Fabrication of novel magnetic MnFe2O4/bio-char composite and heterogeneous photo-Fenton degradation of tetracycline in near neutral pH

Iron-based magnetic materials are deemed to be promising catalysts for various catalytic reactions and can be recovered conveniently by an external magnetic field. MnFe2O4 nanoparticle and MnFe2O4/bio-char composite with different bio-char contents were prepared to activate hydrogen peroxide for the degradation of tetracycline (TC). The catalysts were characterized by SEM, BET, XRD, FTIR, VSM and XPS. The results indicated that MnFe2O4 had a spherical shape and was successfully loaded onto the surface of bio-char. The introduction of bio-char effectively suppressed the aggregation of MnFe2O4 and drastically increased the specific surface area. Both MnFe2O4 and MnFe2O4/bio-char composite can be separated easily by an external magnetic field. Using 1:2 composite as heterogeneous photo-Fenton catalyst obtained a degradation of 95% through visible light irradiation of 40 mg L-1solution at natural pH (pH = 5.5) in the presence of 100 mmol L-1 H2O2 for 2 h. Free radical quenching experiment and the ESR results confirm that hydroxyl radicals play the main role for TC degradation. XPS measurements show that both Fe and Mn ions simultaneously participate in the activation of H2O2. The bio-char not only restrains the aggregation of MnFe2O4 leading to the improved removal efficiency of TC, but also has side effects by consuming hydroxyl radicals. By cyclic degradation experiments, the performance of MnFe2O4/bio-char composite is stable and almost unchanged, and the leaching metal ions of both Fe and Mn are neglectful (both below 0.2 mg L-1). Besides, steady performance of MnFe2O4/bio-char catalyst to remove TC from tap water and river water has been certified.