Synthesis of nanosized iron(III) oxide and study of its formation features

Article abstract of DOI:10.1134/S0036023616110127

Nanosized iron(III) oxide has been obtained by thermolysis of iron(III) acetylacetonate using diphenyl ether as a dispersion medium. It has been shown that increase in thermolysis temperature from 180 to 250°C allows one to half the average size of Fe₂O₃ nanoparticles. The introduction of surfactant into dispersion medium also leads to decrease of the average size of particles down to 4 nm. The phase composition of the prepared nano-Fe₂O₃ has been established, the possibility to reduce nano-Fe₂O₃ into iron metal has been shown by temperature-programmed reduction

Full text of DOI:10.1134/S0036023616110127

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2016, Vol. 61, No. 11, pp. 1387–1391. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © A.S. Lyadov, A.A. Kochubeev, L.D. Koleva, O.P. Parenago, S.N. Khadzhiev, 2016, published in Zhurnal Neorganicheskoi Khimii, 2016, Vol. 61, No. 11,
pp. 1440–1444.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis of Nanosized Iron(III) Oxide
and Study of Its Formation Features
A. S. Lyadov*, A. A. Kochubeev, L. D. Koleva, O. P. Parenago, and S. N. Khadzhiev
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, 119991 Russia
*
e-mail: lyadov@ips.ac.ru
Received January 28, 2016
Abstract―Nanosized iron(III) oxide has been obtained by thermolysis of iron(III) acetylacetonate using
diphenyl ether as a dispersion medium. It has been shown that increase in thermolysis temperature from 180
to 250°C allows one to half the average size of Fe O nanoparticles. The introduction of surfactant into dis-
2
3
persion medium also leads to decrease of the average size of particles down to 4 nm. The phase composition
of the prepared nano-Fe O has been established, the possibility to reduce nano-Fe O into iron metal has
2
3
2
3
been shown by temperature-programmed reduction
DOI: 10.1134/S0036023616110127
At present, nanosized iron(III) oxide and compos- time, acetylacetonates of d-block elements are often
ite materials on its basis find a wide application in var- used as precursors to prepare the corresponding
ious fields of science and technology. For example, nanoparticles. These compounds are chosen because
nanosized iron(III) oxide can be used in catalysis as a they are cheap, simple to prepare, show low toxicity,
catalyst in Fisher–Tropsch process [1], cycloconden- low decomposition temperature, and their thermolysis
sation reaction, and photocatalysis [2]. This com- results in formation of particles of the same shape with
pound is used in medicine as a contrast substance in monodisperse distribution [11].
MRT diagnostics [3] or for precise delivery of pharma-
ceuticals [4], it is applied in power technology as elec-
trodes in alkaline batteries [5], etc. Nanosized iron
oxide is also applied in the manufacture of dyes, sor-
bents, and gas sensors. Superparamagnetism is
another useful property of nanosized iron oxide [6].
The aim of this work is to study the features of for-
mation of nanosized iron(III) oxide in the course of
thermolysis of iron(III) acetylacetonate Fe(acac) in
3
diphenyl ether medium under varying synthesis con-
ditions and to study physicochemical properties of
prepared nano-Fe O .
2
3
There is the large number of methods for preparing
nanosized iron oxide, thermolysis of iron-containing
precursors under specially selected dispersion media
plays an important role among them. It should be
EXPERIMENTAL
We used Fe(acac) as a precursor of nanosized
3
noted that variation of precursor nature, dispersion iron-containing particles, the compound is well solu-
medium, and thermolysis conditions provides a possi- ble in organic solvents and contains no water, which is
bility to change considerably the morphology and size favorable for the course of thermolysis and formation
of resulting iron oxide particles. The introduction of of nanosized particles. Iron(III) acetylacetonate was
surfactants into dispersion medium in the course of synthesized by procedure [12] and identified by X-ray
thermolysis process is an important feature because powder diffraction and UV spectroscopy. The synthe-
these compounds provide not only stabilization of sis of nanoparticles was carried out by thermolysis of
nanoparticles but also change of their size and mor- the precursor in diphenyl ether (DPE), which is an
phology. Dispersion media commonly used are high- aromatic ether insoluble in water but well soluble in
boiling thermally stable liquids, for example, paraffin organic solvents; it has boiling point 259°C, which
hydrocarbons [7], ethers [8], and polyhydric alcohols considerably increases with pressure. This compound
[
9]. Thus, glycerol found a wide application in the syn- was selected as a dispersion medium because of rather
thesis of various nanoparticles, while the method itself high boiling point and low toxicity.
is called glycothermal synthesis [10].
To prepare nanosized iron(III) oxide, 0.5 g of
was dissolved in 10 mL of DPE or a mixture
Inorganic salts (halides, nitrate, sulfate, carbonyls, Fe(acac)
3
etc.) and iron complexes are used as precursors for the of DPE with the appropriate amount of surfactant.
preparation of iron oxide nanoparticles. In recent Next, 40 mL of DPE or a DPE–surfactant mixture
1387

