Adsorption of ethylene glycol and its higher homologues at the mercury/aqueous solution interface

Abstract

Adsorption of ethylene glycol, propan-1,2-diol and butan-1,4-diol at the Hg/0.10 mol kg^–1 KCl (aq.) solution interface evaluated through equilibrium double layer capacity measurements indicated congruency of adsorption isotherms with respect to both electrode charge (σM) and potential (E); applicability of Langmuir's adsorption isotherm; quadratic dependence of ΔG° on E and single stable orientation with the hydrocarbon chain facing the electrode and functional group in solution throughout the coverage region for all these compounds. Surface excess, standard free energy of adsorption and the anodic shift of E_pzc are in the order: ethylene glycol < propan-1,2-diol < butan-1,4-diol. The shift of charge corresponding to maximum adsorption towards less negative charges in passing from ethylene glycol to butan-1,4-diol has been explained with the help of an equation given by Damaskin and Frumkin.