Non -covalent LDH/MOF composite formation: a new approach in sustainability for solvent-dependent photocatalytic aerobic alcohol oxidation

Abstract

An Fe^III-based metal–organic framework denoted as MIL-100(Fe) coated with cobalt–aluminium layered double hydroxide (CoAl-LDH) nanoplates has been synthesized. The structural information was obtained through powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), nitrogen sorption (BET and BJH), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and associated energy dispersive X-ray (EDX), transmission electron microscopy (TEM) and diffuse reflectance UV–Vis spectroscopy (UV–Vis DRS) techniques. Such characteristic methods indicate that the bonding between mesoporous CoAl-LDH nanosheets and open metal sites of metal–organic frameworks leads to non-covalent composite formation. Also, CoAl-LDH linkers add the feature of mesoporosity to MIL-100(Fe). Furthermore, the Fe–O bonds resulting from the coordination of surface –OH groups in the layered double hydroxide structure to Fe^III atoms of the crystal create unique optical properties in the hybrid structure, enhancing its photoreactivity. On the other hand, the lack of pore volume changes and differences among the optical properties indicate a non-covalent composite formation between MIL-100 (Fe) and CoAl-LDH. The CoAl-LDH/MIL-100(Fe) as a photocatalyst showed noticeable photocatalytic performance as compared to its aerobic alcohol oxidation reaction components under visible light irradiation. Also, it is noteworthy that the type of product depends on the reaction conditions. The relevant tests were performed in terms of stability and reusability and showed high photocatalytic efficiency after being reused up to ten times. Additionally, the retrieved CoAl-LDH/Fe-MOF nanocomposite underwent FT-IR and PXRD analyses, which confirmed the stability of the catalyst during aerobic alcohol oxidation.