Preparation Of Porous Metal Oxides With Micro/Nano Structures And Study On Their Growth Mechanisms

This dissertation is intended to supplement and develop precursor calcinations routes to synthesize porous inorganic materials and use templates to prepare micro- or nano-scale biomimetic inorganic materials. On the basis of previous work, we have developed some novel mild routes to fabricate porous metal oxides (MgO and CuO) and micron- or nano-scale inorganic biomimetic materials (CdS and ZnO). The control of the morphology and size of the products has also been investigated. The details are summarized as follows:1. The macroporous CuO has been produced with glycine as template and Cu(NO₃)₂ aqueous solution as copper source. The morphologies of the products could be tuned through varying solvent, reaction temperature, copper sources and the reactants concentrations. On the basis of the experimental results and previous literatures, a possible growth mechanism has also been proposed. Moreover, CdS dendrites have been successfully generated using glycine as structure-directing agent.2. On the basis of previous work, combined the traditional templating method with the calcination technique, a template-assisted calcination route has been applied to synthesize porous materials. The morphologies of porous MgO could be controlled through using different templates, such as poly (vinyl pyrrolidone) (PVP) and dextran. Studies found that the templates had an important role on the products. The experimental route has perfected clacinations reactions and can be easily extended into the preparation of other metal oxides crystals. All above studies has increased our understanding on the calcinations techniques and provided efficient routes to porous inorganic materials.3. A facile thermal decomposition route has been developed for the synthesis of metal oxides using inorganic salt solution as precursors. The porous MgO nanoplates have been produced through calcinations of only aqueous Mg(NO₃)₂ solution. The method has also been applied to grow mushroom-like ZnO microcrystals by using Zn(NO₃)₂ solution as precursor instead of Mg(NO₃)₂ solution. Compared with previous methods, our new route has the following features: (i) the system does not need any protective gases; (ii) the raw materials are inexpensive, and the manipulation is simple; (iii) the route has enriched the methods of preparing micro- or nano-scale materials. 4. Based on previous literatures, a feasible solvothermal/hydrothermal approach was enriched and developed. The material with novel morphology — bone-like MgO nanocrystals has been achieved by the thermal decomposition of an organic metal precursor, which was pre-prepared by a solvothermal process. Some crucial factors, such as the solvothermal temperature, the volume ratio of absolute alcohol to water, and the amount of Mg powders, affected the products formation. This is the first report related to the synthesis of nanobones. The products growth mechanism was also discussed. The tlower-like ZnO microcrystals have been synthesized through a precursor process followed by a hydrothermal process. The microcrystals are self-assembled by nanoplates. The precursor is pre-obtained by a precipitation reaction.