26 American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) ISSN (Print) 2313-4410, ISSN (Online) 2313-4402 Β© Global Society of Scientific Research and Researchers http://asrjetsjournal.org/ Room Temperature Synthesis of Bismuth Oxyiodide with Different Morphologies for the Photocatalytic Degradation of Norfloxacin Saifullahi Shehu Imama*, Zakariyya Uba Zangob, Haruna Abdullahic aDepartment of Pure and Industrial Chemistry, Bayero University, P.M.B 3011, Kano, Nigeria bDepartment of Chemistry, Al-Qalam University Katsina, P.M.B 2341, Katsina, Nigeria cDepartment of Applied Chemistry, Federal University Dutsinma, P.M.B 5001, Katsina, Nigeria aEmail: saifaz2005@gmail.com Abstract In this study, both BiOI spheres and BiOI plates were synthesized successfully at room temperature and applied for the photocatalytic degradation of norfloxacin using indoor fluorescent light illumination. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis absorption spectrum, scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET). Although both BiOI spheres and BiOI plates displayed approximately similar absorption band edge, higher photocatalytic degradation was noticed in the case of BiOI spheres as compared with BiOI plates. This was attributed to the unique features of BiOI spheres, such as enlarged specific surface area and enhanced adsorption capacity. The study demonstrated that morphology has a key role in improving the degradation efficiency of a photocatalyst. Keywords: Photocatalytic degradation; Room-temperature synthesis; BiOI spheres; BiOI Plates; Norfloxacin. 1 Introduction Annual worldwide consumption of fluoroquinolones stands around 44 million kilograms [1]. Among the fluoroquinolones, norfloxacin antibiotic is a frequent prescribed medication for both human and veterinary purpose, as it acts against both gram positive and gram negative bacteria [2]. After ingestion, more than 50% of norfloxacin is excreted unaltered, this leads to its frequent detection in water bodies, for example, in hospital wastewater alone, concentrations of over 100 Β΅gL-1 have been reported [3-5]. ------------------------------------------------------------------------ * Corresponding author. http://asrjetsjournal.org/ American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 27 Its presence has serious repercussions, as apart from polluting the water thereby resulting in intense and perpetual lethality, it enhance the development of antibiotic-resistant bacteria [6]. Since conventional treatment methods hardly remove pharmaceuticals from wastewater to the levels required by law, the development of more effective treatment technologies becomes imperative [7]. Many techniques such as adsorption [8], micro- extraction [9], electrochemical oxidation [10], combined photo-Fenton and biological oxidation [11], aerobic degradation [12], nanofiltration membranes [13], ozonation [14] and advanced oxidation processes (AOPs) [15] are now being employed for the destruction of organic pollutants. Among the advanced oxidation processes (AOPs), heterogeneous photocatalysis receives much attention specifically because of its unique properties of being promising and efficient as it converts harmful organic pollutants into safer end products [16]. Infact, its capability at room temperature and pressure have been widely demonstrated. However, the major challenge now is the inadequate number of visible light responsive photocatalysts which represents over 40% of the solar radiation [17]. Bismuth-based compounds such as BiVO4 [18], Bi2S3 [19], Bi2WO6 [20], Bi2O3 [21], Bi4Ti3O12 [22], Bi2MoO6 [23], Bi2O2CO3 [24] and BiOX (X= Cl, Br, I) [25-27] have recently received much attention, as they are able to degrade organic pollutants using visible light radiation. Among the bismuth-based compounds, high emphasis is been placed on the BiOX (X=Cl, Br, I) family, mainly because of their unique