Highly Chemically Stable MOFs with Trifluoromethyl Groups: Effect of Position of Trifluoromethyl Groups on Chemical Stability

Abstract

Metal–organic frameworks (MOFs) are a class of advanced porous crystalline materials. However, numerous MOFs have poor chemical stability, significantly restricting their industrial application. The introduction of trifluoromethyl groups around clusters of MOFs results in a shielding effect caused by their hydrophobicity and bulkiness, thus preventing guest molecules from attacking the coordination bonds. To prove such a shielding effect, the position of the trifluoromethyl groups is rationally adjusted, with trifluoromethyl groups at the ortho positions of carboxyl groups significantly improving the chemical stability of UiO-67. The prepared UiO-67-o-2CF3 remains intact after treatment with boiling water, 8 M HCl, 10 mM NaOH, and 50 ppm of NaF aqueous solutions. As the control experiment, trifluoromethyl groups at the meta positions of carboxyl groups have no shielding effect; hence, UiO-67-m-2CF3 has a stability that is lower than that of UiO-67-o-2CF3. In addition, the shielding effect is also applied to other MOFs, including DUT-5-o-2CF3 and Al-TPDC-o-2CF3, confirming the universality of this strategy.

Improving MOF stability: approaches and applications

“…In addition to the length of the side chain, the position of the hydrophobic groups relative to metal clusters also plays a critical role in improving MOF chemical stability. 99,100 A convincing comparison was made between MOF-508 and its two analogs (SCUTC-18 and SCUTC-19). 99 Compared with bipyridine of MOF-508, there were two methyl-substituents, respectively, located at the ortho-positions and meta-positions of the coordinating N atoms of bipyridine in SCUTC-18 and SCUTC-19.…”

“…Apart from alkyl chains, [96][97][98][99][100][101] introduction of uorinated groups (e.g. -F, -CF 3 , etc.)…”

Water and Metal–Organic Frameworks: From Interaction toward Utilization

“…The access of water to the coordination bonds can be blocked by appending linkers with hydrophobic fluorinated or alkyl functional groups. Trifluoromethyl groups were incorporated into UiO-67(Zr) 90 and Mn 2 L1(Mn) 91 to improve their water stability. The robustness of ZIF-302(Zn), 92 MAF-69(Mo, W), 93 MAF-6(Zn), 94 and CALF-25(Ba) 95 in a water system was confirmed by decorating phenyl, ethyl, ethyl and ethyl ester groups on their linkers, respectively.…”

MOFs Derived Catalysts Prepared by Pyrolysis for Hydrogenation of Bio‐Based Furfural: A Mini‐Review

“…[27,28] Although many stable MOFs materials have been reported continuously, this is still the key to limit the preparation of efficient MOFs catalysts. [29][30][31] Therefore, a series of modification studies have been carried out. Firstly, modified MOFs metal nodes make it exposed the coordination of the unsaturated metal ion center.…”

“…It could be caused by the instability of MOFs materials themselves [27,28] . Although many stable MOFs materials have been reported continuously, this is still the key to limit the preparation of efficient MOFs catalysts [29–31] . Therefore, a series of modification studies have been carried out.…”