Effect Of Thermal Polymerization Atmosphere On The Structure Of Graphite Phase Carbon Nitride And Its Photocatalytic Performance For Hydrogen Production

Graphite carbon nitride semiconductor（g-C₃N₄）as a kind of visible light catalyst and contains no metal components since it has the appropriate band structure,good chemical stability,as well as the advantages of non-toxic,environmentally friendly,the photolysis aquaculture,photocatalytic hydrogen production oxygen selective organic synthesis and photocatalytic degradation of organic pollutants,and other fields have got wide attention and research.However,g-C₃N₄ also has some problems,such as low crystallinity,small specific surface area and few surface active sites.In order to solve the above problems,some explorations and studies have been made in improving the crystallinity and specific surface area of g-C₃N₄ in this paper.The specific work is as follows:1、By changing the flow state of the reaction atmosphere,the assembly structure and photocatalytic activity of g-C₃N₄ under different control conditions were studied.The hydrogen production capacity of g-C₃N₄ prepared under visible light was evaluated by photocatalytic decomposition of water for hydrogen production.The results show that the accumulation of thermal polymerization gas by-products in the reaction system at zero flow static atmosphere inhibits the in-plane polymerization of C₃N₄ and forms a large number of unpolymerized amino C₃N₄ nano-fragments,which significantly increases the specific surface area of g-C₃N₄.At the same time,the interamino hydrogen bond enhances theπ-πconjugated system,improves the crystallinity of g-C₃N₄,promotes the separation of photogenerated carriers,and enhances the dispersion of the catalyst in water.The synergistic effect of the above factors significantly improved the photocatalytic hydrogen evolution activity of g-C₃N₄.2、Urea was pretreated with water to preabsorb a certain amount of water,and then thermal polymerization was carried out in a closed tube furnace and a semi-open muffle furnace respectively to study the structure and properties of g-C₃N₄ photocatalyst.The g-C₃N₄ samples prepared in closed and semi-open environments were characterized and analyzed by various characterization methods.The photocatalytic activity of the prepared g-C₃N₄ samples was evaluated by photocatalytic decomposition of water for hydrogen production.Research results show that the preparation of aqueous urea in the airtight environment g-C₃N₄ samples have excellent photocatalytic activity,this is mainly due to the addition of water to further strengthen the thermal polymerization in gas phase by-products of C₃N₄ surface polymerization inhibition,its fragmentation worsen nanomaterials structure,increasing the g-C₃N₄ specific surface area and pore volume,More reactive active sites are provided.At the same time,the enhanced inhibition of in-plane polymerization leads to the formation of more N defects in g-C₃N₄ samples,which further promotes the separation of photogenerated carriers.The synergistic effect of the above factors makes the g-C₃N₄ sample prepared by aqueous urea in a closed environment have excellent photocatalytic hydrogen evolution activity.