On the Conditions of Deposition of a Two-Component Adsorption Layer for the Frumkin–Damaskin Isotherm

Abstract—A system of two equations of joint adsorption from a liquid solution according to the Frumkin–Damaskin isotherm is investigated. Conditions for the uniqueness of the solution of these equations with respect to the surface concentrations of adsorbates are derived analytically in terms of a three-parameter description of the isotherm at given values of their volume concentrations. Nonuniqueness of solutions is traditionally interpreted as the possibility of separation of the adsorption layer. The results of numerical calculations of the nonuniqueness of these solutions arising when the conditions for uniqueness are violated are presented using particular examples.