Efficiency and Mechanism of Degradation of Methylene Blue with H2O2 Catalyzed by Magnetic Mn0.6Zn0.4Fe2O4@SiO2

To prepare high-efficiency heterogeneous Fenton catalysts with easy solid-liquid separation and good stability, Mn0.6Zn0.4Fe2O4 magnetic nanoparticles (SF-MNPs) were functionally modified through hydrolysis of tetraethylorthosilicate, and Mn0.6Zn0.4Fe2O4@SiO2 (MZF@SiO2) magnetic nanocomposite (MNC) catalysts were prepared. MZF@SiO2 was characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, and a vibrating sample magnetometer. The effect of different initial pH on the catalytic performance of MZF@SiO2 was investigated using methylene blue (MB) refractory azo dye as the target pollutant. Under the initial near-neutral pH condition (pH=6.5), the effects of H2O2dosage, MZF@SiO2 dosage, and temperature on the removal efficiency of MB were investigated. The stability and recycling performance of MZF@SiO2 were studied, and the catalytic reaction mechanism was speculated. The results showed that SF-MNPs were completely encapsulated by amorphous SiO2, and MZF@SiO2 had a "core-shell" structure. Magnetic core SF-MNPs had good crystallinity with a spinel structure. The saturation magnetization of MZF@SiO2 was 18.6 emu•g-1, and the remanence and coercivity were low. The dispersibility and solid-liquid separation performance of MZF@SiO2 were excellent in water. Under the condition of neutral pH, the utilization rate of H2O2 was 74.50%, and the removal rate of MB reached 94.76%. When the reaction time was 120 min, the temperature was 303 K, and the dosage of MZF@SiO2 was 1.0 g•L-1. The first-order reaction rate constant was 0.046 6 min-1, and MZF@SiO2 had good stability and recycling performance. The solid-liquid interface reaction was the rate control step of the process. The reactive oxygen species in the MZF@SiO2+H2O2 system were •OH radicles. The coating layer SiO2 could accelerate the electron transfer rate, and there was a positive synergistic effect between SiO2 and SF-MNPs. The existence of oxygen vacancies in SF-MNPs was also conducive to the electron transfer in the heterogeneous Fenton-like reaction. The as-prepared MZF@SiO2 MNC catalysts had a superior catalytic activity with good stability, and they had the advantages of easy magnetic separation and reusability. Thus, MZF@SiO2 MNC catalysts have a wider range of potential applications in actual printing and dyeing wastewater treatment. © 2022, Science Press. All right reserved.