structure constructed by interleaved [Bi2O2]2+ slabs and [X]2- slabs (X=Cl, Br, I), resulting in the formation of internal electric fields, which obviously facilitates the separation of photogenerated electrons and holes [28-30]. Compared to BiOBr or BiOCl, preference is given to BiOI for its narrow band gap and strong absorption in the visible region. Preparation methods such as hydrothermal [31], solvothermal [32] and soon are commonly employed for the synthesis of BiOX (X=Cl, Br, I), but are tedious, operated at elevated temperature and pressure and are often complicated [33]. The objective of this study is to synthesize BiOI catalysts with different morphologies via room temperature synthesis, characterize them using FTIR, SEM, TEM, BET, UV-Vis absorption spectrum and XRD before finally evaluating their photocatalytic performance on the degradation of norfloxacin using indoor fluorescent light illumination. 2 Materials and Methods 2.1 Chemicals All chemicals used were of analytical grade and used without further treatment. Bismuth nitrate pentahydrate (Bi(NO3)3.5H2O), Potassium iodide (KI) and Absolute ethanol were supplied by QReC Chemicals, while Polyethylene glycol (PEG400) was supplied by Merck Germany and norfloxacin by Sigma Aldrich respectively. 2.2 Preparation of BiOI Catalysts 2.2.1 Preparation of BiOI Spheres 5 mmol of Bi(NO3)3.5H2O were grounded continuously for 5 mins using an agate mortar to ensure evenness, 3 ml of PEG400 was then added, and grinding continues for further 5 mins. Subsequently, 5 mmol of KI were added and grounded together for 20 mins. After that, the product was washed several times with distilled water American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 28 and then with absolute ethanol before dried in an oven at 80 oC [34]. 2.2.2 Preparation of BiOI Plates 2 mmol of Bi(NO3)3.5H2O and 2 mmol of KI were mixed thoroughly and grounded resulting in the formation of black paste. 5 ml of distilled water was then added and mixed well with the black paste. This was subsequently allowed to stand at room temperature for 3 hrs. After that, the product was washed several times with distilled water and then with absolute ethanol before dried in an oven at 80 oC [35]. Figure 1: Possible growth mechanism of BiOI spheres and BiOI plates Based on the above schematic representation, the reaction that occurred in the formation of BiOI may be explained by equation (1) below: Bi(N𝑂𝑂3)3. 5𝐻𝐻2𝑂𝑂 + 𝐾𝐾𝐼𝐼 β†’ 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼 ↓ + 2𝐻𝐻𝐻𝐻𝑂𝑂3 + 𝐾𝐾𝐻𝐻𝑂𝑂3 + 4𝐻𝐻2𝑂𝑂 (1) 2.3 Photocatalytic Experiment Photocatalytic activity was evaluated using norfloxacin as a model pollutant. Different norfloxacin concentrations (10 – 100 mg/L) were prepared using the stock solution. The suspensions were subsequently prepared by adding variable amounts (0.5 – 2 g) of the photocatalyst powder per liter of norfloxacin solution. The photocatalytic reactions were carried out at room temperature in a 500 mL pyrex beaker using indoor fluorescent light illumination and maintaining eco living day light fluorescent (25 W) as the source throughout. Prior to irradiation, the suspensions were stirred in the dark using a magnetic stirrer for 30 mins to reach adsorption-desorption equilibrium. Periodically after irradiation, 5 mL of the suspension was taken out using a syringe and centrifuged for 5 mins at 4000 rpm essentially to remove the catalyst from the norfloxacin suspension and then filtered. Concentration of the filtrate was subsequently analyzed at 273 nm (Ξ»max) using a UV-Vis spectrophotometer (Shimadzu 2600). All experiments were conducted in duplicates and at the inherent solution pH which remain unaltered during irradiations. The photodegradation efficiency (Ξ·) was calculated by the following equation: American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 29 Ξ· (%) = πΆπΆπ‘œπ‘œ βˆ’ 𝐢𝐢𝑑𝑑 πΆπΆπ‘œπ‘œ Γ— 100 (2) Where Co is the initial concentration and Ct is the concentration at time (t) respectively. 