Construction Of ZnIn₂S₄-based Composite Photocatalyst And Study On Photocatalytic Water Splitting For Hydrogen Production

Photocatalytic water splitting into hydrogen can convert solar energy into green hydrogen energy with zero pollution,renewability and high combustion calorific value,which is an important way to realize sustainable development of human society.However,the conversion efficiency of solar energy to hydrogen energy is determined by various factors,such as the spectral response range of the photocatalyst,the separation efficiency of photogenerated electron-hole pair and the surface reaction process.The current efficiency of solar photocatalytic hydrogen production is relatively low,and the development of high-performance photocatalysts for water splitting is still a great challenge.To address these problems,the ultra-thin hexagonal phase Zn In₂S₄ was taken as the research object in this work.And the efficiency and stability of Zn In₂S₄ photocatalysts for the photocatalytic water splitting into hydrogen are greatly improved by intrinsic carrier separation regulation,interfacial photogenerated charge transfer regulation and construction of artificial Z-type organic-inorganic heterojunction,which provide new ideas for the rational construction of efficient and highly stable photocatalysts for photocatalytic water splitting into hydrogen.Moreover,the mechanism of photocatalytic water splitting into hydrogen over Zn In₂S₄-based photocatalysts were investigated in depth by structural characterization,photoelectric characterization and density function theory calculations,the specific research contents are as follows.Firstly,Zn In₂S₄ nanosheets with a thickness of about 3.65 nm were prepared by"top-down"combined with"bottom-up"method.The effect of two-dimensional structure and surface sulfur defects on the separation efficiency of photogenerated carriers on Zn In₂S₄ photocatalyst was studied.Two-dimensional ultrathin structure can provide shorter path for photo-generated carrier migration and more surface active sites on Zn In₂S₄.In addition,the rich sulfur vacancies on the ultra-thin Zn In₂S₄ surface can further promote the separation of photo-generated electrons and holes by capturing photo-generated electrons.Under visible light irradiation（λ≥400 nm）,the photocatalytic hydrogen production rate of ultrathin Zn In₂S₄ was 40.7μmol·h^-1,which was 1.8 times and 2.5 times than that of layered Zn In₂S₄ and 3D Zn In₂S₄ nanoflowers,respectively.Secondly,in order to further improve the activity and stability of Zn In₂S₄ for photocatalytic water splitting into hydrogen,2D/2D Ti₃C₂T_x/Zn In₂S₄heterostructures were constructed by electrostatic self-assembly strategy.The optimal photocatalytic hydrogen production rate from water splitting over Ti₃C₂T_x/Zn In₂S₄ composite was 148.4μmol·h^-1,which was 3.6 times and 9.2times than that of ultrathin Zn In₂S₄ nanosheets and 3D Zn In₂S₄ nanoflowers,respectively,and the apparent quantum efficiency at 400 nm was 12.84%.The related characterization and density functional theory（DFT）calculations show that the tight 2D/2D contact interface can effectively promote the transfer of photogenerated electrons from Zn In₂S₄ to Ti₃C₂T_x,and the sulfur vacancy of Zn In₂S₄ as an electron trap can further enhance the separation of photogenerated electrons and holes.The synergistic effect of sulfur vacancy and Ti₃C₂T_xcocatalyst is the reason for the remarkable improvement of the photocatalytic hydrogen production from water splitting.Finally,copper phthalocyanine（Cu Pc）/Zn In₂S₄ organic-inorganic hybrid artificial Z-type heterojunction was constructed by in-situ growth method.When the Cu Pc content was 7 wt.%,the photocatalytic hydrogen production rate from water splitting over Cu Pc/Zn In₂S₄ under visible light reached 151.2μmol·h^-1,which was 8.1 times than that of Zn In₂S₄ nanoflowers.After photodeposition of 1wt.%Pt,the cyclic stability of Cu Pc/Zn In₂S₄ was significantly improved,and the photocatalytic hydrogen production rate was further increased by 4.7 times.The structure characterization and photoelectric characterization showed that the addition of Cu Pc photosensitizer increased the light absorption range of Zn In₂S₄to the near infrared range,and effectively reduced the aggregation of Zn In₂S₄ and exposed more surface active sites.In addition,the Z-type transfer mechanism of photogenerated electrons and holes between Zn In₂S₄ and Cu Pc also plays a crucial role in improving the efficiency of photocatalytic hydrogen production.