4(h2o)6](h2o), consist a 3d frameworks built by the 1d rod shaped metal carboxylate sbus and 3,5-bis (4-carboxyphenoxy) benzoate (bpa 3) ligands. magnetic mofs can also be explored for the environmental application in removal of arsenic. magnetic nanoclusters have been reported for applications in arsenic removal [147,148] . 6.3 sensing a large number of mofs have been reported to be photoluminescent because aromatic units of linkers in most of the mofs lead to excitation by absorbing uv-visible light and provide luminescence. mofs as luminescent materials or phosphors can find application in cathode ray tubes, projection television, fluorescent tubes and x-ray detectors [149] , small-molecule sensors [150,151] , ph sensors [152] , light concentrators for photovoltaic devices, antennae in photo-sensitive bioinorganic compounds and high-technology optics. trivalent lanthanide metal ions are widely used for synthesis of luminescent mofs due to their electronic transition from dto f shell, with accompanying photon emission. lanthanides like eu, tb, dy, sm, nd, gd, er and yb are used as luminescent metal ions. naphthalene, anthracene, pyrene, perylene and stilbene types of ligands are most commonly used for synthesis of luminescent mofs. both the metal and the linker can be used to give rise to luminescence, and can furthermore interact (via antenna effect) to increase the brightness and the quantum yield. 4,4-[(2,5 dimetoxy-1,4-phenylene)-di-2,1-ethenediyl] bisben toxy-1,4-phenylene)-di-2,1-ethenediyl] bisbenzoic acid (h2pvdc) was used to efficiently sensitise the nir emission of the yb 3+ ions at ca. 1000 nm in an extended [yb2(pvdc)3(h2o)2].6dmf.8.5h2o porous network [153] . the lnmofs co-doped with multiple ln 3+ ions can be used as bimodal (or multicoloured) light emitters. bimodal (or multicoloured) emission may be applied in multiplexed detection and imaging of therapeutic cells [154] . ln-mofs are used in cation sensing, anion sensing as well as molecule sensing. a visible colour change of material is one of the simplest, most powerful sensing strategies. for example, a nanotubular mof, {[(ws4cu4)i2 (dptz)3].dmf}n (dptz = 3,6-di-(pyrid-in-4-yl)-1,2,4, 5-tetrazine, dmf = n,n-dimethylformamide) was reported for sensing small solvent molecules. when accommodating different solvent molecules as guests, the resulting inclusion compounds exhibited different colours depending on the solvent guests, showing a new way of signal transduction as a new kind of sensor [150] . recently, water stable cationic mof [155] has been reported which can adsorb oxoanionic pollutents such as mno4 , cr2o7 2. recently, mofs have been demonstrated as chemical sensor for selective fluorescence quenching of an explosive tnp (2,4,6-tri nitro phenol) in water using urotropin-based metal-organic framework (ur-mof) [156] . nano mofs (nmofs) have experirnced another exciting development and nmofs are used for sensing pesticides. akash deep et al. [157] were the first who demonstrated biosensing application of nano mof [cd(atc)(h2o)2]n (atc = 2-amino terepthalic acid) impedimetrically for the detection of organo-phospate pestiside by developing an anti-paration/nmof/2-aba/ito (aba = 2-amino benzyl amine, ito = indium tin oxide) sensing platform. a novel approach to develop an inkless and erasable printing medium using mofs has been demonstrated by synthesizing photochromic mof containing 1,4,5,8-naphthalenediimide (ndi) and ca, mg, sr and revealed their inkless printing property [158] . the print content was self-erased after 24 hours. this may be useful for reducing paper wastage. 6.4 catalysis the presence of strong metal–ligand interaction in mofs can provide permanent porosity to the material, i.e., it is possible to remove solvent molecules completely without structure collapse. mofs have shown great potential as heterogeneous catalyst. the mofs, in which metal centres are not completely blocked by organic ligands or unsaturated, i.e., labile ligands are introduced, and are 98 good catalysts because when labile ligands are generally solvent molecules and when they are removed leave a free coordination position on the metal. for example, [cu3(btc)2] (btc = 1,3,5 benzenetricarboxylate) material hkust-1, in which coordinated water molecule leaves a coordination vacancy on cu upon thermal activation [159] . a number of organic reactions have been catalyzed by using nanoporous mofs. for example, knoevenag el condensation reaction catalyzed by using either [cd(4-btapa)2(no3)2] (btapa = 1,3,5-benzene tricarboxylic acid tris[n-(4-pyridyl)amide]) [160] or [cr3f(h2o)2o(bdc)3] (bdc = 1,4-benzenedicarboxy late) [161] . xu et al. synthesized a novel bimetal complex [zn4ru2(bpdc)4.4c2nh8.9dmf]n (h2bpd = 4,4’-biphenyldicarboxylic acid), which can adsorb ru(ii) photosensitizer [ru(bpy)3] 2+ and cobalamin derivative such as heptmethyl cobyrinate perchlorate (b12) to form a complex b12-ru@mof. this complex has been reported to catalyse dechlorination reaction and 1, 2-migration reaction in solid state. this is the first example of b12 catalysis using mof system [162] . 6.5 biomedical application mofs offer extremely high drug loading capacity and very long release time. as compared to mesoporous silica materials, mofs can load four times greater drug, i.e., ibuprofen adsorption (upto 1.4 gm per gram of mofs) with longer release time (upto 21 days) [108] . non-toxic mofs are applicable in targeted drug delivery. mil family of metal-orga nic frameworks has a good candidature for storage and controlled release of biologically important molecules due to their enhanced stability, enormous porosity and large pore volume [10,163] . serrey and férey et al. [8] demonstrated encapsulating drug mol ecules (ibuprofen) in chromium carboxylate mofs, mil-100 and mil-101, exhibiting drug storage capacities of 35 wt.% and 140 wt.% respectively and controlled drug release behaviour of 5 to 6 days under physiological conditions. iron (iii) carboxylate mofs such as mil-88a, mil-8, mil-100 and mil-101 are able to entrap anticancer [163] , antitumor and antiretroviral drugs as well as cosmetic agents [8] . férey et al. [164] reported first group of synthesized mofs using trivalent metal centers with carboxylic acid bridging for drug delivery application. a novel type of magnetic mof composite fe3o4/cu3(btc)2, fabricated by incorporation of fe3o4 nanorods with nanocrystals of cu3(btc)2 (hkust-1), adsorbed upto 0.2 gm of nimesulide (an anticancer drug for pancreatic cancer treatment) per gram of composite and it took as long as 11 days for the complete drug release in physiological saline at 37˚c [165] . zhuang et al. demonstrated zif-8 as ph responsive drug delivery system with high cellular uptake efficiency by incorporating camptothecin into zif-8 nanospheres. this encapsulated zif-8 exhibited enhanced cell death [11] . bernini et al. demonstrated the ability of gcmc (grand canonical monte carlo) simulation to predict the microscopic performance of new porous mofs in drug delivery application and validated their simulation, with the available experimental data reported for the adsorption-release of ibuprofen in mil-53(fe), mil-100(fe) and mil-101(cr) [166] . their simulation predicted an outstanding ibuprofen adsorption capacity of 1969 mg g -1 for mesoporous biomof-100 which is six times higher than the values reported for mesoporous silica. the presence of strong electrostatic interactions due to existence of charge compensating ions in mofs enhances the adsorbate-adsorbent interaction which leads to higher drug loading at low pressure. in biomof-100, dimethylammonium cations present in the pores reinforce the attractive interaction with ibuprofen molecules. monte carlo simulation was also used for comparing the drug uptake capacity of two different mesoporous mofs, viz. mil-101 and umcm-1 computationally [9] . anti-bacterial activity of novel mof stam-1 [138] has been compared with that of the hkust-1 against the growth of some bacteria such as clostridium difficle, staphylococcus aureus and pseudomonas aeruginosa. it is found that both the mofs have significant effect against the growth of these pathogens. antimicrobial activity of these mofs has been enhanced when they are impregnated with no. 99 6.6 electrical property and its application mofs have been demonstrated as useful device material for energy storage. electrical storage capacity of mofs in co-doped mof-5, i.e., co8-mof-5 [167] as electrode for supercapacitors has been reported by diaz et al. however, this mof has much lower capacitance than the commercially activated carbon. lee et al. introduced cobalt based mof film [168] which has pseudocapacitor behavior with specific capacitance upto 206.76 f g -1 and energy density of 7.18 wh kg -1 at 0.6 a g -1 . zn-doped ni-based mof [169] with a flowerlike microsphere exhibited high specific capacitance (1620 f g -1 and 860 f g -1 at 0.25 and 10 a g -1 respectively), good rate capability and good cycling stability (91% for the mof with zn/ni of 0.26). in 2014, a series of 23 different nanocrystalline mofs (nmofs) were reported for their electrochemical energy storage capacity. among these nmofs, a zirconium based mof, i.e. nmof-867 exhibited high capacitance. nmof-867 has the stack and areal capacitance of 0.64 and 5.09 mf cm -2 which is about six times higher than that of the supercapacitors made from activated carbon [170] . recently, a mn-based mof is employed as the active coating material to enhance the capacity of li-rich layered li (li0.17ni0.20co0.05 mn0.58)o2 oxide as cathode for li-ion batteries. this surface modified oxide material showed a large discharge capacity, good thermal stability without harming the cycle stability, high initial coulombic efficiency and high rate capability [171] . researches in this direction are needed to further explore the applications of mofs. 7. future scope the knowledge about metal organic frameworks is growing rapidly during recent few years but there are still significant gaps in the completeness of our understanding of their structure, stability and properties. detailed investigations on factors responsible for destruction of crystal structure of certain mofs with time stability and decomposition mechanism have still not been carried out systematically. there are some reports on applications of mofs in drug loading and delivery for some anticancer and antiviral molecules. mofs can be explored for such application for other drug molecules too. detailed toxicological investigation should be carried out commercialization of such products. 8. conclusion in this review article, we have discussed various synthetic methods of mofs along with their applications. different methods lead to the mofs having different properties. mofs introduced a huge number of applications including gas storage and separation, catalysis, magnetism, sensors, electrical energy storage systems etc. several applications of mofs have not been explored yet, for instance, magnetic mofs can be explored for removal of arsenic from environmental sample same as magnetic nano clusters have been demonstrated. research work should be carried out to study degradation mechanism of unstable mof. studies can also be carried out to evaluate the toxicity of degradation products. these studies will be helpful to explore the biomedical application of nontoxic mofs. nontoxic mofs can be explored for application as solid support for natural bioactive molecules to increase their shelf life and effectiveness. mofs should be evaluated for antibacterial and antifungal activities to explore their clinical and biological applications as solid support, uv-screens and synergist. abbreviations used 1. adip — 5,5’-(9,10-anthracenediyl)di-isophthalate 2. bdc — benzene dicarboxylate 3. bodipy — boron dipyromethene 4. btc — benzene tricarboxylate 5. cof — covalent organic framework 6. dabco — diazabicyclooctane 7. hkust — hong kong university of science and technology 8. irmof — isoreticular metal organic framework 9. mil — materials of institute lavoisier 10. mof — metal organic framework 100 11. mw 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2: 19005– 19010. 170. choi km, jeong hm, park jh, et al. supercapacititors for nanorystalline metal-organic frameworks. acs nano 2014; 8: 7451–7458. 171. qiao q, li g, wang y, et al. to enhance the capacity of li rich layered oxides by surface modification with metal-organic frameworks as cathodes for advanced lithium-ion batteries. journal of materials chemistry a 2016; 4: 4440–4447. characterization and application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1691 119 original research article using aqueous extract of eucalyptus grandis to synthesize iron oxide nanoparticles santiago eduardo pabón-guerrero * , ricardo benítez-benítez, rodrigo andrés sarria-villa, josé antonio gallo-corredor departamento de química, universidad del cauca, popayán, colombia. e-mail: santiagopabon@unicauca.edu.co abstract this work presents the evaluation of iron oxide nanoparticles obtained from the aqueous extract of eucalyptus grandis. twenty-three experiments were carried out where the synthesis of nanoparticles was performed by using the aqueous extract together with salts of iron (ii) chloride tetrahydrate and iron (iii) chloride hexahydrate. a characterization was carried out by ir, tem and bet, where bands were presented at 3,440.77, 1,559.26 and 445.31 cm−1, indicating the presence of iron oxide nanoparticles. a relatively high monodispersity was evidenced with particles around 9 nm. by means of bet analysis it was found to present a surface area of 131.897 m2/g. obtaining nanoparticles by this green method presents yield values of 98%, with application in nanotechnology, biomedicine, environmental treatment, among others, making them highly versatile and their production cost is relatively low. keywords: green synthesis; magnetite nanoparticles; plant extract article info received: 22 july 2022 accepted: 14 october 2022 available online: 23 october 2022 copyright copyright © 2022 santiago eduardo pabón-guerrero, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction nanotechnology refers to research and technological development at the atomic, molecular or macromolecular level, in the range of 1 to 100 nm, to provide a fundamental understanding of nanoscale phenomena and materials and on the other hand to create and use structures, devices and systems with novel properties and functions due to their sizes compared to bulk size materials[1]. in recent years the interest in the use of magnetic nanoparticles has been increasing due to the wide range of applications they have, ranging from applications in biomedicine, nanotechnological construction of dna, development of electronic devices, even environmental remediation treatments[1–3]. among the nanoparticles that have been studied are iron nanoparticles given their properties such as magnetite (fe3o4) or maghemite (γ-fe2o3) [4–7]. their nanoferrite structure is characterized by having a spinel crystal structure (figure 1), in which oxygen ions form the compact cubic packing and iron ions are located in the tetrahedral (td) and octahedral (oh) interstices. equation (1) shows the formula of magnetite, in which fe2+ cations occupy only oh positions, while fe3+ ions are distributed between td and oh positions[8]. (1) the magnetization of fe3o4 nanoparticles arises from the antiferromagnetic coupling between fe3+ ions at oh and td interstices, leaving 120 figure 1. spinel structure of fe3o4. source: noval et al.[9]. magnetic moments of fe2+ ions, at oh positions, as the ones responsible for the unit cell magnetization[8,9]. there are many methods that can be used for the synthesis of nanoparticles, some of these methods are classified as mechanical-chemical methods consisting of a top-down system, i.e. a method consisting of the division of a larger solid to reduce it to smaller portions of the same, although unfortunately this method is not recommended when a homogeneous synthesis is sought because it tends to form unequal and amorphous particles[10]. other methods are classified as chemical-physical methods and are called bottom-up system, which consists of the fabrication of nanoparticles through the condensation of atoms, molecules or molecular entities in gas phase or in solution, this type of synthesis being the most popular in obtaining nanoparticles[1,3,10–12]. in the latter case, conditions such as working temperature, solvent used or stabilizing agents and reproducibility are two very important aspects to take into account when choosing the appropriate method, and the most common method used for the synthesis of iron oxide nanoparticles is chemical co-precipitation[1], which is perhaps the simplest and most chemically efficient method to obtain iron oxide nanoparticles (fe3o4 or γ-fe2o3), which are generally prepared by a stoichiometric mixture between ferrous and ferric salts in aqueous medium[1]. equation 2 shows the chemical reaction that takes place in the formation of fe3o4. (2) according to the thermodynamics of this reaction, complete precipitation of fe3o4 is achieved at ph between 8 and 14, with a stoichiometric ratio of 2:1 (fe3+∕fe2+) in an oxygen-free environment to avoid iron oxidation[11]. however, magnetite (fe3o4) is not very stable in the environment and is sensitive to oxidation. therefore, in the presence of oxygen, it transforms into maghemite (γ-fe2o3) as shown in equation 3[11]. (3) oxidation with air not only transforms magnetite (fe3o4) into maghemite (γ-fe2o3), but also transfers various electrons or ions, depending on the ph of the solution, as shown in equation 3. under acidic and anaerobic conditions, the surface of fe2+ ions form hexaaqua complexes in solution, whereas, under basic conditions, the oxidation of magnetite involves oxidation-reduction reactions on the magnetite surface. the main advantage of this method is the large amount of nanoparticles that can be synthesized, however, the control of the particle size distribution is limited because kinetic factors control the crystal growth[11]. thus, the size and shape of the nanoparticles can be controlled with relative success by adjusting parameters such as ph, ionic strength, temperature, nature of the salts used (perchlorates, chlorides, sulfates and nitrates) or the concentration ratio of the fe2+∕fe3+ species. in addition, the addition of chelating organic anions (carboxylates or α-hydroxy carboxylate ions such as, citric, gluconic or oleic acids) or surface polymers as complexing agents (dextran, carboxydextran or polyvinyl alcohol) during magnetite formation can help to control particle size[11,13]. similarly, the synthesis of nanoparticles is achieved by using aqueous plant extracts such as stan et al. in 2017 using grape or lemon peel extracts, robles et al. in 2019 using papaya peel extracts, awwad and salem in 2013 using plants such as carob, and ahmed et al. in 2013 also using papaya peel; they used citrate in order to achieve the synthesis of these materials, reducing the cost of manufacturing, requiring the use of many reagents, as these extracts have multiple functions in the process, in addition to reducing hazardous waste when 121 using this type of extract[4-6,14]. this work is carried out with the purpose of testing the effectiveness of a eucalyptus extract in the synthesis of iron oxide nanoparticles, which can be used in processes for the uptake of heavy metals such as mercury or selenium, or in processes for the degradation of organic molecules present in aqueous media[3,15]. 2. materials and methods 2.1 sample collection and processing site the foliage sample of eucalyptus grandis was obtained from the forest nursery of the cooperativa agroforestal del cauca (cootraforc), located in vereda gonzales, municipality of popayán, department of cauca, coordinates 2°28’34.9’’ n 76°34’03.2’’ w. the study was carried out in the facilities of the laboratory of the environmental analytical chemistry research group (eacrg) and the industrial analysis unit of the chemistry program of the universidad del cauca. since only the leaves would be used, the sample was subjected to a previous classification and manual cleaning in order to separate the foliage from dust, branches or seeds that could later interfere with the development of the research. subsequently, the wet sample was left to dry for about 2 weeks to eliminate excess moisture, moving the leaves periodically to avoid moisture retention in some of the leaves that could generate losses of material, obtaining a dry biomass ready to be ground. subsequently, the sample was completely ground by means of a conventional mill and then classified by size in order to achieve a small particle size of biomass by sieving through a no.18 mesh sieve of 2 mm thickness, thus obtaining a biomass with a very fine particle size of about 2 mm, finally the sieved sample was stored at room temperature. 2.2 obtaining the aqueous extract of eucalyptus grandis for the preparation of the aqueous plant extract, a ratio between plant material and solvent of 1:5 weight/volume, respectively[4], for which the extract is prepared starting from the use of the plant material in this case of foliage of the species eucalyptus grandis in the solvent in this case deionized water, heating at a temperature of 80 °c for 5 minutes, then filtered under vacuum and centrifuged at 1,250 rpm for 5 minutes, deionized water is used in order to complete the total volume of the extract and stored at room temperature for later use[5]. 2.3 preparation of magnetite nanoparticles in a typical execution, the coprecipitation method uses two iron salts, in this case iron (ii) chloride tetrahydrate (fecl2∙4h2o) and iron (ill) chloride hexahydrate (fecl3∙6h2o) in a ratio of 1:2 weights, respectively, heated for 10 minutes with constant stirring, after which a volume of the previously prepared eucalyptus extract is added turning the solution slightly brown, and finally 20 ml of a known concentration of sodium hydroxide (naoh) solution was added after 5 minutes. after this process, since the particle obtained is insoluble in water, it is precipitated, filtered and dried in an oven at 50 °c for 24 hours. finally, the dried particle is macerated and stored in a dry, cool place at room temperature[4,5]. the conditions of both working temperature, volume of the extract used and hydroxide concentration were optimized to find the maximum yield point of the synthesis. table 1. variables considered for the synthesis variable definition units performance particle synthesis performance % extract volume amount of extract to be used ml temperature temperature for synthesis °c naoh concentration concentration used to complete the reaction mol/l source: authors. 2.4 statistical analysis of the synthesis for the analysis of the design and optimization of the synthesis, the statistical program statgraphics centurion xvii.ii was used, with which a central composite experimental design with star points 23 was carried out. table 1 presents the variables taken into consideration for the design and the procedure followed by awwad and salem for obtaining magnetite nanoparticles[5], so that through this experimental design the best synthesis parame 122 ters for the temperature, the volume of extract used and the concentration of the base can be established and thus achieve the highest yield in the process of obtaining magnetite nanoparticles. 2.5 characterization of nanoparticles the characterization of the nanoparticles was performed by instrumental analysis using transmission electron microscopy (tem), ft-ir spectroscopy by kbr pellet and surface area analysis by bet technique. 2.5.1 transmission electron microscopy (tem) to obtain the respective micrograph of the synthesized magnetite, a jeol jem 1200-ex transmission electron microscope was used in the microscopy laboratory of the universidad del cauca, dispersing the nanoparticles by ultrasound, measuring with a micrograph resolution of 4 nm and using the image-pro plus 3.0 image processing program. 2.5.2 infrared spectroscopy the spectra were measured in a thermo® ir-nicolet is10 spectrophotometer with itr (atr) accessory, using the kbr pellet analysis method. in this case, both the infrared spectra for the aqueous extract and the synthesized magnetite nanoparticle were taken by this technique. 2.5.3 bet analysis to determine the estimated surface area of the magnetite nanoparticle, a bet analysis was performed at the universidad del valle in a nova 1000e, quantachrome instruments, using nitrogen (n2) grade 5.0 as adsorbate, a run range between 0.05 to 0.3 p/p0 for an acquisition of 11 points, pressure tolerance of 0.100 mm hg, equilibrium time of 60 seconds, tolerance time of 240 seconds and a liquid n2 temperature of 77 k. figure 2. infrared spectrum of eucalyptus grandis extract. source: authors. 3. results and discussion the aqueous extract of eucalyptus grandis foliage obtained presented a slightly brown coloration which was analyzed by infrared spectrometry (figure 2), finding a band at 3,319.61 cm−1 which is indicative of the hydroxyl groups (-oh) of the polyphenols found in the extract, a band at 1,634.74 cm−1 is also observed which represents the carbonyl group (-co), which together with the hydroxyl group, expresses the presence of carboxylic groups (-cooh) within the extract of eucalyptus grandis. table 2 shows the results obtained from the analysis of variance (anova), performed with the help of the statgraphics centurion xvii.ii software. the statistical significance of 123 each effect was determined by comparing its mean square with the estimated values of the experimental error; in this way, the values of the significant parameters in the yield process of nanoparticles obtained with eucalyptus grandis extract are obtained. for the synthesis yield, a confidence level of 95% was established (maximum permissible error 5%) and, therefore, those effects or parameters with an error (p value) of less than 0.05 are accepted as significant. table 2. results of the analysis of variance for yield source medium square f-ratio p-value a: naoh conc. 589.627 6.35 0.0256 b: temperature 139.913 1.51 0.2412 c: vln extract 10,895.2 117.41 0.0000 ab 91.7335 0.99 0.3382 ac 7.66361 0.08 0.7784 bc 338.65 3.65 0.0784 total error 92.7934 source: authors. the anova table partitions the variability of the percentage of nanoparticle synthesis into separate pieces for each of the effects. testing the statistical significance of each effect by comparing its mean square with an estimate of the experimental error. the p value of the respective experiments was compared with a significance level of α = 0.05 and it is observed that factors a (naoh concentration) and c (extract volume) reject the null hypothesis because it presents a p value less than 0.05, which indicates that they are significantly different from zero with a confidence level of 95%, that is to say that effects a and c do have an influence on the synthesis process of nanoparticles. factor b (temperature) presents a p value greater than 0.05, therefore the null hypothesis is accepted and it is concluded that it has no effect on the percentage of synthesis, in the same way it is established that the correlation coefficient obtained for this experiment reached 91.67% adjusted for the synthesis yield. analyzing the pareto diagram (figure 3), which presents each of the studied effects in decreasing importance, the length of each bar is proportional to the standardized effect, which refers to the estimated effect divided by its standard error. the vertical line presented is used to judge which effects are statistically significant, so that any bar extending beyond this vertical line corresponds to effects that are statistically significant at a confidence level of 95%[16]. figure 3. pareto diagram for nanoparticle synthesis performance. source: authors. therefore, in this case the factors that exceed the significance line are a and c, namely, the concentration of naoh and the volume of extract, respectively, so they are the effects that significantly influence the synthesis process of the nanoparticle, and results that can be corroborated with the analysis of variance. according to the sign presented, the effects can be both positive and negative, therefore, in the case of factor a, it is indicated that there will be a higher percentage of synthesis at higher concentrations of naoh, while on the other side in the case of factor c, there will be a lower percentage of synthesis with higher volumes of eucalyptus extract. the anova made it possible to observe 124 the effects of the factors studied, as shown in figure 4, which presents the main effects for the yield; this analysis makes it possible to establish the optimum points for the synthesis of the nanoparticles. (4) figure 4. main effects plot for yield. source: authors. it is observed then that as previously mentioned in the case of factor a (naoh concentration) and c (volume of the extract), the higher the naoh concentration the higher the yield because the -oh group of the base interacts with the nucleus of the particle in formation generating iron hydroxides which by dehydration allow the formation of the iron oxide crystals of interest (fe3o4), while as the volume of the extract used increases, the yield decreases to a great extent, because a greater number of organic molecules will come into contact with the iron ions, increasing the impediment of the base to interact with the nucleus of the particle in formation[5]. on the other hand, in the case of temperature the values start high, drop to a minimum point and at the end rise, but to a value that is lower. this trend presumably is due to the fact that after a certain temperature, the compounds in the eucalyptus extract degrade, reducing the proportion of them present during the synthesis, however, the yield of the particle synthesis remains above 50% in this case. based on these results, equation 4 is generated which models the performance behavior of the synthesis based on the three parameters previously stipulated. the function led to an estimated response surface plot[16], which is shown in figure 5. it is observed that with a naoh concentration of 1.7 m, with temperatures of 87 °c, with an extract volume close to 1 ml, a % yield of approximately 96% is obtained. at the end of the experimental design and having the values for the optimization of particle synthesis, tests were performed in triplicate of those points, obtaining on average a yield of 98.99% ± 0.21, results that resemble those expressed by alvear et al., who reported yields in the synthesis of magnetite nanoparticles of 94% and exceed the results expressed by robles et al., whose yields in the synthesis reached a maximum of 35.03%[14,17]. for the determination of the nanoparticle size, transmission electron microscopy (tem) was employed and using image-pro plus 3.0 image analysis software with which it is obtained that the average size of the nanoparticles is approximately 8.97 nm, which is an average size close to that exhibited by alvear et al. of 7 nm and that of awwad and salem of 8 nm[5,17]. figure 6 shows the micrograph obtained for the synthesized particle in the nanometer range. to determine the functional groups present in the synthesized magnetite nanoparticle, an analysis was performed by infrared spectroscopy (ir) technique, this technique can be applied for the identification of surface functional groups, which is important to have a general idea of the chemical structure of the possible biomolecules that are responsible for the coating and stability of the nanoparticle[5]. in this case, several functional groups are found on the particle, in figure 6, we see the ir 125 figure 5. estimated response surface plot of nanoparticle synthesis. source: authors. figure 6. transmission electron microscopy of nanoparticles. source: authors. spectrum of the synthesized nanoparticle which shows that around 3,440.77 cm−1 a band of stretching of the hydroxyl group (-oh) is found, although in this case the band is quite attenuated, likewise a band can be seen at 1,559.26 cm−1, which refers to the stretching of the carbonyl group bond (-co). the presence of magnetite nanoparticles can be seen by the appearance of a band at 445.31 cm−1, which corresponds to the stretching band of the fe-o bond of the magnetite core[5]. with these results it can be established that the carboxyl (-coo − ) has interacted with the core by binding on the surface of the magnetite nanoparticles. from this we can say that the polyphenols of the eucalyptus extract have interacted with the particle acting as a reducing and stabilizing agent for the magnetite nanoparticles. a comparison is also made between the spectra of the eucalyptus (eucalyptus grandis) leaf extract (figure 2) and the synthesized magnetite (figure 7), in order to compare the bands between both spectra finding that the band of the hydroxyl groups remains around 3,440.77 cm−1, although in the case of the magnetite spectrum this band, as already said, is greatly attenuated, a fact that is also presented in the studies carried out by awwad and salem for the synthesis of magnetic particles[5]. in addition it can be observed how the band belonging to the carboxyl is also presented in both spectra although slightly displaced, a fact that could be attributed to the same magnetic properties of the nanoparticle that generate this fact. the bet analysis provided a surface area of 131.9 m2/g for the synthesized magnetite nanoparticles, values that are verified by the studies performed by stan et al. where surface area values of 137.4 m2/g are obtained in their experiments of nanoparticle synthesis with aqueous plant extracts[4]. 126 4. conclusions it was possible to synthesize the magnetite nanoparticle with the aqueous extract of euclayptus grandis foliage with a synthesis percentage of 98.99% and with the experimental design the optimal conditions for the synthesis reaction were established (naoh solution 1.7 m, extract volume 0.8 ml, temperature 87 °c), improving the characteristics of the nanoparticles. figure 7. ir spectra of the synthesized magnetite nanoparticles. source: authors. from the results obtained, it is concluded that the iron oxide nanoparticle prepared from aqueous extract of eucalyptus grandis foliage, due to its chemical stability, as well as the nature of the biomass and its low cost, in addition to its large estimated surface area, is presented as an alternative for obtaining this type of materials taking into account the guidelines of green chemistry. conflict of interest the authors declare that they have no conflict of interest. references 1. del rio clar m. application of magnetic iron nanoparticles to the 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remediation of mercury contaminated saltwater with functionalized silica coated magnetite nanoparticles. science of the total environment 2016; 557–558: 712–721. doi: 10.1016/j.scitotenv.2016.03.075. 16. hasnain ms, javed mn, alam ms, et al. purple heart plant leaves extract-mediated silver nanoparticle synthesis: optimization by box-behnken design. materials science and engineering: c 2019; 99: 1105–1114. doi: 10.1016/j.msec.2019.02.061. 17. alvear d, galeas s, guerrero vh, et al. synthesis and characterization of magnetite nanoparticles (in spanish). revista politécnica 2017; 39(2): 61–66. doi: 10.33333/rp.v39i2.545. microsoft word can-v6i2-editorial-online characterization and application of nanomaterials (2023) volume 6 issue 2 doi: 10.24294/can.v6i2.5883 1 editorial editorial for characterization and application of nanomaterials (volume 6, issue 2) naval garg† delhi technological university, new delhi 110042, india; naval.garg@dtu.ac.in † editor of characterization and application of nanomaterials nanomaterials are a recently discovered type of material that is gaining importance and receiving a lot of attention from researchers. due to their numerous advantages, scholars are studying nanoparticles extensively. the articles in this issue that discuss the various applications of nanoparticles are very interesting. the majority of these articles focus on the use of nanoparticles in the medical sector and their contributions to environmental protection. nano-biomaterials have a wide range of applications in the medical field, including medical antibacterial materials, medical intervention/implantation materials, tissue engineering, regenerative medical materials, medical diagnostic imaging contrast agents, cancer photothermal therapy/chemotherapy, drug-controlled release carriers, and more. these materials have excellent physical, chemical, and biological safety properties, making them highly beneficial[1]. researchers have been studying nano-biomaterials for a long time due to their significant impact on social development and human health[2]. cole et al.[3] have reported a simple, economical, and optimized hydrothermal synthesis process for the production of high-purity tadoped potassium titanate nanofibers. they aim to develop functional nanoscale bone tissue substitutes that can be utilized for the regeneration, replacement, or repair of diseased or damaged bone. sanjay et al.[4] have explored the use of bioactive glass nanoparticles doped with antimicrobial compounds, including silver, zinc, and magnesium ions, for medical applications. according to these researchers, nano-biomaterials are essential for optimizing some medical solutions. nanoparticles play a significant role in protecting the environment. in a study by kamyab et al.[5], the use of green resources from cardamom seeds and ginger peels was used to synthesize the zno-cofe2o4 nanostructure by the oxygen evolution reaction (oer), which is environmentally friendly and serves as an effective electrochemical catalyst for the oxidation of water. another study by krishnan and rajendran[6] demonstrated that hydrophilically modified mesoporous ps-mwcnt composites have rapid adsorption and desorption kinetics of xylene isomers, which can effectively remove toxic substances from the environment. biju[7] also found that the article info received: 31 december 2023 available online: 18 janurary 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 copper oxide/zinc oxide nanocomposite effectively reduced water pollution and protected human health by degrading dyes such as methyl red and methyl orange under uv and visible light. the application of nanomaterials in this field shows great potential for reducing the negative effects of toxic substances on the environment. based on historical and contemporary studies, it is evident that nanomaterials provide various benefits that significantly impact several sectors associated with social progress and human welfare. as a result, many academics continue to investigate the applications and qualities of nanomaterials that could be advantageous to human society. lastly, we express our deep appreciation to the authors for granting us permission to share their insightful ideas. conflict of interest the author declares no conflict of interest. references 1. what are the applications of nanotechnology in the industry? available online: https://www.cdstm.cn/gallery/media/mkjx/qcyjswx_6431/202110/t20211025_1058080.html (accessed on 15 january 2024). 2. newsijie. nanobiomaterials have great potential for development in the medical field, and most research has not been commercialized. available online: https://m.ofweek.com/medical/2022-03/art-11106-842030554585.html#:~:text=%e7%ba%b3%e7%b1%b3%e7%94%9f%e7%89%a9%e6%9d%90%e6%96%99% e4%ba%a7%e5%93%81%e7%a7%8d%e7%b1%bb,%e5%85%b6%e7%a0%94%e7%a9%b6%e7%83% ad%e5%ba%a6%e4%b8%8d%e5%87%8f%e3%80%82 (accessed on 15 january 2024). 3. cole p, tian y, thornburgh s, et al. hydrothermal synthesis of valve metal ta-doped titanate nanofibers for potentially engineering bone tissue. characterization and application of nanomaterials 2023; 6(2): 3606. doi: 10.24294/can.v6i2.3606 4. sanjay ss, yadav p, asthana n, et al. an investigation on 45s5 nanobioactive glass using ftir and raman spectroscopy. characterization and application of nanomaterials 2023; 6(2): 4152. doi: 10.24294/can.v6i2.4152 5. kamyab a, khojasteh mh, asadpour-zeynali k. an eco-friendly route for green synthesis of zno-cofe2o4 nanoparticles from cardamom and ginger extract as an efficient electrochemical catalyst for water oxidation. characterization and application of nanomaterials 2023; 6(2): 3182. doi: 10.24294/can.v6i2.3182 6. krishnan mr, rajendran v. sulfonated mesoporous polystyrene-1d multiwall carbon nanotube nanocomposite as potential adsorbent for efficient removal of xylene isomers from aqueous solution. characterization and application of nanomaterials 2023; 6(2): 3516. doi: 10.24294/can.v6i2.3516 7. biju r. photocatalytic degradation of organic dyes using transition metal based mixed metal oxide nanocomposite under different illumination. characterization and application of nanomaterials 2023; 6(2): 3573. doi: 10.24294/can.v6i2.3573 characterization and application of nanomaterials (2019) volume 2 issue 1 doi:10.24294/can.v2i1.562 1 non-destructive determination of chemical effects on fluorescence yields and vacancy transfer probabilities of tin compounds ahmet tursucu1*, mehmet haskul2 and asaf tolga ulgen3 1 department of energy systems engineering, faculty of engineering, sirnak university, sirnak 73000, turkey, ahmettursucu@sirnak.edu.tr 2 department of mechanical engineering, faculty of engineering, sirnak university, sirnak 73000, turkey, mehmethaskul@gmail.com.tr 3 department of electric and electronic engineering, faculty of engineering, sirnak university, sirnak 73000, turkey, ulgen_at@sirnak.edu.tr abstract in the current work, it was investigated to the k x-ray fluorescence efficiency and chemical effect on vacancy transfer probability for some tin compounds. we used br2tin, tini2, setin, tinf2, tinso4, tincl2, tino and tins compounds for experimental study. the target samples were irradiated with 241am annular radioactive source at the intensity of 5 ci which emits gamma rays at wavelength of 0.2028 nm. the characteristic x-rays emitted because of the excitation are collected by a high-resolution hpge semiconductor detector. it has been determined that the experimental calculations of the tin (sn) element are compatible with the theoretical calculation. in addition, we have calculated the experimental intensity ratios, fluorescence yields and total vacancy transfer probabilities for other sn compounds. keywords: vacancy transfer probability; intensity ratio; fluorescence efficiency. 1. introduction the characteristic x-rays are an electromagnetic wave type that is produced by passing the dissociating electron of an inner layer electron from a high-energy level to a low-energy level[1]. when a monochromatic x-ray diffraction onto the material, the scattered, diffracted, and radiographic absorbed events that are the basis of x-ray diffraction occur. a stimulated atom radiative or non-radiative will transition and these transitions continue until reaching the equilibrium state. stimulation of the outer orbit of the atom; it’s internal orbit electrons are possible with stimuli such as accelerated electrons, neutrons, α-particles, photons emitted from radioactive sources. thus, a vacancy is formed in the outer shell of the excited atom, these are filled by radiative or non-radiative transition (auger)[2]. the vacancy transfer is called the vacancy from the bottom layer to the top layer[3]. absorption jump factor and jump ratios are important parameters related to the absorption and emission of x-rays that produce fluorescence effect. in the literature, different experimental methods have been used to calculate k shell absorption leap factor and jump ratios, such as gamma ray absorption method[4-7]. this method is preferred for the analysis of photons and energy-separated x-ray spectroscopy which are absorbed because of compton scattering. absorption jump factor and jump ratio is give (kβ/kα) intensity ratio[8,9] and this parameter is also very important in our study. the calculation of the severity rates of the different elements and compounds has several effects on the sample of stimulating radiation and the characteristic properties of the materials used as target specimens are revealed. the experimental studies of x-ray intensity ratios for different elements are also benefit research areas such as atomic, molecular and radiation physics, geology, medical physics and elemental analysis[10-12]. yılmaz studied the kβ /kα intensity ratio at 16.896 kev excitation energy in the elements with atomic numbers between 28 ≤ z ≤ 39, using si (li) semiconductor detector and compared the calculated experimental values with other theoretical values[13]. baydaş copyright © 2019 ahmet tursucu et al. doi: 10.24294/can.v2i1.562 enpress publisher llc.this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 and öz worked the chemical effect on k and k 1,3 publishing lines in some iron compounds using wavelength dispersive x-ray fluorescence (wdxrf) technique and they observed that the oxidation rate of fe, the main atom in the compounds, is influential in the intensity ratios of the emission lines[14]. porikli et all investigated l x-ray intensity ratios and chemical effects on related line structures in some compounds of la, ce and pr elements[15]. they have proved that, the full width at half maximum (fwhm) values and the spectral lines are susceptible to changes in the molecular structure of the ligand bond. in this paper, we have studied the chemical effects on the kβ/kα x-ray intensity ratio values, k x-ray fluorescence cross sections and k-l shell gap crossing probabilities in sn compounds. moreover, in space researches and its compounds which are frequently used as coating materials in industrial devices have been studied. the br2tin, tini2, setin, tinf2, tinso4, tincl2, tino and tins samples were also investigated with a high-resolution hpge semiconductor detector. 2. materials and methods in this experimental study, we aimed to calculate the kβ /kα x-ray intensity ratio of tin (sn) compounds using gamma rays of 0.2082 nm wavelength emitted from a 241 am annular (ring) source at 5 ci power. the characteristic x-rays which are generated because of gamma rays warping the target sample were collected by a high-resolution semiconductor hpge detector. this detector has a high purity germanium crystal with 16 mm radius, 10 mm long, and 0.12 mm thick be window and its active area is 200 mm2. the schematic diagram of experimental setup is shown in fig.1 and fig.2. a bias voltage of -1500 v was applied to the detector with an ideal resolution of 182 ev at 5.9 kev. the mass thicknesses of the sn compounds used range from 0.244 to 0.538 g/cm2 and these samples were br2tin, tini2, setin, tinf2, tinso4, tincl2, tino and tins. spectrum of sn samples was assessed by using a canberra (accuspec) pc-based multichannel analyzer card. we fixed the time constant of the ortec model 472 amplifier at 6 μs so that we get the best count value from the detector. operating parameters of the experimental system were controlled by the computer program genie-2000. the experimental data were obtained on 1024 channels of the mca. these data were analyzed and illustrated by the origin 7.5 software program. figure 1. experimental setup. 3 figure 2. sample chamber (a=6.5 cm, b=6.3 cm, c=13.5 cm, d=11 cm and e=5 cm). 3. theory 3.1 calculation of k x-ray intensity ratio the intensity ratios of emitted characteristic k x-rays are the result of filling the vacancy formed by the photoionization of the k layer. theoretical atomic parameters of k layer are given by the expression iki = ik e wkfki → i = α, β (1) where ik(e) is x-ray intensity at excitation energy for element k layer[16] and wk is the fluorescence efficiency for k layer[17]. the fki value is partial emission rate for kix-rays. k and k x-rays are given by the expression fkα = [1 + (ikβ/ikα)]−1 and fkβ = [1 + (ikα/ikβ)]−1 . (2) the ikβ/ikα values are taken from the table of scofield et all. studies[16]. the characteristic of the xrf technique is that the x-ray line intensity is experimentally given as iki = nki[i0gεkiβt]−1 (3) 4 where nki is net peak area in counts, i0 is severity of stimulated radiation, g is geometry factor, εki is the detector efficiency for k x-rays group and t is mass thicknesses of samples (g/cm2). β is the self-absorption correction coefficient for incident photons and emitted x-ray photons, as calculated by  1 2 1 2 1exp ( ) ( ) i e ki i e μ /cosθ +μ /cosθ t β = μ /cosθ +μ /cosθ t (4) where μi and μe are the mass absorption coefficients of incident and scattered photons, respectively. θ1 and θ2 are the angles of the excitation photons and the x-rays emitted by the surface normal of the working sample geometry, respectively. in this study, θ1 = 167.5o and θ2 = 0o. μi and μe values can be calculated using the winxcom[18] software. equation 4 can also be written as 1 0 [ ] ik k ki g n i t      (5) if the values of ikα are used in different excitation energies in equation 5, i0gε can be calculated for any energy. if these values ​ ​ are plotted as a function of the excitation energy e, the i0gε value in the excitation photon energy used in the actual measurements in this graph can be calculated. as a function of i0gε energy value;  3 1 2 3 4 0 0 1 2 3 4. . . .k k k k ke log i g a a e a e a e a e            (6) where ekα is energy of kα x-rays and a0, a1, a2, a3, and a4 are constants found by the least squares method. thus, the difference between fitted values and experimental values is less than 2%. since this difference is not the single energetic peak of the kβ or kα , and therefore the average value calculated for energy does not represent energy fully. according to equation (3) is used for the k x-ray intensity ratios, β β α α α α β β k k k k k k k k i n β ε= i n β ε (7) where nkβ and nkα are net counts, βkβand βkα are the self-absorption correction coefficients, and εkα and εkβ are detector efficiency. 3.2 the calculation of k x-ray fluorescence yield for all the selected target samples, the x-ray production cross section at 0.2028 nm wave length excitation energy, as; k k k kw f     (8) where wk is fluorescence yield for k shell and the theoretical calculation of this value is calculated by krause worked[19]. the σk value is the total ionisation cross section of the k shell, and fkαvalue represents the partial emission ratio. as a result, fluorescence effect cross section, as per the relation; ik k k w    (9) the experimental calculation of clearance transitions (ηkl) from layer k to layer l is expressed by ηkl = 2−wk 1+(ikβ+ikα) (10) 4. result and discussion in this work, the clearance transitions probabilities (ηkl), intensity ratios and ( ikβ/ikα ) x-ray fluorescence efficiencies (wk) of the tin, br2tin, tini2, setin, tinf2, tinso4, tincl2, tino ve tins compounds (from layer k to layer l) were calculated by the above equations. the energy dispersive x-ray fluorescence spectra of pure sn element and several sn compounds are given in fig.3. kβ/kα x-ray intensity ratios, k x-ray fluorescence yields and k-l total vacancy transfer probabilities values for the sn sample are given in table 1. at the same time, experimental values and theoretical values were compared for these sample. since there is no previous theoretical study for other samples, only experimental values are given as in table 2. as can be seen from table 1 and table 2. present exp. theoretical other exp. 5 table 1. values of kβ/kα x-ray intensity ratios, k x-ray fluorescence yields and k-l total vacancy transfer probabilities for the tin sample. sample intensity ratios fluorescence yields vacancy transfer probabilities tins 0,2064±0,0003 0,7064 0.1206 1.072 0.1110 br2tin 0,2168±0,0107 0.7004 0.1246 1.067 0.1077 tini2 0,2074±0,0013 0.7058 0.1211 1.072 0.1107 setin 0,2465±0,0404 0.6838 0.1349 1.056 0.0981 tinf2 0,2351±0,0289 0.6902 0.1311 1.0605 0.1018 tinso4 0,2350 ±0,0289 0.6903 0.1309 1.0604 0.1017 tincl2 0,2343±0,0282 0.6908 0.1306 1.0607 0.1019 tino 0,2363±0,0302 0.6896±0.1314 1.0598 0.1013 table 2. experimental values of kβ/kα x-ray intensity ratios, k x-ray fluorescence yields and k-l total vacancy transfer probabilities for the other sn samples. sn compounds are found to be effective on x-ray fluorescence parameters of chemical bond structures. figure 3. energy dispersive x-ray fluorescence graph for pure sn (black dots) and sn compounds (red dots). a) tin and tin(ii)sulfide, b) tin and tin(ii)bromide, c) tin and tin(ii)iodide, d) tin and tinselenide, e) tin and tin(ii)fluoride, f) tin and tin(ii)sulfade, g) tin and tin(ii)chloride, f) tin and tin(ii)oxide. the energy dispersive x-ray fluorescence spectra of pure sn (black dots) and their compounds (red dots) are depicted in fig.3. the difference in the characteristic peaks was caused by chemical bond structure and ligand effect, as can be clearly seen from the spectra. as a result, it is seen that some of the peak count numbers are excessive whereas the other peak count numbers are less. this is mainly due to differences in the binding energies of the electrons in the structures connected to the central atom. the differences in the spectrum are based on the common use of the donor electrons made with the main element and the possibility of interacting with the gamma rays in the 0.2082 nm wavelength sent by the density of the exposed electrons. intensity ratios 0,2061 0,22a 0,2061b 0.20860.011c 0.2260.020d fluorescence yields 0.8620.044 0.862a 0.860b 0.8580.069c 0.7470.060c vacancy transfer probabilities. 0.9250.0008 0.941a 0.952b 0.9420.005c 6 5. conclusion the study was observed to be very consistent when compared with theoretical and other experimental data. we have presented the pure sn element and sn compounds with scattering intensity ratio, k x-ray fluorescence yields and k-l total vacancy transfer probabilities. only experimental and theoretical value of the tin element was given in this study and experimental values were calculated for the tins, br2tin, tini2, setin, tinf2, tinso4, tincl2 and tino compounds which will shed light on other theoretical studies. scattering intensity ratio, k x-ray fluorescence yields and k-l total vacancy transfer probabilities values in all samples are consistent with each other. additionally, scattering intensity ratio is approximately 0.2, fluorescence yields is ~ 0.7 and total vacancy transfer probabilities values is 1.0 in all samples. it is important to perform similar studies in different excitation energies and detection systems to obtain more detailed and stable results. author contributions in the preparation of this manuscript, the first writer contributed 35%, the second writer 30%, the third writer 35%. acknowledgements this work is supported by sirnak university research fund (bap), project no: 2017.03.03.03. references 1. ino s. theory of transmission coefficient of x-rays evanescent wave for grazing incidence. journal of the physical society of japan.1996; 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22(2): 245-258. 12. ertuğral b, apaydın g, çevik u, et al; kβ/kα x-ray intensity ratios for elements in the range 16⩽ z⩽ 92 excited by 5.9, 59.5 and 123.6 kev photons. radiation physics and chemistry.2007; 76(1): 15-22. 13. yılmaz r. kβ/kα x-ray intensity ratios for some elements in the atomic number range 28≤ z≤ 39 at 16.896 kev. journal of radiation research and applied sciences.2017; 10(3):172-177. 14. baydaş e, öz e. chemical effects in the kα and kβ1, 3 of x-ray emission spectra of fe. journal of electron spectroscopy and related phenomena.2012; 185(1-2), 27-31. 15. porikli s. influence of the chemical environment changes on the line shape and intensity ratio values for la, ce and pr l lines spectra. chemical physics letters. 2011; 508(1-3), 165-170. 16. scofield jh. theoretical photoionization cross sections from 1 to 1500 kev (no. ucrl--51326). california univ., livermore. lawrence livermore lab, 1973. 17. hubbell jh, trehan pn, singh n, et al. a review, bibliography, and tabulation of k, l, and higher atomic shell 7 x‐ray fluorescence yields. journal of physical and chemical reference data.2004; 23(2): 339-364. 18. gerward l, guilbert n, jensen kb, et al. 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(1979). atomic radiative and radiationless yields for k and l shells. journal of physical and chemical reference data.1979; 8(2): 307-327. characterization and application of nanomaterials (2019) volume 2 issue 1 doi:10.24294/can.v2i1.659 1 effect of an inverse parabolic confining electric potential on third harmonic generation in cylindrical quantum wires tshipamoletlanyi1 department of physics, university of botswana, gaborone, south east district, botswana. abstract a theoretical investigation of the effect of an inverse parabolic potential on third harmonic generation in cylindrical quantum wires is presented. the wave functions are obtained as solutions to schrödinger equationsolved within the effective mass approximation. it turns out that peaks of the third harmonic generation susceptibility (thgs) associated with nanowires of small radii occur at larger photon energies as compared to those associated with quantum wires of larger radii. the inverse parabolic potential red-shifts peaks of the thgs, and suppresses the amplitude of the thgs. thgs associated with higher radial quantum numbers is diminished in magnitude and blue-shifted, as a function of the photon energy. as a function of the inverse parabolic potential, the thgs is still characterized by peaks, which shift to lower values of the potential as the photon energy increases. keywords: third harmonic generation; confining electric potential; cylindrical quantum wires. 1. introduction advances in nanofabrication techniques have endowed the scientific community with an avenue of obtaining nanostructures of different sizes and geometries[1-3]. these nanostructures have applications in many disciplines like medicine[4,5], chemical sensing[6], optoelectronics[7, 8], energy physics[9-11] and gas sensing[12]. an attractive feature of nanostructures is the emergence of quantization when charge carriers are confined to nanoscopic regions. the charge carriers occupy quantum states with associated energies, which are dramatically different from the bulk values. electrons can make transitions between states if they absorb or lose energy which equals transition energies. this energy could be associated with photons, phonons or any other elementary excitation. transition energies are the differences between energies of states between which transitions can take place, and can be modified by changing the size of the nanostructure or by changing the intrinsic electric potential of the nanostructure[13]. the ability of electrons to make transitions between different states renders nanostructures invaluable to nanodevice applications. some of the interesting phenomena are non-linear optical processes. by making more than one transition to higher states, followed by a transition to a lower states, energy of radiation can be multiplied as required. nth harmonic generation is generation of electromagnetic wave with frequency n times the frequency of the input radiation. examples are second harmonic generation (shg), wherein the frequency of the incident radiation is doubled, third harmonic generation (thg), where the frequency is tripled, and so forth. however, thg has been shown to be more versatile than shg in imaging samples[14]. it is thusinstructive to study thg. khodard theoretically studied third harmonic generation (thg) in a double ring shaped quantum dot and found that phonons have a significant effect on the third harmonic generation susceptibility (thgs)[15]. thgs can also be modified by the geometry of the nanostructure[16]. the effects of electric and magnetic fields on thgs in a morse quantum well have also been investigated[17]. bahari et al also looked at thg in multilayered nanoshells, and found that the thgs strongly depends on the thicknesses of the nanoshells[18]. thg has been experimentally achieved and studied[19], and utilized, for example, to cool beryllium ions[20]. in this communication, the effect of the inverse parabolic potential on the thgs of cylindrical quantum wires is investigated. the inverse parabolic potential is superimposed on an infinite cylindrical square well (icsw). this paper copyright © 2019 tshipamoletlanyi et al. doi: 10.24294/can.v2i1.659 enpress publisher llc.this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 has the following organizational structure: section 2 deals with the theoretical treatment of the problem, section 3 relates the results and discussions, and the conclusions are laid in section 4. 2. theoretical framework the envisaged system is a free standing cylindrical quantum wire (cqw) of radius r and very long length hosting a negatively charged strand coincident with the axis of the wire, nonetheless considered to be much smaller than the radius of the nanowire. through appropriate nanopatterning of the cylinder by varying the lattice composition, an intrinsic confining electric potential of the form    rrrv           1 2 1 2 2 22 0 (1) and infinity elsewhere, may be realized. here,  is the effective mass of the electron and 0 is the angular frequency associated with the classical harmonic oscillator. the hamiltonian in cylindrical coordinates with this type of potential is separable, and the electron wave function can be cast in the form         imzikfcz zml expexp,,  , where mlc is the normalization constant, zk is the axial wave number and m is the azimuthal quantum number that quantifies the quantized angular momentum of the electron. the radial portion of the electron wave function,  f , satisfies the second order differential equation (schrödinger equation)        .02 2 2 21                      fmvmle d df d d  (2) where mle is the radial confinement energy. for the inverse parabolic potential (eq. 1), the radial component of the schrödinger equation is solvable in terms of the bessel functions [13]      .21   ll ycjcf  (3) in the above,   222 02 reml   and 242 0 22 rm   . the nature of the bessel y function is such that it is divergent at the origin ( 0 ), as such has to be discarded ( 02 c ) in the case of a solid cylinder, which leaves the radial wave function as    . ljf  (4) imposing the condition that the electron wave function must vanish at the walls of the quantum wire due to the infinite potential outside the wire avails an expression for the determination of the energy eigen values for the electron as    2 2222 02 1 22 2 0 2 zkr r mlj zemletote   (5) where mlj0 are the zeroes of the bessel j function. third harmonic generation susceptibility consider the system under the influence of an electromagnetic field      tietiete   exp~exp~ incident along the z direction. we can invoke the time-dependent liouville equation to investigate the evolution of the single electron state density matrix ̂       ,ˆˆˆ,ˆˆ1ˆ 0 0 ijijijij ij temh it       (6) with 0ĥ being the unperturbed hamiltonian of the system (with the electromagnetic radiation switched off),  0̂ being the unperturbed density matrix and the perturbing term being    teretem ˆˆ  , where e is the electronic charge and ij is the relaxation rate of ̂ to  0̂ . here, [] denotes the quantum mechanical commutator. the above equation (eq. (6)) can be solved using an iterative approach      n n tt  ˆˆ (7) where 3             .ˆ,ˆ1ˆˆ,ˆ1ˆ 11 0 1 tere i ih it n ij n ijijij n ij n ij           (8) the dependence of the electric polarization of the quantum wire on the electromagnetic field can be written as            cceeeeeeetp tititi .~~~~ 333 30 22 20 22 00 1 0        (9) where 0 is the absolute dielectric permittivity of classical vacuum while  1 ,  2 0 ,  2 2 and  3 3 are the linear, optical rectification, second harmonic generation and third harmonic generation susceptibilities, respectively [21]. c.c. is complex conjugate of the terms in the brackets. the thgs can be expressed as [15]                                                                              212131310101212131313030 010131313232303031312121 303020201010232320201010 101020203030212120202323 302312013 0 4 3 3 32 1 32 1 32 1 32 1 32 1 32 1 32 1 32 1 iiiiii iiiiii iiiiii iiiiii mmmme e          ,(10) where e is the electronic density, ijij rm  the matrix elements of the dipole moment and  ijij ee  the transition frequency. 3. results and discussion the parameters used in these calculations are em067.0 , where em is the free electron mass, relevant to gaas crystals. the other relevant parameters are: 32210  me [22], mf12 0 10854.8  ,   30322110 , 23120   [15], where  mev156.2 [18]. figure 1; the dependence of the product of the matrix elements on the inverse parabolic potential for a quantum wire of radius of r = 100å, for the radial quantum numbers l = 1, 2 and l = 3 figure 1 illustrates the variation of the product of the matrix elements, 30231201 mmmm , with strength of the inverse parabolic potential in a quantum wire of radius r = 100å. the three graphs have been generated for the radial quantum numbers l = 1, 2 and l = 3, as indicated. the overall effect of the inverse parabolic potential is to increase the magnitude of 30231201 mmmm . this is due to the fact that this potential tends to dilate the radial wave functions of electrons, which enhances the radial position vector. this effect is opposite to those ofthe magnetic field and the parabolic potential, which tend to suppress 30231201 mmmm [22]. the variation of 30231201 mmmm corresponding to higher radial quantum numbers is characterized by local minima and maxima, which are due to 4 the effect of the inverse parabolic potential on the electron wave functions [13]. figure 2; thgs as a function of the photon energy in an icsw (  mev00  ). the solid plot is for a quantum wire of radius r = 100å while the dashed curve is for r = 120å figure 2 depicts the (l = 1) thgs as a function of the photon energy for a cylindrical nanowire without the intrinsic inverse parabolic potential (  mev00  ). the solid plot corresponds to a cylindrical quantum wire of radius r = 100å while the dashed is associated with r = 120å. as can be appreciated from the figure, the peaks of the thgs become red-shifted as radius of the nanowire increases. this is due to the relaxation of the electron wave functions as the radius increases, which decreases radial confinement energy and consequently dwindles transition energies. the shifting of the peaks to lower photon energies is accompanied by increase in the magnitude of the thgs, which can be attributed to enhancement of the magnitude of the radial position vector as the radius increases. additionally, the peaks of the thgs converge as the radius of the specimen is increased. figure 3; the variation of the thgs with the photon energy for a quantum wire of radius r = 100å without the inverse parabolic potential  mev00  (solid plot) and with the inverse parabolic potential of strength  mev200  (dashed plot) the effect of the inverse parabolic potential on the thgs can be viewed in figure 3, which depicts the thgs as a function of the photon energy for a cylindrical quantum wire of radius of r = 100å. the solid plot represents thgs of an infinite cylindrical square well (icsw) (  mev00  ) while the dashed curve is of a nanowire with an inverse parabolic potential of strength  mev200  superimposed on the icsw. the inverse parabolic potential affects the lower states than it does the higher, therefore it naturally decreases transition energies. this manifests as the red-shifting of peaks of the thgs. in addition, the inverse parabolic potential moves the peaks apart. this can be advantageous in cases where the peaks of the thgs need to be distinct from each other, for research and/or practical purposes. another advantageous effect of the inverse parabolic potential is the enhancement of the thgs peaks at very low energies (in 5 this case, below the 40 mev region). figure 4; thgs as a function of energy of the radiation field for an icsw (  mev00  ) of radius r = 100å corresponding to radial quantum numbers l = 1, 2 and l = 3 in figure 4, the thgs corresponding to an icsw (  mev00  ) has been plotted as a function of the photon energy for the first three radial quantum numbers, l = 1, 2 and l = 3. the radius of the nanowire is r = 100å. transition energies associated with higher radial quantum numbers are greater than those associated with lower radial quantum numbers, hence the peaks of the thgs corresponding to higher radial quantum numbers occur at higher photon energies. although not shown here for succinctness, the inverse parabolic potential will also red-shift the peaks of the thgs associated with higher radial quantum numbers. it can be seen from the figure that increasing the radial quantum number decreases the magnitude of the thgs, attributable to reduced overlapping of the radial electron wave functions which determine the thgs (eq. 10). figure 5; the dependence of the thgs on strength of the inverse parabolic potential in a quantum wire of radius r = 100å. the wire is irradiated with an electromagnetic field of energy  mev40 . the solid plot is for radial quantum number l = 1 while the dashed is for l = 2 figure 5 illustrates the dependence of the thgs on strength of the inverse parabolic potential for fixed photon energy (  mev40 ) in a cylindrical quantum wire of radius r = 100å. the solid curve represents the thgs corresponding to l = 1 while the dashed curve is associated with l = 2. for a given photon energy, peaks of the thgs associated with greater radial quantum number occur at high values of the inverse parabolic potential. this is because, as already mentioned, transition energies associated with greater radial quantum numbers are usually higher than those of lower l values. concomitantly, high values of 0 are required to reduce transition energies corresponding to large l to equal the photon energy. 4. conclusion the effect of the inverse parabolic potential on third harmonic generation in a cylindrical quantum wire has been investigated. the inverse parabolic potential is superimposed on an infinite cylindrical square well. the wave functions 6 were obtained by solving the schrödinger equation within the effective mass approach. the third harmonic generation susceptibility corresponding to a quantum wire of larger radius is red-shifted and greater in magnitude than the thgs corresponding to a quantum wire of a smaller radius. the inverse parabolic potential red-shifts peaks of the thgs, and enhances peaks in the low energy region. the thgss associated with greater radial quantum numbers have relatively small magnitude compared to those corresponding to lower values of the radial quantum number. references 1. song c, li x, dong h, et al. nondestructive tribochemistry-assisted nanofabrication on gaas surface. 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litao3 crystal. appl. phys. lett. 2017; 110: 111105. 20. carollo ra, lane da, kleiner ek, et al. thrid-harmonic generation of a diode laser for quantum control of beryllium ions. optics express 2017; 25(7): 7220-7229. 21. shao s, guo k-x, zhang z-h, et al. third-harmonic generation in cylindrical quantum dots in a static magnetic field. solid state communications 2011; 151: 289-292. 22. wang g, guo q. third-harmonic-generation in cylindrical parabolic wires with static magnetic fields. physica b 2008; 403: 37-43. microsoft word 4 1412-can-layout 30-38 characterization and application of nanomaterials (2022) volume 5 issue 1 doi: 10.24294/can.v5i1.1412 30  original research article preparation of mof/au composite nanoparticles and their sers properties huihui liu, baichuan zhao, congyun zhang* school of materials science and engineering, north university of china, taiyuan 030051, shanxi province, china. e-mail: z.congyun@nuc.edu.cn abstract surface-enhanced raman scattering (sers) spectrum has the characteristics of fast-detection, high-sensitivity and low-requirements for sample pretreatment. it plays a more and more important role in the detection of organic pollutants. in this study, mil-101 and au nanoparticles were prepared by hydrothermal method and aqueous solution reduction method respectively, and mil-101/au composite nanoparticles were prepared by electrostatic interaction. the sers properties of the composite substrate were optimized by adjusting the size of au nanoparticles and the surface distribution density of mil-101 nanoparticles. the detection limit of rhodamine 6g (r6g) for the composite substrate with the optimal ratio was investigated, which was as low as 10–11 m. it is proved that mil-101/au composite nanoparticles have high sensitivity to probe molecules. when they are applied to the detection of persistent organic pollutants, the detection limit for fluoranthene can reach 10–9 m and for 3,3’,4,4’-tetrachlorobiphenyl (pcb-77) can reach 10–5 m. keywords: mil-101; au nanoparticles; surface-enhanced raman scattering (sers) article info received: 13 november 2021 accepted: 31 december 2021 available online: 8 january 2022 copyright copyright © 2022 huihui liu, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction surface-enhanced raman scattering (sers) spectrum is a substance detection method that can provide fingerprint peak identification. it has high sensitivity and its samples are non-destructive. it has important application value in the fields of environmental chemistry, medical detection, food safety and so on[1–3]. regarding the mechanism of sers enhancement, there are two types to be recognized in academic: physical enhancement and chemical enhancement, in which physical enhancement is dominant. physical enhancement is also called electromagnetic field enhancement. under the irradiation of incident light, electrons on metal surfaces with nanostructures are excited to produce vibration, and localized surface plasmon resonance (lspr) can be formed at a specific excitation frequency. this leads to the enhancement of the local electromagnetic field of the metal substrate and greatly enhances the raman signal of the probe molecules attached to the metal surface. the enhancement effect of sers strongly depends on the metal type, nanostructure and morphology of the substrate. the traditional coin metals such as au, ag and cu have been widely studied because of their excellent surface plasmon resonance characteristics[4–6]. however, some polycyclic aromatic hydrocarbons have poor affinity with the surface of traditional precious metals, resulting in weak or even no detection signal, which further limits the application of sers in detection field. therefore, in order to improve the affinity between probe 31  molecules and metal particles, the functionalization of metal nanoparticles has become a research hotspot. introducing modifiers such as cysteamine[7] and cyclodextrin[8,9]. to modify the surface of nano metals can effectively improve the enrichment effect of molecules[10]. now, the development trend of sers substrate is to composite precious metals with plasma resonance effect and porous materials with adsorption and enrichment ability to build composite particles. porous materials can effectively adsorb solution molecules. however, the application prospects of traditional activated carbon, aluminum silicate[11] and zeolite[12] are limited due to defects such as small specific surface, fixed structure and inability to be modified flexibly. as a new porous material, metal organic framework (mof) material has the characteristics of large specific surface area, excellent adsorption capacity and adjustable structure. it has been widely studied in the field of adsorption and removal of organic molecules. in 2010, haque et al.[13] first reported the study on the adsorption of dyes by mof. for methyl orange in aqueous solution, two cr bases mof materials (mil-101(cr) and mil-53(cr)) show ed better adsorption effect than traditional activated carbon. at the same time, the adsorption capacity of mil-101(cr) was more and the adsorption rate is faster. it is due to the larger specific surface area of mil-101(cr). in addition, the π-π interaction between mof particles and organic molecules can enhance the adsorption of organic molecules[14], such as the adsorption of uio-66 on herbicide methyl chlorophenoxypropionic acid (mcpp)[15]. the probe molecules can be preconcentrated near the metal surface by using the adsorption characteristics of mof. generally, there are three ways to combine mof with metal particles. one is to take metal particles as the core and mof particles as the shell to coat its surface to construct the core-shell composite structure. zhang et al.[16] obtained au/mof-74 core-shell structure by one-pot method to detect 4-nitrothiophene in situ. yang et al.[17] synthesized au@mil-101 through layer by layer self-assembly to realize the detection of hexamethylene tetramine at 10–8 m. au@zif-8 prepared by li shikou, et al.[18] showed a highly sensitive sers response to crystal violet. the defect of this method is that the spacing of metal particles is not easy to control to get the best state of “hot spot”. the second method is to prepare aunps/mil-101 by in-situ reduction of metal embedded in mof by solution impregnation method, which can achieve relatively low sers detection limits for r6g and benzidine[19]. because in-situ reduction cannot control the size and morphology of metal particles, it is difficult to realize sers performance optimization. the third is to connect mof and metal particles with modifiers, specifically to modify mof in preparation or after mof preparation. then reduce the loaded metal particles at the modification position in the metal precursor solution[20], or grafted mof particles on the modified metal surface. this synthetic method has better control over the metal loading position, but the synthesis is cumbersome. additional reagents need to be introduced, and the cost is increased. therefore, this paper explores a simple and easy method which can well control the morphology and spacing of mof and metal particles. the composite sers substrate was prepared by combining negatively charged mil-101 in me thanol dispersion with positively charged au particles coated with cetyl trimethyl ammonium bromide (ctab) by electrostatic adsorption. mil-101 provides adsorption and enrichment of probe molecules, while au particles provide surface electromagnetic enhancement. the substrate enhancement ability is optimized by adjusting the size of au particles and the load density on the surface of mil-101. when the particle size of au particles is 60 nm and the composite volume ratio of mil-101 to au is 1:2, the sers substrate gets the best performance. in the end, sers substrate with best performance is applied to the detection of fluoranthene and pcb-77. it is found that the detection limit of the substrate for typical persistent organic pollutant fluoranthene can reach 10–9 m and 10–5 m for pcb-77, which has important research significance and application value in the field of real-time and highly sensitive detection of environmental persistent organic 32  pollutants. 2. experiment parts 2.1 preparation of mil-101/au composite nanoparticles 2.1.1 laboratory reagent the main reagents used in the experiment are shown in table 1. table 1. main reagents used in the experiment name factories purity chromium (ⅲ) nitrate nonahydrate aladdin ar terephthalic acid china national pharmaceutical group corporation 99% hydrofluoric acid tianjin tianli chemical reagent co., ltd 40% gold acid chloride trihydrate aladdin ar sodium borohydride shanghai sinopharm reagent 98.0% cetyl trimethyl ammonium bromide (ctab) tianjin kaitong chemical reagent co., ltd 99% anhydrous ethanol tianjin damao chemical reagent co., ltd 99.7% n,n-dimethyl formamide aladdin 99.8% methanol tianjin damao chemical reagent co., ltd ar 2.1.2 preparation of mil-101 chromium (ⅲ) nitrate nonahydrate (5 mmol), terephthalic acid (5.2 mmol) and pure water (30 ml) were added to a 50 ml beaker for ultrasound for 30 min, and then 0.25 ml hydrofluoric acid was added. the mixed solution was transferred to a reactor with tetrafluoroethylene lining and maintained at 220 ℃ for 8 h. after the reaction, cool down naturally to room temperature. wash the product alternately with ethanol and n,n-dimethyl formamide (dmf) for three times to remove the incompletely reacted terephthalic acid. reflux with ethanol solution at 85 ℃ for 6 h to remove the residual reactants in the mof channel. finally, wash it twice with anhydrous ethanol and keep it in a vacuum oven at 150 ℃ for 12 h. green powder was obtained after drying, and then dispersed in methanol solution to prepare 0.1 mg/ml suspension. 2.1.3 preparation of au nanoparticles au nanoparticles were prepared by seed growth method. au seed preparation: first, prepare a certain amount of 0.01 m haucl4 and 0.1 m ctab aqueous solution, mix 0.25 ml haucl4 and 7.5 ml ctab solution evenly, and quickly add cold newly prepared nabh4 (0.6 ml, 0.01 m) aqueous solution, stirring at high speed for 1 min to obtain gold seed suspension, and then set aside at room temperature for 1 h. preparation of growth solution: mix ctab (6.4 ml, 0.1 m) and haucl4 (0.8 ml, 0.01 m) solution. add aa (3.8 ml, 0.1 m) and 32 ml ultrapure water. finally, add 10, 20, 30 and 40 μl gold seeds diluted 10 times into the growth solution respectively. gold particle solutions with different particle sizes are obtained after setting aside for 4 h. wash them twice with ultrapure water, and then disperse them in 8 ml methanol solution for standby. 2.1.4 preparation of mil-101/au composite nanoparticles the suspension of mil-101 and au was mixed at different volume ratios (1:1, 1:2 and 1:3) under high-speed stirring for 5 min and stood for 1 h to obtain composite particles with different au loading densities. 2.2 characterization and test method of mil-101/au composite substrate the particle morphology and crystal structure are determined by the scanning electron microscope (su-8010, 10 kv) of hitachi, japan, and german bruker x-ray diffractor (d8adva nce, emission source of cu kα line, acceleration voltage of 35 kv, and scanning angle of 5–70°) and nicolet is50 fourier transform infrared spectroscopy (ftir, scan wavenumber ranging from 500–3,500 cm–1) of thermo fisher, inc. ultraviolet visible absorption spectrum (uv-vis) is measured by ultraviolet spectrophotometer (model: carry500) of agilent company. during the sers performance test, take 0.2 ml r6g and pcb-77 solutions with different concentrations and 0.8 ml suspension of compo 33  site particles. after the composite particles fully adsorb the substance to be tested, remove the free molecules, and suck 20 μl with a pipette gun and drop on the silicon wafer. after vacuum drying, raman measurement was carried out in renishaw invia laser micro confocal raman spectrometer of renishaw company in the uk. the laser wavelength was 785 nm, the acquisition time was 10 s and the laser power was 1.5 mw. 3. results and discussion 3.1 preparation and characterization of mil-101/au figure 1(a, b) shows the sem morphology of mil-101/au composite nanoparticles under different test multiples. it can be seen from the figure that au nanoparticles are evenly distributed on the surface of mil-101, which proves the successful recombination of the two particles from the perspective of morphology. figure 1. (a, b) sem images of mil-101/au composite nanoparticles at different magnification; (c) xrd test diagram; (d) uv visible spectrum curve; (e, f) ftir curve. it can be seen from figure 1(c), the x-ray diffraction peaks of mil-101 are mainly concentrated in the range of 5–20°. after compounding with au nanoparticles, obvious characteristic diffraction peaks belonging to au particles appear, in which the (111), (200) and (220) crystal planes of au correspond to 38.2°, 44.4° and 64.6° respectively. meanwhile, the characteristic peaks attributed to mil-101 after recombination of particles are particularly weak, which is due to the weakening of the signal of mil-101 against the strong characteristic peaks of au. however, these two characterization methods cannot fully express the binding effect of mil-101 and au. therefore, with the help of uv-vis spectrum, the spectral absorption peaks of mil-101, au and the suspension after recombination are studied. figure 1(d) shows the uv spectral curves of mil-101 and au particles alone and after recombination. it can be seen from the figure that the absorption peak of au particles with particle size of 60 nm is at 590 nm and the absorption peak of 34  mil-101 is at 319 nm. after the two are combined, the characteristic absorption peaks of the composite particles appear near the positions of the two absorption peaks at the same time, which only produces a small blue-shift, indicating that the combination of the two by electrostatic adsorption has no effect on their respective characteristics. therefore, the successful recombination of mil-101 and au is proved from the perspective of microstructure. in order to further investigate the interaction between mil-101 and au nanoparticles, the infrared spectrum of the composite particles and pure mil-101 is analyzed. figure 1(f) is the enlarged local spectrum of figure 1(e). according to the comparison of the infrared spectrum curves before and after composite, the composite particles appear new absorption peaks at 1,109 and 912 cm–1, which belongs to the vibrational absorption of c-n bond and c-h bond respectively. they all come from ctab molecules coated on the surface of au particles. this shows that there is no new chemical bond formed in the recombination process of mil-101 and au, and the binding process is a physical change. 3.2 optimization of sers performance the sers effect strongly depends on the morphology, size and particle gap of metal nanostructures. in this experiment, the surface plasmon resonance effect of composite particles was adjusted by controlling the size and distribution density of au nanoparticles on the surface of mil-101, so as to optimize the sers performance of particles. the particle size of au particles is adjusted by changing the amount of seed dispersion added to the growth solution. figure 2(a) shows the uv-vis spectra of au particle dispersion with different particle sizes. it can be seen from the figure that with the increase of au particle size from 40 nm to 60 nm, the absorption peak shifts red and the peak width is relatively narrow, which shows that the particle size distribution is uniform. when the particle size increases to 70 nm, the absorption peak becomes wider and the particle size distribution begins to be uneven. the au particles with four particle sizes are compounded with mil-101 dispersion in a volume ratio of 1:1, and the compounded particles are used as the substrate for sers performance test. figure 2(b) shows the results of sers detection for r6g at 10–5 m. figure 2(c) shows the raman signal intensity of each substrate in 2(b) at 1,509 cm–1. it can be seen from the figure that the signal intensity of gold particles with particle size of 60 nm is the largest and the sers performance is the best. therefore, it is used as the optimal substrate for subsequent experimental research. figure 2. (a) uv-vis spectra of au particle dispersion with different particle sizes; (b) sers test of r6g by composite particles corresponding to au nanoparticles with different particle sizes; (c) corresponding to the raman signal intensity at 1,509 cm–1 in (b). when determining the size of au nanoparticles, another factor, that is, the distribution density of au particles on mil-101, was investigated. the distribution density of au particles was adjusted by controlling the volume ratio of mil-101 to au nanoparticle dispersion. taking 60 nm au particles as the precursor, three substrates were prepared with the volume ratio of mil-101 to au particles of 1:1, 1:2 and 1:3 respectively. the sers properties were investi 35  gated with 10–5 m r6g as the probe molecule. figure 3(a, b and c) is the sem diagram of the particles compounded according to the three volume ratios. it can be seen from the figure that with the increase of au addition from 1:1 to 1:2, the au particle density increases significantly after composite. continuing to increase to 1:3, au particle density no longer increases significantly after composite. figure 3(d) shows the sers performance diagram of r6g test of three substrates. figure 3(e) shows the raman signal intensity at 1,509 cm–1 in 3(d). it can be seen from the sers performance diagram that the raman signal is significantly enhanced with the addition of au particles from 1:1 to 1:2, which is due to the increase of au particle density. on one hand, the increase of au particle density can increase more surface “hot spots”; on the other hand, reducing the spacing between particles will produce stronger surface plasma coupling and stronger surface electromagnetic field effect. with the further increase of the amount of au particles, the loading density of au particles is saturated and the raman signal intensity is basically stable. this is because there is an electrostatic balance between mil-101 and au particles, i.e. potential “zero”. this is also a major advantage of electrostatic interaction to avoid the formation of particle accumulation due to excessive au particle density, which will affect the raman enhancement effect. therefore, the volume ratio 1:2 of mil-101 to au particles is regarded as the optimal composite ratio for the next performance study. figure 3. sem diagram of mil-101 and au compounded according to volume ratio: (a) 1:1; (b) 1:2; (c) 1:3. (d) sers test of r6g after compounding according to different volume ratio; (e) corresponding to the raman signal intensity at 1,509 cm–1 in (d). 3.3 study on sers performance in order to explore the raman enhancement mechanism of the substrate, raman tests were carried out on 10–5 m r6g molecules on three types of substrates: pure silicon wafer, mil-101 and mil-101/au composite particles. the results are shown in figure 4(a). almost no r6g raman signal appeared on the pure silicon wafer. after the introduction of mof, due to its porous and adsorption characteristics, r6g molecules are enriched, the number of r6g molecules per unit volume is significantly increased, and weak signal peaks will appear. further, after mof and au are combined, the r6g signal is significantly enhanced by combining the characteristics of mof materials and the surface plasma coupling effect of precious metal gold particles. due to the introduction of mof materials, the adsorption of probe molecules takes a certain time. therefore, the effect of adsorption time on the sers performance of mil-101/au composite substrate is further explored. figure 4(b) shows the raman 36  spectrum curve of mil-101/au substrate on r6g under different adsorption time. figure 4(c) shows the change curve of peak intensity over time at 1,509 cm–1 in corresponding 4(b). obviously, when the adsorption time is extended, the raman detection signal of the corresponding substrate will increase, but after the adsorption time reaches 40 min or even longer, the corresponding signal intensity will hardly change, indicating that when the adsorption time is 40 min, and the substrate reaches adsorption saturation on the probe molecules, the number of probe molecules that can effectively interact with the substrate will not increase, and the raman signal of the corresponding molecules will not be enhanced. after various substrate indexes have been determined, raman tests are carried out on r6g molecules of different concentrations on the composite substrate. as shown in figure 4(d), the detection limit of r6g by the substrate can reach 10–11 m. it has reached the leading level in the reported literature. figure 4. (a) raman spectra of r6g on different substrates; (b) raman spectra of r6g by mil-101/au at different adsorption times; (c) corresponding to the relationship between raman signal intensity and adsorption time at 1,509 cm–1 in (b); (d) raman detection spectrum curve of mil-101/au composite substrate for different concentrations of r6g. 3.4 study on detection and application of sustainable organic pollutants a large number of persistent organic environmental pollutants such as polychlorinated biphenyls (pcbs) have the characteristics of strong toxicity and easy bioaccumulation, which seriously threaten human health and the environment. therefore, the research on rapid trace detection and efficient treatment of persistent organic pollutants is very urgent. in order to further explore the practical application of composite substrate, in this experiment, raman detection was carried out for two typical organic pollutants: fluoranthene and pcb-77. the test results are shown in figure 5(a) and figure 5(c). the detection limit of the prepared composite substrate for fluoranthene can reach 10–9 m and pcb-77 can reach 10–5 m, successfully realizing the trace detection of pops. figures 5(b) and (d) show the plots of the concentration logarithm and ramanan peak intensity of fluoranthene and pcb-77, respectively. it can be seen from the figure that the raman peak intensity of pcb-77 at 1,599 cm–1 shows a good linear correlation with its logarithm of concentration, and the correlation index r2 can reach 0.993. for fluoranthene, the correlation between the characteristic raman peak intensity and the concentration logarithm is relatively poor, indicating that although the detection limit of the substrate for fluoranthene is lower, 37  the detection stability of the substrate is worse than that of the substrate for pcb-77, which means that there are still difficulties to be overcome in the detection and application of persistent organic compounds. figure 5. (a) raman detection curves of different concentrations of fluoranthene on mil-101/au composite substrate; (b) the relationship between fluoranthene concentration and raman peak intensity (1,607 cm–1); (c) raman detection curves of substrate to different concentrations of pcb-77; (d) relationship between pcb-77 concentration and raman peak intensity (1,599 cm–1). 4. conclusion in this paper, the combination of mil-101 and au nanoparticles was successfully realized by electrostatic adsorption. combining the advantages of the two materials, the high sensitive detection of persistent organic pollutants such as fluoranthene and polychlorinated biphenyls is realized by using the excellent molecular enrichment ability of mil-101 and the significant plasma resonance coupling effect of au nanoparticles. the detection limit of fluoranthene can reach 10–9 m and pcb-77 can reach 10–5 m. through the physical adsorption of mil-101 and π-π conjugation with organic pollutants, it promotes the interaction between substrate and detector, and makes up for the poor adsorption capacity, weak or no detection signal of traditional noble metal sers substrate for polycyclic aromatic hydrocarbons. this paper proves that mil-101/au composite sers substrate has important research significance and application value in the fields of food safety, environmental monitoring, etc. conflict of interest the authors declare that they have no conflict of interest. acknowledgements youth project of national natural science foundation of china (51701186); supported by the key r & d program of shanxi province (201603d421030). references 1. wong cl, dinish us, schmidt mc, et al. non-labeling multiplex surface enhanced raman scattering (sers) detection of volatile organic compounds (vocs). analytica chimica acta 2014; 844: 54–60. 2. indrasekara asds, meyers s, shubeita s, et al. gold nanostar substrates for sers-based chemical sensing in the femtomolar regime. nanoscale 2014; 6(15): 8891–8899. 3. wang 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for high-performance plasmonic sers detection. chemical engineering journal 2019; 371: 26–33. 19. hu y, liao j, wang d, et al. fabrication of gold nanoparticle-embedded metal-organic framework for highly sensitive surface-enhanced raman scattering detection. analytical chemistry 2014; 86(8): 3955–3963. 20. xuan t, gao y, cai y, et al. fabrication and characterization of the stable ag-au-metal-organic-frameworks: an application for sensitive detection of thiabendazole. sensors and actuators b: chemical 2019; 293: 289–295. 24 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1294 original research article template assisted nano-structured nickel for efficient methanol oxidation s mohanapriya*, v raj advance materials research lab, department of chemistry, periyar university, salem-636 011, india. e-mail: priyaechem@gmail.com abstract nanoporous nickel has been prepared by electrodeposition using non-ionic surfactant based liquid crystalline template under optimized processing conditions. physicochemical properties of nanoporous nickel are systematically characterized through xrd, sem and afm analyses. comparison of electrocatalytic activity of nanoporous nickel with smooth nickel was interrogated using cyclic voltammetry (cv), chronoamperometry (ca) and electrochemical impedance spectroscopy (eis) analyses. distinctly enhanced electrocatalytic activity with improved surface poisoning resistance related to nanoporous nickel electrode towards methanol oxidation stems from unique nanoporous morphology. this nanoporous morphology with high surface to volume ratio is highly beneficial to promote active catalytic centers to offer readily accessible pt catalytic sites for mor, through facilitating mass and electron transports. keywords: template deposition; electrocatalysis; methanol oxidation; direct methanol fuel cell article info received: 20 may 2021 accepted: 11 july 2021 available online: 18 july 2021 copyright copyright © 2021 s mohanapriya, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction owing to the simplified system design, high energy density, and ease of transportation of fuel, direct methanol fuel cells (dmfcs) are currently at the forefront as renewable energy sources which involve electrochemical energy conversion and hence suitable for automotive as well as portable power applications[1–4]. till now, platinum (pt) and its alloys represent the most extensively used dmfc electrocatalysts on account of their superior catalytic activity and stability towards oxidation of methanol at the anode side[5–7]. but the catalytic activity of the pt surface could easily be deteriorated by the adsorption of co generated during methanol oxidation reaction (mor). promoting the effect of ni over pt catalytic activity both in acidic and alkaline mediums is well established in the literature[8–10]. earlier studies established the role of nickel in assisting the dissociative adsorption of water molecules to produce-oh ads species, which facilitates the oxidation of co adsorbed on pt surface, thereby favors regeneration of pt catalytic centers. many electrodes involving nickel as a component in their manufacture can be used as catalysts in fuel cells. it is commonly used as an electrocatalyst for both anodic and cathodic reactions in organic synthesis and water electrolysis[15–18]. a very important appl icat ion of nickel as a catalyst is the 25 oxidation of alcohol. several studies on the electro-oxidation of alcohol on nickel have been reported. alkaline direct methanol fuel cells are now receiving considerable attention because they allow the use of anion exchange membranes that reduce methanol cross-over—a serious problem with cation exchange membrane used in acidic methanol fuels[8]. another reason for using an alkaline medium is because the kinetics for both methanol oxidation and oxygen reduction reactions is found to be more facile in an alkaline medium than in an acidic one[9–12]. in recent years, researchers focus on finding cheaper alternative electrocatalysts and improving the overall cell performance. non-noble transition metal electrocatalysts such as copper[13–16], nickel[17–24], which oxidize methanol and other alcohols, offer good alternative electrocatalysts. the activity of nickelbased electrocatalysts depends on the method of preparation of these electrodes. rahim et al.[24] showed that only nickel dispersed in graphite is catalytically active for methanol oxidation while massive nickel is not. in addition, this nickel electrocatalyst loses its performance due to the possible loss of nickel oxide activity after continuous circulation[24]. this is believed to be due to the increased thickness of nio(oh), which acts as a barrier inhibiting the charge transfer process for methanol oxidation. alternative approaches to prepare nickel electrocatalysts that can minimize the buildup of such a barrier layer would be of great interest in the development of non-noble metal electrodes for methanol oxidation. the purpose of the present work is to establish the electro-catalytic oxidation of methanol on nanoporous nickel in a solution of 1.0 m naoh. surfactant mesophases come under the category of soft template systems and electrodeposition through them is a very useful and versatile method for the synthesis of nanostructured materials. in addition, lyotropic liquid crystalline phases possess a longranged spatially periodic architecture with lattice parameters in the range of a few nanometers. this makes them ideal candidate systems for the synthesis of nanomaterials. in this study, we report a simple electrochemical method of preparing a high surface area for nanoporous nickel deposit, using a new hexagonal liquid crystalline phase as a template. this room-temperature deposited nickel has been characterized by electrochemical techniques such as cyclic voltammetry (cv) and electrochemical impedance spectroscopy. besides, scanning electron microscopy (sem), atomic force microscopy (afm), and x-ray diffraction (xrd) are also used for surface characterization. the catalytic efficiency of synthesized nanoporous nickel is evaluated by methanol oxidation using the techniques such as cv, impedance, etc. and morphology and composition of nanoporous nickel cloud easily be tuned through controlling parameters involved in electrodeposition. 2. materials and methods 2.1 chemicals triton x-100 (spectrochem), polyacrylic acid (paa) (aldrich), sodium hydroxide pellets (emerck), ni(ii) chloride (emerck), nickel sulphamate (grauer and wheel), boric acid (sarabhai chemicals) were used in this study. all chemical reagents used were analar (ar) grade. millipore water having a resistivity of 18 m cm was used in all the experiments. 2.2 preparation and characterization of hexagonal liquid crystalline phase the hexagonal liquid crystalline phase was prepared from a ternary mixture of triton x-100, paa, and water. we have carried out our studies at two different weight compositions viz., triton x-100 + water (42/58 vol%). the mixture was stirred in a magnetic stirrer at a temperature of 33–35 ℃ for 1 h and cool down to room temperature. when viewed under a polarized light microscope, the mixture shows the characteristic birefringence of a hexagonal liquid crystalline phase-stable up to 29 ℃. all the electrodeposition using this phase as a template has been done at the room temperature of 25 ℃. 2.3 nickel electroplating through hexagonal liquid crystalline the electrodeposition of nanoporous nickel was performed in a standard three-electrode glass cell using al as a working electrode, a saturated calomel 26 electrode (sce), and pt foil served as a reference and counter electrodes respective. nanoporous nickel synthesizes through electrodeposition at a constant of –1 v for a different periods. for electrodeposition, we have prepared the aqueous phase of the above described hexagonal liquid crystalline system from the standard nickel sulfamate bath[21] of the composition: 300 g/l nickel sulfamate, 6 g/l nickel chloride, and 30 g/l boric acids. 3. results and discussion 3.1 micro-structural analyses interesting electrocatalytic properties is exhibited by mesoporous nickel owing to their high surface area, unique morphology and high conductivity. schematics of synthesis of steps involved in the process of preparation of nanoporous nickel is illustrated in figure 1. triton x 100 forms micelles aggregated in the aqueous phase. nickel ions encapsulated in the micelles of triton x100 undergoes electrochemical reduction in such way that meso domains are created over the surface. textural properties of nickel deposit are modified due to entrapment of nickel ions inside the micelles. figure 1. preparation of the nanoporous nickel. (a) pictorial representation of nickel bath with and without surfactant; (b) schematic representation for preparation of nanoporous nickel. nanoporous nickel was characterized by x-ray powder diffraction (xrd). xrd pattern of nickel deposited electrodes reveals the characteristic peaks expected for nickel with face-centered cubic (fcc) structure in addition to the reflections observed for bare al electrode. nanoporous nickel deposited show the peaks at 44.3° and 51.8° corresponding to (111) and (200) planes respectively and are indicated by the asterisk mark in the figure. the ratio of intensities of (111) and (200) planes associated with these nickel electrodes with and without surfactant suggests that there is a preferential growth and orientation of nickel film along (200) direction in the case of surfactant electro deposition. it can be noticed from the figure that the xrd pattern of nickel deposited electrodes reveals the characteristic peaks expected for nickel with a face-centered cubic structure. figure 2. sem images of (a) nanoporous nickel and (b) smooth nickel. 27 sem pictures of nickel deposited on with and without the addition of triton-x 100 are shown in figure 2. the morphology of an individual deposit depends upon the electrolyte used for deposition. these images display the distinguishable structural features indicating the homogeneous growth of nickel deposits. compared with nickel electrode produced without template, nickel deposited by template shows higher uniform growth. the particles are same-sized spheres with smooth surfaces, the surface area can be related to the average equivalent particle size by d = 6000/(ρ.s) (in nm), where d is the average diameter of spherical particle in manometer; ρ is the theoretical density of nickel (g/cm3 ) and s represents the measured surface area of the powder in m2/g. the size of the particles is in the range of 5–10 μm. compared to the both images, nanoporous nickel surface morphologies present higher roughness. afm studies also validate the above observation as presented by figure 3. afm studies are used to demonstrate the difference in topography of nanoporous nickel and smooth nickel. difference in the surface topographies related to nanoporous nickel and smooth nickel are evaluated through afm analysis. nanoporous structure helps to improve electronic conductivity which is highly advantageous for efficient electrocatalysis. the modulations in the height profile indicate that synthesized nanoporous nickel is associated with high degree of roughness. surface modulations on the nanoporous nickel drastically increase the roughness factor associated with it, however nickel deposited using electrolyte bath without addition of surfactant exhibits two times lower roughness. figure 3. afm images of smooth nickel and nanoporous nickel. it is because that this unique porous structure electrocatalytic activity of nanoporous nickel is higher. distinct porous structure of nanoporous deposits substantially increases the surface area. sem and xrd studies are in good agreement with afm results. 3.2 electrochemical studies the electrochemical activity of mesoporous nickel electrode was studied by cyclic voltammetry, amperometry and electrochemical impedance techniques. the cyclic voltammograms (cv) of nickel deposited with and without the addition of triton-x100 were recorded in alkaline medium. the cv measurements were conducted in 0.1 m naoh at scanning rate of 100 mv/s. the applied potential was limited between 1 and –1 v. when discussing the electrochemical behavior of nickel, it is convenient to consider the three oxide phases formed when a positive potential is applied to the metallic nickel electrode. a cyclic voltammetry (cv) profile of nickel in aqueous alkaline solution reveals features corresponding to the formation of three oxide species as the potential increased from –1 to 1 v vs hydrogen evolution reaction. the an28 odic peak corresponding to the formation of the first surface oxide, α-ni(oh)2, is present in the v range of –1 to 1 v. if the cv scan is reversed at a potential lower than 0.50 v, the full reduction of α-ni(oh)2 to metallic nickel will occur, giving rise to a cathodic peak in the cv profile at –1 ≤ e ≤ 1 v. when the potential is brought to values lower than 0 v, appreciable current density as a result of the hydrogen evolution reaction (her) is observed along with the formation of h2 (gas) bubbles at the electrode. the her overlaps in potential with the reduction of α ni(oh)2. if the forward cv scan continues to have potentials higher than 0.50 v, the αni(oh)2 already present on the electrode converts to β-ni(oh)2, and an additional β-ni(oh)2 is formed. this species forms in the e region between 0.50 v and 1.30 v, which is known as the passive potential region for a nickel. of these two ni(oh)2 structures, the β phase is more stable. the formation of this phase is irreversible, meaning that β-ni(oh)2 cannot be removed from the surface of the electrode by simply reversing the potential and reducing the oxide electrochemically. once formed, β-ni(oh)2 can be removed through chemical etching, mechanical polishing, and thermal reduction in a hydrogen environment. the αand β-ni(oh)2 species have different crystallographic structures; the α phase incorporates either water or alkali cations from the electrolyte and has a lattice constant that is larger than that of β-ni(oh)2. the final oxidation species to be formed is niooh. at e > 1.30 v, the β-ni(oh)2 species is oxidized reversibly to β-niooh, which has a similar crystallographic structure and lattice constant. if an increasing positive potential is continuously applied, a γ-niooh phase is formed. this species adopts a crystallographic structure similar to that of α-ni(oh)2 and can be electrochemically reduced back to β-ni(oh)2. from figure 4a, it is evident that nanoporous nickel deposits present a higher current density compared to smooth nickel prepared without the addition of surfactant. it reports that periodic nanoporous structures with a high surface area can have charge storage capacity by one order over that of the bulk materials. increased electrochemical surface area of nanoporous deposits are due to the presence of triton-x100 molecules during a deposition process. these surfactant molecules act as a template during deposition, create mesopores in the nickel surface, and favor the formation of highly active nanoporous nickel deposits. owing to the larger surface area, electrochemically active surface area is also higher for the nanoporous nickel deposits. higher roughness associated with mesopores nickel is due to the larger number of electrolytes accessing channels formed over nanoporous nickel due to more availability of electrolyte access-electrochemical surface area. in other words, through the nanoporous deposits, electrolytes could easily reach the nickel surface compared to smooth nickel. the electrocatalytic response of prepared nickel deposits is evaluated through the addition of 1 m methanol. cv curves of nickel deposits before and after the addition of 1 m methanol in 0.1 m aqueous figure 4. cyclic voltammetric curves of different nickel materials scanned from –1 to 1v at a rate of 50 mv/s in 0.1 m naoh. (a) nanoporous nickel and smooth nickel; (b) smooth nickel with and without 1m methanol, and (c) nanoporous nickel with and without 1 m methanol. 29 naoh solution are given in figure 4b and figure 4c correspondingly. since niooh was constantly being reduced back to ni(oh)2, once methanol oxidation started, some anodic current could always be attributed to the continuous re-oxidation of ni(oh)2 back to niooh. furthermore, during the cathodic scans, lingering methanol oxidation caused some portion of the electrode surface to be prematurely reduced to the ni(ii) oxidation state before the ni(iii)/ni(ii) reduction occurred, thus decreasing the amount of niooh on the surface and the magnitude of the corresponding peak. by comparing the electrocatalytic response of methanol on nanoporous nickel and smooth nickel, it is clear that the anodic peak current associated with methanol electro-oxidation is higher for nanoporous nickel. an increase in the anodic peak current on the addition of 1 m methanol is 0.0012 and 0.0002 ma/cm2 for nanoporous nickel and smooth nickel respectively. the improved current response demonstrates the significance of nanoporous structure. the onset of methanol oxidation occurs at about 500 mv at the nanoporous nickel electrode whereas methanol oxidation begins from 550 mv with a smooth nickel electrode. a lower onset potential associated with nanoporous nickel evidences higher electrocatalytic activity for mor. the superior catalytic activity of nanoporous nickel may stem from unique porous morphology associated with higher esca. it is evident that the peak potential at which methanol oxidation occurs on nanoporous nickel is 0.75 v, but 0.85 v for a smooth nickel. as well known, the forward current peak (if) is attributed to the oxidation of methanol molecule and the backward current peak (ib) to the oxidation of adsorbed intermediates such as co, chxoh (0 < x < 2), chxo, hcooand so on. hence, the number of oxidizable intermediates adsorbed over the catalytic surface could be predicted by the relative magnitude of backward peak. (if)/(ib) ratio is a measure of the efficiency of a catalyst to tolerate the poisoning of the surface due to adsorption of incompletely oxidized intermediates. (if)/(ib) value for nanoporous nickel and smooth nickel is 1.3 and 1.17 respectively, which are higher than that of pure pt as reported earlier. a higher (if)/(ib) value indicates that most of the intermediate carbonaceous species were oxidized to carbon dioxide in the forward scan on the nanoporous nickel electrode. increased co tolerance of nanoporous nickel electrode may be attributed due to the basic difference in methanol oxidation between nanoporous and nonporous structure, which could be explained on the basis of morphology-dependent co tolerance as demonstrated earlier. based on the results, it could be inferred that nanoporous architecture increases poisoning tolerance of the catalyst through influencing the availability of continuous binding sites for c-h bond cleavage and enhances a greater number of readily accessible active catalytic sites for methanol oxidation reaction (mor). the schematic illustration of the mechanism of co removal over nanoporous nickel is depicted in figure 5. various concentrations of methanol 2 m, 3 m, 4 m, and 5 m were added to smooth nickel and nanoporous nickel. smooth nickel has good electrocatalytic activity, but surfactant tritonx-100 nickel has high electrocatalytic activity shown in figures figure 5. mechanism of electro-oxidation of methanol on nanoporous nickel catalyst. 30 6a and 6b respectively. cv curves were used to examine the electrochemical properties of nanoporous nickel in an aqueous alkaline electrolyte and to relate such acquired insight to their chemical composition and surface characteristics. typical cv curves for bulk nickel in aqueous naoh solution in the –1 to +1 v potential (e) range show the following anodic features: i. oxidation of metallic nickel to α-ni(oh)2 at 0.20 < e < 0.40 v; ii. concurrent conversion of αto β-ni(oh)2 and oxidation of metallic nickel to β-ni(oh)2 at 0.50 < e < 1.30 v; iii. the oxidation state of ni increases from +2 to +3 through the oxidation of β-ni(oh)2 to β-niooh at 1.30 < e < 1.55 v; iv. oxygen evolution reaction (oer) at e ≥ 1.55 v. the β phase of ni(oh)2 is the most stable and thermodynamically favored oxide of nickel; it is the passive layer that develops on the surface of metallic nickel upon contact with the ambient environment. the conversion of αto β-ni(oh)2 is irreversible, and once it takes place, the cathodic peak corresponding to the reduction of α-ni(oh)2 is not observable anymore. the reduction of β-ni(oh)2 cannot be accomplished electrochemically and can be achieved at elevated temperatures in the presence of h2 (g). the anodic and cathodic peaks characteristic of α-ni(oh)2 formation and reduction are not observed because a layer of β-ni(oh)2 has developed as the result of several prior cv scans. the cv curves for nickel nanoporous display the same features as those observed for smooth nickel in alkaline media. the cv curves for nanoporous nickel reveal pronounced differences, especially in the anodic scan. compared to the mesoporous nickel, the peak is shifted towards higher potentials and overlaps the region of oer. the value of is for oer is greater than that of nickel nanoporous; the specific current for the cathodic feature is greater than that of nickel nanoporous, but the difference is small. nickel and nanoporous nickel have very different surface morphologies, and the rough, bubbly surface of nanoporous nickel gives rise to a larger surface area than a smooth nickel. the charges under the two cathodic peaks are similar, thus indicating that both samples have similar amounts of β-niooh on the surface. the difference in qs values for smooth nickel is less than 40%, and that nanoporous nickel has a significantly larger actual surface area, we conclude that β-niooh does not make up the entire surface of nanoporous nickel. 3.3 chronoamperometry to evaluate the long-term activity of the catalyst, the steady-state current responses of nanoporous nickel and smooth nickel were recorded (figure 7). figure 6. cyclic voltametric curves of (a) smooth nickel and (b) nanoporous nickel in various concentration of methanol scanned from –1 to 1v at a rate of 50 mv/s performed in 0.1 m naoh. 31 initial rapid current decay for both catalysts is due to double-layer capacitance. transient current due to methanol oxidation attains a steady state after 820 s and 1600 s with nanoporous nickel electrode and smooth nickel electrode respectively, indicating the better catalytic performance of the former. it could be noticed from chronoamperometric results that the addition of 1 m methanol shows an increased electrocatalytic response on nanoporous nickel surface but the increased current response is not very high with smooth nickel. as evident from the figures, the addition of 1 m methanol causes an increase in current 0.07 a/cm2 for nanoporous nickel and 0.0001 ma/cm2 for smooth nickel. methanol oxidation current tends to decrease due to the accumulation of adsorbed species on catalyst surfaces due to the decomposition of methanol molecules. by comparing the current responses, it is obvious that the nanoporous nickel electrode possesses enhanced catalytic durability. unique nanoporous structure comprising continuous meso channels is highly favorable to provide easy transport paths of electrons and reaction intermediates, therefore, enhances mor activity of nanoporous nickel electrode. 3.4 impedance studies to further extract information about the electro catalytic process, eis studies are performed. figures 8a and 8b represent nyquist plots recorded at 500 mv dc-offset potential in 0.1 m naoh with methanol for nanoporous nickel and smooth nickel electrodes respectively. figure 7. amperometric curves of nanoporous nickel with and without 1 m methanol. figure 8. impedance of (a) nanoporous nickel and (b) smooth nickel deposition, with or without 1 m methanol. general pattern of nyquist plot obtained with electrodes under study is unaltered on changing the concentration of methanol from 0.1 to 4 m, pointing that mechanism of methanol oxidation is not affected by methanol concentration. conversely, diameter of semicircle has been dramatically decreased on increasing the concentration of methanol, denoting that charge transfer resistance (rct) regularly drops. eis analysis was carried out by fitting the data with appropriate equivalent circuit as shown in table 1. equivalent circuit is composed of solution resistance (rs), double layer capacitance (cpe1) and charge transfer resistance (rct) associated with mor. porous nature of electrode is attributed by the presence of additional elements namely cpe2 and rf. the values for all the parameters rct, cpe1, cpe2, and their associated % error determined by the fitting of the experimental eis data are summarized in table 1. 32 the parallel combination of the charge-transfer resistance (rct) and cpe take into account for methanol adsorption and oxidation on porous thin film. from figure 8a, it can be seen that the rct values are found to decrease in the order 1 m methanol > without methanol. without methanol is low resistance compared to 1 m methanol. the diameter of the semicircle is proportional to the value of the impedance. the smaller the value of impedance, the better the conducting property of the coating will be. this can be further confirmed by its low resistance and high capacitance. likewise, the equivalent circuit shown figure 8b is a simplified electrochemical model, which has been used to fit the impedance data obtained for the composite coatings present on substrate. as can be seen from the equivalent circuit, rs refers to the resistance of the solution, cdl is the electric double layer capacitance and rct is the charge transfer resistance that represents the electrochemical activity of the electrode. based on equivalent circuit model proposed, these eis curves were best fitted. various concentration of methanol solution in tritonx-100 surfactant of the deposited nickel has low resistance and high capacitance. the parallel combination rct with cpe leads to a depressed semicircle in the corresponding nyquist impedance plot. it is noteworthy that rct is an order lower for nanoporous nickel than that of smooth nickel, which reflects the enhanced electrocatalytic activity of the former (figure 9). the electrochemical impedance spectroscopic (eis) is a power tool for studying the electrochemical behavior of electrode. table 1. numerical values of elements in the equivalent circuit fitted with nyquist plots of nanoporous and smooth nickel figure 9. impedance of (a) nanoporous and (b) smooth nickel deposition at 2, 3, 4 and 5 m methanol. 33 4. conclusions in a nutshell, a facile and simple approach to produce nanoporous nickel through electrode-position is by using surfactant triton-x100. the developed methods are scalable and reproducible triton-x100 template could be easily removed by washing the electrode with water. nanoporous nickel has been prepared by surfactant assistant assisted electrochemical deposition of nickel under optimized process conditions. surface characteristics of the nanoporous nickel and smooth nickel were systematically characterized through xrd, sem, and afm analyses. nanoporous morphology is highly beneficial to offer readily accessible catalytic sites for methanol oxidation reaction (mor), through facilitating mass and electron transport. the prepared nickel was used as electrocatalyst for dmfc. comparison of electrolytic activity of nanoporous nickel with smooth nickel was interrogated using cyclic voltammetry (cv), chronoamperometry (ca) and electrochemical impedance spectroscopy (eis) analyses. distinctly enhanced electrocatalytic activity with improved co tolerance associate with nanoporous nickel electrode towards methanol oxidation stems from readily accessible high surface area associated with nanoporous structured, which facilitate mass transport of both the reactants and products. conflict of interest no conflict of interest was reported by the authors. acknowledgements one of the authors s. mohanapriya is grateful to university grants commission (ugc), government of india, for providing fund under the scheme of “ugc-dr. d. s. kothari post-doctoral fellowship”. 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characterization and application of nanomaterials (2023) volume 6 issue 2 doi: 10.24294/can.v6i2.3606 1 original research article hydrothermal synthesis of valve metal ta-doped titanate nanofibers for potentially engineering bone tissue parker cole1,2,†, yang tian2,3,†, savannah thornburgh4, mary malloy4, lauren roeder4, lu zhang5, mansi patel6, yiting xiao7, yan huang8, z. ryan tian2,3,5,6,* 1 biomedical engineering, university of arkansas, fayetteville, ar 72701, usa 2 institute for nanoscience/engineering, university of arkansas, fayetteville, ar 72701, usa 3 materials science/engineering, university of arkansas, fayetteville, ar 72701, usa 4 biological sciences, university of arkansas, fayetteville, ar 72701, usa 5 cell/molecular biology, university of arkansas, fayetteville, ar 72701, usa 6 chemistry/biochemistry, university of arkansas, fayetteville, ar 72701, usa 7 biological/agricultural engineering, university of arkansas, fayetteville, ar 72701, usa 8 animal science, university of arkansas, fayetteville, ar 72701, usa * corresponding author: z. ryan tian, rtian@uark.edu † these authors contributed equally to this work. abstract recent research efforts have increasingly concentrated on creating innovative biomaterials to improve bone tissue engineering techniques. among these, hybrid nanomaterials stand out as a promising category of biomaterials. in this study, we present a straightforward, cost-efficient, and optimized hydrothermal synthesis method to produce high-purity ta-doped potassium titanate nanofibers. morphological characterizations revealed that ta-doping maintained the native crystal structure of potassium titanate, highlighting its exciting potential in bone tissue engineering. keywords: nanosynthesis; titanate nanofiber; bone scaffold; tantalum dopant 1. introduction recently, nanomaterials have garnered significant attention for their applications in bone tissue engineering due to their unique physicochemical properties. implant materials can be enhanced by these artificially designed nanostructures to better mimic the native extracellular matrix, improve mechanical properties, support osteoconductive conditions, control drug delivery release, increase surface area and porosity, strengthen the cell-scaffold interaction, and even improve x-ray imaging quality[1–9]. since bone is a natural bio-nanocomposite, it has been our goal to develop functional nanoscale bone tissue substitutes that can be used to repair, replace, or regenerate damaged or diseased bone. regarding recent studies on the impact of nanotechnology on orthopedic applications, the key factors at the nanoscale, including grain size, pore morphology, surface topography, surface area-to-volume ratio, surface wettability, and the corresponding energetics, have been identified as critical determinants for achieving superior performance[8]. to this end, there has been a prolific surge in the exploration, development, and article info received: 12 december 2023 accepted: 12 november 2023 available online: 17 january 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 implementation of diverse nanomaterials and associated nanocomposites within the field of bone tissue engineering[9,10]. titanium dioxide (tio2) has attracted significant attention in recent times, primarily due to the intersection of orthopedics and nanomaterial science. this surge in interest can be attributed to the wellestablished understanding that ti metal undergoes surface oxidation when exposed to atmospheric conditions, culminating in the formation of a robust native tio2 layer on the external face. techniques such as anodization further enhance this process, leading to the development of a passivated surface coating that is biologically compatible and osteogenic. advancements in nanomaterial chemistry have been pivotal in this domain, enabling the controlled assembly of tio2 structures, including nanofibers and nanotubes. furthermore, specific synthetic methods have been identified to produce titanate clusters that exhibit a layered structure, which is conducive to apatite formation—the inorganic composite of native bone tissue. it’s also worth noting that titanium dioxide has the ability to react and transform into titanate nanotubes or nanowires. this characteristic has proven beneficial as it has been demonstrated to facilitate ion-exchange interactions with body fluids, thereby supporting bone tissue growth. specifically, when titanate materials are placed in simulated body fluid, ionic exchange commences and encourages the generation of hydroxyapatite, a fundamental component of natural bone. nanomaterials chemistry has enriched this area of research, and many labs have investigated structurally controlling tio2 morphologies such as nanofibers and nanotubes[11,12]. advancements in synthetic approaches have been identified to produce titanate materials, which are distinguished by their clay-like lattice, composed of edge-sharing tio6 octahedra interspersed with cationic entities[13]. this stratified structure is particularly favorable for apatite formation in simulated body fluid (sbf). more specifically, the hydrothermal reaction involving powdery tio2 minerals, such as rutile and anatase, with aqueous sodium or potassium hydroxide solutions yields naor k-titanate nanotubes or nanowires, depending on reaction conditions. this resulting ionic-layered structure serves a crucial role as a cationic reservoir. it aids in ion-exchange with cations found in body fluids, thus autonomously maintaining cation equilibrium in situ, a process vital for bone tissue growth. in an sbf environment, the concentration gradient between na/k-titanate and calcium (ca2+) prompts the ion-exchange of monovalent na+ or k+ ions with ca2+. this sets the stage for a subsequent interaction: the coordination of phosphate anions {i.e., (po3)3−, (hpo3)2−, and (h2po3)−} from the body fluid with the titanatebound ca2+. the culmination of this interaction is the formation of hydrated calcium phosphate, or hydroxyapatite, an essential building block of natural bone[13]. tantalate-based nanomaterials have been demonstrated to be osteoconductive; however, their syntheses have not become commercially viable for large-scale production[14–16]. in one instance, tantalum-coated polylactic acid (pla) electrospun fibers were found to be more osteoconductive compared to bare pla[17]. cell attachment, cell proliferation and preosteoblast differentiation were all improved in vitro[17]. congruently, ta-pla led to expedited bone tissue formation and provided a conducive environment for osteocytes to thrive in a rabbit calvarial defect model. furthermore, an anodized layer of tantalum was added to a titanate nanotubecoated substrate and was shown to enhance the matrix mineralization rate by 30% compared to a control titanate-coated substrate[14]. the doped titanate has provided an alternative strategy to hybridize other osteogenic elements (such as other valve metals: zr, nb, or ta) into heterogenous nanostructures rather than try and develop difficult and/or costly approaches to obtain pure species such as tantalum oxide and tantalum pentoxide[11,17–21]. through this hydrothermal doping process, we strive to promote the integration of osteogenic elements without incurring risks associated with surface coating delamination (e.g., an inflammatory response to rogue metallic debris)[17]. to evaluate new ta-doped nanomaterials for bone tissue regeneration applications, we conducted a systematic nanosynthesis study to assess the feasibility of producing long and pristine nanofibers of ta-doped titanate. tantalum doping optimization was corroborated using 3 characterization data from scanning electronic microscopy with an energy-dispersive elemental analyzer (sem-edx) together with x-ray diffraction (xrd). 2. materials and methods 2.1. nanofiber synthesis the ta-doped potassium titanate nanofibers were prepared following a published protocol[15,16,21,22] with some modifications. briefly, in a teflon cup containing 50 ml water solution of 10 m koh, 500 mg of tio2 powder (aeroxide p25) was added to the teflon and stirred for about 5 min with a teflon-coated magnetic stirring bar on an electrical stirrer. thereafter, tantalum pentoxide powder (chemical grade, from johnson matthey) was mixed with the koh suspension for 24 h to form a mixture upon stirring. here, the molar ratio of ta-dopant to ti was widely varied from 1%–4%. next, the mixture containing teflon cup was sealed in an autoclave container, heated in an oven at 240 ℃ for 72 h and then allowed to cool to room temperature. the white powdery product was collected, waterwashed until ph = 7, and finally air-dried for characterization. to keep the nanofiber lattice intact, it is important to do the water-washing step carefully, as detailed separately below. 2.2. post synthesis washing the fibers were formed as a slurry from the high alkalinity environment in the autoclave treatment. to remove the residual koh, the white slurry went through a well-controlled neutralization process. the nanofiber slurry was first centrifuged for 5 min at 4000 rpm. the supernatant was decanted and then deionized water was mixed to form another slurry with a lower koh content, which was repeated until the supernatant’s ph = 7. 2.3. characterization the sem-edx analysis was carried out on the fei nova nanolab 200 to assess nanofiber morphology and chemical composition. typically, the fiber sample was placed on an aluminum holder to let the sample dry in air. once dried, the holder was placed in a plasma sputtering coater with an au target to coat the sample surface with au. the xrd was performed with the rigaku miniflex ii desktop x-ray diffractometer using monochromatized cu-kα (λ = 1.5406 å) at 30 kv and 15 ma, in the range of 2θ from 5° to 60° at a speed of 1°/min. to assess crystal structure. 3. results and discussion the ta-doped potassium titanate nanofibers underwent self-assembly, forming a bone-mimetic bioscaffold structure upon desiccation as illustrated in figure 1. these self-assembled nanowires created microsize porous structures, facilitating effective bone tissue adhesion to the bio-scaffold. moreover, the increased surface area provided by these structures enhances osteoblast cell adhesion. at higher magnification (figure 2(a)) under the sem, the well-crystallized long nanofibers in selfentangled sheets can be clearly seen, which is a characteristic of the successfully ta-doped potassium titanate nanofibers. the nanofibers length extends into the microns range whereas their width is typically under 50 nm. additionally, figure 2(a) shows the relatively smooth surface of the high length to width ratio (or aspect ratio) nanofibers, suggesting an optimal control over the nanowires’ nucleation and 1d-growth in nanoscale, which is crucial for the mo-dopant’s good distribution throughout the crystal lattice of all the nanowires from the “one-pot” nanosynthesis. in the energy-dispersive x-ray (edx) map, the ta dopants (figure 2(d)) and ti (figure 2(c)) are evenly distributed on the fibers. this uniformity in distribution suggests the dopant well-dispersed in the ta-doped 4 titanate nanowires, which indicates a quite precisely controlled nano-synthesis process. theoretically, the [tao6] octahedron in the nanowire lattice is larger than the [tio6] octahedra[23]. however, the [tao6] octahedra are well-dispersed allowing for the structural distortion of each [tao6] octahedron to not disrupt the lattice structural continuity as suggested by the edx mapping in figure 2. in other words, the high dispersion of ta dopant in the nanofiber structure suggests the optimal doping conditions that support figure 1. the nanofiber crystal structure can be characterized using the xrd patterns (figure 3). all the xrd peaks of (200), (110), (310), (312), (404), and (020) can be assigned to the layered k2ti6o13 titanate lattice (jcpds no. 40-0403). no residual impurity was detected, as evidenced by no extra peaks in the xrd pattern due to the xrd detection limit, which indicates that the larger [tao6] octahedron is well-doped in the titanate crystal structure to maintain the lattice integrity and nanofiber structure. comparing the xrd pattern with against those without the doping (figure 4(a)), the large ta-dopant increases the d-space between adjacent titanate sheets by shifting the xrd peak to d(200) = 8.1215 å (or a lower 2-theta angle at 2θ = 10.89°) at 4% ta-dopant. this is in contrast with the undoped nanofiber’s smaller d-space of d(200) = 7.7415 å at a higher 2-theta angle (2θ = 11.43°). this interlayer spacing expansion is indicative of ta substitutional doping within the titanate lattice. more specifically, the ionic radius of ta5+ (73 pm) is larger than that of ti4+ (53 pm) which leads to ta5+ species replacing ti4+ within the titanate lattice[23–25]. substitutional doping of larger ions within the native lattice increases lattice parameters and cell volume resulting in shifts to lower diffraction angles[16,24]. moreover, the doped samples’ xrd patterns show no structural impurity. this is because all the xrd peaks are in the same width and can be indexed to that of potassium titanate, matching what our lab reported in the literature before[15,16]. figure 1. sem micrographs of ta-doped potassium titanate. figure 2. the edx mapping of the ta-doped potassium titanate nanofibers. (a) the high-resolution sem of ta-doped potassium with the yellow box for mapping. the edx mapping showed that (b) k, (c) ti, and (d) ta are evenly distributed on the titanate nanofibers. 5 figure 3. x-ray diffraction of nb-doped potassium titanate nanofibers with different doping percentages. figure 4. (a) xrd analysis of ta-doped potassium titanate nanofibers with (b) d-space value. (c) and (d) schematics of ta-dopant impact on the titanate crystal structure. within the clay-like layered crystal structure of k-titanate nanofibers, the ti4+-based [tio6] octahedra were partially substituted with the ta5+-based [tao6] octahedra by the deliberate doping of ta. sterically, the volumetrically larger [tao6] octahedra, in comparison to [tio6], would preferentially orient themselves on the nanofiber surface to minimize disruptions within the predominantly [tio6] crystal lattice. such surfacelocalized [tao6] entities have been identified as promoters of bone-tissue adhesion, as supported by prior literature[26,27]. moreover, the adjacent interlayer k+ cations in proximity to the [tao6] within the k-titanate nanofiber are inclined to undergo rapid substitution by ca2+ cations present in body fluids. this promotes the rapid nucleation of hydrated calcium phosphates, notably hydroxyapatite, on the nanofiber surface, aligning with observations made by other researchers in simulated body fluid (sbf) experiments[13,28]. the strong affinity between the hydroxyapatite layer and the foundational titanate nanofiber ensures persistent bone tissue adhesion on the hydroxyapatite-coated nanofiber, establishing an ideal osteogenic and osteoconductive environment[13]. as such, the enhanced surface properties of titanate nanofibers offer a synergistic strategy to current practices, augmenting the osteoconductivity of bone scaffolds[26,29]. at its core, this study presents an 6 innovative and cost-effective method for integrating ta (v) into the titanate nanofiber matrix, representing a notable advancement in orthopedic nanomedicine. 4. conclusions tantalum-doped potassium titanate nanofibers have been satisfactorily synthesized through a straightforward hydrothermal method. to the best of our knowledge, this approach represents a novel contribution, particularly within the domain of orthopedic nanomedicine. the nanofibers retained their morphological, compositional, and crystalline attributes after doping, demonstrating the efficacy of the hydrothermal method in facilitating crystal framework doping. furthermore, the dopant concentrations were carefully modulated to ensure no deleterious effects on the nanofiber’s lattice structure, a pivotal consideration for preserving the nanofibers’ intrinsic properties for their intended applications. to evaluate the impact of this material on bone tissue engineering, nanofibers with diverse ta-dopant concentrations will be subjected to in vitro and in vivo protocols, aiming to gauge their biocompatibility and osteogenic capacity. ultimately, the goal of this research is to identify the most effective ta-doped titanate nanofiber composition to be used in biomaterial matrices to improve the osteogenic properties of bone cement. understanding the impact of biocompatible transition metal doping on the physicochemical properties of nanofiber-based bone implants is imperative for the design of biomaterials tailored to each distinct application. the interactions between these doped nanofibers and bone cells will garner critical insights into their prospective utility as candidates for bone tissue composites—a standard criterion in determining the appropriateness of materials for clinical applications. a progressive strategy stemming from this research is the doping of titanate nanofibers with dual oxide dopants, potentially facilitating the investigation of a broadening spectrum of bone tissue composites characterized by diverse physiological adaptability. this approach empowers researchers to systematically investigate the effects of doping variations on the material’s properties and efficacy. the insights derived from such studies are crucial for the fine-tuning of these materials, optimizing them for targeted applications within bone tissue engineering and beyond. data availability statement applicable for reasonable request. author contributions investigation, pc, yt, st, mm, lr, mp and yx; writing—original draft preparation, pc, yt and zrt; writing—review and editing, pc, yt, yh, lz and zrt; funding acquisition, pc, st, mm, lr and zrt. all authors have read and agreed to the published version of the manuscript. funding this work was partially supported by the nsf (grant #2230853) and nist (grant #70nanb22h010) of the usa. acknowledgments the team would like to thank paula prescott and connie dixon for ordering lab supplies and managing financial reimbursement. the team also would like to thank kz shein, zay lynn, and david n. parette for their technical support. 7 conflict of interest the authors declare no conflict of interest. the funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. references 1. benedini l, laiuppa j, santillán g, et al. antibacterial alginate/nano-hydroxyapatite composites for bone tissue engineering: assessment of their bioactivity, biocompatibility, and antibacterial activity. materials science and engineering: c 2020; 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“dentistry and nanotechnology”; “dentistry and nanoparticles”; “dentistry and nanomedicine”; “dentistry and nanorobots”. there were found 530 papers in total. some papers belonged to two and more categories. it is revealed that the number of papers versus year does not follow any specific pattern, but the cumulative amount of papers versus year is fitted with the exponential regression. there were also selected papers using certain inclusion/exclusion criteria. only the selected papers were analyzed. nanomedicine is subjected to intensive studies nowadays. there are some promising results that will likely be implemented into praxis soon in the fields of medical diagnostics and clinical therapeutics. the appearance of nanotechnology can have a considerable impact on the treatment of periodontal diseases. keywords: nano dentistry; nanoparticle; nanotechnology; periodontal tissue; periodontal disease; treatment options 1. introduction modern materials science is developing at a very fast pace. this development is felt in almost all areas of science and technology. new materials for sensors [1,2] and medical applications [3,4] evolve. novel materials create excellent opportunities for researchers and engineers to solve long lasting problems. on the other hand, the conservative fields suffer from stagnation for many decades because the existing materials are prone to degradation [5], while new materials have not achieved the required level of performance yet. so to solve the problem of materials, a quite complex design of sensors and measurement systems is required [6,7]. another topical direction of studies is the internet of things [8,9], which also has medical applications [9]. in this paper, we focus our attention only on nanomaterials for dentistry. the field of dentistry is closely connected to materials and often requires the development of new therapeutic materials, along with the necessary equipment, instruments, and treatment techniques. developing new materials and technologies can solve issues in traditional dental care [10]. conventional dental treatment can often citation boitsaniuk s, levkiv m, kochan o. application of nanotechnology in periodontal therapy: narrative review. characterization and application of nanomaterials. 2024; 7(1): 4306. https://doi.org/10.24294/can.v7i1.4306 article info received: 19 january 2024 accepted: 20 february 2024 available online: 11 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 4306. 2 be uncomfortable, painful, and anxiety-inducing for patients due to invasive procedures such as carious cavity preparation, filling, and tooth extraction. nano dentistry presents a promising alternative to these procedures by utilizing nanosized materials, tissue engineering, and dental nanorobots to diagnose, treat, and prevent oral and dental diseases. patients may experience discomfort and hypersensitivity to dentine during recovery from procedures like root scaling, planning, and curettage of periodontal pockets. however, nanorobotics aims to overcome the drawbacks of conventional medical techniques. for instance, inserting medicaments into periodontal pockets and then protecting them with periodontal dressing may cause discomfort for a patient during eating or communicating, and it can also disrupt the mouth’s esthetic appearance. additionally, medicaments may seep out of the pocket. to combat these issues, nanoparticles can be carriers for targeted drug delivery. nanotechnology is the field of science and technology that involves manipulating materials at the scale of nanometers. the term ‘nano’ comes from the greek ‘nanos,’ which means ‘dwarf’. nobel prize-winning physicist richard feynman introduced the concept of nanotechnology in a 1959 lecture titled “there is a plenty of room at the bottom.” he ended the lecture by concluding, “this is a development which i think cannot be avoided” [11–13]. in 1974, norio taniguchi coined the term ‘nanotechnology’ to refer to the ability to precisely engineer materials with the dimension of nanometers. dogra et al. [14] and hamissi et al. [15] first introduced the field of «nanomedicine». at the molecular level, nanostructures and nanodevices are used to observe, control, and treat biological systems within the human body [16,17]. it improved materials’ mechanical and physical properties and introduced new diagnostic modalities and nanodelivery systems, revolutionizing the medical and dental fields [18]. the increasing interest in using nanotechnology in dentistry has led to the emergence of a new field called ‘nano dentistry’ [19,20]. nano dentistry can be approached from two different perspectives. one is called the “bottom-up approach,” where atomic elements are combined to build particles. the other approach is the “top-down approach,” which involves using equipment to create a mechanical nanoscale [21–23]. nanotechnology has a wide range of applications for preventing, diagnosing, and treating oral diseases. periodontitis and gingivitis are prevalent periodontal diseases affecting millions of people worldwide [24]. conventional treatment methods for these diseases involve mechanical debridement, antimicrobial agents, and surgery. however, the emergence of nanotechnology has opened up new possibilities in treating periodontal diseases. periodontics has been used to develop novel drug delivery systems, such as nanofibers and nanoparticles, which can penetrate deep into the periodontal tissues and release drugs over an extended period. moreover, nanotechnology has also been utilized to develop antimicrobial agents, which can effectively eliminate periodontal pathogens while minimizing toxicity and side effects. for example, silver nanoparticles have shown promising results in inhibiting the growth of periodontal pathogens, such as porphyromonas gingivalis and aggregatibacter actinomycetemcomitans. in addition, nanotechnology has been applied in developing tissue engineering and regenerative medicine techniques, which aim to restore damaged or lost periodontal tissues. nanofibrous scaffolds and nanoparticles have been used to promote cell adhesion, proliferation, and differentiation, forming new periodontal tissues. integrating characterization and application of nanomaterials 2024, 7(1), 4306. 3 nanotechnology in the treatment modalities for periodontal diseases represents a significant advancement of periodontics and has a wide range of use (figure 1). it offers new avenues for managing and preventing periodontal diseases, improving oral health outcomes that improve patients’ quality of life. figure 1. areas of applications of nanotechnology in periodontics. this review article aims to provide recent updates on nanotechnology-based approaches for periodontal disease therapy. additionally, the present review will help the reader understand nanoscience and its benefits and limitations by addressing its ethical, social, and health implications. 2. the technique of data preparation for this paper, we chose the form of narrative review [25]. for this narrative review, the search was performed within the scopus database to identify the number of papers found for the keywords and phrases such as “nanodentistry”; “dentistry and nanotechnology”; “dentistry and nanoparticles”; “dentistry and nanomedicine”; “dentistry and nanorobots”. the search considered works published in scopus till 5th of november 2023 (included). only relevant literature in english from the electronic search was selected for the present review. the nanoparticles had to be used in periodontics. the found papers were subjected to the inclusion and exclusion criteria. the inclusion criteria are as follows: i) use of nanoparticles in periodontics; ii) full text journal articles written in english; iii) books and book chapters written in english; iv) scientific works published in 2013 and later (older works are mentioned only in the introduction chapter). the exclusion criteria are as follows: i) case reports (clinical trials); ii) conference papers; iii) materials published earlier than 2013; iv) randomized controlled studies; v) editorials; vi) errata. the search was carried out in scopus, using the keywords and phrases “nanodentistry”, “dentistry and nanotechnology”, “dentistry and nanoparticles”, “dentistry and nanomedicine”, “dentistry and nanorobots”. in total, 530 records were found. 1) we excluded the types of papers that fit the exclusion criteria. 2) the first and second co-authors analyzed the remaining records for compliance with the inclusion and exclusion criteria. some points were clarified with additional hand searching, in particular the peculiarities of the use of triclosan, characterization and application of nanomaterials 2024, 7(1), 4306. 4 bone grafting, and data about periodontal disease. there were 27 additional records identified from the hand search. 3) all selected records were distributed among all authors for reading of the full text articles and preparation of the manuscript. the procedure is generalized in figure 2 in the prisma flowchart. figure 2. prisma (preferred reporting items for systematic reviews and metaanalyses) flow diagram of inclusion/exclusion criteria. 3. results the results of the search are summarized in table 1 and explained in details below this table. table 1. results of the search. nano-dentistry dentistry and nanotechnology dentistry and nanoparticles dentistry and nanomedicine dentistry and nanorobots total (along row) nanodentistry 53 18 8 18 2 99 dentistry and nanotechnology 18 148 19 15 0 200 dentistry and nanoparticles 8 19 169 4 0 200 dentistry and nanomedicine 18 15 4 75 0 112 dentistry and nanorobots 2 0 0 0 1 3 the first column contains key words as well as the first row. the numbers on intersections of rows and columns indicate the number of papers belonging to both key words. the intersection of the key word along the row and column indicates the number of papers that belong exclusively to this particular key word. the table is symmetric, i.e., the number of papers on the intersection of a certain row and a certain column is the same as the number of papers on the intersection of a certain column and row with the same key words. the column entitled “total (along row)” indicates the amount of papers that belong solely to a certain key word and in combination with characterization and application of nanomaterials 2024, 7(1), 4306. 5 other key words. since the table is symmetric, the total amount of papers in each column equals to that of each row. the last row, “total papers” indicates the total amount of papers. numerical analysis of publication in a certain field can be interesting and useful. it can reveal some patterns of development, ties to other fields, and trends of development [19,26]. the total list of unique papers contains 530 ones. this number can also be found when we add the numbers on intersections of a row and a column with the same key word, i.e., along the diagonal. these include 6 editorials, 7 conference papers, 103 book chapters, 222 journal articles, 187 reviews, and 5 other articles (errata, notes, etc.). the distribution of papers by year and cumulative amount of papers by year are given in table 2. table 2. the amount of paper year by year and cumulative amount of papers by year. year papers by year cumulative number of papers 2000 2 2 2006 1 3 2007 1 4 2009 2 6 2010 3 9 2011 14 23 2012 9 32 2013 8 40 2014 9 49 2015 14 63 2016 10 73 2017 9 82 2018 16 98 2019 17 115 2020 56 171 2021 76 247 2022 117 364 2023 166 530 the cumulative amount of papers by year can be expressed with the formula [27]. 𝑁(𝑋 ≤ 𝑥) = 𝑛(𝑥 ) ( ) (1) where 𝑁(𝑋 ≤ 𝑥) is the cumulative amount of papers for a certain year x; n(xi) is the amount of papers for i-th year. these data are also given in figure 3. the left-hand side y-axis is for the blue curve, which shows the amount of papers each year. the right-hand side y-axis is for characterization and application of nanomaterials 2024, 7(1), 4306. 6 the orange curve, which shows the cumulative distribution of papers, i.e., the sum of papers for this particular year and all years prior to this one. figure 3. the amount of paper versus year (left hand side axis y) and cumulative amount of papers (right hand side axis y). as can be seen from figure 2, the number of papers published within 2020–2023 has sharply increased. this rise agrees with the prediction made in the study by kochan [19]. however, it seems to us as a new trend, so it is impossible to fit any curve to describe the data and make any prediction for the field’s future development. we try to fit the curve to data. there are several tools, such as regression analysis [28] and neural networks [29,30] to solve such a task. however, according to spiegelhalter [31], it is preferable to use regressions in relatively simple tasks like this. we applied this approach in the study by kochan [19], and we will follow it in this paper too. we failed to fit the curve to the amount of paper versus year because there is no such a typical equation [28] to fit the amount of papers by year. however, we can fit the cumulative amount of papers. to do it, we need to preprocess the data. first of all, we eliminate the data prior to 2006 to avoid gaps in the independent variable (year). then, to simplify the coefficients, we subtract 2000 from each year (i.e., we use only two last digits to denote a year), and plug is in equation (2). from figure 3, we assume the data can be fitted with the model as follows: 𝐶𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑃𝑎𝑝𝑒𝑟𝑠 = 𝑎 ∙ 𝑎 (2) to estimate the unknown coefficients a0 and a1 we log both sides, so the linear model is as follows: 𝐿𝑜𝑔(𝐶𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑃𝑎𝑝𝑒𝑟𝑠) = 𝑙𝑜𝑔(𝑎 ) + 𝑦𝑒𝑎𝑟 ∙ 𝑙𝑜𝑔(𝑎 ) (3) equation (3) is the simple linear regression [27,28]. having applied the conventional procedure of the least squares we got coefficients of equation (3). the distribution of residuals is given in figure 4. characterization and application of nanomaterials 2024, 7(1), 4306. 7 figure 4. the distribution of residuals for linearized equation (3). we use the coefficients of the linearized model to compute the coefficients of equation (2) according to the procedure described in the study by mendenhall et al. [28]. we plug numerical values of coefficients in equation (2) to get the formula that can be used for calculating the cumulative amount of papers: 𝐶𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑃𝑎𝑝𝑒𝑟𝑠 = 0,649 ∙ 1,334 (4) the coefficient of determination is 0.97, which means the model explains the variation of 97% of the data. according to decoursey [27] and mendenhall et al. [28], in a fully valid linear model, residuals have to be distributed randomly. this was the case in the study by kochan et al. [19]. however, figure 4 shows some pattern in distribution, so the model can be used with some care; that is why we do not use it for forecasting, unlike kochan et al. [19], despite a very high value of the coefficient of determination. however, the forecast can be made according to the technique given in the study by hu et al. [9]. 4. discussion 4.1. properties of nanomaterials nanotechnology refers to the science and art of engineering materials on a scale of less than 100 nanometers [29–31]. the term “nanotechnology” was initially coined by norio taniguchi, a professor at tokyo science university, in 1974. according to scientific research, nanotechnology involves processing materials by manipulating them at the level of individual atoms or molecules [32]. materials with components measuring less than 100 nanometers in at least one dimension are called nanomaterials. this includes synthetic or natural materials such as clusters of atoms, grains less than 100 nanometers in size, fibers with a diameter of less than 100 nanometers, films less than 100 nanometers in thickness, nanoholes, and composites that are a combination of these [33,34]. unique physical and chemical properties are possessed by materials on the nanoscale, commonly referred to as nanomaterials. nanostructures, another name for nanomaterials, can be classified based on their dimension. zero-dimensional nanostructures are known as nanoparticles, while nanowires and nanorods are considered one-dimensional nanostructures. two-dimensional nanostructures are referred to as thin films. all of these structures meet the definition of a nanomaterial or nanostructure, being smaller than 100 nm in at least one dimension (figure 5) [35]. characterization and application of nanomaterials 2024, 7(1), 4306. 8 the characteristics of the material have been enhanced, resulting in improved toughness, stiffness, and transparency, as well as increased resistance to scratches, abrasions, solvents, and heat. furthermore, nanoparticles possess distinctive attributes that distinguish them from other particles, such as varied chemical, optical, magnetic, and electro-optical properties, which are not found in bulk species or individual molecules [35]. figure 5. representation of the structure of nanomaterials that are highly beneficial for medical purposes. reprinted from bonilla-represa et al. [35], 2020 by the authors. licensee mdpi, basel, switzerland. this article is an open access article distributed under the terms and conditions of the creative commons attribution (cc by) license (http://creativecommons.org/licenses/by/4.0/). the shape of nanoparticles and their size distribution vary depending on the method of synthesis used. both top-down and bottom-up approaches can be utilized in the creation of nanoparticles. the synthesis methods for nanoparticles depend on the material classification of the particle, such as metal, ceramic, or polymer. silver nanoparticles are commonly used in dental materials because of their ability to destroy microbes. metal complexes are typically reduced in dilute solutions under carefully controlled reduction reaction conditions to create metal colloidal dispersions containing metallic nanoparticles [36]. drug delivery often employs polymer nanoparticles, such as nanospheres and nanocapsules, which often contain active pharmaceutical ingredients within each particle or have macromolecular substances adsorbed on their surface. polymerization-based methods like emulsion polymerization, dispersion polymerization, interfacial complexation, and polymer participation methods such as single/double emulsion, solvent displacement, or salting out can be used to prepare polymer nanoparticles. drugs can be incorporated either during nanoparticle preparation or after [37]. typical polymers for polymer nanoparticles include chitosan, polyacrylamide, polyacrylate, and polyesters. biodegradable polymer nanoparticles are often employed to release drugs from nanoparticles into the human body. polymer nanoparticles can be used as a drug delivery mechanism, which offers many benefits over traditional drug applications. these benefits include the ability to target specific tissues and cells through ligand specificity, efficient absorption of polymer nanoparticles into cells, lower doses of drugs required for treatment, reduced toxic effects, sustained release of drugs at the target site, and improved therapeutic potential [38]. the fusion of nanotechnology in the treatment modalities for periodontal diseases can be considered one of the breakthroughs in periodontics. characterization and application of nanomaterials 2024, 7(1), 4306. 9 4.2. periodontal diseases periodontal disease, which is a major dental illness, affects millions of people across the globe. the disease is one of the significant public health problems in many countries [39,40], as it possesses the criteria such as being widespread and having severe consequences on individuals, communities, and health services in terms of social, psychological, and economic aspects [41,42]. inflammation and damage to the supportive tissues surrounding the teeth, including the periodontal ligament, alveolar bone, cementum, and gum, often occur due to the invasion of anaerobic gram-negative bacteria (figure 6). this condition is commonly known as periodontal disease [43]. the cause of periodontal disease is the imbalance between the colonization of bacterial pathogens and the host’s immune response toward infection [44,45]. figure 6. schematic representation of healthy periodontal tissues and generalized periodontitis. periodontal treatment aims to address infections and restore the function and structure of periodontal tissues, including cementum, periodontal ligament (pdl) fibres, and bone. however, it is still difficult to fully recover these three tissue types and re-establish the strong attachment of pdl fibres to the new cementum and alveolar bone [46,47]. recent developments in nano-materials and nano-technology have created promising possibilities for the efficient management of periodontitis. various newer techniques, such as the use of bio-adhesive polymers to achieve extended drug release, enhancing intrapocket drug penetration, improving mechanical features through chemical cross-linkers, and the potential of loading multiple drugs in a single delivery system, offer several significant advantages. these benefits pave the way for further research opportunities in advancing dental therapeutics through the development of drug delivery systems [48–51]. 4.3. applications of nanotechnology in periodontics antiseptic treatment of periodontal diseases involves using disinfectants, which can contain irritating compounds and cannot be applied to soft tissues like mucosa. an exciting alternative to these strong disinfectants is the development of ozone water. unlike other disinfectants, ozone water does not damage skin cells, and repeated use does not result in skin roughness or oral mucosa irritation. after use, ozone characterization and application of nanomaterials 2024, 7(1), 4306. 10 decomposes to oxygen and leaves no harmful residues. additionally, ozone nanobubble water, which has been stable for over six months in storage in an electrolyte solution, has been created [52]. nanotechnology in periodontics has touched every aspect of treatment modality, from non-surgical therapy to implant procedures, including regenerative procedures (table 3). table 3. overview of advancements in nanomaterial, and nanotechnology in periodontics. active ingredient/brand name properties and advantages reference/year ozone water ozone water is an exciting alternative to strong disinfectants (i.e. alcohol, povidone iodine) used in antiseptic treatment of periodontal diseases. it can be used on soft tissues like mucosa and does not contain irritating compounds. [52]/2017 year antimicrobial and antibiofilm activity of curcumin-silver nanoparticles curcumin-silver exhibited excellent antibacterial activity against both gram-positive and gram-negative bacteria and were less toxic to human keratinocytes. cur-agnps were effective in inhibiting biofilm formation and exhibited anti-inflammatory effects on human macrophages. [53]/2018 year triclosan it is a noncationic antimicrobial agent that has been proven efficacious against several plaque forming bacteria. [54]/2020 year [55]/2021 year tetracycline microspheres tetracycline microspheres(tm) were more effective in treating chronic periodontitis through clinical parameters and microbiological analysis. additionally, tm had a superior method of local drug in terms of usage and application. [56]/2017 year minocycline microspheres, arestin® the microspheres are combined with the person’s saliva as they are dispensed. this mixture transforms into a semi-solid gel that fills the small crevices of the gum pocket and tooth. the microsphere gel compound can move around the mouth after inoculation, better coating the infected area. the microspheres slowly dissolve over three weeks to a month, releasing minocycline. this allows the drug to target the biofilms around the area and directly attack these species. [57]/2023 year harungana madagascariensis (hypericaceae) h. madagascariensis, a plant found in tropical africa and madagascar, has medicinal properties that have been traditionally used to cure diseases. it has antibacterial potential against both sensitive and mdr bacteria. its anthranoids constituents show promise in developing herbal medicine and pharmaceuticals to combat bacterial drug resistance. [58]/2023 year tricalcium phosphate scaffolds for bone regeneration/vitosso (orthovita, inc., usa) ha+tricalcium phosphate biomaterials made of ceramics, such as cap, are excellent choices for restoring lost function and hard-tissue engineering. the minerals in them are comparable to those found in bones, and they have the ability to induce the growth and specialization of cells.additionally, their relatively low degradation rate can facilitate prolonged guided tissue remodeling and structural support. [59]/2017 year nano-hydroxyapatite for bone tissue engineering, nano crystalline particles of ha ostims commercially available in a syringe as a ready-to-use paste (heraeus kutzer, hanau, germany) hap can promote new bone ingrowth through osteoconduction mechanism without causing any local or systemic toxicity, inflammation or foreign body response. nanocrystaline hydroxyapatite (nha) is a drug delivery carrier that can be used instead of ha ceramics. the reason for this is that it has a reactive surface area that is quite high, nanoscale porosity, and it is capable of in vivo degradability [60]/2019 year chitosan nanohydrogel as a bone regenerative material it has the potential to act as a scaffold material that can enhance the differentiation of osteoprogenitor cells, chitosan hydrogel in combination with a bone graft showed superior bone regenerative potential and could prove to be an excellent candidate for bone regeneration. [61]/2021 year chitosan hydrogels for drug delivery the study tested a prototype toothpaste containing cacl2/chitosan microspheres for remineralization of human tooth enamels. the toothpaste was found to be effective in increasing calcium contents and ca/p weight ratios in treated enamels, resulting in larger remineralization bands compared to the negative control group. [62]/2018 year micro-nanorobots dental nanorobots can quickly relieve dentine hypersensitivity by closing specific dentinal tubes. dentifrobots can prevent cavities by targeting harmful bacteria and allowing good bacteria to thrive. utilizing micro/nanorobots, stem cells have been transported to a damaged area for the purpose of restoring tissue. these uses exemplify that micro/nanorobots could act as foundations for cell-based therapy and regenerative medicine. this has the potential to be particularly advantageous during the later phases of life, as organs and systems may begin to deteriorate. [63]/2023 year [64]/2018 year characterization and application of nanomaterials 2024, 7(1), 4306. 11 understanding their mechanism plays a pivotal role in more efficient usage of nanotechnology, better treatment procedures, and eventually better outcomes. effectively treating periodontal disease involves utilizing nps that can eradicate pathogenic bacteria, as bacterial colonization is among the initial stages that cause this condition. according to available reports, combining azithromycin and clarithromycin with silver nanoparticles (agnps) has been found to have a synergistic antimicrobial effect against microorganisms that cause periodontal disease [53, 65]. in another study, produced glutathione-capped bimetallic nps with great antibacterial potential against the anaerobic oral pathogen porphyromonas gingivalis was suggested [53]. curcuminsilver nanoparticles (cur-agnps) exhibited excellent antibacterial activity against both gram-positive and gram-negative bacteria and were less toxic to human keratinocytes [66]. moreover, cur-agnps exhibited anti-inflammatory effects on human macrophages by reducing the secretion of pro-inflammatory cytokines il-6 and tnf-α compared to chemically synthesized agnps. implants can be coated with titanium oxide nanotubes and infused with silver nanoparticles to help prevent infections and prolong the lifespan of the implants [67]. 4.4. dentinal hypersensitivity dentin hypersensitivity is an area where dental nanorobots may find their use. dentin hypersensitivity is a condition that occurs when changes in pressure are transmitted through the surface of the tooth, affecting the pulp [68]. the density of dentinal tubules on hypersensitive teeth is eight times higher than on non-sensitive teeth. additionally, the diameter of these tubules is twice as large. it is possible to use dental nanorobots to occlude these tubules within a few minutes. this procedure offers patients a fast and permanent solution to their hypersensitivity [69]. the dentinal tubules are reached by tiny nanorobots that move towards the pulp while being directed by chemical gradients and temperature changes, all controlled by a nanocomputer. these nanorobots can get the pulp within 100 s, providing quick relief from sensitivity [63,70]. 4.5. drug delivery in periodontal treatments, local drug delivery is necessary for reliable outcomes. drug delivery systems based on triclosan-incorporated nanoparticles have been developed. triclosan-loaded nanoparticles have been produced by emulsificationdiffusion to obtain a novel delivery system for the treatment of periodontal disease. in this research article [54], the authors investigated the properties of triclosan (tcs), a hydrophobic antibacterial agent with broad-spectrum activity. to improve its antimicrobial and bacteriostatic effects, a novel amphiphilic copolymer containing tertiary amine groups, called monomethyl ether poly (ethylene glycol)-b-poly{α-[4(diethylamino)methyl-1,2,3-triazol]-caprolactone-co-caprolactone} (mpeg-pdcl), was synthesized and designed. this copolymer was used to create micelles that served as carriers for tcs. micelles released the cargo faster in acidic environments and demonstrated excellent antimicrobial ability against s. aureus and e. coli. significant regeneration of the lost bone was revealed for the nanogels-treated group as per another study [55] based on morphometric findings. the developed nano-gel system, characterization and application of nanomaterials 2024, 7(1), 4306. 12 loaded with antimicrobial tcs and anti-inflammatory flb (flurbiprofen-loaded nanogels), showed a superior healing effect in treating periodontitis based on the overall results. the use of microspheres containing tetracycline is presently being evaluated for treating periodontal pockets. based on the study by kumar et al. [56], it was concluded with the help of clinical parameters and microbiological analysis that tetracycline microspheres (tm) were more efficient than commercially available tetracycline fibers (tf) (periodontal plus ab) in the treatment of chronic periodontitis. also, tm had a better mode of local drug delivery in comparison to tf for both dentists and patients in terms of usage and application. arestin is a famous brand of antibiotic minocycline that is claimed to aid in regaining at least 1 mm of gingival reattachment height. this treatment does not require bandages or stitches and is bio-adhesive and bioresorbable, which means that it will not leak or fall out and does not need to be removed by the dentist or hygienist in a follow-up visit. when combined with deep cleaning, using arestin to treat periodontal disease can help keep gum pockets below the threshold for surgical intervention. moreover, the application of arestin is comfortable and does not require anaesthesia. clinical trials have demonstrated that a single dose of microspheres introduced into an infected gum pocket can be released for over three weeks, compared to minocycline oral capsules, commonly prescribed for 15 days [57]. arestin® doses, which contain minocycline hydrochloride impregnated within a polymer, are delivered in 1 mg increments into the gum pocket, allowing the minocycline to be released slowly over three weeks to a month. although several chemical agents are available commercially, the search for alternatives persists, and traditional medicinal plants are considered a viable option, as they contain natural phytochemicals that could serve as substitutes. an african plant called harungana madagascariensis (hypericaceae) possesses antimicrobial properties and contains various antimicrobial components. the leaves were subjected to successive soxhlet solvent extractions to prepare an ethyl acetate extract, which was then tested against several oral pathogens. the extract killed all oral bacteria tested, including actinomyces, fusobacterium, lactobacillus, prevotella, propionibacterium, and streptococcus species. however, the activity of poly(d,llactide-co-glycolide) nanoparticles containing the extract was enhanced. the authors suggested that the polymer’s bioadhesive properties might have led to the extract being in contact with the bacteria for prolonged periods [58]. 4.6. bone regeneration bone loss is a significant hallmark of periodontitis. losing bone support causes tooth movement and dislocation, ultimately resulting in tooth loss [71]. biologic or synthetic biomaterial intended for human implantation to restore bone health, preserve bone structure, or fill bone loss is considered a bone substitute [72]. bone grafts can be conveniently divided into four groups:  the patient himself (autogenous grafts)—“gold standard” for bone replacement [73]; characterization and application of nanomaterials 2024, 7(1), 4306. 13  different donors from the same species (allogeneic grafts), including freeze-dried bone allografts and demineralized freeze-dried bone allografts [74];  donors from different species (xenogeneic grafts), for example, bio-oss [75];  synthetically created materials (alloplastics), for example, tricalcium phosphates [59], a calcium-layered polymer of polymethyl methacrylate and hydroxyethyl methacrylate [76], bioactive glass [77], and hydroxyapatite (ha) [78]. hydroxyapatite (hap) is the primary mineral constituent of vertebrate bones and teeth. hydroxyapatite (hap) powder has been used for biomedical applications such as bone implant substitutes, scaffolds for complex tissue engineering, or superficial coating of implants due to a great chemical similarity with biologically calcified tissues. synthetic hap has been of interest for decades due to its excellent biocompatibility, affinity to biopolymers, and high osteogenic potential. it has been well documented that hap can promote new bone in growth through osteoconduction without causing local or systemic toxicity, inflammation, or a foreign body response [79]. among the various hap structures, nanosized hap, also known as hap nanoparticles, with appropriate stoichiometry, morphology, and purity, have stimulated great interest in basic scientific research and various biomedical applications. nanosized hap, which has a grain size less than 100 nm in at least one direction, has high surface activity and an ultrafine structure, similar to the mineral found in hard tissues. in recent years, bioceramics and biocomposites based on nanosized hap have been the most promising materials for a variety of biomedical applications. nanocrystaline hydroxyapatite (nha) is a drug delivery carrier that can be used instead of ha ceramics. the reason for this is that it has a reactive surface area that is quite high, nanoscale porosity, and it is capable of in vivo degradability. numerous techniques have been created for linking nha with a broad range of antibiotics, especially tetracyclines, gentamicin, and vancomycin. the effectiveness of the delivery mechanism relies on the interplay of antibiotics with the surface of nha, the scaffold’s porosity, the capacity of antibiotic loading on the nha nanoparticles, and the gradual release of antibiotics in the defect [60]. apart from its therapeutic activity, nha also acts as a bioactive matrix for newly formed bone, which may be improved with metal (zn2+ and sr2+) and carbonate substitution (co3 2–) in the apatite structure. methods for the preparation of hap nanoparticles are given in figure 7 [80]. figure 7. methods for the preparation of hap nanoparticles. characterization and application of nanomaterials 2024, 7(1), 4306. 14 various techniques have been developed to enhance the osteogenesis process, including bone grafts [81], scaffolds [82], stem cells [83], and growth factors [84]. all of these techniques have significant clinical drawbacks. autologous grafts are limited in availability, growth factors are often unstable, and biomaterials have a high failure rate. consequently, there is a great need for treatments that are highly effective and efficient in order to pave the way for periodontal tissue renewal. designing scaffolds that imitate the intricate shape and organization of periodontal tissues is a significant challenge in regenerative periodontology. ceramics and polymers are the most commonly used materials for restoring and replacing lost oral tissues in periodontal regeneration. ceramic biomaterials, such as calcium phosphate (cap), calcium sulfate (cs), and bioactive glass (bg), are highly suitable for the construction of complex tissues. they can effectively restore lost function due to their similar composition to bone minerals, ability to stimulate cell proliferation and differentiation, and relatively low degradation rate. the latter is particularly beneficial for promoting long-term guided tissue remodelling and structural support. nevertheless, these materials’ brittleness and low ductility should be considered. polymers, such as polylactic acid (pla), polyglycolic acid (pga), the copolymer poly (lactic-co-glycolic acid), and pcl, are highly adjustable and can be mass-produced [59]. although many options are available, achieving complete regeneration is still challenging. therefore, there is a focus on utilizing natural materials to overcome the limitations of synthetic ones. chitosan is a naturally occurring biopolymer that is abundant [85]. it has the potential to act as a scaffold material that can enhance the differentiation of osteoprogenitor cells, which in turn promotes bone regeneration [86]. the study’s outcome showed that chitosan significantly improved clinical and radiological parameters [61]. when bone grafts were mixed with chitosan gel and used to treat defects, it substantially reduced probing depth, improved clinical attachment loss, and achieved significant defect resolution at six months [87]. 4.7. prevention delivery of nanorobotic dentifrice is possible through toothpaste or mouthwash, allowing it to patrol all surfaces above and below the gum line. it can metabolize trapped organic matter into harmless, odorless vapors while performing continuous calculus debridement [88]. mouthwash or toothpaste can release tiny robots called dentifrice nanorobots (or dentifrobots) onto the surfaces of teeth. these robots, which can be as small as 1–10 microns, move quickly (at a rate of 1–10 microns/second) and can clean up organic residues on both the supragingival and subgingival surfaces of teeth. by doing so, they can continuously prevent the buildup of calculus. dentifrobots are designed to be safe for humans; they are deactivated when swallowed. additionally, if they are correctly configured, dentifrobots can detect and eliminate harmful bacteria that may be present in dental plaque [64]. in scientific research [62], we tested a prototype toothpaste containing cacl2/chitosan microspheres for remineralization of human tooth enamels. the toothpaste was found to be effective in increasing calcium contents and ca/p weight characterization and application of nanomaterials 2024, 7(1), 4306. 15 ratios in treated enamels, resulting in larger remineralization bands compared to the negative control group. antimicrobial peptides can be immobilized on the surface of medical devices and instruments to provide them with antimicrobial properties [89]. 4.8. challenges faced by nano dentistry the healthcare industry is set to undergo a significant transformation through the utilization of nanotechnology, which provides new possibilities for disease diagnosis and prevention, drug delivery, and gene therapy. despite the groundbreaking methods and equipment introduced by nanotechnology in the dental field, certain apprehensions must be addressed (table 4). these include cost-effective mass production of nanorobots, ethical dilemmas and human safety, biocompatibility issues, and the necessity for precision positioning and technical expertise in nanotechnology [90–94]. table 4. problems and challenges of nanotechnology. area problems and challenges engineering feasibility of mass production technique assembly lines for mass production precise monitoring and control of production processes metrological service of measuring instruments biological development of biofriendly nanomaterial development of safe materials for human beings biocompatibility the human body social ethics public opinion and acceptance regulation and human safety affordability accessibility 5. conclusion the field of nanotechnology is relatively new and holds immense potential for advancements. there are numerous paths for its development and progress. it is a rapidly growing area with the potential to produce advanced clinical tools and devices for oral healthcare. the future of periodontics looks incomplete without incorporating nanotechnology in routine periodontal therapy, be it surgical or non-surgical; however, it will take extensive research to develop nanoscale biomaterials, which can be safely instilled in the human body. nanotechnology promises to play an essential role in minimizing patient discomfort and, at the same time, maximizing the effects of a particular periodontal therapy. numerous nanomedicine approaches are being pursued today, and their successful development will likely occur very soon. these approaches are already close enough to the realization that their subsequent incorporation into valuable medical diagnostics or clinical therapeutics is almost inevitable. the fusion of characterization and application of nanomaterials 2024, 7(1), 4306. 16 nanotechnology in the treatment modalities for periodontal diseases is one of the breakthroughs in periodontics. conflict of interest: the authors declare no conflict of interest. references 1. krolczyk g, legutko s, gajek m. predicting the surface roughness in the dry machining of duplex stainless steel (dss). 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distributed under the terms of the creative commons attribution-noncommercial 4.0 international license (http://creativecommons.org/licenses/by-nc/4.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. characterization and application of nanomaterials（2018） original research article solvent thermal method to control lead sulfi de nano/micron crystal and its ni/pbs composites yajia ding,bing bai,jianan peng key laboratory of nanometer materials, university of architecture and technology, fujian, china abstract lead sulfide (pbs) is an important iv-vi semiconductor material with narrow bandwidth and wide wave width, which attracts people's attention. nano-level pbs has many novel optoelectronic properties and has a wide range of applications in the fi eld of optoelectronics, such as infrared optoelectronic devices, photovoltaic devices, light-emitting devices and display devices. in this paper, pbs is produced by solvent thermal method by using lead acetate as lead source, sulfur power as sulfur source, ethylene glycol as solvent, and acetic acid to provide acidic environment. the reaction acidity, type of lead source, amount of sulfur source and other aspects will be explored. the products obtained under diff erent conditions were characterized by x-ray diff raction (xrd), optical microscopy and scanning electron microscopy (sem). the results showed that pbs produced at 140°c for 24 hours, using 14ml ethylene glycol and 1.2ml acetic acid has the best morphology. it has a non-planar six-arm symmetrical structure. finally, we prepare the lead sulfi de composite ni/pbs, and characterized it. keywords: pbs; solvent heat; nanomaterials; composites 1. introduction 1.1. nanomaterials 1.1.1 introduction to nanomaterials nano-materials[1], also known as ultra-fi ne particles, are composed of nanoparticles. nanoparticles, also known as ultrafi ne particles, generally refer to particles in the range of 1 to 100 nm which are in the transitional region between atomic cluster and the macroscopic object boundary. such a system is neither typical in the general point of view of microcosmic and macroscopic system. this system is a typical mesoscopic system with surface eff ect, small size eff ect and macroscopic quantum tunneling eff ect. when subdividing macroscopic objects into ultrafi ne particles (nanoscale), it will show many properties namely optical, thermal, electrical, magnetic, mechanical and chemical properties, and has signifi cant diff erences when compared to its large solid phases. nanoparticles are composed of a limited number of atoms or molecules, able to maintain the chemical properties of the original material and maintain in a metastable atomic group or molecular group. when the linearity of the material decreases, the relative proportion of the number of atoms on the surface increases, so that the surface energy of the single atom can increase rapidly. to the nano-scale, the changes in this form refl ect on the material structure and performance, and will show unique eff ects which can be divided into the following basic characteristics [3]. (1) small size eff ect [4, 5] when the volume of a substance is reduced to a size equal to or smaller than the size of the physical characteristic of light wavelength, deborah wavelength, coherence length or transmittance depth of superconductivity, the periodic boundary conditions of the crystal will be destroyed which lead to a great change in magnetism, internal pressure, light absorption, thermal resistance, chemical activity, catalytic activity, melting point, etc. when compared to ordinary crystal. this is the volume eff ect of nano-materials. when the crystal is in the nano-scale category, the average free path of free electrons in the metal will be reduced resulting in a decrease in conductivity which may cause the original material to convert from metal conductor to an insulator. the stress-strain of a material in nano-scale will change from hall-petch eff ect to anti-hall-petch eff ect. for example, under normal conditions the melting point of gold is 1337 k, yajia ding, et al 31 while the melting point of 2 nm gold particles is 600 k, and the melting point of nano silver can be reduced from 1173 k to 373 k. (2) surface eff ect the surface eff ect of nano-materials is the abrupt increase on ratio of the number of atoms on the surface of the nanoparticles to the total number of atoms with the change of the particle size, which leads to the change of the material properties. it is well known that the specific surface area of the material is inversely proportional to the size of the material. as the size of the material decreases, the number of atoms in the surface area and surface atoms will increase significantly. the increase in the number of atoms on the surface causes a lack of surface atomic coordination and high surface energy, these atoms combine easily with other atoms and stabilize, which has a high chemical activity. it can be widely used in catalysis, adsorption and other fi elds. the ratio of the number of surface atoms to the total number of nanoparticles increases sharply with the decrease of particle size. when the particle size is reduced to 1 nm, the proportion of the number of atoms on the surface has reached 99% and the atoms are almost all concentrated on the surface of the nanoparticles. the increase in the number of atoms on the surface causes a lack of surface atomic coordination and high surface energy, these atoms combine easily with other atoms and stabilize, which has a high chemical activity [6, 7]. this causes the change of surface electron spin conformation and electron spectrum, and the change of atomic transport and confi guration on the surface of nanoparticles. (3) quantum size eff ect when the particle size drops to a certain value, the electron energy level near the fermi level is reduced from quasicontinuous to discrete energy levels, conductive nano particles have discontinuous highest occupied molecular orbit and lowest unoccupied molecular orbit, band gap widening and other phenomena, are known as quantum size eff ect [8] . the band theory suggests that the electron level near the fermi level is generally continuous, which is only true at high temperature or macro size. for ultrafi ne particles with only a limited number of conductive electrons, in low temperature energy level is discrete; for macroscopic material which contains infi nite atoms, by the kubo formula: δ = (4/3) ef / n (1-1) it can be seen that the energy level spacing is δ → 0. which means that the spacing of large particles or macroscopic objects is almost zero; and for nanomaterials, the number of contained atoms is limited, n value is very small, and caused a certain value to δ. the separation of energy level causes the kubo eff ect. when the energy level is greater than the cohesive energy of thermal energy, magnetic energy, magnetostatic energy, electrostatic energy, photon energy, or superconductivity, quantum size eff ects must be taken into account. this can lead to significant difference between nanoparticle magnetism, light, sound, thermoelectric, superconductivity and macroscopic characteristics. (4) macro quantum tunneling eff ect the tunneling eff ect is one of the basic quantum phenomena. when the total energy of the microscopic particles is less than the barrier height, the particles can still pass through the barrier. in recent years, it has been found that some macroscopic quantities such as the magnetization of ultrafine particles and the magnetic flux in quantum coherent devices also have tunneling effects which can change through the potential well of the macroscopic system, known as the macroseopie quantum tunneling [9]. many of the magnetic electrons in the atom (referring to the electrons in the 3d and 4f shells) pass through the barrier in a tunneling manner, resulting in a change in magnetization which is a magnetic macroscopic quantum effect. it can be used to explain the phenomenon where nano-particles at low temperature remain superparamagnetic. the study of macroscopic quantum tunneling is of great signifi cance to basic research and application, which limits the time limit of information storage of magnetic tape and disk. the quantum size eff ect and the macroscopic quantum tunneling eff ect will be the foundation of future microelectronic devices which establishes the limits of further miniaturization of existing microelectronic devices. when the microelectronic devices are further refi ned, the above-mentioned quantum eff ects must be considered. (5) volume eff ect due to the small size of the nanoparticles, the number of atoms contained is very small. therefore, many phenomena such as adsorption, catalysis, diff usion, sintering and other physical and chemical properties related to the interface state will be significantly different from those of the large particle conventional materials, and can not be explained by the nature of the bulk material which is usually infi nitely atomized. this particular phenomenon is often called the volumetric eff ect [10]. (6) dielectric limit eff ect the dielectric confi nement is the phenomenon that the nanoparticles are dispersed in the heterogeneous medium due to the dielectric enhancement of the interface caused by the interface. this dielectric enhancement is usually called the dielectric limit, mainly derived from the enhancement of the surface and the internal of the particles. when the refractive solvent thermal method to control lead sulfi de nano/micron crystal and its ni/pbs composites 32 index of the medium is larger than the refractive index of the microparticles, the refractive index boundary is generated which leads to the enhancement of the fi eld strength of the particles and the internal fi eld. the enhancement of the local field strength is called dielectric limited field. generally, transition metal oxides and semiconductor microparticles may produce dielectric limiting effects. the dielectric confinement of nanoparticles has an important effect on light absorption, photochemistry and optical nonlinearity. therefore, when we analyze the optical phenomenon of a material, it is necessary to consider the quantum size eff ect and dielectric limit eff ect. 1.2. hydrothermal / solvent thermal method 1.2.1 defi nition of hydrothermal method / solvent thermal synthesis in hydrothermal method, a water solution is used as a reaction medium in a specially made closed reactor to create a high temperature and high pressure reaction environment by heating the reaction vessel so that the normally insoluble material dissolves and recrystallizes. the hydrothermal reaction can treat some organic reaction or treat organic wastes that endanger our environment, as well as sintering ceramic materials at relatively low temperatures. however, the process of hydrothermal preparation of nanocrystals using water as solvent reaction is subjected to certain restrictions such as reactants decomposition or some reaction are unable to occur. for example: carbides, nitrides, phosphides and silicides. therefore, by replacing water with non-aqueous solvent such as ethanol, methanol, benzene etc. as a solvent, and by replacing hydrothermal reaction with solvothermal reaction, a large amount of precursors to water-sensitive nanocyrstaline compound. solvent thermal reaction is in the lime light in recent years. solvent thermal reaction is the development of hydrothermal reaction, which is diff erent from hydrothermal reaction where an organic solvent is used rather than water. compared with other preparation method, the main characteristic of solvent thermal reaction is very mild reaction conditions (such as the preparation of diamond), stabilizes phase, prepares new substances, develop new preparation routes and more. in the solvent thermal reaction process, the chemical component involved in the reaction acts as a solvent, mineralization accelerator, and also transmission medium for pressure. solvent thermal reaction is mainly researched and developed by research group lead by mr qian yitai. the most widely used solvent is ethylenediamine. in ethylenediamine system, in addition to being a solvent, ethylenediamine is also a complexing agent or chelating agent. ethylenediamine as a bidentate ligand, due to the strong chelating eff ect of n, together with ion precursor become stable complex ion, where the complex ion then react with reactants to produce products. the reduction properties of methanol, ethanol, etc. in addition to solvent can also be used as a reducing agent. it can be seen, that solvent thermal reaction greatly expands the fi eld of nano-functional materials synthesis. the method is simple and convenient. as long as the suitable solvent is found, the development and application of solvent thermal reaction will have broad prospects. 1.2.2 characteristics of hydrothermal / solvent thermal method (1) advantages and disadvantages of hydrothermal method: (a) hydrothermal method uses medium temperature in liquid phase control. energy consumption is relatively low and has wide applicability. (b) raw material is relatively cheap and easy to obtain, quickly convection in the liquid phase reaction, high yield, uniform phase, high purity, good crystallization, and controllable shape and size. (c) in hydrothermal process, the purpose of effective control of reaction and crystal growth can be achieved by adjusting the reaction temperature, pressure, treatment time, solution composition, ph value, the type of precursor and mineralizer. (d) reaction is carried out in a closed vessel and the reaction atmosphere can be controlled to form a suitable redox reaction condition, and obtain some special phases, which is particularly advantageous for the synthesis reaction in a toxic system and minimizes environmental pollution. limitations of hydrothermal method: this method is only applicable to the preparation of oxides or a few waterinsensitive sulfi de semiconductor nanomaterials. in this context, researchers design solvent thermal synthesis in new solvent system, expanding the application of hydrothermal method. (2) advantages and disadvantages of solvent thermal synthesis method in hydrothermal synthesis, water is the medium to transfer pressure and also played the role of mineralizer. replacing water with a non-aqueous solvent also has the same effect and additional effects. at high temperature and high pressure, the solvent of the synthesis reaction is in critical or near-critical state. the physical and chemical properties of the reactants in the solvent have a great change, and the thermochemical reaction of the solvent is much diff erent from normal. the functional materials and crystal has its own excellent characteristics in terms of its nature. therefore, the solvent thermal reaction is an eff ective method for the synthesis of chalcogenides. yajia ding, et al 33 solvent thermal methods have the following advantages over other methods: (a) solvent thermal method may replace the solid phase reaction and the difficult synthesis reaction due to the change in the reactivity of the reactants under solvent thermal conditions and the improvement of the activity. (b) as intermediate state, steady state, and specific phase is relatively easy to be generated, the synthesis and development of a series of special metastable structure and special condensed products can be produced. (c) able to crystallize compound with low melting point, substance that is non-liquid in high vapour pressure condition, and high temperature decomposition phase. (d) low temperature, isobaric, are solution conditions of the solvent thermal method, are beneficial due to less defects, perfect crystals with good orientation, synthesis of high crystallinity and easy to control the crystal particle size. (e) as the atmosphere under solvent thermal method is easily adjustable, it is beneficial for the formation of compounds in low valence state, intermediate state and special valence state, doping is uniformed, and benefi cial to the synthesis of new structures. although the solvent thermal synthesis of nano-materials has the above advantages, this method has some shortcomings as following: (a) the solubility of the solvent and the rate of crystal growth are unpredictable. (b) it takes a long time to grow crystals of the appropriate size. (c) the infl uencing factors are more complex and have no mature theoretical causality. 1.2.3 advances in hydrothermal / solvent thermal processes reaction systems in hydrothermal synthesis are usually the following: water, inorganic ammonia, inorganic strong complexing agent system, organic amine, organic alcohol, organic alkane, other organic solvent system. various reaction systems have their own characteristics and properties. over the past decade, hydrothermal (solvothermal) synthesis has made considerable progress in the preparation of chalcogenide nanomaterials. the conditions of synthesis of chalcogenide nanomaterials under hydrothermal (solvothermal) were studied in detail, and various binary and ternary chalcogen compounds were synthesized. the results show that the hydrothermal (solvothermal) method is simple and effective for nanocrystalline morphology control and phase control. 1.3. nano lead sulfi de lead sulfi de is a cubic rock salt structure semiconductor material with narrow band gap (0,41 ev) and a large bohr exciton radius (18 nm) [16]. pbs nanocrystals have a strong quantum confinement effect, and their cubic nonlinear optical properties are about 30 times that of gaas and 1000 times of cdse. they are potential application in infrared communication, photon switch, thermal and biological imaging, optoelectronic devices and solar cells. recently, the generation of effective polychromes has been detected in pbs quantum dots, making it the most promising highly effi cient photovoltaic conversion material [17-23]. as an important member of the iv-vi semiconductors, lead sulfi de has a small band gap and a larger bohr radius, and the nanoscale pbs band moves from near-infrared blue to the visible region, showing special optical properties and electrical properties [24], and thus, it has been extensively studied in nonlinear optical devices, infrared detectors and the application of solar receivers. the properties of pbs nanomaterials are directly related to their microstructure. 2. experimental part 2.1. experimental reagents and instruments 2.1.1 experimental reagents table 2-1-1 list of reagents used in the experiment drug name product purity manufacturer high purity lead acetate analytical no. 230 shuguan dao, hebei district, tianjin city sublimation of sulphur chemical chongqing oriental reagent factory ethylene glycol analytical tianjin ke miou chemical reagent co., ltd solvent thermal method to control lead sulfi de nano/micron crystal and its ni/pbs composites 34 glacial acetic acid analytical kaifeng chemical reagent factory lead nitrate analytical tianjin chemical reagent factory anhydrous ethanol analytical anhui ante biochemical co., ltd distilled water analytical university of information materials research institute hydrated nickel chloride analytical tianjin ke miou chemical reagent co., ltd hydrate hydrazine analytical tianjin zhiyuan chemical reagent co., ltd. sodium hydroxide analytical zhengzhou paini technology cetyltrimethylammonium bromide analytical tianjin ke miou chemical reagent co., ltd thioacetamide analytical tianjin ke miou chemical reagent co., ltd note: of all reagents used in the experiment, sublimation of sulfur as pure chemical and the others are analytical. glass equipment used are washed with tap water, rinsed with distilled water, and rinsed with industrial alcohol and dried before use. reactor lining is soaked in water, washed with tap water, rinsed with distilled water, and rinsed with industrial alcohol and dried before use. 2.1.2 experimental apparatus table 2-1-2 list of experimental instruments instrument name and model manufacturer electric mixer shanghai pudong physics optical instrument factory electronic balance beijing sartorius instrument system co., ltd electric constant temperature blast drying oven shanghai yiheng instruments co., ltd. d/max-2200pc x-ray diff raction (xrd) japanese science dgg-9246a electric constant temperature blast drying oven shanghai qi xin scientifi c instrument co., ltd dms-653 optical microscope boyu instrument 85-2 digital thermostat magnetic stirrer shanghai pudong physics optical instrument factory kh 2200 ultrasonic cleaner kunshan wo chong ultrasonic instrument co., ltd 800b centrifuge shanghai anting scientifi c instrument co., ltd. 2.2. experimental steps 2.2.1 preparation of pbs nanocrystals / micrometer crystals (1) 1 mmol (0.379 g) of lead acetate was added to a polytetrafl uoroethylene lined stainless steel kettle, and 10 ml of ethylene glycol was added as a solvent to stir the mixture on a magnetic stirrer. (2) 1.5 mmol of the recovered sulfur powder was added to the kettle of (1), and the mixture was suffi ciently stirred to disperse. (3) 1.5 ml of glacial acetic acid was added to the solution using a pipette and stirring was continued. (4) when the sulfur powder was dispersed uniformly, 4 ml of the ethylene glycol solution was fi nally added, and the mixture was stirred till suffi ciently dispersed. (5) kettle was sealed and placed into the oven. in the constant temperature of 240°c for 24h, after the end of the reaction, let the reactor naturally cooled to room temperature. when cooled to room temperature, the black product is poured out by fi ltration, repeatedly washed with alcohol until the fi ltrate become colorless. a small amount of product is observed under optical microscope and recorded. all the black powder was then dried in a vacuum oven at 60°c. the product is collected for further characterization. 2.2.2 preparation of ni-coated pbs heterogeneous materials (1) 0.2 mmol (0.048 g) of lead sulfi de, 0.4 mmol of nickel chloride hydrate and 8 mmol of hydrazine hydrate were added to a mixed solvent of ethylene glycol / water (30 ml of ethylene glycol, 6 ml of water). (2) 1 ml, 2 ml, and 4 ml of 1 m naoh were each added to the above solution and stirred at room temperature for 30 min on a magnetic stirrer. yajia ding, et al 35 (3) kettle was sealed and placed into the oven, at 140°c for 12h. after the reaction has completed, let the reactor naturally cooled to room temperature. after cooled, the product is poured out, fi ltered, and repeatedly washed with alcohol. a small amount of the product is observed under optical microscope and recorded. use magnet to verify whether the outside of the sulfur has been coated with metal ni, and use the magnetic size to judge the coverage condition under diff erent variables. the black powder was then dried in a vacuum oven at 60°c. the product is collected for further characterization. 2.3. characterization method the phase and purity of the product were measured by a japanese rigalcu d/max-3c x-ray powder deff ractometer (xrd) using cu kα (λ = 1.5418å), a test voltage of 40 kv, and a measurement angle of 2θ 10 to 80°; the morphology and size of the product were observed using an optical microscope and a quanta 200 environmental scanning electron microscope (esem, fei company). 3. results and discussion 3.1. characterization of pbs nanocrystals / micrometers 3.1.1 product phase and purity analysis the phase and purity of the product were examined by xrd. figure 3-1-1 shows the x-ray diff raction spectrum of the product obtained when the molar ratio of lead acetate and sulfur powder is 2: 3, 14ml ethylene glycol is used as solvent and 1.5ml acetic acid is added. it can be seen from the fi gure: the purity of lead sulfi de is relatively high. the diff raction peak is strong and sharp, and all the diff raction peaks can be indexed into cubic phase pbs with a unit cell parameter a = 5.936å which is consistent with the reported literature (jcpds card value 05-0592). xrd does not detect impurity peaks such as s, pbso4, pbo, which indicates that the purity and crystallinity of the product are relatively high. figure 3-1-1 shows the xrd pattern of the product at 140°c for 24 hours 3.1.2 morphological analysis of products the morphology of the product was observed by sem. figure 3-1-1 shows the molar ratio of lead acetate and sulfur powder of 2: 3, with 14ml of ethylene glycol as solvent, adding 1.2ml of acetic acid, at 140°c for 24 hours. figure 3-1-1a is the overall topography of the product at low magnifi cation. as can be seen from the fi gure, the product is mostly tree-like six-arm symmetrical structure and some crystal arm has small bifurcation and some did not. its size is relatively uniform, arm length of about 5 µm. in addition, some six-arm structure is broken, indicating that the tree-like pbs is not easy for long-term ultrasonic dispersion. figure 3-1-1b is a sem image of a single tree structure at high magnifi cation. the structure of the lead sulfi de micrometer crystal can be clearly seen from the fi gure. a single lead sulfi de tree structure consists of six diff erent orientations of arms, each arm size is more uniform, the orientation distribution is also more uniform, but they are not in the same plane. in addition, each arm is distributed with fine bifurcation, they are arranged more uniform, the overall structure is like a symmetrical branch. by the fi gure, each small bifurcation is about 1µm, each arm is about 5µm, each crystal is about 10µm, so we consider it more suitable for micron crystal. figure 3-1-1c is another six-arm lead sulfi de structure we have obtained. compared to the six-arm structure in figure 3-1-1b, its surface is relatively smooth, there is no small bifurcation, but its overall shape and the former is basically the same, the size is similar with the former. solvent thermal method to control lead sulfi de nano/micron crystal and its ni/pbs composites 36 figure 3-1-1 pbs sample obtained from molar ratio of lead acetate to sulfur powder of 2: 3, reaction at 140°c for 24 h 3.1.3 eff ect of sulfur content on product morphology experiments show that the amount of sulfur powder on the product morphology has a greater impact. in this regard, we analyze them through sem image. figure 3-1-3 is the sem image of the product with diff erent amounts of sulfur powder. figure 3-1-3 sem images of pbs with diff erent amounts of sulfur powder (figure a, b, c uses 1mmol, 1.5mmol, 2mmol of sulfur powder, respectively) it can be seen from the fi gure, when the other variables are the same (lead acetate 1mmol, acetic acid 1.2ml, ethylene glycol 14ml, reaction time 24 hours, temperature 140°c), when the sulfur powder is 1mmol, the product morphology is more messy, there are fl ower-like structure, there are square-shaped structure, but less non-planar six-arm structure; when the sulfur powder is 1.5mmol, the product morphology is very uniform, more than 80% non-planar six-arm structure, the size is relatively uniform, the symmetry is also very good, and the results are ideal; when the sulfur powder is 2mmol, although there are still non-planar six-arm structure, but there are also other structures, and the six-arm structures are not very regular, the size is not very uniform. this shows that the amount of sulfur powder has a certain role on the product structure, morphology of the regularity, and the size of uniformity. sulfur powder dosage should not be too less or too much, from the experimental results we know that sulfur powder 1.5mmol is more appropriate. 3.1.4 the eff ect of acetic acid on the morphology of the product experiments show that the amount of acetic acid also has a great impact on the appearance of lead sulfi de. likewise, we analyze the impact through sem image. figure 3-1-4 is the sem image of lead sulfide obtained with different amounts of acetic acid. it can be seen from the fi gure, when the other variables are the same (lead acetate 1mmol, sulfur powder 1.5mmol, ethylene glycol 14ml, reaction time 24 hours, temperature 140°c), when acetic acid dosage is 1ml, its morphology is more messy and the size of each petal is not uniform; when the amount of acetic acid is 1.2ml, the product morphology is very uniform, more than 80% of non-planar six-arm structure, the size is also more uniform, the symmetry is also very good, and the results are ideal; when the amount of acetic acid is 1.5ml, the product is mostly six-arm structure, there are fl ower structure and other cluttered structure, and size is also diff erent; when the amount of acetic acid is 2ml, there are very few six-arm structure, arm lengths are diff erent, mostly are fl ower structure and cubic block structure, the shape and size is not regular. it can be seen that the preparation of lead sulfi de microstructure requires appropriate acidic conditions, where the increase in the amount of acetic acid is conducive to the product to the uniform morphology changes. however, the acidity cannot be too strong; otherwise it is not conducive to the formation of uniform morphology products. from the results, a usage of 1.2ml acetic acid is more appropriate. yajia ding, et al 37 3.1.5 eff ect of lead source on product morphology when diff erent lead sources are used, the morphology of the resulting products is also diff erent. figure 3-1-5 is an image observed under optical microscope of the product obtained using lead acetate and lead nitrate, respectively, as lead sources. figure 3-1-5 image observed under optical microscope of product obtained under diff erent lead sources (figure a and b are lead acetate and lead nitrate, respectively) it can be seen from the fi gure that when the other variables are the same (acetic acid amount, solvent, sulfur source, reaction time, reaction temperature), when lead acetate is used as lead source, the product has a non-planar six-arm structure with uniform size, looks more regular, and has a good symmetry; and when the use of lead nitrate as a lead source, the product has a large size four corner spindle structure, its shape is also more structured but the size is not uniform. when observed by the naked eye: pbs products made with lead acetate are darker, and is of black powder, and pbs prepared by using lead nitrate is of gray powder. at the same time, we tried to use lead chloride as a lead source but failed to get the product. the specifi c reason is unclear. 3.2. characterization of ni / pbs composites 3.2.1 product phase and purity analysis the phase and purity of ni/pbs composites were observed by xrd. figure 3-2-1 shows the x-ray diffraction pattern of the product obtained by coating 0.2 mmol of pbs with nickel at 140°c for 12 hours with polyethylene glycol and water as a composite solvent. in this case, we compare the spectra of lead sulfi de with the products obtained with diff erent amounts of 1 mol/l naoh in the same spectrum. it can be seen from the fi gure: the resulting pbs (05-0592) diff raction peak is strong and sharp, indicating that its purity and crystallinity are relatively high. when naoh is added (under alkaline conditions, the reduction of hydrazine hydrate is enhanced and nickel chloride is more easily reduced to elemental nickel), the strength of the peak varies with nickel, and with the addition of diff erent amount of naoh, the change is not the same. secondly, the product is not of pure ni/pbs composite, from the fi gure we can clearly see the diff raction peak of ni3pb2s2 (26-1287) indicating that in the coating process, bimetallic sulfi de is produced. in addition, with the increase in the amount of naoh, the peak of bimetallic sulfi de has weakened, while the peak of metal nickel initially enhanced and then weakened. when adding 2ml of naoh, nickel peak is the strongest, indicating that at this time there is more ni/pbs heterogeneous materials. figure 3-2-1 xrd pattern of the product obtained at 140°c for 12h (a is the xrd pattern of pbs, b, c, d is the composite product obtained by adding 1, 2, 4ml 1mol/l naoh, respectively) solvent thermal method to control lead sulfi de nano/micron crystal and its ni/pbs composites 38 3.2.2 morphological analysis of products the morphology of the composite product was observed by sem. figure 3-2-2 shows sem image of the product obtained by coating 0.2 mmol of pbs with nickel at 140°c for 12 hours with ethylene glycol and water as a complex solvent (vethylene glycol: vwater = 5: 1). figure 3-2-2 sem image of products obtained at 140°c for 12 h (figure a, b, c were added with 1, 2, 4ml 1mol/l naoh, respectively) it can be seen from the fi gure: when naoh is added to the lead sulfi de, the six-arm structure of lead sulfi de can still maintain its original state. when adding 1ml of naoh, the six-arm structure surface is coated with many small particles, while the surrounding is also scattered with some particles, they are not evenly distributed, and in addition to six-arm structure, there are other clutter structure; when adding 2ml of naoh, the distribution of small particles is more uniform, well coated on the surface of lead sulfi de, it has similar properties as a ‘binder’; when adding 4ml of naoh, the are very thick layer of small particles stuck to the six-arm structure, surrounded by a large number of scattered particles, and the overall phenomenon of agglomeration is very serious, which may be due to slightly stronger alkaline and reaction was too fast. it can be seen, when coating lead sulfi de, 2ml of naoh is more appropriate. when naoh is less, there were more impurities, more reactions which is too fast, and not conducive to dispersion. 4. conclusions in this experiment, the nano-crystal materials with uniform morphology (non-planar six-arm structure) were successfully synthesized at the appropriate temperature by the compound solvent method, and the eff ects of various factors (acetic acid dosage, sulfur content and lead source) are studied. the xrd, sem and microscopy were used to characterize them. finally, nickel-coated lead sulfi de heterogeneous materials were prepared. (1) the amount of sulfur powder on the product morphology has a greater impact. when the amount of sulfur powder is too much or too little, it will affect the regularity and uniformity of the product morphology. different amounts of sulfur powder may be produce diff erent products. the appropriate amount of sulfur powder is 1.5mmol. (2) the amount of acetic acid is another factor aff ecting the product morphology. the preparation of lead sulfi de requires proper acidity, and the increase in acetic acid is benefi cial to the uniformity of the product. however, the acidity shall not be too strong; otherwise it is not conducive to the formation of uniform morphology. from the results: 1.2ml acetic acid is more appropriate. (3) diff erent lead sources also aff ect the product. when using diff erent lead sources, not only the product's color and sedimentation capacity is diff erent, the product also shows a completely diff erent morphology and the size is also very diff erent. (4) when coating with nickel, the amount of naoh used gives a great impact. its amount will not only aff ect the speed of the coating, but also aff ect the purity of the composite material, and product dispersion. the results show that the amount of 2ml is more appropriate. in this experiment, diff erent variables were studied and observed using xrd, sem and microscopy. the target products were the non-planar six-arm structure. the optimal reaction conditions were as follow: 1.2ml acetic acid, 1mmol lead acetate, 1.5mmol sulfur powder, reaction temperature 140°c, reaction time 24 h, 14ml ethylene glycol as solvent. for coating, 2ml of naoh is more appropriate. references 1. d.k. kim, y. zhang, w. voit, et al. synthesis and characterization of surfactant coated superparamagnetie monodispersed iron oxide nanoparticles [j]. j. magn. mater, 2001, 225: 30-32. yajia ding, et al 39 2. xiang hang. 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application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1293 original research article sapindus emarginatus extract embedded with gold nanoparticles: an antiproliferative agent against mcf7 breast cancer cell line s vignesh kumar1*, v kavimani2 1 department of biotechnology, anna university regional centre, coimbatore, india. e-mail: svigneshkum6@gmail. com 2 department of mechanical engineering, anna university regional centre, coimbatore, india abstract there are numerous studies reported on the usage of the sapindus emarginatus (se) fruit in cancer and other treatments in the past few years. in this study, crude se fruit extract was prepared and it was further used to synthesis gold nanoparticles (au nps). the synthesized au nps were left embedded in the se fruit extract. the au nps embedded in the se fruit extract (se-au nps) were characterized using uv-visiable spectroscopy, centrifugal particle size analyzer (cps), scanning electron microscope (sem) and fourier transform infrared spectroscopy (ftir). mtt assay was carried out for both se fruit extract and se-au nps on mcf7 breast cancer cell line and thus compared. the uv-visible absorbance for the se-au nps was obtained at 543 nm. the centrifugal particle size analysis of the au nps embedded in se fruit extract showed the size of the nanoparticles to be widely varying with higher fraction of particles between the size ranges of 15 to 20 nm. the morphology of the au nps embedded in se fruit extract was observed using sem. the presence of au nps in se fruit extract was confirmed using ftir. the results of the mtt assay on mcf7 breast cancer cell line proved that the % cell viability was less for se-au nps than that of the se fruit extract alone. thus, the antiproliferative activity of the se fruit extract was significantly enhanced by embedding it with au nps and it can be effectively used in therapeutic applications after further studies. keywords: gold nanoparticles; sapindus emarginatus; antiproliferative; mcf7 article info received: 25 march 2021 accepted: 11 may 2021 available online: 18 may 2021 copyright copyright © 2021 s vignesh kumar, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction cancer is the abnormal growth of cells with uncontrolled division resulting in increased number of cells[1]. cancer is observed as the most dangerous class of disease categorized by uncontrolled cell growth[2,3]. there is a marginal increase in cancer cases in the last few years, and most of the time, it ends up with taking life[4,5]. breast cancer is a complex and heterogeneous disease[6]. in world, breast cancer represents 9% of the global cancer burden and is the third most common tumour. human breast cancer mcf7 cells represent one of the most widely used experimental models for in vitro studies on breast carcinoma[7]. a considerable part of the current knowledge on breast carcinomas is based on in vivo and in vitro studies performed with cell lines derived from breast cancer. in reference to the treatments available for cancer, the characteristics of the cancer determine the treatment, which may include surgery, medications (hormonal therapy and chemotherapy), radiotherapy and immunotherapy. there are currently three main 2 groups of medications for breast cancer, such as hormone blocking agents (tamoxifen, anastrozole or letrozole), chemotherapy (cyclophosphamide, methotrexate and fluorouracil) and monoclonal antibodies (trastuzumab). radiotherapy is given after surgery to the region of the tumor bed and regional lymph nodes, to destroy microscopic tumor cells that may have escaped surgery. radiation can reduce the risk of recurrence by 50%–60%[8]. most chemotherapy medications work by destroying fast-growing and/or fast-replicating cancer cells, either by causing dna damage upon replication or by other mechanisms. along with the medications chemotherapy and radiation can also affect healthy cells. for example, damage to the heart muscle is the most dangerous complication of doxorubicin. trastuzumab is very expensive and its use may cause serious side effects (approximately 2% of patients who receive it suffer from significant heart damage). due to growing resistance and side effects to these therapies search for new therapeutics for breast cancer has become essential. scientific interest in medicinal plant has bloomed in recent times due to increased efficiency of new plant derived drugs and wide spread concerns about the side effects of modern medicine[9]. sapindus emarginatus vahl found in south india is commonly known as soap nut tree. the tree species is inadequately distributed in diverse geographical provinces like gangetic plains, western ghats and deccan plateau in india[10]. the genus sapindus possesses tremendous medicinal value. since past, it is used as emetic, tonic, astringent, anthelmintic, for asthma, colic, diarrhea, cholera, tubercular glands and paralysis of limbs. methanolic extract of fruit of sapindus emarginatus (se) found to produce cns depressant activity[11]. the fruits are usually used for hair problems and also in preparation of shampoos. traditionally se is used as anti-inflammatory and antipruritic medicine. the seed is an intoxicant and the fruit rind has oxytropic action. its powder is used as nasal insufflations[12]. saponins isolated from different plants and animals have been shown to specifically inhibit the growth of cancer cells in vitro[13–18]. the saponins from se fruit extract found to have significant antihyperlipidemic activity[19]. the combined application of saponins with other antitumor compounds may increase cytotoxic activity of the latter, which is an interesting new possibility in cancer treatment research[20]. the noble metal nanoparticles like gold nanoparticles represent smart and promising candidates in the drug delivery applications due to their unique dimensions, tunable functionalities on the surface, and controlled drug release[21]. another essential aspect while working with au np in bio-applications is safety and biocompatibility (au np is already approved by the us food and drug administration.) biologically synthesized and functionalized, au np provides many desirable attributes for use as carriers in drug delivery systems as the functionalized au np core is essentially inert and nontoxic reported in recent studies[22]. the labeling of aunps with biological ligands to specifically bind to desired cancer cells increases the effectiveness of thermal energy transfer to cancer cells without harming non-cancerous cells[23]. after cellular uptake, the au nps can act as tiny, precise and powerful heaters (thermal scalpels) to kill cancer and they are capable of inducing apoptosis in b-chronic lymphocytic leukemia[24]. it has been found that gold nanoparticles embedded in rubia cordifolia (rc) matrix significantly enhanced anti-inflammatory characteristics by inhibiting nitric oxide release[25]. it was reported in terms of inhibitory concentration for 50% inhibition compared to either rc extract or au nps. hence, in this work the se fruit extract was embedded with gold nanoparticles with the vision of increasing its antiproliferative activity. 2. materials and methods 2.1 preparation of plant extract fresh fruits of se were collected from the nursery of institute of forest genetics and tree breeding (ifgtb), coimbatore, tamilnadu. collected se fruits were dried under shade, mechanically powdered and stored in an airtight container. dried and powdered se fruits were extracted with 95% methanol in a soxhlet extractor. the methanolic extract was concentrated to give a dark brown residue which 3 was partitioned between water-n-butanol (1:1). the n-butanolic layer was evaporated to give the crude saponin fraction as a brown residue[26]. 2.2 synthesis of gold nanoparticles (au nps) embedded in se fruit extract (se-au nps) a solution of 50 ml, 0.001 m (0.39382 mg/ml) gold (iii) chloride trihydrate (haucl4·3h2o) and 50 ml se fruit extract, diluted in 50 ml of distilled water, was added together drop by drop and stirred on a magnetic stirrer. the solution was ultrasonicated at a high frequency of 10 khz for 3 h and then maintained at a stationary position for 2 h at room temperature. 2.3 characterization of se-au nps se-au nps were characterized by uv-visible absorption spectroscopy, centrifugal particle size analyzer (cps), fourier transform infrared spectroscopy (ftir) and a scanning electron microscope (sem). 2.4 uv-visible absorptance spectroscopy studies uv-visible absorptance spectroscopy have been proved to be quite sensitive to the formation of gold colloids because gold nanoparticles exhibit an intense absorption peak around 540 nm due to the surface plasmon (it describes the collective excitation of conduction electrons in a metal) excitation. the sample was analyzed using uv-9000s spectrophotometer (lark, india). distilled water was used as a blank. cps the gold nanoparticles embedded in the plant extract were isolated by centrifugation. diluted suspensions of sucrose, on the order of 0.01–1.0 [wt%], were prepared. the sugar solution and our sample solutions were injected in disc centrifuge. nanoparticle size was analyzed by injection of 350 µl of sample into cps operating at a speed of 20,000 rpm. all analyses were run against a known calibration standard and the particles in the solution were analyzed by size distribution graph. sem morphology of the synthesized au nps in the se fruit extract was analyzed using sem. few drops of the se fruit extract embedded with the au nps was spread on a cover slip and dried. then the sample on the cover slip was coated with gold in a sputter coating unit for few minutes. ftir the samples were completely dissolved in respective solvents, non-sticky and the ph was found to be less than 8 which are necessary conditions to analyze the liquid samples. the sample analysis was carried out using ftir (brucker–tensor 27) in atr mode with a range from 500 to 4000 cm-1. the liquid samples are directly placed onto the znse crystal to obtain the spectrum. 3. cell proliferation assay on mcf7 cell line 3.1 chemicals and reagents mtt (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) invitrogen, usa. acridine orange was obtained from sigma, usa. all other fine chemicals were obtained from sigma–aldrich, st. louis. 3.2 cell culture mcf7 cells obtained from nccs (national centre for cell science, pune) were cultured in rose well park memorial institute medium (rpmi), supplemented with 10% fetal bovine serum, penicillin/ streptomycin (250 u/ml), gentamycin (100 µg/ml) and amphotericin b (1 mg/ml) were obtained from sigma chemicals, mo, usa. all cell cultures were maintained at 37 °c in a humidified atmosphere of 5% co2. cells were allowed to grow to confluence over 24 h before use. 4. cell growth inhibition studies by mtt assay cell viability was measured with the conventional mtt reduction assay, as described previously with slight modification. briefly, mcf7 cells were 4 seeded at a density of 5 × 103 cells/well in 96-well plates for 24 h, in 200 µl of rpmi with 10% fbs. then culture supernatant was removed and rpmi containing various concentrations (0.11–100 µg/ml) of test compound was added and incubated for 48 h. after treatment, cells were incubated with mtt (10 µl, 5 mg/ml) at 37 °c for 4 h and then with dmso at room temperature for 1 h. the plates were read at 595 nm on a scanning multi-well spectrophotometer. data represented the mean values for six independent experiments[27]. cell viability (%) = (mean od/ control od) × 100. 5. results and discussion 5.1 preparation of se fruit extract crude extract of se fruits was obtained as brown colored mixture from the soxhlet apparatus. the mixture was separated into upper phase (butanol and crude saponin) and lower phase. the upper phase was evaporated and the crude saponin obtained was brown in color with a colorless lower phase. 5.2 synthesis of se-au np the change in the brown color of se fruit extract into purple color after its treatment with haucl4·3h2o solution clearly indicated the formation of au nps. the color change was observed within 1 h in room temperature. jannathul firdhouse and lalitha have earlier reported the similar color change as the indicator for the formation of au nps[28]. the reduction of metal ions was roughly monitored by visual inspection as described earlier[29]. the process performed simply at room temperature is comparatively free of toxic chemical hazards. figure 1. synthesized au np. (a) haucl4·3h2o; (b) plant extract + haucl4·3h2o; (c) se-au np. 5.3 characterization of se-au nps uv-visible spectroscopy the uv-visable absorbance for the se-au nps was obtained at 543 nm and it is due to the excitation of surface plasmon vibrations in the gold nanoparticles. the spectra are consistent with previous experimental results. parida et al. reported the synthesis of gold nanoparticles using allium cepa extract as the reducing agent and the absorption peak was broad and found at 540 nm which might be due to polydispersity nature of the nanoparticles[30]. figure 2. uv-visible spectroscopy for se-au nps. cps the particle size analyzer (figure 3) showed various diameter ranges of nanoparticles. the diameter versus % fraction was plotted. the size of the au nps embedded in se fruit extract was found to be widely varying with higher fraction of particles between the size ranges of 15 to 20 nm. the particle size analyzer displayed a total weight of injected gold sample as 57.26 µg. in the injected sample 20 to 15.9 nm diameter of particles are present in high level whereas the 15.9 to 12.7 nm sized particles were in minimum level. this variation may be due to the aggregation of the nanoparticles in the extract. 5 figure 3. particle size distribution of au nps. sem the sem image (figure 4) of se-au nps showed the au nps distributed over the extract. the au nps embedded in the se fruit extract were found to be aggregated and was not clear. the result obtained was similar to that of paz elia et al. who observed the morphology of au nps using plant extracts as reducing agents[31]. figure 4. sem image of se-au nps. ftir ftir spectrum of methanolic fruit extract of se showed characteristic peaks for several functional groups like hydroxyl group in the range 3500 to 3000, c-o-c in the range of 1500 to 1000 and c-br (alkyl) in the range of 1000 to 500. for se-au nps the peak in the range of 3500 to 3000 indicates the presence of -nh2 (amino) group, c-h group at 2119 and carbonyl group c=o in the range of 2000 to 2500. by comparing the spectrum of se-au nps with the spectrum of se fruit extract and the standard spectrum of gold nanoparticles[32], it is clear that the spectra of se embedded with gold nanoparticles indicates the presence of both the extract and the gold nanoparticle in it. 6. cell proliferative study—mtt assay the antiproliferative activity of se fruit extract and se-au nps under in vitro conditions were examined on cell proliferation by the mtt assay. mcf7 cells were exposed to the two samples at varying concentrations for 48 h and cytotoxicity was determined using mtt assays. mtt results have shown that as the concentration of the samples increase, increased cytotoxicity was observed in a dose-dependent manner. in mtt assay, cell viability was significantly reduced to 47, 60 and 81.9% for the concentrations of 100, 10 and 1 µg respectively for se-au nps and 69.9, 85.76 and 90% for 100, 10 and 1 µg respectively for crude se fruit extract (figure 7). the se-au nps was found to be more effective compared to the crude se fruit extract alone which indicates that au nps increases the cytotoxicity and has great potential as conjugate with the fruit extract and can be effectively used as anticancer agent. 6 table 1. mtt assay for cell viability concentration cell viability (%) sample a sample b 100 µg 47.38003 69.93933 10 µg 60.28682 85.76944 1 µg 81.9636 90.12686 100 ng 98.78654 95.58742 1 ng 97.90403 98.67632 7. conclusion the se fruit extract was prepared using the soxhlet apparatus. the se fruit extract was used to synthesize the gold nanoparticles. the synthesized gold nanoparticles embedded in the se fruit extract (seau nps) were confirmed by its absorbance at 543 nm using the uv vis spectrophotometer. the size of the au nps was found to be widely varying with higher fraction of particles between the size ranges of 15 to 20 nm. this may be due to the agglomeration of the particles. morphology of the se-au nps was observed using sem. the ftir analysis of the se-au nps confirmed the presence of gold nanoparticles in the extract. mtt assay was carried out for both se fruit extract and se-au nps on mcf7 breast cancer cell line and compared. the results of the mtt assay on mcf7 breast cancer cell line proved that the % cell viability was less for se-au nps than that of the se fruit extract alone. thus, the antiproliferative activity of the se fruit extract was significantly enhanced by embedding it with au nps and it can be effectively used in therapeutic applications after further studies. the se-au nps can be further taken to in vivo studies and then to clinical applications. conflict of interest no conflict of interest was reported by the authors. references 1. manoharan s, palanimuthu d, baskaran n, et al. modulating effect of lupeol on the expression pattern of apoptotic markers in 7, 12-dimethylbenz (a) anthracene induced oral carcinogenesis. asian pacific journal of cancer prevention 2012; 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and bimolecular spectroscopy 2015; 150: 691–695. can-v4i2 第3次校对 1 can-v4i2 第3次校对 2 can-v4i2 第3次校对 3 can-v4i2 第3次校对 4 can-v4i2 第3次校对 5 can-v4i2 第3次校对 6 can-v4i2 第3次校对 7 microsoft word can-6031 characterization and application of nanomaterials 2024, 7(2), 6031. https://doi.org/10.24294/can.v7i2.6031 1 article super-resolution by converting evanescent waves in microsphere to propagating waves and light transmitted from its surface to nano-jet y. ben-aryeh physics department, technion-israel-institute of technology, haifa 32000, israel; phr65yb@physics.technion.ac.il abstract: the electro-magnetic (em) waves transmitted through a thin object with fine structures are observed by a microsphere located above the thin object. the em radiation transmitted through the object produces both evanescent waves, which include information on the fine structures of the object (smaller than a wavelength), and propagating waves, which include the large image of the object (with dimensions larger than a wavelength). the superresolutions are calculated by using the helmholtz equation. according to this equation, evanescent waves have an imaginary component of the wavevector in the z direction, leading the components of the wavevector in the transversal directions to become very large so that the fine structures of the object can be observed. due to the decay of the evanescent waves, only a small region near the contact point between the thin object and the microsphere is effective for producing the super resolution effects. the image with super-resolution can be increased by a movement of the microsphere over the object or by using arrays of microspheres. both propagating and evanescent waves arrive at the inner surface of the microsphere. a coupling between the transmitted em waves and resonances produced in the dielectric sphere, possibly obtained by the mie method, leads to a product of the em distribution function with the transfer function. while this transfer function might be calculated by the mie method, it is also possible to use it as an experimental function. by fourier transform of the above product, we get convolution between the em spatial modes and those of the transfer function arriving at the nano-jet, which leads the evanescent waves to become propagating waves with effective very small wavelengths and thus increase the resolution. keywords: microsphere; super-resolution; evanescent waves; nano-jet; transfer function; mie method 1. introduction any microscopic image can be magnified by using a microscope. but observing sub-wavelength structures is difficult because of the abbe diffraction limit [1], by which light with wavelength 𝜆 travelling in medium with refractive index 𝑛 and aperture angle 𝜃 will make a spot with radius. 𝑑 = 2(𝑛 𝑠𝑖𝑛 𝜃) 𝜆 (1) the term 𝑛 𝑠𝑖𝑛 𝜃is called the numerical aperture (𝑁𝐴)and the abbe limit is of order 𝜆/2. i analyze in the present article the mechanism by which evanescent waves incident on a microsphere are converted into propagating waves, and by such conversion high resolution is obtained in the image by the microsphere, which is much beyond the abbe limit. there is much interest in the optical properties of the microsphere system. many studies on the super-resolution obtained by the microsphere system were described in recent articles [2–10]. the mechanisms by citation ben-aryeh y. super-resolution by converting evanescent waves in microsphere to propagating waves and light transmitted from its surface to nano-jet. characterization and application of nanomaterials. 2024; 7(2): 6031. https://doi.org/10.24294/can.v7i2.6031 article info received: 26 april 2024 accepted: 15 may 2024 available online: 15 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 6031. 2 which nan-jets are produced in the microsphere system were analyzed [11–16]. these works and many previous ones led to controversy about the origin of the observed super-resolution effects. in certain works, the super-resolution was related to evanescent waves emitted from the object, which include the fine structures of the object. in these works, the production of the nan-jet was considered a separate effect, not related to super resolution. on the other hand, it was claimed in other works that the super-resolution effects are produced by the same mechanisms that produce the nano-jet, while the evanescent waves might have only minor effect. in the present work, i show that the super-resolution effects are produced in two steps, where in the first step the information on the object's fine structures is obtained by the evanescent waves. in the second step, there is a convolution between the spatial modes of the evanescent waves and the spatial modes of the microsphere, which transforms the evanescent waves into propagating waves with very small effective wavelengths [17]. the super-resolution obtained by the microsphere is like the field of scanning near-field optical microscopy (snom), where the resonant effect with the tip detector enhances the super-resolution. we follow in the present analysis the idea that the evanescent wavevectors are coupled to the microsphere by resonances produced by mie theory analysis [18,19]. such mie theory is also used for a good description of the nano-jet [19]. the conversion of evanescent waves to propagating waves, after the transmission through the microsphere surface, is obtained by convolution between the evanescent spatial modes and the transfer function of the microsphere modes [17]. the idea of using such convolution was suggested already in a previous article [20]. my approach to microsphere high resolution will be developed in the next sections by using two steps: 1) in the first step, we use the helmholtz equation, by which large wave vectors are produced above the object, producing high resolutions. 2) the em fields of both evanescent waves and propagating waves arriving parallel to the microsphere surface are preserved during transmission through the microsphere surface due to boundary conditions. the enhancement of the conversion of evanescent waves to propagating waves is due to coupling between evanescent waves and resonances, produced in the microsphere, for example, by mie theory [19]. in the second stage we do not use the helmholtz equation, and the above coupling is described as a convolution between the spatial modes of the evanescent waves and those of the microsphere modes, described by the transfer function [17]. although the propagating waves are stronger than those of the evanescent waves, the modulation of the total intensity by the evanescent waves is the source of the high resolutions obtained by the microsphere system. 2. methods the use of evanescent waves to increase the resolution beyond the abbe limit can be related to helmholtz equation [17]. in homogenous medium this equation is given by (𝑛𝑘 ) = 𝑘 + 𝑘 + 𝑘 (2) where 𝑘 = 2𝜋/𝜆 , 𝜆 is the wavelength in vacuum, 𝑘 , 𝑘 , 𝑘 are the wavevector components. the evanescent waves satisfying the relation: characterization and application of nanomaterials 2024, 7(2), 6031. 3 𝑘 + 𝑘 > (𝑛𝑘 ) (3) are arriving at the microsphere with imaginary 𝑘 . the increase of the components of the wavevector 𝑘 in the plane 𝑥, 𝑦 decreases the “effective” wavelength in this plane, and thus increases the resolution. as described in figure 1, a dielectric microsphere with radius r and a refractive index 𝑛 is located above a thin object at a contact point o. the medium between the object and the microsphere has a refractive index 𝑛 . parallel em waves are transmitted in a direction perpendicular to a thin planar object, which may be transmitted as “propagation” waves and as “evanescent” waves. but the increase of resolution by the microsphere is related to the conversion of evanescent waves to propagating waves. we analyze the conversion of evanescent waves to propagating waves at a point p, which is on the microsphere surface. the incident and transmitted angles for the em waves transmitted into the microsphere at point p are given as 𝛩 and 𝛩 , respectively. at this point, em waves with wavevectors 𝑘 . 𝑘 are arriving at the microsphere, where 𝑘 is imaginary. the increase in the component of the wavevector 𝑘 in the plane 𝑥, 𝑦 decreases the “effective” wavelength in this plane, and thus increases the resolution. but the evanescent waves decay in the perpendicular z direction, so that to “capture” the fine structure that is available in the evanescent waves, we need that the point p will be near the contact point o, so that its perpendicular distance to the object will be of a wavelength order. according to geometric optics, the microsphere has a spherical symmetry under rotation around the z axis, which connects the center of the microsphere at point c with the contact point o. the line connecting the point c with point p has an angle 𝛩 with the symmetric z axis. as shown in figure 1, the em waves transmitted through the microsphere are converging into photonic-jet (pj), where its role in producing the high resolution is controversial. the original work in obtaining high resolution in microsphere imaging was made by zengo wang et al. [21]. that analysis was made with a virtual image as follows from the geometric optics description. since this time, a very large number of papers were published on various effects in the microsphere system. in figure 1, we describe a real image that is produced by using a high-refractive index microsphere (e.g., [22,23]). the focusing of light in the microsphere system is concentrated in the nano-jet sub-diffraction region, which does not obey the classical laws of geometrical optics. but might be explained by diffraction effects, known as photonic-jet (pj) (e.g., [24,25]). exact solutions for non-diffraction beams might be related to the central part of the photonic nano-jet [26,27]. characterization and application of nanomaterials 2024, 7(2), 6031. 4 figure 1. microsphere and nano-jet. propagating em waves are transmitted through a thin object with a certain structure, whose image is produced by evanescent waves, arriving at the microsphere surface at point p, for example. the em transmitted through the microsphere is converging into a non-diffraction region known as a photonic jet (pj). rigorous mie theory predicts the interaction of light with spherical particles, and this theory was used to describe various properties of the pj’s produced by the microsphere system [19]. the exact use of the mie theory is usually done by numerical calculations, as it is obtained by the sum of many terms that do not give an analytical result. using mie theory, optical resonances in microsphere photonic nano-jets were observed [18]. we analyzed the properties of evanescent waves, produced by plane em waves transmitted through nano-corrugated-metallic thin film, which includes information on its fine structures [28]. a microsphere located above the metallic surface collects the evanescent waves, which are converted to propagating waves. the magnification of the nano-structure images is explained by a geometric optics description, but the high resolution is related to the evanescent wave analysis. such an approach for explaining the high resolutions obtained by microspheres was developed by using complex snell’s law [29]. very high resolutions by microspheres were reported also in other works (e.g., [30,31]). maslov and astratov [32,33] studied the origin of super-resolution in microsphere-assisted imaging. the imaging of the nano-jet cannot give a good explanation for the high resolutions obtained in the microsphere system. the characterization and application of nanomaterials 2024, 7(2), 6031. 5 evanescent wave source cannot explain the high resolutions obtained by the microsphere system since its effect is too weak. they suggested using a direct approach to maxwell equations, including optical principles such as point-spread functions, in microspherical imaging. i claim, however, that there are strong arguments that evanescent waves should be included in the theories about high resolutions: a) the propagating distance between the object and the microscope must be small enough to reveal the nanometric features. to generate super-resolution over large areas of the sample, we need to attach the microsphere to a frame, which is scanned on the sample in step-by-step fashion [34] or by using microspheres arrays [6]. b) there is a dependence of the super-resolution on the radius of the microsphere and its index of refraction, which is in good correspondence with the evanescent wave properties [29]. c) the super-resolution is related to information theory, where the information on the fine structures of the object area is available in the evanescent waves. magnification of the image and optical transforms cannot introduce high resolution if the information on the object's fine structures is not available in such transforms. i find, however, that there is an important mechanism that enhances the transformation of evanescent waves into propagating waves after the microsphere surface, which is beyond classical geometric optics (beyond the use of complex snell’s law [29]. to explain this new mechanism, it will be helpful to compare the high resolution obtained by the microsphere with the high resolutions obtained in metallic grating [35,36]. it was shown in these works that a thin film of metallic grating with arrays of subwavelength holes can transmit light at certain frequencies, which is order of magnitude larger than the light intensity incident on the area of these holes. most investigators agree that these experiments, conducted originally by ebessen et al. [35,36], are related to coupling the light with surface plasmons. i explained these phenomena as transmission enhancement by converting evanescent waves, entering the small holes to propagating waves, due to convolution of the evanescent spatial modes with the plasmon spatial modes, producing high spatial wavevectors with very small “effective” wavelengths [37]. such effects were described in a similar way by relating the ‘tunelling’ of evanescent waves to propagating waves due to the convolution of the high spatial frequencies of the source with those of the detector [38]. one should consider that in the dielectric sphere we don’t have plasmons, but we have other coupling mechanisms between the evanescent waves and the microsphere em modes. 3. an analysis for the super resolution, in the microsphere system, obtained in many experiments in experimental studies on microspheres by other authors [2–23,30,31,34], super resolution effects were observed. these works raised the question: is the superresolution related to evanescent waves? or is it related to the existence of the nano-jet? the question led to controversy between the various works. i show in the present theoretical analysis that a combination of two effects produces the high resolution: 1) the evanescent waves produced by the object are incident on the microsphere surface, preserving high resolutions. 2) the same mechanism which produces the nano-jet leads to conversion of the evanescent waves to propagating waves, but with very small wave lengths. the reduction of the wavelength was explained also as a quantum effect characterization and application of nanomaterials 2024, 7(2), 6031. 6 [39,40] where n entangled photons lead to effective wavelength /𝑛, and there is a distribution of such effective wavelengths. we develop the analysis for the microsphere system into two parts: a) in the first part, we describe the propagation of evanescent waves, produced on thin planar objects with fine structures, to the microsphere surface. in this stage, high resolutions of the image are obtained related to the use of the helmholtz equation. b) in the second part, we consider the propagation of both evanescent and propagating waves produced on the inner surface of the microsphere to the nano-jet. this propagation is described by the convolution of these em fields with the microsphere modes described by a transfer function [17], which is related to mie theory, but it is more convenient to use it as an experimental function. 3.1. the use of helmholtz equation for getting high resolutions by evanescent waves let us assume that the planar surface of an object is given by z = 0, and the em field in this plane is given by the fourier transform 𝑈(𝑥, 𝑦) = 𝑢 𝑘 , 𝑘 ∞ ∞ ∞ ∞ 𝑒𝑥𝑝 −𝑖 𝑘 𝑥 + 𝑘 𝑦 𝑑𝑘 𝑑𝑘 (4) where 𝑢 𝑘 , 𝑘 is the distribution of the em spatial modes in the 𝑥, 𝑦plane. then, the em waves propagating from the planar surface of the object into homogenous medium in the space 𝑧 > 0 with a refractive index 𝑛 is given by: 𝑈(𝑥, 𝑦, 𝑧 > 0) = 𝑢 𝑘 , 𝑘 ∞ ∞ ∞ ∞ 𝑒𝑥𝑝 −𝑖 𝑘 𝑥 + 𝑘 𝑦 + 𝑘 𝑧 𝑑𝑘 𝑑𝑘 (5) substituting eq. (5) into the helmholtz equation we get: (𝛥 + 𝑘 )𝑈(𝑟) = 0 (6) obtaining the result: 𝑘 − 𝑘 + 𝑘 + 𝑘 𝑈(𝑥, 𝑦, 𝑧 > 0) = 0 (7) under the condition 𝑘 < 𝑘 + 𝑘 , 𝑘 is imaginary, and for such case we get the evanescent wave solution: 𝑈(𝑥, 𝑦, 𝑧 > 0) = 𝑈(𝑥, 𝑦, 𝑧 = 0) 𝑒𝑥𝑝(−𝛾𝑧)  ; 𝛾 = 𝑘 + 𝑘 − 𝑘 (8) a dielectric microsphere with refractive index 𝑛 and radius 𝑅 is located above a thin film of the object at a contact point 𝑂,where the medium between the object and the microsphere has a refraction index 𝑛 . a plane em wave is transmitted through the thin film of the object in the perpendicular direction and incident on the microsphere at point p. the evanescent waves are incident on the microsphere surface near the contact point 𝑂. for evanescent waves, there is a decay of the wave in the z direction. the resolution obtained by the evanescent waves is limited by the lateral component 𝑘 of the wavelength given by: 𝜆 = 2𝜋 𝑘 = 2𝜋 𝑘 + 𝑘 (9) characterization and application of nanomaterials 2024, 7(2), 6031. 7 as the evanescent waves satisfy the equation 𝑘 = 𝑘 + 𝑘 − 𝛾 , then eq. (9) can be written as 𝜆 (𝑒𝑣𝑎𝑛. ) = 2𝜋 𝑘 + 𝛾 (10) the minimal value of 𝜆 for propagating waves is given by: 𝜆(𝑝𝑟𝑜𝑝. ) 2𝜋 𝑘 , (11) since the minimum is obtained when 𝑘 is in the x, y plane. as by the abbe limit the resolution is of order 𝜆/2, the increase of resolution 𝐹 by using evanescent waves is given by: 𝐹 = 𝜆 (𝑝𝑟𝑜𝑝. )/𝜆 (𝑒𝑣𝑎𝑛. ) = 𝑘 + 𝛾 𝑘 = 1 + 𝛾 𝑛 𝑘 (12) figure 2. evanescent waves on microsphere surface. the distance of the point p from the planar object is given by ℎ = 𝑅(1 − 𝑐𝑜𝑠 𝜙) (see figure 2). for decay constant 𝛾 of the evanescent waves, represented in unit 𝛾/𝑛 𝑘 , the decay of the evanescent wave at point at point p, after transversing the distance ℎ, is given by 𝑒𝑥𝑝(−𝛾ℎ) = 𝑒𝑥𝑝 − 𝛾 𝑛 𝑘 𝑛 𝑘 𝑅(1 − 𝑐𝑜𝑠 𝜙 = 𝑒𝑥𝑝 − 𝛾 𝑛 𝑘 2𝜋(1 − 𝑐𝑜𝑠 𝜙) 𝑅 𝜆 (13) we find that this decay increases very much by increasing 𝜙, so that only a small region around the contact point o is efficient in obtaining the high resolution by evanescent waves. characterization and application of nanomaterials 2024, 7(2), 6031. 8 3.2. microsphere imaging by a transfer function from the microsphere surface to the nano-jet let us assume that the em field 𝐸(𝑥, 𝑦) , which is tangent to the microsphere surface at the point 𝑥, 𝑦 (of evanescent wave in a small region around the contact point o, plus a propagating wave in a larger region), is given by: 𝐸 𝑐𝑜𝑠 𝜙 (14) where 𝐸(𝑥, 𝑦) is the em field before the microsphere surface (see figure 2, and [29]). the em field 𝐸 is preserved during transmission through the microsphere surface due to boundary conditions, and it includes both the evanescent waves and the propagating waves. the em field propagating after the microsphere surface is given as tan'( , ) ( , ) ( , )e x y e x y g x y (15) where the ‘transfer function’ 𝐺(𝑥, 𝑦) can be related by fourier transform [17] to 𝐺(𝑘 , 𝑘 ): 𝐺(𝑘 , 𝑘 ) = 𝐺(𝑥, 𝑦) ∞ ∞ ∞ ∞ 𝑒𝑥𝑝 −𝑖 𝑘 𝑥 + 𝑘 𝑦 𝑑𝑥𝑑𝑦 (16) one should notice that 𝐺(𝑘 , 𝑘 ) should include both evanescent waves for which 𝑘 + 𝑘 > 𝑘 , and propagating waves for which 𝑘 + 𝑘 < 𝑘 . due to the small distance between the points x, y and the contact point o, the evanescent field 𝐸 , (𝑥, 𝑦) is approximately parallel to the x, y plane. this em field is smaller from the evanescent em field on the thin object, by the factor given approximately by eq. (13). the fourier amplitude 𝐴(𝑘 , 𝑘 ) is described by the fourier inverse of 𝐸 , which is given by: 𝐴(𝑘 , 𝑘 ) = 𝐸(𝑥, 𝑦) ∞∫ ∞ ∞∫ ∞ (17) where 𝑘 . 𝑘 are the wavevectors in the x and y directions. the fourier transform of 𝐸′(𝑥, 𝑦), (given by the product of eq. (14)) is obtained by the convolution of the spatial wavevectors 𝐺(𝑘 , 𝑘 ) and 𝐴(𝑘 , 𝑘 ) [17]: 𝐸′(𝑘 , 𝑘 ) = 𝐴 𝑘′ , 𝑘′ ∞ ∞ ∞ ∞ 𝐺 𝑘 − 𝑘′ , 𝑘 − 𝑘; 𝑑𝑘′ 𝑑𝑘′ (18) the convolution given by equation (18) includes spatial wavevectors 𝑘 − 𝑘′ and 𝑘 − 𝑘′ which might be very large, so that the corresponding wavelengths can be reduced to very low values. for example, if approximately, 𝑘 − 𝑘′ = 𝑘𝑛 where n is a large integer, then the effective wavelength will be reduced to 𝜆/𝑛 (see the analysis in [39,40]). we use the convolution effect described by equation (18), to obtain enhancement of the conversion of evanescent waves to propagating waves by reducing the effective wavelength. although the modulation of the em waves by evanescent waves is small relative to the total intensity of the em field, such modulation is effective in producing the high resolution. the spreading of the spatial modes by convolution is like the point spread function used in [32,33], but one should not ignore characterization and application of nanomaterials 2024, 7(2), 6031. 9 the super resolution obtained for the object in the first stage of the imaging process, which is related to the use of helmholtz equation. the above reduction of the effective wavelength by convolution, was also described as a quantum effect where entanglement between the n photons reduces the effective wavelength to 𝜆/𝑛 [39,40]. such entanglement remains true also after the transformation to propagating waves. 4. discussions and results the high resolution obtained in microspheres is due to the following two factors: a) the em radiation transmitted through the object produces both evanescent waves, which include information on the fine structures of the object (smaller than a wavelength), and propagating waves, which include the large image of the object (with dimensions larger than a wavelength). evanescent waves lead to a super-resolution, which is better than the abbe limit, by the factor 𝐹 = 𝑘 + 𝑘 /𝑘 = (𝑘 + 𝛾 )/𝑘 where 𝑘 = 𝑘 + 𝑘 − 𝑘 is the wavevector of the evanescent em field, 𝑘 = −𝑖𝛾 is imaginary, and 𝑘 , 𝑘 are the transversal components. the evanescent waves arrive at the microsphere surface after a decay in the 𝑧 direction by the factor 𝑒𝑥𝑝(−𝛾ℎ). where ℎ is the distance from the object to the microsphere surface, and 𝛾 is a certain decay constant., so that only the evanescent waves which are near the contact point 𝑂 of the object are efficient in conserving the fine structure imaging. but one can attach the microsphere to a frame which moves on the object and scans a large image, or to use arrays of microspheres. b) by using boundary conditions, we get on the inner microsphere surface both evanescent waves and propagating waves. the convolution between the em waves, on the inner surface of the microsphere, and the transfer function, representing the coupling with microsphere em modes, enables propagation with small effective wavelengths (smaller than a wavelength and correspondingly large wave vectors). this effect is due to the spread of the wavevectors due to the above convolution. the transfer function also includes the wavevectors of the evanescent waves and thus enables them to be transferred to the image without evanescent wave decay. the analytical description of this convolution is given in the article by using equations (14–18). it is possible to use mie theory for calculating the transfer function, but such calculations are very complicated and usually give only numerical results. we suggest, therefore, to use the transfer function as an empirical function, which can also be used for a description of the nanojet. figure 1 gives only a geometric optics picture. the incident and transmitted angles 𝜃 and 𝜃 are derived by snell’s law, respectively. there are different features in the microsphere system which can be explained by the geometric optics picture. for example, for a small microsphere index of refraction, we get a diverging beam with a virtual image, while if this index of refraction is large, then the beam is converging with a real image, like that in figure 1. the angle 𝛽 between the beam converging to the nano-jet and the symmetric axis, and the distance 𝑟 from the point p to the symmetric axis, can be obtained by simple geometric calculations. but the microsphere super-resolutions can be calculated, only by using an analysis, similar to characterization and application of nanomaterials 2024, 7(2), 6031. 10 that presented in the present article. some features of the nano-jet may be described by using bessel beams [26,27]. figure 2 describes the transmittance of both evanescent waves and propagating waves from the object to the inner surface of the microsphere, where the fine structures of the object are included in the evanescent waves. 5. conclusion by using the helmholtz equation, it was shown how the fine structures of the object are transferred by the evanescent em radiation to the inner surface of the microsphere. the information on the fine structures of the object is included in the evanescent waves, and this information is transferred from the inner microsphere surface to the nano-jet by using the coupling between the em fields and the em modes of the microsphere, which might be calculated by mie theory (e.g., [19]). this coupling leads to transmittance of both the evanescent waves and propagating waves to the nano-jet by using ‘transfer functions’ (see equations (14–17) and reference [17]), which lead to a very small ‘effective wavelength’ for the evanescent waves, although they are not decaying any more. while the propagating waves are stronger than the evanescent waves, the modulation of the total em radiation intensity in the nano-jet by the evanescent waves is the source of the super-resolutions of the microsphere system. the present analysis solves the controversy about whether the nano-jet or the evanescent waves are the source of the super-resolution effects, as the source of the super-resolution is composed of 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39. ben-aryeh y. nonclassical high resolution optical effects produced by evanescent waves. journal of optics b: quantum and semiclassical optics. 2003; 5(6): s553-s556. doi: 10.1088/1464-4266/5/6/002 40. ben-aryeh y. super resolution of nanomaterials and quantum effects obtained by microspheres. progress in materials science. 2019; 1(3): 1-21. doi:10.21926/rpm.1903003 40 copyright © 2018 -. this is an open access article distributed under the terms of the creative commons attribution-noncommercial 4.0 international license (http://creativecommons.org/licenses/by-nc/4.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. characterization and application of nanomaterials（2018） original research article preparation and properties of silver nanoparticles pengfei xie,wenyuan ji,zhigang wei school of materials science and engineering, shenzhen engineering university, guangdong, china abstract with the progress of science and technology, the research and development of silver nanoparticles has also developed. this paper attempts to prepare a silver nanoparticle by electrolyzing agno3 solution with electrochemical reduction method and citric acid as a complexing agent in a certain current and time. the crystal morphology and sample purity of silver nanoparticles were analyzed by x-ray diff ractometer. the crystal structure of the nanoparticles was analyzed by scanning electron microscopy (sem). the crystal structure of the nanoparticles was analyzed by x-ray diff raction. the particle size distribution of the particles was in the range of 125-199 nm, and the carbon paste electrode was modifi ed with the prepared silver nanoparticles. the electrocatalytic activity of the carbon paste electrode was preliminarily explored. keywords: silver nanoparticles; electrolysis; preparation; characterization 1. introduction 1.1. overview of nanoparticles in the 21st century, the rapid development of nanotechnology has become a new industry. it has a huge market potential in many areas with a wide range of applications, closely related to people's life and production and it has unexpected potential. the particle size of the nanoparticles is usually between 1 and 100 nm, also called ultrafine particles. studies of nanoparticles have shown that nanoparticles should have some novel physical and chemical properties. there are diff erences in the structure of the nanoparticles and the macroscopic objects, which are manifested in the large surface area, while the outer atoms are neither short nor longer. it is presumed that the atoms in the nanoparticles are arranged in an orderly manner, and that the surface atoms are more biased towards the gas state. even so, as the external curvature, small particle size, the internal gibbs pressure is high, the internal structure of a deformation. its unique micro-structure to make it with excellent performance. nanoparticles have the characteristics of small size effect, surface effect, macroscopic quantum tunneling effect and quantum size effect. they have the characteristics of macroscopic materials such as conductive properties, photoelectric properties and photocatalytic ability. they are widely used in various luminescence and display device [1]. 1.2. application of nanoparticles nano-particles external activation of the core, is the preparation of excellent catalyst for raw materials. at present, you can directly use nano-particles in the polymer oxidation, reduction and synthesis reactions in the catalyst such as platinum black, silver and so on. the use of nano-particles as a catalyst to react, can signifi cantly increase the reaction effi ciency, such as rocket fuel combustion reaction using nano-nickel powder as a catalyst, can increase the combustion efficiency of 100 times [2]. the catalytic reaction of the nanoparticles is also selective. for example, when the propionaldehyde is oxidized with nano-nickel as the catalyst, the particle size of the nickel particles has a great infl uence on the reaction. when the reaction is less than 5 nm, the reaction direction is more biased towards the formation of alcohol, and the reaction of the decomposition aldehyde [3]. some materials are usually sintered at high temperatures, such as silicon carbide, tungsten carbide, high alloy, etc., but in the nanometer state at a lower temperature can be sintered to get high-density sintered body, which benefi ted from the volume eff ect of nanoparticles. on the other hand, if the active agent is used in the sintering process, the sintering process can be accelerated, the sintering temperature is lowered, the sintering time is shortened, and the nanoparticles can be used as an active agent. for example, adding 0.1% nano-nickel powder in the tungsten powder, the sintering pengfei xie, et al 41 temperature can be reduced to 12000-1300 ℃, and under normal circumstances tungsten powder at 3000 ℃ high temperature sintering [4]. the sintering of the composite material is diffi cult for the sintering of the composite material because of its diff erent melting point and different phase transition temperature. the surface effect and volume effect of the nanoparticles can be carried out at low temperature. the decomposition reaction reduces the melting point and the phase transition temperature, so that the composite material with good sintering performance can be obtained [5]. pure nano-powder materials can be used to make fine ceramics. ceramic made with these nanomaterials has the function of converting energy and transmitting information, and has the ability to wear, hard, high temperature and corrosion resistance. in addition, it can also be used as infrared absorption materials, such as cr-based alloy nanoparticles to absorb infrared, the eff ect is good [6]. there are many applications of nanomaterials in medicine and bioengineering. 'biological missile' drug technology has been successfully developed [7], which is a nano-magnetic materials for drug carrier targeted drugs. that is, carrying the drug on the surface of the protein, and then coated with magnetic iron oxide nanoparticles, injected into the human blood vessels, and then the role of the magnetic fi eld under the action of drug-oriented movement can be direct lesions, reducing the drug on the human organs produced side eff ects, improve the treatment eff ect. nano-sized nano-sensors can be used to obtain a variety of human body electrochemical information and biochemical reactions of information. you can also use nanotechnology developed into a robot, into the blood of the body, spread to the body, you can conduct a thorough examination of the human body, but also to clear the human brain thrombosis, remove the patient's arterial fat deposits, and even remove the virus, kill cancer cells, etc., the study of nanotechnology on human medical technology is of great signifi cance. it is predicted that the development of nanotechnology and the development of functional materials will develop rapidly in the future. more and more new nanometer materials will be widely used in many high-tech fi elds. 1.3. overview of silver nanoparticles silver nanoparticles refers to the fi ne particles of silver atoms consisting of 1 to 100 nm. studies have shown that the physical and chemical properties of materials are greatly altered when nanosized silver is mosaic on diff erent materials. at present, people interested in silver nanoparticles research interest, promising. silver nanoparticles have very excellent performance, mainly in the information technology, physical components, chemical products, environmental protection and many other aspects, is a high-tech materials. now widely used in ceramic building materials, medical care, environmental protection and coatings, researchers have paid great attention to the research and preparation of silver nanoparticles [8]. chen water and so on [9] people found that the load of silver particles of activated carbon fi ber has a strong bactericidal ability, so the load of silver prepared into silver nanoparticles, the reactivity of the material that is a substantial increase in bactericidal activity, because this do a substantial increase in surface area, increase the proportion of surface atoms. it has always been that the main components of ethylene epoxidation catalysts are silver and the eff ective way to improve the effi ciency of the catalyst is to reduce the particle size. therefore, it is very important to study the preparation of silver nanoparticles with smaller particle size to improve the performance of the catalyst. nano-silver can also improve the methane selective reduction of nox catalyst activity. the addition of an appropriate amount of silver nanoparticles to insulators and semiconductors gives them good optical properties and is suitable for the manufacture of optoelectronic devices [10]. the conductivity, catalytic effi ciency and bactericidal ability of silver nanoparticles are aff ected by their particle size, so it is necessary to precisely control the particle size of silver nanoparticles. in addition, in recent years, the structure and properties of self-assembled and ordered assembled fi lms of silver nanoparticles have become the focus of people's research. among the most interesting ones are silver nanoparticles or semiconducting silver with uniform size distribution and smaller particle size nanoparticles are assembled into ordered superlattices and investigated for their photoelectric properties [11]. the photoelectric properties of the solid composite fi lm are aff ected by the size of the nanoparticles and the distance between the particles, so the research on this is of great signifi cance. 1.4. preparation of silver nanoparticles over the past decade, nanotechnology has flourished, and various physical methods and chemical methods for preparing nano silver particles have been endless. the focus of this fi eld is to develop silver nanoparticle preparation methods that are less costly, more effi cient, and more effi cient and have large-scale industrial production prospects. one of the physical methods [12] have high-energy mechanical ball mill method, light method, evaporation condensation method. the simplicity of the principle is the advantage of the physical method, but its production cost is high, the requirements of the instrument device is also very high, in the silver nanoparticle size and shape of the requirements of the industrial preparation is not applicable. in the high performance requirements of nano-particles in general chemical synthesis of silver nanoparticles, such as optical, electrical and biomedical. it is the key technology to prepare the silver preparation and properties of silver nanoparticles 42 nanoparticles by controlling the particle size of the particles, the smaller particle size distribution and the fabrication of specifi c, single and uniform crystal structures. chemical preparation methods are photochemical reduction method, liquid chemical reduction method, electrochemical reduction method, microemulsion method, chemical precipitation method, sol-gel method and alcoholysis method. in recent years, the development of a new method of electrochemical synthesis of nanoparticles, shen mingming et al [13] by controlling the current density using electrochemical method to prepare a dumbbell, spherical and rod-shaped silver nanoparticles, b raun et al [14 the silver nanoparticles were synthesized by electrochemical synthesis of silver nanowires, and the silver nanoparticles were synthesized by electrodeposition. the eff ects of potential on the morphology of the particles were studied. zhu et al. [16] synthesized the semiconductors by ultrasonic electrochemistry pbse nanoparticles. the current electrochemical method is an eff ective means to synthesize nanomaterials because of its advantages of simple, rapid, non-polluting and high effi ciency [17]. 1.5. research status quo gengtao et al. [9], 'preparation and characterization of silver nanoparticles,' states that they prepared silver nanoparticles with ethylene glycol reduction under solvothermal conditions and characterized by x-ray diffraction (xrd) and transmission electron microscopy (tem). it was concluded that the nano-silver particles prepared by the hydrothermal reduction method of ethylene glycol had a face-centered cubic phase polycrystal structure with an average particle size of about 50 nm, mainly in the form of spherical granules. the agent played a very good dispersion. yang biwen et al [18] with tyrosine as a reducing agent and stabilizer, in 60 ℃ constant temperature water bath under alkaline conditions to restore silver nitrate, reaction 20 min, successfully prepared silver nanoparticles. in the process of the formation of silver nanoparticles, the color of the mixed solution changed from pale yellow to brown, this phenomenon shows the formation of fi ne particles of silver. the uv-vis and uv-vis absorption spectra (tem) were used to characterize the obtained product. the results showed that the uv absorption peak of the particles was near 412 nm, and the diameter of the silver nanoparticles at 15 25 nm, the shape is approximately spherical. sun et al. [19] used silver borohydride to reduce silver nitrate to prepare smaller silver nanoparticles. the silver nanoparticles were characterized by uv-vis absorption spectroscopy (uv-vis), scanning electron microscopy (sem) and cyclic voltammetry (cv). the results show that the size of silver nanoparticles is about 10 nm and can be assembled on the surface of conductive glass in the form of sub-monolayer. cv graph shows that silver nanoparticles have a pair of asymmetric redox peaks, and the concentration of nanoparticles can aff ect redox potential. gu daming [20] and so on in the ph = 1 2, temperature 40 42 ℃ under the conditions of sodium hypophosphite to reduce the silver nitrate solution to get purple silver paste, dried powder products. the results show that the size of the prepared silver nanoparticles is between 10 and 30 nm by tem and xrd. the preparation cycle of this method is about 5 h, the yield can reach 70% 80%. wang et al. [21] et al. used edta as a ligand to prepare spherical nano-silver particles with diff erent particle sizes by electrochemical method. they were characterized by xrd, tem and uv-visible spectroscopy. the results show that the concentration of agn03 solution is diff erent, and the shape and size of the prepared silver nanoparticles are diff erent. liao xuehong [17] and so on with n'-hydroxyethylethylenediamine-n, n, n'-triacetic acid as the complexing agent to prepare dendritic nano silver by x-ray, and xrd and tem were carried out on the nanoparticles. characterization and discovery of the presence of ligands is the key to the formation of nanoparticles, and electrochemical method is an excellent method for the preparation of silver nanoparticles, simple and effi cient pollution. at the same time, they were prepared by using edta as complexing agent and agno3 solution as raw materials. the silver nanoparticles with different spherical and dendritic shapes were successfully prepared by ultrasonic electrochemical method and characterized by xrd and tem. zhang yunhong [22] and so on in 8 14 layer of silver stearate silver l-b fi lm, the electrochemical method of preparation of nano-scale ultra-fi ne silver particles, spherical nano-silver particles detected diameter between 2-3 nm. 1.6. research content this method of preparation of silver nanoparticles is based on the solution of silver ions in a certain electrochemical window, can occur redox reaction, and was reduced to silver atoms. under the specifi c potential, select the appropriate reaction conditions, the price of silver ions can be reduced to zero valence silver. in the electrochemical reaction carried out at the same time, the electrolyte exists in the stabilizer (the experiment is citric acid), the resulting protection of silver atoms isolated, can form dispersed silver nanoparticles. the basic principle is: anode 4oh 4e o2 ↑ + 2h2o cathode 4ag ++ 4e+ stabilizer 4ag / stabilizer pengfei xie, et al 43 total reaction 4agno3 + 2h2o 4ag / stabilizer + o2 ↑ + 4hno3 after the silver nanoparticles were synthesized, they were characterized by x-ray diffraction (xrd), scanning electron microscopy (sem) and nano-particle size analyzer (c-v). 2. the experimental part 2.1. experimental drugs drug manufacturers silver nitrate (agno3, a. r. grade) sinopharm group chemical reagent co., ltd. citric acid (c6h8o7 · h2o, a. r. grade) sinopharm group chemical reagent co., ltd. potassium nitrate (kno3, a. r. grade) sinopharm group chemical reagent co., ltd. anhydrous ethanol (c2h5oh, a. r. grade) sinopharm group chemical reagent co., ltd. ultra pure water shanghai and thailand instrument co., ltd high purity graphite rods china's new materials in jiangsu science and technology co., ltd 2.2. experimental apparatus equipment manufacturers desktop high speed centrifuge (h1850) xiangyi centrifuge instrument co., ltd electronic balance (al204) mettler toledo instruments electrochemical workstation (chi660c) shanghai chen hua instrument company electric thermostatic blast oven (dhg-9140a) shanghai jinghong experimental equipment co., ltd. ultrasonic cleaning device (sk1200e) shanghai branch guided ultrasound instrument co., ltd nano-laser particle size analyzer (bt-90) dandong city baxter instrument co., ltd. x-ray diff ractometer (xrd-7000) shimadzu corporation scanning electron microscope (s-3000n) hitachi (hitachi) 2.3. experimental steps 2.3.1 preparation of silver nanoparticles use a balance to accurately weigh 4g of citric acid (as a complexing agent) and 0.2g of agno3 in a beaker. measure 100ml of ultrapure water with a graduated cylinder until fully dissolved (adding a small amount of kno3 to enhance the conductivity of the solution) to form an electrolyte. it is important to note that the beaker used in the experiment needs to be repeatedly washed with ultrapure water so as not to adhere to cl and ag + to form agcl. the electrode system is a graphite rod-graphite rod (8mm) double electrode system, the two-electrode system line connection for the working electrode caught in a graphite rod, the electrode and the reference electrode together with another graphite rod on the beaker for the electrolytic cell. can be added in a beaker cup lid, on the one hand to catch the electrode to avoid shaking the impact of silver nanoparticles precipitation, on the other hand to prevent impurities fall into the pollution of the electrolyte. the electrochemical workstation was used as the power source and was operated at a constant current of 25 ma for 40 min using the chronopotentiometry mode of operation. after the start of electrolysis need to pay close attention to the phenomenon of the electrolytic cell, can be observed on the working electrode black fl uff y material generation, with the passage of time gradually grow up, the electrode has a small bubble evenly (for oxygen). after the electrolysis is completed, turn off the electrochemical workstation, carefully remove the graphite rod, placed in a clean beaker with ultra-pure water rinse the fi nished silver completely off , the beaker placed in the ultrasonic cleaner in the shock so that the silver particles fully dispersed to facilitate the washing. take the silver suspension in a centrifuge tube and centrifuge for 15 min using a high-speed centrifuge (6500 r / min). remove the supernatant and separate the precipitate again with water and ethanol. after the precipitate was washed and washed, it was placed on a surface dish and dried in an oven (40 ° c) for 12 h to obtain a product and the product was collected and stored. preparation and properties of silver nanoparticles 44 2.3.2 characterization of silver nanoparticles characterization of the product: x-ray diffraction (xrd), scanning electron microscopy (sem) and nano-laser particle size analyzer were used to characterize it. xrd: the silver nanoparticle powder was uniformly fi lled on a glass slide, covered and the surface was fl attened, and the sample was placed in the instrument. the instrument parameters are set to: target = cu voltage = 40kv current = 30ma scan rate of 2 ° / min, scan range of 10 ° 80 °, set up after the start scan sem characterization: the fi rst silver nanoparticle powder shocks fully dispersed, and then use a toothpick to pick a small number of samples applied to the stage, so that the powder paved evenly. after the preparation of the sample is placed in the instrument, respectively, in the magnifi cation of 10,000 times and 20000 times the case to observe the camera. nano-laser particle size analyzer: since the sample is powder, it must be pretreated to be tested. weigh 0.05 g of silver nanoparticles in a 5 ml plastic capsule, and then add 5 ml of ultra-pure water to the capsule, close the capsule and place it in an ultrasonic cleaner for 30 min after ultrasonic shock until the silver particles are fully diff used to obtain silver nano particle suspension. the resulting suspension was transferred to a quartz cuvette and tested. 2.3.3 electrocatalytic activity of silver nanoparticles 1). take 0.02 g of graphite powder in the surface dish, add 5 μl of liquid paraffi n mixed evenly, grinding to paste, fi lled into the ptfe tube, fi lling to ensure that the mixture is empty and smooth contact surface, at the other end a copper paste was inserted as a conductor to obtain a carbon paste electrode. 2) add 1 ml of liquid paraffi n to 0.002 g silver nanoparticle powder, encapsulate the mixture in a closed container, and place it in an ultrasonic cleaner for 30 min to prepare a uniform silver nanoparticle suspension. take 0.02 g of graphite powder in the surface dish, with a pipette to take 5μl suspension in the graphite powder mixed evenly, grinding to paste, fi lled into the ptfe tube, the same fi lling to ensure that the mixture is empty the contact surface is smooth and the copper wire is inserted into the copper wire as the conductor at the other end to prepare the carbon paste electrode modifi ed by silver nanoparticles. 3). the electrode was immersed in potassium ferrocyanide solution and the starting potential of the two electrode reactions and the current through the electrode were measured by cyclic voltammetry respectively. the data were recorded and plotted. the c-v parameter is set to: starting voltage -0.2v, maximum voltage 1v, minimum voltage -0.2v, scanning rate 0.05v / s, sensitivity 10-4a / v. 3. the experimental results and discussion the prepared silver nanoparticles are gray-black solid powders 3.1. characterization of x ray diff ractors pengfei xie, et al 45 fig 1 xrd diff raction of the silver nanoparticles x-ray diff raction measurements can be used to confi rm the presence of silver nanoparticles and to estimate their grain size [23]. it can be seen from fig. 1 that the four diff raction peaks on the curve appear at 2θ = 38.1 °, 44.3 °, 64.56 ° and 77.44 °, respectively. (111), (200), (220) and (311) planes, respectively, which can be judged to be silver crystals, and the peaks are clear and pure other peaks, indicating that the prepared samples were cubic-structured single-phase silver nanoparticles without any other impurities. the average grain size of the silver nanoparticles can be calculated using the x-ray diff raction peak scherrer formula: d = kλ / bcos2θ d is the average thickness of the crystal grains perpendicular to the crystal plane (nm) k is the scherrer constant, if b is the half width of the diff raction peak, k = 0.89; if b is the integral height of the diff raction peak, then k = 1 λ is an x-ray wavelength (cu target) of 0.154056 nm b is the diff raction peak of the measured sample θ is the diff raction angle, refl ected at 2θ = 38.1 °, 44.3 °, 64.56 ° and 77.44 °. the average particle size of the grains is 21.2 nm, which is 18.5 nm, 17.2 nm, 25.4 nm and 23.7 nm, respectively. 3.2. scanning electron microscopy (sem) characterization a b figure 2 silver nanoparticle sem image of the fi rst group (figure a for the amplifi cation of 10k times, figure b for the amplifi cation of 20k times) fig. 2 the fi rst group of the sem image of the silver nanoparticles (figure a is magnifi ed 10k times, and the b is magnifi ed 20k times). c d figure 3 sem chart of silver nanoparticles, the second group (figure c for the amplifi cation of 10k times, d figure for amplifi cation 20k times) fig 2 the second group of the sem image of the silver nanoparticles (figure c is magnifi ed 10k times, and the d is magnifi ed 20k times). figure 2 is a freshly prepared silver nanoparticle sem image, figure 3 for the preparation is completed, placed a week after the shot of the sem. preparation and properties of silver nanoparticles 46 it can be seen that the prepared silver nanoparticles are pineal crystal, the single pattern of the crystal form is symmetrical and the size is uniform and the dispersity is good. also, compared the four pictures, you can clearly fi nd the newly prepared and placed a week of silver nanoparticles sem diagram refl ects the morphology of the nature of the two are almost identical, there is no signifi cant diff erence can explain the preparation of this experiment has a good reproducibility and the preparation of the product of stable nature, a certain period of time basically no change. it is estimated that the particle size of the pineal silver nanoparticles is 50-100 nm by comparison with the sem scale. the coordination agent used in this experiment is citric acid, its existence is very important, is the key to the formation of nanoparticles. previous studies have shown that silver nanoparticles cannot be produced if an appropriate amount of complexing agent is not added to the agno3 solution when the silver nanoparticles are synthesized by electrochemical reduction [17]. i also confi rmed this by the control test, in the same experimental environment electrolysis did not join the citric acid agno3 solution, can be clearly observed in the graphite rod on the precipitation of silver-white large-size silver element particles, and not gray black fl uff y material. this is mainly due to the addition of complexing agent, the solution there is the following coordination dissociation balance: ag + complexing agent ag + + complexing agent under the action of the complexing agent, the free ag + in the solution is surrounded by and bound with the complex, and the concentration of ag + is controlled so that the rate of ag + reduction on the electrode is indirectly controlled to achieve the control of the generation of silver atoms rate, the preparation of nano-level silver particles. since citric acid contains an atom having a strong coordination ability such as a carboxyl group, it can function with ag +, so that the above object can be achieved. the shape of the synthesized silver nanoparticles is also related to the structure of the ligands used. citric acid contains carboxyl, only ag + electrolysis before the role of coordination, in order to control a certain degree of electrolytic reduction. dendritic crystals may be the cause of the fractal growth of particles, that is, within a certain range of particles through the diffusion, adsorption process, continuous growth, and finally grow into pine-like crystals. the results show that the crystal types of silver nanoparticles prepared by the use of different complexing agents are very diff erent in crystal form size. liao xuehong et al. use cysteine as the complexing agent, and the silver nanoparticles are spherical. ] it can be seen that the use of diff erent types and diff erent structures of the complex agent is to achieve the manual control of silver nanoparticles shape and size of the eff ective means. 3.3. nano laser particle size analyzer test particle size and distribution area particle size nm 125-140 140-158 158-177 177-199 interval% 16.88 34.56 33.5 15.06 accumulated% 16.88 51.44 84.94 100 15.1% 33.5% 34.6% 16.9% 125-140nm 140-158nm 158-177nm 177-199nm fig. 4 size and percentage distribution of silver nanoparticles as a result of the nano-laser particle size analyzer, the average particle size of the prepared silver nanoparticles was 157 nm and the particle size range was 125 nm to 199 nm. the results show that the size of silver nanoparticles is very consistent, the particle size is evenly distributed in a small range, a single crystal, successfully control the particle size and crystal structure, and the product is excellent. pengfei xie, et al 47 3.4. electronactivity test results of silver nanoparticles cyclic voltammetry was used to scan the two electrodes for cyclic voltammetry, as shown in the following fi gure fig. 5 comparison of cyclic voltammetry on carbon paste electrode blankcarbon pasteelectrode with silver nanoparticles modifi ed a is the cyclic voltammetry of the carbon paste electrode modified with silver nanoparticles b is the cyclic voltammogram of the blank carbon paste electrode. it can be seen from the above figures that the starting potential of the cv curve of the carbon paste electrode modifi ed with silver nanoparticles is lower than that of the blank carbon paste electrode, indicating that the reaction is easier to proceed and the electrode current is larger, indicating that the reaction proceeds the more intense. from this we can speculate that silver nanoparticles have an eff ect on the electrochemical activity of the carbon paste electrode, which can make it have better electrochemical performance. but the observation curve shows that before and after the modifi cation of the diff erence is relatively weak, given the interpretation of persuasive is not very adequate. the electrochemical knowledge and electrochemical experiments are limited. the experiment is only a preliminary exploration of the electrocatalytic activity of silver nanoparticles. further understanding is still to be studied and studied. 4. conclusion in this paper, high purity silver nanoparticles with uniform size, crystal symmetry and particle size of about 100 nm were prepared by electrochemical reduction method and citric acid as agent. agno3 solution was successfully prepared by cyclic voltammetry. it is concluded that silver nanoparticles have an effect on the electrode properties of carbon paste electrodes but need to be explored. it is very useful and promising method to prepare silver nanoparticles by electrochemical synthesis method. this method can be extended to the preparation of other metal nanoparticles, which is worthy of attention and sustainable development. references 1. zhang lide, mu jiemei nanomaterials [m], shenyang: liaoning science and technology press, 1994,1-6 2. he yan da. nanometer materials application and prospects [j], science and technology wind, 2010.1, (1): 195-196 3. journal of jinzhou teachers college; 2002-04,23 (3): 3-7 4. peng liling. nano-powder surface modification of the necessity and application 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people's liberation army master of medicine, academy of military medical sciences, 2011 23. liu xiaoli, et al. pvp as a protective agent for the preparation of ag nanoparticles [j], applied chemicals, 2014.8,43 (8): 13741376 characterization and application of nanomaterials (2019) volume 2 issue 2 doi:10.24294/can.v2i2.627 42  original research article the variations of hydrophilic self-cleaning properties and refractive index dependence in the zro2 thin films by gamma irradiation d. abayli, n. baydogan* energy institute, istanbul technical university, ayazaga campus 34469, istanbul, turkey. e-mail: dogannil@itu.edu. tr abstract zro2 thin film samples were produced by the sol-gel dip coating method. four different absorbed dose levels (such as ~ 0.4, 0.7, 1.2 and 2.7 gray-gy) were applied to zro2 thin films. hence, the absorbed dose of zro2 thin film was examined as physical dose quantity representing the mean energy imparted to the thin film per unit mass by gamma radiation. modification of the grain size was performed sensitively by the application of the absorbed dose to the zro2 thin film. therefore the grain size reached from ~50 nm to 87 nm at the irradiated zro2 thin film. the relationship of the grain size, the contact angle, and the refractive index of the irradiated zro2 thin film was investigated as being an important technical concern. the irradiation process was performed in a hot cell by using a certified solid gamma ray source with 0.018021 ci as an alternative technique to minimize the utilization of extra toxicological chemical solution. antireflection and hydrophilic properties of the irradiated zro2 thin film were slightly improved by the modification of the grain size. the details on the optical and structural properties of the zro2 thin film were examined to obtain the optimum high refractive index, self-cleaning and anti-reflective properties. keywords: absorbed dose; irradiation; optical properties; thin film; zirconium oxide article info article history: received 27 june 2019 received in revised form 23 july 2019 accepted 25 july 2019 available online 7 august 2019 copyright copyright © 2019 d. abayli et al. doi: 10.24294/can.v2i2.627 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/by/4.0/ 1. introduction thin films of zirconium oxide (zro2) have attracted attention due to their advantageous properties for future thin layers technology. zirconium oxide (zro2) possesses good dielectric, optical, mechanical and chemical properties. additionally, it exhibits high refraction index, very good transparency, great chemical stability and direct wide gap, with an optical band gap in the range of .0–5.85 ev[1,2]. hence, zro2 can be used in a wide range of applications such as optical filters, laser mirrors, barrier layers, buffer layers for super-conducting ceramics, as a biomaterial for prostheses, gas sensor, optical storage elements, scintillators and luminescent oxygen-sensors etc.[1,3]. pure or doped zro2 thin film continues to present sufficiently high thermoluminescence (tl) yield after irradiation with ionizing or ultraviolet (uv) radiation[3]. zro2 thin films with different morphologies are prepared by seve ral methods such as chemical vapor deposition (cvd), spray pyrolysis, reactive rf sputtering, polyol route, hydrothermal method bio-temp late method, ultra-sound assisted precipitation method, room temperature precipitation method, solution combustion method and sol–gel method[4,5]. among these techniques, the sol–gel method can be used in the production of the thin films for electronics and optics. the sol-gel 43  method is of particular intere the production of the thin films for electronics and optics. the sol-gel method is of particular interest because of several advantages such as its simplicity, low processing temperature, stoichiometry control and its ability to produce uniform, chemically homogenous films and the formation of multi and mixed layers[1,2]. the sol–gel process involves the preparation of a “sol” (mostly colloidal), the transformation of the sol into a solid “gel” phase and crystallization by heating at increased temperatures (calcination). the first and second stages determine a chemical composition and the calcination stage controls the phase evolution of zro2 from amorphous to nanocrystalline and crystalline phase transformation (monoclinic to tetragonal, etc.)[3]. the sol–gel process also allows the deposition of films and coatings with variable thick ness from nm to micrometer, in an easy and fast way, by the use of either dip-, spinor spray-coating procedures[6]. the zro2 thin film can be produced with refractive indices n ranging from 1.35 to 2.50 and film thicknesses d from 150 to 1500 nm. the zro2 thin film is hard, durable, and laser-damage resistant thin films with high refractive index and it is widely used to produce multilayered coatings, also for the uv spectral range[7] generation of energy by using clean and environmental-friendly technologies is one of the major aims in industrial and scientific areas. among the various coating techniques, the coating performed with sol–gel method is one of today’s environment protective methods. the sol-gel coating of zro2 att racts attention since it is an environmental-friendly coating method[8]. as the zrocl2ꞏ8h2o is low toxi city of zirconium salts low toxicity of zrocl2ꞏ8h2o makes the use of zrocl2ꞏ8h2o attractive at the pro duction of solution in this study. hence it was possible to avoid the use of high level chemical toxicity by minimizing the production of hazardous che mical solution waste. besides, more economical and environmentally friendly technologies are research ed to adopt more eco-friendly thin film production methods in industrial and scientific areas. the utilization of irradiation treatment at several production steps can be preferred as a practical and rapid process to obtain the efficient performance in the devices containing thin film[9]. in this study, the ionizing radiation effect on structural and optical properties was used in the zro2 thin film. therefore, the improvements in the structural and optical properties were obtained, avoiding the production of extra hazardous chemical solution waste. the irradiation treatment by using the gamma radiation was a key parameter to manage the optical constants and the grain sizes of the zro2 thin film to use them as protective and biomimetic layers. the agglomeration tendency of the irradiated grains at 0.7 gy has resulted with high refractive index and more hydrophilic properties. there was a relation between the refractive index and hydrophilic properties with the rise of the grain size of the irradiated zro2 thin film. 2. experimental part the sol-gel dip coating method at the production of the zro2 thin film seems a candidate as more ecolabel coating method than other zro2 thin film coating methods in the advance future economic coating technology for the industry[8]. zrocl2ꞏ8h2o is an attractive material in several procedures due to its low toxicity[10]. zro cl2ꞏ8h2o can be used for the environmentally frien dly methods[11]. hence, zirconium oxychloride octahydrate (zrocl2ꞏ8h2o) inorganic precursor solution (sigma aldrich puriss grade, ≥99.0%) was used for the production of zro2 thin films. all the substrates were cleaned with ethyl alcohol and rinsed with deionized water and they were sterilized with water vapour in an auto clave furnace (nuve ot 012 ben ch top steam sterilizer) then dried at 100°c in dry ing oven (binder ed 53). the solvent was determined as a mixture of 2-butanol and ethanol (in the ratio 1:1). homogeneous solution including zirconium oxychloride octahydrate (2 wt.%) was produced by mixing 1 mol of zirconium oxychloride octahydrate in 1/3 of the total volume of mixed 2-butanol and ethanol. the solution was stirred for 45 minutes by use of a magnetic stirrer (heidolph mr 3001k). water for hydrolysis and nitric acid for oxidation (water: hno3: acetylacetone = 20: 0.4: 3) were added to the salt–alcohol solution. the stirring was continued for another 90 minutes to obtain 44  clear and transparent solution. the precursor solution prepared at 60°c deposited on cleaned soda lime silicate glass substrates. dip coater (ksv dip coater lmx2) with computer controlled was used and the dip coating parameters were chosen as 10 cm/min lifting speed and 90° vertical lifting. the dip coated films were dried at room conditions and pre-fired at 150°c. this process of coating and dry ing was repeated for 9 times in a heater. zro2 film samples were annealed at 500°c for 1 h in air similar with the literature[12]. after the coating process, the remaining solution was stored in a dark glass b ottle to prevent the degeneration of solution and used within 60 days at the refrigerator. a certified co-60 radioisotope was used as a gamma ray source emitting the photons with two different energies (1.17 mev and 1.33 mev) to examine the rise of the absorbed dose effect on the optical properties. hence, the provided gamma ray beam was assumed as a monochromatic beam at ~ 1.25 mev. the used co-60 radioisotope had an activity level of 0.018021 ci and it was determined as an appropriate irradiation source to evaluate the changes in the structural and optical properties of the zro2 film samples. the absorbed dose level of the zro2 thin film was the important parameter as the cumulative dose for the thin film samples at the irradiation area. the properties of the used co-60 radioisotope were presented at the irradiation process of zro2 thin film samples in table 1. table 1. the properties of the co-60 radioisotope used in the irradiation of zro2 thin film radioisotope k (r m2/ci h) a (ci) t1/2 (y) e (mev) co-60 1.32 0.018021 5.27 1.17 and 1.33 in this study, the zro2 thin film samples were placed around the gamma irradiation source panoramically (in figure 1). the cumulative dose level of the sample was considered as the total dose resulting from the repeated exposures of the ionising radiation. because radiation fields can varies with several irradiation conditions (geometry or time) for a period of time[9]. hence, four different absorbed dose levels were obtained such as ~ 0.4, 0.7, 1.2 and 2.7 gy to examine the details of the changes in the optical and structural properties. all of the irradiation tests were conducted at room temperature. figure 1. irradiation settlement of the zro2 thin film samples. the thicknesses of the zro2 thin film samples were determined by using veeco dektak 6m stylus sur face profilometer after the optical properties of zro2 thin films prepared by sol-gel method were determined employing transmittance and reflectance spectrophotometry in uv and vis range between 190–1100 nm by using pg instruments t80 uv-vis spectrophotometer. thickness measurement was obtained from the coated to the uncoated part of the glass. therefore, the thickness of the thin film was determined as ~ 80 nm[13]. the use of the ionizing radiation was a key parameter to limit the chemical solution toxicity without the generation of the extra hazardous chemical solutions at the environment. 3. results and discussion the surface morphology of the film was examined using 2d scanning electron microscope (sem). there were voids between the grains in some areas of surface as depicted in figure 2(a)-(d). the surface of the irradiated zro2 thin film at 0.4 gy was composed of the equaxial grains (~50 nm) in figure 2(a). the dimension of grains in which induced by gamma irradiation at 0.7 gy had ~ 87.3 nm in figure 2(b) and their dimension was the highest one with respect to the dimension of grains in other ones. the dimension of the grains was ~ 74.5 nm and decrease on the surface of the film at irradiation source 45  1.2 gy in figure 2(c) and the dimension of grains is ~ 64.8 nm of the film at 2.7 gy in figure 2(d). while the grains separated to more small grains due to the absorbed dose of the film, they started to gather and piled up at several places on the surface of the films at 1.2 gy and 2.7 gy. the changes of beta transmission of the zro2 thin films supported the variation of the grain size in our previous study[13]. the properties of the surface started to change obviously at 0.7 gy. the absorbed dose of 0.7 gy was important to investigate the optical constants of the thin film. it was interesting to note that when the absorbed dose of the specimen reached to 1.2 gy, the dimension of the grains decreased again. moreover, the gathering of the grains in the induced film took place more obviously at the certain places. on the surface of the films in figure 2(c-d). the gathering of the grains at the surface of the film increased when the absorbed dose increased. but it was determined that there was the combination of grains with each other on the surfaces of irradiated specimens. the change of the valance state of impurity atoms in the irradiated thin film can be explained with the formation of new electronic order in defect centers as the result of the new configuration of the ions while the gathering of small grains with the rise of the absorbed dose in the thin film structure. (a) (b) (c) (d) figure 2. sem images of the zro2 thin film irradiated at (a) 0.4 (b) 0.7 (c) 1.2 2.7 gy. the changes in transmittance (in figure 3) and reflectance (figure 4) of the irradiated zro2 thin film samples were examined with the rise of the absorbed dose. the colour of the irradiated zro2 thin film samples changed to darker colour tones with rise of the absorbed dose. the transmittance of the irradiated zro2 thin films decreased with the rise of the grain size. besides, the transmittance shi fted towards the higher wavelength (red shift) in uv range as the absorbed dose increased. this behaviour is compatible with the decrease in transparency of the irradiated zro2 thin films depending on the improvement of the optical absorbance. the red shift of the irradiated zro2 thin film at 0.7 gy (in figure 3) distinguished clearly with the improvement of the optical absorbance (in figure 5) as the irradiated thin film (at 0.7 gy ) reached maxi mum grain size from ~50 nm to 87 nm. however, there is not considerable information on the details of the changes in optical constants of the irradiated zro2 thin film by gamma radiation in previous studies[14]. the rise of the grain size resulted with the decrease of the optical transmittance of the irradiated thin film (at 0.7 gy). the rise of the grain size resulted with the decrease of the reflectance of the zro2 thin film. the minimum reflectance of the thin film irradiated at 0.7 gy was determined at the film with maximum grain size reached from ~ 50 nm to ~ 87 nm. the reason of this was the decrease of the grain boundaries around the course grains. the changes in refractive index of the zro2 thin film samples irradiated at different absorbed dose levels were determined from the transmittance according to swanepoel’s envelope method in this study. the details on the determination of the refractive index were presented in the previous studies[15]. the interference fringes shifted towards the higher wavelength (red shift) region. swanepoel’s envelope method stated the minimum and maximum envelops of transmittance spectrum in the weak and medium absorption regions; extrapolating the graph of the refractive index at the strong absorption region in the literature[16]. the optical constants of zro2 thin films were affected by the gamma irradiation. it was possible to determine the ch anges in optical constants such as the refractive in46  dex (n) (in figure 6), extinction coefficient (k) (in figure 7) and absorption coefficient () (in figure 8) with the rise of the grain size in this study. there were the increases in n, k and  values of the irradiated zro2 thin film as the result of the increase in grain size (in figure 2). the rises of n, k and  were related with the enhancement of optical absorption as the result of the controlling of the absorbed dose. the increase of the optical constants of the irradiated films was related with the gathering of the grains at the surface of the film with the controlling of the absorbed dose according to the sem images (in figure 2). photoluminescence (pl) stu dies provide information about the electronic band transitions, structure, defects and chemical composition of the optical materials[2]. the exciton lumen escence and intrinsic defects related luminescence are known in a number of oxides. for zro2, the ph otoluminescence is of much interest for both theoretical and experimental investigations. there are some references to make an evaluation between the results of this study and results in literature by using different irradiation sources. a broad pl emission is observed at ~ 480 nm for zro2 structures after the samples are induced by uv irradiation in the literature[2]. the refractive index increases with the reduction of the transmittance of the films as the absorption region of the transmitance spectra rises to wards higher wavelenght region, in the previous study of berlin et al.[5]. in this study, it was determined that there were the dramatic changes in optical constants at ~ 480 nm. the photoluminescence effect at ~ 480 nm supported the rise of the optical transmittance and decrease of the optical absorbance slightly depending on the increase of the scattered photons. besides, the decrease of the optical absorbance has led the decrease of the optical constants over ~ 480 nm. it was thought that the improvement of the grain sizes in irradiated zro2 thin film at 0.7 gy indicated the enhancement of the ph otoluminescence effect dominantly at the coarse gr ains with 87 nm. (a) (b) figure 3. (a) the changes in transmittance of the irradiated zro2 thin film; (b) the details on the changes in the transmittance. (a) (b) figure 4. (a) the changes in reflectance of the irradiated zro2 thin film; (b) the details on the changes in the reflectance. 47  figure 5. the changes in optical absorbance of the zro2 thin film. figure 6. the changes in the refractive index, n of the irradiated zro2 thin films. figure 7. the changes in extinction coefficient, k of the irradiated zro2 thin film. figure 8. the changes in absorption coefficient, of the irradiated zro2 thin film. figure 9. the relation between static water contact angle and refraction index of the zro2 films. the surface contact angle of the zro2 thin film was determined by using a contact angle measurement instrument. the contact angle values of the thin film decreased slightly and a minimum value of around 24.62° was obtained with the increase of the grain size when the absorbed dose was set to 0.7 gy. the rise of the grain size led to increase the surface roughness and the decrease of contact angle values of the thin film resulted with the improvement of the hydrophilic properties. hence, the contact angle was decreased by irradiation and wettability of hydrophilic nanostructured zro2 surface was modified slightly with increasing surface roughness. the nanoscale roughness having coarse grains (~87 nm) has influenced the surface wettability slightly at 0.7 gy. the zro2 thin film derived on soda-lime glasses has presented a relation between the refractive index and hydrophilic properties as the result of the change in the size of the grains. 48  4. conclusions the zro2 thin film was derived from zro cl2ꞏ8h2o (which is low toxicity of zirconium salt s) by using sol-gel dip coating method as it is a green friendly alternative coating method. the irradiation treatment has played a role in the enhancement of the optical constants (such as refractive in dex, the extinction coefficient and absorption coefficient) of the zro2 thin film. the improvement in the irradiated grain size supported to rise the refractive index by minimizing the production of ha zardous chemical solutions. the rise of the grain size of the irradiated zro2 thin film improved the optical constants. there was a relation between the induced optical constants and the gathering of the irradiated grains by gamma radiation. the red shift in uv range by using gamma irradiation was enhanced with the rise of the grain size. it was possible to control the dimension of grains with the applied absorbed dose. the agglomeration tendency of the irradiated grains has enhanced slightly the refractive index and hydrophilic properties of the zro2 thin film. the grain size reached a maximum value from ~50 nm to 87 nm when the absorbed dose of zro2 thin film attained to 0.7 gy. references 1. bensouyad h, sedrati h, dehdouh h, et al. structural, thermal and optical characterization of tio2: zro2 thin films prepared by sol–gel method. thin solid films 2010; 519(1): 96–100. 2. joy k, berlin ij, nair pb, et al. effects of annealing temperature on the structural and photoluminescence properties of nanocrystalline zro2 thin films prepared by sol–gel route. journal of physics and chemistry of solids 2011; 72(6): 673–677. 3. chernov v, belykh a, meléndrez r, et al. beta radiation induced thermoluminescence in pure zro2 prepared by sol–gel. journal of non-crystalline solids 2006; 352(23-25): 2543–2547. 4. ravichandran at, catherine s, ravichandran k, et al. effect of al doping on the structural and optical properties of zro2 nanopowders synthesized using solution combustion method. superlattices & microstructures 2014; 75: 533–542. 5. berlin ij, lekshmy ss, ganesan v, et al. effect of mn doping on the structural and optical properties of zro2 thin films prepared by sol–gel method. thin solid films 2014; 550: 199–205. 6. garcia rbr, silva fs, kawachi ey. new sol–gel route for sio2/zro2 film preparation. colloids and surfaces a: physicochemical engineering aspects 2013; 436: 484–488. 7. jerman m, qiao z, and mergel d. refractive index of thin films of sio2, zro2, and hfo2 as a function of the films’ mass density. applied optics 2005; 44(15): 3006–3012. 8. li q, zhong x, hu j, et al. preparation and corrosion resistance studies of zirconia coating on fluorinated az91d magnesium alloy. progress in organic coatings 2008; 63(2): 222–227. 9. baydogan n, ozdemir o, cimenoglu h. the impro vement in the electrical properties of nanospherical zno: al thin film exposed to irradiation using a co-60 radioisotope. radiation physics & chemistry 2013; 89: 20–27. 10. mishra s, ghosh r. ecofriendly and sustainable eff icient synthesis of bis(indolyl)methanes based on recyclable brønsted (csa) or lewis (zrocl2.8h2o) acid catalysts. indian journal of chemistry; 2011; 50: 1630–1636. 11. jafarpour m, rezaeifard a, heidari m. a new catalytic method for eco-friendly synthesis of quinoxalines by zirconium (iv) oxide chloride octahydrate under mild conditions. letters in organic chemistry 2016; 8(3): 202–209. 12. berlin ji, lakshmi js, lekshmy ss, et al. effect of sol temperature on the structure, morphology, optical and photoluminescence properties of nanocrystalline zirconia thin films. journal of sol-gel science and technology 2011; 58(3): 669–676. 13. abayli d, baydogan n. the characterization of the irradiated zro2 transparent thin films. procedia — social and behavioral sciences 2015; 195: 2117– 2121. 14. abayli d, baydogan n. the changes in optical absorbance of zro2 thin film with the rise of the absorbed dose. book of abstracts of 9th international physics conference of the balkan physical union. istanbul, tr; 2015 august 24-27. p.175. 15. baydogan n, ozdurmusoglu t, cimenoglu h, et al. refractive index and extinction coefficient of zno: al thin films derived by sol-gel dip coating technique. defect and diffusion forum 2013; 334-335: 290–293. 16. larijani mm, hasani e, safa s. annealing temperature effect on the optical properties of thermally oxidized nano-crystalline zro2 thin films grown on glass substrates. applied surface science 2013; 290: 490–494. can v2i2 2019 4 can v2i2 2019 5 can v2i2 2019 6 can v2i2 2019 7 can v2i2 2019 8 can v2i2 2019 9 can v2i2 2019 10 characterization and application of nanomaterials 2025, 8(2), 11330. https://doi.org/10.24294/can11330 1 article role of aluminium doping in tailoring the structural, electrical, and magnetic characteristics of li-co ferrites using sol-gel auto-combustion synthesis khushal p. mudholkar1, madhu g. kottad1, shivanand v. angadi1, lingaraj d. horakeri1, sushant s. kakati2, shridhar n. mathad2,*, chidanandayya s. hiremath3, rangappa b. pujar1, mahesh s. bannur4 1 department of physics, p. c. jabin science college, hubballi 580021, india 2 department of engineering physics, k. l. e. institute of technology, hubballi 580027, india 3 department of physics, s. k. arts and h. s. kotambari science institute, hubballi 580021, india 4 department of physics, a. g. m. rural college of engineering and technology, varur, hubballi 581207, india * corresponding author: shridhar n. mathad, physicssiddu@gmail.com, physicssiddu@kleit.ac.in abstract: this study examined the impact of aluminium doping on the structural, electrical, and magnetic properties of li(0.5)co(0.75)alxfe(2−x)o4 spinel ferrites (x =0.15 to 0.60). the samples were synthesised using the sol-gel auto-combustion technique, and they were examined using x-ray diffraction (xrd), scanning electron microscopy (sem), fouriertransform infrared spectroscopy (ftir), dielectric measurements, and vibrating sample magnetometry (vsm). all samples possessed a single-phase cubic spinel structure with fd-3m space group, according to xrd analyses. sem images showed the creation of homogeneous particles with an average size of about 21 nm. all samples had spinel ferrite phases, confirmed from ftir spectra. dc electrical conductivity studies showed that the conductivity increased with increasing aluminium content up to x = 0.45 before dropping at x = 0.60. the maximum saturation magnetization value was found at x = 0.45, according to vsm measurements, which demonstrated that the magnetic characteristics were strongly correlated with the amount of aluminium. keywords: ferrites; structural studies; morphology; magnetic materials 1. introduction ferrites are a class of magnetic materials with a wide range of technological applications, including in microwave devices, transformers, and magnetic recording media [1]. ferrites are typically composed of iron oxide (fe2o3) and other metal oxides, such as zinc oxide (zno) or nickel oxide (nio). the properties of ferrites can be tailored for specific applications by doping them with various metal ions. aluminium (al)-doped lithium cobalt (li-co) ferrites are a class of magnetic materials that have gained increasing attention in recent years due to their potential applications in various fields such as microwave absorption [2], magnetic recording [3], and electromagnetic interference (emi) shielding [4]. these materials are composed of a ferrimagnetic spinel structure with a general formula of lico1−xalxfe2o4, where x represents the al doping concentration. the al doping in li-co ferrites results in a significant enhancement in the magnetic properties, such as the saturation magnetization and the coercive field, as well as an improvement in the microwave absorption characteristics. the synthesis of al-doped li-co ferrites can be achieved through various citation mudholkar kp, kottad mg, angadi sv, et al. role of aluminium doping in tailoring the structural, electrical, and magnetic characteristics of li-co ferrites using sol-gel auto-combustion synthesis. characterization and application of nanomaterials. 2025; 8(2): 11330. https://doi.org/10.24294/can11330 article info received: 14 january2025 accepted: 20 march2025 available online: 19 may 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 11330. 2 methods such as solid-state reaction [1], sol-gel[5], the co-precipitation method [6], and hydrothermal synthesis[7]. among these methods, the solid-state reaction method is the most commonly used due to its simplicity and cost-effectiveness. in this method, the starting materials, such as licoo2, coo, fe2o3, and al2o3, are mixed together in a desired proportion and heated at a high temperature for several hours. the final product is then cooled and ground to a fine powder. the magnetic properties of aldoped li-co ferrites are strongly influenced by the al doping concentration. the saturation magnetization increases with increasing al doping concentration, reaching a maximum at x = 0.1. this is due to the substitution of al3+ ions for co2+ ions in the ferrite structure, which results in a decrease in the average spin state of the co ions and a corresponding increase in the magnetic moment. the coercive field also increases with increasing al doping concentration, which indicates an improvement in the magnetic stability of the material [8–12]. in addition to the magnetic properties, al-doped li-co ferrites have been found to have excellent microwave absorption characteristics [9]. the absorption peak of these materials is found to be in the range of 2–18 ghz, making them suitable for use in the microwave frequency range. the absorption performance is also found to improve with increasing al doping concentration, which is attributed to the enhancement of the magnetic loss caused by the substitution of al3+ ions for co2+ ions. the emi shielding performance of the al-doped li-co ferrites is also found to be good [13]. emi is the unwanted interference caused by electromagnetic radiation and it is a major concern in many electronic devices. the shielding effectiveness of these materials is found to increase with increasing al doping concentration, which is attributed to the improvement in the magnetic properties as well as the increase in the electrical conductivity caused by the substitution of al3+ ions for co2+ions.furthermore, the aldoping in li-co ferrites is found to affect the microstructure of the materials. the aldoping leads to the formation of smaller grain size and more homogeneous distribution of the grains. this can lead to an improvement in the mechanical properties of the materials [14]. the al-doped li-co ferrites are a promising class of magnetic materials that have a wide range of potential applications due to their excellent magnetic and microwave properties. the al-doped li-co ferrites concentration was synthesized by the autocombustion method. the detailed structural studies were done through xrd, sem, edax, and ftir studies. dielectrical, ac conductivity, and magnetic properties of these ferrites are also studied and controlled to optimize the properties of these materials for specific applications. 2. experimental 2.1. samples preparation the sol-gel auto combustion method is a commonly used technique for synthesizing oxide materials, including spinel ferrites such as li0.5co0.75alxfe2−xo4 (x = 0.15, 0.30, 0.45, and 0.60). here are the steps to synthesize this material using the sol-gel auto combustion method: characterization and application of nanomaterials 2025, 8(2), 11330. 3 2.2. preparation of precursor sol the first step in the process is the preparation of a precursor sol, which is a stable colloidal suspension of nanoparticles in a liquid medium (water). in this case, the precursor compounds used are lino3, co(no3)2∙6h2o, al(no3)3∙9h2o, fe(no3)3∙9h2o, and c6h8o7∙h2o form sd fine-chem ltd (india). these compounds are dissolved in a suitable solvent (water)used to prepare the sol. a stabilizing agent, such as citric acid, is also added to prevent the agglomeration of nanoparticles. lino3 + co(no3)2∙6h2o + al(no3)3∙9h2o + fe(no3)3∙9h2o + c6h8o7∙h2o → li-co-al-fe-citrate + no2 + h2o 2.3. gelation the sol is then subjected to a gelation process, which transforms the liquid sol into a solid gel matrix. gelation can be achieved by several methods, including evaporation, cooling, or chemical crosslinking. in this case, the gelation is achieved by heating the sol at a temperature of around 80°c for several hours until a solid gel is obtained. li-co-al-fe-citrate → li-co-al-fe-citrate gel 2.4. auto-combustion the solid gel matrix was initially heated at 120℃ to remove excess water, followed by auto-combustion at approximately 250°c, and final sintering at 800°c for 4 h. the solid gel matrix is then heated to a high temperature to trigger the autocombustion process. this process involves an exothermic chemical reaction between the precursor compounds and the stabilizing agent, which generates heat and produces the desired oxide products. in the first step, c6h8o7∙h2o (citric acid) acts as a fuel and reacts with lino3 to produce li5c6h3o7 (lithium citrate), no2, and h2o. the lithium citrate then reacts with the metal nitrates to form the desired oxide products, along with co2, h2o and no2. the exact stoichiometry and properties of the final product depend on the composition and combustion conditions used in the process. 2.5. final product formation li-co-al-fe-citrate gel → li0.5co0.75alxfe2−xo4 + co2 + h2o + no2 the heat generated during the auto-combustion process at ambient air causes the solid products to crystallize and form li0.5co0.75alxfe2−xo4(x= 0.15, 0.30, 0.45, and 0.60). 3. results and discussion 3.1. powder xrd analysis x-ray diffraction (xrd) of samples done by rigaku smartlab se (fully automated computerized powder xrd); x-ray tube: cuangular range (2θ): 2° to 80° with cu-kα radiation (λ = 1.5406 å). the powder specimen of the crystal can be thought of as a group of microscopic crystals that are randomly oriented and present a range of glancing angles to the incident beam. there can only be one value of the characterization and application of nanomaterials 2025, 8(2), 11330. 4 glancing angle that fulfils the equation 2dsin = n, where n = 1, for a given wavelength and a given value of d. such reflected beams, which are slanted at an angle of 2 with the direction of the incident beam, radiate out from the specimen in all directions. 𝑑 = 𝑎 √ℎ2+ 𝑘2+𝑙2 å. where, a = lattice constant, (hkl) = miller indices. the lattice constant is calculated by the relation [14,15], 𝑎 = 𝜆 2sin𝜃 √ℎ2 + 𝑘2 + 𝑙2 where, λ = wavelength of monochromatic x-rays, = glancing angle. knowing the values of and (hkl), the lattice constant may be computed for the prominent line in the spinel diffraction pattern, which corresponds to the (311) plane. we may determine the interplanar spacing by obtaining the values of the miller indices and lattice constant. 𝑑 = 𝜆 2sin𝜃 or𝑑 = 𝑎 √ℎ2+𝑘2+𝑙2 where, λ = wavelength of cu-kα (1.5406 å),= glancing angle. the average particle size of each sample is calculated from the relation [16]. 𝐷 = 0.9𝜆 𝛽cos𝜃 . β= full width half maximum corresponding to the highest peak of the (311) plane. similarly, dislocation density(ρ), lattice strain(ε), and porosity(p) are calculated from the following relations [17]. 𝜌 = 1 𝐷2 , 𝜀 = 𝛽cos𝜃 4 , 𝑃 = 𝑑𝑥−𝑑𝑎 𝑑𝑥 × 100, 𝑑𝑥 = 𝑋 − ray density = 𝑍𝑀 𝑁𝑎3. hopping lengths (la and lb), tetrahedral location for a,𝐿𝐴 = √3 4 𝑎 å. octahedron location for b, 𝐿𝐵 = √2 4 𝑎 å. where z is the number of molecules per cell, n is avogadro’s number (6.02×1023), ais the lattice constant, and da is the actual density, which is equal to the mass divided by the volume of the pellet in grams. the x-ray diffraction (xrd) patterns of the li(0.5)co(0.75)alₓfe(2−x)o4 spinel ferrites are presented in figure 1. all samples exhibit a face-centered cubic (fcc) spinel structure, with no detectable secondary phases, confirming the formation of a single-phase material. the absence of any impurity peaks further supports the phase purity of the synthesized ferrites. among the diffraction peaks, the (311) plane is observed to have the highest intensity, which is characteristic of spinel ferrites and consistent with previously reported data. the indexed diffraction peaks correspond to the (111), (220), (311), (222), (400), (422), (511), and (440) planes, aligning well with standard spinel ferrite patterns and reinforcing the structural integrity of the material. characterization and application of nanomaterials 2025, 8(2), 11330. 5 the lattice parameters, calculated using bragg’s law, exhibit a close correlation with the experimentally observed interplanar spacings, as summarized in table 1. this agreement validates the precision of the structural analysis and confirms the successful incorporation of al3⁺ into the spinel lattice. figure 1.xrd patterns of li0.5co0.75alxfe2−xo4(x= 0.15, 0.30, 0.45, and 0.60). the variation of lattice parameter with composition is shown in table 1. from the table it is observed that the lattice constant (a) decreases with an increase in composition. which is attributed to the fact that as composition al increases, the amount of fe decreases. because the ionic radius of al3+ (0.53 å) is less than that of fe3+(0.77 å), hence the lattice constant tends to decrease with composition, obeying vegard’s law. the observed deviation in lattice parameter is due to the rearrangement of al and fe ions. the variation of crystallite size with composition is depicted in table 1. from the table, it is observed that the crystallite size nearly varies from 9 nm to 28 nm. the size is found to decrease with an increase in the composition of al. the porosity varies from 23% to 48% depending upon the method of preparation, purity of samples, and sintering temperature (table 1). it is due to the fact that x-ray density is greater than that of actual density because of the presence of pores in the material, depending on the method of preparation and sintering condition. table 1. data on lattice constant, average particle size, dislocation density, lattice strain, and x-ray density. composition, x lattice constant, å avg. particle size, d in nm dislocation density, ρ in ×1016m−2 lattice strain, ε×10−3 x-ray density, dx (g/cc) hopping length laå lbå 0.15 8.3462 29 0.121 1.218 5.004 3.613 2.950 0.30 8.3408 20 0.283 1.845 4.912 3.611 2.948 0.45 8.3528 15 0.437 2.293 4.781 3.616 2.952 0.60 8.3663 9 1.274 3.913 4.752 3.600 2.939 characterization and application of nanomaterials 2025, 8(2), 11330. 6 3.2. ftir analysis figure 2 presents ftir spectra. the vibration mode of the space group fd3moℎ 7 exhibits four ir active fundamentals in the spinel ferrites with fcc structure. the largest restoring force is associated with the inherent vibrations of tetrahedral complexes, whereas bond-bending vibrations are associated with octahedral complexes. hence, it is anticipated that 𝜈1 > 𝜈2. table 2 displays two distinct lines in the ranges of 572 cm−1 to 539 cm−1 and 496 cm−1 to 455 cm−1, respectively. fe3+–o2− distance changes in the octahedral and tetrahedral complexes may be the cause of the minor shift in frequency with composition. due to the presence of fe2+, which locally causes lattice deformation because of a non-cubic component of the crystal field potential, the jahn-teller effect splits the bands 𝜈1and 𝜈2. in contrast, fe3+ ions don’t have these effects [18,19]. figure 2. ftir spectra of li0.5co0.75alxfe2−xo4. table 2. data on ftir absorption bands of li0.5co0.75alxfe2−xo4 ferrites. composition, x absorption bands 𝝂𝟏 (cm−1) 𝝂𝟐 (cm−1) 0.15 539 455 0.30 555 457 0.45 539 455 0.60 535 455 3.3. scanning electron microscope analysis the samples’ sem (jeol jsm/jsm-it500la, magnification up to 300,000×resolution: 3nm acc. voltage up to 30kv max. specimen size: 200mm dia×75mm height (fully computer-controlled carbon, gold coating) micrographs are shown in figure 3. the features shown in these micrographs are as follows. the sample’s porosity ranges from 23% to 48% since the sol-gel process was used to characterization and application of nanomaterials 2025, 8(2), 11330. 7 prepare them. the size of the grain varies between 17 and 26 m depending on the heat treatment. if x=0.15, the largest grain size is discovered. at the base of the neck and the neck, porosity forms as a result of uneven diffusion rates. the characteristic microstructure of ferrites, in which residual porosity manifests in intra granular space, is the outcome of the mechanism of pore expansion in conjunction with grain growth. table 3 shows that average grain diameter reduces as aluminium content rises. the presence of a particular number of metal ion vacancies brought on by the oxidation of a suitable dopant is what causes the diameter to expand [20,21]. figure 3. sem spectrum of the li0.5co0.75alxfe2−xo4. table 3. data on actual density, porosity, and grain size. composition ‘x’ actual density g/cc porosity ‘p’% average grain diameter ‘d’ in µm 0.15 3.136 23.10 25.9 0.30 3.179 39.73 22.70 0.45 3.042 36.37 20.22 0.60 2.452 48.42 17.48 characterization and application of nanomaterials 2025, 8(2), 11330. 8 figure 4. eds analysis of the li0.5co0.75alxfe2−xo4. the elemental composition of the synthesized ferrites was confirmed using energy dispersive x-ray spectroscopy (eds). the edx sample peaks are shown in figure 4, revealing that the fcc structure is formed without any impurity. the identified elements from the edx are co, al, fe, and o, in which lithium (li) is absent. lithium is a light element with a low atomic number and is typically not detected using eds due to its weak x-ray emission and other elements detected listed in table 4. table 4. the percentage of trace elements present in the ferrite. x 0.15 0.30 0.45 0.60 elements weight% atomic% weight% atomic% weight% atomic% weight% atomic% c k 3.53 7.90 3.97 8.73 2.97 6.50 4.64 10.03 o k 33.01 55.42 32.62 53.77 33.67 55.37 33.14 53.77 mg k 8.26 9.13 8.76 9.51 9.03 9.77 7.33 7.82 al k 1.95 1.94 4.33 4.23 5.49 5.35 5.77 5.55 fe l 53.24 25.61 50.32 23.76 48.84 23.01 49.13 22.83 3.4. dielectric properties analysis the sample in pellet form is used to measure capacitance (cp) and dielectric loss (ε) at room temperature in the frequency range from 20hz to 1mhz by the two-probe method (hioki-im3570 high-precision impedance analyzer interfaced to a computer in the frequency range from 4 hz to1 mhz). the dielectric constant is calculated by the relation [22]. ∈= 𝐶𝑝𝑡 ∈0𝐴 . where, cp—capacitance of the parallel plate capacitor in farad, t—thickness of the pellet in meter,∈0—permittivity of free space in si unit, a—area of cross section of characterization and application of nanomaterials 2025, 8(2), 11330. 9 pellet in m2. the ac conductivity is related to dielectric relaxation, caused by localized electric charges. the frequency-dependent ac conductivity is calculated from the relation: 𝜎𝐴𝐶 = 2π𝑓 ∈0∈. where, f = frequency of applied electric field in hz, ∈0—permittivity of free space in si unit,∈—dielectric constant. all the samples exhibit dispersion (figure 5a,b) in dielectric constant in the frequency range of 20 hz to 1 mhz. beyond this range, it does not remain constant; it may be constant above 5 mhz. the dispersion in dielectric constant obeys maxwellwagner type interfacial polarization, in agreement with koop’s phenomenological theory. the large values of the parameter at low frequency are due to space charge polarization at grain boundaries, interfacial dislocation, oxygen vacancies, grain defects and predominance of large fe3+ ions [23] and abstraction belonging to the polarization due to changes in valence states of cations and space charge polarization. at higher frequencies the dielectric constant remains independent of frequency (f) due to the lack of ability of electric dipoles to follow the fast variation of the alternating applied electric field [24].when grain size decreases, grain boundary area and porosity decrease, but in this case, porosity increases due to many effects like method of preparation, sintering condition, etc. this substitution of lithium affects grain growth, typically leading to a reduction in particle size, which in turn influences dielectric behavior. smaller particles increase grain boundary resistance, thereby enhancing dielectric constant and loss at lower frequencies. the decrease in the parameter with frequency is due to lagging of polarizability behind the applied field at higher and higher frequency. due to impurities and flaws in the crystal lattice, polarization sometimes lags behind the applied ac field, which results in dielectric loss [17,22– 24]. the period of rest, which is comparable to the applied field duration, is what causes the most loss. the dielectric becomes tiny if the relaxation time is longer than the applied field period, and vice versa. the ac conductivity of li-co ferrites generally increases with increasing frequency, exhibiting semiconducting behavior due to hopping mechanisms of charge carriers, especially electrons between fe2+ and fe3+ ions shown in figure 5c. the conduction mechanism in ferrites is due to electrons and polarons following the hopping model suggested by austin and moot. the inverse tangential increase in conductivity with frequency is attributed to small polarons. such behavior is found in all the ferrite samples. the variation in hopping length is the distance between ions in a and b sites, which governs the conduction mechanism as shown in table 5. the same reports have been reported in the case of li-ni-cu nano ferrites [17]. characterization and application of nanomaterials 2025, 8(2), 11330. 10 figure 5. dielectric studies of li0.5co0.75alxfe2−xo4 nano ferrites (a) dielectric constant; (b) dielectric loss factor; (c) ac conductivity. table 5. data on porosity, hopping length, and ac conductivity at 1 mhz. composition, x lattice constant, a å porosity, p % ac conductivity, σ sm−1 0.15 8.3482 23.10 28,513.712 0.30 8.3408 39.73 50,295.760 0.45 8.3528 36.37 21,300.360 0.60 8.3163 48.42 12,199.196 3.5. magnetic properties analysis the specification of the vsm analyzer: lakeshore, model: 7410 series. the variation of saturation magnetization vs. alternating magnetizing field of all the samples at room temperature (300 k) is shown in figure 6. the data on saturation magnetization, magnetic moment, and hc are given in table 6. characterization and application of nanomaterials 2025, 8(2), 11330. 11 figure 6. magnetic properties study of li0.5co0.75alxfe2−xo4 nano ferrites. table 6. different magnetic parameters for all al-substituted li-co ferrites. composition, x molecular weight, m saturation magnetization, ms 𝝁𝑩 coercivity (hc) (oe) porosity 0.15 219.02 3.97 0.1556 512 37.36 0.30 214.69 1.33 0.0511 498 46.06 0.45 210.36 1.43 0.0538 473 36.37 0.60 206.03 1.36 0.0501 447 52.71 the variation of magnetic moment with al can be explained as follows. both al and li are nonmagnetic in nature. as the amount of al increases, the amount of fe3+ ions on both a and b sites decreases. as a result, magnetization goes on decreasing with an increase in al. however, the variation of ms with composition is attributed to the density of the sample. this then results in the weakening of a–b exchange interactions and decreases the saturation magnetization. at x = 0.15, it exhibits the highest saturation magnetization (~4 emu) due to the strong fe3⁺–o2⁻–fe3⁺ super exchange interactions. as al3⁺ substitution increases (x = 0.30 to 0.60), the magnetization decreases because non-magnetic al3⁺ ions replace fe3⁺, weakening the overall magnetic interactions. this substitution disrupts the spin alignment, leading to a decline in the net magnetic moment. this then results in the weakening of a–b exchange interactions and increases the saturation magnetization [25–27]. due to polarization effects, they prefer tetrahedral and octahedral sites, and the presence of non-magnetic lithium-aluminium ions in these sites results in lower values than both sites and consequently enhancement of ms values [27–29]. similarly, the coercivity is highest for x = 0.15, indicating hard magnetic behavior. as al3⁺ content increases, it decreases, suggesting a transition to a softer magnetic nature. this reduction in coercivity results from the dilution of magnetic interactions and a decrease in anisotropy, making the material easier to magnetize and demagnetize. the observed changes confirm that al3⁺ substitution significantly influences the structural and magnetic properties of li(0.5)co(0.75)alₓfe(2−x)o4 spinel ferrites. microstructure is a significant additional aspect that affects ferrites’ ability to magnetize. every grain possesses a unique magnetic moment. the magnetic circuits between the grains are characterization and application of nanomaterials 2025, 8(2), 11330. 12 broken by the pores. as a result, there are net reductions in magnetic moment and an increase in porosity. smaller numbers of big grains are formed at higher a sintering temperature, which reduces porosity. hence, magnetism rises as sintering temperature rises [26–29]. 4. conclusion in conclusion, the study investigated the effects of aluminium doping on the structural, electrical, and magnetic properties of li(0.5)co(0.75)alxfe(2−x)o4 spinel ferrites (x =0.15 to 0.60) synthesized using the sol-gel auto-combustion technique. the results showed that the samples had a single-phase cubic spinel structure with fd-3m space group, confirmed by xrd analysis. sem images showed the creation of homogeneous particles with an average size of about 21 nm. ftir spectra confirmed the presence of spinel ferrite phases in all samples. the dc electrical conductivity increased with increasing aluminium content up to x = 0.45 before dropping at x = 0.60. the maximum saturation magnetization value was found at x = 0.45, indicating a strong correlation between the magnetic properties and the amount of aluminium. therefore, the study suggests that the addition of aluminium can significantly enhance the magnetic and electrical properties of li(0.5)co(0.75)fe(2)o4 spinel ferrites, up to a certain point, which can be beneficial for various technological applications. author contributions: conceptualization, kpm and mgk; methodology, sva; software, kpm and mgk; validation, ldh, snm, ssk, csh, msb and rbp; formal analysis, rbp, ssk and snm; investigation, kpm and mgk; resources, kpm, mgk and rbp; data curation, kpm and mgk; writing—original draft preparation, kpm, mgk and ssk; writing—review and editing, snm and rbp; supervision, snm and rbp; project administration, csh, ldh and rbp. all authors have read and agreed to the published version of the manuscript. institutional review board statement: not applicable. informed consent statement: not applicable. conflict of interest: the authors declare no conflict of interest. references 1. kakati s, rendale mk, mathad sn. synthesis, characterization, and applications of cofe2o4 and m-cofe2o4 (m = ni, zn, mg, cd, cu, re) ferrites: a 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synthesis and adsorption property of porous carbon/ni nanoparticle composites sailu xu1, yuxin du1, meiqi hui1, zichen wang1, junfeng zhao1,2*, gang yang1,2 1 school of materials engineering, changshu institute of technology, changshu 215500, jiangsu province, china. e-mail: jfzhao@cslg.edu.cn 2 suzhou key laboratory of functional ceramic materials, changshu 215500, jiangsu province, china abstract the porous carbon/ni nanoparticle composite was prepared by a freeze-drying method using nacl as the template. it was applied in the effect of the concentration, adsorption time, and temperature of adsorption on the adsorption behavior. the kinetic model and the adsorption isothermic fitting results show that the adsorption behavior fits with the pseudo-secondary dynamics and the langmuir isothermal model, indicating that the adsorption process is monolayer adsorption. thermodynamic results indicate that the adsorption process is spontaneous physicochemical adsorption. the fitting showed that the porous carbon/ni nanoparticle composites reach 217.17 mg·g–1, at 313 k indicates good adsorption for congo red. keywords: porous carbon; magnetic; congored; adsorption performance article info received: 3 december 2020 accepted: 23 january 2021 available online: 30 january 2021 copyright copyright © 2021 sailu xu, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction with the steady development of the economy and the deepening of industrialization, dye wastewater has become an urgent pollution problem[1]. the adsorption method is simple and highly efficient. porous carbon material (porous carbon material) is a porous material with carbon as the main body, which has the advantages of large than surface area, developed pores, good chemical stability, and a wide source of raw materials, rich resources, low price, and simple production process, which can carry out large-scale production. therefore, it is widely used in energy storage and conversion, catalytic and macromolecular adsorption, and is favored by researchers at home and abroad[2,3]. according to the internationally recognized definition, porous carbon can be divided into three types: microporous carbon material (< 2 nm), iterporous carbon material (between 2–50 nm), porous carbon material (> 50 nm). in recent years, research has found that a single type of hole structure material cannot meet the market demand of high performance and high efficiency. therefore, artificial transformation and design of porous carbon according to performance and application requirements has become a hot research topic, and the development and application of multiporous carbon materials have emerged[4,5]. in terms of sewage treatment, although porous carbon has the advantages of large than surface area and good adsorption performance when porous carbon is added to sewage for adsorption, it will be dispersed in water and cannot be 19 recycled, which leads to waste of resources and cost increase. in this paper, porous carbon/ni nanoparticle complexes were prepared by the freeze-drying method, using water-soluble inorganic salt nacl as a template. the effect of adsorbent dosage, adsorption time, and temperature on the adsorption properties of porous carbon/ni nanoparticle composites was investigated respectively, and the adsorption behavior of porous carbon/ni nanoparticle composite is analyzed using kinetic and isothermic models. 2. experiment 2.1 preparation of porous carbon/ni nanoparticle composites 0.003 mol ni(no3)2•6h2o and 4 g nacl, were dissolved in 20 ml deionized water, quantity 10 ml egg white was added to the above solution, stirred with a magnetic mixer for 30 min, and mixing evenly for standby. the mixture liquid is frozen in liquid nitrogen for 10 min to completely frozen, and the vacuum sublimation treatment for 48 h is removed to completely sublimate the water. frozen dried samples were removed and placed into the crucible. the heat-treated samples were removed at 650 ℃ for 3 h. in n2 atmosphere, ground dispersed in a certain amount of deionized water, the nacl template was sonicated, and the samples were then extracted and separated, repeated to fully remove inorganic salt 3 times. the aspirated/ni nanoparticle-washed samples were prepared by drying in a 60 ℃ vacuum drying tank for 8 h, to obtain a porous carbon/ni nanoparticle composite. 2.2 characterization of the material topography and structure the structure was analyzed by the x-ray diffraction instrument (xrd), the scanning electron microscopy (sem, sigma, 20 kv) and high-resolution transmission electron microscopy (hrtem, jeol2000 cx, 200 kv), and the specific surface area and aperture size analyzer (bet) were used to analyze the specific surface area and pore structure. 2.2 characterization of the adsorption properties the sorbent properties of porous carbon/ni nanoparticle composites were determined using a tu-1901 uv spectrophotometer. the adsorption properties of the adsorbent were studied, using congo red (cr) as a pollutant model, at 20, 40, 60, 80, 100 mg/l concentrations. a solution of cr at 40 mg/ l and investigated the effects of different temperatures (298, 303, 308, 313 k) on the adsorption properties. all the above experiments were performed at 200 r·min–1 oscillations, with 5 ml mixed solution at 15 min, 30 min, 1 h, 2 h, 3 h, placed into a centrifuge tube, centrifugation for 5 min, and the remaining cr concentration was tested using a uv spectrophotometer. 3. results and discussions figure 1 shows the xrd map of the prepared porous carbon/ni nanoparticle composite, showing three sharp diffraction peaks at 2θ at 42.2°, at 51.9° and 76.2°, corresponding to (111), (200), (220) crystal surface diffraction of ni (pdf#65-0380), respectively. furthermore, a bulging, relatively weak diffraction peak was observed at 2θ of 25.6°, analyzed corresponding to the characteristic diffraction peak of amorphous carbon. no other miscellaneous peaks were observed, indicating that there was no impurity phase in the composite product. xrd results show that the products prepared by freeze drying-carbonization are c/ni composite, the carbon component in protein converted to carbon material by high temperature thermolysis; nickel nitrate generates nickel oxide by high temperature, the temperature increases further, nickel oxide by carbon reduction generates magnetic nanoparticle, and eventually form porous carbon/magnetic ni nanoparticle composite material. 20 figure 1. xrd plot of the porous carbon/ni nanoparticle composites. (a) 5,000 times; (b) 20,000 times figure 2. xrd diagram of porous carbon /ni nanoparticle composites. as can be seen from figure 2, the material prepared by freeze-drying-carbonization presents a 3d structure similar to the block material of “frozen tofu”. further observation found that the surface of 3d carbon material presents irregular sheet structure, in layer by layer pit gully successively filled with holes from large to small. it is believed that during the reaction precursor of liquid nitrogen freezing, nacl cubic crystal and nickel nitrate crystal precipitate out rapidly with the sharp drop of temperature, and a large number of nacl cubic crystal particles are self-stacked to form a 3d structure. nickel nitrate crystals are distributed in the 3d structure, and the proteins in the precursor are also precipitated with decreasing temperature and coated in the surface of the nacl cubic crystals. further vacuum sublimation drying completely removes the water from the system, thus forming a protein/nickel nitrate/nacl composite powder product. complex powder at high temperature in an inert atmosphere, nacl structure remains stable at high temperature, the protein carbonization on the surface is transformed into carbon material, and nickel nitrate forms nanoparticles by decomposition and reduction reaction and nanoparticles. the product, removed from the nacl template with simple washing, forming a honeycomb porous carbon structure with more evenly distributed dimensions, interconnected and interconnected. figure 3(a)–figure 3(c) is a tem plot of porous carbon/ni nanoparticle complexes. it can be seen that the sample has a 3d structure of which the matrix is the porous carbon. the porous carbon structure is filled with high-density, ultra-fine nickel nanoparticles with a size of approximately 30 nm. the hrtem plot of figure 3(d) shows a distinct crystal surface orientation in the local region, corresponding to the crystal surface spacing of ni in the composite, covered with helminth-like disordered ripples of the nickel, corresponding to the amorphous carbon layer. this result is consistent with the xrd results, indicating that nanoparticles distributed in graded porous carbon form a composite structure. figure 3. (a) (b) (c) tem figures of multiwell carbon/ni nanoparticle composites and (d) hrtem figure. according to the bet adsorption/desorption of figure 4(a) porous carbon/ni nanoparticle composite, the sample presents a i/iv mixed adsorption model indicating the presence of a hierarchical porous structure of the material. first, the significant uptrend at p/p0 < 0.01 was attributed to type i isotherms, indicating the presence of a micropore structure in the structure. at p/p0 = 0.4–0.9, there is a distinct suction attachment hysteresis loop in the relative pressure range, in line with the iv isothermic model, showing a large number of interpore structures in the structure. besides, when p/p0 > 0.9, the adsorption/desorption is further increased, 21 indicating that large pore structures still exist in the structure[6–7]. therefore, the material prepared in this experiment is a graded porous structure. the analysis of brunauer-emmett-teller (bet) showed that the specific surface area of porous carbon/ni nanoparticle composites is up to 511.532 m2·g–1. the aperture distribution curves of the sample are further given in figures 4(b) and 4(c), and barrett-joyner-halenda (bjh) and dubinin radushkevich (dr) analysis showed that the sample showed a distinct aperture distribution in both the 2–30 nm and the micropore region of 0–2 nm. by the observation, we know that the distribution of pore diameter is relatively concentrated, and the mesole mostly concentrated around 5 nm and the micropore around 0.3 nm, further proving that the sample has a better graded porous structure. among them, the total adsorption pore volume was 0.938 cm3·g–1, bjh adsorption cumulative interpore and total pore volume were 0.859 cm3·g–1, dr method micropore (< 2 nm) volume was 0.236 cm3·g–1. figure 5 shows plots of the adsorption properties of congo red dye in porous carbon/ni nanoparticle composites at 298, 303, 308, 313 k. as can be seen from the figure, the adsorption curve rises sharply when the adsorption time is within 60 min, and then tends to be flat. it shows that the adsorption tends to achieve saturation at 60 min. the intercepted 60 min time point and the adsorption concentration are 40 mg·l–1 (in the order of temperature rise), respectively, are 105.37, 124.37, 158.52, 163.87 mg·g–1, indicating that the adsorption amount will increase as the temperature increases (the increase rate is gradually slowed and reaches saturation at a temperature). it shows that as the temperature increases, the concentration of the adsorption matter will also affect the size of the adsorption quantity. figure 4. diagram of bet and aperture distribution of porous carbon/ni nanoparticle composites. (a) bet adsorption/detachment map; (b) distribution map of interpore aperture map; (c) micropore aperture distribution map. figure 5. effects of different temperatures on the adsorption properties. to further explore the adsorption behavior of porous carbon/ni nanoparticle composites on the organic dye congo red, a pseudo-second-order kinetic model was used to fit the adsorption data at different temperatures, with the exact formula shown in equation (1)[8]. (1) the qe, qt (mg·g–1) represent the adsorption capacity of t (min) at equilibrium and at some time, respectively; k2 represents the pseudo-second-order rate constant (g·mg–1·min–1). figures 6(a)–figure 6(d) shows a pseudo-fitting second-order nonlinear fitting curve for the adsorption behavior of porous carbon/ni nanoparticle 22 complexes at 298, 303, 308, 313 k temperatures. the kinetic parameters (k2 and qe) and regression coefficients (r2) of the fitted model are shown in table 1. for all four adsorption temperatures, the experimental data agree with the regression coefficients (r2 substantially above 0.99) at all initial concentrations. from these r2 values, the model of quasi-second order is suitable to describe the adsorption kinetic behavior. the pseudo-second-order model calculations agree well with the experimental observations. these results confirm that chemical adsorption is a rate control step and depends on the concentration of contaminants exposed to the surface of the porous carbon/ni nanoparticle composite materials[9]. furthermore, the maximum adsorption of the congo red dye at 100 mg·l–1 by the porous carbon/ni nanoparticle composite at 298, 303, 308, 313 k was 119.53, 150.60, 189.04, and 206.19 mg·g–1, respectively. the interaction of adsorbent with adsorbate describes as adsorption isotherms. the well-known model langmuir isotherm describes the adsorption process. figure 6. fof pseudo-second-order dynamics of the adsorption process. langmuir isotherms are based on single-molecule adsorption processes, commonly used to describe equilibrium adsorption isotherms on homogeneous surfaces. the isothermal model can represent as equation (2)[10,11]. (2) ce is the equilibrium concentration of the solute (mg·l–1); qe indicates the adsorption amount table 1. the fitting parameters of pseudo-second order dynamics of porous carbon/ni nanoparticle composites to congo red adsorption 23 (mg·g–1) at equilibrium; qm is the maximum adsorption amount (mg·g–1); and kl indicates the langmuir adsorption constant (g–1). figure 7 shows the fit diagram of the langmuir isothermal model. the relevant parameters obtained from the isothermal model fitting listed in table 2 show that the regression coefficient r2 is above 0.9 at different adsorption temperatures, saying that the bright muir model can well describe the adsorption behavior of porous carbon/ni nanoparticle composite adsorption agent. the isothermal fitting showed that the porous carbon/ni nanoparticle composite is monolayer adsorption, and the adsorption is in a monolayer. once the adsorption cannot be further at that position once the dye molecule occupies the active site on the magnetic porous carbon surface[12]. by the fitting calculation, we can get that the maximum adsorption of congo red by the porous carbon/ni nanoparticle composite was 123.10, 144.95, 197.53, and 217.17 mg·g–1. at 298, 303, 308, 313 k, respectively. figure 7. a fitting of the langmuir isothermic model for the adsorption process. table 2. langmuir fitting parameters for the isotherm model to further evaluate the effect of temperature on the adsorption properties of porous carbon/ni nanoparticles composites, thermodynamic parameters, including enthalpy (δho), gibbs free energy (δgo), and entropy (δso) were calculated, with the specific equations of: (3) (4) r is the gas constant (8.314 j·mol–1·k–1), t indicates the temperature (k), and k is the adsorption equilibrium constant. figure 8 shows a linear plot of lnk and 1/t. the specific values of the thermodynamic parameter enthalpy (δho), gibbs free energy (δgo), and entropy (δso) are calculated by fitting shown in table 3. figure 8. linear plot between lnk and 1/t. table 3. specific values for the enthalpy of thermodynamic parameters (δho), gibbs free energy (δgo), and entropy (δso) from table 3, all of the δgo value is negative, indicating that the congo red adsorption of the porous carbon/ni nanoparticle composite is a spontaneous process. the δgo tends to decrease with the increasing temperature, which indicates that the increased temperature is favorable for adsorption. δho and δso are all positive, which indicates that the adsorption of porous carbon/ni nanoparticle composite to congo red has exothermal properties[13]. δho is 31.25 kj·mol–1, higher than physical adsorption heat (2.1–20.9 kj·mol–1) and less than chemical adsorption heat (80–200 kj·mol–1), indicating that the adsorption of porous carbon/ni nanoparticle composite belongs to a physicochemical adsorption process[14]. 24 4. conclusion the porous carbon/ni nanoparticle composites synthesized by a freeze-drying method by nacl as a template. sem and tem showed that ni nanoparticles equably distributed on porous carbon carriers, which constructed into a 3d-graded porous structure. the bet and pore size distribution results show that the porous carbon/ni nanoparticle composite is a graded porous structure composed of large holes, mesholes and micropores, with 511.532 m2·g–1 and 0.938 cm3·g–1. compared to the surface area and the total adsorption pore volume, respectively, making the porous carbon/ni nanoparticle composite has excellent adsorption properties. the kinetic and thermodynamic results show that the adsorption behavior, which is the composite materials to the organic pollutant congo red, accords with the pseudo-secondary dynamics and langmuir isothermal model. and it is with a maximum adsorption amount of 217.17 mg·g–1 at 313 k. conflict of interest the authors declare that they have no conflict of interest. references 1. lu y, song s, wang r, et al. impacts of soil and water pollution on food safety and health risks in china. environment international 2015; 77: 5–15. 2. chen b, ma q, tan c, et al. carbon-based sorbents with three-dimensional architectures for water remediation. small 2015; 11(27): 3319–3316. 3. de s, balu am, van der wall jc, et al. biomass‐ derived porous carbon materials: synthesis and catalytic applications. chemcatchem 2015; 7(11): 1608–1629. 4. sevilla m, ferrero ga, fuertes ab. one-pot synthesis of biomass-based hierarchical porous carbons with a large porosity development. chemistry of materials 2017; 29(16): 6900–6907. 5. liu r, liu y, zhou x, et al. biomass-derived highly porous functional carbon fabricated by using a free-standing template for efficient removal of methylene blue. bioresource technology 2014; 154: 138–147. 6. gupta k, gupta d, khatri op. graphene-like porous carbon nanostructure from bengal gram bean husk and its application for fast and efficient adsorption of organic dyes. applied surface science 2019; 476: 647–657. 7. song y, wei g, kopec m, et al. copolymer-templated synthesis of nitrogen-doped mesoporous carbons for enhanced adsorption of hexavalent chromium and uranium. acs applied nano materials 2018; 6(1): 2536–2543. 8. ho ys, mckay g. pseudo-second order model for sorption processes. process biochemistry 1999; 34(5): 451–465. 9. pour zs, ghaemy m. removal of dyes and heavy metal ions from water by magnetic hydrogel beads based on poly (vinyl alcohol)/ carboxymethyl starch-gpoly (vinyl imidazole). rsc advance 2015; 5: 64106–64118. 10. hemmati f, norouzbeigi r, sarbisheh f, et al. malachite green removal using modified sphagnum peat moss as a low-cost biosorbent: kinetic, equilibrium and thermodynamic studies. journal taiwan institute of chemical engineers 2016; 58: 482–489. 11. liu y, xu h. equilibrium, thermodynamics and mechanisms of ni2+ biosorption by aerobic granules. biochemistry engineering journal 2007; (35): 174– 182. 12. cheng b, le y, cai w, et al. synthesis of hierarchical ni(oh)2, and nio nanosheets and their adsorption kinetics and isotherms to congo red in water. journal of hazardous materials 2011; 185(2-3): 889–897. 13. zhao j, zha j, yang c, et al. cauliflower-like ni/ nio and nio architectures transformed from nickel alkoxide and their excellent removal of congo red and cr(vi) ions from water. rsc advance 2016; 6: 103585–103593. 