Sol–gel-derived super-hydrophilic nickel doped TiO2 film as active photo-catalyst

Abstract Pure and nickel doped TiO 2 thin films on soda glass substrates were prepared by sol–gel dip coating process. The resulting films were annealed at 500 °C for 1 h and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV–vis-near IR techniques. AFM reveals that doping of Ni ions suppresses the grain growth of crystal in the TiO 2 film. The contact angle with water of these films was measured by sessile drop method. The undoped films could be entirely wetted by water after 1 h UV illuminations, while 0.5 mol% Ni ion-doped films become entirely wetted after 20 min UV illumination. The photo-catalytic activity was characterized by photo-catalytic degradation of aqueous methyl orange under UV radiation. It is found that, with a suitable amount (2–10 mol%), the Ni dopant increases the photo-catalytic activity of TiO 2 films. The mechanism can be attributed to these processes: (1) as the anatase grain sizes decrease with Ni doping and the specific surface areas of doped TiO 2 films increase, the charge transfer in TiO 2 film is promoted; (2) by enhancing the electron–hole pair separation and inhibiting their recombination, the Ni dopant enhances the charge pair separation efficiency for doped TiO 2 films.