The large diameter and fast growth of self-organized TiO2 nanotube arrays achieved via electrochemical anodization

We have carried out a detailed investigation of the effect of water content on the electrochemical anodization of Ti in electrolytes consisting of ammonium fluoride, water, and ethylene glycol. We have explored the possible growth of ordered TiO2 nanotubes in the electrolyte with water concentrations from 1 to 100 vol% and the applied voltage from 10 to 150 V, where large diameter (similar to 600 nm) and fast growth rate (similar to 100 mu m h(-1)) have been successfully realized for the self-organized TiO2 nanotube arrays. The achievement benefits from the clear understanding of the effects of both the water content and the anodization voltage on the formation of TiO2 nanotube arrays. We have further shown crystalline formation of TiO2 nanotubes by simple thermal annealing. The mechanisms of the effect of the water content on the diameter and growth rate revealed here should establish a basis for further optimization of the TiO2 nanotube geometries.