Carbon dioxide radical anion: A novel concept for water purification

Contamination of water and wastewater by hazardous pollutants poses serious environmental and health concerns, demanding advanced remediation strategies. Although oxidative radicals are conventionally utilized, their limited efficacy in treating specific persistent pollutants highlights the urgent need for innovative reductive processes. This study reviews the carbon dioxide radical anion (CO₂^●-) as a novel advanced reduction process for pollutants removal in water and wastewater, with particular emphasis on the historical evolution and key milestones of CO₂^●- research, chemical attributes, detection methodologies, and applications. A first-of-its-kind dataset of reaction rate constants for CO₂^●- with 307 typical compounds is established. CO₂^●- acts as a nucleophilic reducing radical whose reactivity is governed by functional group effects, preferentially attacking electron-withdrawing compounds via single-electron transfer. Notably, three forward-looking application scenarios for CO₂^●- are proposed, including synergistic reduction and oxidation of per- and poly-halogenated contaminants, integrated control of disinfection byproducts (DBPs), and enhanced transition metal recycling in Fenton systems. This review establishes a new paradigm in aquatic contaminant control, transitioning the field from oxidative radical dominance toward reductive CO₂^●- innovation, offering a sustainable and robust strategy for advanced water remediation.