Adaptive Induced-Fit via Engineered Linker Regioisomerization in Biomimetic Zeolitic Imidazolate Frameworks for Boosting SF6/N2 Separation.

Capturing and recovering sulfur hexafluoride (SF6) is a crucial yet formidable challenge in mitigating global warming. Herein, we propose a programmable linker regioisomerization strategy within zeolitic imidazolate frameworks (ZIFs) to modulate their stimulus-responsive structural flexibility, thereby significantly enhancing SF6 capture efficiency from nitrogen (N2) streams. Simultaneous regioisomerization of the methyl group in ZIF-8 and the aldehyde group in ZIF-90 on the imidazolate linkers yields ZIF-94, which exhibits a rare guest-induced reversible framework deformation upon SF6 adsorption. This behavior confers an enzyme-like induced-fit recognition mechanism for SF6 molecules, strengthening host-guest interactions. As a result, ZIF-94 achieves a high SF6 adsorption capacity of 1.97 mmol g-1 and an ultrahigh SF6 stacking density of 1438.69 mg cm-3 at 298 K and 0.1 bar, along with dramatically enhanced SF6/N2 selectivities over ZIF-8 and ZIF-90. In situ experiments and theoretical analyses reveal that the SF6-induced structural flexibility of ZIF-94 allows the framework to dynamically adjust and optimize its cage structure to match gas molecules, thus leading to significantly reinforced SF6/N2 separation performance. The experimental column breakthrough tests and pressure swing adsorption simulations confirm the practical separation performance for SF6/N2 mixtures in ZIF-94. This work offers useful insights for designing flexible adsorbents for gas separation applications.