In situ Raman Spectroscopy of Aza-Arenes Adsorbed at the Aqueous/Silica Interface

Abstract

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 p K_a of the compound. A protonated aza-arene/ClO₄⁻ ion pair interacts with surface sites in aqueous solutions in which the pH is below the pK_a of the compound. These results may be useful in predicting the fate of these environmentally significant compounds in groundwater.