Activation of Peroxymonosulfate by Magnetic MnFe2O4/MWCNT Toward Rhodamine B Degradation: Efficiency, Mechanism and Influencing Factors

A solvothermal route was used to synthesize manganese ferrite/multi-wall carbon nanotubes (MnFe2O4/MWCNT) composite catalyst, which was firstly employed to activate peroxymonosulfate (PMS) to eliminate rhodamine B (RhB) from water. The catalytic activity of the as-obtained MnFe2O4/MWCNT for PMS activation and RhB degradation was higher than that of MnFe2O4 and MWCNT. The optimal MnFe2O4/MWCNT-10 catalyst (0.3 g/L) can remove 98.1% of RhB (20 mg/L) from water by activating PMS (1.0 g/L) after 100 min of reaction, and this catalyst remained stable in the oxidation process. Quenching experiments, X-ray photoelectron spectroscopy (XPS) and electrochemical analysis demonstrated that RhB elimination in the MnFe2O4/MWCNT-PMS system was accomplished by the non-radical (1O2 and electron transfer) and free radical (O2•−, SO4•‒ and •OH) oxidation pathways, and 1O2 played a leading role. The influence of operational factors (PMS dosage, initial solution pH, catalyst dosage, reaction temperature, common inorganic anions and water matrix) on RhB removal by MnFe2O4/MWCNT-10 activated PMS was investigated in detail. The presence of Cl‒ ions significantly boosted RhB degradation due to the production of more 1O2.