Solvent removal from water with hydrophobic aerogels

Hydrophobic aerogels are shown to be efficient absorbers of solvents from water. Solvents miscible with water are separated from it because the solvents are more volatile than water and they enter the porous aerogel as a vapor across the liquid water/solid interface. Solvents that are immiscible with water are separated from it by selectively wetting the aerogel. Adsorption isotherms are presented for hydrophobic silica aerogels, for several solvents (e.g., toluene, ethyl alcohol, trichloroethylene, chlorobenzene) in water mixtures. The adsorption capacities are compared with the standard activated carbon. Our measurements show that the adsorption capacity of the hydrophobic silica aerogels exceed the capacity of comparable granular activated carbon (GAC), on a gram-per-gram basis, for all of the solvents tested. The improved performance of adsorption capacity by the aerogel over the GAC ranged from factors of ∼30 times for low molecular weight, highly soluble solvents, to factors of 130 times for immiscible solvents.