Preparation, charaterization and application of metal oxide nanomaterials

Abstract

Transition metal oxides are an important group of materials, because they form a wide variety of structures, display many interesting properties, and have numerous applications. In particular, metal oxide nanomaterials have attracted great interest in their potential applications as catalysts, magnetic data storage devices, lithium-ion battery materials, and solid-state sensors, because of their chemical stability and magnetic properties. Cobaltous oxide typically crystallizes in two stable phases, cubic rocksalt CoO (c-CoO, space group Fm3m) with octahedral Co2+ and hexagonal wurtzite CoO (h-CoO, space group P63mc) with tetrahedral Co2+ ions. I have synthesized h-CoO and c-CoO nanocrystals with controlled morphologies of hexagonal pyramids, rods, and cubes in a selective manner. The wurtzite and rocksalt phases have been controlled by changing thermal decomposition kinetics of the cobalt precursor, Co(acac)3 (acac = acetylacetonate), in benzylamine. Addition of o-DCB slows down the decomposition rates, and drives the reactions to the thermodynamic control regime. Moreover, through the subsequent air oxidation of both h-CoO and c-CoO nanocrystals, spinel Co3O4 nanocrystals have been produced with retention of the original morphology of CoO. The detailed crystal structures during oxidation reactions have been carefully examined. Finally, the electrochemical properties of h-CoO toward lithium have been investigated for the first time and compared with those of c-CoO and spinel Co3O4 to elucidate their relative electrochemical activities. Synthesis and characterization of [100] directed Cu-doped h-CoO nanorods, which are very stable in an aqueous solution unlike pure h-CoO nanocrystals. Theoretical analyses reveal that Cu-doping leads to a rearrangement of the order of surface energies among the (001), (101), (110), and (100) surfaces, thus causing the nanorods to grow along the [100] direction. The change of surface energy by doping is a crucial factor for det...