Preparation of silica aerogel from rice hull ash by supercritical carbon dioxide drying

Silica aerogel, which is a mesoporous light solid material, was prepared from the rice hull ash by sol–gel followed supercritical carbon dioxide drying. The rice hull ash, which is rich in silica, was extracted using sodium hydroxide solution to produce a sodium silicate solution. The solution was neutralized with sulfuric acid solution to form a silica gel. After washing with water and the solvent exchange with ethanol, the aged gel was dried to produce aerogel using supercritical carbon dioxide drying. The prepared silica aerogel was characterized using SEM, TEM and BET measurements. The specific surface area of the rice hull ash aerogel was as high as 597.7 m2/g with a bulk density of 38.0 kg/m3. The diameters of the pores inside the aerogel are between 10 and 60 nm.