Design And Performance Study Of ZnIn₂S₄/MOFs Heterojunction Photocatalysts

Addressing energy and environmental challenges,photocatalysis has attracted widespread attention worldwide.The rapid development of this emerging field has led to a great interest in the development of highly efficient photocatalytic materials.As an excellent two-dimensional visible light photocatalytic material,indium zinc sulfide（ZnIn₂S₄）has attracted more extensive research due to its non-toxicity,suitable energy band structure,high physicochemical stability and easy synthesis.However,its photocatalytic efficiency is still unsatisfactory due to its slow separation and transfer rate of photogenerated carriers.Metal-organic frameworks（MOFs）,with their semiconductor-like properties,high specific surface area and porosity,diverse and tunable structures,have become potential candidates for building heterogeneous combinations with other semiconductors into efficient photocatalysts.This thesis focuses on the performance of ZnIn₂S₄/MOFs heterojunctions in photocatalytic reactions,taking full advantage of the semiconductor-like structure,ligand-unsaturated metal center sites,and easy functionalization modification of MOFs to synthesize a series of photocatalysts with efficient photocatalytic performance,explore their excellent performance in different photocatalytic reactions,and propose different reaction mechanisms for the research provides a theoretical basis and research ideas for the design and construction of new high-efficiency composite photocatalytic materials.The specific research contents are as follows.（1）Using the opposite surface charged nature of ZnIn₂S₄ and MIL-101（Cr）,the MIL-101@ZnIn₂S₄ composite photocatalyst was synthesized by growing ZnIn₂S₄ nanosheets uniformly on the surface of MIL-101 through a simple oil bath method,which proposed and demonstrated the formation of a new Cr-S bond between ZnIn₂S₄ and MIL-101,thereby achieved a tight interfacial connection,which improved the electron transport efficiency and greatly promoted the separation efficiency of photogenerated electron-hole pairs,and finally realized the efficient visible light photocatalytic Cr（VI）reduction efficiency.The best MIL-101@ZnIn₂S₄ sample can reduce95%of Cr（VI）within 30 min,corresponding to a rate constant of 0.107 min^-1,which is 2.9 times higher than that of pure ZnIn₂S₄.In addition,an apparent quantum yield of 9.7%was able to be achieved at a wavelength of 420 nm.（2）Taking advantage of the easier ligand modification of Zr-MOFs,a series of Ui O-66-X（X=NH₂,OH,（OH）₂）were prepared by the solvothermal method,and the corresponding ZnIn₂S₄/Ui O-66-X composite photocatalysts were subsequently prepared for the photocatalytic O₂reduction in pure water system to produce H₂O₂.The results showed that the absorption range of visible light by ZnIn₂S₄/Ui O-66-NH₂ and ZnIn₂S₄/Ui O-66-（OH）₂ was expanded when modified with the auxochrome groups-NH₂ and-（OH）₂.In addition,the mechanistic analysis showed that the Z-scheme heterojunction formed between ZnIn₂S₄/Ui O-66-NH₂ and ZnIn₂S₄/Ui O-66-（OH）₂facilitated the separation of photogenerated electrons and holes,and ultimately exhibited excellent visible light photocatalytic H₂O₂ production performance.ZnIn₂S₄/Ui O-66-NH₂,ZnIn₂S₄/Ui O-66-（OH）₂ and ZnIn₂S₄/Ui O-66-OH showed H₂O₂ yields of 799,733 and 165μmol·L^-1,which were9.5,8.7 and 2.0 times higher than those of ZnIn₂S₄/Ui O-66,respectively.（3）The spindle-shaped MIL-53（Fe）-NH₂@ZnIn₂S₄ photocatalysts were prepared by in situ growth of ZnIn₂S₄ nanosheets on the surface of Fe-MOFs by grafting the color-coordinating group-NH₂ to enhance the absorption of visible light and deepen the study of Z-scheme heterojunctions.The multilevel structure and Z-scheme heterojunction of the composite catalysts enabled the effective separation of photogenerated electrons and holes,and retained their strong redox ability,ultimately showing a more excellent performance for visible light photocatalytic benzyl alcohol oxidation and Cr（VI）reduction.The best MIL-53-NH₂@ZnIn₂S₄ sample was able to achieve 73%conversion of benzyl alcohol in air atmosphere,corresponding to a yield of 1825μmol·g^-1·h^-1 of benzaldehyde.