Boosting H₂O₂ activation to hydroxyl radicals via electronic modulation of asymmetric Fe-O₃Cl₁-C catalysts for water decontamination

Heterogeneous Fenton technologies are highly promising for organic wastewater remediation, yet their practical application is restricted by the sluggish kinetics of H₂O₂ activation to hydroxyl radicals (•OH). Addressing this, we report the rational design of a chlorine-mediated asymmetric iron single-atom catalyst (Fe-O₃Cl₁-C) to overcome kinetic bottlenecks via coordination symmetry breaking. Density functional theory (DFT) calculations reveal that the introduction of electronegative Cl ligands induces a profound charge redistribution at the Fe center. This electronic reconfiguration optimizes H₂O₂ adsorption thermodynamics and drastically reduces the activation barrier of the rate-limiting step from 0.81 eV (symmetric Fe-O₄-C) to 0.46 eV (asymmetric Fe-O₃Cl₁-C). Consequently, the catalyst exhibits superior Fenton-like reactivity, achieving complete elimination of sulfamethoxazole (SMX) across a broad pH window (3.0-11.0). The observed apparent rate constant (0.202 min^-1) surpasses that of its symmetric Fe-O₄-C analogue by a factor of 4.3. To validate engineering feasibility, a continuous-flow reactor was deployed for treating authentic medical wastewater, successfully reducing the chemical oxygen demand (COD) to compliant levels (<60 mg·L^-1) while completely mitigating biological toxicity. This work elucidates the critical role of asymmetric coordination in single-atom catalysts and provides a scalable strategy for deep water purification.