The Study of Photocatalytic Performance of ZIF-67 and Zn/Co-ZIF for the Removal of Organic Pollutants from Wastewater

Abstract

Due to environmental issues caused by pollution of water resources with organic pollutants, researches to provide effective methods for removing these pollutants has got a lot of attentions. In the present work, the application of Metal Organic Frameworks for the photocatalytic treatment of wastewater containing organic pollutants was studied. Due to the high porosity, suitable band gap, good thermal and chemical stability, ZIF-67 was selected for photocatalytic removal of organic pollutants from wastewater. The ZIF-67 photocatalyst was synthesized and characterized by XRD, FTIR, BET, ICP and UV-DRS techniques. To study the photocatalytic activity of ZIF-67, degradation of methylene blue as an organic model compound has been performed and the effects of catalyst loading, dye concentration and pH on MB removal were studied. Also, the effect of zinc addition to ZIF-67 strucure on the performance of photocatalytic activity was studied. According to the BET results, the specific surface area of catalyst was measured about 1750 m2/g which indicates the high porous structure of ZIF-67. A catalyst loading of 0.5 g/L resulted in 68% removal of MB with initial concentration of 15 ppm after 2 hours of exposure. By addition of zinc to the structure, Zn/Co-ZIF was synthesized and not only showed better crystallization, but also photocatalytic activity increased to 79%. Also, increasing pH and catalyst loading resulted in higher removal efficiency. Both ZIF-67 and Zn/Co-ZIF structures exhibited higher activity in the basic environment (pH 8-12). Although increasing catalyst loading increases removal efficiency but it entails the increase of turbidity which could affect the removal efficiency inversely for higher values. Band gap measurements by UV-DRS analysis indicated that both ZIF-67 and Zn/ZIF-67 can be active under visible light irradiation, and hence may be applicable for degradation of organic pollutant in wastewater.