Origin of Photocatalytic Activity of Nitrogen-Doped TiO_2 Nanobelts

摘要

Experiments combined with the density functional theory (DFT) calculation have been performed to understand the underlying photocatalysis mechanism of the nitrogen-doped titania nanobelts. Nitrogen-doped anatase titania nanobelts are prepared via hydrothermal processing and subsequent heat treatment in NH_3. Both the nitrogen content and the oxygen vacancy concentration increase with increasing the NH_3 treatment temperature. Nitrogen doping leads to an add-on shoulder on the edge of the valence band, the localized N 2p levels above the valence band maximum, and the 3d states of Ti~(3+) below the conduction band, which is confirmed by DFT calculation and X-ray photoelectron spectroscopy (XPS) measurement. Extension of the light absorption from the ultraviolet (UV) region to the visible-light region arises from the N 2p levels near the valence band and from the color centers induced by the oxygen vacancies and the Ti~(3+) species. Nitrogen doping allows visible-light-responsive photocatalytic activity but lowers UV-light-responsive photocatalytic activity. The visible-light photocatalytic activity originates from the N 2p levels near the valence band. The oxygen vacancies and the associated Ti~(3+) species act as the recombination centers for the photoinduced electrons and holes. They reduce the photocatalytic activity although they contribute to the visible light absorbance.