Preparation Of Visible-Light Photocatalyst BiVO₄ And Its Performance Study

Monoclinic BiVO₄ has been paid more and more attention which has amazing photocatalytic performance under the visible light by researchers. In this paper, monoclinic BiVO₄ with high photocatalytic activity and scheelite-type structure was prepared respectively by microwave hydrothermal method with Bi（NO 3）3·5H2O or Bi C l3 as resource of Bi. X-ray diffraction（XRD）, field emission scanning electron microscope（FESEM） and energy dispersive spectra（EDS） were used to characterize the crystalline phase, microscopic morphology and size of BiVO₄ and UV-Vis spectrophotometer was adopted to measure the degradation efficiency of methylene blue solution in the presence of the photocatalyst BiVO₄. The influence of different experimental conditions on properties of samples were also discussed in the thesis. The experimental results are as follows:1. Bi（NO3）3·5H2O, NH4VO3 and ethanolamine were used as raw materials to synthesize bright yellow monoclinic BiVO₄ powder by microwave hydrothermal method. The microscopic morphology and size of BiVO₄ powder varies with the reaction temperature. With the increase of temperature, the microscopic morphology changed from tight arrangement of herringbone structure to loose arrangement of branched structure. When the temperature was raised, crystal would grow along another cr ystal plane orientation. When the temperature reached 180℃, the surface of the sample became very smooth. Besides, the photocatalytic properties of the sample increased significantly with the increase of temperature. When the temperature was 160℃, microscopic morphology of BiVO₄ transferred from the mixed morphology of rod shaped structure, p lane structure and small particle agglomeration to three-dimensional structure, meanwhile, the photocatalytic properties of BiVO₄ increased.2. In the second part, Bi（NO3）3·5H2O was substituted to Bi C l3, and Bi C l3, NH4VO3 and ethanolamine were used to synthesize BiVO₄ by microwave hydrothermal method. When the reaction temperature is raised, the microscopic morphology of BiVO₄ sample changed from disorganized to loose and dispersive nanosheet. The sample which had a microscopic morphology of nanosheet showed the most outstanding photocatalytic properties. With the extension of reaction time, nanosheet was replaced by a large size rod-like bar.3. Comparing the above two experiment under the same experimental conditions except the different Bi sources, it came to a conclusion that Bi source had great influence on the crystalline phase, microscopic morphology, size and photocatalytic activity of BiVO₄. Comparison results showed that chloride ion helps to shape the nano-size slice of monoclinic BiVO₄ and BiVO₄ of this microscopic morphology had better photocatalytic performance than other structures.