Sorption of Phenanthrene from Water onto Alumina Coated with Dianionic Surfactants

Abstract

An aluminum oxide (alumina) coated with three dianionic surfactants (commercial DOWFAX) was examined for its effectiveness to sorb phenanthrene from water, as a function of the surfactant loading rate and the surfactant alkyl chain length. The results showed that the dianionic surfactants adsorbed on alumina are effective phases for the sorption of nonionic organic compounds (NOCs) such as phenanthrene, increasing the apparent distribution coefficient (K*) of phenanthrene onto the solid phase by up to 3 orders of magnitude. The effectiveness of the surfactants as sorptive phases was shown to increase with their carbon content (i.e., the alkyl chain length). To distinguish between the contributions to the sorption of phenanthrene by surfactant monolayers and bilayers, the partitioning of phenanthrene onto the surfactant coated alumina was quantified over a large range of surfactant loading. Compared on a unit surfactant mass basis, the bilayers of the dianionic surfactants are approximately 3−6 times as effective in terms of sorbing phenanthrene from water than the corresponding monolayers, showing that the organic carbon-normalized partition coefficient for these two sorbed surfactant phases differs. It was also shown that, on a per unit surfactant mass basis, the partitioning of phenanthrene between the adsorbed dianionic surfactant phases (monolayers and bilayers) and water is 5−7 (15 in one case) times more effective than that between the corresponding surfactants phases (monomers and micelles) in the aqueous phase and water.