Preparation of Ordered Porous Alumina Through-Hole Membranes with Large Hole Periods by Two-Layer Anodization

Ordered anodic porous alumina through-hole membranes with a hole period larger than 500 nm were fabricated by two-layer anodization. Formation of the ordered anodic porous alumina with a hole period larger than 500 nm was carried out by anodization of Al in phosphoric acid or mixture of malic acid and phosphoric acid. Two-layered structures comprising porous alumina layers with different solubilities were formed by anodization using two electrolytes, one of which was 17.6 M sulfuric acid. The membranes were prepared by selectively etching the lower part of the alumina layer formed in 17.6 M sulfuric acid. The thickness of the membranes was controlled by adjusting the anodization time. The obtained membranes are expected to be used in various applications such as filtration membranes.