Tailor-engineered structural and physico-chemical properties of anodic alumina nanotubes by pulse anodization: A step forward

Abstract

A study on advanced structural engineering of anodic alumina nanotubes (AANTs) manufactured by pulse anodization is presented. In-depth analysis of the electrochemical parameters of pulse anodization was carried out, distinctive sections of the anodization were defined. Evolution of the profiles has been quantified and described with regards to different current density applied and pulse duration during hard anodization. A smart combination of different anodization conditions enables precise control over the nanotubes' geometric features and physiochemical properties. Nanotubes are produced with varying pulse period, current density level and various post-anodization treatments (different sonication time, temperature and thermal annealing of anodic alumina film before fragmentation) under galvanostatic mode in sulfuric acid electrolyte modified with 10% (v) ethanol. The average length of nanotubes is tailor-engineered from 424 ± 92 to 1010 ± 118 nm, with an average inner diameter that ranges from 37 to 48 nm. It is also demonstrated that the level of current density input during pulse anodization has a direct effect on the ζ-potential of nanotubes, which can be tuned between 25 and 8.5 mV. Additionally, it is possible to produce nanotubes with a negative ζ-potential of −6.3 mV upon post-annealing treatment. Separation of nanotubes from the original template is improved by sonication at low temperature, providing a new means of increasing the production yield of these nanostructures. Furthermore, nanotubes are found to increasingly degrade with the bath temperature during separation. To better understand the impact of the fabrication parameters over the physical and chemical properties of nanotubes is a key step to design and tailor-engineer these model 1D nanostructures for specific applications. AANTs provide many attractive features that could find broad applicability in disciplines such as catalysis, drug delivery, nanofabrication and sensing. • In-depth analysis of anodization profile evolution accordingly to process parameters. • Evaluation of process parameters on physiochemical properties of alumina nanotubes. • Improved separation/degradation at lower/higher sonication temperatures. • ζ -potential change with anodization current, pulse duration and thermal annealing. • Morphology and crystalline form can be affected with thermal annealing.