The Improved Performance And Mechanism Of G-C₃N₄ Based Photocatalysts For Uranium Reduction By Electronic Structure Regulation

With the rapid development of industrialization,environmental pollution and energy crisis are becoming more and more serious.Photocatalytic technology can convert solar energy into chemical energy under the action of photocatalyst,and facilitate the purification of environmental pollutants.It shows advantages in solving energy and environmental issues,in which,developing the excellent photocatalytic materials with wide spectral response and high photo-induced carrier mobility is highly important.Carbonized nitrogen?g-C₃N₄?,as a new photocatalytic material with graphite like phase structure,is widely used in photocatalysis field because of its narrow band gap,suitable valence band conduction band location and catalytic stability.In this thesis,the electronic structure and optical absorption properties of g-C₃N₄ were further adjusted by heteroatom doping or carbon materials combination in order to improve the weak visible light absorption and the seperation of photo-induced electron and hole.The main contents and results of this paper are as follows:?1?S-doped g-C₃N₄ photocatalyst was synthesized by a simple high-temperature pyrolysis method,and the content of the doped S was modulated by adding different precursors.A series of characterizations such as XRD,TEM,XPS and UV-vis indicate that S is doped into the g-C₃N₄ crystal lattice and the continuous modulation on the content of sulfur doped into S-g-C₃N₄ samples has been achieved,and the capability of the absorption to visible light increases for S-g-C₃N₄.The photocatalytic activity of S-g-C₃N₄ was evaluated by the UO₂²⁺photo-reduction.The experimental results show that S₃-g-C₃N₄ exhibits the highest photocatalytic activity.The photocatalytic reaction rate constant is 1.86 times than the pure g-C₃N₄.Further studies by PL spectra and photocurrent experiments indicated that the S-g-C₃N₄ material has faster electron transfer and electron-hole separation efficiency than the pure g-C₃N₄.A photocatalytic mechanism of S-g-C₃N₄ materials were also proposed.?2?P-doped g-C₃N₄ with tubular structure were prepared by hydrothermal method combined with high temperature pyrolysis method.The tubular P-g-C₃N₄ photocatalyst was characteruzed by XRD,TEM,XPS and UV-vis.The analysis results indicated that the P-g-C₃N₄ photocatalyst possess a tubular structure.The photocatalytic activity of the tubular P-g-C₃N₄ photocatalyst is significantly better than that of the pure g-C₃N₄ for UO₂²⁺degradation due to the effectively suppressed combination of electron-hole as well as the tuned electronic structure.?3?The CNCs/g-C₃N₄ composites was synthesized by simple chemical impregnation and high temperature pyrolysis.The composites were characterized by XRD,SEM,XPS,UV-vis and Raman.The analysis results indicated that the three-dimensional structure of CNCs can effectively increase the specific surface area of g-C₃N₄.The photocatalytic activity of g-C₃N₄/CNCs composite was analyzed by the UO₂²⁺photo-reduction reaction.It was found that the photocatalytic activity of g-C₃N₄/CNCs composite was higher than the pure g-C₃N₄ photocatalyst,and the optimized amount of the CNCs was 2 wt%.The photocurrent and electrochemical impedance spectroscopy experiments show that the charge transfer efficiency of g-C₃N₄/CNCs composite has a significant increase,which enhances the photocatalytic activity.