Green modification of P84 co-polyimide with β-cyclodextrin for separation of dye/salt mixtures

Novel beta-cyclodextrin (β-CD) incorporated P84 co-polyimide nanofiltration (NF) membranes were prepared via interfacial polymerization between N, N-bis(3-aminopropyl)-1,3-propanediamine (APPD) and beta-cyclodextrin (β-CD) in a green solvent. The effects of concentration and hydroxyl groups of β-CD on separation performance, surface hydrophilicity, and antifouling performance of the prepared membranes were analyzed. The results demonstrate that the 0.3β-CD/APPD/P84 membrane has a pure water permeability of 209.07 Lm−2 h−1 bar−1 at 2 bar. The membrane also shows effective dye/salt separation with a high dye rejection of 99.1 % to Congo red and a high salt permeation of 92.13 % to NaCl. The resultant membranes can also effectively separate binary dye solutions with different molecular weights because of the unique cavity structure of β-CD and inclusion complexation. In addition, the membranes exhibit excellent antifouling characteristics because the unreacted hydroxyl groups in the outer cavity of β-CD initiate strong hydrogen bonding with water molecules, which blocks the interaction between pollutants and the membrane surface. Comparing with other reported membranes, the newly developed nanofiltration (NF) membrane exhibits a higher water permeability and comparable separation performance to dye/salt mixtures. Furthermore, the membrane maintains a high dye rejection (Congo red, 98.67 %) and salt permeation (NaCl, 95.93 %) even at a high NaCl concentration of 40,000 ppm in dye/salt mixtures. Therefore, the novel β-CD incorporated NF membrane has a prominent potential for the treatment of salt-containing dye wastewater treatment with better dye/salt separation.