Adsorption behavior of pyridinecarboxylic acids in acidic solution on a polycrystalline gold electrode surface studied by infrared reflection absorption spectroscopy

Adsorption behavior of three isomeric pyridinecarboxylic acids (picolinic acid: 2-PCA, nicotinic acid: S-PCA, and isonicotinic acid: 4-PCA) in 0.1 M (M=mol dm(-3)) HClO4 solution on a smooth polycrystalline gold electrode surface was investigated by in situ infrared reflection absorption spectroscopy (IRAS). As the electrode potential became more positive, adsorbed 3- and 4-PCAs were found to reorient from a flat configuration to a vertical one that binds to the surface through lone pairs of electrons on two oxygen atoms of the carboxylate group. However, no significant adsorption of 2-PCA occurred an the electrode surface, and this finding indicates the ortho effect on adsorption.