AAO aluminum oxide is a porous template material used for the fabrication of nanostructured membranes and templates. Its advantages include the ability to adjust the thickness of the pores. The pore depth can be controlled and monitored in real time. This property allows for the creation of a wide range of nanostructured templates, including nanowells, nanospikes, nanobowls, and inverted nanocones.
AAO has also been used in a variety of applications, from catalysis to energy storage devices. For example, it was used to create a low temperature thermochemical heat storage system. However, its inherent properties make it a challenging material to fabricate. Specifically, the anodization process presents a challenge for precise control.
In order to precisely monitor the AAO pore depth during the anodization process, a generic electric charge integral approach was developed. As shown in Figure 2b, the integrated charge density of the AAO varies for different anodization voltages. This correlation is robust, and can be used to accurately control the AAO growth process.
Variations in the anodization conditions and minor constituents in the electrolyte affect the rate of growth. Moreover, fluctuations in acid concentration may influence the pore diameter. Nevertheless, a linear relationship exists between the integrated charge density and the AAO pore depth, which can be used to predict the pore depth in real time.
Porous AAO membranes exhibit better retention of the electrolyte. They are also more mechanically stable than commercial separators.
Functionalization methods for AAO membranes include grafting polyelectrolytes and alkenes/alkynes. AAO composites can also be made from various organic and inorganic materials. Examples of such materials include poly(diallylamine) and poly(ethyleneimine).
Because of their large internal surface area, AAO nanostructures can be engineered into a number of variations. Nanopillar-nanowell structures and colorimetric sensors are two examples of such applications.