Copyright © 2011 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 11, 1030–1036, 2011
Synthesis and Electromagnetic Wave Absorption
Properties of Multi-Walled Carbon Nanotubes
Decorated by BaTiO3 Nanoparticles
Cheng Bi1 , Meifang Zhu1 , Qinghong Zhang2 , Yaogang Li1 ∗ , and Hongzhi Wang2 ∗
1
RESEARCH ARTICLE
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University,
Shanghai 201620, People’s Republic of China
2
College of Materials Science and Engineering, Donghua University, Shanghai 201620, People’s Republic of China
A hybrid composite material, consisting of BaTiO3 and multi-walled carbon nanotubes, was synthesized by an efficient solvent-thermal route. Transmission electron microscopy images clearly indicate
that the surfaces of the multi-walled carbon nanotubes were uniformly decorated by well-crystallized
BaTiO3 particles, with diameters of 15–30 nm. Electromagnetic wave absorption properties analysis, determined by the electromagnetic parameters measured by a vector network analyzer, shows
that the reflection loss in the BaTiO3 /multi-walled carbon nanotube composite was higher than that
occurring in pure multi-walled carbon nanotubes or BaTiO3 and that was resulted from a better
matched characteristic impedance and an enhanced complex permeability in the high frequency,
which was improved by the decrease of eddy currents owing to the finite increase in resistivity.
The maximum reflection loss of −37.5 dB in the BaTiO3 /multi-walled carbon nanotube composDelivered
by Publishing
Technology
University
of Waterloo
ite was obtained
at a frequency
of 10.4 GHz
and the to:
absorption
range
under −10 dB was from
On: Wed,
Nov 2015 10:19:42
9.6–13.1 GHz rangeIP:
as213.138.164.228
the absorber thickness
was 2 04
mm.
Copyright: American Scientific Publishers
Keywords: Carbon Nanotubes, Nano Particles, Hybrid Composites, BaTiO3 , Electromagnetic
Wave Absorption Properties.
1. INTRODUCTION
In recent years, electromagnetic interference (EMI) has
become an increasingly serious problem due to rapid
development in navigation, telecommunication, and aircraft and the increasing number of electronic devices. EMI
may not only cause interruption in electronic systems but
also be potentially harmful to human health.1–3 To overcome EMI problems, electromagnetic (EM) wave absorbing materials have been studied extensively. It is now
very important to synthesize effective EM wave-absorbing
materials of low density and with strong absorption capacity over a wide frequency range. Conventionally, ferromagnetic or metal particles, such as Fe3 O4 , Fe2 O3 , Ag and Ni,
have been used as materials that absorb EM waves through
magnetic loss. However, while these materials offer good
EM absorption properties, they have drawbacks, including high specific gravity and a relatively high tendency to
corrosion, especially drastic reduction of permittivity ability at giga–hertz range in some generally used ferromagnetic materials, which limit their practical applications.4–8
∗
Authors to whom correspondence should be addressed.
1030
J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 2
Furthermore, in some cases, magnetic absorbers may suffer problems during formation. For example, when producing EMI clothing fabrics from a magnetic particle/polymer
composite, magnetic particles can stick on the iron-made
spinneret and cause agglomeration during the spinning
process. To overcome these problems, appropriate absorptive materials should be relatively lightweight and structurally stable, with a low magnetic permeability.
BaTiO3 is physical and chemical stable for its ternary
perovskites-type structure and has excellent dielectric and
polarization properties but no high magnetic permeability.
It has therefore received increasing attention as a dielectric
absorber, functioning through ohmic losses and polarization. Recent reports state that nanoscale BaTiO3 particles show EM waves absorption with a matrix of epoxy
resin in the X band (8.2–12.4 GHz) and Ku band range
(12.4–18 GHz), which can be characterized by a decrease
in dielectric constant and peak in the dielectric loss with
increasing frequency.9–12 However, single components of
these absorber materials are only effective over a narrow
bandwidth and have low reflection loss (RL), as is typical for other dielectric loss materials. Thus, composites
1533-4880/2011/11/1030/007
doi:10.1166/jnn.2011.3046
Bi et al.
