Molecular soldered COF membrane with crystalline-amorphous heterointerface for fast organic solvent nanofiltration

Covalent organic frameworks (COFs) featuring high porosity and well-defined pore structures are attractive candidates for organic solvent nanofiltration (OSN). However, preparing defect-free COF membrane and manipulating pore size for precise molecular separation in OSN remains a significant challenge. Herein, we address this challenge by developing composite membranes through molecular soldering a benzimidazole-linked polymer (BILP-101x) onto a continuous ACOF-1 membrane. The shared monomer of ACOF-1 and BILP-101x promotes good compatibility, allowing the amorphous BILP-101x chemically stitch the grain boundary defects of the crystalline ACOF-1 layer and create narrow, staggered pores at the interface, thereby enhancing the OSN performance. Non-equilibrium molecular dynamics simulations were employed to reproduce and explain the permeability order of the solvents and dyes, revealing a hydrogen-bond cluster permeation mode for alcohols. Furthermore, the optimized BILP-101x/ACOF-1 composite membrane exhibits excellent ethanol permeance (13.2 ​L ​m⁻² ​h⁻¹ bar⁻¹) and outstanding rejection towards various dye molecules, together with desirable and stable OSN performance under continuous filtration operation. This work opens a new avenue for improving the separation performance of continuous COF membranes in OSN applications.