In situ growth of hierarchical Al2O3 nanostructures onto TiO2 nanofibers surface: super-hydrophilicity, efficient oil/water separation and dye-removal.

Developing a facile strategy to synthesize template-free TiO2 membrane with stable super-hydrophilic surface is still a daunting challenge. In this work, super-hydrophilicity (close to 0°) and underwater super-oleophobicity (165°) have been successfully demonstrated on a hierarchical Al2O3/TiO2 membrane, which is prepared via a facile electrospinning method followed by simple calcination in air. The precisely-tuned Al2O3 heterojunctions grew in situ and dispersed uniformly on the TiO2 surface, resulting in an 'island in the sea' configuration. Such a unique feature allows not only achieving super-hydrophilicity by maximizing the surface roughness and enhancing the hydrogen bonding, but also improving the adsorption capacity toward different toxic dyes utilizing the abundant adsorption sites protected by the hierarchical nanostructure during sintering. The new Al2O3/TiO2 nanofibrous membrane can serve as a novel filter for gravity driven oil/water separation along with dye removal, achieving 97.7% of oil/water separation efficiency and 98% of dye capture, thanks to their superb wettability and the sophisticated adsorptive performance. Our presented fabrication strategy can be extended to a wide range of ceramic materials and inspires their advanced applications in water purification under harsh liquid-phase environments.