Heteroatom Engineering in Robust Al-Based MOFs for Efficient Separation of Xenon over Krypton

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Xenon (Xe) and krypton (Kr) separation is crucial for industry and environmental safety.
• Their similar physical properties (no permanent dipoles, low polarizability, similar kinetic diameters) pose significant separation challenges for traditional porous adsorbents.

Purpose of the Study:

• To investigate the impact of pore geometry and surface polarity in aluminum-based metal-organic frameworks (Al-MOFs) on Xe/Kr separation.
• To explore the effectiveness of heteroatom engineering in enhancing Xe/Kr separation performance.

Main Methods:

• Synthesis and characterization of a series of Al-MOFs (CAU-10-H, MIL-160, KMF-1, CAU-23) with varying pore characteristics.
• Utilized Ideal Adsorbed Solution Theory (IAST) and Grand Canonical Monte Carlo (GCMC) simulations to predict and analyze separation performance.
• Employed first-principles density functional theory (DFT) calculations to understand binding mechanisms.
• Validated performance through dynamic breakthrough experiments.

Main Results:

• MIL-160, featuring a polar furanyl linker, demonstrated superior Xe/Kr separation performance.
• At 298 K and 1.0 bar, MIL-160 achieved a Xe uptake of 4.12 mmol g⁻¹ and an IAST selectivity of 7.63 for a Xe/Kr (20/80) mixture.
• Dynamic breakthrough experiments confirmed a Xe breakthrough time of 42.9 min g⁻¹.
• GCMC and DFT revealed that cooperative confinement and polarization effects, particularly Xe-binding at furanyl oxygen sites, enhance separation.

Conclusions:

• Established clear structure-property relationships for Xe/Kr separation in Al-MOFs.
• Heteroatom engineering, specifically incorporating polar functional groups like furanyl oxygen, is a promising strategy for designing efficient noble gas adsorbents.
• The findings highlight the potential of tailored Al-MOFs for practical Xe/Kr separation applications.