Preparation and characterization of Fe₃O₄/ZIF-8 and Fe₃O₄–MnO₂/ZIF-8 composites

Metal–organic frameworks (MOFs) have been employed in many studies recently because of their stability, porosity, and high surface area. Although zeolitic imidazole frameworks (ZIF-8) have many advantages among MOFs, they have disadvantages such as low activity, conductivity, and reusability depending on the application. To overcome these drawbacks, Fe₃O₄ and a mixture of Fe₃O₄ and MnO₂ were added into the structure of ZIF-8. The SEM and STEM analysis of the synthesized materials showed that the polyhedral structure of ZIF-8 was hardly affected by the integration of metal oxides into the structure. FTIR and XPS results showed the presence of peaks arising from organic ligands and metal bonds with ZIF-8 in metal oxide/ZIF-8. Addition of Fe₃O₄ and Fe₃O₄–MnO₂ to structure of ZIF-8 decreased the surface area of ZIF-8 with the formation of mesopores and accumulation of metal oxide particles in pores. When the synthesized metal oxide/ZIF-8 samples were tested in supercapacitor applications, MnO₂/ZIF-8 electrode showed the highest specific capacitance. In addition, the presence of metal oxides in the ZIF-8 improved conductivity of the material. Based on the properties of metal oxide/ZIF-8 composites, the materials have also a potential for applications such as gas storage, adsorption, catalysts, and membranes.