Study of the Efficiency of UV and Visible-Light Photocatalytic Oxidation of Methanol on Mesoporous RuO2-TiO2 Nanocomposites

Mesoporous RuO2-TiO2 nanocomposites at different RuO2 concentrations (0-10 wt%) are prepared through a simple one-step sol-gel reaction of tetrabutyl orthotitanate with ruthenium(III) acetylacetonate in the presence of an F127 triblock copolymer as structure-directing agent. The thus-formed RuO2-TiO2 network gels are calcined at 4508 degrees C for 4 h leading to mesoporous RuO2-TiO2 nanocomposites. The photocatalytic CH3OH oxidation to HCHO is chosen as the test reaction to examine the photocatalytic activity of the mesoporous RuO2-TiO2 nanocomposites under UV and visible light. The photooxidation of CH3OH is substantially affected by the loading amount and the degree of dispersion of RuO2 particles onto the TiO2, which indicates the exclusive effect of the RuO2 nanoparticles on this photocatalytic reaction under visible light. The measured photonic efficiency xi = 0.53% of 0.5 wt% RuO2-TiO2 nanocomposite for CH3OH oxidation is maximal and the further increase of RuO2 loading up to 10 wt% gradually decreases this value. The cause of the visible-light photocatalytic behavior is the incorporation of small amounts of Ru4+ into the anatase lattice. On the other hand, under UV light, undoped TiO2 shows a very good photonic efficiency, which is more than three times that for commercial photocatalyst, P-25 (Evonik-Degussa); however, addition of RuO2 suppresses the photonic efficiency of TiO2. The proposed reaction mechanism based on the observed behavior of RuO2-TiO2 photocatalysts under UV and visible light is explored.