14. liu s, ding y, li p, et al. adsorption of the anionic dye congo red from aqueous solution onto natural zeolites modified with n, n-dimethyl dehydroabietylamine oxide. chemical engineering journal 2014; 248: 135-144. microsoft word can-5756 characterization and application of nanomaterials 2024, 7(1), 5756. https://doi.org/10.24294/can.v7i1.5756 1 article enhanced photocatalytic performance by zno/graphene heterojunction grown on ni foam for methylene blue removal lucas f. melia1, maría v. gallegos2, luciana juncal1, marcos meyer1, francisco j. ibañez3, laura c. damonte1,* 1 instituto de física la plata (iflp), conicet-unlp, la plata 1900, argentina 2 centro de investigación y desarrollo en ciencias aplicadas (cindeca), conicet-unlp-cic, la plata 1900, argentina 3 instituto de investigaciones fisicoquímicas, teóricas y aplicadas (inifta), universidad nacional de la plata-conicet, la plata 1900, argentina * corresponding author: laura c. damonte, damonte@fisica.unlp.edu.ar abstract: zno nanostructures were obtained by electrodeposition on ni foam, where graphene was previously grown by chemical vapor deposition (cvd). the resulting heterostructures were characterized by x-ray diffraction and sem microscopy, and their potential application as a catalyst for the photodegradation of methylene blue (mb) was evaluated. the incorporation of graphene to the ni substrate increases the amount of deposited zno at low potentials in comparison to bare ni. sem images show homogeneous growth of zno on ni/g but not on bare ni foam. a percent removal of almost 60% of mb was achieved by the ni/g/zno sample, which represents a double quantity than the other catalysts proved in this work. the synergistic effects of zno-graphene heterojunctions play a key role in achieving better adsorption and photocatalytic performance. the results demonstrate the ease of depositing zno on seedless graphene by electrodeposition. the use of the film as a photocatalyst delivers interesting and competitive removal percentages for a potentially scalable degradation process enhanced by a non-toxic compound such as graphene. keywords: ni foam; electrodeposition; zinc oxide; photocatalysis; graphene; methylene blue degradation 1. introduction it is known that water pollution is an environmental problem that worsens year after year. human activities, such as industry and agricultural production, affect bodies of water and, consequently, human health [1]. it is believed that of all wastewaters generated by human activities, 80% are discharged without prior treatment. poorquality drinking water is a problem that is associated with 80% of childhood illnesses and 50% of child deaths worldwide [2]. among water contaminants, organic dyes play a leading role: around 100,000 different types of dyes are produced annually, totaling more than 700,000 tons, with approximately 100 tons being dumped [3,4]. in addition to many of them being carcinogenic and dangerous for humans [5,6], they have good stability in environmental conditions [7] and cause, among other drawbacks, loss of transparency, reduction in the penetration of sunlight, retard biological activity of plants and animals, increase chemical oxygen demand (cod) and biochemical oxygen demand (bod), etc. [8,9]. in this context, organic dyes contribute significantly to this environmental problem since they are one of the main sources of contamination of surface and groundwater [10]. one of the most commonly used dyes is methylene blue (mb). mb, from the thiazine class, is a heterocyclic aromatic compound; see figure citation melia lf, gallegos mv, juncal l, et al. enhanced photocatalytic performance by zno/graphene heterojunction grown on ni foam for methylene blue removal. characterization and application of nanomaterials. 2024; 7(1): 5756. https://doi.org/10.24294/can.v7i1.5756 article info received: 15 april 2024 accepted: 30 april 2024 available online: 29 may 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 5756. 2 1 [11]. this cationic dye is commonly used in the textile industry to dye wool, cotton, etc., where 15% is transferred to wastewater during this process as an industrial pollutant [12–14]. these dyes have also long been used in medicine and scientific purposes, such as in microscopy or as redox indicators [15]. although this dye can be used as a drug against some diseases, such as malaria, it is also toxic to human health and the environment and can cause vomiting, nausea, irritation, and tachycardia, among other diseases, in humans. this pollutant can inhibit plant growth and reduce the pigment and protein content of algae [16–18]. for these reasons, the elimination of these pollutants from water is now one of the main areas of study [3]. figure 1. schematic representation of methylene blue (mb) dye. the removal mechanisms of mb and other contaminants from wastewater are frequently studied [19–21]. photodegradation via photocatalysis using semiconductors is a preferred way to eliminate contaminants in various sources of water [22,23]. one of the main advantages of photocatalysis relies on the generation of non-harmful products, such as co2, h2o, and inorganic salts, after activating the process with light [24,25]. although there are various kinds of semiconductors that adapt well to these systems, including fe2o3, cds, and zns [3], tio2 and zno are the most used in photocatalysis applications [10]. most likely due to their low toxicity, outstanding thermal and chemical stability, and relatively low cost [26]. in particular, zno presents higher percentages of contaminants degradation in water than tio2 [27], which could be due to the higher exciton binding energy and the higher electrical conductivity of zno compared to tio2, in addition to the zno band potentials (of valence and conduction) being lower than tio2 ones. this combination of properties allows an increase in the effectiveness of the degradation reactions [28,29]. in this context, the use of thinly supported zno films is most desired since it allows a very simple separation process, which consists of removing the catalyst from the solution and also facilitating the recycling of the catalyst. on the other hand, the use of zno powder involves separation by some subsequent process. in addition to this, it is known that the photodegradation efficiency increases as the specific surface increases [30]. this is why the use of porous supports, such as nickel foams, can obtain very high performance, comparable to powders. zno thin films can be obtained through various methods, such as metal-organic chemical vapor deposition (cvd) [31,32], magnetron sputtering [33,34], molecularbeam epitaxy [35,36], sol-gel [37], spray pyrolysis [38,39] and electrodeposition [40– 42]. what is interesting about the latter is the simple scalability, film control, and the possibility of depositing structures in many different shapes and sizes without using high temperatures or expensive equipment. growth can be carried out through various solutions that use zn2+ salts with different anions, whether chlorides, nitrates, or sulfates, as precursors [43–48]. by varying the type, concentration, or ph of these characterization and application of nanomaterials 2024, 7(1), 5756. 3 solutions, as well as the applied potential, the deposition time, or the current circulating in the cell, various types of zno films and morphologies can be obtained [49–54]. however, it is desirable to use low currents or voltages, low-concentrated salts with non-toxic precursors, and low times so that the process is profitable and easily scalable. one of the ways to improve the properties of zno is to form heterostructures with graphene. cvd graphene presents outstanding properties such as transparency, flexibility, high carrier mobility, and mechanical stability [55–57]. when graphene is grown in 3d structures, the carbon atoms are exposed on the surface, resulting in a large surface area and a large number of active sites [58]. the three-dimensional znographene heterojunction provides synergetic properties and improves charge separation by zno followed by charge transport offered by highly conductive graphene, which dramatically reduces the probability of electron-hole recombination [59,60]. this happens because the work function of graphene (−4.5 ev) is lower than the conduction band of the semiconductor oxide (−4.1 ev), so the excited electrons in zno are transported toward graphene, which has a high carrier mobility, thus inhibiting recombination in zno and consequently increasing the photocatalysis degradation efficiency of mb [61]. researchers have shown that the photocatalytic activity of zno improves whenever graphene is used as a co-catalyst [62]. in addition, graphene could extend the absorption range of zno to longer wavelengths further from the ultraviolet region [59]. these exceptional properties offered by the zno-graphene heterojunction have been applied in various fields, including photocatalysis, photodetection, solar cells, etc. in this work we propose the electrodeposition of zno on graphene already grown on a ni foam by cvd to be used in photodegradation applications. this heterojunction is interesting both as an adsorbent material and for photocatalysis due to the high specific surface area provided by using ni foam as a substrate, added to the improvement in conductivity and the decrease in electron/hole recombination provided by graphene. 2. materials and methods we proposed to grow zno nanostructures by electrodeposition on ni foam, a low-cost and simple technique that had proved to be successful in obtaining zno films on different flat substrates like ito and fto [40–43]. 2.1. graphene growth in nickel foam nickel foam with 1.6 mm thickness and porosity of 87% was purchased from mti corp (richmond, ca, usa). graphene was grown on ni foam by cvd method on ni foam following the protocol described by messina et al. [63]. briefly, the bare ni foam was sonicated in acetone for 20 min and placed in a quartz tube under a vacuum pressure of 8 × 10−5 torr. during the synthesis, a constant flow of h2 was maintained at a rate of 75 ml min−1. at 950 ℃ a flow of ch4 was introduced at a rate of 35 ml min−1 for 5 min leading to the growth of graphene on the entire surface of ni. finally, the furnace was cooled down at a rate of 16 ℃ per minute until reaching room temperature. characterization and application of nanomaterials 2024, 7(1), 5756. 4 2.2. electrodeposited zno films a thin layer of zno was grown on ni with and without graphene by the electrodeposition technique using a teq4 potentiostat from nanoteq, argentina. the aqueous solution was 0.01 mol/l zn(no3)2 (sigma aldrich, 98%) in 0.1 mol/l kcl (anedra, 99.6%) and 0.1 mol/l kno3 (anedra, 99.8%). the electrolytic cell is a three-electrode setup where ni foam, pt wire, and ag/agcl electrodes immersed in 3.0 m kcl acted as working, counter, and reference electrodes, respectively. figure 2 shows a scheme of the cell. before electrodeposition, the working electrode was washed with soapy water, sonicated in distilled water for 10 min, and then sonicated in isopropyl alcohol for 10 min. electrodeposition was performed at constant temperature (70 ℃) and stirring (200 rpm) to ensure homogenous distribution. the applied voltage was −800 mv (chosen after performing cyclic voltammetry on the studied system) for 60 min. the initial ph of the solution is 5.3. the samples obtained were called ni/g (ni foam + graphene), ni/zno (zno on ni foam), and ni/g/zno (zno on ni foam with graphene). figure 2. scheme represents the three-electrode set-up under the parameters used in this work. 2.3. sample characterization cyclic voltammetry and subsequent amperometry were performed using a teq4 potentiostat from nanoteq co., argentina. x-ray diffraction (xrd) patterns were acquired using a philips pw1710, panalytical x’pert pro diffractometer at 45 kv and 45 ma with monochromatized cukα radiation in the range of 20° ≤ 2θ ≤ 40° with a step of 0.02 °/s and a grazing angle of 3°. optical images were obtained through a leica dm il led optical microscope. sem images were obtained from an fei quanta 250 environmental scanning microscope (esem) at an operating voltage of 20 kv. the equipment has an x-ray detector, edax, through which the chemical composition was studied qualitatively using energy dispersive spectroscopy (eds). 2.4. mb degradation the photodegradation of mb was evaluated by immersing ni, ni/g, ni/zno, and ni/g/zno in 1.3 ppm methylene blue (mb) solution. the solution was kept in the dark characterization and application of nanomaterials 2024, 7(1), 5756. 5 for 15 min to reach adsorption equilibrium. then, it was irradiated with an 8 w fluorescent lamp (bte lighting, argentina) with a wavelength ranging from 250 to 600 nm. the uv lamp was kept on for 165 min and the experiment was carried out at room temperature. figure 3 shows the experimental set-up. at the indicated times, the sample was removed from the solution, and the absorbance of the remaining solution was measured using a shimadzu uv-2600 spectrometer. figure 3. scheme of the experimental set-up used to measure mb adsorption and degradation. 3. results in this section details of the electrodeposition method are presented along with the structural and morphological characterization of the obtained heterostructures. also, the use of these samples on the mb removal is analyzed. 3.1. cyclic voltammetry (cv) and amperometry cvs were run from negative from 0 to −1.1 v and back to 0 v at 100 mv/s scan rate. figure 4 shows only the cathodic sweep that is of interest for the zno deposition. the cv reveals significant differences based on the electrode substrate. our group successfully electrodeposited zno on different substrates, including ito and fto, by applying potentials between −700 mv and −1000 mv. we identified −800 mv as the optimal potential. therefore, we applied −800 mv which resulted in a noticeable increase in the steep curve for ni/g as compared to the naked ni electrode shown in figure 4. due to the increase in slope observed in both cases, this potential was chosen and applied for 1 h. after amperometry, the ni/g sample exhibited a white deposit to the naked eye, while no apparent change in color was observed for ni foam. figure 4. cyclic voltagrams corresponding to ni (black) and ni/g (red) electrodes. characterization and application of nanomaterials 2024, 7(1), 5756. 6 3.2. x-ray diffraction (xrd) figure 5 shows the diffractograms for ni/zno and ni/g/zno samples measured at angles between 20° and 40°, a region where the characteristic diffraction peaks of zno become more evident after smoothing the original signal using the savitzkygolay method. amperometry was performed for 1 h on both samples. as it can be seen, no characteristic peak for zno was detected within the ni/zno sample. this does not necessarily rule out the deposition of zno since there may be a low amount of mass that is below the limit of detection. on the other hand, for ni/g/zno samples, three peaks clearly evolved, corresponding to (100), (002), and (101) crystallographic orientations that matched the peaks for icsd no. 01-080-0074. this clearly confirms the successful deposition of the zno semiconductor onto the ni/g sample. furthermore, there is no evidence of preferential growth in the (002), as the intensity of this peak (at 34.335°) is not dominant. this is consistent with the literature, which has also shown predominant (101) peaks using electrodeposition and other techniques [30,64–66]. these results suggest that the as-deposited zno film does not display a nanocolumnar morphology [67]. additionally, no other diffraction peaks are detected, as ni exhibits diffraction peaks for 2θ > 40° [68]. the technique also allows us to confirm that no other crystalline material was deposited in large quantities, since the diffractograms do not present other peaks, nor amorphous ones, since no bands were observed at low angles. figure 5. xrd diffractogram comparing ni/zno and ni/g/zno samples. blue lines that correspond to card no. 01-080-0074 are used as a comparison. 3.3. optical microscopy figure 6a exhibits multiple pores within the naked ni foam structure. no apparent changes were detected for graphene grown on ni foam (not shown), most likely due to the poor resolution of the optical microscope. figures 6b and 6c clearly exhibits the as-deposited zno; however, the amount of deposit seems not to be uniform along the entire ni/g/zno sample. characterization and application of nanomaterials 2024, 7(1), 5756. 7 figure 6. optical images. (a) ni foam; (b) ni/g/zno sample; (c) ni/g/zno sample. 3.4. sem-eds figure 7 shows sem images for ni (a), ni/g (b), ni/zno (c), and ni/g/zno (d). notable differences in the surfaces are observed between the electrodeposition of zno on bare ni and on ni/g using the same deposition parameters. figure 7b clearly shows the growth of graphene on the surface of bare ni. it can be seen there is a large amount of graphene in the center of the foam and that, close to the edge of the pores, that decreases. to confirm that it was a different material, it was analyzed with backscattered electrons, since in this type of image the contrast is based on the atomic number. figure 7. sem images. (a) ni; (b) ni/g; (c) ni/zno; (d) ni/g/zno. figure 8 shows a sem image of the ni/g sample obtained by backscattered electrons. in these images the contrast is achieved with the difference in atomic number, which allows us to confirm that they are two different materials since the ni substrate appears bright while the graphene deposit appears dark. this confirms that characterization and application of nanomaterials 2024, 7(1), 5756. 8 the cvd deposit was successful. figure 8. sem image of the ni/g sample obtained by backscattered electrons. on the other hand, the ni/zno sample does not present changes with respect to the ni sample, except for the appearance of localized structures that are observed as white dots in figure 7c. the amount of zn provided by eds in this sample is very low (about 3.5% by weight), consistent with a very low amount of zno deposited. as for other elements, the percentage by weight of o, k, n, and cl revealed 40%, 25%, 13%, and 5% by weight, respectively. the presence of various elements, besides zn, suggests the potential formation of kno3 and kcl crystals that arose during the drying-off process after electrodeposition. figure 7d shows the homogeneous growth of zno on the ni/g substrate. eds measured at various points in the sample indicated 27% and 31% by weight of zn and o, respectively. in addition, a similar amount of c (31% by weight) was detected, consistent with the growth of graphene. this confirms the successful deposition of zno and indicates that graphene remains even after the voltage application in the synthesis. figure 9 shows the ni/g/zno sample with a higher magnification, where an increase in the exposed surface can be seen due to the irregularity of the deposit. this type of morphology is comparable to those reported in the literature, despite using a different zno deposition technique [64,65]. finally, figure 10 shows a color map obtained by eds, which shows the location of the evaluated elements. it is confirmed that zno is deposited throughout the foam, unlike graphene, which is mostly located in the center of it. figure 9. sem image of the ni/g/zno sample at higher magnification, showing the uniformity of the deposit. characterization and application of nanomaterials 2024, 7(1), 5756. 9 figure 10. eds color map showing the location of ni, c, zn, and o elements within the ni/g/zno sample. 3.5. removal of mb from a solution an absorption spectrum was initially obtained after immersing the samples in 1.3 ppm mb solution for 15 min under dark conditions. in this way, the percentage of mb adsorption in the first min of the experiment was obtained. then, the lamp was turned on and absorbance measured at 45 and 165 min. to calculate the percentage removal of mb in the solution, we choose to measure the area under the curve for the absorption band located at 662 nm. finally, equation (1) was applied to obtain the mb removal percentages: mb removal [%] = (1 − at/a0) 100 (1) where at is the absorption measured at a certain time t and a0 is the initial absorbance. figure 11 shows the absorbance spectra for each sample measured at the indicated times. figure 11. absorbance spectra of the samples measured at different times: under dark (black curve), after 15 min exposure to light (red curve), after 45 min (blue curve) and 165 min (green curve). (a) ni; (b) ni/g; (c) ni/zno; (d) ni/g/zno. table 1 shows the mb removal percentages for each sample for two different periods of time: while the light was off, that is, the black and red curves indicated in figure 11, and then once the light was turned on, that is, between the red and green curves of the same figure. it is clear that the ni/g/zno sample exhibits a higher characterization and application of nanomaterials 2024, 7(1), 5756. 10 removal percentage than the other samples (almost double) in both time periods, thus improving both adsorption and degradation of the contaminant. the ni foam and ni/g foam are characterized by their abundance of microscopic-sized pores, which provide a large surface area leading to high contaminants adsorption capacity. the significant enhancement in adsorption observed in the samples with g/zno can be attributed to two concurrent factors. firstly, the morphology of the deposited zno increases the contact surface, thereby facilitating increased adsorption. this fact is corroborated by sem images (figures 7 and 9), where the nanostructured feature of zno is clearly appreciated. secondly, the ph of the mb solution is 6, which results in the formation of zn(oh)+ on the zno surface. in contrast, the functional groups of mb carry a negative charge (−so3−). this allows the formation of an ionic bond that increases the adsorption capacity [69]. figure 12 shows percentages of mb removal from the solution achieved for each sample after irradiation with uv light, represented by the black and green curves in figure 11. numerous studies [18,70,71] have corroborated that zno serves as a photocatalyst in this reaction. it is particularly noteworthy that the sample composed of ni/g/zno exhibits the greatest efficiency, achieving about 60% removal of mb from the solution. table 1. mb removal percentages from the solution for each sample before and after light irradiation. sample mb removal without light [%] mb removal with light [%] ni 24 10 ni/g 20 14 ni/zno 20 14 ni/g/zno 41 28 figure 12. percent removal of mb achieved by the different samples. 4. discussion this work reports on the growth of zno on ni and ni/g foams by electrodeposition and its possible application in the removal of dyes in water bodies. in the case of bare ni foam, zno deposition is evidenced by the presence of zn in eds analysis, although zno growth could not be observed by xrd. on the other hand, characterization and application of nanomaterials 2024, 7(1), 5756. 11 when the ni/g foam is used as a substrate, a large amount of zno deposition is observed by both techniques used. unlike the work of fei et al. [30], here, the growth of zno was achieved in a single step, without the need of adding seeds and performing heat treatments. this behavior could be due to the presence of defects and wrinkles in the graphene, which act as nucleation sites for zno. then growth occurs in all directions. it is worth highlighting that our starting solution has a low concentration of precursors compared to the growth solution used by lv et al. [64]. the salt that contains the zn2+, zn(no3)2, has a concentration 20 times lower, while the supporting electrolyte kcl has a concentration 48 times lower. this makes our process more affordable and accessible. furthermore, the application of a potential difference of −800 mv in our synthesis results in a more efficient and less demanding method in terms of equipment compared to the use of −10 v in the aforementioned study. regarding the incorporation of graphene, two benefits were found: in addition to allowing nucleation at lower applied voltages, it increases the percentage of mb removal from the solution (57%). in this context, it is interesting to note that graphene is an organic, non-toxic, and inexpensive material. the results obtained in this work are close to those obtained by various authors who grow zno on different substrates [3,72]. fei et al. [30] do photocatalysis and photoelectrocatalysis using the ni/zno and ni/zno/mos2 heterojunction. the results obtained with both techniques with the ni/zno electrode are less efficient than our findings doing photocatalysis with the ni/g/zno heterostructure. however, fei and co-workers achieved higher removal when using the ni/zno/mos2 heterostructure, although it should be noted that graphene is a less toxic and cheaper compound. on the other hand, kulis-kapuscinska et al. [10] have studied the photodegradation of mb by growing zno films by sputtering on si(100) with a subsequent thermal treatment and have managed to remove 64% of mb from the solution in 540 min. that is, with a more complicated growth method they have achieved a result similar to that obtained in this work with a substantial difference in time: their experiment lasts 9 h while ours lasts 3 h, reducing the cost involved in maintaining the light on. this result is very important from the point of view that the degradation rate is usually a limiting factor for the selection of the photocatalyst. this could be due, in addition to the graphene, to the chosen substrate, since the ni foam, being so porous, has a large active surface. the improvements occur mainly due to the use of a nickel foam that increases the active surface compared to other flat substrates [30], added to the incorporation of graphene, which inhibits the recombination of electrons and holes according to the mechanism that can be seen in figure 13. the conduction band of zno (−4.05 ev vs. vacuum) is aligned with the graphene in such a way that the electron excited in the semiconductor can be transferred to the graphene (also taking advantage of the high electron mobility), separating the charges and reducing, thus way, recombination. then, the electron and the hole interact with the water in the solution: the molecular oxygen is reduced, generating the superoxide anion o2 − and the water is oxidized to obtain hydroxyl radicals (oh*), which finally degrade the mb, and co2 and h2o are obtained as products of this [59,62,73]. characterization and application of nanomaterials 2024, 7(1), 5756. 12 figure 13. scheme of the process with the zno and graphene bands. 5. conclusion in this study, zno was successfully electrodeposited on ni/g foam substrates to obtain new materials with high specific surface area. large amounts of zno were observed on ni/g due to the presence of graphene, whose defects acted as nucleation sites. sem images confirmed a homogeneous distribution of zno nanorods along the substrate. instead, scarce deposition was observed for the bare ni foam. the combined presence of zno and graphene increased the mb removal capacity, giving around 60% higher than what is achieved with the other heterostructures. the percentage improvement in terms of adsorption is due to the ionic bond that occurs between the zno surface and the negatively charged functional groups of the mb, while in photocatalysis it is probably due to a decrease in electron/hole recombination that leads to better charge separation. furthermore, the electrodeposition technique is a highly scalable method, so the synergistic effects of g/zno heterojunctions on a porous substrate become an interesting alternative for outperforming in areas of water cleaning and environmental remediation. this study highlights the importance of the efficient synthesis of zno on ni/g substrates via electrodeposition, not only for its applications in environmental remediation but also for its contribution to the development of sustainable practices within the framework of green chemistry. author contributions: conceptualization, lcd; methodology, lcd, lfm, mvg; validation, lcd, mvg and lfm; formal analysis, lfm and lj; investigation, lfm; resources, lcd, fji and mm; data curation, lfm, mvg and lj; writing—original draft preparation, lcd and lfm; writing—review and editing, lcd, fji, lfm and mvg; visualization, lfm; supervision, lcd and fji; project administration, lcd and mm; funding acquisition, lcd and fji. all authors have read and agreed to the published version of the manuscript. funding: this research was funded by conicet, grant numbers pip0901 and pip 0001 and unlp grant numbers 11x933 and x-887. acknowledgments: lfm, mvg, lj, mm, fji and lcd are members of conicet, argentina. the authors acknowledge sebastian rabal, technical personnel of characterization and application of nanomaterials 2024, 7(1), 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gabriel báez gonzález2, carlos abel amaya guerra2, sergio arturo galindo rodríguez2* 1 facultad de ciencias de la salud, universidad de montemorelos, montemorelos 67515, nuevo león, mexico. 2 facultad de ciencias biológicas, universidad autónoma de nuevo león, san nicolás de los garza 66450, nuevo león, mexico. e-mail: sagrod@yahoo.com.mx 3 facultad de medicina, universidad autónoma de nuevo león, monterrey, 64460, nuevo león, mexico. abstract deficiencies in postharvest technology and the attack of phytopathogens cause horticultural products, such as tomatoes to have a very short shelf life. in addition to the economic damage, this can also have negative effects on health and the environment. the objective of this work is to evaluate an active coating of sodium alginate in combination with eugenol-loaded polymeric nanocapsules (al-np-eug) to improve the shelf life of tomato. using the nanoprecipitation technique, nps with a size of 171 nm, a polydispersity index of 0.113 and a zeta potential of −2.47 mv were obtained. using the hs-spme technique with gc-fid, an encapsulation efficiency percentage of 31.85% was determined for eug. the shelf-life study showed that the al-np-eug-treated tomatoes maintained firmness longer than those without the coating. in addition, the pathogenicity test showed that tomatoes with al-np-eug showed no signs of damage caused by the phytopathogen colletotrichum gloesporoides. it was concluded that the formulation of eug nanoencapsulated and incorporated into the edible coating presents high potential for its application as a natural nanoconservative of fruit and vegetable products such as tomato. keywords: shelf life; edible coatings; eugenol; polymeric nanoparticles; hs-spme article info received: 29 june 2022 accepted: 11 august 2022 available online: 22 august 2022 copyright copyright © 2022 andrés mauricio piña-barrera, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction mexico is the producer of agrifood products currently among the world’s top 10. tomato (solanum lycopersicum) is one of mexico’s most important fruit and vegetable products. unfortunately, its very nature, the deficiencies in post-harvest technology and the attack of phytopathogens cause that, in general, fruit and vegetable products have a very short shelf life and post-harvest losses of up to 50% of total production, according to information from the food and agriculture organization of the united nations[1]. in recent years, the use of natural preservatives in the food industry has become a trend due to consumer demand for natural products. in particular, essential oils (eos) are secondary metabolites of aromatic plants and have a wide range of biological activities (e.g. antioxidant and antimicrobial) that have made them emerge as an alternative for the control and reduction of postharvest losses[2,3]. in fact, the antimicrobial properties of eos and their components have been exploited to control fungi and phytopathogenic bacteria[4,5]. eugenol (eug) is a phenolic derivative commonly known as 48 clove essence, which is extracted from the eos of pepper, bay, cinnamon and camphor, among others. eug has been shown to exhibit significant antimicrobial activity against bacteria and fungi[6], moreover, the u.s. food and drug administration (fda) has classified it as a gras (generally recognized as safe) substance and it has been approved by the european commission as a food additive[7]. unfortunately, the application of compounds such as eug, as food additives, has limitations as they exhibit strong lipophilic character, high volatility, are insoluble in water and are easily deteriorated by environmental factors, such as light and oxygen, making it difficult to incorporate them into commercial products[8,9]. in recent years, nanotechnology in the food industry has presented an important development, offering new alternatives to overcome these impediments. nanoencapsulation involves the incorporation, adsorption, solubilization or dispersion of bioactive compounds (e.g., eug) in or on a nanoscale polymeric structure. incorporation of these biocompounds into polymeric nanoparticles (nps) based on preformed polymers (e.g., eudragit l 100-55) can protect them against degradation, thus improving their physical and chemical stability. in addition, the combination of these nps with so-called edible coatings (rc) has emerged as an important alternative in food preservation. an rc is defined as a thin, continuous layer of some material that is incorporated on the food. alginate (al) is a linear glycosidic anionic polysaccharide consisting of monomeric units of d-mannuronate and l-guluronate and is obtained mainly from two sources: brown algae (phaeophyceae) (40% of dry matter) and bacteria[10,11]. this polymer has been used in the food industry as a coating or packaging material, in addition, it is also recognized by the fda as a gras substance. the incorporation of nanomaterials and antimicrobials, including essential oils and their components, in cr has been studied to give new properties to the coating and to improve the safety and shelf life of fruits and vegetables[12,13]. in this context, a combined system of nps, crs and compounds exhibiting biological activity, such as eug, may have potential as an alternative to synthetic agrochemical preservatives. therefore, the present study focuses on evaluating the efficacy of a combined np-eug system with an alginate rc to extend the shelf life of tomato (solanum lycopersicum) and inhibit the phytopathogenic action of colletotrichum gloesporoides. 2. materials and methods 2.1 materials alginate (pm 216.12 g∙mol−1) and eug (eugenol reagent plus 99%) were purchased from sigma aldrich® brand. polyvinyl alcohol (mowiol 4-88 with a pm 26.000 g∙mol−1 and hydrolysis degree of 88%) was kindly donated by omya ag. commercial tomatoes (solanum lycopersicum) which presented homogeneous characteristics of color, texture and size were used for the shelf-life tests. acetone and methanol were purchased from tedia® brand. eudragit l 100-55 polymer (methacrylic acid: ethyl acrylate (1:1), pm 320,000 da) was kindly donated by evonik industries®. sodium hydroxide was purchased from merck® brand and 75 μm carboxen/polydimethylsiloxane spme (car/pdms) fiber from supelco-sigma aldrich brand®. 2.2 nanoformulation with eugenol and its incorporation into an edible coating nps with eug were prepared by the nanoprecipitation technique[14]. for this purpose, 4 ml of organic phase containing eudragit l 100-55 polymer (55 mg) and eug (60 mg) dissolved in acetone were injected into an aqueous phase (25 ml) containing 0.5% (w/w) pva surfactant. the diffusion of the organic phase into the aqueous phase induced the aggregation of the eudragit l 100-55 polymer and thus the encapsulation of the eug (np-eug) inside it. finally, the solvent was removed with using a rotary evaporator (control laborota 4003, heidolph instruments, ger). nps without eug (np-bco) were obtained following the same procedure described above. the average particle size and poly-dispersity index (pi) of np-eugs were measured at a scattering angle of 90 degrees using dynamic light scattering, whereas, zeta potential measurement was 49 performed by laser doppler microelectrophoresis (zetasizer nano-zs90, malvern instruments, uk). for the formation of the edible coating, al was used as the forming agent. the solid al was incorporated into an aqueous dispersion of np-eug with magnetic stirring until complete dissolution. 2.3 analysis of the nanoformulation by gas chromatography with flame ionization detector (gc-fid) and headspace mode solid phase microextraction (hs-spme) to determine the percent encapsulation efficiency (%ee), the np-eug dispersion was centrifuged (allegra 64r centrifuge, beckman coulter, usa) and the sediment formed by the np-eugs was subjected to the hs-spme technique using a carboxen/polydimethylsiloxane (car/pdms) fiber of 75 μm coating thickness to quantify the eug in the nps by gc-fid (clarus 480, perkin elmer, usa). a capillary column (elite-5, perkin elmer, usa) (30 m × 0.25 mm × 0.25 μm) was used for the chromatographic method. the injector and detector temperatures were 270 °c. the oven temperature was programmed as follows: 70 °c for 1 min, increased by 30 °c∙min−1 to 190 °c, increased by 10 °c∙min−1 to 210 °c and finally increased by 20 °c∙min−1 to 270 °c and held for 1 min. the flow rate of helium carrier gas (99.999% purity, infra®) was 1 ml∙min−1. subsequently, the percent encapsulation efficiency (%ee) was calculated using the following formula: %ee = (eugc/eugt) × 100 (1) where eugc is the amount of eug quantified in the np-eugs (mg) and eugt is the amount of total eug (mg) used in the organic phase of the nanoformulation. 2.4 evaluation of the preservative effect of nanoformulation in combination with an edible coating on the shelf life parameters of tomato tomatoes (solanum lycopersicum) with homogeneous characteristics of color (ripening), size and without mechanical damage were selected for the application of the different treatments. they were washed with distilled water and dried. the fruits were distributed in five groups of three tomatoes each. the first group was used as control (no treatment). the second group was put in contact by immersion with a 0.5% (w/w) al solution (alg) for 1 min. the third group was applied by immersion, under the same conditions as above, a rc treatment of al with eug without nanoencapsulation (alg-eug). the fourth group was treated with a np dispersion without active, i.e., without eug (np-bco). finally, the fifth group was immersion-treated with an aqueous dispersion of the 0.5% (w/w) rc of al with the nanoformulation with eug incorporated (alg-np-eug). all groups were maintained at 25 °c and 35% humidity for 16 days. after this time, each group underwent the evaluations mentioned below: evaluation of firmness. firmness of tomatoes was measured by using a texture analyzer (ct3 texture analyzer, brookfield-ametek, usa) equipped with a cylindrical probe of 2 mm diameter. firmness was expressed in newton (n). evaluation of color change. color values (cie l* a* and b*) of tomatoes were determined by direct measurement of the fruit surface using a colorimeter (colorflex ez, hunterlab, usa). total color change (δe) was measured using the following equation: δe* = ((l*1 − l*2 )2 + (a*1 − a*2 )2 +(b*1 − b*2)2)1/2 (2) where δe* is the total color change. l*1/l*2 is initial brightness/lightness obtained. a*1/a*2 is initial red-green color/red-green color obtained and b*/b*2 is initial yellow-blue color/yellow-blue color obtained. evaluation of total soluble solids content. the total soluble solids (tss) content of tomato juice was obtained directly by refractometry (abbemat 200, antonpaar, aut). evaluation of titratable acidity. for the analysis of postharvest fruit quality, titratable acidity (ta) was determined by titration of tomato juice using a 0.1 n naoh solution until the end of titration (ph = 8.2). the result was expressed in grams of citric acid per 100 ml of juice. all parameters were determined in triplicate at the beginning and at the end of the shelf-life study. 50 in addition, the results were analyzed in the statistical program startical product and service solutions (spss statistics version 23) by means of an anova (p = 0.05). 2.5 evaluation of the protective effect of nanoformulation in combination with edible coating on tomato fruits inoculated with the phytopathogen colletotrichum gloesporoides the tomato fruits were cleaned and disinfected. each of the treatments was applied by immersion. under aseptic conditions, three wounds were made on their surface. in one of them, the phytopathogen colletotrichum gloesporoides was inoculated by striation and another wound by puncture. the fruits were placed in a humidity chamber at 25 °c for 5 days. at the end, the absence or presence of the phytopathogen growth on the tomato was observed. 3. results and discussion 3.1 obtaining and physicochemical characterization of the nanoformulation with eugenol generally, eudragit polymers have been used to modify drug release profiles by offering protective and sustained release properties[13]. due to the properties exhibited by such polymers (e.g., good stability, controlled release, and taste and odor masking), their use confers protection to bioactive compounds of unstable chemical nature, not only in the pharmaceutical industry, but also in the food industry. in the present study, eudragit l 100-55 polymer was used, which is an anionic copolymer derived from acrylic and methacrylic acid (figure 1). this polymer is proved to be very attractive for usage in the food industry, as it exhibits excellent off-flavor masking properties as well as controlled release in a ph-dependent manner[15]. in the present study, np-bcos with an average size of 164.2 ± 6.6 nm, a pi of 0.084 ± 0.018 and a zeta potential of −1.80 ± 0.64 were obtained. the physicochemical characteristics for the np-eug nanoformulation are presented in table 1. figure 1. basic structure of eudragit l 100-55 polymer. table 1. physicochemical characteristics of np-bcos and eugenol-incorporated nanoformulation obtained by the nanoprecipitation technique (n = 3; �̅�𝑥 ± ds) size (nm) ip1 zeta potential (mv) %ee2 np-bco 164.0 ± 6.6 0.084 ± 0.018 -1.80 ± 0.64 na np-eug 171.0 ± 3.0 0.113 ± 0.036 -2.47 ± 0.61 31.85 ± 12.77 note: 1polydispersity index ranging from 0 to 1. a higher value corresponds to a less homogeneous size distribution; 2percentage encapsulation efficiency; na: np without eugenol. the nanoprecipitation technique has been successfully used for the encapsulation of eos and their components, such as eug[16–18]. the incorporation of these environmentally unstable components into nps may offer advantages for their application and incorporation into commercial products in the food industry. for example, due to their nanometric size and multiparticulate character, eug-loaded nps can enhance np/fruit surface interaction and subsequently gradually release the eug[19,20]. moreover, compared to large particles (e.g. microparticles), nanosystems present a better surface/volume ratio, therefore, it is possible to have a larger surface of the fruit in direct contact with the nps[21]. in addition, the polymer wall of the nps allows retaining the eug inside the structure, thus decreasing its evaporation rate, favoring its application, increasing the residence time on the feed surface and improving the incorporation of eug in aqueous systems[22]. the average size of the np-eugs (i.e. 171.0 ± 3.0 nm) was similar to that reported by gomes et al.[23] who obtained plga 51 nps with eug incorporated with an average size of 179 nm. in addition, the authors report that in the release trials performed, a slower release rate of the eug incorporated into the nps was presented, which would improve their overall application. on the other hand, pi is a parameter associated with the homogeneity of the nano-system dispersion. for this study, the ip value of np-eug was 0.113 ± 0.036, which indicates a high homogeneity of nanoparticles that would allow individual np interactions (e.g. bioadhesion and eug release) to be homogeneous on the fruit surface as well. for the zetasizer nano-zs90 (malvern instruments) used, the pi values range from 0 to 1. a value below 0.200 indicates a homogeneous distribution of nanoparticle size[24]. the electrostatic potential at the boundary dividing the compact layer and the diffuse layer of the colloidal particles, called zeta potential, was −2.47 mv for the np-eugs. this negative potential can be attributed to the molecules of the polymer wall-forming anionic polymer (eudragit l 100-55) that imparts a negative charge to the obtained nps due to their methacrylic acid groups. the zeta potential of the nps depends mainly on the chemical nature of the polymer, in addition to the chemical nature of the stabilizing agent. therefore, when nps are prepared for methacrylate-derived polymers using nonionic stabilizing agents, negative zeta potential values are obtained due to the presence of terminal carboxylic groups of the polymer[25]. therefore, it follows that eudragit effectively formed an envelope that constitutes the outer wall of the nanoparticles. the core will correspond to the nano-encapsulated eug. similarly, the zeta potential can be considered as an indicator of the stability of the np dispersions. although it is considered as a general rule that absolute values around 30 mv provide good stability. but when using surfactants (i.e. pva), which act mainly by steric stabilization, values below 20 mv or much lower can provide sufficient stabilization of the dispersions[24,26]. this negative potential is also important because it could facilitate the interaction of np-eug with the membrane of plant pathogenic microorganisms which would ensure that the interaction of eug is directly from the np to the microorganism, thus improving, therefore, its antimicrobial effectiveness[27]. figure 2. chromatogram of eug (40 μg∙ml−1) and carvacrol (10 μg∙ml−1) with car/pdms coating (75 μm) by gc-fid. to complete the physicochemical characterization of the np-eug, eug was extracted from the nps using the hs-spme technique and quantified by a gc-fid analytical method to determine the encapsulation efficiency (%ee) (table 1) using equation (1). regarding the hs-spme technique, a 75 μm car/pdms fiber was used because eug is a partially polar component (log po/w = 2.7) of low molecular weight (164.20 g∙mol−1) that has affinity for this type of fibers. figure 2 shows the chromatogram of eug extracted by the hs-spme technique and the internal standard (carvacrol) used 52 to determine the %ee by the gc-fid analytical method (figure 2). the %ee obtained for the np-eug was 31.85 ± 12.77 (table 1) indicating that more than 30% of the eug added during formulation was encapsulated in the np using the nanoprecipitation technique, therefore, it is likely that this active compound is gradually released from the np to the fruit surface. 3.2 evaluation of the preservative effect of nanoformulation in combination with an edible coating on the shelf-life parameters of tomato (solanum lycopersicum) firmness. figure 3 shows the results of firmness tests performed on tomatoes after 16 days of storage at room temperature. the firmness of the tomatoes was 1.5 n at the beginning of the experiment. this parameter decreased for all groups of tomatoes tested. a 42.7% decrease in firmness was observed in tomatoes without any treatment (ctrl) (0.86 n). tomatoes treated with alg (0.68 n) and alg-eug (0.71 n) showed a loss of 54.7 and 52.7%, respectively, while tomatoes treated with np-bco (0.87 n) had a firmness value similar to the initial one. no significant difference was found between the alg, alg-eug and np-bco groups with respect to the ctrl group. figure 3. firmness, day 0 and day 16, of tomatoes after storage for 16 days at 25 °c. ctrl = no treatment, alg = alginate, alg-eug = alginate + free eugenol, np-bco = np without active, alg-np-eug = alginate + np with eugenol (n = 3; �̅�𝑥 ± ds). * significant difference with respect to the ctrl group. tomatoes treated with np-eug in combination with rc (alg-np-eug) showed higher firmness (1.10 n) compared to the four previous treatments, representing only 22% loss compared to untreated fruit (ctrl). this difference was statistically significant. firmness of fruits and vegetables is related to cell wall structure, which depends on the turgor, cohesion, shape and size of the cells that make up the cell wall. water loss is closely related to the loss of turgor of mesocarp cells, decreasing fruit firmness[28]. in this work, the presence of the rc alg-np-eug could interfere with the decrease in fruit transpiration rate, resulting in a lower loss of firmness of the treated tomatoes. similarly, the loss of firmness is related to an increase in the activity of hydrolytic enzymes (i.e. polygalacturonase) that act on cell wall pectins, resulting in tissue changes, which in turn cause fruit softening[29]. this enzyme activity is low during the first stage of fruit development, and then increases and reaches a maximum in the climacteric stage of the ripening process[30]. similar results were reported by fagundes[31] who obtained firmness results similar to the initial ones in tomatoes treated with hydroxypropyl methylcellulose and beeswax coatings after 15 days of storage. the authors attribute this firmness retention in coated tomatoes to the reduction in enzyme activities caused by the modification of the internal atmosphere of the fruit. that is, to a lower respiration rate. similarly, in our study, the al of the rc alg-np-eug had the ability to act as a barrier that interfered with gas exchange, which led to a reduction in the respiration rate of the tomatoes and prevented water loss. furthermore, it is possible that the biological activity of the nanoencapsulated eug decreased the en 53 zymatic activity of the fruit, resulting in slower ripening. color change. in the food industry, to measure color change in a product such as tomato, coordinates expressed in numerical values have been established to correlate color with maturity. in this study, color changes were determined by the ciel a* b* color scale, where a* is the red/green coordinate (+a* indicates more red and −a* indicates more green), while b* is the yellow/blue coordinate (+b* indicates more yellow and −b* indicates more blue). figure 4 shows the analysis of the 3 coordinate values obtained, presented as the color change (δe), using equation (2), produced in each of the groups treated and stored for 16 days. a δe value of 219.75 was obtained for ctrl, 255.71 for alg and 210.80 for alg-eug, 167.76 for np-bco and 190.47 for rc alg-np-eug. less color change is interpreted as preservation of tomato quality. although there was no significant difference between the groups, it can be observed that the presence of the np in combination with the alg-np-eug rc on the fruit surface could have an effect on color preservation. it is important to mention that tomato, upon reaching commercial maturity, undergoes minimal changes in color, which is the characteristic of climacteric fruits. different authors have mentioned that the application of coatings can delay color changes in tomatoes during storage by creating a modified atmosphere in the fruit[23,31]. total soluble solids and titratable acidity. tss of fruits tended to increase during ripening. the tss value (figure 5) for tomatoes at the beginning of the experiment was 3.64 °brix. after 16 days of storage, this parameter increased for control tomatoes (4.83 °brix), as well as for tomatoes treated with alg-eug (4.74 °brix), alg (5.21 °brix), np-co (5.08 °brix) and rc alg np-eug (4.31 °brix). figure 4. color change of tomatoes after storage for 16 days at 25 °c. ctrl = no treatment, alg = alginate, alg-eug = alginate + free eugenol, np-bco = np without active, alg-np-eug = alginate + np with eugenol (n = 3; �̅�𝑥 ± ds). figure 5. total soluble solids, day 0 and day 16, of tomatoes after storage for 16 days at 25 °c. ctrl = no treatment, alg = alginate, alg-eug = alginate + free eugenol, np-bco = np without active, alg-np-eug = alginate + np with eugenol (n = 3; �̅�𝑥 ± ds). 54 the increase in tss during storage is due to respiration. during the ripening process, sugar accumulation will depend on the degradation of starch, the main energy storage compound in green tomato. in addition, metabolic activity continues as a result of fruit ripening, leading to the conversion of carbohydrates and organic acids into sugars to be used in various metabolic processes[10]. on the other hand, compared to the control group, the coating in combination with np-eug (alg-np-eug), showed the lowest tss values. this behavior could be attributed to the presence of al cr and a synergy with np-eug, which causes a more effective deceleration of respiration and metabolic activity, delaying the fruit ripening process. these results are similar to that reported by sucharitha, beulah and ravikiran[33] who treated tomatoes with chitosan coatings and reported a significant difference at the end of the storage period (15 days) between samples coated and not coated with chitosan. in our study, a difference in tss was observed between rc alg-np-eug (4.31 °brix) and alg alone (5.21 °brix). this could be due to the presence of the nps with encapsulated eug on the fruit surface for a longer time and, in addition to the barrier properties of the coating, the sustained release of eug from the nps could have extended the biological activity of eug (e.g. antioxidant) on the surface of the tomato, which contributed to better fruit preservation. finally, as shown in figure 6, the ta of tomatoes was 1.6 g 100 ml−1 at the beginning of the experiment and after 16 days of storage, ta values decreased for all groups. this reduction in ta values is associated with the metabolism of organic acids in the fruits during the ripening process. organic acids are responsible for fruit acidity which is expressed as ta. during the ripening of tomatoes, the amount of organic acids decreases, and this is due to the fact that organic acids are metabolized mainly to ensure the additional supply of carbon for obtaining sucrose, glucose and fructose in the fruit[34]. as for the groups of tomatoes with treatments, the ta results had the same trend as those obtained for tss. after 16 days of storage, tomatoes in the control group had the most significant decrease in ta, while those in the alg-np-eug had the lowest decrease in ta. this means that the coating in combination with the np-eug was the most effective treatment in delaying ripening, which can be attributed to the presence of the al coating that acted as a barrier and decreased the respiration rate (metabolism) of the tomatoes. figure 6. titratable acidity, day 0 and day 16, of tomatoes after storage for 16 days at 25 °c. ctrl = no treatment, alg = alginate, alg-eug = alginate + free eugenol, np-bco = np without active, alg-np-eug = alginate + np with eugenol (n = 3; �̅�𝑥 ± ds). 3.3 evaluation of the protective effect of nanoformulation in combination with edible coating on tomato fruits inoculated with the phytopathogen colletotrichum gloesporoides the tomato crop is affected by various postharvest diseases, many of which are caused by fungi. among the main postharvest phytopathogenic agents of tomato are: fusarium solani, botritys cinerea, alternaria alternata, penicilium expansum and, particularly, colletotrichum gloesporoides[35]. in the present study, tomatoes with each of the aforementioned treatments were inoculated by 55 puncture with the phytopathogen colletotrichum gloesporoides and their development was observed for 5 days at room temperature in humidity chambers. the results are shown in figure 7. after 5 days, the tomatoes treated with rc alg-np-eug showed no fungal growth (figure 7e), while the rest of the fruit showed characteristic colonies of the fungus colletotrichum gloeosporioides. this protection is due to the antimicrobial capacity and effect on phytopathogens of eug[36–38]. hong[39] demonstrated that clove eo and eugenol exhibited significant inhibition of colletotrichum gloeosporioides growth by reducing the diameter of a lesion in immature green bell pepper inoculated with this phytopathogen. in addition, the incorporation of eug into the polymeric structure of the np may cause an increase in residence time on the fruit surface by decreasing its rapid evaporation when applied freely. it has been proposed that the mechanism of action of the antifungal activity of eo components appears to depend on their chemical structure and their ability to pass through the cell wall and penetrate between the fatty acid chains of the lipid bilayer, making the cell membrane much more permeable and, as a result, cause cell death or inhibition of sporulation and germination of fungi or other spoilage-causing microorganisms[40–42]. taking into account this mechanism, the eug incorporated in the nps in combination with the rc helped to have a more intimate and prolonged contact between the active and the microorganisms on the fruit surface. figure 7. pathogenicity test with c. gloesporoides after 5 days of storage of tomatoes with different treatments. a) = control, b) = alginate, c) = alginate + free eugenol, d) = white np, e) alg-np-eug. 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78: 61–71. can v3i1 2020.pdf characterization and application of nanomaterials (2020) volume 3 issue 1 original research article department of mechanical engineering, celal bayar university, manisa daire 45030, muradiye, turkey. e-mail: simge. gencalp@cbu.edu.tr keywords: et al et al. et al. et al. dagpsf psf g a d et al. et al. et al. et al. et al. et al. et al. et al. dis psf et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. microsoft word can-6401 characterization and application of nanomaterials 2024, 7(2), 6401. https://doi.org/10.24294/can.v7i2.6401 1 article qca-based design of polar encoder circuit sravan kumar vittapu, ravichand sankuru, chepuri rakshana, beeradhar mahesh*, amudha naga teja department of ece, nalla narasimha reddy education society’s group of institutions, chowdariguda, hyderabad 500088, telangana, india * corresponding author: beeradhar mahesh, beeradharmahesh@gmail.com abstract: in the last few decades, nano-electronic devices have been manufactured using vlsi technology. over the past four decades, ic technology has been growing by using cmos technology successfully, but this cmos technology has a scaling limitation. to overcome this scaling limitation, qca (quantum dot cellular automata) emerges as an alternative. this work is the implementation of the design of a polar encoder using qca technology. this design is a single-layered and even bottom-up approach technique. the polar code is more efficient and has less energy dissipation compared to the turbo code and conventional codes (cc). this design explores (8:4). a polar encoder is designed to have fewer cells and area compared to the turbo encoder and conventional encoder. the proposed design is implemented using the qca designer tool. keywords: alu; cmos; nano technology; polar encoder; qca; vlsi 1. introduction the ic technology is growing faster and is using vlsi technology successfully. however, the scaling limitation of the cmos technology is the main disadvantage. this leads to a switch to an alternative approach. qca is a nano technology that has emerged as an alternative to cmos technology. an encoder is an electronic digital circuit that compares the inputs and outputs. an encoder is used in error correction and communication networks. at the nanoscale level, quantum-dot cellular automata (qca) is an emerging computing technology beyond the current paradigm. qca uses charge to encode binary values. information is processed with the aid of the intercellular coupling mechanism and the qca cell’s configuration or magnetization. in comparison to cmos devices, qca might provide high device density, high integration, and high switching speed with extremely low energy dissipation. up until now, qca has been used to design and implement a large number of sequential and combinational logic circuits. in addition, a simple processor design strategy and complex arithmetic circuits demonstrate the qca’s efficiency as a viable nano computer. inherent shift-register capacity in qca, as opposed to conventional characteristics of logic circuits, results in cyclic 4-phase clocking in qca devices. circuits have been investigated in a number of studies. the key design element for storage is “memory-in-motion” and for computation, it is “logic-in-wire”, in order to achieve high performance and device density. the issue of “layout = timing” in qca design is illustrated by using variables like wire length, clock zone width, wasted space, and physical feedback. these factors are taken into account when designing qca circuits in an effective and dependable manner. additionally, a number of design guidelines are put forth by the researchers to accomplish dependable and effective nano-scale digital circuit citation vittapu sk, sankuru r, rakshana c, et al. qca-based design of polar encoder circuit. characterization and application of nanomaterials. 2024; 7(2): 6401. https://doi.org/10.24294/can.v7i2.6401 article info received: 14 may 2024 accepted: 8 july 2024 available online: 26 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 6401. 2 design in qca. in qca, nano communication has drawn interest from a broad spectrum of researchers. numerous nano communication architectures based on qca have previously been documented by scholars. however, there are still many different domains in which to construct a qca-based architecture for nano communication. this study investigates the design. 2. related work to build the qca architectures for nano communication, several works have been proposed [1–28]. to maximize channel utilization, a multiplexer (mux) and demultiplexer (demux)-based router architecture was created in qca, as proposed by tirthji maharaja jagadguru [1]. the computational fidelity for channels composed of qca devices in nanocomputing has been calculated by van loan [2]. an array of qca cells is used as the noisy channel for the estimation. the random flaw in the array has been taken into account during measurement. a nano-router circuit employing demux, piso converter, and crossbar architecture is suggested by hashemi and navi [3] in contrast to the method presented by das and de [4]. a detailed description is given of how well this nano-router routes information. a 4-bit data processor circuit was implemented in qca by sardinha et al. [5]. that data processor can be used for various multifunctional tasks, including sigmoid function creation and information preprocessing. sayedsalehi et al. [6] presented a strong qca architecture with serial communication capabilities. this design includes a sipo converter, a piso converter, a parity checker, and a hamming code generator. the turbo encoder design process and its implementation in qca are illustrated by yao et al. [7]. the use of reversible logic in qca and its application in the design of nano communication architecture are discussed. to further achieve security during nano communication, a number of cryptographic and steganographic architectures have been developed by kamaraj et al. [8], kianpour et al. [9], and angizi et al. [10]. an enhanced arithmetic logic unit (alu) design in qca has been demonstrated in zhang et al. [11]. the alu is made up of a 1-bit full adder, a 2:1 mux, and a two-input xor gate. additionally, it has been explained in sheikhfaal et al. [12] how those i/o interfaces can be used to solve the issue with conventional tri-state gates. sayedsalehi et al. [13], an effective. qca sram cell implementation has been investigated. one 3-input mv, one 5-input mv, and a 2:1 mux are included in this design. accurate descriptions are also provided for energy efficiency and structural strength. a brand-new programmable qca circuit is shown in ahmad et al. [14]. crossbar architecture is used in the design of the circuit. you can use this proposed circuit to build any type of boolean logic. the architecture helps create and model area-efficient, stable, and consistent qca circuits. a synchronous counter with a reliable and effective architecture is described in kalogeiton et al. [15], das and de [16,17]. dflip-flip and edge-to-level converter circuits make up the design. a proposed efficient fredkin gate with qca implementation can be found in das and de [18] and chandra das and de [20]. the fredkin gate is then used to create an authenticator circuit that uses the user’s password to identify the authorized user. compared to previous qca-fredkin gates, this one has a lower cell count, latency, and device area. in order to investigate circuit stability, the characterization and application of nanomaterials 2024, 7(2), 6401. 3 computational functionality under thermal randomization is also assessed. by zhang et al. [21], the qca design of a block cipher employing an electronic code book (ecb) is demonstrated, and qca technology is used to implement it. a proposed encoder circuit with dual functionality as a decoder circuit is able to construct block ciphers. polar code a polar code is an error-correcting code. polar code uses recursive cascading, which converts the physical medium into a virtual medium. the main advantage of the polar code is that there is less polarization. a polar code has 4 tuples (i.e., n, r, a, ua). here, n represents the block length; r represents the code rate; a is the bit position; and ua is the fixed rate. this polar code has k inputs and n outputs. this design explorer (8:4) in the polar encoder, the code rate is calculated by (k/n). the code rate of this proposed design is (1/2), which is the code rate. a polar code, often known as an error-correcting code, is a kind of linear block code that ranges from 23 to 25. cascaded recursively over the short kernel code is employed in the creation of the polar code, which transforms the tangible medium into a virtual one by azimi et al. [22] and zhang et al. [23]. for a high quantity of repeat. the information bits are allocated to the most dependable virtual medium based on whether the virtual medium has low or high polarization during the simulation process. with polynomial dependence by premananda et al. [24] on the gap to capacity, it was built to achieve the capacity of symmetric binary-input discrete memory-less channels (b-dmc). in formal terms, a polar code is defined as a 4-tuple (n, r, a, ua), in which n is the block length (i.e., the length of information bit travelled via the communication channel) by teen et al. [25]. the code is represented by r ∈ [0,1]. a polar code, often known as errorcorrecting code, is a kind of linear block code that ranges from 23 to 25 by dehbozorgi et al. [26] and siddaiah et al. [27]. it cascaded recursively over the short kernel code. 3. proposed work figure 1. block diagrams of (a) g2; (b) g4; (c); g8 [9]. characterization and application of nanomaterials 2024, 7(2), 6401. 4 the proposed polar encoder has 4 inputs and 8 outputs, which represents the (8:4) polar encoder. this encoder has g8 and ‘a’ be the input (ai = a1, a2, a3, a4, …, an) and the ‘b’ the output (bi = b1, b2, b3, b4, …, bn). actually, this encoder is given 8 inputs, of which 4 are frozen or fixed with values, and the remaining 4 are for giving inputs. so, here, a1, a2, a3, and a5 are frozen inputs, and a4, a6, a7, and a8 are given inputs, as shown in figure 1. 3.1. construction of g8 the g8 structure can be denoted by gn. to achieve the construction of g8, firstly, the construction of g2 is made. by using g2, the g4 is made, and lastly, by using g4, the construction of the g8 is made. one way to define it is by using a simple recursive rule. this section deals with the construction of g8. to attain the structure of g8, first the building of g2 has been completed. after that, g4 was constructed using the structure of g2. lastly, employ g2 and g4, the building blocks of g8. 3.1.1. design of g2 the outputs of g2 are two (b1, b2) and two inputs (a1, a2). figure 2 (where ⊕ indicates the xor operation and the input-output mapping is displayed) and figure 3 demonstrate that the output b2 is equal to the input a2, and the output b1 is the xor value of the inputs a1 and a2. therefore, building the structure of g2 just requires a single xor operation. b1 = a1 ⊕ a2 b2 = a2 figure 2. design of g2. figure 3. implementation of g2 design. characterization and application of nanomaterials 2024, 7(2), 6401. 5 3.1.2. design of g4 the structure of g4 can be easily created by concatenating four copies of g2, as fig-4 illustrates. it maps inputs (a1, a2, a3, and a4) to outputs (b1, b2, b3, and b4). b1 = a1 ⊕ a2 ⊕ a3 ⊕ a4 b2 = a3 ⊕ a4 b3 = a2 ⊕ a4 b4 = a4 as said, one xor operation is needed for the production of g2. as a result, to complete the qca implementation of g2, corresponding to figure 3, as illustrated in figure 4, one qca xor circuit is sufficient. figure 5 displays the qca layout. figure 4. design of g4 [9]. figure 5. implementation of g4. characterization and application of nanomaterials 2024, 7(2), 6401. 6 3.1.3. design of g8 the construction of g8 includes 4 blocks of g2 design and two blocks of g4 design, as shown in figure 6. it has 8 inputs (a1, a2, a3, a4, a5, a6, a7, a8) and 8 outputs (b1, b2, b3, b4, b5, b6, b7, b8). figure 7 illustrates the implementation of g8. b1 = a1 ⊕ a2 ⊕ a3 ⊕ a4 ⊕ a5 ⊕ a6 ⊕ a7 ⊕ a8 b2 = a5 ⊕ a6 ⊕ a7 ⊕ a8 b3 = a3 ⊕ a4 ⊕ a7 ⊕ a8 b4 = a7 ⊕ a8 b5 = a2 ⊕ a4 ⊕ a6 ⊕ a8 b6 = a6 ⊕ a8 figure 6. design of g8. figure 7. implementation of g8. characterization and application of nanomaterials 2024, 7(2), 6401. 7 4. experimental results the design of g8 has no fixed cells and has (8:4). the g8 design has fixed polarized input cells, and 36 are fixed polarized qca cells. totally, the g8 design consists of 40 fixed polarized cells. the design is simulated using the qca designer program. the qca implementation of g2 is accomplished by using the wire crossing technique suggested by abedi et al. to implement single-layer wire crossing in qca, the four-phase clocking approach of qca designer, with its benefit of two clock zones, is helpful. it is demonstrated by angizi et al. [10] that clock zones 0 and 2 can be combined to build a wire cross. the same thing plotting the simulation result corresponds to figure 6. the legitimate outputs are displayed in a rectangle box. figure 6 illustrates that when a1 = 0 and a2 = 0, the resulting values are b1 = 0 and b2 = 0. the results are b1 = 1 and b2 = 1 for a1 = 0 and a2 = 1. in a similar vein, every output appears in accordance with every input. this outcome validates the theoretical values, demonstrating the accuracy of the design. another interesting finding from figure 6 is that the output appears during the second clock cycle, meaning that it is delayed by one clock cycle after the input. in the work of vangala et al. [28], algorithms for polar encoders were proposed, and in the work of babar et al. [29], polar encoder types were designed using qca. two g2 copies are needed for the production of g4. as seen in figure 4, the qca implementation of g4 will thus be done utilizing two qca circuits in g2. figure 8 displays the qca layout from figure 9. the design is simulated using qca. figure 8. output waveform of g2. characterization and application of nanomaterials 2024, 7(2), 6401. 8 figure 9. output waveform of g4. figure 10 displays the simulation results that correlate. the legitimate outputs are displayed in a rectangle box. as can be seen from figure 6c, the output is b1 = 0, b2 = 0, b3 = 0, and b4 = 0 when a1 = 0, a2 = 0, a3 = 0, and a4 = 0. the result is b1 = 1, b2 = 1, b3 = 1, and b4 = 1 when a1 = 0, a2 = 0, a3 = 0, and a4 = 1. in a similar manner, the input combinations determine how each output appears. therefore, the outcome validates the theory. figure 10. output waveform of g8. characterization and application of nanomaterials 2024, 7(2), 6401. 9 figure 10 describes the simulation result corresponding to the (8:4) polar encoder as it is displayed in figure 7. the valid results are displayed using the rectangle box. according to figure 8b, the outputs for data bits a4 = 0, a6 = 0, a7 = 0, and a8 = 0 are b1 = 0, b2 = 0, b3 = 0, b4 = 0, b5 = 0, b6 = 0, b7 = 0, and b8 = 0. this is because all of the frozen bits (i.e., a1, a2, a3, and a5) are set to zero. the outputs are b1 = 1, b2 = 1, b3 = 1, b4 = 1, b5 = 1, b6 = 1, b7 = 1, and b8 = 1 for the data bits a4 = 0, a6 = 0, a7 = 0, and a8 = 1. in the same vein, every output appears in accordance with the data bits. as a result, the outcome validates the theoretical values, proving the design’s accuracy. figure 10 also shows that the output is six clock cycles behind the input; that is, the legitimate output appears at the eleventh clock cycle. the performance comparison of the proposed schematic with the existing one is shown in table 1. from table 1, it is clear that the proposed schematic outperforms the existing [11] in terms of cell count, area, and complexity. table 1. comparison of proposed vs. existing [11]. parameters existing [11] proposed cells count 2275 1188 area (um2) 5.4320 1.915 complexity more less 5. conclusion in this work, the (8:4) polar encoder circuit is designed for nano scale communication and implemented using the qca platform. here, the bottom-up approach is used to reduce the complexity, and it is performed by a single layer, which reduces the complexity even during the physical device fabrication. the code proposed has a lower cell count and less area compared to other encoders that use turbo and cc codes [11]. the top-down method has been taken into consideration to simplify the design. the implementation is done in a single layer, which helps lower complexity while fabricating devices. the communication procedure with the polar encoder is depicted in the communication architecture. it is helpful to give fault-free design with the stuck-at-fault effect analysis. the suggested test vectors are robust enough to enable 100% fault coverage. the simulation result validates the encoder circuit’s design accuracy. device area and circuit latency demonstrate the quicker speed at which the polar encoder circuit may work at the nanoscale. the low dissipated energy of the proposed polar encoder circuit is verified through energy dissipation estimation. author contributions: conceptualization, skv and cr; methodology, cr, bm and ant; software, cr; validation, skv and rs; formal analysis, cr; investigation, skv, rs; resources, cr; data curation, cr; writing—original draft preparation, skv and cr; writing—review and editing, skv and cr; visualization, cr, bm and ant; supervision, skv; project administration, cr, bm and ant. all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. characterization and application of nanomaterials 2024, 7(2), 6401. 10 references 1. 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nanomaterials (2022) volume 5 issue 1 doi:10.24294/can.v5i1.1680 59 review article nanotechnology, architecture and art adriana lira oliver1*, alicia oliver2 1 facultad de arquitectura, universidad nacional autónoma de méxico, mexico. e-mail: adrianalira@post.harvard.edu 2 instituto de física, universidad nacional autónoma de méxico, mexico abstract in the past three decades, nanotechnology has attracted extensive attention. people have many expectations on the utilization of nanotechnology in medicine, but unfortunately, these expectations are unlikely to be realized. in the field of nanotechnology, the niche for building commercial products has not been developed yet. however, metal nanoparticles have attracted people’s attention since ancient times because of their optical properties, which are very different from those of bulk metals. by understanding the origin of these optical properties and using current technology, these nanoparticles can be manipulated to build a palette. using micro measurement equipment, the palette can be printed with very good resolution. keywords: metal nanoparticles; plasma; photoprinting article info received: 7 january 2022 accepted: 26 february 2022 available online: 9 march 2022 copyright copyright © 2022 adriana lira oliver, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction in the past decade, the word “nanotechnology” has appeared on countless occasions, referring to great inventions that will change our lives. unfortunately, we live in a world that is distorted by mass media transmission. we believe that the trivialization of the term nanotechnology is due to two basic factors: (1) after an important discovery, scientists’ emotions confuse them and sometimes have high expectations for future applications; and (2) the media exaggerate the news coverage of this discovery. therefore, the new discoveries realized by science through dissemination to others distort the meaning of social life and produce high expectations that are often difficult to achieve. at the end of the second world war, the great potential of nuclear energy emerged. it is generally believed that nuclear energy will solve human problems in this regard, but it didn’t happen. in the 1980s, when the high-temperature superconductor was discovered, the superconductivity of this material was higher than the temperature of liquid helium, higher than -269 °c. it was also said that the energy problem would be solved to a great extent: in our daily life, the current of a conductor is expected to be maintained indefinitely, but this did not happen. however, it is undeniable that apart from its negative uses, nuclear energy is beneficial to people’s lives in many ways. on the other hand, at more accessible temperatures, such as -196 °c, superconductivity has opened up a new research field. the same is true for nanotechnology. there is no doubt that nanotechnology is bringing great benefits to the fields of biomedicine, energy, environment, and photonics (aimed at replacing electronics). 60 metal nanoparticles, due to their surface plasmon resonance characteristics, produce a very strong near nanoscale electric field at nano distance, making them high-sensitivity and high-resolution sensors in two-state systems and photonics[1,2]. in order to understand what we are going to write about architecture and art, we must first understand what nanotechnology is. 2. nanotechnology nanotechnology originates from the understanding of nanostructures in nanoscience. from the perspective of size, the nanostructure is a collection of atoms or molecules, and its size is on the non-metrological scale (1 nm = 10−9 meters, 1000 times that of 1 micron). a cell with a size between 5 and 50 microns is tens of thousands of times larger than what we mean by nanostructures. however, nanostructures have always existed and been produced. but these structures were not understood until a few years ago. for nanoscience, the nanostructures that make up nanotechnology are those basic elements, whether atoms or basic crystal cells. in nanoscale aggregates, they show characteristics different from the mass properties we are used to in our daily life. not all nanostructures show characteristics different from large volume structures, so these characteristics are not considered in nanotechnology. at present, however, nano-sized materials, whether or not they have properties different from those in large volume, are considered a part of nanotechnology products. in the field of architecture, there are few truly commercialized and large-scale nanotechnology products. this paper describes the real nanotechnology materials used in architecture and the materials currently being developed for printing. 3. metal nanoparticles and plasma plasma is a new branch of science. the term was coined by a group of scientists at the california institute of technology in 2000[3]. plasma refers to the surface plasma that produces light when being hit by metal particles. we know that light is an electromagnetic wave composed of oscillating electric and magnetic fields. when the electric field of the wave acts on the metal nanoparticles, the free electrons of the super surface metal oscillate with the electric field of the wave. through some physical mechanisms, the nanoparticles absorb a large amount of light. at some wavelengths, this absorption occurs in a privileged form, which is called surface plasmon resonance. this phenomenon only occurs when the size of metal particles is much smaller than the wavelength of the incident light, from some nanometers to 100 nm, so it will not occur in a large volume of materials[4]. this particularity bestows these nanoparticles’ interesting optical properties in nonlinear optics[5], photonics[6], and biomedicine[1,7]. interestingly, this phenomenon leads to the absorption of metal nanoparticles in the ultraviolet and visible regions. in special cases, nanoparticles over 100 nm absorb in the infrared range of the electromagnetic spectrum[8]. 4. light and color light is an electromagnetic wave, which is part of the electromagnetic spectrum. the electromagnetic spectrum is very broad, including wavelengths ranging from picometers to kilometers. in this large range, light occupies the so-called visible region, which is a very small region of the electromagnetic spectrum. white visible light disperses through a prism and is separated into its component colors. this is because visible light consists of wavelengths between 380 and 780 nm, which are perceived by the eyes and detected as color in our brain. we know that the color of objects is caused by the different lengths they absorb and the different lengths reflected by other objects and detected by the eyes. therefore, metal nanoparticles up to 100 nm absorb the visible light band and show a color that metals do not have in a large volume. 5. the wonderful world of color in metal nanoparticles in the previous section, we have said that metal nanoparticles selectively absorb visible light at some visible wavelengths. specifically, this absorption is carried out in some nanoscale to 100 nanoscale structures. in addition, nanoparticles can 61 have different shapes. according to the size and shape of nanoparticles, surface plasmon resonance, when the light is absorbed to the greatest extent, can move and expand in the spectrum, so as to change the color. we know that if it absorbs blue light, the color will turn yellow. this is why the surface plasmon resonance wavelength of silver nanoparticles embedded in glass with a spherical diameter of about 10 nm is 380 nm and the width extends to blue. this is why these nanoparticles appear yellow. if the size and shape of these particles change, surface plasmon resonance can occur at higher or lower wavelengths, or can be expanded according to the situation to produce different colors. if the green color is absorbed, the color will be red. another example is gold nanoparticles. if these nanoparticles are spherical, they are between 4 nm and 20 nm, and their surface plasmon resonance is 520 nm. therefore, they have strong absorption of green, making them look red. if their size increases to about 90 nm, they will appear blue. nanoparticles can have a range of bright colors depending on their shape and size. figure 1 shows a series of solutions containing metal nanoparticles of different elements of different shapes and sizes. when these nanoparticles are embedded in glass, they will show different colors according to the nanoparticles involved. figure 1. metal nanoparticles in solution. source: josé i. garcía laureiro, isqch. blog promotion of institute of chemical synthesis and homogeneous catalysis higher scientific research council (csic) of the university of zaragoza, spain. 6. design of nanodevices the synthesis of metal nanoparticles can be carried out by chemical or physical methods. it is relatively simple to synthesize in an aqueous solution by chemical method. the color is really bright. as early as 1875, michael faraday already had the solutions. he first described these colors scientifically, referring to very small particles with optical properties different from large volume metals. one physical method is ion implantation. through the particle accelerator, the required metal atoms are introduced into the dielectric one-to-one[9]. the obtained material is then treated at a high temperature and special atmosphere. figure 2 shows two different amounts of high-purity silica-implanted gold. these materials were obtained at the pelletron accelerator laboratory of the unama institute of physics. although the properties of metal nanoparticles had already be explained in the 19th century, the discipline of nanoscience and nanotechnology has only emerged recently after completely repeatable synthesis and analysis methods have been developed. this is the result of scientific and technological progress. the synthetic methods of these systems, both physical and chemical, have made great progress. nowadays, people are designing the particles to be manufactured. if coupled with the extraordinary scientific instruments in the 20th century, a series of analytical methods would be able to produce microscale materials; this progress would usher in the nanoscale ear at a faster pace. for example, the emergence of nanoparticles expedites the development of ultra-high-resolution transmission electron microscopy. this technology enables us to view the location of nanoparticles and their atoms (figure 3). on the other hand, really complex calculations have been carried out on desktop computers, so that they can simulate and predict what shapes correspond to surface plasmon resonance so as to determine its specific optical characteristics. this makes it possible to produce dispersible materials with very special properties. figure 2. high-purity silica with spherical gold nanoparticles with an average diameter of 10 nm. (a) low gold ion inflow. (b) high gold ion inflow. source: authors’ images. 62 figure 3. high-resolution transmission electron microscopy micrograph of gold nanoparticles in ion-implanted silicon. source: authors’ image. therefore, at present, science and technology allow the use of nanostructures to design, operate and, in some cases, build devices for different applications[10]. 7. there is nothing new in the sun colored glass and colored glass beads have always attracted people. humans have learned to make colored glass since ancient times. the main glass products are colored bead necklaces. as early as 1200 bc, egypt had a blue or green transparent glass. of course, it was also in egypt people found out that adding metal oxides to molten glass would produce beautiful colors. however, the people who did glassblowing are phoenicians. during the roman empire, the manufacture of glass products spread throughout the empire and germany. figure 4. likugo rome cup at british museum. (a) illumination on the observer’s side. (b) rear illumination relative to the observer. source: figures (a) and (b) were photographed by john bode and mary ranran, respectively. in ancient times, craftsmen were already utilizing nanotechnology in producing glass products with colors. an indisputable example is the beautiful likugo cup in rome. the cup was made in the 4th century ad, and its owner had been troubled by the influence of light on the cup for a long time. when illuminated from the observer’s side, it shows green emerald (figure 4(a)), and the glass looks opaque, but when illuminated from the back relative to the observer, it shows translucent and bright red (figure 4(b)). the secret was discovered in 1990. small fragments of the glass were analyzed by electron microscope. the results showed that the glass contained a very accurate mixture of gold and silver particles below 50 nm. through the invention of this cup, we can deduce that knowledge of contemporary nanotechnology was practiced and utilized in manufacturing products in ancient times. perhaps, the most famous building of nanotechnology is the glass window of the gothic cathedral. gothic architecture originated in northern france in normandy in the 12th century. it first spread to the kingdom of france, and then to the holy roman empire. this new architectural style engendered a new form of buildings that were infused with different proportions of romanesque and gothic architecture styles: thinner and higher vaults. in order to withstand the thrust of the vault, the architects designed buttresses with stumps. the exterior wall has a huge gap, and the interior wall produces greater brightness. this gave rise to what is known today, the medieval glass art that embodies its colorful interior. the holy church in central paris is a good example. the walls of this building, which was built in the early 13th century, were replaced by huge windows covered with glass (figure 5). figure 5. holy church of paris. source: photograph by b. didier. 63 the bright indoor environment brings a very special effect to the atmosphere. unlike the effect produced by a normal window, the window used in the building can let all the white light in the solar radiation pass through. these craftsmen, the original nanotechnology experts, know very well what to put in the molten glass and their proportions to obtain the whole color range of the glass. even today, we still appreciate the richness of these works of art (figure 6). figure 6. the glass windows of cologne cathedral. source: photograph by jan van der crabben. figure 7. schematic diagram of the plasma pixel configuration of aluminum nano disk: (a) different arrangement of nanodisk in size and spacing; (b) palette of the basic layout of nanodisk; (c) a hybrid palette that provides different sizes of nanodiscs with a spacing of one pixel; and (d) a palette that combines the size and spacing of nanodiscs into one pixel. source: adapted with the permission of tan et al.[11]. 8. modern nanotechnology and color palette the color image reproduction system uses filters and prisms to disperse light of different wavelengths. with the miniaturization of integrated devices, the research on the image sensor is growing exponentially. the pursuit of high efficiency, low power consumption, and small size poses a great challenge to the traditional system. 64 in the previous section, it was explained that the surface plasmon resonance of metal nanoparticles absorbs light and makes these nanoparticles reflect the light of a certain color. in 2014, scientists from several institutions in singapore built devices containing specific arrangements of aluminum nanodisks of different sizes with different spatial arrangements[11]. in this way, they built plasma pixels to form a palette. each pixel contains four nanodisks of different sizes to create a basic palette. by changing the distance between them and the size of the nanodisk, different colors and tones can be created and converted into the colors and tones of the palette. these nanostructures were obtained by forming nanocolumns on silicon substrate by electron beam lithography. aluminium with a thickness of 20 nm was deposited on silicon substrate by electron beam lithography. the size of each pixel is 800 × 800 nm. as shown in figure 7(a), the basic tray is composed of aluminum nanodisks with the same spacing but different sizes. other colors and tones can be generated using the same size and different spacing. finally, the palette is enhanced by a combination of size, space, and layout geometry. figure 7(b) shows the arrangement of the basic tray, in which only the size changes, the disc diameter is 40 to 330 nm, the step diameter is 10 nm, and the fixed spacing is 400 nm. figure 7(c) shows how the change in size is intertwined with the change in di, where d in each pixel (two nanodisks of one size and two nanodisks of another size) = 80 to 220 nm, with each step of 10 nm. the fixed spacing on the same pixel is 400 nm, 800 × 800 nm, which enriches the palette. in figure 7(d), the color palette is formed by changing the size (d = 80 to 220 nm) and spacing (s = d + 50 to 400 nm) in steps of 10 and 20 nm, respectively, in the arrangement of four nanodiscs in 800 × 800 nm pixels. figure 8. using different strategies of plasma palette to reproduce monet’s sunrise painting: (a) reproduce the original as the input image; (b) copy using only the “primary plasma colors” palette; (c) use the extended palette to reproduce the painting more realistically; (d) enlarge the details in panel (c); and (e) scanning electron microscope micrograph that shows the pixels in different arrays of aluminum nanodisks. source: adapted with permission of tan et al.[11]. 65 these combinations of aluminum nanodisks in pixels produce plasma in the visible palette. in order to show the versatility of their plasma palette contained in the microstructure, these scientists created photo prints of monet’s famous painting dawn. a copy of the original is shown in figure 8(a). in figure 8(b), printing is performed using a limited (basic) plasma palette. in figure 8(c), photo printing with a wider color range can be obtained using an extended palette (a combination of pixel and nanodisk size and spacing). the degree of repeatability is impressive for a micron device, as obtained in the described work. figure 8(d) shows the details, and figure 8(e) shows a scanning electron microscope micrograph of pixels with different arrangements of nanodisks. compared with their gold or silver counterparts, aluminum nanoparticles are very durable and much cheaper. therefore, microdevices with these characteristics have a huge market prospect. 9. conclusion the optical properties of metal nanoparticles are very different from those of large-volume metal nanoparticles. it was first used to decorate objects and is now used as high-resolution photonic microdevices. from the perspective of architecture and art, the charm of color and the effect of light have always influenced mankind. conflict of interest the authors declared no conflict of interest. references 1. heydari e, mabbot s, thompson d. engineering molecularly-active nano-plasmonic surfaces for dna detection via colorimetry and raman scattering. nanoscale imaging, sensing, and actuation for biomedical applications xiii. book series: proceedings of spie 2016; 9721: 972105. 2. kim hs, lee bh, oh gy. significantly enhanced sensitivity of surface plasmon resonance sensor with self-assembled metallic nanoparticles. journal of nanophotonics 2016; 10: 026012. 3. atwater ha. the promise of plasmonics. scientific american 2007; 296: 56–63. 4. kelly kl, ronaldo e, zhao ll, et al. the optical properties of metal nanoparticles: the influence of size, shape and dielectric environment. journal of physical chemistry b 2003; 107: 668–677. 5. torres-torres c, reyes-esqueda ja, cheang-wong jc, et al. optical third-order nonlinearity by nanosecond and 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plasmonic color palettes for photorealistic printing with aluminium nanostructures. nano letters 2014; 14: 4023–4029. http://apps.webofknowledge.com.pbidi.unam.mx:8080/full_record.do?product=wos&search_mode=generalsearch&qid=1&sid=3aubswdqqdbgzcsiuck&page=2&doc=15 http://apps.webofknowledge.com.pbidi.unam.mx:8080/full_record.do?product=wos&search_mode=generalsearch&qid=1&sid=3aubswdqqdbgzcsiuck&page=2&doc=15 http://apps.webofknowledge.com.pbidi.unam.mx:8080/full_record.do?product=wos&search_mode=generalsearch&qid=1&sid=3aubswdqqdbgzcsiuck&page=2&doc=15 http://apps.webofknowledge.com.pbidi.unam.mx:8080/full_record.do?product=wos&search_mode=generalsearch&qid=1&sid=3aubswdqqdbgzcsiuck&page=2&doc=15 35 original research article sedimentation of nanoparticle titanium dioxide in the presence of ammonium duo li1,2, nan xu1,2* 1 school of chemistry, biology and materials engineering, suzhou university of science and technology, suzhou 215009, jiangsu, china 2 jiangsu key laboratory of environmental functional materials, suzhou 215009, jiangsu, china. e-mail: nanxu@ mail.usts.edu.cn abstract due to its physicochemical properties, nanoparticles titanium dioxide (ntio2) is being put into mass production and widespread applications, which inevitably results in their increasing exposure to the water body. after it entering the water body, the chemical properties of ntio2 can be influenced by ion compositions, ion strength and ph, which affects their ecological risk. excess of ammonium (nh4+) fertilizer has contaminated soil and water environments. in this paper, the zeta potentials and hydrodynamic radius of ntio2 were studied in nh4+ solution compared to those in na+ solution. in addition, the sedimentation rate of ntio2 was also investigated. the experiment results show that high ph inhibits the sedimentation of ntio2. moreover, nh4+ increases the stability of ntio2 more than na+ at the same is, which was attributed the more negative zeta potentials and the smaller hydraulic radius. our results provide a theoretical basis for evaluating the ecological risk of ntio2 in aqueous solution containing nh4+. keywords: ammonium; chloride; nanoparticles titanium dioxide (ntio2); sedimentation; zeta potential characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1333 article info received: 13 june 2021 accepted: 5 august 2021 available online: 12 august 2021 copyright copyright © 2021 duo li, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction nanomaterials have small size effects, surface effects, quantum size effects, and macroscopic quantum tunneling effects, so that nanomaterials are widely used in medical[1], chemical[2], environmental[3], microelectronics[4] and other industries. nanotitanium oxide (ntio2), as common nanomaterial, is heavily produced and widely used due to low production cost, good chemical stability and strong photocatalytic capacity[5]. in the production and consumption of ntio2, some ntio2 cannot be released into the natural environment[6,7]. after entering the environment, they will resemble other environmental pollutants and participate in the circulation of the biosphere, where complex migration and transformation processes occur, which will produce ecological effects. for example, yamamoto et al. found that ntio2 increases the generation of reactive oxygen species in skin cells[8], which may damage dna or mutation of the gene and eventually develop to cellular cancer[9,10]. it was found that the nanoparticles affect the properties of the particles themselves. particle size, surface potential, ion species, ion concentration, and ph values all affect the aggregation and settling of nanoparticles in water, hence their reactivity and biotoxicity. therefore, studying the sedimentation capacity of ntio2 in water bodies can 36 provide important theoretical support for assessing the potential ecological risk of ntio2. at present, the global economy is developing rapidly, and science and technology are becoming more and more developed. in agricultural production, a large number of pesticides and fertilizers containing ammonia nitrogen are being used, and the phenomenon of ammonia nitrogen pollution in lakes, groundwater and rivers has become more and more serious. therefore, preventing and controlling ammonia nitrogen pollution is an urgent task in chinese agricultural science, and it is of great practical significance to study the harm of ammonia nitrogen pollution. for example, the fixation of phosphorus in soil was studied by li yanan et al. in the case of synthetic calcium magnesium carbonate, and high ph favored fixation of phosphorus by the material[11]. at the same time, na+ is one of the most widely distributed and abundant ions in groundwater, which is inevitably considered when studying the relevant water environment. it has been shown that ntio2 can be used to remove ammonia nitrogen from sewage[12,13]. after entering the water environment, ntio2 causes aggregation and settlement under van der waals force and electrostatic attraction, which may lead to short stay in water, but also reduce the specific surface area of the particles, affect ntio2 reactivity, reduce photocatalytic performance, and ultimately affect the ability of ntio2 to remove ammonia nitrogen. so far, most reports have been on the effect of ntio2 migration. for example, liu cheng et al. studied the effect of phosphate on ntio2 migration in soil[14], and xu xiaoting et al. studied the effect of phosphate and humic acid on ntio2 migration[15]. however, to date, no report has been reported on the impact of ammonia nitrogen on ntio2 settlement performance, so it is very important to study the aggregation and settlement capacity of ntio2 in water bodies containing ammonia nitrogen. in view of this, the authors mainly studied the mechanism of nh4+ on ntio2 particle settlement, studied the settlement curve of ph values, calculated the settlement rate through zeta potential and nanopularity, and then explained the influence and mechanism of nh4+ on the settlement rate of ntio2 particles in water bodies. 2. materials and methods 2.1 experimental reagents ntio2 was purchased from shanghai gaoquan chemical co., ltd. all other reagents were analytical reagents (ar). 2.2 aggregation experiment of ntio2 accurately measure 1 g of tio2, transfer it to a 100 ml beaker, add 100 ml nh4cl solution and nacl solution with different concentrations (1, 5 and 10 mmol·l–1) respectively, adjust the ph value to 6.0 and 8.0 with hcl and naoh respectively, place the tio2 suspension in the ultrasonic instrument for ultrasonic for 30 min, and then stand for interval sampling, sampling 2 ml each time. the measurement method of ntio2 was measured by diantipyrylmethane method, and the absorbance was measured at 390 nm by shimadzu uv-2450 uv spectrophotometer[16]. dilute 1000 mg·l–1 titanium standard solution to 1–5 mg·l–1 for measurement, and obtain the standard curve of ntio2 concentration (as shown in figure 1). figure 1. curve for ntio2 concentration was determined by uv spectrophotometry. 2.3 the zeta potential and hydraulical diameter measurements of ntio2 accurately weigh 0.01 g of tio2, transfer it to a 100 ml beaker, add 100 ml of nh4cl solution and nacl solution with different concentrations (1, 5 and 37 10 mmol·l–1) respectively, and adjust the ph to 6.0 and 8.0 with hcl and naoh respectively. referring to the research method of fang et al.[17], in order to promote the better dispersion of ntio2 in the solution, the suspension was placed in the ultrasonic instrument for ultrasonic for 10 min, and then each sample was sampled three times. the zeta potential and hydraulic diameter were measured by malvin nano-zs90, and finally the average value was taken. 2.4 settlement efficiency model the sedimentation data were analyzed using the empirical model of quik et al. and velzeboer et al.[18,19]: (1) in which t is the settlement time, ct is the colloidal concentration (g·l–1) at the time t, cres is the residual concentration (g·l–1), c0 is the initial concentration (g·l–1), vs is the sedimentation rate (mm·min–1), h is the height of the water surface distance sampling point, aggregate vs. according to equation (1), assuming not in each solution, the ntio2 samples were dissolved in ionic states. 3. results and discussion 3.1 zeta potential and hydroechanical diameter of ntio2 in nacl solution in figure 2, it studied the zeta potential (a) and hydroechanical diameter (b) of ntio2 at ph = 6.0 and 8.0, in nacl solution. in figures 2(a) and 2(b), the zeta potential becomes slightly less negative with na+ concentration, with particle size (hydroechanical diameter) larger and prone to reunion. when the ph value continues to increase to 8.0, the zeta potential of ntio2 in the water environment becomes more negative and the hydraulical diameter decreases. for specific ph values, both zeta potentials become less negative with increasing na+ concentration, mainly because the charge shielding effect and electrostatic bielectric layer on the ntio2 surface are compressed resulting in reduced net negative charge and reduced zeta potention the particle surface[20,21]. 3.2 zeta potential and hydroechanical diameter of ntio2 in nh4cl solution in figure 3, it studied the zeta potential (a) and hydroechanical diameter (b) of ntio2 at ph = 6.0, were studied in nh4cl solution 8.0. in figure 3(a), the zeta potentials of ntio2 at ph = 6.0 and 8.0 are all negative. at the same nh4cl concentration, the zeta potential at ph = 6.0 is less negative than that at ph = 8.0; in figure 3(b), at the same nh4cl concentration, the particle size of ntio2 decreases with increasing ph values. the possible mechanism leading to this phenomenon is that, zeta, with less than a negative potential. this results in a smaller electrostatic repulsion between the ntio2 particles, making it easier to reunite between ntio2 particles and then leading to a larger particle size. in figure 3(a), the zeta potential of ntio2 becomes less negative with increasing ion concentrations for spefigure 2. zeta potentials (a) and hydraulical diameter (b) of ntio2 in different concentrations of nacl solution under ph= 6.0 and 8.0. 38 cific ph values, consistent with the phenomenon in na+. the increase in the hydrotomechanical diameter in figure 3(b) is consistent with the less negative of the zeta potential in figure 3(a). compared to figures 3 and 2, the zeta potential of ntio2 is more negative and smaller particle size in nh4cl electrolyte solution at the same ph values and the same ion concentration. for example, under the condition of ph = 6.0, the zeta potential and hydroechanical diameter of ntio2 in 1 mmol·l–1 nacl solution are –19.3 mv, 554 nm, and the corresponding value becomes -20.6 mv, 472 nm. when the electrolyte solution is 1 mmol·l–1 nh4cl, the corresponding values are changed to –20.6 mv, 472 nm. 3.3 settlement of ntio2 in the nacl solution figure 4 is the settlement curve of ntio2 in nacl solution in ph = 6.0 and 8.0. the abscissa represents the settling time, and the ordinate represents the ratio of the concentration of ntio2 (c) in the sampled liquid to the initial concentration of ntio2 (c0) under the corresponding settling time. the smaller the ratio, the lower the concentration of ntio2 in the representative sample, and the more ntio2 settled in the corresponding solution. figure 4(a) shows that under the condition of ph = 6.0, although the concentration of nacl solution has no obvious effect on the sedimentation performance of ntio2, on the whole, the higher the ion concentration, the faster the sedimentation rate and the worse the suspension stability. the increase of ion concentration is conducive to the sedimentation of particles, but this effect is not very obvious. according to the sedimentation rate (vs) simulated and calculated according to formula (1), it is found that with the increase of ion concentration, vs only increases from 0.507 mm·min–1 to 0.534 mm·min–1. in figure 4(b), under the condition of ph = 8.0, low nacl concentration (1 mmol·l–1) has obvious sedimentation effect on ntio2, which significantly enhances the suspension stability of ntio2 in water environment. comparing figure 4(a) and figure 4(b), under the condition of 1 mmol·l–1 nacl, ph figure 3. zeta potentials (a) and hydraulical diameter (b) of ntio2 in different concentrations of nh4cl solution under ph = 6.0, and 8.0. figure 4. settlement curves of ntio2 in different concentrations of nacl solution ph = 6.0 (a) and 8.0 (b). 39 value is an important factor affecting the sedimentation performance of ntio2 in water environment; at higher ion concentration, the inhibition effect of high ph value on sedimentation is not obvious. 3.4 settlement of ntio2 in the nh4cl solution as shown in figure 5(a), ntio2 settles at ph = 6.0 with increasing nh4+ concentration, indicating that ntio2 sedimentation performance is affected by nh4+ concentration, and higher sedimentation rate and worse suspension stability, mainly due to the charge shielding effect of the ntio2 surface and electrostatic double electric layer compression theory, and enhanced electrostatic repulsion between particles[19,20].when the ph value increased to 8.0, the suspension stability of ntio2 still weakened with increasing nh4+ concentration. the data in table 1 explain this well: it does increase with ion concentration. this suggests that nh4+ concentration is an important factor influencing the settling properties of ntio2. by comparing figures 5(a) and 5(b), we also found that when the ph increases at the same nh4+ concentration, the smaller the settlement rate, the better the suspension stability. this is consistent with previous zeta potential and hydroechanical diameter results: the zeta potential of ntio2 is more negative and smaller hydraulical diameter at high ph. moreover, the data in table 1 indicate values at ph = 6.0 higher than those at ph = 8.0, indicating that increased high ph improves the suspension stability of ntio2 in the water environment. comparing figures 4(a) and 5(a), it is not difficult to find that nh4+ inhibited the aggregate deposition of ntio2 compared to na+ under the same ionic strength at ph = 6.0. if settlement equilibrium is reached, the value of c/c0 is 0.029 in 10 mmol·l–1 nacl solution, and the ratio is 0.011 in nacl solution. this phenomenon still applies when ph increases to 8.0. the zeta potential and hydraulical diameters in figures 2 and 3 also show that a more negative zeta potential and a smaller hydraulical diameter will make the nanoparticles difficult to settle and enhance stability. it can be seen that nh4+ is conducive to improve the suspension stability of ntio2 in the water environment. figure 5. settlement curve of ntio2 at ph = 6.0 (a) and 8.0 (b) in different concentrations of nh4cl solution. table 1. settlement rates of ntio2 (10 g·l–1) in different electrolyte solutions ph of solution concentration of nh4cl /mmol·l–1 settlement rate vs / mm·min–1 ph of solution concentration of nacl /mmol·l–1 settlement rate vs / mm·min–1 6.0 1 0.570 6.0 1 0.507 5 0.688 5 0.524 10 0.782 10 0.534 0.4598.0 1 0.142 8.0 1 0.214 5 0.196 5 0.459 10 0.363 10 0.466 40 4. conclusion experimental results show that high ph helps to improve ntio2 stability in the electrolyte solution because the increased ph leads to more negative particle surface potential, larger electrostatic repulsion between particles, causing particles to reunite and eventually lead to settle. in the same ph and ionic strength, nh4+ in water than na+ can improve particle stability and suspension, and the settlement rate of ntio2 increases with nh4+ concentration. conflict of interest the authors declare that they have no 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nanosheets on ag using atmospheric pressure plasma for enhanced hardness muhammad mudassar * , muhammad shahid rafique, hafsa mahmood, muhammad arslan, tehreem arshad, ayesha armani, fakhar siddiq, maimoona kanwal, imran shahadat, fazila javed department of physics, university of engineering and technology, lahore 54890, punjab, islamic republic of pakistan * corresponding author: muhammad mudassar, mudassarmuhammadfraz7860@gmail.com abstract: two-dimensional hexagonal boron nitride nanosheets (h-bnns) were synthesized on silver (ag) substrates via a scalable, room-temperature atmospheric pressure plasma (app) technique, employing borazine as a precursor. this approach overcomes the limitations of conventional chemical vapor deposition (cvd), which requires high temperatures (>800 °c) and low pressures (10⁻2 pa). the h-bnns were characterized using ft-ir spectroscopy, confirming the presence of bn functional groups (805 cm⁻1 and 1632 cm⁻1), while fesem/eds revealed uniform nanosheet morphology with reduced particle size (80.66 nm at 20 min plasma exposure) and pore size (28.6 nm). xrd analysis demonstrated high crystallinity, with prominent h-bn (002) and h-bn (100) peaks, and scherrer calculations indicated a crystallite size of ~15 nm. the coatings exhibited minimal disruption to uv-vis reflectivity, maintaining ag’s optical properties. crucially, vickers hardness tests showed a 39% improvement (38.3 hv vs. 27.6 hv for pristine ag) due to plasma-induced cross-linking and interfacial adhesion. this work establishes app as a cost-effective, eco-friendly alternative for growing h-bnns on temperature-sensitive substrates, with applications in optical mirrors, corrosion-resistant coatings, energy devices and gas sensing. keywords: 2d materials; vicker’s hardness; h-bn nanosheets (h-bnns); borazine; surface chemistry; atmospheric pressure plasma (app) 1. introduction boron nitride (bn), a notable member of 2d materials, has been extensively investigated due to its excellent and desirable properties such as high surface toughness, low electrical but high thermal conductivity, surface hardness, versatile thermal and chemical stability, and impermeability to fluids [1–8]. h-bn is white, nontoxic, and impermeable, with a density of 2.27 g/cm3, making it the least dense material in its class. white graphene is the term for the 2-d nanosheets of hexagonal boron nitride [9,10]. owing to their interesting features, they offer considerable potential in a variety of applications, including coatings, stealth, automotive, gas sensing, aerospace, corrosion resistance, catalysts, energy storage, medicine, electronics, high-resolution imaging, water purification and flame retarding [11–17]. boron nitride nanomaterials exhibit exceptional mechanical properties, including a fracture strength of 165 gpa and a young’s modulus of 0.8 tpa [18], alongside high thermal stability (up to 800 °c in air) [19–22] and a low thermal expansion coefficient (−2.72 × 10⁻6 k⁻1) [23,24]. their thermal conductivity (300–2000 w·m⁻1·k⁻1) [24,25] surpasses many conventional materials, making them ideal for thermal management applications. unlike other 2d materials (e.g., graphene, mxene) [26–29], bn nanosheets (bnns) are electrically insulative due to their wide bandgap (~5.6 ev), citation mudassar m, rafique ms, mahmood h, et al. growth of 2d hexagonal boron nitride nanosheets on ag using atmospheric pressure plasma for enhanced hardness. characterization and application of nanomaterials. 2025; 8(2): 11613. https://doi.org/10.24294/can11613 article info received: 20 march 2025 accepted: 21 april 2025 available online: 3 june 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ mailto:mudassarmuhammadfraz7860@gmail.com characterization and application of nanomaterials 2025, 8(2), 11613. 2 low leakage current, and high dielectric strength (12 mv·cm⁻1) [30]. these properties enable bnns-polymer nanocomposites to achieve superior performance in electronics, coatings, and energy devices [31–33]. nanoscale bn is of potential use in nanostructured ceramic materials and nano-dimensional electronic devices [34–36]. hbn is non-cytotoxic and contains an extent of biocompatibility [37,38]. due to its electron affinity being highly negative [39], chemical, physical and thermal stabilities, the bn sheathing may function as an organic covering that is both protective and insulating for the materials it encapsulates. h-bnns have several desirable qualities for potential uses in optics as well. it also has a significant field-emitting factor [40]. h-bnns also exhibit desirable optical properties such as a direct band gap of 5.5 ev and great electromagnetic transparency, confirming its electrically insulating nature [41,42]. in lasers as well as leds, h-bnns are utilized for heat dissipation and protective coating [43,44]. a protective layer of 130 µm thick h-bn was applied to a solar probe because of the outstanding stability of h-bn at high temperatures. it also contains high ratios of solar emissivity to absorptivity [45]. unlike conventional bigger materials or thin films, 2-d boron nitride nanosheets can perform new or better functions. the distinctive anisotropy and mechanical characteristics of 2d materials have greatly spurred interest in their basic mechanics and optics as well as a broad range of applications [46–48]. because of its high reflectivity in the uv-visible region, silver mirrors are an excellent choice for solar energy concentrators and astronomical telescopes [49,50]. nevertheless, as a result of the reaction of ag with sulfurcontaining substances, particularly h2s in the open atmosphere, ag progressively tarnishes, creating black ag2s that reduces uv-vis reflectivity and promotes electrical resistance. ag2s and can be removed using techniques like sanding and dipping in a sodium bicarbonate solution, but they also run the risk of irreversible material loss and the formation of micro-pits, which will eventually encourage more corrosion [51–53]. atomic layer coating of conventional thin layers like alox is also incompatible with metals like ag because it can partially oxidize their surface and reduce their reflectivity [54,55]. while chromate conversion coatings and other tarnish inhibitors work well, they frequently include extremely toxic hexavalent chromium compounds [56]. in addition, the other carbon equivalents of boron nitride like graphene possess similar characteristics, however, a fatal drawback of graphene is that, with time, it may create a galvanic cell with the underlying metal ag and potentially promote oxidation resulting in extended corrosion. these attributes make h-bnns a suitable defensive coating that may be applied to ag in challenging conditions. this work is the first to demonstrate such growth. research on the cvd growth of h-bnns on single [57,58], as well as polycrystalline ag has been conducted [59], but no earlier studies have been made on the h-bnns synthesis on industrially existing ag utilizing a simple but versatile plasma facility [60]. borazine has been used in chemical vapor deposition (cvd) to create nanoporous-like structures of hbn on a variety metal surfaces, like rh(111) and that of ru(001) as well [61,62]. the main drawback of cvd (chemical vapor deposition) was that it requires a high temperature of 800 to 1600 °c and an extremely low pressure of 10-2 pa which is industrially incompatible. moreover, hboron nitride nanosheets cannot be grown on all the substrates by cvd especially temperature sensitive substrates like plastics and polymers. also, some chemicals like diborane, boron trihalides e.g., bcl3, arsenic and characterization and application of nanomaterials 2025, 8(2), 11613. 3 phosphorus are highly toxic, explosive, and corrosive [63] at elevated temperatures and special care is required. due to these reasons atmospheric pressure plasma is applied as it provides us the same growth at atmospheric pressure and room temperature. all the substrates from hard metals to soft polymers can be coated using non-thermal atmospheric pressure plasma. the plasma operating parameters, such as interelectrode spacing, power, interaction time, applied voltage and working gas pressure are easily adjustable. h-bnns were synthesized on ag through a simple plasma facility at room temperature and atmospheric pressure. the resulting h-bnns were characterized using ft-ir analysis, fesem analysis accompanied by eds, xrd analysis, uv-vis spectroscopy, and vickers hardness tests. 2. experimental setup figure 1 exhibits an illustrative schematic and an image of the atmospheric pressure plasma (app) facility for the growth of h-bnns on ag substrates. seven stainless steel capillary tubes act as the anode and are maintained at an elevated voltage to make up the reactor head. the cathode is mounted over a load-lock stage, horizontally aligned beneath the anode, and spaced 2 cm apart. these components are enclosed in an acrylic container with a top-mounted gas inlet pipe. the upper inlet provides nitrogen gas to the capillary tubes (cathode). a double-neck flask containing the precursor is attached to an argon (ar) cylinder, which is then connected to the reactor head in order to transport the precursor fumes. figure 1. (a) an illustrative schematic; (b) an in-situ image of the atmospheric pressure plasma (app) facility for h-bnns growth on ag. experimentation h-bnns were successfully grown on ag with borazine (h3bnh3) serving as the characterization and application of nanomaterials 2025, 8(2), 11613. 4 precursor. for this purpose, commercially available ag (99.9 % pure) with the dimensions of 8 × 8 × 2 mm3 was used as a substrate. to ensure that the substrate was free from surface contaminations, it was washed in ethyl alcohol for two hours prior to treatment. subsequently, the substrate was placed in an airtight desiccator to protect it from ambient exposure. borazine (h3bnh3) was used as a boron nitride precursor. ar was used as a precursor carrier gas while n2 was used to produce plasma. 250 ml of borazine was filled in the double-necked flask having a capacity of 500 ml. the substrate ag was placed on a horizontally mounted cathode. the argon was made to flow at a fine-tuned flow rate of 10 sl/m via the double-necked flask to carry the borazine fumes to the substrate. the n2 was made to flow via the steel capillaries at an optimized flow rate of 10 sl/m. a 10 kv constant dc voltage was applied to the electrodes to generate the plasma. this resulted in the exposure of the substrate to fumes containing the precursor, coupled with plasma. in this way, nanosheets of h-bn were grown on ag for 10, 15 and 20 min. in order to make a comparison, one ag sample was kept untreated. for ease, the samples have been labeled as follows: pristine ag sample as (ag), 10 min. grown sample as (ag gt)10, 15 min. grown samples as (ag gt)15 and 20 min. grown samples as (ag gt)20 respectively (where gt stands for “growth time”). ftir evaluation was performed to confirm the presence of bn bonds and vibrational modes at the surface of grown samples. fesem along with eds was employed to evaluate microstructure and elemental analysis. xrd was implied to govern the hexagonal structure of bnns. diffused reflectance spectra were carried out to check the reflectivity of the samples. to confirm the hardness enhancement, the samples underwent vickers hardness tests post-growth. 3. results and discussions 3.1. ftir analysis ftir analysis was performed to determine the presence of bn functional groups on substrate ag. figure 2 shows the ftir spectra for (ag), (ag gt)10, (ag gt)15, and (ag gt)20. the resolution was set at 2 cm⁻1, with a frequency range spanning from 500 to 4000 cm⁻1. two prominent absorption bands, located at 805 cm⁻1 and 1632 cm⁻1, are visible for (ag gt)10, (ag gt)15, and (ag gt)20, confirming the presence of h-bn functional groups. the dotted boxes in figure 2 draw attention to the absence of these bands in (ag). depending on the type of bn structure, these peaks’ precise locations vary. in h-bn, a prominent peak appears at approximately 805 cm−1. these bands represent, respectively, the bending and stretching modes of the crystalline h-bn lattice bound to sp2 [63–65]. as plasma exposure time increased, ir light reflection, associated with that of bn functional groups, intensified. this enhanced reflection is proportional to the enhanced bn formation for (ag gt)20. this phenomenon can be explained by the decrease in pore size, surface roughness, and particle size, which leads to a greater reflection of ir radiation (also verified in sem section). the bn structure, as well as the existence of impurities or structural defects, can all affect the exact location and form of this peak. furthermore, other functional groups, such as c–h, c≡n, and c–c, which correspond to peak locations at 1367, 2265, and 2920 cm⁻1, arise with longer plasma exposure time [66]. since the characterization and application of nanomaterials 2025, 8(2), 11613. 5 experiment was conducted in the ambient environment, these groups might have arisen from environmental contamination. upon comparison, it can be seen that the h-bnns grown on ag at an operating voltage of 10 kv for 20 min are the best among the others. h-bn 4000 3500 3000 2500 2000 1500 1000 500 100 150 c-c cºn h-bn c-h h-bn c-c cºn c-h h-bn t ra n sm it te n ce % wavenumber (cm-1) c-h h-bn c-hh-bn cºn c=c (ag) (ag gt)10 (ag gt)15 (ag gt)20 figure 2. ftir spectra of (ag), (ag gt)10, (ag gt)15, (ag gt)20. dotted rectangles represent the distinctive bands of h-bn. 3.2. scanning electron microscopy analysis having confirmed the presence of h-bn functional groups via ftir, we next examined the morphological evolution of the nanosheets using sem. figure 3 shows the scanning electron micrographs alongside edx spectra for (ag), (ag gt)10, (ag gt)15, and (ag gt)20 respectively. pristine ag used as a substrate (figure 3a) does not show any deposition; however, a few scratches are seen on the surface. figure 3b reveals the surface morphology of h-bnns grown via plasma operated for 10 min. there are uniformly distributed nanosheets of bn (figure 3b). the high-energy atmosphere of plasma boosts the polarization exhibited by the covalently bound sp2 [67] h-bn. this enhanced polarization of the h-bn bond is a consequence of plasma bond interaction. as a result, electrostatic induction in the ag substrate takes place, increasing the adhesion between the adsorbing bn particles and substrate ag. additionally, huge and unreacted particles are observed over the surface of these hbnns. these particles remained so because there is a layer (nanosheet of bn) between these bigger particles and substrate ag, due to which these particles could not interact with the substrate. also, the plasma exposure time was small, as a result they remained bigger. the existence of b and n was certified through the respective eds spectrum. for (ag gt)15 (figure 3c), the bn nanosheets are more uniformly dispersed compared to (ag gt)10. this is attributed to the enhanced plasma exposure with the fumes containing the precursor, which leads to greater electrostatic induction, ultimately increasing the electrostatic interaction between adsorbing bn particles and the underlying substrate ag. for (ag gt)15, big unreacted precursor particles are less abundant on the surface of h-bnns, as the plasma has sufficient time to break them down. eds examination verified the existence of b and n. figure 3d displays the morphology of (ag gt)20, where the sem image shows that the bn nanosheets (as confirmed by edx) appear to be fused or adhered, likely because of the extended characterization and application of nanomaterials 2025, 8(2), 11613. 6 plasma exposure with both the adsorbing bn particles and that of ag. plasma enhances interfacial properties, including inter-diffusion and the formation of bn surface layers, such as inter-diffusion and plasma-enhanced surface layers of bn. as the plasma exposure time increases, so does the electrostatic induction, resulting in stronger attraction between bn and ag. additionally, a few cracks can be observed in the h-bnns in the fesem micrograph of (ag gt)20. these cracks likely formed after prolonged plasma heating, followed by rapid condensation when the samples were cooled to room temperature after the growth process. boron nitride nanosheets interact strongly with ag via van der waals attractions as well as coulombic forces [68]. the underlying ag substrate appears as dark regions in the fesem micrographs (as illustrated in figure 3b–d), on the other hand, h-bnns exhibits different shadows of grey. since h-bn is a semiconductor or insulator, the electron charging from the fesem beam causes the nanosheets to appear brighter. upon comparison, distinct differences in the morphology of these nanosheets are observed. as plasma growth time increases, the sheets become more uniform. consequently, (ag gt)20 shows more uniform h-bnns as compared to the others, which is attributed to the prolonged plasma exposure time. figure 3. scanning electron micrographs alongside edx spectra for (a) (ag); (b) (ag gt)10; (c) (ag gt)15; (d) (ag gt)20. the fesem micrographs were processed by software called fiji imagej to evaluate the particle size of bn, porosity of bnns, and average surface roughness of characterization and application of nanomaterials 2025, 8(2), 11613. 7 the grown h-bnns. figure 4 presents the graph of particle size as a function of plasma exposure time while average surface roughness, pore size are functions of plasma exposure time. figure 4a shows a decrease in particle size with extended plasma exposure. the average particle sizes for (ag gt)10, (ag gt)15, and (ag gt)20 are 140.91, 128.43 and 80.66 nm, respectively. because the highly reactive plasma species break down the larger precursor particles into smaller ones, the particle size decreases with increasing plasma exposure duration. furthermore, plasma removes impurities and pollutants from the surface, improving h-bnns growth conditions and encouraging the development of smaller, more uniform bnns. for (ag), (ag gt)10, (ag gt)15, and (ag gt)20, the average surface roughness (ra) values were 23.5337 nm, 31.9465 nm, 47.764 nm, and 43.3627 nm, in that order. an increase in surface roughness was noted for (ag gt)10 and (ag gt)15, followed by a decrease for (ag gt)20. this rise in roughness for (ag gt)10 is linked to the presence of larger bn particles on these nanosheets. as seen in the earlier graph depicting particle size and growth time (figure 4a,b), highly energetic and reactive plasma ions and electrons interacting with ag and the encroaching fumes of precursor initiate activation processes, leading to increased surface roughness [69,70]. further enhanced average surface roughness for (ag gt)15 (figure 4b) is attributed to the presence of the prominent cracks in thusly synthesized h-bnns (figure 3c). the reduction in average surface roughness for (ag gt)20 predicts the smoothness of the 2d h-bnns on ag. plasma interaction for a larger time span cleans the surface. this might also be due to the filling of surface defects or voids resulting in a smoother surface. also, the bigger particles were turned into smaller ones (as seen in sem section figure 3d). as a result, surface roughness reduced for (ag gt)20. an observable decrease in porosity with extended plasma exposure time has also been noted (figure 4b). the average pore size reduces a top value of 61.049 to 28.6 nm for (ag gt)10 and (ag gt)20 respectively. the highly reactive species from plasma, including ions, excited atoms, electrons, and free radicals, break down bigger covalently sp2-bonded bn particles into smaller ones, which results in the lowering of pore size. this leads to a decrease in pore size because more tiny particles are contained in a smaller volume. longer plasma exposure causes the boron nitride nanosheets to become more uniform and cover the sample’s surface more successfully. as a result, the particle and pore sizes decrease with an increase in plasma exposure time (figure 4a,b). thus, for (ag gt)20, the average surface roughness is decreased. thus, in comparison to the other samples, (ag gt)20 exhibits the most consistent, homogenous, and flexible boron nitride nanosheets. characterization and application of nanomaterials 2025, 8(2), 11613. 8 10 20 80 90 100 110 120 130 140 150 (ag bn)20 (ag gt)15 p a rt ic le s iz e (n m ) growth time (min.) (ag gt)10 (a) 0 2 4 6 8 10 12 14 16 18 20 22 20 25 30 35 40 45 50 55 60 65 average roughness pore size growth time (min.) a v er a g e r o u g h n es s (n m ) 20 25 30 35 40 45 50 55 60 65 p o re s iz e (n m ) (b) (a) (b) figure 4. graph showing the relationship between (a) particle size vs. growth time; (b) average surface roughness and pore size vs growth time. 3.3. x-ray diffraction analysis figure 5 shows the x-ray diffraction patterns of (ag), (ag gt)10 and (ag gt)20. the pattern of (ag gt)15 is missing as our aim was to observe the h-bnns growth at minimum and maximum plasma exposure time. in the xrd pattern of (ag) (figure 5), three highly sharp peaks at the positions 2θ = 38.8°, 65.2° and 78.6° which represents ag(111), ag (220) and ag(311) respectively (jcpds ref. code 03-065-2871) [71]. for (ag gt)10 and (ag gt)20, there are two new peaks at the positions of 2θ = 26.2° and 45.2° which correspond to the h-bn(002) as well as h-bn(100) (jcpds ref. code 00009-0012) [72,73]. the appearance of these two new peaks confirms the growth of 2d h-bn on ag via plasma using hexagonal borazine (h3bnh3) [74] as a precursor. the borazine contains the stoichiometry 1:1 between b and n [75]. when borazine is used as a precursor, it facilitates the formation of h-bn at reduced temperatures [76]. before settling down of bn particles from ar fumes on substrate ag, electrons and ions from plasma dissociate borazine (h3bnh3) into bn accompanied with dehydrogenation [77] according to the equation (1) given below [78]. e− + h3bnh3 → bn + 3h2↑ (1) as a result, the dissociated bn readily settles down to the substrate. it is worth noting that despite a large lattice incompatibility between ag (4.036 å) [79] and that of h-bn (2.50475 å) [80], even then there is growth of h-bn on ag. this is due to the reason that the precursor while interacting with the plasma melts and h-bn dissociates in the molten form. since plasma is also in direct contact with the ag substrate as well, it heats up the ag also. this molten h-bn settles down on the preheated ag substrate. consequently, the precursor adheres well to the substrate, leading to more effective growth. furthermore, the difference in the surface energies of ag (1.0–2.2 j/m2) [81] and h-bn (25 mj/m2) [50] is less, which is also in favor of this growth. better wetting is achieved with a fluid with a lower surface tension and a solid with a higher surface characterization and application of nanomaterials 2025, 8(2), 11613. 9 energy [82]. plasma compensates for this lattice mismatch and surface energy difference by improving interfacial interaction between incoming h-bn and the underlying ag substrate [83]. in the case of (ag gt)10 as well as (ag gt)20, it is clearly evident that peaks centered at a diffraction angle of 2θ = 45.2° have slightly higher intensity as compared to peaks situated at 2θ = 26.2° which shows that bn(100) are more abundant/populated than that of bn(002) in the lattice of h-bn [84]. it is also observed that the peaks situated at 2θ = 26.2° and 45.2° for (ag gt)20 have higher intensity than the corresponding peaks at the same positions in (ag gt)10 (figure 5). this is because of enhanced plasma-precursor exposure resulting in more effective and improved bn growth. longer plasma exposure time leads to increased crystallinity [85] by promoting better adhesion, polarization, cleaning, growth and alignment of nanoparticles on ag substrate that aligns well with literature as well [86]. also, the crystallite size determined by scherrer’s equation is ~15 nm for (ag gt)20. consequently, 20 min. seems to be an optimum growth time at which boron nitride nanosheets can be grown with high crystallinity, high purity and high yield on ag substrates. it seems reasonable to state that the optimal condition for the growth of hbnns on ag is achieved with plasma operation at 10 kv for 20 min. 10 20 30 40 50 60 70 80 90 100 0 10000 20000 30000 40000 50000 60000 70000 80000 ag(311) ag(311) ag(220) ag(220) ag(111) ag(111) h-bn(100) h-bn(100) h-bn(002) in te n si ty ( a .u ) 2q (degree) (ag) (ag gt)10 (ag gt)20 h-bn(002) ag(111) ag(220) ag(311) figure 5. diffraction peaks observed in x-ray analysis of (ag), (ag gt)10, and (ag gt)20. 3.4. diffuse reflectance spectra analysis figure 6 showcases the diffuse reflectance spectra for (ag), (ag gt)10, (ag gt)15, and (ag gt)20, and a magnified view (360–800 nm) of (ag), (ag gt)10, (ag gt)15, and (ag gt)20. it appears from the graph that there is no reflection from 200 to 300 nm for all the samples (figure 6a). in this range of the electromagnetic spectrum, all the samples behave as good absorbers. after 300 nm, there is a sharp increase in the reflectivity till 350 nm which lies in the ultraviolet wavelength range. there are two crests corresponding to 550 and 740 nm which show the highest reflectivity for each sample in figure 6b, depicting that these samples are good reflectors for these wavelengths. the curves become smooth from 525 to 675 nm. (ag) shows maximum reflectivity among (ag gt)10, (ag gt)15, (ag gt)20. the characterization and application of nanomaterials 2025, 8(2), 11613. 10 reflectance increases with extended plasma exposure time. as plasma exposure progresses, there is an abrupt decrease in surface roughness of (ag gt)20 (figure 4b), leading to a smoother surface. reflectivity for (ag gt)10 and (ag gt)15 is lower compared to (ag) and (ag gt)20, primarily due to the larger surface particles and surface fractures. the increase in plasma exposure duration introduces new surface chemical groups like c=n, c–c, c≡n, c–h, ag2o as well as c=o on the ag substrate (verified through ft-ir in figure 5 as well as eds analysis in figure 3). through partial absorption of light and possible modification of reflectance, these newly developed groups alter the way light interacts with the ag surface. as the plasma exposure time rises, a decrease in the average particle size was observed (figure 4a). reflectivity decreases when the particle size gets closer to the wavelength of light due to stronger scattering effects. as demonstrated in figure 4b, the nanosheets formed under similar conditions likewise saw a decrease in pore size with extended plasma exposure. scattering and interference processes are responsible for influencing overall reflectivity when the wavelength of incident light matches the pore size in the boron nitride nanosheets. as a result, reflectance is reduced. based on this, (ag gt)20 seems to be the best sample of the rest of the samples. 200 300 400 500 600 700 800 -10 0 10 20 30 40 50 60 70 80 r ef le ct iv it y % wavelength (nm) (ag) (ag gt)10 (ag gt)15 (ag gt)20 (a) 400 450 500 550 600 650 700 750 800 56 58 60 62 64 66 68 70 72 74 r ef le c ti v it y % wavelength (nm) (ag) (ag gt)10 (ag gt)15 (ag gt)20 (b) (a) (b) figure 6. the diffuse reflectance spectra of (a) (ag), (ag gt)10, (ag gt)15, and (ag gt)20; (b) a magnified view (360–800 nm) of (ag), (ag gt)10, (ag gt)15, and (ag gt)20. 3.5. vickers hardness analysis vickers hardness testers with steel balls having a diameter of 1.588 mm and weighing 100 kg were used to measure the hardness of (ag), (ag gt)10, (ag gt)15 and (ag gt)20 at room temperature. the findings of at least two indentations are averaged to produce the hardness values. figure 7 graph illustrates vickers hardness as a function of plasma exposure time for (ag), (ag gt)10, (ag gt)15, and (ag gt)20. from figure 7, it can be concluded that the hardness of each sample shows a near-linear increase with extended plasma exposure time [87,88]. the (ag) has an average value of 27.6 hv, while the (ag gt)20 has an average value of 38.3 hv. there is a maximum increase in the hardness of (ag gt)20 due to the extended plasma characterization and application of nanomaterials 2025, 8(2), 11613. 11 exposure episode. this may be due to the increase in hardness when plasma interacts with ag and bn, leading to cross-linking, ion implantation, and the formation of strong covalent bonds between the substrate and bn. plasma tends to activate the substrate surface enhancing the adhesion between the substrate and bn particles. extended plasma exposure duration has also resulted in enhanced crystallinity of (ag gt)20 (figure 3). with enhanced plasma exposure time, the average pore size as well as the average surface roughness of thusly grown nanosheets has decreased (figure 4b), thus creating a better environment for the adsorbents b and n via cleaning and activating the substrate surface giving rise to hardness. the particle size has also decreased for extended plasma exposure time (as verified in the fesem section figure 4a). this increase in hardness might also be due to an increase in plasma exposure time resulting in prolonged interaction of radiation like uv, x-rays etc., emitted from plasma with the underlying substrate and bn [89,90]. furthermore, when ag is exposed to plasma along with precursor borazine, the b and n atoms imbed and penetrate into the ag surface (as also verified by ft-ir, edx and xrd techniques) as a result, the hardness of the samples increases. hence, 20 min and 10 kv are the best optimum parameters to enhance the surface hardness. 0 5 10 15 20 26 28 30 32 34 36 38 40 h v v a lu e growth time (min.) figure 7. graph illustrating vickers hardness as a function of plasma exposure time for (ag), (ag gt)10, (ag gt)15, and (ag gt)20. figure 8 represents the change in the hv value, average particle size, average surface roughness and average pore size versus plasma exposure time of (ag), (ag gt)10, (ag gt)15, (ag gt)20. it can be inferred from this graph that the average particle size as well as the pore size of boron nitride has reduced with an increase in plasma exposure time. the average surface roughness of the samples increases and then diminishes ultimately for 20 min. interaction time (figure 4b). as a result, the hardness of (ag), (ag gt)10, (ag gt)15, (ag gt)20 increases from an average 27.6 hv value to a 38.3 hv value [91]. characterization and application of nanomaterials 2025, 8(2), 11613. 12 0 5 10 15 20 20 40 60 80 100 120 140 hardness particle size roughness pore size h v v a lu e p a r ti c le s iz e ( n m ) r o u g h n e ss ( n m ) p o r e s iz e ( n m ) growth time (min.) figure 8. comparative graph of hv value, average particle size, average surface roughness and average pore size as a function of plasma growth time for samples (ag), (ag gt)10, (ag gt)15, and (ag gt)20. 4. conclusion h-bnns were synthesized on silver using a simple plasma setup at atmospheric pressure and room temperature. the bn source borazine underwent interaction with the nitrogen plasma for various time spans of 10, 15 and 20 min. h-bnns are found to be grown for all the plasma exposure times; however, the crystallinity of the grown bn sheets is much better for longer plasma exposure times (20 min. in our case). smoother nanosheets have grown as a result of a drop in average particle size, average pore size, and average surface roughness as the plasma exposure period has increased. the hardness of the samples has similarly risen with the increase in plasma exposure time. therefore, it is concluded that the atmospheric pressure plasma facility serves as an excellent, cost-effective, eco-friendly, and versatile approach for growing h-bnns on ag resulting in smoother nanosheets with improved crystallinity and hardness. author contributions: conceptualization, mm and msr; methodology, mm; software, mm; validation, mk, aa and fs; formal analysis, ma; investigation, is; resources, fj and hm; writing—original draft preparation, mm; writing—review and editing, mm; supervision, msr; project administration, ta. all authors have read and agreed to the published version of the manuscript. acknowledgments: the authors express gratitude to the dean, faculty of natural sciences muhammad shahid rafique, at the university of engineering and technology lahore, pakistan, for overseeing and supervising this study through the research group program. special thanks are extended to anwar latif, khurram siraj, muneeb irshad, muhammad irfan and from the laser and optronic center, department of physics, university of engineering and technology lahore, pakistan, for their valuable contributions. institutional review board statement: not applicable. characterization and application of nanomaterials 2025, 8(2), 11613. 13 informed consent statement: not applicable. conflict of interest: the authors declare no conflict of interest. references 1. wang j, ma f, liang w, et al. electrical properties and applications of graphene, hexagonal boron nitride (h-bn), and graphene/h-bn heterostructures. materials today physics. 2017; 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145: 111076. doi: 10.1016/j.diamond.2024.111076 characterization and application of nanomaterials (2020) volume 3 issue 2 doi:10.24294/can.v3i2.567 49 original research article effect of heating and resistance on emission properties of carbon nanotubes sergey v. bulyarskiy 1* , alexander a. dudin 1 , alexander v. lakalin 1 , andrey p. orlov 1 , alexander a. pavlov 1 , roman m. ryazanov 2 , artemiy a. shamanaev 2 1 institute of nanotechnology of microelectronics of the russian academy of sciences, 32a leninskii pr., moscow, 119991, russia; e-mail: bulyar2954@mail.ru 2 scientific-manufacturing complex «technological centre» build 1, shokin sq., zelenograd, moscow, 124498, russia abstract we have studied the effect of the series resistance on the heating of the cathode, which is based on carbon nanotubes and serves to realize the field emission of electrons into the vacuum. the experiment was performed with the single multi-walled carbon nanotube (mcnt) that was separated from the array grown by cvd method with thin-film ni-ti catalyst (nickel 4 nm/ti 10 nm). the heating of the cathode leads to the appearance of a current of the thermionic emission. the experimental voltage current characteristic exhibited the negative resistance region caused by thermal field emission. this current increases strongly with increasing voltage and contributes to the degradation of the cold emitter. the calculation of the temperature of the end of the cathode is made taking into account the effect of the phenomenon that warms up and cools the cathode. we have developed a method for processing of the emission volt-ampere characteristics of a cathode, which relies on a numerical calculation of the field emission current and the comparison of these calculations with experiments. the model of the volt-ampere characteristic takes into account the cnt’s geometry, properties, its contact with the catalyst, heating and simultaneous implementation of the thermionic and field emission. the calculation made it possible to determine a number of important parameters, including the voltage and current of the beginning of thermionic emission, the temperature distribution along the cathode and the resistance of the nanotube. the phenomenon of thermionic emission from cnts was investigated experimentally and theoretically. the conditions of this type emission occurrence were defined. the results of the study could form the basis of theory of cnt emitter’s degradation. keywords: carbon nanotubes; field emission; thermionic emission; volt-ampere characteristic; emitter temperature article info article history: received 11 october 2020 received in revised form 4 november 2020 accepted 9 november 2020 available online 21 november 2020 copyright copyright © 2020 sergey v. bulyarskiy et al. doi: 10.24294/can.v3i2.567 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0) http://creativecommons.org/licenses/by/4.0/ 1. introduction the carbon nanotubes (cnts) have the important practical properties such as high electrical and thermal conductivity, suitable mechanical properties, and ability to absorb and emit electromagnetic waves [1] . scientists from all over the world have developed the variety of convenient technological methods for producing cnts, which promotes the development of studies of this allotropic form of carbon. at present, various practical applications of nanotubes are shown, including field-effect transistors, lithium-ion batteries, radiation receivers, interconnections of integrated microcircuits, conductive composites, etc. [1] cnts have a small diameter. for the case with single-walled cnt, it is from 0.8 to 1.5 nm; for multi-walled cnt — from units to tens nanometers, cnt’s diameter is much less than their mailto:bulyar2954@mail.ru http://creativecommons.org/licenses/by/4.0/ 50 length (large aspect ratio), which results in enhancement of the electric field near the cnt’s tip and contributes to field emission. several papers that appeared in 1995 described the phenomenon of field emission in cnts [2-4] . this phenomenon formed the basis for a number of important applications from the point of view of practical applications: flatscreens [5,6] , miniature x-ray tubes [7,8] , light-emitting devices [9,10] , miniature vacuum lamps [11,12] , terahertz amplifiers [13,14] , and high-freq uency vacuum switches [15] . for widespread use of field emission (fe), it is necessary to study the possibility of achieving high emission current densities and stability of this process. these issues are discussed in detail foremost from the theoretical point of view, in particular, the necessary information can be found in the reviews [16,17] . voltage-current characteristic of cold cathode in the region of prevalence of field emission current is generally described by fowler-nordheim formula. detailed analysis of this model and its transition to the region of thermionic emission was carried out in the studies of rupesinghe et al., eletskii, bocharov & eletskii, and murphy [15,18] . the calculations of field-emission current for cnt were shown in several studies, for example, in the studies of rupesin ghe et al., eletskii, bocharov & eletskii, murphy, as well as mayer & lambin [15-19] . fowler-nordheim dependence in usable form has a formula [20] : (1) where: , , , , e is elementary charge (c); h is plank constant (js); e is the local electric field strength near the emitting surface (v/m);  is work function of an electron from a cnt (j); m is free-electron mass; j is current density of the fe (a/m 2 ). t(y0) и v(y0) are weakly varying functions that can be taken equal to unity without increasing the error in determining the work function. we can neglect the weak power dependence of the functions t(y) and (y) by setting t(y)1 and (y)1. this condition allows us to obtain the following formula for calculating of the work function:          e e j 2/392 6 1083.6 exp1054.1   (2) where: [] = ev; [e] = v/m; [j] = а/m 2 . the experimental results are often represented in the fowler-nordheim coordinates: ln (j/e 2 ) = f(1/e). a straight line approximates these results and the work function is calculated from the slope of which. the amount of the calculation these work function depends on the choice of the initial and final electric field strengths, which specify the region of the current-voltage characteristic. in generally, this choice is not motivated. therefore, the result of calculating contains significant systematic errors. even in the first papers devoted to field emission, it was found that cnt’s tip is heated by flow of field-emission current, and its temperature is proportional to the square of the current density [19,21] , which is quite obvious in accordance with the joule-lenz law. models that are more complex were considered in the studies of bocharov et al. [16] and murphy et al. [17] a single nanotube has a rather large thermal resistance. this resistance prevents the release of heat into the substrate with which the lower end of the nanotube is connected. cnt’s tip heating leads to thermionic emission current, which may be large and even exceed the field emission current. moreover, the resistance of cnt’s changes the voltage-current characteristic as a function of temperature and current value due to an additional voltage drop. cnt’s resistance makes a definite contribution to the form of the voltage-current characteristic, taking part of the voltage to itself at high current densities. thus, cnt’s resistance leads to a deviation of the experimental results from ed. (1). therefore, when researchers involve only fowler nordheim dependence to determine the work function, they admit two systematic errors: firstly, thermionic emission is neglected, and, secondly, they 33.11107.01)( yyt  69.11)( yy           eeh ym yth ee j    eee y  51 don’t take into account the voltage drop on the nanotube. in this paper, the emission currents of a single multi-walled nanotube have been studied experimentally in a wide range of current values. the authors have revealed deviations of the current-volta ge characteristic from the fowler-nordheim dependence. moreover, the calculation of the temperature of cnt’s heating has been carried out, and the conditions under which the nanotube resistance and the thermionic emission current have a significant effect on the voltage-current characteristic shape were analyzed, and the algorithm for cnt parameters calculating was presented, namely, the electrical resistance, the dependence of the cnt heating temperature from the current value. 2. experimental results carbon nanotubes were grown by the chemical vapor deposition (cvd) method in plasmalab system 100 (oxford instruments) on silicon substrate on which a catalyst was deposited consisting of a two-layer metal film: titanium 10 nm and nickel 2 nm. the film of the catalyst was covered with silicon oxide, in which windows were opened with a diameter of 0.7 μm. the cnt growth was carried out by cvd method. gas flow consisted of an acetylene with addition of ammonia in a 3:1 ratio rate. it was constant during the growth process. the synthesis temperature was 600°c. as a result, single multi-walled carbon nanotubes 2-3 μm in height were obtained (figure 1). figure 1. sem image of single multi-walled carbon nanotube (cathode) and tungsten tip (anode). the measurements were carried out in a high vacuum in the chamber of two-beam fei helios nanolab 650i system. a measuring electron microscope could obtain images with a resolution of not worse than 0.7 nm at an accelerating voltage of not more than 1 kv. the pressure in the measuring chamber was 510 -5 pa. in this chamber there was a probe system kleindiek nanotechnik with 4 separate independent manipulators that can operate at voltages up to 150 v. each probe had its own coaxial connector. for current-voltage measurements on dc currents, a programmable two-channel source meter source meter 2634b from keithley was used. this device can measure currents up to 10 -15 a. it is equipped with special shielded three axial leads with the function of ultra-low currents compensation. the input impedance of source-meter (over 100 volts) provides a minimum level of the introduced distortions and errors in tested circuits during the measurements for this class of instruments. the voltage-current characteristic of emission current of the single multi-walled cnt is shown in figure 2. it was the starting point for further processing. the electrical circuit in which the emission current flows is shown in the inset of figure 2. this current consists of two components: its nonlinear resistance characterizes field emission and thermionic emission, each of these processes (rfe and rte). the total voltage applied to the circuit (u) is composed of the sum of the voltages, one of which falls on the resistance of the nanotube (ur), and the other one — on the nonlinear resistance of the emitting tip of the nanotube (ue). we must divide the current of the current-voltage characteristic into two components. one component is the field emission current, and the second component is the thermionic current. these components are determined by the following sequence of actions: 1) the field emission current is calculated (the calculations are shown in the following subsection). the work function is selected in such way that the field-emission current coincides with the initial section of the experimental voltage-current characteristic (figure 2). this calculation allows us to determine ue. 52 figure 2. voltage-current characteristic of the emission current of the single multi-walled cnt: 1 — experimental; 2 — modeling by formula; top corner: equivalent circuit of cnt. 2) the voltage of the model curve, there is a deduction from the voltage of the experimental curve for each current value. the difference of these voltages makes it possible to determine ur (figure 2), to construct the current-voltage characteristic of the series resistance of a carbon nanotube and calculate this resistance r=10 mω. then the model value of the voltage drop across the series resistance of a nanotube is: ur =i·r. 3) we are conducting the second stage of modeling the volt-ampere characteristic. the total theoretical voltage (ut), which should be on the emission system, is calculated as the sum of the voltage on the nonlinear resistance of the emitting tip of the nanotube (ue) and the series resistance (ur). we calculate the difference between the theoretical and experimental voltage drops at each current value: ut－u=ue＋ur－u. the result is a voltage-current characteristic of the section, which contains two parallel non-linear resistances (rfe and rte). the result of the transformations is shown in figure 3. this figure shows the initial experimental current ed. (1); field emission current ed. (2); the experimental section of negative resistance ed. (3). the voltage reaches a critical value (uc) at a critical value of the current (ic). further increases of the current leads to a heating of the nanotube, as a result of which, the resistance for the thermionic current decreases. this leads to a decrease in voltage drop across the parallel connection section of nonlinear resistances. the voltage at the end of the nanotube, which emits electrons, falls and the emission current decreases. it is evident that when cnt’s tip is heated to a certain critical temperature, a thermionic emission current appears, and the voltage at the emitting end (ue) falls. a section of negative resistance is present, then: i＞ic. the current that exceeds the critical region is thermionic in fact. the field emission current does not exceed the critical current. thus, the thermionic current component dominates when the total current density exceeds a critical value. this is because the end of the tube is heating when the current flows. the temperature of the end of the tube grows. its temperature can reach several thousand degrees. this temperature leads to cnt destruction and the emission current degrades. the phenomenon of degradation of the field emission current is due to overheating of the nanotube. below, we will carry out the necessary calculations to determine the conditions under which the emission process will be stable. 3. modeling 3.1. calculation of the currents of the field emission of a carbon nanotube (cnt) the efficiency of field emission depends essentially on the electric field strength near the emitting surface. therefore, the electric field strength requires an exact calculation. the calculation is carried out in two stages: first, the potential distribution and the magnitude of the electric field at the end of the tube are calculated; secondly, the current density of the cathode is calculated. the calculation of the electric field potential distribution is carried out in the classical approximation. we applied a model in which a cnt is a solid body of cylindrical shape. the end of this body represents a hemisphere (cnt with a closed end) or half a torus (cnt with an open end). this body has a metallic type of conductivity. the potential of the electric field is found by solving the 3-dimensional laplace equation in the boundary element with the conditions given on its boundary. the solution of the laplace equation was found by the boundary element 53 method, which is described in detail in the studies of banerjee & butterfield and brebbia et al. [22, 23] . this method involves splitting the surface of a solid body into triangular elements and forming the computational grid. then the boundary conditions are given on its boundaries. as a result, instead of solving the integral equation, a system of linear algebraic equations is solved. by solving, we obtain the coefficients required for calculating the potentials in corresponding space points of emission system. figure 3. current-voltage characteristics of the investigated cnt: 1 — experimental i-v characteristic; 2 — modeling i-v characteristic (ed. 3); 3 — i-v characteristic of the section, which contains two parallel non-linear resistances (rfe and rte). partitioning of the boundary surface to boundary elements (be), on the one hand, need to be quiet detailed to consider all special aspects of surface and on the other hand should not exceed a certain value due to the computing power used by the computer (memory capacity, processing speed). based on these conditions, in this case, the entire boundary surface is divided into 20000–30000 triangular be. electric field strength distribution must be calculated near all points of the cnt surface, since the cathode current is caused not only by emission from its end, but also from regions near it. figure 4 shows the emission system under investigation consisting of a single cnt (cathode) and an anode electrode, as well as its idealized model, which was later used to calculate the distribution of the electric field and the field emission current. figure 4. model of a single cnt (cathode) and an anode electrode. geometric parameters of the calculation were obtained as a result of determining the size of a real experimental system, which is shown in figure 4. а system of equipotential surfaces was obtained after the implementation of the above mentioned calculation algorithm. the electric field strength was calculated as the potential gradient near the surface. the cathode current is the sum of the current of the total boundary elements. electrons, which are emitted by these elements, moved along a certain trajectory and, at the end of their path, hit the anode. the motion of an electron along a trajectory causes the formation of an elementary electric current. the sum of these currents over the area of the cathode creates an emission current (cathode current), as well as the components of this current that fall on other elements of the emission system (anode current, leakage current, etc.). such approach is permissible on the basis of an estimate of the electron velocity in the system. the velocity of an electron in the corresponding electric field can be estimated from the law of energy conservation: 2 2 0 2 01         eucm cm cv , where: c is light velocity; m0 is electron rest mass; u is accelerating voltage between cathode and anode. in the experiments, u did not exceed 150 v, therefore v  5·10 6 m/s. thus, the electron velocity is much smaller 54 than the speed of light, so they move with nonrelativistic velocities and the laws of classical mechanics can be used to calculate their trajectories of motion. we will assume that the coulomb force acts on the electron, which must be used in the motion equation. the numerical integration was done by euler’s method [24] . it should be noted that in the case of random cathode geometry (not flat) in eqs. (1) and (2), e is understood as the field strength near the surface of the emitting elementary cathode pad, rather than the average value obtained by dividing the applied voltage by the distance between the anode and the cathode. when calculating the field-emission current from a single cnt, it is assumed that each be of the cathode emits a current ii, which is defined as ii =jisi , where ji is the current density of the i-th be of cathode, si is the surface area of the i-th cathode be (the surface area of the entire cathode s=∑si ). the current density ji is calculated from the fowler-nordheim ed. (1), in which the electric field strength ei is taken from the solution of the laplace equation for a given initial point at the center of each i-th be. then the total field emission current of the cathode is found by summing the currents over all sites si:            i i i i i i i ii s eeh ym yth ee sji 3 )(28 exp )(8 2/3 2 23   (3) 3.2. calculation of the heating temperature of the end of a single carbon nanotube the nanotube is heated when an electric current flows in it. its temperature is not the same at its two ends. it is assumed that the temperature of the nanotube end, which is in contact with the substrate, is equal to the temperature of the substrate. the temperature of the opposite end was calculated by solving the heat-transfer equation taking into account the radiative cooling and the release of heat, which is caused by the current flow [21,25] :   0 )( 2)( 24 0 4       dx l tr idxttrdx dx dt tk dx d s  (4) where: is cross-section area of cnt; r is outer radius of cnt; r0 is inner radius of cnt; k(t) is coefficient of heat conductivity along the cnt axis; t=t(x) is the temperature along the cnt axis; t0 is the temperature of surrounding bod ies (substrate); l is length of cnt; r(t)/l is electrical resistance of a unit length of cnt; η is the coefficient of the grayness of the thermal radiation of cnt (η＜1) in our case, which was taken equal to 0.9; )/(1067.5 428 kmw is stefan-boltz mann constant; i is the current flowing through cnt (emission current). the boundary conditions for equation (4) have the formula: .0 )( ,)0( 0  dx ldt tt (5) in the study of vincent et al. [21] , the analytical solution of ed. (4) was obtained in the absence of radiative cooling and provided that the thermal conductivity coefficient k, as well as the resistance r of the nanotube, which do not depend on temperature. however, for the case with cnts there is a temperature dependence of k and r, therefore the results of vincent et al.’s study [21] should be considered as approximate. it was assumed in bocharov & eletskii’s study [25] that the thermal conductivity coefficient k and the resistance r are described by power functions of temperature. for the case: k=at 3 , r=bt 4 +c in bocharov & eletskii’s study [25] , an analytic solution of ed. (4) was obtained. in the study of bocharov et al. [26] , it was assumed that: , ， where  is an adjustable parameter, and equation (4) was solved numerically. however, power-law dependence with the form for the thermal conductivity coefficient occurs only at temperatures below the debye characteristic temperature [27] . at high temperatures, due to the anharmonicity of long-wave oscillations and other causes, the thermal conductivity of a solid body decreases according to the law1/t, namely in the study of ziman [27] : (6) where:  is debye temperature. the energy of the debye phonon of carbon nanotubes is 0.103 ev [28] . accordingly, the debye temperature is =1190k. it is the dependence that dominates in the high temperature region, when thermionic emission is possible. therefore, for calculating the heating of ctk  )( 2 0 2 rrs   )/( 00 ttkk  )/( 00 ttrr  t kk   0 55 the nanotube, the dependence ed. (6) was chosen. the correct calculation of the temperature of nanotubes should be taken into account both their heating due to joule heat, and cooling due to the notingham effect [29] . the nottingham effect is manifested in the cooling of the cathode. this effect is the result of the difference between the average energy of the electrons that leave the cathode and the electrons from the volume of the nanotube that takes their place. the electron that leaves the cnt carries away from the nanotube energy equal to the average energy of the thermal motion (3/2)kbt [30] . the number of electrons that are emitted from the cathode per unit time is i/e. then the boundary condition ed. (5) at the point x=l will have the formula: the first term describes the cooling of cnts by radiation from the end surface [29,30] , the second term due to the nottingham effect [30] . in addition, the temperature dependence of the resistance of cnts has the formula [30,31] : )1()( 2/3 0 tt s l tr   (7) where: 0 is the resistivity of cnts. the heat conduction ed. (4) takes the form with allowance for ed (6), (7):                                          s lt ek iltk tlt lt k dx ldt tt s tt ittr dx dt tdx td s t k b   (8) the system that is given by ed. (8) is solved by a numerical method to determine the temperature of the end of a nanotube that emits electrons. the values of the parameters were assumed to be equal to: =8.510 -4 k -1[31] ; β=9.810 -6 k -3/2[31] ; 0=2.3310 -3 m [31] ; l=2.36 µm; r=20 nm; r0=15 nm; t0=300 k; i=10 ua; =1190 k; k0=140 w/(mk). at the selected values of k0 and  in the temperature range 200-1000 k, the thermal conductivity coefficient k lies in the range 55÷830 w/(mk). this corresponds to the literature data according to which k can vary from 25 to 3000 w/(mk) [25] . the results of the calculations are shown in figure 5, curve 1 (curve 2 — calculation without taking into account the nottingham effect). figure 5. temperature distribution along the axis of the carbon nanotube: 1 — taking into account (1) the nottingham effect; 2 — without taking into account the nottingham effect. the values of the coefficients are indicated in the text. figure 6. the temperature of the emitting end of cnts on the value of the flowing emission current, taking into account the nottingham effect. 1 — k=k0 (/t); 2 — k=const. the values of the coefficients are shown in the text. figure 6 shows the temperature dependence of the emitting end of the cnts (tl) as a function of the flowing emission current, taking into account the nottingham effect (for comparison, the curve for k=const is also given there). the calculation is   eks iltk tlt kdx ldt b  2 )(3 )( )( 4 0 4 56 made for the values of the coefficients, which are given in the text before that. the temperature of the emitting end of the cnt in the case k=k0 (/t) turned out to be higher than in the case k=const in the whole considered range of emission currents. the nanotube length varied from 0.5 to 4 μm when calculating the temperature. the temperature of the cold end of the nanotube contacted to the substrate was assumed to be t0 = 300 k. equation (4) was solved for different values of the current i, and thus a dependence was obtained, where tl is the temperature of the emitting end, as is shown in figure 7. figure 7. dependence of the superheating temperature of the emitting end of a cnt on the flowing current for cnts of different lengths: 1 — 0.5 μm; 2 — 1.0 μm; 3 — 1.5 μm; 4 — 2.0 μm; 5 — 3.0 μm; 6 — 4.0 μm. in this figure, the exact solution of ed. (4) is compared with the approximate analytical solution obtained under the condition that there are no radiative cooling, no nottingham effect, the thermal conductivity coefficient and the resistance of cnts are constant [21] : l ks ri ttl 2 2 0  (9) the results of the calculations in figure 7 show that the simplified solution gives an overestimate value of the superheat temperature of the emitting end of the nanotube for all values of its length. a simplified solution approximates the exact solution with increasing current strength. we assume that the temperature dependence of the thermal conductivity ed. (6) is compensated by additional cooling due to the nottingham effect. the temperature of the cathode overheating increases in proportion to the square of the emission current. the current strength of the 1 ua is a critical value in our case, exceeding which results in the appearance of thermionic emission currents and the appearance of unstable volt-ampere characteristics. 4. results and discussion the emission current is composed of the field and thermionic components according the electrical circuit of the current flow is shown in figure 2. this current is represented by curve 3 in figure 3. field emission current is represented by curve 2. it is obvious that at the maximum values of the voltage (uc) at which the negative resistance region starts, the currents of field-electron and thermionic emission are approximately equal. further current growth is due to the thermionic component, and the field current decreases, while changing along curve 2. thus, the region of negative resistance of the voltage-current characteristic (figure 3) is due to the fact that the current of thermionic emission predominates over the field emission current. the end of the nanotube is already overheated to such an extent that it can be destroyed. the voltage (uc) and current (ic) at which the negative resistance region starts can be considered as critical. as soon as the total current exceeds this value, the emission becomes unstable and the degradation processes begin. it is important to estimate the conditions under which degradation of emission currents is possible. there is a conditional current limit, the excess of which causes a rapid overheating of the nanotube end and the degradation of the emission. at the boundary, the total current is equal to the sum of the currents of the field electron emission and the thermionic emission, i = ite+ife . subsequently thermionic current predominates. therefore, as a condition for changing the emission mechanism, one can choose the equality of currents )(0 ifttl  57 ite = ife or ite (t) = i/2. this condition allows us to estimate the geometric dimensions of the carbon nanotubes of the cathode at a fixed value of the flowing current at which their heating begins. the temperature of cnt end warming up is determined by the current of thermionic emission (ite) and the geometric dimensions of the nanotube, which ultimately determine the magnitude of its electrical resistance ed. (9). for rough estimation of the overheating temperature, it is enough to restrict ourselves to ed. (9). the resistance of a nanotube is estimated by the formula: s l r  , 0 0 0 l s r (10) where: — cnt cross-section area. the values of these parameters were calculated from the experiments r0 = 10 м; s0 = 5.510 2 nm 2 ; l0 = 2.36 μm;  = 2.3310 -3 ·m. the expression for the thermionic emission current is:           tk ee kt h m si b n cntte )4( exp)( 4 0 3 2 3 *  (11) where: is the area of cnt emitting surface (hemisphere surface area); is effective mass of electron in cnt; kb is boltzmann constant; t is absolute temperature; 0 is electrical constant. the conditional boundary of the transformation of a stable process to an unstable process is calculated from formulas (10) and (11). if we neglect the decrease in the height of the barrier in the formula (11) by the electric field, then the condition ite (t)=i/2 will be written in the formula:          )( exp)( 2 1 2 ltk ltasi b cnt  (12) substituting ed. (9) into ed. (12), we obtain:                           2 22 0 2 2 22 0 2 exp 2 2 ks li tk ks li ta s i b cnt   (13) for the case with given cnt radius r, formula (13) allows us to calculate the cross-sectional area s and the length l, which correspond to the beginning of the appearance of the thermionic emission current (ite) for a given value of the total current i, as is shown in figure 8. figure 8. dependencies for current values i: 1 — 2 μa; 2 — 3 μa; 3 — 4 μa; 4 — 5 μa; 5 — 6 μa; 6 — 7 μa. this figure represents several regions in the space of length — cnt area. this space is divided into regions by the curves, which are calculated for certain currents. these curves represent the boundary behind which the regime of thermionic emission and degradation of cnts occurs. for each curve, the following statement is true: if the length of the nanotube is larger and the area is smaller, then we cross the boundary and fall into the degradation region. with inverse relations between the parameters, namely, the length is less than the boundary one, and the area is larger, and then we fall into the region of stability of the emission. 5. summary and conclusions the analysis of emission processes with a single nanotube showed that when the current density increases, the end that emits electrons is heated. in this case, along with the field emission current, a thermionic emission current appears. the growth of the total current causes overheating of the end of the nanotube. this current is almost completely associated with the phenomenon of thermionic emission. at the same time, the emission process be22 rscnt  mmn 3.0*  )( 2 0 2 rrs   58 comes unstable. so the temperature of overheating can exceed 1000°с, and then the nanotube begins to break down. to analyze these processes, within the framework of this work, an algorithm has been developed that relies on numerical calculations of the field emission current and the overheat temperature. it is shown that when there is overheating, a negative resistance region occurs. at this moment, the thermionic current begins to predominate. the correlation between the current density, length and cross sectional area of the nanotube was calculated, whi ch allows estimating the regions in which cathode degradation can progress and the emission becomes unstable. acknowledgements the work was carried out with the financial support of the ministry of education and science of russia (project no.: 16.9007.2017/бч). references 1. bulyarskiy sv. carbon nanotubes: technology (in russian). manage properties application. ulyanovsk: strezhen; 2011. p.479. 2. chernozatonskii la, gulyaev yv, kosakovskaja zj, et al. electron field emission from nanofilament carbon films. chemical physics letters 1995; 233(1-2): 63–68. 3. de heer wa, chatelain a, ugarte d. a carbon nanotube field-emission electron source. science 1995; 270: 1179–1180. 4. rinzler ag, hafner jh, nikolaev p, et al. unraveling nanotubes: 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breakdown. physics review letter 2004; 93: 075501. characterization and application of nanomaterials (2022) volume 5 issue 1 doi:10.24294/can.v5i1.1431 52 review article research progress in applying nanomaterials in the field of functional textiles fang wu1,2,3, jinlong ge1,2,3*, yingyue qin1,2,3, zongqun li1,2,3, qiulin li4 1 anhui provincial engineering laboratory of silicon-based materials, bengbu 233030, china. e-mail: jinlongge2005@126.com 2 engineering technology research center of silicon-based materials, bengbu 233030, china 3 school of material and chemical engineering, bengbu university, bengbu 233030, china 4 college of materials science and engineering, suzhou university of science and technology, suzhou 215011, china abstract the ways of developing functional textiles based on nanomaterials were introduced, and the latest research achievements of nanomaterials in such aspects as flame retardancy, antibacterial, super-hydrophobic, self-cleaning, uv resistance, and anti-static textiles were reviewed. the main technical obstacles to the large-scale application of nanomaterials in functional textiles were pointed out, the possible solutions were discussed, and the development of functional textiles by nanomaterials has been prospected. keywords: nanomaterials; functional textiles; flame retardancy; antibacterial; self-cleaning article info received: 17 december 2021 accepted: 4 february 2022 available online: 24 february 2022 copyright copyright © 2022 fang wu, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4 .0/ 1. introduction with the continuous improvement of people’s living standards and the rapid progress of science and technology, functional textiles have penetrated into every field of the national economy. using nanomaterials to develop textiles with special functions is helpful to enhance the competitiveness of china’s textile industry. the combination of nanomaterials and functional textiles can accelerate the innovation of the textile industry and lead the development of the textile industry. 2. methods of modifying functional fabrics by nanomaterials there are four methods to modify functional textiles by using nanomaterials[1]: one is the blending spinning method, in which the nanomaterials are evenly dispersed in the polymer melt, and then the nanomaterial modified functional fibers are prepared by granulation, melt spinning and other processes. this method has little effect on the finishing process and is mainly used to produce chemical fibers or regenerated fibers modified by nanomaterials. the second is the post-finishing method, which uses physical and chemical methods to treat the surface of the fiber or fabric, and then adds the nanomaterials to the finishing agent, and combines the nanomaterials with the fabric through impregnation, coating and spraying. the third is the graft modification method, which endows the surface of nanomaterials with nanomaterials to the surface of textile materials. the fourth is the in 53 situ generation method, in the surface and interior of the fiber in situ generation of nanomaterials to achieve specific functions. 3. application of nanomaterials in functional fibers and fabrics in recent years, the application of plasma technology, self-healing technology and other new technologies is conducive to the composite of nanomaterials with fibers and fabrics, realizing the rapid development of single nanoparticle modification to multiple nanoparticle compounding, multi-functional composite direction, and the development of many nano-modified functional textiles. 3.1 flame retardancy most of the fibers belong to combustible fibers, and the flame retardant finishing of the fabric is helpful to reduce the risk of fire. at present, nano flame retardants used in the textile field include nano phosphorus and nitrogen flame retardants, inorganic nanomaterial flame retardants, organic-inorganic mixed nano flame retardants, biological flame retardants. compared with halogen flame retardants, phospho-nitrogen flame retardants have lower toxicity and smoke emission and meet environmental requirements[2]. inorganic nano flame retardants include carbon nanomaterials such as carbon nanotubes, graphene[3], and oxides such as tio2 [4], sio2 [5], zno[6], hydroxyl oxide[7], hydroxide[8], etc. bio-based flame retardants contain deoxynucleotides, etc.[9] nano flame retardants are usually added into the fibers by means of self-assembly, compounding, surface modification, and microencapsulation to improve the flame retardant property of the fibers. wang et al.[3] applied the impregnation method to finish the pgo on the surface of cotton fabric, which significantly enhanced the flame retardant performance of the cotton fabric. pgo with a large layered structure can effectively insulate oxygen and volatile combustible gases from permeation, thus reducing the heat release rate. at the same time, the presence of phosphorus contributes to catalytic carbonization during combustion, promoting the formation of carbon slag and preventing the infiltration of oxidation and pyrolysis products. wang et al.[8] constructed a safety coating consisting of polydopamine, layered dihydroxide, and polydimethylsiloxane on cotton fabric, which significantly improved the flame retardant performance of the cotton fabric and gave it excellent oil-water separation characteristics. polydopamine and layered dihydroxide inhibit most smog, while coated polydimethylsiloxane enhances stain resistance and durability. ortelli et al.[9] applied the mixture of nano tio2 and dna on the surface of cotton by impregnation curing method, which significantly improved the flame retardant performance of the cotton fabric. 3.2 antibacterial the active components of nano-antibacterial materials used in the textile are mainly heavy metal ionic and photocatalytic. specifically, metal ion type nano antibacterial materials include nanometer-scale ag[10], au[11], cu[12], etc. in the process of use, metal ions dissolve out, destroy the respiration, metabolism, and reproduction pathways of bacteria, to achieve the antibacterial effect. photocatalytic antibacterial agents mainly use tio2 [13], zno[14], bivo4 [15], and other semiconductor materials to produce oh– with strong oxidation capacity under the action of photocatalysis, which destroys the respiration of bacteria and interferes with the material delivery pathway to achieve the antibacterial purpose. in order to combine antibacterial nanoparticles firmly with fiber surface, the impregnation method, layer deposition method, and in situ synthesis method are adopted. in order to make full use of the surface plasmon resonance effect of silver nanoparticles to present brilliant colors and their efficient and safe antibacterial properties, wu et al.,[10] adopted a simple solution impregnation method. a cotton fabric with adjustable color and antibacterial, durable, self-healing, and super-hydrophobic properties was prepared by coating the surface of cotton fabric with f–poss/agnps/pei. the self-healing super-hydrophobicity of f–poss/agnps/pei coated cotton fabric significantly improved the color fastness of agnps to washing and mechanical wear, 54 and retained the antibacterial properties of agnps. ran et al.[15] fixed cuo/bivo4 nanocomposite photocatalyst on cotton fabric through the polydopamine template, endowed the fabric with photocatalytic properties, and made it have good antibacterial activity and uv resistance. ibrahim et al.[13] prepared anatase tio2 nanoparticles doped with cu2o nanoparticles as nano antibacterial composite materials, and treated them into cotton fabric by impregnation method, endows cotton fabric with self-cleaning, uv resistance and antibacterial functions. the cotton fabric has high antibacterial activity due to the production of reactive oxygen species under sunlight. 3.3 super-hydrophobic in the field of super-hydrophobicity, fibers and fabrics are treated with nanomaterials to construct micro/nano rough structures. meanwhile, the fiber was chemically modified with low surface energy materials. micro/nano rough structure can adsorb gas and form nano-sized air film, so that oil or water cannot penetrate into the fabric, thus showing super-hydrophobic or oil-phobic properties[16]. commonly used nanomaterials include sio2[17], tio2[18], zno[19], al2o3 [20], etc. the commonly used methods include chemical vapor precipitation, layer-by-layer self-assembly, sol-gel and so on. these nanomaterials not only improve the super-hydrophobic properties of the fabric, but also have antibacterial, self-cleaning, flame retardant, uv resistance and other properties. yao et al.[17] combined the bio-based l benzoxazine monomer with sio2 nanoparticles and prepared a bio-based polybenzoxazine/sio2 coating on polyethylene terephzoate (pet) non-woven fabric by spraying and thermal curing, endows the non-woven fabric with super-hydrophobic/super oleophilic function. the surface contact angle between the finished fabric and water is (156.2 ± 1.5)°, rolling angle is (5.2 + 1.0)°, with good adhesion strength, can be used for various types of oil-water separation. the fabric still shows super-hydrophobic stability after severe treatment such as mechanical wear, acid and alkali immersion, and solvent immersion. guo et al.[18] deposited super-hydrophobic and flame retardant coatings on cotton fabrics with a simple two-step spraying method, and prepared fabrics with both flame retardant and super-hydrophobic functions. the super-hydrophobic and superoleophilic coatings are composed of layered tio2 and pdms, while the flame retardant coatings are composed of alkylamine sesimiloxane/phytic acid. the finished cotton fabric exhibits high thermal stability, flame retardancy, super-hydrophobicity, self-cleaning and oil-water separation properties. in addition, after 50 wear tests and 5 washing treatments, the cotton fabric still maintained good hydrophobicity and self-extinguishing ability. xiao et al.[20] deposited al2o3 layer and al2o3 nanoparticles on the surface of the wool fabric by atomic layer deposition technology, effectively increasing the surface roughness of wool fabric, increasing the static contact angle between wool fabric surface and water from 130° to about 160°, and achieving higher durability. although the fluorine-containing finishing agent has good water-repellent and oil-repellent properties, its high price and bio-cumulative effect limit its further development. in addition, in the actual use process, the modified super-hydrophobic and superoil-phobic surface structure are vulnerable to mechanical damage and chemical action, resulting in a decrease in durability. in order to solve this problem, lahiri et al.[21] deposited the sio2–alkyl silane coating mixed with boric acid on cotton fabric through a simple dip rolling finish, and then modified it with pdms to prepare fluorine-free super-hydrophobic composite coating on the surface of cotton fabric. the static contact angle between the finished fabric and water reaches (157.95 ± 2)°, rolling angle reached (3.8 ± 0.6)°, showing excellent super-hydrophobic characteristics. coated fabrics demonstrate excellent robustness and durability, as well as self-healing and oil-water separation. 3.4 self-cleaning self-cleaning fabrics can be divided into super-hydrophobic self-cleaning and photocatalytic self-cleaning according to the way of self-cleaning. super-hydrophobic self-cleaning mainly refers to the use of bionics principles to treat fabrics with 55 super-hydrophobic treatment to achieve self-cleaning performance. commonly used inorganic nanomaterials include layered bimetal hydroxide[8], sio2 [21,22], etc. chen et al.[22] prepared super-hydrophobic fabrics by the sol-gel method by deposition of sio2 on the fabric and grafting of the finishing agent. the fabric remains highly oil-repellent and water-repellent under various harsh conditions (such as ultraviolet radiation, alkali (ph 12) or acid (ph 2) solution, water treatment at 2 ℃ or 95 ℃), and has excellent self-cleaning and antifouling performance. photocatalytic self-cleaning mainly uses nano-semiconductor materials with photocatalytic effects, such as bioi[23], tio2[24,25], zno[26], carbon nitride[27], etc., to generate free radicals under the action of light and degrade organic pollutants on the fabric into co2 and h2o, so as to achieve the purpose of self-cleaning. zahid et al.[24] prepared manganese-doped nano tio2 by sol-gel method, and applied organosilicon adhesive to finish it on textiles. using methylene blue dye to simulate pollutants, the fabric showed a good self-cleaning effect under ultraviolet and visible light irradiation. at the same time, the functional fabric has good biocompatibility and shows antibacterial properties in natural sunlight. jaksik et al.[25] reported that tio2 modified by ag/au nanoparticles was deposited on cotton fiber through gel sol process to prepare self-cleaning cotton fabric with photocatalytic properties. tio2 coating with au and ag nanoparticles endow cotton fabric with self-cleaning and antibacterial properties. pedrosa et al.[27] prepared functional fabrics with high antibacterial and self-cleaning properties by treating g–c3n4 and go on cotton fabric with a simple impregnation method. using caffeine and rhodamine b as simulated pollutants, the finished cotton fabric effectively degraded the pollutants under visible light irradiation and showed excellent photocatalytic activity, indicating that it has an excellent self-cleaning function. 3.5 uv resistance adding uv absorbent or blocking agent to fabric can effectively reduce the damage of excessive uv to the human body. however, some organic anti-uv protective agents are prone to allergic reactions and may be toxic to the human body. inorganic nanomaterials with non-toxic, stable properties and long-lasting uv resistance are easier to be accepted by the market. commonly used uv blocking agents of nanomaterials include nano au[11], bioi[23], zno[28], ag[29], metal-organic skeleton materials[30], tio2 [31], graphene[32], etc. these nanomaterials, when combined with the fiber, can enhance the fiber’s uv reflection and scattering effect, thus achieving enhanced uv absorption and shielding effect. yuan et al.[29] successfully deposited ag/zno composite films on polyester fabrics with pure silver and zinc targets by dc magnetron sputtering and rf magnetron reactive sputtering techniques. the results show that zinc coating on silver film before rf reactive sputtering can effectively protect the silver film from oxidation. ag/zno composite film can produce structure color on polyester fabric, and give the fabric excellent uv resistance and antistatic properties. xiao et al.[31] successfully deposited nano tio2 onto silk fiber by atomic layer deposition technology, which enhanced the thermal stability and mechanical properties of silk fiber and endowed the fiber with excellent uv protection characteristics. li et al.[30] fixed the inof–1 nanocrystals generated in situ on the surfaces of three kinds of fabrics (cotton, polyester and aramid) based on the solid-phase hot pressing method without adding solvents or adhesives, significantly improving the uv resistance of the fabrics. cao et al.[32] prepared a multifunctional silk fabric with conductivity, uv resistance and water repellency by repeatedly impregnating go and chemical reduction methods by finishing rgo onto silk fabric. 3.6 antistatic fiber due to the friction electrostatic effect, the fabric is easy to produce spark discharge in the process of use, and the high voltage electrostatic is harmful to health and easy to induce a variety of diseases. in inflammable and explosive places, high voltage static electricity can easily cause hidden dangers, in addition, high voltage static electricity will damage 56 precision electronic instruments, so it is necessary to develop antistatic fabrics. compared with antistatic materials such as antistatic agents, metal fibers, carbon fibers and conductive polymers, nano conductive particles are more suitable for preparing permanent antistatic fabrics due to their simple preparation and wide application range. conductive particles such as carbon nanotubes[33], mxene[34], go[35] and sio2/tio2 [36] are often compounded with fibers by post-finishing method or blending spinning method to improve the antistatic properties of fabrics. li liang et al.[35] prepared polyester fabrics with good antistatic properties by using dopamine in situ polymerization to construct polydopamine films on the surface of polyester fabrics and then loading go. the antistatic fabric has good washing durability thanks to the super adhesive effect of polydopamine. kelly et al.[37] prepared a new type of silver nanoparticles wool composite by chemical reduction method. silver nanoparticles give the composites excellent antibacterial and antistatic properties. 4. technical obstacles and solutions of nanomaterials application at present, the main obstacles in the application of nanomaterials in the textile field are as follows: one is the problem that the nanoparticles are difficult to disperse evenly in spinning and on the fiber surface. the particle size of nanomaterials is small, the surface energy is high, easy to agglomerate; in addition, the polarity difference between some nanomaterials and the spinning solution makes it difficult for the nanoparticles to disperse evenly in the spinning solution, which affects the rheology and spinnability of the spinning solution. the second is to improve the bonding firmness of nanoparticles with fibers and fabrics. the durability and stability of functional textiles can be enhanced by increasing the binding degree of nanomaterials and fibers. solutions: (1) in situ synthesis of nanomaterials on the surface or inside the fiber. this method takes advantage of the porous structure of the fiber material, effectively solves the agglomeration problem of the nanomaterial in use, and enhances the binding degree between the nanomaterial and the fiber matrix to a certain extent. (2) the fiber surface is modified, such as plasma treatment, chemical etching, radiation, etc., to improve the roughness of the fiber surface and increase the number of active groups, so as to improve its binding ability with nanomaterials. (3) surface coating and modification of nanomaterials. based on graft polymerization reaction, gel-sol method, and so on, use coated modification agents such as surfactants, super-dispersants to achieve the purpose of modifying nanomaterials, so as to enhance the binding ability of nanomaterials and fibers. 5. conclusion using nanomaterials to develop functional textiles has become one of the main trends in the textile industry. however, due to the unpredictability of nanomaterials in nano-toxicology and their own characteristics, as well as the standardization of functional textiles modified by nanomaterials, all these hinder the further development of functional textiles. how to further accelerate the application of nanomaterials in the field of functional textiles can be carried out from the following four aspects. (1) develop nano textile standards. nano-modified functional fabrics are popular in the market because of their excellent properties. very few businesses take the opportunity to hype nano, shoddy, seriously disrupted the market order. in order to solve the chaos of the nano textile market and further standardize the market, it is necessary to standardize the performance testing of functional textiles and accelerate the formulation and improvement of the standard of nano-modified functional textiles. (2) due to the unique nano-size effect of nanomaterials, while benefiting mankind, they may cause harm to the human body and the environment[38]. nanotoxicology has formed new interdisciplinary research on the biological effects of nanomaterials. at present, the research on nano-toxicology is still in its infancy, so it is necessary to establish reasonable, effective, and rapid evaluation methods and establish safety evaluation 57 systems and detection standards of nanomaterials, so as to promote the rapid development of nanomaterials. (3) at present, china has made a series of research achievements in the development of nano-modified functional textiles, and occupies a certain market share. but in general, most are still experimental. (4) the development of new nanomaterials and the application of nanotechnology, micro-electronics, bionic technology, 3d printing technology and textile technology have greatly promoted the development of multi-functional textiles. at present, smart fibers and smart textiles are in the ascendant. our country should speed up the pace of research and development, and constantly develop functional textiles with multi-function and high added value to form core competitiveness. acknowledgment this article is supported by the key project of natural science research of universities in anhui province “dilute soil doped pure silicon mcm 41 gentle oxidation and product separation of aromatic ring compounds” (kj2019a0850), and major project of natural science research in anhui province “controllable preparation and surface functionalization regulation of highly dispersed spherical porous silica” (kj2019zd62). conflict of interest the authors declare that they have no conflict of interest. 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technology, suzhou 215009, china. e-mail: nanxu@mail.usts.edu.cn 2jiangsu key laboratory of environmental functional material, suzhou 215009, china abstract we studied zeta potentials of nanoparticles titanium dioxides (ntio2) in different concentration of nano3 and phosphate (p) solutions. in addition, the effect of flow rate on the transport of ntio2 in p was investigated at ph = 6.5. experimental results show that the zeta potential of ntio2 is compressed with the increasing ion concentration (ic) of nano3 at ph = 6.5. the negative charge increases with the augment of p. therefore, the high p and low nano3 induce the stabilization of ntio2 aggregates. the transport experiments suggest that the rapid flow rate is favorable for the transportability of ntio2 and soluble phosphate. the breakthrough transport curves (btcs) of ntio2 in sand columns can be fitted well with two-site kinetic attachment model. the modeling results suggest that the values of first-order attachment rate coefficients (k2) and detachment rate coefficients (k2d) on site 2 and first-order attachment rate coefficients (k1) on site 1 are responsible to the attaching efficiency of ntio2 on sands and their transportability. keywords: ntio2; zeta potential; transport; phosphate article info received: 14 january 2021 accepted: 28 february 2021 available online: 6 march 2021 copyright copyright © 2021 gang feng, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ nano titanium dioxide (ntio2) is one of the mass-produced metal oxide nano materials. due to the ultra-high photocatalytic ability of nano materials, it has been more and more used in various fields and commercial products[1–5]. in mass production and wide application, some ntio2 cannot be avoided to be released into natural water and soil environment. a large amount of evidence shows that after artificial ntio2 enters the water body, it has adverse effects on aquatic organisms, including microorganisms, algae, invertebrates and fish[6,7]. therefore, the study of the relationship between nanoparticles attached to soil saturated particles and nanoparticles in soil particle saturated porous media has become a hot spot in the study of the environmental behavior of nanoparticles. at present, the artificial nano materials studied internationally are mainly industrial fullerene nc60, carbon nanotubes and silica nanoparticles. the mobility of these nano materials in saturated porous media is different. the flow rate of solution, ion concentration and surface potential of nanoparticles will affect their migration behavior[8,9]. therefore, it is necessary to explore the changes of surface properties of ntio2 under different environmental conditions and its migration in the natural world. in agricultural production and people’s life and production, a large number of phosphorus containing substances are used, which makes phosphorus containing substances enter into 56 soil and water. ntio2 particles have certain adsorption on phosphate, which changes its surface properties, and finally changes the migration properties of ntio2 in soil[10,11]. therefore, this paper will explore the changes of surface zeta potential of ntio2 under different environmental conditions and the effects of different environmental water flow velocities on its migration in phosphate environment. 1. materials and methods 1.1 preparation of the ntio2 phosphate suspension all chemicals used in the experiment are analytical pure and purchased from sinopharmgroup. 20 nm ntio2 was purchased from shanghai gaoquan chemical co., ltd., 1 g·l–1 tio2 was weighed and dissolved in 0.1 mm phosphate solution (nah2po4) and 10 mm nano3 electrolyte solution, and ultrasonic was used with an ultrasonic cleaner (kq 2200b, ultrasonic instruments co., ltd., hunshan, china) for 30 mins for migration experiment. 1.2 test of the zeta potential on the ntio2 particle surface accurately weigh 0.01 g of tio2 particles into a 100 ml beaker and prepare suspensions under different conditions. the different conditions are electrolyte nano3 concentration (0.1–5 mm) and phosphate solution (0.1–5 mm), in which the ph value of all suspensions is adjusted to ph = 6.50 with diluted hcl and naoh. then, the suspension of ntio2 particles with adjusted ph value was placed on the ultrasonic instrument for 30 mins. after ultrasonic treatment, the suspension was placed on a stirrer and stirred for 30s. finally, the zeta potential of ntio2 particles was tested with marvin nano-zs90. all samples were tested three times, and the average value was taken as the final zeta potential value. 1.3 migration experiment of quartz sand column referring to fang, et al., column leaching experiment was used to study the migration behavior of ntio2 [2]. a chromatographic column with a length of 17.5 cm and an inner diameter of 25 mm was selected. the chromatographic column was filled with quartz sand and saturated with deionized water for 12 h. inject 200 ml (10 mm nano3) of background solution into the saturated chromatographic column with a peristaltic pump, and collect 10ml of effluent every 10 mins with an automatic sample partial collector (bs-100a, huxi, shanghai). then, about 5 pore volumes (pv) of the ntio2 suspension were injected into the chromatographic column, and 20 tubes of effluent were collected with an automatic partial collector. after the suspension is injected, continue to inject 5 pv nano3 background solution, collect the effluent and wait for test. 1.4 analysis and determination of the titanium and phosphorus concentrations analysis and determination of titanium (ti): take 2 ml of ntio2 suspension and put it into a 25 ml beaker, add 1–2 ml of sulfuric acid ammonium sulfate digestion solution to the beaker, place it on a heating plate and heat it at 220 ℃ for 1–1.5 h. after digestion, transfer the solution to a 50 ml volumetric flask for constant volume, then transferring 5 ml into a 50 ml volumetric flask, and successively adding 8 ml (vhydrochloric acid:vdeionized water = 5:1) dilute hydrochloric acid, 2 ml (10 g·l–1) ascorbic acid and 10 ml diantipyrylmethane hydrochloride solution with constant volume. the concentration of ti was measured with an ultraviolet spectrophotometer (tu-1901, shimadzu, japan) at a wavelength of 390 nm. dilute 1000 mg·l–1 titanium standard stock solution (matrix is 0.15 mol·l–1 hno3) into a series of standard solutions (concentration gradient is 1–5 mg·l–1), and then obtain the standard curve and measure the concentration of titanium. analysis and determination of total phosphorus: determine the phosphorus concentration by molybdenum blue chromogenic method, put the solution to be measured into a 50 ml volumetric flask to volume, and successively add a drop of phenolphthalein, a drop of 1 mol·l–1 naoh solution (shake well), a drop of 1 mol·l–1 sulfuric acid solution (shake well to colorless), 1 ml (100 g·l–1) anti chemical acid and 2 ml molybdate to volume[12]. after 20 mins of 57 color development, the absorbance of phosphorus (p) was measured with an ultraviolet spectrophotometer at the wavelength of 700 nm. in addition, dilute the phosphorus standard stock solution into a series of standard solutions with a concentration gradient of 1–5 mg·l–1, measure the absorbance at the same wavelength, then obtain the standard curve and determine the phosphorus concentration. analysis and determination of dissolved phosphorus: take 5 ml of ntio2 suspension into 7 ml high-speed centrifuge tube, place the centrifuge tube in ultra-high-speed centrifuge (gl-21m, thermo fisher technology company), and centrifuge at 4 ℃ and 15,000 r·min–1 for 1 h. pass the supernatant over 0.22 μm porous filter membrane, test the concentration of dissolved phosphorus according to the above method of testing total phosphorus. 1.5 a two-point kinetic model a two-point kinetic adsorption model (tskam) was chosen with the equation[13,14]. (1) among them, θ is the porosity of the quartz sand column, and c represents the concentration of ntio2 particles in the solution, ρb represents the unit weight of quartz sand, x represents the spatial vertical coordinate axis, and d represents the hydraulic dispersion coefficient, ν represents the water flow velocity, s1 and s2 represent ntio2 sites l and 2, respectively. the core of tskam model is to divide the sites on the quartz sand surface conducive to the adsorption of tio2 particles into site 1 and site 2. the ntio2 particles retained at site 2 are controlled by convection dispersion, and the mass conservation equation is the first-order kinetic adsorption and desorption equation. (2) k2 and k2d are the adsorption and desorption rates at site 2, respectively, and the adsorption of the ntio2 particles at site 2 belongs to the reversible adsorption. the mass conservation equation on site 1 is: (3) k1 is the adsorption rate at the colloidal site 1. adsorption at site 1 is irreversible adsorption. ψx is a function related to the depth of the filled column[13]. (4) where, dc is the average particle size of quartz sand and x0 is the distance on the coordinate axis. at this distance, the reten of ntio2 particles is related to the column depth. β is an empirical coefficient that controls the shape of the spatial ntio2 curve. the smaller the values of site 2 adsorption efficiency (k2), analytical efficiency (k2d) and site 1 adsorption efficiency (k1) are, the less the reten ntio2 of particles on quartz sand and the higher their mobility will be. the penetration curve of ntio2 particles is simulated by hydrus-1d software to obtain parameters k1, s1, k2 and k2d [15]. 1.6 migration parameters the ntio2 particle mass recovery can be obtained by performing area integration of its migration curves. (5) in formula, q is the pore flow velocity (ml·min–1), c0 and c are the inflow and outflow tio2 concentration (mg·l–1), t is time (min) and t0 is pulse duration (min). the probability of ntio2 particles adsorbing on the quartz sand surface is called the adsorption efficiency (α). (6) in formula, l is the length of the column. θ is 58 the porosity of the filled column. dc is the diameter of sand and η0 is the theoretical single medium contact efficiency. net bed penetration coefficient: (7) particulate deposition rate coefficient: (8) in formula, vp is the flow velocity and k is the coefficient of time and distance correlation. the maximum migration distance of the ntio2 particles was defined as the distance at which the ntio2 particles move when 99.9% of the ntio2 particles are trapped, that is, (9) the results of the various migration parameters for the above formula are shown in table 1. table 1. physical and computational parameters of ntio2 particles and quartz sand columns in the migration experiments number nano3 concentrated/mm p concentrated/mm flow speed/ ml· min–1 outflow ratio/% single medium contact efficiency adsorption efficiency adsorption efficiency/ cm–1 sedimentation rate coefficient/h–1 maximum migration distance/cm 1 10 0.1 0.5 3.9 35.9 3.56 × 10-4 0.19 2.705 37.3 2 10 0.1 1 12 35.9 2.32 × 10-4 0.12 3.536 57 3 10 0.1 2.5 38 35.9 1.06 × 10-4 0.06 4.034 124.9 2. results and discussion 2.1 effect of different concentrations of nano3 electrolytes on the zeta potential on the ntio2 surface when ph = 6.5, the change of surface zeta potential of ntio2 in different concentrations of nano3 is shown in figure 1(a). at different electrolyte concentrations, the zeta potential on the surface of tio2 particles is negative, which indicates that the surface of tio2 particles is negatively charged at different concentrations of nano3. with the increasing concentration of nano3 in the solution, the zeta potential on the surface of ntio2 particles decreases (the absolute value decreases, that is, the negative is getting smaller and smaller). when the nano3 concentration increased from 0.1 mm to 5 mm, the corresponding zeta potential changed from –19 mv to –6.09 mv. this is mainly because with the increasing solubility of nano3 in the solution, the charge shielding effect and electrostatic double layer on the surface of ntio2 particles are compressed, and the net negative charge on the surface of tio2 particles decreases[16,17]. as a result, the zeta potential on the figure 1. zeta potentials of ntio2 particles with different nano3 concentrations (a) and different phosphorus concentrations (b) in the 10 mm nano3 background solution (ph = 6.5). 59 surface of ntio2 particles is reduced, so the dispersion stability of ntio2 particle suspension is also reduced. 2.2 effect of different phosphorus concentrations on the zeta potential on the ntio2 surface as shown in figure 1(b), when ph = 6.5 and background solution nano3 is 10 mm, the zeta potential on the surface of ntio2 particles increases with the increase of p concentration. for example, when the p concentration is 0.1 mm, its surface zeta potential is –28.6 mv, while when the p concentration is increased to 5 mm, its surface zeta potential increases to –32.43 mv. the results show that because phosphate is adsorbed on the surface of ntio2 particles, the charge density on the surface of ntio2 particles is improved through the deprotonation of surface carboxyl groups[18]. therefore, the electrostatic repulsion between the ntio2 particles and the ntio2 particles adsorbing p is strengthened, which eventually leads to the improvement of the dispersion stability of the ntio2 particle suspension[19]. 2.3 effect of water flow velocity on the migration of ntio2 particles suspended in a phosphate solution the effects of different water flow velocities (0.5–2.5 ml·min–1) on the migration of tio2 particles and p in quartz sand column were investigated when the suspension ph was 6.5, the phosphate concentration was 0.1 mm and the background solution nano3 concentration was 10 mm. the flow velocity selected in this group of experiments is within the range of groundwater flow velocity. figure 2 shows the penetration curve of ntio2 particles at different water velocities. with the increase of water flow velocity, the outflow ratio (c/c0) of ntio2 particles increases continuously. when the water flow velocity increases from 0.5 ml·min–1 to 2.5 ml·min–1, the outflow ratio of ntio2 particles increases from 3.9% to about 38.0%, which is similar to the migration law of nano-hydroxyapatite in quartz sand column under different water flow velocities[21]. the above phenomenon is mainly because with the increase of water flow velocity in the quartz sand column, the total sites on the quartz sand surface that can be adsorbed by ntio2 particles in the quartz sand column also decrease. when the water flow velocity is very high, the total sites on the quartz sand surface that can be adsorbed by ntio2 particles decrease sharply due to the action of hydraulic shear force. the retention of ntio2 particles in quartz sand column also decreases. in addition, when the water flow velocity is very low, it is difficult to provide enough kinetic energy for ntio2 particles to penetrate the quartz sand column in the quartz sand column with small porosity, and a large number of ntio2 particles are retained in the quartz sand column[21–23]. in addition, it can be seen from table 1 that when the water flow rate increases from 0.5 ml· min–1 to 2.5 ml·min–1, the adsorption efficiency of ntio2 particles on the surface of quartz sand reduces from 3.56 × 10–4 to 1.06 × 10–4, the retention of ntio2 particles in quartz sand column is reduced and the migration ability is continuously improved. although the deposition rate coefficient increased from 2.705 h–1 to 7.699 h–1, due to the increase of water flow velocity, the continuous improvement of hydraulic shear force improves continuously, the active collision increases continuously during migration, the retention of ntio2 particles on the surface of quartz sand decreased constantly, and more ntio2 particles penetrated the quartz sand column. in addition, the maximum migration distance of ntio2 particles is also increasing with the increase of water flow velocity, and the maximum migration distance is greater than the height of the column by 17.5 cm, which shows that ntio2 particles can smoothly penetrate the quartz sand column under these three different water flow velocities. therefore, the increase of water flow velocity promotes the migration of ntio2 particles in the quartz sand column. as for the effect of water velocity on the migration of ntio2 particles in saturated quartz sand column, the two-point dynamic model can well simulate the penetration curve of ntio2 particles in quartz sand column. as shown in table 2, the water flow velocity is 0.5–2.5 ml·min–1, and the simulated r2 are 0.983, 0.996 and 0.990 respectively, indicating that the model has 60 high fitting degree. with the increase of water flow velocity, the adsorption efficiency of site 1 (k1), site 2 (k2) and the first-order desorption rate (k1d) on site 1 decrease, which indicates that the adsorption of ntio2 particles on the surface of quartz sand is less, resulting in the increase of their migration, which is more conducive to their migration. figure 2. penetration curve of ntio2 particles at different water flow speeds. 2.4 effect of water flow velocity on phosphate migration as shown in figure 3, the outflow ratio of total p increases with the increase of water flow rate. when the water flow rate was 0.5 ml·min–1, the outflow ratio of total p was 38.0%; when the flow rate increases to 1 ml·min–1, the outflow ratio of total p is 50%. continue to increase the flow rate to 2.5 ml·min–1, and the outflow ratio of total p increases to 67.9%. this is mainly because with the increase of water flow velocity in the quartz sand column, the ability of ntio2 particles to penetrate the quartz sand column increases, so that the p adsorbed on the ntio2 particles also migrate out of the quartz sand column. after digestion, the measured total p concentration also increases. however, with the increase of water flow velocity, the outflow ratio of dissolved p does not change significantly, as shown in figure 4. at this time, the outflow ratio of dissolved p is basically maintained at about 21.5%. there is no obvious change in the outflow ratio of dissolved p, mainly because the change of water flow velocity will not affect the adsorption capacity of ntio2 particles for p. therefore, no matter how the water flow velocity changes, the concentration of dissolved p in the solution will not change. in addition, the dissolved p is obtained by subtracting the total phosphate from the bound p of ntio2 particles. therefore, when the velocity is changed and the concentration of dissolved p remains unchanged, the water flow rate is at 0.5 ml·min–1, the dissolved p in the effluent is the main, and only a small part of the bound p with ntio2 particles exists. when the water flow rate increases, most of the p in the effluent exists in the form of bound p with ntio2 particles, and only a small part exists in the form of dissolved p. figure 3. penetration curves of total phosphorus suspended in (0.1 mm) phosphate solution at different flow rates. table 2. simulation parameters of two-point kinetic adsorption model under different experimental conditions number site 2 adsorption efficiency site 2 resolution efficiency maximum value of retention at point 1 site 1 adsorption efficiency person mean square correction factor 1 14.470 6.271 97.15 0.230 0.983 2 14.160 6.028 45.67 1.152 0.996 3 3.138 1.224 33.50 0.067 0.990 61 figure 4. penetration curves of dissolved phosphorus suspended in (0.1 mm) phosphate solution by different flow velocities. 3. conclusion (1) when ph = 6.5, with the increase of electrolyte nano3 concentration, the zeta negative potential on the surface of ntio2 particles decreased gradually; (2) the surface negative charge of ntio2 increases with the increase of p concentration, and its dispersion stability also improves constantly; (3) high flow velocity promotes the mobility of ntio2, and the migration of soluble phosphate also increases continuously; (4) the two-point kinetic adsorption model can well simulate the migration and penetration curve of nano materials in quartz sand column. the model results show that with the increase of flow rate, the adsorption efficiency of site 2 (k2), analytical efficiency (k2d) and site 1 adsorption efficiency (k1) decrease, and the adsorption efficiency of ntio2 particles on quartz sand decreases, so that more ntio2 particles penetrate the quartz sand column. conflict of interest the authors declare that they have no conflict of interest. acknowledgements general research project of national natural science foundation of china, no. 21377090. references 1. fang j, shan x, wen b, et al. stability of titania nanoparticles in soil suspensions and transport in saturated homogeneous soil columns. environmental pollution 2009; 157(4): 110–109. 2. higashi mm, jardim wf. remediation of pesticide contaminated soil 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paradelo m, et al. facilitated transport of copper with hydroxyapatite nanoparticles in saturated sand. soil science society of america journal 2012; 76(2): 375–388. 21. gargiulo g, bradford sa, simunek j, et al. transport and deposition of metabolically active and stationary phase deinococcus radiodurans in unsaturated porous media. environmental science & technology 2007; 41(4): 1265–1271. 22. gargiulo g, bradford sa, simunek j, et al. bacteria transport and deposition under unsaturated flow conditions: the role of water content and bacteria surface hydrophobicity. vadose zone journal 2008; 7(2): 406–419. 23. bradford sa, torkzaban s, wiegmann a. pore-scale simulations to determine the applied hydrodynamic torque and colloid immobilization. vadose zone journal 2010; 10(1): 252–261. characterization and application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1683 9 review article application of the nano drug delivery system in the treatment of cardiovascular diseases ramaiyan velmurugan*, shankar swabanu faculty of pharmaceutical sciences, saveetha institute of medical and technical sciences, chennai, india. email: ramaiyan.dr@gmail.com abstract in the last several decades, cardiovascular diseases (cvds) have emerged as a major hazard to human life and health. conventional formulations for the treatment of cvd are available, but they are far from ideal because of poor water solubility, limited biological activity, non-targeting, and drug resistance. with the advancement of nanotechnology, a novel drug delivery approach for the treatment of cvds has emerged: nano-drug delivery systems (nddss). nddss have shown significant advantages in tackling the difficulties listed above. cytotoxicity is a difficulty with the use of non-destructive dna sequences. ndds categories and targeted tactics were outlined, as well as current research advancements in the diagnosis and treatment of cvds. it’s possible that gene therapy might be included into nano-carriers in the delivery of cardiovascular medications in the future. in addition, the evaluation addressed the drug’s safety. keywords: nano-drug delivery system; cardiovascular disease; targeting strategy; application progress; safety article info received: 3 may 2022 accepted: 30 june 2022 available online: 14 july 2022 copyright copyright © 2022 ramaiyan velmurugan, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction cvds have become a major public health issue across the world, and their morbidity and death ranks number 1 among all other diseases in the globe[1]. development of medications for the treatment of cvd is now a primary focus. new ways of treating cardiovascular illness have emerged as a result of the rapid advances in nanoscience and nanomaterials’ exceptional performance. to enhance the safety and efficacy of pharmaceuticals, researchers use nddss, a family of nanomaterials that can boost drug stability and water solubility, extend the cycle duration, raise the absorption rate of target cells or tissues, and limit enzyme degradation[2]. as nddss may be supplied by a variety of methods, such as inhalation or intravenous injection, their bioavailability is improved. more researchers have begun to create nano-drug carrier systems for the detection and treatment of cardiovascular diseases in the last few years. furthermore, when the use of nanomaterials in clinical applications develops, the risk of exposure to nanomaterials in blood vessels, blood, and their components increases, which will have a significant influence on human health as a result. consequently, this paper focused on nddss, their targeting methodologies, and their application in cvds, as well as the safety of nanomaterials. 2. classifications of nddss to add to this, nanomaterials will have more opportunities to inter 10 act with blood vessels, blood, and their components as they become more widely used in clinical applications. this means that nanomaterials will have a greater impact on human health as they become more widely used in clinical applications. consequently, this paper focused on nddss, their targeting methodologies, and their application in cvds, as well as the safety of nanomaterials. 2.1 liposomes liposomes are lipid vesicles with a cell-like structure generated by an organized phospholipid bilayer[3]. as a form of drug carrier, liposomes demonstrate a number of advantages, such as non-toxicity, non-immunogenicity, and long-term drug release, as well as modifying drug distribution in vivo, enhancing the treatment index, and minimizing the risks associated with drug interactions. in addition to being simple to make, liposomes may also be used to encapsulate hydrophilic and ionic compounds, as well as hydrophobic medicines[4]. phospholipids and liposomes can be used to encase hydrophobic medications, whereas liposomes can encase hydrophilic pharmaceuticals, such as those carrying genes. material modifications can change particle size, potential and surface chemistry. these liposomes, known as cationic liposomes, are positively charged, which indicates that they may cause dose-dependent cell death and inflammation, and as a sort of complex, they may interact with negatively charged serum proteins in an untargeted manner. these issues can be addressed by neutral lipids and ph-sensitive liposomes[5]. 2.2 polymer micellar co-delivery system it is possible to categorize polymer nanoparticles into non-biodegradable materials and biodegradable materials for the delivery of drugs. poly(lactic-co-glycolic acid) (plga), polyvinyl imine (pei), polycaprolactone (pcl), and polyvinyl alcohol (pva) are examples of synthetic polymer materials. biocompatibility, nontoxicity, and teratogenicity are all demonstrated by these polymers. oligomerization and final products of degradation have no harmful effects on cells and can coexist peacefully with the majority of medications. polysaccharides, peptides, chol, and cyclodextrin inclusion complexes are the most common types of natural polymers[6], although there are many others. amphiphilic block copolymers, which comprise the core of polymer nanoparticles, can be employed to intercept insoluble medicines through self-assembly[7]. particle size uniformity and drug release control may be improved by the stable structure of polymer nanoparticles, which can effectively withstand the effects of gastrointestinal environment during oral delivery[8]. drug absorption is enhanced by their small size and wide surface area, which facilitates greater bioavailability. polymer nanoparticles, however, not all of them are created equal. since chitosan, a naturally occurring polymer, is incompatible with biological fluids, it can lead to particle disintegration and lower operating efficiency. its deficit can be remedied structurally. the conjugate’s endocytosis and macrophage phagocytosis mechanisms are unusual since they combine chitosan and polyethylene glycol. furthermore, the addition of a polypeptide to chitosan can increase its working efficiency[9]. 2.3 dendritic macromolecules synthetic macromolecules may take on a variety of shapes and are frequently branched. nano-carriers, such as macromolecules structured like spheres, can be utilized to administer and dissolve insoluble medications in a monodisperse environment. in addition to being monodispersed, dendritic macromolecules with a unique branch structure also have a variable molecular weight. in addition, the package has a significant number of pre-made surface functional groups and a hydrophobic environment, making it an ideal drug delivery medium[10]. dendritic macromolecules are frequently employed in the biomedical and pharmaceutical industries because of their good biological characteristics, however, the presence of a surface cationic charge also restricts their clinical applicability. 2.4 metal nanomaterials there are a wide variety of metal nanomaterials that can be separated into/like gold, silver, and 11 platinum nanomaterials, each of which may be categorized into/like nanoparticles, rods, capsules, nanocuboids, and wire[11]. gold nanoparticles are employed in photothermal therapy of malignancies and rheumatoid arthritis in addition to being a nano-contrast agent for ct and surface-enhanced raman spectroscopy. antibacterial, anti-infection, and anti-tumor are among the various uses for silver nanoparticles that have been demonstrated in several studies. another option is to use hollow nanostructures to hold therapeutic pharmaceuticals[12] or chemically bind them to the surface of nanoparticles to transport the medications. gold and silver nanoparticles can be used to treat chronic illnesses, however, the elimination of gold nanomaterials in the human body is too slow, and silver ions are poisonous in vivo. 2.5 inorganic non-metallic nanomaterials there are a wide variety of nonmetallic inorganic nanomaterials, such as quantum dots, iron oxide, silicon, and grapheme for example[13]. fluorescence imaging with qds, or semiconductor nanocrystals, is the primary focus of qd research, whereas iron oxide nanoparticles are being exploited to develop novel mri contrast agents. because of their enormous surface area and porous structure, mesoporous silicon nanoparticles have become increasingly popular in recent years as a therapeutic tool. drugs and genes can be transported more efficiently in mammalian cells by integrating diverse functional groups into inorganic nanomaterials. in the meanwhile, they’re being touted as a type of joint carrier with room for growth. however, the bio-safety of inorganic non-metallic nanoparticles would be a significant barrier to their clinical use[14]. 2.6 composite nanomaterials additionally, several research are focusing on the development of composite nanomaterials with a variety of characteristics. to generate multifunctional nddss, for example, metal or inorganic non-metallic nanomaterials are inserted into polymer or lipid nanoparticles. organic materials are used to decorate or modify metal and inorganic nanomaterials to improve their physical and chemical properties, in vivo kinetic behavior, and biocompatibility, and some nddss with special structure and diverse functions can be prepared by combining different metals and inorganic materials. 3. targeting strategy of the nddss lesion cells or tissues of cvds may also be targeted, making them easier to target than tumor tissues that have various physiological hurdles to overcome, according to new studies in the field. if you’re using nano-transporter medications, the time it takes for them to enter the bloodstream may be longer than if you were using traditional pharmaceuticals. it is possible to alter the rate of those targeted nano-transporter medications by adjusting ph, temperature, light, ultrasound, or biological enzyme[15]. 3.1 passive target transfer enhanced vascular permeability high permeability and high retention (epr) effects are the primary means by which passive targeted transport is accomplished[16]. there are some chemicals or particles that tend to collect in tumor tissues, and this is known as epr. normal tissue has a thick and intact microvascular endothelial cell space, making it difficult to pass through the vascular wall nddss loaded with drugs of a high molecular weight. despite its high blood artery density, tumor tissue is structurally weak. high molecular weight nddss loaded with drugs can preferentially pass through the vascular wall and stay in the tumor tissue. nano-drug carriers with a particle size of less than 100 nm have been proven to be able to find and target solid tumor tissues using epr. the nano-drug carrier can boost the drug’s bioavailability by more than ten times when compared to the direct delivery approach[17]. however, it has been revealed that the epr effect may be exploited to treat a variety of cardiovascular diseases, not just malignancies. to provide one example, the development of as in some cvds may be traced to an ongoing inflammation that leads to abnormally high levels of blood vessel permeability—a phenomenon strikingly similar to that seen in solid tumors. for the ndds to reach the inside of the plaque, vascu 12 lar endothelial permeability is a crucial factor in the process. aside from being consumed by inflammatory cells (monocytes or macrophages), nano-drug carriers entering the blood are also taken up by these cells, allowing medications to be given in a different manner[18]. nanomaterials are inappropriate for medications with lengthy cycle durations because of their quick clearance from the circulation upon intravenous administration due to their size and surface properties. the nano-system may be covered over using nano-coating technology, and the rate at which the coating agent is administered can be precisely regulated and changed. nddss can benefit from this technology in the treatment of cardiovascular disease. poly (ethylene glycol) (peg) has been used in particle creation by ndds developers. a hydrophilic polymer known as peg may be grafted onto any surface to create an effective coating of water that prevents proteins from adhering to the surface. so that tissue plasminogen activator is protected from plasma inhibitor inactivation and its half-life is prolonged. it is enclosed in nanoparticles that conceal the nanosystem[19]. 3.2 shear-induced targeting for patients with severe coronary artery disease (cad), thrombosis or microthrombus formation develops, which leads to stenosis of the blood arteries, which restricts blood flow through the plaque, and therefore raises the fluid shear stress. compared to the normal vasculature, the blood fluid shear force in the as plaque stenosis can reach up to 1,000 dyne·cm2 on a daily basis[20]. as a result, the difference in blood fluid shear force between as plaque and normal blood arteries may be used to develop blood fluid shear-sensitive nanoparticles to accomplish physicochemical targeting. lipid nanoparticles were formed into convex, two-sided lenticular nanoparticle vesicles, according to holme et al. as blood flow is increased to the as plaque, the drug-loaded nanoscale is able to preserve its structural stability, and its configuration change may be leveraged to release the medication. it was based on platelet activation and adherence to plaque blood vessels in as plaques that prompted the development of a nanoparticle aggregate that may be built locally in plaques[20]. to begin, the researchers synthesized plga nanoparticles with a diameter of 180 nm, encapsulated tissue plasminogen activator, and then used spray drying to produce a 3.8 nm plga nanoparticle aggregate. plga nanoparticles of 180 nm were formed after exposure to the high fluid shear stress of the as plaque, and these nanoparticles were then able to penetrate the plaque’s local thrombus because of the nanoparticles’ great penetrability. the thrombolytic impact increased effectiveness while minimizing thrombolysis’ negative effects and dosage requirements. cardiomyopathy is characterized by an endothelial gap that widens and polysaccharide from ophiopogon japonicus polysaccharides in ischemic myocardium that is twice as high as that of normal rats. both shear stress and blood flow shear rate of the vascular wall can influence the aggregation of nanoparticles, according to tan et al.[21]. 3.3 magnetically guided a “pseudo-passive” targeting approach using a magnetically guided nanoparticle seems intriguing. in theory, magnetic nanoparticles may be directed to the illness location by the application of an external magnetic field. cvd patients may benefit from this approach, as evidenced by recent studies. the effects of several nano drug carriers on atherosclerotic plaque imaging were examined[22]. ultra-tiny, superparamagnetic iron oxide nano-carriers, and extremely small superparamagnetic iron oxide nanoparticles are some of the nanoparticle forms of iron oxide. one collection of ultra-small superparamagnetic iron oxide nanoparticles performed significantly better than others in terms of vascular wall penetration and plaque retention. external magnetic fields may aid in the movement of particles from the cell-free layer, which lacks red blood cells, to the artery wall, some studies have suggested[23]. figure 1 illustrates the passive and active targeting strategy. 13 figure 1. drug targeting strategy. (a) passive targeting (b) active targeting. 3.4 active targeted transhipment passive targeting may be utilized to build an active targeting approach for cvds based on their unique pathological characteristics, which has piqued the interest of researchers interested in improving the targeted delivery efficiency of medications to cvd lesions. nddss with one or more targets are the primary focus of active targeting in order to facilitate medication delivery to a specific location[24]. in other words, the ability of carriers to target sick tissues or cells will be improved by adding a functional group or active material to the surface of the nano-drug carrier. 3.4.1 active targeting of vascular endothelial cells the vascular endothelial cells of cvds are in an inflammatory activation state at different phases of the disease. one of the main targets for nddss is the overexpression of certain small molecules in these cancerous endothelial cells, such as icam-1 and vcam-1. other small molecules that are overexpressed include integrins and selectins[25]. liposomal delivery of anti-inflammatory liposomes to the pulmonary vascular system is improved by conjugating lung-specific single-stranded variable fragment/liposome with pecam-1 (platelet endothelial cell adhesion molecule 1) antibody[26]. anti-vcam-1 monoclonal antibody was used to silica nanoparticles in 2013. before being absorbed by endothelial cells, the nanoparticles were able to attach to inflammatory sites. the antibody anti-icam-1, which actively targets icam-1 on the liposome surface and loads contrast chemicals[27] based on the pathological characteristics of elevated icam-1 expression in early vascular endothelial cells of as (gadolinium). anti-icam-1 and icam-1 have been proven in studies to have a particular effect on liposomes that activates the targeting of vascular endothelial cells and as plaques. liposomes’ ability to target as plaques may be compromised if circulating white blood cells compete for binding to the icam-1 site and blood flow shearing occurs. liposome binding to icam-1 was improved by testing liposome particle size, antibody concentration, and lipid concentration ratios. as an endothelial cell glycoprotein, e-selectin promotes the attachment of monocytes/macrophages and lymphocytes to trigger an inflammatory response, ultimately leading to cvds such as (atherosclerosis-related cardiovascular disease)[28]. also, nano-transport medicines might leverage the target of e-selectin. human umbilical vein endothelial cells triggered by interleukin-1 (il-1) and umbilical cord vein endothelial cells not 14 stimulated by il-1 (il-1) were treated with functional liposomes containing mouse h18/7 mab (an e-selectin-specific antibody). the capacity of functional liposomes to target activated human umbilical vein endothelial cells was shown to be 275 times more than that of the non-activated form of liposomes[29]. when a myocardial infarction or heart failure occurs, at1 levels increase in myocardial tissue. polyethylene glycol liposomes (1,428 nm) were developed[30] to deliver medicinal payloads (such as growth factors, cytokines, etc.) in a regulated way. gly-arg-val-tyr-ile-his-pro-phe (binding sequence of at1 receptor) is connected to these liposomes, which might lead the nanoparticles to the infarction heart. 3.4.2 active targeting of macrophages or foam cells foam cells, also known as macrophages, play an important part in the development of as. some inflammation-related molecules, including as cd44 and interleukin-4 (il-4) receptors, were overexpressed in an inflammatory environment by mononuclear/macrophages in the early stages of as. in order to track the course of as and administer medication, nddss can be used for imaging and drug administration into macrophages or foam cells. when the carboxyl group of the ha skeleton was chemically coupled to 5-cholic acid and the fluorescent dye cy5.5, nanoparticles (ha-nps) were generated by self-assembly[31]. it was shown that in comparison to nanoparticles (hgc-nps) made with chitosan backbones that did not target cd44 receptors, ha-np could greatly improve the absorption of activated macrophages, and the plaque site of apoe/mice (as model) was more targeted. co-localization experiments showed that ha-np was mostly found in macrophages in plaques. amphiphilicity of the il-4 receptor peptide was improved by the application of phage library screening technology and chemical bonding to amphiphilic chitosan (with ethylene glycol chitosan as the backbone and 5-cholate attached). self-assembled nanoparticles having the function of targeting macrophages in as plaques are then produced. 3.5 targeting vascular basement membrane collagen damaged blood arteries and inflammatory areas have collagen iv (col iv)-rich vascular basement membranes, according to research. collagen iv-targeting nanoparticles (ac2-26 col iv nps) were developed in 2013 by kamaly et al. by attaching the 7 amino acid oligopeptides to the peg end of the plga–peg block copolymer, and using it to package act-26 (with anti-inflammatory and inhibition of leukocyte extravasation). act-26 col iv nps were shown to limit neutrophil migration and adherence to the inflammatory site and to prevent inflammation development. il-10 nanoparticles (col-iv il-10 nps) were also created in 2016 by combining plga-peg-col iv and pdla-peg-ome targeting collagen lv with self-assembly[32]. col-iv il-10 np considerably boosted the plaque’s il-10 content after being administered intravenously to ldlr/mice and had a greater impact on as therapy than free il-10. additional research has focused on nanocarriers that can deliver numerous anti-inflammatory agents to distinct types of cells in the body. platelet-mimetic discoid morphology and flexibility were integrated with the platelet-mimetic biochemical heteromultivalent interactive functions by dendritic presentation of multiple peptides that bind simultaneously to both activated natural platelets and injured endothelial sites by dendritic presentation of multiple peptides[33]. nanoparticles’ biological and physical features determine whether they are passively targeted or actively targeted. particle size and distribution, targeting unit kinds, surface chemistry, morphology, and density are all examples of biological and physical features. the development stage, type and location of cvds and tumors, vascular wall shear rate, blood composition and its fluid type, as well as other elements, will have a significant impact on the targeting efficiency for the body[34]. however, even though the use of active targeted nddss in clinical diagnosis and treatment is exceedingly appealing, their development is still hampered by several dif 15 ficulties. as a result of these issues, there are two primary aspects: one is the inability to locate an optimal target; the other is the difficulty in designing and preparing effective nanosystems. 4. multifunctional responsiveness nddss with the principles of the aforementioned two targeting mechanisms, nano-drug carriers could be produced that would have a superior ability to target. these nanocarriers are often constituted of stimulatory responsive materials, which may be released under the stimulation of a specific environment, thereby decreasing release in normal tissue and enhancing drug accumulation at the focal site. when combined with other diagnostic compounds like volatile organic compounds, halogen containing compounds and many, nanocarriers can form an integrated diagnosis and treatment system. 5. application of the nddss in the diagnosis of cvds effective cvd prevention and therapy depend on early, quick, and precise identification. there has been an increase in the use of molecular imaging in the diagnosis of cardiovascular diseases in the last few years. additionally, new contrast agents are essential for real-time high sensitivity and high resolution diagnostics, in addition to the continual invention of various imaging modalities. nano-contrast agents have the following benefits over traditional contrast agents. there will be improvements in the following areas: (1) in vivo stabilization; (2) controllable physical and chemical properties (like chemical composition and size) and imaging performance; (3) specific identification of specific biomolecules; (4) multimodal imaging capability; (5) potential benefits for personalized treatment and diagnosis. nano-probes with distinct chemical signal molecules of sick tissues defined by pathological investigations can be used to drive the contrast agent to the lesion location for mri, x-ray imaging, fluorescence imaging, and contrast-enhanced ultrasound (us) imaging in the early stages of the illness. also optical coherence tomography (oct) using aunps and photoacoustic molecular probe are in existence to diagnose cvds. 5.1 magnetic resonance imaging magnetic resonance imaging (mri) is a non-invasive, safe, and high-resolution imaging technique that is particularly useful for studying soft tissues. however, mri’s sensitivity ranges from 103 to 109 m, which isn’t very high. t1-weighted imaging contrast agents, such as gadolinium complexes, are routinely employed in clinical practice; nonetheless, gadolinium has some nephrotoxicity. non-toxic t2-weighted mri contrast agents are fe3o4 nanoparticle[35]. in comparison to tinctures, their sensitivity, tissue compatibility, and superparamagnetism are far higher, and they’re also more potent. a high signal to noise ratio is achieved by using targeted contrast agents to collect mri probes at a high concentration (in micrograms to milligrammes) in the target tissue. preliminary vascular imaging may be conducted at an early stage of cardiovascular illness, and medications can be provided after the magnetic nanoparticles are infused in the body. diethylenetriamine pentaacetic acid (dtpa) was used[36] to chelate gadolinium in hydrophilic lipid (amphiphilic) micelles, which were subsequently encased in dendritic polymers and linked with fibrin binding agent. an improved targeting of atherosclerotic plaques and the ability to identify thrombus at an early stage have been achieved by this method. new zealand white rabbits were injected intravenously with paramagnetic nanoparticles targeting integrin v3 by winter et al. to identify neovascularization in plaques during the early stages of as[37]. 5.2 x-ray imaging nuclear medicine relies heavily on radionuclides for imaging[38]. in addition to being highly sensitive, radionuclides also have the ability to be quantified. imaging techniques use positron emission tomography (pet) and single photon emittance computed tomography (spect)[39]. radiation-labeled nanoparticles can now be used to track the embolization process and nanomedicine delivery in order to gain more precise imaging. these liposomes were utilized to conduct spect, which 16 can monitor the distribution of pharmaceuticals in the body, as well as enhance drug release. for example, researchers employed 186re-bmeda and 99mtc-pegylate-labeled doxorubicin liposomes. to detect atherosclerotic plaques, ct may be utilized to detect the nanoparticles, which can also be used to predict the prognosis of the disease. using a venous injection, galperin and colleagues administered iodine nanoparticle contrast agent (n1177) to animals. in macrophage-rich tissue, the contrast agent was shown to congregate, and the signal of atherosclerotic plaques was greatly amplified, and the enhancement period may continue for more than 30 min. when researchers utilized 11-muda (11-mercaptoundecanoic acid), they discovered that gold nanoparticles might concentrate in foam cells of atherosclerotic plaques and boost the contrast of imaging[40]. 5.3 fluorescence imaging optics is a strong imaging approach that has no radiation, no invasion, great resolution and good controllability, but it has a low penetrating ability. fluorescein is commonly used to create fluorescence signals in fluorescence imaging. it is common to utilize near infrared fluorescence (nirf) probes due to their high penetrating power and safety. small animal live imaging systems and clinical tumor transformation have utilized them. nano-drug carriers, such as liposomes, metal, or non-metallic nanoparticles, can encapsulate nirf to enable optical imaging of blood arteries at present. a growing amount of focus has been placed on its use in cardiovascular disease imaging. they created diagnostic and therapeutic nanoparticles by combining near infrared light activated therapy (nilat) with macrophage-targeted magnetic nanoparticles (mnp). within 24 hours of injection, the nanoparticles had spread across the study region. using profilin-1 as a target[41] injected atherosclerotic mice with profilin-1-targeting magnetic iron oxide nanoparticles (pf1cy5.5-dmsa-fe3 o4 nps). carotid atherosclerotic plaques contained magnetic iron oxide nanoparticle aggregates. fluorescence intensity measured in vitro was found to be in good agreement with the mri signal from animals injected with pc-nps. 5.4 ultrasound imaging ultrasound imaging provides a number of advantages to fluorescence imaging, including the fact that it is less invasive, more convenient, and can be used in real time. materials that can be targeted to certain vascular indicators have been produced. to give one example, vascular ultrasound nanoparticles that target vegfr2 increase drug localization in blood vessels by increasing the clarity of ultrasound imaging of tumor blood vessels. vegfr2 is an endothelial growth factor receptor 2 (vegfr2). streptokinase-carrying perfluorocarbon nanoparticles were created by marsh and colleagues for the diagnosis and treatment of thrombus[42]. ultrasonic imaging may be performed on the drug-loaded particles, which are made using the evaporation/dispersion approach and have a diameter of around 250 nm. 5.5 multi-modal bioimaging a mixture of diverse imaging technologies, known as multi-modal imaging technology, may now be used to achieve synergistic effects, resulting in more complete and accurate images for the diagnosis and treatment of cardiovascular diseases. for example, 64cu-labeled spio-loaded doxorubicin nanoparticles can be employed for mri and pet imaging, for example[43]. according to one study, gold nanoparticles mixed with cy5, sputum, and folic acid can provide trimodal optical imaging as well as mri and ct imaging in mice[44]. cardiovascular nanomedicine’s future development will take a fresh turn in the direction of multimodal imaging and diagnostic and therapy integration. 6. application of the nddss in the treatment of cvds 6.1 the nddss in as as is the most prevalent kind of cvd, and it frequently results in a stroke or heart attack. endothelial dysfunction is the first step in the development of as. ischemic cardiomyopathy can be caused by plaque-induced coronary artery narrowing, whereas acute myocardial infarction might be 17 caused by plaque rupture. peptideases and macrophages can be candidates for intervention in the pathophysiology of plaque instability because of increased vascular permeability, increased pecam expression, and macrophage aggregation. in order to maximize the concentration of lesions and decrease side effects, the medicine can be administered to atherosclerotic plaques using a nano-drug carrier. with these nano-drug carriers, you can regulate lipoprotein levels and reduce inflammation as well as prevent the formation of new vessels. in order to stop the formation of as, reduce plaque area, or stabilize susceptible plaques, these therapeutic options are employed[45]. 6.2 the nddss in hypertension today, a wide variety of medications are used to treat hypertension, including aten inhibitors, vascular angiotensin antagonists, central sympathetic nerve agents, adrenergic receptor blockers, diuretics and vasodilators, among other classes of medication[46]. antihypertensive therapeutic medications have evident flaws such as short plasma half-lives, limited bioavailability and toxic and side effects such as upper respiratory tract abstraction, angioedema, reflex thyrotomy, excessive hypotensive effects, etc. nano-drug carriers, on the other hand, can offer the advantages listed above. olmesartan has been developed into a nanoemulsion system by certain researchers. the nanoemulsion group exhibits greater blood pressure-lowering effects, a longer maintenance period, and nearly three times the dosage decrease than the standard dose group[47]. 6.3 the nddss in pulmonary hypertension increased pulmonary vascular resistance and raised pulmonary artery pressure are the hallmarks of pulmonary hypertension. pulmonary hypertension is commonly treated with vasodilators such as prostaglandin i, endothelin receptor antagonist, type 5 phosphodiesterase inhibitor, and others. the therapeutic potential of these vasodilators is limited, however they have demonstrated some results. in order to address this issue, nano-mediated drug delivery systems have become increasingly relevant. in nanoparticle form, bosentan is an endothelin receptor antagonist that is seven times more soluble than bosentan that hasn’t been treated[48]. 6.4 the nddss in myocardial infarction apoptosis, calcium overload, and reactive oxygen species have all been linked to reperfusion therapy, which is most commonly employed in the early stages of a myocardial infarction. apoptosis and necrosis of cardiomyocytes are promoted by the opening of the mptp and the rise in mitochondrial outer membrane permeability as a result of these factors[49]. growth factors, cytokines, and other small molecular substances are mostly used in clinical practice to treat myocardial ischemia. the drawbacks of these pharmaceuticals are the same as those of the standard medications listed above. in ischemic heart disease, high blood permeability and an abundance of monocytes can be utilized to deliver medications through the targeting ability of nano-carriers. 6.5 the nddss in other cvds additionally, the nano-drug delivery method works effectively in the treatment of various cardiovascular diseases. allogeneic angiopathy of the coronary arteries is an inflammatory process of proliferation that threatens the long-term effectiveness of heart transplantation. using methotrexate or paclitaxel-coated lipid nanoparticles, researchers administered them intravenously to rabbits receiving an ectopic heart transplant and fed them a cholesterol-rich diet[50]. insufficient oxygen supply and unstable myocardial energy metabolism are the primary causes of myocardial ischemia, a condition that can’t sustain the heart’s regular functions. thin film dispersion was used to make liposomes coated with phenytoin (pht, a non-selective vgsc inhibitor). pht-encapsulated liposomes partly suppressed i/r injury-induced cd43+ inflammatory monocyte growth and decreased infarct size and left ventricular fibrosis after intravenous injection of the rat myocardial i/r injury model[51]. after an angioplasty, an arteriotomy, or the implantation of an endovascular stent, the blood arteries might become stenotic and blocked again, a condition known as vascular restenosis. catheter-intervention methods may be employed to pump 18 drug-loaded nanoparticles into the damage site to enable angioplasty and topical delivery in one step. through the compromised endothelium, the nanoparticles can infiltrate the artery wall, locate, and then slowly release the medicine[52]. a high concentration of medicine in the lesion vessel may be maintained for a long length of time, which is advantageous to maximizing the drug’s action and preventing vascular restenosis as well. 7. application of the co-loaded nano-system in the cvds when two or more medications are administered to a patient at the same time, we say that we are using drug combination therapy. this treatment has been widely utilized in the medical community to treat a variety of diseases. the synergistic effect of medications, or the therapeutic benefit of numerous drugs which is larger than that of a single drug, is typically a factor in the use of this combination treatment. recent years have seen the development of several co-loaded nano-systems that carry medications and/or genes, particularly sirna, for the treatment of cardiovascular disease. 8. application of rnai in the treatment of cvds rna interference (rnai) is a gene-specific silencing process that is present in eukaryotic cells and an essential tool for preventing the spread of alien genes and viruses. when rnai was initially identified in c. elegans, it was later shown to be present in human cells[53]. a variety of rna interference mechanisms exist, including mirna, sirna, piwi-interacting rna, and long non-coding rna (lncrna) (lncrna). cell-specific genes may be silenced using rnai technology, which involves introducing double-stranded rna (dsrna) into cells, degrading mrna homologously complementary to the dsrna and limiting its expression. development of rnai research has led to it becoming a therapeutic development tool for the treatment of cvds[54]. additionally, rna interference therapy for the treatment of cvd has its own set of obstacles, including toxicity, targeting, temporal impact, and effective delivery method, which restrict its broad usage in the clinic and are urgently needed to be resolved and improved[55]. rna interference in the cardiovascular system is expected to take a new turn. 9. co-loaded gene and drug nano-system in order to overcome the difficulties in the delivery process and realise the full potential of rnai-based therapies, safe and effective nano delivery devices are essential. the liposome vector was used to contain the apolipoprotein b (apob) sirna. when the liver apob mrna was tested after 48 hours, the silencing rate was over 90%. when apob protein and blood cholesterol levels began to fall 24 hours after therapy, the effects lasted until day 11 of treatment[56]. researchers have created and packaged small interfering rna (sirna) against the pdgf-b mrna expression vector using chitosan nanoparticles, and then employed therapeutic ultrasound to transfect the vascular smooth muscle cells (vsmc) of rabbit artery wall injured by balloon catheter. according to the findings, the nanoparticles dramatically decreased intimal vsmc pcna and pdgf-b mrna expressions as well as local intimal thickness and area when applied to cells. the infarcted myocardium expresses considerably more nox2-nadph. nox2-sirna was delivered to the post-mi heart via acid-degradable polyketal particles[57], which decreased both sirna degradation and inflammation. sirna can be delivered to the proper cells at the right time in nano-doses created by several pharmaceutical firms. alnylam pharmaceuticals’ aln-pcs or placebo were given intravenously into healthy individuals with serum ldl values of 3 mmol/l or higher[58]. a sirna, aln-pcs, is integrated in lipid nanoparticles to block pcsk9 production. a single intravenous injection of aln-pcs decreased human pcsk9 protein levels by 70%, while ldl was lowered by 40%. using a combination of nanotechnology, gene interference technology, and the packaged chemicals, the therapeutic impact is far superior than a single therapy due to the synergistic effect. a medicine called carvedilol, which inhibits adrenergic 19 receptors in several organs concurrently, is extensively used and effective. cardiovascular hypertrophy can be effectively prevented by silencing p53 in the dna. however, cancer can spread to other organs as a result. these bioactive compounds were successfully encapsulated with stearic acid modified carboxymethyl chitosan (cmc) nanopolymers linked to a homing peptide for distribution in vivo to hypertrophied cardiomyocytes. 10. safety of the nddss although nanomaterial nddss are becoming more common, their unknown toxicity and lack of systematic research into the materials themselves limit their continued use. the surface effect, small scale effect, quantum scale effect, and macroscopical quantum tunnelling effect will all become apparent when the particle size reaches the nanoscale scale[59]. only a few research have looked at the potential dangers of ndds on the cardiovascular system. because of this, cardiovascular system tissue has been identified as a primary nddss target, which can have a significant influence on illness prognosis. nanomaterials have been shown to enter the bloodstream via the respiratory, digestive, skin, and other mucous membranes, where they interact with the blood, immune system, and other tissues, including plasma proteins and immune proteins, blood cells and immune cells, and so on. toxicological studies of the health effects are the primary focus of the ndds safety evaluation. nanomaterials’ cardiovascular toxicity has been linked to a number of adverse consequences, including oxidative stress, inflammation, apoptosis, blood aggregation, and cardiac signal transduction, in animal and cell studies[60]. inflammation and oxidative stress are two of the most important pathways for cardiovascular damage caused by nanomaterials, according to this research. hypertension, myocarditis, as, acute myocardial infarction, and heart failure can all be exacerbated by an inflammatory response to a variety of factors. when nano-carriers are not removed in a timely manner, they can reach all organs via blood, triggering a sequence of cytokines, which in turn raises the risk of cardiovascular events if they aren’t eliminated[61]. as a result of nanomaterials’ many surface atoms and high reactivity, free radicals and reactive oxygen species (ros) can be generated, posing a threat to antioxidant systems[62]. dna and proteins, which are macromolecular molecules, can be damaged by oxidative stress, resulting in decreased cell development, irregularities in the cell cycle, and even cell death. caenorhabditis elegans was used to test the biological safety of ph-responsive carrier system (ffpff self-assembling into a nanosphere structure, ffpff nps), which was designed for anti-tumor drug delivery and the results showed that exposure to high doses of ffpff nps did not have a significant impact on the survival rate, growth, development, movement, and reproduction of caenorhabditis elegans. the preliminary evaluation of the overall biological model of caenorhabditis elegans shows that ffpff nps has good biological safety[63]. potential toxicities that are associated with nanocarriers, mechanisms of toxicity, major target organs, and factors influencing these toxicities have also been discussed[64]. nanoparticles, due to their nanosize, easily traverse through biological barriers and may be accumulated in the body, where the ingredients incorporated in the formulation development might accumulate and/or produce toxic manifestation, leading to cause severe health hazards. therefore, the toxic profile of these delivery systems needs to be evaluated at the molecular, cellular, tissue and organ level[65]. the research of nanomaterial-induced cardiovascular system injury is still in its infancy across the world. nanoparticle physicochemical factors (shape, size, size distribution, surface structure, electrochemical properties) and the toxic effects of the cardiovascular system are poorly understood in terms of their link to the physiochemical parameters. more study into the cardiovascular system hazardous effects and processes of ordinary nanomaterial exposure is therefore needed by scientists in order to better utilise nanomaterials’ good properties to avoid, mitigate, or eliminate potential detrimental health consequences. nanomaterial safety evalua 20 tion technologies and standards would also have theoretical and technological foundations provided by this study. 11. conclusion in conclusion, the nano-carrier, as an efficient, specific and controllable intracellular drug delivery method, has shown unique advantages in the diagnosis and therapy of cvds. it can effectively solve the problems of targeting, local drug delivery, controlled release, sustained release, and reducing toxicity while it is developing toward the multifunctional and integrated direction of diagnosis and therapy. with the innovation of nanotechnology and the deepening studies on molecular pathological mechanism of cvds, the application of nddss will be promoted, and new techniques and methods will be provided for clinical diagnosis and therapy. in addition, since the study on these nano-carriers is in its infancy, many problems still remain unclear. the main challenge is how to solve the biocompatibility of nano-drug-loaded particles themselves or their degradation products, which is need to be solved in the field of nano-biomedicine in the future. conflict of interest the authors declared no conflict of 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science, king abdulaziz university, jeddah 80203, saudi arabia * corresponding author: md. mahmud alam, alam-mahmud@hotmail.com, mmalam@zhsust.ac.bd abstract: water splitting has gained significant attention as a means to produce clean and sustainable hydrogen fuel through the electrochemical or photoelectrochemical decomposition of water. efficient and cost-effective water splitting requires the development of highly active and stable catalysts for the oxygen evolution reaction (oer) and hydrogen evolution reaction (her). carbon nanomaterials, including carbon nanotubes, graphene, and carbon nanofibers, etc., have emerged as promising candidates for catalyzing these reactions due to their unique properties, such as high surface area, excellent electrical conductivity, and chemical stability. this review article provides an overview of recent advancements in the utilization of carbon nanomaterials as catalysts or catalyst supports for the oer and her in water splitting. it discusses various strategies employed to enhance the catalytic activity and stability of carbon nanomaterials, such as surface functionalization, hybridization with other active materials, and optimization of nanostructure and morphology. the influence of carbon nanomaterial properties, such as defect density, doping, and surface chemistry, on electrochemical performance is also explored. furthermore, the article highlights the challenges and opportunities in the field, including scalability, long-term stability, and integration of carbon nanomaterials into practical water splitting devices. overall, carbon nanomaterials show great potential for advancing the field of water splitting and enabling the realization of efficient and sustainable hydrogen production. keywords: oxygen evolution reaction (oer); hydrogen evolution reaction (her); carbon nanomaterials; surface functionalization; optimization of nanostructure and morphology 1. introduction water splitting, the process of converting water into oxygen and hydrogen gases, has emerged as a promising avenue for sustainable energy production and storage. it offers a pathway to generate clean and renewable hydrogen fuel, which can be used as a versatile energy carrier. the efficient catalysis of the oxygen evolution reaction (oer) and hydrogen evolution reaction (her) remains a critical challenge in water splitting technologies [1,2]. catalysts used in the oxygen evolution reaction frequently experience stability problems when exposed to harsh oxidative environments, resulting in degradation and a decrease in catalytic performance over time. the oxygen evolution reaction generally necessitates a high overpotential to achieve a substantial reaction rate, diminishing overall efficiency. many of the best catalysts for oer and her use noble metals such as platinum, iridium, and ruthenium, which are rare and costly. this restricts their widespread use and highlights the need for affordable and citation shahazi r, saddam ai, islam mr, et al. carbon nanomaterials for efficient oxygen and hydrogen evolution reactions in water splitting: a review. characterization and application of nanomaterials. 2024. 7(2): 8543. https://doi.org/10.24294/can.v7i2.8543 article info received: 13 august 2024 accepted: 10 october 2024 available online: 28 october 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 8543. 2 abundant alternatives. achieving high efficiency and selectivity in both oer and her is difficult because of competing side reactions and the necessity for precise control over the reaction environment and catalyst properties [3–5]. to address this challenge, researchers have turned their attention to carbon nanomaterials, which exhibit unique structural and electronic properties that make them attractive candidates for efficient catalysis in water splitting. carbon nanomaterials, such as carbon nanotubes, graphene, and carbon nanofibers, possess exceptional characteristics, including high surface area, excellent electrical conductivity, and chemical stability [6,7]. the high surface area of carbon nanomaterials provides a large number of active sites for catalytic reactions, facilitating the adsorption and activation of reactant molecules. this leads to increased reaction kinetics and improved catalytic efficiency. furthermore, the excellent electrical conductivity of carbon nanomaterials enables efficient charge transfer during electrochemical reactions, reducing energy losses and enhancing overall catalytic activity [8–10]. the chemical stability of carbon nanomaterials is another advantageous attribute for water splitting. their robust nature allows them to withstand harsh reaction conditions, such as high temperatures and corrosive environments, ensuring long-term durability and catalytic performance [11,12]. in recent years, extensive research efforts have been dedicated to exploring the catalytic properties and performance of carbon nanomaterials in water splitting. various strategies have been employed to optimize their catalytic activity, including surface functionalization, heteroatom doping, and incorporation of other active materials. these approaches aim to enhance the catalytic efficiency, selectivity, and stability of carbon-based catalysts for both the oer and her [13,14]. this review aims to provide an overview of the recent advancements in the utilization of carbon nanomaterials for efficient oer and her in water splitting. it will discuss the fundamental mechanisms underlying their catalytic activity, highlight the strategies employed to enhance their performance, and address the challenges associated with their implementation in practical water splitting systems. additionally, future research directions and opportunities for the development of carbon nanomaterial-based catalysts will be explored. 2. importance of water splitting for sustainable energy production water splitting is of paramount importance for sustainable energy production because it can harness and utilize hydrogen as a clean and renewable energy source. 2.1. hydrogen fuel water splitting enables the production of hydrogen gas (h2), which can be used as a fuel in various applications. hydrogen is a versatile energy carrier that can be used in fuel cells to generate electricity or directly combusted. unlike fossil fuels, hydrogen combustion or utilization in fuel cells produces only water as a byproduct, making it a clean and environmentally friendly energy option [15]. characterization and application of nanomaterials 2024, 7(2), 8543. 3 2.2. renewable energy storage one of the significant challenges with renewable energy sources like solar and wind is their intermittent nature. water splitting offers a way to store excess renewable energy by converting it into hydrogen [16]. the generated hydrogen can be stored and used later when energy demand exceeds supply, providing a reliable and controllable energy storage option. this helps to balance the intermittent nature of renewables and ensures a consistent energy supply. 2.3. decarbonization hydrogen produced through water splitting can play a vital role in decarbonizing various sectors of the economy. when hydrogen is produced using renewable electricity, the entire process becomes carbon-neutral or even carbon-free [17]. by substituting hydrogen for fossil fuels in transportation, heating, and industrial processes, we can significantly reduce greenhouse gas emissions and mitigate climate change. 2.4. industrial applications water splitting and the production of hydrogen can revolutionize various industrial processes. hydrogen can be used as a feedstock for producing chemicals, such as ammonia and methanol, replacing fossil fuel-based methods [18]. this enables the decarbonization of industries and promotes a more sustainable and environmentally friendly manufacturing sector. 2.5. transportation water splitting enables the production of hydrogen fuel for transportation applications. hydrogen fuel cells can power vehicles, including cars, buses, trucks, and trains [19]. hydrogen fuel cell vehicles emit only water vapor, offering a zeroemission alternative to conventional fossil fuel-powered vehicles [20]. by transitioning to hydrogen-powered transportation, we can significantly reduce air pollution and dependence on fossil fuels. 2.6. grid flexibility water splitting and hydrogen production contribute to grid flexibility and stability. by utilizing excess renewable energy to produce hydrogen, we can effectively store energy and balance the electricity grid. hydrogen can be converted back to electricity during peak demand periods, ensuring a stable power supply and enhancing the resilience of the grid [21]. 3. potential of carbon nanomaterials as catalysts or catalyst supports carbon nanomaterials, such as carbon nanotubes (cnts), graphene, and carbon nanofibers, show significant potential as catalysts or catalyst supports for watersplitting reactions. here are some key reasons for their attractiveness in this field: characterization and application of nanomaterials 2024, 7(2), 8543. 4 3.1. high surface area carbon nanomaterials possess a large surface area per unit mass or volume. this high surface area provides abundant active sites for catalytic reactions, allowing for efficient utilization of the catalyst and enhancing reaction rates [22,23]. 3.2. chemical stability carbon nanomaterials exhibit excellent chemical stability, which is crucial for withstanding the harsh conditions of water-splitting reactions. they are resistant to corrosion and degradation, ensuring long-term catalytic activity and durability [24,25]. 3.3. electrical conductivity several carbon nanomaterials, such as cnts and graphene, exhibit excellent electrical conductivity. this property enables efficient charge transfer during electrochemical reactions, minimizing energy losses and improving overall catalytic performance [26,27]. 3.4. tailorable properties carbon nanomaterials offer versatility in terms of their structural and surface properties. their morphology, surface chemistry, and functionalization can be tailored to optimize catalytic activity, selectivity, and stability for specific water-splitting reactions [28,29]. 3.5. catalyst support carbon nanomaterials can serve as excellent supports for other catalyst materials, such as metal nanoparticles or metal oxides. the high surface area and unique structural features of carbon nanomaterials facilitate the dispersion and stabilization of active catalyst particles, enhancing their catalytic performance [30,31]. figure 1 demonstrates the use of graphene sheets as catalyst supports. figure 1. graphene as catalyst support. 3.6. abundance and low cost carbon is an abundant and relatively low-cost element. carbon nanomaterials can be synthesized from various carbon sources, making them economically favorable for large-scale production and implementation in water splitting technologies [32,33]. 3.7. synergistic effects carbon nanomaterials can exhibit synergistic effects when combined with other characterization and application of nanomaterials 2024, 7(2), 8543. 5 catalyst materials. for example, the integration of carbon nanomaterials with transition metal-based catalysts can lead to enhanced catalytic activity and stability through synergistic interactions and improved electron transfer pathways [34,35]. while carbon nanomaterials hold great potential, challenges still exist. these include further enhancing catalytic activity, improving mass transport limitations, minimizing side reactions, and addressing potential issues such as catalyst poisoning or surface fouling. continued research and development efforts are focused on optimizing carbon nanomaterials and harnessing their full potential as catalysts or catalyst supports for water splitting, contributing to the advancement of sustainable energy production. 4. carbon nanomaterials for oer and her carbon nanomaterials have shown great potential as catalysts for both the hydrogen evolution reaction (her) and the oxygen evolution reaction (oer), which are essential processes in water splitting for hydrogen production and in various energy conversion and storage technologies. figure 2 depicts a range of carbon nanomaterials. here’s an overview of the potential of carbon nanomaterials for her and oer: figure 2. various types of carbon nanomaterials. 4.1. carbon nanotubes (cnts) cnts possess high electrical conductivity, a large surface area, and unique tubular structures, making them attractive catalysts for both her and oer. their conductivity facilitates efficient charge transfer during the electrochemical reactions, while their high surface area provides abundant active sites. functionalization of cnts with metal nanoparticles or heteroatoms can further enhance their catalytic activity for both her and oer [36–39]. 4.2. graphene graphene, a two-dimensional carbon material, exhibits excellent electrical conductivity and a large surface area, making it a promising catalyst for her and oer. pristine graphene itself has limited intrinsic activity. strategies such as functionalization, doping, or hybridization with other materials have been explored to enhance its catalytic performance for both reactions [40,41]. characterization and application of nanomaterials 2024, 7(2), 8543. 6 4.3. carbon nitride (c3n4) carbon nitride-based materials, such as graphitic carbon nitride (g-c3n4), have emerged as metal-free catalysts for both her and oer. the structure of graphitic carbon nitride is demonstrated in figure 3. these materials are abundant, low-cost, and environmentally friendly. their unique electronic structure enables efficient charge transfer and catalytic activity during both reactions. further modifications and optimization are required to improve their intrinsic activity and stability [42,43]. modifications may include tailoring the shape and surface characteristics of g-c3n4, doping with other elements, or forming composites with other materials. these changes are intended to improve light absorption characteristics, expand the number of active sites accessible for catalytic reactions, and strengthen the material’s overall resilience to operating conditions [44,45]. figure 3. structure of graphitic carbon nitride (g-c3n4). 4.4. carbon quantum dots (cqds) carbon quantum dots, small carbon nanoparticles, have shown promise as catalysts for both her and oer. their unique quantum confinement effects and tunable surface properties enable efficient charge transfer and catalytic activity. surface functionalization or doping of cqds with heteroatoms or metal species can further enhance their performance for both reactions [46–48]. 4.5. defect-engineered carbon materials introducing defects or heteroatoms into carbon nanomaterials can significantly influence their electronic structure and surface reactivity, enhancing their catalytic activity for both her and oer. defect engineering provides additional active sites and improves charge transfer kinetics. tailoring the defect density and distribution can optimize the performance of carbon nanomaterials for both reactions [49,50]. while carbon nanomaterials hold promise for her and oer catalysis, challenges remain in enhancing their intrinsic activity, stability, and mass transport properties. additionally, understanding the underlying mechanisms and optimizing the catalyst design are ongoing research areas. nonetheless, carbon nanomaterials offer exciting opportunities to advance her and oer catalysis and enable efficient and sustainable energy conversion and storage technologies [51]. characterization and application of nanomaterials 2024, 7(2), 8543. 7 5. carbon nanomaterial hybridization with other materials for enhanced catalysis hybridization of carbon nanomaterials with other materials has been extensively explored to enhance water splitting catalysis, particularly in the context of the hydrogen evolution reaction (her) and the oxygen evolution reaction (oer). here are some examples of carbon nanomaterials hybridized with other materials for enhanced water splitting catalysis. 5.1. carbon nanotubes (cnts) and metal nanoparticles cnts can be hybridized with metal nanoparticles, such as platinum (pt), palladium (pd), or nickel (ni), to form composite catalysts. metal nanoparticles may be applied to the surface of carbon nanotubes (cnts) to create a composite material, as seen in figure 4. the metal nanoparticles provide high catalytic activity, while the cnts act as conductive supports, facilitating electron transfer during the reactions. the hybridization enhances the overall catalytic performance and stability [52,53]. figure 4. deposition of metal nanoparticles on carbon nanotube. 5.2. graphene and metal oxides graphene can be combined with metal oxides, such as titanium dioxide (tio2), iron oxide (fe2o3), or cobalt oxide (co3o4), to form composite catalysts. the metal oxides provide high catalytic activity, while graphene offers excellent electrical conductivity and large surface area. the hybrid structure promotes efficient charge transfer and provides additional active sites, enhancing the water splitting catalysis [54–56]. 5.3. carbon nitride (c3n4) and transition metal compounds carbon nitride-based materials, such as graphitic carbon nitride (g-c3n4), can be hybridized with transition metal compounds, including metal oxides or sulfides, to form composite catalysts. the transition metal compounds provide catalytic activity, while carbon nitride offers a stable and conductive support. the hybridization promotes synergistic effects, leading to enhanced water splitting catalysis [57–60]. 5.4. carbon quantum dots (cqds) and semiconductor nanomaterials carbon quantum dots can be combined with semiconductor nanomaterials, such as metal chalcogenides (e.g., mos2, ws2) or metal oxides (e.g., zno, wo3), to form characterization and application of nanomaterials 2024, 7(2), 8543. 8 hybrid catalysts. the semiconductor nanomaterials provide light absorption and charge separation capabilities, while carbon quantum dots contribute to improved charge transfer and catalytic activity. the hybridization enables efficient utilization of solar energy for water splitting [61–65]. 5.5. carbon-based heterostructures carbon nanomaterials, such as cnts or graphene, can be integrated with other functional materials, such as metal nanoparticles, metal oxides, or semiconductor nanomaterials, to form complex heterostructures. the combination of different materials in the heterostructures allows for synergistic effects, enhanced catalytic activity, and improved charge transfer kinetics [66–68]. hybridization strategies enable the integration of the unique properties of carbon nanomaterials with those of other materials, leading to enhanced water splitting catalysis. the resulting hybrid catalysts can exhibit improved activity, stability, and efficiency, which are crucial for advancing water splitting technologies for sustainable hydrogen production and energy storage. 6. challenges and future perspectives carbon nanomaterials have shown great potential for water splitting applications, but there are several challenges that need to be addressed for their effective implementation. additionally, there are several future perspectives that can drive further advancements in this field. here are the challenges and future perspectives of carbon nanomaterials in water splitting: 6.1. challenges catalyzing the oxygen evolution reaction (oer) and hydrogen evolution reaction (her) is crucial for efficient water splitting and sustainable energy production. several challenges exist in developing effective catalysts for these reactions. both oer and her are kinetically sluggish processes, meaning that the reaction rates are relatively slow. this limits the overall efficiency and scalability of water splitting systems [69,70]. catalysts need to accelerate the reaction rates and improve the kinetics to enhance the performance of the reactions. these reactions typically require a significant overpotential, which is the additional energy input needed to drive the reactions. high overpotentials result in increased energy losses and reduced overall efficiency [71–73]. developing catalysts that can minimize the overpotential required for these reactions is a major challenge. catalysts for oer and her must be stable and durable under the harsh conditions of water splitting, including high temperatures, corrosive electrolytes, and repeated cycling. many catalyst materials suffer from degradation, corrosion, particle detachment, or surface restructuring over time, leading to reduced activity and performance. an illustration of carbon corrosion and particle detachment is shown in figure 5. developing catalysts with high stability and durability is crucial for long-term and practical applications. the widespread adoption of water splitting technologies depends on the availability and affordability of catalyst materials. some catalysts, such as those based on precious metals like platinum [74,75] and iridium [76,77], are expensive and scarce, limiting their large-scale deployment. characterization and application of nanomaterials 2024, 7(2), 8543. 9 developing catalysts based on earth-abundant elements or low-cost materials is important for making water splitting economically viable. efficient water splitting systems require the integration of oer and her catalysts with other components, such as electrodes, membranes, and electrolytes. achieving optimal compatibility and synergy among these components is challenging. catalyst designs that can facilitate effective coupling with other system components are crucial for maximizing overall performance. achieving high selectivity for either oer or her is desirable to minimize energy losses and maximize overall water splitting efficiency. catalysts may exhibit side reactions or undesired reactions, leading to reduced selectivity. developing catalysts that can selectively promote either oer or her without significant crossover or side reactions is a challenge. for practical implementation, catalysts need to be scalable, meaning they should be easily synthesized, fabricated, and deployed at a large scale. some catalyst materials may face limitations in terms of scalability due to complex synthesis methods or high-cost fabrication techniques. developing scalable catalyst synthesis and manufacturing processes is important for commercialization. figure 5. the reduction of catalyst activity through carbon corrosion and particle detachment. thus, addressing these challenges requires a multidisciplinary approach involving materials science, electrochemistry, catalysis, and engineering. researchers are actively exploring new catalyst materials, nanostructured architectures, surface modifications, and advanced characterization techniques to overcome these hurdles and develop efficient and stable catalysts for oer and her in water splitting systems. the key points are presented in the forthcoming paragraphs. 6.1.1. limited catalytic activity carbon nanomaterials, such as carbon nanotubes and graphene, often exhibit limited intrinsic catalytic activity for water splitting reactions. enhancing their catalytic performance is crucial for achieving efficient water splitting. future research should focus on developing strategies to improve the catalytic activity of carbon nanomaterials through doping, functionalization, and structural modifications. 6.1.2. stability and durability carbon nanomaterials can suffer from degradation and oxidation under harsh water splitting conditions, leading to reduced stability and durability. improving the stability and durability of carbon nanomaterials is essential for long-term performance. characterization and application of nanomaterials 2024, 7(2), 8543. 10 future research should investigate protective coatings, surface modifications, and composite structures to enhance the stability and durability of carbon nanomaterials. 6.1.3. mass transport limitations carbon nanomaterials often possess high surface area but limited porosity, which can hinder the mass transport of reactants to the catalytic sites. improving mass transport is crucial for efficient water splitting. future research should focus on optimizing the porous structure and surface morphology of carbon nanomaterials to enhance reactant diffusion and accessibility to active sites. 6.1.4. cost and scalability the cost-effective synthesis and large-scale production of carbon nanomaterials remain a challenge. many carbon nanomaterials are still produced through complex and expensive methods. future research should explore scalable synthesis routes and cost-effective fabrication techniques to enable the widespread implementation of carbon nanomaterials in water splitting technologies. integration with other components: carbon nanomaterials often need to be integrated with other components, such as electrodes and membranes, in water splitting systems. achieving effective integration and compatibility between carbon nanomaterials and other components is crucial for overall system performance. future research should focus on developing suitable interfaces and interfacial engineering strategies to enable efficient integration of carbon nanomaterials with other functional components. 6.2. future perspectives 6.2.1. advanced catalyst design future research should focus on the rational design of carbon nanomaterial-based catalysts. this includes tailoring the morphology, structure, and composition of carbon nanomaterials to optimize their catalytic activity. additionally, exploring novel carbon nanomaterials and hybrid systems can lead to breakthroughs in water splitting catalysis. 6.2.2. synergistic hybrid materials the combination of carbon nanomaterials with other functional materials, such as metal nanoparticles or metal oxides, can create synergistic effects and enhance water splitting performance. future research should explore the development of hybrid materials that leverage the unique properties of carbon nanomaterials and other materials to achieve improved catalytic activity and stability. 6.2.3. electrocatalysis and photocatalysis carbon nanomaterials can be employed in both electrocatalytic and photocatalytic water splitting systems. future research should investigate the fundamental mechanisms and optimize the parameters for efficient electrocatalysis and photocatalysis using carbon nanomaterials. this includes exploring new carbon nanomaterial-based electrode architectures and tuning their band structures for enhanced performance. 6.2.4. integration with renewable energy sources carbon nanomaterials can be integrated with renewable energy sources, such as characterization and application of nanomaterials 2024, 7(2), 8543. 11 solar energy or wind energy, to achieve sustainable and clean water splitting. future research should explore the synergistic integration of carbon nanomaterials with renewable energy systems to develop efficient and environmentally friendly water splitting technologies. 6.2.5. environmental impact assessment as with any nanomaterial, it is essential to consider the potential environmental impact of carbon nanomaterials. future research should focus on comprehensive environmental impact assessments to ensure the safe and sustainable implementation of carbon nanomaterials in water splitting technologies. addressing these challenges and exploring the future perspectives will drive the advancement of carbon nanomaterials in water splitting, enabling the development of efficient and sustainable hydrogen production systems. continued research, collaboration, and innovation are crucial for realizing the full potential of carbon nanomaterials in this field. 7. conclusion in conclusion, carbon nanomaterials have emerged as promising catalysts for efficient oxygen and hydrogen evolution reactions in water splitting. they offer several advantages, including high surface area, tunable properties, and chemical stability. there are still challenges that need to be addressed to fully exploit their potential. enhancing the catalytic activity and stability of carbon nanomaterials is a key focus for future research. strategies such as doping, functionalization, and structural modifications can be employed to improve their intrinsic activity and durability. additionally, optimizing the porous structure and surface morphology of carbon nanomaterials can enhance mass transport and reaction kinetics. the scalability and cost-effectiveness of carbon nanomaterials also require attention. developing scalable synthesis methods and cost-effective fabrication techniques is essential for their large-scale production and practical implementation in water splitting technologies. future perspectives include advanced catalyst design, exploring synergistic hybrid materials, and leveraging carbon nanomaterials in electrocatalytic and photocatalytic systems. the integration of carbon nanomaterials with renewable energy sources holds promise for sustainable water splitting. additionally, comprehensive environmental impact assessments are crucial to ensuring the safe and responsible use of carbon nanomaterials. overall, with continued research, innovation, and interdisciplinary collaborations, carbon nanomaterials have the potential to play a significant role in achieving efficient and sustainable water splitting, contributing to the development of clean energy systems, and addressing global energy challenges. conflict of interest: the authors declare no conflict 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10.1021/acsnano.1c08506 76. pi y, xu y, li l, et al. selective surface reconstruction of a defective iridium‐based catalyst for high‐efficiency water splitting. advanced functional materials. 2020; 30(43). doi: 10.1002/adfm.202004375 77. chen z, duan x, wei w, et al. iridium-based nanomaterials for electrochemical water splitting. nano energy. 2020; 78: 105270. doi: 10.1016/j.nanoen.2020.105270 microsoft word 8291-38398-2-le characterization and application of nanomaterials 2025, 8(1), 8291. https://doi.org/10.24294/can8291 1 article polymeric nanoparticles for protein and peptide delivery nijhawan monika, neerude sirisha, sneha nawale* department of pharmacognosy, gokaraju rangaraju college of pharmacy, hyderabad 500090, india * corresponding author: sneha nawale, sneha.nawale11@gmail.com abstract: proteinand peptide-based medications are recognized for their effectiveness and lower toxicity compared to chemical-based drugs, making them promising therapeutic agents. however, their application has been limited by numerous delivery challenges. polymeric nanostructures have emerged as effective tools for protein delivery due to their versatility and customizability. polymers’ inherent adaptability makes them ideal for meeting the specific demands of protein-delivery systems. various strategies have been employed, such as enzyme inhibitors, absorption enhancers, mucoadhesive polymers, and chemical modifications of proteins or peptides. this study explores the hurdles associated with protein and peptide transport, the use of polymeric nanocarriers (both natural and synthetic) to overcome these challenges, and the techniques for fabricating and characterizing nanoparticles. keywords: drug delivery; nanoparticles (nps); protein delivery; therapeutic effect 1. introduction protein is derived from the greek word “protos”, meaning the first or the supreme. proteins are large organic molecules composed of amino acids linked together in a linear chain by peptide bonds, with proteins typically containing more than 50 amino acids. peptides are short polymers formed by the linkage of amino acids in a specific order (a peptide contains < 50 amino acids). proteins exhibit various structural forms: the primary structure, which is the sequence of amino acids; the secondary structure, consisting of regularly repeating local structures stabilized by hydrogen bonds; the tertiary structure, representing the three-dimensional configuration of the polypeptide; and the quaternary structure, formed by the assembly of multiple protein molecules (polypeptide chains) [1]. proteins and peptides can be classified into different types, including polypeptides, oligopeptides, fibrous proteins, globular proteins, and oligomeric proteins, based on the number of amino acids present. proteins are essential to the body as they participate in various biological roles in the form of enzymes that catalyze virtually all chemical reactions (e.g., 6gdh), help in the transport of hemoglobin of erythrocytes, contract muscles (actin and myosin), maintain the structure of the body (collagen in bones), provide defensive activity (immunoglobulins and antibodies), regulate secretions (insulin), provide nutrition and storage in the body (ovalbumin), generate and transmit nerve impulses, provide immune protection through antibodies, and control growth. bioapplications of proteins and peptides include the use of erythropoietin to stimulate red blood cell production, tissue plasminogen activator for treating heart attacks and strokes, oxytocin to manage labor pain, bradykinins to enhance peripheral circulation, somatostatin to reduce bleeding in gastric ulcers, gonadotropin to induce citation monika n, sirisha n, nawale s. polymeric nanoparticles for protein and peptide delivery. characterization and application of nanomaterials. 2025; 8(1): 8291. https://doi.org/10.24294/can8291 article info received: 30 july 2024 accepted: 7 november 2024 available online: 2 december 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterialst is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 8291. 2 ovulation, and insulin to regulate blood sugar levels. although proteins and peptides offer many benefits, their delivery poses challenges due to their large size and instability. their structures are maintained by weak noncovalent forces, making them susceptible to degradation under mild storage conditions and gastric juices [2–4]. 2. problems with protein and peptide the primary challenges in delivering proteins and peptides are proteolysis by exo/endo proteases, small-size proteins getting filtered out by kidneys very easily, causing elimination of b and t cells, and may show unwanted allergic reactions (even toxicity), and less therapeutic activity of proteins due to insolubility/adsorption [5]. 3. barriers to protein and peptide delivery 3.1. enzymatic barriers proteins and peptides can be degraded by enzymes in two distinct ways. one method involves the hydrolytic breaking of peptide bonds by enzymes that degrade insulin, convert angiotensin, and renin. since proteolysis is an irreversible event, it may harm medications that include proteins and peptides. others include chemical modification of proteins by oxidizing them using glucose oxidase or xanthine oxidase or phosphorylating them with kinases [6]. 3.2. intestinal epithelial barrier it prevents protein medications from passing through the intestinal epithelium. transport of protein and peptide medicines across the intestinal epithelium is accomplished by several processes, including paracellular movements, endocytosis, transcytosis, passive transport, and carrier-mediated transport. dipeptides and tripeptides from the small intestine are extensively absorbed through active transport. proteins and peptides that are too large to be absorbed through carrier-mediated transport can be taken up via endocytosis, which is one of the processes by which cellular internalization of proteins and peptides occurs that include pinocytosis (cell drinking) and phagocytosis (cell eating). paracellular migration and persorption are the two mechanisms involved in drug absorption. the epithelial mucosa of the small intestine serves as a barrier against macromolecule penetration [7]. 3.3. capillary endothelial barrier proteins and peptides must either cross the endothelial cells themselves or move between the cells to pass through the capillary endothelium. cytoplasmic enzymes can alter or metabolize solutes that pass through endothelial cell membranes. therefore, the endothelial passage presents an enzymatic or metabolic barrier to the passage of the proteins and peptides [8]. 3.4. blood-brain barrier one of the main barriers to protein delivery to the brain compartment is the bloodbrain barrier (bbb). it is made up of the blood-cerebrospinal fluid barrier and the vascular bbb. bbb is made up of a monolayer of cells at both locations that are joined characterization and application of nanomaterials 2025, 8(1), 8291. 3 by tight junctions and contain additional mechanisms to prevent or slow the flow of plasma into the central nervous system, permitting only the passage of uncharged, tiny, lipophilic molecules and gases. proteins and other large molecules cannot cross the bbb [9]. different barriers to protein and peptide drug delivery are illustrated in a visual format in figure 1. figure 1. intestinal barrier, capillary endothelial barrier and blood brain barrier for protein and peptide delivery. glycoproteins tight junctions adherence junctions desmosomes brush border transporter epithelial cells basement membrane tight junctions astrocyte foot process tight junctions pericyte capillary lumen endothelial cell characterization and application of nanomaterials 2025, 8(1), 8291. 4 4. polymeric nanocarriers for protein and peptide delivery polymeric nanoparticles (nps), which are solid colloidal carriers ranging from 10 to 100 nm in size, can be formulated with synthetic, semi-synthetic, or natural polymers. the choice of materials used to synthesize these nps affects their drug delivery performance and therapeutic effects. proteins can be chemically attached, adsorbed, or encapsulated on the surface of polymeric nps [10,11]. 4.1. natural polymers therapeutic proteins can be delivered to specific sites for distinctive benefits with natural polymers. the natural polymers may be of plant, animal, and marine origin and are generally inexpensive. the existence of reactive sites in natural polymers is significant in drug delivery systems because it facilitates ligand conjugation, crosslinking, and other modifications that make the polymers perfect drug carriers for a variety of therapeutic proteins. however, natural polymers are more susceptible to processing parameters. 4.1.1. polysaccharide-based natural polymers polysaccharides exhibit structural and functional diversity because of their vast number of reactive groups, wide range of molecular weights, and varied chemical composition. being naturally occurring biomaterials, polysaccharides are safe, nontoxic, and biodegradable and exhibit remarkable stability in biological fluids. polysaccharides are also known as mucoadhesive polymers because of their mucoadhesive qualities (polysaccharides, which are hydrophilic in nature, create noncovalent connections with biological tissues) due to the presence of many derivable groups on the molecular structure, such as hydroxyl, carboxyl, and amino groups. mucoadhesive polysaccharide-based nps have been demonstrated to improve the residence and absorbance time of integrated therapeutic protein. various polysaccharides used for the transport of proteins and peptides are represented in table 1. table 1. list of various polysaccharide polymers for proteins and peptide drug delivery. polysaccharide polymers properties role of polymers in transportation of protein and peptides reference chitosan biocompatible, non-toxic aid in facilitating the intestinal epithelial mucosal absorption of therapeutic proteins with high molecular weight. [12,13] cyclodextrins utilized as potential carriers in pharmaceutical biotechnology and non-toxic improve the bioavailability of the protein molecule by delivering it directly to the barrier membrane [14,15] alginates excellent mucoadhesive qualities, biocompatibility, biodegradability, high degree of flexibility and nontoxic helps in transport of therapeutic proteins that are heat sensitive. alginate also transports labile proteins and peptides safely to the colon while shielding them from the stomach environment. [16,17] pectins mucoadhesive activity inert for physiological fluids and non-toxic stops integrated proteins from being broken down by gastric enzymes and greatly boosts the intestinal absorption by its unique mucoadhesive activity on the intestinal epithelium. [18,19] xanthan gum biocompatible, non-toxic, biodegradable and bioadhesive properties preserves the integrity of the therapeutic protein and extends its sustained release [20,21] characterization and application of nanomaterials 2025, 8(1), 8291. 5 4.1.2. protein-based polymers amidst natural polymers, protein-based polymers have garnered significant attention because of their attributes such as abundance, accessibility, minimal toxicity, modifiability due to their intricate heterogeneity, and adaptability in delivery methods as depicted in table 2. there is still more work to be done to make protein-based polymers stable enough to be used as the perfect therapeutic polymers. table 2. list of various protein polymers for proteins and peptide drug delivery. protein polymers properties role of polymers in transportation of protein and peptides reference lectins sugar-binding proteins ability to improve the active transport of therapeutic proteins with large molecular weights from the intestinal epithelium [22] albumin non-toxic, biocompatible deliver therapeutic proteins across the blood-brain barrier and nuclear membrane [23] collagen biocompatible easily modifiable and available synergic with bioactive components facilitates the delivery of therapeutic proteins and extends the sustained release of the incorporated proteins. [24] gelatin biocompatible biodegradable thermo-reversible properties are utilized for delivering therapeutic molecules through targeted drug delivery systems [25] 4.2. synthetic polymers formulators are focusing on synthetic polymers for the delivery of therapeutic proteins and peptides. it has been demonstrated that these polymers lengthen the pharmacokinetic and circulation periods of integrated medicinal compounds. drug carriers made of synthetic polymers frequently serve a passive purpose as tabulated in tables 3 and 4. table 3. list of various synthetic biodegradable polymers with their properties and transport of proteins and peptide drug delivery. synthetic polymers properties role in transportation of protein and peptides reference polyethylene glycol non-immunogenic, nontoxic, highly soluble in water pegylation of therapeutic proteins protects them from enzymatic degradation and reduces immunogenicity, thereby extending their residence time in the body, enhancing stability, and modifying pharmacokinetics by altering various physicochemical properties [26,27] polaxomers thermosensitive inert and stable helps to sustain the stability of incorporated therapeutic proteins and peptides more effectively than other prolonged release drug delivery systems [28,29] poly (lactic-coglycolic acid) biocompatible and biodegradable several types of plga-peg block copolymers have been developed for the proteins and peptides sustained delivery [30,31] pluronic f127 non-irritant biocompatibility good mechanical strength bioadhesive properties ensures greater stability of incorporated therapeutic proteins and peptides compared to other prolonged release drug delivery systems [32] characterization and application of nanomaterials 2025, 8(1), 8291. 6 table 4. list of various synthetic non-biodegradable polymers with their properties and transport of proteins and peptide drug delivery. synthetic polymers properties role in transportation of protein and peptides reference silicons high loading capacity, surface functionalization, biocompatibility, physicochemical and thermal stability protection of proteins from degradation, increase the half-life of protein, targetted delivery, ability to functionalize their surfaces [33] polyacrylate versatile, non-toxic, mucoadhesive safe delivery of protein, controlled and sustained release of proteins and peptides [34] 4.2.1. synthetic biodegradable polymers biodegradable polymers offer significant advantages in biomedical applications, especially for drug delivery. their capacity to break down into smaller, absorbable molecules eliminates the need for surgical removal, improving patient comfort and compliance. moreover, their biocompatibility and non-toxicity make them ideal for use in a range of medical devices and treatments, reducing the risk of adverse reactions and promoting better integration within the body. this makes them a favored option for many cutting-edge therapeutic solutions [35,36]. 4.2.2. synthetic non-biodegradable polymers non-biodegradable polymers present considerable challenges in medical applications, as they require surgical removal once the medication, they deliver is exhausted. this limitation confines their use to cases where the implant can be easily retrieved. on the other hand, biodegradable polymers naturally break down within the body, providing a more convenient and less invasive alternative for drug delivery systems. this distinction highlights the importance of choosing the appropriate polymer type based on the specific medical requirements and desired treatment outcomes. 5. method of preparation of nanocarriers typically, two primary approaches are utilized, which are the dispersion of prefabricated polymers or the polymerization of monomers. the lists of commonly used techniques are presented in figures 2 and 3. characterization and application of nanomaterials 2025, 8(1), 8291. 7 figure 2. methods of preparation of nps. figure 3. preparation of nps. 5.1. solvent evaporation method an emulsion is prepared by dissolving the polymer in an organic solvent like chloroform, acetone, or ethyl acetate using polyvinyl alcohol as a stabilizer. if the homogenization procedure is carried out for a long enough duration, it can help to evaporate the organic solvent [37]. ultracentrifugation is used to gather the nps at the end of the homogenization process. the desired particle size and other characteristics can be attained by modifying process variables, including the ratio of polymer to characterization and application of nanomaterials 2025, 8(1), 8291. 8 organic solvent, the type of organic solvent, and the speed and duration of homogenization [38]. 5.2. spontaneous emulsification/solvent diffusion method this method utilizes water-immiscible solvents such as dichloromethane or chloroform as the organic phase, while water-miscible solvents like methanol or acetone serve as the organic phase. nps are formed when these two phases are combined, resulting in interfacial turbulence and leading to the formation of nps. despite producing nanosized particles, this approach has certain drawbacks, such as the existence of leftover organic solvent [39,40]. 5.3. salting out/emulsion diffusion method in the salting-out process, the polymer is first dissolved in a water-miscible organic phase, such as acetone or tetrahydrofuran, and then added to the aqueous phase containing the emulsifier [39]. the fast addition of water to the emulsion, combined with gentle stirring, decreases the ionic strength, causing the water-soluble organic solvent to migrate to the aqueous phase and resulting in the formation of polymeric nanoparticles [41]. 5.4. phase separation method this technique works with both lipophilic and hydrophilic medications. the hydrophilic medications are typically introduced to the organic phase after being dissolved in water. conversely, the medications that are lipophilic are dissolved in polymer solutions. after the aqueous and organic phases are combined to form an emulsion, a second organic nonsolvent, such as silicone oil, is added while stirring vigorously. silicone oil is miscible with the initial organic phase but does not dissolve the medication. consequently, the first organic solvent is extracted, reducing the solubility of the polymer and causing phase separation, leading to the formation of a polymer coacervate. drug-loaded nanoparticles are formed when this polymer coacervate adsorbs onto active pharmaceutical ingredients [42]. 5.5. emulsion polymerization method emulsion polymerization is a widely used technique for synthesizing polymeric nps. in this process, the monomer is emulsified in a continuous phase of an immiscible liquid. a polymerization reaction occurs in situ, resulting in nanospheres. the choice between water-in-oil (w/o) or oil-in-water (o/w) emulsion systems depends on the hydrophobicity of the desired monomer. surfactants play a crucial role in stabilizing emulsions and controlling particle size. high-speed mixing, homogenization, or ultrasound sonication are common methods for carrying out this process [43]. 5.6. nanoprecipitation the nanoprecipitation technique utilizes two miscible solvents: one acts as a good solvent (usually an organic solvent such as acetone, isopropanol, or ethanol), while the other functions as a non-solvent for the polymer or lipid used to form the nps. for instance, water can be a non-solvent. the procedure involves preparing an characterization and application of nanomaterials 2025, 8(1), 8291. 9 organic phase and a non-solvent phase (often referred to as the aqueous phase). both phases ensure complete solubility of all starting materials. the organic phase may include polymers, solid or liquid lipids, surfactants with low hlb values, and active compounds dissolved in organic solvents. the solubility of the active molecule in the solvent affects the drug loading capacity of the particles. meanwhile, the non-solvent phase includes stabilizing agents dissolved in water, facilitating np formation and ensuring system stability [44,45]. 5.7. ion gelation ionotropic gelation is a well-studied method for preparing nanocarrier systems due to its mild conditions and straightforward procedures. in this technique, polyelectrolytes (such as chitosan, alginate, hyaluronic acid, and carrageenan) are cross-linked in the presence of counterions. the cross-linking process involves the formation of a network through ionic bridges between macromolecular chains. typically, a charged ionic entity with a defined molecular weight serves as the crosslinking agent. researchers frequently use this procedure to prepare nps [46,47]. 6. characterization of protein loaded nps 6.1. size, polydispersity index (pdi), and zeta potential particle size characterization of protein-loaded nps involves morphological examination by transmission electron microscopy (tem), scanning electron microscopy (sem), and atomic force microscopy (afm) [46]. transmission electron microscopy (tem) provides direct visualization of np size and provides detailed images of np morphology. dynamic light scattering (dls) is commonly used to measure the hydrodynamic diameter and pdi of nps [48–50]. 6.2. stability and surface properties surface charge (zeta potential), hydrophilicity, and wettability are vital for determining the interactions between nps and biological systems. zeta potential measurements predict the stability of np dispersions and can be measured by a zeta sizer. this measures the surface charge of nps, which influences their stability in suspension. a higher absolute zeta potential value typically indicates better stability due to electrostatic repulsion between particles. nps with zeta potential of more than 30 mv (+/−) have been reported to be stable in the deposit because the surface charge prevents the particles from clotting. 6.3. encapsulation efficiency the encapsulation efficiency is determined by measuring the amount of protein in the supernatant after centrifugation of the nps. the protein content is quantified using methods like lowry’s assay or bca assay. the encapsulation efficiency is calculated as: (total protein ‒ protein in supernatant)/total protein × 100% characterization and application of nanomaterials 2025, 8(1), 8291. 10 release kinetics: the drug release behaviour of nps is evaluated in simulated biological fluids to understand how they release their therapeutic load over time. this assessment is conducted using techniques like dialysis or sample-and-separate methods. biodegradability and degradation rate: gel permeation chromatography (gpc) and mass spectrometry (ms) are used to track the degradation of polymeric nps over time. cellular uptake studies: nps internalization by cells is measured and visualized through techniques such as confocal microscopy and flow cytometry, which help assess how effectively the nps are delivered to target cells. cytotoxicity: the compatibility of nps with cells is tested using various assays like mtt, xtt, or live/dead assays to evaluate their potential toxicity to healthy cells. haemolysis and protein binding: haemolysis tests determine how nps interact with red blood cells and are analysed through sds-page or mass spectrometry that investigates how serum proteins attach to nps and potentially affect their behaviour. in-vivo characterization: it focuses on how polymeric nps perform inside living organisms, providing critical information for preclinical evaluation.  pharmacokinetics (pk): the absorption, distribution, metabolism, and excretion (adme) of nps are examined using techniques such as hplc, lc-ms, and fluorescence imaging. prolonged circulation times of nps are often preferred for better bioavailability.  biodistribution: nps distribution across different organs or tissues is analysed using radioactive labelling or fluorescent dyes in combination with imaging technologies like mri, pet, or bioluminescence imaging to ensure that nps reach their target, such as tumours.  in-vivo toxicity: the safety of nps is evaluated by examining major organs (e.g., liver, kidneys, lungs) using histopathological analysis, blood tests, and immune response monitoring. both acute and chronic toxicity assessments are conducted to detect any adverse effects.  in-vivo efficacy: these studies evaluate whether the nps effectively deliver their therapeutic payload in animal models. endpoints like tumour shrinkage, inflammation reduction, or changes in specific biomarkers are monitored to assess therapeutic success.  immunogenicity and immune response: nps should not trigger harmful immune reactions. the immune response is gauged by measuring levels of cytokines, antibodies, and other immune markers using elisa or multiplex assays.  targeting efficiency: the effectiveness of targeted delivery mechanisms (e.g., ligand-receptor binding or enhanced permeability and retention (epr) effect) is studied. imaging techniques or tissue analysis help determine the extent of nps accumulation at the target site [51–57]. each of these techniques provides insights into different aspects of protein-loaded nps, helping to optimize their design for specific applications, such as drug delivery or therapeutic interventions (table 5). characterization and application of nanomaterials 2025, 8(1), 8291. 11 table 5. applications. polymer used type of polymeric np /method of preparation route of administration drug/active agent treatment reference chitosan ion crosslinking method nasal quercetin allergic rhinitis (ar) [58] chitosan cs-au based on gold nps and chitosan (cs) intravenous myricaria germania immunization [59] poly (β-amino esters) (pbaes) encapsulation of the synthetic mrna encoding bevacizumab, an anti-vegf antibody in nps intravenous mrna encoding bevacizumab non-small cell lung cancers (nsclcs) [60] chitosan mtx was entrapped in the chitosan nps topical application methotrexate (mtx) rheumatoid arthritis [61] chitosan encapsulation of amp nrc-07 in cs-nps by ionotropic gelation intravenous antimicrobial peptide nrc-07 antibacterial and in vitro anticancer activities [62] elastin-like peptides (elps) supramolecular nps based on elastin-like peptides modified capsid protein intravenous doxorubicin murine melanoma and colorectal cancer. [63] poly(nisopropylacrylami de) temperature-responsive polymer nps intravenous paclitaxel anticancer activity [64] albumin elastin-targeted nps intravenous doxycycline lps-mediated lung inflammation [65] polymeric and lipid-based levodopa-loaded nps intravenous, transdermal delivery and intranasal administration levodopa parkinson’s disease [66] hydrogel ph-responsive polymeric nanocarriers intravenous il-12 immunotherapy of cancer [67] chitosan concanavalin a (cona) coated chitosan (cs) nanocarrier intravenous short antimicrobial peptide (cm11) helicobacter pylori gastric infection [68] glutenin glucose-conjugated glutenin nps intravenous camptothecin breast cancer [69] chitosan peptides in chitosan nps coated with zein oral antihypertensive peptides, isoleucineproline-proline and leucine-lysineproline antihypertensive activity [70] ros-responsive polymer modified emulsion approach intravenous dexamethasone acute lung injury (ali) [71] chitosan hyaluronic acid coated chitosan nps oral insulin hypoglycemic activity [72] phenylboronic ester phenylboronic ester-modified polymeric nps nano vaccine trp2 peptide antigen delivery cancer immunotherapy [73] poly(lactic-coglycolic) acid (plga) double emulsion technique oral capreomycin peptide impact of stress conditions on peptide degradation: thermal, mechanical, chemical [74] chitosan self-assembled chitosan nps by ionic crosslinking technique intranasal recombinant protein interleukin-17 receptor c (il-17rc) asthma [75] ph-sensitive polymer d-melittin polymeric nps intravenous d-melittin anti-cancer treatment [76] chitosan cross-linked nps percutaneous delivery betamethason contact dermatitis [77] characterization and application of nanomaterials 2025, 8(1), 8291. 12 table 5. (continued). polymer used type of polymeric np /method of preparation route of administration drug/active agent treatment reference hypoxiaresponsive polymer pla targeted and nontargeted self-assembled polymeric nps intravenous doxorubicin (dox) hypoxic, triplenegative breast tumors [78] chitosan self-gelation method oral insulin diabetes [79] poly (lactic-coglycolic acid) (plga) double emulsion modified method intravenous recombinant adrenomedullin-2 angiogenesis [80] plga, peg s2p peptide-conjugated plga-maleimidepeg nps, modified emulsion/solvent evaporation technique. intravenous imatinib atherosclerosis [81] poly (lactide-coglycolide)-b-poly (ethylene glycol) nps polymeric nps functionalized with musclehoming peptides intravenous phosphatase and tension homology inhibitor to skeletal muscle duchenne muscular dystrophy (dmd) [82] human serum albumin (hsa) synthetic protein nps (spnp), polymerized hsa equipped with irgd intravenous sirna against signal transducer glioblastoma [83] 7. conclusions and future prospects peptides and proteins are essential for numerous biological reactions and play significant roles in various pathological conditions. however, their therapeutic application in treating life-threatening disorders encounters several challenges, including instability, poor absorption, enzymatic degradation, a short biological halflife, and rapid elimination. polymeric nps have shown considerable potential in enhancing the absorption of macromolecules. these polymers are typically inert, biocompatible with biological fluids, biodegradable, and can be removed from the body as inert biodegradable products. the choice of polymers used to deliver therapeutic proteins and peptides significantly impacts their therapeutic efficacy. polymeric nps hold promise for various delivery routes, including nasal, pulmonary, oral, and ocular delivery; nonviral gene delivery; and crossing the blood-brain barrier. a versatile system that can ensure the delivery and systemic stability of various proteins and peptides would be highly beneficial in the near future. author contributions: conceptualization, nm and ns (nawale sneha); methodology, nm; software, ns (neerude sirisha); validation, nm, ns (nawale sneha) and ns (neerude sirisha); formal analysis, nm; investigation, ns (nawale sneha); resources, ns (neerude sirisha); data curation, nm and ns (nawale sneha); writing—original draft preparation, ns (neerude sirisha); writing—review and editing, nm and ns (nawale sneha); visualization, ns (neerude sirisha); supervision, nm; project administration, nm; funding acquisition, ns (neerude sirisha). all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. references 1. srivastava s, sharma v, bhushan b, et al. nanocarriers for protein and peptide delivery: recent advances and progress. journal of research in pharmacy. 2021; 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disease biomarker detection; early diagnosis; biosensing; cancer; cardiovascular diseases; infectious diseases; neurodegenerative disorders 1. introduction emerging as quite promising systems for identifying disease biomarkers are cnt/go-based biosensors. carbon nanotubes (cnts) and graphene oxide (go) are attractive for this use. firstly, cnts and go have outstanding electrical conductivity, which helps detect biomolecules sensitively. between biomarkers and recognition elements, their electrical characteristics can transduce particular binding events into detectable electrical signals [1,2]. secondly, cnts and go have a high surface areato-volume ratio, offering a lot of binding surfaces for biomarker capture. this improves the biosensor’s sensitivity. selective detection of target biomarkers becomes feasible by functionalizing cnts and go with particular recognition elements like antibodies or aptamers [3–5]. the label-free detection capability of cnt/go-based biosensors adds still another benefit. this simplifies the assay process and removes the necessity of extra labeling steps. moreover, cnts and go fit microfabrication methods, which enables integration with miniature devices [6,7]. this makes point-of-care diagnostics portable, and successful detection of several disease biomarkers has been shown by cnt/go-based biosensors [8–10]. they have shown great sensitivity and specificity for identifying particular tumor markers in cancer diagnosis, thus facilitating early citation saddam ai, islam mr, shahazi r, et al. emerging frontiers: harnessing the power of cnt/go-based biosensors for early disease biomarker detection. characterization and application of nanomaterials. 2025; 8(1): 9917. https://doi.org/10.24294/can9917 article info received: 28 october 2024 accepted: 9 december 2024 available online:17 february 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 9917. 2 cancer detection and treatment monitoring [11,12]. by identifying cardiac biomarkers linked with heart failure and myocardial infarction, they have also shown promise in diagnosing cardiovascular disease [13–15]. cnt/go-based biosensors have been applied for fast and sensitive identification of pathogen-associated biomarkers in infectious disease diagnostics, enabling early identification of infectious agents [16]. furthermore, these biosensors could identify disease-specific biomarkers in neurodegenerative diseases, supporting early diagnosis and disease progression monitoring [17,18]. this review intends to analyze the progress in cnt/go-based biosensors, emphasizing their fabrication techniques, functionalization approaches, and integration with transducing components to improve sensitivity and selectivity. it examines the particular applications of these biosensors in identifying various disease biomarkers, including those linked to cancer, cardiovascular diseases, infectious diseases, and neurodegenerative disorders. additionally, the review highlights the superior performance of cnt/go-based biosensors, such as their high sensitivity, low detection limits, and real-time monitoring capabilities, which contribute to their potential in facilitating early disease diagnosis. finally, it discusses the challenges and future trajectories in the domain, highlighting the necessity for standardization, scalability, and commercialization to enhance personalized medicine and optimize patient outcomes. 2. cancer diagnosis biosensors using graphene oxide (go) and carbon nanotubes (cnt) have shown significant potential for cancer detection [19,20]. these biosensors possess exceptional qualities such as high sensitivity, selectivity, and compatibility with biological systems. [21,22]. they can identify specific cancer biomarkers, such as proteins and nucleic acids, in diverse biological specimens, including blood, urine, and saliva [23]. the elevated surface area and superior electrical conductivity of cnts and go enhance the immobilization of capture probes that specifically attach to target biomarkers [24,25]. the detection of cancer utilizing a biosensor is depicted in figure 1. binding events induce alterations in electrical, optical, or electrochemical signals, facilitating the sensitive detection of cancer biomarkers [26,27]. liquid biopsy is a non-invasive method utilized for cancer diagnosis and monitoring [28–30]. cnt/go-based biosensors have been investigated to detect circulating tumor cells (ctcs) and circulating tumor dna (ctdna) in blood specimens. these biosensors can detect circulating tumor cells (ctcs) or assess genetic modifications in circulating tumor dna (ctdna), yielding critical insights regarding tumor existence, advancement, and therapeutic response [31]. characterization and application of nanomaterials 2025, 8(1), 9917. 3 figure 1. detection of cancer using biosensor. another advantage is the potential for multiplexed detection, allowing simultaneous analysis of multiple cancer biomarkers [32–34]. by integrating different capture probes specific to distinct biomarkers, cnt/go-based biosensors can detect and quantify multiple analytes in a single assay. multiplex biomarker detection employs modern techniques such as microarrays, multiplexed enzymelinked immunosorbent assay, mass spectrometry, and biosensors to recognize many targets at once [35]. techniques use unique probes, spectral signatures, or chemical interactions to provide high-throughput and specific detection [36]. this multiplexed approach improves diagnostic accuracy and efficiency by providing a comprehensive profile of the disease [37]. cnt/go-based biosensors are also well-suited for pointof-care cancer testing due to their portability, rapid response, and ability to detect low analyte concentrations [38]. they can be integrated into portable devices or wearable sensors, enabling real-time and on-site cancer diagnosis. by continually monitoring physiological or chemical signals from the body, wearable sensors can identify cancer biomarkers. these devices detect cancer-related markers in physiological fluids such blood, saliva, perspiration, or interstitial fluid by using cutting-edge materials and technology [39]. point-of-care testing facilitates early detection, personalized treatment, and improved patient outcomes, particularly in resource-limited settings [40–42]. furthermore, cnt/go-based biosensors have been investigated for cancer imaging and visualization. functionalized cnts or go can act as contrast agents in various imaging techniques such as photoacoustic imaging, fluorescence imaging, and magnetic resonance imaging (mri) [43–46]. these biosensors enhance sensitivity and specificity in cancer imaging, aiding in tumor localization, staging, and monitoring [47,48]. it’s important to note that while cnt/go-based biosensors hold promise for cancer diagnosis, further research and development are necessary to optimize their performance, validate their clinical utility, and ensure integration into routine clinical practice [49,50]. the field of biosensors is rapidly evolving, and recent advancements may have occurred since my knowledge cutoff. therefore, referring to the latest scientific literature and characterization and application of nanomaterials 2025, 8(1), 9917. 4 research updates is recommended for the most recent progress in cnt/go-based biosensors for cancer diagnosis. 3. infectious disease diagnosis biosensors based on cnt/go have shown great promise as tools for diagnosing infectious diseases. these biosensors allow for the quick and accurate identification of particular biomarkers linked to contagious agents using the unique qualities of graphene oxide (go) and carbon nanotubes (cnts). they can identify various biomarkers that indicate the presence of pathogens or host immune responses, such as proteins, nucleic acids, and other molecular targets [51,52]. figure 2 shows how infectious diseases are detected. the high sensitivity and selectivity of cnt/go-based biosensors is one of their main benefits. they improved sensitivity results from the effective capture of biomarkers made possible by the high surface area-to-volume ratio of go and cnts [53–55]. accurate diagnosis is also ensured by functionalizing cnts and go with particular recognition elements, like aptamers or antibodies, which allow for the selective detection of target biomarkers. multiplexed detection is another significant characteristic of cnt/go-based biosensors [56–58]. these systems enable the simultaneous detection of multiple infectious disease biomarkers by attaching multiple capture probes to the biosensor. this feature allows for thorough disease profiling and improves diagnostic efficiency and accuracy [59,60]. figure 2. infectious disease detection. ongoing research efforts in this field focus on enhancing the sensitivity, stability, and scalability of cnt/go-based biosensors for infectious disease diagnosis. additionally, there is a concerted effort to address challenges related to standardization, validation, and the integration of these biosensors into routine clinical practice. 4. neurological disorder diagnosis the use of cnt/go-based biosensors in diagnosing neurological conditions, such as parkinson’s and alzheimer’s diseases, has shown encouraging results [61,62]. these biosensors can detect specific biomarkers closely linked to the pathophysiology of these disorders, such as alpha-synuclein and amyloid-beta proteins. amyloid-beta plaques and tau protein tangles are two characteristics of alzheimer’s disease found in the brain [63,64]. amyloid-beta peptides or tau characterization and application of nanomaterials 2025, 8(1), 9917. 5 proteins in blood or cerebrospinal fluid can be detected by cnt/go-based biosensors, allowing for the early diagnosis and tracking of alzheimer’s disease progression. similarly, lewy bodies, which are aggregates of alpha-synuclein proteins, are a hallmark of parkinson’s disease [65,66]. figure 3 shows a schematic diagram for detecting neurological diseases using a biosensor based on cnt/go. one possible diagnostic tool for parkinson’s disease is biosensors based on carbon nanotubes and graphene oxide that detect alpha-synuclein in blood and cerebrospinal fluid. initiating effective treatments, tracking disease progression, and enhancing patient outcomes depend on early and accurate diagnosis of neurological disorders [67–69]. the creation of biosensors based on carbon nanotubes and graphene oxide shows potential for the sensitive and selective detection of biomarkers linked to these diseases, which could lead to earlier diagnoses and more tailored treatments. clinical translation of these biosensors for neurological disorder diagnosis will be advanced by ongoing research and validation studies [70–73]. figure 3. schematic diagram of neurological disease detection using cnt/go based biosensor. 5. glucose monitoring in diabetes management one exciting development in diabetes management is using biosensors based on carbon nanotubes and gonads (cnts/go). these biosensors provide an alternative to the invasive and time-consuming finger-prick test for monitoring glucose levels. they reduce patient pain and infection risk by detecting glucose in non-invasive bodily fluids such as saliva, sweat, or tears rather than blood [74–76]. thanks to their distinct electrical characteristics, cnts and go make it possible to track glucose levels in real-time. changes in electrical conductivity or other sensing mechanisms provide quick feedback on glucose fluctuations, enabling patients to make timely adjustments to their diabetes management. wearable devices like smartwatches, patches, or contact lenses can incorporate these biosensors, allowing for more accessible and convenient continuous glucose monitoring [77,78]. patients can benefit greatly by having their glucose profiles monitored continuously throughout the day. glucose detection using cnt/go-based biosensors is exact and sensitive— figure 4 displays glucose monitoring for diabetes management. accurate readings characterization and application of nanomaterials 2025, 8(1), 9917. 6 are guaranteed by functionalizing the biosensor surface with molecules or enzymes specific to glucose, increasing sensitivity and selectivity [79,80]. patients can then better manage their diabetes as a whole because they can control their blood glucose levels through dietary, exercise, and medication choices [81]. however, there are still challenges to address in the field. researchers are actively working on improving sensor stability, calibration, and long-term performance to enhance the reliability, accuracy, and durability of cnt/go-based biosensors [82,83]. figure 4. glucose monitoring in diabetes management. standardization and regulatory approval are also vital for the widespread adoption of these biosensors in clinical practice. despite these challenges, cnt/gobased biosensors hold significant potential to transform diabetes management by providing non-invasive, real-time glucose monitoring [84,85]. continued research and development efforts aim to overcome the current limitations and pave the way for their integration into routine clinical care. 6. cardiovascular diseases detection the promising diagnosis of cardiovascular disease is cnt/go-based biosensors. in this discipline, biosensors have many advantages. accurately identifying cardiovascular disease biomarkers, including cardiac troponins, crp, and bnp, which expose heart muscle damage, inflammation, and heart failure [86–88], they expose to diagnosis and track cardiovascular disease, cnt/go-based biosensors measure biomarkers in blood or other non-invasive samples. figure 5 shows cardiovascular disease detection methods. high sensitivity and selectivity are cnt/go biosensor strengths [89,90]. they can detect low cardiovascular biomarker concentrations in complex biological matrices, enabling early cardiac event detection and precise disease progression monitoring. early intervention and treatment may improve patient outcomes. the detection and monitoring of cardiovascular disease using cnt/go-based biosensors from blood or saliva samples is easy and patientfriendly. eliminating invasive treatments helps biosensors lower patient discomfort and improve monitoring [91–94]. real-time tracking of cnt/go-based biosensors would help management of cardiovascular diseases. their dynamic character and rapid biomarker feedback help to enable quick medical interventions and treatment plan modifications related to cardiovascular diseases. characterization and application of nanomaterials 2025, 8(1), 9917. 7 figure 5. detection technique of various cardiovascular disease. moreover, the use of cnt/go-based biosensors aligns with the principles of personalized medicine. by providing real-time monitoring and precise quantification of cardiovascular biomarkers, these biosensors facilitate tailored treatment plans and patient-specific interventions, optimizing patient outcomes. while ongoing research and development are still needed, cnt/go-based biosensors hold great promise for the detection and monitoring of cardiovascular diseases. continued collaboration among researchers, clinicians, and industry partners is essential to further refine the technology, establish robust validation protocols, and ensure the successful integration of these biosensors into routine clinical practice [95]. 7. challenges and future directions in the field of cnt/go-based biosensors, there are several challenges that need to be addressed for their widespread adoption, standardization, scalability, and commercialization. these challenges include: 7.1. standardization of fabrication processes one of the key challenges is the standardization of fabrication processes for cnt/go-based biosensors. variations in synthesis methods, functionalization techniques, and sensor assembly can lead to inconsistent performance and hinder reproducibility. establishing standardized protocols and quality control measures is crucial to ensure consistent and reliable biosensor performance across different laboratories and manufacturing facilities. 7.2. sensor stability and longevity the stability and longevity of cnt/go-based biosensors are important factors for their practical implementation. the performance of these biosensors should be maintained over extended periods, ensuring reliable and accurate detection of cardiovascular biomarkers. addressing issues related to sensor degradation, biofouling, and long-term stability will be crucial for their successful commercialization. characterization and application of nanomaterials 2025, 8(1), 9917. 8 7.3. scalability and manufacturing processes for wide-scale adoption, cnt/go-based biosensors need to be manufactured in large quantities using scalable and cost-effective processes. it is important to develop manufacturing techniques that can produce biosensors with consistent quality, while also ensuring affordability and accessibility for healthcare settings. 7.4. integration with point-of-care devices the integration of cnt/go-based biosensors with portable and user-friendly point-of-care devices is a significant challenge. these biosensors need to be compatible with miniaturized and low-power electronics, enabling their integration into handheld or wearable devices. this integration would facilitate on-site testing, remote monitoring, and real-time data analysis, thereby enhancing their clinical utility. point-of-care (poc) cancer detection technologies include i-stat for prostate-specific antigen assessment, lateral flow assays for visual biomarker detection, and wearable microneedle biosensors for noninvasive monitoring. 7.5. regulatory and commercialization aspects the regulatory landscape and commercialization pathways for cnt/go-based biosensors need to be addressed. meeting regulatory requirements, obtaining necessary certifications, and navigating the complex commercialization process are critical steps for bringing these biosensors to the market and making them available for widespread clinical use. 7.6. additional challenges robust clinical validation studies are essential to demonstrate the efficacy, accuracy, and clinical relevance of cnt/go-based biosensors for cardiovascular disease detection and monitoring. collaboration between researchers, clinicians, and industry partners is crucial for conducting large-scale clinical trials, validating the biosensor performance, and refining the technology based on feedback from endusers. future directions in the field of cnt/go-based biosensors should focus on addressing these challenges. collaborative efforts among researchers, regulatory agencies, and industry partners are necessary to establish standardized protocols, optimize manufacturing processes, ensure sensor stability, and navigate the regulatory and commercialization landscape. by overcoming these challenges, cnt/go-based biosensors can become valuable tools for cardiovascular disease diagnosis and management in clinical settings. 8. conclusion in conclusion, cnt/go-based biosensors have shown significant potential in various areas of medical diagnosis, including cancer, infectious diseases, neurological disorders, diabetes management, and cardiovascular diseases. these biosensors offer advantages such as high sensitivity, selectivity, multiplexed detection, and real-time monitoring. they can detect specific biomarkers associated with different diseases, enabling early diagnosis, treatment monitoring, and characterization and application of nanomaterials 2025, 8(1), 9917. 9 personalized medicine approaches. the non-invasive 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technology, changshu 215500, china. e-mail: han@cslg.edu.cn 4 jiangsu key laboratory of advanced functional materials, changshu 215500, china abstract in recent years, nanoporous alloys have presented the advantages of a large specific surface area, low density, and simple operation, and they have been widely used in the fields of catalysis, magnetism, and medicine. nanoporous pt-si alloy was prepared by melt-spun and chemical dealloying, and was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscope, and transmission electron microscopy. pt-si alloys possess a three-dimensional bicontinuous structure and an average size of 5 nanometers. compared with commercial pt/c catalysts, nanoporous pt-si alloys exhibit excellent electrocatalytic activity and stability in ethanol-catalyzed oxidation reactions. it is taken into consideration to be a promising catalyst in direct ethanol fuel cells. keywords: dealloying; nanoporous; electrocatalysis; ethanol oxidation reaction characterization and application of nanomaterials (2021) volume 4 issue 1 doi:10.24294/can.v4i1.1325 article info received: 14 december 2020 accepted: 3 february 2021 available online: 10 february 2021 copyright copyright © 2021 nali lu, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction the fuel cell is an energy conversion device, which can directly convert the energy generated by fuel through chemical reactions into electric energy, and only water is generated in the entire process[1]. a fuel cell combines the best characteristics of an internal combustion engine and battery, like an internal combustion engine that can run only with fuel without any mechanical conversion process. fuel cells are similar to those under load conditions[2]. direct ethanol fuel cell (defc) uses ethanol as fuel, which has attracted more and more attention. ethanol, as a small alcohol organic molecule, converts the chemical energy into electrical energy, has higher capacity density, low toxicity, and is convenient for storage and transportation, as well as the advantages of large-scale preparation of biomass products, it is widely used in mobile devices such as automobiles, mobile phones and computers[3–5]. the research of wang et al.[6] shows that the permeability of ethanol through the electrolytic membrane is lower than that of methanol. under acidic conditions, the reaction process of ethanol is as follows: total reaction: c2h5oh+3o2 → 2co2+3h2o anode process: c2h5ooh+3h2o → 2co2+12h++12e– cathode process: 3o2+12h++12e– → 6h2o the reaction mechanism of ethanol is very complex, involving 12 e transfers, accompanied by the fracture of the c–c bond, the interme26 diate products dominated by coads are generated, which gather on the surface of the catalyst and produce poisoning phenomenon that reduces the activity of the catalyst. in practical application, the catalytic oxidation of ethanol requires a high overpotential. therefore, developing new anode catalysts with high activity and high stability has become a research hotspot. the existing research shows that the improvement of the performance of pt-based catalysts is due to the shortening of pt metal bonds, the enhancement of bond energy, and the easier adsorption of oxygen after alloying; the microstructure between materials is changed, the alloying effect of different elements, the specific surface area increases, and the active sites increase. to mix pt with other non-noble metals[7–9], and the microstructure of pt is optimized to prepare nano pt catalyst with controllable morphology[10], which can prevent the aggregation of pt particles due to the synergistic effect between bimetallic metals and is helpful to improve the stability of the catalyst[11,12]. based on the different properties of different elements, the dealloying method uses chemical or electrochemical methods[13] to remove the more active components in the alloy. then the remaining components finally obtain more stable elements through diffusion and aggregation to form the framework of nanometal materials[13–15]. in recent years, chen et al.[16] proposed a reverse dealloying method to prepare nanosilver. to selective remove the inert component au in au-ag alloy. meanwhile, thiourea plays a role in promoting gold dissolution and passivating silver in the process of forming the porous silver framework[16]. according to liu et al.[17], by changing the time sequence of dealloying, a series of nanoporous metal compound products with bimodal porous metals and single peak pores can be synthesized[17]. at present, pt and 3d transition metals m (such as ti, cr, v, mn, fe, co, ni, cu[18–20]) form alloys and are loaded on carbon carrier, which can effectively improve the stability of catalysts. relevant literature reports pt-sn[21], pt-w[22], and other alloy catalysts also show co tolerance and are excellent catalysts[21,22]. considering the small radius of the si atom, the introduction of the si atom reduces the distance between pt-pt and enhances the catalytic activity. in addition, si is relatively stable under acidic conditions and can obtain better stability. therefore, that alloying pt and si expects to improve the electrocatalytic performance of the material. although studies have shown that bulk pt-si alloy[23] has great electrocatalytic oxidation activity for methanol and carbon monoxide, nano-scale pt-si alloy and its catalytic performance have not been reported[23]. in this study, we successfully prepared a 3d framework nanoporous ptsi (np ptsi) binary alloy through the combination of melt rapid quenching technology and dealloying. meanwhile, it also studied its electrocatalytic oxidation activity and stability for ethanol. 2. experiment 2.1 sample preparation the purity of metal materials pt, si and al is more than 99.99%, and the corresponding stoichiometric ratio is 9:3:88. then calculate their respective elemental mass. put the prepared materials into a water-cooled copper crucible electric arc furnace, and inject ar gas to melt repeatedly 3–4 times to obtain pt9si3al88 alloy ingot. cut the melted pt9si3al88 alloy ingot into small pieces, put it into the fired quartz glass tube and melt the material slowly to obtain the alloy strip with basically the same thickness. weigh about 50 mg of the strip and put it in 5 wt% hcl solution to produce lots of bubbles at the beginning. when the reaction is slow, put it into a constant temperature water bath at 50 ℃ celsius for 48 h, take out the sample, centrifuge and wash it repeatedly 5–6 times. finally, it obtains the np-ptsi by drying in a vacuum drying oven for 24 h. 2.2 characterization of materials we used the sa-hf3 x-ray powder diffractometer (xrd) of rigaku company from japan to analyze the crystal structure of the materials. detecting the chemical composition and surface atomic state of the material by the x-ray photoelectron spectroscopy (xps) of axis ultra, which is a wholly-owned subsidiary of shimadzu group in japan. the sigma 27 scanning electron microscope (sem) of zeiss company in germany was used to observe the micromorphology of the material, the accelerating voltage is 20 kv. tecnaig220s-twin transmission electron microscope (tem) and high-resolution transmission electron microscope (hrtem) of american fei company are used, which not only could detect the microstructure of materials but also obtain the crystal plane spacing of atoms. the electrochemical properties of materials are measured by the electrochemical workstation of model 760e of shanghai chenhua instrument co., ltd. 2.3 electrode preparation and electrochemical test weigh 1 mg of np-ptsi and 1.5 mg of carbon black with an electronic balance into a 2 ml centrifuge tube, and put 980 μl absolute ethanol and 20 μl 5 wt% nafion with a pipette gun respectively into a centrifuge tube. then put into an ultrasonic cleaner for about 1h to obtain the catalyst suspension. commercial pt/c catalyst with the same concentration was prepared by the same method. firstly, the glassy carbon electrode (gce, diameter 3 mm) was applied on the foot skin with 0.05 μm polishing powder shall be polished and cleaned with ultrapure water, and then placed in the mixed solution of 0.1 mol/l kcl + 1 mol/l potassium ferricyanide to measure the redox potential difference. when the value is less than 70 mv, it shall be washed with ultrapure water and dry naturally for standby. all electrochemical tests were carried out in a three-electrode system. before the reaction, introducing saturated n2, removing o2 from the solution, and the reaction temperature was 25 degrees celsius. 3. results and discussion 3.1 characterization of np-ptsi 3.1.1 xrd characterization of np-ptsi figure 1 is the xrd diagram of pt9si3al88 alloy before and after dealloying. it shows from the diagram that the diffraction peak of ptsial alloy is very complex, and it is difficult to distinguish the alloy phase of ptsial, and there is no diffraction peak corresponding to pure pt, al, and si, indicating the formation of pt-si alloy. np-ptsi sample has three diffraction peaks, i.e. 2θ = 40.140°, 46.599°, and 68.317°, corresponding to (111), (200), (220) crystal planes of face-centered cubic ptsi. compared with the standard pure pt card (jcpds 04-0802), it finds that the diffraction peak of each crystal plane deviates slightly to a high angle, which may be because si atoms with small atomic radius are added into the alloy to replace some pt atoms, which reduces the distance between pt-pt and finally forms pt-si alloy. figure 1. xrd spectra of pt9si3al88 alloy before and after dealloying. standard spectra: pt (jcpds04-0802), si (jcpds35-1158), al (jcpds 04-0787). 3.1.2 xps characterization of np-ptsi figure 2(a) is the full spectrum of np-ptsi. by that, we can see the peaks of pt 4f, si 2f, o 1s, c 1s, and other elements, in which o 1s and c 1s belong to water or carbon dioxide physically or chemically adsorbed on the material surface, which fits with xps peak fit[13]. figure 2(b) is the peak diagram of pt 4f. there are two peaks at 71.2 ev and 74.6 ev, corresponding to pt and pt2+ in the metal state. the results show that some pt is oxidized to pt2+, but it mainly exists in the form of pt in a metal state, which is consistent with the internal xrd test results of the material. figure 2(c) is the sub-peak diagram of si 2p. both si0 and si4+ can be detected, and the binding energy belongs to si0 at 99.5 ev; the binding energy belongs to si4+ at 103.2 ev. on the surface, si mainly exists in the form of si4+. it also can observe some metallic si. 28 figure 2. (a) xps full spectrum of np-ptsi; (b) pt 4f peak diagram; (c) si 2p peak diagram. 3.1.3 sem, tem and hrtem characterization of np ptsi figure 3(a) is the sem diagram of pt9si3al88 strip after dealloying, which shows that it forms a uniform nanoporous structure composed of nanopores and ligaments. the pore size is 5–20 nm, the specific surface area increases, and the active sites of an electrochemical reaction in the material increase. figure 3(b) is the cross-sectional view of np-ptsi, from which the uniform pores can be seen. this confirms that the fine nanoporous structure is obtained in the whole sample. the tem diagram can observe the microstructure of the sample from the nano size, as shown in figure 3(c). the uniformly distributed bright white areas can be seen more clearly from the tem diagram. compared with the sem diagram, the structure with pores in the multi-level pores is more significant. it is conducive to improving the kinetics of oxygen diffusion. figure 3(d) is the hrtem diagram of np-ptsi, and it is clear that the continuous lattice diffraction fringes. figure 3. characterization diagram of np-ptsi alloy. (a) (b) sem diagram; (c) tem diagram; (d) hrtem diagram. 3.2 electrochemical performance test of np-ptsi in 0.5 mol/l h2so4 deoxidized solution, the stable cv curve of np-ptsi alloy is shown in figure 4 (a), and commercial pt/c catalysts can be compared. in the whole potential scanning range, np-ptsi and commercial pt/c catalysts show the same cv curve characteristics, including hydrogen adsorption and desorption zone: –0.25–0.1 v vs. sce; electric double layer area: 0.1–0.35 v vs. sce; high potential region: 0.35–1.2 v vs. sce. in the hydrogen adsorption and desorption region, the peak of np-ptsi alloy becomes wider and shifts to high potential compared with commercial pt/c, which is due to the increase of hydrogen adsorption strength on pt due to the interaction between pt and si. compared with commercial pt/c catalyst, np-ptsi shows a significant current peak at about 0.45 v vs. sce, which shows that lots of oh species adsorb on the surface of the catalyst. figure 4. cyclic voltammetric curves of pt/c and np ptsi catalysts in deaeration solution. (a) 0.5 mol/l h2so4 solution; (b) 0.5 mol/ l h2so4 + 1 mol/l ch3ch2oh mixed solution. 29 it believes that the activity of the catalyst is related to the electrochemical activity area (ecsa). we use origin software to calculate the desorption peak area of h, and the formula is ecsa = qh/(m × c). in the formula, q is the coulomb charge mc ∙cm–2 in the h region, m is the pt load, mg∙cm–2, and c is the charge density adsorbed by the monolayer of h of pt, which is 0.210 mc∙cm–2. it shows in figure 4(a) that the electrochemically active area of np-ptsi is much larger than that of commercial pt/c, indicating that the number of active sites of np-ptsi catalyst after dealloying is increased, which is conducive to the catalytic oxidation of ethanol. figure 4(b) shows the cv curve of np-ptsi and commercial pt/c catalyst in the mixed solution of 0.5 mol/l h2so4 + 1 mol/l ch3ch2oh. during the potential positive scanning, there are two oxidation peaks. during the negative scanning, there is a reduction peak. the pt-based catalyst surface will adsorb -oh and be oxidized to pto. during the negative scanning, pto is restored. the oxidation peak (i) is about 0.7 v, which is usually taken into consideration as the characteristic peak of ethanol oxidation to co2. it is one of the basis for judging the performance of the catalyst. the oxidation peak (ⅱ) is about 1.1 v, which is related to the secondary oxidation of intermediate products. the peak onset potential is also a key index for evaluating the activity of the catalyst. the peak onset potential of np-ptsi alloy is negative compared with that of commercial pt/c catalyst, which shows that the catalyst can improve the catalytic oxidation kinetics of ethanol and has good application value. we further explored the stability of np-ptsi alloy and commercial pt/c catalyst by the potentiostat method. figure 5 is the i-t curve with a constant potential of 0.7 v. it shows from the figure that at the beginning, the current density of np-ptsi and pt/ c catalyst decreased sharply due to the formation of electric double-layer capacitance. the subsequent decrease in current is due to the loss of surface activity sites caused by the adsorption of oxygen-containing intermediate species on the catalyst surface. after 500 s, the current density tends to be stable, which attributes to the continuous reduction of catalyst concentration during the reaction. although the current density of both decreased to varying degrees within the entire 3,000 s, the current density of np-ptsi is always higher than that of commercial pt/ c catalyst, indicating that the addition of si makes np-ptsi alloy show better stability than commercial pt/c catalyst. figure 5. potentiostatic i-t curve of pt/c and np-ptsi catalysts in mixed solution of 0.5 mol/l h2so4 + 1 mol/l ch3ch2oh (constant potential is 0.7 v). 4. conclusion nanoporous pt-si alloy was prepared by the combination of melt rapid quenching technology and dealloying. np-ptsi alloy has a three-dimensional bi-continuous structure, with an average pore size of 5 nm and a large specific surface area. compared with commercial pt/c catalyst, np-ptsi alloy has excellent ethanol electrocatalytic activity and stability under acidic conditions, and the operation is simple, the conditions are easy to control, the cost is low, and it can produce on a large scale, which makes np-ptsi alloy have more application potential in the field of electrocatalysis. conflict of interest the authors declare that they have no conflict of interest. acknowledgements project: the national natural science foundation of china project “research on low temperature phase effect of phase separation and exchange biasing of alloy of ni-mn based magnetic shape memory alloy” (51371004). 30 references 1. hou m, yi b. development status of fuel cell technology (in chinese). chinese journal of power sources 2008; 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kaushikphys-ics@gmail.com) 1*center for nanotechnology (cnt), school of engineering and applied sciences, nile university, sheikh zayed, 16453 giza, egypt. 2* department of nanotechnology, bharath university, biher research park, 173 agharam road, selaiyur, chennai, tamil nadu 600073, india. 3department of physics, faculty of science, tanta university, tanta, gharbia, egypt. 4petrochemicals department, egyptian petroleum research institute, nasr city, cairo, egypt. abstract synthesis of macro-mesoporous titania (titanium dioxide-tio2) nanospheres was successfully achieved using a modified template-free methodology to incorporate macroporous channels into a mesoporous tio2 framework to form mixed macro-mesoporous tio2 spheres (mmpt), which were doped with carbon dots (c-dots) to form improved nanocomposites (c-dots@mmpt). elemental composition, surface bonding and optical properties of these nanocomposites were characterized by x-ray diffraction (xrd), fourier transform infrared spectroscopy (ftir) and ultraviolet-visible absorption spectroscopy (uv-vis). evaluation of photocatalytic activity for each (c-dots@mmpt) sample was performed via degrading the methylene blue (mb) dye compared with bare samples (mmpt) under visible light irradiation using 300-watt halogen lamp. keywords:photocatalysis; macro-mesoporous tio2; up-conversion photoluminescence; mb degradation 1. introduction for many years, there has been a large interest in the synthesis of semiconductor nanostructures and the investigation of their properties due to their vital applications in electronic and optical devices. among the transition metal oxide semiconductors, titania possesses many outstanding features such as the strong oxidizing ability, cost-effectiveness, environmentally-benign and high chemical and thermal inertness [1], titanium dioxide is also recognized as the most efficient, non-toxic, insoluble and stable photocatalyst. titania has three crystalline phases such as: anatase (tetragonal), rutile (tetragonal) and brookite (orthorhombic). the anatase phase shows superior photocatalytic activity compared to other polymorphs of titania [2]. unfortunately, the technological usage of bare tio2 is hampered by two main limitations. first, it has a wide band gap (3.2, 3.02, 2.96 ev) for the anatase, rutile and brookite phases, respectively. thereby it is only activated by ultraviolet (uv) light which represents 2-3% of the total solar spectrum. second, the short time for recombination of photo generated electron-hole pairs (in the order of nanoseconds). these limitations deteriorate the quantum efficiency of tio2 [3]. many authors reported different strategies to overcome such drawbacks and improve the photocatalytic performance by tailoring the semiconductor heterojunction [4], including the doping of noble metals such as ag [5], au and pt [6] or modification of tio2 by means of doping with non-metal ions such as sulfur [7], chlorine [8]and nitrogen [9]. copyright © 2018 m. abd elkodous et al. doi: 10.24294/can.v2i1.585 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 furthermore, “it was supposed that doping with metal-ions could improve the electronic energy band structure of tio2 and thus enhances the photocatalytic performance by effective charge transform from the doping metal ions to ti4+ ions” [10]. in addition, the combination with carbon nanotubes [11,12] and graphene [13-16] has proven their efficiency to provide high electron mobility to extend electron-hole separation lifetime [17]. carbon dots are a recent class of carbonaceous nanomaterials, discovered during the purification of single-walled carbon nanotubes [18], which received remarkable attention as the most reliable and green approach to promoting effective energy conversion. it has been reported that c-dots doped photocatalyst significantly improving the photocatalytic reaction based on their ability to absorb long wavelength photons in the visible region and emit light of the shorter wavelength in the ultraviolet region and vice versa (up-conversion down-conversion photoluminescence) [19-23], this eventually leads to an efficient utilization of the solar spectrum. furthermore, c-dots inhibited the recombination of the electron-hole pairs generated during photocatalysis [ 24]. the present work introduces an improved methodology to synthesize macro-mesoporous tio2 spheres (mmpt). all as-prepared samples were doped with c-dots, and their performance against degradation of an aqueous solution of methylene blue (mb) dye under visible light irradiation was examined. schematic diagram of figure 1(a-c) represents hierarchical c-dots dispersed macro-mesoporous tio2 composites with (0.4 wt.%) of carbon explored an enhanced photocatalytic activity, while in the mechanism of tio2 photocatalytic activity for microorganism inactivation, water treatment and air purification dramatically presented in the figure 1(d). figure 1, (a-c); the hierarchical c-dots dispersed macro-mesoporous tio2 composites with low loadings (0.4 wt.%) of carbon showed an enhanced photocatalytic activity in the photodegradation of acetone in air, and (d) the mechanism of tio2 photocatalytic activity for microorganism inactivation, water treatment and air purification 3 2. experimental details 2.1 materials all chemicals used were of extra pure grade of 99.5%, purchased from sigma aldrich and were used as received without further purification. 2.2 methods 2.2.1 preparation of mixed macro-mesoporous tio2nanospheres mmpt spheres were prepared by a surfactant-free method, through assembly of tio2 nano-crystalline particles using ammonium citrate as a chemical linker [25]. in a typical procedure, (0.0015 mole) citric acid was mixed with (2 ml) deionized water diw) and then (20 ml) ammonia was added portion-wise to the mixture. then the mixture was dipped directly into the ethanol solution of titanium (iv) isopropoxide (6 ml of titanium (iv) isopropoxide dissolved in (40 ml) of absolute ethanol). the mixed solution was stirred for 4 h and left to stand for overnight. the resulting white precipitate was then filtered, washed several times with diw and ethanol and dried at 60 o c for 8 h, finally the powder was calcined at 500 o c for 4 h to obtain pure anatase crystal structure. four mmpt samples with different sizes were synthesized by controlling the concentration of ammonium hydroxide solution (nh3.h2o), 28%, 29%, 30% and 32%, the corresponding samples were named mmpt 28%, mmpt 29%, mmpt 30% and mmpt 32%, respectively. 