Molecularly Welded “Cellulose‐Like” Membrane with Extensive H‐Bond Networks Enabling Robust and Tunable Nanofiltration

Abstract Targeted removal of ionic species presents a bottleneck in designing advanced water purification technologies. Nanofiltration (NF) holds potential yet suffers from the trade‐off between fractionation efficiency and operational stability. Here a “cellulose‐like” composite membrane is developed using D (+)‐glucosamine (DGA) as the primary building block via molecular‐welding‐mediated interfacial polymerization (IP). Trace aliphatic diamines with different pendant functional groups are incorporated to both create an aperture‐tunable structure and facilitate the formation of extensive hydrogen‐bond networks. Specially, the optimized membrane, cross‐linked with 1,3‐diamino‐2‐propanol (DAP), featured an ultrathin polyester‐amide layer with high water permeance, smooth surface, strong hydrophilicity, near‐neutral charge, exceptional NO 3 − removal (84.1%), and tunable NaCl rejection (30–90%), outperforming the state‐of‐the‐art polyamide membranes. Detailed characterization revealed that ester/amide and H‐bonds conferred desirable anti‐fouling ability, superior chlorine resistance, and robust pH stability. This study offers a versatile platform for designing high‐performance NF membranes addressing critical needs in sustainable water management.