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Preparation and Photocatalytic Property of Bismuth-based One-dimensional Nanomaterials

Author: ZhangMingYi
Tutor: ShaoChangLu
School: Northeast Normal University
Course: Materials Physics and Chemistry
Keywords: Electrospinning technique Photocatalytic Nanofibers Bismuth-based Heterostructures
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Type: PhD thesis
Year: 2013
Downloads: 585
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Abstract


It is possible to converse the low density solar energy to chemistry and electricity energy bythe photocatalytic technologies, which provide great potential for the applications insterilization,remediation of environment, H2production by water splitting and dye-sensitizedsolar cell,and so on. However, the photocatalytic technologies still have at least twodisadvantages. First, most of these applications suffer from its dissatisfactory quantumeffciency. Second, the rapid recombination of photoinduced electrons and holes greatlylowers the quantum efficiency. Therefore, to design and develop highly efficient and easy tobe recovered photocatalyts has become the focus of current research. Generally, highly activephotocatalysts have the features of narrow band gap, high quantum efficiency, large specificsurface area, high stability and can be easy recovered. However, in fact, many programs ofimproving photocatalytic activity are still unable to meet the above points. In this dissertation,we focus on development of bismuth-based heterojunctions as photocatalysts, usinghydrothermal and solvothermal methods to control their composition and morphology. Themain contents were discussed as follows:（1） Bi2MoO6microtubes （BMO-MTs） were obtained by a two-step fabrication route. Byusing the electrospun polyacrylonitrile （PAN） microfibers as structure-directing hard templateand through ethylene glycol solvothermal method, polyacrylonitrile/Bi2MoO6（PAN/BMO）hybrid microfibers with core–shell structures were prepared. Through heat treatment of theas-prepared PAN/BMO to remove the PAN core, Bi2MoO6with tubes-structured wereobtained. Photocatalytic tests show that the BMO-MTs possess a much higher degradationrate of Rhodamine B （RB） than that of Bi2MoO6prepared by solid-state reaction andconventional P25. The improved photocatalytic performance could be ascribed to the hollowmulti channelled structure and large surface area. The BMO-MTs could be reclaimed easilyby sedimentation from the photocatalytic reaction solution due to the large length to diameterratio of one-dimensional tubes structures. Moreover, such simple and versatile strategy canprovide a general way to fabricate other tubes structures of Bi（III）-containing oxides, such asBi2WO6and BiVO4microtubes. Carbon-modified BiVO4microtubes embedded by Agnanoparticles （BVO@C/Ag MTs） were obtained by by a combination of hydrothermaltechnique and ion exchange reaction. The photocatalytic studies revealed that theBVO@C/Ag MTs exhibited the highest photocatalytic activity for photodegradation ofRhodamine B （RB） as compared with the pure BiVO4MTs, BiVO4@C MTs under visiblelight irradiation. The high separation efficiency of photogenerated electron–hole pairs basedon the photosynergistic effect among the three components of BiVO4, carbon, and Ag and the improved visible light utilization from the sensitizing effects of carbon layers both contributeto the enhanced photocatalytic activity. The BVO@C/Ag MTs did not exhibit any significantloss of activity after three cycles of the photodegradation process of RB, which results fromthe fact that the presence of carbon layer could inhibit the oxidized and lost of Ag NPs duringrepeated applications.（2） One-dimensional Bi2MoO6/TiO2hierarchical heterostructures with different secondaryBi2MoO6nanostructures grown on primary TiO2nanofibers have been obtained by acombination of electrospinning and a solvothermal technique. The morphology of thesecondary Bi2MoO6nanostructures could be controlled by adjusting precursor concentration,and then two different morphologies of Bi2MoO6/TiO2heterostructures with Bi2MoO6nanoparticles and nanosheets were successfully achieved. Photocatalytic tests displayed thatthe Bi2MoO6/TiO2heterostructures possessed a much higher degradation rate of Rhodamine B（RB） than the unmodifed TiO2nanofibers and Bi2MoO6under UV and visible light.Moreover, the heterostructures could be reclaimed easily by sedimentation without a decreaseof the photocatalytic activity.（3） A two-step synthesis route combining an electrospinning technique and solvothermalmethod has been accepted as a straightforward protocol for the exploitation ofBi2MoO6/carbon nanofibers （CNFs） hierarchical heterostructures which are composed ofBi2MoO6nanosheets on the surface of CNFs. Photocatalytic tests display that theBi2MoO6/CNFs heterostructures possess a much higher degradation rate of Rhodamine B（RB） than pure Bi2MoO6under visible light. The enhanced photocatalytic activity could beattributed to the extended absorption in the visible light region resulting from the Bi2MoO6nanosheets, and the effective separation of photogenerated carriers driven by thephotoinduced potential difference generated at the Bi2MoO6/CNFs heterojunction interface.Moreover, the heterostructures could be reclaimed easily by sedimentation without a decreaseof the photocatalytic activity. The morphology of the secondary Bi2MoO6nanostructurescould be controlled by adjusting the experimental parameters including precursorconcentration, temperature and solvent during the solvothermal process. As a result, differentmorphologies of Bi2MoO6/CNFs heterostructures with Bi2MoO6nanosheets, nanoparticles,nanoflowers and nanorods were successfully achieved.（4） A two-step synthesis route combining an electrospinning technique and solvothermalmethod has been accepted as a straightforward protocol for the exploitation of BiOCl/carbonnanofibers （CNFs） hierarchical heterostructures which are composed of BiOCl nanosheets onthe surface of CNFs. Photocatalytic tests display that the BiOCl/CNFs heterostructurespossess a much higher degradation rate of4-nitrophenol （4-NP） than pure BiOCl under UVlight. The enhanced photocatalytic activity could be attributed to the effective separation ofphotogenerated carriers driven by the photoinduced potential difference generated at the BiOCl/CNFs heterojunction interface. Moreover, the heterostructures could be reclaimedeasily by sedimentation without a decrease of the photocatalytic activity. Moreover, suchsimple and versatile strategy can provide a general way to fabricate other BiOX （X=Cl, Br,I）/CNFs heterostructures, such as BiOBr/CNFs and BiOI/CNFs.（5） A novel AgBr/BiOBr/CNFs heterostructures was prepared by a rational in situ ionexchange reaction between BiOBr and AgNO3in ethylene glycol. Photocatalytic tests displaythat the AgBr/BiOBr/CNFs heterostructures possess a much higher degradation rate ofmethyl orange （MO） than BiOBr/CNFs heterostructures under visible light. The enhancedphotocatalytic activity could be attributed to the extended absorption in the visible lightregion resulting from the AgBr and BiOBr nanosheets, and the effective separation ofphotogenerated carriers driven by the photoinduced potential difference generated at theAgBr/BiOBr/CNFs heterojunction interface.

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