In-situ construction of a polydopamine@ZIF-8 functional layer on PES ultrafiltration membranes for high-flux, antifouling dye/salt separation

This study reports the one-step in-situ assembly of a polydopamine (PDA)@ZIF-8 functional layer on polyethersulfone (PES) ultrafiltration (UF) membranes for high-flux, antifouling dye/salt separation. Leveraging the synergistic effect of dopamine (DA) self-polymerization and the in-situ growth of ZIF-8 during the nonsolvent-induced phase separation (NIPS) process, a highly integrated PDA@ZIF-8 functional layer was successfully constructed on the PES membrane surface. Strong coordination and chelation interactions among Zn 2 + ions, the catechol moieties of PDA, and 2-methylimidazole (2-MIM) increase the casting solution viscosity, triggering delayed demixing and promoting the migration of hydrophilic precursors toward the membrane interface. Structurally, the in-situ assembly of PDA@ZIF-8 significantly increased the selective layer thickness from 4.73 μm to 33.10 μm. The resulting ultrafiltration membrane exhibited exceptional separation efficiency, delivering a Congo Red (CR) rejection rate of over 99.5% while maintaining a salt rejection rate under 5%, enabling the efficient fractionation of dyes and salts. A high pure water flux of 455 L·m −2 ·h −1 at 0.1 MPa is attained, which is attributed to the enhanced surface hydrophilicity and the intrinsic sub-nanometer microporous channels of ZIF-8. Furthermore, the functionalized layer demonstrates remarkable antifouling properties toward anionic dyes, with a stable flux recovery ratio (FRR) exceeding 85% after multiple cycles of CR filtration. This research presents an effective membrane preparation strategy that enhances separation performance while ensuring excellent long-term antifouling stability.