[Degradation of OG with Peroxymonosulfate Activated by a MnFe₂O₄-graphene Hybrid]

The rG-MnFe₂O₄ was synthesized by hydrothermal method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectra. The rG-MnFe₂O₄ was used to activate peroxymonosulfate (PMS) to decolorize azo dyes, e.g., Orange G, and the effect of PMS dosage, rG-MnFe₂O₄ loadings, initial pH, and the concentration of Cl^- were investigated. The results indicated that the degradation rate of OG was 100% within 27 min with 0.3 g ·L^-1 of rG-MnFe₂O₄ and at a 40:1 of PMS:OG molar ratio. The decolorization efficiency of OG increased with increasing PMS concentration and increasing rG-MnFe₂O₄ dosage. The initial pH had a significant effect on OG degradation, and pH 5.00 was most favorable for its decolorization. In addition, the addition of Cl^- accelerated the decolorization of OG, and the decolorization rate increased with increasing concentration of Cl^-. The rG-MnFe₂O₄ also exhibited an excellent reusability, and its activation of PMS was still observed after five rounds of tests. From the analysis of UV-vis spectra and gas chromatography-mass spectrometry (GC/MS), the naphthalene ring and azo band were found to be destroyed, with p-nitrophenol and phthalic acid as the main degradation products. Finally, a TOC analysis indicated that a certain degree of OG mineralization was obtained in the rG-MnFe₂O₄/PMS system.