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.