Effect of transition metal elements addition on the properties of nitrogen-doped TiO₂ photocatalysts

Nitrogen-doped TiO₂ (TiO_2-xN_y) nanoparticles with and without adding the transition metal ions, such as Co ⁺ and Ni⁺, were synthesized by thermohydrolysis of TiCl₃. The samples were characterized by X-ray diffraction, specific surface area determination, UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the sample was investigated by employing the oxidative destruction of nitric oxide as a probe reaction using a continuously flowing gases-solid system. Although the doping of transition metal ion in the lattice of titania was not useful to improve the photocatlytic activity, loading of transition metal oxides on the surface of titania resulted in an improvement of the photoreactivity of the nitrogen-doped TiO₂. The beneficial effect was explained by an increased separation efficiency of the photogenerated electron-hole pairs.