The key role of heteroatom effects in COF separation of SF6/N2: A theoretical study

Sulfur hexafluoride (SF6) is particularly important for purification and recovery in environmental management and resource optimization due to its extremely high global warming potential and widespread industrial applications. In this study, we employed grand canonical Monte Carlo simulations and density functional theory calculations to investigate heteroatom (C, N, and O) functionalization modifications of covalent organic framework (COF)-637, aiming to evaluate its selective adsorption performance for SF6/N2 mixtures. The results indicate that at 298 K and 1 bar, the selectivity values of heterocyclic COF-2O and COF-2N for SF6/N2 (10:90 v:v) mixtures are 400.79 and 353.57, respectively. The introduction of heteroatoms effectively enhances the selective separation performance of the original framework. By analyzing the adsorption isotherms of SF6 in the mixed components within the framework at pressures ranging from 0.1 to 1 bar, it is confirmed that heterocyclic modification can effectively enhance the selective capture of SF6. Further analysis, including charge difference density, Bader charges, and the independent gradient model for weak interactions, reveals the interactions between SF6 and the framework. This study provides theoretical support for understanding the adsorption mechanisms of COFs and for designing highly efficient materials for SF6 purification.