Fe-based metal–organic frameworks as heterogeneous catalysts for highly efficient degradation of wastewater in plasma/Fenton-like systems

Abstract

Fe-based metal organic frameworks (Fe-MOFs) were successfully synthesized with the dielectric barrier discharge (DBD) plasma method and FeSO₄·7H₂O as the Fe precursor. Fe-MOFs were used as Fenton-like catalysts in DBD plasma/Fenton-like technology to treat wastewater, which addressed the issues with iron solubility. Since the valence state of iron will affect the catalytic performance, the Fe precursor FeSO₄·7H₂O was added to regulate the valence state and adjust the catalytic performance by improving the availability of active sites. The influences of discharge voltage, catalyst addition amount, H₂O₂ addition amount and pH on the degradation efficiency of methyl orange (MO) were systematically examined. Through free radical capture experiments, the reaction mechanism of the plasma/Fenton-like catalytic degradation process was deduced primarily as the coordinated oxidation process of hydroxyl radicals (·OH), photo-generated holes (h⁺) and superoxide radicals (·O₂⁻). The reusability experiments proved that the catalyst was stable and reusable. The possible degradation pathways were proposed based on the identification of intermediate products generated in the degradation process by liquid chromatography-mass spectrometry (LC-MS) analyses.