High specific surface area TEOS-based aerogels with large pore volume prepared at an ambient pressure

The experimental results on the synthesis of tetraethoxysilane (TEOS)-based silica aerogel with high specific surface area and large pore volume, via ambient pressure drying (APD) route, are reported. The silica aerogels were prepared by the acid-base sol-gel polymerization of TEOS precursor followed by the drying of the alcogels at an ambient pressure. The solvent present in the alcogel (i.e. ethanol) was replaced by a non-polar solvent such as hexane prior to the surface modification step. In order to minimize the drying shrinkage, the surface of the gels was modified using trimethylchlorosilane (TMCS) before the APD. The FTIR spectra of the surface modified aerogels showed Si-CH₃ peaks at 2965 and 850 cm⁻¹. The effect of the base catalyst (NH₄OH) addition to the sol, at different time intervals (T), on the physical and textural properties of the resulting aerogels has been investigated. It has been observed that the surface area and the cumulative pore volume of the aerogels enhanced considerably from 819 to 1108 m² g⁻¹ and 2.65 to 4.7 cm³ g⁻¹, respectively with an increase in the T value from 6 to 48 h. Silica aerogels with very low bulk density (0.06 g cm⁻³), extremely high specific surface area (1108 m² g⁻¹) and large cumulative pore volume (4.7 cm³ g⁻¹) could be synthesized by drying the alcogels at the ambient pressure. The aerogels were mesoporous solids with the average pore size ranging from 12 to 17 nm. The results have been discussed by taking into consideration the hydrolysis and condensation reactions during the sol-gel polymerization of the TEOS precursor.