Synthesis, characterization and electronic structure of nitrogen-doped TiO2 nanopowder

Nanopowders of TiO2:N were synthesized in a two step process. At first, TiO2 was prepared from titanium tetraisopropoxide (TTIP) in form of crystalline powder by flame spray synthesis (FSS). In a second step TiO2-FSS with a specific surface area (SSA) of 54 m2/g and TiO2-P25 as a reference material were ammonolysed in a rotating tube furnace. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate crystallinity before and after ammonolysis. Based on the X-ray photoelectron spectroscopy (XPS) studies it has been established that the N 1s peak at 395.9 eV can be assigned to substitutional nitrogen. New electron transitions and resulting band gap changes in respect to undoped sample have been observed in TiO2−xNx. Diffusive reflectance and the resulted band gap energy were determined by diffuse reflection spectroscopy (DRS), where the correlation between differential reflectance and Tauc plot, known as a second method of the band gap determination, is discussed for pure and N-doped TiO2 nanopowders. The photocatalytic performance of the nanopowders under visible light irradiation (400–500 nm) was studied by the degradation of methylene blue (MB) in aqueous suspensions.