Synthesis of Ruthenium-Doped TiO₂ Nanotube Arrays for the Photocatalytic Degradation of Terasil Blue Dye.

The oxidation of terasil blue dye (TB) has been achieved by photocatalysis under UV light using well organized nanotubes of Ti/TiO₂ doped with ruthenium (Ru/Ti/TiO₂). Ru/Ti/TiO₂ were fabricated by Ti anodization followed by impregnation with 0.04, 0.08 and 0.16 wt% of RuCl₃ · H2O or KRuO₄ as precursor salts. Ti foil anodization was carried out in non-aqueous solutions and in aqueous solutions at pH 7 and pH 12.6. Scanning electron microscopy analyses revealed a morphology of well-defined, organized nanotubes of Ti/TiO₂ and Ru/Ti/TiO₂. The ruthenium was evenly distributed over Ti/TiO₂ surface. Cluster formation was also observed for 0.16 wt% Ru loading. The X-ray diffraction spectra showed anatase and rutile phase in pure Ti/TiO₂ and Ru/Ti/TiO₂ nanotubes. Therefore, ruthenium doping did not modify the crystalline phase of Ti/TiO₂. Raman spectra did not reveal the rutile phase of TiO₂ in the composites which is attributed to the laser characteristics used. The optical band gap energies of the Ti/TiO₂ and Ru/Ti/TiO₂ nanotube arrays showed that ruthenium-doping on Ti/TiO₂ had slight effect on the band-gap energy. A decrease in the band gap energy of pure Ti/TiO₂ ( 2.88 eV) was observed by Ru loading of 0.04 wt% in the Ti/TiO₂ nanotube arrays ( 2.60 eV). The kinetic rate constant of the photocatalytic oxidation of TB, using 0.08 wt% Ru load, was 1.56 and 1.39 times of that on Ti/TiO₂ composite (0.01 min) synthetized at pH 12.6 impregnated in RuCl₃ (0.0156 min) and KRuO₄ (0.0139 min) solutions, respectively. Nevertheless, the highest rate constant value of TB degradation (87.8%) was 0.0172 min using 0.16 wt% Ru loading on Ti/TiO₂ composite synthetized at pH 7 impregnated in RuCl₃; this represents 1.15 times of that on Ti/TiO₂ composite (0.0150 min; 81.4% color removal) synthetized under the same conditions.