Solvent-switch-driven covalent organic framework nanosheets for ultra-robust and recyclable gas separation membrane

Covalent organic frameworks (COFs) exhibit significant potential for gas separation applications, primarily due to their remarkable stability and precisely adjustable pore structures. However, creating sustainable COF-based gas separation membranes remains unachieved and is confronted with significant challenges, including high defect sensitivity, poor recyclability, high-cost and poor pressure resistance. To address these challenges, a molecular knitting strategy is applied for reconstructing long-range ordered COF nanosheets (CONs) into super-robust and nearly defect-free COF membranes using tris(2-aminoethyl)amine (TREN) as the suture. Notably, the disassembly and self-assembly of designated CONs into membranes can be achieved through thermodynamic control by solvent switching in the presence of TREN. The underlying mechanism of this thermodynamically driven molecular structure transformation is elucidated using density functional theory calculations. The COF membranes derived from dynamically knitted CONs exhibit excellent self-healing and recycling capabilities and superior ideal selectivity for gas separation. It demonstrates an ultrahigh Young’s modulus of 19.68 GPa, corresponding to an approximate 992-fold enhancement over that of original COF membranes (0.021 GPa). Ultimately, the fabricated COF membranes exhibit outstanding pressure-resistant (ΔP > 6 bar), anti-plasticizing and H2/CO2 selectivity (113 ~ 52), largely surpassing the Robeson upper bound. The performance of covalent organic framework-based gas separation membranes is limited by high defect sensitivity, poor recyclability, high-cost and poor pressure resistance. Here the authors overcome these limitations with a molecular knitting strategy to transform long-range ordered covalent organic framework nanosheets into robust and defect-free COF membranes.