Capacitive Deionization for Targeted Anion Removal: Mechanisms, Advances, and Future Directions

Abstract

The escalating prevalence of anionic contaminants in water sources presents a critical challenge to global water security. Conventional treatment methods are frequently limited by secondary pollution, high energy consumption, and suboptimal efficacy in complex aqueous matrices. Capacitive deionization (CDI), an emerging electrochemical desalination technology, offers a compelling alternative for selective anion removal, distinguished by its low energy footprint, environmental compatibility, operational simplicity, and designable electrode architectures. This review provides a systematic overview of recent progress in CDI for the removal of key anions, including fluoride, chloride, phosphate, sulfate, and arsenate. It elucidates the fundamental mechanisms underlying ion removal, tracing the evolution from classical electric double layer adsorption toward multi-mechanistic systems that synergistically integrate redox reactions, ion exchange, and surface complexation. The structural characteristics and comparative advantages of various CDI configurations are critically assessed. Furthermore, this review highlights key innovations in functional electrodes and discuss their role in achieving anion-specific selectivity. Despite substantial progress, persistent challenges remain, including material costs, unresolved microscopic adsorption dynamics, and limited industrial scalability. Finally, prospective research directions are outlined, aimed at material multifunctionalization, system intelligence, and application diversification, offering a roadmap for translating CDI from laboratory innovation to practical water treatment solutions.