Enhancing capacitive deionization for water desalination: the role of activated carbon in contaminant removal

The desalination of saline water is of great importance in water-stressed areas. Therefore, the energy efficiency and secondary contaminants of emerging desalination technologies need to be addressed. Heavy metal ions that exist in industrial wastewater may cause permanent damage to human health. Capacitive deionization (CDI) is a promising desalination technology, attracting increasing interest. It stands out for its operational efficiency and minimal maintenance requirements. Compared to traditional methods such as reverse osmosis (RO), electrodialysis (ED), and ion exchange (IE), CDI offers a more energy-efficient and eco-friendly approach to water treatment. Among the existing electrode materials, activated carbon exhibits great potential with intriguing advantages, such as low cost, high adsorption properties, and ease of integration with other materials. This paper reviews the science of CDI and reports on the removal of seven contaminant ions in brackish water by modifying AC electrodes or coupling them with ion exchange membranes/coatings in CDI technology. In addition, this paper discusses the factors that may reduce the energy efficiency caused by electrode materials in seawater desalination as well as modification strategies.