Adsorption and stability of phthalic acid on a colloidal silver surface: surface-enhanced Raman scattering study

Abstract

The adsorption characteristics of phthalic acid on a silver surface were investigated by means of surface-enhanced Raman scattering (SERS). For a reliable analysis of the SER spectrum, we also performed an ab initio vibrational wavenumber calculation, The SER spectral features dictated that the phthalic acid molecules should be bound to silver as dicarboxylate, but in contrast with earlier reports, with a strongly tilted orientation with respect to the surface normal. The degree of tilt appeared to increase with increase in the bulk pH, Such a tilted orientation was presumed to occur by the simultaneous sigma- and pi-type coordination of carboxylate groups to silver caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups. Probably owing to the latter effects, phthalic acid on silver was easily displaced with aromatic mono-acids that could be bound to silver by forming only sigma-type coordination. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for an aromatic carboxylic acid derivative to assemble a robust monolayer on a silver surface. Copyright (C) 2000 John Whey & Sons, Ltd.