Abstract
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 (N2) to induce the TiO2 anatase phase. Better crystallinity of anatase is achieved for the N2-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 N2 at 600 ℃ exhibited an excellent photocatalytic activity under simulated solar light. The conversion of Cr(VI) to Cr(III) reached ∼89% within 2 h. N2 insertion within the oxide was possible, which narrowed the energy band gap, allowing photocatalytic properties under the visible light region.
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