Enhanced activation of persulfate by magnetic NiFe2O4@CuO coupled with ultrasonic for degradation of oxytetracycline: Activation mechanism and degradation pathway

Coupled advanced oxidation processes (AOPs) based on ultrasound and transition metal-activated persulfate (PS) have attracted considerable attention for the degradation of antibiotics. NiFe2O4@CuO composites with core–shell structure were prepared by hydrothermal-freeze-drying-synchronous pyrolysis and coupled with ultrasound to degrade oxytetracycline (OTC) via activated PS. The coupled oxidation process (15-NFO@CuO/US/PS) can substantially enhance the degradation rate of OTC due to the synergistic effects from both ultrasonic and metal activation. X-ray photoelectron spectroscopy reflects that the synergistic interaction between the metals on the 15-NFO@CuO surface can effectively enhance the redox cycling process of metal ions and promote PS activation. Free radical quenching experiments and electron paramagnetic resonance spectroscopy (EPR) identified and confirmed the presence of sulfate radicals (SO4•−), hydroxyl radicals (•OH), and superoxide radicals (O2•−). In addition, the degradation pathways and intermediates of OTC were proposed based on liquid chromatography-mass spectrometry (LC-MS) and three-dimensional excitation-emission matrix (3D-EEM) analysis.