Self-assembled anodic TiO2 nanotube arrays: electrolyte properties and their effect on resulting morphologies

Self-assembled TiO2 nanotube arrays fabricated by electrochemical anodization of titanium are of great interest having been successfully used in many applications including gas sensing, water photoelectrolysis, drug delivery and photovoltaics. Nanotube array synthesis techniques have been studied and developed through several electrolyte systems, however, the key parameters controlling self-organization of the nanotubes have remained unclear. Herein we examine nanotube array morphological growth parameters as dependent upon electrolyte conductivity and titanium concentration. Electrolyte properties establish a regime wherein the TiO2 nanotube arrays self-assemble. Nanotube morphological parameters, including pore diameter, wall thickness and tube-to-tube spacing, are all found to increase with electrolyte conductivity. Using diethylene glycol (DEG) based electrolytes as a model, we detail how manipulation of electrolyte conductivity enables control of nanotube array morphological features.