Effects of fluorine doping and co-doping and of noble metal nanoparticles deposition on the photoactivity of TiO2

A detailed analysis of the effects produced by fluorine doping or co-doping with nitrogen and boron on the UV-vis photoactivity of TiO2 in both down-hill (decomposition of organics) and up-hill reactions (hydrogen production by methanol photoreforming) reveals that fluorine doping is the sole responsible for the photoactivity increase in the UVA region observed with full anatase, highly crystalline doped TiO2 calcined at high temperature, possibly due to the formation of surface oxygen defects. Noble metal (Au or Pt) nanoparticles on the photocatalyst surface contribute in increasing the separation of photoproduced charge carriers resulting in increased photocatalytic performance of the surface and bulk-modified photocatalyst systems. Almost identical bell-shaped photoactivity trends were obtained for the naked, Au- and Pt- modified titania with increasing the dopant content, demonstrating the crucial role that the electronic structure of the doped materials has in determining the absorption features and the separation and mobility of photoproduced charges within the doped oxide photocatalysts. The main role of the noble metal is limited to an increased efficiency of electron-hole separation by “capturing” conduction band electrons, Pt always being more efficient than Au, in line with their work functions. TiO2 doping with fluorine provides a synergistic positive contribution to the beneficial effect that noble metal nanoparticles have in the reduction paths leading to hydrogen production from methanol photoreforming.