Xinhua Xu

High-valent iron-oxo species (Fe(IV)=O) play a pivotal role in advanced oxidation processes (AOPs), offering high redox potentials and intrinsic selectivity for contaminant degradation. However, stabilizing Fe(IV)=O generation and elucidating their formation mechanisms remain longstanding challenges in Fenton-like catalysis. Herein, we employ a sulfur-coordination engineering strategy to construct asymmetric Fe–N3S1 sites in Fe-SNC single-atom catalysts (SACs). The optimized Fe–SNC catalyst markedly enhances peroxymonosulfate (PMS) activation, affording an exceptional Fe(IV)=O selectivity of 97%. Consequently, the Fe–SNC/PMS system enables ultrafast degradation of diverse contaminants within minutes, surpassing the performance of most reported analogues under comparable conditions. Density functional theory (DFT) calculations reveal that S doping enriches the electron density at Fe sites, bolstering PMS adsorption while concurrently lowering the energy barrier for Fe(IV)=O formation. This work establishes a feasible paradigm for the rational regulation of sulfur coordination environments in single-atom catalysts, paving the way for the design of high-efficiency Fenton-like systems toward practical wastewater purification.

Nonradicals relying on peroxymonosulfate (PMS) activation face inherent kinetic and thermodynamic limitations in pollutant mineralization. This is overcome using asymmetric iron single‐atom catalysts (Fe‐SACs) with Sabatier‐adjusted d ‐band centers that establish a synergistic nonradical network of pathways, achieving exceptional mineralization (≈85%) with only one‐tenth conventional PMS dosage. Direct coordination of high‐loading Fe (≈10 wt.%) with controllable p ‐block elements (S, P, B) simultaneously facilitates electron‐transfer pathways and selective generation of nonradicals ( ¹ O ₂ , Fe ^IV  = O). Compared to symmetric Fe ₁ ‐N ₄ , they enhance pollutant removal and mineralization by 4.2‐fold and 6.3‐fold, respectively. Atomic‐resolution characterization and theory reveal that the dopant's electronegativity governs the electronic perturbations of the Fe center, dictating PMS adsorption. Pollutant‐specific charge transfer and adsorption affinity critically determine nonradical activity. The asymmetric Fe SACs exhibit excellent stability and applicability in complex matrices and continuous‐flow wastewater treatment. This work provides a transformative strategy to overcome fundamental limitations in advanced oxidation processes and a design framework for sustainable environmental technologies.

Sulfidized zero-valent iron (S-ZVI) holds promise in the remediation of chlorinated hydrocarbons. However, S-ZVI is susceptible to corrosion in aquifers with elevated dissolved oxygen (DO) levels. This study demonstrates, for the first time, that a trade-off between the passivation and oxidative corrosion of aged S-ZVI can be achieved in the presence of silicate to promote its dechlorination performance on trichloroethylene. The electron transfer from aged S-ZVI to target contaminants and DO can be promoted to generate reactive oxygen species (ROS), simultaneously enhancing reductive and oxidative dechlorination. Silicate interactions contribute up to an 18.9% decrease in the electron resistance, a 23.3% increase in oxidative dechlorination, a 61.1% increase in the dechlorination rate constant, and an 85.7% increase in the degradation capacity of aged S-ZVI as compared to the control. Furthermore, the decrease in the reductive sulfur species over an extended aging time promotes the depolymerization of silica polymers into monomer silicate on S-ZVI, which is conducive to mitigating silicate passivation and promoting the release of dissolved silicate in aged S-ZVI systems. This process, in turn, facilitates ferrous iron dissolution and ROS production, thereby enhancing the redox reactivity of aged S-ZVI. This study provides new insights into the effect of silicate on the aging of S-ZVI, which will help develop novel strategies for remediation using S-ZVI-based techniques.