216 © Published by College of Education for Pure Science (Ibn Al-Haitham), University of Baghdad. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License Synthesis and Characterization Two Nanocomposites of Fe3O4 Nnanoparticles and Using Them as a Chemical Sensors Ameer Abdul Raheem Nemea1* and Basim I. Al-Abdaly2 1,2Department of Chemistry, College of Sciences, University of Baghdad, Baghdad, Iraq. *Corresponding Author. Received: 24 February 2023 Accepted: 30 March 2023 Published: 20 July 2024 doi.org/10.30526/37.3.3293 Abstract The sensor aspect is one of the most critical disciplines due to its wide application in life. This work has studied the performance of the Fe3O4 nanocomposite, which was prepared by the synthesis of Fe3O4 nanoparticles (NPs) by the co-precipitation method through its precursors, which are ferric chloride and ferrous chloride. On the other hand, graphene oxide was synthesized using the Hummers method. Chemical sensing is a process that converts a chemical or physical change of a specific analyte into a measurable signal whose magnitude is usually proportional to the concentration of the analyte. The chemical sensor is an analyzer that responds to a particular analyte and reflects that response into an analytical electrical signal. The carbon nanotubes (CNTs) have been purchased to provide two matrixes (substrates) for nanocomposites. The sonication technique has been used to prepare the composites: the first nanocomposite is made of iron oxide NPs and graphene oxide NPs, and the second is made of iron oxide NPs with CNTs. Many techniques, such as AFM, SEM-EDX, FTIR, and XRD, have been used for characterization. There are specific factors indicated in the sensing, which are sensitivity, response time, and recovery time. In the Fe3O4/CNT nanocomposite state, the sensitivity is higher than that of Fe3O4/GO, and there is also a difference between them in response and recovery times. It has been observed that there was a difference between the two nanocomposites in the pattern of the cyclic voltammetry curve, with Fe3O4/CNTs being more regular than Fe3O4/GO for sensing glucose molecules. Keywords: Nanocomposite, ferric oxide nanoparticles, gas sensor, biosensor, matrix, cyclic voltammetry. 1. Introduction The chemical sensor is an analyzer that responds to a particular analyte and reflects that response into an analytical electrical signal. Although the chemical sensor topic has been a modern discipline, it has gained increasing attraction due to its applications in environmental monitoring, gas composition analysis, industrial processes, medicine, public contributed to by multidisciplinary studies like chemistry, biology, electricity, and semiconductor security, etc., https://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-4770-0250 mailto:ameer.abdulraheem1205m@sc.uobaghdad.edu.iq https://orcid.org/0000-0001-7111-3959 mailto:Basim.ibrahim@sc.uobaghdad.edu.iq IHJPAS. 2024, 37( 3 ) 217 and that returns to its attractive properties such as its small size, sound sensitivity, low cost, and ease of preparation and use. The chemical sensor topic was developed and technology principles, and the most common types are gas sensors for trace gas monitoring, ion sensors represented by the pH sensor, humidity sensors, and biosensors [1]. This work deals with gas sensors when using oxidizing NO2 gas and biosensors when using glucose molecules in a particular electrolyte. The development trend of chemical sensors is linked with environmental protection and monitoring, and metal oxide nanoparticles (NPs) are typically used to prepare a sensor owing to their excellent sensitivity. Both gas and biological sensors played a pivotal role in many applications; their critical performance was based on the sensitivity of the target element [2]. The Fe3O4 NPs have been applied in biological and gas sensor fields because of their inexpensive fabrication process, low toxicity, high adsorption performance, and fast electron transfer capability [3]. They are an excellent sensing material and have been extensively studied because of their good characteristics, such as high sensitivity