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

Abstract

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.