3 Results and Discussions 3.1 Characterization Results 3.1.1 XRD Analysis The crystal structure of both BiOI spheres and BiOI plates were analyzed by X-ray diffraction (XRD), no impurity peaks were detected, which indicates that pure BiOI was successfully synthesized using both routes. As shown in Fig. 1, all diffraction peaks from both BiOI spheres and BiOI plates can well be indexed to (002), (101), (102), (110), (111), (103), (004), (200), (114), (212), (213), (204) and (220) planes of the tetragonal phase of BiOI. The results were in good agreement with the results of XRD patterns of BiOI reported by JCPDS (file no. 73.2062) for samples synthesized in the presence of KI. However, the intense and sharp diffraction peaks of BiOI spheres indicates the high crystallization of the BiOI spheres. Figure2: XRD pattern of as-synthesized BiOI spheres and plates. 3.1.2 FTIR Analysis Fourier transform infrared spectroscopy (FTIR) analysis was conducted for dual purposes. First was to determine the surface functional groups and second was to confirm the complete eradication of PEG400 from the surface of BiOI spheres. As shown in Fig. 2, the absorption peaks of BiOI spheres and BiOI plates are almost identical. Both spectra have peaks at low frequency around 500 cm-1 which are assigned to Bi – O American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 30 vibration of chemical bonds in BiOI [36]. Absorption peaks at around 1045 cm-1 may be assigned to asymmetric stretching vibration peaks of Bi – I band in BiOI structure, while absorption peaks at 1650 cm-1 are the H – O – H of physical adsorbed water [37]. Broad absorption peaks at 3450 cm-1 are due to the O – H stretching vibration over the samples [38]. Figure 3: FTIR spectra of as-synthesized BiOI spheres and plates. 3.1.3 SEM Analysis Since solvents with different viscosity were used in the synthesis of BiOI. This would have direct impact on its morphology, basically solvent of low viscosity facilities high diffusion rate of ions, while high viscosity solvent slows the diffusion rate of ions. Morphologies of the as-synthesized BiOI catalysts were first examined by SEM (Fig. 3). Low magnification images show that the BiOI catalysts have spherical-like shape (Fig. 3a) and plate-like shape (Fig. 3d). This served as a first stage confirmation of the unique role of PEG 400 in the synthesis of BiOI spheres, It has prevented the agglomeration of plates (Fig. 3f) and resulted in a self-assembly of numerous plates, loosely packed and intercrossed each other (Fig 3c). 3.1.4 UV – Vis Absorption Spectrum UV – Vis absorption spectrum analysis was also conducted for dual reasons. First was to determine the band gaps of both BiOI spheres and BiOI plates, second is to confirm that BiOI spheres has no added advantage over American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 31 BiOI plates in terms of optical absorption. It can be observed from Fig. 4 that both synthesized samples showed noticeable absorption at wavelength close to 700 nm, with an absorption edge of 675 nm and 668 nm for BiOI spheres and BiOI plates respectively. The band gap energies (Ebg, eV) of the prepared samples were estimated using the following equation: Ξ» = 1240 𝐸𝐸𝑏𝑏𝑏𝑏 (3) Based on the above equation, the band gap energies for BiOI spheres and BiOI plates were calculated to be 1.835 eV and 1.856 eV, which are close to the values reported in literature [39]. From the calculated band gap energies, it is clear that the synthesized BiOI samples were theoretically feasible for photocatalytic degradation of organic pollutants under visible light radiation. Figure 4: SEM images of the as-synthesized BiOI spheres (a,b,c) and BiOI plates (d,e,f). American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 32 Figure 5: UV-Vis absorption spectrum of BiOI spheres and BiOI plates. 