Interfacial polymerization modulated by COFs interlayer to fabricate efficient mono/divalent ions separation nanofiltration membrane

Thin-film composite (TFC) membranes have been recently applied in the mono/divalent ions separation, which is essential for resource recycle, wastewater treatment, and lithium resource extraction. However, the TFC membranes fabricated between the polyethyleneimine (PEI) and trimesoyl chloride (TMC) usually show a low water permeance. Herein, piperazine (PIP) is added in the PEI aqueous phase solution to fabricate a polyamide (PA) layer for the enhancement of water permeance. Meanwhile, the diffusion rate of PIP to the two-phase interface is reduced by the hydrogen bond effect between PIP and MPDTp COFs interlayer, which can weaken the reaction of PIP and TMC and maintain a high ion rejection. Pure water permeance of the obtained PA-PIP/Fe-COF/PES membrane is 16.1 L m−2 h−1 bar−1, and the Li+/Mg2+ separation factor is 73.0, which is almost two times higher than the PA-PIP/PES under Li+/Mg2+ mass ratio of 1:20. Besides, the membrane also keeps satisfactory performance in Na+/Mg2+, Cl−/SO42−, Na+/Ca2+ separation, and ten days of long-term testing. Therefore, this work raises a new strategy to prepare a high-efficiency mono/divalent ions separation nanofiltration membrane.