The effect of redox potential on the removal characteristic of divalent cations during activated carbon-based capacitive deionization
Journal
Chemosphere
Journal Volume
274
Date Issued
2021
Author(s)
Abstract
The main objective of the study is to explore the removal characteristics of Cu2+ and Zn2+ ions in activated carbon-based capacitive deionization (CDI). In this work, CDI experiments were performed to remove divalent ions (e.g., Cu2+, Zn2+, and Ca2+) from single- and multicomponent aqueous solutions. As evidenced, divalent heavy metals could be successfully removed by charging the CDI cell at 1.2 V. Notably, the preferential removal of Cu2+ ions over Zn2+ and Ca2+ ions was observed in the charging step. The removal capacities for Cu2+, Zn2+, and Ca2+ ions in a competitive environment were 29.6, 19.6, and 13.8 μmol/g, respectively. In contrast, the regeneration efficiencies for the removal of Cu2+ and Zn2+ were much lower than that of Ca2+, suggesting the occurrence of irreversible Faradaic reactions on the cathode. X-ray photoelectron spectroscopy analysis demonstrated that Cu2+ ions were reduced to Cu(I) and Zn2+ ions were transformed to ZnO/Zn(OH)2 on the cathode. Therefore, there were two major mechanisms for the removal of divalent heavy metal ions: capacitive electrosorption and cathodic electrodeposition. Specifically, the reduction potential played a crucial role in determining the removal characteristics. When regarding divalent cations with similar hydrated sizes, the divalent cation with a higher reduction potential tended to be separated by cathodic electrodeposition rather than double-layer charging, indicating the high removal selectivity of activated carbon-based CDI. This paper constitutes a significant contribution to promoting the application of CDI for contaminant sequestration. © 2021 Elsevier Ltd
Subjects
Capacitive deionization; Divalent heavy metals; Electrodeposition; Electrosorption; Reduction potential
SDGs
Other Subjects
Activated carbon; Cathodes; Copper metallography; Electrodeposition; Heavy metals; II-VI semiconductors; Metal ions; Oxide minerals; Positive ions; Redox reactions; Reduction; X ray photoelectron spectroscopy; Zinc metallography; Zinc oxide; Capacitive deionization; Cathodic electrodeposition; Competitive environment; Double layer charging; Faradaic reactions; Reduction potential; Regeneration efficiency; Removal characteristics; Copper compounds; activated carbon; calcium ion; copper; cuprous ion; divalent cation; zinc; zinc ion; charcoal; divalent cation; aqueous solution; copper; electrochemistry; experimental study; pollutant removal; redox conditions; transformation; zinc; adsorption; aqueous solution; Article; comparative study; controlled study; desorption; electrodeposition; energy dispersive X ray spectroscopy; heavy metal removal; isotherm; oxidation reduction potential; pH; pore size distribution; pore volume; qualitative analysis; scanning electron microscopy; static electricity; surface area; X ray photoemission spectroscopy; electrode; oxidation reduction reaction; water management; Cations, Divalent; Charcoal; Electrodes; Oxidation-Reduction; Water Purification
Type
journal article