and good stability. Graphene oxide (GO) has been considered an exceptional candidate to develop the electrical conductivity of Fe3O4 NPs, thus the sensing applications, due to the following merits: (1) the two-dimensional honeycomb structure, which will quickly provide a high surface area and therefore high sensitivity to various materials (2) The high quality of the crystal lattice leads to low electric noise [4]. These merits help to improve the capturing and migrating of electrons between nanocomposites and tar Fe3O4 get material and could be used in carbon nanotubes (CNTs) for the same reason. The sol-gel method for Fe3O4 NPs is most suitable owing to the use of a small quantity of low-cost precursors, low temperature, and a simple synthesis technique [5]. Iron oxide exists in three forms in nature: magnetite (Fe3O4), maghemite (γ- Fe3O4), and hematite (α- Fe3O4). Actually, the crystalline iron oxide NPs were found with a mixture of magnetite and maghemite [6]. As mentioned before, chemical sensors can be used in different applications. In this work, we will consider the following two factors: 1) Gas sensing. In this study, CNTs and GO are compared while creating nanocomposites and employing them as sensors for the oxidizing gas NO2. Gas sensing technology relies on tracking changes in the target material's direct resistance to adsorption and desorption [4]. Measures of gas sensing can be classified into a number of categories, including sensitivity, stability, selectivity, response, and recovery time [7]. The concentration of NO2 gas on sensitivity will be between (80-100) ppm flow rate [8]. Heat it to various temperatures until it reaches the ideal temperatures; 2) Bio-sensing. All researchers who investigate biosensors share a similar interest in glucose biosensors because of the critical role they play in the treatment and management of diabetes. Recently, bio-applications of iron oxides have been attracting attention [9]. Due to their exceptional biocompatibility, super- paramagnetic characteristics, and electrical activity, Fe3O4 NPs are, in fact, regarded as suitable biosensors [10]. Cyclic voltammetry will be used in bio-sensing. An ITO conductive slide will be used, and after depositing nanocomposites on it with binding material (Nafion) and dipping in a specific electrolyte, this slide was connected to a cycle by using a platinum electrode to connect both sides of the electric circuit with a cyclic voltammetry device. Also, this sensing has been observed by gradually adding glucose [11]. IHJPAS. 2024, 37( 3 ) 218 2. Materials and Methods 2.1 Materials In the present study, all materials from Sigma-Aldrich, including ferric chloride (FeCl3.6H2O) and its purity= 99.9%, for ferrous chloride (FeCl2)= 98%, ammonium hydroxide (NH4OH)= 25%, CNTs (C)= 98%, and for graphite (C)= 99.99%. The de-ionized water was from local markets. 2.2 Methods 2.2.1 Preparation of iron oxide Fe3O4 NPs by co-precipitation method Iron chloride can be used as a precursor, and ammonium hydroxide can be used as a reducing agent to create iron oxide NPs quickly and efficiently (Shenmin et al., 2013). About 1.35 g of FeCl3.6H2O and 0.5 g of FeCl2 were dissolved in 50 mL of de-ionized water at 60 ͦ C; after 30 minutes of proper mixing, 33 mL of ammonium hydroxide dropwise was added. Ammonium hydroxide dropwise was added to the mixture at room temperature to adjust the pH of the solution. After that, the solution's color turned black, which indicated that for the reduction process, the solution was left for 2 hours for proper mixing to complete reduction. After centrifuging the solution, it filtered out the black color, washed with de-ionized water and ethanol several times to remove the unwanted impurities, and dried, forming a black powder. 2.2.2 Preparation of graphene oxide NPs by hummer's method About 1 g of graphite in 25 mL of sulfuric acid was put in an ice bath, vigorously stirring; 3 g of potassium permanganate was added very slowly, keeping the temperature below 20 ͦ C, and stirring for 3 hours. Distilled water (50 mL) was added dropwise, keeping the temperature below 50 ͦ C. After some time, the color of the colloidal changed to dark brown, indicating the formation of GO. Then, 100 mL of distilled water was added for complete oxidation. To stop the reaction, 5 mL of hydrogen peroxide was added carefully. After centrifuging, it is filtered out, washed several times with distilled water, and dried to get black powder [12]. 