High Aspect Ratio TiO2 Nanotube Layers Obtained in a Short Time

Abstract

In the last two decades, anodic TiO2 nanotube (TNT) layers have gained considerable attention for both their unique physical and chemical properties practical applications [1-3].One of the key parameters that characterize TNT layers is the aspect ratio, which is the ratio between the TNT layer thickness and the nanotube diameter. In particular, TNT layers with a high aspect ratio (HAR) due to their 1D ordered structure, an exceptional morphology and a high surface area, have a great potential in different applications, such as filtration and micro-photo reactors [4,5]. In the last decade, ethylene glycol (EG)-based electrolytes containing small amounts of NH4F and H2O [6] were the most widely used electrolytes to produce high-aspect ratio TNT layers. However, using these electrolytes very long anodization times i.e., several hours or up to several days [7], are needed. Apparently, the synthesis of long and extremely robust HAR TNT layers in a relatively short time remains very challenging until now. Recently, it has been shown that the addition of lactic acid (LA) to EG-based electrolytes can shift the dielectric breakdown potential to significantly higher potentials due to the strong adsorption of lactic acid on TiO2 during the anodization [8]. Thus, considerably higher anodization potentials and increased electrolyte temperatures can be employed and HAR TNT layers can be obtained within less than one hour of anodization.In this presentation we will demonstrate that HAR TNT layers can be obtained within short anodization times using an optimized anodization protocol. The key feature is the use of NH4F/H2O/EG electrolytes containing LA with optimized electrolyte [9].Experimental details and some recent anodization results will be presented and discussed.