Low-cost and facile synthesis of mesocellular carbon foams

Article abstract of DOI:10.1039/b208642e

Mesocellular carbon foam composed of nanometer sized primary particles was synthesized using hydrothermally synthesized MSU-F silica as a template and poly(furfuryl alcohol) as a carbon source.

Full text of DOI:10.1039/b208642e

Low-cost and facile synthesis of mesocellular carbon foams†
Jinwoo Lee, Kwonnam Sohn and Taeghwan Hyeon*
National Creative Research Initiative Center for Oxide Nanocrystalline Materials and School of Chemical
Engineering, Seoul National University, Seoul 151-744, Korea. E-mail: thyeon@plaza.snu.ac.kr
Received (in Cambridge, UK) 4th September 2002, Accepted 30th September 2002
First published as an Advance Article on the web 16th October 2002
Mesocellular carbon foam composed of nanometer sized
primary particles was synthesized using hydrothermally
synthesized MSU-F silica as a template and poly(furfuryl
alcohol) as a carbon source.
mesocellular carbon foams composed of nanometer-sized
primary particles, designated as C-nano-MSU-F, using MSU-F
silicas as templates, and through the use of a simple incipient
wetness method using furfuryl alcohol. This MSU-F silica, with
nanometer-sized primary particles, was synthesized by means
of a modified version of the original synthetic procedure,
employing post hydrothermal treatment at 100 °C. The
nanometer-sized primary particles should allow better diffusion
of large molecules to the active sites in the framework pores.
For the purposes of comparison, we also synthesized mesocel-
lular carbon foams using MCF silicas as templates and furfuryl
alcohol as the carbon precursor.
MSU-F was synthesized following the procedure reported by
Kim et al.,10 except for the application of additional hydro-
thermal treatment at 100 °C for 24 h. After calcination at 550 °C
for 4 h, alumination (Si/Al = 20) was performed, by means of
the impregnation method, to generate acidic catalytic sites for
the polymerization of furfuryl alcohol inside the mesopores. In
a typical synthesis, 1 g of AlMSU-F is wetted with 2 ml furfuryl
alcohol using the incipient wetness technique, and is then
polymerized at 85 °C for 24 h. The resulting AlMSU-F/
poly(furfuryl alcohol) composite is heated at 850 °C for 3 h
under a nitrogen atmosphere. The dissolution of the AlMSU-F
template using 3 M NaOH at 100 °C generates the mesocellular
carbon foam designated as C-nano-MSU-F.
Mesoporous carbons have attracted much attention because of
their use as catalyst supports, adsorbents for bulky pollutants,
and electrode materials.1 Recently, new mesoporous carbons
with connected pores have been synthesized using mesoporous
silica materials as nano-scale templates.2 Following the de-
signed synthesis of MCM-48 templated mesoporous carbons by
our group and by others, numerous ordered and disordered
mesoporous carbons with connected pore structures have been
synthesized using various mesoporous silicas as templates. To
date, cubic,2a disordered,2b hexagonal,2c and foam-like2d me-
sostructured carbon materials have been synthesized. This
technique of carbonization inside the pores of mesoporous
materials has also allowed the elucidation of their pore
structures. The 3-D wormhole-like pore structure in HMS
silica3 and the presence of complementary pores inside the
channel walls of SBA-15 silica4 were elucidated using this
procedure. These novel mesoporous carbons have been success-
fully employed as electrodes for electrochemical double-layer
capacitors5 and fuel cells.6 They have also been used as catalyst
supports in the process of hydrogenation.7 Generally, the pore
sizes of these mesoporous carbons are limited by the wall
thickness of the template silica materials, because these pores
are generated from the dissolution of the silicate framework.
Controlling the wall thickness of mesoporous silica has turned
out to be a very difficult challenge, and the wall thickness is
generally in the range of 2U4 nm.8 In order to permit the facile
diffusion and reaction of bulky molecules, mesocellular carbon
foams with pore size ranging from 20 nm to 30 nm were
synthesized by our group through the controlled incorporation
of a carbon precursor (phenol resin) selectively into the
complementary pores of the mesocellular silica foam templa-
tes.2d Although the mesocellular silica foam (MCF),9 developed
by Stucky and his coworkers, was successfully utilized as a
template for mesocellular carbon foams, MCF is synthesized
under strongly acidic conditions using an expensive silica
source, TEOS. It is preferable to have a low-cost route for
manufacturing silica templates, because the template has to be
sacrificed when synthesizing the templated carbons. Recently,
