Electrochemical Growth of Vertically-Oriented High Aspect Ratio Titania Nanotubes by Rabid Anodization in Fluoride-Free Media

Abstract

Vertically-oriented high aspect ratio titania nanotube bundles have been grown by a potentiostatic anodization of titanium sheet in fluoride-free electrolytes. The anodization conditions like the applied voltage were optimized for the synthesis of titania nanotubes in HClO4 and NaCl electrolyte. The resulting nanotubes have a length of about 30 microm, outer diameter about 40 nm, inner pore size of about 10 nm and the aspect ratio was 750:1 by anodization in 0.1 M perchloric acid of pH approximaately 1 at applied voltage of 20 V. While for nanotubes prepared in 0.3 M NaCl of pH 4.3, the length was above 50 microm with the aspect ratio of 1250:1. A method to increase the uniformity of nanotube was demonstrated by pretreatment the titanium sheet by (4 wt% HF + 5 M HNO3) solution prior to anodization. Titania nanotubes were prepared, for the first time, by anodization in aqueous H2SO4 electrolyte alone with tube length above 500 nm. Annealing studies were performed, on high aspect ratio Titania nanotube layers produced in HClO4 electrolyte, in the temperature interval of 300 to 550 degrees C. The XRD patterns and TEM data confirmed the formation of single anatase phase after annealing at 450 degrees C with perfect nanoubular structure. While the rutile titania phase starts to emerege after annealing at about 500 degrees C and the evidence for the appearance of rutile phase due to the oxidation of the underlying Ti metal at the interface between nanotube/Ti-metal was given. On the other hand, the nanotubular structure starts to destroy upon annealing temperature of approximate 550 degrees C by tube flattening and losing of roll-up characteristics as indicated in SEM images. The superior morphology of these high aspect ratio nanotubes and their rapid growth rate foreshadow a bright future in wide applications like dye-sensitized solar cells, water photolysis and nanobiomedical.

Forming Process of Anodic TiO2Nanotubes under a Preformed Compact Surface Layer

“…12 In summary, TiO 2 nanotubes could be obtained not only in the fluoride or chloride-containing electrolytes, but also in the halidefree electrolytes. 22 The interesting results demonstrate that the J e generation and oxygen bubbles are necessary to form nanopores or nanotubes, because the J e becomes the predominant mode of charge transport under the breakdown condition. 24 Anion incorporation and generation mechanism of electronic current.-Electronic current and oxygen evolution during anodizing process are admitted in many literatures.…”

“…When the applied voltage is high and anodic oxide is localized breakdown, porous anodic oxide can be obtained. Fahim et al 22 have demonstrated that TiO 2 NTs could be obtained during Ti anodization in H 2 SO 4 solutions. The current-time curve during Ti anodization in H 2 SO 4 is quite similar to that obtained in fluoride-containing electrolytes.…”

TiO2 Nanotubes on Transparent Substrates: Control of Film Microstructure and Photoelectrochemical Water Splitting Performance

“…Self-organized oxide tube arrays can be fabricated by electrochemical anodization of a suitable metal foil under specific anodic conditions and proper electrolytes [18][19][20][21][22][23]. For instance, highly ordered TiO 2 nanotube arrays are typically grown by electrochemical anodization of titanium foils [23].…”

Recent advances in the use of TiO2 nanotube powder in biological, environmental, and energy applications

“…The titanium dioxide white layer leaves the substrate and breaks down gradually in one dimension developing vertically oriented nanotubes in the electrolyte in the powder form as indicated by eqn (1)-(4). 15,16,38 Ti + 2H 2 O / TiO 2 + 4H + + 4e À…”