Spectroscopic evidence for a pi-cation sorption mechanism for polycyclic aromatic hydrocarbons on hydrated mineral surfaces
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abstract
The spectroscopic evidence for a pi-cation sorption mechanism for PAH (naphthalene and pyrene) on hydrated mineral surfaces was studied. Linear equilibrium sorption isotherms were observed for sorption of naphthalene and pyrene to all cation-saturated silica gels. For both sorbates, Cs-saturated gels had the highest partition coefficients. The NMR spin-lattice relaxation time (T 1 ) value of deuterated benzene (C 6 D 6 ) decreased with increasing salt concentration, e.g., NaCl, KCl, CsCl, AgNO 3 ; the greatest decreases in T 1 occurred in the AgNO 3 and CsCl solutions. The coordination of Ag + by NH 3 H 2 O significantly increased the T 1 of C 6 D 6 as compared to AgNO 3 solutions without NH 3 H 2 O. The pi-cation interactions could exit between PAH and selected cations in aqueous solutions. Pi-cation interactions between PAH and exchangeable cations of hydrated minerals might explain variation in partition coefficients observed for sorption of naphthalene and pyrene to silica gels and other minerals saturated with different cations.
