Adsorption of 4‐hydroxybenzoic acid on silver investigated by surface‐enhanced Raman scattering

Abstract

AbstractSurface‐enhanced Raman scattering (SERS) of 4‐hydroxybenzolc acid (4HBA) was investigated in a silver sol and at a silver electrode. The adsorption behaviour of 4HBA on the sol surface appeared different from that on the electrode surface. It was concluded that the molecule binds to the sol particle surface as either oxidobenzoate or hydroxybenzoate assuming a flat orientation. The former species that was bonded to silver via both the lone pair electrons of the oxido group and the π orbitals of the carboxylate group was more stable in a basic environment On the electrode surface, the molecule seemed to bind as hydroxybenzoate mainly through the oxygen lone pair electrons of the carboxylate group, with the hydroxyl group being pendent to the surface. From the pH dependence of the SER spectral pattern, the acid strength of the hydroxyl group was estimated to become 104 times stronger on the sol surface in comparison with that in the bulk. The nature of the different adsorption mechanisms observed on the sol and electrode surfaces is not yet certain. Tentatively, the difference was attributed to the different surface morphology along with the intrinsic difference in the nature of SERS active sites on the two surfaces.