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Hydrothermal Synthesis and Physical Properties Study of Hierarchical Cobalt-based Micro/Nanomaterials

Author: PangZhanWen
Tutor: WuMingZai
School: Anhui University
Course: Materials Physics and Chemistry
Keywords: Hydrothermal Nano-materials Synthesis Properties
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 59
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Abstract


From the view of functional materials development, Co-based micro/nanomaterials have shown broad application foreground due to their unique characters of structure and performance. Moreover, the physical properties of the products were reported to be dependent on the shapes and sizes of the products. Hence, the synthesis and physical properties study of complex Co-based micro/nanomaterials have become an important topic in the field of materials science. In the thesis, we present the synthesis of Co-based micro/nanomaterials with special shapes. The influences of some parameters on the morphology of the products have been investigated. Besides, the relationship between the physical property and morphology of the Co-based micro/nanomaterials is also studied. The main achievements and innovations in this thesis are summarized as follows:1. Three-dimensional cobalt microcrystals composed of well-aligned dendrites radiating from the center were prepared using cobalt chloride hexahydrate as starting materials via a facile hydrothermal route. The dosages of ethylenediamine, sodium hydrate were found to play an important role in the morphology control of the final products. A unique growth mechanism for the radial cobalt microcrystal was tentatively discussed, which offer a fresh and possible solution to the design and fabrication of materials with hierarchical structure. Additionally, the products exhibited ferromagnetic characteristics with a saturation magnetization of151.7emu/g and a coercivity of355.8Oe at room temperature, showing a potential applications in ferrofluids and other related magnetic application.2. Different morphologies of CO3O4microcrystals including octahedron, netlike, and sphere have been prepared using cobalt chloride hexahydrate as starting materials through the change of hydrazine dosages, whih was found to exert important influences on the size, structure and shapes based on the SEM measurements. Charge-discharge of Li ions was performed on the coin battery made of spherical particles and the measurement results shows that the first charge-discharge specific capacitance is as high as1073mAhg-1. In addition, the gas sensing properties of the as-synthesized spherical microcrystals are investigated, which reveals that the as-prepared spherical CO3O4microcrystals exhibit superior sensitivity to C2H5OH, as well as short response times.3. Successful phase control synthesis of Co(OH)2via a magnetic field-assisted hydrothermal route. Two-dimensional platelets of Co(OH)2are selectively synthesized by an in situ magnetic field assisted hydrothermal method with COCl2·6H2O) and hydrazine as the starting materials. It was found that the dosage of hydrazine and the application of magnetic field exerted much infulence on the phase and final morphologies on the products. In addition, magnetic field was found to promote the phase of the products. Additionally, the electrochemical performances of the products were investigated by constant current charge/discharge techniques. The test results show that an high specific capacitance value of313F/g is achieved inl mol/L KOH electrolyte in the potential range of-0.1-0.4V (vs SCE) at the charge-discharge current of1mA, and the products is a promising electrode material for supercapacitor.4. CoFe2O4nanostructures with different morphologies were prepared using cobalt chloride hexahydrate as starting materials via a magnetic field-assisted hydrothermal route. It was found that the application of magnetic field and the reaction time can exert a significant effect on the morphologies and magnetic properties of CoFe2O4. In the absence of magnetic field, the products are granular, and the saturatioin magnetization of the products increase with the elongation of reaction time; while in the presence of magnetic field, the granular products.are transformed to be platets, and the saturatioin magnetization of the products firstly increase and then decrease with the elongation of reaction time.

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