Study On The Preparation Of G-C₃N₄/Metal Oxide Bniary Composite Materials And Their Visible Light Photocatalytic Properties

WO3 are semiconductors with narrow band gaps, which can absorb visible light and act as popular photocatalyst in the photocatalysis field. However, the recombination rate of photo-generated carriers is high, which affects the photo catalytic efficiency of g-C3N4 and WO3. Furthermore, the large band gaps of brookite TiO2 and SnO2 allow high-energy ultraviolet light absorption, which greatly limits their utilization of sunlight. To optimize the catalytic activity and extend the application scope, it is highly essential to prepare composites of different types of semiconductors. In this thesis, we focused on the synthesis of g-C3N4 based composites and study on their photocatalytic properties. The main composites include g-C3N4/WO3, g-C3N4/SnO2 and brookite TiO2/g-C3N4. The physicochemical propoties of these composites were systematically characterized by TG, XRD, FT-IR, HR-TEM, BET, DRS, XPS, PL, and EIS. The primary results could be summarized as follows:(1) g-C3N4/WO3 composite materials are synthesized by calcination method with different temperature for the first time; Comparing to the components g-C3N4 and WO3, the composites showed the enhanced photocatalytic performance on MO degradation under visible light irradiation; Photocatalytic activity of these compostes is closely related to the calcination temperature, and the highest degradation rate is achieved when calcination of the composite is set at 400℃; The enhanced photocatalytic activity is attributed to the synergic effect between g-C3N4 and WO3, the decreased number of defects, and the increased specific surface areas;(2) g-C3N4/SnO2 composites with different contents of SnO2 were synthesized by calcination method; These composites exhibited a significantly enhanced photocatalytic activity towards MO degradation under visible light irradiation, the optimum photocatalytic performance is achieved at a loading of 47.5 wt% SnO2; The optimized g-C3N4/SnO2-47.5% composite with Pt additives is also successfully applied to high-efficiency production of hydrogen from water splitting; The strong interactions between both components are confirmed by PL, EIS, variations inbinding energies and lattice parameters of Sn in SnO2 and g-C3N4/SnO2-47.5%, which is the main reason for the improved catalytic performance;(3) Brookite TiO2/g-C3N4 composites with different contents of g-C3N4 (g-C3N4=20,35,50wt%) were synthesized by calcination method. These composites absorbed visible light because of the existence of g-C3N4; the composite exhibited a high activity towards MO degradation superior to g-C3N4 or brookite TiO2; For the content of g-C3N4 with 35%, the composite achieved an optimum photocatalytic activity; The optimized brookite TiO2/g-C3N4-35% composite is successfully applied to high-efficiency As3+ oxidation; even with Pt additives, it can also has activity in hydrogen generation; The enhanced photocatalytic activity is ascribed to the separation of photogenerated carriers as induced by semiconductor compound.