Edmiston, P. L.; Underwood, L. A. “Absorption of Dissolved Organic Species from Water Using Organically Modified Silica that Swells.” Separation and Purification Technology 66: 532-540 (2009).
Organically modified silica that rapidly and reversibly swells to >3 times their dry volume have been recently described. Here, these organosilica materials were demonstrated to have the ability absorb trichloroethylene (TCE), perchloroethylene (PCE), methyl t-butyl ether (MTBE), toluene, naphthalene, acetone, 1,4-dioxane, and 1-butanol from water. Direct experimental comparisons indicated that swellable organically modified silica (SOMS) has in many instances greater capacity than activated carbon and molecular sieves and possesses the ability to capture a wide range of dissolved polar and non-polar organic contaminants. The absorption of organic species to SOMS is enhanced by matrix expansion leading to non-selective capture of organics beyond what could only be attributed to physisorption. This process appears to be facilitated by initial adsorption events unlatching the collapsed matrix leading to the opening of nanometer-scale pores within the tensioned SOMS material, thus providing volume for absorption. Partition coefficients for the absorption of organic species from water by SOMS ranged from 2.8 × 105 to 1.0 × 102, and vary depending on polarity of the contaminant, concentration, and the total mass of contaminant absorbed. Maximum capacity exceed three times the dry weight of the absorbent under conditions of high contaminant concentration. SOMS was repeatedly regenerated with mild thermal treatment (60–110 °C) in air to evaporate absorbates from the matrix which could be subsequently collected. Only a slight decrease in effectiveness is observed after regeneration. Absorption is equally effective from salt water. Minimal loss of capacity and affinity is lost when extracting environmentally relevant concentrations of TCE from a topsoil/water mixture, presumably due to a molecular sieving effect.