Mn-O Covalency Governs the Intrinsic Activity of Co-Mn Spinel Oxides for Boosted Peroxymonosulfate Activation.

Transition metal (TM)-based bimetallic spinel oxides can efficiently activate peroxymonosulfate (PMS) presumably attributed to enhanced electron transfer between TMs, but the existing model cannot fully explain the efficient TM redox cycling. Here, we discover a critical role of TM-O covalency in governing the intrinsic catalytic activity of Co _3-x Mn _x O ₄ spinel oxides. Experimental and theoretical analysis reveals that the Co sites significantly raises the Mn valence and enlarges Mn-O covalency in octahedral configuration, thereby lowering the charge transfer energy to favor Mn _Oh -PMS interaction. With appropriate Mn ^IV /Mn ^III ratio to balance PMS adsorption and Mn ^IV reduction, the Co _1.1 Mn _1.9 O ₄ exhibits remarkable catalytic activities for PMS activation and pollutant degradation, outperforming all the reported TM spinel oxides. The improved understandings on the origins of spinel oxides activity for PMS activation may inspire the development of more active and robust metal oxide catalysts.
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