Construction Of 2D/2D Carbon Nitride Heterojunction And Its Photo/enzyme Coupled Catalytic CO₂ Reductio

Carbon dioxide（CO₂）is one of the main components of greenhouse gases,which contributes to serious environmental problems such as global warming,melting glaciers and rising sea levels."Carbon neutrality"and"carbon neutrality"are two major national goals for environmental protection and economic development,which further illustrate the importance of"green and low-carbon".In order to ensure the dynamic balance of the environment and avoid irreversible disasters caused by the linear increase of atmospheric CO₂concentration,carbon fixation has become a research hotspot in recent decades.Among them,photocatalysis is considered as a promising research direction due to mild reaction conditions and green materials.However,the reduction potential required by various products of CO₂reduction is not very different,resulting in product confusion and increased production costs.Inspired by the carbon fixation process of the dark reaction of photosynthesis in plants,a photoenzyme coupled artificial photosynthesis system was constructed.Linking the high efficiency of photocatalytic reactions with the specificity of enzyme catalysis,such as the specific reduction of CO₂to formic acid（HCOOH）by formate dehydrogenase,ensures high efficiency and specificity of products,which is of great significance for environmental and energy mitigation.In this paper,graphite phase carbon nitride（g-C₃N₄）and carbon azide nitride（C₃N₅）were prepared by thermocondensation using dicyandiamide and 3-amino-1,2,4-triazole as precursors respectively.The photocatalytic reduction of nicotinamide adenine dinucleotide（NADH）and HCOOH of PDI/CN and Ti₃C₂/C₃N₅heterojunction which were combining two kinds of carbon nitrides with cocatalyst Perylene imide（PDI）and Titanium carbide（Ti₃C₂）was investigated.The main research contents are as follows:（1）A novel visible ligh t（λ<660 nm）nonmetallic heterojunction of perylene imide/g-C₃N₄（PDI/CN）to achieve a photoenzyme-catalyzed cascade system that can efficiently regenerate NADH and selectively reduce carbon dioxide to HCOOH.The yield of NADH and formic acid in 0.6%PDI/CN samples reached 75%and 1.269 mmol g^-1h^-1,respectively.The selectivity was close to 100%.The PDI/CN heterojunction has a unique photoenzyme catalytic cascade system,heterogeneous interface effect,good electrical conductivity and a wide range of sunlight response.（2）Carbon azides-C₃N₅was prepared by changing the molecular structure of g-C₃N₄to achieve strong aborption of visible light,and Ti₃C₂/C₃N₅complex was prepared by loading Mxenes material Ti₃C₂,so as to achieve rapid charge separation and multiple active sites involved in the reaction.Due to the defect of product diversity in the photocatalytic CO₂process,the photocatalytic system was coupled with the enzyme system to achieve the photocatalytic highly selective production of HCOOH.The reduction rate of NADH of 5%Ti₃C₂/C₃N₅reached 96.4%,close to 100%,under simulated sunlight irradiation without the addition of other electronic intermediates.The amount of formic acid produced by illumination for 9 h can reach 315.2μmol.And enhanced site activity to provide a new way for directed conversion of carbon dioxide to formic acid.