Enhancing the Water Flux and Antifouling Properties of PES Membranes via the Construction of a Bimetallic Polyphenol Network

High-performance polyethersulfone (PES) ultrafiltration membranes integrating antibacterial activity and antifouling performance were fabricated via the in situ construction of bimetallic polyphenol networks (BMPNs) throughout the membrane architecture. Tannic acid (TA) functioned as a multifunctional molecular bridge, functionalizing silver metal–organic frameworks (Ag-MOFs) to yield hydrophilic T-Ag-MOFs and chelating Fe3+ ions from the coagulation bath to form a polyphenol network during phase inversion. T-Ag-MOF incorporation generated asymmetric morphologies featuring highly porous surfaces and sponge-like cross-sections, improving pure water permeability, mechanical integrity, and bovine serum albumin (BSA) rejection. TA-mediated functionalization increased hydrophilicity, imparted a negative surface charge, suppressed nonspecific protein adhesion, and enhanced flux recovery with low irreversible fouling. At an optimal loading of 0.4 wt%, the resultant T-Ag-MOF/Fe3+/PES composite membrane achieved a pure water permeability of 593.4 L m−2 h−1 bar−1—1.77-fold higher than that of the pristine PES control—while sustaining a BSA rejection of 96.5%. Notably, interfacial compatibility between the T-Ag-MOFs and PES matrix was enhanced, facilitating strong, covalent-like filler–matrix adhesion. Moreover, the composite membrane delivered synergistic multifunctionality, including exceptional long-term aqueous stability, precisely tuned Ag+ release kinetics, and potent antibacterial activity, as evidenced by negligible uncontrolled ion leaching and a lack of structural degradation under prolonged hydration.