Single-step synthesis of Fe-TiO2 nanotube arrays with improved light harvesting properties for application as photoactive electrodes

Highlights: • Fe-TiO₂ nanotubes were synthesized by an innovative single-step anodization method. • The Fe²⁺ doping of TiO₂ nanotubes was induced by the complexing agent DTPA. • Fe-TiO₂ arrays developed photocurrent 2.5 times greater than that of the pure TiO₂. Research on TiO₂ nanotubes gained prominence in the past years due to their photoelectrochemical behavior. Metallic ion doping via a simple and fast method of production can dictate a path in order to achieve and improve such application. This work reports an innovative single-step anodization synthesis of iron-doped TiO₂ nanotubes. Titanium foils were anodized at three potentials (20, 40 and 60 V) for 1 h. The resulting arrays were characterized by scanning electron microscopy, X-ray diffraction, Raman, XPS and UV–Vis diffuse reflectance spectroscopy. SEM images showed that higher anodization potentials successfully produced Fe-TiO₂ nanotubes without a passivating top-layer. XRD and Raman results indicate that Fe ions were introduced in the anatase framework. Fe-doping produced a shift in the UV–Vis absorption edge towards the visible region, which reflected onto the photoelectrochemical performance of the electrodes. The Fe-TiO₂ sample anodized at 60 V developed a current density of 1.9 × 10⁻⁴ A·cm⁻², i.e., 2.5 times greater than that of the undoped TiO₂ sample. The results indicate that the obtained Fe-TiO₂ nanotube arrays are promising materials for application as photoactive electrodes.