Templated synthesis of TiO₂ nanotube macrostructures and their photocatalytic properties

Controlled synthesis of hierarchically assembled titanium dioxide (TiO₂) nanostructures is important for practical applications in environmental purification and solar energy conversion. We present here the fabrication of interconnected TiO₂ nanotubes as a macroscopic bulk material by using a porous carbon nanotube (CNT) sponge as a template. The basic idea is to uniformly coat an amorphous titania layer onto the CNT surface by the infiltration of a TiO₂ precursor into the sponge followed by a subsequent hydrolysis process. After calcination, the CNTs are completely removed and the titania is simultaneously crystallized, which results in a porous macrostructure composed of interconnected anatase TiO₂ nanotubes. The TiO₂ nanotube macrostructures show comparable photocatalytic activities to commercial products (AEROXIDE TiO₂ P25) for the degradation of rhodamine B (RhB). Moreover, the TiO₂ nanotube macrostructures can be settled and separated from water within 12 h after photocatalysis, whereas P25 remains suspended in solution after weeks. Thus the TiO₂ nanotube macrostructures offer the advantage of easy catalyst separation and recycle and can be a promising candidate for wastewater treatment.