Tunable Methylation in Imide-Linked Covalent Organic Frameworks Enables Highly Selective SF₆ Capture

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Rational design of covalent organic frameworks (COFs) for energy-efficient sulfur hexafluoride (SF₆) capture is limited by a lack of mechanistic understanding regarding structure-property relationships.
• Developing effective SF₆ capture materials is crucial due to its potent greenhouse gas properties.

Purpose of the Study:

• To investigate the impact of methyl-group engineering in imide-linked COFs on SF₆ capture and separation performance.
• To elucidate the structure-property relationships governing SF₆ adsorption in tailored COFs.

Main Methods:

• Systematic methylation of triazine building units in imide-linked COFs.
• Characterization of structural evolution from AA to ABC stacking modes.
• Gas sorption analysis and breakthrough experiments for SF₆/N₂ separation.
• Molecular simulations to understand adsorption mechanisms.

Main Results:

• Methylation induced a stacking transition from AA to ABC, optimizing ultramicropore size (0.66 nm) for SF₆.
• Dimethyl-functionalized NMUCOF-5 achieved high SF₆ uptake (42.5 cm³·g^-1) and selectivity (126) for SF₆/N₂.
• Performance attributed to size-sieving and enhanced C-H···F interactions within methyl-enriched pores.

Conclusions:

• Methyl-directed stacking modulation is an effective pore-engineering strategy for imide-linked COFs.
• Substituent-controlled packing significantly influences SF₆ capture and separation efficiency.
• This work provides mechanistic insights for designing advanced COFs for gas separation applications.