Lattice-driven gating in a Cu-based zeolitic imidazolate framework for efficient high-temperature hydrogen isotope...

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Traditional kinetic quantum sieving (KQS) for hydrogen isotope separation (H2/D2) relies on flexible linkers and framework breathing, typically observed below 77 K.
• Porous materials with narrow channels can create diffusion barriers crucial for isotope separation.

Purpose of the Study:

• To investigate the potential of a copper-based zeolite imidazolate framework (Cu-ZIF-gis) for hydrogen isotope separation at elevated temperatures.
• To elucidate the mechanism of kinetic quantum sieving (KQS) in Cu-ZIF-gis, focusing on temperature-dependent pore dynamics.

Main Methods:

• Adsorption isotherms of H2 measured across a temperature range of 40-150 K.
• Quasi-elastic neutron scattering (QENS) experiments to probe molecular mobility of H2 and D2 above 150 K.
• Temperature-variation powder X-ray diffraction (PXRD) from 20-300 K to analyze structural changes.

Main Results:

• Cu-ZIF-gis exhibits significant kinetic quantum sieving (KQS) for H2/D2 separation at temperatures above 120 K.
• Lattice-driven gating (LDG) in Cu-ZIF-gis, characterized by temperature-dependent pore size modulation (ca. 2.4 Å aperture), is identified as the key mechanism.
• QENS confirmed distinct molecular mobilities for H2 and D2 even above 150 K, while PXRD showed gradual unit cell expansion with increasing temperature.

Conclusions:

• Cu-ZIF-gis enables efficient hydrogen isotope separation via KQS at temperatures significantly higher than previously reported.
• The observed KQS is attributed to lattice-driven gating (LDG) and the temperature-sensitive pore aperture of the material.
• These findings pave the way for developing sustainable isotope separation technologies compatible with existing cryogenic infrastructure like LNG.