Preparation Of ZnIn₂S₄ Based Composites And Their Photocatalytic Performance

Zinc indium sulfide（ZnIn₂S₄）with a relatively narrow band gap can absorb visible light,which has attracted wide attention in the field of photocatalysis.However,ZnIn₂S₄suffers from fast recombination of photogenerated electrons and holes,short lifetime of charge carriers and limited light absorption capacity.The photocatalytic performance of ZnIn₂S₄ cannot meet the requirements of practical applications.Therefore,in this paper,a series of ZnIn₂S₄-based composites materials were designed and synthesized,which effectively improved the photocatalytic hydrogen production performance of ZnIn₂S₄driven by visible light.The main research contents are as follows:（1）Direct Z-scheme BiVO₄/ZnIn₂S₄ photocatalysts were prepared by a facile hydrothermal method.The structure,micromorphology,light absorption properties and photoelectric properties of BiVO₄/ZnIn₂S₄ were characterized in detail.The photocatalytic performance for hydrogen production from water was studied under the excitation of visible light.The Z scheme system was constructed by loading ZnIn₂S₄nanoparticles onto BiVO₄blocks.Compared with pure ZnIn₂S₄ and BiVO₄bulk,BiVO₄/ZnIn₂S₄ had better light response ability and better hydrogen evolution performance.It can be obtained that when the load reaches the optimal ratio,the mass percentage of BiVO₄ is 10%,and the hydrogen production efficiency can reach 345.6μmol·g^-1·h^-1.The performance improvement can be attributed to the combination of photogenerated electrons in the conduction band of BiVO₄ and photogenerated holes in the valence band of ZnIn₂S₄ during the catalysis process,which promotes the transfer of carriers and effectively reduces the recombination rate between photogenerated electrons and holes.As a result,the improvement of photocatalytic hydrogen evolution performance is realized.（2）SnS₂ hexagonal microplates were loaded on ZnIn₂S₄ flower-shaped microspheres by hydrothermal method,and SnS₂/ZnIn₂S₄ composite material with type II heterojunction was prepared.The effect of the loading amounts of SnS₂ on the activity of photocatalytic hydrogen production was researched.Among the composite catalysts,2.5-SS/ZIS showed the highest photocatalytic activity for hydrogen production,and the hydrogen evolution rate reached 769μmol·g^-1·h^-1,which was about 10.5 times higher than that of pure ZnIn₂S₄.The results of PL,EIS and photocurrent measurements confirmed that the effective separation of electron-hole pairs was achieved in 2.5-SS/ZIS,which leaded to enhancement of the photocatalytic performance of ZnIn₂S₄.（3）By controlling the mass ratio of Mo S₂ microspheres,g-C₃N₄ nanosheets and ZnIn₂S₄ nanosheets,a series of new g-C₃N₄/ZnIn₂S₄/Mo S₂ composite photocatalysts were prepared.The composite photocatalyst with a content of 5%g-C₃N₄ and 5%Mo S₂（ZGM-5）exhibited the highest rate of hydrogen production(3.26 mmol·g^-1·h^-1),which is 2.16 times of that of pure ZnIn₂S₄.After ZnIn₂S₄ was combined with g-C₃N₄ and Mo S₂,on the one hand,the light absorption capacity was improved,on the other hand,the recombination rate of photogenerated electron-hole pairs was reduced.Therefore,the hydrogen evolution performance driven by visible light is improved.（4）A new type of ZnIn₂S₄/g-C₃N₄/WS₂ ternary heterojunction composites were synthesized by hydrothermal method.The composite photocatalyst showed excellent photocatalytic performance of hydrogen evolution under visible light irradiation.Among them,the sample with a content of 5%g-C₃N₄ and 5%WS₂（ZGW-5）displayed the highest rate of hydrogen evolution(3.33 mmol·g^-1·h^-1),which is about 2.21 times of that of pure ZnIn₂S₄.After ZnIn₂S₄ is combined with g-C₃N₄ and WS₂,the light absorption capacity of the composite is improved.Two I-type heterojunctions were formed in sequence between g-C₃N₄,ZnIn₂S₄ and WS₂,which promote the effective separation and rapid transfer between photogenerated electrons and holes.Therefore,the composite catalyst exhibits better hydrogen evolution performance.