Green fabrication of magnetic recoverable graphene/MnFe2O4 hybrids for efficient decomposition of methylene blue and the Mn/Fe redox synergetic mechanism

Herein, we report an environmentally benign synthesis of a high-performance reduced graphene oxide/MnFe2O4 (RGO/MnFe2O4) catalyst for methylene blue (MB) decomposition in neutral solution using a GO/MnSO4 suspension from a modified Hummers method and FeSO4 as the precursors. The as-prepared RGO/MnFe2O4 catalyst shows exceptional performance towards the MB decomposition in the presence of H2O2. In particular, 10 mL of MB (50 mg L-1) can be thoroughly decolorized in 130 min and 78% mineralized with 5 mg of RGO/MnFe2O4 hybrid at room temperature. More interestingly, the catalysts can be magnetically recycled. The good catalytic performance of the RGO/MnFe2O4 hybrid is not only attributed to the synergetic effects of RGO, MnFe2O4, H2O2 and MB molecules, but also related to the redox couples of Fe/Mn ions during the reaction. We have firstly experimentally demonstrated that the catalytic performance of MnFe2O4 is dominated by Fe3+/Fe2+ in the initial stage (<70 min) then by Mn3+/Mn2+ in the later stage (>70 min), while Fe2+/Mn3+ redox in turn benefits the redox cycles of Fe3+/Fe2+ and Mn3+/Mn2+. Our results not only provide an alternative strategy for green synthesis of high-performance functional nanomaterials, but also promote a deep understanding of the mechanism of MnFe2O4 catalyst for MB decomposition.