Influence of ruthenium doping on UV- and visible-light photoelectrocatalytic color removal from dye solutions using a TiO nanotube array photoanode.

The photocatalytic activity of TiO anodes was enhanced by synthesizing Ru-doped Ti|TiO nanotube arrays. Such photoanodes were fabricated via Ti anodization followed by Ru impregnation and annealing. The X-ray diffractograms revealed that anatase was the main TiO phase, while rutile was slightly present in all samples. Scanning electron microscopy evidenced a uniform morphology in all samples, with nanotube diameter ranging from 60 to 120 nm. The bias potential for the photoelectrochemical (PEC) treatment was selected from the electrochemical characterization of each electrode, made via linear sweep voltammetry. All the Ru-doped TiO nanotube array photoanodes showed a peak photocurrent (PP) and a saturation photocurrent (SP) upon their illumination with UV or visible light. In contrast, the undoped TiO nanotubes only showed the SP, which was higher than that reached with the Ru-doped photoanodes using UV light. An exception was the Ru(0.15 wt%)-doped TiO, whose SP was comparable under visible light. Using that anode, the activity enhancement during the PEC treatment of a Terasil Blue dye solution at E(PP) was much higher than that attained at E(SP). The percentage of color removal at 120 min with the Ru(0.15 wt%)-doped TiO was 98% and 55% in PEC with UV and visible light, respectively, being much greater than 82% and 28% achieved in photocatalysis. The moderate visible-light photoactivity of the Ru-doped TiO nanotube arrays suggests their convenience to work under solar PEC conditions, aiming at using a large portion of the solar spectrum.