Page 224 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 4 CONTROL OF NANOSTRUCTURE OF MATERIALS
their structures and morphologies in nanometer-size starting material. A gold film was made on the sheet
level. Carbon nanotubes, discovered by Iijima have by evaporation for the electrical condition of the
been reported to possess unique electrical and material, and then methyl methacrylate (PMMA)
mechanical properties different from those of was polymerized inside of the pores. After the result-
conventional carbons such as graphite and fullerene ing films were treated with NaOH aqueous solution
[1]. The fundamental studies on the electrical to remove the Al O , resulting in the formation of
2
3
conductivities and the formation mechanism of car- the PMMA replicated negatively. Subsequently,
bon nanotubes are in progress. Carbon nanotubes electrochemical deposition techniques in the PMMA
have realized a high performance as a cantilever mold were used to form TiO . After the chemical
2
(mechanical probe) for a scanning probe microscope, dissolution of the polymer, titania nanotubes with
and field emission display. Carbon nanocoils have inner diameter of 70–100 nm were obtained. The
been reported to show excellent electromagnetic wave porous alumina membrane prepared by an anodic
absorption properties. oxidization method consists of highly oriented alu-
The novel functionalities are expected to be gener- mina pillars and, the shapes of the resulting titania
ated by controlling the shape, size, and composition crystals are reflected by the mold derived from the
of materials: (1) shapes such as tube, layer, sheet, or pillars.
wire; (2) sizes in nanometer or micrometer level; and After this report, some works on the preparation of
(3) composition such as carbon, alumina, or titania the nanotubes using polycarbonate, carbon nanotubes,
are quite important. surfactants as replica or template materials were
Since the discovery of carbon nanotubes, there have reported. Table 4.3.2 shows some reports on titania
been numerous works on the preparation of various nanotubes prepared by replica methods.
non-oxide nanotubes such as, BN, B-C-N, WS , and Imai et al. reported that the direct preparation of
2
oxide-based nanotubes such as SiO , Al O , and TiO . titania nanotubes in nanochannels of porous alu-
2
3
2
2
In the present section, TiO -based nanotubes with mina membranes using a deposition technique from
2
photocatalytic activities [2], in various fields involv- TiF solution. After dissolving the alumina mem-
4
ing (1) the removal of NO and gases associated with brane, titania nanotubes with an outer diameter of
x
aldehyde decomposition; (2) environmental purifi- 200 nm, and an inner diameter of 100–150 nm were
cation processes such as water purification and obtained [6].
decomposition of pollutants; (3) catalytic reactions Michailowski et al. reported that titania nan-
for hydrogen generation; and (4) electrode materials otubes with a diameter of 50–70 nm and a wall
for dye-sensitizing solar batteries, are briefly thickness of 3 nm were prepared by filling pores in
reviewed. aluminum oxide membrane with titanium iso-
propoxide and subsequent heating [8]. Varghese et
(1) Preparation methods of titania nanotubes al. prepared titania nanotubes by the anodic oxida-
Two significant routes for the preparation of titania tion of a pure titaniumu sheet in an aqueous HF
nanotubes have been reported: (a) a replica or tem- solution [10, 11].
plate method, (b) a chemical treatment or hydrother-
mal method. Some of these works were summarized (b) The soft-chemical method
in Ref. [3] by Suzuki et al. In 1998, Kauga et al. reported for the first time that
titania nanotubes were prepared by using a soft-
(a) The replica method chemical method [14]. Needle-shaped titanium oxide
In 1996, titania nanotubes were prepared for the first crystals with an inner diameter of approximately 5 nm
time using a replica method by Hoyer [4, 5]. and an outer diameter of 8 nm were obtained when
Anodically grown aluminum oxide was used as the titania nanopowders were treated chemically with
Table 4.3.2
Titania nanotubes prepared by a template or a replica method.

Author Template mold Raw solution
Hoyer [4, 5] Anodic alumina, PMMA TiCl 3
Imai [6] Anodic alumina TiF 4
Adachi [7] Surfactant Titanium alkoxide
Michailowski [8] Anodic alumina Titanium alkoxide
Caruso [9] Fibrous polymers Titanium alkoxide
Gong [10, 11] Anodic oxidation of pure titanium HF solution
Sun [12] Carbon nanotubes TiCl 4
Shin [13] Polycarbonate filters Titanium alkoxide

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