| SiO2 aerogel is a lightweight nanoporous amorphous material. It has nano-porous structure, high surface area, high porosity, low density and low thermal conductivity. So it has broad application prospects in the field of aerospace, military, medical, insulation, electronics, environmental protection and industrial catalysis. But the high cost of SiO2 aerogels restrict its practical application, which just limited to the aerospace and other high-tech fields. To promote the application of commercial or industrial SiO2 aerogels, the production cost should be reduced.In the paper, online in situ infrared and other technologies were used to study the reaction mechanism of synthesis of SiO2 aerogels. In the microwave and ultrasonic irradiation conditions, TEOS used as raw materials, sol-gel two-step acid-base as catalyzing method. SiO2 aerogels, with high surface area, were prepared by ambient dying. This method can reduce the production cost. The surface modification of SiO2 aerogels , process optimization, aerogels drying technics were investigated. Atmospheric CO2 drying method and supercritical drying method were compared respectively. Adsorption properties of aerogels were also investigated. They were used to deal with the water polluted by oil.1. The online in situ infrared analysis system was applied to monitor the reaction process of SiO2 aerogels, tracking reactants, intermedias and products's real time changes. The reaction mechanism was analyzed. The effect of acid catalyst, reaction temperature, pH, and reaction solvent on the hydrolysis reaction were studied.2. The trimethylchlorosilane(TMCS) , dimethyldichlorosilane(DMCS) , methacrylate-based trimethoxysilane (KH570) were used to prepare SiO2 aerogels. The hydrophobically modifed process was discussed and the grading of hydrophobic modification process were proposed. The results show that: TCMS suits the hydrophobically modified technique for classification, the prepared SiO2 aerogels SBET=695.23-m2/g, the nanoparticle size are 50-100 nm, pore size distribution are 2-70 nm, heat-stable temperature is 440℃, hydrophobic angle is 160o. DMCS are suit for the surface modification process. The prepared SiO2 aerogels SBET=656.55m2/g, particle size are 20-40 nm, pore size distribution are 2-120 nm. Silica aerogels modified with KH-570 exhibited good hydropholic performance with the surface area of 877.17 m2/g. This material was composed by the accumulated spherical nano-particles. The particles'size was in the range of 10-50 nm and that of the pore size was 1.9-2.5 nm. They are the typical nano-mesoporous materials. It exhibites good hydrophobic performance with heat resistance of 407℃. If the carbon-carbon double bonds and a reactive carbonyl functional groups were connected to the surface of the aerogels , it can be used for the preparation of new polymer composites.3. The microwave was introduced to the SiO2 aerogel synthesis reaction as energy. The microwave inner heating methods could change the microstructure of aerogels, strengthen the network structure. It can avoid follow-up pressure drying of nanopores'collapse. The aerogels prepared by ambient drying have SBET=1092.11m2/g, which reduced the production cost. The aerogels prepared by microwave exhibited internal porous surfaces with a closed structure. It is not easy to absorb moisture in the air. This can solve the problem that the hydrophilic aerogels easy to collapse after adsorption water. The aerogels exhibited superior thermal stability than that prepared by a water bath. Microwave prepared hydrophobic SiO2 aerogels have hydrophobic angle 153o, they exhibte good heat stability with SBET=831.56m2/g and pore size distribution of 214 nm.4. SiO2 aerogels synthesis was in response to the introduction of ultrasonic waves as an auxiliary energy. The mechanical and cavitation effects of ultrasound could effectively promote the hydrolysis reaction and nano-particles dispersed in the sol-gel system. Aerogels are deposited by the nano-scale spherical particles with particle size of 30-100 nm, which has open porous structure. Ultrasound improves the specific surface area and the porous structure of aerogels. Under ambient pressure drying, the SBET of hydrophilic aerogels are 763.52 m2/g and that of TMCS modified aerogels are 801.71 m2/g. The pore size distribution are 0.5-1 nm, hydrophobic angle is 160o, heat stable temperature is 460℃.5. Surface aera and packing density used as the standard for evaluation the aerogels. Drying temperature, drying pressure, CO2 flow rate, drying time are the experimental factors. Design the orthogonal experiment with four factors and three levels, optimizing the CO2 supercritical drying process. The optimun conditions are as follows: CO2 flow rate 12kg/h, drying temperature 45℃, drying pressure 13 MPa, drying time 6 h. The SiO2 aerogels prepared by bath supercritical drying were deposited by spherical nanoparticals. Their characteristics are: SBET=927.37 m2/g, density 0.1956 g/cm3, particle size 10-30 nm, pore size distribution around 10 nm. They are typical nano-mesoporous materials. Microwave SiO2 aerogels prepared by supercritical drying had pore structure with large holes. This method destroyed the dense outer surface of the aerogels. Their SBET are 901.59m2/g, which are smaller than that of the aerogels prepared by microwave ambient pressure drying.6. The adsorption properties of SiO2 aerogels were investigated. The surface area, pore structure and pore size distribution variation law of SiO2 aerogels before and after adsorption organic solvents were analyzed. Aerogels kept high surface area, pore structure and pore size distribution without change after adsorption. These kind of aerogels can use for adsorbing organic matter in the water and can be recycled. The hydrophobic SiO2 aerogels prepared by microwave can adsorb organic solvent most effectively, the adsorption rate could be up to 763%. If they adsorb kerosene, the kerosene content was 0.08163 g/g before adsorption, which was 9.85×10-7 g/g after adsorption. If they adsorb crude oil, the crude oil content was 0.08352 g/g, which was 1.59×10-6g/g after adsorption. The preformance of SiO2 aerogels is excellent if used in oil pollution control.
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