Photocatalytic Activity for Water Decomposition to Hydrogen over Nitrogen‐doped TiO2 Nanoparticle

Nitrogen‐doped TiO₂ nanoparticle photocatalysts were obtained by an annealing method with gaseous ammonia and nitrogen. The influence of dopant N on the crystal structure was characterized by XRD, XPS, BET, TEM and UV‐Vis spectra. The results of XRD indicate that, the crystal phase transforms from anatase to rutile structure gradually with increase of annealing temperature from 300 to 700 °C. XPS studies indicate that the nitrogen atom enters the TiO₂ lattice and occupies the position of oxygen atom. Agglomeration of particles is found in TEM images after annealing. BET results show that the specific surface areas of N‐doped samples from 44.61 to 38.27 m²/g are smaller than that of Degussa TiO₂. UV‐Vis spectra indicate that the absorption threshold shifts gradually with increase of annealing temperature, which shows absorption in the visible region. The influence of annealing condition on the photocatalytic property has been researched over water decomposition to hydrogen, indicating that nitrogen raises the photocatalytic activity for hydrogen evolution, and the modified TiO₂ annealed for 2 h at 400 °C under gas of NH₃/N₂ (V/V=1/2) mixture shows better efficiency of hydrogen evolution. Furthermore, the N‐doped TiO₂ nanoparticle catalysts have obvious visible light activity, evidenced by hydrogen evolution under visible light (λ>400 nm) irradiation. However, the catalytic activity under visible light irradiation is absent for Degussa as reference and the N‐doped TiO₂ annealed at 700 °C.