Photo-electro-catalytic performance of highly ordered nitrogen doped TiO₂ nanotubes array photoanode

Highly ordered nitrogen doped TiO₂ nanotube arrays (N-TNTAs) were synthesized via a one step anodization method at 40 V for 1 hour, in the electrolyte containing ammonium fluoride (NH₄F), water and triethylamine solution, followed calcination under N₂ atmosphere at 450^oC for 3 h. The obtained samples were characterized by means of FE-SEM image showed that the N-TNTs are in a highly ordered array, having inner diameters, wall thickness, tube length of 65 nm, 30 nm and 900 nm, respectively. The X-ray diffraction (XRD) patterns of N-TNTAs and undoped TiO₂ nanotubes arrays (TNTAs) are identical consists of anatase phase, which suggests that the doping of N does not affect the crystalline structure. X-ray photoelectron spectroscopy (XPS), revealed that N atom was incorporated into the lattice of a TiO₂ nanotube array film. The infrared spectra, showed a new peak at 1240 cm^-1 may indicate the incorporation of N into the lattice of TiO₂ through substituting O atoms, in the form of ∼N-Ti-O∼. A red shift of the absorption edge toward the visible region of N-TNTAs are observed by diffuse reflectance spectroscopy (DRS), which is corresponding to a band gap of 2.8 eV. The photo-electro-catalytic (PEC) degradation efficiency toward methylene blue solution under visible light illumination of the N-TNTAs electrode was 89%, in which the rate constant of N-TNTAs electrode was 8 times better compared to that the undoped TNTAs photo-electrode.