Polyamide Covalent Organic Framework Membranes for Molecular Sieving

Polyamide is an important class of membrane materials for separation technology. The polyamide membranes currently used are amorphous, and thus, their pore structures are disordered, which inevitably decreases their performance in separation. Herein, we report a new type of polyamide membranes which are fabricated from amide-linked covalent organic frameworks (COFs), a class of crystalline porous polymers with well-ordered pore structures. Thanks to the structural advantages of amide-linked COFs, the polyamide COF membranes not only exhibit high permeability (482.3 L m^-2 h^-1 bar^-1 to water) and high rejection rate to organic dyes (>99% for methylene blue) but also display excellent stability under a harsh environment. The vantage of the polyamide COF membranes is also manifested by the comparison of their mechanical property, stability, and separation performance with that of the membranes fabricated from the COFs having the same building blocks but linked with imine and amine linkages. This work demonstrates that amide-linked COFs, which combine the structural features of COFs and polyamide, could be a new type of advanced materials for the fabrication of high-performance separation membranes.