Water Annealing of TiO(2)Nanotubes for Photocatalysis Revisited

摘要

Over the past years, so-called water annealing of TiO(2)nanotube (NT) arrays has attracted considerable attention as a tool to enhance the nanotubes' photocatalytic properties. The present work investigates the effect of different water-annealing treatments on TiO(2)nanotubes and compares it to thermally annealed tubes. We find that the most effective water annealing is water immersion of TiO2NT arrays at 70 degrees C for several days. The two main effects are i) a partial crystallization of the tubes to anatase, and ii) an etching of the tube walls that leads to a roughening of the walls and, thus, to a higher surface area. Under the best conditions, water annealing is almost as effective in providing enhanced photocatalytic AO7 degradation as a classic thermal annealing of the tubes. We, however, find that water annealed tubes - due to their only partial crystallization - do not perform well when used as photoelectrodes. For photocatalysis, most efficient is a combination of water annealing, followed by thermal annealing, which provides both a larger surface area and a high crystallinity.