FeO_x/MnO_y modified oxidized carbon nanotubes as peroxymonosulfate activator for organic pollutants degradation

In this work, the FeO_x/MnO_y decorated oxidized carbon nanotubes (CNTs-Fe-Mn) composites were synthesized and used as catalysts to activate peroxymonosulfate (PMS) for organic pollutants degradation. The catalytic ability of the CNTs-Fe-Mn catalyst was strongly correlated with the oxidation of CNTs and the molar ratio of Fe/Mn. When the CNTs was oxidized by 30 wt% HNO₃ and the modified molar ratio of Fe/Mn was 0.5, the 30%-CNTs-Fe-Mn-0.5 showed highest efficiency for rhodamine B (RhB) degradation via activating PMS, and the removal rate of 95% was achieved in 60 min at room temperature in 15 mg L^-1 RhB solution with catalyst dosage of 0.1 g L^-1. Fe and Mn multivalent oxide species coexisted were randomly distributed on the outer surface and encapsulated into the channels of oxidized CNTs in the 30%-CNTs-Fe-Mn-0.5 catalyst. The XPS results of catalysts before and after reaction proved that the redox cycles between the multivalent states of Fe and Mn ensured the superior catalytic activity of the 30%-CNTs-Fe-Mn-0.5 for PMS activation. The radical quenching tests and D₂O experiments confirmed that SO₄^-, HO· and O₂^- radicals were the main reactive oxidized species for the oxidation of pollutants in the 30%-CNTs-Fe-Mn-0.5/PMS system. In addition, the influences of operation parameters including initial pH, pollutant concentration, catalyst dosage, and PMS dosage on catalytic degradation were investigated.