Isotopic separation of helium through graphyne membranes: a ring polymer molecular dynamics study

Area of Science:

• Materials Science
• Computational Chemistry
• Chemical Engineering

Background:

• Understanding 2D membrane separation mechanisms is crucial for technological applications.
• Helium (He) purification is vital due to production shortfalls.
• Isotope separation requires precise control at the molecular level.

Purpose of the Study:

• To investigate the microscopic separation mechanism of helium isotopes using graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes.
• To compare the efficacy of ring polymer molecular dynamics (RPMD) with rigorous quantum calculations for He isotope separation.
• To elucidate the role of quantum effects, such as zero-point energy and tunneling, in He isotope selectivity.

Main Methods:

• Application of the ring polymer molecular dynamics (RPMD) method.
• Utilizing graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes with varying pore sizes.
• Comparison with rigorous quantum mechanical calculations.

Main Results:

• The transmission rate of He isotopes through Gr3 membranes is significantly higher (orders of magnitude) than through Gr2 membranes.
• Selectivity between ⁴He and ³He isotopes at low temperatures is governed by a balance between zero-point energy and quantum tunneling.
• A notable quantum tunneling effect was observed in Gr2 membranes at 10 K, enhancing the permeation of the lighter ³He isotope.

Conclusions:

• RPMD is an efficient computational approach for studying He isotope separation, accurately capturing quantum effects of light nuclei at low temperatures.
• Quantum effects, particularly tunneling, play a critical role in the separation of He isotopes by 2D membranes.
• The findings provide insights into designing advanced membranes for efficient helium purification and isotope separation.