Role of Mg in mesoporous MgFe2O4 for efficient catalytic ozonation of Acid Orange II

BACKGROUND: An ozonation catalyst needs to be recycled easily and to exhibit high activity in view of its practical application in wastewater treatment. In this study, magnetic mesoporous MgFe₂O₄ was successfully prepared and used as a new ozonation catalyst for degradation of Acid Orange II (AOII). The role of Mg in MgFe₂O₄ was revealed to explain the high activity by catalytic experiments and XPS analysis. RESULTS: The degradation efficiency of AOII in the MgFe₂O₄/O₃ process exceeds 90% over a wide pH range of 4.6–9.6, slightly affected by the solution pH. The catalytic activity of MgFe₂O₄ is much higher than that of MgO, Fe₂O₃ and also their mixture (MgO+Fe₂O₃) with identical molar ratio of Mg²⁺ to Fe³⁺, indicating the first role of Mg, i.e. coupling with Fe to present a synergistically catalytic effect. Furthermore, MgFe₂O₄ possesses a reaction rate constant at least 2.3 times that of NiFe₂O₄, MnFe₂O₄, and CuFe₂O₄. It illustrates the second role of Mg, i.e. causing the high electron density on lattice oxygen in MgFe₂O₄ indicated by XPS and thus favoring activation of the electrophilic ozone. CONCLUSIONS: This study demonstrated the easy recycling and high activity of MgFe₂O₄ in catalytic ozonation, and revealed the role of Mg in MgFe₂O₄. © 2015 Society of Chemical Industry