Synthesis Of Functional Nanostructures Assisted By Cellulose-based Polymeric Surfactants

Metal oxide and complex metal oxide nanostructures have exhibited great application potentials, and become a popular research subject in materials chemistry. Single crystals have a basic property of anisotropy and exhibit different physical and chemical properties on various facets or in diverse directions. Therefore, it is believable that the controllable synthesis of metal oxide and complex metal oxide nanostructures with different morphologies and assembling behaviors to further tune their chemical and physical properties will benefit the improvement of their optical, magnetic and catalytic properties for basic research and technology applications.In this thesis, a series of novel metal oxide and complex metal oxide nanostructures have been synthesized through hydro-/solvo-thermal approaches in the presence of cellulose-based polymeric surfactants. The morphologies of these nanostructures were successfully controlled by changing the reaction conditions. The properties of the nanomaterials were studied and the relationship between the properties and morphology of the nanomaterials were discussed. The main contents of our work are summarized as follows:1. Self-assembled structures with highly specific morphology could bring brand-new properties. Hierarchically complex hollow cage-like ZnO superstructures assembled by nanorods have been successfully constructed in the presence of sodium carboxymethyl cellulose. The number of the hollow cage could be adjusted from single-cage, double-cage, multi-cage to connected-cage. A possible formation mechanism of the hollow superstructures has also been proposed. The catalytic properties on the decomposition of AP of the various ZnO superstructures have been studied. The results showed that all the superstructures have good catalysis properties, and the single-cage superstructures show enhanced activity over other multicage superstructures.2. The CMC, a kind of water-soluble polymer, is not only reactant but also crystal growth modifier. By adjusting the experiment conditions such as the molar ratio of the reactants, the reaction temperature, and the reaction time, several manganese-based (with the Mn oxidation states from+2to+4) nanostructures including Mn3O4octahedrons, MnOOH nanorods, MnO2nanowires and aggregated MnCO3nanoparticles in the form of spindles can be obtained through the redox reaction between KMnO4and CMC. The study of the direct electrochemical behavior of cytochrome c (Cyt. c) immobilized on octahedral Mn3O4modified glassy carbon (GC) electrode shows that the octahedral Mn3O4nanoparticles could promote the direct electron transfer between Cyt. c and the electrode.3. Because high-index facets usually have high surface energy, these facets can endow nanocrystals with high catalytic activities or bring brand-new properties. We report for the first time two kinds of iron oxide crystals in the hexagonal crystal system:tetrakaidecahedra and oblique parallelepipeds with high-index facets exposed. Owing to the fact that iron oxide belongs to the hexagonal system, these exposed high-index facets are very special, and the two kinds of brand-new polyhedra have never been reported before. Magnetic studies uncovered that these two forms of iron oxide have distinct differences. The tetrakaidecahedral iron oxide nanocrystals might be spin-canted ferromagnetically controlled at room temperature, and the ferromagnetism disappears at temperatures lower than Tm. The oblique parallelepiped nanocrystals might have coexistent spin-canted and defect ferromagnetism at room temperature and be defect ferromagnetically controlled at low temperature.4. Inorganic crystals with highly specific morphology by a self-assembling process may have brand-new properties. Hierarchically novel drum-like Cd(OH)2superstructures have been successfully obtained. The drumlike superstructures are accumulated by numerous polyhedral units, and the polyhedral unit is an incomplete structure of a double hexagonal pyramid. A possible formation mechanism of the drum-like Cd(OH)2superstructures has also been proposed. The as-prepared Cd(OH)2could be transformed into CdO superstructures by calcining in air. These Cd(OH)2and CdO superstructures have been demonstrated to have good catalytic properties to decrease the decomposition temperature of ammonium perchlorate.5. Surface-dependent physical and chemical properties are very important in crystals, which makes it very important to control exposed surfaces of a functional material. The polyhedral ZnSnO3crystals with different exposed facets have been prepared successfully in the reaction system of methylcellulose alcohol solution via a solvothermal method. Simply by adjusting the amount of the added NaOH in the reaction system, the polyhedral crystals include hexahedron, truncated hexahedron,14-faceted polyhedron, truncated octahedron, and octahedron can be obtained.6. Other relevant work. Various ZnO with various distinct morphologies have been successfully synthesized via a simple double-solvent thermal method in the presence of glycine. The morphologies of the products can be successfully controlled from superstructures to microplates by adjusting the amount of water in the EtOH/H2O system. The catalytic properties on the decomposition of AP and photoluminescence properties of the various ZnO superstructures have been studied.Cobalt ion-based coordination nanostructures have been synthesized by using acetylacetone and hydrazine as chelating agents by a simple solution-based method in the absence of surfactant. The morphology of products can be controlled from spheres to nanowires by adjusting the reaction temperature and time.