Spectroscopic evidence for a cation-p sorption mechanism for polycyclic aromatic hydrocarbons on hydrated mineral surfaces
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abstract
Spectroscopic evidence for a cation-p sorption mechanism for PAH on hydrate mineral surfaces was presented. NMR spin-lattice relaxation tomes (T1) for predeuterated benzene in electrolyte solutions suggested that cation- interactions existed between aromatic hydrocarbons and selected cations in aqueous solutions. An overall binding energy sequence of Ag+ Cs+> K+> Na+, Li+in the aqueous phase was derived based on T1measurements corrected for viscosity effects. Linear equilibrium sorption isotherms were observed for sorption of naphthalene and pyrene to all cation-saturated minerals. Quadrupolar splitting was observed for predeuterated benzene and deuterated water (natural abundance) in Na-montmorillonite suspensions, while no splitting was observed for deuterated methanol under the same experimental conditions. The quadrupolar splitting of deuterated benzene in Na-montmorillonite suspensions demonstrated the ordering of sorbed benzene molecules, which likely resulted from the cation-p interaction between benzene and exchangeable cations. Although methanol was more polar than benzene, it was not polar enough to compete with water for exchangeable cations. No significant sorption of methanol to mineral surfaces was expected, and as a result, no quadrupolar splitting could be observed for deuterated methanol.
