Characterization of the photoactivity of nanotube layers grown on Ti-35Nb and Ti-35Nb-4Sn alloys

摘要

TiO2 nanotube arrays, grown on titanium metal by anodizing, have been widely used as a photoelectrode. Titanium alloys have also been anodized to obtain doped TiO2 nanotubes or as oxide heterojunctions with enhanced photoactivity, in some cases with absorption extending over the region of visible light. In this paper, samples of Ti-35Nb and Ti-35Nb-4Sn (wt) alloys were anodized in a dilute HF electrolyte to grow a self-ordered nanotube layer and were heat treated for crystallization of anatase phase of TiO2. Characterization by X-ray diffraction and photoelectron spectroscopy revealed that the oxide layers were composed of anatase-TiO2/Nb2O5 and anatase-TiO2/Nb2O5/SnO2 phases. TiO2/Nb2O5 nanotubes showed a photoresponse compared with TiO2 nanotube arrays, with photoactivity extending to the region of visible light as a consequence of a band gap energy lower than that of TiO2. A band gap energy of 2.5 eV was calculated by fitting data from the diffuse reflectance spectroscopy (Tauc plot) using the Kubelka-Munk function.