Fabrication of hollow fiber nanofiltration membrane with high permselectivity based on “Co-deposition, biomineralization and dual cross-linking” process

In this work, the organic-inorganic hybrid separation layer containing BaSO4 or CaC2O4 was fabricated on the membrane outer surface through the combination of polyvinylamine (PVAM)-tannic acid (TA)-metal ion co-deposition, dual cross-linking and biomineralization. Based on the synergistic coordination effect between TA and PVAM, metal ions were anchored within the separation layer. The strong interaction ability between functional groups of organics and metal ions enhanced the attaching stability of mineralized substances. Characterizing the chemical composition, hydrophilicity, microstructure, and potential of the NF membrane's outer surface allowed for a thorough investigation and comparison of the impact of mineralized substances on the separation performance of NF membrane. The results indicated that the introduction of mineralized substances provided the permeance path for water molecule and reduced the water transmission resistance, which not only increased the permeability (53.4 L m−2 h−1 bar−1) by 2.7 times, but also remained ultrahigh removal capacity for both Mg2+ and Ca2+ (>99%). Furthermore, the NF membrane also exhibited satisfactory acid resistance, anti-fouling capacity and favorable operation stability. This work demonstrated excellent potential in wastewater recovery and rapid desalination, serving as a reference for the development of high-performance NF membrane with positively charged surface.