Synergism between Activated Carbon and Fenton Reaction for Organic Pollutant Degradation: The Hitherto Overlooked Role of Dynamic Single-Atom Sites

Fenton process and activated carbon are widely used for water treatment, yet both encounter significant challenges, such as slow Fe³⁺/Fe²⁺ conversion and rapid adsorbent saturation. Herein, a category of hitherto overlooked dynamic single-atom sites on heteroatom-doped carbons (HDCs) that mitigate the above problems was observed by coupling Fenton and activated carbon. Specifically, the defects on the carbon surface, particularly the heteroatom defects, coordinated with Fe³⁺ in the bulk solution to form dynamic single-atom sites that simultaneously suppress the Fe³⁺ hydrolysis and promote the Fe³⁺/Fe²⁺ conversion. This synergy sustains the efficient oxidation process of the coupled system through up to 5 cycles due to the optimized Fe³⁺/Fe²⁺ cycling. Moreover, dynamic single-atom sites enable the continuous removal of adsorbates from the carbon surface, extending the time before adsorption saturation and maintaining nearly 100% efficiency for 480 h. Mechanistic analysis revealed that dynamic single-atom sites optimize the Fe³⁺/Fe²⁺ redox cycle through forming a carbon → ligand atoms → Fe ↔ H₂O₂ electron flux pathway. Their bidirectional electron flux with H₂O₂ enhances OH· production, thereby improving the Fenton oxidation process. These findings offer crucial insights for overcoming challenges in environmental engineering technologies and underscore the potential superiority of coupled systems in practical applications.