Adsorption States of Pyridinecarboxylic Acids on Gold Electrode Surface Studied by Infrared Reflection Absorption Spectroscopy

• Published in: BUNSEKI KAGAKU Vol. 56; no. 6; pp. 457 - 464
• Main Authors: NANBU, Noritoshi, KITAMURA, Fusao, OHSAKA, Takeo, TOKUDA, Koichi
• Format: Journal Article
• Language: Japanese; English
• Published: Tokyo The Japan Society for Analytical Chemistry 2007; Japan Science and Technology Agency
• Subjects: adsorption; FT-IRAS; gold electrode; ortho effect; pyridinecarboxylic acid
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.56.457

Adsorption behavior of three isomeric pyridinecarboxylic acids (picolinic acid: 2-PCA, nicotinic acid: 3-PCA, and isonicotinic acid: 4-PCA) on a smooth polycrystalline gold electrode surface was investigated in three electrolytic solutions, 0.1 mol dm−3 HClO4, NaClO4, and NaOH aqueous solutions, by in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). The reversible adsorption/desorption and reorientation of the PCAs were observed over the potential range investigated. The adsorbed PCAs existed as either zwitterions or anions, i.e., the carboxylate group of the PCA molecule was not protonated. In the HClO4 aqueous solution, it was found that as the electrode potential became more positive, adsorbed 3- and 4-PCAs reoriented from a flat (parallel) configuration to a vertical one that binds to the surface through lone pairs of electrons on the two oxygen atoms of the carboxylate group. In the NaClO4 aqueous solution, adsorbed 3-PCA and 4-PCA anions showed the flat configurations. In the NaOH aqueous solution, 3-PCA and 4-PCA anions adsorbed in the flat and the vertical configuration, respectively. No significant adsorption of 2-PCA was observed in the HClO4 and the NaOH aqueous solution. 2-PCA anion adsorbed in the flat configuration only in the NaClO4 aqueous solution. These findings indicate the ortho effect on adsorption.