Preparation of multiple-doped TiO2 nanotube arrays with nitrogen, carbon and nickel with enhanced visible light photoelectrochemical activity via single-step anodization

The main objective of this research is to enhance the photocatalytic activity of TiO2 nanotube aligned arrays (TNAs) for the visible light by multiple-doping with nitrogen, nickel and carbon for the first time. This has been achieved through anodization of titanium foils in ethylene glycol based electrolytes containing NH4F and various concentrations of K-2[Ni(CN)(4)]. The method proposed allows for a simple one-step multiple-doping of TNAs during its electrochemical formation. The surface morphology, structure and composition of undoped and Ni-N-C-doped TNAs were investigated by field emission scanning electron microscopy (FESEM), XRD, XPS and EDX. The characterization results indicate that Ni, N and C atoms have been incorporated into the lattice of the TiO2 nanotubes. UV-Vis DRS spectroscopy and photo-electrochemical measurements showed that multiple-doping results in the broadening of the absorption region of visible light and the reduction of bandgap energy. Accordingly, multiple-doping of TNAs improves photogenerated electron hole separation and increases transfer rate of surface charge carriers from the interior to the surface of semiconductors. Under the visible-light irradiation, the average photocurrent density of the optimal multiple-doped TNAs is 10 times greater than that of the undoped TNAs tested under the same conditions. Accordingly, Ni-C-N-doped TNAs may be considered as a promising photocatalytic material for various potential applications like water splitting under sunlight irradiation for hydrogen generation. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.