Optimization of electrochemical doping approach resulting in highly photoactive iodine-doped titania nanotubes

The paper focuses on the optimization procedure concerning the synthesis method resulting in highly ordered titania nanotubes doped with iodine atoms. The doping process was based on the electrochemical treatment of a titania nanotube layer immersed in a potassium iodide (KI) solution acting as an iodine precursor. A number of endeavors were undertaken in order to optimize the doping conditions. Electrolyte concentration, reaction voltage, and time/duration were the main factors that influenced the iodine (I)-doping effect on the photoactivity. The parameters of electrochemical doping that result in a material characterized by the highest photocurrent density are as follows: reaction voltage of 1.5 V, duration of 15 min, and 0.1 M KI. Different spectroscopic techniques, i.e., UV–Vis spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the absorbance capability and the crystalline phase, to confirm the presence of iodine atoms and to study the nature of chemical compounds. The morphology inspection performed by means of scanning electron microscopy shows that the doping process does not affect the ordered tubular architecture. The photocurrent densities of the I-doped sample were six times higher in comparison to those generated by the pure titania nanotube electrode. Moreover, doped samples act as a much better catalyst in the photodegradation process of methylene blue and formation of hydroxyl radicals (•OH) than undoped samples.