Photocatalytic Performance Of Carbon-Deficient Carbon Nitride Controlled By Elemental Bismuth

As a metal-free semiconductor photocatalyst,graphitic carbon nitride（g-C₃N₄）,has attracted much attention due to its excellent stable structure,high specific surface area,suitable band gap,tunable electronic structure,high efficiency and utilization of sunlight.These properties make graphitic carbon nitrides have great potential for artificial photocatalysis.However,problems such as low light absorption threshold,high electron-hole recombination rate,and slow surface reaction kinetics limit the photocatalytic activity of graphitic carbon nitride.Therefore,in order to obtain a photocatalyst with better performance,g-C₃N₄ must be efficiently modified.Defect engineering is one of the important modification methods for carbon nitride materials.Defect sites are active sites for photocatalytic graphitic carbon nitride redox reactions.Firstly,defects can be introduced into the carbon nitride surface or inside by designing a controllable adjustment scheme.Secondly,the utilization of bismuth metal has the characteristics of small electron effective mass,low carrier concentration,long mean free path,anisotropy,and surface plasmon resonance（SPR）.The combination of the two can act synergistically to enhance the photocatalytic effect.Therefore,in this paper,carbon nitride（V-CN）with carbon defects was prepared by traditional thermal polymerization method using urea and melamine as precursors,respectively.On this basis,it was compounded with elemental bismuth（Bi）to explore Photocatalytic hydrogen production and nitric oxide conversion performance of composite products.（1）A defective carbon nitride（V-CN）was synthesized by etching bulk carbon nitride（CN）three times at high temperature to form carbon-defective carbon nitride with a large specific surface area under weak oxygen conditions.The bulk carbon nitride was first prepared by conventional thermal polymerization,and then the optimal carbon vacancy concentration of the catalyst was explored by modifying the calcination atmosphere,temperature program and time.The photocatalytic ammonia synthesis performance of different carbon nitrides was evaluated and compared.The results show that the introduction of carbon vacancies increases the specific surface area from 68.9m²·g^-1to 555.3 m²·g^-1.And the band gap of carbon nitride is enlarged from 2.82 e V to3.03 e V,which improves the charge separation efficiency and helps to improve the performance of photocatalytic ammonia synthesis.（2）Firstly,suitable vacancy sites are constructed in the CN polymer framework by thermal polymerization at higher temperature to enhance the photocatalytic redox ability.Then metal Bi was supported on carbon-deficient carbon nitride catalysts by chemical reduction.Experiments show that Bi,as a plasmonic metal,can concentrate incident photon energy into plasmonic oscillations,and the concentrated resonance energy can be transferred to V-CN or converted into a local electromagnetic field,which is also beneficial for e^-/h⁺in V-CN.In addition,the photocatalytic performance of Bi-V-CN for degrading pollutants can be improved.This paper provides a preparation method to simultaneously introduce carbon defects and bismuth metal into carbon nitride,which shows that the separation of photogenerated carriers can be effectively promoted by defect engineering strategy and metal loading,which is very important for improving the photocatalytic performance of carbon nitride.