Effect of Cetyl trimethylammonium bromide (CTAB) amount on phase constituents and magnetic properties of nano-sized NiFe2O4 powders synthesized by sol-gel auto-combustion method

Article abstract of DOI:10.1016/j.jallcom.2015.02.192

Abstract In this research nano-sized NiFe₂O₄ powders were synthesized with and without Cetyl trimethylammonium bromide (CTAB) surfactant addition by sol-gel auto-combustion method. Phase constituents, microstructure and magnetic properties as a result of different CTAB addition amounts were evaluated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscope (FESEM) and vibration sample magnetometer (VSM) techniques. XRD results designated that the combustion product consists of NiFe₂O₄ as the main phase and some amount of α-Fe₂O₃ and FeNi₃ phases. Raman spectroscopy represents the formation of NiO phase in addition to the mentioned phases. CTAB addition affects the phase constituents and elimination of α-Fe₂O₃ residuals from the combustion product while facilitating the formation of FeNi₃ phase. Also its addition leads to powder refinement based on FESEM images. Mean crystallite sizes of the samples by calculated by Scherrer equation showed a decreasing trend from 46 to 27 nm with increasing the amount of CTAB. Magnetic measurements showed that saturation magnetization increased from 36.96 emu/g to 51.07 emu/g by CTAB addition as a result of increased FeNi₃ amount. The intrinsic coercivity values (_iH_c) of the samples are in the range of 164-175 Oe.

Full text of DOI:10.1016/j.jallcom.2015.02.192

Journal of Alloys and Compounds 638 (2015) 121–126
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Effect of Cetyl trimethylammonium bromide (CTAB) amount on phase
constituents and magnetic properties of nano-sized NiFe O powders
2
4
synthesized by sol–gel auto-combustion method
⇑
S. Alamolhoda , S.M. Mirkazemi, T. Shahjooyi, N. Benvidi
School of Metallurgy and Materials Engineering, Iran University of Science & Technology (IUST), Narmak, Tehran 13114-16846, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In this research nano-sized NiFe O powders were synthesized with and without Cetyl trimethy-
2
4
Received 28 December 2014
Received in revised form 7 February 2015
Accepted 25 February 2015
Available online 12 March 2015
lammonium bromide (CTAB) surfactant addition by sol–gel auto-combustion method. Phase con-
stituents, microstructure and magnetic properties as a result of different CTAB addition amounts were
evaluated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscope
(
FESEM) and vibration sample magnetometer (VSM) techniques. XRD results designated that the com-
bustion product consists of NiFe as the main phase and some amount of -Fe and FeNi phases.
Raman spectroscopy represents the formation of NiO phase in addition to the mentioned phases. CTAB
addition affects the phase constituents and elimination of -Fe residuals from the combustion pro-
duct while facilitating the formation of FeNi phase. Also its addition leads to powder refinement based
2
O
4
a
2
O
3
3
Keywords:
Ceramics
Sol–gel processes
Microstructure
Magnetic measurement
SEM
a
2 3
O
3
on FESEM images. Mean crystallite sizes of the samples by calculated by Scherrer equation showed a
decreasing trend from 46 to 27 nm with increasing the amount of CTAB. Magnetic measurements showed
that saturation magnetization increased from 36.96 emu/g to 51.07 emu/g by CTAB addition as a result of
X-ray diffraction
increased FeNi
75 Oe.
3
amount. The intrinsic coercivity values (
i
H
c
) of the samples are in the range of 164–
1
Ó 2015 Elsevier B.V. All rights reserved.
1
. Introduction
influences the composition and microstructural characteristics of
the synthesized powders [2,16].
Nickel ferrite (NiFe
2
O
4
) is one of the most important materials
Sol–gel auto-combustion method is a unique combination of
the ignition and the chemical gelation processes. This method
has the advantages of simple preparation, cost-effectiveness and
gentle chemistry route resulting in ultra-fine and homogeneous
powder [9].
There are some reports representing that in the aqueous wet
chemistry methods, presence of surfactants and their concentra-
tion influences the morphology and size of the synthesized nano-
in the inverse spinel family exhibiting ferromagnetic properties
with high saturation magnetization, excellent chemical stability
and mechanical hardness, electrical resistivity and low eddy cur-
rent loss in alternating current applications [1–4]. Nano ferrites
are potential candidates for various applications which include
their usage in microwave control components such as circulators,
isolators, and phase shifters [5]. Also they are applicable for gas
and humidity sensing, drug-delivery technology, high density
magnetic storage media, MRI contrast agents, color imaging,
ferro-fluids, high frequency (ꢀGHz) devices electric and electronic
applications, water treatment, biomedical and biotechnology
fields, magnetic refrigerators and catalysts applications [4–9].
Nickel ferrite nano particles have been prepared by several
methods such as hydrothermal [10], co-precipitation [11], micro
emulsion [12], ball milling [13], sol–gel [14] and sol–gel auto-com-
bustion [15]. It should be mentioned that the preparation method
particles of different materials (e.g.
SrFe12 19) [17–20].
2 3 2
a-Fe O , Cu O, Au and
O
Barati et al. reported that Cetyl trimethylammonium bromide
(CTAB) addition resulted in formation of single phase nickel ferrite
and reduction of its crystallite size using sol–gel auto-combustion
method [21]. But they did not report the effect of the amount of
CTAB surfactant on the microstructure and magnetic properties
2 4
of NiFe O . It was reported that CTAB amount influence on sat-
uration magnetization and coercivity values of strontium hexafer-
rite synthesized by co-precipitation method [22]. Up to our
knowledge there is no report about the effect of CTAB amount on
⇑
Corresponding author. Tel.: +98 21 77240540x2885.
E-mail address: alamolhoda@iust.ac.ir (S. Alamolhoda).
http://dx.doi.org/10.1016/j.jallcom.2015.02.192
925-8388/Ó 2015 Elsevier B.V. All rights reserved.
0

