Assessing Guest-Molecule Diffusion in Heterogeneous Powder Samples of Metal-Organic Frameworks through Pulsed-Field-Gradient (PFG) NMR Spectroscopy.

摘要: Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is major importance since many porosity-related properties MOFs are influenced by effects. The dimethylsulfoxide (DMSO) the framework (MOF) MIL-53-NH2(Al) was investigated through pulsed-field-gradient (PFG) NMR spectroscopy. microporous material synthesized small crystallites (under 500 nm), which agglomerated a large range particle sizes, giving morphologically very heterogeneous sample. No special agglomeration pattern could be observed, makes PFG-NMR investigation challenging, yet it represents realistic situation for molecules materials. We were able to distinguish between two regimes existing parallel with each other over total from 15 ms up 200 observation times as accessible experiments: In crystal agglomerates (diameters above 20 µm) movement found sub¬diffusive, time exponent κ = 0.8 (rather than 1 normal diffusion). Guest remaining, smaller host particles followed within bed spheres impenetrable external surfaces, size distribution good agreement that under study. Diffusion rather complex system thus referred two-region model novel potentials application systems intricate topology.