Visible light-driven iodine-doped titanium dioxide nanotubes prepared by hydrothermal process and post-calcination Original Research Article

A novel class of iodine-doped TiO2 nanotubes (I-TNTs) has been synthesized via a hydrothermal route using Degussa P25 as a precursor and subsequent calcination. The photocatalytic ability of the products was evaluated in terms of phenol degradation in an aqueous solution under visible light irradiation. The structural properties of the catalysts were characterized by X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra. According to the XRD data, I-TNTs are pure anatase, revealing a shift of crystallite phase for P25 from rutile to anatase. The surface area of I-TNTs is significantly larger than that of I-doped TiO2 (I-TiO2) nanoparticles, which is an important advantage of the photocatalysts formed with a hydrothermal procedure. XPS and UV–vis spectroscopy show that iodine was incorporated into the TiO2 lattice, and such incorporation extends the photoresponse of TiO2 from UV to the visible light region. As far as phenol degradation is concerned, the I-TNTs are clearly superior to I-TiO2 nanoparticles, pure TNTs and P25. The photocatalytic activity of I-TNTs hydrothermally synthesized at 150 °C had a significantly higher level than that synthesized at 200 °C. This is attributed to the increase of reactive sites and the enhancement of mass transfer that result from the large surface areas associated with the tubular morphology. Additionally, the increase of Ti3+ content also contributes to the improvement of photocatalytic activity of I-TNTs.