Advanced Materials Research Vol 1112 (2015) pp 172-175
© (2015) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.1112.172
Submitted: 2014-09-02
Revised: 2015-02-10
Accepted: 2015-02-10
Synthesis of Mesoporous Silica Particles with Fibrous Morphology via
Self-Assembly Process in Micromulsion System
Erna Febriyanti1,Rino R. Mukti1,2,a, Veinardi Suendo1,2, I Nyoman Marsih1,
Sugeng Triwahyono3, Suryadi Ismadji4 and Ismunandar1
1
Division of Inorganic and Physical Chemistry, Faculty of Mathematics and Natural Sciences, Institut
Teknologi Bandung, Jln. Ganesha No. 10, Bandung40132, Indonesia
2
Center for Advanced Sciences, Institut Teknologi Bandung, Jln. Ganesha No. 10, Bandung 40132,
Indonesia
3
Ibnu Sina Institutefor Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM
Johor Bahru,Malaysia
4
Department of Chemical Engineering, Widya Mandala Surabaya Catholic University, Kalijudan 37,
Surabaya 60114, Indonesia
a
rino@chem.itb.ac.id
Keywords: silica particle, mesoporous, fibrous morphology, self-assembly, microemulsion
Abstract. In this research, several precursors were chosen to solve the drawbacks of using toxic and
expensive chemicals in the synthesis of fibrous mesoporous silica particle via self-assembly process
in microemulsion system. The synthesis of this emerging material normally is realized by using toxic
cetylpyridinium bromide (CPB) as common structure directing agent in conjunction with combined
cyclohexane and n-pentanol as expensive solvent and co-solvent, respectively. Less toxic
cetyltrimethylammonium bromide (CTAB) can be the replacement for CPB but the use of this
surfactant may drastically reduce the surface area of the resulting product. Herein, we report that the
use of CTAB with combined toluene and n-butanol as affordable solvents can be used to synthesize
fibrous mesoporous silica particle with high surface area. The material was well characterized by field
emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), N2
adsorption/ desorption, X-ray difraction (XRD)and thermal gravimetry (TG). This material might be
applied in potential applications such as catalysis, drug delivery and adsorption. Moreover, it can be
used as a hard-template for fabricating another novel fibrous materials.
Introduction
The need of material with high surface areas host to guest molecule is one of great importance to
improve the performance of catalyst system [1,2,3], drug release properties [4], wide-bandgap oxide
nanomaterials performance [5], and gas-sensing properties [6]. This can be realized by introducing a
highly distribution of mesopore within the internal surface of material or by modifying the
morphology into fibrous-type in nanometer scale. Nowadays, a family of mesoporous silica particles
can possess both of latter properties. The realm of mesoporous silica materials is getting more
advance after the discovery of fibrous silica nanosphere (KCC-1) [1]. The unique fibrous morphology
is believed to be responsible for its superior activity and stability as catalyst support for some essential
reactions [7-8].
The synthesis of this fibrous mesoporous material involves surfactant as template molecules, with
cetylpyridinium bromide (CPB) as the most common. Additionally, the preparation uses two kinds of
organic solvent with different composition. Typical synthesis uses cyclohexane and n-pentanol as
solvent and cosolvent, respectively. The synthesis modification was done by replacing those
precursors. Gai and co-workers [9] showed that the substitution of CPB with less toxic
cetyltrimethylammonium bromide (CTAB) could result in bigger KCC-1 particles (730 nm) but
displaying a very low surface area (77 m2g-1). In the present work, newly combined precursors were
chosen in the synthesis of fibrous mesoporous silica to solve the drawbacks of using toxic and
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expensive chemicals as well as to improve the final product to have a high surface area. The fibrous
mesoporous silica particle was synthesized via self-assembly process in microemulsion system
implementing CTAB as less toxic chemical than CPB and also replacing the cyclohexane and
n-pentanol with toluene, n-butanol as affordable solvent and co-solvent, respectively.
Experimental
Figure 1 illustrates the formation of fibrous mesoporous silica particle by self-assembly process
using mild solvothermal treatment. In a typical synthesis, 0.7 mL of n-butanol was dissolved in 17 mL
of toluene, followed by adding 1.456 g (6.9 mmol) of tetraethyl orthosilicate (TEOS). Subsequently, a
solution containing 0.552 g (1.5 mmol) of CTAB, 0.346 g of urea and 17.3 mL of deionized water was
quickly mixed into the first solution. After vigorous stirring for 30 min, the mixture was transferred
toTeflon-lined autoclave with capacity of 100 mL and heated at 120 °C for 4 h. The resulting solid
was isolated by centrifugation, washed with deionized water, acetone and dried in air for 24 h. Finally,
the as-synthesized material was then calcined at 550 °C for 6 h in air.