Synthesis and Electromagnetic Wave Absorption Properties of MWCNTs Decorated by BaTiO3 Nanoparticles
2. EXPERIMENTAL DETAILS
2.1. Sample Preparation
A BaTiO3 /MWCNT composite was synthesized by the
solvent-thermal method, using a mixture of BaTiO3
precursors and oxidized MWCNTs. Barium acetate
(Ba(CH3 COO)2 ) and tetrabutyl titanate (Ti(OC4 H9 4 ) were
used to prepare BaTiO3 precursors. The Ba and Ti
J. Nanosci. Nanotechnol. 11, 1030–1036, 2011
X-ray diffraction (XRD) analysis was performed in a
Rigaku D/max 2550V X-ray diffractometer, using Cu
K-radiation to measure the phase purity and crystal
form of the as-synthesized products. Transmission electron
microscopy (TEM) and high-resolution TEM (HRTEM)
images, with corresponding selected area electron diffraction (SAED) pattern, were taken on a JEOL-2100F electron microscope, at an operating voltage of 200 KV for
1031
RESEARCH ARTICLE
formed by two or more component have received concations were controlled at a 1:1 molar ratio. The
siderable attention for absorber technology. Traditional
main reaction medium was supplied by a mixture
carbon black-coated or fiber-based composites have been
of ethanolamine (NH2 CH2 CH2 OH) and ethylenediamine
studied widely and show good absorbing capability but
(NH2 CH2 CH2 NH2 ) in a 1:1 volume ratio, with a small
require a high loading, resulting in bulky and fragile
amount of deionized water introduced with Ba(CH3 COO)2
materials.7 13 Additionally, some recent reported EM wave
and NaOH aqueous solutions. Oxidation of MWCNTs was
absorption composites with core/shell structure, such as
carried out in hot, diluted nitric acid. All raw materials
Fe3 O4 /Fe/SiO2 nanorods, Ni/Ag nanoparticles or ZnOand solvents were analytical grade and purchased from
coated Fe nanocapsules, have excellent efficiency of EM
Sinopharm Chemical Reagent Co. Ltd (China), except
wave absorption, especially the broad absorption band for
MWCNTs, which were provided by Shenzhen Nanotech
the Fe3 O4 /Fe/SiO2 core/shell nanorods. However, these
Port Co. Ltd (China).
metal or metal-oxide based composites still have some
Typically, 0.6 g MWCNTs were treated by a 60 ml mixdisadvantages for their applications, including high speture of HNO3 /H2 O, at a volume ratio of 2:1, at 120 C
cific gravity, no resistance to acid or easy corroded.14–16
for 36 h, to obtain oxidized MWCNTs with a large numTo produce a lightweight, flexible and strong composber of carboxyl and hydroxyl groups on the ends and
ite absorber, carbon nanotubes (CNTs) are suitable candisidewalls.29 The oxidized MWCNTs were then collected
dates as supporting media for the composite because of
by centrifugation, without drying after washing. 0.008 mol
their low density, novel nanostructure and good chemiTi(OC4 H9 4 was dissolved in 10 ml of ethanol with magcal and thermal stability. CNTs, including single-walled
netic stirring. A white Ti(OH)4 precipitate was obtained as
and multi-walled carbon nanotubes (MWCNTs), have been
0.25 M ammonia solution was slowly added to the mixstudied extensively for many potential engineering appliture of Ti(OC4 H9 4 and ethanol. Precipitated Ti(OH)4 was
cations, including EMI shielding, because of their fasciseparated from the suspension by centrifugation, rinsed
nating electronic and chemical properties.17–19 Work on
with distilled water and then dispersed in a 50 ml mixture
CNTs decorated by metal or metal-oxide composites, such
of NH2 CH2 CH2 OH and NH2 CH2 CH2 NH2 with stirring.
as Fe3 O4 /MWCNT, CoO/MWCNT, Fe-filled or Ni-coated
2 ml of 4 M Ba(CH3 COO)2 aqueous solution, the oxidized
MWCNT, is emerging as a promising and exciting domain
MWCNTs and 1.5 ml of polyvinyl alcohol 200 liquid were
of research because of their outstanding performance and
thento:
added
to the mixed
solution. After the mixture was
Delivered by Publishing Technology
University
of Waterloo
extensive applications.20–23 It isIP:well
known that CNTs,
213.138.164.228
On: Wed,
04 Novfor
2015
10:19:42
sonicated
30 min,
3.5 ml of 8 M NaOH aqueous soluthemselves, are good EM wave absorbers,
throughAmerican
dielec- Scientific
Copyright:
tion wasPublishers
used to titrate to approximately pH 12 under
tric loss. Considering the above advantages of BaTiO3
magnetic stirring. The suspension was stirred for 1 h and
and MWCNTs, a BaTiO3 /MWCNT composite can be prethen transferred into an 80 ml stainless steel Teflon-lined
pared to combine the properties of BaTiO3 and CNTs and
autoclave. The autoclave was sealed and heated at 200 C
enhance the absorption capability.
in an oven for 12 h and then cooled to room temperature.
