TiO₂ nanotubes with tunable morphology, diameter, and length: Synthesis and photo-electrical/catalytic performance

This article reports on the synthesis of TiO₂ nanotubes (NTs) with tunable morphologies by adjusting the reaction conditions during anodization to balance electrochemical reaction and chemical etching. Nanoporous and free-standing NTs with different lengths and diameters are thus obtained in a controlled manner, solving the bundling, sealing, and etching pit issues in the conventional anodization. The high growth speed (60 μm/h) of TiO ₂ NT arrays with the pore diameter of 120 nm was achieved. The photoelectrochemical response of the NT photoelectrodes is studied under both UV and visible illumination from 250 to 600 nm, showing that the photoresponse occurred between 300 - 400 nm with the maximum value at 355 nm. The nanoporous TiO₂ film has the higher photocurrent density than the nonporous NTs array because of fewer defects and perfect alignment. However, the photocatalytic performance to degrade methylene blue showed an inverse trend: the free-standing TiO₂ NTs have better photocatalytic degradation than the nanoporous TiO₂ NT film probably due to the larger effective contact area.