Preparation of TiO_2 Nanotube Arrays and Their Photoelectrochemical Properties

TiO2 nanotube arrays were fabricated by anodization of the Ti foils in aqueous phosphoric acid and sodium fluoride solutions at 20V under ultrasonic field.The resulting nanotubes had the similar tube diameter(100nm) and the similar wall thickness(15-20nm).The tube lengths of the nanotubes anodized for 1h,3h and 7h were 600,1000,900nm,respectively.Employing a 500W high-pressure mercury lamp as the light source,the open-circuit potential and the photocurrent,the flat band potential and the charge carrier densities of TiO2 nanotubes arrays annealed at 500℃ were analyzed by the open-circuit potential curves,the voltammetry curves and Mott-Schottky plots.The re-sults showed that the photocurrent,the flat band potential,the charge carrier densities of the resultant samples reduced with the increase of oxidation time.The decrease of photocurrent density was more than that of the open-circuit poten-tial.It can be ascribed to partial fracture and detachment of the nanotubes and the growth of the barrier layer with the inrease of anodization time,which led to the augment of the charge transfer resistance and the decrease of the charge carrier densities.