Many preparation pathways and treatment methods for
Finally, the slurry product was separated from the suspenCNTs have been applied to combine the unique propersion by centrifugation and washed six times with distilled
ties of CNTs and metal-oxides.24–26 Compared with other,
water and ethanol. A small quantity of BaCO3 impurity
traditional, preparation methods, solvent-thermal synthesis
could be removed by an acid washing process. The prodhas advantages for preparing BaTiO3 and BaTiO3 composuct was dried at 80 C for 24 h. For EM wave absorption
ites with a homogeneous microstructure for good control
control experiments, pure BaTiO3 particles were prepared
of crystallization and particle growth, without requiring a
using a similar synthesis procedure to that of the composhigh temperature calcination process. Although nanoscale
ite but oxidized MWCNTs were not introduced, and the
metal-oxide-coated CNT composites have attracted much
sample of MWCNTs were purified through an acid treatattention for their potential applications, solvent-thermal
ment to remove the residual catalyst, which may affect the
synthesis and EM wave absorption properties of MWCresults of EM parameters measurement.
NTs decorated with BaTiO3 nanoparticles have rarely been
27 28
studied.
2.2. Characterization
Synthesis and Electromagnetic Wave Absorption Properties of MWCNTs Decorated by BaTiO3 Nanoparticles
RESEARCH ARTICLE
morphological, size and crystallinity analyses. The synthesized composite powders were uniformly mixed with
epoxide resin, which is transparent for EM wave because
of its low permittivity and permeability as an insulator.10 13
The mixture was pressed into a cylindrical shape and then
cut into toroidal sample with a thickness of 4 mm for EM
parameters measurements. The samples for the both pure
BaTiO3 and MWCNTs powders are processed by the same
procedure. The EM parameters of the toroidal shaped samples loaded 20 wt% synthesized composite, pure BaTiO3
and MWCNTs, respectively, were measured by a reflection/transmission technique, using an Agilent E8363A vector network analyzer with the testing frequency bands in
the range from 2 to 18 GHz. The RL of the samples
were calculated based on a model of a single-layered plane
wave absorber, using transmission line theory and the EM
parameters, including the real and imaginary parts of complex permittivity ( and ) and complex permeability
( and ).
Bi et al.
Fig. 1. XRD patterns of the BaTiO3 /MWCNT composite with hybrid
nanostructure.
because of the formation of ionic bonds between Ti cations
hanging on the surface of the BaTiO3 particles and the car3. RESULTS AND DISCUSSION
boxyl and hydroxyl groups of oxidized MWCNTs, which
3.1. Structure and Morphology of BaTiO3 /MWCNT
was reported by previous studies.30 Figure 2(c) shows the
Composite
SAED pattern taken from the sample, which displays polycrystalline diffraction rings. The diffraction rings, repreFigure 1 shows the XRD pattern of the BaTiO3 /MWCNT
senting corresponding crystal faces, coincide well with
composite prepared by the solvent-thermal method at
the to:
cubic
perovskites
structure and the first five indicated
Delivered
Technology
University
of Waterloo
200 C for 12 h. XRD
patternbyofPublishing
as-synthesized
IP: 213.138.164.228 On: Wed,
04 Nov
2015
crystal
faces
are10:19:42
(100), (110), (111), (200) and (210),
BaTiO3 /MWCNT composite not only
has the American
diffrac- Scientific Publishers
Copyright:
respectively. HRTEM images of the BaTiO3 /MWCNT
tion peaks of the MWCNTs but also those of diffraccomposite are shown in Figure 2(d). Clear, square lattice
tion peaks for the standard pattern of BaTiO3 crystals
fringes, with d100 = 3.9 Å and d010 = 3.9 Å observed in
(JCPDS, No. 31-0174). The diffraction peak assigned to
the (0 0 2) plane at 2 = 26.3 is the typical Bragg peak
of MWCNTs,26 indicating that the CNT structure was not
destroyed during the solvent-thermal treatment. The crystal
structure of the BaTiO3 nanoparticles, revealed by clearly
resolved diffraction peaks, can be classified as a cubic perovskite structure, without any detectable crystalline impurities, such as TiO2 or BaCO3 . The average crystallite size
of BaTiO3 particles was calculated to be 26.2 nm from
the width of X-ray diffraction peak, using the Scherrer’s
equation.
