Synergistic heteroatom-engineered pore chemistry in aluminum-based metal-organic frameworks for efficient sulfur...

Sulfur hexafluoride (SF₆) is a potent greenhouse gas with an exceptionally high global warming potential. Developing adsorbents that combine high SF₆/N₂ selectivity, low regeneration energy, and low cost remains a key challenge. Herein, three aluminum-based metal-organic frameworks (Al-MOFs), CAU-10-Py, MIL-160, and CAU-23, were systematically investigated to clarify how heteroatom identity (N, O, and S) affects SF₆/N₂ separation. Among them, CAU-23 exhibited the best performance, with an SF₆ uptake of 1.76 mmol g^-1 at 0.1 bar and an ideal adsorbed solution theory (IAST) SF₆/N₂ selectivity of 659 for a 10/90 SF₆/N₂ mixture. CAU-23 can also be synthesized through a water-based route using inexpensive precursors, giving an estimated precursor cost of approximately 50 USD kg^-1. Its relatively low isosteric heat of adsorption (24.9 kJ mol^-1) further supports energy-efficient regeneration. Experimental and theoretical analyses suggest that the favorable separation performance of CAU-23 arises from the combined effects of suitable pore architecture and specific S···F interactions between the thiophene-based ligand and SF₆. The high polarizability and weak Lewis basicity of sulfur generate a positively polarized site on the thiophene ring, promoting favorable electrostatic interactions with the fluorine atoms of SF₆. These results demonstrate that the cooperative engineering of heteroatom functionality and pore environment is an effective strategy for tuning pore-surface electrostatics while balancing SF₆/N₂ selectivity and regeneration energy. This work highlights heteroatom-engineered Al-MOFs as promising adsorbents for sustainable and energy-efficient SF₆ capture.