Highly water-permeable and stable hybrid membrane with asymmetric covalent organic framework distribution

Although covalent organic frameworks (COFs) have received tremendous attention in recent years due to their unique advantages, their application in membrane processes for liquid mixture separation has not been explored. In this study, COF-based hybrid membranes were fabricated by incorporating COF SNW-1 into sodium alginate (SA) matrices and used for ethanol dehydration. Due to the remarkable density difference between SNW-1 and the membrane casting solvent, majority of SNW-1 nanoparticles floated to the top of the membrane and minority of SNW-1 nanoparticles were entrapped in SA during the slow evaporation of the solvent, resulting in asymmetric distributions. The surface hydrophilicity and water sorption capacity of the hybrid membrane are enhanced by the enriched SNW-1. And the porous structure of SNW-1 could render additional selectivity and free volume cavities for water molecules transfer. As a result, the hybrid membrane shows high separation factor and permeation flux of 1293 and 2397 g/m2 h, respectively. Moreover, the incorporation of SNW-1 also endows membranes with enhanced thermal and mechanical stability, good anti-swelling properties and desirable long-term operation stability. This study offers a novel approach to design high performance hybrid membranes by incorporating fillers with the density different from that of the membrane casting solvent.