Figure 2 shows the representative TEM images of the
as-synthesized BaTiO3 /MWCNT composite. Figure 2(a)
reveals that BaTiO3 particles with diameters in the range
of 15–30 nm were synthesized and assembled on the sidewalls of the MWCNTs. The sphere-like morphology and
homogeneous microstructure of the particles can also be
identified from the image. Moreover, Figure 2(b) shows
an overview image at a low TEM resolution. It was found
that the MWCNTs were densely decorated with nanoscale
BaTiO3 particles. The phenomenon of slight agglomeration of small particles could be also observed. Although
Fig. 2. Representative TEM micrographs of BaTiO3 /MWCNT composthe sample was sonicated at high power in ethanol before
ite with hybrid nanostructure synthesized by the solvent-thermal method:
the TEM measurement, the structure of the nanoscale
(a–b) BaTiO3 /MWCNT composite; (c) selected SAED; (d) HRTEM
BaTiO3 -coated MWCNTs was not destroyed probably
images of BaTiO3 nanoparticles.
1032
J. Nanosci. Nanotechnol. 11, 1030–1036, 2011
Bi et al.
Synthesis and Electromagnetic Wave Absorption Properties of MWCNTs Decorated by BaTiO3 Nanoparticles
the image, provide evidence that the particles were cubic
perovskites structure with high crystallinity, which corresponds to the XRD and SAED results.
According to the results of TEM and the report of
Huang,30 the mixture of NH2 CH2 CH2 OH and NH2 CH2
CH2 NH2 , as a strong reducing agent, seems to contribute
to the inhibition of crystal growth compared with other
reaction media. With the introduction of small amounts
of water, which is usually considered to improve the
crystallization, homogeneous shapes and well-crystallized
BaTiO3 particles with small size would be formed on the
sidewalls of MWCNTs through a dissolution-precipitation
mechanism during the solvent-thermal treatment.
3.2. EM Wave Absorption Properties of
BaTiO3 /MWCNT Composite
To investigate the EM wave absorption properties of the
as-synthesized composite, EM parameters of the samples
were measured on an Agilent E8363A network analyzer
and the RL was calculated according to transmission line
theory,31–33 using the formula:
Zin − 1 (1)
RLdB = 20 log
Zin + 1 Fig. 3. Calculated RL of BaTiO3 /MWCNT composite, MWCNTs and
BaTiO3 using the transmission line theory in the frequency range
2–18 GHz at constant thickness.
J. Nanosci. Nanotechnol. 11, 1030–1036, 2011
1033
RESEARCH ARTICLE
between 8.6 and 16 GHz, similar to the RL enhancement
by decoration of CNTs in electrical conductive polymers
and metal-oxides. The minimum RL of −37.5 dB was
located at 10.4 GHz, with a relatively broad absorption frequency band having losses above −5 dB over a frequency
range from 8.8 to 14.5 GHz. The RL less than −10 dB
was also found for the BaTiO3 /MWCNT composite in the
The normalized input impedance (Zin ) is given by the
9.6–13.1 GHz range. The composite was approximately
equation:
Delivered by Publishing Technology
to: University
of Waterloo
similar
to the BaTiO
3 sample in the absorption region
On: Wed, 04 Nov 2015 10:19:42
IP: 213.138.164.228
but
improved
in
the
absorption
ability, which was indi
2ft Copyright:
√
American Scientific Publishers
(2)
tan h j
Zin =
cated
that
the
MWCNTs
contribute
to the developed abil
c
ity in the composite. As many metal or metal-oxide-filled
According to the formula, there are six characteristic
MWCNTs composite, including CoFe2 O4 /CNTs, Er2 O3 parameters, c, f , t, r , r , r and r , where c, f and t
filled MWCNTs and Co-filled MWCNTs, a sharp peak
are the velocity of the EM wave, the frequency of the EM
was obtained in the BaTiO3 /MWCNTs, which was probwave and the wall thickness of the absorber, respectively.
