Preparation of high-performance nanofiltration membranes with quaternized cross-linked microgels as intermediate layer

The high-performance nanofiltration (NF) membranes were fabricated by using hydrolyzed polyacrylonitrile (HPAN) ultrafiltration (UF) membranes with negatively surface charges as the substrate membranes, quaternized crosslinked microgels (PNI6) with positive charges as the intermediate layer, piperazine (PIP) and trimesoyl chloride (TMC) as the monomers for the formation of polyamide selective layer via interfacial polymerization (IP). The introduction of positively charged PNI6 microgels as the intermediate layer improved the hydrophilicity of resultant NF membranes and rendered the NF membranes with surface positive charges. The obtained NF membranes (MG-NF) with PNI6 microgel interlayer simultaneously achieved excellent water flux and the rejection of salts including Na2SO4, MgSO4, MgCl2, and CaCl2. Increasing the deposition time of PNI6 microgels on the HPAN UF substrate membranes increased the water flux and rejection of MgCl2 of the resultant MG-NF series NF membranes. The nanofiltration performance of obtained MG-NF series NF membranes exhibited thermo-sensitivity and long-term stability. For MG-NF-6 NF membrane, the water flux and rejection of MgCl2 reached 10.1 L·m−2·h−1·bar−1 and 93.4 % at 25 °C, respectively. With increase of temperature, the water flux of MG-NF-6 membrane was significantly enhanced to be 13.4 L·m−2·h−1·bar−1 at 45 °C, while the rejection of MgCl2 slightly decreased to be 90 %.