Fig. 1 Schematic formation of mesoporous silica particle with fibrous morphology by self-assembly
process. (a) TEM image and (b) XRD pattern with FE-SEM image as inset of resulting material.
The morphology of material was characterized by field emission scanning electron microscopy
(FE-SEM, JSM-6701F) and transmission electron microscopy (TEM, JEOL JEM 1400). The surface
area and mesoporosity were obtained by calculating the N2 adsorption-desorption isotherm using
Brunauer-Emmet-Teller,BET (P/Po range of 0.05 to 0.25) and NL-DFT model, respectively. The
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isotherm was measured using Autosorb iQ-MP, a Quantachrome instrument. The lattice ordering was
measured in low angle of 2-Theta by powder X-ray difraction (XRD, Rigaku Ultima III) equipped
with Cu Kα X-ray source. The sample was measured by thermogravimetry (TG, NETZSCH STA
449F1) with heating rate of 10 °C min-1 to reveal the combustion profile and obtain the maintained
weight percentage. Powder X-ray difraction pattern were measured by using a Rigaku Ultima III
Instrument equipped with Cu Kα X-ray source.
Result and Discussion
FE-SEM image revealed the fibrous morphology in the uniform spherical particles of calcined
sample and TEM image further verified the presence of fibers grown from the center of spherical
particle (Figure 1). The material posseses spherical particles with diameter range from 250 to 450 nm.
A highly magnified observation shows that the dendrimeric-type fibers is present which are linked
and arranged to form spheres with open pore channels and complex three dimensional morphology.
However, the fibers were not clearly seen in the FE-SEM image which may due to the high density of
linked fibers.The observed fibrous morphology has a wavy structure rather than a straight fibrous in
comparison to the previous reports [1,9].
The broadened diffraction pattern in the low angle of 2-Theta confirms the lattice ordering from the
narrow mesoporosity within the amorphous silica network (Fig. 1b).The BET surface area was found
to be higher that that of sample reported in literature by having this combined CTAB, toluene, and
butanol (Table 1). However, the current surface area is lower than that of the origin KCC-1
synthesized using CPB surfactant (550 m2g-1)[1]. The mesopore size distribution estimated by
NL-DFT method reveals the presence of uniform pores centered at 3.2 nm.We also would like to
further investigate the contribution of small microporosity that may exist in the concentrically wall of
the linked fibers.
Table 1. Textural parameters of fibrous silica particles prepared by using CTAB as template
SBET
Vtotal
Average diameter of Pore size
Ref.
Sample
(m2g-1) (cm3g-1)
particles (nm)
(nm)
Fibrous silica
508
0,929
350
3,2
Current work
Ibrous silica
77
0,093
730
8,9
9
Fig. 2 TG curve of theas-synthesized fibrous mesoporous silica particle.
The as-synthesized sample was analyzed by thermogravimetry from room temperature to 900 °C
(Figure 2). A weight loss of up to 24 % was observed and the material shows a slight weight loss (~
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175
4%) below 120 °C that corresponds to the desorption of physisorbed water (or ethanol and butanol) in
the voids within the particle aggregation. Above 120 °C, cleavage of organic fragments seem to occur
and the large (~ 14%) weight change at 120-350 °C is attributed to the lost of occluded water (and
ethanol molecules) or the thermodesorption of alkyl chains resulting from the surfactant
decomposition. Above 350 °C, combustion of residual organics occurs in a small quantity (~ 4%
weight lost) and the last 2 % weight lost at above 450 °C might be attributed to the water lost from the
dehydroxilation at the silicate surface [10]. From this experiment, it appears that the resulting fibrous
mesoporous silica particle displays a good thermal stability, however further investigation needs
to be carried out.
Conclusion
In summary, mesoporous silica particles with fibrous morphology was successfully synthesized via
self-assembly process using solvothermal treatment. The resulting material shows a remarkable
surface area if compared to the sample reported in literature under similar precursor, i.e. CTAB as
structure-directing agent. The key to this success is to replace the cyclohexane and n-pentanol with
toluene and n-butanol as the affordable solvent and co-solvent. As this material is very promising for
various applications due to its unique fibrous morphology, further investigation shall be carried out to
reveal the formation mechanism as well as to find other uses that leads to a scientific breakthrough.
Acknowledgement
We acknowledge partial financial support from theAsahi Foundation-Japan program and “Program
Riset dan Inovasi ITB 2014”. EF is grateful for receiving a scholarship under PMDSU program from
the Higher Educational Ministry of Indonesia.
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