Manganese-Based Metal-Organic Frameworks Photocatalysts for Visible Light-Driven Oxidative Coupling of Benzylamine under Atmospheric Oxygen: A Comparative Study

Abstract

Research on the utilization of sustainable and renewable energy sources has increased as a result of the world’s expanding energy demand. In this regard, we report the photocatalytic performance of two synthesized Mn-MOFs: MnII3(tp)6/2(bpy)2.(dmf) (C47H35Mn3N5O13) and Mn2(tpa)2(dmf)2 (C22H22Mn2N2O10). The two MOFs were characterized using different spectroscopic and analytical techniques: powder X-ray diffraction, thermogravimetric analysis, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. MnII3(tp)6/2(bpy)2.(dmf) possesses a band gap value of 2.5 eV, which exhibits significant photocatalytic activity when exposed to simulated visible light irradiation. Mn2(tpa)2(dmf)2 shows a larger band gap of 3.16 eV, which renders the photocatalytic performance under visible light. The oxidation of benzylamine to N,N-benzylidenebenzylamine by a photocatalytic reaction was selected to evaluate the photocatalytic activities of MnII3(tp)6/2(bpy)2.(dmf) and Mn2(tpa)2(dmf)2 in the visible region. In addition to its high photocatalytic performance, MnII3(tp)6/2(bpy)2.(dmf) also showed high thermal stability up to 430 °C. Accordingly, the strategy of designing frameworks possessing mixed ligands provides stability to the frameworks as well as enhancing the photocatalytic performance of frameworks containing bipyridine ligands such as MnII3(tp)6/2(bpy)2.(dmf).