Advanced Mg2+/Li+ separation nanofiltration membranes by introducing hydroxypropyltrimethyl ammonium chloride chitosan as a co-monomer

In recent years, the global demand for lithium resources has been constantly rising thanks to the rapid development of the new energy industry. Nanofiltration (NF) membranes with positive charge could achieve high efficiency separation performance of magnesium ion (Mg2+)/ lithium ion (Li+), which provides a useful solution for the extraction and recovery of lithium resources from brine. In this work, hydroxypropyltrimethyl ammonium chloride chitosan (HACC) was introduced into the interfacial polymerization (IP) as co-monomer with piperazine (PIP) to react with trimesoyl chloride (TMC) for preparing positively charged NF membranes. Based on the modulation of IP process by HACC, the thickness of the modified NF membrane separation layer reduced and the hydrophilicity increased, while the pore size had no obvious variation. In addition, the introduction of the quaternary ammonium group in HACC also increased the antibacterial properties of the NF membrane. The optimized NF-HACC-0.3 not only improved the separation factor significantly, but also increased the flux by 2 times compared with the original membrane. This strategy provides a new valuable idea and insight for the preparation and development of Mg2+/Li+ separation NF membranes.