Electrospun Hollow Oxide Nanomaterials And Their Photocatalytic Properties

Electrospinning technique is one of methods for preparing nanomaterials, which has the most potential for development. It has the advantages of simple device, facile preparation process, various electrospun nanomaterials and a wide range of application.In many applications, the electrospun nanomaterials used in photocatalytic decomposition of organic pollutants have been attracted. At present besides nanofibers, elecreospinning can aslo be used to fabricate nanotubes, nanospheres and other nanomaterials with hollow structure, which has greatly enriched the application of electrospinning technique. In the thesis, electrospinning is used to prepare porous TiO2nanotubes, hollow ZnO nanospheres and Sn02/Fe2O3heterojunction nanotubes, and the photocatalytic properties of these hollow nanomaterials are investigated in detail. The main contents of this thesis are as the following:1.Porous TiO2nanotubes and TiO2nanofibers are prepared by controlling the content of mineral oil in precursor solution during electrospinning. The two nanomaterials have anatase phase and rutile phase, and the proportion of the two phases is different. The ratio of anatase phase to rutile phase in the porous TiO2nanotubes is77:23, which is close to the ratio of commercial P25. Porous TiO2nanotubes have larger specific surface area of38.39m2/g, which is more than two times the surface area of TiO2nanofibers. Under ultraviolet light of250W, porous TiO2nanotubes show higher photocatalytic properties than TiO2nanofibers. After120min, porous TiO2nanotubes can completely decompose RhB dye. This is mainly due to that large surface area of porous TiO2nanotubes can increase the contact area between photocatalyst and dye, which can promote the catalytic reaction.In addition, anatase TiO2nanocrystal and rutile TiO2nanocrystal of nanotubes can form homojunction structure, which increases the separation of electrons and holes, and improve photocatalytic efficiency of samples.Porous TiO2nanotubes has good ultraviolet photocatalytic activity, however, their utilization rate of light is greatly limited, because the ultraviolet light in solar spectrum only is5%.In order to further improve the photocatalytic activity of porous TiO2nanotubes, we combine electrospinning method and hydrothermal method to prepare the graphene (GR)/porous TiO2nanotubes composite photocatalyst. Results show that GR/porous TiO2nanotubes composite photocatalyst have better photocatalytic activity than pure porous TiO2nanotubes under visible light. After150min, the GR/porous TiO2nanotubes composite photocatalyst can completely degrade RhB dye. This is due to that the combination of graphene and porous TiO2nanotubes expands the light absorption of TiO2from the UV light range to visible light range and enhances the utilization rate of light. Moreover, graphene has high electrical conductivity, so the combination can quickly transfer photoinduced electrons and holes, which increases the separation of electrons and holes and improve photocatalytic efficiency.2. Hollow ZnO nanospheres with diameter of about300nm are successfully parpared by electrospinning and thermal treatment process. The samples are self-assembled by large numbers of ZnO nanocrystallites with diameter in about30nm during annealing process. Under ultraviolet light of250W, ZnO hollow nanospheres show higher photocatalytic activity than commercial nano ZnO. After150min, ZnO hollow nanospheres can completely decompose RhB dye. The excellent catalytic activity of ZnO hollow nanospheres is attributed to large surface area of samples, which is favorable for photocatalytic reaction. At the same time, hollow spherical structure of ZnO samples has light trapping effect, which can enhance the ability of capturing light and increase the number of photogenerated carriers, thus photocatalytic efficiency of hollow ZnO nanospheres is improved.3.SnO2/Fe203heterojunction nanotubes are prepared by electrospinning technique. The heterojunction nanotubes with diameter of about200nm are uniformly distributed by SnO2and nanocrystals and present the obvious interfaces between them, which form perfect nanoheterojunctions. A possible mechanism based on self-polymer-templates is proposed to explain the formation of SnO2/Fe2O3heterojunction nanotubes. SnO2/Fe2O3heterojunction nanotubes have good absorption property of visible light. Under the irradiation visible light. The SnO2/Fe2O3heterojunction nanotubes show higher photocatalytic activity than pure SnO2nanotubes and Fe2O3nanofibers. After180min, SnO2/Fe2O3heterojunction nanotubes can break down about80%of the RhB dye. However, SnO2nanotubes and Fe2O3nanofibers were as photocatalysts, most RhB dye molecules are not decomposed. The efficient visible light photocatalytic activity is attributed to that tubular structure of samples increase the contact area of dye and sample, and heterojunction structure formed by Fe2O3and SnO2nanocrystalline can improve the separation of photogenerated electron-hole pairs, which ultimately promotes the photocatalytic reactionIn this thesis, we use the simple electrospinning method to prepare three hollow nano-photocatalysts, the three materials show higher photocatalytic properties, and the formation mechanism of materials and the reason for high photocatalytic efficiency are explored.