Preparation and gas separation properties of fluorinated covalent organic frameworks/polyimide mixed matrix membranes

Mixed matrix membranes, which combine the flexibility of polymer membranes with the gas separation properties of porous fillers, have attracted much attention in the field of gas separation in recent years. Covalent organic framework materials (COFs) are distinguished by a high specific surface area, high porosity, and facile functionalization. Their all-organic structure exhibits favorable compatibility with polymers, which is regarded as an optimal filler for mixed matrix membranes. Accordingly, in this study, the fluorinated covalent organic framework material TpPa-CF₃ was synthesized via a solvothermal method, and TpPa-CF₃/6FDA-ODA mixed matrix membranes were prepared through a blending method utilizing TpPa-CF₃ as a filler and polyimide 6FDA-ODA as a matrix. The structure and properties of TpPa-CF₃ and its mixed matrix membranes were investigated through a series of analytical techniques, including FT-IR, XRD, TGA, SEM, and gas permeability tests. The results showed that the homogeneous pores of TpPa-CF₃ provided fast channels for gas molecule transport, the microporous structure of the framework enhanced the interaction of gas molecules with functional groups on the pore walls, and the dipole-quadrupole interactions of C—F bonds with CO₂ elevated the interactions of the framework with CO₂. At a loading of 5 wt% of TpPa-CF₃, the CO₂ and O₂ permeability exhibited an improvement of 149% and 138%, respectively, in comparison to the 6FDA-ODA matrix membrane. Additionally, the CO₂/N₂ and O₂/N₂ separation factors were elevated to 24.4 and 4.8, respectively.