Solid-State Characterization of the Nuclear and Electronic Environments in a Boron-Fluoride Co-doped TiO2 Visible-Light Photocatalyst

摘要

We describe the synthesis of a visible light absorbing boron-fluoride co-doped TiO2 photocatalyst by a sol-gel methodology and its structural characterization using magnetic resonance techniques.The formation of photoactive sites was induced by pyrolysis under anaerobic conditions at temperatures of 400 to 500°C,followed by a short exposure to air or oxygen gas and rapid cooling.nB solid-state nuclear magnetic resonance analysis of B/F-TiO2 shows that the chemical environment of the photochemically active B/F co-doped TiO2 can be described as tetrahedrally coordinated BO4 units(delta=-1.4 ppm).~(19)F NMR indicates that fluorine species form part of the Ti coordination sphere and are of the form TiO5F(delta=-152 ppm).Similarly,X-ray photoelectron spectroscopy indicates that fluorine is found at lattice positions forming O-Ti-F fragments.Electron paramagnetic resonance spectroscopy,coupled to spectral simulation of the sample calcined at 485°C,shows that the radicals formed in this material are mainly located on two distinct Ti~(3+)species.The UV/vis characterization of B/F co-doped TiO2 shows the presence of intraband gap states likely responsible for its absorption of visible light(2.4 eV),while the indirect band gap transition remains unaltered(3.1 eV).The B/F co-doped TiO2 material shows good visible light photocatalytic activity for the photochemical oxidation of methylene blue.