Surface-crumpled thin-film nanocomposite membranes with elevated nanofiltration performance enabled by facilely synthesized covalent organic frameworks

Hydrophilic and porous nanofillers have shown great benefits in the attainment of high-performance nanofiltration (NF) membranes. In this work, a novel nanoporous covalent organic framework (NCOF) was facilely synthesized under mild conditions and deposited onto a polyethersulfone substrate to induce formations of crumpled polyamide layers via interfacial polymerization. With the incorporation of NCOFs, the surface of the COF-based thin-film nanocomposite (CTN) membranes gradually transformed from tent-like to mesh morphology, which significantly enhanced the water permeance owing to the increased effective membrane filtration area and additional water transport channels provided by NCOFs. Besides, the favorable compatibility between NCOFs and the polyamide layer endowed the CTN membranes with high rejection capacities to a variety of solutes. The optimal membrane with the NCOF deposition density of 19.27 μg cm−2, CTN9 membrane, showed nearly twice higher water permeance of 15.5 L m−2 h−1 bar−1 while maintaining high rejections of Na2SO4 and MgCl2 (98.9% and 94.2%, respectively). In addition, the CTN membranes exhibited a satisfying stability during the long-term filtration of saline solutions as well as an improved antifouling ability to the model foulants of bovine serum albumin. The superior NF performance rendered the NCOF functionalized membranes highly promising for water treatment.