Effect of cathode size on the morphology of the anodized TiO2 nanotube photocatalyst

Titanium dioxide nanotubes (TNTs) were synthesized via an electrochemical anodization process. The influence of increasing the cathode surface area on the microstructure and order of the final product was investigated. To study the microstructure of the synthesized nanotubes, field emission scanning electron microscopy (FESEM) was employed. The degree of crystallinity and the characteristic of synthesized nanostructure was evaluated by X-ray diffraction (XRD). The porous initiation layer covering the tube-top became thinner and lost its’ integrity, as a consequence of employing a larger cathode. This is due to the enhanced reaction sites followed by intensifying the electrochemical reaction in the anodic oxidation processes. In contrast, a small surface area of the cathode made it possible to control the obtained nanostructure with no damages to the surface morphology. The average diameter of the surface nanopores increased from 60 to 67 nm by increasing the cathode surface area. Optical characterization demonstrates that the bandgap of the synthesized TiO2 nanotubes is about 3.2 eV. In the process of methylene blue (MB) degradation, the photocatalytic activity of the TNTs with an ordered initiation layer reaches 69% after 480 min irradiation.