Fluorinated-cardo-based thermally rearranged membranes with enhanced gas separation performance for CO2 capture and hydrogen separation

Thermally rearranged (TR) material has emerged as a focal point in gas separation membranes. However, further enhancing the gas separation performance of TR materials remains a key hurdle. In this study, fluorinated-cardo-based diamine (FFDA) was strategically incorporated into the polybenzoxazole structure to improve the gas selectivity. The size-sieving ability of the polymers was significantly enhanced through the interchain hydrogen bonding and π-π stacking induced by the cardo groups. Furthermore, the aromatic fluorine atoms in FFDA exhibited superior CO 2 adsorption capacity. As the thermal rearrangement progressed and the polybenzoxazole structure developed, pores with a diameter of approximately 3 Å were formed, leading to increased diffusion rate of CO 2 and H 2 . The TR400 °C membranes surpassed the 2018 CO 2 /CH 4 mixed-gas upper bound. Particularly, the 6FDA-FFDA/6FAP(1:1)-TR400 membrane achieved a CO 2 permeability of 185.3 Barrer and a CO 2 /CH 4 selectivity of 79.9—representing increases of 227.3 % and 37.5 %, respectively, compared to the precursor membranes. Moreover, the robust structure of the membrane demonstrated enhanced plasticization resistance, with no discernible plasticization observed under CO 2 /CH 4 mixed-gas conditions up to 20 bar. Our design approach paves the way for developing mechanically robust and highly selective TR membranes, with significant potentials for application in CO 2 separation under aggressive conditions.