Parameters of n-hexanol adsorption on Au (111). Comparison between differential capacity and chronocoulometry results

The adsorption behaviour of n-hexanol on a Au (111) single-crystal electrod e from aqueous 0.2 mol dm(-3) NaClO4 was studied on the basis of dynamic ca pacity measurements and of capacitive charge measurements by chronocoulomet ry. The charge density, sigma(M), as a function of the applied potential, E , and of the n-hexanol concentration was analysed thermodynamically, yieldi ng the Gibbs surface excess, Gamma, and the Gibbs energy of adsorption, Del ta(ads)G degrees, of n-hexanol as a function of potential and concentration . The results of the thermodynamic analysis of the adsorption data at the p otential of maximum adsorption are discussed in comparison with the literat ure data for the adsorption of this compound on Hg [1,2] and on silver sing le-crystals [3,4]. The results obtained show that the adsorption process co uld be described by a Frumkin isotherm, the parameters of which were determ ined and discussed. The values of the standard Gibbs energy of adsorption s uggest physical adsorption of the alcohol, without the existence of specifi c interactions of the adsorbed molecules with gold. Differences and inconsi stencies for the results obtained from the analysis of charge and capacity data are discussed in terms of the experimental technique. (C) 1999 Elsevie r Science Ltd. All rights reserved.