2.2.2 preparation of c-dots c-dots were fabricated facilely by one-pot green method [26]. in a typical synthesis, (1.7 g) ascorbic acid was dissolved in (100 ml) d.i. water, followed by adding (0.2 g) copper (ii) acetate. the mixture was then stirred for 10 min. at room temperature and then maintained at 90 o c under stirring for 8 h. c-dots were obtained after centrifugation at 9000 rpm, then the precipitate was washed several times with diw and dried at 80 oc for 1 h. 2.2.3 preparation of photocatalytic composites (c-dots@mmpt) a typical amount of 0.8 g mmpt powder was dispersed in c-dots solution (0.6 g c-dots dissolved in 50 ml diw) with ultrasonic vibration for 45 min, the mixture was then dried in vacuum oven at 70 o c for 6 h. the four composite samples were denoted c-dots@mmpt 28%, c-dots@mmpt 29%, c-dots@mmpt 30% and c-dots@mmpt 32%. 2.2.4 photocatalytic degradation of mb dye an aqueous suspension of mb dye (100 ml, with an initial concentration of 20 ppm) and photocatalyst prepared in the previous step (0.06 g) were placed in a beaker (250 ml). prior to irradiation, each suspension was magnetically stirred in dark for 2 h to get the adsorption-desorption equilibrium (between photocatalyst and dye), followed by visible light irradiation using 300 w halogen lamp fixed at a distance of about 10 cm. after a given time interval (20 min.) during the visible light irradiation, the suspension was filtered to separate the photocatalyst and the supernatant. the percentage of dye degradation was calculated as (c/c0) where (c) was the concentration at each time interval and (c0) was the initial concentration when the adsorption-desorption equilibrium is reached. 2.3 spectroscopic characterization of materials the crystal structure was verified by x-ray diffraction (xrd) on a brucker axis d8 diffractometer with crystallographic data software topas 2 utilizing cu kα (λ = 1.54060 å) radiation operating at 40 kv and 40 ma. ftir pattern was recorded using ftir-4100 ft-ir fourier-transform infrared spectrometer. the uv-vis absorption spectrum was recorded on a perkinelmer lambda 950 uv-vis.-nir spectrophotometer. 3. results &discussion 3.1 morphology analysis by high resolution transmission electron microscopy (hr-tem) in figure 2 depicts the as-prepared photocomposite (c-dots decorated mmpt nanosphere), and the chemical linkages between titania nanosphere and the hydrophilic c-dots. 4 figure 2; schematic illustration of the as-prepared photocomposite (a) hr-tem image of monodispersed c-dots with an average particle size ≈ 4 nm, and (b) c-dots decorated macro-mesoporous titania nanosphere as displayed by ‘white circle’ in hr-tem image 3.2 purity and crystal structure nano-structure is examined by xrd analysis. figure 3 shows typical xrd patterns of mmpt 28% and mmpt 30% samples prepared via template-free method. the observed peaks of both samples are in good agreement with those of standard anatase tio2 (jcpds card number 04-0477). figure 3; xrd pattern of mmpt 28% and mmpt 30% nanospheres calcined at 500 oc for 4 h 5 os k c d     typical narrow peaks of titania reveal the formation of tio2 nanospheres with relatively larger crystalline domain size compared with tio2 nanoparticles [27]. according to debye-scherrer equation (1), the particle size (d) based on the peak corresponding to (101 reflection) is found to be (41.3 nm for mmpt 28% and 51.7 nm for mmpt 30%) as shown in table 1. where (d) is the particle size, (k) is the shape factor and has a value of about (0.9), (λ) is the wavelength of the x-ray radiation (1.54060 ǻ for cu-kα), (β) is the full width at half maximum (fwhm) of the intensity and (θ) is the angle of diffraction. sample 2θ (degree) phase fwhm (degree) particle size (nm) mmpt 28% 25.4 anatase 0.1968 41.3 mmpt 30% 25.4 anatase 0.1574 51.7 table 1. particle size of both mmpt 28% and mmpt 30% nanoshperes 3.3 optical properties of c-dots uv-visible absorption spectrum of as-prepared c-dots are shown in the figure 4, shows an absorption peak centered in the uv region nearly at 247 nm with a tail extending to the visible range revealing the formation of c-dots [28]. figure 4; uv-visible absorption spectrum of c-dots to explore the optical properties of the as-prepared c-dots, photoluminescence (pl) study was carried out at various excitation wavelengths. in agreement with previous literature reports, the as-prepared c-dots exhibit an excitation dependent pl behavior. the as-prepared c-dots exhibit a clear up-converted and down-converted pl properties. figure 5, (a-b); reveals the up-conversion and down-conversion photoluminescence emission spectra of c-dots excited by short (270 nm) and long wavelength (600 nm) light and the excitation wavelengths were (540 nm) and (300 nm) respectively. this phenomenon could be attributed to a multiphoton active process [29]. 6 figure 5; photoluminescence (pl) properties of asprepared c-dots, (a) up-conversion pl spectrum of c-dots (λex = 270 nm and λem = 540 nm), and (b) down-conversion pl of as prepared c-dots (λex = 600 nm and λem = 300 nm) 3.4 surface bonding ft-ir spectrum of as-prepared mmpt 28% and c-dots@mmpt 28% samples as shown in figure 6. in fact, mmpt 28% the broad band centered at 550 cm-1 is likely due to ti-o-ti stretching vibrations within tio2 lattice, absorbance peak at 1630 cm-1 originates from -oh bending vibrations, while the peak at 2920 cm-1 reveals the presence of atmospheric co2 and finally the peak at 3439 cm-1 corresponds to -oh stretching vibrations [30]. figure 6; ft-ir spectrum of as-prepared mmpt 28% and c-dots@mmpt 28% samples however, upon doping mmpt 28% with c-dots, another peak at 1045 cm-1 is observed and corresponds to ti-o-c is bridging vibrations, indicating the physical adsorption of c-dots on tio2 surface and the formation of c-dots@ mmpt 28% photocomposite. 3.5 photocatalytic degradation of mb dye a study of photocatalytic activity of as-prepared samples are performed by degrading fixed volume and concentration of mb dye under visible light irradiation using 300 w halogen lamp as a light source. hence, in the figure 7 depicts the mb decomposition as a result of photocatalytic degradation under visible light illumination. during the reaction, the catalytic activity of c-dots@mmpt 28% sample deteriorated, such result revealed that the formation of the mmpt sample with very small particle sizes, decreased the number of pores and facilitated the 7 formation of large aggregates. the photocatalytic activity of c-dots@mmpt 29% was slightly better than c-dots@mmpt 32%, which could be attributed to the relatively higher surface area of c-dots@mmpt 29% sample. while c-dots@mmpt 30% sample showed the highest photocatalytic activity among all samples due to the relatively higher surface area than c-dots@mmpt 32% sample and the better particle sizes than c-dots@mmpt 29% and c-dots@mmpt 28% samples, promoting the formation for the relatively increased number of pores (macropores and mesopores) which facilitated the diffusion of reactants , provided a large number of readily accessible active sites and fostered the light transfer into the inner surface of the photocatalyst. figure 7; photocatalytic efficiency of the as-prepared samples under visible light irradiation after adsorption-desorption equilibrium is reached 4. conclusion c-dots have been used to improve the photocatalytic efficacy of tio2 nanospheres prepared via a template-free methodology using ammonium citrate crystals as a chemical linker, in a trial to develop cost-effective technology for effective waste water recycling. c-dots@mmpt 30% sample showed superior photocatalytic activity due to the combination and the benefits of a relatively high surface area of mesoporosity with the readily accessible diffusion pathways of microporous channels. our novel findings could provide a new route to support current wastewater treatment modules, in terms of improving water quality and could complement ongoing efforts in developing treatment systems. acknowledgements the authors acknowledge the financial support of science and technology development fund (stdf), researchers and operators form nanotechnology department, nile university, egypt. also, dr. kaushik pal also grateful to dean (research) giving opportunity at nanotechnology department from bharath institute for higher education and research (biher), bharath university, chennai (india). conflict of interest all the authors have declared that there is no competing financial interest in this contribution. references 1. pelaez m, nolan nt, pillai sc, et al. a review on the visible light active titanium dioxide photocatalysts for environmental applications. appl. catal. b environ 2012; 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authors: prof.(dr.) kaushik pal was born in india. he received his ph.d. from university of kalyani, nadia, (india), most significant prestigious awards “marie-curie experienced researcher (postdoctoral fellowship)” offered by the european commission at aristotle university of thessaloniki, greece and “brain korea national research foundation visiting scientist fellowship” at cnu, south korea also achieved in his career. he was appointed “senior postdoctoral fellow” at wuhan university, china and after he achieved the most prestigious position “scientist & faculty cas fellow” by chinese academy of science. most recently he has been working as a “research professor (independent scientist & pi)”, at the department of nanotechnology, bharath university, biher research park, chennai. based on his research back ground, he was selected “editor-in-chief” of the international peer reviewed journals and publishers ‘pan-standford,’enpress, and ‘intech’, as well as he edited significant numbers of the book chapters, partially reviewed 55 research articles. prof. pal is an expert group leader as well as associate member in various scientific societies, reorganizations and professional bodies. since last year he organized around 10 national and international events, symposium, conferences, workshops and himself contributed around 6 keynote and 15 invited lectures as well as attained distinguish chief-guest of honor worldwide nanotechnology and materials science research community. mohamed abd elkodous, working as a research assistant at center for nanotechnology (cnt), nile university, egypt. he obtained his bachelor degree of special sciences in bio-physics from tanta university, egypt with excellent honor. currently, he is pursuing his masters in nano science and technology. based on his outstanding research capabilities, experimental skills and knowledge, he was awarded many prestigious young fellowship awards like daad scholarship and erasmus+ credit mobility fellowship at oviedo university in spain for 6 months to complete his master thesis project entitled “recyclable nanostructured composites for effective waste water treatment. most recently he is coordinating international conferences on materials science and nanotechnology with his co-supervisor prof. dr. kaushik pal. characterization and application of nanomaterials 2025, 8(1), 8899. https://doi.org/10.24294/can8899 1 review nanoparticles’ classification, synthesis, characterization and applications— a review muhammad sharf u. din awan1, muhammad tuoqeer anwar1,*, hasan izhar khan2, muhammad rehman asghar3, muhammad rafi raza1, naveed husnain4, muzamil hussain1, tahir rasheed5,* 1 department of mechanical engineering, comsats university islamabad, sahiwal campus, sahiwal 57000, pakistan 2 automotive engineering center, university of engineering and technology, lahore 54890, pakistan 3 institute for energy research, jiangsu university, zhenjiang 212013, china 4 department of mechanical engineering, faculty of engineering and technology, bahauddin zakariya university, multan 60800, pakistan 5 interdisciplinary research center for advanced materials, king fahd university of petroleum and minerals, dhahran 31261, saudi arabia * corresponding authors: muhammad tuoqeer anwar, engr.tauqeer137@gmail.com; tahir rasheed, tahir.rasheed@kfupm.edu.sa abstract: this review provides an overview of the importance of nanoparticles in various fields of science, their classification, synthesis, reinforcements, and applications in numerous areas of interest. normally nanoparticles are particles having a size of 100 nm or less that would be included in the larger category of nanoparticles. generally, these materials are either 0-d, 1-d, 2-d, or 3-d. they are classified into groups based on their composition like being organic and inorganic, shapes, and sizes. these nanomaterials are synthesized with the help of top-down bottom and bottom-up methods. in case of plant-based synthesis i.e., the synthesis using plant extracts is non-toxic, making plants the best choice for producing nanoparticles. several physicochemical characterization techniques are available such as ultraviolet spectrophotometry, fourier transform infrared spectroscopy, the atomic force microscopy, the scanning electron microscopy, the vibrating specimen magnetometer, the superconducting complex optical device, the energy dispersive x-ray spectrometry, and xray photoelectron spectroscopy to investigate the nanomaterials. in the meanwhile, there are some challenges associated with the use of nanoparticles, which need to be addressed for the sustainable environment. keywords: nanomaterials; nanoparticles; characterization; top-down synthesis; bottom-up synthesis 1. introduction over the last few decades, nanotechnology has expanded at an incredible rate. nanotechnology specializes in creating materials and devices at the nanoscale, allowing for precise manipulation of size, shape, and functionality. nano has become a ubiquitous buzzword in advertising efforts. the greek term “nano” means “dwarf,” while the latin “nanos” means “nanus.”. nanotechnology has broad potential uses across all of the technological and scientific domains. nanoscience facilitates the investigation at atoms and molecules level that affect their fundamental properties, whereas, nanotechnology seems to be the act of manipulating substances on the atomic scale to develop unique nanomaterials with exceptional features. richard p. feynman first used word “nanotechnology” in his 1959 lecture, “in 1959 capacity that at bottom”, since then, the field has made great progress. several new types of nanoscale materials have been created, thanks to the advancements in nanotechnology. as it was found that a substance’s size can affect its citation awan msud, anwar mt, khan hi, et al. nanoparticles’ classification, synthesis, characterization and applications—a review. characterization and application of nanomaterials. 2025; 8(1): 8899. https://doi.org/10.24294/can8899 article info received: 30 august 2024 accepted: 23 october 2024 available online: 29 november 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 8899. 2 physiochemical properties, including its optical qualities, therefore, the importance of these materials became clear. nanoparticles (nps) of gold (au), platinum (pt), silver (ag), and palladium (pd) with varying size were synthesized. for instance, gold nps of varying sizes and shapes, each with its own distinct hue and set of properties that could be put to use in biomedical, were introduced. changes in the solution’s defining properties are reflected in the color of the solution (viewing angle, nano shell width, and gold concentration). changes from any of these variables affect the nps’ ability to absorb light and, by extension, their color [1]. figure 1. significance of nanoscience and nanotechnology in fields of engineering and science. the public is unaware of the myriad ways nanotechnology is being employed in areas such as medical, building, nature conservation, electronics, national security, and even personal safety [2–6], despite the fact that it is getting increasing attention from scientists and engineers as depicted in figure 1. even if a lot of work already has been done with this technology, there is still opportunity for generating the new unique nanomaterials in a variety of fields for the development of humanity. scientists spend their time, effort, and resources to advancing human understanding because they are passionate about the subject. miniaturizing equipment while keeping prices down is thus a priority in different sectors. at some point in the future, nanotechnology will be able to dictate every facet of human existence. people’s curiosity in nanotechnology is piqued, and they begin discussing the field’s underlying principles and innovative uses. nanotechnology cannot exist without nanomaterials. nanomaterials are those with lengths approximately 100 nm or less. nanoparticles have physicochemical properties that are unique from that of bulk material because of their size and shape. nanomaterials take on a surprise new persona with unique characteristics and abilities when their quantum structure and size are altered. several types of nanomaterials, like nanostructures, nanoclusters, and nanosheets, can be distinguished entrenched on their extent of range. as particles interact with one another, their physical properties will evolve. characterization and application of nanomaterials 2025, 8(1), 8899. 3 2. classification of nanomaterials on the basis of size • one kind of nanomaterials is called zero-dimensional (or 0-d) because its dimensions are under a nanometer. • with a 2-d nanomaterial, both dimensions are larger than a nanometer, whereas, in a 1-d nanomaterial, only one dimension is. this category includes structures like nanorods, nanotubes, and nanowires. • 2-d nanomaterials have just two dimensions that are tiny, whereas the remaining dimension is macroscopic. nanofilms, nanolayers, and nanocoating’s are all examples of such materials. • three-dimensional or large nanomaterials (3-d) have a size of >100 nm in three arbitrary dimensions. nanowire and nanotube bundles, as well as core-shell structures, multi-nanolayers, and nanocomposites are all examples of 3-d nanomaterials [7]. table 1 provides classification of nanomaterials on the basis of dimensions. table 1. dimension, types in different forms of occurrence, properties, and potential applications of nanomaterials [8]. dimensionality type of nanomaterial properties potential applications zero dimensional nanoparticles, carbon dots high surface rea, isotropy, and confined electronic movement applications include bio imaging, electronics, drug delivery, and catalysis. one dimensional nanowires, nanorods, nanotubes high aspect ratio, anisotropy, outstanding electrical conductivity. application areas comprise energy storage devices, nanoelectronics, and composite materials. two dimensional graphene, mxenes excellent surface area, better in-plane electrical and thermal conductivity, layered structure. such materials have applications in catalysis, electronics, and energy storage. three dimensional or higher order a bunch of nanowires, core shells, nanocubes, nanocages porous structure, multifunctionality, enhanced mechanical strength. application areas include tissue engineering, filtration, supercapacitors, and catalysis. many kinds of nps exist, each with its own unique size, shape, characteristics, and synthesis. nanomaterials may range from those based on carbon to those based on metal, semiconductors, polymers, or lipids. different nanomaterials along with their synthesis procedure and specific examples are provided in table 2. table 2. nanomaterials, synthesis procedures [9], and corresponding examples [10]. nanomaterials methods of synthesis examples metal nanoparticles (nps) biochemical synthesis, photochemical, thermochemical process, electrochemical zns, pt, pd, ir, ag, au, cu, rh, co, fe, ni, cu au, ni, coni, cdte, cdse. carbon nano-materials arc-discharge technique, chemical vapor deposition, laser ablation method cylindrical carbon nanotube like single walled nanotubes (swnt) and multi walled nanotubes (mwnt) fullerenes polymer nanomaterials polymerization and electrochemical techniques nanowire of polypyrene, polyaniline, poly (3,4-ethylenedioxythiophane) dendrimers (pamam) nanocomposite innovative processes nanocomposite of polyethylene oxide and polyethyleneimine; carbon nanotubes (cnts) epoxy composites include hydrocarbon polymer composites, polyethylene glycol, polyester polyamides, conjugated polymer composites, cnts with polycarbonates, fluoropolymers, and so forth bio nanoparticles biological operations protein nps, plasmids and viruses [11], characterization and application of nanomaterials 2025, 8(1), 8899. 4 3. nanoparticles and related terminologies nanoparticles are defined as “particles having a nanometric size of 100 nm or less would be included in the larger category of nps”. the british standards institution [12] officially presented the following definitions for the terminologies being used: • nanometer-scale refers to distances between 1 and 1,000,000 of them. • nanoscience, refers an extremely small range, aims to explain how different materials behave depending on their atomic or molecular composition or bulk size. • nanotechnology is the application of scientific knowledge to the controlling and manipulating of matter at the nanoscale. • nanomaterials are defined as those that include or exhibit structures on the nanometer scale. • nano-objects are those made of materials with at least one peripheral element on the nanometer scale. • an item with three exterior dimensions on the nanometer scale is called a nanoparticle. when the lengths of the nanotube are varied, the term nanoparticle is replaced with nanorod or nanoplate. • a nanomaterial is said to be a nanofiber if it has three dimensions, two of which are on the nanoscale and one of which is much bigger. • when at least one of a multiphase structure’s phases are on the nanoscale, we call it a nanocomposite. • to put it simply, a nanostructure is a collection of tiny components that are linked together. a brief history and recent developments of nps is presented in figure 2. figure 2. history and recent developments of nps. 4. classification of nps 4.1. organic nps nanoparticles with composition of carbon or the one which are synthesized by characterization and application of nanomaterials 2025, 8(1), 8899. 5 organic molecules are called organic nanoparticles. common examples of polymers or organic nps include micelles, dendrimers, ferritin, liposomes, etc. some of these nps (liposomes, micelles, etc.) contain a hollow core (also called a nano capsule) and are sensitive to thermal and electromagnetic radiation (heat and light) [7]. because of their productivity and ability to reach peculiar areas of the physical body, organic nps are widely used in the biomedical field, for example in drug delivery systems. 4.2. inorganic nps nanoparticles without composition of carbon are called inorganic nps. most of inorganic nps are made up of metals or metal oxides. 4.2.1. metal nps metal based nps are mainly synthesized using constructive and destructive processes. these types of nps are made from all kinds of commonly used metals. ascribable to their effective surface to volume correlation and quantum effect, they have excellent thermal, antibacterial, catalytic, and ultraviolent sensitive properties. as there are many atoms on their surface and being small in size, they exhibit marvelous conductivity. 4.2.2. metal oxide nps nanoparticles of metal oxides exist for nearly all metals. some commonly used metals are aluminum (al), copper (cu), cobalt (co), lead (pb), manganese (mn), silver (ag), and zinc (zn). however, nps can be made using chemical techniques like electrochemical or photochemical ones. metal oxide nanoparticles can be created by reducing metal-ion antecedents in solution with reducing agents. they may absorb small molecules due to their high surface energy. there are several potential applications for these nps, including biomolecule detection and surveillance, and analytical and environmental testing. samples are occasionally coated with gold nps before being seen using a scanning electron microscope (sem). this typically increases the quality of its electrical current, which in turn produces higher-resolution sem images. because of their remarkable optical properties, metal oxide nps have several potential applications. 4.2.3. ceramic nps ceramic nps are inorganic solids formed by heating and cooling a mixture of materials such as carbonates, oxides, carbides, carbonates, and phosphates. forms ranging from polycrystalline to amorphous, dense to porous to hollow, are all accessible. researchers are paying a lot of attention to these nps due to their potential in various fields, in addition to catalysis, photocatalysis, and the photodegradation of dyes. these nps may be employed into a drug delivery system by adjusting certain physical characteristics; this is particularly useful for treating cancers, eye diseases and some bacterial and viral infections. 4.2.4. semiconductor nps nanoparticles made of semiconductors show characteristics similar of both metals and nonmetals. these may be located in groups ii–vi, iii–vi, or iv–vi of the periodic table. these particles have large bandgaps, the tuning of which reveals new characterization and application of nanomaterials 2025, 8(1), 8899. 6 characteristics. their applications range from water splitting and photocatalysis to electronics and photo-optics [13]. nps of semiconductors include the elements such as silicon and germanium from group iv and gallium nitride (gan), gallium phosphide (gap), indium phosphide (inp), and indium arsenide (inas). 4.2.5. polymeric nps in the scientific literature, these particles are commonly referred to as polymer nanoparticles (pnps) since they are often made of organic materials. they can be in the form of nanospheres or nano-capsules, depending on the method of manufacturing. the former are adsorbate molecules along the surface’s periphery. these are easy to operate. pnps provide a wide range of benefits, including controlled release, drug molecule protection, combined treatment for imaging, targeted delivery, and many more. they may be used in the medical diagnostics and medication delivery industries. pnps used for medication delivery have excellent biodegradability and biocompatibility. 4.2.6. lipid-based nps nanoparticles made of lipids are typically round and have a diameter between 10 and 100 nm. almost predominance of lipid-based nps are spherical platforms, comprise minimum one lipid bilayer and encompass one internal organic and aqueous compartment. there is a lipid solid in its center and a matrix of soluble lipophilic molecules around it. surface agents and emulsifiers stabilize the nps’ outer core. lipid-based nps consist of a wide range of component configurations. lipid-based nps have many benefits including easy formulation, conscious arrangement, renewability, high bioaccumulation, capacity for carrying massive cargo loads, and a variety of properties to modulate their characteristics. these are mainly used in the treatment of cancer including both medication delivery and rna release. 4.3 carbon-based nps carbon nanotubes and buckminster fullerenes are the two most common forms of these nps. graphene is simply rolled up into cnts. they are widely used for reinforcing existing structures. the two most common types of cnts are singlewalled carbon nanotubes and multi-walled nanotubes. carbon nanotubes are unique in a way that they conduct heat only in one direction, making them ideal for uses that necessitate fine-tuned regulation of temperature. fullerenes are a type of carbon allotrope distinguished by their hollow cage structure made up of sixty or more carbon atoms. these frameworks have a polyhedral and hexagonal agreement in place of carbon units [14]. due to their high strength, electronic configuration, and ionic properties, these have useful applications in industry. sub (swnts), two-fold (dwnts), and multi-walled carbon nanotubes are defined by the number of walls given in the rolled sheets. deposition of starting material, notably the atomic carboxylic acids, evaporated from tungsten by laser or by electrical discharge, is a common method of polymerization for these substances. chemical vapor deposition (cvd) is a new method for synthesizing them. nano-composites made from some of these materials are employed as supplements, effective gas biosorbents, in pollution control, and as assist medium for multiple organic as well as inorganic catalysts [15]. characterization and application of nanomaterials 2025, 8(1), 8899. 7 nonetheless, they are also utilized in their basic state for a wide range of commercial applications. 4.3.1. fullerenes fullerenes, which are carbon-based nps with a spherical shape, are bound through sp2 hybridization. depending on the number of layers, fullerenes may range in size from 4–36 nm in diameter for poly-layered fullerenes and to 8.3 nm in size for mono-layered fullerenes [16]. 4.3.2. graphene graphene is the name given to isomorphous type of carbon that have a hexagonal structure and two-dimensional flat surface. a single layer of graphene is just 1 nm thick [17]. 4.3.3. carbon nanotubes carbon monolayer nanotubes have a diameter of less than 0.7 nm. however, there is some variation in length of multilayer carbon nanotubes i.e., it may vary in micrometers to several centimeters, and their ends can be closed or hollow [18]. carbon nanotubes are manufactured by winding the carbon atoms of micro graphene into hollow pipes. 4.3.4. nanofibers of carbon most of nano-foils are coiled in cylindrical shapes of cup or cone shapes, rather than straight tubes, to create carbon nanofibers [19]. 4.3.5. carbon black black nanocarbon have a diameter of 20–70 nm and are amorphous in structure. when agglomerates of around 500 nm are produced, the interactions between the particles become very strong and the particles mix to create larger aggregates [19]. figure 3 demonstrates the classification of nanoparticles. figure 3. overview of the classification of nanoparticles. characterization and application of nanomaterials 2025, 8(1), 8899. 8 5. synthesis of nps nanoparticles are fabricated by different approaches i.e., bottom-up along with top-down one and biological synthesis, that have been developed on behalf of synthesizing nps. these approaches are briefly explained in the following section. 5.1. bottom-up methods one example of a bottom-up or constructive approach is the construction of materials from their atomic level to the cluster or bunch of their nanoparticle level. the most commonly used prevalent bottom-up techniques for producing nanoparticles include sol-gel, spinning, chemical cvd, and pyrolysis. 5.1.1. sol-gel a used prevalent colloidal solution is a suspension of solids particles in a liquid. the sol-gel approach appears to be the best bottom-up method because most nanostructures can be made using it. common precursors used in the sol-gel method include metal oxides and chlorides [20]. the precursor in host liquid can be broken up into a liquid and a solid phase by shaking or sonicating the mixture. phase separation methods like sedimentation, filtration, and centrifugation is used to remove the nanoparticles, and then they are dried to remove any remaining moisture. figure 4 presents the mechanism for the synthesis of batio3 nps. figure 4. suggested route for the synthesis of of batio3 nps along with byproducts (reused with permission from wiley‐vch verlag gmbh & co. kgaa, weinheim [21]). characterization and application of nanomaterials 2025, 8(1), 8899. 9 5.1.2. electrodeposition electrodeposition is a method which involves the reduction of metal ions from a solid metal being coated on a substance or in a solution when electric current is applied. its basic principle is use of an electrolytic cell containing a metal salt solution [22]. when current is supplied, it results in reduction of metal cations from cathode in solution and then gives a metal coated surface of the nanoparticle. 5.1.3. hydrothermal method hydrothermal synthesis of nps is chemical based which involves extraction of nanomaterials from hydrolysis reaction at high or wide range of temperatures [23]. this process is performed using a specific solvent below critical point at both pressure and temperature over wide range under supercritical conditions. however, this is convertible method for synthesis of nonorganic nps at both extreme hot temperatures and pressures. 5.1.4. spin-synthesized nanoparticles are spin-synthesized in a furnace using a spinning like disc (sdr). it uses a disc and spins inside a closed chamber/reactor to control physical parameters. reactors are routinely purged of oxygen, to nitrogen or any other inert gases to prevent chemical reactions. the precursor or water are placed inside the disc and spun at different speeds to create the liquid. atomic or molecular fusion can be precipitated, gathered, and dried with the use of spinning [24]. variables in the sdr’s operation, such as fluid, disc engine speed, liquid/precursor ratio, feeder position, etc., all influence the characteristics of the produced nanoparticles. 5.1.5. deposition of chemicals from gases chemical vapor deposition is a method of coating a substrate with some thin layer of gaseous reactants. reaction causes the deposition i.e.; the joining of gas molecules takes place in a reactor at room temperature. a reaction happens when the mixed gas contacts a heated substrate [25]. the reaction product is a thin coating that is deposited on the substrate and can be removed and recycled for further use. substrate temperature plays an important impact in chemical vapor deposition. nanoparticles made using cvd are superior because they are pure, consistent, rigid, and robust. there are certain downsides to cvd, such as the fact that it requires specialized equipment and results in very toxic gaseous by-products. figure 5 represents step by step procedure for the synthesis of carbon nanofibers. figure 5. step-by-step representation of synthesis route for carbon nanofibers. (a) creation of sic through reduction of sio2 with the help of carbothermal reaction; (b) characterization and application of nanomaterials 2025, 8(1), 8899. 10 coalescence of sic nps; (c) the degradation of sic and formation of carbon caps on its surface (reused with permission from american chemical society [26]). 5.1.6. pyrolysis as far as industrial production is concerned, pyrolysis is the standard method for making nps. in a flame, a precursor is burned up. precursors are introduced into the furnace through a small hole and burned under extreme heat and pressures [27]. most of the other furnaces use lasers in place of flames to generate the extremely feverish temperatures required for spontaneous evaporation of material. advantages of pyrolysis include its simple operation, high throughput, minimal material and labor costs, and scalability. 5.2. top-down methods the top-down also known as destructive method is breaking down a substance into smaller pieces until it reaches nanometer size. some of the most common ways to create nps are by mechanical milling, nanolithography, laser ablation, sputtering, and thermal breakdown. 5.2.1. mechanical milling the most common top-down method for creating nps is milling. mechanical milling is used for milling, following annealing of nanostructures during synthesis, with each component milled inside an inert environment [28]. particle shape is affected by ductile materials during mechanical milling, while particle size is affected by fracture and cold-welding. 5.2.2. nanolithography nanolithography is the study of making things that are often on a scale from 1 to 100 nm. it encompasses a wide range of techniques, including but not limited to nanoimprint lithographic technique, scanning probe photoresistor, and electron-beam lithography. in lithography, a light-sensitive substance is combined with a printing procedure that selectively removes material to create the desired shape and structure. the main benefit of nanolithography is that it can scale up the production of nanoparticles of a specific shape and size. there is a prohibitive cost associated with the complicated machinery. 5.2.3. etching etching is a chemical process of layers separation from some substance like wafer. it is mainly used for micro or nanofabrication. however, to protect other parts of the wafers from etching, special masks are used which provides resistance from this process. these masks are made of photoresist material which is contrived from photolithography [29]. 5.2.4. laser ablation laser ablation is a popular method for fabricating nanoparticles in a wide range of materials. nanoparticles can be created by concentrating a plume from plasma created by irradiating a metal coated in a fluid medium with a laser. it is reliable topdown method that can be used instead of the conventional method of chemically degrading metals to produce metal-based nps. in water emulsion solvents, lasis characterization and application of nanomaterials 2025, 8(1), 8899. 11 (laser ablation in liquids) might be called a “green” approach for manufacturing nanoparticles because no chemical or bonding agent is required. 5.2.5. sputtering this process includes the deposition of some nanostructures on surface as a consequence of wrenching with ions. a covering of nps is first deposited through sputtering and then it is annealed to harden. layer thickness, processing temperature and surface texture, etc. are important parameters to be considered while using this method. 5.2.6. thermal decomposition when anything is broken down by heat, it undergoes an endothermic chemical reaction. when an element reaches its breakdown temperature, it completely disintegrates chemically [30]. the nps are the product of a chemical reaction triggered by the metal’s breakdown at specific temperatures. 5.3. biological synthesis of nanoparticles the following procedures are used in the biological production of nps: 5.3.1. plant-based synthesis the synthesis using plant extract is non-toxic, making plants the best choice for producing nps. plant extracts such as geranium, sun-dried cinnamon menthol, azadi acta indica, etc., may be used to create gold and silver nps [25]. in the meanwhile, plant-based synthesis poses some challenges as well, such as inconsistency in yield, size, and shape of the nps due to the variation in the nature of plant extracts which is further related to the change in geographical locations, seasons, and species. 5.3.2. synthesis by bacteria the vast potential for synthesis of zinc oxide nanoparticles in the past has led to a dramatic expansion of the field. the capacity of bacillus species to produce extracellularly has made them popular in the synthesis of metal nanoparticles. the dimensions are between 10 and 20 nm. furthermore, gold nps may be synthesized [27]. 5.3.3. synthesis by fungi aspergillus nagger, aspergillus orizae, and fusarium solan are just a few examples of the types of fungus that may be used to create the nps. the effectiveness of silver nps against scherichia coli, staphylococcus aureus, and pseudomonas aeruginosa has been evaluated [31]. 5.3.4. synthesis by yeast here, cadmium nps are synthesized using the yeasts candida glabrata and schizosaccharomyce pombe. extremophilic yeast strain obtained from acid mine drainage is also used to study silver and gold nps. stable lead sulfur nps have been synthesized using the marine fungi rode sporidium diazoate [32]. 5.3.5. synthesis by biological compounds nanoparticles may be synthesized using biological compounds such as proteins, peptides, viruses, and enzymes [23]. the mineralization of sulfides is aided by the tobacco mosaic virus. viruses cause cowpea chlorotic mottle which is also present characterization and application of nanomaterials 2025, 8(1), 8899. 12 on the m13 like bacteriophage’s outer membrane. figure 6 provides different routes for the synthesis of nps. figure 6. synthesis routes for nanoparticles. the advantages, disadvantages, and practical applications of top-down and bottom-up synthesis of nps are provided in the table 3. table 3. pros and cons of different synthesis approaches for nps. methods advantages disadvantages practical applications top-down synthesis these methods offer large scale production e.g., milling. the synthesis procedures are simpler one realized through mechanical and chemical processes. there is precise control over the shape and size of the nps. usually, no complex chemicals are employed the surface defects may lead to roughness thus affecting the characteristics of the nps. there is requirement of higher amounts of energy. there may be a lot of waste associated with these processes. different electronic components such as microchips, thin films, and nanoscale circuits can be produced using these methods. catalysts can be synthesized using these methods. optical devices can be manufactured using these methods. bottom-up synthesis there is a better control over the structure. there is less likelihood towards the defects. uniform size distribution can be achieved. these methods are versatile and energy efficient. comparatively, these methods are time consuming and complex. they require costly chemicals. the scalability is limited. there is tendency towards the incorporation of impurities. these methods are employed to produce nps for fuel cells, drug delivery, catalysis, batteries, and supercapacitors. environmental remediation is also key area of application for these methods. 6. characterization of nps several physicochemical characteristics are shown by the nps. changing even a single nanometer in size causes a noticeable shift in behavior. nanoparticles need to be characterized using a variety of tools so that their characteristics may be studied. a few examples are the ultraviolet (uv), spectrophotometer, the fourier transform infrared spectroscopy (ftir), dispersive energy x-ray spectrometry (eds), sem, atomic force microscopy (afm), vibrating sample magnetometry (vsm), and superconducting quantum interference device (squid). characterization and application of nanomaterials 2025, 8(1), 8899. 13 6.1. structural arrangement, morphology, surface area, size, and shape of nps the size and shape of nps are key determinants of their unique physical and chemical properties. you may examine the surface morphology using an afm, field emission scanning electron microscopy (fesem) or transmission electron microscope (tem). the results obtained from these methods will help to determine whether the nps are spherical, rod-shaped, or porous. nanoparticle diameter may also be calculated. when put next to sem and tem, ability to reveal nps’ composition, morphology, and crystallinity stands out. signals are generated when an electron beam strikes atoms in a sample. these signals will reveal the structure and content of the sample’s surface. thus, the samples’ exterior needs to have some degree of electrical conductivity. surface coating with ultrathin electrically charged material may be used for nonconductive samples. afm examines materials that are dry ones. high resolution transmission electron microscopy (hrtem) and fesem are commonly utilized for subsequent processes of nanoscale. tem’s image resolution is superior to that of light microscopes. this will allow a comprehensive understanding of nps. tem is a simple method for determining the nanoparticle’s size [33]. scherrer’s equation may be used to determine the particle size using x-ray diffraction (xrd) spectroscopy. nanoparticle size may be easily determined using the distinct xrd peaks. nevertheless, the xrd peaks are wide and it is more difficult to identify the size of non-crystalline nps as compared with tem. the size of nps is too tiny to be determined by xrd. dynamic light scattering (dls), mossbauer spectroscopy (ms), and photon correlation spectroscopy (pcs) may be used to determine particle sizes and distributions. the surface area on nps may be calculated using the brunauer emmett teller (bet) technique. in addition to determining crystal orientation and aggregation section, electronic morphology, lattice structural spacing and particle phase shift all may be attained. 6.2. determination of elemental and mineral conformation elemental composition and surface interrelation may be determined using eds in conjunction with sem and tem devices. elemental percentages may be determined with the use of the methods like atomic spectrometry and inductively coupled plasma mass spectroscopy (icp-ms). nevertheless, hard nps will not directly used for these spectroscopic applications. they need proper dissolution with acids or strong bases compounds. mineral detection is achieved using x-rays diffraction which results in making up the nanoparticle’s aggregated crystalline form [34]. elemental composition data may also be obtained using xps. 6.3. investigation of structural arrangement and nodes in nanoparticles there are a number of techniques to produce the coveted structure with bonding qualities. standard procedures such as ftir, x-ray photoelectron spectroscopy (xps), thermogravimetric analysis (tga), and raman spectroscopy (rs) might be helpful. the xps and ft-ir can verify the presence of oxygen bonding in the metal. nanoparticle’s surface arrangement may also be studied using xps. it has the potential to keep track of statistics like the oxidation number in addition to their characterization and application of nanomaterials 2025, 8(1), 8899. 14 elemental composition. spinel symmetry and structure may be determined by raman spectroscopy. x-ray absorption spectroscopy (xas) will provide a wealth of data, including calcination states, adjacent molecules, collaboration numbers, length of bond, and the electronic formation of the necessitate element [35]. 6.4. analyzing the intrinsic attributes of nanoparticles it is possible to learn more about the magnetic characteristics of nanoparticles by using vsm, electron paramagnetic resonance (epr) and squid. the epr method can identify paramagnetic facilities along with unbound alkyl. the squid instrument will be accustomed to evaluating distinct varieties of samples like translucent, emaciated films, particles, moisture, and vaporish. it is an overly sensitive piece of equipment. the hs, magnetic partial pressure, and residual magnetic polarity can be measured with squid and vsm, at a persistent extrinsic load magnetic flux density [36]. mossbauer technique of spectroscopy provides access against wealth of features. electronegativity, oxidation states, spin, and covalent character can be determined, as well as bonding, structural, and magnetic characters. table 4 exhibiting the advantages, limitations, and specific uses of different characterization techniques is presented below. table 4. pros, cons and specific applications of different characterization techniques for nps. technique advantages limitations specific uses tem surface topography images of ultra-high resolution, crystallographic information, atomic scale imaging. difficult sample preparation methods, expensive setup. determination of atomic structure, imaging of nps, investigation of microstructure. sem images of surface characteristics, provision of analysis of wide range of materials, ease of sample preparation. internal structure cannot be examined, low resolution, require conductive samples. analysis of surface morphology, inspection of surface defects including cracks and fractures. ftir identification of functional groups and chemical bonds, agile analysis, provision of quantitative and qualitative analysis. low sensitivity, not appropriate for metals, provides surface attributes only. identification of functional groups and compositions. xrd no destructive approach, analysis of material phases. usually limited to crystalline materials. determination of phases and crystal attributes. squid detection of magnetic behavior at low temperatures. expensive due to the use of cryogenic conditions, only for magnetic materials specific uses include paramagnets, ferromagnets, and superconductors. 7. applications of nps nanomaterials are practically amazing due to their magneto strictive, electronic, luminescence, and electrochemical properties. their usage is present in almost every field from medical to advanced manufacturing. they are being used in the fields of medicine [37], water purification, catalysis, mechanical engineering, and computer science as well as in fields like electrochemistry, luminescence, piezoelectric, and magneto strictive ones [38]. they can be used as electrodes in batteries and supercapacitors, two common types of energy storage devices [39–45]. they can also be used in recording media, like voice/video tapes. additionally, they also find some applications in isolators, sprockets, and circulators. they have applications inside the dyeing industry and the treatment of wastewater [46]. characterization and application of nanomaterials 2025, 8(1), 8899. 15 7.1. mechanical engineering nanoparticles play a vital role in mechanical engineering due to their inimitable properties and their corresponding effects. nanotechnology shows remarkable results in materials by enhancing their strength, flexibility, mobility, elasticity, resistivity to environmental concerns and toughness. reinforcement of composites materials, for example, graphene or nanotubes in metals or polymers ultimately results in improving the mechanical strength and stiffness of newly formed or advanced materials which gives extraordinary durability in terms of structural and wear resistance to environment. with the advancement of technology and evolution of nps, the conventional measures of manufacturing have been evolved and nanomanufacturing has been adopted to increase output by escalating technical performance, and, excessively shows reduction in production cost. automobiles being fabricated with help of nanotechnology have observed lower rate of failure and self-degrading properties. thus, on basis of co2 free nanotechnology, environment friendly and sustainable transport, which might call as nano cars, where safe, clean and quiet driving is possible with less or no emission of harmful substances in atmosphere, is possible. in a lucid way, these additives improve efficiency and lifespan of machinery. moreover, oxides of aluminum and boron nitride are being used to incorporate heat dissipation in mechanical systems. now a days, additive manufacturing is one of the most advanced methods for manufacturing of 3-d mechanical parts with advanced nanomaterials along with complex geometries in an efficient way [37]. 7.2. photocatalysis photocatalysis is a method which involve use of photon (light) to actuate the chemical reaction by means of some particles or substance. this process actually leads to initiating a redox reaction along with the electron hole pairs. it is an encouraging approach for sustainable green environment [47]. it is a non-hazardous, safe and reliable technique for deteriorating a large number of pollutants from the environment. nps act as catalyst to absorb substantial number of pollutants due to their large surface area. it is observed that nps of gold and aluminum have higher reaction rates of eliminating the organic dyes from environment. moreover, nps of platinum are used in most of the catalytic converters of automobiles, which significantly reduces the cost and speed up the reaction by improving its overall mechanical performance [38]. 7.3. waste treatment environmental pollutants are one of the major concerns along with gradual increase of urbanization and industrialization. however, some preventive measures have been taken along with the passage of time to solve this problem like sedimentation, activated sludge process, chlorination, aerobic digestion, and chemical treatment etc. meanwhile, with some advancement of technology, nps and their composites are used due to their extraordinary physiochemical properties to counter aforesaid issues [48]. they are well known in waste treatment processes as they have adsorption properties like activated carbon nps act as adsorbents to characterization and application of nanomaterials 2025, 8(1), 8899. 16 eliminate maximum pollutants. for removal of heavy metals, this adsorption mechanism is adaptable due to their surface energy and affinity of surrounding atoms present in the outer most shells [45]. photocatalysis technology, adsorption, nanomembrane technology, and disinfection are some of the methods which help in treatment of wastewater and nps play a pivotal role in that. 7.4. water purification water purification is one of the common challenges for most of the developed and developing countries. some of the traditional methods for purification of water are ultrafiltration, microfiltration, biological treatments, distillation, uv treatment, and reverse osmosis (ro). but these methods have some limitations as they will purify the water up to some extent. there comes the need of nps for water purification. this technology mainly contains oxides of metals and nonmetals and efficacious membranes for hindering and filtering of microbes and harmful pollutants in water. meanwhile zeolite-based nanomaterials are also used for water purification. almost 40 morphological kinds of this materials are found naturally and can also be made in laboratory as per requirement. it has a 3-dimensional structure in which si4+ can be replaced with al3+. these ceramics have special membrane like structure which made it special to filter up to ultra range of soluble particles. meanwhile carbon nanotubes, graphene and nano absorbent with metals, ag, zno and tio2 nanoparticles are most frequently used for water purification [46]. particularly, titania-based materials have been reported for extraction of antibiotics, dye contaminants along with oxidative sterilization [49]. 7.5. medicine and health care the use of nanotechnology in healthcare dates back to 1965. their versatile properties make them useful in medical imaging. targeted pharmaceuticals, tissue engineering, molecular engineering, biosensors, and diagnosis are the primary areas of application [50–54]. nanoparticles are used in the field of targeted pharmaceuticals, where they are administered directly to the disease sites like cancer tumors. the smallest possible size of the nps is required for this method of delivering the drug to the desired location via the bloodstream. when stimulated, the nanoparticles might release their cargo of drug at the site of action. physicalchemical, biological, temperature and electrical-based materials are all examples of the many types of stimuli that exist. the drug’s release will be triggered by these stimuli. gold, titanium, magnetic nps, and quantum dots are commonly used for drug delivery and targeting. good and enhanced output is what you can expect when you mix these nps with polymers. metal nps are by far the most effective ones for targeting drugs. gold nps’ special spectroscopic properties have a significant impact on photothermal therapy in diagnosis of cancer. nanoparticles of gold, silver, or magnetite ones, all work well as nanocarriers [55]. nanocarriers are built to transport cancer drugs to the affected area. nanoparticles are small enough to penetrate deeply but not so small that they disrupt the body’s healthy tissues. that way, healthy cells will not be harmed. drug delivery is facilitated in part by silver nps. some of these nps are enriched with rare earth elements, including fe, ni, co, and their oxides. characterization and application of nanomaterials 2025, 8(1), 8899. 17 magnetic dipole-dipole interactions can also lead to their clustering. both organic and inorganic coatings, as well as magnetic core-shell nps find widespread applications. nanoparticles of the quantum dots (qd) have been found to be effective tumor targeting agents. magnetic resonance imaging (mri) makes use of the electrical properties of qds. diagnosis and treatment are two areas where mesoporous silica nps shine [56]. this technology can also be used to precisely administer medication for cardiovascular conditions. 7.6. nanoparticles as catalysts reducing the acceleration, binding to reagents to antagonize bonds, getting effective collisions by attempting to bring the superoxide radicals close together, and increasing the percentage yield are some of predominate mechanisms in which catalysis come. stimulus helps in reducing the reaction heat because they cut down unwanted byproducts. surface area per unit mass is increased because they seem to be so small in size. because of this, catalytic chemical reactions can take advantage of a larger surface area. when compared to conventional catalytic reactions, which use bulk materials, nano catalytic reactions are more reactive [57–63]. there are many different types of nano catalysts, including those based on metals, carbon, and ceramics [64]. cobalt ferrites, coin ferrites, copper terbium, zinc ferrites, alloys, and core-shell ferrites are all examples of metal-based catalysts. for example, copperbased nano-catalysts can be used to improve the selectivity, catalytic performance, and stability while treating the wastewater. they are preferable due to reusability and ease of the recovery in wastewater treatment [65]. in the recent years, co2 reduction reactions (co2-rr) are in the limelight due to the environmental concerns. in this backdrop, nps of noble and other transition metals are being employed for co2-rr. for instance, nps of gold and copper have been reported as electrocatalysts for co2rr. it was observed that reduction efficiency and stability tremendously increased which was ascribed to the heterometallic interactions between the two metals and mwcnts [66]. 7.7. fuel cell application a fuel cell is an electrochemical device that uses two redox reactions to transform the chemical energy of fuel and oxidizing agent into electricity. an oxygen/hydrogen fuel cell produces electricity with zero emissions of carbon monoxide. every type of vehicle and instrument, from airplanes to cars, ships, submarines, and weapons now features fuel cells. fuel cells come in many forms, including the fuel cell using proton exchange membranes (pemfc), direct methanol fuel cells (dmfcs), alkaline fuel cell (afc), phosphoric acid (pa) fuel cell (pafc), the molten carbonate fuel cell (mcfc), and a solidoxide fuel cell (sofc) [67]. one major problem with using fuel cells is platinum (pt) dependent catalysts that are prohibitively expensive. researchers have not yet succeeded in fully substituting another metal for platinum. pt-co, pt-mn, pt-ru, pt-ir, pt-cu, and pt-fe, are platinum-dependent catalysts that have been introduced. catalysts based on carbon, iron, and transition metal oxides are also used. for instance, the use of doped titanium oxide as pt catalyst support has been reported. traditionally, carbon-based characterization and application of nanomaterials 2025, 8(1), 8899. 18 supports are employed which are prone to corrosion, degrading overall performance of the pemfcs, however, titania nps-based support exhibited superior durability as compared to the commercially available catalyst pt/c [68]. carbon-based catalysts make extensive use of graphene, carbon nanotubes [69], and carbon nanofibers. 7.8. electronics researchers have been interested in discovering new uses of nps for their amazing magneto strictive, electronic, luminescence, and electrochemical capabilities. memory devices, like biosensors, cpu systems, transmitter cores, high storage capacity system, optical data storage, transformer cores etc. are all familiar places to find them. they will only be successful if they exhibit a set of characteristics [70,71]. high-hs ferrite nps, for instance, have practical use in magnetic recording [72]. that highly magnetized hs can be shielded from demagnetization and has been investigated. low hs is preferred in transformers. high ms and hs with minimal residual magnetization are necessary for use in recording medium like audio and video cassettes. nanoparticles with magnetic properties have several applications in fluids, data analysis circuits in digital computers, and digital recorders. their magnetic ferrites reveal high electrical conductivities, thus, can be pertinent to the biomedical fields. the magnetic and electrical characteristics of cobalt ferrites are very impressive [73]. the electrifying and magnetic properties of the polymers were escalated by the incorporation of pearlites. figure 7 demonstrates the application of nanoparticles in different fields. figure 7. applications of nps. 8. issues and challenges apart from its advantages, that have been achieved by use of nanotechnology in various fields of life, there are a number of issues in different areas which need to be characterization and application of nanomaterials 2025, 8(1), 8899. 19 resolved [74]. some of the challenges are given below as: • synthesis of nps is a vital challenge. normally high-quality nps are manufactured using diverse instruments under extreme conditions which results in controlled production at large scale. the scalability is challenging as processes like vapor chemical deposition, laser ablation, and hydrothermal synthesis is difficult to scale up. in the meanwhile, scalability requires more energy, costly materials, more sensitive equipment, thus adding up to the overall cost of processing. • the change in starting material and process parameters can lead to the inconsistencies, ultimately affecting the reproducibility. • although nps are remarkably effective and useful in cancer and drug delivery, however, presence of impurities, defects and discontinuity in their length suppress their strength. • nanoparticles have been found to be harmful for the humans as they can penetrate the human body and cause severe health issues. there is likelihood of entering in the respiratory system and other important organs of the human body. for instance, metallic nanoparticles like au are toxic and reactive in nature, which might cause skin and lungs’ cancer. under certain conditions, it shows phototoxic effect which leads to health problems. additionally, most of cosmetic and beauty products contain titanium dioxide nps, long term use may cause cell damage and respiratory issues. prolong interaction of carbon nanotubes causes inflammation and fibrosis as it has potential of toxicity. there are regulatory challenges as well as they are evolving at the moment. stable revelation of zinc oxide nps may raise challenges of skin and eye irritation [75]. • another challenge which needs to be addressed is environmental impact of nps during their synthesis, utilization, and disposal. their accumulation in the environment may have drastic effect on aquatic life. in addition to that, sustainability is another factor which needs to be kept in mind. use of toxic and expensive chemicals and energy-intensive methods, proliferation of nps in the fresh water, and utilization of larger amounts of water raises sustainability concerns. there is little understanding of their end-of -life disposal as well. 9. conclusion and future prospects in this review, a brief overview of nps, their types based upon their dimensions, synthesis routes, and emerging applications in various fields of science and technology have been discussed. several physicochemical characteristics of the nps are characterized using a variety of tools like ultraviolet, spectrophotometer, the ftir, afm, sem, tem, which reveal that these particles exhibit distinct properties. the synthesis using plant extracts is non-toxic, making plants the best choice for producing nanoparticles. due to small size and large surface area or volume, ability to absorb and scatter rays of light in visible and infrared region is possible. these properties make it ideal for early diagnosis and treatment of neuro-degenerative diseases. besides its advantages, substantial number of health, environmental and safety issues rise due to the refractory use of these particles. it has the potential to characterization and application of nanomaterials 2025, 8(1), 8899. 20 cause detrimental effect like asthma, urticaria, hypertension, parkinson, dermatitis, alzheimer, and many other cancers in human body. thus, there should be a controlled use and discharge of the particles in the environment. there is dire need to divert the future research direction towards the improvement of homogeneity during the synthesis and control over shape and size, while keeping in view the consistency and scalability especially for the green approaches such as plant-based ones. the priority should be given to addressing the toxicity concerns by introducing biodegradable and non-toxic nanoparticles. the innovation will be driven by 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10.3390/pharmaceutics13101615 characterization and application of nanomaterials (2022) volume 5 issue 1 doi:10.24294/can.v5i1.1681 66 review article application of nanotechnology in ophthalmology: where are we? marcela gómez-garzón1, m. alejandra martínez-ceballos1*, arley gómez-lópez1,2, adriana rojas-villarraga1,2 1 división de investigaciones, fucs, cl. 10#18-75, bogotá, colombia. e-mail: mariamace9@gmail.com 2 instituto de investigaciones. fundación universitaria de ciencias de la salud (fucs), bogotá, colombia abstract nanotechnology is a subject that studies, processes, and applies various functional materials, equipment, and systems, and controls substances on a nanoscale. nanomedicine refers to its application in diagnosing, treating, preventing, and monitoring various diseases. drugs administered through eye drops must travel a long distance to avoid various eye barriers reaching the posterior segment of the eye, to achieve the lowest drug level. this review focuses on nanotechnology-based eye disease treatment systems and highlights the obstacles affecting the drug management of eyes and nano-systems for the treatment of eye diseases. this paper summarizes the development prospect of nanotechnology and the challenges it faces in the treatment and diagnosis of ophthalmic diseases, to provide information and new ideas for the implementation of treatment and the development of a refractory eye disease management system. keywords: ophthalmology nanotechnology; nanomedicine; nanoparticles article info received: 18 january 2022 accepted: 20 march 2022 available online: 31 march 2022 copyright copyright © 2022 marcela gómez-garzón, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction the world health organization estimates that in 2018, about 1.3 billion people suffered from some form of visual impairment, mainly due to uncorrected ametropia and cataracts. about 36 million blind people are blind due to cataracts, trachoma, corneal scar, glaucoma, diabetic retinopathy, age-related macular degeneration, and congenital malformations. it is estimated that 80 percent of these cases could have been avoided. the eyes are divided into anterior and posterior segments. the anterior segment includes the cornea, conjunctiva, anterior chamber, iris, ciliary body, and lens. eye drops are widely used in the treatment of anterior segment diseases because of their accessibility. however, due to the corneal barrier and the rapid filtration of tears, the bioavailability of topical eye drops is poor. the posterior segment is composed of the choroid, vitreous, and retina. eye drops must go through a long distance and pass through several eye barriers to reach the posterior pole of the eye, which leads to low bioavailability when the drug reaches its action site[2]. nanotechnology is a discipline that studies, designs, synthesizes, operates, and applies various functional materials, equipment, and systems, and controls substances at the nanoscale (1–100 nm). according to the national nanotechnology initiative, the essence of nanotechnology is the ability to work atom by atom at the molecular level in order to create a huge structure and a new molecular organization. the aim is to develop these properties by controlling structures and devices at the atomic, molecular, and supramolecular levels, and to learn how to 67 manufacture and use these devices efficiently. it can be used to diagnose, treat, prevent and monitor various diseases. nanotechnology is widely used in different fields. for example, in the field of molecular biology, the biological detection method of dna sequencing is developed through a nanopore sequencer[4,5]. in clinical pharmacology, it is used to prepare nano drugs[6]. recently, the us food and drug administration approved a number of nano drugs, including polymer nano-particles, polymer-drug conjugates, and degradable polymer structures classified by material type. their function is to promote the diffusion of drugs through anatomical barriers, improve the bioavailability and half-life of drugs, and promote the controlled release mechanism. it is also used to optimize diagnostic imaging, using inorganic iron oxide nanoparticles as a reagent[7] to enhance image contrast. the application of nanotechnology in the treatment of eye diseases has become the hope of millions of patients with vision diseases. nano-carriers and nano suspensions react by releasing drugs at specific sites, thereby reducing the drug dose and minimizing the risk of side effects. for example, brimonidine, cyclosporine, corticosteroids, intravitreal sustained-release implants, etc. in terms of diagnosis and follow-up, noninvasive intraocular pressure measurement for detecting high intraocular pressure and remote monitoring of nanodevices will contribute to the early diagnosis of progressive optic atrophy and clinical monitoring of patients with glaucomatous optic neuropathy[9,10]. in this review, we focus on the eye disease treatment system based on nanotechnology. firstly, the anatomical structure of the eye and the obstacles to drug administration were briefly introduced. subsequently, ophthalmic diseases and nano-systems for the treatment of these diseases are reviewed. finally, the application prospects and challenges of nanotechnology in the treatment and diagnosis of ophthalmic diseases are summarized. this review will provide information and new ideas for the implementation of treatment and the development of a common eye disease management system. 2. ocular anatomy and ocular barrier figure 1 shows nanotechnology delivers ophthalmic drugs through the various ocular anatomical structures. table 1 depicts different eye structures and possible therapeutic targets. its thickness, function, physiology, and composition are emphatically introduced. these special functions can promote or prevent the effect of topical drugs. it also outlines possible action goals to understand the progress of nanotechnology in ophthalmology. table 1. different eye structures and possible therapeutic targets obstacle barrier thickness function physiology constitution other components tear film 3 μm thick, 3 μl volume[11] lubrication, debris removal, antibacterial protection, stem cell nutrition, and corneal transplantation maintenance; affect the refractive index of the visual system[12]. dynamic functional units: three chambers (fornication, lacrimal meniscus, and anterior lacrimal membrane). surfactant and stability of tear film lipid component, water component, and mucus component[12]. immunoglobulin, lysozyme, lactoferrin, oc, and β[14]. corneal 540–600 μm a barrier against infection and ocular mechanical injury. two-thirds of the eye refraction (image perception)[15]. corneal epithelium: 5–7 layers of non-stratified squamous epithelium are connected by desmosomes and connected through gap junctions, allowing the diffusion of small molecules <1,000 dalton. it is in direct contact with aqueous humor through the na+-k+-atpase pump[16] present in endothelial cells. avascular lens. viscoelastic structures are rich in glucosamine and proteoglycans[17]. sixth floor: bowman, stroma, dua layer, descemet, endothelial layer, corneal epithelium. collagen 1, iii, v and viii. proteoglycans (decorin, lumican, keratin, mimecan, disaccharide, and fibromodulin) and glycoproteins[15,17]. 68 table 1. (continued) obstacle barrier thickness function physiology constitution other components conjunctival 44.9 ± 3.4 μm through mucus, it helps to diffuse the tear film, maintain the stability of the tear film and prevent the adhesion between infection and mucus[19]. corneal epithelial healing[20]. the outermost layer of the eyeball. bulbar conjunctiva, eyelid, and forceps. goblet cells produce mucin[21]. multilayer non keratinized columnar epithelium (goblet cells) in contact with lamina propria (highly vascularized connective tissue)[21]. tff1 and tff3 proteins are involved in the scarring process of corneal tissue[19]. scleral 0.53 ± 0.14 mm viscoelastic properties give eye strength and resistance when intraocular pressure increases[14]. the matrix is composed of proteoglycan, elastin, and large collagen fibers. it is indirectly nourished by the sclera and irrigated by long and short posterior ciliary vessels and choroids. venous drainage occurs in the vortex vein[22]. five-sixths of the eye robe. the innermost layer (lá mina fusca)[14]. use iris and ciliary bod y: 1–2 mm iris, light input regulator. ciliary body: regulates, produces (apigenin) and regulates (electrochemical gradient) aqueous humor flow and secretes hyaluronic acid to the vitreous. aqueous humor: nutrition of avascular ocular structure, homeostasis of ocular tissue, clearance of metabolites, transport of neurotransmitters, and stability of ocular structure[23]. ciliary body cornea scleral junction (iris angle): the space where aqueous humor flows from the posterior chamber to the anterior chamber. aqueous humor contributes to the circulation of inflammatory cells and mediators under pathological conditions and the diffusion of drugs to different tissues[24]. the middle part of the eyeball is composed of the iris, ciliary, body, and choroid. iris (three layers): posterior iris (pigment epithelium), anterior iris muscle (round or contractile, radial or dilator of the pupil), and matrix (vascularized connective tissue). the ciliary body (flat part and fold part)[24]. aqueous humor consists of organic and inorganic ions, carbohydrates, glutathione, urea, amino acids, proteins (collagenase, immunoglobulin), oxygen, carbon dioxide, and water[23]. crystalline 3.5–5 mm reflex power (20% of the total eyeball). an image focused on the outside of the retina. enzyme-mediated oxidant defense mechanisms (glutathione reductase and catalase)[25]. it is nourished by aqueous humor. metabolic activity is involved in ion exchange through sodium, potassium, calcium, and chloride channels, as well as glucose, amino acids, and antioxidants (glutathione) [26]. no vascular structure, transparent. it is divided into the capsule, crystalline epithelium, cortex, and nucleus. 60% protein (crystalline α, β, γ). it is surrounded by collagen capsules (mainly type iv and xviii) and laminin, entactin, proteoglycan (heparan sulfate), pearl, and fibronectin. in the banded region, the main components are fibrin and elastin[25,26]. membrane proteins (different cell connections of lens epithelial cells): cadherin, calmodulin, type ii neural adhesion molecule, endogenous major protein (hydrophobic), and apigenin 0 enzyme (glyceraldehyde 3 phosphate dehydrogenase). the cytoskeleton includes actin, α-actin, anquirina, trompomudulina, myosin, and spectria[25,26]. 69 table 1. (continued) obstacle barrier thickness obstacle barrier thickness obstacle barrier thickness choroid 220–350 μm flush the retina and replenish oxygen and nutrition. absorb light, regulate body temperature, and adjust intraocular pressure by controlling blood flow[27]. drainage of aqueous humor from the anterior chamber through the uveoscleral pathway (accounting for 35% of its drainage volume)[27]. blood vessels, melanocytes, fibroblasts, immunocompetent cells, and supporting structures (collagen and elastic connective tissue). four layers: chorion, chorionic column, two layers of blood vessels, and suprachoroidal[27]. vitreous humor 4 cc its transparency allows light to pass through the retina and gives the eye structure. due to its physicochemical properties and ionic charge, it poses obstacles and challenges to drugs working at the posterior pole level[28]. the viscoelastic gel is located between the lens and retina. it contains water (98%), collagen fibers (ii, v, ix, and xi), polyurealic acid, electrolyte (sodium, potassium, calcium, and chlorine), prealbumin, and transfer protein. equivalent to 80% (4 cc) of eye volume[29.30]. more than 1,205 proteins[30]. retinal pigment epithelium 0.4–1 mm[31] the light energy gathered at the macula is absorbed through the ocular refraction system (cornea and lens) to improve the visual quality. the cell’s own dna repair mechanism includes the defense mechanism against reactive oxygen species[33]. high infusion of chorionic gonadotropin (1400 cc/min/100 g tissue)[34]. antioxidants: superoxide dismutase and catalase. retinal pigment epithelium 0.4–1 mm[31] through the melanin in epr melanosomes, carotenoids (lutein and zeaxanthin), and ascorbic acid in light receptors, photooxidation, and oxidative damage are prevented through the light absorption mechanism[32]. it transports ions and water from subretinal space to chorionic capillaries through the na+-k+-atpase pump and k+/cl transporter and maintains intraocular pressure to a certain extent[33,35] the maintenance of intracellular ph is mediated by the chloride bicarbonate exchanger on the basement lateral membrane of epr[33]. retinal nerve sensation light transduction of external images[36]. it is perfused by the central retinal artery and receives metabolic input through the choroid[31]. the self-regulation of retinal pressure is mainly mediated by the increase in retinal vascular resistance[37]. the outer membrane (photoreceptor and muller cell), outer nuclear layer (photoreceptor nucleus), outer plexiform layer (photoreceptor axon), inner nuclear layer (bipolar cell), inner plexiform layer (bipolar cell and amacrine cell), ganglion cell layer, nerve fiber layer, inner limiting membrane (basement membrane formed by muller cell extension)[31,36]. 70 figure 1. nanotechnology delivers ophthalmic drugs through different ocular anatomical structures. np: nanoparticles. 3. nanotechnology concept nanotechnology is a discipline that studies, designs, synthesizes, operates, and applies functional materials, equipment, and systems by controlling nanomaterials (1–100 nm). the application of nanotechnology in the diagnosis, treatment, and control of various diseases is being implemented rapidly. this new branch of science is called nanomedicine. with the advancement of nanotechnology in medicine and surgery, its application in ophthalmology has made progress. therefore, new eye nano-systems with different shapes and characteristics to optimize the bioavailability of drugs, prolong the contact time and reduce the eye removal process had been designed[39]. there are many nano-systems that have been applied in the treatment of different eye diseases. nanoparticle-filled contact lenses with acetazolamide for the treatment of glaucoma[40], biodegradable subconjunctival implants for the treatment of xerophthalmia [41,42], the development of diclofenac eye release nano colloid system based on hydrogel[43,44], polymer nano colloid system for inflammatory diseases[45,46], and nanostructured lipid transporters for controlling drug delivery in ocular infections[47,48]. 3.1 liposome liposomes are lipid vesicles comprising one or more phospholipid double chains that surround an aqueous core. according to the size of liposomes and the number of phospholipid double chains, liposomes can be divided into small monolayer vesicles (10 and 100 nm), and large monolayer vesicles (100 and 300 nm) and multi membrane vesicles[49] containing more than one phospholipid double chain. liposomes are ideal because they encapsulate both hydrophilic and hydrophobic drugs and show good compatibility with eye tissues[50,51]. examples of applications of such nanoparticles include intravitreal nanoliposome suspensions of prednisolone and infliximab[52,53]. 3.2 polymer nanoparticles polymer micelles are self-assembled nanoscopic core-shell structures formed by amphiphilic copolymer inside water. the core/shell structure allows the hydrophobic drug to be encapsulated in its hydrophobic core. because the core is protected by the hydrophilic crown, the bioavailability of the drug in the local administration of ocular tissue is significantly prolonged[54,55]. an experimental study conducted by mittal et al. in rabbits showed that timolol maleate was biocompatible with the 71 cornea, and the intraocular pressure (iop) decreased for a longer time.[56]. 3.3 nano suspension nano suspensions are colloidal dispersions in which the hydrophobic phase is uniformly dispersed in the aqueous medium with the help of surfactant[9]. for example, prednisone, dexamethasone, hydrocortisone, and other corticosteroids have been administered through nanosuspensions to treat anterior inflammation without the expected side effects of high-dose application, such as cataract and glaucomatous optic neuropathy. 3.4 dendrimer dendrimers are monodisperse macro-molecules. several reaction end groups form an inner cavity around a small molecule. its tree branch structure presents various repeated terminal groups. in particular, low-generation dendrimers can encapsulate hydrophobic drug molecules in their inner cavities. due to this unique structure, dendrimers allow the dissolution of drugs with poor water solubility. in addition, dendrimers can be considered real simulations of globular proteins. they are called “artificial proteins” because of their systematicness, electrophoresis, size scale, and other bionic properties[57,58]. drugs developed using this technology include intravitreal injection of fluocinolone acetoacetate for retinitis pigmentosa and subconjunctival carboplatin for retinoblastoma[59,60]. 3.5 nano micelles nano micelles are drug delivery systems composed of hydrophobic nuclei and hydrophilic caps, which allow the dissolution of hydrophobic drugs and produce transparent aqueous preparations when they are ready to be administered to the anterior segment of the eyeball. one of the drugs used in this nanotechnology is cyclosporine. a phase iii clinical trial has proved that it is effective, safe, and rapid in the treatment of keratoconjunctivitis sicca[61]. 3.6 niosome niosomes are two-layer non-ionic surfactant vesicles that can capture hydrophilic and lipophilic drugs. niosomes are chemically stable, and their non-ionic properties make them less toxic. due to its hydrophilic surface, niosomes can easily interact and cross the tear film barrier, so they can reach the cornea/conjunctival tissue[63]. niosomes have been evaluated as anticholinergic and antibiological agents[62,64,65]. the most important characteristics of the drug delivery carrier for the eye are: (i) the size of the gallbladder is large enough to resist the drainage caused by reflex tear and blinking; (ii) the presence of an irregular shape so that it can be correctly installed at the bottom of the eye bag and accommodated on the surface of the eye; (iii) it is preferable to be heat sensitive and release the drug content in a controlled manner, but at the same time, before removal with blinking and nasolacrimal duct drainage[66,67]. 3.7 cube the structure of the cube consists of a continuous, highly distorted lipid double chain with two disjoint and consistent waterways. compared with the simple liposome structure, the cube has increased surface area and the ability to encapsulate various hydrophilic, hydrophobic, and amphiphilic molecules. due to the strong electric repulsion and the high proportion of liposomes[68–70], cuboids have higher physicochemical stability than liposomes. the use of dexamethasone in eye drops is associated with this nanoparticle, indicating a higher availability of the drug in aqueous humor[71]. 3.8 hydrogel hydrogels are a network composed of multifunctional monomers and relays, which react to form a flexible underwater structure. because the porosity of the hydrogel matrix can be adjusted by changing the crosslinking density, the hydrogel network has been widely studied as a controlled and continuous drug delivery system. the ability to change with the surrounding environment is of great significance for the formation of hydrogels in situ. hydrogels will be crosslinked when the temperature rises from room temperature to body temperature, and their phase-controlled release is affected by ph value or light stimulation[72,73]. 72 controlled release silicone and hydrogel contact lenses containing timolol are a new technology developed in recent years[74]and have good application prospects. 3.9 polymer nanofibers nanofibers are made of solid fiber materials with a diameter of less than microns. they have a porous structure and a very high surface area. nanofibers are nonwoven fiber structures similar to the extracellular matrix. they are composed of highly organized polymer fibers and aqueous compounds comprised of protein polysaccharides to support tissue formation. therefore, tissue engineering is one of its main applications. the device developed and studied is regenerative therapy. this is to protect the biocompatibility, physiology, and transparency of the cornea[75,76[. in addition, because the diameter of nanofibers is very small and the surface area is very large, higher drug content can be loaded in a very small part of[77,78] packages. 3.10 nano preparation for treating eye diseases most ophthalmic products on the market are topical preparations for anterior administration. the biggest disadvantage is that only 5% of the injected dose reaches the anterior chamber. also, the dose penetrating the posterior chamber is small due to multiple and complex anatomical barriers of the eyeball. nano-sized ophthalmic drugs (figure 1) have the advantages of good solubility, large dissolution area, fast dissolution speed, strong biological adhesion, and strong corneal penetration. it is suggested that the particle size should be less than 10 μm to minimize the irritation to the eye structure and reduce the tear and bleeding of the drip dose, so as to improve the effectiveness of eye treatment. 3.11 nano suspension nano suspension is a submicron colloidal dispersion of pure drug particles in the external liquid phase. an important feature of nanosuspension is to increase the saturated solubility, so as to improve the dissolution rate of compounds. in this system, the drug is bound or dissolved in the structure, encapsulated or captured in the structure by binding to the matrix, and a general drug delivery system is generated, including microemulsion, liposome, niosomes, dendrimer, and cyclodextrin[79,80]. advantages of using nanoparticles include improved local delivery of macromolecules and low water-soluble molecules, such as glucocorticoids or cyclosporine, for the treatment of immune diseases affecting vision[81]. other unstable macromolecules, such as nucleic acids, are administered through nanoparticles, providing promising results for gene transfer in the treatment of retinopathy[82,83]. nanoparticle-mediated drug delivery increases the contact time between the administered drug and the target tissue, such as brimonidine, one of the traditional glaucoma treatment methods, or corticosteroids for the treatment of autoimmune uveitis[78,84]. some nano-formulations allow the nonsteroidal anti-inflammatory drug indomethacin to reach the posterior internal structure of the eye through a transmucosal pathway[85]. new applications include the use of gold nanoparticles to make the possibility of targeted drug delivery reach specific types of cancer, such as choroidal melanoma, and keep normal cells intact[86]. 3.12 contact lenses contact lenses are hard or soft polymer devices designed to directly adapt to the cornea to correct refractive abnormalities. in 1965, wichterle et al.[87] patented the idea of using hydrogel contact lenses as drug delivery devices. the patent refers to the inclusion of drugs in the lens hydration process to provide higher drug availability in use. wrapping drug-loaded nanoparticles in the polymer matrix of contact lenses is an effective strategy to prolong drug delivery. the incorporation of drugs is achieved by printing, simple immersion, and colloidal nanoparticles[88–90]. the diameter of nanoparticles must be very small and used in contact lenses to prevent particles from hindering users’ vision. therefore, it is necessary to delay the release of drugs in other ways. this can be achieved by combining the drug with the particles or dispersing the particles through separable chemical bonds so that the affinity of the drug to the particles is greater 73 than that to the surrounding lens material[89]. this method allows the sustainable release of drugs, which can be adjusted from hours to weeks according to the needs of patients, and allows the treatment of anterior segment lesions. different nanoparticles, lead liposomes and microemulsions have been patented, which contain pharmaceutical products and then loaded into contact lenses. liposomes are used in various drug delivery applications due to their high biocompatibility, transparent permanent lens, and several days of drug release. the initial release is due to the unpackaged drug in the lens. contact lenses loaded with releasing microemulsion will be administered for 4–8 days, and the initial peak is attributed to the unpackaged drug[89]. in 2013, jung et al. dispersed timolol nanoparticles in silica gel contact lenses for 30 days. preliminary studies in beagle dogs have shown promising results in treating glaucoma. the incorporation of nanoparticles into silicon hydrogels leads to the decrease of ion and oxygen permeability and the increase of modulus. the impact on each precursor is directly proportional to the charge of particles[74]. in 2018, maulvi et al. added gold nanoparticles into contact lenses to improve the absorption of timolol from drug solvent solution, and obtained satisfactory release kinetics in vivo, while maintaining the characteristics of contact lenses[91]. the device studied has excellent mechanical properties, and the researchers believe that this material is suitable for administration from daily reusable contact lenses. 3.13 intraocular implant ocular implants are a new treatment method for the controlled release of drugs by reducing the dose and increasing the drug load. in addition, the systemic side effects are lesser and closer to the target site, namely the posterior segment of the eye. biodegradable or non-biodegradable polymers can be used in eye implant systems. although biodegradable implants do not need to be removed after implantation into the eye, non-biodegradable implants require additional intervention to remove or fill the implant, which brings additional costs and intraoperative or postoperative surgical risks. the latest development of a biodegradable implant system is the env705™ implant envisia therapeutic agent and zordera[92] nanoporous membrane device. the invention discloses a nanoporous membrane skunk device, which comprises two layers of biodegradable waterproof films there are nanopores with the same diameter as the active material on one side, and only one drug molecule is allowed to flow out of the reservoir of each pore at a time. when injecting the device into the vitreous body, it is very thin, only 40 μ m in diameter, and the drug release order is close to 0. when most drugs are released, the polymer layer then degrades, eliminating the need to remove the device. this implant controls the release rate by adjusting the size of the hole and has been shown to last for 4 months. therefore, it may become the best biodegradable implant for the treatment of chronic retinal diseases[93]. a similar situation occurred when sirolimus was released to the posterior pole[94] through the same device. 3.14 clinical application in order to clearly understand the anatomy, histology, and physiology of different eye barriers, as well as the main nanoparticles developed in the research field, table 2 lists the most common eye diseases treated with nanotechnology at different action sites of eye tissue and the most influential eye diseases on vision. 4. expectation nanotechnology and nanomedicine are widely used in the field of ophthalmology. in many ways, the use of these devices and nano agents contributes to the bioavailability of drugs, allows diffusion through anatomical barriers which may reduce the side effects of the traditional use of topical ophthalmic drugs, and is likely to reduce invasive intervention to the posterior pole to some extent as well as reducing complications after using some drugs that need surgical treatment. finally, the benefits of drugs have been optimized and the negative effects have been reduced, opening a huge window within the scope of so-called personalized drugs, which likely require further research on people with 74 table 2. common eye diseases and treatment application pathology drugs/devices therapeutic target associated nanoparticles mechanism of np action keratitis ofloxacino, colirios, aciclovir[95] fluoroquinolone. inhibition of topoisomerase ii and iv. herpes polymerase dna inhibitor polyethylene glycol oxide and eudragit® in the form of microspheres acyclovir drug encapsulated by polylactic acid microspheres improve the bioavailability and controlled release of antibiotics. delay the degradation of acyclovir prodrug conjunctivitis tobramicina, colirios[96] inhibit the synthesis and binding of polypeptides in ribosomes. solid lipid np they increase the bioavailability of the corneal surface and help retain it in the conjunctival sac dry keratoconjunctivitis ciclosporina a, colirios[97] immune modulators that prevent t lymphocyte activation. chitosan sustained release carrier uveitis nano suspension of prednisone[52] subconjunctival prednisolone injection[52] intravitreal injection of infliximab[53] prostaglandin and leukopenia monoclonal antibody synthesis inhibitors that inhibit tnf-α activity. submicron colloidal carrier of hydrophobic drugs in surfactant stabilized medium sustained release and controlled release of drugs, as well as higher bioavailability and lower toxicity cataract lithium with metabolic activity[98] inhibit ros activity and regulate the level of h2o2 and lipid peroxidation in the surrounding environment. deposition of platinum nanoparticles by magnetron sputtering inorganic catalytic antioxidant glaucoma nano transporters: pilocarpine, timolol, carbonic anhydrase inhibitor, acetazolamida, dorzolamida, brinazolamida and brimonidina[99] silicone and hydrogel contact lenses hydrogel contact lenses containing thymolol[74] thymolol-containing contact lenses[91] wireless sensors[95] traditional treatment of non-selective β-blockers to reduce aqueous humor. continuous intraocular pressure monitoring. dendrimers, liposomes, nanocapsules, nanospheres, hydrogels pgt (triglyceride) np gold drug sustained release increases the loading and absorption of the thymus wet dmre hyaluronic acid implant: bevacizumab[100] nanopore devices: ranibizumab biodegradable[92] humanized monoclonal antibody against vascular endothelial growth factor. chitosan na sustained release vehicle drug release through nanopores diabetic retinopathy reservoir stimulation response device: nintedanib[101] vascular kinase inhibitor, blocking vegf receptor, platelet-derived growth factor receptor, fibroblast growth factor receptor polylactic acid glycolic acid microspheres and nitrobenzene monomer uv stimulates drug release retinitis pigmentosa vitreous fluorooctane sulfonate microglia activity attenuation. polyamide dendritic molecule drug sustained release retinoblastoma subconjunctival carboplatin[60] photodynamic therapy and vertepofina[102] alkylating agent, inhibiting dna replication, rna transcription, dano protein synthesis, selective neovascular endothelial cells, inducing apoptosis and autophagy. np dendritic polyamidoamine non-thermal laser activated liposome vertebral body. sustained release and controlled release of drugs reactive oxygen species production and cell death in tumor cells. 75 table 2. 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coo-cu-mgo catalyst for vapor phase simultaneous synthesis of ortho-chloroaniline and γ-butyrolactone from ortho-cholonitrobenzne and 1,4-butanediol hari prasad reddy kannapu1,2,3*, young-woong suh2,3*, veeralakshmi vaddeboina1, anand narani1, david raju burri1, seetha rama rao kamaraju1 1 catalysis, indian institute of chemical technology, hyderabad 500007, india. e-mail: kannapuhari@gmail.com/ hari83@hanyang.ac.kr 2 department of chemical engineering, hanyang university, seoul 133-791, republic of korea. e-mail: ywsuh@hanyang.ac.kr 3 research institute of industrial science, hanyang university, seoul 133-791, republic of korea abstract the article aims at developing an efficient and stable catalysts for simultaneous hydrogenation of o-chloronitrobenzene to o-chloroaniline and 1,4-butanediol dehydrogenation to γ-butyrolactone. a series of coo-cu-mgo catalysts, composed of 10 wt% of copper, various amount of cobalt loadings (1, 5 and 10 wt%) and remaining of mgo were developed by co-precipitation followed by thermal treatment. o-chloroaniline and γ-butyrolactone were the main products with high yield of 85% and 90%, respectively. the advantage of the coupling process is that the hydrogenation reaction was conducted without external hydrogen, demonstrating minimize the hydrogen consumption known as hydrogen economy route. from n2o characterization results, the high activity of 5coo-10cu-mgo was found that it has high amount of cu species (cu0/cu+1) which govern the stable activity and selectivity on time on stream study in presence of cobalt in cu-mgo. keywords: transfer hydrogenation; ortho-chloro aniline; γ-butyrolactone; atomic h2; basic sites; nano coo-cumgo 1. introduction owing to an enormous importance of aromatic halo amines in the chemical industry, specifically for synthesis of herbicides, dyes, drugs, and pesticides, synthesis of aromatic halo amines from halo nitrobenzene research has been gained a great attention in academia and industry point of view[1–9]. despite high demanding of this reaction, the hydrogenation of ortho-chloronitrobenzene (o-cnb) to ortho-chloroaniline (o-can) has been studied extensively over precious metals e.g., platinum, palladium, nickel, rhodium, ruthenium and iridium[1–9]. moreover, it has been mostly carried out under external hydrogen at an elevated temperatures and pressures which makes this process more complex and cost-ineffective in the industry point of view. further, dehalogenation and ring hydrogenation are common side reactions that lead to formation of common side reactions that lead to formation of aniline and cyclohexylamine particularly over pt, pd and ni catalysts. in this scenario, developing a highly selective and cost-effective cat2 alytic system still remains a challenge. generally, alcohols are highly active for dehydrogenation over supported copper catalysts[10–18]. 1,4-butanediol (bdo) is one of the alcohols that can make γ-butyrolactone (gbl) and two moles of hydrogen in its cyclodehydrogenation over copper-based catalysts. another important point is noticed that the gbl has been demonstrated to be involved in the synthesis of n-vinylpyrrolidone, n-methylpyrrolidone, herbicides, and rubber additives and more over it is a green solvent. commercially, the major production route for gbl is gas-phase dehydrogenation of bdo over supported copper metal catalysts, especially copper chromite catalysts, which are environmentally unacceptable. as described above, owing to the high commercial value of these products, these two reactions would have great impression. currently, coupling of hydrogenation and dehydrogenation[10–17] is a promising and an alternative method to the conventional hydrogenation. in this method, the above mentioned two reactions can be carried out simultaneously at a time over a same catalyst bed. copper-based catalysts were found to be outstanding for the coupling of hydrogenation and dehydrogenation reaction[10–16]. however, the activity and stability of catalysts mainly depends on the preparation of the catalysts. a numerous results documented in the literature have found that the addition of second metal oxide to base catalyst will result in the local composition, the size and structure of active species significantly affecting the catalytic activity and selectivity of supported metal catalysts[19]. it is generally agreed that for supported metal catalysts, highly dispersed active species can provide more active sites and thus confer the resulting catalysts with higher catalytic activity[20]. to best of our knowledge, selective o-cnb hydrogenation to o-can has not been reported using 1,4-butanediol (bdo) dehydrogenation over nano coo-cu-mgo. herein, we have investigated the vapor phase selective hydrogenation of o-cnb to o-can with dehydrogenation of bdo to γ-butyrolactone (gbl) over coo-cu-mgo catalysts. all the catalysts were developed by co-precipitation followed by thermal treatment. catalysts preparation, characterization using different analytical techniques such as bet surface area, n2o pulse chemisorption, xrd, tpr-h2, and tem analysis and activity in hydrogenation and dehydrogenation have been delineated. 2. experimental 2.1 preparation of catalysts an aqueous homogeneous mixed metal nitrate solution containing cu(no3)2•3h2o and mg(no3)2•6h2o was prepared followed immediate precipitation by drop-wise addition of 10% aqueous k2co3 solution at a ph of 9.0 under constant stirring at room temperature. the resultant mixed cu-mg precipitate (precipitate of 10 wt% cu-mgo catalyst, ppt1) has been separated under reduced pressure and washed thoroughly with hot distilled h2o until the complete removal of potassium ion. in a separate experiment, requisite amount of co(no3)2•6h2o aqueous solution has been precipitated at a ph of 9 with k2co3 solution under vigorous stirring. the obtained cobalt precipitate (ppt2) was filtered and washed thoroughly with hot distilled water. cu-mg precipitate (ppt1) and co precipitate (ppt2) were mixed in water under neutral condition and the resultant slurry was subjected to hydrothermal treatment at 373 k for 12 h followed by filtration with repeated washings. the precipitate was dried in oven at 393 k for 12 h followed by calcination at 723 k for 5 h. similar procedure has been adopted for the preparation of other coo promoted cu-mgo catalysts. the prepared catalysts were labeled as 1coo-10cu-mgo, 5coo-10cu-mgo, and 10coo-10cu-mgo, here the numerical value represents the loadings of co and cu by weight percentage. for example, 1coo-10cu-mgo represents a catalyst containing 1 wt% co, 10 wt% cu and the remaining balance mgo. 2.2 characterization techniques all the coo-cu-mgo catalysts were thoroughly characterized by using the following analytical techniques. the brunauer, emmett and teller (bet) surface area of all catalysts was measured by n2 physisorption after degasification at 473 k for 4 h, under liquid nitrogen adsorption at 77 k using 3 quadrasorb-si surface area analyzer (m/s. quantachrome instruments, usa). the surface properties of all coo-cu-mgo catalysts such as cu metal surface area (msa), cu dispersion (dcu), particle size (pcu) and surface coverage of cu atoms (scu ) were estimated by n2o pulse chemisorption on pre-reduced (553 k for 3 h) catalyst under dynamic conditions. the detailed procedure was described elsewhere[10–13]. the x-ray diffraction (xrd) patterns of both calcined and reduced catalysts were recorded on a miniflex diffractometer (m/s. rigaku instruments, japan) using ni filtered cu kα radiation in the 2θ range of 10°–80° at a scan rate of 2° min–1. the average crystallite size of copper was calculated using debye-scherrer principle. transmission electron microscopy (tem) was recorded using a phillips tecnai g2 fei f12 electron microscope. the reduction behavior of the catalysts was determined by temperature programmed reduction (tpr) studies on a home-made system as per the procedure described elsewhere[10]. the chns elemental analysis was carried out on elementar, model: variomicrocube to estimate the carbon content in the catalyst before and after the reaction. 2.3 activity studies a down flow fixed-bed reactor was used to investigate the activity of the coo-cu-mgo catalysts for the individual hydrogenation of o-cnb (dissolved in ethanol) to o-can and dehydrogenation of bdo to gbl as well as coupling of both reactions. for separate experiments, first tests were carried out on o-cnb hydrogenation. approximately, 500 mg of the catalyst powder (sieved to < 200 µm) diluted with an equal amount of quartz beads was charged to the reactor and supported on a quartz wool bed. the catalyst was reduced at 553 k for 3 h under hydrogen. then, the reactor was fed with o-cnb under h2 (18 ml∙min–1), using as a reducing gas. similarly, the dehydrogenation of bdo was conducted under n2 atmosphere. finally, the coupling of o-cnb hydrogenation and bdo dehydrogenation was performed at the molar ratio of 2:3 under nitrogen atmosphere. the liquid products, such as o-can and gbl were analyzed by using gc-17a (m/s. shimadzu, japan) with zb-wax capillary column equipped fid detector. the products were identified and analyzed by using gcms–qp5050 (m/s. shimadzu instruments, japan) equipped with zb-5 capillary column (25 m × 0.32 mm) supplied by m/s. j&w scientific, usa. 3. results and discussion 3.1 catalyst characterization 3.1.1 bet surface area studies table 1 presents bet surface area, crystalline phases of various cobalt loadings of cu-mgo catalysts both in calcined and reduced form. the surface area of the coo-cu-mgo catalysts is higher compared to mgo (42 m2∙g–1) alone. this indicates that addition of cobalt to cu-mgo increases the surface areas of cu-mgo. the bet surface area of catalysts increases with table 1. bet surface area and xrd results of coo-cu-mgo catalysts catalyst bet surface area (m2∙g–1) xrd phases cu0 (nm) reduced cu0 (nm) spent calcined reduced 1coo-10cu-mgo 78 cuo, mgo cu0, cu2 o,mgo 20 30.48 5co-10cu-mgo 88 cuo, mgo cu0, cu2 o,mgo 15 20.30 10coo-10cu-mgo 50 cuo, mgo cu0, cu2 o,mgo 13 26.48 increasing in coo loading and displayed maximum surface area (88 m2∙g–1) at 5 wt% coo loading and thereafter decreases with further increasing in the co content. it was found that hydrothermal treatments of fe/mgo catalysts transformed into lamella-like fe/ mg(oh)2 catalysts, resulted in increasing the specific surface areas[21]. since, in the present study, due to hydrothermal treatment, coo-cuo-mgo interacted species in large number is responsible for high surface area of 5coo-10cu-mgo catalyst. formation of an interacted phase (cuco3o4) between cu and co was reported to be appeared at a temperature of 573 k which was stable up to 1073 k[22]. such interacted phase might be accountable for the increasing trend of surface area and pore volume with the increase in co content up to 5 wt%. contrarily, beyond 5 wt% 4 co loading, a reverse trend was observed due to surface coverage by cobalt oxide. the crystallite size of copper in reduced and spent catalysts is calculated and depicted in table 1. it is obvious that the development of copper size influenced by the cobalt addition is inevitable. in the case of reduced catalysts copper crystallite size linearly minimized whereas in spent catalysts, only 5coo-10cu-mgo has stability and maintain lower crystallite size among other two catalysts. 3.1.2 x-ray diffraction studies (xrd) the xrd patterns of calcined catalysts are shown in figure 1. a low intense diffractions of cuo phase (d values of 2.52 at 2θ = 35.6°, 2.32 at 2θ = 38.78 and 2.53 at 2θ = 35.45°, icdd card no. 5-661) and high intensity of mgo (d values of 2.11 at 2θ = 42.82°, 1.49 at 2θ = 62.25° and 1.22 at 2θ = 78.30°, astm card no. 4-829) are observed in all cobalt loading catalysts. interestingly, no diffractions were noticed for coo oxide phase at all loadings which indicates amorphous form of cobalt species. it was reported that in 11% co-mgo catalyst, mgo is in amorphous form when it is calcined at 673 k and it is in crystalline phase above 973 k[23]. in addition, coo is formed after calcination at 773 k through the decomposition of co(no3)2 and might have diffused into the matrix of mgo or form a solid solution or oxidized to co2o3, which on reaction either with coo or with mgo to yield co3o4 or mgco2o4 [24]. figure 1. xrd patterns of calcined coo-cu-mgo catalysts. (a) 1coo-10cu-mgo; (b) 5coo-10cu-mgo; (c) 10coo-10cumgo. figure 2. xrd patterns of reduced coo-cu-mgo catalysts. (a) 1coo-10cu-mgo; (b) 5coo-10cu-mgo; (c) 10coo-10cumgo. xrd patterns of reduced (at 523 k in h2 flow) coo-cu-mgo catalysts are shown in figure 2. the cu0 phase with corresponding d values of 2.09 at 2θ = 43.25°, 1.81 at 2θ = 50.37° and 1.28 at 2θ= 73.99°, icdd card no. 4-836 is observed for all catalysts. but, the d values of cu0 and mgo are closer; therefore, the diffraction lines are not separated properly. as evidenced from the xrd results almost all cuo phases are reduced to cu0 or cu2o. it can also be seen that mgo phase decreased with addition of cobalt oxide representing the formation of amorphous mgco2o4 species particularly at 10 wt% coo. xrd pattern of 10coo-10cu-mgo catalyst revealed that cu0, cu2o and mgo crystallites were lower than other two catalysts. 3.1.3 n2o pulse chemisorption the estimated surface properties of cu-mgo with cobalt catalysts such as (i) number of surface copper sites, (ii) dispersion, (iii) metal surface area, and (iv) particle size are shown in table 2. n2o pulse chemisorption is a facile and proven technique for the estimation of metal area and allied surface properties of supported copper catalysts. even though co oxides are hard to get reduced at 523 k (the temperature at which the catalysts of the present investigation are reduced prior to n2o pulse chemisorption), small amount of lower oxidation states of co species might have resulted to participate in the decomposition of n2o thus giving 5 a chance to over estimation of cu dispersion[12]. as shown in table 2, the number active surface sites of copper catalysts are higher in 5coo-10cu-mgo. similarly, dispersion of active metal (copper plus cobalt) and active metal surface area (copper plus cobalt) are higher in all the cobalt promoted catalysts. contrarily, the particle size (copper plus cobalt) of metal is lower in all cobalt promoted catalysts. 5coo-10cu-mgo catalyst possesses a little higher surface density (copper plus cobalt) compared to other co promoted catalysts. the surface density of 5coo-10cu-mgo catalyst is nearly double than that of 1coo-10cu-mgo catalyst. 3.1.4 tem analysis figures 3a, b and c are copper particles with an appearance of dark contrasts as well as copper-free mgo particles with an appearance of light contrasts. at lower cobalt loadings the morphology of catalysts seems to be rod type structure, whereas at 10coo-10cu-mgo, catalyst regains its particle type structure. such a gathering of copper species in coo-cu-mgo catalysts has also been reported in the literature[21–25]. however, no obvious copper particles can be found in the hydrothermal-treated catalyst (figure 4). figure 3. tem images of coo-cu-mgo. (a) 1coo-10cu-mgo; (b) 5coo-10cu-mgo; (c) 10coo-10cu-mgo. figure 4. suggested mechanism of hydrothermal treatment and nanoparticle growth. 3.1.5 temperature programmed reduction (tpr) studies the reducibility of the catalysts can be determined by temperature programmed reduction with h2/ar mixture and results are depicted in figure 5. according to the tpr results of 10cu-mgo catalyst, the catalyst characterized by a single symmetric peak centered at a temperature maximum (tm) of 710 k[16]. the present results showed that the 1coo-10cumgo catalyst exhibits a single reduction, indicating the 1 wt% coo did not affect cu-mgo interactions. however, presence of a shoulder on an asymmetric peak is the indication of two-stage reduction: (i) cuo to cu0 and (ii) partial reduction of cuco2o4/ mgco2o4. in the case of 5coo-10cu-mgo catalyst, the high temperature signal corresponds to the reduction of interacted species formed between coo precursor and cuo. it is noteworthy to mention that the amount of cobalt oxide species are less at 5 wt% cobalt oxide compared with that of 10 wt% coo. the reaction between cuo and coo can make more cuco2o4 species in 5coo-10cu-mgo. whereas, the high cobalt oxide content in 10coo-10cu-mgo might have resulted to have less cuco2o4 and more mgco2o4 which are reduced at 850 k. the threestage reduction including copper oxide, cobalt oxides and spinals (cuco2o4 and mgco2o4) providing high acidity for 10coo-10cu-mgo. table 2. n2o pulse chemisorption results for different coo-10cu-mgo catalysts catalyst scu atoms × 10–19 (atoms g–1) d cu (%) metal surface area (m2∙g–1) particle size (nm) surface density scu/bet s.a 1coo-10cu-mgo 10 19 07 13 10/78 5coo-10cu-mgo 18 21 13 06 18/88 10coo-10cu-mgo 12 14 11 10 12/50 note: smetal = number of surface metal sites (cu); dmetal = dispersion of metal (cu); sametal = surface area of metal (cu); pmetal = particle size of metal (cu) 6 figure 5. tpr patterns of coo-cu-mgo. (a) 1coo-10cu-mgo; (b) 5coo-10cu-mgo; (c) 10coo-10cu-mgo. due to high cobalt oxide content in 10coo10cu-mgo, the reduction behavior is unlike to other two catalysts. it was reported that the peaks at 650 and 730 k were assigned to reduction of large crystalline co3o4 to coo and coo to co metal, respectively, but a shoulder peak at 850 k was attributed to the reduction of mgco2o4 [26]. as reported by wang and ruckenstein[24], co3o4 is getting reduced below 773 k while mgco2o4 below 973 k and the solid solution of co-mgo at higher than 1273 k temperature. the tpr results of this study are well collaborated with those reported in the literature[12]. the shifting of tmax to lower temperature in 5 wt% and 10 wt% co catalysts is an indication of interaction between co and cu species. it was reported that when a mixture of cu and co oxides were supported on al2o3, cobalt oxide reacts during calcination not only with cuo but also with al2o3, which leads to formation of the spinel coal2o4 [27]. when the same oxides were supported on non-interacted supports like silica, they interact to form the spinel cuco2o4 [28]. thus, the tpr patterns clearly indicate the presence of co oxide interacted species with both cu and mg-oxides. 3.2 activity studies 3.2.1 hydrogenation of ortho-chloronitrobenzene (o-cnb) the catalytic activity of coo-cu-mgo catalysts evaluated for the vapor phase selective hydrogenation of o-cnb to o-can at atmospheric pressure with h2/o-cnb required mole ratio at a reaction temperature in the range of 548 k–723 k and results are shown in figure 6. the conversion of o-cnb to o-can increases significantly with the increasing of temperature from 540 k to 680 k. thereafter conversion is nearly about 95% and 90% for 5coo-10cumgo and 1coo-10cu-mgo, respectively. precisely, 5coo-10cu-mgo has shown highest conversion about 98% at 720 k. but, the conversion of o-cnb to o-can is maximum of 63% at 673 k and reached to 50% at final temperatures over 10coo-10cumgo. these results demonstrated the effect of cobalt loadings on hydrogenation of o-cnb to o-can over coo-cu-mgo. the high activity of 5coo-10cumgo is associated to the presence of more number of surface active cu0 particles as observed from n2o pulse chemisorption. figure 6. effect of temperature on hydrogenation of ortho chloronitrobenzene over coo-cu-mgo catalysts. figure 7. time on studies over 5coo-10cu-mgo at 623 k for 10 h. 7 figure 7 shows the conversion of o-cnb to o-can at 623 k over a period of 10 h reaction. it is found that the activity of the catalyst is stable with 90% conversion up to 6 h and then reached to 85% at final hours. it is concluded that agglomeration of copper might responsible for loss of the activity. these results are good agreement with that the crystallite size of copper after reaction is bigger than reduced copper as shown in table 1. 3.2.2 dehydrogenation of 1,4-butanediol (bdo) figure 8 illustrates bdo conversion as a function of temperature. the dehydrogenation of bdo is an endothermic reaction; hence the conversion of bdo to gbl increases with the rise of temperature over coo-cu-mgo catalysts. the result shows that the maximum catalytic activity of coo-cu-mgo catalysts is noticed at 523 k, which is best temperature to obtain the gbl with high yields. in contrast, conversion of bdo is falling gradually for all catalysts except over 5coo-cu-mgo. the highest bdo conversion (> 97%) and gbl selectivity (99%) can be seen at 5 wt% coo loading cu-mgo. importantly, the selectivity towards gbl is all most same for all the catalysts. figure 8. effect of temperature on bdo dehydrogenation over coo-cu-mgo catalysts. figure 9. time on stream study of bdo dehydrogenation over 5co-10cm-h catalyst. based on above results, the stability of 5coo10cu-mgo for bdo to gbl was evaluated for 10 h at 523 k. the conversion of bdo is above 95% at beginning of the reaction whereas with increasing in the time the conversion declines slowly from 95% to 75%. interestingly, selectivity to gbl remains constant up to 10 h (figure 9). the deactivation of the catalyst is mainly due to agglomeration of copper particles during course of the reaction. 3.2.3 coupling of o-chloronitrobenzene hydrogenation and 1,4-butanediol dehydrogenation figure 10. time on stream study coupling of bdo dehydrogenation and o-cnb hydrogenation over 5co-10cm-h catalyst. the independent reactions: (i) hydrogenation of o-cnb to o-can and (ii) dehydrogenation of bdo to gbl provide the best catalyst and temperature to conduct the titled reactions. the mole ratio of bdo 8 versus o-cnb is 1.5:1, which is an optimum for coupling process and results are shown in figure 10. the reaction results clearly demonstrate that conversions of bdo and o-cnb are 90% and 85%, respectively, in early hours. when reaction time increases, the conversion of both reactions linearly dropped which could be attributed to the agglomeration of copper and finally reached to 54% and 50% with 99% selectivity of their corresponding products. surprisingly, the individual hydrogenation of o-cnb at 523 k with 1.5 moles of external hydrogen is very low (< 5%). but, in coupling process, hydrogenation of o-cnb with dehydrogenation of bdo was substantially increased from 5% to 90%. this enhancement of o-cnb conversion in the coupling reaction is ascribed to the active role of in-situ production of hydrogen atom from bdo to gbl reaction which gets instantaneously utilized[10–18]. the deactivation of catalysts may be due to agglomeration copper. the color of the catalyst physically changed to black, which further indicates the coke deposition on the catalyst during course of the reaction. 4. conclusions the different amount of coo incorporated 10cu-mgo prepared by co-precipitation followed by hydrothermal treatment has shown excellent catalytic activity compared to unpromoted cu-mgo catalyst. the best catalytic activity of 5co-10cu-mgo is due to the addition of cobalt increased number of surface copper atoms and decreased the reduction ability of copper as observed from tpr results. contrarily, in 10coo-10cu-mgo the high amount of cobalt oxide covered active copper sites. deactivation of catalyst in coupling reaction is mainly due to agglomeration as well the coke formation during the course of reaction. in summary, two industrially important reactions can be carried out over coo-cu-mgo catalyst simultaneously. conflict of interest the authors declare that they have no conflict of interest. acknowledgements authors gratefully thank csir-ugc (india) for the financial support. this research was also financially supported by basic science research program through the national research foundation of korea (nrf) funded by the ministry of education (nrf-2016r1a6a1a03013422) and new & renewable energy core technology program of the korea institute of energy technology evaluation and planning (ketep), granted financial resource from the ministry of trade, industry & energy, 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science 2000; 157: 159. microsoft word can-4671 characterization and application of nanomaterials 2024, 7(1), 4671. https://doi.org/10.24294/can.v7i1.4671 1 article influence of green synthesized aluminum oxide nanoparticle concentration on wear and coefficient of friction of vegetable oil-based lubricants stephen yebosoko tsado1, tijani jimoh oladejo2, uzoma gregory okoro1, daniel ipilakyaa tertsegha3, ibrahim ogu sadiq1, joseph abutu4, emmanuel ogo onche5, antwi afari acheampong6, alhassan sullaiman6, ebenezer adu kyeremeh6, sunday albert lawal1,6,* 1 department of mechanical engineering, federal university of technology minna, minna 920101, nigeria 2 department of chemistry, federal university of technology minna, minna 920101, nigeria 3 department of mechanical engineering, joseph sarwuan tarka university, makurdi 970101, nigeria 4 department of mechanical engineering, taraba state university, jalingo 660213, nigeria 5 department of mechanical engineering, university of abuja, giri 900105, nigeria 6 department of mechanical engineering, university of mines and technology tarkwa, tarkwa 000031, ghana * corresponding author: sunday albert lawal, lawalsunday@futminna.edu.ng abstract: green manufacturing is increasingly becoming popular, especially in lubricant manufacturing, as more environmentally friendly substitutes for mineral base oil and synthetic additives are being found among plant extracts and progress in methodologies for extraction and synthesis is being made. it has been observed that some of the important performance characteristics need enhancement, of which nanoparticle addition has been noted as one of the effective solutions. however, the concentration of the addictive that would optimised the performance characteristics of interest remains a contending area of research. the research was out to find how the concentration of green synthesized aluminum oxide nanoparticles in nano lubricants formed from selected vegetable oils influences friction and wear. a bottom-up green synthesis approach was adopted to synthesize aluminum oxide (al2o3) from aluminum nitrate (al(no3)3) precursor in the presence of a plant-based reducing agent—ipomoea pes-caprae. the synthesized al2o3 nanoparticles were characterized using tem and xrd and found to be mostly of spherical shape of sizes 44.73 nm. al2o3 nanoparticles at different concentrations— 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, and 1.0 wt%—were used as additives to castor, jatropha, and palm kernel oils to formulate nano lubricants and tested alternately on a ball-on-aluminum (sae 332) and low-carbon steel disc tribometer. all the vegetable-based oil nano lubricants showed a significant decrease in the coefficient of friction (cof) and wear rate with ball-on(aluminum sae 332) disc tribometer up to 0.5wt% of the nanoparticle: the best performances (ecof = 92.29; ewr = 79.53) came from al2o3-castor oil nano lubricant and al2o3-palm kernel oil; afterwards, they started to increase. however, the performance indices displayed irregular behaviour for both cof and wear rate (wr) when tested on a ball-on-low-carbon steel disc tribometer. keywords: nanoparticles; green synthesized; wear; coefficient of friction; lubricants 1. introduction in recent times, vegetable oils have been identified as a favorite substitute for mineral oils as base oils in lubricant formulations. this is because vegetable oils possess high biodegradability and lubricity and, hence, can return to nature upon consumption after their useful lives. this property of vegetable oils makes them environmentally friendly alternatives to mineral oil-based lubricants. researchers have carried out studies using vegetable oils as the base oil for lubricants while using citation tsado sy, oladejo tj, okoro ug, et al. influence of green synthesized aluminum oxide nanoparticle concentration on wear and coefficient of friction of vegetable oil-based lubricants. characterization and application of nanomaterials. 2024; 7(1): 4671. https://doi.org/10.24294/can.v7i1.4671 article info received: 18 february 2024 accepted: 26 march 2024 available online: 18 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 4671. 2 various nanoparticle additives to improve its tribological performance [1–3]. vegetable oils comprise the chemical composition of molecules of triacylglycerol made up of esters derived from glycerol and long chains of polar fatty acids [4]. other vegetable oils are also composed of esters of glycerin and long-chain fatty acids (triglycerides), which have molecular structure with three long-chain fatty acids attached at the hydroxyl groups via ester linkages [5]. the chemical structure of a typical vegetable oil is shown in figure 1. figure 1. chemical structure of triglyceride of a typical vegetable oil [5]. other parameters that are determined through the process of formulating the oilbased lubricants are the acid value, saponification, and free fatty acid of the oil [6,7]. nanoparticles ranging between 1 nm and 100 nm have all three external dimensions in the nanoscale, and their longest and shortest axes do not have a significant difference, typically being a factor of at least 3. some examples are nonporous pd nps (0d), graphene nanosheets (2d), ag nanorods (1d), polyethylene oxide nanofibers (1d), urchin-like zno nanowires (3d), and wo3 nanowire network (3d) [8]. nanoparticles demonstrate desirable physical and optical characteristics such as shape and size, which makes them suitable to confine their electrons and produce quantum effects. these properties help in a complete description of its behavioural and operational functionalities, which deal with the size, shape, surface properties, crystallinity, and dispersion state [9]. the use of nanomaterials as additives to oil-base lubricants to produce nano lubricants with improved tribological properties has been gaining research attention in the industry in recent times [10]. this is essentially a result of their anti-wear, extreme pressure, and friction-modifying properties. although there are different types of nanomaterials used in the formulation of nano lubricants, about 72% of nano lubricants are formulated using metal-containing nanomaterials as lubricant additives [11]. among the various metallic nanoparticles that could be used as additives to lubricants, the cu nanoparticles have received wide research attention for their superior performance in comparison with other metallic nanoparticles [12]. metal nanoparticles are produced by the addition of reducing agents, while metal oxide nanoparticles are manufactured by the addition of oxidizing/precipitating agents during their synthesis [13]. generally, when compared with metal-containing nanoparticles, the metal oxide nanoparticles are larger in size. metal oxide nanoparticles have been shown to improve the viscosity of lubricants at low temperatures and the rolling effect of the lubricant at high temperatures, with characterization and application of nanomaterials 2024, 7(1), 4671. 3 deposition of the metal oxide nanoparticles on the interacting surfaces leading to improved anti-wear performance [11]. utilizing metal oxide nanoparticles will improve the nano lubricant properties. these properties include the nanoparticle size, morphology/shape, surface functionalization, and nanoparticle concentration. in synthesizing the nanoparticles, the green synthesis method was used for this work. this is a bottom-up approach of the two methods of synthesizing. the other method, the top-down approach, emphasizes the preparation of nanoparticles from the process of breaking down complex metal ions through physical, chemical, or thermal methods [14], which is more costly to undertake. several nanoparticles have been used as additives to vegetable oils to investigate their effect on the tribological properties of lubricating oils. the major parameters varied are the size, shape, and concentration of the nanoparticles. among other nanoparticles investigated, al2o3 nanoparticles, a metal oxide nanoparticle, have the potency of improving the tribological performance of base oils. also, most nanoparticles investigated are chemically synthesized, and this becomes a subject of interest and consideration when considering potential impacts on the environment on a large scale. therefore, the investigation of the tribological performance of green synthesized al2o3 nanoparticles as additives to vegetable oils for the development of nano lubricants as alternatives to mineral oil-based lubricants holds considerable potential in eco-friendly lubrication. 2. materials and methods the materials used in the study are vegetable oils, aluminum oxide (al2o3) nanoparticles, aluminum nitrate (al(no3)3) salt, beach morning glory (stem) (ipomoea pes-caprae), aluminum sae 332 disc, low carbon steel disc, and distilled water. the vegetable oils are palm kernel oil (pko), jatropha oil, and castor oil, and they were all locally sourced off the shelf. the aluminum oxide nanoparticles were synthesized based on the green synthesis method, as summarized in figure a1. the aqueous leave extract (ale) was produced based on the hot extraction method as presented in figure 2. this involves mixing a milled leaf in distilled water at a ratio 1 g to 20 ml in a beaker and heating the mixture to a temperature range of 60–80 ℃ for 1 h. the mixture is allowed to cool to room temperature and afterwards filtered using a whatman-grade 540 filter paper. the ale was further used in the synthesis of al2o3 nanoparticles using a 0.1 m al(no3)3 solution as a precursor. the extracts were used to synthesize al2o3 nanoparticles within 5 min of extraction. in synthesising the al2o3 nanoparticles, an aqueous solution of 0.1 m al(no3)3 was prepared by dissolving 4.8286 g of the salt into 200 ml of distilled water. the mixture was stirred for 5 min at room temperature using the magnetic stirrer at a stirring speed of 300–320 rpm to ensure proper dissolution of all salt particles in the mixture. using a ratio of 1:4 for the aqueous solution and plant extract, respectively, the plant extract was poured into the beaker with the stirring bar and placed on the magnetic stirrer. the temperature of the stirrer was set at 60 ℃, and the speed was set at 320 rpm. uv-visible adsorption spectra analysis was conducted to determine the wavelength and absorption of the synthesized mixture using the uv-vis spectrophotometer. the result of the analysis gave the size distribution of the al2o3 nanoparticles. synthesized al2o3 nanoparticles characterization and application of nanomaterials 2024, 7(1), 4671. 4 were further subjected to drying and calcination in order to obtain dried and powdered nanoparticles. the synthesized mixture was centrifuged at a rotational speed of 8000 rpm to remove excess moisture content and impurities that may be less dense compared to the precipitate using a high-speed refrigerated centrifuge. the resulting mixture was further subjected to freeze drying using a freeze dryer. the freeze dryer removed moisture content and produced the powdered al2o3 nanoparticles. furthermore, in order to get rid of residual moisture content and impurities, the dried nanoparticles were calcined at a temperature of 700 ℃ for 1 h using an electric oven. figure 2. plant extraction process. the characterization of the al2o3 nanoparticles was done based on transmission electron microscopy (tem) to determine the particle size distribution and morphology of the synthesized al2o3 nanoparticles and x-ray diffraction analysis (xrd) to determine the structure of the synthesized al2o3 nanoparticles. vegetable oils comprising of palm kernel oil, jatropha oil, and castor oils at 0 wt% concentration of nanoparticles were characterised to serve as control experiments of the vegetable oils before addition of the nanoparticles. the properties examined are dynamic viscosity @24 ℃ (mpa/s), dynamic viscosity @40 ℃, dynamic viscosity @100 ℃, kinematic viscosity @40 ℃ (m2/s), kinematic viscosity @100 ℃, density (g/cm3), specific gravity, flash point (℃), fire point (℃), pour point (℃), cloud point, smoke point, acid value (koh/g), saponification (koh/g), and free fatty acids (ffa). the oils were tested using a rotor labeled “3” at a rotational speed of 60 rpm. to determine the smoke point, flash point, and fire point, a volume of the oil sample was poured into a 5 ml crucible, placed on a heating element, and temperatures were taken at smoke, flash, and fire conditions. furthermore, cloud and pour points were determined using a freezer with temperatures taken at cloud and pour conditions. the acid value, saponification, and free fatty acid of the oils were determined by the use of 25 mol of methanol that was prepared, and n-hexane was added in a ratio of 1:1. the study adopted the two-step method in the preparation of the lubricants. the nanoparticles synthesized and characterized were dispersed into the base oil. the base vegetable oils used are palm kernel oil (pko), jatropha oil (jo), and castor oil (co). 50 g of nano lubricants were prepared by dispersing dry powder nanoparticles of size 44.73 nm at concentrations of 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, and 1.0 wt% into the vegetable oils as shown in table 1. the mixture was stirred for 10 min at a speed of 300–320 rpm and a stirring temperature of 60–80 ℃ using a magnetic stirrer. the characterization and application of nanomaterials 2024, 7(1), 4671. 5 nanoparticles were weighed using a chemical weighing balance. a total of 18 samples were prepared, including control samples. table 1. mixture ratio for preparation of nano lubricants. nanoparticle concentration (g) pko (g) jo (g) co (g) 0 50 50 50 0.05 49.95 49.95 49.95 0.15 49.85 49.85 49.85 0.25 49.75 49.75 49.75 0.35 49.65 49.65 49.65 0.5 49.5 49.5 49.5 the concentration was computed using the equation (1). mass (wt%) = mass of solute (nps) mass of solution (oil + nps) × 100% (1) the tribological test for the formulated nano lubricants was done using a ball-ondisc tribometer to determine the coefficient of friction (cof) and wear rate of the nano lubricants formulated. the parameters for the tribological tests used are shown in table 2. a total of 38 metal disc samples of 30 mm diameter each were prepared from aluminum (sae 332) and low-carbon steel. the samples were cast from the waste piston and engine block. they were further machined into discs of 30 mm diameter, polished, and etched to improve the surface finishing. the chemical composition of aluminum sae 332 and low-carbon steel discs is presented in tables 3 and 4, respectively. table 2. parameters for the tribological tests. s/n parameter value 1 track radius 5 mm 2 linear speed 10 cm/s 3 normal load 8 n 4 run time 1500 s 5 linear distance 150 m 6 acquisition rate 10 hz 7 dimension of ball 6 mm 8 disc diameter 30 mm 9 temperature 29 ℃ 10 humidity 55% 11 stop condition 4775 laps table 3. chemical compositions of aluminum sae 332 disc. element si cu mg al % composition 9.5 3.0 1.0 86.5 characterization and application of nanomaterials 2024, 7(1), 4671. 6 table 4. chemical compositions of low carbon steel disc. element c si mn p s cr mo ni cu co fe % composition 0.105 0.034 1.450 <0.005 <0.127 0.082 0.005 0.208 0.336 0.023 97.757 to identify the phase of the al2o3 nanoparticle samples, the result of the xrd analysis was compared with the positions and intensities of the already known crystallographic structure of the same material. in the process of characterization of the vegetable oils, the total quantity of naoh added to the solution to turn it purple-like was observed as recorded as the titer value. the titer value was substituted into equation (2) to determine the acid value. half the acid value is the ffa, as shown in equation (3). the reverse order of this process is used to determine the saponification value. the value of the density was obtained using a specific gravity bottle. the mass and volume of the oil were obtained, and the density was obtained using equation (4). in the determination of the coefficient of friction (cof), the value of the cof was computed by the instrumx software based on the principle of equation (5). this value was recorded for each test carried out. the scar made on the aluminum sae 332 and low-carbon steel discs represented the wear track for the determination of the wear rate. the diameter of the outer and inner wear tracks is measured. the difference gives the wear volume, which is used to compute the specific wear rate using equation (6). the size of the diameter is indicative of the lubricant’s ability to resist wear. the efficiencies of the nano lubricants were determined by comparing performance and results obtained for the coefficient of friction and the wear rate with the results obtained for the control samples (i.e., samples of vegetable oils at 0% nanoparticle concentration). equations (7) and (8) were used to ascertain the efficiency of the prepared and tested nano lubricants for the coefficient of friction and wear rate, respectively. acid value = titer value × concentration of naoh × molar mass of naoh mass of oil (2) ffa = acid value 2 (3) density = mass volume (4) cof = 𝑇√6 2𝑊𝑟 (5) specific wear rate = wear volume load × sliding distance (6) 𝜀 = cof − cof cof × 100% (7) 𝜀 = wr − wr wr × 100% (8) where: t = frictional torque (kg/mm); w = applied load (kg), r = distance from centre of contact surface on the lower ball to the rotation axis (mm), 𝜀 = efficiency of lubricant for coefficient of friction, 𝜀 = efficiency of lubricant for wear rate, cof = coefficient of friction of nano lubricant, cof = coefficient of friction of control sample, wr = wear rate of nano lubricant, wr = wear rate of control sample. characterization and application of nanomaterials 2024, 7(1), 4671. 7 3. results and discussion the results of the phytochemical screening of plant extract for green synthesis revealed a high presence of tannins, saponins, flavonoids, glycosides, and alkaloids. this is presented in table 5. (++ imply high presence of phytochemicals in the plant extract.) figure 3 shows the one-factor graphs, whose plots indicate the effect of each parameter varied on the size of the synthesized al2o3 nanoparticles. the parameters are volume of plant extract (a), volume of aqueous solution (b), temperature (c), speed (d), and time (e). the graphs show that only volume of the extract and volume of the solution have significant impact on the particle size. table 5. phytochemical screening of ipomoea pes-caprae. plant metabolite extract content tannins ++ flavonoids ++ saponins ++ glycosides ++ alkaloids ++ figure 3. one-factor graphs (a–e). the result of the uv-vis analysis is shown in figure 4. a strong and conspicuous absorption peak is observed at 283.00 nm. this confirms the formation of al2o3 nanoparticles in agreement with selma et al. [15] the result of the nanosizing shows peaks at 9.142 nm, 44.73 nm, and 1210.00 nm corresponding to 10.9% vol, 88.9% vol, and 0.2% vol, respectively, of the synthesized nanoparticles, as shown in figure 5. the result of the nanosizing indicates a close correlation with the predictions from the characterization and application of nanomaterials 2024, 7(1), 4671. 8 doe using design expert software, with the various doe responses as shown in table 6, which compares the results of the predicted and the actual results of the experiment. the result shows the predicted mean from the doe to be 44.78 nm, while the experimented mean is 44.73 nm from the nanosizing analysis. a percentage difference of 0.12% was recorded. figure 4. uv-vis analysis of synthesized al2o3 nanoparticles. (a) (b) figure 5. (a) al2o3 nanoparticles size distribution (nanosizing); (b) al2o3 nanoparticles size distribution by intensity. table 6. comparison of predicted and experimented responses. response predicted mean experimental mean difference % difference particle size 44.784 nm 44.73 nm 0.054 0.12 the characterization of al2o3 nanoparticles through the transmission electron microscopy (tem) micrographs shows spherically shaped nanoparticles with size distributions of 2 nm as shown in figure 6a, 20 nm in figure 6b, and 50 nm as shown in figure 6c. furthermore, figure 6d presents the selected area electron diffraction (sead), which shows bright continuous diffraction rings, indicating the formation of amorphous al2o3 nanoparticles. characterization and application of nanomaterials 2024, 7(1), 4671. 9 (a) (b) (c) (d) figure 6. tem micrographs at (a) 2 nm; (b) 20 nm; and (c) 50 nm; and (d) saed. figure 7 shows the x-ray diffraction (xrd) analysis, with observed peaks recorded over a wide range of bragg angle 2θ (20° ≤ 2θ ≤ 80°). this confirmed the formation of al2o3 nanoparticles by the transformation of al to al2o3 using al(no3)3 salt as precursor and ipomoea pes-caprae plant extract as reducing agent. the results of the tribological test for cof of the nano lubricants on low-carbon steel and aluminum sae 332 discs are presented in figures 8–10. all nano lubricants of castor oil, jatropha oil and pko have significantly lower cof on aluminum sae 332 discs compared to pko without al2o3 nanoparticles. figure 8 (l) shows that nano lubricants with 0.5 wt% and 1.0 wt% have significantly lower cof on aluminum sae 332 discs compared to castor oil without al2o3 nanoparticles. figure 7. xrd pattern of al2o3 nps using ipomoea pes-caprae extract. figure 8. cof of castor oil (l) and jatropha oil (r) on aluminum sae 332 discs. characterization and application of nanomaterials 2024, 7(1), 4671. 10 figure 9. cof of palm kernel oil on aluminum sae 332 discs (l) and cof of castor oil on low carbon steel disc (r). figure 10. cof of jatropha oil on low carbon steel disc (l) and cof of pko on low carbon steel disc (r). figure 8 (r) shows that nano lubricant with 0.3 wt% al2o3 nanoparticles concentration gave the most desirable result with cof of 0.030 against a cof of 0.090 at 0 wt% concentration. figure 9 (l) shows that nano lubricant with 0.5 wt% al2o3 nanoparticles concentration gave the most desirable result with cof of 0.066 against a cof of 0.098 at 0 wt% concentration and figure 8 (r) shows a significantly lower cof was observed at 0.5 wt% al2o3 nanoparticles, beyond which the nano lubricant demonstrated higher cof compared to castor oil at 0 wt% al2o3 nanoparticles. figure 10 (l) shows that the nano lubricants demonstrated significantly higher cof compared to jatropha oil without al2o3 nanoparticles, making jatropha oil demonstrate better performance in inhibiting friction on low-carbon steel discs compared to samples with al2o3 nanoparticle additives. figure 9 (r) shows nano lubricant with 0.3 wt% demonstrated significantly lower cof on low-carbon steel discs compared to castor oil without al2o3 nanoparticles. the results of the tribological test for wear rate of the nano lubricants on low-carbon steel and aluminum sae 332 discs are presented in figures 11–13. figure 11. wear rate of castor oil (l) and jatropha oil (r) on aluminium sae 332 discs. characterization and application of nanomaterials 2024, 7(1), 4671. 11 figure 12. wear rate of palm kernel oil on aluminium sae 332 discs (l) and wear rate of castor oil on low carbon disc (r). figure 13. wear rate of jatropha oil (l) and palm kernel oil (r) on low carbon steel disc. figure 11 (l) shows that the nano lubricant with 0.5 wt% demonstrated a slightly lower wear rate on aluminum sae 332 discs compared to castor oil without al2o3 nanoparticles. figure 11 (r) shows that the addition of al2o3 nanoparticles at 0.1 wt% and 0.5 wt% concentrations significantly increased the wear rate, and the nano lubricant with 1.0 wt% al2o3 nanoparticle concentration demonstrated a wear rate of 0.004727 mm3n−1m−1, compared to the wear rate of 0.005064 mm3n−1m−1 at 0 wt% concentration. figure 12 (l) shows that nano lubricant with a 0.5 wt% al2o3 nanoparticle concentration gave the most desirable result with a wear rate of 0.003915 mm3n−1m−1, compared to a wear rate of 0.006037 mm3n−1m−1 at a 0 wt% concentration. figure 12 (r) shows that all nano lubricant formulated demonstrated a higher wear rate compared to castor oil without al2o3 nanoparticles, with a wear rate of 0.002627 mm3n−1m−1. figure 13 (l) shows a steady reduction in wear rate upon addition of al2o3 nanoparticles to jatropha oil was observed from 0.1 wt% to 0.5 wt%, demonstrating the lowest wear rate. figure 13 (r) shows that all nano lubricant formulated demonstrated a higher wear rate compared to castor oil without al2o3 nanoparticles with a wear rate of 0.004191 mm3n−1m−1. on the efficiency of the base oils and nano lubricants, the efficiency of castor oil, jatropha oil, and pko with nano lubricants on cof on aluminum sae 332 discs has the nano lubricant with 0.5 wt% al2o3 nanoparticles had the highest efficiency with 92.29%, 0.3 wt% al2o3 nanoparticles recorded the highest efficiency of 92.54% and 0.5 wt% al2o3 nanoparticles recorded the highest efficiency of 83.58%, respectively. the computation of the efficiency of oils and the nano lubricants with castor oil, jatropha oil, and pko as base oils on cof using a low-carbon steel disc has the nano lubricant with 0.5 wt% al2o3 nanoparticles recording the highest efficiency of 87.80%, while jatropha oil without al2o3 nanoparticle additives recorded the highest efficiency of 89.43%, with the closest nano characterization and application of nanomaterials 2024, 7(1), 4671. 12 lubricant recording an efficiency of 81.30 at 0.5 wt% al2o3 nanoparticle concentration and the nano lubricant with 0.3 wt% al2o3 nanoparticles recorded the highest efficiency of 80.49% for pko. the computation of the efficiency of castor oil, jatropha oil, and pko and the nano lubricants with the oils as base oils on wear rate using aluminum sae 332 discs has the nano lubricant with 0.5 wt% al2o3 nanoparticles had the highest efficiency with 76.20% for the castor oil, while the nano lubricant with 1.0 wt% al2o3 nanoparticles recorded the highest efficiency of 75.29% jatropha oil and the nano lubricant with 0.5 wt% al2o3 nanoparticles recorded the highest efficiency of 79.53% for pko. the computation of the efficiency of the oils and the nano lubricants with castor oil without al2o3 nanoparticle additive recorded the highest efficiency of 64.65%, while jatropha oil with 0.5 wt% al2o3 nanoparticle concentration recorded the highest efficiency of 47.65%, and for pko, all nano lubricant had lower efficiency compared to pko without al2o3 nanoparticle additives with an efficiency of 43.61%. 4. conclusion al2o3-castor oil nano lubricant significantly reduced cof on aluminum sae 332 and low-carbon steel from 0.084 without al2o3 nanoparticles to 0.031 and from 0.084 to 0.060 at 0.5 wt%, respectively. al2o3—jatropha nano lubricant reduced cof on aluminum sae 332 from 0.090 without al2o3 nanoparticles to 0.030 when al2o3 nanoparticles were added at 0.3 wt%. on low-carbon steel, an increase in cof was recorded across all concentrations of al2o3 nanoparticles. similarly, al2o3—palm kernel oil on aluminum sae 332 demonstrated a reduction in cof from 0.098 to 0.066 at concentrations of 0.5 wt%. on low-carbon steel, the cof mostly increased. the test for the wear rate of al2o3—castor nano lubricant indicated an increase in wear rate on aluminum sae 332 and low-carbon steel. similarly, al2o3—jatropha nano lubricant on aluminum sae 332 demonstrated an increase in wear rate. however, on lowcarbon steel, the wear rate reduced from 0.007265 without al2o3 nanoparticles to 0.003891 at 0.5 wt% al2o3 nanoparticle additives. al2o3—pko nano lubricant on aluminum sae 332 demonstrated a reduction in wear rate from 0.006037 without al2o3 nanoparticles to 0.003915 at 0.5 wt% of al2o3 nanoparticles. on low-carbon steel, however, the wear rates increased across all concentrations. author contributions: conceptualization, syt, tjo and sal; methodology, syt, and tjo; software, ugo; validation, ja, ios and eoo; formal analysis, dit and aaa; investigation, as and eak; resources, sal; data curation, sal and ugo; writing—original draft preparation, syt; writing—review and editing, sal and ugo; visualization, ja; supervision, sal and tjo; project administration, sal; funding acquisition, syt and sal. all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. references 1. dai w, kheireddin b, gao h, et al. roles of nanoparticles in oil lubrication. tribology international. 2016; 102: 88-98. doi: 10.1016/j.triboint.2016.05.020 characterization and application of nanomaterials 2024, 7(1), 4671. 13 2. ghaednia h, hossain ms, jackson rl. tribological performance of silver nanoparticle–enhanced polyethylene glycol lubricants. tribology transactions. 2016; 59(4): 585-592. doi: 10.1080/10402004.2015.1092623 3. hwang y, lee jk, lee jk, et al. production and dispersion stability of nanoparticles in nanofluids. powder technology. 2008; 186(2): 145-153. doi: 10.1016/j.powtec.2007.11.020 4. mohan d, pittman cu, bricka m, et al. sorption of arsenic, cadmium, and lead by chars produced from fast pyrolysis of wood and bark during bio-oil production. journal of colloid and interface science. 2007; 310(1): 57-73. doi: 10.1016/j.jcis.2007.01.020 5. lawal sa, choudhury ia, nukman y. application of vegetable oil-based metalworking fluids in machining ferrous metals—a review. international journal of machine tools and manufacture. 2012; 52(1): 1-12. doi: 10.1016/j.ijmachtools.2011.09.003 6. salimon j, abdullah bm, salih n. saponification of jatropha curcas seed oil: optimization by d-optimal design. international journal of chemical engineering. 2012; 2012: 1-6. doi: 10.1155/2012/574780 7. mahesar sa, sherazi sth, khaskheli ar, et al. analytical approaches for the assessment of free fatty acids in oils and fats. anal methods. 2014; 6(14): 4956-4963. doi: 10.1039/c4ay00344f 8. jeevanandam j, barhoum a, chan ys, et al. review on nanoparticles and nanostructured materials: history, sources, toxicity and regulations. beilstein journal of nanotechnology. 2018; 9: 1050-1074. doi: 10.3762/bjnano.9.98 9. griffis c, wilson t, schneider j, pierpont p. unmanned aircraft system propulsion systems technology survey. available online: https://commons.erau.edu/cgi/viewcontent.cgi?article=1042&context=publication (accessed on 2 january 2024). 10. trofymov i, svyryd m, matveyeva o, sydorenko o. influence of electromagnetic treatment of fuels and oils on the formation of wear resistance of friction pairs. in: selected aspects of providing the chemmotological reliability of the engineering. national aviation university; 2019. pp. 141-153. doi: 10.18372/38236 11. dai c, zhang a, liu m, et al. hollow alveolus-like nanovesicle assembly with metal-encapsulated hollow zeolite nanocrystals. acs nano. 2016; 10(8): 7401-7408. doi: 10.1021/acsnano.6b00888 12. kart hh, yildirim h, ozdemir kart s, et al. physical properties of cu nanoparticles: a molecular dynamics study. materials chemistry and physics. 2014; 147(1-2): 204-212. doi: 10.1016/j.matchemphys.2014.04.030 13. rastogi a, zivcak m, sytar o, et al. impact of metal and metal oxide nanoparticles on plant: a critical review. frontiers in chemistry. 2017; 5. doi: 10.3389/fchem.2017.00078 14. nadaroğlu h, güngör aa, nce s. synthesis of nanoparticles by green synthesis method synthesis of nanoparticles by green synthesis method. international journal of innovative research and reviews. 2017; 1(1): 6-9. 15. selma ma, sarya dma, wafaa kk. characterization of laser ablated nanostructured al2o3/p-solar cells. iraqi journal of applied physics. 2015; 11(1): 29-32. characterization and application of nanomaterials 2024, 7(1), 4671. 14 appendix figure a1. graphical abstract. characterization and application of nanomaterials (2019) volume 2 issue 1 doi:10.24294/can.v2i1.541 1 improved mathematical model of polluted insulators nonlinear behaviour under ac voltage based on experimental tests mousalreza faramarzi palangar1, mohammad mirzaie2 1,2faculty of electrical and computer engineering, babol university of technology, babol, iran. r_faramarzi@stu.nit.ac.ir abstract in this paper, an improved mathematical model for flashover behavior of polluted insulators is proposed based on experimental tests. in order to determine the flashover model of polluted insulators, the relationship between conductivity and salinity of solution pollution layer of the insulator is measured. then, the leakage of current amplitude of four common insulators versus axial, thermal conductivity and arc constants temperature was determined. the experimental tests show that top leakage distance (tld) to bottom leakage distance (bld) ratio of insulators has a significant effect on critical voltage and current. therefore, critical voltage and current were modeled by tld to bld ratio index (m). also, salinity of solution pollution layer of the insulators has been applied to this model by resistance pollution parameter. on the other hand, arc constants of each insulator in new model have been identified based on experimental results. finally, a mathematical model is intended for critical voltage against salinity of solution pollution layer of different insulators. this model depends on insulator profile. there is a good agreement between the experimental tests of pollution insulators obtained in the laboratory and values calculated from the mathematical models developed in the present study. keywords:flashover; mathematical model; polluted insulators; salinity 1. introduction pollution phenomena constitute a serious problem, which must be taken into account in the design and the operation of hv insulating devices, under difficult environmental conditions, a pollution layer is entrusted on the insulator surface and when humidity is present due to frost sediment, fog or rain, a humid conducting layer is formed and a leakage current starts to stream[1-23]. the curtailment of the discharge current leads to the formation of dry tape on the surface which results in arcing. the arcs may intrusively extend among the humid surface, leading to a total flashover[1-18]. some researchers have done very good work on the problem of polluted flashover. several models to calculate the flashover of polluted insulators have been proposed[1,3.6-9,12,13]. the expansion of models for the flashover of contaminated insulators which could take into account the real empirical situation is not an easy labor since of the intricacy of the phenomena which can happen[6-14]. however, many efforts have been made to produce models letting one to forecast almost the critical specifications of the contaminated insulators [6]. for this order, the supposition that there is a lone major arc, a uniform contamination distribution and monotone wetting have been made. so, the arc is supposed to move alone on the surface of the insulator. but there is still no consensus as to what amounts of n and n should be used in instance of different polluted atmosphere. in fact, the optimal combination of a and n may be dependent on the chemical nature of the pollutants[16]. the experimental results allowed a great exact evaluation of the discharge constants of the insulator by means of mathematical method. it has been ascertained that the calculated values of the arc constants are autonomous of the insulator kind and the type of pollution[17]. the performance of polluted insulation has been the subject of extensive research and development, and the mechanism of flashover has been elucidated qualitatively. a detailed account of this work is given in[1-6], but the mechanism can be described briefly copyright © 2019 mousalreza faramarzi palangar et al. doi: 10.24294/can.v2i1.541 enpress publisher llc.this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 as follows. notwithstanding the complication of operations evolved in the flashover mechanism, several test and theoretical studies have been assigned to the comprehension of the phenomena leading to flashover of contaminated insulators in order to expansion models letting one to predict the critical voltage and critical current[1-8]. prevalent feature between all these models is a simple display of an arc promotion arc included of a partial arc in series with the resistance of the cross section of contaminated layer. often of these models are confined to the static state of the phenomenon and do not include to the dynamic state of some particular parameters of the flashover. in addition to, the few available dynamic models reported in literature[20]. the above discussion manifests that agreement has not been reached on the value of n, the differences of n when ac function, respectively, the relationship between n and degree of pollution, and the relationship between n and pollution level. on the other, often works offered in literature uses communication giving the critical flashover voltage deduced from the simplified equivalent electrical circuit in[13]. in these relationships, the critical voltage dependent two experimental discharge characteristic constants n and n, the quantities of which is different from one author to another[1-12]. the present work deals with the development of a mathematical model to predict flashover voltage of polluted insulators energized with ac voltages. the objective is to involve the major parameters, namely, profile of the insulator, pollution salinity, the critical current and the environmental conditions such as humidity and temperature. an analytical model letting one to predict the critical voltage, critical current and arc length for contaminated insulators. also constants arc are dependent insulators profile and type of pollution, given the different insulators profile and different types of pollution, each insulator has its own constant. in this paper, is determined the arc constants using programs written. for each insulator is determined an arc constant in which case the answer to experimental result have many similarities and the results are satisfactory. the experimental results allowed a highly exact estimation of the arc constants of the insulator by using a mathematical method. background model[12] among the first flash overs models is presented for contaminated insulators. the equivalent circuit model of contaminated insulators composed of two resistance together series one the contaminated layer resistance pr and a dry bond resistance ar and supplied by a voltage u (figure 1). thus, one can display arc voltage av : v =ra a axi (1) a p au v r i  where ai is the creepage current, whereas n and n are the arc constants and pr is the pollution layer and supplied by a voltageu . pr indicative comprehensive segment of the contamination layer: ( )p pr r l x  where pr resistance per unit length and l is the total creepage length of insulator. on the other, the electrical field discharge is ae . according to [6, 20] is such as: na a a v e ni x   where n and n are the arc constants. the values of these constants depend upon the environment (i.e., the experimental conditions) in which the discharge is burning [20]. by integrating relations (1), (2) and (3): ( )n p au xni r l x i   the purpose of scrutiny is development an analytical model that allowing to predict the critical voltage levels. 3 figure 1, (a), contaminated insulation layer and dry band. (b), model of discharge according to obenaus. the critical length, critical current are determined using the following relations [17, 18]: 0u x    0u i    using equations (5), (6) and (7), one can display the critical length of the arc: cx , the critical current ci and the critical voltage cv [1, 6, 8, and 20]: 1c lx n   1 1( ) nc p ni r  1 1 1 n n nc pv ln r  arc propagation can occur when a pe e (ep is electrical field contaminated layer) . the proposed model 3.1 determine the electrical conductivity and polluted linear resistance in order to determine the surface conductivity, according to the severity of pollution salinity, experiments have been performed in laboratory nano chemistry department babol university of technology. the amount of salt needed after measuring its weight by digital scales in 1000 ml of distilled water dissolved and then by conductivity meter, electrical conductivity of the solution was measured. this experiment were carried out for different amounts of salt in the range [0-100] (g) and 40(g) kaolin were in the range of all kinds of pollution intensity (light, moderate, heavy and very heavy) will be covered. in figure 2 measured values for conductivity in salinity at these experiments is given. using data obtained and programs written in matlab, mathematical linear relationship for conductivity according to pollution salinity is determined: 1.6 30p s    (11) where s and p are the salinity in (g/l) and surface conductivity in ( s ). 0 10 20 30 40 50 60 70 80 90 100 0 50 100 150 200 salinity (g/l) co nd uc tiv ity (u s) experimental data eq. 11 figure 2: curve fitting experimental data of conductivity according[8] to the total resistance of the pollution layer, it is defined by the following equation: 4 p p fr   (12) where f is the form factor of the insulator: 0 ( ( )) l dlf d l   (13) ( )d l is the diameter of the insulator, varying across its leakage length l . using equations (11) and (12) one can define the linear resistance per unit pollution layer: p p fr l  (14) 3.2 investigated insulators and testing of pollution different type of insulator is currently used in iran distribution network. standard cap & pin glass and porcelain insulators are widely used in most of the old system. some 4 different types of insulators were investigated for the purposes of this paper. the characteristics and a view of picture these insulators are presented in table 1 and figure 3. (a) (1) (2) (3) (4) (b) figure 3, a; 3d profile of insulatorb: glass and porcelain insulators number of insulator 1 2 3 4 d(mm) 255 280 280 255 h(mm) 146 146 170 127 l(mm) 440 442 370 320 tld(mm) 320 297 240 190 bld (mm) 120 145 130 115 material porcelain glass porcelain glass table 1. characteristics value of glass and porcelain insulators 5 3.3 laboratory setup the experimental arrangements have been prepared according to iec60507 as shown in fig. 4. all experiments were carried out in a fog chamber in the high voltage laboratory of babol university of technology with a volume of (200cm × 200cm × 200cm). the main power supply is a single phase, (220 v/100 kv), 5 kva, and 50 hz transformer. supplied voltage by tables controlling and feeders by a cable with the appropriate dielectric durability, to testing insulators in the fog chamber is applied. (figure.4) figure 4: laboratory investigation setup (right: hv transformer and regulator – left: fog chamber and fog generator). figure 5 illustrates the schematic diagram of the experimental setup, which consists of a 500 kv ac high voltage system, a capacitance divider (c1=100 pf and c2=2500 pf) for applied voltage measurements, a shunt resistor (r =510 ω) to measure the leakage current flowing through the test object, a data acquisition system, and a vertical circulation climate room, making possible not only very realistic simulation of different types of pollutions, but also the collection of natural frost, fog in particular. figure 5: circuit of the laboratory test setup 3.4 determining the leakage current and arc resistans for an arc burning in air and water vapour at atmospheric pressure, radiation losses are small and the majority of the electrical dissipation heats the surrounding gas. by considering that the energy p is dissipated only by thermal condition in the arc[11], one obtains. a a dqp e i dt   q being the quantity of heat. according to fourier’s law[11]: dq ta dt n      where  , a , n and t are respectively the thermal conductivity, the isothermal surface element, the normal in the direction of the temperature gradient and the temperature of the medium[11]. by using an appropriate assumption (assuming the isothermal surfaces of the arc channel to be hemispherical and the temperature propagation equation to be one-dimensional), the energy balance can be expressed as[11]: 6 a a ave i t where t , the axial temperature is required to provide the necessary amount of thermal ionization and av is the thermal conductivity. the thermal conductivity of such a gas mixture is not readily calculated. some available expressions have been used to give an approximate value according to[11]. (1 )1 v i av i ii a i a v v        where i , iv and ia are the thermal conductivity, volume fraction and a kinetic gas coefficient respectively for each constituent; indices a and v are related to air and water vapour respectively [11]. on the other hand, according to ohm's law: n a a a ae r i ni   by combining (17) and (19), it yields 1 (1 ) ( ) nav a t i n    resistance per unit of the discharge is function of temperature based on relations (1) and (4): ( 1)n a ar ni   3.5 the new model of critical current arc length and voltage at the critical condition to wit a circle that before the complete flashover, the leakage current is called critical current. due to the influence of the insulator geometry on the critical parameters in the most recent article of this effect is not seen in the critical current. in others, such as the [15] constant factor ( ( 1)2( ) 1.3 nk   ) was considered. in this paper, according to the impact of insulator geometry and contamination on the leakage current, a mathematical relation is presented to have a good agreement with experimental results. 1 1( )nc p mni r  where m is: tldm bld  (23) where tld is equivalent top leakage path per shed and bld is equivalent bottom leakage path per shed. for arc length according to [1-15]: 1c lx n   hence, the critical voltage is obtained by substituting ci and cx into equation (5). thus, the critical flashover voltage will be: 1 1 1 1 1 ( ) 1 n nn n nc p lv n r m m n n      the relationship 25 by approximation (n<1, 1nm   ) is modified to relationship 26. to obtain this relationship, the approximation does not greatly influence the critical voltage, and numerical value calculated through these two equations. 1 1 1 1 1 n n n nc pv ln r m   (26) the above equations ((22) to (26)) indicates that the critical current and the critical voltage depend to the profile insulators, type of contamination and temperature of discharge band. 7 the relationship (26) indicates that having the exact values of the arc constants can be polluted insulator behaviour until complete flashover is studied. 3.6 determining the arc constants using the analytical relations, which are based on the polluted insulator model, the most important agent, is the determination of the arc constants n and n . the pervious literature illustrates s that the real values of constants n and n , in the case of thin pollution layers, are in the range of (10-500) and (0-1), respectively [6, 14, 15]. constants arc are dependent insulators profile and type of pollution, given the different insulators profile and different types of pollution, each insulator has its own constant. in this paper, to determine the arc constants using programs written in the software matlab, for each insulator is determined by an arc constant in which case the answer to experimental result the same insulator have many similarities and the results are satisfactory. the experimental data ( cu , against s) and the geometric characteristics of the tested insulators were put in equation (26), thus leading in relations with unknowns the discharge constants n and n . this equation, with unknowns the arc constants n and n were solved using different method (genetic algorithm, newton-raphson and other statistical methods) that the minimum the difference between critical voltages tested with the mathematical model presented in equation (26). in table 4, the results obtained by these tests are given. (n, ) minimumcu f n  (27) insulator n n 1 66.9218 0.5293 2 64.0350 0.5402 3 67.5785 0.5279 4 65.2565 0.5579 table 4. the arc constants n and n for tested insulators performance model the accuracy of the model was verified by comparing the mathematical results with measurements found in the literature besides the already presented experimental results. fig. 6 shows a collation of the presented model and experimental results. according to [17], it can be seen that there is a good relation and accurate between the presented model and the measured data at every contamination severity. this is of great concern in act especially for the prediction of occurrence flashover. consequently, the mathematical model developed in this work represents a good relation for predicting the critical flashover voltage and the critical current. 0 10 20 30 40 50 60 70 80 90 100 1 1.5 2 2.5 3 3.5 x 104 salinity(g/litter) c ri tic al v ol ta ge (v ol t) model (insulator: no1) [17] experimental data very heavy heavy medium light a. 0 10 20 30 40 50 60 70 80 90 100 1 1.5 2 2.5 3 3.5 x 104 salinity(g/litter) c ri tic al v ol ta ge (v ol t) model (insulator: no2) [17] experimental data very heavy heavy medium light b. 8 0 10 20 30 40 50 60 70 80 90 100 0.5 1 1.5 2 2.5 3 3.5 x 104 salinity(g/litter) c ri tic al v ol ta ge (v ol t) model (insulator: no3) [17] experimental data heavy very heavy medium light c. 0 10 20 30 40 50 60 70 80 90 100 0.5 1 1.5 2 2.5 3 x 104 salinity(g/litter) c ri tic al v ol ta ge (v ol t) model (insulator: no4) [17] experimental data very heavy medium light heavy d. figure 6: critical voltage model in compared experimental test and [17] a: no.1, b: no.2, c: no.3, d: no4 figure 7 displays changes critical voltage in the pollution resistance using the relationships (22) and (26) . 0 1000 2000 3000 4000 5000 6000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 pollution resistance(ohm/cm) c ri tic al c ur re nt (a ) model(equation.29) figure 7: critical current variation versus pollution resistance 5. conclusion in this paper, we presented a new mathematical model for critical parameters of polluted insulators based on experimental tests. the validity of these models was verified by comparing the computed results of critical flashover voltage based on experimental tests and theoretical data for different insulators. by using arc constants of each insulator in different polluted condition it is possible to estimate the critical voltage close to real condition. it is expected that intricate tests for the prediction of this behavior can be considerably decreased or even eliminated. references 1. alston ll, zoledziowski s. gowth of discharges on polluted insulation, proc. iee,1963;(10): pp1260-1266. 2. eha, rahal m sur les mécanismes physiques du contournement des isolateurs haute tension,thèse de doctorat ès sciences physiques, université paul sabatier, toulouse, france,1 1979. 3. claverie p. predetermination of the behaviour of polluted insulators, ieee trans. power app. syst. 1971;(90):pp 1902-1908,. 4. crawford fw and edels h,the reignition voltage characteristics of freely recovering proc. iee, 1960;(107):pp 202-212. 5. renyu z., deheng z., and zhicheng, g.a study on the relation between the flashover voltage and the leakage current of naturally or artificially polluted insulators’. presented at 4th international symposium on high voltage engineering, athens, 1983;paper 46.01, vol. ii 6. rizk fam. mathematical models for pollution flashover,electra. 1981;(78):pp 71-103. 7. hampton bf.flashover mechanism of polluted insulation.1964; iee(11):pp. 985-990. 8. wilkins r. “flashover voltage of hv insulators withuniform surface pollution films”, proc iee, 1969;(116):pp 9 457-465. 9. sundararajan r,rs. gorur, “dynamic arc modelling of pollution flashover of insulators under dc voltage”, ieee trans. electr. insul., 1993(28):pp. 209-219. 10. guan zhanga and zhang renyu, “calculation of dc and ac flashover voltage of polluted insulators”, ieee trans. electr. insul.,1990;(25):pp 723-728. 11. dhahbi-megriche n., beroual a. and krähenbühl l. a new proposal model for polluted insulators flashover. j. phys. d. appl. phys.1997(30):pp. 889-894. 12. obenaus f. fremdschichtüberschlag und kriechweglänge. deutsche electrotechnik, 1958;(4):pp 135-136. 13. p. claverie, y. porcheron, “how to choose insulators for polluted areas”, ieee trans. power app. syst., 1973;(92): pp. 1121-1131. 14. danis j. a stochastic pollution flashover model. presented at 4th international symposium on high voltage engineering, athens. 1983; paper 46.12, vol. ii. 15. ghosh pj and chatterjee n. polluted insulators flashover for ac voltag. ieee trans. dielectr. electr. insul.1995; (2): pp. 128-136. 16. topalis fv, gonos if, stathopulos ia. “dielectric behaviour of polluted insulators”, proc. iee gener. transm. distrib. 2001; (148): pp.269 274, 2001. 17. slama mel-a, hadi h and flazi s. investigation on influence of salts mixture on the determination of flashover discharge constant part i: a preliminary study. ieee conf. electr. insul. dielectr. phenomena (ceidp). vancouver canada. 2008; pp. 674-677. 18. labadie jc, etude de la validité de modèle électrique du contournement des isolateurs h.t pollués, ph.d. disseration. university paul sabatier toulouse, france, 1977. 19. slama mel-a, beroual a, hadi h. analytical computation of discharge characteristic constants and critical parameters of flashover of polluted insulators. ieee transactions on dielectrics and electrical insulation.2010; (17): december. 20. l. shu y. shang x. jiang q, et al. comparison between ac and dc flashover performance and discharge process of ice-covered insulators under the conditions of low air pressure and pollution. iet gener. transm. distrib.2012; (6): iss. 9, pp. 884–892. 21. bingbing dong, xingliang jiang, jianlin hu, et al. effects of artificial polluting methods on ac flashover voltage of composite insulators. ieee transactions on dielectrics and electrical insulation. 2012; (19): no. 2 april. 22. mousalreza faramarzi palangar, mohammad mirzaie. designation of an indicator for flashover prediction of porcelain and glass insulators based on experimental tests. journal of operation and automation in power engineering. 2015;(3): no.2, pp. 147-157, july. 23. suda t. frequency characteristics of leakage current waveforms of a string of suspension insulators. ieee trans. power del. 2005; (20): no. 1, jan. pp. 481–487. 24. mousalreza faramarzi palangar, mohammad mirzaie. diagnosis of porcelain and glass insulators conditions using phase angle index based on experimental tests. ieee transactions on dielectrics and electrical insulation,2016; (23): issue 3, pp. 1460-1466, june, doi: 10.1109/tdei.2015.005586. 25. mousalreza faramarzi palangar, mohammad mirzaie. detection of critical conditions on ceramic insulators based on harmonic analysis of leakage. journal of electric power components and systems. 2016; (44): issue 16, pp. 1854-1864, october, doi: 10.1080/15325008.2016.1183723. microsoft word can-4654 characterization and application of nanomaterials 2024, 7(1), 4654. https://doi.org/10.24294/can.v7i1.4654 1 review carbon nanomaterial-based electrochemical sensor in biomedical application, a comprehensive study srabani majumdar1, razu shahazi1, amirul islam saddam1, mohammed muzibur rahman2,3, md. mahmud alam1,2,*, ajoy kumer4, giti paimard5 1 department of chemical engineering, z. h. sikder university of science and technology (zhsust), shariatpur 8024, bangladesh 2 center of excellence for advanced materials research (ceamr), king abdulaziz university, jeddah 21589, saudi arabia 3 chemistry department, faculty of science, king abdulaziz university, jeddah 21589, saudi arabia 4 department of chemistry, college of arts and sciences, iubat-international university of business agriculture and technology, dhaka 1230, bangladesh 5 laboratory of nanoscale biosensing and bioimaging (nbab), school of ophthalmology and optometry, school of biomedical engineering, state key laboratory of ophthalmology optometry, and vision science, wenzhou medical university, wenzhou 325027, china * corresponding author: md. mahmud alam, alam-mahmud@hotmail.com, mmalam@zhsust.ac.bd abstract: recently, carbon nanocomposites have garnered a lot of curiosity because of their distinctive characteristics and extensive variety of possible possibilities. among all of these applications, the development of sensors with electrochemical properties based on carbon nanocomposites for use in biomedicine has shown as an area with potential. these sensors are suitable for an assortment of biomedical applications, such as prescribing medications, disease diagnostics, and biomarker detection. they have many benefits, including outstanding sensitivity, selectivity, and low limitations on detection. this comprehensive review aims to provide an in-depth analysis of the recent advancements in carbon nanocomposites-based electrochemical sensors for biomedical applications. the different types of carbon nanomaterials used in sensor fabrication, their synthesis methods, and the functionalization techniques employed to enhance their sensing properties have been discussed. furthermore, we enumerate the numerous biological and biomedical uses of electrochemical sensors based on carbon nanocomposites, among them their employment in illness diagnosis, physiological parameter monitoring, and biomolecule detection. the challenges and prospects of these sensors in biomedical applications are also discussed. overall, this review highlights the tremendous potential of carbon nanomaterial-based electrochemical sensors in revolutionizing biomedical research and clinical diagnostics. keywords: carbon nanocomposites; sensitivity; selectivity; low detection limits; detecting biomolecules; monitoring physiological parameters; diagnosing diseases; electrochemical sensors 1. introduction because electrochemical sensors can identify and measure the different biochemicals present in human fluid, they are essential in biomedical applications. it provides excellent sensitivity and selectivity for identifying target analytes and can quickly and precisely identify certain compounds or biomarkers in complex biological samples. because of this, electrochemical sensors’ sensitivity and selectivity make them useful instruments for monitoring and diagnosing diseases early on [1–5]. as known, the electrochemical sensors provide rapid analysis, delivering real-time results within minutes or seconds, which is essential in critical medical situations for timely diagnosis and treatment decisions [6–8]. thus, it eliminates the step of sending citation majumdar s, shahazi r, saddam ai, et al. carbon nanomaterial-based electrochemical sensor in biomedical application, a comprehensive study. characterization and application of nanomaterials. 2024; 7(1): 4654. https://doi.org/10.24294/can.v7i1.4654 article info received: 15 february 2024 accepted: 12 march 2024 available online: 12 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 4654. 2 samples to a clinical laboratory and deletes the late medical interventions. in addition, electrochemical sensors are often cost-effective compared to traditional laboratorybased analytical techniques, making them accessible in resource-limited settings [9,10]. multiplexed analysis can be made possible by designing the electrochemical sensors to detect numerous analytes at once. this is another potential feature. this function is very helpful for biomarker profiling, as the combination of several biomarkers can yield more thorough diagnostic data [11,12]. in terms of long-term monitoring, the electrochemical sensors can be integrated into implantable or wearable devices for long-term monitoring of physiological parameters or drug delivery. this allows continuous monitoring of patient health and therapeutic efficacy over extended periods, providing valuable insights for personalized medicine and treatment optimization [13,14]. thus, electrochemical sensors have diverse applications in biomedicine, including disease diagnosis, drug discovery, monitoring of therapeutic interventions, environmental monitoring, and biosecurity. their versatility allows them to be adapted for various biomedical needs. in short, electrochemical sensors offer high sensitivity, selectivity, rapid analysis, and versatility, making them indispensable tools in biomedical applications. they have the potential to revolutionize medical diagnostics, patient monitoring, and personalized medicine by providing accurate, real-time, and cost-effective solutions. 2. instrumentation of electrochemical sensors electrochemical sensors are widely used for detecting and quantifying various analytes in fields such as environmental monitoring, healthcare, and industrial processes. the instrumentation of electrochemical sensors typically involves several key components and techniques. the basic setup of an electrochemical sensor consists of an electrochemical cell. this cell typically includes an electrode system, which consists of a working electrode, a reference electrode, and a counter electrode. the analyte of interest interacts with the working electrode surface, leading to an electrochemical reaction. to control and measure the electrical potential or current during electrochemical measurements, a potentiostat or galvanostat is used. these instruments provide a stable potential or current to the working electrode and maintain it at the desired value throughout the experiment. potentiostats are commonly used for most electrochemical measurements. the reference electrode is a stable electrode with a known and constant potential. it provides a reference point for measuring the potential at the working electrode. common reference electrodes include silver/silver chloride (ag/agcl) and saturated calomel electrode (sce). the counter electrode completes the electrical circuit in the electrochemical cell. it compensates for the current flowing through the working electrode during the electrochemical reaction. common counter electrodes are made of materials such as platinum, graphite, or gold. the electrochemical signal generated at the working electrode is typically small and requires amplification and conditioning for accurate measurement. signal amplifiers and filters are used to enhance the signal-to-noise ratio and remove unwanted noise or interference. a data acquisition system is used to collect and process the output from the electrochemical sensor. it typically includes analog-to-digital converters (adcs) characterization and application of nanomaterials 2024, 7(1), 4654. 3 to convert the analog electrochemical signal into a digital format, which can be further processed and analyzed by a computer or microcontroller. electrochemical sensors often require calibration to establish a relationship between the measured signal and the analyte concentration. calibration involves measuring the sensor response with known concentrations of the analyte and creating a calibration curve. standardization ensures the accuracy and reliability of the sensor measurements by using certified reference materials. in recent years, there has been a trend toward miniaturizing electrochemical sensors and integrating them with portable or wearable devices. this allows for on-site and real-time monitoring of analytes in various applications, including point-of-care diagnostics and environmental sensing. in figure 1, the instrumentation of an electrochemical sensor is illustrated. figure 1. instrumentation of electrochemical sensor. 3. reagent and biomolecules for electrochemical sensing electrochemical sensors utilize specific reagents and biomolecules to facilitate the detection and quantification of analytes. the choice of reagents and biomolecules depends on the nature of the analyte and the sensing mechanism employed. enzymes are widely used in electrochemical sensors due to their high catalytic activity and specificity. they can be immobilized on the electrode surface or incorporated into the sensor matrix. examples include glucose oxidase for glucose sensing, lactate oxidase for lactate sensing, and cholinesterase for acetylcholine sensing [15–17]. antibodies or antibody fragments (e.g., monoclonal antibodies) are used in immunosensors for the detection of specific antigens or biomarkers. the antibodies are immobilized on the electrode surface or on nanoparticles that are subsequently captured by the electrode. this allows for highly specific recognition and measurement of target analytes [18,19]. besides this, dna or rna probes are employed in nucleic acid sensors for the detection of specific dna sequences or rna molecules. probes can be designed to hybridize with the target sequence, leading to changes in the electrochemical signal. various strategies, such as hybridization chain reaction (hcr) or strand displacement amplification (sda), can be used to enhance the sensitivity of nucleic acid sensors [20,21]. moreover, redox mediators are small molecules that facilitate the transfer of electrons between the electrode and the analyte, enhancing the electrochemical signal. examples include ferrocene derivatives, methylene blue, and quinones. redox mediators can be incorporated into the sensor system to mediate the electrochemical reaction and amplify the signal [22,23]. reducing or oxidizing agents can be added to the sensor system to modulate the electrochemical reaction or enhance characterization and application of nanomaterials 2024, 7(1), 4654. 4 the signal. for example, in amperometric glucose sensors, a reducing agent (e.g., ascorbic acid) can be added to minimize interference from other electroactive species [24,25]. in addition, electrochemical sensors often require buffer solutions to maintain a stable ph and optimize the electrochemical reactions. common buffer systems include phosphate-buffered saline (pbs), tris-hcl, or acetate buffers. the buffer composition and ph are chosen based on the requirements of the specific electrochemical reaction and the stability of the biomolecules involved [26,27]. 4. role of carbon nanomaterials in electrochemical sensor development the creation of electrochemical sensors greatly benefits from the use of carbon nanomaterials. its remarkable mechanical, chemical, and electrical characteristics make it an excellent choice for applications involving electrochemical sensing. due to its huge reactive surface area and strong electrical conductivity, it can move electrons efficiently and has increased sensitivity. the performance of conventional electrodes can be enhanced by using carbon nanomaterials as modifiers or by directly integrating them into the electrode structure [28,29]. besides this, it can serve as excellent support for electro-catalysts in electrochemical sensors. the high surface area and good mechanical stability of carbon nanomaterials enhance the catalyst’s activity and stability, leading to improved sensor performance [30,31]. in addition, carbon nanomaterials can act as electrochemical sensing platforms themselves. carbon nanomaterials can be utilized to amplify the electrochemical signals generated during electrochemical sensing processes. a schematic setup of an electrochemical sensor is demonstrated in figure 2. figure 2. schematic diagram of an electrochemical sensor. thus, this signal amplification approach improves the electrochemical sensor’s sensitivity, enabling the detection of trace analytes [32,33]. on the other hand, the carbon nanomaterials can be tailored to exhibit selective interactions with target analytes, enabling the development of highly specific electrochemical sensors. functionalization of the carbon nanomaterial surface with specific receptors, such as antibodies, enzymes, or molecular imprints, allows for the selective recognition and detection of target molecules in complex samples [34,35]. therefore, carbon nanomaterials have revolutionized the field of electrochemical sensing by providing enhanced sensitivity, excellent electrical conductivity, versatile functionalization, stability, and integration capabilities. ongoing research continues to explore new synthesis and functionalization techniques, as well as innovative sensor designs, to characterization and application of nanomaterials 2024, 7(1), 4654. 5 further optimize the properties of carbon nanomaterials and expand their applications in various fields, including environmental monitoring, healthcare diagnostics, and food safety. 5. types of carbon nanomaterials there are several types of carbon nanomaterials, each with unique structures and properties. 5.1. carbon nanotubes (cnts) carbon nanotubes are cylindrical structures made of rolled-up graphene sheets. they can be classified as single-walled (swcnts) or multi-walled (mwcnts) depending on the number of graphene layers. cnts possess excellent mechanical strength, high electrical conductivity, and large surface area. various types of carbon nanotubes are illustrated in figure 3. they are widely used in various applications as electronics, energy storage, and composite materials. figure 3. structure. (a) single-walled carbon nanotube (swcnt); (b) double-walled carbon nanotube (dwcnt); (c) multi-walled carbon nanotube (mwcnt). thus, carbon nanotubes can serve as excellent transducers in electrochemical sensors due to their unique electrical properties. when cnts are functionalized or modified with specific biomolecules or receptors, they can selectively recognize and bind to target analytes, such as disease-specific biomarkers or molecules indicative of a particular disease [36–38]. thus, the unique properties of carbon nanotubes, including their high sensitivity, excellent electrical conductivity, electrochemical activity, and compatibility with functionalization and integration, make them highly valuable for electrochemical sensing applications. ongoing research aims to further optimize the properties of cnts, explore new synthesis and functionalization techniques, and develop innovative sensor designs for enhanced performance and broader application domains. 5.2. graphene a further important aspect of the carbon nanomaterial family is graphene, which is a substance made up of just a single layer of carbon atoms organized in a twodimensional in nature honeycomb lattice. the structure of graphene is shown in figure 4. it is a highly conductive, flexible, and incredibly thin material. because of its remarkable mechanical, electrical, and thermal features, ranging graphene receives application throughout a variety of fields, including medicinal devices, electronics, sensors, and energy storage. to achieve high selectivity and specificity towards the target biomarker, graphene-based electrochemical sensors can be functionalized with characterization and application of nanomaterials 2024, 7(1), 4654. 6 particular receptors, such as antibodies, aptamers, or molecularly imprinted polymers. functionalization lowers false-positive or false-negative readings by enabling the sensor to distinguish between the target biomarker and other interfering species present in the sample. graphene, like carbon nanotubes, can be used in sensor arrays to allow for the simultaneous multiplexed detection of several biomarkers. an array of graphene-based sensors can be functionalized with distinct receptors for various biomarkers, enabling simultaneous analysis and thorough illness diagnosis [39–42]. the application of graphene in electrochemical sensing has shown great promise, and ongoing research aims to further optimize its properties, explore new fabrication techniques, and develop innovative sensor designs. graphene-based electrochemical sensors have the potential to revolutionize fields such as environmental monitoring, healthcare diagnostics, food safety, and many other areas where sensitive and selective detection of analytes is crucial. figure 4. structure of graphene and graphene oxide. 5.3. graphene oxide (go) graphene oxide is derived from graphene by introducing oxygen-containing functional groups. the structure of graphene oxide is shown in figure 4. go exhibits good dispersibility in water and other solvents, making it easier to process and functionalize. it is used in various fields, including sensors, membranes, drug delivery systems, and composites [43,44]. thus, the application of graphene oxide in electrochemical sensors has shown great promise in various fields, including environmental monitoring, healthcare diagnostics, and food safety. ongoing research is focused on further optimizing the properties of go-based sensors [45,46] and exploring new applications in areas such as energy storage, wearable devices, and point-of-care diagnostics. 5.4. carbon nanofibers (cnfs) carbon nanofibers are elongated structures composed of graphene sheets stacked together in a fibrous form. the structure of carbon nanofiber is illustrated in figure 5. they can be produced through various methods, including chemical vapor deposition and electrospinning. cnfs possess high mechanical strength, electrical conductivity, and thermal stability. they find applications in composite materials, energy storage, and sensors. therefore, carbon nanofibers offer a range of advantages for electrochemical sensing applications, including high surface area, excellent conductivity, versatile functionalization, and compatibility with other materials characterization and application of nanomaterials 2024, 7(1), 4654. 7 [47,78]. ongoing research aims to further optimize the properties of cnfs, explore new synthesis techniques, and develop innovative sensor designs for various analytical applications. figure 5. structure of carbon nanofiber. 5.5. fullerenes fullerenes are closed-cage carbon molecules with a hollow spherical or ellipsoidal structure. the most well-known fullerene is c60, also called buckminsterfullerene or buckyball. fullerenes exhibit unique electronic and optical properties and have applications in electronics, photovoltaics, and biomedical research. thus, fullerene, specifically c60 (buckminsterfullerene), has shown promising potential for various electrochemical sensor applications. while fullerene-based sensors are not as extensively studied as other carbon nanomaterials like graphene or carbon nanotubes, they offer unique properties that make them attractive for certain sensing applications. here are some potential applications of c60 as an electrochemical sensor [49–51]. while the use of c60 as an electrochemical sensor is still an active area of research, its unique properties, including redox activity, electron transfer kinetics, stability, and the ability to detect reactive species, make it an intriguing material for certain sensing applications. further research and development are needed to explore and optimize the potential of c60-based electrochemical sensors and to understand their performance characteristics in various sensing scenarios. the larger c70 molecule, similar to c60, belongs to the fullerene family. it resembles the ellipsoidal cage structure of a rugby ball. the structures of c70 and c60 fullerene are shown in figure 6b,c. a fullerene c70 cube is used for sensing volatile aromatic solvent vapors [52,53]. figure 6. structure. (a) carbon nanohorn; (b) c70 fullerene; (c) c60 fullerene. 5.6. carbon dots carbon dots are small carbon nanoparticles with sizes typically less than 10 nanometers. they exhibit strong fluorescence properties and can be easily functionalized. as illustrated in figure 7, cds are comprised of graphene quantum dots, carbon quantum dots, carbon nanodots, and carbonized polymer dots. these dots characterization and application of nanomaterials 2024, 7(1), 4654. 8 are categorized based on the particular characteristics of their carbon core structure, surface groups, and properties [54]. figure 7. classification of carbon dots. carbon dots find applications in bioimaging, optoelectronics, and sensing. therefore, carbon dots as electrochemical sensors are an active area of research, with ongoing efforts focused on optimizing their properties, exploring new synthesis techniques, and developing innovative sensing strategies. the unique characteristics of cds, including their electrochemical activity, high surface area, sensitivity, and versatility, make them attractive for a wide range of electrochemical sensing applications [55–57]. 5.7. carbon nanohorns carbon nanohorns (cnhs) are unique carbon nanostructures that have gained significant attention in various fields, including electrochemical sensor applications. cnhs are three-dimensional, hollow, horn-shaped carbon nanoparticles with a high surface area and unique electronic properties. the structure of carbon nanohorn is shown in figure 6a. these properties make them promising candidates for sensor development, particularly in electrochemical sensing [58,59]. ongoing research and development in this field aim to further optimize the performance of cnh-based sensors and explore new applications in sensing and detection. 6. carbon nanomaterial-based electrochemical sensors due to its special qualities, which include strong electrical conductivity, a huge surface area, and exceptional chemical stability, carbon nanomaterials have demonstrated significant potential in the field of electrochemical sensors, as was previously mentioned. their ability to efficiently transport electrons and offer a large surface area for analyte adsorption makes them excellent choices for sensing applications. a summary of the electrochemical sensors that have been developed utilizing various carbon nanomaterials is presented in table 1. applications for carbon nanomaterial-based electrochemical sensors are numerous and include food safety, industrial process control, healthcare diagnostics, and environmental monitoring [60,61]. target analytes can be detected swiftly, cautiously, and exquisitely attributable to the distinctive characteristics of carbon nanomaterials. the goal of ongoing research is to further improve the performance of these sensors by the integration of cuttingedge signal transduction techniques, the optimization of carbon nanomaterial manufacturing, and the investigation of novel functionalization procedures. characterization and application of nanomaterials 2024, 7(1), 4654. 9 table 1. carbon nanomaterials based modified electrochemical sensors [62]. modified electrode drug method linear range limit of detection mwnt-cooh/gce 6-mercaptopurine amperometry mwnt-cooh/gce 6-mercaptopurine amperometry 0.4–100 μm 0.2 μm swnt-dcp/gce epirubicin linear sweep voltammetry 0.05–50 μm 0.02 μm cnt-ctab/gce daunorubicin cyclic voltammetry 20–500 nm 10 nm mwcnt/gce enrofloxacin ciprofloxacin linear sweep voltammetry 2.0–780.0 μm 0.5 μm mwcnt/gce ciprofloxacin linear sweep voltammetry 40–1000 μm 6.0 μm mwcnt/gce gatifloxacin differential pulse voltammetry 21.3–1700 um 4.5 nm ag nps/mwcnts-cooh/gce adriamycin differential pulse voltammetry 8.2–19 nm 1.7 nm cyclodextrin-gr ns/gce doxorubicin methotrexate differential pulse voltammetry 10 nm–0.2 μm 0.1 nm mwcnts/cpe 6-mercaptopurine linear sweep voltammetry 0.5–900 μm 0.1 μm o-mwnts/gce methotrexate differential pulse voltammetry 0.1–8.0 μm 0.015 μm q-mwnts/gce methotrexate amperometry 0.01–20 mg/l 0.2 μm/l dsdna-modified ppymwcnts/pge 6-mercaptopurine differential pulse voltammetry 0.2–100 μm 0.08 μm cqds/gce etoposide differential pulse voltammetry 0.02–10.0 μm 0.005 μm gqd/gce doxorubicin hydrochloride differential pulse voltammetry 0.018–3.600 μm 0.016 μm gqd/gce doxorubicin hydrochloride differential pulse voltammetry 0.018–3.60 μm 0.016 μm mwcnt/gce 6-mercaptopurine linear sweep voltammetry 0.5–3.0 μm 8.41 nm mwcnt/pt e doxorubicin cyclic voltammetry 0.2–4.0 μm/ml 0.002 μm/ml dna/swcnts/ppy/pge ciprofloxacin differential pulse voltammetry 0.008–30.0 μm 4 nm cb/b-cd/spe flutamide differential pulse voltammetry 0.05–158.3 μm 0.016 μm mwcnts/gce dacarbazine differential pulse voltammetry 0.4–2500 nm 0.12 nm mwcnt-pufix/hf-pge capecitabine erlotinib differential pulse voltammetry 7.70–142.00 μm 0.11 μm n-rgo-cs/au doxorubicin differential pulse voltammetry 0.010–15 μm 10 nm cnps/n/gce azathioprine cyclic voltammetry 0.2–50 μm 80 μm ndg/cs/gce azathioprine cyclic voltammetry 0.2–100 μm 65 μm 7. working principles of electrochemical sensors the cornerstone for the functioning of electrochemical sensors is the principle of converting an electrical signal from a chemical signal, such as the presence or concentration of an analyte. usually, they are made up of an electrode/electrolyte system that aids in the electrochemical reactions necessary for sensing. these comprise the general working principles of electrochemical sensors; however, they might differ based on the particular design and configuration as: 7.1. potentiometric sensors potentiometric sensors measure the potential difference (voltage) between two or more electrodes in an electrochemical cell. the potential difference is related to the concentration of the analyte under investigation. these sensors typically employ ionselective electrodes (ises), such as ph electrodes or ion-specific electrodes, that selectively respond to specific ions in the solution. the potential difference generated characterization and application of nanomaterials 2024, 7(1), 4654. 10 by the ise is measured and correlated with the analyte concentration using a calibration curve. 7.2. amperometric sensors amperometric sensors detect the current generated by an electrochemical reaction at an electrode surface. the current is proportional to the concentration of the analyte. these sensors usually consist of a working electrode, a reference electrode, and sometimes a counter electrode. the working electrode is typically modified with a catalyst or specific molecules that facilitate the electrochemical reaction of the analyte. when the analyte comes into contact with the working electrode, it undergoes an oxidation or reduction reaction, resulting in the generation of a current that is measured and correlated with the analyte concentration. 7.3. voltammetric sensors voltammetric sensors involve the measurement of the current as a function of the applied potential (voltage) at an electrode. these sensors utilize techniques such as cyclic voltammetry, differential pulse voltammetry, or square wave voltammetry. the potential is scanned over a specific range, and the resulting current response provides information about the analyte concentration. voltammetric sensors are commonly used for the detection of redox-active species or for studying the electrochemical behavior of analytes. 7.4. impedimetric sensors impedimetric sensors track variations in the electrode-electrolyte interface’s impedance, or frequency-dependent resistance, in response to analyte interaction. usually, these sensors use highly surface-aread electrodes or certain surface treatments to increase sensitivity. the electrical characteristics of the electrode-electrolyte interface, such as capacitance or charge transfer resistance, change in the presence of the analyte and are measured in order to ascertain the analyte concentration. 8. fabrication methods of electrochemical sensor the fabrication of electrochemical sensors involves several key steps, including the selection of materials, electrode preparation, immobilization of sensing elements, and assembly of the sensor. here is a general overview of the fabrication process: 8.1. material selection the first step is to select suitable materials for the sensor components. this includes choosing appropriate electrode materials, such as metals (e.g., gold, platinum), carbon-based materials (e.g., graphite, carbon nanotubes), or conductive polymers. the selection depends on factors such as the target analyte, desired sensitivity, and compatibility with the chosen fabrication techniques. 8.2. electrode preparation the electrodes can be prepared through various techniques, such as physical deposition, screen printing, or lithography. for example, metal electrodes can be characterization and application of nanomaterials 2024, 7(1), 4654. 11 fabricated by depositing a thin layer of the metal onto a substrate using techniques like sputtering or evaporation. carbon-based electrodes can be prepared by screen printing a carbon ink onto a substrate or by directly growing carbon nanomaterials on the electrode surface. 8.3. surface modification surface modification is often performed to enhance the sensitivity and selectivity of the sensor. this can involve functionalizing the electrode surface with specific molecules or nanoparticles. functionalization can be achieved through self-assembled monolayers (sams), electrodeposition, or chemical modification techniques. the functionalized surface allows for the immobilization of sensing elements or recognition elements that interact with the target analyte. the surface of nanotubes can be functionalized in different ways as illustrated in figure 8. figure 8. surface functionalization of carbon nanotubes. 8.4. immobilization of sensing elements sensing elements, such as enzymes, antibodies, or dna probes, are immobilized onto the electrode surface to enable the selective detection of the target analyte. immobilization techniques can include physical adsorption, covalent attachment, or entrapment within a polymer matrix. the immobilization method should ensure the stability and activity of the sensing element while allowing for efficient analyte interaction. 8.5. sensor assembly once the electrode and sensing elements are prepared, the sensor is assembled. this typically involves placing the prepared electrode into a suitable housing or cell that allows for the introduction of the analyte and the connection to measurement equipment. the assembly can include additional components, such as reference electrodes or counter electrodes, depending on the sensor design. characterization and application of nanomaterials 2024, 7(1), 4654. 12 8.6. sensor characterization and testing after fabrication, the sensor needs to be characterized and tested to evaluate its performance. this includes calibrating the sensor response, determining the detection limit, assessing the selectivity, and evaluating the stability and reproducibility of the sensor. various electrochemical techniques, such as cyclic voltammetry or amperometry, are commonly used for characterization and testing. 9. biomedical applications of electrochemical sensor electrochemical sensors have found numerous applications in the field of biomedicine due to their ability to provide sensitive and selective detection of various biomolecules and analytes. here are some key biomedical applications of electrochemical sensors: 9.1. detection of biomolecules the detection of biomolecules, such as proteins, dna, and other analytes, is frequently accomplished through the use of electrochemical sensors. thus, there are electrochemical sensors that can identify dna using a variety of approaches, such as amplification and dna hybridization. the particular binding between a dna probe that has been mounted on the sensor surface and its complementary target dna sequence is what drives dna hybridization-based sensors. a change in the electrochemical signal, such as a change in voltage or current, is caused by the hybridization event and can be monitored to determine whether the target dna is present or concentrated [48–50]. additionally, it could detect proteins using a variety of methods, including immunosorbent assays involving enzymes (elisas) and antibody-based tests. target proteins in the sample attach to particular antibodies that have been permanently selected on the sensor surface in antibody-based sensors. protein identification is made conceivable by the binding event, which causes a modification in the electrochemical signal. enzyme-labeled antibodies that react with the target protein to produce an electrochemical signal are used in elisa-based electrochemical sensors [63–66]. in addition, enzymatic activity, which is frequently employed to quantify the presence of particular biomolecules, can be detected by electrochemical sensors. immobilized enzymes that have been immobilized that catalyze particular reactions with the target analyte are used in enzyme-based sensors. an electrochemical signal, such as a shift in potential or current, has been generated by the enzymatic process and can be evaluated for determining the quantity of the target biomolecule [67–69]. aptamers, which are short single-stranded dna or rna molecules, can bind to target molecules with high specificity. electrochemical sensors can be functionalized with aptamers, allowing for the selective detection of various analytes, including small molecules, proteins, and toxins. the binding of the target analyte to the aptamer leads to changes in the electrochemical signal, enabling sensitive and specific detection [70–72]. in addition, electrochemical sensors can be integrated with nucleic acid amplification techniques, such as polymerase chain reaction (pcr) or loop-mediated isothermal amplification (lamp), to enhance the sensitivity of dna or rna detection [73–75]. these amplification techniques produce characterization and application of nanomaterials 2024, 7(1), 4654. 13 multiple copies of the target nucleic acid sequence, which can be detected by the electrochemical sensor. 9.2. disease diagnosis in the detection and monitoring of cancer, infectious diseases, and other medical disorders, electrochemical sensors have demonstrated considerable promise in the field of disease diagnostics. it may be useful in the early identification and treatment of cancer. prostate-specific antigen (psa) for prostate cancer and carcinoembryonic antigen (cea) for colorectal cancer are two examples of specific biomarkers that they can identify. electrochemical sensors can provide important information for cancer screening, diagnosis, and treatment response monitoring by detecting the concentration of these biomarkers in patient samples [76–78]. besides this, electrochemical sensors are also employed for the rapid and sensitive detection of infectious agents, including bacteria, viruses, and parasites. by targeting specific nucleic acid sequences or antigens associated with the pathogens, electrochemical sensors can identify infections such as hiv, hepatitis, malaria, and respiratory infections. these sensors offer the potential for point-of-care testing, enabling early diagnosis and timely treatment [79–81]. in addition, electrochemical sensors are commonly used for continuous glucose monitoring in diabetes management. by measuring glucose levels in body fluids, such as blood or interstitial fluid, electrochemical sensors provide real-time information about glucose concentration. this helps individuals with diabetes to monitor and manage their blood sugar levels, ensuring proper insulin administration and dietary adjustments [82,83]. it is also employed for the detection of cardiac biomarkers, such as troponin, creatine kinasemb (ck-mb), and brain natriuretic peptide (bnp). these biomarkers are indicative of heart damage or dysfunction and are used in the diagnosis of acute myocardial infarction (heart attack), heart failure, and other cardiac conditions [83–86]. thus, electrochemical sensors can provide rapid and sensitive measurements of these biomarkers, aiding in early diagnosis and risk assessment. moreover, electrochemical sensors can be used for genetic disease screening, such as detecting mutations or variations in specific genes associated with inherited disorders. by incorporating dna probes or aptamers specific to the target genetic sequence, electrochemical sensors can identify genetic mutations and variations linked to diseases like cystic fibrosis, sickle cell anemia, and genetic predisposition to certain cancers [87–88]. again more, electrochemical sensors have applications in the diagnosis and monitoring of neurological disorders. they can measure neurotransmitters, such as dopamine and serotonin, in the central nervous system, providing insights into conditions like parkinson’s disease, depression, and schizophrenia. it can also detect biomarkers associated with neurodegenerative diseases, such as alzheimer’s and huntington’s diseases [89–91]. 9.3. electrochemical biosensing in drug delivery the use of biosensors in drug delivery systems to track and regulate different medication administration parameters is known as “biosensing in drug delivery”. medication delivery can be tailored and optimized with the help of biosensors, which characterization and application of nanomaterials 2024, 7(1), 4654. 14 can offer real-time data on medication release, drug concentration, physiological parameters, and patient reaction. drug release from delivery methods like implants, patches, or nanoparticles can be tracked using biosensors. biosensors ensure the intended therapeutic impact by providing feedback on the release profile through the incorporation of sensing devices that react to changes in medication concentration or release kinetics. the drug delivery mechanism can be improved or the dosage can be changed with the use of this information [92,93]. drug monitoring, biosensors can measure drug concentrations in biological fluids, such as blood or interstitial fluid, enabling the monitoring of drug levels in real-time. this information helps in maintaining therapeutic drug concentrations within the desired range, ensuring efficacy while minimizing side effects or toxicity [94–96]. besides this, biosensors can be designed to detect specific drugs or drug classes using various sensing mechanisms, including enzymatic reactions, immunoassays, or affinity-based interactions. moreover, it can be integrated into drug delivery systems to monitor relevant physiological parameters. for example, biosensors can measure parameters such as ph, temperature, oxygen levels, or biomarkers indicative of disease progression or treatment response. this information can be used to optimize drug delivery parameters or trigger drug release in response to specific physiological cues. in addition, biosensors can be coupled with drug delivery systems to create closedloop or feedback control systems. biosensors continuously monitor drug concentrations or physiological parameters and provide feedback to control drug delivery rates or adjust dosing algorithms in real-time. this enables personalized and adaptive drug delivery, ensuring optimal therapeutic outcomes [97,98]. 10. challenges and future perspectives of electrochemical sensors because of their special qualities and possible uses, carbon-based electrochemical sensors—such as carbon nanotubes (cnts) and graphene—have drawn a lot of interest. but they also have to deal with some difficulties. because of their high electrical conductivity and huge surface area, carbon-based sensors frequently show great sensitivity. however, achieving consistent and reproducible sensor performance can be challenging due to variations in material properties and fabrication techniques. future research aims to optimize sensor performance by developing standardized fabrication processes, improving material quality, and enhancing the understanding of surface interactions and electrochemical properties. selectivity is a crucial aspect of sensor performance, as it determines the ability to distinguish the target analyte from interfering species. thus, carbon-based sensors may suffer from non-specific adsorption or interference from other components present in complex samples. future efforts focus on surface functionalization, selective modification, and integration with specific recognition elements (e.g., antibodies or aptamers) to enhance selectivity and mitigate interference effects. long-term stability is a challenge for carbon-based sensors, as they can be susceptible to fouling, surface contamination, or material degradation over time. researchers are exploring surface modification techniques, protective coatings, and encapsulation strategies to improve the stability and longevity of carbon-based sensors, especially in harsh or dynamic environments. scalability of carbon-based characterization and application of nanomaterials 2024, 7(1), 4654. 15 sensors for mass production is an important consideration for their practical applications. challenges exist in translating lab-scale fabrication techniques to scalable manufacturing processes while maintaining sensor performance and consistency. future research aims to develop cost-effective and scalable manufacturing methods for carbon-based sensors, including roll-to-roll printing, solution processing, and other high-throughput techniques. integration of carbonbased sensors into compact, portable devices or wearable systems is a key area of development. miniaturization of these sensors requires addressing challenges related to electronics integration, power management, and device packaging. future perspectives involve advancements in flexible electronics, wireless communication, and microfabrication techniques to enable the seamless integration of carbon-based sensors into various form factors. carbon-based sensors have the potential for multifunctionality and multimodal sensing by combining their electrochemical properties with other sensing modalities, such as optical or mechanical sensing. integrating multiple sensing mechanisms can provide complementary information and enhance overall sensor performance. future research focuses on developing hybrid sensor platforms that combine carbon-based materials with other functional materials or transduction principles for multimodal sensing capabilities. as with any technology, environmental considerations are important for carbon-based electrochemical sensors. efforts are being made to develop eco-friendly and sustainable fabrication processes, minimize the use of hazardous materials, and explore recycling or disposal strategies for sensor devices. 11. conclusion in conclusion, carbon-based electrochemical sensors offer unique properties and tremendous potential for various applications. these sensors exhibit high sensitivity, a large surface area, excellent electrical conductivity, and can be functionalized to enhance selectivity. however, they also face challenges such as achieving consistent and reproducible sensor performance, addressing selectivity and interference issues, ensuring stability and longevity, enabling scalable manufacturing, facilitating integration and miniaturization, and considering environmental sustainability. despite these challenges, ongoing research and technological advancements are paving the way for the future of carbon-based electrochemical sensors. efforts are focused on optimizing sensor performance through standardized fabrication processes, improving material quality, and understanding surface interactions. selectivity is being enhanced through surface functionalization, selective modification, and integration with recognition elements. stability and longevity are being 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article a theoretical study of (9, 0) singlewalled carbon nanotubes using quantum mechanical techniques deepa sharma1*, neena jaggi2 1 sus govt. college, matak-majri (indri), haryana-india. e-mail: bhargava.dp@gmail.com 2 national institute of technology, kurukshetra-(haryana)-india abstract first principles simulation studies using the density functional theory have been performed on (9, 0) zigzag singlewalled carbon nanotube (swcnt) to investigate its electronic, optical and thermodynamic properties using castep (cambridge sequential total energy package) and dftb (density functional based tight binding) modules of the material studio software version 7.0. various functionals and sub-functionals available in the castep module (using pulay density mixing treatment of electrons) and various eigen-solvers and smearing schemes available in the dftb module (using smart algorithm) have been tried out to chalk out the electronic structure. the analytically deduced values of the band gap obtained were compared with the experimentally determined value reported in the literature. by comparison, combination of anderson smearing scheme and standard diaogonalizer produced best results in dftb module while in the castep module, gga (general gradient approximation) functional with rpbe (revised-perdew-burke-ernzerh) as sub-functional was found to be the most consistent. these optimized parameters were then used to determine various electronic, optical and thermodynamic properties of (9, 0) singlewalled nanotube. (9, 0) singlewalled nanotube, which is extensively being used for sensing nh3, ch4 & no2, has been picked up in particular as it is reported to exhibit a finite energy band gap in contrast to its expected metallic nature. the study is of utmost significance as it not only probes and validates the simulation route for predicting suitable properties of nanomaterials but also throws light on the comparative efficacy of the different approximation and rationalization quantum mechanical techniques used in simulation studies. keywords: simulation; density functional theory; molecular modeling; castep; dftb; swcnt article info received: 26 december 2020 accepted: 12 february 2021 available online: 21 february 2021 copyright copyright © 2021 deepa sharma, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction since the advent of carbon nanotubes by iijima in 1991[1] and subsequent synthesis of singlewalled carbon nanotubes (swcnts) by iijima[2] & bethune[3], singlewalled carbon nanotubes have grabbed utmost attention because of their mesmerizing electrical[4,5], mechanical[6,7] and optical properties[8,9]. this multifaceted seamless one-dimensional roll of a single layer of graphite (graphene) has revealed highly promising applications in future molecular electronics[10,11] over the last few decades. the remarkable electronic properties of these 1-d structures make them suitable for various applications in nanotechnology, optics, electronics, and other fields of materials science as chemical sensors[12–19], actuators[20], nano biomaterial[21,22] , conductive heating film[23,24], conductive transparent electrode[25,26], conductive nanoink [27], nano device[28–32], and display (backlight, flat lamp and field emitter) [32,33] etc. this has invoked interest in the experimentalists as well as theore32 ticians. experimentalists are trying to develop new methods of synthesizing, purifying and functionalizing swcnts and exploring possibilities of their use into new devices and applications. on the other hand, theoreticians are implying theory and computational modeling to determine the structural, mechanical, thermal and electronic behaviour with accuracy by using computational nanotechnology. the simulation techniques are being used for predictions. various concepts and designs have been theoretically evolved through modeling and simulation and then realized or verified experimentally[34]. in this paper, the electronic structure of a (9, 0) swcnt has been investigated using dftb & castep modules of the material studio software version 7.0, and relative efficacy of various functionals and subfunctionals has been compared and electronic, optical and thermodynamic properties have been studied using the optimum combination of the functional & sub-functional and diagonalization technique & density mixing scheme. the motive behind choosing (9, 0) swcnt as the target material has on the one hand been its current extensive application as a gas sensor for the poisonous gases like nh3 [12], ch4 [13] and no2 [14]. on the other hand, the reported finite band gap in contrast to the expected metallic nature also served as a driving force for this study. 2. theory beginning with the bottom-up, a few tens to hundreds of atoms can be simulated using quantum mechanics based first principle methods, which involve the solution of the complex quantum of many body by schrödinger equation of the atomic system using different computational algorithms[35]. the atoms are treated as a group of quantum mechanical particles governed by the schrödinger equation: where, is the many-body hamiltonian operator. however, with born-oppenheimer approximation, a many body problem is reduced to a many electron problem. current first principle methods are based on the density functional theory (dft) [36,37]. dft is based on the concept that the ground state total electronic energy is a unique functional of the density of the system. kohn and sham[36,37] have shown that the dft can be reduced to a single electron problem with self-consistent effective potential, which takes into consideration the exchange correlation effects of the interactions of the electrons. this reformulation of schrödinger equation into a single electron problem is known as kohn-sham equation. many approximations like local density approximation (lda), general gradient approximation (gga), hartree fock approximation (hf), hartee fock-local density approximation (hf-lda), etc[34–47]. were proposed to approximate the effective exchange-correlation potential[36,40]. to be more specific, certain sub-functional are associated with the approximation functional like lda, ca-pz, gga-pbe, gga-rpbe, gga-pw91, gga-wc, gga-pbesol, etc[34–47]. these approximation based first principles methods have been successful in various modeling and simulation tasks planned for structural, chemical & electronic characterization of nanomaterials. for practical applications, these simulation methods are implemented with a pseudo-potential approximation (ultrasoft, normconserving or on the fly) and a plane wave basis expansion of single electron wavefunctions[47]. these approximations convert the electronic structure problem into a self-consistent matrix diagonalization problem[34,45,46]. when the iterative matrix diagonalization procedure completes, the eigen values obtained correspond to energy states of the system. the eigen functions provide information about the electronic density distribution. castep (cambridge sequential total energy package) and dftb (density functional tight binding) are immensely effective dft simulation programs available through accelrys material studio software as user-friendly modules through a license agreement[47]. 3. computational details this paper elaborates first principles investigations on a zigzag singlewalled carbon nanotube with chirality (9, 0) using the software material studio version 7.0 installed on an 8 core intel(r) core(tm) i7-3770 cpu @ 3.40 ghz with windows 33 operating system. to start with, structural unit was simulated via molecular modelling, which comprised of 144 electrons in the 36 carbon atoms of the specific nanotube giving rise to 87 energy bands in its electronic band structure. the band gap studies were performed using castep as well as dftb modules. initially the task was set up using dftb module. static calculations were performed with self-consistent charges using the smart algorithm. different combinations of diagonalization techniques (standard/divide & conquer) and smearing schemes (anderson/broyden/diis/linear) were tried. suitable choice of various tolerance parameters is very crucial for geometry optimization. the same task was then set up using castep module. the structure of the cnt was first electronically minimized through pseudo-atomic calculations using lda( ca-pz) , gga(rpbe), gga(wc), gga(pw91), gga(pbesol) functionals with pulay density mixing treatment of the electrons, choosing a suitable cutoff energy & tolerance values for various parameters like energy, maximum force, maximum stress, maximum displacement, charge spilling parameter etc. ultrasoft pseudo-potential was used in the reciprocal lattice with fixed basis set quality using gaussian smearing scheme with suitably chosen smearing width without any periodic dipole correction. bfgs algorithm which implements variable cell method with geometry line minimiser was initiated to calculate the ground state eigen values, eigen functions and density. continuing with the ground state wavefunction thus determined and ground state density thus calculated, general k-point calculations for band structure and density of states were performed. in comparison with the experimental results, the calculation performed in castep module with gga (rpbe) and the calculation performed in dftb module with standard diagonalizer & anderson smearing scheme were found to deliver the best match. hence thereafter, electronic, optical and thermodynamic studies were performed using the same combination of functional & sub-functional. 4. results and discussions 4.1 geometry optimization 4.1.1 dftb module while performing static calculations with self-consistent charges for geometry optimization using the smart eigen-solver in the dftb module, different combinations of diagonalization techniques (standard, divide & conquer) and mixing schemes (anderson, broyden, diis & linear) were tried keeping scc tolerance value at 0.1 × 104, energy tolerance value at 0.05 kcal/mol, force tolerance value at 0.05 kcal/mol/ao and ewald alpha parameter ≈ 0.22 (figure 1). the optimization process was carried out with respect to the parameters like energy change, force constant and normal stress component (figure 2a) and converged at different energies for different mixing schemes & diagonalization techniques, finally leading to an optimized hexagonal geometry (figures 2b & 2c). in all the tasks set up using dftb, thermal smearing with smearing parameter 0.005 hartree was used without any dipole correction. the results obtained may be summarized as follows: mixing scheme parameter standard diagonalization divide & conqure diagonalization anderson broyden diis linear anderson broyden diis linear total energy (hartree) –61.84978 –61.57981 –61.57979 –61.57985 –61.57981 –61.57981 –61.57979 –61.57985 total enthalpy (kcal/mol) –38777.3 –38598.7 –38598.7 –38598.7 –38598.7 –38598.7 –38598.7 –38598.7 free energy (hartree) –61.85235 –61.58217 –61.58217 –61.58215 –61.58216 –61.58217 –61.58217 –61.58215 volume (a0)3 0.288 × 104 0.269 × 104 0.269 × 104 0.269 × 104 0.269 × 104 0.269 × 104 0.269 × 104 0.269 × 104 pressure (-pa) 0.260 × 108 0.139 × 108 0.054 × 108 0.511 × 108 0.082 × 108 0.139 × 108 0.054 × 108 0.511 × 108 rms force (kcal/mol/a0) 7.479 8.573 8.573 8.573 8.573 8.573 8.573 8.573 max. force (kcal/mol/a0) 12.90 14.69 14.69 14.69 14.69 14.69 14.69 14.69 rms stress (gpa) 88.59 95.10 95.10 95.10 95.10 95.10 95.10 95.10 max. stress (gpa) 167.6 184.3 184.3 184.3 184.3 184.3 184.3 184.3 table 1. dftb geometry optimization: (9, 0) singlewalled carbon nanotube 34 figure 1. dftb geometry optimization w.r.t. a) energy b) density c) cell lengths & d) cell angles. figure 2. a) geometry optimization convergence curve. b) optimized geometry3d view c) optimized geometrycross-sectionalview. 35 it can be seen that the structure is the most stable and relaxed when treated with anderson mixing scheme under standard diagonalization (minimum energy, minimum force and minimum stress) and hence may be expected to produce the best results. hence, anderson smearing scheme in combination with standard diagonalization implemented using smart algorithm is strongly recommended for studying singlewalled nanotubes. 4.1.2 castep module in the castep module, electronic minimization of the system was performed using pulay density mixing treatment of the electrons. cut-off energy for density mixing was chosen to be 240.0 ev with a charge density mixing g-vector of 1.5/ao. pseudo-atomic calculations using lda (ca-pz), gga (rpbe), gga (wc), gga (pw91) & gga (pbesol) functionals with an energy tolerance value of 2 × 10–5 ev/atom and maximum force tolerance value of 0.05 ev/ao were performed with a charge spilling parameter for spin component 1 equal to 1.06%. geometry of the system was optimized with respect to energy change, max. displacement, max. force and max. stress (figure 3). figure 3. castep geometry optimization a) energy evolution b) optimization convergence w.r.t. i) energy ii) max. displacement iii) max. force & iv) max. stress. ultrasoft pseudo-potential was used in the reciprocal lattice with fixed basis set quality using gaussian smearing scheme with smearing width of 0.1 ev without any periodic dipole correction. geometry of the system was optimized using bfgs algorithm implementing variable cell method with geometry line minimiser of tolerance 0.4. lattice parameters obtained after geometry optimization were a = 10.392983 ao, b = 10.392983 ao & c = 4.260000 ao (cell volume = 398.492992 (a0)3) with cell angles 90o, 90o & 120o confirming the suggested hexagonal geometry (figure 4). figure 4. optimized geometry obtained by supercell approach using castep a) lateral view b) 3-d view. the unit chosen comprised of 36 units. as ex36 pected, the first brullion zone obtained was also hexagonal. supercell approach was adopted. 6 k-points were chosen for bz sampling. 4.2 electronic properties continuing with the ground state wavefunctions during the geometry optimization task and the ground state density thus calculated, general k-point calculations for band structure were performed using complex wavefunction with 84 bands per k-point and a band convergence tolerance of 0.1 × 10–4 ev. fermi energy for the spin-degenerate system with electrical quadrupole moment 0.0332700 barn was calculated keeping 23 basis set k-points under consideration. general k-point calculations for density of states were also performed treating the system as non-spin-polarized with total energy/atom convergence tolerance value equal to 0.2 × 10–5 ev, all bands spilling parameter for spin component 1 & eigen energy convergence tolerance value equal to 0.8276 × 10–6 ev. 4.2.1 dftb module band structure and density of states of the optimized structural unit were determined and investigated using smart algorithm without any dispersion correction using various combinations of diagonalization techniques (standard/divide & conquer) and mixing schemes (anderson/broyden/diis/linear) (figure 5). thermal smearing with smearing parameter equal to 0.005 hartree was used during all these band structure calculations. the values of band gap of (9, 0) swcnt calculated using dftb module can be summarized as below: band structure and density of states of (9,0) swcnt calculated using density functional tight binding module figure 5a). band structure deduced with eigen-solver “divide & conquer”, mixing scheme—anderson. on the basis of the measurements made by leiber et al. under ultrahigh vacuum conditions at 5 k on a au (111) substrate, the experimental value of the band gap of (9, 0) swcnt has been found to be 0.080 ev[48]. by comparing the simulation results with this experimental value, it can be inferred that dftb module tends to drastically underestimate the band gap value. however, the results obtained with standard diagonalizer and anderson mixing scheme with mixing parameter 0.05 are comparatively close enough. 4.2.2 castep module band structure and density of states were also standard diagonalization divide & conqure diagonalization anderson broyden diis linear anderson broyden diis linear 0.063 ev 0.003 ev 0.005 ev 0.004 ev 0.003 ev 0.003 ev 0.005ev 0.004ev table 2. band gap evaluation using dftb: (9, 0) singlewalled carbon nanotube 37 figure 5b). band structure deduced with eigen-solver “divide & conquer”, mixing scheme—broyden. figure 5c). band structure deduced with eigen-solver “divide & conquer”, mixing scheme—diis. figure 5d). band structure deduced with eigen-solver “divide & conquer”, mixing scheme—linear. 38 figure 5e). band structure deduced with eigen-solver “standard”, mixing scheme—anderson. figure 5f). band structure deduced with eigen-solver “standard”, mixing scheme—broyden. figure 5g). band structure deduced with eigen-solver ‘standard’, mixing scheme—diis. 39 figure 5h). band structure deduced with eigen-solver “standard”, mixing scheme—linear. determined and investigated with the help of the castep module of the software using various available functionals and subfunctionals (figure 6). fermi energy for the spin-degenerate system with electrical quadrupole moment 0.0332700 barn was calculated keeping 23 basis set k-points under consideration. the values of band gap of (9, 0) swcnt calculated using castep module can be summarized as below: table 3. band gap evaluation using castep: (9,0) singlewalled carbon natotube comparing these results with the measurements made by leiber et al. (eg = 0.080 ev), it can be seen that some of the functional-subfunctional combinations in the castep module tend to overestimate the value of the bond gap while others underestimate the value. however, the value of the band gap obtained with gga functional and rpbe subfunctional is very close to the experimentally observed value. hence, it can be concluded that gga-rpbe exchange correlation approximation is the most effective theoretical tool for predicting band gaps in swcnts. as (3 m, 0) swcnts are supposed to be of metallic nature, the finite band gap determined theoband structure and density of states of (9,0) swcnt calculated using castep module figure 6a). band structure deduced with functional—“lda” and subfunctional—“ca-pz”. lda gga ca-pz rpbe pbesol wc pw91 0.190 ev 0.097 ev 0.161 ev 0.063 ev 0.003 ev 40 figure 6b). band structure deduced with functional—“gga” and subfunctional—“rpbe”. figure 6c). band structure deduced with functional—“gga” and subfunctional—“pbesol”. figure 6d). band structure deduced with functional—“gga” and subfunctional—“wc”. 41 figure 6e). band structure deduced with functional—“gga” and subfunctional—“pw91”. retically (as well as experimentally by leiber et al.) is somewhat unusual. this can however be explained on the basis of σ*-π* hybridization effects caused by the curvature of small-diameter cnts. in these small cnts, the π* and σ* states mix and repel each other, leading to lower pure π* states. 4.3 optical properties pseudo atomic calculations performed on c (2s2 2p2) converged in 17 iterations to a total energy of –145.6516 ev. pulay density mixing treatment with gaussian smearing was used with finite basis set correction. partial and full phonon density of states and phonon dispersion curves were determined using linear response phonon calculation (figure 7). figure 7. phonon dispersion w.r.t. a) partial phonon density of states b) full phonon density of states. 42 group theory analysis of eigenvectors reveals that the simulated structure displays point group 27: d6h, 6/mmm, 6/m 2/m 2/m symmetries and allows scope for 24 symmetry operations. frequency calculation at 23 wavevectors was performed using gonze variational method with tpa preconditioning scheme. the optimized structure was found to belong to the point group 27: d6h, 6/mmm, 6/m 2/m 2/ m. with 24 symmetry operations. various optical properties of the optimized geometry were investigated using 6 k-point bz sampling over 84 bands (figure 8). figure 8. (9, 0) swcnt: optical properties a) absorption b) real & imaginary part of photoconductivity c) real & imaginary part of dielectric function d) loss function. from the above curves, the refractive index n and the extinction coefficient k can be easily calculated for any frequency as from the maxwell’s relation: n*= ɛ ½ here n* is a complex number. its real part gives the refractive index n and the imaginary part gives the extinction coefficient k. i.e. refractive index n = re (n*) & extinction coefficient k = im (n*) further, the absorption coefficient α and reflection coefficient r for normally incident radiation of any frequency may also be calculated as: α = 2ωκ/c r = | (n* − 1)/ (n* + 1)| 2 where c is the velocity of light. it is clearly evident from the definition that the reflectivity is always positive in the scheduled range of the frequency and is dimensionless. r is sometimes regarded as the index of refraction as a function of the wavelength of light used. 43 the conductivity σ (ω) is related to the dielectric constant via the relation σ (ω) = σ1 + iσ2 = −iω 4π (ε − 1) the loss function, which is a direct measure of the collective excitations of the systems may be calculated as im[−1/ε]. some straightforward algebra may easily reveal that im[−1/ε)] = ε2 / ε1 2 + ε2 2 at the plasma frequency, the above expression attains the higher value when ε1 → 0 and ε2 < 1. 4.4 thermodynamic properties various thermodynamic properties calculated using first principles method through dftb and castep module of the software have already been discussed in table 1. also, the variation of debye temperature with respect to the ambient temperature was determined (figure 9a) for the simulated super-cell structure (figure 9b). figure 9. a). debye temperature vs ambient temperature b) supercell approach. it can be seen that the debye temperature shows striking variations at extremely low temperatures. however, the general formula for the debye temperature derived from fundamental quantum and thermodynamic assumptions has been very well known as: td = ћωd/2π kb where ωd is the debye frequency and kb is the boltzmann constant. having a casual look at the relation may make one wonder whether temperature dependence of the debye temperature makes any sense. as per the relation, debye temperature should rather be independent of the ambient temperature. at this instance, it may be emphasized that the relation arrived at involves various approximations and the debye temperature has very important physical meaning associated to it, which must be clearly understood. the maximum energy which can be reached by acoustic thermal vibration of a crystalline solid may be expressed as: umax acoustic =∑∑∑ nna e max acoustic where emax acoustic is the maximum acoustic thermal vibration energy of an atom. beyond this energy, interacting or organized lattice vibration does not exist and the thermodynamic behavior of the system is described by independent lattice vibration. the temperature where the collective or acoustic vibration shifts to an independent thermal vibration is the debye temperature, which can be defined as: t = td when umax acoustic = uthermal in other words, debye temperature is the temperature needed to activate all the phonon modes in a crystal. thus, higher value of debye temperature may be associated with stiffness of the material. the strikingly high value of the debye temperature at extremely low ambient temperature thus points towards exceptional stiffness of the swcnt under extreme cold conditions. at average room temperature and higher temperatures, it is more or less constant as expected. 44 5. conclusions this first principles study has been performed on (9, 0) singlewalled carbon nanotube and an effort has been made to determine their electronic, optical and thermodynamic properties using castep (cambridge sequential total energy package) and dftb (density functional based tight binding) modules of the material studio software version 7.0. various available algorithms, eigen-solvers, diagonalization techniques, density mixing methods, smearing schemes, functionals, subfunctionals have been tried out and their relative efficacy has been adjudged by comparing with the available experimental data. combination of standard diagonalizer, smart algorithm and anderson mixing scheme in the dftb module and the combination of gga functional and rpbe sub-functional in the castep module have provided fairly good results. these optimized quantum-mechanical calculations not only provide an insight into the structural behaviour of nanomaterials but also present themselves as an effective, convenient and timesaving tool for predicting their physical properties. it may further be mentioned that the unit simulated was a periodic nanostructure (specific tasks on non-periodic structures not covered under the license agreement) and the length of the nanotube simulated was therefore taken at default. variations in the length may 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with numeric atom-centered orbitals. computer physics communications 2009; 180: 2175–2196. 46. kresse g, furthmüller j. efficient iterative schemes for ab initio total-energy calculations using a planewave basis set. physics review b 1996; 54: 11169– 11186. 47. segall m, linda p, probert m, et al. materials studio castep, version 2.2. accelrys: san diego, ca; 2002. 48. matsuda y, tahir-kheli j, goddard iii wa. definitive band gaps for single-wall carbon nanotubes. the journal of physical chemistry letters 2010; 1(19): 2946–2950. characterization and application of nanomaterials (2023) special issue: nanocomposites processing, characterization, and applications doi:10.24294/can.v6i2.3361 1 review article cutting-edge conjugated nanocomposites—fundamentals and anticorrosion significance ayesha kausar1,2,*, ishaq ahmad1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, china. 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa. * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract this review is merely designed to throw light on the cutting-edge conjugated nanocomposites based on conjugated or conducting polymers and appropriate nanofillers. an important aspect of the conjugated nanocomposites has been observed in the anticorrosion of metals or metallic substrates. particularly, including carbon nanoparticles (fullerene, graphene, and carbon nanotube) and inorganic nano-additives to the conjugated matrices have enhanced the physical features (morphology, electrical conductivity, mechanical stability, adhesion, and barrier properties) as well as corrosion resistance. to access the anti-corrosion potential, the conjugated nanocomposites have been coated on metal substrates using facile techniques of solution, spraying, dipping, and others. accordingly, competent anti-corrosion conjugated nanocomposites have found potential for energy or electronic devices, engineering structures, and so on. keywords: conjugated; nanocomposites; matrix; conductivity; anti-corrosion article info received: 20 november 2023 accepted: 6 december 2023 available online: 30 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction nanocarbon nanoparticles have been considered important fillers for nanocomposites and applied for technical applications[1,2]. corrosion has been identified as a serious problem for metals employing industries[3]. to thwart corrosion related challenges, polymer based materials and nanomaterials have been focused in literature[4]. here, conjugated or conductive materials have gained special emphasis to treat the corrosion issues of metals or other affected materials[5]. a basic problem has been documented as the interaction of corrosion causing species to metal surfaces causing harmful effects[6]. in this concern, the coating of conjugated materials on metal surfaces has been used to prevent corrosion[7]. mechanism of corrosion prevention has also been examined[8]. adding nanoparticles in conjugated nanocomposites has been found to further enhance the performance of these anti-corrosion coatings[9]. the conjugated nanocomposite coatings have been explored using numerous chemical, electrochemical, and physical practices[10,11]. according to the literature, the application of conjugated coatings on metal surfaces enhanced the adhesion strength and wear resistance, relative to neat steel metal[12]. fine nanoparticle dispersion has been found to enhance the nanocomposite coating performance to prevent the corrosion issue. 2 this article basically offers a cutting-edge review of conjugated nanocomposite coatings for anticorrosion of metal surfaces. fundamentals of corrosion, corrosion protection mechanisms, and coating processes have been stated. the importance of using nanocomposites and conjugated nanocomposites for corrosion protection utilizations has been analysed. specifically, adding nanocarbon nanoparticles has been found to considerably enhance the anti-corrosion performance of these conjugated nanocomposite coatings. morphology, physical features, and anti-corrosion performance of the conjugated nanocomposites have been deliberated. resulting anti-corrosion coatings have been used in essential technical sectors. this is an allembracing, revolutionary, and up-to-date review of corrosion resistance of conjugated polymers and derived nanocomposites covering design, properties, and technological relevance. to the best of our knowledge, the anticorrosion potential of conjugated polymer/nanocarbon nanocomposites has not been reviewed comprehensively in the literature before. consequently, this article is undoubtedly a radical contribution in the field of corrosion resistance conjugated nanocomposites. future growths in the field of anticorrosion conjugated polymer/nanocarbon nanocomposites are not possible for the field scientists or researchers before getting prior compiled literature knowledge on these materials. 2. conjugated materials for corrosion protection conjugated polymers or conducting polymers have been considered as important materials for corrosion protection of metals[13–15]. conjugated polymers like polyaniline, polypyrrole, and others have been frequently applied in anti-corrosion coatings. corrosion effects can be perceived in these coatings due to the surface cracking leading to the approach of corrosive species to metal surfaces. polyaniline coatings have been deposited on the steel or iron surface to prevent corrosion effects[16]. a direct relation has been observed between the electrical conductivity and corrosion resistance of the materials. an increase in electrical conduction has improved the electrochemical and anti-corrosion performance of the conjugated polymers[17]. the corrosion process is usually prevented by increasing the electrical conductivity of the anticorrosion coating applied on the metal surface. therefore, a direct relationship exists between the rise in electrical conductivity and improving corrosion resistance. metal corrosion usually occurs when metal atoms interact with atmospheric molecules to form oxides, hydroxides, and other molecules to cut the electron flow of metal atom’s orbitals. in other words, when metal atoms are corroded, electrons cannot hop through the metal for electron conduction. once the metal surface is corroded, electron flow pathways are restricted, so lowering the electrical conductivity. conjugated polymers usually form a protection layer over the metal surface. research revealed that the formation of a conductive polymer layer on the metal surface offers corrosion protection via the formation of passive oxide layer involving oxidation-reduction reactions and also the barrier effect. consequently, the likelihood of the corrosion phenomenon is delayed. nevertheless, complex corrosion protection mechanisms have been found to be involved in corrosion protection by conducting polymers. the mechanism of corrosion protection by conducting polymers is in turn affected by numerous parameters. the amount of coated material may also affect the corrosion rate. in addition, polypyrrole has been used to form anti-corrosion coatings on iron or aluminum metal surfaces[18,19]. the corrosion rate greatly relies on factors like amounts, surfactants, ph, and other ecological factors. for conjugated polymers, anti-corrosion performance has been found to be upsurged using nanofillers as well as inhibitors[20,21]. 3. nanocomposites of conjugated polymers for corrosion resistance undoubtedly, conjugated polymers have been found functional for the anti-corrosion of metals[22]. conjugated polymers have the efficiency to better interact with the metal surfaces to avert the harmful effects[23]. metal surfaces commonly act as anodes and conjugated polymers perform as cathodes to encounter corrosion issues through electrochemical reactions[24]. temporarily, anti-corrosion occurs due to metalconjugated polymer interface reactions[25]. adding additives or nanoparticles has been preferred to supplement 3 the anti-corrosion performance by averting the corrosive media from the metal surfaces[26]. consequently, conjugated nanocomposites have been designed to have superior anti-corrosion and scratch/wear resistance features, than pristine conjugated polymers[27]. high performance coatings of conjugated nanocomposites of polyaniline, polypyrrole, and others have been reported[28,29]. these nanocomposite coatings have been frequently deposited using the chemical or electrochemical approaches and electron conduction and charge transference effects have been examined. 4. conjugated nanocomposites with nanocarbon for anti-corrosion conjugated nanocomposites have been designed using the conducting polymer matrix and carbon nanoparticle reinforcements[30–32]. adding nanocarbons to conjugated nanocomposites has resulted in efficient coatings with facile synthesis, physical features, and technological uses. among carbon nano-reinforcements, carbon nanotube has been adopted as a widely used and effective nanofiller to the conjugated polymers to augment the physical profile[33–35]. deshpande et al.[36] specified nanocomposite coatings of polyaniline filled with multi-walled carbon nanotubes to protect carbon steel. open circuit potential studies were used to assess the corrosion resistance performance. anti-corrosion coatings of polypyrrole and carbon nanotube have also been developed[37]. han et al.[38] formed high performance anti-corrosion polypyrrole/multi-walled carbon nanotube nanocomposite coatings. richard prabakar and pyo[39] designed multi-walled carbon nanotube reinforced poly(3,4-ethylenedioxythiphene) nanocomposite coatings for corrosion prevention. the nanomaterial coatings had electrostatic repulsions to avert the corrosion causing anions from the metal surface. mariano et. al.[40] reported on polyaniline and carbon nanotube based nanocomposites focusing on electron conduction and corrosion resistance profiles. including 1 wt.% carbon nanotube revealed high electrical conductivity of 0.06 scm–1, i.e., five orders higher than neat polyaniline (figure 1). on the other hand, lower carbon nanotube loading of 0.25 wt.% exposed minor electrical conductivity of about ∼10−7 scm–1. figure 2 presents a model for the conductive carbon nanotube filled polyaniline matrix. it was proposed that the carbon nanotube bundles were uniformly aligned in the matrix and separated by an insulating polyaniline layer. the aligned nanofillers developed conduction paths through the polymer for efficient electrical conductivity. it was suggested that the coupling may occur among adjacent carbon nanotube bundles for better passage of electrons, in the direction of applied electric field. the tunnelling effects between the carbon nanotube bundles may be hindered due to the polymer layer in between. in addition to carbon nanotubes, graphene and graphene oxide nanofillers have been used to improve the electron conductivity, barrier, mechanical, and thermal features of the conjugated polymers[41–43]. owing to the large surface area and surface properties, graphene and related nanoparticles exposed fine barrier properties and anti-corrosion resistance[44]. chang et al.[45] studied tortuous ways in polyaniline/graphene nanocomposite coatings, responsible for averting h2o and o2 molecules due to barrier effects, so producing anti-corrosion effects[46]. lin et al.[47] fabricated epoxy nanocomposite coatings filled with polyaniline functional graphene figure 1. conductivity as a function of carbon nanotube wt.% at 1 v[40]. reproduced with permission from acs. 4 figure 2. (a) schematic of polyaniline/carbon nanotube nanocomposite; and (b) fibrillar conduction path through two carbon nanotube bundles separated by an insulating polyaniline layer. this junction is modelled by two domains (open and filled) with two conductivities in series[40]. reproduced with permission from acs. oxide. the coatings have been reported for fine barrier and anti-corrosion features due to mutual interactions between the polyaniline, graphene oxide, and epoxy[48]. corrosion inhibition effects of graphene oxide have been explored in literature[49]. ramezanzadeh et al.[50] designed polyaniline nanocomposite coatings filled with graphene oxide and cerium. the nanomaterial coatings were coated on the mild steel and corrosion effects were studied. functionalization of graphene oxide with nanoparticles further boosted the anti-corrosion performance of these coatings by developing twisted diffusion paths throughout the nanocomposites. sheng et al.[51] fabricated polyaniline nanocomposites filled with graphene oxide and p-phenylenediamine functional graphene oxide nanofillers. the nanomaterials were prepared using the in situ redox polymerization. this study explored the synergistic effects between matrix and nanofiller on the morphology and anti-corrosion characteristics of the nanocomposites. scanning electron microscopy and transmission electron microscopy micrographs of graphene oxide and p-phenylenediamine functional graphene oxide are given in figure 3. it can be observed that the p-phenylenediamine functional graphene oxide had a more wrinkled nanosheet nanostructure owing to interactions between the p-phenylenediamine and graphene oxide. comparatively, pristine graphene oxide has a lesser crumpled and smooth nanosheet nanostructure. owing to the wellinteracted phenylenediamine-graphene oxide nanostructure, the nanosheets avoid reaggregation tendency. figure 4 depicts the nyquist plots of polyaniline/phenylenediamine/graphene oxide nanocomposites with various nanofiller loading. adding nano additives enhanced the semicircle diameters due to improvement in the charge transfer resistance or polarization of the nanomaterials. consequently, the addition of nanofiller averted the diffusion of corrosive electrolyte molecules through the nanocomposite coating. according to equivalent circuit studies, electrolyte resistance, polarization resistance, and charge transfer resistance revealed corrosion resistance of the nanocomposite coatings. figure 5 depicts the proposed model for the nanocomposites with corrosion diffusion pathways. dispersion of functional nanofiller in polyaniline caused considerable hindrance to the penetrating corrosive molecules through nanocomposite coating towards metal. on the other hand, neat polymer coating had no resistance to the seeping corrosion species, so affecting the metal surface. henceforth, these nanocomposite coatings had up to 99.9% anti-corrosion efficiency, as per potentiodynamic polarization results. catt et. al.[52] filled graphene oxide in poly(3,4-ethylenedioxythiphene) matrix to develop the nanocomposite coatings using electro-polymerization. for anti-corrosion studies, the magnesium surface was focused. figure 6 depicts the cracked surface of poly(3,4-ethylenedioxythiphene)/graphene oxide coating after corrosion. in corrosion current vs. voltage scans, lower or more positive corrosion current was experiential for coated sample, related to the non-coated surface. the result depicted higher anti-corrosion efficiency of the nanocomposite material. 5 figure 3. high magnification scanning electron microscopy images of (a) graphene oxide and (b) p-phenylenediamine functional graphene oxide; and transmission electron microscopy images of (c) graphene oxide and (d) p-phenylenediamine functional graphene oxide[51]. reproduced with permission from acs. figure 4. (a) nyquist plots; and (b) equivalent circuit model of polyaniline/p-phenylenediamine functionalized graphene 3 wt.% (ppcc03), polyaniline/p-phenylenediamine functionalized graphene 5 wt.% (ppcc05), and polyaniline/p-phenylenediamine functionalized graphene 10 wt.% (ppcc10)[51]. reproduced with permission from acs. figure 5. the model of corrosive diffusion pathways through the coatings[51]. ppc = polyaniline/p-phenylenediamine functionalized graphene; psc = pristine polyaniline. reproduced with permission from acs. (a) (b) figure 6. (a) scanning electron microscopy image of a crack in pedot/go film after corrosion with cracked scale like morphology indicated by an arrow; and (b) corrosion current vs. voltage scans of coated and uncoated surface[52]. pedot/go = poly(3,4ethylenedioxythiphene)/graphene oxide. reproduced with permission from elsevier. (a) (b) 6 the inclusion of graphene and derives in conjugated polymers has promoted electron conductivity. this rise in electrical conductivity can be attributed to the fine electron conduction of graphene having high symmetry. graphene has advantage of developing widespread π electron delocalization[53]. the rise in electrical conduction of graphene coatings in turn supports oxidation-reduction reactions and barrier effects for corrosion resistance. fullerene is a significant zero dimensional carbon nanofiller used in corrosion resisting polymeric nanocomposites[54–56]. here, fullerene has capability to develop van der waals or π-π interactions with the polymers[57]. the mutual interactions industrialised better diffusion trails for corrosion species and supported electron conduction through the coatings[58]. consequently, the corrosion mechanism can be explained on the basis of matrix-nanofiller associations in charge of transporting conjugated polymer/fullerene systems[59]. polyaniline and fullerene based nanomaterials have been designed[60–62]. polyaniline has been reported to form a charge transfer complex with fullerene nanoparticles[63]. cheng et al.[64] fabricated fullerene c60 filled polyaniline nanocomposites. the electrical conductivity was found to increase from 9 × 10–10 to 63.7 sm–1, leading to efficient anti-corrosion performance. gizdavic-nikolaidis et al.[65] also prepared a nanocomposite coating of c60 nanoparticles reinforced polyaniline. dispersion in the nanocomposite was premeditated using transmission electron microscopy. the nanoparticle sizes of 50–100 nm were observed in the matrix. fine dispersion produced better electron transference routes to support charge transfer and anti-corrosion performance. wang et al.[66] developed polyaniline and fullerene c60 nanowhisker derivative nanocomposites. figure 7 illustrates the microstructure of polyaniline doped fullerene c60 nanowhiskers according to scanning electron microscopy. adhesion of a thin polymer layer can be experiential on a fullerene nanorod surface due to the formation of a charge transfer complex. such nanostructures have improved the electrical conductivity, leading to better corrosion confrontation[67]. polypyrrole has also been filled with fullerene nanoparticles to form high-tech nanocomposites[68–70]. wysocka-zolopa et al.[71] reported on the polypyrrole and fullerene c60 based nanocomposites using chemical oxidative polymerization. figure 8 depicts the in situ synthesis of polypyrrole and fullerene c60 resulting in nanocomposite. here, the in situ route seemed effective in developing the well-interlinked polypyrrole-fullerene nanomaterial. polythiophene is another conjugated matrix polymerized via electrochemical polymerization[72]. a doping process has been used to upsurge the electron conduction of polythiophene even higher than 100 scm–1[73]. polythiophene derived forms like poly(3-octylthiophene), poly(3-hexylthiophene), poly(3-octadecylthiophene), etc., have also been focused[74,75]. zabihi et al.[76] developed fullerene c60 filled poly(3-hexylthiophene) nanocomposite coatings. the nanomaterial had superior charge transfer and anti-corrosion due to matrix (a) (b) figure 7. scanning electron microscopy images of (a) fullerene nanowhiskers; and (b) polyaniline doped nanowhiskers[66]. reproduced from hindawi (published open access). 7 figure 8. development of polypyrrole and fullerene c60 derived nanocomposites[71]. reproduced with permission from acs. table 1. design, synthesis, and corrosion efficiency of conjugated polymer and nanocomposites. material synthesis corrosion efficiency ref polyaniline in situ or electrochemical polymerization icorr 0.112 µa cm–2; ecorr –0.596 v 3.5% nacl; 8 h [77] polyaniline in situ polymerization ammonium persulfate; sulfuric acid ∼ 0.06 scm–1 [40] polyaniline/carbon nanotube in situ polymerization ammonium persulfate; sulfuric acid ∼ 10−7 scm–1; tunneling 11-15 å vs. carbon nanotube contents [40] polyaniline in situ chemical oxidative polymerization; ammonium persulfate 5.30 × 10–3 scm–1 [78] polyaniline/carbon nanotube 20 wt.% in situ chemical oxidative polymerization; ammonium persulfate 2.72 × 10–1 scm–1; visibly decreased corrosion relative to pristine sample [78] polyaniline in situ chemical oxidative polymerization icorr –610 µa cm–2; ecorr 0.718 mv [79] polyaniline/carbon nanotube 2 wt.% in situ chemical oxidative polymerization; ammonium persulfate icorr –467 µa cm–2; ecorr 0.31 mv [79] polypyrrole in situ polymerization icorr –0.943 µa cm–2; ecorr 17.5 mv [80] polypyrrole/carbon nanotube 1 wt.% in situ polymerization icorr –0.294 µa cm–2; ecorr 21.5 mv [80] polythiophene in situ method electrical conductivity σ 9.9 × 10–12 scm–1 [81] polythiophene/carbon nanotube in situ method electrical conductivity σ 1.2 × 10–10 scm–1 [81] polyaniline electrodeposition icorr 2.46 × 10–8 a cm–2; ecorr 0.086 v [82] polyaniline/graphene oxide electrodeposition icorr 5.04 × 10–9 a cm–2; ecorr 0.247 v [82] polythiophene solution method icorr 3.47 × 10–5a cm–2; ecorr –0.62 v [83] polythiophene/graphene oxide solution method icorr 5.70 × 10–5a cm–2; ecorr –0.578 v [83] poly(3-hexyl-thiophene): phenyl-c61-butyric acid methyl ester solution method increase in corrosion efficiency to 100%; 100 h [84] nanofiller associations. table 1 demonstrates important literature examples on the design, synthesis, and corrosion efficiency of pristine conjugated polymers as well as nanocarbon nanocomposites for comparison. including nanocarbons have found to enhance the electrical conductivity as well as anticorrosion potential of the nanocomposites. 8 5. prospects and conclusions conducting nanocomposite coatings has gained an immense stance in the methodological and engineering industries[85,86]. conjugated polymers may have optimum electron conductivity, however, there is a lack of structural resilience, limiting major applications. in this context, nanoparticles have been filled in the conjugated polymers to improve the adhesion, durability, and wear properties, when applied on the metal surfaces[87]. especially, carbonaceous nanoparticles have been used to improve the barrier effects and corrosion inhibition features of the conjugated polymers. the main factors contributing to the anti-corrosion performance include the matrix-nanofiller associations, interface formation, development of charge transportation paths, and formation of resistive paths for the seeping of corrosive species[88]. all these aspects can contribute to the prevention of corrosive species approaching the metal surface for corrosion purposes. corrosion prevention mechanisms have been mostly investigated in terms of barrier effects as well as the electrochemical defense of metals against corroding species[89]. for anti-corrosion coating fabrication, mostly in situ polymerization, electro-polymerization, and solution practices have been applied. recently, sophisticated techniques like spin coating, spray coating, and dipping routes have been considered for the formation of evenly layered nanocomposites on metal surfaces. the fate of conjugated nanocomposite coatings depends upon the design and fabrication of efficient innovative self healing materials[90]. consequently, the self-healing phenomenon can better promote the corrosion resistance of the nanocomposite coatings[91]. in effect, the self healing coatings have the potential to release self healing particles to recuperate the corrosion damage in the materials[92]. in such coatings, self healing nanocapsules can be loaded which can act in specific corrosion conditions[93]. future labors are demanded to generate the self healing coatings of the conducting polymers and conjugated nanocomposites having outstanding anti-corrosion efficiency[94]. in this way, self healing anticorrosion coatings need to be designed for future electronics, automobile, and engineering industries[95]. this article is planned to schematically portray the impact of conjugated polymer and conjugated nanocomposites in the corrosion protection of metals. for the formation of conjugated nanocomposite coatings, conducting polymers like polyaniline, polypyrrole, polythiophene, and related derivatives have been used as matrices. these polymers were filled with nanocarbon nanofillers to enhance the anti-corrosion features. facile routes have been adopted to fill the conjugated matrices with carbon nanoparticles. subsequently, anticorrosion properties and involved mechanisms were examined. carbon nanoparticles have resulted in improved anti-corrosion performance due to fine nano-additive dispersion, mutual interactions, and the formation of charge or electron diffusion pathways throughout the nanocomposite. all these synergistic effects led to a fine anti-corrosion performance. hence, the conjugated nanocomposites have been efficiently used to protect the metals and metallic components from harmful corrosion effects. author contributions conceptualization, ak; 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2019. doi: 10.1039/9781788016667 can v3i1 2020.pdf characterization and application of nanomaterials (2020) volume 3 issue 1 original research article *key laboratory for magnetism and magnetic materials of the ministry of education, school of physical science and technology, lanzhou university, lanzhou 730000, gansu province, china. *e-mail: pengshl@lzu.edu.cn. e-mail: zhangjch@lzu.edu.cn keywords: et al. et al. et al. et al. et al. ii i i i et al. et al. et al. et al et al. et al. et al. et al. et al. et al. et al. et al et al et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. characterization and application of nanomaterials (2022) volume 5 issue 1 doi:10.24294/can.v5i1.1408 10 original research article synthesis and in vitro anticancer properties of cu2–xse–aiph nanomaterials juan lu, yini mao, jun yang* school of chemistry and chemical engineering, southwest university, chongqing 400715, china. e-mail: jyang@swu.edu.cn abstract the cu2–xse nanoparticles were synthesized by high temperature pyrolysis, modified with aminated polyethylene glycol in aqueous solution and loaded with compound 2,2′–azobis[2–(2–imidazolin–2–yl)propane] dihydrochloride (aiph). the obtained nanomaterials can induce photothermal effect and use heat to promote the generation of toxic aiph radicals under the irradiation of near-infrared laser (808 nm), which can effectively kill cancer cells. a series of in vitro experiments can preliminarily prove that cu2–xse–aiph nanomaterials have strong photothermal conversion ability, good biocompatibility and anticancer properties. keywords: cu2–xse nanoparticles; aiph; photothermal effect; anticancer properties article info received: 26 september 2021 accepted: 19 november 2021 available online: 30 november 2021 copyright copyright © 2022 juan lu, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4 .0/ 1. introduction cancer has now become one of the major threats to people’s health all over the world, and countless people lose their lives due to cancer every year. however, there are problems lying in treatment methods of traditional chemotherapy, radiotherapy, and surgery, such as great side effects and low treatment efficiency. therefore, it is urgent to develop some novel and effective cancer treatment methods[1–5]. in recent years, photothermal therapy (ptt) has attracted more and more scientists’ attention in the field of cancer treatment due to its low invasiveness[6–8]. the therapeutic principle is that photothermal materials can effectively convert light energy into heat energy after absorbing the external light energy, thereby triggering the withering or death of cancer cells. based on this, batches of excellent photothermal materials have been created continuously, including binary chalcogenides with unique physical and chemical properties[9]. at the same time, near-infrared light is also closely connected to cancer treatment due to its deeper penetration depth in biological tissues compared with ultraviolet light[10–12]. take advantage of the photothermal effect of selenide cu2–xse and combine it with other therapeutic agents. cu2–xse nanoparticles with a particle size of 20–40 nm were synthesized by a classical high-temperature pyrolysis method, and the compound 2,2′–azobis[2– (2–imidazoline–2–yl)propane] dihydrochloride (aiph), an azo compound that rapidly decomposes during heating to produce toxic alkyl groups, was loaded after aminated polyethylene glycol modification. 11 due to the large tumor cell gap, the tumor microenvironment has high enhanced permeability and retention effect (epr), and anti-tumor nanomaterials will passively be targeted to tumor sites to play a role of treatment; without extra light and heating, the body temperature about 37 ℃ will not cause the decomposition of aiph to generate free radicals. therefore, aiph itself will not cause damage to the normal tissues of the organism. due to the lack of copper atoms, cu2–xse nanoparticles have strong plasmon resonance absorption (lspr) and excellent photothermal properties in the near-infrared region where the penetration of biological tissues is strong, and have been increasingly used in the field of photothermal therapy. the cu2–xse–aiph nanoparticles synthesized by this system can generate photothermal temperature up to 48 ℃ after absorbing 808 nm near-infrared light, which is sufficient for photothermal therapy. under the action of near-infrared light, the photothermal effect of cu2– xse nanoparticles can play a synergistic effect with aiph free radicals to kill tumor cells. the anticancer properties of cu2–xse–aiph materials were preliminarily proved through a series of in vitro experiments. 2. experiment 2.1 experimental reagents the reagents used in this experiment including cuprous chloride (cucl), aminated polyethylene glycol (nh2–peg(2000)–nh2), 1–(3–dimethy laminopropyl)–3–ethylcarbodiimide hydrochloride (edc), n–hydroxysuccinimide (nhs), oleylamine, octadecene, and anhydrous ethanol (c2h5oh) were all at an analytical grade and were used directly in the experimental process without further purification. all chemicals were purchased from sigma-aldrich, except for the selenium powder (se) which was purchased from sinopharm chemical reagent co., ltd. 2.2 preparation process cu2–xse nanoparticles were synthesized by a typical solvent injection method with slight modifications from the previous literature[13]. the preparation process was mainly divided into two stages. first, the precursor of se–oam (selenium-oleylamine) was synthesized. weigh 10 mmol of selenium powder and 10 ml of oleylamine into a three-necked flask, set up a pyrolysis device, add nitrogen, and heat it to 140 ℃ with a heating mantle for 10 min to remove moisture and some low-boiling impurities. then the temperature was raised to 320 ℃ for a period of time, and the obtained brown solution was the precursor se–oam. at the same time of the constant temperature reaction, take another four-necked bottle, weigh 0.5 mmol of cucl, 8 ml of octadecene (ode) and 2 ml of oleyl amine in it, also keep it in a nitrogen environment for 10 min, and then heat it up to 200 ℃ and immediately inject the se–oam solution prepared in the previous step, and then continue to heat it up to 220 ℃ for a period of time. the obtained black-brown solution was washed three times alternately with ethanol, cyclohexane and ethanol to obtain cu2–xse nanoparticles, wherein the amount of each washing solvent was equal to the volume of the reaction solution, about 10 ml. the synthesized cu2–xse nanoparticles were then modified with amino groups to improve their hydrophilicity for subsequent compound loading and testing applications. the prepared nanoparticles were mixed with 10 mg of eds and 20 mg of nhs in methanol solvent and stirred for 1.5 h in the dark environment. then 40 mg of nh2–peg(2000)–nh2 was added to the above solution, and the obtained solution was washed with methanol and deionized water and centrifuged after the reaction was continued for 12 h. subsequently, 0.2 g of aiph and the aminated product were kept in a water bath at 70 ℃ for 4 h. finally, the reactant was washed several times with ethanol to remove excess aiph, and the precipitate was collected[14]. 2.3 characterization of properties phase analysis was performed using a rigaku d/max–ttr–iii diffractometer (cu–kα radiation λ = 0.15405 nm), the scanning range 2θ = 10°–90°, 10°/min of the scanning speed; a fei tecnai g2s– twin transmission electron microscope was used to observe the morphology (the sample was first dispersed in cyclohexane or ethanol solvent, and then dropped on a carbon support film for observation 12 after the solvent was volatilized); confocal laser scanning microscope observation was performed on a leica sp8 device (clsm); x-ray electron spectroscopy (xps) measurements were performed using a surface analysis system (thermofisher escalab xi+) with alkα radiation (hν = 1486.6 ev) from a monochromatic x-ray source and a spot size of 500 μm. the above characterizations were all done at room temperature. 3. results and discussion 3.1 morphology, phase and elemental analysis figure 1(a) is the xrd pattern of the product synthesized by the high temperature pyrolysis method in the first step. it can be seen that the xrd pattern of the product shows the position and relative intensity of the main characteristic peaks, which are consistent with the standard pattern of cu2–xse (jcpds no.06–0680), proving the successful synthesis of cu2–xse crystals with good crystallinity. figure 1. (a) xrd pattern of cu2–xse nanoparticles; (b) dynamic light scattering particle size distribution of cu2–xse and cu2–xse– aiph nanoparticles. figure 2. (a) tem of cu2–xse nanoparticles; (b) tem of cu2–xse–aiph nanoparticles. figure 2 shows the morphology of cu2–xse and cu2–xse–aiph nanoparticles. it can be clearly seen from figure 2(a) that the particle size of cu2– xse nanoparticles prepared by high temperature pyrolysis is 20–40 nm, and the morphology is mostly square or spherical with clearly visible outline. after transferring water and loading aiph, it can be seen from figure 2(b) that the particle size increases to about 80 nm, and the morphology changes to a single spherical shape. it can be concluded that the increase in the particle size of nanoparticles may be due to the coagulation of the oily cu2–xse nanoparticles in the subsequent reaction process of the aqueous solution. the mapping images of cu, se, c, n, and o elements in figure 3 further verify the successful synthesis of the product. figure 1(b) shows the dynamic light scattering particle size distribution of cu2–xse and cu2–xse– aiph. it can be seen from the figure that the particle size of the particles is basically the same as the 13 value in the previous transmission diagram. figure 3. elemental mapping images of cu2–xse–aiph nanoparticles. figure 4. xps spectra of cu 2p (a) and se 3d (b) in cu2–xse–aiph nanoparticles. figure 4 is the xps spectrum of cu and se elements in cu2–xse–aiph nanoparticles. specifically, the binding energy of the characteristic peaks of cu 2p in figure 4(a) is 952.2 ev and 932.4 ev, proving the existence of monovalent copper in the material; the binding energy of the characteristic peaks of se 3d in figure 4(b) is 54.7 ev, which proves that selenium in the material is negative divalent. the change of zeta potential during the reaction also confirmed the progress of each step of the reaction. figure 5(a) is the zeta potential change diagram of each step of the reaction product aqueous solution (cu2–xse, nh2–cu2–xse, cu2–xse– aiph). it can be seen that the potential of the initial cu2–xse particle solution was –10.35 mv, which increased significantly after the introduction of amino groups (–1.3 mv). the potential was further increased to 16 mv. the value of zeta potential can reflect the stability of the system to some extent. the lower the zeta potential value (positive or negative) is, when the attractive force exceeds the repulsive force, the more likely the nanoparticles in the system are to agglomerate. therefore, combined with the change of the zeta potential value, the change of the particle size and morphology in the transmission image can be explained to a certain extent. at the beginning, the potential of the cu2– xse particle solution was –10.35 mv, and the particles began to have a tendency to coagulate, but it was relatively stable; after the amino group was modified in the aqueous solution, the potential of the material became –1.3 mv, and the negative value of zeta potential became lower , the system began to become unstable, and the particles will coagulate to a certain extent; finally, the zeta potential of the cu2–xse–aiph material became 16 mv, the positive value of zeta potential was higher, and the system gradually tended to be stable. after the square or spherical cu2–xse particles coagulated in the solution, the particle size of the final material increased and the morphology changed to a single spherical shape. 14 figure 5. (a) zeta potential change diagram of products of each step in the reaction process; (b) standard absorption curve of aiph. figure 5(b) is the standard curve of the supported compound aiph. from the figure, the linear relationship between the concentration (x) of aiph and its uv-vis absorbance (y) can be obtained: y = 0.01207x – 0.05899. figure 6(a) is the uv-vis absorption curve of the cu2–xse material before and after loaded with aiph. it can be seen that, compared with the absorption curve of cu2–xse nanoparticles, that of cu2–xse–aiph appeared at 360 nm. the characteristic absorption peaks of aiph proved the successful loading of aiph. combined with the linear relationship obtained from the aiph standard curve, the loading of aiph can be calculated to be 8.1%. to verify the generation of aiph radicals, 1 mg/ml 2,2′–azobis(3–ethylbenzothiazoline–6– sulfonic acid) (abts) and cu2–xse–aiph of the same concentration were mixed and reacted for 2 h in a water bath at 45 ℃, and the uv-vis absorption spectrum of the reaction solution was measured. figure 6(b) is the characteristic absorption curve of the reaction product abts, indicating that aiph decomposes to generate free radicals under the heating condition of 45 ℃, which further react with abts to generate abts free radicals. figure 6. (a) uv-vis absorption curves of cu2–xse, cu2–xse–aiph and aiph; (b) the reaction curve of aiph and abts when heated at 45 ℃. 3.2 photothermal conversion performance since the photothermal effect of nanoparticles plays a key role in the subsequent treatment of tumor cells, the related photothermal properties of synthetic materials were first explored in aqueous solution[15–17]. the temperature curves of cu2–xse, cu2–xse–aiph solution and solvent water recorded by an infrared thermal imager under the irradiation of near-infrared light (808 nm) are shown in figure 7(a). it can be clearly seen that the temperature of the solvent water basically fluctuates around room temperature, while the temperature of cu2–xse and cu2–xse–aiph materials increases significantly under the irradiation of 808 nm laser, which preliminarily proves the photothermal conversion properties of the materials. moreover, the temperature of the material can reach 48 ℃ or above in a short period of 5 min, meeting the temperature requirements for the treatment of cancer cells in vitro and in vivo. the subsequent connection of amino groups and loading of aiph may block the absorption of near-infrared light by the photothermal agent cu2–xse to a certain extent, but happily, on the contrast, the temperature 15 rise rate of cu2–xse–aiph nanoparticles every 50 s and the final stable temperature value only decrease slightly, which does not affect the performance and application of the material[18]. figure 7. (a) heating curves of cu2–xse, cu2–xse–aiph solution and water under 808 nm laser irradiation; (b) temperature variation curves of cu2–xse–aiph solution with different concentrations under 808 nm laser irradiation. all laser power is 1 w/cm2. then, the temperature changes of cu2–xse– aiph solutions with different concentrations (31.25, 62.5, 125, 250, 500 μg/ml) during the irradiation time of 500 s were further explored. it can be seen from figure 7(b) that the temperature of each group of solutions increases regularly with the prolongation of infrared light irradiation time and the greater the concentration, the faster the temperature rises. when the material’s concentration is 31.25 μg/ml, the heating rate is the smallest, and the final stable temperature is only about 33 ℃, which is lower than the normal temperature of the human body; when the material’s concentration is 500 μg/ml, the heating rate is the largest, and the final stable temperature can reach around 48 ℃, which is enough to induce apoptosis and death of cancer cells[19,20]. figure 8. infrared thermal images of the cu2–xse–aiph material (500 μg/ml). in order to observe the photothermal effect of the cu2–xse–aiph material more intuitively, we used an infrared thermal imager to record the every-minute infrared thermal imaging pictures of 500 μg/ml material when the material was irradiated by 808 nm laser for 5 min. it can be seen from figure 8 that with the extension of time, the color of the thermal imaging picture of the material gradually changes from light yellow to dark red to white-hot. it can be determined that the material can generate a large amount of heat after absorbing near-infrared light, causing a significant increase of the solution temperature. compared with the standard temperature bar, it can be roughly judged that the final photothermal temperature of the material can reach about 48 ℃. the above tests show that cu2–xse– aiph nanomaterials can effectively convert near-infrared light into thermal energy, and thus have the potential for photothermal therapy. 3.3 anticancer properties in vitro before carrying out biological experiments, the biocompatibility of the materials must be effectively evaluated to avoid unnecessary side effects to the organism[21]. after co-culturing cu2–xse–aiph materials of different concentrations (15.6, 31.3, 62.5, 125, 250, 500 μg/ml) with l929 fibroblasts for 24 h, the cell biocompatibility was evaluated by mtt analysis. figure 9(a) shows the state of cells after cultured with different concentrations of cu2– xse–aiph nanomaterials. it can be seen that even 16 when the material’s concentration is as high as 500 μg/ml, the cell viability is still as high as 85%, which preliminarily proves cu2–xse–aiph nanomaterials have good biocompatibility. figure 9. (a) biocompatibility of cu2–xse–aiph nanomaterials with different concentrations; (b) cytotoxicity of cu2–xse and cu2– xse–aiph nanoparticles with different concentrations to hela cells. next, the cytotoxicity of nanoparticles to hela cells was analyzed by a similar mtt method. figure 9(b) is a histogram of the viability of hela cells cultured for the same time under different conditions. as shown in the figure, the cells were divided into four groups, namely: aiph, nir, cu2– xse+nir, cu2–xse–aiph+nir. it can be seen from the figure that the survival rate of cells in all aiph and nir groups can reach more than 95%, which proves that aiph culture alone or infrared light irradiation has basically no effect on cells. the cell viability of the cu2–xse+nir group dropped to about 50% (with a concentration of 500 μg/ml), which was attributed to the good photothermal properties of cu2–xse nanoparticles under the action of near-infrared light, while the cell viability of cu2–xse–aiph+nir group can be reduced to 20% (with a concentration of 500 μg/ml). it can be seen from the analysis that this is because compared with cu2–xse+nir, aiph in the cu2–xse–aiph material can also be decomposed into free radicals under the photothermal action of cu2–xse, and the synergistic effect of the two further enhances the ability of the system to kill cancer cells[22,23]. in order to illustrate the above cytotoxic results more intuitively, a staining experiment was performed using propidium iodide (pi) (this staining method can only mark dead cells with red)[24,25]. figure 10 shows the clsm images of hela cells under different incubation conditions. after similar incubation in the cytotoxicity experiment, similar results were obtained in the staining experiment, namely: in the aiph and nir groups, the number of dead red cells was the least; the number of dead red cells in cu2–xse–aiph+nir was the highest, i.e., the treatment effect was the best, followed by cu2–xse+nir. in conclusion, the above cell experiments can preliminarily prove that the cu2–xse– aiph material has good biocompatibility and anticancer properties[26]. figure 10. clsm images of hela cells incubated under different conditions (the scale bar of all images is 100 μm). 4. conclusion in summary, a series of experiments have proved that the photothermal conversion temperature of the constructed cu2–xse–aiph system is as high as 48 ℃, which can be used for photothermal therapy; in vitro cell experiments prove that the biocompatibility of the material is better, and the cell 17 survival rate is as high as 85%, when the material concentration is 500 μg/ml; the survival rate of cancer cells in the cu2–xse–aiph+nir group could be reduced to 20%, when the material concentration was 500 μg/ml. the above work shows that the cu2–xse–aiph material has the potential for tumor therapy and can be further developed for biological applications. conflict of interest the authors declare that they have no conflict of 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characterization and application of nanomaterials 2025, 8(1), 8349. https://doi.org/10.24294/can8349 1 article significance of zno nano photocatalysts in the clean hospital environment: effective bacterial disinfection and antibiotic waste (ciprofloxacin) disposal jeno blair noble jebakumar1, pavithra murugan2, jessie raj maruthanayagam baktharaj2,* 1 faculty of medicine, seu georgian national university, tbilisi 0144, georgia 2 department of physics, bishop heber college, tiruchirappalli, tamilnadu 620017, india * corresponding author: jessie raj maruthanayagam baktharaj, drjessiebhc@gmail.com abstract: hospital waste containing antibiotics is toxic to the ecosystem. ciprofloxacin is one of the essential, widely used antibiotics and is often detected in water bodies and soil. it is vital to treat these medical wastes, which urge new research towards waste management practices in hospital environments themselves. ultimately minimizes its impact in the ecosystem and prevents the spread of antibiotic resistance. the present study highlights the decomposition of ciprofloxacin using nano-catalytic zno materials by reactive oxygen species (ros) process. the most effective process to treat the residual antibiotics by the photocatalytic degradation mechanism is explored in this paper. the traditional coprecipitation method was used to prepare zinc oxide nanomaterials. the characterization methods, x-ray diffraction analysis (xrd), fourier transform infrared spectroscopy (ftir), ulraviolet-visible spectroscopy (uv-vis), scanning electron microscopy (sem) and x-ray photoelectron spectroscopy (xps) have done to improve the photocatalytic activity of zno materials. the mitigation of ciprofloxacin catalyzed by zno nanophotocatalyst was described by pseudo-first-order kinetics and chemical oxygen demand (cod) analysis. in addition, zno materials help to prevent bacterial species, s. aureus and e. coli, growth in the environment. this work provides some new insights towards ciprofloxacin degradation in efficient ways. keywords: hospital antibiotic waste; ciprofloxacin; zno nanomaterials; photocatalytic degradation; bacterial control 1. introduction in recent decades, the disposal of hospital harmful wastes, such as antibiotic drugs, directly into municipal wastes has been the major concern to the environment that will affect the animals and human health [1]. the antibiotics in the environment are also a main issue of public concern, since an antibiotic-resistant was formed in exposed non-target organisms [2]. it is urging the development of new guidelines and strategies to detoxify the antibiotic contaminants in the disposal [3]. there are many techniques available for waste treatment, such as advanced oxidation processes, photocatalysis, photolysis, electrolysis, and sonolysis, that are used for the removal of antibiotic toxins [4]. among various methods, photocatalytic degradation of antibiotic pollutants exhibits low cost and high efficiency. the nanomaterials are serving as an effective photocatalyst for the antibiotic pollutant removal and applications of disinfection in the hospital environment [5]. nanotechnology plays a great role in the removal of the antibiotic contaminants. zinc oxide active photocatalysts play an important role in developing environmental citation noble jebakumar jb, murugan p, maruthanayagam baktharaj jr. significance of zno nano photocatalysts in the clean hospital environment: effective bacterial disinfection and antibiotic waste (ciprofloxacin) disposal. characterization and application of nanomaterials. 2025; 8(1): 8349. https://doi.org/10.24294/can8349 article info received: 2 august 2024 accepted: 5 november 2024 available online: 4 december 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterialst is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 8349. 2 challenges such as hospital waste degradation. it paves the way for the efficient oxidation of contaminants under uv or visible irradiation. ciprofloxacin is one of the widely used antibiotic medicines to treat infections and antibacterial genes in microorganisms, chosen as a test sample in the present work [6]. the literature revealed that the ciprofloxacin concentration in wastewater treatment plants, raw drinking water, hospital wastewater, lakes, and discharges of the pharmaceutical industry has been reported as 11–99 mg/l, 0.032 mg/l, 150 mg/l, 6.5 mg/l and 31–50 mg/l, respectively. in addition, ciprofloxacin in the hospital environment leads to antibiotic-resistant bacterial formation, and as a result, antibiotic requirements will be higher doses in bacterial infections. the antibiotic ciprofloxacin with zno photocatalyst was tested for finding the degradability of this pharmaceutical pollutant [7]. the present plan is to carry out the uv photocatalysis for the mitigation process, and the usage of zno (catalyst) with the different concentrations of antibiotics was discussed in detail [8]. the outcome of the research would meet the great demand of disposal of hospital wastes. considering the significant detection of ciprofloxacin in hospital environments, the necessity of removing it emerges and leads the way for further large-scale practical applications. 2. materials and methods 2.1. synthesis of zno nanoparticles zinc acetate (zn (ch3coo)2 (h2o)2) and ammonium hydroxide (nh4oh) were taken as precursors to prepare zno nanoparticles by the co-precipitation. after zinc acetate was completely dissolved in double deionized water, ammonium hydroxide precursor was added dropwise until reaching the ph value of 9. the solution was stirred for 3 h at room temperature, and the homogeneity of the solution was attained by continuous agitation using a magnetic stirrer [9]. the resultant white, creamy solution was left to cool down for an hour. the precipitate was washed several times using ethanol and distilled water to reach the neutral value of ph and then filtered. then the precipitate is kept in the muffle furnace at 350 ℃ for 3 h. the steps to prepare zno nanoparticles are pictorially shown in figure 1 [10]. figure 1. steps to synthesize zinc oxide nanoparticles. characterization and application of nanomaterials 2025, 8(1), 8349. 3 2.2. photocatalytic detoxification of antibiotic contaminants the photocatalytic antibiotic degradation process was carried out using zno (catalyst). the different concentrations of ciprofloxacin solution were prepared by taking 10 mg, 20 mg, 30 mg, 40 mg, and 50 mg dissolved with the distilled water separately [11]. the catalyst (zno) of 5 mg is added to the prepared ciprofloxacin solution and stirred at 500 rpm for 30 minutes. after stirring, the solution is exposed to a 254 nm 220v-15w uv lamp in a photo reactor for 30 minutes. the sample of 5 ml can be taken out from the solution of different concentrations, and the absorbance study is analyzed by uv spectroscopy [12]. the degradation capability of catalysts was estimated by finding absorbance with the help of a uv-vis spectrometer (shimadzu/uv-2600) and estimated using the formula: percentage of dye degradation = [c0‒c]/c0 × 100 here, c0 = [initial adsorption], ct = [adsorption at time t]. 2.3. results and discussion characterization of synthesized zno nanoparticle samples x-ray diffractometer is used to study the phase identification of crystalline material and the structural properties of zno. figure2(a) shows the xrd pattern of zno nanoparticles. the sharp diffraction peaks of zno nanoparticles are observed at 2θ values of 31.68º, 34.10º, 36.49º, 47.41º, 56.81º, 66.36º, 67.98º, 69.27º and 77. 55º is associated with the (100), (002), (101), (110), (103), (200), (112), (201) and (202) planes respectively. these peaks correspond to the phase with hexagonal crystal geometry (jcpsd card no. 01-007-2551). the observed diffraction peaks are consistent with the reported values, and the absence of any peaks associated with impurities indicates the purity of this phase [13]. the crystallite size of nanoparticles is calculated by using the debye-scherrer formula. d = 𝑘𝜆 â cos𝛳 where, d—crystallite size, k—shape factor (0.9), λ—wavelength of the x-ray source, β—full-width half maximum height, θ—is the angle of diffraction [14]. the maximum intensity of zno nanoparticles occurs at 2θ = 36.49º is associated with (101) plane. the average crystallite size of zno nanoparticle is calculated as 23.38 nm. the ftir spectrum was recorded using perkin elmer ftir spectrometer in the range at 400–4000 cm−1. fourier transform infrared spectrum of zno is shown in figure 2b. the observed absorption peaks are 3439 cm−1, 1708 cm−1, 1643 cm−1, 1449 cm−1,1027 cm−1, 863 cm−1, 767 cm−1and 608 cm−1 [15]. the typical peaks at 608 cm−1, 767 cm−1 and 1027 cm−1 related to stretching vibrations of zn–o bonds. the absorption at 863 cm−1 is due to the formation of tetrahedral coordination of zn. the peak at 3439 cm−1 corresponds to the stretching vibration of the –oh molecule, while the band at 1643 cm−1 shows the effect of the bending vibration of h–o–h bond a water molecule and is also observed in the significant absorption peak at characterization and application of nanomaterials 2025, 8(1), 8349. 4 1449 cm−1. the peak at 1708 cm−1 can also be related to an additional common band attributed to the bending mode of absorbed water. the optical absorption of zno nanoparticle samples was determined at room temperature using the uv-visible spectrophotometer in the range of 100–1400 nm. figure 2c shows the absorption spectrum of zno, which exhibits an absorption edge in the range of 376 nm, which relates to the uv region. the outcome reveals that there is a strong absorption in the uv band and weak absorbance in the visible region. therefore, these zno samples can be used as an efficient photocatalyst under irradiation with uv light of wavelength less than 400 nm [16]. figure 2d is the sem image of zno nanoparticles, captured under 10.00 kx magnifications. it is predicted from the sem image that zno nanoparticles are homogeneously scattered, and also the randomly oriented hexagonal shapes of nanosized particles with uniform distribution are presented [16]. the exhibited agglomeration of hexagonal-shaped nanoparticles is correlated with the outcome of x-ray diffraction analysis. figure 2. (a) x-ray diffraction; (b) ftir vibrations; (c) uv-vis absorption; (d) sem micrograph characterization of zinc oxide nanoparticles. 3. applications 3.1. antibacterial activity the bacterial strains of staphylococcus aurous—902 (gram—positive species) and escherichia coli—443 (gram—negative species) for agar well diffusion was purchased from mtcc, chandigarh, india and the antibacterial activity of zno nanoparticles was tested against these bacterial strains [17]. petri plates containing 20 ml nutrient agar medium seeded with the bacterial strains were cultured for 24 h, characterization and application of nanomaterials 2025, 8(1), 8349. 5 and adjusted to 0.5 od value according to mcfarland standard (staphylococcus aurous—902 and escherichia coli—443). figure 3 shows the synthesized zno materials exhibit zones against pathogenic bacteria in the petri plates. the diameter of the zone is measured in millimeters and also exhibits the degree of susceptibility of microorganisms. the zones of inhibition of zno nanoparticles are (14.91 ± 0.16) mm and (17.25 ± 0.35) mm for e.coli and s.aureus respectively, as comparable with the standard values of positive control (e.coli:16.75 ± 0.06, s.aureus: 17.25± 0.21 in mm). the result proves that the effective antibacterial activity of zno samples. figure 3. antibacterial activities of the zno nanoparticles. 3.2. photocatalytic degradation mechanisms of ciprofloxacin (figure 4a–d) depicts when the ultraviolet light was irradiated on the zno semiconducting nanomaterial, the valence band electrons absorbed the energy and shifted to the conduction band. as a response, charged particles (holes in the valence band and electrons in the conduction band) develop [18]. the excitation of electrons from the valence band to the conduction band of zno catalyst due to uv illumination and the excitation process continuously produces the electron-hole pairs. following that, the antibiotic waste components interact directly with the released charged particles, either degrading them or transferring them to the surface of the zno semiconductor photo catalyst. as the active sites are decreased, the compound is greatly absorbed by the catalyst. zno possesses high photocatalytic performance, well-separated reductive and oxidative active sites, generation of reactive oxygen species (ros), and strong redox ability [19]. this reduces the reaction between the holes and the electrons. when the holes (h+) are reacted with the water molecules to form hydroxyl free radicals (oh.) and the electrons (e−) are reacted with dissolved oxygen to produce superoxide free radicals (o2 .−). free radicals such as (oh.) and (o2 .−) are the end products [20]. these two products (oh.) and (o2 .−) are strong oxidizing agents and are reacted with the ciprofloxacin to degrade it as a simple substance such as co2, h2o and mineral acids. the maximum absorbance of ciprofloxacin is obtained at the wavelength of 272 nm [21]. the elimination rate of an antibiotic is greatly improved by considering low initial concentration. from the study, the least concentration of antibiotics achieves a high removal rate that is due to more reactions taking place for a lower number of antibiotic molecules [22]. the effect of different concentrations of the antibiotic characterization and application of nanomaterials 2025, 8(1), 8349. 6 ciprofloxacin treated with zno nanoparticles and the degradation plot is shown in figure 4a. the mechanisms are expressed in equations (1)–(4). 𝑍𝑛𝑂 + ℎ𝜈  𝑍𝑛𝑂 𝑒 + ℎ (1) 𝑒 + 𝑂  𝑂 . (2) ℎ + 𝐻 𝑂  𝑂𝐻. (3) 𝑂𝐻. + 𝑂 . + 𝑐𝑖𝑝𝑟𝑜𝑓𝑙𝑜𝑥𝑎𝑐𝑖𝑛  𝐶𝑂 + 𝐻 𝑂 + 𝑚𝑖𝑛𝑒𝑟𝑎𝑙 𝑎𝑐𝑖𝑑 (4) the antibiotic ciprofloxacin is degraded and exposed to subsequent processes, resulting in non-toxic chemicals. when the polluting substance is present in higher concentrations, a smaller number of photons only penetrate through the surface catalyst that reduces the degradation studies.  kinetic model the kinetic model indicates the photo degradation of contaminants fits well with the pseudo-first-order kinetic plot. the high r2 values (more than 0.9) of the linear plot obey first-order reaction kinetics, supporting that the degradation of ciprofloxacin degradation using zno [23]. figure 4b has the pseudo-first-order rate constants of pollutants at 0.0507 min−1.  recycling and reusage after the reaction is completed using a simple centrifugation method, zno nanoparticles were separated and dried at room temperature. then the possibility of recycling of the used samples was analyzed for further degradation of antibiotic ciprofloxacin contaminants. zno nano-catalyst was tested for its photocatalytic degradability up to four cycles and retains its stability as in figure 4c. hence its reusability, it is recommended that zno might be a suitable photocatalyst for degrading antibiotic molecules [24]. figure 4. uv absorbance of effect of different concentration of antibiotic ciprofloxacin. characterization and application of nanomaterials 2025, 8(1), 8349. 7 3.2.1. chemical oxygen demand (cod) analysis the chemical oxygen demand (cod) test is used to determine the natural chemicals in a solution that are prone to pollutant degradation due to light illumination. a higher cod suggests the presence of more organic contaminants in the environment. in our study, the required quantity of chemical oxygen was calculated for the photocatalytic breakdown of antibiotics in hospital waste as an outcome of ultraviolet light exposure. oxidation of organic molecules produced co2. in addition to h2o, electrons were generated, the oxidizing reagent was reduced, and the liberated electrons were embraced. the cod of the solution was evaluated using the formula below to determine photo catalytic efficiency [(% = (cod0‒codt). 100%/cod0 where cod0 and codt] are the (cod0‒codt) and cod values of the solution before photodegradation and during this process at a given time [25]. figure 4d shows the results in (22.5%) chemical oxygen demand eradication, which equates to (80%) decomposition process. while decomposing ciprofloxacin, hydroxyl radicals are more readily released; this results in the photocatalytic degradability. this indicates that the photocatalytic process is quite effective in removing the ciprofloxacin from the solution. 3.2.2. x-ray photoelectron spectroscopy x-ray photoelectron spectroscopy (xps) was taken for zno samples to illustrate their electronic states and surface materials. xps describes the elemental bonding, chemical composition, and oxidation states in the environments of zno surfaces. figure 5 confirmed the the surface compositions and related valence states of the high-resolution spectra of zn 2p. the zn 2p3/2 and zn 2p1/2 of zn2+ are responsible for the peaks centered at 1022.2 and 1045.3 ev, respectively [26]. xps characterization results of the catalyst before and after the reaction indicate that the presence of only zn2+. furthermore, the xps spectra confirmed that zno is wellformed and the purity of the samples was retained. figure 5. xps plots of zno samples before and after usage for photo degradation. 4. conclusion the photo catalyst zno is a potent nonmaterial for hospital drug waste treatment. zno nano materials were prepared by the co-precipitation chemical method. the samples purity, crystalline nature and crystallite size were studied using characterization and application of nanomaterials 2025, 8(1), 8349. 8 x-ray diffraction analysis. the functional groups of prepared samples were confirmed by ftir technique. uv-v is analysis confirmed its suitability as an efficient photo catalyst for the removal of the antibiotic ciprofloxacin in the wastewater. sem photo images revealed the homogeneous growth of hexagonally edged zno nanoparticles, and the crystallite sizes are 20 nm to 30 nm comparable to the calculated value of 23.38 nm by debye-scherer in xrd. the effective photocatalytic degradation of ciprofloxacin antibiotic was achieved in the presence of ultraviolet light illumination. the highest degradation was found in the lowest concentration of the antibiotic (10 mg). zno mixed with ciprofloxacin is against s. aurous (gram—positive species) and e. coli (gram—negative species) bacterial strains. therefore, this can be concluded that the proposed nano photocatalysis is an economic, low-time-consuming, and good photocatalytic degradation takes place with the antibiotic ciprofloxacin. highlights • zno nanoparticles are chosen as an efficient photocatalyst for ros generation. • effectively decompose the hazardous ciprofloxacin (test sample) in hospital waste. • efficient antibacterial agent to control s. aurous and e. coli growth. author contributions: investigation, jbn; resources, jbn; data curation, jbn and pm; writing—original draft preparation, jbn and pm; antibiotic—ciprofloxacin and antibacterial activity, jbn; experimental work, pm; conceptualization, jrmb; project administration, jrmb; supervision, jrmb; validation, jrmb; visualization, jrmb; writing—review and editing, jrmb. all authors have read and agreed to the published version of the manuscript. acknowledgments: the authors like to thank bishop heber college tiruchirappalli, tamilnadu, india to carry out uv characterization. conflict of interest: the authors declare no conflict of interest. references 1. williams m, kookana rs. fate and behavior of environmental contaminants arising from health-care provision, 1st ed. elsevier b.v. 2018. doi: 10.1016/b978-0-444-63857-1.00003-6 2. kumari a, maurya ns, tiwari b. hospital wastewater treatment 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nanotechnology in alfalfa (medicago sativa l.) as alternatives for a sustainable crop carmen maría ramos-ulate, sandra pérez-álvarez*, sergio guerrero-morales, abdon palacios-monarrez facultad de ciencias agrícolas and forestales, universidad autónoma de chihuahua, campus delicias, chihuahua 33000, mexico. e-mail: spalvarez@uach.mx abstract alfalfa is considered the most used forage crop in the world, its main use is for cattle feeding, due to its high nutritional value, specifically in protein and digestible fiber. currently, the trend in agriculture is to reduce the application of chemicals and among them are fertilizers that pollute soil and water, so the adoption of new technologies and other not so new is becoming a good habit among farmers. nanotechnology in the plant system allows the development of new fertilizers to improve agricultural productivity and the release of mineral nutrients in nanoforms, which has a wide variety of benefits, including the timing and direct release of nutrients, as well as synchronizing or specifying the environmental response. biofertilizers are important components of integrated nutrient management and play a key role in soil productivity and sustainability. while protecting the environment, they are a cost-effective, environmentally friendly and renewable source of plant nutrients to supplement chemical fertilizers in the sustainable agricultural system. nanotechnology and biofertilization allow in a practical way the reduction in the application of chemicals, contributing to the sustainability of agriculture, so this work aims to review the relevant results on biofertilization, the use of nanotechnology and the evaluation of the nutritional composition of alfalfa when grown with the application of biofertilizers. keywords: agriculture; biofertilizers; nanomaterials; nanomaterials article info received: 19 august 2022 accepted: 9 october 2022 available online: 21 october 2022 copyright copyright © 2022 carmen maría ramos-ulate, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction the demand for food in the world is increasing exponentially, more so in developing countries where land and agricultural resources hardly contribute to efficient crop production needed to meet such an urgent demand for food. there is a need to intensify agricultural production in a sustainable manner through efficient use of resources considering the full biochemical diversity of the agroecosystem and its potential to mitigate the adverse impacts of low soil fertility, abiotic stresses, pathogens and pests[1]. nutrients are essential for plant growth and development and some of them are not available in the soil, due to many factors such as leaching, degradation by protolysis, hydrolysis and decomposition, so it is necessary to reduce the loss of these nutrients during fertilization and increase crop production through new technologies[2]. one of these technologies is nanotechnology and nanomaterials (nms), because nanofertilizers could have effective qualities for crops, such as being able to release nutrients according to demand, controlled release of chemical fertilizers that regulate plant growth and development and improve target activity[2]. another technology is the application of biofertilization. bioferti 112 lizers are used to supplement chemical fertilizers mainly to maintain soil fertility. these fertilizers are organic, biodegradable, contain microorganisms, provide nutrients, antibiotics, hormones such as auxins, cytokinin, vitamins that enrich the root rhizosphere[3]. legumes contribute to the sustainability of agriculture: they reduce mineral fertilizers, thus decreasing n2o production and increasing n2 fixation, renew and enrich soil fertility due to their deep rooting systems, rapidly decompose their root biomass and accumulate in the soil[4]. alfalfa (medicago sativa l.) has the ability to accumulate significantly greater amounts of nitrogen than other legumes through its deep rooting system and, in addition, fixes atmospheric n2 by 40 to 80% through biological fixation of this element[5]. therefore, the objective of this work is to review the relevant results on biofertilization and the use of nanotechnology in alfalfa cultivation, illustrating how these technologies can lead to a reduction in the application of chemical fertilizers. 2. alfalfa, generalities, uses and applications alfalfa is a perennial legume, representative of temperate regions and is mainly used as livestock feed, and is universally considered one of the highest quality forages. it is a valuable crop because among its many agronomic and environmental advantages are the preservation of soil fertility and biodiversity, protection against soil erosion, mitigation of climate change impacts, reduction of nitrate contamination of groundwater, reduction of fossil fuel consumption, reduction of greenhouse gas emissions, among others[6–9]. this legume (alfalfa) has a set of variable morphological and physiological characteristics of importance in world agriculture and contributes with its high and stable performance as a nutritious grass[10]. its economic importance is based on its high biomass production potential, exceeding 80 t∙ha−1 green and about 20 t∙ha−1 dry matter[11]. alfalfa forages are characterized by a high crude protein content[12], well balanced with respect to amino acid. it is enriched with vitally important vitamins and several microelements essential for normal animal growth and development. alfalfa is the basic component in the feeding program for dairy cattle, as well as for cattle, horses, sheep and other livestock[13]. alfalfa has also become interesting as a potential source of secondary metabolites, because it is considered an alternative of phytoestrogens useful in health (human food ingredient and supplements), so its growth has become widespread in different continents, due to its high adaptability to different types of soils, ph values and environmental conditions, as well as the possibility of sustainable and ecological production[14,15]. in mexico[16], 385,992 ha of green alfalfa have been planted, of which 384,693 ha have been harvested for a production of 15,360,646 and a yield of 39,930 t∙ha−1. in this country, the main use of alfalfa is to feed dairy cattle in arid, semi-arid and temperate regions. the crop is cut at medium intervals to harvest the highest forage yield per year per unit area, as well as for its good crude protein content, digestibility and degree of acceptance by cattle[17,18]. this plant can be used as fodder in different ways, fresh, hayed and ensiled in mixture with one or more grasses[19,20]. 3. biofertilization in alfalfa the development of a country is directly proportional to the amount of food or nutrients available to the population. the growing increase in world population creates an ever-increasing demand for food and to supply it, fertilizers are used which are defined as any substance used to increase the productivity of the soil, promoting its fertility by adding nutrients, which aids in plant growth. fertilizers that are composed of crude chemicals in solid or liquid form made in factories targeted to the nutritional requirements of plants are, by definition, called a chemical fertilizer. nitrogen (n), phosphorus (p) and potassium (k), called npk, are normally present in these chemical fertilizers along with other nutrients[21]. the excessive use of chemical fertilizers has generated several problems in nature such as, for example, water acidification; damage to the ozone 113 layer; the greenhouse effect; using them for a long time can change the ph of the soil, eutrophication of the water where the nutritional content in these environments increases, causing algae proliferation and, consequently, the reduction of oxygen in the water, which damages marine life[22]. a current solution to decrease the use of these fertilizers in agriculture is the use of biofertilizers[23]. biofertilizers are microbial inoculants containing live or dormant cells of efficient strains of nitrogen fixing, phosphate solubilizing and cellulose decomposing microorganisms[3]. these are intended to be applied primarily to soils to improve soil fertility and plant growth by increasing the number and biological activity of beneficial microorganisms[3]. some of the advantages of biofertilizers are that they are cost-effective and environmentally friendly, gradually improving soil quality. the microorganisms contained in the biofertilizer promote the supply of nutrients to the plants, thus ensuring their development, growth and physiological regulation. in addition, crop yields can increase by 10 to 25% and plants are less prone to soil diseases. among the main limitations of biofertilizers are that they act more slowly than chemical fertilizers; they are difficult to store due to their high sensitivity to changes in temperature and humidity; they cannot replace other fertilizers completely; and the scarcity of particular or local strains of microorganisms reduces their availability[24]. the types of biofertilizers available[22] are: 1. nitrogen fixing biofertilizer: rhizobium, azotobacter, azospirillium, bradyrhizobium. 2. phosphorus solubilizing biofertilizer: bacillus, pseudomonas, aspergillus. 3. phosphorus mobilizing biofertilizer mycorrhiza. 4. biofertilizer plant growth promoters: psuedomonas, trichoderma. the effects of the above mentioned biofertilizers in terms of nitrogen fixation in the soil is carried out through the root nodules of the leguminous crop, making n2 available to the plant. other microorganisms that can be used as biofertilizers are: azolla which is a heterogeneous fern with seven species that are endosymbionts with anabaena azollae, a nitrogen fixing cyanobacterium[25] and blue green algae can fix nitrogen in the anaerobic environment due to a specialized cell called heterocyst[26]. phosphate-solubilizing bacteria produce organic and inorganic acids such as gulconic acid and ketogulconic acid that solubilize phosphorus[27]. gluconic acid produces a carboxyl and hydroxyl group, this group will function as a chelator of fe2+, al3+ and ca2+, which will reduce soil ph. it is also important to mention that there is a positive interaction between gluconacetobacter spp and burklderia spp to increase dehydrogenase activity in soil. dehydrogenases are involved in the soil oxidation process and are used as an indicator of soil microbial activity[28]. in alfalfa, some studies have been conducted using organic cultivation, which includes the use of biofertilizers. the application of liquid microbial inoculants to legume seeds is a sustainable agricultural practice that can improve plant nutrient uptake and increase crop productivity. after application to legume seeds the inoculants should provide long-term survival of rhizobia in the final product and to study the survival of sinorhizobium (ensifer) meliloti l3 si, ten different media formulations of microbial inoculants (yeast mannitol broth with the addition of agar, sodium alginate, calcium chloride, glycerol or ferric chloride and combinations thereof) were examined. for survival of l3 si, for a storage time of 150 days, the medium formulation containing glycerol in combination with agar or sodium alginate was applied, which was used as a liquid inoculant. alfalfa seeds were pre-inoculated with four formulations (mannitol yeast broth (ymb), ymb with agar (1 g·l−1), ymb with 1 or 5 g·l−1 sodium alginate) for three months. seeds pre-inoculated and stored for one month produced successful alfalfa plants. nitrogen content in alfalfa obtained from seeds pre-inoculated one month before sowing increased between 3.72%–4.19%[29]. the ability of 17 rhizobacterial strains to improve physiology, nutrient uptake, growth and yield of alfalfa plants grown under desert agricultural conditions in saudi arabia was studied by some 114 authors[30]. the 17 rhizobacterial isolates were confirmed as plant growth promoting rhizobacteria by classical biochemical tests and using 16s rdna gene sequence analysis, the strains were identified as bacillus, acinetobacter and enterobacter. inoculation of alfalfa with any of these 17 strains improved relative water content; chlorophyll a; chlorophyll b; carotenoid content; n, p and k content; plant height; leaf-to-stem ratio; fresh and dry mass. acinetobacter pittiijd-14 was more effective in increasing alfalfa fresh and dry mass by 41 and 34%, respectively, compared to uninoculated control plants. however, all strains improved crop characteristics compared to control plants, indicating that these desert rhizobacterial strains could be used to develop an environmentally friendly biofertilizer for alfalfa and possibly other crop plants to improve sustainable production in arid regions. 4. evaluation of the nutritional composition of alfalfa (m. sativa) when grown with the application of biofertilizers six biofertilizer doses of cattle manure fermented in a biodigester (0, 25, 50, 100, 200 and 400 m3∙ha−1) and five replicates were used. the chemical characteristics of the biofertilizer were: 0.300 g n (nitrogen) l−1; 0.057 g p (phosphorus) l−1; 0.188 g k (potassium) l−1; 0.105 g ca (calcium) l−1; 0.057 g mg (magnesium) l−1, 1 mg mn (manganese) l−1; 1 mg fe (iron) l−1, and 1 mg zn (zinc) l−1. as a result, the best absorption of n, k, ca and mg was obtained with the dose of 400 m3∙ha−1. in the case of n, it was 22% more than in the control and was linear with the increase in biomass. the levels of the micronutrients cu, mn and zn did not differ significantly among the doses applied, as did the crude protein concentrations[31]. on the other hand, the effect of s. meliloti strain enrri a12 and chicken manure (0, 2, 4, 6, 6, 8 and 10 t∙ha−1) on alfalfa cultivar (m. sativa) “hegazi” was studied under pot and field conditions. in the pot experiment, s. melioti inoculation and chicken manure levels significantly increased plant height, root fresh and dry mass, and nodule number and dry weight. in the field experiment, both s. melioti and chicken manure significantly increased plant density, fresh forage yield and protein content, and significantly decreased crude fiber percentage. fresh forage yield and chicken manure level were highly correlated (r > 0.99)[32]. 5. nanotechnology in alfalfa nanotechnology is one of the latest technological innovations. the term “nanotechnology” was first coined by norio taniguichi, a professor at tokyo university of science, in 1974[33]. although the term “nanotechnology” has long been introduced in multiple disciplines, the idea that nanoparticles (nps) could be of interest in agricultural development is a recent technological innovation and is still under progressive development[34]. nps are organic, inorganic or hybrid materials with at least one of their dimensions ranging from 1 to 100 nm (nanoscale). nps that exist in the natural world can be produced from photochemical reaction processes, volcanic eruptions, forest fires, erosion, plants and animals or even by microorganisms[35]. the production of nps derived from plants and microorganisms has become an efficient biological source of green nps attracting additional attention from scientists in recent times due to their environmentally friendly nature and the simplicity of the production process compared to the other routes[36]. nps, depending on their properties, interact with plants causing various morphological and physiological changes. the efficiency of nps is determined by their chemical composition, size, surface coverage, reactivity, and most importantly, the dose at which they are effective[37]. researchers report both positive and negative effects on plant growth and development when using nps and the impact of nps depends on the composition, concentration, size, chemical and physical properties, as well as the plant species[38]. for the exploitation of green nanotechnology, a number of plant species and microorganisms, including bacteria, algae and fungi, are currently being used for the synthesis of nps. for example, the plant species m. sativa and sesbania are used to formulate gold nanoparticles. similarly, inorganic nanomaterials, made of silver (ag), nickel (ni), 115 cobalt (co), zinc (zn) and copper (cu), can be synthesized within living plants, such as brassicqjuncea, m. sativa and heleanthusannus[36]. synthesized nanofertilizers have a specific use to regulate nutrient release according to crop requirements, while minimizing differential losses. for example, conventional nitrogen fertilizers are characterized by large losses to the soil through leaching, evaporation or even degradation of up to 50%–70%, which ultimately reduces fertilizer efficiency and raises the cost of production[39]. on the other hand, nitrogen fertilizer nanoformulations synchronize the release of n-fertilizer with its uptake demand by crops. consequently, nanoformulations prevent undesirable losses of nutrients through direct internalization by crops and thus avoid nutrient interaction with soil, water, air and microorganisms[36]. micronutrient deficiency decreases not only crop productivity, but also affects human health through the consumption of micronutrient-deficient foods. for example, iron deficiency causes anemia, impaired growth, reproductive health problems, and even decreased cognitive and physical performance in humans[40]. in this regard, the use of nano-formulated micronutrients for slow or controlled release of nutrients would stimulate the process of plant uptake, promote crop growth and productivity, and also contribute to maintaining soil health[41]. for example, in zinc deficient soils, application of nano zinc oxide at low doses positively influences growth and physiological responses such as shoot and root elongation, fresh dry weight and photosynthesis in many plant species compared to control[42,43]. 6. nanotechnology applications in alfalfa cultivation boron (b) is among the nutrients that are necessary for plant growth and yield production and can improve the nutritional properties of forage crops. however, at higher levels, it can be toxic and negatively affect plant growth and forage quality. the concentration of b in plants is affected by different parameters, such as fertilization with this same micronutrient, soil, climate, plant species, etc. for all these reasons, the effects of different b treatments in alfalfa on b concentration and pigment content, including chlorophyll, b, total and carotenoids, were studied. experimental treatments were: (1) six soil types (s1–s6); (2) b sources, including boricicide (b1) and nano boron (b2) fertilization; and (3) number of sprays (zero, one, two and three times). results indicated that soil type, b source and number of sprays significantly (p ≤ 0.01) affected alfalfa b concentration and pigment content. spraying three times significantly increased b concentration as it resulted in 207.81% increase compared to the control treatment and equally increased pigment content (p ≤ 0.05) including chlorophyll, b, total and carotenoids compared to the other treatments[44]. a greenhouse study was conducted to explore the effect of various doses of potassium sulfate (k2so4) nps on alfalfa growth and physiological response under salt stress. a salt-tolerant genotype (me-sa-sirsa) and a salt-sensitive genotype (bulldog 505) were selected on the basis of germination under salt and planted in pots containing 2 kg of sand. the two genotypes were subjected to salt levels of 0 and 6 ds∙m-1 using cacl2·2h2o:nacl (2:1) mixed with hoagland’s solution. three treatments of k2so4nps consisting of 1/4, 1/8, and 1/10 of the k level in full-strength hoagland solution (235 mg·l−1) were applied. the highest shoot dry weight, relative yield, root length and root dry weight in both genotypes were obtained when using k2so4nps at the 1/8 level. the different doses of k2so4nps significantly affected the na/k ratio and ca, p, cu, mn and zn concentrations in plant tissue. application of k2so4 nps at a rate of 1/8 improved plant physiological response to salt stress by reducing electrolyte leakage, increasing catalase and proline content, and increasing antioxidant enzyme activity. these results suggest that the application of knps may have better efficiency than conventional k fertilizers in providing adequate plant nutrition and overcoming the negative effects of salt stress in alfalfa[45]. the toxicity of zinc oxide nanoparticles (znonps) on seed germination/root elongation and uptake of znonps and zn2+ in alfalfa (m. sativa), 116 cucumber (cucumis sativus l.) and tomato (solanum lycopersicum l.) seedlings was investigated by the literature[46]. seeds were treated with znonps at 0–1,600 mg·l−1 as well as at 0–250 mg·l−1 of zn2+ for comparison purposes. the results showed that at 1,600 mg·l−1 of znonps, germination in cucumber increased by 10% and germination of alfalfa and tomato was reduced by 40 and 20%, respectively. with 250 mg zn2+ l−1, only tomato germination was reduced with respect to the controls. the highest zn content was 4,700 and 3,500 mg∙kg−1 dry weight (dw), for alfalfa seedlings germinated in 1,600 mg∙l−1 of znonps and 250 mg∙l−1 of zn2+, respectively. alfalfa in nanotechnology has also been used to obtain nps. scientists have found a way to grow and harvest gold (au) from crop plants. the nps could be harvested industrially. for example, alfalfa plants grown in an environment rich in aucl4 showed uptake of metallic gold. aunps can be mechanically separated by dissolving the organic material (plant tissue) after harvest[47]. alfalfa plants can also adsorb ag from a solid medium rich in this element with subsequent formation of ag nps[48]. 7. conclusions (1) the indiscriminate and unbalanced use of chemical fertilizers, especially urea, together with chemical pesticides and the lack of organic fertilizers leads to a considerable reduction in soil health, so the use of biofertilizers is on the rise in various countries and crops. the cultivation of microbial communities induces high productivity with negligible energy investments and, therefore, significantly reduces the effects on the environment. 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tehran 1684613114, iran * corresponding author: mostafa mahinroosta, mahinroosta2010@gmail.com abstract: the present study deliberates the recovery of sodium fluoride (naf)-natrite (na2co3)-sodium chloride (nacl) ternary fluxing agent from hazardous aluminum dross waste using three types of heating methods, including direct heating on a hotplate, heating by a drying oven, and microwave heating. deionized water was used as a green solvent for the recovery experiments. investigating the effects of time and temperature on recovery percentage showed that a recovery percentage of around 96.5% can be achieved under time and temperature of 90 min and 95 ℃, respectively. the recovered fluxing agent salt was characterized by xrd, ftir spectroscopy, fesem, and energy dispersive x-ray spectroscopy (eds) elemental analysis. rietveld fitting analysis of phases detected in the xrd patterns showed that the recovered fluxing agent contained 74–81 wt.% naf, 8–11 wt.% nacl, and 11–14.7 wt.% na2co3. the fesem micrographs revealed that the retrieved salts were in nano scale. the recovered fluxing agent showed different morphologies including needle-like, round shape, and a mixture of both, corresponding to microwave, drying oven, and hotplate heating methods, respectively. the nano-needles exhibited diameter of the tip and base in the range of 39–60 nm and 50–103 nm, respectively. keywords: waste; sodium fluoride; needle-like; microwave-assisted; nanostructure 1. introduction with a general look at the current situation of the industry in the world, industrial production is associated with challenging issues such as waste accumulation and natural resource depletion. the accumulation of industrial wastes over time generates environmental and public health problems [1]. in recent years, public awareness on improving the quality and preservation of the environment has coerced legislators into passing strict regulations on air and water pollution [2]. aluminum black dross (abd) as a hazardous industrial waste is a salty-metallicoxidic waste of aluminum ingot production process formed in casting units [3,4]. the abd also contains about 8%–10% of soluble salts, mainly alkali fluorides and chlorides [5,6]. in aluminum production process, a fluxing agent (usually a salt mixture containing sodium and potassium chlorides as well as a small amount of a mineral fluorine compounds (na3alf6 or caf2) is used to protect al metal from oxidation under favorable conditions (high temperature and the presence of oxygen) [1]. naf is formed as a result of the disintegration of na3alf6 (also known as cryolite) which plays the role of an electrolyte in the melting process as well as a fluxing agent in the process of smelting alumina and turning it into metallic aluminum [7,8]. also, naf may directly come from the molten salt flux [7]. citation mahinroosta m, allahverdi a. green recovery of naf-na2co3-nacl ternary fluxing agent from aluminum dross. characterization and application of nanomaterials. 2024; 7(1): 5593. https://doi.org/10.24294/can.v7i1.559 3 article info received: 18 december 2023 accepted: 6 march 2024 available online: 1 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 5593. 2 in europe, stockpiling of this kind of waste is prohibited because the soluble salts are a major source of surface and groundwater pollution [9] and may have some disadvantages such as cost and safety risks [5,6]. the presence of excess fluoride in drinking water often results in skeletal fluorosis, weakening bone structure, as well as discoloration and speckling of teeth, cancer or adverse effects on the brain and kidney [10]. also, high levels of sodium in drinking water exacerbate chronic congestive heart failure, blood pressure and hypertension [11]. therefore, finding an appropriate solution to eliminate or reduce the environmental pollution of the waste is a necessity. halite (nacl), natrite (na2co3), and naf are water-soluble and recoverable mineral salts. the recovered salt can be mixed with fresh fluxing agent and returned to aluminum smelting furnace. this is economically beneficial and also reduces the toxicity of the abd waste [12]. recently, naf pellets have been applied for the adsorption of gaseous hf as an impurity in the industrial generation of fluorine gas [13]. inasmuch as the adsorption of gaseous pollutants can be noticeably enhanced by developing nano-structures [14], the last mentioned application of naf seems more important. naf in a bulk scale is prepared by neutralizing hydrofluoric acid with sodium hydroxide [15]. in nano scale, the synthesis of nanoparticles of sodium halide salts (naf; nacl, nabr, nai) having sizes of less than 3.0 nm using reverse micelles methods with capping agent has been reported by abdelkader and buckner [16]. sodium carbonate (na2co3) can be used to remove iron oxide in some stages of aluminum production and cause further purification of aluminum. in addition, sodium carbonate can improve the flotation performance and play a role as a ph regulator [17]. in the aluminum smelting process, sodium carbonate improves the performance of the fluxing agent [18]. sodium fluoride, sodium chloride, and sodium carbonate can be used as roasting agents in the processes of extracting valuable materials from primary and secondary sources [19–21]. within the scope of this work, facile green recovery of fluxing agent nanostructures from the abd is investigated for the first time. the recovery of soluble salts in the form of nanostructures implies to the principles 3 (substances with little or no hazard), 5 (safer solvents and auxiliaries), and 12 (safety considerations) of the twelve principles of green chemistry [22]. after removing the soluble salts from the abd, its pollution is significantly reduced, and the soluble salt-free residue can be subjected to subsequent processes such as the recovery of alumina as a valuable and widely used material [23,24]. 2. materials and methods 2.1. materials the abd used herein was obtained from iranian aluminum company (iralco) situated in markazi province, iran. the as-received bad was medium gray in color with the actual and bulk densities of 2.22 and 0.85 g/cm3, respectively. the mineralogy of the abd will be discussed in section 3.2. figure 1 shows the particle size distribution of the abd. as seen, about 55% of the abd particles are below 250 µm, whereas about 90% of which are less than 2.38 mm. characterization and application of nanomaterials 2024, 7(1), 5593. 3 figure 1. particle size distribution of abd. table 1 gives oxide composition of the abd which was determined by x-ray fluorescence (xrf) technique. according to data in table 1, the abd contains almost 61 and 15 wt.% aluminum oxide and silicon dioxide, respectively. the loss on ignition (loi) was obtained around 9 wt.% and the remaining 15 wt.% accounts for the other oxides. deionized (di) water (tds = 5 mg/l) was utilized at all recovery experimental tests as a green solvent. table 1. chemical composition of abd. oxide (wt.%) al2o3 62.56 sio2 7.53 cao 5.87 fe2o3 2.73 na2o 4.68 mgo 1.25 p2o5 0.17 so3 0.10 k2o 0.81 tio2 0.32 mno 0.31 cl 3.35 f 1.32 cuo 0.11 loi* 8.89 characterization and application of nanomaterials 2024, 7(1), 5593. 4 2.2. methods 2.2.1. determination of water leachable salt content of abd to determine the water leachable salt content of the abd, the method described in din 38414-s4 standard for determination of leachability by water was used. according to this standard, first 100 g of dry abd sample is loaded into a 2 l beaker and then 1 l of di water is added. the mixture is then stirred for 24 h. after the mixing time has elapsed, the mixture is filtered through a vacuum filtration system. the filtrate should be transparent at this stage, otherwise it must be re-filtered with a filter paper with a mesh size of 0.45 μm. the determination of the chemical analysis of leachate is performed using inductively coupled plasma atomic emission spectroscopy (icpaes). at the end of the experiment, the mass of the leached substance is calculated by the following equation (1). wes = (β × ve)/ms (1) where, wes is the mass of the leached substance (in mg/kg), β is the mass concentration of the leached substance (in mg/l), ms is the dry mass of initial sample (in kg), and ve is the volume of the filtrate (in l). 2.2.2. salt recovery experiments to perform salt recovery experiments, the setup shown in figure 2 was used. figure 2 shows a three-neck glass reactor, graham condenser, a water bath for homogenizing the recovery temperature, and a magnetic stirrer. after accurate weighing, 5.00 g of the abd is loaded into the reactor. then 100 ml of deionized water is added to it. the rinsing starts at a specified temperature under the stirring speed of 600 rpm. after a certain period of time, the suspension is filtered using a vacuum filtration system. figure 2. experimental setup used for salt recovery from abd. as illustrated in figure 3, in order to evaporate the water content of the obtained filtrate, three types of heating methods including microwave irradiation, heating by a drying oven (pars khazar, ot 650p), and heating by a hotplate (ika c-mag hs7 characterization and application of nanomaterials 2024, 7(1), 5593. 5 digital) were applied. the microwave irradiation was provided using a domestic microwave oven (sapor, 1500 w, 2450 mhz). at the end of the heating, a white solid was achieved. the heating processes were performed at 95 ± 1 ℃ for 2 h by hotplate and at 95 ± 0.5 ℃ for 1 h by drying oven. the microwave irradiation continued for a preset time of 15 min. figure 3. three types of heating methods (left: microwave irradiation, middle: heating by a drying oven, right: heating by a hotplate). 2.2.3. characterization methods to obtain x-ray diffractograms of the samples, philips expert system x-ray diffractometer was utilized with cukα-radiation and ni-filter at voltage and current of 40 kv and 30 ma, respectively. the xrd analyses were carried out at 2θ angles of 10°–80° (scanning speed: 2 °/min; anti-scatter: 1°; receiving slit: 0.01 mm). fourier transform infrared spectroscopy (ftir) spectra of the recovered salts were recorded employing a ftir spectrometer device (shimadzu ir spectrophotometer 8400 s) in the wavenumber range of 400–4000 cm−1. the spectra were recorded with a sensitivity of 4 cm−1 and 64 scans per spectrum taken. morphological and elemental analyses were obtained employing two kinds of microscopes including sigma vp-500 fesem microscope (zeiss) and tescan mira3 at accelerating voltages of 15 and 10 kv, respectively. for sample preparation, an adequate amount of the recovered salts is adhered on a holder. then they are coated with a thin layer of gold. the chemical composition of the abd was determined using a xrf pw2404 device with a measurement range of 20 ppm to 100 wt.%. 3. results and discussion 3.1. chemical analysis of leachate the icp-aes chemical analysis of the leachate obtained according to din 38414-s4 standard is presented in table 2, indicating significant amount of sodium and minor amounts of potassium and aluminum. table 2. chemical analysis of the leachate obtained according to din 38414-s4 standard. element na k al ca concentration (mg/l) 5662.40 37.23 74.77 nd* mass% 98.06 0.64 1.30 *nd: not detected. characterization and application of nanomaterials 2024, 7(1), 5593. 6 based on the data in table 2, the water leachable salt content of the abd was 5.77 mass%. the ph value of the leachate was around 11.25. the previous studies [23,24] revealed that the abd contains aluminum oxide (al2o3), spinel (mgal2o4), quartz (sio2), diaoyudaoite (naal11o17), villiaumite (naf), cryolite (na3alf6), silicon (si), aluminum nitride (al) and iron oxide (fe2o3) as well as minor traces of halite (nacl), graphite (c), and fluorite (caf2). considering the aforementioned compounds, the presence of sodium in the leachate is majorly due to the dissolution of naf and nacl. the presence of aluminum in the leachate originates from the partial hydrolysis of aluminum nitride in water [25,26]. a trace amount of potassium is more likely due to the dissolution of potassium chloride which is used along with sodium chloride as salt flux in melting process of aluminum. 3.2. effects of time and temperature on salt recovery efficiency before performing any salt recovery experiment, the moisture content of the abd sample was removed in a drying oven at 105 ± 0.5 ℃. this is a necessary step to obtain exact recovery efficiency data. the previous study [24] showed that a drying time of 50 min is enough to completely remove the moisture. in order to investigate the possibility of faster recovery of soluble salts, water leaching of the abd was carried out at different temperatures and times. in these experiments, the water leaching of the abd was performed at 25, 45, 65, 85 and 95 ℃ for 30, 60, 90, and 120 min at each temperature. each experiment was performed twice. the results are depicted in figure 4. figure 4. the effects of time and temperature on salt recovery efficiency. from figure 4, it is clear that the salt recovery efficiency generally increases with increasing temperature and time. such an enhancement was expected, since the solubility of naf in water increases with temperature [27]. at 95 ℃, after 60 min, the recovery efficiency is about 96%, and more increase in time does not significantly change the percentage of salt recovery. also, recovery times of more than 1 h are not practically interesting. figure 5 shows the xrd patterns of the raw abd and waterleached abd. characterization and application of nanomaterials 2024, 7(1), 5593. 7 figure 5. xrd patterns of (a) raw abd and (b) water-leached abd. figure 5a shows that the abd contains aluminum oxide (al2o3), spinel (mgal2o4), defect spinel (al1.83mg0.87o3.61), quartz (sio2), diaoyudaoite (naal11o17), villiaumite (naf), cryolite (na3alf6), silicon (si), aluminum nitride (al) and iron oxide (fe2o3) as well as minor traces of halite (nacl), graphite (c), and fluorite (caf2). among all these phases, only naf and nacl are highly soluble in water. as can be clearly observed from the peaks surrounded by rectangles in figure 5, almost all villiaumite (naf) has been dissolved in water. reduced intensity of the diaoyudaoite phase shows that this phase has also partially been dissolved in water. unfortunately, there is not enough information on the solubility of this material in the literature. 3.3. characterization of the recovered salts 3.3.1. xrd patterns figure 6 presents the x-ray diffractograms of the recovered salts using the mentioned three types of heating methods. the peaks of the recovered salts correspond to those of naf, nacl, kcl, aln, and sio2 phases according to the standard cards of icdd-01-089-2956, icdd-01-088-2300, icdd-01-077-2121, icdd-01-089-3446, and icdd-01-081-0069, respectively. because xrd data are substantially qualitative and also due to the proximity of the intensities of some peaks, a reasonable comparison between the three patterns requires the quantification of data and gaining the mass fraction of each phase. to calculate the mass fraction of each phase, the xrd data were quantified applying the rietveld fitting analysis. the rietveld fitting analyses were performed using crystallographic information files (cifs) of villiaumite (naf), halite (nacl), and natrite (na2co3). according to the quantitative data shown in figure 6, the recovered salts consist of predominantly naf, accounting for 74–81 wt.%. the remaining 20–25 wt.% is dedicated to the presence of sodium chloride and sodium carbonate. the higher amount of naf improves the performance of fluxing agent. therefore, according to figure 6, heating by a drying oven is more suitable. in characterization and application of nanomaterials 2024, 7(1), 5593. 8 fact, this type of drying method is a type of indirect heating method, which is mainly done through convection. figure 6. xrd patterns of the recovered salts. heat source: (a) microwave irradiation, (b) drying oven, and (c) hotplate. the average crystallite size was obtained using scherrer equation: l = kλ/βcosθ (2) in which l is the average crystallite size, θ the bragg’s angle, λ the incident x-ray wavelength (λ = 1.541874 å), and β the full width at half maximum (fwhm) of the peak. β and 2θ values were obtained from each xrd pattern using highscore plus software. the results are presented in table 3. characterization and application of nanomaterials 2024, 7(1), 5593. 9 table 3. values of 2θ, β, and average crystallite size of the recovered salts. recovered salt sample 2θ (degree) β (degree) β (rad) average crystallite size (nm) salt recovered by microwave irradiation 38.9254 0.1653 0.00288 61.9 salt recovered by drying oven heating 38.9232 0.1968 0.00343 52.0 salt recovered by hotplate heating 38.7726 0.2952 0.00515 34.5 according to table 3, the salt recovered by hotplate heating has the most minute average crystallite size (34.5 nm) and the salt recovered by microwave irradiation has the largest one (61.9 nm). the larger crystal size of the salt recovered by microwave irradiation is due to the fact that the heating rate is very rapid (only one tenth to one hundredth of the time needed by conventional ways), which leads to the supersaturation of the solution. crystals in a supersaturated solution can grow faster and become larger [28,29]. 3.3.2. ftir analysis figure 7 depicts ftir spectra of the recovered salts. figure 7. ftir spectra of the recovered salts. heat source: (a) microwave irradiation; (b) drying oven; and (c) hotplate. all three samples show absorption bands at 697, 880, 1158, 1436, 2366, 2924, and 3429 cm−1. the bands observed at 697 and 880 cm−1 are assigned to the presence of aln. this is in agreement with the literature that the main excitation of the al-n bonds by infrared radiation take place at the range 200-1000 cm−1 [30]. the band at 1158 cm−1 is caused by the asymmetric stretching of the oxygen atom in the si-o-si chain [31]. the absorption band at 1436 cm−1 is allocated to (ohf)− complexes with a hydrogen bond [32,33]. the presence of (ohf)− complex may be due to some amount of water at the surface of the recovered salts, which dissolves some naf and produces fluoride ions. thus, the generated fluoride ions are surrounded by oh groups due to hydrogen bonding. considering this peak, it is realized that its intensity in the salt recovered by hotplate heating is higher than that in two other samples. the reason characterization and application of nanomaterials 2024, 7(1), 5593. 10 may be the formation of more hydrogen bonds and thus the formation of more (ohf)− complexes. this evidence suggests that the hotplate heating method is less effective in evaporation of water content of the recovered salt compared to other two heating methods. the absorption band at 3429 cm−1 shows a small amount of water in the recovered salts. 3.3.3. microstructural and elemental analyses to gain appropriate insight into the morphological and elemental information of the recovered salts by three types of heating sources, fesem/eds analyses were used. figure 8 depicts the fesem images and corresponding eds elemental analyses of the recovered salts. figure 8a shows that the evaporation of water of the leached salt from the abd through heating by a hotplate has caused the formation of a needle-like nanostructure on surfaces of relatively larger particles (a few to several microns) that seems to be amorphous. observations at high magnification (figure 8a1), however, reveals that the relatively large particles are aggregation of numerous round shape nanoparticles with a diameter in the range of 33–40 nm. as it can be clearly seen from figure 8b, a pure needle-like morphology has emerged due to the removal of water of the leached salt by microwave heating. figure 8b1 shows that the needle-like particles grown with different orientations are in nano scale. the nano-needles show diameter of the tip and base in the range of 39–60 nm and 50–103 nm, respectively. this is despite the fact that the evaporation of water of the leached salt through heating by a drying oven has resulted in the formation of aggregates of round shape nanoparticles only. as can obviously be observed from figure 8c, the agglomerates include nanoparticles with the sizes larger than 20 nm (as shown in figure 8c1). all eds elemental analyses disclosed na, f, o, cl, al, c, si, and k as the chemistry of the formed nanostructures. characterization and application of nanomaterials 2024, 7(1), 5593. 11 figure 8. fesem images and corresponding eds elemental analyses of the recovered salts. heat source: (a, a1) hotplate; (b, b1) microwave irradiation; and (c, c1) drying oven. the mechanism for the formation of different nanostructures can be interpreted as follows: water-soluble halides are ionized in water according to the following reaction [16]: nay(solid) ↔ na+ (aqueous) + y− (aqueous) (3) driving force for the formation of nanostructures of sodium halides or any watersoluble particles is the evaporation of water from a confined space which allows the size and shape control. considering the type of heating source for evaporation of water of the leached salts, two main parameters that may have a key role in the appearance of different nanostructures are temperature gradient and supersaturation. as shown in figure 3, heating through a hotplate causes the temperature of regions from the solution close to the hot plate to be higher than the temperature of the surface regions of the solution in the vicinity of the air. this results in the formation of a sharp temperature gradient in the solution, which in turn leads to a different evaporation rate and, ultimately, a different crystallization rate. the heat generated by a drying oven with heating elements embedded in top and bottom of the oven chamber creates a characterization and application of nanomaterials 2024, 7(1), 5593. 12 milder temperature gradient compared to the previous heating state. consequently, the evaporation rate and the rate of crystallization are more uniform. as a result, morphology is expected to be more uniform. also, the nanoparticles obtained by drying oven and hotplate heating methods tend to severe agglomeration [28] and this is clear in figure 8a,c. the microwave heating as a green heating method, has a mechanism fundamentally different from the common heating methods. this difference is significant from two perspectives: firstly, in common heating methods, i.e., conduction, convection, and radiation, heat is supplied through an external source. while in microwave heating, heat generated from microwave energy is absorbed by the material depending on its position in the microwave field. secondly, common heating methods produce a sharp temperature gradient in the material, while the microwave heating method does not create any temperature gradient and the temperature of the whole material is almost the same. in addition, microwaves deliver heat uniformly and simultaneously throughout the bulk of a material and also have the potential to penetrate deeply into material bulk [34,35]. as another important reason, experimental results have revealed that the crystal characteristics such as size distribution, crystal morphology and degree of agglomeration are also strongly influenced by the degree of supersaturation at the beginning of crystallization [29,36]. the crystals in a relatively high supersaturated solution focus on extending along the longitudinal direction. with the progress of the process, the supersaturation descends around the tips of the crystals and this causes the tips have a smaller diameter than the bases. as a result, a more orderly and uniform structure is expected. 4. conclusions in the present work, naf-na2co3-nacl ternary fluxing agent ternary was recovered from aluminum black dross as a hazardous solid waste. despite a significant reduction in waste toxicity, the recovery of fluxing agent in the form of a nanostructured salt can provide economic benefits. the recovery process was performed using water as a green solvent followed by the evaporation of water. the heat for the evaporation process was supplied using three sources of heating including a hotplate, microwave irradiation, and a drying oven. investigating the effects of time and temperature revealed that a recovery efficiency of 96.5% can be achieved under optimum temperature and time of 95 ℃ and 90 min, respectively. the recovered fluxing agent salt was found to contain more than 74 wt.% of naf by employing the rietveld fitting analysis. microstructural study by fesem disclosed that the ternary fluxing agent has been recovered in the form of highly aggregated round shape nanoparticles, needle-like nanoparticles, and a combination of both. author contributions: conceptualization, mm; methodology, mm; software, mm; validation, mm and aa; formal analysis, mm; investigation, mm and aa; resources, mm and aa; data curation, mm and aa; writing—original draft preparation, mm; writing—review and editing, mm and aa; visualization, mm; supervision, aa; project administration, mm and aa; funding acquisition, mm and aa. all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. characterization and application of nanomaterials 2024, 7(1), 5593. 13 references 1. xiao y, reuter ma, boin udo. aluminium recycling and environmental issues of salt slag treatment. journal of environmental science and health, part 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islamabad 45320, pakistan 2 department of physics, faculty of sciences, international islamic university, islamabad 45320, pakistan 3 department of microelectronics science and technology, school of microelectronics science and technology, sun yat-sen university, zhuhai 510275, china * corresponding author: javed iqbal, javed.saggu@qau.edu.pk abstract: the rapid growth of portable electronics and electric vehicles has intensified the global demand for high-performance energy storage devices with superior power density, energy density, and long cycle life. among transition metal oxide-based electrode materials with potential for energy storage, we report the development of mno2–v2o5 nanocomposite electrodes for supercapacitor applications. pure mno2 and v2o5 were successfully fabricated via a simple and economical sol–gel method, while (mno2)x–(v2o5)1−x (x = 1, 0.75, 0.50, and 0) nanocomposites were fabricated through an ex situ method. analytical techniques, including x-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, and uv-visible spectroscopy, were employed to investigate the structural, morphological, and optical properties of the electrodes. furthermore, the electrochemical properties were systematically analysed using cyclic voltammetry, galvanostatic charge– discharge measurements, and electrochemical impedance spectroscopy. the (mno2)0.75– (v2o5)0.25 nanocomposite demonstrated a remarkable specific capacitance of 666 f/g at a current density of 0.5 a/g in 1 m koh electrolyte. additionally, the electrode material exhibited an energy density of 23 wh/kg and a power density of 450 w/kg, while maintaining a capacitance retention of 95% after 1,500 cycles. the incorporation of v2o5 boosted the conductivity and significantly optimised the number of lattice defects. this work substantially reinforces the importance of metal oxide-based nanocomposites for future energy storage devices. keywords: manganese dioxide; supercapacitor; vanadium pentoxide; electrochemical properties; nanocomposites 1. introduction in the modern era, increasing energy demands that primarily rely on nonrenewable fossil fuels present a significant risk to human well-being. to address these challenges, efforts have been directed toward developing renewable, ecofriendly, and economical energy storage devices [1,2]. renewable energy storage devices are widely utilised in the present era, spanning from portable devices and electric vehicles to large-scale grid storage systems [3]. although li-ion batteries are prevalent owing to their high energy density, there is a critical need for innovative materials and designs capable of delivering higher specific capacitance (cw) and faster charging rates [4,5]. supercapacitors have recently emerged as a desirable option for various energy storage applications due to their increased power density, rapid charge and discharge rates, and long lifespan [6,7]. researchers have encountered challenges citation khalid a, iqbal j, jabeen s et al. (2025). electrochemical properties of transition metal oxide-based nanocomposites for energy storage systems. characterization and application of nanomaterials. 8(3): 11706. https://doi.org/10.24294/can11706 article info received: 24 april 2025 accepted: 6 november 2025 available online: 24 november 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(3), 11706. 2 in improving the energy density of supercapacitors [8,9], which involves optimising the selection and fabrication of appropriate electrode materials that possess a large surface area, low solution resistance, high chemical stability, and high conductivity [10,11]. transition metal oxides (tmos) are prominent pseudocapacitive materials owing to their unique properties, including low cost, abundant oxidation states, reversible surface redox reactions, minimal toxicity, and high theoretical cw [12]. pseudocapacitors are based on reversible redox reactions at the electrode surface. this redox process entails ion migration between distinct oxidation states of the electrode material. charges or ions in pseudocapacitive materials can be stored through mechanisms such as adsorption, intercalation, and surface redox reactions [13‒15]. owing to the synergistic interactions of metal cations, mixed tmos potentially exhibit superior physical and chemical properties [16], such as improved electrical conductivity and enhanced charge storage capacity in comparison to individual metal oxides [17]. the primary disadvantage of tmos is their low electrical conductivity. to address this, various studies have aimed to increase the electrical conductivity of tmos by creating composite materials [18‒20]. extensive research has focused on tmos, such as ruthenium dioxide (ruo2) [21], hafnium dioxide (hfo2) [22], iron(iii) oxide (fe2o3) [23,24], vanadium pentoxide (v2o5) [25], tungsten trioxide (wo3) [26], and manganese dioxide (mno2) [27], for their application in supercapacitors. the pseudocapacitor electrode material mno2 is gaining attention because the singleelectron redox process in each manganese (mn) atom contributes to a relatively large theoretical capacitance of 1,370 f/g. it is affordable, abundant, non-toxic, and has low conductivity [28‒30]. mn exists in a 2d tunnelling structure that facilitates electron transfer, resulting in a relatively high capacitance value, known as α, β, γ, λ, and δ forms, through distinct configurations of mno6 octahedra, where the mn atom is centrally located, surrounded by six oxygen atoms at each corner [31,32]. however, their low conductivity and volume expansion during discharge present significant challenges. to address these issues, numerous studies have been undertaken. wu et al. [33] examined fe-doped mno2 electrodes, enhancing their cw to 340 f/g at a current density of 2 a/g. tatrari et al. [34] compared 3d graphene hydrogel and wo3–mno2 composites, demonstrating their superior performance in asymmetric supercapacitors, with the mno2 composite achieving a cw of 430 f/g at a current density of 1 a/g. shen et al. [35] presented the synthesis of δ-mno2/soybean pod carbon via in situ hydrothermal methods, showcasing its high-performance application with a cw of 380 f/g at a current density of 1 a/g. alternatively, v2o5 is emerging as an excellent option for addressing the aforementioned issues by constructing heterostructured binary metal oxides. v2o5 is distinguished by its high theoretical cw of 2,120 f/g, multiple oxidation states (v5+, v4+, v3+, and v2+), cost-effectiveness, excellent chemical stability in electrolyte solutions, and a wide potential window, making it a promising material in this context [36‒39]. v2o5-based electrodes exhibit superior supercapacitive performance compared with other vanadium oxides, owing to their layered structure and stability [40]. specifically, the contiguous layers, bonded solely by weak van der waals forces, significantly contribute to achieving a high energy density through efficient ion characterization and application of nanomaterials 2025, 8(3), 11706. 3 diffusion. nevertheless, mno2, a pseudocapacitive material, is employed not only to improve the conductivity through composite formation with v2o5 but also to enhance the capacitance and reduce the electrode resistance [41,42]. jia et al. [43] prepared a v2o5 nanobelt array–nio nanosheet array composite, achieving a cw of 950 f/g at a current density of 1 a/g, showcasing a significantly enhanced performance. jyothibasu et al. [44] investigated graphite nanoplatelet–v2o5 nanotube composite electrodes, attaining a cw of 420 f/g at a current density of 1 a/g, emphasizing the synergistic effects of the composite material. according to our understanding, there is limited research on mno2–v2o5 nanocomposites as electrode materials for emerging supercapacitor applications. in this research, we investigate the (mno2)x–(v2o5)1−x nanocomposites as electrode materials for supercapacitors prepared with different stoichiometric ratios (x = 1, 0.75, 0.50, and 0) using a versatile ex situ method to enhance cw, ionic conductivity, and cyclic stability. in a 1 m koh aqueous electrolyte, (mno2)0.75– (v2o5)0.25 exhibited a higher cw of 725 f/g at 5 mv/s, along with a high rate capability with an energy density of 23 wh/kg. after 1,500 cycles at 0.5 a/g, cycling stability tests showed excellent coulombic efficiency, chemical stability, and 80% capacitance retention rate. 2. materials and methods 2.1. materials all substances were acquired from sigma aldrich (united states [us]) and used as received, without any additional refinement or purification. these included ammonium metavanadate (nh4vo3), oxalic acid (c2h2o4), potassium permanganate (kmno4), manganese sulphate (mnso4·4h2o), polyvinylidene fluoride (pvdf), nmethyl-2-pyrrolidinone (nmp), acetone (c3h6o), and carbon black. a sheet of pure 1.6 mm-thick nickel (ni) foam was sourced from sigma-aldrich (china). chemical solutions were prepared using deionised water (diw). 