ADSORPTION OF N-HEXANOL ON AG(100) AND AG(110) FROM AQUEOUS 0.05 M KCLO4

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, Delta G degrees(ads) 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 Delta G degrees(ads) 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 Delta G degrees(ads) values for NHEX adsorption is in fairly good agreement with that based on Trasatti's interfacial parameter Delta X (S. Trasatti, J. Electroanal. Chem., 329 (1992) 237), with the hydrophilicity increasing in the order Hg << Ag(111) < Ag(100) < Ag(110); however, the Delta G degrees(ads) Value for Ag(110) is anomalously low.