Summer Program Report
Prepartion of Silica and Titanium Oxide
Particles by Microwave Method
Han-Lang Wu
Advisor: Prof. Chen-Chi M. Ma
D3, Chemical Engineering, National Tsing-Hua University
2006, Jul. 3 to Sep. 1 stay in Japan
Advisor in Japan: Prof. Yoshiki Chujo
Department of Polymer Chemistry, Kyoto University
mail:
Mobile:
Tel:
Fax:
d913650@oz.nthu.edu.tw
+886 929103102
+886 3 5715131 ext 33694
+886 3 5725924
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Introduction
This is the report of my summer study program in Japan. There are two parts in this
report, which are Experiments and Life & Experiences. I (Han-Lang Wu) am a third
year PhD graduate student of National Tsing-Hua University. My advisor is Prof.
Chen-Chi M. Ma. My major is chemical engineering. I am interested in polymer
chemistry, polymer physics, polymer composites, hybrids and proton exchange
membrane for fuel cell. Because of this summer program, I have a chance to visit Prof.
Chujo’s laboratory, Department of Polymer Chemistry, graduate school of engineering,
Katsura campus, Kyoto University. Current research fields of Prof. Chujo’s laboratory
focus on the development of polymerization reaction, reactive polymer, environmentally
responsible polymer, intelligent polymer, organic-inorganic polymer hybrid, metal
nanoparticle, and template mineralization on the basis of synthetic organic chemistry as
well as inorganic chemistry. There are two other faculties, associate professor, Kensuke
Naka, and assistant professor, Yasuhiro Morisaki in Prof. Chujo’s laboratory. I stayed in
Prof. Chujo’s laboratory from July 3 to September 1.
In this study, microwave was utilized to synthesize spherical particles, which can be
prepared rapidly with uniform sizes. The SiO2 particles were firstly synthesized
following the synthesis with TiO2 precursor in order to form core-shell structure.
Generally, the microwave method is fast, simple, and highly energy efficient. In Prof.
Chujo’s lab they have been used microwave-assisted sol-get method to synthesis hybrid
materials from an organic polymer and a sol-gel precursor. Recently, the microwave
method has been applied to the preparation of metal oxide nanoparticles. For example,
using a microwave assisted polyol method, TiO2 nanocrystallites, SnO2 sols and BaTiO3,
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Ba6Ti17O40, BaZrO3, PbTiO3 nanoparticles have been prepared.1-6 Among the inorganic
particles, TiO2 and its related materials are widely investigated due to its widespread
applications in photovoltaic cells, batteries, separations, sensing, optical emissions,
photonic crystals, catalysis and photo-catalysis, selective adsorption, ion exchange,
ultraviolet blockers, smart surface coatings, and as functional filling materials in textile,
paints, paper, and cosmetics.
Experiments
Synthesis of silica particles by microwave method
Adachi et al. have been firstly proposed synthesis of sub micrometer silica spheres
in non-alcoholic solvent by microwave-assisted sol-gel method.7 The synthesis
procedure is shown below: 40 ml bis(2-methoxymethyl)ether (diglyme), 1 ml
tetramethoxysilane (TMOS) and 0.5 ml 0.1 M HCl solution were added into 50 ml
sample bottle. The mixture was stirred for 1 hour at room temperature. The solution was
poured into 50 ml Teflon beaker. The beaker was put at the center of the microwave
oven and the irradiation power and time. To get the most uniform silica sphere, the
irradiation power is 1000 W for 3 minutes. After being microwave irradiated, the Teflon
beaker was taken out of the microwave oven and cooled down at room temperature. The
white solution was precipitated by centrifuging with 2500 rpm for 30 minutes. The
upper solution was removed and the white product was washed by tetrahydrofuran
(THF). The centrifuge tube was capped with tissue paper and the product was dried
under vacuum at 60 oC.
