Soft and highly permeable COFs nanofiltration membranes for ultrafast small organic molecules separation

Covalent organic frameworks (COFs) are a novel materials platform that combines covalent connectivity, structural regularity, and molecularly precise porosity. However, COFs usually form insoluble aggregates, which limits their wide application in separation membranes. Here, we adopted “reaction-separation-assembly” strategy to produce continuous and uniform COFs membranes with controllable thickness. Our experimental data showed that the strategy can manipulate colloidal COFs suspensions to create tailored selective layer. The obtained membranes exhibited high pure water flux of 150 L m ^-2 h^-1 bar^-1, good salt/dyes separation factor and superior molecular sieving ability (> 90 % for active pharmaceutical ingredients, >97 % for dyes molecules), which is substantially higher than that of commercial NF1. In addition, the prepared composite membranes showed superior stability, especially under harsh conditions such as strong acids (4 mol L^-1 HCl) and strong bases (2 mol L^-1 NaOH). Overall, this work provides a promising approach for highly permeable and stable COFs membranes, and facilitates rapid recycling of small organic molecules such as active pharmaceutical ingredients and dyes.