Enhancement Mechanism Of Photocatalytic CO₂ Reduction By Amination And Iodene Modification Of G-C₃N₄

My country’s CO₂ emissions ranks first in the world,and in response to environmental problems such as the greenhouse effect caused by carbon emissions,China has formulated a medium-and long-term strategic goal of"carbon peaking and carbon neutrality".Photocatalytic CO₂ reduction technology converts CO₂ into usable energy substances through light energy,which is an ideal carbon reduction pathway.Among them,the development of inexpensive,efficient and green semiconductor photocatalysts is the core of photocatalytic technology.g-C₃N₄ is one of the most promising photocatalysts due to its low cost of raw materials and the ability to utilize visible light.However,its disadvantages such as small specific surface area,poor adsorption capacity,and easy recombination of photogenerated electrons and holes limit its CO₂ conversion efficiency and require further modification.to improve its photocatalytic performance.The main research contents and results are as follows:（1）In view of the problem that adsorption affects the photocatalytic reduction activity of g-C₃N₄,an amination grafting method was designed to modify the surface of g-C₃N₄.A series of g-C₃N₄ photocatalysts with different numbers of surface amino groups were prepared and tested for CO₂ reduction under visible light.The results show that the CO₂ adsorption capacity of carbon nitride after amination treatment for 24 h is 1.2 times that of untreated carbon nitride,and its CO production under visible light catalysis is 8.58μmol g^-1,which is the same as the original 6 times that of C₃N₄.After four cycles,the CO yield of aminated g-C₃N₄ was 8.03μmol g^-1 with excellent cycling stability.Electrochemical experimental studies show that the newly prepared aminated g-C₃N₄ increases the basic site can reduce the CO₂ adsorption energy barrier,fix the photogenerated holes,improve the CO₂ adsorption and electron-hole separation and transfer ability,and then promote the photoelectricity.Improvement of catalytic CO₂ reduction performance.（2）At the same time,two-dimensional flakes of iodine（FLI₂）were prepared by ultrasonic liquid phase exfoliation method,and FLI₂/CNNS heterojunction photocatalysts with different loading ratios were synthesized by molecular self-assembly.In the visible light（λ>420 nm）catalytic CO₂ reduction test,the ability of the composites to reduce CO₂ to CO is greatly improved compared with the original carbon nitride.Among them,FLI₂/CNNS-2 showed the best catalytic activity,and the CO yield was 7.76 times that of CNNS.With the help of light absorption characteristics and electrochemical analysis,it is shown that FLI₂/CNNS has a wider light absorption range and stronger photogenerated electron-hole separation ability.Density functional theory（DFT）calculations confirmed that the introduction of FLI₂ resulted in band bending of carbon nitride at the composite interface.Due to the effect of energy level difference,the photogenerated electrons generated by photoexcitation could be enriched to the surface of FLI₂,which promoted the photogenerated carrier.The separation of the electrons improves the efficiency of photocatalysis.This efficient electron shunting method is the main factor to enhance the photocatalytic activity of CNNS.In view of the shortcomings of the original g-C₃N₄ photocatalyst,which has poor adsorption performance and easy recombination of carriers,a new amination g-C₃N₄ and FLI₂/CNNS non-metallic heterojunction photocatalyst were prepared,which greatly improved the photocatalysis CO₂ reduction efficiency,and analyze its performance improvement mechanism.This study will promote the practical application of g-C₃N₄ in the field of photocatalysis and provide theoretical guidance for the design of efficient non-metal-based carbon conversion materials.