Preparation and characterization of TiO₂ photocatalyst co-doped by nitrogen and nickel with concentration gradient distribution

Nitrogen and nickel co-doped TiO₂ photocatalyst was synthesized by the combination of precipitation with layer-by-layer impregnation, in which titanium tetrachloride was used as Ti-precursor and ammonia, nickel chloride as doping-ion donors. The samples were characterized by means of X-ray diffraction (XRD), nitrogen adsorption-desorption, X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy (UV-Vis). The as-prepared photocatalyst was dominantly in anatase phase and a mesoporous structure. The doped nitrogen and nickel impurities were found to be NO_x and Ni₂O₃, NiO species, which were confirmed by XPS. The photocatalytic activity of co-doped TiO₂ was higher than that of both pure and single doped one. Visible light response was due to NO_x and the doped nickel maintains the charge balance at the same time. Simultaneously, the special concentration gradient distribution of Ni in this work reduced the possibility of recombination of photogenerated holes and electrons, which seemed to contribute to the enhancement of the photocatalytic activity of nitrogen and nickel co-doped TiO₂.