Research On The Construction,Characterization And Photocatalytic Performance Of Carbon Nitride Based Composite Materials

In the modern society,with continuous development of industrial civilization,energy crisis and environmental pollution are major challenges in sustainable development of industry.With the development of science and technology,semiconductor photocatalysis is hope to overcoming those challenges.Therefore,photocatalytic technology is considered as one of the most promising technologies in the field of alleviating environmental pollution and energy crisis.Nevertheless,the traditional photocatalyst has a wide band gap,such as TiO₂ and ZnO,which could only be excited by Uv-light that accounts for only a small fraction（4%）of the sun light.Hence,it is important to develop high reliability photocatalysts which could be excited by visible light and have the effectively separation ability of photoelectrons-hole.As a metal-free polymeric semiconductor photocatalyst,graphitic carbon nitride（g-C₃N₄）possesses favourable physical and chemical stability,easily preparation,low cost,non-toxic,narrow band gap and suitable energy level structure,which has been widely used in the photocatalysis field.However,the pure g-C₃N₄ shows poor photocatalytic performance due to its high photogenerated electron-hole recombination rate and low specific surface area.To improve the photocatalytic performance of it,pure g-C₃N₄was combined with other semiconductor or metal,which could be able to enhance photocatalytic performance of g-C₃N₄ based nanocomposite materials in this article.The main contents of this article were as follows:（1）The Ag/g-C₃N₄ nanocomposite was synthesized by one-step method.In this system,Melamine,NH₄Cl and AgNO₃ were selected as carbon and nitrogen source,swelling agent and silver source,respectively.All three chemical reagents were mixed together and calcining at high temperature to obtain Ag/g-C₃N₄ nanocomposite.In this process,Ag nanoparticles were simultaneously synthesized by thermal decomposition of silver nitrate during the synthesis of g-C₃N₄ nanosheets by the pyrolysis of carbon and nitrogen precursors.According to the result of SEM and TEM,Ag nanoparticles was homodispersed on the surface of g-C₃N₄ nanosheets.Ag nanoparticles could enhance the efficiency of photogenerated electron-hole separation on the surface of g-C₃N₄,because Ag nanoparticles possess the SPR effect.Moreover,the photocatalytic performance of the obtained sample consisting of different Ag radios were researched in detail by using RhB solution as model pollutant.The possible mechanism and stability was studied systematically.（2）The two different binary composite materials were prepared by hydrothermal method.In this section,g-C₃N₄ was synthesized by thermal polymerization method firstly.And then inorganic semiconductor materials,such as LaFeO₃ and Ag₂MoO₄,were composited by hydrothermal method in order to construct a g-C₃N₄ based binary composite photocatalyst.RhB was used as a simulated contaminant to evaluate the photocatalytic degradation of the photocatalyst.The mechanism of the photocatalyst was researched by free radical trapping experiments.It is of great value for the construction and research of the subsequent g-C₃N₄ based binary composite photocatalytic system.（3）Preparation and study of carbon nitride ternary composite photocatalysts:Firstly,carbonitride nanosheets was prepared by thermal polymerization and HCl protonation method,and then MOF（UiO-66）was loaded on the surface of carbon nitride by solvothermal method,and then Cd_0.5Zn_0.5S was loaded on the surface of MOF/g-C₃N₄ composite by in-situ deposition method.It exhibited excellent photocatalytic performance in photocatalytic degradation of MO and photocatalytic hydrogen production.The stability of the photocatalyst was measured by cycling experiments.Simultaneously,the photocatalytic mechanism of photodegradation of MO and photocatalytic hydrogen production was studied according to the experimental characterization results.