- Email: [email protected]
Preparation of Monodispersed Iron Nanoparticles by Thermal Decomposition
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications
Preparation of Monodispersed Iron Nanoparticles by Thermal Decomposition SHAD Hui-ping ', LEE Hyo-Sook", SUH Yong-Jae 2 , KIM Jong-Hee', LI Ying4 , KIM Chong-Oh' (I. Department of Materials Science and Engineering, Chungnam National University, Daejeon 305-764, Korea;
2. Nano-materials Group, Korea Institute of Geoscience and Mineral Resources, Daejeon, 305-350, Korea; 3. Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon 305-764, Korea; 4. School of Materials Science and Engineering, Shanghai University, Shanghai, 200072 China)
Abstract: Monodispersed iron nanoparticles were prepared by thermal decomposition of iron carbonyl at low temperatures of 160-180 'C in kerosene. The iron nanoparticles were spherical and their average size was decreased from 11.2 nm to 8.6 nm with increasing decomposition temperatures in the range of 160 'C to 180 ·C. The as-prepared iron nanoparticles were amorphous, but the surface of the particles was easily oxidized to be spinel structured.
Key words: iron nanoparticle; iron carbonyl; thermal decomposition; low temperature
1 Introduction
cially available, which were used without further puri-
Nanometer-sized particles have been attracting an
fication. Iron carbonyl and oleylamine were purchased
ever growing interest over the last decades!", Par-
from Aldrich, kerosene and n-hexane from Junsei. The
ticularly, magnetic nanoparticles exhibiting single-
experimental setup for thermal decomposition is
domain magnetism can be used in magnetic tapes,
schematically shown in Fig.l. The experimental
ferrofluids, magnetic refrigerants, ultrahigh-density
process is as follows: 90 mL kerosene (d=0.80, bp:
magnetic recording media[2] and biomedical appli-
180-190 'C) as a solvent and 2 rnL (0.0425 M)
cations, such as magnetic resonance imaging, cell and
oleylarnine (d=0.813, 70%) as a surfactant were mixed
DNA separation, drug delivery, gene cloning, and
together in a four-distillation flask of 250 rnL, and the
hyperthermia for cancer therapy, because of their size less than single magnetic domain [3.4]. The nano-
high purity N 2 gas was flushed into the flask for 10 min to eliminate O2. The flask was heated to the decom-
particles have been synthesized in a variety of methods
position temperatures of 160-180 'C, and then iron
ranging from sputtering, chemical vapor deposition,
pentacarbonyl [Fe(COh] was added to react for 60 min.
sonochemistry, decomposition
A circulatory water condenser was attached on the
and [5-8].
salt reduction to thermal A strong magnetic interaction
flask, and the high purity N2 was flushed through the
among iron particles makes it difficult to form stable
system during all experimental processes.
colloids. Therefore, it is very important to select a
finishing the reaction, the magnetic particles were well
suitable surfactant to coat the particles. In this work,
dispersed to fluidize. The synthesized particles were
iron nanoparticles were synthesized by thermal decom-
obtained by washing the as-prepared magnetic fluid
position of iron carbonyl at low temperatures below
with n-hexane and acetone to remove the surfactant.
180 ·C. Also oleylamine and kerosene were used as
The particles were dried in a vacuum and characterized
surfactant and solvent, respectively.
using
transmission
vibrating
2 Experimental
sample
electron
microscope
magnetometer
(VSM),
After
(TEM), X-ray
diffraction (XRD) analyzer, and high resolution TEM
All reagents were of an analytical grade commer-
(HRTEM).
