Chitooligosaccharide/Polydopamine Co-Deposition Modifying Substrates for High-Performance Forward Osmosis Membranes with Enhanced Antibacterial and Antifouling Properties

Forward osmosis (FO) membranes have garnered widespread research interest in water treatment, yet their permeability–selectivity trade-off, internal concentration polarization, and membrane fouling remain critical challenges. Herein, a chitooligosaccharide/polydopamine (COS/PDA) co-deposition strategy was proposed to modify polyethersulfone (PES) substrates for constructing high-performance thin-film composite (TFC) FO membranes. COS suppressed excessive PDA aggregation, reduced substrate roughness, and improved substrate hydrophilicity. This substrate modification regulated interfacial polymerization by increasing the adsorption capacity for m-phenylenediamine (MPD) while slowing its diffusion rate, thereby forming thinner, smoother, and more densely crosslinked polyamide (PA) layers. The optimized C4P1-TFC membrane delivered water fluxes of 42.2 and 23.5 L m−2 h−1 in pressure-retarded osmosis (PRO) and FO modes, respectively, representing 43.1% and 40.2% improvements over the pristine membrane. Its specific salt flux decreased to 0.07 and 0.15 g L−1 in the two modes, respectively, suggesting enhanced selectivity. Meanwhile, the C4P1-TFC membrane showed antibacterial rates of 85.7% against Escherichia coli and 86.9% against Staphylococcus aureus, together with improved antifouling performance against bovine serum albumin and lysozyme. This work presents a simple and effective co-deposition approach for simultaneously improving the separation, antibacterial, and antifouling performance of TFC FO membranes, showing promising potential for practical applications.