Alkali-mediated synthesis of uncharged colloidal β-ketoenamine-linked COFs for membrane construction

Covalent organic frameworks (COFs) are ideal materials for engineering molecular sieves membranes. Colloidal COFs play an important role in the preparation of defect-free COF membranes. Herein, we present the alkali-mediated approach to synthesize uncharged β-ketoenamine-linked COFs with high colloidal dispersibility that can serve as preferred membrane-forming materials. The colloidal β-ketoenamine-linked COFs are synthesized in the single solution-phase system and alkali is employed to regulate the reversible dynamic amine-aldehyde condensation process by directing the weak hydrogen bond networks. The colloidal COFs obtained from alkali-mediated synthesis exhibit promoted crystallinity and outstanding dispersity for membrane construction. Furthermore, the alkali-mediated synthesis approach is universal and suitable for synthesizing a series of colloidal β-ketoenamine-linked COFs without the limitations of charged monomers or frameworks. The colloidal COFs are further assembled into COF membranes by vacuum-assisted assembly. Thanks to the intrinsic regular pore structure of COFs, the COF membranes exhibit high permeability (58 L m⁻² h⁻¹·bar⁻¹) and can achieve accurate screening of dye molecules. This work provides a facile and scalable synthesis strategy for uncharged colloidal COFs, and can be employed to develop COF membranes for on-demand molecule separation.