Improved desalination by zinc oxide nanorod induced electric field enhancement in capacitive deionization of brackish water

Ion adsorption in capacitive deionization is a function of the electric field strength present at the electrode surface. We show enhancement in the electric field strength by coating activated carbon cloth (ACC) electrodes with zinc oxide (ZnO) nanorods, where the effective field was shown to vary with respect to the length, diameter and proximity of the coated ZnO nanorods. Deionization of a 17 mM NaCl solution in a single pass experiment using the composite electrodes showed a desalination efficiency of 35%, a 40% improvement as compared to plain ACC electrodes. The composite electrodes also desalinated at a charge efficiency of 78% with a salt uptake of 7.7 mg/g of the electrode. An enhancement in the ion adsorption rate led to a 30% reduction in the energy consumption per mole of salt removed for the desalination process. A theoretical model showing further enhancement in the desalination efficiency by reducing the diameter of the rods is also discussed. (C) 2014 Elsevier B.V. All rights reserved.