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

Highly ordered mesoporous MnFe 2 O 4 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 MnFe 2 O 4 was far superior than that of spinel MnFe 2 O 4 , 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 MnFe 2 O 4 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 MnFe 2 O 4 was reusable over five consecutive cycles and negligible leaching of metal ions was observed during catalytic reaction. The balance among Mn 2+ /Mn 3+ , Fe 2+ /Fe 3+ 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.