Characterization and photocatalytic activity of N-doped TiO2 prepared by thermal decomposition of Ti–melamine complex

Nitrogen doped spherical TiO2 has been prepared by thermal decomposition of Ti–melamine complex in air atmosphere. A clear shift in the onset light absorption from UV region (<400) to visible region (>520 nm) has been observed for the N-doped samples. It has been deduced from the optical absorption spectra that the higher calcination temperature results in the decrease in the amount of N-doping. The XRD results revealed the phase transition of TiO2 from anatase to rutile crystalline phase, starting at calcination temperature ≥600 °C. The electron microscopic images reveal the formation of spherical and flakes of TiO2 nanocrystals (25 nm). The chemical nature of N in the N-TiO2 has been evolved through X-ray photoelectron spectroscopy. The presence of different types of N species have been observed corresponding to different oxidation states and the presence of Ti–N and O–Ti–N have been confirmed from the observed binding energy values. Photocatalytic decomposition of methylene blue has been carried out both in the visible region and UV + visible region. In the visible region, N-TiO2 showed higher activity compared to the undoped commercial TiO2 (Degussa P25).