Capacitive Deionization for Selective Removal of Eutrophic Ions, Fluorides, and Bromides: Material Design Strategies and Mechanism Elucidation

Water eutrophication driven by nitrates (NO₃ ^-), phosphates (PO₄ ^3-), and ammonium salts (NH₄ ⁺), along with groundwater contamination caused by fluorides (F^-) and bromides (Br^-), collectively poses significant threats to both ecological systems and human health. Capacitive Deionization (CDI) has demonstrated significant potential for selectively removing these pollutants due to its low energy consumption, absence of chemical byproducts, and cost-effectiveness. However, systematic mechanistic analyses and material design strategies focusing on this specific area remain insufficient. To this end, against the backdrop of water eutrophication and groundwater contamination, this paper presents a relatively comprehensive review of the research progress regarding the removal of NO₃ ^-, PO₄ ^3-, NH₄ ⁺, F^-, and Br^- using CDI technology. The review first discusses the advantages and limitations of conventional methods for removing these pollutants. It elaborates on the ion storage mechanism of CDI and addresses its fouling mechanisms and mitigation strategies. Subsequently, for different ions, the review systematically sorts out various types of electrode materials and explains in detail the intrinsic mechanisms through which they achieve ion selectivity. Finally, the review discusses current challenges in CDI technology, such as ion selectivity, electrode fouling, complexity of real water matrices, cost, and long-term stability, and proposes specific future research directions.