Preparation And Photocatalytic Performance For Hydrogen Production Analysis Of TiO₂/g-C₃N₄ Composites

In recent years,with the rapid development of economy,environmental contamination and the energy crisis have become two key issues for human society,so it is urgent to develop a sustainable and clean energy to satisfy the increasing global energy demand.Solar energy is one of the most abundant energy resources on the earth.Hydrogen is considered as an ideal energy carrier in the future due to its high mass-specific energy density and zero emission character-istics.Thus,the conversion from solar energy to valuable hydrogen energy has provided an ideal solution to mitigate global energy and environmental issues.Photocatalytic water splitting has become a promising approach for clean,low-cost,and environmental-friendly production of hydrogen by utilizing solar energy in the presence of semiconductor photocatalysts.As one of the most promising photocatalysts,TiO₂ has been widely studied and applied on the photocatalytic hydrogen production because of its proper properties,such as excellent stability,low cost,nontoxic and so on.However,the limited visible light utilization for the wide band gap（Eg=3.2 e V）and low quantum yields for the quick electro-hole recombination have hindered its further application.Thus,significant attention has been drawn to design and construct TiO₂-based heterojunction photocatalysts with good matchable band gap to enhance the visible light absorption and promote electron-hole separation efficiency.Owning to its suitable conduction band and valence band with a smaller band gap,graphitic carbon nitride（g-C₃N₄）seems to be a good candidate for producing heterojunction photocatalyst with TiO₂ nanomaterial because they can absorb visible light and easily form a favorable band alignment for the efficient photo-generated charge separation.Consequently,up until now,many efforts have been devoted to the combination of TiO₂ and g-C₃N₄ with different approach.However,the hydrogen production performance of TiO₂/g-C₃N₄ heterojunction photocatalysts are still relatively low,which severely limits their practical application.In this thesis,the photocatalytic activity of TiO₂/g-C₃N₄ heterojunction was improved by the method of AgBr coupling and co-catalyst Ni Cop loading.The main research contents are as follows.（1）Firstly,TiO₂ and g-C₃N₄ were prepared by hydrothermal and calcination methods,respectively.Then,the TiO₂/g-C₃N₄ heterostructure photocatalyst was perpared by directly mixing TiO₂ and g-C₃N₄.Finally,the narrow-band semiconductor AgBr was used to modify TiO₂/g-C₃N₄ to construct TiO₂/g-C₃N₄/AgBr composite photocatalyst.The hydrogen production activity of the composite photocatalyst was explored,and it was found that the hydrogen production rate of the TiO₂/g-C₃N₄/AgBr composite material was as high as 188.1μmol g^-1 h^-1,which was 3.03 and 2.72 times higher than that of pure TiO₂ and TiO₂/g-C₃N₄.The reason for the improved photocatalytic performance is that the recombination of g-C₃N₄ and AgBr leads to a significant increase in the separation and transport efficiency of photogenerated carriers.（2）Sphere TiO₂ was prepared by hydrothermal method.Then,the TiO₂/g-C₃N₄heterostructure photocatalyst was prepared by calcination and growth of cyanamide（CY）on the surface of TiO₂.Finally,the co-catalyst NiCoP was loaded to construct TiO₂/g-C₃N₄/NiCoP composite photocatalyst.The hydrogen production activity of the composite photocatalyst was explored,and it was found that the hydrogen production rate of the TiO₂/g-C₃N₄/NiCoP composite material was as high as 481.97μmol g^-1 h^-1,which was 21.12 and 3.24 times higher than that of TiO₂ and TiO₂/g-C₃N₄.The main reason for the improvement of photocatalytic performance is that the recombination of g-C₃N₄ and NiCoP significantly improves the separation and transport efficiency of photogenerated carriers.