Preparation Of G-C₃N₄-Based Nano-Heterojunction And Study On The Performance Of Photocatalytic Decomposition Of Water To Hydrogen

In recent years,the problem of energy shortage and environmental pollution are increasingly serious.Photocatalytic technology is considered to be one of the effective ways to solve the energy crisis and environmental problems.The development of high efficiency visible light-driven photocatalysts is a hot research topic at present.g-C₃N₄ has attracted much attention because of its unique energy band structure and excellent visible light catalytic activity.In this paper,g-C₃N₄ as the research object was used to improve the photocatalytic activity of g-C₃N₄ by constructing heterojunction composite catalyst,and it was applied to the photocatalytic hydrogen production.The photoabsorption ability,carrier separation ability and the mechanism of photocatalytic enhancement of the modified composite samples were studied in detail,the main findings are as follows:?1?SnS₂/g-C₃N₄ was prepared by high temperature polymerization and solvent evaporation method.Through a series of characterization,it was found that SnS₂ nanoparticles were uniformly loaded on g-C₃N₄ nanocrystals and formed tightly bound heterostructures.It was found that the 5 wt%SnS₂/g-C₃N₄ exhibited excellent photocatalytic hydrogen production performance under visible light irradiation,and the hydrogen production rate reached 972.6?mol·h^-1·g^-1,which is 2.9 times and 25.6 times than that of bulk g-C₃N₄ and SnS₂,respectively.At the same time,the cycle experiment shows that SnS₂/g-C₃N₄ composite has good reproducibility and stability in photocatalytic experiment.By means of the active factor capture experiment,it is proved that the holes migration pathway in the heterojunction.The holes in the SnS₂ valence band will be transferred to the g-C₃N₄ valence band to participate in the oxidation reaction.?2?First,Au supported g-C₃N₄ was prepared by microwave assisted chemical reduction,then Z type composite heterojunction SnS₂/Au/g-C₃N₄ was prepared by solvent evaporation method.Under the co-modification of Au nanoparticles and SnS₂ nanoparticles,the visible light absorption ability of the sample was further improved.The Schottky junction between Au nanoparticles and g-C₃N₄ nanoparticles facilitates carrier separation.The active factor capture experiments show that the ternary system has formed a typical Z-type electron transfer mechanism,the electrons excited on the SnS₂ conduction band are transferred to the g-C₃N₄ valence band by good conductivity of the Au nanoparticles and recombine with the holes,the reduction reaction is carried out on the g-C₃N₄ conduction band,and the oxidation reaction is carried out on the SnS₂ valence band.?3?SnSe₂/g-C₃N₄ heterojunction was prepared by in-situ growth method.The introduction of SnSe₂ not only broadens the absorption range of visible light,but also enhances the optical absorption intensity.15wt%SnSe₂/g-C₃N₄ showed excellent photocatalytic hydrogen production performance,which was 1.9 times and 3.5 times than that SnSe₂ and g-C₃N₄,respectively.The construction of heterojunction promotes carrier transport efficiency and inhibits the recombination of photoinduced e^-/h⁺pairs,the electrons on the g-C₃N₄ conduction band and the holes in the valence band transfer to the SnSe₂ valence band and conduction band to participate in the redox reaction.