Adsorption of n-Butanol from Aqueous Solutions on an Sn-Ga Electrode in the Absence of a Metal-Water Chemisorption Interaction

Abstract

Data on the dependence of the differential capacitance on potential at the Sn-Ga/H2O interface in 0.05 M solutions of Na2SO4 with various additives of n-butanol are obtained by a bridge method at a frequency of 420 Hz and a temperature of 32°C. In the region of potentials studied, the chemisorption interaction (Sn-Ga)-H2O is completely absent. The adsorption parameters of n-butanol are obtained by a method of a regression analysis of these data. The data obtained are compared with similar data on various hydrophobic electrodes. Shown is that, on the Sn-Ga and Pb-Ga electrodes, whose “electronic” capacitance is similar, the free energies of adsorption of n-butanol are also similar but differ from the adsorption energy on electrodes of Hg, Bi-Ga, and Tl-Ga. The results that are obtained on an Sn-Ga electrode nicely fit a general correlation dependence between the reciprocal value of the electronic capacitance of various electrodes in the absence of a metal-water chemisorption interaction, (C m −1 ), and the free energies of adsorption of molecules of n-butanol on these, ΔG A 0 . The dependence of the free energies of adsorption of molecules of n-butanol in the absence of a metal-water chemisorption interaction on the magnitude of the electronic capacitance of the metal confirms the assumption that we had put forth previously that it is necessary to introduce corrections to criteria of hydrophilicity of metals based on a comparison of quantities ΔG A 0 and potentials of cathodic peak of adsorption-desorption Edes, which are expressed in a rational scale. With the obtained correlation relationships taken into account, criteria of hydrophilicity are suggested, which take into account these correlation relationships.