Adsorption of butane-1,4-diol at the Hg–aqueous solution interface. Transition with polarization between two ideal adsorption models

Abstract

The adsorption of butane-1,4-diol on a polarized Hg electrode from both NaF and Na₂SO₄ solutions has been studied by means of electrocapillary and capacity curves. Analysis has been carried out both at constant charge and at constant potential. Irrespective of the choice of the electrical variable, adsorption has been found to conform to congruent Langmuir isotherms on the negative side of the adsorption maximum, and to non-congruent isotherms on the other side. Results suggest that molecules adsorb flat on the surface. Non congruence may be described in terms of a saturation coverage linearly decreasing with electric field. The inner layer capacity at constant amount adsorbed has been determined up to saturation coverage over a wide range of electric field. Results are discussed in terms of a polarization-dependent adsorbate–solvent interaction on the surface. A detailed molecular model of the adsorption layer is suggested.