Preparation And Photocatalytic Activity Of Graphitic Carbon Nitride Multiphase Materials

With the advancement of technology,the conditions for the development and utilization of solar energy have been greatly improved,and solar energy has shown broad development prospects.Photocatalytic technology is considered to be a green technology by converting solar energy into chemical energy through photocatalyst to degrade pollutants in water.The core of photocatalysis technology is to design and synthesize suitable photocatalysts.The early common TiO₂ and ZnO are limited by its large forbidden band width,so it can only use part of the ultraviolet light in sunlight,and does not make good use of visible light.As a new type of non-metallic high-polymer semiconductor,graphitic carbon nitride（g-C₃N₄）has a wide range of visible light response,which can effectively improve the utilization of solar energy.However,pure g-C₃N₄ also has problems such as a small specific surface area and a high recombination ratio of electron-hole pairs.Studies have shown that the construction of composite materials based on g-C₃N₄ can effectively solve those problems.（1）The yield and morphology of g-C₃N₄ synthesized by direct calcination of melamine,thiourea and urea as precursors at different temperatures were investigated.The soft template method was used to synthesize g-C₃N₄ using melamine as a precursor.The photocatalytic test was carried out on each g-C₃N₄ synthesized at a calcination temperature of 550℃.The experimental results show that the photocatalysis of g-C₃N₄ synthesized by urea as precursor and g-C₃N₄ synthesized by soft template method is higher.The photocatalytic performance of g-C₃N₄ synthesized by soft template method is significantly higher than that of g-C₃N₄ synthesized by direct calcination.（2）Ag-CeO₂ nanospheres were synthesized by hydrothermal method,and the Ag-CeO₂/g-C₃N₄ composites were prepared by simple solvent evaporation method.The effects of Ag-CeO₂ on the structure,morphology and photocatalytic properties of g-C₃N₄ were investigated,and the photocatalytic stability of the composites was evaluated.The experimental results show that the Ag-CeO₂/g-C₃N₄ composite can expand the visible light response and effectively suppress the electron-hole pair recombination.When the Ag-CeO₂ mass is 20%of the mass of g-C₃N₄,the composite photocatalyst exhibits the highest photocatalytic activity and remains stable after repeated four photocatalytic experiments.Finally,through the addition of scavengers,the real active substances in the photocatalytic experiment were found to be h⁺and·O^2-,and the photocatalytic mechanism of the composites was attempted.（3）The WO₃ nanorods were synthesized by hydrothermal method,and the preparation of WO₃/Ag/g-C₃N₄ composites was realized by simple solvent evaporation and photodeposition.The effects of WO₃ and Ag on the structure,morphology and photocatalytic properties of g-C₃N₄ were investigated,and the photocatalytic stability of the composites was evaluated.The experimental results show that the WO₃/Ag/g-C₃N₄ composite can form a Z-scheme photocatalytic structure and inhibit the recombination of electrons and holes.When the mass percentage of WO₃ is 15,the composite photocatalyst exhibits the highest photocatalytic activity,and the activity of the photocatalyst is greatly improved with the addition of nanosilver.The composite photocatalyst remained stable after four photocatalytic repeat experiments.Finally,the real active substances in photocatalytic experiments were·OH and·O^2-by adding scavengers,and the photocatalytic mechanism of the composites was explored.