Rechargeable N ‐Halamine Functionalized Ultra‐Thin PES Ultrafiltration Membranes

Biofouling and permeability‐selectivity trade‐offs remain fundamental challenges in ultrafiltration. In this study, a permeable, biofouling‐resistant, ultra‐thin PES membrane was fabricated by incorporating a custom‐synthesized N‐ halamine polymer. Utilizing a 3D printer‐assisted platform, an ultra‐thin membrane with a dry thickness of 28.2 μm was reproducibly fabricated, demonstrating the precise control afforded by automated casting. Morphological optimization, particularly maintaining the coagulation bath at 30°C, promoted a favorable membrane structure that provided sufficient mechanical stability while maintaining low hydraulic resistance. The functionalized membrane displayed a pure water flux of 271 L m −2 h −1 without compromising the size‐exclusion selectivity (BSA rejection > 94%). During cyclic filtration, the rechargeable N‐ halamine chemistry disrupted irreversible protein adhesion, delivering a flux recovery ratio of 98.6% in the first cycle and maintaining 81.6% after the second. Furthermore, following chlorination, the membrane demonstrated rapid bactericidal response, achieving complete inactivation (> 5.7‐log reduction) against both S. aureus and E. coli within 15 min. These results indicate that combining automated 3D‐assisted casting with regenerable N‐ halamine chemistry is a practical approach to the precise fabrication of ultra‐thin ultrafiltration membranes with enhanced biofouling resistance.