Quantitative studies of benzonitrile adsorption at the low-index gold single crystal electrodes

Abstract

The adsorption of benzonitrile (BN) on the Au(111), Au(100), and Au(110) electrodes in aqueous solutions was investigated. The chronocoulometric technique was used to measure the charge density at the metal surface as a function of the electrode potential for BN concentrations ranging from 0 to 0.030 M. The adsorption parameters such as the film pressure, the surface concentration of the organic adsorbate, the standard Gibbs energy of adsorption (Δ G ads 0), and the charge flowing to the interface per one adsorbed molecule, were determined from the thermodynamic analysis of the charge density data. The analysis was carried out at constant electrode potential and at constant charge density. In addition, subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) was employed to determine the orientation of BN molecules at the Au(111) surfaces. The thermodynamic and spectroscopic data indicate that BN molecules assume a flat (π-bonded) state at the negatively charged surface and progressively reorient from the flat to the tilted (N-bonded) state as the charge at the metal surface becomes more positive. At very positive potentials the character of BN adsorption becomes reactive and the adsorbed molecules partially hydrolyze to form benzamide (BA).