Molecular Mechanism of Loading Sulfur Hexafluoride in γ-Cyclodextrin Metal-Organic Framework.

γ-Cyclodextrin metal-organic framework (γ-CD-MOF) is a new type of highly porous carrier for potential loading of therapeutic or diagnostic gas like sulfur hexafluoride (SF6). Here, loading of SF6 into γ-CD-MOF was investigated for its mechanism by molecular simulation and quantitative determination of SF6 using quantitative nuclear magnetic resonance (qNMR). For the SF6 loading, γ-CD-MOF was first degassed to remove the air without thermal decomposition or loss of framework crystallinity, then placed in the copper tube, and sealed to adsorb SF6 under 1.2 MPa and 25 °C for 12 h. The qNMR was employed for the determination of SF6 loaded in γ-CD-MOF using Span 80 as suspending agent and trifluoroacetic acid as internal standard. Then, the thermodynamic parameters had been estimated. Finally, molecular modeling combining with 19F NMR spectra was conducted to reveal the status of SF6 molecules in γ-CD-MOF. The results demonstrated that the content of SF6 loaded in γ-CD-MOF was 2.67 ± 0.46 wt %. After exposing to the environment of free SF6 at 0.1 MPa for 10 days, the relative content was 74.7%. It was confirmed that SF6 preferred to stay in the cavity of γ-CD-MOF cubes rather than in the γ-CD molecular pairs, which was a nonchemical adsorptive process. In conclusion, this research has established qNMR method and molecular simulation to demonstrate SF6 molecules in γ-CD-MOF and its loading mechanism.