New approaches to prepare nitrogen-doped TiO2 photocatalysts and study on their photocatalytic activities in visible light

Nitrogen-doped TiO₂ nanocatalysts were successfully synthesized by adjusting a pH range using the ammonium nitrate and ammonia water as the nitrogen source. The samples were characterized by XRD, XPS and UV-DRS. When the total amount of ammonium nitrate and ammonia water was unchanged, different pH values were modified by changing the NH₄NO₃/NH₃·H₂O ratio to prepare nitrogen-doped TiO₂. The prepared photocatalyst showed the highest photo-activity for the degradation of 2,4-dichlorophenol (2,4-DCP) under visible light when prepared at pH 5.87. XPS analysis showed the presence of nitrogen in two states doped in TiO₂. The results indicated the photocatalytic activity of N-TiO₂ is varied with the change of pH values, the amount of the nitrogen sources and water. The experimental results showed that the higher activity is due to the variation in the concentration and states of nitrogen-doped in TiO₂. In the preparation methods, the photocatalyst was treated with the hydrogen peroxide before calcination, resulting in the decrease of nitrogen doped into the lattice and the photo-degradation rate of 2,4-DCP. The results suggested that the nitrogen source could be doped into the crystal lattice only in the form of reduction state as NH₄⁺ ion during the calcination process.