Phenoxyl radical-mediated peroxymonosulfate activation for efficient water remediation

Radicals are central to advanced oxidation processes (AOPs). However, the formation and role of organic radicals, particularly phenoxyl radicals, during the remediation of phenolic pollutants remain largely overlooked and misunderstood, often being considered as inactive byproducts or precursors to polymerization. Herein, we demonstrate that phenol spontaneously interacts with Co₃O₄ to form surface-stabilized phenoxyl radicals, which, contrary to conventional wisdom, do not directly degrade pollutants but predominantly act as essential mediators for activating peroxymonosulfate (PMS). Combined experimental and theoretical analyses reveal that the phenoxyl radicals facilitate the elongation of the OO bond in PMS, thereby significantly lowering the activation barrier. Driven by this unique mediation, the system achieves a remarkable 65.2% enhancement in the pollutant degradation rate and a 70.8% increase in the PMS activation efficiency. The synergy between phenoxyl radicals and the ZnO-derived neutral microenvironment in designed Zn/Co composite oxide enables efficient pollutant degradation over a wide pH range with minimal cobalt leaching. Moreover, this synergy substantially improved the biodegradability of actual industrial wastewater. This work unveils a previously unrecognized but critical pathway in heterogeneous Fenton-like catalysis and provides a novel strategic paradigm for designing highly efficient and environmentally benign oxidation technologies.