Printed polyamide membranes with controllable doping of covalent organic framework nanosheets for high-performance desalination

To enhance the water permeability of polyamide (PA) based reverse osmosis (RO) membranes, nanomaterials have been integrated into the polyamide layer during the interfacial polymerization process. However, challenges such as nanoparticle aggregation and uneven dispersion in the PA layer continue to present significant obstacles. In this study, we report a novel printing technique to fabricate thin-film nanocomposite (TFN) membrane that uses an electrospray method to deposit covalent organic framework (COF) nanosheets and monomers for PA polymerization onto a substrate. The COF nanosheets are evenly doped within the polyamide layer. The doping amount of COF nanosheets can be rationally controlled by printing times and dispersion concentration. When the COF nanosheet loading mass is 0.39 mu g cm- 2, the printed TFN membrane shows water permeance of 2.41 L m- 2 h- 1 bar- 1 and NaCl rejection of 98.4 %. Water permeance increases 81.2 % compared with that of without doping COF nanosheets. Moreover, thanks to the negatively charged smooth surface constructed by the printing method, the TFN membranes demonstrate superior resistance to fouling compared to commercial RO membranes. This work proposes a novel methodology for the fabrication of high-performance nanocomposite membranes.