able caused by enhanced dielectric loss resulting from a
r = r –jr and r = r –jr , the complex permeability
improved polarization, especially interface and molecular
and complex permittivity, respectively, can be investigated
polarization.27 34 The optimal absorption peak for BaTiO3
by the microwave network analyzer.
in previous reports was around 13 GHz, which was in
Assuming t = 2 mm, and with c and f as known values
good agreement with the above results.11 12 However, the
at 25 C, the RL of pure MWCNTs, pure BaTiO3 and the
presentation for the dips of −37.5 dB at 10.4 GHz in the
as-synthesized BaTiO3 /MWCNT composite were calcuBaTiO3 /MWCNTs may be influenced by the MWCNTs
lated using Eqs. (1) and (2) in the frequency range from 2
of the composite for its low frequency absorption region.
to 18 GHz and displayed in Figure 3. In general, the RL of
Figure 4 shows the frequency dependence of the RL of the
pure MWCNTs was almost constant at −2 dB, except for
sample containing with 20 wt% BaTiO3 /MWCNT coma peak of −11.5 dB at 5.9 GHz, and the bandwidth with a
posite for the calculated layer thickness ranging form 1.6
loss above −5 dB was in the frequency range 5.2–7.5 GHz.
to 2.2 mm in the frequency range 2–18 GHz. It indicates
This shows that the RL of pure MWCNTs was poor
that the absorption frequency region and its peak shifted
throughout the whole frequency range. Also, the RL of
to a low frequency with the increasing calculated layer
pure BaTiO3 from the corresponding layer was smaller
thickness.31–33 Additionally, it can be also noted that the
than −5 dB between 9.4 and 15.1 GHz, with a minimum
peak values were enhanced with the increase in thickness,
of −9.3 dB at 14 GHz. It is clearly shown, therefore,
and get the maximum with the matched thickness of 2 mm.
that BaTiO3 only weakly absorbed EM waves, with the
The complex permeability and complex permittivity of
whole bandwidth of RL being less than −10 dB. In conthe three samples were studied and transformed into curves
trast, when the surfaces of the MWCNTs were decorated
to investigate the effects that lead to enhancement of the
with nanoscale BaTiO3 particles, the BaTiO3 /MWCNT
wave-absorbing ability. The complex permittivity and percomposite exhibited a greatly enhanced RL at frequencies
meability of pure MWCNTs are presented in Figure 5.
Synthesis and Electromagnetic Wave Absorption Properties of MWCNTs Decorated by BaTiO3 Nanoparticles
RESEARCH ARTICLE
Fig. 4. The thickness dependent of RL for BaTiO3 /MWCNT composite
in the frequency range 2–18 GHz.
Bi et al.
materials should be designed to be nearly equal to the
free space (377 ) to reduce wave reflection at the front
surface of the material.33 Because of their high electric
conductivity, pure MWCNTs with the weak electromagnetic impedance matching are hardly to show considerable
EM wave absorption.
From the complex permittivity of BaTiO3 /MWCNT
composite and pure BaTiO3 shown in Figure 6(a), it can
be seen that the r and r of BaTiO3 /MWCNT composite were clearly larger than those of pure BaTiO3 at almost
all frequencies between 2 and 18 GHz, which can be
attributed to formation of a whole conductive network by
the BaTiO3 /MWCNT composite in the matrix, resulting in
a larger dielectric loss arising from interface polarization
and induced microcurrent, causing more efficient absorption than by separate particles. Moreover, the large distance
between adjacent clusters and the absence of electrical conductivity, led to the low absorbance ability of pure BaTiO3 ,
whose resistivity is about 6.65 × 107
mm. In contrast,
as shown in Figure 6(b), r and r in both samples were
similar and were both small, except for a peak in the curve
It can be seen from the curves that the real and imaginary parts of the complex permeability were negligibly
small, compared with the real and imaginary parts of the
complex permittivity at whole frequencies ranging from
2 to 18 GHz. This shows that the main contribution to
RL is dielectric loss. For the imaginary part of complex
permittivity r , the values increased with increasing frequency and even exceeded 20 at higher frequencies, with
a distinct peak at frequencies ranging from 6 to 8 GHz.
