From branched self-assemblies to branched mesoporous silica nanoribbons

Article abstract of DOI:10.1039/b812016a

Branched left-handed twisted mesoporous silica nanoribbons were prepared via a template method. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b812016a

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From branched self-assemblies to branched mesoporous silica
nanoribbonsw
Baozong Li,a Yuanli Chen,a Huanyu Zhao,a Xianfeng Pei,a Lifeng Bi,a Kenji Hanabusab
and Yonggang Yang*a
Received (in Cambridge, UK) 14th July 2008, Accepted 28th August 2008
First published as an Advance Article on the web 4th November 2008
DOI: 10.1039/b812016a
Branched left-handed twisted mesoporous silica nanoribbons
in 1.0 mL of pure water, a white suspension was obtained. An
were prepared via a template method.
optical micrograph shows many short ribbons and fibers of
mm-size floating in water (Fig. 1a). It is interesting to find that
huge branched organic self-assemblies were identified when
10 mg of L-16Phe6PyBr were dissolved in 1.0 mL of 1-propanol.
According to our previous results,11,12 branched silica nano-
structures are potentially obtained via the sol–gel transcription
method.
Recently, branched, hyperbranched, Y- and star-shaped nano-
particles have attracted many researchers, because they can be
potentially applied in the fields of electronics and photonics.
However, only a few methods have been used to control the
branched nanostructures. For example, branched e-MnO2
nanostructures were synthesized via a hydrothermal method.1
Hyperbranched PbSe nanowire networks were synthesized via
a vapor–liquid–solid mechanism.2 Star-shaped Bi2S3 was
formed by the splitting crystal growth mechanism.3 Star-
shaped gold nanoparticles were synthesized using a surfactant
direct method.4 Boron nanowire Y-junctions were synthesized
in a self-assembled manner by fusing two individual boron
nanowires grown inclined toward each other.5 Multibranched
carbon nanotubes were synthesized using flow fluctuation.6
Y-junction carbon nanotubes were grown by a chemical vapor
deposition method using nanochannel alumina as a template.7
Because it is hard to transfer the morphologies of the self-
assemblies of L-16Phe6PyBr in pure 1-propanol, the sol–gel
transcriptions were carried out in mixtures of water and
1-propanol. A typical synthetic procedure is as follows: com-
pound L-16Phe6PyBr (10 mg, 0.016 mmol) was dissolved in a
mixture of 0.2 mL of 1-propanol and 0.8 mL of NH3 aq.
(5.0 wt%), then 20 mg (0.096 mmol) of tetraethoxyl orthosilicate
(TEOS) were dropped into the suspension under strong stirring
at 0 1C. After it turned white at 90 s, stirring was stopped.
The mixture was kept at 0 1C for 1 day and 80 1C for 4 days
under static conditions. Finally, the template was removed
by washing with a mixture of HCl aq. and methanol, and
calcination was performed in a box furnace in air at 550 1C
Low-molecular-weight amphiphiles show
a variety of
morphologies. Recent results indicated that sol–gel transcrip-
tion is a powerful method to control inorganic, organic–
inorganic hybrid, and organic nanostructures using the self-
assemblies of these amphiphiles as templates.8–13 The
morphologies of organic templates can control those of in-
organic nanomaterials. Up to now, nanofibers, nanotubes, and
mesoporous nanofibers have been prepared. For the prepara-
tion of branched nano-silicas through a sol–gel transcription
process, branched organic self-assemblies should be selected as
templates, at least, branched organic self-assemblies as inter-
mediates can be formed during the sol–gel transcription
process. Here we successfully obtained branched mesoporous
silica nanostructures through a dynamic templating process.
The branched mesoporous silicas have potential to be used as
templates to prepare other nanomaterials.
for 5 h, with a ramp rate of 1 1C minꢀ1
.
To visually study the morphologies of the obtained silica, we
used field emission scanning electron microscopy (FESEM).z
Before taking FESEM images, 10 nm Pt–Pd was covered on
the surface of samples. Although the obtained silica combined
some nano-sheets, branched silica nanoribbons were identified
(Fig. 2 and Supporting information, Fig. S1w). All of these
nanoribbons are left-handed twisted with a uniform helical
pitch of around 3.0 mm. Generally, these nanoribbons are less
than 10 mm in length. Lamellar pore architecture was identified
from transmission electron microscope (TEM) images (Fig. 3
and Supporting information, Fig. S2w). This nanostructure is
different from the twisted ribbons constructed by many tubes
in a single layer.11 It is very interesting to find that the
Amphiphile L-16Phe6PyBr which is composed of
L-phenylalanine was synthesized according to Scheme 1 (ESI w).12
It can gel THF, benzene, nitrobenzene, 1,4-dioxane, and
chlorobenzene. When 10 mg of L-16Phe6PyBr were dissolved
a Key Laboratory of Organic Synthesis of Jiangsu Province, College
of Chemistry and Chemical Engineering, Suzhou University, Suzhou
215123, P. R. China. E-mail: ygyang@suda.edu.cn
b Department of Functional Polymer Science, Faculty of Textile
Science and Technology, Shinshu University, Ueda 386-8567, Japan
