Photoactivity of nitrogen-doped anodic TiO2 under UV and VIS light irradiation
M.V. Diamanti, M. Ormellese, M.P. Pedeferri
Politecnico di Milano, IT
Keywords: Photocatalysis, titanium dioxide, doping
Abstract:Titanium dioxide is probably the most efficient among the known photocatalysts, and undoubtedly the most studied one. An appealing route to tune obtain TiO2 films morphology and structure is to exploit the anodizing process to induce the growth of the oxide layer directly on titanium substrates. This research was aimed at obtaining and characterizing photoactive TiO2 films with different semiconductive properties and morphologies by performing Anodic Spark Deposition (ASD) and anodizing in fluoride-containing electrolytes, the former giving roughened semicrystalline oxide containing anatase crystals, the latter generating amorphous nanotubolar oxide with enhanced specific surface area. Thermal treatments in nitrogen atmosphere were applied to anodized substrates to dope TiO2 and therefore modify its absorption characteristics towards light. The presence of nitrogen in treated oxides was proved by means of Glow Discharge Optical Emission Spectroscopy; crystal structure was investigated by X-Ray Diffraction analyses. Doped TiO2 layers showed enhanced efficiency in the photodecomposition of rhodamine B under visible (VIS) radiation. Nevertheless, an interesting factor arose from thermal treatments in air: unexpectedly, so-treated oxides exhibited photoactivity under VIS irradiation. ASD-generated oxides displayed lower efficiency due to the lower surface area; though, these oxides also presented photoactivity without thermal treatment, which simplifies the photocatalyst production procedure.