Influence of functional groups and substituents on the adsorption of aromatic non-ionic surfactants at the Hg/ethylene glycol interface

Abstract

The adsorption of a number of benzene derivatives with —CH₃, —NH₂, —OH and —CO₂H functional groups on an Hg electrode from solutions of ethylene glycol as solvent has been studied by measuring the differential capacitance as a function of the electrode potential. Charge–potential and surface pressure curves were derived by back-integration of the capacitance curves. The investigation has also been based on the analysis of surface excess, adsorption potential shift and standard Gibbs energy of adsorption. Aromatic compounds can be classified in two groups according to the occurrence or non-occurrence of specific interactions with the metal surface through the π-electron system. Results have been discussed in terms of the prevalence of one or more of the factors governing adsorption at electrodes: solute–solvent, adsorbate–electrode, solvent–electrode and adsorbate–adsorbate interactions. The relative magnitudes of the interactions and orienting effects have been found to depend on the nature of the solvent and of the substituents. Metal-interacting compounds exhibit two-step isotherms indicating the occurrence of adsorption in the two different orientations.