1
22
S. Alamolhoda et al. / Journal of Alloys and Compounds 638 (2015) 121–126
phase constituents and magnetic properties of nano-sized NiFe
powder synthesized by sol–gel auto-combustion method.
In this research nickel ferrite nano sized powders have been
synthesized by sol–gel auto-combustion method. The effect of
CTAB amount on phase formation, microstructure and magnetic
properties of nickel ferrite nano-sized powders has been studied.
2
O
4
3
combustion route [24]. The reason of FeNi formation is explained
to be the existence of citric acid which consumes most of the oxy-
gen surrounding the precursor at the combustion stage. Therefore
Fe and Ni metal ions as a result of scarcity of oxygen form FeNi
phase [24].
3
With CTAB addition the identified phases in the XRD pattern
consists of NiFe and FeNi . Although there is a report that sur-
factant addition causes formation of single phase NiFe [21],
phase is observable in all of the XRD patterns
2
O
4
3
2 4
O
2
. Materials and methods
presence of FeNi
shown in Fig. 1.
3
In order to synthesize nickel ferrite stoichiometric amounts of metal nitrates:
7
.35 g Fe(NO
3
)
3
ꢁ9H
2
O (99% Merck) and 2.56 g Ni(NO
3
)
2
ꢁ6H
2
O (99% Merck) were dis-
XRD patterns illustrate that with CTAB additions hematite
peaks are disappeared. Since Fe/Ni ratio was set to be 2/1, and
solved into 50 ml distilled water to make an aqueous solution. The molar ratio of Ni/
Fe was fixed to 1/2. Then 5.25 g citric acid (C .99% Merck) was added to the
above mixture as a chelating agent with a nitrate to citrate ratio of 1:1. The solution
was heated at 60 °C on magnetic stirrer with a rotating speed of 300 rpm to form a
clear and green sol with pH < 1. The pH of the solution was raised to 7 by ammonia
solution addition. Then different amounts of Cetyl trimethylammonium bromide
6 8 7
H O
FeNi
ence of the other compounds consisting of iron is expected. The
most probable phase is maghemite ( -Fe ) since peaks of
Fe phase also overlap with NiFe peaks in the XRD pattern.
It was reported that the oxidation product of magnetite (Fe
3
phase with Fe/Ni ratio of 1/3 is observed in the sample, pres-
c
2
O
3
c-
2
O
3
2 4
O
(
CTAB) C19H42BrN (99% Merck) was added to the solution as a surfactant. The
3 4
O )
CTAB amount was calculated according to the weight of metal nitrates. The result-
ing sol was heated at constant temperature of 80 °C on magnetic stirrer to complete
the formation of the gel precursor. Then the gel undergoes a self-ignition reaction to
form a very fine brown foamy powder. The codes of the combustion products with
different CTAB addition amounts are shown in Table 1.
is maghemite; and hematite could be formed by heat treatment
of maghemite at temperatures of 400–700 °C [25–27]. The oxida-
tion state of hematite is higher than that of maghemite therefore
scarcity of oxygen in the combustion atmosphere might be the rea-
son for the formation of maghemite. Also in addition to citric acid,
CTAB plays the role of fuel in the sol–gel auto-combustion method
for its hydrocarbon chain [21]. F/O (fuel/oxygen) ratios of different
samples are shown in Table 2. When the molar ratio of metal
The phase identification of the combustion products has been performed by
Philips X’pert Pro X-ray diffractometer (XRD) using Cu
k = 0.1541 nm). The XRD patterns were submitted to a quantitative analysis by
the Rietveld method using MAUD (material analysis using diffraction) software
23]. Raman spectroscopy was performed on a BRUKER model SENTERRA Raman
Ka radiation
(
[
spectrometer. The morphology and microstructure of the nano particles were stud-
ied by a field emission scanning electron microscope (FESEM) model (TESCAN).
Magnetic properties have been taken out at room temperature at the maximum
applied field of 14 kOe by vibrating sample magnetometer (VSM) model MDK.
Table 2
F/O ratio of the synthesized samples.
Sample code
F/O ratio
C0
C1.5
1.54
C3
C6
C9
3
. Results and discussions
1.35
1.74
2.13
2.52
X-ray diffraction patterns of the combustion products for the
samples synthesized with and without CTAB addition are repre-
sented in Fig. 1. XRD results represent that the combustion product
of the sample C0 mainly consists of nickel ferrite coexisting with
some residual
researchers also reported presence of FeNi
tion products in the synthesis process of NiFe O
2 4
a
-Fe
2
O
3
and small amounts of FeNi
phase in the combus-
by sol–gel auto-
3
phase. Other
3
Table 1
Codes of the combustion products with different CTAB amounts.
Sample code
C0
0
C1.5
1
C3
2
C6
4
C9
6
Wt.% of CTAB addition
2 4
Fig. 2. XRD pattern of the sample C0 and JCPDS cards of NiFe O and NiO phases.
Fig. 1. XRD patterns of the combustion products of the samples synthesized with
and without CTAB addition. h: NiFe -Fe , N: FeNi , j: NiO.
2
O
4
,
D
:
a
2
O
3
3
Fig. 3. Raman spectra of samples C0, C1.5, C3 and C9.

