Crystal phase engineering of Ru for simultaneous selective photocatalytic oxidations and H 2 production.

Noble metal nanoparticles are often used as cocatalysts to enhance the photocatalytic efficiency. While the effect of cocatalyst nanoparticle size and shape has widely been explored, the effect of the crystal phase is largely overlooked. In this work, we investigate the effect of Ru nanoparticle crystal phase, specifically regular hexagonal close-packed (hcp) and allotropic face-centered cubic (fcc) crystal phases, as cocatalyst decorated onto the surface of TiO 2 photocatalysts. As reference photocatalytic reaction the simultaneous photocatalytic production of benzaldehyde (BAD) and H 2 from benzyl alcohol was chosen. Both the fcc Ru/TiO 2 and hcp Ru/TiO 2 composites exhibit enhanced BAD and H 2 production rates compared to pristine TiO 2 due to the formation of a Schottky barrier promoting the photogenerated charge separation. Moreover, a 1.9-fold photoactivity enhancement of the fcc Ru/TiO 2 composite is achieved as compared to the hcp Ru/TiO 2 composite, which is attributed to the fact that the fcc Ru NPs are more efficient in facilitating the charge transfer as compared to hcp Ru NPs, thus inhibiting the recombination of electron-hole pairs and enhancing the overall photoactivity.