1388
LYADOV et al.
The indexing of X-ray diffraction patterns of the
(а)
H
C−
prepared compounds was conducted by homology
method on the basis of data taken from the ICDD
PDF-4 international database.
3
50
00
50
00
3
2
2
O
O
Particle size and sample morphology was deter-
mined by transmission electron microscopy (TEM)
on a Tecnai Spirit 120 kV electron microscope. Ana-
lyzed specimen was dispersed in methanol using ultra-
sound and then applied on a copper support.
Fe3+
O
O
C−
C−
O
O
1
50
H
H
100
The features of reduction of nanosized iron(III)
oxide were studied by temperature-programmed
reduction (TPR) on a Micromeritics Auto Chem II
instrument. For this purpose, a specimen was placed
into a quartz U-shaped reactor equipped with a ther-
mocouple and heated in a gas mixture (5 vol % of
hydrogen in argon) to 900°C. Gas mixture supply rate
was 50 mL/min, heating rate 0.167 K/s, temperature
inside the reactor being measured (the thermocouple
was disposed at 5 mm from specimen surface) and
reducing agent consumption was measured with a
thermal conductivity detector (TCD).
5
0
0
6
8
10 12 14 16 18 20 22 24 26 28 30
θ, deg
b)
2
(
2
.5
.0
H
C−
2
1.5
O
O
Fe3+
O
O
1.0
O
C−
C−
O
RESULTS AND DISCUSSION
H
H
Prepared Fe(acac) was analyzed by XRD analysis
3
0
.5
and UV spectroscopy to identify the obtained com-
pound. Figures 1a and 1b show the obtained results.
The diffractogram (Fig. 1a) shows the presence of dis-
0
2
00
300
400 500
600
700
800
tinct peaks, which indicates that obtained Fe(acac)
3
λ, nm
has well formed monophasic crystal structure. On the
basis of comparison of the obtained diffraction pattern
with data taken from ICDD PDF-4 database, one can
Fig. 1. X-ray diffraction pattern of Fe(acac) (a) and UV
spectrum of Fe(acac) in ethanol (b).
3
3
draw a conclusion that the prepared Fe(acac) is iso-
3
structural to the complexes described in the literature.
The UV spectrum of iron(III) acetylacetonate solution
in ethanol (Fig. 1b) exhibits four peaks in the wavelength
region 200–800 nm [13]. The first (≈436 nm) and sec-
ond (≈350 nm) weak peaks in the visible and near UV
spectral regions are caused by d–d transitions (the
transitions of central ion electrons between split ener-
getic levels, difference between them is determined by the
strength and symmetry of the given ligand field). The
weak intensity of these peaks is caused by the fact that
these transitions are forbidden by selection rules. The
presence of chromophore groups in acetylacetonate
ligands (C=C, C=O) provides the emergence in spec-
trum of peaks typical for nπ* (the third peak at ≈275 nm)
was heated to required temperature on an oil bath with
vigorous magnetic stirring in a two-necked round-bot-
tomed flask equipped with a reflux condenser. Next, a
solution of Fe(acac) was quickly added via a syringe
3
into the hot DPE or DPE–surfactant solution. The
resultant mixture was kept for 2 h with vigorous stirring
for complete thermolysis and formation of nanosized
particles. Then, the mixture was cooled and analyzed.
The thermal analysis of the precursor was con-
ducted on a Q-600 thermal analyzer in temperature
range 25–1000°C in air at heating rate 10 K/min.
Absorption spectra in the visible and ultra-violet and ππ* (the fourth peak at ≈230 nm) transitions.
region were recorded on a Shimadzu UV-2401РС
Since the synthesis of iron oxide nanoparticles was
spectrometer in the range 200–800 nm in quartz
performed by thermolysis of iron acetylacetonate, it
cuvettes transparent in the UV region. Optical path
was of interest to carry out its thermal analysis. Figure 2
length of cuvette was 1 mm.
shows the obtained thermogram. The decomposition
of Fe(acac) begins at 169°C, while the most active
Iron(III) acetylacetonate and prepared samples
were studied by X-ray powder diffraction analysis
3
weight loss is observed in the range 169–295°C and
results in 60% weight loss. The decomposition of iron
acetylacetonate is characterized by a set of exo effects.
(
XRD) on a Rigaku X-ray diffractometer with an
Ultima IV θ–θ goniometer using CoK radiation with
α
scanning step of 0.02° and counting time 1 s. The
range of measurement angles 2θ = 10°–100°.
Figure 3 displays the micrographs of nanosized
iron oxide particles obtained in the absence of surfac-
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 61
No. 11
2016

