Exploring the electrosorption selectivity of nitrate over chloride in capacitive deionization (CDI) and membrane capacitive deionization (MCDI)
Journal
Desalination
Journal Volume
497
Date Issued
2021
Author(s)
Abstract
The electrosorption selectivity of nitrate (NO3−) over chloride (Cl−) was investigated in capacitive deionization (CDI) and membrane capacitive deionization (MCDI). In CDI, the selectivity depended on several key operational factors, including the charging time, initial NO3− and Cl− concentration ratio (CNO3−/CCl−) and applied voltage. The NO3− selectivity increased with prolonged charging time and in proportion to the initial CNO3−/CCl−, suggesting that the differences in ion-carbon affinity results in the preferential electrosorption of NO3−. Increasing the applied voltage decreased the NO3− selectivity, revealing that the electrical force kinetically controlled the competitive electrosorption of anions. Therefore, our results indicate that the electrosorption selectivity for NO3− ions in CDI was determined by the contributions of ion-carbon affinity and electrical force during the charging period. In comparison, the NO3− selectivity was found to be significantly reduced in MCDI due to the presence of an ion-exchange membrane controlling ion kinetics on the basis of charge rather than affinity. The electrosorption selectivity of NO3− over Cl− in CDI was 2.44, which was approximately 1.9-fold higher than that in MCDI (1.28). These results provide a practical understanding of the NO3− selectivity in the studied electrosorption processes.
SDGs
Type
journal article