Photocatalytic Hydrogen Performance Of All-Organic Heterojunction Based On G-C₃N₄

Energy shortage and environmental problems have always been the focus of global research.Hydrogen,as a clean and renewable energy has attracted wide attention in recent years.Among the numerous hydrogen production methods,photocatalytic hydrogen production technology is considered to be one of the most promising methods due to its advantages of being renewable,safe,clean,and economical.Among many photocatalysts,graphitic carbon nitride（g-C₃N₄）is widely used in photocatalytic hydrogen production due to its excellent properties.However,pure g-C₃N₄ severely limits its practical application in photocatalysis due to its large band gap（about 2.7 e V）and high recombination rate of photogenerated electron-hole pairs.Selecting two or more semiconductor materials to rationally construct heterojunctions is an effective way to enable photocatalysts with the advantages of broad light absorption,fast charge separation and strong redox capabilities.In this thesis,the defects of weak light absorption and low carrier separation efficiency of g-C₃N₄ are improved by introducing organic matter and g-C₃N₄ to construct an all-organic heterojunction,thereby improving the activity of photocatalytic hydrogen production.The preparation,optimization and application of g-C₃N₄-based semiconductor heterojunctions are analyzed.The main research contents are divided into the following three parts:（1）Basic process and performance testing technology of photocatalytic hydrogen production.（2）The heterojunction system between halogenated small molecules and g-C₃N₄ was constructed,and it was found that the series of halogenated small molecules could improve the catalytic activity of g-C₃N₄ to a certain extent.Among them,the ortho-chloro-substituted small-molecule composite photocatalyst has the best catalytic performance,reaching a H₂generation rate of 7.7 mmol h^-1g^-1 and exhibiting an apparent quantum efficiency of 5.5%at420 nm.The experimental study found that the main reason for the enhanced photocatalytic activity in this heterojunction system is that the introduction of halogenated small molecules promotes the efficient separation and transfer of photogenerated electrons and holes in the composite sample.（3）The heterojunction system of terpolymer DIn（DI1,DI2,DI3）and g-C₃N₄ was constructed and it was found that the catalytic activity of g-C₃N₄ could be effectively improved after the introduction of this series of polymers.When the introduced polymer is DI1,the best photocatalytic activity can reach 16.0 mmol h^-1g^-1 and the H₂ generation rate can be increased by more than 20 times compared with the activity of g-C₃N₄ alone.The experimental study found that the g-C₃N₄/DIn composite can broaden the absorption spectrum to the near-infrared for efficient utilization of visible light,and at the same time promote the effective separation and transfer of photogenerated electrons and holes to improve the photocatalytic activity.