Preparation and Gas Separation Performance of Ionic Liquid Modified Covalent Organic Framework/Fluorinated Polyimide Mixed Matrix Membranes

ABSTRACT In this work, a novel fluorinated diamine monomer, 3‐methoxy‐4‐fluoro‐4,4′‐diaminotriphenylamine (FMBDA), was synthesized through molecular design. And then copolymerized with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4,4′‐oxydianiline (ODA) to prepare fluorinated polyimide (FPI). Subsequently, the covalent organic framework (TpDT) was modified with the imidazolium ionic liquid [Emim][Tf 2 N] (IL) via solution impregnation, and the resulting IL@TpDT was doped into FPI to prepare IL@TpDT/FPI mixed matrix membranes (MMMs) with varying mass fractions. The obtained MMMs exhibited excellent thermal properties ( T g > 295°C, T 10% > 528°C), commendable mechanical properties (tensile strength > 81.08 MPa), and outstanding hydrophobic properties (contact angle > 86.90°). IL modification endows TpDT with improved CO 2 affinity and a smaller pore size, thereby enhancing the membrane material CO 2 adsorption selectivity. Simultaneously, the porous structure of the nanocomposite boosts gas adsorption and diffusion, further improving gas separation performance. At an IL@TpDT loading of 3 wt%, CO 2 and O 2 permeability increased by 222% and 123%, respectively, compared to the FPI matrix membrane. The CO 2 /N 2 and O 2 /N 2 separation factors rose to 27.27 and 4.81, respectively.