Synthesis and characterization of nitrogen-doped titanium dioxide nanomaterials derived from nanotube sodium titanate precursor

Nitrogen-doped titanium dioxide (denoted as N-doped TiO2) nanomaterials were prepared through the ion exchange of sodium titanate nanotube (the precursor; denoted as STN) with aqueous NH4Cl and follow-up sintering at different temperatures in air. The morphology, structure, surface component, and optical properties of as-obtained N-doped TiO2nanomaterials have been analyzed by transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and ultraviolet–visible light diffuse reflectance spectrometry. The formation mechanism and the origin of the visible light absorption for N-doped TiO2nanomaterials have been discussed. Moreover, the thermogravimetric analysis and differential thermal analysis of N-doped TiO2nanomaterial calcined at 100 °C are conducted as an example to examine the thermal stability of as-synthesized N-doped TiO2. It has been found that, as the calcination temperature rises, the initial nanotubular morphology of STN is transformed to the final nanoscale granular one, accompanied by a phase transformation from orthorhombic crystalline system to anatase TiO2. The N content in N-doped TiO2is 7.04%, 6.22%, 3.20%, 1.14%, 0.61%, and 0.40% (atomic percentage), depending on calcination temperature rising from 100 to 600 °C. Moreover, N-doped TiO2samples experience three stages of weight losses, and that calcinated at 300 °C and above have strong visible light absorption, due to the formation of Ti–O–N bonds thereat.