Dependence of nitrogen doping on TiO2 precursor annealed under NH3 flow

N-doped TiO2 photocatalysts were prepared by annealing two different precursors, P25 and a TiO2 xerogel powder under NH3/Ar flow at 500, 550, and 600 °C. The xerogel powder prepared by peptizing Ti(OH)4 with HNO3 was composed of nanoparticles and had large specific surface area. During the annealing process, the xerogel powder underwent increase in crystallinity, grain growth and phase transformation, whereas P25 did not show obvious changes. Compared with the N-doped TiO2 photocatalysts from P25, the N-doped TiO2 photocatalysts from the xerogel powder possessed higher concentrations of the substitutional nitrogen and exhibited more obvious absorption in the visible light region. The N-doped TiO2 photocatalysts from the xerogel powder exhibited obvious visible-light activities for photodegrading methylene blue and the sample prepared at 500 °C achieved the best performance with a rate constant (k) about 0.44 h−1, whereas those from P25 did not exhibit improved visible-light activities.