Role of polyol in the synthesis of Fe particles

Article abstract of DOI:10.1016/j.jmmm.2006.10.1132

Though there have been reports on the synthesis of Fe particles by using polyol process, the role of polyol has not been understood well and it still remains unclear. We report the successful synthesis of Fe nanoparticles in liquid polyols, their magnetic

Full text of DOI:10.1016/j.jmmm.2006.10.1132

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Journal of Magnetism and Magnetic Materials 310 (2007) 2393–2395
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Role of polyol in the synthesis of Fe particles
Ã
R. Justin Joseyphusa, D. Kodamaa, T. Matsumotob, Y. Satoa, B. Jeyadevana, , K. Tohjia
aGraduate School of Environmental Studies, Tohoku University, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579, Japan
bDivision of Materials Control, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
Available online 30 November 2006
Abstract
Though there have been reports on the synthesis of Fe particles by using polyol process, the role of polyol has not been understood
well and it still remains unclear. We report the successful synthesis of Fe nanoparticles in liquid polyols, their magnetic properties and
also the influence of polyols for the formation of Fe nanoparticles. The oxide phase fraction and the magnetic properties are found to
depend on the particle size of the Fe synthesized in various polyols like trimethylene glycol, propylene glycol and ethylene glycol.
r 2006 Elsevier B.V. All rights reserved.
PACS: 75.50.Bb; 75.50.Tt; 74.25.Ha
Keywords: Polyol process; Fe nanoparticle
1. Introduction
taken in a reaction vessel containing 100 ml of polyol
and heated to the desired temperature with constant
mechanical stirring. The synthesized samples were washed
and stored in alcohol. The structure, morphology and
magnetic properties of the particles were analyzed by X-ray
diffraction (XRD) using a Cu target, scanning electron
microscope (SEM) and vibration sample magnetometer
(VSM).
Among various chemical techniques available for the
synthesis of metallic and alloy nanoparticles, polyol
process stands out since the polyol medium prevents the
particle from coming into contact with the oxidizing
atmosphere. Though most of the transition metals were
reduced successfully by polyol, the formation of iron in
polyol is claimed only through disproportionation reaction
of ferrous salts [1]. However, the formation of alloys such
as FePt [2], FePd, FeCo, etc. were reported recently and
cast a doubt on the disability of the polyol in reducing iron.
Therefore, in this paper, we attempted the synthesis of Fe
nanoparticles using polyol process and elucidate the role of
polyol. The magnetic properties of the particles are also
reported.
3. Results and discussion
3.1. Synthesis of Fe in various polyols
The synthesis of Fe in polyols was attempted by reducing
ferrous ions (FeCl2 Á 4H2O) in the presence of hydroxyl ion.
The formation of the iron particles as a function of (a) type
of polyol, (b) ferrous salts, (c) ferrous ion concentration,
(d) hydroxyl ion concentration and (e) reaction tempera-
ture were studied in detail. However, this report will discuss
the results pertaining to the Fe molar concentration of
0.02 M, OH/Fe ratio of 10 and reaction temperature of
393 K in different types of polyol. Fig. 1 shows the XRD
pattern of the products synthesized in TMEG, PG and EG.
Average grain sizes of the Fe nanoparticles synthesized in
TMEG, PG and EG are 15, 23 and 32 nm, respectively,
determined using Scherrer’s formula. Depending on the
2. Experimental
The precursors used for the synthesis of Fe nanoparticles
are FeCl2 Á 4H2O and NaOH. The synthesis was attempted
using polyols like trimethylene glycol (TMEG), propylene
glycol (PG) and ethylene glycol (EG). The precursors were
Ã
Corresponding author. Tel.: 81 22 795 7412; fax: 81 22 795 7412.
E-mail address: jeya@mail.kankyo.tohoku.ac.jp (B. Jeyadevan).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2006.10.1132

