Room temperature synthesis of high-quality Ce(IV)-based MOFs in water

Abstract

There is a growing interest in the sustainable synthesis of Metal-Organic Framework materials (MOFs). This work addresses the exceptional ability of Ce(IV) for the preparation of high-quality MOFs based on carboxylates at room temperature, in water as solvent, and without any energy input. Thus, crystalline terephthalate-based UiO-66(Ce), fumarate-based UiO-66(Ce) and Ce-MOF-808 were successfully synthesized at room temperature by various new approaches. All these methodologies are novel, rapid, simple, reproducible, inexpensive, energetically efficient and relatively environmentally benign compared with the usual conventional methodologies and, unlike other room-temperature synthesis, leads to highly-crystalline samples. In particular, (i) both terephthalate- and fumarate-based UiO-66(Ce) were synthesized using water as a sole solvent and in the absence of any modulator or any other additive; (ii) terephthalate-based UiO-66(Ce) was prepared under systematically-designed different water/DMF molar ratio, selecting these solvents in order to start from clear solutions of both metal and linker sources, respectively; and (iii) terephthalate-based UiO-66(Ce) and Ce-MOF-808 were prepared in the presence of either acetic acid or formic acid as modulators, respectively. Therefore, this work provides novel strategies for the preparation of tetravalent metal based MOFs, which are in general scarce with respect to the whole number of known MOFs, particularly at room temperature.