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

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-2CF(3) 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-2CF(3 )has a stability that is lower than that of UiO-67-o-2CF(3). In addition, the shielding effect is also applied to other MOFs, including DUT-5-o-2CF(3) and Al-TPDC-o-2CF(3), confirming the universality of this strategy.