Adsorption of t-butanol from aqueous solutions on a polarized mercury electrode

Abstract

The adsorption isotherms of t-butanol on polarized Hg electrodes, studied from 0.1 mol dm^–3 Na₂SO₄ aqueous solutions by means of both electrocapillary and capacity measurements, are congruent with respect to neither charge nor potential. Using analysis at constant charge, the charge of maximum adsorption indicates that at the potential of zero charge the alcohol in preferentially orientated with the positive end of the dipole towards the metal surface. Adsorption obeys a Frumkin isotherm with the interaction parameter decreasing quadratically and the saturation coverage decreasing linearly as the charge is moved away from the value of maximum adsorption. Results are discussed in terms of strong interaction of the organic adsorbate with water molecules which is very likely to be the main reason for the peculiar behaviour of this alcohol. This hypothesis enables also the change in inner layer capacity at constant amount adsorbed with coverage to be rationalized.