On the adsorption of pure ethylene glycol on mercury

Abstract

The standard Gibbs energy of adsorption of pure liquid ethylene glycol (EG) on mercury is assessed to range between −50 and −60 kJ mol −1, about two–three times with respect to water (−21 kJ mol −1). This evidence is obtained on the basis of a series of indirect and independent experimental results. Moreover, ab-initio calculations are performed to account for the interaction energy relating the isolated EG molecule and a cluster of seven (or four) Hg atoms: three different geometrical approaches of the EG molecule with respect to the cluster are considered (top, hollow, bridge) as well as three EG conformations ( trans, cis, cis-OH, the last one with an intramolecular hydrogen bond). The deepest minimum in the energy versus (Hg cluster–EG molecule) distance potential energy curve, amounting to −80 kJ mol −1, is obtained in the case of the cis conformation of EG. In particular, it is found that this stabilizing energy is essentially due to the oxygen–mercury atoms interaction, giving rise also to an appreciable charge transfer coefficient from the EG molecule to the Hg cluster. Finally, in this conformation, the EG adsorbed layer is also stabilized by an attractive energy term effective among vicinal interacting molecules.