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2394
Fig. 2. XRD pattern of the Fe particles synthesized in EG.
Fig. 1. XRD pattern of the Fe nanoparticles synthesized in various
polyols.
reducing ability of the polyols, the yield of metal iron and
iron oxide fraction in the product varied. The Fe3O4
fraction is the highest for the particles synthesized in
TMEG, and almost no oxide peak is visible for the
particles synthesized in EG as shown in Fig. 1. The particle
size for the Fe synthesized in EG and TMEG are around
100 and 60 nm as observed from SEM and TEM (not
shown), respectively. The larger particle size confirms
that the particles are polycrystalline since the grain sizes
observed from the XRD pattern are much smaller. The
results suggest that the formation of oxides is due to the
oxidation of iron and their fraction is related to the size of
the nanoparticles. The highly reducing TMEG gives rise to
the formation of smaller particles, which subsequently gets
oxidized. On the other hand, the Fe particles synthesized in
EG are large in diameter and the oxide fraction is below the
detection limit of XRD. This has also been confirmed from
the magnetic properties of the products. The saturation
magnetizations for the particles synthesized in TMEG, PG
and EG are 70, 82 and 126 A m2/kg, respectively. The
saturation magnetization is higher than that of magnetite
nanoparticles (60 A m2/kg) but less than that of bulk Fe
(220 A m2/kg). The magnetization value lower than the
bulk is due to the distribution in the particle sizes with
smaller particles getting converted to magnetite resulting in
the reduction of magnetization. The yield and particle size
of Fe synthesized in polyols varied depending on the
reduction potential of the polyols. This suggests that the
reaction mechanism for the formation of Fe nanoparticles
in polyols is by reduction and not through disproportiona-
tion, where reaction does not depend upon the type
of polyols. To confirm this further, we attempted the
synthesis of iron particles in EG under various experi-
mental conditions.
Fig. 3. SEM micrograph of sub-micron Fe particles synthesized in EG.
200
150
100
50
0
-50
-100
-150
-200
-1500 -1000 -500
0
500
1000
1500
Applied field (kA/m)
Fig. 4. Hysteresis loop at room temperature for the Fe particles
synthesized in EG.
and heating rate were varied to obtain highly pure Fe
particles. Among these, NaOH is found to play a major
role in reducing any metal ion to metal atom. In the present
case, the excess OHÀ helps in reducing the reduction
potential, Eh, of the species [3] as well as enhances the
reaction rate by facilitating the formation of acetaldehyde.
The XRD pattern of the product obtained under optimum
conditions is shown in Fig. 2. Fig. 3 shows the typical SEM
3.2. Synthesis of Fe in EG
As mentioned earlier, since the distribution of particles
with smaller sizes would result in the oxidation of Fe, the
reaction parameters such as OHÀ/Fe ratio, temperature

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2395
micrograph of Fe particles obtained above. The shape of
the sub-micron size particles is found to be cubic. Fig. 4
shows the hysteresis loop at room temperature for the Fe
particles synthesized in EG. The saturation magnetization
of the particles is as large as 182.5 A m2/kg suggesting that
the oxide fraction was very low. The absence of magnetite,
which should be present in equal amount in the case of
disproportionation reaction, suggests that the particles are
produced through the reduction of iron ions into metal as
in the cases of reducing any other noble or transition
metals.
Fe nanoparticles synthesized by polyol process due to
the oxidation of smaller iron particles. The magnetic
properties of the Fe nanoparticles are thus influenced by
the particle size, where the smaller particles undergo
oxidization and thereby the overall saturation magnetiza-
tion is reduced. The synthesis of Fe at low temperatures
will pave the way for Fe-based alloy nanoparticles such
as FePt and FeCo with better magnetic properties at low
temperatures.
References
4. Conclusion
[1] G. Viau, F. Fievet-Vincent, F. Fievet, J. Mater. Chem. 6 (1996) 1047.
[2] B. Jeyadevan, A. Hobo, K. Urakawa, C.N. Chinnasamy, K. Shinoda,
K. Tohji, J. Appl. Phys. 93 (2003) 7574.
We could conclude that the polyol acts as a reducing
agent rather than a medium for the disproportional
reaction as claimed earlier. The oxide peak appears in the
[3] F. Fievet, F. Fievet-Vincent, J.P. Lagier, B. Dumont, J. Mater. Chem.
3 (1993) 627.