Tailored design of highly permeable polyamide-based nanofiltration membrane via a complex-dissociation regulated interfacial polymerization

Nanofiltration (NF) that can separate neutral/charged solutes is considered as a key industrial technology in water softening and wastewater treatment. However, commercial polyamide (PA) NF membranes, with undesirable surface properties and excessive mass transfer resistance, seriously restrict the permeability and are easily attached by pollutants. In this study, a novel complex-dissociation regulated interfacial polymerization (CDRIP) strategy was proposed to prepare highly permeable polyamide-based (PA-based) NF membranes, in which tannic acid (TA)/Ca(II) complex was in situ formed on substrate surface and then dissociated by sodium citrate (SC) after interfacial polymerization. Interestingly, SC can not only adjust surface properties of PA, such as hydrophilicity and surface charge, but also form water-soluble SC/Ca(II) complexes for constructing additional transport channels within the separation layer to reduce mass transfer resistance. After the dissociation of TA/Ca(II) complex, TA remained on the membrane surface to further regulate the surface properties of separation layer. The results showed that the PA/TA/Ca(II)-SC NF membrane maintained a high Na2SO4 rejection (98.5 %) and a remarkable water permeability of 31.7 L·m−2·h−1·bar−1, which is 2-fold that of the pristine PA NF membrane. Moreover, the prepared NF membrane exhibits favorable operation stability and anti-fouling ability. Therefore, by employing the CDRIP method, the permeability of NF membrane can be further improved almost without sacrificing the rejection of Na2SO4, which provides a green and efficient strategy for the fabrication of high-performance PA-based NF membranes.