Synthesis Of BiVO₄ Composite Semiconductors And Their Visible-light Induced Photocatalytic Property

In rencent years, the sharp consumption of fossil fuels destroyed the balance of the earth, causing a variety of environmental problems. Currently, there are still some problems in the process of dealing with environmental pollution treatment, such as the incomplete decomposition of the pollution and the high cost of the procession. The visible-light-driven photocatalystic materials can utilize the solar energy, which is free and inexhaustible. And thy can decompose almost all organic pollution into small inorganic molecules by the photocatalytic oxidation The general reaction can be achieved by completely mineralization, whitout secondary pollution. The technology of photocatalytic degradation has been the focus of current research topics.This paper mainly reported the preparation of monoclinic phase BiVO4, Bi2WO6/BiVO4 and CdS/BiVO4 heterojunction photocatalysts by a hydrothermal method, the optimization of the process conditions to enhance the photocatalytic activity. The effects of the reaction conditions on the phase composition, microstructure and photocatalytic performance of the product were also analysised. Eventually, we discussed the degradation mechanism of organic dyes over BiVO4 composite semiconductors. The main research contents are summarized as follows:(1). The pure BiV04 nano-powders have been prepared by a hydrothermal synthesis with Bi(NO3)3·5H2O and NH4VO3 as raw materials under different process conditions. The samples were characterized by XRD, SEM and UV-vis spectroscopy. At the same time, rhodamine B (RhB) was used as a degradation model for visible light photocatalytic degradation experiments to study the effects of different hydrothermal conditions, such as reaction temperature, pH and surfactants, on the particle size, morphology, and photocatalytic activity, to find the optimum reaction conditions. In this part, the sample prepared at 160℃ under pH 2 exhibited the highest photocatalytic activity.(2). The different component proportion of Bi2WO6/BiVO4 composite semiconductors have been synthesized by a hydrothermal method with Bi(NO3)3·5H2O、Na2WO6·2H2O and BiVO4 as raw materials. The photocatalytic activity was estimated by the degradation of RhB under visible light irradiation. It was found that the superior photocatalytic performance could be yielded at an equimolar ratio of the components. Compared with the pure phase BiVO4, the photocatalystic performance was greatly improved. The rhodamine B degradation rate increased from 67.1% to 96.8% in 3 h. And the photocatalytic mechanism of Bi2WO6/BiVO4 composite semiconductor was also discussed.(3). The CdS/BiVO4 compound semiconductor has been synthesized by hydrothermal with CdCl2、Na2S-9H2O and BiVO4 as raw materials. The photocatalytic activity was estimated by the degradation of RhB under visible light irradiation. Compared with pure phase BiVO4, we found the photocatalyst performance is improved. The removal rate of rhodamine B could reach as much as 71.1% in 3 h. And the photocatalytic principle of CdS/BiVO4 compound semiconductor was also studied.