Reduction of Cd(II) ions in the presence of tetraethylammonium cations: adsorption effect on the electrode process

Abstract

The effect of the adsorption of tetraethylammonium (TEA) cations, which present both ionic and organic characteristics, on the reduction of Cd(II) ions have been studied from dc and ac measurements at the dropping mercury electrode. The resistance to the charge transfer (Rct) and Warburg coefficient (s) parameters have been determined through impedance measurements. Thus, the global velocity constant has been obtained. The reduction process of Cd(II) in perchloric media is reversible and is affected by the adsorption of TEA cations, especially at high TEA concentrations. Values of E1/2, half wave potential, and DO, diffusion coefficient, obtained from both dc and ac measurements agree. The velocity constants show a decrease as TEA concentration increases, with values ranging from 0.6 to 0.01 cm·s-1. The inhibitory effect of TEA adsorption on the electrode process and the relationship between electrode coverage, ¿, and velocity constants, K, using several isotherm equations, have been discussed. The best fit was obtained with the equation K = 0K(1 - ¿)a with an a value close to three, indicating a blocking effect and electrostatic repulsion due to TEA