Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

Summary

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

Abstract

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

Introduction

AAOs which were formed by anodizing Al substrate in an acidic electrolyte, have attracted great interest in diverse fundamental science and industry, for example, hard templates for nanotubes/nanowires^1,2,3,4,5, energy storage devices^6,7,8,9, bio-sensing^10,11, filtering applications^12,

Protocol

Please be aware of all the related materials safety data sheets (MSDS) before beginning. In spite of the eco-friendly nature of this protocol, a few acids and oxidizers are used in the corresponding procedures. Also, use all the proper personal protective equipment (lab coat, gloves, safety glasses, etc.).

1. Preparation of Solution

Note: After complete sealing of the solution-containing vessel, vigorous magnetic stirring was applied to all the solutions at room temperature in sufficient time.

1. Preparation of perchloric acid solution
   1. Mix 100 mL of perchloric acid (....

Results

Flow chart of n_th AAO fabricating sequence mainly consisting of two-step SMSAs, SRBs-detachment, and related chemical etching was presented schematically in Figure 1a. Each inset show a scanning electron microscope (SEM) image of the corresponding surface morphology at each individual procedure and a photograph taken immediately after SRBs-detachment. A schematic illustration after the total 5^th repetition of the unit sequence e.......

Discussion

In this paper, we successfully demonstrated a facile, high yield, and environmentally clean method to fabricate nanoporous AAOs through SMSA and SRBs-detachment, which could be repeated to the same Al substrate for significantly enhancing mass-producibility as well as usability of limited natural resource. As shown in the flow chart of Figure 1a, our AAO fabricating strategy is based on the conventional two-step anodization, which was modified on multi-surfaces situation. Individual procedur.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sulfuric Acid >98%	DUKSAN reagent	5950
Oxalic Acid Anhydrous, 99.5-100.2%	KANTO chemical	31045-73
Phosphoric Acid, 85%	SAMCHUN chemical	P0463
Perchloric Acid, 60%	SAMCHUN chemical	P0181	Highly Reactive
Chromium(VI) Oxide	Sigma Aldrich	232653	Strong Oxidizer
Ethanol, 95%	SAMCHUN chemical	E0219
Absolute Ethanol, 99.9%	SAMCHUN chemical	E1320
Double Jacket Beaker	iNexus	27-00292-05
Low Temperature Bath Circulator	JEIO TECH	AAH57052K
Programmable DC Power Supply	PNCYS	EDP-3001
Aluminum Plate, >99.99%	Goodfellow
Platinum Cylinder	Whatman	444685
Pure & Ultra Pure Water System (Deionized Water)	Human Science	Pwer II & HIQ II