Anti-fouling TiO2 nanowires membrane for oil/water separation: Synergetic effects of wettability and pore size

TiO2 nanowires (NWs) membranes with varied wettability ranging from superhydrophilic to superhydrophobic have been facile fabricated via dip-coating for oil/water separation. Incorporating TiO2 NWs results in the increase of roughness and the formed hierarchical structure from TiO2 NWs micro-aggregations enlarges the wettability. Separation efficiency and permission flux of the as-prepared membranes increase first and decrease with the increment of TiO2 NWs. These superhydrophilic/hydrophilic membranes eliminate water from oil/ water mixtures and the separation efficiency declines with the increasing water contact angle until the membrane lose the oil/water separation property at around 90 degrees. Membranes with water contact angle of 90-100 degrees cannot separate oil/water mixtures while membranes with water contact angle larger than 120 degrees become oilremove type with separation efficiency around similar to 99% and high permission flux. The study illustrates that relatively large pore size (similar to 15 mu m) attributes to the high separation efficiency and permission flux. The synergetic effects of wettability and pore size indicate that surface wettability is critical for efficient oil/water separation. Both hydrophilic and superhydrophilic membranes show high separation efficiency and outstanding anti-fouling performances after long term oil/water separation.