Preparation of anodic aluminum oxide tubular membranes with various geometries

Tubular anodic aluminum oxide (AAO) membranes with various geometries, including circle, square and triangle, were fabricated using the “external anodizing” method (i.e., anodic oxidation takes place from the outside of an aluminum tube) with preformed aluminum tubes. The radical cracks which mostly occur in tubular AAO membranes could be eliminated effectively by adjusting the membrane thickness through the second anodization time. Successful preparation of crack-free membranes with highly ordered nanopores demonstrates that the “external anodizing” method is applicable for fabricating tubular AAO membranes with the maximum curvature up to ∼60°, which implies its predominance in constructing AAO membranes with complex structures.