Adsorption of bromide and iodide anions on a renewable liquid (Cd-Ga) electrode from acetonitrile solutions. Effect of (Cd-Ga)-solvent chemisorption interaction on the anion adsorption energy

摘要

The specific adsorption of bromide and iodide anions was studied at a (Cd-Ga)/acetonitrile (AN) interface from mixed solutions of [0.1 m M LiBr + 0.1 (1-m) M LiBF4] and [0.1 m M LiI + 0.1 (1-m) M LiBF4] 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 main experimental method was measurement of differential capacitance on a renewable liquid (Cd-Ga) electrode. The obtained experimental results can be described quantitatively by the Frumkin isotherm in a wide range of charge densities (sigma). The adsorption parameters of halide anions (Hal-) were determined using regression analysis of two-dimensional pressure isotherms. It is shown that the adsorption energies (Delta Gads) of Br- and I- at the (Cd-Ga)/AN interface practically coincide. It follows that the difference in the interaction energies of Br- and I- with (Cd-Ga) is equal to the difference of the solvation energies of these anions: (Delta G(Cd-Ga)-Br- - Delta G(Cd-Ga)-I-)approximate to(Delta GAN-Br- - Delta GAN-I-) and therefore Delta G(Cd-Ga)-I - < G(Cd-Ga)-Br - . The adsorption parameters of Hal- obtained on the (Cd-Ga)/AN interface are compared with the similar data for the (Cd-Ga)/DMF interface. The adsorption energy of Br- and I- on a (Cd-Ga) electrode increases significantly in AN as compared to DMF. This result can be unambiguously explained by a significant decrease in the energy of chemisorption interaction between a (Cd-Ga) electrode and solvent molecules in the Helmholtz layer upon transition from DMF to AN. The Delta Gads,sigma -dependence obtained at the (Cd-Ga)/AN interface in the first approximation characterizes the change of the free energy of (Cd-Ga)-Hal- interaction with sigma. It is shown that the slope of the Delta Gads, sigma dependence decreases upon transition from the (Cd-Ga)/AN interface to the (Cd-Ga)/DMF interface due to a significant increase in the energy of the chemisorption interaction of (Cd-Ga) with