Electric-field induced effects in ion separation processes through an ionic-liquid-functionalized graphene-oxide membrane: insights from a computational approach

Effects of the application of an electric field in ion-separation processes from saline solutions through multilayered graphene-oxide membranes functionalized with the 1-Ethyl-3-methylimidazolium/Glycine ([EMIM+][Gly-]) ionic liquid, were examined by means of non-equilibrium molecular dynamics simulations. Electric field with constant or oscillating intensity was applied to probe the effects in ion separation of monoatomic ions (Na+, Cl-, Mg2+) and of the polyatomic cation of the ionic liquid, EMIM+, through the membrane. It was found that even at high constant-field intensities (ranging from 0.1 V/Å to 0.3 V/Å) the migration characteristics of the monoatomic ions and the water permeability of the membrane, were not altered significantly compared to those under zero-field conditions. In contrast, the partitioning of the polyatomic cations of the ionic liquid changed notably upon the application of the constant-intensity field. This behavior was found to be consistent with free energy changes associated with the interaction of the cationic species with the membrane. The application of an oscillating electric field at a sub-THz frequency affected the migration charcateristics of water between the different compartments of the system and resulted in notable changes in the membrane’s ion adsorption profiles and the migration characteristics also of the monoatomic ions. This behavior was rationalized by considering a restructuring of the hydrogen-bonding network, which allowed a more efficient energy transfer to the rotational and translational motion of water and affected the ions’ membrane adsorption profiles and their transport properties.