2.2. synthesis of v2o5, mno2, and their nanocomposites the synthesis procedures for v2o5, mno2, and (mno2)x–(v2o5)1−x nanocomposites (x = 1, 0.75, 0.50, and 0) are explained individually and illustrated schematically in figure 1. vanadium pentoxide nanoparticles were fabricated through an easy, straightforward, and cost-effective sol–gel method, in which nh4vo3 and c2h2o4 were used as precursors. in this process, the solutions were prepared separately in two different beakers. in beaker “a,” 3.580 g of c2h2o4, and in beaker “b,” 7.018 g of nh4vo3 were each dissolved in 50 ml of diw. following preparation, the solution from beaker “a” was added dropwise into beaker b to achieve the desired ph, and then the resulting mixture was stirred at 60°c for 2 h to form a gel. during synthesis, the ph of the solution was adjusted to 12 to promote phase formation and stabilise the v₂o₅ nanoparticles. the prepared gel was dried at 80°c for 24 h, and the resulting powder was repeatedly centrifuged with ethanol and diw. subsequently, the product characterization and application of nanomaterials 2025, 8(3), 11706. 4 was ground for 2 h and annealed at 400°c for 4 h in a muffle furnace, yielding yellowish nanoparticles. figure 1. schematic diagrams of the synthesis of mno2, v2o5, and (mno2)x–(v2o5)1−x nanocomposites (x = 1, 0.75, 0.50, and 0). similarly, a simple sol–gel method was used to synthesise mno2 nanoparticles, using kmno4 and mnso4·4h2o as precursors in a 1:2 molar ratio. during this procedure, 2 g of kmno4 was dissolved in 60 ml of diw and stirred at standard room temperature using a magnetic stirrer. simultaneously, in another beaker, 4 g of mnso4·4h2o was dissolved in 30 ml of diw. subsequently, the aqueous kmno4 solution was added dropwise into the mnso4·4h2o solution while maintaining the desired ph, and the mixture was stirred for 4 h at 80°c to form a gel. the resulting gel was then centrifuged multiple times with diw and ethanol to remove impurities. the wet precipitates were dried for 24 h at 80°c in a hot-air oven. after drying, the samples were finely ground and annealed at 500°c for 8 h in a muffle furnace, yielding a light greyish-black mno2 nanopowder. the (mno2)x–(v2o5)1−x nanocomposites were synthesised via an ex situ method using different stoichiometric ratios (x = 1, 0.75, 0.50, and 0) of mno2 and v2o5. the precursor powders were mixed and ground in a mortar and pestle for 2 h. during the grinding process, acetone was added dropwise 4–5 times to facilitate the formation of characterization and application of nanomaterials 2025, 8(3), 11706. 5 a homogeneous mixture. after fine grinding, the sample was dried in a hot-air oven at 80°c for 24 h to ensure complete evaporation of residual acetone and moisture. 2.3. characterisation of materials the crystal structure, crystallite size, and phase identification of the fabricated materials were analysed using x-ray diffraction (xrd), covering a 2θ range from 10° to 70° with a step size of 0.02°. the morphology, average particle size, and elemental composition of the synthesized samples were examined using scanning electron microscopy (sem) and energy-dispersive x-ray spectroscopy. fourier transform infrared (ft-ir) spectroscopy was employed to identify the functional groups and molecular vibrations of the samples across the wavenumber range of 4,000–400 cm−1, utilising kbr as a reference. the optical bandgap energy (eg) was determined by uvvisible spectroscopy within the range of 200–800 nm, and further estimated from the tauc plot relation. 2.4. fabrication of working electrodes for electrochemical measurements to analyse the electrochemical performance of the working electrode, ni foam, used as the electrode substrate, was first activated through sequential washing with 3 m hcl, ethanol, and diw to remove surface contaminants and impurities, followed by drying overnight at 60°c. next, the slurry for the working electrode was prepared using the active material, conductive additive, solvent, and binder. in this process, the electrode active material (80%), carbon black (10%), and pvdf (10%) were ground together for 30 min. the resulting mixture was then mixed with 5% nmp and stirred for 12 h to obtain a slurry. the resulting slurry was coated onto a ni foam electrode (surface area: 1 cm2) to form a thin and uniform layer. then, the coated electrode was dried in an electric oven at 70°c for 6 h to remove any residual solvent. the average active material loading on the ni foam surface was approximately 2 mg. the same procedure was followed for all samples. the supercapacitor device was assembled using two identical electrodes coated with the (mno2)x–(v2o5)1−x nanocomposite as the active material. a porous polypropylene membrane served as a separator, placed between the electrodes to allow for ionic transport while preventing electrical shorting. the entire assembly was immersed in an aqueous electrolyte (1 m koh), as shown in figure 2, and the components were pressed together to ensure good contact. a current collector was used to complete the symmetric supercapacitor cell configuration. characterization and application of nanomaterials 2025, 8(3), 11706. 6 figure 2. schematic representation of the supercapacitor assembly and the corresponding charge storage mechanism in the (mno2)x–(v2o5)1−x nanocomposites. 3. results and discussion 3.1. structural analysis the structural properties and phase formation of mno2, v2o5, and (mno2)0.75– (v2o5)0.25 electrode materials were analysed using xrd with cu–kα radiation (a wavelength of 1.5406 å) as the source. the mno2 nanostructures exhibited intense diffraction peaks corresponding to a tetragonal crystal structure [45], observed at 2θ angles of 21.8°, 35.1°, 36.9°, 42.1°, 47.7°, 55.4°, 56.9°, 63.1°, and 65.1°, which correspond to the crystal planes (110), (101), (020), (111), (210), (211), (220), (002), and (310), respectively. these reflections are consistent with the standard joint committee on powder diffraction standards (jcpds) card number 81-2261 [46], as presented in figure 3. similarly, the v2o5 sample displayed characteristic peaks of an orthorhombic structure [47] at 2θ angles of 20°, 21.3°, 26.1°, 30.9°, 32.50°, 34.1°, 41.23°, 45.45°, 47.50°, 48.7°, 51.3°, 55.6°, 60.9°, and 61.9°, corresponding to the crystal planes (001), (101), (110), (301), (011), (310) (002), (411), (600), (021) (020), (012), (321), and (710). these match well with the standard jcpds card number 41-1426 [48], as depicted in figure 3. the absence of extra peaks in the nanocomposite indicates the formation of a pure crystalline material without additional phases or impurities [49]. the diffraction pattern of (mno2)0.75–(v2o5)0.25, depicted in figure 3, exhibited a minor shift of diffraction peaks towards lower 2θ angles, which can be attributed to the formation of structural defects within the crystal lattice [50]. furthermore, compositional changes characterization and application of nanomaterials 2025, 8(3), 11706. 7 caused by the intercalation of vanadium ions can change the lattice parameters, potentially affecting both electronic conductivity and structural stability. the average crystallite sizes of mno2, v2o5, and (mno2)0.75–(v2o5)0.25 were calculated to be 18.2 nm, 28.1 nm, and 26.3 nm, respectively, using the scherrer equation. the decrease in the crystallite size of mno2–v2o5 was accompanied by an increase in the full width at half maximum of the diffraction peaks, indicating that the incorporation of v2o5 disrupts the crystal structure and induces stress/strain. this structural distortion facilitates the creation of additional ion diffusion channels and active sites, thereby enhancing the electrochemical performance of the material [51]. additional parameters are presented in table 1. figure 3. x-ray diffraction pattern of v2o5, (mno2)0.75–(v2o5)0.25 nanocomposite, and mno2. table 1. parameters of mno2, (mno2)0.75–(v2o5)0.25, and v2o5. serial no. sample peak position (2θ [°]) fwhm (2θ [°]) crystallite size (nm) 1 mno2 65.1 0.51 18.2 2 (mno2)0.75–(v2o5)0.25 48.5 0.33 26.3 3 v2o5 51.8 0.31 28.1 abbreviation: fwhm: full width at half maximum. 3.2. vibrational analysis characterization and application of nanomaterials 2025, 8(3), 11706. 8 vibrational studies were performed using ft-ir spectroscopy to analyse the functional groups of mno2, v2o5, and (mno2)x–(v2o5)1−x nanocomposites, as depicted in figure 4. the absorption bands observed at 524 cm−1, 589 cm−1, and 667 cm−1 corresponded to the vibration modes of the mn–o bond. the bands at 1,211 cm−1 and 1,365 cm−1 were attributed to the v=o stretching vibrations characteristic of v2o5. peaks present between 814 cm−1 and 1,001 cm−1 were attributed to the v–o–v stretching vibrations. the absorption peaks at 1,729 cm−1 and 3,407 cm−1 were linked to the o–h stretching and bending vibrations of h2o molecules, respectively. the main characteristic bands, such as the mn–o, v=o, and v–o–v bands, in the (mno2)x–(v2o5)1−x composites (x=1, 0.75, 0.50, 0) exhibited a slight shift towards lower wavenumbers, indicating chemical bonding interactions between mno2 and v2o5 phases. figure 4. fourier transform infrared spectra of (mno2)x–(v2o5)1−x nanocomposites (x = 1, 0.75, 0.50, and 0). 3.3. optical analysis the optical characteristics of mno2, v2o5, and (mno2)x–(v2o5)1−x nanocomposites were studied using uv-visible spectroscopy over the wavelength range of 200–800 nm. a significant and extensive absorption peak for mno2 was observed at 374 nm, attributed to the d–d transition of mn ions within the mno2 nanostructure (figure 5a). for v2o5, a strong absorption peak appeared at 254 nm, indicating the formation of a single-phase structure (figure 5d). the minor shift towards lower wavelengths in the absorption peaks of the nanocomposites was attributed to the interaction and synergistic effects between the two materials in the nanocomposites, as depicted in figure 5b,c). the energy band gap of the (mno2)x–(v2o5)1−x nanocomposites was determined using the well-defined tauc’s relation: (𝛼ℎ𝑣)2 = 𝐴(ℎ𝑣-𝐸𝑔)n (1) characterization and application of nanomaterials 2025, 8(3), 11706. 9 where n signifies the nature of the electronic transition (n = 1/2 for indirect transitions and n = 2 for direct transitions), hν is the photon energy, and a is ascribed to absorbance corresponding to the energy band gap (eg) [52,53]. the computed energy band gap values for mno2, (mno2)0.75–(v2o5)0.25, (mno2)0.50–(v2o5)0.50, and v2o5 were 1.37 ev, 1.40 ev, 1.65 ev, and 2.1 ev, respectively, as depicted in figure 5a– d. the gradual decrease in energy band gap with increasing mno2 content demonstrates the semiconducting nature of the nanocomposites and effectively tunes the energy band gap towards the visible region. this narrowing of the band gap facilitates enhanced charge transfer during faradaic redox reactions, thereby improving electrical conductivity and cw. through surface redox reactions, mno2 contributes to rapid charge storage, whereas v2o5 provides more redox-active sites and facilitates electron mobility. enhanced charge transfer at the interface between the two materials is achieved by their close contact, which reduces internal resistance, enhances conductivity, and improves charge storage behaviour. figure 5. uv-visible absorption spectra and energy band gap of (a) mno2, (b) (mno2)0.75–(v2o5)0.25, (c) (mno2)0.50– (v2o5)0.50, and (d) v2o5. 3.4 scanning electron microscopy analysis characterization and application of nanomaterials 2025, 8(3), 11706. 10 the surface morphology of synthesised samples—mno2, v2o5, and (mno2)0.75– (v2o5)0.25—was examined at various magnifications using sem, as depicted in figure 6. the nanostructural characteristics were found to be strongly influenced by particle size and distribution. the average particle size, calculated using imagej software (national institutes of health, us), confirmed the nanoscale nature of the synthesised materials. the sem micrographs of the nanocomposites revealed that the mno2 nanoparticles were adsorbed across the surface of v2o5 nanoflakes, as shown in figure 6d–f. pure mno2 exhibited spherical morphology with discernible agglomeration (figure 6a–c), which can be attributed to their high surface energy and the natural tendency of unbound nanoparticles to form clusters through strong intermolecular interactions during synthesis and drying. in contrast, pure v2o5 exhibited a nanoflake-like structure. in the nanocomposite, the degree of agglomeration was substantially reduced, resulting in a larger effective surface area, improved adsorption capacity, and enhanced charge storage performance. the average particle diameters of (mno2)x–(v2o5)1−x (x = 1, 0.75, 0.50, and 0) were in the nanometre range, consistent with xrd results, with minor deviations attributed to particle agglomeration. sem observations effectively revealed a porous nanoarchitecture, which provides numerous active sites and multiple channels for efficient ion and electron transport—key factors in enhancing faradaic reactions and overall electrochemical performance. furthermore, eds analysis confirmed the elemental composition of mno2 and (mno2)0.75–(v2o5)0.25 samples. figure 6g presents elemental mapping of the composite. mn, v, and o elements were uniformly distributed in the nanocomposite structure. characterization and application of nanomaterials 2025, 8(3), 11706. 11 figure 6. scanning electron microscopy images of (a–c) mno2 nanoparticles, (d–f) (mno2)0.75–(v2o5)0.25, and (g) v2o5 nanoflakes. scale bars: (a & g) 1 µm, (b & f) 500 nm, (c & e) 10 µm, (d) 2 µm; magnifications: (a & g) 18 000×, (b & f) 20 000×, (c & e) 1000×, (d) 5000×. (h) energy-dispersive x-ray spectroscopy (edx) of mno2. (i) edx of (mno2)0.75–(v2o5)0.25. 3.5 electrochemical studies the study of electrochemical properties involves understanding the response and interaction of electrode materials under the influence of electric current and voltage. this aspect is needed for the advancement of batteries, supercapacitors, and various energy storage devices [54]. the electrochemical properties, such as electrical conductivity, charge storage capacity, and electrochemical stability, influence the performance and efficiency of electrochemical devices [55]. all measurements of the fabricated electrodes were tested using an electrochemical workstation (gamry interface 1000e potentiostat, gamry instruments, us) equipped with a three-electrode system at room temperature. the setup consisted of a counter electrode, an ag/agcl reference electrode, and a working electrode (mno2–v2o5), all of which were immersed in 1 m koh electrolyte. the abovedescribed procedure (fabrication of working electrode) was repeated for all samples. the electrochemical characteristics of the working electrode were examined through various techniques, such as galvanostatic charge–discharge (gcd) measurements, which were performed at various current densities ranging from 0.5–2 a/g within a potential window of 0–0.5 v to ensure electrochemical stability, show reversible charge–discharge behaviour, and avoid decomposition of electrolyte; cyclic voltammetry, which was conducted at several scan rates (5–100 mv/s) over a potential range of 0–0.6 v to demonstrate the redox behaviour and capacitive response of the electrodes; and electrochemical impedance spectroscopy (eis), which was carried out with a frequency range of 0.1–100 khz. additionally, coulombic efficiency and capacitance retention were analysed over 1,500 cycles. cyclic voltammetry was used to examine the electrochemical responses of the prepared mno2, v2o5, and (mno2)x–(v2o5)1−x nanocomposites. a cyclic voltammogram reveals the adsorption and desorption of electrolyte ions on the electrode surface, forming an electric double layer known as the helmholtz layer. meanwhile, rapid and reversible faradaic redox reactions occur due to ion intercalation at the electrode–electrolyte interface within the tmos (mno2 and v2o5). the redox peaks demonstrate the pseudocapacitive nature of the electrode, and the cw is calculated as follows: 𝐶𝑤 = a 2𝑚𝑘∆𝑉 (2) where m is the mass of active materials, a is the area of the cyclic voltammetric curve, ∆v is the potential window, and k corresponds to the scan rate. the current response and area under the curve increased progressively with scan rate from 5–100 mv/s in 1 m koh electrolyte within a potential window of 0–0.6 v (figure 7a–d). the voltammograms exhibited faradic peaks that corresponded to redox reactions and a diffusion-controlled mechanism occurring at the electrode– electrolyte interface during cathodic and anodic sweeps. these peaks were particularly characterization and application of nanomaterials 2025, 8(3), 11706. 12 noticeable at the lower scan rate of 5 mv/s, where electroactive species and electrolyte ions had sufficient time to interact. the trend of cw is depicted in table 2. as the scan rate increased, the cw gradually declined, which can be attributed to the limited time for ions to reach the inner active sites of the electrode materials. additionally, the oxidation peaks shifted towards more positive potentials, whereas the reduction peaks moved towards more negative potentials, indicating the presence of internal resistance within the electrode. notably, the cw of (mno2)0.75–(v2o5)0.25 nanocomposite achieved 725 f/g, outperforming the individual electrodes of mno2 (230 f/g) and v2o5 (553 f/g). this enhancement can be ascribed to the formation of a heterojunction at the mno2–v2o5 interface, which facilitates efficient interfacial charge transfer. the incorporation of v2o5 introduced additional active sites and promoted faster ion diffusion, thereby reducing charge transfer resistance. this effect accelerated faradaic redox reactions and electric double-layer formation, resulting in enhanced overall charge storage capacity. figure 7e,f depicts the comparison of cw for each sample at varying scan rates. figure 7. cycle voltammetry measurements of (a) mno2, (b) (mno2)0.75–(v2o5)0.25, (c) (mno2)0.50–(v2o5)0.50, and (d) v2o5. (e) specific capacitance vs. scan rate. (f) reliance of ic and ia currents on the sweep rate scan rate. to further elucidate the charge storage mechanism, b-value analysis was conducted using the power-law relationship: 𝑖 = 𝑎𝑣𝑏 (3) where v is the scan rate, i is the peak current, and b indicates the slope obtained from the linear fit. the b value provides insight into the dominant charge storage process: when b = 1, the current response is capacitive-controlled; whereas b = 0.5 corresponds to a charge storage mechanism controlled by ion diffusion. the obtained b value for the cathodic and anodic peaks of the nanocomposite fell between 0.54 and 0.60, characterization and application of nanomaterials 2025, 8(3), 11706. 13 suggesting the k+ cation storage in (mno2)0.75–(v2o5)0.25, which is a characteristic of pseudocapacitive processes. table 2. specific capacitance (cw) of the nanocomposites measured at various scan rates. serial no. materials cw (f/g) 5 mv/s 20 mv/s 40 mv/s 60 mv/s 80 mv/s 100 mv/s 1 mno2 230 129 88 71 62 53 2 (mno2)0.75–(v2o5)0.25 725 493 393 319 263 223 3 (mno2)0.50–(v2o5)0.50 615 426 311 244 199 165 4 v2o5 553 389 284 224 187 160 the charge storage behaviour at the electrode–electrolyte interface was further studied using gcd measurements for mno2, v2o5, and (mno2)x–(v2o5)1−x nanocomposites. the gcd plots for all samples, recorded at current densities of 0.5– 2.0 a/g in 1 m koh electrolyte, are illustrated in figure 8a–d, while the corresponding cw values are listed in table 3. for each sample, the charge–discharge curve clearly demonstrated the pseudocapacitive behaviour of the materials within a potential window of 0–0.5 v. at the beginning of the discharge cycle, a noticeable voltage drop was observed, which was attributed to the internal resistance of the electrode material. the maximum discharge time was recorded at the lowest current density of 0.5 a/g, as the electrolyte ions have sufficient time to diffuse and interact with the electrode’s active sites [56]. conversely, at higher current densities, the cw decreased due to insufficient interaction time, resulting in increased kinetic irreversibility of the ions [57]. the cw was determined from the gcd curve using the following equation: 𝐶𝑤 = i×∆t ∆v×m (4) where ∆v is the potential window, i and m represent current density, and ∆t is the discharge time. the cw for mno2, (mno2)0.75–(v2o5)0.25, (mno2)0.50–(v2o5)0.50, and v2o5 were calculated to be 214 f/g, 666 f/g, 607 f/g, and 515 f/g, respectively, at the lowest current density of 0.5 a/g. figure 8e,f illustrates the cw for each sample at varying current densities. the energy density and power density of the electrochemical supercapacitor were estimated from the gcd plots using the following equations: 𝐸 = 1 2 𝐶𝑤∆𝑉2 (5) 𝑃 = 𝐸 ∆𝑡 (6) characterization and application of nanomaterials 2025, 8(3), 11706. 14 figure 8. galvanostatic charge–discharge curves of (a) mno2, (b) (mno2)0.75–(v2o5)0.25, (c) (mno2)0.50–(v2o5)0.50, and (d) v2o5. (e) specific capacitance vs. current density. (f) graphical comparison of specific capacitance vs. varying current densities. the (mno2)0.75–(v2o5)0.25 electrode demonstrated outstanding electrochemical performance at a maximum current density of 2 a/g, with an impressive energy density of 23 wh/kg and a power density of 450 w/kg. these results aligned with the cw values measured at numerous scan rates for the (mno2)x–(v2o5)1−x (x = 0, 0.75, 0.50, and 1) nanocomposites using cyclic voltammogram. table 3. specific capacitance (cw) of (mno2)x–(v2o5)1−x nanocomposites measured at various current densities. serial no. materials cw (f/g) 0.5 a/g 1.0 a/g 1.5 a/g 2.0 a/g 1 mno2 214 194 186 180 2 (mno2)0.75–(v2o5)0.25 666 640 635 619 3 (mno2)0.50–(v2o5)0.50 607 574 554 548 4 v2o5 515 507 495 489 the measurements of eis were obtained to analyse the charge transfer properties of the electrode–electrolyte interface of the nanocomposites. in the nyquist plot, the real component (z’), plotted along the x-axis, represents the ohmic characteristics, whereas the imaginary component (z”), plotted on the y-axis, denotes the capacitive or inductive properties of the electrochemical cell [58]. the smaller semi-circle observed for the (mno2)0.75–(v2o5)0.25 electrode indicates a notably lower charge transfer resistance. additionally, the nyquist plot of the (mno2)0.75-(v2o5)0.25 electrode was fitted with an equivalent circuit model, wherein the alternating current characterization and application of nanomaterials 2025, 8(3), 11706. 15 signal passes through the solution resistance connected in series across all frequencies, as shown in figure 9e. the solution resistance values for (mno2)x–(v2o5)1−x (x = 1, 0.75, 0.50, and 0) were determined as 0.51 ω, 0.24 ω, 0.44 ω, and 0.84 ω, respectively, as represented in figure 9a–d. the irregularity of the electrode surface and the reduced pore size contributed to increased solution resistance and electrolyte ion resistance. at lower frequencies, the linear response reflects the diffusion of electrolyte ions at the electrode surface, contributing to considerable resistance. the combined electrochemical activities of v2o5 and mno2 accounted for this remarkable performance. both pseudocapacitive metal oxides were distinguished by their high redox activity and stability. figure 9. nyquist plots of (a) mno2, (b) (mno2)0.75–(v2o5)0.25, (c) (mno2)0.50–(v2o5)0.50, and (d) v2o5. (e) fitted nyquist plot with an equivalent circuit. abbreviation: esr: equivalent series resistance. the cyclic stability of mno2, v2o5, and (mno2)x–(v2o5)1−x nanocomposites was evaluated using gcd testing over 1,500 cycles at 0.5 a/g to assess the behaviour of the working electrodes. as shown in figure 10, the (mno2)0.75–(v2o5)0.25 electrode achieved a capacitance retention of 95% and an outstanding coulombic efficiency of 98%, demonstrating excellent stability compared to the capacitance retention of the individual mno2 (74%) and v2o5 (80%). the increased cyclic stability of the nanocomposite electrode can be attributed to the incorporation of v2o5, which not only improves the conductivity but also increases capacity and stabilises the mno2 nanostructure. in contrast, when the gcd process was carried out over several cycles in tmos (mno2 and v2o5), redox reactions at the electrode–electrolyte interface can slowly disrupt the contact between conductive particles within the composite. this instability may lead to the steady dissolution of mn and v ions into the electrolyte, characterization and application of nanomaterials 2025, 8(3), 11706. 16 resulting in inactive material degradation, structural instability, and reduced electrochemical performance over time. overall, the enhancement in stability implies enhanced structural integrity, reduced degradation rate, and consistent electrochemical performance, confirming the potential of the nanocomposite electrode in energy storage applications [59]. figure 10. cyclic stability and coulombic efficiency of mno2, (mno2)0.75–(v2o5)0.25, and v2o5 nanocomposite. 4. conclusion in conclusion, we successfully fabricated (mno2)x–(v2o5)1−x (x = 1, 0.75, 0.50, and 0) nanocomposites as electrode materials for supercapacitor applications through a simple chemical method. xrd studies confirmed the phase purity and crystalline structure of all samples, while sem and eds mapping verified their morphology. uvvisible spectroscopy revealed that the energy band gap of the nanocomposite shifted towards the visible region due to defect sites present in the crystal structure. electrochemical studies demonstrated that the (mno2)0.75–(v2o5)0.25 nanocomposite electrode showed outstanding electrochemical performance, achieving a cw of 666 f/g at a current density of 0.5 a/g, with a low resistance (0.24 ω), excellent cyclic stability (95%), and high coulombic efficiency (98%) after 1,500 cycles. moreover, the energy density (23 wh/kg) and power density (450 w/kg) for the (mno2)0.75–(v2o5)0.25 nanocomposite were enhanced due to the synergistic effect of mno2 and v2o5. overall, the advancement of tmo-based nanocomposites highlights their potential use for characterization and application of nanomaterials 2025, 8(3), 11706. 17 efficient energy storage. furthermore, the nanocomposite electrode exhibited significant energy density and consistent electrochemical characteristics, suggesting the nanocomposite is a promising material for supercapacitors. author contributions: conceptualization, javed iqbal; visualization, sobia jabeen; writing–original draft, amna khalid; writing–review and editing, sobia jabeen. all authors have read and agreed to the published version of the manuscript. acknowledgments: the authors would like to express their sincere gratitude to their supervisor, prof. javed iqbal, for his valuable guidance and support throughout this research. the authors acknowledge the department of physics, lnt laboratory, and quaid-i-azam university, islamabad, pakistan, for providing the necessary research facilities. appreciation is also extended to all the institutes affiliated with the authors of this manuscript for their cooperation and assistance. data availability statement: the data supporting the findings of this study are available upon request. conflict of interest: the authors declare no conflict of interest. references 1. strielkowski w, civín l, tarkhanova e, et al. renewable energy 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2024; 318: 129233. doi: 10.1016/j.matchemphys.2024.129233 characterization and application of nanomaterials (2022) volume 5 issue 1 doi:10.24294/can.v5i1.1407 1 original research article study on the preparation and antibacterial properties of ctab-coated aunps yayun ma, mei liu*, jiao li, xuanyi li, zongqi yang school of food engineering and nutritional science, shaanxi normal university, xi’an 710119, china. e-mail: liumei@snnu.edu.cn abstract in this paper, spherical gold nanoparticles (aunps), rod-shape aunps and triangular aunps were synthesized using ctab as the coating reagent, and their bactericidal properties against staphylococcus aureus (s. aureus) and escherichia coli (e. coli) were studied. by the plate count method and turbidity method, the minimum bactericidal concentrations (mbc) and the minimum bacteriostasis concentrations (mic) to the two kinds of bacteria were determined. the mic of rod-shape aunps, triangular aunps and spherical aunps to e. coli were 0.65 μg/ml, 3.71 μg/ml, 21.21 μg/ml, and mbc were 1.30 μg/ml, 11.09 μg/ml, 21.21 μg/ml, respectively. the mic to s. aureus were 0.26 μg/ml, 0.56 μg/ml, 2.65 μg/ml, while mbc were 0.52 μg/ml, 1.11 μg/ml, 2.65 μg/ml, respectively. the results showed that the bactericidal effect of rod-shape aunps on e. coli and s. aureus was higher than that of the other two forms, and the bactericidal effect of three different forms of aunps on s. aureus was better than that on e. coli. keywords: aunps; different forms; s. aureus; e. coli; antibacterial properties article info received: 8 september 2021 accepted: 21 october 2021 available online: 5 november 2021 copyright copyright © 2022 yayun ma, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4 .0/ 1. introduction food safety issues have become a public health hotspot in today’s world, while foodborne pathogenic bacteria are one of the main causes of foodborne diseases, and the emergence of antibiotics has played a big role in controlling such diseases. however, the abuse of antibiotics makes bacteria have gradually produced drug resistance to traditional antibiotics, and the emergence of antibiotic resistance pathogens has seriously jeopardized human health. therefore, the research about new, safe, and efficient antibacterial materials is imminent[1]. in recent years, with the development of nanotechnology, the antibacterial study of nanomaterials has become a hot spot in current research. antibacterial nanomaterials have been reported[2] including nanocrystallized traditional antibacterial materials (such as nanofibae, nanoplastic antimicrobial peptide, etc.), inorganic metals and metal oxide nanoparticles (such as gold, silver, copper, zinc oxide, etc.), and new surface modified nanoparticles. nanoparticles are used as a new type of antibacterial drugs, which is considered to have a mechanism different from conventional drugs. it is difficult to induce bacterial resistance compared to traditional antibiotics. therefore, it has become one of the novel drug research and development directions, attracting great interest of researchers[3,4]. aunps, highly representative nanoparticles, have a wide range of applications in the fields of catalytic[5], biomedicine[6] and other fields 2 with its good stability, dimensional effect, surface effect, optical effect, and unique biological affinity. in the field of biomedicine, “aunps” has become a favored nanomaterial, widely used in biological sensing[7–9], as drug delivery carriers[10,11], and as a new type of antibacterial drug after its surface is modified by different antibacterial drugs[3]. however, there is little study of aunps’ self-antibacterial properties compared to that of the silver nanoparticles that are widely concerned. in 2015, z. vivian feng’s topic group[12] obtained aunps with different charges by coating different agents on the surface and compared the antibacterial properties. they found that aunps with negative charges do not have bactericidal effect, while aunps with positive charges have bactericidal effect; with the increase of charge density, the bactericidal effect is constantly enhanced. in 2017, jelle penders’s topic group[13] studied the effects of negative aunps, gnfs, gold nanostars on the lag time and exponential growth rate of s. aureus growth, and observed an obvious concentration and shape dependency effect. the change of shapes caused significant difference in the antibacterial effect. it is speculated that this is due to the large surface area and more surface protrusions, which may make gnfs more easily attached to the bacteria, then break the membrane, resulting in cell death. hexadalkyl trimethyl ammonium bromide (ctab) is the most commonly used coating agent to synthesizing aunps with positive charges, and the ctab coated method has been found to be able to synthesize aunps in many shapes such as rod, triangle, sphere, and cube[14], of which rod-shape aunps, spherical aunps, triangular aunps have better stability, a simpler synthetic method, and are applied in a wide range of fields. based on this, we chose to use ctab as a coating agent to study the antibacterial activity of positively charged aunps with spherical, rod-shape and triangular morphology. in this paper, three kinds of positively charged aunps with spherical, rod-shape and triangular morphology were synthesized by using ctab as the coating reagent, and s. aureus from gram-positive bacteria and e. coli from gram-negative bacteria were used as test strains. by the plate count method and turbidity method, we determined the minimum bactericidal concentrations and minimum antibacterial concentrations of the two bacteria, and studied the antibacterial effect of the three different forms of positively charged aunps on test strains. and the mechanism of antibacterial action is discussed. 2. experiment 2.1 reagents and instruments chlorogenic acid (haucl4), ctab, silver nitrate (agno3), sodium borohydride (nabh4), ascorbic acid (aa), trisodium citrate (c6h9na3o9), isopropyl alcohol (c3h8o), anhydrous ethanol (c2h5oh), sodium chloride (nacl), potassium iodide (ki), phosphate buffer solution (pbs), agar powder, cerebral flux culture medium (bhi), broth medium (lb). the above reagents are all commercially available analytical reagents, and the experimental water is ultrapure water. the s. aureus (cicc 10384) and e. coli (k12) for the experiment is purchased in china center of industrial culture collection. ldzx–30kbs vertical pressure steam sterilizer, shanghai shenan medical device factory; yt–cj–2d ultra-clean workbench, beijing yatai kelong instrument technology co., ltd.; dh4000ii electric heating incubator, telles instrument (tianjin) co., ltd.; pb–10 satorius basic ph meter, sartorius scientific instruments (beijing) co., ltd.; zd–85a dual-function constant temperature air bath shaker, youlian instrument research institute, jintan city, jiangsu province; hc–3018r high speed refrigerated centrifuge, zhonghai branch of kdcs co., ltd.; df–101s collective temperature heating magnetic mixer, gongyi yuhua instrument co., ltd.; uv–1800 uv-visible spectrometer, japan hitachi; jem–2100 transmission electron microscope, japan jeol; cannon 500d digital camera, canon co., ltd. 3 2.2 preparation of aunps 2.2.1 preparation of spherical aunps according to the literature[15], 20 ml haucl4 (2.5 × 10–4 m) solution was stirred with 0.0015 g trisodium citrate to make the concentration of trisodium citrate 2.5 × 10–4 m. then 0.6 ml nabh4 solution (0.1 m) with ice water was added, and the solution immediately turned pink and was stirred continuously to act as seed fluid. 6 g ctab was added to 200 ml haucl4 (2.5 × 10–4 m) solution to make the concentration of ctab 0.08 m, then the solution was heated at 45 ℃ until it turned orange, and cooled to room temperature to be used as a growth solution for later use (note: if crystals form, slowly dissolve them at a mild temperature). add 0.05 ml prepared vc (0.1 m) into 9 ml growth solution, add 1 ml seed solution under intense agitation, continue stirring for 10 min, then add 0.05 ml vc (0.1 m) into 9 ml growth solution, add 1 ml dark red solution under intense agitation, continue stirring for 10 min to turn them into brownish red. the spherical aunps with a particle size of 17 ± 2.5 nm can be obtained. post-treatment: undertake centrifugation at 10,000 r/min at 30 ℃ for 15 min, remove the supernatant, replenish water to 10 ml, repeat the centrifugation process twice, and finally dilute the sediment to half of its original volume with water, and store it under 4 ℃ away from light. 2.2.2 preparation of rod-shape aunps according to the method in the literature[16], 5 ml haucl4 (5.0 mm) solution was added to 5 ml ctab (0.2 m) solution and stirred, and the solution changed from bright yellow to orange. continue stirring and add 0.6 ml nabh4 (0.01 m) solution (prepared when necessary), stir for 2 min, and the solution turned yellowish-brown. finally, the aunps solution was heated at constant temperature for 2 h in a 30 ℃ water bath, and then used as seed liquid. in 5 ml ctab (0.2 m) solution, 0.1 ml agno3 (0.004 m) solution was added in the process of stirring, followed by 5 ml haucl4 (1 mm) solution, and 70 ml aa (0.0788 m) solution. after the solution became colorless, add 12 μl crystal seed. continue stirring for 15 min, and the solution turned purple. finally, the solution of aunps was heated in a 30 ℃ water bath for 2 h at constant temperature. the solution turned dark blue and the rod-shape aunps could be obtained. the post-treatment process is the same as that of spherical aunps. 2.2.3 preparation of triangular aunps according to the literature[17], 0.4 ml haucl4 (2.5 × 10–4 m) and 1 ml sodium citrate (10 mm) were added to 37.6 ml water, followed by 1 ml nabh4 solution with ice water (0.1 m). after vigorously stirring for 2 min, the solution turned orange-red, and then stood for 2 h to ensure that the unreacted nabh4 was completely hydrolyzed to make seed liquid. 100 ml growth solution containing 2.5 × 10–4 m haucl4 solution and 0.05 m ctab was added with 55 μl ki (0.1 m), 0.55 ml vc (0.1 m), and 0.55 ml naoh (0.1 m), stirred gently until the solution turned orange, then cooled to room temperature as a growth solution for later use. 0.1 ml seed liquid was added to the growth solution, and the color of the growth solution changed from transparent to light red, and then to deep red within 30 min (the reaction solution was kept at 30 ℃), then triangular aunps were obtained. the post-treatment process is the same as that of spherical aunps. 2.3 characterization of samples a uv–1800 uv-visible spectrometer (uv-vis, japan’s compnay) was used to record the uv spectrum of the samples for quickly distinguishing spherical aunps, rod-shape aunps and triangular aunps. the morphology and particle size of the three different aunps were observed by tem (jeol, japan). 2.4 test of antibacterial performance the minimum bactericidal concentration (mbc) and minimum inhibitory concentration (mic) to e. coli and s. aureus were detected by the plate count method and 96-well plate method. 2.4.1 preparation of medium take 37 g brain heart infusion and culture it in 1 l distilled water, boil it to make it fully dissolved, 4 adjust ph to 7.2–7.3, add 15 g agar powder (agar powder is not needed if liquid medium is prepared). after boiling and dissolving, sterilize it at 121 ℃ for 20 min, and pour it to the plate on an aseptic operating table for later use. broth medium was prepared by the same method. 2.4.2 preparation of bacterial suspension the bacteria cryopreservation tube was taken out from the refrigerator at 80 ℃. after the solution was dissolved, the bacteria solution was diluted to 10–2, 10–4, 10–6 times by the two-fold dilution method[18,19]. 100 μl of each was applied to the plate and cultured at 37 ℃ for 18 h. take out 20 ml sterilized liquid medium and transfer it to a 100 ml conical flask, then use a 10 μl pipetting gun to absorb a complete colony. put the spear tip into the conical flask and incubate it on a shaker (37 ℃, 260 r/min) for 14 h. centrifuge (6,000 r/min, 2 min) for removing the supernatant, add 5 ml normal saline, mix well and centrifuge (6,000 r/min, 2 min), repeat twice, then add 5 ml normal saline to the bacteria removed from the medium, mix evenly and set aside for use. 2.4.3 minimum bactericidal concentration add aunps diluted to different concentrations to pbs buffer solution, then add 100 μl of bacterial solution with a dilution ratio of 2 × 104 and mix them to make the reaction system 1,000 μl. after incubation in a shaker for 4 h, take out 100 μl and spread it on the culture plate, culture upside down at 37 ℃ for 18 h, and observe the colony growth. the mixture of pbs buffer solution and bacteria solution was used as the blank control. three parallel experiments were performed. the colony growth was observed, and the concentration corresponding to the sample with less than 5 colonies was taken as the mbc value. 2.4.4 minimum inhibitory concentration add aunps diluted to different concentrations into the liquid medium, and then add 100 μl bacterial solution with a dilution ratio of 2 × 104 to make the reaction system 1,000 μl. add 200 μl to the area of 96-well plate as the experimental group; the aunps solution in the experimental group was replaced with the same amount of normal saline, and then 200 μl was added to the corresponding area of the 96-well plate as the positive control. change the bacteria liquid and liquid medium of the experimental group into the same amount of normal saline, and add 200 μl to the 96-well plate area as the negative control. the 96-well plate was placed in a constant temperature incubator and incubated at 37 ℃ for 24 h. the mic was the concentration of aunps that could prevent the sample from forming obvious turbidity. 3. results and discussion 3.1 characterization of aunps 3.1.1 uv-visible absorption spectrum analysis figure 1 shows the results of uv-absorbable spectrum analysis after the synthesis of aunps. uv spectrum analysis shows that: absorption peaks of spherical aunps were at 520 nm, that of rod-shape aunps were at 525 nm and 604 nm, and that of triangular aunps were at 728 nm and 928 nm, which were basically consistent with the absorption peaks in the references, confirming the successful synthesis of spherical aunps, rod-shape aunps and triangular aunps. figure 1. uv-vis absorption spectra of spherical aunps (a), rod-shape aunps (b) and triangular aunps (c) coated by ctab. 5 3.1.2 transmission electron microscopy (tem) through tem, three different forms and particle sizes of the synthesized aunps can be intuitively observed, as shown in figure 2. it can be seen from the figure that the three different forms of aunps were successfully prepared, and were relatively uniform with good dispersion among the particles. the diameter of the spherical aunps is about 17 ± 2.5 nm, the length of the rod-shape aunps is about 52.31 ± 0.86 nm, with the width about 22.49 ± 0.56 nm and the aspect ratio about 2.3. the synthesized triangular aunps are equilateral with the side length of 100 ± 25 nm. figure 2. tem images of spherical aunps (a), rod-shape aunps (b) and triangular aunps (c) coated by ctab. 3.2 study on bactericidal effect of different forms of aunps 3.2.1 minimum bactericidal concentration of spherical aunps as shown in figure 3, the mbc of spherical aunps to e. coli: when the concentration of aunps is greater than 21.21 μg/ml, the number of bacterial colonies on the plate is less than 5, so the mbc is 21.21 μg/ml; for the mbc to s. aureus: when the concentration of aunps is greater than 5.30 μg/ml, the number of bacterial colonies on the plate is less than 5, so the mbc of spherical aunps is 5.30 μg/ml. figure 3. plate diagram of e. coli (a) and s. aureus (b) under different concentrations of spherical aunps. note: aunps reacted with bacterial solution for 4 h, and the plate was cultured at 37 ℃ for 18 h. 3.2.2 minimum bactericidal concentration of rod-shape aunps as can be seen from figure 4, when the concentration of rod-shape aunps was greater than 1.30 μg/ml, the number of bacterial colonies on the plate was less than 5, so the mbc to e. coli was 1.30 μg/ml. when the concentration of aunps was greater than 0.52 μg/ml, the number of bacterial colonies on the plate was less than 5, and the mbc to s. aureus was 0.52 μg/ml. 6 figure 4. plate diagram of e. coli (a) and s. aureus (b) under different concentrations of rod-shape aunps. note: aunps reacted with bacterial solution for 4 h, and the plate was cultured at 37 ℃ for 18 h. 3.2.3 minimum bactericidal concentration of triangular aunps as can be seen from figure 5, when the concentration of aunps is greater than 11.09 μg/ml, the number of bacterial colonies on the plate is less than 5, so the mbc to e. coli is 11.09 μg/ml. for the mbc to s. aureus, when the concentration of aunps is greater than 1.11 μg/ml, the number of bacterial colonies on the plate is less than 5, so the mbc of triangular aunps is 1.11 μg/ml. figure 5. plate diagram of e. coli (a) and s. aureus (b) under different concentrations of triangular aunps. note: aunps reacted with bacterial solution for 4 h, and the plate was incubated at 37 ℃ for 18 h. 3.3 study on inhibitory effects of different forms of aunps 3.3.1 staphylococcus aureus taking s. aureus as the research object, the different forms of synthesized aunps were diluted, respectively, the dilution ratio of spherical aunps was 10, 20, 40, 80, 160 times, and that of rod-shape aunps was 1,000, 2,000, 4,000, 8,000, 10,000 times, and that of triangular aunps was 50, 100, 200, 400 and 800 times. the concentration of aunps corresponding to the dilution ratio was used to determine the minimum inhibitory concentration, and the results of the 96-well plate were shown in figure 6. the results showed that the mic of spherical aunps to s. aureus was 2.65 μg/ml, that of rod-shpe aunps was 0.26 μg/ml, and that of triangular aunps was 0.56 μg/ml. figure 6. the mic of spherical aunps (a), rod-shape aunps (b) and triangular aunps (c) coated by ctab to s. aureus cultured at 37 ℃ for 24 h. note: the figure is the concentration of aunps, in μg/ml. 7 3.3.2 escherichia coli e. coli was taken as the research object, and the different forms of aunps were diluted. respectively, the dilution ratios of spherical aunps were 5, 10, 20, 40, 80 times, that of rod-like aunps were 400, 800, 1,000, 2,000, 4,000 times, and that of triangular aunps were 30, 60, 120, 240, 800 and 480 times. the mic of aunps of different forms was determined at the concentration corresponding to different dilution ratios, and the results of 96-well plates were shown in figure 7. the results showed that to e. coli, the mic of spherical aunps was 21.21 μg/ml, that of rod-shape aunps was 0.65 μg/ml, and that of triangular aunps was 3.70 μg/ml. figure 7. the mic of spherical aunps (a), rod-shape aunps (b) and triangular aunps (c) coated by ctab to e. coli cultured for 24 h at 37 ℃. note: the figure is the concentration of aunps, in μg/ml. in conclusion, the mbc and mic of aunps with different forms to s. aureus and e. coli were determined by the plate counting method and 96-well plate method, as shown in table 1 below. the bactericidal effect of rod-shape aunps is the best among the three forms of aunps. and no matter what form of aunps, its bactericidal effect on s. aureus is obviously better than that on e. coli. table 1. mic and mbc of aunps with different forms mbc /μg∙ml–1 mic /μg∙ml–1 e. coli s. aureus e. coli s. aureus spherical aunps 21.21 5.30 21.21 2.65 rod-shape aunps 1.30 0.52 0.65 0.26 triangular aunps 11.09 1.11 3.70 0.56 3.4 discussion on antibacterial mechanism in 2014, xingyu jiang’s research group[20] studied the bactericidal mechanism of aunps against gram-negative bacteria e. coli by means of transcription and proteomics, and found that there are two ways of action: one is to inhibit the activity of atpase and reduce the level of atp by destroying the membrane potential of bacterial cell membrane. the other is to inhibit ribosomal subunit binding to transport rna. it was found that although ros generation is the main reason for the bactericidal effect of most antibiotics and antibacterial nanomaterials, the antibacterial activity of aunps does not induce any related processes. zhang et al.[21] used polyethylene imine and bovine serum protein modified aunps and aunps rod as gene carriers, and found that the tip of rod-shape aunps had large curvature, resulting in higher charge density than spherical aunps. moreover, most of the rod-shape particles will contact the cell membrane through the tip, leading to higher gene transfection efficiency when using rod-shape particles as the gene carrier. due to its special form, rod-shape aunps have advantages in contacting with bacteria. in our experimental results, the bactericidal effect of rod-shape aunps is better than that of the other two forms of aunps, which may be due to this special contact mode. the surface charge of nanoparticles plays an obvious role in their antibacterial ability[22]. for example, angelique’s team[23] studied the effects of different particle diameters and zeta potential on the bactericidal activity of titanium dioxide nanoparticles, and found that titanium dioxide nanoparticles with about the same diameter showed stronger antibacterial effect when zeta potential was higher. this indicates that the enhancement of surface charge is also a way to enhance the bactericidal effect, and the negatively charged nanoparticles will have a certain repulsion effect on negatively charged bacteria[24,25]. we conducted zeta potential to verify the relationship between the bactericidal effect and charge density of different forms of aunps in this experi 8 ment. the zeta potential of rod-shape aunps was 56.8 mv, that of spherical aunps was 42.1 mv, and that of triangular aunps was 33.2 mv. as shown in figure 8, three forms of aunps really are positively charged, and rod-shape aunps are with higher charge density compared with other two forms of aunps. at the same time, our experimental results show that compared with other two forms, rod-shape aunps have better bactericidal effect, which further illustrates that aunps with positive charges on the surface will see an enhanced bactericidal effect with the increase of charge density. figure 8. zeta potentials of spherical aunps, rod-shape aunps and triangular aunps coated by ctab. 4. conclusion ctab-coated aunps of different forms (spherical, rod-shape, triangle) were prepared and s. aureus and e. coli were used as test strains. it can be seen in the study of antibacterial properties, no matter against s. aureus and e. coli, and the bactericidal effect of rod-shape aunps is higher than the other two forms of aunps. the surface of bacteria is with negative charges, and positively charged nanoparticles are attracted by bacteria with negative charge on the surface, contacting and destroying the cell membrane of bacteria to enter and kill bacteria. rod-shape aunps are easier to contact bacteria from spatial effects, which is why they have a higher bactericidal property. the three forms of aunps are demonstrated to have better bactericidal effect against s. aureus than that against e. coli, which may be due to the different cell walls of the two bacteria. all these results laid the foundation for further work. conflict of interest the authors declare that they have no conflict of interest. acknowledgements project of central university basic research business fund (gk201802012); shaanxi science and technology plan project (2017ny-121). references 1. dizaj sm, lotfipour f, barzegar-jalali m, 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s. the bacterial cell envelope. cold spring harbor perspectives in biology 2010; 2(5): a000414. 25. dickson js, koohmaraie m. cell surface charge characteristics and their relationship to bacterial attachment to meat surfaces. applied and environmental microbiology 1989; 55(4): 832–836. microsoft word can-5834 characterization and application of nanomaterials 2024, 7(1), 5834. https://doi.org/10.24294/can.v7i1.5834 1 review advancements in water splitting for sustainable energy generation: a review razu shahazi1, amirul islam saddam1, srabani majumdar1, md. rakibul islam1, mohammed muzibur rahman2,3, md. mahmud alam1,2,*, ajoy kumer4, giti paimard5 1 department of chemical engineering, z. h. sikder university of science and technology (zhsust), shariatpur 8024, bangladesh 2 center of excellence for advanced materials research (ceamr), king abdulaziz university, jeddah 21589, saudi arabia 3 chemistry department, faculty of science, king abdulaziz university, jeddah 21589, saudi arabia 4 department of chemistry, college of arts and sciences, iubat-international university of business agriculture and technology, dhaka 1230, bangladesh 5 laboratory of nanoscale biosensing and bioimaging (nbab), school of ophthalmology and optometry, school of biomedical engineering, state key laboratory of ophthalmology optometry, and vision science, wenzhou medical university, wenzhou 325027, china * corresponding author: md. mahmud alam, alam-mahmud@hotmail.com, mmalam@zhsust.ac.bd abstract: water splitting, the process of converting water into hydrogen and oxygen gases, has garnered significant attention as a promising avenue for sustainable energy production. one area of focus has been the development of efficient and cost-effective catalysts for water splitting. researchers have explored catalysts based on abundant and inexpensive materials such as nickel, iron, and cobalt, which have demonstrated improved performance and stability. these catalysts show promise for large-scale implementation and offer potential for reducing the reliance on expensive and scarce materials. another avenue of research involves photoelectrochemical (pec) cells, which utilize solar energy to drive the water-splitting reaction. scientists have been working on designing novel materials, including metal oxides and semiconductors, to enhance light absorption and charge separation properties. these advancements in pec technology aim to maximize the conversion of sunlight into chemical energy. inspired by natural photosynthesis, artificial photosynthesis approaches have also gained traction. by integrating light-absorbing materials, catalysts, and membranes, these systems aim to mimic the complex processes of natural photosynthesis and produce hydrogen fuel from water. the development of efficient and stable artificial photosynthesis systems holds promise for sustainable and clean energy production. tandem cells, which combine multiple light-absorbing materials with different bandgaps, have emerged as a strategy to enhance the efficiency of water-splitting systems. by capturing a broader range of the solar spectrum, tandem cells optimize light absorption and improve overall system performance. lastly, advancements in electrocatalysis have played a critical role in water splitting. researchers have focused on developing advanced electrocatalysts with high activity, selectivity, and stability for the oxygen evolution reaction (oer) and hydrogen evolution reaction (her). these electrocatalysts contribute to overall water-splitting efficiency and pave the way for practical implementation. keywords: water splitting; oxygen evolution reaction (oer); hydrogen evolution reaction (her); photoelectrochemical (pec) cells; scarce materials; catalyst 1. introduction in the quest for sustainable energy generation, the development of efficient and clean technologies is of paramount importance. among the various renewable energy sources, hydrogen has emerged as a promising candidate due to its high energy content and versatility. water splitting, a process that involves separating water into its constituent elements, hydrogen and oxygen, offers a viable pathway for the production citation shahazi r, saddam ai, majumdar s, et al. advancements in water splitting for sustainable energy generation: a review. characterization and application of nanomaterials. 2024; 7(1): 5834. https://doi.org/10.24294/can.v7i1.5834 article info received: 16 april 2024 accepted: 6 may 2024 available online: 31 may 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 5834. 2 of hydrogen as a clean fuel [1,2]. traditionally, water splitting has relied on electrolysis, a process that utilizes electricity to drive the reaction. however, electrolysis methods have faced challenges in terms of energy efficiency and costeffectiveness, limiting their large-scale implementation [3,4]. to overcome these barriers, researchers and scientists around the world have been working diligently to break new ground in water splitting technology. in recent years, significant advancements have been made in the field of water splitting, leading to the development of novel and efficient approaches. these breakthroughs have the potential to revolutionize the renewable energy landscape and pave the way for a sustainable future [5,6]. one of the key areas of focus in water splitting research has been the development of catalysts. catalysts play a crucial role in facilitating the water splitting reaction by reducing the energy requirements and increasing the reaction rates. traditional catalysts, such as platinum, are effective but expensive, hindering their widespread adoption. however, researchers have made remarkable progress in developing lowcost and earth-abundant catalysts, such as transition metal oxides and molecular catalysts, which exhibit excellent catalytic activity and stability [7–9]. another significant advancement in water splitting technology is the exploration of photoelectrochemical (pec) cells. pec cells utilize semiconductor materials to harness solar energy and drive the water splitting reaction. by combining light absorption and catalytic activity in a single device, pec cells offer a promising approach to achieve solar-driven water splitting. researchers have been actively investigating various semiconductor materials, such as metal oxides and perovskites, to enhance the efficiency and stability of pec cells [10–12]. furthermore, advancements in nanotechnology have opened up new avenues for improving water splitting efficiency. nanostructured materials provide a high surface area, improved charge transport, and enhanced light absorption, making them ideal candidates for water splitting applications. nanoparticles, nanowires, and nanotubes have demonstrated remarkable performance in catalyzing the water splitting reaction, offering unparalleled opportunities for efficient and cost-effective hydrogen production [13–15]. moreover, the integration of water splitting technologies with renewable energy sources, such as wind and solar, holds tremendous potential for sustainable energy generation. by utilizing excess electricity generated from renewable sources during off-peak hours, water splitting can store the energy in the form of hydrogen, which can be used later for power generation or as a clean fuel for transportation [16–18]. countries such as japan, the united states, germany, china, and south korea have been actively researching and developing water splitting technologies [19]. they have made notable advancements in terms of increasing efficiency, reducing costs, and developing new materials for electrocatalysts [20]. japan has a strong research community and has been actively collaborating with universities, research institutes, and industries to advance sunlight-driven water splitting technology [21]. institutions such as the university of tokyo, kyoto university, and the national institute of advanced industrial science and technology (aist) have been at the forefront of this research. japanese researchers have been working on the development of efficient and stable photoelectrochemical (pec) cells and photoelectrodes for water splitting. the characterization and application of nanomaterials 2024, 7(1), 5834. 3 united states has a vibrant research community dedicated to advancing water splitting technology. many universities, national labs, and private research institutions have been conducting research to improve the efficiency, durability, and cost-effectiveness of water splitting systems [22]. electrolysis, particularly proton exchange membrane (pem) electrolysis and solid oxide electrolysis cells (soec), has been an area of focus in the usa. besides this, researchers have been working on developing efficient and stable photoelectrodes, exploring new materials, and improving light absorption and charge separation processes. in addition, germany, china, and south korea have been actively researching and developing water splitting technologies [23,24]. in a short, advancements in water splitting technology are breaking the barriers that have hindered its widespread implementation for sustainable energy generation. the development of efficient catalysts, exploration of photoelectrochemical cells, utilization of nanostructured materials, and integration with renewable energy sources are propelling the field forward. these advancements offer a promising pathway towards a clean and sustainable future, where hydrogen can play a vital role in meeting our energy needs while minimizing environmental impact. 2. development of efficient and cost-effective catalysts for water splitting water splitting is a promising technology for producing clean and renewable hydrogen fuel. it involves the separation of water into hydrogen and oxygen gases through electrochemical reactions. the process typically requires the use of catalysts to enhance the reaction rates and efficiency. over the years, researchers have been working on developing efficient and cost-effective catalysts for water splitting. 2.1. platinum group metals (pgms) pgms, particularly platinum and iridium, have traditionally been used as catalysts for water splitting. however, their high cost and limited availability hinder large-scale applications. researchers are exploring ways to reduce or replace the use of pgms with more abundant and cost-effective materials [25–27]. 2.2. earth-abundant catalysts efforts have been focused on developing catalysts based on earth-abundant elements, such as transition metal oxides, sulfides, phosphides, and nitrides. these materials offer the advantages of low cost and scalability. for example, metal oxides like iron oxide (fe2o3) and cobalt oxide (co3o4) have shown promising catalytic activity [28–30]. an illustration of catalysis by earth-abundant materials is shown in figure 1. figure 1. water splitting with earth-abundant elements. characterization and application of nanomaterials 2024, 7(1), 5834. 4 2.3. bimetallic and alloy catalysts combining different metals into bimetallic or alloy catalysts can enhance their catalytic properties. for instance, combining nickel (ni) with iron (fe) or cobalt (co) has shown improved activity for water splitting. these catalysts can be synthesized using various methods, including electrochemical deposition, sol-gel techniques, and physical mixing [31–33]. 2.4. molecular catalysts researchers are also exploring molecular catalysts, especially based on abundant and inexpensive organic compounds. these catalysts typically contain metal complexes with ligands that facilitate the water splitting reactions. a molecular catalytic reaction is demonstrated in figure 2. molecular catalysts offer precise control over the catalytic properties and can be designed to optimize efficiency [34– 36]. figure 2. schematic diagram of homogeneous catalysis with soluble molecular catalyst. 2.5. nanostructured catalysts nanostructured catalysts, such as nanoparticles, nanowires, and nanotubes, have attracted attention due to their high surface area and unique electronic properties. these structures can enhance catalytic activity by providing more active sites and improving charge transport. examples include metal nanoparticles supported on conductive substrates or semiconductor nanomaterials [37–40]. several nanoparticles and nanowires are shown in figure 3. figure 3. an illustration of nanoparticles and nanowire. characterization and application of nanomaterials 2024, 7(1), 5834. 5 2.6. computational design advances in computational modeling and machine learning have enabled the rational design of catalysts with enhanced activity. by simulating the electronic structure and reaction kinetics, researchers can identify promising catalyst candidates for experimental validation, accelerating the discovery process [41–43]. 3. solar energy to drive the water-splitting reaction utilizing solar energy to drive the water-splitting reaction is a promising approach for sustainable hydrogen production. it involves harnessing the energy from sunlight and converting it into chemical energy stored in the form of hydrogen gas. there are two common methods for using solar energy in water splitting: 3.1. photovoltaic (pv) electrolysis this method involves using photovoltaic cells, commonly known as solar cells, to directly convert solar energy into electricity. the generated electricity is then used to power an electrolyzer, which splits water into hydrogen and oxygen gases. the electrolyzer consists of two electrodes (cathode and anode) immersed in an electrolyte solution. when an electric current is applied, water molecules at the cathode are reduced to produce hydrogen gas (h2), while water molecules at the anode are oxidized to produce oxygen gas (o2). catalysts are employed at the electrodes to enhance the reaction rates and improve overall efficiency [44–46]. 3.2. photoelectrochemical (pec) water splitting pec water splitting combines the principles of solar cells and electrolysis into a single device. a photoelectrochemical cell is used, which typically consists of a semiconductor electrode immersed in an electrolyte solution [47]. a schematic diagram of photoelectrochemical water splitting is depicted in figure 4. the semiconductor electrode absorbs photons from sunlight, generating electron-hole pairs. the excited electrons participate in the reduction reaction (hydrogen evolution), while the holes contribute to the oxidation reaction (oxygen evolution) [48–51]. catalysts are essential in pec cells to facilitate the reaction kinetics and improve efficiency. both pv electrolysis and pec water splitting have their advantages and challenges: figure 4. schematic diagram of photoelectrochemical water splitting. characterization and application of nanomaterials 2024, 7(1), 5834. 6 3.2.1. advantages • utilization of abundant and renewable solar energy. • production of clean and sustainable hydrogen fuel. • compatibility with existing infrastructure for hydrogen storage and utilization. • potential for decentralized hydrogen production. 3.2.2. challenges • efficiency: maximizing the efficiency of solar energy conversion and the watersplitting reaction to maximize hydrogen production. • catalysts: developing efficient and stable catalysts that can enhance the reaction rates and reduce energy losses. • materials: exploring and optimizing semiconductor materials with desirable properties for efficient solar energy absorption and charge separation. • durability: ensuring the long-term stability and durability of the materials and catalysts under harsh operating conditions. • cost: reducing the cost of materials, catalysts, and system components to enable widespread adoption. ongoing research and development efforts are focused on improving the efficiency, stability, and cost-effectiveness of solar-driven water-splitting technologies. by addressing these challenges, solar energy can be harnessed to drive the water-splitting reaction, enabling the production of clean and sustainable hydrogen fuel. 4. natural photosynthesis to hydrogen fuel by integrating light-absorbing materials, catalysts, and membranes, artificial photosynthetic systems aim to mimic the complex processes of natural photosynthesis and produce hydrogen fuel from water. these systems, often referred to as artificial photosynthesis or artificial leaf systems, seek to harness solar energy and use it to drive the water-splitting reaction, generating hydrogen gas (h2) as a clean and renewable fuel. here’s a breakdown of the key components: 4.1. light-absorbing materials light-absorbing materials, such as semiconductors or molecular dyes, capture sunlight and convert it into usable energy. these materials should have a broad absorption spectrum, efficient light harvesting, and good charge separation properties to generate the necessary energetic electrons [52–54]. 4.2. catalysts catalysts facilitate the water-splitting reaction by reducing the energy barriers and increasing the reaction rates. they are typically used at the cathode (hydrogenevolving reaction, her) and anode (oxygen-evolving reaction, oer) to promote the respective electrochemical reactions. catalysts can be based on various materials, including earth-abundant metals, metal oxides, molecular complexes, or even biological enzymes [55–57]. characterization and application of nanomaterials 2024, 7(1), 5834. 7 4.3. membranes membranes are employed to separate the her and oer compartments, preventing the mixing of hydrogen and oxygen gases and enhancing the overall system efficiency. proton-exchange membranes (pems) or other selective ion-conductive membranes are used to enable the transport of protons while blocking the crossover of gases [58–60]. 4.4. electron transfer pathways efficient pathways for electron transfer are essential to transport the generated electrons from the light-absorbing materials to the catalytic sites. electron-conductive materials or structures, such as conductive electrodes or nanowires, are used to facilitate the movement of electrons to the respective electrodes [61–63]. by integrating these components, artificial photosynthetic systems emulate the fundamental processes of natural photosynthesis, where plants and algae convert sunlight, water, and carbon dioxide into chemical energy in the form of carbohydrates. in the case of artificial photosynthesis for hydrogen production, the focus is on generating hydrogen fuel from water using sunlight as the primary energy source. these systems hold promise for sustainable and carbon-neutral energy production, but there are still challenges to overcome, such as improving the efficiency, stability, and scalability of the components, as well as reducing costs. extensive research and development efforts are ongoing to advance the field of artificial photosynthesis and enable its practical implementation as a viable technology for hydrogen production and energy storage. 5. tandem cells to enhance the efficiency of water-splitting systems tandem cells have emerged as a strategy to enhance the efficiency of watersplitting systems in artificial photosynthesis. tandem cells are multi-junction devices that combine multiple light-absorbing materials with different bandgaps in a stacked configuration [64–66]. this configuration allows for the efficient capture of a broader range of the solar spectrum, thereby increasing the overall energy conversion efficiency. here’s a closer look at how tandem cells work: 5.1. bandgap combinations different semiconductor materials have different bandgaps, which determine the range of light wavelengths they can efficiently absorb. in tandem cells, materials with varying bandgaps are carefully selected and arranged in a series to create a cascade of absorption layers. the bandgap of each layer is tailored to match the energy level of a specific portion of the solar spectrum, enabling efficient utilization of a wider range of photons [67,68]. 5.2. efficient light harvesting as sunlight passes through the tandem cell, each layer absorbs a specific portion of the solar spectrum. the absorbed photons generate electron-hole pairs (excitons) in the respective layers, leading to the production of electrical current [69,70]. the light harvesting technique is demonstrated in figure 5. characterization and application of nanomaterials 2024, 7(1), 5834. 8 figure 5. light harvesting technique. 5.3. charge separation and collection the excited electrons and holes generated in each layer are rapidly separated due to the different bandgaps and internal electric fields. efficient charge collection mechanisms are employed to extract the electrons and holes from each layer and direct them to their respective contacts or electrodes. 5.4. water-splitting reactions the separated electrons and holes can be utilized for the water-splitting reaction. the excited electrons are directed to the cathode, where they participate in the reduction reaction (hydrogen evolution) by converting protons (h+) from water into hydrogen gas (h2). the holes are directed to the anode, where they participate in the oxidation reaction (oxygen evolution) by oxidizing water molecules (h2o) to produce oxygen gas (o2). by combining materials with different bandgaps in tandem cells, a larger portion of the solar spectrum can be effectively harvested, leading to improved light-tohydrogen conversion efficiency. this approach allows for better utilization of solar energy and has the potential to achieve higher efficiencies compared to single-junction devices. tandem cells are an active area of research, and scientists are exploring various material combinations, device architectures, and fabrication techniques to optimize their performance. the development of efficient and stable tandem cells is crucial for advancing the field of artificial photosynthesis and enabling more efficient solar-driven water-splitting systems for sustainable hydrogen production. 6. development and optimization of oer and her the development and optimization of the oxygen evolution reaction (oer) and hydrogen evolution reaction (her) electrocatalysts are crucial for advancing various energy conversion and storage technologies. here are some key aspects involved in the development and optimization of oer and her processes: 6.1. catalyst screening and design initial stages involve screening and evaluation of various catalyst materials to characterization and application of nanomaterials 2024, 7(1), 5834. 9 identify candidates with high activity for oer and her. the catalyst design considers factors such as electronic structure, surface area, crystal structure, and surface chemistry to enhance catalytic activity and stability. computational modeling and high-throughput screening techniques are often employed to accelerate catalyst discovery [71,72]. 6.2. nano-structuring and surface modifications nano-structuring techniques, such as nanoparticle synthesis, thin-film deposition, or nanowire fabrication, are employed to increase the surface area and expose more active sites. surface modifications, such as doping, alloying, or surface functionalization, can tailor the catalyst’s electronic properties and surface reactivity, leading to improved performance [73–75]. surface functionalization of catalysts is illustrated in figure 6. figure 6. surface functionalization of catalyst. 6.3. interface engineering the catalyst-support interface plays a crucial role in the overall catalytic activity and stability. interface engineering techniques, such as optimizing the catalyst-support interaction, introducing interlayers, or using conductive substrates, can enhance electron transfer kinetics and catalytic performance [76–78]. 6.4. co-catalysts and synergy effects co-catalysts, such as metal nanoparticles, metal oxides, or molecular complexes, can be combined with the primary catalyst to enhance catalytic performance. synergistic effects between different catalyst components can promote electron transfer, modify reaction kinetics, and improve overall efficiency [79,80]. 6.5. ion and mass transport efficient ion and mass transport within the electrochemical system is crucial for optimizing oer and her. strategies to enhance mass transport include designing porous electrode structures, optimizing electrolyte composition, and improving gas diffusion pathways [81,82]. 6.6. stability and durability long-term stability and durability of oer and her catalysts are essential for practical applications. researchers focus on understanding degradation mechanisms, developing strategies to mitigate catalyst degradation (e.g., corrosion resistance), and exploring protective coatings or encapsulation techniques [83,84]. characterization and application of nanomaterials 2024, 7(1), 5834. 10 6.7. advanced characterization techniques advanced characterization techniques, such as scanning electron microscopy (sem), transmission electron microscopy (tem), x-ray photoelectron spectroscopy (xps), and in-situ spectroscopy, provide insights into catalyst structures, active sites, and reaction mechanisms. these techniques help in understanding the structureactivity relationships and guide catalyst optimization efforts. the development and optimization of oer and her catalysts involve a multidisciplinary approach, combining materials science, surface chemistry, electrochemistry, and computational modeling. continued research efforts aim to enhance catalytic activity, selectivity, stability, and cost-effectiveness to enable efficient and sustainable energy conversion and storage systems. 7. catalyst for oer and her researchers have indeed focused on developing advanced electrocatalysts with high activity, selectivity, and stability for the oxygen evolution reaction (oer) and hydrogen evolution reaction (her). these electrocatalysts play a critical role in facilitating efficient and sustainable water splitting, which is essential for various applications, including artificial photosynthesis and renewable energy storage. here’s an overview of the advancements in electrocatalyst development for the oer and her: 7.1. oxygen evolution reaction (oer) 7.1.1. metal oxides and mixed metal oxides metal oxides, such as ruthenium oxide (ruo2), iridium oxide (iro2), and manganese oxide (mnox), have shown excellent catalytic activity for the oer. researchers have been exploring the synthesis of nanostructured and well-defined metal oxide catalysts to enhance their surface area and expose more active sites. mixed metal oxides, combining different elements, can exhibit improved oer activity and stability compared to single-metal oxides [85–87] (table 1). table 1. comparison of oxygen evolution reaction (oer) performance with various transition metal oxide and hydroxide [88]. materials ph overpotential for 10 ma cm−2/v tafel slope/mv decade−1 mnco-g 14 0.33 48 ruo2 14 0.3 42 ni5mn-ldh-mwcnt 14 0.35 (ir-corrected) 83 co5mn-ldh-mwcnt 14 0.3 (ir-corrected) 74 coni-ldh/fe-pp-m 14 0.32 53 cuco2o4/n-rgo 14 0.36 64 co3s4@mos2 14 0.33 59 comoo4 14 0.31 56 cop 14 0.36 66 cofe ldh 13 0.36 49 nife ldh 14 0.33 41 characterization and application of nanomaterials 2024, 7(1), 5834. 11 7.1.2. perovskite oxides perovskite oxides, with a general formula of abo3, have garnered significant attention for oer electrocatalysis. materials such as strontium titanate (srtio3), strontium iridate (sriro3), and barium strontium cobalt iron oxide (bscf) have demonstrated promising oer activity. doping, surface modification, and nano structuring techniques are employed to optimize the performance of perovskite oxides [89–92]. 7.1.3. earth-abundant talysts to overcome the cost and scarcity associated with noble metals, researchers are actively exploring earth-abundant catalysts for the oer. materials like cobalt-based compounds (e.g., co3o4), nickel-iron-based compounds (e.g., nife layered double hydroxides), and metal phosphides (e.g., nickel phosphide, cobalt phosphide) have shown promising oer activity [93,94]. 7.2. hydrogen evolution reaction (her) 7.2.1. platinum group metals (pgms) pgms, particularly platinum (pt) and palladium (pd), are highly efficient her catalysts due to their excellent activity and stability. researchers are working on developing advanced ptand pd-based catalysts with enhanced activity through alloying, nano structuring, and developing hybrid materials. 7.2.2. earth-abundant catalysts to address the cost and sustainability issues associated with pgms, researchers are actively exploring earth-abundant alternatives for her. materials such as transition metal sulfides (e.g., molybdenum sulfide, nickel-molybdenum sulfide) and metal phosphides (e.g., nickel phosphide, cobalt phosphide) have shown promising her activity [93,94]. several earth-abundant catalysts and their properties are shown in table 2. table 2. examples of earth-abundant her electrocatalysts. catalyst material η at −10macm−2 (mv) tafel slope (mv per decade) ph faradaic yield nimo 200 (100 macm−2) 122 14.8 na como 170 (100 macm−2) 92 14.8 na nimo 185 (100 macm−2) 112 14.8 na nimo 70 (20 macm−2) na 14.3 na nimo 34 (20 macm−2) na 14 na mos2 260 50 0 na pt 50 140–150 13 na ni 58 81.6 14 na mo 65 76 14 na mos2 200 (15 macm−2) 40 −0.3 100%* mos2 ~150 41 0 na mos2 170 60 0.2 na cos2 145 51 0 na characterization and application of nanomaterials 2024, 7(1), 5834. 12 table 2. (continued). catalyst material η at −10 macm−2(mv) tafel slope (mv per decade) ph faradaic yield cos2 ~175 93 7 100% comosx 250 85 7 −100% ws2 ~250 60 0 na cose2 90 39 0 na mos1.0sel.0 ~200 56 0 100%* nise2 ~140 49 0 na ni2p 130 (20 macm−2) 46 0 100%* cop 85 (20 macm−2) 50 0 100%* fep 55 38 0 100% mop 64 na 0 100% conx 170 75 14 na conx 140 30 0 na nimonx 225 (5 macm−2) 35.9 1 na α-mob ~225(20 macm−2) 55 −0.3 100% mo2c 130 53 0 na moc 124 43 0 na moc 77 50 14 na ni/c 34 41 0 100%* cu95ti5 60 110 13 na 7.2.3. molecular catalysts molecular catalysts, typically based on metal complexes or metalloporphyrins, offer precise control over the active sites and electronic properties. researchers are designing and synthesizing molecular catalysts with tailored structures to optimize her activity, selectivity, and stability. the development of advanced electrocatalysts with high activity, selectivity, and stability is crucial for improving the overall efficiency and commercial viability of water-splitting technologies. researchers continue to explore new materials, catalyst designs, and strategies to enhance the performance of electrocatalysts for the oer and her, aiming to enable efficient and sustainable hydrogen production. 8. conclusion in conclusion, significant progress has been made in the development and optimization of catalysts and technologies for water splitting, which has advanced the production of sustainable energy. catalysts based on abundant and inexpensive materials, such as nickel, iron, and cobalt, have shown improved performance and stability, reducing the need for costly materials. photoelectrochemical (pec) cells, which utilize novel materials like metal oxides and semiconductors, aim to maximize the conversion of solar energy into chemical energy for water splitting. artificial photosynthesis approaches, inspired by natural photosynthesis, integrate lightabsorbing materials, catalysts, and membranes to produce hydrogen fuel from water, offering a potential solution for clean energy production. tandem cells, which characterization and application of nanomaterials 2024, 7(1), 5834. 13 combine multiple light-absorbing materials, optimize light absorption and enhance system efficiency. furthermore, advancements in electrocatalysis have led to the development of advanced electrocatalysts with high activity, selectivity, and stability for the oxygen evolution reaction (oer) and hydrogen evolution reaction (her). these advancements collectively pave the way for the practical implementation of water splitting in various energy conversion and storage systems, bringing us closer to a sustainable and clean energy future. conflict of interest: the authors declare no conflict of interest. references 1. hota p, das a, maiti dk. a short review on generation of green fuel hydrogen through water splitting. international journal of hydrogen energy. 2023; 48(2): 523-541. doi: 10.1016/j.ijhydene.2022.09.264 2. mohsin m, ishaq t, bhatti ia, et al. 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characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1334 review article review of super-hydrophobic materials research chengbao liu1,2*, minjia li1, xiaojie liu1,2, zhigang chen1,2 1 school of chemistry, biology and materials engineering, suzhou university of science and technology, suzhou 215009, jiangsu province, china. e-mail: lcb@mail.usts.edu.cn 2 jiangsu key laboratory for environmental functional materials, suzhou 215009, jiangsu province, china abstract we reviewed the research on super-hydrophobic materials. firstly, we introduced the basic principles of super-hydrophobic materials, including the young equation, wenzel model, and cassie model. then, we summarized the main preparation methods and research results of super-hydrophobic materials, such as the template method, soft etching method, electrospinning method, and sol-gel method. among them, the electrospinning method that has developed in recent years is a new technology for preparing micro/nanofibers. finally, the applications of super-hydrophobic materials in the field of coatings, fabric and filter material, anti-fogging, and antibacterial were introduced, and the problems existing in the preparation of super-hydrophobic materials were pointed out, such as unavailable industrialized production, high cost, and poor durability of the materials. therefore, it is necessary to make a further study on the application of the materials in the selection, preparation, and post-treatment. keywords: super-hydrophobic materials; basic principles; preparation method; application article info received: 22 june 2021 accepted: 14 august 2021 available online: 21 august 2021 copyright copyright © 2021 chengbao liu, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction super-hydrophobic material refers to a material with a contact angle of the material surface and water greater than 150° and a rolling angle less than 10°[1,2]. in nature, many plant foliage and waterfowl feathers have super-hydrophobic water characteristics, such as dragonfly wing[3], water strider leg[4], lotus leaf[5], etc. (figure 1), among which the most typical is the “lotus leaf effect”. the surfaces of these moving, plants contain special geometry with contact angles with water above 150°. in the lotus leaf[6–8], the lotus leaf surface (figure 2) is composed of many papillae with an average diameter of 5 to 9 m, and the contact and rolling angles of water on that surface are (161.0 ± 2.7)° and 2°, respectively[6–8]. each papilla is composed of a nanostructured branching with an average diameter of (124.3 ± 3.2) nm. these nanostructures on micromastoid especially, play an important role in super-hydrophobicity. figure 1. dragonfly wings (a), water strider legs (b), lotus leaf (c). 72 through the research, people do not only find many super-hydrophobic phenomena in nature and their surface structures but also make artificial synthetic super-hydrophobic surfaces by various methods. at present, there are two ways to prepare super-hydrophobic surfaces[9]: (1) modification of low surface energy material on a surface with micro-nano rough structure; and (2) construction of a micro-nano rough structure on the surface of the material with low surface energy. in recent years, the preparation of super-hydrophobic surface materials with biological tissues and structures as bionic objects has become one of the hotspots in the field of material research. jiang lei research group is the first research group involved in this field in china. their main preparation methods are the template method, soft etching method, electrospinning method, and at present, its research focus is ultra-super-hydrophobic materials, namely ultra-hydrophobic ultra-hydrophobic oil. it will introduce the super-hydrophobic materials from the basic principles of super-hydrophobic water, its preparation method and its application. 2. the rationale of super-hydrophobic water the wettability of the solid surface is mainly determined by the chemical composition of the solid surface and surface microstructure. the wettability of the solid liquid, that is, hydrophilic and hydrophobicity is generally expressed by the contact angle θ of the liquid and solid phase. the shape formed when the droplet stays on a smooth solid surface by the droplet on its surface is determined by the interface tension of the three-phase contact surface of the solid, liquid and gas, whose contact angle can be described by the young equation[10]: cosθ = (γsa – γsl)/γla (1) γsa, γsl and γla represent the interface tension of solid-gas, solid-liquid and liquid-gas individually. at this time, the three surface tension interactions are at equilibrium. but the young equation is an idealized model suitable only for ideally smooth solid surfaces. if it is a solid surface with a certain roughness, there are some d-value between the apparent and intrinsic contact angles. the actual contact area of solid and liquid is more than the apparent contact area. the droplets fully enter the empty groove of the rough surface structure. therefore, it must consider the impact of roughness on the hydrophobic performance. at present, wenzel model[11] and cassie model[12] are figure 2. microstructure of the surface of the lotus leaf. 73 relatively mature in the related basic theoretical research. the schematic diagram shows in figure 3. 2.1 wenzel model the wenzel model considers that the droplets contact with the solid surface, and infiltrate into the surface groove. it increases the surface contact area, and the apparent geometrically observed contact area is less than the actual solid-liquid contact area when the apparent contact angle is greater than the intrinsic contact angle: cosθw =r(γsa – γsl)/γla = rcosθ (2) in the formula, r is the surface roughness factor, the ratio of the actual surface area to the projected area, and θw is the apparent contact angle of the rough surface. from equation (2), increasing the value of the surface rough factor r can make the original hydrophobic surface more hydrophobic. however, the wenzel model also has its limitations, which do not apply in the case of solid surfaces composed of different types of chemicals. 2.2 cassie model the cassie model suggests that water droplets are suspended on solid surface convex grooves and that liquid droplets fall on a composite phase composed of solid-liquid and solid-gas interfaces. therefore, its equation is: cosθ′ = f1cosθ1 + f2cosθ2 (3) θ′ is the apparent contact angle in the cassie model, f1 and f2 are the ratio of liquid contact to the solid surface and air, respectively, and 1 and 2 are the contact angles of liquid to solid surface and air, respectively. where f1 + f2 = 1, 2 = 180°, the formula (3) can be written as: cosθ′ = f1cosθ1 – f2 = f1cosθ1 + f1–1 (4) from the above model, preparing a surface with a special structure can improve the contact angle of the surface. the cassie model suggests that droplets are suspended on solid surface convex grooves and do not seep into the surface topography. in the cassie model, droplets are usually scrollable on the surface. the wenzel and cassie models provide a strong theoretical basis for the preparation of super-hydrophobic surfaces, and although they are currently under some controversy[14,15]. moreover, the contact angles in the above three cases characterize the performance of water droplets on the horizontal surface and are more oblique in reality. the state of the droplet on the slope can be characterized by the rolling angle, the critical surface tilt angle of the drop when the droplet begins to roll on the solid surface. the smaller tilt angle if the droplet begins to roll indicates that the super-hydrophobic water on this surface is better[16]. in conclusion, the contact and rolling angles jointly characterize the mutual permeability of the solid-liquid and the hydrophilic-hydrophobicity exhibited. the larger contact angle and the smaller rolling angle indicate the stronger hydrophobicity of the material surface[17–19]. 3. preparation method of super-hydrophobic materials figure 3. schematic diagram of the wenzel and cassie models[13]. 74 3.1 template method the template method takes a substrate with a cavity structure as a template, and covers the casting film liquid on the template by dumping, casting and spin coating. the proposed method has the advantages of simplicity, effectiveness and large area replication, and has good application prospects in practice. zheng jianyong et al. used calcium carbonate particles to form a polymer super-hydrophobic surface by thermal pressure and acid etching[20]. after the test, its droplet static contact angle reached 152.7° while its rolling angle was < 3°. liu et al. coated a pdms film with candle soot as a template, and calcination removed the template to form super-hydrophobic fiberglass cotton with a rough fiber mesh surface on the glass substrate[21]. after detection, the material has a contact angle with the water of up to 163° and can be used to optimize oil-water separation and air filtration, showing excellent thermal stability. ke et al. took taro leaves as the parent plate, constructed the surface structure with subtle cavity by template method, and then modified by an impregnated coating method, which significantly improved the hydrophobic performance[22]. 3.2 etching method etching technology refers to the process of etching the target surface into a micro rough appearance by physical or chemical methods. laser etching, plasma, chemical and, photo etching are several commonly used micro etching methods. the etching method can make more accurate operation and design of the surface structure to regulate surface hydrophobicity. while the cost is high, and it is not suitable for large-scale production. qi et al.[23] used the chemical etching method assisted by metal ions (e. g., ag+, cu2+, cr3+) to process zinc substrate to get rough structure surface, and the water contact angle measured by fluoro silane modification is up to (161 ± 2)°. in addition, they explored the effects of different metal ions on the surface morphology and hydrophobic properties, and then they found that the addition of metal ions could enhance the strength and stability of the super-hydrophobic surface. sung-woon et al.[24] took sf6 as a plasma source, obtained with the plasma etching method, and then c4f8 as a plasma source, and then a carbon-fluorine membrane was deposited on the silicon surface with a micron-grade rod structure. after testing, the contact angle with water is 165°. 3.3 phase separation method the phase separation method is the membrane form in which the system produces two or multiple phases during the control conditions. this method is easy to regulate and simple to operate. it can prepare uniform and large areas of superhydrophobic films, which has great value in practical aspects. liu et al.[25] put butyl methacrylate (bma) and glycol dimethyl acrylic (edma) in a mixture of 1, 4-cis-butanediol (bdo) with n-methyl-pyrrolidone (nmp) to in situ polymerization. a super-hydrophobic porous polymer surface with a micro-nano rough structure with a water contact angle of 159.5° and a rolling angle below 3.1°. liu jianfeng et al.[26] used butyl methyl acrylate (bma) and ethylene glycol dimethyl acrylate (edma) as monomers and azo diisonitrile (aibn) as an initiator for thermal polymerization on the glass substrate, thus forming a micro/nanocomposite roughness structure on the surface with a static water contact angle of up to 159.5°. 3.4 chemical vaporous deposition chemical vapor deposition is a simple, efficient, inexpensive, and effective method, which prepares rough structures without the limitation of substrate shape. deng tao et al. prepared aligned dense nanowire structures on silicon wafers by chemical vapor deposition[27]. they placed washed silicon wafers in inductively coupled plasma bins, deposited silicon nanowires while etching, and then modified them with fluoro silane to create a silicon nanowire surface structure with a line width of about 100 nm. 75 3.5 electrospinning method electrospinning is a new technology to prepare micro/nanoscale fibers. it places a polymer solution or melt in a high-pressure electrostatic field, and is stretched under the electric field coulomb force to form a jet fine flow that falls on the substrate to form a micro/nanofiber membrane. jiang lei et al.[28] used electrospinning technology to build a rough surface and then used cheap low surface-energy silicon oil during calcination to prepare tio2 super-hydrophobic surfaces with a contact angle greater than 150° and a rolling angle less than 5°. huang et al.[29] constructed a coating with sio2 nanoparticles and silicic acid solution. they adjusted the roughness of the coating by changing the ratio of sio2 nanoparticles and silica acid. the coating was modified by perfluorooctyl trichlorosilane with a water contact angle of 160°, less than 10°. it also has high light transmittance, excellent thermal stability and mechanical stability. however, when the organic modifier of the coating surface contacts water for a long time, the turnover of its hydrophilic group results in poor hydrophobic stability, increasing the uncertainty in its practical application. li fang et al.[30] used polyvinylidene difluoride (pvdf) and n, n-dimethylformamide (dmf) as the test materials, and prepared the ultra hydrophobic material with hollow microsphere structure by electrospinning. and the ultra hydrophobic material has super lipophilic properties. the contact angle between the material and the water was 153.5°. 3.6 layer upon layer assembly method layer assembly technology refers to the technology of membrane layer by layer deposition under the action of electrostatic action, hydrogen bonding, and coordination bonding. zhang qunbing, wang jun et al. of ningbo university used layer by layer assembly method to prepare the superhydrophobic surface of sea urchin tio2 with silicon sheet as the substrate[31]. the contact angle of the surface was 151.2° and a rolling angle of 4.5°. shang et al.[32] used polypropylene dimethyl ammonium chloride (pdda) and poly4-styrene sodium sulfonate (pss) as the polyelectrolyte, and then dipped the glass in the polyelectrolyte solution. then dipped it in polystyrene modified sio2 particle suspension. finally, a high transparent superhydrophobic porous sio2 glass coating made from perfluoroctane by chemical gas deposition, measuring water contact angle greater than 150° and a rolling angle of less than 10°. 3.7 sol-gel method the sol-gel method is a preparation method for condensing the solvent obtained after hydrolysis of high chemical activity compounds and drying the resulting gel to form a micro/nanopore structure to make it superhydrophobicity, but there are disadvantages such as long preparation process route, poor surface structure control, and solvent contamination. sanjay et al.[33]. prepared a methyl triethoxysilane (mtes) and porous silicon membrane into superhydrophobic surfaces with contact angles up to 160° on a glass substrate by solvent-gel method it is shown that the superhydrophobic films prepared by this method are transparent, adherent, good thermal stability and moisture resistant. wei et al.[34] used potassium titanate and teos as precursors and used a solvent-gel method to prepare a perfect titanium-silicon mesh composite aerosol structure, and the water contact angle of aerogel samples obtained after trimethylchlorosilane modification reached (145 ± 5)°. after zheng yansheng et al.[35] hybridized tfe with a sio2 solvent modified by epoxy propoxy propyl trimethoxysilane, the glass was coated with a hyper-hydrophobic coating with a contact angle of up to 156°. 3.8 electrochemical deposition method su et al.[36] deposit a layer of nickel on the copper substrate, and then fluoro silane modification yields a superhydrophobic surface with a contact angle of 162°. the material is capable of maintaining superhydrophobic by moving 1 m on silicon carbide (sic) sandpaper for 800 at a load pressure of 4.8 kpa, indicating that the surface has excellent micro 76 hardness and mechanical wear resistance. ding, et al. used electrochemical method, and deposited a layer of micro/nanostructure copper oxide (cu2o) membrane on the conductive glass (ito) surface. it has a water contact angle up to about 170°, achieving a superhydrophobic effect. meanwhile, it could obtain the cu2o films of different micromorphology by regulating electrodeposition time. xu et al.[38] electrochemical deposition of tridecafluoroctyl triethoxysilane (pots) on a films of poly pyrene and sio2 prepared a superhydrophobic complex coating of petal micronano layered structures highly transparent, thermal and mechanical stability with a static water contact angle up to (163 ± 1)° and a rolling angle below 2° hyper hydrophobic zno films were prepared on an aluminum alloy substrate after huang et al.[39] functionally tionalized nanozno to 0. 01 mol·l–1 stearate ethanol solution, a mixture of isopropanol and butanol. it found that the roughness of the surface and the water contact angle of the surface gradually increased with the deposition temperature, and the film obtained at 50 ℃ had excellent superhydrophobic properties, with a water contact angle reaching (1553)°. 3.9 solution immersion method li et al.[40] first impregnated the aluminum alloy plate in lanthanum nitrate aqueous solution for heat treatment to form a nano structure similar to ginkgo biloba leaves on the surface, and then modified the super hydrophilic aluminum alloy surface with dodecafluoroheptyl propyl trimethoxysilane. the water contact angle reached 160°, and the superhydrophobic surface had a relatively good surface strong thermal stability, corrosion resistance, wear resistance and other advantages. yao jiannian et al.[41] prepared superhydrophobic materials by solution soaking. after first soaking the smooth copper sheet in a specific [ag(nh3)2]oh solution for 6 h, a structure similar to the rose petals could appear on the surface of the copper sheet, and its contact angle reached 156°. 3.10 other methods yang and et al.[43]were prepared by microemulsion, then heated on a glass plate to form porous rough structural films during the volatile process, and then modified with xinji trimethoxysilane to make honeycomb-like superhydrophobic films with a contact angle of 156.3°, which is simple, fast and economical[42]. furthermore, inspired by the microstructure of plant leaf surfaces, researchers like liu et al. prepared superhydrophobic surfaces with a high contact angle of around 170° and a rolling angle of about 6° on an aluminum alloy by a one-step anodized method. 4. application of hytra hydrophobic materials hyper hydrophobic materials have self-cleaning, pollution resistance and other characteristics, therefore, superhydrophobic materials can be developed and applied, so that they have broad prospects in the fields of aerospace and military industry, agriculture, pipeline nondestructive transportation, housing construction, as well as the equipment working in various open-air environments. 4.1 application of superhydrophobic materials in fabric and filter materials various micronanostructural fibers with superhydrophobic water are produced by electrophospinning or treatment of the material surface to obtain anti-polluting superhydrophobic fabrics. such materials can be used to make waterproof film, hydrophobic filter film, etc., or make the fabric have new functions such as hydrowaterproof, pollution prevention and dust prevention due to hydrophobic properties. for example, xue et al. creates a friction-resistant superhydrophobic fiber fabric coating with sodium hydroxide etched polyethylene terephthalate (pet) fiber fabric[44]. 4.2 application of superhydrophobic materials in building coatings due to their unique hydrophobic properties, superhydrophobic materials have wide application prospects in water resistance, snow prevention and pollution resistance. at present, the ultra-hydropho77 bic surface materials in building pollution prevention materials are mainly coating and protective fluid, for example, ji haiyan, chen gang et al.[45] using etching glass also prepared ultra-hydrophobic glass surface. yang et al.[46] developed a modified dodecthiol zno/pdms complex with a water contact angle of 159.5° and 8.3° and excellent ice resistance at –10 and –5 ℃, showing great potential for application. 4.3 application of superhydrophobic materials in fog prevention and self-cleaning liquidation of water vapor in the air forms water mist covering the surface of transparent materials such as glass can cause reduced visibility of these materials[47]. some bionic ultra-hydrophobic surface effectively reduce the condensation of water vapor, to achieve a certain anti-fog, self-cleaning effect. after alternating self-assembly of raspberry polystyrene and sio2 particles on slides, a highly transparent porous sio2 coating was obtained by high-temperature calcination. finally, an ultra-hydrophobic transparent coating was obtained by chemical vapor deposition with a water contact angle of (1592)°. the coating improves the evaporation rate of water mist with excellent anti-fog performance. 4.4 application of superhydrophobic surface materials in metal anticorrosion protection hyperhydrophobic materials have corrosion-resistant properties because a membrane of air occurs between solid and liquid, making it difficult for corrosive ions to contact the surface of the material[49,50]. many people have researched in this regard, such as guo haifeng et al.[51] praying the inner surface of the natural gas pipeline to prepare superhydrophobic films to further improve the corrosion resistance of the pipeline. the subject group, lu si et al., adhered the disordered carbon nanotubes to the surface of the substrate aluminum plate to form a composite structure surface and then modified with ptfe to form a hyper-hydrophobic ptfe. 4.5 application of superhydrophobic surface materials in other aspects mobina et al.[52] co-modified the trimonomomer copolymer with methanol and nano sio2 and the water contact angle of the composite superhydrophobic coating was greater than 150° and could be applied to the surface of biomedical materials. wang et al.[53] immersed aluminum alloy, silicon plates, polypropylene and other substrate in a buffer of dopamine-hydrochloride for a period, transferred to different concentrations of silver ammonia solution, added formaldehyde solution, and finally modified the substrate into a mixture of ethanol and dodecyl thiol to make a superhydrophobic silver substrate with a water contact angle up to 170°. 5. conclusion the application range of superhydrophobic materials is quite wide, which has had certain development in various aspects, and its application prospect is very broad. however, due to the current technology and development costs are limited, the actual industrialization and commercialization are not much[54,55]. first, from a theoretical perspective, the geometry of superhydrophobic, size, functional group influence of superhydrophobic surface structure needs to be deepened. secondly, in the preparation process, the low surface energy substances used are more expensive, mostly fluoride or silane compounds. finally, in terms of technology, it is mainly the durability and aging resistance of surface coating. many superhydrophobic structures are prone to lose superhydrophobicicity due to infirmness. therefore, in the selection of materials, preparation process and post-processing, further research and solution. research on how to automatically recover or 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engineering 2011; 1(5): 93–98. 55. liang w, zhang y, wang b, et al. biological applications of biomimetic superhydrophobic surfaces. acta chimica sinica 2012; 70(23): 2393–2403. characterization and application of nanomaterials (2020) volume 3 issue 2 doi:10.24294/can.v3i2.595 60 original research article coal combustion residues characterization using scanning electron microscopy & energy dispersive x-ray (sem-edxa) analysis ritesh kumar 1 , sadanand sharma 1 , ajit kumar 1 , charu arora 2* 1 csir-central institute of mining & fuel research (cimfr), barwa road, dhanbad-826001, jharkhand, india. 2 guru ghasi das vishwavidyalaya, bilaspur-459005, chhatisgarh, india; e-mail: charuarora77@gmail.com abstract the objective of the present study is to observe the surface morphology, structure and elemental composition of the ash particles produced from some thermal power stations of india using scanning electron microscopy (sem) and energy dispersive x-ray analysis (edxa). this information is useful to better understand the ash particles before deciding its utility in varied areas. keywords: coal combustion residues; characterization; xrd; sem-edxa; ftir article info article history: received 24 october 2020 received in revised form 21 november 2020 accepted 26 november 2020 available online 7 december 2020 copyright copyright © 2020 ritesh kumar et al. doi: 10.24294/can.v3i2.595 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/by/4.0/ 1. introduction power sector is the major consumer of coal in our country. with rapid industrialization, since independence and improvement in the quality of life, the demand for power has increased tremendously and this has led to the increase in the consumption of coal. the increasing population has further increased the coal consumption. india is the world’s third largest producer and the fourth largest consumer of electricity. more than 51% of india’s commercial energy demand is met through the country’s vast coal reserves [1] . the indian power sector generated approximately 1160.141 bu of electricity in 2016-2017 [2,4] . during the last two decades, the growth in the power sector has been phenomenal. of the total power generated more than 50% has been contributed by coal-fired power station [3,4] . the electricity demand owing to increase in the population and industrialization during last one and a half decade has increased tremendously, which has led to the per-capita increase in power consumption in india to 1010 kwh in 2014-2015 and 1075 kwh in 2015-2016. the installed capacity, which was 72,320 mw in 1993-1994, has now reached 329,226 mw as on august, 2017 [5,6,7] . coal-fired power stations still dominates the energy sector in india. india has vast reserves of thermal grade coal that is cheaply and readily available as a raw material for power generation. the estimated coal reserves as on 01.04.14 in india are 301.564 bt [8,9,10] . the production of coal has increased from about 70 mt in early 1970s to 639.234 mt in 2015-2016 [11] . coal that is used for power generation in the country is mostly low-grade coal containing 30–50% ash [12,13,14] . the combustion of coal at the coal-fired power stations produces ash http://creativecommons.org/licenses/by/4.0/ 61 residues of inorganic minerals. around 132 thermal power stations are there in the country that meets 51% of india’s commercial energy demand. these thermal power stations produce around 150mt of coal combustion residues (ccrs) per year that is causing great environmental concern in the form of air, water and land pollution besides its proper handling and disposal [3] . disposal of such a huge amount of ccrs craves for huge tract of land besides having several environmental implications in the disposal environment. in country like india, where land resources is very limited, proper management of ccrs is the need of the hour not only in our country but also throughout the world and all these requires proper understanding of ccrs through its characterization study. mostly two types of ashes namely, fly ash and bottom ashes are produced by thermal power stations in india. fraction that tries to escape along with flue gas, are trapped by electrostatic precipitators and mechanical dust collectors and is referred as fly ash. this constitutes about 80 percent of the ash produced. the other fraction collects at the bottom of the furnace and is named as the bottom ash. this is coarser in nature and constitutes about 20 percent of the ash produced. the two ashes in the wet system of disposal (as practiced in our country by most of the coal based thermal power plants) are made into slurry form and pumped to the disposal area especially made for this purpose. the ash in such disposal pond is known as pond ash. table 1. status of world energy at the end of 2016[18] (bp, 2017) 2016 change 2016 over 2015 (%) electricity generation (twh) 24816.4 2.2 coal reserves (mt) production (mt) production (mt of oil equivalents) consumption (mt of oil equivalents) 1139331 7460.4 3656.4 3732.0 -6.5 -6.2 -1.7 table 2. year-wise coal consumption, power generation and generation growth in india (2003-2004 to 2013-2014)[19,20,21,22] year coal consumption (million tonnes) generation (bus) generation growth (%) 2003-2004 558.30 2004-2005 278.00 587.40 5.21 2005-2006 281.00 617.50 5.12 2006-2007 302.00 662.50 7.29 2007-2008 330.00 704.50 6.34 2008-2009 355.00 723.80 2.74 2009-2010 367.00 771.551 6.60 2010-2011 387.00 811.143 5.13 2011-2012 417.56 876.887 8.11 2012-2013 545.60 912.056 4.01 2013-2014 489.40 967.150 6.04 2014-2015 530.40 1048.673 8.43 2015-2016 545.90 1107.822 5.64 2016-2017 1160.141 4.72 2017-2018 1229.400 (target) 5.97 the major challenge before the nation is to effectively utilize these coal combustion residues in bulk and that too in environmentally benign manner. the increasing number of thermal power stations and also the ever increasing population will add more pressure for immediate utilization. the ash utilization in india in 1992-1993 was 2–3% [15] , which has now increased to 60.97% of ccrs as per the latest report [16] . however, the percentage of ash utilized is still low as compared to other developed countries of the world where utilization is close to 100% [17] . though in our country the situation has changed since last one and a half decade, we have to go a long way to fulfill the promise of 100% uti 62 2 7 8 2 8 1 3 0 2 3 3 0 3 5 5 3 6 7 3 8 7 4 1 7 .5 6 5 4 5 .6 4 8 9 .4 5 3 0 .4 5 4 5 .9 0 100 200 300 400 500 600 coal consumption (million tonnes) 5 5 8 .3 5 8 7 .4 6 1 7 .5 6 6 2 .5 7 0 4 .5 7 2 3 .8 7 7 1 .5 5 1 8 1 1 .1 4 3 8 7 6 .8 8 7 9 1 2 .0 5 6 9 6 7 .1 5 1 0 4 8 .6 7 3 1 1 0 7 .8 2 2 1 1 6 0 .1 4 1 0 200 400 600 800 1000 1200 1400 2 0 03 -0 4 2 0 04 -0 5 2 0 05 -0 6 2 0 06 -0 7 2 0 07 -0 8 2 0 08 -0 9 2 0 09 -1 0 2 0 10 -1 1 2 0 11 -1 2 2 0 12 -1 3 2 0 13 -1 4 2 0 14 -1 5 2 0 15 -1 6 2 0 16 -1 7 generation (bus) lization. table 1 shows the status of world energy at the end of 2016. table 2 and table 3 show the year-wise coal consumption and power generation in india from 2003-2004 to 2013-2014 and per-capita electricity consumption in india from 2005-2006 to 2015-2016, respectively. table 4 shows the per-capita consumption of electricity by leading countries of the world. table 5 shows the india’s ccrs utilization scenario. similarly, table 6 provides the data on ccrs utilized by the leading countries of the world. figure 1 shows year-wise power generation in bus and coal consumption in mt in india. this paper provides a detailed characterization study of ccrs from indian thermal power station. the paper covers sem-edxa analysis of the ccr samples. the actual aim of this paper is to understand ccrs suitability in various applications using the characterization data so that the material can be used in an environmentally friendly manner. figure 1. year-wise power generation (bus) and goal consumption (mt) in india. table 3. year-wise per-capita electricity consumption in india (2005-2006 to 2015-2016)[23,24] year consumption (kwh) 2005-2006 631 2006-2007 673 2007-2008 717 2008-2009 734 2009-2010 779 2010-2011 819 2011-2012 884 2012-2013 914 2013-2014 957 2014-2015 1010 2015-2016 1075 table 4. comparative per-capita consumption of electricity (kwh)[25,26] countries consumption (kwh) for 2013 canada 15520 usa 12987 australia 10067 japan 7836 france 7382 uk 5409 world 3026 india 957 table 5. year-wise ccrs utilization in india (1993-1994 to 2005-2006) year utilization (%) 1992-1993 2-3% 2002-2003 22.68 2003-2004 29.39 2004-2005 38.04 2005-2006 45.69 2006-2007 50.86 2007-2008 53.00 2008-2009 57.11 2009-2010 62.60 2010-2011 55.79 2011-2012 58.48 2012-2013 61.37 2013-2014 57.85 2014-2015 54.31 2. materials and methods 2.1 selection of thermal power stations for assessing the environmental characteristics of coal combustion residues (ccrs) five thermal power stations, viz. three of damodar valley corporation (dvc), namely, bokaro thermal power station (btps), chandrapura thermal power sta 63 tion (ctps) and durgapur thermal power station (dtps), one fluidised bed combustion (fbc), plant of tata iron & steel company (tisco) and one of fertilizer corporation of india ltd. (fci), sindri unit were chosen. all the thermal power stations are either located on the banks of damodar river or in its immediate vicinity in the states of jharkhand and west bengal. these thermal power stations were chosen for the following reasons:  these form the life-line of an industrial belt in damodar river basin  power plants and the ash ponds are close to surface water bodies.  there is probability of surface and ground water contamination due to leaching of trace elements from the ash ponds of these plants. also, these thermal power stations were easily accessible and it was possible to get desired facilities for the studies. figure 2 shows the locations of the power stations under study along river damodar. similarly, table 7 gives the composition of coal be ing used at different thermal power stations. table 6. utilization of fly ash by various countries[15] s.no. country utilization (%) 1 australia 40 2 canada 40 3 china 35 4 czechoslovakia 40 5 denmark 85 6 france 70 7 germany fr 85 8 greece 45 9 hungary 50 10 india 41 11 israel 80 12 japan (a) 40 13 netherlands 100 14 poland 100 15 south africa 35 16 u.k. 60 17 u.s.a 35 figure 2. location of bokaro thermal power stations along the river damodar. table 7. composition of coal being used at different thermal power stations[27] parameters btps ctps dtps fbcp fcil fixed carbon (%) 36.28–47.77 41.75 55.30 26.67 45–47 volatile matter (%) 15.8–18.12 16.20 24.50 16–19 moisture (%) 0.9–1.11 0.60 2.80 1.1 0.5 ash (%) 34.23–40.25 41.45 27.40 65 30–35 gross calorific value (kcal/kg) 4670–4970 4665 5560 2200 4800 64 2.2 sampling fly ash (fa) and bottom ash (ba) samples were collected on five different days over a week and a final homogenized sample for each of the fly ash and bottom ash were prepared by mixing the appropriate portions. similarly, pond ash samples were collected from the ash ponds site from five different locations on five different days over a week and a final homogenized sample was prepared mixing appropriate portions. the ccr samples after coning and quartering method were then taken for characterization studies adopting analytical methods. 2.3 scanning electron microscopy & energy dispersive x-ray analysis the scanning electron microscopy (sem) [29,30] allows high-level magnifications, which can be used for studying morphology of the sample of finer materials. it uses a focused electron beam to scan small areas of solid sample surfaces. secondary electrons are emitted from the sample and are collected to create an area map of the secondary emissions. this secondary emission is very much dependent on the surface characteristics and so the area obtained is a magnified image of the sample. this technique is also referred to as energy dispersive x-ray analysis (edxa). the back-scattered electrons also produce x-rays and the same can be utilized by many instruments for the qualitative compositional analysis of microscopically small portions of the sample. this technique is also referred to as energy dispersive x-ray analysis (edxa). the sample requirement for the sem analysis is that the solid samples, viz. thin films, powder, fibers and bulk materials should be vacuum compatible. the principle of working of the instrument is that an electron beam, accelerated at 25 kv energy, is generated at electron gun. the electron beam is passed through various electro-magnetic lenses. it first passes through condenser lens forming an electron beam spot. the fine electron beam is then focused by objective lens. the focused electron beam is deflected by beam deflection coil throughout the specimen. as soon as the focused electron beams falls on the specimen, the secondary electron beams are emitted as per the sample topography. the secondary electrons are processed to secondary electron image in the display unit through a secondary electron detector assembly. the scanning electron microscopic studies were carried out using model s-415a (figure 3), hitachi instruments ltd., tokyo, japan. the fine powders are sonicated in test tube with methanol solvent in a sonicator machine for 1 hour. the fine particles were then suspended in the medium. it was then pipetted out through a pipette in a cover slip and dried. after properly drying, it was subjected to gold coating to eliminate the charging effect of the electron beam during sem observation. this was done in an ion coater (model 1132, eiko engineering, japan) by sputtering technique at a 1400v d.c., 8-10 ma current for 3 minutes. after gold coating, it was placed in the evacuation chamber of sem. after evacuation, the electron beam was generated at 25 kv energy and the secondary electron ashi pentax camera was attached to the instrument to record images and the photomicrographs were taken one by one. figure 3. scanning electron microscope, hitachi instruments ltd., japan, model 415a. 2.4 results and discussion the results of the characterization of coal combustion residues (ccrs) from five thermal power stations, viz. btps, ctps, dtps, fbcp and fci, sindri for assessing their characteristics for va rious uses as determined by instrumentation techniques such as sem-edxa is discussed below. 65 3. sem-edxa the morphological features of the leached and unleached ccr samples were examined with the help of scanning electron microscope using scanning electron microscopy (sem) technique. table 8 gives the observation made with respect to sem studies of ccr samples under study. these are also shown in figure 4 to figure 8. the study of the micrographs of the unleached ccr samples in general indicated that ccr consisted primarily of spherical particles with nodules present on it. the particles were of different sizes and ranged from 1µ to 100µ. similarly, study of the micrographs of leached ccr samples clearly shows the leaching pattern that has taken place. the particles in the leached samples lacked agglomeration and were more dispersed than one can observe in the case of unleached samples. thus, one can conclude that the surface film or the irregularities caused the unleached particles to agglomerate. figure 9 shows few micrographs of the leached ccr samples. one can easily observe the leaching phenomena that have taken place and that the surfaces of the leached particles were observed to be smoother. it means that the material residing on the surface has been washed away during the leaching. surficial element mostly present included alkali and alkaline earth metals, i.e. sodium, potassium, calcium and magnesium. as these got washed away due to the first flush phenomenon, their presence in the leached samples also decreased considerably. decrease in concentration of these elements with time can be very well observed from the plot of the open column percolation experiment results for these elements. some of the particles on the leached samples were found distorted as can be seen from the micrographs of the leached samples. distortion of particle surface is due to dissolution or disruption of the surface, making the wall thinner and thinner and finally rupturing the wall. as is pointed out, the particles are mostly spherical in shape and they are either hollow spheres commonly known as cenospheres or solid spheres or may be containing many smaller spheres within a sphere known as plerosphere. all three can be seen from the micrographs. cenospheres and plerospheres are present in very low amount. some spongy morphology can also be noticed from the micrographs. a point of special importance is the fact that most of the particles are found to be of spherical nature. due to being spherical mixed with cement, it can add workability to cement concrete mix. being spherical and hollow can be used as filler in paints and so on. table 8. summary of sem study of ccr samples from a few thermal power stations of india plant samples sem (observations) ps fa#a; fa#b; ba#a; ba#b; pa  mostly spherical in shape with size varying from less than 1 micron to 100 micron.  particles were found mostly spherical in shape with nodules present on it.  some cenospheres could also be seen from the micrographs.  a few plerospheres could also be seen from the micrographs.  cenospheric particles show frequent bursts which are inductive of chemical activity having occurred within them.  surfaces of some particles show extensive mechanical damage caused by impactation.  small size particles were seen sticking to the larger spherical particles possibly on account of the convexity of the surfaces.  leached particles were observed to be smoother. this shows the washout of the elements residing on the surface with time. plot of opce also shows this decreasing trend.  some spongy morphology could also be seen from the micrographs. ctps fa#1; fa#2; ba#1; ba#2; pa dtps fa; ba; pa fbcp fa; pa fcil s1; s2; s3; s4 66 (a) (b) (c) (d) (e) figure 4. scanning electron micrographs of btps (a) fa#a; (b) fa#b; (c) ba#a; (d) ba#b and (e) pa. 67 (a) (b) (c) (d) (e) figure 5. scanning electron micrographs of ctps (a) fa#1; (b) fa#2; (c) ba#1; (d) ba#2 and (e) pa. 68 (a) (b) (c) figure 6. scanning electron micrographs of dtps (a) fa; (b) ba and (c) pa. (a) (b) figure 7. scanning electron micrographs of fbcp (a) fa and (b) pa. 69 (a) (b) (c) (d) figure 8. scanning electron micrographs of fci (a) s1; (b) s2; (c) s3 and (d) s4. 70 the observations of edxa analysis are given in the table 9. this study was performed to determine the trace element contents in the ccr samples. the study shows that the ccr samples are typically formed of si-al-fe system with traces of sodium, potassium, calcium, magnesium, sulphur and titinium. table 9. summary of edxa of ccr samples from a few thermal power stations plant samples si al fe na k ca mg s ti btps fa#a 25.97 14.85 3.34 2.52 1.63 0.62 0.12 0.02 0.97 fa#b 21.67 14.56 3.75 6.35 1.42 0.89 0.92 0.06 2.16 ba#a 25.88 17.36 2.07 1.93 1.27 0.09 0.02 1.32 ba#b 26.40 15.93 1.36 1.10 1.66 0.32 0.64 1.04 pa 23.20 12.20 8.54 4.36 1.16 0.37 0.90 0.21 1.06 ctps fa#1 27.35 14.54 5.09 0.01 1.11 0.44 0.05 0.72 0.91 fa#2 25.66 16.94 2.92 1.16 0.15 0.50 0.02 0.53 ba#1 27.34 14.70 2.78 0.84 1.15 0.31 0.21 0.28 1.61 ba#2 22.90 15.90 7.28 1.41 1.23 0.90 0.64 1.69 pa 24.64 14.88 4.25 0.65 1.06 0.41 1.01 0.38 0.79 dtps fa 25.73 13.36 3.11 2.78 1.62 0.71 0.86 1.42 ba 24.87 12.49 4.81 4.73 1.31 1.51 1.13 0.15 0.06 pa 18.05 22.62 1.01 1.43 0.75 0.34 0.46 0.05 1.03 fbcp fa 24.97 13.11 4.63 1.77 2.61 2.77 0.80 0.51 1.34 pa 22.27 19.64 2.31 0.35 1.28 0.78 0.63 0.59 1.66 fci s1 26.10 14.28 1.98 1.27 0.31 0.55 1.39 s2 21.51 13.17 11.91 0.94 0.50 0.23 1.14 s3 25.78 15.59 2.84 1.45 0.72 0.25 1.16 s4 26.59 14.40 2.54 1.26 0.35 0.65 1.73 figure 9. scanning electron micrographs of ccr samples after leaching. 71 4. conclusion the sem studies of the ccrs have shown that ccrs consisted primarily of spherical particles with nodules present on it. the particles varied in size from less than 1 micron to 100 micron. the particles consisted of cenospheres (hollow spheres), solid spheres and plerospheres (spheres within a sphere). spongy morphology and a small amount of angular shaped particles were also seen. this was due to the presence of unburned carbon and other minerals. being spherical and hollow these particles can be used as filler in paints and so on. on the other hand, the sem studies of the ccr particles after leaching have clearly shown the leaching pattern that has taken place. the particles after leaching lacked agglomeration compared to the original particles. some of the particles were also observed distorted in shape while walls of some of the particles were found ruptured. this distortion and rupturing may be accounted due to the dissolution of the surficial elements making the wall of the sphere thinner and thinner and finally the wall ruptures. list of abbreviations ccrs coal combustion residues dtps durgapur thermal power station btps bokaro thermal power station ctps chandrapura thermal power station tisco plant of tata iron & steel company fcil fertilizer corporation of india limited dvc damodar valley corporation sem scanning electron microscopy edxa energy dispersive x-ray 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author: devendra kumar, dkumar@dce.ac.in abstract: herein, we developed a non-enzymatic biosensing platform using polyaniline (pani) polymer matrix grafted with ceo2. the one-pot synthesized nanocomposite has been used for the detection of 17β-estradiol (e2). the homogeneous distribution of ceo2 onto the pani matrix leads to an increase in surface area, conductivity, and effectiveness of the synthesized nanocomposite pani@ceo2. the pani@ceo2 nanocomposite was characterized using structural and morphological techniques. further, the electrode fabrication was performed electrophoretically by depositing the pani@ceo2 nanocomposite onto the ito electrode. the pani@ceo2/ito showed enhanced electrochemical behavior as compared to pani/ito. detection of e2 was carried out using the differential pulse voltametric technique (dpv). linearity has been observed through the detection range of 1 µm–100 µm with lod = 2.15 µm. the developed biosensor has been found to be stable and selective towards e2. it has been successfully utilized for the detection of e2 in real samples like tap water and human urine samples. thus, this research encourages its use for more applications in clinical diagnosis and biomedical sciences. keywords: polyaniline; 17β-estradiol; biosensor; tap water; urine; ceo2 1. introduction the excessive use of steroid growth hormones has resulted in the widespread presence of 17β-estradiol (e2) in food commodities such as meat and dairy products. these hormones are excreted by animals into the environment, serving as prevalent forms of environmental endocrine disruptors [1]. at low concentrations, the abuse of steroid growth hormones can mimic the effects of female sex hormones in the human body and disrupt hormone actions through different mechanisms. this interference with the endocrine system can lead to adverse effects such as infertility, diabetes, birth defects, pcod, and reproductive dysfunctions in humans. exceeding a certain threshold concentration, exogenous e2 can disturb the balance within the human body. it has been reported that elevated levels of e2 lead to an increased incidence of prostate cancer in men and breast cancer in women [2,3]. during the last decade, many analytical methods have been reported for the determination of e2, such as hplc, lc-ms, gc-ms, etc. these methodologies use expensive instruments, require intricate operation, extended assay time, and personnel with specialized training. some alternative methods that have been introduced for detecting e2 are surface plasmon resonance biosensors, surface molecular imprinting techniques, colorimetric methods, and enzyme-linked immunosorbent assays. despite the appreciable sensitivity of these newly developed methods for detecting e2, most of them still require expensive instruments, similar to citation dam a, rajput t, verma s, kumar d. non-enzymatic detection of 17βestradiol in real samples using pani@ceo2 nanocomposite. characterization and application of nanomaterials. 2024; 7(2): 4768. https://doi.org/10.24294/can.v7i2.4768 article info received: 20 february 2024 accepted: 22 july 2024 available online: 19 august 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 4768. 2 chromatography techniques. as a result, they are not suitable for on-site detections due to cost and instrument dependency limitations [4–6]. also, the detection of hormones based on enzyme immobilization mobility is gaining popularity due to its high selectivity, easy fabrication, and rapid response. despite this popularity, this technique comes with various limitations, like high cost, low sensitivity, and leaking of enzyme from the transducer surface. therefore, there is a strong demand for reliable, rapid, and user-friendly biosensors that can effectively detect low concentrations of e2 in samples [7,8]. conducting polymers (cp) due to their electrochemical activity, mechanical elasticity, biocompatibility, electrical conductivity, and environmental stability are the most liable to be used as sensing elements in analytical and bioanalytical systems. electrochemical biosensors based on enzymatic and non-enzymatic methods have gained tremendous attention throughout the world. however, enzymatic methods are known to have some drawbacks, such as thermal and storage stability, environmental selectivity, etc. [9,10]. hence, scientists have been more focused on the development of non-enzymatic biosensors in the last decade because of their high selectivity and lower cost than enzymatic ones. the most common among them is the mip-based sensors, which do not require any biologically recognized element. the principle for these nonenzymatic biosensors for the detection of e2 is based on the direct oxidation of the hydroxyl group. the sensing properties of cp’s can be modified by alternating their surface and morphology, such as by developing a metal-based structure grafted with conducting polymer. n-type inorganic semiconductors such as ceo2, zno, tio2, and wo3 can be used efficiently with conducting polymers as a sensing material [11,12]. polyaniline (pani) displays exceptional advantages, including easy synthesis, superior electrical conductivity, and reversible redox behavior. despite the numerous positive characteristics of the polymer, pani-based chemical sensors can face limitations in terms of sensitivity, linearity, selectivity, or stability. one way to overcome these limitations is by incorporating a secondary material into the pani, resulting in the formation of a polymeric composite. the integration of pani with a secondary nanocomponent, such as metallic nanoparticles, metal oxide nanoparticles, carbon compounds, or polymers, leads to enhanced functionality and improved performance, providing an effective design approach [13,14]. the synergistic interactions between the constituents in nanocomposites of pani and metal oxides such as ceo2 result in improved properties, making them highly valuable for applications such as sensors and biosensors, photovoltaics, and batteries. nanocomposites of pani with ceo2 have been extensively explored for sensing applications. the enhanced sensor response of these composites can be attributed to the formation of electron-conducting pathways within the material, leading to improved device efficiency. the inclusion of semiconductor metal oxide ceo2 into polymer matrices pani has been shown to improve the mechanical, thermal, dielectric, and optical properties of polymers, enabling high carrier mobilities [15]. this research work reveals the biosensory fabrication of electrodes using synthesized pani@ceo2 nanocomposite, which acts as an effective sensing platform for e2 detection (figure 1). the performance of pani@ceo2 composite as a sensing platform has been analysed in real samples, i.e., human urine and tap water. characterization and application of nanomaterials 2024, 7(2), 4768. 3 figure 1. schematic diagram of the synthesis of pani@ceo2 and its deposition on ito. 2. materials and methods 2.1. materials required for synthesizing the pani, ceo2, and pani@ceo2 nanocomposite, we used aniline and ammonium persulfate, bought from central drug house (pvt), [ce(no3)3·6h2o], 99% trace metal basis, procured from sigma aldrich (france), hydrochloric acid (hcl, 25%), and liquor ammonia (25% ammonia) procured from thermofisher scientific, india. other chemicals, i.e., di-sodium hydrogen orthophosphate dihydrate, potassium ferrocyanide, sodium dihydrogen orthophosphate, and potassium ferricyanide, were purchased from qualigens fine chemicals for preparing pbs and ferro-ferri solution (ph = 7.4). the cleaning was done using 100% acetone and 99.9% ethanol, which were purchased from central drug house (pvt). 2.2. synthesis of polyaniline for the synthesis of pani, we took 1 ml aniline and mixed it with 15 ml hcl (1 m) to get solution-a. then solution b was prepared by dissolving ammonium persulfate in 15 ml hcl (1 m). the molar ratio of aniline with respect to ammonium persulfate was taken to be 1:1.15, respectively. in an ice bath maintaining 0–5 ℃, solution-b was added dropwise into solution-a, followed by 3 h of stirring under the same condition. at last, the resultant solution was kept overnight in the refrigerator and rinsed with acetone and distilled water the next day to remove impurities. the obtained product was then left to dry in an oven at 60 ℃ to get dark green-colored pani [16]. characterization and application of nanomaterials 2024, 7(2), 4768. 4 2.3. synthesis of ceo2 for the preparation of ceo2 nanoparticles, 1.5 m mol of cerium (iii) nitrate hexahydrate was dissolved in distilled water (50 ml) with the addition of 1.5 ml of liquid ammonia. the resulting solution was stirred for around 30 min using a magnetic stirrer. following this, the solution mixture was shifted to an autoclave (120 ml) (teflon-lined stainless steel) and left at 180 ℃ in an oven for 24 h. the obtained stagnant was then cooled at room temperature, rinsed with both distilled water and ethanol repeatedly for the excretion of excessive ammonium hydroxide, and left at 60 ℃ for 24 h to get the dry, desired pale-yellow, white-colored product. 2.4. synthesis of pani@ceo2 nanocomposite for synthesis of pani@ceo2 nanocomposite, 40% (w/w) of synthesized ceo2 was mixed with 1 ml of aniline in 15 ml of hcl (1 m) to get solution-a, followed by the same procedure as mentioned in synthesis of pani. 2.5. electrophoretic deposition (epd) on electrode a gx300c (genetix) electrophoretic unit was used to carry out the process of electrophoretic deposition, where platinum was used as the counter electrode. we deposited all three synthesized compounds on an ito (indium tin oxide) coated glass electrode. for that, we mixed 1 mg of each compound with 10 ml of distilled water separately and ultrasonicated them for 3–4 h. the epd process was conducted at a constant voltage of 10 v provided via a dc power supply for stable and efficient deposition and optimized at 7 s for pani and cerium (iv) oxide suspension, and for pani@ceo2 nanocomposite suspension, it was optimized at 15 s. after epd, the electrodes were removed from the suspension and stored in a refrigerator for further use. 2.6. characterization for the study of x-ray diffraction of the synthesized materials, cu kα radiations with a wavelength of λ = 1.5406 å based on a bruker d-8 advance x-ray diffractometer (xrd) have been used. for the study of the presence of functional groups and saturation in materials, the perkin elmer fourier transform infrared (ftir) spectrum (model spectrum 2) has been used. we used a zeta potential analyzer (malvern instruments ltd.) for analysing the charge of the materials. tga 4000, perkinelmer, was used in the range of 0–600 ℃ in an atmosphere of nitrogen with a constant heating rate of 10 ℃/min for studying the degradation of materials with temperature. similarly, dsc 8000, perkin elmer, was used for differential scanning calorimetry for the analysis of thermal characteristics. for electrochemical studies, we used autolab potentiostat/galvanostat (eco-chemie, the netherlands), which is a three-electrode cell having ito, platinum, and ag/agcl as a working, inert, and auxiliary electrode in phosphate buffered saline (pbs; ph 7.4; 100 mm) mixed with ferrocyanide and ferricyanide [fe(cn)6]3−/4− of 5 mm concentration each. characterization and application of nanomaterials 2024, 7(2), 4768. 5 3. results and discussion 3.1. x-ray diffraction study the powder xrd pattern of ceo2 and pani@ceo2 nanocomposite and pani has been shown in figure 2a and figure s1. it has been observed that ceo2 shows clearly distinct xrd peaks at 2θ = 28.5°, 33.1°, 47.7°, 57.1°, 59.3°, 69.6°, 77.0° and 79.2° respectively. no other peaks are obtained, which indicates the successful synthesis of ceo2. the observed x-ray patterns of the synthesized ceo2 satisfied the fluorite-type crystal cubic phase of ceo2 (jc-pds card no 01-075-8371) [17]. figure 2. (a) xrd spectra; (b) ft-ir spectra; (c) tga plot of pani@ceo2 and ceo2. the results here indicate that both the compounds maintained its characteristic in the composite mixture. in the xrd pattern of pani@ceo2 nanocomposite, it was observed that the diffraction peaks of pani and ceo2 overlapped with each other. both the pani and pani@ceo2 nanocomposite show a wide peak located at 2θ = 26° satisfying the amorphous (semi-crystalline) nature of pani. the synthesized pani@ceo2 nanocomposite shows its peaks at 2θ = 28.5°, 33.1°, 47.7°, 57.1°, 59.3°, 69.6°, 77.0° and 79.2° respectively which resembled the (111), (200), (220), (311), (222), (400), (331) and (420) bragg’s crystal plane reflections [18]. 3.2. fourier transform infrared study the ftir spectra of ceo2, pani@ceo2 nanocomposite, and pani are shown in figure 2b and figure s2. the vibration peaks of the as-prepared pani@ceo2 nanocomposite sample appear at 503, 689, 803, 1130, 1299, 1244, 1487, and 2822 (cm−1). the c–n stretching of a secondary aromatic amine is responsible for a minor, distinct peak observed at 1299 cm−1. the wide and sharp peaks at 1130 cm−1 characterization and application of nanomaterials 2024, 7(2), 4768. 6 correspond to the bending vibration of c–h. the very small and clear peaks at 803 cm−1 indicate the metal-oxygen bands. the minor peak at 1244 cm−1 showed the c– n stretching and c–c stretching bands of pani. the sharp peak at 1487 cm−1 showed the benzenoid ring stretching of pani. the broad peak at 503 cm−1 corresponds to the metal-oxygen stretching frequency. as the percentage of ceo2 in the pani@ceo2 composite increases, the intensity also increases. for pure ceo2 this peak was observed at 496 cm−1, and moved at 503 cm−1 in the case of pani@ceo2 which illustrates the weak interaction between ceo2 and pani, while other prominent peaks of pure ceo2 are 619, 1126, 1356, and 1569 (cm−1) attributes to the stretching band of the metal-oxygen bond [17,19–21]. 3.3. thermogravimetric analysis study from the tga of ceo2 and pani@ceo2 as shown in figure 2c, it is observed that pure ceo2 crystals are superiorly stable and thermally resistant in the temperature range of 20–600 °c whereas pani@ceo2 nanocomposite shows a loss in its mass in two steps. the first decrease in mass of about 10% occurs in the range of 40–100 °c owing to the deprivation of water from pani chains. in the second step, loss of mass occurs in the range of 250–600 °c, corresponding to the breaking of polymeric chains. it is observed that when the ceo2 to aniline ratio is about 40% in the pani@ceo2 nanocomposite, it shows highest thermal stability. the higher the content of ceo2 in the composite, the more strengthening occurs between the polymeric chains and ceo2 and the thermal decomposition of the chains is restricted accordingly [22–24]. 3.4. morphological studies the surface morphology of pani and pani@ceo2 was analysed using scanning electron microscopy (sem), as shown in figure 3a,b, respectively. the morphology of pani appeared as a grain-like structure that contains some pores and voids. from the morphology of pani@ceo2 nanocomposites, it was observed that pani@ceo2 has some spherical and irregularly shaped grains with diameters in the nanorange, where the ceo2 nanoparticles are homogeneously compacted in the pani matrix, leading to homogeneous morphology and the higher conductivity of pani@ceo2 nanocomposite. figure 3. (a) sem images of pani; (b) sem images of pani@ceo2 nanocomposite. indicating more homogeneously compacted morphology of the nanocomposite. characterization and application of nanomaterials 2024, 7(2), 4768. 7 4. electrochemical studies 4.1. electrochemical studies of electrodes electrochemical studies of the pani/ito and pani@ceo2/ito electrodes have been performed using cyclic voltammetry (cv) technique in pbs (ph—7.4; 100 mm) carrying [fe(cn)6]3−/4− solution of 5 mm concentration. at 50 mv/s, it was noticed that pani@ceo2 electrode exhibits higher current with respect to the pani/ito electrode, which illustrates the better electron conduction ability of the pani@ceo2/ito electrode (figure 4a). a scan rate study has also been performed for both electrodes, as shown in figure 4b and figure s3. it is observed that the anodic peak potential rises from 10 mv/s to 300 mv/s and the cathodic peak potential collapses with an increase in the scanning rate for both the pani and pani@ceo2 modified ito electrodes. this led to a linear relation between the cathodic and anodic peak potentials (epa and epc) of pani and pani@ceo2 with respect to logarithmic scan rate (logν) (figure 4d) [equations (1)–(4)] [25]. a linear correlation between the cathodic and anodic peak currents (ipa and ipc) with respect to the square root of scan rates (ν1/2) has also been observed from the scan rate studies of pani and pani@ceo2 grafted ito electrodes (figure 4c) and has been depicted by equations (5)–(8). epa [pani@ceo2/ito] (v)= 0.04968 log(ν) + 0.148; r2 = 0.9492 (1) epc [pani@ceo2/ito] (v) = −0.0708 log(ν) + 0.183; r2 = 0.9710 (2) epa [pani/ito] (v) = 0.1075 log(ν) + 0.1187; r2 = 0.9833 (3) epc [pani/ito] (v) = −0.2257 log(ν) + 0.3403; r2 = 0.8701 (4) ipa [pani@ceo2/ito] (a) = 2.75 × 10−5 × ν1∕2 + 4.483 × 10−5; r2 = 0.994 (5) ipc [pani@ceo2/ito] (a) = −1.77 × 10−5 × ν1∕2 – 7.008 × 10−5; r2 = 0.978 (6) ipa [pani/ito] (a) = 1.66 × 10−5 × ν1∕2 + 5.6315 × 10−5; r2 = 0.9905 (7) ipc [pani/ito] (a) = −9.31 × 10−6 × ν1∕2 – 6.422 × 10−5; r2 = 0.9855 (8) the value of electron transfer co-efficient (α) for both pani and pani@ceo2 grafted ito electrodes was obtained to be 0.9138 and 0.8874, respectively (equation s1). using the value of (α) and the equation (s2), the value of the charge transfer rate constant (ks) is found to be 0.1804 s−1 and 0.8185 s−1 for pani and pani@ceo2 respectively. further, the value of average surface coverage (λ) is to be calculated using equation s3, which is found to be 1.515 × 10−4 m−2 and 2.07 × 10−4 m−2 for pani and pani@ceo2 respectively. the value of diffusion coefficient for [fe(cn)6]3−/4− solution (d) and effective surface area of electrodes (a) are calculated using the gradient of lines established by the linear connection between ip and ν1/2, using the randles-sevcik equation as shown in equation (s4). the effective surface area of pani having d = 4.964 × 10−4 m2 s−1 and pani@ceo2 having d = 9.5 × 10−4 m2 s−1 is found to be 5.22 × 10−7 m2 and 6.32 × 10−7 m2 respectively. the values of d and a are greater for pani@ceo2 nanocomposite than pani because pani@ceo2 performs better diffusion of redox ions through its active detection area and electrode interface [26,27]. all the parameters have been summarized in table 1. characterization and application of nanomaterials 2024, 7(2), 4768. 8 table 1. comparison of the electrochemical behaviour of the pani/ito and pani@ceo2/ito electrodes. modified electrodes electron transfer co-efficient (α) charge transfer rate constant (ks) (s−1) average surface coverage (λ) (m−2) diffusion coefficient (d) (m2s−1) effective surface area (a) (m2) pani/ito 0.9138 0.1804 1.515 × 10−4 4.964 × 10−4 5.22 × 10−7 pani@ceo2/ito 0.8874 0.8184 2.07 × 10−4 9.5 × 10−4 6.32 × 10−7 figure 4. (a) cv studies of pani@ceo2, pani and bare electrode demonstrating the higher conduction ability of pani@ceo2; (b) different scan rates with pani@ceo2 electrode (10–300 mv/s); (c) plot of ipa, ipc vs. square root of scan rate for pani@ceo2 electrode; (d) plot of potential vs. logarithm of scan rate for pani@ceo2 electrode. 4.2. optimization of ph parameter for an effective sensing methodology of the electrodes, it is mandatory to optimize the value of ph of the electrolyte solution, as the ph affects the sensitivity of the electrode towards the analyte. thus, we performed the optimization of buffer solution from ph 5.5 to ph 8.5 using the dpv. maximum current has been observed at ph 7.4, and thus we used ph 7.4 buffer for all the sensing studies (figure s4). this can be attributed to the fact that the rate of deprotonation of phenols declines with the rise in ph of the solution. also, human body serum has an optimum ph of 7.4, hence this ph is favourable for clinical studies as well [8]. 4.3. electrochemical biosensing of e2 the electrochemical sensing of e2 was performed using the dpv technique in pbs (ph 7.4) carrying 5 mm [fe(cn)6]−3/−4 solution, as shown in figure 5a. it was noticed that the peak current declined linearly with the concentration of the e2 as analyte (1–100 µm). this can be justified as, with an increase in concentration, the analyte tends to bind with iron coming from [fe(cn)6]−3/−4 solution to make an iron complex, which retards the analyte from getting onto the electrode surface of the characterization and application of nanomaterials 2024, 7(2), 4768. 9 pani@ceo2 modified ito electrode [28]. the linear correlation between the concentration and peak current of the analyte is illustrated in figure 5b, which follows the equation: i (a) = 7.6 × 10−5 − 9.012 × 10−8 [e2]; r2 = 0.9865 from the slope of the equation, the sensitivity of the biosensor obtained is 142.6 µa µm−1 m−2. the fabricated electrode offers an lod of 21.53 µm towards e2 with reference to the equation: lod = 3σ/s. (σ = standard deviation, s = sensitivity, which is determined from the slope of the calibration curve) [29]. the aromatic ring of e2 consists of the hydroxy group, which is liable to make phenoxyl radicals in an aqueous medium during the process of oxidation. the radical on further oxidation leads to the formation of commensurate ketone derivatives, which conclude the effective electrocatalytic direct oxidation of e2 using pani@ceo2 [30]. figure 5. (a) dpv response for pani@ceo2 electrode with increase in concentration of e2 as an analyte (1–100 µm); (b) calibration plot between magnitude of current response vs. concentration of the analyte where linearity is observed. 4.4. interference, shelf life and stability study to understand the specificity for analyte e2, an interference study has been performed by testing e2 (100 µm) in the presence of equal amounts of interferants like ascorbic acid (100 µm), glucose, nacl, urea, estriol, and uric acid, which might restrict the sensing of e2 while its detection in urine and water samples. it has been observed from the current response for different interferants that the target analyte maintained its specificity in different interferants (figure 6a). further, the shelf life of the developed electrode was examined for 21 days in the interval of 7 days. from this study, no change in the current response is observed till 14 days. whereas a sudden diminution in peak current of around 12.1% is noticed on the 21st day of this study. therefore, we confirm the good stability of the developed biosensor for a period of up to 15 days (figure 6b). however, the stability of the biosensing electrode has been confirmed by repeating each result thrice. characterization and application of nanomaterials 2024, 7(2), 4768. 10 figure 6. (a) interference study for different analytes indicating the specificity of e2 analyte; (b) shelf study of the pani@ceo2 modified electrode in 7.4 ph pbs containing 5 mm [fe (cn)6]3−/4− for 100 µm e2; from this result, we confirmed a shelf life of up to 15 days for the developed biosensor. 4.5. real sample analysis to examine the precision and practical applicability of our biosensor, we performed electrochemical analysis in two different samples, viz., human urine (healthy female) and tap water (dtu, delhi). for analysis, each real sample was infused with different concentrations of e2 (1–100 µm) [31]. from the above analysis, we observed recovery of e2 in the range of 98.3%–99.7% for human urine and 97.1%–98.1% for tap water which validates the good productivity and effectuality of the pani@ceo2 electrode (table 2). table 2. recovery percentage data of e2 in real samples. sample added amount (µm) found amount (µm) recovery (%) human urine 10 9.85 98.5 40 39.88 99.7 60 59.64 99.4 100 98.3 98.3 tap water 10 9.71 97.1 40 38.92 97.3 60 58.86 98.1 100 97.6 97.6 5. conclusion in this study, a method was incorporated to detect e2 using a non-enzymatic approach. we synthesized and characterized a pani@ceo2 nanocomposite, which was then electrophoretically deposited onto an ito substrate. the electrochemical behaviour of the pani@ceo2 modified electrode was compared to a pani modified electrode. after considering the results, this work can be summarized as: a) the incorporation of ceo2 in the conducting polymer (pani), forming pani@ceo2 acts as an effective sensing platform for e2. pani matrix grafted characterization and application of nanomaterials 2024, 7(2), 4768. 11 with ceo2 increases the surface area, density, electrical conductivity, and sensitivity of nanocomposite. b) pani@ceo2 modified electrode persisting higher current as compared to pani modified electrode has been depicted, indicating better diffusion of redox ions. c) the study also included a quantitative analysis of three important parameters: sensitivity (275.4 ma (µm)−1), linear range (1–100 µm), and limit of detection (2.15 µm). these results demonstrated the reliability and performance of the developed biosensor in terms of sensitivity, range, and detection limit. the experiments showed good repeatability, stability, and reproducibility, further validating the effectiveness of the non-enzymatic biosensor for detecting e2. d) for better evaluation, the applicability of the biosensor is demonstrated by conducting the analysis in real samples, viz., human urine and tap water, which showcase the practicality and potential of the biosensor in real-world scenarios. supplementary materials: consists of supporting equations, xrd and ftir pattern of pani, and ph optimization results. author contributions: conceptualization, ad, and tr; methodology, sv; software, ad; validation, sv and dk; formal analysis, sv; investigation, ad and tr; resources, ad; data curation, tr; writing—original draft 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2021; 235: 122782. doi: 10.1016/j.talanta.2021.122782 63 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1337 original research article preparation and characterization of branched micro/nano se yongjun wu* software and food engineering department, maanshan teacher’s college, maanshan 243041, anhui, china. e-mail: wyj0555@126.com abstract branched micro/nano se was prepared by the redaction of l-cys•hcl and h2seo3 in hydrothermal method, as β-cd was used as soft template. the structures of products were characterized by sem, tem and xrd. some important factors influencing the morphology of products were studied and discussed, including the amounts of soft template, the reaction temperature and the reaction time. the results showed that external causes had a potent effect on the morphology of micro/nano se. the uniform branched micro/nano se prepared under the optimal reaction condition was rhombohedral trigonal selenium t-se0, but its crystallinity degree was low. keywords: branched se; β-cd; micro/nanoparticles; morphology; rhombohedral phase article info received: 15 augest 2021 accepted: 8 october 2021 available online: 15 october 2021 copyright copyright © 2021 yongjun wu. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction selenium is an important elemental semiconductor material with excellent photoelectronic and catalytic properties and is widely used in photosensitive elements, solar cells, ceramic coatings, functional catalytic materials and other application fields[1]. meanwhile, as an essential trace element in human body, selenium has important physiological functions such as scavenging free radicals, antagonizing toxins, promoting reproduction, regulating metabolism and enhancing immunity[2]. in the traditional selenium supplement products, inorganic selenium and organic selenium have some disadvantages, such as higher toxicity, difficult absorption and high price. in contrast, nano-selenium has significant low toxicity and high efficiency, making it an ideal selenium source for selenium supplement preparations[3]. at present, the reported synthesis methods of nano-selenium mainly include template method, microemulsion method, ultrasonic chemistry method, temperature control method, interface chemistry method, etc.[4,5]. in this study, se0 was prepared by hydrothermal method with reductive l-cys•hcl and h2seo3, and β-cd was used as template agent to control the growth of se0 particles. the effects of surfactant dosage, reaction temperature and reaction time on the morphology, particle size and structure of micro-nano se0 were studied. 2. materials and methods 2.1 materials and instruments materials: seo2(a.r), l-cys•hcl(a.r), food-grade β-cd, industrial alcohol, re-steam water, deionized water. 64 instruments: s-4,800 scanning electron microscopy (hitachi), fei tecnai g2 f20 transmission electron microscopy (jeol), y-4q x-ray diffractometer (dandong ray), dhg-9101-3sa type air blowing drying oven (shanghai sanfa), ds-8510dth ultrasonic cleaning instrument (shanghai sxsonic), tgl-16a centrifuge (jintan huanyu), f1004b electronic balance (shanghai yueping). 2.2 experimental methods l-cys•hcl with a weight of 0.6306 g (4.0 mmol was placed in a reaction kettle. a certain amount of template β-cd solution (0.5 g/l) was dropped and shaken evenly, then 80 ml 0.05 mol/l h2seo3 was added. at this time, n (l-cys•hcl) : n (h2seo3) = 1:1 in the reaction system. after shaking well, the product was placed in a drying oven with air blast and heated at constant temperature for a certain time. the product was ultrasonic cleaned with deionized water for 4 times, and then ultrasonic cleaned with industrial alcohol for 4 times. se0 product was obtained after centrifugation and natural drying. the effects of β-cd dosage, reaction temperature and reaction time on se crystal morphology and crystal state were studied by single factor experiment. 3. experiment and analysis 3.1 the influence of the ratio of reactant substance to the reaction rate fixed h2seo3 dosage as 4.0 mmol (80 ml 0.05 mol/l); used different reactant molar ratios, namely, n (l-cys•hcl) : n (h2seo3) = 1:3, 2:3, 1:1, 4:3, 5:3, 2:1; no β-cd template was added, and the reaction was conducted at 110 ℃. three parallel experiments were conducted for each mole ratio, and the time of the solution turning into light orange was recorded and the average value was taken. the result is shown in figure 1. with the increase of the amount of l-cys•hcl in the reactants, the discoloration time of the reaction solution is rapidly shortened within the range of 1:3 to 4:3 when the ratio of (l-cys•hcl : h2seo3) to the amount of reactants increases, indicating that the reaction speed is accelerated, but the ratio of the amount of reactants is greater than 4:3, the discoloration time basically remained unchanged, indicating that increasing the amount of l-cys•hcl could not significantly accelerate the reaction rate. 3.2 influence of the ratio of reactants to reactants on product yield fixed h2seo3 dosage as 4.0 mmol (80 ml 0.05 mol/l); used different reactant molar ratio, namely n (l-cys•hcl) : n (h2seo3) = 1:3, 2:3, 1:1, 4:3, 5:3, 2:1; no β-cd template was added and the reaction was conducted at 110 ℃ for 2 h. three parallel experiments were performed for each mole ratio. the product was cleaned by ultrasonic cleaning with deionized water once, and then by ultrasonic cleaning with industrial alcohol once. after natural drying, the product was weighed and the average yield was calculated. the result is shown in figure 2. figure 2. effect of the ratio of reactants to substances on the yield. figure 1. effect of the ratio of reactants to substances on the reaction rate. 65 with the increase of the dosage of l-cys•hcl, the yield of reactant mass ratio n (l-cys•hcl) : n (h2seo3) was in the range of 1:3–1:1, but the increase rate gradually decreased. when the molar ratio of reactants was 1:1, the yield fluctuated slightly but did not increase significantly, indicating that the selenium in selenite could not be reduced by hydroxylamine hydrochloride under experimental conditions. compared with the preparation of se0 by vc and h2seo3, the lower selenium yield in this method also confirms the weak reducibility of l-cys•hcl. the fluctuation of yield after the molar ratio of 1:1 was related to the quality loss caused by cleaning products. based on the above facts, the molar ratio of the reactants n (l-cys•hcl) : n (h2seo3) = 1:1 is appropriate. 3.3 influence of dosage of template agent on product morphology using the experimental method in 2.2, the reaction temperature was fixed at 110 ℃ and the reaction time was 2 h, and 0.5 g/l β-cd solution 0, 2.0, 4.0, 8.0, 16.0 ml (equivalent β-cd is 0, 1.0, 2.0, 4.0 and 8.0 mg) was added respectively, and the single factor comparison test is carried out. after ultrasonic cleaning, the product is detected by sem, as shown in figure 3(a) ~ figure 3(e). the product prepared without β-cd was severely adhered selenium balls, similar to ginger cubes, as shown in figure 3(a). at this time, because there is no soft template in the reaction solution, the selenium grains cannot be stable after generation, and inevitably adsorb and combine with each other. in the deposition, the nucleation rate in solution is less than the nuclear growth rate, and the small-scale selenium nanoparticles cannot be obtained. when 2.0 ml β-cd solution was added, the aggregation and adsorption of selenium grains were prevented under the control of β-cd macromolecules, and the products were dispersed to a certain extent. at this time, dispersed selenium pellets were obtained, with cracks visible on the surface, as shown in figure 3(b). when 4.0 ml β-cd solution was added, selenium pellets increased and a large number of short selenium buds grew on some selenium pellets, as shown in figure 3(c). when 8.0 ml β-cd solution was added, the buds of selenium grew significantly and became selenium filaments. some of the selenium filaments connected to each other and formed branched selenium, as shown in figure 3(d). when 16.0 ml β-cd solution was added, the selenium in the branches was significantly reduced and the diameter of selenium pellets was slightly increased, as shown in figure 3(e). figure 3. effect of the amount of β-cd on the morphology of the product. 66 figure 4. the self-assembly principle for β-cd adsorbing se. the appearance of selenium with the above morphology is related to the soft template β-cd, which has many hydroxyl groups in the structure, and its self-assembly principle is as follows[6]: the se nuclei generated in aqueous solution preferentially adsorb on the active hydroxyl groups through hydrogen bonds (figure 4a, figure 4b), and complete self-assembly in two directions with the assistance of template agent β-cd. among them, β-cd molecules interact longitudinally (figure 4c), extending and assembling into a one-dimensional long chain structure as a whole. in the transverse direction (figure 4d), under the guidance of its special inner hydrophobic and outer hydrophilic structure, β-cd assembles a planar two-dimensional structure. finally, β-cd self-assembled into a three-dimensional ordered supramolecular shell, which became a reticular limiting template to guide the growth of selenium grains. selenium nanocrystals are deposited and grown into selenium spheres. with the increase of the concentration of β-cd, the volume of the cross-linked macromolecules will increase, and the particle size of the selenium materials grown by its guiding limit will inevitably increase. based on the above experimental results, the optimal concentration of β-cd solution (0.5 g/l) was determined to be 8.0 ml (equivalent to 4.0 mg β-cd). 3.4 influence of reaction temperature on product morphology using the experimental method described in step 2.2, the amount of soft template β-cd solution was 8.0 ml (equivalent to 4.0 mg β-cd). the reaction temperature was set at 90, 110, 130, 150, 170 ℃ for 2 h, and the single factor comparison test was conducted. the morphologic changes of ultrasonic cleaning products were shown in figure 5(a) ~ figure 5(e). figure 5. effect of reaction temperature on the morphology of products. 67 a small number of light red products were prepared at 90 oc. the morphologies were relatively smooth selenium spheres with a diameter of about 500 nm, as shown in figure 5(a). at 110 oc, slender selenium filaments grow on the surface of some selenium pellets. the surface of these selenium pellets is uneven, and the protrusions are suspected to be selenium buds without growth and formation, as shown in figure 5(b). at 130 oc, selenium filaments increased significantly, and selenium appeared as shown in figure 5(c). the products prepared at 150 oc contained both smooth selenium balls and a selenium ball with large selenium buds, shaped like sea urchins, as shown in figure 5(d). when the reaction temperature was set at 170 oc, the selenium pellets disappeared and the products turned into large particles bonded together, as shown in figure 5(e). relevant studies have shown that β-cd has different inclusion ability at different temperatures[7]. at low temperature, β-cd has a strong inclusion ability for (quasi-) metallic elements, and it is easy to obtain selenium pellets with large particle size under the guidance of β-cd limit, as shown in figure 5(a). with the increase of reaction temperature, the solubility of β-cd increases, which is conducive to the formation of cysteine-cyclodextrin copolymerization hydrogel that can better disperse and stabilize selenium grains, resulting in the emergence of fine selenium buds and selenium branches, as shown in figure 5(b) and (c)[8]. however, heating also has adverse effects: on the one hand, it will intensify the thermal movement of grains, increase the probability of collision and binding of crystal nuclei, and destroy the stability of β-cd soft template on selenium grains, resulting in the fusion of small selenium filament and selenium bud, and selenium bud becomes significantly thicker. as shown in figure 5(d), johnson’s sintering model shows that reaction temperature has a great influence on grain growth, and grain agglomeration will become more serious with increasing sintering temperature[9]. therefore, high temperature causes selenium crystals to “sinter” together, as shown in figure 5(e). according to the above facts, the optimum temperature for the growth of selenium was determined to be 130 oc. 3.5 effect of reaction time on product morphology using the experimental method described in step 2.2, the amount of fixed template agent β-cd solution (0.5 g/l) was 8.0 ml, and the reaction temperature was set at 130 oc. the reaction time was set as 0.5, 1, 2, 3 and 4 h, respectively, and the single-factor comparison test was conducted. the products obtained were repeatedly cleaned by ultrasonic and detected by sem, as shown in figure 6(a) to figure 6(e). the products prepared by reaction of 0.5 h are selenium balls of different sizes, as shown in figure figure 6. effect of reaction time on the morphology of products. 68 6(a). after heating for 1 h, a large number of selenium buds appeared, as shown in figure 6(b). after 2 h of reaction, selenium buds grew and cross linked with each other, and a large number of selenium shoots began to emerge, as shown in figure 6(c) and figure 6(c1). after reaction for 3 h, there were few selenium buds, selenium filaments and selenium branches, and cracks appeared on the surface of selenium ball, as shown in figure 6(d). after heating for 4 h, the selenium pellets continued to increase, and the diameter was 2–4 μm. the selenium sticks were obviously stuck together, as shown in figure 6(e). the morphology was not significantly different from that of the product after heating for 3 h. the reason for the above changes may be that β-cd can self-assemble into supramolecular shells through adsorption and hydrogen bonding, but this process requires time, and prolonged reaction time is conducive to β-cd self-assemble into supramolecular shells[10]. under the guidance of β-cd supramolecular shells, selenium crystals grow in a limited position in this three-dimensional template, and finally the dendritic selenium with neat appearance is obtained. however, at higher temperatures, the longterm reaction will lead to aggregation and fusion of small-scale products. gao shanmin et al. pointed out that there is a competitive process of grain dissolution and crystallization in the reaction system[11]. if the reaction time is prolonged at a higher reaction temperature, the crystallization speed will gradually exceed the dissolution speed, resulting in the gradual reduction of small grains, the continuous settlement of large grains, the smaller and smaller suspended grains in the solution, and the product has an obvious tendency of floccumulation. based on the above facts, the optimum reaction time for selenium growth was determined to be 2 h. figure 8. hrtem spectra of branched micro nano selenium. 3.6 xrd and tem characterization the branched selenium prepared under the corresponding experimental conditions in figure 6(c) was naturally dried and made into powder. dandong y-4q x-ray diffrotometer was used for detection. the xrd pattern (figure 7) showed that the absorption peak intensity was weak, but the background intensity was large. the whole peak shape was basically consistent with the tripartite selenium absorption peak data in jcpds card (no.73-0465), and only a few weak absorption peaks could not be displayed. figure 8 shows the hrtem (high resolution transmission electron microscopy) pattern of the dendritic selenium. the illustration shows the saed (selective electron diffraction) pattern of the corresponding region. the aperture diameter is 0.1 μm, and the diffraction pattern shows that the product has a single crystal structure. the crystal lattice fringes in figure 8 are clear, indicating that the product has good crystallinity. the distance between adjacent crystal planes is about 0.380 nm, which is very close to that of t-se (100) crystal plane at 0.3781 nm. the above figure 7. xrd pattern of branched micro nano selenium. 69 detection indicated that the prepared selenium was tripartite t-se under experimental conditions, and the micro-nano se0 of such a dendritic structure had not been reported in the literature before. 4. conclusions the results showed that the reducibility of l-cys•hcl was weak, and the yield of selenium was not high. β-cd soft template has a great influence on the morphology of selenium nanoparticles. β-cd has hydrophilic outer surface and hydrophobic inner surface, under the combined action of hole effect, coordination effect and steric hindrance effect, it can effectively inhibit the growth and agglomeration of selenium nuclei, slow down the growth rate of selenium nuclei, promote the rapid nucleation and slow growth of selenium crystals, and finally obtain dendritic selenium with unique morphology. selenium spheres with large particle size also appeared in the test. according to the hydrogen bond theory explaining powder agglomeration, the hydrogen bond initiated by hydroxyl group is the root of hard agglomeration[12]. β-cd, as a macromolecular, contains a lot of hydrogen bonds, and its ability as a soft template to stabilize nanoparticles is weaker than that of anionic surfactant. hence, the particle size of selenium crystal prepared with β-cd as template is large. in this study, the amount, reaction temperature and reaction time of β-cd have different effects on the morphology of the product. after comparison, the most suitable reaction conditions for the growth of branch selenium are as follows: adding in 0.6306 g l-cys•hcl in turn 8.0 ml of β-cd solution (0.5 g/l), 80 ml of h2seo3 solution (0.05 mol/l), and n (l-cys•hcl): n (h2seo3) = 1:1 in the reaction system. after the reaction kettle is shaken evenly, it is placed in a blast drying oven and heated at 130 ℃ for 2 h to prepare gray products. the gray products are cleaned for many times with deionized water and industrial alcohol, centrifuged and naturally dried to obtain dendritic micro nano selenium. conflict of interest no conflict of interest was reported by the author. acknowledgements project: provincial key research project of natural science in anhui province “preparation and properties of nano-selenium compound nutrition sustained-release agent” (kj2014a246). references 1. du y, liu x. research progress of trace element selenium (in chinese). studies of trace elements and health 2007; (3): 56–58. 2. li l, lin q, chen h. the biological functions of selenium and research development of se-enriched 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department of biotechnology, lahore college for women university, punjab 44444, pakistan; asmashahzad87@gmail.com abstract: gold nanoparticles (aunps) have been known to possess exceptional electric, biochemical, and optical characteristics and are ‘the topic of discussion’ these days, especially relating to the field of biomedicine. several plants, bacteria, and fungi have been utilized for the generation of aunps, besides other physical and chemical methods. while some studies have been reported with gold nanoparticles, less are aimed at fungi and its optimization factors. these parameters can allow us to design aunps of our choice depending on the use. the present review focuses on and inspects aunps with green synthesis through fungus optimization parameters followed by applications, aiming specifically at their antibacterial activity. their antibacterial characteristics can open new doors for the pharmaceutical industry in the future. keywords: gold nanoparticles; green synthesis; optimization; fungi; antibacterial activity 1. introduction nano-biotechnology is the subdivision of nanotechnology that is expanding day by day and includes the development and fabrication of nanomaterials [1]. nanoparticles (nps) can be generated by utilizing several plants, bacteria, and fungi by using different approaches comprising of physical, chemical, and biological methods. various microorganisms can be employed for both extracellular and intracellular nanoparticles owing to their incomparable characteristics; however, separation of intracellular nps is laborious and requires extra processes [2]. the credit for discovering aunps in particular goes to michael faraday, who in 1857 observed these small particles (˂100 nm) radiating a red colour. this phenomenon is also known as the tyndall effect, which is in fact dispersion of the light as a ray of light passes through a colloid. although these particles were not visible at that time, they gave a ‘golden-coloured glow’. it is known that light’s wavelength is more in contrast to the gold nanoparticles owing to their size. this is the basis of present-day nanotechnology, and it has allowed a lot of researchers to work in this field [3]. the nanoparticles can easily be characterized using multiple instruments; their varying size and morphology in particular can be identified by using transmission electron microscope (tem), scanning electron microscope (sem), zeta sizer, or atomic force microscope (afm). moreover, their surface plasmon resonance (spr) band can be detected by using uv-vis spectrophotometer whereas their functional groups can be exposed using fourier transform infrared spectroscopy (ftir). in order to find out the nature of a certain nanoparticle, x-ray diffraction (xrd) is also carried out [4,5]. additionally, the process of nanoparticle formation can be enhanced by altering citation shahzad a. biosynthesis of gold nanoparticles via fungi: a review of their optimization, antibacterial action and applications. characterization and application of nanomaterials. 2024. 7(2): 8205. https://doi.org/10.24294/can.v7i2.8205 article info received: 26 july 2024 accepted: 12 october 2024 available online: 28 october 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 8205. 2 a few factors like biomass weight of fungi, temperature, synthesis or incubation time, ph, and concentration of substrates, etc. still further studies are necessary to regulate the size, assembly, conformation, and other physico-chemical characteristics of nps developed by employing fungi [5,6]. 2. methods of nanoparticle development there are three ways to generate nanoparticles: firstly, physical, then chemical, and finally biological. physical techniques include ball milling, laser ablation, lithography, thermal evaporation, etc., which basically require the application of external force. these procedures are high maintenance and call for higher temperatures in addition to reaction time. on the other hand, chemical procedures are most commonly used to produce nps but use and emit chemical and harmful gases along with contaminated end products. additional steps like hydrolysis and reduction are also part of the chemical synthesis. lastly, the biological technique has been gaining popularity these days and involves extracts from various plants, microbes like fungi, bacteria, algae, and viruses for its production. green synthesis of nanoparticles is not only harmless towards the environment and cost-effective but is known to have fewer inadequacies in contrast to the chemical and physical techniques discussed above; additionally, they are also excellent candidates for upscaling. hence, fungi in particular have been selected for much research these days due to their easy availability, harmless nature, wide variety, and novel strains. fungi are also known to produce natural metabolites and excrete enzymes and proteins that act as capping agents and support the reduction process during np formation. moreover, fungi itself have more surface area owing to their mycelial structure, releasing more proteins in return, forming nps rapidly and effectively [7]. 3. attributes of gold nanoparticles many metals have been employed for the synthesis of nps, but gold nanoparticles have amazed researchers due to their unmatched properties, which allow alterations on their surface. gold nanoparticles, specifically, are known for their surface plasmon resonance (spr) phenomenon and give out a range of colours, i.e., red, purple, and orange, as the size of nps increases. owing to this factor, the spr band is formed between 500 and 550 nm, which is validated later by a uv-vis spectrophotometer; moreover, highly charged particles have the ability to either be suspended or stay diffused in a solution, as hammami and alabdallah [5] described. gold nps have enhanced adsorption capacity along with great biocompatibility, chemical, and opto-electronic capabilities, which also determine their morphology, permitting them to be used in various sectors, especially biomedical. gold is a valuable metal known for its stability and for being inert henceforth allowing it to be used in many applications, specifically its role in antibacterial studies, which has gained popularity among researchers as microbe resistance towards antibiotics has become a dilemma these days [8]. characterization and application of nanomaterials 2024, 7(2), 8205. 3 4. green technique by employing fungi by using the green technique and choosing fungi over bacteria and plant extracts has more benefits, like they can withstand additional agitation along with pressure. another important factor is temperature, which makes fungi a suitable candidate for biosynthesis; also, their scaling up is easy [8]. quite a few inspections were aimed towards the biosynthesis of aunps by a variety of fungi giving off different sizes (figure 1), such as candida albicans (15 nm), aspergillus niger (20 nm), fomes fomentarius (50 nm), ganoderma lucidum (30 nm), gliocladium roseum (45 nm), lentinula edodes (35 nm), myrothecium verrucaria (40 nm), phanerochaete chrysosporium (40 nm), pleurotus florida (50 nm), schizophyllum commune (45 nm), trichoderma harzianum (40 nm), and tolypocladium ophioglossoides (60 nm) [9]. after their generation, they were used in various applications like drug delivery, biosensors, preservation of paintings, effluent treatment and management, antifungal glazes, food preservation, optics, and environmental monitoring [8]. figure 1. overview of the fungi-mediated synthesis of gold nanoparticles. similarly, many more reports regarding aunps from fungi include pleurotus sajor-caju [10], fusarium solani [11], jahnula aquatica [12], botryosphaeria rhodian [13], aspergillus terreus [14], pleurotus ostreatus [15], aspergillus tamarii [16], ganoderma neo-japonicum [17], morchella esculenta [18], cladosporium sp. [19], and aspergillus flavus, etc. [20]. furthermore, aunps were also produced by employing some strains such as alternaria sp. (9.5 nm), trichoderma viride (24.7 nm), ganoderma sessile (13.6 nm), trichoderma asperellum (16.4 nm), and botrytis cinerea (92.9 nm) [21]. additionally, some more research on aunps was also conducted using helminthosporum solani, neurospora crassa, [22] penicillium citrinum, m. phaseolina, [3] fusarium oxysporum, colletotrichum sp., fusarium semitectum, phoma glomerata, etc. with varying sizes and shapes. it was observed that aunps were generated both intracellularly and extracellularly by trichothecium sp. with a variety of shapes consisting of triangular and spherical forms [23]. characterization and application of nanomaterials 2024, 7(2), 8205. 4 5. mechanism of gold nps there are many benefits in the generation of gold nps via fungi, such as little or no energy is required, additional supplements or agents are not needed, and they are highly functional. furthermore, the process of production is quite simple, followed by purification. during research, several fungi have been utilized in the formation of gold nps, as mentioned previously, and they can be both extracellular (outside the cell) and intracellular (inside the cell) with varying unique morphologies. it has been reported that phenols, peptides, and enzymes located on the outside of the fungal cell are mainly in charge of the extracellular production of gold nps, whereas the intracellular process basically revolves around the concept of absorption through mostly proteins plus enzymes and reduction of gold ions occurring within the cytoplasm or in the cell wall through enzymes or proteins. we can attain nps with varying sizes and forms along with unique characteristics by optimizing the parameters. in order to improve the function of nps, we can also adjust substrate concentrations, ph, process time, temperature of incubation, biomass weight, etc. [24]. it was reported earlier that reduction within the aunps occurs within the cytoplasm or the surface of the cells due to the presence of nicotinamide adenine dinucleotide phosphate (nadph) or nicotinamide adenine dinucleotide (nadh). additionally, it was exposed that reduction occurs firstly with au+3 which is further reduced to au+ and finally into its elemental form, i.e., au0, but the enzymes or proteins involved are yet to be investigated [25]. moreover, it was also reported that other metabolites, i.e., flavin adenine dinucleotide (fad)-dependent glutathione reductase alongside nadh, have performed a major task in the generation of aunps via fungi. other than that, quinine was also involved in the process of reduction along with phytochelatin when substrate concentration was increased to a certain level [26]. mainly, the development of nanoparticles involves two processes occurring side by side: first, reduction, which transforms au+3 into au0; and second, particles' growth and equilibrium amongst them are monitored by capping agents. the nps are guarded by these ligands, which prevent any form of aggregates and additional development with the assistance of electrostatic charges. it is also reported that some amino acids or chemical metabolites are capable of working as both reducing and capping agents. proteins and enzymes use van der waals forces and adhere to the surface of gold nps or alternatively attach by bonds among sulfur along with nitrogen atoms within the protein. they are known to bind even at points of zero charge, but it decreases their bonding capability [27]. 6. optimization factors the aunps can be acquired by altering several parameters one at a time of our choice with varying physical and chemical properties. some of the important factors are discussed below in table 1. characterization and application of nanomaterials 2024, 7(2), 8205. 5 table 1. synthesis of gold nanoparticles by various fungi and their characterization. fungi incubation conditions size (nm) zeta potential (mv) spr band (nm) functional groups shape antibacterial studies references cladosporium sp. 1 mm, (haucl4) fungal extract/ haucl4 (70 ml: 30 ml) temperature 37 ℃ agitation rate 180 rpm reaction time 24/h 5–10 524 o-h c=o spherical, irregular [19] epicoccum nigrum 1 mm, (haucl4) temperature 28 ℃ dark condition agitation rate 180 rpm reaction time 24/h 2–30 550 o-h c=o c-h quasispherical bacillus subtilis with 100, 200, 300 mg/l (aunps) [28] fusarium chlamydosporum 0.1 mm, (haucl4) cff (10 ml) temperature 25 ℃ dark condition 120 rpm agitation rate reaction time 24 h 25 g biomass weight 22.1 37.6 530 spherical escherichia coli and pseudomonas aeruginosa [29] fusarium solani temperature 25 ℃ dark condition concentration 1 mm (haucl4) ph 8.5 fungal extract/ haucl4 (1: 99) incubation time 48 h 40–45 2.5 551 c-n c-h needle, flower [11] jahnula aquatica reaction time 48 h reaction temperature 70–90 ℃ 8, 20, 60 −43.5 560 n-h o-h c=o c-h c-n c-c spherical [12] aspergillus flavus filtrate concentration (10%) haucl4 1mm tween 20 (0.1%) incubation period 30 min with light temperature (30 °c) reaction time (15 min) 10–50 positive 530 c-o-o c=o c-n n-h o-h spherical, hexagonal, rectangular b. subtilis, s. aureus, e. coli, p. aeruginosa yeast, c. albicans no zoi observed [20] pleurotus ostreatus ph 5 salt concentration (5mm) agitation 200 rpm incubation time 48 h temperature 30 ℃ ratio of salt and ecf (5:1) 10–30 −24.0 550 n-h spherical b. subtilis (30 mm), e. coli (30 mm), s. aureus (30 mm), c. albicans (13 mm) [15] morchella esculenta 1mm hauci4 extract: gold chloride solution ratio (1:5) 16.51 511 o-h c=c c-h c=o cubic s. aureus p. aeruginosa (10 mm) [18] fusarium oxysporum temperature 37 ℃ and 80 ℃ 50 −28 541 spherical [30] candida tropicalis temperature 37 ℃ ctab 12.4 +57.5 482 spherical [31] characterization and application of nanomaterials 2024, 7(2), 8205. 6 table 1. (continued). fungi incubation conditions size (nm) zeta potential (mv) spr band (nm) functional groups shape antibacterial studies references thermoascus thermophilus ph (4.7) temperature 35.0 ℃, 45.0℃ and 55.0 ℃ reaction time 3–20 h czapek-dox medium 40 450– 650  spherical [27] fusarium acuminatum acidic ph 1 mm (gold chloride) temperature 37 ℃ 8–28 520– 550 spherical [32] aspergillus trinidadensis 2–12 ph 48 and 72 h culture ages 1 mm substrate concentration shaking (160 rpm) biomass weight (80–240 mg/ml) 35 530– 570 n-h c-n c=o spherical [33] bipolaris tetramera 1 mm substrate concentration 58.4– 261.7 570 spherical, triangular, hexagonal b. subtilis, b. cereus, s. aureus, e. coli, e. aerogenes [34] agaricus bisporus 1 mm of haucl4 solution (10 ml) 1 ml of mushroom extract 25 −45.8 510– 570 n-h c-n c-o-c c-oh spherical [35] aspergillus terreus haucl4 solution (1mm) ph (4–12) temperature (25°c to 60 ℃) fungal extract intensity (10–200 ppm) shaking (150 rpm) haucl4 solution (1 mm) ph (5–10) 10–16 2–29 −28.2 536 550 o-h c-h c=o c-n c-h, n-h −sh spherical elongated, triangular, rod s. aureus, v. cholera, s.typhimurium escherichia coli [36] [37] candida rugopelliculosa 1 mm of haucl4 solution temperature (35 ℃), shaking (120 rpm) 10–30 550 c-h c=o c-n −nh2 [38] pycnoporus sanguineus substrate concentration (0.5–2.0 mm) temperature (30 ℃), shaking (165 rpm) 29.3– 61.4 520– 560 o-h c=o c-n c-h −nh2 spherical, pseudospherical, triangular, triangular, pentagonal hexagonal [22] 6.1. temperature and time of synthesis nps typically attain large-size to small-size during the synthesis at high temperatures. usually, elevated temperatures favour bigger nps as it is suitable for growth alongside the nucleation stage. in contrast to this, lower temperatures support ‘growth’ leading to an increase in the rate of reaction. due to an alteration in temperature, nps of many conformations are generated, and the number of substrates characterization and application of nanomaterials 2024, 7(2), 8205. 7 secreted is also affected, which also shifts the equilibrium between growth and nucleation. in order to obtain small-sized nps, higher temperatures are needed, which will trigger the reduction rate, use up the metal ions, and obstruct secondary reduction progress, which can still take place [39]. many studies have evaluated the aunps with varying temperatures. in a study with pleurotus ostreatus, aunps were optimized by employing varying temperatures such as 30 ℃, 37 ℃ and 40 ℃. it was seen that 30 ℃ gave the highest yield of aunps [13]. aspergillus terreus was also utilized for the generation of gold nps, and temperature was optimized at 30 ℃ within a period of twelve hours [14]. moreover, verticillium luteoalbum was also used for the formation of gold nanoparticles, and varying temperatures of 25 ℃, 35 ℃ and 50 ℃ were assessed. it was observed that rapid development of nps occurred with rise of temperature in contrast to lower temperatures. most of the growth and development was revealed in the first hour with a spherical shape and size of about 10 nm. at a temperature of 50 ℃ no further changes were detected [40]. in another study with fusarium oxysporum, aunps were synthesized after incubation with two varying temperatures, one at 37 ℃ and subsequently at 80 ℃. aunps slightly above 50 nm were generated, but it was also seen that at higher temperatures they are more suitable, taking less time, and it was realized that this also allows the formation of smaller nanoparticles [31]. similarly, in a study with aspergillus flavus, various temperature ranges were applied and aunps were monitored; temperatures from 20 ℃ to 100 ℃ were analyzed. in this study, 30 to 40 ℃ proved to be the most suitable for monodispersed aunps, whereas after 60 ℃ a decline was observed, and later at 80 ℃ clumping of the nanoparticles was noticed. no aunps were formed at lower temperatures of 20 ℃ [20], whereas the time of synthesis was observed from 25 min to 55 mins. it was detected that the gold nps started forming right after 15 mins of mixing cff and gold chloride solution. it is known that time of reaction plays a significant role in molding the shapes and sizes of any nanoparticles, together with the yield of nps [41]. in the recent studies, many shapes have been revealed with the changes in temperatures with aunps, such as spherical, triangular, hexagonal, etc. it was stated that generation of nps can be boosted by raising the temperature up to 50 ℃ and substrate concentration up to 0.7 mm. hammami and alabdallah [3] found that the ideal temperature for the production of aunps was between 28–55 ℃ by maintaining the incubation temperature of the fungal cell-free extract [3]. 6.2. ph during the synthesis of nanoparticles, a change in ph can play a significant role. it is reported that at a low ph, the biomass itself clutches onto more positive charges and produces small-sized nanoparticles rapidly due to the weakened reduction power and binding site being nearby. moreover, ph plays a vital role in the initial stages of aunp generation with respect to size and shape. it was described that gold nps specifically do not form at lower ph, but greater ph values help establish extracellular aunps. furthermore, an increase in ph means a higher rate of reaction along with a reducing rate, thus producing a variety of shapes and sizes [42]. characterization and application of nanomaterials 2024, 7(2), 8205. 8 in an interesting investigation with the fungus verticillium luteoalbum, ph was adjusted several times using different levels, commencing from 3, 5, 7, and later 9. it was established that altering the ph greatly impacts the shape and size of nps. a size of 10 nm aunps (spherical) was observed with a ph of 3, and a similar outcome was realized. furthermore, a ph 5 exposed triangular-shaped or rod-shaped nps as well after the synthesis. ph 7 and 9 revealed small-sized nanoparticles with spherical shapes [40]. a similar study with the fungus penicillium brevicompactum was employed for the formation of gold nps, and its ph was optimized by varying it between 5 and 8 [43]. besides, aspergillus terreus was also utilized for the formation of gold nanoparticles, and its ph was also optimized. no change was noted with ph 1 and 2, whereas at ph 3, pink to violet colour transformations were observed. later, at ph 7, stable nps were seen, and colour intensified at a ph of 10, with little or no synthesis at higher ph [14]. likewise, in a study with aspergillus flavus, various phs commencing from 3 to 4 to 7, 9 and 12 were tested to enhance the functioning of gold nps, but it was noted that alteration in ph did not influence the process of np formation. rapid synthesis was observed with the distilled water alone, and changes in ph only reduced the absorbance capacity, so it can be said that the reduction process was disturbed due to fluctuations in ph within the cell-free filtrate (cff) [20]. another experiment with pleurotus ostreatus evaluated aunps; they were optimized by applying ph 5, 6, and 7. it was established that a ph of 5 gave a suitable outcome with aunps; however, little or no effect was felt on the nanoparticles themselves [15]. moreover, another study with aspergillus trinidadensis described the effect of ph on the stability of aunps. varying phs from 2 to 12 were applied to the aunps for a period of 12 h, and it was revealed that a ph of 7.4 enhanced the monodispersion and nps were steady under all the tested ph ranges [33]. another study states that the most optimum ph for aunps development is between 5 and 9 of the cell-free extract that can be easily maintained with the help of buffers. it was also stated that a change in ph can alter the conformation of aunps, like it was observed that a lower ph of 2 revealed rod-shaped (large) nps, whereas a ph of 4 produced smaller rods. likewise, it was noted that ph of 8 and 9 normally yielded spherical to oval-shaped nps, while ph of 10 exposed rod-shaped morphology, though nanowires were exhibited at a ph of 11 [3]. in an examination of aunps with aspergillus terreus, it was noted that nps of varying sizes (20 to 29 nm) were developed with varying ph ranges. at a ph of 8, nps were mostly polydispersed, establishing themselves with rod and spherical conformation, while at a ph of 5 to 7, nps with triangular to rod-shaped shapes were attained along with broad spr peaks. ph 9 and 10 showed monodispersed nps, and size varied from 10 nm to 19 nm, and it can be stated that there was a reduction in size with the increasing ph towards alkalinity [37]. this also shows that the environment was ideal for the aunps and led towards small-sized nanoparticles. characterization and application of nanomaterials 2024, 7(2), 8205. 9 6.3. agitation rate optimizing the rate of agitation is important, as it plays a substantial part in the reduction of the nanoparticles. static agitation will give low absorbance along with a low reaction rate during the process of the development of nanoparticles, resulting in low performance and efficiency in contrast to the experiment conducted with agitation [44]. however, in a study with pleurotus ostreatus, aunps were optimized by using varying agitation rates, i.e., 100 rpm, 150 rpm, and 200 rpm; nevertheless, it was noted that the most suitable agitation rate was 200 rpm, which gave the greatest response [15]. similarly, in a study with aspergillus flavus, it was analyzed that the agitation speed of 120 rpm did not affect or boost the process of gold nanoparticle formation [20]. it was also noted in a study that trichothecium sp. produced intracellular aunps quickly with a spherical shape with shaking. however, surprisingly, without agitation, it produced both intracellular and extracellular nanoparticles, giving rise to triangular and spherical nps [23]. 6.4. substrate concentration metal salt concentration also leaves an impact on the size of the nanoparticles. it was described that nanoparticles may develop with very large sizes if the concentration is extremely high, as struggle between the capping agents and ions (metal) may possibly escalate to form nps, and excess substrates may form aggregates [45]. many studies were conducted to optimize the aunps with fungi, and interesting results were revealed in an investigation with aspergillus terreus. 1 mm substrate concentration proved to be the most optimum even though aucl3 of many intensities was applied from 1 mm to 10 mm, but they simply failed to generate nps [14]. likewise, after investigation with penicillium brevicompactum, it was seen that after 2 mm gold, nps started to form aggregates and also increased in size, probably due to saturation of the environment [40]. in another study with pleurotus ostreatus, aunps were optimized by using different substrate concentrations at 1 mm, 2.5 mm, and 5 mm. the most optimum substrate concentration was found to be 5 mm and showed a rapid reduction soon after its addition [15]. similarly, in a study, aspergillus flavus gold chloride solutions of varying molarities starting from 0.5 mm to 2 mm were applied to control the functionality of aunps. results displayed that at 1 mm some synthesis took place, whereas at 0.5 mm a broad spr band was revealed, while 2 mm exposed reduced absorbance [20]. it was also stated in an investigation that lower intensities of substrates along with reduced weight of biomass give rise to aunps with a smaller size, but on the other hand, their yield becomes restricted if upscaled [8]. 6.5. fungal filtrate fungal filtrate concentration clearly effects the formation of nanoparticles. in order to analyze fungal filtrates and the functionality of aunps, varying concentrations of 5% to 40% were applied in a study with aspergillus flavus. it was seen that at a higher percentage of fungal filtrate, a broad spr band was obtained in contrast to a reduced concentration of 5 to 10%, which probably occurred due to the characterization and application of nanomaterials 2024, 7(2), 8205. 10 presence of exceedingly reducing agents [20]. in a study with agaricus bisporus, it was seen that fungal filtrate of ‘1 ml’ generated aunps of approximately 25 nm with great stability of −45.8 mv by zeta sizer [35]. 6.6. biomass weight biomass weight is another important factor that must be kept in mind while optimizing nanoparticles. it was reported that if the biomass quantity is increased during the synthesis of nps, its size begins to modify, and if the enzymes become saturated while the process is taking place, researchers may have to deal with largesized nps as the enzymes are secreted in excess, which might lead to aggregation later [46]. another study was conducted using aspergillus terreus to produce nps with varying biomass weights, such as 10 g/100 ml to 30 g/100 ml. it was noted that the increase in the biomass weight did not work for the biosynthesis of gold nps, probably due to the occurrence of additional reducing agents; however, at a weight of 10 g/100 ml, np formation was observed as the environment must be in equilibrium and not saturated with enzymes [14]. furthermore, aspergillus trinidadensis was also studied with varying biomass intensities until optimization was achieved. initially, experiments were conducted with biomass of 160 mg/ml; later, more ranges were introduced, starting from 40–240 mg/ml with 1 mm of haucl4 solution. finally, 4 g (160 mg/ml) of biomass was found to be ideal along with the rest of the optimization variables like culture, temperature of incubation, ph, etc. [33]. 6.7. fungal culture age in an inspection with the fungus verticillium luteoalbum, different time periods, i.e., 24 h, 48 h, and 72 h, were applied and aunps were monitored. initially it was observed the fungal culture age did not seem to affect the aunps, but it was perceived that as the reaction time progressed and culture grew old, generation of the nps was reduced, which probably means the rapid development occurred in the exponential phase, reducing the gold ions right away. the older culture hence has a low rate of reduction and reaction and is less active, declining the production of nps. at low reaction rates, spherical particles were formed in contrast to high rates, which yielded rods and a platelet-like appearance [40]. furthermore, in an investigation with aspergillus trinidadensis, the effect of different fungal cultures was examined with gold nanoparticles. cultures of 36 h, 48 h, 72 h, and 96 h were employed with 160 mg/ml intensity, and it was observed that 72 h produced the best results and was optimized using these conditions [33]. 6.8. supplementation with surfactants microbes such as bacteria, fungi, and yeast are known to produce extracellular bio-surfactants comprising both hydrophobic and hydrophilic elements. stabilization of the nanoparticles is usually established by the addition of surfactants during the generation of nps that consist of mostly fats and sugar. due to the addition of surfactants, an even distribution occurs with the nps colloidal solution; moreover, it characterization and application of nanomaterials 2024, 7(2), 8205. 11 is eco-friendly and non-hazardous. they are also utilized for designing nps with varying shapes and sizes [47]. likewise, in a study with aspergillus flavus, surfactants were added to enhance the performance of gold nps. various surfactants such as sodium dodecyl sulphate (sds) 0.1% along with tween 20, 0.1% were used in the experiment with aunps. it was observed that tween 20 stabilized the aunps, and the spr band persisted and remained unaffected for approximately three months, whereas others were able to keep them steady for less. it was also reported earlier that surfactants like tween 20 are biocompatible; moreover, they are utilized for surface modifications [20]. 7. antimicrobial activity antimicrobial resistance has become a major problem all over the globe these days. it is basically the capability of the microbes to resist a variety of antibiotics, hence making the medicine ineffective [48]. the entire concept of antimicrobial activity of gold nanoparticles revolves around the gram-negative and gram-positive bacteria occurring on the surface of the membrane. it was previously described that the reduction of adenosine triphosphate (atp) is perceived, along with obstruction of ribosomal structures and an increase in oxidative stress, in the presence of aunps; hence, they are successful antimicrobial agents. after interaction between microbes and nps, an increase is felt in the production of ros, which initiates degeneration together with degradation in the cell membrane and overall cell structure, proving their antibacterial nature (figure 2) [41]. it was reported earlier that small nanoparticles approximately 20 nm are able to penetrate the cell wall of bacteria and cause degradation in organelles, hence leading towards death, which makes aunps a good contender for antibiotics [49]. figure 2. antibacterial activity of gold nanoparticles. size and dimensions both play a significant role in determining the efficiency of the antibacterial properties of nanoparticles. consequently, gold nanoparticles with smaller sizes usually demonstrate a substantial amount of antibacterial activity [50]. thus, a study with inonotus obliquus showed antibacterial properties of gold nps against various stains like s. aureus, e. coli, and b. subtilis. after analysis, zoi were characterization and application of nanomaterials 2024, 7(2), 8205. 12 noted down for the afore mentioned strains. a zone of 14 nm was observed with e. coli, whereas s. aureus displayed 16 mm while b. subtilis established a zoi at 12 mm. in earlier studies, it was reported that the positive charge occurring within the gold ion directs the antimicrobial activity of any microbe. the cell membrane supporting a negative charge along with nps carrying a positive charge makes the whole mechanism work. it was also proposed that cell death occurs when the nps creates perforations within the cell walls elevating its penetrability, forcing the cellular environment to change and contents to leak, hence another idea towards mechanism [18]. likewise, in another recent investigation with aspergillus terreus, antibacterial activities were revealed, showing maximum zoi against vibrio cholerae (9.31 ± 0.14) and staphylococcus aureus (8.58 ± 0.28) with aunps at 400 μg/ml. the antibacterial activities are again thought to be using processes affiliated with ros or deterioration of enzymes or cell membranes to kill bacteria [43]. similarly, in another evaluation with bipolaris tetramera, antibacterial activity was also assessed. the bacterial pathogens like b. subtilis, b. cereus, s. aureus, e. coli, and e. aerogenes were tested against aunps with varying concentrations from 10 μm to 150 μm. the highest zoi of 1.3 cm was formed against s. aureus at a concentration of 100 μm, whereas the lowest was observed with e. coli at 0.5 cm with 100 μm intensity. overall, 10 μm formed the lowest zoi of less than 0.5 cm with all the pathogens, and it was noted that as the intensities of the aunps were increased, the antibacterial activities also increased, which could be due to its small size [34]. another study with aspergillus terreus exposed the antibacterial abilities of gold nps against some stains like s. aureus, v. cholera, and s. typhimurium with concentrations ranging from 100 to 400 µg/ml. after investigation, it was revealed that maximum zoi appeared at 400 µg/ml with s. aureus and v. cholera, i.e., 8.58 ± 0.28 mm and 9.31 ± 0.14 mm, respectively. other concentrations did not reveal any significant results [36]. 8. applications aunps are known to have many applications in different fields of life as they occur in their natural form (figure 3). firstly, as the gold nps are biology compatible and less harmless, they are utilized in drug deliveries and are used in early detection for various ailments related to cancer and heart along with gene therapies [42] and photoacoustic imaging [48]. the anti-tumor activities with the aunps are being carried out by employing varying categories of nps, which include nanoshells, nanotubes, nanostars [51], nanocages, etc. these are inserted in the body, which then incorporate themselves into the tumor; later, they are subjected to infrared followed by heat, which destroys the cancerous cells after raising the temperature, avoiding the healthy cells. it is an efficient tool for the treatment of cancer without comprising any more healthy cells. two of these successful methods include thermo-chemotherapy (tct) and gene therapy (gt), which are worth mentioning. aunps have also proved themselves in immunotherapy, where these small-sized nps can pass through and penetrate various tissues, such as lymphoid tissue, and harm the immune cells [3]. characterization and application of nanomaterials 2024, 7(2), 8205. 13 also, they are being used as reliable antimicrobial agents against various infections [52]. figure 3. some applications of gold nanoparticles. gold nanoparticles have also been used in drug delivery in which they were coupled up with the medicine or antibiotics using simple covalent or ionic bonds or by absorption approach. for instance, an anti-cancer treatment involved the coupling of folic acid with 13 nm aunps to interrupt the cancer cells during folate metabolism [53]. aunps have also been applied in the treatment of various skin diseases like psoriasis, pemphigus, hives, etc., and illnesses related to joints such as lupus, etc. secondly, aunps have good chemical and thermal properties, which enable them to act as sensors. they have also been utilized in cleaning of the air, like removing carbon monoxide or any odour from an enclosed space [3]. thirdly, gold nanoparticles can be controlled, their size and shapes can be varied according to your requirements, permitting them to be used in various processes, like food preservation. additionally, they are consumed in some food items as ‘nano-capsules that transfer varying nutrients without comprising the taste or its presence [3]. other applications include optics, conservation of paintings, environmental assessment, waste water treatment, and control. when fungal extract is revealed to metals, they usually generate nanoparticles from it, and it overpowers the toxic elements present within the wastewater by reducing it; hence, it develops into a less harmful form and persists the metal toxicity. in this way, the metal toxicity is reduced from varying sources, ensuring a better and cleaner environment through the use of gold nanoparticles. some species of fungi have developed high tolerance towards heavy metal pollution, like penicillium sp. and aspergillus sp. [54], but their mechanisms still need to be studied further to develop new techniques [55–58]. moreover, during the production of aunps via green synthesis, no external agent is required, so no capping agents are added, which stabilizes the nps by themselves, allowing researchers to alter their form easily [41]. besides, they can also be used as an insecticide [39] and in agriculture too [48,59]. the agriculture sector is also suffering due to depletion of nutrients and increasing human population; thus, new techniques must be developed for increasing the productivity of the crops. hence, nps are employed as agro-chemical ‘agents’ and have been introduced to eradicate characterization and application of nanomaterials 2024, 7(2), 8205. 14 pesticides. moreover, they are designed to enhance crop productivity and are being utilized as fertilizers as well. some biosensors have also been introduced to protect the crops and detect various diseases occurring in a specific crop. additionally, they are also being employed as growth regulators for the plants and help improve the overall yield of the crops [60]. 9. future perspectives and challenges even though the gold nanoparticles have proven to be non-toxic and have great potential as antibiotics, further research is required, and doses need to be administered before they can actually be used in the biomedicine field on a larger scale. experiments are essential to make sure that they are safe and can be used as drugs alone. we need to indulge in this notion a bit more, as the antimicrobial resistance and its overuse are growing day by day, and it is becoming challenging for the pharmaceutical companies to come up with novel strains for this purpose; therefore, we need to find treatments that are innovative [49]. 10. conclusion the green technique of synthesizing gold nanoparticles is an interesting approach as it is simple, safe, economical, stable, and biocompatible in contrast to old methods. after synthesis, unique shapes and sizes can be expected and controlled, which can be utilized in many applications, specifically biomedical. these intriguing aunps can be optimized according to the need by altering various parameters like temperature, ph, amount of biomass, agitation rate, surfactants or enhancers, metal concentration, etc. the gold nps are unique due to their antimicrobial properties, and their small size and large surface area are another plus, which makes them excellent candidates for future antibiotic investigations. conflict of interest: the author declares no conflict of interest. references 1. iranmanesh s, shahidi bonjar gh, baghizadeh a. study of the biosynthesis of gold nanoparticles by using several saprophytic fungi. sn applied sciences. 2020; 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dr.ayeshakausar@yahoo.com abstract: quantum dot can be seen as an amazing nanotechnological discovery, including inorganic semiconducting nanodots as well as carbon nanodots, like graphene quantum dots. unlike pristine graphene nanosheet having two dimensional nanostructure, graphene quantum dot is a zero dimensional nanoentity having superior aspect ratio, surface properties, edge effects, and quantum confinement characters. to enhance valuable physical properties and potential prospects of graphene quantum dots, various high-performance nanocomposite nanostructures have been developed using polymeric matrices. in this concern, noteworthy combinations of graphene quantum dots have been reported for a number of thermoplastic polymers, like polystyrene, polyurethane, poly(vinylidene fluoride), poly(methyl methacrylate), poly(vinyl alcohol), and so on. due to nanostructural compatibility, dispersal, and interfacial aspects, thermoplastics/graphene quantum dot nanocomposites depicted unique microstructure and technically reliable electrical/thermal conductivity, mechanical/heat strength, and countless other physical properties. precisely speaking, thermoplastic polymer/graphene quantum dot nanocomposites have been reported in the literature for momentous applications in electromagnetic interference shielding, memory devices, florescent diodes, solar cells photocatalysts for environmental remediation, florescent sensors, antibacterial, and bioimaging. to the point, this review article offers an all inclusive and valuable literature compilation of thermoplastic polymer/graphene quantum dot nanocomposites (including design, property, and applied aspects) for field scientists/researchers to carry out future investigations on further novel designs and valued property-performance attributes. keywords: thermoplastics; graphene quantum dot; nanocomposite; emi shielding; memory devices; bioimaging 1. introduction continuous advancements in the field of high-performance nanocomposites have introduced wide-ranging nanoadditives to upsurge intrinsic features of matrices, especially polymers [1]. for polymeric nanocomposites, carbonaceous nanoparticles have been distinctively used to attain desired physical properties and performance [2]. in addition to unique carbon nanoparticles, like graphene, carbon dots own further enhanced physical properties and applications [3]. in polymeric matrices, adding graphene quantum dots has been documented to develop compatible matrix-nanofiller associations depending upon its surface functionalities, matrix type, and processing strategies used [4]. particularly, polymer/graphene quantum dot nanomaterials may have physical interactions (hydrogen bonding, electrostatic, van der waals, etc.) [5] or covalent bonding to form robust interfacial contours [6]. thermoplastic polymers (a major polymer grouping) with graphene quantum dots have been investigated for superior microstructure, strength, heat stability, electrical/thermal conductivity, and a citation kausar a. graphene quantum dot for thermoplastic nanocomposites— scope and opportunities. characterization and application of nanomaterials. 2025; 8(2): 11484. https://doi.org/10.24294/can11484 article info received: 7 february 2025 accepted: 17 february 2025 available online: 7 april 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 11484. 2 number of allied properties leading to technical end uses [7]. incidentally, thermoplastic polymer/graphene quantum dot nanocomposites revealed applied potential for devices, radiation shields, and biological arenas [8,9]. this comprehensive review article covers essential design, characteristics, and technical aspects of multifunctional thermoplastic polymer/graphene quantum dot nanocomposites prepared via facile processing techniques. in this concern, we have tried to report almost all important thermoplastic matrices explored so far in the literature with graphene quantum dots for significant structural, physical, and applied characters. herein, the type of thermoplastic matrix and graphene quantum dot surface functionalities govern their mutual amalgamation and final structure-property profiles needed for next-level industrial applications. 2. thermoplastic nanocomposites the thermoplastics or thermoplastic polymers form a major cataloging of synthetic as well as naturally occurring polymers [10]. thermoplastic polymers are either amorphous or semicrystalline in nature owing to the distribution of high molecular weight polymeric chains [11]. in semicrystalline thermoplastics, a few of the macromolecular chains may get orderly arranged to form small ordered chain fragments, rendering partial crystallinity to these polymers [12]. conversely, amorphous polymers own nearly all randomly oriented chains throughout the polymer, so having no crystallinity in the backbone [13]. these polymers usually have restricted temperature ranges for rubbery to glassy state transformations and so show phase transformations above their glass transition temperatures [14]. notable physical, electrical, thermal, barrier, anticorrosion, and chemical properties of lightweight and low-cost thermoplastics have been reported for methodological applications in a myriad of applications, including automotive, civil, households, toys, cosmetics, pharmaceuticals, etc. [15]. to enhance essential features and performance aspects of thermoplastic polymers, inorganic and carbon additives or nanoadditives have been used to form composite or nanocomposite materials [16]. an important use of nanoadditives in thermoplastic polymers has been observed in upsurging the intrinsically low mechanical properties of these matrices via nanoparticle dispersion and interface formation effects [17,18]. in addition, nanoparticle dispersion may form a percolation network throughout the polymers for facilitated electron, charge, or ion flow through the nanocomposite phases [19]. in these nanocomposites, the increase in physical properties seemed to be reliant upon nanofiller functionalities, amount/orientation in the matrix, and interaction/compatibility with matrices [20–22]. in this way, by optimizing the nanofiller type, amount, and surface properties, desired highperformance thermoplastic nanocomposites have been reported [23]. 3. graphene quantum dot a quantum dot is a nanoentity having a size of a few nanometers, usually 2–10 nm, an enormously high surface area, surface features, and marvelous electronic, optical, fluorescence, and physical attributes [24]. quantum dots can be formed using inorganic or organic materials, and so resulting nanoparticles may have distinct characterization and application of nanomaterials 2025, 8(2), 11484. 3 features and technical significance [25]. among organic quantum dots, carbon-based nanodots of 5–10 nm in size have been reported [26]. carbon-structured quantum dots can be broadly listed as polymer dots, carbon nanodots, and graphene quantum dots depending upon their backbone compositions, as presented in figure 1 [27]. figure 1. carbon structured quantum dots. owing to the graphene backbone, the graphene quantum dot owns sp3 and sp2 hybridization in its structure [28]. however, unlike parent graphene, the quantum dot has zero dimensions, a size of < 10 nm, and quantum-related effects (figure 2) [29]. due to armchair or zigzag edge-related effects, valued electronic, optical, photoluminescence, magnetic, non-toxic, and biocompatible properties have been observed for graphene quantum dots [30]. here, it is important to understand key differences between carbon quantum dots and graphene quantum dots. firstly, carbon quantum dots have sp3 hybridization in structure, whereas graphene quantum dots are sp2 hybridized; secondly, carbon quantum dots are amorphous, while graphene quantum dots are crystalline in nature, having relatively superior semi-conductivity properties; third, carbon quantum dots usually have a diameter/nanosize of ˂ 10 nm, characterization and application of nanomaterials 2025, 8(2), 11484. 4 while on the other hand, graphene quantum dots may have a size of up to 2–20 nm to show the fluorescence phenomenon; finally, carbon quantum dots can be synthesized using any type of carbon precursor; conversely, precursors for graphene quantum dots must be some graphene-based material. due to progressive research on graphene quantum dot, a range of top down (carbon nano-cutting, exfoliation, solution, etc.) and bottom up (hydrothermal, chemical vapor deposition, microwave, plasma, electrochemical, chemical, etc.) synthesis methods have been used [31]. ensuing graphene quantum dots have been examined in the literature for capacitors, batteries, leds (light-emitting diodes), solar cells, sensors, nems (nanoelectrochemical systems), labs on a chip, and biomedical sectors [32]. another worthwhile application of graphene quantum dot has been observed for the formation of nanocomposites having superior physical features and applied prospects [33]. figure 2. structures of graphene, graphene oxide, and graphene quantum dots. characterization and application of nanomaterials 2025, 8(2), 11484. 5 4. thermoplastic/graphene quantum dot nanocomposites thermoplastic polymer/graphene nanocomposites have been frequently explored in the literature using innumerable matrices (polyethylene, polystyrene, poly(vinyl fluoride, nylon, and so on), synthesis techniques, advantageous physical properties and applications [34–36]. similarly, graphene quantum dots have been reinforced in the thermoplastic matrices to attain versatile nanocomposite nanomaterials [37,38]. among thermoplastics, polystyrene is one of the most recurrently used commodity polymers, having low cost, light weight, and facile processing [39]. in spite of this, brittleness of polystyrene limits its potential applications in significant engineering fields [40]. consequently, recent researches on polystyrene suggest its processing as nanocomposite materials employing beneficial nanoadditives, like graphene, to enhance its inherent properties [41]. hence, reports on superior mechanical, thermal, and physical features of polystyrene/graphene nanomaterials suggest further use of graphene derivatives (e.g., graphene quantum dot) to form high performance nanocomposites [42]. ma et al. [43] formed carbon-functional graphene quantum dots via the pyrolysis technique and processed them with polystyrene using the pickering emulsion polymerization method, as outlined in figure 3a. the resulting polystyrene/carbon functional graphene quantum dot nanocomposites with 0.1–2 wt.% nanodot contents were investigated for microstructure, thermal, and flame resistance properties. figure 3b (a & b) show scanning electron microscopy micrographs for neat polystyrene and polystyrene/carbon functional graphene quantum dot nanocomposite, respectively. as per results, pristine polystyrene microspheres formed by pickering emulsion method had uniform surface. on the other hand, surface roughness and wrinkling of the nanocomposite microspheres can be observed in the micrographs due to the deposition of polymer chains. according to thermogravimetric analysis, neat polystyrene had one-step degradation (350 °c–450 °c), whereas 860 w g−1 nanocomposite showed additional weight loss steps (280 °c–380 °c and 520 °c–600 °c) due to the presence of nanodot nanoparticles (figure 3c). figure 3d shows heat release rate curves for pristine and composited polystyrene-based nanomaterials. here, the decrease in the peak heat release rate of unfilled polystyrene (~860 w g−1) in polystyrene/carbon functional graphene quantum dot (~520 w g−1) confirmed the enhancement in the flame resistance of the nanocomposites with the nanodot addition. this fact was explained on the basis of the formation of a flame protection layer causing a barrier effect by quantum dot nanoparticles, so limiting the decomposition of polystyrene during the combustion process (figure 3e). the overall enhancement in heat/flame resistance of the nanocomposites can be credited to the modified graphene quantum dot-based designs as well as the effectiveness of the fabrication technique used in this attempt. however, literature shows limited reports on polystyrene/graphene quantum dot nanocomposites. characterization and application of nanomaterials 2025, 8(2), 11484. 6 figure 3. (a) schematic for formation of ps/c-gqds nanocomposites; (b) scanning electron microscopy images for (a) neat ps and (b) ps/c-gqd 5; (c) thermogravimetric analysis curves of ps and ps/c-gqds nanocomposites; (d) heat release rate (hrr) curves of ps and ps/c-gqds nanocomposites; and (e) mechanisms of flame retardancy of ps nanocomposites [43]. ps = polystyrene; cgqds = carbon-modified graphene quantum dots; ps/c-gqds = polystyrene/carbonmodified graphene quantum dots. reproduced with permission from springer. characterization and application of nanomaterials 2025, 8(2), 11484. 7 polyethylene is another common low-price plastic material having high molecular weight and hydrophobic properties [44]. moreover, polyethylene has fine flexibility, toughness, chemical resistance, etc., for commercial applications [45]. it is commonly practiced as low-density polyethylene, high-density polyethylene, as well as ultra-high molecular weight polyethylene forms [46]. to upsurge the industrial significance, polyethylene was composited with metal or inorganic nanoparticles as well as carbon nanoadditives, like graphene, carbon nanotube, etc. [47]. accordingly, plenty of research can be seen for polyethylene/graphene nanocomposites [48]. few attempts have been observed on polyethylene/graphene quantum dot hybrids in the literature to date. for example, yin et al. [49] investigated polyethylene/carbon quantum dot/silica for microstructural and fluorescent emission spectral behavior. for this purpose, stöber method was used to form silica microspheres and then polyethylene/carbon quantum dot/silica were designed using compression molding approach. using this method, polyethylene chains were believed to be confined between silica nanoparticles to ensure fine dispersion and interaction towards the nanodot (figure 4a). accordingly, high resolution transmission electron microscopy of the nanocomposite depicted lattice spacing (~2.1 å) and lattice plane (100) confirming the structural integrity and dispersion of carbon quantum dot in the nanocomposite (figure 4b). figure 4c illustrates fluorescent emission spectra of polyethylene/carbon quantum dot/silica hybrid with red shift (340 to 380 nm) and blue shift (380–500 nm) at lower and higher wavelengths, respectively. such results also confirmed the surface defects and fluorescent features of carbon quantum dots. figure 4d shows rectangle, triangle, and circle shapes for pristine polystyrene, polyethylene/carbon quantum dot, and polyethylene/carbon quantum dot/silica hybrids, respectively, studied simultaneously under daylight and uv excitation (~360 nm). thus, fluorescence can be seen for the nanocomposite sample shapes under uv excitation, relative to unfilled matrix shapes. additionally, among polyethylene derivative thermoplastics, poly(ethylene glycol) nanocomposites reinforced with graphene quantum dot have been designed and reported [50,51]. kim et al. [52] stated the nanomaterials based on poly(ethylene glycol) filled with fluorescent graphene quantum dot, obtained through a solution processing technique (water solvent). the poly(ethylene glycol)/graphene quantum dot nanocomposite had a higher fluorescence quantum yield of ~5% with excitation at a 320 nm wavelength, compared with pristine graphene quantum dot. in addition, low toxicity and chemical stability features of the nanomaterials have been observed. consequently, the as-designed poly(ethylene glycol)/graphene quantum dot nanocomposites were suggested to be useful for light-emitting diode applications. the resulting device depicted luminance > 800 cd m−2. similarly, other articles can be seen in the literature regarding the synthesis and fluorescence features of poly(ethylene glycol)/graphene quantum dot nanocomposites [53,54]. characterization and application of nanomaterials 2025, 8(2), 11484. 8 figure 4. (a) polyethylene in cavities/pores of silica nanoparticle aggregates; (b) high resolution transmission electron microscopy of polyethylene/carbon quantum dot/silica; (c) fluorescent emission spectra polyethylene/carbon quantum dot/silica hybrid at varying wavelengths; (d) photos of pure polyethylene (rectangles), polyethylene/carbon quantum dot (triangles), and polyethylene/carbon quantum dot/silica (circles) films in: (a) daylight and (b) upon excitation with ~360 nm light [49]. reproduced with permission from acs. poly(vinylidene fluoride) appeared as a widely studied unique high performance thermoplastic, especially for the formation of nanocomposites [55]. its important properties can be listed as optical, electronic, piezoelectric, ferroelectric, and dielectric characteristics, especially useful for energy/electronic device applications [56,57]. out of carbon nanofillers, graphene-based poly(vinylidene fluoride) nanocomposites have been explored for technical features and performance [58]. like graphene, its quantum dot nanostructures have been amalgamated with poly(vinylidene fluoride) to form high-performance nanocomposites [59]. adding graphene quantum dots in poly(vinylidene fluoride) has been found to affect the piezoelectric features of the nanomaterials, e.g., β polymorph formation in the matrix [60]. cho et al. [61] formed poly(vinylidene fluoride)/amino-modified graphene quantum dot nanocomposites. including modified quantum dots developed hydrogen bonding and resulted in α→β form changes of poly(vinylidene fluoride) matrix. moreover, these nanomaterials had a high dielectric constant of ~61. recently, tay et al. [62] formed silver-modified graphene oxide quantum dots for a poly(vinylidene fluoride) matrix by the solution method. the poly(vinylidene fluoride)/silver-modified graphene oxide quantum dot nanomaterials had antimicrobial features against the e. coli bacterial strain. zhang et al. [63] prepared important nanofiber designs of graphene oxide quantum dot using a poly(vinylidene fluoride) derivative, i.e., poly(vinylidene fluoride)(tetrabutyl titanate)/poly(vinyl pyrrolidone) (tetrabutyl titanate) by electrospinning method. for this purpose, graphene oxide quantum dots were synthesized using the hydrothermal method. in this way, pristine poly(vinylidene fluoride)(tetrabutyl titanate)/poly(vinyl characterization and application of nanomaterials 2025, 8(2), 11484. 9 pyrrolidone)(tetrabutyl titanate) as well as poly(vinylidene fluoride)(tetrabutyl titanate)/poly(vinyl pyrrolidone)(tetrabutyl titanate)/graphene quantum dots nanocomposite nanofibers have been prepared. figure 5a shows luminescent behavior of pristine nanodots at wavelength of 365 nm. figure 5b, c show transmission electron microscopy micrographs of graphene quantum dots with uniform discrete nanoparticle dispersion. accordingly, figure 5d presents a size distribution spectrum of pristine nanodots around 1.8–3.0 nm. figure 5e, f present neat polymer and graphene quantum dot-filled nanocomposite nanofibers, respectively. relative to the smooth surface morphology of unfilled poly(vinylidene fluoride)(tetrabutyl titanate)/poly(vinyl pyrrolidone)(tetrabutyl titanate) nanofibers, the quantum dot-filled nanocomposite nanofibers had visible deposition of graphene quantum dots on the surface. these nanocomposite nanofibers were studied and found effective for photocatalytic degradation features regarding rhodamine b. figure 5. (a) photograph of graphene quantum dot under 365 nm ultraviolet light; (b,c) transmission electron microscopy (tem) images of quantum dot at low and high magnifications; (d) size distribution chart of graphene quantum dot; scanning electron microscopy of (e) poly(vinylidene fluoride)(tetrabutyl titanate)/poly(vinyl pyrrolidone)(tetrabutyl titanate) nanofiber; and (f) poly(vinylidene fluoride)(tetrabutyl titanate)/poly(vinyl pyrrolidone)(tetrabutyl titanate)/graphene quantum dot nanofiber [63]. reproduced with permission from mdpi (open access). poly(vinyl alcohol) is also a common name among thermoplastics for nanocomposite formation [64,65]. it has advantageous features of water solubility, facile processing, and environmental friendliness. owing to its abundant use as matrix material, inorganic and carbon nanofillers have been used to form the corresponding [66]. graphene is a commonly reinforced nanocarbon in a poly(vinyl alcohol) matrix. likewise, graphene quantum dot has been investigated for poly(vinyl alcohol) nanocomposites [67,68]. adding quantum dots in a poly(vinyl alcohol) matrix was not characterization and application of nanomaterials 2025, 8(2), 11484. 10 observed to repress the solubility, dispersion, luminescent properties, and quantum yield of the nanodots [69–72]. fauzi et al. [73] developed poly(vinyl alcohol)/graphene quantum dot nanomaterial by the spin-coating method. the asobtained nanocomposite was applied as a sensor for carbaryl detection, having a limit in the range of 0.001–0.007 ppb. ogi and workers [74] filled graphene quantum dots in a poly(vinyl alcohol) matrix via a hydrothermal technique. these nanocomposites had remarkable photoluminescence intensity and a high quantum yield of 44%. elumalai et al. [75] reported on solution-formed poly(vinyl alcohol)/graphene quantum dot nanocomposites. figure 6a depicts a facile route for the formation of these nanomaterials having intense blue color illumination in uv light. according to the differential thermal analysis data of unfilled and filled matrix given in figure 6b, the neat poly(vinyl alcohol) sample had crystalline melting peaks around 220 °c and moisture peaks at 120 °c. on the other hand, the nanocomposite depicted altogether different thermograms with a glass transition temperature of about 59 °c and exothermic peaks due to matrix-nanofiller interfacial interactions. hence, poly(vinyl alcohol)/graphene quantum dot nanocomposites have been mostly explored for fluorescence emission properties, as per available reports so far. 5. applications of thermoplastic/graphene quantum dot nanocomposites as discussed in preceding sections of this review, graphene quantum dots have several structure-property advantages of extremely tiny sizes, zero dimensions, and high surface area, as well as quantum confinement effects, relative to pristine graphene nanosheets, which are in turn useful in varying technological devices and biomedical appliances [76–78]. an important application of graphene quantum dots and derived nanocomposites has been observed for electromagnetic interference (emi) shielding [79]. for radiation shielding, literature reports on countless designs of carbonaceous nanocomposites using carbon nanotubes, graphene, carbon black, and other nanocarbons [80–82]. generally, nano-sizes, compatibility with polymers, interface formation, and electron conduction or percolation behavior of nanocarbons were found useful for shielding the effects of ecologically hazardous electromagnetic radiations continuously emitted by functional electronics and allied equipment. the emi defense was mainly accredited to the conducting behavior of nanocarbon. amongst nanocarbon nanofillers, graphene is an exclusive two-dimensional nanosheet nanocarbon graphene, which has been commonly used for emi defense applications [83–85]. graphene quantum dot-based nanomaterials have lightweight, fine nanoparticle dispersion, electrical conductivity, dielectric, and electromagnetic features for high-end emi shielding applications [86]. all these emi shielding-related features of the nanocomposites rely upon graphene quantum dot dispersion as well as matrix-nanofiller associations. characterization and application of nanomaterials 2025, 8(2), 11484. 11 figure 6. (a) fabrication of pristine pva and pva/gqd nanocomposite films; (b,c) differential thermal analysis data of neat pva and pva/gqd nanocomposite films, respectively [75]. pva = poly(vinyl alcohol); pva/gqd = poly(vinyl alcohol)/graphene quantum dots nanocomposite. reproduced with permission from mdpi (open access). lakshmi et al. [87], for instance, explored electromagnetic shielding effectiveness of the poly(vinylidene fluoride)/graphene decorated graphene quantum dots and poly(vinylidene fluoride)/graphene decorated graphene quantum dots/silver characterization and application of nanomaterials 2025, 8(2), 11484. 12 nanoparticles nanocomposites. according to the results for the nanocomposites having 2 wt.% nanofiller loadings, the poly(vinylidene fluoride)/graphene decorated graphene quantum dots/silver nanoparticles (with contents) had a total shielding effectiveness of 43 db, i.e., ten times higher than that of the poly(vinylidene fluoride)/graphene decorated graphene quantum dots (31 db) as shown in figure 7a. upsurges in the total shielding effectiveness of the graphene-decorated graphene quantum dots/silver nanoparticles-based nanocomposites seemed to be due to their mutual nanostructural effects between the quantum dots and the metal nanoparticles, therefore resulting in their uniform dispersions and an interconnecting network formation for a facilitated electron flow through the epoxy matrix. accordingly, the graphene-decorated graphene quantum dots/silver nanoparticles were capable of shielding around 99.9% of electromagnetic radiations, relative to the neat epoxy matrix. additionally, as shown in figure 7b, both absorption and reflection of electromagnetic waves for the graphene-decorated graphene quantum dots/silver nanoparticles-filled nanocomposites were observed to be higher, as compared to the non-modified graphene-decorated graphene quantum dots nanocomposites. herein, superior reflection/absorption from the graphene-decorated graphene quantum dots/silver nanoparticles-based nanocomposites was attributed to their better dispersion in the poly(vinylidene fluoride) matrix, therefore, facilitating more surface charges and higher conductivity of their nanocomposites, relative to the non-modified quantum dots-based system. moreover, electromagnetic wave attenuations of the poly(vinylidene fluoride)/graphene decorated graphene quantum dots (left image in figure 7c) and poly(vinylidene fluoride)/graphene decorated graphene quantum dots/silver nanoparticles nanocomposites (right-hand image in figure 7c) were investigated. it was suggested that graphene-decorated graphene quantum dots/silver nanoparticles developed a denser interconnecting network in the epoxy matrix, relative to that of the non-modified graphene-decorated graphene quantum dots, therefore resulting in superior tunneling phenomena and wave attenuation characteristics of their nanocomposites. since pristine polymeric matrices are usually nonconductive and do not absorb radiation. including semiconducting nanoparticles, like graphene quantum dots, in polymers has been reported to enhance the electrical conductivity and electromagnetic absorption properties of polymeric nanocomposites. the electrically conducting graphene quantum dots usually have the capability to dissipate electrical charges, thereby reducing electromagnetic field buildup. in addition, emi shielding mechanism of polymer/graphene quantum dot nanocomposites seemed to be relying upon network formation, alignment, and selective localization of quantum dots nanoparticles at matrix-nanofiller interfaces, so contributing to emi shielding competence. in this way, semiconducting quantum dots exhibited fine electromagnetic reflection/absorption characteristics to effectively enhance radiation shielding of nanocomposites. characterization and application of nanomaterials 2025, 8(2), 11484. 13 figure 7. (a) total shielding effectiveness of poly(vinyledene fluoride)/graphene decorated graphene quantum dots, pvdf/g-d-gqds, and poly(vinyledene fluoride)/graphene decorated graphene quantum dots/silver nanoparticles, pvdf/gd-gqdsag, nanocomposites in the x-band range and (b) reflection and absorption of the pvdf/g-d-gqds and pvdf/gd-gqdsag nanocomposites in the x-band range; (c) schematic of attenuation of electromagnetic (em) wave of pvdf/g-d-gqds nanocomposites (left) and pvdf/gd-gqds/ag nanocomposites (right) [87]. reproduced with permission from taylor and francis. due to the charge-storing properties of graphene quantum dots, interesting applications can be seen regarding the memory and charge-trapping devices [88,89]. nevertheless, such applications demand low-cost and facile material fabrication on a commercial scale without environmentally harmful effects. in this concern, kou et al. [90] hydrothermally formed poly(methyl methacrylate) filled with graphene quantum dots. a transmission electron microscopy study was used to confirm the consistent dispersion of graphene quantum dots having 7 nm in size throughout the matrix. figure 8a shows the final design of a flexible memory device of poly(ethylene terephthalate)/indium-tin-oxide/poly(methyl methacrylate)/graphene quantum dot (pet/ito/pmma:gqds/al). figure 8b presents comparative photoluminescence characterization and application of nanomaterials 2025, 8(2), 11484. 14 spectra of pristine poly(methyl methacrylate), graphene nanosheet, graphene quantum dot, and pmma/gqd nanocomposite. figure 8. (a) a graphic of a flexible poly(ethylene terephthalate)/indium-tinoxide/poly(methyl methacrylate)/graphene quantum dot (pet/ito/pmma: gqds/al) memory device; (b) photoluminescence spectra of poly(methyl methacrylate), pmma, graphene nanosheet (gns), gqd, and pmma/gqd nanocomposite films excited at 260 nm, where inset: photograph of gqd chlorobenzene solution taken under visible light and 365 nm uv light, from left to right, respectively [90]. gqd = graphene quantum dots; pmma/gqd = poly (methyl methacrylate) and graphene quantum dots-based nanocomposites; gns = graphene nanosheet. reproduced with permission from elsevier. as per results, the nanocomposite revealed a photoluminescence peak of visibly higher intensity at a wavelength of 405 nm, relative to neat graphene quantum dots. the change in fluorescence spectral intensity indicated homogeneous dispersion and compatibility of nanodots in the nanocomposite matrix, which was found useful for manufacturing the desired memory device. on the other hand, graphene showed a broad photoluminescent peak at 510 nm owing to the broad size distribution of characterization and application of nanomaterials 2025, 8(2), 11484. 15 nanosheets. however, few researches have been seen on the use of thermoplastic polymer/graphene quantum dots for these systems, and future studies may unveil important results for designing advanced high-tech memory devices. regarding optoelectronic applications of thermoplastic polymer/graphene quantum dot nanomaterials, few important studies have been noticed so far on systems having fine electronic, optical, and luminescence features [91]. in this concern, liu et al. [92] designed starch and nitrogen-doped reduced graphene oxide quantum dotbased nanocomposites having conductivity and fluorescence properties. including 10 wt.% nitrogen-doped reduced graphene oxide quantum dot led to low resistivity of ~0.08 ω·m, reasonably high light transmittance of 80%, and fluorescence intensity of up to 9000 cps. these multifunctional, ecologically friendly nanocomposites were suggested for wearable optoelectronic devices. chen et al. [93] proposed meltprocessed thermoplastic starch and graphene quantum dots-based fluorescent nanocomposites. adding 10 wt.% nanofiller depicted low resistivity and notable photoluminescence intensity properties of the nanocomposites. according to the results, these environmentally friendly nanocomposites exhibited high-end potential application as optoelectronic packaging materials. photocatalytic performance of thermoplastic polymer/graphene quantum dot nanocomposites has been found valuable for environmental remediation [94]. in this concern, mafukidze et al. [95] formed solution-processed polystyrene and zinc phthalocyanine functional graphene quantum dot-derived nanocomposites and photocatalytic activity for the remediation of 4-chlorophenol from water. these nanocomposites followed second-order kinetics for photocatalytic oxidation of 4chlorophenol. apostolaki et al. [96] formed polystyrene and titania-modified graphene quantum dot-based photonic crystals. the ensuing nanocomposite exhibited blue luminescence at 350 nm due to n-π* transitions. the polystyrene/titania-graphene quantum dot photonic crystals were found useful for photocatalytic degradation of salicylic acid. similarly, few studies on thermoplastic polymer/graphene quantum dots mentioned potential towards chemical sensing applications [97–99]. notably, majid masteri-farahani et al. [100] developed poly(methyl methacrylate)/graphene quantum dots-based fluorescent nanosensors using the molecular imprinting method for methamphetamine detection. these nanocomposites had a fine detection limit of ~1.7 μg/l for methamphetamine. in the biomedical sector, carbon nanodots, especially graphene quantum dots, attained significance owing to their biocompatibility and non-toxic nature [101,102]. furthermore, these nanoparticles have remarkable fluorescent and surface/edgerelated quantum effects for biomedical uses [103,104]. besides, graphene quantum dots have been reported for their biologically inert nature, leading to technical utilization in fluorescent bioimaging probes [105]. zhu et al. [106] formed fluorescent graphene quantum dot-based bioimaging probes using the solvothermal method. the obtained graphene quantum dot had a high quantum yield of > 11%. nurunnabi et al. [107] reported on graphene quantum dots coated with polydopamine obtained by oxidation/exfoliation techniques. the as-formed polydopamine/graphene quantum dot nanocomposites depicted notable properties, like in vivo stability, non-toxicity, photoluminescence, etc. such nanocomposite architectures were discovered to be characterization and application of nanomaterials 2025, 8(2), 11484. 16 advantageous for drug delivery as well as optical imaging applications [108]. as per literature, figure 9 illustrates the use of bioactive graphene quantum dots for malignancy diagnosis via the bioimaging method [109]. for designing fluorescent bioimaging probes, photoluminescence properties of graphene quantum dots were found valuable [110,111]. similarly, sheng et al. [112] fabricated polyvinylpyrrolidone/nitrogen-doped graphene quantum dot hybrids via hydrothermal means. the ensuing nanocomposites have high quantum efficiency (> 64%), which was found beneficial for employment in fluorescence probes for chromium (vi) detection. thus, bioactive graphene quantum dots have been effectively explored in manufacturing fluorescent bioimaging probes [113]. nonetheless, future attempts in this direction may lead to the formation of reproducible commercial designs of fluorescent graphene quantum dots for bioimaging applications. figure 9. use of bioactive graphene quantum dots (gqd) for malignancy diagnosis via bioimaging [99]. reproduced with permission from mdpi. furthermore, scientific attempts have been observed on the antimicrobial activity of graphene quantum dots-based nanomaterials [114]. in this concern, rajendiran et al. [115] functionalized graphene quantum dots with poly(ethylene glycol), polyethyleneimine, and poly-l-lysine polymers. these non-toxic polymer/graphene quantum dot nanocomposites showed antibacterial and antifungal activities. liu et al. [116] formed polyethylenimine/graphene quantum dot/zinc oxide nanocomposites using sol-gel and solution methods. these nanomaterials showed fine antimicrobial activity towards the e. coli bacterial strain. however, limited literature has been seen so far in this important biomedical area of graphene quantum dots. 6. conclusions and views in short, thermoplastic polymers have been decisively reviewed with graphene quantum dot nanofillers, considering different matrices, fabrication techniques, physical features, and applied prospects. amalgamation of thermoplastic polymer characterization and application of nanomaterials 2025, 8(2), 11484. 17 with graphene-structured quantum dots revealed interesting structural, morphological, and wide-ranging physical attributes. the upsurges in these properties of thermoplastic polymer/graphene quantum dot can be credited to the quality of these polymers to consistently disperse the nanodot for robust interfacial interactions. here, functional graphene quantum dots seem to effectively interact with thermoplastics for the formation of compatible nanocomposite nanostructures. among prominent application zones, thermoplastic polymer/graphene quantum dot nanocomposites revealed success for radiation shielding, memory devices, optoelectronics, photocatalysts, sensing, antibacterial, and bioimaging. for future high-performance designs and applications, challenges regarding polymer and nanodot functionalities, synthesis, mutual compatibility, and large-scale production need to be technically resolved. broadly speaking, graphene quantum dots have been found to develop fine interfacial miscibility with thermoplastic polymers, thereby leading to unique microstructures, electron/charge transference, fluorescence, heat stability, nonflammability, biomolecular sensing, catalytic, and antibacterial properties. all these key advantageous characteristics and applied aptitudes of polymer/graphene quantum dot nanomaterials depend upon seamless nanoparticle dispersion and network formation in matrices, which can be attained via appropriate processing techniques to develop strong matrix-nanofiller interactions. for synthesizing thermoplastic polymer/graphene quantum dot nanocomposites, most studies focused on facile solution processing and pickering emulsion polymerization techniques. few reports have also been observed on melt mixing or compression molding methods for the formation of graphene quantum dots filled nanomaterials. beside conventional solution and melt techniques, sophisticated approaches, like spin coating and hydrothermal/solvothetmal have also been used to integrate quantum dots in polymeric nanocomposites. here, selection of an appropriate technique seems to directly influence the physical features of the as-prepared polymer/graphene quantum dot nanocomposite. all these techniques used so far have certain advantages and disadvantages, which must be considered before nanocomposite synthesis. out of these, solution processing has been considered a lowcost and environmentally friendly method for the formation of polymer/graphene quantum dot nanocomposites. this technique has been used to attain fine nanofiller dispersion in the matrices. the melt method has also been reported for fine nanofiller dispersion in polymeric matrices; however, it has its own limitations of using extreme temperature/shear conditions. relative to solution/melt methods, the spin coating method has been found more effective for uniform quantum dot dispersion in polymers. consequently, homogeneous nanofiller dispersion may ensure strong interfacial bonding with polymers, thereby leading to desirable enhancements in physical properties (microstructure, structural integrity, heat stability, electrical percolation, etc.) of the nanocomposites. along with the choice of an appropriate technique, control of processing parameters seems indispensable for large-scale processing to attain high-performance 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industries making substantial use of synthetic chemicals, resulting in significant environmental consequences. in this research investigation, the co-precipitation approach was employed for the synthesis of cellulose-based ferric oxide (fe2o3/cellulose) and copper oxide nanoparticles (cuox-nps). scanning electron microscopy (sem) analyses were conducted to determine the properties of the newly synthesised nanoparticles. furthermore, the synthesized nanoparticles were employed for eliminating chromium from aqueous media under various conditions, including temperature, contact time, adsorbent concentration, adsorbate concentration, and ph. additionally, the synthesised materials were used to recover cr(vi) ions from real samples, including tap water, seawater, and industrial water, and the adsorptive capacity of both materials was evaluated under optimal conditions. the synthesis of fe2o3/cellulose and cuox-nps proved to be effective, as indicated by the outcomes of the study. keywords: nanocomposites; cellulose-derived nps; (fe2o3/cellulose); (cuox-nps) and sem 1. introduction heavy metal ions, which are transported into aquatic environments via industrial effluents, affect aquatic life. they are harmful because of their hazardous bioaccumulative nature. one of the most hazardous heavy metal contaminants is chromium cr(vi), which has been utilized extensively and on a massive scale in a number of sectors, including metal cleaning, dyes, leather, textiles, and plating. cr(vi) is a transition metal, steel-gray, lustrous, stiff, and having a brittle appearance [1–4]. cr(vi) has a high degree of oxidation resistance even at high temperatures. cr(vi) is exceedingly poisonous and carcinogenic; therefore, its excess presence in food, water, or the environment may seriously harm the biota. for this reason, several environmental protection agencies have established a chromium limit that is acceptable as long as no acute or long-term effects on human health have been documented. according to the world health organization (who 1958), 0.05 mg/l of chromium is the maximum level that should be present in water. the maximum contaminant limit (mcl) and maximum contaminant limit goal (mclg) for chromium in water were both set at 0.1 parts per million (ppm) by the united states environmental and protection agency (us epa) in 2012 (100 ppb). the maximum contaminant limit (mcl) for chromium in drinking water is 0.05 mg/l, according to a 2013 report from the california department of public health. the public health objective for cr(vi) is 0.02 ppb; however, the maximum contamination level is established at 10 ppb [4,5]. the quick removal of cr(vi) ions from contaminated water citation khan su, khan a, hassan a, abbas b. synthesis, characterization and analytical prospects of cellulosederived nanoparticles of ferric-oxide (fe2o3/cellulose) and copper-oxide (cuox). characterization and application of nanomaterials. 2024; 7(1): 5300. https://doi.org/10.24294/can.v7i1.5300 article info received: 18 march 2024 accepted: 29 april 2024 available online: 29 may 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 5300. 2 has been focused on for the last few decades, and numerous techniques have been utilized, such as electrochemical deposition, ion exchange, adsorption, biological methods, and membrane separation. adsorption separation is the fastest, most practical, and least expensive method for the quick removal of harmful pollutants. the adsorptive removal of cr(vi) ions from wastewater has occasionally been accomplished using a variety of adsorbents, including zeolite, activated carbon, metal oxides, waste industrial material, and nano-composites, etc. for the quick removal of heavy cr(vi) ions, a variety of metal oxide nanostructures have been employed, including cellulose-based iron oxide nanoparticle composites, titanium oxides, aluminum oxides, and copper oxides [6,7]. in the present research investigations, synthesised fe2o3/cellulose nanocomposites and cuox-nps are being characterised and used for the direct removal of cr(vi) ions from an aqueous environment. additionally, the adsorption properties of these adsorbents are being compared. the results obtained suggest that the synthesised fe2o3/cellulose and cuox-nps are useful for adsorption and can potentially be used multiple times without losing their effectiveness. 2. materials and methods 2.1. materials the used papers served as a source of cellulose and were purchased from the local market. all of the reagents utilised in the experiment were of analytical grade. iron(iii) oxide, sodium hydroxide, copper chloride, copper nitrates, and urea were acquired from the commercial supplier sigma-aldrich. 2.2. synthesis of fe2o3/cellulose nanocomposite synthesis of fe2o3/cellulose using the precipitation method involves a two-stage process. during the initial phase, previously utilised copy paper was fragmented into smaller segments, subjected to three rounds of washing with distilled water, and afterwards immersed in a solution containing 40% h2so4. the mixture was subjected to filtration and afterwards washed four times with distilled water. following this, the mixture was dried in an oven maintained at a temperature of 50 ℃. in addition, a quantity of 3.3 g of dried material was introduced into a solution containing naoh, thiourea, and urea at a temperature of 261.15 kelvin. the solution was then stirred for a duration of 25 min in an environment saturated with nitrogen [8]. during the second stage of the experiment, a solution containing 15 ml of fe2cl3.6h2o (weighing 13.51 g) and fecl2.4h2o (weighing 4.97 g) was prepared. this solution was then added drop by drop to the cellulose solution and vigorously stirred for a duration of 180 min at room temperature. the composite material that was synthesised underwent a filtration process, followed by rinsing with distilled water, ethanol, and acetone. the synthesised substances were further dried in an oven at a temperature of 323.15 k and thereafter stored. characterization and application of nanomaterials 2024, 7(1), 5300. 3 2.3. synthesis of cuox-nps copper oxide nanoparticles (cuox-nps) were synthesised utilising the precipitation method, employing copper chloride (cucl2) and copper nitrate (cu(no3)2.3h2o) as precursor materials. to initiate the experiment, every precursor was initially dissolved in 100 millilitres of distilled water to achieve a concentration of 0.1 m. subsequently, a 0.1 m naoh solution was gradually introduced into the mixture under constant stirring until the ph level reached 14, resulting in the formation of black precipitates indicative of the presence of n2 gas. the black precipitate was collected and later subjected to washing procedures until the ph was adjusted to 7.0. distilled water was used initially, followed by a wash with 100% ethanol. the yields were thereafter subjected to a drying process at a temperature of 80 °c for a duration of 16 h, as indicated in references [9,10]. subsequently, the synthesised materials passed through a calcination process at a temperature of 500 ℃ for a duration of 4 h. 2.4. characterization and batch adsorption study the synthesised materials, which are fe2o3/cellulose and cuox-nps, were subjected to comprehensive characterization using essential analytical techniques. in order to determine the characteristics of the freshly synthesised nanoparticles, the morphological and elemental analyses were investigated through the jsm-it800 schottky field emission scanning electron microscope, jeol ltd. investigation involved the utilisation of synthesised materials for the purpose of conducting an adsorption study. to establish the standard stock solution of chromium (vi) ions with a concentration of 500 parts per million (ppm), a mass of 0.5 g of chromium was solubilized in 1000 ml of distilled water. the initial concentrated solution was subjected to additional dilution in order to attain the desired concentrations, employing the dilution formula denoted as c1v1 = c2v2. a solution was prepared and supplemented with 0.1 g of copper oxide nanoparticles (cuo-nps) and iron (iii) oxide (fe2o3) composite. the specimen underwent agitation for approximately 30 minutes within a water bath shaker. subsequently, the sample was subjected to filtration in order to isolate any remaining cr(vi) species. the quantification of cr(vi) was accomplished using atomic absorption spectroscopy (aas) through the application of equation (1). 𝑞 𝑚𝑔 𝑔 = 𝐶 – 𝐶 𝑊 × 𝑉 (1) initial and equilibrium concentrations of chromium (vi) metal, denoted as co and ce (mg.l−1) respectively, are of interest in this context. additionally, the quantity of chromium (vi) adsorbed at equilibrium, represented as qe (mg/g), and the volume of the solution, denoted as v (ml), are also relevant parameters. the influence of different parameters on the adsorption process was investigated, encompassing temperature, initial concentration, contact time, ionic strength, and ph. the identical methodology was also employed to explore the efficacious elimination of hexavalent chromium (cr(vi)) from a true sample. characterization and application of nanomaterials 2024, 7(1), 5300. 4 3. results and discussion 3.1. characterization the synthesis of fe2o3/cellulose and cuo-nps was achieved using the coprecipitation method, and the sem analysis conclusively validates the successful synthesis of these nanomaterials, as shown in figure 1. sem analysis reveals a densely packed surface with cr(vi) ions attached to the adsorbent materials. this observation corresponds to favorable electrostatic interactions and efficient metal adsorption in the acidic environment due to the presence of elevated hydronium ions (h+). conversely, under extremely acidic conditions, sem images show a weakened and less stable adsorbent surface due to surface oxidation processes. this phenomenon aligns with the decrease in metal adsorption observed in these conditions. this shift adversely affects the attachment of chromium oxyanions to the adsorbent surface. the sem analysis also suggests that at higher ph levels, the presence of an increased concentration of hydroxyl groups (oh−) in the solution leads to repulsion between chromium oxyanions and oh− ions, reducing the availability of adsorption sites and competition for these sites. figure 1. sem analyses of cuox nanoparticles (i-iii) and feox nanoparticles (iv-vii). 3.2. effect of ph adsorption and contact time the adsorption behavior of cr(vi) ions onto the surfaces of fe2o3/cellulose and cuox nanoparticles (nps) was investigated across a ph range spanning from 2.0 to 10.0, utilizing a fixed concentration of 300 mg/l. the experimental outcomes are presented graphically in figure 2a. the adsorption of cr(vi) ions on fe2o3/cellulose and cuox-nps displays a significant dependency on ph. maximum adsorption of cr(vi) ions was observed at ph values of 2.0 and 4.0. this phenomenon can be attributed to the elevated concentrations of hydronium ions (h+) present on the characterization and application of nanomaterials 2024, 7(1), 5300. 5 adsorbent surface within an acidic environment, thereby intensifying the electrostatic interactions between the negatively charged chromium ions and the protonated sorbent. this enhanced interaction enhances the efficiency of metal adsorption. however, it should be noted that the adsorbent surface experiences a weakening and loss of stability under extremely acidic conditions, primarily due to surface oxidation processes, which in turn diminishes the capacity for metal adsorption. these observations are consistent with the fact that cuox nanoparticles possess a nearly neutral point of zero charge, around 6.9. consequently, as the ph level rises from its optimal value (ph 3.5) towards the alkaline range, the degree of protonation of the cuox nanoparticles surface gradually decreases. beyond this point, the surface acquires a net negative charge, rendering it less favorable for the attachment of chromium oxyanions. moreover, at higher ph levels, the concentration of hydroxyl groups (oh−) in the solution increases, leading to repulsion between chromium oxyanions and oh− ions, resulting in competition for the limited available adsorption sites. this competition reduces the removal efficiency of cr(vi) ions from the solution [11,12]. to establish the optimal experimental conditions for the adsorption of cr(vi) ions onto cuox nanoparticles (cuox-nps) and fe2o3/cellulose composites, we conducted contact time experiments. the findings demonstrated that equilibrium for cr(vi) ion adsorption on cuox-nps was attained after 120 min, while equilibrium for adsorption on fe2o3/cellulose was reached within 60 min, as illustrated in figure 2b. initially, the rapid adsorption of cr(vi) ions was facilitated by the abundance of unoccupied binding sites on the surfaces of cuox-nps and fe2o3/cellulose composites, coupled with a substantial concentration gradient between the adsorbate and the solid phase of the synthesized materials. however, with prolonged contact time, the number of available active sites for adsorption diminished, and there was an increase in repulsive forces between the ions that had already adsorbed onto the adsorbent surface and those still in the solution. consequently, the adsorption of cr(vi) ions proceeded more slowly as the system approached equilibrium due to ion competition for the limited accessible binding sites [13,14]. figure 2. (a) influence of ph on cr adsorption; and (b) impact of contact time on cr adsorption using fe2o3/cellulose and cuo-nps. characterization and application of nanomaterials 2024, 7(1), 5300. 6 3.3. effect of adsorbent dosage and adsorbate concentration figure 3. (a) influence of adsorbent on cr adsorption; and (b) effect of adsorbate concentration on cr adsorption; (c) dose dependent adsorbent removal efficiency, using fe2o3/cellulose and cuox-nps. table 1. various adsorbent utilized for cr(vi) adsorption. s. no adsorbent type qmax (mg/g) percent, % reference 1 n77 cation exchange resins 35.38 mg/g 95 [15] 2 skn1 cation exchange resins 46.34 mg/g 95 [15] 3 carbon aerogel electrodes 94.69 [16] 4 c1 activated carbon 98.86 [17] 5 c2 activated carbon 98.6 [17] 6 c3 activated carbon 93 [17] 7 al electrodes 97.76 [18] 8 chemical precipitation method 99.74 [18] 9 eucalyptus bark (eb) 99 [19] 10 cation exchange resins 1200h 84.04 mg/g [20] 11 cation exchange resins 1500h 188.67 mg/g [20] 12 cation exchange resins irn97h 58.14 mg/g [20] characterization and application of nanomaterials 2024, 7(1), 5300. 7 table 1. (continued). s. no adsorbent type qmax (mg/g) percent, % reference 13 dried green alga u. lactuca 8.91 mg/g 52.54 [21] 14 activated carbon 93.92 mg/g 99.52 [21] 15 activated carbon 28.019 mg/g [22] 16 electrochemical method 86.45 [23] 17 amidoxime adsorb 31.68 mg/g [24] we conducted an investigation into the effect of adsorbent dosage, with the results presented in figures 3a and 3c. upon increasing the adsorbent dose, the removal of cr(vi) ions exhibited a sharp rise, increasing from 50% to 74.08% for fe2o3/cellulose and from 41% to 78% for cuox-nps when initial cr(vi) ion concentrations were in the range of 1.25 mg/l. further increases in adsorbent dose led to a gradual enhancement in removal efficiency, reaching 86.97% and 87.44% for fe2o3/cellulose and cuox-nps, respectively (figure 3c). conversely, when examining the adsorption capacity of fe2o3/cellulose and cuox-nps for an initial cr(vi) ion concentration of 24 mg/l, it was observed that the adsorption capacity gradually decreased from 80 mg/g to 78 mg/g as the adsorbent dose increased. this phenomenon can be explained by the fact that the ratio of available binding sites to the amount of metal ions in the system affects the adsorbent's capacity for adsorption. at higher doses of cr(vi) ions, the saturation of binding sites on the surface of cuox-nps and fe2o3/cellulose composites was not achieved, resulting in a reduced adsorption capacity per unit mass of cuox nanoparticles. furthermore, the increased availability of surface area and open adsorption sites with higher adsorbent dosages contributed to the elevated removal of cr(vi) ions. however, it should be noted that as equilibrium was approached, additional increases in adsorbent dosage resulted in only marginal improvements in cr(vi) ion removal. consequently, a dose of 1.25 g/l was selected for subsequent studies, as it balanced the desirable values of high removal efficiency and adsorption capacity per unit mass of fe2o3/cellulose and cuox-nps adsorbent [25,26]. in comparison table 1, various adsorbents utilized for cr(vi) adsorption, we examined the impact of varying cr(vi) ion concentrations on the adsorption behavior of fe2o3/cellulose and cuox nanoparticles (cuox-nps), with the results shown in figure 3b. it was observed that the highest removal efficiencies, reaching 90.04% and 94.08%, were achieved at a relatively low initial metal ion concentration of 5 mg/l. as the initial concentration of cr(vi) ions was progressively increased from 5 to 50 mg/l, the removal efficiency exhibited a consistent decline, dropping to 69.16% and 62.5%. this phenomenon can be attributed to the availability of a greater number of active surface areas and binding sites on fe2o3/cellulose and cuox-nps when exposed to lower cr(vi) ion concentrations, resulting in optimal adsorption performance. conversely, at higher initial concentrations of cr(vi) ions, fewer sites were available for the acceptance of cr(vi) ions on the synthesized materials, thereby leading to a decrease in the adsorption efficiency [27]. 3.4. influence of temperature on adsorption a comprehensive investigation into the influence of temperature, spanning from characterization and application of nanomaterials 2024, 7(1), 5300. 8 15 ℃ to 45 ℃, on the adsorption behavior of cr(vi) onto the surfaces of fe2o3/cellulose and cuox nanoparticles (cuox-nps), and the resultant data are visually shown in figure 4. the findings unveiled a distinct temperature-dependent impact on the adsorption process. specifically, an elevation in temperature within this specified range elicited divergent responses: a notable augmentation in the adsorption of cr(vi) ions onto cuox-nps, in stark contrast to a conspicuous reduction in adsorption observed for fe2o3/cellulose composites. this intriguing phenomenon can be ascribed to the noteworthy reduction in solution viscosity with increasing temperature, a well-recognized phenomenon in the realm of chemical kinetics. elevated temperatures serve as a catalyst, enhancing the diffusion rate of adsorbate molecules. this accelerated diffusion occurs both within the exterior boundary layer and, crucially, within the intricate network of pores intrinsic to the adsorbent particles. consequently, the heightened thermal energy facilitates more efficient interaction between the cr(vi) ions and the cuox-nps, leading to an augmented adsorption capacity. in stark contrast, the adsorption performance of cr(vi) onto fe2o3/cellulose composites exhibits a counterintuitive decline with rising temperature. this paradoxical behavior can be attributed to complex interplays between temperatureinduced changes in the physicochemical properties of the adsorbent and the nature of adsorbate interactions. these interactions influence the availability of active adsorption sites and, consequently, the overall adsorption efficiency [28,29]. figure 4. effect of temperature on chromium adsorption utilizing fe2o3/cellulose and cuo-nps. 3.5. kinetic study theoretical studies were conducted to study the nature of adsorption and establish potential adsorption mechanisms. to achieve this, well-known adsorption equations and models were utilized to analyze the acquired data. in the kinetic studies, common kinetic models/equations were applied to analyze the adsorption kinetics of the newly developed adsorbent. characterization and application of nanomaterials 2024, 7(1), 5300. 9 3.5.1. pseudo second order kinetic model the model/equation is expressed as: 𝑑𝑞 𝑑𝑡 = 𝐾 (𝑞 − 𝑞 ) the linear form of this model/equation is given as: 𝑡 𝑞 = 𝑡 𝑞 − 1 𝐾 𝑞 where qe is the amount of sample adsorbed (mg/g) at equilibrium, qt is the amount of sample adsorbed (mg/g) at any given time (t) (min), and k2 is the pseudo-second-order reaction rate constant for adsorption (g/mg.min). the constant k2 = to calculate the initial adsorption rate (h) (mg/g.min), at t → 0 as follows; ℎ = 𝐾 𝑞 where k2 is the pseudo-second-order reaction rate constant for adsorption (g/mg.min) and qe is the amount of sample adsorbed (mg/g) at equilibrium. from the equilibrium time adsorption data, the time (t) (min) plotted with t/qt (figures 5a and 5b) with correlation co-efficient (r2) of 0.9958 (slope = 1/qe 0.05418, cuox), plus r2 = 0.9958 (1/qe = 0.05762, for fe2o3/cellulose) and the pseudo-second-order-kinetic equation/model were constructed. figure 5. pseudo second order kinetic model of (a) cuox; and (b) fe2o3/cellulose. 3.5.2. langmuir adsorption isotherm model it is important to establish the most appropriate correlation for the equilibrium curves. an adsorption isotherm/model describes the relationship between the amount of adsorbate that is adsorbed on the adsorbent and the concentration of dissolved adsorbate in the liquid at equilibrium. isotherm models such as those have been used to describe the equilibrium nature of adsorption; the langmuir adsorption isotherm/model is the most frequently used model for the adsorption of an adsorbate from a liquid solution onto the adsorbent. this model is obtained under the ideal assumption of an adsorption surface. it is assumed that adsorbate occupied a site, and no further adsorption occurred. a saturated value is reached, and no further adsorption can take place. the langmuir adsorption isotherm/model is used and is expressed by the following equation: characterization and application of nanomaterials 2024, 7(1), 5300. 10 𝑞 = 𝐾 𝐶 1 + 𝑎 𝐶 in a linear form of this equation is given as; 𝐶 𝑞 = 1 𝐾 + 𝑎 𝐶 𝐾 where ce is the equilibrium concentration of sample (bpb) in the solution (mg/l), qe is the amount of sample adsorbed (mg/g), kl and al are the langmuir adsorption isotherm/model constants and are related to the maximum adsorption capacity (l/g) and bonding strength (l/mg), respectively. the theoretical monolayer adsorption capacity (qo, mg/g) is numerically equal to kl/al. 𝑄 = 𝐾 𝑎 the ce (mg/l) was then plotted with ce/qe (figures 6a and 6b) with correlation co-efficient (r2) of 0.9907 and the langmuir adsorption isotherm/model was constructed. in the present study, it is highlighted that the adsorbent is favorable for the adsorption onto the newly developed adsorbent under the studied conditions. figure 6. langmuir adsorption isotherm/model of (a) cuox and (b) fe2o3/cellulose. 3.6. effectiveness of samples in the pursuit of evaluating the effectiveness of removing cr(vi) from authentic and synthetic wastewater samples, we employed fe2o3/cellulose and cuox nanoparticles (cuox-nps) under carefully optimized adsorption parameters, as illustrated in figure 7. this comprehensive assessment encompassed the utilization of three distinct true water samples (comprising tap water, well water, and river water), an industrial effluent sample, and a synthetic wastewater sample. to commence the evaluation process, each of these samples underwent individual spiking with a cr(vi) concentration of 25 mg/l. following the completion of the adsorption procedure, we meticulously quantified the amount of adsorbed cr. the results unveiled a noteworthy accomplishment in the removal of cr(vi) ions, with removal percentages ranging from 53.52% to 70.97% for authentic water samples and 49.78% to 68.93% for wastewater samples, all facilitated by the utilization of the synthesized composites. these outcomes affirm the practical applicability of the synthesized materials in the purification of authentic water samples, wastewater, and industrial effluents. characterization and application of nanomaterials 2024, 7(1), 5300. 11 remarkably, it is worth noting that fe2o3/cellulose outperformed cuox-nps significantly in these diverse applications, underscoring its superior performance [29,30]. figure 7. adsorption of cr (vi) ion using fe2o3/cellulose and cuonps in true samples. 4. conclusions in this study, cellulose-based ferric oxide (fe2o3/cellulose) and copper oxide nanoparticles (cuox-nps) were successfully synthesized using the co-precipitation approach. these newly synthesized nanoparticles were extensively characterized. the synthesized materials demonstrated promise for the removal of hazardous hexavalent chromium (cr(vi)) ions from aqueous solutions. the investigation into the effect of ph on cr(vi) adsorption revealed that the optimal ph for maximum adsorption was 2.0 and 4.0. the impact of adsorbent dosage indicated that an increase in dosage led to enhanced cr(vi) ion removal, with saturation observed at higher doses. furthermore, the influence of adsorbate concentration on adsorption performance demonstrated that lower initial cr(vi) ion concentrations resulted in higher removal efficiencies. thermal influence on adsorption was investigated, with cuox-nps exhibiting increased adsorption at higher temperatures, attributed to enhanced diffusion rates. conversely, fe2o3/cellulose composites showed decreased adsorption at elevated temperatures, likely due to altered surface properties. the practical applicability of fe2o3/cellulose and cuox-nps was confirmed through successful cr(vi) ion removal from real water samples, including tap water, well water, river water, and industrial effluent. these findings highlight the potential of these nanomaterials for efficient and sustainable heavy metal ion removal from aqueous environments, addressing environmental contamination concerns. author contributions: literature, experimental investigation, suk and ba; 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7(6): 225. doi: 10.3390/met7060225 characterization and application of nanomaterials 2025, 8(3), 11815. https://doi.org/10.24294/can11815 1 perspective evaluation of static atomic charges in elementary nanostructures: boron planar clusters tornike odishvili1,2, levan chkhartishvili1,3* 1 engineering physics department, faculty of informatics and control systems, georgian technical university, tbilisi 0160, georgia 2 radiophysics, optics and acoustics reference division, georgian national agency for standards and metrology, tbilisi 0178, georgia 3 semiconducting and powder composite materials laboratory, ferdinand tavadze metallurgy and materials science institute, tbilisi 0186, georgia * corresponding author: levan chkhartishvili, levanchkhartishvili@gtu.ge abstract: static atomic charges affect key ground-state parameters of boron quasi-planar clusters bn, n ≤ 20, which serve as building blocks of borophenes and other two-dimensional boron-based materials promising for various advanced applications. assuming that the outer valence shells partial electron density of the constituent b atoms are shared between them proportionally to their coordination numbers, the static atomic charges in small boron planar clusters in the electrically neutral and positively and negatively singly charged states are estimated to be in the ranges of –0.750e (b7 0) to +0.535e (b20 0), –0.500e (b7 +, b8 +, and b9 +) to +0.556e (b17 +), and –1.000e (b7 –) to +0.512e (b20 –), respectively. keywords: static atomic charge; coordination number; valence electron; cluster; boron 1. introduction the combination of atoms into a bound structure with subsequent redistribution of the valence electron densities of individual atoms can lead to the appearance of nonzero static atomic charges. their influence on the polarity of chemical bonds in a substance and the associated physicochemical properties is most significant in chemical compounds with large differences in the electronegativity of the constituent elements. however, static charges of atoms are found even in elementary structures with different coordination of atomic sites. this effect is most noticeable in small clusters with comparable numbers of central and peripheral atoms. good examples of such kind are all-boron clusters consisting of up to 20 atoms with quasi-planar ground states. evaluating static atomic charges in bn, n = 1, 2, 3, …, 20, nanoclusters is not only of academic, but also quite high practical interest, because they are considered as the building blocks of borophenes [1–3], a class of twodimensional materials promising for nanoelectronics (wiring in nano-ic and nanocapacitor plates) [4–9], radiation protection (from neutron fluxes and accompanying gamma-rays), formation of hard and corrosion-resistant coatings, etc. in the present work, this problem is solved within the framework of a model approach, which assumes that the partial electron density of the outer valence shells of the constituent b-atoms is redistributed between them in dependence on their coordination. 2. model to estimate the effective values of the static atomic charges in an elementary citation odishvili t, chkhartishvili l. (2025). evaluation of static atomic charges in elementary nanostructures: boron planar clusters. characterization and application of nanomaterials. 8(3): 11815. https://doi.org/10.24294/can11815 article info received: 23 june 2025 accepted: 27 november 2025 available online: 28 november 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(3), 11815. 2 structure, it is natural to assume that the effective number of valence electrons centered on a given atomic site and participating in the electron transfer to/from the nearest neighbors is proportional to its coordination number [10]. this study describes the corresponding simple model of the distribution of static atomic charges in elementary structures. let the structure consist of 𝑛 identical atoms, each of which gives up 𝜈 valence electrons participating in the electron transfer to/from the remaining constituent atoms. then the total number 𝑁 of such electrons is: 𝑁 = 𝑛𝜈. (1) denoting the coordination number of the 𝑖th site by 𝐶𝑖 ( 𝑖 = 1, 2, 3, … , 𝑛 ), the corresponding effective number 𝜈𝑖 of localized electrons were found: 𝜈𝑖 = 𝑁𝐶𝑖 ∑ 𝐶𝑗 𝑗=𝑛 𝑗=1 = 𝑛𝜈𝐶𝑖 ∑ 𝐶𝑗 𝑗=𝑛 𝑗=1 . (2) the difference between 𝜈 and 𝜈𝑖 values give the desired effective charge numbers 𝑧𝑖: 𝑧𝑖 = 𝜈 − 𝜈𝑖 = 𝜈 (1 − 𝑛𝐶𝑖 ∑ 𝐶𝑗 𝑗=𝑛 𝑗=1 ). (3) an isolated b atom has 3 valence electrons: 2 and 1, respectively, in the inner 2s and outer 2p-states. the energy level of 2s-electrons is located much deeper than the 2p-level. this means that practically only 2p-electrons are involved in the transfer: 𝜈 ≈ 1 . then, for all-boron structures in the electrically neutral state, the static atomic charge numbers 𝑧𝑖 0 are: 𝑧𝑖 0 ≈ 1 − 𝑛𝐶𝑖 ∑ 𝐶𝑗 𝑗=𝑛 𝑗=1 . (4) the multiply positively charged atomic structures are metastable due to their high ability to capture electrons from the environment or to annihilate with negatively charged ones, while the multiply negatively charged atomic structures are not stable at all. for this reason, the study considers only singly positively and singly negatively charged all-boron structures with 𝑁 − 1 ≈ 𝑛 − 1 and 𝑁 + 1 ≈ 𝑛 + 1 electrons participating in the transfer, respectively. this gives their static atomic charge numbers 𝑧𝑖 + and 𝑧𝑖 − : 𝑧𝑖 + ≈ 1 − (𝑛−1)𝐶𝑖 ∑ 𝐶𝑗 𝑗=𝑛 𝑗=1 , (5) 𝑧𝑖 − ≈ 1 − (𝑛+1)𝐶𝑖 ∑ 𝐶𝑗 𝑗=𝑛 𝑗=1 . (6) why, despite its simplicity, can the coordination number-based method for estimating static atomic charges be valuable? this is explained by the necessity of representing the bonds polarity in clusters through the interatomic transfer of static point charges, when: (1) a diatomic model is used to calculate their binding energy; (2) the constituent atoms are identical and, consequently, their non-zero static characterization and application of nanomaterials 2025, 8(3), 11815. 3 charges cannot be attributed to differences in quantum-chemical properties such as ionization energy, electron affinity, and electronegativity; (3) for convenience of calculation, the lengths of all bonds between identical atoms are assumed to be the same, which makes the difference in coordination numbers the only cause of interatomic charge transfer. 3. results figure 1 shows the structures of boron small planar clusters bn, n = 1, 2, 3, …, 20, selected for the ground-state isomorphs [11], while tables 1‒3 present the static atomic charges evaluated using equations (4)‒(6) for electrically neutral, positively and negatively charged clusters, respectively. note that the charge numbers given in these tables are obtained by rounding the calculated values (to the third decimal place): the charge balance relationships for clusters are only approximately observed. figure 1. ground-state isomorphs of boron small planar clusters [11]. table 1. static atomic charge numbers × atomic site numbers in neutral boron small planar clusters. cluster coordination number 0 1 2 3 4 6 b1 0 ±0.000 × 1 b2 0 ±0.000 × 2 b3 0 ±0.000 × 3 b4 0 +0.200 × 2 –0.200 × 2 b5 0 +0.286 × 2 –0.071 × 2 –0.429 × 1 b6 0 +0.333 × 3 –0.333 × 3 b7 0 +0.125 × 6 –0.750 × 1 b8 0 +0.429 × 1 +0.143 × 4 –0.143 × 2 –0.714 × 1 characterization and application of nanomaterials 2025, 8(3), 11815. 4 b9 0 +0.438 × 2 +0.156 × 2 –0.125 × 4 –0.688 × 1 b10 0 +0.211 × 6 –0.053 × 2 –0.579 × 2 b11 0 +0.476 × 1 +0.214 × 4 –0.048 × 4 –0.571 × 2 b12 0 +0.250 × 6 ±0.000 × 3 –0.500 × 3 b13 0 +0.250 × 6 ±0.000 × 4 –0.500 × 3 b14 0 +0.500 × 2 +0.250 × 2 ±0.000 × 7 –0.500 × 3 b15 0 +0.500 × 3 ±0.000 × 9 –0.500 × 3 b16 0 +0.515 × 2 +0.273 × 2 +0.030 × 8 –0.454 × 4 b17 0 +0.528 × 1 +0.292 × 4 +0.056 × 7 –0.417 × 5 b18 0 +0.308 × 6 +0.077 × 6 –0.385 × 6 b19 0 +0.321 × 6 +0.095 × 6 –0.357 × 7 b20 0 +0.535 × 2 +0.302 × 2 +0.070 × 10 –0.395 × 6 table 2. static atomic charge numbers × atomic site numbers in singly positively charged boron small planar clusters. cluster coordination number 0 1 2 3 4 6 b1 + +1.000 × 1 b2 + +0.500 × 2 b3 + +0.333 × 3 b4 + +0.400 × 2 +0.100 × 2 b5 + +0.429 × 2 +0.143 × 2 –0.143 × 1 b6 + +0.444 × 3 –0.111 × 3 b7 + +0.250 × 6 –0.500 × 1 b8 + +0.500 × 1 +0.250 × 4 ±0.000 × 2 –0.500 × 1 b9 + +0.500 × 2 +0.250 × 2 ±0.000 × 4 –0.500 × 1 b10 + +0.282 × 6 +0.053 × 2 –0.421 × 2 b11 + +0.524 × 1 +0.286 × 4 +0.048 × 4 –0.429 × 2 b12 + +0.313 × 6 +0.083 × 3 –0.375 × 3 b13 + +0.308 × 6 +0.077 × 4 –0.385 × 3 b14 + +0.536 × 2 +0.304 × 2 +0.071 × 7 –0.393 × 3 b15 + +0.533 × 3 +0.067 × 9 –0.400 × 3 b16 + +0.545 × 2 +0.318 × 2 +0.091 × 8 –0.364 × 4 b17 + +0.556 × 1 +0.333 × 4 +0.111 × 7 –0.333 × 5 b18 + +0.346 × 6 +0.128 × 6 –0.308 × 6 b19 + +0.357 × 6 +0.143 × 6 –0.286 × 7 b20 + +0.535 × 2 +0.302 × 2 +0.070 × 10 –0.233 × 6 table 3. static atomic charge numbers × atomic site numbers in singly negatively charged boron small planar clusters. cluster coordination number 0 1 2 3 4 6 b1 – –1.000 × 1 characterization and application of nanomaterials 2025, 8(3), 11815. 5 b2 – –0.500 × 2 b3 – –0.333 × 3 b4 – ±0.000 × 2 –0.500 × 2 b5 – +0.143 × 2 –0.286 × 2 –0.714 × 1 b6 – +0.222 × 3 –0.556 × 3 b7 – ±0.000 × 6 –1.000 × 1 b8 – +0.357 × 1 +0.036 × 4 –0.286 × 2 –0.929 × 1 b9 – +0.375 × 2 +0.063 × 2 –0.250 × 4 –0.875 × 1 b10 – +0.132 × 6 –0.158 × 2 –0.737 × 2 b11 – +0.429 × 1 +0.143 × 4 –0.143 × 4 –0.714 × 2 b12 – +0.188 × 6 –0.083 × 3 –0.625 × 3 b13 – +0.192 × 6 –0.077 × 4 –0.615 × 3 b14 – +0.464 × 2 +0.196 × 2 –0.071 × 7 –0.607 × 3 b15 – +0.467 × 3 –0.067 × 9 –0.600 × 3 b16 – +0.485 × 2 +0.227 × 2 –0.030 × 8 –0.545 × 4 b17 – +0.500 × 1 +0.250 × 4 ±0.000 × 7 –0.500 × 5 b18 – +0.269 × 6 +0.026 × 6 –0.462 × 6 b19 – +0.286 × 6 +0.048 × 6 –0.429 × 7 b20 – +0.512 × 2 +0.267 × 2 +0.023 × 10 –0.465 × 6 excluding from consideration the three smallest clusters with identically coordinated atoms, it can be stated that the static atomic charges in small planar bn clusters in the electrically neutral and positively and negatively singly charged states are estimated as –0.750e (b7 0) to +0.535e (b20 0), –0.500e (b7 +, b8 +, and b9 +) to +0.556e (b17 +), and –1.000e (b7 –) to +0.512e (b20 –), respectively. the largest absolute values of the static charge numbers are obtained in b7 – and b20 0: –1.000 and +0.535, respectively. 4. conclusion it has been shown previously that the ground-state parameters of boron small clusters and, consequently, their relative stability and probability of formation can be successfully estimated in the so-called diatomic model or the approximation of pair interatomic potentials [12–15]. in such an approach, replacing the redistributed charge density of valence electrons with point charges does not introduce additional errors, but, on the contrary, taking into account the partial polarity of the bonds increases the reliability. in addition, this allows one to estimate the electric dipole moments of clusters and associated physical interactions with other species, as well as solid surfaces, for example, those that serve as substrates for the borophene growth. the results obtained here for planar boron clusters may have broader applications in future research directions, since nanostructures, clusters, nanoparticles, or structured materials, composed of a single element, such as only carbon atoms or only gold atoms, are materials that exhibit unique properties, often distinct from their bulk counterparts, due to quantum effects and high surface-to-volume ratios. characterization and application of nanomaterials 2025, 8(3), 11815. 6 author contributions: idea proposed: lc; calculation: to; result summarization: to & lc; manuscript writing: lc. both authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. references 1. kiran b, bulusu s, zhai hj, et al. planar-to-tubular structural transition in boron clusters: b20 as the embryo of single-walled boron nanotubes. proceedings of the national academy of sciences. 2005; 102(4): 961-964. doi: 10.1073/pnas.0408132102 2. alexandrova an, boldyrev ai, zhai hj, et al. all-boron aromatic clusters as potential new inorganic ligands and building blocks in chemistry. coordination chemistry reviews. 2006; 250(21-22): 2811-2866. doi: 10.1016/j.ccr.2006.03.032 3. li wl, chen q, tian wj, et al. the b35 cluster with a double-hexagonal vacancy: a new and more flexible structural motif for borophene. journal of the american chemical society. 2014; 136(35): 12257-12260. doi: 10.1021/ja507235s 4. becker r, chkhartishvili l, martin p. boron, the new graphene? vacuum technology & coating. 2015. 16(4): 38-44. 5. chkhartishvili l. ch. 7: all-boron nanostructures. crc concise encyclopedia of nanotechnology crc press; 2016: 53-69. 6. tian y, guo z, zhang t, et al. inorganic boron-based nanostructures: synthesis, optoelectronic properties, and prospective applications. nanomaterials. 2019; 9(4): 538. doi: 10.3390/nano9040538 7. li d, gao j, cheng p, et al. 2d boron sheets: structure, growth, and electronic and thermal transport properties. advanced functional materials. 2019; 30(8): 1904349. doi: 10.1002/adfm.201904349 8. boustani i. molecular modelling and synthesis of nanomaterials. springer international publishing; 2020. doi: 10.1007/978-3030-32726-2 9. matsuda i, wu k, eds. 2d boron: boraphene, borophene, boronene. springer international publishing; 2021. doi: 10.1007/978-3-030-49999-0 10. chkhartishvili l. relative stability of boron planar clusters in diatomic molecular model. molecules. 2022; 27(5): 1469. doi: 10.3390/molecules27051469 11. odishvili t, chkhartishvili l. all-boron planar clusters with electric dipole moment. solid state sciences. 2025; 160: 107833. doi: 10.1016/j.solidstatesciences.2025.107833 12. chkhartishvili l. quasi-planar elemental clusters in pair interactions approximation. open physics. 2016; 14(1): 617-620. doi: 10.1515/phys-2016-0070 13. chkhartishvili l. relative stability of planar clusters b11, b12, and b13 in neutraland charged-states. characterization and application of nanomaterials. 2020; 3(2): 73-80. doi: 10.24294/can.v3i2.761 14. chkhartishvili l. nanoclusters binding energy in diatomic model. international journal of advanced nano computing and analytics. 2021; 1(1): 80-83. doi: 10.61797/ijanca.v1i1.109 15. chkhartishvili l. effect of static atomic charges on small elemental clusters: evidence from boron. international journal of advanced nano computing and analytics. 2023; 2(1): 13-21. doi: 10.61797/ijanca.v2i1.150 microsoft word can-4912 characterization and application of nanomaterials 2024, 7(1), 4912. https://doi.org/10.24294/can.v7i1.4912 1 article enhancing the thermal properties of paraffin wax as latent heat storage material using hybrid nanomaterials a. a. el-sebaii1, s. aboul-enein1, m. r. i. ramadan1, n. samy1, a. r. el-sayed2, s. m. shalaby2,* 1 physics department, faculty of science, tanta university, tanta 31511, egypt 2 engineering physics and mathematics department, faculty of engineering, tanta university, tanta 31511, egypt * corresponding author: s. m. shalaby, saleh.shalaby@f-eng.tanta.edu.eg abstract: paraffin wax is the most common phase change material (pcm) that has been broadly studied, leading to a reliable optimal for thermal energy storage in solar energy applications. the main advantages of paraffin are its high latent heat of fusion and low melting point that appropriate solar thermal energy application. in addition to its accessibility, ease of use, and ability to be stored at room temperature for extended periods of time, nevertheless, improving its low thermal conductivity is still a big, noticeable challenge in recently published work. in this work, the effect of adding nano-cu2o, nano-al2o3 and hybrid nano-cu2o-al2o3 (1:1) at different mass concentrations (1, 3, and 5 wt%) on the thermal characteristics of paraffin wax is investigated. the measured results showed that the peak values of thermal conductivity and diffusivity are achieved at a wight concentration of 3% when nano-cu2o and nano-al2o3 are added to paraffin wax with significant superiority for nano-cu2o. while both of those thermal properties are negatively affected by increasing the concentration beyond this value. the results also showed the excellence of the proposed hybrid nanoparticles compared to nano-cu2o and nano-al2o3 as they achieve the highest values of thermal conductivity and diffusivity at a weight concentration of 5.0 wt%. keywords: thermal characteristics; phase change materials; paraffin wax; hybrid nanocomposites 1. introduction paraffin wax (pw) is one of the most important materials used as phase change materials (pcms) in the thermal energy storage system [1]. a lower thermal conductivity is considered the main disadvantage of pcms, which causes a lower heat transfer rate during the charging and discharging processes. many studies have been conducted to overcome this property, such as adding metallic or nonmetallic nanoparticles with high thermal conductivity [2], inserting fins [3], fibrous materials [4], macro-micro and nano-encapsulations [5,6], metal foams [7], carbon nanotubes [8]. the above-mentioned techniques used to improve the thermal conductivity of the pw include the addition of high-conductive nanomaterials, which is the simplest and most practicable technique. the influence of adding nano-graphite (ng) on the pw thermal conductivity was experimentally studied by li [9]. the results showed that the thermal conductivity of the composite pcms with 1% and 10% ng is 2.89 times and 7.41 times that of pure paraffin. nano-silicon nitride (si3n4) at different mass fractions (1, 2, 3, 4, 5, 10 wt%) was studied by yang et al. [10] to enhance the thermal properties of pw. they observed an improvement of 35% in thermal conductivity and also found an improvement in thermal diffusivity, reaching 47% at 10 wt% si3n4 citation el-sebaii aa, aboul-enein s, ramadan mri, et al. enhancing the thermal properties of paraffin wax as latent heat storage material using hybrid nanomaterials. characterization and application of nanomaterials. 2024; 7(1): 4912. https://doi.org/10.24294/can.v7i1.4912 article info received: 29 february 2024 accepted: 25 march 2024 available online: 18 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 4912. 2 additional fraction. wang et al. [11] experimentally studied the effect of dispersing copper oxide (cuo) as a nanomaterial at different mass fractions of 0.3, 0.6, 0.9, and 1.2% into the pw. they concluded that the thermal conductivity of nanocomposite pcms with a weight fraction of 1.2% had improved by 24.4%. pise et al. [12] experimentally evaluated the improvement of thermal performance of pw integrated with nano-alumina (al2o3) particles at various mass concentrations of nanoparticles of 1, 3, and 5%. they reported that the thermal performance of paraffin wax is enhanced up to 14% compared to pure paraffin. another experimental study concerning the thermophysical properties of al2o3 nanoparticles/paraffin emulsions with two mass fractions of 5 wt% and 10 wt% [13]. the measured results showed that the increase in thermal conductivity is nonlinear with the increase in nanoparticle mass fraction. yanqi et al. [14] examined how interfacial thermal resistance and particle size affected the thermal conductivity of paraffin/expanded graphite (eg) composites. they found that the increase in thermal conductivity is directly correlated with larger particle sizes. the small eg particles have less of an enhancement in thermal conductivity because interfacial thermal resistance predominates in their impact on the composite thermal conductivity. sari et al. [15] also examined the paraffin/eg composite material and revealed that the thermal conductivity of the composite increased to 0.82 w/mk at 10 wt% eg. huang et al. [16] investigated the enhancement of thermal conductivity of paraffin composites using non-equilibrium molecular dynamics simulation. the simulation results indicated that the thermal conductivity of pw is significantly enhanced by adding graphene oxide, which is more efficient than graphene. maher et al. [17] investigated the effect of the addition of nanosilicon carbide (sic) and nanosilver (ag)-based paraffin composites on the thermal characteristics of pcm. the results revealed that the thermal conductivity of the paraffin/sic composite improved by 58.2%, which is much higher than the thermal conductivity of the paraffin/ag composite, which improved by 31.2% at the same mass fraction of 15 wt%. qusay et al. [18] found that the thermal conductivity of the pw is improved by 18.2% when adding 3 wt% of nano-sic into the pw. the impact of silver nanoparticles on the thermal conductivity of the pw was experimentally studied by pradeep et al. [19]. their results showed that thermal conductivity increases with the increase of the mass concentration of ag nanoparticles. sahan et al. [20] concluded experimental research evaluating the effect of adding nanomagnetite (fe3o4) on the thermal properties of pw. they found that the thermal conductivity increased by 48% and 67% when adding 10 wt% and 20 wt% nano magnetite, respectively. according to several studies, pcm could benefit from the addition of two or more hybrid nanoparticles [21–23]. when hybrid nanoparticles are used instead of single nanoparticles, the researchers conclude that the thermal conductivity increases at the same additional mass fraction compared to individual nanoparticles. from this point forward, several practical, numerical, and experimental investigations focus on the use of hybrid nanoparticles. kumar et al. [24] studied the influence of hybrid nanoparticles containing sio2 and ceo2 nanoparticles on the thermo-physical characteristics of the pw as pcm with various mass fractions (0.5, 1.0, and 2.0 wt%). they observed that the highest paraffin’s thermal conductivity (0.298 w/m k) is achieved at 2.0 wt%. kalbande et al. [25] carried out the addition of cuo and multi-walled carbon characterization and application of nanomaterials 2024, 7(1), 4912. 3 nanotubes (mwcnt) hybrid nanoparticles into the pw for thermal energy storage applications. they found that the thermal conductivity of nano-enhanced paraffin wax (pcm) was 6.125% higher than that of pure paraffin wax. harikrishnan et al. [26] investigated the effect of dispersed hybrid nanoparticles cuo-tio2 into pw, which includes several mass concentrations of 0.25%, 0.5%, 0.75%, and 1 wt% to improve its thermal performance. they reported that the optimum studied concentration of hybrid nano-phase change material (hnpcm) is 1.0 wt%, and the improvement of thermal conductivity reaches 46.81% compared to pure paraffin. ibrahim et al. [27] added nano-tio2, nano-mgo, and a 50% mixture of the two kinds into pw at different mass fractions of 0.25%, 0.5%, 0.75%, and 1 wt% to find the maximum thermal storage characteristics of pcm. they observed that the highest enhancement is achieved when adding 1% of the nanoparticles, and the thermal conductivity at this fraction is 4.6%, 3.9%, and 4.6% for nano-tio2, nano-mgo, and hybrid nanoparticles, respectively. in this work, the experimental investigations were conducted thoroughly to analyze the variation of thermo-physical properties of paraffin wax based as pcm under the influence of various weight concentrations (1%, 3%, 5%) of the nanoparticles, namely: cu2o and al2o3. it is very important to mention here that cu2o nanoparticles are used for the first time, as authors know, to improve the thermal properties of paraffin wax. a thorough investigation into the impact of additional hybrid nanoparticles on the thermo-physical properties of paraffin is also rare in the literature. therefore, the hybrid nanoparticles were also prepared by mixing equal masses of cu2o and al2o3 to study their effect on the thermo-physical characteristics of the pcm. it was found that the hybrid nanoparticles at a mass fraction of 5.0 wt% presented significant potential for enhancing the thermal storage properties of the paraffin wax. 2. experimental work in this study, the effect of adding cu2o, al2o3 nanoparticles, and hybrid cu2oal2o3 nanoparticles into pw under different mass fraction concentrations (1%, 3%, 5%) on its thermal characteristics has been studied. to determine the accurate weights of pure pw, cu2o, al2o3, and hybrids of the two nanoparticles, a digital balance with an accuracy of 0.0001 g was employed. using a water path, 100 g of pure pw was melted at a melting point of 56 ℃ in order to prepare a specific pw/nanocomposite to obtain paraffin/nano-cu2o (npcm-1), paraffin/nano-al2o3 (npcm-2) and paraffin/hybrid nano-cu2o-al2o3 (1:1) (npcm-3) as shown in table 1. after the completely melted pw, nano-cu2o, nano-al2o3 and hybrid nanoparticles were added to the pw individually under continuous stirring for around 15 min to reduce the precipitation of the droplet’s nano-additives into the pw and make the mixture homogenous. these steps were repeated at each of the nano-additives with various mass concentrations (1%, 3%, 5%). all samples are allowed to cool at room temperature and then shaped into a disc shape in the press designed for this process, where all prepared samples of pw, npcm-1, npcm-2, and npcm-3 were impressed at 15 mm diameter and 3 mm thickness, as shown in figure 1. the thermal properties of pw before and after adding the nano-additive materials were measured using the characterization and application of nanomaterials 2024, 7(1), 4912. 4 hot disc transient (hot disc tps 500 s). repeating the test twice produces more accurate, very flexible, fast, non-destructive, and reliable thermal properties of pw before and after adding the nano-additive materials, including thermal conductivity, thermal diffusivity, and specific heat. the size of the samples must be determined when a suitable disc radius for a particular material has been chosen and the best test times for the disc and material combination are known. taking into consideration that the nickel spiral sensor 7577 has a has a radius of 2.1 mm with kapton insulation sandwiched between two sample portions to ensure tight contact with the sensor to minimize the amount of air gap. more details about al2o3 nanoparticle preparation and characterization can be found elsewhere [28]. while cu2o nanoparticles are purchased from qualikems fine chem pvt. ltd., vadodara, gujarat, india. table 1. sample labelling and compositions. s. no. sample label composition (wt%) 1 pure paraffin 100 pw 2 1% npcm-1 99 pw + 1.0 nano-cu2o 3 3% npcm-1 97 pw + 3.0 nano-cu2o 4 5% npcm-1 95 pw + 5.0 nano-cu2o 5 1% npcm-2 99 pw + 1.0 nano-al2o3 6 3% npcm-2 97 pw + 3.0 nano-al2o3 7 5% npcm-2 95 paraffin+ 5.0 nano-al2o3 8 1% npcm-3 99 pw +0.5 nano-cu2o + 5.0 nano-al2o3 9 3% npcm-3 97 pw + 1.5 nano-cu2o + 1.5 nano-al2o3 10 5% npcm-3 95 pw + 2.5 nano-cu2o + 2.5 nano-al2o3 figure 1. photograph of the prepared paraffin nanocomposites. 3. results and discussions in this section, the measured values of different thermal properties of the prepared samples of pure paraffin and nanocomposites are presented, discussed, and evaluated. the compromise between adding individual or hybrid nanoparticles into the pw is also of great interest in this section. figure 2 shows the variation of the thermal conductivity of npcm-1, npcm-2, and npcm-3 with the concentrations. for samples npcm-1 and npcm-2, it was observed that the thermal conductivity of samples npcm-1 and npcm-2 reaches its peak value of 0.2760 w/m k and 0.2708 w/m k at 3.0% mass fraction of nano-cu2o and nano-al2o3, respectively, with an improvement of 10.98% and 9.27% compared to the measured value for pure pw (0.2457 w/mk). but such a tendency is declined characterization and application of nanomaterials 2024, 7(1), 4912. 5 at 5.0 wt% for both samples. the improvement of thermal conductivity is calculated as: 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝑖𝑚𝑝𝑟𝑜𝑣𝑒𝑚𝑒𝑛𝑡 = × 100, figure 2. the thermal conductivity of the nepcms at different concentrations of 1.0, 3.0 and 5.0 wt%. the improvement of thermal conductivity of the pw is primarily because these additive nanomaterials have higher thermal conductivity and the combination performance of the nano-additives into the paraffin wax to enable the use of phasechange heat at higher temperatures to enhance the released rate of heat in paraffin. the results of figure 2 also show that the thermal conductivity of pw/nano-cu2o is higher than that of pw/nano-al2o3 at all studied mass concentrations. while it is higher than those values measured for pw/hybrid nanoparticles except at a mass fraction of 5.0%. this situation of decline happens at higher concentrations (>3%) in npcm-1 and npcm-2 samples due to the poor combination between the nano-additives and paraffin, which causes an interfacial thick layer [29], hence augmenting the interface thermal resistance between the paraffin and nano-additives. this layer is unable to contribute to the phase change temperature as phase change does not take place in the interface layer, so it decreases the thermal storage unit volume. furthermore, the thicker thermal storage layer also diminishes the heat conduction performance of the nepcms. the same non-linear trend of thermal conductivity of nano cu–paraffin composites has been reported by lin and al-kayiem [30]. the results reveal that the increased mass percentage of nanoparticles in the base material may form their repressible agglomeration due to the prevailing cohesive forces, which would account for the diminished slope in the magnitude of thermal conductivity at the upper mass fractions. the phenomenon of an increase and sudden decrease in thermal conductivity of nano-al2o3 was also reported by arshad et al. [31] due to randomly molecule motion within the disordered microstructure of paraffin in the liquid phase. the hybrid nano-cu2o and nano-al2o3 show different effects as shown in figure 2, where the thermal conductivity increases with incrusting the mass fraction (under the studied values) to reach 0.2780 w/m k at a mass concentration of 5.0% compared to 0.2441 w/mk and 0.2133 w/mk for nano-cu2o and nano-al2o3, respectively. this improvement achieved by adding hybrid nanomaterials is considered the best among characterization and application of nanomaterials 2024, 7(1), 4912. 6 the studied cases, reaching 11.62% compared to pure paraffin. keep in mind that this improvement was achieved at a higher concentration (5.0%). the results of figure 2 also show that the improvement percentages of the thermal conductivity of paraffin/nano-cu2o, paraffin/nano-al2o3 and paraffin/hybrid nanoparticles at 1.0 wt% are 7.28%, 1.56%, and 1.17%, respectively, compared to pure paraffin. while these improvements reached 10.98%, 9.27%, and 7.87%, respectively, at a mass concentration of 3.0% compared to pure paraffin. the results also showed a drop of 0.65% and 13.19% in the thermal conductivity of pw/nano-cu2o and pw/nano-al2o3 at 5.0 wt%, respectively. figure 2 also shows that the thermal conductivity improvement for pw/nano-cu2o is higher by about 5.8% and 1.88% than for pw/nano-al2o3 and pw/hybrid nanoparticles, respectively, at mass fraction 1%, while these percentages increase to 6.19% and 3.37%, respectively, when mass fraction 3.0 wt% is used. on the other hand, the thermal conductivity of pw/hybrid nanoparticles at 5 wt% is higher than the corresponding measured values of pw/nanocu2o and pw/nano-al2o3, which are 12.19% and 23.27%, respectively. among the physical properties, thermal diffusivity is considered one of the most important properties because it measures the facility of a material to conduct thermal energy, corresponding to its ability to store thermal energy. considering the fact that thermal diffusivity has a great significance in thermal management, this property was investigated in the current study, as shown by the results presented in figure 3. this figure shows that the thermal diffusivity of samples npcm-1 and npcm-2 reach their maximum values of 0.1595 m2/s and 0.1252 m2/s at 3.0% mass fraction of nano-cu2o and nano-al2o3, respectively, compared to 0.1130 m2/s for pure paraffin. so the maximum improvements achieved by adding nano-cu2o and nano-al2o3 are 29.15% and 9.74%, respectively, compared to pure paraffin. accordingly, the thermal conductivity is directly proportional to the thermal diffusivity, so the behavior observed in thermal diffusivity is the same in thermal conductivity. increasing the mass fraction of nano additives causes an increase in the thermal diffusivity except at concentrations of 5.0 wt% for each of the nano-cu2o and nano-al2o3 where the decline occurs, decreasing to 0.1006 and 0.0692 m2/s, respectively, in comparison to pure paraffin. figure 3. the thermal diffusivity of the nepcms at different concentrations of 1.0, 3.0 and 5.0 wt%. characterization and application of nanomaterials 2024, 7(1), 4912. 7 from the results of figure 3, the thermal diffusivity enhanced to 0.1245 m2/s, 0.1493 m2/s and 0.2440 m2/s at 1.0, 3.0, and 5.0 wt%, respectively. in comparison to nano-al2o3 and hybrid nano, the paraffin wax/nano-cu2o composite exhibits a percentage improvement of 19.21% and 16.39% at a weight concentration of 1% and 21.50% and 6.39% at a weight concentration of 3%, respectively, as shown in figure 3. however, the hybrid nano has a percentage rise of 58.77% and 71.64% greater than nano-cu2o and nano-al2o3 at a weight concentration of 5.0%, respectively. this means that the higher the dispersion of suspended nanoparticles, the higher the thermal diffusivity, which accelerated heat transmission from the top to the bottom of the nanocomposite. the limited dispersion of suspended nanoparticles will affect the value of thermal diffusivity, which will create a reduced heat transfer rate even though the ratio of added nanoparticles is higher. the comparison between the thermophysical properties of all established samples is summarized in table 2. table 2. enhanced thermal properties of the pure paraffin wax. samples thermal conductivity (w/mk) percentage of enhancement (%) thermal diffusivity(m2/s) percentage of enhancement (%) pure paraffin 0.2457 0.1130 1% npcm-1 0.2650 7.28 0.1489 24.11 3% npcm-1 0.2760 10.98 0.1595 29.15 5% npcm-1 0.2441 0.1006 1% npcm-2 0.2496 1.56 0.1203 6.07 3% npcm-2 0.2708 9.27 0.1252 9.74 5% npcm-2 0.2133 0.0692 1% npcm-3 0.2486 1.17 0.1245 9.24 3% npcm-3 0.2667 7.87 0.1493 24.31 5% npcm-3 0.2780 11.62 0.2440 53.69 the specific heat is the only measured property that decreased with the nanocu2o, nano-al2o3 and hybrid additions into pw as it is inversely proportional to the thermal conductivity and diffusivity as shown in the following equation: 𝛼 = 𝑚 𝑠. where 𝛼 and 𝑘 are thermal diffusivity (m2/s), and thermal conductivity (w/m k), respectively, 𝜌 is the density (kg/m3) and 𝑐 is specific heat (j/𝑚 𝑘). the reduction rates as shown in figure 4 were 15.52%, 20.88%, 2.31%, and 2.80% for the addition of nano-cu2o and nano-al2o3 at concentrations of 1.0 and 3.0 wt%, respectively, in comparison to pure paraffin. according to the decrease in thermal conductivity and also thermal diffusivity for nano-cu2o and nano-al2o3 at 5.0 wt%, the specific heat increased to 2.427 j/𝑚 𝑘, 3.081 j/𝑚 𝑘, respectively, which equals 2.1739 j/𝑚 𝑘 for pure paraffin. as shown in figure 4 the peak reduction percentage is 48.43%, compared to pure paraffin in the case of hybrid nanoparticles at 5.0 wt%. since the specific heat capacity of nano-cu2o is lower than that of nanoal2o3 by about 13.52%, 18.60%, and 21.23% at 1.0, 3.0, and 5.0 wt%, respectively. the same conclusion is revealed by kok [32]. the author integrated paraffin wax as characterization and application of nanomaterials 2024, 7(1), 4912. 8 pcm with alumina (al2o3) and copper oxide (cuo). his results showed that copper oxide has a lower specific heat capacity than alumina. also, the influence of the occupied volume variation of nanoparticles immersed into the paraffin was studied by sushobhan and kar [33]. their results agree with the present work since the specific heat of the composites decreased by increasing the volume fraction of nanomaterials through the composite. figure 4. the specific heat of the nepcms at different concentrations of 1.0, 3.0 and 5.0 wt%. from the above results, the hybrid nano-cu2o-al2o3 paraffin wax composite at a concentration of 5 wt% is the best among the studied nepcms in this work for thermal energy storage systems because it has the highest thermal conductivity and diffusivity. it also has the lowest specific heat, which is considered a good feature in this case as it quickly reaches the melting point. 4. conclusions in this study, high-thermal-conductive nano-additives materials were used to prepare nepcms by adding different concentrations of cu2o, al2o3, and a mixture of the two oxides in a ratio of 1:1 into the paraffin wax. in general, adding high thermally conductive nano-additives increases the thermal conductivity and thermal diffusivity of the paraffin nano-oxide composites while decreasing the specific heat in comparison to pure paraffin. the peak values of thermal conductivity and diffusivity are achieved at a weight concentration of 3.0% when nano-cu2o and nano-al2o3 are added to paraffin wax with significant superiority for nano-cu2o. while both of those thermal properties are negatively affected by increasing the concentration beyond this value. the results also showed the excellence of the proposed hybrid nanoparticles compared to nano-cu2o and nano-al2o3, as they achieved the highest values of thermal conductivity and diffusivity at a weight concentration of 5.0 wt%. it also has the lowest specific heat among the studied samples at a weight concentration of 5.0%. increasing the weight concentration in the case of hybrid nanoparticles may lead to more improvement in the thermal properties. so, it is strongly recommended for future work to study the proposed hybrid nanoparticles of paraffin wax at higher weight concentrations. characterization and application of nanomaterials 2024, 7(1), 4912. 9 author contributions: conceptualization, sms, aaes and mrir; methodology, sae; software, ares; formal analysis, ns; investigation, ns; data curation, ns; writing—original draft preparation, ns; writing—review and editing, sms; visualization, ares; supervision, aaes, sae, mrir, sms; project administration, aaes. all authors have read and agreed to the published version of the manuscript. acknowledgments: this paper is based upon work supported by science, technology and innovation funding authority (stifa), capacity building project, code: 42922. conflict of interest: the 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improvement of thermal energy storage. energy procedia. 2017; 109: 385-392. doi: 10.1016/j.egypro.2017.03.035 characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.2068 1 original research article water vapor permeability of smooth cellulose nanofiber film prepared via spraying kirubanandan shanmugam1*, narendhar chandrasekar2, ramachandran balaji3 1 saveetha school of engineering, saveetha institute of medical and technical sciences, chennai 602107, india. email: kirubanandan.shanmugam@gmail.com 2 department of bionano technology, gachon university, seongnam 13120, republic of korea. 3 department of chemical engineering and biotechnology, national taipei university of technology, taipei 10608, china. abstract eco-friendly and greener barrier materials are required to replace the synthetic packaging materials as they produce a threat to environment. these can be fabricated by natural polymers such as cellulose nanofiber (cnf). the sustainability of cnf was so amazing due to its potential for circular economy and provides alternative platform for synthetic plastics. the challenging task to fabricate cnf films still existed and also current methods have various limitations. cnf films have good oxygen permeability and the value was lower than synthetic plastics. however, cnf films have poor water vapour permeability and higher than that of synthetic plastics. the fabrication method is one of strong parameters to impact on the water permeability of cnf films. the deposition of cnf suspension on the stainless-steel plate via spraying, is a potential process for fabrication for cnf films acting as barrier material against water vapour. in spraying process, the time required to form cnf films in diameter of 15.9 cm was less than 1 min and it is independent of cnf content in the suspension. the uniqueness of cnf films via the spraying process was their surfaces, such as rough surface exposed to air and smooth surface exposed to stainless steel. their surfaces were investigated by sem, afm and optical profilometry micrographs, confirming that the smooth surface was evaluated notable lower surface roughness. the spray coated surface was smooth and glossy and its impact on the water vapor permeability remains obscure. the spraying process is a flexible process to tailor the basis weight and thickness of cnf films can be adjusted by the spraying of cnf suspension with varying fibre content. the water vapour permeability of cnf films can be tailored via varying density of cnf films. the plot between water vapour transfer rate (wvtr)/water vapour and density of cnf films has been investigated. the wvp of spray coated cnf films varied from 6.99 ± 1.17 × 10−11 to 4.19 ± 1.45 × 10−11 g/m.s.pa. with the density from 664 kg/m3 to 1,412.08 kg/m3. the wvp of cnf films achieved with 2 wt% cnf films (1,120 kg/m3) was 3.91 × 10−11 g/m.s.pa. these values were comparable with the wvp of synthetic plastics. given this correspondence, cnf films via spraying have a good barrier against water vapour. this process is a potential for scale up and commercialization of cnf films as barrier materials. keywords: cellulose nanofiber (cnf); spray coating; water vapour permeability; water vapour transfer rate (wvtr); synthetic plastics 1. introduction cellulose nanofiber (cnf) is a type of nanomaterial derived from natural cellulose fibres, which is the main component of plant cell walls. the notable properties of cnf are high mechanical strength, high surface area, biodegradability, and biocompatibility[1]. there are several types of nanocellulose, including cellulose nanocrystals article info received: 27 april 2023 accepted: 13 june 2023 available online: 21 june 2023 2 (cncs), cellulose nanofibrils (cnfs), and bacterial cellulose (bc)[2]. cncs were produced from acid hydrolysis of cellulose fibres and are typically rod-shaped with dimensions on the order of 5–20 nm in diameter and several hundred nanometres in length[2]. cnfs were also produced by mechanical processing of cellulose fibres from the wood pulp and non woody pulp and the size of cnf typically has widths ranging from 5 to 50 nm and lengths ranging from several microns to several millimeters. bacterial cellulose is produced by bacteria and has similar properties to plant-derived cellulose, but with higher purity and consistency[3]. cellulose nanofiber (cnf) is a sustainable fibrous nanomaterial used as feed stock for the fabrication of free-standing films and composite with various nano-inorganic materials. past decade, cnf was getting improved attention to play as alternative for synthetic plastics in packaging application. cnf has a good potential for recyclability and biodegradability. cnf was produced by the fibrillation of cellulose pulps from lignocellulosic biomass through mechanical process such as homogenization, chemical process such as acid hydrolysis and tempo and enzymatic process. cnf has low density and toxicity and provides a platform for sustainability and circular economy. the film prepared from cellulose nanofibrils has translucency and good strength[3]. cnf films were reported as a good barrier against oxygen, however poor barrier against water vapour. the challenge in this area is to bring the value of water vapour permeability (wvp) of free-standing cnf films near to synthetic plastics. the fabrication of cnf films is one of the strong parameters controlling the water vapour barrier performance of the film[2]. the reported fabrication methods for cnf films were solvent casting, hot pressing, roll to roll (r2r) coating, vacuum filtration and spray coating[3]. vacuum filtration is the most common process for fabricating cnf films. in this method, the filtration time to form cnf films exponentially increased with cnf suspension consistency. the time for forming cnf films on the filter mesh consumes 10 min[4] to 4 h[3]. the filter marks were appeared on cnf films when the film was peeled from the filter mesh. these marks affect the uniformity of the film indirectly effects on the barrier properties and mechanical properties of cnf films. solvent casting is a laboratory scale method to fabricate cnf films for various applications. however, the evaporation of water from cnf suspension consumes time more than a day to form the film on the petri dish. the limitation of cast cnf films consists of shrinkages which affects the uniformity and various properties of cnf films. this method has time constraint and not fit for scale up for commercialization via large scale production[3]. recently, spraying cnf suspension on the polished metal surface is a novel process for fabrication of free-standing cnf films[5,6]. in the spraying process, cnf suspension was deposited on the stainless-steel plate via spray coating and then allowed to dry in standard laboratory copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 3 conditions. dried cnf films were smoothly and easily peeled from the stainless-steel plate. in the case of fabricating cnf films via spraying, the thickness and basis weight of cnf films can be tailored via spraying cnf suspension with various fibre content. the operation time for spraying cnf suspension was independent of their solid content. the spraying process was rapid in the formation of wet cnf films[6]. the mechanical and barrier properties of the film can be tailored via spraying various concentration of cnf on the stainless-steel plate[2]. even though the film made from cnf has a good barrier against oxygen and also incomparable with synthetic plastics[7]. cnf films have poor barrier properties against water vapour due to high affinity between cellulose nanofibrils and water molecules. cnf is a highly hydrophilic polymer and capable for susceptible to water molecules. but cnf is much better than nominal cellulose fibres such as paper and paper board substrates in terms of water vapour permeability[3]. this is why cellulose nanofiber was used as high-performance barrier material as it forms a compact network/mesh of cellulose nanofibrils to free standing cnf films[6]. apart from this, cnf films have very minute pores and complex tortuous pathway for water vapour and air than that of normal cellulose substrates[1,8]. it was noticed that the fabrication methods also control the wvp of cnf films and other barrier properties of cnf films, such as air permeance and oxygen permeability[3]. having spraying process for scale up potential, the wvp of spray coated cnf films should be investigated and their water vapour transfer mechanism across cnf films should be investigated. this paper deals the effect of cnf films density on the water vapour transfer rate and the water vapour permeability of cnf films and the wvp of cnf films was compared with cnf films from synthetic plastics. 2. materials and methods the number of terminologies for cellulose nanofiber (cnf) has been mentioned in various scientific literatures. generally, cellulose nanofibers are also called as nano-fibrillated cellulose, cellulose nano-fibrils, micro fibrillated cellulose and nanocellulose, etc. but in this scientific study, cellulose nanofiber/nanocellulose has been reported throughout in this paper[2]. the cnf was used as a feed stock for fabrication of cnf films. the used raw cnf is ky 100s received from diacel chemical industries, japan. the cnf content in ky100s was 25 wt.% and the mean diameter of cellulose nanofibrils in cnf was 73 nm. the aspect ratio of raw cnf (ky100s) was investigated to be 142 ± 28 and the crystallinity index of the ky 100s was evaluated to be 78%. the sem micrographs of the raw cnf have been shown in figure 1[6]. figure 1. sem micrograph of cellulose nanofiber (ky 100s)—diacel chemical industries, japen. 2.1 preparation of cnf suspension for spraying the cnf suspension was prepared with concentration varying from 1 wt.% to 2 wt.% of cnf content in the water. the raw cnf quantity of interest was added into the double distilled water and disintegrated at 15,000 rpm for 15 min to make cnf suspension of interest. in this way, the cnf suspension from 1 wt.% to 2 wt.% was produced for spraying process. 2.2 fabrication of cnf films via spraying the experimental set up for spray system was shown in figure 2. the cnf suspension was sprayed on the polished stainless-steel plate via the professional wagner spray system. the process conditions for spraying process have been followed 4 as per the reported in our previous scientific literature. there are two important parameters in the spray coating experimental system to control/tailor the thickness and basis weight of cnf films were velocity of the conveyor and cnf suspension consistency. in this study, the velocity of the conveyor was maintained a constant parameter at a velocity of 0.32 cm/sec and then cnf suspension was varied from 1 wt.% to 2 wt.% for spraying on the stainless-steel plate. the spray distance between spray tip to the circular stainless-steel plate was 30 ± 1 cm. the diameter of the orifice in spray nozzle was 0.38 mm and produces elliptical pattern and spray width of 50 cm[6]. figure 2. experimental system for spray coating setup. 2.3 drying of cnf films and its characterization the wet film on the stainless-steel plate was formed and dried under standard laboratory conditions. in drying spray coated wet cnf films, the film was kept in laminar flow chamber with constant flowrate for faster removal of water from the wet film. the dried film was easily peeled from the stainless-steel plate and subjected to the measurement of thickness and basis weight of the film. the apparent density of cnf films was evaluated from its thickness and basis weight of the film. the surface topography and morphology of spray coated cnf films was evaluated by scanning electron microscopy as per the reported procedure previously[2]. the surface roughness of cnf films was evaluated by atomic force microscopy and optical profilometry[6]. 2.4 evaluation of water vapour barrier of spray coated cnf films the water vapour barrier of cnf films was performed as the per standard of astm e96/e96m-05[9]. the films/specimen size having diameter of 76 mm was used as specimen and dried in an air oven at a temperature of 105 ℃ for 4 h. this would help the complete removal of moisture from the specimen to evaluate water vapour permeability of the film perfectly. as per the astm standard, the brass cups were filled with dried anhydrous calcium chloride and then covered with cnf films as experimental cups and cups covered without cacl2 as control in the experimental study. this test was carried out at 23 ℃ and 50% rh and the weight of the cup was increased/measured due to the absorption of water vapour across cnf films. from the data, the water vapour transmission rate (wvtr) is the slope derived from the plot between weight of the cup and time[2,9,10]. 푊푉푇푅 = 퐺 푡 × 퐴 where g/t refers to the slope of a straight line (g h−1) and a is the surface area of the films (m2). the water vapour permeability of cnf films was evaluated from the wvtr normalized with thickness of cnf films. the permeance of cnf films was found to be: 푃푒푟푚푒푎푛푐푒 = 푊푉푇푅 푆(푅1 − 푅2) where s is the saturation vapor pressure per mmhg (1.333 × 102 pa) at the tested temperature, r1 is the relative humidity of the source and r2 is the relative humidity of the vapor sink, expressed as a fraction. finally, the wvp of the films can be evaluated as 푊푉푃 = 푃푒푟푚푒푎푛푐푒 × 푇ℎ푖푐푘푛푒푠푠 표푓 퐶푁퐹 푓푖푙푚 the mean of wvp from three replicates in the experiment was reported in this work. the value of wvp of cnf films was compared with the synthetic plastics to show the potential of cnf films as a good barrier against water vapour. 3. results and discussion spraying nanofibers is a new concept for fabrication of film for various applications[11–13]. nanofiber spraying has several advantages over traditional fibre production methods, including a higher surface area to volume ratio, enhanced mechanical 5 properties, increased porosity, and improved biocompatibility[3]. applications of nanofiber spraying include drug delivery, tissue engineering, air filtration[1,8], and energy storage such as fabrication of sustainable electrodes[13,14]. however, there are still challenges in scaling up nanofiber spraying for commercial production and optimizing the process parameters[6] for specific applications such as food packaging and barrier materials[7,10]. spraying cnf suspension on the polished stainless-steel plate is a flexible method to fabricate cnf films with unique surfaces[6]. the spray coated cnf has two unique surfaces namely rough surface exposed to air and smooth surface exposed to the stainless-steel plate. spraying cnf suspension on the metal surface produce the film with glossy and shiny and the smoothness of the film was replicated from the stainless-steel plate[6]. figure 3 shows the spray coated cnf films and shows the two surfaces of the film. spray coated cnf films have very compact and cellulose nanofibrous network[6]. the basis weight and the thickness of cnf films were tailored by varying cnf suspension for spraying[10]. the compactness of cnf films was achieved via the coalescence of the atomized cnf suspension from the spray jet in the spraying process. the atomized cnf suspension formed together via forming hydrogen bonds between the hydroxyl group of the cellulose nanofibrils, results in forming the compact film[3,11]. 3.1 scanning electron microscopy micrograph figure 4 reveals the rough and smooth surface of spray coated cnf films. the rough side of cnf films was porous and high surface roughness. the roughness of the film was high due to the distribution of various fibres. the smooth side of cnf films was glossy and shiny. the surface roughness of the film on the smooth side was very low and fibres compressed and mimics the surface smoothness of the film from stainless steel plate. however, the effect of surface roughness on the barrier performance of cnf films remains obscure[10]. figure 3. spray coated cnf films. (a) (b) figure 4. (a) rough surface of spray coated cnf films’ sem micrographs. (b) smooth surface of spray coated cnf films’ sem micrographs. 3.2 optical profilometry images figure 5a–b reveals the optical profilometry of cnf films confirming the rough surface and smooth surface of cnf films. in this investigation, the rms of both surfaces were evaluated. the 6 rms of rough and smooth side was reported to be 2000 nm and 400 nm, respectively[6,10]. the effect of surface roughness on the rough side and surface smoothness on the smooth side of cnf films were obscure on the barrier performance against water vapour. (a) figure 5. (a) optical profilometry image of rough side of cnf films. (b) optical profilometry image of smooth side of cnf films. 3.3 atomic force microscopy images afm micrographs of cnf films confirms the surface roughness of the both surfaces at nanoscale dimension. it confirmed that the rough side of the film was very porous and high surface roughness due to various size distribution of cellulose nanofibrils. the smooth side of the film was very glossy and shiny and their surface roughness was too low. the rms for rough surface and smooth surface was reported to be 51.4 nm and 16.7 nm[6]. see figure 6a–b. (a) figure 6. (a) afm micrograph of rough side of spray coated cnf film. (b) afm micrograph of smooth surface of cnf films. 3.4 water vapour barrier performance of cnf films water vapour permeability (wvp) refers to the ability of a material to allow the passage of water vapour through it. this property is important in packaging, as it affects the moisture resistance of the material. the wvp of a material depends on their structure, thickness, and other factors. the performance of cnf films as water vapour barriers has been attributed to their ability to form dense, nano porous networks that impede the movement of water molecules. it has been noticed that the fabrication method for cnf films is one of the main 7 criteria for controlling water vapour barrier performance of the films. figure 7 reveals the effect of film’s density on the water vapour transmission rate of cnf films. the apparent density of cnf films is defined as the ratio between basis weight and thickness of cnf films[6]. the basis weight and thickness of the cnf can be tailored by varying cnf suspension concentration for spraying process to fabricate the cnf[6]. the relationship between thickness and basis weight of cnf films was linear[6]. as a result, the water transmission rate of cnf films was tailored via thickness and basis weight of the film[10]. the wvtr of cnf films was comparable with synthetic plastics. the wvtr was normalized with thickness of cnf films to give the value of wvp[2]. 800 900 1000 1100 1200 1300 1400 1500 0 20 40 60 80 100 120 140 160 180 200 w at er v ap ou r t ra ns fe r r at e ( g /m 2. da y) density of cnf film (kg/m3) figure 7. effect of film’s density on water vapour transfer rate. figure 8 shows the effect of apparent density on the wvtr of cnf films. the spraying process was carried out in two different conditions. one of the conditions from fixed cnf concentration and varied velocity of the conveyor in the experimental set up was performed[2]. the other was from the fixed velocity of the conveyor and varied cnf suspension concentration from 1 wt.% to 2 wt.% was carried out to fabricate the cnf films. this plot confirms that the lower density of cnf films gives good barrier against water vapour. figure 9 shows the effect of density on the water vapour permeability of cnf films. it is noted that the wvp of cnf films was comparable with synthetic plastics. the lower density of the film gives good barrier against water vapour. however, 700 800 900 1000 1100 1200 1300 1400 1500 0 20 40 60 80 100 120 140 160 180 200 spraying process 1 spraying process 2 w at er v ap ou r t ra ns fe r r at e ( g /m 2. da y) density of cnf film (kg/m3) figure 8. effect of density on water vapour transmission rate. 660 680 700 720 740 760 780 800 820 0 1 2 3 4 5 6 7 water vapour permeability (g/m.s.pa* 10-11) d en si ty o f c n f fi lm (k g/ m 3) water vapour permeability figure 9. effect of density on the water vapour permeability of the cnf films. the higher density of cnf films has poor barrier performance against water vapour[2]. figure 10 shows the effect of cellulose nanofibrils on the water vapour permeability. this is due to the reducing effect of cellulose nanofiber. it means that cellulose nanofibrils is a hydrophilic polymer, reduced the water vapour permeability of the film when fibre diameter reduced. when the fibre diameter of cnf is reduced, the water vapour diffusion rate was increased across the tortuous pathway in the film. cnf films with lowest fibre diameter forms rigid fibrous network which acts as a good resistance against gaseous substances including water vapour[15]. the diameter of cnf reduction was performed by the mechanical process such as high-pressure homogenization, chemical 8 methods such as acid hydrolysis and enzymatic process[16]. the data in figure 10 was derived from the spraying of high pressure homogenized cnf suspension on the stainless-steel plate to fabricate cnf films which acts as high-performance barrier against water vapour[10]. 10 20 30 40 50 60 70 80 0 1 2 3 4 w ater v apo ur p erm eab ility (g /m .s .p a * 10 -11) fi br e d ia m et er (n m ) figure 10. effect of fibre diameter on the wvp of cnf films. 3.5 comparison with synthetic plastics figure 11 reveals the potential of spray coated cnf films as a good water vapour barrier and comparable with synthetic politics. however, the thickness of packaging film also decides the barrier performance of the film against water vapour. this is why water vapour permeability was used to describe the water vapour barrier performance of the film and this value was calculated via the normalizing thickness of the film with their wvtr values. figure 12 shows the comparison of spray coated cnf films with synthetic plastics in terms of wvp. this plot confirms that the wvp of spray coated cnf films has comparable with synthetic plastics[17]. apart from this advantage, cnf is an eco-friendly friendly nanomaterial that has capacity to degrade in environment[18,19]. 3.6 barrier mechanism of cnf films figure 13 reveals the mechanism of water vapour passage across the spray coated cnf films. the nanocellulose/cnf suspension was well mixed during the spraying process and sprayed on the stainless-steel plate[6,12]. it results in the formation of smooth cnf films[6]. it has been concluded that cnf films are an effective barrier against water vapour due to its physical and mechanical properties[17]. the barrier mechanism of cnf films can be commented as the following factors. the nanostructure of cnf films is a predominant reason for good barrier mechanism even though cnf is a hydrophilic polymer[20,21]. generally, cnf has high aspect ratio and high surface area to volume ratio[24]. this unique nanostructure the cnf film spray coated (96.5 g/m2) the cnf film vacuum filtration (100 g/m2) recycled cellulose film from spray coated nc cellulose nano fibrils acetylated cnf (acetylation time-30 mins) polyvinylidene chloride polyethylene (pe) plasticized (pvc) aluminium foil ldpe hdpe oriented nylon 6 oriented polystyrene eva evoh pa pet pc ps pp 0 50 100 150 200 250 wvtr in g/m2 day wvtr figure 11. comparison of wvtr of cnf films with conventional synthetic plastics. 9 the cnf film spray coated (96.5 g/m2) the cnf film vacuum filtration (100 g/m2) recycled cellulose film from spray coated nc cellulose nano fibrils acetylated cnf (acetylation time-30 mins) polyvinylidene chloride polyethylene (pe) plasticized (pvc) aluminium foil ldpe hdpe oriented nylon 6 oriented polystyrene eva evoh pa pet pc ps pp 0 2 4 6 8 10 watervapour permeability (g/m.s.pa) x 10-11 watervapour permeability figure 12. comparison of wvp of cnf films with synthetic plastics. figure 13. water vapour barrier mechanism of spray coated cellulose nanofiber film. of cnf forms a compact network of cellulose nanofibrils during the fabrication of cnf films via spraying[6]. it results a compact and dense film which acts as barrier against gaseous molecules. the dense packing of cnf produces a tortuous pathway for diffusion of water vapours, which reduces the permeability of the film to water vapour[21,22]. cnf has high source of hydroxyl groups (–oh) present in their surface of cellulose nanofibrils and offers for strong intermolecular hydrogen bonding between adjacent fibres[18]. in addition to that, cnf films were densified via crosslinking of the fibres via hydrogen bonding and it strengthens the intermolecular and intramolecular hydrogen bonds in the film[23]. as water vapour is polar in nature and forms hydrogen bonds, the strong intermolecular hydrogen bonding between the cellulose nanofibers creates a strong barrier to water vapour diffusion. overall, the combination of the unique nanostructure and the strong intermolecular hydrogen bonding in cellulose nanofiber films results in a highly effective water vapour barrier, making it an ideal material for a wide range of applications where water vapour barrier properties are required[17,21,22]. 3.7 recommendations for improving the wvp of cnf films the following recommendations have been mentioned to improve the water vapour barrier performance of cnf films. 10 1) use a higher concentration of cellulose nanofibers: increasing the concentration of cellulose nanofibers in the film can lead to smaller pores and increased density, improving the film’s ability to block water vapour[6,10]. 2) incorporate hydrophobic materials: adding materials that repel water, such as hydrophobic nanoparticles like silica or graphene or montmorillonite[24], can improve the water vapour barrier properties of the film[25,26]. 3) modify the surface of the cellulose nanofibers: the surface of cellulose nanofibers can be modified with various chemicals to increase the surface charge or to introduce hydrophobic/hydrophilic functionalities. this can help to alter the water interactions of the film[24]. 4) increase the number of layers: building up multiple layers of cellulose nanofiber films can reduce the size of the film’s pores, improving its water barrier properties[21,22]. 5) increase the degree of orientation: by subjecting the cellulose nanofiber films to mechanical or thermal treatments, it is possible to achieve higher degrees of alignment in the fibres, which can improve water vapour barrier properties[27]. 6) add plasticizers: incorporating plasticizers, such as glycerol or sorbitol, can improve the flexibility of the cellulose nanofiber film, reducing the possibility of cracks or gaps that can allow water vapour to pass through[28]. 3.8 cnf for packaging applications cellulose nanofibers (cnfs) are a promising natural and renewable material for use in packaging. the unique properties of cnfs, including their high strength, low weight, and excellent barrier properties, make them an attractive alternative to other packaging materials such as plastics[7]. several packaging applications of cnfs have been explored, including: 1) food packaging: cnfs have been used to produce films and coatings for food packaging, providing excellent barrier properties against oxygen and water vapor. cnf-based packaging can also prolong the shelf life of food products, preventing spoilage. 2) biodegradable packaging: cnfs can be used to produce biodegradable packaging materials that are environmentally friendly and fully compostable. this makes them an excellent alternative to traditional plastic packaging, which can take hundreds of years to decompose. 3) medical packaging: cnfs have been used for the packaging of medical devices and other healthcare products due to their excellent biocompatibility and low toxicity. 4) electronics packaging: cnfs can also be utilized in electronic packaging due to their excellent electrical insulation properties. cnf-based packaging can help protect electronic devices from moisture, dust, and other environmental contaminants. overall, the use of cnfs in packaging can reduce the environmental impact of packaging while providing excellent protection to the packaged product. as the demand for sustainable packaging continues to grow, cnfs are likely to play a significant role in the future of packaging materials[7,22]. 4. conclusion the spray coated cellulose nanofiber (cnf) film is a renewable, biodegradable and sustainable material that has attracted attention for its unique mechanical properties, high surface area, and good barrier properties. the film is produced by a process called spray coating, which involves spraying cellulose nanofibers onto a stainless-steel surface to form a compact film which has a notable smoothness on the spray coated side. the resulting film has two unique surfaces, potential barrier against water vapour. it is a sustainable material that can be produced in large quantities via spraying, a scalable process, making it an attractive alternative to petroleum-based materials in conventional packaging. the water vapour permeability of cnf films can be tailored by varying the density of the film through tailoring the thickness and basis weight of the film. it can be done by spraying various cnf concentration on the stainless stee plate to fabricate the film. given this correspondence, spraying cnf suspension on the polished stainless steel surface is a flexible process for fabrication of cnf films and capacity to tailor barrier properties of the film. 11 conflict of interest the authors declare no conflict of interest. references 1. abitbol t, rivkin a, cao y, et al. nanocellulose, a tiny fiber with huge applications. current opinion in biotechnology 2016; 39: 76–88. doi: 10.1016/j.copbio.2016.01.002. 2. shanmugam k. spray coated nanocellulose filmsproduction, characterisation and applications [phd thesis]. melbourne: monash university; 2019. 3. shanmugam k, browne c. nanocellulose and its composite films: applications, properties, fabrication methods, and their limitations. in: thomas s, balakrishnan p (editors). nanoscale processing. amsterdam: elsevier; 2021. p. 247–297. 4. varanasi s, batchelor wj. rapid preparation of 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article relative stability of planar clusters b11, b12, and b13 in neutraland charged-states levan chkhartishvili department of engineering physics, georgian technical university, tbilisi, georgia; e-mail: chkharti2003@yahoo.com abstract theoretically, within the diatomic model, the relative stability of most abundant boron clusters b11, b12, and b13 with planar structures in neutral, positive and negative charged-states is studied. according to the specific (per atom) binding energy criterion, b12 + (6.49 ev) is found to be the most stable boron cluster, while b11 – + b13 + (5.83 ev) neutral pair is expected to present the preferable ablation channel for boron-rich solids. obtained results would be applicable in production of boron-clusters-based nanostructured coating materials with super-properties such as lightness, hardness, conductivity, chemical inertness, neutron-absorption, etc., making them especially effective for protection against cracking, wear, corrosion, neutronand electromagnetic-radiations, etc. keywords: cluster; charge state; specific binding energy; diatomic model; relative stability; clusters-based coating material; boron article info article history: received 12 june 2020 received in revised form 4 july 2020 accepted 7 july 2020 available online 20 july 2020 copyright copyright © 2020 levan chkhartishvili. doi: 10.24294/can.v3i2.761 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/by/4.0/ 1. introduction boron-clusters-based nanostructured coating materials due to their super-properties such as lightness, hardness, conductivity, chemical inertness, neutron-absorption, etc. can serve for effective protection against cracking, wear, corrosion, neutronand electromagnetic-radiations, etc. [1,2] . this makes boron clusters bn, n=1,2,3,…, interesting to be investigated in details. summarizing experimental and theoretical data available in the literature on all-boron nanomaterials (e.g. see our overviews on subject [3-5] ), one can conclude that, according to the specific (per constituting atom) binding energy criterion, ultra-small, with , boron clusters prefer (quasi)planar structures, while at higher , they should be wrapped first into cylinders and then into spheres forming boron nanotubes or boron fullerenes, respectively. in (quasi)planar clusters, increases with because of increasing in mean coordination number of constituent atoms. within the initial approximation, specific binding energy of boron clusters is expected to be almost saturated around . but, when the polarity deal into the bonding — commonly characteristic of structures of identical atoms with differently coordinated atomic sites — is taken into account, there is expected a weak maximum instead. in general features, the experimental mass-spectra fits these theoretical findings. however, formation probability peak is well-pronounced for species b11, b12, and b13. naturally, 20n n  n 10n http://creativecommons.org/licenses/by/4.0/ 74 such a behavior is related not only to the energy-factor, but mainly to the process kinetics. usually, boron clusters are formed by the ablation of elemental boron or boron-rich solid materials, main structural motifs of which are slightly deformed regular icosahedra of boron atoms b12 [6] . present paper aims to theoretically study the relative stability of most abundant boron clusters b11, b12, and b13 with (quasi)planar structures in different charged-states. 2. method of calculations in clusters of identical atoms, binding energy per atom, i.e., specific binding energy, serves for the key factor determining their relative stabilities and, consequently, concentrations of clusters with different numbers of atoms in the products of ablation of corresponding solid materials. based on various ab initio methods specif ic binding energy and some other important physical characteristics of boron clusters were numerically calculated by boustani et al. (summarizing of these studies see in the study of boustani [7] ) and some other teams (see above cited reviews and references therein). but, more vividly these species can be descried based on the diatomic model. it should be noted that such model-based approach provides quite good quantitative results as well. the application of the fermi’s old diatomic model [8] to the multi-atomic structures is based on the property of interatomic bonding to be saturated. in the initial, i.e., pair interactions, approximation the binding energy of a structure simply equals to the sum of energies of interactions between neighboring atoms. based on the pair interactions approximation, microscopic theory of expansion and its generalization to the periodical structures allow correct estimation of the thermal expansion coefficient for number of crystalline substances [9] . despite its simplicity, the diatomic model is still successfully used to calculate anharmonic effects in solids [10] . an analogous approach was used by us to explain isotopic effects of thermal expansion and melting in all-boron lattices [11-15] . suppose that the index i = 1,…, n numbers the atoms constituting cluster of n atoms, and ci are their coordination numbers, respectively. in the initial approximation, binding energies between each pair of adjacent atoms e0 are equal, and it turns out that:     ni i ic n e 1 0 2  (1) here, the factor ½ is introduced to correct the double sum which includes every pair of neighboring atoms twice. we used approximated formula (1) to estimate ground-state binding energy of all-boron nanostructures, mainly, boron nanotubes [16-18] . however, clusters are finite structures of atoms and, consequently, coordination numbers of sites at center are higher than that at periphery. this leads to the redistribution of the outer valence shell electrons and, as a result, differences between binding energies of neighboring atomic pairs. note the report [19] on high-pressure experiments and ab initio evolutionary crystal structure predictions that explore the structural stability of boron under pressure and reveal a partially ionic high-pressure boron phase. our formulation of the first approximation to the diatomic model theory takes into account corresponding polarity of the bonds. in case of identical constituent atoms, it is obvious to assume that these electrons between the atoms are divided proportionally to their coordination numbers. this implies that the atoms develop non-zero effective static atomic charges with charge numbers zi determined from the relation:     nj j j ii c nc v nz 1 1 (2) respectively, here v is the total number of the outer valence shell electrons in the atoms constituent cluster. thus, the binding energy per atom in the first approximation, i.e., including correction related to the interatomic bonds polarity, is: 75        ni i ck k kii ii i i zzece n 1 110 )( 2 1  (3) where the index ki = 1,…,ci numbers the nearest neighboring atoms of i -atoms, respectively; d e e 0 2 1 4  (4) is the energy-dimension parameter (e and are elemental charge and electric constant, respectively); and d is the initial bonds length in the equilibrium. in our previous studies [20-23] , relations (2), (3), (4) are used to estimate effective static atomic charges, dipole moment, and specific binding energy in the boron planar clusters. further improvement of this approximation means determination of the equilibrium bond length in the first approximation as well. it can be done by the minimization of the system potentials energy including bond length-dependent vibrational and electrostatic interaction energies [24] . within the frame of the diatomic approach, further refinement of the clusters’ binding energy and other ground-state parameters can be achieved by abandoning the requirement for equality of all the bond lengths. in another study of mine [25] , a general theoretical frame for further studying is provided. finally, we have got a set of linear equations determining not precisely planar, but quasi-planar equilibrium cluster configurations. finally, all the above described theory-levels of the diatomic approach are summarized in the mini-review [26] . by definition, cluster binding energy is the difference between sum of energies of isolated atomic particles and energy of their bounded structure. energy of a neutral atom exceeds that of positive ion by the ionization potential (ip), while is less by the electron affinity (ea) that of negative ion. let q=0, ±1,…,±n be the ionic charge number of the cluster, then, n qeq q  (5) should be the specific binding energy correction related to its charge state if eq is ip or ea depending on the sign of q. taking into account this correction, in present work, specific binding energy of planar boron clusters are estimated from the relation:              qezzece n q ni i ck k kii ii i i1 110 )( 2 11  (6) 3. species studied and results because b12 icosahedral clusters are the main structural units of structural modifications of boron and boron-rich compounds, here we studied stability of planar boron clusters b11, b12 and b13 with almost the same number of constituent atoms both in neutraland charged-states. for obtaining numerical results, one needs input parameters such as e0 and e1 (or d) characteristic of pair interaction between two boron atoms. they can be found e.g. from the quasi-classical b– b potential [27] : e0 ≈ 2.80 ev, e1 ≈ 8.09ev; and d ≈ 1.78 å. note that this potential was successfully applied to explaining of the above mentioned isotopic effects of boron atoms also in geometric models for boron nanostructures [28] . as for ip and ea of boron atom, they equal to e+1 ≈ 8.30 ev and e–1 ≈ 0.28 ev, respectively [29] . outer valence shell of the isolated b-atom contains a single 2p-electron. consequently, their total number v=10 in b11 + , v=11 in b11 0 and b12 + , v=12 in b11 – , b12 0 and b13 + , v=13 in b12 – and b13 0 , and v=14 in b13 – , respectively. obtained results of calculations confirmed the expectation that cluster-isomers with symmetrical shapes and without holes (vacant sites) in their structure, i.e., with the maximal number of interatomic bonds, should be most stable. correspondingly, in the tables below, we present structures and characteristics only for ground-state isomers. table 3-1 shows that among the neutral clusters studied, the atomic charges are maximal in b11, apparently because of its asymmetric structure. on contrary, symmetric clusters b12 and b13 reveal higher polarity of bonding in their charged-states. 0 76 table 3-1. static charge number of atomic sites in most abundant boron clusters ground-state isomer cluster coordination number number of sites static charge number b11 + 2 1 + 11/21 3 4 + 2/7 4 4 + 1/21 6 2 – 3/7 b11 0 2 1 + 10/21 3 4 + 3/14 4 4 – 1/21 6 2 – 4/7 b11 – 2 1 + 3/7 3 4 + 1/7 4 4 – 1/7 6 2 – 5/7 b12 + 3 6 + 5/16 4 3 + 1/12 6 3 – 3/8 b12 0 3 6 + 1/4 4 3 0 6 3 – 1/2 b12 – 3 6 + 3/16 4 3 – 1/12 6 3 – 5/8 b13 + 3 6 + 4/13 4 4 + 1/13 6 3 – 5/13 b13 0 3 6 + 1/4 4 4 0 6 3 – 1/2 b13 – 3 6 + 5/26 4 4 – 1/13 6 3 – 8/13 table 3-2. specific binding energy of most abundant boron clusters clusters binding energy per atom, ev b12 + 6.49 b13 + 6.34 b11 + 6.21 b13 0 5.60 b12 0 5.47 b11 0 5.34 b13 – 5.25 b11 – 5.24 b12 – 5.10 from the table 3-2, one can see that positively charged clusters are certainly more stable than neutral clusters, while lasts are more stable than negatively charged ones. table 3-3. specific binding energy of neutral pairs of most abundant boron clusters pairs of clusters binding energy per atom, ev b11 – + b13 + 5.83 b12 + + b12 – 5.79 b11 + + b13 – 5.69 b11 0 + b13 0 5.48 b12 0 + b12 0 5.47 according to the date presented in the table 3-3, preferably channels of ablation of icosahedral boron-rich materials are related to the formation of neutral pairs of differently charged clusters. 4. discussion and conclusions before making conclusions based on results 77 obtained by us, we need to discuss shortly the theoretical data available in the literature on b12 cluster isomers stability. as is known, boron atoms are unique in their strong preference for forming icosahedral structural units. in the icosahedral cage b12, each atom has 5 other atoms as nearest neighbors. such b12 units are unstable by themselves, but distorted b12 icosahedra do form a stable framework for boron and many bo ron compounds. in particular, the α-rhombohedral crystalline boron may be considered an almost perfect cubic close packing of b12 icosahedra. in general, the persistence of the icosahedral structure is explained by the fact that the chemical valence of boron is not completely saturated under 5-fold coordination and that there exist outwardly directed bonds which serve to link icosahedra. the xα-method of the scattered-wave self consistent-field (scf–xα–sw) with muffin-tin-pot ential and local exchange was applied [30] to determine quantitatively electronic structure and binding energy of icosahedral b12. then the binding energy was used to estimate the cohesive energy of the b12 units in the α-rhombohedral structure. from this, an effective b12–b12 interaction potential in the solid was constructed. the binding energy of 35.6 ev was obtained at an equilibrium bond distance of 1.96 å, which is within 10 % of the bond distance of 1.77 å found in b12 icosahedra in bulk boron. the electronic structure of b12 corresponded to an open-shell configuration so that such an isolated cluster would be chemically unstable. geometries and electronic structures of the b12 cluster have been investigated using a car–parrine llo ab initio molecular dynamics simulation [31] . the icosahedral structure was found to be locally stable, but with a few dangling bonds. on annealing or melting, this structure rearranges to a more open geometry. the new structure has a significantly lo wer energy despite a lower coordination. but, bonds are stronger and there are no dangling bonds. the structure and stability of small boron clusters were investigated employing density functional theory (dft) [32] . the search for minima was performed using gradient methods at the local spin density (lsd) level. most of the final structures prefer planar or quasi-planar forms and can be considered to be fragments of planar or spherical surfaces. a group of spherical boron clusters may exist. however, their energies are generally higher than those of the convex or quasi-planar clusters. this also means that clusters of real bulk, sections of the boron lattice, have less stable configurations. they try to close the open spheres with a small number of atoms. in particular, the distorted icosahedral b12 cluster with closed structure has energy by 2.01–3.28 ev higher than that of the convex b12 structure. based on ab initio quantum-chemical methods, accurate calculations on small boron clusters were carried out to determine their electronic and geometric structures [33] . the geometry optimization with a linear search of local minima on the potential-energy surface (pes) was performed using analytical gradients in the framework of the restricted hartree-fock scf approach. most of the final structures of the boron clusters are composed of two fundamental units: either of hexagonal or of pentagonal pyramids. the resulting quasi-planar and convex structures can be considered as fragments of planar surfaces and as segments of nanotubes or hollow spheres, respectively. in particular, the most stable isomers of b12 clusters are 2 planar and 1 convex clusters. in contrast to the convex or the quasi-planar clusters, the structures of the cage-clusters are rather similar to those of the well-known and -rhombohedral boron crystals, or to those of the boron hydrides. the energies of the cage-clusters on average are between 2 and 5 ev higher than those of the convex or the quasi-planar clusters. taking into account that interesting features of elemental boron and boron compounds are the occurrence of highly symmetric icosahedral clusters and rich chemistry of boron also dominated by cage-structures, in the study of zhai et al. [34] , the authors reported experimental and theoretical evidences that small boron clusters prefer planar structures and exhibit aromaticity and antiaromaticity according to the huckel rules, akin to planar 78 hydrocarbons. the electronic and geometric structures, including binding energies, of small and neutral boron clusters have been investigated using dft [35] . linear, planar, convex, quasi-planar, open-cage and cage structures have been found. none of the lowest energy structures and their isomers has an inner atom; i.e., all the atoms are positioned at the surface. within size range under the consideration, the planar and quasi-planar (convex) structures have the lowest energies. in particular, 11 different structures of b12 cluster were investigated. their binding energies are ranging from 4.037 to 4.599 ev/atom. the first lowest energy isomer is a convex structure containing three dovetailed hexagonal pyramids. only ninth and tenth isomers are cages, slightly distorted icosahedral structures without the central atom. among the several aromatic boron clusters, b12 and b13 + are unique. they show three distinct sets of sextets, resulting in extraordinary kinetic stability. a novel way to analyze them was proposed in the study of kiran et al. [36] , in which the cluster is partitioned as inner and outer rings. the molecular orbital analysis, based on this fragmentation, reveals that the delocalized valence electrons in b12 and b13 + clusters can be trifurcated leading to triple aromaticity, which is unique to these clusters. recently, bhattacharyya et al. [37] conducted a comprehensive numerical study of the ground-state structures of isomers of b12 cluster. geometry optimization was performed at a level of theory employing the extended basis sets. once the geometry of a given isomer was optimized, its ground state energy was calculated more accurately at the level of theory employing even larger basis set. thus, computed values of binding energies of various isomers are expected to be quite accurate. geometry optimization revealed 10 distinct isomers. the vibrational frequency analysis performed on the 3 lowest energy isomers showed them to be stable. while, in boron-rich solids, icosahedron is the basic structural unit, in the isolated form, it was demonstrated to be unstable. the disc-like lowest-energy structure of b12 cluster can be seen as a consequence of the jahn–teller distortion of its icosahedral isomer. computed binding energies per atom are 4.60 and 4.31 ev for quasi-planar and icosahedral isomers with c3v and c2h point group symmetries, respectively. this work, based upon ab initio geometry optimization, verifies early results and predicts the b12 icosahedron to be higher in energy as compared to the lowest energy quasi-planar b12 cluster. this clearly illustrates the tendency of the icosahedral structure towards distortion to a lower symmetry one, consistent with the jahn–teller theorem. thus, neutral b12 icosahedral clusters constituting boron-rich materials, on ablation have to be converted into (quasi) planar disc-like isomer with higher specific binding energy. the charged cluster b13 + also should have higher stability. consequently, the formation of b11, b12 and b13 clusters in different charged-states is expected. our calculations performed within the diatomic model using quasi-classical b–b interatomic potential, lead to following hierarchies in the formation probabilities of single boron clusters in various charged states and their neutral pairs: b12 + > b13 + > b11 + > b13 0 > b12 0 > b11 0 > b13 – > b11 – > b12 – and b11 – + b13 + > b12 + + b12 – > b11 + + b13 – > b11 0 + b13 0 > b12 0 + b12 0 , respectively. the obtained results would be helpful in controlling the synthesis of nanoboron materials with specific engineering properties. references 1. becker r, chkhartishvili l, martin p. boron, the new graphene? vacuum technology & coating 2015; 16 (4): 38–44. 2. becker r, chkhartishvili l, martin p. tribological applications for boron. vacuum technology & coating 2015; 16 (10): 36–41. 3. chkhartishvili l. microand nano-structured boron. in: perkins gl (editor). boron. compounds, production and application. new york: nova science publishers; 2011.p. 221–294. 4. chkhartishvili l. nanoboron (an overview). nano studies 2011; 3: 227–314. 5. chkhartishvili l. all-boron nanostructures. in: kharisov b i, kharissova o v, ortiz–mendez u (editors). crc concise encyclopedia of nanotechnology. boca raton: crc press; 2016. p. 53–69. 79 6. albert b, hillebrecht h. boron: elementary challenge for experimenters and theoreticians. angewa ndte chemie international edition 2009; 48(46): 8640–8668. 7. boustani i. towards novel boron nanostructural materials. in: springborg m (editor). chemical mo delling: applications and theory. cambridge: royal society of chemistry; 2011. p. 1–44. 8. fermi e. molecules, crystals, and quantum statistics. new york, amsterdam: w. a. benjamin inc; 1966. 9. novikova si. thermal expansion of solids. moscow: nauka; 1974. 