Rational design and synthesis of molecular-sieving, photocatalytic, hollow fiber membranes for advanced water treatment applications

Photocatalytic, hollow fiber membranes based on nanocomposites of titania nanoparticles and carbonaceous char were simultaneously fabricated in a single calcination step, and then optimized for the photo-degradation of pollutants and water recovery in an integrated membrane operation in this study. The physicochemical, mechanical and photocatalytic properties along with separation performance of two series of membranes were finely-tuned by systematically changing the calcination temperature (series 1: 500–1000 °C for 8 h holding time) and calcination time (series 2: 2–8 h at 600 °C). The calcined membranes were extensively characterized for morphology, thermal stability, microstructure, modulus and chemical compositions. Both constituents of titania and char are essential in deriving the desirable hollow fiber properties and membrane performance for photocatalysis and water recovery. By controlling the calcination conditions, membranes prepared at 600 °C for the 3 and 6 h duration displayed an optimal balance between enhanced mechanical strength (34 MPa) and high photo-degradation of acid orange 7 (90.4%). Membrane performance demonstrated water fluxes of 6.9 (H₂O/dark), 12.9 (H₂O/UV) 4.8 (AO7/dark) and 7.9 L m^–2 h^–1 (AO7/UV) with excellent organic dye rejection. Both membranes exhibited photo-induced super-hydrophilicity and defouling potential under the influence of UV light due to the photo-activation of exposed TiO₂ nanoparticles on the membrane surface. The detailed mechanism of property correlation and separation performance for the photocatalytic hollow fibers is proposed and elucidated. This work offers an innovative material for the research avenue of photocatalytic, hollow fiber membrane reactors for advanced membrane treatment applications.