Preparation Of GC₃N₄-based Heterojunction And Its Enhanced Visible Light Catalytic Mechanism

According to reports,with the development of the social chemical industry,air,soil and water resources have been seriously polluted,especially the pollution of water resources poses a threat to people’s lives and health.Photocatalysis technology has become a new way to effectively treat sewage because it can directly utilize the characteristics of solar energy,green and pollution-free,and high catalytic efficiency.At present,the photocatalysts commonly developed and used include Ti O₂,Zn O,etc.However,because the light source used is only 3-5%of ultraviolet light from sunlight,this condition limits the practical application of the catalyst in the field of photocatalysis.Therefore,it is still a challenge to research and develop semiconductor catalysts that respond to visible light and improve their utilization of sunlight.Graphite-phase carbon nitride（g-C₃N₄）has good photocatalytic performance due to its stable photoelectrochemical properties,suitable band gap,and response to visible light.However,as a powder semiconductor catalyst,g-C₃N₄is prone to agglomeration and deposition,and the absorption rate of visible light is low,and the photogenerated electron-hole pairs generated by it are also easy to recombine.These problems hinder the development and application of g-C₃N₄.Therefore,this paper improves the catalytic performance by constructing composite materials,the introduction of conductive media,and element doping,and further investigates its photocatalytic degradation path and reaction principle.In order to improve the catalytic performance of a single semiconductor g-C₃N₄,a g-C₃N₄/Ag₃PO₄heterojunction composite was first prepared by calcination-deposition method in this paper.A new g-C₃N₄/Ag₃PO₄-H₂O₂catalytic system was successfully constructed by adding H₂O₂.Secondly,in the reaction system,H₂O₂is used as a sacrificial agent to suppress the photoetching phenomenon of Ag₃PO₄,thereby protecting the structural stability of Ag₃PO₄.Studies have shown that the construction of g-C₃N₄/Ag₃PO₄heterojunction can increase its response range to visible light.The close contact between g-C₃N₄and Ag₃PO₄interface can improve the photo-generated electron-hole pairs can be effectively separated and promote their photocatalytic activity.In addition,the active components that play a leading role in the photocatalytic degradation were studied by free-radical capture experiments,and the possible photocatalytic reaction mechanism of g-C₃N₄/Ag₃PO₄-H₂O₂was further proposed.A novel g-C₃N₄/WO₃/NCDs Z-scheme heterojunction catalyst was prepared by in-situ calcination and physical deposition.Studies have shown that the introduction of NCDs and the construction of g-C₃N₄/WO₃Z-scheme heterojunctions can significantly improve the utilization of visible light.Secondly,NCDs as a conductive medium facilitate the migration of photogenerated charges,promote the effective separation of photogenerated electron-hole pairs,and then enhance the photocatalytic activity of g-C₃N₄/WO₃/NCDs.The results of photocatalytic cycling experiments and XRD diffraction peaks before and after the experiment verified the structural stability of g-C₃N₄/WO₃/NCDs.In addition,the main active ingredients in the photocatalytic degradation process were investigated through free radical capture experiments,and the photocatalytic reaction mechanism of g-C₃N₄/WO₃/NCDs was proposed and discussed.Studies on g-C₃N₄/WO₃/NCDs Z-scheme heterojunctions have shown that NCDs as a conductive medium can further promote the catalytic performance of heterojunction composites.In order to explore the role of NCDs in catalyst design,a new type of g-C₃N₄/Bi₂WO₆/NCDs Z-scheme composites was constructed by a combination of calcination and hydrothermal methods.The study shows the following:i)The construction of g-C₃N₄/Bi₂WO₆heterojunction and the introduction of NCDs can promote the visible light utilization efficiency of the catalyst g-C₃N₄/Bi₂WO₆/NCDs;ii)Due to the excellent conductivity of NCDs,the migration and separation efficiency of photo-generated carriers in the g-C₃N₄/Bi₂WO₆/NCDs composite has also been further enhanced;iii)Because NCDs can serve as acceptors and donors of electrons,they can promote the catalytic reaction of electrons and holes at the catalyst interface,thereby enhancing the redox capacity of the catalyst.The above three factors jointly promote the catalytic activity of g-C₃N₄/Bi₂WO₆/NCDs.Moreover,the structural stability of g-C₃N₄/Bi₂WO₆/NCDs was evaluated by XRD characteristic diffraction peaks of the catalyst before and after the photocatalytic cycling experiments.In addition,the active substances in the photocatalytic reaction process were verified by free radical capture experiments.Subsequently,the photocatalytic degradation principle of g-C₃N₄/Bi₂WO₆/NCDs was proposed and discussed to systematically understand the interfacial reaction of photocatalysts.