Preparation of silica aerogel from rice hull ash by drying at atmospheric pressure

The silica aerogel was prepared by a sol–gel process followed the drying process at atmospheric pressure and 40 °C. The silicon source was the rice hull ash, which is an agricultural waste and rich in silicon. The rice hull ash was extracted with sodium hydroxide solution to get a sodium silicate solution. The solution was neutralized with sulfuric acid solution to form silica hydrosol, which was immediately added appropriate quantity of tetraethyl orthosilicate (TEOS), and then gelated to be a gel. The aged gel was washed successively by water and ethanol, and finally dried at the atmosphere. The prepared material was characterized using transmission electron microscope (TEM) and Brunauer–Emmett–Teller (BET) measurements. The specific surface area of the prepared material is high as 500 m2/g with a bulk density of 0.33 g/cm3. The diameters of the pores inside the prepared materials are between 5 and 60 nm.