Synthesis of magnetic MFe2O4@PC (M = Fe, Cu, Co, and Mn) composites and application of heterogeneous photo-Fenton efficient removal of metronidazole under visible light

Nanoscale magnetic spinel ferrite composites with the general formula MFe2O4@PC (M = Fe, Cu, Co, and Mn; PC = biochar) were prepared by a facile impregnation and pretreatment method. MFe2O4@PC particles were deliberated by X-ray Diffractometer (XRD), Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM), Brunauer–Emmett–Teller adsorption–desorption isotherm (BET), X-ray Photoelectron Spectroscopy (XPS) and Vibrating Sample Magnetometer. The results showed that MFe2O4 coating, which is evenly distributed on the surface of HNO3-pretreated biochar, can provide more active sites to enable MFe2O4@PC to be activated by visible light. The XRD confirmed that the crystallite sizes of MFe2O4 ranged from 10.0 to 27.9 nm. With the help of surface-OH, PCoF has a rapid adsorption performance on metronidazole (MNZ) and can degrade 99% of MNZ within 20 minutes at an optimal pH of 3.0. Meanwhile, the PCuF composites showed excellent photo-Fenton catalytic performance for the degradation of MNZ under neutral pH conditions, and 96.0% of MNZ (300 mg/L) could be removed within 120 min. This study confirmed OH is the main reactant, while O2− and h+ contributed to the degradation of MNZ during photocatalysis. MFe2O4@PC composite can be separated easily by an external magnetic field. The synthesized PCoF was reused for 5 cycles and it was clear that it had no significant loss, indicating its excellent ability to remove MNZ from wastewater.