Mixed Matrix Membranes Based on Nanoporous Organic Cages and a Noncoplanar Polyimide for Gas Separation

Mixed-matrix membranes (MMMs) have attracted considerable attention for gas separation because nanoscale engineering of filler structure and polymer/filler interfaces can improve overall separation performance. In this study, a monomer, 4,4′-diamino-4″-dibenzofuran-triphenylamine (DATPA), was synthesized, and a noncoplanar copolyimide was subsequently prepared using DATPA, 9,9-bis(4-amino-3-fluorophenyl)fluorene (FFDA), and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). MMMs were then fabricated by solution blending using Noria as a nanoporous organic cage filler and the copolyimide as the matrix. Owing to the intrinsic subnanometer cavities of Noria and the resulting nanoscale transport features introduced into the membrane structure, the incorporation of Noria significantly enhanced gas separation performance. At a Noria loading of 9 wt %, the permeabilities of He, CO2, O2, and N2 increased by 96%, 134%, 57%, and 41%, respectively, compared with the pure polyimide membrane. Furthermore, at a 6 wt % loading, the ideal selectivities for He/N2 and CO2/N2 reached 77.9 and 26.0, corresponding to improvements of 42% and 57%, respectively. These results demonstrate that nanoporous organic cage incorporation is an effective strategy for tuning membrane microstructure and improving gas separation performance.