Ozone catalytic oxidation of biologically pretreated semi-coking wastewater (BPSCW) by spinel-type MnFe2O4 magnetic nanoparticles

In this study, spinel-type MnFe2O4 magnetic nanoparticles were successfully synthesized employing the purified sol-gel method and used for the advanced treatment of biologically pretreated semi-coking wastewater (BPSCW) by the O-3/H2O2 catalytic system. Results showed that the MnFe2O4 magnetic catalysts did not have a regular surface morphology, and their surface contained numerous fine particles that showed a particle accumulation state and formed a good nano-spinel structure. Their surface morphology, ratio, size, and X-ray photoelectron spectroscopy revealed two active metal elements in the catalyst, namely, Fe3+ and Mn2+, which were consistent with the elemental composition and valence of MnFe2O4. Under optimal reaction conditions, the removal efficiency of O-3/H2O2/MnFe2O4 catalytic system for chemical oxygen demand (COD) and volatile phenol (VP) can reach 85.2% and 94.1%, respectively (catalyst dosage = 2.0 g.L-1, O-3 dosage = 1.2 mg.min(-1), H2O2 concentration = 0.15 mol.L-1, pH = 7.0, and treatment time = 70 min). The free radical quenching experiment and electron paramagnetic resonance (EPR) experiment verified that hydroxyl radicals (center dot OH) played a role in the deep treatment of BPSCW in the O-3/H2O2/MnFe2O4 catalytic system. Phosphate experiments proved that lewis acid sites on the surface of the MnFe2O4 magnetic catalysts were the catalytically active sites. The superparamagnetic properties of the MnFe2O4 magnetic catalysts (67.8 emu.g(-1)) facilitated magnetic separation from the treated wastewater. After 10 cycles, the activity of the MnFe2O4 magnetic catalysts remained high, and the removal efficiencies of COD and VP only decreased by 13.6% and 11.9%, respectively. Considering excellent degradation performance, easy magnetic separation and high stability, this study provided important insights into the practical application of the O-3/H2O2 catalytic system for the advanced treatment of BPSCW.