3.1.5 BET Analysis A vital factor that affects the photocatalytic ability of a semiconductor is its surface area, as semiconductors with larger specific surface areas displayed much better efficiency in their performance. This is because larger surface area may favour the adsorption of more effluents onto the surface of the semiconductor, which in turn facilitates photocatalytic activity [40]. In view of the above importance, surface areas of both BiOI spheres and BiOI plates were determined. Fig. 5 below is the nitrogen adsorption-desorption isotherm and Barret-Joyner-Halender (BJH) pore size distribution curves. The isotherms according to IUPAC classification corresponds to type IV with BiOI spheres having a H3 hysteresis loop, a common feature of mesoporous solids, while BiOI plates lacks hysteresis loop, a common feature of non-porous solids. In line with that, the pore size distribution curves also reveals that BiOI spheres have a mesoporous structure, while BiOI plates is nearly non porous. The BET specific surface areas (ABET) of BiOI spheres and BiOI plates were calculated to be 16.05 m2/g and 4.99 m2/g, an indication that the surface area of the former is more than three times larger than the later. Based on the above observations, BiOI spheres is expected to have higher adsorption capacity and photocatalytic activity for the degradation of norfloxacin. 200 300 400 500 600 700 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Ab so rb an ce Wavelength (nm) BiOI Spheres BiOI Plates American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 33 Figure 6: Isotherms of N2 adsorption-desorption and BJH pore size distribution curves (insets) for (a) BiOI spheres and (b) BiOI plates. 3.2 Photocatalytic Activities of BiOI 3.2.1 Influence of Catalyst Morphology BiOI spheres and BiOI plates have quite different morphologies, which is expected to result in difference of performance. This was confirmed by subjecting equal amounts of both BiOI spheres and BiOI plates to photocatalytic degradation of norfloxacin of similar concentrations, which is resistant to photolytic reactions as reported in literatures [41, 42]. As shown in Fig. 6, higher degradation efficiency was recorded by BiOI spheres as compared to BiOI plates, this was attributed to the high adsorption of norfloxacin onto the surface of BiOI spheres due to its mesoporous structure, resulting in enhanced photocatalytic activity. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 34 Figure7: Influence of BiOI morphology on the photodegradation of norfloxacin 3.2.2 Influence of Catalyst Dosage At this stage, variable amounts of BiOI spheres (0.5 – 2 g/L) were used as photocatalysts for the degradation of norfloxacin solutions of the same concentration. As shown in Fig. 7, when catalyst dosage increases from 0.5 g/L to 1 g/L, degradation efficiency also increases. At 1 g/L, the optimum dosage was attained, and hence any further increase does not increase surface area but results in agglomeration of particles thereby increasing the turbidity of the solution which inturn blocks radiation, a paramount requirement for photodegradation [43]. Figure 8: Influence of BiOI spheres dosage on the photodegradation of norfloxacin 3.2.3 Influence of Pollutant Concentration 0 10 20 30 40 50 60 70 80 -50 0 50 100 150 De gr ad at io n ef fic ie nc y (% ) Time (min) BiOI Spheres BiOI Plates 0 10 20 30 40 50 60 70 80 90 -50 0 50 100 150 De gr ad at io n ef fic ie nc y (% ) Time (min) 0.5g/L 1g/L 2g/L American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 35 This was studied by varying the norfloxacin concentration from 10 – 20 ppm at a catalyst loading of 1 g/L. It can be observed from Fig. 8, a high degradation efficiency was recorded at low concentration, but begins to decline with increase in concentration. An explanation to that is, as concentration increases, more reactive