CQD-mediated homogeneous covalent organic framework membranes for ultrafast molecular sieving

Self-standing COF membranes with precisely defined channels enable selective separation and rapid solvent transport, showing the potential to overcome the trade-off between selectivity and permeability. However, self-standing COF membranes formed through conventional interfacial polymerization often suffer from structural heterogeneity, resulting in numerous gaps and defects that impair membrane integrity and separation performance. In this work, we present a simple method to increase the structural homogeneity of COF membranes via a carbon quantum dot (CQD)-mediated interfacial polymerization process. CQDs controllably release amine monomers at the reaction interface, enabling the COF layer to nucleate and grow slowly, resulting in a highly ordered and uniform membrane structure. The resulting COF‒membrane composite membranes, characterized by uniform, dense, and smooth surfaces, achieve precise separation between dyes and salts and exhibit an exceptionally high water flux of 92.1 L/m² h bar. Furthermore, the separation process of the COF membrane aligns with a pore flow model, where the permeation flux for different solvents inversely correlates with their viscosity, reaching up to 213.6 L/m²·h·bar for acetonitrile. This work offers a promising strategy for the fabrication of highly crystalline and structurally precise COF membranes for energy-efficient environmental remediation and resource recovery.