Novel Poly(piperazinamide)/poly(m-phenylene isophthalamide) composite nanofiltration membrane with polydopamine coated silica as an interlayer for the splendid performance

Nanofiltration (NF) is a potential separation technology in the field of water treatment. However, NF membrane generally has the bottleneck problems of low permeability and poor selective separation. Therefore, this study proposed to use polydopamine coated silica microspheres as the intermediate layer to modify the poly(m-phenylene isophthalamide) (PMIA) substrate, then to prepare poly(piperazinamide) composite NF membrane via interfacial polymerization technique. Because both dopamine and silica contain a large number of hydroxyl groups, which can limit the diffusion of aqueous monomers to the water/oil boundary due to the hydrogen bonding force. The obtained NF membrane presented a nano-tubular Turing structure. As a result, the membrane exhibited extremely high permeability with the pure water flux of 31.37 ± 1.06 LMH/bar, and the corresponding rejection to Na₂SO₄ could reach to 97.0%, which was three times that of traditional polyamide NF membrane. Moreover, the performance of one-valent/bivalent salt was excellent. The composite nanofiltration membrane made of polydopamine coated silica as the intermediate layer provides a potential strategy to construct polyamide membrane with improved permeation and selectivity, which will be beneficial to save energy consumption during the actual application.