J Supercond Nov Magn (2015) 28:901–904
DOI 10.1007/s10948-014-2794-7
ORIGINAL PAPER
Preparation and Characterization of Hematite-Multiwall
Carbon Nanotubes Nanocomposite
M. Krajewski · A. Malolepszy · L. Stobinski ·
S. Lewinska · A. Slawska-Waniewska · M. Tokarczyk ·
G. Kowalski · J. Borysiuk · D. Wasik
Received: 7 June 2014 / Accepted: 12 September 2014 / Published online: 16 October 2014
© The Author(s) 2014. This article is published with open access at Springerlink.com
Abstract The aim of this work is to study the preparation
and characterization of a new nanocomposite which consists of chemically-modified multiwall carbon nanotubes
covered by randomly-deposited nanoparticles of hematite.
The morphology, structural and physical properties of the
investigated nanomaterial were determined by means of
transmission electron microscopy, X-ray diffraction and
vibrating sample magnetometry at ambient conditions. The
presence of residual catalyst nanospheres inside multiwall
carbon nanotubes was confirmed by transmission electron
microscopy. The signal coming from this contamination was
under the detection limit of X-ray diffractometer, therefore
it was not registered.
Keywords Hematite · Multiwall carbon nanotubes ·
CVD · TEM · XRD · VSM
M. Krajewski () · M. Tokarczyk · G. Kowalski · J. Borysiuk ·
D. Wasik
Faculty of Physics, Institute of Experimental Physics,
University of Warsaw, Hoza St.69, 00-681 Warsaw, Poland
e-mail: marcin.krajewski@fuw.edu.pl
A. Malolepszy
Faculty of Materials Science and Engineering, Warsaw University
of Technology, Woloska St. 141, 02-507 Warsaw, Poland
L. Stobinski
Institute of Physical Chemistry, Polish Academy of Sciences,
Kasprzaka St. 44/52, 01-224 Warsaw, Poland
L. Stobinski
University Research Centre “Functional Materials”, Warsaw
University of Technology, Woloska St. 141, 02-507 Warsaw,
Poland
S. Lewinska · A. Slawska-Waniewska · J. Borysiuk
Institute of Physics, Polish Academy of Sciences, Al. Lotnikow
32/46, 02-668 Warsaw, Poland
1 Introduction
In 1991, Iijima managed to prepare the first multiwall carbon nanotubes (MWCNTs) via arc discharge process [1].
Since then, carbon nanotubes (CNTs) became the source
of advanced studies in the field of physics, chemistry and
material sciences. At the same time, CNTs started to play
a significant role in numerous applications in many fields
including: medicine [2], high-performance adsorbents [3],
sector of energy storage and conversion [4, 5], etc.
There are four commonly-used CNTs fabrication techniques: arc discharge [1], laser ablation [6], chemical vapor
deposition (CVD) [7] and vapor–liquid–solid (VLS) method
[8]. However, the two latter techniques seem to have certain advantages over the other. For instance, they are not
high temperature processes. The growth and dimensions of
CNTs (via CVD or VLS) can be easily-controlled by fitting
reaction parameters such as: temperature, source of carbon,
or catalyst concentration. However, CNTs growth complications arise when using metallic catalysts such as iron (Fe),
cobalt (Co) or nickel (Ni) because they form metal carbides together with carbon precursors which become the
seeds for carbon nanotubes growth. Therefore, they often
remain built into the tubes and become an integral part of
the nanomaterial.
So far, it has been reported that the purification of contaminated CNTs could be achieved via the functionalization
of carbon nanotubes [9]. Through this procedure, it is possible to cover the CNTs surface by various chemical groups
such as: -OH, -COOH, COONH4 , etc. Furthermore, it has
been proven that the traces of catalyst are gradually removed
from the nanotubes at the same time [10].
Another material which is interesting in the case of this
work is hematite (α-Fe2 O3 ). This oxide belongs to the group
of low-cost and environmentally-friendly transition metal
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J Supercond Nov Magn (2015) 28:901–904
Fig. 1 TEM images of
MWCNTs-COONH4 (a),
multiwall carbon nanotube filled
by the trace of catalyst (b), and
MWCNTs-COONH4 coated
randomly by α−Fe2 O3 (c)
oxides. Moreover, α-Fe2 O3 is the most thermodynamically
stable iron oxide and it is extensively used in the production
of pigments, jewelry, catalysts, sensors, hard and soft magnets, devices for energy storage and conversion, etc. [11].
The purpose of this work is to synthesize and characterize a new nanocomposite which consists of chemicallymodified multiwall carbon nanotubes (MWCNTs) covered by randomly-deposited nanoparticles of hematite
(α-Fe2 O3 ). Such nanomaterial promises to combine the
features of both MWCNTs and α-Fe2 O3 making it an
useful material in many fields for future applications.
2 Experimental Details
The raw multiwall carbon nanotubes (MWCNTs; 93 %
of purity; CNT CO., Ltd. from South Korea) were
manufactured via CVD process with iron (Fe) as the
catalyst. Such MWCNTs were chemically-modified by
heating at 120 ◦ C in concentrated nitric acid (68 %
HNO3 ) for 50 h under a reflux. Then, they were filtered and washed with distilled water until the pH value
of the filtrate reached 6. Thereby, the MWCNTs were
Fig. 2 XRD patterns of MWCNTs-COONH4 (a), α−Fe2 O3 /
MWCNTs (b), and commercial α−Fe2 O3 (c)
oxidized and formed carboxylic groups attached to the
ends and the walls of CNTs (MWCNTs-COOH) [12].
