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

TL;DR

This study shows how modifying aluminum-based metal-organic frameworks with heteroatoms can improve the separation of xenon from krypton, which is important for industry and the environment.

Contribution

The study introduces a heteroatom engineering strategy to enhance Xe/Kr separation performance in Al-based MOFs.

Findings

MIL-160, with a furan-based polar linker, achieved the best Xe uptake and selectivity.

Dynamic experiments showed a long Xe breakthrough time of 42.9 min g−1 for MIL-160.

Simulations and calculations confirmed that furanyl oxygen atoms optimize Xe binding.

Abstract

The separation of xenon (Xe) and krypton (Kr) is very important for industrial applications and environmental protection. However, the lack of permanent dipoles, low polarizabilities arising from their spherical nature, and similar kinetic diameters make their efficient separation by porous adsorbents exceptionally challenging. This study explored the effects of pore geometry and surface polarity of a series of aluminum-based metal–organic frameworks (CAU-10-H, MIL-160, KMF-1, CAU-23) on Xe/Kr separation performance using a heteroatom engineering strategy. These MOFs are composed of AlO6 clusters and bent dicarboxylic acid linkers, enabling us to systematically investigate the effects of pore size and heteroatom types on Xe/Kr separation performance. Among them, MIL-160 has a polar linker based on furan, showing the best balance performance. At 298 K and 1.0 bar, the uptake of Xe is 4.12 mmol g−1 and the IAST selectivity is 7.63 for a Xe/Kr (20/80) mixture. The practical performance was verified by dynamic breakthrough experiments, which yielded a long Xe breakthrough time of 42.9 min g−1. Grand Canonical Monte Carlo (GCMC) simulations and first-principles density functional theory (DFT) calculations revealed that the enhanced performance originates from cooperative confinement and polarization effects, with the furanyl oxygen atoms providing optimal Xe-binding sites. This work clarifies the structure–property relationships governing Xe/Kr separation in aluminum-based MOFs (Al-MOFs), highlighting the potential of heteroatom engineering for designing efficient noble gas adsorbents.

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