Strong enhancement effect of bisulfite on MIL-68(Fe)-catalyzed Fenton-like reaction for organic pollutants degradation

Abstract

Metal organic frameworks (MOFs) have shown a great potential to act as heterogeneous Fenton-like catalysts. However, the lower catalytic efficiency and reaction rate are limiting their practical applications. Herein, a facile and efficient strategy was studied to boost the catalytic oxidation performance of MIL-68(Fe)-mediated Fenton-like process with the addition of a minor amount of bisulfite. The factors affecting the catalytic oxidation capacity of the MIL-68(Fe)/HSO3−/H2O2 system were investigated using methyl orange (MO) as model pollutant. Under the optimal condition, the degradation rate of MO could be increased by 11.5 times compared to that in MIL-68(Fe)/H2O2 system, and the total organic carbon (TOC) removal in 120 min reached 46.8%. The MIL-68(Fe)/HSO3−/H2O2 system also displayed a wide applicable pH range. Besides MO, other organic contaminants such as acid red 18 (AR18), rhodamine B (RhB), methylene blue (MB), xylenol orange (XO) and tetracycline hydrochloride (TC) could be effectively degraded in the MIL-68(Fe)/HSO3−/H2O2 system as well. The quenching tests and electron paramagnetic resonance (EPR) spectrometry confirmed that OH, SO4−, HO2, and 1O2 were the main reactive species for MO degradation in the MIL-68(Fe)/HSO3−/H2O2 system. The coumarin fluorometry further disclosed that much more hydroxyl radicals were generated in the MIL-68(Fe)/HSO3−/H2O2 system than in MIL-68(Fe)/H2O2 system. Cyclic voltammetry analysis, on the other hand, indicated that the presence of HSO3− facilitated the Fe(III)/Fe(II) cycle in the MIL-68(Fe)/HSO3−/H2O2 system. Based on these results, the enhancement mechanism of the Fenton-like MIL-68(Fe)/HSO3−/H2O2 system was proposed. Finally, the cyclic experiments manifested the MIL-68(Fe)/HSO3−/H2O2 system had good stability and reusability. This study suggests that the addition of bisulfite being an excellent approach to construct the Fe-MOFs mediated Fenton systems for eliminating organic contaminants in water with high efficiency.