Surface fluorination of single-phase TiO2 by thermal shock method for enhanced UV and visible light induced photocatalytic activity

• Fluorination of TiO2 anatase/rutile by thermal shock at different temperatures.
• Fluorination creates F ions, increases the OH groups and oxygen/titanium vacancies.
• Fluorination below 600 °C improves the photocatalytic activity of TiO2.
• Fluorination above 600 °C leads the formation of K2Ti6O13 phase.
• The presence of K2Ti6O13 phase may decrease the photocatalytic activity.

Fluorinated TiO2 was prepared from anatase and rutile monophasic TiO2 nanopowders by thermal shock method at different temperatures (400–950 °C), then characterized by XRD, SEM, XPS in order to elucidate the influences of thermal shock fluorination on the crystallite structure, morphologies and surface structure of TiO2 in different phases. Their photocatalytic activities were evaluated via the degradation of methylene blue. According to the results, the fluorination below 600 °C did not change the crystallite structure or the particle size. However, the surface hydroxyl groups content is increased with the creation of fluoride ions and oxygen/titanium vacancies on the surface of anatase/rutile TiO2 which are all involved in the improvement of the photocatalytic activity. The TiO2 anatase fluorinated at 500 °C showed the best photocatalytic behaviour under UV light whereas the TiO2 rutile fluorinated at 500 °C is the best photocatalyst under visible light. At higher thermal shock temperatures, the photocatalytic activity decreased, which was assigned to the decrease of the surface hydroxyl groups and vacancies content and the formation of the K2Ti6O13 phase.

The influences of fluorination by thermal shock method at different temperatures on the surface of TiO2 have been investigated by XPS analyses. The F 1s spectra of all fluorinated samples from anatase (a) and rutile (b) TiO2 show two F 1s peaks located at 684.5 and 686.7 eV, which are respectively assigned to the fluoride ions chemisorbed on the surface and fluorine atoms in oxygenated environment of solid solution TiO2−xFx.Figure optionsDownload as PowerPoint slide