An Efficient Two-Step Technique for Nitrogen-Doped Titanium Dioxide Synthesizing:  Visible-Light-Induced Photodecomposition of Methylene Blue

A series of nitrogen-doped TiO2 nanocatalysts have been synthesized successfully by a two-step hydrolysis-calcination method in which condensed HNO3 (∼16 mol/L) was first used. In contrast to the traditional hydrolysis method, the time consumed in the hydrolysis process was shortened greatly. The content of nitrogen decreases as the calcination temperature increases, resulting in the variation of bandgaps of the as-synthesized N-doped TiO2 from 1.55 to 2.95 eV. Decomposition of methylene blue under visible light irradiation (λ ≥ 400 nm) has been carried out to evaluate the photocatalytic activity of the as-synthesized N-doped nanocatalysts. Compared to P25, greatly improved photocatalytic activity for water contaminant decomposition under visible light irradiation was obtained due to the doping of nitrogen into the titania system. The crystallinity of the photocatalysts was found to be less influential than the nitrogen content in determining the photocatalytic activity.