Ascorbic acid enhanced MnFe2O4/peroxymonosulfate oxidation of organic pollutant: Key role of singlet oxygen generation and Fe/Mn cycling

The activated peroxymonosulfate (PMS) process has been widely applied for degrading organic pollutants. However, its application is limited by low metal cycling, and the contribution of oxygen species remains unclear. Here, the crystal structure, surface morphology, and elemental valence of the synthesized manganese ferrite (MnFe2O4) catalyst were investigated by SEM, HRTEM, XRD, and XPS. A novel MnFe2O4/PMS/ascorbic acid (AA) system was constructed to enhance the Fe/Mn cycling on the surfaces of the MnFe2O4 catalyst. The addition of AA can significantly increase the decomposition of organic pollutants, and the apparent rate constant of the MnFe2O4/PMS/AA system is 8.2 times higher than that of MnFe2O4/PMS. AA facilitates the reduction of Fe/Mn(III) and the dissolution of Fe/Mn(II), creating a Fe/Mn cycle between the heterogeneous and homogeneous interfaces of the catalyst. Furthermore, AA greatly increases the activity of adsorbed oxygen on the catalyst surfaces, generating a large amount of singlet oxygen (1O2), which contributes significantly to the destruction of organic pollutants. The efficient, fast, and environmentally friendly PMS activation method in this study can provide reliable technical support for treating refractory organic pollutants in water.