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 · xH2O 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 (Eg 2.88 eV) was observed by Ru loading of 0.04 wt% in the Ti/TiO₂ nanotube arrays (Eg 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-1) synthetized at pH 12.6 impregnated in RuCl₃ (0.0156 min-1) and KRuO₄ (0.0139 min-1) solutions, respectively. Nevertheless, the highest rate constant value of TB degradation (87.8%) was 0.0172 min-1 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-1; 81.4% color removal) synthetized under the same conditions.