Such functionalized CNTs were treated with a 25 % aqueous solution of ammonia and then rinsed with distilled water
during filtration to obtain the ammonium salt (MWCNTsCOONH4 ). After that, 1 g of MWCNTs-COONH4 was
dispersed in 500 ml of distilled water and cooled to 4 ◦ C.
In two other beakers 0.215 g of iron dichloride tetrahydrate (FeCl2 · 4H2 O; 98 % of purity; Sigma-Aldrich) and
0.588 g of iron trichloride hexahydrate (FeCl3 · 6H2 O; 97 %
of purity; Sigma-Aldrich) were dissolved in distilled water
and added by droplets to the previously prepared carbon
nanotube dispersion mixed with a magnetic stirrer. After
30 min, the pH of dispersion was brought up to 10 with 1 M
NaOH. The obtained product was heated up to 100 ◦ C on
a hot plate with magnetic stirring for 30 min. Finally, the
prepared nanocomposite was centrifuged and washed with
distilled water until the value of pH reached 7.
The obtained nanomaterial was studied using a Phillips
X’Pert diffractometer (XRD) equipped with a Cu X-ray
source and a parallel beam Bragg reflection mirror, a JEOL
JEM 3010 transmission electron microscope (TEM) and
an Oxford Instruments Ltd. vibrating sample magnetometer
(VSM) in the range of magnetic field between −0.6 T and
Fig. 3 Magnetization hysteresis loops of MWCNTs-COONH4 (a)
and α−Fe2 O3 /MWCNTs (b)
J Supercond Nov Magn (2015) 28:901–904
0.6 T. The XRD and VSM measurements were performed
under ambient conditions.
Additionally, the results for commercially-available reference samples of α-Fe2 O3 powder (99.98 % of purity; Carl
Roth GmbH) and the chemically-modified multiwall carbon nanotubes (MWCNTs-COONH4 ) are presented in this
work.
3 Results and Discussion
TEM images of chemically-modified MWCNTs and
α-Fe2 O3 /MWCNTs nanocomposite are presented in Fig. 1a
and 1c. A residual amount of catalyst coming from the
preparation process can also be seen built into the nanotube (Fig. 1b). TEM studies show that MWCNTs are
very disordered, braided, and are successfully coated by the
randomly-dispersed hematite nanoparticles. The diameter of
CNTs varies from 10 to 40 nm. The average diameters of αFe2 O3 and traces of catalyst are approximately 50 nm and
12 nm, respectively.
XRD has great advantages in comparison with the other
experimental techniques because it is simple in terms of
implementation and it also has the ability of measuring
for a long period of time without any negative effects
on the sample. Therefore, the XRD technique is a good
tool to study the structure of α-Fe2 O3 /MWCNTs nanocomposite and reference samples. These results are presented
in Fig. 2. Recorded XRD patterns confirm that MWCNTs are successfully coated by hematite. The positions
of peaks originating from α-Fe2 O3 and the chemicallymodified MWCNTs lie at the same angle positions for all
structures. Moreover, no significant changes in the functionalized MWCNTs structure after deposition of hematite are
observed.
Figure 3 presents the magnetization hysteresis loops of
MWCNTs-COONH4 and α-Fe2 O3 /MWCNTs. The differences in curve shapes indicate different magnetic behaviors. The functionalized MWCNTs contain the encapsulated
traces of catalyst coming from the CVD process. The previous studies performed on this nanomaterial have shown that
the residual amount of catalyst is associated with the presence of non-stoichiometric iron carbide (Fex C), α-Fe and
ferrihydrite [10]. Most of these iron compounds are ferromagnetic, therefore magnetization hysteresis of MWCNTsCOONH4 reveals the ferromagnetic behavior. On the other
hand, the shape of the magnetization curve for the studied nanocomposite exhibits more complex behavior with a
coercivity and large high field susceptibility. It is related to
the strong influence of α-Fe2 O3 deposited on the surface
of carbon nanotubes being superimposed on the ferromagnetic behavior of the catalyst residue, of which the content in
the investigated material is much lower than hematite. The
903
recorded values of saturated magnetization (MS ), remnant
magnetization (MR ) and coercivity (HC ) for MWCNTsCOONH4 are equal 0.26 emu/g, 0.10 emu/g and 0.04 T
(400 Oe), respectively. For α-Fe2 O3 /MWCNTs, the remnant magnetization equals 0.11 emu/g and the coercivity
equals 0.03 T (300 Oe). Taking into account that all magnetic moment values are given in this work per unit of
total mass (emu/g), considering all compounds inside and
outside of CNTs and also the nanotubes mass, it is very
difficult to perform further analysis of the obtained results.
Nevertheless, the presence of encapsulated catalyst traces
in CNTs and diamagnetic contribution of the graphitic nanotubes play important roles for the magnetic properties of
both MWCNTs-COONH4 and α-Fe2 O3 /MWCNTs.
4 Conclusion
This work confirms that α-Fe2 O3 /MWCNTs nanocomposite could be simply prepared via the proposed chemical
method. Morphology and structural and magnetic features
of this material were determined. Moreover, the investigated
nanomaterial is interesting due to the variety of possible
applications; for example in the lithium-ion batteries [4, 13]
and/or the supercapacitors [5, 14]. Therefore, it is supposed
to be a very perspective material with regards to future
research.
Acknowledgments This work was supported by the Foundation for
Polish Science International PhD Projects Programme co-financed by
the EU European Regional Development Fund, A.M. thanked the support from the European Union funds by the European Social Fund and
L.S. thanked the National Center for Research and Development for
support by the project no. PBS1/A5/15/2012. Sincere thanks towards
Dr. J. Syzdek for the research consultations.
Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s)
and the source are credited.
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