the preparation of C-MSU-H10 was reported, whose structure is
identical to that of the CMK-3 carbons, using MSU-H silicas11
as templates. Because MSU-H is synthesized under neutral
conditions using inexpensive sodium silicate as the silica
source, the preparation of C-MSU-H is very cost-effective. The
structure of MSU-F11 is similar to that of MCF, and MSU-F is
also synthesized under neutral conditions using inexpensive
sodium silicate as the silica source. In our previous study, MCF
carbons were synthesized by means of the vapor-phase
infiltration of phenol, which is not a suitable method for large-
scale production. Herein, we demonstrate the preparation of
Fig. 1 shows the N2 isotherms and pore size distributions of
C-nano-MSU-F and MCF-carbon calculated using the BJH
(BarrettUJoynerUHalenda) method. There are two types of pores
which can be distinguished in C-nano-MSU-F. These are the 22
nm cellular pores and the 3.6 nm disordered pores. The BET
surface area and single point total pore volume at P/Po = 0.98
are 716 m2 g21 and 1.12 cm3 g21, respectively. The cellular
pores of the AlMSU-F template were preserved during the
Fig. 1 N2 adsorption (filled circles) and desorption (empty circles)
isotherms of (a) C-nano-MSU-F and (b) MCF-carbon. Corresponding pore
size distributions of (c) C-Nano-MSU-F and (d) MCF-carbon, calculated
from the BJH method.
† Electronic supplementary information (ESI) available: N2 adsorptionUde-
sorption isotherms, TEM and SEM images. See http://www.rsc.org/
suppdata/cc/b2/b208642e/
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CHEM. COMMUN., 2002, 2674–2675
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synthesis, because the furfuryl alcohol was polymerized around
the acidic sites present in the surface of the AlMSU-F silicas. In
contrast to CMK-5,6 which is made using a similar method, it is
not required that the unpolymerized furfuryl alcohol (FA) be
removed before carbonization. The unpolymerized FA seems to
be removed during heat treatment under an N2 atmosphere. The
3.6 nm pores were generated by the dissolution of the silicate
framework. MCF-carbon, synthesized using MCF silica as a
template, also has 22 nm cellular pores and 4 nm disordered
pores. The BET surface area and single point total pore volume
of the MCF-carbon at P/Po = 0.98 are 893 m2 g21 and 1.46 cm3
g21, respectively.
Fig. 3 Scanning electron microscopic images (SEM) of C-nano-MSU-F (a)
and MCF-carbon (b).
Fig. 2 shows transmission electron microscopic images
(TEM) of C-nano-MSU-F and MCF-carbon. At low magnifica-
tions, the difference between C-nano-MSU-F and MCF-carbon
is significant. The individual particles of C-nano-MSU-F are
much smaller than those of MCF-carbon. The individual
particle size of C-nano-MSU-F is around 300 nm. The presence
of individual particles with a small size is highly desirable in
mesoporous materials, because this favours the approach of
large molecules to the framework pores. At higher magnifica-
tions, the two mesocellular carbons (C-nano-MSU-F and MCF-
carbon) exhibit very similar pore structures. Both carbons have
~ 20 nm sized cellular pores and ~ 4 nm sized disordered pores.
As expected, the smaller individual particle size of C-nano-
MSU-F, compared to that of MCF-carbon, is derived from the
smaller individual particle size of the MSU-F template in
comparison to that of the MCF template (ESI† 2).
C-nano-MSU-F is comprised of 200U300 nm particles, while
MCF-carbon is comprised of micrometer sized particles.
In conclusion, mesocellular carbon foams comprised of
nanometer sized particles were fabricated using furfuryl alcohol
as a carbon source and hydrothermally synthesized MSU-F
silicas as templates. These mesocellular carbon foams possess
large cellular pores ( ~ 20 nm) and disordered uniform pores
( ~ 4 nm), and are composed of nanometer sized primary
particles. This combination of factors facilitates the diffusion of
large molecules within these materials, thereby rendering them
more effective for applications in catalysis and adsorption. The
availability of an inexpensive and facile synthetic method for
this novel mesocellular carbon foam will undoubtedly trigger
research into its practical applications.
We are grateful to the Korea Research Foundation (KRF-
2001-041-D00172) for financial support.
The smaller size of the individual particles in C-nano-MSU-F
is confirmed by the scanning electron microscopy (SEM)
images of C-nano-MSU-F (a) and MCF-carbon (b) (Fig. 3). The
Notes and references
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Fig. 2 Transmission electron micrographic images (TEM) of C-nano-MSU-
F (a, b) and MCF-carbon (c, d).
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