Electrosorption of tri(n)octylphosphine oxide from methanol and water-methanolic solutions on a polarized mercury electrode

Abstract

The adsorption of tri(n)octylphosphine oxide on the mercury electrode in methanolic and water-methanolic solutions of LiCl has been examined from electrocapillary measurements. In methanolic solutions this substance shows the typical characteristic features of an organic adsorbate. The isotherms are congruent only with respect to potential on the negative side of the electrocapillary maximum and in this region a Frumkin isotherm is obeyed with an interaction parameter equal to α = 0.3 corresponding to intermolecular attraction. On the positive side the isotherms are non congruent with respect to both the electrical variables, while the system may be described by a Frumkin isotherm either with constant Γ s = 1.03 × 10 −10 mole cm −2 and α decreasing with the increase of the positive charges on the electrode or with constant α = 0.3 and decreasing Γ s . In water-methanolic solutions the adsorption of tri(n)octylphosphine oxide increases, due mainly to the decrease of its solubility. In parallel a clear dependence of Γ s on the amount of water in solutions is detected. Γ s is seen to increase with the water content of the solutions probably due to a partial overlap of the hydrocarbon chains of this substance.