Preparation And Photocatalytic Property Of Bismuth-based One-dimensional Nanomaterials

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.