-205-
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications
nanoparticles. At the same other reaction conditions, the nucleation rate was faster with higher concentrations of the precursor solution. On the contrary, large particles were formed at lower concentrations of the precursor solution. If the whole of precursor were fast decomposed, the most part take part in nucleation, forming a large number of particles with very small size. If the precursor were slowly decomposed for several steps, the first added precursor is attended by the nucleation of particles, and the subsequently added precursor by the growth instead of the nucleation; i.e., large particles are partly formed as well as small particles. Therefore, the concentration of precursor is a very important factor in growing the particle size. FigA shows TEM images of the iron particles prepared with different injection steps at the same precursor concentration. When the precursor was (I) High purity N2 flow tube; (4) Stirrer;
(2) Thermocouple;
injected in once, the size of the prepared particles was
(3) Water condenser;
almost homogeneous, whereas when it was injected in
(5) Temperature controller
Fig. 1 Schematic diagram of experimental setup for thermal decomposition
3 Results and Discussion Fig.2 shows TEM images of the iron nanoparticles obtained with 0.296 M iron carbonyl and 0.0425 M oleylamine at the decomposition temperatures of 160 °C and 180 °C for 60 min. The average particle size was decreased from 11.2 nm to 8.6 nm (counted with 220-280 particles) as increasing the temperature from 160 °C to 180 °C. This means that in such a range of the decomposition temperature, the nucleation rate was much more sensitive to temperature change compared with the growth rate. Therefore, the average particle size became smaller at higher temperatures. Also, the shape of synthesized iron particles was spherical and their size was uniformly distributed. Fig.3 shows the magnetization curves
of
the
iron
nanoparticles
obtained
at
decomposition temperatures of 160 °C and 180 °C. All of the iron nanoparticles exhibited superparamagnetic behavior. The saturation magnetization value of the iron nanoparticles was decreased from 193.26 emu/g to 167.66 emu/g with increasing the decomposition temperatures.
(a) 160 'C;
The precursor concentration was directly related to the nucleation and growth rate of the iron -206-
(b) 180'C
Fig. 2 TEM images of iron nanoparticles prepared at different decomposition temperatures
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications
1BO'C(a}
200
(a) (b)
180'C(b)
1SO
This size distribution is attributed to the secondary nuclei formed by the second injection. Fig.5 shows HRTEM image of the iron particles.
HlO
~ E
so
~
"
0
'"111 '" Q)
twice, small particles existed among large particles.
-50
The inside of the iron particles was amorphous, but
"~ -100 '"
their surface structure was spinel crystalline. The surface of the particles should be partly oxidized to
-,so -200 -10000
-5000
5000
ioooo
magnetic field (De)
become iron oxide during carrying out the analysis. A selected-area electron diffraction (SAED) is also shown in the inset of Fig.5. Fig.6 shows XRD patterns
Fig. 3 Magnetization curves of iron nanopartic1es prepared at different decomposition temperatures
of the iron nanoparticles synthesized with 0.0425 M oleylamine and without oleylamine. The particles obtained without oleylamine formed the iron crystal (BeC), but the iron nanoparticles coated with oleylamine appeared amorphous.
450 400 350
(110)
300
?;o 250 ·iii
.! 200
without surfactant
.s
150 100 50
0 10
20
30
40
50
60
70
60
90
2 theta
Fig. 4 TEM images of iron nanopartic1es obtained from iron carbonyl injected (a) in once and (b) in
Fig. 6 XRD patterns of iron nanopartic1es prepared with
twice
0.0425 M oleylamine and without oleylamine
4 Conclusions The iron nanoparticles were successfully prepared by thermal decomposition using kerosene solvent at low temperatures below 180 'C. The shape of as-prepared particles was spherical. An average size of the particles was decreased from 11.2 nm to 8.6 nm with increasing decomposition temperatures in the range of 160 'C to 180 'C, and their corresponding saturation magnetization was also decreased from
Fig. 5 HRTEM image of as-prepared iron nanopartic1es
193.26 emu/g to 167.66 emu/g. The phase of the iron particles was amorphous, but their surface was easily oxidized in air to become a spinel-structured iron oxide. -207-
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications (2002) 289.
References: [1]
[6]
C. Petit, S. Rusponi, and H. Brune, J. Appl. Phys., 95 (8) (2004) 4251.
F. Guo, H. Zheng, Z. Yang, Y. Qian, Mater. Lett., 56 (2002) 906.
[7]
S. Wirth, S. von Molnar, M. Field, and D. D. Awschalom, J.
[2]
L. Bronstein, E. Kramer, B. Berton, C. Burger, S. Forster,
[3]
C. Liu, T. J. Klemmer, N. Shukla, X. Wu, D. Weller, M.
Bhattacharya, Y. Yeshurun, and 1. Felner, J. Magn. Magn.
Tanase, D. Laughlin, J. Magn. Magn. Mater., 266 (2003) 96.
Mater., 268 (2004) 95.
