| Environmental pollution has been a difficult problem for people. The application of photocatalytic technology in sewage treatment and air purification is very good to ease the environmental problems. TiO2 has played an important role in the photocatalytic degradation of harmful substances, but its structural defects also limit its use. For example, it can only be carried out under the ultraviolet light catalysis, and the band gap is large, etc. In recent years, scientists have developed a lot of new un-doped single-phase metal composite oxide photocatalyst such as BiVO4, CaBi2O4, BiOBr, which shows photocatalytic ability on the range of the visible light, but the photocatalytic activity of these new materials is very limited. Smaller surface area and long distance migration of the excited electrons and holes increase the probability of composite phase with losing of energy, which leads to lower photocatalytic activity. It is one of the important means to improve the photocatalytic activity of the composite photocatalyst by using two element or multi-component structure. In this paper, we designed two kinds of photocatalytic composite materials (n-n, p-n) and the photocatalytic activities have been evaluated by photodegradation experiments of Rhodamine B (RhB) and methylene blue (MB) under visible light irradiation. In this dissertation, the following several parts of work have been done:1. BiOBr and BiVO4 were both synthesized by hydrothermal methods. BiOBr/BiVO4 composites were obtained by ultrasonic mixing the as-prepared BiOBr and BiV04 powder in ethanol solvent and then drying at 80℃. Two different semiconductor hybrid, the band gap of the heterostructure photocatalytic materials is narrower (2.1 eV) than single-phase metal oxide photocatalysts BiOBr (2.88 eV) and BiVO4 (2.3 eV). The results of photocatalytic degradation experiment of RhB show that the degradation rate is up to 92%, higher than the degradation rate of BiVO4 and BiOBr when BiOBr: BiVO4=1:1. Obviously, the synergistic effect of BiOBr and BiVO4 can enhance the photocatalytic activity under visible light.2. BiOBr was synthesized by hydrothermal methods and CuO was obtained by calcination of Cu (NO3) 2·3H2O. And then the uniform p-CuO/n-BiOBr heterojunction composite photocatalytic materials with different mass ratios were prepared by mechanical mixing. The prepared materials are used for the degradation of MB and their photocatalytic properties were studied. The results showed that when the mass ratio of CuO to BiOBr was 1:1, the photocatalytic degradation rate was the highest and the photocatalytic activity of hybrid composites was stronger than that of single phase.The above results show that the reasonable design of n-n and p-n heterostructures composite will improve the absorption efficiency of photocatalyst in the visible light range. The formed heterogeneous structure between the semiconductors will promote the effective separation of the photo-generated carriers, and realize the efficient degradation of organic pollutants under the visible light. This paper provides a feasible method for the design and preparation of the visible-light-responded photocatalysts of the heterogeneous structures, which provides a valuable reference for the further application and development of photocatalysis. |
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