Technology to: University of Waterloo
compared by
to Publishing
those for carbon
The high values of r , asDelivered
IP: 213.138.164.228 On: Wed, 04 Nov 2015 10:19:42
black, graphite and their composites,Copyright:
are stronglyAmerican
related Scientific Publishers
to the excellent conductive properties of MWCNTs and
network formation of the conducting MWCNTs in an insulating organic background.35 However, the relatively high
electric conductivity of the pure MWCNTs, which was
mm, makes the effecmeasured to be about 0.53 × 102
tive permeability in the high frequency decrease drastically due to the eddy currents induced by EM wave.7 13
Furthermore, another important parameter, the concept of
matched characteristic impedance, limits the RL of pure
MWCNTs so the characteristic impedance of the absorbing
Fig. 5. Complex permittivity and permeability of the MWCNTs in the
frequency range 2–18 GHz.
1034
Fig. 6. Real and imaginary complex permittivity (a) and real and imaginary complex permeability (b) of BaTiO3 /MWCNT composite and
BaTiO3 in the frequency range 2–18 GHz.
J. Nanosci. Nanotechnol. 11, 1030–1036, 2011
Bi et al.
Synthesis and Electromagnetic Wave Absorption Properties of MWCNTs Decorated by BaTiO3 Nanoparticles
China (Nos. 50772022, 50772127), Shanghai Leading
Academic Discipline Project (B603), the Cultivation Fund
of the Key Scientific and Technical Innovation Project
(No. 708039), and the Program of Introducing Talents of
Discipline to Universities (No. 111-2-04).
References and Notes
Fig. 7. Schematic of the EM wave absorption process in a BaTiO3 /
MWCNT composite.
J. Nanosci. Nanotechnol. 11, 1030–1036, 2011
1. Y. B. Feng, T. Qiu, and C. Y. Shen, J. Magn. Magn. Mater. 318, 8
(2007).
2. M. Nakanishi, Y. Uchida, T. Fujii, J. Takada, Y. Kusano, and
T. Kikuchi, Carbon 45, 2460 (2007).
1035
RESEARCH ARTICLE
of BaTiO3 /MWCNT composite, indicating that magnetic
on the sidewalls of MWCNTs. Then, through interactions
between the electric field and mobile electrons, the EM
loss cannot be considered to be the primary cause of
wave tends to induce a microcurrent through the network
RL enhancement with frequency. It can be found that the
formed by the MWCNTs with finite conductivity, simienhancement in dielectric loss for BaTiO3 /MWCNT comlar to the carbon black composite but not identical, which
posite as compared with pure BaTiO3 led to the improvecould hardly form a network in the matrix.13 Additionment of EM wave absorption. The negative values for
ally, molecular polarization and interface polarization phepure BaTiO3 are probable from the error of equipment.
nomena generated by the interaction between EM wave
However, recent reports found that Fe3 O4 /SnO2 core/shell
penetrating the surface of the BaTiO3 particles and the
nanorods and MWCNTs/wax composite had the negative
electric field intensified by the microcurrent arising from
values of r due to left-hand properties of the materiMWCNTs, occurs in the BaTiO3 particles and induces
als and the magnetic energy being radiated out from the
current. In the last step, the electrical energy (including
composites, respectively.36 37 Thus, the negative values for
the energy loss owing to molecular polarization) transBaTiO3 /MWCNTs composite and MWCNTs may not be
formed from the EM wave energy is rapidly dissipated
the error, and more detail mechanism needs further study.
as heat by the resistance of the material. Thus, the dissiComparing Figure 5 with Figure 6, for BaTiO3 /MWCNT
pated energy is considered to have been ‘absorbed’ by the
composite, whose resistivity was measured to be about
2
composite.38 39
mm, the real and imaginary parts of the
3.32×10
complex permittivity show prominent attenuation, compared with pure MWCNTs, which have been caused by a
4. CONCLUSIONS
decrease in the electrical conductivity. Although, the comIn conclusion, a novel, hybrid, nanostructured BaTiO3 /
plex permittivity of BaTiO3 /MWCNT composite decreased
MWCNT composite was successfully synthesized by
in the whole frequency, when the MWCNTs was deco
a simple and highly efficient solvent-thermal method.
