Synthesis And Photocatalytic Properties Of Complex Catalysts Based On Carbon Nitride

The increasingly serious energy crisis and environmental pollution are gradually threatening the healthy survival of human beings.Semiconductor photocatalysis technology can use visible light to achieve photodecomposition of water and photodegradation of organic pollutants,which has attracted widespread attention.Graphite carbon nitride（g-C₃N₄）is a typical two-dimensional layered non-metallic semiconductor carbon materials.It has good chemical stability,non-toxicity,easy preparation,and can be driven by visible light.The band gap width is about 2.7e V,crossing the reduction potential for hydrogen production in water,it can not only be used to degrade of organic pollutants,but also realize the reduction of water to hydrogen.However,single g-C₃N₄has disadvantages such as small specific surface area,low utilization of visible light and easy recombination of photogenerated electron-hole pairs,resulting unsatisfactory photocatalytic performance and severely limiting its application in practical production.Therefore,how to improve the photocatalytic performance of g-C₃N₄ is of great significance for follow-up research.The study found that the combination with some other semiconductor materials or metal materials can effectively inhibit the recombination of photogenerated electron-hole pairs,broaden the utilization of visible light,and improve the photocatalytic performance.Therefore,this paper intends to improve the photocatalytic performance of g-C₃N₄ with iron oxide semiconductor and loading metal Ag on the surface of g-C₃N₄.Part one:The flake g-C₃N₄ was prepared by two-step calcination with dicyandiamide as the precursor by thermal polymerization.Then spherical iron oxide nanoparticles were obtained by direct precipitation method.The Fe₂O₃/CN2-D composite catalyst was prepared by compounding CN2-D with Fe₂O₃ by the hydrothermal method,and the ability to degrade methylene blue（MB）under visible light was studied.The morphology,crystal structure,chemical composition and light absorption properties of the samples were characterized by SEM,XRD,FT-IR,UV-Vis,PL and other characterized methods.The results show that the carbon nitride material has a lamellar structure,the size of which is about 500nm to 4000nm,and the Fe₂O₃ spherical particles with an average diameter of about 53.5nm are successfully loaded on the surface of CN2-D material.Compared with single CN2-D nanosheets,Fe₂O₃/CN2-D composite has enhanced visible light absorption ability,which effectively inhibits the recombination of photogenerated electron-hole pairs.When the amount of iron oxide loaded on CN2-D is 1wt%,Fe₂O₃/CN2-D composite catalyst has the best degradation performance,and the degradation rate can reach 99%within120min,which is close to complete degradation,indicating the loading of iron oxide can obviously improve the catalytic degradation capacity of graphite phase carbon nitride.The second part:The flake g-C₃N₄ was prepared by thermal polymerization method,and then the Ag nanoparticles were deposited on g-C₃N₄ by sodium citrate reduction method toobtain Ag/g-C₃N₄ composite catalyst.The morphology,crystal structure,chemical composition and light absorption properties of g-C₃N₄ and Ag/g-C₃N₄ samples with different mass fractions were also characterized.The results show that the carbon nitride material has a lamellar structure,and the Ag nanoparticles were uniformly loaded on the surface of CN2-D material.Compared with the single CN2-D nanosheet,the Ag/CN2-D composite catalyst has a wider response range to visible light and has a lower recombination rate of photogenerated electron hole pair.The hydrogen production performance of CN2-D and Ag/CN2-D composite materials has been tested under visible light.And the hydrogen production rate was up to 14.3404μmol·h^-1·g^-1.while no hydrogen was detected in single graphite phase carbon nitride,indicating that Ag loading can significantly improve the catalytic hydrogen production capacity of graphite phase carbon nitride.