Fig. 1 is the SEM images of the silica particles by microwave method. Comparing to
the conventional heating method, the silica particles by microwave method are less
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aggregated and their surfaces are fairly flat. Surprisingly, the diameter of these silica
particles is uniform. The diameter of silica particles is depends on the power and the
time of microwave processing. The input energy of Fig. 1(a) and (b) is 180 kJ and 120
KJ, respectively. The higher the input energy, the larger silica particles can be derived.
The average particle size in Fig. 1(a) is 700 nm, while is 400 nm in Fig. 1(b).
The growth of silica particles by microwave method was assumed as the following
steps. Firstly, the silica precursors, TMOS, were reacted to form oligomer during the
stirring at ambient temperature. The oligomer can be regarded as silica seeds. When
these silica seeds were irradiated in the microwave, the energy of microwave was
absorbed at the surface of these slilca seeds directly because of the presence of polarized
silanol groups. The elevated surface energy causes the enhanced reactivity on the
surface of silica seeds that makes TMOS reacted rapidly on it. On the other hand, the
non-alcoholic solvent absorbs lower irradiation energy, so that the solution temperature
is low comparing to that of the surface of silica particles. The temperature difference
leads to the greatly different reactivity between the surface of silica particles and the
solution hence the uniform silica particle sizes were derived. However, in the
conventional heating the temperature was uniform in whole environment, so that the
energy is transferred slowly through the vibration of the solvent molecules and the silica
particle formation is slow. In such case, the silica seeds grow irregularly and the
aggregation is easily occurred.
Synthesis of silica-titanium oxide core-shell particles
The procedure of silica-titanium oxide core-shell particles is described as the
followings. The silica particles are re-dispersed in 50 mL diglyme. 0.5 mL 1M base
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solution (tributylamine) and 1 mL titanium tetraisopropoxide (Ti(OPri)4 or TTIP,
99.999%), which is the precursor of the TiO2, were added into the solution. Tertiary
amines or quaternary ammonium hydroxides were employed as catalysts for
polycondensation in order to ensure a crystalline product. The mixture was stirred at
room temperature for one hour and was further microwave irradiated for 3 minutes with
the power of 1000 W.
Cozolli et al have been found that the easy crystallization process in the mild
conditions (at as low a temperature as 80 °C), which can be attributed to a specific
action played by bulky amines and alkylammonium hydroxides during the synthesis.8
They suggested that amines could promote a chemical reversibility in the Ti-O bonding
formation. The amine/alkoxy or amine/titanyl exchange can occur when the alkoxide
precursors of a partially formed titania network attack the electrophilic titanium center,
therefore, a Ti-O bond breaking and forming. The SEM images of silica/titanium oxide
particles were shown in Fig. 2. Instead of the core-shell structure, the TiO2 precursors
form many cubic structures. As the increase of irradiation time and input power, those
TiO2 cubic particles grow larger and cover the whole surface of silica particles.
The reactivity of silanol is quite lower than that of titanium tetraisopropoxide, hence
the TTIP reacted with itself instead of silanol thus the formation of TiO2 cubic instead
of core-shell structure. At room temperature, TTIP solution turns from transparent
liquid to white solid in short times. Even quickly inject TTIP into diglyme, the small
and transparent particles can be found in the solution. Besides, the crystalline of TiO2
restricts the formation of sphere shape, i.e. growing randomly. The crystalline can be
investigated via X-ray diffraction.
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Conclusion
In this study, the silica particles with uniform diameter have been synthesized by
microwave-assisted sol-gel method. Effects of the input power and the irradiated time
have been discussed. In this stage, the core-shell silica-titanium oxide structure has not
been synthesized successfully, but it is the good beginning to study this issue.
