Theoretical study on the selective adsorption of SF₆/N₂ by covalent triazine frameworks

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Sulfur hexafluoride (SF₆) is a potent greenhouse gas with significant industrial applications.
• Sustainable utilization and management of SF₆ are critical under dual-carbon goals.
• Covalent organic frameworks (COFs) show promise for gas separation applications.

Purpose of the Study:

• To investigate the impact of 2D stacking modes (AA, AB, SS) in covalent triazine frameworks (CTFs) on SF₆/N₂ adsorption and separation.
• To identify CTF structures with optimal pore characteristics for selective SF₆ adsorption.
• To elucidate the adsorption mechanism of SF₆/N₂ in CTFs.

Main Methods:

• Computational screening of four CTFs with varying 2D stacking modes (AA, AB, SS).
• Grand Canonical Monte Carlo (GCMC) simulations to predict adsorption and selectivity.
• Analysis of pore size, porosity, surface area, adsorption snapshots, charge density difference (CDD), and independent gradient model based on Hirshfeld partition (IGMH).

Main Results:

• CTF-FUM-SS exhibited the highest SF₆/N₂ selectivity (2321.738 at 1 bar) due to optimal pore size.
• Staircase-like stacking (SS) demonstrated superior selective adsorption compared to AA and AB stacking.
• SS-stacked CTFs showed higher SF₆ adsorption capacity despite minor reductions in porosity and surface area.
• Pore size optimization and pore shape modification enhance SF₆ adsorption strength and saturation kinetics.

Conclusions:

• The 2D stacking mode significantly influences the SF₆/N₂ separation performance of CTFs.
• Staircase-like stacking (SS) offers a promising strategy for designing high-performance COFs for SF₆ capture.
• Tailoring pore characteristics in CTFs is essential for efficient gas separation and sustainable greenhouse gas management.