Channel-molecule attraction mediated molecule transport in confined nanochannels of COF membranes for nanofiltration

Porous membranes, a type of material widely used in nanofiltration, are confronted with the limitation that the influence of channel-molecule interactions on transport behaviors has yet been investigated in detail. Herein, covalent organic framework membranes with adjustable pore sizes (similar to 2.5 nm and similar to 1.2 nm) and chemical groups (-F, -OH, and -CO-) were prepared by interfacial polymerization. We demonstrate that strong channel-molecule attraction induces the formation of stable solvent layers along nanochannel walls, which protect central molecules from the attraction of chemical groups. Significantly, stable solvent layers permit fast transport of ethanol (245.6 L m(-2) h(-1) bar(-1)) with reactive black (RB) rejection of 96%. Likely, for membranes with weak channel-molecule attraction, no solvent layers are formed and molecules also transport smoothly. Interestingly, membranes that exhibit moderate channel-molecule attraction exert metastable solvent layers, thus displaying high transport resistance. This hindrance effect on molecule transport becomes more pronounced in smaller nanochannels.