Switching Peroxymonosulfate Redox Routes by Manipulating Spinel Tetrahedral and Octahedral Site Activity for Multi-Scenario Wastewater Treatment.

Abstract

For diverse wastewater treatment scenarios, achieving controllable switching of reactive oxygen species within a unified catalytic system remains a major challenge. Here, an inert cation substitution strategy is proposed to regulate tetrahedral and octahedral Co activity in Co₃O₄, enabling controllable switching between radical and nonradical pathways. Octahedral-Co-enriched ZnCo₂O₄ (ZCO) selectively directs peroxymonosulfate (PMS) activation toward the ¹O₂ pathway (95.8% contribution), whereas tetrahedral-Co-dominated CoAl₂O₄ (CAO) favors radical oxidation, with •OH (76.4%) and SO₄ ^•- (21.7%) dominating. This polyhedral-dependent pathway control leads to distinct oxidation behaviors. Notably, the ZCO/PMS system achieved nearly 100% o-nitrophenol (ONP) degradation within 4 min, with a k-value of 71.81 min^-1 M^-1, 32.2 times that of Co₃O₄. Multiple lines of evidence reveal that polyhedral-site engineering governs PMS adsorption geometry, interfacial charge redistribution, and O─O bond activation, thereby determining pathway selection. These differentiated functions were further translated into bench-scale municipal wastewater treatment, with ZCO/PMS increasing the effluent Biochemical oxygen demand/chemical oxygen demand (BOD/COD) ratio from below 0.3 to consistently above 0.5 over 80 h and CAO/PMS decreasing the effluent TOC from ∼25 mg L^-1 to below 12 mg L^-1 over 60 h. Both systems exhibited low biotoxicity and favorable sustainability, offering a practical route toward selective energy-efficient advanced oxidation.