SYNTHESIS OF NANOSIZED IRON(III) OXIDE
50
1389
169°C
(a)
0
20
40
60
80
295°C
40
30
20
–
–
–
–
10
0
–
10
–100
200
400
600
T, °C
800
1000
Fig. 2. Thermogram of iron(III) acetylacetonate.
100 nm
(b)
tant. It is seen that at low-temperature thermolysis
180°C, Fig. 3a) the particles differ in form, there is a
(
trend to form particles of triangle shape, the average
size is 12–15 nm. Increase in thermolysis temperature
leads not only to decrease of average particle size but
also formation of particles of uniform shape (Fig. 3b).
Increase in thermolysis temperature from 180 to
2
50°C provides more than twofold decrease of average
size of iron(III) oxide particles (Fig. 3c).
The introduction of surfactants is known to allow
the preparation of particles of smaller size, other syn-
thesis conditions being equal. In this work, we used a
mixture of oleic acid, oleylamine, and oleyl alcohol in
1
: 1 : 1 weight ratio as a surfactant. The introduction
of 5 wt % of the surfactant into dispersion medium
leads to formation of uniform in shape nanosized parti-
cles even at thermolysis temperature of 180°C (Fig. 4a),
increase in surfactant concentration allows one to
decrease considerably the size of particles (Fig. 4b).
Thus, at surfactant concentration of 15 wt % and ther-
molysis temperature of 180°C, the average size of iron
oxide particles is only 4 nm.
60 nm
(c)
13
1
2
1
1
1
0
To study the physicochemical properties of nano-
sized iron(III) oxide, we used a sample obtained by the
9
8
7
6
thermolysis of Fe(acac) in DPE in the absence of sur-
3
factant at 200°C. The average size of particles of such
a sample was 8–9 nm. To study the phase composition
of nano-Fe O and its ability to reduction, we
2
3
5
4
obtained solid iron(III) oxide nanoparticles as a black
powder by the removal of DPE in a vacuum.
3
Figure 5a shows X-ray diffraction pattern for nano-
sized iron(III) oxide with average particle size of 8–9 nm,
which is characterized by the presence of well-formed
slightly broadened peaks indicating a small size of
crystallites. The nanosized Fe O has a cubic structure
170
190
210
T, °C
230
250
2
3
(
PDF #39-1346). The use of the Scherrer equation
14] allowed us to calculate the average size of crystal-
Fig. 3. TEM image of nano-Fe O : (a) thermolysis at
2
3
[
1
80°C, (b) thermolysis at 250°C, dependence of particle
lites for this sample:
size on thermolysis temperature (c).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 61 No. 11 2016

1390
LYADOV et al.
I, arb. units
(a)
(а)
8000
1
4
000
0
Fe O (PDF #39-1346)
2
3
2
0000
1
5000
0000
000
2
1
5
Fe O (PDF #85-1436)
3 4
0
1
2000
9000
6000
3000
3
0
20 30
40 50 60 70 80
θ, deg
b)
90
2
(
1
1
1
1
.8
.6
.4
.2
6
70°C
80 nm
(b)
750°C
13
1
.0
430°C
12
0.8
11
0.6
0
0
.4
.2
10
9
8
7
6
5
4
3
0
200
400
600
T, °C
800
1000
Fig. 5. X-ray diffraction patterns (a): (1) nano-Fe O ;
2
3
(
2) the sample after reduction at 430°С; (3) the sample
after reduction at 670°С; TPR profile of nano-Fe O (b).
2
3
II peak: Fe O → Fe1 – xO,
3
4
0
2
4
6
8
10
12
14
Surfactant content, wt %
III peak: Fe1 – xO → Fe.
To confirm this scheme, we determined the phase
Fig. 4. TEM image of nanosized iron(III) oxide prepared
in the presence of surfactant by thermolysis at 180°C (a),
effect of surfactant concentration on the average size of
resulting nano-Fe O particles (b).
composition of reduction products. The X-ray diffrac-
tion patterns of these samples are shown in Fig. 5a. In
the reduction of nano-Fe O at 430°C until comple-
2
3
2
3
tion of hydrogen absorption, a phase of magnetite
really forms, which has a cubic structure like initial
0
.94λ
0.94 × 0.178897
nano-Fe O (PDF #85-1436). The crystallographic
L =
=
= 9 nm.
2
3
B
(
2θ
)
cos(θ) 0.019cos(20.51)
difference in the cubic structure of Fe O and Fe O is
2 3 3 4
not larger 1%, therefore the X-ray diffraction patterns
of these compounds are very similar and their identifica-
tion by this method is often difficult. Further increase in
magnetite reduction temperature up to 670°C leads to
formation of multiphase product (Fig. 5a, 3). The X-ray
diffraction pattern shows numerous reflections,
including reflections related to iron monooxide (wüs-
tite), iron metal, and different carbide forms of iron.
The formation of carbides is possible because of
incomplete removal of diphenyl ether during vacuum
distillation. Diphenyl ether residue undergoes decom-
The obtained from XRD data crystallite size (9 nm)
agrees well with the results of TEM for the sample
under study.
The TPR profile of nanosized iron oxide (Fig. 5b)
has three peaks of hydrogen absorption, which corre-
sponds to three consecutive reduction processes. The
following processes are most likely to take place in the
course of reduction [15]:
I peak: Fe O → Fe O ,
2
3
3
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 61
No. 11
2016

