Optimization of the synthesis of UiO-66(Zr) in ionic liquids

In order to rationalize the production of porous Metal-Organic Frameworks (MOFs) in ionic liquids (ILs) as main solvent, we selected the archetype UiO-66(Zr) to analyze its precipitation in four commercial candidates of ILs commonly used in the literature. We did the choice to investigate the reactivity of two hydrophobic salts, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][NTf2]) and 1-butyl-3-methylimidazolium hexafluorophosphate [Bumim][PF6]), as well as two other salts considered as hydrophilic, ([Omim][Cl]) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim][TFO]). Whereas the synthesis in hydrophilic ILs gave rise to the crystallization of pure UiO-66(Zr), the solvo-thermal reaction (120 °C) performed in hydrophobic salts did not lead to the same results. In the case of [Bumim][PF6], we noted the precipitation of zirconium phosphate Zr(HPO4)2 H2O, while the synthesis in [Emim][NTf2] favored the formation of distinct zirconium terephthalate called hcp UiO-66. These different phases have been characterized by powder X-ray diffraction, BET, IR and SEM.