Spectroscopic evidence for a cation-P sorption mechanism for polycyclic aromatic hydrocarbons on hydrated mineral surfaces
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NMR spin-lattice relaxation times (T1) for perdeuterated benzene in electrolyte solutions suggest that cation- interactions exist between aromatic hydrocarbons and selected cations in aqueous solutions. An overall binding energy sequence of Ag+ Cs+> K+> Na+, Li+in the aqueous phase is derived based on T1measurements corrected for viscosity effects. Softer metal cations present on hydrated mineral surfaces can directly enhance the sorption of PAH through cation- interactions. Quadrupolar splitting is observed for perdeuterated benzene and deuterated water (natural abundance) in Na-montmorillonite suspensions, while no splitting is observed for deuterated methanol under the same experimental conditions. Because of cation-p interactions and the entropy gradient caused by dissolution of benzene ("iceberg formation" process), benzene can efficiently compete with water for exchangeable cations. On the other hand, methanol is miscible with water due to their structural similarity. This is an abstract of a paper presented at the 222nd ACS National Meeting (Chicago, IL 8/26-30/2001).