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436
Chemistry Letters Vol.35, No.12 (2006)
Three-dimensionally Ordered Array of Nanoporous Starburst Carbon Spheres
Ã
Tadashi Nakamura, Yuri Yamada, and Kazuhisa Yano
Toyota Central R & D Laboratories, Inc., Nagakute, Aichi 480-1192
(Received September 27, 2006; CL-061124; E-mail: e1014@mosk.tytlabs.co.jp)
A three-dimensionally ordered array consisting of highly
(a)
(b)
monodispersed nanoporous carbon spheres with a novel star-
burst structure was successfully fabricated via the self-assembly
of mesoporous silica/carbon composite spheres and the subse-
quent dissolution of the silica templates.
1
µm
1 µm
Microporous and/or mesoporous carbons are expected to be
prepared with desired morphologies to meet the requirements of
various applications such as catalyst supports, adsorbents, and
electrode materials. In particular, monodispersed colloidal
porous carbon spheres are of great interest because they can be
applied to construct a three-dimensional structure with high
packing efficiency, and also the diffusion of guest species
through the structure can be tuned by changing the particle
(c)
(d)
Carbon replica
MMSS
(100)
1
,2
diameters and/or pore sizes of the carbon spheres. In addition,
submicrometer-sized carbon spheres with satisfactorily narrow
size distributions have the potential to be used as building blocks
(110)
(200)
100 nm
2
4
6
8
10
3
to fabricate photonic band-gap crystals or other nanodevices.
Although a few reports exist for the synthesis of monodispersed
2
θ
/ deg, Cu K
α
Figure 1. (a) and (b) SEM image of MMSS and their carbon
replicas. (c) TEM image of the carbon sphere. (d) XRD patterns
of MMSS and their carbon replicas.
1
–5
colloidal porous carbon spheres, three-dimensionally ordered
arrays consistiong of the carbon spehres have not yet been suc-
cessfully fabricated.
A nanocasting strategy using monodispersed mesoporous
silica spheres (abbreviated as MMSS hereafter) with radially
6
by polymerization at 423 K in air and subsequent carbonization
at 1173 K in N2 flow. The dissolution of silica templates from the
carbonized sample with hydrofluoric acid resulted in carbon
materials.
7
aligned mesopores that we previously reported is expected to
provide a promising route to obtain highly monodispersed nano-
porous carbon spheres, because the macroscopical morphology
as well as the mesostructure of the silica template is retained
Electron micrograph images and small-angle XRD patterns
of MMSS and their carbon replicas are shown in Figure 1. The
EDX analysis confirmed that the content of residual silica was
less than 0.5% in the carbon replicas. It can be observed from
Figure 1 that the carbon replicas exhibit spherical morphology
with the retention of the high monodispersity. The average diam-
eter and the standard deviation of the carbon replicas were esti-
mated to be 0.66 mm and 2.2%, respectively. The slight decrease
in the average diameter of carbon spheres is attributed to the
shrinkage of the incorporated polymer precursors during carbon-
8
in the carbon replica by the nanocasting. Since MMSS can be
9
self-assembled into a three-dimensionally close-packed array,
the replicated carbon spheres are also assumed to have the poten-
tial to form an ordered array. Furthermore, it is anticipated that
the resulting carbon sphere possesses a novel internal structure
which inversely replicates the radially aligned mesopores of
the MMSS. Herein, we first describe the controlled synthesis
of monodispersed nanoporous carbon spheres with a novel inter-
nal structure by the nanocasting process. Then, we for the fist
time demonstrate the fabrication of a three-dimensionally
close-packed array consisting of the monodispersed nanoporous
carbon spheres.
8
c
ization.
Internal structure of the carbon spheres was clarified by
TEM observation. As shown in Figure 1c, a starburst structure,
which radiates form the center to the circumference, can be
clearly observed in the carbon sphere. This internal structure in-
dicates that the carbon sphere is composed of a radial collection
of carbon nanorods formed inside the radially aligned mesopores
in the silica template. However, we could not observe carbon
nanorods clearly by a high-resolution TEM. This result and the
contrast at the outside of the sphere in Figure 1c suggest that
adjacent carbon nanorods coalesce into bundles and that the
ordered structure in the silica template is thereby not perfectly
retained in the carbon sphere. XRD analysis supported this
suggestion. The small-angle XRD pattern for the carbon spheres
MMSS templates were prepared using a cetyltrimethyl-
ammonium chloride as a templating agent and a tetramethoxy-
silane (TMOS) as a silica source, employing a previously report-
7
ed procedure. The average diameter and the standard deviation
of the silica spheres used in this study were 0.72 mm and 2.5%,
respectively (Figure 1a). In the synthesis of carbon replicas,
1
0
furfuryl alcohol was used as a carbon source. Furfuryl alcohol
was first introduced into MMSS until the incipient wetness was
achieved and subsequently polymerized in air at 423 K. Then,
the sample was heated at 773 K under N2 atmosphere. The
remaining pore was filled with furfuryl alcohol again, followed
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ꢀ
exhibits broad reflections in the 2ꢀ range 2–4 and 4–8
Copyright ꢀ 2006 The Chemical Society of Japan
Nakamura, Tadashi
