Visible-light-driven nitrogen-doped TiO2 photocatalysts: effect of nitrogen precursors on their photocatalysis for decomposition of gas-phase organic pollutants

Yellow-colored N-doped TiO2 (NTO) powders were synthesized by spray pyrolysis from a mixed aqueous solution containing TiCl4 and an N-precursor (urea, guanidine, or ammonium fluoride). All resulting powders possessed spherical particles with an average particle diameter of 0.45 μm, however, the surface morphologies of particles significantly depended on the N-precursors. A porous surface was observed for the particles prepared by using NH4F as N-precursor. Acetaldehyde and trichloroethylene decompositions were used as probe reactions to evaluate the photocatalytic activity of these NTO powders under visible-light (vis) irradiation. The NTO powder prepared from a mixed solution of TiCl4 and NH4F demonstrated the highest photocatalytic activity among three N-precursors, and it was much higher than that of commercial P 25. This high photocatalytic activity was ascribed to a synergetic effect of several factors: its porous and acidic surface, doped N atoms, and simultaneously codoped F atoms during nitrogen introduction. However, no correlation between N-concentration and photocatalytic activity was observed.