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

A weak magnetic field (WMF) was employed to enhance the degradation of 4-nitrophenol (4-NP) by the advanced Fenton process (Fe-0/H2O2) in this study. Although the oxidation rates of 4-NP by Fe-0/H2O2 and WMF-Fe-0/H2O2 dropped sharply upon increasing the initial pH (pH(ini)), the introduction of WMF could remarkably improve the 4-NP degradation by Fe-0/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 pH(ini) 4.0 and the cumulative concentration of HOc in the WMF-Fe-0/H2O2 system was about 3-fold that in Fe-0/H2O2 system. The superimposed WMF increased the generation of HOc in the Fe-0/H2O2 process by accelerating the Fe0 corrosion and FeII generation, which was the limiting step of the Fe-0/H2O2 process. The application of WMF largely enhanced the mineralization of 4NP 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-Fe-0/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 Fe-0 and H2O2 dosages were beneficial for 4-NP degradation by WMF-Fe-0/H2O2. Among the three factors (pH(ini), Fe-0 dosage, and H2O2 dosage) investigated, pH(ini) was the most important factor affecting the performance of the WMF-Fe-0/H2O2 process. The WMF-Fe-0/H2O2 technology provides a newalternative for scientistsworking in the field of water treatment.