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-cardobased 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 it-it stacking induced by the cardo groups. Furthermore, the aromatic fluorine atoms in FFDA exhibited superior CO2 adsorption capacity. As the thermal rearrangement progressed and the polybenzoxazole structure developed, pores with a diameter of approximately 3 & Aring; were formed, leading to increased diffusion rate of CO2 and H2. The TR400 degrees C membranes surpassed the 2018 CO2/CH4 mixed-gas upper bound. Particularly, the 6FDA-FFDA/6FAP(1:1)-TR400 membrane achieved a CO2 permeability of 185.3 Barrer and a CO2/CH4 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 CO2/CH4 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 CO2 separation under aggressive conditions.