Adsorption of isomers of butanol on bismuth single crystal plane electrodes

Abstract

Cyclic voltammetry, impedance and chronocoulometry have been employed for quantitative study of normal butanol ( n-BA), iso-butanol ( iso-BA), sec-butanol ( sec-BA) and tert-butanol ( tert-BA) adsorption at the bismuth single crystal plane¦aqueous Na 2SO 4 solution interface. The adsorption isotherms, Gibbs energies of adsorption, the surface excess and other adsorption parameters have been determined. As found, the adsorption characteristics of the isomers of butanol depend on the crystallographic structure of the electrodes, as well as on the geometrical structure of hydrocarbon chains of adsorbate. The adsorption characteristics obtained from the impedance and chronocoulometric measurements are in good agreement within the limits of surface charge densities — 24 < σ < 3 μC cm −2. The adsorption of n-BA, sec-BA, iso-BA and tert-BA on Bi single crystal planes is physical and is limited by the rate of diffusion of organic molecules to the electrode surface. The adsorption activity of adsorbates at the bismuth¦solution interface increases in the sequence tert-BA < sec-BA < iso-BA < n-BA as the adsorption at the air¦solution interface increases. In the case of all compounds studied, the adsorption activity of planes increases in the sequence (̄10̄1) ≤ (001) < (2̄1̄1) < (01̄1) as the superficial density of atoms increases. According to the values of the standard Gibbs energy of adsorption, it was established that the hydrophilicity of electrodes increases in the sequence Sb(111) < Bi(01̄1) < Bi(211¯) < Bi(̄10̄1) ≤ Hg < Bi(001) < Bi(111) < Cd(0001) < Zn(0001) < Ag(111) < Ag(100) < Ga.