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 COF 2 membrane showed an excellent rejection (>96%) for dye molecules. This work opens a new fabrication route for COF-based membranes.