Promotional effect of Rh nanoparticles on WO 3 /TiO 2 titanate nanotube photocatalysts for boosted hydrogen production

Abstract In this work, we explore the hydrogen production via the water splitting process on Rh-WO 3 photocatalysts supported on nanotubes of TiO 2 . H 2 production tests were performed in a 2-propanol-water solution. The support (titanate nanotubes, NT) was obtained, first, by the sol-gel method followed by the hydrothermal method. The surface of the titanate nanotubes was decorated with nanoparticles of rhodium and tungsten by applying microwave irradiation. The photocatalysts were characterized by XRD, HR-TEM, UV-vis, S BET , H 2 -TPR and XPS. For the photocatalytic tests, we employed two photocatalysts with 0.3 and 0.5 wt.% of Rh on WO 3 /TiO 2 (3 wt.% of WO 3 ) under UV-A light radiation at 365 nm and visible light at 450 nm. We found that 56 μmol h −1 of hydrogen were produced by photolysis. The support (NT) produced 59 μmol h −1 of hydrogen. The addition of 3 wt.% of WO 3 to the nanotubes increased slightly the H 2 production (66 μmol h −1 ). However, a promotional effect was observed when rhodium was added to the 3WO 3 /NT photocatalysts. In fact, the highest hydrogen production was obtained on the 0.5Rh-3WO 3 /NT photocatalyst (234 μmol h −1 ), even after seven cycles of 8 h. We suggest that Rh acts as co-catalyst of the WO 3 during the water splitting process. A diagram for the density of states, based on the UV–vis and XPS results, is proposed.