In Situ Converted High‐Loading Membranes With Molecularly Dispersed Porous Organic Cages for Superior CO ₂ /N ₂ Separation

ABSTRACT Porous organic cages (POCs) based mixed‐matrix membranes with characteristics of molecular‐size pores and operation efficiency are promising for gas separation; however, the imbalance between high loading and molecular dispersion impedes the further development of POCs in the field of membrane gas separation. Herein, we propose an in situ cage conversion strategy to construct solid‐solution membranes: RCC3, a highly soluble yet nonporous cage, is first synthesized via the reduction reaction, followed by its homogeneous dispersion in PIM‐1 to form a uniform membrane. Paraformaldehyde, involved in situ nucleophilic addition, converts nonporous RCC3 to rigid porous FT‐RCC3 directly in the membrane. FT‐RCC3 membrane exhibits permanent porosity and molecularly dispersed cages with the highest loading (26.6 wt%) achieved ever for POC‐based membranes. Permeation measurements of CO 2 and N 2 gases show that the obtained FT‐RCC3 membrane demonstrates superior CO 2 /N 2 separation performance with CO 2 permeability (9321 Barrer) and CO 2 /N 2 selectivity (68.9) largely exceeding the 2019 upper bound and other POCs membranes. Both CO 2 permeability and CO 2 /N 2 selectivity are substantially enhanced in comparison to pristine PIM‐1 and RCC3/PIM‐1 membranes.