γ-Fe2O3/MIL101(Fe)-NH2/COF-MT as a novel ternary photocatalyst for the selective oxidation of alcohols through a dual S-scheme pathway under sunlight irradiation

In this study, γ-Fe2O3/MIL101(Fe)-NH2/COF-MT, a hybrid material, capable of absorbing visible light, was designed and synthesized easily through growth of COF-MT by imine bond formation using amine groups of supported melamine on γ-Fe2O3/MIL101(Fe)-NH2. The structure, morphology and optical properties of γ-Fe2O3/MIL101(Fe)-NH2/COF-MT were investigated using various techniques, including FT-IR, UV-vis DRS, PXRD, TGA, XPS, FESEM, EDS mapping, TEM, VSM, BET, BJH, PL, ICP, EIS and Mott-Schottky plots. This hybrid material was effectively utilized as a ternary heterostructure photocatalyst to achieve efficient and selective oxidation of alcohols into aldehydes under sunlight irradiation and air bubbling in ethanol. The remarkably improved photocatalytic performance is attributed to enhanced charge separation, increased visible light absorption, and the strengthened redox capabilities of photogenerated electrons and holes through a dual S-scheme charge transfer mechanism. Based on our knowledge, this is the first report on the photo-oxidation of alcohols catalyzed by γ-Fe2O3/MOF/COF as a hybrid material. This work highlights the potential of γ-Fe2O3/MIL101(Fe)-NH2/COF-MT as a sustainable catalyst for the synthesis of aldehydes as fine chemicals due to the improved light absorption and charge separation, energy-saving (sunlight irradiation), mild reaction conditions (room temperature and ambient pressure), using a small amount of the catalyst, air as a safe and plentiful oxidant (generating water as the only by-product), ethanol as a green solvent, and the ease of catalyst isolation and reuse by an external magnet without a remarkable change in the catalyst structure and activity.