Effect of metal nature on specific adsorption of Cl−, Br−, and I− ions from N-methylformamide solutions

The differential capacitance curves were measured with an ac bridge in the M/[N-MF + 0.1m M KCl + 0.1(1 − m) M KClO4], M/[N-MF + 0.1m M KBr + 0.1(1 − m) M KClO4], and M/[N-MF + 0.1m MKI + 0.1(1 − m) M KClO4] systems (where M = In–Ga, Tl–Ga) at the following values of molar fraction m of the surface–active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. The I−, Br− and Cl− (Hal−) anions specific adsorption in the above systems can be described quantitatively by the Frumkin isotherm. The main parameters of adsorption of the I−, Br−, and Cl− anions were determined for the studied interfaces. Unlike Ga/N-MF interface, where the adsorption energy (ΔGads) increased in the sequence Br− ≈ I− < Cl−, at the (In–Ga)/N-MF and (Tl–Ga)/N-MF interfaces, same as at the Hg/N-MF interface, it increased in the reverse sequence: Cl− < Br− < I−. It is found that the values of ΔGads, energy of metal–Hal− interaction ( Δ G M - Hal - ), and difference ( Δ G M - Hal 1 - - Δ G M - Hal 2 - ) grow in the series of (Tl–Ga) < (In–Ga) < Ga. The metal–Hal− interaction energy increase in the sequence of Δ G M - Cl - > Δ G M - Br - > Δ G M - I - . The values of difference ( Δ G M - Hal 1 - - Δ G M - Hal 2 - ) are higher for the Ga electrode and lower for the (In–Ga) and (Tl–Ga) electrodes than the values of difference between the Hal− solvation energies ( Δ G S - Hal 1 - - Δ G S - Hal 2 - ), which determines the sequences of Hal− adsorption.