Enhancement of the advanced Fenton process by weak magnetic field for the degradation of 4-nitrophenol

Xiong, Xinmei; Sun, Yuankui; Sun, Bo; Song, Weihua; Sun, Jingyi; Gao, Naiyun; Qiao, Junlian; Guan, Xiaohong

Enhancement of the advanced Fenton process by weak magnetic field for the degradation of 4-nitrophenol

2015

A weak magnetic field (WMF) was employed to enhance the degradation of 4-nitrophenol (4-NP) by the advanced Fenton process (Fe⁰/H₂O₂) in this study. Although the oxidation rates of 4-NP by Fe⁰/H₂O₂ and WMF–Fe⁰/H₂O₂ dropped sharply upon increasing the initial pH (pHᵢₙᵢ), the introduction of WMF could remarkably improve the 4-NP degradation by Fe⁰/H₂O₂ at pHᵢₙᵢ ranging from 3.0 to 6.0. The quenching and electron paramagnetic resonance experiments verified that the hydroxyl radical was the primary oxidant responsible for the 4-NP degradation at pHᵢₙᵢ 4.0 and the cumulative concentration of HO˙ in the WMF–Fe⁰/H₂O₂ system was about 3-fold that in Fe⁰/H₂O₂ system. The superimposed WMF increased the generation of HO˙ in the Fe⁰/H₂O₂ process by accelerating the Fe⁰ corrosion and Feᴵᴵ generation, which was the limiting step of the Fe⁰/H₂O₂ process. The application of WMF largely enhanced the mineralization of 4-NP but it did not change the 4-NP degradation pathways, which were proposed based on the degradation products detected with LC-MS/MS. The optimum intensity of the magnetic field for 4-NP oxidation by WMF–Fe⁰/H₂O₂ was determined to be 20 mT. Response surface methodology (RSM) was applied to analyze the experimental variables and it was found that lower pH and higher Fe⁰ and H₂O₂ dosages were beneficial for 4-NP degradation by WMF–Fe⁰/H₂O₂. Among the three factors (pHᵢₙᵢ, Fe⁰ dosage, and H₂O₂ dosage) investigated, pHᵢₙᵢ was the most important factor affecting the performance of the WMF–Fe⁰/H₂O₂ process. The WMF–Fe⁰/H₂O₂ technology provides a new alternative for scientists working in the field of water treatment.

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