Cost-effective synthesis of silica aerogels from fly ash via ambient pressure drying

Silica aerogels were synthesized from the industrial fly ash by ambient pressure drying method. The process consists of two stages, preparation of sodium silicate solution from fly ash by hydrothermal reaction with sodium hydroxide, and synthesis of porous silica aerogels from the obtained sodium silicate solution. Silica wet gels were formed by vitriol-catalysis or resin-exchange-alkali-catalysis of the obtained sodium silicate solution. The trimethylchlorosilane(TMCS)/ethanol(EtOH)/hexane mixed solution was used for solvent exchange/surface modification of the wet gel so as to obtain porous silica aerogels via ambient pressure drying. The results indicated that the synthesized silica aerogels were lightweight and hydrophobic. The BET specific surface area, pore volume and average pore diameter were 362.2–907.9 m2 g− 1, 0.738–4.875 cm3 g− 1, and 7.69–24.09 nm respectively. Particularly, the synthesized silica aerogels by resin-exchange-alkali-catalysis method showed uniform mesoporous structure, and had much higher specific surface area (907.9 m2 g− 1) and pore volume (4.875 cm3 g− 1) than that of by vitriol-catalysis process.