2.2.3 Preparation of nanocomposites Following the creation, as mentioned above, of Fe3O4 NPs, two nanocomposite materials will be made from this metal oxide, the first of which will contain GO and the second of which will contain CNTs. The ratio of the matrix mixture (GO or CNTs) to the metal oxide NPs was 2:8. The process for both nanocomposites involved placing metal oxide NPs (200 mg) in an appropriate volume of absolute ethanol and ultrasonically processing it for 20 minutes, followed by placing matrix material (800 mg) in a proper volume of deionized water and ultrasonically processing them for 30 minutes. Then, the two solutions were mixed vigorously for 20 minutes and transferred to ultrasonic for 30 minutes. The last steps were centrifuging and drying to get two black powders that represent two nanocomposites for the same Fe3O4 NPs but with different matrixes. 2.3 Chemical sensing techniques 2.3.1 Gas sensing technique Before presenting the data for the NO2 gas sensing, it must explain some factors of sense, like sensitivity (S), which is connected with the resistance (R) of the sensor (nanocomposites), because there is a difference in resistance when the flow of the gas (80–100 ppm) concentration is on and off. Then, the sensitivity was calculated according to the following relation and the other important factors in data are response and recovery times [7]: IHJPAS. 2024, 37( 3 ) 219 𝐒% = (𝐑 𝐨𝐧−𝐑 𝐨𝐟𝐟) (𝐑 𝐨𝐧) ×100% (1) The response time was defined as the time to reach a 90% maximum value of conductance when using reducing gas or the minimum value of conductance when using oxidizing gas. On the other hand, the recovery time is the time required to recover within 10% of the original baseline when the flow of reducing or oxidizing gas was removed [8]. 2.3.2 Bio-sensing technique The sample was prepared to be examined through cyclic voltammetry by following the steps [15]: ● About 20 μm from Nafion (binding material), 25 mL of ethanol, and 25 mL of de-ionized water were added to a beaker containing 100 mL of nanocomposite and let under sonication for (10-15) minutes using an ultrasonic cleaner. ● Then, a piece of the slide (ITO) was put on a hot plate, and a mixture (already prepared) was precipitated drop by drop until the precipitation was completed, using a pipette. ● The electrolyte in question was prepared from 10 mL of (0.1 M) NaOH in distilled water at a scan rate of 50 mV.S-1. ● The amperometric responses to the successive additions of glucose concentration in the solution were at +0.13V (VS. Ag/AgCl). ● About 10 mL of 0.1 M glucose solution was prepared and added millimeter after millimeter for each cycle of the cyclic voltammetry and the change on screen was observed using platinum electrodes. 3. Results 3.1 Characterization of Fe3O4/GO and Fe3O4/CNT nanocomposite Firstly, the nanoscale of Fe3O4 was insured through AFM images before the preparation of each nanocomposite. The AFM (2D and 3D) image showed that the surface morphology was not smooth and had agglomerated particles, which are represented by the white peaks. This aggregation can be caused by the measurement method [13]. The average diameter of Fe3O4 NPs was 31.27 nm, GO NPs was 63.94 nm, and CNTs was 43.5 nm [14, 15], as shown in Figures 1 and 2 . Figure 1. The AFM images (2D and3D) of Fe3O4 NPs. IHJPAS. 2024, 37( 3 ) 220 3.1.1 The SEM-EDX for Fe3O4/GO There is a distribution of iron (spinal) oxide NPs on the surface of GO, as the SEM technique shows, and the components of nanocomposites are (C) 51.2%, (O) 15.4%, and (Fe) 33.4% [13,14], as EDX shows in Figure 2. Figure 2. The AFM images (2D and3D) of A: GO NPs and B: CNTs. 3.1.2 The FTIR for Fe3O4/GO The results of the FT-IR spectrum of Fe3O4 / GO showed there is a reaction between the (O-H) groups of Fe3O4/GO at 1604.66 cm-1, which is ascribed to the (H-O-H) bending mode. The peak at 1344.29 cm-1 is referred to as (C-O) stretching, 1099 cm-1 is for (H-O-Fe) stretching, and 611.39 cm-1 and 567 cm-1 are referred to as (Fe-O) bonds [13, 14], as shown in Figure 3. Figure 3. The SEM and EDX images of Fe3O4/ GO nanocomposite. 