References
1. W. Wang, B. H. Gu, L. Y. Liang, and W. A. Hamilton, J. Phys. Chem. B, 107,
12113 (2003)
2. J. E. G. J. Wijnhoven and W. L. Vos, Science, 281, 802 (1998)
3. P. Jiang, J. F. Bertone, and V. L. Colvin, Science, 291, 453 (2001)
4. O. D. Velev and E. W. Kaler, Adv. Mater., 12, 531 (2000)
5. Y. N. Xia, B. Gates, and Z. Y. Li, Adv. Mater., 13, 409 (2001).
6. W. Stober and A. Fink, J. Colloid Interface Sci., 26, 62 (1968).
7. K. Adachi, T. Iwamura, Y. Chujo, Chem. Lett., 33, 1504 (2004)
8. P. D. Cozzoli, A. Kornowski, H. Weller, J/ Am. Chem. Soc., 125, 14539.
(2003)
9. Chemseddine, A.; Moritz, A. Eur. J. Inorg. Chem., 235. (1999)
10. Bischoff, B. L.; Anderson, M. A. Chem. Mater., 7, 2. (1995)
11. Murakami, Y.; Matsumoto, T.; Takasu, Y. J. Phys. Chem. B, 103, 1836.
(1999)
12. Poznyak, S. K.; Talapin, D. V.; Kulak, A. I. J. Phys. Chem. B, 105, 4816.
(2001)
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(a) 1000 W, 3 minutes
(b) 500 W, 4 minutes
Fig. 1. The silica particle by microwave irradiation.
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(a) 500 W, 4 minutes
(b) 1000 W, 3 minutes
Fig. 2. The silica/titanium oxide particles by microwave method.
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Life & Experiences
This is my first time to visit Japan and also my longest time for me to stay abroad
that I have ever been. Japan is really a clean and fine country. People work very hard at
there. Japanese students are very cooperative, they like to work together.
In Japan, there are three teachers in one laboratory. Generally, they are professor,
associate professor and assistance professor. In Prof. Chujo’s laboratory, they are around
20 graduate students; the ratio of teacher to student is high, so that students at there can
get more time to discuss with their teachers.
The facilities in Prof. Chujo’s laboratory are very good. They have nuclear magnetic
resonance (NMR), gel permeation chromatography (GPC), mass-gas chromatography
(GC-mass), scanning probe microscopy (SPM), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), X-ray diffraction (XRD), polymer crystalline
measurements, infrared spectroscopy (IR), differential scanning calorimeter (DSC), etc.
In Taiwan, one laboratory could not have so many equipment. It is very suitable for
doing experiments in Japan.
In addition, the Katsura campus of Kyoto University is very beautiful. This campus
is on the mountainside, one can view the whole Kyoto city in Katsura campus. The
night view of Kyoto city is also very nice. The landmark in Katsura campus is its clock
tower. This clock tower has LED display, which has high brightness.
The meals in the student restaurant are delicious. There are so many dishes such as
pork, beef, chicken, fish, noodles, etc. The environment of restaurant is also good.
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Because Japanese food and Taiwanese food are not so different, there is no problem for
me to get use to Japanese food.
Acknowledgement
So many people and organizations I want to acknowledge. First of all, I would like
to thank Interchange Association Japan (IAJ) and National Science Council (NSC) for
their financial support. Thanks to my advisor, Prof. Ma, for allowing me to stay two
months in Japan. I also want to thank Ms. Tsunoda-san and Ms. Yokoi-san for their
kindly help. Still, I would like to appreciate Kokado-san for the assistance on my
experiments. A lot of thanks are giving to Wada-san, Inagi-san, Ouchi-san and
Nakahashi-san for taking me to many interesting places. I really have fun with all of
you. Thank you, Nakamura-san, for teaching me Japanese, taking me home after mini
soccer games, playing table tennis with me. I would also like to acknowledge Saito-san
for introducing such beautiful city, Kobe, to me. Furthermore, I would like to thank
Fujita-san for many pleasant talking. Special thanks are giving to Huang-san and
Lin-san. I feel comfortable to stay in this foreign place, Japan, because I can talk with
you in Chinese. In addition, I am appreciated Dr. Lee of MRL, ITRI for introducing me
to Prof. Chujo, so that I can have these wonderful days in Japan.
Last but not the least, I would like to dedicate much thanks to Prof. Chujo for giving
me so nice research environment and thoughtful care. I really learned and enjoyed a lot,
thank you very much.
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