SYNTHESIS OF NANOSIZED IRON(III) OXIDE
REFERENCES
1391
position on the surface of nanoparticles to produce
carbon, which reacts at high temperature with iron-
containing compounds to give carbide phases. Iron
metal is the final product of complete reduction of
1
2
3
4
5
6
7
8
9
. S. N. Khadzhiev, A. S. Lyadov, M. V. Krylova, and
A. Y. Krylova, Petrol. Chem. 51, 24 (2011).
. S. Dadashi-Silab, Y. Yasemin, H. Acarb, and Y. Yagci,
Polym. Chem. 6, 1918 (2015).
nano-Fe O .
2
3
. D. B. Shieh, F. Y. Cheng, C. H. Su, et al., Biomater. 26,
Thus, we performed the synthesis of nanosized
iron(III) oxide by the thermolysis of iron(III) acetyl-
acetonate in diphenyl ether. The effect of external fac-
tors on the morphology and size of resulting particles
was studied. It was shown that increase in temperature
and surfactant concentration in dispersion medium
leads to considerable decrease of average particle size.
This method is convenient, inexpensive, and low-
toxic approach to the synthesis of nanosized iron(III)
oxide with average particle size of 4–15 nm. It was
found that the thermolysis of iron(III) acetylacetonate
results in formation of nano-Fe O of cubic structure.
7183 (2005).
. M. Mahmoudj, S. Sant, B. Wang, et al., Adv. Drug
Deliv. Rev. 63, 24 (2011).
. B. Zhao, Y. Wang, H. Guo, et al., Mater. Sci. (Poland)
25, 1143 (2007).
. L. Zhang, W.-F. Dong, and H. -B. Sun, Nanoscale 5,
664 (2013).
. H. Gu and M. D. Soucek, Chem. Mater. 19, 1103
2007).
. X. Teng, X. Liang, S. Maksimuk, and H. Yang, Small 2,
49 (2006).
7
(
2
2
3
. H. S. Kil, Y. J. Jung, J. I. Moon, et al., J. Nanosci.
Nano-technol. 15, 6193 (2015).
The ability of nano-Fe O to reduction in hydrogen
2
3
flow was studied by TPR. The reduction proceeds in
three stages to give iron metal as a final product.
1
1
0. M. Inouse, J. Phys.: Condens. Matter. 16, 1291 (2004).
1. A. L. Willis, Z. Chen, J. He, et al., J. Nanomater. 2007,
(2007).
2. W. C. Fernelius, Inorg. Synth. 2, 27 (1946).
3. O. V. Sverdlova, Electronic Spectra in Organic Chemistry
(Khimiya, Leningrad, 1985) [in Russian].
1
1
1
ACKNOWLEDGMENTS
This work was supported by the Russian Academy
of Sciences (the program no. 25 of the Presidium of 14. P. Scherrer and N. G. W. Gottingen, Math.-Phys. Kl. 2,
the RAS “Fundamental Chemical Aspects of Carbon
96 (1918).
Power Engineering,” the project “Research on the 15. W. K. Jozwiak, E. Kaczmarek, T. P. Maniecki, et al.,
Design of Process for Oxidative Desulfurization of Oil
and Petroleum Products in the Presence of Nanosized
Oxide Catalytic Systems”).
Appl. Catal. A: Gen. 326, 17 (2007).
Translated by I. Kudryavtsev
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 61 No. 11 2016