ABSTRACT
The pore size, surface area, and density of silica gel were controlled by drying silica alcogel in ambient conditions and using supercritical ethanol extraction to obtain silica xerogel and silica aerogel, respectively, in the present study. The samples were characterized by N2 gas adsorption at −196°C, scanning electron microscopy and Fourier transform infrared (FTIR) spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The effect of time on surface characteristics of silica aerogel up to three-month storage time was investigated by N2 gas adsorption. The functional groups of the xerogel and silica aerogel and a commercial mesoporous silica gel were examined by FTIR transmission spectroscopy. The effects of pressure, relative humidity, and temperature on hydration–dehydration behavior of silica aerogel and silica xerogel were investigated using a temperature and pressure-controlled chamber in diffused reflectance cell of FTIR spectrophotometer. It was observed that free water was eliminated from the samples 142under vacuum at ambient temperature. Hydrogen-bonded OH groups and isolated OH groups were eliminated partially by heating the samples up to 500°C. The samples heated up to 500°C and cooled to ambient conditions had still had the capability of adsorbing free water.
