Self-replenishing neutral Fenton-like treatment for emerging contaminants through single Fe atom electron configuration regulation

Fenton technology is promising for removing recalcitrant and toxic organic contaminants for wastewater purification. Neutral Fenton technology is preferred for its reduced acid usage and improved operational convenience. However, the challenges are the low production of reactive species and the limited conversion of high-valent iron (Fe) to low-valent Fe. This study introduced a new cycle employing high-valent iron-oxo species [Fe(IV)=O], which directly participates in degradation, facilitating Fe regeneration. To achieve it, we developed an O-doped single Fe atom catalyst (SACs, Fe-N₃O₁) to promote the efficient Fe(IV)=O generation. The O-doping improved the acetaminophen degradation rate constant and turnover frequency of Fe-N₃O₁ by approximately tenfold, and elevated the steady-state concentration of Fe(IV)=O 65 times over. The normalized degradation rate constant of Fe-N₃O₁/H₂O₂ was superior to other reported catalysts. Density functional theory calculations indicated that O-doping decreased the charge density of Fe site, enhanced the metal–oxygen bond strength, and reduced the energy barrier for the key reaction intermediate (*O + *H₂O), facilitating the efficient and selective formation of Fe(IV)=O. Fe-N₃O₁/H₂O₂ demonstrated wide pH tolerance, high resistance to complex water matrices, and excellent stability, making it promising for practical applications. This study provides a new perspective on controlling the selective generation of reactive species to achieve sustainable neutral Fenton-like reactions.