Double-wall anodic titania nanotube arrays for water photooxidation.

Vertically oriented double-wall titania nanotube (external diameters of 82 and 206 nm) arrays are synthesized by a sonoelectrochemical anodization technique in combination with a unique room-temperature ionic liquid and organic electrolyte. Compared to similar single-wall nanotubes (0.638 mA/cm(2)) and commercial nanoparticles (0.365 mA/cm(2)), these double-wall nanotube arrays show 2-4 times more photoactivity to split water under solar light illumination to generate hydrogen and oxygen. Partial doping of B and C into the TiO(2) matrix gives rise to these double-wall nanotubes which absorb visible solar light more efficiently than the intrinsic TiO(2). The structural properties of these novel structures have been studied extensively using various spectroscopic, analytical, and electrochemical techniques.