Competition of quantum effects in H2/D2 sieving in narrow single-wall carbon nanotubes

Abstract

Nanoporous materials have the potential to be used as molecular sieves to separate chemical substances in a mixture via selective adsorption and kinetic sieving. The separation of isotopologues is also possible via the so-called quantum sieving effect: the different effective size of isotopologues due to their different Zero Point Energy (ZPE). Here we compare the diffusion coefficients of Hydrogen and Deuterium in (8,0) Single Walled Carbon Nanotubes obtained with quantum dynamics simulations. The diffusion channels obtained present important contributions from resonances connecting the potential wells. These resonances, which are more important for H2 than for D2, increase the low-temperature diffusivity of both isotopologues, but prevent the inverse kinetic isotope effect reported for similar nanostructured systems.