Specific adsorption of bromide and iodide ions on the (Cd–Ca)/dimethylformamide interface

Abstract

The specific adsorption of bromide and iodide ions from mixed solutions [0.1 m M LiBr + 0.1 (1 – m) M LiBF₄] and [0.1 m M LiI + 0.1 (1 – m)M LiBF₄] in dimetylformamide (DMF) with the following fractures m of surface-active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 is studied on a renewable liquid (Cd–Ga) electrode by means of an ac bridge. The data on the specific adsorption of Br^– and I^– anions can be quantitatively described by the Frumkin isotherm, the same as the data on Cl^–. It is found that in contrast to Hg/DMF and Bi/DMF interfaces for which the adsorption energy of halide (Hal^–) anions (ΔG _ads) increases with the transition from Cl^– to Br^– and further to I^–, on the (Cd–Ga)/DMF interface, the ΔG _ads values increase in the inverted sequence I^–< Br^–< Cl^–. It is found that the energy of (Cd–Ga) interaction with Hal^– anions ($\Delta {G_{\left( {{\text{Cd - Ga}}} \right) - Ha{l^ - }}}$) also increases in the sequence I^– < Br^– < Cl^–. The comparative analysis of the results on the Hal^– adsorption on the (Сd–Gа)/DMF and (In–Gа)/DNF interfaces shows that the interaction energies metal–DMF and metal–Hal^– correlate with one another. For (Cd–Ga) and (In–Ga) electrodes which have virtually the same energy of metal–DMF interaction, the corresponding values of $\Delta {G_{\left( {{\text{Cd - Ga}}} \right) - Ha{l^ - }}}$ and $\Delta {G_{\left( {{\text{In - Ga}}} \right) - Ha{l^ - }}}$ turn out to be close not only for Cl^– but also for Br^– and I^–.