Hierarchically structured anatase nanotubes and membranes

Hierarchically structured anatase membranes containing both macro- and mesopores were synthesized by liquid phase deposition of porous anodic aluminum oxide (AAO) templates at 50 °C. It was observed that titania initially forms nanotubes held together by residual AAO, then takes on completely the shape of the AAO template by displacing alumina and finally forms ‘capped’ membranes in which a layer of mesoporous titania covers the ends of the template. Besides the sub-250 nm diameter tube holes, nitrogen physisorption also revealed that the tube walls were mesoporous with pore diameters centered around 4 nm with extremely high specific surface areas ranging from 179 to 552 m2/g. Active photodegradation of aqueous solutions of methylene blue indicated that the membranes were photocatalytically active and the highest degradation constant was observed for AAO templates that had been treated for 5 h by liquid phase deposition.