Effect of surface modification on physical properties of silica aerogels derived from fly ash acid sludge

• Silica aerogel was successfully synthesized from fly ash acid sludge.
• Effect of surface modification on the properties of silica aerogel was investigated.
• The modified aerogel exhibited better performance than that of the unmodified aerogel.
• The modified aerogel exhibited strong hydrophobicity.

The silica aerogels were synthesized using fly ash acid sludge via ambient pressure drying. The silica in the fly ash acid sludge was extracted using a NaOH solution to form the sodium silicate solution. Silica wet gels were formed by sol–gel process of the obtained sodium silicate solution. To prevent the condensation and shrinkage of the wet gel structure during drying, the surfaces of wet gel were modified using trimethylchlorosilane (TMCS) via solvent exchange and surface modification. The effects of surface modification on the textural and physical properties of the silica aerogels were investigated. The properties of the synthesized silica aerogels were analyzed with SEM, BJH, FT-IR, DTA-TG and contact angle measurement. The results indicated that the silica gel modified using TMCS could undergo reversible shrinkage during ambient pressure drying and thereby preserved mesoporous structure. The modified aerogel had much lower density (0.085 g/cm3), higher specific surface area (700 m2/g) and larger pore volume (3.29 cc/g) than those of the unmodified aerogel. The contact angle measurements indicated that the modified aerogel had a hydrophobic property with contact angle of 140°.

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