Abstract
Nanoporous anodic aluminum oxide (AAO) films play an important role in nanotechnology due to their easily adjustable morphological properties and wide range of applications. Thus, a deep and systematic characterization of the morphological properties of these coatings is essential. The most important variables in the synthesis of nanoporous AAO films include the anodization voltage, nature, concentration and temperature of the electrolyte, which, combined, result in pores of different sizes and geometries. In the present work, AA 1050 alloy was used to synthesize AAO films, using 0.3 and 0.9 M oxalic acid as the electrolyte and combining different electrolyte temperatures (20, 30 and 40 °C) and anodizing voltages (30, 40 and 60 V), with the aim to correlate the morphological properties of the coatings with the synthesis parameters of a single anodization step. The coatings obtained were characterized by optical microscopy and scanning electron microscopy, determining pore diameter, interpore distance, pore density and coating thickness. The results showed that, by varying the anodic synthesis conditions, it is possible to obtain coatings with a pore diameter between 21 and 97 nm, an interpore distance between 59 and 138 nm, pore density between 2.8 × 1010 and 5.4 × 109 pores/cm2 and thicknesses between 15 and 145 µm. In this way, the right combination of synthesis variables allows synthesizing AAO coatings with morphological characteristics best suited to each particular application.
Highlights
Aluminum anodic oxidation is a simple, low-cost and versatile electrochemical process that allows obtaining nanoporous coatings of different morphology, by varying the electrochemical parameters of synthesis such as the nature, concentration and temperature of the electrolyte and the anodization voltage [1].Over the years, many efforts have been made to optimize the use of nanoporous anodic aluminum oxide (AAO) films in applications such as molecular filtration and separation, catalysis, electronics and photonics, energy generation and storage, sensors and biosensors, drug delivery and template synthesis to obtain nanotubular materials [2,3,4]
Based on the fact that it is fundamental to select the synthesis conditions that best adapt to each particular application, we studied the correlation between the synthesis conditions, the current density vs. time curves [3,4,11,31]
From 2019, the analysis of the curves, current density vs. time of Figure 1a,b, we summarized in Figure the anodic pore formation in four characteristic curves related to the conditions of anodic synthesis
Summary
Many efforts have been made to optimize the use of nanoporous anodic aluminum oxide (AAO) films in applications such as molecular filtration and separation, catalysis, electronics and photonics, energy generation and storage, sensors and biosensors, drug delivery and template synthesis to obtain nanotubular materials [2,3,4] In this sense, Masuda and Fukuda [5] developed a two-step anodization technique to obtain self-ordered nanostructures and hexagonal packaging of pores, without the need for expensive lithographic techniques [5,6], which was a breakthrough in obtaining nanomaterials from AAO templates. Another way to minimize AAO film synthesis costs is to use commercial aluminum alloys such as AA 1050 (99.5% Al) [1,16,17,18,19] as the substrate, high-purity aluminum anodizing allows obtaining higher order films [11,15,20,21]
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