Array of electrodeposited Ru-decorated TiO2 nanotubes with enhanced photoresponse
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Although TiO2 anatase phase has been widely chosen as the main photocatalyst, it presents high electron/hole recombination rate. However, today, what is sought is a semiconductor material with enhanced photocatalytic activity with higher photon to electron conversion efficiency by introduction of electrons trap dopants. In this paper, TiO2 nanotubes arrays obtained by anodization of Ti substrates were decorated with Ru via electrodeposition, and their photo-response was investigated. First, voltammetric experiments were performed to elucidate the route of Ru reduction on the TiO2 surface and to select the range of potentials for Ru deposition. The reduction potentials were used for controlling the amount of Ru distributed all over the surface. Although Ru was electrodeposited at potentials over the range from − 0.025 to − 0.188 V vs. Ag/AgCl, the deposition of 3.7 mC cm−2 at − 0.100 V for 30 min resulted in a tenfold greater photocurrent when compared to the recorded photocurrent for the undecorated TiO2 nanotubes array. Next, Ru-decorated TiO2 nanotubes with a length of 323 ± 18 nm and inner and outer diameters of 91 and 104 nm, respectively, were characterized using SEM-WDS, SEM-FEG, XRD, and XPS. UV-Vis-NIR diffuse reflectance spectroscopy and photoluminescence (PL) measurements, which revealed a maximum PL emission at 445 nm, showed that for the array of Ru-decorated TiO2 nanotubes, the electron-hole recombination may be effectively inhibited by the presence of ruthenium electrodeposited, which can make this photocatalyst even more attractive for environmental applications. The performances of the TiO2 and Ru-decorated TiO2 catalysts were compared in heterogeneous photocatalysis experiments for color removal of an azo-dye, which presented a pseudo-first-order rate constant more than twofold greater for the Ru-decorated TiO2 catalysts.
KeywordsRuthenium electrodeposition TiO2 nanotubes Ru decoration Photocatalysis
The authors thank FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo (Process Number 06/61261-2) for financial support. The authors acknowledge the support of LNNano - Brazilian Nanotechnology National Laboratory, CNPEM/MCTI for MEV-FEG and XPS characterization, IQ-Unesp/Araraquara for the UV-Vis diffuse reflectance spectroscopy (DRS) experiments and Prof. Máximo Siu Lic for the photoluminescence analyses.
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