Fabrication Of G-C₃N₄-based Nano-heterojunction And Studies On The Performance Of Photocatalytic Removal Of Nitrogen Oxides

In recent years,Nitrogen oxides?NO_x?pollution has become increasingly serious due to the combustion of industrial fossil fuels and the large amounts of vehicle exhaust emissions,which has seriously affected human health.Currently,the methods to removal NO_x include NSR?NO_x Storage-Reduction?and SCR?Selective Catalytic Reduction?,which depend on equipment and are subject to temperature restrictions,and require precious metal Pt or replenishment of reducing agent?urea and ammonia,etc.?.It is generally used for denitrification of high-concentration NO_x in factory exhaust gas and gasoline or diesel engine exhaust.For ppb-level NO_xin the air,photocatalytic technology is widely used because of its mild reaction conditions,simple operation and low energy consumption.graphitic carbon nitride?g-C₃N₄?,as a new two-dimensional?2D?layered semiconductor with visible light response,has broad application prospects in photocatalytic removal of NO_xdue to its cheap and abundant raw materials,suitable electronic band structure and easy to modify.In this paper,two-dimensional?2D?g-C₃N₄ nanosheets were used as a substrate to construct heterojunction with Bismuth-based or metal oxide semiconductors,which could widen its visible light absorption range and improve the efficiency of transfer and separation of photo-generated carriers to improve the photocatalytic degradation effect.The main research contents are as follows:?1?First,the zero-dimensional?0D?-2D Ag VO₃-g-C₃N₄ heterojunction was synthesized by in situ growth method to promote the separation of light-induced charges.In order to further accelerate the migration of photo-generated electrons,we combined graphene,as an electron transporting medium,with the above composite.Finally,the porous morphology of the three-dimensional?3D?hybrid aerogel promotes gas adsorption and circulation,and the layered structure is also conducive to the layer-by-layer retention of NO exhaust gas,which is eventually fully degraded.Compared to binary Ag VO₃-g-C₃N₄ composite,the degradation effect of ternary composite was increased by 10%and showed excellent cycle stability.In addition,the immobilization of the powder catalyst is also convenient for subsequent recycling.?2?The ZIF-67-derived Co₃O₄ semiconductor was wrapped by g-C₃N₄ nanosheets by the template method.The low-temperature calcined Co₃O₄ almost retained the rhombic dodecahedron morphology of ZIF-67 and showed the microstructure of hollow mesopores,which promoted the circulation of exhaust gas.Furthermore,3D Co₃O₄/2D g-C₃N₄constitutes a space conductive network framework,achieving a degradation efficiency of 57%and suppressing the generation of NO₂.The capture experiments also verified that the enhanceed mechanism was due to the oxidation of holes?h⁺?,superoxide radicals?·O₂^-?and hydroxyl radicals?·OH?.?3?Considering the characteristics of oxygen vacancies?OVs?in substrate adsorption,electron capture,and reactant activation,we prepared Bi OBr nanoflowers modified with surface OVs by a mixed solvothermal method and constructed a heterojunction with g-C₃N₄.In terms of the mechanism,on the one hand,the formation of heterojunction establishes the preliminary carrier separation;on the other hand,surface OVs capture and confine photogenerated electrons on the surface of stacked Bi OBr nanosheets,which fully exposed reaction sites and promoted the formation of reactive oxygen species.In this system,the OVs and heterojunction synergize to achieve a NO removal rate of 63%.Additionally,considering the excellent electron capture capability of OVs,we also applied it to CO₂ photoreduction experiments and achieved 96% selectivity for carbonaceous products?i.e.,carbon monoxide and methane?.