Functional Metal Oxide Nanomaterials: Solution-Based Synthesis And Property Investigation

Metal oxide nanomaterials have exhibited promising applications in catalysis, sensing, optics, magnetism and batteries. Preparation of nanomaterials with well-defined size, morphology, dimensionality and diversity through novel synthesis approaches and investigations of their formation mechanism should be a key precondition to reveal the relations between the structures and properties, assemble the nanocrystals into superstructures and pave the way to the real applications. In this dissertation, valuable explorations have been carried out on new solution-based manipulated synthetic strategies for functional metal oxide nanostructures along with their formation mechanisms and novel properties, emphasizing on the relationship between crystal symmetry and morphology manipulation as well as the connection between properties and size/morphology of nanomaterials.A rational low-temperature hydrothermal synthetic way has been developed to selectively prepare vanadium oxide nanobelts with different valent status. The formation mechanism is investigated in details and believed to be closely related to their layered structure. A highly selective and stable ethanol sensor was designed based on the intrinsical layered structure of vanadium pentoxides and the advantages of nanobelts. The investigation on the electrical transport and magnetic properties of vanadium dioxide nanobelts shows their potential applications in nanodevices.A synthesis and self-assembly approach assisted with oleic acid molecules is developed to fabricate luminescent Ln3+ doped LaVO4 nanocrystals (NCs) and rare earth vanadates. A transparent luminescent film of uniform nanocrystals, which could absorb UV light and down-convert it to visible light, prepared by coating approach could greatly improve the cell performance when applied in dye-sensitized solar cells. Catalytically active gold catalysts have been designed via monodispersed gold colloids on LaVO4 nanocrystals with controlled size as more well-defined nanocatalysts. The use of rare earth vanadates as supports for active gold catalysts opens up new routes in the research work for high performance catalysts.Bismuth vanadate micro/nanocrystals with different morphologies were synthesized by surfactant assisted hydrothermal/solvothermal methods. The studies on the crystal growth reveal the relationship between the crystal structures and the morphology. Low dimensional potassium niobate nanostructures with different compositions were achieved by simply controlling pH value of the hydrothermal system. It was found that the solvent plays an important role in the phase control of the KNbO3 nanocrystals.Study on the catalysis properties of iron oxide nanocrystals with different size and morphology showed that the catalytical activities were influenced not only by the size and BET of the materials, but also by the crystal planes due to the facts that the reactivity, coming from different active sites on certain reactions, varies with crystal planes. Redispersible TiO2 nanocrystals with hydrophobic surface were prepared by controlled solvothermal reactions, followed by a newly developed microemulsion-based method to assemble the nanocrystals to colloidal spheres with hydrophilic surface. Mesoporous spheres, which are expected to show excellent properties in applications such as catalysis, could then be achieved by annealing of colloidal spheres.