Improved selectivity of CH₄/CO₂ within 1D channel of COFs realized by pore wall functionalization strategy

CO₂ removal is a critical step in natural gas purification to upgrade the gas stream for practical use. Although covalent organic frameworks (COFs) show promise for gas separation, research in this area remains in its early stages, and their separation performance requires further improvement. Here, a combined quantum chemical calculations and molecular dynamics simulations were performed to elucidate the fundamental mechanisms governing CH₄/CO₂ separation in COF materials. Calculated results demonstrated that the adsorption of CO₂ within the one-dimensional (1D) channels of COF10 is more favorable than that of CH₄, and the adsorption selectivity (S_ads) exhibits a significant enhancement by Cl-functionalization. Moving rate of CH₄ is much larger than that of CO₂ in the 1D channel of COF10, and Cl-functionalization creates stronger diffusion barriers for CO₂ than for CH₄. Cl-functionalized COFs exhibit substantially stronger CH₄/CO₂ selectivity than COF10. It is verified that the interaction energies of more polarized CO₂ on the pore wall of COF10 are larger than those of CH₄, and the increased polarity induced by the highly electronegative Cl groups strengthens the framework’s affinity for gas molecules. As a result, improved CO₂/CH₄ selectivity of COF10 by Cl-functionalization can be explained.