Specific ion adsorption at liquid vertical bar liquid interfaces: effect of the ionic charge

The effect of the charge of adsorbed ions on their surface concentration wa s examined for a series of negatively charged ions at the water \ 1,2-dichl oroethane (DCE) interface. Langmuir and Frumkin isotherms and Coulomb law w ere used to fit the experimental data. The limiting surface concentration G amma(s), as determined from the surface tension measurements, was found to be related to the charge number z of the adsorbed ions, in agreement with t he derived formula Gamma(s) = 1.42 x 10(-6)/z(4/3) mol(-2). Application of this formula to the determination of the dissociation and equilibrium const ants of surface reactions is demonstrated for slightly soluble calix[4]aren e ligands. (C) 2000 Elsevier Science S.A. All rights reserved.