Selective Two-Electron Phenol Oxidation Polymerization for Water Purification

Highly reactive phenoxonium ion (PhO⁺), generated via two-electron oxidation, exhibits remarkable efficacy in polymerizing and removing phenolic contaminants. However, the sequential two-electron abstraction from phenol to form PhO⁺ remains a significant kinetic and thermodynamic challenge. Herein, we report an N-bridged double-iron site (≡Fe─N─Fe ≡) catalyst that enables PhO⁺ generation through peroxymonosulfate (PMS) activation. In situ spectroscopy and theoretical calculations reveal that PMS adsorbs onto the ≡Fe─N─Fe ≡ site via both peroxide oxygen atoms (─O─O─), forming a ≡Fe-(μO─O)─Fe≡ intermediate. This unique structure provides dual low-lying Fe─O σ*( $d_{z^2}$ -p_z) orbitals, and minimizes the energy gap between the Fe $d_{z^2}$ orbital and the O─O σ* orbital, thereby catalyzing two-step single-electron transfer from phenol to the ─O─O─ and enabling the PhO⁺ formation. This PhO⁺-induced C─O coupling polymerization achieves an 81.8% polymerization transfer ratio, significantly higher than that obtained via the phenoxy radical (PhO•)-mediated process (35.0%). This system enables the rapid phenol removal (98.1% in 3 min) and the effective treatment of coking wastewater, maintaining > 97% phenol removal over 10 d in a continuous-flow reactor. Our work provides an atomic-level design principle for steering oxidation pathways, opening a sustainable route for water purification that simultaneously eliminates pollutants and recovers carbon resources.