Highly effective nanoporous materials for hydrogen isotope separation

Abstract

Deuterium is widely used for numerous applications such as nuclear fusion, non-radioactive isotopic tracing, neutron scattering as well as a host of others. Extracting deuterium from hydrogen isotopes mixture is, however, difficult business since its isotopes share similar size and shape. Conventional separation method such as thermal diffusion and centrifugation tends to be time and energy intensive. The development of a cost-effective separation method is therefore required. In this study, quantum sieving effect for isotope separation of light gas using Metal-organic frameworks (MOFs) is discussed. The mechanism of isotope separation by quantum effects is quite different from the normal separation by size exclusion. The isotope separation is possible when quantum effects become significant; which can be observed if the difference between entrance pore diameter and size of the molecule become comparable to the De Broglie wavelength. When decreasing the pore diameter close to molecule size, the zero-point energy can overcompensate the attraction of the wall, leading to an energy barrier for molecules entering the pore. This barrier is greatest for the molecule with the highest zero-point energy. Owing to this effect, at low temperature heavier isotope molecules are diffusing faster than lighter molecules, resulting in kinetic isotope quantum molecular sieving. Additionally, D2/H2 selectivity is only inferred from the isotherm of pure hydrogen and pure deuterium which would be different from D2/H2 mixture due to its surface adsorption competition. Therefore, recent experimental results of the kinetic isotope quantum molecular sieving effect in equilibrium and kinetic adsorption of H2/D2 mixture on MOFs will be presented in here.