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.