| Due to the conspicious chemical and physical properties, metal oxide nanostructures have great application potentials in many fields, and become popular research subject in material chemistry. Since the properties are depend on he morphologies and assembling behaviors of materials, it is believed that the controllable synthesis of metal oxide nanostructures with different morphologies and assembling behaviors can further tune their chemical and physical properties and will improve their supercapacitor and lithium ion battery performances.Using the precursor method, metal oxides assembled by nanoparticles can be obtained after the heat treatment of the precursors,and we can control the assembling way of the nanoparticles through the morphology control of the precursors. And then, the problems of fusion of small particles and the great resistance produced by the bad connection between the particles can be solved to a certain extent. In this thesis, we successfully regulated morphology and structure of a series of metal oxides by controlling the morphology and structure of precursors. The growth mechanism of the nanomaterials and the relationship between the morphology and property of the nanomaterials have also been investigated and discussed. The main contents of our work are summarized as follows:One-dimensional (1D) cobalt acetate hydroxide (Co5(OH)2(CH3COO)8-2H2O) prisms were obtained through a low temperature re-crystallization process in ethanol and then converted to cobalt oxide by calcining in the air. Cobalt oxide keeps the outside configuration of the 1D cobalt acetate hydroxide but turns to be boxes with hollow structure inside through the Kirkendall effect. The precursor prisms and polycrystalline boxes both have length of 3μm, width of 300 nm and height of 300 nm, characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical measurement results show that the hollow Co3O4 structures exhibit wonderful capacitive properties with high capacitance and good cyclicity by supercapacitor test.2. Synthesis and performance test of cobalt oxide,nickel oxide and their multiple oxideOne-dimensinal 2Co(C7H4O3)Co(OH)(C7H5O3)·6H2O (cobalt salicylate hydroxide) helical nanowires were obtained through a simple solvothermal method and the precursors have been converted to Co3O4 by calcining in the air. Cobalt oxides compose of small particles and keep the outside configuration of the 1D salicylate hydroxide. The precursor and polycrystalline boxes were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical measurement results show that the helical Co3O4 nanowires exhibit great capacitive properties with high capacitance and good cyclicity both in supercapacitor test and lithium in battery test. Using the same solvtherrmal method, NiO and NiCo2O4 with similar spiral morphology to Co3O4 helical nanowires have both been successfully synthesized.3. Controllable synthesis and performance test of MnOxThe MnCO3 precursors with two different morphologies (fusiform and cubic) have been obtained through a green route under hydrothermal conditions with orange pericarp extracting solution as the reducing agent and with KMnO4 as manganese source. Manganese oxides with different crystalline phases and morphologies have been controllably prepared by calcining MnCO3 precursors at different temperatures and in different atmospheres. MnOx with different valences, such as, fusiform MnO, MnO2, Mn2O3, and cubic MnO, MnO2, Mn2O3, Mn3O4, can be obtained. The supercapacitor performances of these MnOx nanostructures have been researched systematically, MnO2 and MnO electrodes exhibiting great supercapacity with high specific capacity and good cyclicity.4. Green synthesis of carbon quantum dots (CQDs)In this chapter, fluorescent carbon quantum dots (CQDs) was obtained through hydrothermal technique with extracting solution of orange pericarp as raw materials direclly. Hydrothermal temperatures and times were adjusted to control the particle sizes and the quantum yields of the obtained CQDs. Furthermore, good morphology of carbon spheres with high purity and uniform size can be easily obtained as the reaction byproducts. |
