Activation of peroxymonosulfate by α-MnO₂ for Orange Ⅰ removal in water

Developing high-efficiency catalysts for peroxymonosulfate (PMS)-based advanced oxidation processes is important for eliminating pollutants in water. Herein, α-MnO₂ with major exposed {110} and {100} facets prepared via a hydrothermal method were used as catalysts to activate PMS for the degradation of Orange Ⅰ (OⅠ). α-MnO₂-100, with more abundant surface hydroxyl groups and greater reductive ability, performed remarkably better than α-MnO₂-110 for degrading OⅠ. OⅠ removal of 86.20% was obtained in the α-MnO₂-100/PMS system. The apparent rate constant of OⅠ removal over α-MnO₂-100 was 2.11 times higher than that of α-MnO₂-110. The effects of PMS concentration, catalyst dosage, OⅠ concentration, initial pH, anions and humic acid (HA) on OⅠ degradation in the α-MnO₂-100/PMS system were systematically investigated. Quenching experiments and electron paramagnetic resonance (EPR) demonstrated that SO₄^•-, •OH, O₂^•- and ¹O₂ were the reactive oxygen species (ROS) in the α-MnO₂-100/PMS system. Moreover, the possible degradation pathway of OⅠ in the α-MnO₂-100/PMS system was proposed. This work provides an ideal metal oxide catalyst for sewage remediation.