Improving the visible light photoelectrochemical activity of synthesized TiO2 nanotube arrays in an organic electrolyte containing sodium carbonate with doping by copper via single-step anodization

Abstract

The main aim of this research is to improve the photocatalytic activity of TiO₂ nanotubes by co-doping with copper and sodium for application in the water splitting process as a photoanode. The doping was performed simultaneously to the anodizing process through a single-step treatment. The synthesized TiO₂ nanotube array (TNA) was characterized by applying FESEM (Field Emission Scanning Electron Microscopy), XRD (X-ray Diffraction), DRS (Diffraction Reflection Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) analyses. The results of XPS analysis proved the presence of copper with valence (2+) and carbon and sodium with valence (1+). Moreover, DRS tests showed a reduction in the band gap energy of the nanotubes from 3.2 eV for pure nanotubes to about 2.61 eV for doped ones. UV-visible tests confirmed the development of the absorption edge of pure nanotubes from UV-light (380 nm) to visible light (525 nm) for doped samples. Furthermore, it was exhibited that doping with copper and sodium leads to a decrease in the potential needed to separate the photoinduced electrons and promote them to the outer orbital. This slows the electron–hole recombination and allows the photocatalytic activity of TiO₂ nanotubes to occur. In addition, photoelectrochemical measurements indicated that the photocurrent density of the doped nanotubes was enhanced about 12 times relative to the pure nanotubes.