Shape-Controlled Synthesis Of Sio₂ Micro-nano Structure

It is great significance for the production of micro-nano materials with special morphology, size and hierarchical structure from viewpoint of both in basic scientific research and practical applications, and is attracting ever-increasing attention by researchers. So it is an important topic to design and fabricate these materials with special morphology, size and hierarchical structure, and to study on the relations of their structure and properties.In this thesis, we focused on the preparation of SiO2 with different morphology and micro-nano structure by evaporation-induced self-assembly (EISA) using the cetyltrimethyl-ammonium bromide (CTAB) as template and sodium silicate (SS) as silicon source in the mixed medium of ethyl acetate and water. In the process of the EISA, the hydrolysis and polycondensation of silicate species were adjusted and controlled by the hydrolysis of ethyl acetate (EA) in SS/CTAB/H2O synthesis system, which lead to the change of the acidity and basicity of sythnsis system. Self-assembly was undergone between surfactants and inorganic precursors by the electrostatic charge-matching, silicate species interact with the cationic head groups of the CTAB, Finally, the resulting materials were characterized by N2 adsorption-desorption, FT-IR, XRD, SEM, TEM.It was found that the formation of the SiO2 with micro-nano structure is determined on the formation of crystal nucleus of SiO2. The crystal nucleus grows into SiO2 spheres, and links into fibers forming into three-dimensional space. Finally, coral SiO2 with micro-nano structure was fabricated. We also found that the SiO2 nanocages can be produced for the lowering of the surface free energy of the coral SiO2 by aging of coral silica in alcohol. The morphologies and structures of macroporous silica cages were strongly affected by various synthetic conditions, including the molar compositions of reactants, the evaporation time of solvent, and the ageing conditions.Porous silica nanotubes with similar structure of silica nano cages were also produced by changing of the parameters of the synthesis system. Porous silica nanotubes show that their microscopic structures are identical to the synthesized silica cages, indicating the formation of porous morphologies due to the different nucleation-controlled process and the similar mechanism of silica cages. Interestingly, silica chiral nanotubes with well-distributed pore size and order structure were also obtained by altering of the parameters in the same synthesis system. It suggested that a new methods to prepare the chiral nanotubes not using achiral surfactant as template was developed.In conclusion, a new reaction system was developed in this thesis, a variety of micro-nano SiO2 with different morphology and structure was synthesized by controlling the experimental conditions. It is also considered as promising materials possess many potential applications in catalysis, chiral catalysis, drug delivery, material separation etc.