M. Antonietti, Chern. Mater., 11 (1999) 1402.
[4]
Appl. Phys., 85 (8) (1999) 5249. [8]
N. Wu, L. Fu, M. Su, M. Aslam, K. C. Wong, and V. P. Dravid, NanoLetters, 4 (2) (2004) 383.
[5]
C. J. Choi, O. Tolochko, B. K. Kim, Materials Letters, 56
-208-
M. Sivakumar, A. Gedanken, W. Zhong, Y. W. Du, D.
Preparation of Monodispersed Iron Nanoparticles by Thermal Decomposition SHAD Hui-ping ', LEE Hyo-Sook", SUH Yong-Jae 2 , KIM Jong-Hee', LI Ying4 , KIM Chong-Oh' (I. Department of Materials Science and Engineering, Chungnam National University, Daejeon 305-764, Korea;
2. Nano-materials Group, Korea Institute of Geoscience and Mineral Resources, Daejeon, 305-350, Korea; 3. Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon 305-764, Korea; 4. School of Materials Science and Engineering, Shanghai University, Shanghai, 200072 China)
Abstract: Monodispersed iron nanoparticles were prepared by thermal decomposition of iron carbonyl at low temperatures of 160-180 'C in kerosene. The iron nanoparticles were spherical and their average size was decreased from 11.2 nm to 8.6 nm with increasing decomposition temperatures in the range of 160 'C to 180 ·C. The as-prepared iron nanoparticles were amorphous, but the surface of the particles was easily oxidized to be spinel structured.
Key words: iron nanoparticle; iron carbonyl; thermal decomposition; low temperature
1 Introduction
cially available, which were used without further puri-
Nanometer-sized particles have been attracting an
fication. Iron carbonyl and oleylamine were purchased
ever growing interest over the last decades!", Par-
from Aldrich, kerosene and n-hexane from Junsei. The
ticularly, magnetic nanoparticles exhibiting single-
experimental setup for thermal decomposition is
domain magnetism can be used in magnetic tapes,
schematically shown in Fig.l. The experimental
ferrofluids, magnetic refrigerants, ultrahigh-density
process is as follows: 90 mL kerosene (d=0.80, bp:
magnetic recording media[2] and biomedical appli-
180-190 'C) as a solvent and 2 rnL (0.0425 M)
cations, such as magnetic resonance imaging, cell and
oleylarnine (d=0.813, 70%) as a surfactant were mixed
DNA separation, drug delivery, gene cloning, and
together in a four-distillation flask of 250 rnL, and the
hyperthermia for cancer therapy, because of their size less than single magnetic domain [3.4]. The nano-
high purity N 2 gas was flushed into the flask for 10 min to eliminate O2. The flask was heated to the decom-
particles have been synthesized in a variety of methods
position temperatures of 160-180 'C, and then iron
ranging from sputtering, chemical vapor deposition,
pentacarbonyl [Fe(COh] was added to react for 60 min.
sonochemistry, decomposition
A circulatory water condenser was attached on the
and [5-8].
salt reduction to thermal A strong magnetic interaction
flask, and the high purity N2 was flushed through the
among iron particles makes it difficult to form stable
system during all experimental processes.
colloids. Therefore, it is very important to select a
finishing the reaction, the magnetic particles were well
suitable surfactant to coat the particles. In this work,
dispersed to fluidize. The synthesized particles were
iron nanoparticles were synthesized by thermal decom-
obtained by washing the as-prepared magnetic fluid
position of iron carbonyl at low temperatures below
with n-hexane and acetone to remove the surfactant.
180 ·C. Also oleylamine and kerosene were used as
The particles were dried in a vacuum and characterized
surfactant and solvent, respectively.
using
transmission
vibrating
2 Experimental
sample
electron
microscope
magnetometer
(VSM),
After
(TEM), X-ray
diffraction (XRD) analyzer, and high resolution TEM
All reagents were of an analytical grade commer-
(HRTEM).
-205-
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications
nanoparticles. At the same other reaction conditions, the nucleation rate was faster with higher concentrations of the precursor solution. On the contrary, large particles were formed at lower concentrations of the precursor solution. If the whole of precursor were fast decomposed, the most part take part in nucleation, forming a large number of particles with very small size. If the precursor were slowly decomposed for several steps, the first added precursor is attended by the nucleation of particles, and the subsequently added precursor by the growth instead of the nucleation; i.e., large particles are partly formed as well as small particles. Therefore, the concentration of precursor is a very important factor in growing the particle size. FigA shows TEM images of the iron particles prepared with different injection steps at the same precursor concentration. When the precursor was (I) High purity N2 flow tube; (4) Stirrer;
(2) Thermocouple;
injected in once, the size of the prepared particles was
(3) Water condenser;
almost homogeneous, whereas when it was injected in
(5) Temperature controller
Fig. 1 Schematic diagram of experimental setup for thermal decomposition
3 Results and Discussion Fig.2 shows TEM images of the iron nanoparticles obtained with 0.296 M iron carbonyl and 0.0425 M oleylamine at the decomposition temperatures of 160 °C and 180 °C for 60 min. The average particle size was decreased from 11.2 nm to 8.6 nm (counted with 220-280 particles) as increasing the temperature from 160 °C to 180 °C. This means that in such a range of the decomposition temperature, the nucleation rate was much more sensitive to temperature change compared with the growth rate. Therefore, the average particle size became smaller at higher temperatures. Also, the shape of synthesized iron particles was spherical and their size was uniformly distributed. Fig.3 shows the magnetization curves
of
the
iron
nanoparticles
obtained
at
decomposition temperatures of 160 °C and 180 °C. All of the iron nanoparticles exhibited superparamagnetic behavior. The saturation magnetization value of the iron nanoparticles was decreased from 193.26 emu/g to 167.66 emu/g with increasing the decomposition temperatures.
