Photocatalytic Activity vs Structural Features of Titanium Dioxide Materials Singly Doped or Codoped with Fluorine and Boron

TiO2photocatalysts, either doped with different amounts of fluorine or boron, or codoped with boron and fluorine, were prepared by sol–gel synthesis, followed by calcination at different temperatures (500–700 °C), and characterized by XRPD, BET, XPS, and UV–vis absorption analyses. The oxidative decompositions of both formic and acetic acid were employed as photoactivity test reactions, also in comparison with previous results obtained with NF-codoped TiO2. A detailed XPS analysis revealed the presence of B2O3on the surface of B-doped and BF-codoped TiO2, which could be removed by washing under acidic conditions and had no beneficial role in phototocatalysis. A correlation was found between the photoactivity of full anatase TiO2materials calcined at 500 °C, singly doped or codoped with nitrogen, fluorine, and boron, and their specific surface area, pointing to a major role of the latter, not of the different dopants, on photoactivity. Only samples containing fluorine, as dopant or codopant, exhibit a photoactivity increase with increasing the calcination temperature to 700 °C. This fact, together with an action spectra analysis on photocatalysts calcined at different temperatures, evidenced that only fluorine is responsible for the photoactivity increase in the UVA region observed with full-anatase, highly crystalline doped TiO2calcined at high temperature.