Adsorption of adipic acid conjugates at the Au(1 1 1) electrode|aqueous solution interface

The adsorption of adipic acid, an aliphatic dicarboxylic acid, has been studied at the Au(1 1 1) electrode|aqueous solution interface by cyclic voltammetry, chronocoulometry and in situ infrared spectroscopy. The voltammograms recorded at different pH values in adipic acid, biadipate and adipate solutions point to the adsorption of anionic species. A potential dependent order–disorder phase transition is apparent from the voltammetric curves, the transition potential being directly influenced by the solution pH. From infrared spectra it is concluded that as the electrode potential is made more positive, the amount of carboxylic groups in the adsorbed layer increases. The maximum surface excess concentration, Γ = (4.4 ± 0.6) × 10−10 mol cm−2, and the adsorption free energy, −ΔadsG = 125–190 kJ mol−1, have been determined by a thermodynamic analysis of the chronocoulometric data.