Study Of Construction And Mechanism Of Hollow Metal Oxide Spheres

Template strategy is becoming an efficient and promising method to obtain nano-materials. In present years, nano/micro materials with zero dimensional, one dimensional, two dimensional and three dimensional structures have been synthesized by template strategy and their formation mechanisms have been brought out. In the dissertation, nano/micro Fe2O3, Co3O4, NiO hollow spheres were synthesized by carbon sphere template strategy. The influences of preparation parameters on the morphologies were investigated. The formation mechanisms and growing models of carbon spheres and three metal oxides are proposed and established on the basis of experimental results. The main Points are summarized as follows:In the process of preparation of carbon spheres, carbon spheres were synthesized hydrothermally in a glucose-water mixed solution system. Repeated to clean the carbon spheres by alcohol and water. The samples were characterized by a series of methods and the influences of reaction temperature, reaction time, volume of ethanol on the final morphologies of carbon spheres were investigated.The formation mechanism was proposed on the basis of experimental results. The cooperative mechanism between the nuclear cohesion and the surface free energy plays a key role. The hydrothermal reaction is to start the carbon particles generated as the core to make carbon elements gradually attract growth together. This attraction is nuclear cohesion. With moderate increase in pressure, reaction in molecular aggregation nucleating is more likely. The lattice distortion of the powder is mainly caused due to the surface energy and surface tension effects, can be used for qualitative interpretation according to the fundamental thermodynamic characteristics of nano crystal if the carbon nanospheres as small spherical particles, and then gradually formed carbon sphere. The reason of the effect of the reaction factors on the final morphologies was explained by the mechanism.Hollow iron oxide spheres were synthesized by hydrolysis with FeCl3 serving as the precursor and carbon spheres as templates in the aqueous solution system. Then the samples were calcined at 450℃. The samples were characterized by a series of methods and the influences of reaction temperature, reaction time, the concentration of FeCl3 on the final morphologies of Fe2O3 were investigated. The formation mechanism was proposed on the basis of experimental results and explained the reason of the influence of the reaction factors on the morphologies. In the process of coating system, the pH value of the solution changes and the electrification of particles plays a key role. Through this mechanism, solution to form a spherical nucleus adsorbed onto the surface of carbon spheres. Then Fe2O3 became hollow structure by the increase of reaction time.Hollow cobalt oxides and nickel oxides spheres were synthesized with urea,cobalt and nickel salts serving as the precursor by carbon spheres as templates in the aqueous solution system. Cobalt oxides and nickel oxides with the same morphology were obtained when the samples were calcined at 450℃. The samples were characterized by a series of methods and the influences of molar ratio of salts to urea, reaction time, reaction temperature were investigated. Ionic strength and ion charged changes determine the morphology of the product in the process of growth system. The early stage of growth pattern aggregation is dominant, then continuous growth process of solute molecules is the main way. In the homogeneous precipitation process, solution particles have experienced the process of nucleation and aggregation growth and continuous growth.