Built-in Electric Field Regulation Of Graphene Carbon Nitride And Exploration Of Photocatalytic Hydrogen Production

In recent years,energy consumption and environmental pollution caused by the development of science and technology have gradually become a major challenge in the process of human development.In this context,the development and utilization of solar energy has become an important means to effectively balance energy utilization and pollution prevention.With the development of photocatalysis,the rational use of solar energy is benefiting thousands of households in step.Chemical energy plays an important role in the process of converting solar energy into direct energy such as heat energy and electric energy,so it is necessary to develop excellent photocatalysts for solar energy absorption,storage and conversion.Graphene carbon nitride（g-C₃N₄）as photocatalyst has been concentrated explored due to its stable chemical structure,easy availability and good photochemical ability.However,there are still some drawbacks such as low visible light utilization rate and low photoelectron-hole separation efficiency.In this paper,based on the traditional study of g-C₃N₄,a built-in electric field was constructed in g-C₃N₄ by heteroatom doping,defect regulation and heterojunction construction,thus improving the photocatalytic hydrogen production performance of g-C₃N₄,which provides promising strategy for the effective utilization of g-C₃N₄.1.On the basis of tri-s-triazine phase carbon nitride（BCN）synthesized with melamine as precursor,in situ protonation treatment was carried out with phosphoric acid,and the oxygen deeply doped carbon nitride（Od-UCN）was prepared by high temperature calcination after hydrothermal process.The deep doping of oxygen atoms in catalysts was confirmed by FT-IR and XPS,and the doping sites of oxygen atoms were accurately simulated by density functional theory（DFT）.The hydrogen production rate of the catalyst under simulated sunlight reaches 1.49 mmol·g^-1·h^-1,which is 3.5 times that of BCN(0.42 mmol·g^-1·h^-1).The enhancement of hydrogen production performance of the catalyst is mainly due to the built-in electric field enhanced by deep doping of oxygen,which effectively prevents photoelectron-hole pair recombination.2.Alkali metal chloride（Li Cl,Na Cl,KCl）was selected as the molten salt system,and a series of M metal（M=Li,Na,K）doped carbon nitride（CCN）with high crystallinity was prepared by changing the type of molten salt.The results show that prepared Li/Na/K-CCN has high crystallinity and excellent photoelectric response,which makes the rate of hydrogen production under simulated sunlight reach 3.38mmol·g^-1·h^-1,with 6 times higher than that of BCN.In addition,the hydrogen production rate of Li/Na/K-CCN under visible light irradiation is as high as 0.75mmol·g^-1·h^-1.The improved performance of the catalyst is mainly attributed to the synergistic effect between the doped alkali metal ions to enhance the built-in electric field,which greatly improves the transfer and separation of photogenerated carriers.3.Band gap matched vanadium penoxide（VO）was embedded on traditional carbon nitrode（BCN）matrix by in-situ calcination to form Z-type heterojunction.By comparing different compiste approach and composition ratios of heterojunction,it is found that the hydrogen production rate of 5%VO/CNs heterojunction prepared in situ is 0.95 mmol·g^-1·h^-1 under visible light irradiation,which is 10 times of BCN(0.10mmol·g^-1·h^-1).In addition,the cyclic stability of plasma-etched catalysts has been greatly improved.The excellent photoelectric characteristics of VO and the enhanced built-in electric field on the interface are shown in VO/CN heterojunction,which are attributed to the effective separation of photogenerated carriers and the improvement of photocatalytic performance towards hydrogen production.