Controllable synthesis of TiO2 nanoflowers and their morphology-dependent photocatalytic activities

Different surface morphologies of TiO2 films were prepared through hydrothermal synthesis method on transparent fluorine-doped tin oxide (FTO) substrates by changing reaction temperatures. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectrometer (XPS). As the hydrothermal temperatures increases, the surface morphologies of the TiO2 changes from nanorods (150 °C) to nanobuds (180 °C), and finally to nanoflowers (210 °C). Evolution of these structures are accompanied by great variations of optical properties and photocatalytic activities including a narrowing of band gap from 3.01 to 2.97 eV, increase of UV–visible absorption intensity and specific surface area, and photocatalytic degradation efficiencies from 88.18 to 95.56%. Under ultraviolet light (UV light) irradiation, the TiO2 nanoflowers exhibit significantly activity (95.56%) in degradation of methyl orange (MO) compared to commercial P25 (76.15%). The outstanding photocatalytic activity of the TiO2 nanoflowers can be attributed to the synergetic effect of much larger specific surface area, the larger content of oxygen vacancy, and higher intensity of absorption. These findings help to grow unique TiO2 films with desired structure and activities for photocatalyst applications.