Abstract
Hydrophobic and lipophilic silica aerogel was prepared from water-glass by gelling, aging, silylation, and drying under atmospheric pressure and characterized by FT-IR and SEM. The effect of preparation process on aerogel density and the aerogel density on contact angle of water on it were investigated in detail. pH 6 is most beneficial to shorten gelling time and to obtain the lowest density of silica aerogel. Increasing TEOS concentration of aging solution to 25 v% could decrease aerogel density to 0.093 g/cm3. The silica aerogel exhibits good hydrophobicity even though its density is 0.30 g/cm3. There are few changes in their adsorption capacities after 3 cycles of adsorption-desorption. The adsorption performance of the silica aerogel to organic solvent in water is different from in pure solvents. The critical surface tension (γC) of the silica aerogel prepared here is about 30.8 mN/m. If the surface tension of aqueous solvent solution (γ) is greater thanγC, it will wet the aerogel surface partially. Ifγ ≤ γC, the solution will wet all aerogel surface and be adsorbed well. This work delivers us a method to adsorb solvents from their waste water by adjusting the surface tension of the waste water to lower thanγCof the adsorbent.
Highlights
Silica aerogel [1,2,3,4] is a nanostructured material with open foam-like structures having very low density, high specific surface area (700–1000 m2/g), and extremely high porosity (98%-99%) [5]
Wang et al investigated the adsorption of six volatile organic compounds in vapor, liquid, and aqueous solution on hydrophobic aerogels and found that the rate for adsorption are very different, with the uptake time in the order of about 100 min for vapor, 10 min for solution, and 10 s for liquid
Standeker et al synthesized some silica aerogels and used them to adsorb toxic organic compounds from water. They found that the adsorption capacity of both hydrophobic silica aerogel adsorbents M9 and E6 exceeded the capacity of Advances in Materials Science and Engineering comparable granular activated carbon, for all toxic organic compounds tested in ranges of factors from 15 to 400 [3]
Summary
Silica aerogel [1,2,3,4] is a nanostructured material with open foam-like structures having very low density (as low as 3 kg/m3), high specific surface area (700–1000 m2/g), and extremely high porosity (98%-99%) [5]. Various applications such as thermal super insulation, catalyst support, microfilters, controlled release of drugs, and inertial confinement fusion targets have already been investigated and reported [6, 7] Because of their very high specific surface area and porosity as well as hydrophobicity, silica aerogel is an ideal adsorbent for organic compounds. Its uptake capacity for organics from their aqueous solution cuts down sharply, for example, 87 mg benzene, 223 mg toluene, or 1064 mg p-xylene per gram silica aerogel, respectively [10]. It is the hydrophobicity of silica aerogel that prohibits the aqueous solution of organic compounds entering into the interior pores of silica aerogel, and only external space but not internal space of the aerogel adsorbs the organic compounds. The uptake capacity of these adsorbent will increase greatly in the presence of penetrating agent
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