One-step synthesis of Zn doped titania nanotubes and investigation of their visible photocatalytic activity

Highly oriented undoped and Zn-doped titania (TiO₂) nanotubes were electrochemically fabricated by one-step anodization of titanium foil in a freshly prepared aqueous solution of zinc fluoride (ZnF₂) and ethylene glycol (EG). XRD and Raman spectroscopy unveiled the typical characteristic of anatase phase of TiO₂ nanotube without any distinct dopant related peaks. SEM and AFM observation confirmed the formation of nanotubes and revealed that the Zn doping did not distort the tube morphology of TiO₂. The doping of Zn was confirmed by energy dispersive X-ray as well as X-ray photospectroscopy. Due to one-step anodization process, instead of surface doping, the Zn²⁺ ions were incorporated into the bulk of TiO₂ nanotubes. With increasing Zn doping in nanotubes, a gradual decrease in the band gap of TiO₂ (2.84 eV) was observed. Photoluminescence measurements revealed that the doping of Zn enhanced the number of charge carriers, which eventually boosted the photocatalytic activity of TiO₂ nanotubes. Compared to undoped nanotubes, the as prepared Zn-doped TiO₂-nanotubes showed excellent photocatalytic activity for methylene blue degradation (reaction rate constant k = 0.19 min⁻¹) under visible light irradiation. - Highlights: • A facile one-step anodization method is used for Zn doped TiO₂-nanotubes synthesis. • Zn²⁺ ions are doped into the bulk of TiO₂ nanotubes. • Doped TiO₂-nanotubes unveil pure anatase phase and reduced band gap. • Compared to undoped, doped TiO₂ nanotubes exhibit enhanced photocatalytic activity