Adsorption of cresols at the mercury-solution interface

Abstract

The adsorption of cresols at the mercury-solution interface from NaF and from NaOH solutions has been studied by electrocapillary and capacitance methods. An interpretation of results has been attempted with special reference to o-cresol adsorption. The curves obtained in NaF solutions are similar to those obtained for phenol adsorption from neutral media. In NaOH solutions the capacitance minima are well above the capacitance of the supporting electrolyte except when the concentration of cresol is nearly as large as that of the base electrolyte. Adsorption isotherms, pressure-area isotherms, and adsorption potential vs. surface excess curves have been calculated at the p.z.c. These results correspond to a model of four capacitors for the adsorption of o-cresol from NaF solutions, the dielectrics being monolayers of oriented water molecules, flat-as well as vertical-oriented cresol molecules, and a polylayer of flat-oriented cresol molecules. From NaOH solution, however, the adsorption of o-cresol leads only to an incomplete monolayer and an S-shaped adsorption potential curve; the reason is that the adsorbate in this case is the cresoxide ion which exerts a lateral repulsion and undergoes a sharp reorientation. The general model suggested for the adsorption of cresol from neutral or alkaline media consists of six capacitors, the dielectrics constituting monolayers of oriented water molecules, flat- and vertical-oriented cresol molecules, flat- and vertical-oriented cresoxide ions and a polylayer of flat-oriented cresol molecules.