Novel anti-fouling Fe2O3/TiO2 nanowire membranes for humic acid removal from water

• Interwoven Fe2O3/TiO2 nanowire membranes are fabricated.
• High removal of humic acid is achieved with anti-fouling ability under sunlight.
• Fe2O3 enhances HA adsorption and photocatalytic activity under visible light.
• Interfacial charge transfer between Fe2O3 and TiO2 nanowires is important.

Membrane fouling is one of the major obstacles inhibiting the wide application of membrane technologies for water treatment. Membranes with surface modification of titanium dioxide (TiO2) nanoparticles or TiO2 nanowire membranes (Ti–NWM) have demonstrated reduced membrane fouling due to the photocatalytic capability of TiO2 in degrading foulants on the membrane surface. However, the wide band gap of TiO2 makes it only absorb ultraviolet light, which limits its applications under solar irradiation. In this study, a novel membrane made of interwoven iron oxide (Fe2O3) nanowires and TiO2 nanowires (FeTi–NWM) has demonstrated superior anti-fouling capability in removing humic acid (HA) from water. Results showed that under simulated solar irradiation the FeTi–NWM achieved nearly complete HA removal during a 2 h short-term test at an initial HA concentration of 200 mg/L, compared with 89% HA removal by Ti–NWM. During a 12 h long-term test, the FeTi–NWM maintained 98% HA removal, while the Ti–NWM showed only 55% removal at the end. Without solar irradiation, the FeTi–NWM was severely contaminated and by contrast, a clean surface was maintained under solar irradiation after the 12 h test and the transmembrane pressure change was minimal. The improved HA removal by FeTi–NWM compared with Ti–NWM and its excellent anti-fouling capability under solar irradiation can be attributed to (1) the enhanced HA absorption by Fe2O3 nanowires and (2) the formed Fe2O3/TiO2 heterojunctions that increase photo-induced charge transfer and improve visible light activity.

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