Interfacial structural defects in biochar-decorated MnCo spinel nanosheets for boosted peroxymonosulfate activation:...

Spinel-based transition metal oxides are potential activators for peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) in water purification, yet their sluggish redox cycling, stemming from poor conductivity, remains a critical limitation. In this work, a distiller's grain-derived porous biochar (BC)-decorated MnCo spinel nanosheet catalyst (MnCoO_x@BC) is developed and applied for PMS activation. The catalyst exhibits high efficacy in degrading ibuprofen (IBU), achieving complete removal within 5 min with an apparent reaction rate constant of 1.08 min^-1 ([IBU] = 10 mg L^-1, [catalyst] = 200 mg L^-1, [PMS] = 200 mg L^-1), which is 18 and 15 times for pristine BC and unsupported MnCoO_x, respectively. Characterization and DFT calculation results indicate that the introduction of biochar could improve the conductivity and induce the formation of abundant oxygen defects, which accelerate the redox cycles of Co (III)/Co (II) and Mn (IV)/Mn (III) catalytic centers. This interfacial configuration facilitates the conversion of PMS into peroxysulfate radical (SO₅•^-) and superoxide radical (O₂•^-) species, and finally towards singlet oxygen (¹O₂), establishing a non-radical dominant pathway where ¹O₂ accounts for over 95% of the reactive species contribution. This work presents an effective strategy for developing defect-controlled catalytic interfaces to modulate the d-band center of metal sites and steer the interfacial electron transfer pathway, offering profound insights into non-radical-dominated mechanisms for the degradation of emerging micropollutants.