Adsorption o n-hexanol on Ag(100) and Ag(110) from aqueous 0.050 M KCl04

The adsorption behaviour of n-hexanol (NHEX) on a Ag(100) single-crystal electrode surface from aqueous 0.05 M KClO4 was investigated on the basis of capacitive charge measurements carried out by a computerized chronocoulometric apparatus. The adsorption data were analysed thermodynamically and the resulting parameters were compared with a molecular model (R. Guidelli and M.L. Foresti, J. Electroanal. Chem., 197 (1986) 103), leading to the conclusion that the NHEX molecules are adsorbed in a flat orientation just as on mercury and on Ag(111). The standard Gibbs energy of adsorption, ΔGads°, on Ag(100) was determined as a function of the electrode potential and of the capacitive charge density. The differential capacity at the interface between Ag(110) and aqueous 0.05 M KClO4 was found to be only very slightly depressed upon saturating the solution with NHEX: this points to a vanishingly small adsorptivity of NHEX on this face. The adsorption parameters for NHEX adsorption on Ag(100) are compared with those on Ag(111); in particular ΔGads ° at the potential of maximum adsorption equals -17.7 kJ mol-1 on Ag(100) and -18.4 kJ mol-1 on Ag(111). The scale of hydrophilicity for sp metals, Ag(100) and Ag(111), based on the corresponding ΔGads° values for NHEX adsorption is in fairly good agreement with that based on Trasatti's interfacial parameter ΔX (S. Trasatti, J. Electroanal. Chem., 329 (1992) 237), with the hydrophilicity increasing in the order Hg ≪ Ag(111) < Ag(100) < Ag(110); however, the ΔGads° value for Ag(110) is anomalously low.