Spaced Titania Nanotube Arrays Allow the Construction of an Efficient N‐Doped Hierarchical Structure for Visible‐Light Harvesting

Regularly spaced TiO(2) nanotubes were prepared by anodizing a titanium substrate in triethylene glycol electrolyte at elevated temperature. In comparison to conventional TiO(2) nanotubes, spaced nanotubes possess an adjustable spacing between the individual nanotubes; this allows for controlled buildup of a hierarchical nanoparticle‐on‐nanotube structure. Here, we use this principle for layer‐by‐layer decoration of the tubes with TiO(2) nanoparticles. The hierarchical structure after N doping and NH(3) treatment at 450 °C shows a significant enhancement of visible‐light absorption, although it only carries a low doping concentration of nitrogen. For optimized N‐doped and particle‐decorated spaced TiO(2) nanotubes, a considerable improvement in photocatalytic activity is obtained in comparison with conventional N‐doped TiO(2) nanotubes or comparable N‐doped nanoparticle films. This is attributed to an enhanced visible‐light absorption through the N‐doped nanoparticle shell and a fast charge separation between the shell and the one‐dimensional nanotubular core.