Isotopic Separation of Helium through Nanoporous Graphene Membranes: A Ring Polymer Molecular Dynamics Study

TL;DR

This study uses ring polymer molecular dynamics to investigate helium isotope separation through nanoporous graphene membranes, revealing quantum effects' importance and membrane pore size impact on separation efficiency.

Contribution

It introduces RPMD as an effective method for modeling quantum effects in helium isotope separation through 2D membranes, highlighting differences between graphdiyne and graphtriyne.

Findings

Transmission rate through Gr3 is much higher than Gr2.

Selectivity depends on zero-point energy and tunneling effects.

RPMD captures quantum effects missed by classical methods.

Abstract

Microscopic-level understanding of the separation mechanism for two-dimensional (2D) membranes is an active area of research due to potential implications of this class of membranes for various technological processes. Helium (He) purification from the natural resources is of particular interest due to the shortfall in its production. In this work, we applied the ring polymer molecular dynamics (RPMD) method to graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes having variable pore sizes for the separation of He isotopes. We found that the transmission rate through Gr3 is many orders of magnitude greater than Gr2. The selectivity of either isotope at low temperatures is a consequence of a delicate balance between the zero-point energy effect and tunneling of $^4$He and $^3$He. RPMD provides an efficient approach for studying the separation of He isotopes, taking into account quantum effects of light nuclei motions at low temperatures, which classical methods fail to capture.