Fabrication of 3D Nanotubular Networks

AAO templates having periodic 3D nanotubular network templates have been prepared by a two-step anodization of aluminum,³⁵ being the second anodization process a pulsed anodization. To begin with, ultrapure (99.999%) aluminum foils (Advent Research Materials, England), were cleaned and degreased by sonication in acetone, water, isopropanol, and ethanol. Foils were then electropolished in a solution of perchloric acid/ethanol (1/3) under a constant voltage of 20 V for 4 min. After that, the first anodization was achieved for 24 h. A 0.3 M sulphuric acid (Panreac AC Química, Spain) solution was used under a voltage of 25 V and at 0 °C. Then, the first anodic layer was removed by chemical etching in a mixture of phosphoric acid (7 wt. %) and chromic oxide (1.8 wt. %). A pulsed anodization process was then carried out in the conditions specified along the text. Afterwards, the underlying Aluminum substrate was etched with an acidic solution of CuCl₂ at 1 °C and the barrier layer was dissolved using a 10 wt. % aqueous H₃PO₄ solution at 30 °C. Finally, the samples were submerged into a 5 wt. % aqueous H₃PO₄ solution at 30 °C in order to create the transversal nanochannels.