Structures and properties of N-doped TiO2 nanotubes arrays synthesized by the anodization method for hydrogen production

Abstract

The films of TiO2 nanotube arrays were fabricated by the anodization of Ti metal sheets for photocatalytic hydrogen production. The anodization was carried out in electrolytes prepared by mixing ethylene glycol (EG), ammonium fluoride (0.3 wt% NH4F) and deionized water (2 Vol% H2O). DC power supply was used at a constant voltage of 50 Volts. The nanotube arrays were aged in different amounts of ammonia (NH3) as nitrogen dopants. The morphology of the nanotube arrays was characterized by scanning electron microscopy (SEM). The phase and structure of the TiO2 nanotube arrays were determined by X-ray diffraction (XRD). The phase of the nanotubes is transformed from anatase to rutile when annealing temperature is changed from 450 °C to 500 °C or higher. The phase of the nanotubes became completely rutile when the nanotube arrays were 700 °C or higher, and the nanotubes were transformed to nanacrystalline. X-ray Photoelectron spectroscopy (XPS) was used to determine the dopant presenting in TiO2 structure. UV-vis spectroscopy was used to study the optical property of the nanotubes. The diameters of TiO2 nanotubes were about 200 nm. The highest density of TiO2 nanotubes was obtained when the nanotubes were doped with 6% by volume of ammonia. The photocatalytic activity was examined without an external applied potential. The maximum photocurrent density was 2.7 mA/cm2 under illumination of 100 mW/cm2 corresponding with photoconversion efficiency of 3.3%.