Titania nanotubes prepared by anodization in fluorine-free acids

Recently, we reported the discovery of new high-aspect ratio titania nanotubes. These nanotubes were synthesized by means of anodization in an oxalic acid electrolyte containing chlorine ions and were found to have significant carbon content. In this article, the synthesis of similar titania nanotubes in oxalic, formic, trichloroacetic, gluconic, hydrochloric, and sulfuric acid is reported. Differences in carbon content and morphology are analyzed, which in turn provides information on the chemistry of the formation of these nanotubes. Our results suggest that the carbon content in the nanotubes can be controlled by the use of an appropriate organic acid.