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Synthesis of Three-dimensional Bi-based Photocatalyst Nanostructures and Their Controllable Photocatalytic Activities

Author: GeMing
Tutor: ChenWei
School: Nankai University
Course: Environmental Science
Keywords: three-demensional nanostructures Bi-basednano-photocatalysts solvothermal/hydrothermal method photodegradation controllable photoactivity
CLC: X52
Type: PhD thesis
Year: 2012
Downloads: 26
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Abstract


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.

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CLC: > Environmental science, safety science > Environmental pollution and its prevention > Water pollution and its control
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