Hydration of pyridine-4-carbaldehyde at the silver–water interface: a pH-dependent surface enhanced Raman study

Abstract

Surface enhanced Raman (SER) spectra of samples in silver sole have been used to monitor the relative concentration of protonated and neutral pyridine-4-carbaldehyde (4PCA) on the silver surface, which is shown to depend on the solution pH. At low pH, the relative amount of adsorbed free aldehyde decreases as the molecule becomes hydrated.

When the pH value is in the range 5 < pH < 6, most of the aldehyde is protonated and consequently the presence of free aldehyde is not shown in the SER spectrum. As the pH increases further, the neutral hydrate becomes the adsorbed species. The identical nature of the SER spectra of 4-PCA and 4-pyridylmethanol at pH 6.45 confirms the complete hydration of surface adsorbed 4-PCA molecules.