β-Cyclodextrin enabled ultrahigh-permeance loose nanofiltration membrane for efficient dye separation

Traditional loose nanofiltration (LNF) membranes show great advantages in dyeing wastewater treatment, however, their applications are limited by the “trade-off” effect. β-Cyclodextrins (β-CD) demonstrate excellent hydrophilicity and hydraulic conductivity owing to the existence of the hydrophilic ends and hydrophobic inner lumen. This study reports an LNF membrane with outstanding permeance and dye rejection capabilities achieved through the immobilization of β-CD within the pores of the substrate membrane via the thermal shrinkage of sulfonated polysulfone and the electrostatic synergy of polydopamine. The introduction of β-CD and PDA changed the surface potential, hydrophilicity, and pore structure of the membrane. Furthermore, it displays specific recognition with dyes, thereby further enhancing both permeance and rejection rates. As anticipated, both permeance and dye rejection (Methylene Blue) increased to remarkable levels, reaching up to 225 L·m −2 ·h −1 ·bar −1 and 97.8 %, respectively. These values far exceeded those achieved by conventional polymeric NF membranes or hybrid NF membranes. Besides, the permance and dye rejection didn't change much with the increase of the dye feed concentration, salt concentrations or under different pH conditions. Furthermore, both permeance and rejection rates remained stable during the cyclic filtration tests, with stability further enhanced in deionized water at 40 °C. These findings highlight the potential of strategies aimed at modifying membrane pore transport channels for applications in dye separation, particularly in treating printing and dyeing wastewater.