Fabrication of hollow fiber loose nanofiltration separation layers based on nucleophilic addition and Schiff base reactions and the investigation on separation performance of low molecular weight dye/salt systems

Efficiently achieving selective separation of low molecular weight dye/salt systems is significant to promote the development of membrane technology in the field of wastewater treatment. In this work, polyvinyl amine (PVAM), a linear polymer with a large number of primary amine groups (-NH2) and a part of formamide groups (–NH–CHO), was chosen as the primary cross-linker. The primary cross-linked membrane with a thin and compactness separation layer was prepared via nucleophilic addition and Schiff base reactions on the surface of hollow fiber ultrafiltration membrane. Then, the unreacted –NH2 on the membrane surface were used for secondary cross-linking with glutaraldehyde (GA) and terephthalaldehyde (TPA) to obtain two cross-linked membranes with different separation layer structures, respectively. The influences of the cross-linker's rigidity and flexibility on the compactness of the separation layer are expounded detail and the evolution process in the microstructure of the separation layer is revealed. Neutral Red (MW = 288.8 g mol−1) can be completely removed while maintaining high flux (42.6 L m−2 h−1 bar−1). Moreover, the rejection to dyes was almost uninfluenced by salt. This study provides a reference for preparing LNFs with stable microstructures and high efficiency for the selective separation of low molecular weight dye/salt systems.