Modification of nano-TiO₂ by doping with nitrogen and fluorine and study acetaldehyde removal under visible light irradiation

P25–TiO₂ nanoparticles were doped with fluorine, nitrogen, and their combination. Samples of N-doped, F-doped, and N–F-codoped TiO₂ were prepared by physical and chemical treatments. The products were characterized by X-ray diffraction, Fourier transform infrared, Brunauer–Emmett–Teller technique, and ultraviolet–visible diffuse reflectance spectroscopy. It was revealed that absorption spectra of N-doped, F-doped, and F–N-codoped TiO₂ were extended to the visible region wavelengths, and the photocatalytic experiments showed enhancement of acetaldehyde removal under visible light irradiation. The photocatalytic activity of the powders was evaluated through the process of acetaldehyde degradation under visible light scattering in a continuous stirred tank reactor. F–N-codoped nano-TiO₂ calcinated at 500 °C possessed the highest photocatalytic activity. The photocatalytic kinetic consumption of acetaldehyde was studied on N–F–TiO₂ powders under 80 W Hg lamp irradiation, and a Langmuir-type kinetic model was developed for the reaction with appropriate kinetic parameters.