Capture of heavy hydrogen isotopes in a metal-organic framework with active Cu(I) sites

Abstract

The production of pure deuterium and the removal of tritium from nuclear waste are the key challenges in separation of light isotopes. Presently, the technological methods are extremely energy- and cost-intensive. Here we report the capture of heavy hydrogen isotopes from hydrogen gas by selective adsorption at Cu(I) sites in a metal-organic framework. At the strongly binding Cu(I) sites (32 kJ mol−1) nuclear quantum effects result in higher adsorption enthalpies of heavier isotopes. The capture mechanism takes place most efficiently at temperatures above 80 K, when an isotope exchange allows the preferential adsorption of heavy isotopologues from the gas phase. Large difference in adsorption enthalpy of 2.5 kJ mol−1 between D2 and H2 results in D2-over-H2 selectivity of 11 at 100 K, to the best of our knowledge the largest value known to date. Combination of thermal desorption spectroscopy, Raman measurements, inelastic neutron scattering and first principles calculations for H2/D2 mixtures allows the prediction of selectivities for tritium-containing isotopologues.

From coherent quasi-irreversible quantum dynamics towards the second law of thermodynamics: The model boron rotor B13+

“…Delocalization is also supported by the effect of interfering partial waves, or lobes of the wavefunction. A prominent example is observed at ca 8 ps when the frontier lobes of the two branches of the wavefunction that tunnel in clockwise and anti-clockwise directions "collide" in approximately the domains of GM 30 , GM 1 , GM 2 , opposite to the initial domain of GM 16 . Subsequently, this collision causes rather complex interference patterns of the wave function that tend to populate all GMs: this contributes to the quasi-irreversible delocalization of the density in all GMs and, therefore to the rather large mean value of the entropy S(t) of occupying the GMs, which is recalled in the time domain of ca 6 ps, as documented in Fig.…”

“…neighbors (ca 520 fs per step). For comparison, the density and flux for coherent periodic tunneling in the cyclic double-well potential 30 are shown in the right panels of Fig. 3.…”

“…c, d, Coherent periodic tunneling of a system with cyclic double-well potential. 30 For reference, the horizontal lines mark the values of the entropies ln2, ln3,..., ln30 for equal populations of 2,3,...,30 GMs, respectively.…”

“…One cycle of the wheel rotating with respect to the bearing corresponds to motion along a cyclic potential energy surface with N w ×N b = 30 equivalent wells. The potential wells support thirty equivalent global minimum structures that are arranged in cyclic order, GM 1 , GM 2 , ..., GM 30 . These are separated from each other by thirty equivalent transition states, again in cyclic order, TS 1,2 , TS 2,3 , ..., TS 30,1 , and all with the same low potential barrier (V b ≈ 106.4 h c cm -1 ).…”

“…Will the tunneling in the cyclic multi-well potential exhibit new phenomena that are fundamentally different from the familiar tunneling in cyclic double-well potentials observed in examples such as B 2 Cl 2 F 2 29 and T 2 captured in a metal-organic framework with active Cu(I) sites. 30 Will the quantum dynamics induce the increase of the entropy for occupying the GMs? On what time scale?…”