Effect of carbon nanotube incorporation on the photocatalytic activity of TiO₂ nanotubes

Arrays of titanium dioxide (TiO₂) nanotubes were prepared on commercially pure titanium (Ti) foils by anodic oxidation in a 0.5 M hydrofluoric acid (HF)-based electrolyte with multiwalled carbon nanotubes (MWCNTs) up to 0.035 g/l. The samples were annealed at 450°C for 1 h after anodic oxidation to form a crystalline anatase structure. The effect of MWCNT addition on the morphology and photocatalytic activity of the nanostructures was characterized by scanning electron microscopy, Raman spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and methylene blue degradation tests. The results showed that MWCNTs were successfully incorporated into the titanium dioxide nanotube structure and significantly affected its photocatalytic activity. The best photocatalytic performance was achieved with the use of 0.025 g/l MWCNTs in the electrolyte composition. However, when the MWCNT content in the electrolyte increased, the electron–hole recombination rate and photon absorption ability of the structure deteriorated, resulting in a decreased photocatalytic activity.