Fluorine-engineered two-dimensional covalent organic frameworks for enhanced C₂H₂/CO₂ separation

Efficient separation of C₂H₂ from CO₂ remains a significant challenge owing to their closely matched molecular dimensions and physicochemical properties. Developing adsorbents capable of discriminating between these two gases is therefore of considerable importance for acetylene purification. Herein, we report two isoreticular two-dimensional covalent organic frameworks (COFs), TP-TFPB-COF and TP-NFPB-COF, featuring an hcb topology and constructed via [3 + 3] imine condensation. By increasing the fluorine content within the framework, TP-NFPB-COF exhibits enhanced C₂H₂/CO₂ separation performance, delivering an IAST selectivity of 2.86 at 298 K and 1 bar, compared with 2.04 for TP-TFPB-COF. Grand canonical Monte Carlo simulations reveal that the improved selectivity arises from increased pore polarity and strengthened C-H⋯F interactions with C₂H₂ molecules. This work highlights fluorination as an effective strategy for tuning pore environments and advancing COF-based acetylene separation.