10. slutsker ai, gilyarov vl, luk’yanenko as. energy features of an adiabatically loaded anharmonic oscillator. physics of the solid state 2006; 48(10): 1947–1953. 11. chkhartishvili l, gabunia d, tsagareishvili o, et al. estimation of isotopic composition effect on substance melting temperature. bulletin of the georgian national academy of sciences 2004; 170(3): 530–532. 12. chkhartishvili ls, gabunia dl, tsagareishvili oa. estimation of the isotopic effect on the melting parameters of boron. inorganic materials 2007; 43(6): 594–596. 13. chkhartishvili ls, gabunia dl, tsagareishvili oa. effect of the isotopic composition on the lattice parameter of boron. powder metallurgy and metal ceramics 2008; 47(9-10): 616–621. 14. gabunia d, tsagareishvili o, chkhartishvili l, et al. isotopic composition dependences of lattice constant and thermal expansion of -rhombohedral boron. journal of physics: conference series 2009; 176(012022): 1–10. 15. chkhartishvili l, tsagareishvili o, gabunia d. isotopic expansion of boron. journal of metallurgical engineering 2014; 3 (3): 97–103. 16. chkhartishvili l. on quasi-classical estimations of boron nanotubes ground-state parameters. journal of physics: conference series 2009; 176(1): 1– 9. 17. chkhartishvili l. molar binding energy of the boron nanosystems. in: konuk a, kurama h, ak h, et al. 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2(12): 827–833. 35. atis m, ozdogan c, guvenc zb. structure and energetic of bn (n = 2–12) clusters: electronic structure calculations. international journal of quantum 80 chemistry 2007; 107(3): 729–744. 36. kiran b, kumar gg, nguyen mt, et al. origin of the unusual stability of b12 and b13+ clusters. inorganic chemistry 2009; 48(21): 9965–9967. 37. bhattacharyya p, boustani i, shukla a. first principles electronic structure study of b12 isomers: jahn– teller distortion flattens the icosahedron into a disc. arxiv:1802.01072v1 [physics.atm-clus] 4 feb 2018; 1–32. 49 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1335 original research article defocused image restoration method based on micro-nano scale yongjun liu1,2*, qiuyu wu1, mingxin zhang1, yi wang2 1 school of computer science and engineering, changshu institute of technology, changshu 215500, china. e-mail: yongjun1981@126.com 2 school of computer science and engineering, northeastern university, shenyang 110819, china abstract an image adaptive noise reduction enhancement algorithm based on nsct is proposed to perform image restoration preprocessing on the defocused image obtained under the microscope. defocused images acquired under micro-nano scale optical microscopy, usually with inconspicuous details, edges and contours, affect the accuracy of subsequent observation tasks. due to its multi-scale and multi-directionality, the nsct transform has superior transform functions and can obtain more textures and edges of images. combined with the characteristics of micro-nanoscale optical defocus images, the nsct inverse transform is performed on all sub-bands to reconstruct the image. finally, the experimental results of the standard 500 nm scale grid, conductive probe and triangular probe show that the proposed algorithm has a better image enhancement effect and significantly improves the quality of out-of-focus images. keywords: micro-nano scale; defocused image; nsct; image restoration 1. introduction when observing samples with optical microscope, there is a problem of “abbe limit” due to the limitation of diffraction limit[1,2]. when the observation scale reaches the micro-nano level, the observed images show fuzzy circular spots no matter how to adjust the focal length. therefore, the images collected under micro-nano optical microscope have poor resolution, and unclear edges, details and contours not only affect the quality of the image, but also are not conducive to the subsequent observation of “depth” and other information[3]. traditional image enhancement and preprocessing methods include histogram equalization algorithm[4], retinex algorithm[5,6], homomorphic filtering algorithm[7], wavelet transform algorithm[8], etc., which have made great progress in recent years[4–8]. however, they have their own advantages and disadvantages, such as serious block effect and relatively complex operation in local equalization algorithm. global equalization algorithm is also easy to cause color distortion due to over fitting. retinex algorithm is based on color constancy. homomorphic filtering algorithm needs to select reasonable filter parameters in frequency domain to realize image enhancement, but it is very difficult to select appropriate parameters. for the defocus image collected under the microscope, we hope to avoid adding new noise as much as possible and make the enhanced image quality better. non-subsampled contourlet transform (nsct) article info received: 27 july 2021 accepted: 17 september 2021 available online: 24 september 2021 copyright copyright © 2021 yongjun liu, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 50 has superior transformation function due to multiscale and multi-directional, and can obtain more textures and edges of the image[9,10]. therefore, this paper chooses nsct transform. firstly, the input image is transformed from spatial domain to frequency domain to obtain high-frequency sub-band and low-frequency sub-band; secondly, the low-frequency coefficients are enhanced by anti-sharpening mask algorithm, and the high-frequency coefficients are enhanced by adaptive filtering algorithm[11,12]; thirdly, nsct is used to inverse transform the image to construct a new image; finally, in order to further enhance the effect of image details, the anti-sharpening mask algorithm is used for image processing. 2. nonsubsampledcontourlet transformation (nsct) nsct is conducive to better maintain the image edge information and contour and enhance the translation invariance of the image. it is divided into two processes: multi-scale decomposition and directional filtering. the two processes are independent of each other. figure 1 is the overall structure diagram. figure 1. overall structure diagram. in view of the translation invariance of laplace filter, the multi-scale nature of nsct can be guaranteed by using non-subsampled pyramid for image decomposition. nsct consists of low-pass decomposition filter module h0(z) and high pass decomposition filter module h1(z) = 1 − h0(z), and some low-pass synthetic filtering modules, which are composed of high pass filtering module g0(z) = g1(z) = 1. figure 2. a schematic diagram of the decomposition of three layers of the pyramid. figure 2 is the decomposition diagram of three layers of the non-subsampled pyramid, in which the ideal band-pass support region of the low-pass filter decomposed in layer j is [(π/2j), (π/2j)]2, while the ideal band-pass region of the high pass filter is the complement of the low-pass sub-bands [(−π/2j), (π/2j)]2/[(−π/2j), (π/2j)]2. non-subsampling direction filter banks: the filter is based on two channels and decomposes the coefficients into different sub-bands through a tree like structure. the non-subsampling direction filter banks remove the down-sampling module and up-sampling module in the directional filter bank, so that the sampling results at different scales are consistent, and effectively improves the distortion in the sampling process. 3. micro-nano optical image enhancement algorithm based on nsct due to the multi-scale and multi-directional nature, nsct has superior transformation function and can effectively improve the image quality. therefore, we propose a micro-nano optical image enhancement algorithm based on nsct to preprocess the defocus image obtained under the microscope. firstly, nsct decomposes the input image to generate a series of low-frequency and high-frequency components; secondly, the low-frequency coefficients are enhanced by anti-sharpening mask algorithm; adaptive filtering algorithm is used for high-frequency coefficients; finally, all sub-bands are reconstructed by nsct in51 verse transform. 3.1 nsct low-frequency coefficient transformation the low-frequency coefficients obtained by nsct decomposition contain some basic information in the image. in this paper, the anti-sharpening mask algorithm is used to enhance it. (1) where, in the formula represent the input image and output image respectively, and k is the adjustment coefficient, taking 2. is the blurred image or approximate image, which can be obtained from equation (2). (2) where, w is the filter window. 3.2 nsct high-frequency coefficient conversion high-frequency coefficients represent detailed information, such as image edges and textures, but also contain a lot of noise. high-frequency coefficient transformation aims to achieve enhancement based on noise reduction. high-frequency coefficients with large values contain image edge details and should be retained. noise is distributed in nsct high-frequency coefficients with small values. threshold noise reduction is to set an appropriate threshold, and noise reduction is performed by comparing the absolute value of nsct coefficient with the threshold. when the absolute value is greater than the threshold, nsct coefficient is considered to contain important image information and is retained. when the absolute value of nsct coefficient decreases or becomes 0 accordingly, it is used to filter noise. by using the coefficient processed by threshold, the nsct inverse transformation is used to reconstruct the image, so as to eliminate the noise. threshold de-noising eliminates the noise and retains the image coefficient as much as possible. therefore, the key of de-noising is to determine the threshold. less than the threshold is regarded as the noise to be suppressed, and more than the threshold is regarded as the edge information to be enhanced. (3) t1,k is the noise threshold in the k direction of the 1 layer, and p is the coefficient value of the subband. in this paper, an adaptive filtering algorithm based on bayesshrink is used. the threshold can be calculated by equation (4). (4) where, c is a constant between 0 and 1, σ2 is the noise variance, and σ2 x is the signal variance. the standard deviation of noise can be calculated by equation (5). (5) where, cj,k is the high-frequency coefficient of the first layer of the image after nsct decomposition, i.e., take the median of the absolute value of nsct coefficients, and calculate the noise standard deviation with 0.6745 as the adjustment coefficient. (6) where, m and n represent the length and width of the image respectively, and the coefficient located in x(i, j) in the k direction image of layer 1 is xi, j(1, k). the obtained threshold is used to suppress the noise. (7) where, xi,j is the coefficient of the high-frequency sub-band of the original image and is the coefficient of the processed image. the main steps of the algorithm are as follows: step 1: nsct decomposes the defocus image obtained under the microscope to generate a series of low-frequency and high-frequency components; step 2: calculate the low-frequency coefficient obtained by equation (1) to obtain a higher contrast of the image; step 3: adaptive filtering algorithm is used for threshold de-noising of high-frequency coefficients; 52 step 4: the image is inversely transformed into the spatial domain by nsct, and the new image is reconstructed; step 5: the reconstructed image is further processed by anti-sharpening mask technology to obtain the optimized clear image. 4. experimental results and analysis the experiments are carried out by using the traditional histogram equalization algorithm (he), retinex image enhancement algorithm (msr) and the algorithms proposed in this paper. the experiments are carried out by using the standard nano grid image obtained under the actual optical microscope, the conductive probe and triangular probe sample images collected under the atomic force microscope. figure 3, figure 4, figure 5 show the results of preprocessing three kinds of images by three algorithms. among them, (a) is the original image, (b) is the image enhanced by histogram equalization algorithm (he), (c) is the image enhanced by retinex algorithm (mer), and (d) is the image enhanced by the algorithm proposed in this paper. 4.1 subjective evaluation (1) standard 500 nm raster image (2) conductive probe image (3) triangular probe image figure 3. grid image preprocessing results of three algorithms. as can be seen from figure 3, figure 4, figure 5, compared with the original image, the clarity and contrast of the three images processed by he algorithm are greatly improved, and the overall enhancement effect is better. however, the image processed by this algorithm has more noise, and the processing of the edge details of the image is not ideal. sometimes there will be local distortion and block phenomenon. for example, the standard 500 nm scale grid image is obviously noisy after being processed by he algorithm; after the conductive probe and triangular probe are processed by he algorithm, the probe tip appears local distortion. figure 4. preprocessing results of three algorithms on conductive probe. figure 5. preprocessing results of three algorithms on triangular probe. retinex algorithm decomposes the image into illumination image and reflectance image, and then eliminates or weakens the influence of illumination, so as to achieve the effect of image enhancement. therefore, compared with the original image, the clarity and contrast of the three kinds of images processed by retinex algorithm are greatly improved, and the overall enhancement effect is better. however, due to the logarithmic processing, the display range of the bright area of the image is compressed, resulting in the weakening of the details of the image. for example, the details of the edges and corners of the standard 500 nm scale grid, the needles of the conductive probe and the triangular probe are significantly weakened. compared with the original image, the sharpness and contrast of the three images processed by the proposed algorithm are improved, and the over53 all effect is better; moreover, the algorithm adopts an adaptive filtering algorithm for high-frequency coefficients to determine the noise determination threshold suitable for different sub-band coefficients. therefore, compared with the original image, the noise of the three images processed by the algorithm proposed in this paper is very low. 4.2 objective evaluation sharpness, contrast and peak signal-to-noise ratio are three objective indexes commonly used to measure the effect of image enhancement. these three indexes have been used for objective calculation and evaluation in this paper. (1) clarity it mainly reflects the vein part of the image. the larger is the measured value, the clearer is the representative image, as shown in equation (8). (8) ∆mx(i, j), ∆nx(i, j) are the difference points of points (i, j) in vertical and horizontal directions. (2) contrast it represents the overall contrast intensity of the image. generally, the greater is the contrast, the better is the image enhancement effect. the contrast calculation formula is: (9) where, µx represents the average value of gray scale, m and n represent the number of pixels in image rows and columns. var is the variance of image, and the calculation formula is: (10) (3) peak signal-to-noise ratio according to the ratio of maximum signal power and noise power, the greater is the psnr, the better is the image enhancement effect. the calculation formula of psnr is: (11) where, l is the gray level range, usually 255, and mse is the mean square error, which can be calculated by equation (12). (12) where, fij and oij are the gray values of the input image and the output image at points (i, j), and m and n represent the number of pixels in the rows and columns of the image. table 1, table 2 and table 3 respectively show the objective evaluation indexes of the images of standard nano grid, triangular probe and conductive table 1. comparison of objective evaluation indexes of three algorithms for raster image processing evaluating indicators original image he algorithm retinex algorithm textual algorithm clarity 3.63 21.02 13.65 5.71 contrast 10.92 64.65 41.98 14.56 peak signal-to-noise ratio — 10.84 15.79 20.49 table 2. comparison of objective evaluation indexes of three algorithms for processing conductive probe images evaluating indicators original image he algorithm retinex algorithm textual algorithm clarity 3.68 19.03 12.11 5.16 contrast 20.35 64.50 29.64 26.76 peak signal-to-noise ratio — 10.68 15.12 17.67 table 3. comparison of objective evaluation indexes of three algorithms for processing triangular probe images evaluating indicators original image he algorithm ritinex algorithm textual algorithm clarity 3.71 25.32 17.52 5.91 contrast 13.39 64.63 28.80 15.51 peak signal-to-noise ratio — 9.88 14.94 18.67 54 probe in atomic force microscope processed by three algorithms. (1) standard 500 nm scale grid (2) conductive probe (3) triangular probe from table 1 to table 3, it can be seen that the clarity of different defocused images processed by he algorithm and retinex algorithm is relatively high. although the clarity of defocused images processed by the algorithm proposed in this paper is not very high, it also improves the clarity of different defocused images to a certain extent and can effectively improve the image quality. the contrast of different defocused images processed by he algorithm and retinex algorithm is relatively high. although the contrast of defocused images processed by the algorithm proposed in this paper is not very high, it also improves the contrast of different defocused images to a certain extent and can effectively improve the image quality. it can be seen from the peak signal-to-noise ratio data that compared with he algorithm and retinex algorithm, the proposed algorithm has the largest peak signal-to-noise ratio, the most information retained, the least distortion and better visual effect. therefore, through the comparative experiments of standard nano-grid images obtained under the actual optical microscope, triangular probe and conductive probe sample images collected under the atomic force microscope, it can be seen that the image enhancement effect of the proposed algorithm is relatively better than that of histogram equalization algorithm (he) and retinex algorithm (mer), and can effectively improve the image quality. 5. conclusion the out of focus images collected under micro-nano optical microscope are not very clear in detail, edge and contour. combined with nsct image transformation method, which has multi-scale and multi-directional, and superior transformation function, more texture and edge of the image can be obtained. at the same time, an adaptive noise reduction and enhancement algorithm of micro-nano optical image based on nsct is proposed to restore the defocus image obtained under the microscope. the experimental results of standard nano-grid images, triangular probe images and conductive probe images show that the enhanced image effect of the algorithm proposed in this paper is better than histogram equalization algorithm (he) and multi-scale retinex algorithm, which not only improves the quality of defocused images, but is also conducive to the depth information recovery of subsequent defocused images. conflict of interest no conflict of interest was reported by the author. acknowledgements project: the next generation internet technology innovation project of saier network of the ministry of education, “emergency and critical intelligent medical cloud platform based on ipv6” (ngii20170709). references 1. hu r. scanning near-field optical microscopy: instrumentation and applications [master’s thesis]. nanjing: nanjing university; 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nano biotechnology; nanoparticles 1. introduction the route of administration is the direction of the drug preparation. oral administration is the key to the fi rst eff ect. the first effect affects the role of drugs, such as proteins, peptide drugs and so on. the effects of drugs are usually targeted to human organs and tissue-specifi c specifi c structures such as human immune system, reticuloendothelial, and blood-brain barrier transport. on the one hand, the body's self-protection system is used for macromolecular drug eff ects to reach the lesion's ability. for example, a normal body, blood brain barrier, the general monoamine in the central nervous system cannot pass. on the other hand, the drug cannot be applied directly, but must be carried out by certain reagents and mainly hinders the application of the drug in the drug with greater side eff ects and the physical properties of the drug itself (e.g. poorly soluble drugs). overcoming the obstruction of the human health drug administration is the direction of modern medicine research to improve the physical properties of drugs (solubility, dissolution rate, etc.) to reduce the adverse eff ects of drugs, for enhanced performance of drugs, increased bioavailability, there are also ways to solve this problem by combining nanotechnology with biomedicine. traditional pharmacy, pharmacology and other multidisciplinary and nano medical combination of modern nanotechnology products. according to the american health association, the use of nanotechnology to control drug effi cacy, diagnosis, monitoring and nanotechnology of biological systems. drug formulations that explore the transport and targeting characteristics of the theoretical formula and diagnostic mode of effi cacy of the nano pharmaceutical problem at the forefront, mainly including precise and specifi c clinical pathology to determine the location of the environment associated with the lesion and at the same time the risk of adverse eff ects to select the appropriate nano-carrier to meet specifi c requirements. therefore, they need to fi nd a way to mass production of nano-drug convenience. 2. introduction 2.1. objective and signifi cance of nano-drug carrier research nano-drug carriers are usually synthesized from natural or polymeric materials at a size of 10-1000 nm because of their targeted and slow release, so the carrier material has other signifi cant advantages of biocompatible biodegradability, which has been widely used in pharmaceuticals preparation development. the nanoparticles are used as drug carriers in which the therapeutic drug is encapsulated into the nanoparticles or adsorbed on the surface thereof by means of jianping wu, et al 13 targeted molecules, for effi cient delivery and gene therapy. nano-carrier technology is an important development of nano-biotechnology [1]. nanotechnology and nanomaterials will be applied to the pharmaceutical fi eld to form nano complex carriers, in vivo drugs that carry nanoparticles of drugs or embedded in their surface after adsorbing nanoparticles, to form a stable nano sized drug delivery system. nano-carrier drug delivery methods are hydrophobic, electrostatic, hydrogen bonding, and covalent role. in the fi eld of drug discovery. which has the following advantages: (a) enhance the dissolution of insoluble drugs. the hydrophobic drug will be precipitated in the blood circulation and the drug is diffi cult to reach the lesion site. therefore, the hydrophobic drug will be packaged in the nano-drug carrier, and the outer layer of the nano carrier is usually a hydrophilic layer, which can better avoid the drug aggregation and precipitation, thereby ultimately enhancing the solubility of the drug. (b) to prevent drug degradation, improve the stability of the drug, for the biological activity of drugs, such as easily degraded in the human camptothecin, and therefore lose the drug eff ect. and the use of nano-drug carrier can be wrapped to achieve the purpose of avoiding its degradation. (c) improving the properties of the drug dispersion in the body to reduce or eliminate tissue damage caused by leakage of the resulting drug. after this, by the reticulate endothelial system of phagocytic nano into the human body, you can quickly phagocytic cells in the region. for example, doxorubicin can not only destroy cancer cells, but also greatly damage the normal cells, nano-drug carrier can focus on the lesion site (targeted release), so that can reduce the damage to normal tissue. (d) improving the absorption of drugs. because the nano-drug carrier is too dispersed, the surface area and the surface has a special function, which can better improve the drug contact area and time, in the lesion, so that the effi ciency of the drug can be improved. (e) membrane transduction mechanisms that enhance the permeability of drugs that are benefi cial to some of the special parts of the biofi lm. 2.2. types and characteristics of nano-drug carriers according to the preparation of nano-drug carrier material can be divided into nano-particles, nano-milk, nanomicelles, nano-suspension, and drug-like body [2]. the nanoparticle nanoparticles are solid colloidal particles smaller than the lttm polymer colloid drug delivery system [3]. is a solid formed in the polymer backbone, in which the drug can be dissolved or coated on a solid adsorbent by preparing different drug cladding modules into nano spheres and nano capsules. when the drug is dissolved, dispersed or adsorbed, ball-forming polymer drugs are called nano spheres; nano capsules are spherical nanoparticles [4] formed by the encapsulation of solid or liquid drugs, wrapped by polymer fi lms of natural or synthetic polymers. nano emulsion is also known as micro emulsion, particle size 10-100nm between, usually, nano-emulsion is composed of oil, water, surfactant and surfactant composition of the colloidal dispersion system, the general formation of spherical droplets can make the size of the more uniform, transparent or translucent, and have the thermodynamic stability, mild preparation conditions make nano-emulsion physical stability better, can enhance the stability of the drug; by dissolving the oil phase and surfactant chain, can improve the drug the solubility of drugs and promote drug absorption, improve drug utilization of nano emulsion is a new type of drug carrier [5]. nano micelles can be prepared by block polymer nano-micelles as a drug carrier, self-assembled structure formed in water is amphiphilic block polymer dissolved synthesis, the particle size is generally 5nm-100nm. its advantages are: high drug dose, wide range, strong stability, the role of a long time, the unique distribution, high utilization, toxicity, is widely used as anti-cancer drugs, antibiotics, antihypertensive drugs and genes treatment of drugs and other hydrophobic drugs contained [6]. nanoparticles suspension nano-suspensions under certain conditions, special techniques and equipment are used to pulverize the drug to obtain nano-suspensions. in addition to increasing the adhesion and the crystalline structure of the amorphous particles compared to conventional dosage forms, it also increases the rate of dissolution of the poor solubility of the poorly soluble drug, especially for large doses of soluble or injectable poor absorption of oral medications. such as the anti-aids drug bupravaquone in the mucosal adhesion of nano-suspension preparation, bioavailability of up to 40%, and the eff ect is improved, and the dose is greatly reduced [7]. drugs are formed by covalent bonds with lipids to form drug bodies, which are automatically formed due to changes in the solubility characteristics in the medium. drug quality is a new type of drug delivery system; particle size range is generally 10-200nm. drugs are nanoparticles, and they also overcome the shortcomings of drug leakage and skeleton instability, improve drug targeting and biocompatibility, and increase stability [8]. advances in synthesis and application of nanometer drug carriers 14 nano-drug carrier types are rich and varied, more common with polymer micelles, liposomes nanoparticles, polymer-drug copolymers, ceramic nanoparticles, carbon nanotubes, etc., according to its characteristics are applied to diff erent drug delivery system the nano-drug carrier structure. 2.3. transport of nano-drug carriers in general, nanoparticles are engulfed by the reticular endothelial system during circulation, and the flow of nanoparticles is aff ected by their size and surface characteristics [9]. diameter size can be adjusted to be one of the advantages of nanoparticles. but the particles cannot be too large, otherwise it is engulfed by the macrophages of the reticuloendothelial system. particle size of 100-150nm nanoparticles for the most eff ective. in addition to particle size, in the vascular circulation is also affected by the surface characteristics. ideally, the nanoparticles will have a longer cycle time on the hydrophilic surface of the blood vessel. can be obtained by two methods, namely, nanoparticles modifi ed by hydrophilic polymers, or hydrophobic and hydrophobic copolymerization to form hydrophobic core, hydrophilic shell of nanoparticles. however, changing the surface charge of nanoparticles can aff ect their fate, for example, neutral nanoparticles are negligible compared to negative and positive nanoparticles when ingested cells are ingested. meet the above conditions, can better reach the recipient tissue. binary complex in the drug transport target eff ect is not satisfactory, only on the macrophages are more concentrated organs have a certain eff ect [10]. but can be selected specifi c ligand or antibody linked to the binary match to overcome the above problems. active targeting refers to a drug delivery system constructed by specifi cally interacting and enriching specifi c organs, tissues, or cells by means of certain specifi c biochemical environments in the organism, or by the antigen-antibody response mechanism of the organism. according to diff erent mechanisms of action, active targeting is divided into antigen-antibody binding targeting and ligand-receptor binding targeting. 3. preparation methods of nanometer drug carriers 3.1. liposomes the overall structure of the nano-drug carrier is liposomes, which are the earliest developed nano-drug carriers before, until now, liposomes have also improved and used in more disease treatments. membrane evaporation [11], jianping wu, et al 15 reversed-phase evaporation [12], thin-fi lm ultrasonic dispersion [13] and so on are the main methods for the synthesis of nano-liposomes. membrane evaporation method in the organic solvent to the drug and cholesterol, phospholipid compatibility, the liposomal suspension is the evaporation of the solvent so that drugs and phospholipids and other fi lm-forming materials to form a symmetrical lipid fi lm in the fl ask wall and added to the wash fi lm rinse obtain. lvwen li et al. synthesized 50nm liposomes by combining thin fi lm evaporation and freeze-drying with 187.5 mg of phospholipid, cholesterol, 93.8 mg and 37.5 mg lamp and 30 ml of dichloromethane as the main raw material. the aqueous solution of the drug is added to the mixed solution of lecithin, cholesterol and organic solvent to form a relatively stable cde type emulsion. the organic solvent is removed and the phosphate buff er is added to hydrate and continue to short-term evaporate at low milky yellow liposomal suspension. l. liu and other use of reverse phase evaporation with lecithin, cholesterol, streamside made of particle size of 562 nm coverage of 55% to 65% of the cationic liposomes. thin film ultrasonic dispersion method first synthesis of phospholipid bilayer, by ultrasonic hydration dispersed liposomes. y. gu, y. shi, who used emodin, cholesterol, phospholipids, chloroform prepared a particle size of about 25 nm liposomes. 3.2. emulsion method nano-drug in the emulsion synthesis method known as the emulsion method. the small particles are obtained by nucleating the small droplets formed by the action of the surfactant dispersion and the external force. but also by nature in the emulsion polymerization self-assembled nuclei. the main methods: emulsion polymerization, emulsion selfassembly method and membrane emulsion interface polymerization method emulsion polymerization emulsion polymerization nucleation is a discontinuous process. particle size obtained by emulsion polymerization varies in size, typically between 100 nm and several ums. c. chauvierre, c. v authier, d. labarre et al. [14] with dextran, dextran coated polyisobutylcyanoacrylate nanoparticles synthesized by anionic polymerization and two mechanisms of emulsion radical polymerization. the self-assembly polymer nanocomposite has a core-shell structure by dissolving the amphiphilic polymer in an organic solvent and adding water to form an emulsion. the organic solvent is removed by vacuum distillation or solvent diff usion. y. li, s. ikeda, k. nakashima, h. nakamura et al. prepared polymethyl methacrylate micelles, and have a core-shell structure. membrane emulsification interface polymerization membrane emulsification interface is a special interfacial polymerization that occurs by the addition of an initiator to the uniform emulsion prepared in the nano porous membrane. membrane emulsifi cation can not only obtain a monodisperse, stable emulsion by a simple and eff ective method, but also an eff ective means of preparing functional microspheres and microcapsules. 3.3. micro emulsion method there is a fundamental diff erence between the micro emulsion and the emulsion. in the thermodynamic stability conditions can be spontaneously formed transparent or translucent micro emulsion dispersion system. but the eff ect is not stable, placed for a period of time will automatically stratify. the micro emulsion can form nano cells, and if the reaction is carried out in the reaction pool, the reaction product can be regarded as nano. moreover, the micro emulsion reaction conditions are very mild, by changing the micro emulsion preparation method, the external conditions change more so that it changes, the small pool to change the shape, the product of the nano-structure is diff erent. the most attractive is the micro emulsion, which can dissolve a large amount of water and a large amount of oil at the same time. it can make the above oil-soluble substances and water-soluble substances fully mixed, which greatly improves the effi ciency of the reaction. at present, micro emulsion method has many people at home and abroad to study, according to the type of micro emulsion can be divided into normal phase micro emulsion (o/w) [15] and reverse micro emulsion (w/o) [16]. 3.4. ultrasonic method liquid phase internal molecules in the ultrasonic vibration occurs, the molecules change, when the intensity of ultrasound to a certain extent, will produce holes or cavitation bubble liquid molecules, this phenomenon is called ultrasonic cavitation technology [17]. cavitation bubbles continue to produce and violate the collapse, when the cavitation bubble collapse, resulting in local high temperature and high pressure, temperature changes, and accompanied by a strong impact and a 400km projection rate. therefore, ultrasonic cavitation has a very special physical and chemical environment, through its conditions to achieve some special chemical reactions. for example, the phacoemulsifi cation on a two-phase liquid interface can cause the reaction even in the absence of a catalyst. now a lot of polymerization advances in synthesis and application of nanometer drug carriers 16 reactions are used in ultrasonic technology. by exploring the preparation of drug carriers under ultrasonic conditions, many methods have been improved and a better performance nanometer drug carrier has been prepared. 3.5. dialysis and solvent evaporation method the drug carrier is dissolved, the resulting solution is dispersed, evaporated or dialyzed into an organic solvent, and the drug or carrier is nucleated and aggregated due to drastically reduced solubility. z. yan et al. the preparation of methoxypolyethylene glycol-polylactic acid copolymer nanoparticles by phase separation/dialysis method and the study on the distribution of drugs in the nose. (tp-pla-np), tp-pla-the average particle size of np was determined by dynamic laser particle size analyzer (167 nm). the results showed that tp-pla-np as a nano-carrier can signifi cantly reduce the toxicity of tripterygium wilfordii. 3.6. precipitation method the product is precipitated in solution by chemical reaction, and the size of nano-drug particle size is aff ected by the reaction conditions. y. wu and so on in the preparation of nano-magnetic materials used in the method. pillar calvo [18] used an interfacial deposition method to prepare chitosan and polyline-coated nano capsules to study the effi cacy of capsules as indomethacin. the study found that the effi cacy of coated chitosan increased by a factor of two, while the effi cacy of coated with polyline did not change. 4. application and prospect of nanometer drug carrier 4.1. application of nanometer drug carrier in clinical medicine oral drug carriers: drugs and drugs are aff ected by the route of administration. oral effi cacy is mainly aff ected by two primary eff ects, biogenic enzymes and liver enzymes on the gastrointestinal tract that are epithelial cells. many drugs are mostly due to the first effect and metabolic failure, such as peptides, protein drugs have not been a good therapeutic eff ect, oral route of administration usually must be changed to intravenous injection. as the non-targeted drug through the injection pathway steps can be evenly distributed in the systemic blood circulation, and then reach the lesion tissue, protein binding, excretion, degradation, etc., only a small amount of drugs to reach the lesion. the purpose of targeted drug delivery is to improve the drug concentration in the target area and improve the effi ciency of the drug to reduce the side eff ects of drugs in the fi eld has been an important research topic, nano-drug carrier research eff ectively solves these problems. after some oral medication in the nanoparticle wrapped under the gastric acid, pepsin on the drug decomposition decreased. in addition, the nanoparticles can easily promote the delivery of drugs with poor oral absorption specifi city in the human body, prolonging the action time of the drug, and cyclosporine is usually used as an anti-rejection drug in clinical organ transplantation, and the waterslow absorption, oral use of low bioavailability. anti-tumor drug carrier: in recent years, nano-capsule for anti-cancer drug carrier particles research has become the focus of attention of medical workers. most of the anti-cancer drugs, in the cancer treatment of specificity is poor, the key is how to target the drug delivery to the tumor cells without damage to normal cells. liposomes or microcapsules as a drug carrier can improve the water solubility of drugs, so that drug targeting, reduce drug toxicity and prolong the residence time, prolonged the survival time of tumor animals. soma et al. [19] explored the eff ects of macrophages on the presence of doxorubicin-containing nanoparticles, and the results showed that cancer cells with nanoparticles containing doxorubicin toxicity were much more toxic than free doxorubicin. as a new anti-cancer drug paclitaxel encapsulated in pvp nanoparticles in vivo experiments, the tumor size of tumor-bearing mice was reduced and the survival time was evaluated for effi cacy. the results showed that paclitaxel was less than the free paclitaxel nanoparticles the efficacy of the concentration was significantly increased. the experiment also prepared a package of plga nanoparticles targeting drug paclitaxel, as well as linked to a specifi c targeting malignant melanoma, breast cancer, mouse-derived anti-tumor-related antigen monoclonal antibody sm5-1 single chain antibody, the results show that it can be designed to kill liver cancer cells [20]. targeting the carrier of the brain: the presence of the blood-brain barrier, the usual drug is not easy to enter the brain, so the part of the diagnosis and treatment is very diffi cult. studies have shown that modifi ed nanoparticles can pass through the blood-brain barrier, which acts as a drug delivery to the central nervous system. camptothecin solid lipid nanoparticles were injected into mice and found that camptothecin was enriched in rat brain, liver, heart, spleen, brain auc/dose and mrt increased by 10.4 and 4 times, so this nano granules can pass the blood-brain barrier, which is of special signifi cance for the treatment of brain tumors [21]. vector is a gene delivery: antisense oligonucleotide technology is one of the gene therapy methods aimed at designing antisense nucleic acids against a specific target sequence based on the principle of nucleic acid hybridization, thereby inhibiting the expression of a particular gene. antisense oligonucleotide drugs can hybridize to a particular target gene and interfere with the production of a pathogenic protein at the gene level. as the exonuclease and endonuclease of the in vivo are ubiquitous and degrading, jianping wu, et al 17 the bioavailability of oligonucleotides is reduced. the use of nanotechnology gene transfer can overcome this shortcoming; nano-drugs have more than other carriers do not have many advantages in clinical applications has a very good prospect. 4.2. application of nano-drug carrier in pharmaceutical the drug-loaded nanoparticles are nanotechnology combined with modern medical products and are a super-ball drug carrier. in recent years, it is a new drug delivery and sustained release dosage form, including nanoparticles and nano capsules. its advantage is smaller than the cells (10-loonm), so it can be absorbed through the organization and cells, after special treatment can be guided to the organization and management of the organ. controlled release of drug particles: with the previous control of the preparation of different formulations, the release of drug-loaded nanoparticles has a specifi c law of the process, due to the dissolution of the wall and the role of enzyme micro-organisms, drugs can make nanoparticles in the local stay and to achieve eff ective concentration, without causing systemic toxicity. for some of the immune system and the central nervous system drugs, the disease of the treatment of chronic diseases, long-term medication. drug-loaded nanoparticles as a new type of drug-controlled release formulations, especially for these drugs. it was found that rats were subcutaneously injected with insulin nanoparticles. the hypoglycemic eff ect could last for three days and had a signifi cant reaction with the absorption of the drug. it was also found that the hypoglycemic eff ect of insulin nanoparticles was almost three times a day with conventional insulin therapy have the same eff ect, thus proving that insulin can be made under the nano-carrier particles can prolong the role of time and lower blood sugar, more eff ective than the same dose of insulin. drug-loaded nano-enhancing drug targeting eff ect: such micro particles are prepared by the use of various human tissues or vectors of diff erent affi nity for the preparation of drug-loaded micro particles according to clinical needs, or the monoclonal antibodies are bound to the vector, the drug can be highly selective the dispersion in the role of the object, thereby enhancing effi cacy and reduce side eff ects. from target organs, target cells to the most advanced intracellular target mechanisms, these three targeted therapy can be done through drug nanoparticles. when the drugloaded nanoparticles and the drug form a complex, depending on the purpose of the treatment, the choice of blood through the circulation or diff erent ways to selectively enter the body's specifi c tissue and cells to achieve treatment. characteristics of nanoparticles into the cell structure and to achieve gene therapy. now the study of more objects with liver, blood system, gastrointestinal tract, lung, etc. in the liver, etc., for example, drug nanoparticle composite material in two ways to achieve positioning: the complex is kuepfer cell phagocytosis, in the liver drug accumulation, and then gradually fall into the blood circulation, so that the increase in liver drug concentration, reduce other organs side eff ects, known as passive targeting side eff ects; when the nanoparticles are small enough (100-150 nm), and covered with a special coating layer surface, kuepfer cells can escape phagocytic cells, connect monoclonal antibodies and other positioning in the role of liver parenchymal cells, known as active targeting [22]. regardless of the approach taken, the size and shape of the particles is critical to achieving targeting in order to achieve localization while the specifi city of the antibody on the cell surface can improve the selectivity. manufacturing nano-robots to replace traditional drugs: nano-robot, also known as molecular robots, is a combination of nano-mechanical devices and biological systems (such as enzyme and nano-gear combination). nano-robot with its unique structure and nature, so that in many areas have shown extraordinary vitality, to solve the traditional drug mouth problems [23]. in the fi eld of cardiovascular, nano-robot can be injected into the body, a blood vessel operation of the robot. these molecular robots capture energy in blood glucose and oxygen to remove blood vessel thrombosis, remove heart and internal arterial lipid deposits; in genetic engineering, gene assembly can be performed by nano robots, that is, the gene can be removed or harmful dna, or in the normal dna assembly into the chromosome, so that the normal operation of the human body; nano-robot can be used for organ repair, such as repair damaged tissue and organs, complete cosmetic surgery; in addition, nano-robot also swallowed bacteria and kill cancer cells in the body to monitor the disease. 5. conclusion the direction of exploration of nano-drug carriers is to be intelligent, the study of the preparation of nano-carrier and a specifi c drug combination to get with automatic targeting and quantitative timing of the release of nano-intelligent drugs to address the diagnosis and treatment of major diseases. the application of nanotechnology in the field of biopharmaceuticals is one of the most promising research directions for nanotechnology in the 21st century. the use of nano-drug carriers makes some of the better effi cacy but diffi cult to dissolve, slow to dissolve, highly toxic, easily degradable in the body of the drug has been applied to fi nd a new drug dosage form of excellent performance, its signifi cance is no less than found new drugs. now, there are several kinds of nano-drugs into commercial production, not only to human disease to bring a new gospel, but also created a considerable economic benefi ts. but the development of nano-drugs has many problems to be solved, such as nanodrugs into the human 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alzheimer's disease: genes, proteins and therapy. phys rev. 2001, 81: 741-766 42 characterization and application of nanomaterials (2021) volume 4 issue 2 doi:10.24294/can.v4i2.1324 original research article research progress of nanoarray structure transport layers in perovskite solar cells fangxin tan1, shan cong1*, qinghua yi1, zhida han1,2, yushen liu1 1 school of electronic and information engineering, changshu institute of technology, changshu 215500, china. e-mail: congshan@cslg.edu.cn 2 jiangsu laboratory of advanced functional materials, changshu institute of technology, changshu 215500, china abstract the electron/hole transport layer can promote charge transfer and improve device performance, which is used in perovskite solar cells. the nanoarray structure transport layers can not only further promote carrier transport but also reduce recombination. it also has a great potential in enhancing perovskite light absorption, improving device stability and inhibiting the crack nucleation of different structure layers in perovskite solar cells. this paper reviewed the research progress of perovskite solar cells with different nanoarray structure transport layers. the challenges and development directions of perovskite solar cells based on nanoarray structure transport layers are also summarized and prospected. keywords: perovskite solar cells; nanoarray; transport layers article info received: 5 july 2021 accepted: 29 august 2021 available online: 5 septemper 2021 copyright copyright © 2021 fangxin tan, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction organic-inorganic hybrid perovskite materials have attracted much attention because of their adjustable bandgap, long carrier diffusion length and high light absorption coefficient. they are the preferred materials for solar cells prepared by the low-temperature solution method[1,2]. at present, the certified conversion efficiency of perovskite solar cells (psc) has exceeded 25%[3]. conventional perovskite solar cells mainly include planar perovskite solar cells and mesoporous perovskite solar cells. the electron/hole transport layer can accelerate the electron/ hole transport in the device and reduce the interface recombination, which plays an important role in improving the efficiency and stability of the device. at present, various organic and inorganic materials are widely used in perovskite solar cells, such as 2,2’, 7,7’ -tetra [n, n-bis (4-methoxyphenyl) amino]-9,9’-spiro-ometad, poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (ptaa), titanium oxide (tio2), zinc oxide (zno), tin oxide (sno2), nickel oxide nio, and so on[4–7]. the researchers found that the transport layer of nanoarray structure ,such as titanium oxide nanorodarray, zinc oxide nanoarray, not only could promote charge transmission but also reduce interface recombination. it also could enhance perovskite light absorption, inhibit crack nucleation of different structural layers in perovskite solar cells, and improve the stability of flexible devices[8–10]. this paper introduces the research progress at home and abroad, which includes the design and prepara43 tion of nanoarray structures of different electron and hole transport layer materials. 2. research progress of nanoarray electron transport layer 2.1 metal oxide nanoarrays the electron transport layer materials of a metal oxide represented by tio2, zno, and sno2, are widely used in perovskite solar cells, photodetectors and other optoelectronic devices with their excellent electron transport capacity, relatively good environmental stability and convenient preparation process[11–14]. 2.1.1 titanium oxide tio2 tio2 is easy to prepare, low-cost, with appropriate energy level and electron transport capacity. psc use tio2 as an electron transport layer material widely. at present, the research on tio2 nanoarray mainly focuses on the preparation method and structural composition to optimize its performance and structure. it improve electron transport efficiency using tio2 nanoarray, reduces interfacial recombination, enhances the light absorption of photoactive layer, playing a good role in improving the stability of the device. kim et al. reported an efficient perovskite solar cell using submicron (~0.6 μm) rutile tio2 [15]. tio2 nanorods were grown by hydrothermal method, and the reaction time adjusted the length of nanorods. experiments showed that the current density would decrease due to the increase of nanorods. it is mainly due to the tilt of the nanorods during the growth process, which affects the filling of perovskite and ultimately affects the device efficiency (figure 1). huh et al. enhanced the performance of psc by selectively growing tio2 nanorods[16]. they selectively grew tio2 nanorod substrate by nanoimprint lithography and hydrothermal growth method. experiments show that tio2 nanorods, as an electron transmission channel, can effectively improve the electron-hole separation energy, reduce interface recombination, and obtain an open circuit voltage of 1.12 v. in addition, tio2 nanorods can increase the optical path of the incident light, enhance the light absorption of the active layer and improve the device performance. hu et al. prepared a tio2 nano column array by grazing angle deposition[17]. scanning electron microscope studied the tio2 nano column array, scanning near-field optical microscope, and uvvis absorption. it found that the tio2 nano column transport layer can enhance the optical absorption of perovskite through a large number of precursor penetration paths, near-field light concentration, and partial uv shielding. thus it improves the short circuit current and stability of the device. liu et al. deposited the optimized cds shell on tio2 nanoarray at room temperature by a simple chemical bath method, which significantly improved the efficiency and stability of pscs[18]. experiments show that, on the one hand, the cds shell can passivate oxygen vacancies on the tio2 surface, prevent electron-hole recombination and protect the calcium titanium layer. on the other hand, the insertion of cds shell on the surface of tio2 is helpful to form a type-ii structure, which can further accelerate electron transfer and the cds@tio2 coaxial nanoarray structure provides enough space for perovskite implantation. xiao et al. successfully doped nb in titanium oxide array by hydrothermal method[19]. the research shows that in the interface between tio2 and perovskite, tio2 doped with nb is more efficient for electron transport and charge separation, which (a) ~ (c) effect of different tio2 nano array height on device performance; (d) ~ (f) scanning electron microscope images of different tio2 nano array heights[15]. figure 1. application of tio2 nanoarray. 44 provides an effective way to prepare pscs with high performance and high stability. 2.1.2 zinc oxide zno similar to tio2, zno is also a common electron transport material in perovskite solar cells. its electron mobility is higher than tio2, and it is more controllable jn form and has a lower synthesis temperature. these advantages make it widely used in psc[20,21]. at present, the research on zno nanoarrays mainly focuses on many ways, such as how to improve preparation methods,interface modification, increase perovskite filling, reduce carrier recombination as well as improve device efficiency. tulus et al. deposited gold nanoparticles on the surface of zno nanorod array using vacuum deposition technology to increase the hole schottky barrier at the interface of zno perovskite active layer, as shown in figure 2(a). further block holes, passivate carrier composite defects on the surface of zno nanorods, reduce the loss of open-circuit voltage of devices, and improve the filling factor, thus, the conversion efficiency of the battery improved[22]. dong et al. doped the zno nanorod array with al and formed an al-zn-o layer on the surface of the zno nanorod. while passivating the surface defects of the zno nanorod, they also adjusted the energy level to make the energy level of the active layer better match that of the electron transport layer, improve the electron transport efficiency, and finally improve the device[23]. mahmood et al. combined with the dual characteristics of polyethyleneimine (pei) as dipole layer and selective polymer cover, prepared n: zno nanoarrays with high aspect ratio and electron-rich nitrogen doping through low-temperature solution-phase hydrothermal growth[24]. then he applied them in psc to effectively improve the penetration of calcium titanium ore in the array, inhibit carrier recombination and improve device efficiency (figure 2). at the same time, they successfully applied pei coating on the n: zno array adjusted the work function, and obtained stable and hysteresis-free devices with device efficiency > 16%. more interestingly, zhao et al. prepared highly ordered zno nanorod arrays at low temperatures (90°c)[25]. this nanoarray structure has excellent mechanical stability when combined with a flexible substrate, and its performance remains 90% after 1,000 bending cycles with a radius of curvature of 4 mm. it has excellent bending resistance and durability and has great application potential in foldable photovoltaic devices. 2.1.3 stannic oxide sno2 in recent years, planar pscs with sno2 etls have developed rapidly due to the excellent characteristics of sno2 materials, such as appropriate energy level, high electron mobility, good transmittance, excellent chemical stability, and inactive uv catalysis. similar to zinc oxide, stannic oxide also faces many problems of morphology and defect states. optimize the stannic oxide nanorod arrays using the same passivation strategy[26]. song et al. doped sno2 nanocrystals with y3+ by typical solvothermal method[27]. the results show that y dopant has a more appropriate energy level structure and better carrier dynamics performance, and obtains devices with a total efficiency of 20.71%. gao et al. proposed an effective in-situ template self-etching method on the basis of a series (a) device structure diagram of conventional low aspect ratio (lar) zno nanoarrays and (b) high aspect ratio (har) zno nanoarrays with pei coating (illustration: pei as a capping agent for controlling nanotube growth); based on the scanning electron microscope cross-sectional images of 1,070 nm intact cells of lar n: zno nrs (c) and har n: zno nrs (d) without pei coating, the results show that harzno nanoarrays have better perovskite wetting properties[24]. figure 2. application of zno nanoarrays. 45 of controllable experiments, stannic oxide nanotube arrays were prepared with zinc oxide nanorods as sacrificial templates, and the growth mechanism of nanotubes was studied[28]. by comparing stannic oxide nanotube array psc devices with similar sno2 or zno pscs, psc with stannic oxide nanotube array as transport layer has better long-term stability and uv stability (figure 3). this work emphasizes the importance of the material selection of an electron transport layer and provides an idea for realizing ideal electron transport layer/substrate homogeneous junction to promote electron transport. (a) schematic diagram based on sno2 nanoarray and its devices; (b) the corresponding scanning electron microscope cross-sectional image, with a scale of 500 nm; (c) comparison diagram of long-term stability based on sno2, tio2, and zno nanoarrays; (d) based on the uv stability comparison diagram of sno2 and tio2 nanoarray perovskite solar cells, the results show that sno2 nanoarray perovskite solar cells have better stability[28]. figure 3. application of sno2 nanoarray. 2.2 other nanoarray electron transport materials through previous work, it finds that zinc compounds usually have excellent electrical properties. so it is also an important topic to develop the electron transport layer materials of zinc compound. tavakoli et al. introduced zn2sno4 nanorod array as electron transport layer into perovskite solar cells, although the short-circuit current of the obtained devices increased and the hysteresis significantly reduced. however, the open-circuit voltage loss caused by energy level mismatch still needs to solve[29]. 3. research progress of hole transport layer of nanoarray the hole transport materials commonly used in psc mainly include organic materials and inorganic hole transport materials. these holes materials need to meet the conditions of good hole transport capacity, high stability, and matching with perovskite energy level. organic hole transport materials, such as polyethylene dioxythiophene-poly(styrene sulfonate) (pedot: pss), poly[bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (ptaa), are of relatively complex synthesis, and it is not easy to prepare nanorod array structure. in addition, the acidity of pedot: pss and the instability of unsaturated carbon bonds in organic materials are not conducive to the long-term stable operation of the device. the preparation process of inorganic hole transport materials, such as nickel oxide nio, cuprous iodide cui, cuprous thiocyanate cuscn, is relatively simple and convenient structural regulation[30–32]. gan et al. successfully synthesized cuscn nanorod arrays with good crystallinity and electrical properties at room temperature by adjusting the synthesis temperature and deposition potential, which opened an opportunity for their application in the field of optoelectronic devices[33]. xi et al. applied cuscn nanowire array and its similar derived microstructure to perovskite solar cells to achieve a photoelectric conversion efficiency of more than 7.5%. at the same time, the research results show that the introduction of cuscn nanowire array and its derived microstructure is conducive to obtaining a more regular perovskite active layer interface, improving the crystal orientation of perovskite and reducing crystal defects at the active layer and interface, reducing carrier recombination and improving device performance[34]. 46 anandan et al. introduced the wet prepared cuo nanorod array into the dye-sensitized solar cell and obtained a cell with 0.29% conversion efficiency, which proved that the cuo nanorod array could be used as the photoanode (hole transport layer) of the dye-sensitized solar cell. but the cuo band gap was small (about 1.2 ev), such natural defect makes it impossible to completely separate photogenerated electron-hole pairs, resulting in the recombination of a large number of carriers at the cuo interface, affecting the efficiency of the device and greatly limiting its application[35]. cong et al. prepared well-crystallized nickel oxide nanorod arrays at room temperature by grazing angle deposition. it proved that the introduction of nickel oxide arrays reduced the reflection of the light incident surface, increased the light capture of the device, passivated the interface defects between the hole layer and the active layer, induced perovskite crystal growth, obtained high-quality perovskite films, and finally obtained more than 20% photoelectric conversion efficiency. at the same time, the advantages of low-temperature preparation make this structure also have a conversion efficiency of more than 17% on the flexible substrate. moreover, due to the mesoporous structure of the array, the device stress is relieved and the stable operation of the devices on the flexible substrate is guaranteed, which proves the application potential of nanorod array in flexible devices[36] (figure 4). zheng et al. introduced copper phthalocyanine (cupc) nanorod arrays into organic solar cells. through close engagement with pcbm molecules in the active layer, the dark current intensity of the device reduces, and the device performance is doubled compared with the device based on planar cupc structure. it also shows that this structure can effectively passivate the defects between the active layer and the electrode[37]. zhang shows that it can effectively replace the current mainstream spiro-ometad hole transport materials doped with a lithium salt, which integrates the undoped cupc nanorod array with the electrode from the perspective of chemical stability. and obtain a battery with high repeatability with an efficiency of 16.1%[38]. 4. conclusion this paper describes the application and research progress of nanoarray transport layer materials in psc. generally, these devices mainly focus on the preparation and optimization of oxide materials. the preparation methods are a popular such as hydrothermal method, vacuum deposition, template method. generally, the devices with nanoarray transport layer materials can improve the carrier transport efficiency, and enhance the absorption of the photoactive layer. at present, most of the devices prepared by these materials are still small-area devices based on a glass substrate. there is still great potential in the preparation of flexible devices and large-area de(a) grazing angle deposition of nio nanoarrays; (b) the finite element analysis of the electric field distribution diagram with/without nio nanoarray substrate. the results show that nio nanoarray structure is conducive to increasing light transmission and reducing light reflection; (c) the finite element analysis stress distribution diagramof the flexible substrate with/without nio nanoarray.the results show that the nio nanoarray structure has better bending resistance[36]. figure 4. application of nio nanoarrays. 47 vices. in the future, it is necessary to select appropriate flexible substrates for the high-quality growth of nanoarrays through interface modification or doping to improve the carrier mobility, reduce the carrier recombination, improve the device stability, and realize the preparation and application of flexible wearable devices. conflict of interest the authors declare that they have no conflict of interest. acknowledgements project: the national natural science foundation of china project “study on stability mechanism of perovskite solar cells based on nio nano arrays” (62005027); jiangsu natural science foundation project “growth of efficient and stable tio2 array 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crystalline molecular nanorods. organic electronics 2009; 10(8): 1621–1625. 38. zhang f, yang x, cheng m, et al. boosting the efficiency and the stability of low cost perovskite solar cells by using cupc nanorods as hole transport material and carbon as counter electrode. nano energy 2016; 20: 108–116. review article on polymeric nanoparticle final work 20240304 characterization and application of nanomaterials 2025, 8(1), 9274. https://doi.org/10.24294/can9274 1 article advanced tungsten-containing materials manufacturing from its scrap levan chkhartishvili1,2,*, natia barbakadze3, otar tsagareishvili2, archil mikeladze2, tamaz batsikadze4, manana buzariashvili3, tamar dgebuadze3, roin chedia2,3 1 engineering physics department, georgian technical university, tbilisi 0160, georgia 2 semiconducting and powder composite materials laboratory, ferdinand tavadze metallurgy and materials science institute, tbilisi 0186, georgia 3 petre melikishvili institute of physical and organic chemistry, ivane javakhishvili tbilisi state university, tbilisi 0186, georgia 4 structural and physical-chemical properties research laboratory, ferdinand tavadze metallurgy and materials science institute, tbilisi 0186, georgia * corresponding author: levan chkhartishvili, levanchkhartishvili@gtu.ge abstract: we develop a relatively cheap technology of processing a scrap in the form of already used tungsten-containing products (spirals, plates, wires, rods, etc.), as well not conditional tungsten powders. the main stages of the proposed w-scrap recycling method are its dispersing and subsequent dissolution under controlled conditions in hydrogen peroxide aqueous solution resulting in the pta (peroxpolytungstic acid) formation. the filtered solution, as well as the solid acid obtained by its evaporation, are used to synthesize various tungsten compounds and composites. good solubility of pta in water and some other solvents allows preparing homogeneous liquid charges, heat treatment of which yield wc and wc–co in form of ultradispersed powders. go (graphene oxide) and pta composite is obtained and its phase transition in vacuum and reducing atmosphere (h2) is studied. by vacuum-thermal exfoliation of go–pta composite at 170–500 ℃ the rgo (reduced go) and wo2.9 tungsten oxide are obtained, and at 700 ℃—rgo–wo2 composite. wc, w2c and wc–co are obtained from pta at high temperature (900–1000 ℃). by reducing pta in a hydrogen atmosphere, metallic tungsten powder is obtained, which was used to obtain sandwich composites with boron carbide b4c, w/b4c, and w/(b4c–w), as neutron shield materials. composites of sandwich morphology are formed by sps (spark-plasma sintering) method. keywords: tungsten scrap; hydrogen peroxide; peroxpolytungstic acid; graphene oxides; composites; vacuum-thermal exfoliation; tungsten carbides and alloys; spark-plasma sintering; tungsten–boron carbide sandwich composites 1. introduction modern technologies widely use the tungsten-containing alloys, compounds and composites to produce hard materials, cutting tools, drills, heating elements, weapons, electronics, catalysts, sensors, coatings, abrasives, dry lubricants, colorants, etc. this results in permanent increasing the demand for such class of materials. tungsten w is a rare metal (it makes up just a miniscule of the earth’s crust). usually, it is found in the form of ferberite and huebnerite minerals. the main industrial applications have scheelite and wolframite. currently, china controlling 80% of tungsten world production partially restricts the export due to which the price of tungsten (as well as its compounds) on the world market has increased significantly. for example, metallic tungsten is separated from ore by turning it into ammonium paratungstante, the price of which increased 9 times from 2003 to 2011. at present, the development of economical and efficient technologies for the mining and processing of ores or scraps citation chkhartishvili l, barbakadze n, tsagareishvili o, et al. advanced tungsten-containing materials manufacturing from its scrap. characterization and application of nanomaterials. 2025; 8(1): 9274. https://doi.org/10.24294/can9274 article info received: 24 september 2024 accepted: 5 november 2024 available online: 22 november 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 9274. 2 is of great importance [1,2]. unconditioned powders, plates, spirals, rods and other products of tungsten and its alloys are collected in various technological processes, which can be processed by various methods. tungsten has a high melting temperature (3410 ℃), so it is impossible to separate metallic tungsten from scrap by melting. for this purpose, chemical processes, which include several steps, are widely used. one commonly used method (in simplified scheme) is to obtain a tungsten compound from scrap, mainly wo3. its reducing with hydrogen to metallic tungsten, adding other components, and sintering yield the final product. therefore, the recycling and utilization of tungsten and its compounds from used materials, machine parts, or tools is of great importance [3–7]. in particular, cobalt-cemented tungsten carbide wc–co is produced in large quantities and, therefore, a large amount of scrap is collected. its processing methods (so-called direct and chemical recycling and melting metallurgical processes) are quite well optimized [1,8,9]. in the paper [10], the recycling of industrial scrap (i.e., new scrap) and used products (i.e. old scrap) was discussed. because of tungsten’s diverse uses, numerous types of scrap were available for recycling by a wide variety of processes. in 2000, around 46% of us tungsten supply was derived from scrap. the percentage ratio of tungsten consumed from new scrap to that consumed from old scrap was estimated to be of 20:80. of all the tungsten in old scrap available for recycling, around 66% was either consumed in the us or exported to be recycled. for last decades, to remove it from tool scrap and utilize by making the new hard instruments a number industrial technologies of tungsten extracting from tungstencontaining scrap have been developed. the methods implemented so far usually are characterized both by some examples of strengths and weaknesses. generally, when selecting ways to recycle a tungsten waste, it is important to take into account technological process’ simplicity, productivity, energy costs, and environmental friendliness [11–14]. the description of currently available ways of processing of tungsten-containing hard materials has been given in paper [15]. here we list the main methods used to recycle such kind waste in the production of tungsten-containing hard alloys: (i) dispersion of sintered waste first with a crusher and then product grinding into fine fractions; (ii) waste decomposition by chemical-metallurgical methods with strong oxidizers, product pouring, crushing and leaching; (iii) waste chlorination in the presence of carbon dioxide to obtain tungsten chloride, product purification, conversion into tungsten oxides and reducing; (iv) waste heating to high temperature, product oxidizing in air and reducing wo3; (v) first waste oxidizing and then product chlorinating to trap the tungsten chloride; (vi) electrochemical processing of waste solution in ammonia, alkaline or salts; (vii) hydroor pyrometallurgical processing of sawdust; (viii) fine-grained grinding, quenching and crushing the forged mass; (ix) dissolution with sodium hydroxide, precipitation in hydrochloric acid, precipitation and purification of ammonium paratungstate with ammonia, and reduction to tungsten with hydrogen; (x) thermal regeneration in oxidation–reduction–carbidization process; etc. as mentioned, tungsten carbide–cobalt wc–co hard alloy is widely used tool material. it is why frequently, tungsten-containing waste contains cobalt as well. presence of cobalt makes a problem because forming the cobalt tungstate hampers the characterization and application of nanomaterials 2025, 8(1), 9274. 3 complete removal of tungsten itself. analysis of studies on the tungsten waste regeneration from hard alloys containing cobalt showed that selective extraction of cobalt could be done by chemical (chlorine and zinc) and thermochemical and hydro and pyrometallurgical methods, as well as a technology based on explosive energy consumption. development in such industrial technologies solves the tungsten-containing superhard alloys and scrap materials recycling problem and, in this way, helps in their rehabilitation and, respectively, savings of these expensive raw materials. the regeneration process of hard alloys under the influence of shock waves is also processed. through the direct regeneration of secondary raw materials, this highly efficient production technology allows, without thermochemical and metallurgical processes, obtaining the powders of hard alloys useful to create the tools. this technology differs from the existing ones in terms of high technical and economic indicators, high performance, low energy consumption and environmental friendliness. the recovery of the tungsten-containing mixture is carried out under conditions of high-pressure gradients and delivery velocities in cylindrical reaction ampoules subjected to the impact caused by the detonation of an axially symmetric explosive charge. in our opinion, the processing of unconditioned tungsten powders by using spirals, plates and other products into tungsten compounds is best done by a relatively simple environmentally friendly technology, which involves obtaining of pta (peroxpolytungstic acid) from scrap metal by reacting it with hydrogen peroxide. unlike other methods, only oxygen is released in this process, which is not a harmful substance for the environment. by crushing tungsten spirals and dissolving the obtained powder in hydrogen peroxide solution (30%), pta was obtained in [16]. the optimum dissolving temperature is 60 ℃. the ability of w and mo as well to dissolve in h2o2 solution was used to remove and separate them [17]. investigation of thermal decomposition of peroxotungstic and peroxomolybdic acids confirmed that peroxomolybdic acid showed a preferable stability compared with pta. this thermal stability difference can serve for the basic principle of the separation of w and mo. method of dissolving tungsten in a solution of hydrogen peroxide and converting it into pta is often used to deposit tungsten on various surfaces to obtain tungsten oxides. wo3 obtained by this method has many applications in modern technologies as photocatalyst in water splitting, electrode materials for lithium-ion batteries, photochromic films and electrochromic displays [18–20]. during the manufacturing the penetrators from fine powder of tungsten and some other metals (nickel, iron, cobalt, chromium, aluminum, etc.) three types of scraps are generated: compaction scrap (powder), machining scrap (turnings) and defective products (penetrators on form of solid rods), which may contain up to 90% w. methods for the extraction of tungsten from this scrap developed in [21] include electrical leaching of turnings from solid rods, soda annealing and leaching of turnings/powder, impurity removal from powder scrap by acid leaching and physical enrichment of powder scrap. copper was effectively removed from w–cu scrap with increasing fecl3 concentration in dissolver. a weight ratio of fecl3 to scrap of 2:1 at room temperature for 24 h resulted in 97% copper removal and 75% tungsten recovery. characterization and application of nanomaterials 2025, 8(1), 9274. 4 complete removal of copper occurred at increased temperatures and acidic conditions, however, at the efficiency of direct tungsten reduction dropped to 50% [22]. on the one hand, metalperoxy compounds have the ability to form complex compounds with many organic compounds. for example, in work [23] is discussed synthesis of peroxotungstate (vi) complexes containing benzene core carboxylic, benzoic, 2-chlorobenzoic and 3-aminobenzoic acids. as go (graphene oxide) may contain many oxygen functional groups (carboxyl, carbonyl, hydroxyl, peroxy groups, etc.), it can be considered as a macroligand and has to form complexes with metal compounds. on the second hand, the properties of hydrophilicity and hydrophobicity are combined in go, therefore they will affect the adsorption ability of these composite materials toward both inorganic and organic species [24]. these properties can used to obtain go and pta composites. it is confirmed, that the oxide semiconductors can be strongly coupled with the go sheets to form hybrid composites, which have to be promising platforms for the design of electronic devices. in particular, competition between the growth of tungsten oxide nanowires and the reduction of go sheets leads to the formation of sandwichstructured tungsten oxide–rgo (reduced go) composite [25,26]. g (graphene) and its derivatives such as go and chemically obtained rgo composites are promising materials for photocatalysis, making lithium battery electrodes, sensors, photocurrent generation, etc. in the paper solvothermal process simultaneously enables [27] the reduction of go and the formation of tungsten oxide of composition w18o49 making it suitable for the preparation of other g-based composites. a systematic investigation on the incorporation of wo3 nanorods and g for high-efficiency visible-light-driven photocatalysis and no2 gas sensing was given in paper [28]. thus, by obtaining pta from tungsten scrap it is possible to produce many tungsten compounds and composites that are now used in different fields. among them, the composites of go–pta type are especially promising materials for modern developments in science and technology. 2. experimental 2.1. materials graphite flake (natural, 325 mesh, 99.98 % metals basis) used to obtain graphene oxide, reduced graphene oxide and graphene itself, and boron carbide powder (1–7 μm) were purchased from alfa aesar and used without prior purification. reagents such as kmno4, h2so4 (98%) and hcl (37%) were purchased from sigma aldrich and used without prior purification. organic compounds and polymers (carbohydrates, glucose, sucrose, cellulose, polyvinyl alcohol, polyvinylpyrrolidone, etc.) were used as a carbon source (for carbidization and as a reducing agent), which pyrolysis produces activated amorphous carbon, so-called carbon black. the purity of chemical reagents and solvents used for synthesis reached 99.00–99.99% purity. inert environment in the reaction area was created using nitrogen (99.95%) or argon (99.95%) gases. hydrogen gas with purity of 99.95% was used to reduce the tungsten oxide and obtain wc–co. characterization and application of nanomaterials 2025, 8(1), 9274. 5 tungsten scrap (unconditioned powders, plates, spirals, rods, etc.) was collected from the ferdinand tavadze metallurgy and materials science institute (tbilisi, georgia). it was crushed in a steel ball mill and sieved in a vibrating screen. for pta syntheses, powders < 250 μm in size, as well powders with as larger grain sizes of 1– 3 mm, were used. 2.2. equipment to grind the powders there was used planetary mill pulverisette 7 premium line with grinding cup and balls made from wc–co hard alloy. for the ultrasound treatment and homogenization of suspensions it was used an ultrasonic cleaner (45 khz) and jy92–iidn touch screen ultrasonic homogenizer (20–25 khz, 900 w). thermal treatment (< 1500 ℃) of samples was conducted in the high-temperature vacuum furnace kejia. in the same furnace, metal oxides deposited on boron nitride were reduced in hydrogen flow. to obtain wc–co, tungsten oxide also was reduced in the kengo digital generator. compaction of powder samples or simultaneous synthesis and compaction were carried out by using the sps (spark-plasma sintering) facility operating in dc (direct current), pulsed dc and pulsed ac (alternating current) modes, which was designed at the georgian technical university (tbilisi, georgia). the morphology and microstructure of the powders were studied with sem (scanning electron microscope) jeol–jsm 6510 lv equipped with energy dispersive analyzer: dispersive micro-x-ray spectral analyzer x-maxn (oxford instruments). an eds (energy-dispersive spectrometer) and tabletop sem tm3030 plus (hitachi) were be used to determine the samples elemental composition. xrd (x-ray diffraction) patterns were obtained with dron–3m (cu kα, ni filter, 2°/min) and xzg–4 (cu kα, λ = 1.5418 å) diffractometers. the powder particle sizes were determined by the scherrer method. particle sizes were also analyzed by photon correlation nanoparticle size analyzer winner 802 dls and malvern instruments mastersizer. the powder specific surface area was measured on micromeritics gemini vii instrument. samples ftir (fourier transform infrared) spectra were recorded on agilent cary 630 spectrometer (at 350–5000 cm–1). 2.3. chemical synthesis methods the synthesis methods used in this study were previously used by authors to solve some other research tasks and are described in the papers [29–32]. below are described their versions modified to fit the task of producing tungsten compounds and composites from its scrap. method 1: synthesis of pta 5.0 g of tungsten powder is slowly dissolved in 40 ml of 20%–25% h2o2. the h2o2 solution is added to the tungsten powder in three portions during 2 h (note that the reaction is very exothermic!). then 15 ml of hydrogen peroxide solution is again added to the reaction mixture and stirred at room temperature for 5 h. the solution is left for 12 h and then filtered. a yellowish transparent solution is obtained. excess h2o2 is decomposed using a platinum spiral and the solution is evaporated under characterization and application of nanomaterials 2025, 8(1), 9274. 6 vacuum. an orange crystalline substance containing 85.4% wo3 is obtained (at 600 ℃ for 4 h). method 2: preparing pta solution to obtain different composite materials, it is convenient to use pta solutions of a certain concentration. the production of pta is carried out by the process described above with the difference that after filtering the obtained solution is diluted with distilled water and a solution with a w concentration of 50–100 mg/ml is prepared. method 3: synthesis of go 40 ml of 98% sulfuric acid and 1 g graphite powder (325 mesh) is added into a glass reactor. the mixture is stirred at 30–40 ℃ for 0.5 h and 3 g of kmno4 is added at 40–45 ℃ under 1 h (the temperature can reach 50 ℃). the mixture is stirred for 3 h. a gray viscous mass is obtained, which is cooled to 10 ℃ and 100 ml of ice water is added to the reactor. the mixture is diluted to 500 ml and 2 ml of 30% of h2o2 solution is added. a yellowish suspension of graphite oxide is obtained. during the washing of the sediment, its color gradually changes to dark brown. 20 min later solution is removed by decantation. this process is repeated twice. for the rapid precipitation of graphite oxide from the suspension, a 5% solution of hydrochloric acid (500 ml) is added. decantation is repeated 3 times in 10 min intervals. an aqueous gel-like mass is obtained. washing of this precipitate is continued until the ph of the solution reached a value of 5–6. go is separated from the obtained suspension by centrifugation and dried in a vacuum at 60 ℃ for 4 h. in many cases, to obtain composites containing pta, it is more convenient to use go suspension without separation from the reaction mixture. go suspension with a go concentration of 12 mg/ml is used in this process. method 4: vacuum-thermal exfoliation of go and obtaining of rgo vacuum exfoliation of go temperature depends on its synthesis method, chemical composition, preparation time, heating rate and pressure. the vacuum exfoliation temperature range of go obtained by methods known in the literature is of 150–250 ℃. 0.5 g go plates are cut into small pieces (2–4 mm) and placed in 1 l glass flask. after vacuuming the flask, it is heated at rate of 5 ℃/min to 160–170 ℃. in this temperature range, a volumetric exfoliation of the go plates takes place and a fluffy black powder is formed. vacuuming is continued for 1 h and then the flask is cooled under vacuum. the bulk density of the obtained powder reaches 20–30 mg/ml. method 5: obtaining of go–pta composite 40 ml suspension containing 480 mg go is sonicated for 1 h and placed in a 100 ml flask. the suspension is heated to 50 ℃ and 1ml solution of pta (50 mg w/ml) is added. the resulting suspension is stirred for 1 h at 50 ℃. the obtained suspension is dried in air at 100 ℃ (3 h). black plates (0.645 g) are obtained. it is kept in a desiccator. carbon black–pta composite can be obtained in a similar procedure. method 6: vacuum-thermal exfoliation of go–pta composite 0.315 g of go–pta composite is placed in a quartz flask. after vacuuming the flask, it is heated at a rate of 5 ℃/min to 170–175 ℃. in this temperature range, volumetric exfoliation of the composite powder takes place. material heating at this temperature is continued for 1 h and then it is cooled in argon. the powder volume increases in 50–70 times. black 164 mg composite – 1st sample is formed: powder rgo–pta-170. the 2nd sample of the composite obtained by this method is heated at characterization and application of nanomaterials 2025, 8(1), 9274. 7 500 ℃ in vacuum for 1 h and cooled to room temperature under argon: powder rgo– pta-500. method 7: reduction of powder rgo–pta-170 with h2 at 700 ℃ and obtaining of rgo–w composite 0.5 g of rgo–pta-170 composite powder is placed in a quartz boat-like vessel and put in high temperature vacuum furnace. the sample is heated in argon flow at rate of 10 ℃/min. at 400 ℃, argon is replaced by hydrogen and the temperature is raised to 700 ℃ and kept under for 2 h. after that, the furnace is turned off and cooled in argon stream. to prevent oxidation of metallic tungsten, the sample is kept in an argon desiccator. as a result, the rgo–w composite is obtained. method 8: obtaining of rgo–wo2 composite 0.5 g of rgo–pta-170 composite powder is placed in a quartz boat-like vessel and put in high temperature vacuum furnace. the sample is heated to 700 ℃ in an argon stream at a rate of 10 ℃/min and kept for 2 h. after that, the furnace is turned off and cooled in argon stream. the sample is stored in an argon desiccator. rgo–wo2 composite is obtained. method 9: obtaining wc–w2c composite from carbon black–pta and rgo– pta-170 wc–w2c tungsten carbides are obtained by the interaction of acetylene carbon black and pta solution, drying the obtained paste to 180–200 ℃ and sintering the obtained powder at 1000 ℃ in a hydrogen atmosphere for 1 h. wc–w2c composite was obtained from rgo–pta-170 powder in similar way. method 10: obtaining wc–co from pta–co(ch3coo)24h2o–c12h22o11 (sucrose). a mixture of 2.65 g pta, 2.1 g co(ch3coo)24h2o and 4 g c12h22o11 (sucrose) is dissolved in 50 ml of water. the obtained solution is evaporated and the paste is dried at 180–200 ℃ for 2 h. the obtained black mass is ground, placed in a quartz tube and heated at 600 ℃ in an argon flow (30 ml/min) for 2 h. the obtained material is milled in nanomill. then the pre-ceramic precursor powder is transferred into a quartz boat-like vessel, placed in muffle furnace tube, and thermally treated in h2 flow (heating rate of 10 ℃/min, holding time of 2 h at 1000 ℃). the obtained powder of wc–co is of a gray color. method 11: preparation w–b4c powder composite 1 g pta is dissolved in 20 ml of 1% hydroxyl ethyl cellulose (hes 30000) aqueous solution, containing 5 ml of ethylene glycol. 6 g of boron carbide b4c powder are added to the obtained solution. the suspension is evaporated under stirring and the obtained mass is burned in a high temperature furnace at 600 ℃ for 1 h in argon. the resulting wo3/b4c composite is reduced at 700 ℃ in h2 flow for 2 h. a powder composite w/b4c containing 9%–10% metallic tungsten is formed. method 12: obtaining of sandwich-like w/(w–b4c) composite by sps method 12 mm diameter graphite press-form lined with graphite foil is placed together with a certain amount of w wet powder, which was obtained by heating pta at 600 ℃ and then by the reduction of wo3 at 700 ℃ in a h2 stream for 2 h. poured tungsten powder is pressed and wet w–b4c powder obtained by the method described above is also poured on top. this surface is covered with graphite foil and a graphite punch is characterization and application of nanomaterials 2025, 8(1), 9274. 8 placed on top. the press form is placed in the sps facility, and after vacuuming its chamber, the powder is pressed at 30–50 mpa (holding at 1500–1700 ℃ for 10 min. pulsed ac mode with pulse duration of 5 μs and pause of 1 μs is used to sinter these ceramics. the sample heating rate reaches 100–200 ℃/min. the samples are cooled in vacuum. w/(w–b4c) sandwich-like composite is obtained similarly. 3. results and discussion tungsten scrap is a fragile material and it breaks easily under mechanical impact. in laboratory practice, it is possible to obtain powder from scrap (spirals, plates) using a steel mortal, and a steel ball mill was used to crush rods with large diameter. a fine fraction with a particle size of < 250 μm and a relatively large fraction of 1–3 mm were obtained from the scrap. the interaction of the powders with the hydrogen peroxide solution takes place energetically resulting in the formation of a weak yellowish solution. as a result of solution evaporation, an orange crystalline substance is obtained, the eds analysis of which shows that it consists of tungsten and oxygen and does not contain other metals as impurities (figure 1). for example, from 74w land 8o kseries analysis in a point there are obtained: 21.16at.%w and 78.84at.%o. figure 1. eds spectrum of pta obtained from tungsten scrap. the main processes of scrap recycling are given in figure 2. obtaining pta from tungsten scrap by this method is advantageous for several reasons. the simplicity of the method and the synthesis of a water-soluble substance, from which many promising and scarce materials or substances can be obtained are remarkable. for example, it is possible to obtain tungsten oxides (wox), metallic tungsten powder, carbides, borides, composites for various functional purposes, radiation-resistant metal ceramics, catalysts, metallized coatings, sensor materials and others. 0 2 4 6 8 10 kev 0 5 10 15 20 25 30 cps/ev w w w w o characterization and application of nanomaterials 2025, 8(1), 9274. 9 figure 2. general scheme of technological route of obtaining pta from tungsten scrap. 3.1. phase transitions in go–pta composite it is very promising to obtain composites containing tungsten compounds from g and its oxides—gos. this needs studying the phase transitions in go–pta composite due to the interaction of go with pta in different environments and temperature regimes. corresponding results are summarized in figure 3. figure 3. scheme of obtaining different materials from go–pta composite. at the initial stage, go–pta composite was obtained. the formation of this composite is easy because the components consist of many oxygen-containing functional groups, which interact with each other and form a stable homogeneous suspension, by drying of which, the polymer films are obtained. they are flexible and can be used to coat various surfaces with tungsten oxides. we aimed to study the effect of temperature increase on the synthesized composite under vacuum, inert and reducing atmospheres. it should be noted that the process of vacuum-thermal exfoliation of composites go–me compounds was previously studied by authors and in this way, it was obtained rgo–me (me = ag, pt and pd) and rgo–mexoy (mexoy = cuo, cu2o, tio2, fe2o3, fe3o4, coo, etc.) characterization and application of nanomaterials 2025, 8(1), 9274. 10 composites. their biocidal (rgo–ag, rgo–cuo, rgo–tio2, rgo–fe2o3) and magnetic properties, as well as effects of g on morphology, fracture toughness and electrical conductivity of titanium dioxide composite (g–tio2), were studied [32–35]. the developed methods were used for vacuum-thermal exfoliation of go–pta composite. it is determined that the exfoliation temperature of the composite, when using newly synthesized go, is 170–175 ℃ and practically coincides with the temperature of vacuum exfoliation of go (160–170 ℃). because of exfoliation, a fluffy powder is obtained, the volume of which is in 200–300 times greater, than the volume of the initial composite. for comparison, we present the corresponding images in figure 4. (a) (b) (c) figure 4. (a) go–pta composite; (b) and (c) composite rgo–pta-170 obtained from it by vacuum-thermal method. it is confirmed that the volume of the rgo–pta-170 powder composite depends on several factors. for example, if the drying temperature of the initial rgo–pta composite is increased to 150 ℃, the volume of the obtained powder decreases by 5– 7 times. also, the volume of the rgo–pta-170 powder composite depends on the go: pta mass ratio. the maximum volume of powdered rgo–pta-170 is obtained when the amount of pta in the go–pta composite is in the range of 8–20% of go. when obtaining similar powders by vacuum-thermal exfoliation, the preparation time of the go suspension sample should be taken into account. in the case of using a suspension made 3 months earlier or more, powders of a significantly smaller volume are obtained from the go–pta composite. a similar result was obtained when obtaining composites of compounds of other elements, with the difference that the vacuum exfoliation of the composite of go–metal nitrates actually takes place by explosion. this is caused by the presence of nitrate ions in the system, which with any organic compound produces explosive materials. exfoliation of non-nitrate systems is safe and easy to do even in glassware. we note here that the separation of the matrix (go) is caused by the decomposition of the oxygen-containing functional groups contained in it, the generation of gases (co2, h2o and vapors of organic compounds) and the characterization and application of nanomaterials 2025, 8(1), 9274. 11 development of a certain pressure between the layers of go, which causes the exfoliation of the layers. without vacuum, i.e. in air or any gas flow the films of go itself or its composites do not change their geometric shape and remain in the form of plates. thus, the method of vacuum-thermal exfoliation can be considered as a new method for obtaining composites of tungsten compounds and gos. further heating of the rgo–pta-170 composite up to 500 ℃ literally does not change the phase composition and the rgo–wo2.9 composite is obtained, which transforms into the rgo–wo2 composite at 700 ℃ (figures 5 and 6). figure 5. xrd patterns of rgo (green) and composites rgo–(rgo–wo2.9-170) (blue) and rgo–(rgo–wo2.9-500) (red). figure 6. xrd patterns of rgo–wo2-700 composite (green) and wo2 phase (red). comparing these diffractograms, it can be concluded that in the rgo–wo2.9-170 and rgo–(rgo–wo2.9-500) composites, the wo2.9 phase is not fully formed, while in the rgo–wo2-700 composite, the wo2 phase is well defined (figure 6). in general, pta gradually undergoes dehydration and deoxygenation during heat treatment, and at 600 ℃ the wo3 phase is obtained and metallic tungsten is obtained in hydrogen environment [18–20]. it is also known that in a reducing environment wo3 reduces to metallic w. in our case, rgo–pta-170, as well as rgo–wo2.9-170 composites in a reducing atmosphere (h2) are reduced to metallic tungsten and rgo–w is obtained. characterization and application of nanomaterials 2025, 8(1), 9274. 12 it is known [8] that in the temperature range of 700–1000 ℃ the w–c system produces tungsten carbides. different types of organic compounds are often used for carbon sources, which, when the temperature rises, produce active carbon, both carbonizing and reducing agent in the carbonizing process. using organic reagents, we have obtained nanopowders of many metal carbides and multicomponent metalceramics – see the earlier papers [36–38]. in general, the go–pta composite is a w– c type system containing a tungsten compound and a carbonizing agent (carbon source) in the form of go. by their heating to 900 ℃ in hydrogen (or argon) flow tungsten carbides wc and w2c are obtained (figure 7). figure 7. xrd patterns of wc and w2c phases obtained from go–pta composite at 900 ℃ in h2 flow. figure 8. xrd patterns of wc and w2c phases obtained from carbon black–pta mixture at 900 ℃ in h2 flow. for comparison, we carried out carbon black–pta mixture carbonization at 900 ℃ in h2 flow. as can be seen from the xrd patterns, as it was expected wc and w2c phases are also obtained in this case (figure 8). the diffractogram also shows the peak of excess carbon. in the case of go–pta, a carbon low intensity peak is visible. such a difference is due to the fact that go forms g with a defective structure at high temperature (a chemical method of graphene synthesis) because the oxygencontaining groups are removed from it. therefore, the carbon present in go is spent characterization and application of nanomaterials 2025, 8(1), 9274. 13 both on carbonization and formation of low-molecular carbon-containing compounds. in the case of carbon black, the oxygen content is low (1%–3%), while the oxygen content in go is in the range of 20%–34%. these results are presented in our previous works [33,35,39]. 3.2. preparation wc–co from pta with the proposed method, it is possible to transform tungsten scrap into wc– co, which is an important metal-ceramic in metalworking technology (drills, cutters, abrasives, coatings, etc.). carbothermic process is mainly used to obtain the mentioned material, which involves the carbonization of a mixture of tungsten powder, cobalt and carbonaceous material (amorphous coal, black carbon obtained by various methods) in a hydrogen environment at 900–1000 ℃. the technological process requires dispersed tungsten powder, which is obtained by long grinding in mills, due to which the target product is contaminated with wear materials of the mill and balls. besides, the grain size of the wc–co powder obtained by the traditional method is several micrometers. currently, much attention is being paid to the technologies that lead to obtaining ultradisperse (nanosize) powders of hard materials [36,40]. using traditional methods, it is impossible to achieve the goal, because it is practically impossible to grind the components of the starting material down to the nanosize. one of the ways to solve this problem is to obtain pre-ceramic precursors from liquid charge, where the components are broken down into molecules and ions [37,38,41]. figure 9. xrd pattern of wc–co obtained from pta–co(ch3coo)2(4h2o– c12h22o11 (sucrose) precursors at 1000 ℃ in h2 flow. to obtain wc–co, we selected the system pta–co(ch3coo)24h2o–c12h22o11 (sucrose), which contains water-soluble components. specifically, pta is an ideal precursor candidate for obtaining wc–co as it is highly soluble in water and can be obtained as a solution up to 50%. cobalt acetate (or cobalt nitrate and chloride) is also soluble in water. it is possible to use water-soluble synthetic and natural polymers, carbohydrates, alcohols and other organic compounds as carbonizing agents. by mixing the component solutions and drying them by vaporization at 300–400 ℃, a preceramic precursor is obtained, in which tungsten, cobalt and carbon compounds are characterization and application of nanomaterials 2025, 8(1), 9274. 14 homogeneously distributed, and wc–co is obtained by their carbonization in a hydrogen atmosphere. this technology does not require scarce metal powders: the target product is obtained from available reagents. the wc–co diffractogram obtained by heating the preceramic precursor obtained from pta–co(ch3coo)24h2o– c12h22o11 (sucrose) at 1000 ℃ in the hydrogen environment is shown in figure 9. 3.3. obtaining of radiation resistant sandwich-like composites w/b4c and w/(w–b4c) boron carbide–tungsten b4c–w thin-layered sandwich structures are known as effective shield composite materials, in which lowand high-z atoms (z is the atomic number), b and w, serve as effective absorbers for, respectively, (epi)thermal neutrons and secondary gamma-quanta accompanying the neutrons capture by 10b nuclei [42– 44]. to obtain them, first note that wo3 is obtained from tungsten scrap by heating of pta, which is reduced above > 500 ℃ to metallic tungsten in h2 flow [19,45,46]. pta solutions are also used for tungstenizig (metallizing with tungsten) of various surfaces [47,48]. we obtained both metallic tungsten powder and powder of composite w–b4c containing 8–10% tungsten from pta using a similar method. the obtained powders were used to obtain w/b4c and w/(w–b4c) sandwiches. it is known that boron carbide reacts with metals at high temperatures and forms borides, which are also binding (cement) phases of composites. many composites were obtained by this method, which found use in obtaining radiation resistant materials [49]. thus, the w– b4c powder composite obtained by us from pta is a promising material for making radiation-resistant sandwiches. sintered composites of wc–wb–w2b were prepared from b4c–w–wc powders using a reactive energization hot-pressing technique that initiated a solid state reaction between b4c and w [50]. it is established that the resulting sandwiches do not undergo exfoliation because at the contact boundary between the metal and boron carbide, a transitional bonding phase w2b5 is formed, which is also the best neutron absorber compound [51]. when tungsten and boron carbide powders are sintered by sps method, actually a three-layer sandwich w/w2b5/b4c is formed. if we selectively remove the tungsten layer with a hydrogen peroxide solution, the sandwich w2b5/b4c will remain. xrd analysis of such composition detects both w2b5 phase and b4c. for xrd analysis, half the surface of the w2b5/b4c cylindrical sample was peeled off at an angle of approximately 40–45 degrees to expose the b4c layer [31]. w/b4c and w/(w–b4c) sandwiches were made by sps method, in which tungsten powder was obtained by reduction of pta separated from scrap (in h2 flow at 700 ℃). in this case, the sintering method was partially changed. in the sem image of the w/b4c sample fragment, the separation boundary between tungsten and boron carbide is clearly seen in figure 10. it seems that there is a mutual diffusion of tungsten and boron carbide, as a result of which the w2b5 phase is formed, whose irregular layer is well separated between the white and black layers. figure 11 shows the edx (energy dispersive x-ray) mapping images and distributions of each element in the sandwich structure. w/(w–b4c) sandwiches were obtained by a similar method. characterization and application of nanomaterials 2025, 8(1), 9274. 15 (a) (b) figure 10. sem images of composite b4c–w obtained by sps from b4c and w powders at 1500 ℃: fracture surfaces with different magnifications. (a) × 90; (b) × 10,000. (a) (b) (c) (d) figure 11. edx mapping of all elements (a) and separately b (b) c (c) and w (d) distributions in b4c and w phases contact regions. if we consider these processes, it can be concluded that the w2b5 phase, which is a powder binder, is formed on the contact surface of the w–b4c composite powder particles. this is important because it allows pressure-free sintering of pressed composites (green products) at relatively low temperatures (1400–1500 ℃). thus, characterization and application of nanomaterials 2025, 8(1), 9274. 16 pta is a necessary component for obtaining w–b4c powder composites, so it’s obtaining from tungsten scrap is a promising direction. 4. conclusions methods for obtaining solution and crystalline pta from tungsten scrap are developed. by mechanically crushing tungsten scrap and dissolving the resulting powder in hydrogen peroxide solution, a pta solution is obtained. in addition, by its evaporating a crystalline pta is formed. they are used in the preparation of metallic tungsten w powder; tungsten–boron carbide composite w–b4c powder, gos containing composites go–pta, rgo–wo2.9, rgo–wo2, and rgo–w; tungsten carbides w2c, wc, and wc–co; and sandwich composites w/b4c and w/(w–b4c). it is established that by thermal treatment of pta in the hydrogen environment at 600– 700 ℃, metallic tungsten w powder is obtained, which has many applications. phase transitions of go–pta composite in vacuum and hydrogen atmosphere at 170–900 ℃ is studied. by the interaction of pta solution and go suspension, an amorphous go–pta composite is obtained. in addition, rgo–wo2.9 composite powder is formed by their vacuum thermal explosion at 170–500 ℃. it is determined that wo2.9 phase transforms into wo2 at 700 ℃ and rgo–wo2 composite is formed. by reduction the latter in a hydrogen atmosphere (700 ℃), rgo–w composite containing metallic tungsten is obtained. using the pta solution, a liquid charge containing the pta– co(ch3coo)24h2o–c12h22o11 (sucrose) system is prepared. a preceramic precursor powder is obtained from this charge. it is determined by xrd analysis that through carbonization in hydrogen atmosphere at 1000 ℃ wc–co is obtained, in which cobalt content reaches 6–20wt.%. obtaining possibilities of sandwich composites containing boron carbide and metallic tungsten layer using metallic tungsten powder obtained from pta also are studied. it is confirmed that by sps process it is possible to obtain sandwich-like w/b4c and w/(w–b4c) composites at 1500–1700 ℃. on the contacting surface of tungsten and boron carbide, formation of the w2b5 intermediate phase is detected, which serves for an additional binder phase. thus, from the point of view of implementing environmentally friendly technologies, replacing commercial tungsten powder with tungsten scrap obtained from pta and processing with appropriate methods, it is possible to obtain many scarce and widely used tungsten-containing composites and materials. we note here that when tungsten scrap is dissolved in an aqueous solution of hydrogen peroxide, oxygen is formed as a by-product, which is not an environmental pollutant. author contributions: conceptualization, lc and rc; 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nano communications networks; parity generator; parity checker; reversible logic; vlsi 1. introduction given that people must utilise electronics, it is regrettable that common electronic gadgets based on cmos technology have flaws. there are some significant drawbacks to this technique, such as short-channel effects. as cmos technology nears its physical limits, issues like power dissipation and the quantum effect are becoming more noticeable. the design complexity increases much further when cmos technology is down to the nanoscale. reversibility processing is one of the most important subjects in nanotechnology, the science that complements cmos technology. this is due to the physical constraints of cmos technology, which include its larger dimensions compared to qca. we work on both hardware and software components to attain great efficiency. power analysis is therefore important since it can assist designers in identifying the positive long-term consequences [1]. on the whole, circuit designers were able to construct new goods utilising qca technology because the logic value model relies on where electrons are located in each cell of quantum dots. the zero-and-one logic paradigm in cmos is based on low and high voltages. irreversible logic generally causes some input data to be lost, which could lead to increased power consumption. when this happens, the output information is not recoverable, so we must retrieve the data from the main memory [2,3]. according to landauer’s research, every bit of information lost results in the citation vittapu sk, sankuru r, bolimera r, et al. reversible logic-based parity generator circuit for nano communication network using qca. characterization and application of nanomaterials. 2024; 7(2): 6236. https://doi.org/10.24294/can.v7i2.6236 article info received: 6 may 2024 accepted: 8 july 2024 available online: 26 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 6236. 2 loss of ktln2 joules of heat energy, where t is the operation’s absolute temperature and k is boltzmann’s constant [4]. a circuit must be made up of reversible gates in order to prevent this energy dissipation [5]. energy dissipation is decreased by reversible logic, which produces a one-to-one connection between input and output vectors. reversible computing is limited primarily by minimising the quantum cost, minimising input constants, minimising garbage outputs, and employing the fewest number of gates possible [6,7]. parity and feynman diagrams are crucial components of arithmetic computing [8]. this study proposes an optimised reversible feynman design implementation using parity generators, parity checker gates, and the efficient xor proposed by ahmed and naz [8]. to show expandability, we then create a nano communication design with fewer garbage outputs. moreover, the proposed nanocommunication designs are reversible and provide fault tolerance. 2. related works the design of the nano communication network reversible based parity generator circuit using qca has involved numerous research projects. below is a discussion of some of them. numerous issues and inadequacies have been noted in recent decades as a result of the emergence of significant limitations on the complementary metal oxide semiconductor (cmos) technology’s capacity to scale physically. a few of the challenges that come with this technology are short channel effects and high leakage power consumption. reversible gates are used in conjunction with a procedural technique in the study of bagherian khosroshahy et al. [1] to minimise latency in the system design, which is based on output conformance and a requirements self-checking approach. the reversibility logic will be the focus of the suggested circuit. in comparison to the study of danehdaran et al. [2], the technique is obtained with enhanced reliability. since there is no fan-out in the reversible logic gates, there is no power dissipation [3]. the output terms and garbage values are both present in the reversible logic. the relationship between the trash value, the input, and the output [4]. the primary parameters to be discussed in reversible logic are quantum cost, garbage, constant input, and latency. every circuit needs a delay calculation feature in order to adjust efficiency. the parity generator circuit implements a novel feynman-based, reversible, and fault-tolerant nano communication arithmetic architecture with several trash outputs [5]. according to panahi et al.’s research, every bit of information lost results in the loss of ktln2 joules of heat energy, where t is the operation’s absolute temperature and k is boltzmann’s constant [6]. reversibility is crucial for error detection in nanocircuits since it allows for lossless transmission and the absence of data loss. additionally, latency and cell count are not described independently in the majority of these irreversible circuits. although their circuits contain more cells and a delay, the parity generator, parity checker, and their nano-communication circuit have been created reversibly using odd parity bits in the study of panahi et al. [7]. feynman and parity are crucial components of arithmetic computing in the study of ahmed and naz [8]. the suggested feynman gate uses an xor gate based on ahmed and naz [8], despite certain limitations in cell placement leading to greater overhead areas. equation [9] can be used to calculate the electrostatic interaction force between each characterization and application of nanomaterials 2024, 7(2), 6236. 3 cell’s two electrons. qca technology flaws are mostly associated with the deposition process, which may be classified into four distinct kinds [10–14]. the transmitted data from the parity generator is controlled by the odd parity checker, which verifies its accuracy. an error during transmission will occur if the parity output of the four bits (the three message bits plus the parity bit) is even. as a result, the binary information that was originally transferred was strange [12,15–17]. in the study of mohaimeed and rabee [18], new nano composite thin films were fabricated that outperformed tio2 films in terms of transmittance and energy gap. in the study of najm et al. [19], a new technique was employed named solvothermal, which is used for the deposition of nano particles into nano thin films. figure 1 shows a high-level representation of a four-dot qca cell. a square is created by positioning four quantum dots. little semi-conductor or metal islands known as quantum dots have a diameter that is small enough to cause their fluctuating energy to be more than kbt (where t is the operating temperature and kb is boltzman’s constant). (they will eventually shrink to fit within specifically made molecules.) they will trap individual charge barriers if this is the case. figure 1. qca cell polarization and representations of binary 1 and binary 0. through electron tunnelling, exactly two mobile electrons are loaded into the cell and are able to travel to various quantum dots within the qca cell. in 2.1, the lines that join the quantum dots depict the tutoring routes. the electrons will only occupy the corners of the qca cell due to repulsion, creating two distinct polarisations. there are two types of cells with 90° and 45° rotations that are commonly used in semiconductor qca technology. both types can be represented as zero and one logic, but there is a slight variation in the forms of the cells that are placed, even though each cell’s computation remains the same. a 90° cell would become a 45° cell if it were rotated by 45°. it is assumed that potential barriers between neighbouring qca cells, which are raised and lowered by capacitive plates, provide total control over electron tunnelling. figure 2. a qca wire. a qca wire depicted in figure 2 is created by electrostatic interaction between cells arranged in a row next to one another; any input value can propagate across the wire, and the output cell will have a value equal to the input cell. because of this, each characterization and application of nanomaterials 2024, 7(2), 6236. 4 cell can perform the three important functions of wire, processor, and memory all at once. generally speaking, a lot of work has gone into creating an inverter gate, as shown in figure 3. all the gates are identical in terms of functioning, but because they are utilised for distinct purposes, each inverter gate has a unique map and overall design. random input values are applied to the input cell of every inverter gate. based on the electrostatic interactions between electrons, any amount of propagation on a gate occurs in between. this is caused by a change in the middle cell’s placement, which charges the middle values in the opposite direction. the output cell then provides the reverted value. figure 3. inverter gate. potential barriers (that would be beneath the cell) that can be increased and reduced between neighbouring qca cells using capacitive plates are considered to be the only means of controlling electron tunnelling. majority gate: the majority and inverter gates are essential gates in qca technology that designers can utilise to create any kind of new circuit. there should be an odd number of cells in the majority. we now want to talk about a three-input majority gate, which has three inputs, one voter cell, and one output cell—as the name suggests. the function of this gate is indicated in equation. the majority gate and the inverter gate share the same electrostatic interactions. the structure of the three input majority gates is shown in figure 4. majority = ab + bc + ac (1) figure 4. the fundamental qca logical device—the majority gate. 3. the proposed method 3.1. the reversible feynman gate more energy is being used by computers than ever before, with over a billion of them in use globally. computers with reversible features can use less power in several areas, such as the cpu and memory. to run on a computer, a process has to divide the characterization and application of nanomaterials 2024, 7(2), 6236. 5 calculation into smaller units. reversible hardware ensures that no result is wasted since occasionally, for a process or set of pieces to be completed, it requires the other parts. therefore, fetching from main memory is not necessary. when a cpu based on reversible hardware executes instructions, for instance, middle registers do not need to keep the results of prior computations; this helps to lower a device’s energy consumption and overall calculation time. reversible circuit design has generally received far more attention in recent decades [13]; the feynman gate is one of the most well-known reversible arithmetic logic gates. one of the numerous circuits that can use the feynman gate is the alu. the feynman gate is a two-by-two device with two inputs, a and b, and two outputs, q and p. the correspondence between the inputs and outputs is one to one. p = a and q = (a ⊕ b) are the respective output equations. when a = 0 and b = 0, this gate’s functioning would result in p = 0 and q = 0 as output. in a similar vein, if a = 0 and b = 1, the result would be p = 0 and q = 1, and the cycle would repeat. the reversible feynman gate suggested by the qca layout is depicted in figure 5. figure 5. layout of feynman gate. 3.2. the reversible odd-parity generator and checker when designing circuits, the most crucial element is extensibility. a reversible parity generator and checker circuit’s complexity is dependent on several variables and necessitates careful evaluation of performance trade-offs. among the methods most frequently employed for data transmission fault detection is the parity-generating technique. binary data in digital systems is susceptible to noise during transmission and processing, which can change 0 s (of the data bits) to 1 s and 1 s to 0 s. below is a block schematic of the parity generator depicted in figure 6. figure 6. block diagram of odd-parity generator. characterization and application of nanomaterials 2024, 7(2), 6236. 6 therefore, to make the number of 1 s even or odd, a parity bit is added to the word containing the data. a new reversible odd-parity generator is shown to illustrate the benefit. it has three inputs, x1, x2, and x3, and one output parity bit. the oddparity generator’s qca configuration is displayed in figure 7. one way to characterise the suggested 3-bit reversible gate is as follows: x1 = gar 1 (2) x2 = gar 2 (3) x3(parity)= x1 xor (x2 xnor x3) (4) the schematic of the parity checker is shown in figure 8. figure 7. the schematic of the parity generator. figure 8. layout of parity checker. the odd-parity generator yields gar1 = 0, gar2 = 0, and a parity bit of 1 if x1 = 0, x2 = 0, and x3 = 0. on the other hand, the outputs become gar1 = 0, gar2 = 0, and parity bit = 0 when the inputs are x1 = 0, x2 = 0, and x3 = 1. the entire set of combinations for this generator is shown in table 1. a circuit known as a parity checker is used to verify the receiver’s parity. check bit = 1 indicates an error occurs when the data word (three input bits plus the parity bit) turns even; check bit = 0 indicates no error occurs. the parity checker generates one output from four inputs characterization and application of nanomaterials 2024, 7(2), 6236. 7 (x1, x2, x3, and the parity bit). the mathematics for this circuit, which the parity checker uses, are displayed below. x1 = gar 1 (5) x2 = gar 2 (6) x3 = gar 3 (7) check bit = ((x1 xor x2)′ xor (x3 xor parity bit)′)′ (8) table 1. truth table of the parity generator and parity checker system. x1 x2 x3 check bit parity bit gar1 gar2 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 1 0 1 1 0 1 0 1 1 0 0 0 0 1 0 1 0 1 0 1 1 0 1 1 0 0 1 1 1 1 1 1 0 0 1 1 3.3. the proposed nano-communication system generally speaking, vulnerabilities in communications networks can be found by utilising a nano-communication system constructed with checkers and parity producing units. the three proposed components for nano-communication are the transmitter, the transmission medium, and the receiver. we solely used fault-tolerant components when designing the suggested nano-communication system, like faulttolerant inverters and xor [11]. • in addition to the three-input message, the transmitter generates a second bit known as the parity bit. the transmitted bit pattern has an odd number of 1s, or odd parity. • the communication link between the source and the destination is provided by the transmission medium. the transmission medium (communication channel) is used to send the transmission bit pattern that the transmitter generates to the receiver. • the receiver takes the transmission message word that the transmitter sent, along with the parity bit. at the receiver, the parity bit is examined in order to detect errors. an error has occurred through the transmission medium, indicating that one bit has changed if the received transmission bit pattern contains an even number of 1. if not, there has been no error. since actual clocking can lower fabrication costs and simplify the physical design, designing circuits based on it is a crucial component. implementing qca circuits based on real clocking has been the subject of numerous attempts; some solutions have been developed in a dynamic approach, while others have been built in a pipeline fashion [14]. therefore, the pipeline format approach in the study of jain et al. [14] would be the optimum option in the event of a loop-less circuit where the clock phase placement is sorted in increasing order. this has been taken into consideration in the case of the suggested nano-communication circuits, and the fundamental ideas characterization and application of nanomaterials 2024, 7(2), 6236. 8 of our suggested technique readily apply to actual clocking. qca schematic of the overall nano communication network is shown in figure 9. in figures 10–12 show the simulation results of each block as depicted in figure 9. figure 9. qca circuit diagram of nano communication circuit. figure 10. simulation waveforms of feynman gate. characterization and application of nanomaterials 2024, 7(2), 6236. 9 figure 11. simulation of parity generator and checker. figure 12. simulation of nano communication circuit. 4. experimental results performance evaluation and simulation results: the most potent programme for simulating circuits based on qca technology is qca designer. qca cell size = 18 nm, quantum dot diameter = 5 nm, number of samples = 50,000, convergence tolerance = 0.001, radius of effect = 65 nm, relative permittivity = 12.9, clock low = 3.8 × 10−23 j, clock high = 9.8 × 10−22 j, clock amplitude factor = 2.000, layer separation = 11.5 nm, and maximum iterations per sample = 100 are some of the simulation parameters for this well-known tool. 5. conclusion in summary, a major advancement in the fields of nanotechnology and communication systems has been made with the design of the nano communication network reversible based parity generator circuit employing qca. through the utilisation of quantum-dot cellular automata (qca) special features, this circuit presents a viable path towards effective nanoscale data processing and transmission. in addition to guaranteeing low energy consumption (31.2%), its reversible design improves data transmission reliability by enabling error detection through parity creation. this method highlights the potential of nanotechnology to transform a number of industries, such as biomedical devices, the internet of things, and more, thereby influencing the direction of communication networks in the future. building strong, high-performing systems in the nanoscale world requires the integration of characterization and application of nanomaterials 2024, 7(2), 6236. 10 qca-based circuits, such as the reversible parity generator, as we continue to explore the domain of nano communication. author contributions: conceptualization, skv and kmr; methodology, skv, rs and rb; software, kmr, mrr and mmr; validation, skv, ra and rb; formal analysis, kmr; investigation, skv; resources, kmr; data curation, skv and rs; writing—original draft preparation, skv; writing—review and editing, skv, rs and rb; visualization, kmr; supervision, skv; project administration, kmr, mrr and mmr. all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of 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word can-4945-online(1)(1) characterization and application of nanomaterials 2024, 7(2), 4945. https://doi.org/10.24294/can.v7i2.4945 1 review fullerene in water remediation nanocomposite membranes—cutting edge advancements ayesha kausar1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, china; dr.ayeshakausar@yahoo.com 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa abstract: among carbon nanoparticles, fullerene has been observed as a unique zerodimensional hollow molecule. fullerene has a high surface area and exceptional structural and physical features (optical, electronic, heat, mechanical, and others). advancements in fullerene have been observed in the form of nanocomposites. application of fullerene nanocomposites has been found in the membrane sector. this cutting-edge review article basically describes the potential of fullerene nanocomposite membranes for water remediation. adding fullerene nanoparticles has been found to amend the microstructure and physical features of the nanocomposite membranes in addition to membrane porosity, selectivity, permeation, water flux, desalination, and other significant properties for water remediation. variations in the designs of fullerene nanocomposites have resulted in greater separations between salts, desired metals, toxic metal ions, microorganisms, etc. future investigations on ground-breaking fullerene-based membrane materials may overcome several design and performance challenges for advanced applications. keywords: fullerene; nanocomposite; membranes; water remediation; permeation 1. introduction benefits of membrane skills have been observed for technical utilization due to low cost, efficient working, low energy consumption, and scaled-up processing [1]. in traditional membrane technologies, pressure-driven membrane assemblies have been used for filtration [2]. developments in this field have led to the implication of polymer-based membranes and materials. consequently, numerous polymers have been used as filtration membranes to enhance their robustness, selectivity, permeability, and desalination performance at low pressure [3,4]. polymeric membranes have been fabricated using a range of techniques, such as simple solution casting, phase inversion, sol-gel procedures, and efficient electrospinning techniques [5–7]. the efficiency of polymeric membranes has been found to be reliable on the surface area, microstructure, porosity, crystallinity, hydrophilicity, etc., enhancing flux, fouling resistance, and desalination performances [8–10]. in this regard, applying nanocomposite membranes instead of pristine polymeric membranes has been found advantageous [11]. consequently, carbon nanostructures like graphene, carbon nanotubes, nanofibers, etc. have been employed to develop nanocomposite membranes [12,13]. most competent fullerene nanoparticles have been applied to polymeric membranes [14]. hence, water remediation has been investigated using polymerand fullerene-derived nanocomposite membranes [15–17]. citation kausar a. fullerene in water remediation nanocomposite membranes—cutting edge advancements. characterization and application of nanomaterials. 2024; 7(2): 4945. https://doi.org/10.24294/can.v7i2.494 5 article info received: 1 march 2024 accepted: 1 april 2024 available online: 1 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 4945. 2 this state-of-the-art article presents fullerene-filled nanocomposite membranes for water purification. inclusion of fullerene in filtration membranes caused significant effects on the separation performances owing to the high surface area, pore size, porosity, surface roughness, and other surface properties [18]. fullerene-based membranes revealed fine potential to overcome the performance challenges of the filtration of unwanted pollutants [19]. 2. fullerene fullerene is a hollow, symmetrical carbon nano-allotrope with sp2 hybridization [20,21]. owing to structural features, π conjugation has been observed in the fullerene molecule [22]. this cage-shaped nanostructure has a size of about 1 nm. its discovery dates back to 1985 [23]. fullerene molecules have been found as c20, c24, c60, c70, c120, etc., depending upon the number of carbon atoms in the hollow ball-like ring structure (figure 1) [24]. fullerene c60 is the most frequently adopted form, known as buckminsterfullerene. this marvelous molecule has been studied for its optical, electronic, mechanical, thermal, and biomedical properties [25]. a number of techniques have been used to form the fullerene molecules, like the plasma method, chemical vapor deposition, arc discharge, and many others [26,27]. advancements in fullerene research have been observed in the form of nanocomposite structures [28,29]. for nanocomposite formation, the solubility of fullerene molecules has been considered [30]. various solvents like water, poly(vinylpyrrolidone), and organic solvents have been used for fullerene molecules [31]. consequently, better-processed fullerene nanomaterials have been applied for photovoltaics, optoelectronics, sensors, and biomedical applications [32–35]. furthermore, high-performance fullerene-based nanocomposite membranes have been designed. the membrane performance was dependent upon the type of fullerene molecules, dispersions, and interactions with the matrix materials used [36]. figure 1. some fullerene molecules. 3. nanocomposite membranes various technological sectors have focused on the application of membranes [37,38]. in this regard, membranes have been effectively applied for the removal of environmental contaminants from water [39]. most importantly, polymer-based nanocomposite membranes have been designed with numerous potential benefits for water separation [40]. accordingly, the pollutants from ground, domestic, sea, and industrial water have been removed using the advanced membranes [41]. the membrane filtration efficiency definitely relies on the permeability and selectivity features [42]. moreover, nanocomposite membranes have been explored for improved characterization and application of nanomaterials 2024, 7(2), 4945. 3 physicochemical properties [43,44]. important membrane features studied in this regard include porosity, hydrophilicity, selectivity, fouling, mechanical, and heat stability [45]. a range of different filtration nanocomposite membranes have been prepared, such as microfiltration, nanofiltration, ultrafiltration, reverse osmosis, mixed matrix, and so on [46,47]. the membrane properties also depend on the nanofiller type, quantity, and dispersion features of the polymeric systems [48]. for nanocomposite membrane formation, various nanocarbon nanoparticles have been used, including graphene, carbon nanotubes, nanodiamonds, etc. [49,50]. similarly, wide-ranging polymers have been adopted to form efficient membranes [51]. for example, reports on polysulfoneand graphene-based nanocomposite membranes have been observed [52,53]. the polysulfone/graphene nanocomposite membranes were fabricated using the phase inversion technique [54]. these membranes have been investigated for crystallinity, morphology, and matrix-nanofiller interactions, enhancing their physical properties and water remediation performance [55]. similarly, countless polymer/nanocarbon nanomaterials have been reported for membrane applications. 4. fullerene in nanocomposite membranes for water remediation fullerene-filled nanocomposite membranes have been prepared and examined for membrane properties like desalination, toxic ion removal, metal ion removal or recovery, and microorganism separation from water [56]. various toxic metals like lead, mercury, arsenic, etc. have been removed using the efficient fullerene-filled membranes [57–59]. the separation performance of these membranes relies on the porosity and surface defects of these membranes [60,61]. perera and colleagues [62] reported on fullerene-based reverse osmosis membranes. the membranes revealed a high water flux of 26.1 l/m2h and salt rejection properties. the nanocomposite membranes were effectively used to separate the lithium ions from seawater [63]. polyamide is a commodity thermoplastic polymer with amide bonds in the main chain [64,65]. polyamide has been effectively adopted for membrane application [66,67]. plisko and co-researchers [68] designed the polyamide and hydroxy functional fullerene-derived nanocomposite membranes for water remediation. adding 5 wt.% nanofiller aided the antifouling properties. in addition, the removal of organic matter has been observed for the nanocomposite membranes. dmitrenko et al. [69] used polyamide polyphenylene isophthalamide and filled it with fullerene nanoparticles along with other carbon fillers. the mixed matrix pervaporation membranes have been fabricated through the solid-phase synthesis method. figure 2 displays a simple route for the formation of polyphenylene isophthalamide/c60 pervaporation membranes. the inclusion of nanofiller increased the transport properties of the nanocomposite membranes. the membranes were tested for the transport properties of an azeotropic methanol-toluene mixture. adding fullerene nanoparticles has considerably improved the permeation flux of the membranes [70]. here, permeation flux was observed in the range of 0.084–0.214 kg/(m2h) with 5 wt.% fullerene contents. in addition, a selectivity of 96 wt.% was observed. the porosity, permeability, and selectivity of the pervaporation membranes were dependent on the fullerene contents and interactions with the polymers [71,72]. characterization and application of nanomaterials 2024, 7(2), 4945. 4 figure 2. graphical representation of development of novel polyphenylene isophthalamide pervaporation (pv) membranes modified with various types of c60 derivatives [72]. reproduced with permission from mdpi. liu et al. [73] reported on epoxy-derived nanocomposite membranes filled with fullerene c60 and graphene oxide. the resulting membranes have been studied for their ion permeation and desalination properties. figure 3 shows a transmission electron microscopy micrograph of fullerene and graphene oxide-based nanomaterials. the interlayer spacing between the fullerene-grafted graphene nanosheets was found to be around 100 nm due to the insertion of 0.7–1 nm fullerene nanoparticles. due to interlayer spacing, a low permeation rate was observed. figure 4 expresses the fabrication and water desalination setup for the formation of water permeation membranes of epoxy and fullerene-grafted graphene nanoparticles. including fullerene molecules led to a high water flux of up to 10.85 l/m2hbar. better desalination and water permeation have been observed. figure 5 displays the variations in ion concentrations on permeation vs. time for the fullerene-based membranes. the stability features of the nanocomposite membranes were found to affect the desalination performance [74]. table 1 exhibits examples of some fullerenefilled nanocomposites-based filtration membranes. table 1. specifications of few polymeric membranes with fullerene nanofiller for water purification. nanoparticles fullerene nanoparticle size (nm) membrane pore size filtration (l/m2h.bar)/lmh.bar ref c60 14–59 34 to 55 nm [68] functional c60 ~1 0.86 to 0.59 nm 26.1 lmh [62] polyhydroxylated c60 0.64 nm 6.7 lmh.bar [63] c60 0.14 [75] c60 large pore size [76] c60 17 nm [77] c60 9–15 5 wt.% nanoparticles small pores 0.084–0.214 kg/(m2h) [69] c60 0.375 [78] characterization and application of nanomaterials 2024, 7(2), 4945. 5 figure 3. (a) transmission electron microscopy (tem) image of pure go layer (very thin layer with a little folding edge represents go layer, at scale bar of 100 nm); (b) schematic illustration of grafting c60 on go layer through lithiation reaction; and (c) tem image of c60 grafted go layer (smooth layer with irregular shape represents go layer and dark dots represent c60 nanoparticles, at scale bar 20 nm). the go layer is around 150 nm, whereas the c60 nanoparticles are 1–2 nm) [73]. go = graphene oxide; c60 = fullerene. reproduced with permission from acs. figure 4. fabrication process and water desalination setup using c60 grafted graphene oxide membranes. the photograph shows: (a) graphene oxide membrane without c60; (b) c60 grafted graphene oxide membrane; (c) optical micrograph of cross-sectional area with scale bar 100 µm. the micrograph shows 148 µm thick graphene oxide laminates embedded in 81 µm thick epoxy; (d) graphene oxide-c60 membrane encapsulated with epoxy in plastic disk of 47 mm; (e) graphene oxide-c60 membrane inside water desalination setup; (f) and (g) are schematic setup of flat membrane made of graphene oxide and c60 hybrid for water desalination [73]. go = graphene oxide; c60 = fullerene; reproduced with permission from acs. characterization and application of nanomaterials 2024, 7(2), 4945. 6 figure 5. ion concentration on the permeation side through go/c60 membrane over time period (the red, blue, and green lines indicate the feed ratios of go:c60 = 1:2, 1:1, and 2:1, respectively) [73]. go = graphene oxide; c60 = fullerene. reproduced with permission from acs. polysulfone is a marketable thermoplastic polymer commonly used [79]. polysulfone has several advantageous features, like chemical, mechanical, and thermal robustness. polysulfone has been used to form membranes, coatings, and other practical nanostructures for methodological fields [80]. penkova and colleagues [81] reported on polysulfone and fullerene-derived mixed-matrix membranes. adding 5 wt.% fullerene c60 enhanced the membrane transport features, especially pervaporation of the ethyl acetate-water mixture [82]. including fullerene nanofiller also elevated the membrane surface area and hydrophilicity. the solution-diffusion processes were used to promote pervaporation through the membrane [83]. consequently, mass transfer and permeability were found to increase through the membranes. nafion is another important matrix for membrane formation [84,85]. nafionbased commercial membranes have been widely adopted for environmental, energy, and energy/electronics applications [86,87]. here, fullerene-filled nafion membranes have been produced [88]. the antimicrobial properties of the nanocomposite membranes were considered. tasaki and colleagues [89] formed the nafion/fullerene nanocomposite membrane using the solution casting method. the solvent technique was efficient in forming compatible fullerene-filled membranes [15]. the membranes were studied using molecular dynamic simulations, and fine fullerene nanoparticle dispersion was deliberated. layon et. al. [90] developed fullerene nanocomposites using poly(vinyl pyrrolidone) as well as different solvent media. the resulting membranes were used for wastewater remediation. figure 6 shows that the sonication technique better dispersed the fullerene nanoparticles in the medium relative to aqueous dispersion and in tetrahydrofuran. fullerene nanoparticles had a size of 30– 100 nm. in poly(vinyl pyrrolidone), aggregated fullerene nanoparticles have been observed [91]. the effects of minimal inhibitory concentrations on aggregate surface area can be seen in figure 7. there was no linear relationship between the minimal characterization and application of nanomaterials 2024, 7(2), 4945. 7 inhibitory concentrations and aggregate surface area. however, enhanced surface area increased membrane performance due to better interactions. figure 6. transmission electron microscopy micrographs of (a) aq/nc60; (b) son/nc60; (c) thf/nc60; and (d) pvp/nc60 [90]. reproduced with permission from acs. figure 7. relationship between minimal inhibitory concentrations (mic) and aggregate surface area. there is no linear relationship between the mean mic and the surface area to volume ratio calculated, indicating that the difference in surface area alone does not account for the difference in mic between the small and large aggregates [90]. reproduced with permission from acs. 5. prospects and conclusions fullerene nanostructures have brought about revolutions in a range of methodological industries, including organic photovoltaics, energy, biomedical characterization and application of nanomaterials 2024, 7(2), 4945. 8 purposes, biopharmaceuticals, etc. [92–94]. fullerene nanocomposite membranes have been widely used in filtration systems. other water decontamination strategies have also been considered, such as sedimentation, distillation, biological processes, flocculation, chlorination, ultraviolet light, etc. [95]. various combinations and types of polymer/fullerene membranes have been developed (figure 8). in fullerene-based membranes, remarkable morphology, mechanical, and barrier features have significantly contributed towards water remediation [96]. fullerene molecules have contributed to the matrix-nanofiller interactions, enhancing the compatibility of these nanostructures. the main challenging aspect has been recognized as nanoparticle dispersion in polymeric membranes [97]. figure 8. design of fullerene-based membranes. better fullerene dispersion throughout the membrane ultimately defines the controlled pore size or structure, morphology, surface roughness, and wettability of efficient membranes. in this regard, separation mechanisms need to be explored to further improve the fullerene membrane-based filtration processes. theoretical studies on fullerene nanocomposite membranes may also help to resolve the performance challenges. in the future, variations in membrane designs may also bring about revolutions in this field. this cutting-edge review presents an analysis of applying fullerene nanocomposite membranes for water purification purposes. polymer-based nanocomposite membranes with fullerene nanoparticles have been found to transform waste water remediation. efforts on fullerene nanocomposite membranes have led to improved surface properties, permeability, selectivity, separation, antifouling, and other features. these membranes have a low price and lasting stability for large-scale filtration. further research may lead to a number of enhanced membrane parameters to overcome these drawbacks. conflict of interest: the author declares no conflict of interest. references 1. kausar a, ahmad i. graphene and nanocomposites—imprints on environmentally sustainable production and applications based on ecological aspects. characterization and application of nanomaterials. 2024; 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tungsten carbide; b-c-w system; composite; nanodispersed state 1. introduction boron and tungsten carbides, b4c and wc, are well-known hard materials widely used in modern technologies. improvement of their performance characteristics involves the development of new composites with b4c and wc matrices in a nanodispersed state. good examples of this kind are the boron carbide-titanium diboride b4c-tib2 quasieutetic and tungsten carbide-cobalt wc-co ceramic alloys. in nanodispersed form, some additional attractive physical-mechanical properties are exhibited (for example, see the research of chkhartishvili et al. [1,2] and shabalin [3]) by more complex composites containing both boron and tungsten carbides, which serve as matrix and modifying components, respectively, or vice versa. this makes the development of newer boron and tungsten carbide-based and/or related composites very promising (for example, see the recent reviews of manzar et al. [4] and singh et al. [5] on various techniques for the development of hard boron carbon nitride nanoscale coatings on metal surfaces). the present article aims to give only a short review of available in the literature research on b-c-w systems not illustrated with self-drawn or reproduced figures and tables and not provide criticism towards the described results. authors are not claiming to provide exhaustive information about the huge number of publications in this field. nevertheless, we believe that the data presented here are representative and thus will be useful in future studies on boron and tungsten carbide-based composite materials. 2. b-w systems using the tungsten coatings saturated with boron of compositions w-(13wt.%23wt.%)b to substrates from austenitic steel was found [6] to be suitable. obtained structures revealed much more resistance to corrosion and wear losses in material mass than uncoated steel. the beta-wb and w2b (tungsten boride high-temperature phases) coatings of titanium ti and steel surfaces containing tungsten can be formed [7] citation tsagareishvili o, chkhartishvili l, matcharashvili m, dekanosidze s. boron and tungsten carbides based and related nanodispersed composites—a review. characterization and application of nanomaterials. 2024; 7(2): 5454. https://doi.org/10.24294/can.v7i2.5454 article info received: 26 march 2024 accepted: 4 june 2024 available online: 18 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 5454. 2 applying the shaped charge explosion technique. microhardness of coated material achieved 42 gpa. the hardness and stability of the highest tungsten borides, when they are built of tungsten atoms separated by borophene layers, were studied in the study of gonzalez szwacki [8]. shift of so-called dbtt (ductile-to-brittle transition temperature) in tungsten foil was found by studying the neutron irradiation effect. processing techniques, possible applications, as well as some physical characteristics of multilayered materials (ceramic-c and ceramic-metal structures) with an operating temperature higher than 1200 ℃ were considered in the study of sorokin et al. [9]. this problem is of interest because of the applicability of boron compound-tungsten compound composites as effective neutron-shield materials. aiming to increase the physical-mechanical properties of tungsten tetraboride wb4 (which is a lower-cost transition-metal boride), its solid solutions with metals, namely, chromium cr, manganese mn, and tantalum ta, were synthesized and characterized [10]. and the concentrations of these transition metals up to 50.0at.% were tested. the listed solutions, which are the refractory compounds, were obtained from component elements by arc melting method. samples chemical composition was examined using x-ray eds (energy-dispersive spectroscopy). the xrd (x-ray diffraction) results indicated that the solubility limits of cr, mn, and ta in wb4 are <10at.%, <20at.% and >20at.%, respectively. vickers hardness optimized values measured by microindentation were of 53.5, 53.7, and 52.8 gpa when wb4 was added with 10at.%, 4at.% and 2at.% of cr, mn, and ta, respectively. it was also produced the tungsten tetraboride-based ternary solid solution with a ta concentration fixed at 2at.%, while varying mn and cr concentrations. the values of hardness measured for w0.93ta0.02cr0.05b4 and w0.94ta0.02mn0.04b4 compositions equal to 57.3 and 55.8 gpa, respectively. according to the high-pressure (<65 gpa) in situ xrd measurements, for the hardest wb4-based solid solution, w0.93ta0.02cr0.05b4, the bulk modulus is 335 gpa, and a phase transition induced by pressure, which is observable in pure tungsten tetraboride, was suppressed. obtaining of powder tungsten tetraboride by reactive hpv (hot pressing in vacuum) method from powders of its component chemical elements (amorphous boron a-b and tungsten w) was systematically investigated [11] in dependence on temperature of synthesis, molar ratio between boron and tungsten in charge, applied pressure, and duration of phase formation. metastable wb4 was obtained at a molar ratio of b:w = 8:1 and a temperature of 1350 ℃ under uniaxial pressure of 30 mpa for 1 h. both sem (scanning electron microscopy) and tem (transmission electron microscopy) studies revealed that particles of the obtained powder tend to agglomerate. besides, a-b trace was detected in the product. at the same time, xrd pattern analysis of the as-synthesized powders conforms formation of the wb4 crystalline phase. 3. c-w systems in general, hard alloys are the wear-resistant metal materials that can retain their advanced properties at 900–1200 ℃ and are mainly made from carbides of tungsten, titanium, tantalum, or/and chromium and bonded with metal binders with varying characterization and application of nanomaterials 2024, 7(2), 5454. 3 cobalt or nickel content. hard alloys produced by industry can be divided into four groups according to the metal carbides present in them: tungsten, titanium-tungsten, titanium-tantalum-tungsten, and tungsten-free alloys [12]. one can see that the tungsten carbide presence is critical.  the first group consists of alloys of the tungsten carbide-cobalt (wc-co) system. they can be marked with the letters wco and a number indicating the cobalt content as wt.%; for example, wco10 alloy contains 10wt.% co and the rest (up to 100wt.%) is wc. these alloys are characterized by maximum strength but reduced hardness. they are heat-resistant up to temperatures of 800 ℃. as the content of cobalt increases, impact toughness increases as well, but wear resistance decreases. alloys of the wco-group are used for processing workpieces made of brittle metals such as cast iron, bronze, and other non-ferrous metals and alloys, as well as some non-metallic materials.  the second group is formed by alloys of the tungsten carbide-titanium carbidecobalt (wc-tic-co) system. they can be marked with the letters ti and co and numbers. the numbers after the letters ti and co mean the wt.% of tic and co, respectively, and the rest (up to 100wt.%) is wc. for example, the ti5co10 alloy contains 5wt.%, 10wt.% and 85wt.% of tic, co, and wc, respectively. alloys in this group are more wear-resistant but less durable. as the tic content increases, wear resistance increases, but strength decreases. the heat resistance of tico-group alloys is higher, about 900–1000 ℃. the heat resistance performance increases as the amount of tic increases. tools made from alloys of this group provide higher cutting speeds. they are most often used for processing carbon and alloy steels.  the third group is formed by alloys of the tungsten carbide-titanium carbidetantalum carbide-cobalt (wc-tic-tac-co) system. these alloys are usually marked with the letters tita and co. the numbers after the letters tita and co indicate the wt.% of titanium and tantalum carbides together, tic-tac and co, and the rest (up to 100wt.%) is tungsten carbide wc. for example, the tita5co15 alloy contains 5wt.%, 15wt.%, and 80wt.% tic-tac, co, and wc, respectively. these alloys differ in greater strength and better resistance to vibration and chipping. alloys of this group are used under the most severe cutting conditions—roughing of steel ingots, castings, and forgings.  to rationally use scarce tungsten, a fourth group of tungsten-free hard alloys was developed. they contain titanium carbides (tic) and titanium carbonitrides (ticn) bonded with a nickel-molybdenum (nimo) metallic alloy. their manufacturing technologies are quite similar to the above-listed hard alloys containing tungsten; however, they have lower bending and impact strengths and, because of lower thermal conductivity, are more sensitive to changes in temperature. their advantages are: higher (up to 1000 ℃) heat resistance and lower adhesion during cutting and, consequently, not prone to buildup to materials being processed. this is why tools made from tungsten-free hard alloys are recommended for finishing turning and milling processes. thus, according to the chemical composition, hard alloys are divided into tungsten-cobalt (wco), titanium-tungsten-cobalt (tico), and titanium-tantalumtungsten-cobalt (titaco) alloys. as for the production method, such classification of characterization and application of nanomaterials 2024, 7(2), 5454. 4 hard alloys divides them into two groups: sintered and casted alloys. products from sintered hard alloys are manufactured by powder metallurgy, and they can be processed by physical or chemical methods (dispersing and grinding, treatment with us (ultrasound) and laser, etching in acids, etc.) and, most perfectly, by electrical erosion. casted hard alloys intended for surfacing tools can be subjected to mechanical and thermal treatments (annealing, hardening, aging, etc.). finally, the iso (international organization for standardization) standards classify the hard alloys according to their intended purpose:  p: steel castings and materials, processing of which forms the drain chips;  m: processing difficult-to-cut materials (for example, stainless steel);  k: processing cast iron fe;  n: processing aluminum al, other non-ferrous metals and metallic alloys;  s: processing heat-resistant alloys and titanium-based alloys; and  h: hardened steel. in hard alloys, as a result of combining their matrix and reinforcing modifiers, a complex of properties of the composition is formed, which not only reflects the initial characteristics of components but also includes properties that the isolated components do not possess. in particular, the presence of interfaces between reinforcing components and matrix significantly increases the crack resistance of the material, and in hard composites, unlike homogeneous metals, an increase in static strength does not lead to a decrease but, as a rule, to an increase in fracture toughness characteristics. hard alloy tools have high hardness and heat resistance, typically of 80–90 hra and 800–1000 ℃, because of refractory metal carbide components. products made from them can be processed at several times higher speeds in comparison with the characteristic speeds of cutting high-carbon steels. the main disadvantages of hard alloys are fragility and difficulty in machining their products. they have reduced bending strength, 1000–1500 mpa, and very low impact toughness. due to their high hardness, hard alloys are low-tech. for example, it is impossible to shape tools from them. in addition, hard alloys can be ground to a limited extent—only with a diamond tool. in this regard, frequently there are used their plates, either soldered or fixed to the tool holders. as entropy is a key characteristic of thermodynamic systems, its calculation allows studying the equilibrium state, in particular, component contact interaction, when the composite is formed. a study by syrovatko [13] introduced such calculations for tungsten carbide phases wc-w2c eutectic by statistically processing the digitalized photos of scanned component phases. entropies of wc and w2c phases were found to be 29.22 and 58.38 j/mol∙k, respectively, which are in satisfactory agreement with reference data [14]: 32.21 and 56.28 j/mol∙k, respectively. ultrafast compacting possibility for tungsten carbide wc without adding any binder phase was explored [15] for a technology combining sintering processes assisted with uniaxial pressure and limited ac (alternating current). in modern production, wc-co hard alloy parts are mainly made either by casting or powder metallurgy methods. therefore, details with complex geometry often require further mechanical processing, which is associated with difficulties due to the high hardness of the material. so-called additive manufacturing technology was proposed [16] for producing details of small dimensions and complex configurations. characterization and application of nanomaterials 2024, 7(2), 5454. 5 it includes slm (selective laser melting), sebm (selective electron beam melting), inkjet additive production of binder, gel 3d printing, and melting stages. product properties depend on wc particle size and co amount in the composite. due to the uneven distribution of energy, the microstructures of samples obtained by slmand sebm-methods are not uniform. for this reason, their properties are unstable. in addition, in the samples obtained by slm, due to the high energy density, co and c are burned. these losses lead to cracked and brittle samples, and if the energy density is reduced, the cobalt cannot melt completely and the samples turn out to be porous. using the method of obtaining nanocrystalline tungsten carbide with co component developed in gachechiladze et al.’s study [17], the ultradispersed wc-co alloys were synthesized from the precursor in the form of a suspension of ethyl alcohol solution of tungsten chloride wcl6·6h2o and a mixture of aqueous solution of cobalt chloride cocl2·6h2o and an alcohol solution of urotropin c6h12n4. it is known that in the process of synthesizing tungsten carbide, the presence of some intermediate complex carbides, mainly w3co3c and w6co6c, in the final product is expected, which cause degradation of the material's physical-mechanical properties. however, optimizing the technological parameters made it possible to obtain the final product without these intermediate carbides. a systematic analysis of wc-co alloys was carried out [18] on samples obtained under identical conditions. namely, the influences of wc matrix particle size, co binder content, and temperature on their complex mechanical properties were studied. by determining the mechanical characteristics during bending tests, the three temperature intervals with different mechanisms of plastic deformation, temperatures of ductile-brittle transition, and strain hardening coefficients, as well as their indicators, were established. impact toughness increases and hardness decreases with increasing both co content and average wc grain size, with some exceptions, where impact toughness and, consequently, cracking resistance can be increased at hardness expense and, thus, wear resistance. the maximum strength limit is reached when the average wc grain size varies in the range of 1.4–5.3 μm, and the co amount in the alloy is 6 wt.%. the maximum compressive strength is achieved when the average wc grain size changes in the range of 1.4–1.7 µm. as for the bending strength limit, it practically does not change with further reduction of the average grain size. tungsten carbide compound produced by powder metallurgy methods, which is widely used to develop the tool materials necessary for high-speed processing, consists of carbide particles—usually tungsten carbide wc itself and a relatively soft metal binder. currently, hundreds of wc-based alloys are known, most of which use cobalt co, nickel ni, and chromium cr as binders, as well as other binders with various metallic and non-metallic additives. at room temperature, tungsten carbide wc is characterized by high hardness, which is largely maintained at higher temperatures. but it lacks sufficient high-temperature strength, the cutting tool's key property. to maintain the high hardness of tungsten carbide while increasing its toughness, the special metal binders should be used. the composite obtained in this way must have a much higher hardness than high-speed steel and a higher rate of service life as well. an increase in the amount of metal binder in the wc-co alloy leads to a decrease in its hardness. the hardness of this material also depends on the size of the tungsten carbide particles; the hardness of the alloy decreases with the increase in the carbide characterization and application of nanomaterials 2024, 7(2), 5454. 6 grain size [19]. the work of pereira et al. [20] presents the wc-based composites with various binder metal systems: wc-co, wc-coni, wc-ni, wc-cocr, wc-conicr, wcnicr, and wc-nicrmo. wear in such samples was studied, and it has been determined that chromium-containing metal binders are characterized by higher wear resistance compared to other investigated composites. the operational properties of hard alloys are improved not only by the influence of carbide additives but also by optimizing the composition of the cementing metal components. in this sense, the partial or complete replacement of cobalt in the wcco alloy still seems like a relevant task. complex metal alloys have been proposed not only to replace cobalt but also to improve the high-temperature characteristics of the alloy. it is worth noting the creation of a cementitious multi-component metal alloy fenicocr [21], in which the chromium content exceeds 8 wt.%. the characteristics of the wc-fenicocr composite depend on the grain size of the matrix material, i.e., wc. in it, compared to wc-co of the corresponding composition, the hardness value is essentially preserved and the toughness is reduced by 25%. the wc-tic-co system alloys of various compositions are widely used in practice. such compositions are characterized by high hardness, chemical stability at high temperatures, and wear resistance. it has been established that obtaining wctic-co systems in an ultradispersed state and maintaining such a state after compaction significantly improves the physical-mechanical and operational characteristics of the material. wc-tic-co systems can be obtained in a nanocrystalline state by sputtering liquid charge and chemical and mechanical methods. if the composition of the alloy is fixed, then the important factors that lead to the improvement of the material's mechanical characteristics are the size of the particles, the degree of homogeneity of the structure, and the purity of the initial powder. thus, it is recommended that the sizes of the carbides, wc and tic, which make up the wc-tic-co system, should be as small as possible—ultradispersed and their mixture—homogeneous. the sputtering method can be considered promising for obtaining high-purity nanopowders for industrial purposes. however, its application is hindered by the problem related to the titanium dioxide tio2 reduction in the wctic-co nanostructured system preparation process. a mechanical-chemical method was successfully used to obtain an ultra-dispersed wc-tic-co composite. in particular, its powder with 200 nm particle size was obtained [22] in this way. the effect of tic on wc-co was studied [23], when it replaced wc by 5 wt.%– 20 wt.%. this composite was consolidated by isostatic htp (high-temperature pressing) at a temperature of 1350 ℃ and a pressure of 50–150 mpa. when replacing with 5wt.% and 20wt.% tic, the required pressures were 50 and 150 mpa, respectively. it led hardness to increase from 1050 up to 1330 and 1600 hv. such a high rate should be not only due to the addition of tic but also to the reduction of porosity during high-pressure compaction. young’s modulus, on the contrary, decreases with the addition of tic. when the young’s modulus of wc-co was equal to 570 mpa, it became 420–490 mpa with the addition of tic. the impact toughness and composite density also decrease slightly with the addition of tic. by discussing [24] the heat treatment processes in two-carbide, wc, and tic alloys and the laser impulse effect on their structure, as well as operational mode characterization and application of nanomaterials 2024, 7(2), 5454. 7 parameters, it has been established that the microcracks in the surface layers of ti15co6 alloy increase by 150–200 units due to laser-pulse impact. such strengthening is associated with structural and phase transformations caused by electrical-physical effects: a new phase w2c is formed in the surface layers, and the binding cobalt phase is saturated with tungsten and titanium carbides. in addition, laser heat treatment increases the operational characteristics of тi15co6 alloy by 2–3 times. physical-mechanical properties and structure of tungsten-cobalt wc-co hardmetals, which contained different amounts of cobalt and alloyed tantalum and vanadium carbides (tac and vc), were investigated in the work of falkovsky et al. [25]. it was shown that the addition of 0.5 wt.%–2 wt.% tac increases the hardness, while the bending strength remains practically unchanged. then the content of tac was kept at the constant level of 5 wt.%, while the vc amount changed from 0.4 wt.% to 10 wt.%. if the vc amount was less than its solubility in co, the materials showed structure with basic carbide phase (wc) ultrafine grains: 0.2–0.5 µm. at 6 wt.% and 10 wt.% of co, typical physical-mechanical parameters of these hardmetals were: hardness of 93.5 and 93.0 kgf/mm2, bending strength of 1670 and 1870 mpa, cracking coefficient of 11 and 16 mpa·m1/2 and coercive force of 417 and 383 oe, respectively. a process was developed [26] to produce wc in nanopowder form applying a plasmachemical reduction method. the carbide grain size value was adjustable from 0.01 to 0.05 µm. two more routes were suggested as alternatives to obtain wc-co ultrafinegrade powder mixtures. depending on the sintering mode variable parameters, the size of carbide phase grains was kept in ranges of 0.1–0.2 or 0.3–0.4 µm. the hardness of these hardmetals proved sharply increased, while their strength rose by 25%–30%. it has been shown in the research of ruziev et al. [27] that the addition of 1wt.%– 12wt.% vanadium carbide vc in the wc-6wt.%co alloy slightly, no more than by 3%, increases the hardness of the material, but significantly, by 33%–50%, improves its wear resistance, compared to unmodified wc-6wt.%co. also, properties and characteristics of wc-6wt.%co hard alloy separately modified with vc and rhenium carbide rec were discussed. in particular, with the addition of rec to 5 wt.%, the wear efficiency of wc-6 wt.%co increases to 66.3%, while the working resource of the tool made from it increases to 35.0%. the wc-13 wt.%co composite with added iron fe can be obtained [28] by pressureless sintering. material structure, porosity, and size of grains, as well as mechanical properties, were studied using sem, xrd, x-ray eds, and vickers hardness tests. the fe atoms position, when they are added in component phases, was determined: in eutectic, at 2 wt.%–4 wt.%, it exists both in low-carbon etaand binder phases. in the eta-phase lattice, fe atoms occupy the co sites, being uniformly distributed in the binder simple cubic lattice. tungsten boride growth in melted iron was found to be strongly limited. in w-c-co-fe systems, wc grain size increases up to 1.14–1.21 µm, when iron content increases to 4 wt.%. thus, the wc growth process in melted cofe metallic alloy should differ from that in melted iron and be closer to that in melted cobalt. when both 2 wt.% fe and 1 wt.% c are added, the sample possesses the optimal combination of hardness/toughness: hardness is increased up to 1070 hv (from 980 hv for the sample without fe and c additives) at a slight increase in toughness. interface models of dccc (diamond-coated cemented carbide) wc-co, with characterization and application of nanomaterials 2024, 7(2), 5454. 8 interface terminals tic, tin, crn, and sic but without intermediate layers, were suggested in yang et al.’s study [29]. according to the conducted calculations, adding four corresponding intermediate layers increases the work of interface adhesion. interface adhesion improvement of this dccc could be ranked as: sic > crn > tic > tin. adding the intermediate layer changes the interface junction charge distribution and forms a more stable chemical bond as a result of interface junction electron cloud overlapping. in the energy overlapping area, an additional intermediate layer increases the interface atoms dos (density-of-states). and the dccc interface bonding enhances as well. the most obvious should be diamond/sicc-si/wc-co interface interatomic electron cloud overlapping. corresponding bond length was found to be the shortest: 1.62 å, while the energy resonance peak-forming region was the largest, from −5 to +20 ev, and bonding was the strongest. at the diamond/tinti/wc-co interface, on the contrary, these characteristics were the longest: 4.11 å, the smallest from −5 to +16 ev, and the weakest, respectively. among the considered intermediate layers, the best and the worst for improving the dccc interface bonding were sic and tin, respectively. 4. b-c-w systems wc tool cutting edges treated by ld (laser doping) of boron nitride bn revealed extra-long cutting distance. in view of this, wc-co, the base material of the tool, was processed [30] similarly to the study, resulting in changes in crystal structure. x-ray and electron backscatter diffractions allow to observe the effect in the near-surface 50 nm thick ld: increased by ~11.7% strength at maintained wc structure. some physical-mechanical and tribological properties of wc-tib2 composites, as well as their microstructure, at sliding (against stainless steel-201) conditions were studied in zhang et al.’s study [31]. mechanical properties and relative density improved, while concentration of microstructural defects decreased when the tib2 component increased from 10 wt.% to 30 wt.%. as for the friction coefficient, it decreased both with increasing applied load and sliding speed. as the fracture effect is important for composite coatings contact surfaces, it led to the formation of abrasive and adhesive wear mechanisms. for wc-tib2 compositions, the rate of specific wear increased with increasing sliding velocity and normal load. in particular, the sample of intermediate composition wc-30wt.%tib2 possessed better tribological properties than wc-10 wt.%tib2 and wc-20 wt.%tib2 ones. tool materials from tib2-wc compositions can be produced [32] using the hpv technique with sintering additives such as co and ni metals and nimo metallic alloys as well. sem-, xrd-, and eds analyses showed that tib2-wc ceramic composites microstructure consisted of tib2 uniform and wc fine grains. in composition tib2wc-ni, there are observed few pores and ni3b4 brittle phase inclusions. as for the composition tib2-wc-co, it contains a lot of pores and co2b and w2cob2 brittle phases. coarse-grained tib2 phase and pores are formed as a result of the reaction consuming the liquid cobalt. coarse-grained components, brittle phase inclusions, and pores in significant volume fractions were harmful to the tib2-wc compositions mechanical properties and density. using nimo alloy as a sintering additive had significantly improved these characteristics. the accompanying process of moni4 characterization and application of nanomaterials 2024, 7(2), 5454. 9 intermetallic compound formation not only inhibited nimo liquid phase consumption and related coarse grains and pores growth but also strengthened the wc/tib2 interface interaction between grains of different components. as grains were fine, the relative density of tib2-wc-nimo composite in average was up to 99.1%. material vickers hardness, flexural strength, and fracture toughness were of 22.7 gpa, 1307 mpa, and 8.2 mpa∙m1/2, respectively. boron carbide and its different nanocomposites manufacturing parameters were studied [33] for an effective two-stage technology. at the first stage, the combustion method is used to obtain boron carbide in nanopowder form, and then, at the second stage, metalceramic-ceramic nanocomposites on the basis of boron carbide are produced in the process of joint melting, milling, and sintering. at well-adjusted composition b4c-25wt.%tib2-10wt.%(wc-10wt.%co), the boron carbide-titanium diboride-tungsten carbide-cobalt nanocomposites powder morphology shows the reduction of b4c particles in size from 500–5000 to 200–600 nm. the synthesized composite powder xrd pattern proves the presence of all the target phases: b4c, tib2, wc, and co. wc peaks are of relatively low intensity, which can be explained by some transformations taking place in the wo3 reagent phase. the obtained product may contain graphite with ultrafine grains, a mixture of various tungsten borides with “amorphous” structure, and trace phases as well. the different b:c:ti:co ratios according to the charge composition and experimentally obtained from the eds spectra showed the combination of carbon reduction and cobalt evaporation yielding the ultrafine-grained tungsten borides formation. such a mixture behaves as an amorphous-like inclusion. from xrdand eds-analyses, it can be concluded that the synthesized fine-grained powders contain both ceramic b4c-tib2 and ceramic wc-co components of the target composite; however, there are also some amorphous-like trace phases that are not visible on the xrd patterns. to find the sources, it is suitable to analyze chemical reactions taking place in the system at elevated, >1500 ℃, temperatures. to examine the corresponding reaction, a test process was conducted with a powder mixture of b4c-tib2-(wc-co) at 1800 ℃. the presence of crystalline b4c, tib2, w2b5 and graphite traces is clearly visible on the product xrd pattern. therefore, the sintering temperature of powders synthesized in this way should not exceed 1600 ℃, as tungsten boride w2b5 is expected to form at higher temperatures. a wet chemical method can be used [34] to prepare preceramic precursors for low-temperature synthesis of ultrafine powders of tungsten boride composite with boron carbide matrix ceramics. that technique includes the thermal treatment of ammonium paratungstate-zirconium oxide-cobalt acetate tetrahydrate-sucroseamorphous boron mixture viscous paste in air at 200 ℃ and then in argon at 600 ℃ for 2 h, grinding of the intermediate powder product, and its additional thermal treatment at 800–1500 ℃. these complex ceramic powders were pressed at 1000– 1700 ℃ by using the sps (spark-plasma sintering). phases wo3–x, co3o4, coo, and amorphous carbon were formed at 600 ℃. xrd-analysis data confirmed the relatively low-temperature (800–1000 ℃) formation of wc-co, b4c, and metal boride (zrb2 and w2b5) phases. finally, wc was completely converted into w2b5. for boron carbide-based composites production, the ultradispersed powders of preceramic precursors were obtained [35] by their relatively low-temperature (200– characterization and application of nanomaterials 2024, 7(2), 5454. 10 1000 ℃) synthesis from liquid charge consisting of commercially available compounds (oxides and salts). these ceramics with boron carbide matrix were consolidated by their sps at 1500–1700 ℃. the xrd peaks of monoclinic zirconia zro2 and wc phases visible in the preceramic precursors disappeared when the sps process was conducted at 1500 ℃. it was demonstrated that additive compounds of tungsten and cobalt promoted not only ceramic components low-temperature synthesis in powder form but also their sintering processes. according to the eds analysis, the ceramic products contain a small amount of co (0.8 wt%–2 wt%). the cobaltcontaining ceramic b4c-zrb2-w2b5-co density exceeds that of co-free ceramics (such as b4c-zrb2-w2b5). 5. b4c-w systems compositions b4c-w with 5 vol.%, 10 vol.%, 15 vol.%, and 20 vol.% w were synthesized [36] by sps in vacuum at uniaxial pressure of 40 mpa and temperature of 1500–1600 ℃ for 4 min (at a heating rate of 100 ℃/min). for initial materials served the commercial powders of b4c and w with particle sizes of 0.7 and 60 μm and purity of 99.5% and 99.8%, respectively. the initial mixture of these powders was prepared by milling for 24 h in ethanol with wc balls. tungsten pentaboride w2b5 formed as the result of a reaction between particles of the b4c and w component phases. when the tungsten amount increased, part of the carbon remained unbounded, forming the graphite phase inclusions. on the one hand, the free carbon presented in these composite materials deteriorated their physical-mechanical properties. but, on the other hand, metallic tungsten addition improved some technological properties of initial powder mixtures, in particular, their sinterability. besides, it densifies the matrix like boron carbide samples with almost theoretical densities. studies of neutronand gamma-radiation attenuation by carbide-tungsten composites lead to the conclusion that increasing the tungsten concentration in the b4c-w system yields the higher gamma-attenuation property of this composite, whereas it provides a lower neutron shielding capacity than that of pure b4c. for b4c-based ceramics, pressureless sintering of powders can be considered an industry method. however, it possesses a disadvantage as well: the impossibility to sinter to high density without densification additives. parts of sintering additives, tungsten among them, and appropriate methods of sintering are described in the review [37]. from b4c-w-wc system powders, it was obtained [38] wc-wb-w2b composites using reactive hot pressing, which initiated energization by a solid-state reaction between b4c and w components. at 76.9 mol.% wc in the starting powder, phases of wb and wc were formed in the reaction b4c + 5w + xwc = wb + (1 + x)wc. these two plus w2b phases were produced at 85.4 mol.% wc. pure wc in densely sintered state was not obtained. as for wc-wb-w2b compositions obtained at (5.4 mol.%–95.6 mol.% wc), they were fully consolidated, having high mechanical characteristics (young’s modulus, vickers hardness, and fracture toughness) comparable with pure wc. toughness, hardness, and crack density of fine-grained wc-co compositions were investigated in tamizifar et al.’s [39] work. namely, about 30 experimental and characterization and application of nanomaterials 2024, 7(2), 5454. 11 commercial hard metal grades with different additives, such as boron b4c, vanadium vc, chromium cr3c2, and silicon carbides sic, were obtained in an hpv commercial isostatic sintering furnace. microstructural and physical-mechanical properties were investigated to construct a representative hardness/crack density measurement band useful to estimate the most effective temperature for sintering, as well as amounts of additives. comparison of grain growth inhibitors effect in optimal conditions showed that b4cand vc-doped grades for growth inhibitors exhibit the maximal hardness. however, addition of cr3c2 is found to favor the toughness improvement. boron carbide coatings can be synthesized using the method of an rf (radio frequency) plasma source and an external magnetic field [40]. the nanohardness of steel surfaces coated in this way was 14.0–16.6 gpa. such b4c coatings were found to have the hardness 1.73–3.89 times higher than uncoated (bare) steel surfaces served as targets. this technique would be useful for coating tungsten substrates with boron carbide. due to the high cross section of (epi)thermal neutrons captured by boron 10b isotope nuclei, all-boron and boron-rich systems—compounds and composites—are widely used as materials that intensively interact with neutron radiation. in the finedispersive form, they have the improved performance characteristics. preparation methods of some fine-dispersive important boron-containing b4c-w composites useful in neutron shielding were reported in the studies of chkhartishvili et al. [41,42]. using the spin coating technique on the b4c surface, first a wo3 layer was deposited to reduce it to metallic α-w at a temperature of 600–800 ℃ under a hydrogen atmosphere. usually, such α-w layer was weakly attached to the boron carbide. the sandwich composites can be effectively obtained by sps at 1300– 2000 ℃. for this purpose, the method by which previously tungsten-contained multicomponent ceramics with boron carbide matrix were synthesized was modified. the substrates used were compacted by sps at temperatures of 1500–2000 ℃ from ultradispersive boron carbide powders prepared from liquid charge systems like amorphous boron-carbohydrates-water and boron acid-organic compound-water. during heating at temperatures exceeding 1300 ℃, in these sandwich structures, it starts the formation of tungsten pentaboride w2b5, while at >1600 ℃ it converts into a new sandwich composite b4c-w2b5. from two-component sandwiches, applying the sps, one is able to manufacture similar multicomponent structures: b4c-w-b4cw, w-b4c-w-b4c, and the like. monolithic b4c-w samples were obtained from b4c and w powders in sps processes as well. first, the powder of metallic w was compacted and placed in a graphite press mold with a graphitic foil lining. then b4c powder was sprinkled on the w layer. after leveling the surface, again the graphitic foil was placed on it. during the described method, including rapid heating together with applying a certain pressure, powder consolidates and a sandwich composite is obtained. the sem and eds investigations showed the presence of the fracturing on the contact interface between b4c and w consolidated in the sandwich structure. there are the opposite directions of diffusion of b and w atoms, and an intermediate-phase w2b5 forms. the thickness of layers can be adjusted within wide limits. after removing metallic tungsten and tungsten boride layers, the sample sintered at 1600 ℃ revealed the relative density of boron carbide as 87%–92% of the theoretical value. xrd patterns characterization and application of nanomaterials 2024, 7(2), 5454. 12 of the cleaned surface unambiguously confirmed boron carbide presence, as well as metallic tungsten removal from the sandwich surface. to obtain similar composites using tungsten plates instead of their powders, a new method was developed. conclusion was made that heating and pressing of the boron carbide powder-metallic tungsten foil structure leads to the intermediate phase w2b5 formation and provides a strong bonding between these phases. based on theoretical simulations [43–45], b4c-w thin-layered sandwich compositions are considered effective shield materials containing both lowand highz atoms (here z denotes the atomic number), boron and tungsten, serving as effective absorbers for, respectively, (epi)thermal neutrons and secondary gamma-quanta, which accompany the neutrons captured by 10b nuclei. the thin film materials based on w and b and including b4c, wc, and wb3 phases can display too high a hardness. compounds of composition wb3+x were shown to have vickers hardness approaching 40 gpa for relatively small x. thin film materials based on w and b and including b4c, wc, and wb3 display very high hardness. also, borophene doped with w was found to exhibit superior hardness. in martin’s [46] study, w1−yb3+x structures elastic properties were summarized. among them, only the stoichiometric wb3 phase can be considered as superhard material. contamination with extra b-atoms is energetically unfavorable and affects the hardness: it lowers the shear modulus while maintaining the bulk modulus, effectively leading to a softer material. the w-vacancies, e.g., in w0.75b3+x composition, form structures with hardness less sensitive to variations in boron content. interface roughness influences the b4c-w multilayer reflectivity and varies with bilayer number n [47]. in particular, multilayers of b4c-w composition with equal design period thickness (2.5 nm), a real-structure model can be used to calculate the variation of reflectivity with n (n = 50, 100, 150, and 200). dc (direct current) magnetron sputtering system was used to fabricate such multilayers. the xrd measurement of their reflectivity and scattering intensity indicates that the reflectivity is a function of bilayer number, and interface roughness slightly increases from layer to layer during the growth of the multilayer. 6. b4c-wb2 systems from b4c and wb2 as initial raw materials, the densified compositions b4c-wb2 were produced by the hpv method at a temperature of 1950 ℃ [48]. the b4c-68.7 vol.%wb2 composition obtained in this way demonstrated a quite good set of physical-mechanical properties such as superior hardness of 34.8 gpa, high flexural strength of 696 mpa, acceptable fracture toughness of 3.3 mpa∙m1/2 and low density of 5.59 g/cm3. these compositions, in addition, showed good electrical conductivity of 3.3 × 105 s/m, which, together with the above mechanical properties, make them interesting for various applications, e.g., as armor protection and cutting tool materials. based on the explored b4c-tib2 compositions fine microstructure, it was proposed [49] an overall evolution picture of their microstructure, starting from the processing of raw powders to sintering and compacting. it was found that structures with small-scale grain and their local mechanical properties (measured applying the nanoindentation method) are correlated and thus provide a trend in their mechanical characterization and application of nanomaterials 2024, 7(2), 5454. 13 behavior. in particular, dense ceramics can be typified by the core-shell structure development in titanium boride grains, where shells comprise two-component solid solution tib2-wb2 with different assemblage and variable (in dependence on the technological route) content of tungsten atoms, i.e., guest cations. analyses conducted by tem revealed some morphological and chemical differences that can be related to the densification mechanisms. to extract the composite and component phases (core tib2, shell wb2, and matrix b4c) properties, it was used the nanoindentation highlighting modulus and hardness variations as functions of lattice perturbation from nominally pure boride coarse to shell regions. 7. b4c-w2b5 systems to understand the wc and tic additions effect on mixtures of compositions b4c-b-si on the sintering process and final product mechanical properties, a special investigation was undertaken [50]. in the process of milling in attrition, the starting component powders are alloyed with wc, tic, and co phases by the hard metal spheres. in the case of long milling, the rate of material wear decreased strongly. powder products milled for 2 and 4 h, respectively, contained 39 wt.% and 47 wt.% wc-tic. during the heating, the components of the starting powder milled for 2 h (b, b4c, si, co, wc, and tic) reacted to form b4c, tib2, and w2b5. some chemical reactions took place in the temperature range of 800–1500 ℃. the w2b5 boride phase started formation at 1100 °c and its maximum amount is reached at 1600–1800 ℃. the content of w2b5 phase very strongly decreases at higher temperatures. the tib2 phase started its formation at 1050 ℃ and at further heating the system up to a temperature of 1200 ℃ its content increased. within the temperature range of 1200–1800 ℃, the tib2 phase amount remains almost unchanged, and when temperature is higher than 1800 ℃, a strong increase in the tib2 amount takes place. increasing in tib2 amount and decreasing in w2b5 amount at same temperatures lead to the conclusion that the solubility of w in tib2 increases with temperature. it is why the three different phases in form of boron compounds are observable. these are boron carbide, tungsten pentaboride, and titanium diboride. the grain size of these boron compounds is about 1 μm. the 72 vol.%, 20 vol.% and 8 vol.% of component phases b4c, tib2 and w2b5, respectively, contained the alloy compositions prepared by powder attrition milling for 2 h. the material porosity was less than 3 vol.%. the increase in temperature causes the decrease in density because of w2b5 dissolution and subsequent formation of the diboride system tib2-wb2. this reaction lowers both the hardness and bending strength of the material after its compacting. the above-presented observations can be summarized as follows: attrition milling of mixtures containing b4c, b, and si powders with wc-tic-co spheres decreases the hot-pressing temperature and increases the strength of boron-carbide-based hard material. during heating, the starting components reacted and formed boron carbide and tib2 and w2b5 boride phases, which are more stable than corresponding carbides. pure boron carbide and boron carbide-based composite ceramics b4c-w2b5 were prepared [51] by the hot-pressing method. their microstructure and chemical and phase compositions were characterized by means of xrd, tem, and epma (electron characterization and application of nanomaterials 2024, 7(2), 5454. 14 probe microanalysis). measuring results of their electrical conductivity and seebeck coefficient temperature dependences in the range of 300–1500 k showed that the b4cw2b5 composite electrical conductivity strongly exceeds that for pure boron carbide, while the composite seebeck coefficient is somewhat lower if compared with that for the b4c ceramic. note that both of these characteristics increase with temperature. the figure-of-merit of this composite ceramic was found to be higher than that of the b4c, though its thermal conductivity is somewhat higher in comparison with that of boron carbide. two, wb and w2b5, tungsten borides, were experimentally prepared [52] by the shs (self-propagating high-temperature synthesis) process, during which borothermic reduction of tungsten oxide wo3 and interaction between b and w proceeded concurrently. two series of molar proportions, wo3:b:w = 1:5.5:x with x = 1.16–2.50 and 1:7.5:y with y = 0.50–1.33, were adopted for powder mixtures to produce wb and w2b5 phases, respectively. the reactants compact starting stoichiometry substantially affected the combustion regime and the final product composition. increasing in tungsten and boron contents reduced the overall exothermicity of the reaction, which leads to some decrease in both reaction front velocity and combustion temperature. the initial composition of the reactant compact should be optimized for the predominant synthesis of wb or w2b5. the compact wo3-5.50b-2.00w powder system dominantly produced wb together with small amounts of w2b and w2b5 additive phases. as for the w2b5 phase optimal formation, it was observed from the initial system of wo3-7.50b-0.85w composition. excess in boron amount about 10 mol.%–13 mol.% was experimentally found to be favorable for the formation of mentioned wb and w2b5 trace phases. pressureless sintering at 2150 ℃ can be used [53] to compact boron carbidebased ceramic powders to a relative density of 96.1% with the co-incorporation of tungsten carbide wc and pyrolytic carbon c phases. the specific surface of asbatched boron carbide powder was 7.89 m2/g. in the bw-6c composite, the fracture toughness value of 5.80 mpa∙m1/2 was achieved. as for the sintering aids for tungsten boride and carbon, they were formed in an in-situ reaction. the observed improvement in material toughness should be attributed to the residual thermal stresses as well as the presence of w2b5 phase platelets. thus, b4c-w2b5 composites have the potential to be used as structural materials. boron carbide matrix graphite-containing composites and in situ-formed w2b5 were obtained [54] by the sps method. starting powders of b4c containing 5 vol.%w were shaped into the composite bulk. the sintering was conducted under vacuum at 1500, 1550, and 1600 ℃. sintering temperature and tungsten addition influences on material microstructural and phase properties, densification degree, hardness, and fracture toughness were examined by xrd and sem in-lens mode, as well as vickers indentation technique and palmqvist method. results showed that these composites possess high hardness and improved fracture toughness. the ceramic compositions b4c-(wc-tic) containing different amounts of wctic solid solution were obtained in the work of deng et al. [55] by the hot-pressing method. a chemical reaction taking place during the process resulted in b4c-tib2w2b5 composite with high density and mechanical properties improved in comparison with monolithic boron carbide. addition of wc-tic solution affects the rates of characterization and application of nanomaterials 2024, 7(2), 5454. 15 densification of the composite. increasing in wc-tic content increased the densification rate, while the b4c-(wc-tic)c composites sintering temperature was lowered to 1850 ℃ from that of 2150 ℃ for monolithic boron carbide. with an increase in wc-tic content up to 50 wt.%, the composite material's hardness decreased while its flexural strength and fracture toughness increased continuously. the boron carbide matrix composites b4c-(tib2-zrb2)-w2b5 and their cobalt co additive can be obtained from commercially available initial compounds on the basis of preparing corresponding precursor pastes and their processing in controlled thermal regimes [56]. all the component phases (b4c, tib2, zrb2, w2b5 and co) can be synthesized at relatively low temperatures (around 1000 ℃) from cobalt-containing liquid charges. note that from cobalt-free precursors only zirconium diboride formation can be observed under the same conditions. maintaining the initial grain size by inhibiting their sps growth in boron carbide matrix composite powders with cobalt additive is one more advantage of this approach. 8. w layers surfaces of different types coated with metallic tungsten are widely used in dra (dynamic random access) and flash memories, microprocessors, image sensors, and a number of other modern technologies. the thin-layer coatings of semiconducting surfaces with w are mainly carried out applying cvd (chemical vapor deposition) technique using for precursor materials wf6, sih4 and h2. maintaining the vacuum in the reaction chamber at pressure within the range of 20–760 torr increases both the tungsten deposition rate and reflectivity of the produced w-surface [57]. using the lpcvd (low pressure cvd) method, thin w film was deposited [58] (see plyushcheva et al.’s [59] work as well) on si(100) substrate. wf6 and sih4 were used for source and tungsten-reducing (from wf6) gases, respectively. the deposited tungsten thin film was formed either on sih4 or si substrates by the wf6 reduction in cold wall conditions and by the sih4 reduction under the hot wall conditions. the nmlayer tungsten silicide w5si3 was formed at the w-si interface only during the gas phase deposition. growth of other tungsten silicide wsi2 layers commences at 700 ℃ for cvd layers and above 750 ℃ for plasma-chemically deposited films. this drastic increase increases the material's electrical resistance: under optimal conditions, wfilms with a resistivity of 8 × 10–6 ohm∙cm can be obtained. dissolving of tungsten in hydrogen peroxide and subsequent evaporating the residual solvent yielded [60] the water-soluble powder of tungsten-ipa (inorganic peroxopolytungstic acid). the obtained w-ipa solution was mixed with organic solvent and spin-coated on wafer. films of metallic tungsten were formed by the reduction process. appropriate selection of organic solvent and uv (ultraviolet) irradiating leads to the film with remarkably decreased sheet resistance. frequently obtained tungsten powders are nanosizes. reduction of wo3 at 600 ℃ by using in situ produced hydrogen gas [61] could be considered for a w nanopowder production route. according to the xrd patterns, the final product's alphaand betaw phases are presented in nanostructured form. dta (differential thermal analysis) showed that phase transition from beta-w to alpha-w takes place at a temperature of 435 ℃. pastes and suspensions of powders of this type were used for coating various characterization and application of nanomaterials 2024, 7(2), 5454. 16 surfaces. tungsten alpha-w layer can be formed by reducing wo3 oxide layer preliminary formed by spin coating in hydrogen at a temperature of 600–800 ℃ [62]. applying the wox(oh)y chemical vapor transport, the morphology of the tungsten surface can be transformed into star-shaped cracking, floret, irregularly fibrous, rodlike, and spherical particles. technologies of tungsten deposition on different metal substrates are also used [63]. commonly applied metals are aluminum, copper, and titanium. pnl (pulsed nucleation layer) and ald (atomic layer deposition) methods can be used to grow layers of tungsten nucleation. the ultrafine tungsten powder reduction industrial process evolution is described in gao et al.’s [64] study. in industrial push furnaces, the blue oxides of tungsten were used for reduction in hydrogen counter-current flow. reduction was carried out according to the following scheme: wo2.9 → wo2.72 → wo2 → w. quite often, the pure tungsten films are deposited using pvd (physical vapor deposition) or evaporation/sputtering and cvd. the hwald (hot wireassisted ald) method, which was developed in yang et al.’s [65] work, forms a tungsten layer from w-filament heated up to a temperature of 1700–2000 ℃. atomic hydrogen generated by molecular hydrogen dissociation can react with wf6 at the substrate to form the deposit. typically, nucleation cvd layers are deposited in argon carrier gas from sih4 and wf6. a cheap and, at the same time, practical method is the metallic tungsten coating on the ceramic surface, which uses the applicability of chemical solution deposition to form films on the alumina tubules inner surfaces. this approach includes the tungsten oxide layer preparation from pta (peroxotungstic acid) precursor solutions and subsequent reduction to tungsten under hydrogen [66]. the patent [67] proposes a technological route of formation of the sandwich structures, namely, a method of metallization of boron carbide ceramics. this invention describes the four-step process: step 1: mixing of metal powder containing 10 wt.%–40 wt.% mo, ni, and w (according to wt.% ratio) during ball milling and 300-mesh sieving; step 2: mixing the obtained in the step 1 metal powder with 5 wt.% ethylcellulose solution in wt.% ratios of (100–120):30 to prepare the metalized paste; step 3: printing the obtained in the step 2 metalized paste on the boron carbide ceramic part to be metalized to a layer of thickness of 20–30 μm and its drying; and step 4: metalizing the obtained in the step 3 dried boron carbide part by its placement for metallization into a sintering furnace and for 30–35 min at temperature from the range of 1650–1680 ℃ in hydrogen, keeping the dew point at 0–10 ℃ and cooling along with the furnace. the proportioned moniw metallic alloy layer is close to the boron carbide thermal expansion system. its bonding strength is high, while the metalized stress is small. due to the sub-μm network structure, the formed metal layer is not prone to falling off after brazing. the spin coating allows to reduce the previously formed wo3 tungsten oxide layer to an alpha-w layer at a temperature of 600–800 ℃ in hydrogen [68]. hardness and wear resistance of such tungsten layers, when they are sequentially implanted with boron b (and carbon c as well) 60 kev ions at temperatures of 300–350 k, were investigated. for sample hardness testing, they were modified by fluences of 1 × 1015– 3 × 1015 and 1 × 1016–3 × 1017 ion/cm2. nanoand micro-indentations showed that hardness and wear resistance of obtained composites are improved with 1.3–4.5and 2.0–6.7-times, respectively. characterization and application of nanomaterials 2024, 7(2), 5454. 17 the superior mechanical properties characteristic of tungsten foils at room temperature can be expanded [69] by fabricating the metallic laminate composites containing tungsten. 9. utilization of w-containing waste as mentioned, tungsten-containing alloys are widely used in modern technologies. for this reason, the demand for this type of material is increasing day by day. the scarcity of tungsten led to its removal from tool scrap and reuse to make hard instruments. methods for extracting tungsten from tungsten-containing scrap have been developed for decades. a number of methods implemented in practice have certain strengths and weaknesses. in general, when selecting ways to process such waste, it is important to take into account the productivity and simplicity of the technological process, its environmental friendliness, and also low energy costs. the description of main ways of processing wastes of tungsten-containing hard materials is given in the book of panov and chuvilin [70]. here are listed the main methods used to recycle such kind of waste in the production of tungsten-containing hard alloys.  crude dispersion of sintered waste with different types of crushers and then grinding of the obtained mixtures into finely dispersed fractions (a version of this method is to extract cobalt from waste by heating it to 2300–2500 ℃ and dispersing the rest material);  complete decomposition of waste by chemical-metallurgical methods in a special furnace with strong oxidizers—alkaline nitrates and nitrites, product pouring, crushing, and leaching in hot water;  selective separation of cobalt from the solution by heating and treating it with acid or alkali;  multistep chlorination in the presence of carbon dioxide to obtain tungsten and cobalt chlorides and their separation in distillation columns, purification, conversion into oxides, and reducing;  heating to 1100 ℃, oxidizing it in air, and reducing wo3 together with forming cobalt tungstate hampering complete removal of tungsten;  oxidizing and then chlorinating to trap the tungsten chloride and leave the cobalt dioxide in the chlorinator;  electrochemical processing of solutions of ammonia, alkaline, and salts;  hydro-/pyrometallurgical sawdust processing;  processing with regenerators, including fine-grained grinding with a high-energy air stream, quenching of hard alloys in ice water at 1300–1400 ℃ and crushing the forged mass;  dissolution with sodium hydroxide, precipitation in hydrochloric acid, precipitation and purification of ammonium paratungstate with ammonia, and reduction to tungsten with hydrogen;  thermal regeneration as an oxidation-reduction-carbidization process; and  cobalt extraction with zinc and vacuum distillation. a comparative economic analysis [71] of different regeneration technologies of producing the metalceramic alloys demonstrated the ability of shock-wave processing characterization and application of nanomaterials 2024, 7(2), 5454. 18 as a stimulating factor for powder products (of any configuration) destruction to obtain high-quality powder for further molding and sintering to produce tools of various purposes, eco-friendly technology of processing superhard materials, as well as metalceramic components of obsolete military equipment. industrial tests of rock destroying tool batches, die-blanks for non-ferrous metallic drawing pipes, and mandrel-blanks confirmed the high quality, effectiveness, and feasibility of the developed technology. an analysis of available methods to study the tungsten waste regeneration from hard alloys containing cobalt was conducted. these are chemical (chlorine and zinc) and thermochemical and hydroand pyrometallurgical methods, as well as technology based on explosive energy consumption. metalceramic solid alloys are heterogeneous mixtures, in bulk of which there are surfaces with gaps in any microscopic parameter values. industrial technology development solves the superhard alloys and scrap materials recycling problem and also helps in their subsequent rehabilitation and, respectively, significant savings of expensive raw materials. the regeneration process of hard alloys under the influence of shock waves is also processed. through the direct regeneration of secondary raw materials, this highly efficient production technology allows, without thermochemical and metallurgical processes, obtaining the powders of hard alloys useful to create the tools. this technology differs from the existing ones in terms of high technical and economic indicators, high performance, low energy consumption, and environmental friendliness. the recovery of the tungsten-containing mixture is carried out under conditions of high-pressure gradients and delivery velocities in cylindrical reaction ampoules subjected to the impact caused by the detonation of an axially symmetric explosive charge. 10. conclusions in summary, there is a review of scientific publications on boron and tungsten carbide-based and related nanodispersed composites, the hard materials, with a perspective of wide technological applications. it covers a class of hard materials such as boron-tungsten b-w, carbon-tungsten c-w, boron-carbon-tungsten b-c-w, boron carbide-tungsten b4c-w, boron carbide-tungsten diboride b4c-wb2 and boron carbide-tungsten pentaboride b4c-w2b5 systems, as well as tungsten w layers. especially is discussed one of the related important 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2024). 71. shapoval aa, dragobetskii vv, savchenko iv. analysis of processes of shock-wave regeneration of solid alloys (russian). kharkiv national technical university bulletin. 2018; 31(1306): 100-105. characterization and application of nanomaterials (2018) volume 1 doi:10.24294/can.v1i2.540 1 study on doctor blade and spin coated cuingase2 thin films abhay kumar singh1,2*, tien-chien jen1 1 department of mechanical engineering science, university of johannesburg south africa 2 department of physics, mahatma gandhi kashi vidhyapith, varanasi, india e-mail: abhaysngh@rediffmail.com abstract �rim �e＀o�� dealm m\n�remim o� �u䁙n䀀a (�䁙䀀) nano ma�e�ialm alon� �i�r doc�o� �lade and m＀in coa�ed �rin �ilmm meleni�a�ion and �rei� ＀r\mical ＀�o＀e��iem. �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm �ric�nemmem a�e o��ained 2 �m and 2.95 �m. �aman m＀ec��omco＀\ o� �reme �rin �ilmm leadm �re cralco＀\�i�e ＀rame �o�ma�ion �\ e[ri�i�in� �re ＀ea� a� �ave num�e� 1r1 cm-1. �re �ell-develo＀ed ��ain ��o��rm o� m＀in coa�ed �rin �ilm a�e a＀＀ea�ed in �re mu��ace mo�＀rolo�\. wrile �re ��ain ��o��rm develo＀men�m in doc�o�al �lade coa�ed �rin �ilm im �a�re� ra�d and �u��\. ed* meamu�emen� �eco�nimed �re e[im�ence o� �re com＀omi�ional �a�io ＀�emence o� �re allo\in� elemen�m �u, 䁙n. 䀀a and *e. �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm a�e e[ri�i�ed �re uvvimi�le ��anmmimmion ＀ea� in �re �ave len��r �an�e 240 nm 320 nm. �re o＀�ical ene��\ �and �a＀m �o� �re doc�o� �lade and m＀in coa�ed �䁙䀀* �rin �ilmm a�e o��ained 1.41ev and 1.5 ev. keywords: cigs; thin films; raman spectra; uv-visible. 1. introduction ene��\ conmum＀�ion �imin� in ruman dail\ li�e and mo�e demandm in �u�u�e. �o �ul�illin� �u�u�e ene��\ demandm invem�i�a�o�m rave �eco�ni�ed �re ＀�omimin� �ene�a�le ene��\ �emou�cem one o� �re ＀o�en�ial �ecrnolo�\ �ricr can delive�. bamed on �re �ac� mun in ou� mola� m\m�em ＀�ovidem um an a�undan� mou�ce o� mum�aina�le ene��\. �re a�undan�l\ ＀�ovidem mun ene��\ im enou�r �o� common rumani�\ ume. �re enou�r amoun� o� munli�r� can �e ume �o� �re common elec��ici�\ �\ conve�min� ＀ro�ovol�aic (pv) devicem[1]. �re mul�ila\e�ed pv li�e �u䁙n䀀a*2 (�䁙䀀*), �u(䁙n,䀀a)*e2 (�䁙䀀*e) a�e iden�i�ied am an ＀o�en�ial a�ea �o� �re �emea�cr, due �o �rei� enranced e��icienc\, �i�r lon�-�ime m�a�ili�\ and e[cellen� du�a�ili�\[2-4]. *＀eci�icall\ ac�ive la\e� �䁙䀀* ma�e�ial ram �een �eco�ni�ed am e[ce＀�ionall\ �ell due �rei� ri�r a�mo�＀�ion coe��icien� (a�ound 105 cm-1) �i�r m��on� munli�r� a�mo�＀�ion a�ili�\. am a＀＀lica�ili�\ ＀oin� o� vie� �䁙䀀* ac�ive la\e� ma�e�ial �rin �ilmm a�e demi�ed. �re �\＀ical �ric�nemm o� �rim la\e� im �ell de�ined in �re �an�e 1.5 �m �o 3 �m �o� �re �em� ＀e��o�min� devicem. �re va�ioum advan�a�em �䁙䀀* ac�ive la\e� ma�e�ial ma�e �rem an e[cellen� candida�e am an a�mo��e� la\e� �o� la��e mcale ＀�oduc�ion o� �rin �ilm pv modulem[5]. umuall\ ri�r \ield �䁙䀀* devicem e��icienciem a�e �e＀o��ed �i�r �re vacuum ＀�ocemmem li�e co-eva＀o�a�ion and m＀u��e�in� [4].wi�r �re meve�al advan�a�em vacuum ＀�ocemm �ecrnolo�iem almo rave me�ioum immuem �o� �re la��e mcale manu�ac�u�in�, due �o �rei� lo� ＀�oduc�ivi�\, ri�r ＀�oduc�ion com�m and com＀omi�ional uni�o�mi�\[5]. �o ove�come �reme mro��comin�m invem�i�a�o�m rave ＀aid a��en�ion �o�a�d al�e�na�ive non-vacuum ＀�ocemmem. �re non-vacuum ＀�ocemmem can rave mi�ni�ican� advan�a�em li�e lo�e� �a��ica�ion com�m, ri�re� ＀�oduc�ivi�\, uni�o�mi�\ and �ell m�oicriome��ical �a�io. ye�, i� im �eali�\ �re al�e�na�ive non-vacuum ＀�ocemmem �amed �䁙䀀* devicem could no� acrieve mame e��icienciem am ri�r-vacuum ＀�ocemmem. bu� al�e�na�ive non-vacuum ＀�ocemmem m�and ou� am com＀e�i�ive ＀�oduc�ion �ou�em in �re �u�u�e[6]. �re �䁙䀀* non-vacuum a＀＀�oacrem ＀�edomina�el\ rave �een invem�i�a�ed ��om �re �ecrniquem li�e elec��ode＀omi�ion, m＀�a\ ＀\�ol\mim, ＀�in�in� e�c[r9]. �o＀\�i�r� © 2018 a�ra\ kuma� *in�r et al. doi: 10.24294/can.v1i2.540 enp�emm pu�limre� ���.�rim �o�� im licenmed unde� �re ��ea�ive �ommonma���i�u�ion-non�omme�cial 4.0 䁙n�e�na�ional �icenme (�� by-n� 4.0). r��＀://c�ea�ivecommonm.o��/licenmem/ �\/4.0/ 2 䁙nm＀i�e o� di��e�en� m��a�e�iem e[im� �o� �educin� ca��on con�amina�ion in molu�ion-＀�ocemmed �䁙䀀* �ilmm. �re ri�rem� device e��icienc\ �o� �re molu�ion-＀�ocemmed �䁙䀀* pv ram �een acrieved �i�r �re meleni�ined r\d�a�ine-de�ived molecula� �eac�an�m [10].wi�r �rim ＀�ocemm majo� d�a��ac� i�m ri�r �o[ici�\, ＀o�en�ial e[＀lomive and com� o� r\d�a�ine �o� �re manu�ac�u�in� ＀�ocemm[10]. �o �emolve �reme immuem invem�i�a�o�m rave ＀�emen�ed meve�al �ecrnical �e＀o��m on �䁙䀀 nano in� m\n�remim and �rei� �rin �ilmm on di��e�en� mu�m��a�em ��om di��e�en� �ecrniquem[11]. *＀in coa�in� and doc�o�al �lade coa�in� a�e almo iden�i�ied crea＀e� de＀omi�ion �ecrniquem �o� �re la��e mcale. 䀀oal o� �rim �e＀o�� �o ＀�emen� non-�o[ic ni��a�e �ou�e �䁙䀀 nano in� and ＀em� m\n�remim �o� �re �rin �ilmm de＀omi�ion ��om m＀in coa�in� and doc�o� �lade coa�in� �ecrniquem. �re �ive �imem m＀in and doc�o�al �lade coa�ed meleni�ed �rin �ilmm �ric�nemm ＀�o�ile, cralco＀\�i�e ＀rame �o�ma�ion �aman ve�i�ica�ion, *cannin� elec��on mic�omco＀ic (fe*em) ��ain ��o��rm �o�ma�ion �i�r com＀omi�ional ene��\ dim＀e�mive *＀ec��um (ed*) anal\mim, uv-vimi�le ��anmmimmion ＀�o�ile and o＀�ical ene��\ �and �a＀m a�e m�udied. 2. experimental details: p�ecu�mo� molu�ion o� �re �䁙䀀 �am ＀�e＀a�ed �\ dimmolvin� �re a＀＀�o＀�ia�e amoun�m o� �u(no3)2•[h2o (99.999%), 䁙n(no3)3•[h2o (99.99%), and 䀀a(no3)3•[h2o (99.999%) in e�ranol (80 m�) �i�r �e�＀ineol (20 ml). �re molu�ion �am �ren m�i��ed vi�o�ouml\ �o� 3 r, unde� main�ained �em＀e�a�u�e a�ound 500�, a vimcome �lue colou� �u䁙n䀀a (�䁙䀀) molu�ion �i�r �reolo�ical ＀�o＀e��iem �am o��ained �o� �re m＀in coa�in�. a��e��a�d ral� ＀a�� o� �re o�i�inall\ ＀�e＀a�ed molu�ion �am me＀a�a�ed. �re me＀a�a�ed molu�ion a�ain rea�ed a� 1500� unde� �re con�inuoum m�i��in� a vimcome da�� ��een colou� �䁙䀀 ＀em� �am acrieved �o� �re doc�o� �lade coa�in�. �re �䁙䀀 molu�ion m＀in coa�in� �am ＀e��o�med on 2.5 cm [ 2.5 cm moda lime �lamm (*�䀀) mu�m��a�e a� 3000 �＀m. *u�mequen�l\ �re m＀in coa�in� de＀omi�ed �rin �ilm �am d�ied on ro� ＀la�e a� 1500�.�rim ＀�ocemm �am done �o� all �ive �imem. wrile, �䁙䀀 vimcome da�� ��een colou� ＀em� �am de＀omi�ed on �re 2.5 cm [ r cm *�䀀 mu�m��a�e ��om �re doc�o� �lade coa�e�. du�in� �re m＀in and doc�o� �lade coa�in� o� �䁙䀀 �re a��en�ion �am on romo�enei�\ o� �rin �ilmm �ric�nemm. �re m＀in coa�ed and doc�o� �lade coa�ed �ell d�ied �rin �ilmm �e�e umed �o� �re meleni�a�ion. *am＀lem meleni�a�ion ＀�ocemm �e�e done a� 3500�±200� unde� �re con�inuoum �lo� o� n2 in *e va＀ou� envi�onmen�. 䁙� �am enmu�ed �re �䁙䀀* �rin �ilmm com＀omi�ion �a�io 1:0.r:0.3:2. �re mcrema�ic includin� ＀�e＀a�ed �䁙䀀 nano ma�e�ial �o� m＀in and doc�o�al �lade coa�in�, coa�in� ＀�ocemm, meleni�a�ion m�e＀ and ＀ro�o��a＀rm o� �re meleni�ed �rin �ilmm im �iven in figure 1. figure 1: *crema�ic, (a-i) �䁙䀀 ＀em� �o� �re doc�o� �lade coa�in�, (ii) �䁙䀀/*�䀀 �rin �ilm de＀omi�ion m�e＀, (iii) m�e＀ o� meleni�a�ion, (iv) doc�o� �lade coa�ed �䁙䀀* �rin �ilm ＀ro�o��a＀r. 3 *crema�ic, (�-i) �䁙䀀 nano in� �o� �re m＀in coa�in�, (ii) �䁙䀀/*�䀀 �rin �ilm de＀omi�ion m�e＀, (iii) m�e＀ o� meleni�a�ion, (iv) m＀in coa�ed �䁙䀀* �rin �ilm ＀ro�o��a＀r. �ric�nemmem o� �re �o�r me�rodm made �䁙䀀*/*�䀀 �rin �ilmm �e�e de�e�mined ��om �re �ric�nemm ＀�o�illomen�e�. �o con�i�m �re cralco＀\�i�e ＀rame in �reme �rin �ilmm �re �aman m＀ec��omco＀ic meamu�emen� �e�e ＀e��o�med. �re mu��ace m��uc�u�al mo�＀rolo�iem o� �re �rin �ilmm �e�e e[amined ��om �re *cannin� elec��on mic�omco＀e (fe*em). �o con�i�m �re ＀�e＀a�ed �䁙䀀* ma�e�ial nano �o�ma�ion and evalua�e �re o＀�ical ene��\ �and �a＀m �o� �re uvvimi�le ��anmmimmion m＀ec��a �e�e �eco�ded ��om �re m＀ec��ome�e�. 3. results and discussion: �re �ive �imem m＀in coa�ed and analo�uem doc�o� �lade coa�e� adjum�ed dim�ance mcale �e��een �re �ni�e and mu�m��a�e ＀�ocemm, �䁙䀀 /*�䀀 �rin �ilmm a�e o��ained. a��e� meleni�a�ion (�䁙䀀* /*�䀀) �rin �ilmm a＀＀�o＀�ia�e �ric�nemm �no�led�e im an im＀o��an� ＀a�ame�e� �o� �re o＀�imi�a�ion o� m＀in and doc�o� �lade coa�ed ac�ive la\e�. �re �ric�nemm meamu�emen� o� �re m＀in and doc�o� �lade coa�ed �䁙䀀* /*�䀀 �rin �ilmm im ＀e��o�med ��om �re �ric�nemm ＀�o�illome�e�. �re o��ained �ric�nemm ＀�o�illome�e� �emul� ＀lo�m �o� �reme di��e�en� ＀�ocemmem coa�ed �䁙䀀*/*�䀀 �rin �ilmm im �iven in fi�u�e2. figure 2: �ric�nemm ＀�o�ile ＀lo�m �o� �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm. f�om �re ＀lo� i� im clea� doc�o�al �lade coa�ed meleni�ed �ilm �ric�nemm (2 �m) lemme� �ran �re m＀in coa�ed �䁙䀀* �ilm (2.95 �m).�rim �emul� almo �ivem �ric�nemmem o� �reme di��e�en� ＀�ocemmem de＀omi�ed �䁙䀀*/*�䀀 �rin �ilmm a�e �allin� in �ell �eco�ni�ed �an�e (1.5 �m �o 3 �m) �o� �re �䁙䀀* ac�ive la\e� ma��ial[12]. fo� �re ve�i�ica�ion o� �re cralco＀\�i�e ＀rame �o�ma�ion in �reme ��o di��e�en� ＀�ocemmem de＀omi�ed �䁙䀀*/*�䀀 �rin �ilmm �e �e�e ＀e��o�med �re �aman m＀ec��omco＀ic meamu�emen�, in �re �ave num�e� �an�e u＀�o 600 cm-1. �re o��ained �aman m＀ec��um �o� �reme �䁙䀀*/*�䀀 �rin �ilmm im e[ri�i�ed in fi�u�e3. 4 figure 3: �aman m＀ec��um �o� �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm. �aman ＀ea� o� pv ac�ive cralco＀\�i�e ＀rame �䁙䀀* ma�e�ial a＀＀ea�m a� 1r1 cm-1 �o� m＀in and doc�o� �lade coa�ed �rin �ilmm[13,14].�re ri�re� value o� �re �aman ＀ea� in�enmi�\ �o� �re doc�o� �lade coa�ed �䁙䀀*/*�䀀 �rin �ilm mi�r� �e due �o i�m ri�r o�de� mu��ace �e�lec�ivi�\ in com＀a�imon �o m＀in coa�ed �rin �ilm. �re non a＀＀ea�ance o� o�re� ＀�ominen� �aman ＀ea�m in m＀in and doc�o� �lade coa�ed �䁙䀀*/*�䀀 �rin �ilmm �evealm a romo�eneoum cralco＀\�i�e ＀rame �o�ma�ion. �re romo�eneoum cralco＀\�i�e ＀rame �o�ma�ion ma�em �rem ＀o�en�ial �䁙䀀*/*�䀀 �rin �ilmm �o� �re pv a＀＀lica�ion[13,14]. �o ve�i�\ �re mic�om��uc�u�al mu��ace ��ain ��o��rm in �reme �rin �ilmm ＀e��o�med �re fe*em meamu�emen�. *u��ace mo�＀rolo�\ and ed* ＀a��e�m �o� �re m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilm im e[ri�i�ed in figure 4 (a, �). figure 4: fe*em mu��ace mo�＀rolo�\ and ed* m＀ec��um; (a, �) �o� �re m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilm; (c, d) �o� �re doc�o� �lade coa�ed �䁙䀀*/*�䀀 �rin �ilm. 5 wrile �re mu��ace mo�＀rolo�\ and ed* ＀a��e�m �o� �re doc�o� �lade coa�ed �䁙䀀*/*�䀀 �rin �ilm im �iven in fi�u�e. 4 (c, d). �re mu��ace mo�＀rolo�ical anal\mim o� m＀in de＀omi�ed �䁙䀀*/*�䀀 �rin �ilm �ivem �ell develo＀ed ��ainm ��o��rm �i�r a com＀ac� ��ain connec�ivi�\ (*ee fi�u�e.4 (a)), �rile a �eve� ��ain ��o��rm (�i�id ra�d and �u��\) and �ainm connec�ivi�\ im a＀＀ea�ed �o� �re doc�o� �lade coa�ed �䁙䀀*/*�䀀 �rin �ilm (*ee fi�u�e.4 (c)). �rim ma\ �e due �o involvemen� o� ��o dim�inc� de＀omi�ion �ecrniquem. ho�eve�, �o�r ＀�ocemmem de＀omi�ed �rin �ilmm ed* ＀a��e�m �ivem �re ＀�emence o� allo\in� elemen�m �u, 䁙n, 䀀a and *e in �rei� com＀omi�ional �a�io. 䁙� im �ell em�a�limred �ac� �ra� nano dimenmion ma�e�ialm mrould e[ri�i� uv-vimi�le a�mo�＀�ion o� ��anmmimmion ＀ea� u＀�o 500 nm �an�e[15,16]. �re�e�o�e, �e rave ＀e��o�med �re uv-vimi�le ��anmmimmion meamu�emen� �o� �reme m＀in and doc�o� coa�ed �䁙䀀*/*�䀀 �rin �ilmm. �re o��ained uv-vimi�le ��anmmimmion m＀ec��umm o� �reme ��o di��e�en� ＀�ocemmem de＀omi�ed �䁙䀀*/*�䀀 �rin �ilmm im e[ri�i�ed in figure 5 (a, �). figure 5, (a, �); uv-vimi�le ��anmmimmion m＀ec��a �o� �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm. bo�r ＀�ocemmem de＀omi�ed �䁙䀀*/*�䀀 �rin �ilmm rave mro�n �re uv-vimi�le ��anmmimmion ＀ea� �elo� �re 280 nm. �rim con�i�mm �re nano dimenmion �o�ma�ion o� �䁙䀀* ac�ive la\e� ma�e�ial. addi�ionall\, �i�r �re rel＀ o� uv-vimi�le ��anmmimmion m＀ec��a can almo o��ain o＀�ical ene��\ �and. kno�led�e o� �re o＀�ical ene��\ �and �a＀ im an im＀o��an� ＀a�ame�e� �o� �re pv ac�ive la\e� ma�e�ial. �o evalua�ed �re di�ec� o＀�ical ene��\ �and �a＀m �o� ��o di��e�en� ＀�ocemmem de＀omi�ed �䁙䀀*/*�䀀 �rin �ilmm �auc� ＀lo�m im �iven in figure 6 (a, �). figure 6, (a, �); �auc� ＀lo�m �o o��ain o＀�ical ene��\ �and �o� �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm. 6 o＀�ical ene��\ �and �a＀m �o� �reme �rin �ilmm can �e o��ained �\ e[��a＀ola�ion o� no�mal line �r�ou�r �re m＀ec��um cu�ve a�e. �re [-a[im cu� ＀oin� o� �re e[��a＀ola�ed no�mal line di�ec�l\ �ivem �re value o� �re o＀�ical ene��\ �and �a＀ �o� �reme �rin �ilmm. �re evalua�ed o＀�ical �and �a＀ (1.41 ev) o� doc�o� �lade coa�ed �rin �ilm im �eve� �ran m＀in coa�ed �rin �ilm (1.5 ev). �rim �emul� demonm��a�em m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilm o＀�ical ene��\ �and �a＀ im mo�e a＀＀�o＀�ia�e �o� �re pv ume �ran doc�o� �lade �䁙䀀*/*�䀀 �rin �ilm. 4. conclusions 䁙n conclumive �ema��m, �e rave m\n�remi�ed �䁙䀀 ma�e�ial �i�r �re non �o[ic �ou�e and de＀omi�ed �rei� �rin �ilmm on *�䀀 mu�m��a�em �\ �re doc�o� �lade and m＀in coa�in� me�rodm. �o ma�e �䁙䀀* cralco＀\�i�e ＀rame com＀omi�ion �re de＀omi�ed �䁙䀀 �rin �ilmm rave meleni�ed. �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm �ric�nemmem rave demonm��a�ed, i� �allm in �re �\＀ical a＀＀lica�le �an�e �o� �re pv ac�ive la\e� ma�e�ial. �aman m＀ec��omco＀ic �emul� ram �evealed �re cralco�enide ＀rame �o�ma�ion in doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm. �re fe*em mu��ace mo�＀rolo�ical ou�come ram ve�i�ied �re �ell develo＀ed ��ain ��o��rm �i�r mu＀e�io� ��ainm connec�ivi�\ �o� �re m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilm am com＀a�e �o doc�o� �lade coa�ed �rin �ilm. *�oicriome��\ o� �re �䁙䀀* com＀omi�ion �o� �re m＀in and doc�o� �lade �rin �ilmm rave �een ve�i�ied ��om �re ed* ＀a��e�nm. wi�r �re rel＀ o� uv-vimi�le ��anmmimmion ＀a��e�m o� �re doc�o� �lade and m＀in coa�ed �rin �ilmm �re nano dimenmion �o�ma�ion in �䁙䀀* ac�ive la\e� ram con�i�med. �re o＀�ical ene��\ �and �a＀m �o� �re doc�o� �lade and m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilmm rave o��ained 1.41 ev and 1.5 ev. on �re �amim o� �re ou�lined �ecrnical ＀r\mical ＀�o＀e��iem �re m＀in coa�ed �䁙䀀*/*�䀀 �rin �ilm can rave mo�e u�ili�\ �ran doc�o� �lade coa�ed �rin �ilm. acknowledgement: au�ro� ak* �ran��ul �o unive�mi�\ o� jorannem�u��, de＀a��men� o� mecranical en�inee�in� *cience (apk), facul�\ o� en�inee�in� and �re buil� envi�onmen� (febe), �o� �re mu＀＀o�� unde� �re *enio� �emea�cr ammocia�e ＀�o��am. references 1 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https://doi.org/10.24294/can10834 1 review present scenario and futuristic applications of nanomaterial-based products in the industry—a review c. j. panchal1,*, b. h. patel2 1 department of applied physics, faculty of technology and engineering, the maharaja sayajirao university of baroda, vadodara 390001, india 2 department of textile chemistry, faculty of technology and engineering, the maharaja sayajirao university of baroda, vadodara 390001, india * corresponding author: c. j. panchal, cjpanchal_msu@yahoo.com abstract: the article’s proposed engineering uses are based on theories presented in the reviewed research articles and on findings from online investigations into companies that claim to use nanoengineering in their wares. several pre-existing online consumer inventories and nanotechnology news were examined as part of the internet inquiry. the data about the nanoparticles (np), or nanostructure, used in commercially available products comes from the remarks made by the manufacturer. nanoengineered coating agents and textile additives are examples of commercial items developed for industrial clients that fall under the aforementioned uses. keywords: automotive; chemical; construction; electronic; engineering; nanomaterial; textiles 1. introduction nanotechnology is the technology domain that concentrates on manipulating and controlling structures, devices, and systems at the nanoscale, including their design, characterization, production, and application. it possesses significant commercial viability across a wide range of businesses. the traditional techniques and the conventional material employed by the industry require attention owing to the strict environmental rules and constraints in energy consumption. this is primarily because traditional procedures used in preparing various items typically do not yield lasting effects and eventually become ineffective. in addition, applying nanoparticles to various materials will not compromise their breathability or tactile sensation. nanotechnology enhances materials by providing properties such as wrinkle resistance, hydrophobicity, uv protection, flame retardation, antibacterial and antistatic capabilities, soil resistance, and improved dyeability. the present and potential engineering applications outlined in figure 1 are derived from the hypotheses put forth in the analyzed research publications, as well as from internet research on manufacturers who assert the utilization of nanoengineering in their products. the internet investigation was conducted by analyzing several existing online consumer inventories and news articles relevant to nanotechnology. the information concerning the employed nanoparticle or nanostructure in commercially available products is sourced from the manufacturer’s statements. the aforementioned applications include commercial products that are intended for industrial clients, such as textile additives or nanoengineered coating agents. citation panchal cj, patel bh. present scenario and futuristic applications of nanomaterial-based products in the industry—a review. characterization and application of nanomaterials. 2025; 8(2): 10834. https://doi.org/10.24294/can10834 article info received: 10 december 2024 accepted: 13 february 2025 available online: 30 april 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 10834. 2 nevertheless, textile coating or impregnation compounds that are intended for the end consumer are not included, as they are not classified as “textile products” [1]. the research on nanotechnology in the web of science is utilized to create a comprehensive range of functional materials that can be accomplished through nanoengineering. the text highlights the various np and production processes that are presently being examined. the literature delineates the mechanisms that elicit the intended effects for each textile function, encompassing specifics regarding the np/nanostructure, the textile matrix, the employed production method, and the form of the np in the final fabric. the commercial utilization of various functional textiles relies on the findings presented in the analyzed research articles and on online searching for nanoengineered consumer products that are now available. the suggested products are categorized into the following product groups: apparel, protective garments, interior trim and upholstery, sports and leisure, household, cosmetics, medical equipment, building materials, industrial purposes, and auxiliary/intermediate products for industrial operations [2]. the final product category encompasses all items that are not directly sold to the ultimate consumer but rather acquired by industrial customers and employed in the manufacturing process of a nanoengineered final product. examples of such auxiliary or intermediate items include additives, textile composites that are further processed into garments or furniture, as well as licenses for the use of specific production procedures or technologies. figure 1. overview of applications of nanomaterial-based products in different areas. 2. nanoengineered materials for the automotive industry nanomaterials can be utilized in car bodies to create lightweight structures that maintain rigidity and crash resistance, reducing material usage and fuel consumption. this section discusses the integration of nanotechnology into the safety features and fuel efficiency of modern vehicles. it also highlights the significance of sustainable development in the application of these technologies and the analysis of the materials used in their life cycle. this is done to align with societal trends and meet customer characterization and application of nanomaterials 2025, 8(2), 10834. 3 demands for improved comfort, safety, and ecology. the present status and potential application of nanoparticles in automotive engineering are shown in table 1. table 1. potential application of nanoparticles automotive engineering. industry nanoparticles nanoparticle-based product/conventional application potential industrial application automotive engineering carbon nanotubes nano clay silica alumina cerium oxide platinum graphene paints and coatings: improve scratch resistance, uv protection, and color stability. composites: enhance strength, stiffness, and impact resistance in polymer matrix composites. tires: improve tread wear, traction, and fuel efficiency. batteries: increase energy density, power, and charging speed in lithium-ion batteries. catalysts: improve fuel efficiency, reduce emissions, and enhance catalytic converter performance. sensors: enable the development of smaller, more sensitive sensors for temperature, pressure, and gas detection. fuel additives: improve fuel efficiency, reduce emissions, and clean engine components. self-healing materials: to create materials that self-heal cracks and damages. vehicle bodies and chassis engine components (e.g., pistons, cylinders) transmission and drivetrain components battery electric vehicles (bevs) hybrid electric vehicles (hevs) fuel cell electric vehicles (fcevs) 2.1. lightweight body construction and catalysts the need for novel and sophisticated materials in automotive applications arises from vehicle safety, performance, and fuel efficiency requirements. nanomaterials used in automotive applications aim to reduce engine emissions, enhance driving safety, minimize vehicle noise, and provide self-healing capabilities for vehicle bodies and windscreens. the concept of utilizing nano-fluids to enhance the efficiency of coolants was introduced a considerable time ago [3,4]. the suggestion resulted in a 100% improvement in liquid thermal conductivity by utilizing nanometer-scale particles, leading to a proliferation of scientific research efforts in this field [5,6]. nevertheless, the enhancements in the performance of coolants may catalyze driving and inspire additional advancements in engine efficiency, as well as the reduction in size and weight of cooling systems. additionally, there are ongoing investigations that specifically target the enhancement of thermal and rheological characteristics of lubricants by the use of nanoparticles [7]. enhancing the decrease of weight in cars is a crucial concern for motor vehicles, as reducing weight is the primary method to enhance fuel efficiency. the increasing global standards for fuel efficiency and pollution in manufacturing and transportation are generating a need for affordable, high-performing lightweight materials as substitutes for metals. a nanocomposite refers to a solid matrix that contains nano-objects, such as a new type of polymeric materials that have exceptional mechanical, thermal, and processing capabilities. these materials are suited for replacing metals in several applications, including the automobile industry [8]. the nanoparticles are highly effective, typically requiring just 0.5%–5% of their weight to be added. a nanocomposite possesses qualities that surpass those of traditional microscale composites and may be synthesized at a low cost utilizing a straightforward process [9]. nanocomposites are anticipated to enhance manufacturing speed, environmental and thermal stability, recycling, and weight reduction in automotive parts and systems. by restricting the use of this technique to non-essential structural components like front and rear sections, cowl vent grills, characterization and application of nanomaterials 2025, 8(2), 10834. 4 valve/timing covers, and truck beds, it is possible to achieve a significant weight reduction, amounting to several billion kilograms per year [8]. nanotechnology is currently being employed in the mass production of car components. for instance, audi and daimler chrysler utilize multi-layered nanocoating on glass instruments to provide an anti-reflection effect. general motors corp. has implemented a thermoplastic olefin (tpo) nanocomposite in an optional step-assist feature for the chevrolet astro and gmc safari minivans. replacing reinforced polymers in car body components is a viable strategy for reducing weight, but it is crucial to ensure that safety, affordability, and other desired qualities are not compromised [3]. buses utilize sun protection glazing that has nanolayers inserted into glass sheets to reflect infrared rays. gmc utilizes thermoplastic nanocomposites with nanoflakes to manufacture rigid and lightweight external components, such as the stepassist. in their study, presting and koning [10] predicted that a 30% enhancement in roll resistance, air resistance, car weight, or powertrain might potentially lead to a reduction in fossil fuel consumption by 4%, 6%, 15%, or 28%, respectively. therefore, carbon dioxide emissions will decrease. nanotechnology can also play a role in enhancing fuel injection and reforming processes, improving hydrogen storage capabilities, optimizing cell electrodes, and enhancing the performance of proton exchange membranes (pem). in addition, the application of nano jets can enhance engine combustion efficiency by reducing surface tension losses during aerosol production. porous nanocomposites can also be utilized as pollution filters, effectively reducing the release of soot particles or harmful gases by mechanical means or catalytic reactions [3,4,11]. 2.2. automotive painting the field of automotive painting has undergone significant advancements since its inception, transforming into a highly intricate procedure that not only boosts the visual attractiveness of automobiles but also offers vital safeguarding against environmental factors. the base coat clear coat paint method is a groundbreaking approach that has proved essential to the automotive industry. nanotechnology has been included in vehicle paints, leading to the development of nano-coatings. these coatings offer an extra layer of protection, providing resistance against scratches, chemical pollutants, and uv radiation. nano-coatings not only increase the durability of the paint but also improve the gloss and shine on the surface of the car [12]. 3. nanoengineered materials for the chemical industry 3.1. nanocomposite-based coating system a nanocomposite coating is a substance consisting of a minimum of two phases that are incapable of mixing and are separated by a region known as the interface. the material must possess nanoscale dimensions in at least one dimension, with the primary component referred to as the matrix, within which fillers are scattered [13]. the categorization of nanocomposite coatings is determined by different approaches that consider either the type of nanostructured fillers or the type of matrix in which the characterization and application of nanomaterials 2025, 8(2), 10834. 5 filler nanostructures are distributed. there are three primary categories of nanocomposite coating, which are as follows [14]: 0d nanocomposite coatings consist of nanoparticles as fillers, which have diameters in the nanoscale in all three dimensions. 1d nanocomposite coatings consist of nanotubes or whiskers as fillers, which have dimensions on the nanoscale in two dimensions. 2d nanocomposite coatings consist of nanolayers as fillers, which have a dimension in the nanometer scale. there are two types of matrices: organic matrix and inorganic matrix. there are four primary categories of nanocomposite coating, classified based on the combination of matrix and nanofiller: coatings are made of a combination of organic and inorganic materials, known as organic/inorganic nanocomposite coatings (o/i nanocomposite coatings). coatings are made of a combination of organic materials, known as organic/organic nanocomposite coatings (o/o nanocomposite coatings). coatings are made from a combination of inorganic and organic materials, known as inorganic/organic nanocomposite coatings (i/o nanocomposite coatings). coatings are made from a combination of inorganic materials, known as inorganic/inorganic nanocomposite coatings (i/i nanocomposite coatings). 3.2. exceptional characteristics of nano-coating thin films, nanoscale coatings, and nanostructured surfaces have extensive applications across various industry sectors and serve as excellent illustrations of how nanotechnology may enhance or disrupt existing technology sectors, as well as generate new ones. nano coatings offer notable performance benefits compared to conventional coatings while also being more cost-effective in the medium to long run. nanostructured materials significantly enhance various properties, including antimicrobial activity, product durability, thermal insulation, gloss preservation, resistance to dirt and water, hardness, corrosion resistance, flame retardancy, stability against ultraviolet radiation, improved energy efficiency, resistance to graffiti, selfcleaning ability, moisture absorption, gloss preservation, and chemical and mechanical properties. 3.3. paper industry the paper production business utilizes mechanical and chemical processes, known as pulping, to transform various materials into different types of board goods and paper [15]. due to advancements in the paper industry, there has been an increased focus on manufacturing high-quality paper in a cost-efficient manner [16]. the ultimate characteristics of the paper, including its excellence, mass, sheen, evenness, and decreased ink absorption, are significant [17–19]. by incorporating nanostructured materials and small amounts of organic compounds into the paper formation, it is anticipated that the qualities of the resulting paper will be improved. nanotechnology is employed to modify the production process in response to shifts in resource-based and industrial knowledge, leading to corresponding adjustments, with a significantly heightened focus on stability. the core of the work characterization and application of nanomaterials 2025, 8(2), 10834. 6 revolves around the utilization of nanofibers, nanofillers, nanocomposites, and nanoscale compounds in paper applications. scientists and researchers have been interested in using nano-additives in the paper industry because they significantly enhance the attributes of manufactured papers. these improvements include mechanical strength, printability, glossiness, and gas barrier capabilities. the alleged advantages of nano-additives are manifold, including a large surface area, strength, low weight, high stiffness, and sustained sustainability. nevertheless, the implementation of nanotechnology in the paper sector has been hindered by several obstacles, including elevated expenses, inadequate compatibility between materials, and a gap in understanding. the initial phase of the paper manufacturing process includes material preparation, pulp production, pulp bleaching, paper production, and fiber recycling [20]. the processed wood pulp, which may undergo bleaching if needed, is made as a thin mixture with various additions, particularly fillers, to achieve the desired paper quality. nanotechnology plays a crucial role in nearly all contemporary sectors, with a focus on achieving high-quality and efficient market opportunities [21–23]. the significant interest in the nanoscale range stems from the fact that nano additives exhibit superior characteristics in comparison to their bulk counterparts [22]. nanotechnology is currently at the forefront of driving global economic growth and progress. nano-scale techniques are widely used in various fields, offering insights into promising advancements in materials, electronics, and systems [23,24]. nanoadditives possessing distinctive benefits are anticipated to revolutionize the aspects of controlled technology. in this context, nanotechnology primarily aims to exercise control and manipulation over materials to achieve certain functionality. nanotechnology advancements offer gradual and progressive improvements [25] and have recently become a valuable tool in various applications, including the pulp and paper industry. the distinctive benefits and characteristics of the paper can be enhanced by the use of nano-additives. the progress in nanotechnology has led to the creation of several nano-additives, which are the outcome of considerable research in the field of nanotechnology. the size of nano-additives is substantial, as a result of many variables [23–26]. the light scattering properties are influenced by nano-additives, gloss and opacity, the calendaring process, the drying rate, and the ability of the paper to absorb ink. the nanoparticles tend to agglomerate [27]. obtaining bigger-diameter nanoadditives is challenging because of the limited specific surface area. for instance, furnishings that contain nano-additives with microscopic particles have a larger surface area that competes with the sizing agent, making them more resistant. 3.4. switchable adhesives nano-based adhesive bonding incorporates the incorporation of nano-scale particles, such as nano-fillers and nanocrystals, to enhance the strength, flexibility, and durability of contemporary adhesives. these adhesive matrices, loaded with nanoparticles, possess improved characteristics in comparison to traditional adhesives [28–30]. characterization and application of nanomaterials 2025, 8(2), 10834. 7 3.5. nanofillers in adhesives the adhesive matrices, which are infused with nanoparticles, exhibit enhanced properties as compared to conventional adhesives. the use of nanofillers is an effective method for improving the performance of these base polymers. nanofillers enhance the mechanical characteristics of polymeric adhesives, including their ability to withstand cracks, resist wear, and prevent corrosion [31]. several types of nanofillers, such as nanoclays, carbon nanotubes, metal or metal oxide particles, ceramic fillers, and cellulose nanomaterials (cnms), have been studied for their incorporation into polymeric adhesive nanocomposites. studies have demonstrated that cnms are especially proficient in improving polymeric adhesive matrices. carbon nanomaterials (cnms) possess the advantageous properties of reusability, biodegradability, non-toxicity, and lower energy requirements during the manufacturing process. an example of this is when the addition of 5 wt.% nano-silica to an epoxy coating resulted in a 30% reduction in mass loss during abrasive tests. comparable enhancements were noted for acrylic adhesive composites reinforced with cnm, specifically with a fiber loading of 10 wt.% [32]. due to their excellent crystallinity and aspect ratios, cncs are much sought after as adhesive reinforcements. the use of cncs in adhesive formulations enhances bond strength and enhances the resistance to joint creep and stiffness. the nanocrystals’ high modulus of elasticity is crucial for improving the stiffness of the composite, making it essential for structural applications. nanostructured epoxy adhesives are widely used because of their improved properties, including higher mechanical strength, enhanced heat and chemical resistance, and reduced curing time. nanoscale materials enhance adhesion on uneven or rough surfaces as a result of their increased surface area-to-volume ratio. the adhesives supplemented with nanomaterials demonstrate a substantial enhancement in bonding strength, hardness, and durability. their ability to cure quickly is extremely beneficial in businesses that require fast manufacturing procedures. in addition, the process of nano-structuring improves the ability of these adhesives to withstand harsh chemicals and high temperatures, thereby making them well-suited for challenging settings and maximizing their performance for specific industrial uses. 3.6. nano-based adhesives in aerospace the aerospace sector actively utilizes nano-based adhesives because of their exceptional tensile features, including fatigue resistance and improved mechanical properties. nonetheless, the effectiveness of their performance in aircraft and space flight applications is heavily influenced by the specific nanoparticles or fillers utilized, their dimensionality, and the fabrication procedures applied. carbon fibers have been integrated into adhesive epoxy matrices to provide lightweight and specialized structural materials that are specifically designed for modern spacecraft. these materials have demonstrated their suitability for use in aircraft applications (table 2). the utilization of nanoparticles of various shapes, including planar, tubular, and spherical, in adhesives is a novel method for improving the characteristics of adhesive connections in contemporary airplanes [33]. characterization and application of nanomaterials 2025, 8(2), 10834. 8 table 2. potential application of nanoparticles in aerospace engineering. industry nanoparticles nanoparticle-based conventional product/potential area of application aerospace engineering carbon nanotubes graphene nano clay metal nanoparticles (e.g., silver, gold) ceramic nanoparticles (e.g., silica, alumina) composite materials: create lightweight, high-strength composites for structural components. coatings: provide corrosion resistance, thermal protection, and reduced friction. energy storage: batteries and supercapacitors to improve energy density and power. propulsion: fuel additives, propulsion systems, and rocket engines. sensors: detecting temperature, pressure, and chemical changes. self-healing materials: create materials that can self-heal cracks and damages. thermal management: improve heat transfer and thermal management in aerospace systems. radiation protection: create lightweight radiation shielding materials. 3.7. the futuristic nano-based adhesives due to current progress in manufacturing, adhesives are constantly enhancing, and the integration of nanoparticles is providing important characteristics. the present emphasis is on employing ecologically sustainable techniques to improve contemporary adhesives. research in the field of bio-based adhesives enhanced with nanofillers is showing great potential. continued advancements are anticipated in the realm of nano-based adhesives. 3.8. magnetic fluids the topic of magnetic soft materials is a rapidly growing interdisciplinary scientific discipline that has developed in the past several decades. the tasks largely involve condensed matter physics, magnetism, magnetic hydrodynamics, inorganic and organic chemistry, colloid chemistry, computational and computer modeling, acoustics, engineering, and applied sciences. magnetically soft materials include magnetic fluids, magnetic elastomers, and magnetic gels that contain magnetic nanoparticles. these materials can be modified by adding different types of magnetic or non-magnetic substances. traditionally, magnetic fluids (mfs) were at the forefront, consisting of a colloidal system where nanoparticles coated with magnetic material were dispersed in a liquid medium. the magnetic fluid contains single-domain superparamagnetic nanoparticles, which are typically approximately 10 nm in size. the early materials mentioned here are recognized as the forerunners of intelligent nano-dispersed materials [34,35]. these materials have been extensively studied in scientific literature [36–38] and are used in a wide range of devices and technologies [39–42]. magnetic fluid possesses a distinctive blend of fluidity and the capacity to react to an external magnetic field. as a result, it has been used in seals [40], controlled shock absorbers [39], diverse sensors [41], and acoustic systems [42]. the significant advancements in nanotechnology and the capacity to create materials and structures have allowed for the development of magnetic fluids as multiphase systems. in this particular situation, magnetic nanoparticles work as separate components with a regulated arrangement that can experience modifications on their surface with the help of particular surfactants. these modifications allow them to engage preferentially with specific biological entities or organic molecules [43]. characterization and application of nanomaterials 2025, 8(2), 10834. 9 a nano-dispersive magnetic fluid is a colloidal system consisting of magnetic nanoparticles (mnps) with diameters ranging from 5 to 20 nm. the mnps are covered with a stabilizing shell of a surfactant dispersed within a liquid carrier. investigation and academic curiosity surrounding nano-disperse magnetic fluids article [44] provides a comprehensive explanation of the mechanism by which stable colloids are created from magnetic nanoparticles, which usually have a diameter of approximately 10 nm or greater. the name “magnetic fluids” was initially used to refer to these colloids [44], and their dynamics were referred to as ferrohydrodynamics [45]. magnetic fluids are distinct materials that are artificially produced. magnetostatic bacteria can detect magnetic nanoparticles (mnps) [46], but there are currently no stable liquid systems that display ferromagnetic characteristics. during the early 19th century, renowned physicists michael faraday and thomas j. seebeck conducted research on the behavior of magnetic dust when subjected to external magnetic fields [47]. the system under investigation was characterized by instability and exhibited rapid settling. elmore subsequently conducted measurements of the magnetization curves of micro-sized particles that were scattered in a carrier liquid [48]. the synthesis of magnetic fluids, as now investigated, originated in the united states approximately 60 years ago [34]. they were recognized as groundbreaking artificial nano-dispersed material and became the focus of scientific investigation [35]. magnetic fluids have been utilized in much technical equipment [35,49,50], even before the word ‘nanotechnology’ was coined [51]. nanotechnology has been evolving over the past 15 years, sparking renewed interest in magnetic fluids. researchers have started viewing magnetic fluid from a different perspective. currently, magnetic fluid is recognized as a multiphase system where magnetic nanoparticles exist as distinct elements with controlled structures and properties. magnetic fluid and magnetic nanoparticles find numerous applications, particularly magnetic fluid and magnetic nanoparticles find numerous applications, particularly in the field of biomedicine [52–54]. these particles serve as contrast agents in magnetic resonance imaging [55,56]. researchers are actively investigating interactions between particles, the formation of chain aggregates and flexible clusters, and the impact of the microstructure on the macroscopic properties of magnetic fluid through both experimental and theoretical studies [57,58]. the development of magneto-fluidic systems has made it possible to significantly alter viscosity under the influence of an external magnetic field, showcasing a giant magneto-viscous effect. presently, the exploration of magneto-fluidic systems constitutes a multidisciplinary field, encompassing condensed matter physics, magnetism, hydrodynamics, inorganic and organic chemistry, colloidal chemistry, computational and computer modeling, acoustics, engineering, and applied sciences. positive anisotropic mnps are achieved through extensive efforts in refining production methods that control the material, size, shape, structure, and modification of the mnp surface [59–61]. 4. nanoengineered materials for the engineering industry table 3 describes the potential application of nanoparticle mechanical engineering. characterization and application of nanomaterials 2025, 8(2), 10834. 10 table 3. potential application of nanoparticles mechanical engineering. industry nanoparticles application nanoparticle-based traditional product/potential area of application mechanical engineering titanium dioxide (tio2) zinc oxide (zno) iron oxide (fe2o3) carbon nanotubes (cnts) graphene silver (ag) gold (au) water treatment plants air pollution control systems soil remediation sites wastewater treatment plants environmental monitoring systems water treatment: • nanoscale’s water treatment systems (nanoscale corporation) • nanostellar’s water treatment catalysts (nanostellar inc.) • altair’s water treatment membranes (altair nanotechnologies inc.) air pollution control: • nanohmics’ air pollution control systems (nanohmics inc.) • nanoscale’s air pollution control catalysts (nanoscale corporation) • komatsu’s air pollution control filters (komatsu ltd.) soil remediation: • nano remediation’s soil remediation systems (nano remediation inc.) • nanostellar’s soil remediation catalysts (nanostellar inc.) • altair’s soil remediation membranes (altair nanotechnologies inc.) wastewater treatment: • nanoscale’s wastewater treatment systems (nanoscale corporation) • nanostellar’s wastewater treatment catalysts (nanostellar inc.) • nanohmics’ wastewater treatment membranes (nanohmics inc.) environmental monitoring: • nano sensor’s environmental monitoring systems (nano sensor inc.) • nanostellar’s environmental monitoring sensors (nanostellar inc.) • altair’s environmental monitoring membranes (altair nanotechnologies inc.) 4.1. wear protection for tools and machines nanocoating for external protection and building in addition to acting as corrosion inhibitors for reinforced steel, nanomaterials are especially well suited to shield the surfaces of many building materials, including glass, concrete, sand, limestone, and marble, from environmental factors like water staining, moss, and algae as well as soot and oil stains. commercially available paints and surface coatings produce a low-energy face, making a building’s surface extremely hydro and oleophobic, extending maintenance cycles and requiring less cleaning. the most common uses in the building and external protection sectors are photocatalytic coatings and dirt-repellent protective paints. building upkeep is greatly hampered by dirt collection (buildup) on building exteriors. typically, high-pressure water jets, scrubbing, wiping, and detergents are used to clean these types of building surfaces. these procedures have several drawbacks, including the need for chemical detergents, significant energy use, and labor costs. high maintenance costs follow naturally from this, which is why an efficient self-cleaning coating is preferred. anti-fouling and easily cleanable coatings are manufactured by several major international corporations, such as evonik degussa, dupont, schott, 3m, and corning, for a range of applications. characterization and application of nanomaterials 2025, 8(2), 10834. 11 recently, photocatalytic self-cleaning coatings have been developed. titanium dioxide (tio2) has drawn a lot of interest from the industry. tio2 has two special qualities that it can achieve with the help of minimal uv light from a fluorescence source or sunshine. • strong oxidation power, and, • super hydrophilicity. strong oxidation power can be utilized to eliminate odors from toilet stains and kill microorganisms that have attached themselves to the wall (commercially available products include tio2-coated glass and tile). when a coating of this kind is put on external surfaces, its superhydrophilic qualities facilitate the easy removal of dirt and stains with water or sunlight. because nanoparticle tio2 self-cleaning coatings eliminate the need for expensive surface cleaning, they are especially beneficial for skyscraper maintenance. by lowering the quantity of volatile organic compounds and other hazardous chemicals that people are exposed to in hotels, restaurants, commercial buildings, university laboratories, hospitals, and homes, photocatalyst coatings are also used to enhance indoor air quality. because of their non-stick qualities, nano coatings make surfaces both inside and outside less stained and easier to clean. because of their anti-graffiti qualities, stains like graffiti that formerly required thorough cleaning can be removed with a high-pressure hose. table 4. potential application of nanoparticles biomedical engineering. industry nanoparticles application area nanoparticle-based traditional products/potential area of application biomedical engineering liposomes polymeric nanoparticles (e.g., plga, peg) metallic nanoparticles (e.g., gold, silver, iron oxide) ceramic nanoparticles (e.g., silica, alumina) quantum dots carbon nanotubes graphene oxide cancer diagnosis and treatment neurological disorders (e.g., alzheimer’s, parkinson’s) cardiovascular disease infectious diseases (e.g., hiv, tuberculosis) ophthalmic applications (e.g., glaucoma, age-related macular degeneration) drug delivery systems: to release drugs in a controlled manner, reducing side effects and improving efficacy. diagnostic imaging: as contrast agents for mri, ct, and pet scans, improving image resolution and accuracy. biosensors: to detect biomarkers for diseases, such as cancer, diabetes, and infectious diseases. tissue engineering: to create scaffolds for tissue regeneration and repair. wound healing: to create dressings that promote wound healing and tissue repair. implantable devices: to improve the biocompatibility and functionality of implantable devices, such as pacemakers and prosthetics. cancer treatment: to deliver chemotherapy directly to cancer cells, reducing side effects and improving efficacy. commercially available are water-based, volatile organic compound (voc)-free, transparent impregnating nanoparticle wood coatings with nanoscale uv absorbers. they offer enhanced water repellence, lower efflorescence, and noticeably better abrasion resistance. they are intended for use on masonry and concrete surfaces. new and creative coating applications are mostly driven by nanotechnology, and nanocoatings have seen significant growth in the last several years. high transparency, novel features, and high-quality performance are becoming more and more crucial needs in the coatings industry. however, protection from ice, pollutants, uv light, fire, heat, bacteria, marine life, touch, and corrosion is the main benefit that nanostructured coatings offer. these elements can be extremely dangerous to the public’s health and cost the worldwide industry billions of dollars in lost production, maintenance, and characterization and application of nanomaterials 2025, 8(2), 10834. 12 downtime annually. for instance, worldwide, direct corrosion expenses represent 3%– 4% of a nation’s gdp. extraordinary attributes nanostructured surfaces, thin films, and nanoscale coatings are extensively used in several industry domains and serve as excellent illustrations of how nanotechnology may advance, upend, or even create new technology sectors. in the medium to long term, nano-coating is more cost-effective than standard coatings and exhibits notable performance advantages. some applications of nanoparticles biomedical engineering is mentioned in table 4. nanostructured materials significantly improve a variety of properties, including antimicrobial, product longevity, heat insulation, gloss retention, dirt and water repellency, hardness, corrosion resistance, flame retardancy, stability against ultraviolet radiation, improved energy efficiency, anti-graffiti, self-cleaning, moisture absorbing, gloss retention, and chemical and mechanical properties. primary markets for coatings with nanostructures are: • medical supplies (both long-term and short-term reusables). • producing food, leather and textiles. • coatings for marine use. • treatment of water. • taking care of the home. • building. • transport/automobile. • engineering & tools. • energy. 4.2. lubricant-free bearings nanoparticles can be particularly useful as lubricating additives in lowering friction and preventing wear. the tribological characteristics of tio2 nanoparticles are good [62–67]. to comprehensively investigate the impact of particle size and shape on friction qualities, hwang and kalyani dispersed different carbon-based particles in mineral oil [68,69]. numerous organic substances, including oxygen, nitrogen, sulfur, halogens, phosphorus, and sulfur, have been employed as anti-wear additives. under lubricating circumstances, additives containing active elements are adsorbed on the metal’s contact surface and form a tribochemical film. by lowering wear and friction, kalyani, zhou, and tomala increased machine efficiency [70–72]. to reduce wear and friction under boundary lubrication conditions, rabaso and rapoport incorporated inorganic fullerene (if) nanoparticles into their lubricants [73,74]. pena-paras investigated the impact of al2o3 and cuo nanoparticles on the load capacity and tribological characteristics of the gl4 and pao 8 oils, respectively [75]. according to liu’s investigation of the mending properties of copper nanoparticles on contact surfaces, these particles indeed exhibit a very good mending effect [76]. lee discovered that the lubrication enhancement of nano-oil was greatly enhanced by nanoparticles distributed in the mineral oil; the friction coefficient of the disc specimen submerged in the nano-oil was significantly lower than that of the disc specimen submerged in the mineral oil [77]. hu produced the nanoparticles and carried out the experiment; the outcomes demonstrated that the addition of nanoparticles characterization and application of nanomaterials 2025, 8(2), 10834. 13 enhanced the 500 sn base oil’s wear resistance and load-carrying capability while lowering its coefficient of friction [78]. researchers have found sio2 to be a valuable common nanoparticle due to its superior controllability, dispersion, and confined distribution range. the tribological characteristics and anti-wear mechanism of water-based lubricants containing sio2 nanoparticles were studied by wang and zhu [79,80]. however, the relationship between surface roughness and nanoparticles has not been thoroughly examined. peng’s objective was to investigate the tribological characteristics of liquid paraffin, including sio2 nanoparticles as additives. the findings suggest that liquid paraffin containing appropriate quantities of sio2 nanoparticles exhibits superior tribological qualities in comparison to pure paraffin oil [81]. 5. nanoengineered materials for electronic industry electronic paper, field emission displays (feds), organic leds (oleds), and electronic devices are the three main types of display technologies, which are the visual devices used to display digital information, images, and videos (table 5). table 5. potential application of nanoparticle electronics engineering. industry nanoparticles application area nanoparticle-based traditional product/potential area of application electronics engineering silver gold copper carbon nanotubes graphene cadmium selenide zinc oxide titanium dioxide smartphones laptops tablets smartwatches televisions solar panels energy storage systems conductive inks: • dupont’s silver nanoparticle ink (dupont) • cabot’s silver nanoparticle ink (cabot corporation) • nanograde’s copper nanoparticle ink (nanograde ltd.) displays: • samsung’s quantum dot technology (samsung electronics) • lg’s nano cell technology (lg electronics) • nanosys’ quantum dot technology (nanosys inc.) solar cells: • nanosolar’s solar cells (nanosolar inc.) • solarmer’s solar cells (solarmer energy inc.) • nanoco’s quantum dot solar cells (nanoco group plc) memory devices: • micron’s phase change memory (micron technology inc.) • samsung’s phase change memory (samsung electronics) • intel’s phase change memory (intel corporation) sensors: • sensirion’s gas sensors (sensirion ag) • abb’s temperature sensors (abb ltd.) • nanosensor’s biosensors (nanosensor inc.) energy storage: • tesla’s battery electrodes (tesla inc.) • lg chem’s battery electrodes (lg chem ltd.) • nanotech’s battery electrodes (nanotech industries inc.) thermal management: • nanocool’s thermal interface materials (nanocool inc.) • indium’s thermal interface materials (indium corporation) • nanotherm’s thermal interface materials (nanotherm ltd.) printed circuit boards: • dupont’s conductive inks for pcbs (dupont) • fujikura’s conductive inks for pcbs (fujikura ltd.) • nanograde’s conductive inks for pcbs (nanograde ltd.) semiconductors: • intel’s transistors • ibm’s transistors characterization and application of nanomaterials 2025, 8(2), 10834. 14 more sophisticated, superior, and energy-efficient displays are made possible by the research and manufacturing of display technologies, which heavily rely on nanotechnology. through careful engineering of materials at the nanoscale, scientists and engineers can attain enhanced performance and novel capabilities that are unattainable with traditional materials and production techniques. one kind of display technology that produces light using organic materials is called an organic led. oleds are perfect for televisions, mobile devices, and other applications because they are thin, flexible, and have great contrast, quick response times, and wide viewing angles. nanotechnology is employed to develop the organic materials in oled displays that make images and emit light. organic materials at the nanoscale are carefully designed to release light when an electric current is applied. e-paper, or electronic paper, is a term for a kind of display technology that simulates the look of regular ink on paper. because they are high contrast, low power consumption, and reflective, e-paper displays are perfect for wearable technology, digital signage, and e-readers, among other applications. to create electronic inks for e-paper displays, nanotechnology is employed. these inks can show text and images because they contain nanoparticles that, when exposed to an electric field, can change color. a sort of display technology called field emission displays (feds) employs electron emitters to produce images on a screen. feds are the perfect choice for applications like projectors and large screen displays since they are light, thin, and have high brightness, quick reaction times, and wide viewing angles. nanotechnology is utilized in field emission displays to construct the electron emitters that generate images. all things considered, display technologies have advanced significantly in recent years and are still developing, giving consumers a wider variety of choices for visual display. 5.1. advanced olets and oleds organic light-emitting diodes, or oleds, hold great potential for a variety of useful uses. oled technology is already utilized in small electronic device displays found in digital cameras, mp3 players, mobile phones, and some tv screens. it is based on the phenomenon that some organic materials generate light when fed by an electric current. large-scale organic solar cells, windows that might be utilized as nighttime light sources, and ultra-flat, extremely bright, and power-saving oled televisions are all achievable with more affordable and efficient oled technology. an oled’s emissive electroluminescent layer is made up of a thin layer of organic chemicals, as opposed to ordinary leds. oleds are very appealing since they don’t need a backlight, which means they use less electricity to run. moreover, because they’re thinner than similar leds, they can be printed on nearly any surface. nanomaterials and nanofabrication techniques are applied in the production of oleds in two areas: transparent electrodes (where thin-film carbon nanotubes are becoming more and more popular) and coatings based on nanoparticles that are used to pack oleds to protect them from environmental damages (such water). techniques for depositing materials based on nanoparticles may also be able to tackle unresolved characterization and application of nanomaterials 2025, 8(2), 10834. 15 problems with oled manufacture, such as material damage, yield, and thickness uniformity. furthermore, a completely new design for oleds with a transparent conductor made of a few manometers of graphene has just been devised by researchers. this made it possible to produce oleds in big quantities at minimal cost on flexible plastic substrates that could be virtually put anywhere and rolled up like wallpaper. however, photon loss and exciton quenching still restrict the brightness and efficiency of oleds. organic light-emitting transistors (olets) are substitute planar light sources that integrate an electroluminescent device’s and a thin-film transistor’s switching mechanism into a single architecture. olets therefore have the potential to usher in a new age in organic optoelectronics and act as experimental platforms for addressing broader basic optoelectronic and photonic problems. 5.2. quantum dot leds, or qleds one of the most promising optoelectronic materials, quantum dots (qds), will be at the heart of next-generation displays due to their unique physical features and ability to be both photoactive (photoluminescent) and electroactive (electroluminescent). qd-based materials have cheaper manufacturing costs, longer lifetimes, purer hues, and lower power consumption than organic luminescent materials used in organic light-emitting diodes (oleds). because qds can be deposited on almost any substrate, you may expect printable, flexible, and even rollable displays of all sizes. this is another important benefit of quantum dot displays. an example of a passive matrix quantum dot light-emitting diode (qled) display that is fully integrated with flexible electronics has been demonstrated by researchers. 5.3. digital paper electronic paper reflects light like regular paper and can keep text and images endlessly without draining electricity, unlike standard flat panel displays that utilize a power-hungry backlight to illuminate their pixels. it also allows for image modification afterward. electrophoretic displays are regarded as leading instances of the electronic paper category because of their ability to be manufactured on thin, flexible substrates and because of the way they resemble paper. there are currently commercially available electrophoretic displays, such as those found in the sony reader and kindle; however, they are primarily black and white at this time. color displays continue to have problems with quality and pricing. researchers studying nanotechnology have demonstrated that organic ink nanoparticles may be able to improve the process of making electronic ink, leading to the production of e-paper with better brightness, a better contrast ratio, and a more affordable manufacturing cost. 5.4. field-based emission displays to develop a new type of vast area, high-resolution, low-cost flat panel displays, researchers have resorted to carbon nanotubes. some predict that the largest challenge to lcd’s hegemony in the panel display market will come from field emission display characterization and application of nanomaterials 2025, 8(2), 10834. 16 (fed) technology, which uses carbon nanotubes (cnt) as an electron emitter. fed is also the preferred technology for ultra-high-resolution, wide-screen televisions. feds can be thought of as a cross between liquid crystal displays (lcd) and cathode ray tube (crt) televisions. by combining the dot matrix cellular structure of lcds with the proven cathode-anode-phosphor technology found in full-sized crts, they profit from this technology. to produce colored light, the grid-mounted electron emitters are individually controlled by “cold” cathodes (in contrast to regular crts, which boil off electrons by heating the cathode). the narrow panel of today’s lcd is made feasible by field emission display technology, which also gives a broader field of view, great image quality comparable to that of crt displays, and lower power consumption. 5.5. optical switch the development of an ultra-fast and ultra-small optical switch could hasten the day when photons take the place of electrons in consumer goods like cell phones and cars. trillions of times every second, the new optical technology may be turned on and off. it is made up of discrete switches with diameters of just 200 nanometers, or onefifth the width of a human hair. this size is significantly smaller than the optical switches of the current generation, and it readily overcomes one of the main technological obstacles to the widespread use of light-detecting and light-controlling electrical devices: the shrinking of ultrafast optical switch sizes. a manmade substance with features not seen in nature is used to make the ultrafast switch. in this instance, the “metamaterial” is made up of nanoscale vanadium dioxide (vo2) particles, which are coated with a “nanomesh” of minute gold nanoparticles and deposited on a glass substrate. vo2 is a crystalline solid that can rapidly transition between an opaque, metallic phase and a transparent, semiconducting phase. the vanadium dioxide undergoes a phase change in a few trillionths of a second when hot electrons from an ultrafast laser are briefly exposed to the gold nanomesh. this process is attributed to the scientists. 5.6. filters (ir-blocking) preventing infrared radiation from affecting a detector’s performance is crucial. metal-mesh infrared-blocking filters have been developed as a highly efficient solution to overcome this problem for superconducting tunnel junction particle detectors. one of the better structures in this type is formed by freestanding cr/cu films that are 590 nm thick, a tiny membrane, and a sequence of circular holes that have a diameter of roughly 2 µm. a transmission of 300 k radiation is just 1%, according to the data transmission efficiency. from an alternative perspective, the ion transmission efficiency is close to 20%, which is consistent with values that are predicted geometrically. because they can simultaneously analyze and elucidate ion charge states and mass values through kinetic energy measurement, superconducting particle detectors are thought to be extremely advantageous for mass spectrometry applications. this is not possible with traditional ion detectors like ion multipliers or microchannel plates. the quality of shielding radiation is essentially the main technology in mass spectroscopy using a cryogenic particle detector. in particular, characterization and application of nanomaterials 2025, 8(2), 10834. 17 until atoms or molecules may be received on the detector, there must be an open chamber for a flight path. as a result, when operating in a linear mode, the detector under cryogenic circumstances is exposed to 300,000 blackbody radiation throughout the flight. as a result, in the absence of radiation protection measures, the performance of cryogenic detectors based on superconducting materials is significantly impacted [82]. 5.7. antistatic and conductive coatings using advances in plastic anti-static coatings, ocsial created a concentrated graphene nanotube that offers thermoplastics-specific conductivity for electrostatic painting, allowing automakers to reduce costs by streamlining the painting procedure. the powder coatings created by erie powder coatings in canada utilizing tuball graphene nanotubes from ocsial are an additional illustration of an efficient antistatic coating for plastic materials. these coatings exhibit high resistance, conductivity, and static dissipative qualities, which eventually improve aesthetic performance. taking a closer look at anti-static coatings and additives for resins, anti-static resin flooring commonly seen in workplaces and factories, serves as an example. to prevent esd, an anti-static resin coating is added to the flooring, which either inhibits or redirects electrical charges or produces no electrical charge at all. this eventually saves lives and is crucial in industry, especially in settings where volatile materials are used. rubber anti-static matting and sheeting used in the electronics sector and the flooring business are two examples of industrial anti-static agents. because graphene nanotubes may function at low working dosages while maintaining or enhancing the characteristics of rubber, they hold considerable promise as anti-static agents. the use of single-walled carbon nanotubes in static control flooring has several advantages, including increased quality and cost-effectiveness. moreover, because they occupy less space in the coating, more materials with even more desirable qualities can be applied. 6. nanoengineered materials for the construction industry the construction sector is attracted to the remarkable features and characteristics of these materials. although they are modest in size, they are well recognized and esteemed for their extremely commendable qualities in practically every domain nowadays. nanomaterials are being extensively utilized in the construction industry, alongside other fields. they not only assist in the construction operations but also serve as a means of eliminating the spread of toxicity that occurs thereafter. nanografi enhances the characteristics of construction materials by using nanotechnology, hence advancing the creation of cutting-edge materials. the features of nanomaterials are exceptionally distinctive, encompassing both their physical and chemical characteristics. the materials at large and tiny scales exhibit significant differences due to the challenges faced by particles of such sizes in identifying their physical and chemical properties. the key factors include the obvious features such as the shape, size, surface qualities, and inner structure. they can also be referred to as aerosols, which encompass both solids and liquids suspended in the characterization and application of nanomaterials 2025, 8(2), 10834. 18 air. additionally, they can be described as suspensions, indicating the presence of particles in liquids, and emulsions, which are mixtures of liquids. by introducing other substances, the characteristics of these materials can be modified and potentially impeded by certain deviations. creating a single nanoparticle requires a high level of intricacy, making the process of assembling one quite challenging. the interaction or combination of chemicals or particles is determined by their specific properties. the chemical processes they are involved in are mostly unknown due to their complexity and the need for meticulous attention and keen observations. nanomaterials exhibit a wide range of distinct modes of interaction, both among themselves and with other substances. the decision to live freely or in groups lies entirely with them, contingent upon the nature of the forces acting upon them, which can be either enticing or repellent. characterizing them is challenging due to their intricate relationships and the presence of dynamic factors. an inherent characteristic of nanomaterials is their ability to maintain a stacked arrangement when suspended in a gas, as opposed to when they are in a liquid form. 6.1. applications of nanomaterials in the construction sector nanomaterials have made significant inroads into the construction industry, resulting in a profound transformation of products, services, and sectors, including construction. recording the effects or impacts that they have on the environment and humans is of utmost importance. the potential application of nanoparticles in civil engineering is shown in table 6. table 6. potential application of nanoparticles civil engineering. industry nanoparticles application area nanoparticle-based traditional product/potential area of application civil engineering nano-silica nano-alumina nano-titania nano-iron oxide carbon nanotubes graphene oxide nano-clay buildings and bridges highways and pavements water treatment plants dams and canals environmental remediation geotechnical engineering structural health monitoring nanocrete: a concrete additive that improves strength and durability. nano-sealants: sealants that use nanoparticles to provide improved water resistance and durability. durabuild: a coating that protects concrete from corrosion and degradation. nanoguard: treatment that improves the durability of asphalt pavements. smartcoat: coating that provides self-healing properties for concrete structures. nanocem: a cement additive that improves strength and sustainability. aquashield: a water treatment system that removes contaminants and improves water quality. nanosensors: sensors that monitor structural health and detect environmental changes. ecopave: an asphalt additive that improves durability and reduces environmental impact. nanocon: a concrete additive that improves strength and reduces shrinkage. nanomaterials offer numerous advantages to the construction industry, and their remarkable ability to safeguard the ecosystem is remarkable. nanomaterials possess a very small size, which enhances their performance in various areas such as catalysis, characterization and application of nanomaterials 2025, 8(2), 10834. 19 conductivity, magnetism, mechanical strength, and optical sensitivity. these properties contribute to a diverse variety of applications and are highly suitable for use in the construction sector and its associated operations. hardened mixture of cement, sand, and water used in construction. concrete is one of the many applications of nanomaterials in the realm of building. concrete exhibits the largest annual production among all other materials, mostly due to the incorporation of carbon nanotubes (cnts) and nanosized sio2. these additives significantly improve the concrete mixture, including both the binding phase and the aggregates. concrete contains a significant quantity of nanoparticles, which enhances its suitability for use in the building industry. although their weightage is rather little, the collective impact of all the nanomaterials significantly influences the overall criterion and the scenario itself [83,84]. steel is a versatile material that is commonly utilized in the construction industry for building structures and bridges. these encounter hurdles in terms of strength, resistance, and formability. this is attributed to their incorporation into the realm of metal nanoparticles (nps). in addition, copper particles are utilized to reduce surface roughness, hence enhancing anti-corrosion properties. transparent material is used to cover openings in buildings, allowing light to enter while keeping out the elements. window glass, like concrete and steel, can serve several purposes when tio2 and sio2 nanoparticles are added. by applying a photochemical method, tio2 nanoparticles can be coated onto windows. this coating enables the nanoparticles to effectively react with sunshine and indoor light, resulting in the elimination of dirt and bacterial films, if present. the silica layers or sheets, in the form of nanoparticles, are utilized to make windows fireproof and are quite reliable. the extensive promotion of nanoparticles is attributed to their properties and many factors [85]. reducing the impact on the environment: while there are certainly advantages, it is important to acknowledge that there are also potential negative consequences associated with the products and materials employed in this particular industry. nevertheless, nanoparticles exist in the form of nano-electromechanical and microelectromechanical systems (nems and mems). these sensors are composed of either nanoor micro-sized materials, which have recently received significant interest. nanomaterials are extensively employed to safeguard both the environment and humans from potential harm resulting from excessive use. it is worth noting that nanomaterials themselves serve as a protective measure to mitigate adverse environmental effects. 6.2. nanomaterial-enriched concrete common nanomaterials used in concrete to improve density, strength, and ultimately fire resistance include silica, titanium dioxide, iron oxide, and carbon nanotubes [86–88]. concrete is made denser and less porous by adding silica particles to fill the spaces between the cement grains. increased mechanical strength is the outcome of this [88]. silica fume and nano-silica, sometimes referred to as “fumed silica”, are the two forms of nanoparticles used in concrete [89]. concrete that is selfcleaning and toxin-free can benefit from the use of nanosized titanium dioxide [87]. characterization and application of nanomaterials 2025, 8(2), 10834. 20 abrasion resistance and compressive strength can be increased by using iron oxide nanoparticles [88]. it has been determined that the presence of carbon nanotubes (cnts) in concrete can result in robust, electrically conductive, and self-healing concrete [87]. the use of nanomaterials to help with post-fire curing of concrete that improves the capability to recover strength post-fire event [90,91] is a novel and promising development in nanotechnology in concrete. using carbon nanotubes or carbon black nanoparticles, these nanoparticles can impart self-sensing properties that have implications for better assessing a building’s structural safety during or after a fire [92–94]. 6.3. advanced glass and windows glass can have its insulating, self-cleaning, and fire-resistant qualities enhanced by a nanomaterial layer [86,87]. another kind of nanomodified material is fire safety glass, which forms an intumescent layer between two glass plates and can offer high levels of fire protection by utilizing either nano-silica or silica fume [86,87]. the intumescent layer offers a high degree of integrity and insulation during a fire by expanding and becoming opaque. for more than 30 years, this kind of glass has been available, although mostly for applications requiring a high degree of thermal insulation, including escape routes [86]. 6.4. nanomaterials for insulation aerogels based on silica are excellent thermal insulators that can be utilized in vacuum-insulated panels, translucent windows, and insulation blankets [89]. these materials are not commonly utilized and are expensive to produce [86,87]. one more thing preventing them from being widely used is their low mechanical strength [95]. however, as demand for energy-efficient building materials rises, costs may be lowered with better production techniques and scale. although the application of nanotechnology as an insulator depends on its capacity to lower the thermal conductivity of the building material, some applications of nanomaterials in construction may raise thermal conductivity, which could be dangerous in the event of fire protection unless the material composite additionally possesses fire-retardant qualities. 6.5. advanced steel steel can have nanomaterials integrated into its construction or applied as a nanocoating. the use of coatings and nanocomposite polymers on steel structures can lower the warmth and enhance fire resistance [96]. through the process of refining materials to the nanoscale and eliminating impurities such as carbides, steel is enhanced in strength, corrosion resistance, and tensile strength, which can reach 100 times that of regular steel [96]. according to manufacturers, employing nanomaterial in steel is more cost-effective and equally effective than using stainless steel. more efficient than more conventional techniques for shielding steel against corrosion, like coated with epoxy [86]. steel constructions lose some of their strength and stiffness when exposed to high temperatures. structural steelwork typically needs fire-resistant materials, such as cement-based sprays, boards, batt materials, and intumescent coatings, to protect characterization and application of nanomaterials 2025, 8(2), 10834. 21 occupants and minimize loss; however, steel coatings often lose their endurance [97]. nanomaterials with good fire resistance can be achieved with structural steel [97,98]. when a structure reaches a critical temperature in a fire, it may collapse. better steel integrity can guarantee the integrity of the structure both during and after a fire, making it safer for rescue personnel. this would offer inhabitants more time to leave during a fire and cause less harm to property. 6.6. nano-coated wood in north america, wood is the most often used building material for residential construction and one of the most extensively used building materials overall. as a building material, timber has excellent mechanical qualities, and if forest resources are maintained well, they can be an endless renewable supply with the capacity to store atmospheric carbon for lengthy times if the lifespan of timber goods is prolonged [99]. nevertheless, wood is a little more durable and fireproof than non-renewable building materials like steel and concrete. untreated wood burns quite easily. building standards restrict the use of wood in residential buildings because, unless it is coated with fire-resistant materials, it has a low fire resistance. conventional chemical fire retardants can be used to increase fire resistance. still, conventional fire-resistant coatings can release harmful gas [100]. the substances are connected with dangers to the environment and human health, and they are less effective than nanomaterials found in wood composites or nanocoatings consisting of sio2 and tio2 oxides and nanoclay [101]. better technologies are required because most fire-retardant coatings are not very resistant to weathering and environmental influences [102]. the app/per/ma intumescent method for wood discovered is the most dependable and financially feasible, and evidence suggests it could be improved with the production of nano clay, nanostructured carbon [100], or amorphous silicon dioxide. researchers have developed nano-coatings that can offer fire-resistant qualities without endangering human health, and they are working on nanotechnology wood coatings that have bestowed on wood fire-resistant qualities [103–107]. one intriguing breakthrough in a wood structure fire safety measure is the hydrothermal synthesis of mnfe2o4 onto the wooden surface, producing an electromagnetic wave-absorbing and fire-resistant layer covering [108]. from a safety standpoint, this could be a good alternative because manganese ferrite is already used in medications based on nanoparticles and is soluble, meaning it won’t stay in the respiratory system if ingested, and there’s proof that the body can get rid of it without harming any organs [109]. the application of an environmentally friendly polyelectrolyte complex that gives wood self-extinguishing and fire resistance when coated is another intriguing, advanced behavior, a longer igniting period, and a lower peak heat release rate [110]. this layer enhanced the wood’s strength as well. these prospective innovations in building materials could have a significant positive impact on society by making wood more fire-resistant, which can save financial loss and avoid injuries and fatalities. in all things considered, using nanoparticles in wood construction can make fire-resistant building materials better and more sustainable, but further study is required to fully comprehend their lifetime and toxicological consequences. characterization and application of nanomaterials 2025, 8(2), 10834. 22 6.7. nanocomposites and nanocoating in architectural materials a variety of architectural materials can be coated with nano-coatings. they create an intumescent coating on drywall and paint. the intumescent layer charges when it comes into contact with heat. because char is a poor conductor, it provides better fire protection for the substance behind it, acting as a fire retardant. it was discovered that adding nanoand micron-sized boron nitride (bn) as fillers to fire-resistant coatings improved the coatings’ thermal stability, particularly at high temperatures [111]. wang et al. [98] compared the expanding and char structure of organic and inorganic intumescent coatings and discovered that while organic intumescent coatings produce smoke and solvent-toxic gas during a fire, they also have a good expanding effect. inorganic intumescent coatings, like salt silicate coatings, have low levels of smoke and harmful gas emissions during application. they also don’t produce organic solvents when heated. nevertheless, only at low temperatures do inorganic intumescent coatings provide fire protection and are susceptible to moisture [95]. further investigation is required to comprehend the life cycle of the product and the toxicological consequences of nanocoating [112]. the use of nano-coating materials has farreaching consequences. the usage of nanocomposites, like nanoclay, can strengthen construction materials and help in resistance against fire. nanoclays have use in coatings and as construction material composites. the advantages of construction materials’ strength and density have risen thanks to nanoclays [113]. although there are currently no goods available for use in building, nanoclays can be synthetic or naturally occurring, created with layers of silicate-based materials, and employed in polymers to improve functioning in various ways [89]. if nano clay brick is put into the construction material market, it could have a significant positive impact on fire safety [87]. 7. nanoengineered materials for textile/non-woven industry nanotechnology possesses significant commercial possibilities for the textile sector. this is mostly due to the fact that traditional techniques employed to bestow various features on fabrics sometimes fail to provide lasting results and tend to lose their functionality after laundering or use [114]. nanotechnology enhances fabric durability due to nanoparticles’ substantial surface area-to-volume ratio and elevated surface energy, resulting in improved affinity for fabrics and increased functional longevity. furthermore, the use of a nanoparticle coating on textiles will not compromise their breathability or tactile quality. consequently, the interest in employing nanotechnologies within the textile business is on the rise. coating is a prevalent method employed to deposit nanoparticles onto fabrics. various techniques can be employed to impart coatings onto fabrics, including spraying, transfer printing, washing, rinsing, and padding. among these strategies, padding is the most frequently employed. nanotechnology bestows textiles with attributes such as water repellence, soil resistance, wrinkle resistance, antibacterial qualities, anti-static characteristics, uv protection, flame retardancy, and enhanced dyeability, among others. this paper characterization and application of nanomaterials 2025, 8(2), 10834. 23 emphasizes some notable qualities conferred by nano-treatment in the textile sector, amidst the diverse prospective uses of nanotechnology. • water repellence. • thermal protective finish. • uv-protection. • easy care finish. • anti-bacteria. • flameproof and retardant finish. • anti-static. • wrinkle resistance. • self-cleaning textiles. • odor control finish. • hydrophilic nano finishes. • lotus effect. nanoparticles possess a high surface area-to-volume ratio, facilitating their adhesion to fibers or fabrics and enhancing the longevity of the capabilities conferred by the particles. the nanoparticle coating does not compromise the breathability or tactile quality of the material. the most prevalent functions include wrinkle resistance, stain and soil repellency, water repellency, as well as anti-static, anti-bacterial, and anti-ultraviolet protection. 7.1. nano-enhanced wrinkle resistance textiles wrinkling transpires when the fiber is significantly wrinkled. when fiber or fabric is flexed, hydrogen bonds among the molecular chains in the amorphous regions fracture, permitting the chains to slide past one another. the linkages are reformed in new locations, and fiber or fabric maintains increased configurations. the drawbacks of traditional resin applications encompass a reduction in fiber strength, abrasion resistance, water absorbency, dyeability, and breathability. 7.2. nano-enhanced stain resistance textiles fabric staining results from the re-deposition of soil during laundering or dry cleaning, the accumulation of airborne dry soil, or contact with extraneous substances. silicon compounds and fluorochemical coatings can verify resistance against soil, water, and oily stains. the stain-resistant textiles from nano-tex consist of billions of minuscule fibers, each about nanometers (0.0000004 inches) in length, integrated within conventional cotton or linen. the waterproof fibers, referred to as “nanowhiskers” by nano-tex, enhance the fabric’s density, elevating surface tension to prevent liquid absorption—similar to raindrops on a newly waxed automobile. the firm asserts that this nano-care treatment will endure 50 home launderings before its efficacy diminishes. the most advanced application of nanotechnology in textiles is presently focused on stain, oil, and water repellency, stain release, and wrinkle resistance. nanotechnology can be utilized to apply stain resistance, stain repellent, and dual-action repel-and-release coatings. repellent treatments reduce the crucial surface tension of the fabric, preventing it from attracting stains or dirt. oil and water bead up and roll off the fabric. when a characterization and application of nanomaterials 2025, 8(2), 10834. 24 repellent finish is applied to textiles, the imperceptible treatment offers enhanced water and oil resistance, as well as protection against spills and stains. stain-release materials permit stains and spills to penetrate the fabric; oil and water may bead slightly, and when stains are introduced, the fabric exhibits minor oil/water repellency. however, the imperceptible stain-release finish facilitates the effortless removal of embedded stains during laundering. this concludes with the incorporation of a hydrophilic component that facilitates the removal of absorbed stains by conventional laundering. the dual action repel and release is the latest stain release finish in the industry. the finish amalgamates the benefits of both stain release and repellent finishes into a singular formulation. this dual protection provides a distinctive equilibrium of repellency that operates in conjunction with an improved stain release, effectively eliminating the most stubborn stains, including entrenched ones. featuring dual-action repel and release finishes, this fabric provides consumers with double the stain prevention in a single, easy-to-maintain material. 7.3. nano-enhanced water repellent textiles water-repellent coatings alter the fiber’s surface without obstructing the interstices. consequently, the fabric allows the passage of air and water vapor. initial water-repellent coatings were readily detachable for dry cleaning or laundry. currently, wax emulsions, pyridinium compounds, n-methylal compounds, silicones, and fluorochemicals are employed to enhance water repellency in both natural and synthetic fibers. recently, various products have been produced to enhance wrinkle resistance, stain resistance, and water repellency. the nano whisker introduced by nanotex is among the most superior alternatives. they are permanently affixed to the cloth, in contrast to the conventional topical coatings or cumbersome laminated fabrics formerly employed for this purpose. the whiskers are hydrocarbons incorporated into the fibers within an aqueous solution. the modifications to the fibers do not impact the inherent tactile quality and breathability of the fabric. the fabric has excellent wrinkle resistance, the processing is imperceptible, and a “peach fuzz” look has been noted. the finish can be applied to textiles by a nanoscale emulsification technique that is more complete, uniform, and precise than conventional approaches. woven cotton fabric rolls from textile mills are submerged in liquids containing trillions of nanowhiskers. they possess waterproof properties and enhance the fabric’s density. the treated cotton is subsequently dried in ovens, adhering the minute fibers to the significantly larger cotton strands. this enhances the surface tension of the fabric’s outer layer, preventing liquid absorption. although the end product appears unaltered, it offers an almost impermeable barrier against liquids and wrinkles, for example. nanowhiskers ensure uniform application without altering surface qualities, in contrast to conventional finishes. nanoparticles are minuscule, rendering their incorporation into fabric imperceptible to tactile examination [115]. nanoparticles incorporated into textile materials are imperceptible to the naked eye, therefore preserving the original color of the products. nanoparticles create a protective coating on the surface of textile materials without altering their chemical properties; hence, they do not release harmful compounds and exhibit no adverse consequences. textile items treated with nanoparticles exhibit greater durability characterization and application of nanomaterials 2025, 8(2), 10834. 25 compared to conventional finishes after multiple washes. nano-finishes can enhance fabrics by providing both wrinkle and stain repellency in a single treatment. nanotech clothes may exhibit suboptimal performance if not adequately maintained. appropriate maintenance for these outfits entails utilizing gentle machine washes and drip drying, refraining from dry cleaning, and eschewing chlorine bleach and wringing of the fabric. 7.4. nano-enhanced anti-static textiles static commonly builds up in synthetic fibers such as nylon and polyester because they absorb little water. traditionally, surfactants are employed to distribute a minimal quantity of moisture over the fiber’s surface to facilitate charge dissipation. silver is among the most effective electrically conductive nanoparticles. silver nanoparticles easily remove static charge [116,117]. 7.5. nano-enhanced anti-bacterial textiles quaternary ammonium compounds are frequently utilized as antibacterial agents. numerous chlorinated organic chemicals and organometallic compounds, including copper, silver, iron, manganese, or zinc, enhance the antibacterial resistance of fabrics. the use of nanosilver particles provides a long-lasting antibacterial treatment for textiles [118–120]. 7.6. nano-enhanced ultraviolet protective textiles various nanocompounds or nanoparticles can be utilized to provide uv protection to textile materials. the most prevalent nanocompounds utilized are titanium dioxide and zinc oxide in nanoscale dimensions. they offer a protective advantage by reflecting, scattering, or absorbing detrimental uv radiation [121]. at present several research organizations and industries are offering nanotechnology and its application techniques for textiles. some of them are as follows: • nanotex, llc, greensboro, n.c., usa. • texcote technology (international) ltd, sweden. • schoeller textiles ag, switzerland. • beijing zhong-shong century nanotechnology co. ltd, beijing, china. 8. environmental aspects and health safety the anticipated widespread application of nanotechnologies in the textile industry, along with other sectors utilizing nanotechnology, is raising environmental and health safety concerns. nanoparticles have a large surface area relative to their volume, which makes them more adsorbent to other materials and increases the duration of their effects. in this regard, it consumes less material compared to the bulk or conventional material required for the same industrial application. the distinctive characteristics of nanomaterials have captivated not only scientists and researchers but also enterprises, due to their significant economic potential. the national science foundation indicates that nano-related products and services will expand to a market value of 1 trillion dollars by 2015. this sum exceeds the total of the characterization and application of nanomaterials 2025, 8(2), 10834. 26 telecommunications and information technology sectors. it is projected that nanotechnology will generate several hundred billion euros during the next decade. the nanomaterials market may reach 4 billion dollars by 2007. it was anticipated that 2 million new job opportunities would be generated to satisfy the global annual production need of 1 trillion dollars within 10 to 15 years [122]. due to the less surface-active energy, the bulk materials utilized in traditional procedures reduce performance, lead to increased material consumption, and eventually contribute to increased energy consumption and environmental degradation. on the other hand, nanotechnology may positively influence the environment as well. nanotechnology has the potential to conserve raw materials and enhance the quality of life by utilizing fewer resources without compromising performance. table 7 illustrates the prospective utilization of nanoparticle environmental engineering. table 7. potential application of nanoparticles environmental engineering. industry nanoparticles application area nanoparticle-based traditional product/potential area of application environmental engineering titanium dioxide (tio2) zinc oxide (zno), iron oxide (fe2o3) and carbon nanotubes (cnts) graphene silver (ag) gold (au) water treatment plants air pollution control systems soil remediation sites wastewater treatment plants environmental monitoring systems water treatment: • nanoscale’s water treatment systems (nanoscale corporation) • nanostellar’s water treatment catalysts (nanostellar inc.) • altair’s water treatment membranes (altair nanotechnologies inc.) air pollution control: • nanohmics’ air pollution control systems (nanohmics inc.) • nanoscale’s air pollution control catalysts (nanoscale corporation) • komatsu’s air pollution control filters (komatsu ltd.) soil remediation: • nanoremediation’s soil remediation systems (nanoremediation inc.) • nanostellar’s • soil remediation catalysts (nanostellar inc.) • altair’s soil remediation membranes (altair nanotechnologies inc.) wastewater treatment: • nanoscale’s wastewater treatment systems (nanoscale corporation) • nanostellar’s wastewater treatment catalysts (nanostellar inc.) • nanohmics’ wastewater treatment membranes (nanohmics inc.) environmental monitoring: • nanosensor’s environmental monitoring systems (nanosensor inc.) • nanostellar’s environmental monitoring sensors (nanostellar inc.) • altair’s environmental monitoring membranes (altair nanotechnologies inc.) 8.1. potential impact of nanomaterial on environment the extensive application of nanoparticles inevitably results in heightened emissions into the environment via air, groundwater, and soil. the unique characterization and application of nanomaterials 2025, 8(2), 10834. 27 characteristics of nanoparticles may lead to adverse environmental impacts if released into the ecosystem. furthermore, in addition to possessing inherent hazardous effects, nanomaterials, owing to their unique morphology, surface characteristics, or charge, may interact with molecules in an undesirable manner or sequester nutrients. nanomaterials may infiltrate the environment throughout their lifespan. the duration of their survival and the manner in which they persist remain subjects of inquiry, with estimated ambient nanoparticle concentrations anticipated to be in the mg/l range in air, soil, and water. compared to existing toxicity data for lethal and sublethal effects, these doses were markedly lower than those expected to induce biological consequences, suggesting a minimal risk threshold. it is essential to acknowledge that as novel particles and applications are created, and as additional information on their fate, behavior, uptake pathways, and atmospheric entry emerges, these predictions may evolve. furthermore, once nanomaterials infiltrate the environment, they possess the capacity to accumulate inside environmental organisms. the exposure pathways arising from production, processing, and utilization necessitate the monitoring of the initial products of nanoscale compounds and their transformation products (life-cycle studies, exposure scenarios) within the designated compartments. it is essential to adhere to several steps: first, identify the nanoparticles that persist and accumulate in the environment using appropriate measurement methods for detection in water, soil, and sediment; next, analyze the behavior of the nanomaterials post-use, during disposal, landfilling, incineration, or reutilization; finally, conduct ecotoxicity testing throughout the entire lifecycle. the stability of nanoparticles is a critical aspect in assessing the danger of exposure to nanomaterials; specifically, it is essential to evaluate their stability and longevity, as well as the conditions in which they may undergo alterations upon entering the environment. knowledge regarding the potential fate scenarios of nanoparticles in the environment is progressively emerging. recent studies have emphasized that the behavior of nanoparticles in the environment is influenced not only by the physical and chemical properties of the nanomaterial and their concentration but also by the characteristics of the receiving environment. due to their small size, nanoparticles can be extensively dispersed through the air, allowing for the partial application of research findings regarding the behavior and effects of natural ultrafine dust or ultrafine dust generated during incineration. groundwater is at risk from nanoparticles in soil because of their broad, active surfaces, which can bind and mobilize contaminants like organic materials or heavy metals. if nanomaterials are not broken down or dissolved, they will eventually tend to collect and settle onto the substrate, depending on the receiving environment. typically, industrial products and waste are disposed of in waterways that eventually flow into the ocean. upon the discharge of water, dispersed nanoparticles are anticipated to exhibit behaviors consistent with the principles outlined in colloid science. the assessment of concentrations, surface characteristics of nanomaterials, and the physicochemical features of the aqueous phase are critical elements in ascertaining the interactions of these nanoparticles with organic matter and their potential for adsorption. there is less published research on the absorption or interaction of nanoparticles with plants; however, it details the creation of cadmium nanocrystals on phytoplankton. a nearly linear correlation was observed between toxicity and the characterization and application of nanomaterials 2025, 8(2), 10834. 28 release of silver ions from the particles, which accumulated in the phytoplankton. it has been proposed that plant tissues could serve as a scaffold for the in situ aggregation of metallic nanoparticles and that lipophilic nanoparticles, such as carbon nanotubes, may be absorbed by microbial communities and root systems, leading to their accumulation in plant tissues. in conclusion, understanding the behavior and impacts of nanoparticles in the environment and living creatures is rapidly expanding due to significant interest from the scientific community and greater financing. nevertheless, the field is far from being mature. current forecasts indicate that environmental concentrations are expected to be substantially lower than those that induce biological effects in laboratory settings, and the probability of considerable ecotoxicological harm is minimal. the impact of nanoparticles utilized in food packaging on the overall ambient concentration appears to be insignificant. furthermore, the presence of nanoparticles in the environment may also be advantageous. numerous studies are emerging about the application of nanotechnology for the remediation and detoxification of environmental toxins. the in situ method known as nanoremediation involves the utilization of reactive nanomaterials to facilitate chemical reduction and catalysis for the remediation of targeted pollutants, without the extraction of groundwater for surface treatment or the relocation of soil for treatment and disposal. nanoremediation is purported to have the capacity to lower the overall expenses associated with the remediation of extensive contaminated sites, decrease cleanup duration, obviate the necessity for the treatment and disposal of contaminated dredged soil, and diminish certain contaminant concentrations to nearly zero, all achievable in situ. to mitigate any detrimental environmental repercussions, a comprehensive review, including extensive ecosystem-wide studies of these nanoparticles, must be conducted prior to the widespread application of this technology. using nanoparticles as ‘nano-additives’ for two opposing purposes—the breakdown and stabilization of polymers under different environmental circumstances and durability under varied environmental conditions—is another intriguing aspect of nanoparticles’ impact on the environment. a new study summarizes the current state of research on this novel use of nanoparticles, which has the potential to be extensively used in the near future. 8.2. possible impact of nanomaterial on human health three distinct methods of nanoparticle entry into the organism are possible: inhalation, dermal penetration, and ingestion. increasing scientific data indicates that unbound nanoparticles can traverse biological barriers, and exposure to some nanoparticles may result in oxidative damage and inflammatory responses. concerns with nanomaterials in food packaging primarily revolve around the possibility of indirect exposure stemming from the potential migration of nanoparticles from the packaging. the inhalation and dermal penetration of nanoparticles in food packaging predominantly concern workers in factories that produce these substances. it is advisable for these personnel to utilize personal protective equipment, including gloves, goggles, and masks equipped with high-efficiency particulate filters. there is less knowledge regarding the consequences of nanomaterials entering the human body. the risk evaluation of nanomaterials upon consumption has been examined for only a limited number of nanoparticles utilized in food packaging. characterization and application of nanomaterials 2025, 8(2), 10834. 29 research indicates that tio2, ag nanoparticles, and carbon nanoparticles/nanotubes can penetrate the circulatory system from the gastrointestinal tract. the processes are likely contingent upon the physicochemical parameters of the nanoparticles, including size, and the physiological condition of the entrance organs [123]. the translocation fractions appear to be quite low; yet, this is the focus of ongoing rigorous investigation. upon entering the bloodstream, the liver and spleen serve as the primary organs for nanoparticle distribution. the circulation time significantly rises when nanoparticles are hydrophilic and possess a positive surface charge. certain nanoparticles pose a risk to all organs, as the chemical makeup of the nanoparticles or the nanoparticles themselves have been discovered in every organ examined, showing their diffusion to these organs. the organs encompass the brain and testis, as well as the reproductive system. fetal distribution in pregnancy has also been documented. given the poor understanding of the long-term behavior of nanoparticles, a cautious estimate must posit that insoluble nanoparticles could collect in secondary target organs over prolonged exposure, with ramifications that remain unexamined. there is a particular concern over the potential migration of nanoparticles into the brain and the developing fetus. investigations in both domains must be undertaken to either validate or refute the idea regarding the relationship of nanoparticles with various neurological disorders. the impact of various particles utilized in food packaging on health is now being examined, including zno nanoparticles and fullerenes [124]. 9. summary the advancement in the utilization of nanoparticles, nanocomposites, and nanospheres has accelerated significantly in recent years, especially within the domain of textile finishing. nanoscale materials can improve the physical attributes of traditional textiles, including antimicrobial efficacy, water repellency, soil resistance, antistatic characteristics, infrared resistance, flame retardancy, dyeability, and tensile strength. in the future, the utilization of these remarkable nanoparticles may be expanded to create textiles with healthcare and wound-healing capabilities, as well as self-cleaning and self-repairing properties. future developments of nanotechnologies in smart materials will have a twofold focus: 1) upgrading existing functions and performances of materials. 2) developing smart and intelligent engineering materials with unprecedented functions. the latter is more urgent from the standpoint of homeland security and the advancement of technology. the new functions with nano-enriched material to be developed include: a) wearable solar cell and energy storage, b) sensors and information acquisition and transfer, c) multiple and sophisticated protection and detection, d) healthcare and wound healing functions, and, e) self-cleaning and repairing functions. characterization and application of nanomaterials 2025, 8(2), 10834. 30 undoubtedly, nanotechnology holds an enormously promising future for smart engineering materials. it is estimated that nanotechnology will bring hundreds of billions of dollars of market impact on new materials within a decade. institutional review board statement: not applicable. informed consent statement: not applicable. conflict of interest: 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applications of stimuli-responsive polymers in pharmaceutical and biomedical field rabinarayan parhi department of pharmaceutical sciences, susruta school of medical and paramedical sciences, assam university (a central university), silchar 788011, assam, india; bhu_rabi@rediffmail.com abstract stimuli-responsive, smart, or intelligent polymers are materials that significantly change their physical or chemical properties when there is a small change in the surrounding environment due to either internal or external stimuli. in the last two decades or so, there has been tremendous growth in the strategies to develop various types of stimuli-responsive polymer (srp) materials/systems that are suitable for various fields, including biomedical, material science, nanotechnology, biotechnology, surface and colloid sciences, biochemistry, and the environmental field. the wide acceptability of srps is due to their availability in different architectural forms such as scaffolds, aggregates, hydrogels, pickering emulsions, core-shell particles, nanogels, micelles, membranes, capsules, and layer-by-layer films. the present review focuses on different types of srps, such as physical, chemical, and biological, and various important applications, including controlled drug delivery (cdd), stabilization of colloidal dispersion, diagnostics (sensors and imaging), tissue engineering, regenerative medicines, and actuators. the applications of srps have immense potential in various fields, and the author hopes these polymers will add a new field of applications through new concepts. keywords: stimuli-responsive polymer; scaffold; nanogel; actuator; artificial muscle; gripper 1. introduction polymers are considered a class of material of either natural or synthetic origin and are composed of macromolecules, which are multiples of simpler chemical units termed monomers. these diverse elements are the backbone of drug delivery applications and have immense applicability in biomedical fields such as tissue engineering, biosensors, imaging devices, cosmetics, etc. natural polymers such as protein (e.g., gelatin), polysaccharides (e.g., starch cellulose, chitosan), and nucleic acids are present as basic components in living systems and are widely used due to their suitable qualities, including biodegradability, biocompatibility, and non-toxicity[1]. their synthetic counterpart is fabricated/designed to not only simulate these biopolymers but also modify them through a variety of functional group attachments and combine two polymers to cater to present-day requirements. these polymers include homopolymers, block/statistical copolymers, graft copolymers (including grafted on/from surfaces), and molecular brushes[2]. the applicability of polymers in various fields is confronted with challenges today, which increase demand for sensitive and efficient systems. in this context, there is an immense need for a polymeric system that not only enhances sensitivity but also minimizes side effects[3]. amongst various natural and synthetic article info received: 20 november 2023 accepted: 18 december 2023 available online: 25 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 polymers, a specific class of polymers that respond to various stimuli are termed stimuli-responsive polymers (srps), stimuli-sensitive, smart, or intelligent polymers. the response of a polymer can be expressed in diverse ways. srps in the solution can be classified as those that change their shape, size/chain dimensions, solubility, secondary structure, and degree of intermolecular association. whether these changes are permanent or temporary, the polymers return to their initial shape or state after the removal of the stimulus[4]. these responses are mostly caused by either the formation or destruction of secondary forces such as electrostatic interactions, hydrogen bonding, hydrophobic effects, etc., simple acid-base reactions of moieties present on the backbone of the polymer, and differential osmotic pressure[2]. the stimulus that causes these responses may be external/exogenous, such as a light, electrical field, magnetic field, ultrasound, or internal/endogenous, including ph, ionic strength, etc.[5]. endogenous stimuli do not require a special procedure to be activated. however, the exogenous stimulus activates a reversible mechanism, leading to the fabrication of on-of systems that allow on-demand drug release[6]. all the external and internal stimuli are categorized into three groups: physical, chemical, and biological. the physical stimuli mainly refer to the physical factors that can cause energy changes in intermolecular interaction, such as electric field, magnetic field, temperature, ultrasound, etc. chemical stimuli such as ph, ionic strength, and solvents induce changes in molecular structure and interactions with the addition of chemical agents in smart polymers. biochemical stimuli involved in the change in responses of smart polymers are enzymes, proteins, antibodies, etc. these srps can be developed into different types of architecture, such as scaffolds, aggregates, hydrogels, pickering emulsions, core-shell particles, nanogels, micelles, membranes, capsules, and layer-by-layer films. given their unique properties and different architectures, smart polymers are being employed in diverse fields such as drug delivery, diagnosis sensors, and actuator system fabrication[7]. the current review mainly discusses different types of srps and various important applications, including cdd, stabilization of colloidal dispersion, diagnostics (sensors and imaging), tissue engineering, regenerative medicines, and actuators. 2. classification of stimuli-responsive polymers figure 1. classification of srps based on the stimulus type. srps are commonly grouped under three main headings: physical, chemical, and biological[8] as depicted in figure 1. 3 2.1. physically-responsive polymers these are the polymers stimulated by various physical stimuli such as temperature, electric field, light/photo, ultrasound, and magnetic fields. 2.1.1. thermo-responsive polymers thermo-responsive polymers have drawn huge consideration in the biomedical field because certain diseases demonstrate temperature changes. they are being taken into various architectures including hydrogel, film, micelles, spherical particles, etc. thermo-responsive polymers exhibit a sudden change in their total volume and dissolution state, which is termed the cloud point. these polymers have a critical solution temperature (cst) near which the hydrophilic and hydrophobic interactions between the aqueous media and polymeric chains suddenly change within a small temperature range. this resulted in the disruption of inter and intramolecular electrostatic and hydrophobic interactions, which may lead to chain expansion or collapse due to volume phase transition. these polymers also own upper cst (ucst) beyond which a single phase exists and lower cst (lcst) under which one polymer phase exists[3]. 2.1.2. electric-field-responsive polymers these are smart polymers that change their properties such as size and shape through swelling, shrinking, or bending in response to an external electric field and are termed electro-responsive or electric-fieldresponsive polymers[9]. these polymers are extensively employed in various research fields because of their merits of precise control via the duration of an electric pulse or the magnitude or the interval between the pulses. the responses showed by these polymers upon exposure to an external electric field are (i) development and swelling of redox-active polyelectrolyte multilayers, (ii) voltage-induced motion of ions and solvent molecules resulting in a rise in osmotic pressure in the polymer and thus volumetric expansion, (iii) regulation of the filling or desorption of polyelectrolyte on to conversely charged porous materials, (iv) ionic polymermetal complexation and electrically active complex formation[3,10]. 2.1.3. light-responsive polymers light-responsive polymers when exposed to light with appropriate wavelength/biologically friendly window, intensity and exposure time of near-infrared (nir)/ultraviolet (uv)/visible change their physical properties such as swelling/contraction, mechanical stiffness, shape, and rate of degradation, and chemical properties like surface hydrophilicity[9]. these changes are due to structural changes in specific functional groups of the polymer such as light-sensitive chromophores (azobenzene, spiropyran (sp), or nitro-benzyl groups)[3]. among all the sources nir showed promising potential as it can penetrate deeper into the tissue and is less harmful as more absorbed by polymers than that of a cell. these polymers showed better advantages over other responsive polymers including adjustable therapeutic light dose, (iii) availability of a wide spectrum of wavelengths that can be positively applied to the polymer, (iii) material sensitivity can be four dimensional (4d)-controlled, and (iv) it facilitates proper regulation of the in-vivo response[8]. 2.1.4. ultrasound-responsive polymers the drug delivery system has ultrasound-responsive polymers that respond to externally applied ultrasound waves and release the loaded drug into the targeted tissue. the mechanism through which the drug release is triggered is cavitation, pressure variation, acoustic fluid flow, and hyperthermia. in addition, ultrasound wave enhances the permeability of drugs across the biological membrane. the frequencies of ultrasounds that are used in the biomedical field are three levels including <1 mhz (low), 1–5 mhz (medium), and 5–10 mhz (high)[10]. 4 2.1.5. magnetic field-responsive polymers the magnetic field-responsive feature is not a property of the polymers, but a property generated by adding magnetic particles into these polymers. thus, magnetic field-responsive polymers are hybrid species in which magnetic particles (<100 nm) such as magnetite (fe3o4) or maghemite (γ-fe2o3) are either embedded in the polymeric chain or stabilized with polymers. other magnetic particles like co, ni, fept, and fen are also used to develop magnetic field-responsive polymers[11]. 2.2. chemically-responsive polymers these polymers respond to various factors such as ph, co2, ion, and redox chemicals and thereby induce alteration of molecular interactions. 2.2.1. ph-responsive polymers ph-responsive polymers are polymers containing ionizable, weakly acidic, or weak basic parts which join to a hydrophobic backbone (e.g., polyelectrolytes). with the change in ph of the solution, these polymers undergo ionization and result in chain conformation, solubility, and surface activity through electrostatic repulsions generated charges. these are broadly classified into two broad categories; acidic ph-responsive polymers with weak acidic groups (e.g. carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, and boronic acid groups) that release protons at high ph in aqueous media and basic ph-responsive polymers with weak basic groups (e.g. tertiary amine groups, morpholine, pyrrolidine, piperazine, pyridine and imidazole containing rings) that are protonated at low ph values aqueous media[12]. these are widely used in diverse applications including drug release as ph changes occur naturally in many body parts, gene transfer, membranes, sensors, and so on so forth. 2.2.2. co2-responsive polymers co2-responsive polymers involve a change in the ph of the solution by simply adding co2. since the co2 stimulus can be found in an aqueous environment and can penetrate the inner parts of the polymer, thereby enhancing the co2 sensitivity of the concerned polymers. co2-responsive polymeric systems have several advantages such as being environmentally friendly, recyclable, non-toxic, and abundant presence in nature. in addition, co2 has good permeability with human cells and shows good biocompatibility leading to its immense applicability in the biological field[13]. 2.2.3. ion strength-responsive polymers certain polymers (ion strength-responsive polymers) containing ionizable or neutral groups respond to alterations in ionic strength leading to alterations in the size of polymeric nano aggregates or structure, the solubility of polymers, swelling and shrinkage of gels, and fluorescent quenching kinetics of chromophores of polyelectrolytes[14]. the interactions (coulombic) between oppositely charged species induce the insolubility of polymers in deionized water but soluble due to the existence of electrolyte concentration at a vital level. this led to the shielding of attractive charges and thus changes the above-mentioned properties[15]. 2.2.4. redox-responsive polymers redox-responsive polymers that have electroactive residues or groups such as acid-labile moieties, and disulfide groups in their structure induce oxidization and/or reduction[12]. this redox reaction alters the hydrophilic and hydrophobic properties of the polymer chains leading to swelling and deswelling of the polymers. these polymers have wide applications in the pharmaceutical field (active and cdd), biosensors, optoelectronic devices and electrochromic devices as their properties can be precisely tuned by changing the oxidation step. in addition, these polymers have biological applications due to the presence of redox chemicals in the physiological fluid[16]. 5 2.3. biochemical dependent stimuli here biological analytes and biomolecules such as enzymes, inflammation, oxygen-free radicals, glucose, antigen, and hypoxia. 2.3.1. enzyme-responsive polymers various bacterial species present in the colon of the human body produce special enzymes such as hydrolytic enzymes (e.g. glycosidases) and reductive enzymes (e.g. azoreductase) that are effective in breaking naturally occurring polymers including chitosan, dextrin, amylase, amylopectin, pectin, and cyclodextrin[17]. therefore, these polymers along with other polymers designed to be degraded by colon enzymes or any other enzymes produced inside the body have immense importance in pharmaceutical and biomedical fields. this is because of the unique advantages of the non-requirement of external stimuli for triggered degradation of polymers, high selectivity, and capability of performing in mild conditions[3]. 2.3.2. inflammation-responsive polymers the inflammatory process is started by b and t-lymphocytes and proceeded by polymorphonuclear leukocytes and macrophages. the oxygen-free radicals formed by these polymorphonuclear cells and macrophages are the stimuli for inflammation-responsive polymers[3]. 2.3.3. glucose-responsive polymers to circumvent all the problems associated with insulin delivery via injection for the treatment of diabetes, glucose-responsive polymers change their properties due to changes in glucose concentration in the body. these types of polymers are categorized into three types: (i) glucose oxidase-mediated enzymatic oxidation of glucose, (ii) binding of glucose with concanavalin a and (iii) reversible covalent bonds between glucose and boronic acids (10). these polymer types can be utilized as one which regulates insulin release and another used in the glucose concentration diagnosis either employing feedback-controlled or closed-loop insulin release systems. 2.3.4. antigen-responsive polymers interaction between antigen and antibody (glycoproteins having specific binding sites for an antigen) is very specific and selective[18]. this concept is being utilized to develop antigen-responsive polymers, wherein antigen and antibody groups interacting with each other are grafted onto different polymeric chains leading to the formation of crosslinked structures of polymers. when the free antigen is added to the medium it causes the displacement of the already bound antigen grafted immobilized polymer chain and thus results in the gelsol formation, change in pore size in the membrane, or gel swelling behaviour. 2.3.5. hypoxia-responsive polymers hypoxia is defined as a condition in which a part of the body or the whole body lacks adequate oxygen supply at the tissue level. hypoxia is more relevant to diseases such as cancer where it affects tumours in the process of angiogenesis, invasiveness, metastasis, and epithelial to mesenchymal transformation. major reducing agents generally accumulated in hypoxia cells are alkaline phosphatase, nicotinamide adenine dinucleotide phosphate (nadph), nicotinamide adenine dinucleotide hydrogen (nadh), nitroreductase, and azoreductase. in addition, the tumour microenvironment under hypoxia is highly acidic due to the presence of lactic acid produced through the metabolic cellular pathway. consequently, in cancer therapy hypoxia is induced to create acidic ph conditions and intracellular redox potential where stimuli-responsive polymers can deliver the drugs due to a change in ph[19]. different types of srps are listed in table 1. 6 table 1. various types of srps with examples. stimuli-response types polymer types examples of polymers physically-dependent stimuli thermo-responsive polymers polyethylene oxide-poly(propylene oxide)polyethylene oxide, poly(n-isopropyl acrylamide) (pnipam), poly(n-vinyl caprolactam), poly(methyl vinyl ether), polyvinyl alcohol electric-field-responsive polymers polythiophene, polystyrene sulfonate light-responsive polymers spiropyran (sp), polyacrylic acid (paa) chemically-responsive stimuli ph-responsive polymers polyethylenimine (pei), poly(amidoamine), chitosan, poly(glycolic acid) (pga), poly[2(dimethylamino)ethyl methacrylate] redox-responsive polymers poly(lactic-co-glycolic acid) (plga), polyanhydride biochemical dependent stimuli enzyme-responsive polymers dextran sulphate, chitosan inflammation-responsive polymers glycidylether cross-linked hyaluronic acid glucose-responsive polymers glucose oxidase conjugated chitosan hypoxia-responsive polymers hyaluronic acid 3. application of stimuli-responsive polymers srps have wide applications in various fields. figure 2 depicts different applications which are discussed below with case studies. figure 2. schematic depiction of various applications of srps. 3.1. control drug delivery the application of srps is one of the best ways to improve the effectiveness of the drug delivery system (dds). this concept was first tried in the 1970s for the local release of drugs via hyperthermia employing thermosensitive liposomes. thereafter, a large number of researches about srps were performed keeping the basic desirable properties for smart ddss, including (i) simplicity of administration, (ii) site-specific drug delivery in response to stimulus, (iii) controlled drug release in a predetermined time, (iv) possibility to monitor 7 the delivery, and (v) composition-wise they should be non-toxic, biodegradable and biocompatible. sitespecific drug delivery is subject to different biological barriers such as abnormal blood flow, intestinal pressure gradients, the blood-brain barrier, reticuloendothelial systems, and a complex network of blood vessels[20]. this resulted in reducing the efficacy of the treatment or completely preventing its effect. however, these obstacles can be circumvented through proper design and approaches used to deliver the drugs to the body. different major srp-based cdds used are (i) hydrogel, microgel, and nanogel, (ii) microneedle, (iii) block copolymer self-assembled structures such as micelles and liposomes, (iv) polymeric vesicles or polymersomes and (v) nanoparticles and nanocapsules. 3.1.1. hydrogel, microgel, and nanogel hydrogels are 3d cross-linking polymeric systems that can hold large amounts of water within their polymeric network structure. hydrogels-based drug delivery devices are widely accepted because they require a lower amount of drugs and lower frequency in administration compared to the conventional mode of drug administration. in addition, hydrogels offer their adjustment in terms of physical, mechanical, and biodegradation leading to controlled drug release with site-specificity via interactions with therapeutic moieties. furthermore, hydrogel is a drug delivery platform capable of regulating the way of the accessibility of the drugs to the cells. thus, hydrogels can be employed in diverse medical fields of almost all organs and tissues. moreover, they can encapsulate both hydrophilic and hydrophobic drugs in their structure[21]. however, the lower loading or poor release capacity of conventional hydrogels, particularly hydrophobic ones has limited its wide acceptability as dds. in this scenario, smart/stimuli-responsive hydrogel can circumvent the problems associated with drug release and provide a more regulated and precise drug release. further, the combination of particulate materials with stimuli-responsive hydrogels improves the prospects of dds such as better targeting, minimizing possible risk factors, and enhanced therapeutic outcomes[22,23]. microgels are one of them which has advantages over bulk gels including much faster response to external stimuli, can be modified chemically to increase circulation time in the bloodstream, sustained release of loaded drugs, and quick clearance from the body via biodegradation. based on the above concept, a ph-responsive microgel-based drug carrier was fabricated by sandwiching a thin film of microgel comprised of poly(n-isopropyl acrylamide)-co-acrylic acid (pnipam-co-aac) between two thin au layers (all on glass support), which in turn coated with sio2. the sample drug crystal violet was incorporated into the microgel layer via electrostatic interaction between its positive charge and negative charges on the deprotonated acrylic acid groups at a ph greater than 6.5. upon exposure to ph 3 solutions, the drug was found to release due to the neutralization of the acrylic acid group and the release rate of the drug was controlled by the thickness of the sio2 layer, with a thin layer providing a faster release rate and a thick layer provides slow-release rate[24]. in another investigation, model drug methylene blue was incorporated into a ph-responsive single microgel-based reservoir with two polymers with different chemistries such as pnipam-co-aac and pnipam-3-(acrylamido)phenylboronic acid) (pnipam-co-apba). here, the model drug was loaded through electrostatic interaction between its positive charge and aac group of pnipam-co-aac microgel and the apba group of pnipam-co-apba microgel. this microgel showed a pulse pattern of drug release with the first phase of drug release at ph 7.0 where apba groups got neutralized and then, the second phase of drug release when the ph of the medium reached 3.0 due to neutralization of aac groups[25]. stimuli-responsive nanogels are another type of potential drug carrier due to the advantage of nanosize. in one investigation, ph-responsive pegylated nanogel of doxorubicin with 2-(n,n-diethylamino)ethyl methacrylate (eama) and modified peg through emulsion copolymerization. there was no initial burst release of drug from the nanogel at ph prevailed physiologically, while endosomal ph induced significant drug release[26]. zhu et al.[27] fabricated dual-responsive (ph and temperature) nanogel from polyethyleneimine 8 (pei) and pnipam loaded with 5-fluorouracil for synergistic therapy for mastocarcinoma. the drug release from the nanogel was induced by the formation of autophagosomes, followed by their fusion with lysosomes. this lysosomal-dependent apoptosis was attributed to activatable protonated pei at low ph which led to lysosomal membrane destruction and release of enzyme cathepsin b. the released cathepsin b further increased the mitochondria membrane permeability and facilitated cytochrome c release that induced apoptosis. a ph-responsive nanogel for gene delivery (small interfering rna, sirna) was fabricated with dendritic polyglycerol and positively charged pei. this nanogel successfully released the drug in a controlled manner due to the loading of ph-sensitive benzacetal-bonds within the nanogel network during manufacturing. encapsulation of sirna in the nanogel was able to silence the green fluorescent protein-induced expression of hela cells[28]. 3.1.2. microneedle drug delivery via microneedle is regarded as a novel physical technique involving micron-sized needles to create pores across the skin thereby facilitating the delivery of drug molecules of diverse sizes. this technique provides a minimum or no invasiveness and is painless as the needles penetrate the viable epidermis across the stratum corneum (sc) without making any contact with blood vessels and nerves. there are different types of microneedles being used for the delivery of drugs, including solid, coated, hollow, dissolving, and hydrogel-forming microneedles[29]. among all, hydrogel-forming microneedle arrays are more recently fabricated which can rapidly imbibe skin interstitial fluid to form in situ hydrogel bulbs. this resulted in the drug administration at a higher rate than the traditional patches. additionally, it provides scope to incorporate srps to induce on-demand drug release by external stimuli. for instance, a light-sensitive hydrogel-forming microneedle arrays-based novel device loaded with ibuprofen was fabricated with 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate. the device could deliver 3 doses of ibuprofen (50 mg) for up to 160 h upon the application of light. in addition, the system could also be operated based on the on-andoff principle[30]. to fulfil the ultimate goal of diabetes management through painless insulin administration, a microneedlearray patch of insulin comprised of boronate hydrogel with semi-penetrated silk-fibroin was fabricated. the presence of boronate hydrogel supplies glucose-responsive diffusion control insulin release. the microneedle patch provided sustained as well as acute glucose-responsive insulin delivery and was able to control glycemia in both an acute and continuous manner with remarkable stability and safety[31]. another glucose-responsive microneedle patch amalgamated with hypoxia-responsive hyaluronic acid-based self-assembled vesicles loaded with insulin and glucose oxidase. these microneedles released insulin in response to the local generation of hypoxia, which in turn is achieved through the conversion of 2-nitroimidazole (hydrophobic) to 2-aminoimidazoles (hydrophilic) in a hypoxic prevailing condition. in response to high blood glucose levels, the dissolved oxygen in the blood is quickly consumed because of the glucose oxidation reaction. this resulted in the formation of local hypoxia that reduces 2-nitroimidazole leading to rupturing of vesicles and releasing insulin[32]. a novel infection-responsive dissolving microneedle array loaded with carvacrol and polycaprolactonebased nanoparticles was developed for the site-specific and sustained antimicrobial effect against chronic wound infections. the drug release from the nanoparticles was higher in the presence of bacteria at the site of a wound. the nanoparticles-loaded microneedles demonstrated enhanced skin retention (more than 11-fold) of carvacrol after 24 h compared to free drug-loaded microneedles[33]. 9 3.1.3. block copolymer self-assembled structures the structures including micelles, vesicles, liposomes, and polymersomes are another class of srpderived architectures widely used in cdd. important case studies for the above architecture are described below. a temperature-responsive block copolymer comprised of poly(ethylene oxide)-block-pnipam (peo-bpnipam) self-assembled into micelles at greater than 32 ℃ with integrated hydrophobic fluorescent dye into their membrane and encapsulated hydrophilic doxorubicin. the micelles disassembled and released the drug in a controlled manner through the disintegration of the vesicles when the temperature reached below 32 ℃[34]. polymersomes or polymeric vesicles are hollow spheres in the nanometric range involving an aqueous core encircled by a polymeric bilayer membrane. these are synthetic analogues to liposomes and are developed by the self-assembly of amphiphilic molecules. like liposomes, polymersomes can load and deliver both hydrophilic and lipophilic drugs. in addition, they showed very little or no immunogenicity, increased toughness and decreased membrane permeability. furthermore, control release of drugs from these selfassembled vesicles can be attained by the inclusion of srps[35]. for example, photochromic polymersomes comprised of a diblock copolymer peo-b-poly(sp) (peo-b-psp) and loaded with dye molecule 4',6diamidino-2-phenylindole (dapi). upon self-assembling into polymersomes, sp moieties undergo reversible photo-triggered isomerization between hydrophobic sp moieties and zwitterionic merocyanine (mc) within the vesicles. these polymersomes demonstrated reversible photo-triggered transition with accompanied permeability switching from the state of impermeability to selectively permeability and zwitterionic small molecule species below critical molar masses. the loaded drug showed two types of drug release upon uv actuation: (i) sustained release of dapi upon short uv-irradiation duration due to slow spontaneous mc-tosp transition in the dark and (ii) switchable and on-demand drug release with alternated uv-vis light irradiation[36]. macromolecular supra-amphiphiles are a type of macromolecular amphiphiles whose hydrophobic and hydrophilic components are joined by noncovalent forces and these types of amphiphiles showed great potential in diverse fields including drug delivery, biomedical, and sensor systems. therefore, chi et al.[37] fabricated the first pillararene-based supra-amphiphilic polypseudorotaxane, incorporated with azobenzene derivatives. these self-assembled vesicles exhibited dual-responsiveness of the molecular recognition motif with thermos-responsiveness and photo-responsiveness due to the pillararene and azobenzene, respectively. this dds was successfully employed for the controlled release of calcein molecules. in one study an amphiphilic alternating multiblock copolymer poly[oligo(ethylene glycol)fumarate-codithiodiethanol fumarate with multiple -enes and disulfides in hydrophobic part was developed in the form of micelles. these micelles were capable of encapsulating modified doxorubicin (with a mercapto group) through conjugation and core-crosslinking reactions with 1,6-hexanedithiol in the core of micelles. this resulted in a nano-prodrug micelle which showed minimum drug release at physiological ph, while a rapid drug release was observed at lower ph (5.8) prevailed in the cancer-infected tissue induced by the breaking of disulfide bonds in the micelles[38]. 3.1.4. nanoparticles and nanocapsules developing smart nanoscale systems such as nanoparticles and nanocapsules could be one of the ways to breach or circumvent the efficient biological barriers and allow the medicaments to be delivered to the target site safely and efficiently. capsules can load more drugs compared to micelles and nanogels. these nanosized capsules can store and protect various drugs encapsulated and are capable of releasing the loaded drugs following their internalization within the cell. they also provide options to conjugate drugs with other macromolecules and allow adjustment in the kinetics of drug release. in addition, with the alteration of the 10 outer shell with peo brushes, prolonged circulation in vivo can be accomplished. furthermore, precise target drug delivery can be achieved by incorporating specific ligands on the particle surface as well as the capsule shell[3]. for instance, ph-dependent dds should be designed so that the conditions prevailing in the target organ or tissue provide a triggering mechanism to release the drug. in this regard, a lipid-polypeptide hybrid nanoparticle loaded with doxorubicin was fabricated with a ph-sensitive hydrophobic core with poly-lhistidine and a monolayer shell with pegylated lipid. the smart nanoparticles showed phase transition in two steps at two different ph values in the tumour environment: (i) at ph 6.5–7.0, which prevails in the tumour environment the nanoparticles swell leading to the conversion of negative potential to neutral and facilitate cellular uptake and (ii) at ph 4.5–6.5 that prevails in endo-lysosome after internalization, dissociating the nanoparticles and release of doxorubicin into the cytoplasm[39]. dendrimers are a novel and distinct class of polymeric materials which have huge potential applications in dds. these polymers are capable of encapsulating or conjugating big lipophilic or hydrophilic molecules through their branches and also show ph-sensitive drug release. in one such instance, dendrimers composed of carboxymethyl chitosan-modified polyamidoamine were used to encapsulate doxorubicin. the system exhibited negatively charged physiological conditions due to the presence of carboxymethyl chitosan which was found to accumulate at the site of the tumour. however, by releasing chitosan moiety under the influence of acidic conditions at the tumour site (ph 6.5), the system regained positive charge leading to high intracellular uptake in tumour cells through electrostatic adsorptive endocytosis[40]. in another study, a dual responsive (ph and redox) nanocarrier dds of letrozole was fabricated with heparin-conjugated poly(amidoamine) dendrimer via a redox-sensitive disulfide bond. the spherical nanocarrier with an average diameter of about 11nm effectively loads the drug more than 20% and could not only increase the biocompatibility under the reductive environment of glutathione but also deliver the drug at the desired site thereby showing the effectiveness of cancer therapy after removal of heparin from the particle surface[41]. zhang et al.[42] developed enzymesensitive dendrimer-based nanoparticles of gemcitabine for the treatment of cancer. in this, lysine peptide coupled with peg and drug with nanoparticles through click reaction. the resulting nanoparticles showed a very rapid release of gemcitabine in the condition having cathepsin b due to the presence of a breakable linker (glycyl phenylalanyl leucyl glycine) in the presence of cathepsin b. the presence of cathepsin b enhanced gemcitabine release (up to 90%) more than the environment without cathepsin b. an inflammation-sensitive nano-system was developed for indomethacin by bijukumar et al.[43] with multi-macromolecular polyelectrolytic complex nanoparticles composed of alginate, hyaluronic acid, and chitosan. the resulting nanoparticles were effectively encapsulated and delivered the drug to the target site of arthritis due to the breakdown of hyaluronic acid in response to potential inflammation activities characterized by hydroxyl radicals’ presence at the arthritis site. luo et al.[44] fabricated light and redox-responsive nanoparticles loaded with doxorubicin and comprised of porphyrin zirconium metal-organic framework at the center and selenium-based polymer as the outer layer. the resulting nanoparticles were found to release the drug in a controlled manner through the cleavage of nanoparticles induced by the formation of reactive oxygen species. 3.2. stabilization of colloidal dispersions colloidal particles with amphiphilic responsive properties can be incorporated into the interface between two immiscible fluids (liquid/liquid or liquid/gas), where the large surface area of particles induces their firm adherence. the formation of these layers as mechanical barriers led to the stabilization of emulsion and foams (called pickering dispersions). as a result, coalescence of the dispersed phase was prevented along with the bending rigidity of the interface. the key feature in this is the choice of particles for either phase as more 11 hydrophobic particles are preferred to stabilize w/o emulsions and vice versa. this is due to asymmetric orientation in the interface inducing a tendency to curve towards the minimum preferred phase. li et al.[45] employed laponite/lauric arginate complexes for the stabilization of alkyl ketene dimer pickering emulsion with tunable shells. it was observed that the laponite and lauric arginate complexes interacted close to the water/oil interface, thereby resisting the agglomeration and hydrolysis of oil globules for a considerable period. in addition, there was a synergistic effect of lauric arginate complexes with laponite, when employed for the biodegradable and food-grade emulsifiers. in one study, a magnetic (fe3o4) cellulose nanocrystal (mcnc) stabilized pickering emulsions based on red palm olein and curcumin were developed for the stimuli-responsive controlled drug release for the treatment of human colon cancer. the exposure of mcnc pickering emulsion to an external magnetic field triggered the drug to release 53.30%  ±  5.08% of the initial loading over 4 days. the stabilized emulsion inhibited the human colon cancer cell growth to 18% and reduced the 3d multicellular spheroids of hct116 by 2-fold as compared to the control sample[46]. in another study, a dual responsive toluene-in-water pickering emulsion was stabilized by magnetic nanoparticles (fe3o4) that were modified hydrophobically by ferrocene azine (fc+a) through electrostatic interaction. fc+a modified fe3o4 nanoparticles layer between toluene and water demonstrated reversible switching between unstable and stable states by alternately adding oxidizing (h2o2) and reducing agent (n2h4·h2o). the above system proved to be a good extraction system for the purification of aqueous solution that is contaminated by rhodamine b[47]. 3.3. diagnostics early intervention to prevent disease progression necessitates essential drug delivery predicaments of accurate and non-invasive diagnostic tools. the various diseases are generally associated with a significant imbalance in chemicals such as biomolecules and analytes in the body or variations in environmental factors. proper monitoring of these alterations and factors is very crucial to the diagnosis of those diseases. this can be performed through the use of polymer-based sensors that are sensitive to the above changes in chemical and environmental factors. another function of a nanodevice made up of responsive polymer is its ability to take an image of the site-specific delivery location of the drug[3]. 3.3.1. sensor a sensor may be defined as a self-reliant integrated device which can take up input from its surroundings and transform it into an output signal that can be converted into a readable form[48]. along the same line, a biosensor is a tool employed for the detection and quantification of desired biomolecules from a complex mixture of analytes and gives accurate and precise results in a quick time. thus, biosensors have advantages such as specificity, high degree of sensitivity, simplicity, cost-effective manufacturing, point-of-care analysis, and short response time and function in resource-limited settings. they are fabricated by combining responsive polymers to nearer stimuli such as temperature, ph, biomolecules, ionic strength, and light[49]. particularly, smart responsive hydrogel-based biosensors include the following components: (i) recognition of signal (ii) signal transfer to the gouging electrode, and (iii) converting the signal to the response[50]. in one study, pnipam-based stimulus-sensitive hydrogels were employed as a spacing transducer in between a nanodiamond and magnetic nanoparticles to develop a quantum sensor for the measurement of various biochemical parameters. here, the polymer coating was covalently attached to the nanodiamond quantum sensor leading to the development of a shell with magnetic nickel nanoparticles. when heated the pnipam hydrogel disintegrates owing to the phase transition leading to a considerable reduction in the gap between magnetic nanoparticles and nanodiamonds, and thus a considerable change in magnetic field detected employing optical magnetic resonance[51]. yan et al.[52] used graft copolymers comprised of cncs with azoc6ma-co-dmaema)-based fluorescent nanosensors sensitive to temperature, ph and uv light. when exposed to uv irradiation, the 12 azobenzene group underwent isomerization and thereby reversible transformation of fluorescence intensity. in addition, the change in ph and temperature led to a conformational change in pdmaema that induced fluorescence intensity. recently, enzyme-responsive polymers with functional groups have been studied intensively for their change in physiochemical properties in the presence of an enzyme. in this context, chitosan-based hydrogels functionalized with three different colourimetric substrates such as 4-nitrophenyl-βd-glucuronide, 5-bromo-4-chloro-3-indolyl-β-d-glucuronide (both are chromogenic substrate) and the fluorogenic substrate 4-methylumbelliferyl-β-d-glucuronide were developed for the detection of the βglucuronidase enzyme that is secreted by almost sent-percent of escherichia coli strains. the presence of βglucuronidase led to the cleavage of these functional groups and the emission of different wavelengths of light. the different colours were visible in less than 80 minutes, which can reduce the false-positive tests[53]. a hydrogel-based microfluidic sensor with a short response time was fabricated with acrylamide, 3acrylamidophenylboronic acid n-[3(dimethylamino)propyl] methacrylamide, n,n’-methylenebisacrylamide. this smart hydrogel network demonstrated a pillar-like structure that improved surface area/volume ratios when comes in contact with an aqueous solution having a target analyte resulting in their swelling or shrinking. this change in shape caused an altering of the resistance of the microfluidic channel to current flow when a small voltage was applied to the system[54]. 3.3.2. imaging bioimaging is a technique of visualizing biological behaviour over a specific period that does not disturb different life cycles including respiration, movement, etc., and provides a 3d structure of the specimens. it is useful in visualizing subcellular structure observations of the organism with multicellular structures. smart polymers are used for bioimaging as small alterations in the condition are sufficient to influence changes in the properties of polymers[55]. various imaging techniques including optical imaging, ultrasound imaging, magnetic resonance imaging (mri), positron emission tomography (pet), single-photon computed tomography (spect), and photoacoustic imaging (pa) are being used in clinical settings[56]. here, the most recent developments are mentioned. the fluorescent polymeric sensors used in the previous section can be used reversible for imaging various cells or tissues. in one study, unique switchable liposomes that were self-assembled from peg grafted amphiphilic copolymer were fabricated for imaging-assisted chemo-photothermal therapy for cancer. the tumour microenvironment induced peg shell detachment from the vesicles leading to the change in surface charge on the vesicle surface from neutral to positive, thereby enhancing cellular uptake[57]. in another study, j-aggregates having absorption at 1360 nm and emission at 1379 nm were fabricated from amphiphilic cyanine dye fd1080 and 1,2-dimyristoyl-sn-glycerol-3-phosphocholine through self-assembly. the resulting aggregates showed non-invasive brain and hindlimb vasculature bioimaging[58]. ultrasound-based imaging involves the use of sound waves at 2mhz or more that are transmitted to the patient’s body. these sound waves are reflected differently by different tissues followed by their conversion into images. a novel theranostic nanobubble system comprised of pei-grafted poly(lactic-co-glycolic acid) (plga) nanoparticles loaded with doxorubicin and condensed p-glycoprotein shrna for treatment of doxorubicin resistance human breast cancer. the nanobubble system showed ph-responsive drug release (>80%) at ph 4.4 and the system provided enhanced imaging of cancer cells[59]. another nanobubble liposomal system of paclitaxel was fabricated and observed that the system exhibited ultrasound-responsive paclitaxel delivery and imaging. the nanobubble system also demonstrated better stability, 2.5-fold higher uptake and 300-fold higher anticancer activity compared to commercial formulation (abraxane)[60]. shang et al.[61] reported a novel ultrasonic nanobubble fabricated from block copolymer polylactic acid (pla)-peg-nh2 and span 60 and tween 80 for the treatment of tumour imaging and therapy. 13 mri is a non-invasive procedure involving both radio waves and a powerful magnet linked to a computer and is used to generate detailed pictures of areas inside the body. here, the applied magnetic field arranges the magnetic moments of hydrogen atoms in tissues and is transmitted by an external radio wave[62]. after the relaxation of protons to their ground state, a radiofrequency signal is produced which is identified and transformed into an image. in this imaging technique, an mri contrast agent is essential to improve the contrasting power of the image through the alteration of the relaxation times of protons in different tissues/organs by involving the external magnetic field. however, the use of a large amount of contrast agent may lead to systemic toxicity. to circumvent this problem, these contrast agents can be encapsulated or chelated by stimuli-responsive polymers with specific tumour-specific stimuli-sensitive (e.g. acidic ph, overexpressed reactive oxygen species, ros) polymeric nanoparticles may be used in case of cancer diagnosis[63]. in one research, magneto-polymersomes were fabricated through in situ self-assembling by combining 2 diblock copolymers comprised of peg-terminated 2-hydroxypropyl methacrylate or carboxylic acid terminated poly(2-methacryloyloxyethyl phosphorylcholine) block. these magneto-polymersomes demonstrate a temperature increase of 6 ℃ throughout in vitro magnetic hyperthermia leading to intrinsic power loss. these particles offered the added potential for further functionalization and tuning concerning drug delivery[64]. aouidat et al.[65] developed nanoconjugates (gd(iii)-biopolymer-au(iii) complex) of gold coreshell nanoparticles and observed a strong absorption of these nanoconjugates by hepatocytes in the liver and simultaneously maintaining a t1 contrast within the cells which offered robust imaging by mr. radionuclide imaging includes pet and spect. pet is the latest imaging technology containing positron-emitting isotopes (annihilating γ-rays) such as 18f (most widely used) is introduced into the body, allowing the correct location in the physiological processes through the detection of positron released by the isotopes[66]. spect employs the same logistics and technologies as used by pet and provides cross-sectional 3d images. the 18f used in the imaging process has a low half-life. therefore, research has focussed on developing specific polymeric nanovesicles to subside the disadvantage. a multifunctional polymeric nano platform of a farnesylthiosalicylate-based triblock copolymer poegb-pvba-b-pfts (povf) with a poly(oligo(ethylene glycol) methacrylate) (poeg) hydrophilic block, a poly(4-vinylbenzyl azide) (pvba) middle block and a poly(fts) hydrophobic block for simultaneous imaging and therapeutic applications. the mixed micelle system was able to encapsulate paclitaxel effectively and azide groups in the block polymer helped in the incorporation of pet imaging modality. the micelle-based radiolabelled nanocarriers demonstrated their rapid uptake and slow clearance in the tumour tissues vis pet imaging and it also delivered both farnesyl-thiosalicylate and paclitaxel into the tumour cells leading to inhibition of tumour growth in 4t1.2 tumour bearing mice model[67]. in one investigation, a multifunctional nanosystem comprised of pei-entrapped gold nanoparticles, modified with pegylation and conjugation with tumour-specific ligand (buthus martensii karsch chlorotoxin), 3-(4′-hydroxyphenyl)propionic acid-osu (hpao), and fluorescein isothiocyanate. thereafter, the nanosystem was converted into a novel nanoprobe through radiolabelling of the surface with 131i via hpao for both diagnosis (spect/ct) and treatment. the above system showed suitability in imaging and radionuclide therapy of cancerous cells in in-vitro and also in an in vivo xenograft tumour model[68]. photoacoustic imaging is a recently developed non-invasive biomedical imaging modality involving the generation of ultrasonic waves via material irradiation with a pulsed laser. here, the irradiation is absorbed by the concerned tissue and thereby, generates localized heat and thermoelastic stress waves leading to the formation high-resolution image. this technique has many advantages such as better penetration, improved spatial resolution than optical imaging, and higher contrast than ultrasound. the materials used in this 14 technique are lacking degradability and photostability. therefore, a polymer-based system can avoid these material limitations[69]. in one study, first-of-kind biocompatible electron-donor-acceptor conjugated semiconducting polymer (ppor-peg) nanoparticles with light-harvesting units were fabricated for cancer theranostic involving both photoacoustic imaging-guided photothermal therapy. the system showed remarkable cell-killing ability with 100% success against tumour elimination[69]. in another study, lyu et al.[70] fabricated a semiconducting polymer nanoparticle to simultaneously boost in vivo imaging and cancer therapy through photoacoustic brightness and phototherapy. this intraparticle optoelectronic interaction between nir absorbing semiconducting polymer and fullerene (an ultrasmall carbon dot) resulted in a 2.6 and 1.3-fold increase in photoacoustic signal and photothermal temperature. 3.4. tissue engineering and regenerative medicine these are parts of life sciences combining cells or tissues, biomaterials/engineered bioactive molecules, and biochemical factors to either repair/improve or replace biological functions of tissues or organs which are injured beyond the level of identification. tissue engineering has many advantages such as no pain at the graft site, better survival rate, lower cost, and better availability than other conventional techniques viz. allografts and autografts[71]. in this context, various biopolymers including collagen, chitosan, alginate, etc. are being widely employed in the fabrication of stimuli-sensitive scaffolds and related constructs. the basic requirements for these scaffolds are the provided cellular linkage, propagation, progression, disparity, and relocation. these scaffolds are used to repair or replace almost all tissues including bone, cartilage, cardiac, skin, neural tissue, and blood vessels. 3.4.1. bone tissue engineering bone is constituted of organic matrices composed of collagen and non-collagenous proteins and inorganic matrices composed of carbonated hydroxyapatite. bone tissue engineering implies the application of a matrix with or without biomaterials or cells or a mixture of all of them to address defects in bone or bone regeneration. the use of bio-scaffold and other constructs in bone tissue engineering not only enhances the healing process but also reduces the healing period and therefore, minimizes postoperative complications. in this context, the use of srps can provide trigger-release of encapsulated active ingredients during fracture healing because of their osteoinductive influence for enhanced bone regeneration[72]. a dual responsive (temperature and ultrasound) hydrogel based on p(alg-g-nipaam) mixed with hydroxyapatite was fabricated. the developed hydrogels showed an excellent ultrasound-induced capacity for the on-demand release of various therapeutic agents such as bovine serum albumin, sodium fluorescein, and bone morphogenetic protein. these hydrogels hold promise for osteo-regeneration[73]. in another study, ding et al.[74] fabricated a dual functional (antibacterial and tissue generation) enzyme-responsive implant using ag nanoparticles loaded in mesoporous silica nanoparticles, followed by assembling poly-l-glutamic acid (pga) and polyallylamine hcl on the resulting particles. when exposed to glutamyl endonuclease (secreted by staphylococcus aureus) the pga component of the implant degraded and released ag nanoparticles in a concentration-dependent manner thereby showing antibacterial potential. in addition, the presence of pga led to excellent biocompatibility and enhanced regeneration capacity. tissue engineering involving cartilage poses a challenge due to limited blood supply to them. in this situation, the integration of cells, biomaterials, and factors with pertinent functions and attributes holds the key to tissue engineering. cartilage engineering involves an enhancement in cell number, followed by the induction of cells to form specific cartilaginous phenotypes[71]. in one study, tri-stimuli-responsive (temperature, ph, and ion) biphenyl-tripeptide supramolecular hydrogels were fabricated to stimulate an extracellular matrix scaffold. these hydrogels showed better support adhesion and proliferation of l929. in addition, they induced 15 the secretion of chondrocytes from the extracellular matrix in vitro and facilitated the phenotype support to hyaline cartilage[75]. another smart hydrogel with dual responsiveness to ph and ionic strength was fabricated with chitosan and carrageenan. the hydrogel showed ex-vivo enhancement of chondrogenic differentiation of atdc5 cells[76]. 