Hierarchical Cellulose–COF Composite Membranes with Dual-Sieving Channels for High-Flux and High-Selectivity Separation

Covalent organic framework (COF) membranes, with their programmable pore structures and tunable chemical environments, hold great promise for water purification and pollutant separation. However, simultaneously achieving high permeability and selectivity remains a key challenge. Inspired by the biomineralization mechanism of diatom cell walls, we constructed a bioinspired hierarchical nanofiltration membrane by integrating electrospun cellulose nanofibers with in situ grown COF layers (ECNF/COF membrane). The membrane features multiscale transport channels comprising neck-bridged microsphere junctions, intraparticle tortuous pathways, and intrinsic COF nanopores, enabling efficient and selective molecular transport. Thiol–ene click functionalization with sulfonic acid groups produced the ECNF/SCOF membrane and simultaneously regulated wettability (water contact angle from 150.4° to 2.7°), surface charge (zeta potential from −1.5 to −21.8 mV), and pore size (from 2.8 to 1.4 nm). The ECNF/COF and ECNF/SCOF membranes exhibited excellent separation efficiencies (> 99%) for W/O and O/W emulsions, respectively. In mixed dye/salt systems, the ECNF/SCOF membrane achieved over 99% dye rejection while maintaining high salt permeability (salt rejection below 10%). Molecular dynamics simulations confirmed a synergistic “size-sieving plus electrostatic-barrier” mechanism, clarifying the interplay between structure and surface chemistry. This work proposes a programmable, multiscale structure–interface co-regulation strategy that offers new insights into high-performance purification in complex liquid pollution systems. Graphical