The fabrication of highly-ordered
TiO2 nanotube
arrays up to 134 µm
in length by anodization of Ti foil has recently been reported (Paulose et al 2006 J. Phys.
Chem. B 110 16179). This work reports an extension of the fabrication technique to achieve
TiO2 nanotube
arrays up to 220 µm
in length, with a length-to-outer diameter aspect ratio of
≈1400, as well as their initial application in dye-sensitized solar cells and
hydrogen production by water photoelectrolysis. The highly-ordered
TiO2
nanotube arrays are fabricated by potentiostatic anodization of Ti foil in fluoride ion
containing baths in combination with non-aqueous organic polar electrolytes including
N-methylformamide, dimethyl sulfoxide, formamide, or ethylene glycol. Depending upon the
anodization voltage, the inner pore diameters of the resulting nanotube arrays range from
20 to 150 nm. As confirmed by glancing angle x-ray diffraction and HRTEM studies, the
as-prepared nanotubes are amorphous but crystallize with annealing at elevated
temperatures.
Described is the fabrication of self-aligned highly ordered TiO(2) nanotube arrays by potentiostatic anodization of Ti foil having lengths up to 134 mum, representing well over an order of magnitude increase in length thus far reported. We have achieved the very long nanotube arrays in fluoride ion containing baths in combination with a variety of nonaqueous organic polar electrolytes including dimethyl sulfoxide, formamide, ethylene glycol, and N-methylformamide. Depending on the anodization voltage, pore diameters of the resulting nanotube arrays range from 20 to 150 nm. Our longest nanotube arrays yield a roughness factor of 4750 and length-to-width (outer diameter) aspect ratio of approximately 835. The as-prepared nanotubes are amorphous but crystallize with annealing at elevated temperatures. In initial measurements, 45 mum long nanotube-array samples, 550 degrees C annealed, under UV illumination show a remarkable water photoelectrolysis photoconversion efficiency of 16.25%.
We report on the anodic formation of a self-standing 720 μm thick TiO2 nanotubular membrane by complete
consumption of a 250 μm thick titanium foil sample. By employing double sided electrochemical oxidation
of titanium in an electrolyte comprised of water, NH4F, and ethylene glycol, we obtain two highly ordered,
hexagonal close-packed titania nanotube arrays 360 μm in length that are separated by a thin compact oxide
layer; the individual nanotubes in each array have an aspect ratio of ∼2200. The potentiostatic anodization
of titanium in an ethylene glycol, NH4F, and water electrolyte dramatically increases the rate of nanotube
array growth to approximately 15 μm/h, representing a growth rate ∼750−6000% greater than that seen,
respectively, in other polar organic or aqueous based electrolytes previously used to form TiO2 nanotube
arrays. We consider the effects of electrolyte composition, applied potential, and anodization duration on the
length and diameter of the resulting nanotubes in terms of a growth rate model, with results suggesting that
reduced hydroxyl ion injection from the electrolyte, which enables faster high field ionic conduction through
the barrier layer, is responsible for the high nanotube growth rates achieved. Furthermore, as reported herein
for the first time, we are able to make self-standing TiO2 nanotube array films ranging in thickness from 50
to 360 μm.
We report for the first time fabrication of self-aligned hexagonally closed-packed titania nanotube arrays of
over 1000 μm in length and aspect ratio ≈10 000 by potentiostatic anodization of titanium. We describe a
process by which such thick nanotube array films can be transformed into self-standing, flat or cylindrical,
mechanically robust, polycrystalline TiO2 membranes of precisely controlled nanoscale porosity. The self-standing membranes are characterized using Brunauer−Emmett−Teller surface area measurements, glancing
angle X-ray diffraction, and transmission electron microscopy. In initial application, such membranes are
used to control the diffusion of phenol red.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.