(a) 160 'C;
The precursor concentration was directly related to the nucleation and growth rate of the iron -206-
(b) 180'C
Fig. 2 TEM images of iron nanoparticles prepared at different decomposition temperatures
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications
1BO'C(a}
200
(a) (b)
180'C(b)
1SO
This size distribution is attributed to the secondary nuclei formed by the second injection. Fig.5 shows HRTEM image of the iron particles.
HlO
~ E
so
~
"
0
'"111 '" Q)
twice, small particles existed among large particles.
-50
The inside of the iron particles was amorphous, but
"~ -100 '"
their surface structure was spinel crystalline. The surface of the particles should be partly oxidized to
-,so -200 -10000
-5000
5000
ioooo
magnetic field (De)
become iron oxide during carrying out the analysis. A selected-area electron diffraction (SAED) is also shown in the inset of Fig.5. Fig.6 shows XRD patterns
Fig. 3 Magnetization curves of iron nanopartic1es prepared at different decomposition temperatures
of the iron nanoparticles synthesized with 0.0425 M oleylamine and without oleylamine. The particles obtained without oleylamine formed the iron crystal (BeC), but the iron nanoparticles coated with oleylamine appeared amorphous.
450 400 350
(110)
300
?;o 250 ·iii
.! 200
without surfactant
.s
150 100 50
0 10
20
30
40
50
60
70
60
90
2 theta
Fig. 4 TEM images of iron nanopartic1es obtained from iron carbonyl injected (a) in once and (b) in
Fig. 6 XRD patterns of iron nanopartic1es prepared with
twice
0.0425 M oleylamine and without oleylamine
4 Conclusions The iron nanoparticles were successfully prepared by thermal decomposition using kerosene solvent at low temperatures below 180 'C. The shape of as-prepared particles was spherical. An average size of the particles was decreased from 11.2 nm to 8.6 nm with increasing decomposition temperatures in the range of 160 'C to 180 'C, and their corresponding saturation magnetization was also decreased from
Fig. 5 HRTEM image of as-prepared iron nanopartic1es
193.26 emu/g to 167.66 emu/g. The phase of the iron particles was amorphous, but their surface was easily oxidized in air to become a spinel-structured iron oxide. -207-
Proceedings of 19th International Workshop on Rare Earth Permanent Magnets & Their Applications (2002) 289.
References: [1]
[6]
C. Petit, S. Rusponi, and H. Brune, J. Appl. Phys., 95 (8) (2004) 4251.
F. Guo, H. Zheng, Z. Yang, Y. Qian, Mater. Lett., 56 (2002) 906.
[7]
S. Wirth, S. von Molnar, M. Field, and D. D. Awschalom, J.
[2]
L. Bronstein, E. Kramer, B. Berton, C. Burger, S. Forster,
[3]
C. Liu, T. J. Klemmer, N. Shukla, X. Wu, D. Weller, M.
Bhattacharya, Y. Yeshurun, and 1. Felner, J. Magn. Magn.
Tanase, D. Laughlin, J. Magn. Magn. Mater., 266 (2003) 96.
Mater., 268 (2004) 95.
M. Antonietti, Chern. Mater., 11 (1999) 1402.
[4]
Appl. Phys., 85 (8) (1999) 5249. [8]
N. Wu, L. Fu, M. Su, M. Aslam, K. C. Wong, and V. P. Dravid, NanoLetters, 4 (2) (2004) 383.
[5]
C. J. Choi, O. Tolochko, B. K. Kim, Materials Letters, 56
-208-
M. Sivakumar, A. Gedanken, W. Zhong, Y. W. Du, D.