Photocatalytic activity vs structural features of TiO2 singly doped or codoped with N, F and B

An extended series of singly doped or co-doped TiO2 photocatalysts containing different amounts of N, F and B dopants were prepared by the sol-gel method and calcined at different temperature (500-700°C). Their photocatalytic behavior was investigated, also as a function of the irradiation wavelength, in both thermodynamically down-hill reactions, such as formic and acetic acid degradation in aqueous suspension and gas phase mineralization of acetaldehyde, and up-hill reactions for solar fuels production, such as hydrogen production from methanol-water vapor mixtures. The photoactivity of full anatase TiO2 materials calcined at 500°C, singly doped or co-doped with N, F and B, increases with their specific surface area, pointing to a major role of the latter, not of the different dopants, on photoactivity. Time-resolved photoluminescence spectroscopy analysis revealed a clear correlation between the photoactivity of the materials and the long-lasting component of the PL signal, related to the formation of surface defects. 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 fluorine only is responsible for the photoactivity increase in the UVA region observed with full anatase, highly crystalline doped TiO2 calcined at high temperature.