Unveiling the critical roles of nascent MnO₂ in accelerating permanganate carbocatalysis

To probe the underlying mechanisms of carbocatalysis in enhanced permanganate (PM) oxidation and identify the exact roles of nascent MnO₂, graphene aerogels (GA) were fabricated to activate PM for naproxen (NPX) degradation. All the three GA samples could accelerate NPX oxidation by PM, the rate constants and reaction stoichiometric efficiency (RSE) followed the order of GA900 > GA600 > GA300. Mechanistic studies revealed that Mn(VI), Mn(V) and Mn(III) were not the major reactive species involved in NPX oxidation, but highlighted the essential contribution of electron transfer pathway (ETP) mediated directly by GA and indirectly by nascent MnO₂. For GA300 with strong electron-donating capability, it mainly served as the electron donor for PM decomposition, and indirectly oxidized NPX via nascent MnO₂ mediated ETP, thereby exhibiting inferior RSE as well as mediocre recycling performance. GA600 and GA900 could serve as the electron shuttle to directly mediate the ETP for NPX degradation, the nascent MnO₂ accumulated on GA framework during the reaction would also mediate the ETP from NPX to PM, thus displaying an obvious accelerating recycling performance. This work provides novel insights into the structure-dominated PM carbocatalysis, which contributes better to development of promising carbocatalysts and utilization of nascent MnO₂.