Scientists reveal the effect of Cu(I) structure on quantum sieving for hydrogen isotope separation

Recently, a research team led by Prof. CHEN Changlun from Institute of Plasma Physics, Hefei Institutes of Physical Science of Chinese Academy of Sciences, studied Cu(I)Cu(II)-BTC, a kind of hydrogen isotope separation material and proved its crucial role in tuning quantum sieving without a complex structural design, which provided a new strategy for the intelligent design of highly efficient isotope systems.

The result was published in ACS Applied Materials & Interfaces.

High pure deuterium (D₂) is an important industrial and scientific gas, which has been widely used as an irreplaceable raw material, neutron moderator, isotopic tracer, and in other fields. Despite the huge demand for it, the mole fraction of natural deuterium is only up to 0.0156% of natural hydrogen in the oceans. Moreover, D₂ and its isotope (H₂ or T₂) molecules have almost identical classical dimensions, associated with very similar physicochemical properties, and the separation of hydrogen isotope mixtures in high purity has been considered as one of the greatest difficulties and challenges in modern separation technology.

In this study, HKUST-1 crystals in the presence of hydroquinone were reduced to construct Cu(I)Cu(II)-BTC, featured by dual micropore size distribution and mixed-valence of Cu metal, and had been chosen to study H₂/D₂ separation in detail.

The study showed that unique Cu(I) and Cu(II) coordination network of Cu(I)Cu(II)-BTC could significantly facilitate D₂/H₂ isotope separation. Density functional theory (DFT) calculations indicated that the introduction of Cu(I) macrocycles in the framework decreased the pore size and further led to relatively enhanced interaction of H₂/D₂ molecules on Cu(II) sites. The significantly enhanced selectivity of Cu(I)Cu(II)-BTC at 30 K was mainly attributed to the synergistic effect of kinetic quantum sieving (KQS) and chemical affinity quantum sieving (CAQS).

In addition, a large angle of 156° for the O-Cu(I)-O configuration in Cu(I)Cu(II)-BTC exhibited weak binding strength of hydrogen adsorption since the dz² orbital and small positive of Cu(I) couldn't effectively participate in the hydrogen interaction, and didn't show a strong CAQS effect at above liquid nitrogen temperature.

This research verified the effect of Cu(I) structure in D₂/H₂ separation. "We believe that this study will provide a new strategy for reasonable design of porous materials with OMSs at highly efficient isotope and gas separation systems," said HU Xiaoyu, first author of the paper.