N-Doping of anodic TiO2 nanotubes using heat treatment in ammonia

Self-organized TiO2 nanotube-layers were formed by electrochemical anodization of Ti in a HF/H2SO4 electrolyte. The nanotube layers were then treated at different temperatures (300–600 °C) in pure NH3. The samples were characterized by photoelectrochemistry, SEM, XRD and XPS. The results show clearly successful N-doping of the TiO2 nanotubes. The magnitude of the effect is strongly dependent on the duration and temperature of the ammonia treatment. Besides N-doping, the heat treatment causes – in one step – a conversion of the amorphous tubes to anatase. Both effects drastically improve the photoresponse of the TiO2 nanotubes.