Controlled fabrication of porous double-walled TiO2 nanotubes via ultraviolet-assisted anodization

Abstract

Double-walled TiO₂ nanotubes with porous wall morphologies are fabricated by anodization under ultraviolet (UV) irradiation. TiO₂ formed by anodization of Ti is activated to generate electrons and holes by UV and the anodization process is influenced by the photo-generated charges. As a consequence, morphologies of the fabricated TiO₂ nanotubes can be adjusted by controlling the UV illumination. Double-walled TiO₂ nanotubes or single-walled nanotubes can be selectively formed by switching on/off the UV illumination. The thickness of the inner and outer walls of the double-walled nanotubes can be tailored by changing the UV power. Due to their larger surface areas compared to single-walled nanotubes, the porous double-walled nanotubes exhibit an enhanced photo-degradation rate for methylene blue (MB). The mechanism of the porous double-walled TiO₂ nanotubes is proposed based on the photoactive semiconducting property of the as-growing TiO₂ nanotubes under UV.