Controlled Synthesis And Properties Of G-C₃N₄/Cu Based Layered Composites

Due to the high electrical conductivity of Cu-based nanomaterials and the localized surface plasmonic resonance effect（LSPR）similar to precious metals,it can effectively reduce the photogenerated carrier recombination rate and improve the light absorption of materials.In this paper,Au/Cu nanoparticles（NPs）were introduced into graphite carbon nitride（g-C₃N₄）nanomaterials to improve the photocatalytic performance.In addition,g-C₃N₄/Cu₂O and g-C₃N₄/Cu Se heterojunctions were prepared,the formation of heterojunctions and the mechanism of photocatalysis were studied,and the materials were used for photocatalytic H₂ generation.The specific research contents are as follows:In order to improve the photogenerated carrier separation efficiency of ultra-thin g-C₃N₄nanosheets,Au/Cu NPs were introduced to g-C₃N₄ and investigate their photocatalytic performance.Ultra-thin g-C₃N₄ nanosheets supported by Cu,Au and Au Cu NPs were prepared by mechanical chemical pre-reaction and secondary high temperature thermal polymerization.The photo-electro-chemical results show that the loading of Cu NPs significantly enhances the photocurrent response of the material and reduces the interfacial charge transfer resistance.In addition,in order to further improve the absorption ability of g-C₃N₄ to visible light,precious metal Au NPs were introduced to form bimetallic Au Cu NPs.The LSPR effect of precious metal Au was used to improve the absorption ability of visible light region of the material.The photocatalytic hydrogen evolution rate of Au Cu/g-C₃N₄ nanocomposites is 930.2μmol g^-1 h^-1,36.9 times that of pure g-C₃N₄,when the atomic molar ratio of Au and Cu is 1:1 and the load content is 1%.The results show that loading Au Cu bimetallic NPs can effectively make up for some shortcomings of g-C₃N₄,improve its photoinduced charge separation and transmission efficiency,improve its absorption capacity of visible light,and promote the photocatalytic reaction.Z-scheme g-C₃N₄/Cu₂O heterojunction was constructed to further expand the light absorption and improve the photogenerated carrier separation efficiency to explore the evolution of photocatalytic hydrogen generation.Z-scheme g-C₃N₄/Cu₂O flake heterojunction was prepared by the recrystallization of melamine with copper salt solution and a two-step thermal polymerization at high temperature.The presence of copper salt solution not only affects the recrystallization process of melamine,but also introduces a small amount of Cu ions into the precursor.Ultra-thin g-C₃N₄/Cu₂O nanosheets were formed and the specific surface area of g-C₃N₄ was increased under the two-step thermal polymerization process at 650 and700℃.Cu²⁺are reduced to Cu₂O NPs after heat treatment.Due to the presence of Cu₂O NPs,the visible light absorption capacity of g-C₃N₄ nanosheets is enhanced.With 3wt%Pt as cocatalyst,sample g-C₃N₄/Cu₂O（650-700-Cu₂O/RCNs）nanosheets showed the best photocatalytic hydrogen evolution rate of 5776.4μmol g^-1 h^-1,which is about three times that of pure g-C₃N₄（650-700-CN）nanosheets.In addition,the photocatalytic hydrogen evolution rate of 650-700-Cu₂O/RCNs without Pt cocatalyst is 266.3μmol g^-1 h^-1,which is about 18 times that of 650-700-CN.The g-C₃N₄/Cu Se heterojunction was synthesized by using narrow band gap flake Cu Se to further improve the optical absorption and carrier transport efficiency,and the evolution of its photochemical properties was studied.The layered heterojunctions of g-C₃N₄/Cu Se nanosheets were prepared by solvothermal method.Both g-C₃N₄ and Cu Se exist as nanosheets,forming two-dimensional/two-dimensional layered heterostructure.The surface area of the interaction between the two components is improved,and more active sites are generated between g-C₃N₄ and Cu Se,which is conducive to the rapid transfer of photogenerated charge.The photocatalytic H₂ separation efficiency was greatly improved after loading Cu Se nanosheets.When the loading capacity of Cu Se nanoparticle was 2%,the optimal photocatalytic property was 187.8μmol g^-1 h^-1,which was 12.3 times that of pure g-C₃N₄.Various test results also show that the improvement of its photocatalytic properties can be attributed to the heterogeneous structure formed by Cu Se and g-C₃N₄.Cu Se exhibits higher electrical conductivity compared with g-C₃N₄,which benefits from the rapid transfer of photogenerated electrons.In addition,the interfacial interaction between Cu Se and g-C₃N₄ also provides a fast channel for the rapid transfer of photogenerated electrons and inhibits the rapid recombination of photogenerated carriers,thus improving the utilization rate of photogenerated electrons and speeding up the photocatalytic H₂ evolution reaction.