Magnetic Fe3O4@CoFe-LDH nanocomposite heterogeneously activated peroxymonosulfate for degradation of azo-dye AO7

In this study, a novel core@shell magnetic nanocomposite Fe3O4/CoFe-layered double hydroxide (Fe3O4@CoFe-LDH) was successfully synthesized by the co-precipitation method, and then employed as an efficient heterogeneous catalyst for activation of peroxymonosulfate (PMS) in removal of azo-dye acid orange 7 (AO7). The as-obtained nanocomposite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results from these characterizations showed Fe3O4@CoFe-LDH to possess good ferromagnetism and a perfect crystalline structure with a typical core@shell morphology. The system of Fe3O4@CoFe-LDH11/PMS (cobalt : iron molar ratio of 1 : 1) achieved 95.1% removal rate of AO7 (40 mg L-1) within 15 min under the optimized conditions, which outperformed bare Fe3O4 and raw CoFe-LDH11. Meanwhile, Fe3O4@CoFe-LDH11 displayed good adaptability in a wide pH range from 4 to 9 and relatively low PMS activation energy (39.9 kJ mol(-1)). The interference tests revealed HCO3- to possess the strongest restriction effect. Only 57.7% AO7 was removed when 10 mM HCO3- was introduced, which was ascribed to HCO3- not only serving as a radical scavenger, but also increasing the pH of the system. The radical quenching tests demonstrated SO4- as the dominant reactive species during the catalytic reaction. Based on X-ray photoelectron spectroscopy (XPS) analysis, the core structure of Fe3O4 served as an electron donor for accelerating the cycle of Co(ii)/Co(iii) at the active site of the LDH outer shell. Also, Fe3O4@CoFe-LDH exhibited outstanding stability and recyclability, and maintained high degradation efficiency of AO7 even after five cycles. In sum, the proposed magnetic Fe3O4@CoFe-LDH nanocomposite has great potential for remediation of wastewater contaminated with synthetic dyes.