G-C₃N₄/TiO₂ Composite Structure And Its Photocatalytic Performance

Graphite carbon nitride(g-C₃N₄)is composed of two elements C and N,which are abundant in the earth.It has low cost and friendly environment.It can be directly prepared by simple thermal polymerization and has good thermal stability and physical and chemical stability,so it is a promising semiconductor photocatalytic material.However,the material also has some shortcomings,such as low specific surface area,narrow light absorption range,insufficient visible light utilization,fast composite rate of photogenerated carriers,weak redox ability,few active sites,etc.,which seriously limit the development of the material.To solve the above problems,starting with the hydrothermal treatment of nitric acid(HNO₃)of g-C₃N₄,this paper improved the photocatalytic activity of g-C₃N₄and g-C₃N₄/TiO₂Z-type heterojunction through HNO₃hydrothermal treatment.The research work is as follows:1.The bulk phase g-C₃N₄(CN)prepared by thermal polymerization of melamine was used as raw material,and the thermal polymerization temperature was controlled.Then,different acid etched samples(HCN)were obtained by hydrothermal treatment of HNO₃for comparison.Various characterization methods were used to characterize and analyze the prepared samples,and the effect of HNO₃etching on the photocatalytic activity of g-C₃N₄prepared at different temperatures was explored using photocatalytic hydrogen evolution as the model reaction.The results show that with the increase of the polymerization temperature of g-C₃N₄,the degree of fragmentation caused by acid etching is intensified.The more obvious the quantum confinement effect is,the more significant the decrease of the valence band position is,which enhances the photocatalytic reoxidation and reduction ability of g-C₃N₄.Fragmentation resulted in a significant increase in the specific surface area of g-C₃N₄,providing more active sites for photocatalytic reactions.At the same time,a large number of unpolymerized amino groups are produced,and the hydrogen bond between the amino groups strengthens the?-?stacking,reduces the surface spacing,and promotes the transport and separation of charge carriers.The synergistic effect of several factors significantly improves the visible light catalytic hydrogen evolution performance of g-C₃N₄.2.g-C₃N₄coated TiO₂direct Z-type heterojunction composites were prepared by thermal polymerization using monocyandiamide as precursor.Then,the g-C₃N₄coating was etched by HNO₃hydrothermal treatment to prepare g-C₃N₄/TiO₂direct Z-type heterojunction materials exposed to TiO₂surface and heterojunction interface.The prepared photocatalyst samples were characterized and analyzed by a variety of characterization methods,and the photocatalytic activity was explored by using photocatalytic hydrogen evolution as a model reaction.The results show that nitric acid etching fully exposes the TiO₂surface and heterojunction interface,significantly improves the specific surface area of g-C₃N₄/TiO₂direct Z-type heterojunction,promotes the separation of photogenerated carriers,and effectively improves the photocatalytic hydrogen evolution performance of the heterojunction.