Cocatalyst Modification of Rutile TiO2 Nanorods for Photocatalytic Water Oxidation

Rutile TiO2 nanorods (NR) with different aspect ratios were synthesized using glycolic acid (GA) or lactic acid (LA) as a structure-directing agent in a hydrothermal method. Various cocatalysts were loaded on NR(GA) and NR(LA), and their O2 evolution rate was examined using K2S2O8 as a sacrificial electron acceptor. We used three different methods for loading cocatalysts such as Pt, Ag, Cu2+, Fe3+, and RuO2. Time-resolved diffuse reflectance spectra of all samples indicated that a lifetime of trapped electrons in the range of picoseconds was varied depending on the loaded cocatalysts. Pt was the best as the cocatalysts for the photocatalytic water oxidation because neither dissolution of Pt ion in the solution nor O2 evolution in the dark was observed. For comparison, we synthesized near-spherical TiO2 nanoparticles, TiO2(sol–gel), using a sol–gel method. Comparison of the lifetimes and the O2 evolution rate obtained with NR(GA), NR(LA), TiO2(sol–gel), and their Pt-loaded materials revealed that a shorter lifetime of the trapped electrons in the bulk was beneficial for getting the higher O2 evolution rate. Pt-loaded NR(GA) exhibited the highest O2 evolution rate because of the shortest lifetime of electrons in the bulk and efficient suppression of the recombination on the surface.