species (OHβˆ™ and O2 βˆ™βˆ’ ) are needed for the successful photodegradation of norfloxacin, which in this case keeps on decreasing with increase in concentration, due to fall down in the amount of light reaching BiOI. It is worth noting here that the insufficiency of reactive species (OHβˆ™ and O2 βˆ™βˆ’ ) resulted in continuous decrease of degradation efficiency with increase in concentration [44]. Figure 9: Influence of pollutant concentration on the photodegradation of norfloxacin 3.3 Reaction Mechanism This process gets initiated when a photon of visible light having energy greater than the band gap of BiOI (i.e. hΟ… > 1.835 eV for BiOI spheres or hΟ… > 1.856 eV for BiOI plates) strikes its surface, electron then leaves the valence band (VB) thereby creating a hole (i.e. hVB +) and moves to the conduction band (CB) making it electron rich (i.e. e ΜΆ CB). 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼 + β„ŽΟ… (visible) β†’ 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼 (β„Žπ‘‰π‘‰π‘‰π‘‰+ + π‘’π‘’πΆπΆπ‘‰π‘‰βˆ’ ) (4) Electron in the conduction band converts the adsorbed oxygen on the surface of the photocatalyst to superoxide radical (𝑂𝑂2.βˆ’). 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼(π‘’π‘’πΆπΆπ‘‰π‘‰βˆ’ ) + (𝑂𝑂2)π‘Žπ‘Žπ‘Žπ‘Žπ‘Žπ‘Ž β†’ 𝑂𝑂2.βˆ’ (5) The hole in the valence band abstract an electron from the adsorbed water molecule or hydroxyl ions forming hydroxyl radicals. 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼(β„Žπ‘‰π‘‰π‘‰π‘‰+ ) + 𝑂𝑂𝐻𝐻 βˆ’ β†’ 𝑂𝑂𝐻𝐻 βˆ™ (6) 0 10 20 30 40 50 60 70 80 90 -50 0 50 100 150 De gr ad at io n ef fic ie nc y (% ) Time (min) 10ppm 20ppm American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 41, No 1, pp 26-39 36 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼(β„Žπ‘‰π‘‰π‘‰π‘‰+ ) + 𝐻𝐻2𝑂𝑂 β†’ 𝑂𝑂𝐻𝐻 βˆ™ + 𝐻𝐻+ (7) The superoxide radical gets protonated, resulting in the formation of perhydroxyl radicals. 𝑂𝑂2βˆ™βˆ’ + 𝐻𝐻+ β†’ 𝐻𝐻𝑂𝑂2βˆ™ (8) Subsequent step involves formation of hydrogen peroxide 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼(π‘’π‘’πΆπΆπ‘‰π‘‰βˆ’ ) + 𝐻𝐻𝑂𝑂2βˆ™ + 𝐻𝐻+ β†’ 𝐡𝐡𝐡𝐡𝑂𝑂𝐼𝐼 + 𝐻𝐻2𝑂𝑂2 (9) This is the followed by the cleavage of hydrogen peroxide producing hydroxyl radicals 𝐻𝐻2𝑂𝑂2 + β„ŽΟ… β†’ 2 𝑂𝑂𝐻𝐻 βˆ™ (10) The final stage involves degradation of norfloxacin by hydroxyl radicals 𝑂𝑂𝐻𝐻 βˆ™ + 𝐻𝐻𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝐡𝐡𝑁𝑁 β†’ 𝐷𝐷𝑒𝑒𝐷𝐷𝑁𝑁𝑁𝑁𝐷𝐷𝑒𝑒𝐷𝐷 𝑁𝑁𝑁𝑁 π‘šπ‘šπ΅π΅π‘π‘π‘’π‘’π‘π‘π‘π‘π‘π‘π΅π΅π‘™π‘™π‘’π‘’π·π· 𝑝𝑝𝑁𝑁𝑁𝑁𝐷𝐷𝑝𝑝𝑁𝑁𝑝𝑝𝑙𝑙 (11) 4 Conclusion In this study, both BiOI spheres and BiOI plates were successfully fabricated using low cost and eco-friendly room temperature solid-state synthesis method. Difference in morphology was achieved using PEG400, which due to its viscosity resulted in self-assembly of plates forming spheres. Although low concentration of norfloxacin was tested for photodegradation in the presence of both BiOI spheres and BiOI plates. Higher degradation efficiency was achieved using BiOI spheres as compared with BiOI plates. This is due to the morphology, surface area and pore volume of BiOI spheres, resulting in higher adsorption of norfloxacin, which is essential for decomposition. Moreover, the facile methods presented in this research can be adopted for the easy, fast and large scale synthesis of other bismuth-oxyhalides based photocatalysts. References [1]. Simoens, S., et al., Consumption patterns and in vitro resistance of Streptococcus pneumoniae to fluoroquinolones. Antimicrobial agents and chemotherapy, 2011. 55(6): p. 3051-3053. [2]. Hirsch, R., et al., Occurrence of antibiotics in the aquatic environment. Science of the Total Environment, 1999. 225(1): p. 109-118. [3]. BabiΔ‡, S., M. PeriΕ‘a, and I. Ε koriΔ‡, Photolytic degradation of norfloxacin, enrofloxacin and ciprofloxacin in various aqueous media. Chemosphere, 2013. 91(11): p. 1635-1642. [4]. 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