A cost-effective and fast synthesis of nanoporous SiO2 aerogel powders using water-glass via ambient pressure drying route

Considering the need for large-scale production of silica aerogel powders, the present research was aimed to develop a simple, cost-effective and rapid process based on water-glass precursor via ambient pressure drying (APD) route. It has been shown that the surface chemical modification of hydrogels can rapidly be carried out with extremely low doses (e.g. 5 g of hexamethyldisilazane (HMDS) for 100 g of hydrogel) of HMDS by a co-precursor method which makes this process quite cost-effective. The surface modification in the aqueous phase essentially resulted in the displacement of the pore water and the simultaneous one-step solvent exchange using n-hexane converted the hydrogel into an organo-gel in 3 h and thus the total processing time of the aerogel powder production via APD could drastically be reduced to 5 h. The solvent n-hexane could be recollected during the drying stage and it does not add much to the material cost. The aerogel powders with tapping densities and specific surface areas in the range of 0.100–0.309 g/cm3 and 473–776 m2/g, respectively, could be synthesized using this novel route. The surface modification of the aerogel powders was explored by means of X-ray photoelectron spectroscopy (XPS) in conjunction with the Fourier transform infrared (FT-IR) spectroscopy. The textural investigations revealed that the aerogel powders with a wide variation in their pore size distributions and average pore diameters can easily be synthesized by varying the silica content in the sol.