Study On The Preparation Of SiO₂ Membrane By Bimimetic Synthesis

Biomimetic synthesis imitates the mechanism of biomineralization. In the process of bimineralization, the growth of inorganic material is guided by the organic macromolecules. The elemental way is to form self-assembled organic material as template at first. And then inorganic precursor reacts at the interface of template and solution and forms inorganic-organic composite. Removing the organic template from the composite, we can get inorganic material with special shape and structure. Biomimetic synthesis can produce material with special microstructure, and then improve flow and transport behaviour, catalytic activity, separation efficiency, storage and release kinetics of inorganic material. This paper aimed to synthesize SiO2 membranes with several kinds of microstructures under different conditions by biomimetic synthesis. SiO2 membranes with different microsphere diameters and orders were produced, and composite SiO2 membrane and stratiform SiO2 membrane were also synthesized in the experiment. Microstructure of membrane became further various. The mechanism of production of SiO2 membrane by biomimetic synthesis was also investigated.Organic additive and electric field could control the microstructure of membrane. In the experiment four main factors that affected the microstructure of membrane were discussed. They were concentration of cetyltrimethyl ammonium bromide (CTAB), the concentration of ethyl silicate (TEOS), pH value and temperature. Optimum condition was got though orthogonal experiment with particle size as judgement criteria. At this condition optimum voltage was also got. DSC and TG results showed that all of the template and organic additive could be removed by calcinations at 550℃. And the structure of SiO2 shell was not damaged at this temperature verified by infrared spectroscopy. That the membranes were made by vacant SiO2 microspheres was ascertained by SEM. Microsphere's diameter was different from microsphere's produced at other condition. Diameter of microsphere of 1-3μm or 20-30μm could be got. And these membranes had different microstructures. Combining the results of XRD and TEM, microsphere's structure could be deduced. The shell of the microsphere was made by SiO2 nanometers which distributed stratiformly. The space between stratiforms was occupied by surfactant before calcination. Cell dimension was 3.2-3.7nm and diameter of nanosphere was 15-48nm. The membrane was nanostructure material.Experimental model was S+X-I+(X-=Cl-,Br-)derived from analysis result. Organic additive and electric field were both useful for improving the utilization of TEOS and morphology of membrane. Microsphere's diameter became bigger when organism solved inside the micelle. Diameter of microsphere became smaller in electric field.