Spectroscopic evidence for a pi-cation sorption mechanism for polycyclic aromatic hydrocarbons on hydrated mineral surfaces
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Sorption mechanisms of nonpolar organic chemicals (NOCs) to inorganic surfaces are not fully understood. The NMR spinlattice relaxation time (T1) of deuterium labeled compounds can be related to molecular rotational correlation times. This provides direct observation of NOC interactions with ionic solutes and mineral surfaces. The T1 value of deuterated benzene decreased with increasing salt concentration (e.g., NaCl, KCl, CsCl, AgNO3); the greatest decreases in T1 occurred in the AgNO3 and CsCl solutions. Complexation of Ag+ by NH3-H2O reduced the influence of Ag+ on the molecular rotation of d6-benzene. These results suggest that pi-cation interactions can exist between polycyclic aromatic hydrocarbons (PAHs) and selected cations in aqueous solutions. Additionally, pi-cation interactions between PAHs and exchangeable cations of hydrated minerals may explain variation in partition coefficients (Kd) observed for sorption of naphthalene and pyrene to silica gels and other minerals saturated with different cations.
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ACS Division of Environmental Chemistry, Preprints