Abstract
We report a novel synthetic procedure for the high-yield synthesis of metal–organic frameworks (MOFs) with fcu topology with a UiO-66-like structure starting from a range of commercial ZrIV precursors and various substituted dicarboxylic linkers. The syntheses are carried out by grinding in a ball mill the starting reagents, namely, Zr salts and the dicarboxylic linkers, in the presence of a small amount of acetic acid and water (1 mL total volume for 1 mmol of each reagent), followed by incubation at either room temperature or 120 °C. Such a simple “shake ‘n bake” procedure, inspired by the solid-state reaction of inorganic materials, such as oxides, avoids the use of large amounts of solvents generally used for the syntheses of Zr-MOF. Acidity of the linkers and the amount of water are found to be crucial factors in affording materials of quality comparable to that of products obtained under solvo- or hydrothermal conditions.
Highlights
Zirconium-based metal−organic frameworks (MOFs) (Zr-MOFs) are currently considered benchmark materials for their high chemical and thermal stability, structural versatility, and employment in a vast range of applications, ranging from gas separation,[5−7] catalysis,[8,9] water sorption,[10,11] proton conductivity,[12] and drug delivery.[13]. Their structure is based on the different connectivities of hexanuclear clusters of the formula Zr6O4(OH)412+ with polytopic carboxylic linkers, designing MOFs with variable degrees of connectivity and topologies, such as fcu (UiO-66 and MOF-801), csq (NU1000), reo (DUT-67), and spn (MOF-808).[14−17] Other topologies based on different secondary building units (SBUs), such as dodecanuclear clusters, were recently reported.[18]
A remarkable effort has been recently made for ensuring safer and cleaner procedures for the synthesis of MOFs using different approaches able to minimize the use of hazardous reagents and solvents with high boiling points and the generation of large amounts of waste byproducts.[20−25]
Concerning Br- and NH2-UiO-66, the trend observed so far is reversed: the products with higher crystallinity are those resulting from syntheses in the presence of a higher water quantity. This effect is more pronounced for Br-UiO-66, where the samples obtained with less than 75 μL of water display a different Powder X-ray diffraction (PXRD) pattern from that of UiO-66, whereas samples obtained with 75 and 100 μL of water are highly crystalline, and the BET surface area (724 m2 g−1) is consistent with that reported for conventional syntheses in DMF.[41]
Summary
The development of green and scalable procedures for the synthesis of metal−organic frameworks (MOFs) is currently considered the main factor to enable widespread industrial application and commercialization of these materials.[1,2] The focus is primarily on the production of highly stable MOFs at low cost, in high yield, and fulfilling most of the requirements of sustainability and atom economy.[3,4] Zirconium-based MOFs (Zr-MOFs) are currently considered benchmark materials for their high chemical and thermal stability, structural versatility, and employment in a vast range of applications, ranging from gas separation,[5−7] catalysis,[8,9] water sorption,[10,11] proton conductivity,[12] and drug delivery.[13]. Concerning Br- and NH2-UiO-66, the trend observed so far is reversed: the products with higher crystallinity are those resulting from syntheses in the presence of a higher water quantity This effect is more pronounced for Br-UiO-66, where the samples obtained with less than 75 μL of water display a different PXRD pattern from that of UiO-66, whereas samples obtained with 75 and 100 μL of water are highly crystalline, and the BET surface area (724 m2 g−1) is consistent with that reported for conventional syntheses in DMF.[41] In this case, quantitative 1H NMR analysis (Figure S13) reveals the presence of a significant amount of AcOH and the proposed formula is Zr6O4(OH)4(Br-BDC)5.06(AcOH)1.88. Almost 4 g of good quality MOF (Figure S18) was obtained, demonstrating the easy scalability of the procedure up to a 10-fold scale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
