Effects of Fe(II)/Fe(III) of Fe-MOFs on catalytic performance in plasma/Fenton-like system

Abstract

Fe-MOFs with FeSO4·7H2O and FeCl3·6H2O precursor were successfully prepared by dielectric barrier discharge (DBD) plasma method to regulate the Fe(II)/Fe(III) ratios. Different Fe(II)/Fe(III) ratios of Fe-MOFs were studied to reveal the catalytic mechanism of degradation in DBD plasma/Fenton-like system. Herein, for the first time, Fe-MOFs could be transformed between Fe(II) unsaturated metal sites (CUS) and Fe(III)CUS by the photo-generated electron (e−) generated with plasma, thereby promoting Fe(II)/Fe(III) cycle. The similar ratio of Fe(II) and Fe(III) in the fresh and used Fe-MOF-4 might account for the high catalytic activity and indicated the existence of a certain electronic cycle. In addition, Fe(II) and Fe(III) had synergistic effect in plasma/Fenton-like system and the degradation rate of 200 mL (200 mg/L) methyl orange (MO) reached 99.2 % at 6 min. Through free radical capture experiments, the reaction mechanism of the plasma/Fenton-like catalytic degradation process was deduced mainly as the coordinated oxidation process of hydroxyl radicals (∙OH), photo-generated holes (h+) and superoxide radicals (∙O2−). More importantly, the Fe-MOFs showed excellent stability and reusability during degradation processes for six cycles.