Fast and one-pot synthesis of silica aerogels via a quasi-solvent-exchange-free ambient pressure drying process

Abstract

A very fast (less than 2 h) and one-pot synthetic strategy was developed for the synthesis of silica aerogels. Organic silica gel was first formed under basic condition by adding a predetermined amount of hexane to a freshly prepared silica sol. After aging at elevated temperature for several minutes, the organogel was mechanically crushed and vigorously stirred in a mixture of trimethylchlorosilane and hexane. Finally, silica aerogel was produced by drying the hydrophobized organogel at temperatures higher than 180 °C. The effects of gelation conditions, amount of modification agents, and drying temperatures on the physical properties of the silica aerogels were investigated. The N2 adsorption and desorption measurements indicated that high BET surface areas (up to 725.8 m2/g) could be obtained for the aerogels sintering at 350 °C, while that of the silica aerogels dried at 180 °C were relative lower (from 379.4 to 564.8 m2/g based on the modification conditions). Similar trend was also found in the thermal conductivities of the aerogels, e.g., lower values of thermal conductivity (∼0.025 W/mK) were obtained for the sintering samples, while that of the samples without sintering were relative higher (∼0.034 W/mK). In summary, a fast ambient pressure drying method has been developed, which show a great potential to synthesize silica aerogels in the industrial scale.