rated with BaTiO3 as an insulator, the values of r for
BaTiO3 nanoparticles in the form of regular dots, with a
BaTiO3 /MWCNT composite were enhanced in the high frenarrow
particle size distribution in the range of 15–30 nm
quency region resulting from a decrease of eddy currents
were
uniformly
attached on the external surface of
induced by EM wave, owing to the finite increase in resisMWCNTs
after
the
solvent-thermal treatment. The RL
tivity. Therefore, it can be concluded
increase in
the
Deliveredthat
by the
Publishing
Technology
to: University
of Waterloo
provided
by
the
BaTiO
3 /MWCNT composite was around
resistivity improved the matched
impedance
IP:characteristic
213.138.164.228
On: Wed, 04 Nov 2015 10:19:42
−10
dB
in
the
frequency
range 9.6–13.1 GHz and achieved
Copyright:
American
and enhanced the complex permeability
in the high
fre- Scientific Publishers
a
minimum
RL
of
−37.5
dB at 10.4 GHz, indicating that
quency and thus contributed to the developed EM wave
such
a
composite
can
be
applied as a shielding material
absorption in the BaTiO3 /MWCNT composite for high freagainst
EMI.
Investigation
of the complex permeability
quency region.
and
permittivity
indicates
that
the improved RL properTo reveal the possible EM wave absorption mech/MWCNT
composite
in high frequency
ties
of
the
BaTiO
3
anism of the novel hybrid nanostructure, a simulation
region
can
be
attributed
to
a
better
matched
characteristic
scheme, illustrating the EM wave absorption process of the
impedance
and
an
enhanced
complex
permeability
in the
as-synthesized BaTiO3 /MWCNT composite, is displayed
high
frequency
because
of
the
eddy
currents
decreasing
in the schematic of Figure 7. In the first step, the incident
owing to the finite increase in resistivity. The conductivity
EM wave penetrates into the regions where MWCNTs,
network in the matrix formed by MWCNTs may generate
decorated with nanoscale BaTiO3 particles, exist. In the
highly efficient electrical energy dissipation in the comsecond step, reflected and transmitted waves are generated
posite, compared with isolate particles.
when the incident EM wave contacts the surface of the
composite. Compared with pure MWCNTs, less reflected
Acknowledgments: We gratefully acknowledge the
EM wave in the BaTiO3 /MWCNT composite can be generfinancial supports by Shanghai Municipal Education Comated due to the high electric resistivity of BaTiO3 particles
mission (No. 07SG37), Natural Science Foundation of
RESEARCH ARTICLE
Synthesis and Electromagnetic Wave Absorption Properties of MWCNTs Decorated by BaTiO3 Nanoparticles
Bi et al.
3. G. H. Mu, H. G. Shen, J. X. Qiu, and M. Y. Gu, Appl. Surf. Sci.
21. L. R. Kong, X. F. Lu, and W. J. Zhang, J. Solid State Chem. 181, 628
253, 2278 (2006).
(2008).
4. G. V. Ramesh, K. Sudheendran, K. C. J. Raju, B. Sreedhar, and T. P.
22. H. Zhang, N. Du, P. Wu, B. D. Chen, and D. R. Yang,
Radhakrishnan, J. Nanosci. Nanotechnol. 9, 261 (2009).
Nanotechnology 19, 315604 (2008).
5. F. Ma, J. J. Huang, J. G. Li, and Q. Li, J. Nanosci. Nanotechnol.
23. H. T. Pu and F. J. Jiang, Nanotechnology 16, 1486 (2005).
9, 3219 (2009).
24. L. H. Tang, Y. H. Zhu, X. L. Yang, J. J. Sun, and C. Z. Li, Biosens.
6. C. M. Yang, H. Y. Li, D. B. Xiong, and Z. Y. Gao, React. Funct.
Bioelectron. 24, 319 (2008).
Polym. 69, 137 (2009).
25. C. Q. Li, N. J. Sun, J. F. Ni, J. Y. Wang, H. B. Chu, H. H. Zhou,
7. N. Guskos, V. Likodimos, S. Glenis, M. Maryniak, M. Baran,
M. X. Li, and Y. Li, J. Solid State Chem. 181, 2620 (2008).
R. Szymczak, Z. Roslaniec, M. Watkowska, and D. Petridis,
26. Y. Liu, W. Jiang, Y. Wang, X. J. Zhang, D. Song, and F. S. Li,
J. Nanosci. Nanotechnol. 8, 2127 (2008).
J. Magn. Magn. Mater. 321, 408 (2009).
8. J. J. Huang, Y. Qin, J. G. Li, X. D. Jiang, and F. Ma, J. Nanosci.
27. L. Zhang, H. Zhu, Y. Song, Y. M. Zhang, and Y. Huang, Mater. Sci.
Nanotechnol. 8, 3967 (2008).
