Highly ordered TiO₂ nanotube arrays with controllable length for photoelectrocatalytic degradation of phenol

Highly ordered TiO₂ nanotube array prepared by a potentiostatic anodization shows a considerable potential for improving the transport of the photogenerated electrons in the TiO₂ film, since the ordered architecture can provide a unidirectional electric channel and reduce the grain boundaries. Here, we report on the application of highly ordered TiO₂ nanotube arrays with different lengths for the photoelectrocatalytic degradation of phenol. The lengths of the nanotube arrays can be controlled by the electrolyte media, anodization time, or both. The photoelectrocatalytic activity shows a dependence on the length of the nanotube arrays. Under 3.1 mW/cm² irradiance of ultraviolet light, a short nanotube array shows better photoelectrocatalytic activity than a long nanotube array, which can be explained by the reduced recombination effects. When compared with a P25 TiO₂ particulate film with similar thickness and geometric area, the nanotube array shows a stronger attachment to the parent titanium substrate and a better photoelectrocatalytic activity for phenol degradation owing to the improved electron transport and reduced charge recombination. This superior electron transport is further supported by the remarkably enhanced anodic photocurrent response in the degradation of phenol.