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.