Double-wall TiO₂ nanotube arrays: Enhanced photocatalytic activity and in situ TEM observations at high temperature

By decreasing the water content in an NH₄F and glycerol-water electrolyte, the transition from single-wall to double-wall TiO₂ nanotube arrays was successfully achieved using an anodization method. The double-wall TiO₂ nanotube structures exhibited better photocatalytic activity than the typical single-wall structures. After modification with platinum nanoparticles, the photocatalytic activity of both the singleand double-wall TiO₂ nanotubes was improved further. In situ observations at the annealing temperature of the TiO₂ nanotubes were performed using a transmission electron microscopy (TEM) system. A slower structural failure of the nanotubes was obtained with the introduction of oxygen gas into the TEM column compared with the structural changes observed under high-vacuum conditions without the introduction of oxygen gas. These behaviors suggest that oxygen injection is an important factor in stabilizing the TiO₂ nanotubes during the in situ TEM annealing process. The high-magnification TEM images of the double-wall TiO₂ nanotubes revealed that the sintering of the inner wall can draw a clear distinction between the inner and outer walls. (Graph Presented).