Fabrication and photo-electrocatalytic properties of highly oriented titania nanotube arrays with {1 0 1} crystal face

Highly oriented titania nanotube (TN) arrays with {1 0 1} crystal face were prepared on the surface of titanium substrate by liquid chemical deposition method. The obtained titania samples were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), BET measurements, diffuse reflectance spectroscopy (DRS), and electron paramagnetic resonance (EPR) spin trap technique. Results indicate that the nanotubes grown in this study are well-aligned and organized into high-density uniform arrays. The typical dimensions of the hollow tube are ∼90 nm in outer diameter, ∼60 nm in inner diameter, ∼15 nm in wall thickness and ∼300 nm in height. The BET surface area of the obtained titania nanotube is 275 m2/g. The EPR signals reveal that hydroxyl radical ({radical dot}OH) species can be produced in the nanotube system, and no {radical dot}OH radical EPR signals were detected under dark and/or nanotube non-existing situations. The catalytic degradation of a textile azo dye, acid orange 7 (AO7), in aqueous solution with titania nanotube arrays electrode was carried out using photo-electrocatalytic (PEC) process, comparing with electrochemical process (EP) and photocatalytic (PC) process. A significant photo-electrochemical synergetic effect was observed, which is due to the efficient charge separation and transfer at the surface-interface of titania nanotube arrays. The kinetic constant of PEC degradation of AO7 using TN electrode was 48.7%, which is higher than that using P-25 TiO2film and TiO2particular film electrode. The enhanced degradation rate of AO7 using titania nanotube arrays could be attributed to their larger specific surface area and nanotubular structure with preferred reactive crystal face, which would increase their absorption capacity to the targeted substrates and the rate of surface-interface charge transfers in titania nanotube semiconductor redox systems.