3.4.2. cardiac tissue engineering among the various strategies employed to prevent death due to cardiovascular diseases, the use of tissue engineering with stem cells derived from adipose tissues is the most successful in regenerative medicine. this is because of the ability of stem cells for self-renewal and multi-lineage differentiation[77]. further, it acts as an angiogenic growth factor like hepatocyte and vascular endothelial growth factor. however, its application in cardiac tissue engineering is limited by cell death within 72 h of transplantation if injected directly into the myocardium. to circumvent the above problem, stem cells should be loaded into a biomaterial carrier to maintain both their angiogenic and viability[71]. in this context, li et al.[78] successfully fabricated a polyvinyl alcohol-based hydrogel system for rosinduced delivery of fibroblast growth factor to the myocardial infraction site in the heart. the resulting system demonstrated a low invasive choice for the regeneration of myocardial tissue with an associated higher degree of angiogenesis. most recently, a hybrid macroporous scaffold based on chondroitin sulfate, and gold nanorods for the on-demand release of stromal cell-derived factor 1 (sdf-1) and cytokines. the scaffold showed on-ofrelease of sdf-1 on account of electric stimulation due to the presence of gold nanorods. in addition, when transplanted into the heart of a rat, the sdf-1 was found to be released on a daily basis by electric stimulation and promoting blood vessel-developing cell infiltration and vascularization[79]. 3.4.3. neural tissue engineering mature neurons do not undergo cell division and also have limited healing and regeneration capacity[71]. therefore, any type of neural damage and injury to recover is considered a huge challenge. thus, direct regeneration of endoneurial tubes is a possible option that can be accomplished through two strategies such as grafting and tubulation for bridging and end-to-end nerve stump suturing. the former method is considered more efficacious as it nullifies the stress across the repair site of the neuron. however, the coherence between nerve fibres and schwann cells is not sufficient due to the low internal surface area[80]. thus, there is a need for biomaterial to fill the gap. in one research, conductive composites based on hydrogel were fabricated with conductive carboxymethyl chitosan and poly(3,4-ethylenedioxythiophene). the resulting electroconductive-responsive hydrogel showed exceptional cytocompatibility without any cytotoxicity when phaeochromocytoma cells of rats. in addition, it provided higher cell bioavailability, conductivity, cell viability, multiplication, and adhesion[81]. in another research, dong et al.[82] fabricated a light-sensitive conducting polymer with stretchable properties using copolymerized polyacrylamide and polyaniline to create a conductive bridge to restore the lost sciatic nerve. when illuminated with nir light, it showed higher conductivity that enhanced bioelectric signal transmission. in addition, the hydrogel had a higher degree of adaptability to the immediate strain of nerve tissues caused during the course of movement. 3.4.4. dermal tissue engineering (wound healing) the disadvantages, including frequent infections, pain, and flawed healing associated with traditional skin tissue engineering such as allogenic graft, autogenic graft, etc. propel the researcher toward safe and biocompatible scaffolds[83]. in this scenario, tissue-engineered skin is considered to be the best alternative to traditional methods. stimuli-responsive hydrogels have demonstrated significant potential as wound dressing material due to their cell growth and multiplication-enhancing properties. 16 for instance, palem et al.[84] used carboxy methylcellulose, polyvinyl-pyrrolidone, and agar strengthened with nano-sepiolite clay to develop nanocomposite hydrogel film loaded with 5-fluorouracil. the resulting hydrogel film was sensitive to ph for the release of 5-fluorouracil and showed significant skin regeneration potential. most recently, zhang et al.[85] developed a temperature-responsive nanocomposite hydrogel with gelatin-methacryloyl and polydopamine loaded with aspirin. the nanocomposite system showed a significant amount of aspirin release at 40 ℃ compared to 37 ℃ and 25 ℃ and also showed successful healing both in vitro and in vivo. 3.5. actuators actuators are defined as devices that generate motion by converting energy and signal to go into a system. thus, polymers used to fabricate actuators are the materials capable of converting energy from external stimuli such as light, heat, ph, and electricity to mechanical forces, resulting in shape changes[86]. srps with a distinctive ability to demonstrate considerable and adaptable variations in their volume regarding the extrinsic or intrinsic stimuli are being used widely in actuator models. actuators based on the polymer can be developed from different materials such as shape-memory polymers, hydrogels (used for delicate biological applications), and liquid crystal polymers[86]. actuation in srps is associated with various stretching of attached polymeric macromolecules because of strong repulsion between the grafted chains adjacent to one another. in the transformation of extrinsic stimuli into apprehensible distortion, specific structures such as hierarchical structures, gradient structures, and homogenous structures are required to incorporate these srps[49]. this actuator system has numerous applications in biomedicine, artificial muscle, grippers, etc. 3.5.1. biomedicine therapies based on stem cell transplantation have limitations such as low targeting accuracy, poor retention rate, and spontaneous transformation. to circumvent these, yasa et al.[87] fabricated a magneticresponsive 3d printed microactuator, which was able to recapitulate the physical and biochemical characteristics of the stem cell niche encoded at the single-cell level to achieve unique targeted cell delivery. in addition, stem cell-loaded micro-transporters were mobilized inside the microchannels under rotating magnetic fields and the mesenchymal stem cells were found to exhibit their differentiation capacities to commit to the osteogenic lineage when stimulated inside the microswimmers in vitro. more recently, magnetic microparticles were combined with hydrogels based on pedga to fabricate a novel actuator employing 3d printing. one-half of the magnetic particles were coated with silica and the other half with peg-coated au. these magnetic particles showed diverse programmed shape transformations and functions for future implementation at the cell level as organ-on-a-chip and other biomedical applications[88]. 3.5.2. artificial muscle natural muscles convert chemical energy into mechanical energy involving transmission of the electrical pulse from the brain which induces the release of ions within the sarcomere, followed by hydrolysis of adenosine triphosphate (atp) and eventually conformational variation along the natural muscle fibres[85]. to mimic the above phenomenon, layered polymers having stimuli-responsive properties were investigated for artificial muscles or robotics[89]. for instance, a film was fabricated with polypyrrole and partly reduced graphene oxide. the film showed excellent humidity and electrochemical responses and thus can be used for versatile stimulated actuations that are desired in advanced actuators, including artificial muscles[90]. in another case, a humidity-responsive selfbending bilayer-based actuator was fabricated with microgels of poly (n-isopropylacrylamide) and polydiallyldimethylammoniaum chloride. the resulting bilayer structure demonstrated bending upon drying, which was influenced by the presence of surrounding humidity. this was attributed to 17 polydiallyldimethylammonium chloride composed of both phases, where the amorphous layer absorbs moisture leading to its actuation, and the crystalline phase exhibits the bending property of the device[91]. 3.5.3. grippers grippers are the devices or tools that are installed at the end of a robot manipulator to induce device interaction with the environment. breger et al.[92] have fabricated a soft microgripper depending on pnipamco-acrylic acid (pnipam-aac) hydrogel with self-folding properties in response to stimuli such as temperature and magnetic field. to impart better qualities pnipam-aac was combined with the nonswellable and stiff-segmented polymer polypropylene fumarate. the magnetic response was derived through the incorporation of iron oxide nanoparticles into the porous hydrogel layer. molla et al.[93] fabricated a lightresponsive nanometer-sized actuator by intercalating a molecularly thin interfacial layer that is assembled from azobenzene and diblock copolymer peg-azo-pla within a robust glassy membrane. the fabricated thin layer showed a reversible and long-lived perturbation along greater than 500 chemical bonds. the photochemical trans-cis isomerization of the azo group was responsible for the out-of-equilibrium actuation in the middle of the interfacial layer. this system has the potential to be used as cargo for loading and its on-demand release in vivo. various applications of srps are presented in table 2. table 2. different applications of srps with types of stimuli, active ingredients encapsulated and results are presented. application types of formulations srps types of stimuli drugs result references control drug delivery microgel poly(nisopropylacrylamide)co-acrylic acid (pnipam-co-aac) ph-responsive crystal violet sustained drug release [24] microgel pnipam-co-aac and pnipam-3(acrylamido)phenylbor onic acid) (pnipamco-apba) ph-responsive methylene blue pulse pattern of drug release [25] pegylated nanogel 2-(n,ndiethylamino)ethyl methacrylate (eama) and modified peg ph-responsive doxorubicin controlled drug release [26] nanogel polyethyleneimine (pei) and pnipam ph and temperatureresponsive 5-fluorouracil lysosomaldependent apoptosis [27] nanogel dendritic polyglycerol and pei ph-responsive small interfering rna (sirna) controlled drug release [28] microneedle 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate light-sensitive ibuprofen extended drug release with onand-off principle [30] microneedle-patch boronate hydrogel with semi-penetrated silk-fibroin glucoseresponsive insulin sustained as well as acute glucoseresponsive insulin delivery [31] microneedle hyaluronic acid glucoseresponsive insulin released insulin in response to the local generation of hypoxia [32] 18 table 2. (continued). application types of formulations srps types of stimuli drugs result references microneedle array loaded with nanoparticles polycaprolactone infectionresponsive carvacrol site-specific and sustained drug release [33] micelles poly(ethylene oxide)block-pnipam (peob-pnipam) temperatureresponsive fluorescent dye and doxorubicin controlled manner [34] polymersomes or polymeric vesicles peo-bpoly(spiropyran) (peo-b-psp) photo-sensitive 4',6-diamidino2-phenylindole (dapi) sustained release, switchable and on-demand drug release [36] vesicles polypseudorotaxane, pillararene and azobenzene thermoand photoresponsive calcein controlled release [37] micelles poly[oligo(ethylene glycol)fumarate-codithiodiethanol fumarate ph-responsive doxorubicin rapid drug release in acidic conditions ph 5.8 [38] nanoparticles poly-l-histidine and pegylated lipid ph-responsive doxorubicin drug release in ph 4.5–6.5 [39] dendrimer carboxymethyl chitosan-modified polyamidoamine ph-responsive doxorubicin high intracellular uptake of drug at ph 6.8 [40] dendrimer heparin and poly(amidoamine) dendrimer ph and redoxresponsive letrozole drug release in the reductive environment of glutathione and at the desired site [41] dendrimer lysine peptide and peg enzymesensitive gemcitabine cathepsin binduced drug release (up to 90%) [42] polyelectrolytic complex nanoparticles alginate, hyaluronic acid, and chitosan inflammationsensitive indomethacin oh-radicals induced drug release [43] nanoparticles porphyrin zirconium metal-organic framework and selenium-based polymer light and redoxresponsive doxorubicin reactive oxygen species induced controlled drug release [44] stabilization of colloidal dispersions alkyl ketene dimer pickering emulsion laponite/lauric arginate complexes resisting the agglomeration and hydrolysis of oil globules [45] pickering emulsions magnetic (fe3o4) and cellulose nanocrystal (mcnc) magneticresponsive curcumin controlled drug release [46] toluene-in-water pickering emulsion magnetic nanoparticles (fe3o4) magneticresponsive purification of aqueous solution that is contaminated by rhodamine b [47] 19 table 2. (continued). application types of formulations srps types of stimuli drugs result references diagnostics hydrogel pnipam magneticresponsive magnetic nanoparticles and nanodiamonds quantum sensor for the measurement of various biochemical parameters [51] --cncs with azoc6ma-codmaema) temperature, ph and uv light-responsive fluorescent nanosensors [52] hydrogels chitosan enzymeresponsive chromogenic and fluorogenic substrate detection of the β-glucuronidase enzyme [53] hydrogel acrylamide, 3acrylamidophenylboro nic acid n[3(dimethylamino)pro pyl]methacrylamide, n,n’methylenebisacrylami de microfluidic sensor the change in shape caused an alteration of the resistance of the microfluidic channel to the current flow [54] liposomes peg grafted amphiphilic copolymer imagingassisted chemophotothermal therapy [57] cyanine dye fd-1080 and 1,2-dimyristoylsn-glycerol-3phosphocholine non-invasive brain and hindlimb vasculature bioimaging [58] nanobubble system pei-grafted poly(lactic-co-glycolic acid) (plga) ph-responsive doxorubicin and pglycoprotein shrna theranostic for cancer [59] nanobubble liposomal system ultrasoundresponsive paclitaxel better stability, higher uptake and higher anticancer activity compared to commercial formulation [60] nanobubble system block copolymer polylactic acid (pla)peg-nh2 and span 60 and tween 80 ultrasoundresponsive treatment of tumour imaging and therapy [61] polymersomes peg-terminated 2hydroxypropyl methacrylate or carboxylic acid terminated poly(2methacryloyloxyethyl phosphorylcholine) magneticresponsive imaging and tuning the drug delivery [64] core-shell nanoparticle nanoconjugates (gd(iii)-biopolymerau(iii) complex) of gold mr imaging of hepatocytes [65] 20 table 2. (continued). application types of formulations srps types of stimuli drugs result references micelle triblock copolymer poeg-b-pvba-bpfts (povf), poly(oligo(ethylene glycol) methacrylate) (poeg), a poly(4vinylbenzyl azide) (pvba), and a poly(fts) pet farnesylthiosali cylate and paclitaxel simultaneous imaging and therapeutic applications [67] nanoprobe pei-entrapped gold nanoparticles radioactiveresponsive diagnosis (spect/ct) and treatment of cancer [68] nanoparticles pp or-peg photoacoustic imaging high-resolution image [69] polymeric nanoparticles photoacoustic theranostic for cancer [70] tissue engineering and regenerative medicine hydrogel p(alg-g-nipaam) mixed with hydroxyapatite temperature and ultrasoundresponsive bovine serum albumin, sodium fluorescein, and bone morphogenetic protein osteoregeneration [73] implant mesoporous silica nanoparticles, poly-lglutamic acid (pga) and polyallylamine hcl enzymeresponsive ag nanoparticles osteoregeneration [74] hydrogel-based scaffold biphenyl-tripeptide temperature, ph, and ionresponsive cartilageregeneration [75] hydrogel chitosan and carrageenan ph and ionicresponsive enhancement of chondrogenic differentiation [76] hydrogel polyvinyl alcohol ros-responsive fibroblast growth factor regeneration of myocardial tissue [78] hybrid macroporous scaffold chondroitin sulfate, and gold nanorods electricresponsive stromal cellderived factor 1 (sdf-1) and cytokines on-demand release [79] composites based on hydrogel carboxymethyl chitosan and poly(3,4ethylenedioxy thiophene) electricresponsive neural tissue engineering [81] hydrogel polyacrylamide and polyaniline light-sensitive restore the lost sciatic nerve [82] nanocomposite hydrogel film carboxy methylcellulose, polyvinyl-pyrrolidone, agar and nanosepiolite clay ph-responsive 5-fluorouracil significant skin regeneration potential [84] nanocomposite hydrogel gelatin-methacryloyl and polydopamine temperatureresponsive aspirin wound healing [85] 21 table 2. (continued). application types of formulations srps types of stimuli drugs result references actuators 3d printed microactuator magneticresponsive mesenchymal stem cells targeted cell delivery [87] 3d printed microactuator pedga, magnetic microparticle, silica and peg-coated au magneticresponsive organ-on-achip and other biomedical applications [88] film polypyrrole and reduced graphene oxide humidity and electrochemical responses formation of artificial muscles [90] bilayer actuator poly (nisopropylacrylamide) and polydiallyldimethylam moniaum chloride humidityresponsive formation of artificial muscles [91] soft microgripper pnipam-co-acrylic acid (pnipam-aac), iron oxide and polypropylene fumarate temperature and magneticresponsive interaction with the environment [92] nanogripper azobenzene and diblock copolymer peg-azo-pla light-responsive interaction with the environment [93] 4. conclusions the rapidly developing field of srps has already shown their efficiency for a variety of applications, including cdd, stabilization of colloidal systems, designing and fabrication of sensors, various imaging techniques, actuators (such as artificial muscles and grippers), and prevention of corrosion. the fields that most benefit from stimuli-responsive polymer materials are biomedical, environmental, and biochemistry. in addition, responsive systems are capable of providing functionality at a low cost, as only a nanometric, thin coating is desired. apart from that, nanocarriers with srps such as micelles, liposomes, polymersomes, and nanoparticles might show synergistic activity due to the presence of an active polymer matrix and a stimulus component. despite the above advantages, stimuli-responsive polymers suffer due to the following challenges: the first challenge is to fabricate complex systems that are responsive to biomarkers or biochemical signals generally available in nanomolar concentrations. thus, such systems inside the human body essentially require a complex hierarchical organization (compartmentalization) of the responsive particles to accommodate different amplification mechanisms. the second challenge is to fabricate systems that can greet various extrinsic stimuli smartly. for instance, surface-encoded assemblies of nanoclusters and biocomputing systems have been developed more recently, which is far less than the present-day demand. the third challenge is the safety of the used polymer or its modified compounds, including the toxicity profile, different disease conditions that can alter the moieties, and the difference observed between the in vitro and in vivo efficacy in the presence of various stimuli. last but not least, the list pertains to the long-term stability against uv light, nir, temperature, solvent, etc., and durability, including mechanical stability, abrasion resistance, etc. the applications of srps discussed in this review have immense potential in various fields, and the author hopes these polymers will add a new field of applications through new concepts. 22 conflict of interest the author declares no conflict of interest. abbreviations srp: stimuli-responsive polymer cdd: controlled drug delivery cst: critical solution temperature ucst: upper cst lcst: lower cst nir: near-infrared uv: ultraviolet nadph: nicotinamide adenine dinucleotide phosphate nadh: nicotinamide adenine dinucleotide hydrogen pnipam-co-aac: poly(n-isopropylacrylamide)-co-acrylic acid pnipam-co-apba: pnipam-3-(acrylamido)phenylboronic acid) eama: 2-(n,n-diethylamino)ethyl methacrylate pei: polyethylenimine sirna: small interfering rna sc: stratum corneum peo-b-pnipam: poly(ethylene oxide)-block-pnipam sp: spiropyran peo-b-psp: peo-b-poly(spiropyran) dapi: 4',6-diamidino-2-phenylindole mc: merocyanine mcnc: magnetic (fe3o4) cellulose nanocrystal mri: magnetic resonance imaging pet: positron emission tomography spect: single-photon computed tomography pa: photoacoustic imaging plga: poly(lactic-co-glycolic acid) pla: 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dongguan 523808, china * corresponding authors: yihong ding, 20195205@wzu.edu.cn; tianbiao zeng, tianbiaozeng@126.com abstract: cobalt-based sulfides have emerged as promising candidates for next-generation high-performance anode materials for lithium-ion batteries (libs) due to their high theoretical specific capacity and reversible conversion reaction mechanisms. however, their practical application is hindered by volume expansion effects and relatively low rate performance. guided by theoretical principles, this study synthesizes nanoscale bi/cos-c and bi/co4s3-c (denoted as bi/cs-c) composite materials using co and bi2s3 as precursors via a solid-state ball milling method. the electrochemical properties of these materials were systematically investigated. when employed as anodes for libs, bi/cos-c and bi/cs-c exhibit excellent rate capabilities. at current densities of 0.1, 0.5, 1, 4, and 10 a/g, the reversible capacities of bi/cos-c were 939.2, 730.7, 655.6, 508.1, and 319 mah/g, respectively. in contrast, bi/cs-c exhibited reversible capacities of 760.4, 637.6, 591.9, 484.3, and 295.4 mah/g, respectively. moreover, co4s3, as an active component, enables superior long-cycle performance compared to cos. after 300 cycles at 0.2 a/g, the bi/cos-c and bi/cs-c electrodes retained capacities of 193.1 and 788.8 mah/g, respectively. this study demonstrates that nanostructure design and carbon-based composite materials can effectively mitigate the volume expansion issue of cobalt-based sulfides, thereby enhancing their rate performance and cycling stability. this strategy provides new insights for the development of high-performance anode materials for lithium-ion batteries and is expected to accelerate their practical application in next-generation energy storage devices. keywords: lithium-ion batteries; anode materials; nanoparticles; bi/cos-c; bi/co4s3-c 1. introduction with the rapid development of renewable energy technologies, libs have become the key energy storage devices for electric vehicles, portable electronic devices, and large-scale energy storage systems due to their high energy density, long cycle life, and environmental friendliness [1–3]. however, the theoretical specific capacity of conventional graphite anode materials is only 372 mah/g. their relatively low specific capacity and rate performance fail to meet the demands of next-generation high-performance energy storage devices for high energy density, high power density, and long cycle life [4,5]. therefore, the development of novel anode materials with higher specific capacity, superior rate performance, and enhanced cycling stability has become a key research focus [6]. among various emerging anode materials, transition metal sulfides (tmss) are considered one of the most promising candidates due to their reversible conversion reaction mechanisms citation zhang l, yue t, ding y, et al. solidstate ball milling synthesis of highcapacity multiphase nanoscale bi/co4s3-c as an anode material for lithium-ion batteries. characterization and application of nanomaterials. 2025; 8(2): 11620. https://doi.org/10.24294/can11620 article info received: 21 march 2025 accepted: 28 april 2025 available online: 29 may 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 11620. 2 and high theoretical specific capacity [7–9]. in particular, cobalt-based sulfides (coxsy) have attracted significant attention in lib anode material research due to their high electronic conductivity, excellent lithium-ion diffusion kinetics, and appropriate electrochemical reaction potential [10,11]. however, pure coxsy undergoes significant volume expansion during charge/discharge cycles, leading to electrode structural degradation, poor rate performance, and rapid capacity fading, which severely limit its practical application. to address these challenges, researchers have proposed various strategies to mitigate the volume expansion of coxsy and enhance its lithium storage performance, including: (1) rationally designed composite structures, incorporating other metals or constructing multiphase tms composite materials to form stable heterostructures [12,13]; (2) nanostructuring electrode materials, reducing particle size to increase specific surface area and accelerate lithium-ion diffusion kinetics [14–16]; (3) incorporating carbon-based materials (e.g., porous carbon, graphene, and its derivatives) to construct conductive networks and buffer volume expansion, thereby improving cycling stability [17,18]. notably, the introduction of carbon-based materials plays a crucial role in enhancing the electrochemical performance of coxsy anode materials, with key advantages in three aspects: (i) excellent interfacial regulation, effectively encapsulating coxsy particles and enhancing their structural stability; (ⅱ) superior electrical conductivity and mechanical strength, facilitating fast electron/ion transport and alleviating volume expansion; (ⅲ) a highly porous structure and large specific surface area (typically > 1000 m2/g), increasing the electrode-electrolyte contact area and providing more active sites for li+ storage. recent studies have highlighted the potential of bismuth (bi) and its compounds as promising anode materials for lithium-ion batteries, owing to their high theoretical capacity (385 mah/g for bi) and a distinctive alloying/dealloying mechanism that enables fast kinetics and reversible lithium storage [19,20]. furthermore, compared with other alloy-type anode materials, bi exhibits a relatively low volume expansion (~220%), which helps mitigate structural degradation. when bi is composited with cobalt-based sulfides, it can regulate internal stress and suppress local phase transitions during cycling. notably, yu et al. synthesized co4s3 nanoparticles embedded in a carbon-based interface using a phase-inversion strategy that integrates in situ sulfidation and carbonization [21]. this material significantly enhanced interfacial selectivity and maintained a specific capacity of 563.5 mah/g after 400 cycles at 4.0 c. in addition, jiang et al. developed an environmentally friendly in situ method to fabricate nitrogen-doped co9s8/co4s3 nanoparticles coated with carbon and anchored onto reduced graphene oxide sheets (n-cs@c/g) [10]. in this composite, co4s3 provides additional electrochemically active sites for lithium storage, enabling the n-cs@c/g electrode to exhibit progressive cycling stability with a capacity of 662 mah/g at 2 a/g. these findings underscore the remarkable advantages of bi-based and co4s3-containing composites in enhancing the structural stability and electrochemical performance of lithium-ion battery anodes, especially when synergistically integrated with conductive carbon frameworks. based on these insights, this study selected co and bi2s3 as precursors to synthesize bi/cos and bi/co4s3 composite materials via a solid-state reaction. these characterization and application of nanomaterials 2025, 8(2), 11620. 3 materials were then anchored onto exfoliated graphite through ball milling, forming nanoscale heterostructured bi/cos-c and bi/co4s3-c (bi/cs-c) composites. among them, the bi/cs-c composite exhibited the most significant synergistic enhancement, with key advantages in the following aspects: (1) the introduction of bi, through the formation of a nanocomposite structure with co4s3, plays a role in modulating internal stress and mitigating local structural distortions. this contributes to enhanced structural stability of the electrode material during charge-discharge cycles and helps suppress structural degradation caused by the volume changes of co4s3 [19,22]; (2) the synergistic effect of carbon-based materials further enhanced the electronic conductivity and rate performance of the material, accelerated li+ diffusion kinetics, and alleviated mechanical stress during charge/discharge cycles through the flexible carbon framework; (3) the optimized nanostructure provided a larger specific surface area and more active sites, enhancing electrode-electrolyte interactions, improving li+ storage capacity, and increasing interfacial stability. experimental results demonstrated that nanostructure design and carbon-based material incorporation effectively mitigated the volume expansion of cobalt-based sulfides, significantly enhancing their rate performance and cycling stability. this strategy offers new insights for the development of high-performance anode materials for libs. 2. materials and methods 2.1. synthesis of bi/co1−xs-c and bi/co4s3-c materials cobalt powder (co), graphite (c), and bismuth sulfide (bi2s3) were purchased from shanghai macklin biochemical co., ltd. all chemicals were used as received without further purification. first, co and bi2s3 were mixed in molar ratios of 1:1, 2:1, 3:1, and 4:1 and ground in an agate mortar until no visible particles remained. the mixtures were then loaded into a quartz tube, vacuum-sealed, and placed in a tube furnace. the temperature was increased at a rate of 5 °c/min and maintained at 600 °c for 6 h. after the reaction, the obtained samples were cooled to room temperature and ground into fine powders using an agate mortar, yielding four different products. based on x-ray diffraction (xrd) analysis, the bi/cos and bi/co4s3 (bi/cs) products obtained from the 3:1 and 4:1 molar ratios were selected and mixed with 15 wt.% graphite. the mixtures were then subjected to ball milling at a rotational speed of 900 r/min under a nitrogen atmosphere for 10 h to obtain the bi/cos-c and bi/co4s3-c (bi/cs-c) composites. 2.2. material characterization the crystallographic information of the samples was studied using an x-ray diffractometer (xrd, shimadzu-xrd-7000s, cu kα, 40 kv, 40 ma) with a scan range of 10°–80° and a step size of 0.02°. the morphology and microstructure of the prepared samples were characterized using a scanning electron microscope (sem, nova 200 nanosem) and a high-resolution transmission electron microscope (tem, jem-2100f). characterization and application of nanomaterials 2025, 8(2), 11620. 4 2.3. electrode preparation and electrochemical performance evaluation the active material, acetylene black, and carboxymethyl cellulose sodium salt were mixed in a mass ratio of 8:1:1 and stirred with an appropriate amount of deionized water for 2 h to form a slurry. the slurry was then uniformly coated onto copper foil using a 50 μm film applicator and dried in a vacuum oven at 60 °c for 2 h. the coated copper foil was punched to form disks with a diameter of 12 mm, which were used as anodes. the sample mass on each electrode was 1.5 ± 0.1 mg/cm2. the cr2032 coin cells were assembled in an argon-filled glove box, where the levels of water and oxygen in the glove box were both below 0.1 ppm. the electrolyte was 1 mol/l lipf6 dissolved in a mixture of ethylene carbonate (ec), dimethyl carbonate (dmc), and ethyl methyl carbonate (emc) in a volume ratio of 1:1:1 (vol%), with 5.0% fluoroethylene carbonate (fec). the separator used for the libs was a porous polypropylene membrane (celgard-2300). the assembled libs were tested for charge/discharge, galvanostatic intermittent titration technique (gitt), and rate performance using a land battery tester. cyclic voltammetry (cv) tests were conducted using an ec-100b electrochemical workstation. 3. results and discussion 3.1. theory the equations for the co and bi2s3 system were written based on the final energy/atom values of each crystal from the materials project website, and the calculation of the gibbs free energy ∆g of the reactions is given by equation (1) [23,24]: ∆g = gproducts − greactants (1) where gproducts and greactants represent the gibbs free energies of the products and reactants, respectively. the changes in ∆g for a series of predicted chemical reactions are shown in equations (2)–(5) below: 27 8 co + bi2s3 = 2bi + 3 8 co9s8, ∆g = −1.3397 (2) 9 4 co + bi2s3 = 2bi + 3 4 co3s4, ∆g = −0.5832 (3) 2co + bi2s3 = 2bi + co2s3, ∆g = −0.3342 (4) 3co + bi2s3 = 2bi + 3cos, ∆g = −0.7411 (5) from the above calculation results, it is evident that all the ∆g values are negative, indicating that these reactions are thermodynamically feasible. next, the gibbs free energy for each mole of co was normalized, with the formula ∆g/n, where n is the coefficient of co in the chemical equation. the ∆g/n values for reactions (2)–(5) are −0.3969, −0.2592, −0.1671, and −0.2740 ev, respectively. thus, it can be concluded that the driving force for the reaction of co with bi2s3 to form co9s8 is the greatest, followed by the formation of cos, co3s4, and co2s3. therefore, to systematically study the effect of the co/bi2s3 molar ratio on the reaction products and further explore the formation patterns of possible cobalt characterization and application of nanomaterials 2025, 8(2), 11620. 5 sulfide phases, this study chose co:bi2s3 molar ratios of 1:1, 2:1, 3:1, and 4:1 for solid-state reactions to cover the above reaction systems. 3.2. characterization after performing solid-state reactions with co:bi2s3 molar ratios of 1:1, 2:1, 3:1, and 4:1, the obtained products were characterized by x-ray diffraction (xrd), and their diffraction patterns are shown in figure 1a–c. as observed in the figure, for molar ratios of 1:1 and 2:1, diffraction peaks corresponding to bi were detected in the reaction products, indicating that bi2s3 was partially reduced. however, residual bi2s3 was still present, suggesting that the reaction was incomplete. in contrast, at molar ratios of 3:1 and 4:1, bi2s3 was fully converted, forming bi/co1−xs and bi/co4s3 (bi/cs) composite materials, respectively. this indicates that a higher co/bi2s3 ratio facilitates complete reaction and the formation of a stable cobalt sulfide phase. the value of x was determined using equation (6): 𝐶 = 𝑛 × 𝐹/[3.6 × (𝑀bi2s3 + 𝑀𝐶𝑜y)] (6) where f is the faraday constant (f = 96485.6 c/mol, given that 1 ev = 96485.6 j/mol), n = 12 represents the total number of electrons transferred per mole of bi2s3 during li+ storage, and 3.6 is the conversion factor between coulombs and milliampere-hours. 𝑀bi2s3 and 𝑀𝐶𝑜 represent the molar masses of bi2s3 and co, respectively, and y is the co/bi2s3 molar ratio. based on the calculations, when the co:bi2s3 molar ratio is 3:1, the target materials are cos and bi, yielding x = 0. additionally, chen et al. conducted xrd characterization of cos@c, and the xrd patterns of co1−xs synthesized in this study closely matched their results [25]. this confirms that the synthesized bi/co1−xs theoretically corresponds to the predicted bi/cos composite material [26,27]. since residual unreacted bi2s3 was still present in the 1:1 and 2:1 reaction systems, they were not further investigated. to further explore the optimal molar ratio for the reaction between co and bi2s3, the bi/cos and bi/cs materials synthesized at 3:1 and 4:1 molar ratios were ball-milled with 15 wt.% graphite, yielding bi/cos-c and bi/cs-c, respectively, as shown in figure 1b,c. notably, no xrd peaks corresponding to graphite were observed in the bi/cos-c and bi/cs-c composite materials, suggesting that the graphite may have been partially or completely transformed into an amorphous disordered structure during the ball-milling process. moreover, compared to bi/cos and bi/cs, the peak intensities of bi/cos-c and bi/cs-c were significantly reduced. this is primarily attributed to the high-energy mechanical forces applied during the ball-milling process, which induce a certain degree of disorder in the bi/cos and bi/cs active materials, thereby affecting their crystalline structure and xrd diffraction characteristics. meanwhile, the exfoliated graphite, serving as a conductive framework, is uniformly distributed throughout the composite system and contributes to structural stabilization, although it is not the main cause of the observed crystallographic disorder. furthermore, as shown in the raman spectra in figure 1d, two prominent characteristic peaks are clearly observed at approximately 1350 cm−1 (d band) and 1580 cm−1 (g band) in the bi/co4s3-c and bi/cos-c samples. these peaks correspond to disordered carbon (d band) and graphitic carbon characterization and application of nanomaterials 2025, 8(2), 11620. 6 (g band), which are typical raman features of carbon-based materials. in contrast, the bi/co4s3 and bi/cos samples without carbon composites exhibit negligible raman signals in the same wavenumber range, indicating the absence of carbon components in these materials. figure 1. (a) xrd patterns of samples with co:bi2s3 molar ratios of 1:1 and 2:1; (b) xrd patterns of bi/co1−xs and bi/co1−xs-c composites (co:bi2s3 = 3:1); (c) xrd patterns of bi/co4s3 and bi/co4s3-c composites (co:bi2s3 = 4:1); (d) raman patterns of bi/co4s3, bi/co4s3-c, bi/cos and bi/cos-c. to analyze the effects of different molar ratios and ball milling treatment on the microstructure of the materials, sem was used to examine the bi/cos, bi/cos-c, bi/cs, and bi/cs-c composites at a 20 μm scale. figure 2a,c present the morphology of the bi/cos and bi/cs composites, both of which exhibit large agglomerated structures with relatively rough surfaces. notably, the bi/cs composite shows a certain degree of interfacial distribution between particles, indicating good integration between different phases in the material. figure 2b,d display the sem images of the bi/cos-c and bi/cs-c composites. compared to bi/cos and bi/cs, bi/cos-c and bi/cs-c exhibit a more uniform and finer particle distribution. this suggests that the introduction of graphite during the ball milling process may have played a role in dispersion, preventing further particle agglomeration. additionally, the overall reduction in particle size is likely attributed to the fragmentation effect induced by mechanical ball milling. characterization and application of nanomaterials 2025, 8(2), 11620. 7 figure 2. sem images of (a) bi/cos; (b) bi/cos-c; (c) bi/co4s3; and (d) bi/co4s3-c composites at a 20 μm scale. to further verify the regulatory effect of ball milling on the crystal structure of the materials, the crystallite sizes of the samples were calculated based on the characteristic diffraction peaks from the xrd patterns shown in figure 1b,c, as summarized in table 1. the crystallite sizes were calculated using the scherrer equation (7), 𝐷 = 𝐾𝜆 βcos𝜃 (7) where d is the crystallite size, k is the shape factor (typically 0.9), λ is the x-ray wavelength (cu kα, 0.15406 nm), β is the full width at half maximum (fwhm) of the main xrd peak (in radians), and θ is the bragg angle of the corresponding peak. the results indicate that, compared to the non-carbon-coated bi/cos and bi/cs samples, the corresponding bi/cos-c and bi/cs-c samples exhibit significantly broader diffraction peaks across multiple crystallographic planes. the fwhm values increased markedly, with the average crystallite sizes decreasing from 26.84 nm (bi/cos) and 54.05 nm (bi/cs) to 12.14 nm (bi/cos-c) and 9.94 nm (bi/cs-c), respectively. this further corroborates that the synergistic effect of ball milling significantly refines the particle size, thereby promoting the formation of more stable characterization and application of nanomaterials 2025, 8(2), 11620. 8 electrochemical reaction interfaces and enhancing the exposure of additional active sites. table 1. fwhm values of xrd characteristic peaks and corresponding crystallite sizes of different samples calculated based on the scherrer equation. sample 2θ (°) fwhm (°) β (rad) cos (θ) crystallite size (nm) bi/co4s3 27.17045 0.15469 0.0027 0.9719 52.25 29.83264 0.14919 0.00261 0.9667 54.39 39.6288 0.18724 0.00327 0.9424 44.56 52.05749 0.1345 0.00235 0.8991 65.01 average 54.05 bi/co4s3-c 27.11967 0.65054 0.01136 0.972 12.48 29.95035 0.89421 0.01561 0.9664 9.02 39.60183 0.73836 0.01289 0.9426 10.61 51.96184 1.14691 0.02001 0.8994 7.65 average 9.94 bi/cos 27.17189 0.29735 0.00519 0.9719 27.13 37.9771 0.31609 0.00552 0.9478 26.43 39.63194 0.31626 0.00552 0.9424 26.96 average 26.84 bi/cos-c 27.13421 0.55814 0.00974 0.972 14.46 37.9551 0.76598 0.01337 0.948 10.91 39.60505 0.71549 0.01249 0.9426 11.04 average 12.14 figure 3 presents the tem images of bi/cos-c and bi/cs-c composites along with the corresponding energy-dispersive x-ray spectroscopy (eds) elemental distribution analysis to further reveal the microscopic morphology and elemental distribution of the materials. figure 3a,b show the tem images of bi/cos-c and bi/cs-c composites. both materials exhibit a distinct nanoparticle aggregation structure, with the core region displaying a higher electron density, indicating the coexistence of bi and cos or co4s3 particles. furthermore, the peripheral region exhibits a lower electron density, which is presumed to correspond to the graphite distribution. this suggests that graphite may have uniformly coated the bi/cos-c and bi/cs-c composite particles during the ball milling process. figure 3c,d show the eds elemental distribution maps of bi/cos-c and bi/cs-c composites. the uniform distribution of co, bi, s, and c elements further confirms that bi and cos or co4s3 are homogeneously dispersed and closely connected with exfoliated graphite at the nanoscale. the tem and eds results indicate that the ball milling process facilitates the uniform distribution of graphite within the bi/cos and bi/cs composites. additionally, distinct lattice fringes can be observed in the highresolution tem images, as shown in figure 4a,c. in figure 4a, the interplanar spacings are measured as 1.03 å and 1.55 å, corresponding to the (114) plane of cos and the (107) plane of bi, respectively. similarly, in figure 4c, the interplanar characterization and application of nanomaterials 2025, 8(2), 11620. 9 spacings of bi and co4s3 are measured as 1.65 å and 2.87 å for the (024) and (222) lattice planes, respectively. these findings suggest that the nanoscale bi2s3 particles are separated by bi nanoparticles and that the nanosized bi/cos and bi/cs particles are encapsulated within graphite layers. figure 4b,d present the selected area electron diffraction (saed) patterns of bi/cos-c and bi/cs-c, showing distinct diffraction rings. this further confirms the coexistence of bi and cos or co4s3 in the bi/cos-c and bi/cs-c composites, indicating their well-defined polycrystalline nature. figure 3. (a,b) tem images of bi/cos-c and bi/co4s3-c; (c,c1–c4) elemental distribution maps of bi, co, c, and s in bi/cos-c; (d,d1–d4) elemental distribution maps of bi, co, c, and s in bi/co4s3-c. figure 4. (a,b) tem and saed images of bi/cos-c; (c,d) tem and saed images of bi/co4s3-c. characterization and application of nanomaterials 2025, 8(2), 11620. 10 3.3. testing based on this, to further investigate the lithium storage mechanisms of bi/cos, bi/cs, bi/cos-c, and bi/cs-c composites, cyclic voltammetry (cv) tests and differential charge/discharge curve (dq/dv) analyses were conducted for each electrode material. the dq/dv profiles of bi/cos and bi/cs are shown in figure 5a,c, respectively, while the cv curves of bi/cos-c and bi/cs-c at a scan rate of 0.1 mv/s are presented in figure 5b,d. during the initial cathodic scan, bi/cos and bi/cs electrodes exhibit pronounced reduction peaks at 1.16 v and 1.11 v, respectively. in contrast, bi/cos-c and bi/cs-c electrodes show similar irreversible current peaks at 0.63 v and 0.56 v, which can be primarily attributed to the formation of the solid electrolyte interphase (sei) and the initial structural activation of the electrode materials during the first charge-discharge cycle. this process consumes a portion of lithium ions, leading to shifts in the position and intensity of current peaks in subsequent cycles. from the second to the fifth scan, the cv curves of the bi/cos-c and bi/cs-c electrodes progressively overlap, indicating excellent electrochemical reversibility and cycling stability. as shown in figure 5b, during the second to fifth scans of bi/cos-c, the reduction peak at 1.32–1.36 v is associated with li+ insertion, forming lixcos. a strong reduction peak at 0.75~0.78 v corresponds to the conversion reaction of lixcos, leading to the formation of co and li2s [28]. subsequently, the reduction peak at 0.63–0.66 v corresponds to the alloying reaction of bi, forming the li3bi phase [25]. additionally, the oxidation peaks at 0.88–0.90 v and 2.00–2.02 v correspond to the multi-step dealloying reaction of li3bi and the reverse conversion reaction of co, respectively. to gain deeper insight into the lithium storage mechanism, the above reactions can be described by the following equations (8)–(13): discharge process: xli+ + xe− + cos → lixcos (8) lixcos + (2−x)li+ + (2-x)e− → co+li2s (9) 3li+ + 3e− + bi → li3bi (10) charge process: li3bi → 3li+ + 3e− + bi (11) co + li2s → lixcos + (2−x)li+ + (2−x)e− (12) lixcos → xli+ + xe− + cos (13) as shown in figure 5d, after the first cycle activation, a significant reduction peak was observed at 1.29–1.32 v for the bi/cs-c electrode. this is likely the initial reaction of li+ insertion into the co4s3 structure, forming liyco4s3 (14) [17,29]. a new peak was detected at 0.77 v, corresponding to the conversion reaction of liyco4s3, leading to the formation of co and li2s (15) [10]. it is further speculated that the reduction peak at 0.61 v corresponds to the alloying reaction of bi, forming li3bi (16) [21,30,31]. during the anodic scan, the oxidation peak observed at 0.93– 0.94 v is likely attributed to the delithiation reaction of li3bi. the oxidation peak at characterization and application of nanomaterials 2025, 8(2), 11620. 11 2.04–2.07 v likely represents the desorption process of li2s and co, leading to the formation of liyco4s3, as well as a more extensive reversible delithiation process, which essentially restores the co4s3 active material to its initial state, completing a full cycle. yli+ + ye− + co4s3 → liyco4s3 (14) liyco4s3 + (2−y)li+ + (2−y)e− → co+li2s (15) 3li+ + 3e− + bi → li3bi (16) based on this, the reaction sequence of bi/cs-c composite with lithium should be co4s3 → liyco4s3 → bi. it can be seen that both bi/cs-c and bi/cos-c exhibit good electrochemical stability. however, bi/cs-c, with its higher oxidation/reduction peak currents and broader potential range, may have superior performance in energy storage applications. this suggests that co4s3 has a stronger synergistic effect on the electrochemical behavior of bi compared to cos. figure 5. (a,c) differential capacity curves (dq/dv vs. v) of bi/cos and bi/bi/co4s3 electrodes at 0.1 a/g; (b,d) cyclic voltammetry (cv) curves of bi/cos-c and bi/bi/co4s3-c at a scan rate of 0.1 mv/s. to further evaluate the electrochemical performance of bi/cos, bi/cos-c, bi/cs, and bi/cs-c electrodes during the charge-discharge process, the cycling performance of the materials was tested at a low current of 0.2 a/g, as shown in figure 6a. the experimental results indicate that the initial specific capacities of the bi/cos-c and bi/cs-c electrodes reached 959.7 mah/g and 852.6 mah/g, respectively, significantly outperforming the reversible capacities of bi/cos and bi/cs electrodes at 647.4 mah/g and 690.4 mah/g. this suggests that the incorporation of carbon materials effectively enhances the lithium storage capacity of the electrode materials. however, during prolonged cycling, the specific capacity of bi/cos and bi/cs electrodes showed a rapid decay trend. after 50 cycles, their characterization and application of nanomaterials 2025, 8(2), 11620. 12 reversible capacities decreased to about 100 mah/g, indicating poor structural stability and irreversible morphological or phase structure changes of the electrode materials during repeated charge-discharge cycles. in contrast, bi/cos-c and bi/csc electrodes exhibited superior cycling stability, with the bi/cs-c electrode maintaining a high reversible capacity of 788.8 mah/g after 300 cycles, demonstrating excellent long-term stability. although bi/cos-c has a higher initial specific capacity, its capacity begins to decay significantly after 150 cycles. this indicates that co4s3 has better structural stability compared to cos, which contributes to improving the cycling life of the electrode materials. the incorporation of carbon materials not only enhanced the specific capacity of bi/cos and bi/cs electrodes but also effectively improved their cycling stability. additionally, co4s3, as an active component, is more effective than cos in suppressing the volume expansion and structural collapse of the material, thereby achieving superior long-cycle performance. figure 6. (a) cycling stability of bi/cos, bi/cos-c, bi/co4s3, and bi/co4s3-c at a current density of 0.2 a/g; (b) rate performance of bi/co4s3, bi/cos-c, and bi/co4s3-c; (c) comparison of rate performance with previously reported literature; (d) galvanostatic charge-discharge curves of bi/co4s3, bi/cos-c, and bi/co4s3-c at 1 a/g; (e) galvanostatic charge/discharge curve of graphite (c) at 1 a/g. to investigate the charge-discharge capabilities of bi/cs, bi/cos-c, and bi/cs-c electrodes over a period of time, we conducted rate performance tests, as shown in figure 5b. at current densities of 0.1, 0.2, 0.5, 1, 2, 4, 6, 8, and 10 a/g, the reversible capacities of bi/cos-c were 939.2, 779.7, 730.7, 655.6, 584.9, 508.1, 427.9, 371.5, and 319 mah/g, respectively. in contrast, the reversible capacities of bi/cs-c were 760.4, 661.4, 637.6, 591.9, 544.4, 484.3, 404.2, 344.1, and 295.4 mah/g, respectively. it can be observed that the bi/cos-c electrode exhibited higher specific capacities at all current densities, indicating its superior rate performance. further analysis revealed that at a low current density of 0.2 a/g, although bi/cos-c exhibited a higher initial capacity, its capacity decayed more rapidly over long characterization and application of nanomaterials 2025, 8(2), 11620. 13 cycles, while the bi/cs-c electrode showed better cycling stability. this suggests that cos, as an active component, effectively enhances the rate performance of the material, but its long-term stability still requires optimization compared to the bi/csc electrode. furthermore, throughout the rate testing, the specific capacities of bi/cos-c and bi/cs-c electrodes were always higher than those of the bi/cs electrode, indicating that the incorporation of graphite significantly enhanced the rate performance and charge-discharge capabilities of the material. particularly after high-rate cycling, when the current density was restored to 0.1 a/g, the reversible capacities of the bi/cos-c and bi/cs-c electrodes increased to 719.2 mah/g and 661.6 mah/g, respectively, while the reversible capacity of the bi/cs electrode only increased to 134.2 mah/g. this further verifies that the incorporation of graphite effectively enhances the structural stability and rate performance of the material. this could be attributed to the high conductivity of graphite and its buffering effect on volume expansion, allowing the electrode to maintain good structural integrity during high-rate charge-discharge cycles, thereby improving cycling life and rate performance. this performance surpasses that of many previously reported cobaltbased sulfide anode materials for libs (see figure 6c), demonstrating the significant advantage of the bi/cos-c and bi/cs-c electrodes in terms of rate capability [16,18,25,28,32–34]. to further evaluate the cycling stability of bi/cs, bi/cos-c, and bi/cs-c electrodes at high current densities, we conducted long-term cycling tests at 1 a/g (as shown in figure 6d). the experimental results showed that the bi/cs-c electrode maintained a high reversible capacity of 515.4 mah/g after 150 cycles, demonstrating excellent cycling stability. in contrast, the specific capacity of bi/cos-c electrodes exhibited a continuous decrease with increasing cycle numbers, further proving its poor cycling stability, which may be related to the gradual collapse of its structure or loss of active materials during long cycles. in this study, the carbon content and its contribution to the total capacity were estimated based on the designed precursor ratios and independent electrochemical test results. bi2s3 and co powder were reacted in a molar ratio of 1:4 to produce bi and co4s3, which were then mixed with exfoliated graphite at a mass ratio of 0.85:0.15 via ball milling to obtain the bi/cs-c composite. therefore, the theoretical mass fraction of carbon in the final composite was approximately 15%. additionally, the exfoliated graphite was independently tested in half-cell configuration, yielding a discharge capacity of approximately 613.6 mah/g at the 10th cycle, as shown in figure 6e. based on this, the capacity contribution of the active components in the composite was estimated using the following weighted average formula: capacity estimation for the bi/cs-c electrode (taking the 10th cycle as an example), according to equation (17): 𝐶𝑡𝑜𝑡𝑎𝑙 = 𝑤𝑐 × 𝐶𝑐 + 𝑤𝑎𝑐𝑡𝑖𝑣𝑒 × 𝐶𝑎𝑐𝑡𝑖𝑣𝑒 (17) 514.4 = 0.15 × 613.6 + 0.85 × 𝐶𝑎𝑐𝑡𝑖𝑣𝑒 → 𝐶𝑎𝑐𝑡𝑖𝑣𝑒 ≈ 496.9mah/g. capacity estimation for the bi/cos-c electrode: 667.5 = 0.15 × 613.6+0.85 × 𝐶𝑎𝑐𝑡𝑖𝑣𝑒 → 𝐶𝑎𝑐𝑡𝑖𝑣𝑒 ≈ 677.0mah/g. characterization and application of nanomaterials 2025, 8(2), 11620. 14 these results suggest that the majority of the total capacity of the bi/cs-c electrode originates from the bi/cs active matrix, while the graphite additive, apart from enhancing structural stability, also provides a modest contribution to capacity. in contrast, although bi/cos-c contains the same carbon content, its active components exhibit higher capacity, which is likely attributed to the activation behavior of cos during the initial cycles and stronger synergistic interactions between cos and bi. to further explore the lithium storage mechanism of bi/cs-c composites, cv tests were performed at different scan rates, as shown in figure 7a. in the scan rate range of 0.2 to 1.0 mv/s, the peak current increases as the scan rate increases. the relationship between scan rate (v) and peak current (i) can be expressed by equation (18) [10,35]: ln i = ln a + bln v (18) a is a constant, and b is the slope, which is related to the ratio of the conversion mechanism and pseudocapacitive behavior. based on the v and i values at the typical peaks, the b value is calculated (as shown in figure 7b). the results show that the b values of bi/cs-c electrodes are all greater than 0.65, indicating that their electrochemical behavior is predominantly governed by a capacitive control mechanism. furthermore, to further compare the pseudocapacitive contributions of bi/cs, bi/cs-c, and bi/cos-c, cv tests were conducted at different scan rates for these three electrode materials, and the results were analyzed using equation (19): i = k1v + k2 v1/2 (19) in this equation, k1v and k2 v1/2 represent the contributions of pseudocapacitive behavior and conversion reactions, respectively. based on this relationship, the pseudocapacitive contribution ratio was calculated, as shown in figure 7c. notably, at a scan rate of 1.0 mv/s, the pseudocapacitive contribution of the bi/cs-c electrode reached 91.6%, while the pseudocapacitive contribution of the bi/cos-c electrode was 88.2%, indicating that bi/cs-c has a more significant pseudocapacitive effect. moreover, throughout the entire test range, the pseudocapacitive contribution of bi/cs-c remained above 80%, which is significantly better than the other two electrode materials. these results strongly demonstrate that the introduction of exfoliated graphite plays a crucial role in enhancing the electrochemical performance of bi/cs-c and bi/cos-c electrodes: (1) exfoliated graphite provides a rich conductive network, reducing the internal resistance of the electrodes and facilitating fast electron/ion transport; (2) the interlayer structure of graphite provides more active sites for the storage and diffusion of li+, thereby improving the additional capacity; (3) the flexible skeleton structure of exfoliated graphite can effectively buffer the volume expansion of the material during charge/discharge cycles, improving the structural stability and cycle life of the electrodes. the results of this study further confirm that co4s3, as an active component in bi/cs-c composites, can effectively enhance the cycling life of the material, showing superior lithium storage performance compared to cos, and providing important theoretical and experimental support for the development of high-performance lib anode materials. characterization and application of nanomaterials 2025, 8(2), 11620. 15 figure 7. (a) cv curves of bi/co4s3-c at different scan rates; (b) determination of the b value based on the sharp peaks of the cv curves of bi/co4s3-c at different scan rates; (c) pseudocapacitive contribution ratio of bi/co4s3, bi/co4s3-c, and bi/cos-c at different scan rates; (d) surface pseudocapacitance of bi/co4s3-c at 1.0 mv/s. 4. conclusion guided by theoretical considerations, bi/cos-c and bi/cs-c composites were successfully synthesized via a cost-effective and scalable solid-state ball milling approach. the electrochemical performance of these composites as lib anodes was systematically evaluated. ball milling facilitated the homogeneous integration of bi with cos or co4s3 and nanoscale graphite, yielding a rough, dense microstructure that enhanced li+ diffusion kinetics and introduced abundant active sites for improved lithium storage. simultaneously, the lamellar architecture of exfoliated graphite offers abundant reactive sites and constructs a stable conductive network, thereby enhancing cycling stability and rate capability. moreover, co4s3, as the active component, more effectively suppresses volume expansion and structural degradation compared to cos, thereby imparting superior long-term cycling stability. notably, the bi/cs-c electrode retained a high reversible capacity of 788.8 mah/g after 300 cycles at 0.2 a/g. in rate capability tests, when the current density was reduced back to 0.1 a/g, the reversible capacities recovered to 719.2 and 661.6 mah/g for bi/cos-c and bi/cs-c, respectively. this solid-state ball milling strategy offers a low-cost, efficient, and scalable route for the design and optimization of multicomponent transition metal sulfide-based anodes, laying a robust foundation for the development of next-generation high-performance libs. author contributions: investigation, ty and lz; data curation, ty and lz; formal analysis, lz; writing—original draft preparation, lz; writing—review and editing, tz, and yd; supervision, tz; project administration, hj; funding acquisition, tz and yd. all authors have read and agreed to the published version of the manuscript. funding: this work was supported by the natural science foundation of china youth program (22405042), and the national natural science foundation of china (22073069 and 21773082). characterization and application of nanomaterials 2025, 8(2), 11620. 16 institutional review board statement: not applicable. informed consent statement: not applicable. data availability statement: applicable for reasonable request. conflict of interest: the authors declare no conflict of interest. references 1. navia simon d, diaz anadon l. power price stability and the insurance value of renewable technologies. nature energy 2025. 10(3): 329–341. doi: 10.1038/s41560-025-01704-0 2. kan x, reichenberg l, hedenus f, daniels d. renewable export cost index as an indicator of global renewable energy trade potential. communications earth & environment. 2025; 6(1): 112. doi: 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doi:10.24294/can.v6i1.3406 1 original research article morphology, structural and thermal degradable properties of carboxymethyl cellulose/cuo nanoparticles for tetracycline removal in model aqueous solution win pa pa phyo1, yamin thet1,2, may thazin kyaw1, ngwe sin1, aung than htwe1,3* 1department of chemistry, university of yangon, kamaryut 11041, yangon, myanmar. e-mail: aungthanhtwe76@gmail.com 2 department of chemistry, bamaw university, bamaw 01132, kachin state, myanmar. 3 department of chemistry, mohnyin university, mohnyin 01162, kachin state, myanmar. abstract broad-spectrum antibiotics, such as tetracyclines, are used to treat and manage a range of infectious disorders. since the kidneys are the primary organs responsible for excreting tetracyclines, clinicians should refrain from prescribing them to patients who have renal failure. tetracyclines are one of the clinical waste products of today. one of the biggest problems in the field of pollution of the environment today is the persistence of different pharmaceutical residues, drug residues, pesticides, and metal ion species of the new-generation pollutants in surfaces and groundwater. in the present work, carboxymethyl cellulose (cmc)-cuo nanoparticles (cmc-cuo nps) were synthesized using cuo nps within different amounts of cmc (0.5, 1.0, 1.5 and 2.0 g) at 85 °c. the synthesized nanoparticles were characterized by xrd, ft ir, sem, and tg-dta analysis. according to xrd and sem, the crystallize size and morphology influenced the dosage of cmc. ft-ir analysis confines the layer of cmc to the cuo nanoparticle surface. tg-dta results indicated that the cmc content of cmc-cuo nps was between the range of 69% and 75% by weight. the effects of some parameters such as initial concentration, ph, adsorbent dosage, and contact time on the adsorption of tetracycline from aqueous model solutions on cmc-cuo nps were investigated with batch studies. it was found that the removal of tetracycline was obtained about 80% with optimized parameters of 10 mg/l concentration, 180 min contact time, 5 ph, and 0.3 g/25 ml dose. the synthesized cmc-cuo nps nanocomposite may be a promising material for the removal of tetracycline in environmental pollution and toxicology. keywords: carboxymethyl cellulose; cuo nps; morphology; removal of tetracycline article info received: 9 april 2023 accepted: 22 may 2023 available online: 4 june 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction they are discharged into water sources and domestic wastewater by some pharmaceutical companies. due to their widespread use worldwide, antibiotics are among the pharmaceutical products and drug residues of greatest concern. this is due to the harmful effects of antibiotics on the hepatocytes and other organs of gastrointestinal organs. many microorganisms, including beneficial bacteria such as proteobacteria, cyanobacteria, algae, bacteria, and ammonium-oxidizing bacteria, are harmful to antibiotics in water. an antibiotic called tetracycline is commonly used to treat various diseases in humans. this is the second-most-used antibiotic in the world. tetracycline also inhibits nitrification, soil microbial respiration, and iron(iii) reduction[1]. in view of these facts, several adsorption techniques have been reported to remove tetracycline antibiotics from water[2–5]. the nanocomposite material is 2 made from a polymer-coated substrate that functions as a hybrid adsorbent to remove pollutants. the mixture widely used in environmental cleaning is formed by polycations that attach to carboxymethylcellulose, which carries a negative charge. these synthetic materials are used to remove organic pollutants such as heavy metals, antibiotics, organic dyes, and pesticides. on the other hand, neither polyanion adsorption on positively charged minerals nor microbial respiration in soil have been reported as new synthetic materials for antibiotic removal[1]. these results led to the publication of several adsorption techniques to remove tetracycline antibiotics from water[6]. as a linear polymer with high molecular weight, high crystallinity, and strong intramolecular hydrogen bonds, cellulose is organic, renewable, and biodegradable. most organic solvents cannot dissolve it[7,8]. one way to improve the efficiency of cellulose is to convert it into derivatives such as carboxymethyl cellulose (cmc), based on the ether reaction of b. williamson[9,10]. the long-chain, anionic, and water-soluble properties of cmc make it important. due to its low cost, low toxicity, ability to form transparent films, high viscosity, biodegradability, and biocompatibility, cmc is considered a substitute for synthetic polymers[11]. the abundance of hydroxyl (-oh) and carboxyl (-cooh) groups in carboxymethyl cellulose (cmc) increases its hygroscopicity. copper oxide (cuo) is widely used in many fields, including catalysts, ceramics, glass, and antibacterial agents. the production of cuo nps is inexpensive compared to gold and silver nanoparticles. in addition, cuo nps also have excellent and strong antibacterial activity, and appreciation for their unique crystal structure. when it comes to how the nanoparticles ultimately interact with target cells, their size, state of aggregation in liquids, and surface charge are among their physical and chemical characteristics that matter[12]. in the current work, the specific objective of the present study was to synthesize carboxymethyl cellulose/cuo nanoparticles (cmc-cuo nps), involving the co-precipitation of cmc polymer network in the presence of cuo nps, to characterize the cmc-cuo nps nanoparticles synthesized by modern technique as xrd, ft ir, sem, and tg-dta, and to evaluate synthesized cmc-cuo nps as adsorbents to remove tetracycline from model aqueous solution. 2. materials and methodology 2.1 materials sodium carboxymethyl cellulose (cmc) with a degree of substitution (ds) 0.55–1.0 and a viscosity of 15,000 mpa/s (1% in h2o, 25 ℃) was obtained from nippon paper chemicals co., ltd., japan. other chemicals such as epichlorohydrin (99.5%), copper(ii) sulphate pentahydrate (cuso4·5h2o), sodium hydroxide (naoh), acetic acid glacial (ch3cooh, 100% (v/v)) and hydrochloric acid (hcl) were purchased from merck (indonesia). 2.2 preparation of the cuo nanoparticles the copper(ii) oxide nanoparticles (cuo nps) were prepared by co-precipitation method. firstly cuso4·5h2o was dissolved in 100 ml distilled water and stirred continuously. sodium hydroxide (5 m) was added dropwise into the mixture until the solution reached ph 12 and stirred continuously for 6 h at 85 c. the black precipitation was obtained and washed several times with distilled water to remove any alkali metals until a neutral state (ph 7). and then, this was washed again with ethanol 5 times. samples were dried in a hot air oven at 80 c for 16 h. the sample was calcined at 500 c for 4 h and crushed in mortar and pestle. finally, the sample in the crucible was allowed to cool at room temperature. 2.3 preparation of carboxymethyl cellulose/cuo nanoparticles a total of 1.0 g of copper oxide nanoparticles was mixed with epichlorohydrin (2.5 ml) and 25% acetic acid (30.0 ml). the mixture was stirred for 12 h on a magnetic stirrer to obtain the cuo nps mixture solution. the different amounts of 0.5, 1.0, 1.5, and 2.0 g of cmc sample were added to the cuo np mixture solution and then stirred for 30 min. this was endorsed to stand for 24 h. finally, cucmc was dried for 12 h at 60 oc and collected. the obtained samples are coded as 0.5cmc-cuo nps for 0.5 g of cmc, 1.0cmc-cuo nps for 1.0 g 3 of cmc, 1.5cmc-cuo nps for 1.5 g of cmc, and 2.0cmc-cuo nps for 2.0 g of cmc. 2.4 characterization and analysis x-ray characterization of the synthesized products was performed by x-ray diffractometer at room temperature using cu k radiation (  = 1.5406 a) with the 2 range 5–80. the crystallite size of the cmc-cuo nps was evaluated from x-ray analysis data using a modified debye-scherrer equation. the chemical groups involved in synthesized cmc-cuo nps were identified using the fourier transform infrared spectroscope (ftir perkin-elmer, rx1) method. the size, and morphology of the synthesized product of cmc-cuo nps were determined by scanning electron microscopy (sem). tga and dta were performed with a tg setaram instrument (france) in the air of argon (30 to 600 c). 2.5 adsorption studies adsorption by the batch technique was used to study tc removal using cuo nps and cmc-cuo nps. first, the accurate tc amount was dissolved in methanol and deionized water to make stock solutions of tc at a concentration of 100 mg/l. then, the stock solutions were taken for dilution to make a daily solution. at 25 °c, different adsorbent volumes were mixed with 25 ml of tc solution in 100 ml erlenmeyer flasks. the concentration of the solution, contact time, ph of the solution, and adsorbent dose are a few important parameters that affect the removal of tc. all concentrations of tcs in aqueous solutions were analyzed by the ultraviolet-visible (uv-vis) method at 277.4 nm using a genesys 10s (thermo scientific) uv-vis spectrometer. removal efficiency (%) = -c × 100 % (1) where ci and cf are the initial and final concentrations of tc (mg/l). 3. results and discussion 3.1 characterization of cuo nps and cmc/cuo nps 3.1.1 xrd analysis the xrd pattern of the cuo nps and cmc/cuo nps in the 2 range of 20–80 is shown in figure 1. the diffractogram of the cmc/cuo nps is assigned to diffractions at 2 values of about 32, 35, 38, 48, 53, 58, 61, 65, 66, 72, and 75, which assigned to the (110), (–111), (111), (–202), (020), (202), (–113), (–311), (220), (311) and (044) diffractions of cuo nps, respectively[13]. all the peaks match well with those of monoclinic-phase cuo nps and confirm the formation of cmc-cuo nps matrix. no impurity peaks were observed in the xrd patterns, indicating the high purity of the obtained cuo particles. a wide peak at 24 is due to the polymer networks. briefly, the xrd results confirmed the crystallinity of the prepared cmc/cuo nps with the presence of cuo[1,14]. using scherrer’s equation, the calculated average crystallite size of the cuo nps, 0.5cmc-cuo, 1.0cmc-cuo, 1.5cmc-cuo and 2cmc-cuo were found as 21.22, 38.16, 50.07, 59.99 and 61.28 nm, respectively. there was no change in the crystal structure, which showed diffraction peaks at the same 2 position in all diffractograms. however, the crystallite size changed. furthermore, crystallite size increased with the increasing amount of cmc. the higher the cmc content, the higher the crystallite size of cmc-cuo nps produced. figure 1. xrd patterns of the cuo nps and cmc-cuo nps. 3.1.2 sem analysis sem images of the cuo nps and cmc-cuo nps are shown in figure 2. in figure 2, a clear and uniform surface morphology was observed for the cuo nps. however, there are visible spherical par 4 (a) cuo nps (b) 0.5cmc-cuo nps (c) 1.0cmc-cuo nps (d) 1.5cmc-cuo nps (e) 2.0cmc-cuo nps figure 2. sem images of the cuo nps and cmc-cuo nps. ticles in the case of nanoparticles containing cmc (figure 2(b) to (e)). sem results showed that the cmc matrix was dispersed in the cuo nps solution. however, figure 2(e) found that some aggregation and bigger particles can be seen for cmc-cuo nps containing increasing cmc content. 3.1.3 ftir analysis the functional groups present in cuo nps and cmc-cuo nps were studied by fourier transform infrared (ftir) spectroscopy. the ftir spectra of cuo nps and cmc-cuo nps were recorded in the range of 4,000–400 cm–1 using kbr pellet technique perkin elmer spectrometer. the ft ir spectra of cuo nps and cmc-cuo nps are shown in figures 3(a) and (b). the broad absorption bands that appeared at 3,469–3,272 cm–1 were due to oh stretching of the alcoholic oh group while oh bending appeared at 1,356 cm–1. the band at 2,993 cm–1 and 2,867 cm–1 showed asymmetric and symmetric c-h stretching vibration of ch2 groups and their c-h bending vibration occurred at 1,442 cm–1. the bands at 1,735 cm–1 and 1,649 cm–1 showed the stretching vibration of , –unsaturated carbonyl groups. the absorption bands at 1,263 cm–1 and 1,052 cm–1 appeared by stretching vibration of cyclic ether groups[15]. additionally, the peaks at 626– 687 cm−1 can be attributed to the cu-o vibration of copper oxide nanoparticles. this result corroborated that cmc-cuo could be synthesized. 3.1.4 tg-dta analysis the thermal properties of cuo nps and cmc-cuo nps were investigated by analytical techniques of tg-dta. figure 4(a) shows that the 5 (a) (b) figure 3. ft ir spectra of (a) cuo nps and (b) cmc-cuo nps. cuo nps have a total weight loss of 4.8% in the range of 37 °c to 243 °c. this is due to the evaporation of water or oh groups adsorbed on the surface of the cuo. according to the cucmc-cuo nps curves in figure 4(a), the temperature range between 37 °c and 280 °c lost 43.50% for 0.5cucmc-cuo nps, 42.05% for 1.0cucmc-cuo nps, 44.92% for 1.5cucmc-cuo nps, and 57.66% for 2.0cucmc-cuo nps, corresponding to exothermic peaks at 265 °c [0.5cucmc-cuo nps in figure 4(b)], 230 °c [1.0cucmc-cuo nps in figure 4(b)], 237 °c [1.5cucmc-cuo nps in figure 4(b)], and 243 °c [2.0cucmc-cuo nps in figure 4(b)]. this is due to the dehydration process of moisture on cmc-cuo nps. the loss in weight of 31.22% for 0.5cucmc-cuo nps, 35.06% for 1.0cucmc-cuo nps, 29.54% for 1.5cucmc-cuo nps, and 10.8% for 2.0cucmc-cuo nps were observed to take place within the temperature range of 281 °c to 480 °c. figure 4(b) shows sharp broad exothermic peaks at 342 °c (0.5cucmc-cuo nps), 324 °c (1.0cucmc-cuo nps), 334 °c (1.5cucmc-cuo nps), and 330 °c (2.0cucmc-cuo nps). this is due to the decomposition of the substituted sites in the methylated derivatives. as a result, aside from depolymerization and pyrolysis, the main polymer chain weight loss was caused by cmc decomposition on the 6 cuo nps. it was also confirmed that the cuo nps were successfully dispersed by cmc. (a) (b) figure 4. (a) tga curves and (b) dta curves for cuo nps and cmc-cuo nps. 3.2 investigation of the removal percent of tetracycline (tc) 3.2.1 effect of initial concentration of tc different initial tc concentrations in cuo nps, and cmc-cuo nps are shown in figure 5. tc adsorption percentage at different tc concentrations ranging from 10 mg l–1 (ppm) to 50 mg l–1 (ppm). figure 5 shows that when tc concentration increased, tc removal decreased because there were few active sites on the surface of the sorbent. as the data clearly show that removal percent of tc by cmc-dispersed cuo nanoparticles (0.5cmc-cuo nps (60.12%), 1.5cmc-cuo nps (61.22%), 1.5cmc-cuo nps (63.31%), and 2.0cmc-cuo nps (63.63%)) was considerably higher than that of cuo nps (42.12%). therefore, the optimum initial concentration of 10 ppm of tc was chosen for further studies. figure 5. effect of initial concentration on the tc removal using cuo nps and cmc-cuo nps. 3.2.2 effect of ph the effect of ph on the tc removal using cuo nps and cmc-cuo nps is shown in figure 6. the experiment on the ph effect was conducted in the ph range of 3–9 to find out the best ph for tc removal using cuo nps and cmc-cuo nps. figure 6 shows that the tc removal using cuo nps and cmc-cuo nps reached the maximum at ph 5 and then decreased from ph 6 to 9. as the data clearly show that the removal percent of tc by cmc-dispersed cuo nanoparticles (0.5cmc-cuo nps (67.85%), 1.0cmc-cuo nps (70.39%), 1.5cmc-cuo nps (72.19%), and 2.0cmc-cuo nps (80.20%)) was considerably higher than that of cuo nps (50.39%) at ph 5. tc has three different pka values: 3.3, 7.7, and 9.7. as a result, in aqueous solutions, tc can be found in the cation, zwitterion, or anion form in the ph range 3.3–7.7 below ph 3.3 and in the ph range 3–9 above ph 7.7[16]. at ph 4, the negative charge surface of cmc is convenient for attaching the cationic and zwitter ionic species of tc. this result is similar to the previous report by parolo et al.[17]. because the negative percentage of the tc zwitterionic form grew as the ph rose from 6 to 8, tc removal was reduced. on the other hand, we found less adsorption at ph > 8 because of stronger electrical repulsion between the negatively charged cmc surface and the anionic tc. as a result, ph 5 is chosen and maintained for 7 tc removal using cmc-cuo nps. figure 6. effect of ph on the tc removal using cuo nps and cmc-cuo nps (ci = 10 mg/l). 3.2.3 effect of contact time the influence of contact time on tc removal using cuo nps and cmc-cuo nps is shown in figure 7. the contact time increased from 30 to 240 min. figure 7 indicates that tc removal using cuo nps and cmc-cuo nps increases from 42.11% to 85.16% when increasing time in the prior 30–180 min. when the contact time exceeded 180 min, the tc removal efficiency decreased insignificantly. the data clearly show that the removal percent of tc by cmc-dispersed cuo nanoparticles (0.5cmc-cuo nps (76.12%), 1.0cmc-cuo nps (81.20%), 1.5cmc-cuo nps (84.73%), and 2.0cmc-cuo nps (85.16%)) was considerably higher than that of cuo nps (63.93%) at 180 min so that 180 min is the best contact time for tc removal. figure 7. effect of contact time on the tc removal using cuo nps and cmc-cuo nps (ci = 10 mg/l, ph 5). 3.2.4 effect of adsorbent dosage the effect of adsorbent dosage on tc removal using cuo nps and cmc-cuo nps was investigated in the range of 0.1–0.5 g at 180 min and is indicated in figure 8. as can be seen in figure 8, the tc removal increased when the adsorbent dosage increased from 0.1 to 0.5 g as the result of rising the net surface charge or specific surface area of the adsorbent. the tc plateau removal efficiency was achieved at 0.3 g as 63.14% (cuo nps), 79.2% (0.5cmc-cuo nps), 80.23% (1.0cmc-cuo nps), 84.13% (1.5cmc-cuo nps), 86.97% (2.0cmc-cuo nps), and was not changed significantly when the amount of adsorbent was above 0.3 g. therefore, we used 0.3 g dosage for further study on tc removal. figure 8. effect of adsorbent dosage on the tc removal using cuo nps and cmc-cuo nps (ci = 10 mg/l, ph 5, 180 min). 4. conclusion in this research, the pure cuo nps and cmc-cuo nanoparticles were successfully prepared by the co-precipitation method and applied for the removal of tetracycline from an aqueous model solution. the prepared cuo nps and cmc-cuo nanoparticles were characterized by xrd, ftir, sem and tg-dta techniques. the cmc-cuo nps were completely consistent with the diffraction peaks of cuo nps. x-ray diffraction (xrd) studies confirmed the formation of cuo nanoparticles in the cmc matrix with an average crystallite range of 38.16–61.28 nm with the cmc matrix. ftir spectra showed that cmc attached 8 cuo nps were formed successfully after the chemical effect of cmc on cuo nps. the sem image of cuo nps revealed the aggregated morphology. the sem images of all cmc-cuo nps show a cluster due to agglomeration. in tgdta thermograms, it was found that the total weight loss of cmc-cuo nps is higher than that of pure cuo nps. however, the ftir and tg-dta data indicate that the functional groups were successfully attached to the surface of the nanoparticles. the sorption capacities of prepared samples were studied for the removal of tetracycline from aqueous model solutions with varying experimental conditions of the initial concentration, ph, contact time, and dosage. it is found that the removal percent of tetracycline increases with not only a decrease in initial concentration, but also an increase in contact time and amount of dosage. these carboxymethyl cellulose/cuo nanoparticles may be intended to have a good potential, effective nanoadsorbents for rapid removal of tetracycline which are a problem of clinical wastewater and other sources of the water system. on account of the outcomes, we do advise that carboxymethyl cellulose/cuo nanoparticles can also be used to remove tetracycline in an aqueous solution. it is recommended that the researchers of polymer-based nanomaterials be kept informed of this study. future researchers are encouraged to investigate other factors that may affect the performance of carboxymethylcellulose/cuo nanoparticles. acknowledgments the authors fully acknowledged the ministry of education (moe), department of higher education and department of chemistry, university of yangon for the approved support which makes this important research. author contributions conceptualization, wppp and yt; methodology, wppp; software, ath; validation, wppp, mtk and ns; formal analysis, wppp; investigation, wppp; resources, wppp; data curation, wppp; writing—original draft preparation, yt, mtk, ns and ath; writing—review and editing, yt and mtk; visualization, ns; supervision, ath; project administration, ath; funding acquisition, ath. all authors have read and agreed to the published version of the manuscript. conflict of interest the authors declare no conflict of interest. references 1. alothman za, badjah ay, alharbi oml, et al. copper carboxymethyl cellulose 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cellulose versus biopolymer-based hydrogels for controlled release of fertilizer. polymer-plastics technology and materials 2021; 60(17): 1884–1897. doi: 10.1080/25740881.2021.1934017. 16. chen w-r, huang c-h. adsorption and transformation of tetracycline antibiotics with aluminum oxide. chemosphere 2010; 79(8): 779–785. doi: 10.1016/j.chemosphere.2010.03.020. 17. parolo me, savini mc, vallés jm, et al. tetracycline adsorption on montmorillonite: ph and ionic strength effects. applied clay science 2008; 40(1– 4): 179–186. doi: 10.1016/j.clay.2007.08.003. microsoft word can-3665 pb online characterization and application of nanomaterials (2023) volume 6 issue 2 doi:10.24294/can.v6i2.3665 1 original research article synthesis of vanadium oxide nanoparticles/psi heterojunction photodetector maysoon h. ismail1,*, alaa h. ali1, sabah m. thahab2 1 department of electrical engineering, university of technology, iraq, baghdad 10066, iraq 2 nanotechnology and advanced materials research unit (namru), faculty of engineering, university of kufa, kufa 540011, najaf, iraq * corresponding author: maysoon h. ismail, eee.19.03@grad.uotechnology.edu.iq abstract nanoparticle v2o5 is prepared by the measurement of x-ray diffraction (xrd) and atomic force microscopy (afm) analyses. the crystallite size = 19.59 nm, optical energy gap = 2.6 ev, an average particle size of 29.58 nm and, rms roughness of ~6.8 nm. also, fourier transformer infrared spectrophotometer (ftir) showed a porous free morphology with homogeneity and uniformity on the sample surface. the film surface exhibited no apparent cracking and, the grains exhibited large nicely separated conical columnar growth combined grains throughout the surface with coalescence of some columnar grains at a few places. the fabrication of a thin film of v2o5 nps/psi heterojunction photodetector was characterized and investigated. keywords: v2o5; nanoparticles; porous silicon; afm; xrd; heterojunction photodetector article info received: 13 november 2023 accepted: 14 december 2023 available online: 22 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction numerous fields could greatly benefit from nanotechnology. by creating brand-new approaches to resolving environmental issues, nanomaterials have the potential to enhance the environment. the potential for nanotechnology to overcome the chemical and physical constraints of materials comprised of microparticles has been widely acknowledged. an important class of materials used in a variety of industrial applications, vanadium oxides exhibit an intriguing and varied concern of chemical and physical properties due to diverse metal oxidation situations (from +ii to +v) and v-o organization geometries. for more than 50 years, the theoretical and experimental condensed matter and materials communities have researched vanadium oxygen structures (v2o5, vo2), a sample of powerfully associated resources[1,2]. in comparison to other vanadium oxides, vanadium pentoxide (v2o5) has good electrical and chemical properties, making it a possible contender for electronic applications[3]. according to studies, v2o5 is used to make field effect transistors (fet), chemical sensors, energy harvesters, and other devices[4,5]. also, it is a great option for optoelectronic applications like photo-detectors due to its direct bandgap of 2.2 ev to 2.7 ev which has been the subject of a great deal of fundamental research[6,7]. metal-semiconductor transition, which is distinguished by a sudden 2 shift in optical and electrical properties, has been demonstrated to exhibit a variety of chromogenic properties, including vanadium pentoxide elements used for solar cells and transmittance modification in smart windows, and the technological features of conversion metal oxides have been the focus of study in the latest years among a variety of oxygen-containing compounds with various chemical, optical, and structural characteristics phases including vo, vo2, v2o3, and v2o5 exhibit significant changes in their properties depending on their structural makeup, which also affects other characteristics[8–11]. several systems of vanadium oxides may be created via altering the statement development factors otherwise through post-process management, such as added annealing[12,13]. in terms of applications, the maximum exciting vanadium oxides are vo2 and v2o5. it’s an ideal applicant for thermochroic coverings according to the modification from semiconducting to semimetal properties approximately of 68 ℃ and v2o5, made an object of several theoretical and applied studies, due to their industrial importance for many technological applications. moreover, vanadium pentoxide (v2o5) is a thermodynamically steady system, which displays electrochromic properties. v2o5 thin films can be used in optical filters, reflectance mirrors, as well as surfaces with tunable emittance for temperature mechanism control of space vehicles[14,15]. the aim of this study was to focus on the preparation of v2o5 nps by hydrothermal method and study the structural, topographical and optical properties to reach the optimum condition in manufacturing the photodetector. 2. experimental part 2.1. prepared of v2o5 nanoparticles the hydrothermal method refers to material preparation by chemical reaction to facile the controlling of the reaction parameters such as temperature and reaction time to obtain highly homogeneous products. v2o5 nps synthesized, where 1.8 g powder of material was added into 100 ml of distilled water, and the solution was placed on a magnetic stirrer for 15 min at 50 ℃, after cooling to room temperature, the addition of 1 g of polymethyl methacrylate (pmma) to 50 ml of acetone at various concentrations of materials (1:9, 1.5:8.5 and 2:8) at the first step and 2 g of pmma at the second stage. 2.2. fabrication of porous silicon in the etching process, a teflon container was used because it does not react with hf, which has a very offensive nature. the etching cell consisted of two, upper and lower parts, and the si pieces steadied between them, as shown in figure 1. the upper part contained a circular cavity in the center to keep the etchant and it provided with an o-ring to prevent the etchant from leaking. the edge of the lower part formed as a screw to relate the parts together. porous silicone was created by photo electrochemical etching approach, the surface of a si wafer using a combination of hydrofluoric acid 45% and 100% ethanol, and then placing the wafer in the bottom of teflon cells in a ratio of 1:1, an au ring was used as an electrode with a current density of 15 ma·cm–2 to generate an etched area of the sample of (0.785) cm2 . figure 1. schematic of etching cell and processing. 3 2.3. thin film deposition by drop casting method glass slides of 1.50 × 1.50 cm2 area, were used as a substrate. they were cleaned with alcohol in an ultrasonic bath in order to remove the impurities and residuals from their surface. then, four drops of the colloidal were used in preparing the v2o5 thin film using a specific syringe (ye3k061872:10100ml). this process begins with depositing the droplets of v2o5 via syringe in a certain amount on the glass sample, which is then heated to dry for 20 min. figure 2 shows the x-ray diffraction analysis of v2o5. the shape and size of v2o5 nanoparticles were investigated by using afm (aa 3000 scanning probe microscope). the analysis from x-ray diffraction when v2o5 nps that deposited on a glass substrate by drop casting method at 80 ℃. it notes that the sample has a polycrystalline structure, with 7 peaks in the diffraction spectrum which are (110), (200), (001), (101), (400), (411) and (600). figure 2. xrd diffraction of v2o5 nanostructure. 3. results and discussions 3.1. structural properties the structural properties of the deposited thin film at room temperature were studied by using an x-ray diffractometer (xrd-6000, shimadzu x-ray diffractometer). the optical absorption of the colloidal v2o5 nps was measured using a spectrophotometer (cary, 100 conc plus, uv-vis-nir, splitbeam optics, dual detectors) in the range of 350–1100 nm, using a quartz vessel. the crystallite size values of v2o5 were calculated by measuring the half width of the peak maximum intensity (fwhm), and 2θ of the directions’ peaks using formulae given by equation (1). scherer’s equation is shown in table 1. the strong and narrow peaks can be attributed to v2o5 preferential development along the (200) and (110) planes. d = . (1) the average crystallite size (d), which can be estimated using scherrer’s formulae; λ is the wavelength of cukα (= 1.5405 å), b is the full width at half maximum (fwhm). the fwhm of the preferred orientation (peak) could be measured since it is equal to the width of the line profile (in radian) at the half of the maximum intensity; and θ is bragg’s diffraction angle. the single line method is one of the several line profile analysis methods based on a voigt function to determine the size–strain parameters (microstrains and crystallite sizes) was computed strain (ƞ) and dislocation density (ơ) as shown in table 1. 0 200 400 600 800 1000 1200 1400 1600 10 20 30 40 50 60 70 80 i( a. u. ) 2theta(deg) (110) (200) (400) (001) (101) (411) (600) 4 table 1. summary of xrd characterization for v2o5 powder. crystalline size (nm)  × 1014 lines·m–2 η × 10–4 lines–2·m–4 29.24 11.84 11.69 30.46 11.37 10.77 14.91 23.22 44.92 16.24 21.32 37.89 16.80 20.61 35.40 21.82 15.87 20.99 figure 3 shows the 3d afm micrographs and histograms of v2o5. the atomic force microscopy analysis showed a porous free morphology with homogeneity and uniformity on the sample surface. there was no visible breaking on the film’s surface. the grains had huge beautifully separated conical columnar development joined grains all over the surface, with some columnar grains coalescing in a few locations. it had an average particle size of 29.58 nm and an rms roughness of 6.8 nm. it should be noted that significant sample roughness is essential for photovoltaic applications since rough surfaces have a substantially larger total surface area than smooth surfaces. figure 3. afm image histogram of v2o5. figure 4 shows ftir spectra of v2o5 were analyzed in the range of 450–4500 cm–1 wave number that identifies the chemical bonds and functional sets in the composite. the large broad band at 3450 and 3431 cm– 1 is ascribed to the o-h. the peak at 3000 and 2928 cm–1 for c-h groups. the absorption at 2362 and 2358 cm–1 is ascribed to the c=c bond. the peaks at 1652, 1655, 1658 and 1617 cm–1 are due to vibration of c=o, n-o and c=c, respectively. while the peaks at 1457, 1143, 1138 and 1056 cm–1 are ascribed to the c=h, c-n and c-o, respectively. v2o5 ftir spectra revealed three distinct vibration styles: v=o feelings at 975 cm–1, v-o v symmetric stretch around 500 and 540 cm–1, and v-o-v asymmetric bounce at 770 cm–1. the bands perceived between 950 and 1020 cm–1 were unambiguously ascribed to stretching modes (v-o). the bridge v-o-v stretching was assigned bands between 700 and 900 cm–1. 5 figure 4. fti r of v2o5 nps. 3.2. optical property the band gap of v2o5 nps is shown in figure 5 as a plot of (αhυ)2 versus photon energy hυ (where α is the absorption coefficient). the energy of the band gap was calculated using the tauc relation as in equation (2). the band gap of v2o5 nps was discovered to be 2.6 ev by projecting the linear component of the curve toward the photon energy axis. (αhν) = a(hν–eg) (2) where a is the absorption coefficient; hν is the photon energy; eg is the energy of the band gap, for direct band gap n = 1/2. a photoluminescence (pl) research at room temperature was performed to explore the optical characteristics of v2o5 that was drop cast onto a glass substrate. figure 6 depicts the pl spectra. the emission peak, which was locked at around 476 nm, revealed that the luminescence is connected to band edge recombination in v2o5 thin film. this agrees with the optical features of the samples, where the energy gap was 2.6 ev. figure 5. tauc’s plot of v2o5 nps. 50 55 60 65 70 75 450 950 1450 1950 2450 2950 3450 3950 4450 t % wavenumber (cm–1) o-h c=c c=o c-h c-n c-o v-o 0 1 2 3 4 5 6 7 8 9 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 (α hv )² (e v /c m )² × 10 7 photon energy (ev) eg = 2.6 ev 6 figure 6. pl spectrum of v2o5 thin film. 3.3. ag/v2o5/psi/n-si/ag heterojunction characterizations v2o5/psi/n-si/ heterojunction photodetector consists of two layers. the first place of junction is between the v2o5 layer and porous silicon (psi) and the second place of junction is made up between the porous silicon layer and crystalline (substrate) silicon (psi/n-si), so there are two depletions regions as shown in figure 7. all samples are made up of the diverse concentrations of (1:9, 1.5:8.5 and 2:8) once with 1 g and the second stage with 2 g. figure 7. diagram of detector connection circuit ag/v2o5/psi/n-si/ag heterojunction photodetector. 3.3.1. responsivity the responsivity of structures was examined in the wavelength range of 350–1000 nm with 3v bias and it is calculated by equation (3). 𝑅 = (a/w) (3) where iph is the photocurrent, and 𝑃 is the input power. figure 8 depicts the responsivity plots as a function of the wavelength of v2o5/psi/n-si structures generated at various concentrations (1:9, 1.5:8.5, and 2:8) with 1 g pmma:acetone. the responsivity curve of v2o5/psi/n-si is observed to have three response peaks; the first peak is located at 440–550 nm due to the absorption edge of v2o5 nanoparticles, the second region is located at 700–750 nm, due to the absorption edge of psi, and the third peak is located at 800–850 nm due to the absorption edge of silicon. 0 15 30 45 60 75 90 105 350 450 550 650 750 850 950 1050 p l i nt en si ty ( a. u) wavelength (nm) at 476 nm = 2.6ev 7 figure 8. responsivity as a function of wavelength of v2o5/psi/ n-si photo-detectors with different concentrations (1:9, 1.5:8.5 and 2:8) with 1 g pmma:acetone. 3.3.2. detectivity the detectivity is an important metric for photo-detectors since it represents a minimum detectable power; hence, the detector’s performance is associated with this value. the specific detectivity as a function of wavelength for v2o5/psi/n-si photo-detectors at different concentrations (1:9, 1.5:8.5, and 2:8) with 1 g pmma:acetone. figure 9 shows the detectivity curve consists of two peaks; the first peak is situated in the visible area, while the second region is located in the nir region. 0 0.003 0.006 0.009 350 550 750 950 r  (a /w ) wavelength (nm) a psi/si v2o5/psi = 550 nm 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 350 550 750 950 r  (a /w ) wavelength (nm) b psi/si v2o5/psi = 460 nm 0 0.01 0.02 0.03 0.04 0.05 350 550 750 950 r  (a /w ) wavelength (nm) c psi/si v2o5/psi = 500 nm 8 figure 9. detectivity plots for v2o5/psi/n-si photo-detectors respectively at different concentrations (1:9, 1.5:8.5 and 2:8) with 1 g pmma:aceton. d ∗ = 𝑅 𝐴. δ𝑓 𝐼 (4) 0 15 30 45 60 75 90 105 120 350 450 550 650 750 850 950 d et ec ti vi ty (c m h z1/ 2 w -1 ) × 10 9 wavelength (nm) a 0 800 1600 2400 3200 4000 4800 350 450 550 650 750 850 950 d et ec ti vi ty (c m h z1/ 2 w -1 ) × 10 9 wavelength (nm) b 0 100 200 300 400 500 600 700 800 350 450 550 650 750 850 950d et ec ti vi ty (c m h z1/ 2 w -1 ) × 10 9 wavelength (nm) c 9 𝐼 = (2𝑞𝐼 𝑓) (5) where δf is the bandwidth, a is active area of the detector, 𝐼 is dark current and q is electron charge. the maximal d* for sample was determined to be 4.1 × 1012 w–1·cm·hz1/2 at 460 nm (b). 3.3.3. carrier lifetime circuit voltage decay ocvd is a fundamental parameter for a metal-insulator transition (mit) material industry which influences the performances of the device. the lifetime is a free path for the charge carriers providing the time required for both the hole current and the electron current to generate the necessary current. time is calculated from the inverse of the frequency. the forward current flows through the device, then the circuit is abruptly opened and forward voltage drop decay is measured. the accuracy of the ocvd measurement depends on the precision of the oscilloscope, the temperature measurement and the affected noise. figure 10 represents images for the lifetime for v2o5/psi/n-si at different concentrations (1:9, 1.5:8.5 and 2:8) with 1 g pmma:acetone and the value of the time calculated as shown in table 2. (a) (b) (c) figure 10. the lifetime of structure v2o5/psi/n-si with different concentrations (1:9, 1.5:8.5 and 2:8) with 1 g pmma:acetone. table 2. lifetime of structure v2o5/psi/n-si with different conditions. number samples lifetimes (msec) a 1:9 pmma:acetone 1 g 7.1 b 1.5:8.5 pmma:acetone 1 g 12.5 c 2:8 pmma:acetone 1 g 3.6 3.4. statistical analysis and experimental results of ag/v2o5/psi/n-si/ag statistical analyses have been achieved by spss 24.0 window using least significant difference (lsd) between variables means to calculate a significant variation among all samples of v2o5/psi/n-si with different concentrations (1:9, 1.5:8.5 and 2:8) with three samples of 1 g and, three samples with 2 g of pmma:acetone. lsd analysis is defined as particular two values at levels of statistical probability indicated as the statistically significant function at α = 0.05 level and significant at α = 0.0l level. the analysis of the experimental results showed that there are significant differences between the variable of the samples s and the variable wavelengths λ which affect the variable of responsivity r of the light to the material, as shown in table 3, and the effect of s and λ on efficiency q of the system as shown in table 4, also, the effect of s and λ on important parameter of detectivity d as shown in table 5. 10 in addition, there is a correlation between the parameters of the system, as shown in table 6, where the coefficient of correlation (r = 1). there is a very strong positive relationship between the two variables of the parameters, and also concerning the symbol sig, which means that there is a statistically significant function between the parameters. for example, the value between two parameters, wavelength and efficiency is sig = 0.035, which is less than α value, if compared when the value is at the level α = 0.05, which means that this is an accepted value with a large statistically significant function and the percentage of error is small. while for the level α = 0.01, there is a very strong positive relationship and the rate of error percentage in this experimental work is externally small. table 3. effect of s and λ on responsivity. λ (nm) s mean of (λ) s1 s2 s3 s4 s5 s6 350 0.0077 0.1227 0.0096 0.0077 0.0096 0.0402 0.0329 400 0.0012 0.0833 0.0094 0.0075 0.0110 0.0337 0.0244 450 0.0009 0.2923 0.0140 0.0091 0.0126 0.1202 0.0749 500 0.0003 0.0988 0.0231 0.0069 0.0081 0.0421 0.0299 550 0.0029 0.0974 0.0174 0.0066 0.0061 0.0467 0.0295 600 0.0016 0.0957 0.0167 0.0067 0.0058 0.0437 0.0284 650 0.0011 0.0746 0.0198 0.0063 0.0054 0.0523 0.0266 700 0.0024 0.0562 0.0400 0.0073 0.0084 0.1133 0.0379 750 0.0022 0.1271 0.0296 0.0068 0.0104 0.1144 0.0484 800 0.0032 0.0623 0.0458 0.0070 0.0088 0.1664 0.0489 850 0.0037 0.1259 0.0438 0.0076 0.0116 0.1433 0.0560 900 0.0006 0.0838 0.0370 0.0069 0.0077 0.1064 0.0404 950 0.0006 0.0640 0.0253 0.0068 0.0074 0.0890 0.0322 1000 0.0002 0.0590 0.0233 0.0067 0.0050 0.0890 0.0305 mean of s 0.0020 0.1031 0.0253 0.0071 0.0084 0.0858 lsd (0.05) for (s) = 0.0041, lsd (0.05) for (λ) = 0.0029, lsd (0.05) for (s × λ) = 0.052. table 4. effect of s and λ on q. λ (nm) s mean of (λ) s1 s2 s3 s4 s5 s6 350 2.725 43.468 3.407 2.725 3.407 14.240 11.6620 400 0.371 25.823 2.904 2.317 3.398 10.440 7.5422 450 0.245 78.783 3.866 2.525 3.479 33.868 20.4610 500 0.067 24.514 5.723 1.705 2.003 10.445 7.4095 550 0.652 21.953 3.923 1.499 1.367 10.535 6.6548 600 0.337 19.769 3.453 1.392 1.209 9.021 5.8635 650 0.206 14.239 3.774 1.201 1.029 9.979 5.0713 700 0.428 9.951 7.084 1.285 1.483 20.067 6.7163 750 0.365 21.011 4.891 1.119 1.722 18.910 8.0030 800 0.489 9.654 7.104 1.088 1.360 25.799 7.5823 850 0.540 18.370 6.382 1.114 1.688 20.903 8.1662 900 0.089 11.550 5.091 0.948 1.059 14.659 5.5660 950 0.084 8.352 3.302 0.890 0.971 11.622 4.2035 1000 0.025 7.319 2.891 0.830 0.615 11.041 3.7868 mean of s 0.4731 22.4826 4.5568 1.4741 1.7707 15.8235 lsd (0.05) for (s) = 0.297, lsd (0.05) for (λ) = 1.889, lsd (0.05) for (s × λ) = 2.115. 11 table 5. effect of s and λ on d. λ (nm) s mean of (λ) s1 s2 s3 s4 s5 s6 mean × 1011 350 1.100 17.542 1.375 1.100 1.375 5.747 4.7065 400 0.171 11.910 1.339 1.068 1.567 4.815 3.4783 450 0.127 41.787 2.006 1.295 1.805 17.183 10.7005 500 0.038 14.133 3.299 0.983 1.155 6.022 4.2717 550 0.414 13.922 2.488 0.950 0.867 6.681 4.2203 600 0.233 13.677 2.389 0.963 0.836 6.241 4.0565 650 0.154 10.672 2.829 0.900 0.771 7.479 3.8008 700 0.346 8.032 5.718 1.037 1.197 16.197 5.4212 750 0.316 18.170 4.230 0.968 1.489 16.353 6.9210 800 0.452 8.905 6.553 1.003 1.254 23.798 6.9942 850 0.530 18.005 6.255 1.092 1.655 20.487 8.0040 900 0.092 11.986 5.284 0.984 1.099 15.213 5.7763 950 0.092 9.149 3.617 0.975 1.064 12.730 4.6045 1000 0.028 8.440 3.333 0.957 0.709 12.730 4.3662 mean of s 0.292 14.738 3.623 1.020 1.203 12.263 lsd (0.05) for (s) = 0.899, lsd (0.05) for (λ) = 1.275, lsd (0.05) for (s × λ) = 2.33. table 6. correlation among parameters. r q d wavelength r 0.050 –0.567* 0.051 sig. 0.865 0.035 0.862 r r 1 0.746** 1.000** sig. 0.002 0.000 q r 1 0.746** sig. 0.002 *. correlation is significant at the 0.05 level (2-tailed). **. correlation is significant at the 0.01 level (2-tailed). 4. conclusion in conclusion, this work demonstrated how to create v2o5 thin films to manufacture and characterize heterojunction photodetector used in electronic systems. according to xrd and afm analyses, the pictures show that considerable roughness of the sample is necessary for photovoltaic applications was concluded since the total surface area is substantially larger when the surface is rough than when the surface is smooth. due to the good photo-detector performance, the method employed has been confirmed by the findings of responsivity in the visible and near infrared regions, where this approach is used to construct silicon photodetectors for detecting a low optical signal power with ultra-small size and low cost. author contributions dr. sabah m. thahab conceived the experiments. dr. sabah m. thahab and dr. alaa h. ali planned and supervised the project. dr maysoon h. ismail carried out the experiments. dr. alaa h. ali and dr. maysoon h. ismail contributed to samples preparation. dr. maysoon h. ismail contributed to the interpretation of the results and took the lead in writing the manuscript. all authors provided critical feedback and helped shape the research, analysis and manuscript. conflict of interest the authors declare that they have no conflicts of interest. 12 references 1. ismail mh, ali ah, thahab sm. fabrication and characterization of a vo2:pvp/psi/ and n-si heterojunction for photodetector applications. optics continuum 2023; 2(6): 1301–1314. doi: 10.1364/optcon.484653 2. chuah r, gopinath scb, anbu p, et al. synthesis and characterization of reduced graphene oxide using the aqueous extract of eclipta prostrata. 3 biotech 2020; 10: 364. doi: 10.1007/s13205-020-02365-4 3. ramanathan s, gopinath scb, md arshad mk, et al. 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application of nanomaterials (2023) volume 6 issue 2 doi: 10.24294/can.v6i2.4226 1 review article graphene and nanocomposites—imprints on environmentally sustainable production and applications based on ecological aspects ayesha kausar1,2,*, ishaq ahmad1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, shaanxi province, china 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract graphene, an innovative nanocarbon, has been discovered as a significant technological material. increasing utilization of graphene has moved research towards the development of sustainable green techniques to synthesize graphene and related nanomaterials. this review article is basically designed to highlight the significant sustainability aspects of graphene. consequently, the sustainability vision is presented for graphene and graphene nanocomposites. environmentally sustainable production of graphene and ensuing nanomaterials has been studied. the formation of graphene, graphene oxide, reduced graphene oxide, and other derivatives has been synthesized using ecological carbon and green sources, green solvents, non-toxic reagents, and green routes. furthermore, the utilization of graphene for the conversion of industrial polymers to sustainable recycled polymers has been studied. in addition, the recycled polymers have also been used to form graphene as a sustainable method. the implication of graphene in the sustainable energy systems has been investigated. specifically, high specific capacitance and capacitance retention were observed for graphene-based supercapacitor systems. subsequently, graphene may act as a multi-functional, high performance, green nanomaterial with low weight, low price, and environmental friendliness for sustainable engineering and green energy storage applications. however, existing challenges regarding advanced material design, processing, recyclability, and commercial scale production need to be overcome to unveil the true sustainability aspects of graphene in the environmental and energy sectors. keywords: graphene; sustainability; environmentally friendly; recycled; energy 1. introduction sustainable carbon materials and nanomaterials have been the focus of recent technical research, especially in the high-tech energy and environment sectors[1]. in addition to sustainability, carbon nanomaterials have countless structural and physical benefits like strength, durability, and recyclability[2,3]. graphene can be marked as the most competent nanocarbon owing to two dimensional nanosheet nanostructure and methodological aspects[4]. resourceful approaches have been discovered for the formation of graphene[5]. however, sustainable synthesis paths have been preferred for graphene employing less cost, environmentally safe solvents, and chemicals[6]. the properties of graphene have been further improved by its structural modification, doping, or nanocomposite formation[7]. furthermore, graphene has been used to recycle waste plastic resins. for sustainable graphene nanocomposite formation, the use of green fabrication strategies and green polymers has been favored[8]. high performance article info received: 28 october 2023 accepted: 14 november 2023 available online: 31 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 sustainable graphene nanocomposites have been found functional in energy, electronics, engineering, biomedical, and environmental sectors[9]. to enhance the sustainability aspects of existing energy devices like supercapacitors, green electrode materials have been used for easy recyclability as well as lower pollution impacts[10]. hence, supercapacitors based on sustainable, biodegradable, and recyclable materials have been developed[11]. in this way, sustainable graphene and derived nanomaterials have found wide scope for green energy and environmental applications. to the best of our knowledge, this article is novel in terms of design, framework, and assembled literature regarding sustainable green based nanomaterials. here, essential green routes and matrices have been covered for the formation of sustainable graphene nanomaterials. the resulting graphene has been further applied to recycle industrial waste plastics. the use of sustainable graphene nanocomposites has also been essentially explored for energy storage devices like supercapacitors. consequently, this novel article presents a combination of green technologies for the production of graphene, the formation of sustainable nanomaterials, and the practical application of green graphene. such collective research directions have not been presented in any of the reported review articles of ecologically derived or resulting ecological nanocomposites using green graphene. thus, in this article, the design and properties of waste-derived graphene, the resulting sustainable nanomaterials, and green graphene based applications have been scrutinized. accordingly, the formation of green derived graphene has been highlighted to promote future research in this direction. the need for this review article also rises due to remarkably increased research reports on graphene and graphene nanocomposite research for environmentally sustainable production of graphene and practical and ecological features. therefore, this review can be claimed to be novel as the most demanding to grow future research in the field of ecological graphene nanomaterials. consequently, this innovative review article will definitely be beneficial for field-related scientists and researchers dealing with sustainable research on green graphene. hardly any recent topical comprehensive review reports have been observed on these nanomaterials. future of sustainable engineering recycled resin industries and energy sectors deficiently rely on overcoming the challenges of producing green graphene nanomaterials using sustainable practices. 2. environmentally sustainable production of graphene and derived materials environmentally sustainable graphene and derived materials have been examined[12–14]. to meet marketable demands to manufacture graphene, numerous safe techniques have been applied[15]. unfortunately, effective graphene synthesis approaches use toxic chemicals and reagents for synthesis[16–18]. any technique employing noxious solvents is not sustainable or ecological. a few sustainable, environmental, and safe methods may be listed such as mechanical exfoliation of graphite[19], chemical vapor deposition with green precursors[20], and others[21,22]. a very modest green way of forming graphene is the ball milling method[23]. hence, the existing graphene synthesis techniques can be modified towards sustainability through using ecofriendly precursors, solvents, chemicals, and sustainable pathways[24–26]. efforts have been observed regarding the use of sustainable carbon sources for graphene synthesis[27]. ruan et al.[28] used biscuits and chocolate as carbon sources to form graphene using chemical vapor deposition technique. kalita et al.[29] employed camphor plant extracts as green carbon source for graphene. zhang et al.[30] picked glucose as carbon precursor for graphene. all these green methods can be safely used for mass level graphene synthesis. tavakoli et al.[31] adopted a green sustainable method for the formation of graphene from graphene oxide using pomegranate juice. graphene oxide was formed using green hummer’s process from graphite precursor. figure 1 shows graphene formation from graphene oxide in the presence of pomegranate juice (naturally having anthocyanins as reducing agent). thus, due to electron deficient nature, pomegranate juice better 3 reduced the graphene oxide to graphene. gu et al.[32] synthesized green sustainable nanocomposites of chitosan, reduced graphene oxide, and silver nanoparticles. figure 2 illustrates the mechanism for the formation of reduced graphene oxide and silver nanoparticles based nanomaterial due to electrostatic interactions. these associations led to formation of a compatible nanostructure. according to transmission electron microscopy based morphology studies, reduced graphene oxide/silver nanoparticles revealed wrinkled graphene nanosheet on which silver nanoparticles were found homogeneously scattered. the silver nanoparticles of 15 nm were observed in the micrographs. the silver nanoparticles were also uniformly coated with polymers. fine dispersion revealed also effectiveness of the green method thus, the morphology studies supported the formation of a compatible matrix-nanofiller nanostructure. in addition, the green nanomaterials revealed antibacterial effects towards the e. coli and s. aureus bacterial strains. figure 1. mechanism of synthesizing graphene nanosheets by using pomegranate via green route[31]. reproduced with permission from elsevier. figure 2. (a) preparation mechanism of rgo/agnps; and (b) and (c) tem images of go and rgo@agnps[32]. red arrows = two dimensional nanosheets of go and rgo; tem = transmission electron microscopy; go = graphene oxide; rgo = reduced graphene oxide; rgo@agnps = reduced graphene oxide@silver nanoparticles. reproduced with permission from elsevier. 4 upadhyay and co-workers[33] extracted reduced graphene oxide from vitis vinifera of grapes. this green method was low cost and facile for commercial graphene production (figure 3). starting materials was graphene oxide which was formed by hummer’s technique. this process also used green materials for synthesis. according to x-ray diffraction studies, differences in the graphite, graphene oxide, and reduced graphene oxide were analysed. structures of graphene oxide and reduced graphene oxide were confirmed through peaks at 10.4° and 23.7°, respectively. transparent graphene nanosheet nanostructure was further verified using the transmission electron microscopy analysis. graphene was observed as thin transparent nanosheet which was lightly wrinkled but has fine even surface morphology. li et al.[34] formed the cellulose, polyaniline, and graphene oxide-based nanocomposite through green in situ polymerization. the 3.5 wt.% nanofiller loading was used in these nanocomposites. this method involves simple solution and in situ polymerization techniques (figure 4). in addition, green starting materials and hummer’s method were also employed for the formation of sustainable materials. x-ray photoelectron spectroscopy was used to study the chemical bonding and structure of the nanomaterial (figure 5a). in addition to c and o elements, nitrogen, sulfur, and chloride were also identified in the study. according to cyclic voltametric curves (figure 5b), the cellulose/graphene oxide/polyaniline nanomaterial had significant electrical response, relative to cellulose/graphene oxide and cellulose/polyaniline. the superior cyclic response of the cellulose/graphene oxide/polyaniline was observed due to the synergistic effects of the conjugated polymer and graphene oxide with green polymer. gas adsorption-desorption isotherms of cellulose, polyaniline, and graphene oxide based nanocomposite aerogel were studied using brunauer-emmett-teller (bet) technique as given in table 1. the surface area, pore volume, and pore sizes of cellulose/graphene oxide/polyaniline nanocomposite were observed as 66.7, 0.37 cm3/g, 22.5 nm, respectively. these values were observed lower than the cellulose/graphene oxide and cellulose/polyaniline nanocomposites. these nanocomposites have been used as efficient ecological nanocomposites. figure 3. (a) geen synthesis of reduced graphene oxide; (b) x ray diffraction of graphite, go, and rgo; and (c) tem image of rgo sample[33]. go = graphene oxide; rgo = reduced graphene oxide; tem = transmission electron microscopy. reproduced with permission from elsevier. 5 figure 4. synthetic route to cellulose/graphene oxide/polyaniline nanocomposite[34]. go = graphene oxide; pani = polyaniline; ani = aniline; hcl = hydrochloric acid. reproduced with permission from mdpi. figure 5. (a) x-ray photoelectron spectroscopy spectra of pristine graphene oxide (go), neat polyaniline (pani), and the cellulose/go/pani nanocomposite; and (b) typical cyclic voltammogram (cv) curves of the cellulose/go, cellulose/pani, and cellulose/go/pani electrodes at 50 mv/s[34]. reproduced with permission from mdpi. table 1. brunauer-emmett-teller (bet) analysis of the regenerated cellulose, cellulose/go, cellulose/pani, and cellulose/go/pani[34]. sample sbet pore volume (cm3/g) pore size (nm) cellulose 137.6 0.38 10.9 cellulose/go 147.0 0.46 12.5 cellulose/pani 68.7 0.36 20.8 cellulose/go/pani 66.7 0.37 22.5 go = graphene oxide; cellulose/go/pani = cellulose/graphene oxide/polyaniline nanocomposite. reproduced with permission from mdpi. 6 gao et al.[35] used vitamin c and amin reducing agent/stabilizer to fabricate green graphene. the vitamin c was proved as an active reducing agent to form graphene in large quantity. no harmful solvent was used in this technique[36]. ren et al.[37] formed a nanocomposite based on chitosan matrix, reduced graphene oxide, and gold nanoparticles. homogeneous dispersion of gold nanoparticles was observed. effect of increase in the molecular weight of chitosan was studied on the size of gold nanoparticles. sayed et al.[38] used green sonication route to form the chitosan, erythritol, and graphene oxide derived nanocomposites. the nanocomposite was applied to detect the hg2+ ions and methylene blue dye. the removal efficiency was observed in the range of 186–205 mg g−1. sharif and researchers[39] formed ecological chitosan/graphene oxide nanocomposites using green solution method. the interfacial, load transfer, and physical properties were studied and found to enhance with the nanofiller loading levels. meera and colleagues[40] developed green nanocomposites based on the carboxymethyl chitosan, cashew gum, and boehmite nanoparticles. including 7 wt.% boehmite nanoparticles augmented the ac conductivity of the nanocomposites. the nanocomposites were found suitable to be applied in the green eco-electronic devices. 3. graphene for sustainable energy since decades, sustainable energy devices and systems have been researched and industrialized[41–43]. one of simple example is the wind turbines with green natural composite based blade materials by replacing the metal blades[44,45]. the sustainable composite materials have low weight, low cost, and high mechanical properties. for sophisticated energy devices like supercapacitors, solar cells, etc., use of sustainable materials has been concerned[46]. among energy storage strategies, supercapacitors have been categorized as most effective devices and so focused for the use of sustainable materials. in this concern, numerous sustainable green polymers (starch, cellulose, chitosan, etc.) have been used to form supercapacitor electrodes[47–49]. to further enhance the performance of supercapacitor electrodes based on green polymers, matrices have been reinforced with nanoparticles to form high performance nanocomposites. hence, sustainable synthesis techniques as well as green materials have been used to form sustainable supercapacitors[50]. sustainable fabrication strategies and materials for supercapacitor electrodes not only produce safe energy but also minimize the environmental risks[51]. nevertheless, limited research attempts have been observed in literature regarding the sustainable supercapacitor materials[52]. in this context, attaining high efficiency using sustainable supercapacitors has been found efficient. two-dimensional graphene nanosheets have been considered as best choices for energy storage devices like supercapacitors[53–55]. in addition to superior charge storing competence, graphene owns the advantageous properties like fine microstructure, durability, conductivity, strength, thermal stability, and other physicochemical properties. the functionalized or doped graphene nanosheets have revealed further enhanced electrical conduction and specific capacitance values[56]. conversion of graphene to high performance nanocomposites has also formed active materials for efficient supercapacitor electrodes. zhang et al.[57] adopted green techniques like freeze drying and hydrothermal method for the formation of three-dimensional graphene hydrogel or nitrogen doped (n-doped) graphene hydrogel. figure 6 shows simplistic routes towards the formation of hydrogels. in green freeze drying and hydrothermal techniques, water solvent was used[58,59]. then, ammonium bicarbonate was used to form ndoped graphene hydrogel with density of 0.034 g cm−3. figure 7 illustrates the cycling performance of neat graphene aerogel and n-doped graphene aerogel at current densities of 0.1 a g−1 and 10 a g−1, above > 200 cycles. at 100th cycle, specific capacity of 209 ma h g−1 was observed with 93.4% capacitance retention for n-doped graphene aerogel (0.1 a g-1), whereas the specific capacity was decreased at higher current density. under same conditions, the values were comparatively lesser for the pristine graphene aerogels. n-doping was so found effective to improve the supercapacitor performances. 7 figure 6. schematic illustration of synthesis steps for the n-doped graphene aerogel: (a) photographic images of graphene oxide suspension (5 mg ml−1); (b) freeze-dried graphene hydrogel obtained after hydrothermal reaction, (c) freeze-drying treatment; (d) 3d graphene aerogel; and (e) n-doped graphene aerogel; and (f) schematic illustration of a n-doped graphene aerogel sheet with three nitrogen doping types[57]. reproduced with permission from springer nature. figure 7. comparison of cycling performance of graphene aerogel and n-doped graphene aerogel at a current density of (a) 0.1 a g−1; and (b) 10 a g−1[57]. reproduced with permission from springer nature. çıplak and group[60] reinforced polyaniline with graphene oxide, reduced graphene oxide, and gold nanoparticles to form the nanomaterials aiming the sustainable supercapacitor electrodes. the nanocomposites were prepared using green in situ polymerization technique. an ecological method was also used to form graphene oxide. figure 8 illustrates the specific capacitance scans for unfilled polyaniline, polyaniline/graphene oxide-gold nanoparticle, and polyaniline/reduced graphene oxide-gold nanoparticle nanocomposites. the specific capacitance results revealed that the polyaniline/reduced graphene oxide-gold nanoparticles had value of 212.8 fg−1, which was observed 64 % higher than the unfilled matrix. superior specific capacitance results were obtained due to better π-π interacted nanostructure supporting the high electron conduction through the system. arthisree et al.[61] fabricated the polyaniline, polyacrylonitrile, and graphene quantum dot based sustainable nanocomposites as supercapacitor electrode material. figure 9 shows the design of supercapacitor based on nanocomposite with 1.5 wt.% loading and image of voltage generation for the optimal nanocomposite designed device. the specific capacitance of the sustainable electrode was recorded between 100 to 600 fg−1[62]. the supercapacitor represented reasonable output power of 1.4 v. fine performance was due to synergistic effects in the matrix-nanofiller and electron conductivity features[63]. hence, the formation of sustainable nanomaterials has contributed towards the green charge storage devices[64]. cellulose matrix has been explored as low cost green material for energy systems[65–67]. green supercapacitor electrodes based on cellulose and graphene have high electron conduction, charge transportation, and capacitance values[68]. three dimensional cellulose/graphene oxide sponges had high capacitance performance[69–71]. conductive polymers have been widely used in supercapacitors[72]. green prepared graphene and synthesis route has been applied to form conductive polymer/graphene supercapacitor a b 8 electrodes[73–75]. high performance electrodes have high surface area, specific capacitance, charge density, and electrochemical properties[76]. figure 8. the specific capacitance dependence on the scan rate (5–200 mvs−1) for neat pani, go-au@pani, and rgoau@pani[60]. pani = polyaniline; go-au@pani = graphene oxide-gold nanoparticle@polyaniline; rgo-au@pani = reduced graphene oxidegold nanoparticle@polyaniline. reproduced with permission from elsevier. figure 9. schematics of pan/pani@g-1.5 wt.% based supercapacitor along with the characteristic digital photograph of optimal nanocomposite for voltage generation[61]. pan/pani@g = polyacrylonitrile/polyaniline/graphene quantum dot. reproduced with permission from elsevier. 4. graphene for conversion of recycled resin to graphene or sustainable materials globally, plastic based industries are generating greenhouse emissions and environmental pollution, since decades[77–79]. according to worldwide surveys, 200 million tons of plastic waste can be generated annually[80– 82]. out of which only 10% of plastics is usually recycled and rest causes ecological hazards[83]. consequently, there is stern need of developing recycling strategies for waste plastics. however, the recycled plastics usually have low mechanical and physical properties for further technical uses and advanced techniques must be invented[84]. for the formation of graphene, various sustainable and non-toxic carbon sources have been employed[27]. el essawya et al.[85] established a route to form graphene using the recycled poly(ethylene terephthalate) (basically waste bottles). this method is commonly referred as waste-treats-waste[86,87]. here, synthesis of graphene using poly(ethylene terephthalate) waste bottles is given in figure 10. the waste bottles were treated with very high temperature of 800 ℃ for 1 h. resulting dark colored product was ground to form graphene. the as prepared graphene was used to treat the methylene blue dye. 9 figure 10. schematic representation for the synthesis of graphene from pet recycled bottles[85]. pet = poly(ethylene terephthalate). reproduced with permission from elsevier. numerous reinforcing agents and compatibilizers have been used to elevate the features of recycled polymer resins[88]. furthermore, blends of recycled polymers have been prepared, as a solution to attain enhanced properties[88]. to improve the performance and applications of recycled polymers, effective nanofillers used are graphene, few-layer graphene, graphene nanoplatelets, and other graphene derivatives[89]. among these nanocarbons, few layer graphene has been found to improve the heat constancy, strength, and chemical stability features[90]. moreover, doped graphene like sulfur doped graphene has been filled in recycled polymers to enhance the physical characteristics[91,92]. few layers graphene has been industrialised on commercial scale for desired sustainability applications[93]. among recycled polyethylene resins, high density polyethylene has been efficiently recycled on large scale[94,95]. to augment the mechanical or thermal features of recycled polyethylene resins, commercial highdensity polyethylene has been added through melt mixing[96]. the blend of recycled and non-recycled highdensity polyethylene has been filled with different graphene nanoparticles like few layer graphene and graphene nanoplatelets using melt compounding technique. specifically, few layer graphene has been used to improve the morphological, rheological, thermomechanical, and chemical resistance features of polyethylene resins[97–99]. diallo et al.[100] researched on polyethylene resin which has been used to form recycled resin with reasonable physical features for industrial purposes. the recycled polyethylene/polypropylene blend as well as few-layer graphene filled recycled polyethylene/polypropylene nanocomposites have been prepared. influence of adding nanofiller on the mechanical, thermal, and rheological characters were explored. inclusion of few layers graphene was effective to form large amount of recycled polyethylene resin. sultana et al.[101] also investigated the effect of adding few-layer graphene on the processing of recycled polyethylene. the recycled polyethylene/polypropylene blend filled with few-layer graphene was also formed. consequently, the morphology and mechanical properties of the resulting nanomaterials were explored. the nanocomposites were developed using the melt extrusion method. figure 11 displays scanning electron micrographs of unfilled recycled polyethylene/polypropylene blend as well as recycled polyethylene/polypropylene/few-layer graphene nanocomposites with varying nanofiller contents. 10 figure 11. scanning electron microscopy images of the fractured surface of the (a) neat pe/pp; (b) r-(pe/pp)/flg = 96/4; and (c) r-(pe/pp)/flg = 90/10. the arrows indicate a few of the flg, visible on the fractured surface of the r-(pe/pp)/flg composites[101]. pe/pp = polyethylene/polypropylene; r-(pe/pp)/flg = recycled polyethylene/polypropylene/few-layer graphene; flg = few-layer graphene. reproduced with permission from mdpi. neat blend matrix formed a phase separated structure with globular areas. whereas the nanocomposite did not revealed phase separated structure and instead waves like pattern was observed on the fractured surface. increasing the amount of nanofiller affected the surface morphology of the blend matrix. graphene layers can be seen dispersed in the recycled blend matrix. it can be analysed that the nanocomposite with higher graphene loading had better consistent morphology at fractured surface due to compatible morphology. in other words, with the rising nanofiller contents compatible nanostructure was formed and homogeneous microstructure was observed. figure 12 shows the tensile and flexural strength, tensile and flexural modulus and impact strength of the nanocomposites vs. rising graphene contents. the mechanical results were well supported by the morphology studies. all the tensile and flexural strength and modulus and impact strength properties were found to enhance with the few layer graphene loadings. conclusively, 10 wt.% nanoparticle addition led to superior mechanical profile due to fine interactions in the nanocomposite and load transfer effects and resistance to crack propagation effects. upsurge in tensile strength, flexural strength, and impact strength were found as 9%, 23%, and 9%, respectively, relative to pristine polymers. table 2 displays change in the mechanical features of 4 wt.% nanofiller loaded samples to analyse the performance of the samples. in this way, the recycled resins have been modified for industrial uses towards sustainability applications[102,103]. 11 figure 12. (a) tensile strength and flexural strength; (b) tensile modulus and flexural modulus; and (c) impact strength of r(pe/pp)/flg composites as a function of flg concentration[101]. r-(pe/pp)/flg = recycled polyethylene/polypropylene/few-layer graphene; flg = few-layer graphene. reproduced with permission from mdpi. table 2. mechanical property variation (%) in compounds showing a significant change in properties compared to the neat r(pe/pp). properties neat polymer blend 4 wt.% nanofiller tensile strength 24 mpa +9% tensile modulus 1.4 gpa +37% flexural strength 30 mpa +23% flexural modulus 0.9 gpa +34% elongation at break 34% −80% 5. challenges and future all above discussed green approaches for graphene and nanocomposite synthesis offer remarkable opportunities towards the future sustainable engineering and supercapacitor expertise (table 3 and figure 13). furthermore, the continuous ongoing research efforts may resolve the underlying design, feature, and 12 performance challenges in these fields. important challenges have been encountered for large scale fabrication of graphene and derived forms through green routes. some attempts have been performed on using safe, recyclable, and green bio-based carbon sources to form graphene. however, these methods have not been applied for graphene production on commercial scale. although various studies have been reported for the formation of graphene from sustainable sources, formation of high quality graphene is still uncertain[104]. consequently, the graphene obtained from ecological sources may have defects, impurities, non-homogeneous morphology, and oxidized surface, relative to the graphene obtained through frequently used techniques. in addition, strength and charge transportation properties of graphene nanostructure have been greatly affected using waste derivation method. hence, it has been found challenging to use the waste derived graphene for technical applications. these challenges also hinder the large scale production of useful graphene nanostructure. in this regard, further research efforts have been found desirable for the production of high quality graphene through green methods, especially from waste and biomass. continuous research on sustainable graphene materials have led to the formation of sustainable and recyclable supercapacitor electrode materials with superior reliability, capacitance, charge density, power density, charge-discharge, and cyclic performance. for recyclable electrodes, sustainable polymers and green synthesis routes have been applied. nevertheless, limited material designs and fabrication methods have been explored so far for sustainable graphene based energy devices. furthermore, sustainable supercapacitors have yet not been used for industrial scale energy applications. future research may expand the use of graphene nanomaterials towards the more sustainable energy and electronic devices like micro-supercapacitors and microelectronics. here, research progress in the field of ecologically sustainable production of graphene and graphene nanocomposite membranes need to be analyzed according to the demands for the production of high quality of graphene keeping in view the crucial foremost difficulties in this field and also according to the end applications focused using green graphene research progress in this field need to be categorized according to the possible waste or ecological sources used for the production of green graphene. design and characteristics of sustainable and ensuing graphene nanocomposite need to be studied comprehensively. mechanisms for the conversion of ecological sources to green graphene also need to be analyzed. consequently, focused research efforts have been required on the structure, microstructure, mechanical, and physical properties of the green graphene and nanocomposites. in the nanocomposite form, future studies must focus the dispersion patterns of green graphene in nanomaterials. as green graphene is not pure and high quality having lots of surface defects, therefore, it has been found indispensable to study the matrix-nanofiller interactions, miscibility, interfacial, and miscibility effects in the resulting nanomaterials. research must focus the advanced methods to deal with the structural issues in the nanomaterials arising due to the use of waste derived graphene nanostructures. the durability of the green graphene based nanomaterials must also researched to find out improved methods for production. in the waste derived graphene production methods, optimum parameters and identification of perfect graphene design need to be investigated. major challenges identified in this sector are towards the commercial scale production of the green graphene. in addition, there is lack of targeted research in the area of conversion of plastics or recycled wastes into graphene. more focused research efforts have been certainly desirable in these discussed research directions to form high performance sustainable graphene nanostructures. 13 table 3. features of sustainable graphene and graphene based nanocomposites. graphene, derivative, or nanocomposites green fabrication techniques properties/potential ref. reduced graphene oxide vitis vinifera from grape extracts for graphene oxide reduction; hummer’s method x-ray diffraction peaks for graphene oxide and reduced graphene oxide at 10.4° and 23.7, respectively [33] reduced graphene oxide pomegranate juice for graphene oxide reduction mechanism studies [31] reduced graphene oxide vitamin c as reducing agent large scale production [35] graphene chemical vapor deposition; biscuits/chocolate carbon source green technique [28] graphene camphor plant extracts as green carbon source mass level synthesis [29] graphene glucose carbon source efficient carbon source [30] chitosan/reduced graphene oxide/gold nanoparticles chitosan as as stabilizer and reducing agent low molecular weight chitosan enhance kinetic rate constant of 0.21 min−1 [37] chitosan/erythritol/graphene oxide sonication methylene blue dye and hg2+ ions removal efficiency of 186.23 mg g−1 and 205 mg g−1, respectively. [38] carboxymethyl chitosan/cashew gum/boehmite nanoparticles water solvent ac conductivity and low activation energy [40] epoxy/chitosan encapsulated graphene oxide biodegradable chitosan interface formation between epoxy and chitosan-graphene oxide; elastic modulus enhanced by 65%, load transfer [39] chitosan/reduced graphene oxide/silver nanoparticles electrostatic method; corn stalk for silver nanoparticles morphology; antibacterial activities against the e. coli and s. aureus bacterial strains [32] polyaniline/graphene oxide/gold nanoparticles and polyaniline/reduced graphene oxide/gold nanoparticles cetraria islandica l. ach lichen for reducing graphene oxide; green in situ synthesis supercapacitor electrode has scan rate of 5–200 mvs−1; specific capacitance and capacitance retention of 212.8 fg−1 and 86.9%, [60] cellulose/graphene oxide/polyaniline in situ technique electron conductivity 1.15 scm−1; areal specific capacitance 1218 mfcm−2; energy density 1201 µw/cm2 [34] chitosan/reduced graphene oxide/silver nanoparticles green materials and methods; phosphate buffer saline anti-bacterial packaging against e. coli and s. aureus bacterial strains. [32] three dimensional graphene hydrogel; nitrogen doped graphene hydrogel freeze drying; hydrothermal green methods; current densities 0.1-10 a g−1, specific capacity 209 ma h g−1; capacitance retention 93.4% [57] polyaniline; graphene oxide, reduced graphene oxide, gold nanoparticles green in situ polymerization specific capacitance 212.8 fg−1; capacitance retention 64 % [60] polyaniline, polyacrylonitrile, graphene quantum dot in situ; solution specific capacitance 100-600 fg−1 [61] recycled poly (ethylene terephthalate) to form graphene waste-treats-waste high temperature stability 800 ℃; methylene blue dye adsorption [85] recycled polyethylene/few-layer graphene melt extrusion technique tensile strength, flexural strength, and impact strength were found as 9%, 23%, and 9%, respectively [101] 14 figure 13. graphene nanostructures in sustainable applications. an important ecological application of graphene has been reported for the energy storage devices. a benign solution for commercialization of energy storage technology is to use the green processing approaches. incidentally, ecological friendly solvent, process, and materials have been preferred along with the green formed graphene. materials compatible with the green solvents like water, ionic liquid, etc. need to be used. applying green solvents depicted low noxiousness and facile processability effects. however, there are challenges in utilization of green nanotechnologies for energy storage devices. for example, using water or non-toxic solvents for sustainable materials may not be suitable for all type of efficient energy designs. conjugated systems have been found most efficient for energy devices; however, the green synthesis techniques cannot be adopted for all combinations of conducting graphene nanocomposites. applying green solvents like water may result in poor dispersion and conductivity properties, so decreasing the supercapacitor performance. future research is desirable is needed in this regard to form some novel ionic liquid based green solvents in place of water or toxic chemicals. comprehensive future efforts are required to use green polymers like cellulose and green graphene to form the supercapacitor electrodes. moreover, future research on functionalization of graphene to form green nanostructures must be focused. 6. conclusions this state-of-the-art overview fundamentally sheds light on the ecological aspects of graphene, which of course define the next technological sustainability vision. here, three sustainability characteristics of graphene have been engrossed, including the (i) environmentally sustainable production of graphene and nanocomposites; (ii) applying graphene to convert waste industrial resins into valuable recycled polymers; and (iii) using graphene in sustainable energy devices and systems. the first important stage is the identification of sustainable techniques to form green graphene on a large commercial scale. then, there is a need to 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2021; 5: 100275. doi: 10.1016/j.clet.2021.100275 94 characterization and application of nanomaterials (2021) volume 4 issue 1 doi:10.24294/can.v4i1.1329 original research article synthesis of titania fibers by electrospinning and its photocatalytic degradation properties yan lv1, feng chen1, yuanzheng tang1, zhigang chen1,2* 1school of chemistry, biology and materials engineering, sust, suzhou 215009, china 2jiangsu key laboratory of environmental functional materials, suzhou 215009, china. e-mail: czg@ujs.edu.cn abstract the electrospinning precursor solution was prepared by dissolving polyvinyl pyrrolidone as template, tetrabutyl titanate as titanium source, and acetic acid as inhibitor. the tio2 nanofilms were prepared by precursor solution electrospinning and subsequent calcination. thermal gravimetric analysis (tg), scanning electron microscopy (sem), x-ray powder diffraction (xrd), and transmission electron microscopy (tem) were used to characterize and analyze the samples. the influence of technological parameters on spinning fiber morphology was also studied. the results indicate that the tio2 nanofibers morphology is good when the parameters are as follows: voltage 1.4 × 104 v，spinning distance 0.2 m，translational velocity 2.5 × 10–3 m·s–1, flow rate 3 × 10–4 m·s–1, and needle diameter 3 × 10–4 m. the diameter of the fibers is about 150 nm. with the 1 × 10–4 mol·l–1 methylene blue solution used as simulated degradation target, the degradation rate is 95.8% after 180 minutes. keywords: titania; electrospinning; morphology; structure; photocatalytic degradation article info received: 17 february 2021 accepted: 8 april 2021 available online: 15 april 2021 copyright copyright © 2021 yan lv, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction in recent years, the environmental problems caused by the rapid development of industrialization have become increasingly serious. dyes are widely used in many industries, but they are not fully discarded. the water and soil pollution caused by waste dyes has caused serious harm to human health and ecosystem[1]. at present, there are many methods to treat dye wastewater, the more common ones are adsorption method, membrane separation method, microbial degradation[2], electrochemical method, etc.[3] among them, photocatalytic degradation technology has the characteristics of low cost, high efficiency, low energy consumption and environment-friendly, so it has developed rapidly[4]. among many semiconductor photocatalysts, titanium dioxide is favored for its stable chemical performance, strong oxidation ability, low price, easy availability, non-toxic and harmless and no secondary pollution in the process of organic degradation[5]. at present, the degradation of organic pollutants by using titanium dioxide as photocatalyst has gradually shifted from experimental research to the development of practical products[6]. the photocatalytic degradation process is divided into two steps: adsorption and photochemical reaction. only when organic matter is adsorbed to the material surface can photocatalytic degradation be carried out. therefore, the photocatalytic degradation 95 efficiency is closely related to the adsorption performance of materials to organic molecules and their photocatalytic ability. nowadays, nano titanium dioxide photocatalytic materials include nano powder and nano film[7]. for nano powder, although the particles are fine and easy to combine with organic matter in solution, agglomeration will occur, which will make the catalyst inactive, thus reducing the photocatalytic efficiency. moreover, the nano particles are difficult to separate and recover, which is not conducive to the regeneration and reuse of the catalyst. although nano films are easy to recover and recycle, their practical application is limited because of their small specific surface area and low photocatalytic efficiency. the film composed of one-dimensional titanium dioxide nanofibers can not only be recycled, but also improve the photocatalytic performance by increasing the specific surface area of the nano film. wu mingchung, andrá sápi et al. synthesized palladium modified titanium dioxide composite nanofibers through cellulose/catalyst composite system, which greatly improved the photocatalytic performance of the materials[8]. electrospinning technology is the only one method that can directly and continuously prepare nanofibers[9,10]. this is a spinning method to obtain nano fibers by spray stretching of polymer solution or melt under electrostatic action. it has the advantages of simple equipment, strong operability and high efficiency and has played an important role in many fields such as nano fiber preparation[11]. the process parameters affecting the spinning were studied by electrospinning, and anatase titanium dioxide films mainly composed of fibers with a diameter of about 150 nm were synthesized[12]. the fibers are disorderly and cross arranged, and have certain toughness. the crystal structure and micro morphology were studied by xrd, sem and tem. the material has high photocatalytic activity and is not easy to inactivate. the advantages of morphology and structure make it reusable and easy to separate and recover. the photocatalytic performance of methylene blue solution was studied by degrading it under ultraviolet light. 2. experiment 2.1 raw material tetra-n-butyl titanate (c16h36o4ti, chemically pure), absolute ethanol (analytically pure), glacial acetic acid (analytically pure), all of which are produced by sinopharm chemical reagent co., ltd. polyvinylpyrrolidone (pvp, analytical purity, mw = 1,300,000, aladdin reagent co., ltd.), self-made deionized water, p25 powder (nano titanium oxide, degussa, germany, with an average diameter of about 20 nm). 2.2 preparation weigh 2 g of polyvinylpyrrolidone (pvp) with molecular weight of 1.3 million, fully dissolve it in 40 ml of absolute ethanol, drop 2 ml of glacial acetic acid to keep the solution acidic, and stir at room temperature for 3 h. transfer 3.7 ml of tetra-n-butyl titanate with a pipette gun and add it slowly, and then stir at room temperature for 6 h to prepare a slightly viscous light yellow transparent spinning solution. use a 5 ml disposable medical syringe to suck a certain amount of spinning solution and install it on the ss electrospinning machine. first set the injection speed, injection distance, left-right translation speed of the nozzle and the distance between the nozzle and the plane receiving steel plate, turn on the led observation lamp, apply high voltage at the nozzle through the high-voltage dc power supply, and adjust the voltage through the knob. make the spinning fiber form taylor cone pattern. in the spinning process, the nozzle is required to have neither spinning liquid accumulation nor spinning splash. after spinning, the obtained nanocomposite fiber material was placed in a vacuum drying oven for 6 hours, the temperature is set at 40 ℃ to remove the residual solvent. then, the fiber was calcined to 600 ℃ in muffle furnace at 5 ℃·min–1 for 1 h to prepare nano-tio2 fiber film material. 2.3 characterization and testing it was characterized by thermogravimetric analysis (tg) and differential scanning calorimetry (dsc). the test conditions are: heating rate 96 20 ℃·min–1, air flow 2 × 10–3 l·s–1, the injection amount is about 2 mg, and the temperature range is 25–800 ℃. s-4800 field emission scanning electron microscope (fesem) of hitachi was used to observe the morphology of the samples. the powder was identified by d8 x-ray diffraction (xrd) produced by bruke company. the prepared nano materials were analyzed by x-ray diffraction (xrd). the xrd measurement parameters were: cukα radiation line, filtered by curved graphite crystal monochromator, working voltage 40 kv, working current 40 ma, scanning speed 5°·min–1. the particles were observed by jem-2100 transmission electron microscope (tem) made in japan, and the working voltage was 200 kv. the preparation concentration is 300 ml of 1 × 10–4 mol·l–1 methylene blue solution, add 0.1 g of sample, stir magnetically in the dark for 60 min to establish the adsorption balance between dye and catalyst, and put it into the photocatalytic reaction device for reaction. the light source is four 15 w uv lamps. the constant temperature is 30 ℃, and in the same proportion, p25 is also placed in the photocatalytic reaction device for reaction. take samples at every certain time, centrifuge and take the supernatant. measure the concentration after degradation with a spectrophotometer to obtain the degradation rate of dyes. degradation rate = [(initial concentration – post-degradation concentration)/initial concentration] × 100%. 3. results and discussion 3.1 thermogravimetric analysis figure 1 is the tg-dsc diagram of the composite obtained after electrospinning. from figure 1, it can be observed that there is an obvious weight loss process of the sample before 100 ℃ accompanied by the endothermic of the system, which is the desorption of h2o physically adsorbed on the sample surface and the volatilization of residual solvent. there are two obvious exothermic peaks at about 380 ℃ and 516 ℃, and the exothermic peak near 380 ℃ is due to the oxidation and decomposition of n-tetrabutyl titanate to form titanium dioxide in air. pvp began to decompose at 400 ℃, and there was a significant exothermic peak at 516 ℃, and pvp completely decomposed near 550 ℃. after 600 ℃, the weight and heat flow curve of the sample will not decrease. in order to obtain pure titanium dioxide, the calcination temperature of the material can be set to 600 ℃. figure 1. tg-dsc diagram of pvp/tetra-n-butyl titanate spinning film. 3.2 exploration on the best spinning process the titanium dioxide nanofiber film prepared by electrospinning has snow white, slightly ductile, flake and no cracks. the micro fiber morphology is affected by the spinning process, including voltage, spinning distance, nozzle translation speed, jet speed, needle inner diameter and so on. through the control variable method, the five variables are regulated, and the micro morphology of the sample is analyzed by scanning electron microscope. the more uniform the fiber distribution, the smaller the diameter, the better the material morphology. and there is no fracture and adhesion, so as to obtain the best spinning process. 3.2.1 voltage effect take the voltage as the variable, and the other variables remain unchanged. at 8 × 103 v, 1.4 × 104 v, 2.5 × 104 v, the samples were spun to obtain sem photos (figure 2). figure 2(a) shows voltage at 8 × 103 v, the fiber thickness is uneven and beads appear. figure 2(b) shows voltage at 1.4 × 104 v, the fiber thickness is uniform, and the fiber surface is smooth and continuous. figure 2(c) shows voltage at 2.5 × 97 104 v, the fiber is fine, messy, and a large number of fractures occur. from this analysis, in figure 2(a), when the spinning voltage is too low, the formed electric field force is small, but to overcome the surface tension of the solution, the electrostatic field force is insufficient, resulting in that the spinning solution cannot be stretched into silk in time, so beads are formed. in figure 2(c), when the voltage is too high, during jet operation, the electric field is strong, so that the fibers are pulled very thin and disorderly, and even some fibers are pulled off. therefore, it is necessary to select an appropriate voltage so that the electrostatic field force can overcome the surface tension of the solution without being too large to break the fiber. in figure 2(b), when the positive voltage is 1.4 × 104 v, the spinning is not only uniform in thickness, but also free of beads and fracture, and the morphology is intact. to sum up, when the voltage is 1.4 × 104 v, the spinning effect is the best. 3.2.2 influence of spinning distance the spinning distance is the distance between the spinning needle and the receiving plate. take the spinning distance as the variable, keep the rest unchanged, and set the receiving distance as 0.15 m, 0.2 m and 0.25 m, then the samples were spun, and the sem photos of the samples were obtained (figure 3). it can be analyzed that the spinning distance has an obvious effect on the uniformity of fiber thickness. the change of curing distance mainly affects the electric field strength and whether the solvent in the fiber can volatilize completely. in figure 3(a), when the spinning distance is 0.15 m, the spinning distance is short, so that the fiber cannot be fully stretched, the thickness of the spinning fiber is uneven, and some filaments are thicker, so as to form a large number of curls. the solvent cannot be fully volatilized, so that the fiber can be partially bonded. in figure 3(b), when the spinning distance is 0.2 m, the distance is moderate; the fiber thickness is uniform; the arrangement is relatively orderly, and the spinning morphology is intact. in figure 3(c), when the spinning distance is 0.25 m, the spinning distance figure 2. sem of titanium dioxide film at positive voltage of 8 × 103 v (a), 1.4 × 104 v (b), 2.5 × 104 v (c). figure 3. sem of titanium dioxide film at spinning distance of 0.15 m (a), 0.2 m (b) and 0.25 m (c). 98 is long. although the solvent is fully volatilized, the spun fiber cannot be received in time, and the electric field strength is relatively reduced, resulting in turbulence, and a large number of fiber fractures, more disorder and uneven fiber thickness. to sum up, the spinning distance, that is, the curing distance, is 0.2 m, the spinning effect was the best. 3.2.3 translation speed taking the translational velocity of the needle as the variable, the other quantities remain unchanged. at the speed of 0 m·s–1, 2.5 × 10–3 m·s–1, 5 × 10–3 m·s–1 respectively, the spinning was carried out, and the scanning electron microscope photos of the samples were obtained (figure 4). as can be seen from figure 4, in figure 4(a), when the needle does not move, for no longitudinal traction, the fibers accumulate was in a fixed position, so the fibers are curled and the diameter is too large. in figure 4(b), when the needle translation speed is 2.5 × 10–3 m·s–1, the spinning is smooth, fiber is uniform thickness and intact morphology. in figure 4(c), when the translation speed is 5 × 10–3 m·s–1, the needle moves rapidly left and right, causing partial fracture of the figure 4. sem of titanium dioxide film at nozzle translation speed of 0 m·s–1 (a), 2.5 × 10–3 m·s–1 (b), 5 × 10–3 m·s–1 (c). figure 5. sem of titanium dioxide film of pinning speed at 3 × 10–4 m·s–1 (a), 5 × 10–4 m·s–1 (b), 7 × 10–4 m·s–1 (c). figure 6. sem of titanium dioxide film at the inner diameter of 7 × 10–4 m (a), 5 × 10–4 m (b), 3 × 10–4 m (c). 99 fiber. it can be analyzed that the translation speed has a significant impact on the fiber morphology. in order to control the phenomenon of fiber curling and fracture, it is necessary to select the appropriate translation speed. to sum up, the translation speed is set to 2.5 × 10–3 m·s–1, the spinning effect was the best. 3.2.4 jet speed taking the injection speed as the variable, the other quantities remain unchanged. at the speed of 3 × 10–4 m·s–1, 5 × 10–4 m·s–1, 7 × 10–4 m·s–1, the samples were spun to obtain sem photos (figure 5). in figure 5(a), when the injection speed is 3 × 10–4 m·s–1, the spinning is continuous, smooth, uniform, without fracture, and the fiber is fine. in figure 5(b), when the injection speed is 5 × 10–4 m·s–1, the spinning is relatively uniform and partial fracture occurs. in figure 5(c), when the injection speed is 7 × 10–4 m·s–1, the spinning fiber is thicker and has accumulation. it can be analyzed that the spinning speed has a significant impact on the diameter of the fiber. from figure 5(a) to figure (c), the diameter of the fiber is gradually increasing with the increase of the jet speed, because the jet amount per unit time is increased with the increase of the jet speed, and the taylor cone receiving surface formed by spinning is relatively fixed, so the tensile degree of the electrostatic field on the spinning solution must be reduced. moreover, in the spinning process, the spinning liquid will accumulate in the needle due to the large injection volume and failure to spin in time. of course, the smaller the jet speed, the better. if the amount is too small, there will be spinning discontinuity and fiber disconnection. to sum up, the injection speed is set to 3 × 10–4 m·s–1, then the spinning effect was the best. 3.2.5 needle size the needle size is variable, and the other quantities remain unchanged. under the inner diameter of 7 × 10–4 m, 5 × 10–4 m, 3 × 10–4 m, the samples were spun to obtain sem photos (figure 6). in figure 6(a), when the needle of inner diameter 7 × 10–4 m is selected, the prepared fiber is thicker and the fiber is not straight. select the needle of inner diameter 5 × 10–4 m in figure 6(b), the prepared fiber is uniform in thickness, but slightly broken. select the needle of inner diameter 3 × 10–4 m in figure 6(c), the prepared fibers are evenly distributed and the fiber diameter is much thinner. it can be analyzed that the thickness of the needle will also affect the diameter of the spinning fiber, because the thickness of the inner diameter of the needle directly affects the amount of spinning jet. from figure 6(a) to figure 6(c), as the needle becomes thinner, the prepared fibers not only have small diameter, uniform distribution, but also have intact morphology. therefore, the fiber prepared by selecting the needle with an internal diameter of 3 × 10–4 m is better. based on the above scanning morphology of fiber film under different voltage, spinning distance, jet speed and needle inner diameter, it can be concluded that the voltage is set to 1.4 × 104 v for electrospinning parameters, spinning distance 0.2 m, translation speed 2.5 × 10–3 m·s–1, injection speed 3 × 10–4 m·s–1, needle inner diameter 3 × 10–4 m, the titanium dioxide fiber film with the smallest fiber diameter and the best uniformity and no fracture agglomeration can be obtained. the titanium dioxide film with this morphology is the best morphology. 3.3 structure and morphology analysis figure 7 is at a voltage of 1.4 × 104 v, spinning distance 0.2 m, translation speed 2.5 × 10–3 m·s–1, injection speed 3 × 10–4 m·s–1 and needle inner diameter 3 × 10–4 m xrd pattern of titanium dioxide fiber film with the best spinning morphology prepared. wide diffraction peaks appeared at 2θ = 25.4°, 37.5°, 48.1°, 54.0°, 55.1°, 62.7°, 68.8°, 70.3° and 75.0°. corresponding to the characteristic peaks of (101), (004), (200), (105), (211), (204), (116), (220) and (215) crystal planes of anatase tio2, narrow diffraction peaks also appeared at 2θ = 27.4°, 36.1°, 41.2° and 56.6°. corresponding to the characteristic peaks of (110), (101), (111) and (220) crystal planes of rutile tio2, it can be seen that the titanium dioxide synthesized by electrospinning is mainly anatase phase (jcpds21-1272), and there is also a small amount of more stable rutile phase (jcpds21-1276). according 100 to scherrer formula, the average grain size of tio2 nanofibers is about 14.3 nm. figure 7. xrd diffraction pattern of titanium dioxide fiber film. figure 8 is a tem photograph of nano titanium dioxide fiber film material at different resolutions. it can be observed from figure 8(a) that titanium dioxide is fibrous, the fiber morphology is well preserved, and has a large aspect ratio. it can be seen in figure 8(b) that the fiber is actually assembled from nano-sized titanium oxide particles. at the same time, it can be seen that the diameter of the fiber is about 150 nm. under the high-power observation shown in the hrtem photo (figure 8(c)), it can be seen that there are a large number of lattice lines of titanium dioxide crystal. the measured spacing of lattice lines is 0.35 nm, which corresponds to the crystal plane of anatase phase (101), and the rutile phase is not observed due to the small amount. 3.4 photocatalytic performance in order to investigate the photodegradation effect of titanium dioxide fiber membrane material on common dye methylene blue solution, compare it with p25, and the degradation rate is shown in figure 9. under the same experimental conditions, the degradation rate of methylene blue solution by titanium dioxide film was 95.8%, while the degradation rate of p25 was 66.9%. therefore, titanium dioxide fiber membrane material has better photocatalytic activity. this is because the fluffy fiber structure of the sample makes the material have strong adsorption capacity, which makes methylene blue molecules easier to adsorb on the active sites of the material. the photogenerated hole transmission rate of titanium oxide is fast, which reduces the recombination probability of photogenerated electrons and holes, thus avoiding the rapid deactivation of the catalyst. moreover, titanium fiber oxide surface is rich in hydroxyl group and has strong adsorption water capacity. water and hydroxyl groups can react with surface holes to form strong oxidative hydroxy radicals, which can decompose the methyl blue solution in a short time. figure 9. degrade rate of titanium dioxide fiber membrane samples and p25 on methylene blue solution. figure 8. tem photos of nano titanium dioxide fiber membrane material at different magnification. 101 4. conclusion pvp/tetra-n-butyl titanate composite nanofibers were prepared by electrospinning and calcined in a muffle furnace at 600 ℃. by exploring the influencing factors of electrospinning, the optimum spinning conditions were obtained: the voltage was 1.4 × 104 v, spinning distance 0.2 m, translation speed 2.5 × 10–3 m·s–1, injection speed 3 × 10–4 m·s–1, needle inner diameter 3 × 10–4 m. xrd and tem characterization showed that the products obtained under the optimum conditions were mainly composed of anatase titanium oxide long fibers, with uniform fiber distribution and good morphological structure. the diameter of the fibers was about 150 nm. titanium oxide grains of about 14 nm are deposited. the degradation ability of this material to methylene blue dye is much higher than that of commercial p25 titanium dioxide material, and the membrane structure of the material is more conducive to the recovery and reuse of the material, so it has great application potential. conflict of interest the authors declare that they have no conflict of interest. acknowledgements this work was supported by the national natural science foundation of china (51478285), natural science foundation of jiangsu province—youth fund (bk2014, 280) and natural science foundation of colleges and universities of jiangsu province (16kja430008). 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characterization and application of nanomaterials 2024, 7(1), 4581. https://doi.org/10.24294/can.v7i1.4581 1 review graphene in gas separation membranes—state-of-the-art and potential spoors ayesha kausar1,2,*, ishaq ahmad1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, china 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract: graphene and derivatives have been frequently used to form advanced nanocomposites. a very significant utilization of polymer/graphene nanocomposite was found in the membrane sector. the up-to-date overview essentially highlights the design, features, and advanced functions of graphene nanocomposite membranes towards gas separations. in this concern, pristine thin layer graphene as well as graphene nanocomposites with poly(dimethyl siloxane), polysulfone, poly(methyl methacrylate), polyimide, and other matrices have been perceived as gas separation membranes. in these membranes, the graphene dispersion and interaction with polymers through applying the appropriate processing techniques have led to optimum porosity, pore sizes, and pore distribution, i.e., suitable for selective separation of gaseous molecules. consequently, the graphene-derived nanocomposites brought about numerous revolutions in high-performance gas separation membranes. the structural diversity of polymer/graphene nanocomposites has facilitated the membrane selective separation, permeation, and barrier processes, especially in the separation of desired gaseous molecules, ions, and contaminants. future research on the innovative nanoporous graphene-based membrane can overcome design/performance-related challenging factors for technical utilizations. keywords: graphene; polymer; nanocomposite; membrane; gas separation; selectivity; permeation 1. introduction for environmental remediation purposes, membrane technology has been widely adopted, especially for the separation of desired or toxic gaseous species [1]. among membranes, polymeric membranes have durability, long functioning, and efficient performance, so they have achieved significance for separation applications. the graphene-filled nanocomposite membranes possess superior characteristics for technical fields such as gaseous, water molecules, and chemical separations [2]. the subsequent membranes were formed for large-scale gas separation, water decontamination, fuel cells, and several other applied fields [3,4]. primarily, the graphene-derived nanocomposite membranes have been developed with torturing pathways in the matrices to promote gaseous, water molecules, ions, or diffusion of other species [5]. consistent graphene dispersion in the membranes was found to improve the targeted impurities and toxic molecules from the medium of interest [6,7]. the membrane processes studied for these nanocomposites include ultrafiltration, microfiltration, nanofiltration, and reverse osmosis [8–10]. the resultant membranes were competently applied for eliminating the pollutants [11]. the graphene-reinforced citation kausar a, ahmad i. graphene in gas separation membranes—state-of-theart and potential spoors. characterization and application of nanomaterials. 2024; 7(1): 4581. https://doi.org/10.24294/can.v7i1.4581 article info received: 7 february 2024 accepted: 27 february 2024 available online: 9 april 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 4581. 2 membranes revealed superior structural benefits than the pristine polymer designs due to facile manufacturing and performance advantages [12]. research developments have reported technical growth of these membranes for numerous sectors [13]. in the polymeric membranes, graphene, graphene oxide, and other modified graphene forms have been applied [14]. it is worth mentioning that the thin layer of neat graphene nanosheet has been designed for selective permeation of gaseous molecules [15]. in polymeric matrices, graphene has revealed fine reinforcement effects relative to other carbon nanofillers (fullerene, carbon nanotube, etc.) [16]. including multilayered graphene or graphene oxide in the polymer membranes has been known to form two-dimensional nanochannels for the selective permeation and barrier effects of gaseous molecules [17]. efficient and facile processing technologies have been applied, such as solution casting, doctors blading technique, in situ method, phase inversion, infiltration, lift-off/float-on, etching, etc. [18,19]. mostly, thermoplastic matrices have been examined to form graphene-derived nanocomposites and membranes for gas separation [20–22]. the pore sizes and graphene dispersion patterns directly affect the gaseous molecular permeability and diffusivity features of these membranes [23–25]. consequently, graphene scattering and layering in matrices have been known to develop percolation trails for the diffusing gaseous molecule [26]. however, fine graphene dispersion, optimization of pore sizes, and processing conditions have yet to be attained towards high-performance commercial-scale gas separation membranes. applications of gas separation membranes for gaseous pollutants and desired molecules were found in the fields of fuel cells, gas sensors, chemical industries, etc. [27,28]. this review basically focuses on the design, development, and aspects of graphene-derived nanocomposite membranes for selective gas permeation applications. fine graphene dispersion, interface effects, and optimum pore formation in the membranes have broadened the potential of the gas partition membranes. this overview is groundbreaking to portray the methodical progressions of graphene resultant membranes for gas separation. for the separation of gaseous species from mixtures, various polymer matrices have been filled with the graphene nanofillers to form the selectively permeable membranes. to the best of knowledge, this state-ofthe-art review is innovative to depict the advancements in gas separation membranes, including the membrane designs, physical properties, and effect of graphene inclusion on the gas transportation features. this manuscript has been found indispensable for the future advances of gas separation graphene nanocomposite membranes, and so it can be a helpful guide for the interested field researchers. 2. graphene a two-dimensional nanosheet like carbon nanostructure is referred to as graphene [29]. it is constituted of sp2 hybridized carbon atoms, discovered in 2004 [30]. graphene was synthesized using numerous strategies like mechanical or liquid exfoliation of graphite, chemical vapor deposition, laser technique, plasma practice, and chemical synthesis methods [31–33]. graphene is a thin, layered, transparent nanostructure [34]. graphene has high electron mobilization of around 200,000 cm2v−1s−1 and high thermal conductivity of 3000–5000 w/mk [35]. excellent characterization and application of nanomaterials 2024, 7(1), 4581. 3 mechanical properties of graphene include a high young’s modulus of 1 tpa and a strength of >200 times that of steel [36]. graphene nanosheets have a wrinkling effect due to the van der waals interactions [37]. to enhance the dispersion effects and final features, graphene nanosheets have been functionalized to introduce various surface functionalities such as hydroxyl, carbonyl, carboxylic, epoxide, etc. [38]. the properties of graphene have been synergistically combined with other nanomaterials to form the nanocomposites. graphene-based nanocomposites revealed numerous superior electrical, mechanical, thermal, and physical features [39–41]. consequently, the graphene-derived nanomaterials have been applied in wide-ranging technological structures and applications like electronics, sensors, actuators, energy devices, including fuel cells, batteries, membranes, engineering structures, and biomedical advanced devices [42]. 3. graphene and nanocomposites in gas separation graphene-based nanoporous membranes have been applied for gas molecule transport [43–45]. the ultrathin graphene nanosheets have been designed for gas separation [46–48]. lee et al. [49] studied the selective separation of carbon dioxide co2 molecules from co2/ch4, co2/o2, and co2/n2 gas mixtures. graphene nanosheets have affinity for co2 molecules, and pores in graphene nanosheets were suitable for the passage [50–52]. among the gas mixtures, a high gas flux was observed for co2/o2 at 0.43 [53]. jiang et al. [54] used first principles density functional theory to examine the permeability and selectivity of nanoporous graphene nanosheets. figure 1 shows graphene nanosheet with hydrogen-passivated pore. the nanopore width was 0.02 å according to electron density isosurface isovalue. the snapshot of gas molecules passing is given in figure 2. figure 1. (a) an all-hydrogen passivated pore in graphene; (b) pore electron-density isosurface isovalue is at 0.02 e/å3 [54]. reproduced with permission from acs. characterization and application of nanomaterials 2024, 7(1), 4581. 4 figure 2. molecular dynamics simulations of h2 diffusing through nitrogen functional pore (600 k) [54]. reproduced with permission from acs. according to geometry optimization studies, h2 molecules entered through pores at 244 fs, and molecules stayed there for 180 fs. then molecules diffuse out through pores at 424 fs. high h2/ch4 permselectivity was observed, as per first principles molecular dynamics simulation studies on porous graphene. it has been observed that hydrogen atoms on graphene nanopores decreased the pore width to 2.5 å, while the pore length remained the same as 3.8 å (figure 3). consequently, the interaction energy of incoming molecules with graphene nanosheets and diffusion barriers affected molecular adsorption or transportation. the resulting van der waals density functional barrier for h2 and ch4 was observed as 0.22 and 1.60 ev, respectively. figure 3. interaction energy between h2 vs. adsorption height. inset: adsorption height and orientation of h2. red squares/solid lines = vdw-df; black circle/dashed lines = pbe [54]. reproduced with permission from acs. the graphene membranes having porous nanostructures were designed and studied aiming for gas separation [55–57]. graphene and graphene oxide membranes were designed with fine pores for molecular sieving purposes. koenig and colleagues [58] deposited the single-layered graphene on a silicon oxide substrate. the graphene layer was studied for the permeation of gas molecules. the etching process was characterization and application of nanomaterials 2024, 7(1), 4581. 5 applied for the separation of the membrane from the substrate. the pristine graphene nanosheet is not permeable to gas molecules; however, the etched graphene membrane had a porous nanostructure for gas molecule passage. consequently, the etched graphene nanosheet was permeable to h2 and co2 gas molecules [59–61]. li and researchers [62] designed the ultrathin porous graphene oxide membranes with pore sizes of −0.34 nm to 1 nm. the membranes were studied for permeability and selectivity properties of co2, h2, n2, and gases. the h2/co2 selectivity of 3400 and h2/n2 of 900 were observed [63,64]. smaller gas molecules revealed facile permeation relative to the larger molecules through the porous membranes [65–67]. for gas separation applications, poly(methyl methacrylate) was applied for effective membrane thermoplastic material [68–70]. for the formation of polymer/graphene nanocomposite membranes, facile methods have been used [71,72]. most commonly, the solution casting procedure has been applied [73]. in this method, the polymer is dissolved in an appropriate solvent. the nanoparticles of interest are also dispersed in a solvent. afterwards, both the dispersions are mixed to yield a consistent phase. the mixed solution is spread on an open surface to evaporate the solvent. the phase inversion method has also been used for the fabrication of graphene-filled nanocomposite membranes [74]. in this procedure, polymer is transformed from the liquid to solid phase. during this process, controlled solution evaporation and immersion precipitation are involved. additionally, interfacial polymerization has been used for the formation of graphene nanocomposite membranes [75]. interfacial polymerization consists of various steps such as oil phase formation, emulsification, and finally solvent evaporation. all the membrane formation methods have capabilities for fine dispersion of graphene nanofiller in the polymeric matrices. baldanza and co-workers [76] developed the graphene-filled poly(methyl methacrylate) nanocomposite membranes by applying the wet deposition process. here, the ‘lift-off/float-on’ method was used for obtaining membrane [77–79]. for the preparation of fine graphene nanosheets, the chemical vapor deposition practice was used. figure 4 illustrates the lift-off/float-on procedure for the membrane formation. the poly(methyl methacrylate)/graphene nanocomposite membrane with 0.06% loading had a thickness of 550 nm. according to the scanning electron microscopy images, graphene nanosheets were found to be sequentially layered in the polymeric membranes. according to permeability coefficients of humidified or pure o2 and co2 measured for varying r.h. levels for poly(methyl methacrylate) and poly(methyl methacrylate)/graphene, the resultant membranes own a lower permeability coefficient of 1.30 × 10−17 and 0.21 × 10−17 mol·m·m−2·pa−1·s−1, respectively, for co2 and o2, than the unfilled polymeric membrane (figure 5 and table 1). the reduced permeability values of gases were attributed to the formation of better dispersion and the development of more twisted gas diffusion paths for gas molecule permeation [80]. nevertheless, few studies have reported the poly(methyl methacrylate) and graphene nanocomposite-based gas separation systems, and more concentrated future research efforts may lead to the formation of high-performance selective gas permeation membranes. characterization and application of nanomaterials 2024, 7(1), 4581. 6 figure 4. (a) ‘lift-off/float-on’ and wet depositions adopted to produce poly(methyl methacrylate); (b) thickness of single nanocomposite layer on si wafer (inset: crosssection afm); (c) sem cross-section plane of nanolaminate [76]. reproduced with permission from mdpi. figure 5. gas permeability coefficients (25 ℃), pmma (blue bars) and gr-pmma (red bars): (a) co2 and humidified co2; (b) o2 and humidified o2 [76]. reproduced with permission from mdpi. table 1. permeability coefficients of co2 or o2 through pmma nanocomposite [76]. reproduced with permission from mdpi. nanolaminate/permeating gas p [mol·m·m−2·pa−1·s−1] p [barrer] pmma/co2 21.9 (± 0.8) × 10−17 6.5 (± 0.2) × 10−1 gr-pmma/co2 1.30 (± 0.1) × 10−17 0.39 (± 0.03) × 10−1 pmma/o2 4.79 (± 0.01) × 10−17 1.434 (± 0.003) × 10−1 gr-pmma/o2 0.21 (± 0.01) × 10−17 0.063 (± 0.003) × 10−1 poly(dimethyl siloxane) was investigated towards essential material aiming membrane formation [81–83]. the separation processes of carbon dioxide and other toxic gases have been studied using the poly(dimethyl siloxane) membranes. here, membrane thickness has been found to affect the gas permeability and separation properties [84]. to enhance the membrane features, nanofillers have been reinforced in the matrices for fine performance. ha and co-workers [85] reported on the graphene oxide-filled poly(dimethyl siloxane) membranes through solution processing. the characterization and application of nanomaterials 2024, 7(1), 4581. 7 kinetic diameters of co2, o2, n2, and ch4 gases (in the range of 0.16 to 0.50 å) affected the selectivity and permeability performance according to membrane porosity and microstructures. the membrane permeability was observed up to 99.9% by including 8 wt.% graphene oxide. moreover, selectivity properties of the co2/ch4, co2/o2, and co2/n2 have been observed. the gas transportation features were found to be reliant on the fine nanoparticle scattering in the polymer matrix. the microstructure and matrix-nanofiller interactions were also observed to be linked with the nanofiller alignment and scattering in the matrix for the formation of gas transportation pathways. koolivand and researchers [86] fabricated the poly(dimethyl siloxane) and graphene oxide-derived membranes. facile hummer’s method was used to form graphene oxide [87]. for these membranes, the combination of solution and ultrasonication processing methods have been applied. adding 5 wt.% graphene oxide loading, co2 permeability and co2/ch4 selectivity of 29% and 112%, respectively, were observed. berean et al. [88] opted for solution processing and ultrasonication for the formation of poly(dimethyl siloxane)/graphene nanocomposite membranes. due to the interactions, graphene dispersion and matrix-nanofiller interactions have been perceived. figure 6 shows a change in the permeability behavior of the membranes with graphene loading. the membrane permeability was about 60% enhanced with the nanofiller loading for co2, n2, ar, and ch4 gases. among these, co2 had greater permeation with the 0.5 wt.% graphene than other gases showing permeation at 0.25 wt.%. the greater permeation of co2 at higher nanofiller contents was observed due to its fine affinity towards graphene nanosheets. figure 6. (a) change in permeability for gas species with graphene concentration; (b) experimental data, maxwell model & nielson model for co2 permeation (0.25 wt.% nanocomposite) [88]. reproduced with permission from acs. figure 7 depicts the formation and behavior of diffusion pathways in poly(dimethyl siloxane) and graphene-reinforced poly(dimethyl siloxane) nanocomposites. aligned graphene nanosheets developed layered nanostructures with voids in the matrix. the formation of continuous gas diffusion trails was responsible for the passivation of the gaseous molecules through the matrix. gas permeability of n2, co2, ar, and ch4 was enhanced up to 60% with just 0.2 wt.% graphene contents. consequently, neat poly(dimethyl siloxane) had co2/ch4 selectivity of 3.6, which was increased up to 4.2 in the poly(dimethyl siloxane)/graphene membrane. characterization and application of nanomaterials 2024, 7(1), 4581. 8 figure 7. diffusion paths for pdms and pdms/graphene nanocomposites, path length = l; diffusion path (dα) = red; diffusion path through interfacial void (dβ) = green [88]. reproduced with permission from acs. polysulfone has been used as a popular matrix for membrane formation and also for the gas separation application [89–91]. in this context, the mixed matrix membranes of polysulfone have been reported [92–94]. the resulting polysulfone membranes have been observed to be functional for toxic gas separation such as carbon dioxide, nitrogen, and sulfur oxides [95]. zahri and co-workers [96] reported on polysulfone and graphene oxide-based membranes through the dry wet phase inversion process. the polysulfone-based nanocomposite membranes revealed high co2 permeability of 64–87 gpu. in addition, with the nanofiller loading, co2/ch4 selectivity was increased in the range of 19–25. the fine selectivity of the nanocomposite membranes was credited to the dispersal patterns in the polymer matrix [97]. sainath and co-worker [98] designed the mixed matrix gas separation polysulfone/graphene oxide nanocomposite membrane for gas separation using the solution method. as compared to a pristine polysulfone membrane, the graphene oxide-filled system revealed >3 times higher selectivity for co2/ch4. fine selectivity was attributed to the homogeneous dispersion and formation of efficient diffusion trails in the matrix. zhu and co-workers [99] opted for the vacuum infiltration process to form graphene oxide-filled nanocomposite membranes of the phosphotungstic acidgrafted polyphenylsulfone-pyridine matrix. transmission electron micrographs of polyphenylsulfone-pyridine, phosphotungstic acid, and graphene oxide-based systems are given in figure 8. the nanofiller was observed to be homogeneously dispersed in the polymer matrix. with the increasing nanofiller concentrations, fine nanoparticle distribution was observed in the matrix. in addition, with increasing nanoparticle loading, pore diameter as well as porosity have been found to enhance. it has been observed that the grafting of polymer matrix was also effective to disperse the nanofiller particles in the matrix. henceforth, polysulfone and derivative-based membranes with graphene or graphene oxide have been developed with superior morphology, gas separation, selectivity, and permeation performance. some membrane systems based on polyimide and graphene have been reported for efficient gas separation [100–102]. an attempt by melicchio and colleagues [103] used the knife casting method to form graphene oxide-filled matrimid® 5218 polyimide-derived membranes. the membranes were studied for the permeability and selectivity of h2 and co2 gases. h2/co2 selectivity was found as 3.5, while the permeability of h2 and co2 gases was 8–28 barrer. the nanocomposite membrane characterization and application of nanomaterials 2024, 7(1), 4581. 9 permeability and selectivity were found to rely on the nanofiller contents and dispersion in the polymer matrix. figure 8. transmission electron microscopy images with different pyridine moiety proportions in ppsu-pyx (polyphenylsulfone-pyridine) (a) 20%; (b) 60%; (c) 100%; (d) porosity and diameter of membranes [99]. reproduced with permission from acs. for membrane application, poly(1-trimethylsilyl-1-propyne) matrix material has been found useful [104–106]. albertoa and co-workers [107] formed graphenereinforced poly(1-trimethylsilyl-1-propyne for co2 separation. accordingly, the co2 permeability of poly(1-trimethylsilyl-1-propyne)/graphene nanocomposite membrane was 3.5  × 103 barrer, i.e., 39% lower than the neat polymer membrane. for poly(1trimethylsilyl-1-propyne), graphene oxide has been rarely used as a nanofiller. olivieri et al. [108] designed the graphene oxide-filled poly(1-trimethylsilyl-1-propyne) using solvent technique with chloroform. for the membranes, the co2, n2, and ch4 gases had diffusion coefficients of 25%, 14%, and 9%, respectively. the membrane systems based on poly(2,6-dimethyl-1,4-phenylene oxide) have also been researched [109– 111]. rea and colleagues [112] developed 0.3–15 wt.% graphene-filled poly(2,6dimethyl-1,4-phenylene oxide) membranes. according to scanning electron micrographs, the matrix-nanofiller interfaces have been observed with the nanofiller flakes dispersed in the membrane matrix (figure 9). the membrane permeability was studied at 35 and 65 ℃ (figure 10). for he, co2 and n2, the membrane permeability was found to slightly decrease with the nanofiller loading levels. the decreasing permeability was attributed to the increased nanofiller dispersion and membrane selectivity towards these gases. the dispersed graphene nanoplatelets were supposed to develop percolation pathways for the diffusion of gaseous species. table 2 shows the permeability behavior of the membranes with different nanofiller loadings at 35 and 65 ℃. in this way, efficient graphene-filled nanocomposite membranes have been designed for the selective gas separation or permeation properties [113–115]. the selective permeability of the membranes was found to depend upon nanofiller scattering plus alignment in the matrix [116,117]. future studies on advanced graphene nanocomposite membranes may lead to better gas molecule separation from mixtures of gases. characterization and application of nanomaterials 2024, 7(1), 4581. 10 figure 9. sem images of membranes. (a) ppo/0.3 wt.% graphene; (b) ppo/1 wt.% graphene [112]. sem=scanning electron microscopy; ppo = poly(1-trimethylsilyl-1propyne). reproduced with permission from mdpi. figure 10. gas permeability. (a) 35 ℃; (b) 65 ℃; and after graphene addition (as a function of graphene loading in poly(1-trimethylsilyl-1-propyne) matrix [112]. reproduced with permission from mdpi. table 2. permeability of the various gases in ppo and nanocomposite membranes [112]. ppo = poly(1-trimethylsilyl1-propyne). reproduced with permission from mdpi. permeability at 35 ℃, barrer ppo ppo/0.3 wt.% graphene ppo/1 wt.% graphene ppo/5 wt.% graphene ppo/15 wt.% graphene he 78 ± 3.8 86 ± 4.2 86 ± 4.1 68 ± 2.0 38 ± 3.2 n2 3.0 ± 0.2 3.5 ± 0.2 3.6 ± 0.2 2.8 ± 0.1 1.8 ± 0.2 co2 61 ± 2.0 62 ± 2.9 60 ± 2.9 51 ± 1.5 27 ± 2.3 permeability at 65 ℃, barrer ppo ppo/0.3 wt.% graphene ppo/1 wt.% graphene ppo/5 wt.% graphene ppo/15 wt.% graphene he 114 ± 5.0 116 ± 6.7 81.0 ± 2.4 51.6 ± 4.4 n2 5.00 ± 0.4 4.64 ± 0.3 3.31 ± 0.1 co2 69.3 ± 2 61.9 ± 3.6 42.3 ± 1.2 27.6 ± 2.4 4. prospects, challenges and gaps in the formation and application of graphene nanocomposites as highperformance membrane materials, numerous challenges have been faced during the field research efforts. generally speaking, not much effort has been observed for various categories of polymer/graphene nanocomposite membranes such as poly(dimethyl sulfoxide)/graphene, polysulfone/graphene, poly(methyl methacrylate)/graphene, polyimide/graphene, polyamide/graphene, etc. the experimental designs of the polymer/graphene nanocomposite membranes have been reported using the matrices, graphene nanofillers, processing techniques (solution, phase inversion, infiltration, etc.), and related preparation parameters. characterization and application of nanomaterials 2024, 7(1), 4581. 11 table 3 outlines the experimental design of the gas separation nanocomposite membranes used in important studies. adding graphene in polymer matrices affected the membrane morphology, physical properties, permeability, selectivity, and separation properties. polysulfone-based nanocomposite membranes have efficient co2/ch4 selectivity of 45%–74%. for gas separation membranes of poly(dimethyl siloxane) nanocomposites, n2, co2, and other gases permeability was observed >99.9%. similarly, higher selectivity values for gases like co2/ch4 have been observed. hence, there is huge scope for fabrication and investigations on graphene-based air/water purification membranes. development and investigation of more designs definitely can lead to better analysis of optimum fabrication, selectivity, permeation, and gas separation performance, along with better understandings on the structure-property relationship and mechanism of innovative graphene membranes [118]. major challenges hindering the gas separation membrane performance have been observed as graphene dispersion depending upon nanofiller contents, functionality, matrix nanofiller interactions, and interface formation [7]. the formation of interweaving pathways due to graphene dispersion in the polymer matrices has directly influenced the gas transportation properties. controlled pore sizes, shapes, and distribution in the matrices have also been found indispensable to promote the gas membrane performance. important solutions to the nanofiller dispersion have been proposed depending upon the graphene modification as well as by applying appropriate processing techniques and steps with the optimized conditions [119]. further challenges have been observed regarding the fabrication of graphene-based membranes on a large scale and subsequent commercialization. here, the appropriate fabrication techniques and processing parameters need to be implemented for the massive production of graphene nanocomposite membranes. in this case, the development of nanofibrous polymer/graphene membranes must be developed with a high surface area and welldispersed nanoparticles for separating the desired gaseous molecules [120]. by controlling and overcoming all the above-mentioned graphene and graphene nanocomposite membrane design and processing challenges leading to the fine microstructure, robustness, permeability, selectivity, and barrier characteristics [121]. briefly speaking, further research on the mentioned line may lead to the proposition of high-tech future gas transportation membranes for commercial purposes. table 3. significant features of polymer/graphene nanocomposite membranes for gas separation. polymer nanofiller fabrication way physicochemical properties membrane properties references polymer graphene or graphene oxide solution casting ion-molecule interaction; 1.8– 20 nm thickness h2/n2 selectivity 900; h2/co2 selectivity 3400; pore size 0.34 nm [62] poly(dimethyl siloxane) graphene oxide solution casting matrix-nanofiller interactions; interaction between graphene oxide and polymer 8 wt.% nanofiller; h2, o2, n2, ch4 and co2 permeability 99.9% [85] poly(dimethyl siloxane) graphene oxide solution/ultrasonication methods; tetrahydrofuran solvent interfacial interactions between functional groups of graphene oxide and polymer; density 1.09–1.12; thickness 1.9–2.8 nm 5 wt.% nanofiller; co2/ch4 selectivity 112%; co2 permeability 29%. [86] characterization and application of nanomaterials 2024, 7(1), 4581. 12 table 3. (continued). polymer nanofiller fabrication way physicochemical properties membrane properties references poly(dimethyl siloxane) graphene solution casting; pxylene solvent π-π interactions in matrixnanofiller 0.2 wt.% nanofiller; n2, co2, ar, and ch4 permeation 60%; co2/ch4 selectivity 4.2 [88] polysulfone graphene phase inversion; hollow fiber mixed matrix membrane nanosize synthesized graphene; interfacial interaction between graphene and polymer matrix co2/n2 selectivity 158%; co2/ch4 selectivity 74% [97] polysulfone graphene oxide solution route; nmethyl-2-pyrrolidone solvent physical interaction between oxygenated functional groups of graphene oxide and polymer; interactions between functional groups of nanocomposites and gas molecules co2/ch4 selectivity 45 [98] polyphenylsulfon e-pyridine graphene oxide vacuum infiltration technique wettability and surface charge response to ph; acidic ph = 3 form hydrophilic state contact angle 63.3°; alkaline ph = 11 form hydrophobic state contact angle 106.5°; charge-densitytunable nanoporous; power of ≈ 0.76 w m–2 dispersion; morphology [99] poly(1trimethylsilyl-1propyne) graphene oxide solution casting; chloroform solvent anchoring of graphene oxide nanosheets lowers membrane flexibility; less free volume; covalent cross-linking of polymer 1 wt.% graphene; diffusion coefficients co2 (25%); n2 (14); ch4 (9%) [108] poly(1trimethylsilyl-1propyne) graphene solution route interaction between filler andpolymer matrix; 0.93–1.36 mpa; 38–44 mpa 0.05 wt.% nanofiller; co2 permeability 3.5  × 103 barrer [107] poly(2,6dimethyl-1,4phenylene oxide) graphene solution route void formation at interface; glassy polymer filled with graphene; graphene inclusion for physical constraint to relaxation of polymer chains 0.3–15 wt.% nanofiller reduced permeability [112] the research progress on the polymer/graphene nanocomposite membranes has led to several advances in the kinds, design, and applications to overcome the crucial foremost problems in this field. these separation membranes have been used for the efficient removal of gaseous pollutants with optimally high flux and permeation. for this purpose, microstructure and mechanical features like strength and flexibility have been considered important. for the enhancements in these properties, nanoparticle dispersion has been found significant for the matrix-nanofiller interactions to advance the ultimate membrane characters. in this context, compatibility of graphene nanoparticles with matrices must be enhanced for better miscibility and reinforcing effects. the pore shape, size, and distribution in the matrices have been found to affect the membrane selectivity/permeability features. the most important challenges of graphene-based gas separation membranes include graphene nanosheet aggregation, phase separation, and uncontrolled and undefined fabrication parameters. such undefined conditions may lead to the different pore shapes, sizes, and random distribution in the matrices. the membranes with various pore sizes and shapes may cause major hinderances towards the separation of particular gaseous molecules of characterization and application of nanomaterials 2024, 7(1), 4581. 13 specific types. the random pore distribution in membranes also affects the strength, durability, and life of the membranes. in addition, poor membrane performance may result in restricted cyclic uses. consequently, the uncontrolled membrane features may cause poor barrier effects and selective molecular transportation. hence, perfect membrane design features need to be identified before commercial-scale production of these membranes. investigations on the membrane separation mechanisms may be used to overcome the barrier, molecular selective diffusion, and performance challenges. in addition, advanced and facile fabrication methods need to be designed to form efficient membranes with controlled pore dimensions and essential features. future research to resolve the stated challenging directions can be beneficial for the formation of high-performance gas separation membranes. 5. conclusions in this state-of-the-art review article, the design, physical properties, and gas partition features have been scrutinized for important graphene and nanocompositebased membranes. consequently, graphene has been filled in various polymeric matrices to form the efficient gas separation membranes. these membranes have been studied for the selective separation or permeation of various toxic or desired gas molecules such as o2, n2, co2, ch4, etc. from the gas mixtures. consequently, the membrane performance has been analyzed based on the microstructure, pore size, pore distribution, and specific tests related to the separation or permeation of the gaseous molecules. it has been observed that by varying the nanofiller contents and nanofiller functionalities, as well as polymer type and fabrication methods, the resulting membrane performance has been rehabilitated. in addition, the graphene alignment and dispersion pattern in the polymer matrices resulted in advanced membrane performance with optimum porosity and tortuous pathway formation for the passage of gas molecules. in the future, well-organized graphene-based membranes need to be designed by overcoming the dispersion and processing challenges behind the development of high-performance systems. conflict of interest: the authors declare no conflict of interest. references 1. bellucci s. decontamination of surface water from organic pollutants using graphene membranes. characterization and application of nanomaterials. 2023; 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10.1016/b978-0-323-99311-1.00016-7 characterization and application of nanomaterials (2019) volume 2 issue 1 doi:10.24294/can.v2i1.736 1 design and development of sulfonated tetrafunctional epoxy nanocomposites for advanced engineering applications duraibabu dhanapal1*,alagar muthukaruppan1, ananda kumar srinivasan1 1department of chemistry, anna university, chennai, 600 025, tamil nadu, india. abstract attempts were made in the present study to design and develop skeletally modified ether linked tetraglycidyl epoxy resin (tgbapsb), which is subsequently reinforced with different weight percentages of amine functionalized mullite fiber (f-mf). the f-mf was synthesized by reacting mullite fiber with 3-aminopropyltriethoxysilane (aptes) as coupling agent and the f-mf structure was confirmed by ft-ir. tgbapsb reinforced with f-mf formulation was cured with 4,4’-diamino diphenyl methane (ddm) to obtain nanocomposite. the surface morphology of tgbapsb-f-mf epoxy nanocomposites was investigated by xrd, sem and afm studies. from the study, it follows that these nanocomposite materials offer enhancement in mechanical, thermal, thermo-mechanical, dielectric properties compared to neat (tgbapsb) epoxy matrix. hence we recommend these nanocomposites for a possible use in advanced engineering applications that require both toughness and stiffness. keywords: surface modification; nanocomposites; thermo-mechanical properties; dielectrical properties; phase separation. 1. introduction in modern decades, an increasing research trend in the area of thermosetting polymer like dgeba epoxy resin widely used as an extensive range of advanced high performance applications such as adhesives, coatings, textiles, civil construction, aircraft, automotive and aerospace components owing to phenomenal performance properties, and low cost. generally dgeba epoxy resin is a thermosetting polymer and has been widely used as aerospace, automotive, electronic devices, civil construction, machinery and textiles etc.[1,2] nevertheless, some drawbacks of dgeba epoxy resin, namely brittleness and poor impact resistance to crack propagation, restricts its application for high performance materials.[3,4] in order to overcome these problems, modifiers are needed (such as organic fillers, inorganic fillers, metal oxides, carbon nanomaterial, nanofibers and nanorods etc).[5,6] incorporation of nanofillers into the dgeba epoxy resin caused significant enhancement of mechanical and thermal properties of dgeba epoxy nanocomposites.[7,8] especially silica reinforced epoxy resins have been widely used as an adhesive and encapsulate for electronic industry, for the reason of possessing superior mechanical and electrical properties in addition to the low cost.[9]additionally, alumina (al2o3) reinforced epoxy nanocomposites demonstrated significant improvement in mechanical properties, even with a low percentage of loading.[10-11]moreover, the alumina (al) and silica (si) combined compounds used as a reinforcement agent into the dgeba epoxy resin could possess a greater extent mechanical and physical properties. on the other hand, one of the most promising well-known compounds like mullite (3al2o3–2sio2) contains both alumina and silica ceramic material that possesses attractive properties like high chemical, thermal stability, mechanical strength and low thermal expansion coefficient.[12-14] mullite fibers, which are generally mullite monolithic ceramic materials, exhibit an excellent flexibility at relatively high stress and are commonly used as a reinforcement phase between polymer and oxide ceramic matrix to enhance the composite strength.[15-17] furthermore, the functional groups introduced into the nanofiller, could either react with polymer molecules and good chemical bonding together between nanofiller and the polymer.[18-19]therefore, amine functionalized mullite fiber reinforced epoxy matrix system has a great attention to the development of advanced nanocomposites with adequate features of high performance applications. in the present copyright © 2019 duraibabu dhanapal et al. doi: 10.24294/can.v2i1.736 enpress publisher llc.this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 study amine functionalized mullite fiber (f-mf) was chemically modified by 3-aminopropyltriethoxysilane (aptes) to enhance the properties of the epoxy nanocomposites. in addition, skeletally modified ether linked tetraglycidyl epoxy resin (tgbapsb) was reinforced with different amounts of f-mf and cured with 4, 4’-diamino diphenyl methane (ddm). the amine functionalized nanocomposite materials possess good chemical bonding with dgeba epoxy matrix and f-mf leading to simultaneous enhancement of mechanical, thermal, thermo-mechanical, dielectric and water absorption properties for advanced engineering applications. 2. materials and methods 2.1 materials all chemicals were of reagent grade and were used without further purification except for dimethylformamide (dmf), which was purified by distillation under reduced pressure over calcium hydride. p-chloronitrobenzene, potassium carbonate (k2co3), 10% palladium on activated carbon (pd/c), aluminium isopropoxide, aluminium nitrate nonahydrate, o-xylene, absolute ethanol, hydrazine hydrate (80 wt% water solution), epichlorohydrin (epc), sodium hydroxide, acetone and benzene were obtained from sd fine chemical. the 3-aminopropyltriethoxysilane (aptes), tetraethyl orthosilicate (teos) and di-hydroxy diphenylsulphone were purchased from sigma aldrich, india. 4,4’ -diaminodiphenylmethane (ddm) curing agent, obtained from huntsman (usa), was used as received. 2.2 synthesis of tgbapsb epoxy resin the synthesis of tgbapsb epoxy resin was performed in our laboratory as per the literature reported.[20] the tgbapsb epoxy resin was dissolved in epc and bapsb. the solution was stirred and refluxed for 2h. consequently the addition of 40% naoh solution was added drop wise into the reaction mixture for 1hr after that the reaction mixture was further reflux period of 5h at 50-55°c. the resultant product a pale brown coloured tgbapsb epoxy resin obtained (yield 80%) was percolating and conserved for further use. the reaction sequence is illustrated in figure 1. figure 1; flow chart representation for the preparation of tgbapsb epoxy resin 2.3 synthesis of surface functionalization of mullite mullite fiber was synthesized from aluminium isopropoxide, aluminium nitrate nonahydrate and teos as per the procedure reported in the literature.[21] 4g of mullite fiber and an appropriate amount of 3-aminopropyltriethoxysilane (4.4g) placed into a 100 ml rb flask equipped with a stirrer and a reflux condenser under nitrogen atmosphere, and 50ml of o-xylene solvent were added into the mixture, the reaction mixture was refluxed for 24 h at 150°c. after the reaction completed, the reaction mixture was filtered and washed several times with acetone to remove the unreacted aptes and dried under vacuum for 24 h. the sequence of reactions involved is illustrated in scheme 1. o si (ch2)3 nh2 o om m mullite msio o o h2n 3-aminopropyltriethoxysilane amine functionalized mullite fiber (f-mf) scheme 1. surface functionalization of mullite fiber (f-mf) 2.4 preparation of f-mf reinforced epoxy nanocomposites in order to prepare the epoxy nanocomposites of tgbapsb epoxy resins with f-mf (1, 2, and 3 wt%) is placed in mechanically stirred at 70-80°c for 24 h. subsequently, the stoichiometric amounts of curing agent (ddm) were added 3 to the mixture and then the reaction mixture was poured into preheated teflon coated iron mould (table 1). it was thermally cured firstly at 120 ºc for 2 h and secondly post cured at 180 ºc for 3 h are shown in figure 2 and scheme 2. system tgbapsb f-mf curative a 100 0 ddm b 100 1 ddm c 100 2 ddm d 100 3 ddm table 1. nomenclature of neat and tgbapsb/f-mf epoxy nanocomposites figure 2; schematic diagram of sample preparation tgbapsb o s o n o o n o o o si (ch2)3 nh2 ddm o s o n h2 c c h2nh2 c c h2 o o o o f-mf o o o si (ch2)3 n o o osi(ch2)3n o o osi(ch2)3n o o o si (ch2)3 n o o c h oh h c oh c h h c oh oh m m m m m scheme 2. schematic representation of tgbapsb epoxy/f-mf nanocomposites 3. characterization the ft-ir spectra were recorded on a perkinelmer 781 ftir spectrometer to determine the chemical structure of neat tgbapsb epoxy resin and f-mf/tgbapsb epoxy nanocomposites cured with ddm. a small portion of the cured epoxy resin and nanocomposites was ground to a fine powder, mixed with kbr powder, and pressed into a pellet which is used to obtain the spectrum. thermo gravimetric analysis of neat tgbapsb epoxy matrix and f-mf/tgbapsb epoxy nanocomposites was carried out using tga-thermal analyst netzsch sta 409 pc (ta instruments usa) at a heating rate of 10°c/min from 0°c to 800°c under a continuous flow of n2 atmosphere to determine thermal degradation temperature, percentage weight loss and char yield formation. about 5mg of samples were taken for each analysis. dynamic mechanical behavior of the samples was measured using a dynamic mechanical analysis netzsch 242 at a heating rate of 10°c per minute from 30°c to 300°c. xrd patterns were recorded at room temperature by monitoring the diffraction angle 2θ from 10° to 70° as standard and 0.5° to 10° as low angle on a rich seifert (model 3000) x-ray powder diffractometer. the diffractometer was equipped with a copper target (λ 1.5405 å) radiation using guinier type camera used as focusing geometry and a solid state detector. a curved nickel crystal was used as the monochromator. the step width (scanning speed) was 2θ= 0.04 deg/min. a jeol jsm-6360 scanning electron microscope was used for the sample analysis and the fractured samples were prepared by coating, gold on the surface of the samples and analyzed further. the surface topology of the impact fractured surface was investigated using 4 afm seiko spi3800n, series spa-400 (tokyo, japan). the dielectric constant measurements were carried out with the help of an impedance analyser (solartron impedance/gain phase analyzer 1260) at room temperature (rt) using platinum (pt) electrode at 30°c at a frequency range of 1 mhz. the experiment was repeated for four times at the same conditions. the water absorption measurements of tetraglycidyl epoxy and its nanocomposites were carried out according to astm d570-81, the samples were immersed in water for 24 h at 25°c and the percentage of water absorbed by the specimens was calculated using the following equation (1). % water absorption = (w2-w1) × 100/w1(1) where, w1 is the initial weight of the sample and w2 is the weight of the sample after immersion in water for 24 h at 25°c. 4. results and discussion 4.1 ftir spectra figure 3. shows the ft-ir spectra of amine functionalized mullite fiber (f-mf), tgbapsb epoxy resin and tgbapsb epoxy resin cured with ddm. the ft-ir spectrum of f-mf (figure 3a) shows band at 1565 cm-1 corresponding to the n-h bending (scissoring) of the amine functional group of f-mf, this attributed that the chemical bond are formed between mullite fiber with aptes. the appearance of the band at 2929 cm-1, 1418 cm-1 due to the symmetric methylene stretch (ch2) and 1014 cm-1 to si-ostretching vibrations of the mullite fibers respectively. figure 3(b) shows the band at 912 cm-1 assigned to the presence of oxirane ring. the bands appearing at 2984 cm-1 and 1630 cm-1 correspond to the aromatic rings. the broad peaks at 1499 cm-1 (c–o–c) 820 cm-1 (c–n) and 750 cm-1 (c–s) result of the stretching and bending vibrations of the tgbapsb epoxy matrix. ft-ir spectra of tgbapsb epoxy resin cured with ddm showed the absence of oxirane ring peak at 912 cm-1. the appearance of secondary oh group at 3340 cm-1 confirming the covalent bonding between tgbapsb epoxy resin and ddm curing reaction which is depicted in figure 3(c). 4000 3500 3000 2500 2000 1500 1000 500 % t ra ns m itt an ce wave number (cm-1) (a) (b) (c) 33 40 29 84 16 30 14 99 91 2 82 0 75 0 29 29 15 65 14 18 10 14 figure 3. ft-ir spectra of (a) amine functionalized mullite fiber (f-mf) (b) tgbapsb epoxy resin (c) tgbapsb epoxy resin cured with ddm 5 4.2 mechanical properties the investigations on the mechanical properties were done with tensile strength, flexural strength and impact strength of the neat tgbapsb epoxy matrix and tgbapsb epoxy nanocomposites are reported in table 2. it was found from the data that the incorporation of 1 wt% (system ‘b’) and 2wt% (system ‘c’) of f-mf reinforced nanocomposites leads to the increase of tensile strength, flexural strength and impact strength (figure 4). for instance, the values of tensile strength, flexural strength and impact strength of 2wt% (system ‘c’) are 147.3 mpa, 225.4 mpa and 256.5 j/m2 respectively, when compared to the neat tgbapsb epoxy matrix system ‘a’. this phenomenon could be attributed to the homogeneous deposition of f-mf, having stronger interfacial interaction between amine functionalized mullite fiber nanocomposites, thereby imparted a covalent bonding f-mf with the tgbapsb epoxy matrix as reported by qiang et al.[22] however, the mechanical property values decreased in the case of the high percentage loading f-mf (3wt%) reinforced nanocomposites (system ‘d’) due to filler non-homogeneous in the polymer matrix, which leads to release the stress from the crack tips, thus, enhances the growth of micro voids into the tgbapsb epoxy nanocomposites was found to be decreasing the values of mechanical performance.[23] matrix table 2. data on mechanical properties of neat and tgbapsb/f-mf epoxy nanocomposites tensile strength flexural strength impact strength 0 50 100 150 200 250 a b c d figure 4; mechanical properties of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites 4.3 thermogravimetric analysis the tga thermograms of the neat tgbapsb epoxy matrix and f-mf nanocomposites are presented in table 3 and figure 5. the incorporation of f-mf reinforcement into tgbapsb epoxy resin improvement the thermal stability and char yield increases up to 2wt% when compared to neat tgbapsb epoxy matrix system ‘a’. for example the initial degradation temperature (idt) and char yield of a system ‘a’ was found to be 329°c and 15%, whereas the idt and char yield of the systems ‘b’ and ‘c’ drastically enhanced to 341°c and 347°c, 26% and 33% respectively. this could be attributed to the presence of inorganic moieties like alumina (al) and silica (si) in the systems. the system tgbapsb/%f-mf tensile strength (mpa) flexural strength (mpa) impact strength (j/m) a 100/0 83.5±5 171.1±1 195.8±3 b 100/1 112.4±3 199.5±2 229.5±3 c 100/2 147.3±3 225.4±2 256.5±1 d 100/3 122.5±1 203.5±3 234.3±1 6 improvement of thermal properties of the tgbapsb epoxy nanocomposites is owing to its strongly bonded to the -si-ogroups and better compatibility between f-mf and tgbapsb epoxy.[24] nonetheless, the high percentage loading system ‘d’ (3 wt%) f-mf led to the aggregation of the f-mf in the tgbapsb epoxy, which results were found to be degradation of the thermal properties. a similar observation was made by kumar et al (2017).[25] table 3. data on thermal properties of neat and tgbapsb/f-mf epoxy nanocomposites 100 200 300 400 500 600 700 0 20 40 60 80 100 a b c d w ei gh t ( % ) temperature (c) figure 5; tga of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites 4.4 dynamic mechanical analysis the values of storage modulus increased as the percentage content of f-mf nanoreinforcement is increased up to 2 wt%. despite, the values decreased beyond 3 wt% are shown in table 4. after the incorporation of 1 and 2wt% of f-mf into the tgbapsb epoxy system ‘b’ and ‘c’, the storage modulus value of system ‘c’ significantly increased, when compared to that of other systems namely 'a ' and 'b ' (table 4, figure. 6). the enhancement of the value of storage modulus exhibited by system 'c ' may be due to the presence of crosslinked network between tgbapsb epoxy and f-mf. nevertheless,the raise of storage modulus is probably homogenous distribution within the tgbapsb epoxy which offers the chemical interaction between the inorganic and organic material of f-mf of the resultant tgbapsb epoxy nanocomposites respectively.[26] however, at higher concentration of f-mf 3wt% (system ‘d’), the storage modulus value decreased. this may be due to non-uniformity in the dispersion of the higher loading of f-mf nanoparticles, it was found that the higher loading of 3wt% of f-mf, reduced the storage modulus value (system ‘d’) and this was complimented by sem observation and afm studies (figure 9) as a result of which, there exists a stress concentration regions, which increases the segmental mobility and concomitantly decreased the mechanical properties.[27] matrix system tgbapsb/%f-mf initial decomposition temperature (℃) char yield (%) a 100/0 329 15 b 100/1 341 26 c 100/2 347 33 d 100/3 343 31 7 table 4. dma analysis of neat and tgbapsb/f-mf epoxy nanocomposites 50 100 150 200 0 1x1010 2x1010 3x1010 4x1010 5x1010 6x1010 a b c d temperature (c) e' (p a) figure 6; storage modulus of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites 4.5 damping parameter (tanδ) the values of glass transition temperature (tg) of neat tgbapsb epoxy matrix, f-mf reinforced tgbapsb epoxy nanocomposites obtained from the damping parameter (tan δ) are presented in table 4 and figure 7. the tg values of the neat tgbapsb epoxy matrix were found at 146°c where as the incorporation of f-mf into the tgbapsb epoxy systems ‘b’, ‘c’ and ‘d’ slight increase in the tg values up to 188°c. for example, the systems ‘a’ and ‘b’ show the tg values 146°c and 178°c than that of a system ‘a’ this should be attributed that the covalent linkage between tgbapsb epoxy and f-mf that means of uniformly dispersed across the entire surface of the tgbapsb epoxy matrix, as a result are restricting the segmental mobility of the chain segment.[28] the substantially decreased tg value of the system ‘d’ (3 wt%) of f-mf this could be attributed that the aggregation of f-mf in the tgbapsb epoxy, which was indicated by the deteriorated crosslink of tgbapsb epoxy, leading to reduced cross-linking density and decreased tg. a similar observation was made by colorado et al (2013).[29] 50 100 150 200 a b c d ta n  temperature (c) figure 7; tan δ of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb matrix system tgbapsb/%f-mf storage modulus (gpa) glass transition temperature, tg (℃) a 100/0 3.1 146 b 100/1 3.3 178 c 100/2 5.4 188 d 100/3 2.4 173 8 (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites 4.6 xrd studies x-ray diffraction spectra were used to analyze the morphology of the neat tgbapsb epoxy matrix and different weight percentage of f-mf reinforced tgbapsb epoxy nanocomposites. the results are shown in figure 8. the xrd pattern of tgbapsb epoxy nanocomposites was found to be exhibiting a peak corresponding to mixed intercalated and exfoliated morphology. however, varying weight percentage of loading f-mf in to the tgbaspb epoxy, the 2θ value shifts towards the lower angle this can be attributed that the mixed intercalated and exfoliated of polymer chain linkages, hence a decrease in the peak intensity from 18.6° to 13.5° was observed (figure8).[30] 10 20 30 40 50 60 70 13.5 d c b in te ns ity (a .u ) 2 (degrees) a 18.6 14.6 figure 8; xrd spectra of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites 4.7 sem and afm analysis in order to analyze the morphology of the f-mf/tgbapsb epoxy nanocomposites and neat tgbapsb epoxy matrix, the sem and afm images are represented in figure 9.figure 9 (a) shows the smoothsurface of a neat tgbapsb epoxy matrix when compared than that of f-mf/tgbapsb epoxy nanocomposites. however, upon loading of varying weight percentage of f-mf, the surface morphology changes for the systems ‘b’, ‘c’ and ‘d’. it can be assumed that the surface roughness increases with increasing f-mf content. for illustration, the surface roughness of 2 wt% of the system ‘c’ (figure 9b) shows good interfacial adhesion between f-mf and tgbapsb epoxy. this result correlates with the improvement of storage modulus, mechanical properties and thermal properties owing to bonding together between the polymer matrix and organic and inorganic (f-mf) reinforcement respectively.[26, 31] furthermore, the better dispersion may be due to strong interactions between the f-mf and tgbapsb epoxy matrix. it was found that highly intercalated and partially exfoliated structure was assumed in xrd studies (figure 8). on the other hand, the higher content of 3 wt% (system ‘d’) f-mf tgbapsb epoxy nanocomposites were found to be heterogeneous morphology along with f-mf and tgbapsb epoxy (figure 9c). this indicated that the poor bonding between f-mf and tgbapsb epoxy, leads to worse mechanical, thermal properties and storage modulus.[32-33] 9 figure 9; sem and afm photographs of systems (a) neat tgbapsb epoxy matrix (b) 2 wt% f-mf/tgbapsb and (c) 3 wt% f-mf/tgbapsb epoxy nanocomposites 4.8 dielectric behavior and water absorption properties the values of dielectric constant of the neat tgbapsb epoxy matrix and f-mf/tgbapsb epoxy nanocomposites are represented in table 5 and figure 10. it was noticed that the loading of f-mf into the tgbapsb epoxy systems 'b ' (3.55) 'c ' (3.50) and 'd ' (3.45) displays the low dielectric constant values, when compared to neat tgbapsb epoxy matrix system 'a' (4.10). this could be attributed to the increase in free volume and reducing dipole dipole interaction between mullite fiber and tgbapsb epoxy respectively.[34]figure 11. shows the graphical representation of water absorption of neat tgbapsb epoxy matrix and f-mf loading in tgbapsb epoxy nanocomposites. it’s indicated that upon the increasing in f-mf content, the water absorption values decrease. this may be due to the low polar content and absorbed less water uptake than that of neat tgbapsb epoxy matrix.[35] the data is presented in table 5. table 5. dielectric and water absorption properties of neat and tgbapsb/f-mf epoxy matrix system tgbapsb/%f-mf dielectric constants (mhz) water absorption a 100/0 4.10 0.065 b 100/1 3.55 0.060 c 100/2 3.50 0.058 d 100/3 3.45 0.055 10 dielectric constants (mhz) 0 1 2 3 4 dcb a figure 10; dielectric constants of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites water absorption 0.00 0.02 0.04 0.06 d cb a figure 11; water absorption of (a) neat tgbapsb epoxy matrix (b) 1 wt% f-mf/tgbapsb (c) 2 wt% f-mf/tgbapsb and (d) 3 wt% f-mf/tgbapsb epoxy nanocomposites 5. conclusion in the present study, the surface modified amine functional groups introduced into mullite fibers (f-mf) prepared by using aptes as a coupling agent. f-mf reinforced with varying weight percentage (1 wt%, 2 wt% and 3 wt%) of the tgbapsb epoxy nanocomposites were developed and characterized. the incorporation of f-mf leads to the enhancement of mechanical, thermal, thermo-mechanical, dielectric and water absorption properties of the resulting tgbapsb epoxy nanocomposites. the molecular level dispersion of f-mf in the tgbapsb epoxy was further confirmed by xrd, sem and afm, results which revealed uniform dispersion of f-mf in the tgbapsb epoxy up to 2wt% nanofiller content. the optimum concentration produced significant improvements in mechanical, thermal, thermo-mechanical of the tgbapsb epoxy nanocomposites, these materials can be used as advanced nanocomposites in the field of 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ricardo albis arrieta* facultad de ingenierí, universidad del atlántico, carrera 30 número 8-49, puerto colombia, atlántico, colombia. e-mail: albertoalbis@uniatlantico.edu.co abstract this work shows the results of the biosynthesis of silver nanoparticles using the microalga chlorella sp, using growth media with different concentrations of glycerol, between 5%–20%, and different light and temperature conditions. the synthesis of nanoparticles was studied using supernatants and pellets from autotrophic, heterotrophic and mixotrophic cultures of the microalga. the presence of nanoparticles was verified by ultraviolet-visible spectroscopy and the samples showing the highest concentration of nanoparticles were characterized by scanning electron microscopy. the mixotrophic growth conditions favored the excretion of exopolymers that enhanced the reduction of silver and thus the formation of nanoparticles. the nanoparticles obtained presented predominantly ellipsoidal shape with dimensions of 108 nm × 156 nm and 87 nm × 123 nm for the reductions carried out with the supernatants of the mixotrophic cultures with 5% and 10% glycerol, respectively. keywords: green chemistry; silver nanoparticles; biosynthesis; microalgae article info received: 4 february 2022 accepted: 20 april 2022 available online: 26 april 2022 copyright copyright © 2022 fredy andrés gonzalez ortiz, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction the emergence of microorganisms resistant to common disinfectants has prompted an extensive search for new products that are effective in killing or inhibiting bacterial growth, and at the same time are harmless to humans. silver nanoparticles (np ag) are a possible nanotechnology response to this challenge, as their high surface area per unit volume increases the already known antibacterial properties of silver[1]. np ag can be synthesized by various methods, such as chemical reduction reaction, photochemical reaction, thermal decomposition, radiation-assisted methods, electrothermal processes, sonochemical and microwave-assisted synthesis[2]. these methods produce silver nanoparticles efficiently, however, often these methods involve the use of toxic and hazardous chemicals, which present several harmful effects to the environment and human health[3], also the final product requires several stages of purification, in which reducing agents are used that are often adsorbed on the surface of the nanoparticles, it is also necessary to use stabilizers to avoid agglomeration of silver nanoparticles[4]. some plant extracts can act as reducing leveling agents in the synthesis of silver nanoparticles. the reduction of ag+ ions by combinations of biomolecules found in these extracts such as enzymes/proteins, amino acids, polysaccharides and vitamins[5,6], are environmentally benign, although chemically complex. an extensive body of literature reports the successful synthesis of np ag using compounds from biorganic living things; for example, the extract of unicellular green algae chlorella vulgaris was used to synthesize crystalline ag nanosheets at 101 room temperature[7]. the proteins in the extract provide dual functions of ag+ reduction and a morphology control in np ag synthesis. where carboxyl groups on aspartic and glutamine residues and hydroxyl groups on tyrosine residues of proteins emerged as architects of ag+ ion reduction[7], which is confirmed by ag reduction by the single bifunctional tripeptide asp-asp-tyr-ome. this synthesis process generated small ag nanoplates with low polydispersity with good yield (55%)[8]. various microorganisms have been used to grow silver nanoparticles intracellularly or extracellularly[9,13]. for example, ag+ containing nanocrystals of different compositions were synthesized by the bacterium pseudomonas stutzeri (ag259)[9]. in the fungus fusarium oxysporum, the reduction of ag+ ions is attributed to an enzymatic process, involving nadh reductase which is due to nadh reductase dependence[12]. the white-rot fungus, phanerochaete chrysosporium, also reduced ag+ ion to form nanoparticles; suggesting that a protein from its metabolism caused the reduction. a protein was suggested to cause the reduction[13]; noting the possible involvement of proteins in np ag synthesis in filamentous cyanobacteria, plectonema boryanum (utex 485)[14]. on the other hand, ag+ reduction by culture supernatants of klebsiella pneumoniae, escherichia coli (e. coli), enterobacter cloacae and enterobaceteriacae produced silver nanoparticle formations[15]. in this work, one of the methodologies to synthesize silver nanoparticles, considered as part of the green synthesis group, was used, since the microalga chlorella sp. was used as an agent for the formation of exopolymers[16,17], which promotes the formation of these nanoparticles. these exopolymers are products of the metabolism of chlorella sp. when using glycerin as a substrate or when cultured under stress conditions, and being composed of monomeric units of sugars (with a large amount of hydroxyl groups)[18], it has the ability to easily attract silver ions from the silver nitrate solution, thus forming np ag. 2. methodology 2.1 stock culture of the microalgae chlorella sp. the strain of chlorella sp. was tested by the microalgae biotechnology laboratory of the universidad del atlántico. the culture started with 500 ml of a seed culture of the microalgae, which was diluted with sterile water to a volume of 2,000 ml, adding 4.7 ml of a 2.14 m solution in total nitrogen of nutrifoliar® previously sterilized, to obtain a final nitrogen concentration of 5 mm. the cultures were grown in duplicate and provided with aeration, feeding and illumination (2,710 lm, philips tl 65 w 25 fluorescent tubes, white light) and incubated for a period of 20 days, with light/dark cycles of 12 hours, respectively, using artificial light and room temperature of 24 °c. cultures were gauged to 2,000 ml every 15 days using sterile water and 5.8 ml of nutrifoliar® at 2.14 m total nitrogen. 2.2 biosynthesis of silver nanoparticles for the study of the synthesis of reducing agents produced by microalgae, under different culture conditions and their effect on np ag production, using a factorial design with two independent variables: illumination and temperature conditions, with three levels and glycerol concentration, as an organic carbon source, with 5 levels (0, 5, 10, 10, 15 and 20%) (table 1). table 1. factors and experimental levels experimental factor levels lighting and temperature conditions ambient temperature with continuous illumination ambient temperature in continuous darkness −18 °c in continuous darkness glycerol concentration (% vol/vol) 0 5 10 15 20 the cultures were incubated for three days and then the cells were separated by centrifugation (10 min at 8,000 rpm). the synthesis of np ag was performed using reducing agent, the supernatant and precipitate solutions separately, in order to determine whether the microalgae actively participate in the synthesis of np ag or only the excreted metabolic products are responsible for the synthesis. the synthesis procedure was as follows: 2 ml of precipitate or supernatant, for each of the exper 102 imental combinations, were transferred to 10 ml culture tubes and 2 ml of silver nitrate (agno3 j.t. baker) with a concentration of 2 mm were added, and then subjected to vortex mixing for 2 min. the homogenized medium was again incubated under continuous artificial light for 3 days at room temperature. the experimental response variable was the uv-visible spectrum of the samples, which allows the identification of the possible formation of silver nanoparticles. all assays were performed in duplicate. the uv-vis spectra were obtained in a genesys 60 s spectrophotometer (thermofisher) using quartz cells with a step length of 1 cm and a spectrometric range from 290 to 900 nm. 2.3 scanning electron microscopy (sem) the equipment used for this measurement is a sem model vega3 tescan. before the measurement, it was necessary to remove the organic matter, through successive washes of the samples using a volatile solution of 95% ethanol, as follows: the samples were centrifuged for 10 min at 8,000 rpm, followed by discarding the supernatant, adding 5 ml of 95% ethanol and resuspending the np ag in ultrasound for 10 min. subsequently, for the second step, the np ag were centrifuged at 10,000 rpm, for 10 min. the supernatant was discarded and resuspended with 5 ml of 2-propanol in ultrasound for 10 min. this procedure was repeated 12 more times to ensure the removal of organic matter. the images obtained were processed with image software to determine the shapes and sizes of the np ag. 3. results and discussion 3.1 uv-vis spectra of blank solutions the uv-vis spectra obtained from the aqueous solutions of silver nitrate and different concentrations of glycerol (5%, 10%, 15% and 20%) show flat absorption profiles in most of the photometric range analyzed, with slight absorption of light at wavelengths below 400 nm (figure 1). this behavior is characteristic of non-reduced silver solutions[19]. these solutions were used as targets in the photometric measurements of the subsequent tests performed. figure 1. uv-vis spectra of silver nitrate solutions with different concentrations of glycerol. 3.2 effect of culture conditions on the production of silver nanoparticles figure 2 shows the uv-vis absorption spectra of the silver nitrate and glycerol solutions subjected to each of the experimental treatments, using the cell-excretion metabolite-rich medium (supernatant, figures 2a, 2b and 2c) and some representative treatments using chlorella sp. cells (precipitate, figure 2d). it is observed that most of the treatments in which silver reduction was performed using the supernatant of chlorella sp. cultures grown at room temperature show the characteristic absorption peak of the plasmon effect in the wavelength range comprised between 400 nm and 500 nm (figures 2a and 2b), as well as the characteristic shift to a reddish-brown color[20,21]. in contrast, samples that underwent reduction with the culture supernatant obtained in the absence of light and low temperatures, as well as those in which precipitates were used, show no absorption peak between 400 nm and 500 nm. this suggests that the experimental treatments in which the reduction was done using as reducing agent the supernatant of the cultures of the microalgae grown at room temperature and under light or dark conditions there was formation of silver nanoparticles, while in the treatments in which supernatants of cultures obtained at low temperatures or the precipitate of any of the fermentations (cells) were used there was no reduction of this element. in the case of the reduction carried out with the supernatants of the culture performed in the presence of light at room temperature, it is observed that the presence of glycerol in the culture medium 103 stresses the microalgae (probably osmotic stress) in such a way that it produces excretion metabolites that favor the reduction in the presence of light, at least up to glycerol concentrations of 10%. above this glycerol concentration, a decrease in the intensity of the absorption peak corresponding to the plasmon effect, and thus of the np ag concentration, is observed, probably because at high glycerol concentrations, the microalga grows at a slower rate and is likely to produce fewer reducing metabolites[22,25]. this decrease in the intensity of the absorption peak associated with the plasmon effect at high concentrations also indicates that glycerol is not the reducing agent for silver, but rather the extracellular metabolites produced during microalgal growth. when comparing silver reduction with supernatants from microalgae cultures grown in the presence and absence of light at room temperature, a lower peak intensity (less than 50% in cases where there is evidence of np ag formation) associated with the plasmon effect is observed in the reductions carried out using supernatants from cultures grown in the dark, when compared to the curves corresponding to the same glycerol concentrations and cultures grown in the presence of light. this points to the fact that more reducing metabolites are formed during the microalgae growth process under mixotrophic conditions than under autotrophic (0% glycerol concentration) or heterotro phic (in the absence of light) conditions[23]. on the other hand, the results shown in figure 2c indicate that in the absence of growth the silver-reducing metabolites are not produced. the results point out that the presence of glycerol during growth is determinant for the production of reducing metabolites and the formation of np ag and even these metabolites can be produced during strictly heterotrophic growth using glycerol as carbon source. however, the production process is favored under mixotrophic conditions, probably because higher growth rates are present under these conditions. figure 2. uv-vis spectra of silver nitrate solutions with different concentrations of glycerol. (a) supernatants of cultures grown in the presence of light at room temperature; (b) supernatants of cultures grown in the absence of light at room temperature; (c) supernatants of cultures grown in the absence of light at -18 °c; (d) precipitates obtained with 15% glycerol cultures and different culture conditions. the results shown in figures 2a and 2b suggest that at concentrations of 20% glycerol, the microorganism also produces extracellular metabolites, which can reduce the nanoparticles that produce silver. however, the effect is less marked than for the 5% and 10% glycerol concentrations, particularly in assays with growth under mixotrophic conditions: for the 20% glycerol concentration, the peak of the surface plasmon effect has 0.4 absorbance units in the spectrum in the absence of light and 0.65 in the presence of light, for a difference of 0.25 absorbance units, whereas in the case of the spectra of the supernatants at 5% and 10% glycerol concentrations, these differences amount to 2.5 and 1.2 absorbance units, respectively. it has been reported that the mixotrophic growth of chlorella sp. generates greater production of exopolymers than its growth under heterotrophic and autotrophic conditions[17]. these natural polymers are made up of both reducing and non-reducing sugar mono 104 mers[16,17]. sugars have been reported as reducing agents of silver and np ag production[26,29], so we suggest that it is the exopolymers produced by chlorella sp. and found in the supernatant that are responsible for the production of np ag under the conditions studied in this work. the use of supernatants from bacterial[15,30,31], fungal[32,33], and microalgae cultures for the production of np ag has been reported. 3.3 characterization of silver nanoparticles the assays that showed peaks of higher intensity in the wavelength range between 400 nm and 500 nm, correspond to the reductions carried out with the supernatants of the cultures performed at room temperature and in the presence of light and initial glycerol concentrations of 5% and 10%. the nanoparticles obtained with these assays were characterized by scanning electron microscopy, as shown in figures 3 and 4. in the case of the np ag obtained with the culture supernatant at room temperature, in the presence of light and 5% glycerol, they showed a predominantly ellipsoidal shape with typical dimensions of 108 nm × 156 nm and a standard deviation of 27 nm for both dimensions (figure 3). on the other hand, np ag reduced with the culture supernatant carried out at room temperature, illumination and 10% glycerol showed ellipsoidal and spherical shapes, with average dimensions of 87 nm × 123 nm ± 15 nm × 27 nm. in both cases, the np ag were found to be aggregated on organic matter, despite the extensive washes performed on the samples, possibly the same exopolymers aiding in their reduction. in a similar study, but without overexpression of exopolymers[33], due to the presence of glycerol, predominantly spherical and smaller silver nanoparticles were obtained, suggesting that the use of glycerol may serve as an equalizing factor for the shapes and sizes of the nanoparticles produced. 4. conclusions silver nanoparticles were successfully synthesized using the metabolites excreted during the mixotrophic culture of chlorella sp. the use of glycerol as a source of organic carbon in the mixotrophic culture up to concentrations of 10% in figure 3. sem image of the silver nanoparticles obtained from the supernatant of the chlorella sp. culture at room temperature and 5% glycerol. figure 4. sem image of the silver nanoparticles obtained with the supernatant of the chlorella sp. culture at room temperature and 10% glycerol. creases the height of the peak associated with the plasmon effect, which suggests an increase also in the concentration of silver nanoparticles when compared to the results obtained with the reduction using the supernatant of the chlorella sp. culture obtained under autotrophic conditions. the culture conditions that promoted to a greater extent the production of reducing metabolites were the culture at room temperature and under mixotrophic conditions with initial glycerol concentration of 5% and 105 10%. the nanoparticles thus obtained presented predominantly ellipsoidal shape with dimensions of 108 nm × 156 nm, in the case of the np ag obtained with the supernatant of the culture at room temperature, in the presence of light and 5% glycerol; while the np ag reduced with the supernatant of the culture carried out at room temperature, illumination and 10% glycerol showed average dimensions of 87 nm × 123 nm. conflict of interest the authors declare that they have no conflict of interest. references 1. deshmukh sp, patil sm, mullani sb, et al. silver nanoparticles as an effective disinfectant: a review. materials science and engineering: c 2019; 97: 954–965. 2. shinde nm, lokhande ac, lokhande cd. a green synthesis method for large area 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supernatant of raphanus sativus. journal of genetic engineering and biotechnology 2017; 15(1): 31–39. microsoft word can-4946 characterization and application of nanomaterials 2024, 7(2), 4946. https://doi.org/10.24294/can.v7i2.4946 1 review modernizations of graphene nanocomposites using synthesis strategies— state-of-the-art ayesha kausar1,2,*, ishaq ahmad1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, china 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract: graphene has been ranked among one of the most remarkable nanostructures in the carbon world. graphene modification and nanocomposite formation have been used to expand the practical potential of graphene nanostructure. the overview is an effort to highlight the indispensable synthesis strategies towards the formation of graphene nanocomposites. consequently, graphene has been combined with useful matrices (thermoplastic, conducting, or others) to attain the desired end material. common fabrication approaches like the in-situ method, solution processing, and melt extrusion have been widely involved to form the graphene nanocomposites. moreover, advanced, sophisticated methods such as threeor fourdimensional printing, electrospinning, and others have been used to synthesize the graphene nanocomposites. the focus of all synthesis strategies has remained on the standardized graphene dispersion, physical properties, and applications. however, continuous future efforts are required to resolve the challenges in synthesis strategies and optimization of the parameters behind each technique. as the graphene nanocomposite design and properties directly depend upon the fabrication techniques used, there is an obvious need for the development of advanced methods having better control over process parameters. here, the main challenging factors may involve the precise parameter control of the advanced techniques used for graphene nanocomposite manufacturing. hence, there is not only a need for current and future research to resolve the field challenges related to material fabrication, but also reporting compiled review articles can be useful for interested field researchers towards challenge solving and future developments in graphene manufacturing. keywords: graphene; nanocomposite; synthesis; technique; in situ; melt extrusion 1. introduction due to the technical utilization of graphene nanostructures, considerable literature has been reported on the structure and synthesis methods [1]. particularly, matrix-nanofiller compatibility has been found important to enhance the optical, electronic, thermal, mechanical, and other important properties of the graphene nanocomposites [2,3]. consequently, the miscibility effects in the nanocomposite nanostructure resulted in synergistic property improvements in the high-tech nanomaterial [4]. the interfacial interactions in the matrix-nanofiller system greatly depend on the synthesis strategies used [5]. in this context, choice of an appropriate synthesis method may lead to advanced nanocomposite with superior physical features [6]. traditional methods used to form the polymer/graphene nanocomposites include the in situ, solution, and melt methods [7]. in addition, various efficient advanced processes have been used to form the graphene nanocomposites, like printing, spinning citation kausar a, ahmad i. modernizations of graphene nanocomposites using synthesis strategies—state-of-the-art. characterization and application of nanomaterials. 2024; 7(2): 4946. https://doi.org/10.24294/can.v7i2.4946 article info received: 1 march 2024 accepted: 6 may 2024 available online: 1 july 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(2), 4946. 2 lithography, and several others [8,9]. consequently, thermoplasts, thermosets, and conjugated matrices have been filled with graphene nanoparticles to attain superior properties and applications [10–12]. the resulting graphene nanocomposites have enhanced physical properties due to suitable processing techniques applied to gain improved interfacial aspects of these nanomaterials [13]. hence, noteworthy chemical and physical properties of graphene have been widely inspected by the researchers over the past decades. graphene has been used in numerous potential fields due to its high surface area and excellent electrical, mechanical, thermal, and other structural and physical characteristics. consequently, graphene has been found applicable for energy devices, electronics, sensors, nanocomposites, biomedical devices, drug delivery, and tissue engineering. to enhance the practical use of graphene nanocomposite in technical fields, it has been found important to fabricate the graphene-based materials by opting for appropriate synthesis strategies. advanced fabrication techniques have well-controlled parameters to attain specific properties of graphene nanocomposites for desired end applications. this review focuses on the designs and synthesis strategies for the highperformance graphene nanocomposites. according to analysis, this article is novel to present manufacturing approaches of novel graphene-derived nanocomposites. for graphene nanocomposites, various traditional and modified methods have been used. developments in the synthesis techniques of graphene nanocomposites can enhance the technical potential of these nanomaterials. consequently, the designing, features, and appropriate processes for the graphene nanocomposites have been explained here. literature research reports so far have been observed on the fabrication of graphenebased nanomaterials using appropriate synthesis strategies. however, no compiled review article is seen on technical fabrication techniques and comprehensive debates towards structural developments using modified methods and controlled parameters. the aim or objective of this review is to develop a comprehensive article on the most frequently used methods for graphene nanomaterial synthesis. accordingly, the resulting graphene nanocomposites have been discussed under numerous categories of solution, melt, and other fabrication techniques in this article. then, the design, characteristics, and applications of the nanocomposites have been explained with respect to the fabrication methods used. thus, such a specific overview on graphene nanocomposite fabrication has not been seen in literature before, with well-explained recent literature and an outline. despite the advancements so far, devoted future research efforts are still required on the fabrication of high-performance nanocomposite to overcome the related design and parameter control challenges. 2. graphene graphene is a two-dimensional single nanosheet of sp2 hybridized carbons [14]. detection of graphene is linked back to 2004 [15]. graphene has been formed using many technical approaches, like exfoliation approaches, laser methods, chemical vapor deposition, and chemical synthesis approaches [16]. graphene has been explored for a range of structural and physical features [17]. graphene has countless enhanced features, including a very high young’s modulus of 1 tpa, electron mobilization of 3000–5000 w/mk, and thermal conductivity of around 200,000 characterization and application of nanomaterials 2024, 7(2), 4946. 3 cm2v−1s−1 [18]. essential properties of graphene have been found to be dependent on the graphene nanostructure [19]. owing to van der waals forces, the nanosheet displays wrinkling effects [20]. to augment the structural features of graphene, the nanosheet has been functionalized to introduce oxygen-bearing groups on the surface [21]. such a surface functional graphene nanosheet with hydroxyl, carbonyl, epoxide, carboxylic acid, etc. groups has been often termed graphene oxide. graphene and some linked nanostructures are shown in figure 1. graphene and derivative nanostructures own fine electronic, mechanical, thermal, and chemical characters [22]. consequently, applications of graphene have been observed towards electronics as well as energy devices and countless other technological sectors [23,24]. figure 1. graphite to graphene and graphene oxide and interconversions. 3. in situ technique towards graphene nanocomposites one of the simple and efficient methods for the formation of graphene nanocomposites is the in situ polymerization, or in situ method [25]. this synthesis strategy has been found effective for better graphene dispersion [26]. fine nanoparticle scattering in turn generated better interactions in matrix-nanofiller phases [27]. the main benefits of the in situ synthesis strategy include the environmental friendliness, use of non-toxic solvents, room-temperature processing, and one-step processes involved to form the graphene nanocomposites [28]. subsequently, countless graphene nanocomposite designs have been reported using the in situ synthesis strategy [29]. the in situ technique is a facile, low-cost, and environmentally benign method to physically or covalently functionalize graphene nanosheets. in this method, monomers are in situ polymerized in the presence of graphene or graphene oxide to form the nanocomposites. in situ polymerization has been used as a common method for the polymerization of ε-caprolactam monomer to form the polyamide 6 backbone [30]. adding 1–2 vol.% graphene contents along with ε-caprolactam monomer during in situ polymerization resulted in a reasonable electrical conductivity of ∼0.028 sm−1. in addition, the resulting in situ polymerized polyamide 6/graphene nanocomposites have revealed the superior thermal conductivity of around 0.27 wm−1k−1 [31,32]. in characterization and application of nanomaterials 2024, 7(2), 4946. 4 situ synthesis strategy has also led to enhanced mechanical properties of the polyamide 6/graphene nanocomposites [33]. elevated tensile strength and young’s modulus were found with a 0.1 wt.% graphene nanofiller addition. the improved properties were accredited to the mutual interactions between the matrix and nanofillers leading to compatibility effects. xu et al. [33] synthesized the polyamide 6 and graphene-derived nanocomposites using the in situ polymerization method. the caprolactam monomer was in situ polymerized by the ring-opening polymerization reaction [34]. the reaction was carried out in the presence of graphene oxide nanoparticles to follow the in situ process (figure 2). this method involved the use of 6 aminocaproic acid for an in situ process. this technique caused fine dispersion of monomers as well as graphene nanoparticles in solvent medium, followed by the in situ polymerization to form the polyamide 6/graphene nanocomposite. figure 3 displays the stress strain curves of unfilled polyamide 6 as well as 0.01 and 0.1 wt.% nano-additive reinforced graphene nanocomposites. the 0.01 and 0.1 wt.% graphene-loaded nanocomposite had tensile strengths of 84 and 123 mpa, respectively, relative to the neat matrix (56 mpa). hereafter, the mechanical properties of the nanocomposites were found to be more than 50% higher than the unfilled matrix. hence, this method has been suggested to minimize the nanoparticle dispersion responsible for improved features of the nanomaterials. figure 2. in situ synthesis strategy of graphene nanocomposite by in situ ring opening polymerization of caprolactam occurring in the presence of graphene oxide [33]. reproduced with permission from acs. figure 3. stress strain curves of neat polyamide 6 and nano-graphene (ng) nanocomposites with 0.01 and 0.1 wt.% graphene additions [33]. reproduced with permission from acs. characterization and application of nanomaterials 2024, 7(2), 4946. 5 polystyrene, another commodity thermoplastic, has also been polymerized by in situ technique [35,36]. in the presence of styrene monomer and graphene dispersion, the in situ polymerization method is applied using surfactants [37,38]. styrene monomer is absorbed on graphene surface and then polymerized, leading to fine dispersion of nanoparticles and compatibility with the matrix [39,40]. in this way, in situ-produced nanocomposite had fine interactions leading to high electron conduction, heat stabilization, glass transition, and other improved properties [41,42]. poly(methyl methacrylate) and graphene-derived nanocomposites have also been formed using the in situ method and polymerizing the methyl methacrylate monomers [43,44]. physical as well as covalent bindings have been observed between the poly(methyl methacrylate) and graphene nanoparticles [45]. reports on waterborne polyurethane and graphene-based in situ-formed nanomaterials have also been found in the literature [46,47]. here again, interfacial interactions between matrix and nanofiller led to enhanced performance, thus depicting the efficiency of the in situ technique [48]. 4. solution strategies for graphene nanocomposites another common synthesis strategy to form graphene nanocomposites is solution casting, solution synthesis, or solvent-based processing approaches [49,50]. the solvent method is facile and low-cost for the formation of graphene nanocomposites [51]. in this technique, polymers are dissolved in a suitable solvent, and graphene nanosheets are also dispersed in an appropriate solvent [52]. both the dispersions are mixed and stirred to form a homogeneous nanocomposite mixture (figure 4). the nanocomposite formation occurs through the solvent evaporation step. numerous thermoplastic polymers have been successfully formed by solution technique [53,54]. for example, polystyrene and graphene-based nanocomposites have been prepared using solution processing [55]. n-methyl-2-pyrrolidinone was used as a solvent to dissolve polystyrene and disperse graphene nanoparticles. the addition of 10 wt.% nanofiller enhanced the electrical conductivity of the polystyrene matrix to 1.5 × 10−7 sm−1 [56]. in this concern, the microstructure and matrix-nanofiller interactions in solution-formed nanomaterials have been investigated [57]. figure 4. a simple route of solution method. characterization and application of nanomaterials 2024, 7(2), 4946. 6 figure 5. (a) electrical conductivity versus filler content for neat polystyrene (ps) and its nanocomposites; (b) double-logarithmic plot of electrical conductivity versus ϕϕc, where ϕ is the filler volume fraction and ϕc is the percolation threshold; and (c) transmission electron microscopy image of ps:pla (6:4) composite with ∼0.46 vol.% (∼1.0 wt.%) graphene additives. the selective localization of graphene in the polystyrene region is evident from the image [58]. ps/cnt = polystyrene/carbon nanotube; ps = polystyrene; pla = poly (lactic acid); ps/pla = polystyrene/poly (lactic acid). reproduced with permission from acs. characterization and application of nanomaterials 2024, 7(2), 4946. 7 qi et al. [58] synthesized polystyrene/graphene, polystyrene/graphene/poly (lactic acid), and polystyrene/carbon nanotube nanocomposites using solution strategy. figure 5 demonstrates an increase in the electrical conductivity of the polystyrene/graphene nanocomposites with the addition of 0.1 to 0.69 vol.% nanofiller. high electrical conductivity of 3.49 sm−1 was observed with 1.1 vol.% graphene contents. nanoparticle dispersion formed a conducting network in the matrix to improve the electrical conductivity values at the percolation threshold. furthermore, double-logarithmic plots of the polystyrene/graphene (0.33 vol.%) and polystyrene/carbon nanotube (0.50 vol.%) nanocomposites depicted values at 3.80 and 2.58, respectively. transmission electron microscopy image of polystyrene/poly(lactic acid) blend showed two-phase morphology. graphene nanoparticles can be seen dispersed in the polystyrene matrix. poly (methyl methacrylate) and graphene-based nanocomposites have been reported using the solution technique [59]. these nanomaterials have been studied for morphology, electrical conductivity, and mechanical characters [60]. the poly(methyl methacrylate) filled with 2.0 wt.% graphene contents had a high electrical conductivity of 0.04 sm−1. enhancement in electrical conductivity was attributed to the formation of interlinked graphene networks in the matrix [61]. polyethylene and graphene based nanocomposites were also formed using the solution method [62,63]. similarly, poly(vinyl alcohol) and graphene-based nanomaterials have been developed using the solvent method [64]. inclusion of 6.5 vol.% graphene to the matrix led to a high conductivity of 0.06 scm−1. in addition, the young’s modulus of poly(vinyl alcohol) was enhanced by 58% [65]. consequently, the low-cost, simple, and ecofriendly solution technique has been applied to a variety of thermoplastics and graphene nanofillers. the resulting high-performance nanocomposites have superior dispersion, electrical and thermal conductivity, glass transition temperature, thermal stability, and mechanical strength performances [66,67]. 5. melt strategy for graphene nanocomposites figure 6. schematic of melt strategy. subsequently, numerous thermoplastic matrices have been melt processed with characterization and application of nanomaterials 2024, 7(2), 4946. 8 graphene nanoparticles [75]. polystyrene and graphene-based nanocomposites have been developed using melt blending [76,77]. these nanomaterials have revealed fine dispersion and electron conduction features. shen and colleagues [78] industrialized the polystyrene and graphene derivative nanocomposites through melt blending. figure 7 shows a schematic for the development of π-π stacking interactions in melt blending of polystyrene/graphene nanomaterials. due to high shear forces, polymer chains are inserted between the graphene nanosheets. figure 8 reveals the thermogravimetric analysis of the polystyrene/functional graphene nanocomposites. inclusion of 5 to 60 wt.% nanofiller considerably boosted the thermal stability of the polystyrene matrix. figure 7. schematic for the formation of π-π stacking during melt blending [78]. ps = polystyrene. reproduced with permission from acs. figure 8. thermogravimetric analysis curves of nanocomposites. psfg = polystyrene/functional graphene. 5, 10, 30, 60 = nanofiller contents in designations [78]. reproduced with permission from acs. the graphene-filled polypropylene nanocomposites were processed using the melt blending technique for enhanced electrical, thermal, and mechanical features [79]. the elevated performance was attributed to the interfacial interactions in the matrix-nanofiller [80]. melt-processed graphene-filled polyethylene and polyethylene terephthalate nanocomposites have been developed with elevated strength features [81,82]. the poly(methyl methacrylate) nanocomposites with graphene have also been prepared through melt blending practice [83]. the melt strategy has been found facile, characterization and application of nanomaterials 2024, 7(2), 4946. 9 low-cost, and large-scale processable [84,85]. controlling the reaction temperature, time, and shear and extrusion rate may define fine dispersion in the polymeric matrices [86,87]. 6. more synthesis strategies for graphene nanocomposites, solution approaches have been applied as effective methods; however, complex posttreatments must be used for solvent evaporation [88]. a range of other synthesis strategies have been found effective for the formation of graphene nanocomposites. essential processing techniques include threeor four-dimensional printing approaches [89]. among printing methods, stereolithography [90], inkjet printing [91], selective laser sintering [92], direct ink writing [93], fused deposition modeling [94], and others have been used. printing techniques have been used to enhance the dispersion as well as the end properties and performances of the graphene nanomaterials [95,96]. choice of a particular printing technique has been found critical to form the desired material and properties. accordingly, the performance of printed material relies on the polymer type, nanoparticle dispersion, interactions, and printing parameters. the direct threedimensional printing involves the extrusion of viscous material from the pressurized syringe to form the three-dimensional shapes. the fused deposition modeling printing performs with controlled filament extrusion. by controlling the printing parameters, product quality can be managed. the selective laser sintering uses high power lasers to fuse the powder, and product resolution depends upon the powder specifications, laser power, and scan speed. electrospinning has also been adopted as an efficient and sophisticated method to form the high-tech nanomaterials [97,98]. by using electrospinning, finely reinforced graphene nanocomposites have been designed [98,99]. this technique may include a syringe, spinneret, collector, and voltage-based system [100,101]. resulting electrospun graphene nanocomposite nanofibers have been tested for high electrical, mechanical, thermal, and other advanced technical features [102]. table 1 displays essential details of some literature-reported graphenefilled nanocomposite designs formed using efficient synthesis strategies. hence, the manufacturing technique relies on the inherent features of graphene nanomaterials. table 1. specs of graphene nanocomposites thru various synthesis strategies. matrices nanofiller manufacturing ref. polystyrene graphene in situ polymerization [35] polyamide 6 graphene in situ polymerization [31] polyamide 6 graphene in situ polymerization [32] polystyrene graphene solution method [56] poly (methyl methacrylate) graphene solution method [60] poly (methyl methacrylate) graphene solution method [61] poly (vinyl alcohol) graphene solution method [64] polystyrene, polycarbonate, polypropylene, high density polyethylene, low density polyethylene graphene melt compounding [75] poly (methyl methacrylate), polystyrene, polybutyl acylate graphene atom transfer radical polymerization [103] polystyrene, poly (methyl methacrylate), poly (vinyl fluoride) graphene colloid method [104] characterization and application of nanomaterials 2024, 7(2), 4946. 10 7. scenarios and conclusions graphene nanocomposites have been designed using several simple and sophisticated synthesis strategies (figure 9) [105]. choice of a particular technique always relies on the cost, ease of processing, and opportunities for large-scale production [106,107]. accordingly, graphene dispersion, matrix-nanofiller interactions, and interface developments were influenced. consequently, suitable synthesis technique has been found important to improve the nanocomposite features and end uses of the graphene nanocomposites [108]. here, each synthesis method owns relevant advantages and disadvantages towards the formation of graphene nanomaterials [109]. figure 9. synthesis strategies for graphene nanocomposites. solution synthesis is a simple method; however, this may include the drawback of using toxic solvents. the in situ technique, on the other hand, has resolved this issue by using environmentally friendly solvents [110]. the melt method has also been found beneficial, avoiding the use of any toxic solvent. sometimes the melt extrusion method may have the drawback of poor graphene dispersion in the nanocomposites. therefore, the nanofiller dispersion depends on the type of synthesis strategy used. sophisticated techniques like printing and electrospinning have been found effective to form well-dispersed high-performance graphene nanocomposites [111]. however, these techniques have drawbacks of high cost and limitations for large scale processing [112,113]. moreover, nanoparticle aggregation has been found challenging in sophisticated techniques like coating and prating [114]. beside studying the experimentally processed graphene nanocomposites, theoretical approaches like molecular dynamics or simulation must be applied for graphene nanomaterials [115]. henceforth, research efforts have focused on the use of appropriate synthesis techniques and controlled processing parameters to attain high-performance graphene nanocomposites. main application areas recognized for the well-processed graphene nanocomposites include batteries, supercapacitors, solar cells, fuel cells, coatings, membranes, engineering structures, space, automobiles, and other transportation sectors. in short, this article summarizes the synthesis strategies widely used for the formation of graphene nanocomposites. most importantly, in situ strategy, solution processing, melt blending, printing, spinning, and numerous other methods can be characterization and application of nanomaterials 2024, 7(2), 4946. 11 adopted for the development of efficient graphene-filled nanomaterials. here, a suitable method may reveal fine graphene dispersion, matrix-nanofiller associations, and physical property enhancements. in this context, important microstructure, electrical, thermal, and mechanical features were improved with the graphene additions. consequently, the nanocomposite performance was enhanced by controlling the parameters of the synthesis strategies used. future progress on the processing of graphene nanocomposites may lead to the development of advanced next-level approaches for the formation of high-tech nanomaterials. conflict of interest: the authors declare no conflict of interest. references 1. kausar a, ahmad i, lam td. high-tech graphene oxide reinforced conducting matrix nanocomposites—current status and progress. characterization and application of nanomaterials. 2023; 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268: 191-198. doi: 10.1016/j.jhazmat.2014.01.015 115. rissanou a, power a, harmandaris v. structural and dynamical properties of polyethylene/graphene nanocomposites through molecular dynamics simulations. polymers. 2015; 7(3): 390-417. doi: 10.3390/polym7030390 can v2i2 2019.pdf characterization and application of nanomaterials (2019) volume 2 issue 2 review article nanochemistry department, istituto italiano di tecnologia, via morego 30, 16163 genova, italy. e-mail: rongmeijiao yin@gmail.com keywords: et al. et al. et al et al et al et al et al et al et al et al. et al et al et al. et al. et al. et al. et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al ; et al et al et al et al et al et al et al et al et al et al et al et al characterization and application of nanomaterials 2025, 8(2), 10461. https://doi.org/10.24294/can10461 1 article insight into zero-valent iron at the nanoscale and its silica composites: synthesis and characterization elsayed el-mossalamy1,*, ahmed al-owais2, ibrahim el-hallag3 1 chemistry department, faculty of science, benha university, benha 13511, egypt 2 chemistry department, college of science, king saud university, riyadh 11451, saudi arabia 3 chemistry department, faculty of science, tanta university, tanta 31527, egypt * corresponding author: elsayed el-mossalamy, alsayed.almosallamy@fsc.bu.edu.eg abstract: nanoscale zero-valent iron (nzvi) is thought to be the most effective remediation material for contaminated soil, especially when it comes to heavy metal pollutants. in the current high-industrial and technologically advanced period, water pollution has emerged as one of the most significant causes for concern. in this instance, silica was coated with zerovalent iron nanoparticles at 650 and 800 ℃. ferric iron with various counter-ions, nitrate (fn) and chloride (fc), and sodium borohydride as a reducing agent were used to create nanoscale zero-valent iron in an ethanol medium with nitrogen ambient conditions. x-ray diffraction (xrd) and field emission scanning electron microscopy (fe-sem) techniques were employed to describe the structures of the generated zero-valent iron nanoparticles. further, we investigated the electrical properties and adsorption characteristics of dyes such as alizarin red in an aqueous medium. as a result, zero-valent nano iron (nzvi), a core-shell environmental functional material, has found extensive application in environmental cleanup. the knowledge in this work will be useful for nzvi-related future research and real-world applications. keywords: nanoscale; nzvi; ferric nitrate; ferric chloride; alizarin 1. introduction because of their unique properties that distinguish them from bulk materials, nanoscale materials have garnered a lot of attention recently. it’s interesting to note that zerovalent metal nanostructures, such as galdames et al. [1]; krebsz and pasinszki [2]; pereira et al. [3]; and petrarca et al. [4], or their related composites, may find use in research and technology. among the many possible applications for metallic nanostructures are biomedicine [4], environmental remediation [5], energy storage and harvesting, and catalysis [6]. this is a result of their exceptional physical characteristics. for uses in computer technology, bioimaging, electronics, optics, photonics, data storage, and high-frequency applications. it is crucial to keep in mind that the conditions and techniques employed during synthesis have a significant impact on the final materials’ structure, dielectric characteristics, and magnetic characteristics [7]. farzana et al. [8] used hydrothermal preparation at various reaction temperatures to create a range of cobalt ferrite nanoparticles. they discovered that the sample with the highest saturation magnetisation, 150.67 emu/g, was the one made at the highest temperature. the dielectric characteristics, however, are unaffected by the synthesis temperature. at the nanoscale, metallic particles can be created essentially in two ways: “top-down” and “bottom-up”. bulk metal grinding serves as an example of how top-down citation el-mossalamy e, al-owais a, elhallag i. insight into zero-valent iron at the nanoscale and its silica composites: synthesis and characterization. characterization and application of nanomaterials. 2025; 8(2): 10461. https://doi.org/10.24294/can10461 article info received: 21 november 2024 accepted: 31 december 2024 available online: 2 april 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 10461. 2 approaches struggle with narrow particle size distributions [9]. conversely, bottomup methods offer a precise, suitable distribution of particle sizes. atomic or molecular precursors in the gas or solution phase serve as the starting point for this process, which builds up nuclei that gradually increase until they form nanoparticles. temperature, the type of stabilizing agent, and concentrations are kinetic characteristics that affect the nanoparticle’s ability to form various structures, shapes, and sizes. precipitation methods have been used to create manufactured nanoparticles (mnps) for zero-valent iron throughout the past few decades [10]. the following reaction equation (1) [11] illustrates the most popular technique for environmental reasons: the reduction of fe (ⅱ) or fe (ⅲ) cation solutions using borohydride anion. 2fecl3 + 6nabh4 + 18h2o → 2fe0 + 6nacl + 6b(oh)3 + 21h2 (1) maintaining iron in its zerovalent forms requires a range of aqueous media types. zero-valent iron makes up the majority of the ore, whereas mixed oxides such as f3o4, fe2o3, and feooh make up the shell of the nzvi particle [12]. as a result of its effective electron donation, this type of metallic iron forms a mixed oxide/hydroxide shell that influences the bulk composition, surface charge, and morphologies of nzvi. consequently, surface oxidation, aggregation propensity, magnetic characteristics, and environmental interactions were affected. the iron metal can react with oxygen carriers in a variety of ways, oxidising to produce a suboxide shell. it is expected that this oxidation reaction will generate a very high rate of heat, particularly for the ultra-small particle [13]. numerous investigations have been carried out on the oxidation of metallic nanoparticles, the oxidation of bulk iron by oxygen and water vapour [14,15], and the oxidation of metal films at low temperatures when exposed to oxygen gas [16,17]. three steps were involved in the oxidation of iron nanoparticles: fe3o4 partially oxidised into the α-fe2o3 structure, fe3o4 and iron core fully oxidised into the αfe2o3 phase, and then the iron core oxidised into crystalline iron oxides and disordered phase formation. the size, shape, and morphologies of iron metal nanoparticles have been shown to affect the degree of heat sensitivity. it is essential to comprehend the high-temperature oxidation processes that include various nanoscale particle sizes. additionally, zvi (zero valent iron) materials are used in a wide range of sectors, particularly in soil and groundwater remediation, such as the removal of heavy metals, organophosphates, dyes, antibiotics, and other organic pollutants [18–22]. the synthesis of nzvi under aqueous circumstances has been the subject of numerous research articles in recent years. however, not enough research has been done on how iron nanoparticles are produced in ethanol. in order to avoid severe oxidation, the objective of this endeavour is to synthesise nzvi outdoors using ethanol while simultaneously describing the materials’ size and surface characteristics [11]. in this study, we synthesised and investigated iron-based nanoparticles in the zero-oxidation condition. the materials were described by means of xrd, fe-sem, electrical conductivity, real and imaginary components of the dielectric constant, and the loss tangent (tan δ) approach. furthermore, it was characterization and application of nanomaterials 2025, 8(2), 10461. 3 assessed if nzvis derived from different precursors could adsorb a model dye such as alizarin red. 2. experimental 2.1. materials alizarin red dye [sodium alizarin sulphonate (c14h7nao7s), ferric nitrate [fe(no3)3.9h2o], sodium borohydride (nabh4), and ferric chloride anhydrous (fecl3) were supplied by sigma-aldrich chemical company. all of these materials were employed without additional refinement. aluminium foils, aluminium scrapes, and plates with 98% sodium hydroxide were employed, along with commercial sodium silicate solution with a solid concentration of 45%. the other reagents were all analytical reagent grade, and deionized water was used. figure 1 depicts the chemical structure of alizarin red dye. figure 1. alizarin red dye’s chemical structure. 2.2. method the creation of nanoscale zero-valent iron (nzvis) from various counter-ions impregnated with silica is the focus of this work. it was used as an adsorbent to remove the alizarin red dye from aqueous media. figure 2 shows how to produce of the iron nanoparticles by reduction with sodium borohydride (nabh4) in a flask reactor in an ethanol medium with three open necks. the following is the reaction: 2fexn + 6nabh4 + 18h2o → 2fe0 + 6nax + 6b(oh)3 + 21h2 (2) where x = cl− and no3 −. characterization and application of nanomaterials 2025, 8(2), 10461. 4 figure 2. schematic diagram for the synthesis of iron and its composite nanoparticles. 2.2.1. preparation of nzvi particles for the synthesis of nanoscale zero-valent iron (nzvis) (a and b), where a is (fe0/cl−)] and b is (fe0/no3 −) from different anions such as chloride (cl−) and nitrate (no3 −), a 0.6 m solution of each salt was dissolved in a 4/1 (v/v) ethanol/water mixture (24 ml ethanol + 6 ml deionized water) and stirred well. however, a 0.8 m sodium borohydride solution was made, which is equivalent to dissolving 3.028 g of nabh4 in 100 ml of deionized water. this is because promoting the synthesis of iron nanoparticles requires a greater amount of borohydride. poured into a burette, the borohydride solution is added drop by drop— one drop every two seconds—to each solution while being vigorously stirred. as soon as the first drop of sodium borohydride solution was added, black solid particles appeared. to speed up the reduction reaction, the remaining sodium borohydride was subsequently added drop by drop. the entire borohydride solution was added to the mixture and stirred for a further thirty minutes. the liquid phase was separated from the black iron nanoparticles using the vacuum filtration process. in order to eliminate all of the water, the solid particles were thoroughly cleaned three times using 25 ml parts of 100% ethanol. the washing process is perhaps the most crucial step in the synthesis process because it prevents the rapid oxidation of zero-valent iron nanoparticles. last but not least, the produced nanoparticles were dried for an entire night at 60 ℃. to prevent the nano iron particles from oxidizing, a thin layer of ethanol was applied before storage. 2.2.2. preparation of sio2 nanoparticles sio2 nanoparticles were created using a sol-gel auto-combustion process with two distinct fuels—fructose and glucose. fuels were used as the reductant precursor and nitric acids as the oxidant precursor to create sio2 nanoparticles. sg and sf, respectively, are the sio2 samples that are made utilizing glucose and fructose as fuels. the total oxidising and reducing valences of the fuel and oxidiser are used to characterization and application of nanomaterials 2025, 8(2), 10461. 5 determine the stoichiometric compositions of the redox mixtures for combustion. this ensures that the energy released during combustion is maximized for each reaction by ensuring that the equivalency ratio, ɸc, is unity (i.e., ɸc = 1) [23]. 6 g of silica gel were dissolved by swirling in a hot (50 ml, 4 m) solution in a standard synthesis procedure. naoh. 50 ml of 4m hno3 was subsequently added to the created solution dropwise, resulting in a colourless gel. the surplus sodium hydroxide was eliminated from the generated gel by thoroughly washing it multiple times with diluted hno3. using 0.1 m hno3, the mixture’s ph was brought to 8. heat the reaction with an aqueous hot solution (20 ml) containing (3.963 g, 0.02 mol glucose or 3.603 g, 0.02 mol fructose) to 80 ℃ and stir for an hour. as the mixture heated to 120 ℃, it gelled. after the gel was created, it was burnt on a hot plate at 350 ℃ to produce a dry, gray mass. this mass was then calcined for four hours at 800 ℃ in an electric furnace to produce samples sg and sf, respectively. 2.2.3. impregnation of nzvi with silica the nzvi carrier was silicon. the process of creating the nzvi using silica involved two steps: f is fe0/no3 − impregnated with sf, and fe is fe0/cl− impregnated with sg. initially, ferric salts, like ferric chloride or ferric nitrate, were adsorbed or wet-impregnated onto silica. then, loaded iron was reduced by nabh4 to fe0 [24]. in the adsorption process, 20 ml of a ferric salt solution—such as ferric chloride or ferric nitrate solution—containing 1 mol/l was mixed with 2 g of silica. a rotary shaker set at 25 ℃ was used to shake the mixture for 24 h. after that, the mixture was mixed with 15 ml of ethanol and 15 ml of water. subsequently, 50 ml of 1 mol/l nabh4 was added to the mixture while vigorously swirling and dropping the liquid. ultimately, the produced nanoparticles were dried for an entire night at 60 ℃ in an oven. 2.3. characterization methods the generated products were measured by x-ray powder diffraction using an 18 kw diffractometer (bruker; model d8 advance) with monochromatic cu-ka radiation, 1.54178 (å). x-ray diffraction was used to evaluate the as-prepared nanomaterials for crystallinity and phase purity. with a step size of 0.02° (2 θ) and a scan step length of 0.4 s, the diffraction patterns were rearranged at room temperature within the angular range of 30°–90° (2 θ). with an accelerating voltage of 20 kv, a field emission scanning electron microscope (fe-sem, jeol jsm-6510lv) was used to examine the morphology and elemental content of the as-prepared nanomaterials. the frequency range used for the ac measurements was 500 hz to 5 mhz. using a programmed automatic rcl meter (hiok3532lcr hitester), the values of impedance (z), capacitance (c), resistance (r), and phase angle (υ) can be immediately read. the real part of the dielectric constant, έ , the imaginary part, ε″ , and the dielectric loss tangent, tan δ, were calculated using the data of z, c, r, and ϕ at any frequency f. figure 3 depicts the sample holder that was utilized for the ac measurements. characterization and application of nanomaterials 2025, 8(2), 10461. 6 figure 3. the sample holder was used for ac measurement. 3. results and discussion 3.1. x-ray diffraction study figure 4a,b illustrate the xrd analysis of fc and fn nanoparticles, respectively, in the characterization of produced nzvi particles. when α-fe0 nanoparticles are present in the sample for fc and fn nanoparticles, the peaks at 2θ 44.87° and 44.68°, respectively, show 100% intensity. it was discovered that the average crystalline diameters of the fc and fn nanoparticles were 3.166 and 1.83 nm, respectively. the peaks at 2 θ 44.87° and 44.68°, respectively, indicate the existence of iron nanoparticles (fe0). particle size can be presumed with the xrd by using the scherer equation [25]: 𝐷 = 0.9λ 𝛽 cos 𝜃 (3) where θ is the bragg angle derived from 2 θ, which corresponds to the greatest peak intensity, β is the full width at half maximum (fwhm), d is the particle size (in nanometres), and λ is the wavelength of the cu kα radiation, which is 0.154 nm [26,27]. accordingly, the crystalline particle size was found to be 50 nm and 59 nm, respectively. (a) (b) figure 4. (a) x-ray diffraction (xrd) pattern of fc and (b) fn. characterization and application of nanomaterials 2025, 8(2), 10461. 7 3.2. fe-sem particle size and morphology of the produced nzvi (fc and fn samples) were examined at different magnifications using an fe-sem (figure 5). fe-sem pictures of produced nzvi nanoparticles are displayed in figure 5a–d. the photos show the presence of crystalline, ultrafine, spherical shapes with aggregation. aggregation of iron nanoparticles is thought to be caused by the large surface area of the individual particles and the magnetic dipole-dipole interactions. the average particle size of the nzvi nanoparticles (fc sample) was determined using fe-sem images, and it was discovered to be between 50 and 100 nm. given that the measured size is greater than the size inferred from the xrd pattern, densification is likely the cause of the appearance of the small particles colliding with one another. furthermore, fe-sem images (figure 5e–h) show the morphologies of crystalline spherical networks for fn, with average particle sizes between 50 and 63 nm. figure 5. (a–d) fe-sem images of the fc-based nzvi nanoparticles; (e–h) fesem images of the fn-based nzvi nanoparticles. characterization and application of nanomaterials 2025, 8(2), 10461. 8 3.3. dielectric properties this article measured, examined, and described the electrical characteristics of different compositions of nzvi as a function of frequency. two basic electrical properties of nzvi materials are defined with the help of dielectric analysis. its two main characteristics are its capacitive insulating nature, which indicates its capacity to retain electrical charge, and its conduction nature, which demonstrates its electrical charge transmission capability. the dielectric characteristics of ferric chloride (fc), ferric nitrate (fn), impregnated zero-valent iron prepared from ferric chloride with silica that calcined at 650 ℃ (fcs650), impregnated zero-valent iron prepared from ferric nitrate with silica that calcined at 650 ℃ (fns650), impregnated zero-valent iron prepared from ferric chloride with silica that calcined at 800 ℃ (fcs800), and impregnated zero-valent iron prepared from ferric chloride with silica that calcined at 800 ℃ (fns800) of nzvi in the frequency range of 500 hz to 7 mhz. as a general aspect of the obtained results, the frequency and composition dependency of the dielectric constant’s imaginary (ε‶) and real (ε‵) components are examined and explained. as seen in figure 6a–c, the real and imaginary dielectric constants for nanoscale zero-valent iron (nzvi) compositions for fc, fn, fcs800, fns800, fcs650 and fns650 fluctuate with frequency (f). for every composition, it can be seen that when frequency increases at room temperature, the real part of the dielectric constants (ε‵) and the imaginary part of the dielectric constant (ε‶) both drop in value. at low frequencies, the values of ε‵ and ε‶ reach a maximum value; at higher frequencies, they become frequency dependent, finally reaching a virtually constant value. in the cases of fc and fn, table 1 provides the values of the real part (ε‵) and the imaginary part (ε‶) of the dielectric constant at a chosen range of frequencies. as frequency increases, it was discovered that the values of ε‵ decrease. this is because, for polar material, ε‵ at low frequencies is explained by the combined effects of polarizability, deformational (ionic and electronic), and relaxational (orientational and interfacial) polarization [27]. initially, valence electron displacement with respect to the positive nucleus is the source of electronic polarization. at frequencies as high as 1016 hz, this kind of polarization occurs. positive and negative ions are displaced relative to one another, resulting in ionic polarization, which is the second kind. third, dipolar polarization happens when a material has molecules with a permanent electric dipole moment that are able to modify their orientation relative to the applied electric field. dipolar polarization arises at frequencies as high as 1010 hz. space charge polarization is the last one, which is brought on by interfaces that impede mobile charge carriers. 1 to 103 hz is the usual frequency range where space charge polarization happens. total polarization for dielectric materials is the sum of the four polarization types mentioned above [28,29]. the current study’s acquired results demonstrate that the ionic polarization has little effect on the overall polarization. as a result of taking longer than ionic and electronic polarization, orientational polarization diminishes with increasing frequency. as a result, at higher frequencies, which correspond to interfacial polarization, the value of ε drops and approaches a nearly constant value. characterization and application of nanomaterials 2025, 8(2), 10461. 9 furthermore, the real dielectric constant (ε‵) and imaginary dielectric constant (ε‶) characteristics at high frequencies for a particular sample indicate that the sample has better optical quality and fewer defects; this parameter is crucial for different nonlinear optical materials and their applications [30]. figure 6a and table 1 show how ε‵ and ε‶ vary in frequency for fc and fn compositions. it is also observed in figure 6a–c that the values of ε‵ and ε‶ vary with the composition of nzvi. this is explained by the expectation that altering the composition of nzvi will modify the structure of the nanoscale zero-valent iron host, resulting in a change in the density of charge defect states and, ultimately, dielectric properties [30]. table 1. the values of the dielectric constants’ real (ε‵) and imaginary (ε‶) parts for fc and fn at a chosen range of frequencies (f). fc fn log f log ε‵ log ε‶ log f log ε‵ log ε‶ 2 8.517141 10.29946 2 6.0634 7.028084 2.30103 8.168969 9.898106 2.30103 5.837691 6.866628 2.477121 7.996137 9.559789 2.477121 5.684614 6.731304 2.60206 7.861884 9.412483 2.60206 5.566078 6.614058 2.69897 7.752451 9.286082 2.69897 5.467662 6.511132 2.778151 7.661404 9.183051 2.778151 5.38337 6.419377 2.845098 7.586409 9.100253 2.845098 5.30951 6.336554 2.90309 7.519962 9.02646 2.90309 5.245341 6.26439 2.954243 7.461461 8.962467 2.954243 5.187464 6.197963 3 7.408675 8.906876 3 5.134203 6.135486 3.30103 7.068762 8.526559 3.30103 4.783538 5.71765 3.477121 6.865173 8.294816 3.477121 4.575465 5.465311 3.60206 6.721027 8.131624 3.60206 4.435062 5.300488 3.69897 6.607467 8.002585 3.69897 4.321597 5.162792 3.778151 6.491816 7.985738 3.778151 4.225777 5.043593 3.845098 6.408754 7.880472 3.845098 4.146264 4.945795 3.90309 6.340503 7.803268 3.90309 4.077407 4.860372 3.954243 6.279319 7.733654 3.954243 4.018498 4.790034 4 6.22234 7.669767 4 3.961002 4.716288 4.30103 5.846071 7.211311 4.30103 3.587046 4.234645 4.477121 5.624173 6.942541 4.477121 3.36456 3.939705 4.60206 5.467767 6.75456 4.60206 3.21189 3.737767 4.69897 5.343517 6.608181 4.69897 3.088393 3.566371 4.778151 5.248755 6.492814 4.778151 2.994286 3.439241 4.845098 5.169851 6.39393 4.845098 2.915626 3.331743 4.90309 5.100702 6.306038 4.90309 2.84939 3.241104 4.954243 5.045411 6.244957 4.954243 2.791734 3.161801 5 4.993901 6.181048 5 2.741091 3.091871 characterization and application of nanomaterials 2025, 8(2), 10461. 10 table 1. (continued). fc fn log f log ε‵ log ε‶ log f log ε‵ log ε‶ 5.30103 4.686685 5.847292 5.30103 2.440615 2.67782 5.477121 4.534939 5.706617 5.477121 2.287085 2.466494 5.60206 4.438793 5.626987 5.60206 2.187863 2.331016 5.69897 4.370959 5.587526 5.69897 2.116544 2.235103 5.778151 4.340539 5.375195 5.778151 2.061252 2.161343 5.845098 4.307531 5.377124 5.845098 2.0163 2.102435 5.90309 4.282338 5.37698 5.90309 1.979197 2.054243 5.954243 4.266863 5.383636 5.954243 1.947821 2.014583 6 4.256274 5.403648 6 1.920216 1.979585 6.30103 4.476008 6.100774 6.30103 1.757499 1.785652 6.477121 1.677107 1.706453 6.60206 1.62716 1.922624 6.69897 1.574856 1.898534 figure 6. the variation of the real part of the dielectric constant (ε‵) and the imaginary part of the dielectric constant (ε‶) with frequencies (f) in the case of (a) fc, fn, fcs800, and fns800; (b) fcs650, and fns650; and (c) fc, fn, fcs800, and fns800. characterization and application of nanomaterials 2025, 8(2), 10461. 11 for the two prepared samples, fc and fn, with nzvi compositions, figure 7a displays the frequency dependence of the dielectric loss tangent (tan (δ)). similar trends to those seen for ε‶ at low frequencies can be seen in the variation of tan (δ) with frequency at constant temperature. this could be because, up until a frequency of 10, the polarizability contribution from ionic and orientation sources decreases; after that, the dielectric loss tangent tan (δ) increases because of their inertia effect [31]. figure 7. the variation of loss tangent (tan δ) with frequency (f) for (a) fc, fn; (b) fcs650, fns650; and (c) fcs800, fns800 for nzvis. the loss tangent’s fluctuation with frequency for various nzvi compositions is depicted in figure 7b,c. ionic conduction via nzvi segmental motion is represented by the fingerprint of the single relaxation peak’s [32]. the initial increase in the loss tangent at a lower frequency area can be ascribed to the ohmic (active) component’s dominance over the capacitive (reactive) component. however, the loss tangent falls, and the inverse trend becomes apparent as the frequency rises due to the independent nature of the ohmic part and the increasing reactive component with frequency. the characterization and application of nanomaterials 2025, 8(2), 10461. 12 resonance peak, which represents the highest energy transfer upon the application of a field, is likewise in good agreement with the debye theoretical method [33]. 3.4. electrical conductivity to better visualise, figure 8 shows the frequency dependence of conductance (σ) for different compositions of nzvi. the mentioned figure revealed that the conductivity of the various compositions is significantly high at low frequencies and low at high frequencies. this phenomenon is in line with the well-known debyefalkenhagen (df) hypothesis, which states that the velocity of an ion is dynamically influenced by its ion environment. an external electric field cannot cause the atmosphere to follow the motion of the center ion when it moves in an electrolyte solution. this results in an asymmetrical effect that slows down the ion’s speed. the center ion oscillates under an oscillating electric field, which also reduces the amount of time the ion atmosphere has to unwind and maintains its asymmetry. this results in an enhancement of the conductivity at low frequencies and a reduction of the relaxation force, which raises the rate of electron mobility. due to the ions’ rapid oscillation, which reduces the net ionic motion in a given direction when there is no static or low-frequency field present, conductivity drops at high frequencies [34]. figure 8. the variation of conductance (σ) of nzvi with frequency (f) for fc, fn, fcs800, and fns800. 3.5. alizarin removal via nzvi 3.5.1. effect of contact time one of the most important factors affecting the performance of adsorption processes for alizarin removal is the contact time between adsorbate and adsorbent. the effect of the contact time of fc and fn samples on the adsorption of alizarin red dye was investigated at ph 3 with a dosage of 0.01 g of adsorbent and an initial concentration of 150 mg/l. figure 9 illustrates the alizarin red dye adsorption capacities of synthesized adsorbents as a function of stirring times ranging between 10–240 min and 10–180 min for fc and fn, respectively. the rate of uptake was characterization and application of nanomaterials 2025, 8(2), 10461. 13 rapid at first and gradually increased in the later stages until it reached saturation, as shown in figure 9. the maximum alizarin red dye removal was achieved in 180 and 120 min for fc and fn, respectively. figure 9. effect of contact time on the adsorption capacities of fc and fn adsorbents for the removal of alizarin red dye. 3.5.2. effect of initial dye concentration the effect of varying the starting quantity of alizarin red dye from 50 to 350 mg/l on fc and fn was studied. these adsorption studies were carried out with a ph of 3 and a dosage of 0.01 g of adsorbent. the adsorbent was separated by centrifugation after 180 min for fc and 120 min for fn of stirring, and the residual dye concentration in the supernatant was determined using uv–vis spectrophotometry. the rate of uptake was high at first and quickly approached saturation. as time passed, the active sites were blocked, and the rate fell, as indicated in figure 10 by the relationship between the adsorption capacity and the original dye concentration. from figure 10, the adsorption capacities increased with increasing the initial concentration until they reached the maximum and constant high initial concentrations. from the data, the adsorption capacities of fc and fn samples were determined to be 139.029 and 99.416 mg/g, respectively. figure 10. effect of initial alizarin red dye concentration on adsorption capacities of fc and fn adsorbents for the removal of alizarin red dye. characterization and application of nanomaterials 2025, 8(2), 10461. 14 3.5.3. effect of adsorbent dose one of the most important parameters that determines the adsorbent’s capacity for a given initial adsorbate concentration is the adsorbent dosage. using various doses of adsorbent (0.001–0.01 g), the effect of adsorbent dosage on the adsorption of alizarin red dye was investigated. at equilibrated time, the adsorbent was added to 50 ml of alizarin red dye solutions with initial concentrations of 150 mg/l for fc and fn. after the solutions had reached equilibrium, they were centrifuged and tested for dye content. the adsorption results are depicted in figure 11. because the adsorbent surface active size grows, the results suggest that increasing the adsorbent dosage increases dye removal efficiency. the maximum alizarin red dye removal percentages for fc and fn were found to be 92.786% and 85.206%, respectively, of the boundary layer enclosing the sorbent decreases. the adsorbate mass transfer resistance in the boundary layer decreased. this might have happened because, as the temperature increased, the dye’s mobility increased (due to an increase in kinetic energy). the removal percentage of the alizarin red dye over the fabricated samples increased as the temperature of the dye solution decreased. figure 11. effect of adsorbent dose on the alizarin red dye removal efficiency using fc and fn adsorbents. 4. conclusion nzvi were successfully prepared in the zero-oxidation state with 100% intensity at 2θ of 44.87° and 44.68° for fc and fn, respectively, with mean crystalline sizes of 3.166 and 1.83 nm, respectively, and there was no oxidation during storage for weeks through visual observation. sem results showed that nzvi appear as spherical particles and take the shape of chain-like structures with a particle size in the range of 50–100 nm, and that nzvi have a strong trend to agglomerate in nanoscale aggregates due to the weak surface charges. the electrical properties of the various prepared nzvi compositions showed great variation with the use of different iron salt precursors. further, the prepared nzvi obtained from iron chloride salt precursors were proven to be more capable adsorbents for alizarin red dye in aqueous solutions than those obtained from iron nitrate salt precursors. so, it is concluded that the type of salt precursor appears to have a high impact on the characteristic physical properties of the synthesized nanomaterial. characterization and application of nanomaterials 2025, 8(2), 10461. 15 author contributions: completed the electrical conductivities of nzvi, ieh; wrote the article under consideration, ieh; explained the obtained results, ieh; proposed the idea of the present work, aao; revised the present article, aao; prepared the nzvi, described the structure via fe-sem, and xrd, eem. all authors have read and agreed to the published version of the manuscript. institutional review board statement: not applicable. informed consent statement: not applicable. conflict of interest: the authors declare 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relaxation in na-doped bi–pb–sr–ca–cu–o glasses. journal of non-crystalline solids. 1998; 226: 155–161. doi: 10.1016/s0022-3093(97)00482-1 63 characterization and application of nanomaterials (2021) volume 4 issue 1 doi:10.24294/can.v4i1.1291 original research article preparation and characterization of magnetic graphene oxide nanocomposite (go-fe3o4) for removal of strontium and cesium from aqueous solutions sule aytas1, sabriye yusan1*, senol sert1, cem gok2 1 institute of nuclear sciences, ege university, 35100 bornova, izmir, turkey. e-mail: sabriye.doyurum@ege.edu.tr 2 faculty of technology, department of metallurgical and materials engineering, pamukkale university, 20160 kinikli denizli, turkey abstract magnetic graphene oxide nanocomposites (m-go) were successfully synthesized by partial reduction co-precipitation method and used for removal of sr(ii) and cs(i) ions from aqueous solutions. the structures and properties of the m-go was investigated by x-ray diffraction, fourier transformed infrared spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer (vsm) and n2bet measurements. it is found that m-go has 2.103 mg/g and 142.070 mg/g adsorption capacities for sr(ii) and cs(i) ions, respectively. the adsorption isotherm matches well with the freundlich for sr(ii) and dubinin–radushkevich model for cs(i) and kinetic analysis suggests that the adsorption process is pseudo-second-ordered. keywords: graphene oxide; magnetite; nanocomposite; strontium; cesium, sorption article info received: 26 january 2021 accepted: 12 march 2021 available online: 18 march 2021 copyright copyright © 2021 sule aytas, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction nuclear and industrial safety agency (japan) reported that the fukushima daiichi reactor meltdowns have thus far released 15,000 tera becquerels of radioactive cesium-137 into the environment[1]. also, strontium was measured in plant samples in four others villages, with values ranging from 12 to 61 bq/kg for sr-89 and 1.8 to 5.9 bq/kg for sr-90[2]. this accident caused a great environmental disaster for living metabolisms and plants. furthermore, diverse anthropogenic activities like nuclear research reactors, the production and use of radioisotopes and radiopharmaceuticals bring about the spread of radioactive wastes in the environment[3]. some radionuclides as cesium and strontium are biologically toxic and of great importance due to their long-lasting nature and high solubility in aqueous systems[4]. for this reason, it is a significant subject to find out efficient, economic method that can be used in the removal and recovery of cesium and strontium from contaminated environments. different types of physicochemical methods as ion exchange, chemical precipitation, membrane separation and adsorption, etc. are used for removal and recovery of radionuclides. considering many parameters, one of these techniques comes to the forefront. adsorption is widely-used technique that is fast and effective approach in eliminating pollutants from aqueous solutions[5]. 64 the most critical point in the development of new adsorption methods is developed new adsorbent materials. among the previously developed adsorbents, nanomaterial and especially nano-composites have been received great attention owing to high adsorption capacity, selectivity, high surface area, fast kinetic performances, and reusability for several cycles use[6,7]. furthermore, nano-engineered magnetic adsorbents can be widely applied in contaminant removal due to the magnetism and high surface area. the magnetic particles can be quickly separated from the water after adsorption and this provides easily controlled process[8]. in recent years, graphene oxide nanomaterials, which has a large theoretical surface area and high sorption capacity for the metallic cations, has with wide range of surface oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl[9,10]. according to literature, graphene oxide has a notable affinity toward hard and semi-hard cations like uranium, thorium, lanthanides, and also strontium. these superior properties make graphene oxide proper for efficient adsorbent of cesium and strontium. unfortunately, disadvantage of the graphene oxide is colloidal behavior of its dispersion, which makes separation of its reaction products with metallic cations quite unfairable[9]. preparation of composite is one of the possible solutions to solve this problem. in this study, magnetic-nano composites were synthesized by using graphene and also magnetite, which is economic and readily available material; on the other side it is not selective. integration of these two materials solved agglomeration problem and chemical instability in acidic media[11,12]. preparation of nano-composite material with graphene and magnetite, not only brings about the chemical resistance, but also increase adsorption capacity. in recent years, combining of magnetite and graphene into nanocomposites has become an important subject of research due to their new and/or enhanced functionalities that cannot be obtained by either component alone. so, this topic holds a great promise for a wide variety of applications in removal of contaminants from wastewater, surface enhanced raman scattering, biomedical fields, catalysis, etc.[13,14] in despite of various studies, there is lack of efficient, low cost, secure, high capacity, modifiable, dopeable and reusable technique about cesium and strontium removal from aqueous solution. based on that, magnetic-nano graphene composites were synthesized and characterized to investigate the removability of radiotoxic strontium and cesium ions from aqueous solutions. adsorption performance of prepared composite by batch experiment was studied by physicochemical parameters. the adsorption isotherm parameters were estimated by linear regression analysis, thermodynamic and kinetic parameters have been also calculated to clarify the adsorption mechanism. the interaction mechanism of cesium and strontium on the magnetic nano-composites was discussed from the experimental results. 2. experimental procedure 2.1. reagents and materials the graphene oxide powder was purchased from the sigma aldrich. the stock standard solutions of strontium and cesium were prepared by dissolving an appropriate amount of sr(no3)2 (merck) and csno3 (merck) in distilled deionized water. considering the radioactivity of the 90sr, non-radioactive 88sr was used. all reagents used were of analytical reagent grade. 2.2. instrumental and analytical conditions the strontium and cesium concentration measurements were done using a perkin-elmer optima 2000 dv icp–oes. the shaking was carried out in a thermostated electronic shaker bath (gfl-1083 model). to analyze the characteristics of the m-go, scanning electron microscope (sem, coxem em30), transmission electron microscopy (tem, fei 120kv ctem), fourier transform infrared spectroscopy (ftir, perkin elmer spectrum two), x-ray diffraction (xrd, thermo scientific arl k-alpha), x-ray photoelectron spectroscopy (xps, thermo scientific al k-alpha), vibrating sample magnetometer (vsm, vsm550-100, dexing magnet tech. co) and n2-bet adsorption–desorption were 65 determined at 77 k using micromeritics asap 2020. 2.3. synthesis of m-go the m-go nanocomposite was prepared by co-precipitation method, as reported in the literature[15]. 0.05 g graphene oxide powder was used during the synthesis of the nanocomposite. 2.4. batch adsorption experiments all sorption experiments were performed by the batch technique using 0.01 g of the sorbent suspended in 10 ml of strontium/cesium solution in a polyethylene (pe) flask at selected ph (2–9) and ph (2–12) for sr(ii) and cs(i), respectively. the effects of sorption parameters such as contact time (15–300 min), sr(ii) concentration (10–50 mg/l), cs(i) concentration (200–500 mg/l), adsorbent dosage (m/v) ratio (1–10) and temperature (25–45 °c) on the sorption of sr(ii)/cs(i) were determined by changing a parameter and keeping others constant. the ph was adjusted by adding 0.1 mol/l hcl and naoh to the solutions at the each experiment. after reaction, the solid and liquid was separated by the magnetic separation method. the concentrations of total sr and cs were determined by using icp-oes. each experiment was repeated three times and average values were used for calculation. the percentage sorption of metal ions from aqueous solution was computed as follows: where ci and ce are the initial and final metal ions concentration, respectively. 2.5 kinetic studies kinetic studies were carried out in a thermostated shaker with polyethylene tubes at room temperature. in each run, 0.01 g of m-go was added to 10 ml of sr and cs solution (50, 100, 150 mg/l and 200, 250, 300 mg/l), respectively and adjusted to the desired ph level. the contact time varied from 5 to 180 min. samples were filtered from each tube at specified time intervals and analyzed for the remaining sr/cs ion concentrations by icp-oes. 3. results and discussion 3.1. characterization the micro-structure of the fe3o4-go(m-go) was characterized by xrd (figure 1). the peaks at 2θ values of 30.42°, 35.06°, 43.48°, 53.22°, 57.78° and 63.06° are the characteristic peaks of the fe3o4 crystal with the cubic spinal structure for magnetic graphene nanocomposites matching well with those from the jcpds card (19-0629) [16,17]. the small peak at 2θ = 26.5° corresponds to well-ordered graphene layers of go skeleton and indicates that this way the formation of the magnetic composite as reported by other groups[18]. generally we can conclude from the xrd pattern, the nanocomposite contains mostly fe3o4 and it was synthesized with go. figure 1. xrd pattern of m-go. sem and tem images of the obtained m-go nanocomposite are showed in figure 2 and figure 3. sem images confirm the fe3o4 nanoparticles are attached to the surface of the go sheet in homogeneously. nevertheless, tem images of the m-go shows that fe3o4 nanoparticles are well decorated and clearly observed on the surface of graphene sheet. xps technique was used to verify the chemical state of m-go and the results were shown in figure 4. the wide scan xps spectra of the m-go shows the binding energy peaks about 285, 530 and 710 ev, which are attributed to c1s, o1s and fe 2p, respectively[19,20]. in the figure spectrum, the peaks of fe 2p 3/2 and fe 2p 1/2 were located at about 711.12 and 724.79 ev, confirming that fe3o4 was fairly synthesized on the go. 66 the ft-ir spectrum of go and m-go is depicted in figure 5. the go sheet showed apparent adsorption bands for the carboxyl groups (stretching vibrations from c=o; 1,716 cm−1), aromatic (c=c; 1,580 cm−1), and alkoxy (stretching vibration from c– o (1,041 cm−1). the intense peak at 1,415 cm–1 can figure 2. sem image of m-go. figure 3. tem image of m-go. 67 be attributed to epoxy groups (c=c vibration) also showed at 1,122, 897 and 799 cm–1 in m-go spectrum that related to symmetric stretching, asymmetric stretching, and deformation vibrations, respectively[18]. for m-go, band at 1,635 cm−1 is assigned to h– o bending vibration. the peak at 553 cm−1 showed fe–o bond from fe3o4 the peak around 1,400 cm–1 can be explained by symmetric vibration of coo groups which indicates the carboxylate groups of go coordination with the iron cations[21]. the magnetic properties of the fe3o4 nanoparticles, go and the m-go nanocomposite were determined at room temperature. the hysteresis loop of magnetite, go and m-go composite are shown in figure 6, where the magnetization hysteresis loops appear s-like, and saturation magnetization is 16.16 and 10.74 emu/g for magnetite and m-go, respectively. nevertheless, as shown in the figure, go sample has no magnetic property. the reduction in the saturation magnetization could be related to existence of go and impurities on the surface of the magnetite nanoparticles[22]. however, m-go still could be separated rapidly under the external magnet. bet analysis was performed to investigate the specific surface area and pore size of the synthesized material. the bet surface area and pore size of m-go was found as 124.37 m2/g and 0.386 nm, respectively. in the literature, cheng et al. and hur et al. found the bet surface area for magnetic graphene oxide composites are 111. 8 m2/g and 49.9 m2/g, respectively[23,24]. the results obtained in this study are consistent with the literature. figure 6. magnetization versus magnetic field for magnetite, go and m-go. 3.2 adsorption studies 3.2.1 ph effect the ph value of solutions is a determining factor of the removal efficiency because it affects surface charge of the sorbent, and also the degree of ionization and speciation of the metal in solution. the effect of ph on sr2+ and cs+ adsorption is shown in figure 7 (a-b). as can be seen, the strontium and cesium removal on m-go adsorbent are affected by the ph change of the solution. the maximum strontium and cesium uptake were found 40% at ph 4 and 17.92 mg sr(ii)/g and 59.5% at ph 10 and 148.77 mg cs(i)/g as adsorbent, respectively. for this reason, ph 4 and ph 10 were used in subsequent experiments for sr(ii) and cs(i), respectively. in addition, m-go depicted higher adsorption capacity for cs+ than for sr2+ under the same experimental conditions. this can be attributed to the smaller hydrated ionic figure 4. xps survey scan spectrum of m-go. figure 5. ft-ir spectra of m-go. 68 radius of cs+[25]. 3.2.2 concentration effect the sr(ii) and cs(i) ions adsorption capacities of the m-go were given as a function of the initial concentrations of metal ions in figure 8(a-b). the solution concentration of sr(ii) and cs(i) was varied in the range 25–125 mg/l and 200–500 mg/l, respectively. as shown in figure 8a, when the strontium concentration increased, % adsorption value increased but the concentration value decreased from the 50 mg/l. the highest uptake for m-go adsorbent was calculated as 29.98% at 50 mg/l strontium concentration. this concentration was used in subsequent parameter assays. as shown in figure 8b, when the cesium concentration increased, % adsorption value increased but the concentration decreased from 250 mg/l concentration to the equilibrium. the highest uptake for m-go adsorbent was calculated as 57.2% at a cesium concentration of 250 mg/l. in subsequent parameter assays, this concentration has been studied at maximum adsorption. 3.2.3 effect of dosage (m/v) the adsorption of sr(ii) and cs(i) ions decreases by increasing the ratio of the mass of the m-go to volume of aqueous phase (m/v) (figure 9). the highest values for the adsorption was obtained using 0.01 ml sr/cs solution and 0.01 g adsorbent (m/ v) = 1 and it was taken as the optimum amount for other experiments for sr and cs adsorption. it can be concluded that low amount of nanocomposite can gives higher metals adsorption. increasing the adsorbent dose above 1 g/l have a little or no change on cs(i) removal while it can lead to significant removal for sr(ii). figure 7. a) the effect of ph on the adsorption of sr(ii) ions with m-go (c: 50 mg/l, m: 0.01 g, v: 10 ml, t: 120 min, t: 25 °c); b) the effect of ph on the adsorption of cs(i) ions with m-go (c: 250 mg/l, m: 0.01 g, v: 10 ml, t: 120 min, t: 25 °c). figure 8. a) the effect of initial concentration on the adsorption of sr(ii) ions with m-go (ph: 4, m: 0.01 g, v: 10 ml, t: 120 min, t: 25 °c); b) the effect of initial concentration on the adsorption of cs(i) ions with m-go (ph: 10, m: 0.01 g, v: 10 ml, t: 120 min, t: 25 °c). 69 figure 9. the effect of adsorbent dosage on the adsorption of sr(ii) and cs(i) ions with m-go (sr; ph: 4, c: 50 mg/l, m: 0.01 g, v: 10 ml, t: 120 min, t: 25 °c: cs; ph: 10, c: 250 mg/l, m: 0.01 g, v: 10 ml, t: 120 min, t: 25 °c). 3.3 adsorption equilibrium and isotherm models the adsorption process is a mass transfer operation that can be described mathematically by equilibrium and a rate process. the equilibrium is established between the concentration of the metal ions dissolved in aqueous phase and that bound to the adsorbent. the data obtained from experimental results is fundamental requirements for the design of adsorption systems. the data are used to develop equations and also to calculate isotherm parameters. by this way, the data, provide some insight into both the sorption mechanism and the surface properties and affinity of the sorbent can be used to compare different adsorbents under different operational conditions and to design and optimize an operating procedure[26–28]. in order to analyze the equilibrium data of the adsorption system, experimental data were fitted to langmuir, freundlich, dubinin–radushkevich, temkin, flory-huggins and brunauer, emmer & teller isotherms among the varied models. the constants of isotherm models along with correlation coefficients (r2) have been calculated from the plots for adsorption of cesium and strontium on the composite material and the results are given in table 1. adsorption equilibrium in the concentration range of 25–125 mg/l and 200–500 mg/l was studied with 10 mg of magnetic nanocomposite at 25 °c, 120 min contact time and ph 4 and 10.0 strontium and cesium, respectively. the langmuir isotherm, probably the most widely used model, assumes monolayer coverage of adsorbate over a homogeneous adsorbent surface[29]. the linear forms of the this model are expressed by the following equations: where qe is the amount of cesium and strontium ions adsorbed onto adsorbent; ce is the equilibrium concentration of these metals in solution, and q0 and bl are langmuir constants related to adsorption capacity and adsorption energy, respectively. q0 and bl were calculated from the slope and intercept of linear plots of ce/qe versus ce. the freundlich model has been used to describe adsorption of strontium and cesium from solution onto composite material. this model is not restricted to the formation of the monolayer coverage. it is assumes an empirical expression encompassing the surface heterogeneity and the exponential distribution of the energy of active sites as well as multilayer adsorption. linear form of freundlich model can be represented as follows[30]: where kf represents the adsorption capacity (mg/g), nf is a constant related to adsorption intensity (dimensionless). the data obtained are well described by the freundlich isotherm equation when plotted as logqe versus logce (figure 10). dubinin–radushkevich is the other model that used extensively to determine the type of adsorption for the removal of strontium and cesium[31]. this model was used to calculate the apparent free energy of adsorption, proposed an equation to find out the adsorption mechanism on the basis of the potential theory assuming a porous structure of the sorbent and heterogeneous surface. the linearized equation form of the d-r isotherm is given as: where cads (mmol/g ) is the amount of solute ad70 sorbed per unit weight of solid, xm (mmol/g or mg/ g) is the adsorption capacity, β (mol/k)2 is a constant related to energy and ε is the polanyi potential. polanyi potential can be computed by the following equation: where r is a gas constant in kj/mol and t is the temperature in kelvin. if lncads is plotted against ε2, β and xm can be obtained from the slope and intercept, respectively (figure 11). the adsorption mean energy (e), the free energy change when one mol of ion is transferred to the surface of the solid from infinity in the solution, is assumed by the following equation using the constant β: the temkin isotherm model contains a factor that obviously assuming adsorbent–adsorbate interactions. this model takes into account that heat of adsorption of all molecules in the layer would decrease linearly rather than logarithmic with coverage by neglecting the extremely low and large value of concentrations[32]. the temkin isotherm has generally been applied as follow: where, bte is the constant of temkin related to adsorption heat (j/mol); ate is the temkin isotherm constant (l/mg); r is the gas constant and t is the absolute temperature (k). bte and ate constants were calculated from the intercept and slope of straight line of the plot of the qe versus lnce.. the flory–huggins isotherm model was examined to account for the degree of surface coverage characteristics of the sorbate on the sorbent[33,34]. the equation of the isotherm is as follows: where, θ is the degree of surface coverage, kfh is the flory–huggins model equilibrium constant and nfh is the flory–huggins model exponent. θ is calculated using the following equation: the linearized equation of the model is given as: the constants of isotherm were extrapolated from plots of plot of log(θ/ci) versus log(1-θ), and values of kfh and nfh calculated from the slope and intercept of the plot and are shown in table 1. equilibrium constant (kfh) was used for the calculation of spontaneity of the gibbs free energy (δg0) on following equation: the negative values of δg0 confirmed the feasibility of the process and the spontaneous nature of adsorption ontoadsorbent. brunauer–emmett–teller (bet) isotherm model, related to the liquid–solid interface, is a theoretical equation, most widely applied in the gas–solid equilibrium systems[35]. this equation is presented as: where cbet, cs, qs and qe are the bet adsorption isotherm constants relating to the energy of interaction with the surface (l/mg), adsorbate monolayer saturation concentration (mg/l), theoretical isotherm saturation capacity (mg/g) and equilibrium adsorption capacity (mg/g), respectively[36]. linearized equation of the model is as follows: the curve was plotted between ce/qe(cs–ce) and ce/cs, and values of both constants qs and cbet were calculated from the intercept and slope. bet isotherm parameter for linear regression analyses and error functions are given in table 1. the high determination coefficients for linear 71 models show applicability of the model for metals adsorption using the present adsorbent. according to the correlation coefficients, the adsorption of strontium could be well described by freundlich equation. freundlich’s model theory is regarded as the heterogeneous adsorption and the exponential distribution of the energy of active sites as well as multilayer adsorption. dubinin and radushkevich isotherm provide a particularly good model for the adsorption of cesium. this model has reported that the characteristics of sorption curve is related to the porous structure of the sorbent. according to the results, the maximum adsorption capacities of strontium and cesium were calculated as 2.103 mg/g from freundlich model and 142.07 mg/g from dubinin–radushkevich model, respectively (table 1). the 1/nf value between 0 and 1 indicates that the adsorption is favorable under the experimental conditions. as seen in table 1, cesium adsorption on magnetic graphene composite was found high enough for separation. moreover, the value of 1/nf is known as heterogeneity factor and ranges between 0 and 1; the more heterogeneous the surface, the closer 1/nf value is to 0. the numerical value of 1/nf (< 1) indicates that adsorption capacity is only slightly suppressed at lower equilibrium concentration and the isotherm does not present any saturation of the solid surface of the sorbent by the sorbate[36]. one of the unique features of the dubinin–radushkevich isotherm model lies on the fact that it is temperature-dependent, which when adsorption data at different temperatures are plotted as a function of logarithm of amount adsorbed vs the square of potential energy, all suitable data will lie on the same curve, named as the characteristic curve[36]. the calculated e value is used to estimate the reaction mechanism of adsorption process. if value of e is smaller than 8 kj/mol, it indicates a physical adsorption. if value of e is higher than 8 kj/mol, the adsorption process is of a chemical nature. the e values obtained were 0.016 kj/mol and 0.129 kj/mol for strontium and cesium, respectively. therefore, the magnitudes of e values are in the energy range of physical adsorption for strontium and cesium[7,8]. table 1. isotherm constants of models for strontium and cesium adsorption onto m-go isotherm models parameters strontium cesium langmuir qo (mg/g) 256.410 434.78 bl (l/mg) 0.004 0.035 r2 0.9249 0.2483 freundlich kf (mg/g) 2.103 29.058 nf 0.772 1.973 r2 0.9987 0.4260 dubinin–radushkevich xm (mmol/g) 0.638 1.069 β (mol/kj)2 2.10–4 3.10–5 e (kj/mol) 0.016 0.129 r2 0.8843 0.9611 temkin ate (l/g) 5.820 6.991 bte (kj/mol) 0.245 0.025 r2 0,9235 0.4867 flory-huggins kfh 2.38.10–3 3.93.10–5 nfh 1.190 1.860 ∆g0 (kj/mol) 14.972 25.142 r2 0.1920 0.5004 brunauer, emmer & teller qs (mg/g) 3.753 39.745 cbet (l/mg) 0.421 2.020 r2 0.3481 0.5785 72 figure 10. linear isotherm models of freundlich for strontium adsorption on magnetic graphene oxide composite. figure 11. linear isotherm models of dubinin and radushkevich for cesium adsorption on magnetic graphene oxide composite. 3.4 kinetic parameters of adsorption a study on the kinetics of adsorption is carrying out to obtain information about the adsorption mechanism, which is important for the efficiency of the process[37]. therefore, two well-known kinetic equations were adopted to model the experimental data and identify the adsorption mechanism. in order to analyze the sorption of sr(ii)/cs(i) onto m-go, the pseudo first equation and pseudo second order equation was employed[38–40]: (15) 1 2 2 eet q t qkq t += where, qe is the amount of metal ion adsorbed onto adsorbent at equilibrium (mg/g); qt is the amount of metal ion adsorbed at various times; t (min) is the time of adsorption duration and k1 is the first order rate constant (min–1); k2 (g/mol∙min) is the second-order rate constant. the experiments were conducted at different concentrations 50, 100, 150 ppm for sr(ii) and 200, 250, 300 ppm for cs(i). from the slope ofeach linear trace, the rate constants were calculated and the results are presented in the table 2 and table 3 (pseudo-first-order model was not shown as figure because the r2 values of the adsorption of sr(ii) and cs(i) are low at the studied concentrations). the data obtained separately for each of the kinetic models from the slopes of plots show a good compliance with the pseudo second order equation. high r2 values for the linear plots showed that kinetic data fitted the pseudo second order adsorption kinetic equation for sr(ii) and cs(i) removal (figuer 12 and figure 13). the theoretical values of qe for sr(ii) and cs(i) removal also agree very well with the experimental ones. both facts suggest that the adsorption of sr(ii) and cs(i) onto m-go follows the pseudo-second-order kinetic model. therefore, the rate-limiting step may be chemical sorption or chemisorption through sharing or exchange of electrons between sorbent and adsorbate[5]. figure 12. pseudo-second-order plot for the adsorption of sr(ii) by m-go. table 2. rate parameters for the adsorption of sr(ii) onto m-go at various initial concentrations concentration 50 ppm 100 ppm 150 ppm pseudo-first-order model qe (mg/g) 1.8539 1.2600 4.5790 k1 (1/min) 0.0999 0.0096 0.0145 r2 0.0913 0.3406 0.0321 pseudo-second-order model qe (mg/g) 7.4404 16.7504 33.55 k2 (g/mol∙min) 1.1579 0.0627 1.1100 r2 0.9646 0.9823 0.7632 experimental qe (mg/g) 7.89 18.22 32.30 73 figure 13. pseudo-second-order plot for the adsorption of cs(i) by m-go. table 3. rate parameters for the adsorption of cs(i) onto m-go at various initial concentrations 3.5 thermodynamic studies in this study, the adsorption of sr(ii) and cs(i) onto m-go was examined in the temperature range of 25–40 °c under optimized conditions (sr: ph = 4, c: 50 mg/l, m/v: 1, t: 120 min; cs: ph = 10, c: 250 mg/l, m/v: 1, t: 120 min and adsorbent amount of 0.01 g). figure 14 (a-b) show the effect of temperature on the adsorption of sr(ii) and cs(i) on the nanocomposite, respectively. thermodynamic parameters like enthalpy change (δh0), entropy change (δs0) and free energy change (δg0) were estimated using the following equations. the enthalpy δh0 (kj/mol) and the entropy δs0 (j/molk) of adsorption can be determined from the slope and the intercept of the linear fits which are gained by drawing lnkd against 1/t respectively. the negative amounts δg0 show that the adsorption process is spontaneous for both of the ions. the values are well under those related to chemical bond constitution, showing the physical property of the adsorption process[41]. besides, the enthalpy variation δh0 following adsorption is negative in all cases representing the exothermic nature of the adsorption. the results indicated that the reaction efficiency decreased as the temperature increased for sr(ii) removal but the reaction efficiency increased as the temperature increased for cs(i) removal. the negative value of δs0 for sr(ii) shows the change in the randomness at the m-go-solution interface during the adsorption. the entropy variations δs0 of the system along with the adsorption of cs(i) ions on the m-go is positive in all cases, showing that more discover is generated following adsorption. the results were calculated in table 4. concentration 200 ppm 250 ppm 300 ppm pseudo-first-order model qe (mg/g) 69.47 100.74 120.46 k1 (1/min) 0.0203 0.0205 0.0257 r2 0.9586 0.7875 0.7567 pseudo-second-order model qe (mg/g) 104.17 96.15 86.96 k2 (g /mol min) 0.0051 0.0003 0.0059 r2 0.9965 0.8965 0.999 experimental qe (mg/g) 102.8 95.0 85.5 figure 14. plots of ln kd versus 1/t for sr (a) and cs (b) adsorption on m-go. table 4. thermodynamic parameters for sr(ii) and cs(i) sorption on m-go as a function of temperature m-go δho (kj/mol) δso (j/molk) δgo (kj/mol) 298 k 303 k 308 k 318 k sr(ii) –22.97 –18.37 –17.49 –17.42 –17.33 –17.24 cs(i) –5.17 33.35 –15.11 –15.28 –15.44 –15.61 74 4. conclusion m-go nanocomposite was synthesized using partial reduction co-precipitation method, which is simple, effective, economical and environmentally friendly technique for the removal of sr(ii) and cs(i) from aqueous solutions. prepared nanocomposite was characterized by sem, tem, xrd, ftir, xps and vsm. according to all characterization methods and literature data, we can conclude that m-go was successfully prepared and possessed with the desired properties. the adsorption capacity of m-go for sr(ii) and cs(i) were found as 2.103 mg/g and 142.070 mg/g, respectively. kinetic results indicated that the adsorption process could be defined by the pseudo-second-order kinetic model under the selected strontium and cesium concentration range which provides the best correlation of the data in all cases and the experimental qe values agree with the calculated ones and the adsorption isotherm was fitted well to freundlich model and d-r model for sr(ii) and cs(i), respectively. the thermodynamic analysis of the sorption process for both of the radionuclides indicates that the system is spontaneous and exothermic. the values of δg0 for sr(ii) and cs(i) are well under those related to chemical bond constitution, showing the physical property of the adsorption process. it could be therefore concluded that the sorption mechanism was dominated by physisorption, but the overall observations suggest that the sorption process was administrated by combination of several mechanisms, such as physical sorption, ion exchange and complexation. based on the results, m-go can effectively remove the strontium and cesium ions from aqueous solutions. author contributions sule aytas, sabriye yusan and senol sert performed the experiments and analyzed the data. sule 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chemistry 2010; 174: 756–762. 41. almeida cap, debacher na, downs aj, et al. removal of methylene blue from colored effluents by adsorption on montmorillonite clay. journal of colloid and interface science 2009; 332(1): 46–53. characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.2033 1 original research article decontamination of surface water from organic pollutants using graphene membranes stefano bellucci infn-laboratori nazionali di frascati, via e. fermi 54, frascati 00044, italy. e-mail: bellucci@lnf.infn.it abstract in this paper, we deal with one of the most urgent and relevant topics nowadays, i.e., water pollution. the problem is finding a valid candidate for the absorption and removal of different kinds of pollutants commonly found in water. there are already some indications about graphene oxide as a potential candidate. in the present work, we take a step forward to show how graphene nanoplatelets (rather than the oxide form of this material) are capable of decontaminating water. in this starting step, we use a specific substance as a model pollutant, i.e., acetonitrile, leaving for the future steps, to extend the analysis to additional types of pollutants. in addition to laboratory-produced graphene nanoplatelets, we already examined in the past; now we wish to consider also commercially available ones, so that the new results will not be bound to a laboratory (low technology readiness level) material, but will become interesting also from the industrial point of view, thanks to the scalability of the nanoplatelets production. for this aim, we compare the performance of two types of filters based on two classes of nanomaterials, i.e., those produced by microwave and ultrasound assisted exfoliation, already analyzed in our earlier works, with those commercially distributed by an italian company, i.e., nanesa, http://www.nanesa.com/. the latter is an innovative sme involved in the production of graphene-based nanomaterials. we focus here in the graphene nanoplatelets, commercially available in industrial batches (gxnan grades). the present study leads to determine which filtering membrane, among the various types of commercial graphene considered, shows the greatest stability, and the lack of breakage of the membrane, concentrating on such accessory features, given that all types of graphene showed excellent adsorption properties. keywords: water decontamination; graphene nanoplatelets; acetonitrile; filtering membranes 1. introduction one of the most important problems nowadays is the contamination of the environment and more specifically of surface and underground waters by toxic substances, e.g., heavy metals and organic pollutants. shortage of supplies of potable water is occurring in many areas worldwide, owing to the steady increase of the population, yielding to the harsh exploitation of water resources by human activities, which introduce many contaminants, including organic dyes, heavy metal ions, salts of light metals. in order to contrast what has by now already turned into one of the most severe concerns in the world’s community, it is necessary to carry out the decontamination of wastewater[1,2]. graphene oxide (go) is a valid candidate for the absorption and removal of pollutants in water. recently, several articles have shown that synthetic go has high adsorbing capacities towards dyes, antibiotics and heavy metals[3]. this is probably due to its large surface area and the presence of different functional groups containing oxygen on the surface, which make each atom of this element available to chelate the metal ion. article info received: 17 april 2023 accepted: 8 june 2023 available online: 19 june 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 further experiments were conducted with zinc ions, hypothesizing that the main force of absorption is ion exchange, while electrostatic interaction could also influence the process. in fact, the results show that the absorption depends strongly on the ph of the solution and slightly on the presence of foreign ions and the ionic strength of the solution. also in this case, the thermodynamic parameters indicate a spontaneous and endothermic absorption[3]. another form of graphene commonly used in literature is that of the graphene nanoplatelets (gnp), characterized by a number of sheets between 2 and 11, stacked on one another, which are often called double-, few-, or multi-layered graphene sheets. they are different both from the graphene, composed of a single layer of carbon, and from the graphite, which implies a structure of 8 or more sheets of graphene; they can therefore be considered an intermediate phase, with distinct properties that vary according to the number of layers, until the structure of the graphite is reached. gnps are known as quasi-graphene, and precisely because their properties vary according to the number of sheets, it is good to specify the type of nanoplatelets with which one is working (i.e., to indicate the number of layers from which they are composed). once the 8 layers have been overcome, the electronic properties of the structure change, being more similar to those of graphite, so in these cases the nanostructures are considered[4]. such a low-cost type of graphene has already drawn great interest due to its potential use in large scale industrial production. it has also been used for water decontamination, using filters realized by a disk of pressed graphene nanoplatelets. in the study of ferrigno et al.[5], the fabrication, modeling and experimental characterization of a monitorable and renewable pollution filter based on graphene nanoplatelets was considered. the main goal was to demonstrate a method to monitor the status of such a filter in real time during its operating phases: pollutant adsorption, saturation, and regeneration. the graphene nanoplatelets were obtained by exploiting the thermal expansion of commercial intercalated graphite. this exfoliation method, assisted by microwave irradiation, represents a lowcost and ecologically friendly method to obtain the needed nanomaterial. the filter was used here to adsorb acetonitrile, a water-soluble organic compound with a triple bond, widely adopted in industrial processes, as well as in some industrial solvents and paints. the main results obtained in the study of ferrigno et al.[5] were twofold. firstly, the graphene filter was shown to be effective in adsorbing the selected pollutant, with the additional feature of being fully renewable: all the pollutant can be removed from the filter without the need of costly physical or chemical processes. secondly, monitoring of the time-evolution of the electrical impedance allowed efficient detection of the different phases of the filter life cycle: clean, polluted, saturated and regenerated. let us recall why the measurement of the membrane impedance parameter allows to understand the actual absorption (including possible evaporation) of the pollutant (e.g., acetonitrile). indeed, the method proposed by ferrigno et al.[5] when monitoring the electrical impedance filter in real time, during the filtering operation, relied upon the interpretation of the latter physical observable using an equivalent circuit model, thanks to the well-known high sensitivity of the graphene electrical properties to the presence of external elements adsorbed in its lattice. the variations of the filter’s resistance thus provided the markers to the filter cycle: the peaks of such a variation indicated the start and the end of the adsorption, whereas the reduction of the standard deviation showed that the filter went back to be clean[5]. this article[6] proposed a similar approach, emphasizing the smart monitoring of the life cycle of the same kind of graphene nanoplatelets-based filters for water remediation in the presence of pollutants. the measurement technique was based on suitable figures of merit, analyzing the time variation of the electrical impedance frequency spectrum. the study of miele et al.[6] considered, in addition to the acetonitrile, also the remediation of another toxic industrial pollutant, i.e., the 2,4-dichlorophenol. it is well known that production of graphene nanoplatelets through liquid exfoliation, sonication and centrifugation of graphite in suitable solvents 3 is a practical approach to prepare graphene dispersions. in the study of gomez et al.[7], a detailed experimental and theoretical investigation seeking to explain the liquid exfoliation of graphene in polar solvents at short sonication time was presented, demonstrating that the short-time exfoliation process can only be optimized by dispersing graphene in dimethylformamide (dmf) and that edge-type defects are most noticeable when graphene is exfoliated in ethanol. however, precisely the aim of our production with the assistance by microwave is the avoidance of such non-green chemical compounds. the recent paper[8] studied the temperature dependence of the electrical resistivity of low-cost commercial graphene-based strips, made from a mixture of epoxy and commercial graphene nanoplatelets produced by nanesa[9]. the results suggest that such materials can be used as thermistors in sensing or heating applications. we considered the same commercial (nanesa) graphene nanoplatelets to prepare filters, by the procedure adopted by ferrigno et al.[5] and miele et al.[6], for the graphene nanoplatelets developed within the infn frascati laboratories[10,11], where the anticorrosion properties of the infn laboratory-grade nanoplatelets were explored, suitable for the adsorption of acetonitrile. the advantage of using commercially available nanomaterials is obvious, both for reducing the cost of the filters and the scaling-up of the process, to reach a higher level of technological maturity of the products for environmental remediation. clearly, the topic of water depollution from organic substances, we treat in this paper, has been the subject of extensive investigations over the years. a short list of the published works in this connection can be given as [12–24]. 2. materials and methods the main activity concerned the creation of filters/membranes in graphene that have been used for the decontamination of surface waters polluted with agents of organic nature. we considered essentially two types of filters to compare, consisting of:  graphene nano-platelets (gnp), developed within the infn frascati laboratories[10];  graphene made available by nanesa (g2nan, g3nan, g4nan and g7nan)[9]. the standard procedure for filter creation follows the criteria described here. an amount equal to 200 mg of gnps/graphene nanesa was prepared and dispersed in 400 ml of isopropyl alcohol inside a beaker (the choice of the solvent to be used fell on isopropyl alcohol, being the best from a cost/benefit point of view, in which gnps are completely dispersed), as shown in figure 1. figure 1. 200 mg graphene in 400 ml isopropyl alcohol. the resulting solution was subjected to sonication through the use of the sonics vibracell ultrasonic tip. the ultrasonic tip was set in the following mode: a one-second pulse at 40% power alternating with a one-second rest for a total sonication time of 1 h; the choice of pulse mode and power are both optimal in order not to obtain excessive heating of the solution, also allows a good separation of the graphene planes (figure 2). figure 2. ultrasounds tip sonics vibracell. 4 once sonication was finished, the solution was vacuum filtered using a ptfe (polytetrafluoroethylene) filter with a porosity of 0.2 μm, which allows the passage of isopropyl alcohol molecules but not the dispersed nanoparticles, so that these can be deposited. subsequently, the nanoparticle layer was collected and placed in an oven at 85 ℃ to allow complete evaporation of the isopropyl alcohol, whose evaporation temperature is 82.6 ℃. finally, each gnp/graphenenanesa membrane made by this procedure was pressed in an automated press with a force of 700 n. unfortunately, the properties belonging to the different types of commercial graphene do not allow us to use the same procedure previously used for graphene nano-platelets (gnps) of the infn frascati laboratories[10]. the changes made were as follows:  g2nan: as shown in figures 3 and 4, the amount of graphene is sufficient to maintain the ratio 1:2 (200 mg graphene, 400 ml isopropyl alcohol). the negative note concerns the quality of the membrane, from the images is evident the presence of lumps and a nonhomogeneous distribution of the material, which irreversibly damage the final product. figure 3. g2nan standard procedure. figure 4. g2nan standard procedure.  to overcome these problems, we resorted to a prolonged sonication anticipated by the use of an additional instrument, the mechanical disperser ika t10 basic ultra-turrax® (figures 5 and 6). figure 5. mechanical disperser. figure 6. mechanical disperser in action. 5 standard procedure g2nan procedure ratio graphene/isopropyl alcohol 1:2 ratio graphene/isopropyl alcohol 1:2 mechanical dispersion no mechanical dispersion yes (1 h, 10 min on/ 10 min off at power 3) sonication 1 h sonication 2 h  g3nan: as with g2nan, the use of a mechanical disperser followed by a prolonged sonication phase is necessary (figure 7). moreover, a further problem results from the quantity of the product. in fact, 200 mg of graphene are not necessary to form a disc with adequate thickness (>0.5 mm). therefore, it was decided to switch from a 1:2 ratio to a 1:1 one, thus inserting 400 mg of g3nan inside 400 ml of isopropyl alcohol (figure 8). figure 7. g3nan 200 mg standard procedure. figure 8. g3nan 400 mg standard procedure. standard procedure g3nan procedure ratio graphene/isopropyl alcohol 1:2 ratio graphene/isopropyl alcohol 1:1 mechanical dispersion no mechanical dispersion yes (1 h, 10 min on/ 10 min off at power 3) sonication 1 h sonication 2 h the reason for doubling the amount of g3nan graphene compared to g2nan could depend on the average particle lateral size (average particle lateral size), which for g2nan is 30 µm while for g3nan it is 15 µm.  g4nan: see the g3nan procedure. in this case, we double the amount of graphene compared to g2nan because of the bulk density, which for g2nan is about 0.036 g/cm3 (average between 0.020 and 0.042 g/cm3), while for g4nan is 0.07 g/cm3. so, for the same weight, g2nan will take up much more space than g4nan. differences between g4nan discs at 200 mg and 400 mg are shown in figures 9 and 10. figure 9. g4nan 200 mg. figure 10. g4nan 400 mg. 6 standard procedure g4nan procedure ratio graphene/isopropyl alcohol 1:2 ratio graphene/isopropyl alcohol 1:1 mechanical dispersion no mechanical dispersion yes (1 h, 10 min on/ 10 min off at power 3) sonication 1 h sonication 2 h  g7nan: with this last type of graphene, it was not possible to create discs/filters, because of the properties that characterize it. the apparent density (bulk density) is remarkable compared to the other products, equal to 0.2 g/cm3, therefore a considerable weight was derived. in addition, the average lateral particle size (average particle lateral size) is extremely small (about 12 µm), giving g7nan considerable fineness. therefore, attempts to create a membrane using 200 mg, 400 mg, and 800 mg (thus with a 2:1 graphene/isopropyl alcohol ratio) of g7nan were not sufficient (figures 11, 12, and 13). figure 11. g7nan 200 mg. figure 12. g7nan 400 mg. figure 13. g7nan 800 mg. once the filter formation procedure was completed, their ability to absorb acetonitrile (ch3cn), the simplest organic nitrile, was evaluated. this was accomplished through the use of mfia. the mfia (from zurich instruments, zurich, switzerland) is a digital impedance analyzer and precision lcr meter that sets the new standard for impedance measurements in the frequency range of 1 mhz to 5 mhz. the mfia features a basic accuracy of 0.05%, high measurement repeatability, and small temperature variation. the mfia meter was connected to the graphene membrane through metal rings used as “inductive plates” (figure 14). the plates have an outer diameter of 4.5 cm, an inner diameter of 2.5 cm, and a thickness of 4 mm, perforated in the center to allow the insertion of a ppr (a type of plastic for plumbing uses) tube, into which acetonitrile is inserted during the experiment. the graphene membrane, being a conductor, is then inserted in contact with the two plates and the tube. by doing so, the set-up allows the measurement of the impedance parameter of the membrane, allowing in turn to understand the actual absorption (along with any evaporation) of the acetonitrile released during the experiment. figure 14. inductive plates. 3. results and discussion impedance measurements determined with the mfia instrumentation involved the following steps:  once the membrane was inserted inside the inductive plates, the mfia was operated, beginning to measure the impedance value for 30 min; 7  after 30 min, 1 ml of acetonitrile was released inside the ppr tube leading directly to the membrane;  finally, the impedance was calculated for a minimum time of 2 h after release. in table 1, for each variety of commercial graphene, the thickness, the number of tests performed, and the weight change during the phases of the membrane use are specified. table 1. thickness, number of tests performed, and weight change of the membrane g2nan g3nan g4nan diameter 33.8 mm thickness 0.8 mm 1.3 mm 0.7 mm 1st test initial weight 0.1948 g 0.3757 g 0.2318 g final weight 0.1943 g 0.3757 g 0.2309 g 2nd test initial weight 0.1942 g 0.3757 g 0.2309 g final weight 0.1942 g 0.3741 g 0.2270 g 3rd test initial weight 0.1942 g 0.2244 g final weight 0.1941 g 0.2202 g one can be puzzled about the reason why the thicknesses of the tested membranes differ significantly. this is due to the different characteristics (e.g., porosity) of the different types of graphene used, which yielded also in different values of the membrane mass, resulting from filtration. nevertheless, there was no effect of the thickness on membrane fracture during testing. as one can see from the table:  the diameter of the discs will always remain unchanged and equal to 33.8 mm, while the thickness will vary depending on the material (as has been seen before);  as far as weight is concerned, a slight decrease is observed at each test performed, mainly caused by the fragile and extremely delicate nature of graphene, which involves minimal but inevitable losses every time the filter is handled to set-up. the decrease in weight is also an indication of total evaporation of the acetonitrile once the tests are completed;  finally, it must be taken into account that for the two filters g3nan and g4nan, the end of the second and third test (respectively) corresponds to the breakage of the filter itself, confirming once again the fragility of the product. with the exception of the membrane obtained using g2nan, which is much more stable, a property that can be understood from the minimal weight variations with respect to the other two membranes. the data released by mfia measurements mainly provide the trend of the absolute value of the impedance (퐴푏푠(푍) = |푍� + 푗푍��| = �(푍�)� + (푍��)�), a function of frequency (with a range from 80 hz to 1 mhz). three frequencies were taken as reference, in an attempt to cover the entire measured range. they are 50 khz, 500 khz and 1 mhz. the graph in figure 15 shows the behavior of impedance as the frequency varies. the increase in frequency involves the formation, a few minutes after the release of acetonitrile, of a depression (probably due to the acceleration of the evaporation process due to higher frequencies). this trend was found for each type of graphene studied. figures 16–21 show the behavior of abs(z) as time varies for the different tests performed, the frequencies taken into account will be 50 khz and 1 mhz. 8 figure 15. g4nan, influence of frequency in the behavior of abs(z). figure 16. g2nan, time dependence of abs(z) at 50 khz. figure 17. g2nan, time dependence of abs(z) at 1 mhz. figure 18. g3nan, time dependence of abs(z) at 50 khz. figure 19. g3nan, time dependence of abs(z) at 1 mhz. figure 20. g4nan, time dependence of abs(z) at 50 khz. figure 21. g4nan, time dependence of abs(z) at 1 mhz. from the above graphs, it can be seen that the abs(z) curve tends, after the initial surge due to the release of acetonitrile (which occurs around 1,800 s), to stabilize within 5,000 s, which corresponds to 9 about 50 min after release. in the abs(z) curves, there are, however, several problems:  not all of them start from the same impedance value and no correlation is visible between the different values calculated in the different tests performed;  the frequency dependence does not make the curves regular, especially for those at high frequencies (1 mhz);  the final impedance values are usually different from the initial ones. these problems are also found in table 2. in the table, the following values of abs(z) have been selected:  initial, equal to the average of the values calculated from the mfia meter power-up to the time of release (thus 30 min);  release;  after 15 min, equal to 900 s from release;  after 30 min, equal to 1,800 s from release;  after 1 h, equal to 3,600 s from release;  after 2 h, equal to 7,200 s from release. the reference frequency is 50 khz because, as mentioned earlier, at low frequencies, the curves tend to be more regular. next to the value of abs(z), there is its percentage value, established in the range that varies from the initial value and the maximum point obtained during the release phase of the organic substance. table 2. values of abs(z) at the reference frequency of 50 khz (frequency = 50 khz) g2nan g3nan g4nan abs(z) percentage abs(z) percentage abs(z) percentage 1st test initial 0.54774 0 0.41605 0 0.43705 0 release 0.82347 100 0.57156 100 0.69511 100 after 15 min 0.74348 70.98974 0.50505 57.23105 0.59532 61.33070 after 30 min 0.65852 40.17698 0.40843 −4.90001 0.46182 9.59854 after 1 h 0.6129 23.63181 0.37106 −28.93062 0.40946 −10.69131 after 2 h 0.59107 15.71465 0.355 −39.25793 0.3738 −24.50980 2nd test initial 0.57837 0 0.57666 0 0.26446 0 release 0.94365 100 0.88898 100 0.41087 100 after 15 min 0.8012 61.00252 0.7406 52.49103 0.35029 58.62304 after 30 min 0.67368 26.09231 0.57691 0.08005 0.29362 19.91667 after 1 h 0.59391 4.254271 0.43246 −46.17059 0.27005 3.81805 after 2 h 0.56059 −4.86750 0.40175 −56.00346 0.25738 −4.83574 3rd test initial 0.49303 0 0.26947 0 release 0.85536 100 0.42716 100 after 15 min 0.74755 70.24536 0.37514 67.01122 after 30 min 0.64928 43.12367 0.30658 23.53352 after 1 h 0.58137 24.38109 0.27652 4.470797 after 2 h 0.5599 18.45556 0.25804 −7.24840 the dependence of the abs(z) curve on frequency can only depend on the behavior of one of its two components, the real part z′ and the imaginary part z′'. 푍 = 푍� + 푗푍�� figure 22 below allows us to understand that the frequency dependence comes mainly from the real part of the impedance z′, which follows almost at every point the trend of abs(z), thus forming in turn the depression caused by high frequencies (in this case 1 mhz). 10 figure 22. time dependence of the real and the imaginary parts of the impedance z, at the reference frequency of 1 mhz. the imaginary part z′', less affected by the frequency, shows a very regular curve, in which the final values are close to the initial ones. for this reason, it has been taken as a reference in figures 23–25. for visual purposes, in the graphs, the value of the imaginary part shown will be � � ����� �. figure 23. time dependence for g2nan, at the frequency of 1 mhz. figure 24. time dependence for g3nan, at the frequency of 1 mhz. figure 25. time dependence of abs(1/(1+z′') for g4nan, at the frequency of 1 mhz. in table 3 (as it was done in table 2), certain values of abs(1/(1+z′') and their reference percentages have been taken into account. table 3. values of abs(1/1+z′') at the reference frequency of 1 mhz (frequency = 1 mhz) g2nan g3nan g4nan abs(1/1+z′') percentage abs(1/1+z′') percentage abs(1/1+z′') percentage 1st test initial 0.96959 0 0.98036 0 0.93482 0 release 1.32846 100 1.15287 100 1.20272 100 after 15 min 1.22302 70.61888 1.10348 71.36977 1.09462 59.64912 after 30 min 0.98264 3.63641 0.99076 6.02863 0.9398 1.85890 after 1 h 0.98012 2.93421 0.98984 5.49533 0.94005 1.95222 after 2 h 0.97962 2.79488 0.98964 5.37939 0.94712 4.59126 2nd test initial 0.98224 0 0.95113 0 0.97639 0 release 1.51257 100 1.41321 100 1.06982 100 after 15 min 1.31348 62.45922 1.2376 61.99575 1.03621 64.02654 after 30 min 1.01198 5.60782 1.04427 20.15668 0.97805 1.77673 after 1 h 0.9993 3.21686 0.9753 5.23069 0.97868 2.45103 after 2 h 0.99866 3.09618 0.97126 4.35638 0.97936 3.17885 3rd test initial 0.97363 0 0.9761 0 release 1.35176 100 1.0615 100 after 15 min 1.23131 68.14587 1.03219 65.67915 after 30 min 0.99927 6.78073 0.97634 0.28103 after 1 h 0.98095 1.93584 0.97729 1.39344 after 2 h 0.98032 1.76923 0.97801 2.23653 11 from the percentages in table 3 it is evident that, for all types of graphene (g2nan, g3nan and g4nan), 30 min after the release of acetonitrile, the values of z′' have returned almost completely to their original values, which implies the total evaporation of our organic compound. in the curves depicting the behavior of z′', there are small “jumps”, which can also be seen in figure 26 and figure 27. these small deviations allow us to understand the sensitivity of the mfia instrumentation, because they are most likely due to imperceptible movements or vibrations in the vicinity of the conductive plates that contain the membrane. figure 26. evidence of small jumps in the time dependence of figure 25. figure 27. magnified view of the inset in figure 26. furthermore, we can conclude that all types of graphene show excellent adsorption properties, with virtually total evaporation of the absorbed acetonitrile after about 30–40 min after its release inside our filters (table 3 and figures 23–25), also clear from the total absence of additional weight at the end of processing (table 1). clearly, more work is needed to optimize, from the industrial viewpoint such devices, e.g., in testing the additional feature of being fully renewable and then regenerating them, in view of their possible use in relation to industrial processes, where industrial solvents and paints are involved. nevertheless, the present device already represents a low-cost and ecologically friendly method to obtain the needed nanomaterial and the related membranes, to be employed as filters. 4. conclusions the study shows, first of all, that all types of graphene show excellent adsorption properties. moreover, it leads to the following conclusions, i.e., that among the three types of graphene seen, g2nan shows the greatest stability, evident from the virtually no decrease in weight during measurements (as seen in table 1) and the lack of breakage of the membrane (unlike g3nan and g4nan). the results we obtained in the present investigation, corroborate the idea that graphene materials yield is a valid candidate for the absorption and removal of pollutants in water, owing to their high adsorbing capacities towards pollutants, which appear to be due to the effect of a large surface area available. acknowledgments we acknowledge the participation of a. lustrissimi and the support and encouragement by f. bertocchi during the early stages of this work, data availability statement data are available by the 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destruction of pollutant. composites part b: engineering 2020; 184: 107666. doi: 10.1016/j.compositesb.2019.107666. 24. asefi d, arami m, sarabi aa, mahmoodi nm. the chain length influence of cationic surfactant and role of nonionic co-surfactants on controlling the corrosion rate of steel in acidic media. corrosion science 2009; 51(8): 1817–1821. doi: 10.1016/j.corsci.2009.05.007. characterization and application of nanomaterials (2023) volume 6 issue 1 doi: 10.24294/can.v6i1.2538 1 original research article surface grafting of cellulose triacetate hollow fiber membranes with ag@zno-hyperbranched polyglycerols nanoparticles for constructing antifouling and antibacterial surfaces xiujing huang, yingbo chen* state key laboratory of separation membranes and membrane processes, school of materials science and engineering, tiangong university, tianjin 300387, china. e-mail: bocy2009@hotmail.com abstract in recent years, using novel nanomaterials to improve the antifouling and antibacterial performance of reverse osmosis membranes has received much attention. in this study, hydrophilic ag@zno-hyperbranched polyglycerols nanoparticles were fabricated by ring-opening multibranched polymerization of glycidyl acid with the core-shell ag@zno nanoparticles. the cellulose triacetate composite membranes were prepared by grafting ag@zno-hpgs nanoparticles on the surface of cellulose triacetate membranes. the surface of the nanoparticles with active functional group –oh was confirmed by x-ray photoelectron spectroscopy and fourier transform infrared spectroscopy. surface morphology, charge, and hydrophilicity of the composite membranes were characterized by scanning electron microscope, zeta potential, and contact angle analysis. the results showed that grafting the ag@zno-hpgs nanoparticles onto the cellulose triacetate membrane surface improved the physical and chemical properties of the cellulose triacetate composite membranes. the water flux of cellulose triacetate composite membranes increased while the salt rejection rate to nacl slightly decreased. meanwhile, the cellulose triacetate composite membranes showed excellent antifouling properties of having a high flux recovery. the antibacterial performance of the cellulose triacetate composite membrane against e. coli and s. aureus was prominent that the antibacterial rates were 99.50% and 92.38%, and bacterial adhesion rates were as low as 19.12% and 21.35%, respectively. keywords: core-shell nanoparticles; hyperbranched polyglycerol; cellulose triacetate; reverse osmosis membrane; antifouling 1. introduction reverse osmosis (ro) technology, as an advanced technology for wastewater treatment and seawater desalination, has received continuous and extensive attention due to its efficient removal of small molecules and salt ions and is considered to be an effective way to solve the current water shortage[1–3]. whereas, the ro membrane is polluted inevitably by a variety of organics, inorganic matters, colloids, and microorganisms in the practical application process[4,5]. these substances are adsorbed and deposited on the ro membrane surface, leading to a decrease in permeate flux and an increase in operating pressure. membrane fouling increases the costs of operation and maintenance and limits the application and development of ro membranes[6,7]. in previous research, the ro membrane with the surface characteristics of high hydrophilicity and neutral charge shows remarkable antifouling performance because the interaction between pollutant article info received: 9 march 2023 accepted: 28 april 2023 available online: 7 may 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 and membrane surface is reduced[5,7,8]. two mainly common modification methods for membrane surface are surface coating and surface grafting[9,10]. the surface coating method is simply coating with a layer of hydrophilic polymer on the membrane surface. although the preparation process of the surface coating method is very simple, the coating is gradually washed off during subsequent application since no chemical bond between the modifier and the membrane surface[11]. different from the surface coating method, surface grafting anchored the modifier on the membrane surface through a chemical reaction, which provides the possibility for long-term and stable practical operation and endows the membrane with long-term and effective antifouling performance. in recent years, nanocomposite membranes consisting of polymers and inorganic or organic nanomaterials have been widely developed for modifying ro membranes. the permeability, selectivity, and stability of composite membranes were improved by introducing the inorganic nanomaterials into polymer membranes. the composite membranes have even gained excellent fouling performance by selecting an appropriate nanomaterial. nanomaterials have been reported including silver (ag)[12], copper[13], titanium dioxide[14], silicon dioxide[15], graphene oxide[16,17], and graphene quantum dots[18]. ag nanoparticles, as one of the most common antibacterial nanomaterials, were applied in many studies to improve the antifouling performance of separation membranes and could be modified to obtain better properties[19–21]. researchers conducted several studies that showed the great potential of ag nps in areas such as antimicrobial action and the degradation of organic pollutants[22–25]. however, inorganic nanomaterials generally have poor hydrophilicity and need further modification. hyperbranched polyglycerols (hpgs) have the hydrophilic structure of polyether polyols and are one of the most popular hyperbranched polymers. hpgs with highly active functional hydroxyl terminal groups are easily synthesized in one reactor on a large scale and show good water solubility[26–28]. in addition, hpgs have received extensive attention in the field of antifouling surface modification due to their dendritic structure, low toxicity, stable chemical properties, easy-to-be synthetic, and good hydrophilicity[28,29]. in our previous research, hydrophobic silver@zinc oxide (ag@zno) nanoparticles with the core-shell structure were synthesized[30]. on this basis, in this study, hydrophilic ag@zno-hyperbranched polyglycerols (hpgs) nanoparticles with a surface layer of hpgs were prepared by ring-opening multi-branched polymerization of glycidyl. the cta composite membranes were fabricated by grafting ag@zno-hpgs nanoparticles on the cta ro membrane surface with bonding sites of acyl chloride groups. ring-opening multi-branched polymerization has the advantages of easy handling and high yields[31]. the morphology, size, crystal structure, and surface chemical composition of the nanoparticles were studied in detail. the effects of ag@znohpgs nanoparticles on the hydrophilicity, surface charge, surface morphology, and permeability of the cta composite membranes were systematically analyzed. the antifouling performance of the composite membranes was evaluated with bsa as a model foulant. finally, e. coli and s. aureus were used as microbial models to investigate the antibacterial properties of the composite membrane, and the longterm release of ag+ was evaluated. this work suggested a modification of the ro membrane for longterm use and provided a research way for the development of an antifouling ro membrane with high performance. 2. experimental 2.1 materials hollow fiber cellulose triacetate (cta) reverse osmosis membranes (outside diameter = 400 μm, inside diameter = 200 μm, thickness = 100 μm) were provided by tianjin motimo membrane technology co. ltd. (tianjin, china). silver acetate, zinc acetylacetonate, oleyl amine, glycidol, succinyl chloride, and bovine serum albumin (bsa) were supplied by aladdin chemistry co. ltd. (shanghai, china). 1dodecanol, ethyl alcohol, n-hexane, methylbenzene, triethylamine, and nitric acid were obtained from kemiou fine chemical research institute (tianjin, china). sodium chloride (nacl) and acetone were 3 supplied by fengchuan fine chemical research institute (tianjin, china). e. coli and s. aureus were used for the anti-bacterial experiments and were supplied by tianjin medical university (tianjin, china). phosphate buffer saline (pbs, ph = 7.4) solution was prepared with the following salts (nacl: 8.00 g/l, kcl: 0.20 g/l, na2hpo4: 1.56 g/l and kh2po4: 0.20 g/l) which were obtained from fengchuan fine chemical research institute (tianjin, china). yeast extract was purchased from guangfu technology development co. ltd. (tianjin, china). peptone and agar were provided by beijing aoboxing bio-tech co. ltd. (beijing, china). all chemicals were used as received. in the above experimental materials, bsa, yeast extract, peptone, and agar powder were pure as biological reagents, while the rest of the reagents were analytically pure and were not further purified in the process of use. 2.2 synthesis of ag@zno and ag@znohpgs nanoparticles the core-shell ag@zno nanoparticles were synthesized by a two-step method[30]. first, 1-dodecyl alcohol (50 ml) and oleyl amine (10 ml) were mixed in a 250 ml three-neck flask under stirring and heated to 210 ℃. after adding silver acetate (0.55 g), the reaction lasted for 1 h before cooling to 140 ℃, and then zinc acetylacetone (1.32 g) was added to the mixture and continued the reaction for another 2 h. the dark brown mixture was cooled to room temperature and precipitated by adding ethanol. the sediments were collected by centrifugation (rotational speed was 10,000 r/min), which were further purified by washing with hexane and ethanol 2–3 times. finally, the dispersion of the hydrophilic ag@zno nanoparticles was obtained by dispersing the product in hexane. the powder of ag@zno nanoparticles was obtained after drying in a vacuum oven at 100 ℃ for 24 h. ag@zno-hpgs nanoparticle was prepared by grafting hpgs over the ag@zno nanoparticles via ring-opening multibranched polymerization, as shown in figure 1. first, 1-dodecyl alcohol (50 ml) and oleyl amine (10 ml) were mixed in a 250 ml three-neck flask under stirring and heated to 210 ℃. after adding silver acetate (0.55 g), the reaction lasted for 1 h before cooling to 140 ℃, and then zinc acetylacetone (1.32 g) was to the mixture and continued the reaction for another 2 h. the mixture was cooled down to 120 ℃ and glycidyl was added slowly. the reaction was performed for 12 h under the n2 atmosphere after the temperature no longer changed. the brown mixture was cooled to room temperature and precipitated by adding acetone. the sediments were collected by centrifugation (rotational speed was 8,000 r/min), which were further purified by washing with water. the suspension solution was extracted by centrifugation (rotational speed was 6,000 r/min) and added acetone to precipitate again. the sediments were collected by centrifugation (rotational speed was 8,000 r/min) and dried in a vacuum oven at 100 ℃ for 24 h to obtain ag@zno-hpgs nanoparticles. figure 1. reaction scheme for the synthesis of ag@zno and ag@zno-hpgs nanoparticles. 