(566g) First Observation of Microscopic H2 Isotope Dynamics in Flexible MOFs for Hydrogen Isotope Separation

Development of cost efficient and environmental friendly methods of hydrogen isotope separation is of a very high importance today due to the rapidly increasing demand in medical healthcare such as imaging and cancer therapy. Unfortunately, the current separation methods suffer from low separation efficiency due to their nearly same chemical properties and thus high purity isotopes are not easily achieved. Recently nanoporous materials have been proposed as alternatives, which are supported by the newly proposed separation mechanism, quantum sieving (D2, which has a shorter de Broglie wavelength than H2, can diffuse faster through the confined pore at a cryogenic temperature). A few research groups have been investigated for this hydrogen isotope separation using rigid nanostructure up to now.

Structural flexibility is a unique property of some metal−organic frameworks (MOFs) that clearly distinguishes them from other inorganic porous materials. A MIL-53(Al), one of the most well-known flexible MOF, leads to dynamic changes as closed pore transitions to open pore, also called ‘breathing’ phenomenon. During the flexible and reversible transition, the pore apertures are continuously adjusted, thus providing the tremendous opportunity to separate mixtures of hydrogen isotope that require precise pore tuning.

Here, we report quasielastic neutron scattering studies of H2-D2 diffusion in MIL-53(Al), demonstrating remarkable quantum effects, with significant diffusivity difference even at high temperature. Such flexible porous materials exhibit the its dynamic behavior of adsorbed hydrogen isotopes during ‘breathing’ phenomenon which will enable novel processes for kinetic molecular sieving of hydrogen isotopes.