Cr(VI) reduction by nitrogen annealed free-standing anodic TiO2 nanotubes formed in ethylene glycol-Na2CO3 electrolyte

Free-standing anodic TiO2 films consisting of vertically oriented nanotubes (NTs) were produced by the anodization of titanium (Ti) in ethylene glycol (EG) added with 1 M Na2CO3. The volume of Na2CO3 gives effect on the adhesion of TiO2 oxide with Ti substrate. The film is easily removed from the Ti foil for the addition of <= 2 vol% 1 M Na2CO3 only, which resulted in free-standing TiO2 NTs (FSTNTs). The FSTNTs then were annealed in different atmospheres, either in air or nitrogen (N-2) to induce the TiO2 anatase phase. Better crystallinity of anatase is achieved for the N-2-annealed sample compared to the air-annealed sample. The annealing temperature also gives effect on the anatase formation. A photoreduction experiment was performed on all samples, and the results showed that the FSTNTs annealed in N-2 at 600 degree celsius exhibited an excellent photocatalytic activity under simulated solar light. The conversion of Cr(VI) to Cr(III) reached similar to 89% within 2 h. N-2 insertion within the oxide was possible, which narrowed the energy band gap, allowing photocatalytic properties under the visible light region.

Automated summary

Free-standing anodic TiO2 films consisting of vertically oriented nanotubes can be produced by anodizing titanium in ethylene glycol with the addition of Na2CO3. Annealing in different atmospheres and temperatures can affect the crystallinity and photocatalytic activity of the TiO2 films.