Two facile synthesis routes for magnetic recoverable MnFe2O4/g-C3N4 nanocomposites to enhance visible light photo-Fenton activity for methylene blue degradation

High-efficiency photocatalyst MnFe2O4/g-C3N4 nanocomposites were successfully synthesized to degrade methylene blue (MB). Two types of magnetic recoverable nanocomposite (MG1 and MG2), which were fabricated using co-precipitation and calcination methods, were characterized using various analytical techniques and applied as heterogeneous catalysts for H2O2 activation under simulated sunlight irradiation. The results revealed that composing g-C3N4 in the composites improved the MnFe2O4 crystallinity and increased the material magnetism which facilitated them for efficient recovery using an external magnet. The MG2 synthesis strategy effectively suppressed particle aggregation and immensely increased the active surface area more than for MG1. The quenching experiments revealed that photogenerated electrons played an important role in the catalytic reaction and singlet oxygen (O-1(2)) was a dominant reactive species for MB degradation. The XPS analysis before and after treatment confirmed that the generated O-1(2) was derived from the interaction of metal ions and oxygen vacancy in the H2O2 activation. While both nanocomposites exhibited excellent catalytic ability at near-neutral pH levels and for different real water matrices, MG2 had better MB degradation performance but greater difficulty with gravity settling due to its much smaller particle sizes. Therefore, MG2 large-scale production may require more cumbersome steps. However, both nanocomposites showed high crystallinity and very low metal leaching after several uses and still maintained their magnetism. These observations support the use of our MG nanocomposites as potential photocatalysts to activate H2O2 for the degradation of an organic contaminant in water.