Chemistry Letters Vol.33, No.5 (2004)
505
2), no remarkable change in the thickness was observed by
changing the amount of TEOS. This finding enables us to con-
clude that in the surface mechanism the presence of the secon-
dary ammonium cations on the nanotube surfaces is crucial for
the control of the thickness.
In conclusion, when adding solution catalysts into the reac-
tion medium, we are not able to control the adsorption or depo-
sition of silica. While in the case without catalysts, the sol-gel
reaction mostly occurs near the surfaces of the organic template,
as defined as a surface mechanism. Therefore, the concentration
of the TEOS around the surface may affect the degree of the hy-
drolysis and condensation and thus affect the wall thickness of
the resultant silica nanotubes. This situation allows us to control
the dimension of the silica nanotubes within 4-nm precision.
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Figure 2. TEM images for silica nanotubes before calcination,
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As a contrast experiment, we used a solution catalyst, so-
dium hydroxide, for the sol-gel transcription into silica. Al-
though the wall thickness of the obtained silica nanotubes was
relatively thicker than those without solution catalysts (Figure
Published on the web (Advance View) March 30, 2004; DOI 10.1246/cl.2004.504