Sustainable Preparation of MIL-100(Fe) and Its Photocatalytic Behavior in the Degradation of Methyl Orange in Water

Abstract

The real industrial establishment of metal–organic frameworks (MOFs) requires significant advances in economic and chemical sustainability. This work describes a novel and simple method to prepare one of the most widely studied MOF materials, i.e., MIL-100(Fe), which significantly improves the sustainability of the conventional process in several aspects. This MOF material is prepared (i) at room temperature (instead of 150 °C used in the conventional method), (ii) after a few hours (instead of 6 days), (iii) in the absence of any inorganic corrosive acid (significant amounts of HF and HNO3 are used in the conventional method), and (iv) it is washed at room temperature (unlike the washing at 80 °C for 3 h). Interestingly, the only difference in the preparation method of MIL-100(Fe) compared with that of semiamorphous Fe-BTC (MOF material commercialized as Basolite F300 having the same metal and linker, and which can be also prepared under similar sustainable conditions) is to start from Fe(II) or Fe(III) sources, respectively, which opens certain versatility options in the room temperature synthesis procedures of MOF materials. The prepared samples were characterized using X-ray diffraction, thermogravimetric analysis, N2 adsorption/desorption isotherms, Cs-aberration corrected scanning transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. These two room-temperature-made Fe-BTC materials were tested in the industrially demanded photocatalytic degradation of methyl orange under both ultraviolet and solar light radiation. MIL-100(Fe) was a very active photocatalyst in comparison with its homologue. That difference was mainly attributed to the presence of larger cavities within its structure.