Genesis of selectivity and reversibility for sorption of synthetic aromatic anions onto polymeric sorbents

Many environmentally significant synthetic aromatic compounds such as penta chlorophenol, benzene and naphthalene sulfonates, and benzene carboxylates exist as anions in water over a wide range of pH values. Understandably, bo th ionic charges and nonpolar moieties of these organic compounds govern th eir sorption characteristics. This study reports the results of very favora ble sorption behaviors of these anthropogenic aromatic compounds onto polym eric anion exchangers. Such favorable sorption equilibria are, however, dis tinctively unique because they are all endothermic processes and accompanie d by high positive entropy changes. Solvent dielectric constant, polarity o r moisture content of the ion-exchanger matrix, and the nonpolar moiety (NP M) of the aromatic anion are the three fundamental process variables which govern the overall sorption equilibrium. Anomalous enthalpic and entropic c hanges associated with such sorption processes are explained from a mechani stic viewpoint after taking into consideration appropriate NPM-solvent and NPM-matrix interactions. Experimental observations made in this study are q uite analogous to the transfer of hydrophobic methane from self-associated, polar water phase to nonpolar cyclohexane phase.