2.3 preparation of cta composite membrane cta hollow fiber membranes were cut into 30 cm in length and dried at room temperature for 24 h before sealing the ends with epoxy resin. the cta hollow fiber membrane was immersed in succinyl chloride/toluene solution with different concentrations at 50 ℃ for 15 min. the excess solution was removed before the membrane was soaked in the ag@zno-hpgs/triethylamine aqueous solution for 4 5 min at 30 ℃. triethylamine was an acid-binding agent and acted as a catalyst. after draining the excess aqueous solution, the membrane was undergone heat treatment in an oven at 60 ℃ for 5 min. finally, the cta composite membrane was fabricated and immersed in deionized water for 24 h before measuring. the specific process of the modification was shown in figure 2. figure 2. schematic diagram for the modification process of cta composite membranes. 2.4 characterizations of ag@zno and ag@zno-hpgs nanoparticles the chemical structures of ag@zno and ag@zno-hpgs nanoparticles were characterized by an ultraviolet-visible spectrometer (uv-vis spectrometer, uh4150, hitachi, japan) and fourier transform infrared spectroscopy (ftir, nicolet is50, thermo fisher scientific, usa). the crystal structures of the nanoparticles were analyzed by x-ray diffraction (xrd, ultima iv, rigaku corporation, japan) with 2θ ranging from 10° to 80° (scanning speed: 2° min−1). to characterize the morphology of the nanoparticles, samples were prepared by drying a drop of the suspension of ag@zno nanoparticles in hexane or ag@zno-hpgs nanoparticles or dopamine-modified ag@zno nanoparticles in deionized water on 230 mesh ultra-thin amorphous carboncoated copper grids and measured by transmission electron microscopy (tem, h7650, hitachi, japan). ag@zno nanoparticles were transferred from nhexane to water by using dopamine. dissolve 20 ml of dopamine hydrochloride in 4 ml water, and adjust ph to neutral with naoh solution. then the solution was into the nanoparticle dispersion, and the mixture was stirred overnight at room temperature. the mixture was precipitated by adding ethanol. the sediments were collected by centrifugation, which was further purified by washing with water and ethanol 2–3 times. finally, the dispersion of the dopaminemodified ag@zno nanoparticles was obtained by dispersing the product in water and preserving it in a dark place at room temperature for 30 days before analysis. the size of the nanoparticles was carried out using a dynamic light scattering particle size analyzer (dls, lb-550, horiba company, japan) to test the suspension of ag@zno nanoparticles in hexane or ag@zno-hpgs nanoparticles in deionized (di) water. the thermal degradation process was carried out by a thermal gravimetric analyzer (tga, sta449f3, netzsch company, germany) with a temperature ranging from 80 ℃ to 800 ℃ (heating speed: 10 ℃ min−1) under n2 atmosphere. in addition, the elemental contents were analyzed by x-ray photoelectron spectroscopy (xps, thermo fisher scientific, usa) with a monochromatic al ka x-ray source (1486.6 ev photons). to measure the contents of ag and zn of ag@zno-hpgs nanoparticles, ag@zno-hpgs nanoparticles (20 mg) in 5% hno3 aqueous solution (20 ml) were completely dissolved with ultrasonic for 30 min and detected by inductively coupled plasma optical emission spectrometer (icp-oes, 725es, agilent company, usa). 5 2.5 characterization of membranes the surface morphologies of the membranes were observed by scanning electron microscope (sem, gemini sem500, zeiss company, germany) operating at 10  kv, and the specimens were sputter-coated with gold. automatic contact angle measurement (dsa30s, kruss gmbh co., germany) was used to evaluate the surface hydrophilicity of the membranes by microtitration system at 25 ℃ and 50% relative humidity. the resulting contact angle and standard deviation are based on 5 measurements per sample at least. the electronegativity of the membrane surface was measured by a solid surface zeta potential analyzer (surpass-3, anton paar gmbh, austria). the feed solution was 0.001 m kcl at 25 ℃ and used sodium hydroxide (naoh) or hydrochloric acid (hcl) solution to adjust the ph value during the measurement. 2.6 evaluation of membrane performance the self-made filtration apparatus was used to evaluate the separation performance of the membranes by cross-flow filtration. the water flux and salt rejection to nacl of the membranes were estimated with an aqueous solution of nacl at a concentration of 2,000 mg/l at 1.5 mpa and 25 ℃. the conductivity meter (fe38, mettler toledo co., ltd., switzerland) was used to measure the electrical conductivities of feed and permeate solutions. evaluations of water flux (jw, lmh) and salt rejection to nacl (r) were as follows. 퐽� = 푉 퐴 × ∆푡 (1) 푅 = �1 − 퐶� 퐶� � × 100% (2) where v is the volume of the collected permeate (l), a is the effective area of the membrane (m2), and t is the permeation time. cp and cf are the solute concentrations in permeate and feed solutions, respectively[6]. 2.7 assessment of membrane antifouling and anti-bacterial properties 2.7.1 antifouling property the antifouling performance of the membrane was detected by using the filtration apparatus with bsa as the model foulant at 25 ℃. for this filtration test, the membrane was pre-compacted with di water for 0.5 h at 1.5 mpa before testing. to obtain a stable initial pure water flux, the membrane was filtered for 1 h using di water at 1.5 mpa. then, bsa solution (1 g/l) was used as feed solution to filter for 8 h at 1.5 mpa, followed by forward washing with di water at 0.4 mpa for 10 min before filtration for 1 h at 1.5 mpa. the flux was measured every 10 min in the filtration of di water while the flux was measured every 30 min in the filtration of bsa solution. the initial flux of di water was recorded as jw0, and all fluxes obtained were normalized. 2.7.2 anti-bacterial property bacterial activity the antibacterial properties of the membranes were investigated by using gram-negative e. coli and gram-positive s. aureus as microbial models. bacterial suspensions with a concentration of 4 × 107 cfu/ml were diluted with pbs solution (ph = 7.4) to 4 × 105 cfu/ml. after uv sterilization, 2.5 cmlong hollow fiber membranes were immersed in 20 ml bacterial suspension and cultured for 24 h at 37 ℃. the concentration of bacterial suspension was taken to test its absorbance by using a microplate spectrophotometer at a wavelength of 600 nm and bacterial activity was calculated by equation (3). 퐵푎푐푡푒푟푖푎푙 푣푖푎푏푖푙푖푡푦 = 퐴 퐴� × 100% (3) where a0 and a are the absorbances of the bacterial solution before and after adding the membrane, respectively[8,10]. bacterial adhesion the bacterial suspension (2 ml) at a concentration of 4 × 108 cfu/ml was centrifuged at 2,700 rpm for 10 min to remove the supernatants. after two times washing with pbs solution, bacterial suspension with a concentration of 4 × 107 cfu/ml was obtained by dilution with pbs solution. twenty hollow fiber membranes 2.5 cm in length were sterilized by uv before being immersed in 20 ml bacterial suspension, followed by cultivation for 4 h at 37 ℃[14]. five hollow fiber membranes were taken from 6 the bacterial suspension to soak in the aqueous solution of 3% glutaraldehyde for 8 h at 4 ℃, followed by dehydration with 25%, 50%, 75%, and 100% ethanol, respectively. after drying at room temperature, the morphology of bacteria on the surface of the membranes was observed by sem. after washing the remaining membranes with pbs solution, membranes were divided into 3 groups (5 membranes in each group) and steeped in 4 ml of pbs solution. to release the bacteria attached to the membrane surface, the solution with the sample was treated with ultrasonic for 7 min, and shaken for 30 s to obtain bacterial suspension. after dilution with pbs solution, the plate smearing method was carried out to count the number of bacterial cells, and the average value was calculated. the membrane without nanoparticles was the control group, and the adhesion rate of it was regarded as 100%. evaluations of bacterial adhesion rate was as follows. 퐴푑ℎ푒푠푖표푛 푟푎푡푒 = 퐵 퐵� × 100% (4) where b0 and b are the number of bacterial cells of the control group and cta composite membrane, respectively[25,32]. 2.8 releasing of silver ions (ag+) from the cta composite membrane to assess the releasing rate of ag+ from the cta composite membrane, one hundred m3 composite membranes 2.5 cm in length were put in a bottle wrapped in tinfoil. after adding 20 ml di water, the bottle was placed in a thermostatic incubator shaker at 120 rpm and 37 ℃, and di water to replace the solution every 24 h. the solution collected daily was acidified with 5% hno3 aqueous solution before using inductively coupled plasma mass spectrometry (icp-ms, agilent 7700, agilent company, usa) to detect the ag content of the solution. ag+ content per liter of permeate solution was calculated by 퐶�� = 퐶� × 푉 24 × 퐽� × 푆 (5) the released amount of ag+ per membrane area was calculated by 퐶��� = 퐶� × 푉 푆 (6) where ct is the concentration of ag+ in the solution collected daily, v is the total volume of solution collected, s is the effective area of one hundred 2.5 cmlong membranes, and jw is the water flux of the membrane. one hundred m3 composite membranes 2.5 cm in length were put in a bottle wrapped in tinfoil. after adding 20 ml of 5% hno3 aqueous solution, the bottle was treated by ultrasonic for 30 min to release the total ag of membranes. 3. results and discussion 3.1 characterization of ag@zno and ag@zno-hpgs nanoparticles figure 3a showed the uv-vis absorption spectra of ag, zno, ag@zno, and ag@zno-hpgs nanoparticles. the uv absorption peak of pure ag and ag in ag@zno nanoparticles occurred at 405 nm, while the peak in ag@zno-hpgs nanoparticles occurred at 433 nm. a red shift of the characteristic absorption peak indicated that the particle size of ag@zno-hpgs nanoparticles was larger than that of ag@zno nanoparticles[32]. meanwhile, the uv absorption peaks of pure zno and zno in ag@zno and ag@zno-hpgs nanoparticles both appeared at 361 nm. figure 3b showed the xrd patterns of ag@zno and ag@zno-hpgs nanoparticles. the xrd pattern of ag@zno nanoparticles was observed with a wide peak at 38.1°, which was the diffraction peak of ag (111) due to the tiny size of the nanoparticles. however, no obvious diffraction peak was found at other positions, and a wide diffraction peak occurred at the low diffraction angle because of amorphous zno, which was similar to the xrd pattern of ag@fe2o3 nanoparticles with amorphous fe2o3 reported by chen et al.[33]. four characteristic diffraction peaks of ag and seven characteristic peaks of zno were found in the xrd patterns of ag@zno-hpgs nanoparticles, which were matched with the jcpds cards of silver and zincite (jcpds, no. 04-0783 and jcpds, no. 36-1451), respectively. moreover, the wide peak of zno near 27° was shifted to 24°, which confirmed that hpgs were grafted on the zno shell[34]. the results of xrd patterns indicated that part of zno would change from 7 an amorphous state to a crystal state during the process of grafting hpgs. figure 3c showed the ftir spectra of ag@zno and ag@zno-hpgs nanoparticles. as shown in ftir spectra of ag@zno nanoparticles, the peak at 3,360 cm−1 was stretching vibration of –oh from the surface of zno and –nh of oleyl amine. the peaks at 1,460 cm−1, 2,850 cm−1, 2,920 cm−1, and 2,950 cm−1 were –ch2 in-plane bending vibration, –ch2 symmetric and antisymmetric stretching vibration, and =c–h stretching vibration, respectively. the peak of =c–h in-plane bending vibration and peak of c–n vibration overlapped at 1,410 cm−1. the peak at 1,570 cm−1 could be due to the c=c stretching vibration. the ftir spectra of ag@zno nanoparticles only showed the vibration peak of oleyl amine since oleyl amine was a capping agent of ag@zno nanoparticles. nevertheless, the peak of –oh at 3,440 cm−1 became stronger, and the peak appeared at 1,380 cm−1 for –oh bending stretching, as shown in the ftir spectra of ag@zno-hpgs nanoparticles. new peaks at 1,090 and 1,040 cm−1 for c–o–c antisymmetric and symmetric stretching vibration were observed while the characteristic peak of oleyl amine disappeared. the results indicated that hpgs were successfully grafted on the surface of ag@zno nanoparticles, and ag@zno-hpgs nanoparticles contained large amounts of c–o–c and –oh, as illustrated in figure 3d. figure 3. (a) uv-vis absorption spectra; (b) xrd patterns; (c) ftir spectra of ag@zno and ag@zno-hpgs nanoparticles; and (d) schematic illustration of ag@zno-hpgs nanoparticles. the size and morphology of ag@zno and ag@zno-hpgs nanoparticles were observed by tem, as shown in figure 4a. the hydrophobic ag@zno nanoparticles had good dispersion in nhexane with a diameter from 6 to 16 nm. the coreshell structure of ag@zno nanoparticles had been demonstrated in a previous study of our research group[30]. the tem image of dopamine-modified ag@zno nanoparticles after storing in water for 30 days, with some hollow zno shells, indicated that ag ions were released through the shell of the amorphous zno. after surface grafting of hpgs, ag@zno-hpgs nanoparticles with a diameter from 20 to 50 nm were changed to be hydrophilic and showed excellent dispersibility in di water. however, the agglomeration of ag@zno-hpgs nanoparticles in water was more serious than that of ag@zno nanoparticles in n-hexane. figure 4b showed the size distributions of ag@zno and ag@zno-hpgs nanoparticles measured by dls. the size distributions of the particles were narrow, and the size distribution of ag@zno nanoparticles was narrower than that of ag@znohpgs nanoparticles. the size distribution range of ag@zno nanoparticles was from 5 to 21 nm with an average particle size of 11.07 nm in n-hexane, while the size distribution range of ag@zno-hpgs nanoparticles was from 38 to 68 nm with an average particle size of 51.65 nm in di water. therefore, the average thickness of the hpgs layer for ag@znohpgs nanoparticles was 20.97 nm. the thermal degradation process of ag@zno 8 and ag@zno-hpgs nanoparticles was examined by tga. as shown in figure 4c, tga thermograms of ag@zno nanoparticles were observed that the weight loss at 200 ℃, 353 ℃, and 800 ℃ was 0.81%, 4.18%, and 9.79%, respectively, which was mainly attributed to the evaporation of organic solvents and water molecules, the loss of –oh from amorphous zno and the degradation of oleyl amine. in addition, for ag@zno-hpgs nanoparticles, due to the evaporation of adsorbed water and bound water in particles, the weight loss rate at 250 ℃ was 5.07%. the weight loss in the temperature range of 250–550 ℃ was related to the degradation of hpgs, and the weight loss rate was 18.96%. figure 4. (a) tem images of ag@zno, dopamine-modified ag@zno (after storing in water for 30 days) and ag@zno-hpgs nanoparticles; (b) size distribution; and (c) tga thermograms of ag@zno and ag@zno-hpgs nanoparticles. figure 5 showed the xps o 1s spectra of ag@zno and ag@zno-hpgs nanoparticles. both nanoparticles had only one absorption peak of o at 529.7 ev, corresponding to the lattice oxygen of zno in ag@zno nanoparticles. however, the absorption peak of o at 532.3 ev corresponded to the c–o of hpgs in ag@zno-hpgs nanoparticles. the results proved that the surface of ag@zno was grafted with a layer of hpgs. besides, in table 1, compared with ag@zno nanoparticles, the elemental percentages of c and o in ag@zno-hpgs nanoparticles significantly increased while the elemental percentages of zn and ag were extremely low. since the measuring depth of xps was less than 10 nm, the data of tem and dls showed that the thickness of the hpgs layer was greater than 10 nm, which exceeds the detection limit of xps. figure 5. (a) xps o 1s spectra of ag@zno; and (b) ag@zno-hpgs nanoparticles. 9 table 1. the surface elemental percentage for ag@zno and ag@zno-hpgs nanoparticles is based on xps spectra. nanoparticles c (at%) o (at%) zn (at%) ag (at%) n (at%) ag@zno 41.06 19.16 28.79 4.76 6.23 ag@zno-hpgs 72.56 26.45 0.84 0.14 therefore, to explore the elemental percentage of ag and zn for ag@zno-hpgs nanoparticles, further investigation was necessary due to the unreliable result of xps. the percent contents of ag and zn in ag@zno-hpgs nanoparticles were determined by icp-oes after digestion with hno3. the percent contents of ag and zn in ag@zno-hpgs nanoparticles were 4.40 w/w% and 32.17 w/w%, respectively. 3.2 effect of the concentrations of succinyl chloride on the nanoparticles grafting on the membrane surface to explore the influence of different concentrations of succinyl chloride on the grafting degree of ag@zno-hpgs nanoparticles on the surface of the cta membrane, the cta composite membrane was prepared according to the reaction conditions in table 2, and the surface morphology of the cta composite membrane was observed by sem. figure 6 showed the surface sem images of cta composite membranes with different concentrations of succinyl chloride. the granular spheres that appeared on the surface of the cta composite membrane were ag@zno-hpgs nanoparticles which were grafted on the membrane surface via succinyl chloride. the number of granular spheres on the surface of the cta composite membrane increased with the increase of succinyl chloride concentration, indicating that the more ag@zno-hpgs nanoparticles grafted on the membrane surface, the higher the degree of grafting. the number of nanoparticles on the surface of the sc4 and sc5 cta composite membranes were similar, but the agglomeration of nanoparticles on the surface of the sc5 cta composite membrane was more likely. therefore, the concentration of succinyl chloride at 1 wt% was selected for grafting in the subsequent preparation of composite membranes due to the uniform dispersion of nanoparticles on the surface of the sc4 membrane. figure 6. surface sem images of cta composite membranes with different concentrations of succinyl chloride. table 2. reaction conditions of cta composite membranes with different concentrations of succinyl chloride. membrane succinyl chloride (wt%) ag@zno-hpgs (wt%) triethylamine (wt%) sc1 0.25 0.1 0.15 sc2 0.5 0.1 0.15 sc3 0.75 0.1 0.15 sc4 1 0.1 0.15 sc5 1.25 0.1 0.15 10 3.3 effect of the concentrations of triethylamine on the nanoparticles grafting on the membrane surface the cta composite membrane was prepared under the reaction conditions in table 3, and the effect of different concentrations of triethylamine on the grafting degree of ag@zno-hpgs nanoparticles on the surface of the cta membrane was further investigated by sem. figure 7 showed the surface sem images of cta composite membranes with different concentrations of triethylamine. with the increased concentration of triethylamine, the number of granular spheres on the membrane surface grew. at a mass ratio of ag@zno-hpgs nanoparticles to triethylamine equal to or larger than 1:2, the nanoparticles began to distribute unevenly on the membrane surface, and the further increase of the mass ratio would affect the surface structure of the cta composite membrane. hence, the mass ratio of ag@zno-hpgs nanoparticles to triethylamine was 1:1.5 for the subsequent preparation of the composite membranes. table 3. reaction conditions of cta composite membranes with different concentrations of triethylamine. membrane succinyl chloride (wt%) ag@zno-hpgs (wt%) triethylamine (wt%) t1 1 0.1 0.1 t2 1 0.1 0.15 t3 1 0.1 0.2 t4 1 0.1 0.25 t5 1 0.1 0.3 figure 7. surface sem images of cta composite membranes with different concentrations of triethylamine. 3.4 characterization of cta composite membranes the reaction conditions for the preparation of cta composite membranes with different concentrations of ag@zno-hpgs nanoparticles were determined by the results in section 3.2 and section 3.3, as shown in table 4. figure 8 showed the surface sem images of the cta composite membranes with different concentrations of ag@zno-hpgs nanoparticles. the surface of the pristine cta membrane was smooth, while a large number of granular spheres appeared on the surface of the cta composite membranes. the small granular spheres were ag@zno-hpgs nanoparticles with a diameter of about 50 nm, as shown in the locally enlarged image of figure 8. the number of nanoparticles on the surface of the cta composite membranes increased with the incremental concentration of the nanoparticles. too high concentrations of nanoparticles would lead to aggregation and uneven distribution of nanoparticles on the membrane surface, such as the m4 membrane. 11 table 4. reaction conditions of cta composite membranes with different concentrations of ag@zno-hpgs nanoparticles. membrane succinyl chloride (wt%) ag@zno-hpgs (wt%) triethylamine (wt%) cta m1 1 0.05 0.075 m2 1 0.1 0.15 m3 1 0.2 0.3 m4 1 0.3 0.45 figure 8. surface sem images of cta composite membranes. the surface water contact angle of cta composite membranes was shown in figure 9a. the water contact angle of the pristine cta membrane was 76.62° ± 2.45°. with the increased concentration of ag@zno-hpgs nanoparticles, the water contact angle of cta composite membranes augmented at first and then declined. the water contact angles of m1, m2, m3 and m4 membranes were 79.87°, 78.2°, 76.03° and 75.76°, respectively. nanoparticles were grafted onto the surface of the cta membrane via succinyl chloride, as shown in figure 1. the hydroxyl groups on the membrane surface were transformed into acyl chloride groups by grafting succinyl chloride, followed by a reaction with hydroxyl groups of ag@zno-hpgs nanoparticles to obtain cta composite membranes. however, the remanent unreacted acyl chloride groups on the membrane surface converted into carboxyl groups in water, and the number of carboxyl groups decreased with the increased grafting degree of nanoparticles. since the surface of nanoparticles was filled with hydroxyl groups, the number of hydroxyl groups on the surface of the cta composite membrane increased while the number of carboxyl groups decreased with the increased grafting degree of nanoparticles. this would lead to the reduction of water contact angle and the enhancement of hydrophilicity. therefore, the water contact angle of cta composite membranes increased firstly and then declined with the rising concentration of nanoparticles, grafting a great many ag@zno-hpgs nanoparticles was beneficial to improve the surface hydrophilicity of cta composite membranes. the separation performance of the ro membrane was usually related to its surface electronegativity, and the surface zeta potential of cta composite membranes were shown in figure 9b. the zeta potential of pristine cta and cta composite membranes decreased with the increase in ph. the isoelectric point of pristine cta membrane was 4.05, while those of m1, m2, m3, and m4 membranes were 3.49, 3.42, 3.96, and 4.10, respectively. due to the combined effects from carboxyl groups of cta composite membrane and hydroxyl group of ag@zno-hpgs nanoparticles, the isoelectric point of cta composite membranes decreased at first and then increased. the acyl chloride groups of the cta composite membrane were consumed by ag@znohpgs nanoparticles. thus, the carboxyl groups decreased and the zeta potential of cta composite membranes increased with the increased concentration of nanoparticles at a ph value equal to 7. 12 figure 9. (a) surface water contact angle; and (b) surface zeta potential of cta composite membranes. 3.5 membrane performance the effect of the concentration of ag@znohpgs nanoparticles on the separation performance of cta composite membranes was shown in figure 10a. the water flux and nacl rejection of pristine cta membrane were 9.20 lmh and 93.06% respectively. with the increase of nanoparticle concentration, the water flux of cta composite membranes decreased first and then increased, which was opposite to the changing trend of the water contact angle. the water fluxes of m1, m2, m3, and m4 composite membranes were 8.89, 9.51, 10.65, and 13.95 lmh, respectively. however, the changing trend of salt rejection was opposite to that of water flux, and the nacl rejections of m1, m2, m3, and m4 membranes were 93.12%, 92.81%, 91.10%, and 87.34%, respectively. the water flux increased with the amounts of nanoparticles, due to the enhancement of hydrophilicity of the cta composite membranes effected by the introduction of ag@zno-hpgs nanoparticles. meanwhile, the salt rejection decreased with the number of nanoparticles, which was caused by the corrosivity of triethylamine[35]. triethylamine would break down the hydrogen bonds among the amorphous region of cta. this led to the augmentation of the transition channel of the membrane, thus decreasing the salt rejection, as well as enhancing the water flux. when the concentration of triethylamine was too high, the salt rejections of cta composite membranes were severely affected, such as m4 membranes. to evaluate the antifouling performance of the cta composite membrane, the normalized flux variation of membranes during bsa filtration was detected by using bsa as a model foulant, as shown in figure 10b. the pollutant was gradually deposited and adsorbed on the membrane surface over time during bsa filtration, which caused the flux of cta membranes to be less than that during water filtration. as time went by, the normalized flux became lower, and the fouling degree of the membrane surface was getting more serious. after an 8 h bsa filtration, the normalized fluxes of cta, m1, m2, m3, and m4 membranes were 0.74, 0.72, 0.82, 0.81, and 0.82, respectively. then, after forward washing with di water for 10 min, the normalized fluxes of cta composite membranes recovered, especially of m2, m3, and m4 composite membranes. the influences of ag@zno-hpgs nanoparticles on the antifouling performance of the membranes were basically due to the following reasons. one was that the membrane surface approached electrically neutral, which was good for reducing the adsorption of pollutants. second, a large number of ag@zno-hpgs nanoparticles with abundant hydroxyl groups loaded on the membrane surface made it easy to form a water film on the membrane surface. furthermore, ag@znohpgs nanoparticles were grafted on the membrane surface via succinyl chloride so that space existed between the nanoparticles and the membrane. ag@zno-hpgs nanoparticles shook with the water flow on the membrane surface, which is more conducive to removing the pollutant during forward washing. after 600 min filtration, the normalized fluxes of cta, m1, m2, m3, and m4 membranes were 0.83, 0.79, 0.94, 0.98, and 0.94, respectively. m4 composite membrane showed the best fouling resistance with a flux recovery rate of 97.69%. 13 figure 10. (a) water flux and salt rejection of cta composite membranes with different amounts of ag@zno-oac nanoparticles (feed solution: 2000 mg/l nacl); and (b) time-dependent normalized flux of cta composite membranes during bsa filtration. e. coli and s. aureus were used as microbial models to assess the antibacterial properties of cta composite membranes by bacterial activity and adhesion experiments. as shown in figure 11a, the bacterial activity decreased, and the antibacterial effect of the cta composite membrane on e. coli and s. aureus became more significant with the increase of ag@zno-hpgs nanoparticles concentration. the antibacterial rates of m3 and m4 composite membranes to e. coli were above 99.50%, while the antibacterial rates of them to s. aureus were 92.38% and 99.88%, respectively. the hydroxyl radicals and reactive oxygen species generated by zno[36] and ag[37] gave the cta composite membranes such excellent antibacterial properties. figure 11. (a) bacterial viability; (b) viable adherent fractions of the cta composite membranes; and (c) sem images of the cta composite membrane surfaces after exposure to e. coli or s. aureus (5 × 107 cells ml−1) for 4 h. figure 11b showed the bacterial adhesion rates on the surface of cta composite membranes. with the increased concentration of nanoparticles, the viable adherent fractions of the composite membranes decreased. for m1, m2, m3, and m4 composite membranes, adhesion rates to e. coli were 37.08%, 25.74%, 19.12%, and 17.29% while to s. aureus were 52.25%, 32.67%, 21.35% and 18.28%, respectively. the surface chemical groups of ag@znohpgs nanoparticles grafted on the membrane surface were mainly hydroxyl, which helped improve hydrophilicity and from a water film on the membrane surface to resist the adhesion of bacteria. the sem images of the cta composite membrane surfaces after exposure to e. coli or s. aureus for 4 h were shown in figure 11c. single or cluster bacterial cells were observed on the surface of the pristine cta membrane. the number of bacterial cells on the surface of cta composite membranes 14 declined with the increased concentration of nanoparticles. the morphology of e. coli on the surface of the cta composite membranes was incomplete, and the cell membrane had shape change, even cavities, leading to leakage of cell fluid and bacterial death. however, s. aureus was still spherical with intact cell morphology, and no cell membrane breakage was found on the surface of the cta composite membranes. cta composite membrane achieved an antibacterial effect by destroying the cell membrane of e. coli and inhibiting the further division and growth of s. aureus. although the antibacterial properties of m3 and m4 composite membranes were similar, the nacl rejection of the m4 membrane was lower than 90%. therefore, the m3 composite membrane was selected as the test sample to evaluate the long-term release stability of ag+ for the membrane by monitoring the release behavior of ag+ under a simulated water environment for 30 days. figure 12 showed the concentration of ag+ in permeate solution per liter and the released amount of ag+ per square centimeter from the m3 composite membrane. during 30 days, a low concentration of ag+ released by the m3 composite membrane maintained steady long-term, and the releasing rate of ag+ was between 3.40 × 10−5 and 6.20 × 10−5 mg l−1. in addition, according to the national standard of drinking water[38], the concentration of ag+ in permeate water per liter must be less than 0.05 mg l−1 to meet the standard (the dotted line in figure 12), and that from m3 composite membrane was markedly lower than the standard. the released amount of ag+ was 8.80 × 10−4 μg cm−2 day−1 and the daily average for daily released amount was 1.23×10−5 μg cm−2 day−1. moreover, the total content of ag+ on the m3 membrane surface was 0.38 μg cm−2 day−1, which helped the m3 composite membrane continue to exhibit antibacterial activity over 306 days. the results showed that the m3 membrane could keep lower releasing rates of ag+ for a long period. figure 12. releasing rate and released amount of ag+ ions from the m3 cta composite membranes. 4. conclusions in this paper, novel hydrophilic ag@znohpgs nanoparticles with a large number of hydroxyl groups were successfully anchored on the surface of cta membranes by grafting succinyl chloride on the surface of cta membranes to endow acyl chloride bonding sites, and cta composite membranes were prepared. the introduction of ag@zno-hpgs nanoparticles greatly improved the physical and chemical properties of cta composite membranes and increased the water flux of cta composite membranes. in particular, the cta composite membranes showed excellent fouling resistance, and the flux recovery rate was up to 97.69% during the bsa solution filtration test. in addition, cta composite membranes exhibited remarkable antibacterial properties and excellent antiadhesion to e. coli and s. aureus. the antibacterial rates of e. coli and s. aureus for the m3 composite membrane were 99.50% and 92.38%, and bacterial adhesion rates were as low as 19.12% and 21.35%, respectively. the release of ag+ from the cta composite membrane was much lower than the 15 national standard of drinking water. this study provided a new approach for the development of new antifouling ro membranes with great potential for applications in biomedical, environmental, and other fields. author contributions methodology, validation, formal analysis, writing—original draft preparation, xh; resources, data curation, writing—review and editing, supervision, yc. all authors have read and agreed to the published version of the manuscript. acknowledgments the authors acknowledge the financial support from the science and technology plans of tianjin (no. 20yfzcsn00930). the authors would like to thank the analytical & testing center of tiangong university for ftir, xps, and tem tests. conflict of 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water quality (chinese). ministry of health of the people’s republic of china; 2006. characterization and application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1768 99 original research article development, optimization, and evaluation of cisplatin-loaded plga nanoparticles purushothaman bhuvaneshwaran, ramaiyan velmurugan* faculty of pharmaceutical sciences, saveetha institute of medical and technical sciences, chennai, tamil nadu 602105, india. e-mail: ramaiyan.dr@gmail.com abstract nanoparticle drug delivery systems are engineered technologies that use nanoparticles for the targeted delivery and controlled release of therapeutic agents. cisplatin-loaded nanoparticle formulations were optimized utilizing response surface methods and the central composite rotating design model. this study employed a central composite rotatable design with a three-factored factorial design with three tiers. three independent variables namely drug polymer ratio, aqueous organic phase ration, and stabilizer concentration were used to examine the particle size, entrapment efficiency, and drug loading of cisplatin plga nanoparticles as responses. the results revealed that this response surface approach might be able to be used to find the best formulation for the cisplatin plga nanoparticles. a polymer ratio of 1:8.27, organic phase ratio of 1:6, and stabilizer concentration of 0.15 were found to be optimum for cisplatin plga nanoparticles. nanoparticles made under the optimal conditions found yielded a 112 nm particle size and a 95.4 percent entrapment efficiency, as well as a drug loading of 9 percent. the cisplatin plga nanoparticles tailored for scanning electon microscopy displayed a spherical form. a series of in vitro tests showed that the nanoparticle delivered cisplatin progressively over time. according to this work, the response surface methodology (rsm) employing the central composite rotatable design may be successfully used to simulate cisplatin-plga nanoparticles. keywords: cisplatin; plga; nanoparticles; response surface methodology; central composite rotatable design article info received: 2 august 2022 accepted: 28 september 2022 available online: 12 october 2022 copyright copyright © 2022 by purushothaman bhuvaneshwaran, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction tumors form when cells grow and divide improperly and uncontrollably, which is the hallmark of the cancerous condition. new technologies that can distinguish between healthy and cancerous cells followed by the targeting of the tumor with precision are attracting a lot of attention. with (transdermal drug delivery) tdd, the medicine is encapsulated inside of a nanocarrier like liposomes or liposomal particles to transport it directly to the patient. both the effectiveness and toxicity of the medicine may be improved by tdd, and it can overcome a broad variety of difficulties, such as drug solubility and instability, and the ease of delivery to the target cells. passive and active medication targeting methods are available[1]. on the basis of the enhanced permeability and retention (epr) effect, which occurs in most solid tumors, passive targeting relies on molecules of specific sizes being preferentially taken up and retained by the tumors[2]. however, the reticuloendothelial system (res) rapidly removes intravenously delivered nanocarriers containing anticancer medicines from circulation. these nanocarriers have a hydrophilic polymer, for example, polyethylene glycol (peg) coating applied on top of them to increase their circulation duration and consequently 100 their targeting of tumor tissue[3]. the adsorption of plasma proteins (opsonin), which is critical for phagocytosis, would be prevented, resulting in a longer period for blood to circulate[4,5]. nanoparticles (nps) are regarded as drug delivery mechanism that allows for novel approaches to cancer therapy, and one of the most important methods used in nanomedicine. there are several np delivery techniques, in which the medication is dissolved, encapsulated, and entrapped inside the matrix[6]. the potential of nps coupled with biodegradable polymers such as plga to actively and passively target tumors has drawn considerable interest[7]. the exterior diameters of nps can range from a few nanometers to over 1,000 nanometers in length. due to the epr effect, nps coated with peg can accumulate in a variety of solid tumors, making them ideal carriers for hydrophobic medicines, which can provide effective tumor targeting with the fewest adverse responses[8,9]. nanoprecipitation[10], solvent evaporation[11], dialysis[12], and salting out[13] have all been used for the formation of nps. for the treatment of a wide range of solid malignancies, including cervical cancer, cisplatin is a powerful anticancer drug[14]. in order to eliminate cancer cells, cisplatin causes cross-linking of dna, which leads to cell death. although cisplatin has a powerful anticancer impact, its severe side effects such as nephrological and neurological toxicities[15] limit its effectiveness. chronic and acute kidney damage are common side effects of cisplatin, while neurotoxicity is cumulative-dose dependent. cisplatin’s immediate inactivation in the systemic circulation is one of the greatest concerns[16,17]. as a result, cis-dichlorodiammineplatinum (ii) (cis-[ptcl2(nh3)2], cisplatin (cddp’s) pharmacological effect must be protected and its systemic circulation must be prolonged. drug must be delivered over an extended period of time in order to maximise its anticancer properties and minimise its negative effects. for passive targeting following intravenous delivery, researchers are trying to integrate cisplatin into poly (lactic-coglycolic acid) (plga) nps. response surface methodology central composite rotatable design will be used to optimise the nanoparticles created. after optimizing cisplatin loading, we will conduct in vitro drug release and physicochemical evaluations of the plga nps. 2. materials and method dichloromethane and sodium cholate were provided by madras pharmaceuticals, india. cisplatin and plga was purchased from sigma-aldrich, india. all other chemicals were of analytical grade and used as such. 2.1 preparation of cisplatin nanoparticles in order to create nanoparticles, a solvent evaporation approach was used[18]. sonication was used for 5 min to create an emulsion between an organic polymer solution (o) and an aqueous solution (w) containing the medication (5 mg of cisplatin in 2 ml distilled water). it was then mixed with 50 ml of water and sonicated to create the double-emulsion, which was then dissolved in an equal amount of water. a mild magnetic stirring at room temperature was used to evaporate the solvent. recovered nanoparticles were rinsed with distilled water, dried, and kept in cold temperatures (2–8 °c) for future use. 2.2 experimental design according to preliminary investigations, the variables including drug polymer ratio, water to organic phase ratio, and stabilizer concentration during synthesis of the cisplatin nanoparticles, had the greatest impact on particle size, distribution, entrapment, and drug loading efficiency. these responses were considered for optimization as they accounts very much for rapid drug absorption and drug availability. in order to study the impact of these three essential formulation factors on particle size, entrapment efficiency, and drug loading efficiency, a central composite rotatable design–response surface methodology (ccrd–rsm) was adopted[19]. table 1 lists the design specifications. preliminary tests and the possibility of making nanoparticles at extreme levels were used to select the experimental ranges for each component. for the drug polymer ratio (x1), the range was 1:1–1:7; for the aqueous-to-organic phase ratio (x2), it was 1:1–1:5, and for the stabilizer concentration (x3), it was 0.1–0.5%. there were a 101 total of 20 tests carried out. in these tests, every formulation was made in two separate batches. since it may investigate many variables at multiple levels with a small number of tests, the central composite rotating design–response surface methodology (ccrd–rsm) is an excellent alternative strategy. after conducting exploratory trials, we came up with the factors in table 1. particle size distribution, drug loading, and entrapment efficiency were all examined in table 2 of the experiments. 94–104 nm, 75– 94 %, and 4–13% were the three dependent variables. design-expert® 7.0 software was used to perform response surface regression analysis on variables and parameters. table 1. independent variables and their corresponding levels of nanoparticle preparation for ccrd independent variables levels −1 0 +1 drug/polymer ratio 1:1 1:5 1:9 aqueous to organic phase ratio 1:1 1:3.5 1:6 stabilizer concentration 0.1 0.55 1.0 table 2. central composite design consisting of experiments for the study of three experimental factors in coded and actual levels with experimental results s. no trial drug polymer ratio aqueous organic phase ratio conc. of stabilizer particle size entrapment efficiency drug loading 1 1 1 1 0.1 100.335 84.076 7.231 2 2 9 1 0.1 99.3895 83.012 8.254 3 3 1 6 0.1 96.8928 81.123 9.014 4 4 9 6 0.1 96.3544 79.089 8.543 5 5 1 1 1 97.9656 87.12 11.239 6 6 9 1 1 95.3729 75.13 13.231 7 7 1 6 1 103.267 85.065 10.123 8 8 9 6 1 102.642 89.87 11.435 9 9 −1.72717 3.5 0.55 102.176 92.1009 5.098 10 10 11.7272 3.5 0.55 104.079 79.34 11.675 11 11 5 −0.704482 0.55 102.726 84.012 9.233 12 12 5 7.70448 0.55 94.2578 90.012 5.987 13 13 5 3.5 −0.206807 96.3522 89.122 9.234 14 14 5 3.5 1.30681 104.532 93.9741 5.123 15 15 5 3.5 0.55 98.5098 91.012 4.098 2.2.1 particle size analysis a malvern zetasizer 3000 hsa was used to measure particle size using dynamic light scattering (dls) (malvern instruments, uk). the polydispersity index (pi), a measure of the breadth of the size distribution, and the mean diameter are both obtained using dls. temperatures of 25 °c were used to measure the mean diameter and the proportional index (pi). an acceptable scattering intensity was achieved by diluting all samples with double-distilled water prior to testing. 2.2.2 zeta potential zeta potential, which reflects the electric charge on a particle’s surface and indicates its physical stability, was determined by measuring electrophoretic mobility using the malvern zetasizer 3000 hsa (figure 9) (malvern instruments, uk). sodium chloride solution (0.9% w/v) was used to modify the conductivity of the sample to 50 is/cm in double distilled water. the applied field strength was 20 v/cm and the ph ranged between 5.5 and 7.5. 2.2.3 scanning electron microscopy (sem) measurement using a hitachi s4800 field emission scanning electron microscope (fesem), the surface and surface morphology of the particles were analyzed in detail (hitachi, gaithersburg, 102 md, usa). analysis settings comprised a vacuum pressure of 40 pascals, an accelerating voltage of 10 kev, and a working distance of 13.5 mm 2.2.4 differential scanning calorimetry (dsc) analysis pure cisplatin, plga, physical mixtures, and cisplatin nanoparticles were all examined using a differential scanning calorimeter (dsc) (shimadzu dsc-60, columbia, md, usa). it was crimped non-hermetically in an aluminum pan and heated at a rate of 10 °c/min from 23 °c to 300 °c under a nitrogen purge for dsc analysis (3–5 mg). 2.2.5 fourier transform infrared spectroscopy (ftir) analysis ftir analyses of cisplatin, plga, physical mixture and cisplatin nanoparticles were carried out using ir prestige-21 (shimadzu, columbia, md, usa). the sample was placed in direct contact with atr crystal ensuring good contact. all the spectra were recorded as a mean of 20 scans, with a resolution of 4 cm−1 and in the range of 800 to 4,000 cm−1. 2.2.6 chromatographic conditions chromolith rp-18e (e-merk, 4.6 × 50 mm) column was used to measure the cisplatin concentration in the hplc system[20]. an acetonitrile-water mixture containing 0.1% formic acid (40:60) was utilized as the mobile phase. a flow rate of 0.5 ml/min was measured. 10 µl of injection was used with a 490 nm laser and a wavelength of 10 nm. 2.2.7 determination of drug entrapment efficiency (ee) and drug loading (dl) centrifuged nanoformulations were evaluated by hplc[21], and the supernatant containing the free drug, which was recovered, was further studied. unentrapped nanoparticles of drug may be determined using this method. in order to determine the amount of drug encapsulated in nanoparticles, a subtraction was made from the total amount of drug added to the formulation. for the evaluation of the formulations, the following formula was used: 𝐸𝐸𝐸𝐸 = 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐴𝐴𝑜𝑜 𝑑𝑑𝑑𝑑𝐴𝐴𝑑𝑑 𝑖𝑖𝐴𝐴 𝐴𝐴𝑛𝑛𝐴𝐴𝐴𝐴𝑛𝑛𝑛𝑛𝑑𝑑𝐴𝐴𝑖𝑖𝑛𝑛𝑛𝑛𝑛𝑛 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐴𝐴𝑜𝑜 𝑑𝑑𝑑𝑑𝐴𝐴𝑑𝑑 − 𝐿𝐿𝐴𝐴𝑛𝑛𝑑𝑑𝑛𝑛𝑑𝑑 𝐴𝐴𝑛𝑛𝐴𝐴𝐴𝐴𝑛𝑛𝑛𝑛𝑑𝑑𝐴𝐴𝑖𝑖𝑛𝑛𝑛𝑛𝑛𝑛 × 100 𝐷𝐷𝐿𝐿 = 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐴𝐴𝑜𝑜 𝑑𝑑𝑑𝑑𝐴𝐴𝑑𝑑 𝑖𝑖𝐴𝐴 𝐴𝐴𝑛𝑛𝐴𝐴𝐴𝐴𝑛𝑛𝑛𝑛𝑑𝑑𝐴𝐴𝑖𝑖𝑛𝑛𝑛𝑛𝑛𝑛 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝐴𝐴𝑜𝑜 𝑑𝑑𝑑𝑑𝐴𝐴𝑑𝑑 𝑜𝑜𝐴𝐴𝑑𝑑 𝑛𝑛𝐴𝐴𝑛𝑛𝑑𝑑𝑖𝑖𝐴𝐴𝑑𝑑 × 100 2.2.8 in vitro release study dialysis bags (cellulose membrane, 12400mw, sigma) were used to contain nanoparticle samples, which were incubated in 30 ml of pbs (ph 7.4) at 37 °c under gentle agitation in a water bath at 37 °c (20). samples were taken from the incubation mixture at predefined intervals and tested for cisplatin using the hplc technique as described above. every time a sample was taken, the incubation media was changed with new pbs. in addition, a control experiment was conducted to assess the free drug’s release behavior. dialysis bags were filled with pbs, pbs at 37 °c, and dissolved cisplatin in 1 ml of this solution, which was deposited in 30 ml of pbs. it was determined that cisplatin was released in the manner stated above. 2.3 data analysis design-expert® software was used to analyze the connections between model responses and their corresponding formulation factors. stepwise linear regression and response surface analysis were used in the statistical study. in the final equations, only significant terms (p < 0.05) were used. linear, quadratic, and special cubic models are all suitable for three-component models. on the basis of statistical comparisons of a number of statistical parameters, including the coefficient of variation (cv), the multiple correlation coefficient (r2), and an adjusted multiple correlation coefficient (adjusted r2) proved by design-expert software, the best fitting mathematical model was selected. student’s t-test and one-way anova were used to determine the significance of differences at a 0.05 significance level. 103 3. results and discussion 3.1 optimization of formulas according to the most statistically significant factors on the examined parameters, 3d response surface graphs are provided in figures 1–3. the experiment yielded a desirability of 0.542 (figure 4). particle size and entrapment efficiency improve with a rise in polymer content and the aqueous to organic phase ratio. polymer concentration and aqueous to organic phase ratio both reduce drug loading. the correlation coefficients (r) of the optimized variables were 0.9365, 0.9289, and 0.9698, respectively, for the second-order polynomial equation. the r value reduced significantly to 0.9112, 0.2089, and 0.9312 after model simplification with backward stepwise solution. at a 95% confidence level, there was a substantial lack of fit. at p < 0.05, all of the remaining variables were significant. the best-fitting model was the quadratic model, and the comparative values of r, sd, and percent cv along with the regression equation developed for the selected answers are shown in table 3. the following polynomial equations were derived from the statistical analysis of the results: ps = +98.57 – 0.1099a – 0.5967b + 1.47c + 0.2968ab – 0.2167ac + 2.38bc + 1.25a2 – 0.3845b2 + 0.3050c2 ee = +91.17 – 2.32a + 1.16b + 1.32c + 1.98ab – 0.5109ac + 2.45bc – 2.90a2 – 2,44b2 – 0.8352c2 dl = +4.04 +1.09a – 0.4612b + 0.4446c – 0.2717ab + 0.3440ac – 0.6230bc + 1.93a2 + 1.65b2 + 1.50c2 figure 1. three-dimensional (3d) response surface plots showing the effect of drug/polymer ratio and aqueous to organic phase ratio on particle size. 104 figure 2. three-dimensional (3d) response surface plots showing the effect of drug/polymer ratio and aqueous to organic phase ratio on entrapment efficiency. figure 3. three-dimensional (3d) response surface plots showing the effect of drug/polymer ratio and aqueous to organic phase ratio on drug loading. 105 figure 4. contour plot showing the desirability with a value of 0.542. table 3. reduced response models and statistical parameters obtained from anova responses regression model adjusted r2 model p value % cv adequate precision particle size ps = +98.57 – 0.1099a – 0.5967b + 1.47c + 0.2968ab – 0.2167ac + 2.38bc + 1.25a2 – 0.3845b2 + 0.3050c2 0.9365 0.0001 2.86 6.47 entrapment efficiency ee = +91.17 – 2.32a + 1.16b + 1.32c + 1.98ab – 0.5109ac + 2.45bc – 2.90a2 – 2,44b2 – 0.8352c2 0.9289 0.0001 3.12 9.10 drug loading dl = +4.04 +1.09a – 0.4612b + 0.4446c – 0.2717 ab + 0.3440ac – 0.6230bc + 1.93a2 + 1.65b2 + 1.50c2 0.9698 0.0001 3.98 11.28 acceptance criteria 1 <0.05 <4 >4 a drug polymer to aqueous/organic phase ratio of 1:6 and a stabilizer concentration of 0.1% produced nanoparticles with high ee, high dl, and a small mean diameter, according to the fitting findings. data from the two batches that were created in optimal ranges were extremely near to the projected values, with a minimal percentage bias. this indicates that the optimized formulation was trustworthy and reasonable. figures 5–7 show the effect of an independent factor on a specific response, with all other characteristics maintained constant at a reference factor. a high inclination or curve indicates that the reaction to a given element is very sensitive. the aqueous-to-organic phase ratio, drug polymer ratio, and stabilizer concentration are all shown to have significant effects on particle size in figure 5. following stabilizer concentration and drug polymer ratio, the aqueous to organic phase ratio had the most significant influence on entrapment efficiency, as shown in figure 6. drug polymer ratio, stabilizer concentration, and aqueous-to-organic phase ratio are shown in figure 7 to have the most significant effect on drug loading. response surface methodology (rsm) using the central composite rotatable 106 design model was used to optimize formulations of dihydroartemisinin nanostructured lipid carrier. the experimental values of the nanoparticles prepared under the optimum conditions were mostly close to the predicted values (table 4)[22]. the ansamycin-loaded polymeric nanoparticles were optimized using the central composite rotatable design–response surface methodology by fitting a second-order model to the response data and the experimental values of the nanoparticles shows that it deliver the encapsulated drug well to the target site[23]. figure 5. perturbation plot showing the effect of independent variables on particle size where a, b and c are drug/polymer ratio, aqueous to organic phase ratio and stabilizer concentration respectively. figure 6. perturbation plot showing the effect of independent variables on entrapment efficiency where a, b and c are drug/polymer ratio, aqueous to organic phase ratio and stabilizer concentration respectively. 107 figure 7. perturbation plot showing the effect of independent variables on drug loading where a, b and c are drug/polymer ratio, aqueous to organic phase ratio and stabilizer concentration respectively. table 4. predicted and experimental values under predicted optimal conditions drug/polymer ratio aqueous to organic phase ratio stabilizer concentration (%) particle size (nm) entrapment efficiency (%) drug loading (%) 1:8.27 1:6 0.1 predicted 114 83.5 8.6 experimental 112 85.4 9.0 bias % 1.75% 2.27% 4.6% acceptance criteria 6% bias was calculated as (predicted value experimental value)/predicted value × 100 3.2 particle size, zeta potential and sem measurement it was discovered that the average cisplatin nanoparticle particle size was 112 nm (figure 8). as shown in figure 9, the zeta potential of this compound is high enough to allow for the creation of a stable pharmaceutical formulation. figure 10 shows the sem images taken of the improved cisplatin nanoparticles to offer information on their shape. these nanoparticles have been fine-tuned to be spherical. the nanoparticles had the higher absolute values of zeta potential, indicating a better stability of this colloid system[24]. zeta potential under −30 mv showed good physical stability[25]. figure 8. size distribution of cisplatin plga np. 108 figure 9. zeta potential of cisplatin plga np. figure 10. scanning electron microscopy of cisplatin plga np. 3.3 differential scanning calorimetry (dsc) analysis after the preparation, dsc was used to examine the cisplatin’s physical condition within the plga particles. drug-loaded nanoparticles did not exhibit the glass transition peak seen in the dsc thermogram of plga (figure 11). the cisplatin thermogram revealed an exothermic peak at 280–285 °c. it is possible that the drug is scattered in an amorphous form due to its lack of this characteristic peak. 3.4 fourier transform infrared spectroscopy (ftir) analysis ftir analysis is used to study the interactions between cisplatin and plga during the entrapment procedure and the ftir spectrum obtained for cisplatin, plga, physical mixture and the drug loaded nanoparticle is presented in figure 12. figure 11. dsc thermogram of plga (polymer), cisplatin (drug), plga cisplatin mixture, cisplatin plga np. figure 12. ftir spectra of plga (polymer), cisplatin (drug), plga cisplatin mixture, cisplatin plga np. the pure cisplatin obtained the characteristic peaks that includes amine stretching (3,208 cm−1), symmetric amine bending (1,302 cm−1) and chloride stretching (766 cm−1). plga nanoparticles obtained its characteristic peaks that include c = o stretching (1,728 cm−1) and c-o stretching (1,020–1,280 cm−1). the ftir spectra of the cisplatin loaded nanoparticles obtained a peak for amine stretching (3,279 cm−1), indicating the presence of cisplatin in the formulation. the ftir data obtained indicates that there were no chemical interactions between plga and the study drug cisplatin. 3.5 in vitro drug release study in vitro cisplatin release from plga nanoparticles is presented in figure 13. biphasic 109 release pattern with an initial fast release for the first 48 hrs, followed by a steady release for six days is observed. the drug may have accumulated on the nanoparticle surface during manufacturing, resulting in a fast release. comparison of cisplatin release profiles with those of cisplatin solution demonstrates that nanoparticle entrapment greatly slowed cisplatin’s release from the solution. according to the data (figure 13), roughly 90% of cisplatin in phosphate buffer solution was released in 24 hours. for the next six days, the cisplatin nanoparticles released at a consistent and modest rate. in vitro, the cisplatin nanoparticles showed a clear sustained-release impact as compared to cisplatin. the decreased percentage of cumulative drug release may be due to the enhanced particle size and also hence smaller sized surface area at greater polymer concentration. an additional description for reduced cumulative drug release at greater polymer concentration might be the enhanced concentration of the polymer existing which impedes the drug release by diffusion[26]. figure 13. in-vitro drug release study of pure cisplatin and cisplatin plga nps in pbs (ph 7.4). 4. conclusion the cisplatin-loaded plga nanoparticles were made using the double emulsion solvent evaporation process. a second-order model was fitted to the response data of the cisplatin plga nanoparticles using the central composite rotatable design–responsive surface approach. most of the nanoparticles’ experimental values were in line with their projected values. the obtained nanoparticles were found to be spherical in shape confirmed by scanning electron microscopy. nanoparticle-mediated drug release followed a biphasic pattern, with early burst releases followed by a sustained release. in vitro drug release trials using nanoparticles showed a long-term effect. according to these findings, the nanoparticles developed in this work might be used therapeutically as a carrier with an initial dosage and a sustained plasma level in vivo. conflict of interest the authors declare that they have no conflict of interest. references 1. attia mf, anton n, wallyn j, et al. an overview of active and passive targeting strategies to improve the nanocarriers efficiency to tumor sites. journal of pharmacy and pharmacology 2019; 71(8): 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nanomaterials (2023) volume 6 issue 2 doi:10.24294/can.v6i2.3516 1 original research article sulfonated mesoporous polystyrene-1d multiwall carbon nanotube nanocomposite as potential adsorbent for efficient removal of xylene isomers from aqueous solution mohan raj krishnan1,*, venugopal rajendran2 1 college of science and general studies, alfaisal university, p.o. box 50927, riyadh 11533, saudi arabia. 2 research department of chemistry, pachiyappa’s college for men, kanchipuram 631502, tamil nadu, india. * corresponding author: mohan raj krishnan, mkrishnan@alfaisal.edu abstract xylene isomers are notorious chemical hazards, and their efficient removal from water solutions is still challenging. the current study reports a polymer nanocomposite as a potential adsorbent for successfully removing dissolved xylene isomers from contaminated water. polystyrene-1d multiwall carbon nanotube nanocomposite (ps-mwcnt) adsorbent was prepared using the one-step bulk polymerization method. mesoporous ps-mwcnt was prepared using the nanocrystallization phase separation method. the sulfonation of the mesoporous ps-mwcnt nanocomposites was carried out by treating the samples with concentrated sulfuric acid at elevated temperatures. the sulfonated ps-mwcnt (ho3sps-mwcnt) was found to be a potential adsorbent for dissolved xylene isomers from water solution. in addition, the ho3s-ps-mwcnt can be efficiently recycled for up to 10 consecutive cycles with negligible decline in adsorption values. the exhibited equilibrium adsorption, rate of adsorption, and rapid regeneration of the ho3s-ps-mwcnt are clear indications for the possibility of practical utilization of these adsorbents in large-scale water treatment plants. keywords: polystyrene; carbon nanotube; nanocomposites; sulfonation; adsorption; xylene isomers article info received: 16 november 2023 accepted: 25 december 2023 available online: 29 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction produced water is oil-contaminated water that is co-produced in huge quantities during oil and gas production[1,2]. the volume of water produced by the oil/gas industry does not remain constant and rapidly increases yearly[3,4]. as per the us department of energy, the annual production of produced water exceeds about 882 billion gallons only from the usa and about 2100 billion gallons from the rest of the world[5]. though various efforts exist to reduce the produced water from the wells[6–12], excessive water production remains one of the biggest challenges. the high volume of the produced water demands immediate action in constructing rapid and effective treatment plants[6–9]. the water produced by gas industries contains high amounts of low-molecularweight aromatic hydrocarbons, including saturated aliphatic hydrocarbons, polycyclic aromatics, organic acids, phenols, toluene, xylenes, and volatiles[10–13]. notably, xylenes are one of the potentially hazardous chemicals and pose a significant threat to human health[14,15]. the excessive health risks caused by the xylene isomers are well documented in the recent literature[16–18]. conventional contaminated water treatment technologies such as coagulation, flocculation, and gravity separations do not meet the high 2 purity requirement of the water treatment process[19,20]. the membrane separation processes, such as ultrafiltration (uf)[21,22] and nanofiltration (nf)[23–25], are being applied for the removal of macro/micro oil droplets present in produced water. removing dissolved oil and organic components at their saturated concentration is still challenging[26,27]. among the possible techniques for water treatment, adsorption by porous solids is prominent as it is one of the most efficient ways to treat organic compounds in contaminated water[19,28–31]. adsorption has the advantage over the other simple design methodologies and low investment[32]. the search for low-cost adsorbents with high adsorption capacities has recently intensified[33–36]. there has been a constant demand for solid-phase adsorbents with improved adsorptive capacity, selectivity, stability, and analyte recoveries[37,38]. the search for a new porous solid seems to be a never-ending task, as the current efforts are at finding an optimum adsorbent for specific applications[39–42]. since there is a growing tendency to use adsorption as an effective tool for removing dissolved aromatic hydrocarbons, discovering new porous materials exhibiting very high adsorption capacity with rapid regeneration characteristics is inevitable. moreover, numerous absorbent polymers or porous polymer-based systems are exploited in oil and gas[9,43–57] and other industries[54,58–65]. carbon nanostructures-based composite adsorbents are emerging as potential adsorbents for removing dissolved organic compounds from water solutions[66–68]. however, their adsorption capacity values and recyclability can further be improved. these issues can be successfully addressed by suitable processing of the composite adsorbents into mesoporous structured materials and subsequent hydrophilic surface modifications. moreover, the application of polymers are well-known in various stages of oil and gas extraction processes[43,47,55,57,58,69–76]. therefore, we have developed a nano-crystallization phase separation approach for fabricating mesoporous polymers from various commodity polymers[12,13,39,41,77]. these unique mesoporous polymers that contain high specific surface area and narrow pore distribution also exhibit excellent adsorption properties of different aromatic compounds dissolved in water and, at the same time, can be rapidly regenerated for repeated use in several cycles. the present study evidences the ultrafast adsorption and desorption dynamics of xylene isomers by the hydrophilically modified mesoporous ps-mwcnt composites. 2. experimental 2.1. materials polystyrene (mw 280,000) and multiwall carbon nanotube (mwcnt, 50–90 nm diameter, >95% carbon basis) were purchased from sigma aldrich. azoisobutyronitrile (aibn, 98% purity) was also purchased from sigma aldrich. n, n-dimethylformamide (dmf, mw 73.09, gc purity 99.7%), methanol (mw 32.04, gc purity 99.8%), sulfuric acid (96% gc purity), and ethanol (99.5% gc purity) was obtained from loba chemie. all these chemicals were as received and without any further purification. 2.2. methods 2.2.1. synthesis of ps-1d mwcnt nanocomposite the ps-1d mwcnt was synthesized using a one-step, in-situ bulk polymerization method. to prepare the sample, a mixture of 5 ml of styrene and 0.005 g of mwcnt was taken in a test tube and sonicated for 30 min. for complete mixing. then, 0.005 mg of aibn was added and sonicated for another 30 min. afterwards, the mixture’s temperature was raised to 70 ℃ for polymerization. the sample is kept at the same temperature for 72 h. then, the sample is thoroughly washed with hot methanol (45 ℃) several times and dried in a vacuum oven to remove non-reacted monomers, oligomers, and homopolymers. 2.2.2. mesoporous ps-1d mwcnt nanocomposite to prepare mesoporous ps-1d mwcnt nanocomposite, the sample is firstly dissolved in dmf (40 wt.% of polymer nanocomposite). then, the solution is immersed into liq. n2 and allowed to stand for 15 min to 3 make the deep-frozen polymer nanocomposite solution. excessive methanol that is pre-cooled to –80 ℃ was added to the above-frozen solution and subsequently transferred to a refrigerator (–80 ℃) and kept for five days for the complete exchange of the dmf (solvent) with methanol (non-solvent). then, the sample was brought to room temperature, and the excessive methanol was removed. finally, the sample was dried in a vacuum chamber for 12 h. 2.2.3. sulfonation of mesoporous ps-1d mwcnt nanocomposite (ho3s-ps-mwcnt) to prepare ho3s-ps-mwcnt, the mesoporous mesoporous ps-1d mwcnt nanocomposite samples were treated with an excess of concentrated sulphuric acid (h2so4) at 70 ℃ for 2 h. after the preferred reaction time, the samples were removed from the acid and subsequently washed in anhydrous methanol several times, followed by d.i. water until the ph of the washed water was around 6–7. this step ensures the complete removal of the sulfuric acid from the polymer samples. after washing, the samples were dried in a vacuum oven. 2.2.4. determination of ion-exchange capacity (iec) of mesoporous ho3s-ps-mwcnt the mesoporous ho3s-ps-mwcnt was characterized by its ion exchange capacity values (iec). the iec of a sulfonated polymer is defined as the number of replaceable h+ ions. this iec value of the sulfonated polymer is directly related to the extent of substitution of sulfonic acid groups. when the sulfonated polymer was added to the dilute nacl solution, the na+ ion replaced the h+ ion from the introduced sulfonic acid group (-so3h) onto the polymer surface. if the replaced h+ ion is back titrated with diluted naoh solution, we can estimate the iec of the sulfonated polymer. to determine the iec, 100 mg of sulfonated ho3s-ps-mwcnt was treated with 10 ml of 1m nacl solution in a 50 cc glass bottle and stirred for 24 h. then, a ph meter removed the sample from the nacl solution and titrated it with 0.1m naoh. the iec can be determined by equation (1) from the required titration volume. 𝐼𝐸𝐶 = [𝑉𝑜𝑙. 𝑜𝑓 𝑁𝑎𝑂𝐻 (𝑚𝑙) × 𝐶𝑜𝑛𝑐. 𝑜𝑓 𝑁𝑎𝑂𝐻 (𝑀)] 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑖𝑒𝑑 𝑝𝑜𝑙𝑦𝑚𝑒𝑟 (𝑔) (1) 2.2.5. adsorption of xylene isomers from aqueous solution equilibrium adsorption a 0.05 wt.% of xylene isomers stock solution was prepared using d.i. water at room temperature and diluted to other subsequent experimental concentrations. in a typical equilibrium adsorption experiment, 70 g/l of mesoporous ho3s-ps-mwcnt was used, whereas the xylene isomer solutions of different concentrations of 1 mg/l to 500 mg/l were used. before use as an adsorbent, the mesoporous ho3s-psmwcnt was added to ethanol to remove the air inside the pores. then, the polymer is filtered and used. the adsorption reaction has been carried out at different temperatures of 30 ℃ and 50 ℃. the mesoporous ho3sps-mwcnt was added to the xylene isomers solution, which was continuously stirred and kept in a water bath at the abovementioned temperatures. a decrease in the concentration of xylene isomer was monitored using uv-vis spectroscopic measurements. the adsorption experiment was stopped by filtering off the adsorbents from the solution when no more decrease in the solution concentration was observed. adsorption kinetics the xylene isomer solution of 500 mg/l was used to study the adsorption kinetics. 70 g/l of sulfonated polystyrene was used in each of the experiments. the kinetics of xylene isomer adsorption onto the sulfonated mesoporous ho3s-ps-mwcnt was investigated at different temperatures of 30 ℃ and 50 ℃. the adsorbent was added to the xylene isomers solution, continuously stirred, and kept in the water bath at the above temperatures. at an equal time interval (every 10 min), a decrease in the concentration of xylene isomers was monitored using uv-vis spectroscopic measurements. the adsorption experiment was stopped when no more 4 reduction in the solution concentration was observed. desorption kinetics the desorption kinetics was studied by adding the xylene-adsorbed mesoporous ho3s-ps-mwcnt in hot ethanol (60 ℃). after adding the adsorbed polymer samples to the desired desorption medium, the increase in the ho3s-ps-mwcnt concentration in the desorbing liquid was monitored by uv-vis spectra. 2.3. characterization bulk and mesoporous morphologies of the samples were analyzed using field-emission scanning electron microscopy (fe-sem, jeol jsm-7401f). the surfaces of the examined sample were coated with au nanoparticles to avoid charging. the images were recorded at an accelerating voltage of 10 kv. 3. results and discussion 3.1. fabrication of mesoporous ps-1d mwcnt nanocomposite the mesoporous ps-1d mwcnt nanocomposite was prepared using the nano-crystallization-induced phase separation method (flash-freezing route). when the temperature of the polymer solution is rapidly decreased to –196 ℃ (liq. n2), the solvent molecules are frozen among the polymer chains. if the temperature of the frozen polymer solution is slowly increased to a temperature (–80 ℃) that is lower than the solvent's melting point, then nano-crystallization of the solvent molecules occurs. consequently, the entangled polymer chains will be expelled due to the nano-crystallization of the solvent molecules while the forming network structure, in turn, effectively suppresses the further growth of the solvent crystals. a mesoporous structure can be obtained by extracting the size-controlled solvent crystals with a non-solvent. figure 1 shows the fesem images of ps-mwcnt (as-prepared), mesoporous ps-mwcnt, and sulfonated ps-mwcnt (ho3sps-mwcnt) samples. as evident from figure 1(b), the ps-mwcnt exhibited a disordered mesoporous structure, while the as-prepared one showed a non-porous structure (figure 1(a)). figure 1. fe-sem images of (a) as prepared ps-mwcnt; (b) mesoporous ps-mwcnt; and (c) ho3s-ps-mwcnt. the samples’ pore sizes can be evaluated from the sem images. the pore sizes of the mesoporous psmwcnt samples range from 10 nm to 25 nm. the observed mesoporous structures of ps-mwcnt support the proposed nano-crystallization-induced phase separation mechanism. 3.2. sulfonation of mesoporous ps-1d mwcnt nanocomposite the hydrophobicity of mesoporous ps-1d mwcnt nanocomposite highly limits its applications in aqueous mediums, but it can be hydrophilically modified to have good contact with water. the hydrophilic surface modifications of the mesoporous ps-1d mwcnt nanocomposite can be achieved by controlled sulfonation reactions without much affecting the mesoporous morphology of the polymer by treating it with a mild sulfonating agent like sulfuric acid. electrophilic substitution introduced the hydrophilic sulfonic acid (-so3h) groups in the mesoporous ps-1d mwcnt nanocomposite surface phenyl group. the mesoporous ps-1d mwcnt nanocomposite will predominantly be homogenously sulfonated on the polymer surface in 5 this methodology. the extent of surface modification by sulfonation reactions was determined as ion-exchange capacity (iec). the sulfonation conditions were optimized based on the requirement of a minimal loss in the specific surface area and the pore structure of the mesoporous polystyrene. the optimized condition was the reaction of ho3s-ps-mwcnt with conc. h2so4 for 2 h at 70 ℃, and the corresponding iec value was found to be 0.011 meq/g. the sulfonated mesoporous ps-1d mwcnt nanocomposite shows excellent contact with water in this condition. figure 1(c) shows the mesoporous morphology of the ho3s-ps-mwcnt samples. interestingly, the mesoporous structure of the sample was not much affected due to the sulfonation reactions. 3.3. equilibrium adsorption figure 2 shows the equilibrium adsorption conditions of xylene isomers’ adsorption by ho3s-psmwcnt. the adsorption reaction was carried out at different times and with varying amounts of ho3s-psmwcnt. as evident from figure 2, the amount of xylene adsorption is increased with the increase in ho3sps-mwcnt adsorbents and reaches saturated adsorption with 70 g/l of adsorbent with >99% removal. therefore, it can be said that the optimized amount of ho3s-ps-mwcnt was 70 g/l for the treatment of saturated concentration of dissolved xylene isomers in water. on the other hand, the amount of adsorption also increases with time. as shown in figure 2, with two h of adsorption, % of removal reached a maximum of only 85%, whereas that of 4 h of adsorption time reached a maximum of >99%. also, the adsorption time of 8 h exhibited >99% of removal. therefore, the minimum time to reach the equilibrium adsorption of xylene isomers from water solution with optimized 70 g/l of adsorbent can be four h. the efficient and fast adsorption of xylene molecules to the ho3s-ps-mwcnt adsorbent is correlated to the phenyl-phenyl (hydrophobic) interaction of xylene and styrene moiety of the polymeric chains. figure 2. adsorption of xylene isomers from water solution with different amounts of ho3s-ps-mwcnt adsorbent and contact times. 3.4. adsorption kinetics and effect of temperature figure 3 shows the adsorption kinetic curves of xylene isomers from water solutions at different temperatures of 30 ℃ and 50 ℃. the kinetic studies have been carried out with the optimized adsorbent amount of 70 g/l. compared to 30 ℃, the adsorption rate is higher at 50 ℃ while the overall adsorption amount was decreased at higher temperatures. for instance, the maximum % of removal has reached >99% at 30 ℃ (in 4 h of contact time) while it was only 85% at 50 ℃ (in 2 h of contact time). at lower temperatures, the adsorption process is initially controlled by the concentration gradient (primary diffusion of xylene into the mesopores) of xylene molecules. afterward, the adsorption process occurs due to the secondary diffusion of xylene molecules into the hydrophobic polymeric chains. however, the diffusion rate into mesopores is highly favored at higher temperatures due to the increased kinetic energy of the xylene molecules compared to that at lower temperatures. 6 figure 3. adsorption kinetics of xylene isomers from water solution at different contact times and temperatures. table 1 shows a comparative performance of xylene removal by various solid-phase adsorbents reported in the literature against the ones reported in this study. as evident from table 1, ho3s-ps-mwcnt exhibited higher adsorption capacities (499 mg/g) and % of removal (>99%) for xylene adsorption in comparison to the other adsorbents reported in the literature. table 1. xylene removal efficiency by various adsorbents. adsorbent adsorption capacity (mg/g) % of removal reference porous biomass carbon foam 322.36 98 [78] polyvinyl chloride-sio2-melamine sponge 93 [79] cellulose modified fe3o4 nanoparticles 595 53 [80] single walled-carbon nanotubes 210 [81] ho3s-ps-mwcnt 499 >99 this study 3.5. recyclability figure 4 shows recyclability curves of ho3s-ps-mwcnt adsorbent for ten consecutive adsorptiondesorption cycles. after each cycle of adsorption, the desorption of adsorbed xylene molecules or regeneration of the adsorbent was carried out by treating the adsorbent in hot ethanol at 60 ℃. as evident from figure 4, the reduction in the amount of adsorption after each adsorption cycle is only marginal. interestingly, the adsorbent showed >99% of removal at the first adsorption cycle, and the same adsorbent exhibited >97% of removal after the 10th cycle. the complete desorption or regeneration characteristics of adsorption sites of any porous solid in a given adsorption system are essential for their practical applications. therefore, the demonstrated rapid regeneration of ho3s-ps-mwcnt adsorbents by simple treatment with ethanol ensures they are beneficial and advantageous adsorbent materials. 7 figure 4. recyclability of ho3s-ps-mwcnt adsorbent for xylene isomers adsorption from water solutions. a1–a10: adsorption cycles; d1–d10: desorption cycles. 4. conclusions the ps-mwcnt samples were prepared using the one-step bulk polymerization method. mesoporous structures in ps-mwcnt were created using the nano-crystallization phase separation method. sulfonated ps-mwcnt nanocomposites were prepared by treating the samples with concentrated sulfuric acid. the sulfonated ps-mwcnt (ho3s-ps-mwcnt) was found to be a potential adsorbent for dissolved xylene isomers from water solution. the sulfonated mesoporous ps-mwcnt (ho3s-ps-mwcnt) has been studied as a potential adsorbent for the efficient adsorption of xylene isomers from the aqueous solution of nearsaturated concentration. this unique adsorbent exhibits excellent sorption characteristics with enhanced kinetics and excellent recyclability. the equilibrium and kinetics studies indicate that the adsorption process occurs not just by simple diffusion but by strong migration between the adsorption sites or cavities. author contributions conceptualization, mrk and vr; methodology, mrk; validation, vr; formal analysis, mrk; investigation, mrk; resources, mrk; data curation, mrk and vr; writing—original draft preparation, mrk; 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degradation properties aiza maqbool department of physics, university of agriculture faisalabad, faisalabad 38040, pakistan; aizamaqbool12@gmail.com abstract: photocatalysis, an innovative technology, holds promise for addressing industrial pollution issues across aqueous solutions, surfaces, and gaseous effluents. the efficiency of photodegradation is notably influenced by light intensity and duration, underscoring the importance of optimizing these parameters. furthermore, temperature and ph have a significant impact on pollutant speciation, surface chemistry, and reaction kinetics; therefore, process optimization must consider these factors. photocatalytic degradation is an effective method for treating water in environmental remediation, providing a flexible and eco-friendly way to eliminate organic contaminants from wastewater. selectivity in photocatalytic degradation is achieved by a multidisciplinary approach that includes reaction optimization, catalyst design, and profound awareness of chemical processes. to create efficient and environmentally responsible methods for pollution removal and environmental remediation, researchers are working to improve these components. keywords: catalyst dosage; pollutant degradation; environmental remediation; catalytic activity; reaction kinetics; water treatment; catalyst optimization; sustainable chemistry; environmental impact assessment introduction photocatalytic degradation refers to a process in which a substance is broken down into smaller, less harmful compounds under the influence of light and a photocatalyst. this phenomenon is often employed in environmental and industrial applications for the removal or transformation of pollutants, contaminants, or other undesirable substances. here are some key aspects of photocatalytic degradation properties: 1. photocatalyst the photocatalyst is a material that facilitates the degradation process when exposed to light. the novel oxidation process known as photocatalysis works by using sunlight to cause electron-hole pairs to form on a photocatalyst’s surface. an enhancement in this field is represented by composite photocatalysts, which improve doping, coupling, and sensitization of individual photocatalysts like zno, ago2, and tio2. these developments could lead to more innovative uses of environmental therapy [1]. titanium dioxide (tio2) and zinc oxide (zno) are commonly used photocatalysts due to their stability, efficiency, and non-toxic nature. they are suitable for photocatalytic applications due to their broad bandgap, especially when subjected to ultraviolet (uv) light [2]. 2. light source typically, photocatalytic reactions require ultraviolet light to activate the catalyst. citation maqbool a. photocatalytic degradation properties. characterization and application of nanomaterials. 2024; 7(1): 5523. https://doi.org/10.24294/can.v7i1.5523 article info received: 28 march 2024 accepted: 23 april 2024 available online: 31 may 2024 copyright copyright © 2024 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2024, 7(1), 5523. 2 however, advancements in photocatalytic materials and technologies have expanded the range of light sources to include visible light, making the process more practical and applicable in various settings. photocatalysts produce electron-hole pairs when exposed to uv light, which excites electrons from the valence band to the conduction band. the breakdown of organic contaminants or the creation of beneficial compounds can result from these charge carriers engaging in redox reactions with adsorbed species on the oxide’s surface [3]. electrons in the valence band may be induced to move to the conduction band, forming a hole in the valence band, when a material absorbs photons with energy equal to or greater than the bandgap energy. the generation of superoxide radicals (o2•−) is triggered by interactions between electrons in the conduction band and oxygen molecules on the crystal surface [4]. concurrently, water molecules on the crystal surface may interact with positively charged holes in the valence band, resulting in oxidation processes that generate hydroxyl radicals (·oh) [5]. figure 1 shows the process of photocatalytic water splitting [6]. these reactive oxygen species (ros), which break down dye molecules and other organic pollutants, are essential to the photooxidation process. some instances of ros include superoxide and hydroxyl radicals [7]. figure 2. process of photocatalytic water splitting. 3. substrate the substance targeted for degradation is referred to as the substrate. photocatalytic degradation is effective for various pollutants, including organic compounds, dyes, pesticides, and even some inorganic contaminants. tio2 [8], ag, and zno [9] nanoparticles are the most commonly used substrates in the photocatalytic degradation of dyes in water and are effective due to their antimicrobial properties, uv radiation blocking capabilities, and photocatalytic characteristics [9]. these nanoparticles are commonly employed in the textile industry for various purposes such as self-cleaning, uv protection, and antibacterial properties. by harnessing their photocatalytic abilities, these nanoparticles facilitate the degradation of dyes present in water, thus aiding in water purification processes [1,2]. this multifunctional approach not only removes dyes but also provides additional benefits such as characterization and application of nanomaterials 2024, 7(1), 5523. 3 microbial control and uv protection, making it a versatile solution for water treatment and environmental remediation [10]. heterogeneous photocatalysis has undergone a significant change in the last ten years, especially in the application of titania in its anatase form [1,2]. the majority of the applications for this photocatalyst were moderate oxidation processes in gaseous or liquid organic phases. but in more recent times, there has been a shift towards using it for the complete oxidation and breakdown of different organic chemicals and contaminants, especially in situations with humid air or water [1,2,11]. reaction mechanism: the photocatalytic degradation process involves the generation of ros on the surface of the photocatalyst when exposed to light. these ros, such as hydroxyl radicals (•oh), superoxide radicals (o2 • −), and others, then react with the substrate molecules, leading to their degradation into simpler and less harmful byproducts. the production of oh° radicals resulting from the presence of water has been ascribed to this alteration in photocatalytic behavior. this process’s mechanism is based on the interaction of titania with water, which produces oh• radicals. these radicals are essential for promoting the complete oxidation and destruction of organic molecules and environmental contaminants. for instance, water molecules react with e−-hole pairs on the tio2 surface and generate radicals. these highly reactive species are the cause of photocatalytic degradation of organic molecules [12] through equations (1)–(4): tio + hv → tio (e + h ) (electron-hole pair generation) (1) tio (e ) + o → o. (superoxide radical anion) (2) tio (h ) + h o → oh (hydroxyl radical) (3) tio (e + h ) + organic pollutant → degraded product (4) 4. factors influencing efficiency 4.1. catalyst surface area a larger surface area provides more active sites for the photocatalytic reaction. surface area can be increased by different strategies like coating, treating plasma, heating or cooling, and changing the shapes (thin films, cylindrical, etc.). using ionic liquids for surface modification offers dual advantages as both a supply and an agent for enhancing the photocatalytic properties of materials. through the introduction of external elements or functional groups onto the surface of photocatalysts, such as nitrogen or sulfur in bismuth oxyhalides, additional active sites can be created, impacting the material’s electrical properties positively. when a semiconductor material is illuminated, positive charges (h+) are produced that combine with oh-anions to produce hydroxyl radicals. when water and oxygen are available, these radicals are crucial for the oxidation of organic materials [13]. therefore, increasing the coating surface area helps to increase the photocatalytic activity of the coating. the increased specific surface area boosts the film’s hydroxyl group concentration. when a semiconductor is exposed to light in the context of heterogeneous photocatalysis, electron-hole pairs (e and h+) are produced. hydroxyl radicals are produced when the negatively charged oh ions and positively charged holes (h+) interact. the hydroxyl radicals generated at the photocatalyst's surface characterization and application of nanomaterials 2024, 7(1), 5523. 4 function as oxidizing agents, which ultimately increase the efficiency of the photocatalytic activity [14]. additionally, the incorporation of organic groups facilitates improved charge carrier separation and enhanced adsorption of contaminants, thereby increasing surface area and photocatalytic efficiency. this surface modification process aims to capture photogenerated electrons, thus inhibiting the recombination of electron-hole pairs generated during photoinduction. ultimately, the utilization of ionic liquids as a means of surface modification presents a versatile approach to optimize photocatalytic performance, leveraging their unique properties to enhance material functionality and effectiveness in environmental remediation and other applications [15]. 4.2. light intensity and duration the duration and intensity of light are important factors in photodegradation, especially in photocatalysis, where light is utilized to start chemical reactions. higher light intensity and longer exposure times generally enhance the degradation process. through photocatalysis, a substance is activated by light, speeding up chemical reactions without permanently altering the catalyst’s chemical composition. in contrast, conventional thermal catalysts require heat to activate them. the activation mode is the primary difference: photosensitive catalysts are activated by light, whereas thermal catalysts are activated by heat [16]. the rate of photodegradation is directly impacted by the light source intensity. since more photons are available to activate the photocatalyst and produce reactive species, higher light intensities usually lead to faster degradation rates. beyond a certain optimal intensity, nevertheless, additional increases might not appreciably speed up the rate of degradation. the optimal intensity varies based on the target pollutant and the particular photocatalyst. another important consideration is the period spent in the light. extended exposure periods typically result in higher deterioration rates because the photocatalyst absorbs more photons over time, producing a greater number of reactive species. like light intensity, there might be an ideal time frame, though, after which the rate of degradation plateaus or increases just slightly. reaction kinetics principles lead to the link between light intensity, duration, and photodegradation rate. first-order kinetics, which states that the rate of reaction is proportional to the concentration of the pollutant and the concentration of the active species produced by the photocatalyst, is typically followed by the photodegradation process. the concentration of these active species is influenced by both the length and intensity of the light, which affects the overall response rate. although photodegradation rates can be increased by longer exposure times and stronger light, there are realistic concerns about cost and energy efficiency. in large-scale applications, it might not be practical or cost-effective to use extremely high-intensity light sources or extended exposure times. to attain the intended degradation rate while consuming the least amount of energy, light intensity and duration must be optimized. 4.3. ph and temperature the ph of the solution and the temperature can affect the rate of photocatalytic degradation. advanced oxidation processes, or aops, are finding a broader characterization and application of nanomaterials 2024, 7(1), 5523. 5 application in environmental applications such as wastewater cleaning. these reactions are based on oxidation by reactive species and are usually catalyzed by photocatalysts like zno, tio2, cds, co3o4, or wo3. these semiconductor photocatalysts undergo photoexcitation when they come into contact with an intense light source and an oxidizing agent such as air or oxygen, which produces reactive species [17]. the organic contaminants in the wastewater are then efficiently oxidized by these reactive species, leading to their elimination. the semiconductor used, the ph of the solution, and the light source intensity are some of the variables that affect the process efficiency [18]. the adsorption and interaction between the target pollutants and the photocatalyst are influenced by ph, which also changes their surface charges. the ideal ph range for many photocatalytic processes is one in which the photocatalyst surface charge and chemical makeup are most advantageous to the degradation process. reduced efficiency may result from ph deviation because of variations in surface charge, surface chemistry, or pollutant speciation. the stability and solubility of the photocatalyst, which in turn impacts its duration and efficacy in the degradation process, can also be influenced by ph. temperature modifies the reaction kinetics, which affects how quickly photodegradation processes occur. since more energy is available to activate surface reactions at higher temperatures, reactions often proceed more quickly. nevertheless, overly high temperatures may cause the photocatalyst and the intended pollutants to thermally degrade, which would reduce the process’ overall effectiveness. the ideal temperature range is frequently found through experimentation and can change based on the particular photocatalyst and contaminants present. reaction kinetics may also be affected by temperature changes in the physical characteristics of the reaction environment, such as the viscosity and diffusion rates of reactants and products. 4.4. catalyst dosage and pollutant degradation catalyst dosage plays a crucial role in pollutant degradation efficiency. ongoing research and literature reviews indicate that an appropriate catalyst dosage can significantly enhance degradation rates, leading to more effective pollutant removal. the need to strike a balance between increased catalyst dosage and economic feasibility. excessive dosages may not proportionally improve degradation rates and can lead to diminishing returns in terms of cost-effectiveness. photocatalysis using nanoparticles (nps) is a promising method for dye removal from water due to their exceptional and highly tunable surface properties compared to bulk materials. nps offer a wider scope in catalytic processes thanks to their unique surface characteristics, and they have higher diffusion rates coupled with lower reinforcing capabilities, all of which collectively enhance their catalytic performance [8,9,19,20]. like the potential of rgo-250 as a robust photocatalyst for dye degradation, highlighting its adaptability and efficiency in well-defined circumstances that require ph, dye concentration, catalyst dosage, and recyclability into consideration. these results facilitate the creation of effective and long-lasting methods for environmental remediation that make use of cutting-edge substances like catalysts based on graphene [21]. characterization and application of nanomaterials 2024, 7(1), 5523. 6 5. challenges 5.1. selectivity ensuring that the photocatalytic process selectively targets the desired pollutants without causing unintended side reactions. the method of utilizing photocatalysts and light energy to decompose organic pollutants in wastewater or other environmental contaminants is known as photocatalytic degradation. selectivity, or the photocatalyst’s capacity to preferentially target and break down particular contaminants while mostly unaffected by other chemicals, is a crucial component of this process. because it maximizes the effectiveness of pollution removal while minimizing the formation of hazardous byproducts, selective photocatalytic degradation is desired. selectivity is attained via several factors: catalyst choice, reaction conditions, targeted modification, light source, and controlled reaction pathways. different photocatalysts exhibit varying affinities for different types of pollutants. by selecting a suitable photocatalyst based on the nature of the contaminants, researchers can enhance selectivity. parameters such as ph, temperature, and the presence of co-catalysts or electron donors can influence the selectivity of the photocatalytic process. optimizing these conditions can help tailor the degradation process toward specific pollutants. surface modification of photocatalysts with specific functional groups or nanoparticles can enhance their affinity towards certain pollutants, thus improving selectivity. the wavelength and intensity of the light source used for photoexcitation can also influence selectivity. tuning the light source to match the absorption spectrum of the target pollutant or photocatalyst can enhance the efficiency of degradation. understanding the reaction pathways involved in photocatalytic degradation allows researchers to design strategies that promote the selective degradation of target pollutants while minimizing the formation of unwanted byproducts. 5.2. catalyst recyclability strategies for reusing and recycling the photocatalyst to improve the economic and environmental sustainability of the process. the potential of catalyst recyclability is one of the major benefits of photocatalytic degradation. when subjected to light and an oxidizing agent, photocatalytic degradation is the process of breaking down organic contaminants in wastewater using catalysts, usually semiconductors such as tio2 [22], zno [23], cds, co3o4, or wo3. by absorbing photons, these catalysts create electronhole pairs, which when combined with oxygen and water, produce extremely reactive species like hydroxyl radicals. these free radicals can oxidize and break down organic contaminants into innocuous byproducts like water and co2. the catalyst may frequently be recovered and utilized again after the degrading process, which lowers operating costs and minimizes waste. to extract the catalyst from the wastewater that has been treated, a variety of techniques, including centrifugation and filtration, can be used. furthermore, methods such as catalyst immobilization onto support materials can improve recyclability by limiting catalyst loss in the process. overall, the combination of photocatalytic degradation and catalyst recyclability offers a characterization and application of nanomaterials 2024, 7(1), 5523. 7 promising approach for efficient and sustainable wastewater treatment, contributing to environmental protection and resource conservation. 5.3. scale-up transitioning from laboratory-scale experiments to large-scale applications poses challenges in maintaining efficiency and cost-effectiveness. many semiconductor materials have been investigated for photocatalytic water splitting since 1972. their limited ability to absorb visible light has presented a significant obstacle, impeding their practicality for widespread use [24]. significant progress has been achieved in the last few years in the identification and synthesis of semiconductor materials specifically designed for solar water splitting, especially in the visible light spectrum [25]. scale-up in photocatalytic degradation involves transitioning laboratory-scale processes to larger industrial or municipal scales. this scaling-up process requires careful consideration of various factors to ensure efficient and effective operation: reactor design: designing reactors suitable for larger volumes while maintaining optimal contact between the photocatalyst and wastewater is crucial. different reactor configurations, such as slurry reactors, fixed-bed reactors, or immobilized photocatalyst reactors, may be employed depending on the specific requirements. light source: ensuring adequate and uniform illumination across the entire reactor volume is essential. this may involve using powerful and efficient light sources, such as uv lamps or natural sunlight, along with appropriate light distribution mechanisms. catalyst preparation: developing scalable methods for preparing and immobilizing photocatalysts onto suitable supports or substrates is necessary. these methods should ensure consistent catalyst properties and performance at larger scales. mass transfer: optimizing the mass transfer of pollutants to the catalyst surface and products away from it is critical for efficient degradation. this may involve adjusting flow rates, agitation methods, or reactor geometries to minimize mass transfer limitations. operational parameters: identifying and optimizing operational parameters such as ph, temperature, catalyst loading, and residence time for larger-scale systems is essential to maximize degradation efficiency while minimizing operational costs. safety and environmental considerations: ensuring safety protocols are in place for handling potentially hazardous materials and byproducts and assessing any potential environmental impacts of the scaled-up process. overall, successful scale-up of photocatalytic degradation processes requires interdisciplinary collaboration between scientists, engineers, and stakeholders to address technical, economic, and regulatory challenges while realizing the full potential of this environmentally friendly wastewater treatment technology. conflict of interest: the author declares no conflict of interest. characterization and application of nanomaterials 2024, 7(1), 5523. 8 abbreviations tio2 titanium 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and reproduction in any medium, provided the original work is properly cited. characterization and application of nanomaterials （2018） original research article nylon 66/nano caco3 composites peipei yuan,jianshu zhong,xisheng liu school of materials science and engineering, suining university of technology, sichuan, china abstract the nylon 66/nano-caco3 composites were prepared by melt blending on a twin-screw extruder. scanning electron microscopy (sem), polarized light microscopy (plm), thermal loss (tga) and differential scanning calorimetry (dsc) the eff ects of nanometer calcium carbonate on the polycrystalline behavior and thermal properties of nylon 66/nano caco3 composites were investigated. the results show that the nanometer calcium carbonate particles are dispersed in the nylon 66 matrix and exist in the form of aggregates. the nanometer calcium carbonate has the eff ect of heterogeneous nucleation, which can reduce the size of the spherules. the decomposition temperature of the nylon 66 is 400 ℃, the addition of nano-caco3 to reduce the decomposition temperature. at the same time, dsc test showed that the β-crystalline form in the material reduced the melting temperature of the material. the addition of nano-caco3 in the nylon 66 matrix resulted in the decrease of the crystallization temperature and the increase of the half-height width of the endothermic peak. the lower the crystallization temperature, the wider the crystallization temperature range. keywords: nanometer calcium carbonate; nylon 66; crystallization; cooling rate 1. introduction 1.1. nylon 66 nylon 66 (pa-66) is the most important varieties of nylon, the output of about 70% of nylon engineering plastics [1]. nylon 66 is made from hex methylene diamine and adipic acid, nylon is a semi-crystalline crystalline material, pa66 pa series is the highest mechanical strength, the most widely used varieties, because of its high crystallinity, so its rigidity, heat resistance are higher. as the nylon 66 amorphous part of the amide is easy to combine with water molecules, nylon 66 at room temperature, the higher water absorption. compared with the general plastic, nylon 66 toughness, excellent wear resistance, friction noise is small, in addition, nylon 66 on hydrocarbon solvents, especially gasoline and lubricants are more resistant. nylon 66 has a low viscosity and is temperature sensitive and can therefore be used to process very thin components, but to strictly control the temperature. due to the presence of the amide polar groups, the nylon 66 is extremely water-absorbent and must be dried before the product to take into account the impact of moisture absorption; nylon 66 molding process is good, can be used for extrusion, blow molding, injection molding, casting molding. the structure of nylon 66 is shown in figure 1-1: figure 1-1 structure of nylon 66 the nylon 66 is easily crystallized by hydrogen bonding between hydrogen and oxygen. the crystals of nylon 66 are shown in figure 1-2 below: nylon 66/nano caco3 composites 20 figure 1-2 nylon 66 crystal structure the modifi cation of nylon can be divided into physical modifi cation and chemical modifi cation. the main methods of chemical modifi cation are: graft copolymerization and functionalization of polymer. the main methods of physical modifi cation are: blending, sex, etc. [2]. in the plastic processing process generally use physical modifi cation. nylon 66 can be reinforced in nylon 66 fi lled with fi ber reinforced materials, to maintain its excellent performance on the basis of the heat resistance, chemical stability and mechanical properties improved [3]; nylon 66 by the capacity of toughening (mah) grafted pp, pe, will increase the impact strength of the material, and grafted elastomer epdm, poe due to its own impact performance, the impact of the impact of nylon 66 more and the toughening agent is also a non-polar polymer, the water absorption is small, and the polar group of the toughening agent after grafting is the same as that of the nylon 66 the reaction of the group results in a decrease in the water absorption of the composite. 1.2. nanometer calcium carbonate nano-calcium carbonate is a new type of nanomaterials that are used in many fi elds and have been industrialized. nano-calcium carbonate and other nano-materials compared to the raw materials easy to obtain, high performance, low cost, non-toxic and tasteless; compared with ordinary calcium carbonate, small particle size, large surface area, high whiteness, high activation rate, structure and so on. at present, the application technology of nano-calcium carbonate is the most mature in the plastics industry. the nanometer calcium carbonate has four nano-effects (quantum size eff ect, small size eff ect, surface eff ect and macroscopic quantum tunneling eff ect), which can improve the mechanical properties and improve the thermal stability and reduce costs. china's plastics, rubber, coatings and other industries led to the rapid development of nano-calcium carbonate, the increasing demand for him, therefore, nano-calcium carbonate has a strong market competitiveness. 1.3. preparation of polymer/nano caco3 composites polymer nanocomposites are prepared by a variety of methods, including intercalation, blending, in situ polymerization, sol-gel, and blending in this experiment. 1.3.1 interlayer insertion method interlayer insertion method is an important method to prepare polymer nanocomposites, which is the hotspot of current research. interlayer insertion method is the use of inorganic nano-particles layered structure, the organic polymer dispersed into the inorganic layer, the inorganic material was stripped into a nano-scale layered structure, evenly dispersed in the nylon matrix and made nylon inorganic nano composites. the method can be divided into four kinds: melt intercalation polymerization, solution intercalation polymerization, polymer melting intercalation, polymer solution intercalation. the melting intercalation polymerization method is the most widely used. the intercalation method is rich in raw materials, low price, and the nanoparticles are ordered in the material. therefore, the obtained materials have anisotropy, high interfacial strength, good barrier property and good dispersibility, but have some claim. this method also has drawbacks, such as the uneven dispersion of the catalyst between the layers, nano-minerals will reduce the catalyst activity, which will have an impact on the performance of composite materials. 1.3.2 blending method blending is the easiest way to prepare polymer nanocomposites, similar to polymer blending. blending can be divided into four methods: solution blending, emulsion blending, melt blending, mechanical blending, wherein the melt blending is a method in which the polymer is blended with the nanoparticles in a molten state to produce a composite material, the application is more extensive. melt blending less energy consumption; no use of organic solvents, no harm to the environment and reduce waste; can be used conventional processing technology for production, simple process, easy to industrial; cannot be used in situ polymerization of the polymer can be used blending the however, the melt peipei yuan, et al 21 blending has some limitations. if the decomposition temperature of the polymer is lower than the melting point, this method cannot be used and the particles are easy to agglomerate during heating. therefore, attention should be paid to the surface treatment with the coupling agent and the dispersant. 1.3.3 in situ polymerization method in situ polymerization [16] is a method in which inorganic nanoparticles are uniformly dispersed in a polymer monomer and a suitable catalyst is initiated to initiate monomer polymerization. this method is suitable for the preparation of most polymer nanocomposites and maintains excellent properties of the material. compared with other preparation methods, the reaction conditions of the method are mild and there is no hot working, so that the nanoparticles in the material are dispersed uniformly and the performance is not damaged. in situ polymerization can be used to prepare reinforced polymer nanocomposites, but the use of certain limitations. 1.3.4 sol-gel method sol-gel method is the most commonly used and mature method for preparing nylon inorganic nanocomposites. the principle of this method is colloidal chemical method, that is, the precursor is dispersed in a certain organic solvent to form a homogeneous solution, by adding acid, alkali, or neutral salt catalyzed hydrolysis of the formation of sol, and then by heating or solvent evaporation the sol is converted to a gel. the preparation method is simple and easy to operate, and the surface of the material can be controlled by controlling the process of hydrolysis of the precursor to make the material excellent. however, in the process of drying the gel, the small molecules in the material are easily volatilized, resulting in the generation of shrinkage stress, so that the performance of the composite material. the purpose and signifi cance of this research with the development of china's automobile, electronics, aviation and other industries, the requirements of the material performance are getting higher and higher, the development of high-performance pa66 new varieties become the focus of research. the research on nylon nanocomposites has achieved great success, especially in the case of nylon 6/clay nanocomposites. on the use of nano-sio2, nano-montmorillonite pa66 reported a lot, but for the use of nanocaco3 modifi ed pa66 reported very little. nano-caco3 with other nano-materials and ordinary calcium carbonate does not have excellent performance, if the successful preparation of nylon 66/nano caco3 composite material, will save a lot of cost, application prospects. in this study, nano-caco3 modifi ed pa66, nano-caco3 as a nucleating agent [18-20] with heterogeneous nucleation, can change the crystallinity of the polymer and crystalline morphology, thereby aff ecting the performance of composite materials. 2. experimental part 2.1. experimental principle 2.1.1 eff ect of nano-caco3 nucleating agent on pa66 the eff ect of nano-caco3 nucleating agent on pa66 is mainly through the following two aspects: 1) nano caco3 on the crystallization behavior of pa66. nylon 66 in the general case only α crystal form, and nylon nanocomposites in addition to α crystal form, as well as β crystal form, nano-caco3 is through heterogeneous nucleation to make nanocomposite polymorphic, and thus aff ect its performance. nano-caco3 as a nucleating agent will make the polymer to form a small spherule, and the crystal structure is uniform. the addition of nano-caco3 will limit the movement of nylon 66 molecular chain, induced β crystal form, the crystallization rate and crystallinity increased, the crystallization temperature decreased. 2) eff ect of nano caco3 on the interface of pa66. nano-particles in nano-particles with a large contact area of the polymer, and nano-particles with four nano-eff ect, his surface area, high surface activity, and polymer affi nity, strong physical and chemical eff ects, this eff ect will aff ect the performance of the material. 2.1.2 principles of test instruments a) scanning electron microscopy (sem) test scanning electron microscopy is a new type of electronic optics developed in the 1960s to evaluate the interaction of the interface. he combines the advantages of optical microscopy and transmission electron microscopy, which can directly observe large chunks of samples like optical microscopes, as well as high resolution and magnification as transmitted microscopes, and his sample preparation is simple and observes the depth, image three-dimensional, so he is widely used to study the nylon 66/nano caco3 composite morphology characteristics. nylon 66/nano caco3 composites 22 b) polarizing microscopy (plm) test optical microscopic analysis technology is to use visible light to observe the material, the use of the nature of light to analyze the microstructure and crystal phase composition. polarizing microscopy is the most eff ective tool for optical microscopy. nowadays, due to the rapid development of science, polarizing microscope observation technology can not only qualitative analysis, but also quantitative analysis. c) thermogravimetric analysis (tga) thermogravimetric analysis is a technique for measuring the relationship between material temperature and mass at programmed temperature. substances in the heating or cooling process will sublimation, vaporization, decomposition of the gas or loss of crystal water and the quality of change, by analyzing the quality of different temperature changes, you can study the nature of the material changes in the crystal and some physical and chemical phenomena. thermogravimetric analysis is highly deterministic and widely used in various fi elds related to chemistry. d) diff erential scanning calorimetry (dsc) differential scanning calorimetry is an important method of thermal analysis and is a technique for measuring the relationship between the power diff erence between the input sample and the reference and the temperature at the programmed temperature. because diff erential thermal analysis technology can only be semi-quantitative or qualitative analysis work and many factors, so the development of differential scanning calorimetry, he not only differential thermal analysis of the general function, can be quantitative analysis, but also to obtain the process of change sample temperature and various thermodynamics, kinetic parameters. 2.2. experimental drugs and equipment 2.2.1 experimental drugs see table 2-1 for experimental drugs table 2-1 experimental drugs drug name level production business nylon 66 1300s3j1 asahi kasei chemicals nano caco3 industrial grade shanxi ruicheng huaxin nano materials co., ltd. manufacturing liquid paraffi n industrial grade commercial 2.2.2 test equipment the experimental instruments are shown in table 2-2 table 2-2 major laboratory equipment model name manufacturer gh-10 high speed mixer beijing yingte plastic machinery plant cet35 mixing with twin screw extruder kobelongkuoya (nanjing) machinery co., ltd dgf30022b electric blast oven china chongqing galaxy test instrument co., ltd tk-c921ec polarized light microscope (plm) victor company of japan limited q200 diff erential scanning calorimetry (dsc) ta s-4800-1 scanning electron microscope (sem) japan hitachi stare system thermogravimetric analysis (tga) mrttler toledo peipei yuan, et al 23 2.3. preparation of composite materials 2.3.1 preparation of pellets 1000 g of nylon 66 was dried in an electro thermal blast oven at a set temperature of 102 ° c for 6 hours and then mixed with nano-caco3 in a high-speed mixer, and an appropriate amount of liquid paraffi n was added and mixed at room temperature for three minutes. mixed with a good material into the twin-screw extruder extrusion, and fi nally with a cold pelletizer for pelletizing. the process parameters of the twin-screw extruder are shown in table 2-3, where the mass fraction of nano-caco3 is 1%, 2%, 3% and 5%. the composite samples are designated pnc-01, pnc-02, pnc -03, pnc-04, pure nylon 66 is designated as pnc-05. table 2-3 process parameters of twin-screw extruder process parameters parameter value/℃ process parameters parameter value/℃ a district temperature control 180 district temperature control 260 two district temperature control 240 eight district temperature control 260 three district temperature control 250 nine temperature control 260 four district temperature control 260 area temperature control 260 five district temperature control 260 head temperature control 260 six district temperature control 260 1) speed: 75r/min; feeding frequency: 3/hz 2.3.2 preparation of experimental samples the granular nylon nanocomposites were dried, placed in a melt index instrument to melt, and then manually pressed, the prepared sheet material will be used for scanning electron microscopy to observe the dispersion of nanocalcium carbonate. the granular nylon nanocomposite material is heated and melted, and then produced under a certain pressure, natural cooling to room temperature, the prepared sample will be used for polarizing microscope to observe the shape and size of spherules. the granular nylon nanocomposites were cut into fi ne particles with a mass of 10 mg or less and dried for dsc and tga to test their properties. 2.4. performance test and characterization of nylon 66/nano caco3 composites a) scanning electron microscopy (sem) the dispersion of nano caco3 in the samples was observed by scanning electron microscopy. the acceleration voltage of the scanning electron microscope is 3.0kv, the magnifi cation is 8000 times. b) polarization microscopy (plm) the morphology and size of spherules were observed by polarizing microscope. the magnifi cation of the selected eyepiece is 10x and the magnifi cation of the objective lens is 20x. c) thermogravimetric analysis (tga) tga detection in a nitrogen atmosphere, the temperature was raised at a rate of 10 ° c/min, and the change in sample weight with temperature was recorded. d) diff erential scanning calorimetry (dsc) dsc analysis was carried out using tzero aluminum as a reference sample under nitrogen at a fl ow rate of 50.0 ml/ min. eff ect of nano-caco3 content on the crystal form of nylon 66/nano-caco3 composites. the samples were heated at a heating rate of 40.00 ° c/min to 270.00 ° c and then kept at a constant temperature of 3.00 min to eliminate the thermal history and then equilibrated to 50.00 ° c, and fi nally 40.00 ℃/min heating rate to 320.00 ℃, and recorded during the heating process with the temperature changes in the heat fl ow. eff ect of isothermal crystallization time on the crystal form of nylon 66/nano-caco3 composites. take the sample with a mass fraction of 5%. the sample was heated to 280.00 ° c at a heating rate of 40.00 ° c/min and then kept at a constant temperature of 3.00 min to eliminate the thermal history. the sample was heated to 240.00 ° c at a heating nylon 66/nano caco3 composites 24 rate of 40.00 ° c/constant temperature of 10.00min (the second constant temperature 30.00min), the material to create a thermal history, followed by a balance to 50.00 ℃, and fi nally to 40.00 ℃/min heating rate of heating up to 320.00 ℃, and record the heating process with the temperature changes happening. eff ect of heating rate on the crystal form of nylon 66/nano-caco3 composites. a sample with a mass fraction of 5% was fi rst heated to a temperature of 300.00 ° c at a heating rate of 40.00 ° c/min and then at a constant temperature of 3.00 min to eliminate the thermal history and then equilibrated to 50.00 ° c. finally, the samples were heated at 10.00 ° c/min and 40.00 ° c/min heating rate up to 320.00 ℃, and record the heating process with the temperature changes in temperature. eff ect of cooling rate on the crystal form of nylon 66/nano-caco3 composites. take the sample with a mass fraction of 5%. the sample was heated to 280.00 ° c at a heating rate of 40.00 ° c/min and then kept at a constant temperature of 3.00 min to eliminate the thermal history. the samples were cooled at 10.00 ° c/min and 40.00 ° c/min the temperature from 250.00 ℃ down to 50.00 ℃ and fi nally to 40.00 ℃/min heating rate to 320.00 ℃, and record the heating process with the temperature changes in temperature. 3. results and discussion 3.1. dispersed morphology of nanometer caco3 in nylon 66 figure 3-1 shows a scanning electron microscope image of the pnc-01 section showing the dispersion of nanocalcium carbonate in nylon 66, where the spherical particles are dispersed nano-calcium carbonate in the nylon 66 matrix. it can be seen from the figure that the effect of nano-calcium carbonate dispersion in the nylon 66 matrix is not ideal, mainly in the form of aggregates. the scale in the figure shows that the nanometer calcium carbonate aggregates have a particle size of about 1000 nm to 2000 nm, which is much larger than the size required for the nanocomposites (1 nm to 100 nm), and a signifi cant interface boundary can be observed, calcium in the nylon 66 matrix was agglomerated, nano-calcium carbonate and nylon 66 matrix interface adhesion is very weak. there are two reasons for the agglomeration of nano-calcium carbonate: first, nylon 66 melt and nano-calcium carbonate particles interface is relatively weak; second, nano-calcium carbonate particles surface area is very large, exposed to the outer layer of particles in the high atomic activity, so there is higher than the surface energy of ordinary particles, in order to reduce the surface energy, the interaction between particles agglomeration. figure 3-1 sem image of pnc-01 section the dispersion of nano-calcium carbonate particles in nylon 66 matrix and the interfacial adhesion of nylon 66 to nano-calcium carbonate are very important for the properties of the materials. in order to disperse the nanoparticles evenly and have some interface adhesion, the most common the method is to surface treatment of nanoparticles. the nano-calcium carbonate is subjected to organic surface treatment, that is, the intercalation of the organic reagent into the layers of the nanoparticles can not only make the hydrophilicity of the surface of the nano-calcium carbonate particles become lipophilic and increase the interface adhesion with the nylon 66; will increase the interlayer spacing of nanocalcium carbonate, is conducive to nylon 66 into the interlayer, nylon 66 and nano-calcium carbonate in the nanouniform mixing; the same time, non-reactive surface treatment will reduce the surface tension of nylon 66, and then make between the nanoparticles, the interaction between the nanoparticles and the polymer decreases. the results show that diff erent kinds of intercalation agent, amount of intercalation agent and organic time will aff ect the eff ect of nanoparticles on the surface treatment of nano-particles. as the nano-calcium carbonate particles used in this experiment were not surface treated, the nanoparticles were easily agglomerated, which affected the properties of nylon 66/nano caco3 composites. in order to prevent the agglomeration of nano-calcium carbonate particles, in addition to organic surface treatment, but also from the following aspects can be improved: fi rst, without causing nylon 66 decomposition of the case, as far as possible to extend the peipei yuan, et al 25 mixing time; second, improve the twin screw extruder screw structure, or the use of a combination of screw with a mixer to enhance the cutting eff ect; third, change the process parameters, such as barrel temperature, screw speed, so that the performance of the material to achieve better. 3.2. eff ect of nano-caco3 on the crystal morphology of composites figure 3-2 nylon 66 molecules in the presence of hydrogen bonds, hydrogen bonding of the positioning of the material to show anisotropy, the crystal has a birefringence eff ect of the crystal, so that the morphology of the crystal can be observed by a polarizing microscope. figure 3-2 shows a picture of the natural cooling of the material after melting the observed material under a polarizing microscope. it can be seen from the fi gure that the nucleating agent has a signifi cant eff ect on the crystal morphology of nylon 66. the crystal of pure nylon 66 has a clear black extinction phenomenon, and the spherules are radially grown from the center along the radial direction to the surroundings, the spherical interface is clear and larger (see 3-2a). when the nanometer calcium carbonate nucleating agent was added, the size of the spherule became smaller. when the nucleating agent content was 1% (see 3-2b), the size change of the spherule was less obvious. with the increase of the nucleating agent content, the size of the spherules is getting smaller and smaller until the added content is 5% (see 3-2d), and the complete spherules have not been seen, just some fi ne crushed crystals. it is clear that the size of the spherule is signifi cantly reduced as the amount of calcium carbonate nucleating agent increases. this is because the nanometer calcium carbonate nucleating agent in the crystallization process from the nucleus, can increase the probability of heterogeneous nucleation, change the crystallization behavior of the polymer to promote the formation of spherules, and the increase in grain crystal of the distance becomes smaller, the spherules squeeze each other to make the size of the spherules smaller, therefore, the addition of nano-calcium carbonate nylon spherule size and uniform shape. figure 3-2 polarization microscope of nylon 66/nano caco3 composites a (pnc-05) b (pnc-01) c (pnc-03) d (pnc-04) 3.3. thermal stability of nylon 66/nano caco3 composites tga was used to study the thermal stability of composites. figure 3-3 shows the thermal weightlessness curves for nylon 66 and pnc-04. it can be seen from the fi gure that nylon 66 and pnc-04 have only one weight loss stage, between 0 ° c and 400 ° c, the quality of nylon 66 decreases slightly as the temperature increases and decreases from about 100 ° c initially, the decrease in the quality of nylon 66 is due to the evaporation of water. after 400 ° c, the mass of nylon 66 decreased rapidly due to the decomposition of nylon 66; from 470 ° c to 600 ° c, the mass change of nylon 66 was zero and the residue was carbonized by nylon 66. for pnc-04, the mass change at 520 ° c is zero due to the decomposition temperature of nanometer calcium carbonate of 897 ° c and the last remaining 5% of nanometer calcium carbonate. the tga curve of the pnc-04 is somewhat higher than the tga curve of the nylon 66 to the low temperature region. the decomposition temperature of nylon 66 is about 400 ℃, while the decomposition temperature of pnc-04 is about 380 ℃, which is lower than that of nylon 66, which indicates that the addition of nano-caco3 particles reduces the thermal stability of the composites. under normal circumstances, the nylon 66/nano caco3 composite material than the pure nylon 66 decomposition temperature is higher, because when the nano-calcium carbonate particles dispersed evenly into the nylon 66 matrix, with nylon 66 will have a strong interface reaction; and dispersed nano the particles can block the heat conduction and gas diff usion eff ect, to prevent heat transfer can protect the polymer section, so that it nylon 66/nano caco3 composites 26 is not easy to break down, thereby reducing the generation of combustible gas, while the polymer particles can prevent combustible gas diff use into the object the thermal properties of the nylon 66/nano caco3 composites are improved by reducing the surface heat and reducing the combustion heat, thereby preventing excess segments from decomposing to produce combustible gases. figure 3-3 tga curves for nylon 66 and pnc-04 this experiment is not the same as the results obtained from predecessors may be nano-calcium carbonate particles scattered uneven, occurred reunion, as observed by scanning electron microscopy. the nano-calcium carbonate particles used in the experiment were subjected to non-thermodynamically stable state without surface treatment. in order to reduce the surface energy, the atomic interaction was agglomerated together. the agglomerates of nanoparticles have two eff ects: fi rst, nano-calcium carbonate particles have hydrophobic oleo phobic surface heat, weak affi nity with nylon 66, the formation of large aggregates will make defects in the material, thermal stability decreased the second, the agglomerates of nanoparticles improve the thermal conductivity of the composites, so that heat can easily be transferred to the polymer matrix, resulting in the rapid decomposition of the segment, while the decomposition of the segment will increase the combustion gas to further accelerate the decomposition of materials. therefore, in order to prepare the nylon 66/nano-caco3 composite with good thermal stability, the key is to improve the dispersion of nano-calcium carbonate in nylon 66. 3.4. melt crystallization behavior of nylon 66/nano caco3 composites study on the melting crystallization behavior of composites by dsc. figure 3-3 shows the dsc curve of the composite. in the melt crystallization process, the nucleating agent content, constant temperature time, heating rate and cooling rate will have an impact on the crystallization of nylon 66. 3.4.1 eff ect of diff erent mass fraction of nylon 66/nano caco3 composites on crystallization figure 3-4 dsc curves of nylon 66/nano caco3 composites with diff erent mass fractions figure 3-4 shows the composite dsc curves of nylon 66 and diff erent mass fraction of nano-calcium carbonate, with heating rates of 40 ° c/min. bill has pointed out that nylon 66 has α and β two crystal form, under normal circumstances nylon 66 is α crystal form, α crystal form is more stable. nylon 66 can form a diff erent crystal form, is due to the presence of nylon 66 amide groups to make a strong hydrogen bond between the molecular chain, the different arrangement of molecular chains so that the formation of hydrogen bonds in different ways, so nylon 66 produced a polymorphic phenomenon the as can be seen from the fi gure, all the curves are bimodal, they correspond to nylon 66 alpha crystal form and β crystal form. however, the shape of the peaks and the crystallization temperature are peipei yuan, et al 27 diff erent. with the increase of the content of nano-caco3, the increase of the nano-caco3 increases the crystallization temperature of the material, and the crystallization temperature range widen. the crystallization temperature of nanocomposites decreases with the increase of nano-caco3 content because a large amount of nano-calcium carbonate particles cannot be uniformly dispersed in the matrix leading to the fi nal agglomeration. and these reunited particles cannot promote nucleation. the increase in the endothermic peak of the nanocomposite may be due to two reasons: the first reason may be the increase in the viscosity of the nanocomposite melt system, which is caused by the interaction of nanometer calcium carbonate with the molecular chains in the nylon 66 matrix. the addition of nanometer calcium carbonate limits the diff usion of the nylon 66 molecular chain, resulting in pa66 crystal growth rate decreased. due to the heterogeneous nucleation of nano-calcium carbonate, the crystal growth rate plays a decisive role in the total crystallization rate. thus, a decrease in crystal growth rate means a decrease in the total crystallization rate. that is, the crystallization needs to be in a wider temperature range, and thus the endothermic peak increases. the second reason may be the uneven dispersion of nano-calcium carbonate, which will lead to uneven growth of the crystal, diff erent content of nano-calcium carbonate nylon 66 molecular chain between the diff erent crystal growth rate. 3.4.2 the eff ect of diff erent constant temperature on the crystallization of the material figure 3-5 dsc curves for pnc-04 for diff erent constant temperature times figure 3-5 for the diff erent temperature of the pnc-04 material dsc curve, the solid line at 240.00 ℃ constant temperature 10min, dotted line at 240.00 ℃ constant temperature 30min. compared to the two curves found that the temperature of the crystallization of nylon 66 did not have much impact. according to the theoretical analysis, the longer the thermostatic time, the longer the nylon chain has a more suffi cient time to form a stable α crystal form, but from the two curves found that with the increase in temperature, α melting peak and β melting the area of the peak did not change, that is, the alpha crystal did not increase. this may be due to uneven dispersion of nano-calcium carbonate caused by the two selected pnc-04 material, nano-calcium carbonate content of 5%, but doing constant temperature 30min experiment, the selected material may contain of the nano-calcium carbonate is more, it is conducive to the formation of β crystal form, α crystal growth trend cannot be revealed. 3.4.3 eff ect of cooling rate on crystallization of composites figure 3-6 dsc curves for pnc-04 at diff erent cooling rates nylon 66/nano caco3 composites 28 figure 3-6 shows the dsc curves of the pnc-04 composites at different cooling rates. the solid line is the cooling rate of 10 ° c/min and the dotted line is the cooling rate of 30 ° c/min. compared with the two curves, two melting peaks were found on the two dsc curves, and as the cooling rate increased, the curve moved toward the low temperature and the peak shape became broad. these phenomena can show that there are α crystal form and β crystal form in the nylon 66 nanocomposite matrix, and the crystallization temperature decreases and the crystallization temperature range increases with the increase of the cooling rate. this may have two causes: one is undercooling, each material has a theoretical crystallization temperature, but because the cooling rate is too fast, the actual crystallization temperature of the material than the theoretical crystallization temperature is lower, the diff erence between them value is undercooled. an increase in the cooling rate causes the degree of sub cooling to rise, so that the crystallization temperature at 30 ° c/min is lower. second, because the material molecular chain from the chaotic into a regular order, from the amorphous state or semi-crystalline state into a complete crystalline state, take some time to complete, the faster the cooling rate, the same temperature range to stay less time, the more obvious the temperature hysteresis, so the curve to the low temperature movement and the shape of the curve widened. 3.4.4 eff ect of heating rate on crystallization of composites figure 3-7 dsc curve for pnc-04 at diff erent heating rates figure 3-7 shows the dsc curves of pnc-04 composites at diff erent heating rates. the solid line represents the heating rate of 10 ℃/min and the dotted line represents the heating rate of 40 ℃/min. compared with the two curves, it can be found that although there are two melting peaks, the two peaks are diff erent in area, and the material with the heating rate of 10 ℃/min is basically α crystal (designated as material 1), and the heating rate for the material at 40 ° c/min, there are α crystal form and β crystal form (designated as material 2), which shows that although the two experimental materials are the same, the crystallization rate is the same when the thermal history is eliminated, but the resulting material is not complete the same. theoretically speaking, the faster the rate of temperature rise, the stronger the temperature hysteresis, the higher the temperature of the crystal melted, but the reaction in figure 3-7 is just the opposite, which is due to the two diff erent materials used in the experiment caused. material 1 is mostly stable because of its large α crystal form, until the temperature is high when the melting peak occurs; and material 2 due to β crystal form, at a lower temperature β crystal will melt, β crystal melt will make the heat of the material increases, and the melting of the α crystal is accelerated, so that the temperature of the melting peak is lowered. 4. conclusiond the nylon 66/nano caco3 composites were successfully prepared and the polycrystalline behavior and thermal properties of the nanocomposites were characterized. the electron microscope image shows that the nano-calcium carbonate particles are dispersed in nylon 66 in the form of aggregates, because the nano-calcium carbonate has not been surface modifi ed, the surface can be high and hydrophilic oleo phobic, the atoms easily interact with the polymer binding capacity is weak, easy to use to form aggregates. through the tga image shows that the addition of nanocalcium carbonate nylon composite materials to reduce the decomposition temperature, the thermal stability of the material decreased. the thermal behavior of pa66 and pa66/nano-caco3 composites shows that the thermal history has a strong infl uence on the polycrystalline transformation behavior of the samples. for pa66/m calcium carbonate composites, after heat treatment at 280 °c for 3 minutes, there was a significant change at different cooling rates. pa66/nanocalcium carbonate composite material in the molten state heat treatment led to β crystal form to become the main crystal type and higher cooling rate of this phenomenon is more obvious, probably because of nano-calcium carbonate with peipei yuan, et al 29 heterogeneous nucleation, can make the material crystal the size of the material decreases and the melting temperature of the material is reduced. the difference of polymorphism between pure pa66 and pa66/nano-calcium carbonate composites reflects the complexity of the melting behavior of pa66/nano-calcium carbonate composite system. the addition of nanocomposite will limit the movement of nylon 66 molecular chain, induce the formation of β crystal form, increase the crystallization rate and crystallinity, and decrease the crystallization temperature. references 1. wj. tang, f. wu. advances in polyamide modifi cation technology. plastics science and technology, 2002,1 (2): 38-4l 2. wj. tang. world polyamide engineering plastics market and forecast. engineering plastics applications, 2003,3 (2): 56-58 3. qf. zhou, xc. lu, p. wang. high performance and modifi cation of polyamide. plastics science and technology, 2005,4 (5): 59-64 4. wp. chen, qy. gao, ch. mi. research progress of nylon 66 modifi cation. journal of henan university (natural science edition), 2000,30 (2): 71-72 5. jl. zhang, j. he, x. li. research on present situation and application of modifi ed. engineering plastics, 2000, 28 (5): 19-23 6. j. zhu, bz. li research progress of polymer/inorganic nanocomposites. new chemical materials, 2000,28 (10): 3-13 7. dreamy province. application of nanotechnology in polymer modifi cation. new chemical materials, 2001,29 (2): 3-6 8. y. gu. powder surface modifi cation technology and its application. chemical progress, 1994, 2 (1): 33-41 9. zf. ding, sh. huang. eff ect of ultrafi ne particle dispersion on properties of polymer materials. plastic processing, 1998,2 (3); 45-50 10. sc. lu. powder processing technology. china light industry press, 1990 (2): 25-30 11. j. zhu, bz. li research progress of polymer/inorganic nanocomposites. new chemical materials, 2000,28 (10): 3-13 12. vaia r a, wagner h d. framework for nanocomposites. materials today, 2004, 5 (11): 32-37 13. pinnavaia t j, beall g w. polymer-clay nanocomposites. polymer, 2000, 10 (5): 18 to 23 14. j. wang, yc. zong, cx. feng. pyrolysis of polycarbosilane/nano nickel powder. applied chemistry, 1997,14 (2): 90-92 15. l. chen, wj. yang, c. huang. preparation of nanometer iron oxide particles by polymeric materials as medium. polymer materials and engineering, 1998,14 (4): 53-55 16. david i a, scherer g w. an organic-iorganic single-phase composite. composites science and technology, 1995, 7 (7): 1967-1967 17. cy. shen, zx. zhang. preparation and dispersion stability mechanism of polymer/nano particle composites. chemistry and adhension, 2000, 5 (4): 178-118 characterization and application of nanomaterials (2020) volume 3 issue 2 doi:10.24294/can.v3i2.1069 81 original research article subnanophase coatings as new type low-dimensional nanomaterials: ultra-high-vacuum synthesis, properties and application nikolay plusnin institute of automation and control processes, far east branch, russian academy of sciences, vladivostok, russia; e-mail: plusnin@dvo.ru abstract in this paper, a classification of low-dimensional nanomaterials is given, and new type of these nanomaterials — subnanophase coatings are proposed. experimental results on the formation of a wetting layer of a transition metal on a silicon substrate by physical deposition in vacuum and results of this layer identification by the eels method are given. based on these results, a new approach to the formation of subnanophase coatings has been proposed by creation of an interface stresses structuring wl. the possible properties and application prospects of subnanophase coatings are considered. keywords: low-dimensional nanomaterials; subnanophase coatings; wetting layer; ultrahigh-vacuum; formation; properties; application article info article history: received 24 june 2020 received in revised form 18 july 2020 accepted 23 july 2020 available online 3 august 2020 copyright copyright © 2020 nikolay plusnin. doi: 10.24294/can.v3i2.1069 enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/by/4.0/ 1. introduction in the world there are many major scientific, educational and technological centers that are engaged in researches and various applications of nanotechnology and nanomaterials. in particular, there are a number of manufacturers of nanophase materials. the most famous among them is the company ―nanophase technologies‖, which produces nanodispersed powders ―nanogard‖ and ―nanotech‖ based on zinc and aluminum oxides, respectively [1] . usually, nanophase materials are obtained by compacting bulk materials from nanodispersed particles with a diameter of 2 to 50 nm. as a result, after compacting, they consist of grains 4-30 nm in size. in their atomic structure, nanophase materials are neither amorphous, nor crystalline, nor even quasicrystalline. it is believed that they are in a low-dimensional-nanophase state. this production technology of nano phase materials is still relevant today. considering the main role of effects underlying their basis, low-dimensional nanomaterials can be classified as follows: 1) low-dimensional heterocrystalline ones with the effect of intercrystalline proximity. 2) low-dimensional heterophase amorphous ones with the effect of interphase proximity. 3) low-dimensional ones with the quantum effect in their constituent particles. 4) two-dimensional ones with the effect of interaction with the http://creativecommons.org/licenses/by/4.0/ 82 substrate. 5) two-dimensional ones with the effect of interaction with the vacuum. 6) two-dimensional ones with a transboundary quantum size effect. besides, various types of low-dimensional nanomaterials are possible, including thin-film, dispersed and composite nanomaterials, which are combination of these types of nanomaterials. here, we will focus on subnanophase coatings (snp) consisted of low-dimensional clusters with a decisive influence on these coatings of interaction effects with the substrate and vacuum. due to the influence of the strained interface on their structure and properties, these coatings can have a set of unique properties that are absent in bulk coatings, as well as in massive nanophase materials. it is assumed that snp coatings will be used in areas of the nano industry where the use of massive (with a thickness of more than 1 nanometer) and high-stable coatings is not required. namely, when the coating can be non-equilibrium and metastable and have a nanometer thickness. the problem of creating snp coatings is associated with the methods of their synthesis, as well as with the methods of structural-phase diagnosis of their state and diagnosis of their properties, both in the process of obtaining these coatings and at its completion. the combination of the synthesis and growth control of snp coatings in an ultrahigh vacuum environment allows reducing the number of control cycles and, thus, more effectively finding nanomaterials with the required properties. ultra-high vacuum (uhv) is the most convenient and cleanest medium for controlling the atomic and electronic structure and various properties of coatings. uhv allows you to synthesize coatings from atomic or molecular beams [2] and use electron, ion, and photon beams to diagnose coatings [3] . in addition, uhv-vacuum provides the ability to control the surface state of the coatings during their synthesis and allows cyclically controlling the formation of ultrathin layers and their interfaces, creating the necessary composition and structure in them. in addition, uhv technology (uhvt) similar to nanotechnology (nt) is high-tech technology and use controlled manipulations with individual atoms and molecules. in a vacuum, particle beams and fields can interact on a solid surface without interference. this property gives uhvt a unique advantage over nt in other environments. first of all, it is the controllability of the synthesis of coatings. another important advantage of uhvt is the pure conditions for the synthesis and control of coatings. as for the lower level of practical application of uhvt due to the high cost, this is offset either by the high cost of the product (for example, in nanomedicine) or by the ability to produce a product in the form of a coating on large substrates (for example, in the field of solar energy, microelectronics and nanoelectronics). currently, methods and devices for the synthesis and control of coatings in vacuum have evolved significantly and reached a high level of perfection [4] . this allows, in the main, focusing not on creating these methods, but on their use. however, the specificity of snp coatings, their non-equilibri um, subnanostructural state, requires more precise regulation and a wider range of growth parameters. for this, it is necessary to develop methods for producing directed atomic beams, which will have a higher density and simultaneously lower temperature or kinetic energy. in addition, the structure-phase specificity of snp coatings, which differs in their atomic density and interatomic bonding configuration from bulk phases, requires the further development of more adequate methods of structural-phase analysis directly during synthesis. therefore, it is necessary to increase the sensitivity of these methods or adapt them to the subnanometric sample thickness and to work in real time. the solution of these problems will allow creating new types of nanomaterials in a subnanophase state. the purpose of this work is to develop an approach to the self-organizing synthesis of subnano phase coatings using physical deposition of vapor phase in ultrahigh vacuum. 83 2. creating subnanophase coatings in vacuum for the synthesis of snp coatings in vacuum, both new methods of obtaining atomic vapor beams with low thermal energy of vapor are needed. also methods of electron spectroscopy, microscopy and probe measurements adapted to snp coatings are needed. in addition, it is necessary to solve the following list of main tasks for obtaining snp coatings: (1) to develop design principles for their electronic and atomic structure. (2) to develop the principles of management of their growth and self-organization by regulating the density and temperature of the atomic vapor stream, as well as the temperature of the substrate. (3) to develop principles of subnanoscale diagnostics in real time of their structural-physical and other properties. for this, it is necessary to conduct both theoretical studies (including computer simulation) and experimental studies. deposition from the vapor phase in vacuum at a low substrate temperature usually provides a non-equilibrium and, in particular, nanophase state of the coating [5] . however, to obtain a thinner coating in a sub-nanophase state, this is not enough. high kinetic energy of vapor and latent heat of phase transitions in coating lead to mixing at the interface and the formation of alloys or compounds and additionally cause cluster fusion into larger islands and, thus, coarsening of the grains and transition to the bulk phase [6] . the obvious way to solve this problem is to evaporate the material at a source with a low vapor temperature [6,7] , as well as decreasing the diffusion and chemical interaction of the coating with the substrate using a subor single-molecular intermediate layer [8] . also, it is necessary to modify the methods for monitoring the structural state of the coating and the interface layer thickness during the growth of coatings [7,9,10] . the possibility of realizing the self-organizati on of snp coatings from the vapor phase or atomic beam was first shown by the example of metal growth on the surface of a single-crystal silicon substrate. such a coating was first called by a surface multilayer phase [11,12] , and then, a two-dimensi onal nanophase [13,14] . the first of these names reflected the view on the stabilizing role of the substrate, and the second on the two-dimensional nature of the snp coating. subsequently, the snp coating got the short name ―ν-phase‖. in this name, the uncertainty and low dimension structure of the snp coating and, accordingly, the difficulty of its identification from experimental data were reflected. indeed, the existing variety of experimental research methods (x-ray, electron, ion, probe microscopy and spectroscopy) is well developed for the study of single-crystal, amorphous and even quasicrystalline homogeneous structural state. but, in the case of low-dimensional, disordered and, in general, non-uniform coating, most of these methods do not allow identifying this coating and separating them from bulk homogeneous phases. as a result, the snp coating is often interpreted as a mixture of some bulk phases. nevertheless, the method of electron spectroscopy of characteristic electron energy loss (eels) allowed us to identify the integral structure of the ν-phase, namely the structure of its electron density and, indirectly, of its atomic density. indeed, the energy position of the loss peak in the eels spectrum connected with the excitation of a volume plasmon gives information about the oscillation frequency of the plasma of valence electrons in the local region in which the electron loses its energy. and the oscillation frequency, in turn, gives information about the density of valence electrons and, indirectly, about the density of atoms that donate their electrons to a valence bond of one or another type. for a solid, an approximation of solid balls is usually used. in this model, atoms are very tightly packed like solid balls. with this, the densest packing is realized in an ordered lattice — in a crystal. but, in the crystal, one can break the dense structure of the packing by means of subjecting this body to 84 stretching, inserting vacancies and rotating interatomic bonds, forming clusters and intercluster (intergranular) defective interfaces, as well as rotating the clusters themselves relative to each other. something similar seems to be realized in the ν-phase under the action of tensile stresses caused by the substrate and under the action of its conjugation with this phase. it leads to the fact that the atoms in the phase at the interface are not closely connected to each other and their packaging is not compact. due to this, in the eels spectrum of the ν-phase, shifted bulk plasma loss (bpl) peak is formed. but if the ν-phase has an inhomogeneous structure, there will form a whole group of peaks. each peak in this group corresponds to a local collective interaction with electrons of the same type of configuration of interatomic bonds and with the same electron density. the adaptation of the atomic and electron density in the phase to the density of the substrate, as well as the non-uniform nature of this density, cause the bpl peak to shift, expand, and decrease in intensity. thus, it is possible to distinguish the ν-phase from the bulk coating and determine the range of thickness on which the ν-phase is formed by use the shift, the degree of expansion of the bpl peak, and a decrease in its intensity. 3. experimental observation of met al snp on silicon a series of experiments was carried out to study the initial stage of growth of transition metals on silicon using the methods of aes, leed, eels, afm, as well as measurements of conductivity, optical reflection and magnetization. namely eels data showed the formation of an snp coating. based on eels data, we previously called these coatings by the ν-phase, and then we called them by the wetting layer (wl). the latter name reflects the adaptation of the atomic density of the snp coating to the atomic density of the substrate. figure 1 and 2 present the eels spectra families, showing changes of electron density in fe and cr layers and at the metal-substrate interface, during growth of fe and cr on si (001) and si (111), respectively. in figure 1a and 1b, electron density changes are shown in the case of mixing fe with the si substrate and in the case of the growth of pure fe at elevated and lowered temperatures of metal’s vapor, respectively. figure 1c shows the eels spectra of the fe–si phases obtained after annealing the samples of figure 1b. figure 1. eels fe on si (001) in the case of fe growth at elevated (a) and lowered (b) vapor temperature, respectively; (c) eels of fe–si phases on si (001) after moderate annealing of the fe coating in figure (b)[15]. in each case, we see transitions of: 1) a pure silicon surface (si) into the surface phase (sp); 2) sp into the wetting layer (wl); and 3) wl of maximum thickness into the bulk phase (bp) of the metal or metal-silicon compound (silicide). these transitions show a change in the position of the peaks of the surface (e1) and bulk (e2) losses. the transition into sp ends when the surface loss shift ceases. and the transition into wl is completed when the energy position of the peak of bulk losses stabilizes without reaching the position of the peak of bulk losses in bp (eb). figure 1a and 1b also show a non-monotonic increase in the energy of the peak of bulk plasmon losses, corresponding to transitions from sp to wl and from wl to bp. the formation of wl in non-equilibrium conditions is a general phenomenon of the formation of the metal/silicon interface. with this, in the case of solid-phase epitaxy, even ordering wl occurs, as is shown in figure 2. and that evokes compacting wl. therefore atomic density of wl becomes closer to the density of bulk silicide. 85 however, as can be seen from figure 1b and figure 1c, the amplitude of the peak of volume plasmon losses at the stage of wl formation is much smaller, and the peak width is greater than in bp. this can be explained only by the formation of snp coverage. moreover, in the case of snp coverage of pure fe on si (001) (figure 1b), these differences are more pronounced, since this coating is in a more non-equilibrium state and has a more pronounced gradient of the atomic density. figure 2. eels and leed of cr-si phases on si (111) obtained by the deposition of cr with an elevated vapor temperature and annealing[15]. indirect evidence of the formation of the fe snp on si (001) at the wl formation stage was obtained on the basis of aes and afm data. at this stage, for samples in figure 1c, the stability of the coating in composition decreased according to aes, and the height of the surface relief was significantly less than at the stage of bp formation [14] . at the same time, on the afm images, the wl relief was not seen due to the diameter of the afm needle near 1 nm. invisible relief at this thickness can be explained only by a subnanophase structure of the coating. additional confirmation of such structure of the metal wls is also provided by data of on their electrical, optical and magnetic properties [16] . these data show a resistive type of conductivity (independence of resistance on the temperature) of cr wl, a high uv absorption (low uv reflection) in wl of fe on si (001). moreover, the dependence of polarized light reflection on the magnitude of the magnetic field perpendicular to fe wl corresponds to the superparamagnetism of this wl. and as it is known, resistive type of conductivity, high uv absorption and superparamagnetism are most pronounced in coatings and films of metals with a nanophase or finely dispersed structure. 4. properties and application of snp coatings cluster or subnanoscale structure, uneven along the plane and subnanoscale gradient of structural properties in the transverse direction, determine the specific properties of coatings. examples of specific properties of snp coatings can also be increased wetting ability, increased surface area, increased surface curvature and latent energy of stresses. due to the reduced atomic density, the presence of clusters, near amorphous type structure, a large number of vacancies, they will also have their modified electronic structure and modified optical, magnetic and electrical properties. and, as a result, there will be coatings with high uv absorption, magnetic-soft coatings and coatings with resistive conductivity type [16] . in addition, in snp coatings, by analogy with multilayer coatings, a chemi cal potential gradient is possible and, as a consequence, the presence of an embedded electric field. due to the low thickness of snp coatings and due to the vacuum environment during physical vapor deposition, the scope of applications of snp coatings will be limited to the element base of electronics, optoelectronics, and telecommunications. in addition, they can be used for various specialized applications where there is no mechanical damage and the influence of the corrosive environment and the atmosphere (for example, in biosensors). it is assumed that the main application of snp coatings will focus in the range of nanoelectronics, nanospintronics, nanooptics, nanoplasmonics, and analytical instrumentation for ecology, biology and medicine. another application of snp is the use of a tension energy hidden in them for solid-phase reactions, crystallization and other processes of formation of ultra-thin coatings. 86 5. conclusion the subnanophase coatings as a class of new materials have been proposed based on the classification of low-dimensional nanomaterials. synthesize these coatings using physical deposition from low-temperature vapor with control them in ultrahigh vacuum, and use the eels method to identify their subnanophase structure have been proposed. the experimental observations of subnanophase coatings in the form of a metal wetting layer on silicon substrate and also the indirect evidences of their subnanophase structure on data of afm, optical, electrical and magnetic measurements have be en presented. the properties and possible applications of subnanophase coatings are considered. references 1. hannink rhj, hill aj (editors). nanostructure control of materials. cambridge: woodhead publishing limited, 2006. p. 368. 2. voorhoeve rjh. molecular beam deposition of solids on surfaces: ultrathin films. in: treatise on solid state chemistry. new york, london: plenum press; 1976. p. 241–342. 3. o’connor dj, sexton ba. smart rstc (editors). surface analysis methods in material science. new york, berlin: springer verlag; 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plusnin ni. the use of aes and eels for complex analysis of two-dimensional coatings and their growth process. modern electronic materials 2017; 3: 131–141. 11. plusnin ni. from physics of the interface formation to low-dimensional nanocoatings and nanomaterals based on them. vestnik of far east branch of russian academy of science 2016; 4(188): 27–35. available from: https://cyberleninka.ru/article/n/ot fizki-formirovaniya-granitsy-razdela-k-nizkorazmer nym-nanopokrytiyam-i-materialam-na-ih-osnove. 12. plusnin ni, galkin ng, lifshits vg, et al. formation of interfaces and templates in the si(111)-cr system. surface review and letters 1995; 2: 439– 449. 13. plusnin ni, il’iashchenko vm, kitan’ sa, et al. metal thin-film nanophases and their interface with silicon. journal of physics conference 2008; 100: 052094. 14. plusnin ni, il’yashchenko vm, kitan’ sa, et al. formation, electronic structure, and stability of film nanophases of transition metals on silicon. journal of surface investigation. x-ray, synchrotron and neutron techniques 2009; 3(5): 734–746. 15. plusnin ni. atomic-scale aes-eels analysis of structure-phase state and growth mechanism of layered nanostructures. advances in materials physics and chemistry 2016; 6: 195–210. 16. plusnin ni. metallic nanofilms on single crystal silicon: growth, properties and applications. modern electronic materials 2017; 3(2): 57–65. microsoft word can-4152-online characterization and application of nanomaterials (2023) volume 6 issue 2 doi: 10.24294/can.v6i2.4152 1 original research article an investigation on 45s5 nanobioactive glass using ftir and raman spectroscopy sharda sundaram sanjay1, pratibha yadav1, nidhi asthana2, mrigank mauli dwivedi2, kamlesh pandey2,* 1 department of chemistry, ewing christian college, university of allahabad allahabad, uttar pradesh 211002, india 2 national center of experimental mineralogy and petrology, university of allahabad allahabad, uttar pradesh 211002, india * corresponding author: kamlesh pandey, kamleshpandey@allduniv.ac.in abstract bioactive materials are those that cause a number of interactions at the biomaterial-living tissue inter-face that result in the evolution of a mechanically strong association between them. for this reason, an implantable material’s bioactive behavior is highly advantageous. silicate glasses are encouraged to be used as bioactive glasses due to their great biocompatibility and beneficial biological effects. the sol-gel method is the most effective for preparing silicate glasses because it increases the material’s bioactivity by creating pores. glass densities are altered by the internal network connectivity between network formers and network modifiers. the increase in the composition of alkali or alkaline oxides reduces the number of bridging oxygens and increases the number of non-bridging oxygens by retaining the overall charge neutrality between the alkali or alkaline cation and oxygen anion. higher drying temperatures increase pore densities, while the melt-quenching approach encourages the creation of higher density glasses. band assignments for the bag structure can be explained in detail using fourier transform infrared (ftir) and raman spectroscopic investigations. raman spectroscopy makes it simple to measure the concentration of the non-bridging oxygens in the silica matrix. keywords: bioactive glass (bag); ft-ir; raman spectra; melt-quench; epma 1. introduction bioactive materials are becoming an essential component of everyday life. these materials are in between inert and resorbable materials. bio active materials have the ability to form natural bonds with living tissue[1,2]. during the 1970, this new class of materials, i.e., bioactive glass (bag), gained attention[3–7]. the first bioactive glass (bioglass 45s5 with compositions of 45 wt% sio2, 24.4 wt% cao, 24.5 wt% na2o, and 6 wt% p2o5) was developed and studied by jones[8] and hench[9]. bag is mostly used for biomedical applications and consists of a silicate network incorporating sodium, calcium, and phosphorus in different relative proportions. it exhibits high bioactivity and may attach to soft tissues. recently, bioactive glass nanoparticles doped with antimicrobial agents such as silver, zinc, and magnesium ions have been widely developed for medical applications. the bioactive glass nanoparticles in a polymeric composite system enable us to develop potential materials for orthopedic applications to avoid health risks[10]. to study the structural changes during the synthesis of bag, zachariasen[11] observed that the silicate crystals had a threearticle info received: 10 november 2023 accepted: 12 december 2023 available online: 31 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 dimensional network structure, which allowed them to easily form glasses upon melting and cooling. it is necessary to keep the cations as far apart as possible and to ensure that each oxygen ion is linked to no more than two cations. failure to do so would prevent linkage distortion from producing a random network topology. in order to avoid an inflexible octahedral or cubic unit, the coordination number of the oxygen ions surrounding the glass-forming cation must be modest, four or less. with sio2, sio4 2− tetrahedra connected at the corners will form a glass on the basis of the radius ratio. according to smekal[12], a material’s bonding needs to be mixed rather than entirely ionic or totally covalent in order to obtain glass. the covalent bonds have stern bond angles and are strongly oriented. therefore, a random network structure, which is characteristic of glass, cannot be produced by purely covalent bonding. ionic bonds, on the other hand, are non-directional and unable to form networks. thus, a glass needs to have a mixed-character binding[13]. sio4 tetrahedra are the basic building blocks of silicate glasses, which are materials that lack long-range order and crystallinity. the sio4 tetrahedra can form different types of rings, such as 3-, 4-, or 6-membered rings, depending on the si–o–si bond angles and the degree of distortion. some examples of how sio4 tetrahedra contribute to directional characteristics in the glass network are: in pure silica glass, the sio4 tetrahedra form a random network of mostly 6-membered rings, which have an average si–o–si bond angle of 144°. this angle is close to the ideal tetrahedral angle of 109.5°, which minimizes the strain and energy of the network. the 6-membered rings also have a high degree of rotational symmetry, which makes the glass isotropic and transparent. in soda-lime-silica glass, the addition of sodium and calcium oxides as network modifiers reduces the amount of sio4 tetrahedra and introduces non-bridging oxygens (nbos) in the network. the nbos break the symmetry of the rings and create more 3and 4-membered rings, which have smaller and more distorted si– o–si bond angles. these rings increase the directionality of the network. in phosphate glasses, which are a type of bioactive glass that can bond with living tissues, the addition of phosphorus pentoxide as a network former creates a composite structure of separate sio4 and po4 domains. the po4 tetrahedra have a higher charge than the sio4 tetrahedra, which makes them more prone to dissolution and precipitation in simulated body fluid. the po4 domains also have different ring sizes and shapes than the sio4 domains, which create a heterogeneous and adaptable network that can respond to different biological conditions. based on the cation’s electronegativity, the oxides used in the present study are categorised into two distinct groups. the cation’s electronegativity serves as a gauge for the ionic character of the connection because the anion is always oxygen; a lower ionic character is indicated by a higher electronegativity. (i) group i cations form bonds with oxygen that have an ionic character larger than fifty percent. they ought to form glass on their own and be network formers. we refer to them as “network formers”. (ii) group ii cations are marginally less electronegative. they can substitute for some of the cations in group i, but they cannot make glass on their own. we refer to them as intermediates. we produced a nano bioactive glass (nbag) using the sol-gel process and melt quench techniques based on an appraisal of the literature. the precursors teos, nano3, cacl2, and p2o5 are gradually added in four stages of the sol-gel process. according to albert-mercier et al.[14] and deshmukh et al.[15] the network condenses by adding p2o5 to the glasses. an increase in p2o5 increases the polymerization of the silicate network by increasing the connectivity of the silicate network. p2o5 increases the amount of orthophosphate groups in the glass structure, which are the precursors of phosphate compounds that precipitate on the glass surface. the compound, such as hydroxyapatite, forms a strong bond with the bone tissue and enhances the bioactivity of the glass. p2o5 coexists with other network former sio2 in separate domains within the glass, which creates a composite structure that allows for both dissolution and precipitation processes to occur 3 simultaneously. the na2o content in bag affects the glass transition temperature (tg). an increase in na2o content decreases tg. the sintering process of glasses depends on properties like the glass transition temperature and the peak crystallization temperature. a large difference between tg and crystalline temperature (tc) is required to ensure that the glass sinters without crystallizing. crystallization of a bag inhibits its bioactive properties in the presence of crystalline phases[16–18]. in this process, the hydrolysis and poly-condensation of precursors result in the formation of the disordered glass network, and the addition of sodium and calcium salts triggers the gelation of the sol. there is limited literature regarding temperature-dependent ftir studies conducted at different stages for bioactive glasses. the comprehensive data in this work provides a panoramic view of the intermediate constituents and their influence on bonding during the process, which is therefore crucial. in the present study, we report the changes in structural behaviour during the process of gelification as well as the melt-quench method by ftir, laser raman technique, and electron-probe micro analyser. 2. experimental we have synthesised the following five bioactive glass compositions using both melt quench and sol gel synthesis method: (i) 70% sio2-30% cao (bag-1) (ii) 45% sio2-24.5% na2o-24.5% cao-6% p2o5 (45s5) (bag-2) (iii) 53% sio2-23% na2o-20% cao-4% p2o5 (bag-3) (iv) 58% sio2-33% cao-9% p2o5 (bag-4) (v) 53% sio2-6% na2o-20% cao-12% k2o-5% mgo-4% p2o5(bag-5) in the present study the composition 45s5 was considered. in the melt-quenching method, glass is obtained by mixing, homogenizing, calcining, and fusing glass precursors such as oxides or carbonates at 1500 ℃. the starting materials were sio2 (99%, renkem, india), caco3 (98%, renkem, india, na2co3 (98%, renkem, india) and p2o5 (99.9%, glaxo, india). glass batches of 5 g were prepared by meltquenching. for that, the starting materials were mixed homogeneously in acetone as mixing media for 2 h and then dried at 110 ℃. the mixtures were melted in a platinum crucible in a two-step process. firstly, they were heated up to 1500 ℃ with a heating rate of 10 ℃/min, with a holding step for 1 h. finally, the melted compositions were quenched in cold water (0 ℃). this procedure was repeated twice to ensure homogeneity of the specimens. afterwards, the glasses were ground in an agate mortar and pestle. while synthesing bag through sol-gel technique, the composition by weight percent was maintained as 45 sio2 24.5 na2o 24.5 cao 6 p2o5. tetraethyl-orthosilicate (teos), si(oc2h5)4, supplied by acrosorganics, was used as the si network precursor, while sodium nitrite nano3 and calcium nitrate/chloride ca(no3)2 (98%, lobachem, india),were selected as na and ca network modifiers respectively. two separate solutions were prepared. first contains the network precursor and other network modifier. in network precursor teos (9 ml ∼ 4.5 g sio2) was hydrolysed in ethanol and acidified with acetic acid in the 1:4:1 ratio under the magnetic stirring for 120 min, until a transparent sol was formed. the other solution of sodium nitrate and calcium nitrate (equivalent to 1.22 g of each na2o and cao) were dissolved in 10 ml double distilled water for one hours. afterward both solutions were mixed in teos sol separately. finally, p2o5 powder (300 mg) was dissolved in same sol and the final solution was stirred for 24 h at room temperature. this solution was stored at 70 ℃ for 120 h to get the gel. to promote a relatively fast sol-gel transition, the gel was kept at 200 ℃ for 24 h, after this the xerogel was crushed with agate pestle and mortar into a fine powder and then calcined at 350 ℃ and 700 ℃ for 10–15 h. the ftir spectra (in the wave 4 number range 1200–700 cm−1) of sol with different time span reaction (0–3000 s) was also recorded. the sintered specimen powder was characterized by atr-ftir (bruker-alpha, germany) in the wavenumber 4000 cm−1 to 400 cm−1, raman spectra were collected with uniram confocal raman spectrophotometer with laser sources at 785 nm with variable power in the spectral range (100–2000 cm−1). the surface morphology and compositional analysis of the melt quench synthesised bag was analysed by jeol-jxa-8100, electron probe micro-analyser. for this the sample was mounted on epoxy resin and then grinded and polished to a very smooth surface and then coated with 20–30 nm layer of carbon for making the surface conducting. 3. results and discussion the ftir spectra of bioactive glass in range 4000 cm−1–2500 cm−1 and 1500 cm−1–600 cm−1 at different stages is shown in figure 1. the figure 1a, shows a broad peak present around 3300 cm−1 assigned as –oh stretching in the ftir range of 2000 cm−1–4000 cm−1, in sol-gel prepared bag 45s5. when gel is dried at 200 °c, then this peak completely disappeared. in figure 1b different ftir spectra of sol gel prepared bag-2 are recorded at various stage of gelification. the comparative study of these spectra (in range 1500– 600 cm−1) clearly indicates the chemical changes and continuous decrease in their intensity up to 150 h at 70 °c (temperature of gelification), a new peak pattern at same temperature indicates the intermediate phase formation in between 150–170 h. at 200 °c (gel drying temperature), this peaks pattern almost disappeared. figure 1c, explains the effect of na2o, cao and p2o5, here, it is clear that peaks at 783 cm−1 and 1166 cm−1 of hydrolysed teos are completely vanished when nano3 is mixed in the solution. similar effect of cano3 is also observed. the effect of p2o5 in the matrix, reduces the broadness of peak around 1400 cm−1. this effect is also observed in the figure 1d, where glass sample without p2o5 have no peak around the 1400 cm−1 region. figure 1. (continued). 5 figure 1. different stages of ft-ir spectra of bioactive glass (a) in the region (4000–2500 cm−1); and (b) in the region (1500–600 cm−1); (c) effect of different constituents (i) sodium nitrate (ii) calcium nitrate (iii) p2o5; (d) ftir spectra of melt quench glasses with and without na2o and p2o5. in figure 2 the rapid three dimensional time span reaction (with time in seconds) is presented from starting material to partial stabilisation of reaction process of bag formation. the other important features in the gelification process with small interval of time (figure 2) is as follows the ftir spectrum at 30 s. in the homogeneous solution of teos, h2o and acetic acid show strong bands at 1110 cm−1, 1070 cm−1, and 955 cm−1 and medium and small bands at 1165 cm−1 and 809 cm−1, all attributed due to teos. the peak at 1052 cm−1 and 880 cm−1 are due to ethanol. figure 2. ft-ir spectra of bag formation starting from hydrolysis of teos with time 0–3000 s in 1200 cm−1–600 cm−1 range. 6 with the increasing time, the intensity of the of the main peaks of teos tries to reduce their intensity and the intensity of ethanol peaks 1052 cm−1 and 880 cm−1 increases and after 500 s, it becomes almost constant. it is also observed that the absorbance values of si–o–c stretching bands of teos at 1105 cm−1 and 1080 cm−1 show a sudden enhancement during the time span 200 s. this shift is possibly due to the alteration of the dipole moment of the si–o–c vibrations as a result of the reaction of acetic acid during hydrolysis. after 400 s. most of the teos peak disappeared, but the intensity of the peak 950 (si–oh, silanol group) increases. peaks at 805 cm−1 and 1165 cm−1 (i.e., si–o–si sym. and lo components respectively) appears in later stage due to the formation of sio4 network formation of sio2. in the initial stage some peaks tries to overlap/superimpose. a comparative ft-ir spectra of liquid teos, hydrolysed teos and final silica powder are given in figure 3. the raman spectra of teos hydrolysis process with sol-gel bag-2 and melt—quench synthesised bag-2 is shown in figure 4. figure 3. ft-ir spectra of teos, hydrolysed teos and sio2 powder in 1500 cm−1–600 cm−1 range. 7 figure 4. raman spectra of bag (a) at different stages of temperature; (b) bag and sio2 powder by sol gel; (c) bag by melt quench with compositional image of bag by epma. on the basis of these stepwise interaction’s studies (mainly peaks of the ft-ir and raman spectra), following reaction mechanism for the final glass formation can be deduced[19–22]. the logical explanation for each reaction mechanism is given along with each equation:  disappearance of red shift of intense c–h rocking peak at 959 cm−1 due to ch3 of teos to a less intense broad peak at 951 cm−1 indicated the formation of si–oh group (equation (1)). (1)  si–o–si bend frequency mode at 782 cm−1 is revealing hydrolysis. this is also confirmed in raman spectral peak at 1050 cm−1, which confirms the formation of siloxane network on condensation (equation (2)). (2)  red shift of the peak at 1042 cm−1 due to stretching and bending vibrations shows the change in dipole moment of si–o–c fragment. in raman spectra peak at 880 cm−1 is of c–c–o stretching vibrations of ethanol which disappears at higher temperature indicating the evaporation of ethanol (equation (3)). (3)  peak at 1081 cm−1 c–o asymmetric stretch in ethanol (equations (1) and (3)).  decreasing intensity at 1167 cm−1 shows the disappearance of –oc2h5 group due to repeated hydrolysis and condensation giving following product (equation (4)). 8 (4)  the incorporation of na and ca in the silica lattice is observed in their hydrolysed form at 1657 cm−1 and 1641 cm−1 respectively (equations (5) and (6)). (5) (6)  intense peak at 878 cm−1 indicates the formation of sio4 network. a characteristic vibrational mode of [p2o7]4– (pyrophosphate) were also observed at 878 cm−1 which persist even at 700 ℃ with a little red shift at 784 cm−1 indicating the presence of bridge p–o–p within the silaxanol lattice (equation (7)). (7) the raman spectra (figure 4) also reveals the fact: (i) the sharp peak at 1500 cm−1 is due to –ch2 bending vibrations and is also red shifted and become broad after gelification and the broadness reduces after drying the sample. (ii) it is also important to observe the appearance of some new peaks during the process of gelification. at 750 cm−1 the peak is due to p–o–p bridging oxygen (equation (6)) there is a clear increase in the intensity of 1050 cm−1 peak is due to dominant role of phosphorus in gel matrix (equation (4))[23–26]. (iii) another evidence of the existence of the phosphorus in the form of p = o (1376 cm−1—raman peak) of p2o5. it may be due to the formation of pπ–dπ dative bond (figure 5) along with p–o σ bond, introducing double bond character, which in turn strengthen the p–o (nbo) bonds. this p exist up to 800 ℃ and finally forming pyro-phosphate. on comparing figure 4b,c, clearly indicating that the pyro-phosphate does not exist in the melt-quench bag π structure, but the peak at 1050 cm−1 red shifted with very small intensity at 950 cm−1, which is the indication of the formation of o-phosphate (nbo) in the matrix. this o-phosphate is formed because there is rapid increase and quenching of the temperature during the glass formation. 9 figure 5. showing p–d overlap between o and p orbital. this result is also confirmed in ‘electron probe micro analysis’ (epma) of melt quench bag-2 powder in the inset of figure 4 the presence of p2o5 (estimated quantity in final glass 4.8%) is more or less same amount as in the host matrix. 4. conclusion a study confirms that sio4 tetrahedra provide some directional characteristics to form a sort of network, while sodium and calcium introduc randomness in the structure. p2o5 helps in the reinforcement of stable bonds to form an efficient bioactive glass. a systematic mechanism of the glass formation is deduced with the help of ir and raman spectra; 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28(8): 1595–1602. doi: 10.1016/j.jeurceramsoc.2007.11.006 26. mohan babu m, syam prasad p, hima bindu s, et al. investigations on physico-mechanical and spectral studies of zn2+ doped p2o5-based bioglass system. journal of composites science 2020; 4(3): 129. doi: 10.3390/jcs4030129 characterization and application of nanomaterials (2018) volume 1 doi:10.24294/can.v1i2.202 1 comparison between using generalized differential quadrature method and analytical solution in analyzing vibration behavior of nonuniform nanobeam systems hessam bakhshi khaniki1, shahrokh hosseini hashemi 2, hossein bakhshi khaniki2,* 1 department of industrial engineering, sharif university of technology, tehran, iran 2 school of mechanical engineering, iran university of science and technology, tehran, iran abstract in this article, generalized differential quadrature method (gdqm) is used to study the free vibrational behavior of variable cross section nano beams. eringen's nonlocal elastic theory is taken into account to model the small scale effects and nonuniformity is assumed by exponentially varying the width of nano beam. governing equation of motion is solved using generalized differential quadrature method with different numbers of sampling points. effects of increasing the sampling points in reaching more accurate results for first three frequency parameters are presented and it is shown that after a specific number of sampling points, results merge to a certain accurate number. it is concluded that generalized differential quadrature method is able to reach the correct answers comparing to analytical results. moreover, due to the stiffness softening behavior of small-scale structures, necessity of using eringen's nonlocal elastic theory to model the small scale effects due to the frequency variation is observed. keywords: generalized differential quadrature method; gdqm; nanobeam; nonlocal beam; nonuniform beam; variable cross section. 1. introduction beams are one of the important structures used in most mechanical designs ever since. with the improvements done in new devices, scale of such structures have been reduced to micro/nano in order to reach a smaller and lighter machines. in this study, generalized differential quadrature method is used to solve the governing equations of nonuniformnanobeams. scale effect is defined using eringen's nonlocal elastic theory and beam is modeled using euler-bernoulli beam theory. nonuniformity is proposed using exponential width variation while thickness remains constant through the beam in which a schematic model is presented in fig. 1 and used is previous studies (ece et al. 2007, khaniki and hashemi 2016, hashemi and khaniki 2017). figure 1. schematic representation of nonuniform small scale beam 2. problem formulation general equation of motion for nonlocal euler-bernoulli nonuniformnanobeam is achieved as: copyright © 2018 hessam bakhshi khaniki et al. doi: 10.24294/can.v1i2.202 enpress publisher llc.this work is licensed under the creative commonsattribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ � ���� 2       4 3 2 2 2 2 2 2 22 2 2 2 0 0 04 3 2 2 2 22 2 0d w di d w d i d w d w da dw d aei e e e a a e a e a w a w dx dx dx dx dx dx dx dx dx               (1) where e is the young's modulus term, i and a are the second moment inertia and cross section terms, e�a are the small scale parameters, ω is the frequency term and ρ is the mass density. in this study as mentioned before, exponential variation is presented for width of nonuniformnanobeam with constant thickness. therefore nonuniformity terms are presented as: 3 0 0 1( ) , ( ) 12 nx nxa x b he i x b h e  (2) where b� is the width of the beam at x = � , h is the thickness of the beam and n is the exponential nonuniformity term and by defining new parameters to have same range of scales between terms as: 4 2 2 0/ , / l, , / , alx x l y y nl e a l ei         (3) in which by using these new parameters and nonuniformity terms, equation of motion of nonuniformnanobeam could be rewritten in nondimensional form as:     4 3 2 2 2 2 2 2 2 2 2 4 3 22 1 0d w d w d w dw w dx dx dx dx                (4) where λ denotes the nondimensional frequency term. 3. solution procedure as mentioned before, in order to solve the nondimensional equation of motion of nonuniformnanobeam presented in eq.(5), generalized differential quadrature method (gdqm) is employed. this theory uses monomials coefficients and sampling points to introduce the deflection variable as:         1 1 1 2 ( ) (k) ( ) ( ) (k) ( ) 1 1 0 0 2 0 ) 1 ( n n r r r r i k i j i j nk i n ik k k j k k r x h x w h x w h x ww e u              (5) where eik represent the monomials coefficients and n is the number of sampling points. hik (r) are the hermite interpolation shape functions as:            0 ( ) 2 2 222 2 ( ) 1 , 1, ; 0,1, 2 1 1 2,3,/ ..., 1                         r jl i ij lr pi pi pi pi p j j j j h x h x a x b x c l x p n i h x x x x l x j n (6) and li are the off diagonal terms defined as:       1, 1, (1) , 12,3,...,                   n i i n i k ik k k x x x l i k n a x x nd k x i (7) (r 1) (r) (r 1) (1) , 12,3,..., , 1           ik ik ii ik i k al r a a i k n and k i r x x (8) and api, bpi andcpi are the coefficients defined as     (2)2(1) (1)1 1 1 1 1 1 2(1 10 11 1 1 2 ) 1 ( )( ) 2 1 2 ( ) 2 ( ) 2 1 2                l xl x l x l a a x a (9)  10 10 1 (1) 1 1 1 11 12 1 1 1 ( ) 2 2 1 2            ab l x x b x b a x (10) 3 10 10 11 2 (1) 1 1 1 1 1 11 12 1 2 1 1 ( ( ) 2) ( 1) 2              c x x l x c x a x xc a (11)     (2)2(1) (1) 2( 0 1 ) 2 1 ( )( ) 2 1 2 ( ) 2 ( ) 2 1 2                n n n nn n n n n n n a a l xl x l x a x l (12)  0 0 1 1 (1) 2 ( ) 2 2 1 2            n n n n n n n n n n b l x x b x b x a a (13) 0 0 1 2 (1) 1 2 2 1 ( ( ) 2) ( 1) 2              n n n n n n n n n n n n c x x l x x x a c x a c (14) in this study, boundary conditions are assumed to be simply-supported therefore the boundary equations are achieved as: 2 2 ( ): ( ) 0, 0 1&i i d w xsimply supported w x i n dx     (15) it should be mentioned that although this solution is done for simply-supported nonuniformnanobeams but it could be also assigned to other kinds of boundaries. using these equations and rewriting eq. (4) leads to     2 2 2 2 (4) (3) (2) 2 (2) (1) 1 2 1 2 2 02 1 n n ik ik ik k ik ik ik k k k e e e u e e e u                 (16) where��� could be defined using previous literatures (wu and liu 1999 and 2000). equations achieved for each sampling point in eq. (16) could be written in a matrix form as:                         24 4 4 4 4 4 4 4 ( 1) ( 1) ( 1) ( 1) ( 1) ( 1) ( 1) ( 1) 0 0 0b bbb bd db dd db ddn n n n n n n nd d u us s s s q qu u                                               (17) and accordingly, generalized eigenvalue equation could be reached as:              1 12 0dd db bb bd dd db bb bds s s s q q s s     (18) by calculating the results for eq. (18), frequency mode numbers are achieved. 4. results and discussion as shown in previous sections, free vibration equation of motion of nonuniform nonlocal beam is presented and solution process using gdq method is obtained step by step. in order to study the accuracy of current solution process and methodology, frequency terms are obtained for different numbers of sampling points and compared to those calculated using analytical solution. for this reason, first three nondimensional frequency terms are calculated and presented in table 1. different number of sampling points is chosen which is varied from 5 to 8 sample points. moreover, average error with respect to analytical results obtained by hashemi and khaniki (2017) is calculated and presented. it can be seen that increasing the number of sampling points reduces the average related errors. after a number of sampling points, results merge to specific numbers which compared to analytical ones, are in a great agreement. from the results once again it is seen that increasing the nonlocal term reduces the frequency term in all first three modes of vibration. solution method � = th� � = th� � = th� � = th� � = tht error(%) analytical 2.624137 2.787796 2.948800 3.076059 3.126165 4 (hashemi and khaniki 2017) gdqm 5 nodes 2.648128 2.790631 2.975591 3.103779 3.141507 6.63278 e-3 gdqm 6 nodes 2.623994 2.787297 2.948568 3.077145 3.127054 1.89918 e-4 gdqm 7 nodes 2.624128 2.787754 2.948798 3.076066 3.126171 4.67371 e-6 gdqm 8 nodes 2.624128 2.787754 2.948798 3.076066 3.126171 4.67371 e-6 table 1. first mode of vibration frequency term in nonuniform nanobeam with η = � solution method � = �h4 � = �h3 � = �h2 � = �h� � = �h� error(%) analytical (hashemi and khaniki 2017) 3.795550 4.315183 5.004425 5.820408 6.290498 gdqm 5 nodes 3.810800 4.321869 5.005180 5.840437 6.302245 2.20534 e-3 gdqm 6 nodes 3.796457 4.3160276 5.005812 5.821824 6.292014 2.39225 e-4 gdqm 7 nodes 3.795564 4.315108 5.004471 5.820398 6.290454 7.79473 e-6 gdqm 8 nodes 3.795564 4.315108 5.004471 5.820398 6.290454 7.79473 e-6 table 2. second mode of vibration frequency term in nonuniform nanobeam with η = � solution method � = �h4 � = �h3 � = �h2 � = �h� � = �h� error(%) analytical (hashemi and khaniki 2017) 4.768500 5.442014 6.467170 8.073308 9.432419 gdqm 5 nodes 4.767854 5.441456 6.466045 8.072585 9.430874 1.33063 e-4 gdqm 6 nodes 4.768421 5.442874 6.466924 8.072987 9.432010 5.91514 e-5 gdqm 7 nodes 4.768472 5.441987 6.467122 8.073358 9.432371 5.90749 e-6 gdqm 8 nodes 4.768472 5.441987 6.467122 8.073358 9.432371 5.90749 e-6 table 3. third mode of vibration frequency term in nonuniform nanobeam with η = 5. conclusion free vibration analysis of variable cross section nonlocal small scale beam is done using gdq method. nanobeam is modeled using euler-bernoulli beam and eringen's nonlocal elastic theory. generalized differential quadrature method is presented step by step for the current problem. calculation is done for different number of sampling points and results for first three frequency parameters are presented and compared to those achieved by analytically solving the problem. average related error is presented for different number of sampling point and accuracy of current method is discussed. it is shown that gdqm method has a great ability and accuracy in solving this problem formulation and frequency term is achieved with high accuracy. it is mentioned that increasing the nonlocal parameter in exponential cross section variable nonuniformnanobeam leads to smaller frequency parameters in all the first three mode shapes using simply support as boundary conditions and it is necessary to add nonlocal effects in analyzing nonuniformnanobeams. references 1. ece mc, aydogdu m, taskin v. vibration of a variable cross-section beam. mechanics research communications 2007; 34(1): 78-84. 2. khaniki hb, hashemi sh. free vibration analysis of nonuniform microbeams based on modified couple stress theory: an analytical solution. international journal of engineering-transactions b: applications 2017; 30(2): 311-320. 3. hashemi sh, khaniki hb. analytical solution for free vibration of a variable cross-section nonlocal nanobeam. international journal of engineering-transactions b: applications 2016; 29(5): 688-696. 4. hashemi sh, khaniki hb. vibration analysis of a timoshenko non-uniform nanobeam based on nonlocal theory: an analytical solution. international journal of nano dimension. 2017; 8(1): 70-81. 5 5. hashemi sh, khaniki hb. free vibration analysis of functionally graded materials non-uniform beams. international journal of engineering-transactions c: aspects 2016;29(12): 1734-1740. 6. wu ty, liu gr. a differential quadrature as a numerical method to solve differential equations. computational mechanics 1999; 24(3): 197-205. 7. wu ty, liu gr. application of generalized differential quadrature rule to sixth‐order differential equations. international journal for numerical methods in biomedical engineering 2000; 16(11): 777-784. characterization and application of nanomaterials 2025, 8(3), 11474. https://doi.org/10.24294/can11474 1 review insights of prototyping hierarchical bottom-up of optical active materials for multimodal energy coupling and functional biophotonic nano-, microwearable devices sofia mickaela martinez1, cecilia s. tettamanti1, m. valeria amé2, daniela alejandra quinteros1, a. guillermo bracamonte3,4,* 1 unity of research and development in pharmaceutical technology (unitefa), conicet, department of pharmacy, faculty of chemical sciences, national university of córdoba (unc), córdoba 5000, argentina 2 research center in clinical biochemistry and immunology (cibici), department of biochemistry, national university of córdoba (unc), córdoba, córdoba 5000, argentina 3 academic department, faculty of chemical sciences, national university of córdoba (unc), córdoba x5000hua, argentina 4 national scientific and technical research council (conicet), córdoba research institute in physical chemistry, córdoba x5000hua, argentina * corresponding author: a. guillermo bracamonte, gbracamonte@fcq.unc.edu.ar, guillermobrac@yahoo.ca abstract: in this review are developed insights from the current research work to develop the concept of functional materials. this is understood as real modified substrates for varied applications. so, functional and modified substrates focused on nanoarchitectures, microcapsules, and devices for new nanotechnologies highlighting life sciences applications were revised. in this context, different types of concepts to proofs of concepts of new materials are shown to develop desired functions. thus, it was shown that varied chemicals, emitters, pharmacophores, and controlled nano-chemistry were used for the design of nanoplatforms to further increase the sizes of materials. in this regard, the prototyping of materials was discussed, affording how to afford the challenge in the design and fabrication of new materials. thus, the concept of optical active materials and the generation of a targeted signal through the substrate were developed. moreover, advanced concepts were introduced, such as the multimodal energy approach by tuning optical coupling from molecules to the nanoscale within complex matter composites. these approaches were based on the confinement of specific optical matter, considering molecular spectroscopics and nano-optics, from where the new concept nominated as metamaterials was generated. in this manner, fundamental and applied research by the design of hierarchical bottom-up materials, controlling molecules towards nanoplatforms and modified substrates, was proposed. therefore, varied accurate length scales and dimensions were controlled. finally, it showed proofs of concepts and applications of implantable, portable, and wearable devices from cutting-edge knowledge to the next generation of devices and miniaturized instrumentation. keywords: nanomaterials; modified substrates; nano-optics; nanophotonics; nanodevices; microdevices 1. basis of prototyping new nanomaterials towards modified substrates and devices in this first part of the communication, it is intended to highlight why it is important to prototype nanomaterials in the design and synthesis of new nanomaterials. in this regard, the methodology to afford new designs nominated as “prototypes” is highlighted. incorporate the concept of prototyping macromaterials in the absence of developing reactions, and wet chemistry could be proposed citation martinez sm, tettamanti cs, amé mv, et al. insights of prototyping hierarchical bottom-up of optical active materials for multimodal energy coupling and functional biophotonic nano-, microwearable devices. characterization and application of nanomaterials. 2025; 8(3): 11474. https://doi.org/10.24294/can11474 article info received: 5 february 2025 revised: 16 march 2025 accepted: 21 march 2025 available online: 20 june 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(3), 11474. 2 theoretically by the use of microand macroscopic materials that could be held by hands. from this theoretical proposal based on fundamental knowledge, the strategy for the study and applied research is begun. this is the beginning, and we contemplate the basis and fundamental knowledge in relation to the desired matter incorporation and potential new chemical properties. therefore, the design using real materials in the macroscale with shapes that emulate the nanoscale and contemplating chemical surfaces could be visualized. sometimes the use of the blackboard and 3d imaging software could provide interesting approaches; however, the capability to manipulate real materials emulating the molecular and nano-world is the final targeted aim that should be developed and shown. the prototyping could facilitate different strategies using varied materials to support the idea of the use of the nanoscale for the targeted objective. then, after obtaining the design and developing the synthetic methodology, it could be applied to the iteration and optimization depending on the results obtained. maybe these first insights could produce advice for students and young researchers for the next generation of experiments and materials [1,2]. in these perspectives is noted the important theme of nano-optics that could be developed in order to study and design optical active nanomaterials, light matter interactions, quantum phenomena, and metamaterials as well [3]. the metamaterials are generated by the incorporation of different optical active materials confined that produce unexpected electronic properties. in this regard, nanomaterials could produce meta-material properties based on their close matter compositions. the electron and photonic matter coupling modify their intrinsic free properties, accompanied logically by new electronic densities from the bulk. in this context, quantum phenomena could provide high sensitivity to modulate new properties. as an example, from recent advances and the perspective of quantum metaphotonics, it is highlighted that meta-optics employ subwavelength resonators and their planar structures, such as metasurfaces, to generate, manipulate, and detect quantum states of light. in this approach to developing materials, the design of nano-patterns by laser-assisted techniques affords coupling optics from individual signaling to collective nano-arrays. thus, electronic waves and quantum properties interact between nano-volumes surrounded with optical active matter that modify signaling. thus, it is recently noted from literature that the proper selection of polarization states in the heralding arm of the entangled photon source, either normal image or edge image, was obtained. thus, a high signal-to-noise ratio at the same photon flux level was generated. this improved state of quantum light was applied for nonlocal weak-measurement microscopy imaging [4]. thus, quantum light affords high nanoscale resolution by diminishing sizes and augmenting intensities. in this context, it is important to note that from this point of view, the prototyping is related as well to the methodology to develop the know-how to create a new nanomaterial with particular new non-classical optical properties. it involves the design of the idea based on the incorporation of varied physical and chemical phenomena. thus, it should incorporate many strategies from different sources of materials and associated properties. this fact could be achieved by incorporating different optical components within varied scales and physical phenomena associated (figure 1). schematically, in the prototyping, it is possible to organize 3d structures from nano-spheres connecting molecular interphases of varied optical components activated by different sources depending on the targeted modified substrates to be characterization and application of nanomaterials 2025, 8(3), 11474. 3 incorporated in devices and miniaturized instrumentation. the schema looks easy; however, it is the current challenge to develop further knowledge as well as to improve the performances of optical materials from the market. in this context, physics and chemistry involve different electronic and quantum properties that could govern the final optics developed. this principle is related to the atomic level interacting with other ones with different optoelectronic properties, as for example [5]. thus, the knowledge about nanochemistry is required for the bottom-up of the nanoplatforms. spectroscopy of materials should also be considered in order to produce smart, optically active matter. this is the theory, and sometimes it is not as straight as expected. in this context, it could present many challenges in this theme, where prototyping is a very important step in the design and synthesis of the nanooptical material. by this manner it is possible to think of the potential performances as well as any inconvenient interferences, etc., in the process of the fabrication. hence, these concepts focused on how to proceed; it could be expected to develop nano-optics from the desk to the bench and laboratory. figure 1. scheme of prototyping hybrid modified optical active nanomaterials controlling the molecular level, nanoscale, and higher-sized substrates in the micro and macro-scales. therefore, opto-electronics and biophotonics applications could be proposed for targeted applications. notes: nanospheres are supports of varied chemical structures such as single molecules, molecular wires, and polymeric fibers acting as linkers with varied functions to switch different targeted functions schemed as fibers, lamps, chips, etc. in these perspectives, it was led to highlight some reports in literature showing varied approaches and strategies depending on the involved study or targeted application. hence, prototyping nanomaterials is a basic step in the design, synthesis, and fabrication of optical active single nanoplatforms and nanoand microarrays. it was noted that the concept is related to the proposal of the targeted design based on well-known molecular and nanocomponents joined in a way not previously achieved before for a desired functionality of study [6]. in this manner, innovation could be proposed as challenges as well. in this manner, physics below the nanoscale could be tuned and generate improved performances, such as plasmonics coupling within core-bi-shell structures [7]. this approach was formed by a silver core (ag) covered with titania (tio2 nps) and an extra organic layer of benzoic acid-fullerene (ag@tio2@pa). the optical setup showed improved properties based on synergistic effects (optical and electrical phenomena). for example, organic solar cells led to enhancements of 12%–20% with characterization and application of nanomaterials 2025, 8(3), 11474. 4 a maximal power conversion efficiency of 13%, while the plasmonic core-bi-shell nanostructure produced an enhancement of 10%, from 18.4% to 20.2%. the constitution of this bi-layered core-shell permitted an improved short circuit current from within the nanoparticle and through the cell material by light excitation with electronic current generation. this fact could lead to the development of enhanced light emitter devices (leds) [8] and new futuristic non-classical light generation by plasmonics-leds [9]. therefore, opto-electro-active materials could afford to further fundamental studies as well as applied technology. the same concept is developed when different materials are combined with unknown properties looking for the study of some property not well known or a new one. this last mention is because not always are all the properties of materials known. in many cases they were recently synthesized, and partial characterization was developed. in this context, the prototyping of optical active nanomaterials by the combination of different matter compositions is an interesting fundamental research field as well as an applied field and is required for the fabrication of new optical materials within a varied scale of lengths [10]. the prototype is the first proposed model of the design of the nanomaterial. this should be logically well justified based on knowledge and hypothesis of functionality. it could be related to inventions as well as fabrication processes, or both at the same time. as all prototypes, it should be developed from an idea to a simple scheme, theoretical model, calculation, and physical model fabricated maybe in the macroscale to show the nanoarchitecture, permitting in this manner the visualization of the different components and functions [11]. all these strategies can provide different manners of evaluation of the fundamentals or basis involved in the targeted final properties of the desired proposed study. when it is mentioned the targeted property or function [12,13], it is focused on the objective of the research work or fabrication process [14]. in this context and just to finish, it highlighted the need to keep in mind a large window of materials types from where it could be prototyped new ones. thus, soft materials, organized systems, and biomaterials could be joined to inorganic and hard materials depending on the targeted function or study of interest. in this regard and considering methodological issues, it is noted that the required multidisciplinary research to develop these types of projects. so, in the next subsection, it was afforded the development of nano-optics and beyond from varied sources of materials. 2. from prototyping towards the design of multi-modal energy approaches for fundamental research and applications so, prototyping from atoms to molecules, joining different fragments with different functions and properties, could afford interesting insights in varied research fields depending on the material involved. this need should be planned on a larger scale, affording the different challenges related to the bottom-up. thus, the incorporation of optically active materials could tune optics by adding optically active molecules and tuning the nanoscale. in this direction is involved fundamental research where the characterization of nanochemistry with varied spectroscopical properties would be of interest, looking to go up in the micro-scale by assembling or applying laser-assisted techniques to make nanopatterned surfaces. characterization and application of nanomaterials 2025, 8(3), 11474. 5 about methodologies involved, it could be mentioned that wet chemistry methods [15] are used to manage colloids and nano-optics, while laser-assisted techniques are used for solid nanopatterned surfaces of substrates [16]. in this regard, it is expected to control the nanospectroscopy from single particles within colloids or placed modified substrates towards collective behaviors from nanoarrays [17]. naturally, materials and methods are different; however, this broad overview should be mentioned to afford a large spectrum of possibilities to produce different properties within the nanoscale. thus, from optics, it is needed to control and track single energy modes that require; i) high accuracy and precision in the measurements, ii) analysis of data, iii) interpretation, and iv) development of applications. this could be the case of near infrared (nir) nanoemitters for labeling and the generation of bioimaging [18]. in this regard, the design and synthesis incorporating different energy modes is highly required for many reasons. thus, whatever expected property with attended applications always involves different phenomena at the same time. but not always are all the possibilities under focus because there are many optical setups to fix in order to record multi-signaling at the same time [19]. in this context, the coupling of different optical set-ups is a challenge to afford. when the properties are originated from the same material, such as for an absorber with the capability to generate electron conduction, the set-up could be simplified [20]; while incorporating different materials accompanied by different properties and generating new ones, it could require more complex optical set-ups for multi-modal signal recording in real time and time-resolved ones as well [21]. in this regard, as an example, it could be required to track electrochemical signaling and luminescence emissions from single nano-optical systems, from where it is unless it needs the incorporation of potentiostats to vary voltages while on the other side laser dyes for light matter interactions [22]. in a similar manner, the optical disposition of optical elements and detectors in the optical bench could add more requirements. by this manner, the matter could be applied a programmed stimulation by different energy pathways upon needs controlled remotely [23]. as an example, it could be mentioned that the design and application for theranostics uses of fluorescent and magnetic nanoparticles [24]. in this study it was fabricated light-responsive janus nanoparticles based on poly (styrene-methyl methacrylate-acrylic acid). this nanoplatform permitted supporting two photobase generators that could react with fluorescamine to produce varied colors. in addition, the incorporation of magnetic fe3o4 afforded the control of nanoparticles by the use of a magnet at the same time that fluorescence with varied colors was produced. previously, the development naturally should have proposed a retro-synthesis in order to link the different optical active parts of the molecules, nanoplatforms, and by this manner, add up on the needs of the required optical set-ups. this planning involves the spatial distribution of atoms and molecules within the nanoscale if it is expected to develop nano-optics; while to focus light, it could be contemplated to vary supports to contain, depose, and get in flow the nano-optical active particles. in this context, it could also be considered the topological factor for photonics developments. thus, topological photonics based on asymmetrical bottom-up nanomaterials and highersized substrates are important further considerations in the development of multimodal approaches [25]. in this manner and incorporating different materials, it was possible characterization and application of nanomaterials 2025, 8(3), 11474. 6 to generate even more energy modes from interactions of different optical matter components accurately placed in 3d spatial distributions (figure 2). the concept could be summarized by the combination of different optical active nanoparticles by molecular wires. by this manner, focusing a laser or applying electron conduction from one side, it stimulates the first energy modes such as plasmonics or semiconductive to then generate in the second electron optical nanomaterial a response modifying the conduction of photons or electrons. this could be applied in varied substrates and techniques such as laser-assisted light waveguiding and light scattering by the use of advanced spectroscopical techniques available on the market such as wols (waveguiding optical light scattering). these interactions generate variations in the electronic distributions, and in many cases, they could modify the waves after interactions. therefore, the electronic density of the material is different, and logically, the optics too. this is the basic concept; however, it is the challenge waiting for further research. in this regard, the pattern of molecules, spectroscopical properties, quantum phenomena, and optics incorporated on the surface and through substrates as well are of interest for a full coverage of possibilities in the tuning towards the control of multimodal signaling [26]. figure 2. modified substrates for nano-, micro-devices, capsules for implantable and wearable therapeutic approaches. the substrate, represented by a rectangle, incorporates different functional nanomaterials as sources of electrons, e-shuttles, photons, or quantum particles. between them there are molecular wires and electromagnetic fields involved affecting the confined spaces. therefore, there are input of energy and output as energy transferred and energy emission, respectively. so, the control of materials, space, distances, patterns, and distributions on surfaces and substrates considering varied scales not only contemplates the energy modes known to be added from materials; it is also the beginning of fundamental research towards the generation of new unknown non-classical energy modes and opto-electronic matter constitution. 3. hierarchical bottom-up of materials: design from molecules towards nanoplatforms and higher sizes of modified substrates there is a broad spectrum of research within functional nanomaterials for varied applications [27]. in this regard, research focuses on specific functions or characterization and application of nanomaterials 2025, 8(3), 11474. 7 multifunctional materials for nanomedicine under development and transfer. this is the case of precision medicine [28] by genotyping, early diagnoses, genomic treatments [29], drugs, and light delivery [30]. particular interest has been paid to the control of chemistry to manipulate chemical bonds to design new pharmacophores [31] and mimetic synthetic membrane ligands such as coronavirus variants [32]. moreover, switch on/off molecular systems to be activated by different strategies [33] for personalized treatments in oncology [34]. these insights and advances showed how the hierarchical structure provided the final targeted function based on accurate compositions and mechanisms involved to accomplish the target function. therefore, it is intended to propose the generation of new ideas for future multidisciplinary studies by controlling the matter constitution. this is mainly focused by incorporating the control of the nanoscale [35], looking for functional nanoplatforms within colloidal dispersions [36]; however, it is desirable as well to scale up the bottom up depending on the aims. in this context, the nanochemistry allowed the design of different sizes of functional platforms in close contact and related with cells and membrane components. by this manner, controlled interactions could be provided with interesting perspectives such as for nano-immune platforms and further biotechnology applications [37]. figure 3. scheme different levels of optical active materials from molecules to varied nanoplatforms and beyond. the nanoplatforms are: (a) i) polymeric chains and assemblies, ii) organized systems formed by lipids, iii) biomolecules and assemblies, iv) synthetic well-defined nanoparticles; (b) i) polymeric nanoparticles, ii) micelles or vesicle-organized systems, iii) nanostructured biomolecules such as protein-based nanoparticles, iv) multi-layered core-shell nanoparticles. different nanoarchitectures could be considered to develop targeted nanomedicine. this could be afforded by controlling small molecules, monomers, and atomic ions (figure 3a) to build the nanoscale towards polymeric nanoparticles, organized systems, nanostructured biomaterials, and other bottom-up systems with different and accurately defined parts within the nanoscale, such as core-shell nanoplatforms (figure 3b) [38]. therefore, new research areas were addressed, and further perspectives could be developed as well. in particular, it could be aimed at being transferred to translating studies and applications in vitro and in vivo, such as for biophotonics clinical translations. in view of this, it is noted that there are varied and different functions, such as drug delivery [39], biosensing, non-classical light delivery [40], bioimaging [41], electronics [42,43], and quantum signaling [44]. however, the factor in common and challenge was focused on how to interact at the characterization and application of nanomaterials 2025, 8(3), 11474. 8 right place within close distance to achieve the desired function. hence, right delivery and specific function were also of particular interest. therefore, it was added higher sizes of substrates such as patches [45] and modified substrates [46] based on variable polymeric compositions [47] to support the materials and associated properties with functions. thus, as stated, the bottom-up could be developed by a hierarchical material with different components acting in close contact with different types of real tissues in order to activate the function upon needs. for example, the permeability and dynamic skin tissue are used to incorporate varied drugs up to needs [48]. moreover, surgical procedures or simple injections into deep tissues allowed being in close contact with the desired type of cells [49]. therefore, implantable nanoand microdevices could be new approaches to be developed in this regard. accordingly, the concept of nanodevices towards the bottom-up of microdevices to be incorporated by different strategies considers: i) implantable strategies by direct deposition and contact with the targeted tissue [50]; ii) injections [51]; iii) deposition or ingestion to be adsorbed through membranes and tissues [52], in addition to other types of strategies such as the use of microcapsules [53]. it is important to underline the role of the specific functions of devices, as well as the support material and strategy to record signaling from the mechanism developed as a strategy for the targeted and desired function. at the same time, colloidal dispersions could afford to nano-optics and drug delivery nanotechnologies that merit being studied and applied. in these perspectives, it is presented this package of ideas for further developments focusing research on nanomaterials and devices for biophotonics and nanomedicine applications to gain insight into implantable and related strategies to activate the desired function at the right place and time within complex biological systems. 4. advances from the cutting-edge of the knowledge of modified substrates to implantable, portable, and wearable devices for biophotonics studies and applications after considering the control on the molecular scale and nanoscale towards modified substrates with higher sizes and specific functions, it could be proposed to deposit the device on different tissues depending on needs in order to look for early diagnoses, biosensing, and drug delivery. it is possible to propose new treatments from precision medicine, where fundamental research and translational clinical applications are highly required. material composition and biocompatibility to avoid immune reactions to the deposed material should be viewed as a device. this device could vary in size according to the application required. in these perspectives, it is known that there are different substrate materials for implantable devices and miniaturized instrumentation [54]. similarly, wearable designs such as thin slides containing highly sensitive points of contact with the tissue provide signal tracking from biological variations (figure 4a). characterization and application of nanomaterials 2025, 8(3), 11474. 9 figure 4. schematic representation of devices within different intervals of sizes and dimensions: (a) multifunctional microand higher sizes of devices interacting with specific functional materials domains and nanoplatforms for multi-modal energy delivery modes, multi-photon delivery, and drug delivery based on variable different remote switch on/off strategies; (b) nano-devices placed on biostructures such as uni-cellular, and pluri-cellular micro-organisms for light delivery and coupling through optical active organelles. for the design of a modified substrate for specific functions, different types of signaling could be tracked, such as light, electronics, quantum, electrical properties, electromagnetic fields, and thermal and chemical signals. all controllable physical and chemical properties are of interest to transduce through space and time. however, being able to record weak signals or amplify them through amplification strategies is still a challenge. and this is not as easy to achieve from the bulk of synthetic materials or synthetic real matrices as well. so, there is a lot of work involved that should be developed for each design and targeted function. light, managing photons and their transmissions through space and time, is particularly useful to develop implantable devices. in addition, other variables should be controlled at the same time, such as the biocompatibility of the materials added. thus, photonic phenomena should be adapted to the desired application. tuning photons and non-classical light should be compatible with tissues in order to avoid immune responses. thus, new biomaterials are currently in progress and should be evaluated for new implantable substrates and related applications, as in signaling for biosensing and delivery treatments. in all these complex processes, interferences and background from tissues need to be considered. it is particularly interesting to develop biomaterials in search of new substrates as in tuning light within waveguides [55], transducing signaling, delivering light, or even producing laser properties [56]. here, plasmonics and control of high electromagnetic fields within the near field towards the far field are under study [57]. these enhanced properties could be generated from varied physical and chemical properties as well as coupling varied phenomena associated from the nanoscale to biostructures (figure 4b). moreover, it could be highlighted how it was designed as a nano-bio-sensor for low concentration levels of dna detection based on metal enhanced fluorescence characterization and application of nanomaterials 2025, 8(3), 11474. 10 (mef) coupled to fluorescence resonance energy transfer (fret) [58]. in addition, recent studies provide insights into light coupling and transmission through the space, addressing different photobiological receptors in unicellular microorganisms, probably developed from bi-colored fret nano-emitters [59]. and this is based on the effect of energy levels and consequent properties by interaction with electromagnetic fields. the electromagnetic fields could be generated from the molecular scale to the nanoscale, varying in nature and intensity, which could also reach the quantum level [60]. thus, it could be considered that the field is so high and versatile for tuning further opto-active properties. note that many of these studies were inspired by the 1946 nobel prize in physics awarded to the study of spontaneous electromagnetic fields generated from metallic particles [61]. it means that these phenomena are relatively new and still studied on the nanoscale and beyond. plasmonic devices and enhanced photodetectors, the basis of new technology, have also been developed, in addition to new strategies in remote switch on/off laserbased applications and miniaturized instrumentation such as light-emitting devices (leds), related oleds, and new plasmonics oleds (p-oled) joined to minioptical setups or within reduced sizes of pre-designed structures. these are new developments of biomaterials with biodegradable properties for biophotonics and implantable applications [62], such as flexible bioelectronic devices from conductive polymers based on living materials [63]. figure 5. schematic representation of flexible devices based on different materials to interact with living systems. thus, the versatility in the design shows the incorporation of different further technological functions such as micro-electronics, circuits and connectivity. reprinted with permissions from roblyer d. et al. [64]. moreover, it should be mentioned that this focused interest on nanotechnology led later to ongoing insights and new roles of devices and data recording in vivo and in real time for remote sensing and diagnoses (figure 5) [64]. thus, it should be highlighted that the internet of nano things is transforming healthcare with the cutting-edge technology in progress [65]. further technological issues even could arrive to be proposed managing semiconductors and photoreceptors to incorporate connectivity and automation, desiring a higher level of bottom-up towards miniaturized instrumentation [66]. in this regard, the control of photons, the development of nanoelectronics, and improved electrical signaling are under study to record weak signals from tissues. as an example, it is noted that the development of implants with highly sensitive sensors characterization and application of nanomaterials 2025, 8(3), 11474. 11 and implants having wireless myoelectric sensors in their re-innervation sites after targeted muscle re-innervation (tmr) [67]. the tmr amplifies the electrical activity of nerves at the stump of amputees by redirecting them in remnant muscles above the amputation. this signaling could be collected and transduced to prosthetics. this technology is based on highly sensitive surface electrode developments using implanted systems. this is a higher level of signal transduction from molecular transduction and electrical signals. thus, the signal was transduced from confined molecular levels towards longer lengths and scales, affording long-term implants of intramuscular sensors and nerve transfers for wireless control of robotic arms in above-elbow amputees. other highly sensitive implants and portable devices were reported from neuroscience, such as neurophotonics, neuroimaging, and neuromedicine, in addition to portable miniaturized instrumentation at different levels, such as mini-microscopes and mini-endoscopes. then, higher-sized approaches and instruments for bioimaging afforded getting connections between neurons in vivo [68]; from where, ion, molecular, and neurotransmitter detections were recorded by a proper combination of miniaturized optical set-ups and molecular sensors, labellers, and nano-platforms [69]. therefore, it was even scaled up the applications to replace the upper part of the human skull with a biocompatible, rechargeable, refillable, and cleanable electrical/molecular device to safely and effectively treat and cure severe and currently intractable brain disorders [70]. nanochemistry and new modified substrates could lead to implantable approaches and wearable designs. the research for biosensing in cells for molecular targeting and tracking, as well as ion and neurotransmitter detection, is a high-impact field [71]. then, if this level of signal transduction is amplified, enhanced, or improved by some strategy through space and time, these facts could afford multimodal imaging approaches. and by this manner, it could lead to new technologies within life science applications. examples of technology already developed and placed on the market include, for example, portable pcr chips [72], lab-on-particles for early diagnosis of sars cov2 [73], and next-generation sequencing (ngs) [74]. the perspective of developments is particularly stimulating in the context of multidisciplinary research fields. 5. conclusions and perspectives this mini-review is intended to present and open the discussion about the design of new nanomaterials and reduced sizes of substrates with perspectives towards functional devices focusing on implantable and wearable applications. thus, it was shown from insights and basis for prototyping molecules, nanomaterials, and substrates. the incorporation of different properties joining different materials controlling molecular connectors permitted proposing signal transductions through space and time. and this capability led to its being used within modified substrates with multifunctional perspectives. so, the fact of getting a microto millimeter-sized polymeric material with a controlled nanostructured and functional pattern showed interesting perspectives from recent reports. in addition, further development could afford to activate or track functionalities remotely. characterization and application of nanomaterials 2025, 8(3), 11474. 12 therefore, from the concept of functional materials towards the control of the nanoscale, it was shown the development of applications such as nanodevices and microdevices for sensing and biophotonics uses. many of these new nanomaterials could be incorporated in substrates, improving performance. it means that within the bottom-up of the functional material, other enhanced pathways could be added. so, higher performances from nanotechnology are highly desired for signal detection and transduction. in these regards, different nanoarchitectures that could be applied were presented. all these nanomaterials could act as support for optical active materials and functions. in addition, the combination of biocompatible materials and controlled physical and chemical properties could develop different strategies for the targeted functions. thus, as an example, the knowledge from plasmonics and coupled phenomena had been shown to enhance signaling, thermal activations, and the development of laser properties. in addition, electrical signaling detection and molecular tracking applied to tissues and organs as in biological event detections to generate bioimaging and early diagnosis and also to optimize mechanical movements by prosthesis were presented as of high interest and impact. hence, there is a broad spectrum of needs and interests that should be addressed by the next generation of therapeutics and new precision medicine accessed through implantable devices and encapsulated multi-functional nanoand micromaterials. in this context, the incorporation of non-classical light and new modes of energy based on coupling optical active materials could afford new implantables considering biocompatible photonic approaches. acknowledgments: special thanks are given to the science and technology of unc (secyt), argentina, for the research grant provided. we would also like to thank copl, laval university, québec, canada, for the long-standing research collaboration in progress, as well as to the canadian grants received. institutional review board statement: not applicable. informed consent statement: not applicable. conflict of interest: the authors declare no conflict of interest. references 1. kathuria y. chapter 6. laser-produced rapid prototyping in manufacturing. in: international trends in applied optics. spie digital library; 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al . et al. et al. et al. et al et al. et al. et al. et al. et al. et al et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al et al. et al. et al. et al et al. et al. et al et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. 77 characterization and application of nanomaterials (2021) volume 4 issue 1 doi:10.24294/can.v4i1.1292 original research article mesoscale computational prediction of lightweight, thermally conductive polymer nanocomposites containing graphene-wrapped hollow particle fillers jianjun wang1,a,*, zhonghui shen2,a, wenying zhou3*, yang shen2, cewen nan2, qing wang1, longqing chen1* 1 department of materials science and engineering, the pennsylvania state university, university park, pennsylvania 16802, united states. e-mail: wjj8384@gmail.com (j wang); lqc3@psu.edu (l chen) 2 school of materials science and engineering, state key lab of new ceramics and fine processing, tsinghua university, beijing 100084, china 3 college of chemistry and chemical engineering, xi'an university of science & technology, xi’an 710054, china. e-mail: wyzhou2004@163.com(w zhou) abstract heat removal has become an increasingly crucial issue for microelectronic chips due to increasingly high speed and high performance. one solution is to increase the thermal conductivity of the corresponding dielectrics. however, traditional approach to adding solid heat conductive nanoparticles to polymer dielectrics led to a significant weight increase. here we propose a dielectric polymer filled with heat conductive hollow nanoparticles to mitigate the weight gain. our mesoscale simulation of heat conduction through this dielectric polymer composite microstructure using the phase-field spectral iterative perturbation method demonstrates the simultaneous achievement of enhanced effective thermal conductivity and the low density. it is shown that additional heat conductivity enhancement can be achieved by wrapping the hollow nanoparticles with graphene layers. the underlying mesoscale mechanism of such a microstructure design and the quantitative effect of interfacial thermal resistance will be discussed. this work is expected to stimulate future efforts to develop light-weight thermal conductive polymer nanocomposites. keywords: thermal conductivity; polymer nanocomposites; materials design; graphene-wrapped hollow nanoparticles article info received: 2 febuary 2021 accepted: 17 march 2021 available online: 25 march 2021 copyright copyright © 2021 jianjun wang, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction the effective thermal management in applications, such as led (light emitting diode) lighting, batteries, automobile cooling systems, and high-power density microelectronic devices, where heat accumulation can have deleterious effects, is critically important to ensure the device performance and reliability, and therefore to enhance the lifetime and accuracy of the system[1–3]. with further miniaturization, integration and functionalization of microelectronics and the emerging applications, such as electronic assembly and packaging, and solar the thermal dissipation has become a challenge[4–6]. addressing this challenge requires the development of novel materials with enhanced thermal conductivity as well as light weight, low cost, good processability, and corrosion resistance. polymers have many of these characa these authors contributed equally to this work. 78 teristics, but they generally have very low thermal conductivity (0.1–0.4 wm−1∙k−1)[7,8]. therefore, heat conductive fillers, such as carbon nanotube[9–13] (> 2,000 wm−1∙k−1), graphene[14–18] (–5,000 wm−1∙k−1), aluminum oxide[19–21] (> 20 wm−1∙k−1), boron nitride[22–26] (–350 wm−1∙k−1), and metal particles[27–31] (> 100 wm−1∙k−1), etc., are traditionally added into polymers to enhance their thermal conductivity while preserving the above-mentioned advantages of polymers. the influences of the filler type, size, shape, alignment, and loading level on the effective thermal conductivity of the resulted polymer composites have been extensively investigated, see e.g., the recent reviews[5,12,32]. it was generally accepted that a high filler loading level (≥ 30% in volume) is necessary in order to achieve the appropriate level (≥ 1 wm−1∙k−1) of thermal conductivity in a polymer nanocomposite. for example, heat sinks in microelectronic systems require polymer nanocomposites with a thermal conductivity approximately from 1 to 30 wm−1∙k−1, which normally needs a filler loading level higher than 30% in volume[7,33]. the high loading level of the filler, particularly for metallic fillers, usually significantly increases the mass density and costs, and weakens the mechanical performances, such as tensile strength and flexibility, and processibility, which prevents the polymer composites from being used commercially, in particular in aerospace where a lightweight is extremely desired[32,34]. therefore, it is imperative to seek for alternative approaches to developing novel material microstructures with enhanced thermal conductivity but low density and costs. to effectively reduce the weight and improve the specific thermal conductivity of filled polymers, in this work, we propose to fill the polymer matrix with hollow nanoparticles to increase the thermal conductivity while preserving a low mass density of the nanocomposite. in particular, we computed the effective thermal conductivity (κeff) and the effective mass density (ρeff) of the polyethene (pe) polymer nanocomposites filled with various hollow nanoparticles. it is predicted that by wrapping a thin graphene layer onto the hollow nanoparticles, the effective thermal conductivity can be further significantly enhanced. materials thermal conductivity (wm−1∙k−1) mass density (kg/m3) literature values (wm−1∙k−1) refs. ag 417 10,490 427 31 al 237 2,700 247 28 fe 40 7,900 67 38 cu 397 8,900 398 28 al2o3 33 3,700 30–36 39 aln 300 3,260 100–300 5 bn 57 2,290 185–300 5,40 graphene 4,000 2,250 2,000–6,000 41,42 pe polymer 0.24 1,000 0.3–0.45 5 air 0.024 1.225 0.024 5 table 1. thermal conductivities and mass density of the filler materials used in the simulation. for bn nanoparticles, the thermal conductivity used is smaller than the literature values which were reported for the in-plane thermal conductivity in bn nanosheets. for pe polymer, the thermal conductivity depends on the density figure 1. computationally-generated microstructures for polymer nanocomposites filled with (a) 20 vol.% solid nanoparticles, (b) 40 vol.% solid nanoparticles, (c) 20 vol.% hollow nanoparticles, and (d) 40 vol.% hollow nanoparticles, (e) the effective thermal conductivity and (f) mass density as function of filler volume fraction for polymer nanocomposites filled with various solid and hollow nanoparticles. 79 2. methods the heat conduction equation in the polymer nanocomposite can be written as: ( ) ( ) ( ) ( ) ( ) ( ) ij p i j t t k q c x x t ρ  ∂ ∂∂ + =  ∂ ∂ ∂  x x x x x x where kij(x), t(x), ρ(x), and cp(x) represent the spatial-dependent thermal conductivity tensor, temperature, the mass density, and the specific heat capacity, respectively. those spatial-dependent material properties such as kij(x), ρ(x), and cp(x) are determined by the microstructure of the polymer nanocomposite specified by a phase-field variable. the internal heat source of the material is represented by q(x). eq. (1) can be solved using the spectral iterative perturbation method which was developed in previous work[35] or using the finite element method via the comsol software. when incorporating the interfacial thermal resistance, slit boundary conditions are applied at the heterointerfaces between phase a and phase b, i.e., ( ) k a b a a a t tt r − − ⋅ − ∇ =n k , ( ) k b a b b b t tt r − − ⋅ − ∇ =n k (2) where na and nb represent the normal directions of the interface pointing to phase a and phase b, respectively. the variable ta and tb represent the temperature at the two boundaries of the heterointerfaces, and ka and kb represent the thermal conductivity of phase a and phase b, respectively. once the temperature distribution is solved, the heat flux density that flows through a unit area per unit time can be determined from the fourier’s law, i.e., ( ) ( ) /i ij jj k t x= − ∂ ∂x x (3) the effective thermal conductivity tensor eff ijk of the polymer nanocomposite can then be determined from eq. (3) by solving ( )eff /i ij jj k t x= − ∂ ∂x (4) where represents the average property per volume. 2. results and discussions figures 1a-d show the microstructures of pe nanocomposites filled with 20 vol.% and 40 vol.% solid nanoparticles, 20 vol.% and 40 vol.% hollow nanoparticles, respectively, computationally generated assuming random distributions of the filler nanoparticles. for hollow nanoparticles, the thickness of the filler layer is about 4% to 7% of the radius of the nanoparticles. the effective thermal conductivity for the polymer nanocomposite is calculated by solving the steady-state heat conduction equation using the phase-field spectral iterative perturbation method[35–37]. the intrinsic thermal conductivities and mass densities of the filler materials, polyethylene (pe) polymer, and air used in the computation are listed in table 1. figure 1e shows the effective thermal conductivity as function of the filler volume fraction for pe nanocomposites filled with various nanoparticles. for all listed nanocomposites, the effective thermal conductivity increases with the volume fraction of the fillers for both the solid and hollow nanoparticles. for a filler material at a given vf, the solid nanoparticles are more effective than the hollow nanoparticles in enhancing the thermal conductivity. for example, at a vf of ∼50%, the polymer nanocomposites filled with solid ag, solid al, solid fe, solid cu, solid al2o3, solid aln, and solid bn nanoparticles have a κeff of ∼28 wm−1∙k−1, ∼14 wm−1∙k−1, ∼3.6 wm−1∙k−1, ∼20 wm−1∙k−1, ∼4.1 wm−1∙k−1, ∼22 wm−1∙k−1, and ∼5.0 wm−1∙k−1, while their counterparts filled with corresponding hollow nanoparticles have a κeff of ∼1.9 wm−1∙k−1, ∼1.2 wm−1∙k−1, ∼0.5 wm−1∙k−1, ∼1.7 wm−1∙k−1, ∼0.5 wm−1∙k−1, ∼1.4 wm−1∙k−1, and ∼0.6 wm−1∙k−1, respectively (see table 2). however, the effective mass density of the pe nanocomposite is significantly increased by the solid nanoparticles compared to the hollow nanoparticles. as shown in figure 1f, at a vf of ∼50%, the nanocomposites filled with solid ag, solid cu, and solid fe nanoparticles respectively have a ρeff of ∼5,646 kg/m3, ∼4,971 kg/m3, and ∼4,374 kg/m3, while their counterparts filled with hollow nanoparticles have a much lower ρeff of ∼1,246 kg/m3, ∼1,135 kg/m3, and ∼1,109 kg/m3, respectively (see table 2). more interestingly, the effective mass density of the polymer nanocomposites filled with hollow al, hollow al2o3, hollow aln, and hollow bn even decreases with (1) 80 the volume fraction of the nanoparticles. more specifically, the effective mass density of the polymer nanocomposites can be reduced from ∼1,000 kg/m3 to ∼681 kg/m3, ∼756 kg/m3, ∼731 kg/m3, and ∼663 kg/m3 when it is respectively filled with hollow al, hollow al2o3, hollow aln, and hollow bn nanoparticles at a vf of 50 percent (see table 2). nanoparticle vf = 50% ag al fe cu al2o3 aln bn solid κeff(wm−1∙k−1) 28 14 3.6 20 4.1 22 5.0 ρeff (kg/m3) 5,646 1,849 4,374 4,971 2,380 2,097 1,663 hollow κeff(wm−1∙k−1) 1.9 1.2 0.5 1.7 0.5 1.4 0.6 ρeff (kg/m3) 1,246 681 1,109 1,135 756 731 663 graphene-wrapped κeff(wm−1∙k−1) ~11 ~11 ~5 ~11 ~5 ~11 ~5 ρeff (kg/m3) 1,290 817 1,153 1,196 877 847 789 table 2. effect thermal conductivity and mass density for polymer nanocomposites filled with various solid, hollow, and graphenewrapped hollow nanoparticles at a volume fraction of 50%. figure 2a shows the mapping result of the κeff as function of the thermal conductivity of the filler material (κfiller) and vf for the polymer nanocomposites filled with hollow nanoparticles. the calculations in figure 1e are included in this more comprehensive mapping result. for example, for nanocomposites filled with 10 vol.% hollow aln, 20 vol.% hollow cu, 30 vol.% hollow al, and 40 vol.% hollow ag nanoparticles, which are marked on figure 2e, they have a κeff of ∼0.31 wm−1∙k−1, ∼0.41 wm−1∙k−1, ∼0.54 wm−1∙k−1, ∼0.91 wm−1∙k−1, respectively, as indicated by the color bar. the κeff increases with both κfiller and vf. at κfiller = 2000 wm−1∙k−1 and vf = 50%, the effective thermal conductivity can be increased to ∼4.8 wm−1k−1. in contrast, figure 2b shows the mapping result for the nanocomposite filled with solid nanoparticles. the solid nanoparticles are indeed more effective in enhancing the κeff than their hollow counterparts. for example, at κfiller = 2000 wm−1∙k−1 and vf = 50%, the κeff can be enhanced to ∼103 wm−1∙k−1 by the solid nanoparticles. however, in order to achieve a specific thermal conductivity by filling different types of nanoparticles into the pe polymer, the nanocomposites filled with hollow nanoparticles are shown to require much less filler materials and hence show much lower mass density. for example, as shown in figure 3a, for a pe nanocomposite with an effective thermal conductivity of ∼1 wm−1∙k−1, the mass density is ∼3,566 kg/m3, ∼1,506 kg/m3, ∼3,206 kg/m3, and ∼1,614 kg/m3 when the nanocomposite is filled with solid ag, solid al, solid cu, and solid aln nanoparticles, respectively. however, their counterparts only show a mass density of ∼1,271 kg/m3, ∼774 kg/m3, ∼1,156 kg/m3, and ∼805 kg/m3 when filled with the corresponding hollow nanoparticles. figure 2. the effective thermal conductivity as function of the volume fraction and the filler thermal conductivity for polymer nanocomposites filled with (a) hollow nanoparticles and (b) solid nanoparticles. 81 furthermore, the materials cost in the nanocomposites filled with the hollow nanoparticles will also be much less. as shown in figure 3b, the unit costs of the polymer nanocomposites filled with hollow ag, hollow al, hollow cu, and hollow aln nanoparticles are ∼0.839 $/cm3, ∼0.001 $/cm3, ∼0.0069 $/ cm3, and ∼0.161 $/cm3, while the unit costs of their counterparts filled with solid nanoparticles are ∼2.35 $/cm3, ∼0.0019 $/cm3, ∼0.019 $/cm3, and ∼0.322 $/ cm3, respectively. therefore, the usage of hollow nanoparticles reduces the weight of the nanocomposite and the materials cost of the nanocomposite. however, the hollow nanoparticles might not yield sufficient enhancement of the effective thermal conductivity. for instance, by filling hollow nanoparticles such as fe, al2o3, and bn into the pe polymer, a target κeff of 1 wm−1∙k−1 may not be achieved unless denser pe polymer with higher thermal conductivity is used as the matrix. figure 3. for a pe nanocomposite with a targeted effective thermal conductivity of 1 wk1m1, (a) the mass density and (b) the unit cost of materials it has when it is filled with various solid and hollow nanoparticles. the inset table of (b) lists the rough costs of different filler materials, which might change depending on the market. in the light of the mapping result for the κeff as function of the κfiller and the vf shown in figure 2a, we propose a hierarchical architecture for the hollow nanoparticles. as shown in figure 4, we suggest wrapping one graphene layer onto the shell of the hollow nanoparticle. this design is rationalized by the super-high thermal conductivity (∼4,000 wm−1∙k−1) of the graphene[41,42], which can be employed to possibly wrap the shell of a hollow nanoparticle[43–45]. the technique of wrapping a graphene layer onto the shell of a nanoparticle has been used to improve the performances of batteries[43–45], and here we predict that it can be used to improve the effective thermal conductivity of the polymer nanocomposites. it can be seen from figure 5a that the effective thermal conductivity of the nanocomposite filled with graphene-wrapped hollow nanoparticles increases much faster with the volume fraction of the filler nanoparticles. at a vf of 50%, the effective thermal conductivity of the nanocomposite can be enhanced to ∼11 wm−1∙k−1, which is about 10 times of their counterparts filled with hollow nanoparticles without a graphene layer. meanwhile, this hierarchical architecture does not increase the effective mass density much. as shown in figure 5b, the effective mass density of the nanocomposite at a vf of 50% is ∼1,290 kg/m3, ∼817 kg/m3, ∼1,153 kg/m3, ∼1,196 kg/ m3, ∼877 kg/m3, ∼847 kg/m3, and ∼789 kg/m3 when filled with graphene-wrapped hollow ag, al, fe, cu, al2o3, aln, and bn nanoparticles, respectively (see table 2). these values are about ∼3.5%, ∼20.0%, ∼3.9%, ∼5.3%, ∼16.0%, ∼15.8%, and ∼19.0% higher than their counterparts filled with corresponding hollow nanoparticles without wrapping graphene. figure 6a shows the comparison of the effective mass density between the nanocomposites filled with solid nanoparticles and graphene-wrapped hollow nanoparticles. it can be seen that a target κeff of 1 wm−1∙k−1 now can be achieved by all listed filler materials. the effective mass densities of the nanocomposites filled with graphene-wrapped hollow nanoparticles are much lower than their counterparts filled with solid nanoparticles. for nanocomposites filled with heavy fillers such as ag, fe, and cu, the effective mass density can be reduced by ∼70% by using graphene-wrapped hollow nanoparticles rather than solid nanoparticles, while still preserving the 82 same κeff of 1 wm−1∙k−1. this is not only beneficial to the reduction of the weight and materials costs, but also beneficial to the preservation of the flexibility performances of the polymers which can easily be damaged by a high loading level[46–50]. as shown in figure 6b, the vf of the nanocomposites filled with graphene-wrapped hollow nanoparticles is universally reduced, compared with the counterpart in the nanocomposites filled with solid nanoparticles. now turn to the underlying mechanisms of the advantages of using hollow nanoparticles and graphene-wrapped nanoparticles over the solid nanoparticles. we consider three nanocomposites, which are filled with solid nanoparticles, hollow nanoparticles, and graphene-wrapped hollow nanoparticles, respectively. the filler materials are same, e.g., cu metal, and the sizes of the filler nanoparticles are assumed to be similar. the volume fraction of cu metal in the three nanocomposites are set to be at the same value of 6%. while in the nanocomposite filled with solid nanoparticles the thermally conductive cu metal concentrates at each solid particle, the cu metal in the nanocomposite filled with hollow nanoparticles distributes on the surface of each hollow particle. since the surface layer volume of the hollow particle is much lower than the whole volume of the solid particle, there must be more hollow particles in the same polymer. as a result, the probability of forming thermally conductive channels through surfaces connection of the hollow particles is increased, leading to the enhancement of the effective thermal conductivity. this can be understood from the comparison of the thermal energy flux distributions shown in figures 7a-b. by wrapping a more thermally conductive graphene layer on the surfaces of the hollow nanoparticles, the formation probability of heat conductive channels and hence the effective thermal conductivity will be 83 further increased, as revealed in figure 7c. figure 6. for a pe nanocomposite with a targeted effective thermal conductivity of 1 wk1m1, (a) the mass density and (b) the filler volume fraction it has when it is filled with various solid and graphene-wrapped hollow nanoparticles. figure 8. effect of the interfacial thermal resistance on the effective thermal conductivity for pe nanocomposites filled with 25 vol.% solid cu nanoparticles, hollow cu nanoparticles, and graphene-wrapped hollow cu nanoparticles. in above simulations, the strategy of adding hollow and graphene-wrapped hollow nanoparticles into the polymer to enhance the thermal conductivity and reduce the mass density is illustrated without considering the interfacial thermal resistance (rk). figure 8a shows the parameterized study of rk effects on the effective thermal conductivity for polymer nanofigure 7. thermal energy flux distributions for polymer nanocomposites filled with (a) solid cu nanoparticles, (b) hollow cu nanoparticles, and (c) graphene-wrapped hollow cu nanoparticles. the volume fractions of cu metal for these three polymer nanocomposites are at the same value of 6%. due to the introduction of the hollow structure, the volume fractions of the hollow nanoparticles are 30%. composites filled with solid, hollow, and graphenewrapped cu hollow nanoparticles. for polymer nanocomposites filled with solid cu and graphenewrapped hollow cu nanoparticles, rk is important when it is great than 10−10 m2∙k/w, whereas it is important when rk > 10−6 m2∙k/w for the polymer nanocomposite filled with hollow cu nanoparticles. specifically, the effective thermal conductivity can be decreased by the interfacial thermal resistance from 1.0 wm−1∙k−1 to 0.19 wm−1∙k−1, from 0.71 wm−1∙k−1 to 0.16 wm−1∙k−1, and from 0.48 wm−1∙k−1 to 0.14 wm−1∙k−1 for polymer nanocomposite filled with 25 vol.% graphene-wrapped hollow cu nanoparticles, solid cu nanoparticles, and hollow cu nanoparticles, respectively. therefore, the effective thermal conductivity predicted in this work should be lower 84 when the interfacial thermal resistance is considered. in order to accurately predict the effective thermal conductivity as function of the microstructure, the knowledge of the interfacial thermal resistance is necessary. while it is challenging to measure the interfacial thermal resistance experimentally, it may be obtained via molecular dynamic simulations[51–53]. 3. conclusions the effective thermal conductivity and effective mass density of the polymer nanocomposites filled with solid nanoparticles and hollow nanoparticles are computed. it is predicted that the usage of hollow nanoparticles rather than the solid nanoparticles as fillers can enhance the thermal conductivity but preserve the low mass density of the polymer nanocomposites. by wrapping a graphene layer onto the surface of the hollow nanoparticles, the effective thermal conductivity can be further significantly enhanced while still preserving a low mass density of the polymer nanocomposite. the underlying mechanism of this microstructure design and the quantitative effect of the interfacial thermal resistance are presented. the present work is expected to stimuli future experimental and theoretical efforts to design light-weight thermally conductive polymer nanocomposites. conflict of interest no conflict of interest was reported by the authors. acknowledgements j. j. wang and l. q. chen are partially supported by the us air force office of scientific research through tasks (fa9550-17-1-0318) and by the hamer professorship. w y zhou gratefully acknowledge the financial supports from the national natural science foundation of china (no.51577154), the key laboratory of engineering dielectrics and its application, ministry of education, harbin university of science and technology (no. jzk201301, kf20151111). references 1. gurrum sp, suman sk, joshi yk, et al. thermal issues in 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mechanical engineering & automation, zhejiang sci-tech university, hangzhou 310018, zhejiang, china. e-mail: yinsm@zstu.edu.cn abstract in order to explore the influence of the ferroelectric surface on the structure and properties of semiconductor oxides, the growth of cds nanocrystals was regulated and controlled by taking single-crystal perovskite pbtio3 nanosheets as the substrate through a simple hydrothermal method. through composition design, a series of pbtio3-cds nanocomposite materials with different loading concentrations were prepared, and their microstructure and photocatalytic properties were systematically analyzed. studies show that in the prepared product, cds nanoparticles selectively grow on the surfaces of pbtio3 nanosheets, and their morphology is affected by the exposed surfaces of pbtio3 nanosheets. there is a clear interface between the pbtio3 substrate and cds nanoparticles. the concentration of the initial reactant and the time of hydrothermal reaction also significantly affect the crystal morphology of cds. photocatalysis studies have shown that the prepared pbtio3-cds nanocomposite material has a significant degradation effect on 10 mg/l of rhodamine b aqueous solution. the degradation efficiency rises with the increase of cds loading concentration. when degrading 10 mg/l of rhodamine b aqueous solution, the pbtio3-cds sample with a mass fraction of 3% can reach a degradation rate of 72% within 120 min. keywords: cds; single-crystal perovskite; pbtio3; nanocomposite material; photocatalysis article info received: 8 october 2021 accepted: 17 december 2021 available online: 23 december 2021 copyright copyright © 2022 mingdong xu, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/4 .0/ 1. introduction nano materials have many characteristics, such as small size effect, surface effect, volume effect and unique photoelectric effect, which make them have broad application prospects in energy environment, electronic devices, biomedicine and so on[1–3]. perovskite phase pbtio3 is a typical ferroelectric oxide material. it was reported by shirane et al.[4] in 1950 that the pbtio3 is with a curie temperature of about 480 ℃, and with high spontaneous polarization intensity, large dielectric constant and small dielectric loss. it is widely used in sensing, storage, infrared imaging and nano generator devices[5,6]. with the in-depth study of perovskite materials, researchers have made breakthroughs in the surface research of nanostructures of perovskite materials, and the research of the special surface ferroelectric polarization characteristics has gradually become an important direction[7]. using the composite-preparation technology and the ferroelectric polarization characteristics on the surface of perovskite nanostructures can regulate the crystal growth of semiconductor oxides, so as to prepare new nanocomposite materials[8]. previous studies have shown that nanocomposite materials have unique electron transport characteristics due to their special energy band structure and surface effects, so 20  they have become a research hotspot in the fields of solar cells, gas-phase catalysis, photocatalysis etc.[9] in 1972, fujishima et al.[10] reported the research on the photolysis of water. in this research, tio2 was used as a photoelectric electrode to decompose water under visible light to prepare hydrogen. semiconductor[11] was used as an important research object of photocatalytic materials. researchers have systematically studied other semiconductor oxide systems, such as g-c3n4 [12,13], zno[14], mos2 [15], and fe2o3 [16]. among many semiconductors, cds[17] is a promising photocatalytic material because of its small band gap (eg ≈ 2.4 ev) and good optical response in the visible band. however, due to its low electron-hole separation efficiency and electron mobility, cds crystal materials prepared by traditional methods are easy to agglomerate and form large particles, resulting in a significant reduction in their specific surface area, which seriously affects the photocatalytic efficiency of cds. in view of the above problems, existing studies mainly promote the photocatalytic efficiency of cds by loading precious metals, such as pt[18], ag[19], and au[20], etc. however, due to the rarity of precious metals and the easy oxidation of cds, the preparation cost of photocatalytic materials increases. in this paper, pbtio3-cds nanocomposite materials were successfully synthesized by a secondary hydrothermal method with single-crystal perovskite phase pbtio3 nanosheets as substrates and cdcl2·5/2h2o and ch4n2s as main reactants. their microstructure and crystal growth were systematically studied. the photocatalytic properties of the prepared pbtio3-cds nanocomposite materials were evaluated by the degradation efficiency of rhodamine b aqueous solution under ultraviolet light and uv-vis diffuse reflectance spectrum, which provided experimental material and theoretical basis for the subsequent exploration of the synthesis and properties of more nanocomposite materials. 2. experiment 2.1 experimental reagents potassium hydroxide (koh, analytical pure, hangzhou gaojing chemical co., ltd.); titanium dioxide (p25 tio2, analytical pure, shanghai aladdin biochemical technology co., ltd.); lead nitrate (pb(no3)2, analytical pure, shanghai zhanyun chemical co., ltd.); cadmium chloride hemihydrate (cdcl2·5/2h2o, analytical purity); thiourea (ch4n2s, analytical purity) and rhodamine b (c28h31cin2o3, analytical purity) were provided by mclean biochemical technology co., ltd.; absolute ethanol (c2h6o, analytical purity, anhui ante food co., ltd.); deionized water (h2o, self-made in the laboratory). 2.2 synthesis of materials 2.2.1 preparation of single-crystal perovskite phase pbtio3 nanosheets single-crystal perovskite phase pbtio3 nanosheets were prepared by the method in the literature[21]. 0.4 g of tio2 powder was added to 6 mol/l of koh aqueous solution to obtain a solution containing ti4+ with the concentration of 0.1 mol/l. in the stirred state, 0.2 mol/l of pb(no3)2 aqueous solution was added to the ti4+-contained solution to adjust the ratio of lead-titanium to 2:0 and stirred for 2 h. the obtained hydroxide solution of titanium and lead was transferred to the inner tank of a 50 ml stainless steel reactor, sealed, and then hydrothermal reaction was carried out at 200 ℃ for 12 h. after the sample was cooled to room temperature, the sample was centrifuged and cleaned with deionized water and absolute ethanol respectively until the washing solution was neutral. finally, the washed sample was dried at 60 ℃ for 24 h to obtain the pbtio3 nanosheet sample to be tested. 2.2.2 preparation of the pbtio3-cds nanocomposite materials 0.2 g of prepared pbtio3 nanosheets were dispersed in 30 ml of deionized water to obtain a white suspension. cdcl2·5/2h2o and ch4n2s were added to the above white suspension at a molar ratio of 1:1 to obtain a mixed solution, which was continuously stirred at room temperature for 30 min. transfer the above mixed solution to the inner tank of a 50 ml stainless steel reactor, seal it, and then conduct hydrothermal reaction at 160 ℃ for 12 h. 21  after cooled to room temperature, the sample was centrifuged and cleaned with deionized water and absolute ethanol respectively until the washing solution was neutral. finally, the washed sample was dried at 60 ℃ for 24 h to obtain the target product sample to be tested. 2.2.3 preparation of cds crystals (contrast samples) using the above synthesis method, cds crystals grown separately were prepared without adding pbtio3 nanosheets. the specific synthesis process is as follows: add cdcl2·5/2h2o and ch4n2s with a molar ratio of 1:1 in 30 ml of deionized water, and obtain the precursor solution by magnetic stirring. after continuous stirring at room temperature for 30 min, transfer the above solution to the inner tank of a 50 ml stainless steel reactor for sealing, and conduct hydrothermal reaction at 160 ℃ for 12 h. after the reaction, cool the sample to room temperature, centrifuge and clean it with deionized water and absolute ethanol respectively until the eluent was neutral. finally, the washed sample was dried at 60 ℃ for 24 h to obtain the contrast product sample to be tested. 2.3 testing and characterization 2.3.1 microscopic characterization of materials the surface morphology of the material was characterized by a zeiss ultra-55 scanning electron microscope (sem), and the acceleration voltage was 5 kv. the powder sample was added to the resin with curing agents, stirred and cured by heating. a leica em trim2 paraffin slicer was used to slice the resin embedded samples. a jeol-200cx transmission electron microscope (tem) was used to characterize the fine structure of the materials, and a high resolution transmission electron microscope (hrtem) was used for imaging analysis, the acceleration voltage of was greater than or equal to 200 kv, the lattice resolution was less than 0.15 nm and the point resolution was 0.21 nm. 2.3.2 phase analysis of materials a shimadzu xrd-6000 x-ray diffractor was used to carry out phase analysis of materials, with cu kɑ (λ = 0.15406 nm) as the radioactive source, with a scanning speed of 3 (°)/min and scanning range of 10.0° to 80.0°. 2.3.3 test of photocatalytic performance 0.2 g of prepared powder sample was dispersed in 50 ml of rhodamine b aqueous solution (10 mg/l) and dark treated for 30 min to reach adsorption equilibrium. then, place it in a photochemical reactor (yz-ghx-a, shanghai yanzheng experimental instrument co., ltd.) and degrade rhodamine b aqueous solution under uv irradiation of 500 w mercury lamp. under continuous stirring and illumination, take out 3 ml mixed solution every 20 min, and centrifuge at the speed of 4000 r/min for 5 min to remove the sediment. measure the absorption peak of the separated supernatant at the wavelength of 554 nm under a uv-vis gradiometer (uv-1800, shanghai mapda instrument co., ltd.). in order to intuitively express the degradation efficiency of rhodamine b aqueous solution, data processing is carried out through formula (1): degradation rate /% = c/c0 × 100 (1) in the formula, c0 is the initial mass concentration of rhodamine b aqueous solution, mg/l; c is the mass concentration of the upper clear liquid at an interval, mg/l. 2.3.4 analysis of uv-vis diffuse reflectance absorption spectrum a shimadzu uv-3600 uv-vis-nir spectrophotometer was used for uv-vis diffuse reflection absorption spectrum analysis. the band gap eg of ahv-hv image fitted by equation (2): αhv = c(hv – eg)2 (2) in the formula, α is the absorbance coefficient, which is directly proportional to absorbance a, and it does not affect the fitting result of the band gap width eg, so in the final image, α is replaced by a, c is a constant. hv is obtained from equation (3): hv = (h × c)/λ (3) in the formula: h is planck constant, h = 6.63 × 10–34 j; c is the speed of light, taken as 3 × 108 m/s; the unit of hv is j. according to 1 ev = 1.6 × 10–19 j, the obtained hv was converted to ev. 22 3. results and analysis 3.1 analysis of the morphology of the pbtio3-cds nanocomposite materials figure 1(a) is the sem diagram of the perovskite phase pbtio3 sample prepared by the hydrothermal method. as can be seen from figure 1(a), the pbtio3 sample is a sheet square with a side length of about 600 nm and a thickness of about 100 nm, with smooth surface, regular morphology and good dispersion. its large-area exposed surface is (001) crystal surface[21]. figure 1(b) shows the contrast sample, that is the morphology of cds particles grown alone without pbtio3 nanosheet substrate. according to figure 1(b), the cds particles grown alone were of micron structure with leaf and branch morphology with size of 2–3 μm. the surface is smooth and flat, with clear particle contour and aggregation tendency. figures 1(c)–(e) are sem images of samples with different cds loading concentrations. as can be seen from figure 1(c), most of the pbtio3 nanosheets in the sample with pbtio3-cds mass fraction of 1% have smooth surface and no obvious adhesion of cds nanoparticles. it can be seen from figure 1(d) that more cds nanoparticles with a size of about 10 nm are grown on the (001) crystal surface of pbtio3 nanosheets in the sample with pbtio3-cds mass fraction of 2%. figure 1(e) shows that in the sample with pbtio3-cds mass fraction of 3%, cds is not only dispersed on the (001) crystal plane of pbtio3, but a small amount of cds is selectively dispersed on the side of pbtio3 nanosheets, that is, the (100) or (010) crystal plane. with the increase of cds loading concentration, the amount of particles grown on pbtio3 nanosheets gradually increases, and its growth crystal surface has obvious selectivity, which may be related to the polarity of the exposed crystal surface of pbtio3 nanosheets. under different initial reactant additions, it can also be observed that there is crystal plane selectivity in the growth of cds nanoparticles on pbtio3 nanosheets, that is, it is preferred to nucleate and grow on the strongly polarized plane, and then composite on other crystal planes. (a) pbtio3 nanopsheet (b) cds particles (c) pbtio3-cds with a mass fraction of 1% (d) pbtio3-cds with a mass fraction of 2% (e) pbtio3-cds with a mass fraction of 3% figure 1. sem images of single-crystal perovskite phase pbtio3 nanosheets synthesized by the hydrothermal method, cds particles and pbtio3-cds nanocomposite materials with different cds loading concentrations. 3.2 phase analysis of pbtio3-cds nanocomposite materials figure 2(a) shows the xrd pattern of perovskite phase pbtio3 nanosheets prepared by the hydrothermal method, with all corresponding diffraction peaks (jcpds: 06-0452), sharp diffraction peaks, good crystallinity and no impurity diffraction peaks. the diffraction peak intensity of its (001) crystal plane is almost equal to the highest peak 23  (101) of the standard diffraction pattern, indicating that the prepared pbtio3 sample has a large number of (001) exposed surface, which is consistent with the observation results reported in the literature[21] and figure 1(a). figure 2(b) shows the xrd patterns of cds particles grown alone and samples with different cds loading concentrations. it can be seen from the figure that the diffraction peaks of cds particle samples synthesized separately all correspond to the standard pdf card (jcpds: 41-1049), with sharp diffraction peaks and no impurity diffraction peaks. the diffraction peaks of pbtio3-cds with a mass fraction of 1%, 2% and 3% are obvious, and the diffraction of pbtio3 is more intense, and the diffraction peak of cds is relatively weak. with the increase of cds loading concentration, the diffraction peak is gradually obvious. it is consistent with the sem results in figures 1(c) to (e). and in the xrd diffraction pattern of pbtio3-cds nanocomposite materials, the diffraction peak intensity corresponding to the (001) crystal plane in pbtio3 (jcpds: 06-0452) decreases, which may be related to the selective growth of cds on the (001) crystal plane of pbtio3 nanosheets. (a) pbtio3 nanosheets (b) single-synthesized cds particles pbtio3-cds with a mass fraction of 1%, 2%, 3% figure 2. xrd patterns of single-crystal perovskite phase pbtio3 nanosheets synthesized by the hydrothermal method, single-synthesized cds particles and pbtio3 cds nanocomposite materials with different cds loading concentrations. 3.3 microstructure analysis of pbtio3-cds nanocomposite materials in order to further explore the growth and morphology of cds nanoparticles on the surface of perovskite pbtio3 nanosheets, the resin embedded sections of pbtio3-cds nanocomposite materials were characterized and analyzed by tem and hrtem. as shown in figure 3(a), cds nanoparticles are dispersed on the upper and lower crystal planes of pbtio3 nanosheets, and an obvious lattice interface is formed, as shown in figure 3(b). the nanoparticle has complete outline and clear lattice, and its crystal plane spacing is 0.316 nm and 0.245 nm respectively, which corresponds to the (101) and (102) crystal planes of cds (jcpds: 41-1049). the crystal plane spacing of pbtio3 nanosheets is 0.415 nm and 0.390 nm respectively, which corresponds to the (001) and (100) crystal planes of pbtio3 (jcpds: 06-0452). therefore, it is further proved that the prepared samples are pbtio3-cds nanocomposite materials, and cds nanoparticles grow selectively on the surface of pbtio3 nanosheets. 24  (a) tem (b) hrtem figure 3. tem and hrtem diagrams of pbtio3-cds nanocomposite materials synthesized by the hydrothermal method. 3.4 growth process of pbtio3-cds nanocomposite materials in order to further explore the growth process of pbtio3-cds nanocomposites, pbtio3-cds nanocomposite materials grown under different hydrothermal reaction time were analyzed. figure 4 and figure 5 show the sem and xrd results of the prepared samples respectively. as can be seen from figure 4: (a) no obvious cds nanoparticles were observed on the surface of pbtio3 nanosheets in the 0.5-h sample, and there was no corresponding diffraction peak in xrd. at this time, cds had not crystallized because the hydrothermal time was too short. (b) fine cds nanoparticles with a size of about 10 nm have appeared on the surface of pbtio3 nanosheets in the 3-h sample. comparing the xrd pattern of this sample with that of the 0.5-h sample, it can be found that the diffraction peak corresponding to cds gradually strengthen. (c) the cds nanoparticles grown on the surface of pbtio3 nanosheets in the 5-h sample gradually increased, and grew on each surface. compared with the xrd pattern of 3-h sample in (b), the diffraction peak corresponding to cds in this sample pattern was enhanced again. with the extension of the reaction time to 7 h in (d), the size and quantity of cds nanoparticles on the surface of pbtio3 nanosheets increase. at this time, cds nanoparticles can be obviously observed on some surfaces of pbtio3 nanosheets, with smooth surfaces and no particle adhesion. therefore, it can be seen that the growth of cds on the surface of pbtio3 nanosheets appears selectivity under the growth conditions. with the further extension of the reaction time (figures 4(e)–(f)), the size of cds nanoparticles on the surface of pbtio3 nanosheets remains stable, and its growth selectivity is more obvious. statistically, a large number of blank exposed crystal surfaces can be observed, while a large number of cds particles grow on other crystal surfaces. figure 5 shows the xrd diffraction results of the prepared samples. it can be seen from the figure that the reaction products have sharp diffraction peaks, which can correspond to two substances of perovskite phase pbtio3 (jcpds: 06-0452) and cds (jcpds: 41-1049) on the standard pdf card. the diffraction results show that both pbtio3 substrate and cds grown on its surface have good crystallinity. according to the above analysis results, with the extension of the reaction time, the growth of cds nanoparticles on pbtio3 nanosheets was significantly regulated. cds nanoparticles selectively grow on a crystal surface of pbtio3 nanosheets. with the increase of the hydrothermal time, according to the crystallization thermodynamics, the size of cds nanoparticles gradually increases and stabilizes. the growth of cds on the surface of pbtio3 nanosheets is a process regulated by thermodynamics and exposed crystal surface of pbtio3. 25  (a) 0.5 h (b) 3 h (c) 5 h (d) 7 h (e) 9 h (f) 12 h figure 4. sem of pbtio3-cds nanocomposite materials synthesized under different hydrothermal reaction time. figure 5. xrd patterns of pbtio3-cds nanocomposite materials synthesized under different hydrothermal reaction time. 3.5 study on the photocatalytic properties of pbtio3-cds nanocomposite materials based on the above research, the photocatalytic degradation properties of the prepared pbtio3-cds nanocomposite materials were studied. figure 6 shows the efficiency curves of self-degra dation of rhodamine b solution and degradation rhodamine b solution by different samples under uv irradiation. as shown in figure 6, rhodamine b solution has slight self-degradation within 120 min, and the degradation rate is 10%, which is caused by the slight increase of the temperature of the stirred solution under uv irradiation in the experiment. pbtio3 nanosheets and pbtio3 nano sheets + cds particles have almost the same degradation ability to rhodamine b solution, and the degradation efficiency is low, which is 40%. it shows that the photocatalytic activity of pbtio3 nanoparticles and cds particles is not high. the rhodamine b solution was significantly degraded by pbtio3-cds with a mass fraction of 1%, 2% and 3% under uv light, and the degradation rates were 60%, 64% and 72% respectively. the above results show that with the increase of cds loading, the catalytic degradation efficiency of pbtio3-cds nanocomposite materials on rhodamine b aqueous solution increases significantly. the degradation efficiency of pbtio3-cds with a mass fraction of 3% is 1.8 times higher than that of pbtio3 nanosheets and pbtio3 nanosheets + cds particles. 26  figure 6. efficiency curves of self-degradation of rhodamine b solution and degradation by different samples. figure 7. uv-vis diffuse reflection absorption spectrum. figure 8. ahv-hv fitting image. figure 7 shows the uv-vis diffuse reflectance spectra of different samples. it can be seen from the figure that the prepared pbtio3-cds nanocomposite materials have obvious absorption peaks between 425 nm and 520 nm, indicating that pbtio3-cds nanocomposite materials have good response to visible light. with the increase of cds loading concentration, the response of pbtio3-cds nanocomposite materials to visible light increased slightly. the ahv-hv fitting image of each sample is fitted 27  according to formula (2), as shown in figure 8, and the band gap width of each sample is shown in table 1. the two band gap widths of pbtio3-cds nanocomposite materials not only improve the band gap width of pbtio3 nanosheets, but also improve the band gap width of cds particles (eg ≈ 2.4 ev), so as to reduce the energy required for electronic transition and improve the photocatalytic performance. with the increase of cds loading concentration to 3%, the light absorption of pbtio3-cds composite samples with a mass fraction of 3% in 425–520 nm band increases significantly. the increase of light absorption is conducive to the formation of electrons and holes in the composites. the absorption edge of pbtio3-cds composite samples with a mass fraction of 3% also has a small amount of red shift, indicating that the band gap of the sample is also reduced accordingly, which is conducive to the absorption of small energy photons, promoting the generation and separation of electrons and holes, and further improving the photocatalytic performance of the sample. this is also consistent with the fact that pbtio3-cds samples with a mass fraction of 3% show the highest photocatalytic activity on rhodamine b aqueous solution under light. based on the above analysis, a possible photocatalytic mechanism is proposed: perovskite pbtio3 nanosheets and cds are used as light absorption centers to absorb photon energy and produce photogenerated carriers respectively. the cds surface is the photocatalytic reaction center. the built-in electric field formed by the spontaneous polarization of pbtio3 nanosheets promotes the separation of electrons and holes, and the electrons are further transferred to the cds surface for photocatalytic reaction, so as to improve the photocatalytic effect of pbtio3-cds. table 1. band gap width of pbtio3 nanosheets and pbtio3-cds with different loading concentrations samples band gap width 1/ev band gap width 2/ev pbtio3 nanosheets 2.76 pbtio3-cds with a mass fraction of 1% 2.24 2.67 pbtio3-cds with a mass fraction of 2% 2.21 2.52 pbtio3-cds with a mass fraction of 3% 2.21 2.46 4. conclusion in this paper, pbtio3-cds nanocomposite materials were successfully prepared by the hydrothermal method, and their microstructure and crystal growth process were systematically charac terized and analyzed. on this basis, the photocatalytic properties of the prepared pbtio3-cds nanocomposite materials were evaluated. the main conclusions are as follows: a) the prepared pbtio3-cds nanocomposite materials have regular morphology and good dispersion; cds nanoparticles (about 10 nm in size) were selectively grown on the surface of perovskite pbtio3 nanosheets with good crystallinity. compared with cds particles with independent nucleation and crystallization, its size decreases sharply, and an obvious interface is formed with pbtio3 nanosheets. the crystal growth of pbtio3-cds nanocomposite materials is a process regulated by the exposed crystal surface of pbtio3. b) hydrothermal reaction time is an important thermodynamic condition that strongly affects the crystal growth process of pbtio3-cds nanocomposite materials. with the increase of time, the more sufficient the nucleation and crystal growth of cds nanoparticles on the surface of pbtio3 nanosheets, the larger the cds grain size. c) the prepared pbtio3-cds nanocomposite materials can degrade 10 mg/l rhodamine b solution. with the increase of the mass fraction of pbtio3-cds, the photocatalytic degradation efficiency of pbtio3-cds nanocomposite materials increases. the degradation rate of pbtio3-cds nanocomposite materials with a mass fraction of 3% was the highest at 120 min, reaching 72%. 28 conflict of interest the authors declare that they have no conflict of interest. acknowledgements national natural science foundation of china (51602286); zhejiang natural science foundation project (ly19e02015). references 1. niu s, peng k, kou j. introduction to the photoelectric materials of nanostructure．journal of liaoning normal university (natural science edition) 2003; 26(1): 63–67. 2. cao j, wu b, peng j, et al. copper-copper iodide hybrid nanostructure as hole transport material for efficient and stable inverted perovskite solar cells. science china chemistry 2019; 62(3): 363–369. 3. zhang m, chen h, yang x, et al. the development and prospect of nanometer materials. missiles and space vehicles 2000; (3): 11–16. 4. shirane g, hoshino s, suzuki k. x-ray study of the phase transition in lead titanate. physical review 1950; 80(6): 1105. 5. yin s. study on the 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generation by a cds-au-tio2 sandwich nanorod array enhanced with au nanoparticle as electron relay and plasmonic photosensitizer. journal of the american chemical society 2014; 136(23): 8438– 8449. 21. chao c, ren z, zhu y, et al. self-templated synthesis of single-crystal and single-domain ferroelectric nanoplates. angewandte chemie international edition 2012; 51(37): 9283–9287. 22. zhong w, tu w, feng s, et al. photocatalytic h2 evolution on cds nanoparticles by loading fese nanorods as co-catalyst under visible light irradiation. journal of alloys and compounds 2019; 772: 669–674. 23. ye k, li y, yang h, et al. an ultrathin carbon layer activated ceo2 heterojunction nanorods for photocatalytic degradation of organic pollutants. applied catalysis b: environmental 2019; 259: 118085. 24. huang x, lei r, yuan j, et al. insight into the piezo-photo coupling effect of pbtio3/cds composites for piezo-photocatalytic hydrogen production. applied catalysis b: environmental 2021; 282: 119586. 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pipelines necessitates the creation of materials of high strength, plasticity, welding and high rigidity. keywords: dynamic crack resistance; austempering; steel; microstructure 1. introduction the subject of this study isto explore the relationship between the dynamic crack strength of low carbon micro alloyed steel at different structure condition and crack surface micro relief. to determine the material crack strength is used three point bending test. the special case is that, in addition to standard sharpy test specimens, test specimens with additional two side notchesare used[3].when performing dynamic tests, the condition for a flat deformed condition must be complied with. a significant amount of energy is consumed to form this state during the tests, which is accompanied and illustrated by the absence of lateral deformation of the test piece in cross-section. in other words, after the flattened deformation state, the shape and dimensions of the cross-section of the test body are preserved the same as the parent–not distort (deformation) the side walls of the test body. in order to increase the resistance of the materials against rupture it is necessary to possess simultaneously high strength and plasticity at the same time. normally, in conventional metals, this is impossible.it is known[5 -11] that sub microcrystalline and nanocrystalline materials exhibit high strength and, in certain cases, unique strength and plasticity properties.one possible method for producing a high crack resistanceand toughness material is the preparation of a bainitic structure. the aim of this research is to obtain astructure of low carbon bainitic steel after isothermal quenching from austenite temperature.different processes like austempering has become the most powerful and effective manufacturing process to satisfy increased hardenability, improved strength, and superior low-temperature toughness[5]. that is why, different structural morphologies have been investigated as a result of cooling from the austenitic temperature at different rates or after annealing. 2. materials and methods specimens of low carbon steel of the chemical composition listed in table 1 were subjected to study. table 1. chemical composition (wt. %) elementcsimncrnialps wt. %)0, 291, 271, 01, 12 0, 050, 070,018 0,018 steel bulk material was initially forged to a 12 x 12 mm square profile to reach approximately 18% deformation texture. the profile is then subjected to recrystallization annealing at 1200 ° c, holding 30 minutes and cooling with the furnace was adopted to remove the texture. from the square are cut samples for metallographic analysis and mechanical tests, which are subsequently subjected to different thermal treatments. copyright © 2019 tatyana avdjieva et al. doi: 10.24294/can.v2i1.650 enpress publisher llc.this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). http://creativecommons.org/licenses/ by/4.0/ 2 the metallographic analysis are performed on pre-prepared screeds after etching with 3% nitric acid, according to e3-95 preparation of metallographic specimens, e407-93 micro etching metals and alloys. analyzes were performed on a sem electron microscope (sem lyra, tescan with quantax eds detector bruker) at various magnifications. the impact was measured at room temperature on all specimens (fig. 1) after each heat treatment. at the base of each concentrator deep 2 mm in all specimens, with a special device, a notch with 1 mm of depth is applied еextra. this was necessary in order to determine the energy for spreading the crack and not the total energy of destruction in the three-point bending test.the fulfillment of the flat deformed condition during the dynamic loading is made possible by increasing the length of the exit initial crack as well as by applying two additional side notches of the same depth (figure 1, b). 55 10 11l b v-notch crack 55 10 11l b v-notch crack b) figure 1. specimens for sharpy test: a) specimen with v-notch and crack, b) specimen with two side notches and crack all thermal treatments of the material begin with austenization at 880 ° c for 30 minutes. the processing temperatures were selected taking into account the martensite transformation temperature, mn = 358 °c experimentallee defined. temperatures of isothermal quenching are selected in the rangefrom 360 till 390ос. results the mechanical properties are summarized in table 2.no significant change in hardness was found ranging from hrc44 to hrc45 in different heat treatments. № heat treatment hardness [hrc] kev [j/sm2] gic[j/sm2] 1 quenching (880 ос) and tempering (350 ос) 45 16,25 12,78 2 austempering at 360ос 43 39,48 31 3 austempering at 380ос 43,5 45,31 41,12 4 austempering at 390ос 44 27,85 22,23 table 2.mechanical properties an especially important parameter of the material, consciously sought, is its crack resistance. rresults obtained in a double sided specimens test are independent of the length of the pre-cracked crack -= l/b (fig. 1, b) and can be considered as the gic dynamic crack resistance of the steel.specific work of fraction propagation (kev) is found to exceed in all cases the work in the plane strain condition (gic). maximum crack resistance is obtained at the processing temperature 380 oc and minimum – after quenching with tempering. the microstructure of the steel after various heat treatments is shown in table 2[1]. at micrographs of steel, ferrite appears gray, bainite appears dark, and both martensite and retained austenite appear white. after quenching and tempering at 350 ° c (table 3, a), the structure has a temperedmartensitic a plate typemartensitic.the individual areas are located within the former austenitic grain. extremely detached structure sharp boundaries between the different phase elements. № heat treatment hardness [hrc] microstructure 1 quenching (880 ос) and tempering (350 ос) 45 tempered martensite troostite 3 table 3.microstructures of cr-mn-si steel the observed at table3, 2microstructure is alow bainite consisting of a number of clusters located within the "paternal" austenitic grain. it consists of ferrite lamellas, some quantity martensitic and residual austenite, which quantity is about 15, 6 %. at a very high magnification in some places there are observed separations along the boundary of the lamellae formationsand individual cement carbides (small rounded formations at high magnification, r ≈0, 20 – 0, 21 m). clusters (individual cereal formations) with bainite ferrite and separate cement separations are observed(table 3, 3). as can be seen in the picture, the sizes of the individual structural formations are extremely small. the structure is low bainite. there is no residual austenite on the x-ray difraction. the structure after 390 oc (table 3.4) is an upper bainite consisting of alternating ferrite lamellas and residual austenite – 21 %. cluster sizes are relatively large. they are located at a different angle within the former austenitic grain. the difference in the microstructure is also the size of the individual lamellae in the clusters with an increase in the temperature of the isothermal quench the size increases. at a temperature of 360 °c, the average size is 0.23 – 0, 25 μm and at 390 °c 1.55 – 1, 72 μm, which thickens the laminates. fractography is a method in failure analysis for studying the fracture surface of materials. the fractured surface are shown at table. 4 to help determinnation of the cause of failure. we can see different modes of failure produce characteristic features on the fracture surface. 2 austempering at 360ос 43 low bainite and martensite 3 austempering at 380ос 43,5 low bainite 4 austempering at 390ос 44 upper bainite 4 heat treatment 1 2 3 4 standard sharpy specimens specimens with 2 v-notches table 4. fracture surfaces the failure in all of the specimens begins along the entire length of the overshoot. in the tempered patterns the direction of the major crack points are arranged fan-shaped from the bottom of the notch to the opposite end of the sample body. in the samples after isothermal quenching there is no visible movement of the crack. at the beginning of the crack propagation (immediately after the bottom of the overshoot) there are areas located transversely to the direction of impact with the presence of secondary cracks in them, which suggest a delay in the movement of the highway crack. there are no deformations in the destroyed test bodies with 2 v-notches, as expected. thus all the energy for has gone to spread the crack. a) b) c) d) a) – after quenching and tempering, b) austempering at 360 ос, c) austempering at 380 ос, d) austempering at 390 ос figure 4. the fracture surface of tested steel after different heat treatment it is known that the crack resistance of the metal is determined by the dominant fracture mechanism in each case[3,4]. the absence of distortion on the fracture surface of two v-notch specimens allowed to test into the influence of structure condition on dynamic crack strength gic. 5 after quenching the crack follows the grain boundaries(intergranular fracture) – intergranular cleavage facets appear together with quasi cleavage facets (fig. 4, a).after isothermal quenching at 360 ос, the structure changes multiple flat dimples appear withcomplex carbides at the bottom (fig. 4, b).numerous flat dimples are combined with few quasi cleavage facets at the fig.4, c. low bainite structure leads to ellimination of the brittle fraction ductile fracture is characterized by a deeper dimple structure. as a result of the presence of an upper bainite in the structure (fig. 4, d, the fracture surface again changes– flat dumples with quasi cleavage facets appears. 3. discussion two low-carbon steel alloyed with cr,si, mn have been tested. the low carbon is preferred for the current steel from the viewpoint of low segregation, good toughness, and superior weldability. conclusion the increasing dynamic crack strength gic to be determine in appearing of low bainite is conditioned by growing of large and deep dimples. the method for determining the dynamic crack resistanceof the metal with 2 v-notch specimens is easy, fast and sufficiently representative. it has been found that bainitic steel has maximum crack resistance references 1. avdjieva t. microstructure features of cr-ni steel after isothermal tempering, annual of sofia university 2016; 109. 2. avdjieva t, et al.(2013). microstructure and crack resistance of low carbon cr-ni and cr-ni-w steel after austempering, central european journal of engineering 2013; 3(3): 484-491. 3. georgiev m, et al. the relation between dynamic crack strength of structural steels and schnook loading fracture structures, material science 2011; 12: 118-128. 4. георгиев м, et al. оценка работы разрушения ударных образцов с боковыми надрезами, заводская лаборатория. 2012; 9: 56-61. 5. litovchenko i, et al. the features of microstructure and mechanical properties of metastable austenitic steel subjected to low-temperature and subsequent warm deformation, russian physics journal 2016; 59(6). 6. lang hf, et al. microstructure and mechanical properties of a low carbonbainitic steel, mat. res. 2013; 84(4): 352–361. 7. yong tiana, et al. the analysis of the microstructure and mechanical properties of low carbon micro alloyed steels after ultra-fast cooling, mat. res. 2017; 20(3). 8. zuo x, et al. study of pipeline steels with acicular ferrite microstructure and ferrite-bainite dual-phase microstructure, materials research 2015;18(1): 36-41. 9. pedrosa irv, et al. study of phase transformations in api 5l x80 steel in order to increase its fracture toughness, materials research 2013; 16(2): 489-496. 10. sung hk, et al. s effects of cooling conditions on microstructure, tensile properties, and charpy impact toughness of low-carbon high-strength bainitic steels, metallurgical and materials transactions a 2013; 44(1): 294-302. 11. gallego j, et al. second phase precipitation in ultrafine-grained ferrite steel. materials research 2014. characterization and application of nanomaterials 2025, 8(3), 10232. https://doi.org/10.24294/can10232 1 review development of coumarin composite with graphene oxide influence: preparation, characterization, and application abdulhaleem abdulkareem ahmad, zhen zhang, yanqiu li, xiao wang, ling li*, peng zhang* school of environmental and chemical engineering, school of materials science and engineering, shanghai university, shanghai 200444, china * corresponding authors: ling li, liling2178@shu.edu.cn; peng zhang, pengzhang@shu.edu.cn abstract: the tunable conduction of coumarin-based composites has attracted considerable attention in a wide range of applications due to their unique chemical structures and fascinating properties. the incorporation of graphene oxide (go) further enhances coumarin properties, including strong fluorescence, reversible photodimerization, and good thermal stability, expanding their potential use in advanced technological applications. this review describes the developmental evolution from go, go-polymer, and coumarin-based polymer to the coumarin-go composite, concerning their synthesis, characterization, unique properties, and wide applications. we especially highlight the outstanding progress in the synthesis and structural characteristics along with their physical and chemical properties. therefore, understanding their structure-property relations is very important to acquire scientific and technological information for developing the advanced materials with interesting performance in optoelectronic and energy applications as well as in the biomedical field. given the expertise of influenced factors (e.g., dispersion quality, functionalization, and loading level) on the overall extent of enhancement, future research directions include optimizing coumarin-go composites by varying the nanofiller types and coumarin compositions, which could significantly promote the development of next-generation polymer composites for specific applications. keywords: coumarin-based polymer; polymeric features; coumarin-go composites; synthesis and structural characteristics; structure-property relations; specific application 1. introduction the field of unique polymeric features (e.g., ease of fabrication, lightweight, exceptional processability, durability and comparatively less cost) dependent technical applications has developed considerably in the past decades [1]. in a recent study, the stimuli-responsive polymers have attracted considerable attention due to their unique capacity to perform the rapid shifting of their physical and chemical properties in response to the surrounding environment [2]. these polymers, especially coumarinbased photoresponsive polymers, have garnered significant interest due to their potential applications in the ranged fields from self-healing materials to drug delivery systems [3]. according to the coumarin dimerization reaction, it is more important to understand the design principles of moieties location in the polymer matrix for making informed choices to optimize their performance for specific applications [4]. therefore, the versatility of light-based triggers offers a promising avenue for the design and fabrication of innovative materials with enhanced functionality and responsiveness [5]. coumarin conjugated with their derivatives has attracted significant attention in various fields of research owing to its exceptional properties and the wide range of citation ahmad aa, zhang z, li y, et al. development of coumarin composite with graphene oxide influence: preparation, characterization, and application. characterization and application of nanomaterials. 2025; 8(3): 10232. https://doi.org/10.24294/can10232 article info received: 12 november 2024 revised: 5 january 2025 accepted: 10 january 2025 available online: 20 june 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterialsis published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(3), 10232. 2 enhancements it offers to polymer matrices [6]. the synthesis of coumarin-based polymers has evolved significantly from classical and modern methods to green synthetic methods to produce versatile materials. how to understand their synthetic mechanism with nanofiller modification is crucial for optimizing the properties and applications of coumarin-based polymers in various fields. as an alternative nanofiller among carbon materials (e.g., carbon nanotube and graphite), graphene oxide (go) with economic feasibility and large-scale manufacturing underscores its importance to significantly enhance the mechanical, thermal, electrical, and barrier properties of polymers [7]. further exploration into the structural dynamics of go has revealed its suitability for integration into nanocomposites, supercapacitors, and electrochemical sensors, attributed to the presence of various oxygen-containing groups and high surface functionality of go [8,9]. several factors from go critically influence the overall extent of polymer properties (e.g., tensile strength, elastic modulus, toughness and electrical, thermal and mechanical properties), such as dispersion quality to prevent agglomeration, functionalization to disrupt the network conductivity and optimal loading to affect the electrical behavior [10]. in line with this trend, the incorporation of go into polymer matrices significantly improves their thermal stability, thermal conductivity, and overall thermal performance, making these composites suitable for various advanced applications [11–13]. recently, the functionalized go as a nanofiller, especially doped coumarin-based polymers, could perform a unique combination of mechanical, thermal, electrical, and chemical properties for meeting the specific application requirements [14–16]. in this review, advancements from go, go-composites and coumarin-based polymers to coumarin-go composites are presented, as well as highlighting the various methods, typical characterizations and specific properties. especially, the contribution of go introduction on property enhancement is summarized dependent on the manufacturing strategy. moreover, the scope of the fabrication of coumaringo composites in demanded applications has been overviewed. to the end, the challenges encountered related to the accomplishment of coumarin-go composite systems for achieving the desired features have been deliberated. 2. structure and property of graphene oxide as a crucial material in nanotechnology, graphene oxide (go) is known for its unique properties and wide range of applications. universal strategies have been developed for go-based material synthesis and property tailoring to address various technological applications in photonics, electronics and optoelectronics [17]. it is always synthesized by subjecting pristine graphite to strong oxidizers and acids to alter the structural functionalities and maintain the layered configuration. during this process, various oxygen-containing functional groups of epoxy (c–o–c), hydroxyl (– oh), and carboxyl (–cooh) groups were introduced to attach both the basal planes and side edges of host graphene layers, resulting in a combination of sp2 and sp3 hybridized carbons within the formation (figure 1) [18]. while characterized by the presence of oxygen-containing functional groups from various synthetic methods, characterization and application of nanomaterials 2025, 8(3), 10232. 3 structures significantly influence their intrinsic properties to explore as an excellent candidate for a wide range of applications. figure 1. summary of synthetic methods, characterization techniques and tunable properties for go. 2.1. synthetic methods the synthesis of go has evolved over time, as well as several methods developed to optimize its production [19]. the primary synthetic methods were summarized as follows. 2.1.1. brodie method the brodie method introduced by benjamin c. brodie in 1859 (figure 1), was the original technique for go synthesis via graphite oxidation involving potassium chlorate (kclo3) in fuming nitric acid (hno3) [20]. despite its historical significance, this reaction is highly exothermic and requires careful control to prevent explosive hazards from violent reactions [21]. 2.1.2. hofmann method the hofmann method is a modified brodie method that employs a mixture of concentrated sulfuric acid (h2so4) and hno3 with kclo3 as the oxidizing agent in 1898 (figure 1). in comparison to the brodie method, the hofmann method improves the safety and efficiency of the oxidation process, while it still involves handling strong acids and oxidizers to cause the significant safety risks [22]. 2.1.3. staudenmaier method as another improvement over the brodie method, the staudenmaier method was developed by l. staudenmaier in 1898 through mixing the intercalant of concentrated h2so4 and h2so4 with kclo3 in a batch reaction (figure 1) [23–25]. the staudenmaier method is capable to produce go with a higher degree of oxidation (i.e., a higher carbon-to-oxygen ratio) and better control over the reaction conditions than the brodie method. however, it still involves handling strong acids and oxidizers, which require careful control to ensure safety [26]. 2.1.4. hummers method the hummers method was developed by william s. hummers and richard e. offeman in 1958, which evolved as one of the most widely used methods for go preparation (figure 1) [27,28]. this synthesis involves the oxidation of graphite using a mixture of concentrated h2so4, sodium nitrate (nano3) and potassium permanganate (k2mno4). this method is favored for its efficiency and relatively safer characterization and application of nanomaterials 2025, 8(3), 10232. 4 procedure than the brodie and hofmann methods, deriving from their conducted reaction at low temperatures to control the exothermic nature of the process [29]. however, it still generates toxic gases such as nitrogen dioxide (no2) and dinitrogen tetroxide (n2o4) during the reaction [30]. therefore, several modifications have been made to the original hummers method to enhance its efficiency and safety. for example, through the removal of nano3 and the partial replacement of k2mno4 with potassium ferrate (k2feo4), this modification reduces the generation of toxic gases and improves the yield of go [31]. another approach includes a pre-oxidation step before the main oxidation reaction, resulting in achieving a higher degree of oxidation and better quality of the final product [32]. 2.2. characterization techniques as a non-stoichiometric substance, the structure of go with oxygen-containing functional groups from different preparations remains a challenge to determine [33]. through the powerful and exact characterization of solid-state nuclear magnetic resonance (nmr), x-ray photoelectron spectroscopy (xps), fourier transform infrared spectroscopy (ftir), and raman spectroscopy, the precise structure of go has been successively determined (figure 1), such as the isotope 13c labeling of c– o–c and c–oh (60.2 ppm and 71.2 ppm) from nmr, sp3 carbon (c–c, 284.4 ev), epoxide group/hydroxyl group (c–o, 285.3 ev) and carbonyl group (c=o, 288.0 ev) from xps, stretching vibration peaks of o–h (3420 cm−1), c=o (1720–1740 cm−1), unoxidized sp2 hybridized c=c (1590–1620 cm−1) and c–o (1250 cm−1) from ftir [34]. unlike the spectral analysis, the examination of surface morphology from electron microscopy of scanning electron microscopy (sem), transmission electron microscopy (tem) and atomic force microscopy (afm) provides complete information about the layered structure of go with a variety of surface formations. 2.3. tunable properties go is a versatile material with a unique combination of mechanical, thermal, electrical, and chemical properties with respect to their structures (figure 1). the ability to tailor its properties through reduction and functionalization was furthered to enhance its utility in advanced materials science [35]. 2.3.1. mechanical properties after disrupting the sp2 hybridization of carbon atoms, the interlayer space increases to approximately 0.7 nm more than pristine graphite (0.34 nm) to cause the buckled structure [36]. while mechanical properties of go could enhance through the facilitated strong covalent bond within the graphene layers and the interlayer interactions by the functional groups (e.g., –c–o–c– and –oh) [37], leading to render go as a suitable nanofiller for reinforcing polymer matrices [38]. 2.3.2. thermal properties generally, go performed lower thermal stability compared to pristine graphene when oxygen-containing groups decomposed at elevated temperatures [39]. from the consideration of oxidation degree and additional functional groups (e.g., –c–o–c– and –c=o) on thermal stability [40], we could still significantly enhance the thermal properties of polymer composites when go is selected as a nanofiller [41,42]. characterization and application of nanomaterials 2025, 8(3), 10232. 5 2.3.3. barrier properties go also exhibits excellent barrier properties against gases and liquids due to its layered structure and the tortuous path created by the functional groups. the functional groups in go result in the chemical reactivity, rendering it potentially active in various chemical reactions and hence versatile for functionalization and composite formation [43]. while the presence of oxygen-containing groups (e.g., –c–o–c– and –cooh) [44] makes go highly hydrophilic for adequate dispersion in water and other polar solvents [45], allowing for applications in packaging and coatings [46]. 2.3.4. electrical conductivity go with high surface area forms conductive networks within the polymer matrix. the dielectric properties of go make it useful in applications requiring materials with high dielectric constants (40 at 100 hz and 80 ℃) and low dielectric losses (5 at 100 hz and 80 ℃) [47]. one of the most notable properties of go is its ability to improve the electrical conductivity of polymers or composites for extending the applications in electronics, sensors, and energy storage devices [48]. 3. structure and properties of coumarin-based polymers referred to as “antenna” or “light-harvesting” polymers, coumarin-based polymers have attracted significant attention due to their unique optical, biological and photochemical properties [49]. 3.1. structural properties the coumarin group can undergo photodimerization, a reversible [2πs + 2πs] cycloaddition reaction upon exposure to uv light. this reaction leads to the formation of cyclobutane dimers, which can be reversed by uv irradiation of higher energy photons, typically at wavelengths greater than 250 nm [50,51]. coumarin-based polymers are recognized by the presence of coumarin units, which consist of a benzene ring fused to an α-pyrone ring (figure 2, blue structure). these polymers feature coumarin moieties as pendant or terminal groups on the polymer chain, exhibiting their structure dependent on fascinating properties. these properties are summarized below: 1) photophysical properties: coumarin-based polymers exhibit strong fluorescence, suitable for applications in optoelectronics [52] and photonics [53]. while the fluorescence behavior is influenced by the conjugated system of the coumarin moiety, which allows for efficient light absorption and emission [54]. 2) photochemical properties: the ability of coumarin derivatives to undergo photoinduced cyclodimerization and subsequent photo-cleavage is a key feature [55]. this reversible reaction is utilized in photo-optical devices for information storage and management [56]. 3) thermal stability: coumarin-based polymers generally exhibit good thermal stability via the incorporation of nanofillers such as go [57], leading to applications requiring high thermal resistance [58]. 4) mechanical properties: the mechanical properties of coumarin-based polymers can be tailored by varying the composition and structure of the polymer matrix. such incorporation of coumarin groups enhances the rigidity and strength of the polymer [59,60]. characterization and application of nanomaterials 2025, 8(3), 10232. 6 5) biocompatibility: coumarin derivatives such as thiazole, azetidinone and oxazole have been found to be effective against bacterial and fungal infections, highlighting their potential in biomedical applications [61]. figure 2. illustrating the synthesis of coumarin-based polymer. 3.2. synthetic methods all above-mentioned properties have propelled coumarin-based polymers into the spotlight as versatile materials with wide-ranging applications. while producing these materials, various synthetic methods have evolved significantly over the past decades (figure 2). all methods are summarized to highlight the pathways, mechanisms, advantages and limitations. 3.2.1. classical synthesis (1) pechmann condensation: the pechmann condensation is one of the earliest and most widely used methods for synthesizing coumarin derivatives [62]. the process is typically carried out using h2so4 or other strong acids as catalysts, involving the acid-catalyzed condensation of phenols with β-keto esters. the method is favored for its simplicity and high yield, but it requires stringent reaction conditions as well as significant amounts of by-product formation [63]. (2) knoevenagel condensation: the knoevenagel condensation involves the reaction of aldehydes with active methylene compounds in the presence of a base (e.g., piperidine or pyridine) [64]. this method is particularly useful for synthesizing coumarin derivatives with various substituents on the aromatic ring. deriving from its characterization and application of nanomaterials 2025, 8(3), 10232. 7 mild reaction conditions and high selectivity, this method was alternatively selected as a popular choice for synthesizing coumarin-based polymers [65]. (3) perkin reaction: the perkin reaction is another classical method for synthesizing coumarin derivatives. it involves the condensation of aromatic aldehydes with anhydrides in the presence of a base, such as sodium acetate. this method is advantageous for producing coumarins with specific substituents, but it often requires high temperatures and long reaction times [66]. 3.2.2. modern synthesis (1) heck-lactonization reaction: in addition to the classical synthesis, the modern synthetic methods include the heck-lactonization reaction, which was particularly useful for producing coumarin-based polymers with enhanced photophysical properties [67]. this method is highly efficient and allows for designing the coumarin derivatives with complex structures through the intramolecular cyclization of aryl halides with alkenes from the palladium coupling reaction [68]. (2) baylis-hillman reaction: another important technique for coumarin production is the baylis-hillman reaction, which involves the coupling of aldehydes with activated alkenes triggered by a tertiary amine [69,70]. this method results in coumarin derivatives with reasonable tolerance to several functional groups and bland conditions of reaction. (3) michael addition reaction: the nucleophilic addition reaction involving a, bunsaturated carbonyl compounds through a michael addition reaction is also a suitable method, widely used in the synthesis of coumarin derivatives with various substituents. the michael addition is suitable for coumarin preparation with high efficiency and selectivity [71]. 3.2.3. green synthesis (1) microwave-assisted synthesis: this is a green chemistry approach to using microwave irradiation for accelerating chemical reactions [72]. this method is advantageous for synthesizing coumarin-based polymers with high yields (95%–99%) and purity under the reduced reaction times and energy consumption [73]. (2) ultrasound-assisted synthesis: assisted with ultrasonic waves to promote chemical reactions, coumarin-based polymers with improved properties (e.g., enhanced mechanical strength, chemical resistance, optical activity and thermal stability) and reduced environmental impact (e.g., energy consumption and waste generation) produced under mild reaction conditions with high efficiency [74]. 3.3. broad applications understanding these synthetic methods is crucial for optimizing the properties and applications of coumarin-based polymers in various fields of science and technology (figure 3). characterization and application of nanomaterials 2025, 8(3), 10232. 8 figure 3. illustration of various applications from coumarin-based polymers. 3.3.1. electronics and optics coumarin-based polymers are increasingly applied in electronics and optics due to their unique photochemical properties. they serve as optical limiters to protect sensitive devices from high-intensity light and act as fluorescent dyes in bio-imaging and chemical sensing. especially in organic light-emitting diodes (oleds), these polymers enhance light emission to be valuable for display technologies. also they are utilized in electronic devices for efficient light guiding and modulation, while their sensitivity allows them to function as real-time sensors for various analytes. additionally, coumarin-based polymers contribute to solar energy conversion in organic photovoltaics, which were applied as protective coatings to enhance the aesthetic and functional properties of surfaces in optics [75,76]. 3.3.2. liquid-crystal materials deriving from their alignment after interaction with liquid crystal phases, coumarin-based polymers are employed in the fabrication of liquid-crystal displays (lcds) and other optical devices. in this way, they tuned liquid crystal features to enhance the responsiveness of lcds by providing improved switching speeds and color ratios in optics. therefore, they are applied in smart windows and adaptive optics, advanced imaging and display technologies, resulting in better flexibility and efficiency [77,78]. 3.3.3. biomedical applications coumarin-based polymers, possessing unique light-responsiveness, serve as effective fluorescent probes for bio-imaging, enabling the visualization of cellular processes and disease markers in biomedicine. for instance, these polymers can be utilized in imaging techniques such as fluorescence microscopy to track cancer cell migration or monitor the expression of specific proteins associated with diseases. characterization and application of nanomaterials 2025, 8(3), 10232. 9 additionally, they enhance the solubility of therapeutic agents, promoting drug delivery systems that improve the bioavailability of poorly soluble drugs. in photothermal therapy, coumarin-based polymers can selectively target cancer cells, generating localized heat upon light irradiation to induce cell death while minimizing damage to surrounding healthy tissues. furthermore, these materials are being developed into biosensors for real-time monitoring of biomolecules, such as glucose or cancer biomarkers, facilitating advancements in diagnostics and personalized medicine [79]. 3.3.4. organic-inorganic hybrid materials coumarin-based polymers integrated into hybrid materials (e.g., polymer nanocomposites, polymer-ceramic composites, polymer-metal composites, and polymer-organic hybrid materials) achieve outstanding photochemical properties and excellent mechanical strength, enhancing their performance in diverse applications, e.g., in optoelectronics for organic light-emitting diodes (oleds) and solar cells, in coatings for enhanced durability and self-healing capabilities [80]. in the field of optoelectronics, these hybrids are utilized in oleds for displays and lighting, where their tunable emission properties improve color purity and efficiency. they also contribute to solar cells by enhancing light absorption and charge transport, leading to higher energy conversion efficiencies. in coatings, coumarin-based polymers provide enhanced durability and self-healing capabilities, making them suitable for protective coatings in the automotive and aerospace industries. additionally, they play a vital role in nanotechnology for packaging applications, where they can provide barrier properties and antimicrobial effects, as well as in sensors for environmental monitoring, detecting pollutants or hazardous substances. in energy storage, these materials are being explored for use in batteries and supercapacitors, where their unique properties can enhance charge capacity and cycling stability [81,82]. 4. property and application of go-coumarin composites the synthesis of coumarin-based polymers has evolved significantly, while the incorporation of go nanofiller into the polymer matrix further enhances their properties as well as expands potential applications in various fields. therefore, how to understand the structure-property relations of coumarin-based polymers, along with the advantages of using go as a nanofiller, is very important for developing the advanced materials with interesting performance. 4.1. go-polymer composites as the hot topics, nanofiller-based polymer composites have been presented with special emphasis on significant industrial potential [83]. the various polymer composites with high performance were widely constructed through the controllable interfacial interaction between the filler and the matrix [84]. among other nanofillers (e.g., carbon, silica and clay minerals), go with the favorable functional properties has been extensively explored as the appropriate candidate in polymer composites [85]. due to π–π stacking and van der waals forces, reactive oxygen moieties on the basal plane and edges of go could contact with the polymer matrix through the covalent bond and hybrid approach. therefore, most of the important polymers commercially characterization and application of nanomaterials 2025, 8(3), 10232. 10 (e.g., polymethyl methacrylate, polyacrylamide, polyethylene terephthalate and polyvinyl alcohol) have been used in the production of go-filled polymer composites [86]. 4.2. go-coumarin composites in comparison to the structural regulation of photoresponsive coumarin by inorganic nanoparticles (e.g., au, pt, pd and sio2), a new set of emerging gocoumarin composites with novel structure-dependent functional properties has been developed, which was interesting both for fundamental research and advanced applications [87]. 4.2.1. synthetic methods through the electrostatic self-assembly of positively charged nitrogenous coumarin and negatively charged go, go-coumarin composite could be obtained as well as improved morphological structure and adsorption capacity [88]. it is speculated that the structure of go-coumarin composite can also be controlled by coumarin-based polymer, although there is little research in the field. this review especially highlighted the development of go incorporation with lactone-ended poly (benzyl methacrylate) (le-pbma/go) and random copolymers of 4-methyl-2-oxo2h-chromen-7-yl methacrylate (couma) and methyl methacrylate (mma) (comcop/go) along with others (figure 4) [89]. figure 4. schematic representation of the formation of go-coumarin composites. 4.2.2. characterization technologies after synthesis, the products were detailedly analyzed using various characterization techniques. characterization and application of nanomaterials 2025, 8(3), 10232. 11 (1) nmr, ftir and xps were utilized for structural characterization to confirm the presence and functionality of various chemical groups within the polymer. from the 1h-nmr spectrum (in cdcl3), the resonance signals of =ch next to the c=o group in the couma unit and the och3 groups of mma at 6.23 and 3.61 ppm were observed (figure 5a). most characteristic bands of couma and mma units are at 1730 cm−1 (c=o stretching) and 1624–1572 cm−1 (c=c stretching), respectively. while the amount of benzyl methacrylate and benzyl alcohol was less produced from le-pbma/go degradation, implying that go has decreased depolymerization of lepbma. for identifying the electronic states of composites, the signals of c 1s (c-c, c-n, c-o and c=o) and o 1s (n-o and o-c) are assigned to the go, while a new peak at approximately 400 ev corresponding to n 1s is observed to prove the successful introduction of coumarin for the coumarin-go [88]. (2) differential scanning calorimetry (dsc) and thermogravimetric analysis (tga) were carried out for detailed analysis of thermal behavior, including stability, melting points and decomposition kinetics (figure 5b). with an incorporation of couma content, the glass transition temperature (tg) of comcop increased to 166 ℃, which was higher than that of the control pmma (109.5 ℃). consistent with the literature, it has been recorded that the tg value of copolymers with increasing ratios of couma units containing butoxyethyl methacrylate has increased [90]. when go content in comcop increased from 10% to 16%, the tg value increased from 162 to 173 ℃ due to the synergic contribution of the coumarin group and go on movement ability. (3) uv-vis spectroscopy was employed to investigate the photophysical properties and photodimerization behavior of the coumarin units (figure 5c), which are integral to the polymer backbone or exist as side chains. it was found that the uv absorption peak of coumarin appears at around 320 nm and a broad peak of go locates between 220 nm and 240 nm, while coumarin-go displays a maximum absorption at 320 nm. from another study, it can be seen that the values of the refractive index of le-pbma increased with increasing wavelength to 590 nm and subsequently decreased due to disperse property with increasing wavelength. while the strong band absorption of le-pbma/go in the uv range (between 400 and 800 nm) leads to a drastic decrease in refractive index, indicating the restricted movement of polymer chains from interaction between go and polymer matrix [91]. (4) the crystal structures are normally characterized by x-ray diffraction (xrd) analysis. in comparison to the sharp characteristic diffraction (001) peak of go at 2θ =11.29° and a shoulder peak of coumarin at around 21°, the composite shows characteristic peaks of both go and coumarin (figure 5d) to demonstrate their successful synthesis through the electrostatic self-assembly [92]. according to the xrd pattern, the (001) peak of coumarin-go with broadening diffraction appears at 10.05°, evidently revealing the coumarin introduction changes the crystal structure of the go and increases their interlayer spacing from 0.79 nm to 0.88 nm. (5) sem and tem are carried out to investigate the structural morphology. as shown from sem images (figure 5e), coumarin-go shows a three-dimensional (3d) close-packed structure similar to a squished multi-porous structure instead of a twodimensional (2d) planar structure of pure go. meanwhile, the 3d close-packed structure of the composite was verified from the tem image (figure 5f), along with characterization and application of nanomaterials 2025, 8(3), 10232. 12 observation of small pores distributed on the surface. the pore size distribution would be characterized based on the barrett-joyner-halenda method, in which the composite displays pore sizes ranging from 1.8 to 2.5 nm to be in line with the specific surface area increment from 56 m2 g−1 to 89 m2 g−1 via the typical type-iv isotherms with h3type hysteresis loops. additionally, from the analysis of tem equipped with energydispersive x-ray spectroscopy, it proved that c, o and n elements uniformly distributed on all material, further clearly demonstrating the successful introduction of coumarin groups in the coumarin-go composite. figure 5. materials characterization of (a) nmr; (b) dsc; (c) uv-vis absorption; (d) xrd; (e) sem; (f) tem. 4.3. unique property stemming from the unique properties (e.g., mechanical, thermal, electrical, and barrier enhancements) of go along with its chemical reactivity and biocompatibility, it is always selected as an exceptional nanofiller for doping coumarin-based polymers with improved properties. 4.3.1. electrical conductivity when go are well dispersed in the polymer medium, they create pathways in the form of a hole or empty space in the conduction band of the material, rendering it ready for electron or charge carrier gain from the valence band of the material to achieve the crucial conductivity [93]. functionalized go normally gives better performance of composites in terms of electrical properties as well as the loading levels related to agglomeration [94]. the electrical properties with respect to the maximum current values increase significantly with the concentration of go loading, demonstrating the strong interfacial interactions between go and the copolymer [94]. while the dielectric constant and loss factor also increase with go contents attributed to the polar functional groups in both go and the copolymer (figure 6a), which further enhanced the dipolar and interfacial polarizations [95]. dielectric analysis of the comcop/go further supports these findings, showing the magnitude of conductivity changes with increasing amounts of go. also, the polymer with go characterization and application of nanomaterials 2025, 8(3), 10232. 13 attachment showed a linear variation between i-v, especially the maximum current values for comcop/go estimated at 8.53 × 10−4 a (figure 6b). similarly, a study conducted by go incorporated into polyvinylpyrrolidone (pvp) created nanocomposites with enhanced dielectric properties [96]. 4.3.2. thermal stability several studies have shown that go can increase the degradation temperature of polymers via a mechanism of barrier creation, which slows down the release of volatile degradation products [65–67]. for instance, the inclusion of go nanosheets in polypropylene (pp) composites has been reported to increase the thermal stability [97]. the superior nanofiller of go-doped coumarin-based polymers significantly improves the mechanical properties of polymers by enhancing tensile strength, elastic modulus, and toughness through strong interfacial interactions [98]. additionally, go enhances the thermal stability of polymer matrices by increasing the activation energy required for thermal decomposition. according to the thermal degradation kinetics, it revealed that decomposition temperatures of le-pbma [99], poly (bma) and le-pbma/go at 10% weight loss were 265 ℃, 273 ℃ and 288 ℃, respectively, while thermal stability of the composite between 308 ℃ and 363 ℃ has increased. also, the decreased activation energy values were consistent with enhanced stability in the presence of go nanofiller (figure 6c), due to the higher tg of the copolymers (comcop/go). another study found that the thermal reduction of graphite oxide in the presence of polymers to produce reduced graphite oxide (rgo) led to decreased thermal stability of the polymer. in line with a study on poly (ethylene oxide) (peo) intercalated in go (peo/go) composites demonstrated a significant decrease in thermal stability [100,101]. similarly, it found that pva/peo composite with go incorporation significantly influences the optical, thermal, electrical, and dielectric properties. the optical bandgap of composites decreased with increasing go concentrations, indicating enhanced charge transport, while thermal stability improved due to chemical interactions between pva and peo [102]. 4.3.3. photochemical transition based on reversible photoresponses of coumarin, the coumarin-go composites are investigated by monitoring the absorbance evolution under uv light (365 nm or 254 nm) irradiation. it found the characteristic peak of coumarin (320 nm) decreases with illumination time under 365 nm uv light due to the photodimerization of coumarin, while it increases with time under 254 nm light illumination due to the photocleavage of coumarin. similar as comcop/go, by preparing very low dilute solutions of coumarin-containing homopolymer or copolymers, when exposed to uv light at λ > 350 nm, it can be controlled by the formation of cyclobutane intramolecularly with a cyclo-addition photodimerization and photocleavage (figure 6d) [103]. the maximum peak intensity for n→π* transition in the coumarin group at 310 nm decreased along the period of irradiation, indicating an increase in the degree of dimerization. however, as time increases, the maximum peak intensity decreases; the peaks reflect the contribution of π→π* transitions of conjugated benzene and pyron subunits in the coumarin chromophores within the copolymer structure. the conjugation between the double bonds and the benzene ring decreased significantly as a result of the homolytic cleavage of the c=c bond next to the c=o. based on previous characterization and application of nanomaterials 2025, 8(3), 10232. 14 studies, four isomeric structures of coumarin dimers have been recorded [104]. this reversible process accounts for the unique behaviors of supramolecular networks and provides a useful reaction pathway in polymer science [105]. figure 6. dependence of e’ and e” as a function of frequency: (a) and current (i)-voltage (v) characteristics; (b) for composites with various concentrations of go; (c) dsc curves of go and their composite; (d) photodimerization recorded from uv–vis spectra after uv irradiation. 4.4. versatile application proper characterization of the polymers is crucial to provide insights into their electrical, thermal and photoresponse properties, which directly helps in optimizing the material design for specific applications. 4.4.1. intracellular imaging the nanoprobe of the coumarin-go composite has a fluorescence on–off response for intracellular imaging via covalently linking coumarin derivatives to go through disulfide bonds [106]. more significantly, from in vitro cytotoxicity study, there was no obvious toxicity observed for composites even at a high concentration of 60 g ml−1, indicating the resultant nanoprobe is not cytotoxic and suitable for cell imaging. according to the time-course fluorescence microscopy experiments using hela and nih-3t3 cells, we found the fluorescence signal from hela cells after 30 min of incubation was clearly detected in the cytoplasm while weakly detected from nih-3t3 cells. however, the nanoprobe exhibited nominal cytoplasm fluorescence in hela cells or nih-3t3 cells even after 4 h of incubation. in vivo tumor imaging, subcutaneous hela tumors in mice were established using the proposed activatable nanoprobe. as the time expanded, the accumulation in tumors and subsequent characterization and application of nanomaterials 2025, 8(3), 10232. 15 fluorescence activation of the nanoprobe is visible as early as 1 h post-injection and even achieves maximum contrast by 4 h post-injection (figure 7a). although the fluorescence emission of the nanoprobe is weakened, the improved signal-to-noise ratio under two-photon near-infrared (nir) excitation affords alternative detection of cancer. also, a coumarin-go-based turn-on fluorescence strategy is proposed for the detection of cu2+ ions [107]. 4.4.2. heavy metal ions removal coumarin introduction produced a large amount of micropores and mesopores on the surface of the coumarin-go composite as well as photo-regulated structure transformation to solve the separation problem through the reversible controlling of adsorption capacity (figure 7b,c). after 365 nm uv light irradiation, the composite displays better adsorption capacities for pb2+ (492.51 mg g−1), cd2+ (419.7 mg g−1), cu2+ (392.1 mg g−1) and zn2+ (375.3 mg g−1) than the intrinsic one (403.97 mg g−1, 340.3 mg g−1, 319.9 mg g−1 and 280.1 mg g−1). additionally, a part of adsorbed heavy metal ions can be desorbed after illuminated by 254 nm uv light, which not only greatly reduces the amount of water or organic reagent for elution of heavy metal ions but also lowers the complexity of the desorption process. from the consideration of practical applications, the adsorption capacity of the composite and their irradiation decreases about 16.5% and 18.4%, respectively, after the consecutive adsorption desorption process (six times). the results indicate that the coumarin-go provides an experimental basis for structurally photocontrollable materials, which can be served as photoreversible adsorbents for effective removal of pb2+ ions from wastewater at low cost. 4.4.3. organic solar cell ternary blends are considered an encouraging model to increase organic solar cell (osc) performance by either increasing charge mobility or incorporating optical materials or both. the incorporation of functional materials such as go with unique properties together with the light harvesting groups of coumarin make them promising materials for ternary blend composites (figure 7d). the osc performances of covalently bonded hybrid materials (coumarin-go) in p3ht: pcbm blends were investigated. the reference device based on the pure p3ht: pcbm blend has displayed a power conversion efficiency (pce) of 2.62% with a fill factor (ff) of 60% and a short-circuit current density (jsc) of 7.1 ma cm−2, while the pce and jsc reached 2.85% and 8.65 ma cm−2, respectively, with coumarin-go. apart from the contribution of go with unique properties on improved electrical conductivity, extended conjugation in coumarin to increase in the benzene ring and improve the electron transfer ability resulted in an enhancement of solar cell efficiency [108]. the increase in the jsc also confirmed using internal power conversion efficiency (ipce) measurements with respect to absorption spectra in wide ranges from around 610 nm to 300 nm. characterization and application of nanomaterials 2025, 8(3), 10232. 16 4.4.4. photodiodes figure 7. in vivo nir images of hela tumor-bearing mice at 0.5, 1, 2, 4 and 8 h post-intratumor injection with 100 μl of the nanoprobe solution: (a) adsorption recyclability of the composite along with irradiation for pb2+; (b) adsorption capacities of the composite along with irradiation in relation to various heavy metal ions; (c) j(v) characteristics of solar cells based on pristine p3ht:pcbm blends and p3ht:pcbm hybrid ternary blends; (d) go:bodipy, go: coumarin, swcnts: bodipy and swcnts: coumarin are referred to as (gb), (gc), (cb) and (cc), respectively. photo of a flexible osc based on p3ht: pcbm hybrid active layer was inset in (d); i–v characteristics of the diodes with various coumarin: go under dark and various illumination intensities: (e) 0.01%; (f) 0.03%; (g) 0.1%. new photodiode-based go-organic semiconductor hybrid materials were well developed over the past decades [109]. the current–voltage characteristics (e.g., i–v, c–v and transient characteristics) of the coumarin-go-based diodes were investigated under dark and various illumination intensities. when the diode is illuminated by solar light, the photogenerated charges are produced to form photocurrent in the reverse bias region, revealing the typical photodiode behavior (figure 7e–g). it was found that the photoconducting behavior of the diodes was also improved with coumarin: go doping, i.e., the diode having 0.01% coumarin: go exhibited the highest photoresponsivity. the ideality factor (n) and barrier height (φb) of the au/coumarin: go-doped bi2o3/p-si diodes with various coumarin: go contents were determined characterization and application of nanomaterials 2025, 8(3), 10232. 17 in the range of 2.5–4.8 and 0.68–0.8 ev, respectively, suggesting the lower coumarin contents clearly improved the photoresponsivity properties. the transient photocurrent measurements indicate that au/go: coumarin/p-si/al diodes are very sensitive to illumination and the precise responsivity of the diodes is tunable by adjusting the go: coumarin fraction. additionally, the capacitance–voltage–frequency (c–v–f) measurements indicate that the capacitance of the diodes depends on voltage and frequency. the ability to tune the photosensitivity in the photoconductive mode through the go: coumarin weight ratio has been shown to lead to a near-constant sensitivity to illumination for an optimal weight ratio. thus, this interlayer of coumarin-go in diodes is a preferable alternative to traditional insulator layers regarding the enhancements in device parameters. furthermore, the diodes exhibited a photocapacitance and photoconductance behavior under solar light illumination to be used as a photocapacitor or photodiode in electro-optic applications. 5. comparative analysis of coumarin-go composites with other similar composites coumarin-go composites boast distinct advantages compared to other types of polymer-graphene oxide composites, such as polythiophene-go and polyaniline-go composites. here’s a detailed comparison focusing on several key aspects: 5.1. photostability the successful photodimerization of coumarin groups in coumarin-go composites enhances their stability under uv exposure [110]. this characteristic is crucial for long-term applications in light-sensitive devices, such as sensors and photonic systems, where prolonged exposure to light is common. even polythiophenebased materials (i.e., polythiophene-go) also exhibit good conductivity; they can degrade under extended uv light exposure, limiting their effectiveness in certain applications [111]. similar to polythiophene, polyaniline composites (i.e., polyanilinego) may experience photodegradation, which could compromise their optical properties over time [112]. 5.2. conductivity and charge carrier mobility coumarin-go composites show enhanced electrical and thermal conductivity due to the effective integration of go, which facilitates improved charge transport [113]. the design of coumarin structures can be tailored to optimize these properties further. known for their excellent electrochemical performance, polythiophene-go typically exhibit high conductivity but may require additional doping to reach optimal levels [114]. while polyaniline offers good conductivity in polyaniline-go composites, its inherent instability and the requirement for oxidation can complicate application processes [115]. 5.3. functional versatility the incorporation of coumarin groups not only enhances conductivity but also introduces unique photochemical characteristics, allowing coumarin-go composites to be used in applications such as targeted drug delivery and bioimaging [116]. the characterization and application of nanomaterials 2025, 8(3), 10232. 18 ability to modify functional groups easily enables tailored responses to specific stimuli. for polythiophene-go composites, they are primarily limited to applications in organic electronics and sensors, with less versatility regarding functional modifications [117]. while polyaniline-go composites are employed in sensors and energy storage, they are less adaptable to dual-functional roles due to the complexities of their synthesis and stability [118]. 5.4. biocompatibility and environmental impact preliminary studies suggest that the biocompatibility of coumarin-based materials is favorable, making coumarin-go composites suitable for biomedical applications and reducing potential environmental hazards [119]. while both polythiophene-go and polyaniline-go composites may exhibit cytotoxicity and environmental concerns depending on their processing and degradation products, which necessitates careful evaluation before biomedical application [120]. 5.5. application scope coumarin-go composites show potential not only in electronics and environmental sensors but also in medical applications such as fluorescent probes for bioimaging [121]. their ability to function both as sensors and therapeutic agents makes them highly versatile. in contrast, polythiophene-go and polyaniline-go composites generally focused on electronic applications, including oleds and solar cells, rather than typically extending into the biomedical realm to the same extent as coumarin-go composites [122]. coumarin-go composites stand out for their unique photostability, enhanced conductivity, functional versatility, and potential biocompatibility. these attributes make them particularly promising for a wider range of applications, especially in fields such as biomedicine and sustainable technologies, compared to traditional polythiophene-go and polyaniline-go composites. as research progresses, further investigations into their unique properties and applications will likely yield exciting opportunities in material science and engineering. 6. conclusion and future prospects during the past several decades, significant developments have been made in the field of coumarin-go composites. this review provides a detailed examination of the various synthetic methods employed to produce graphene oxide (go), go-polymer, coumarin-based polymer, and coumarin-go composites, highlighting their pathways, properties, characterizations, and applications. these fascinating materials are in high demand for optoelectronic and energy applications, as well as in the biomedical field. from our overview of coumarin-go composites, several important implications emerge. firstly, the successful photodimerization of coumarin groups with go imparts unique properties that enhance stability under uv exposure. their electro-optic characteristics make them suitable for sensors and devices requiring light manipulation. secondly, the improved electrical and thermal conductivity of these composites, achieved through careful design and loading of go, suggests their suitability for applications in flexible electronics, solar cells, and energy transfer characterization and application of nanomaterials 2025, 8(3), 10232. 19 materials. lastly, understanding the kinetic and electrical characteristics of coumaringo composites could lead to new polymer materials with tailored functionalities, thereby expanding the scope of specific applications. in particular, examinations of their biocompatibility and environmental impact are crucial for paving the way for practical applications in bioimaging and sustainable technologies. as the field of coumarin-go composites continues to evolve, future research directions should focus on modifying functional groups, incorporating different graphitic nanofillers, and exploring various polymer compositions. however, several challenges must be addressed to achieve coumarin-based composites with enhanced features: • characterization techniques: advanced characterization methods, including extended x-ray absorption fine structure (exafs) spectroscopy, can provide detailed insights into the local structure of materials, including coordination numbers and bonding lengths. this information is vital for validating the composites’ suitability for future applications. • practical scalability: scaling up the production of these composites while maintaining their unique properties and performance is a significant challenge, especially for applications in organic thermoelectric devices and bioelectronics. techniques such as microwaveand ultrasound-assisted synthesis may prove useful for obtaining the large quantities of material needed for practical applications. however, standardizing production techniques without compromising quality remains a key hurdle. • extending applications: the synthesis of composites through copolymerization or in combination with semiconductors (i.e., photocatalysts) could create promising materials for wastewater remediation and solar energy conversion by tailoring the bandgap and enhancing light absorption. future studies should investigate the synergy between these materials and their potential in dualfunctional roles. conclusively, exploring the full potential of coumarin-go composites is essential for developing next-generation applications in electronics, biomedicine, and sustainable technologies. overcoming the challenges of scalability and modification will ultimately contribute to advancements in material science and engineering. funding: this research was funded by the national natural science foundation of china (12375344) and the program for professor of special appointment (eastern scholar) at shanghai institutions of higher learning (tp2019040). institutional review board statement: not applicable. informed consent statement: not applicable. conflict of interest: the authors declare no conflict of interest. references 1. kausar a, ullah-shah m, khan my. an investigation on novel poly(thiourea-amide)-based nanocomposites reinforced with silica nanotubes. 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can-3183-pb online characterization and application of nanomaterials (2023) volume 6 issue 1 doi: 10.24294/can.v6i1.3183 1 original research article green synthesis and characterization of iron nanoparticle using extracted bitter guard leaves used as methylene blue removal thin phyu lin1, kyu kyu khaing1, aung than htwe1,2,*, may thazin oo1, su su soe nyunt1 1 department of chemistry, mohnyin university, mohnyin 01162, kachin state, myanmar. e-mail: aungthanhtwe76@gmail.com 2 department of chemistry, university of yangon, kamaryut 11041, myanmar. abstract zero-valent iron is a moderately reducing reagent that is both non-toxic and affordable. in the present work, iron nanoparticles were synthesized using bitter guard leaf extract (momordica charantia l.) (bgl-fe np). using leaf samples from bitter protectant extract, iron nanoparticles were synthesized with secondary metabolites such as flavonoids and polyphenols acting as capping and reducing agents. polyphenols reduce fe2+/fe3+ to nanovalent iron or iron nanoparticles. iron nanoparticles were synthesized by reducing iron chloride as a precursor with bitter protective leaf extract in an alkaline environment. the obtained bgl-fe nps were calcined for 4 h at various temperatures of 400 c, 500 c, and 600 c. the obtained samples were coded as bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6, respectively. the synthesized bgl-fe nps were systematically characterized by xrd, sem, ftir, uv-vis and tg-dta analysis. the obtained bgl-fe nps were then used as an adsorbent to remove the aqueous solution of basic methylene blue (mb) dye. mb concentration was monitored using uv-vis spectroscopy. keywords: iron nanoparticle; characterization; methylene blue 1. introduction momordica charantia l., a member of the cucurbitaceae family, is also known as bitter guard. simple or alternating leaves measure 4– 10 cm long and have 3–6 deeply divided lobes. tendrils can be unbranched or branched. fruit has an irregular dehiscence as a fleshy capsule or is indehiscent. it is ovoidal, elliptical, or spindle-shaped, packed with flat seeds in pulp, typically with a ridged surface. the fruits are green when they are young and become orange or yellow as they ripen. numerous studies have reported on the environmentally friendly production of iron nanoparticles using a variety of plant extracts. iron nanoparticles (fe nps) have mostly been biosynthesised utilizing the extract of green tea, a readily available and affordable resource. making use of green tea (camellia sinensis) extract, which contains a number of polyphenols, hoag et al.[1] synthesized nzvi. the stable nanoparticles were created at room temperature without the use of a surfactant or polymer. plant polyphenols function as capping and reducing agents, producing stable, green, zero-valent iron particles with special characteristics. according to ghanim et al.[2], dye pollutants are one of the primary sources of environmental contamination in a wide range of sectors. there are several ways to clean up wastewater from all industries, in article info received: 4 may 2023 accepted: 20 may 2023 available online: 4 june 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 cluding textile industry effluent. adsorption is the most often used technique among them since it is efficient and easy to apply[3,4]. in this study, bitter guard leave extracts were successfully used to prepare iron nanoparticles (bgl-fe nps). polyphenols from bitter guard have been found to have capping and reducing properties. it designed an entirely novel synthetic method for sorbent here using green chemistry principles and eco-friendly, cost-effective, nonhazardous, and renewable materials. modern methods, including xrd, ftir, uv-visible, sem, and tg-dta, were used to analyze the properties of the prepared bgl-fe nps. finally, the main objective of this study is to reveal the efficient adsorptive removal of organic waste, such as the cationic synthetic dye methylene blue, by the synthesized bgl-fe nps sorbent. 2. materials and methodology 2.1 collection and extraction the leaves of bitter guard (momordica charantia l.) were collected from nammar township, kachin state, myanmar, in december 2022. the samples were cut into small pieces and dried in the shade at room temperature for one week. the dried leaves samples were ground with a grinder and stored in airtight bottles. 2.2 preparation of iron nanoparticle (bglfe nps) the iron nanoparticles (bgl-fe nps) were prepared by the co-precipitation method. extracts were prepared by heating 20 g of bitter guard leaves powder in 200 ml of distilled water for 30 min at 85 c on a hot plate. the extract was filtered using filter paper. fecl3·6h2o (3.381 g) was dissolved in 250 ml of distilled water and stirred continuously to obtain a 0.1 m fe(iii) solution. the bitter guard leave extract was mixed into a 0.1 m fe(iii) solution for 15 min. the color immediately changed after the addition of bitter guard leaves extract to the ferric chloride solution. and then, sodium hydroxide (1m) solution was added drop by drop into the iron(iii) mixture solution, which was carried out with constant stirring at 80 ºc until the solution reached ph 8. the color of the solution was changed from brown to reddish-brown. the solution was continuously stirred at 80 c for 2 h. then, the solution was centrifuged at 3,000 rpm for 5 min. the synthesized bgl-fe nps were washed several times with distilled water until neutral (ph 7) to remove any alkali metals. the obtained neutral bgl-fe nps were washed again with ethanol and dried for 3 h in the oven at 80 c. after that, the dried bgl-fe nps were calcinied in a muffle furnace at 400 c, 500 c, and 600 c for 4 h to achieve stable bglfe nps. this sample was coded bgl-fe nps-4 for 400 c, bgl-fe nps-5 for 500 c, and bglfe nps-6 for 600 c. all samples were crushed with a motor and pestle and sieved with a 40mesh sieve. finally, the sample was stored in a sealed bottle and placed in a dessicator for further use. the schematic diagram was described in figure 1. figure 1. schematic diagram of preparation of iron nanoparticle (bgl-fe nps) using bitter guard extract. 2.3 characterization of iron nanoparticle (bgl-fe nps) green synthesized iron nanoparticles are characterized through different techniques such as xrd, ftir, sem, uv-vis, and tg-dta to elucidate their properties. x-ray diffraction studies were used to determine the prepared powdered samples (varistors) with the help of rigaku multiflux x-ray diffractometer with cu kα (λ = 1.5418 å) monochromatic radiation. the powdered samples were scanned from 10° to 80° with a scanned speed of 0.01°/sec. the applied voltage and current of the x-ray diffractometer were set to be 50 kv and 40 ma. the identification of functional groups was investigated by ft-ir with a 3 perkin elmer spectrum of 2,000. the analyses were carried out in the range of 400 cm–1–4,000 cm–1. nanoparticles powder samples (varistors) were characterized with the assistance of (jeol, model no. jsm-5610 lv). applied voltage and current of sem were set to be 15 kv, 68 ua, and 94x magnification. 2.4 adsorption experiment adsorption by the batch technique was used to study methylene blue (mb) removal using bgl-fe nps. first, the accurate mb amount was dissolved in deionized water to make stock solutions of mb at a concentration of 50 mg/l. then, the stock solutions were taken for dilution to make a daily solution. at 25 c, different adsorbent volumes were mixed with 25 ml of mb solution in 100 ml erlenmeyer flasks. the concentration of the solution, contact time, ph of the solution, and adsorbent dose are a few important parameters that affect the removal of mb. all concentrations of mb in aqueous solutions were analyzed by the ultraviolet-visible (uv-vis) method at 668 nm using a genesys 10s (thermo scientific) uv-vis spectrometer. removal efficiency (%) = 𝐶 –c 𝐶 × 100 % (1) where ci and cf are the initial and final concentrations of mb (mg/l). 3. results and discussion 3.1 characterization the identity of the synthesized iron nanoparticles was established using the following analytical techniques: 3.1.1 xrd analysis the x-ray diffractogram of the synthesized bgl-fe nps, bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6 (figure 2) shows the presence of characteristic peaks at 2 values of 30.17 and 57.34 corresponding to hematite (α-fe2o3), whereas the peak at 35.45 corresponds to magnetite (fe3o4). in addition, the peaks at 28.50 correspond to geothite (α-feooh) whereas a peak at 45.32 and 62.89 correspond to zerovalent iron (α-fe) phases. it is therefore confirmed that fe nps-jf contain zero-valent iron nanoparticles (nzvi) along with iron oxides and oxyhydroxide[5,6]. using scherrer’s formula, which is provided below, and the peak broadening profile of the peak at all 2 values, the average crystallite size was estimated using the fwhm value of the most intense peak. d = 0.94λ βcosθ where λ is the wavelength (1.5418 å) and β is the full width at half maximum (fwhm) of the corresponding peak[7]. the average crystallite size of synthesized bgl-fe nps calculated from sherrer’s equation was 47.66 nm for bgl-fe nps, 10.55 nm for bgl-fe nps-4, 11.33 nm for bglfe nps-5, 15.72 nm for bgl-fe nps-6, respectively. figure 2. xrd pattern of bgl-fe nps before and after calcination temperature. 3.1.2 ftir analysis the potential extract functionalities that may have been the cause of the edx-found carbon signature were determined using ftir analysis. several peaks were observed in the range of 1,000–3,400 cm–1. in figure 3, the iron nanoparticles correspond to the vibrations of the fe-o bonds. the bands at 3,021 cm–1, 1,636 cm–1, 1,440 cm–1, 870 cm–1, and 540 cm–1 were confirmed as oh, c=c, aliphatic c-h bending, c-h bending, feo stretching. the absorption bands at around 540 cm–1 attributed to the feo symmetrical 4 (a) (b) (c) figure 3. continued. 5 (d) figure 3. ftir spectra data of (a) bgl-fe nps; (b) bgl-fe nps-4; (c) bgl-fe nps-5; and (d) bgl-fe nps-6. stretching. the highest peaks at 3,359–3,361 cm−1 correspond to polyphenols, showing the greater abundance and noticeable presence of phenolic functional groups for the reduction of fe3+ to fe0. other than that, the more available phenolic groups provide a favorable molecular arrangement for the delocalization of unpaired electrons. so, the leaf extract captured the property of successful scavenging of free radicals. the appearance of a peak at 3,359 cm–1 and a shift to 3,361 cm–1 indicate that the phenolic or amine groups of the leaves extract may be involved in the formation of fe nps. it can be concluded from the spectra that the polyphenols in the leaves extract were responsible for the reduction and stabilization of fe nps, which also agrees with the uv-visible analysis[7]. 3.1.3 sem analysis the morphology and diameter distribution of bgl-fe nps are determined by sem. the sem images of bgl-fe nps are shown in figure 4(a)–(d) at 10 kv acceleration voltage and 94x magnification. analysis of sem images of all nanoparticles of bgl-fe nps shows that the nanoparticles are agglomerated and tend to form irregular spherical particles on the surface. aggregated nanoparticles have been shown to have rough surfaces. iron nanoparticles are in close contact with each other due to the magnetic properties of iron species. this may be due to the presence of different polyphenols in the leaves extract, which can significantly affect the final morphology and size of iron nanoparticles. in figure 5(a)–(d), size diameter distributions were evaluated by measuring at least 200 particles from sem micrograph. the results are obtained that the average diameters of the prepared nanoparticles are 12.11 μm for bgl-fe nps, 12.23 μm for bgl-fe nps-4, 16.59 μm for bglfe nps-5, and 12.53 μm for bgl-fe nps-6, respectively. according to the size diameter distribution histograms, the significant size of bgl-fe nps-5 increased among the samples. it indicates that the produced bgl-fe nps possess a narrow size distribution. figure 4. sem spectra data of (a) bgl-fe nps; (b) bgl-fe nps-4; (c) bgl-fe nps-5; and (d) bgl-fe nps-6 and particle size diameter distribution. 6 figure 5. particle size diameter distribution of (a) bgl-fe nps; (b) bgl-fe nps-4; (c) bgl-fe nps-5; and (d) bgl-fe nps-6. 3.1.4 uv-vis analysis uv-vis absorption spectra of iron nanoparticles are represented in figure 6. as seen in figure 6, the absorption spectra of bgl-fe nps nanoparticle peaks were detected at 229 nm and 274 nm for bgl-fe nps, 264 nm for bgl-fe nps-4, 263 nm for bgl-fe nps-5, and 361 nm for bglfe nps-6, respectively. therefore, a sharp and relatively narrow absorption between about 229 nm was observed. the absorption spectrum of bitter guard –fe0 showed a maximum in the range of 216–300 nm, which is identical to the characteristic absorption peak for the reported metallic iron[8]. figure 6. uv-visible absorbance spectra of bgl-fe nps using leaves extract. as seen in figure 7, bgl-fe nps samples give an optical band gap value that shows 4.03 ev for bgl-fe nps, 3.98 ev for bgl-fe nps-4, 3.83 ev for bgl-fe nps-5, and 3.70 ev for bgl-fe nps-6, respectively. due to charge transitions, the absorption decreases and the optical band gap increases. the bgl-fe nps prepared in this study are expected to be more useful in photonic and electronic devices. figure 7. plots of h vs (αh)1/2 of bgl-fe nps using leaves extract. 3.1.5 tg-dta analysis the thermogram profiles of the prepared bgl-fe nps samples are shown in figure 8. the thermogram of bgl-fe np samples exhibits three 7 stages of noticeable weight loss between 37 °c and 600 °c. the first stage in the temperature range is 37.09 °c to 230 °c, with 20.42% weight loss for bgl-fe nps. there is a loss of moisture. in the second stage, the temperature range between 230 °c and 300 °c was observed to cause 10.15% of weight loss for bgl-fe nps. this is due to the dehydration of water molecules. one exothermic peak was seen at 291.30 °c in both samples. the third stage is the loss in weight of 2.28% for bgl-fe nps, which was observed to take place within the temperature range of 300 °c to 600 °c due to the combustion of some residue. the thermogram of bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6 samples in figure 8 shows one phase of weight loss between 38 °c and 300 °c. in this temperature range, it was found that the weight loss of 4.14% for bgl-fe nps-4, 1.54% for bgl-fe nps-5, and 1.47% for bgl-fe nps-6, respectively. in this stage, weight loss may be loss of surface water or oh groups adsorbed on the surface of the iron oxide. the broad endothermic peak was observed between 53 °c and 73 °c. this occurrence is due to the oxidation product of feo. according to the tgdta analysis, it was demonstrated that there is no appreciable weight loss at 300 °c above, indicating that the prepared samples are thermally stable. figure 8. tg-dta thermogram of fe nps-l. 3.2 investigation of the removal percent of methylene blue by iron nanoparticles 3.2.1 effect of concentration the effect of color concentration of methylene blue dye solution on the adsorption of bglfe nps, bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6 was studied under the optimized conditions of time and dosage of adsorbents. the concentrations varied from 50 to 250 ppm. figure 9 showed that the effect of the initial concentration of methylene blue (mb) solution on the adsorption of bgl-fe nps, bgl-fe nps-4, bglfe nps-5, and bgl-fe nps-6. according to figure 9, it was found that the percent removal was decreased from about 97.52% to 62.73% for all iron nanoparticles. these indicated that the initial mb concentration of fe bgl-fe nps-6 was more effective than that of bgl-fe nps. higher the removal percentages were observed for lower concentrations of mb for bgl-fe nps-6. figure 9. effect of the initial concentration on the mb sorption process depending on the phase contact time 3 h: bglfe nps (dosage 0.4 g, ph 7, shaking speed 250 rpm, temperature 25 ℃). 3.2.2 effect of ph figure 10 shows that the lowest removal efficiency of 78.154% of bgl-fe nps, bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6 was recorded at ph = 5 (highly acidic medium). at low ph values, the presence of excess h+ ions on the surface of fe nps can compete with the mb cations for adsorption sites, causing an electrostatic repulsion[9]. a further increase in ph from 5 to 9 resulted in an enhancement of mb removal efficiency from 78.154% to 81.186% for fe nps-l (400 °c) and from 80.092% to 82.982% for fe nps-f (500 °c). the increase in negatively charged sites (due to oh–) resulting in electrostatic attraction and compounds with the cationic dye 8 may be responsible for the finding[10]. an increase in ph value from 5 to 9 resulted in a decrease in mb removal efficiency from 81.16% to 78.154% of bgl-fe nps, and 81.468% to 80.092% in bgl-fe nps-4, respectively. this result may be due to the corrosion or hydrolysis of fe0 in alkaline solutions (e.g., ph around 10), leading to the production of iron ions and ferric iron precipitated as iron oxide/hydroxide[11]. these reactions can be described by the following equations (equations (2)–(4)): fe0  fe2+ + 2ē (2) 2fe0 + o2 + 2h2o  2fe2+ + 4oh– (3) fe0 + h2o  fe2+ + h2 + 2oh– (4) the corrosive results of the bgl-fe nps formation might cover the surface of the nanoparticles, which hindered electron transport from fe0 to mb[12]; as a result, the adsorption process slowed down. similar to this, fan et al.[13] showed that dye removal by bgl-fe nps particles was inefficient under excessively basic or acidic conditions but performed in a mildly acidic range. according to sun et al.[11], the net surface charge of n bgl-fe nps particles turned positive when the solution ph was lower than the point of zero charge (phzpc) of 8.0, which attracted the anionic dye. on the other hand, the adsorbent surface becomes negatively charged when the solution ph approaches phzpc, which strengthens the attraction mechanism with cations. figure 10. effect of ph on the mb sorption process depending on the phase contact time 3 h: bgl-fe nps (dosage 0.4 g, initial concentration 50 ppm, shaking speed 250 rpm, temperature 25 °c). 3.2.3 effect of dosage the efficiency of bgl-fe nps, bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6 sorbents in removing mb from a 50 ppm mb solution was determined by monitoring the contact time. in the investigations, the color intensities of aliquots were spectrophotometrically measured at specified times using a batch approach. the dosage, as seen in figure 11, varied from 0.1 to 0.5 g. the proportion of each adsorbent decreased after 0.4 g, but during the 3 h period, bgl-fe nps-6 sorbent removed the highest mb among bgl-fe nps, bgl-fe nps-4, and bgl-fe nps-5 sorbents. figure 11. effect of dosage on the mb sorption process depending on the phase contact time 3 h: bgl-fe nps (initial concentration 50 ppm, ph 7, shaking speed 250 rpm, temperature 25 °c). 3.2.4 effect of time the mb removal efficiency of bgl-fe nps, bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6 sorbents was tested against 50 ppm ferric chloride solution by measuring the contact time. the experiments were performed using the batch method, where the color intensity of the aliquots was monitored spectrophotometrically at certain time intervals. figure 12 showed that the time varied from 1 to 5 h. from figure 12, it has been observed that the maximum removal of mb dye was achieved at 3 h of reaction with 81.82% bgl-fe nps, bgl-fe nps-4, bgl-fe nps-5, and bgl-fe nps-6. from the results, it can be observed that there was decreased in the percentage of each adsorbent after 3 h, whereas bgl-fe nps-6 sorbent was more removal percent of mb than fe nps sorbent for investigation time periods. 9 figure 12. effect of contact time on the mb sorption process of bgl-fe nps (dosage 0.4 g, initial concentration 50 ppm, ph 7, shaking speed 250 rpm, temperature 25 °c). 3.2.5 effect of temperature temperature plays an important role in influencing the removal efficiency of a mb adsorption process of fe nps. the effect of reaction temperature (25, 30, 35, 40 and 45 c) on the removal efficiency using fe nps is described in figure 13. here, the efficiency of bgl-fe nps-4 for mb removal was 98.96, 89.16, 86.38, 81.38, and 77.86% at 25, 30, 35, 40, and 45 c. it is shown that the removal of mb from bgl-fe nps-4 was an endothermic process. however, the mb removal efficiency of bgl-fe nps at 25, 30, 35, 40, and 45 °c was 85.30, 84.95, 84.12, 83.45, and 83.11%. it was suggested that bgl-fe nps were less effective than bgl-fe nps-6 in removing the mb because the surface of bgl-fe np-6 was more covered by iron oxide and iron hydroxide. thus, the removal efficiency can be improved by increasing the temperature because it promotes the collisions of mb molecules, which in turn leads to more activation energy[14]. increasing the solution temperature can improve the adsorption efficiency[15,16]: (a) increases the solubility and mobility of mb in the solution, which increases the intra-particle diffusion; (b) reduce the amount of dissolved oxygen in the solution, prevent the oxidation of iron nanoparticles; (c) increase the activation energy, create new adsorption sites, and form a complex reaction surface; and (d) facilitates the production of a swelling effect within the internal structure of the absorbent, which facilitates the penetration of molecules into the pores[17]. figure 13. effect of contact time on the mb sorption process of bgl-fe nps (dosage 0.4 g, initial concentration 50 ppm, ph 7, shaking speed 250 rpm, temperature 25 °c). 