Engineering Vanillin-Functionalized TiO2 Nanotube–Polysulfone Membranes with Enhanced Antifouling and Water Filtration Performance

Vanillin-functionalized TiO2 nanotube–polysulfone (PolySulf–VOH@TNT) composite membranes were developed to enhance water permeability, antifouling resistance, and mechanical performance. VOH@TNTs were incorporated into a polysulfone matrix (1–7 wt%) via non-solvent-induced phase separation. Incorporating VOH@TNTs markedly improved surface hydrophilicity, reducing the water contact angle from 83° (pristine polysulfone membrane, PSM) to 59.6° (5 wt%), and increased water uptake and porosity from 36% and 38% to 61% and 52%, respectively. Mechanical strength rose from 5.3 to 8.3 MPa due to strong polymer–filler interfacial bonding. The PolySulf–VOH@TNT (5%) membrane, identified as the best-performing formulation based on its physicochemical properties and humic acid (HA) filtration performance, exhibited a pure-water flux of 195.4 L m−2 h−1, approximately 125% higher than that of pristine PSM, while achieving 98.8% HA rejection and a 19% reduction in foulant adsorption. Antifouling tests showed a flux recovery ratio (FRR) of ~91% and irreversible fouling (Rir) of ~7%. The membrane also achieved >96% rejection for humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA), maintaining ~94% flux recovery after cleaning. These enhancements result from the formation of a VOH- and Ti–OH-derived hydration layer, electrostatic repulsion, and improved pore interconnectivity. The findings demonstrate that VOH@TNT incorporation is a promising approach for improving the permeability, separation efficiency, and short-term antifouling performance of polysulfone ultrafiltration membranes under the investigated experimental conditions. However, further studies are required to establish their long-term stability, environmental safety, and practical applicability in water treatment.