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

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)/HSO 3 − /H 2 O 2 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)/H 2 O 2 system, and the total organic carbon (TOC) removal in 120 min reached 46.8%. The MIL-68(Fe)/HSO 3 − /H 2 O 2 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)/HSO 3 − /H 2 O 2 system as well. The quenching tests and electron paramagnetic resonance (EPR) spectrometry confirmed that OH, SO 4 − , HO 2 , and 1 O 2 were the main reactive species for MO degradation in the MIL-68(Fe)/HSO 3 − /H 2 O 2 system. The coumarin fluorometry further disclosed that much more hydroxyl radicals were generated in the MIL-68(Fe)/HSO 3 − /H 2 O 2 system than in MIL-68(Fe)/H 2 O 2 system. Cyclic voltammetry analysis, on the other hand, indicated that the presence of HSO 3 − facilitated the Fe(III)/Fe(II) cycle in the MIL-68(Fe)/HSO 3 − /H 2 O 2 system. Based on these results, the enhancement mechanism of the Fenton-like MIL-68(Fe)/HSO 3 − /H 2 O 2 system was proposed. Finally, the cyclic experiments manifested the MIL-68(Fe)/HSO 3 − /H 2 O 2 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.