3.1.3 The XRD for Fe3O4/GO Through treatment of the data in the Origin Pro 8 program, we have obtained the following data: FWHM was (1.69387) and 2 thetas were 26.46259, and after using those values with Scherrer equation, take a piece from the plot having the highest peaks and do analysis for them to get crystallite size equal to (16 nm), and by entering the data [13, 14], the plot was drawn as in Figure 4. µm -0.225 -0.2 -0.175 -0.15 -0.125 -0.1 -0.075 -0.05 -0.025 0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 A B IHJPAS. 2024, 37( 3 ) 221 Figure 4. The FT-IR spectrum for Fe3O4/ GO nanocomposite. 3.1.4 The SEM-EDX for Fe3O4/CNT There was a distribution of iron (spinal) oxide NPs on the surface of CNTs, as the SEM technique shows, and the components of nanocomposites are (C) 86.9%, (O) 8.3%, and (Fe) 4.8% [13, 14], as in Figure 5. Figure 5. The XRD pattern of Fe3O4/GO nanocomposite. 3.1.5 The FTIR for Fe3O4/CNT The results of the FT-IR spectrum of Fe3O4 and CNT showed a band at 3500.56 cm-1 to 3429.20 cm-1 attributed to the (O-H) of H2O molecules that were interlayers of composites, and there were weak peaks at 2921.96 cm-1 and 2850.59 cm-1 ascribed to the (C-H) of organic residues. There is a peak at 1614.31 cm-1 is ascribed to the (C=O) group, and the peak at 1367.44 cm-1 is referred to as (C-O) stretching, 1097.42 cm-1 as (H-O-Fe) stretching, and 617.18 cm-1 to 445.53 cm-1 were referred to as (Fe-O) bond [13, 14], as shown in Figure 6. Position [°2Theta] (Copper (Cu)) 20 30 40 50 60 70 Counts 0 1000 2000 86-AAR2 IHJPAS. 2024, 37( 3 ) 222 Figure 6. The SEM and EDX images of Fe2O3 / CNT nanocomposite. 3.1.6 The XRD for Fe3O4/CNT Through treatment of the data in the Origin Pro 8 program, it obtained the following data: FWHM was (1.14111) and 2 theta was 26.41637. After using those values with the Scherrer equation, taking a piece from the plot having the highest peaks, and analyzing them, it was obtained that the crystallite size equals (9 nm). By entering the data [13, 14], it obtained the plot as in Figure 7. Figure 7. The FT-IR spectrum of Fe3O4/ CNT nanocomposite. Figure 8. The XRD pattern of Fe3O4/CNT nanocomposite. IHJPAS. 2024, 37( 3 ) 223 3.2 Gas sensing data 3.2.1 The data sensing of Fe3O4/GO nanocomposite Series (1) refers to the relationship between a response time and temperature, and series (2) refers to the relationship between a recovery time and temperature [16, 23]. To summarize the data of Fe3O4/GO nanocomposites (sensors) for the different temperatures (25, 80, 130, and 200) °C as shown in Table 1. Figure 9. Sensing plots of Fe3O 4/GO nanocomposite. Table 1. The data of Fe3O4/GO nanocomposite for NO2 sensing. 3.2.2 The data sensing of Fe3O4/CNT nanocomposite Figure 10 reveals the sensing plots of Fe3O 4/CNT nanocomposite. The data of Fe3O4/CNT nanocomposite for NO2 sensing are illustrated in Table 2. Figure 10. Sensing plots of Fe3O 4/CNT nanocomposite. 0 20 40 60 80 100 0 5 10 15 20 25 30 0 50 100 150 200 250 R e co ve ry T im e ( S) R e sp o n ce T im e ( S) Operation Temperature (oC) Series1 Series2 0 20 40 60 80 100 120 140 160 0 5 10 15 20 25 30 35 0 100 200 300 R e co ve ry T im e ( S) R e sp o n ce T im e ( S) Operation Temperature (oC) Series1 Series2 No. Temperature (°C) Sensitivity ( S%) Response time (sec.) Recovery time (sec.) 1 25 2.251 26.1 90.9 2 80 2.536 25.2 91.8 3 130 2.971 19.8 70.2 4 200 4.975 27 45 0 1 2 3 4 5 6 0 100 200 300Se n si ti vi ty ( % ) Operation temperature (oC) 0 5 10 15 20 25 30 35 40 0 100 200 300 Se n si ti vi ty ( % ) Operation temperature (oC) IHJPAS. 