Nanostructured Oxides With Unusual Morphologies:Synthesis And Properties

Nanostructured materials with unusual morphologies open up a new opportunity for some unique optical, electrical and magnetic applications, e.g. photodegradation of organics, dye-sensitized solar cells and gas sensors, etc; among these applications, the architecture of nanostructured materials is particularly important. However, the controllable synthesis of nanostructured materials with tuneable shapes and sizes is still a great challenge. In this work, nanostructured TiO2, ZnO and SiO2particles with peculiar morphologies were systematically synthesized, and special consideration was paid to the correlation between the properties of these nanostructured materials and their performances in water pollution treatment, photocatalysis, mechanics and thermotics, etc. The major results of this work are summarized as follows:1. Morphology engineering of nanostructured particles:A systematic approach was applied to solvothermally synthesize nanostructured TiO2particles with five different morphologies, namely spherical flower, thatch, cauliflower, nanocube, octahedron. These nanostructured particles are stoichiometric, crystallized with the anatase structure, the BET surface areas vary for more than one order of magnitude from12.86to172.02m2g-1, and pore size from3.96to16.68nm. The synthesis of nanostructured TiO2particles with tuneable shapes and sizes were achieved through the effective control of the alcoholysis rate of TiF4and the prevention of the aggregation through optimizing the pressure, composition and pH value of the reaction solution. This work provides not only a strategy for controlling the morphology of TiO2particles, but also a universal method that can be applied to the preparation of other nanomaterials.2. Wastewater treatment:Two types of nanostructured TiO2particles with high specific surface areas, namely dandelion and spherical flower, were successfully synthesized. The specific surface areas of the dandelions and spherical flowers were determined by BET to be226and172m2g-1, respectively. The maximum monolayer adsorption capacities of Cd(Ⅱ) for the dandelions and spherical flowers were found to be396and282mg g-1, respectively, and both nanostructured TiO2particles could be repeatedly used without any remarkable loss in the adsorption capacity. The FT-IR, XPS and TG-MS analyses indicated that the Cd(Ⅱ) adsorption was mainly ascribed to the hydroxyl groups on the TiO2surfaces. Both nanostructured particles exhibited great potential for the removal of Cd(Ⅱ) from wastewater in engineering practices.3. Ultraviolet photocatalytic degradation:Nanostructured TiO2/ZnO heterojunctions with the morphologies of hedgehog and fan blade were synthesized by a solvothermal method. The photocatalytic activities of both TiO2/ZnO hedgehogs and fan blades for the degradation of methyl orange (MO) were explored under UV light. The degradation kinetics was pretty fast, which could be completed within30minutes. More importantly, the degradation capacity of the TiO2/ZnO heterojunctions did not show any obvious decrease after five degradation cycles. The hedgehogs had the best photocatalytic activity, which could be ascribed to the hierarchical nanostructure and the higher specific surface area. This work provides a facile and economical strategy for fabricating nanostructured TiO2/ZnO photocatalysts with tuneable morphologies, and will greatly promote their industrial application in eliminating the organic pollutants from wastewater.4. Epoxy composites reinforced by mesoporous SiO2nanoparticles:SiO2particles/epoxy nano-composites were synthesized and their mechanical, thermal and dielectric properties were evaluated; the tensile modulus, tensile strength and toughness of the nanocomposites were enhanced by mesoporous SiO2nanoparticles with high specific surface area, while their storage modulus and glass transition temperature (Tg) decreased.5. Epoxy composites reinforced by multi-dimensional nanostructured materials: epoxy was reinforced by montmorillonite (MMT) with a two-dimensional lamellar structure and TiO2nanoparticles with a quasi zero-dimensional structure, the properties of nanostructured particle/epoxy nanocomposites, such as mechanical, thermal and dielectric properties, were improved due to the synergistic effect of two dimensionally different nanostructured materials. The TiO2nanoparticles with high specific surface area can provide more active sites to strengthen the interaction between the fillers and epoxy resin matrix. The synergistic effect of dimensionally different nanostructured particles is also expected to find applications in the enhancement of the properties of the other composites.