Raman spectroscopy is used to study the effect of pH on the solute/sorbent interactions and the chemical nature of the adsorbed species at the aqueous/silica interface for the aza-arenes acridine, quinoline, and pyridine. The neutral aza-arene is hydrogen-bonded to surface sites in aqueous media in which the pH is above the pKa of the compound. A protonated aza-arene/ClO4 ion pair interacts with surface sites in aqueous solutions in which the pH is below the pKa of the compound. These results may be useful in predicting the fate of these environmentally significant compounds in groundwater.
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