Synthesis And Performance Of Visible-light-driven Bi₂WO₆Photocatalyst

Due to the smaller band gap (2.7eV), novel visible light Bi2WO6photocatalytic materials possessexcellent photocatalytic activity in the degradation of organic pollutants under UV and visible lightirradiation, which attract extensive attention from researchers. In this paper, Bi2WO6were prepared usingBismuth nitrate (Bi(NO3)35H2O) and ammonium tungstate (NH4)6W7O246H2O) as raw materials. Theeffects of synthetic method, biological template agent and graphene on the structure, morphology, theseparation efficiency of photo-induced electrons and holes and absorbence of the Bi2WO6photocatalysthave been investigated. Based on the experimental results, the mechanism and the reason for highperformance of Bi2WO6photocatalyst were proposed, which might provide the useful data for preparinghigh performance photocatalyst. The researches are as follows:(1)3D hierarchical Bi2WO6microspheres are prepared by sol-gel-hydrothermal method at220℃for24h using EDTA as a gelata. Based on the characterization of X-ray diffraction (XRD), scanningelectron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflectancespectra, the structure, morphology and optical property of Bi2WO6were investigated and the formationmechanism of3D hierarchical Bi2WO6microspheres was proposed. Photocatalytic activities of the sampleswere evaluated by the degradation of methylene blue (MB) under visible light irradiation. The resultsindicated that Bi2WO6microspheres exhibited better photocatalytic activities. The enhanced photocatalyticdegradation of MB of Bi2WO6microspheres may be attributed to the synergistic effects of high surface area,small particle size, the special3D hierarchical structure, high utilization rate of photon and diffusion rate ofreagent. In addition, the Bi2WO6microspheres with a hierarchical architecture maintain excellentphotocatalytic activity after several repetitive tests, which show a good future in industrial application forwastewater treatment.(2) Bi2WO6-RGO composites have been synthesized by hydrothermal method in the presence ofionic liquid [BMIM][BF4]. The effects of the content of graphene and ionic liquid on the photocatalyticactivity were investigated and the suitable preparation conditions were obtained. The results show thatBi2WO6-RGO samples synthesized using ionic liquid exhibit the bigger specific area and unique nestmorphology, and have significantly enhanced photocatalytic performance for degradation of rhodamine B.Due to the introduction of graphene, Bi2WO6-RGO composites boost its absorption in UV and visible light and improve the separation efficiency of photo-induced electrons and holes. Moreover, Bi2WO6-RGOcomposites with the amount of graphene of5.0wt%exhibited the highest photocatalytic performance, andthe photocatalytic degradation efficiency could reach99.3%under300W xenon lamp irradiation for120min.(3) Bi2WO6nanoplates have been synthesized by using egg white as a biotemplate via sol-gelmethod at500℃for2h. In this experiment, EBWO sample synthesized with egg white possesses plate-likestructure, while BWO sample prepared without egg white exhibits irregular block structure andagglomerates seriously. In the preparing process, egg white is used as a stabilizer and gelling agent forreducing agglomeration of nanoparticles. Because of high surface area and lower recombination rate ofelectron-hole, degradation efficiency of EBWO can reach91.1%under300W xenon lamp irradiation for120min.