Preparation And Photocatalytic Performances Of Titanium Dioxide/Semiconductor Metal Oxide Composite Nanofibers

As energy crisis and environment pollution become more and more serious, how to protect the environment and save energy have been of important topic nowadays. Since the discovery of photoelectrochemical splitting of water on n-type semiconductor TiO₂ electrodes, TiO₂ has become the focus in the field of semiconductor photoelectrochemistry. However, its practical application is limited due to its excitation by only UV light,low quantum efficiency as well as the difficulty in separation and reuse of the nanoparticles powder. For this, this thesis devotes to the preparation and modification of TiO₂ based nano-photocatalyst, aiming at enhancing the separation efficiency of photogenerated carriers and increasing the spectral response range to visible light region. Via sol-gel process, electrospinning technique, hydrothermal method or their recombination, single phase of TiO₂ or TiO₂/semiconductor metal oxides composite photocatalyst in the form of nanoparticles or nanofibers are prepared, and also their photocatayltic activities are studied. Some interesting and original results are obtained and listed as following:First, pure phase TiO₂ nanomaterials were synthesized by an autoclaving treatment of TiCl₄ with butanol as a single alcohol source. It was found that the control of molar ratio of TiCl₄ to butanol played an important role in determining the TiO₂ crystal phase and morphology. A high molar ratio of TiCl₄ to butanol favored the formation of anatase nanoparticles, whereas rutile nanorods were selectively obtained at a low molar ratio of TiCl₄ to butanol. Evaluation of the photocatalytic activity of the synthesized TiO₂ was performed in terms of decomposition of organic dye rhodamine B under ultraviolet irradiation. It turned out that the as-synthesized TiO₂ crystallites possessed higher photocatalytic activities toward bleaching rhdomine B than Degussa P25, benefiting from their high surface area, small crystal size as well as high crystallinity.Second, heterostructured TiO₂/CeO₂ composite nanofibers were prepared via hydrothermal growth and electrospinning technique of CeO₂ nanostructures on anatase TiO₂ nanofibers templates. The catalytic properties of the sample were studied via rhodamine B degradation as the model reaction. The results showed that CeO₂ nanoparticles could evenly grow on the TiO₂ nanofibers surface and thus heterostructured TiO₂/CeO₂ composite materials were successfully obtained. By selecting different alkaline source, TiO₂/CeO₂ heterostructures with different morphology of CeO₂ nanostructures were facilely fabricated. We found that the TiO₂/CeO₂ heterostructures showed enhanced photocatalytic efficiency compared with the bare TiO₂ nanofibers under UV light irradiation. The presence of CeO₂ in TiO₂ nanofibers could increase its surface area, and effectively achieve the separation of photoelectrons and holes. Last, the mechanism for the enhancement of photocatalytic activity of heterostructured nanofibers was discussed.Third, heterostructured TiO₂/SrTiO₃ composite nanofibers were fabricated by in situ hydrothermal method using TiO₂ nanofibers as both template and reactant. The as-fabricated heterostructures composite included SrTiO₃ nanocubes assembled uniformly on the surface of TiO₂ nanofibers. Compared with the pure TiO₂ nanofibers, TiO₂/SrTiO₃ nanofibers exhibited enhanced photocatalytic activity in the decomposition of Rhodamine B （RB） under ultraviolet light. This material also showed good catalytic stability. Last, the growth mechanism of TiO₂/SrTiO₃ heterojunction and the mechanism for the enhancement of photocatalytic activity of heterostructured nanofibers was discussed.Fourth, a facile two-step synthesis route combining electrospinning method and hydrothermal technique had been accepted as a straightforward protocol for the exploitation of TiO₂/Bi₄Ti₃O₁₂ heterostructures which were composed of Bi₄Ti₃O₁₂ nanosheets on the surface of TiO₂ nanofibers. The thickness of the as-grown nanosheets was about 20 nm and the size of nanosheets increased with the increase of precursor concentration. Photocatalytic test displayed that the TiO₂/Bi₄Ti₃O₁₂ heterostructures possessed much higher degradation rate of rhdomine B （RB） than the unmodified TiO₂ nanofibers under visible light. The enhanced photocatalytic activity could be attributed to the extended absorption in the visible light region resulting from the Bi₄Ti₃O₁₂ nanosheets and the effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the TiO₂/Bi₄Ti₃O₁₂ junction interface, and the decolorizing efficiency of RB solution remains above 97% after 5 times recycle, and was easily separation, removed from the system after reaction and reuse.