Removal of heavy metal ions by capacitive deionization: Effect of surface modification on ions adsorption

Activated carbon cloth (ACC) coated with zinc oxide (ZnO) nanoparticles (NPs) have been used as electrodes in flow-by capacitive deionization (CDI) system. Aqueous solution of individual Pb2+ and Cd2+ ions and mixed Pb2+ and Cd2+ ions were used as test contaminant in CDI system to study the effect of surface modification upon ions removal efficiency. Due to the aggregated structure of ZnO NPs on ACC surface, the modified ACC electrodes develop the additional surface area as well as dielectric barrier therefore resulting in higher specific capacitance. In addition, coating with ZnO NPs effectively reduced physical adsorption whereby enhanced the ions adsorption rate and capacity during electrosorption process. Upon incorporating with ZnO NPs, the electrosorption efficiency was enhanced from 17% to 33% for Pb2+, from 21% to 29% for Cd2+ and from 21% to 35% for mixed Pb2+ and Cd2+ ions. The power consumption of individual ions and mixed ions removal process for ACC and ZnO NPs modified ACC were also discussed. Furthermore, used ACC electrodes surfaces were examined using photoelectron spectroscopy (XPS) and results were also conferred. The CDI ACC electrodes with ZnO NPs showed a promising and an effective way for heavy metal removal applications.