Single-Atom Mn–N₄ Site-Catalyzed Peroxone Reaction for the Efficient Production of Hydroxyl Radicals in an Acidic Solution

Abstract

The peroxone reaction between O₃ and H₂O₂ has been deemed a promising technology to resolve the increasingly serious water pollution problem by virtue of the generation of superactive hydroxyl radicals (^•OH), but it suffers greatly from an extremely limited reaction rate constant under acidic conditions (ca. less than 0.1 M^-1 s^-1 at pH 3). This article describes a heterogeneous catalyst composed of single Mn atoms anchored on graphitic carbon nitride, which effectively overcomes such a drawback by altering the reaction pathway and thus dramatically promotes ^•OH generation in acid solution. Combined experimental and theoretical studies demonstrate Mn-N₄ as the catalytically active sites. A distinctive catalytic pathway involving HO₂^• formation by the activation of H₂O₂ is found, which gets rid of the restriction of HO₂^- as the essential initiator in the conventional peroxone reaction. This work offers a new pathway of using a low-cost and easily accessible single-atom catalyst (SAC) and could inspire more catalytic oxidation strategies.