Green resource utilization of textile and dyeing wastewater: Fabrication of a chlorine-resistant ZIF-L/PDA loose nanofiltration membrane via interfacial polymerization and its performance in dye/salt separation

This study reports the development and performance of a chlorine-resistant, negatively charged loose nanofiltration (LNF) membrane designed for efficient dye/salt separation from textile wastewater. The membrane was constructed by incorporating a synergistic composite of zeolitic imidazolate framework-L (ZIF-L) and polydopamine (PDA) into a polyamide layer on a polyethersulfone (PES) support via interfacial polymerization. In this design, ZIF-L nanosheets create a highly permeable, loose network, while PDA acts as a crucial molecular linker to ensure homogeneous dispersion and structural integration. Characterization using SEM, XRD, FTIR, XPS, and AFM confirmed successful synthesis. The optimal membrane, loaded with 2 wt% ZIF-L/PDA, exhibited superior performance: a pure water flux of 31.56 L·m −2 ·h −1 ·bar −1 , which is 3.19 times greater than the pristine Thin-Film Composite (TFC) membrane. This membrane achieved high dye rejection rates: Eriochrome Black T (99.25 %), Acid Chrome Blue K (97.87 %), Direct Blue 71 (97.56 %), Congo Red (94.09 %), and Direct Red 23 (93.92 %). Simultaneously, it showed low rejection for salts, indicating high permeability: NaCl (7.80 %), MgCl 2 (9.89 %), MgSO 4 (15.39 %), and Na 2 SO 4 (23.97 %). Crucially, the membrane demonstrated robust stability under diverse and harsh conditions, including exposure to strong acid, strong alkali, high pressure, and during long-term continuous operation, along with markedly enhanced chlorine resistance. Therefore, the ZIF-L/PDA loose NF membrane presents significant potential for dye wastewater treatment applications.