Zeolitic Imidazole Framework-67 (ZIF-67) as a heterogeneous catalyst to activate peroxymonosulfate for degradation of Rhodamine B in water

Metal organic frameworks (MOFs) can exhibit chemical, photo and biomimetic catalytic activities. While MOFs have been intensively investigated as photo-catalysts to degrade pollutants in water, studies of wet chemical oxidation catalyzed by MOFs are still quite limited. Particularly, the activation of peroxymonosulfate (PMS) represents a widely-used chemical oxidation reaction for chemical synthesis and environmental remediation. Yet little effort has been made to evaluate MOFs as a catalyst for the PMS activation. In this study, it is proposed to use a cobalt-based MOF, ZIF-67, as a heterogeneous catalyst to activate PMS to degrade Rhodamine B (RB) dye. Through the RB degradation, ZIF-67 as the PMS activation catalyst was evaluated and its underlying mechanism was proposed. Additionally, factors affecting the PMS activation were also examined, including ZIF-67 loading, temperature, pH, UV irradiation and ultrasonication. A ratio of 1/3/1 (RB/PMS/ZIF-67) is the most effective ratio to degrade RB in water. The higher temperature, UV irradiation and ultrasonication also enhanced the RB degradation using PMS activated by ZIF-67. The recyclability test revealed that ZIF-67 can be used continuously with stable and effective catalytic activity. These features reveal that ZIF-67 can be an interesting and promising heterogeneous catalyst to activate PMS for the degradation of organic pollutants in water.