Enhanced photocatalytic activity of CoO/TiO2 nanotube composite

Titania nanotube (TNT) array was fabricated by anodization of titanium in 0.2 wt.% HF aqueous solution. The as-anodized TNT was crystallized to anatase phase with a heat treatment at 450 °C. CoO/TNT nanocomposite was synthesized by cathodic deposition over the annealed TNT in 0.05 M Co(NO3)2. The surface morphology and crystalline structure of the resultant CoO/TNT nanocomposite were characterized by X-ray diffraction (XRD), Raman spectrum and field emission scanning electron microscopy (FESEM). The influences of deposition time and current density on the surface morphology of CoO/TNT were studied. The photoelectrochemical response of CoO/TNT nanocomposite was investigated. All CoO/TNT exhibited higher photocurrent than bare annealed TNT did, which was caused by the enhanced photogenerated electron–hole pairs separation. However, the photocatalytic activity cannot be straightforwardly related to photocurrent response because it also depends on some other factors such as catalyst acidic properties, specific surface area and the adsorption of organic dye. Transient photocurrent measurement should not be used alone for the screening of photocatalytic materials.

► CoO/TNT nanocomposite was fabricated through a facile electrochemical process.
► CoO/TNT showed an enhanced photocatalytic activity.
► Photocatalytic activity cannot be straightforwardly related to transient photocurrent response.