Synthesis of Superhydrophilic Titanium Oxide Spheres and Flowers

The microstructure including crystal phase, morphology and particle size is generally considered to be the primary factor in the design of functional materials, because these elements have unique influence on the physical properties. Although each factor could be well controlled, it is still a big challenge to achieve the complete control on all factors in one system. Here we report a simple hydrothermal method, which can lead to the deliberate control on TiO₂ crystal phase and morphology by using different anions in the reaction system. Anatase TiO₂ with sphere-like structure and rutile TiO₂ with flower-like structure were obtained employing fluorine anion and chlorine anion, respectively. These unique structures exhibit persistent superhydrophilicity without the need of external stimuli, such as the ultraviolet irradiation. Surface roughness and ultraviolet absorption analysis demonstrated that the cooperation of the hierarchical surface and the defects in crystal lattice are considered to be responsible for this superhydrophilic behaviour. This ultimate TiO₂ wetting surface may have environmental friendly applications such as self-cleaning coatings, anti-fogging coatings.