Synthesis and Characterization of Highly Fluorinated Hydrophobic Rare–Earth Metal–Organic Frameworks (MOFs)

Tuning a material's hydrophobicity is desirable in several industrial applications, such as hydrocarbon storage, separation, selective CO₂ capture, oil spill cleanup, and water purification. The introduction of fluorine into rare-earth (RE) metal-organic frameworks (MOFs) can make them hydrophobic. In this work, the linker bis(trifluoromethyl)terephthalic acid (TTA) was used to make highly fluorinated MOFs. The reaction of the TTA and RE³⁺ (RE: Y, Gd, or Eu) ions resulted in the primitive cubic structure (<i>pcu</i>) exhibiting RE dimer nodes (RE-TTA-<i>pcu</i>). The crystal structure of the RE-TTA-<i>pcu</i> was obtained. The use of the 2-fluorobenzoic acid in the synthesis resulted in fluorinated hexaclusters in the face-centered cubic (<i>fcu</i>) framework (RE-TTA-<i>fcu</i>), analogous to the UiO-66 MOF. The RE-TTA-<i>fcu</i> has fluorine on the linker as well as in the cluster. The MOFs were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, and contact angle measurements.