Abstract
In recent years, photocatalytic reactions on anodic TiO2 nanotubes have been intensively investigated. In order to show photocatalytic activity, anodically formed nanotubes need to be crystallized to anatase. This is conventionally done by thermal annealing in air at temperatures 400-600 degrees C. Recently, a so-called "water annealing" treatment has been reported to be effective to also create a highly active form for photocatalysis. Here we report on the feasibility of using a water annealing treatment of TiO2 nanotubes to create a photocatalyst for H-2 production that is as active as conventional thermal annealing. If the water-annealed samples are additionally hydrogenated to a so-called "grey" modification, a further significant improvement of the photocatalytic activity for H-2 evolution can be achieved - this without the use of any noble metal co-catalyst. A combination of water annealing, thermal annealing, followed by hydrogenation can deliver a H-2 generation activity that is more than five times higher than that achieved by thermal annealing of anodic TiO2 nanotubes.