Heterogeneous degradation of Orange II with peroxymonosulfate activated by ordered mesoporous MnFe2O4

• Ordered mesoporous MnFe2O4 shows outstanding catalytic activity for peroxymonosulfate.
• Effect of several important operating parameters on the catalytic activity is evaluated.
• Ordered mesoporous MnFe2O4 exhibits superior reusability and stability.
• Sulfate radicals were identified as the dominant active species.
• A plausible activation mechanism was proposed.

Highly ordered mesoporous MnFe2O4 was fabricated via the nanocasting strategy and innovatively used to activate peroxymonosulfate for the degradation of Orange II in water. The effects of several key parameters including catalyst dosage, peroxymonosulfate concentration, temperature and initial pH on the degradation performance were investigated. Results showed that the catalytic activity of ordered mesoporous MnFe2O4 was far superior than that of spinel MnFe2O4, which can be attributed to its unique structural characteristics. Data fitting showed that the Orange II degradation could be described by the pseudo-first-order kinetics under all conditions tested in this study. Ordered mesoporous MnFe2O4 presented stable and excellent catalytic activity in wide pH range of 5–9. Both the increase of catalyst dosage and temperature favored the enhancement in catalytic efficiency. However, the Orange II degradation tended to have a decline trend after an initial ascent as the peroxymonosulfate concentration increased. Moreover, ordered mesoporous MnFe2O4 was reusable over five consecutive cycles and negligible leaching of metal ions was observed during catalytic reaction. The balance among Mn2+/Mn3+, Fe2+/Fe3+ and peroxymonosulfate decomposed in solution was considered as the proposed activation mechanism, and the generation of sulfate radicals played the dominant role in the Orange II degradation.

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