Structure Design Of ZnIn₂S₄-based Semiconductor Composite Photocatalyst And Study On Their Photocatalytic Performance Of Pollutants Treatment

The water environmental pollution caused by tetracycline antibiotics and lignin waste liquid should be solved urgently.Photocatalysis technology has been proved to be a mild oxidation technology in the effectively treatment of water pollutants.The metal sulfide ZnIn₂S₄has unique photoelectric properties,but the inherent defects of single component catalyst such as poor utilization rate of visible light and high photogenerated carrier recombination rate limit its application.This study aims to design efficient composite photocatalytic systems for tetracycline degradation and lignin model depolymerization using ZnIn₂S₄ semiconductor as the base through the modification method of co-catalyst loading and heterogeneous structure construction,so as to alleviate environmental pollution.Meanwhile,in collaboration with various characterization methods,capture experiment,cycle experiment,DFT simulation calculation,etc.,the internal relationship between material structure and its photocatalytic behavior and stability was explored,so as to clarify the photocatalytic path and mechanism,and provide certain theoretical support for the construction of ZnIn₂S₄-based composite photocatalytic system in the future.The specific research content and innovation of this work are as follows:（1）The g-C₃N₄/ZnIn₂S₄ Type-Ⅱ heterojunction was prepared by calcination and solvothermal method for photocatalytic degradation of tetracycline.g-C₃N₄ and ZnIn₂S₄,both of which are nanosheet structures,are closely combined face to face,forming a 2D/2D heterogeneous interface,providing more nanochannels and active sites,effectively promoting photogenerated carrier separation and further promoting the photocatalytic process.The results showed that the photocatalytic degradation rate of g-C₃N₄/ZnIn₂S₄ for tetracycline was 3.16and 2.35 times higher than that of pure g-C₃N₄ and ZnIn₂S₄,respectively.DFT calculation proved the charge flow at the heterogeneous interface between g-C₃N₄ and ZnIn₂S_4.In addition,the photocatalytic degradation mechanism was determined.（2）Fe₃/g-C₃N₄/ZnIn₂S₄ ternary photocatalytic system was constructed by crystallization and solvothermal method.Under visible light,the degradation efficiency of 50 m L 50 mg/L tetracycline solution was 82.3%by adding only 15 mg composite catalyst,which was higher than 69.5%of g-C₃N_4/ZnIn₂S₄ heterojunction under the same conditions.The further improved photocatalytic activity can be attributed to the addition of Fe₃ clusters,which effectively inhibits photogenerated carrier recombination by trapping photogenerated electrons.The loading of 0D nanoclusters on 2D/2D heterojunction surfaces also supplies more active sites by increasing the specific surface area of the material.·O₂^-and h⁺were proved to be the main active species in the photocatalytic process.The photocatalytic degradation mechanism was determined and the degradation path of tetracycline was analyzed by liquid chromatography-mass spectrometry.（3）2D/2D TiO₂/ZnIn₂S₄ n-n heterojunction photocatalyst was synthesized by solvothermal process to cleavage Cβ-O bond of ligninβ-O-4 model under simulated sunlight.The electron transfer from TiO₂ to ZnIn₂S₄ formed an internal electric field around the heterojunction interface,which effectively promoted the separation of photogenerated carriers.h⁺and e^-act as active species in oxidation and reduction ofβ-O-4 model,respectively.The optimal ratio of TiO₂/ZnIn₂S₄ material achieved 98.5%conversion of ligninβ-O-4 alcohol model,and all substrate were converted into target aromatic products,with the by-product yield only 0.53%.Through a series of characterization methods and DFT calculation,a mechanism of photocatalytic cleavage of lignin bond was described.