Kinetic-quantum-sieving-assisted H2:D2 separation in flexible porous materials is more effective than the currently used energy-intensive cryogenic distillation and girdle-sulfide processes for isotope separation. It is believed that material flexibility results in a pore-breathing phenomenon under the influence of external stimuli, which helps in adjusting the pore size and gives rise to the optimum quantum-sieving phenomenon at each stage of gas separation. However, only a few studies have investigated kinetic-quantum-sieving-assisted isotope separation using flexible porous materials. In addition, no reports are available on the microscopic observation of isotopic molecular transportation during the separation process under dynamic transition. Here, the experimental observation of a significantly faster diffusion of deuterium than hydrogen in a flexible pore structure, even at high temperatures, through quasi-elastic neutron scattering, is reported. Unlike rigid structures, the extracted diffusion dynamics of hydrogen isotopes within flexible frameworks show that the diffusion difference between the isotopes increases with an increase in temperature. Owing to this unique inverse trend, a new strategy is suggested for achieving higher operating temperatures for efficient isotope separation utilizing a flexible metal–organic framework system.
Bibliographical noteFunding Information:
M.J. and J.P. contributed equally to this work. This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSI) (Nos. 2019R1A2C2005162, 2020M2D2A1A02069267, 2020K1A3A7A09078094, 2020R1A2C3008908). The neutron source BER II in HZB is gratefully acknowledged for the allocation of neutron scattering beamtime on NEAT beamlines.
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- flexible porous materials
- hydrogen diffusion
- hydrogen isotope separation
- quantum sieving