Visible-Light-Induced Self-Cleaning Property of Bi2Ti2O7-TiO2 Composite Nanowire Arrays.

Bi2Ti2O7-TiO2 composite nanowire arrays were prepared via a two-step sequential solvothermal and subsequent calcination process. The morphology and structure of the Bi2Ti2O7-TiO2 composite nanowire array composite were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The UV-visible diffuse reflectance spectroscopy analysis indicated that the absorption spectrum of the Bi2Ti2O7-TiO2 composite nanowire array composite was extended to the visible-light region due to the existence of Bi2Ti2O7. The Bi2Ti2O7-TiO2 composite nanowire arrays exhibit superhydrophilicity with water contact angles of 0° after irradiation with visible light, and the superhydrophilic nature is retained for at least 15 days. This effect enables us to consider self-cleaning applications that do not require permanent UV exposure. Compared to pure Bi2Ti2O7 and TiO2, the vertically aligned Bi2Ti2O7-TiO2 composite nanowire arrays showed more significant visible-light self-cleaning performance due to the synergistic effect of superhydrophilicity and significant photocatalytic activity caused by effective electron-hole separation at the interfaces of the two semiconductors, which was confirmed by the electrochemical analysis and surface photovoltage technique.