Enhanced persulfate oxidation of organic pollutants and removal of total organic carbons using natural magnetite and microwave irradiation

Natural magnetite (Fe3O4) and microwave (MW) irradiation were applied to activate persulfate (PS) for the degradation of p-nitrophenol (PNP) with superior activity. The characteristics of natural magnetite were systematically inspected and analyzed. The MW + PS + Fe3O4 system showed a high degradation efficiency for PNP (94.2% within 28 min under the conditions of [PNP] = 20 mg·L−1, [Fe3O4] = 2.5 g·L−1, [PS]/[PNP]molar = 15/1, T = 80 °C), which was better than MW + PS system at the same reaction temperature. With the help of quenching experiment and electron paramagnetic resonance (EPR), we found that of the generated radicals, SO4− was responsible for most the oxidation and OH played a minor role. Regarding the effects of coexisting ions, the different ions exhibited different influence on degradation performance. Specifically, chloride ion showed an accelerating effect, whereas sulfate, phosphate and carbonate showed an inhibitory effect, and nitrate showed negligible effect for PNP decomposition performance. This unique ion effect was ascribed to the generation of ferrous-ligand complexes and the secondary radical reaction between the sulfate radicals and coexisting ions. Both metronidazole and sulfadiazine were also treated well in the present system. The practical and economic applicability of MW + PS + Fe3O4 system were discussed. All in all, our unique MW + PS + Fe3O4 system opens a new path for advanced oxidation.