Dithizone Adsorption at Metal Electrodes. 4. Voltammetric and Surface Raman Spectroelectrochemical Investigation at a Copper Electrode

Cyclic voltammetric and surface Raman spectroelectrochemical behavior of the anion of dithizone (diphenylthiocarbazone), HDz⁻, has been characterized at a Cu electrode in aqueous alkaline media. The cyclic voltammetry suggests very strong interaction of HDz⁻ with the Cu surface. In the presence of HDz⁻, significant oxidation of the Cu surface does not take place until potentials greater than 0.2–0.3 V are reached. The surface Raman spectroelectrochemical data are consistent with strong adsorption of HDz⁻ at the Cu surface at potentials negative of the oxidation potential. Very little control of surface HDz⁻ population can be realized through alteration of the potential. This is in contrast to the previous behavior observed at Ag. The surface species observed at potentials more positive than the oxidation potential of HDz⁻ is the disulfide. The effect of solubility on the extent of adsorption was also investigated. The surface Raman data indicate that adsorption of HDz⁻ in pH 10 solution is significantly greater than that in pH 12 solution in which HDz⁻ is more soluble. On the basis of the similarity of the surface spectra obtained and the spectrum of copper(II) dithizonate, an approximate orientation of HDz⁻ at the Cu/solution interface is proposed.