Short-Time Peeling of Large Anodic Porous Alumina Membranes from Al Substrates by Two-Layer Anodization Using Concentrated Sulfuric Acid

Ordered anodic porous alumina membranes, which have a uniform cylindrical pore array with a high density, are promising materials for the precise filtration of target substances. We previously reported that when a sample that has undergone anodizing is re-anodized in concentrated sulfuric acid, a highly soluble alumina layer is formed at the bottom of the anodized oxide film. When the re-anodized sample was etched, the highly soluble alumina layer was selectively dissolved; thus, it was possible to obtain a large ordered anodic porous alumina membrane without cracks. In this study, we succeeded in reducing the time required for anodization and etching to obtain an alumina membrane by optimizing the anodization conditions using concentrated sulfuric acid. According to this method, after the alumina membrane was peeled off, it was possible to retain a regular pattern of depressions on the surface of the residual Al substrate, which acted as the starting points for the generation of pores during subsequent anodization. By repeating this process on a single Al substrate, we can repeatedly form an ordered anodic porous alumina membrane. The obtained ordered anodic porous alumina membranes can be used as filtration membranes, catalyst supports, and templates for preparing one-dimensional nanostructures.