Research On The Photocatalytic Mechanism Of B-doped G-C₃N₄ Monomer And Heterojunction

g-C₃N₄ is a two-dimensional material similar to graphene,composed of nitrogen and carbon.It have excellent photoelectric properties,high chemical stability,and good photocatalytic performance,which makes it widely studied in the fields such as environmental remediation,energy conversion,and electronic devices.However,due to the high recombination rate of photo-generated carriers and low utilization of visible light in g-C₃N₄,its practical application is greatly limited.In order to improve the photocatalytic performance of g-C₃N₄,researchers have explored various modification strategies and achieved significant results.Based on the previous research,two different types of heterojunctions were constructed in this article,namely g-C₃N₄/Cd S and B-g-C₃N₄/Cd S,and the photocatalytic mechanisms of B-g-C₃N₄,g-C₃N₄/Cd S,and B-g-C₃N₄/Cd S heterojunctions were systematically studied by combining the method of B element doping.The main research contents are as follows:（1）The research on the photocatalytic mechanism of B-doped g-C₃N₄mainly focuses on its electronic structure,optical properties and the effective mass of photogenerated electron holes.After replacing the C₁position of g-C₃N₄with the B atom,an impurity energy level is introduced at the top of the valence band,which narrows the band gap and facilitates photo-generated electron transitions.In the visible light range,B-g-C₃N₄can improve its electrical storage performance,increase the absorption index of incident light,refractive index,and extinction coefficient,and its light absorption ability is better than g-C₃N₄.The effective mass of the electrons and holes of B-g-C₃N₄is smaller than that of g-C₃N₄,that is,the electrons and holes of B-g-C₃N₄can migrate to the surface active site faster,and the photocatalytic activity will be enhanced.（2）The photocatalytic mechanism of g-C₃N₄/Cd S heterojunction was studied by combining g-C₃N₄and Cd S.The results indicate that the heterojunction of g-C₃N₄/Cd S is a type II heterojunction.During the formation of the heterojunction,electrons transfer from the surface of g-C₃N₄to the surface of Cd S,forming an internal electric field from the surface of g-C₃N₄to the surface of Cd S,which effectively promotes the separation of photo-generated electron and holes.From the calculation results of optical properties,it can be seen that in the visible light range,the photocatalytic performance of g-C₃N₄/Cd S is significantly improved compared to g-C₃N₄,and the photocatalytic activity is enhanced.（3）The B-g-C₃N₄/Cd S heterojunction was constructed from B-g-C₃N₄and Cd S,and its electronic structure,optical properties,work function,charge transfer and other photocatalytic properties were simulated.The analysis shows that the B-g-C₃N₄/Cd S heterostructure is a Z-type heterojunction,forming an internal electric field from the surface of B-g-C₃N₄to the surface of Cd S.Under visible light irradiation,the driving force of the built-in electric field makes it difficult for Cd S valence band photo-generated holes and B-g-C₃N₄conduction bands to recombine due to their presence at different spatial positions,increasing their probability of participating in photocatalytic reactions.This is one of the reasons for the significant improvement in their photocatalytic efficiency.Meanwhile,due to the introduction of B atoms,B-g-C₃N₄/Cd S also introduces magazine energy levels,resulting in a smaller bandgap value and promoting photocatalytic activity.