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