Nitrogen doping in Ta2O5 and its implication for photocatalytic H2 production

Nitrogen-doped Ta2O5 (N-Ta2O5) powders were fabricated by nitridation of Ta2O5 in NH3 for 1 h at 600-700 °C. The concentration of nitrogen doping increased as the nitridation temperature increased, and a small amount of Ta3N5 appeared when nitridized at 700 °C. Pure Ta3N5 was obtained by nitridation at 800 °C for 6 h. They were characterized by X-ray diffraction, Raman spectroscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectrometry, and photoluminescence spectroscopy. It is concluded that in the N-Ta2O5 samples nitrogen ions have substituted for oxygen ions, creating some oxygen vacancies and extra energy levels within the band gap. Further, Ta3N5 prefers to form on the surface and acts as the recombination center for electrons and holes. Among all samples, nitridation at 650 °C resulted in the best photocatalytic hydrogen production efficiency that can be explained by more nitrogen doping and no formation of Ta3N5.