Performance and mechanism of magnetic Fe3O4@MnO2 catalyst for rapid degradation of methylene blue by activation of peroxymonosulfate

A flower ball shaped magnetic Fe3O4@MnO2 core-shell catalyst has been synthesized and the average diameter is about 135~180 nm. The Fe3O4@MnO2 (140.6 m2 g-1) showed a larger specific surface area than Fe3O4 (64.6 m2 g-1) due to the thin film like nature of MnO2. The Fe3O4@MnO2 exhibited a great degradation performance for methylene blue (MB, 20 mg L-1, pH=7) after the addition of peroxymonosulfate (PMS, 0.18 g L-1) when the dosage of Fe3O4@MnO2 is 0.3 g L-1, which reached 98% within 20 min. Additionally, the influences of catalyst dosage, PMS concentration and initial pH value of MB solution have been studied to maximize the catalytic performance of Fe3O4@MnO2. Results showed that the increase of catalyst dosage and PMS concentration have improved the degradation efficiency and reaction rate of MB. However, the effect of pH on MB removal was complex and has been analyzed. According to XPS and quenching studies, the degradation effects of free radicals produced by catalyst-activated PMS on MB followed the order 1O2> •OH> SO4•−. This research demonstrates that Fe3O4@MnO2 is an effective catalyst for the degradation of organic dye MB.