Compactness-tailored hollow fiber loose nanofiltration separation layers based on “chemical crosslinking and metal ion coordination” for selective dye separation

In this work, three types of hollow fiber loose nanofiltration membranes (LNFs) with different compactness in an “outside-in” mode were prepared via “chemical crosslinking and metal ion coordination”. The formation and evolution in the microstructural regularity of three types of separation layers (G-PEI, M-PEI and C-PEI) are expounded. The compactness of a separation layer can be effectively tailored by combining chemical cross-linking with metal ion coordination on the membrane surface (achieving mean pore sizes as small as 1.2 nm). The three as-prepared membranes can effectively reject dyes with different molecular weights, 99.5% acid red 27 for G-PEI, 99.3% sunset yellow for M-PEI and 96.1% crystal violet for C-PEI maintaining high flux (41.8, 31.2, and 28.7 L m–2 h–1 bar–1, respectively). The size sieving decolorization mechanism of the membranes was demonstrated from the relationship between the pore sizes of the LNFs and the “hydration, aggregation and absorption” process of dye molecules. In addition, the as-prepared membrane displayed excellent anti-bacterial performance and good stability in the long-term separation of dye/salt system. This work provides a new idea in fabricating hollow fiber LNFs with the separation layer with adjustable microstructure.