Synthesis Of Three-dimensional Bi-based Photocatalyst Nanostructures And Their Controllable Photocatalytic Activities

With the rapid development of modern industry, more and moreorganic pollutants were released into water environment, which posed agreat threat to human survival. Compared with the traditional treatmenttechnology, such as absorption and biological methods, photocatalysisoxidation technology has attracted considerable attention because it canefficiently remove the stable and toxic organic pollutants in water. As awidely used photocatalyst, titania owns some outstanding advantages,such as highly efficient, non-toxic, stable and low-cost. However, titaniais only excited by UV light, which limits its efficient utilization of solarlight because the UV light range accounts for about4%of the solarspectrum. Therefore, it is highly necessary to develop new kinds ofvisible-light-induced photocatalysts using solar light to degrade organicpollutants in water. In this thesis, we mainly focus on design anddevelopment of recyclable sunlight-induced three dimensional （3D） Bi-based photocatalyst nanostructures by one-step facilesolvothermal/hydrothermal route. The as-obtained3D Bi-basedphotocatalyst nanostructures were characterized using various analytictechnologies, and the photocatalytic activities of Bi-based nanostructureswere controlled to enhance their abilities to remove organic pollutants inwater using solar light.3D porous peanut-shaped BiVO₄nano-photocatalysts assembled bynanoparticles were solvothermally synthesized with high yield byemploying bismuth nitrate and ammonium metavanadate as the startingmaterials. The as-obtained BiVO₄nano-photocatalysts were characterizedby X-ray powder diffraction, energy dispersive spectroscopy, scanningelectron microscopy, transmission electron microscopy, UV-Vis diffusereflectance spectroscopy and nitrogen sorption. The possible formationmechanism of3D peanut-shaped BiVO₄nano-photocatalysts wasdiscussed in detail. In the solvothermal condition, ethylene glycol played an important role in controlling the phase and morphology of theas-synthesized3D peanut-shaped BiVO₄nano-photocatalysts. In theH₂O₂-containing system, the photocatalytic ability of3D peanut-shapedBiVO₄nano-photocatalysts was greatly enhanced to degrade RhB inwater using solar light. The photocatalytic mechanism of porousBiVO₄/H₂O₂/sunlight/RhB system was also proposed, and the resulstsindicated that RhB was oxidized by OH and holes. In addition, thestability and reuse of3D peanut-shaped BiVO₄nano-photocatalysts inthe H₂O₂-containing system were also investigated.The effect of Ag⁺ions for the RhB photodegradation in3D BiVO₄suspension was discussed under simulated solar light irradiation. Thephotoinduced electrons on the conduction band of BiVO₄were capturedby Ag⁺ions, which suppressed the recombination of electrons and holes.The theoretical and experimental results indicated that RhB was oxidizedby holes in the Ag⁺/BiVO₄system using simulated solar light. X-ray powder diffraction, energy dispersive spectroscopy, and transmissionelectron microscopy confirmed that metal Ag nanoparticles weredeposited on the3D BiVO₄photocatalysts after the photocatalyticreaction. The Ag/BiVO₄composite photocatalysts showed a higherphotocatalytic activity than pure BiVO₄photocatalysts. Obviously, Ag⁺ions played the dual role to enhance the photocatalytic ability of3DBiVO₄photocatalysts for RhB degradation.3D Bi₂WO₆microspheres assembled by nanosheets were preparedwith high yield via one-step simple hydrothermal method, by employingbismuth nitrate and sodium tungstate as the starting materials. Theas-obtained Bi₂WO₆microspheres were characterized by X-ray powderdiffraction, Raman, scanning electron microscopy, transmission electronmicroscopy, UV-Vis diffuse reflectance spectroscopy and nitrogensorption. Under simulated solar light,3D Bi₂WO₆microspheres showedan excellent photocatalytic ability to degrade RhB in water, and the photodegradation mechanism was also proposed. The results indicatedthat RhB was degraded by holes and O–2radicals. The Bi₂WO₆microspheres could keep stable in acid or basic condition, and thephotocatalytic ability would be decrease in basic condition. Thephotocatalytic performance of the Bi₂WO₆microspheres for phenoldegradation was greatly enhanced with the assistance of a small amountof H₂O₂because of more OH radicals produced.3D Bi₂O₃/Bi₂WO₆composite microspheres were hydrothermallysynthesized by using CTAB as soft template, and bismuth nitrate andsodium tungstate as the starting materials. The as-obtained Bi₂O₃/Bi₂WO₆composite microspheres were characterized by X-ray powder diffraction,X-ray photoelectron spectroscopy, scanning electron microscopy,transmission electron microscopy, UV-Vis diffuse reflectancespectroscopy and nitrogen sorption. Under solar light irradiation,3DBi₂O₃-Bi₂WO₆composite microspheres exhibited a much higher efciency in the photodecomposition of RhB than Bi₂O₃catalyst orBi₂WO₆catalyst. The excellent photocatalytic activity of Bi₂O₃-Bi₂WO₆composite microspheres could be mainly attributed to their strongabsorption in light and low recombination rate of the electrons and holesbecause of the heterojunction formed between Bi₂O₃and Bi₂WO₆.