Growth, Characteristics and Application of Nanoporous Anodic Aluminum Oxide Synthesized at Relatively High Temperature

Abstract

The nanoporous anodic aluminum oxide (AAO) is one important nano-template used for synthesis of nanocomposite materials or as an etching mask for pattern transfer in a variety of applications. Conventional AAO templates were synthesized using two-step potentiostatic method of direct current anodization (DCA) at low temperature (0–10 °C) to avoid dissolution effect. In this chapter, an effective method of hybrid pulse anodization (HPA) with normal positive and small negative voltages has been proposed for AAO synthesis at a relatively high temperature of 15–25°C for enhancing performance of AAO structure from the cheap low-purity (99%), costly high-purity (99.997%) aluminum foils and the aluminum (Al) films on Si substrates. The pore size distribution and circularity of AAO by HPA is much better than DCA due to its effective cooling at relatively high temperature. The HPA not only merits manufacturing convenience and cost reduction but also promotes pore characteristics of AAO at severe conditions of cheap low-purity Al foils and high temperature. Moreover, the pore diameter can be enlarged by wet etching. The etching rate of AAO pore diameter is greatly affected by the electrolyte anions contaminated AAO prepared by HPA at low-to-high concentrations (0.3~0.9 M) of oxalic acid at 25°C. Increasing oxalic acid concentration decreases the widening rate of pore diameter because more anions in the AAO would decrease etching rate during widening. The applications to effective nanoporous membranes fabrication and photocatalysis are presented.