Local structure of vanadium in Ti-6Al-4V alloy anodized in acetic acid aqueous solution and its contribution to visible light response in photocatalysis

• Anodization/annealing of Ti-6Al-4V afforded visible light responsive photocatalysts.
• Vanadium was present on the oxide surface as vanadate.
• Acetaldehyde could be decomposed on the oxide under visible light illumination.
• Visible light absorption by the vanadate contributed to the activities.

Anodization of Ti-6Al-4V alloy in acetic acid aqueous solution resulted in the formation of amorphous oxide on its surface; the amorphous oxide transformed into crystalline oxide primarily consisting of anatase TiO2 by annealing. The annealed anodic oxide, especially those anodized in 1–2 mol L−1 acetic acid aqueous solution, could photocatalytically decompose acetaldehyde under visible light illumination. X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray absorption near-edge structure spectroscopy analyses showed that the vanadium is pentavalent and exists in an oxygen-tetragonal structure composed of VO43− units. When the vanadate absorbs visible light, the excited electrons move into the conduction band of anatase TiO2 so that recombination with holes was restricted. As a result, the anodic oxide exhibited superior photocatalytic activity under visible light illumination.

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