4. conclusion in this research, iron nanoparticles synthesized from aqueous bitter guard leave extracts were characterized by modern methods such as xrd, ftir, sem, uv-vis, and tg-dta. iron nanoparticles rich in iron oxide/oxhydroxide can be easily prepared using aqueous extracts of bitter guard leaves as reducing and capping agents at different calcination temperatures of 400, 500, and 600 °c for 4 h. particle morphology and size were investigated using sem and xrd techniques. sem microscopy of all prepared fe nps showed agglomerated clusters. the crystallite size of bgl-fe nps was observed to vary from 10.55 nm to 47.66 nm before and after annealing temperature. ft ir measurements confirmed the attachment of compounds in the extract to iron nanoparticles. functional groups of phenolic compounds can contribute to the formation of metal nanoparticles. from the ft ir spectral data of all bgl-fe nps, a strong stretching absorption band of the fe-o bond at 543.05 cm–1 was observed. according to the results, the functional groups successfully synthesized bgl-fe nps. the product of bgl-fe nps was confirmed by change of colour and the uv-vis spectra surface plasmon resonance center at 229 nm. from uv-visible data, the band edge-absorption peak of all fe nps is found to be between about 229 nm and 247 nm, and the band gap values are in the range of 4.06 ev to 4.28 ev for fe nps-l with changes the calcination temperature. the absorption decreases, and the optical band gap increases due to charge transfer transitions. 10 in tg-dta thermogram, the total weight loss (%) shows about 32.85% in bgl-fe nps before calcination. after calcination, the total weight loss changes in the range between 4.14% and 1.14% for bgl-fe nps (400 °c, 500 °c, and 600 °c). it is found that the total weight loss of bgl-fe nps after calcination is lower than that of bgl-fe nps before calcination. tg-dta analysis demonstrated that there is no appreciable weight loss at 300 c above, indicating that all fe nps samples are thermally stable. the prepared bgl-fe nps showed promising prospects for mb removal. the removal efficiency was found to depend on the test conditions. the optimum removal occurred at ph 7 and 25 c with 0.4 g fe np. in addition, the removal efficiency increased rapidly after 1 h and then increased more slowly, followed by an equilibrium period after 3 h. the removal percentage of bglfe nps prepared by methylene blue indicator was about 81.18% to 96.53% of the bgl-fe nps sample. this study provides convincing evidence that stabilized nanoparticles of bgl-fe nps can be used to remove mb from a cationic dye solution, potentially leading to an innovative treatment method that is likely to be more cost-effective and less disruptive to the environment. author contributions conceptualization, tpl and ath; methodology, tpl; software, ath; validation, kkk, mto and sssn; formal analysis, tpl; investigation, tpl; resources, tpl; data curation, ath; writing—original draft preparation, mto, sssn and ath; writing—review and editing, ath; visualization, mto and kkk; supervision, ath; project administration, ath; funding acquisition, ath. all authors have read and agreed to the published version of the manuscript. conflict of interest the authors declare no conflict of interest. acknowledgments the authors gratefully acknowledged to professor nyein nyein htwe, head of the department of chemistry, mohnyin university, myanmar for her encouragement and administrative supervision beginning from this research work. we would like to express my special thanks myinzu minn, rector, mohnyin university, myanmar who gave us the opportunity to do this research. references 1. hoag ge, collins jb, holcomb jl, et al. degradation 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al. decoloration of acid violet red b by bentonite-supported nanoscale zero-valent iron: reactivity, characterization, kinetics and reaction pathway. applied clay science 2014; 93–94: 56–61. doi: 10.1016/j.clay.2014.02.020. 15. bao y, zhang g. study of adsorption characteristics of methylene blue onto activated carbon made by salix psammophila. energy procedia 2012; 16: 1141–1146. doi: 10.1016/j.egypro.2012.01.182. 16. chen z, wang t, jin x, et al. multifunctional kaolinite-supported nanoscale zero-valent iron used for the adsorption and degradation of crystal violet in aqueous solution. journal of colloid and interface science 2013; 398: 59–66. doi: 10.1016/j.jcis.2013.02.020. 17. hamdy a, mostafa mk, nasr m. zero-valent iron nanoparticles for methylene blue removal from aqueous solutions and textile wastewater treatment, with cost estimation. water science and technology 2018; 78(2): 367–378. doi: 10.2166/wst.2018.306. characterization and application of nanomaterials (2023) volume 6 issue 1 doi:10.24294/can.v6i1.2637 1 review article high-tech graphene oxide reinforced conducting matrix nanocomposites—current status and progress ayesha kausar1,2,*, ishaq ahmad1,2, tran dai lam3 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, shanxi province, china. e-mail: dr.ayeshakausar@yahoo.com 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa. 3 institute for tropical technology, vietnam academy of science and technology, hanoi 100000, viet nam. abstract graphene oxide can be referred to as oxidized graphene. similar to graphene, oxidized graphene possesses remarkable structural features, advantageous properties, and technical applications. among polymeric matrices, conducting polymers have been categorized for  conjugated backbone and semiconducting features. in this context, doping, or nanoadditive inclusion, has been found to enhance the electrical conduction features of conjugated polymers. like other carbon nanostructures (fullerene, carbon nanotube, etc.), graphene has been used to reinforce the conjugated matrices. graphene can be further modified into several derived forms, including graphene oxide, reduced graphene oxide, and functionalized graphene. among these, graphene oxide has been identified as an important graphene derivative and nanofiller for conducting matrices. this overview covers essential aspects and progressions in the sector of conjugated polymers and graphene oxide derived nanomaterials. since the importance of graphene oxide derived nanocomposites, this overview has been developed aiming at conductive polymer/graphene oxide nanocomposites. the novelty of this article relies on the originality and design of the outline, the review framework, and recent literature gathering compared with previous literature reviews. to the best of our knowledge, such an all-inclusive overview of conducting polymer/graphene oxide focusing on fundamentals and essential technical developments has not been seen in the literature before. due to advantageous structural, morphological, conducting, and other specific properties, conductive polymer/graphene oxide nanomaterials have been applied for a range of technical applications such as supercapacitors, photovoltaics, corrosion resistance, etc. future research on these high-performance nanocomposites may overcome the design and performancerelated challenges facing industrial utilization. keywords: graphene oxide; conductive polymer; nanocomposite; conductivity; supercapacitor 1. introduction conductive, conducting, or conjugated polymers constitute an essential category of polymers with semiconduction or electron conduction properties[1,2]. important types of conjugated polymers include polyacetylene, polyaniline, polythiophene, polypyrrole, and derivatives. conjugated polymers have been recognized for their optical, electrical, thermal, and physical characteristics[3]. technological applications of conductive polymers have been observed for electronics, energy devices, biomedical fields, and so on[4]. graphene is a one-atom-thick two-dimensional nanosheet material[5]. graphene oxide is simply a graphene derivative having oxygen-containing surface functionalities on graphene nano-sheet. graphene oxide has been utilized to form polymer nanocomposites with conducting polymers, thermosets, and thermoplastic matrices[6,7]. particularly conducting polymers are generally article info received: 30 april 2023 accepted: 13 june 2023 available online: 24 june 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterial is published by enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 well-known due to their remarkable properties, such as low price, high conductivity, lightweightness, simple fabrication, and reusability potential. doping of conducting polymers on graphene oxide surfaces usually leads to interface formation, which improves the electrical properties of the resulting nanocomposite[8]. due to interface development between matrix-nanofiller, charge transfer across the interface is greatly promoted. consequently, these nanocomposites possess fine durability, conductivity, corrosion resistance, mechanical strength, wear resistance, and barrier properties[9]. several approaches have been used for the fabrication of conductive polymer/graphene oxide nanocomposite, including in situ, solution, electropolymerization, electrodeposition, etc.[10]. consequently, conducting polymer and graphene oxide derived nanocomposites revealed suitability for application in technical sectors such as photovoltaics, capacitors, sensing devices, radiation shielding, etc.[11–13]. therefore, the major theme behind developing this review article is to gather and portray the field literature and efforts reported on graphene oxide reinforced conducting polymer nanocomposites so far, in a novel way by identifying the property/potential advantages of combining conducting polymers with graphene oxide nanofiller. hence, this overview is designed to cover indispensable properties and potential aspects of graphene oxide reinforced conductive polymer nanocomposites. owing to the unique structural combination of conjugated polymer and graphene oxide, essential features of the conductive nanomaterials have been enhanced. subsequently, conducting polymer and graphene oxide-based nanocomposites were investigated, aiming for energy storage and production devices and anticorrosion nanomaterials. 2. graphene oxide graphene is a nanocarbon nanoallotrope with sp2 hybridized carbon atoms in nanostructure[14]. it is a monolayer of carbon with hexagonal arrangements. graphene is simply a single sheet of stacked graphite nanostructure[15]. graphene is a one-atomthick nanosheet of carbon atoms[16]. due to hybridization and π electron conjugation, the graphene nanosheet reveals semiconductivity features[17]. graphene has been prepared using a number of topdown and bottom-up techniques, such as graphite chemical or mechanical exfoliation, chemical vapor deposition, plasma-based chemical vapor deposition, thermally enhanced chemical vapor deposition, laser ablation, organic synthesis, and other important techniques[18]. graphene oxide is a significant modification of the graphene nanosheet through the incorporation of various surface functionalities[19]. mainly hydrophilic groups like carbonyl, acid, epoxide, hydroxyl, etc. have been observed on the graphene oxide nanosheet. figure 1 gives a comparison of the simple structures of graphene vs. graphene oxide. hummer’s approach and the brodie method have been commonly used for the formation of graphene oxide[20,21]. both of these methods involve using oxidizing agents for the formation of graphene oxide from graphene[22]. graphene oxide possesses high conductivity, heat stability, mechanical strength, and chemical stability features. graphene oxide has been essentially reinforced in polymers to form nanocomposites. polymer and graphene oxide derived nanomaterials have been applied for electronics, energy devices, membranes, and biomedics[23–25]. figure 1. graphene and graphene oxide. 3. conducting polymers conductive polymers have been placed in a separate category of polymers and are not included in thermoplastics or thermosets classifications[26,27]. inherently conducting polymers have conductivity properties similar to semiconductors[28]. therefore, conducting polymers are often referred to as synthetic metals[29]. conductive polymers have light 3 weight and fine processability properties[30]. the πconjugation in conducting polymer backbones formed an electron transportation system and electron affinity properties[31]. the presence of alternate single and double bonds in conducting polymers causes delocalization of electrons in sp2 hybridized orbitals. consequently, conductivity properties are actually due to electron transportation through double bonds and charge transfer by resonance. doping agents and oxidation-reduction processes were applied to enhance the conducting characteristics of conductive polymers. polyacetylene is an intrinsically conjugated polymer[32]. the doping process has been used to improve the electrical conductivity features of polyacetylene[33]. other significant conductive polymers are polycarbazole[34], polythiophene[35], polypyrrole[36], polyaniline[37], and several derived forms (figure 2). hn polyaniline polypyrrole n s polythiophene poly(3-hexylthiophene) n n n s n figure 2. some significant conjugated polymers. among these, polyaniline is the most widely studied conductive polymer. polyaniline is a lowpriced and easily possessable conjugated polymer[38]. polyaniline has been studied for electron transportation and percolation threshold values. consequently, conducting polymers have high electron conductivity and technical applications. 4. graphene oxide nanofiller in conducting polymeric nanocomposites graphene and graphene oxide nano-reinforcements have been used to form polymeric nanocomposites[39]. graphene derivative nanofillers have improved the electronic, strength, heat stability, and other features of the resulting nanocomposites[40]. however, graphene and derivatives can have poor dispersion in matrices because of the wrinkling effect. graphene oxide possesses the advantage of better dispersion in polymers due to its surface functionalities[41]. moreover, graphene oxide has been found to develop better interactions with the polymer matrix. appropriate processing approaches need to be adopted for fine graphene oxide dispersion in polymer matrices[42]. consistent graphene oxide dispersion in matrices has been found to enhance the electron conductivity, heat constancy, robustness, and physical features of the nanocomposites. in this context, conductive polymers have been filled with graphene oxide nanofiller to design efficient nanocomposites[43]. polyaniline (an important conjugated polymer) and graphene oxide derived nanocomposites have been fabricated[44]. li et al.[45] applied in situ polymerization for the development of polyaniline and reduced graphene oxide based nanocomposites. gao et al.[46] also formed polyaniline and reduced graphene oxide based nanocomposites through in situ techniques. the reduced graphene oxide was produced by sodium borohydride. chauhan et al.[47] fabricated polyaniline and reduced graphene oxide derived nanocomposites. increasing reduced graphene oxide contents led to enhancements in electron conduction and specific capacitance properties. graphene oxide was functionalized with sulfonic acid for modification. consequently, the polyaniline and sulfonated graphene oxide revealed fine electron conduction features. hawash et al.[48] fabricated polyaniline and graphene oxide nanosheetimmobilized granular tea waste-derived nanocomposites. the nanomaterial has been applied for effective removal of bromide (br−) from aqueous systems. the nanocomposite revealed bromide adsorption of 26.8 mg–1. figure 3 shows an oxidation technique to form the polyaniline/graphene oxide nanosheet-immobilized granular tea waste nanocomposites. graphene oxide functionalities have been found to interact with the functional groups on granular tea waste, such as carboxylic acid, hydroxyl, amine, amide, etc. consequently, electrostatic as well as hydrogen binding interactions were developed to form the nanocomposite. 4 figure 3. schematic for the formation of pani/go@gtw nanocomposite[48]. pani = polyaniline; go = graphene oxide; gtw = granular tea waste; pani/go@gtw = polyaniline/graphene oxide nanosheet immobilized granular tea waste[48]. reproduced with permission from mdpi. polypyrrole is a significant conductive matrix with facile preparation and electrical conductivity features[49]. several designs have been formed using polypyrrole and graphene nanofiller[50]. similarly, polypyrrole and graphene oxide derived nanomaterials have been reported[51]. graphene oxide dispersion has been used to enhance the physical properties of the polypyrrole nanocomposites, such as electron mobility and thermal transport[52]. these nanocomposites have been developed using in situ, electrochemical, emulsion, and solution polymerization techniques. deng et al.[53] developed polypyrrole and graphene oxide based nanocomposites by the electrochemical synthesis method. the inclusion of 0.5 to 1 wt.% graphene oxide led to an impedance variation of 115 to 26 kω. wu et al.[54] prepared polypyrrole, reduced graphene oxide, gold nanoparticles, and glucose oxidase based multilayered films through the electrodeposition method. figure 4 illustrates the stepwise synthesis process for the formation of polypyrrole/reduced graphene oxide/gold nanoparticles/glucose oxidase nanocomposite. initially, the biosensor was synthesized through the electrodeposition of polypyrrole/reduced graphene oxide on a neat glassy carbon electrode. then, gold nanoparticles and glucose oxidase were immobilized on the electrode surface. the glucose oxidase formed selfassembly along with gold nanoparticles on the polypyrrole/reduced graphene oxide nanocomposite surface. gold nanoparticles can efficiently bond to biomolecules such as enzymes or nucleic acids via covalent linking. figure 5 depicts current-time curves using a glucose biosensor based on polypyrrole/reduced graphene oxide/gold nanoparticle nanocomposite in the applied potential range of 0.35 v to 0.55 v. it has been observed that increasing applied potential increases the current values. for the biosensor, a working potential of up to 0.5 v was used to attain high selectivity or sensitivity. the nanocomposite electrode was found to be efficient in detecting glucose in the range of 0.2 to 8 mm. the detection limit was found to be 5.6 μm. in addition, biosensor was found to has ecofriendly properties. figure 4. schematic illustration of a glucose biosensor using the polypyrrole and reduced graphene oxide (ppy-rgo) and gold nanoparticles and glucose oxidase (aunps-god) multilayer films as the sensitive layer fabricated by the electrodeposition and self-assembly[54]. aunps = gold nanoparticles; god = glucose oxidase; ppyrgo-aunps/god = polypyrrole/reduced graphene oxide/gold nanoparticles/glucose oxidase. reproduced with permission from mdpi. 5 figure 5. current-time curves for ppy-rgo-aunpsgod/gce in 4 mm glucose at different applied potentials from 0.35 v to 0.55 v versus sce[54]. ppy-rgo-aunps/god = polypyrrole/reduced graphene oxide/gold nanoparticles/glucose oxidase/electrode. reproduced with permission from mdpi. polythiophene and derived forms have been utilized to form nanocomposites[55]. shamsayei et al.[56] fabricated polythiophene and graphene oxide based nanocomposites by the electrochemical method. the microstructure and electron conduction features of the nanomaterials have been explored. bora and researchers[57] used the interfacial polymerization method for the formation of polythiophene and graphene oxide based nanomaterials. due to nanofiller loading, dispersion, and the formation of a percolation network, the nanocomposite had a high electrical conductivity of 2.7 × 10–4 s cm–1. thermal stability analysis revealed higher degradation temperatures in the range of 248–260 ℃ for the nanocomposites relative to the neat matrix (200–300 ℃). yang et al.[58] fabricated poly(3-hexylthiophene) and reduced modified graphene oxide based nanocomposite. the morphology studies were performed to study the nanoparticle dispersion in the matrix. the poly(3-hexylthiophene) was found layered on the nanofiller surface. pilo et al.[59] used a polythiophene derivative, poly(2,5-di(2-thienyl)thieno[3,2-b]thiophene, with graphene oxide to form the nanocomposites. the resulting nanomaterials have been utilized for the formation of enzyme-sensing electrodes. the biosensor had a detection limit and sensitivity of 0.036 mm and 9.4 µa mm–1 cm–2, respectively. zamani et al.[60] fabricated the poly(3,4-ethylenedioxythiophene)/graphene oxide nanocomposite. the material was electrodeposited on solid phase microextraction fiber to form the sensing electrode. the nanocomposite electrode had a detection limit of 0.005–0.025 µg l–1 for tricyclic antidepressants (nortriptyline, amitriptyline, desipramine, imipramine, etc.). the sensing electrode revealed drug extraction of up to 105%. 5. significance of graphene oxide filled conducting nanocomposites supercapacitors have been categorized as effective energy storage devices[61]. conductive polymers and derived nanocomposites have been applied to form supercapacitors[62]. polythiophene has been effectively used in supercapacitors owing to efficient charge mobilization, eco and chemical stabilization[63]. moreover, polythiophene and graphene oxide derived nanocomposites have been functional for supercapacitance application[64]. mostly, in situ polymerization route was adopted to attain polythiophene/graphene oxide nanocomposite for supercapacitors. the poly(3,4-ethylenedioxythiophene) nanocomposites filled with graphene oxide possess a high specific capacitance of about 201–320 fg–1[65]. the poly(9-butyl-3,6di(thien-2-yl)-9h-carbazole) and graphene oxide based nanocomposite also have a specific capacitance of up to ~320 fg–1[66]. interactions among polythiophene or polythiophene derivatives and graphene oxide occur via non-covalent bonding and π-π stacking interactions. these interactions have improved electron transfer, specific capacitance, and charge-discharge performance[67,68]. zhou et al.[69] formed polypyrrole and graphene oxide derived nanocomposite through an electrochemical approach. the nanocomposite was electrochemically co-deposited on the fluorine doped tin oxide substrate. then, the layered supercapacitor was formed by sandwiching the nanocomposite layer between the fluorine-doped tin oxide substrates. li et al.[70] developed cellulose and graphene oxide based nanocomposites. then, polyaniline was layered on cellulose/graphene oxide through in situ polymerization of aniline monomers. cellulose/graphene oxide/polyaniline nanomaterial possess a high electron conduction of about 1.15 s cm–1. the supercapacitor electrode had a sufficiently elevated specific capacitance of 6 1,218 mf cm–2 at 1.0 ma/cm2. the flexible supercapacitor electrodes have revealed constant capacitance with twisting, so they can be used for flexible electronics. figure 6 shows a schematic for the formation of nanocomposite. moreover, the contact behavior of water droplets on nanocomposite surfaces was studied for super wettability behavior. due to the porous nature of the nanocomposite, a water droplet was easily penetrated. figure 7 depicts cyclic voltametric curves for in series and parallel devices as compared to a single device. the supercapacitor was used to light a red-light emitting diode for 4 minutes. consequently, the nanocomposites have been used to form flexible, weight-less electronics. figure 6. (a) synthetic route to cellulose/graphene oxide/polyaniline nanocomposites; (b) the water droplet contact process on the nanocomposite surface[70]. go = graphene oxide; pani = polyaniline; ani = aniline; aps = ammonium peroxydisulfate. reproduced with permission from mdpi. figure 7. (a) cv profiles of single device, two devices in series, and two devices in parallel connection at a scan rate of 50 mvs–1; (b) gcd profiles of single devices and three devices in series at a current density of 2 ma cm–2; and (c) optical pictures of three devices in series connection to light a led lamp for 4 minutes[70]. cv = cyclic voltammetry; led = light emitting diode; gcd = galvanostatic charge/discharge. reproduced with permission from mdpi. multipurpose energy production devices have also been focused on the use of conducting polymers[71]. in this context, conjugated polymers have been filled with efficient carbon nanoparticles such as fullerene, graphene, graphene oxide, and carbon nanotubes[72]. ensuing nanocomposites have been used to improve solar cell efficiencies. graphene oxide has been adopted as an efficient electron acceptor nanomaterial in solar cells[73]. graphene oxide has a large surface area and electron-conducting pathways for electron passage through the material. polythiophene and derivatives reinforced with graphene oxide have been integrated into solar cells[74]. stylianakis et al.[75] fabricated and applied poly(3-hexylthiophene) and graphene oxide nanomaterials for bulk heterojunction solar cells. poly(3-hexylthiophene) was used for electron donation, whereas graphene oxide worked for electron acceptance material[76,77]. furthermore, graphene oxide formed a percolation network, allowing electron diffusion through the system[78]. agbolaghi[79] produced the polyaniline and reduced graphene oxide nanomaterials through in situ techniques. the resulting nanocomposite has a solar cell efficiency of up to 7%. corrosion is a critical issue for metal-based industries[80]. in this context, different methods have been developed and applied for the corrosion protection of metals, such as the use of inhibitors and surface coatings[81]. conductive polymers were reinforced with graphene and graphene oxide to develop anticorrosion coatings[82]. moreover, pristine graphene oxide has been used as the a corrosion protective coatings[83]. graphene oxide has been layered on nickel or copper metal for corrosion inhibition[84]. similarly, graphene oxide reinforced polyaniline matrix has also been used as an anticorrosion coating[85]. graphene oxide filled polythiophene nanocomposites have been applied for corrosion protection applications[86]. electron conduction and corrosion defiance features of polythiophene/graphene oxide nanomaterials have been explored. however, few research efforts have been observed regarding polythiophene and graphene oxide derived anticorrosion nanomaterials so far. 7 therefore, further investigations are desirable in this field to attain better designs and properties[87]. 6. prospects and conclusions continuous research efforts have been focused on conductive polymeric materials. essential conjugated polymers such as polyaniline, polythiophene, polypyrrole, and derived polymers have been investigated with graphene oxide nanofiller. in this respect, various processing methods have been used to form the conductive polymer/graphene oxide nanomaterials. consequently, structure, microstructure, and electron transportation properties have been explored. interactions between conjugated polymers and graphene oxide have been found to enhance the features of the ensuing nanocomposites. inclusion of graphene oxide has been reported to enhance the electrical conductivity of the conducting polymer up to 50–90%. enhancement in electrical conductivity depends upon the nanofiller dispersion and interaction with the matrix, which may ultimately lead to the formation of an electronconducting network for percolation[88]. cheng et al.[89] reported the fabrication and electrical conductivity properties of polyaniline and graphene oxide derived nanocomposites. inclusion of 0.45 wt.% graphene oxide in polyaniline led to an electrical conductivity of up to 9.8 s cm–1, which is 90% higher than that of the pristine polyaniline matrix. the synergistic effects between matrix-nanofiller were observed due to interactions between the oxygen functionalities of graphene oxide and amino groups on polyaniline and aromatic ring stackings, leading to fine dispersion and network formation. good dispersion of graphene oxide in the conducting polymer matrix has enhanced surface-to-volume ratio and interfacial interactions, which contributed to overall enhanced electrical conductivity properties. supercapacitors have been developed using conjugated polymer/graphene oxide nanocomposites. an important use of polymer/graphene oxide nanocomposites was observed for photovoltaics. the corrosion resistant features of the conductive polymers and graphene oxide derived nanocomposites have also been studied. the anticorrosion features were enhanced using conducting polymers doped on graphene oxide surfaces. in the future, new design combinations and structure-property relationships of these nanomaterials need to be investigated for further developments in these fields. moreover, research can be extended towards the development of efficient designs for microelectronics and digitally integrated circuits. the biomedical sector also needs to be explored for the application of conductive polymer/graphene oxide nanocomposites. here, synthesis processes and mechanisms need to be investigated for the formation of high-performance conducting nanomaterials. in this review, major problems regarding conducting polymer/graphene oxide nanocomposites have been identified, including the benefits of combining graphene oxide and conducting matrices, overall property/potential advantages, and challenges in this field. graphene oxide has been identified as a low-cost, efficient nanocarbon[90]. in addition, lots of literature has been reported regarding the significant features and technical characteristics of conducting polymers and derived nanocomposites[91,92]. the main challenges discovered for conjugated polymers include poor processability and large-scale coating development. consequently, hardly any conducting polymer/graphene oxide nanomaterials have been used for commercial level applications. however, reports have been observed for the future market of these nanomaterials[93]. therefore, it is essential to investigate present research statistics and future forecasts on the upcoming industrial revolution of conducting polymer/graphene oxide nanocomposite in the form of this comprehensive review article[94]. as portrayed in this article, the detailed analysis of design, approaches, opportunities, and challenges has been found indispensable for the future development of conducting polymer/graphene oxide nanocomposites[95]. in short, this overview comprehensively covered the essential aspects of conducting polymer and graphene oxide derived nanocomposites. the 8 morphology, electronic, thermal, and strength features of the nanomaterials were studied. in addition, the potential 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review mahyar vefaghi 1 , hediyeh rezaei sedehi 1 , omid ashkani 1,* , yones yar-ahmadi 2 , yasemin tabak 3 1 faculty of engineering, islamic azad university, science and research branch, tehran 14515/775, iran 2 kerman university, kerman 7616913439, iran 3 tubitak national metrology institute (tubitak ume), gebze 41470, turkey * corresponding author: omid ashkani, o.ashkani.14@gmail.com abstract: given the increasing demand for sustainable energy sources and the challenges associated with the limited efficiency of solar cells, this review focuses on the application of gold quantum dots (auqds) in enhancing solar cell performance. gold quantum dots, with their unique properties such as the ability to absorb ultraviolet light and convert it into visible light expand the utilization of the solar spectrum in solar cells. additionally, these quantum dots, through plasmonic effects and the enhancement of localized electric fields, improve light absorption, charge carrier generation (electrons and holes), and their transfer. this study investigates the integration of quantum dots with gold plasmonic nanoparticles into the structure of solar cells. experimental results demonstrate that using green quantum dots and gold plasmonic nanoparticles as intermediate layers leads to an increase in power conversion efficiency. this improvement highlights the significant impact of this technology on solar cell performance. furthermore, the reduction in charge transfer resistance and the increase in shortcircuit current are additional advantages of utilizing this technology. the findings of this research emphasize the high potential of gold quantum dots in advancing next-generation solar cell technology. keywords: au-nano particles; au-qds; sustainable energy; solar energy; short circuit current 1. introduction in the last few decades, the rise in population and industrial advancement has placed greater demands on worldwide energy resources. consequently, the necessity to discover sustainable and renewable energy supply solutions has arisen as one of the most pressing global issues. among the various renewable energy sources, solar energy is notable as one of the top choices because of its extensive availability, sustainability, and low environmental impact. nonetheless, numerous obstacles, such as the low efficiency of solar cells and their manufacturing expenses, persist in obstructing the complete achievement of this technology’s capabilities. recent studies have aimed at enhancing the efficiency and lowering the manufacturing expenses of solar cells. to enhance the effectiveness of solar cells, several solutions have been suggested, including the incorporation of different quantum dots. in their research, ashkani and collaborators also noted the impact of graphene on the efficiency of solar cells [1,2]. additionally, a major advancement in this area is the use of gold quantum dots (auqds) technology. gold quantum dots, because of their nanoscale dimensions and distinctive optical characteristics, are capable of absorbing ultraviolet light and transforming it into visible light. this ability enables more effective use of the solar spectrum and enhances energy conversion efficiency. additionally, the plasmonic citation vefaghi m, sedehi hr, ashkani o, et al. recent advances in increasing the efficiency of solar cells using gold nanostructures/quantum dots, a comprehensive review. characterization and application of nanomaterials. 2025; 8(2): 11533. https://doi.org/10.24294/can11533 article info received: 21 february 2025 accepted: 28 march 2025 available online: 14 may 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(2), 11533. 2 effects created by these quantum dots generate intense localized electric fields, which boost light absorption and electron transfer in solar cells. this article explores how gold quantum dots enhance solar cell efficiency and their potential to propel the future of solar technologies. 2. solar energy and solar cells 2.1. solar energy and its advantages over other energy sources the increasing global energy demand is one of the most pressing challenges of the 21st century. driven by population growth and industrial development, energy consumption continues to surge, underscoring the urgent need for sustainable and innovative energy solutions. considering energy sources is therefore crucial, as they play a key role in satisfying the needs of the world’s population. accessible energy is insufficient for many people due to several factors, such as the developmental profile of a country, the economic status of its people, and the technological advancements within the country. the ecosystem is heavily polluted due to the emission of various gases generated from the burning of fossil fuels, which are readily available and commonly used to satisfy the world’s energy demand [3]. it is therefore vital to shift toward eco-friendly energy sources for the betterment of the future world [4]. renewable energy sources such as solar energy, wind energy, hydropower, and geothermal energy are critically important in this regard, as they are eco-friendly [5]. however, solar energy could be the best option for the future for several reasons. in general, sunlight as an energy source has many advantages. the sun is the largest natural energy source that is continuously available, and its energy is produced consistently. this energy is renewable, with the sun emitting it at a rate of 3.8 × 1023 kw, of which approximately 1.8 × 1014 kw is intercepted by the earth [6]. unlike fossil fuels, which have limited resources, the sun will continue to produce energy for billions of years. moreover, the cost of installing solar systems has decreased due to their widespread adoption, making this technology more affordable every day. additionally, solar energy production does not generate pollution and helps protect the environment. the use of solar energy can reduce dependence on foreign sources, which is especially important for countries that rely on importing fossil fuels. today, with the help of storage systems, solar energy can also be utilized during non-daylight hours, such as at night or on cloudy days. solar energy also has a significant impact on economic growth and job creation. table 1 also shows a summary of the increase in the volume of solar cell consumption in recent years, which requires further attention [7]. characterization and application of nanomaterials 2025, 8(2), 11533. 3 table 1. generating electrical energy with solar cells in recent years [7]. year generating electrical energy (twh per year) 2000 less than 100 2004 less than 100 2008 less than 150 2012 150 up to 200 2016 400 2020 1000 2.2. solar cells and their characteristics solar cells introduction a solar cell (also known as a solar panel) is a device used to convert sunlight into electrical energy as can be seen in figure 1. this process occurs through a phenomenon called the “photovoltaic effect”. in this effect, when sunlight (which consists of photons) strikes the surface of a specific material, the photons can excite the electrons of that material, causing them to be released. these free electrons then move and create an electric current. to demonstrate the effectiveness of solar energy, the sunlight radiation on dark disks could provide energy for the entire world. if solar cells with a conversion efficiency of only 8% are installed in suitable positions all over the world, they could generate an average of 18 terawatts of electricity. this amount exceeds the total primary energy output currently obtained from all major energy sources, including coal, oil, gas, nuclear, and hydroelectric [8]. figure 1. a schematic of the mechanism of utilizing solar energy for domestic use and its benefits. 3. quantum dots and gold quantum dots 3.1. introduction to quantum dots characterization and application of nanomaterials 2025, 8(2), 11533. 4 quantum dots (qds) have been recognized as a significant advancement in nanotechnology, representing semiconductor inorganic crystals that contain varying numbers of electrons occupying well-defined, discrete quantum states. while qds share a similar atomic arrangement with bulk materials, their three-dimensional truncation results in a higher proportion of surface atoms compared to bulk counterparts [9]. qds are characterized by their small size, which allows for a wide range of element ratio variations, often leading to remarkable fluorescent properties [10]. these semiconductor nanoparticles exhibit unique features such as sizedependent emission wavelengths, a broad excitation spectrum, and the ability to emit glowing light when stimulated by uv light, resulting in fascinating optical phenomena [11,12]. additionally, the structure of qds can be precisely tailored, adhering to the principles of quantum confinement, which further enhances their versatility and potential for various applications [13]. the emission and absorption spectra corresponding to the energy band gap of quantum dots (qds) [14] are governed by quantum confinement principles [15,16], which describe the energy required to excite electrons from the electronic band to higher energy levels. this excitation spontaneously creates an electron-hole pair, which can emit energy in the form of fluorescent photons [17]. qds can also be viewed as artificial atoms that generate discrete energy levels, with their band gap being precisely modulated by varying their size [18]. the band gap is related to the nano-crystallite size, as it depends on the number of atoms that make up the structure. as a result, qds exhibit optical properties that depend on their size, with smaller nanocrystals having larger band gaps [19,20]. specifically, the energy band gap increases as the quantum dot particle size decreases, leading to corresponding shifts in the wavelengths of emitted light [14]. 3.2. techniques for producing quantum dots there are various widely known methods for producing quantum dots: physical, chemical, and mechanical. there are also different definitions concerning the manufacturing and synthesis of quantum dots. quantum dots’ fabrication involves processes generally divided into two main categories: top-down and bottom-up methods. the choice of methods for fabricating nano-materials depends on the type of material, the desired properties, and the final application. in general, bottom-up methods tend to offer greater precision and control, while top-down methods may be more suitable for larger scales and industrial applications [21]. 3.2.1. top-down methods in top-down approaches, bulk materials are broken down into smaller parts to produce nanostructured materials. these methods include mechanical milling, laser ablation, etching, sputtering, and electro-explosion.  mechanical milling: in this method, materials are converted into smaller and nanometer-sized particles using high-speed mills or similar processes [22].  lithography: this method uses light or other beams to design precise patterns on the surface of materials, creating nanostructures [23].  laser ablation: in this process, a laser is used to vaporize and remove portions of the material, ultimately leading to the production of nanoparticles [24]. characterization and application of nanomaterials 2025, 8(2), 11533. 5  electro-spinning: electro-spinning is a simple method to produce nano-fibers, particularly from polymers, and coaxial electro-spinning enables large-scale production of core-shell and hollow nano-fibers [25].  sputtering: sputtering produces thin nanomaterial films by bombarding solid surfaces with high-energy particles, yielding high-purity materials with compositions similar to the target [26].  arc discharge method: this method generates carbon-based nano-material (e.g., fullerenes, nanotubes, graphene) using arc discharge between graphite rods in a helium atmosphere [27,28]. 3.2.2. bottom-up methods bottom-up methods in nano-material involve assembling structures from atoms, molecules, or small precursors, enabling precise control over size, shape, and properties. unlike top-down approaches that break down bulk materials, bottom-up techniques like self-assembly, sol-gel processes, and chemical vapor deposition utilize natural processes to create nano-scale materials. these methods are widely used in electronics, energy storage, drug delivery, and catalysis, where nano-scale precision enhances performance.  chemical vapor deposition (cvd): cvd produces high-quality nano-material by depositing thin films through chemical reactions of vapor-phase precursors on heated substrates. it is widely used for carbon-based nano-material like carbon nanotubes and graphene, where catalysts determine the material’s morphology [29].  hydrothermal and solvothermal methods: these methods synthesize nanostructures (e.g., nanowires, nano-rods) through reactions in high-pressure, high-temperature environments. the hydrothermal process uses aqueous solutions, while solvothermal employs non-aqueous media. microwave assisted hydrothermal methods are gaining attention in nanomaterial engineering [30].  sol-gel method: the sol-gel method is a wet-chemical process for producing metal-oxide nano-material. it involves precursor hydrolysis, condensation, aging, and calcination, leading to homogeneous, low temperature materials. this economical method supports complex nanostructures and composites [31].  soft and hard templating methods: soft templating uses surfactants to form nanoporous materials with tunable pore sizes, while hard templating involves filling solid templates with precursors to create mesoporous replicas. both methods enable the production of diverse nanostructures like nano-rods and mesoporous graphene [32].  reverse micelle method: this method uses water-in-oil emulsions where reverse micelles act as nano-reactors. by controlling the water-to-surfactant ratio, uniform nanoparticles with precise sizes are synthesized. it is a simple way to create fine, monodisperse nano-reactors [33,34]. 3.3. gold quantum dots and their properties gold quantum dots (auqds) are nanoparticles that display unique electronic and optical properties due to quantum confinement effects. these characteristics make them highly valuable for a wide range of applications, particularly in optoelectronics characterization and application of nanomaterials 2025, 8(2), 11533. 6 and sensing. auqds possess discrete electronic states that lead to distinct optical behaviors, such as photoluminescence. the quantum confinement effect results in size-dependent optical absorption and emission spectra, allowing the optical properties of auqds to be tuned based on their size. this tunability is especially useful in applications like fluorescence resonance energy transfer (fret) systems, where specific wavelength emissions are necessary for efficient energy transfer between molecules. figure 2 schematically shows some of the applications of gold quantum dots. 3.3.1. surface plasmon resonance (spr) and optical properties auqds also exhibit surface plasmon resonance (spr), a phenomenon in which conduction electrons on the nanoparticle surface oscillate in resonance with incident light. this leads to strong light absorption and scattering, with the resonance frequency being highly dependent on the particle size, shape, and local refractive index. the spr properties of auqds are particularly sensitive to the surrounding environment, making them highly responsive to changes in the chemical or biological milieu. this feature is crucial for their use in sensing applications. figure 2. a schematic of some applications of gold quantum dots. 3.3.2. sensing applications the tunable optical properties and spr effects of auqds make them excellent candidates for various sensing applications. auqds can be functionalized with specific ligands or biomolecules, enabling selective interaction with target substances such as proteins, dna, or small molecules. this ability to alter their optical properties upon binding with specific targets forms the foundation of a wide range of biosensors. these sensors can detect subtle changes in the environment, making auqds ideal for real-time monitoring of biological or chemical processes. additionally, their strong scattering and absorption properties allow the detection of even low concentrations of characterization and application of nanomaterials 2025, 8(2), 11533. 7 target molecules, enhancing sensor sensitivity. auqds can also be used in colorimetric sensors, where a visible color change occurs upon interaction with a target molecule, providing a simple and cost-effective detection method. 3.3.3. optoelectronics auqds possess unique electronic properties that are applied in various optoelectronic devices. due to their discrete electronic states, auqds exhibit high quantum efficiency, making them valuable for light-emitting diodes (leds), solar cells, and other optoelectronic devices. the size-dependent emission properties of auqds allow the creation of light sources with specific emission wavelengths, improving the performance of optoelectronic components. for example, in solar cells, auqds can enhance light absorption and improve overall cell efficiency. additionally, their photostability and non-toxicity make them a promising alternative to traditional semiconductors in optoelectronics. the unique properties of auqds, including their tunable optical absorption, surface plasmon resonance, and sizedependent electronic states, position them as key players in advancing the fields of sensing and optoelectronics, offering innovative applications for future technologies [35–37]. it is worth noting that the photo response mechanism of gold is also of interest in some of its applications. in this context, mahmoud et al. [38] investigated the photo response performance of gold-titanium oxide and its importance. chang et al. [39] also investigated the importance of this issue. in the study of chang et al. [39], it was shown that although neodymium vanadate is used in some cases due to its strong absorption of ultraviolet light, its medical applications are weakened due to its weak absorption in the visible light regions that gold can compensate for. also, some experiments showed that ndvo4/au can act as a highly effective anticancer agent in tumor inhibition [39]. 3.3.4. a review of the synthesis of gold nanoparticles gold nanoparticles are synthesized through a variety of physicochemical processes, which have advantages and disadvantages. one of the methods for synthesizing gold nanoparticles is the biological synthesis method [40]. this method is known as one of the suitable methods for producing nanoparticles due to its high efficiency. nanoparticles produced by this method have high stability but may have biological hazards, and for this reason, other synthesis methods, such as green synthesis, have been developed [41]. green routes using plant extracts as reducing and stabilizing agents for preparing gold nanoparticles are of interest [42]. modified nanocellulose is also known as a promising material for extracting gold nanoparticles [43]. it is also possible to synthesize gold nanoparticles with models close to the turkevich model, and in this model, trisodium citrate dihydrate and tetrachloroauric acid can also be used. in general, in some chemical methods, the synthesis of gold nanoparticles depends on the reaction time, acid concentration, and ph [44]. 4. integration of gold quantum dots with solar cells 4.1. enhancing solar cell performance using gold quantum dots characterization and application of nanomaterials 2025, 8(2), 11533. 8 with the continuous advancement of industries and the rapid growth of the global population, the demand for more efficient and sustainable energy sources has become increasingly urgent. among various renewable energy options, solar energy has garnered significant attention, leading to the need for improving solar cell efficiency and generating higher energy outputs. to meet this demand, it is essential to enhance solar cell manufacturing techniques through methods that are not only safe but also minimize the environmental impact compared to traditional approaches, while achieving superior performance over conventional enhancement strategies. scientific research and experimental findings indicate that the use of gold quantum dots has proven to significantly boost the performance of solar cells, delivering results such as higher power conversion efficiency, synergistic effects, and various other benefits. one of the promising solutions for improving the performance of solar cells lies in the incorporation of gold quantum dots, particularly in organic solar cells (oscs). organic solar cells have become a leading contender for renewable energy production due to their lightweight, flexible structure, low manufacturing costs, and ease of fabrication. however, these cells face the challenge of lower efficiency when compared to siliconbased solar cells. this is primarily due to their limited ability to absorb light across a broad spectrum, particularly in the ultraviolet (uv) region. organic materials typically operate efficiently in the visible spectrum, but uv light remains largely unutilized in these cells, which leads to a reduction in the overall power conversion efficiency (pce). in response to this challenge, researchers have employed two advanced technologies: gold quantum dots (auqds) and gold plasmonic nanoparticles (aunps). gold quantum dots, with their extremely small size (less than 2 nanometers), possess unique optical and electronic properties. these properties enable them to absorb ultraviolet light and convert it into visible light, which is then absorbed by the active layer of the solar cell. this ability allows the solar cells to capture a wider spectrum of sunlight, enhancing their overall efficiency. in addition, gold plasmonic nanoparticles help generate strong localized electric fields, improving light absorption within the cell and facilitating the process of charge carrier generation (electrons and holes). to investigate the effects of these technologies, researchers tested three types of quantum dots that emitted blue (b-auqds), green (g-auqds), and red (r-auqds) light. these quantum dots, when combined with plasmonic nanoparticles, were strategically placed as an intermediate layer between the hole transport layer (pedot: pss) and the active layer of the solar cell. the final structure of the solar cell included the following layers: a glass substrate coated with indium tin oxide (ito), quantum dots, a hole transport layer with gold nanoparticles, an active layer, and an aluminum electrode. the key findings from this experiment demonstrated that the combination of green quantum dots and plasmonic nanoparticles achieved the highest performance. specifically, this combination resulted in a 13% increase in power conversion efficiency (from 2.47% to 3.66%). this enhancement is attributed to the ability of the quantum dots to absorb ultraviolet light, convert it to visible light, and subsequently transfer it to the active layer, where it can be absorbed. additionally, the plasmonic nanoparticles generated stronger electric fields, improving the energy transfer process and overall efficiency. the research also revealed that the combination of green quantum dots and plasmonic nanoparticles led to the most significant increase in shortcircuit current (from 6.85 ma/cm2 to 7.61 ma/cm2). this improvement was due to a characterization and application of nanomaterials 2025, 8(2), 11533. 9 greater production of charge carriers and their more efficient transport within the device. therefore, the enhanced short-circuit current (jsc) stands out as one of the key advantages of incorporating quantum dots into solar cells. moreover, the addition of quantum dot and gold nanoparticle layers reduced charge transfer resistance, signifying improved efficiency in the transport of electrons and holes from the active layer to the electrodes. for example, in cells containing green quantum dots and plasmonic nanoparticles, the charge transfer resistance (rct) was reduced to 6.7 ohms, the lowest value recorded across all test samples. this reduction in resistance directly resulted from the synergistic effects of the quantum dots and plasmonic nanoparticles. the combination of quantum dots and plasmonic nanoparticles showed far superior performance compared to using either technology alone. the quantum dots enhanced the plasmonic effects of the gold nanoparticles by generating visible light, which, in turn, boosted the production of optical carriers and overall device performance. this phenomenon is referred to as the synergistic effect. the research demonstrates that pairing quantum dots with plasmonic nanoparticles can effectively address the challenges associated with light absorption in organic solar cells. the innovative design of this system not only improves power conversion efficiency but also enables the utilization of the ultraviolet spectrum, which was previously underused. the results highlight the potential of this technology for further development in the next generation of advanced solar cell applications [45–49]. also, table 2 provides a general summary of the strengths, weaknesses, and efficiency requirements of solar cells [50–55]. table 2. a summary of the efficiency, strengths and weaknesses of auqds in solar cells. increased efficiency reason for increasing solar cell efficiency ref. existing restrictions in a study, solar cell efficiency was increased by 30%. integrating plasmonic nanostructures and enhancing light absorption intensity. [51] high manufacturing cost recycling problems short-circuit current density and power conversion efficiency increase with the presence of gold quantum dots. localized surface the plasmon effect leads to enhanced light trapping. [49] there is a need for industrialization. using gold quantum dots increases efficiency by 104%. absorption coefficient of cadmium selenium quantum dots is improved by the addition of gold nanoparticles. [53] the limitations of using solar cells at night should be examined. increasing the efficiency of inverted organic solar cells gold quantum dots are used in inverted organic solar cells. [54] construction limitations and high costs need to be considered. jsc increases by 14.11% and pce by 19.57%. due to the use of gold quantum dots with green fluorescent color (green-auqds). [55] limitations in size and the need for further investigation to build cells with large dimensions. 4.2. future prospects in the future, the development of gold quantum dot technology could open new horizons in the solar energy industry. further research could focus on the following areas: 4.2.1. optimization of production processes and cost reduction given the relatively high cost of gold quantum dot production, it is essential to develop cheaper and scalable production methods, such as simpler chemical methods or innovative techniques. characterization and application of nanomaterials 2025, 8(2), 11533. 10 4.2.2. material durability under various environmental conditions the resistance of gold quantum dots to environmental factors such as humidity, heat, and prolonged exposure to radiation needs to be improved to be suitable for industrial and long-term applications. results have also been observed that the use of gold quantum dots in this field increases cell durability [50]. the results also show that the greatest improvement in solar cell efficiency compared to reference cells exceeded 30% [51]. 4.2.3. application in next-generation solar cells research on integrating gold quantum dots with perovskite cells, hybrid cells, and thin-film solar cells can enhance the performance of these systems and optimize the use of the solar spectrum. 4.2.4. energy efficiency improvement by studying the interaction between gold quantum dots and other nanoparticles, such as silver nanoparticles or two-dimensional materials like graphene, new synergies could be created to improve efficiency and reduce energy losses. research has shown that the use of aunps/g6/gqdsx composites can play an effective role in enhancing the sers response of solar cells [52]. in this regard, it is necessary to investigate the effect of the simultaneous presence of other quantum dots, such as gold and zinc sulfide, in the future. one of the main challenges in the field of solar cells is their efficiency at night, which limits the efficiency of solar cells. in this regard, more research needs to be done in the future by researchers to be able to use solar energy during the dark period, and especially in rainy conditions. of course, it should be noted that the dimensions of the solar cell can play an effective role in energy storage. figure 3 shows two examples of solar cells coated with nanoparticles in different dimensions. although figure 3a shows smaller dimensions, it has the same efficiency as the example in figure 3b, which is due to the application of nanoparticles and increased cell performance. researchers can also do more research in this area in the future, and it is considered a suitable research area. figure 3. examples of solar cells with different dimensions and different energy efficiencies (cells and image provided by the researchers of this article). characterization and application of nanomaterials 2025, 8(2), 11533. 11 4.2.5. applications in diverse fields in addition to solar cells, gold quantum dots can be used in other fields, such as biosensors, advanced displays, and energy storage devices. ultimately, the development of gold quantum dot technology could play a key role in achieving sustainable development goals and reducing the environmental impact of fossil fuel use. given the growing global demand for energy and advancements in related technologies, a bright future is anticipated for quantum dots in the renewable energy sector. this technology could provide a scientific and practical solution, creating a new path for clean and efficient energy production on a global scale. finally, it is proposed to use multilayer solar cells by applying different layers of gold nano-dots similar to figure 4. such solar cells may be able to have higher efficiency. it should be noted that this is only a theory and needs further investigation in future research. figure 4. schematic of multilayer solar cells as a theory for making cells with higher efficiency. this design has been suggested as a theory to researchers in future research, and whether or not the results are desirable requires future investigation. 5. conclusion the results of this study show that gold quantum dots (auqds), as one of the innovative technologies in enhancing the efficiency of solar cells, have significant potential to improve the performance of these systems. due to their unique optical and electronic properties, such as ultraviolet light absorption and its conversion into visible light, as well as the generation of strong electric fields through plasmonic effects, these quantum dots can significantly enhance the efficiency of the solar light absorption and conversion process. laboratory studies have shown that combining gold quantum dots with gold plasmonic nanoparticles improved the power conversion efficiency of solar cells by up to 13% and significantly reduced charge transfer resistance. this combination also led to an increase in short-circuit current and better charge carrier generation, indicating effective interaction between quantum dots and plasmonic nanoparticles in boosting optical and electronic processes. furthermore, the proposed structures in this characterization and application of nanomaterials 2025, 8(2), 11533. 12 study could serve as economic and efficient solutions for clean energy production in the future. this technology, by reducing dependence on traditional materials and increasing efficiency, represents an effective step toward achieving global environmental and economic goals. at the end of this study, it is suggested that researchers in the future should make more efforts in the field of quantum solar cells. the use of gold quantum dots is a suitable solution to increase the efficiency of solar cells used in spacecraft. the use of carbon-gold composites can also be suggested in the cell. in addition to the above suggestions, cell recycling methods can also be considered or the cell can 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adrián ojeda, adriana maría arias gorman, sonia cecilia sgroppo* universidad nacional del nordeste, facultad de ciencias exactas y naturales y agrimensura, av. libertad 5450. 3400. corrientes, argentina. e-mail: sonia.sgroppo@unne.edu.ar, sonia.sgroppo@hotmail.com ang.ac.kr abstract the application of nanotechnology in the food industry enables prioritization of consumers’ needs. nanotechnology has the ability to provide new forms of control on food structure; therefore, this technology has higher industrial value. this paper briefly introduces the main concepts of nanotechnology and its correlation with size reduction performance. this paper also introduces the main nanobjects and their potential applications in food, and summarizes various studies and their applications in food industry. keywords: nanomaterials; nanocomposites; nanoemulsion; packaging; composition article info received: 13 march 2022 accepted: 9 may 2022 available online: 8 june 2022 copyright copyright © 2022 gonzalo adrián ojeda, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction nanoscience and nanotechnology is expected to become one of the most innovative fields. nanotechnology allows the control and modification of substances and systems at the nano scale, which enables significant change to their properties relative to those observed at the macro scale. the nano size ranges from about 1 to 100 nm[1], and size is a key parameter for identifying nanomaterials (nms). the prefix “nano” originated from greek, meaning “short” and “small.” it is used to represent the coefficient of 10–9 (1 nm = 1 × 10–9 m) in the international system of units. the european commission recommends that nanomaterials should be categorized as natural, incidental or man-made substances, with 50% or more of the particle sizes between 1 and 100 nm[2]. iso defines it as a material with nanoscale external dimensions (nanobject or nanoscale internal or surface structures (nanostructured materials)[1]. therefore, nms is different from reference materials in physical, chemical or biological aspects. these changes are due to its small volume, combined with the surface energy, which gives the number of atoms on the outer surface and the number of atoms inside the material. on the other hand, the electrons in materials are distributed at different energy levels, resulting in different electronic structures, quantum phenomena and different electrical, optical and magnetic properties of the system. nanoparticles (nps) are nanobjects in only external nano sizes, with which the lengths of the long axis and the short axis are not significantly different from each other. they can self-assemble and have different reaction activity, hardness, conductivity, solubility, absorption rate and bioavailability compared with large particles. these characte 2 ristics of nps produce new ingredients and other methods to produce foods with different structures and characteristics, which increase or improve their functions, thereby elevating their commercial values. nanotechnology provides important opportunities for the development of innovative products and is applied in food production, processing, pre-processing and packaging. the availability of nanotechnology-derived food has increased significantly. according to food and agricultural organization[3], 183 “nano” and “food” patents were published from 2009 to 2011, including 47 related to packaging or coating, 19 related to nano additives, and 10 related to nanotechnology detection methods. in addition, developing countries are particularly interested in nanotechnology because it is a productive and economic activity with low requirements for its implementation (e.g., land, maintenance, energy and material availability). aguilera suggests that there are two interrelated basic dimensions or axes in the current and future food industry[4]: 1) the center of the “food chain” starts from the production of raw materials to the packaging and distribution of products. 2) the axis of “consumers” must be considered comprehensively. at present, consumers are interested not only in the contribution and bioavailability of nutrients, but also in the positive effects of diet (satiety, weight control, gastronomical experience, health, etc.). these requirements are the result of social changes in recent years. in this society, consumers have more opportunities to obtain information and are on a constant pursuit for better quality of life. nms used in food are divided into three different groups[5] (table 1): 1) organic nms include lipids, proteins and polysaccharides, which are used to wrap vitamins, antioxidants, dyes, condiments and preservatives to form micelles, liposomes or nanospheres. they have the advantages of increasing intake, absorption, biocompatibility and stability. 2) organic/inorganic bound nms are called surface functionalized nms and are added to the matrix through specific functions (antibacterial agents, antioxidants, permeability and stiffness regulators). 3) inorganic nms are metals and metal oxides, nps of silver, iron, selenium and tio2, which are used as additives, food additives or packaging materials. table 1. classification of nms in food nanomaterials for food and food contact organic organic/inorganic combination inorganic micelle and release system polymers, compounds and emulsions clay surface modification surface modification of metal or metalloid clay metals and metalloids fullerenes and carbon nanotubes source: authors’ elaboration, adapted from peters r[5]. nanocomposites are formed by adding a low percentage (<5%) of nps into the polymer matrix, which is reinforced by these nanofillers with higher rigidity and strength. in addition, the addition of nps will lead to the circuitous flow of gas in nanocompounds, so as to regulate the gas exchange between packaging materials and the environment. the main polymers used can be natural or synthetic, chitosan, cellulose, carrageenan, polyvinyl alcohol, polylactic acid, polyglycolic acid, polyethylene, polyamide, polyvinyl chloride, etc. as fillers, inorganic or organic nps, clay, silicate, cu, ti, cellulose, carbon, etc. with different geometries (spheres, flakes, nanotubes, fibers, etc.) are used. these fillers can be bonded to the matrix in the form of interlayer or delamination[6] and extrusion or coating methods. in the process of adding materials, the quantity and dispersion of nps, their interaction with matrix and possible aggregate should be controlled. nanoemulsion is a dispersion of two incompatible liquids, such as oil and water. it is stabilized by surfactant molecules that form an interfacial layer. the average diameter of each drop is between 20 and 200 nm. if the drop diameter is less than 40 nm, it is suitable for transparent food. they have a large surface area and 3 slow release of bioactive substances, which avoid the deposition or precipitation of cream caused by brownian motion. in addition, they will improve the texture, flavor and color of food and act as an appropriate system to release less water-soluble compounds by increasing the dispersion and stability of drops[7]. the composition and structure of nanoemulsion can be properly designed to protect the compound and achieve the expected performance in vivo. in addition, the ability of nanoemulsion to form gel allows the design of foods with different textures. oil/water nanoemulsion can be used to encapsulate hydrophobic compounds (vitamins, minerals, saponin components, antioxidants, carotenoids), while water/oil/water nanoemulsion can be used to encapsulate water-soluble bioactive substances embedded in aqueous heart. the bioavailability of compounds contained in droplets is inversely proportional to the size of droplets, which may be due to increased enzyme activity, prolonged contact with mucosa, direct transport through epithelium, and increased water solubility of hydrophobic components. in order to be used in industry, nanoemulsion must be prepared with generally recognized as safe (gras)1 ingredients and allow industrial production in operation and economy. in addition, because nanodroplets can increase their bioavailability, in vivo evaluation must be carried out. nanoencapsulation may also improve the solubility, stability and bioavailability of food and prevent adverse interactions between components. nanoliposomes and nanochelates are the main carriers of bioactive substances, which help to control and release nutrients, enzymes, vitamins, antimicrobial drugs and additives. nanochelates stabilize micronutrients and improve the nutritional value of processed foods[8]. 2. food improvement and innovation nanotechnology can be used to prepare innovative foods and add new ingredients and additives with specific functions, such as antibacterial agents, antioxidants, texture enhancers and flavor enhancers. in 1generally recognized as safe (gras) refers to a rule that requires a chemical designated by the u.s. food and drug administration (fda) or a substance added to food, which is considered safe by experts and is addition, it can also be used to design foods with specific nutritional characteristics to meet individual nutritional and health needs (e.g. allergies, chronic diseases) or preferences, or to produce interactive foods that release color and taste according to consumer needs. at present, the formula of dietary supplements used in nutrition, sports and health food market contains mineral nps (sio2, mg, ca, etc.). in australia, nanocapsular provides omega-3 oil, which is only released into the stomach to avoid unpleasant taste. in argentina, liposomes are made of lecithin with stable structure and resistance to gastric digestion. nanoencapsulated iron and omega-3 can increase the absorption of minerals and avoid intestinal discomfort caused by intake (htpps://www.fan.org.ar/potfolios/nutranova-la-linea-de-suplementosdietarios-de-lipomize). unilever has developed ice cream, mayonnaise, and low-fat, low-calorie cream that tastes like cream, while nestle has developed a quick thawing nanoemulsion. aquanova has developed micelles to improve the stability, effectiveness and bioavailability of components (vitamins c, e and fatty acids). novasolare provides nanocapsules of bioactive compounds (dl-α-tocopherol; coenzyme q10, ω-3 fatty acids and vitamins a, d, d3, e and k) and natural dyes (apocaro tenal, β-carotene, turmeric, chlorophyll, lutein). nutralease also provides bioactive compounds (lutein, lycopene, vitamin a, d3, e, q10, phytosterols and isoflavones) for use in a variety of foods and beverages, or nanoemulsions to protect flavor components[9]. at the same time, many scientific papers related to this subject have been published, which are still subject to further evaluation and validation because of their effectiveness. ha et al. showed that by preparing lycopene nanoemulsion added to tomato extract, the in vitro bioavailability of bioactive substances was enhanced, stable in aqueous medium, and poor in oxidation[10]. ban et al. achieved similar results in the oral bioavailability of oil/water nanoemulsified flavonoids[11]. on the other hand, akbas et al. prepared a transparent capsaicin nanoemulsion with inhibitory activity against staphylococcus aureus and escherichia coli[12], which is suitable for functional food, edible coatings or therefore not subject to the tolerance requirements of food additives under the federal food, drug and cosmetic act (ffdca). 4 packaging. meanwhile, lane et al. developed omega-3 linseed oil and seaweed nanoemulsion to make fortified food[13]. silva et al. prepared a stable double emulsion composed of olive oil, flax oil and fish oil[14]. quercetin and gallic acid were added to the internal and external aqueous phases as a substitute for fat in food formula. on the other hand, by adding nanoencapsulated quercetin prepared from a mixture of soybean oil and water to chicken legs, the lipid oxidation of the product was prevented, and a sensory acceptable product was obtained[15]. the treatment of rainbow trout with nanoemulsion of sunflower seed oil/water and eupatorium multiflorum essential oil has similar results[16]. gani and benjakul pointed out that adding coconut oil/sodium caseinate nanoemulsion to surimi gel not only improved the whiteness of the gel, but also improved the texture and appearance of the gel[17]. for isotonic beverages, bovi et al. developed buriti (mauritia flexuosa l.) oil nanoemulsion[18], which contains high content of steroids and provides stable natural colorants for these drinks. wang et al. prepared a functional dehydrated beverage including salt, lipophilic and hydrophilic vitamins through peppermint oil nanoemulsification process and pectinas nanoencapsulated sodium caseinate[19]. meanwhile, ghosh et al. obtained a eugenol nanoemulsion containing sesame oil/tween 80-20/water[20], which extended the shelf life of orange juice by inhibiting the growth of s. aureus and controlling the local flora during storage at 4 °c. 3. food packaging the main purpose of packaging is to ensure the protection and preservation of food quality from production to consumers. container is a kind of goods container, which is convenient for transportation and handling. similarly, a well-designed package must be attractive and easy to use to the consumers, and is able to promote the products (marketing) and provide information about products. at present, the application of nanodevices in packaging aims to improve its function by using nanocomposites as packaging materials or coatings. in this way, gas exchange, temperature, humidity, flexibility, mechanical strength and thermal strength can be controlled. generally speaking, nanocomposites will not change the density or fluidity of the film, nor change its transparency, and have the advantages of recyclability, thus reducing environmental pollution. they allow the synergy of antibacterial compounds, antioxidants, oxygen absorbers and water vapor, and detect and provide information about food (freshness, temperature abuse, etc.). montmorillonite layer (mx(a14xmgx)si8o20(oh)4) is the most commonly used clay filler. it can improve the mechanical and physicochemical properties of polymer composites by improving the gas barrier performance. some companies have developed nanocomposites based on montmorillonite-added nylon polymer matrix and provided them as particles, and used durethan rku2-2601, (nanocor tm)[21] for packaging flavored alcoholic beverages (honeywell international) or pet bottles, and multilayer nanocomposites for beer and carbonated beverages[22]. picouet et al. studied the addition of nanoclay to polyamide 6 (pa6) matrix of vacuum-packed beef loin, and verified the increased rigidity of the packaging and the barrier performance against oxygen and ultraviolet light[23]. at the same time, montmorillonite nano antifungal column was prepared by simple intercalation method with pomegranate residue extract (punica granatum), and the efficacy of apple gray mold was tested in vitro and in vivo[24]. on the other hand, metal/metal oxide nps can also be effectively used as antibacterial agents because they produce reactive oxygen species that can destroy cells and change their structure or function through interaction with metal ions. it must be remembered that one of the most critical aspects of the food chain is the deterioration caused by microbes. nps and nanocomposites of silver are widely used in industry because of their antibacterial properties in fruit, herbal medicine, bread, cheese, soup and meat packaging, and are offered under the name of fresher longertm, bags fresher longertm (usa). they are also added to food trays and sold as nanosilver food containers (korea), zeomic (japan), nanosilver food (china)[20]. to date, some studies have shown that nanocomposites do not or begin to migrate from containers or model systems in contact with food[25,26]. when packaging meat, cheese, lettuce, apples and eggs with ethyl vinyl alcohol (evoh) and agnps, 5 martinez abad et al. found a decrease in salmonella and monocytic e. coli[27]. on the other hand, when lorette et al. put cellulose agnps adsorption pads in chopped meat, kiwi fruit and melon sample containers to determine that the antibacterial activity depends on the food matrix[28]. montmorillonite agnps was also prepared by replacing na+ ions in clay and applying it to fruit salad. by inhibiting changed microorganisms, products with good sensory quality and long shelf life were obtained[29]. in addition, films were made from a mixture of binary agar and banana powder and enhanced with agnps, which proved to have a strong effect on pathogens and gram-negative bacteria[30]. other films based on agar and nps ag-cu have strong inhibitory activity against monocytic proliferative e. coli and salmonella typhimurium, and can be used as packaging materials[31]. in order to preserve freshly cut apples, li et al. prepared polyvinyl chloride bags containing zno nps (200–400 nm) and determined their effectiveness in controlling product degradation, reducing respiratory activity and browning[32]. luo et al. found similar results in freshly cut sweet potato packaged with nano caco3 low density polyethylene (ldpe), and discovered that the browning rate decreased due to the decrease of oxidase activity[33]. marra et al. found that the mechanical properties of the colorless nps of zno-a biodegradable polylactic acid film were improved and the gas permeability was low[34], while zhang et al. found that the mechanical properties of the film were improved, and were effective against e. coli and s. aureus[35]. other authors added nps of cuo (1%) to ldpe film and applied it to cheese ultrafiltration to verify the control of coliform during storage[36]. in addition, benzoic acid and vanillin nico nps in polylactic acid, ethanol polylactic acid and polyethylene glycol biopolymers also inhibit the growth of salmonella typhimurium, e. coli o157:h7 and mononucleosis in raw and cooked chicken[37]. tio2 has the effect of light and enhanced antibacterial properties. it is used to increase the bleaching capability and luster of toothpaste, candy and mayonnaise, and prevent product agglomeration. by adding tio2 nps into polyethylene, xing et al. observed the inhibitory effect on s. aureus and e. coli, which increased after ultraviolet irradiation[38]. at the same time, cozmuta et al. prepared a nanocomposite with ag-tio2 and polyethylene for packaging fresh bread, thus extending the shelf life of the product[39]. on the other hand, dias et al. applied carbon nanotube (cnt) allyl isothiocyanate film to chicken chop to verify their safety and antioxidant capacity[40]. similar results were observed by zimoch korzycka and jarmoluk[41] and dehnad et al.[42] who used chitosan coating on meat or formed nanocomposites with cellulose. the application of chitosan together with cellulose nanocrystals to whole pears (pyrus communis l.) resulted in delayed ripening and the appearance of postharvest deterioration symptoms[43]. on the other hand, kim et al. applied carnauba wax/montgras nanoemulsified oil on grapes (vitis labruscana bailey) and observed the inhibition of pathogens while avoiding mass loss[44]. similarly, fresh strawberries coated with alginate and limonene liposomes can also prolong their shelf life after harvest[45]. pectin/turmeric/cinnamon oil nanoemulsion coatings were also tested on chicken slices, which were effective for microbial control and slow degradation[46]. in low-fat cheese, nanoemulsion was prepared with sodium alginate orange fiber and oregano oil, artiga-artigas et al. determined its effectiveness and appearance retention against s. aureus and native flora[47]. in meat, amna et al. found that packaging materials containing zno olive oil nanofibers were effective against s. aureus and salmonella typhimurium[48], and khan et al. found the same situation was in cnts-containing nisin[49]. 4. nanosensor nanosensor can be an electrode or active layer of nanostructure, as well as an electronic data processor, which is used to convert the detected signal (the presence of light, gas or organic matter) into electronic signal. it has the advantage of being a non-destructive method, with high sensitivity, fast response and recovery. nanosensors can be used as indicators, labels or coatings to add intelligent functions to containers to detect changes in ph, gas composition, components released due to deterioration, container integrity, temperature, time, or microbial safety. in addition, they can be integrated with equipment during processing or storage in gondola or refrigerator to avoid nps from direct 6 contact with food. they are widely used in the field of food safety to detect pathogens, mycotoxins or allergens. they can also be used for environmental monitoring and agriculture to detect pesticides in fruits and water. kraft foods has developed an electronic language, which is included in the package. the language consists of a series of nanosensors that are very sensitive to the gas released by spoiled food. these sensors produce a sensitive freshness signal showing color changes[21]. the application of electronic nose and electronic tongue in beer fermentation and the detection of fungal pollution in grain were introduced through examples. biosensors use various nanotargets, nanofibers, nps and quantum dots to fix antibodies, dna, enzymes, etc. portable devices using nanowires and antibodies are also provided, which can quickly detect, identify and quantify pathogens, interfering substances and allergens. some nanosensors can detect gold nps containing antibodies and can detect and recognize pathogens in milk, apple juice and meat[50], or have immobilized xanthine oxidase, which can be used as an indicator of the freshness of canned tuna[51]. abargues et al. designed a chip containing gold nps to monitor changes in chicken[52], and liu et al. developed a chemically resistant cnt detector modified by co and medium arylmorpholine complex to detect biogenic amines and monitor changes in meat and fish[53]. sensors with nps quantum dots were also used to detect salmonella typhi[54] or e. coli o157:h7 in various meats[55]. due to its photosensitivity, tio2 nps are used to prepare oxygen sensors, as is sno2 nps[56]. biodegradable nanosensors are also being developed to monitor temperature and humidity and to monitor these parameters during transportation and storage of packaged food. recently, a large number of sensors have been designed for different purposes, particularly in line with consumers’ demand for safer and more natural food, which has spawned a series of scientific progress and industrial development. 5. final considerations nanotechnology has a tremendous potential in the food sector, which enables the prioritization of consumers’ needs. at present, many products containing nms in the market, especially additives and food contact materials, are usually consumed and ignored. a major safety concern is the ignorance of the effects of nms entry and accumulation in the body. nps can be ingested directly and intentionally released into food as additives, supplements, pesticide residues or put in contact with packaging materials. although nps have special characteristics of affecting microbial cells or improving the bioavailability of bioactive substances, they may be cytotoxic to human cells or cause inflammatory processes due to oxidative stress. therefore, it is necessary to conduct a comprehensive assessment of the toxicity risk of the nms to be used and develop a specific legislative framework to manage this technology. finally, nanotechnology can control food 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67: 243–247. 55. yang l, li y. simultaneous detection of escherichia coli o157:h7 and salmonella typhimurium using quantum dots as fluorescence labels. analyst 2006; 131: 394–401. doi: 10.1039/b510888h. 56. mihindukulasuriya s, lim l. oxygen detection using uv-activated electrospun poly (ethylene oxide) fibers encapsulated with tio2 nanoparticles. journal of material science 2013; 48: 5489–5498. microsoft word can-3008-online characterization and application of nanomaterials (2023) volume 6 issue 2 doi: 10.24294/can.v6i2.3008 1 original research article nanodemulsifiers with the properties of crystalline liquids, intramolecular interblock activity and eternal intramolecular nanomotors dashdiyev rahim abas1,*, dashdiyeva turana kamil2 1 international oil services kazakhstan llp, baku 1012, azerbaijan 2 azerbaijan state oil and industry university, baku 1012, azerbaijan * corresponding author: dashdiyev rahim abas, dashdiyev51@gmail.com abstract the provided material presents a priority article on the scientific discovery titled “the phenomenon of simultaneous destruction of water-oil and oil-water emulsions”. the authors propose the corresponding formula: the previously unknown phenomenon of simultaneous destruction of water-oil and oil-water emulsions occurs when polynanostructured surfactant demulsifiers with characteristics akin to crystalline liquids, intramolecular interblock activity, and enduring intramolecular nanomotors (such as block copolymers of ethylene and propylene oxides, which act as sources of oligomer homologues of oxyethylene ethers) are added to crude oil during primary oil processing. this phenomenon is attributed to the redistribution of oligomer homologues, with the most hydrophobic oxyethylene ethers being dispersed in water-oil emulsions and the most hydrophilic ones in oil-water emulsions, resulting in robust nanodispersed phases with crystalline liquid properties. keywords: the phenomenon of simultaneous destruction of water-oil and oil-water emulsions; polynanostructured surfactant demulsifiers; crystalline liquids; intramolecular interblock activity; eternal intramolecular nanomotors 1. introduction the authors conducted a thorough analysis of existing literature in the field but found no specific information on the subject of “nanodemulsifiers with the properties of crystalline liquids, intramolecular interblock activity, and eternal intramolecular nanomotors.” as a result, there are certain gaps in applied nanocolloid chemistry, particularly in relation to demulsifiers used in primary oil preparation. however, despite these gaps, the authors consider the presentation of conclusions based on the available literature data to be both intriguing and valuable.  academician a. h. mirzajanzadeh is credited with laying some of the foundational principles of nanotechnology in the global context of oil production[1].  in 2012, for the first time at the zhetibai field of the republic of kazakhstan, under the leadership of r. a. dashdiev, experimentalindustrial tests (eit) were carried out for the destruction of hard to destroy water-oil emulsions (hdwoe) using the nanodemulsifier “nd-1/4”, developed by a group of scientists at the institute “nipi neftegaz” socar (state oil company of azerbaijan republic). the results of the eit were found to be successful[2]; article info received: 11 october 2023 accepted: 23 november 2023 available online: 25 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2  the liquid crystalline nanodemulsifier tnd (tyumen nanodemulsifier) was developed by scientists at tyumen state university. however, there is currently no available data in the literature regarding the widespread application of this reagent[3];  research on mathematical modeling conducted by azerbaijani scientists (g.ch. kalbaliev, s.r. rasulov, etc.) related to the formation and decomposition of oil emulsions is one of the priority issues in this area[4];  the use of reverse demulsifiers, mainly made in china, in the primary preparation of oil (ppo) practice for the purpose of splitting oil-water emulsions has not been confirmed by the results of implementation[5];  the development and large-scale application of nanoecological technologies used for processing petroleum nanocolloids formed using ppo (primary preparation of oil) technologies is one of the priority areas of modern oilfield nanotechnology;  no information was found on the emulsifying properties of hdwoe in relation to reverse and direct emulsions;  no information was found on the use of demulsifiers capable of simultaneously destroying reverse, direct, and medium emulsions (or the intermediate layer, or hdwoe);  the utilization of conventional substances, such as nonionic surfactants, as a wetting component in demulsifier compositions of new generations is regarded as favorable. however, the impact of the nonionic surfactant structure (such as alkyl radical and oxyethylene chain length) on the effectiveness of the demulsifier has been relatively underexplored.  prevention of the formation of persistent water-oil and oil-water emulsions in wells by chemical methods is one of the priorities of modern oilfield chemistry;  the global market currently offers a wide range of surfactant demulsifiers, including oxyalkylene block copolymers derived from polyhydric alcohols, amines, polyamines, phenol-formaldehyde resins, epoxy resins, and silicon compounds. the selection of surfactant demulsifiers available exceeds a thousand. however, the precise distinction between conventional surfactants and surfactant demulsifiers remains an open question.  upon research, no existing information was found regarding the concept of a “desuspensifier” within the framework of the emulsion-emulsifier-demulsifier complex, which complements the concepts of suspension and suspensifier. the concept of a desuspensifier, introducing a new property of substances, holds promising implications for applied colloidal chemistry. this scientific discovery opens potential avenues for further exploration and investigation in the field of desuspension and related phenomena in colloidal systems[6];  for the components of demulsifiers, issues related to the correlation between property, structure, and efficiency have also been little studied[6];  analyzing the relevant literature data, the authors found that nanocolloids in crude oil increase the stability of oil emulsions and form polynanoenergy barriers that reduce the effectiveness of traditional demulsifiers in dispersed and dispersed media[7];  no information was found on nanodemulsifiers with a polynano structure;  no relevant information was also found on the following issues: the phenomenon of simultaneous destruction of oil-water and water-oil emulsions; polynanostructured surfactants demulsifiers with the properties of crystalline liquids, intramolecular interblock activity and eternal intramolecular nanomotors.  the development of multidisciplinary nanotechnology is accompanied by the emergence of certain priority areas, for example, the creation of nanomotors[8–12]. as an example, we can briefly describe a nanomotor made of dna material[8]. the dna nanomotor consists of three components: a base, a 3 platform, and a rotor. the base is about 40 nanometers in height and is attached to the glass plate in solution via chemical bonds on the glass plate. a rotor arm up to 500 nanometers long is mounted on a base so that it can be rotated[8]. physicists from the university of cambridge have managed to develop a unique nanomotor. this motor uses light as its energy source[12]. chinese scientist professor zhong from shanghai university has created eternal nanogenerators (based on triboelectricity) that will produce electricity directly from air[13]. however, zhong’s eternal nanogenerators do not belong to polynanostructured nanodemulsifiers, which have the properties of crystalline liquids, intramolecular interblock activity, and eternal intramolecular nanomotors;  generally, there are certain gaps at the level of scientific discoveries in the field of applied nanocolloidal chemistry and nanophysics in primary preparation of oil. in several specific cases, the european academy of natural sciences (eans) has registered five scientific discoveries by authors in this direction[14–18]. this article is a priority article of the project of the sixth scientific discovery of the authors on the topic “the phenomenon of simultaneous destruction of water-oil and oil-water emulsions”. for this project, a scientific discovery was registered in eans on 5 october 2023[19]. 2. experiment 2.1. objects and methods of research 2.1.1. objects of research the research for this project involved the use of multi-block demulsifiers and complex oil emulsions sourced from the fields of the republic of kazakhstan. multi-block demulsifiers. the following were used as multi-block demulsifiers: opb–oeb–opb knowns three-blocks oeb–opb–oeb knowns three-blocks opb–oeb–opb–oeb–opb five-blocks opb–oeb–opb–oeb–opb–oeb–opb seven-blocks opb–oeb–opb–oeb–opb–oeb–opb–oeb–opb nine-blocks opb–oeb–opb–oeb–opb–oeb–opb–oeb–opb–oeb–opb eleven-blocks where, opb—oxypropylene block; oeb—oxyethylene block. for the research, well-known three-block demulsifiers were utilized: “dissolvan-4411” (oeb–opb– oeb), “dissolvan-4795” (oeb-opb-oeb), “dissolva-4397” (oeb–opb–oeb), “dissolvan5748” (opb– oeb–opb), (“clariant” of switzerland, a subsidiary of “basf” of germany); “randem-2219” (oeb–opb– oeb), “randem-2201” (opb–oeb–opb), “randem-2208” (opb–oeb–opb) (nalco usa); “snpx4315d” (opb–oeb–opb) (russian); “f-929” (“toho chemical industry co., ltd”, japan). the following were used as our own multi-block demulsifiers: “ikhlas-1m-5” (opb–oeb–opb), “ikhlas-1m-7” (opb–oeb–opb), “ikhlas-1m-9” (opb– oeb–opb), “ikhlas-1m-11” (opb–oeb–opb) (azerbaijan-kazakhstan-china). several oil fields in the republic of kazakhstan were selected as research objects for this study. “uzen” “ozenmunaigas” jsc; “zhetibai” “mangistaumunaygas” jsc; “zhalgiztobe”. 4 2.1.2. research methods the quality of oil, in terms of water content (not exceeding 0.5%), chloride salts (not exceeding 100 mg/dm3), and mechanical impurities (not exceeding 0.05%), must meet the requirements outlined in current standards[20,21]. additionally, the quality of formation water, in terms of oil content, should not exceed 50 mg/dm3. the experimental part of the work was conducted following widely accepted standards:  method for determining water in petroleum products and oil[22];  method for determining the content of chloride salts in oil[23];  method for determining the content of mechanical impurities in oil[24];  method for determining oil content in water[21].  the laboratory test results are presented in tables 1 and 2. table 1. comparative results of laboratory tests of polynanostructured demulsifiers “ikhlas” regarding the phenomenon of simultaneous destruction of oil-water and oil-water emulsions of the “jetibay” field[25]. demulsifier residual consentrations dsс, + or – ic for hdwoe, + or – coil, mg/dm3 fosdowo & owe + or – water, % cl salts, mg/dm3 mech imp, % 1 2 3 4 5 6 7 8 “ikhlas-1” traces 11 0.004 + + 16 + “ikhlas-2” 0.12 37 0.01 + + 33 + “ikhlas-3” 0.06 23 0.01 + + 32 + “ikhlas-4” 0.18 44 0.02 + + 45 + “ikhlas-5” 0.15 36 0.01 + + 36 + “ikhlas-6” 0.09 26 0.01 + + 19 + “ikhlas-7” 0.12 29 0.02 + + 43 + “ikhlas-8” 0.34 58 0.01 + + 48 + “ikhlas-9” 0.07 14 0.009 + + 28 + “ikhlas-10” 0.21 45 0.01 + + 49 + “ikhlas-11” 0.09 22 0.02 + + 24 + “ikhlas-12” 0.12 29 0.01 + + 31 + “ikhlas-13” 0.17 42 0.03 + + 25 + “ikhlas-14” 0.12 35 0.01 + + 37 + “ikhlas-15” 0.10 23 0.01 + + 20 + “ikhlas-16” 0.09 29 0.02 + + 41 + “ikhlas-17” 0,.6 76 0.03 + + 47 + “ikhlas-18” 0.27 48 0.01 + + 24 + “ikhlas-19” 0.40 89 0.03 + + 45 + “ikhlas-20” 0.38 91 0.04 + + 43 + “ikhlas-21” 0.12 29 0.02 + + 19 + “ikhlas-22” 0.32 69 0.01 + + 38 + “ikhlas-23” 0.15 29 0.01 + + 33 + “ikhlas-24” 0.41 87 0.025 + + 50 + “ikhlas-25” 0.06 19 0.02 + + 24 + “ikhlas-26” 0.06 23 0.02 + + 17 + “ikhlas-27” 0.10 34 0.01 + + 33 + 5 table 1. (continued). demulsifier residual consentrations dsс, + or – ic for hdwoe, + or – coil, mg/dm3 fosdowo & owe + or – water, % cl salts, mg/dm3 mech imp, % 1 2 3 4 5 6 7 8 “ikhlas-28” 0.38 79 0.04 + + 40 + “ikhlas-29” 044 91 0.03 + + 45 + “ikhlas-30” 0.25 53 0.03 + + 46 + “ikhlas-31” 0.24 35 0.01 + + 32 + “ikhlas-32” 0.09 16 0.005 + + 20 + “ikhlas-33” 0.12 29 0.02 + + 39 + “ikhlas-34” 0.19 15 0.01 + + 25 + “ikhlas-35” 0.32 55 0.01 + + 47 + “ikhlas-36” 0.09 16 0.009 + + 18 + “ikhlas-37” 0.07 20 0.006 + + 19 + “ikhlas-38” 0.27 46 0.01 + + 35 + “ikhlas-39” 0.18 49 0.02 + + 43 + “ikhlas-40” 0.43 92 0.04 + + 47 + “ikhlas-41” 0.39 88 0.04 + + 39 + “ikhlas-42” 0.36 74 0.03 + + 44 + prototip 98 0.83 423 0.07 – – 184 – “randem-2219” (bd) 12.74 5087 1.96 – – 672 – note: test conditions of “ikhlas” and “randem-2219” demulsifiers: t = 64 ℃; xs = 150 g/t; settling time  = 3.5 h; for prototype: t = 70 ℃; xs = 200 g/t;  = 24 h; mech imp—mechanical impurities; dsс—desuspensifier capacity[14,25]; inhibitory capacity (iс) for hdwoe[16,25]; coil—oil concentration in water; bd—basic demulsifier; fosdowo&owe—phenomenon of simultaneous destruction of oil-water and oil-water emulsions. table 2. comparative results of laboratory tests of samples of various demulsifiers of some leading companies in the world for the destruction of oil emulsions from various fields of the republic of kazakhstan to reveal the nanobarrier properties of crude oil[7,17] (in brief form). demulsifier name dem. effic sc, g/t td, ℃ , hours dem. stab con. of wat, % deid rocw, mg/dm3 deder bd, at times init-l wi res-l wr dd, % edierbd, at times 1 2 3 4 5 6 7 8 9 10 11 12 crude oil from the “uzen” field of “ozenmunaigas” jsc of rk 5 (chin com-y pe) pns hed 100 62 3 st da 48 0.17 99.6 46 46 17,0 6 (chin com-y pe) pns sd 100 62 3 st da 48 0.03 99.9 260 39 20,1 7 (chin com-y pe) pns sd 100 62 3 st da 48 0 100  35 22,4 8 (chin com-y pe) pns sd 100 62 3 st da 48 0 100  27 29.0 9 (chin com-y pe) pns sd 100 62 3 st da 48 0 100  34 23.0 10 (chin com-y pe) pns sd 100 62 3 st da 48 0 100  28 27.9 11 (chin com-y pe) pns sd 100 62 3 st da 48 0.08 99.8 97 43 18.2 12 (chin com-y pe) pns sd 100 62 3 st da 48 0.03 99.9 260 31 25.2 proxamine-385 (rus) wd 100 62 3 stable 48 7.8 83.7 1 778 1.00 tnd (rus) wd 100 62 3 stable 48 2.1 95.6 3.71 73 10.7 snpx-4315d (rus) wd 100 62 3 stable 48 8.8 81.7 0.88 290 2.70 flek-d020 (rus) wd 100 62 3 stable 48 8.2 82.9 0.95 271 2.89 6 table 2. (continued). demulsifier name dem. effic sc, g/t td, ℃ , hours dem. stab con. of wat, % deid rocw, mg/dm3 deder bd, at times init-l wi res-l wr dd, % edierbd, at times 1 2 3 4 5 6 7 8 9 10 11 12 nedra-1m (rus) vwd 100 62 3 ves 48 13.9 71.0 0.56 790 0.99 dissolvan-4411 (germ) wd 100 62 3 hlws 48 8.0 83.3 0.97 792 0.99 dissolvan v 5748 (germ) wd 100 62 3 delam 48 7.6 84.2 1.02 789 0.99 dissolvan-4795 (germ) wd 100 62 3 cmf 48 9.0 81.2 0.87 630 1.24 dissolvan-4397 (germ) wd 100 62 3 cmf 48 9.6 80.0 0.81 810 0.97 ikhlas-1 pns sd 100 62 3 st da 48 0 100  18 43.5 ikhlas-3 pns sd 100 62 3 st da 48 0 100  35 22.4 ikhlas-37 pns hed 100 62 3 st da 48 0.13 99.7 60.0 21 37.3 demtrol-2020 (usa dow) vwd 100 62 3 stable 48 21.1 56.0 0.37 882 0.88 demtrol-2025 (usa dow) vwd 100 62 3 stable 48 21.6 55.0 0.36 880 0.89 demtrol-2030 (usa dow) vwd 100 62 3 stable 48 24.4 49.2 0.32 889 0.88 dmo-86520 (usa bh) vwd 100 62 3 ст 48 12.4 74.2 0.63 527 1.48 randem-2208 (usa rn) wd 100 62 3 ves 48 7.0 85.4 1.11 529 1.48 randem-2219 (usa rn) wd 100 62 3 stable 48 9.5 80.2 0.82 789 0.99 сontrol 62 3 48 34.0 29.2 0.23 828 0.95 randem-2201 (bd) wd 100 62 3 ves 48 7.8 (bd) 83,7 783(bd) crude oil from the “zhetybai” field of “mangistaumunaigas” jsc of rk demulsifier name demeffic sc, g/t td, ℃ , hours dem. stab con. of wat, % deid rocw, mg/dm3 deder bd, at times init-l wi res-l wr dd, % edierbd, at times 1 2 3 4 5 6 7 8 9 10 11 12 5 (chin com-y pe) pns hed 100 64 3 st da 45 0.12 99.7 124 47 14.5 6 (chin com-y pe) pns sd 100 64 3 st da 45 0.07 99.8 213 42 16.2 7 (chin com-y pe) pns sd 100 64 3 st da 45 0 100  43 15.8 8 (chin com-y pe) pns sd 100 64 3 st da 45 0 100  31 21.9 9 (chin com-y pe) pns sd 100 64 3 st da 45 0.09 99.8 165 32 21.3 10 (chin com-y pe) pns sd 100 64 3 st da 45 0.03 99.9 496 29 23.4 11 (chin com-y pe) pns hed 100 64 3 st da 45 0.15 99.7 99 49 13.9 12 (chin com-y pe) pns sd 100 64 3 st da 45 0.09 99.8 165 34 20.0 proxamine-385 (rus) vwd 100 64 3 stable 45 12.9 71.3 1,15 647 1.05 tnd (rus) wd 100 64 3 stable 45 3.7 91.8 2,60 81 8.4 snpx-4315d (rus) wd 100 64 3 stable 45 8.9 80.1 1.67 369 1.84 flek-d020 (rus) wd 100 64 3 stable 45 8.1 82.0 1.84 354 1.92 nedra-1m (rus) vwd 100 64 3 ves 45 13.2 70.6 1.13 830 0.82 dissolvan-4411 (germ) vwd 100 64 3 hlws 45 14.8 67.1 1.00 723 0.94 dissolvan v 5748 (germ) wd 100 64 3 delam 45 7.2 84.0 2.07 707 0.96 dissolvan-4795 (germ) wd 100 64 3 cmf 45 7.5 83.3 2 585 1.16 dissolvan-4397 (germ) vwd 100 64 3 cmf 45 9.6 78.7 1.55 764 0.89 ikhlas-1 pns sd 100 64 3 st da 45 0 100  23 29.5 ikhlas-3 pns sd 100 64 3 st da 45 0.06 99.9 248 38 17.9 ikhlas-26 pns sd 100 64 3 st da 45 0 100  24 28.3 ikhlas-37 pns hed 100 64 3 st da 45 0.15 99.7 99 25 27.2 demtrol-2020 (usa dow) vwd 100 64 3 stable 45 22.8 49.3 0.65 705 0.96 7 table 2. (continued). demulsifier name dem. effic sc, g/t td, ℃ , hours dem. stab con. of wat, % deid rocw, mg/dm3 deder bd, at times init-l wi res-l wr dd, % edierbd, at times 1 2 3 4 5 6 7 8 9 10 11 12 demtrol-2025 (usa dow) vwd 100 64 3 stable 45 23.1 48.7 0.64 716 0.95 demtrol-2030 (usa dow) vwd 100 64 3 stable 45 26.0 42.2 0.57 903 0.75 dmo-86520 (usa bh) vwd 100 64 3 stable 45 11.7 74.0 1.27 576 1.18 randem-2208 (usa rn) wd 100 64 3 ves 45 6.7 85.2 2.22 427 1.59 randem-2201 (usa rn) vwd 100 64 3 ves 45 10.2 77.4 1.46 601 1.13 сontrol 64 3 45 31.2 30.7 0.48 875 0.77 randem-2219 (bd) vwd 100 64 3 stable 45 14.9 (bd) 66.9 680 (bd) crude oil from the subsidiary llp “zhalgiztobemunai” field of rk demulsifier name demeffic sc, g/t td, oc , hours dem. stab con. of wat, % deid rocw, mg/dm3 deder bd, at times init-l wi res-l wr dd, % edierbd, at times 1 2 3 4 5 6 7 8 9 10 11 12 5 (chin com-y pe) pns hed 400 80 10 st da 32 0.18 99.4 25 50 17.9 6 (chin com-y pe) pns hed 400 80 10 st da 32 0.12 99.6 37.5 42 21.3 7 (chin com-y pe) pns hed 400 80 10 st da 32 0.09 99.7 50 37 24.2 8 (chin com-y pe) pns sd 400 80 10 st da 32 0 100  27 33.1 9 (chin com-y pe) pns hed 400 80 10 st da 32 0.09 99.7 50 39 22.9 10 (chin com-y pe) pns sd 400 80 10 st da 32 0 100  27 33.1 11 (chin com-y pe) pns ed 400 80 10 st da 32 0.45 98.6 10 46 19.4 12 (chin com-y pe) pns hed 400 80 10 st da 32 0.21 99.3 21.4 33 27.0 proxamine-385 (rus) vwd 400 80 10 stable 32 9.3 70.9 0.48 917 0.97 tnd (rus) wd 400 80 10 stable 32 3.7 88.4 1.21 97 9.2 snpx-4315d (rus) wd 400 80 10 stable 32 5.4 83.1 0.83 911 0.98 flek-d020 (rus) wd 400 80 10 stable 32 4.9 84.7 0.92 599 1.49 nedra-1m (rus) vwd 400 80 10 ves 32 9.8 69.3 0.46 1170 0.76 dissolvan-4411 (germ) vwd 400 80 10 hlws 32 11.2 65.0 0.40 1184 0.75 dissolvan v 5748 (germ) wd 400 80 10 delam 32 6.2 80.6 1.73 925 0.96 dissolvan-4795 (germ) wd 400 80 10 cmf 32 5.9 81.6 0.76 950 0.94 dissolvan-4397 (germ) vwd 400 80 10 cmf 32 7.2 77.5 0.63 1208 0.74 ikhlas-1 pns sd 400 80 10 st da 32 0 100  18 49.6 ikhlas-3 pns hed 400 80 10 st da 32 0.09 99.7 50 38 23.5 ikhlas-26 pns sd 400 80 10 st da 32 0.03 99.9 150 21 42.5 ikhlas-37 pns hed 400 80 10 st da 32 0.25 99.2 18 22 40.6 demtrol-2020 (usa dow) vwd 400 80 10 stable 32 16.4 48.8 0.27 1405 0.64 demtrol-2025 (usa dow) vwd 400 80 10 stable 32 17.6 45.0 0.25 1436 0.62 demtrol-2030 (usa dow) vwd 400 80 10 stable 32 19.1 40.3 0.23 1490 0.60 dmo-86520 (usa bh) vwd 400 80 10 stable 32 9.3 70.9 0.48 1066 0.84 randem-2208 (usa rn) wd 400 80 10 ves 32 5.6 82.5 0.80 902 0.99 randem-2219 (usa rn) vwd 400 80 10 stable 32 7.4 76.9 0.61 1112 0.80 сontrol 80 10 32 28 12.5 0.16 1134 0.77 randem-2208 (bd) wd 400 80 10 ves 32 4.5 85.9 894(bd) notes: dem. effic—demulsifier efficiency; sc, g/t—specific consumption of demulsifiers; td—demulsification temperature; , hours—is the settling time of the bottle tests in a water bath at td; dem. stab—demulsifier stability; con. of water, %—concentration of water in oil; init-l wi—initial water; res-l wr—residual water; dd—degree of demulsification, dd = (wi – wr)/wi100, %; deid—destruction efficiency of inverse emulsions; edierbd—the effectiveness of the destruction of inverse emulsions relative to 8 the base demulsifier. edierbd = wrbd / wrtd, (at times) wrbd—residual water in the case of base demulsifier, wrtd—residual water in the case of test demulsifier; rocw—residual oil concentration in water, мг/дм3; dederbd—destruction efficiency of direct emulsions relative to the base demulsifier, dederbd = rocw (bd) / rocw (td), bd—base demulsifier, td—test demulsifier; in expl—in exploitation; aop—annual oil production per field, t; pns—polynanostructured; st—stable; da—desuspensifier ability; —oil density, kg/m3; tpp—pour point of oil; ves-visco—elastic systems; hlws—high level of water solubility; delam—delamination; cmf—a curd mass is formed; sd—super demulsifier: dd = 99.8–100%; hed—highly effective demulsifier: dd = 99.0–99.8%; ed— effective demulsifier: dd = 97.0%–99.0%; wd—weak demulsifier: dd = 80.0%–97.0%; vwd—very weak demulsifier: dd = up to 80.0%; bh—baker hughes; rn—rauan-nalco. 3. results and discussions 3.1. requirements for demulsifiers building upon the authors’ extensive experience in the field of primary oil preparation (ppo)[26] and considering relevant literature sources[27], a comprehensive set of requirements for demulsifiers was developed for the first time at the nanotechnology level. 1) demulsifiers must be effective, that is, ensure high quality of the resulting oil at minimum specific consumption, minimum settling time and minimum temperature; 2) demulsifiers must have a higher surface activity in the phase into which they are introduced (dispersion medium); 3) demulsifiers must have good dispersion properties in a dispersion medium to increase the contact surface with particles of the dispersed phase water droplets of different sizes with molecular adsorption layers (mal) around the perimeter; 4) demulsifier molecules must have sufficient peptization property (sol-gel transition) to ensure its release due to adsorption on the mal (“protective coating”) formed around the particles of the dispersed phase; 5) the demulsifier molecules must have strong wetting properties towards the mal components; 6) demulsifier molecules should not form a continuous film around particles of the dispersed phase; 7) demulsifiers must have low viscosity (no more than 100 mpas), not be subject to delamination and hardening at low temperatures for a long time (at least during the warranty period, for example 1–3 years); 8) demulsifiers must ensure high quality of formation water separated under ppo conditions, which can allow its use in a reservoir pressure maintenance system (rpm) without additional preparation (removal of oil and mechanical impurities); 9) demulsifiers should not cause corrosion of pipes and equipment and should not have a negative impact on the effectiveness of other reagents used (for example, scale inhibitors, paraffin deposits, corrosion inhibitors, etc.); 10) demulsifiers should not be subjected to coagulation in formation waters; 11) demulsifiers must have anti-foam properties; 12) it is desirable that the demulsifiers be oil-soluble nonionic surfactants (ns); 13) demulsifiers must have a high speed of action; 14) demulsifiers must exhibit thermodynamic and aggregative stability in various technical, thermal, technological and climat conditions of ppo; 15) demulsifiers for the destruction of oil emulsions (w/o—reverse emulsion; o/w—direct emulsion; w/o/w—medium emulsion) and other oil nanocolloids under ppo conditions hdwoe (hard to destroy water-oil emulsions), hdwos (hard to destroy water-oil suspensions), trap oil, pit oil, bottom sediments of technological and commercial tanks, oil sludge, crude oil with viscoelastic properties or crude oil with structural and rheological properties; demulsifiers used to ensure high disintegration of gas hydrates, etc. must be nanodemulsifiers with a polynano structure; 16) the surface pressure for a nanodemulsifier must be at least 40–42 mj/m2; 9 17) to ensure maximum efficiency of the thermochemical method in the processes of demulsification of all types of oil emulsions, it is more expedient for nanodemulsifiers to be in a hybrid state of aggregation of the liquid crystalline type (the concept of “hybrid state of aggregation” for organic substances is used for the first time)[26]; 18) the components of the active phase of the nanodemulsifier should exhibit a synergistic effect during the breakdown of reverse, direct and medium emulsions; 19) the presence of wetting agents in the composition of a highly effective nanodemulsifier, consisting of n-aliphatic alcohols of the neonogenic surfactants type, oxyethylene esters of acids, creates maximum wetting (cos = 0 or cos  0) in the molecular adsorption layers around the particles of the dispersed phase. (“protective coating”), and the emulsions undergo complete decomposition; 20) highly efficient nanodemulsifiers must have minimum values of interfacial tension (m) at the boundaries of the water-oil partition (m = 0 or m  0); 21) highly effective nanodemulsifiers should not exhibit emulsifying properties regardless of the specific application of the nanodemulsifier for all types of petroleum emulsions. it is for this reason that the use of demulsifiers with an antagonistic effect in ppo technologies is absolutely unacceptable; 22) it is advisable to replace surfactants injected into wells, used in these fields to increase the oil recovery factor to nanodemulsifiers (or demulsifiers); 23) by switching to full downhole demulsification using nanodemulsifiers in oil fields, it is possible to achieve the maximum elimination of possible negative consequences in primary oil treatment technologies, including the maximum level of purification of oil from formation water and salt, as well as formation water from oil; 24) critical nanoemulsions that provide a synergistic effect with the active phase are considered one of the most suitable solvents for nanodemulsifiers; 25) the active phase of demulsifiers should not produce viscoelastic systems with a solvent; 26) molecules of the active phase of demulsifiers should easily overcome polynanostructural barriers existing in the dispersion medium and dispersed phase of crude oil; 27) it is inappropriate to include nanopowders in demulsifiers and nanodemulsifier compositions, which can further increase the stability of oil emulsions; 28) the presence of organochlorine compounds in the composition of the demulsifier is unacceptable; 29) surfactants with intramolecular surface activity, characterized by complex interactions simultaneously with hydrophobic and hydrophilic phases, can be highly effective demulsifiers of oil emulsions; 30) demulsifiers may also have depressant, anti-corrosion and bactericidal properties; 31) demulsifiers can also act as a nanodesuspensifer (the terms “nanodesuspensifer” and “desuspensifer” in general are used for the first time), allowing for the cleaning of bottom sediments of reservoirs consisting of a mixture of hdwoe and hdwos; 32) demulsifiers can also perform inhibitory and dissolving functions for viscoelastic systems (ves) under conditions primary preparation of oil; 33) under conditions of primary preparation of oil, demulsifiers can also perform inhibitory and dissolving functions for gas hydrates; 34) demulsifiers can also perform a neutralizing function against hydrogen sulfide and iron sulfide contained in oil; 35) demulsifiers must have high surface activity for the dispersive, dispersed phases of all types of oil emulsions, as well as for the mat phase (or “protective coating”, mat is considered for the first time as a separate phase); 36) demulsifiers must also operate under cold demulsification conditions; 37) the boiling point of demulsifier solvents should not be lower than 50 ℃–60 ℃; 10 38) demulsifier solvents should not be carcinogenic; 39) demulsifiers should not viscoelastic systems create in oil emulsions; 40) the main reason for phase separation in demulsifiers from the point of view of system stability is the thermodynamic incompatibility of the constituent components. therefore, the thermodynamic compatibility condition must be met for the demulsifier components; 41) highly effective demulsifiers must have a polynano structure to easily overcome persistent polynano barriers in crude oil at relatively high asphaltene concentrations (3%) and relatively high crude oil densities (830–840 kg/m3); 42) highly effective demulsifiers must have the properties of crystalline liquids; 43) highly effective demulsifiers should have the properties of eternal intramolecular nanomotors; 44) highly effective demulsifiers should ensure the simultaneous destruction of oil-water and oil-water emulsions due to the redistribution of oligomer homologues of the most hydrophobic oxyethylene ethers in water-oil emulsions, and the most hydrophilic oligomers in oil-water emulsions with high-strength nanodispersed phases that also have the properties of crystalline liquids. in this case, demulsifiers must provide the necessary qualities of commercial oil (residual water of water no more than 0.5%; chloride salts no more than 100 mg/dm3; mechanical impurities no more than 0.05%) and produced water (oil no more than 50 mg/dm3) for reinjection into the reservoir in the reservoir pressure maintenance system (maintaining reservoir pressure); 45) representatives of the newest generation of highly effective demulsifiers should be nanodemulsifiers with a polynano structure, intramolecular and intermolecular synergy, multifunctional and universal nature. we formulated requirements 14–45, while the known requirements (1–13) were edited. therefore, the development and utilization of nanodemulsifiers that effectively meet the demands of ppo conditions is considered a top priority in the field of oilfield nanotechnology. 3.2. crystalline liquids in addition to the traditional states of matter (gaseous, liquid, solid), there are also hybrid states of matter. therefore, liquid crystals can be considered as a hybrid of liquid and solid (crystalline) state of matter. in our perspective, it is crucial to determine which state of aggregation predominantly influences the hybrid version, as this aspect has not been previously addressed[7]. the liquid state of aggregation plays a dominant role in liquid crystalline hybrid states. therefore, it is necessary to conditionally note the cases of hybrid units. it can be assumed that the first letter represents the dominant role in the hybrid. the lc (liquid crystal) symbol is suitable for liquid crystal state hybrids. it is known that the solid state of matter can exist in crystalline and amorphous forms. therefore, in the case of a liquid-amorphous hybrid, if liquid predominates, the corresponding sign will be la. with this approach, the following possible hybrid aggregated cases can be considered: lc; la; cl; al; lg; gl; cg; ag; gc; ga (where l: liquid, к: crystal, a: amorphous, g: gas). the problem being discussed is highly significant as it represents a novel area in colloidal chemistry, modern molecular physics, petrochemicals, petrochemical physics, oilfield nanotechnologies, and petroleum nanotechnologies. this is because there is a lack of information regarding the hybrid aggregative state of organic substances. additionally, according to the adsorption theory developed by academician m.m. dubinin and his students, it is established that the adsorbed gas state in nanoporous adsorbents corresponds to the state of the corresponding liquid[28]. consequently, the state of absorbed water in the form of interconnected nanoheterogeneous associative colloidal water clusters in the nanodispersed phase of water-oil emulsions will be adequate to a hybrid state such as a crystalline liquid. we were the first to observe this phenomenon in nanosuspensions[18]. therefore, the investigation of this issue in 11 emulsions is being examined for the first time. demulsifiers with the visual aggregate state of a crystalline liquid are demonstrated in figure 1: (a) (b) (c) figure 1. some samples of nano-demulsifiers “ikhlas” with visual aggregate states of crystalline liquids (for the first time) in glass bottles in vertical and horizontal positions: (a): “ikhlas”—6003-20; (b): “ikhlas”—5003-15; (c): “ikhlas”—4003-10[29]. 3.3. the phenomenon of simultaneous destruction of water-oil and oil-water emulsions worth noting that such phenomenon is being explored for the first time. it is known that during the synthesis of ethoxylated esters of n-alcohols, acids and other compounds generally non-colloidal surfactants, a certain mixture of oligomer homologues[30–32], is formed, with a certain pattern in the distribution of monomers in the mixture depending on the number of oxyethylene units (n) in surfactant molecules[30]. industrial samples of such ethers are characterized by an average number n[33]. demulsifiers are mainly ester products of block copolymers based on ethylene and propylene oxides[25,34]. consequently, demulsifiers are also mixtures of homologues of oligomers with certain n values, which are often expressed in terms of the mass fraction of the oxyethylene chain in the demulsifier molecules. when dosing a demulsifier into crude oil, a redistribution of oligomer homologues occurs in oil-water and oil-water emulsions. monoesters with relatively low n values, i.e., the most hydrophobic components are distributed in water-oil emulsions, and components with relatively high n values, i.e., relatively hydrophilic components pass into the oil-water emulsion[35]. due to a similar redistribution of oligomer homologues in crude oil, the phenomenon of simultaneous destruction of water-oil and oil-water emulsions occurs and as a result, commercial oil is obtained with a water content of no more than 0.5%, as well as produced water (formation water) with an oil content of no more than 50 mg/dm3, which comply with current standards[20,21]. therefore, demulsifiers of the ihlas (xx) brand with a polynano structure are designed for the simultaneous destruction of oil-water and oil-water emulsions[25]. the polynanostructure of demulsifiers generally contributes to the high intensity of destruction processes of both types of oil emulsions[17]. it should be noted that the results of laboratory tests coincide with the results of pilot industrial tests. as an example, we can show the karazhanbasmunai field. in both cases, the content of residual water in oil (0.06; 0.17) and the content of oil in wastewater (36 mg/dm3; 36 mg/dm3) practically coincide and are confirmation of the discovery in question “the phenomenon of simultaneous destruction of oil-water and oil-water emulsions”. furthermore, the authors of 12 the karazhanbasmunai field discovery have established an empirical formula co = 10.3 m + 36.1 (1) where, co is the residual concentration of oil in the composition of produced water during oil recovery; m— interfacial tension at the water-oil interface. for polynanostructured surfactant demulsifiers with the properties of crystalline liquids, intramolecular interblock activity and eternal intramolecular nanomotors such as block copolymers of ethylene and propylene oxides, the values of m are practically equal to zero. consequently, at m  0 co  36.1 mg/dm3, which also confirms the reliability of the results of laboratory and industrial tests. moreover, the co-author of this discovery, t. k. dashdieva, conducted further extensive research on this topic as part of her dissertation titled “development and implementation of nanodemulsifiers for the purification of formation waters from oil under conditions of primary oil treatment”. work performed by polynanostructured surfactants demulsifiers, which have the properties of crystalline liquids, intramolecular interblock activity and eternal intramolecular nanomotors for overcoming polynanobarriers in crude oil, as well as for the simultaneous destruction of water-oil and water-oil emulsions, is determined precisely by ultra-low values (m = 0 or m  0) of interfacial tension. this is the eternity of intramolecular nanomotors. another condition for highly effective nanodemulsifiers is the requirement for surface pressure, which must be at least 40–42 mj/m2. issues with the synthesis of these nanodemulsifiers are given in our paten[25]. the characteristics of the studied nanodemulsifiers meet all the requirements for demulsifiers and are within the listed criteria (see pages 4–6 of the article for details). 3.4. calculation of the sizes of perpetual nanomotors such as block copolymers of ethylene and propylene oxides for perpetual nanomotors such as block copolymers of ethylene (–ch2ch2o–) and propylene (–сн2сн2–ch2о–) oxides based on glycerine; the cross section (s) of the molecules is s = 78 × 10−20 m2[29]. calculation of the diameter (d) of the cross section or height of the stator (oxypropylene circuit): s =  d2/4 d2= 4 s/ =99.4 × 10−20 m2 d  10 × 10−10 m = 1 nm. it is known that the cross section (s) of the oxyethylene chain is 23 × 10−20 m2[30]. s =  d2/4, d2 = 4, s/ = 29.3 × 10−20 m2, d  5.4 × 10−10 m = 0.54 nm. consequently, the diameter of the rotor (oxyethylene chain) is 1.85 times smaller compared to the stator (oxypropylene chain). the demulsifier surfactant molecule performs the function of a platform for an eternal nanomotor in accordance with the discovery formula. the contact of the rotor at the stator input is determined by the chemical covalent bond of oxygen between the extreme group of the oxyethylene chain and the carbon atom also with the extreme group of the oxypropylene chain, i.e. at the interblock boundary of surfactant demulsifier molecules, i.e., at the interface between the highly hydrophobic oxypropylene chain and the highly hydrophilic oxyethylene chain, due to which there is a rotational movement of the rotor (oxyethylene chain), resulting in interblock activity, which is much stronger than the surface activity of conventional surfactants. it is due to interblock activity that the effect of destruction of oil emulsions is achieved. therefore, the key distinction between conventional surfactants and surfactant demulsifiers in terms of nanocolloid chemistry lies in the presence of interblock activity in demulsifier surfactant molecules based on oxyalkylene oxides, which is not observed in conventional surfactants. the perpetual nanomotor under consideration according to this discovery, in contrast to the only known perpetual nanomotor (works based on triboelectricity) zhong[13], works using polynanostructured nanoemulsifiers, which have the properties of crystalline liquids, intramolecular interblock activity and perpetual intramolecular nanomotors. thus, according to the proposed discovery, the dimensions of perpetual nanomotors are nanosized in all respects: stator with a diameter of 1 nm; rotor with a diameter of 0.54 nm; platform with a length of 19.9 nm. 13 through our research, we have determined that all existing demulsifiers, including block copolymers of ethylene and propylene oxides, fall into the category of triblock polyols. within this category, there are two options: 1st option oeb-opb-oeb water-soluble demulsifiers 2nd option opb-oeb-opb oil-soluble demulsifiers where oeb—oxyethylene block; opb—oxypropylene block. in practice primary preparation of oil mainly uses oil-soluble demulsifiers of the opb-oeb-opb type. in these three-block demulsifiers, there are 2 interphase boundaries in which, thanks to perpetual nanomotors, there is exists interblock activity of surfactant demulsifiers. it would be reasonable to increase the overall interblock activity and thereby enhance the efficiency of the corresponding demulsifiers with an increase in the number of blocks to a certain value: opb–oeb–opb–oeb–opb 5-block opb–oeb–opb–oeb–opb–oeb–opb 7-block opb–oeb–opb–oeb–opb–oeb–opb–oeb–opb 9-block opb–oeb–oeb–oeb–opb–oeb–opb–oeb–opb–oeb–opb 11-block the authors conducted tests using bottle tests and found that for crude oil possessing polynanobarrier properties, the most effective demulsifiers in terms of simultaneously breaking water-oil and oil-water emulsions are 7and 9-block polynanostructured demulsifiers based on monohydric aliphatic alcohols. worth noting that demulsifiers, such as oxyalkylene block copolymers based on monohydric aliphatic alcohols, are being considered for the first time[7,17]. 3.5. experimental proof of the alleged scientific discovery we would like to reiterate that this priority article presents the findings of testing oil emulsions from the uzen, zhetibay, and zhalgiztobe fields as the subject of investigation. the highest specific consumption of demulsifier (up to 580 g/t) and the highest oil treatment temperature (up to 114 ℃) among the oil fields of kazakhstan and other regions are characteristic only of the zhalgiztobe field. worth noting that highly paraffinic (up to 25%–28%) crude oil from the “uzen”, “zhetibai” fields and the highly resinous “zhalgiztobe” field, which have polynanobarrier properties[7,17] including a nanodispersed medium, a nanodispersed phase and a nano-sized moleculars adsorptions layers with nanoparticle components from organic inorganic origin, are over complex nanoheterogeneous systems in relation to “the phenomenon of simultaneous destruction of water-oil and oil-water emulsions”. the data of the tables 1 and 2 are experimentals evidence of the scientific discovery “the phenomenon of simultaneous destruction of wateroil and oil-water emulsions” that occurs with the dosage of polynanostructured surfactants, demulsifiers, which have the properties of crystalline liquids, intramolecular interblock activity and eternal intramolecular nanomotors, unlike all researched known demulsifiers. 3.6. scientific novelty of the discovery (first achieved by the authors of this discovery)  the phenomenon of simultaneous destruction of water-oil and oil-water emulsions;  polynanostructure of surfactant demulsifiers;  new hybrid state of aggregation such as crystalline liquids of surfactant demulsifiers;  intramolecular interblock activity of surfactant demulsifiers;  the property of eternal intramolecular nanomotors of surfactants, demulsifiers such as block copolymers of ethylene and propylene oxides; 14  the phenomenon of redistribution of oligomer homologs of the most hydrophobic oxyethylene ethers in water-oil emulsions, and the most hydrophilic oligomers in oil-water emulsions;  new hybrid state of aggregation such as crystalline liquids also for nanodispersed phases of water-oil and oil-water emulsions. 3.7. area of scientific and practical significance of the proposed scientific discovery 3.7.1. area of scientific significance of the discovery (asssd) the scientific novelty of the discovery is determined based on individual points of scientific novelty of the proposed discovery: 1) for the first time, a previously unknown phenomenon of simultaneous destruction of oil-water and oilwater emulsions was established, due to the redistribution of oligomer homologues of the most hydrophobic oxyethylene ethers in oil-water emulsions, and the most hydrophilic oligomers in oil-water emulsions with high-strength nanodispersed phases, which also have the properties of crystalline liquids. the authors have also, for the first time, explored the hybrid state of aggregation of substances, specifically in relation to the crystalline liquid state[18]. future studies of the physicochemical, colloidal chemical and quantum mechanical properties of crystalline liquids are one of the priority areas of modern molecular physics; 2) the polynanostructure of surfactant demulsifiers is presented by the authors as one of the important requirements for demulsifiers: demulsifiers must have a polynanostructure to easily overcome persistent polynanobarriers in crude oil at a relatively high concentration of asphaltenes (3%) and relatively high densities of crude oil (830–840 kg/m3)[17]; 3) intramolecular interblock activity of surfactant demulsifiers. this is a very important property of surfactant demulsifiers, which determines the difference between conventional surfactants and surfactant demulsifiers. this direction will also be a priority for further research; 4) the property of eternal intramolecular nanomotors of surfactants, demulsifiers such as block copolymers of ethylene and propylene oxides and the phenomenon of redistribution of oligomer homologues of the most hydrophobic oxyethylene ethers in water-oil, and the most hydrophilic oligomers in oil-water emulsions are also innovative priority areas in the field of applied nanocolloid chemistry. 3.7.2. the area of the practical significance (aps) the aps is also determined based on individual points of scientific novelty of the proposed discovery which are closely linked to the name of the discovery itself: “the phenomenon of simultaneous destruction of oil-water and oil-water emulsions”. the practical significance of the discovery is confirmed by the results of pilot testing and the introduction of polynanostructured nanodemulsifiers of the “ikhlas” brand in rather complex fields of the republic of kazakhstan[14–18,25,26,29,34,35]. the annual actual economic efficiency from the implementation of this discovery stands at approximately $10,846,000 and in the period 2021–2023 $32,538,000 (there is an official certificate of economic efficiency from the implementation of the authors’ scientific discoveries in the oil fields of the republic of kazakhstan). furthermore, utilizing the insights provided by this discovery, it is feasible to conduct targeted synthesis of polynanostructured surfactant demulsifiers, such as block copolymers of ethylene and propylene oxides, which possess the characteristics of crystalline liquids, intramolecular interblock activity, and perpetual intramolecular nanomotors. this synthesis can be performed in a specialized installation, employing established technology. the authors of this discovery have strategically set their goal to achieve significant success in the global market for modern demulsifiers by leveraging these unparalleled surfactant demulsifiers, which currently have no alternatives. 15 4. conclusion the presented material is a priority article detailing a scientific discovery regarding “the phenomenon of simultaneous destruction of water-oil and oil-water emulsions”. the authors introduce a corresponding formula that describes this phenomenon. the previously unknown phenomenon of simultaneous destruction of water-oil and oil-water emulsions, which occurs with the dosage of polynanostructured surfactant demulsifiers possessing the properties of crystalline liquids, intramolecular interblock activity and eternal intramolecular nanomotors such as block copolymers of ethylene and propylene oxides (sources of oligomer homologues of oxyethylene ethers) in crude oil under conditions of primary oil preparation, due to the redistribution of oligomer homologues of the most hydrophobic oxyethylene ethers in water-oil, and the most hydrophilic oligomers in oil-water emulsions with high-strength nanodispersed phases, which also have the properties of crystalline liquids. author contributions conceptualization, dra and dtk; methodology, dra; experiments, dra and dtk; software, dra; validation, dra and dtk; formal analysis, dtk; investigation, dra; resources, dtk; data curation, dra; writing — original draft preparation, dra and dtk; writing—review and editing, dra and dtk; visualization, dtk; supervision, dra; project administration, dra. all authors have read and agreed to the published version of the manuscript. acknowledgments the authors of this research express their gratitude to the leaders of the azerbaijan state oil and industry university and “international oil services kazakhstan” llp for their support and collaboration. t.k. dashdieva, as a doctoral student, conducts her dissertation work under the agreement on scientific and technical cooperation between these organizations. conflict of interest the authors declare no conflict of interest. references 1. mirzajanzadeh ak. nanohydrodynamic effects based on the use of micronucleation technology (russian). mirzajanzade ak, bakhtizin rn, mustafaev aa et al. oilfield business, moscow: 2005. 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university of tabriz, tabriz 51666-16471, iran 2 pharmaceutical analysis research center, faculty of pharmacy, tabriz university of medical sciences, tabriz 5166414766, iran * corresponding author: karim asadpour-zeynali, asadpour@tabrizu.ac.ir abstract water splitting has been one of the potential techniques as a clean and renewable energy resource for the fulfillment of world energy demands. one of the major aspects of this procedure is the exploitation of efficient and inexpensive electrocatalysts due to the fact that the water oxidation procedure is accompanied by a delayed reaction. in this research, zno-cofe2o4 nanostructure was successfully synthesized via the green method and green resources from cardamom seeds and ginger peels for oxygen evolution reaction (oer). the modified glassy carbon electrode (gce) with znocofe2o4 is effective for the electrochemical water oxidation interaction since it has sufficient electrical strength and excellent catalytic performance. the creation of rice-like and small granular structures of zno-cofe2o4 nano-catalysts was confirmed by characterization methods such as xrd, fesem, eds and map. according to the achieved results, in the electrolysis of water, with in-cell voltage of 1.40 v and 50 ma cm–2 for current density in a 0.1 m koh electrolyte and oer only has 170 mv overpotentials. keywords: green synthesis; nanoparticles; zno-cofe2o4; cardamoms; ginger peels article info received: 16 october 2023 accepted: 24 november 2023 available online: 4 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction in today’s world fossil fuels are exploited as the primary resource of energy to meet world demands which in turn has led to the energy crisis, great harm to the environment, global warming and other issues[1,2]. thus, the development and application of an eco-friendly and renewable energy resource to decrease the usage of conventional fossil fuel is crucial for a sustainable economy and community[3]. in this regard, hydrogen (h2), as a suitable mass-energy density and non-carbonous emission source, exhibits an efficient capability for sustainable energy production which can be replaced with fossil fuel[4,5]. electrochemical water splitting is an effective method to achieve hydrogen with high purity at the cathode and this electrochemical process includes two half reactions, known as an oxygen evolution reaction (oer) and a hydrogen evolution reaction (her) at the anode at the cathode, respectively[6,7]. in real-world experiments, electrochemical reduction of water involves an excessive overpotential[8] which means, introducing sufficient modifiers to activate proton reduction by the lowest possible overvoltage for the her reaction and enhance the kinetics of oer is an indispensable stage for the current demands[9,10]. the most efficient water splitting 2 performance to date has been developed by means of noble metal-based electrocatalysts, principally pt-based and ir/ru-based electrocatalysts for her and oer procedures, respectively[11,12]. nonetheless, the precious metals’ expensiveness and their scarceness are major reasons for water splitting limitations on an industrial scale. thus, the investigation of non-precious options with sufficient activity and stability is imperative[13–15]. spinel ferrites-based compounds as cobalt ferrite nanostructures have various utilities in information storage and electronic devices[16,17], drug delivery[18], biological[19], and environmental[20] owing to the essential properties like inexpensiveness, mechanical hardness, excellent stability, acceptable curie temperature and high magnetic anisotropy. moreover, cobalt ferrite has a small band gap, which results in an increment in decomposition performance[21,22]. recently, zno semiconductors with exclusive properties like a nonpoisonous nature, band gap of roughly 3.3 ev, remarkable photosensitivity and thermal stabilities[23]. photocatalytic activity results due to the movement of photogenerated holes and electrons to the surface which conduce pollutant degradation under uv and visible irradiations[24,25]. surface modifying, doping and coupling with other compounds like semiconductors are instances of the approaches that are employed to improve the catalytic performance of zno[26–28]. cerium oxide is an excellent example of this agenda that is utilized in diverse research like gas sensors, h2s removal, eco-friendly pigments, catalyst and etc.[29–33]. several procedures have been established to produce zno-cofe2o4, including, hydrolysis of chelated zinc diethylene glycol alkoxide complexes in alkaline diethylene glycol solution at high temperature[34] and hydrothermal method with carbon nanoparticles as the template[24], microwave combustion[35], coprecipitation[36], sol-gel procedure accompanied by hydrothermal technique[37], and combustion process[38,39]. nevertheless, the aforementioned techniques involve sophisticated processes, intricate equipment, consuming chemicals, and high energy consumption, thus contributing to undesirable impacts on the ecosystem. biogenic resources are drawing growing attention because of their sustainability. some biogenic ingredients are recyclable and have possibility to be achieved from waste compounds, which substantially decreases their production expenditure[40–43]. more significantly, biogenic resources have the possibility to be manipulated to include definite catalytic features, making them an effectual choice for selective procedures[44,45]. these resources not only provide eco-friendly substitutes to synthetic catalysts due to biodegradability and nontoxicity, but also show enhanced stability and activity which make them adequate for various applications such as water splitting[46–48]. a promising approach for green synthesis is a hydrothermal method due to the fact that it employs water as a solvent and natural plants leaf extracts such as solanum nigrum[49], aloe vera[50] azadirachta indica[51], and camellia sinensis[52] as capping agents which monitor the nanoparticles of the chosen elements. one more example of a natural component been exploited for this agenda to produce nio nanocrystals is rambutan (nephelium lappaceum l.) peel extract from sapindaceae spices[53]. in this paper, zno-cofe2o4 semiconductor magnetic nanoparticles were produced by consuming cardamom and ginger peel extract. the benefits of this procedure involve the use of inexpensive, harmless and environmentally friendly materials, and an uncomplicated and time-saving process. the main element in cardamom and ginger peel extract is phenolic combinations acting as a capping agent, stabilizer and even chelating agent in order to capture the metal ions and monitor the formation of nanostructures. the morphology and structure of the synthesized zno-cofe2o4 were investigated with xrd, fesem, eds and map techniques. in addition, the electrochemical interactions zno-cofe2o4 in the oer process were assessed by monitoring cyclic voltammetry (cv), linear sweep voltammograms (lsv) and chronoamperometry techniques for stability analysis and tafel calculation in basic conditions. 2. experimental 2.1. reagents zinc acetate dihydrate ([zn(ch3co2)2]·2h2o) and sodium hydroxide (naoh) were bought commercially 3 from sigma-aldrich chemicals. compounds which are employed during this research were analytical grade and did not treat with any purification approaches also, deionized water was utilized in all experiments of this research. fresh cardamom seeds and ginger peels were bought from a local health store. all glassware were completely cleaned before executing each test and protective procedures was taken to prevent any contamination. the potassium hydroxide (koh), iron nitrate (fe(no3)3·9h2o), hydrogen chloride (hcl 37%) solution, cobalt nitrate (co(no3)2·6h2o), and ethanol were provided from merck. 2.2. synthesizing and preparation methods 2.2.1. green synthesis of zno fresh cardamoms were washed with distilled water to eliminate all contaminations, and then fully dried. the standard protocol accompanying little modification was employed to prepare the extract. first 5 g of cardamoms were boiled in 100 ml distilled water for 20 min at 80 °c, and the extract was obtained from filter paper at room temperature. the resulting filtered extract was utilized for further investigation. in order to prepare 0.2 m zinc acetate solution 2.2 g of powdered ([zn(ch3co2)2]·2h2o) was poured in 50 ml of distilled h2o and stirred on a magnetic stirrer until fully dissolution. then, 50 ml of this extract was added gradually to 50 ml of [zn(ch3co2)2]·2h2o accompanying continuous solution stirring, which was followed by drop-bydrop addition of 10 ml of 1 m naoh solution. a yellowish-white sediment was attained instantly after pouring sodium hydroxide solution. in the next step, the precipitate was washed with ethanol three times and centrifugated at 5000 rpm for 10 min and the precipitate was separated and completely dried in a vacuum. finally, zno-nps green sedimentation was calcinated at 400 ℃ in a muffle furnace. 2.2.2. cofe2o4 green synthesis 20 g of ginger root were sliced into 100 ml of deionized water and the admixture underwent a boiling process for 5 min, the color of the solution altered to yellow (ph ~ 6). then temperature of this extract decreased at room temperature and filtered. also, 10 g of cardamom seeds were ground and resulted in yellow-brown sediment was added and stirred in 100 ml of deionized water after 4 h of boiling, the precipitate was separated from the solution and the brown separated sediment was cooled at room temperature. in the next step, metal nitrates (2fe3+:1co2+) were added gradually within stirring conditions to the aqueous seeds extract, respectively. then these combinations (ph ~ 2) were brought to a gel-like concentration with a thermal treatment process at 80 ℃ and these gels were heated at 250–300 ℃ which is accompanied by an initial gel melting process which is followed by a spontaneous self-ignition, leaving behind a magnetic foam (selfcombustion). during this exothermic procedure, the admixture of nitrates and plant extracts acts in the same way as common oxidants and fuels. the final step was the calcination of the magnetic foams at 800 ℃ for 1 h in order to enhance the crystallization degree. 2.3. characterization of catalysts and electrochemical performance the crystalline structure was investigated with the x-ray diffraction analysis with siemens d500 and 2θ spectra range from 10 to 80. in order to investigate the morphology of the synthesized nanostructure fesem (model: tescan and mira3). also, the chemical structure of the developed nanostructures was further investigated with an eds attached to fesem and ft-ir analysis was executed with shimadzu 8400 (japan). electrochemical analyses were executed by mean of an eg&g model 273 potentiostat/galvanostat instrument accompanied with gce as a working electrode, an ag/agcl electrode as a reference electrode and a platinum as a counter electrode (there electrode system), all these electrodes were bought from azar electrode co., urmia, iran. during the study, the standard reversible hydrogen electrode (rhe) was utilized to calculate the electrochemical potentials. the nernst equation (1): erhe = eag/agcl + 0.059 ph (13) + e0 ag/agcl (1) which was employed to convert the obtained potential based on the ag/agcl to the rhe potential (equation 4 2). eag/agcl = 0.198 v (at 25 celsius degree temperature) (2) also, the 0.1 m koh is used as electrolyte. in order to accomplish oer analysis, linear sweep voltammetry (lsv) and cv assessment were performed at a scan rate of and potential limit of 0–1.6 v vs. ag/agcl. furthermore, its stability in the basic solution was studied by the chronoamperometry technique. the tafel slope is achieved from equation (3): 𝜂 = 𝑏 × 𝑙𝑜𝑔 𝑗 𝑗 (3) (ŋ: overpotential, b: tafel slope, 𝑗: current density, 𝑗 : exchange current density[54,55]). 3. result and discussion 3.1. characterization 3.1.1. x-ray diffraction investigation synthesized zno-cofe2o4 nps exhibited sharp diffraction peaks which is a testimony to the decent crystallinity of this synthesis illustrated in figure 1. diverse peaks relating to the 2θ value were obtained in 31.9, 34.5, 36.2, 40.6, 42.7 56.6, 62.9, 66.4, 68 and 69.36. moreover, the characteristic peaks relating to (hkl) values of (111), (220), (311), (222), (400), (511), and (440). these values are in accordance with the hexagonal wurtzite structure of zno based on the joint committee on powder diffraction studies standards. the x-ray diffraction results of the nanostructure attained from the self-combustion procedure utilizing the aqueous extract of ginger and cardamom accepted the correct synthesis of zn-cofe2o4 which is in good agreement previously reported research. the purity of produced nanoparticles was confirmed by the absence of any other peak[56,57]. figure 1. xrd pattern of green synthesized zno-cofe2o4. 3.1.2. fesem & edx in order to investigate the green synthesized zno-cofe2o4 nps morphological characteristics field emission scanning electron microscopy (fesem) was exploited. fesem micrographs of the nanostructure in 200 nm (figure 2) demonstrated the synthesizing of very fine nanograined agglomerates with equiaxed nanocrystals. sem analysis of the nanoparticles in 500 nm (figure 3) confirms the existence of porous nanograined agglomerates structure with the mainstream remaining equiaxed and limited faceted crystals. based on the micrograph image, a rod-shaped and identic ordination is observable which is in good accordance 0 50 100 150 200 250 10 20 30 40 50 60 70 80 in te ns it y a .u . 2 degree (0 02 )* (2 20 ) (3 11 ) (2 22 ) (5 11 ) (4 40 ) (4 00 ) *zno jcpds , card no. 36-1451 cofe2o4 jcpds, card no. 22-1086 (1 01 )* (1 02 )* (1 10 )* (1 12 )* 5 with green approaches for producing zno-cofe2o4 nps. as its observable edx spectroscopy results in the samples attained utilizing ginger and cardamom green extract, all the expected major elements including co, o, fe and zn were detected. xrd and eds graphs are an indication of successful synthesis for a threecomponent nanostructure[58,59]. 3.1.3. ftir analysis in order to investigate the possible interaction between zno and cofe2o4 and sustain the formation of zno-cofe2o4 spinel structure, the ftir spectra of ginger root and cardamom seeds aqueous extracts were accomplished from 400 to 4000 cm–1 and the obtained spectra exhibited major bands of phenolic hydroxyl group (-oh) representing hydrogen bonding in flavonoids (figure 4). the interaction of zno and cofe2o4 causes an alteration in the zn-o and fe-o bond absorption area. furthermore, emerging two significant bands between 400–800 cm–1 wavelength were assigned to the stretching vibration of the fe-o bond and the stretching vibration of zn-o and co-o in the three composite structures[60]. the peaks at 556 and 454 cm–1 are attributed to the stretching vibration of the fe-o and co-o bond. the peaks at around 546 cm–1 are attributed to the stretching vibration of the fe-o bond and the peaks around 410–432 cm–1 to the stretching vibration of zn-o and co-o in the composite samples. figure 2. sem image of zno-cofe2o4 nanostructure in (a) 500 nm and (b) 200 nm scales. figure 3. (continued). o fe fe fe co co co zn zn zn kev0 100 200 300 400 500 600 700 0 5 10 a b a elements w% o 25.15 fe 28.10 co 14.25 zn 32.50 6 figure 3. (a) eds and mapping images of zno-cofe2o4 nanostructures, (b)–(e) its elements mapping separately, (f) the elements mapping simultaneously and (g) mapping and sem simultaneously. b c d e f g 7 figure 4. ftir spectra of zno-cofe2o4 nanoparticles. 3.1.4. uv–vis spectroscopy analysis uv–vis diffuse reflectance analysis was performed to explore the optical properties of the zno-cofe2o4 nanostructure. zno absorbs well in the uv region and it has little stimulation in the visible light wavelength, however, cofe2o4 indicates appropriate absorption in the visible region. as it is observable from figure 5, the characteristic peak of green zno-cofe2o4 was detected around 350 nm which resulted due to a high value of excitation binding energy. this result is in a good agreement with previous research which approves the correct synthesizing of zno-cofe2o4 nps[61]. figure 5. uv-visible spectra zno-cofe2o4 nanocomposite. 3.2. electrochemical measurements in this research, a conventional three electrode system within 1 m potassium hydroxide and 0.6–2.5 v vs. hre voltage range and a scan rate of 10 mv s–1 was employed. as is observable in figure 6, the lsv plots of bare gce and zno-cofe2o4 modified gce were studied in the aforementioned situation. polarization plots evaluation demonstrates the minimum electrocatalytic activity of bare gce, while zno-cofe2o4/gce shows satisfactory catalytic performance for oer with 170 mv for overpotential at 50 ma cm–2, diminishing overpotential defines enhancement in the kinetics of the oer process. what’s more, zno-cofe2o4/gce as 0.4 0.5 0.6 0.7 0.8 0.9 1 10050090013001700210025002900330037004100 t ra ns m it an ce wavenumber(cm-1) zn-o 541 432 m-o 556 fe-o 454 co-o 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 190 390 590 790 a bs or ba n ce (a .u .) wavelength(nm) (-oh) stretching vibration 34 8 noble-metal-free electrocatalysts in basic situations is desperately active for oer, which can be assigned to the synergistic impact of the zno and the cofe2o4 nanoparticles. in addition, the attendance of zno in the zno-cofe2o4/gce heterostructure improves the electrocatalyst electrical conductivity to increase the electrocatalytic performance. moreover, zno and cofe2o4 nanostructures create a 3d zno-cofe2o4 nanostructure with more existing active sites, providing more ways for the operative electrons transfer, and conductive gce offers a platform for growing active materials, which helps electrical conductivity between the gce and the developed electrocatalysts. according to obtained lsv plots, the oxygen evolution peak of zno-cofe2o4/gce is located at ~1.42 v vs. rhe. tafel plot was utilized for the oer catalytic kinetics evaluation. as it is illustrated in figure 7, the znocofe2o4/gce has the lowest tafel slope with 88.56 mv dec–1. also, the zno and cofe2o4 exhibit higher tafel slop of 121.1 and 167.57, respectively, which means zno-cofe2o4/gce displays a faster kinetic and enhanced catalytic performance for oer. figure 6. linear sweep voltammograms of zno-cofe2o4, cofe2o4, zno and bare electrode. considering the lower overpotential and tafel slope, which can be a good proof for the respective activity of zno-cofe2o4/gce synthesized by adequate hydrothermal approach, zno-cofe2o4/gce was selected as an ideal electrocatalyst in this present investigation. based on the lower tafel slope value and overpotential of the zno-cofe2o4/gce catalyst is an illustration for faster performance and sufficient kinetics toward oer activity than other synthesized catalysts. figure 7. tafel plots of zn-cofe2o4, cofe2o4 and zno nano catalysts. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 c ur re nt d en si ty ( ma /c m 2 ) e / rhe (v) \ y = 88.566x 68.514 r² = 0.8013 y = 121.1x 149.31 r² = 0.9677 y = 167.57x 231.16 r² = 0.9842 0 10 20 30 40 50 60 70 80 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 j / ( ma /c m 2 ) e / rhe (v) zno-cofe2o4 cofe2o4 zno 9 one of the major criterions for every catalyst in electrochemistry is its electrochemical stability which can be analyzed with the chronoamperometry method. undoubtedly, the current density and time (j-t) plot indicated the premiere electrochemical stability of zno-cofe2o4/gce for a 15 h electrolysis reaction under a basic situation (figure 8). instantaneously, the catalytic stability of zno-znfe2o4/gce before and after 500 cycles was examined by continuous sweeps and, the polarization plot of zno-cofe2o4/gce after 500 cycles exhibited insignificant variation from that initial condition. figure 8. chronoamperometry plots of zno-cofe2o4 modified electrode with potential steps of (a) 0–1.2, (b) 0–1.1, (c) 0–0.10 and (d) 0–0.9 v in 0.1 m koh solution. in order to compare the efficiency of the catalysis prepared by the green method with other catalysts that have been published for water oxidation in recent years, table 1 has been prepared. as can be seen in this table, the tafel slope and overpotential of this research are comparable to the results in the literature. table 1. comparison of the oer activities of some recently reported catalysts for water oxidation. catalyst tafel slope (mv dec−1) solution over potential (mv) current density references aloe-vera-mediated niox 95 naoh 413 10 ma cm−2 [62] moo4 2− intercalating α-co(oh)2 nanosheet 57.78 1 m koh 303 10 ma cm−2 [63] ni–feooh/ni(oh)2 16.8 1 m koh 264 20 ma cm–2 [64] pr3ir1−xmoxo7 50.52  0.1 m hclo4 259 10  ma cm−2 [65] zn-doped ruo2 41.2 0.5 m h2so4 173 10 ma cm–2 [66] ni-fe-co film 34.7 1 m koh 314 10 ma cm−2 [67] comn-ldh@cuo/cu2o 89 1 m koh 297 10 ma cm−2 [68] cafe6ge6/nf 43.35 1 m koh 322 10 ma cm−2 [69] sf[fe-tol-ni] 103 1 m koh 480 1 ma cm−2 [70] ni-feooh/nf 52 1 m koh 277 100 ma cm−2 [71] co3o4/pr2o3 78 alkaline 257 10 ma cm−2 [72] co3o4@knbo3 61 1 m koh 330 10 ma·cm−2 [73] zno-cofe2o4 88.56 0.1 m koh 170 50 μa cm–2 this work 4. conclusion a green and facile procedure for synthesizing the innovative, effective and stable zno-cofe2o4 electrocatalyst as a modifier for gce was introduced, which exhibits a noteworthy oer performance in alkaline circumstances. additionally, zno-cofe2o4/gce has an acceptable specific surface area and porous structure and enhanced accessible active sites and the rate of electron transfer that provides the oer exceptional performance accompanying a low overpotential of 222 mv and a tafel slope of 88.56 mv dec–1 for oer. the kinetics of water oxidation were studied with the tafel slope technique. demanding a voltage of 1.45 v at 5 ma cm–2 in a water oxidation procedure within three electrode system is a demonstration of -5 0 5 10 15 20 25 30 35 0 100 200 300 400 500 c ur re nt d en si ty (m a /c m 2 ) time (s) a d 10 excellent electrochemical efficiency for the zno-cofe2o4/gce this work developed a mixed transition metal as an inexpensive electrocatalyst for stable and green oer analysis in basic situations, which has the capability to be employed in other applications like renewable energy storage and other energy conversion methods. this research also provides a novel strategy for accomplishing effective water oxidation with nanostructured transition metals. we assign this outstanding water oxidation activity to the excellent synergistic effects, in situ evolution on the stable conductive substrate and attendance of active oer compounds. author contributions conceptualization, kaz and mhbk; methodology, ak and mhbk; software, mhbk; validation, ak and mhbk; formal analysis, mhbk; investigation, ak and mhbk; resources, kaz; data curation, ak and mhbk; writing—original draft preparation, ak and mhbk; writing—review and editing, kaz; visualization, ak and mhbk; supervision, kaz; project administration, kaz; funding acquisition, kaz. all authors have read and agreed to the published version of the manuscript. acknowledgements the financial support from the university of tabriz is gratefully acknowledged. conflict of interest the authors report that there is no conflict of interest to 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grupo de investigación e innovación en formulaciones químicas, escuela de ciencias de la vida, universidad eia, envigado, colombia. e-mail: pedronel.araque@eia.edu.co 2 laboratorio clínico hematológico, carrera 43c no 5–33, medellín, colombia. abstract this study focused on the formulation and characterization of silver nanoparticles (agnp) functionalized with d-limonene. the nanoparticles were functionalized by phase inversion and the synthesis of the nanoparticles was performed in situ; particle size was determined by laser diffraction, zeta potential and optical colloidal stability using multiscan 20 for a period of 24 hours at 37 °c; the minimum inhibitory concentration (mic) and minimum bactericidal concentration (mbc) of the formulated material on escherichia coli atcc 25922, staphylococcus aureus atcc 29213, klebsiella oxytoca atcc 700324, enterococcus casseliflavus atcc 700327, escherichia coli blee, carbapenem-resistant pseudomona aeruginosa were determined. the nanoparticles showed colloidal stability at a d-limonene concentration of 3.93%, silver ions at 1.61 × 10−3%, non-ionic adjuvant at 24% and ascorbic acid at 5.88%; citric acid/citrate (1:1) 0.48m for a ph of 4.5 was used as a buffer system. the formulation was classified as a polydisperse system (pd = 0.0851), with a zeta potential of −11.6 mv and average particle size of 81.5 ± 0.9 nm. a particle migration velocity of −0.199 ± 0.006 mm∙h−1, a constant transmission profile and backscattering profile with variations of 10% were evidenced, which represents a stable formulation. the nanoparticles presented an mic and an mbc of 28 μg∙ml−1 (5.6 × 10−2% d-limonene and 4.7 × 10−5% agnp) against all tested bacteria. keywords: silver nanoparticles; phase inversion; bacterial resistance; minimum inhibitory concentration article info received: 5 june 2022 accepted: 26 july 2022 available online: 13 august 2022 copyright copyright © 2022 julián echeverry-chica, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction due to the indiscriminate use of artificial chemical compounds such as antibiotics and disinfectants for the treatment of infectious diseases in humans and other species, for livestock production, cleaning and disinfection of environments, food production and preservation, many exposed microorganisms quickly develop resistance to these compounds, becoming a worldwide public health problem by generating infections that cannot be treated; additionally, artificial compounds can directly cause diseases in humans and other living beings and contaminate the environment. in 2017, the world health organization pointed out that the battery of antimicrobials available to combat multidrug-resistant bacteria such as pseudomonas aeruginosa, acinetobacter baumannii, mycobacterium tuberculosis and staphylococcus aureus, is insufficient to mitigate their proliferation and cause infection in humans; the design of innovative products is urgently required to control disease-causing microorganisms that endanger human life and increase treatment costs[1–6]. there is a growing trend towards the research and use of natural extracts or essen 36 tial oils (eo) that have been demonstrated in vitro the ability to inhibit the growth of clinically important bacteria, such as antibiotic or disinfectant agents[4,5,7]. additionally, the development of new formulations using inorganic compounds has gained importance, being metal ions, which are known to be very toxic to bacterial cells[3,8]. metal nanoparticles present a better performance to eliminate bacteria by increasing the surface area to react[3,8,9]. the scientific community should contribute to the solution of the problem by researching and carefully selecting active agents and formulations that target multiple bacterial sites and present modes of action less likely to confer cross-resistance. antimicrobial resistance is defined as the acquisition of resistance by a microorganism to an antimicrobial drug to which it was previously sensitive. the acquisition of resistance by bacteria poses a threat to public health; the greatest concern is the increasing spread of multidrug-resistant pathogenic bacteria worldwide, due to the misuse and abuse of antibiotics[10,11]. among the mechanisms expressed by bacteria to resist various groups of antibiotics is the production of enzymes such as extended-spectrum beta-lactamases (esbl) that confer resistance to oxymino-cephalosporins and monobactams (aztreonam), antibiotics that act by inhibiting the synthesis of the bacterial cell wall. when a bacterium is identified as a esbl producer, a group of antibiotics called carbapenems are used as a therapeutic alternative; these act on the cell wall and are highly resistant to hydrolysis against esbl[12]. but bacteria have also created multiple mechanisms to avoid the action of carbapenems, becoming a threat to world health, since for many years they have been the most stable and active antibiotics against bacteria with multiple resistance[13]. citrus plants have high concentrations of eo in the peel of their fruits; its main component is the terpene d-limonene, a molecule with recognized inhibitory power against bacterial growth in vitro. in colombia, citrus fruits are considered the second most important fruit species after bananas, and there is sufficient raw material in colombia to obtain eos with high limonene content[4,14–17]. the antimicrobial activity of d-limonene on the in vitro growth of streptococcus uberis, sthapylococcus aureus, staphylococcus epidermidis, klebsiella pneumoniae, pseudomonas fragi, pseudomonas aeruginosa, escherichia coli, salmonella typhimurium, salmonella enteritidis and listeria monocytogenes has been reported[14,16,18–21]. these results demonstrate the potential advantages of using d-limonene as a naturally occurring antimicrobial. among metal compounds, silver “ag(s)” is a common element in nature and has been used by humans as a disinfecting agent[3,22–24]. silver nanoparticles (agnp) have a strong bactericidal potential due to their higher surface-to-volume ratio, presenting on average a size of 10–100 nm, and being highly reactive molecules can be incorporated as an active ingredient of drugs and disinfectants, offering distinct advantages such as reduced toxicity, overcoming resistance and reduced cost compared to conventional antibiotics[2– 4,8,25]. agnps can act as an antimicrobial agents against nearly 650 species, including antibiotic-resistant bacteria[5,22], exhibit good in vitro performance against gram-positive bacteria such as staphylococcus aureus, streptococcus pyogenes and bacillus subtilis and gram-negative bacteria such as pseudomonas aeruginosa, escherichia coli and salmonella typhi[2,3,8,22–26]. the mechanisms of action of agnp on bacteria begin with binding to the cell membrane, membrane proteins and negatively charged nucleic acids, blocking the respiratory chains, generating reactive oxygen species, which lead to functional changes in the cell until it is destroyed[4,3,22,24,26]. on the other hand, some authors report bacterial strains that present mechanisms of adaptation and/or resistance to agnp[22,24]. in recent studies, it has been demonstrated that nanoparticles functionalized with essential oils increase their antibacterial effect and biocompatibility[4,5,8,27]; the antibacterial effects of agnp in combination with the eo of the zataria multiflora plant have been evaluated, observing that agnp with eo present synergistic effect against the growth of staphylococcus epidermidis and staphylococcus aureus. however, no reports were found indicating the inhibitory potential of bacterial growth of for 37 mulations combining d-limonene and agnp; in this study it is proposed to produce a nanoemulsion containing agnp functionalized with d-limonene and evaluate its effect on antibacterial activity, hoping to obtain a formulation that offers an alternative for the control and eradication of bacterial agents of clinical importance, especially microorganisms that manifest mechanisms to avoid the action of antibiotics and disinfectants currently used. 2. method the process of formulation, characterization and microbiological evaluation of agnp functionalized with d-linomenon is described below. 2.1 formula silver nitrate (>99%), ascorbic acid (>99%), citric acid (>99.5%), sodium citrate (>99%), and tween 20® (for synthesis) were imported by sigma-aldrich co (st. louis, mo). the d-limonene was donated by the fundación de apoyo a la investigación en el grupo interdisciplinario de estudios molecularesfundagiem of the universidad de antioquia. the formulations were prepared in a 50 ml falcon tube, adding non-ionic coadjuvant (tween 20®; glycerin and ethyl alcohol) and d-limonene with continuous agitation; then, silver nitrate solution and the solid mixture composed of citric acid/sodium citrate were slowly added. subsequently, ascorbic acid was slowly added with continuous stirring in vortex (thermo scientific) for the reduction of the silver ion; the volume was made up to 50 ml with deionized water. formula f1 represents agnp functionalized with d-limonene, formula f2 represents agnp without limonene addition and formula f3 represents nanoemulsion with d-limonene and absence of agnp. 2.2 particle size and z-potential analysis the formulations were diluted 1:10 with sterile water for injection. they were then analyzed on the malvern nanosight 300, which uses a technique ideal for polydisperse systems and yields a particle tracking analysis, allowing characterization of nanoparticles from 10 nm to 2,000 nm. 2.3 colloidal stability analysis the colloidal stability of the nanosuspensions was evaluated by the dataphysics multiscan 20. each formulation was stored in closed 40 mm clear glass bottles, where the products were subjected to periodic analysis at 37 °c for 24 hours. the objective was to accelerate the destabilization processes and to detect potentially unstable products at the earliest possible stage to consequently reduce the time for new product development. 2.4 microbiological analysis for antibacterial activity tests, the following bacteria were used: escherichia coli atcc 25922, staphylococcus aureus atcc 29213, klebsiella oxytoca atcc 700324, enterococcus casseliflavus atcc 700327, blee-producing escherichia coli, pseudomona aeruginosa, which showed impermeability to carbapenemics, the latter two isolated from urine samples. all strains were provided by the clinical hematology laboratory. bacteria cryopreserved on bhi brain heart infusion agar, glycerol and fetal bovine serum, were thawed and gram-negative bacilli were seeded by depletion on macconkey agar (biomériux) and gram-positive cocci on columbia cna biomériux agar. they were incubated for 24 hours at 37 °c; the genus and species of each growth were identified by means of the vitek 2 compac biomériux kit. once the genus and species were confirmed, the mic was determined. 2.5 agar dilution method this method made it possible to quantify the in vitro activity of an antimicrobial by determining the growth of a microorganism in a series of dilutions of the antibiotic mixed with culture medium. the agar dilution method made it possible to determine the minimum bactericidal concentration cmb, defined as the lowest concentration of the antimicrobial agent necessary to eliminate 99% of the initial inoculum, and the minimum inhibitory concentration cmi, defined as the lowest concentration of substance that can inhibit the visible growth of a microorganism. to make the dilutions of the anti 38 bacterial product under study, the amount of the antibacterial agent to be analyzed was dispersed in an erlenmeyer flask, then a known amount of sterile agar still molten (50 °c) was added; müeller-hinton agar is usually used, which allows the development of gram-negative bacilli and gram-positive cocci. the mixture is homogenized and poured into an empty sterile petri dish, thus obtaining a müeller-hinton agar plate with the antibiotic diluted to a certain concentration ready to be inoculated[12,28–31]. the mic was that dilution at which no growth of the tested bacteria was observed. the cmb is established by taking a sample with a sterile swab from the surface of the solid agar containing the dilution that allowed the mic to be established and the sample is cultured on müeller-hinton agar. it is incubated for 48 hours at 37 °c, waiting for no bacterial growth to be observed[28]. müeller-hinton agar is a solid, non-selective medium that allows antimicrobial susceptibility testing of aerobic, anaerobic and microaerophilic bacteria[30]. it has a low inhibitory power and high reproducibility; it should be prepared at a ph between 7.2 and 7.4 which can be adjusted with ca2+ (20–25 mg∙l−1) and mg2+ (10– 12.5 mg∙l−1)[31]. 2.6 determination of minimum inhibitory concentration (mic) the mic of formulations f1, f2, f3 was determined by the agar dilution method described in clsi guideline m-7 2018[32], with some modifications; after 24 hours of incubation at 37 °c, three to four colonies of each bacterium are taken with a sterile wooden stick and suspended in 0.85 % saline, until a turbidity standard of 0.5 mcfarland (1.5 × 108 cfu m∙l−1) is reached. each suspension was tested with densichek equipment (biomériux). muellerhinton agar (becton dickinson, usa) was used to perform the dilutions, incorporating the determined amount of the nanoemulsion in the agar when it is still in liquid phase (50 °c), always keeping a final volume of 10 ml; the first dilution contains 1 ml of formulated + 9 ml of agar, the final dilution contains 100 μl of formulated + 900 μl of sterile distilled water + 9 ml of agar. the mixture is deposited in sterile plastic petris dishes and allowed to cool to gel the culture medium. once the mixture is in its solid phase, surface inoculation is performed, 10 μl of each 0.5 mcfarland suspension is taken and deposited as a dot on the medium; incubate for 24 hours at 37 °c. a growth control is performed by inoculating 10 μl of each bacterial suspension on a petri dish with 10 ml of mueller-hinton agar (becton dickinson, usa); a sterility control is performed by leaving in incubation for 24 hours at 37 °c a petri dish with 10 ml of the previously prepared mueller-hinton agar without seeding. as method control the commercially used antibiotic amoxicillin (sigma) is used starting from the concentration 512 μg∙ml−1 up to the concentration of 2 μg∙ml−1 according to the “preparation of dilutions of antimicrobial agents for use in agar dilution susceptibility testing”, available in the clsi guide m100 e28[33]. each analysis is performed in triplicate. the mic of two commercial disinfectant detergents produced by spartan chemical campany, inc, clean by peroxy based on hydrogen peroxide and super hdq neutral based on quaternary ammonium were determined for comparison with the mic of f1. first, the commercial disinfectants were prepared at the dilution recommended on the label, 1:32 for clean by peroxy and 1:250 for super hdq neutral; distilled water was used as diluting agent. dilution in agar was performed to determine the mic of each product on the same group of bacteria previously tested. to evaluate the effect of temperature on the formulations, taking into account that they are added to the liquid phase agar which is at 50 °c, the direct effect of the nanoemulsion at a temperature of 30 °c on the selected bacteria was determined. 2.7 determination of minimum bactericidal concentration (mbc) from the petri dish containing the agar with the dilution of formulated that allowed the mic to be established, a sample is taken from the agar surface with a sterile swab and seeded on a new sterile mueller-hinton agar; incubate for 48 hours at 37 °c and read. 39 2.8 statistical analysis for the systematization of the information and analysis of the results, the statistical software spss version 24, licensed by the university of antioquia, was used. the descriptive tables of the information were constructed in this software. for each of the formulations and commercial disinfectants, the chi-square test was applied to observe the relationship between product concentration and bacterial growth, finding in all experiments the concentration value that allowed no bacterial growth in the three replicates, with no growth in the tested concentrations higher than the mic, which shows the stability of the formulations. subsequently, the student’s t-test was applied, taking as reference the average concentration at which the f1 formulation (with agnp and d-limonene) acted, and it was established whether there were statistically significant differences with the means of the other products evaluated. the “p” values less than or equal to 0.05 were taken as statistically significant in both tests. 3. results 3.1 particle stability table 1 presents the colloidal characterization results of the formulations. f1 (5.6 × 10−2% d-limonene, 4.7 × 10−5% agnp) presented smaller average particle size, lower polydispersity and higher electrostatic stability. figures 1, 2 and 3 show the particle size distributions of the formulations and the effect of in situ d-limonene functionalization on the agnp synthesis process. table 1. colloidal characterization of formulations evaluated f1 f2 f3 average diameter (nm) 81.5 ± 0.9 116.4 ± 9.2 133.7 ± 1.5 fashion (nm) 69.5 ± 1.7 81.8 ± 4.8 9.4 ± 2.7 d10 (nm) 60.5 ± 0.5 72.1 ± 5.6 86.5 ± 0.8 d50 (nm) 75.1 ± 0.8 99.7 ± 8.6 121 ± 3 d90 (nm) 107.8 ± 2.4 186.3 ± 18.2 198.4 ± 4.8 polydispersity 0.0851 0.495 0.0928 zeta potential (mv) −11.6 ± 0.3 −8.3 ± 0.4 −5.1 ± 0.5 figure 1. particle size distribution of formulation f1. 40 figure 2. particle size distribution of the formulation f2. figure 3. particle size distribution of the formulation f3. figure 4. colloidal stability of formulation f1: a) transmission profile; b) backscattering profile. 41 for the colloidal stability of formulation 1, a transmission that remains constant along the height of the vial is observed (figure 4a) which means that no particle migration (creaming or sedimentation) is evidenced during the 24 hours of sample analysis. on the other hand, figure 4b shows the backscattering profile in absolute form; although no isosbestic point is observed, there is no variation in particle size since the backscattering profile is within the ±2% range. 3.2 microbiological bacterial identification. results of vitek 2 compac indicate that all bacterial strain identifications achieve an average of 96% probability. results of mic and bmc of the formulations. formulation f1 containing agnp functionalized with d-limonene presented a mic and wbc of 28 μg∙ml−1 with a concentration of d-limonene and agnp of 5.6 × 10−2% and 4.7 × 10−5%, respectively, against all tested bacteria; the mic and mic for escherichia coli atcc 25922, staphylococcus aureus atcc 29213, klebsiella oxytoca atcc 700324, escherichia coli producing extended-spectrum beta-lactamase blee was 28 μg∙ml−1, against pseudomona aeruginosa was 22 μg∙ml−1 and against enterococcus casseliflavus was 24 μg∙ml−1. table 2 shows the results of each formulation on the bacteria tested. the growth control yielded a positive result in all three replicates and the method control reproduced in the expected mic range of amoxicillin on each bacterium. the commercially available disinfectants based on clean by peroxy hydrogen peroxide and super hdq neutral quaternary ammonium ammonium had mic of 68 μg∙ml−1 and 36 μg∙ml−1, respectively. the percentage of agnp and d-limonene in the cmb of the formulations, taking into account that the minimum amount of the product tested to eliminate the total bacteria tested was 28 μg∙ml−1 for f1, 34 μg∙ml−1 for f2 and 50 μg∙ml−1 for f3, is reported in table 3. table 2. minimum inhibitory/bactericidal concentration of the formulations on the tested bacteria formulated disinfectant bacteria cmi cmb μg∙ml−1* e.coli atcc 25922 e.coli blee p. aeruginosa r carb k. oxytoka atcc 700324 s. aureus atcc 29213 e. casseliflavus atcc 700327 f1 agnp+ d-limonene 28 28 22 28 28 24 f2 agnp only 30 30 22 34 34 26 f3 d-limonene only 40 40 32 46 50 34 hydrogen peroxide (a) 68 68 46 46 46 44 quaternary ammonium (b) 20 20 18 36 20 18 a: hydrogen peroxide-based disinfectant detergent, clean by peroxy, spartan. b: quaternary ammonium-based disinfectant detergent for medical devices, super hdq neutral, spartan. * average of the results of three different experiments. table 3. percentage of d-limonene and agnp in the cmb f1 f2 f3 d-limonene (%) 5.6 × 10−5 n/c* 0.1 agnp (%) 4.7 × 10−5 5.7 × 10−5 n/c *n/c: does not contain table 4 shows the descriptive statistics for the behavior of each disinfectant. the one with the widest range was the hydrogen peroxide-based disinfectant, with a value of 2.4 μg∙ml−1. the maximum concentration used in this was 68 μg∙ml−1. the one with the smallest range of action was the combination of agnp and d-limonene, presenting a minimum value of 22 μg∙ml−1 and a maximum of 28 μg∙ml−1, which shows greater stability among the agents evaluated. when observing the behavior of the mean, it is found that the disinfectants that required on average less volume to inhibit the evaluated agents are the quaternary ammonium-based disinfectants, with a mean of 22 μg∙ml−1, followed by f1 (agnp and d-limonene) 26.3 μg∙ml−1. the two disinfectants with the highest mic were f3 (d-limonene) and hydrogen peroxide-based disinfectant with means of 40.3 μg∙ml−1 and 53 μg∙ml−1 respectively. 42 table 4. descriptive statistics for the formulated volume of disinfectant formulation n (bacteria evaluated) range (μg∙ml−1) minimum (μg∙ml−1) maximum (μg∙ml−1) mean (μg∙ml−1) deviation (μg∙ml−1) f1 agnp + d-limonene 6 0.6 22 28 26.3 2.6 f2 agnp only 6 1.2 22 34 29.3 4.7 f3 d-limonene only 6 1.8 32 50 40.3 6.9 a. disinfectant based on hydrogen peroxide 6 2.4 44 68 53 12 b. disinfectant based on quaternary ammoniums 6 1.8 18 36 22 7 table 5. student’s t-test of means formulation test value = 26.3 t-test gl sig. (bilateral) difference in means agnp + limonene 0.000 5 1.000 0.0 agnp only 1.571 5 0.177 3.0 limonene only 4.999 5 0.004 14.0 disinfectant based on hydrogen peroxide 5.609 5 0.002 26.7 quaternary ammonium-based disinfectant −1.532 5 0.186 −4.3 having the behavior of the average concentrations necessary to inhibit the growth of the different bacteria, student’s t-test was performed taking as reference the mean given for formulation f1 (agnp and d-limonene) 26.3 μg∙ml−1. when performing the student’s t-test with this parameter (see table 5), statistically significant differences were found when comparing f1 with f3, the d-limonene-only formulation (p = 0.004) and the hydrogen peroxide-based disinfectant (p = 0.002). in contrast, the f2 formulations of agnp alone and the quaternary ammonium-based disinfectants did not show statistically significant differences compared to the agnp+d-limonene formulation. 4. discussion the bacteria analyzed in this study are considered human pathogens; reference strains provided by the american type culture collection atcc and bacteria that have shown in vivo and in vitro antibiotic resistance mechanisms, such as blee-producing escherichia coli, are included, enzymes produced by bacteria with the ability to inactivate third-generation cephalosporins (ceftriaxone, cefotaxime, ceftazidime) and aztreonam[12], pseudomona aeruginosa with resistance to carbapenemics, a group of antibiotics used for the treatment of infections caused by blee-producing bacteria[13]. the mixtures used to prepare the nanoemulsions allowed achieving a final formulation called f1, whose physical and chemical properties demonstrate that it is a stable mixture, containing particles with an average size of 81.5 ± 0.9 nm, characteristics that enhance the effect of agnp and d-limonene in microbiological tests; f1 presented the same effect on e. coli and multidrug-resistant e. coli and an mic against carbapenem-resistant p. aeruginosa, lower than that obtained against the other 5 bacteria tested; this suggests that agnp functionalized with d-limonene perform with the same power on bacteria without resistance and bacteria multidrug-resistant to antibiotics. the combination of agnp with essential oils has already demonstrated a synergistic effect against multidrug-resistant bacteria[8]. the mic is considered the amount of antimicrobial that allowed the complete inhibition of growth of all the bacteria tested in all the assays. the formulation named f1 showed an outstanding broad-spectrum antimicrobial activity since it acted similarly on gram-positive cocci and gram-negative bacilli, eliminating the in vitro growth of all the bacteria tested with a mic and 43 bmc of 28 μg∙ml−1 with an average of 26.3 μg∙ml−1; the formulation named f2 presented an mic and a wbc of 34 μg∙ml−1 and formulation f3 showed an mic and a wbc of 50 μg∙ml−1; these data indicate that agnps functionalized in situ with d-limonene in a nanoemulsion type formulation present an antimicrobial additive effect, being necessary less quantity of formulation f1 to eliminate 99.9% of the tested bacteria, compared to f2 and f3. elements such as silver (ag), gold (au), zinc (zn), platinum (pt), iron (fe) and copper (cu) have been used in combination with ec to evaluate their antimicrobial activity, showing a synergistic effect[35]. according to the statistical analysis, f1 presents significantly different mic values compared to f3, a formulation containing only d-limonene, which indicates that f1 acts better at lower concentrations compared to f3; with f2, which only contains agnp, there are no statistically significant differences. despite this, as shown in table 4, a lower amount of the formulation is necessary when combining agnp with d-limonene to inhibit the growth of 5 of the 6 bacteria tested; the percentage of agnp necessary to inhibit 100% of the bacteria tested in f1 was 4.7 × 10−5% and that of f2 was 5.7 × 10−5%, achieving a decrease of 1 × 10−5% when combining agnp with d-limonene. this low decrease of one unit may signify a reduction in the toxicity of the product to eukaryotic cells, reflecting that limonene acts as a stabilizer of the silver nanoparticles and, when combining the two antibacterial agents, their growth inhibitory power is not affected. the effect of f1 (agnp with d-limonene) compared to the f2 formulation (agnp alone) is more noticeable on k. oxytoka and s. aureus, bacteria known for their high pathogenicity and ability to generate and transmit resistance to antibacterials. this finding is important because it proves the addictive effect generated by limonene on agnps. in the comparative tests of the antibacterial effect of the disinfectants versus the f1 formulation, the quaternary ammonium-based disinfectant presented the best inhibitory effect against the bacteria escherichia coli atcc 25922, staphylococcus aureus atcc 2921, enterococcus casseliflavus atcc 700327, escherichia coli blee+, carbapenem-resistant pseudomona aeruginosa, compared to formulation f1 and clean by peroxy disinfectant. but the mic (36 g∙l−1) against klebsiella oxytoca atcc 700324 was higher than the mic (28 g∙l−1) presented by the f1 formulation on the same bacteria. according to this data, the f1 formulation is considered more stable in its effect on the total bacterial group tested, presenting a significant difference with both disinfectants, since a minimum of 28 μg∙ml−1 of f1, 36 μg∙ml−1 of quaternary ammonium and 68 μg∙ml−1 of hydrogen peroxide are needed to eliminate the 6 bacterial genera. the hydrogen peroxide-based disinfectant presented lower inhibitory effect than the f1 formulation on all tested bacteria. these findings suggest that f1 has a broad-spectrum action as a disinfectant agent by acting evenly and at low concentrations on gram-positive and gram-negative bacteria. when analyzing the minimum and maximum values, it is noted that the formulation that had a smaller range of action was the combination of agnp and d-limonene, presenting a minimum value of 22 μg∙ml−1 and a maximum of 28 μg∙ml−1, which shows a greater stability among the agents evaluated. f1 behaved very similar to the commercial quaternary ammonium-based disinfectant; this product is used in places such as laboratories, intensive care units, food industries among others to control dangerous pathogens, therefore, it is concluded that f1 presents a potential as a disinfectant agent that is at the level of the latest generation disinfectants with the advantage that its effect is more even on a heterogeneous group of bacteria compared to quaternary ammonium. the combination of agnp with eo to achieve greater antimicrobial effect against bacteria has been tested in several studies. the additive effect between agnp and the terpene thymol to disinfect vegetative tissue of bermudagrass plant has been reported[36]. agnps combined with the essential oil of oreganum spp exhibited an addictive effect against multidrug-resistant bacteria[34]. the mixture of agnps with the eo of oreganum spp. showed antimicrobial stability against gram-positive bacteria[37]; agnps functionalized with essential oils of the plants cymbopogon citra 44 tus, c. martini, eucalyptus globules, azadirachta indica, ocimum sanctum showed effect against s. aureus bacteria[38]. this is the first report of the in vitro antibacterial effect of a mixture of agnps and d-limonene; the results suggest that the additive effect of agnps functionalized with d-limonene can be used to prevent the growth of bacteria including multi-resistant bacteria that are considered pathogenic for humans and other species; further research on combinations of agnps with products of natural origin is necessary to provide more alternatives against the phenomenon of bacterial multi-resistance. the mechanisms of action of eos on bacterial cells vary depending on their composition and the bacterial strain exposed; eos are characterized by their hydrophobicity and lipophilic nature, which allows them to interact easily with the fatty acids of the microbial cell membrane; they act on cell membrane integrity by changing permeability, leading to electrolyte leakage and loss of vital intracellular contents such as proteins, reducing sugars, while inhibiting energy generation, leading to cell destruction[39–42]. d-limonene derived from citrus essential oil acts on the cytoplasmic membranes of microorganisms, causing a loss of membrane integrity, inhibition of respiratory enzymes and dissipation of proton motive force[27]. the mechanism of action of agnps on bacteria begins with binding to the cell membrane, increasing permeability, producing the release of lipopolysaccharides, membrane proteins and subsequent binding to nucleic acids, blocking the respiratory chains, generating reactive oxygen species, which lead to functional changes in the cell leading to cell death[3,5,22–24,26,35,44]. the effect depends on the surface area that is increased by the presentation in nanometric size, being able to interact in greater proportion with molecules such as enzymes and nucleic acids, causing greater structural changes and deformation in bacterial walls and membranes[2,21,43]. on the other hand, some authors report bacterial strains that present mechanisms of adaptation and or resistance to agnp[22,24], so it is important to continue evaluating whether the mixture of agnp with essential oils with antibacterial power with d-limonene counteracts the resistance effect that has been presented on agnp. however, the results show that the addition of d-limonene to the formulation requires a lower amount of agnp, which decreases the toxicity due to the presence of silver in eukaryotic cells. according to the mechanisms of action of eos and agnps, it can be suggested that the f1 nanoemulsion presents a combined and synergistic mechanism of action; d-limonene by its lipophilic nature interacts easily with the fatty acids of the microbial cell membrane, damaging the integrity of the membrane, agnps also affect the membrane, allowing easy entry of agnps and limonene into the cell cytoplasm, there they disrupt the electron transport process inhibiting the secretion of toxins into the environment, causing dysfunction of ribosomes, interact with the genetic material until degrading it and finally achieving cell lysis[35]. 5. conclusions the problem of bacterial resistance is growing at an alarming rate, considerably increasing morbidity and mortality rates worldwide. the level of evolution of bacteria to survive and multiply in environments with high concentrations of commercially available antibiotics and disinfectants, in the last decade, is occurring at a much higher rate than the evolution in the development of antimicrobials by scientists. there is a need for the development of new products that demonstrate a microbicidal effect on all types of pathogenic bacteria, especially those with higher resistance mechanisms. agnps are considered as a real alternative for the development of antimicrobials against multidrug-resistant bacteria because of their high toxicity to bacterial cells. however, bacteria have been reported to present resistance mechanisms to agnps and it is therefore important to test mixtures of agnps with other agents that present microbicidal potential in search of synergy, in order to achieve a better antibacterial effect and counteract resistance. some eo derivatives have shown broad-spectrum antibacterial effect; d-limonene as the main component of citrus eo showed a good bactericidal effect at low concentra 45 tions, becoming an alternative to combat germs of clinical importance. the formulation containing agnps functionalized with d-limonene produced an additive effect to eliminate the growth of pathogenic bacteria, compared to the nanoemulsion containing only agnp or the nanoemulsion containing only limonene. f1 presented an effect similar to that obtained with commercially 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al. antioxidant and antibacterial activity of silver nanoparticles biosynthesized using chenopodium murale leaf extract. journal of saudi chemical society 2014; 18(4): 356–363. 44. rhim j, wang l, hong s. preparation and characterization of agar/silver nanoparticles composite films with antimicrobial activity. food hydrocolloids 2013; 33(2): 327–335. 11 original research article spin thermoelectric effects of new-style one-dimensional carbon-based nanomaterials yushen liu1*, jinfu feng1, xuefeng wang2 1 school of physics and electronic engineering, changshu institute of technology, changshu 215500, china. e-mail: ysliu@cslg.edu.cn 2 college of physics, optoelectronics and energy, soochow university, suzhou 215006, china abstract based on first-principles methods, the authors of this paper investigate spin thermoelectric effects of one-dimensional spin-based devices consisting of zigzag-edged graphene nanoribbons (zgnrs), carbon chains and graphene nanoflake. it is found that the spin-down transmission function is suppressed to zero, while the spin-up transmission function is about 0.25. therefore, an ideal half-metallic property is achieved. in addition, the phonon thermal conductance is obviously smaller than the electronic thermal conductance. meantime, the spin seebeck effects are obviously enhanced at the low-temperature regime (about 80 k), resulting in the fact that spin thermoelectric figure of merit can reach about 40. moreover, the spin thermoelectric figure of merit is always larger than the corresponding charge thermoelectric figure of merit. therefore, the study shows that they can be used to prepare the ideal thermospin devices. keywords: graphene nanoribbons; carbon chains; graphene nanoflake; spin seebeck coefficients; thermoelectric figure of merit characterization and application of nanomaterials (2021) volume 4 issue 1 doi:10.24294/can.v4i1.1323 article info received: 15 november 2020 accepted: 8 january 2021 available online: 14 january 2021 copyright copyright © 2021 yushen liu, et al. enpress publisher llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 1. introduction carbon is one of the elements widely distributed in nature. as a tetravalent non-metallic element, it can form covalent bonds with metals and non-metals and combine into a variety of carbon-based nanomaterials. graphene, as a two-dimensional allotrope of carbon, has been widely studied because of its unique electrical properties. reviewing its development history, it is found that it has attracted early attention in theory, but the extensive research on its properties began with geim and novoselov, who obtained nearly perfect monolayer and free state graphene by simple mechanical method for the first time[1]. from the atomic level, graphene is composed of sp2 hybrid carbon atoms. it is also an aromatic compound with a large π electron conjugate system. the special energy band structure leads to a semiconductor with zero energy gap. unlike traditional semiconductor materials, graphene follows dirac equation rather than schrodinger equation. the migration rate of carriers in the conjugate system is very high, even close to the speed of light, making graphene one of the materials with the lowest resistivity at present. although graphene has very unique electrical properties, it cannot be directly used in logic devices due to the energy band structure of zero energy gap. in order to open the energy gap, a common method is 12 to shear two-dimensional graphene into one-dimensional nano band structure and introduce quantum confined domain effect and boundary effect. when the width is less than 10 nm, graphene nanoribbons will open the energy gap. the preparation methods of graphene nanoribbons can be divided into two kinds: one is the top-down synthesis method. for example, carbon nanotubes can be cut by physical or chemical methods using carbon nanotubes as basic raw materials. the other is the bottom-up synthesis method, that is, the nanoribbon structure is synthesized from small molecular raw materials. according to the boundary structure characteristics of the ribbons, graphene nanoribbons can be divided into two types: armchair and zigzag. armchair nanoribbons (agnrs) show non-magnetic semiconductor behavior, and the band gap decreases with the gradual increase of width[2]. zigzag nanoribbons (zgnrs) have spin-polarized boundary states due to the presence of non-bonding electrons in boundary carbon atoms. theoretical study shows that the ground state of zigzag nanoribbons (zgnrs) is that the boundary spin has antiferromagnetic order, that is, the directions of different boundary spins are opposite, but on the same side, the boundary spins show ferromagnetic arrangement. with a suitable applied magnetic field, we can realize the ferromagnetic order of different boundary spins[3]. regardless of whether different boundary carbon atoms show ferromagnetic order or antiferromagnetic order, the density of states at the fermi plane is spin degenerate, which limits their application in spintronics. however, using a transverse electric field, we can make zgnrs realize semi-metallic property[4]. here, the semi-metallic property refers to the fact that the fermi surface shows an insulating state for one spin band structure and a metallic state for the other. in addition, the magnetic property and transport property of zgnrs are also affected by chemical element doping or defect[5–7]. interestingly, some studies show that a single spin negative differential resistance is found in the boundary doped zgnrs[5]. in addition to voltage driving electrons or holes in materials to move at a certain direction, temperature difference can also drive electrons. more electrons or holes are often accumulated at the high and low temperature ends, so the voltage caused by temperature difference will appear in this material. this phenomenon is called seebeck effect. recently, with the progress of spin detection technology, k. uchida, et al. firstly observed spin voltage caused by temperature difference in metal magnets, which is called spin seebeck effect[8]. this pioneering experiment inspired people to theoretically study spin-related thermoelectric effects in various systems[9–21]. recently, we have obtained high spin polarizability and large single spin seebeck effect at the fermi plane by doping ferromagnetic zgnrs with boundary non-magnetic elements[16]. at present, a stable carbon atom chain (cac) can be synthesized from graphene by electron irradiation technology using high-resolution transmission electron microscope[22]. shen, et al. found that the channel transport property of cacs does not depend on structural deformation, structural defects and hydrogen adsorption[23]. carbon-based nanostructures exhibit perfect spin filtering effect and giant magnetoresistance under near zero bias. recently, dong, et al. have studied the transport property of zigzag graphene nanoribbons connected with cacs[24]. it is found that the electron transport near the fermi level can be changed by adjusting the position and the number of atoms in cacs. fano resonance effect is an interference effect existing between the local state and the extended state. it was first found in the inelastic scattering of electrons in helium. in 2002, kobayashi, et al. found that the adjustable fano effect was observed in the aharonov-bohm ring embedded in quantum dots[25]. two quantum dots can be coupled into an artificial molecule, and then the electrons will be shared by the two quantum dots. when the electron energy is close to fano linear system, the seebeck effect is significantly strengthened[26]. in this paper, the spin thermoelectric property of one-dimensional spin quantum devices composed of graphene nanoribbons, carbon chains and graphene nanosheets was studied. the first principle calculation shows that the spin-down transfer function at the fermi face is suppressed to almost zero, however, the spin-up transfer function is close to 0.25. 13 therefore, we got distinct semimetal property. in addition, the phonon partial thermal conductivity in the low-temperature region is significantly smaller than the corresponding electron partial conductance. however, in the low temperature region (near 80 k), the spin seebeck coefficient is significantly strengthened, resulting in the charge and spin thermoelectric quality factor close to 40. moreover, in the whole temperature range (0 < t ≤ 400 k), the spin thermoelectric quality factor is always greater than the corresponding charge thermoelectric quality factor, and becomes more obvious in the room temperature region. therefore, this one-dimensional carbon-based nanoribbon can be designed as an ideal spin thermoelectric device. 2. model establishment in this paper, a one-dimensional nano double probe system as shown in figure 1(a) was designed. the left electrode and the right electrode are composed of serrated graphene nanoribbons, and the boundary carbon atoms are saturated with hydrogen atoms. the central scattering region is connected by a graphene nano sheet to a zigzag graphene nanoribbon through two carbon atom chains. the width of the graphene nanoribbon is represented by the number of carbon atoms perpendicular to the transport direction. in this paper, the width is 6. figure 1. thermal spin quantum double probe model and corresponding spin density. all numerical calculations are completed based on the software package atomistix toolkit (atk) of non-equilibrium green’s function and density functional theory[27–28]. the system optimization adopts newton optimization method; the exchange correlation function adopts generalized gradient approximation (gga), and the basis vector adopts dzp (double-zeta-polarized). the size of the reduced brillouin zone is set to (1, 1, 100). in order to avoid the interaction between images, the vacuum layer is taken as 15 å and the truncation energy is taken as 150 ry. using atk software, the transmission coefficient of spin resolvable electrons with energy of e is: (1) here, γl/rσ(e) is the linewidth function of the coupling between the central scattering region and the left/right electrode; σ is the spin index and e is the energy. is the delayed and advanced green’s functions of the center scattering region. it can be determined by the equations and . i is the identity matrix. h is the hamiltonian of the central scattering region. the spin polarizability at the fermi plane is defined as: (2) in order to study the spin thermoelectric effect, we give the expression of spin-dependent seebeck coefficient in the linear region: (3) the thermal conductivity of the electronic part can be written as: here, n = 0, 1, 2. fl(r) is the fermi dirac distribution function. spin seebeck coefficient is expressed as ss = (s↑–s↓)/2, and the corresponding charge seebeck coefficient is sc = (s↑ + s↓)/2 [14]. charge (spin) thermoelectric quality factors are obtained from the following equation: (4) ge(s) is the corresponding charge and spin con14 ductance, which can be obtained by the following equation: (5) the phonon partial heat guide in formula (4) is available in the atk2013 beta. 3. results and discussion figure 1(b) shows that zgnr still has boundary spin state in the buffer region, and the ferromagnetic order is maintained at the three boundaries of graphene nanosheets, that is, the spins of boundary carbon atoms are arranged in parallel. in figure 2(b), we draw the variation trend of spin resolvable transfer function with electron energy, and find a wide energy region near the fermi plane (for example: –0.25 ev < e < 0.1 ev). the spin-up transfer function remains limited, while the spin-down transfer function is suppressed to zero. therefore, this device shows obvious semi-metallic behavior, and the spin polarizability satisfies ζ = 1. in order to reveal the physical reason behind it, we draw the spatial distribution of spin dependent local density of states at the fermi surface in figures 2(c) and (d). obviously, the spin-up local density of states is distributed in the whole central scattering region domain, including zgnr, graphene nanosheets and carbon chains. however, the spin-down local density of states is only distributed in the zgnr in the middle scattering region, and does not appear on carbon chains and graphene nanosheets. this result further confirmed the semi-metallic property at the fermi plane. we also found that the spin-up fano type tunneling spectrum appears in the –0.2 ev region below the fermi plane, but the spin-down fano type tunneling spectrum appears at 0.1 ev on the fermi plane. the corresponding trend of density of state with energy shows that these fano type tunneling spectra come from the local state in the energy region (figure 2(a)). fano resonance is formed when these local states and surrounding electronic states undergo quantum interference effect. figure 2. the spin-dependent transport property. (a) and (b) represent the variation trend of state density and transport function with the electron energy respectively, and the dashed line represents the position of the fermi plane, letting the energy of the fermi surface be zero. (c) and (d) indicate the local spin-up and spin-down density of states at the fermi surface, respectively. fano resonance causes the transfer function to change dramatically with the electron energy, which is bound to strengthen the thermoelectric effect. compared with other energy points, the thermoelectric performance at the fermi surface will attract more attention of researchers. in figure 3(a), we give the change of spin-dependent seebeck coefficient with temperature at the fermi surface. it is found that the spin-up seebeck coefficient is positive while the spin-down seebeck coefficient is negative. this result can be well explained by the following equation. at low temperature, equation (3) can be simplified as: (6) this equation shows that sσ at the fermi surface is directly proportional to the negative value of the slope of the transmission probability τσ and inversely proportional to its size. at the same time, we also note that it is directly proportional to the temperature t. this equation can well explain the behavior of sσ in the low temperature region (0 < t ≤ 50 k). however, when the temperature further increases, we find that the spin-down seebeck coefficient is significantly strengthened, and equation (6) becomes no longer applicable. it is mainly because more nonlinearity participates in the contribution to the spin seebeck coefficient at high temperature[29]. in order to calculate the charge and spin thermoelectric quality factors, in figure 3(b), we give the contribution of the 15 electron and phonon part to the thermal conductivity. the thermal conductivity contributed by the phonon part κph and the thermal conductivity contributed by the electron part κel increase monotonically with the increase of temperature. figure 3. spin-dependent thermoelectric property. (a) spin-dependent seebeck coefficients; (b) electron and phonon partial thermal conductivity; (c) charge and spin seebeck coefficients; (d) trend of spin and charge thermoelectric quality factors with temperature. moreover, it is important that the thermal conductivity of the phonon part is significantly lower than that of the electronic part, especially in the low temperature region (t < 100 k), and the thermal conductivity of the phonon part is one percent of the electronic part (see the embedded diagram in figure 3(b)). interestingly, the spin-down seebeck coefficient is significantly strengthened near the temperature of 80 k, and the maximum value even reaches 2000 μv/k. the charge seebeck coefficient sc and spin seebeck coefficient ss are also significantly strengthened near the temperature of 80 k. in the high temperature region (near room temperature), we find that the value ss is significantly larger than sc, which indicates that the spin thermoelectric effect is significantly stronger than the corresponding charge thermoelectric effect. in figure 3(d), we show the variation trend of spin thermoelectric quality factor zst and charge thermoelectric quality factor zct with temperature t. the results show that their maximum value is close to 40, and the sizes of zst and zct are the same in the whole temperature region. generally speaking, if the thermoelectric quality factor is greater than 3, it is considered that the material has high thermoelectric efficiency. it can be used as an ideal thermoelectric material. more interestingly, in the high temperature region (room temperature region), zst is significantly larger than zct, and zst is close to 3. this shows that this double probe model with carbon atoms can be used as an ideal thermoelectric device at room temperature. 4. conclusion we designed a one-dimensional spin quantum device composed of graphene nanoribbons, carbon chains and graphene nanosheets. it is found that the spin-down transfer function at the fermi surface is almost suppressed to zero, while the spin-up transfer function is close to 0.25, so it has obvious semi-metallic property. in addition, we also found that in this device, the thermal conductivity of the phonon part is significantly smaller than the corresponding electronic partial conductance. in the low temperature region, the phonon partial thermal conductance is only one percent of the electronic partial thermal conductance. however, in the low temperature region (near 80 k), the spin seebeck coefficient is significantly strengthened, resulting in the charge or spin quality factor close to 40. moreover, in the whole temperature range (0< t ≤ 400 k), the spin thermoelectric quality factor is always greater than the corresponding charge thermoelectric quality factor, and this effect becomes more obvious at room temperature. therefore, this one-dimensional carbon-based nanoribbon can be used to design ideal spin thermoelectric devices at room temperature. conflict 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nanoparticles—prevailing progressions ayesha kausar1,2,*, ishaq ahmad1,2 1 npu-ncp joint international research center on advanced nanomaterials and defects engineering, northwestern polytechnical university, xi’an 710072, shaanxi province, china 2 unesco-unisa africa chair in nanosciences/nanotechnology, ithemba labs, somerset west 7129, south africa * corresponding author: ayesha kausar, dr.ayeshakausar@yahoo.com abstract this state-of-the-art overview emphasizes electrospinning technique and resulting electrospun nanofibers and nanofibrous membranes. consequently, the electrospinning method as well as the formation and features of the electrospun nanofiber/membrane nanomaterials have been described. properties of the electrospun nanofibers have found to be enhanced several folds through the incorporation of carbon nanoparticles in the nanofibers. important properties and utilizations of carbon nanocomposite electrospun nanofibers were seemed to be affected by nanoparticle amount and dispersal. importantly, diameter, microstructure, and physical features (thermal, mechanical, conductive, etc.) of the nanofibers and resulting membranes can be affected by the nanofiller behavior. the high performance electrospun nanofibers have been used to form efficient nanocomposite nanofibrous membranes. sequentially, the electrospun nanocomposite nanofibrous membranes have been applied in technical membrane applications. keywords: electrospinning; nanofibers; polymer; nanocomposite; membrane 1. introduction nanofibers, especially polymer structured nanofibers, are one dimensional nanostructures having remarkable properties[1]. for the formation of synthetic polymer nanofibers, various important categories of polymers have contributed such as thermoplasts, thermosets, as well as conjugated polymers[2]. for the formation of polymeric nanocomposites, carbon nanoparticles have been used as essential nano-additives[3]. prominently, carbon nanotube, graphene, fullerene, etc. have been reinforced in polymers and studied. in addition to the usually formed films or precipitated polymeric nanocomposites, nanofibers have been designed[4]. spinning method is among the most widely focused techniques for polymer nanofibers[5,6]. usually, spinning techniques have been found advantageous due to facile controllable process parameters. spinning techniques have been widely categorized as wet spinning, melt spinning, electrostatic spinning, etc. solution blow spinning has been initially opted to form desired nanofibers of polymers as well as nanocomposites[7]. in this technique, varying process parameters have been found to affect the nanofiber diameter and morphology[8]. centrifugal jet spinning has also been applied to fabricate microor nanofibers[9,10]. then, electrohydrodynamic direct writing spinning method has also been adopted to form nanofibers. this method article info received: 16 october 2023 accepted: 7 december 2023 available online: 26 december 2023 copyright copyright © 2023 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attributionnoncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/bync/4.0/ 2 involves electrical/mechanical forces to form nanofibers[11,12]. among spinning techniques, electrospinning has been widely used for the polymer nanofibers. due to better parameter control to form precisely defined nanofibers, electrospinning technique has accomplished success for high performance polymers and nanocomposite nanofibers[13]. the resulting electrospun polymers or polymer/carbon nanocomposite nanofibers own superior physiochemical characters[14]. consequently, electrospinning technique has been described as a facile, and versatile process to form the nanofibers[15]. in nanofibrous form, the nanoparticle loading resulted in high-tech physical profiles of these nanostructures materials[16]. efficient membranes have been reported using the appropriate nanocomposite design and choice of suitable nanofiber processing techniques[17]. electrospinning has been widely studied for the nanocomposite nanofiber formation and the resulting membranes[18]. in this regard, the electrospinning parameters involved in the nanofibers and membranes formation have been focused. carbon nanoparticle filled nanocomposite nanofibers have been used to develop high performance nanofibers aiming membrane applications, energy and electronics devices, and biomedical applications[19]. this review manuscript clarifies basics and potential of electrospinning technique to synthesize the nanocomposite nanofibers and membranes for advanced applications. the electrospun nanocomposite nanofibers covered in this review consist of polymer and carbon nano-additives. in nanofibrous form, the polymer/carbon nanocomposites revealed enhanced physical and methodological features towards membrane application. superior morphology and properties have been observed due to synergistic effects between matrixnanofiller in the nanofibers and derived materials. to the best of the knowledge, this overview is novel and ground-breaking to highpoint the area of electrospinning derived nanocomposite nanofibers and membranes. although, literature research reports have been observed on electrospun nanofibers, however (like our novel comprehensive manuscript) no comprehensive review article has been reported before in this field. consequently, this article explains recent literature in this area in a reorganized and assembled manner. hence, this review is novel in terms of the recent literature included, outline and framework, and related discussions. hence, following this compiled manuscript on nanocomposite nanofibers and membranes will be helpful for the concerned scientists for indispensable future developments towards nanofiber technologies. 2. nanofillers, nanocomposites, and nanofibers carbon nanoparticles have gained research interest in important materials fields[20]. few important carbon nanostructures are given in figure 1. among carbon nan-additives, graphite, carbon nanotube, graphene, fullerene, and countless other forms have been studied[21,22]. these carbon nanoparticles led to the design of some valuable nanocomposites[23]. here, worth mentioning type of the nanocomposites is the polymer and carbon nanocomposites. these materials have been readily prepared through solvent, melt, and in situ techniques[24]. for the conversion of polymeric nanocomposites to nanofibers, spinning approaches have been applied[25]. spinning approaches have definitely improved the dispersion features of the nanoparticles in the nanofibers[26]. consequently, enhanced physical performance of the resulting nanocomposites, prepared through facile methods, was observed[27]. the polymer/carbon nanoparticle nanocomposites have been studied mostly for morphological, thermal, electronic, mechanical, and other profiles[28]. 3 figure 1. some carbon nanostructures. polymer nanofibers are nanostructures with diameter of few nanometers, whereas length up to millimeters[29]. these nanofibers may have uniform, wrinkled, hollow, or other forms depending upon the nature of polymer and technique used[30]. subsequently, the structural and engineering properties of the nanofibers can be varied[31]. innumerable polymers have ability to be processed or formed as nanofibers like epoxies, polyamides, some rubbers, and blends[32]. the technique used to form these nanofibers have been found considered important[33]. spinning methods have been found to be the most effective to develop uniform nanofibers having unique microstructures[34]. nanofiber formation technique and related parameters play important role to define the properties of polymer and nanocomposite nanofibrous materials[35]. the carbon nano-additives have been widely explored to fill the polymer nanofibers[36]. due to high surface area and physical properties, the carbon nanoparticle based nanofibers have important technological applications[37]. in this context, manufacturing strategies have been found important to fabricate the high performance nanofibers[38]. 3. use of electrospinning technique to form nanofibers spinning is the commonly adopted technique reported for the fabrication of polymer nanofibers[39]. in general, spinning methods can be melt or wet spinning based[40]. these techniques rely on using an electrostatic spinning mechanism[41]. spinning methods have easily controllable parameters for fiber formation[42]. in this regard, wet spinning method like solution blow spinning has been focused[43]. solution blow spinning technique has been designed for spinnable polymer solution. this spinning method has also been adopted for nanocomposites, in addition to polymer nanofibers. the set up of this technique includes a spinning chamber, dc motor, and multiple fiber collector. this technique forms stable polymer solution jet through adjusting parameters like polymer concentration and gas pressure[44]. the fiber diameter and mat formation depends upon parameter alteration like polymer type and solution concentration. the non-woven microand nanofibers have been produced using solution blowing method[45]. in this method, fiber production rate has been observed high, therefore parameter control has been found complicated, as compared to the electrospinning. solution blow spinning forms bundled morphology of fiber mats, relative to finely spun electrospun nanofibers and mats. consequently, electrospinning has been found advantageous, relative to solution blow spinning. table 1 shows a comparison of the solution blowing and electrospinning techniques in terms of parameters and nanocomposite used. 4 table 1. comparison on parameters and nanocomposite nanofibers formed using melt blowing and electrospinning. parameters or materials solution blowing electrospinning diameter of nanofibers 40 nm to several µm 40 nm to 2 μm rate of injection 20 μl/min 5 μl/min voltage used na. 10–40 kv variable parameters solution viscosity, nozzle geometry, feeding rate; gas pressure viscosity, feeding rate, needle to collector distance; voltage use of high polymer concentration yes fiber property distortion commercialization yes yes nanofiber alignment yes yes nanocomposite fiber polyaniline/carbon nanoparticle nanofibers; poly(vinyl alcohol)/carbon nanoparticle nanofiber; polystyrene/carbon nanoparticle nanofiber; polyamide/carbon nanoparticle nanofiber; polystyrene/carbon nanoparticle nanofiber; polyaniline/carbon nanoparticle nanofibers refs. [46–48] [49,50] the electrospinning procedures have been applied for both the wet and melt spinning[51,52]. the electrospinning technique involves easily controllable parameters for the formation of polymer and nanocomposite nanofibers[53]. electrospinning has simple set up consisting of a syringe with needle to held polymer solution, a pumping structure, a nozzle, a collector, and a power source. upon the application of applied voltage, polymer or nanocomposite solution is pumped out of the syringe through the needle. under the electric field effect, the ejected nanofiber elongates and moves towards the collector. here, polymer and nanofiller types, voltage applied, and pumping speed, etc. affect the nanofiber surface topology and structural and physical properties[54]. practically, electrospinning set up has been reported in the horizontal and the perpendicular provisions[15]. advanced form of electrospinning is the electrohydrodynamic direct writing mechano-electrospinning method[55]. in this approach, electrical and mechanical forces have been applied to grow viscous ink and resulting nanofibers[12]. hence, the polymer and nanocomposite nanofibers properties have been monitored by varying several parameters of polymer, nanoparticles, as well as the electrospinning set up[56,57]. figure 2 demonstrates a simple demonstration of the electrospinning set up. figure 2. a simple electrospinning set-up. 5 4. nanocomposite nanofibers and membranes formed by electrospinning technique high-tech nanocomposite nanofibers have been designed exhibiting high surface area and physical characteristics[58]. carbon nanotube is one dimensional cylindrical nanostructure made up of sp2 carbons[59,60]. carbon nanotube owns unique features and technical potential. using electrospinning, carbon nanotube has been filled in nanofibers of polymers[59]. the polyamide and poly(ethylene glycol) thermoplastic matrices have been reinforced with carbon nanotube to form electrospun nanofibers[61]. in addition, conducting polymer like polyaniline has been filled with carbon nanotube to synthesize the nanofibers[62]. the polyaniline/carbon nanotube nanofibers have fine nanofiller dispersion, texture, and conductivity properties[63]. simotwo et al.[64] designed the electrospun polyaniline/carbon nanotube nanocomposite nanofibrous membranes as shown in figure 3. scanning electron microscopy and transmission electron microscopy images reveal fine nanoparticle dispersion in the nanofibers (figure 4). no nanoparticle aggregation was observed due to the spinning and electrostatic forces applied in electrospinning technique. figure 5 displays the efficiency of electrospun polyaniline/carbon nanotube nanocomposite nanofibrous membranes for the supercapacitor electrodes. high specific capacitance of 320 f g−1 and capacitance retention of 83% were observed for nanocomposite nanofibers. superior supercapacitor performance was attributed to graphene dispersion and formation of conductive network in the polymer matrix. figure 3. polyaniline/carbon nanotube nanocomposite nanofibrous membranes[64]. reproduced with permission from acs. figure 4. scanning electron microscopy images of (a) polyaniline and (b) polyaniline/carbon nanotube electrospun nanofibers with an average nanofiber diameter of 678 ± 54 nm and 491 ± 86 nm, respectively; (c and d) transmission electron microscopy images of polyaniline/carbon nanotube nanofiber showing distribution of nanotube[64]. reproduced with permission from acs. 6 figure 5. plots showing electrochemical performance of symmetric polyaniline/carbon nanotube for specific capacitance as a function of charge-discharge rates[64]. reproduced with permission from acs. graphene is a two dimensional nanosheet of sp2 hybrid carbon atoms[65,66]. owing to advantageous physical characteristics, graphene has been employed to manufacture high performance nanomaterials[67]. among polymer matrices, nylons or polyamides have been explored for nanocomposite nanofibers[68,69]. accordingly, the graphene oxide reinforced nylon 6 and nylon 6,6 were processed for nanocomposite nanofibers through electrospinning[70,71]. the nanofibers reveal small diameters in the range of 100–200 nm. moreover, the nanofiller loading up to 10 wt.% depicted fine dispersion in nanocomposite nanofibers. leyvaporras et al.[72] fabricated the electrospun nanofibers of nylon 6/nitroxide-functional graphene oxide. nitroxidefunctionalized graphene oxide was formed with oxoammonium salt through the reaction between the aromatic alcohol protons and graphene oxide acid moieties (figure 6). scanning transmission electron microscopy images of modified graphene oxide and nanocomposite nanofibers are displayed in figure 7. in the micrographs, the finely dispersed functional graphene oxide can be seen in the nanofibers owing to matrix nanofiller intersections. effectiveness of electrospinning technique was responsible to form homogeneous electrospun nanofibers. figure 6. exfoliation and functionalization of graphene oxide with nitroxide moieties using oxoammonium salts[72]. et3n = triethyl amine; dmf = dimethyl formamide. reproduced with permission from elsevier (open access, pmc copyright). 7 figure 7. stem images showing (a) few layers of goft platelet (less than 4); and (b) nanocomposite nanofiber containing a thicker go platelet[72]. stem = scanning transmission electron microscopy; goft = nitroxide-functionalized graphene oxide layers; go = graphene oxide. reproduced with permission from elsevier (open access, pmc copyright). xu and gao[73] fabricated the nylon and graphene filled nanocomposites using an in situ technique. the caprolactam monomer was polymerized in the presence of graphene oxide nanosheets to form the nanomaterials. graphene oxide was filled in varying amounts of 0.1–10 wt.%. then, during in situ polymerization, graphene oxide was converted to graphene and grafted to polymerized nylon matrix. figure 8 expresses the route for the in situ formation of graphene and grafting to polymerized nylon 6. during in situ process, consistent graphene nanosheet dispersion was observed. figure 9 displays the scanning electron microscopy images of the nylon/graphene nanocomposites. at low and high resolutions, fine graphene dispersion can be observed in the matrix due to in situ process. figure 10 illustrates the electrospun nanofiber formation of the nylon/graphene nanomaterials. including 0.01 wt.% graphene contents resulted in higher tensile strength of 123 mpa and young’s modulus of 722 mpa, relative to neat nylon 6 nanofibers (50% lower values of properties). the property enhancement was attributed to graphene dispersion and covalent grafting to the polyamide matrix[74]. another important matrix for electrospun nanofiber is poly(vinyl alcohol) with graphene additive[75,76]. the electrical conductivity, optical, and thermal stability features of the poly(vinyl alcohol) nanofibers have been found to enhance with graphene loadings[77]. figure 8. synthesis of nylon/graphene nanocomposites formed using in situ ring opening polymerization of caprolactam[73]. reproduced with permission from acs. a b 8 figure 9. scanning electron microscopy images of 0.5 wt.% graphene grafted nylon nanocomposite, at low and high resolution respectively[73]. reproduced with permission from acs. reproduced with permission from acs. figure 10. (a) apparatus of melt spinning of nylon graphene (ng) nanocomposites nanofibers at 250 ℃; and (b) photograph of 0.5 wt.% nanofibers, optical micrograph with nanofiber diameter 50 μm (inset); and (c) stress-strain curves of neat polyamide 6 and nanocomposite nanofibers with 0.01 and 0.1. wt.% graphene contents[73]. reproduced with permission from acs. in addition to carbon nanoparticles, metal nanoparticles have also been filled in the nanofibers[78]. some important designs of metal and inorganic nanoparticles based electrospun nanofibers include transition metal like fe, co, ni based nanofibers, mg and yb doped in2o3 nanofibers, and conise2@n-carbon nanofibers[79,80]. the resulting high performance inorganic nanoparticle filled nanofibers have been employed for electrocatalysts and energy related devices and systems[81]. table 2 presents an outline of the specifications of various carbon nanoparticle nanocomposite nanofibers formed by electrospinning technique. table 2. specifications of carbon nanoparticle nanocomposite nanofibers. polymer nanocomposite diameter/size solvent/concentration physical properties ref. polyaniline/carbon nanotube nanofibrous membranes average nanofiber diameter 491 ± 86 nm polyethylene oxide solution specific capacitance 320 f g−1; capacitance retention 83% [64] nylon 6/nitroxide-functional graphene oxide 165–190 nm dimethyl formamide physical interactions; well dispersed microstructure [72] nylon/graphene diameter 50 µm melt tensile strength 123 mpa; young’s modulus 722 mpa [73] polyamide/graphene 76–338 nm hexafluoroisopropanol; 0.005–0.01 wt.% increase in tensile strength, young’s modulus fracture, toughness by 56%, 113%, and 250%, respectively [82] polyaniline/poly (methyl methacrylate)/aminofunctionalized graphene 35–133 nm dimethyl formamide thermal stability [83] poly(ε-caprolactone)/graphene oxide 201–264 nm glacial acetic acid; 1.5 w/v% tensile stress increase by 189% [84] poly(ε-caprolactone)/graphene 121–154 nm dichloromethane/methanol; 10–12 wt.% young’s modulus tensile strength of 3771 mpa and 56.08 mpa, respectively [85] poly(ε-caprolactone)/reduced graphene oxide 100–130 nm glacial acetic acid; 1.5 w/v% tensile strength increases by 304% [86] 9 5. applications of nanocomposite nanofibers and membranes prepared by electrospinning technique electrospinning method involves electrostatic spinning of material to form fibers. it has been adopted as an effective technique to form nanofibers having diameter in nanometer range under the influence of electric field. including carbon nanoparticles in nanofibers have numerous advantages, relative to pristine polymer nanofibers. particularly, the production of carbon nanoparticle filled electrospun nanofibers resulted in high surface area, homogeneous surface, topography, precise porosity, variable diameter/shapes, and specific designs/functions, which have not been detected for unfilled polymer nanofibers or membranes (figure 11). figure 11. electrospun nanofibers for nanocomposite membranes. in addition, nanoparticle filled nanofibers own better functionalization tendencies, fine percolation pathways for electrical conductivity and superior mechanical properties than polymer fibers[87]. electrospinning technique has been used to alter the specifications of nanofibers according to the specific desired applications. mainly the fiber parameters such as surface area to volume ratio, diameter, length, surface properties, porosity, morphology, etc. have been controlled by adjusting the electrospinning parameters such as solution/melt viscosity, flow rate, spinning speed, spinning mode, voltage applied distance between needle and collector[88]. applications of electrospinning technique have been found in the fields of filtration, energy sector, textile, biomedical, etc. in filtration processes, electrospinning method has been used to form nanofibers of high surface/volume ratio and controlled porosity for crucial environmental applications like air filtration and water purification[89]. by appropriately controlling the electrospinning parameters, molecular permeability and selectivity can be manages for the filtration of hazardous particulate matter. for textile application, electrospinning has been used to form nanofibers and membranes of very small size, high surface area, and appropriate porosity[90]. the fiber chemistry has bee found essential to choose nanofibers for textile purposes. development of strategies for fine quality regulation of the electrospinning process may form high quality textile nanofibers and membranes for commercialization. biomedical applications require the use of electrospinning technique to form nanofibers maintaining the morphology, strength, biocompatibility, degradation rate, drug release profile, and interactions with living cells for drug deliver as well as tissue engineering purposes[91]. then, wide ranging applications have been observed for the energy sector. in energy sector, electrospinning technique has offered high aspect ratio, robustness, and effective electron or charge transportation of the electrospun nanofibers and membranes[89,92]. consequently, the fields of energy storage and production like supercapacitors, li ion batteries, and solar cells have been focused. electrospinning has been used to create appropriate defects and surface area to support the charge passage and interfacial effects. by controlling the electrospinning parameters, efficient electrodes have been developed to overcome the challenges in current supercapacitor technology[93]. for li-ion batteries, the electrode must be designed with precise electrospinning parameters to attain high capacity, fast charging rates, and long cycle life[94]. electrospinning technique has also been found competent for designing nanofibers for dye-sensitized solar 10 cells for high efficiency[95]. some significant designs of inorganic or metal-organic hybrid based electrospinning nanofibers have been applied for high performance gas sensing and chemiresistive sensing devices[96,97]. this technique offers an efficient way to form ultra-fine nanofibers and nanocomposite meshes for superior gas sensing performance. for polymer/carbon nanocomposite nanofibers, energy storage applications related to supercapacitors have been reported[98]. including carbon nanoparticles can yield efficient supercapacitor electrodes having high surface area, capacitance. electron conduction, and structural properties[99]. zhou et al.[100] reported on polyaniline and graphene nanocomposite nanofibers developed through electrospinning technique. the electrospun nanofibers have been used for supercapacitor electrodes[101]. the potential polyaniline/graphene electrode had higher specific capacitance (250 fg−1) than that of unfilled polyaniline (175 fg−1) electrode. electrospinning was found efficient to form the nanofibers having high conductivity and capacitance properties. significantly, the electrospun nanocomposite nanofibers have been used to form the photovoltaics[102]. photovoltaic systems based on polythiophene and fullerene derivatives have been reported[103]. these devices have high power conversion efficiency of >5%[104]. kurniawan et al.[105] established poly(3hexylthiophene):phenyl-c61-butyric acid methyl ester nanofibers for photovoltaics. as prepared nanofibers were used after thermally annealed. table 3 shows the photovoltaic characters of the nanofibers. the thermally annealed nanofibers at 150 ℃ (30 min) had significantly higher power conversion efficiency, short circuit current density, and fill factor, relative to non-annealed nanofibers. figure 12 also depicts the i-v features of electrospun nanofibers based photovoltaics. better results for thermally annealed nanofibers were observed due to synergistic effect in nanostructure developed after heating. moreover, the polymer nanofibers have wide scope for biomedical relevance. the electrospun nanocomposite nanofibers have also been used in this field. for tissue engineering scaffolds, poly(vinyl alcohol) and graphene based nanofibers have been prepared by electrospinning method[106]. table 3. photovoltaic properties of the nanofibers[105]. pce = power conversion efficiency; jsc = short circuit current density; ff = fill factor; p3ht:pcbm = poly(3-hexylthiophene):phenyl-c61-butyric acid methyl ester; p3ht-nf:pcbm = poly(3-hexylthiophene)nanofiber:phenyl-c61-butyric acid methyl ester; na = non-annealed; ta= thermally annealed. reproduced with permission from acs. sample pce (%) jsc (ma/cm2) ff p3ht:pcbm (na) 1.08 4.56 0.33 p3ht:pcbm (ta) 3.57 8.57 0.66 p3ht-nf:pcbm 2.40 8.21 0.50 figure 12. i-v characteristics of photovoltaic devices fabricated with neat, thermally annealed p3ht:pcbm, and p3ht-nf:pcbm materials[105]. p3ht:pcbm = poly(3-hexylthiophene): phenyl-c61-butyric acid methyl ester; p3ht-nf:pcbm = poly(3hexylthiophene)-nanofiber:phenyl-c61-butyric acid methyl ester; na = non-annealed; ta= thermally annealed. reproduced with permission from acs. 11 mostly, polymer fibers have been researched for wide ranging applications related to membranes, coatings, packages, weaves, tissue engineering, and other arenas[107]. here, the carbon nanoparticle filled nanofibers have high-tech engineering applications[108,109]. the perfectly engineered nanofiber based membranes have been used for separation and purification applications[110]. these electrospun nanofibrous membranes have technical potential for water remediation applications[111]. the topography, permeability, selectivity, porosity, robustness, and other membrane properties have been studied[112]. the nanofiller dispersion and alignment in nanofibers and fiber orientation in membranes define the final membrane potential. electrospun polymer/carbon nanocomposite membranes for nanofiltration, ultrafiltration, distillation, and osmosis have been designed[113]. the electrospun membranes have been observed for the high flux, permeability, and rejection rates, relative to traditional membranes[114]. these innovative membranes have low weight, low price, optimum porosity, and large scale processing characters. hence, electrospinning has been referred as an emergent multipurpose practice to form high performance filtration membrane systems. 6. conclusions key points of this review article include: (i) understanding the fundamentals of nanofillers, nanocomposites, and nanofibers; (ii) basics and use of electrospinning technique to synthesize nanofibers; (iii) effect of electrospinning technique to fabricate the nanocomposite based nanofibers and membranes; and (iv) important applications of electrospun nanocomposite nanofibers and membranes. performance of electrospun nanocomposite nanofibers and membranes depends upon the factors like nanoparticle dispersion in the nanofibers, matrix-nanofiller interactions like electrostatic, hydrogen bonding, and convent interactions, and the adjustment of parameters of electrospinning technique. concisely, the review article explains the design of nanofibers focusing the electrospinning technique. this practice owns facile and efficient set up and easily controllable parameters to develop fine and advanced nanofibers. development of nanofibers and nanocomposite nanofibers through electrospinning has been found remarkable to unfold fine microstructure, physical properties, and technical utilizations in energy devices to membranes. the nanocomposites, particularly, the carbon filled nanofibers have been found technically efficient due to facile manufacturing parameters applied to controlling the final designs. further research in this field may lead to novel nanofiber design by overcoming the challenges related to nanoparticle dispersion, material compatibility, and parameter control. initially in this article, fundamentals of nanofillers, nanocomposites, and nanofibers have been stated to give reader a quick knowledge of these nanomaterials. afterwards, common spinning technique like solution blow spinning has been discussed in addition to electrospinning method to reveal the specifications, advantages, and differences of electrospinning techniques with respect to traditional spinning methods to form high performance nanofibers. consequently, major state-of-the-art of electrospun nanocomposite nanofibers and membranes have been discussed in subsequent section. numerous carbon nanoparticle filled nanofiber designs have been discussed with advantages of including carbon nanoparticles in nanofibers and property benefits compared with the pristine polymer nanofibers. for numerous polymer nanocomposite nanofiber, diameter, solvent used, processing conditions, and physical properties have been discussed. using this technique solution as well as melt samples have been successfully processed. the electrospun nanocomposite nanofibers have uniform nanoparticle dispersion and surface to enhance the physical properties like mechanical, thermal., conductivity, and other features. here, choice of polymer, solution concentration, electrospinning speed, solution flow rate, applied voltage, etc. affect the final characters such as consistency, surface, morphology, and diameter of the nanocomposite nanofibers. then, a detailed section presents the application areas of the electrospun nanofibers in supercapacitors, solar cells, and other probabilities have been discussed. due to better dispersion and conductivity properties, device applications have been preferred for electrospun carbon nanoparticle nanocomposite designs. however, engineered nanofiber membranes have been suggested for 12 future separation or purification utilizations on industrial level. in addition, the future scope of these nanofibers and membranes can be seen in the field of drug transfusion and tissue engineering. future developments in the field of polymer/carbon nanoparticle nanocomposite based nanofibers and membranes have been found 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2025, 8(1), 9187. https://doi.org/10.24294/can9187 article preparation, characterization of telfairia occidentalis stem extract-silver nanocomposite and application in remediation of lead (ⅱ) ions from oilfield produced water leonard mgbeahuruike1, roseline njoku-tony1, tochukwu ebe1, godwin jarkwa1, emereibeole ihediohanma1, ekemini ituen2,*, atim johnson2, ezirim thank god3 1 department of environmental management, school of environmental science, federal university of technology, owerri, nigeria 2 materials and oilfield chemistry research group, department of chemistry, faculty of physical sciences, university of uyo, uyo, nigeria 3 department of mechatronics, school of electrical systems engineering technology, federal university of technology owerri, owerri, nigeria * corresponding author: ekemini ituen, ekeminiituen@uniuyo.edu.ng abstract: every production day in nigeria, and in other oil producing countries, millions of barrels of produced water is generated. being very toxic, remediation of the produced water before discharge into environment or re-use is very essential. an eco-friendly and cost effective approach is hereby reported for remediative pre-treatment of produced water (pw) obtained from nigerian oilfield. in this approach, telfairia occidentalis stem extract-silver nanoparticles (tose-agnps) were synthesized, characterized and applied as bio-based adsorbent for treating the pw in situ. the nanoparticles were of average size 42.8 nm ± 5.3 nm, spherical to round shaped and mainly composed of nitrogen and oxygen as major atoms on the surface. owing to the effect of addition of tose-agnps, the initially high levels (mg/l) of total dissolved solids (tds), biological oxygen demand (bod) and tss of 607, 3.78 and 48.4 in the pw were reduced to 381, 1.22 and 19.6, respectively, whereas do and cod improved from 161 and 48.4 to 276 and 19.6 respectively, most of which fell within who and us-epa safe limits. particularly, the added tose-agnps efficiently removed pb (ii) ions from the pw at temperatures between 25 ℃ to 50 ℃. removal of tose-agnps occurred through the adsorption mechanism and was dependent contact time, temperature and dose of tose-agnps added. optimal remediation was achieved with 0.5 g/l tose-agnps at 30 ℃ after 5 h contact time. adsorption of pb (ⅱ) ions on tose-agnps was spontaneous and physical in nature with remediation efficiency of over 82% of the pb (ⅱ) ions in solution. instead of discarding the stem of telfairia occidentalis, it can be extracted and prepared into a new material and applied in the oilfield as reported here for the first time. keywords: adsorption; heavy metals removal; nanomaterial; oilfield chemical; remediation; water treatment 1. introduction during production of crude oil, water is usually also co-produced. this water is often referred to as produced water (pw) or petroleum wastewater. the pw may originate from reservoir or formation water, or water injected during recovery or enhanced recovery operations [1]. the chemical composition of pw varies depending on geographical region, quality of crude and operating condition [2]. most often, pw is composed of a complex blend of both inorganic and organic compounds. this implies that pw is highly toxic, and when discharged into the environment, it pollutes the environment. being a mixture of complex toxic organic and inorganic in nature, citation mgbeahuruike l, njoku-tony r, ebe t, et al. preparation, characterization of telfairia occidentalis stem extractsilver nanocomposite and application in remediation of lead (ⅱ) ions from oilfield produced water. characterization and application of nanomaterials. 2025; 8(1): 9187. https://doi.org/10.24294/can9187 article info received: 18 september 2024 accepted: 30 november 2024 available online: 14 january 2025 copyright copyright © 2025 by author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/licenses/ by/4.0/ characterization and application of nanomaterials 2025, 8(1), 9187. the chemicals in pw are often resistant to chemical or biological degradation. discharge of pw on soils or into water has been a major cause of environmental degradation in the niger delta region of nigeria [3]. it renders water unfit for consumption, harms aquatic animals, kills biodiversity on the land and renders the soil infertile for cropping. in the end, it leads to decline in food production which may result to famine, malnutrition and even deaths. to guard against these menace, it is very crucial that pw be treated before being discharged into the environment or re-use in injection stream. otherwise, the discharge could be pose harmful (carcinogenic, mutagenic) effects on environment and humans [3] and cause corrosion, scaling and flow problems in transportation pipework [4]. depending on its composition, various techniques have been applied to treat pw. among these include physicochemical, chemical and biological methods of pw treatment described in literature [5,6]. comparatively, chemical methods of treatment are very popular and reputed for good efficiency and selectivity [7–10]. for instance, high concentrations of grease, oil and fats as well as pollutants that may be suspended or dissolved in pw have been resolved by using chemical methods such as coagulation [11]. the coagulants precipitates are dissolved or suspended as colloidal solids which makes it easy to separate them by sedimentation. electrocoagulation may also be efficient especially for resolving very greasy and oily pws [12,13]. experts have opined that a single method may not remove all the toxic components in pw at the same time. therefore, any method used is often designed towards removing either some very toxic inorganic components only or some very toxic organic components only, at a given time [11]. this study was designed from this background and was aimed at removing some major toxic inorganic components in pw. the toxic inorganic substances in pw are basically heavy metals ions such as lead, cadmium, and chromium. these ions are often better removed using adsorbents by the adsorption [11]. adsorption phenomenon is a popular method of treating pw [14]. for instance, activated carbon prepared from various sources is a commonly reported efficient adsorbent for petroleum wastewater treatment [15,16]. in selecting an adsorbent, cost effectiveness, local availability, renewability, durability, stability, biodegradability, eco-friendliness and high adsorption capacity are key factors often considered [14,17]. despite the efficiency, activated carbon is very expensive to buy and laborious to fabricate and characterize. scientists have therefore been in the search for cheap alternative materials, hence the proposed research work. these days, engineered materials from plant extracts have been explored as alternative adsorbents that satisfy many of the requirements mentioned above [18]. among the ones reported, plant-based adsorbents (biosorbents) have been demonstrated to be effective in removing some organic compounds and heavy metal ions from industrial wastewater [19–22]. apart from a recent report by ituen and coworkers [11], to the best of our knowledge, the use of plant biomass-based adsorbents in its nano-form to remove heavy metals from produced water has not been reported in literature, hence the motivation for this study. in this study, we have demonstrated the use of t. occidentalis-silver nanoparticles as adsorbent for treating pw for the first time. characterization and application of nanomaterials 2025, 8(1), 9187. adsorbents derived from plant biomasses appear to be desirable because it will be of low cost, non-toxic and sustainably obtainable. also, since plants contain a wide range of phyto-compounds, it could be multifunctional but, would easily be degraded by biochemical agents [11]. in other words, if stored for long, biochemical degradation of the biomass sets in, then its adsorption capacity and efficiency declines. to overcome these setbacks, the extract needs to be modified using chemical additives [23]. recently, nanoparticles composites prepared by bio-reduction of plant extracts, have been used to remove toxic heavy metal ions, especially pb, cd, cr and organic pollutants from wastewater [11]. since nanoparticles large surface to volume ratio, their reactivity is expected to be high and this could justify the high removal efficiency reported in literature [11]. also, being less difficult to synthesize, with the synthetic process not requiring deployment of expensive equipment or high energy, nanoparticles engineered from plant extracts would be more desirable. therefore, the main objectives of this research was to prepare bio-based silver nanoparticles from t. occidentalis stem extract, characterize the nanoparticles and apply it as adsorbent for remediative treatment of pw, especially to remove pb (ⅱ) ions from the pw. 2. materials and methods 2.1. sample collection and preparation viable seeds of t. occidentalis were obtained from akwa ibom agricultural development program (akadep) and were authenticated by a plant taxonomist in the department of botany and ecological studies in the university of uyo. the plants were cultivated in the field. field experiment adopted a completely randomized design (crd) with three replications. the plants were cultivated in three raised shaped beds and maintained under proper routine agronomic practices [24]. the mature plant was harvested and the edible leaves plucked out. the stem (which is often discarded) were cut into pieces, washed convincingly with distilled water, dried in air at laboratory temperature and macerated (figure 1a–c). (a) de-leaving. (b) cutting into small sizes. (c) maceration. figure 1. t. occidentalis stem after (a) de-leaving; (b) cutting into small sizes; (c) maceration. 2.2. preparation of t. occidentalis stem extract a 10 g of the macerated sample was soaked in 1 l of de-ionized water for 24 h characterization and application of nanomaterials 2025, 8(1), 9187. and filtered using 1 mm filter paper. the filtrate was concentrated to paste form in rotary evaporator at 40 °c, dried in oven at 40 °c and blended in mortar to obtain dry powdery t. occidentalis stem extract (tose). 2.3. preparation of tose-silver nanomaterial solution of 0.001 m agno3 (analar, bdh, england) and 1.0 g/l of tose were prepared in deionized water. both were mixed at various ratios (vol/vol), allowed to react and observed for colour change [11]. every 1 hour, aliquot of the mixture was subjected to uv-vis spectroscopic analysis. after colour change, a portion of the mixture was concentrated in rotary evaporator at 40 °c, then retrieved, washed using de-ionized water and filtered. the filtrate was dried in oven at 30 °c and labelled as tose-silver nanomaterial (tose-agnp) and stored in aluminum foil for characterization. another portion was stored in amber colored glass for future analyses. 2.4. characterization of synthesized materials uv-vis analysis was conducted by scanning both the tose and tose-agnps at 200–800 nm using thermo genesys 10 uv/vis spectrophotometer. the functionalities in small quantity of each of tose and tose-agnp (mixed with kbr) were determined by ftir using agilent cary 630 ftir/atr spectrophotometer. the crystallographic properties of the powder samples of both tose and tose-agnp were also analyzed by xrd at 2 θ = 10°–90° using px1800 x-ray diffractometer. the elemental compositions of each of tose and tose-agnp were determined by eds using phenom prox sem/eds spectrophotometer. the morphology and size of each of tose and tose-agnps were probed by tem using fei technai g2f20 microscope. 2.5. collection and treatment of produced water produced water was collected from total oil drilling platform at amenem near port harcourt and transported to the laboratory the same day. the water sample was analysed to determine the average concentrations of lead ions present following standard procedures already reported by ituen and co-workers [11]. in addition, some physicochemical properties of the water, namely, biochemical oxygen demand (bod5), total dissolved solids (tds), chemical oxygen demand (cod), conductivity, total suspended solids (tss), dissolved oxygen (do) and ph were also analysed following similar procedures reported by ituen and co-workers [11]. 2.6. remediation of heavy metals from produced water the procedures reported by ituen and coworkers [11] were also followed with slight modifications. about 50 ml each of the produced water were placed in several flasks. about 0.5 g/l of tose and 0.1 g/l to 0.5 g/l of tose-agnps was added to each flask and each mixture was shaken in water bath at room temperature for 5 h. after 5 h, each mixture was filtered, and each filtrate was analyzed by aas to determine the concentrations of each of pb (ⅱ) ions. characterization and application of nanomaterials 2025, 8(1), 9187. 2.7. effect of adsorbent concentration the tose-agnps was prepared into five (5) different concentrations to elucidate the effect of its dosage on the remediation efficiency. the concentrations were selected between 0.10 g/l to 0.50 g/l and this was obtained by dilution of the highest concentration using the dilution principle. during this investigation, the contact time, temperature and volume of the pw were not changed. 2.8. effect of time and temperature to determine the effect of time on the remediation efficiency, aliquots of the mixture at room temperature were collected every 1 hour within the shaking process and analysed by aas. also, the influence of temperature on the remediation efficiency was studied by varying the temperature of the solution in the water bath between 25 °c to 50 °c. for this experiment, the highest concentration of tose-agnps (0.50 g/l) was used and the shaking process was carried out at a constant time of 5 h. 2.9. analysis of data the concentration of each metal ion in the produced water before remediation was denoted by co while the equilibrium concentration of each metal ion after filtration was denoted by ce. the remediation efficiency (η) was determined in terms of the ratio of the amount of heavy metal adsorbed by the substrate using equation (1) [11]. 𝜂(%) = 𝐶 − 𝐶 𝐶 𝑥 100 (1) the amount of heavy metal ion adsorbed per unit mass of tose and toseagnps at equilibrium (qe) was determined from equation (2), where m represents the mass of the adsorbent added to heavy metal ions solution of and v is the volume of the solution. 𝑞 = (𝐶 − 𝐶 ) 𝑉 𝑀 (2) 3. results and discussion 3.1. formation of nanoparticles on observation after every 1 h, the colour of the mixtures changed gradually until the nanoparticles were fully developed, signified by a change in colour from dark green to brown. it took different duration for complete development of the nanoparticles to occur depending on the ratio of mix. for instance, for the mixture containing tose:agno3 (vol/vol) at 1:1 formed at about 2 h whereas 1:2 and 2:1 formed at about 5 h and 8 h respectively. only the nanoparticles formed from 1:1 at the shortest duration was used for further studies. characterization and application of nanomaterials 2025, 8(1), 9187. 3.2. characterization of nanoparticles 3.2.1. uv-vis spectroscopy both tose and tose-agnps were subjected to uv-vis analyses and the spectra obtained were shown in figure 2. it can be observed that tose produced absorption maximum corresponding to the maximum wavelength of absorption (𝜆 ) at 433 nm whereas that of tose-agnps was obtained at 485 nm. since the absorption (𝜆 ) for tose and tose-agnps were different, it was inferred that tose-agnps is a different material from tose. also, the (𝜆 ) obtained for toseagnps were compared to others reported in literature for silver nanoparticles [11]. it was observed that the value for tose-agnps falls within 450–520 nm which is the range often obtained for silver nanoparticles. therefore, the (𝜆 ) obtained in the present study agrees with those reported in literature [11,18]. 400 450 500 550 600 0.0 0.5 1.0 1.5 2.0 2.5 3.0 a b s o rb an c e ( a .u ) wavelength (nm) tose tose-agnps 433 nm 485 nm figure 2. uv-vis spectra of tose and tose-agnps. 3.2.2. ftir spectroscopy in order to elucidate the functional groups present in each of the material, the ftir spectra of tose and tose-agnps were obtained and plotted in one frame of axes for easy comparison. the spectra obtained were shown in figure 3. it can be observed from the figures that tose produced several peaks including in the fingerprint region. however, the peaks at around 3120–3530 cm−1, 2975 cm−1 and 1620 cm−1 were of significance to this study. the 3120–3530 cm−1 peak on tose spectra may be assigned to o-h stretching of an aromatic alcohol or n-h stretching of a primary amine group. on formation of tose-agnps, it can be observed that this peak became broader and more prominent than with the crude extract. a similar occurrence was observed with the peak at 2975 cm−1 which may be assigned to n-h stretching of an amine salt. this peak appears sharper and more prominent with toseagnps than tose, suggesting that an amine salt may have been formed with silver. the peak at 1620 cm−1 may be assigned to c = c of alkene or 𝛼, 𝛽-unsaturated ketone. this peak shifted to 1635cm−1 in the spectrum of tose-agnps and became more characterization and application of nanomaterials 2025, 8(1), 9187. prominent. this indicates possibility of interaction of silver ions with tose phytocompounds at the c = c sites to form tose-agnps. figure 3. ftir spectra of tose and tose-agnps. 3.2.3. xrd spectroscopy to determine whether tose-agnps were crystalline, they were subjected to xrd analyses alongside with tose for proper comparison and the spectra obtained were shown in figure 4. it was observed that the spectrum of tose yielded no peaks whereas that of tose-agnps yielded major peaks at 2 𝜃 = 28.0°, 32.5°, 38.2°, 44.0°, 46.4°, 64.3° and 77.6°.these peaks were compared to silver file 04–0283 of joint committee on powder diffraction standards (jcpds) card as well as with other reports on plant extracts mediated silver nanoparticles [11]. it was observed that the peaks at 32.5°, 38.2° and 44.0° correspond to (121), (111) and (200) planes of ag0 phase. the peak at 38.2° was the most prominent, indicating that the silver is mostly distributed in the ag (111) plane. comparing the spectrum of tose with that of tose-agnps, it was clearly observed that while tose was amorphous, toseagnps were crystalline, indicating that tose-agnps may be a nanoparticle. figure 4. xrd diffraction patterns of tose and tose-agnps. characterization and application of nanomaterials 2025, 8(1), 9187. 3.2.4. eds spectroscopy the eds spectra of tose and tose-agnps with prejudice to c, n, o and ag atoms were obtained for comparison as shown in figure 5. the result revealed that ag was present on the surface of the new material (tose-agnps) but not found on tose. though both contain c, n and o, the amounts were different as shown in table 1. it can be inferred from table 1 that the incorporation of silver into the phytocompounds of tose resulted in its binding and formation of a kind of ag-organic framework which increased the visibility of n and o. a similar suggestion was made in a work reported by ituen and coworkers [11]. the eds results obtained also supported that tose-agnps may have been formed and may be nanocomposite. figure 5. eds spectra of (a) tose and (b) tose-agnps. table 1. elemental composition of tose and tose-agnps surface determined by eds. element tose tose-agnps weight (%) atomic (%) weight (%) atomic (%) c 70.02 75.03 46.12 58.16 n 0.46 1.01 1.13 2.21 o 29.52 23.96 39.34 37.73 ag 13.41 1.91 3.2.5. transmission electron microscopy the nanostructure of tose-agnps was probed using transmission electron microscopy and the images captured for both tose and tose-agnps were shown in figure 6. it was observed that tose were shapeless and sized within the microscale whereas tose-agnps were spherical to round and of average sizes of 42.8 nm characterization and application of nanomaterials 2025, 8(1), 9187. ± 5.3 nm. tem results confirmed that tose-agnps was nanomaterial and appeared crystalline. figure 6. morphologies of (a) tose and (b) tose-agnps determined by tem. 3.3. physicochemical properties of produced water the concentration of pb (ⅱ) ions in the produced water (pw) was determined in triplicates and the average values as computed was 1.43 ± 0.08 mg/l. the other physicochemical properties determined are shown in table 2. it has been documented that the usa-epa and who permissible limits of pb (ⅱ) ions for drinking water is 0.015 mg/l and 0.010 mg/l respectively [11], indicating that pb (ⅱ) ions are present in excess amount and remediation is crucial. in addition, the values obtained for key pollution indicator parameters such as tss, tds, bod etc were above who standards, therefore would require remediation to reduce them to safe limits before discharge or re-use for injection. therefore, the pw was initially remediated by addition of tose and tose-agnps and the results from both adsorbents were compared and discussed in the following sub-sections. table 2. physicochemical properties of non-remediated and remediated produced water. parameter non-remediated water sample remediated with tose remediated with tose-agnps ph 8.55 8.52 8.56 conductivity (µscm−1) 4318 3953 2881 tds (mg/l) 607 406 381 bod5 (mg/l) 3.78 1.56 1.22 do (mg/l) 2.16 5.87 6.79 cod (mg/l) 161 242 276 tss (mg/l) 48.4 38.2 19.6 3.3.1. effects of addition of tose and tose-agnps from table 2, it can be observed that remediation of pw with tose reduced ph from 8.55 to 8.52 whereas using tose-agnps, the ph rather increased to 8.56. these levels were well within the permissible limits by both us-epa and who. for conductivity, it can be observed that pw had a very high value of 4318 µscm−1. however, on remediation with tose and tose-agnps, the values reduced to 3953 characterization and application of nanomaterials 2025, 8(1), 9187. µscm−1 and 2881 µscm−1 respectively. this implies that remediation with tose and tose-agnps caused significant reduction in conductivity of pw. although the final conductivity of remediated water was still higher than the permissible level for drinking water (2500 µscm−1) and may require further treatment, the resulting water could still be useful for irrigation purposes and for livestock, which requires conductivity of around 2000–2500 µscm−1 ** [11]. for tds, addition of tose and tose-agnps reduced the value from 607 mg/l to 406 mg/l and 381 mg/l respectively. the upper safe limit of tds in drinking water was 500 mg/l while the who recommended limit is 300 mg/l. this implies that the tds in pw made it unsafe for drinking but on remediation, safe limits were attained. similarly, the safe limits for bod, do, cod and tss are 1–2 mg/l, 6.5–8 mg/l, 250–500 mg/l, 30 mg/l respectively. for do and cod, the values are associated with the amounts of oxygen in the water. the untreated water had low amounts of oxygen. however, on treatment with the new material, the amount of oxygen increased, which indicates its higher propensity to support aquatic life. as can be observed from table 2, on remediation with tose and tose-agnps, significant improvements were obtained, and the physicochemical properties of the remediated water was within ranges of values close to safe or permissible levels. thus, tose and tose-agnps were effective in remediating the pw with tose-agnps which showed better remediating effect than tose. 3.3.2. effects of changing the concentration of tose-agnps the concentration of tose-agnps was varied between 0.1 g/l to 0.5 g/l to elucidate the effect of its dose on the efficiency of remediation of pb (ⅱ) ions. results obtained are displayed in table 3. it was observed that the concentration of pb (ⅱ) ions in pw reduced from 1.43 mg/l to 0.32 mg/l and 0.18 mg/l on addition of tose and tose-agnps respectively, corresponding to an efficiency of 77.5% and 87.6% respectively. this implies that the efficiency of remediation of pb increases with increase in tose-agnps dosage or concentration and is also in agreement with previous observations reported by ituen and coworkers [11]. a possible explanation for this trend is that as the dose of the adsorbent increases, more adsorption sites becomes available per volume of the pw due to the presence of more adsorbent species in solution. the more the adsorption sites, the more the number of pb (ⅱ) ions adsorbed and sequestrated from the pw. on the other hand, even lower concentrations of toseagnps were more efficient than 0.5 g/l tose supporting that tose-agnps performs better than the crude extract. table 3. results for adsorption of lead (ⅱ) ions from pw within 5 h at room temperature using tose and different concentrations of tose-agnps. adsorbent co (mg/l) ce (mg/l) η (%) qe 0.5 g/l tose 1.43 0.41 71.2 102 0.1 g/l tose-agnps 1.43 0.32 77.5 555 0.2 g/l tose-agnps 1.43 0.28 80.4 288 0.3 g/l tose-agnps 1.43 0.26 81.8 195 0.4 g/l tose-agnps 1.43 0.20 86.1 154 0.5 g/l tose-agnps 1.43 0.18 87.6 125 characterization and application of nanomaterials 2025, 8(1), 9187. 3.3.3. effects of temperature the effect of temperature on the amount of pb (ⅱ) ions removed from the pw was investigated by varying the experimental conditions from room temperature (25 °c) to 50 °c and the results obtained are shown in table 4. the results reveal that as temperature increases, the amount of pb (ⅱ) ions removed as well as the remediation efficiency decreases. for instance, in the presence of tose, the amount of pb (ⅱ) ions in pw reduced from 1.43 mg/l to 0.42 mg/l and 0.58 mg/l respectively corresponding to remediation efficiency of 70.7% and 59.7% respectively as temperature increased from 25 °c to 50 °c. this indicates that as temperature increases, there would be a huge reduction in remediation capacity and the qe when tose is used as adsorbent. however, on addition of tose-agnps, the reduction in remediation efficiency was only slightly as could be observed going from 85.2% to 81.6%. this implies that the modification of tose into tose-agnps makes it more thermally stable and efficient than tose. the observed decrease in remediation efficiency as temperature increases is could be ascribed to the weak binding character of the adsorbent—pb (ⅱ) ions adsorptive interaction. such interactions are usually considered as physisorptions and are often driven by physical forces such as electrostatic interaction between positive pb (ⅱ) ions and negative groups on the tose-agnps surface [11]. owing to their weak nature, such interactions weaken with increase in temperature, leading to reduced remediation efficiency. table 4. results for adsorption of lead (ⅱ) ions from produced water within 5 h at different temperatures. temperature (°c) tose tose-agnps co (mg/l) ce (mg/l) η (%) co (mg/l) ce (mg/l) η (%) 25 1.43 0.42 70.7 1.43 0.21 85.2 30 1.43 0.41 71.4 1.43 0.17 88.1 40 1.43 0.48 66.4 1.43 0.22 84.3 50 1.43 0.58 59.7 1.43 0.26 81.6 3.3.4. effects of contact time the effect of contact time between the adsorbent and the heavy metal contaminants in pw was investigated to elucidate the optimum time required to remove the ions from pw. the results obtained were shown in table 5. from the table, it can be observed that the efficiency of remediation increased as contact time increased until it reached a critical time of 5 h after which there was no significant increase in the percentage remediation efficiency. therefore, it was inferred that the time taken for tose-agnps to optimally remove pb ions from pw is 5 h. after this time, equilibrium may have been achieved and an optimal efficiency reached. characterization and application of nanomaterials 2025, 8(1), 9187. table 5. results for adsorption of lead (ⅱ) ions from produced water at room temperature and different times using 0.50 g/l tose-agnps. time (h) parameters co (mg/l) ce (mg/l) η (%) 1 1.43 0.74 48.1 2 1.43 0.61 54.7 3 1.43 0.47 66.8 4 1.43 0.37 74.2 5 1.43 0.26 81.6 6 1.43 0.25 82.1 7 1.43 0.25 82.2 8 1.43 0.25 82.2 3.4. remediation kinetics and adsorption mechanism it has been reported that removal of heavy metal ions from solution by bio-based adsorbents occurs through the adsorption mechanism. adsorption involves attraction and holding of the metal ions on the surface of the adsorbent molecules driven by surface forces. these surface forces could be electrostatic or weak van der waals forces (physical adsorption) or even coordinate covalent bonding (chemical adsorption). to probe the nature of these forces, the values of and obtained were fitted into various adsorption isotherms but the best fit was obtained with the freundlich adsorption isotherm (with r2 = 0.9998) which can be represented as shown in equation (3) [11]: log 𝑞 = log 𝐾 + 1 𝑛 log 𝐶 (3) where kf and n are constants related to the adsorption phenomena and kf can be related to the free energy of adsorption using the equation (4) [11]: δ𝐺 = −𝑅𝑇 ln 55.5𝐾 (4) where 55.5 is a factor that relates with the concentration of water molecules. the obtained isotherms is shown in figure 7 and the associated kinetic parameters deduced. the straight line graph afforded a slope of 0.93 and an intercept of 1.814. the constants n and kf were 0.551 and 1.08 respectively. the value of δ𝐺 obtained was −10.14 kj/mol which can be appropriately associated with spontaneous adsorption of the metal ions on tose-agnps. thus, if deployed for industrial use, tose-agnps would remediate pw on its own without the need for any catalyst or external force. also, since the δ𝐺 value is less negative than −20 kjmol−1, the adsorption therefore proceeded via the physical adsorption mechanism [11]. characterization and application of nanomaterials 2025, 8(1), 9187. -1.0 -0.8 -0.6 -0.4 -0.2 2.2 2.4 2.6 2.8 3.0 lo g q e log c e figure 7. freundlich adsorption isotherm for the adsorption of pb from pw using tose-agnps at room temperature. 4. conclusion telfairia occidentalis stem extract-silver nanocomposites (tose-agnps) were prepared, characterized and assessed as adsorbent for removing treatment of pw, which is usually toxic, before discharge or re-use. the nanomaterial was round shaped and the surfaces were rich in o and n atoms. the tose-agnps was up to 82% efficient in remediating pb (ⅱ) ions from pw. treatment of pw with tose-agnps also helped to reduce the levels (mg/l) of tds, bod and tss while increasing the levels of do and cod to near who and us-epa safe limits. the remediation occurs through spontaneous physical adsorptive interactions between tose-agnps species and pb (ⅱ) ions. the adsorption and remediation depends on contact time, temperature and dose of tose-agnps added. the new material could find application in the petroleum industry for treating associated wastewater. author contributions: conceptualization, ei (ekemini ituen), rnt, gj and lm; methodology, ei (ekemini ituen), aj and gj; software, ei (ekemini ituen); validation, lm, rnt, ei (ekemini ituen) and te; formal analysis, ei (ekemini ituen) and gj; investigation, gj, ei (ekemini ituen), lm, rnt, te, aj, ei (emereibeole ihediohanma) and etg; resources, gj, ei (ekemini ituen) and lm; data curation, gj, ei (ekemini ituen), rnt and lm; writing—original draft preparation, gj and ei (ekemini ituen); writing—review and editing, ei (ekemini ituen); visualization, gj, ei (ekemini ituen), lm, rnt, aj, te, ei (emereibeole ihediohanma) and etg; supervision, rnt, lm and ei (ekemini ituen); project administration, rnt, lm, ei (ekemini ituen), te, ei (emereibeole ihediohanma) and etg; funding acquisition, gj and ei (ekemini ituen). all authors have read and agreed to the published version of the manuscript. conflict of interest: the authors declare no conflict of interest. characterization and application of nanomaterials 2025, 8(1), 9187. references 1. salem f, thiemann t. produced water from oil and gas exploration—problems, solutions and opportunities. journal of water resource and protection. 2022; 14(2): 142–185. 2. al-ghouti ma, al-kaabi ma, ashfaq my, da’na da. produced water characteristics, treatment and reuse: a review. journal of water process engineering. 2019; 28: 222–239. 3. ewim dre, orikpete of, scott,to, et al. survey of wastewater issues due to oil spills and pollution in the niger delta area of nigeria: a secondary data analysis. bulletin of the national research centre. 2023; 47(1): 116. 4. ukhurebor ke, athar h, adetunji co, et al. environmental implications of petroleum spillages in the niger delta region of nigeria: a 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l.) grown with okra (abelmoschus esculentus l.) under raised and sunken bed systems. agronomy. 2021; 11(10): 2087. characterization and application of nanomaterials 2025, 8(2), 10326. https://doi.org/10.24294/can10326 article functionalization of graphene by intercalation: a theoretical insight vittoria urso department of physics, sapienza università di roma, 00185 rome, italy; vittoria.urso@uniroma1.it citation urso v. functionalization of graphene by intercalation: a theoretical insight. characterization and application of nanomaterials. 2025; 8(2): 10326. https://doi.org/10.24294/can10326 article info received: 14 november 2024 accepted: 18 march 2025 available online: 6 may 2025 copyright copyright © 2025 author(s). characterization and application of nanomaterials is published by enpress publisher, llc. this work is licensed under the creative commons attribution (cc by) license. https://creativecommons.org/ licenses/by/4.0/ abstract: the intercalation of alkali metals in graphene monolayers and bilayers has been studied using first-principles calculations in particular density functional theory. alkali metals intercalate into graphite, leading to the formation ofm-graphene layered materials (withm = li, na, k, rb, and cs). intercalated species can modify the very electronic structure of graphene and consequently its electron mobility. thanks to various experimental studies, it has been possible to demonstrate that alkali metal intercalation can be used to modify the electronic structure close to the fermi level of the m-graphene materials and manipulate the carrier mobility and therefore we want to do this also with computational studies. these materials have a wide variety of applications, especially for the development of new batteries and other devices. the first principles are discussed on the effects of the intercalation of a heavy-alkali metal (k) on the electronic structure of graphene monolayers and bilayers. keywords: graphene; alkali metals; intercalation; dirac cone shift pacs numbers: 71.10.−w; 78.20.bh; 81.05.ue 1. introduction graphene is the most studied of two-dimensional (2d) materials [1–6], pristine free-standing graphene has a high electron mobility, which is reduced when deposited on a substrate due to graphene-substrate interactions [7–12]. graphene and carbon nanotube cnts are among the most prominent nanoscale materials currently studied [13]. two-dimensional (2d) graphene [14] has a rather unique sublattice symmetry and is a zero-gap semiconductor with a point-like fermi surface and a linear dispersion at the fermi level; these properties are responsible for observed ballistic transport, dirac-type quasiparticles, and anomalous quantum hall effects [15]. graphene is a flat monolayer of carbon atoms tightly packed in a two-dimensional (2-d) honeycomb lattice and is a basic building block for graphitic materials of all other dimensions [16] as shown in figure 1. its interesting electrical and transport properties have attracted much attention since its discovery in 2004. graphene is one atom thick and its very high mobility allows the quantum hall effects to be observed even at room temperature [17]. alkali metals adsorbed onmetallic substrates have been studied for a long time [18,19], but the nature of the alkali-substrate bond is not yet fully understood. a subset of these studies concerns the adsorption of alkali in graphite [19]. the electronic properties of graphite can change dramatically due to intercalators; for example, electrical conductivity along the planes increases dramatically [19]. potassium (k) has been the most studied of all alkali metals intercalated on graphite [20–24]. the first step in studying the surface structure of k in graphite is the intercalation process [25]. in figure 2 there are some 1 characterization and application of nanomaterials 2025, 8(2), 10326. methods of intercalation of k on graphite, in particular methods for investigating the coverage of k/graphite, in the last column you can find a reference for each experiment: figure 1. carbon allotropes. top left: graphene 2-d; top right: graphite 3-d; bottom left: nanotube 1-d; bottom right: fullerene 0-d [17]. figure 2. critical coverage for k/graphite condensation taken from reference [25]. 2. theory graphene is made out of carbon atoms with a structure shown in figure 3 [26]. the lattice vectors can be written as a1 = a 2 (3, √ 3) a2 = a 2 (3,− √ 3) (1) 2 characterization and application of nanomaterials 2025, 8(2), 10326. where a ≈ 1.42å. the reciprocal-lattice vectors are given by b1 = 2π 3a (1, √ 3) b2 = 2π 3a (1,− √ 3). (2) the two pointsk andk’ at the corners of the brillouin zone (bz) are of particular importance, these are named dirac points, their positions in momentum space are [26]: k = ( 2π 3a , 2π 3 √ 3a ) k′ = ( 2π 3a ,− 2π 3 √ 3a ) . (3) figure 3. honeycomb lattice and its brillouin zone. left: lattice structure of graphene, made out of two interpenetrating triangular lattices (a1 and a2 are the lattice unit vectors, and δi, i = 1, 2, 3 are the nearest-neighbor vectors). right: corresponding brillouin zone. the dirac cones are located at thek andk ′ points [26]. the three nearest-neighbor vectors in real space are given by δ1 = a 2 (1, √ 3), δ2 = a 2 (1,− √ 3), δ3 = −a(1, 0). (4) usually the schrödinger equation is quite sufficient to describe the electronic properties of materials. charge carriers in semiconductors have a non-zero effective mass and their behavior can be well described by schrödinger’s equation. graphene is an exception [27–30]: its charge carriers behave like relativistic particles and therefore it is more natural to describe them with the dirac equation rather than the schrödinger equation [31] (see figure 4). the tight-binding hamiltonian for electrons is: h = −t ∑ <i,j>,σ (a+σ,ibσ,j + h.c.) − t′ ∑ <<i,j>>,σ (a+σ,iaσ,j + b+σ,ibσ,j + h.c.) (5) where t ≈ 2.8 ev is the nearest-neighbor hopping energy and t’ = 0.1 ev (obtained from ab initio calculations) is the next nearest-neighbor hopping energy. the energy bands have the form: e±(k) = ±t √ 3 + f(k)− t′f(k) (6) with 3 characterization and application of nanomaterials 2025, 8(2), 10326. f(k) = 2 cos ( √ 3kya) + 4 cos ( √ 3 2 kya)cos ( 3 2 kxa) (7) where the plus sign applies to the upper (π∗) and the minus sign to the lower (π) band, from equation (7) can be seen that the spectrum is symmetric around zero energy if t′ = 0. for a finite value of t′, the electron-hole symmetry is broken and the π and π∗ bands become asymmetric. in figure 5 there is the full band structure with both t and t′, there is also a zoom in of the band structure close to one of the dirac points (at the k or k ′ point in the bz). this dispersion can be obtained by expanding the full band structure, equation (7), close to the k (or k′) vector, equation (3), as k = k+ q, with |q| ≪ |k| e±(q) ≈ ±vf |q|+o[(q/k)2] (8) where vf is the fermi velocity, given by vf = 3ta/2, with a value of vf ≃ 1×106 m/s. the most important difference between this result and the usual case ϵ(q) = q2/(2m), wherem is the electron mass, is that the fermi velocity does not depend on the energy or momentum. figure 4. (a) charge carriers are normally described by the schrödinger equation with an effective mass m∗ different from the free electron mass (p is the momentum operator). (b) relativistic particles in the limit of zero rest mass follow the dirac equation, where c is the speed of light and σ is the pauli matrix. (c) charge carriers in graphene are called massless dirac fermions, with the fermi velocity vf = 1× 106 m/s playing the role of the speed of light. (d) bilayer graphene provides us another type of quasi-particles: they are massive dirac fermions described by a rather bizarre hamiltonian that combines features of both dirac and schrödinger equations [31]. the coverage-dependent behavior of k/graphite is obtained by means of a combination of one-dimensional low energy electron diffraction (leed) and electron energy loss spectroscopy (eels): low covers can be prepared in which the k atoms are partially ionized and evenly distributed over the surface due to dipole-dipole interactions. as coverage increases, the upper layer compresses uniformly until it reaches a critical coverage (θ) of 0.1 monolayer (ml) [19]. coverages below this limit are defined as dispersed phase, while the critical coverage (0.1 ml) will be referred to as saturated dispersed phase. at 0.1 ml, potassium forms approximately a covering layer (7 × 7 ). above 0.1 ml, islands (2 × 2) start to nucleate until the covering layer 4 characterization and application of nanomaterials 2025, 8(2), 10326. (2 × 2) is fully developed and corresponds to θ = 1 ml. the region between 0.1 and 1 ml will be defined as mixed phase. figure 5. electronic dispersion in the honeycomb lattice. left: energy spectrum. right: zoom in of the energy bands close to one of the dirac points. 3. computational details calculations are performed within the first-principles density functional theory (dft) under the local density approximation (lda). our main goal is to observe the effect of doping on graphene, and since we are not directly interested in describing long-range interactions or structural distortions, we focus on the simplest approach: lda. lda is sufficient to observe charge transfer from the alkali metal to graphene, changes in the electronic bands of graphene, such as filling of conduction bands, and changes in local electronic properties, such as the change of the density of states (dos) near the fermi level. lda is an approximation that works well when dispersion effects (van der waals forces) are not dominant or are not crucial for the interaction between the alkali metal and graphene; there are no large structural distortions in the graphene lattice that significantly affect the geometry or symmetry of the electronic bands. lda is preferred in all cases like these for computational simplicity because it is less computationally expensive than gga making it more suitable for preliminary studies or large-scale simulations and for the description of local electronic changes; and because lda can provide an accurate idea of the change in electron density and energy levels as a result of doping without the need to deal with the weak interactions between the alkali metal and graphene. in practice we use the so-called “rigid band model”, a simple model in which the interaction between graphite and an adsorbate or intercalant is limited to the donation or removal of the charge by the atom, with no other influences on the graphite bands [19]. the model thus allows us to understand the observed binding energy shifts, estimate the amount of charge transferred, etc. the quantum espresso package is used to perform all calculations [32]. the primitive unit cell and the experimental value of the lattice constant are shown infigure 6, my calculated lattice constant is 2.44å = √ 3×1.41å, which is slightly smaller than the experimental value. 5 characterization and application of nanomaterials 2025, 8(2), 10326. figure 6. on the left: model of (a) two-dimensional and (b) three-dimensional graphite together with the structural parameters. in (a), the surface unit cell, containing two c atoms, is highlighted. on the right: a schematic diagram of the (2 × 2) structure formed by k on the graphite surface. both the substrate and the overlayer unit cells are represented [25]. calculations for the isolated graphene layer (2 × 2) and (4 × 4), the isolated adatom layer (2 × 2) and (4 × 4), and the adatom-graphene system (2 × 2) and (4 × 4) are performed with the same hexagonal supercell. the brillouin zone is sampled with a grid of 8 × 8 × 1 k points centered on γ, and gaussian smearing with a width of σ = 0.01 ev is used for the occupation of the electronic levels. a larger supercell improves the description of the interactions between alkalines and graphene, reducing periodic confinement effects and improving the convergence of physical properties. finer sampling of the brillouin zone allows for a better description of electronic bands and densities of states, especially in regions close to the dirac points of graphene. with alkaline intercalation, the effect on electronic bands (e.g., shifting of conduction bands or formation of new states) can be more precisely predicted. the self-consistency convergence threshold was set at 1.0d−9, the convergence threshold on total energy at 1.0d−5, and the convergence threshold on forces (a.u.) at 1.0d−4. we have performed calculations of k on graphite at the h site; see figure 7: figure 7. the three adsorption sites: hollow h, bridge b, and top t [33]. 4. results we have analyzed 11 different systems through self-consistent field calculations with quantum espresso under the local density approximation (lda) and perdew-zunger functionals and the von barth-car method (pz-vbc), including spin polarization, and we have obtained the results showed in table 1: 6 characterization and application of nanomaterials 2025, 8(2), 10326. table 1. the results of all systems, the greater the shift of the dirac cone the greater the doping. system total energy (ev) /num. atoms schift dirac cone (ev) dk−graphene (å) 1. kc8 −138.9405 −1.07 2.89 2. kc32 −150.6698 −0.90 2.73 2bis. kc32 (s = 2) −150.6703 −0.88 2.73 3. k4c32 −138.9397 −1.07 2.93 4. k4c32 (alt. side) −138.9153 −1.18 2.84 5. k4c32 (check.) −138.9153 −1.18 2.83 6. c8kc8 (st. ab) −146.5524 −1.07 2.84 7. c8kc8 (st. aa) −146.5547 −1.18 2.85 8. kc8c8 −146.54465 −1.07 2.91 9. kc8c8k −138.9507 −1.07 2.92 10. kc2 −105.6311 −2.30 2.66 11. k2c32 −146.5225 −0.98 2.83 the following subsections show the systems visualized with xcrysden and the dos visualized with xmgrace. 4.1. kc8 in figure 8 thekc8 system is shown and in figure 9 its dos. figure 8. in the upper there is thekc8 system in top view (on the left) and in side view (on the right) in (2 × 2) unit cell and in the lower there is the replicated kc8 system in the top view (on the left) and in the side view (on the right) in (6× 6) unit cell. the carbon-carbon distance is dc−c = 1.4106å. 7 characterization and application of nanomaterials 2025, 8(2), 10326. figure 9. the dos (density of states) of the kc8 system, on the left the full dos and on the right a range of energy around the fermi level. in figure 10 are shown the pdos (projected dos). figure 10. the full and its partial dos s and p. 4.2. kc32 in figure 11 thekc32 system is shown and in figure 12 its dos. 8 characterization and application of nanomaterials 2025, 8(2), 10326. figure 11. in the upper there is the kc32 system in top view (on the left) and in side view (on the right) in (4 × 4) unit cell and in the lower there is the replicated kc32 system in the top view (on the left) and in the side view (on the right) in (12× 12) unit cell. the carbon-carbon distance is dc−c = 1.4106. figure 12. the dos of the kc32 system, on the left the full dos and on the right a range of energy around the fermi level. only in this case do we have a magnetic case as shown in figures 13 and 14. 9 characterization and application of nanomaterials 2025, 8(2), 10326. figure 13. the dos of thekc32 system with spin = 2, on the left the dos of my calculation and on the right the dos of figure 3 of the reference [34]. figure 14. the dos of thekc32 system with spin = 2, on the left a range of energy around the fermi level of my dos and on the right figure 4 of the reference [34]. 10 characterization and application of nanomaterials 2025, 8(2), 10326. 4.3. k4c32 in figure 15 thek4c32 system is shown and in figure 16 its dos. figure 15. in the upper there is the k4c32 with (4 × 4) cell and in the lower there is the replicatedk4c32 system. the carbon-carbon distance is dc−c = 1.4102. figure 16. the dos of thek4c32 system, on the left the full dos and on the right a range of energy around the fermi level. 4.4. k4c32 with k on alternate side in figure 17 the k4c32 with k on alternate side system is shown and in figure 18 its dos. figure 17. in the upper there is the k4c32 system with (4 × 4) cell and in the lower there is the replicatedk4c32 system. the carbon-carbon distance is dc−c = 1.4119. 11 characterization and application of nanomaterials 2025, 8(2), 10326. figure 18. the dos of thek4c32 system, on the left the full dos and on the right a range of energy around the fermi level. 4.5. k4c32 with k at checkerboard in figure 19 the k4c32 with k at checkerboard system is shown and in figure 20 its dos. figure 19. in the upper there is the k4c32 system with (4 × 4) cell and in the lower there is the replicatedk4c32 system. the carbon-carbon distance is dc−c = 1.4111. figure 20. the dos of thek4c32 system, on the left the full dos and on the right a range of energy around the fermi level. 12 characterization and application of nanomaterials 2025, 8(2), 10326. 4.6. c8kc8 with stacking ab in figure 21 the c8kc8 with stacking ab system is shown and in figure 22 its dos. figure 21. in the upper there is the c8kc8 system with (2× 2) cell and in the lower there is the replicated c8kc8 system. the carbon-carbon distance is dc−c = 1.4131. figure 22. the dos of the c8kc8 system, on the left the full dos and on the right a range of energy around the fermi level. 4.7. c8kc8 with stacking aa in figure 23 the c8kc8 with stacking aa system is shown and in figure 24 its dos. figure 23. in the upper there is the c8kc8 system with (2× 2) cell and in the lower there is the replicated c8kc8 system. the carbon-carbon distance is dc−c = 1.4121. 13 characterization and application of nanomaterials 2025, 8(2), 10326. figure 24. the dos of the c8kc8 system, on the left the full dos and on the right a range of energy around the fermi level. 4.8. kc8c8 in figure 25 thekc8c8 system is shown and in figure 26 its dos. figure 25. in the upper there is the kc8c8 system with (2× 2) cell and in the lower there is the replicatedkc8c8 system. the carbon-carbon distance is dc−c = 1.4083. figure 26. the dos of thekc8c8 system, on the left the full dos and on the right a range of energy around the fermi level. 14 characterization and application of nanomaterials 2025, 8(2), 10326. 4.9. kc8c8k in figure 27 thekc8c8k system is shown and in figure 28 its dos. figure 27. in the upper there is thekc8c8k system with (2×2) cell and in the lower there is the replicatedkc8c8k system. the carbon-carbon distance is dc−c = 1.4100. figure 28. the dos of the kc8c8k system, on the left the full dos and on the right a range of energy around the fermi level. 4.10. kc2 in figure 29 the c8kc8 system is shown and in figure 30 its dos. figure 29. in the upper there is thekc2 system with (1×1) cell and in the lower there is the replicatedkc2 system. the carbon-carbon distance is dc−c = 1.50. 15 characterization and application of nanomaterials 2025, 8(2), 10326. figure 30. the dos of the kc2 system, on the left the full dos and on the right a range of energy around the fermi level. 4.11. k2c32 in figure 31 the c8kc8 system is shown and in figure 32 its dos. figure 31. in the upper there is the kc16 system with (2 × 2) cell and in the lower there is the replicatedkc16 system. the carbon-carbon distance is dc−c = 1.4106. figure 32. the dos of the kc16 system, on the left the full dos and on the right a range of energy around the fermi level. 16 characterization and application of nanomaterials 2025, 8(2), 10326. 5. conclusions chemical doping is a natural way to increase the performance or personalize the properties of graphene or any other 2d material. the band gap can be produced in graphene by chemical doping with a significant reduction in its carrier mobility [35]. however, there are several methods for modifying the band gap of graphene without the use of traditional chemical doping. these approaches exploit geometry, physical interactions (such as quantum confinement [36] or strain engineering [37]), and structural modifications such as oxidation [38] or the use of multilayer structures [39] to achieve semiconductor-like electronic behavior, opening the band gap of graphene, or simply the application of electric fields [40]. after doping graphene, several mechanisms contribute to the reduction of charge carrier mobility. the main ones are the following: impurity scattering [41], phonon scattering (lattice vibrations) [42], defect [43] and dislocation scattering, local structure distortions. the computational results obtained are well compared to the experimental data of reference [44] shown in figure 33 and with some literature dealing with this topic [45–52] and could be useful for predicting material properties [53,54]. figure 33. (a) uv photoemission spectral density of the k-npg system as a function of k exposure (spectra vertically stacked for the sake of clarity). (b) perspective 3d view of the spectral density evolution of the vb close to the fermi level (black line) as a function of k dose; the dirac point energy shift δe due to charge injection is reported as a red line in the top projection of the 3d perspective view. (c) experimental spectral density of k-npg at saturation coverage (red line) compared with clean npg, shifted by −0.6 ev in spectral density (gray filled area) [44]. 17 characterization and application of nanomaterials 2025, 8(2), 10326. the experimental results of figure 33 are obtained with ups, ultraviolet photoelectron spectroscopy, (h̄ν = 21.2 ev and h̄ν = 40.8 ev whose sources are hei and heii, respectively) used to probe the surfaces of materials (see figure 34). the most significant observation is an intensity peak at the fermi energy ef in the intercalation compounds. this peak is mainly due to alkali-like s states [55]. photoelectron spectroscopy is the most powerful and versatile technique to study the electronic structure of the valence bands in atoms, solids, and molecules (ionization energy of molecules, homo). multiplying the dos of the computational calculations with the fermi-dirac distribution f(e), we get the density of conduction electrons at any particular energy n(e) = dos · f(e). for the koopmans theorem we have ii = −ϵi, where ii is the binding energy of an electron in the state i and ϵi is the orbital energy of the state i-th. identification of calculated orbital energies with ionization potentials is possible as shown in figure 35. figure 34. with xps (with hν > 1000 ev) the electron emission is a good reflection of the density of states (weighted by the transition rate across the vb). at low photon energies (hν < 50 ev) as in ups the situation is more complex but richer in information. figure 35. left: computational results for pristine graphene (quantum espresso (qe) c8) and k-doped graphene (qe k4c32 instead of kc8 and kc32) compared with experimental results from reference [44]. right: a zoom of the same data. ups results involving a coverage of 0.3–0.4 ml are very similar to those obtained computationally with quantum espresso for thekc32 system (1 ml→ kc8). finally, it is possible to observe from the total energy values of systems 6,7 and 11 that the bilayer is more favored than the monolayer (it is also possible to verify this for the kc8 systems) and this compares well with other works [56–58]. 18 characterization and application of nanomaterials 2025, 8(2), 10326. the electron donating ability of alkalis, which increases as we move down the group, from li to cs [59–66], changes the electronic balance and therefore shifts the fermi level. li being the lightest and having a low electronegativity has a tendency to easily donate its valence electron to the graphene surface. consequently, the introduction of li is expected to shift the fermi level upwards, potentially increasing the density of electronic states near the fermi level. this could increase the conductivity of the system and, in some cases, lead to metallic behavior. na, although larger than li maintains a similar behavior, the fermi level could shift even higher than pure graphene, but to a lesser extent than li. k being larger than na tends to donate its valence electron even more easily, but the bond strength between graphene and the adatom is generally weaker. it could be observed that the interaction of potassium with graphene leads to a marked upward shift of the fermi level but due to the lower electron affinity the effect may be more transient or less stable. rb and cs [67], the heavier of the family, the adatomics become even more reactive and tend to donate electrons to graphene more easily. however, the chemical stability of systems with rb [68] and cs may decrease, since these alkali atoms tend to have a low adhesion energy to graphene, leading to possible desorption phenomena at relatively low temperatures. in these cases, it could be observed significant shifts of the fermi level, but with a less stable behavior over time, especially at high temperatures. the interaction between graphene and alkali adatomics, as we have seen, also affects the band structure of the system, in particular the dirac cone, li adsorption on graphene may cause minimal distortion of the dirac cone, but the symmetry of the cone should remain fairly intact. however, a shift in the fermi level upwards can make the systemmore conductive. at low concentrations, this effect may not be sufficient to significantly alter the structure of the dirac cone, but at higher concentrations, changes in the symmetry of the band structure may emerge, with stronger coupling between the graphene electrons and the li p-orbitals [69]. when na and k are adsorbed on graphene they can influence the dirac cone more pronouncedly. the stronger coupling between the alkali s-orbitals and the graphene p-orbitals may lead to more pronounced distortions in the dirac cone, changing the shape and position of the conduction and valence bands. in particular, the stronger interaction with na and k may also affect the characteristic symmetry of graphene, leading to asymmetric effects in the cone [70]. for rb [71] and cs [72], the interaction with graphene is weaker, but the change in band structure could be significant in terms of the shift and deformation of the dirac cone. we may see asymmetric deformations in the dirac cone and a reduction in band structure symmetry, as the heavier alkali adatomics can more strongly influence the local electronic properties of graphene. li and na are more stable than their heavier counterparts. their reactivity may be more easily manageable under experimental conditions, although their adhesion to graphene may not be very strong. this means that the adatom can remain stably adsorbed on graphene, with little problem of desorption at moderate temperatures. k, rb, and cs are more reactive and less stable on the graphene surface. these adatomics tend to desorb easily at higher temperatures, and thus the system may not be viable in long-term devices, especially if thermal stability is critical. they could also change the structure of graphene more dramatically, causing structural deformations. li could be 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application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1700 83 original research article preparation and application of carbon-based hollow structured nanomaterials xingmiao zhang, wei zhang, wei li* department of chemistry, fudan university, shanghai 200433, china. e-mail: weilichen@fudan.edu.cn abstract carbon-based hollow structured nanomaterials have become one of the hot areas for research and development of hollow structured nanomaterials due to their unique structure, excellent physicochemical properties and promising applications. the design and synthesis of novel carbon-based hollow structured nanomaterials are of great scientific significance and wide application value. the recent research on the synthesis, structure and functionalization of carbon-based hollow structured nanomaterials and their related applications are reviewed. the basic synthetic strategies of carbon-based hollow structure nanomaterials are briefly introduced, and the structural design, material functionalization and main applications of carbon-based hollow structure nanomaterials are described in detail. finally, the current challenges and opportunities in the synthesis and application of carbon-based hollow structured nanomaterials are discussed. keywords: hollow structure; carbon-based nanomaterials; preparation methods article info received: 25 july 2022 accepted: 15 september 2022 available online: 3 october 2022 copyright copyright © 2022 xingmiao zhang, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction hollow-structured nanomaterials have been one of the most popular materials among advanced nanomaterials due to their low mass density, high porosity and large surface area. the unique properties of hollow-structured nanomaterials have led to their use in a wide range of applications, such as energy storage and conversion, catalytic, water and air purification and adsorption, etc.[1–4]. in recent years, researchers have focused on the synthesis, characterization and application of hollow structures. many studies have provided novel insights into the structural and functional design and synthesis of hollow structured nanomaterials, which have contributed to the development of hollow structured nanomaterials[5–8]. among the many hollow structured nanomaterials, carbon-based hollow structured nanomaterials have attracted much attention due to their great potential applications in energy and catalysis[9]. carbon-based hollow structured nanomaterials are favored by researchers due to their tunable specific surface area, cavity size, morphological structure and composition. based on the needs of different applications, the research on carbon-based hollow structure nanomaterials has focused on the design and synthesis of cavity structure, shell structure and functionality. researchers have focused on obtaining carbon-based hollow structure nanomaterials with the following properties: (1) large specific surface area and effective dispersion and loading of metal nanoparticles or other active substances on their surface, functionalized surface structure; (2) excellent electrical conductivity; (3) 84 tunable porosity and particle size; and (4) high mechanical stability[10]. in order to impart these excellent properties to carbon materials, a series of synthetic strategies have been successfully developed, such as: stöber method, template method, microemulsion method, etc.[11–13]. these works have contributed to the development of carbon-based hollow structured nanomaterials and have played an important role in understanding their synthesis mechanisms and expanding their applications. in this paper, we summarize the basic synthesis strategies of carbon-based hollow structure nanomaterials in terms of synthesis, structure, functionalization design and their related applications in recent years. the structural design and functionalization of carbon-based hollow structured nanomaterials and their main applications are described in detail. the current challenges and opportunities in the synthesis and application of carbon-based hollow structured nanomaterials are discussed. 2. synthesis and application of carbon-based hollow structured nanomaterials 2.1 synthesis of carbon-based hollow structured nanomaterials the synthesis of carbon-based hollow structure nanomaterials is basically the same as the preparation of other hollow structures (figure 1)[9]. it can be divided into hard template method, soft template method and self-template method. the most distinctive feature is that the shell layer is a carbon material. therefore, the successful coating of carbon precursors on the synthesized templates is the key to the preparation of carbon-based hollow structure nanomaterials. the soft and self-templating methods are relatively limited in the preparation of carbon-based hollow structure nanomaterials. the soft template method usually uses stable surfactant micelles or emulsions as templates, which can only be used for the coating of carbon precursors in the liquid phase system, and the morphology and pore size are relatively difficult to regulate[14]. the self-templating method refers to a template-free strategy, and the preparation of carbon-based hollow structure nanomaterials using this method is generally carbonized with some hollow carbon precursors. in addition, in recent years, some new metal-organic skeletal materials can also be obtained through appropriate control of calcination conditions of carbon-based hollow structure, greatly enriching the scope of self-templating method for the preparation of carbon-based hollow structure nanomaterials[15,16]. figure 1. synthesis of carbon-based hollow nanomaterials[9]. compared with soft and self-templating methods, hard template method has more advantages in the design and preparation of carbon-based hollow structure nanomaterials, and in consideration of the price and ease of operation, hard templates such as silica, metal oxides and polymers are often chosen. methane, furfuryl alcohol, glucose, asphalt, and phenolic resins are available as carbon sources. in addition, some nitrogen-containing compounds (e.g., aniline, pyrrole, dopamine, and ionic liquids) have also been used to synthesize heteroatom-doped carbon[17]. 85 the coating strategies of carbon precursors on templates are generally classified into physical and chemical coating. the physical coating is usually performed by vapor deposition (cvd), where the carbon source is usually styrene, acetonitrile, benzene and methane. the main advantage of cvd method is that the thickness of carbon layer can be precisely controlled, especially for depositing atomic layer thickness. however, the size of carbon spheres prepared by this method is mostly limited to larger sizes (>500 nm), and it is difficult to obtain small size hollow carbon spheres by this method. chen et al.[18] used sio2@m-sio2 with core-shell structure as hard template and ethane as carbon source, and deposited the carbon source into the mesoporous silicon oxide pore channel by cvd method, and then etched the silicon oxide template by hydrofluoric acid to obtain hollow mesoporous carbon material. by controlling the size of the template, the shell thickness and cavity size of the hollow mesoporous carbon spheres were controlled. in addition, the hollow mesoporous carbon spheres were obtained with a high degree of graphitization and a specific surface area of 771 m2·g−1 due to the use of ethane as the carbon source. the chemical cladding method uses a chemical reaction to clad the chemical precursors on the outer surface of the template to form a template@carbon precursor core-shell structure complex. finally, the hollow structure is obtained by etching the template. the development of carbon precursor chemistry is the key to this approach. considering that the hydrolytic polymerization process and the structure of phenolic resin are similar to the formation of sio2. the reaction mechanism is shown in figure 2. resorcinol and formaldehyde monomers can form emulsion droplets through the interaction of hydrogen bonds in the mixture system of ethanol and water, and then undergo a polymerization reaction catalyzed by ammonia water to form phenolic resin colloidal microspheres. subsequent studies have shown that this stöber method can be extended to the hydrolytic polymerization of other carbon precursors, such as phenolic resin derivatives, polydopamine and polybenzoxazine[20,21]. figure 2. synthesis of phenolic resin microspheres[19]. inspired by the successful application of the silicate sol-gel process for the preparation of hollow structured materials, the stöber method system was also used for the synthesis of carbon-based hollow structured nanomaterials. using the stöber system to combine the synthesis of sio2 and rf, fuertes et al.[22] synthesized core-shell structured sio2@rf microspheres and hollow porous carbon spheres by a one-pot method with teos, resorcinol and formaldehyde in a mixture of water, ethanol and ammonia. yin, zheng and huo[23–25] have independently investigated the synthesis of hollow or yolk-shell structured carbon-based materials by depositing phenolic resin and cationic surfactant complexes on the surface of silicon oxide or silicon oxide core-shell structured nanoparticles. the 86 co-assembly of positively charged cationic surfactants with phenolic resins (rf) on the negatively charged silicon oxide surface is the key to the rf coating process. the introduction of the cationic surfactant enhances the interaction between the two negatively charged materials, rf and the silicon oxide core, allowing the rf to be successfully encapsulated on the surface of the silicon oxide core. in order to further increase the porosity of hollow carbon spheres, zheng’s group[26] developed a multi-step coating process to synthesize a sandwich structure of sio2@rf/ctab@sio2 complexes. the hollow carbon spheres obtained with this structure have a foam-like shell, which is similar to that of sio2@rf/ctab-derived hollow carbon spheres (specific surface area and porosity of 639 m2·g–1 and 0.56 cm3·g–1, respectively). in comparison, it has a higher specific surface area (1,286 m2·g–1) and a larger pore volume (2.25 cm3·g–1). in addition, in the modified stöber method system, the mechanism of co-assembly of silica-based oligomers, cetyltrimethylammonium chloride (ctac) and rf, qiao et al. developed a silica-assisted process to regulate the structure and size of pores (figure 3)[27]. the sio2@rf/ctac/sio2 composite microspheres were prepared by a one-step reaction using teos, formaldehyde and resorcinol in the ethanol/water/ammonia/ctac system. in the rf/ctac/sio2 composite shell layer, sio2 can be used as a pore-forming agent, and the pore size of the hollow carbon sphere shell layer can be adjusted from 3.2 to 3.6 nm when the template is removed. in addition, the size of the hollow spheres (180–800 nm in diameter) can also be adjusted by the amount of teos and the water/ethanol ratio. figure 3. synthesis of hollow carbon nanostructures via a “silica-assisted” strategy[27]. as researchers gained a better understanding of carbon precursor chemistry, they began to work on simplifying the stöber method for the controlled synthesis of hollow carbon spheres. in recent years, a series of general synthetic methods have been developed for the preparation of hollow carbon spheres, ranging from surfactant-free to silicon oxide free. wang et al.[28] reported a facile synthesis of nitrogen-doped polybenzoxazine microspheres and nitrogen-doped carbon microspheres. the polymer microspheres were obtained by condensation of resorcinol, formaldehyde and 1,6-diaminohexane, and the size could be adjusted by adjusting the temperature parameters. considering that the positively charged polybenzoxazine can be adsorbed on the negatively charged sio2 surface by electrostatic interaction, the nitrogen-doped hollow carbon spheres were further synthesized by the surfactant-free stöber system designed by nanfeng zheng’s group. the synthetic route and the resulting products are shown in figure 4. when resorcinol/formaldehyde/ethylenediamine is used as the polybenzoxazine (pb) precursor and teos as the sio2 precursor, the pb/sio2 composite shell layer can be directly coated on the core surface of sio2 spheres in a solvent mixture of water and ethanol. in this system, ethylenediamine acts as a base catalyst to promote the hydrolysis of teos. the positively charged polybenzoxazine and negatively charged silicon oxide oligomers are coassembled 87 and deposited on the negatively charged sio2 core surface to form the sio2@pb/sio2 core-shell structure. this core-shell structure can be further transformed into nitrogen-doped hollow carbon materials. the structure of hollow carbon spheres can also be changed from a spherical shape to a bowl-shaped hollow structure by changing the ratio of teos and pb[29]. figure 4. silica-assisted polybenzoxazine coating strategy for the synthesis of n doped hollow carbon spheres (a); sem images of as-obtained products (b–f)[29]. figure 5. fabrication of multi-shells hollow carbon spheres using 3-aminophenol/formaldehyde resin[30]. in addition, the hollow carbon spheres were recently prepared by the group of lijun wan by selective dissolution of 3-aminophen/formaldehyde resin microspheres (3-af), which discarded the surfactant and silicon oxide template used in the previous method (figure5)[30]. the polymerization of 3-aminophen and formaldehyde in a mixed system of water and nh4oh produced 3-aminophen/formaldehyde resin microspheres with a heterogeneous chemical composition. the microspheres are composed of 3-af oligomers and high molecular weight 3-af with high polymerization degree, and the overall core-shell structure of oligomers@high polymers. since the internal oligomer 3-af can be dissolved by acetone, the prepared 3-aminophenol/formaldehyde resin microspheres can be treated with acetone to obtain hollow 3-af microspheres. when the hollow 3-af microspheres were used as a template, the growth and dissolution process was repeated to obtain multishell 3-af spheres. the corresponding multishell hollow carbon spheres can be obtained by carbonization. this work provides a controlled pathway for the synthesis of multishell hollow carbon spheres. in addition, the stöber-based strategy for the synthesis of polymeric microspheres has been extended to other 88 polymers in recent years, for example, the successful application of polydopamine provides an effective way to directly prepare nitrogen-doped carbon-based materials[31]. 2.2 morphology and structural design of carbon-based hollow structure nanomaterials the morphology and structure design of carbon-based hollow nanomaterials are similar to other hollow materials, and the morphology and structure of the templates can be controlled to obtain hollow carbon structures with different morphologies. more importantly, the morphological and functional diversity of carbon-based hollow structure nanomaterials can be enriched through the rational design of template@carbon precursor complexes. when a core/shell material is used as a template,two typical sandwich-like intermediates (e.g., sacrificial layer@functional layer@carbon precursor structure and functional layer@sacrificial layer@carbon precursor structure) can be obtained by coating the template with carbon precursors, which can be converted into hollow core/shell carbon based material and yolk@shell hollow carbon based structure after removing the template, respectively. this strategy of modifying hard templates provides an effective way to directly design multifunctional carbon-based functional materials, which greatly facilitates the application of carbon-based hollow structure nanomaterials[32]. carbon-based hollow structure nanomaterials have great potential for applications in catalysis, drug delivery, and batteries. for these applications, the design of the shell structure is an important aspect to further improve the performance of hollow nanomaterials. 2.2.1 ultra-thin shell layer design in carbon-based hollow nanomaterials, the shell structure plays a decisive role in their performance. the thickness of the shell layer directly affects the physicochemical properties of the material, such as electrical conductivity, specific surface area, porosity, density, and the number of active sites available. in energy storage and catalysis applications, nanomaterials with ultra-thin hollow shell layers are preferred by researchers. liu et al. first synthesized sio2@pda core-shell structures under alkaline conditions using dopamine as the green carbon source, and then carbonized and etched the core template to obtain ultra-thin hollow carbon spheres with a shell layer thickness of only 4 nm (figure 6). in addition, au@c yolk⁃shell structure was prepared by using au@sio2 core-shell structure as a template and used in the reduction of nitrobenzene phenol, which showed high catalytic activity and stability[33]. han et al. also developed a template-assisted thermal decomposition method to prepare ultrathin hollow nitrogen-doped carbon spheres loaded with single-atom co active sites (figure 7)[34], with a shell thickness of 5 nm. the ultrathin carbon shell layer loaded with single-atom co is beneficial for improving the utilization of active sites. in addition, the ultra-thin shell layer facilitates the transport of the reacting species. the ma terial showed high catalytic activity and stability for oxygen reduction catalytic reactions under acidic conditions. figure 6. tem image of super-thin hollow carbon spheres[33]. 89 figure 7. schematic illustration of the fabrication (a) and tem of images of super-thin hollow carbon spheres (b,c)[34]. 2.2.2 the porous shell layer design nanomaterials with porous shell layer structure can further increase the specific surface area of hollow structured materials compared to hollow micro/nano structured materials with solid shell layer. most of the research in this area is based on a combination of soft and hard template synthesis methods. in addition to the hard template method for cavity fabrication, porogenic agents are introduced during the coating process of the shell layer material, and hollow micro/nano-structured materials with porous shell layer structure can be obtained after the removal of the cavity template and the shell layer porogenic agents[35]. for example, hollow mesoporous carbon microspheres were also successfully synthesized by the co-hydrolysis of organic polymers and inorganic silica-derived precursors by yu’s group at the university of queensland, australia[36]. a core-shell structure of phenolic resin/silicon composite shell layer with a silicon oxide core was successfully prepared by co-hydrolysis/cross-linking of resorcinol, formaldehyde and silica in an ethanol/water system, followed by carbonization to remove the template to obtain hollow mesoporous carbon microspheres (figure 8). the final hollow structure and mesoporous shell structure can also be controlled by controlling the amount of silicon source and the type of silicon source in the system. the hollow mesoporous carbon was prepared using a combination of soft and hard templates by lou from nanyang technological university. in the alcohol/water system, the carbon source dopamine, the porogenic agent f127, and the pore expander trimethylbenzene were co-assembled and coated on different substrates catalyzed by ammonia water. after high temperature carbonization, core-shell nanocomposites with mesoporous carbon shell layer were successfully obtained (figure 9). the removal of the substrate template resulted in hollow mesoporous carbon spheres with different morphologies[37]. 2.3 functionalization of carbon-based hollow structured nanomaterials 2.3.1 heteroatom doping effects in order to create more active sites and further improve the catalytic activity as well as the interaction between carbon composites and reactants, doping the carbon skeleton with other heteroatoms such as nitrogen (n), boron (b), sulfur (s), phosphorus (p) or a combination has been widely adopted[38]. among them, the chemical reactivity, electrical conductivity, affinity for co2 adsorption and specific capacity for supercapacitors are much better than pure carbon materials due to the introduction of n elements into the carbon skeleton[39,40]. nitrogen-doped carbon materials can be prepared by: (1) direct carbonization of precursors containing heteroatoms to obtain heteroatom-doped carbon materials; (2) post-processing methods, which refers to the heteroatom post-merging in the pure carbon material skeleton. usually, the carbon material is calcined together with precursors containing heteroatoms such as ammonia or thiourea. the biggest disadvantage of the post-treatment doping method is that it is difficult for the heteroatoms to enter the carbon skeleton, only a certain modification of the surface carbon atoms is possible. therefore, most of the efforts have been devoted to the synthesis of homogeneous heteroatom-doped carbon materials using the first approach. to date, significant progress has been made in the design of heteroatom-doped carbon materials based on the molecular level, especially using phenolic resin 90 polymer precursors. a series of nitrogen-containing compounds have been used to prepare nitrogen-doped carbon materials, such as: melamine, aminophenol, 4⁃amino⁃3⁃nitrophenol, 4⁃aminophenol, hexamethylenetetramine, and 1,6⁃diaminohexane. in addition, some nitrogen-containing monomers, such as aniline, pyrrole and dopamine, were also used to prepare nitrogen-doped carbon materials. the content of nitrogen in nitrogen-doped carbon materials can be adjusted by regulating the addition of nitrogen-containing precursors and calcination conditions. similarly, in the preparation of sulfur-doped carbon and boron-doped carbon materials, the corresponding heteroatom-doped carbon materials can be obtained by introducing the corresponding monomers. polyatomic doped carbon materials can be prepared by introducing monomers containing different elements, or by combining various methods to introduce different elements separately. figure 8. fabrication of mesoporous carbon structures via a carbon/silica composite shell method[36]. figure 9. fabrication of mesoporous carbon spheres via a micelle assembly strategy[37]. 2.3.2 surface modification of carbon materials carbon materials are often used as catalyst carriers to enhance the performance of catalytically active materials. two main approaches can be used to functionalize the surface of carbon: (1) deposition of nanoparticles; (2) surface grafting of functional groups. the loading of nanoparticles or single atoms on carbon surfaces is often considered an effective way to tune the interfacial properties and improve the molecular interactions to achieve desirable catalytic and electrochemical properties. for nanoparticles highly dispersed on the surface of carbon ma 91 terials, the size can be adjusted from nanoscale to single atoms, and the smaller the size, the more catalytic sites are exposed, and the corresponding electrochemical and catalytic properties are more desirable. for example, li’s group has successfully loaded highly dispersed cobalt atoms on the surface of hollow nitrogen-doped carbon spheres using a thermal decomposition method. using this material for oxygen reduction reactions, the atomically dispersed cobalt sites expose the maximum number of catalytic sites, and the hollow structure facilitates the rapid transport of oxygen reduction-related species. this combination of structures gives the material a high catalytic performance[34]. in addition, a similar structure was used to load cobalt atoms in co-n5 coordination in nitrogen-doped hollow mesoporous carbon spheres for the co2 reduction reaction, which exhibited nearly 100% co selectivity and high stability[41]. hollow carbon spheres and carbon-based yolk-shell structures were considered as ideal carriers to prevent the precipitation and aggregation of noble metals on the surface of carbon carriers at high temperatures in catalytic reactions. liu et al. prepared ag/agbr@sio2@rf core-shell structure by one-step stöber method, and obtained ag@c yolk⁃shell nanostructured microspheres by carbon etching the template[42]. in addition, galeano et al. confined small size pt nanoparticles in mesoporous hollow carbon materials and used them in electrochemical oxygen reduction reactions with much better stability than commercial pt/c[43,44]. the functional groups on the surface of carbon materials can be used as anchor sites for metal catalysts and contribute to the adsorption of metals on the carbon surface. this usually results in a high dispersion of the metal species on the carbon surface and enhances the chemical properties. commonly used methods such as oxidation, koh activation and sulfonation have been widely used for the grafting of functionalized functional groups on the surface of carbon materials[45]. in addition, the polarity of carbon materials can also be changed by the grafting of functional groups, such as the introduction of various polar groups such as carboxyl, nitrate, sulfonic acid and hydroxyl groups on the surface of carbon materials so that its own non-polar surface is transformed into a polar surface. for example, wang et al. obtained sulfonated hollow mesoporous carbon spheres (arso3h-hmcs) by etching the core-shell structure of sio2@c with hydrofluoric acid and further treatment with chlorosulfonic acid[46]. song et al. successfully synthesized hollow mesoporous carbon spheres functionalized with aryl sulfonic acid by diazo coupling using furfuryl alcohol as the carbon precursor by the hard template method, and the synthetic route is shown in figure 10[47]. the amount of arso3h grafted on the surface of the carbon material could be controlled by the amount of sulfonate. the results showed that the prepared sulfonate-functionalized hollow mesoporous carbon spheres were used as solid acid catalysts with high catalytic activity and stability for the alcoholysis reaction of ethyl levulinate or furfuryl alcohol by esterification of levulinic acid. the strong brönsted acidity of arso3h⁃hmcss plays a crucial role in the catalytic activity. the thin carbon shell layer and its hollow structure shorten the diffusion distance of the reacting species and facilitate the rapid transfer between reactants and products. 2.4 applications of carbon-based hollow structured nanomaterials 2.4.1 applications in energy storage for chemical batteries, high cycle stability and multiplicative performance is a goal to be pursued in the design of any type of battery. fast ion and electron transport requires electrode materials with high conductivity and open structure. high cycling stability requires relatively stable active materials and host electrode materials that can mitigate the large volume expansion of active materials during charging and discharging, or effectively inhibit the dissolution of specific active materials in the electrolyte. due to their unique structural properties, such as high conductivity, open structure and large cavities, carbon-based hollow structure nanomaterials are widely used to load various battery electrode active materials and relieve the volume expansion of active materials. hollow carbon spheres can be used as host materials for loading high-capacity but unstable electrode active materials. for example, when silicon is used as the anode material for ba 92 figure 10. fabrication of arso3h-mesoporous hollow carbon spheres[47]. figure 11. (a) fabrication of silicon nanoparticles confined in double-shell carbon nanoparticles; (b) corresponding tem image of the material, with the selected area electron diffraction (saed) pattern in the inset; (c) structural change of the material during the charge-discharge process[49]. teries, the capacity decays rapidly due to the rupture of the material structure, and the cycling stability is poor[48]. chen et al. confined si nanoparticles in hollow carbon spheres with a bilayer shell structure by a multi-step coating and etching strategy. the inner carbon shell provides voids to buffer the large volume expansion changes of the si nanoparticles, while the outer shell helps to form a stable sei film (figure 11)[49]. similar strategies have been applied to protect other less stable active materials, such as sn, sno2, mos2, etc.[50–52]. li-s batteries are considered to be one of the most promising secondary batteries due to their high energy density. the cathode active material is non-metallic s. despite its high theoretical capacity, s has a lot of shortcomings as a battery electrode material. the low electrical conductivity of s, the shuttle effect of lithium polysulfide, and the high-volume expansion limit the practical application of li-s batteries[53,54]. to alleviate these defects, hollow carbon spheres are widely used as s host materials for li-s cells. carbon-based hollow structured nanomaterials loaded with polar inorganic nanoparticles are the most effective strategy to solve the defects of li-s cells[55–58]. wu et al. used hollow carbon spheres loaded with cobalt oxide nanoparticles (hpcs/coo) for li-s batteries, which showed excellent cycling stability[59]. due to the strong interaction between polar coo nanoparticles and lithium polysulfide, the shuttle effect phenomenon can be suppressed. compared with the hpcs/s electrode material, the cycling stability of the hpcs/coo/s composite electrode material is significantly enhanced, and the capacity can still reach 629 mah·g−1 after 1,000 cycles at a current density of 100 c. in contrast, the specific capacity of the hpcs/s electrode after 1,000 cycles is only 302 mah·g−1 (figure 12). the researchers also developed c/co9s8, c/tio, fe3o4@c, mno2@hcf and other composites for li-s batteries, which ef 93 fectively solved the defect problem of s anode and achieved excellent battery performance[60–63]. figure 12. schematic illustration of the fabrication of hpcs/coo/s and cycling performanceof hpcs/coo/s for li-s battery[59]. unlike the storage of lithium ions in the battery anode material, lithium metal batteries directly utilize lithium metal as the anode material. lithium metal has a higher specific capacity (3,860 mah·g−1) than the conventional graphite anode material used in li-ion batteries[64]. very attractive energy densities (e.g., 3,500 wh·kg−1 for li-o2 cells and 2,600 wh·kg−1 s cells for li-s cells) can be obtained when lithium metal cathodes are coupled with other high-capacity cathode materials, such as oxygen and sulfur cathodes[65]. despite these advantages, lithium metal has inherent defects, including high reactivity, large volume changes during cycling, and formation of lithium dendrites[66]. to solve this problem, surface protection of lithium metal is essential, and hollow carbon microspheres are ideal for solving this problem. the consistent deposition of li metal in hollow carbon spheres is a great challenge due to the difficulty in controlling its morphology and deposition location during lithium metal deposition. until recently, au nanoparticles were first deposited in hollow carbon spheres, and then controlled deposition of li metal was successfully achieved in hollow carbon spheres using au as the seed (figure 13). by avoiding direct contact between the lithium metal and the electrolyte, figure 13. (a) tem images of gold nanoparticles trapped inside hollow carbon nanospheres;(b) lithium deposition process inside the hollow carbon structure;(c) corresponding tem images of the lithium disposition at different stages[67]. 94 this restricted space can effectively improve the stability of the electrochemical cycle of the lithium metal and minimize the undesirable side effects between the lithium metal and the electrolyte. the cycle performance of the lithium metal cell is improved with a coulombic efficiency of 98% in the carbonate electrolyte and excellent cycle stability over 300 cycles[67]. 2.4.2 applications in electrocatalysis electrocatalysis is an important process in the field of clean energy conversion (fuel cells, water splitting and metal-air cells). however, the sluggish kinetics of hydrogen precipitation reactions (her), oxygen precipitation reactions (oer), and oxygen reduction reactions (orr) limit the practical applications in these fields. in addition, carbon dioxide reduction, methanol oxidation and nitrogen reduction are also key factors in the conversion of renewable energy sources. carbon based hollow structured nanomaterials with high electrical conductivity can improve the charge transfer efficiency. in addition, hollow structure and porous structure can improve the mass transfer efficiency. based on the unique structural characteristics of carbon-based hollow structure nanomaterials mentioned above, researchers generally consider carbon-based hollow structure nanomaterials as one of the best candidates for electrocatalysts with high activity and stability. the oxygen reduction reaction (orr) plays a very important role in metal-air cells and fuel cells. pt electrocatalysts exhibit excellent orr activity under acidic and alkaline conditions, but their high cost and poor stability have limited the mass production and further practical application of noble metal pt. in recent years, researchers have focused on the synthesis of low-cost and stable electrocatalysts. carbon based hollow structured nanomaterials are gaining more and more attention due to their low cost, high activity and stability. non-metallic carbon-based materials can be doped with various heteroatoms such as n, s and p to modify their electronic structure and chemical activity. the electronegativity and atomic radius differences between heteroatoms and carbon atoms lead to changes in the electronic structure of c atoms adjacent to the heteroatoms, which facilitate the adsorption and electron transfer of oxygen species and enhance their orr activity. for example, lou’s group developed a strategy to synthesize ultra-thin hollow nitrogen-doped carbon spheres by self-assembling polymer block copolymer f127 and polydopamine composite micelles. the ultrathin shell layer with monolayer mesoporous structure ensured the rapid mass transfer process and high catalytic activity[37]. although the heteroatom-doped carbon materials exhibited stable and efficient orr properties in alkaline solutions, their orr activity under acidic conditions was not satisfactory[68]. to solve this problem, carbon-based materials modified with non-precious metals (fe, co, and ni) have been extensively investigated. 2.4.3 carbon-based hollow structured nanomaterials as nanoreactors for catalytic reactions the design of a suitable reactor is essential in chemical reaction engineering. in order to obtain optimal reaction conditions, fluid dynamics, mass transfer, heat transfer, and reaction kinetics must be taken into account. the development of nanotechnology has transformed the reactor vessel from macroscopic to microscopic structures and opened up the concept of new nano-reactors. from the chemical engineering point of view, the designed and prepared catalysts are considered as nano-reactors. compared to conventional reactors, nanoreactors offer the advantage of parallel chemical reactions, avoiding the formation of undesirable products and enhancing catalytic performance. for example, in hollow carbon-based catalysts, multiple catalytic sites can be located on the inner and outer surfaces of the carbon shell, in the voids of the carbon particles and in anisotropic locations to achieve the best catalytic performance. compared with solid carbon sphere catalysts, hollow carbon sphere catalytic nano-reactors have the following advantages: (1) catalytically active species can be loaded inside the cavity to prevent the migration and agglomeration of active particles during the catalytic reaction, which leads to the reduction of catalytic activity; (2) selective catalytic activity can be further en 95 hanced by the regulation of shell structure; (3) mass transfer process can be further enhanced during the catalytic reaction compared with the same mass of bulk catalyst; (4) the catalytic reaction rate can be improved by regulating the hydrophilicity/hydrophobicity in the cavity to enrich the reaction products in the cavity[69]. figure 14. (a) schematic illustration of the synthesis of ptco@c yolk-shell micro-spheres; (b) tem image; (c) edx mapping images of ptco@c yolk-shell micro-spheres[70]. selective hydrogenation is essential in organic synthesis, such as the synthesis of epoxy compounds. most of the catalysis has to be carried out at high temperatures, which makes the active nanoparticles susceptible to sintering and loss of activity during the reaction. schüth and co-workers developed a simple method to confine 4 nm ptco nanoparticles inside a hollow carbon sphere cavity (figure 14)[2]. the catalytic conversion of 5-hydroxymethylfurfural to 2,5-dimethylfuran within 10 min was achieved with an efficiency of 100% using this material as a catalyst. the yield of 2,5-furan after 2 h was 98%. in another work, wang et al. successfully prepared pd@c yolk⁃shell structured catalysts by hydrothermal treatment of emulsions containing p123/sodium oleate/pdcl42 and polymer precursors of 2,4-dihydroxybenzoic acid and hexamethylenetetramine[70]. recently, tian et al. also reported a yolk⁃shell structured sub-micron reactor loaded with metal nanoparticles in the structure of pd@zn/c yolk⁃shell[71]. when used as a catalyst for the hydrogenation of styrene from phenylacetylene, the catalyst achieved 99% selectivity, high conversion and excellent catalytic stability. 3. conclusions and prospects in the past decade, carbon-based hollow structured nanomaterials have been developed by leaps and bounds, and fruitful results have been achieved in synthesis, characterization and applications. in this paper, we summarize the basic synthesis strategy, structural design, material functionalization and main applications of carbon-based hollow structured nanomaterials. the unique structure of carbon-based hollow structured nanomaterials has shown great potential applications in many fields. it is this promising application that the research, development and application of such materials remain a hot topic in the field of hollow structural materials. the future research should focus on the precise regulation of the composition, shell structure and thickness, inner and outer surface properties and loading composition of carbon-based hollow structural materials. to prepare carbon-based hollow structure materials with desired physical properties for different applications. understanding the conformational relationship between material structure and application properties is the driving force for the development of carbon-based hollow structured nanomaterials and is a 96 major challenge in this field. conflict of interest the authors declared no conflict of interest. references 1. liu j, wickramaratne np, qiao s, et al. molecular-based design and emerging applications of nanoporous carbon spheres. nature materials 2015; 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28(32): 1801737. characterization and application of nanomaterials (2022) volume 5 issue 2 doi:10.24294/can.v5i2.1684 24 original research article effect of an oscillating magnetic field in polymeric columns with magnetic nanoparticles violeta maricela dalgo flores*, gabriela cristina chango lescano, john germán vera luzuriaga escuela superior politécnica de chimborazo, riobamba 060155, ecuador. e-mail: violeta.dalgo@espoch.edu.ec abstract magnetite magnetic nanoparticles (mnp) exhibit superparamagnetic behavior, which gives them important properties such as low coercive field, easy superficial modification and acceptable magnetization levels. this makes them useful in separation techniques. however, few studies have experimented with the interactions of mnp with magnetic fields. therefore, the aim of this research was to study the influence of an oscillating magnetic field (omf) on polymeric monolithic columns with vinylated magnetic nanoparticles (vmnp) for capillary liquid chromatography (clc). for this purpose, mnp were synthesized by coprecipitation of iron salts. the preparation of polymeric monolithic columns was performed by copolymerization and aggregation of vmnp. taking advantage of the magnetic properties of mnp, the influence of parameters such as resonance frequency, intensity and exposure time of a omf applied to the synthesized columns was studied. as a result, a better separation of a sample according to the measured parameters was obtained, so that a column resolution (rs) of 1.35 was achieved. the morphological properties of the columns were evaluated by scanning electron microscopy (sem). the results of the chromatographic properties revealed that the best separation of the alkylbenzenes sample occurs under conditions of 5.5 khz and 10 min of exposure in the omf. this study constitutes a first application in chromatographic separation techniques for future research in nanotechnology. keywords: capillary liquid chromatography; oscillation frequency; nanoparticles; superparamagnetic article info received: 14 may 2022 accepted: 13 july 2022 available online: 27 july 2022 copyright copyright © 2022 violeta maricela dalgo flores, et al. enpress publisher llc. this work is licensed under the creative commons attribution-noncommercial 4.0 international license (cc by-nc 4.0). https://creativecommons.org/licenses/by-nc/ 4.0/ 1. introduction capillary liquid chromatography (clc) is one of the most widely used analytical techniques for the qualitative and quantitative analysis of numerous chemical compounds. for this reason, the development of clc columns has evolved significantly. among the great diversity of columns, monolithic columns stand out because they allow working at high flow rates, therefore, obtaining fast separations without the use of high pressures in the system[1,2]. in addition, the bed is anchored directly to the support wall, so the use of retention fry is not necessary. these columns have been widely used to separate individual components of various samples[3,4]. there are two types of monolithic columns: polymers, which consist of obtaining organic polymers by in-situ polymerization of an organic or hydro-organic mixture, and silicon-based monolithic prepared by sol-gel processes[5,6]. polymer monomers have some advantages over silica, such as fast and simple preparation, versatility of polymer functionalization and improved chemical stability over a wide ph range (2–12)[7]. these monoliths are widely used in the analysis of proteins, high molecular weight molecules and small molecules in food, environmental and pharmaceutical fields[8–11]. 25 therefore, the latter type of monoliths was selected for this study. however, despite the advantages of polymer monolithic columns, it should be noted that their limitation lies in the low surface area values (<10 m/g) compared to silica columns. to solve this drawback, in recent years, various nano-materials have been incorporated into these stationary phases. thus, for example, glycidyl methacrylate (gma) monoliths are described which functionalized with various types of au, ag and ni-co metal nanoparticles resulting in a manipulation in the retention of proteins and other small molecules[12,13]. as nanotechnology advances, new nanomaterials are destined to emerge as powerful materials that enable analytical determinations with improved sensitivity. the most commonly used in separation techniques include: silica and carbon nanoparticles (np) (mainly fullerenes and carbon nanotubes) and metallic (iron oxide, gold, silver and europium)[14]. applications of these nps include their use as adsorbents in solid-phase extraction and microextraction[5,12], as well as the development of stationary phases incorporating these nanostructured materials. for example, recently, vinylated micro nanoparticles have been incorporated into the monolithic columns of gma, which provided an increase in the surface area of the monoliths. this in turn lead to an increase in the retention and effectiveness of the chromatographic column[15]. however, the incorporation of magnetic nanoparticles (mnp) into this type of stationary phases has been little studied[10,15]. hence, the aim of the present investigation which seeks to take advantage of the superparamagnetic behavior of mnp in the efficiency of chromatographic separations. the oscillating magnetic field (omf) is one of the different types of magnetic fields, which is produced by alternating current electromagnets with a periodic change of intensity that depends on the frequency of the magnet and the type of wave. the omf applied in the form of reverse polarity pulses can be homogeneous in the area enclosed by the magnetic field coil or heterogeneous where the intensity decreases as the distance from the center of the coil increases[16]. applying the theory of electromagnetism and the laws of biot-savart, ampère ohm and kirchhoff, the motion of particles affected by a omf is obtained. the biot-savart law states that if the current i passes through the conducting wire, a magnetic field is generated[17]. to denote the presence of a magnetic field in a given region of space, one must work with the magnetic field strength h. this relation is linear in most materials (equation 1). b = μh (1) where: b is the magnetic flux density (teslas) and μ the magnetic permeability of the material (t*m*a−1). with this law, the relation of the magnetic field can be found for any point in space with current i[18]. on the other hand, ampère’s circulation law is represented by equation 2. ∮ b��⃗ ⋅ dl⃗ = μ0i (2) where: dl is the length differential of the curve; μo is the magnetic permeability in vacuum (μo = 4π*10−7 t*m*a−1). the field lines of b are concentric circles lying in planes perpendicular to the axis of the wire, with center in it. if a region of space is available, then the number of field vectors, traversing a surface, gives the magnetic flux conditions. applying the double integral, the flux is divided by a certain surface area s, and b is obtained, as shown in equation 3[19]. b = φ s = μh (3) where: φ is the magnetic flux through an area s in scalar product with b, with weber units. if there is more than one magnetic field source, it will provide intensive movements of the np in different directions and consequently improves mass transfer[20,21]. the magnetic field generates the movement of the mnp contained in the monolith of the polymeric column (figure 1). in the present investigation, the influence of a omf on polymeric monolithic columns with vinylated magnetite magnetic nanoparticles (vmnp) for clc was studied. for this purpose, polymeric monolithic columns were prepared by the copolymerization method with butyl methacrylate (bma) and 26 figure 1. movement of the mnp generated by a magnetic field: (a) position of the mnp in the absence of magmatic field and (b) displacement of the mnp according to the direction of the field line. ethylene glycol dimethacrylate (edma) monomers by thermal initiation and subsequent aggregation of vmnp. then, taking advantage of the magnetic properties of the mnp, the influence of various parameters (resonance frequency, intensity and exposure time) of a omf applied on the synthesized columns was studied. the influence of these parameters on the morphological properties was evaluated by scanning electron microscopy (sem). while, to monitor the effect on chromatographic properties, the separation of alkylbenzenes (abs) samples in clc in reverse elution mode was studied. 2. materials and methods 2.1 obtaining of polymeric monolithic columns monolithic columns were prepared using fused silica capillaries. the polyimide coating of 794 μm external diameter and 500 μm internal diameter, supplied by multi-micro technology (phoenix, usa). in order to ensure covalent bonding with the monolith, the inner wall of the fused silica capillary was modified with 3-(trimethoxysilyl) propyl methacrylate (γ-mps) from sigma-aldrich (milwaukee, usa). for this purpose, the procedure described by petro, svec and fréchet[22] was adopted. the preparation of the polymerization mixtures was carried out in a glass cabinet, using an ohaus model ex224 analytical balance (mexico d.f., mexico). the polymerization mixture was composed of bma from sigma-aldrich (milwaukee, usa) as functional monomer. edma from sigma-aldrich (milwaukee, usa) and a ternary porogenic solvent, consisting of a mixture of 1,4-butanediol from sigma-aldrich (milwaukee, usa), 1-propanol from scharlau (barcelona, spain) and ultrapure water, obtained from a nanopure ii purification system from barnstead (boston, usa), were used as the binding agent. azobisisobutyronitrile (aibn) from fluka (buchs, switzerland) was used as initiator of the polymerization reaction. to the polymerization mixture, vmnp were added up to a final concentration of 2% by weight. the method selected to disperse the vmnp into the polymerization mixture was sonication, since it is the most recommended for the homogeneous distribution of nanomaterials in aqueous media. for this, once the mixture was prepared in a vial, it was agitated in a heidolph vortex, model reax 2000 (schwabach, germany), sonicated in a bransonic ultrasonic bath model 2510r-mt (boston, usa) for 15 min and purged with nitrogen, according to the method proposed by carrasco, ramis and herrero[15]. table 1 shows the composition of the polymerization mixture studied. table 1. composition of the polymerization mixture used components concentration (% weight) butyl methacrylate (bma) 17.9 ethylene glycol dimethacrylate (edma) 12.0 1,4-butane diol 34.6 1-propanol 28.2 water(h2o) 6.9 azobisisobutyronitrile (aibn) 0.4 the pretreated 10 cm long molten silica capillaries were capillary-filled entirely with the polymerization mixture and sealed at their ends. thermal polymerization was carried out in a pol-eko-aparatura model srn 115 std oven (wodzislaw sl¾ski, poland) at 70 °c for 20 h. after the polymerization process was completed, methanol from vwr-prolabo chemicals (paris, france) was passed through the obtained monolithic columns for 15 min in order to remove porogenic solvents and possible unreacted monomers, using a shimadzu lc-10as pump (columbia, usa). 2.2 synthesis and characterization of mnp this section describes the synthesis and characterization of mnp with and without vinylation. the preparation of mnp was carried out by co 27 precipitation, according to the procedure described by yang et al.[23]. after the reaction was finished, the precipitate was collected with the help of a magnet; it was washed repeatedly with water and ethanol from vwrprolabo chemicals (paris, france) and the product was dried in an oven, at 60 °c for 12 h. to modify the surface of mnp with vinyl groups, 4 ml of γ-mps reagent was added over 50 mg of mnps; then, 1 ml of a 1:1 (v/v) water-ethanol mixture was added. the reaction was carried out under nitrogen atmosphere at a temperature of 40 °c for 12 h. finally, the mnp was washed several times with ethanol and dried in the oven at 60 °c for 6 h. the vmnp was characterized using a jasco ftir, model 4100 (oklahoma, usa). 2.3 preparation of the test sample a sample of abs consisting of toluene ethylbenzene propylbenzene and butyl benzene from riedel de haen (hannover, germany), was used as the analyte. the abs stock solution was prepared from a concentration of 1,000 μg⁄ml in acetonitrile (mecn) from vwr prolabo chemicals (paris, france), and kept at −20 °c. from this, a 10 μg⁄ml test mixture of uracil (sigma-aldrich, milwaukee, usa) and abs was prepared. 2.4 instrumental in the generation of the omf the omf is generated and the mnp vibration of the monolithic column is caused using an electromagnet consisting of a coil of 500 coils of copper wire wound around a ferrite core and two pieces of iron forming a slot 5 mm wide and 9.5 cm long where the monolithic columns were placed. the electric current supplied to generate the magnetic field came from an rs pro model gfg-8255a function generator (northants, england), connected to a krohn-hite model 7600/7602 broadband amplifier (massachusetts, usa). electrolytic capacitors were used to store the electric charges and modify the output frequency (table 2). table 2. capacitance of the capacitors used, resonance frequencies and magnetic flux densities obtained capacitor capacitance c(f) resonant frequency fo (hz) comment intensity 1(a) magnetic flux density bg (mt) 4.7 × 10−3 2 1.15 8.028 l.0 × 10−3 8 0.79 5.515 l.0 × 10−6 198 0.10 0.698 l.0 × 10−9 5,500 2.l × 10−6 l.466 × 10−5 l.0 × 10−12 228,000 not measured not measured figure 2. circuit used in the generation of omf. note: a and b: terminals; g: alternating current generator; c: variable capacitor; r: resistor; rb: coil resistance; l: inductor. the current intensity was measured with a fluke model 179 series multimeter. a lab-volt model ac 793g oscilloscope (new jersey, usa) was connected to the system to obtain a graphical 28 representation of the electrical signals, their variation over time, and to monitor the signal voltage. figure 2 shows the circuit designed in matlab with the above representation. in table 3 the parameters and operating conditions of the omf considered in the study of monolithic columns prepared using vmnp are given. table 3. omf parameters and working conditions used in the study capacitors capacity 4700 μf~1 pf coil number of turns 500 resistance 14.6 ω function generator output signal sine wave frequency 2.3 hz ~ 228 khz amplifier amplitude 20 vpp type of electrical component alterna amplitude 25 vpp 2.5 chromatographic conditions monolithic columns at 25 °c with vmnp were connected to the clc equipment with shimadzu uv-vis detector model scl-10a (columbia, usa), and conditioned with the mobile phase until a stable baseline was observed, i.e., a mixture of mecn:water (30:70 v/v) in isocratic elution at a flow rate of 0.15 ml/min. a mixture of abs in concentration of 10 μg⁄ml was used as analyte with an injection volume of 2 μl and a spectrophotometric determination of 214 nm. 2.6 characterization of polymeric monolithic columns the morphological study of the monolithic materials was performed using the jeol scanning electron microscope model jsm-it100 (tokyo, japan). an important aspect here was the stability of the dispersion of vmnps in the polymerization mixture and consequently their homogeneous distribution in the polymeric matrix. therefore, it was decided to study the degree of dispersion of the vmnps in the monolithic beds obtained thermally. for this purpose, mixtures containing 2% of vmnps were placed in several vials polymerized thermally. samples were then taken at different polymerization times. as a result of this procedure, images were obtained in the zhunma optical microscope model xsz 107bn-t (ningbo, china) of monolithic beds with vmnp, taken at 5 and 60 min after polymerization. figure 3. infrared spectra of the surface of mnp: (a) unvinylated and (b) vinylated with γ-mps. 3. results and discussion 3.1 characterization of vinylized mnp figure 3 shows the infrared spectra of unvinylated mnp (trace a) and vmnp (trace b). both show an absorbance band at 562 cm−1, corresponding to the fe-o vibration of the magnetic core. in the vmnp (trace b) an intense band is observed at 29 1,718 cm−1 which is characteristic of the stress vibration of the γ-mps ester carbonyl. the bands found at 1,633 and 3,004 cm−1 are due to the vibrations (stresses) of the c=c and c-h bonds of the γ-mps compound. the conditions for the preparation of the monoliths with vmnp were established considering a previous investigation[14]. the selected vmnp content was 2% in the polymerization mixture (table 1). in the study, uv radiation was used as the polymerization initiation mode which can be performed in short times (15 min). this avoids possible sedimentation problems of the npmv. however, in the present investigation, the capillaries used (internal diameter of 500 μm) are not transparent to uv radiation, so thermal initiation had to be resorted, which involved times of 20–24 h. 3.2 characterization of monoliths with vmnp in order to carry out the present characterization, the degree of dispersion of the npmv in monolithic beds obtained by the thermal process was studied. the samples were taken at different polymerization times and observed by microscope. as a result, a random distribution of vmnp in the polymer matrix was determined, suggesting a homogeneous distribution of vmnps. this can be explained by the rapid formation of polymerization nuclei (oligomers), which act as a support (host) for the vmnps, thus preventing their sedimentation, properties mentioned in the work of yu, dave, zhu, quevedo and pfeffer[24], investigated in depth by ommen, valverde and pfeffer[25]. figure 4. separation of abs using a monolithic polymeric column with 2% vmnp in the absence of magnetic field. note: peaks: 1 uracil; 2 toluene; 3 ethylbenzene; 4 propylbenzene; 5 butylbenzene. 3.3 chromatographic and morphological characterization of the monolith with vmnp figure 4 shows the separation of the abs sample, using the monolithic column with vmnp content in the absence of omf, according to the clc working conditions previously indicated. these conditions presented the best separation results among several tests performed, in which parameters such as mobile phase composition and flow rate, injection volume and analyte concentra 30 tion were measured. in the chromatogram, a partial separation between the toluene and ethylbenzene pair was observed (peaks 2 and 3, respectively). it is intended to improve this separation by applying an external magnetic field to the monolithic columns with vmnp. figure 5 shows the morphology of the column, in which the microglobular structure characteristic of this type of polymers is observed. the existence of vmnp on the surface is not appreciated, since they are embedded (copolymerized) in the polymeric network, which was determined based on the study of the degree of dispersion of vmnp in the monolith. figure 5. sem image of the monolith with 2% vmnp, obtained at 20 kv and x25 k magnification. 3.4 influence of time-constant omf frequency variation as discussed above magnetite np is superparamagnetic so they are oriented and attracted by magnetic fields. for this reason, the influence of omf application on the synthesized polymeric columns was studied. for this purpose, the columns were placed in the electromagnet gap and subjected to different magnetic fields at a fixed exposure time of 5 min. the magnetic field values produced in the air gap (bg) were measured from different resonance frequencies (r), obtained from 2.3 hz to 228 khz for varying values of capacitors with capacities ranging from 4,700 μf to 1 pf. the variation of the resonance frequency gives different maximum current intensity values. in turn, it will influence the magnetic flux density. according to miranda, ferrites resonate at resonance frequencies when subjected to the action of a magnetic field, which influences chromatographic retention[26]. as this is a new study, the trend of better chromatographic separation as a function of column resolution has been seen, as presented in the results. figure 6 shows the separation of abs at different resonance frequencies. as can be seen, as the omf frequency increases, there is an increase in the retention time of the analytes, as described by carrasco, ramis and herrero[15]. also, it is observed that the resolution of all pairs of peaks improves, particularly, that of the toluene and ethylbenzene pair. in order to evaluate the influence of omf on the morphology of the studied monoliths, sem tests were performed. however, in the overall image affected by different frequencies insignificant changes in microsphere size were observed compared to those obtained in the absence of omf (figure 5). although sem images cannot show clear changes in the microgranule level, it is evident that the presence of superparamagnetic np affects the monolith structure. this leads to an increase in the number of mesoscopic and micropores, which is closely related to the surface area and retention of analytes[15,27]. 3.5 influence of varying omf exposure time at constant frequency continuing with the investigation, it was decided to study the influence of omf exposure time at constant resonance frequency. for this purpose, the frequency of 5.5 khz was chosen, which provided the best results in the previous section. in figure 7, it is observed that an increase of the exposure time leads to an increase of the retention time of the analytes and to an improvement in the separation of the toluene-ethylbenzene pair up to 10 min. values of time higher than this imply the decrease of the retention, accompanied by the loss of resolution of the toluene-ethylbenzene pair. 31 figure 6. separation of abs sample using a polymeric monolithic column with 2% npvm. note: (a) in the absence of omf and (b) at different resonance frequencies: (a) 2 hz, (b) 8 hz, (c) 198 hz, (d) 5.5 khz and (e) 228 khz. figure 7. separation of abs using a monolithic polymeric column with 2% vmnp at constant resonance frequency (5.5 khz) and different omf generation times: (a) 1 min, (b) 5 min, (c) 10 min, (d) 20 min and (e) 60 min. table 4. comparison of chromatographic resolution of abs in the absence or presence of omf absence of omf omf* frequency variation time variation of omf** exposure peaks resolution resolution resolution rs (n = 4) rs (n = 4) rs (n = 4) uracil-toluene 1.03 1.13 1.45 toluene-ethylbenzene 1.02 1.27 1.35 ethylbenzene-propylbenzene 1.12 1.78 1.86 propylbenzene-butylbenzene 1.74 2.32 2.40 note: * results obtained at 5.5 khz; ** results obtained at 5.5 khz and 10 min exposure to omf. 32 figure 8. sem images of monoliths with 2% vmnp obtained at constant resonance frequency (5.5 khz) and different omf generation times: (a) 1 min, (b) 5 min, (c) 10 min, (d) 20 min and (e) 60 min. images obtained at 20 kv and x25 k magnification. based on the reported results, it is established that, in the separation of the toluene-ethylbenzene pair using a polymeric monolithic column with 2% vmnp in the absence of magnetic field, the column resolution is 1.02. while the separation of this abs pair using a polymeric monolithic column with 2% npvmv in the presence of magnetic field, under conditions of 5.5 khz and 10 min exposure in omf, the rs increases to 1.35. this chromatographic parameter was quantified based on the literature of roig[28] and analyzed according to the work of bose[29]. the resolution data of the other pairs of peaks are shown in table 4, where it can be evidenced that the variables used in this methodology allowed improving the resolution in the chromatographic column. in order to clarify the influence of exposure time on chromatographic behavior, the morphology of the columns was again studied by sem (figure 8). however, as was the case with the influence of omf frequency variation, no appreciable morphological changes in microglobule size were observed with increasing exposure time. according to jiles and atherton, excess magnetic field exposure time can generate hysteresis in ferromagnetic materials[30]. ultimately, in order to establish reproducibility, five of the columns in the absence of omf were used for chromatographic characterization. then, to analyze the resonance frequency, four columns were used for each frequency, whereby a value of 5.5 khz was determined for the best chromatographic separation. finally, based on this last factor, four monolithic columns were used for each omf 33 exposure time. in this way, retention time, separation factor and column resolution were evaluated, with an optimum value of 1.35. these results are close to those reported by carrasco-correa et al. and dadoo et al.[15,31]. 4. conclusions the influence of the application of omf on methacrylate monoliths containing vmnp and the effects on their chromatographic and morphological properties were studied. the application of increasing omf frequencies resulted in an increase in chromatographic retention. similarly, the influence of omf exposure time at a given frequency also resulted in changes in chromatographic retention, but no morphological modifications were evident. the experimental conditions for the preparation of the monolithic columns and the chromatographic conditions for the analysis were carefully optimized. thus, the best abs separation was established at 5.5 khz and 10 min exposure in the omf. the application of this factor resulted in an increase in column resolution from 1.02 to 1.35. this translates into a better separation of the analyte components. these results make this a novel work for the development of miniaturized systems of analysis and future investigations with the use of other test solutes for the evaluation of changes in selectivity, applying different omf parameters or in the determination of the surface area of monoliths with vmnp subjected to different frequencies and exposure times of omf. conflict of interest the authors declared no conflict of interest. references 1. lynch kb, ren j, beckner ma, et al. monolith columns for liquid chromatographic separations of intact proteins: a review of recent advances and applications. analytica chimica acta 2019; 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