Organic-inorganic polyimide nanofiltration membrane with triazine and SiO₂ cross-linked structures for enhancing dye/inorganic salt separation

Polyimide nanofiltration (NF) membranes with remarkable physicochemical properties have garnered significant attention in dye separation applications due to their high separation efficiency and stability. Inspired by the biological process of mineralization observed in sponges, we introduce a novel net sponge polyimide nanofiltration (PIS) membrane embedded with triazine and SiO₂ cross-linked structures. The PIS membrane was fabricated through a straightforward phase inversion technique, showcasing impressive water permeability (∼168.82 L m⁻²h⁻¹ bar⁻¹). Notably, it achieved a high rejection rate (>90.0 %) both for negatively charged dyes such as Brilliant Blue R and Congo Red, and for positively charged Rhodamine B dyes. Moreover, while obtaining universal rejections of different dyes, the PIS membrane maintained a low rejection rate of inorganic salts (below 10 %). Its long-term stability was assessed in various organic solvents, such as methanol, cyclohexane, acetone, ethyl acetate, ethanol, and toluene. Furthermore, it also exhibited excellent filtration and remarkable organic solvent resistance after seven days of repeated immersion and cleaning in ethanol. The distinct reusability of the PIS membrane was also demonstrated. Overall, these properties render the PIS membrane highly advantageous for applications in the dye/inorganic salt separation field.