The Preparation And Modication Of Bismuth Tungstate And Its Photocatalytic Research

In recent years, photocatalytic oxidation technology has been a research hot topic as a new wastewater treatment technology. Bi2WO6 has attracted widespread attention as a new kind of visible-light catalytic material. Bi2WO6 is an Aurivillius oxide with layered structure, and the band gap is 2.7 eV. It can make full use of sun when excited by visible light. What’s more, the Bi2WO6 is photostable, and it’s a kind of eco-friendly visible-light catalyst. The research and development of Bi2WO6 can improve the utilization rate of solar energy. It has potential practical value in both environmental purification and new materials development.In this article, Bi2WO6, Eu/Bi2WO6 and Bi3.84W0.i6O6.24/Bi2O2CO3 were synthesized respectively through sol-gel method, hydrothermal method and solvothermal method with the metal doping, semiconductor compositing modification mesures. The structure, morphology, optical absorption properties of the photocatalyst were characterized by XRD, SEM, DRS, EDS, XPS and other means. The photocatalytic activity of all the samples were determined through the degradation rate of Rhodamine B (RhB) solution under visible light. Modified bismuth tungstate micro-nano materials with highly photocatalytic performance were prepared. The specific contents and results are as follows:(1) Bi2WO6 micro-nano materials were successfully synthesized by sol-gel method with citric acid as complexing agent at the optimum prepared conditions: calcination temperature 450℃, calcination time 3h, with mole ratio of citric acid to Bi3+3:1, pH=1 for the precursor solution, and PEG-4000 as dispersing agent. The products obtained exhibit the orthorhombic Bi2WO6 structure, which contain large quantities of nano-flakes with grain size about 50 nm. After 1 h irradiation under visible light (200 W tungsten lamp) with the presence of H2O2,the products showed relatively higher photocatalytic degradation rate of RhB by 87.9%.(2) Eu/Bi2WO6 nanomaterials was synthesized by hydrothermal method under the optimal conditions:hydrothermal temperature 160℃, hydrothermal time 16h, pH=1 for the precursor solution, Eu doping amount 5%. After 1 h illumination, the photocatalytic degradation rate of RhB reached 94.2%, better than 75.4% of pure Bi2WO6. The maximum absorption wavelength of Bi2WO6 shifted toward longer wavelength after Eu doped, which promoted the absorption of visible light. With the doping amount of Eu increased, the morphology of samples evolved from planar sheet structure to triaxial layered ball-flower and turned into massive grain at last. Through the photocatalytic performance, it can be deduced that the improvement of photocatalytic efficiency is due to the transport channels and huge storage room for RhB provided by open space between ultrathin nano of triaxial layered ball-flower.(3) Bi202CO3/Bi3.84W0.i6O6.24 composite catalyst was prepared by solvothermal method using ethanediol as solvent, under the conditions:the molar ratio of Bi3+ to W6+ 2:1, reaction temperature 160℃, reaction time 4h, pH=11 for the precursor solution. The photocatalytic degradation rate of RhB reached 92.0% after 15min illumination. The particle size of sample was about 10 nm, which was much smaller than that prepared by hydrothermal method. As the absorption margin moved to longer wavelength, band gap decreased and the visible-light absorption enhanced. According to Mulliken electronegativity theory, while Bi3.84W0.i6O6.24 and Bi2O2CO3 compounded, photogenerated electrons and holes gathered in the conduction band of Bi2O2CO3 and valence band of Bi3.84W0.16O6.24 respectively, which greatly reduced the recombination rate of photoproduction carriers, so as to improve the photocatalytic efficiency.