S. Alamolhoda et al. / Journal of Alloys and Compounds 638 (2015) 121–126
123
Fig. 4. Dependence of approximated weight percentages of different phases to CTAB amount calculated by MAUD software.
Fig. 5. FESEM images of the samples (a) C0 and (b) C3.
nitrates to citric acid is equal and no CTAB addition is used (sample
addition is reported for the synthesis of nanostructured Cu
2
O par-
C0), F/O ratio is calculated to be equal to 1.35. With CTAB addition
the F/O ratio would be increased causing more shortage of oxygen
in the combustion process. By F/O increment formation of maghe-
mite would be facilitated as a result of more deficiency of oxygen.
It was observed that below the crystal size of 30 nm only
maghemite would be produced while above this size only hematite
could be obtained [28]. Reduction of mean particle size by CTAB
ticles [18] by sol–gel auto-combustion method. Therefore in addi-
tion to reducing atmosphere, refinement of the synthesized Fe
particles by CTAB addition may also assist maghemite formation.
Presence of some amount of NiO phase is also probable in the
samples since the peaks of NiFe O phase are overlapping with
2 4
NiO peaks in the XRD pattern (Fig. 1). Fig. 2 demonstrates that
2 3
O
the intensity of (222) reflection at 37.33° in the standard JCPDS

