Powders of amorphous titanium dioxide (titania) nanotubes
have been synthesized by DC (V = 16 V) rapid breakdown anodization
[7–9] of 0.89 mm thick titanium foil (Alfa Aesar, 99.7% metal
basis) for several hours in an aqueous solution containing 0.1 M
ammonium chloride (Alfa Aesar, purity >99.5%). Bundles of nanotubes
were continuously released in the solution from corrosion
sites on the titanium foil surface, forming a white precipitate which
was recovered, washed repeatedly with water and then with isopropanol,
and subsequently dried on a hotplate at about 80 ◦C.
BET (Porous Materials, Inc.) measurements were performed on
approximately 0.5 g of powder which was degassed to 20 mTorr
at 20 ◦C prior to measurements, with nitrogen at −195.76 ◦C used
as adsorbate. Separately, bundles of nanotubes were released on
a conductive substrate or directly on a transmission electron
microscopy (TEM) grid for further examination by scanning electron
microscopy (SEM) (Hitachi S4800) or TEM (JEOL 2010F). In
addition, the powders were further analysed by Raman spectroscopy
(Jobin Yvon LabRam HR800) and X-ray Diffraction (XRD)
(PANalytical X’Pert Pro Philips).