Rapid synthesis of self-standing covalent organic frameworks membrane via polyethylene glycol-assisted space-confined strategy

Owing to their high specific surface area, tunable pore sizes, excellent chemical/thermal stability and ability to allow easy modification of the nature of the surface, covalent organic frameworks (COFs) have shown great promise in membrane separation. However, until now, rapid preparation of self-standing COFs membrane has still been a great challenge. In this work, a polyethylene glycol-assisted space-confined strategy for rapid and simple synthesis of imine-linked self-standing COF (TB-DA COF) membranes was developed for the first time. By using this strategy, the molecular organic building unit 1,3,5-tri-(4-aminophenyl)benzene (TB) is confined in a thin layer of polyethylene glycol in conjunction with molecular organic building unit 2,5-dimethoxyterephthalaldehyde (DA). Therefore, the condensation reaction between TB and DA can occur directly without slow diffusion process. In addition, the amorphous-to-crystalline interconversion process can be completed rapidly. Based on this, the imine-based TB-DA COF membrane with high crystallinity can be synthesized within 2 min, which has been the fastest strategy for preparation of COFs membrane to date. The synthesized TB-DA COF2 membrane showed an excellent rejection (>96%) for dye molecules. This work opens a new fabrication route for COF-based membranes.