Photocatalytic activity of TiO2 thin film non-uniformly doped by Ni

The thin films of TiO2 doped by Ni non-uniformly were prepared by a modified dip-hoisting process of sol–gel method. The transmittance, absorbency, photocurrent and open-circuit potential of the thin films were studied by UV–vis spectrophotometer and electrochemical workstation. The activity of thin films was characterized by photocatalytic degradation of aqueous methyl orange under UV irradiation. The results showed that the photocatalytic activity of TiO2 thin films can be remarkably enhanced by Ni non-uniformly doping compared with the pure ones, while that of the uniformly doped can only be improved a little. The transmittance of the TiO2 thin films doped by Ni uniformly and non-uniformly doping showed “blue shift” and “red shift”, respectively. The absorbency of the non-uniformly doped extended to “red shift”. Under UV irradiation, the non-uniformly doped TiO2 thin films show higher open-circuit potential and photocurrent compared with that of the pure ones, which demonstrated that the photogenerated electron–hole pairs were effectively separated. And the electrode bias influenced the photocurrent of Ni non-uniformly doped TiO2 thin films greatly, which verified the structure of p–n junction. The photocatalytic activity mechanism of the non-uniformly doped TiO2 was discussed by p–n junction theory.