Eng., B 153, 78 (2008).
9. S. M. Abbas, A. K. Dixit, R. Chatterjee, and T. C. Goel, Mater. Sci.
28. R. C. Che, C. Y. Liang, H. L. Shi, X. G. Zhou, and X. N. Yang,
Eng., B 123, 167 (2005).
Nanotechnology 18, 355705 (2007).
10. X. D. Chen, G. Q. Wang, Y. P. Duan, and S. H. Liu, J. Alloys.
29. R. Q. Yu, L. W. Chen, Q. P. Liu, J. Y. Lin, K. L. Tan, S. C. Ng,
Compd. 453, 433 (2008).
H. S. O. Chan, G. Q. Xu, and T. S. A. Hor, Chem. Mater. 10, 718
11. Y. K. Liu, Y. J. Feng, X. W. Wu, and X. G. Han, J. Alloys. Compd.
(1998).
472, 441 (2009).
30. Q. Huang and L. Gao, J. Mater. Chem. 14, 2536 (2004).
12. X. D. Chen, G. Q. Wang, Y. P. Duan, and S. H. Liu, J. Phys. D:
31. P. Xu, X. J. Han, J. J. Jiang, X. H. Wang, X. D. Li, and A. H. Wen,
Appl. Phys. 40, 1827 (2007).
J. Phys. Chem. C 111, 12603 (2007).
13. X. G. Liu, B. Li, D. Y. Gen, W. B. Cui, F. Yang, Z. G. Xie, D. J.
32. P. Xu, X. J. Han, C. Wang, H. T. Zhao, J. Y. Wang, X. H. Wang,
Kang, and Z. D. Zhang, Carbon 47, 470 (2009).
and B. Zhang, J. Phys. Chem. B 112, 2775 (2008).
14. C. C. Lee and D. H. Chen, Appl. Phys. Lett. 90, 193102 (2007).
33. P. Xu, X. J. Han, C. Wang, D. H. Zhou, Z. H. Lv, A. H. Wen, X. H.
15. X. G. Liu, D. Y. Geng, H. Meng, P. J. Shang, and Z. D. Zhang,
Wang, and B. Zhang, J. Phys. Chem. B 112, 10443 (2008).
Appl. Phys. Lett. 92, 173117 (2008).
34. R. C. Che, C. Y. Zhi, C. Y. Liang, and X. G. Zhou, Appl. Phys. Lett.
16. Y. J. Chen, P. Gao, C. L. Zhu, R. X. Wang, L. J. Wang, M. S. Cao,
88, 033105 (2006).
and X. Y. Fang, J. Appl. Phys. 106, 054303 (2009).
35. L. L. Wang, B. K. Tay, K. Y. See, Z. Sun, L. K. Tan, and D. Lua,
17. Z. J. Fan, G. H. Luo, Z. F. Zhang, L. Zhou, and F. Wei, Mater. Sci.
Carbon 47, 1905 (2009).
Eng., B 132, 85 (2006).
36. L. J. Deng and M. G. Han, Appl. Phys. Lett. 91, 023119
18. H. M. Kim, K. Kim, C. Y. Lee, J. Joo, S. J. Cho, H. S. Yoon, D. A.
(2007).
37. Y. J. Chen, P. Gao, R. X. Wang, C. L. Zhu, L. J. Wang, and M. S.
Pejakovic, J. W. Yoo, and A. J. Epstein, Appl. Phys. Lett. 84, 589
Delivered by Publishing Technology Cao,
to: University
of Waterloo
J. Phys. Chem. C 113, 10061 (2009).
(2004).
IP: 213.138.164.228 On: Wed,
04 Nov 2015 10:19:42
38. S. W. Phang, M. Tadokoro, J. Watanabe, and N. Kuramoto, Curr.
19. P. C. P. Watts, W. K. Hsu, A. Barnes, and B. Chambers, Adv. Mater.
Copyright: American Scientific
Publishers
Appl. Phys. 8, 391 (2008).
15, 600 (2003).
39. D. A. Makeiff and T. Huber, Synth. Met. 156, 497
20. D. L. Zhao, X. Li, and Z. M. Shen, Compos. Sci. Technol. 68, 2902
(2006).
(2008).
Received: 12 December 2009. Accepted: 5 February 2010.
1036
J. Nanosci. Nanotechnol. 11, 1030–1036, 2011