Eco-Friendly Synthesis\nof ZnO for Efficient Photodegradation\nof Pharmaceutical Drug Removal by Photocatalysis

In the present work, a comparative study on eco-friendly\nsynthesis\nof zinc oxide (ZnO) sample 1 and sample 2 with 3.17 and 4.17 M NaOH,\nrespectively, is reported. Sample 2 with 4.17 M NaOH is applied in\nthe photocatalytic degradation of paracetamol (pure and raw both)\nusing the ultraviolet (UV, 280–400 nm) and UV/H<sub>2</sub>O<sub>2</sub> reaction systems. Pure paracetamol (PCM1) and raw paracetamol\n(PCM2) from tablets are used for photocatalytic degradation by photocatalysis.\nOur experimental evidence show that ZnO sample 2 was more active in\nthe UV/H<sub>2</sub>O<sub>2</sub> reaction system than under ultraviolet\n(UV, 280–400 nm) irradiation only in the photocatalytic degradation\nprocess. Field emission scanning electron microscopy (FE-SEM) confirms\nthe homogeneous growth of a rod-like structure for sample 1 and brittle\nand randomly aggregated rod-like and wire-like nanostructures for\nsample 2. The peaks observed in the region around 440 to 900 cm<sup>–1</sup> in the FTIR spectra for sample 1 and sample 2 annealed\nat 250 °C confirms the presence of ZnO bonds. UV absorption spectroscopy\nindicates a red shift in the absorption spectra due to the increase\nin the molar concentration of NaOH to 4.17 M for sample 2. In this\nstudy, the band gap values are found to be 3.33 and 3.01 eV for the\nsynthesized ZnO sample 1 and sample 2, respectively, which are 40\nand 360 meV less as compared to that of bulk ZnO (3.37 eV). The oxidation\nrate is increased in the UV/H<sub>2</sub>O<sub>2</sub> reaction system,\nproducing the highest rate for PCM1 drug removal with rate constant\n9.7 × 10<sup>–3</sup> min<sup>–1</sup> and half-life\n71.5 min. The kinetic study results for the removal of PCM1 and PCM2\nshow good results and follow the pseudo-first-order kinetic model\nwith correlation coefficients 0.69556 and 0.90851, respectively, whereas\nPCM2 follows the pseudo-second-order kinetic model with correlation\ncoefficient 0.9993. The experimental and calculated values of removal\ncapacity (<i>q</i><sub>e</sub>) at equilibrium is found\nclose to those of the pseudo-second order kinetic model for the removal\nof both the paracetamol forms PCM1 and PCM2 with the catalyst ZnO\nnanostructure. The photostability of ZnO sample 2 is also tested with\na reusability test in photocatalytic degradation of paracetamol at\nleast four times. The absence of a maxima peak at 243 of PCM1 in the\nUV/H<sub>2</sub>O<sub>2</sub> reaction system indicates nearly 100%\nsuccessful conversion of 20 ppm PCM1 by using synthesized catalyst\nZnO sample 2. The comparative results of both reaction systems, i.e.,\nUV and UV/H<sub>2</sub>O<sub>2</sub>, show that the hydroxyl radicals,\nas the active species, are responsible for major degradation of both\nparacetamol forms (PCM1 and PCM2).