Fabrication of High-Performance Nanofiltration Membrane Using Polydopamine and Carbon Nitride as the Interlayer

In order to recover lithium from brine with a high Mg2+/Li+ratio, a positively charged nanofiltration (NF) membrane was prepared by depositing polydopamine (PDA)-coated graphitic carbon nitride (g-C3N4) as the interlayer (PDA-g-C3N4) and the interfacial polymerization (IP) of polyethyleneimine (PEI) and trimesoyl chloride (TMC) was carried out. Under optimal conditions, the water contact angle of the composite membrane is only 55.5° and the isoelectric point (IEP) is 6.01. The final positively charged NF membrane (M5) exhibits high permeance (10.19 L·m−2·h−1·bar−1) and high rejection of Mg2+(98.20%) but low rejection of Li+(13.33%). The separation factor (SF) is up to 48.08, and the Mg2+/Li+ratio of the permeate is 0.036 in the simulated brine. In conclusion, the M5 membrane shows a good separation performance for salt lake brine (SF = 12.79 and Mg2+/Li+ratio of the permeate = 1.43) and good fouling resistance. Therefore, the positively charged M5 membrane with PDA-g-C3N4as the interlayer has the potential to be used for the recovery of lithium from brine.Keywords:polydopamine;graphitic carbon nitride;nanofiltration membrane;brine;Mg2+/Li+separation