Preparation Of Indium Zinc Sulfide Composite And Its Photocatalytic Degradation Of Pharmaceutical Wastewater

Pharmaceutical wastewater often contains a large amount of drug residues,which can easily lead to large-scale water pollution after discharge and make the ecological environment suffer serious damage.Semiconductor-based photocatalytic degradation as an advanced oxidation technology has been widely studied by researchers and has great potential for application in solving drug wastewater pollution problems.However,the design and preparation of efficient,stable,visible-light responsive semiconductor photocatalysts remains a difficult task in the field of photocatalysis.Among the many semiconductors,indium zinc sulfide（ZnIn₂S₄）has received much attention from researchers because of its good visible light absorption ability,excellent physicochemical stability,narrow band gap and proper redox potential.However,ZnIn₂S₄ exhibits relatively low photocatalytic degradation activity due to the rapid complexation of its photogenerated carriers,and also suffers from photocorrosion as a metal sulfide ZnIn₂S₄.An effective way to overcome these problems is to introduce suitable species to construct heterojunctions.Heterojunctions will promote interfacial charge transfer,thus promoting effective photo-induced electron-hole separation,improving photocatalytic activity and overcoming its photocorrosion problems.In this work,we adopted the method of constructing complex heterojunctions by combining indium vanadate（InVO₄）and ferrous tungstate（Fe WO₄）with ZnIn₂S₄,respectively,to form composite materials,which effectively improve the photocatalytic degradation ability,and the main research is as follows:（1）InVO₄/ZnIn₂S₄ composites were synthesized using a hydrothermal method based on the synthesis of ZnIn₂S₄ using a solvent thermal method.The structural composition was subsequently analyzed using SEM,TEM,XPS,XRD and other characterization means,and the results showed that the main body of the synthesized material was a three-dimensional graded flower-like morphology,which was favorable for the incident light to be absorbed after multiple reflections and scatterings on the surface and inside of the material,and improved the absorption of visible light by the catalyst.Its performance in degrading tetracycline（TET）under visible light irradiation was investigated and optimal degradation conditions were found.Under the optimized conditions,the photocatalytic removal efficiency of InVO₄/ZnIn₂S₄ for TET reached82.96%,and the degradation process was in accordance with the proposed first-order kinetic model.The active substances among the InVO₄/ZnIn₂S₄ photocatalytic degradation system were explored by scavenger experiments,mainly·OH,h⁺and·O₂^-,and the order of active influence ability was h⁺>·OH>·O₂^-.The charge transfer mechanism of the composite S-scheme was also proposed by combining the material energy band positions determined by the Mott-Schottky test and UV-Vis DRS calculation results.The efficient reuse performance of the InVO₄/ZnIn₂S₄ complex was confirmed by recycling experiments,and the good stability of the InVO₄/ZnIn₂S₄complex was confirmed using XRD,XPS and ICP-OES.The TET degradation products were analyzed by liquid mass spectrometry（HPLC-MS）and ion chromatography（IC）,and the possible degradation pathways were proposed.Finally,the inhibition experiments of TET degradation products against Staphylococcus aureus showed that the photocatalytic degradation could effectively reduce the biotoxicity of TET.（2）Fe WO₄/ZnIn₂S₄ complexes were synthesized on the basis of ZnIn₂S₄ by precipitation method and used for the photocatalytic degradation of TET and meloxicam（MLX）.After characterization of the complexes,the morphological features,crystal structure,light absorption properties and other properties of the materials themselves were determined.The characterization results showed that the synthesized material has a three-dimensional flower-like morphology,and the unique flower-like morphology has a large specific surface area and exposes abundant active sites,which is beneficial to improve the catalytic performance of the catalyst.The degradation performance of TET and meloxicam（MLX）was investigated under visible light irradiation and the optimal degradation conditions were found.In addition,H₂O₂ was added to build a photo-Fenton degradation system to achieve higher organic pollutant removal efficiency.Under the optimized conditions,Fe WO₄/ZnIn₂S₄ achieved 96.28%removal efficiency for TET and 95.84%removal efficiency for MLX.The scavenger experiments revealed that·OH,h⁺and·O₂^-were the main active substances in the Fe WO₄/ZnIn₂S₄ photocatalytic degradation system,and the order of the active influence was h⁺>·OH>·O₂^-.Moreover,the conduction mechanism of the S-scheme heterojunction of Fe WO₄/ZnIn₂S₄ composites was proposed by combining the energy band positions determined by the Mott-Schottky test and UV-Vis DRS calculations.The efficient reusability performance of the Fe WO₄/ZnIn₂S₄ complex was confirmed by recycling experiments,and the high stability of the Fe WO₄/ZnIn₂S₄ complex was confirmed using XRD,XPS and ICP-OES.The TET degradation products were analyzed by HPLC-MS and IC,and the possible degradation pathways were proposed.Finally,the photocatalytic oxidation technology was proved to be effective in reducing the biotoxicity of TET by the inhibition experiments of degradation products against Staphylococcus aureus.In conclusion,the InVO₄/ZnIn₂S₄ complex and Fe WO₄/ZnIn₂S₄ complex were successfully obtained by constructing complex heterojunctions,which effectively improved the photocatalytic degradation capacity of ZnIn₂S₄ and showed strong removal ability for TET,MLX and other organic pollutants in water,and reduced the biotoxicity of TET.This study has contributed to the practical application of photocatalytic technology for solving pharmaceutical wastewater treatment problems and has implications for the construction of high-performance photocatalytic heterojunctions.