Preformed covalent organic framework network-based polyimide mixed matrix membranes for high-flux hydrogen separation

Mixed matrix membranes (MMMs), combining the processability of polymers with the separation performance of fillers, have attracted significant attention for industrial gas separations. Nevertheless, achieving a uniformly distributed, highly connected filler phase remains a major obstacle, limiting the separation performance enhancement of MMMs. Herein, we report a family of preformed covalent organic framework (COF) network-based MMMs, which are fabricated by preforming a continuous COF network followed by infiltration of a polyimide matrix. This preforming-filler-network (PFN) method constructs a three-dimensional (3D) interconnected transport scaffold within the membrane. This unique structure eliminates filler agglomeration, a key challenge that has not been resolved by conventional MMM fabrication methods. Consequently, the membranes achieve a 707.7% enhancement in H 2 permeability (to 366.7 Barrer) and a 121.7% increase in H 2 /CH 4 separation factor (to 100.2) compared to pristine polyimide membranes. The COF-network MMM also exhibits excellent stability and plasticization resistance, further highlighting its potential for real-world hydrogen purification.