Towards efficient chemical reduction of perchlorate in water: Mechanisms, design considerations, and future...

Perchlorate (ClO₄^-) contamination poses persistent and global risks to human health and ecosystems through drinking water and the food chain, highlighting the need for effective removal strategies. Unlike separation-based technologies, chemical and electrochemical reduction can convert ClO₄^- to harmless chloride (Cl^-), but the kinetic inertness of ClO₄^- presents substantial challenges. This review summarizes recent advances in ClO₄^- reduction in aqueous systems, including direct reduction, catalytic reduction, and electrocatalysis. For direct reduction, Fe- and Ti-based systems are discussed, underscoring their thermodynamic favorability but severe kinetic limitations and requirements for harsh conditions. In catalytic strategies, the oxygen atom transfer (OAT) and hydrodeoxygenation mechanisms are discussed in homogeneous Re/Mo/Fe complexes and heterogeneous bimetallic catalysts, particularly Re-Pd/C and Mo-Pd/C. In addition, precious group metal (PGM)-based hydrogenation systems and photocatalytic processes are discussed. Electrocatalytic approaches are reviewed in terms of anodic corrosion-generated reductants, metal-mediated OAT at cathodes, and atomic-hydrogen-mediated reduction on PGM and non-noble surfaces. Across these systems, available kinetic rate constants for ClO₄^- reduction to Cl^- are compiled, and the influence of ligands in catalysts, metal composition, supports, and water matrices is analyzed. The major limitations of current strategies are summarized. Finally, research priorities in rational catalyst design, reactor and process engineering, and advanced mechanistic characterization are outlined, with the aim of developing novel ClO₄^- reduction technologies that are faster, capable of operating under mild, environmentally relevant conditions, and suitable for practical water treatment.