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

Abstract

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 CO₂ 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 CO₂ and H₂. The TR400 °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.