Ultrasound-assisted heterogeneous Fenton-like process for methylene blue removal using magnetic MnFe2O4/biochar nanocomposite

Abstract In this study, a MnFe2O4 nanocomposite (MnFe2O4/BC) using biochar as the carrier was prepared by a simple hydrothermal method, and then an ultrasound-assisted heterogeneous Fenton-like process was used to catalytically degrade methylene blue (MB). The catalyst was characterized by SEM, TEM, BET, XRD, FTIR, VSM, and XPS. The results showed that spherical MnFe2O4 was successfully loaded onto the biochar surface. The introduction of biochar inhibited the aggregation of MnFe2O4 and greatly increased the specific surface area from 41.4 m2/g to 95.1 m2/g. When using the MnFe2O4/BC composite as an ultrasound-assisted heterogeneous Fenton-like catalyst, 95% of MB (20 mg/L) was degraded at pH = 5 in the presence of 15 mmol/L H2O2 in 20 min, exhibiting a reaction rate constant of 0.09 min−1 much larger than that over MnFe2O4 (0.00995 min−1). This efficiency may be due to the synergistic effect of ultrasound and MnFe2O4/BC, which simultaneously induced the generation of reactive radicals and increased the mass transfer rate at the solid–liquid interface. Compared with other catalysts, the degradation and mineralization levels of MB over MnFe2O4/BC catalyst are greatly improved. These results indicate that MnFe2O4/BC has significant potential for use as a highly efficient and low-cost catalyst for ultrasound-assisted heterogeneous Fenton-like systems.