A comparative study of electrosorption selectivity of ions by activated carbon electrodes in capacitive deionization

This study has been focused on an experimental investigation of the electrosorption selectivity for alkali- and alkaline-earth cations in activated carbon-based capacitive deionization process. Cyclic voltammetry experiments showed that a large proportion of micropores in activated carbon electrodes were associated with electrical double-layer overlapping, and the specific capacitance of cations increased with the decrease of hydrated radius. A series of electrosorption experiments were conducted to identify the preferential electrosorption in multi-ionic solutions. The electrosorption selectivity of cations can be determined by the ionic charge, hydrated radius, and initial molar concentration. The activated carbon electrodes presented greater selectivity of smaller ions over larger ions due to size-affinity, while divalent cations possessing higher valence to screen the surface charge were more effectively removed than monovalent cations. The increase of initial molar concentration resulted in the increase of electrosorption capacity. Moreover, the ion selectivity can be further enhanced by increasing the applied voltage. The results are relevant to water desalination and softening in electrosorption.

► Micropores in activated carbon electrode resulted in electrical double-layer overlapping.
► Electrosorption selectivity was studied in a competitive multi-ionic environment.
► The electrosorption capacity was dependent on the ionic charge and hydrated radius.
► The molar concentration of cations had a critical effect on the sorption capacity.
► Divalent cations were more effectively removed than monovalent cations.