Interfacial behaviour of triphenylphosphine, triphenylarsine and triphenylantimony at the mercury-methanolic solution interface

Abstract

The adsorption and interfacial behaviour of triphenylphosphine, triphenylarsine and triphenylantimony on polarized Hg electrodes from 0.1 mol dm −3 LiCl methanolic solutions, was studied by means of electrocapillary measurements. The results show that the adsorption isotherms are congruent only with respect to potential on the negative side of the adsorption maximum. At this potential region a Langmuir isotherm is obeyed for all the above substances. On the positive side of the adsorption maximum the isotherms are not congruent with respect to either of the two electrical variables. Under these polarizations the adsorption of these compounds is more realistically described by a Frumkin isotherm with parameters m and α decreasing with the increase of the positive charges on the electrode surface. A detailed analysis of this polarization region reveals that the presence of positive electrode charges causes a shift of the electronic charge of the adsorbed molecules towards the phenyl groups. This change, the extent of which depends on the polarity of the above substances, causes an increase of the attractive electrode-adsorbate and repulsive adsorbate-adsorbate and adsorbate-solvent interactions.