Study On Preparation And Visible Light Catalytic Performance Of Hollow Tubular Graphene Carbon Nitride Composites Materials

With the rapid development of economy and society,energy shortage and environmental pollution are major problems that human beings are facing.Therefore,the development of renewable energy and the control of environmental pollution are of great significance to the development of national economy and the realization of sustainable development strategy.Photocatalytic technology can convert solar energy into chemical energy under mild conditions,showing great potential and good application prospects in solving energy shortage and environmental pollution.Among many photocatalysts,graphite phase carbon nitride（g-C₃N₄）,a semiconductor material with response in visible light region,has attracted many scholars’attention due to its good chemical stability,2.7eV bandgap and layered structure.However,the photocatalytic performance of g-C₃N₄ is limited mainly due to its small specific surface area and serious photogenerated carrier recombination.Therefore,the morphology and band structure of g-C₃N₄ were controlled,and the photocatalytic properties of g-C₃N₄ under visible light were studied.The main contents of this paper are as follows:Using melamine as raw material,g-C₃N₄ with different morphologies was prepared by molten salt method.The crystal structure and morphology of g-C₃N₄ were characterized,and the effects of different preparation processes on its morphology were discussed.The results show that hollow tubular g-C₃N₄（HTCN） with a diameter of 400nm and a wall thickness of 60-70nm has been successfully prepared by molten salt method.The optimum technological parameters are as follows:1:10 of mass ratio of raw material and molten salt,500℃ of calcination temperature,4h of holding time.A possible salt-assisted self-assembly mechanism was also proposed.The specific surface area of HTCN phase is 3.3 times of that of bulk g-C₃N₄ phase,which is beneficial to the improvement of photocatalytic activity.TiO₂/HTCN composites were successfully prepared by one-step in-situ synthesis.The crystal structure,morphology and optical properties were characterized and analyzed.The results show that the introduction of titanium dioxide narrows the bandgap of HTCN,improves the utilization of solar energy and effectively suppresses the recombination rate of photogenerated electron holes.When RhB was used as a simulated pollutant,the degradation rate of the TiO₂ content is 7% of HTCN mass is 92% that is the highest after 60 minutes of visible light irradiation.The main active species in the degradation process are h⁺、·O₂^-,and a possible photocatalytic mechanism is proposed based on the energy band theory.Ag₃PO₄/HTCN composites were successfully prepared by ultrasound-assisted coprecipitation.The crystal structure,morphology,optical properties and photocatalytic properties of Ag₃PO₄/HTCN composites were characterized and analyzed.The results show that the incorporation of HTCN can effectively utilize some silver elements produced by photoetching of Ag₃PO₄ to form a ternary photocatalytic composite system Ag₃PO_4/Ag/HTCN in the process of photocatalysis,which can effectively improve the photocatalytic performance and stability.When RhB was used as a simulated pollutant,the photocatalytic efficiency of the sample with 500 mg HTCN content was 90.0% that is the highest after 120 minutes of visible light irradiation.The main active species in the degradation process are·OH、h⁺ and·O₂^- through the capture experiments of active species.The Z-type catalytic mechanism of photogenerated carriers is proposed based on the energy band theory.