Improved selectivity of CH 4 /CO 2 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 was performed to elucidate the fundamental mechanisms governing CH4/CO2 separation in COF materials. Calculated results demonstrated that the adsorption of CO2 within the 1D channels of COF10 is more favorable than CH4, and the adsorption selectivity (Sads) exhibits a significant enhancement by Cl-functionalization. Moving rate of CH4 is much larger than that of CO2 in the 1-D channel of COF10, and Cl-functionalization creates stronger diffusion barriers for CO2 than for CH4. And then 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.