Construction Of Carbon Nitride-based Heterostructures And Their Photocatalytic Mechanism

My country has experienced a rapid development in recent years,though with some energy crisis and environmental issues.One vital way to convert solar energy into chemical energy is to use the semiconductor photocatalysis technology,but the efficiency of photocatalysis is still very low,so it is of great significance to develop efficient and stable photocatalysts.Graphitic carbon nitride(g-C₃N₄)is a metal-free organic semiconductor catalyst with excellent physical and chemical properties,which is widely used in various photocatalytic reactions.However,as a semiconductor photocatalyst,bulk g-C₃N₄ also has some disadvantages.Combining semiconductors to construct heterojunctions is considered to be one of the most effective ways to improve the photocatalytic efficiency of semiconductors.Therefore,we constructed g-C₃N₄ based heterostructures to improve the performance of photocatalysts by a simple and easy-to-operate method.First,an efficient CN-LDH composite photocatalyst was successfully synthesized by in situ growing of a layer of flaky nickel chromium layered double hydroxide nanosheets(LDH)on tubular C₃N₄(CN)in hydrothermal method.The CN-LDH heterostructures have enhanced hydrogen evolution efficiency(14.5 mmol h^-1 g^-1),which is about 4.7 times that of pure CN(2.7 mmol h^-1 g^-1)and much higher than that of LDH(0.06 mmol h^-1 g^-1).We attribute this performance improvement mainly to the close-knit heterostructure formed between LDH and CN.This tight combination strengthens the diffusion of self-charge between the two semiconductors to form a strong built-in electric field(BIEF)and band bending.Under the action of the BIEF,the photogenerated charge can be efficiently separated and oriented fast transfer,thereby greatly improving the photocatalytic efficiency.In addition,A novel method was reported for the in situ synthesize tubular C₃N₄-Zn In₂S₄ heterostructures(CN-ZIS)and use the composite for efficient photocatalytic H₂O₂ production.In this synthesis method,a supramolecular precursor formed by self-assembly of melamine and solid phosphorous acid is used as a template,a layer of Zn In₂S₄(ZIS)is grown on the precursor by a water bath method,and finally polymerizes the precursor into tubular C₃N₄(CN)by high-temperature calcination.This unique structure can improve the absorption capacity of the catalyst for visible light,and this synthesis method makes the combination of the two more closely and stable,which can effectively promote the separation of photogenerated charges.In addition,through characterization,it is found that the CN-ZIS tends to produce H₂O₂ by the two-electron reduction of O₂,which leads to a significant increase in the production rate of H₂O₂.Finally,CN@Cd S composites photocatalyst was synthesized by in-situ coating of a layer of Cd S nanoparticles on the surface of hexagonal tubular C₃N₄(CN)by a simple water bath method.Tubular CN as an excellent carrier can effectively prevent the aggregation of Cd S nanoparticles,and this structure facilitates the absorption of visible light.The matching energy band structure between the two can form a typical type II heterostructure,which promotes the separation of photogenerated electrons and holes.The performance of the composite material for photocatalytic oxidation of benzaldehyde is significantly improved.