An efficient synthesis of helical mesoporous silica nanorods

Article abstract of DOI:10.1246/cl.2006.190

Helical mesoporous silica nanorods have been synthesized with high efficiency by the addition of 1-alkanol or 1-aminoalkane with proper carbon chain length (C₄-C₈) as a cosurfactant of cetyltrimethylammonium bromide (CTAB) during the synthesis of MCM-41 in a dilute synthesis gel containing CTAB, tetraethyl orthosilicate, ammonium hydroxide, and water. Copyright

Full text of DOI:10.1246/cl.2006.190

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Chemistry Letters Vol.35, No.2 (2006)
An Efficient Synthesis of Helical Mesoporous Silica Nanorods
Ã
Ã
Qinghong Zhang, Fei L u¨ , Changli Li, Ye Wang, and Huilin Wan
State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry,
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China
(Received October 5, 2005; CL-051272; E-mail: zhangqh@xmu.edu.cn, hlwan@xmu.edu.cn)
Helical mesoporous silica nanorods have been synthesized
gies of mesoporous silica under specific synthetic conditions or
–16
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with high efficiency by the addition of 1-alkanol or 1-aminoal-
kane with proper carbon chain length (C4–C8) as a cosurfactant
of cetyltrimethylammonium bromide (CTAB) during the synthe-
sis of MCM-41 in a dilute synthesis gel containing CTAB,
tetraethyl orthosilicate, ammonium hydroxide, and water.
in the presence of an additive.
The formation of mesoporous
silica nanofibers with either circular or longitudinal pore archi-
tecture was observed by the addition of concentrated inorganic
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salts to an acidic synthesis gel. Organic additives such as
1
4
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decane and ethylacetate were also reported to be capable of
changing the morphology of mesoporous silica from sphere to
tube or rod. However, there are only a few reports on the synthe-
sis of mesoporous materials with inerratic helical channels with
Inorganic materials with helical pores have attracted much
attention because they may exhibit peculiar advantages of shape
selectivity in adsorption, separation, and heterogeneous cataly-
3
high efficiency.
Recently, we discovered that helical mesoporous silica
nanorods could be formed with high yields by simply modifying
the synthesis procedure using C4–C8 primary alcohol or amine
as a cosurfactant of CTAB. In a typical synthesis, the surfactant
(CTAB) was first dissolved in deionized water. After the adjust-
ment of pH value of the solution with ammonium hydroxide,
1-hexanol, and TEOS were added, and the mixture with a molar
ratio of CTAB:TEOS:NH3:H2O being 0.11:1:10:525 was al-
1
sis. Thus far, only very scattered reports have succeeded in
the synthesis of this kind of materials. Usually, complicated
structure-directing agents with chiral property have to be ap-
plied, e.g., chiral ligand or chiral metal complex for microporous
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materials, chiral organic templates for mesoporous materials.
A recent paper showed that the use of an achiral ionic liquid
4
as the template could yield helical mesoporous silica. Here,
ꢀ
we report a new route for the synthesis of inerratic helical chan-
nel architecture in mesoporous silica nanorods with high effi-
ciency by using primary alcohol or amine as a cosurfactant.
The current study offers a possibility of simply fabricating
mesoporous materials with regular helical channels.
lowed to react at temperatures of 35–95 C under continuous
stirring for 2 h. The product was recovered by filtration followed
by washing and drying. The organic molecules were removed by
ꢀ
calcination in air at 550 C for 8 h.
Figure 1 shows the SEM micrographs of the samples after
the addition of 1-hexanol as a cosurfactant of CTAB at a
MCM-41, one of the most widely studied ordered mesopo-
rous materials, was synthesized by the self-assembly of organic
template molecules and inorganic silicate ions into an organic–
ꢀ
reaction temperature of 80 C. The particles prepared from the
gel without 1-hexanol were spheres with diameters of 150–300
nm. By adding 1-hexanol, the spheric particles elongated in
one direction, and gradually developed into nanorods as the mo-
lar ratio of 1-hexanol/CTAB increased to 1/1. Further increases
in the ratio to 2/1 led to the formation of small spheric particles
again with diameters of ca. 80 nm. Finally, irregular hollow par-
5
inorganic hybrid as a precursor. It can be expected that the
channel architecture and the morphology of the mesoporous
materials synthesized by this approach are largely dominated
by the assembling behavior of the template molecules. Many
pioneer researches have provided several interesting morpholo-
ꢀ
Figure 1. SEM images of mesoporous silicas prepared at 80 C with and without 1-hexanol co-surfactant. The molar ratios of 1-
hexanol/CTAB are: (a) 0/1, (b) 0.25/1, (c) 0.5/1, (d) 1/1, (e) 2/1, and (f) 7/1. The black bar in each micrograph denotes 400 nm.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.2 (2006)
191
In conclusion, we have discovered a simple route for the
synthesis of helical mesoporous silica nanorods with high effi-
ciency by using alkyl alcohol or alkylamine as a cosurfactant
of CTAB in a dilute synthesis gel containing CTAB, TEOS,
ammonium hydroxide, and H2O. The nature of the cosurfactant
and the ratio of the cosurfactant to CTAB are key factors influ-
encing the morphology. The current route may also be applicable
to the syntheses of other nonsilica helical mesoporous materials,
which may be useful for shape-selective adsorption, separation,
and catalysis. Researches on this direction and the elucidation of
the formation mechanism are underway in our laboratory.
This work was supported by the National Basic Program
of China (Nos. 2005CB221408 and 2003CB615803), and the
Program for New Century Excellent Talents in University of
China (No. NCET-04-0602).
Figure 2. TEM image of the mesoporous silica nanorods pre-
ꢀ
pared at 80 C in the presence of 1-hexanol with 1-hexanol/
CTAB = 1/1.
ticles appeared as the 1-hexanol/CTAB increased to 7/1.
The SEM image in Figure 1d for the rodlike sample showed
equidistant lines going diagonally across the external surfaces,
revealing that the sample possessed perfect helical morphology.
The proportion of this morphology was almost 100%. These
helical silica rods were 70–120 nm in diameter and 400–1000
nm in length.
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Published on the web (Advance View) January 14, 2006; DOI 10.1246/cl.2006.190