Stepwise tuning carbon slits at sub-angstrom scale for dynamical separation of hydrogen isotope
Abstract
Heavier hydrogen isotope is indispensable for many applications such as isotope tracing and labeling, neutron scattering, and nuclear fusion reaction. Thus it calls for efficient hydrogen isotope separation. Cryogenic adsorptive separation is an energy-efficient way for deuterium/protium (D2/H2) separation, requiring nanopores with precisely tuned pore size and suitable geometry to induce the quantum sieving effect. Herein, we report on the stepwise tuned slit-shaped ultramicropores at sub-angstrom (Å) scale for highly efficient D2/H2 separation. The opening width of carbon nanoslits was precisely tuned by the devised thermal-induced molecularly imprinting method. The adsorbent with 4.0 Å centered nanoslits showed an excellent D2/H2 uptake ratio of 1.9 with a high D2 uptake of 10.1 mmol g-1 at 40 K and 100 kPa. Column breakthrough experiments revealed a high D2/H2 selectivity of 10.1 at 40 K. It evidenced that the 4.0 Å centered slits enable an optimal balance between the barrier induced by zero-point energy and the adsorption potential at 40 K, thereby reaching a selectively quantized configurational diffusion of D2/H2. Programmed thermal desorption experiments indicated that a 0.1 Å alteration of the slit size enhanced the quantum sieving effect of D2/H2 by 180%. These results would benefit the understanding of D2/H2 separation behavior, and the design principle may inspire other isotope separations.
