Swift fabrication of thin-film composite membranes with azine-linked covalent organic framework for high-temperature organic solvent nanofiltration

Covalent organic frameworks (COFs) belong to a class of crystalline and porous solids that are generated by the self-assembly of reactive monomers via covalent linkage. Most existing methods for fabricating COF membranes are tedious, and they focus on quality control challenges associated with thickness uniformity, pore size, and mechanical properties. In this study, TraHz and TpaHz COF-based thin-film composite (TFC) membranes were prepared via the swift interfacial polymerization (IP) of hydrazine and aldehyde monomers on a polyacrylonitrile (PAN) support. Hydrazine played a dual role in one-pot synthesis, where PAN was crosslinked and IP was initiated. Varying the polymerization time allowed for fine-tuning the membrane thickness and performance. The membranes displayed robust high-temperature separation performance in polar aprotic solvents at temperatures of up to 80 °C. The toluene permeance of the membranes was remarkable. The permeance was highly dependent on both the applied pressure and temperature; however, the rejection performance was less dependent on these parameters. Based on the results of the nanofiltration performance evaluated using different molecular-weight dyes, a molecular-weight cut-off value of ∼650 g mol−1 and a rejection higher than 98 % for the Congo red and Chicago blue dyes in water, THF, and ethanol were observed. The dye rejection in toluene was higher than 98 % for Rhodanile blue, while maintaining high toluene permeances of 47 and 33 L m−2 h−1 bar−1 using TraHz-30 and TpaHz-30, respectively. In addition, both membranes exhibited stable separation performance. Our TFC membranes demonstrate a new approach for designing robust and high-flux nanofiltration membranes for precise molecular sieving even at high temperatures.