w Electronic supplementary information (ESI) available: Synthesis
of compound L-16Phe6PyBr; FESEM and TEM images; SAXRD
pattern. See DOI: 10.1039/b812016a
Scheme 1 Synthesis of compound L-16Phe6PyBr.
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Fig. 1 Optical micrographs of L-16Phe6PyBr in pure water (a, 10 mg
of L-16Phe6PyBr in 1.0 mL of water) and in 1-propanol (b, 10 mg of
L-16Phe6PyBr in 1.0 mL of 1-propanol).
Fig. 4 N2 adsorption–desorption measurements of left-handedly
twisted mesoporous silica nanoribbons. Sorption isotherms (a) and
BJH pore-size distribution plot (b) from the adsorption branch.
pore-size distribution plot determined from the adsorption
branch shows one sharp peak at 4.0 nm (Fig. 4). This lamellar
pore architecture shows high thermostability, even this silica
was calcined at 550 1C for 5 h. The small-angle X-ray diffrac-
tion (SAXRD) pattern shows no sharp peaks (Supporting
information, Fig. S3w). Several kinds of helical and coiled
mesoporous silica nanostructures have been prepared re-
cently.11,12 Only broad peaks were identified in SAXRD
patterns. For the lamellar mesoporous silica nanoribbons
shown here, possibly due to the twisted morphology and the
ribbons formed only by several silica layers, no sharp peaks
were identified in the SAXRD pattern.
The mechanism of the formation of the branched meso-
porous ribbons was studied using TEM at different reaction times
(Fig. 5).14 Before dropping TEOS, both ribbons and helical
bundles were identified (Fig. 5a). After dropping TEOS,
dendrimer-like organic self-assemblies were identified at 30 s
Fig. 2 FESEM (a, b, and c) images of branched mesoporous silica
nanoribbons.
Fig. 3 TEM image of branched mesoporous silica nanoribbons after
calcination.
thickness of the trunk and the branch of some ribbons is
nearly the same (Fig. 2b and 3). The mesoporous nanoribbons
exhibited a nitrogen Brunauer–Emmett–Teller (BET) surface
area of 306 m2 gꢀ1 and the Barrett–Joyner–Halenda (BJH)
Fig. 5 TEM images of the reaction mixture at different reaction times
(a, 0 s; b, 30 s; c, 30 s; d, 60 s; e, 90 s, and f, 160 s).
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(Fig. 5b). Each twisted nanoribbon is separated into two
twisted nanoribbons (Fig. 5c). Branched nanoribbons were
still identified at 90 s, just after stopping stirring (Fig. 5e).
These branched nanoribbons organized into non-coiled nano-
ribbons with increasing stirring time (Fig. 5d and e). The
non-coiled nanoribbons started to form at 60 s with self-
assembling of twisted nanoribbons (Fig. 5d). Then non-coiled
nanoribbons and branched nanoribbons were obtained finally
(Fig. 5e and Supporting information, Fig. S4w). Compared
with Fig. 5a, c, and d, it was found that the helical pitch of the
morphologies increased with increasing reaction time. The
branched nanoribbon (Fig. 5b) was the intermediate between
the helical bundle (Fig. 5a) and non-coiled nanoribbon (Fig. 5f).
Because of the existence of 1-propanol in the reaction
mixture, ethanol resulting from the hydrolysis of TEOS should
not be the main factor to change the morphologies of the
organic self-assemblies from the nanoribbons and helical
bundles to the dendrimer-like structure. Thus, the adsorption
of silicate anions and silica oligomers should be the main
factors controlling this morphology change. After the poly-
condensation of the silica oligomers on the surface of the
branched organic self-assemblies, branched silica nanoribbons
were formed. Branched mesoporous silica nanoribbons were
obtained by removing the templates. In all, the formation of
branched mesoporous silica nanoribbons follows the dynamic
template process.15 The morphologies of organic self-assemblies
change during the sol–gel transcription process.
formation of non-coiled nanoribbons. Compared with the
other gelators reported previously,11,12,14 the p–p interaction
among the phenyl groups of L-16Phe6PyBr is the main factor
forming the non-coiled nanoribbons.
In summary, branched mesoporous silica nanoribbons were
fabricated through a dynamic templating process. These
branched nanoribbons have a left-handed twist and show high
thermostability. They are templated by the intermediates of
the organic self-assemblies during the sol–gel transcription
process. Based on the mechanism shown here, many other
branched nanoparticles have the potential to be prepared,
which could be used in electronics and photonics.
This work was partially supported by Jiangsu Provincial
Key Laboratory of Organic Chemistry Foundation and Natural
Science Foundation of Jiansu Province (No. BK2007047).
Notes and references
z TEM images were obtained using a TecnaiG220. FESEM images
were taken on a Hitachi S-5000. Specific surface area and pore-size
distribution were determined by the BET and BJH methods using a N2
adsorption isotherm measured by a Gemini V 2380 instrument. The
SAXRD pattern was taken on an X’Pert-Pro MPD X-ray diffracto-
meter. CD and UV spectra were taken on an AVIV 410 spectrometer.
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This journal is The Royal Society of Chemistry 2008
6368 | Chem. Commun., 2008, 6366–6368