1
24
S. Alamolhoda et al. / Journal of Alloys and Compounds 638 (2015) 121–126
8
6-2267 for NiFe
plane reflection at 37.44° is strong in the standard JCPDS 001-
239 for NiO phase. The observed peak in the XRD pattern of sam-
ple C0 is not as weak as the (222) reflection in the standard JCPDS
6-2267 card. So presence of some amount of NiO phase in the
2
O
4
phase is weak. While the intensity of (111)
themselves throughout the sol uniformly [38] which provides a
narrow size distribution in the combustion product.
The complexes are assembled within the template of surfactant
micelle in the sol [37] which restricts the amount of coagulation
and therefore restricts the growth of particulate assemblies. The
small particulate assemblies in the sol form smaller particles after
combustion process.
Mean crystallite size of nickel ferrite in the samples with differ-
ent CTAB amounts is calculated using XRD patterns and Scherrer’s
equation:
1
8
sample may be the reason for differences in peak intensities.
Fig. 3 shows the Raman spectra of the samples. It could be seen
that there are Raman bands at about 212, 331, 482, 572 and a
ꢂ1
strong band at about 700 cm which respectively correspond to
g g 2 4
F2g(1), E , F2g(2), F2g(3) and A vibration modes for NiFe O [29–32].
The shoulder like feature at lower wave number side of the
ꢂ1
D ¼ 0:9k=b cos h
ð1Þ
Raman band at 700 cm is assigned to A1g(1) and A1g(2) modes
reflecting the stretching vibration of Fe3 and O ions in tetrahe-
+
2ꢂ
where D is mean crystallite size, k is the X-ray wavelength, b is the
value of the full width at half maximum of the diffraction peaks, and
h is the diffraction angle at the peak maxima [39]. The results
dral site [30].
It was reported that NiO has Raman bands at 440, 560 and
ꢂ1
ꢂ1
7
40 cm [33]. The observed bands at 440 and 562 cm in the
(Table 3) represent a decreasing trend in mean crystallite size by
Raman spectra of the sample C0 can be attributed to the presence
of NiO in this sample since the other bands of NiO have overlapped
increasing CTAB amount for nickel ferrite particles.
Magnetization curves of the samples obtained from room tem-
ꢂ1
with the broad bands of NiFeO
4
at 700 cm . Raman bands for
perature VSM measurement are shown in Fig. 6. Mmax and
quantities of the samples are listed in Table 4 and plotted in Fig. 7.
The reported M values for nanoparticles of NiFe are equal to
i c
H
ꢂ1
maghemite are reported to be at 365, 500 and 700 cm [34,35].
The peaks at 500 and 700 cm are overlap with NiFe
ꢂ1
2
O
4
broad
s
2 4
O
ꢂ1
peaks. However there is a small peak at about 370 cm at the
Raman spectra of the sample C9 which could be the Raman band
of maghemite. As it was explained earlier, it is expected that with
increasing F/O ratio the amount of maghemite phase increases.
Quantitative analyses performed by Rietveld method using
MAUD software representing the dependence of weight percentage
of different phases on CTAB amount are shown in Fig. 4. It should
5
0.4 [16] and 46.53 emu/g [4] and the reported value for the bulk
Table 3
Calculated mean crystallite sizes of the samples with different
CTAB amounts by Scherrer equation.
Sample code
Mean crystallite size (nm)
be noted that these quantities are not exact; particularly since
c
-
C0
C1.5
C3
C6
C9
46
38
33
31
27
Fe peaks in the XRD pattern overlap with NiFe peaks; how-
2
O
3
2
O
4
ever they can represent relative phase changes by alternation in
CTAB amount. It could be observed that with CTAB addition the
amount of NiFe
Fe amount could reduce about 20% at the same time.
However as mentioned above, these changes may be as a result
of formation of some -Fe phase in the sample.
2 4
O would increase above 25% and residual a-
2 3
O
c
2 3
O
Quantitative analyses also show the presence of NiO phase in
the samples. This enhances the probability of presence of NiO in
the synthesized samples and it is in consistence with the above
mentioned XRD standard cards in Fig. 2. The graph in Fig. 4d shows
about 6–9% reduction in NiO amount by CTAB addition. The
amount of NiO phase reaches to minimum in sample C3 and
FeNi
3
phase amount reaches to a maximum in this sample
(Fig. 4b and d). Fig. 4b shows that with CTAB addition FeNi
3
amount reaches to a maximum and then its amount would be
decreased. F/O ratio is increased with surfactant addition and
therefore it is expected to make the environment more reductive
so FeNi
3
phase amount would be increased. After the increment
amount. This declining trend
there is a declining trend for FeNi
3
may be as a result of the higher exothermicity of the combustion
process caused by surfactant addition [36]. The higher exothermic-
ity of the combustion process may facilitate the interaction of the
precursors by oxygen molecules present in the atmosphere.
Therefore it is observed that NiO amount in the samples increases
simultaneously with the decrease in FeNi
FESEM micrographs of the samples C0 and C3 (Fig. 5) represent
morphology of NiFe nano sized particles and it seems that CTAB
3
amount.
Fig. 6. Magnetization curves of the samples.
2 4
O
addition does not affect the particle morphology. The micrographs
represent formation of smaller particles with a narrow size dis-
tribution with CTAB addition. Presence of CTAB influences the for-
mation process of the particulate assemblies in the sol including
nucleation, growth, coagulation and flocculation [37]. The basic
role for surfactants in the synthesis of nanoparticles arises out of
their ability for compartmentalization. This may reduce the reac-
tion dimensionalities which could facilitate the nucleation process
of the particulate assemblies. Also the reactants distribute
Table 4
Magnetic properties of the combustion products of samples synthesized without and
with different amounts of CTAB addition.
Sample code
Mmax (emu/g)
iHc (Oe)
C0
C1.5
C3
C6
C9
37
48.2
51
30.3
29.4
175.5
163.7
170.7
172
172

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