Peroxymonosulfate activation by Mn3O4/metal-organic framework for degradation of refractory aqueous organic pollutant rhodamine B

Abstract

An environmentally friendly Mn-oxide-supported metal-organic framework (MOF), Mn3O4/ZIF-8, was successfully prepared using a facile solvothermal method, with a formation mechanism proposed. The composite was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and Fourier-transform infrared spectroscopy. After characterization, the MOF was used to activate peroxymonosulfate (PMS) for degradation of the refractory pollutant rhodamine B (RhB) in water. The composite prepared at a 0.5:1 mass ratio of Mn3O4 to ZIF-8 possessed the highest catalytic activity with negligible Mn leaching. The maximum RhB degradation of approximately 98% was achieved at 0.4 g/L 0.5-Mn/ZIF-120, 0.3 g/L PMS, and 10 mg/L initial RhB concentration at a reaction temperature of 23 °C. The RhB degradation followed first-order kinetics and was accelerated with increased 0.5-Mn/ZIF-120 and PMS dosages, decreased initial RhB concentration, and increased reaction temperature. Moreover, quenching tests indicated that •OH was the predominant radical involved in the RhB degradation; the •OH mainly originated from SO4−• and, hence, PMS. Mn3O4/ZIF-8 also displayed good reusability for RhB degradation in the presence of PMS over five runs, with a RhB degradation efficiency of more than 96% and Mn leaching of less than 5% for each run. Based on these findings, a RhB degradation mechanism was proposed.