2024, 37( 3 ) 224 Table 2. The data of Fe3O4/CNT nanocomposite for NO2 sensing. N o. Temperature (°C) Sensitivity ( S%) Response time (sec.) Recovery time (sec.) 1 25 36.84 27.9 131.4 2 80 8.39 28.8 133.2 3 130 9.40 31.5 130.5 4 200 9.72 22.5 91.8 3.3 Bio sensing results By cyclic voltammetry [17, 18, 24], the resulting data of the two nanocomposites (Fe3O4/GO and Fe3O4/CNT) as biosensors have been obtained as follows: 3.3.1 Fe3O4/GO nanocomposite Leaner increasing but not regular, as shown in Figure 10. Figure 10. The bio-sensing chart of glucose using Fe3O4 / GO nanocomposite. 3.3.2 Fe3O4/CNT nanocomposite Linear and regular increasing, as shown in Figure 11. Figure 11. The bio-sensing chart of glucose using Fe3O4/CNT nanocomposite. -2.00E-03 -1.50E-03 -1.00E-03 -5.00E-04 0.00E+00 5.00E-04 1.00E-03 1.50E-03 2.00E-03 2.50E-03 3.00E-03 3.50E-03 -1.50E+00-1.00E+00-5.00E-010.00E+005.00E-011.00E+001.50E+00 (V ) i(A), CH potential (V) vs i(A), CH without glucose with glucose -5.00E-03 0.00E+00 5.00E-03 -1.50E+00-1.00E+00-5.00E-010.00E+005.00E-011.00E+001.50E+00 (V ) i (A) , CH potential (V) vs i(A), CH with glucose without IHJPAS. 2024, 37( 3 ) 225 4. Discussion The main goal of this work is to study the data of sensing, whether in gas-sensing or bio- sensing, for the same metal oxide Fe3O4 when using it with different matrixes (substrates) to form two different nanocomposites [19,25]. When studying the data of the results for two nanocomposites, it was observed that the surface of each of them was different. The GO- based composite surface was made of plates or sheets, as shown in Figure 3. Still, the CNT- based composite surface was as tubes in Figure 6. In EDX images, it was observed that the proportion of (C) (86.9%) in CNTs-based composites was higher than the proportion of (C) (51.2%) in GO-based composites that return to the nature of the matrix. The high proportion of (C) in CNTs-based nanocomposite reflected the presence of a (C-O) bond in the FTIR, which had a somewhat weak peak but was clearer in Fe3O4/GO than in Fe3O4/CNTs. The XRD was observed in the Fe3O4/GO pattern, which contains more peaks than the Fe3O4/CNTs pattern; furthermore, the crystalline size of the Fe3O4/GO nanocomposite was (36.178 nm) and that of the Fe3O4/CNTs was (6.267 nm) respectively [20, 26]. The difference has been observed in two techniques: in gas sensing data, the sensitivity of Fe3O4/CNT is higher than that of Fe3O4/GO, and observing the same thing when comparing response and recovery times, as has been written in the two Tables above [21, 27, 28]. In bio-sensing, the difference between two nanocomposites in their regularity could be seen, although both of them sensed the glucose in the electrolyte. However, with Fe3O4/CNT, the increase of sensing was regular, as in the chart above, but with Fe3O4/GO, it was irregular. It could be said that the chief reason for these differences in data in both techniques with two nanocomposites is the difference in matrixes (substrates) [22, 29, 30]. 5. Conclusion The final result of this work is to try to highlight the real reason for the difference in sensing between Fe3O4/GO nanocomposite and Fe3O4/CNT nanocomposite when using both of them as chemical sensors. After studying their data in two techniques, gas-sensing and bio- sensing, with the same circumstances and apparatus of sense, it could be concluded that the chief reason for that difference is a matrix (substrate). When using CNTs with nanocomposite, the gas sensing data showed high sensitivity and was more regular in the sensing of glucose. Therefore, to improve the capability of the sensor, one should choose the optimal matrix (substrate), which will enhance the electroactivity of the nanocomposite and, ultimately, the sensing behavior. Acknowledgment The authors thank the Department of Chemistry, College of Science, University of Baghdad, and Dr. Fwad Tariq Ibrahim in the Department of Physics, College of Science, University of Baghdad, and the Nano Technological Research Center at the University of Technology. Conflict of Interest The authors declare that they have no conflicts of interest. IHJPAS. 2024, 37( 3 ) 226 Funding The authors declare that they have no conflicts of interest. Ethical Clearance Ethics of scientific research were carried out in accordance with the international conditions followed in dealing with laboratory animals. 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