Study of surface fluorination of photocatalytic TiO2 by thermal shock method

Surface fluorinated TiO2 powders were prepared by thermal shock method and an overall comparative study was achieved on the basis of XRD, SEM, UV–vis and XPS analyses. The main objective was to elucidate the influences of surface fluorination on the crystallite structures, morphologies, optical properties and surface chemistry with the temperature. According to the results, the surface fluorination under thermal shock method below 600 °C did not change the crystallite structure and the particles size, but successfully created chemisorbed fluoride ions, oxygen vacancies and increased the hydroxyl groups on the surface of TiO2. The presence of oxygen vacancies was assigned to the red shift of TiO2 optical absorption edge, which was the origin of visible-light-induced photocatalytic activity of these samples. For the thermal shock temperatures over 600 °C, the K2Ti6O13-like phase was formed, resulting from the decrease of surface hydroxyl groups and the blue shift in absorption edge which reduced the photocatalytic activity. - Graphical abstract: The influence of fluorination on the surface of TiO2 by thermal shock method at several temperatures has been investigated by following the evolution of the F1s spectra obtained by X-ray photoelectron spectroscopy. The blank peaks are assigned to the chemisorbed fluoride ions on the samples surface and the filled peaks to fluorine atoms in oxygenated environment of solid solution TiO2−xFx, which is originated from the substitution of F ions for O ions in the TiO2 lattice. Highlights: ► Surface fluorination of TiO2 P25 by thermal shock method. ► Structure, morphology, surface and photocatalytic properties of fluorinated TiO2. ► Low thermal shock temperatures increase the photocatalytic activity. ► Fluoride ions chemisorbed on the surface without structure and morphology change. ► Formation of K2Ti6O13 phase at high thermal shock temperatures.