RESEARCH PAPER

Fe3O4–graphene hybrids: nanoscale characterizationand their enhanced electromagnetic wave absorptionin gigahertz range

Xinghua Li • Haibo Yi • Junwei Zhang •

Juan Feng • Fashen Li • Desheng Xue •

Haoli Zhang • Yong Peng • Nigel J. Mellors

Received: 6 December 2012 / Accepted: 28 January 2013

� Springer Science+Business Media Dordrecht 2013

Abstract Fe3O4–graphene hybrid materials have

been fabricated by a simple polyol method, and their

morphology, chemistry and crystal structure have

been characterized at the nanoscale. It is found that

each Fe3O4 nanoparticles decorated on the graphene

has a polycrystalline fcc spinel structure and a

uniform chemical phase. Raman spectroscopy, Fourier

transform infrared spectroscopy, thermogravimetry/

differential thermal analysis, X-ray diffraction, and

transmission electron microscopy suggest that Fe3O4

nanoparticles are chemically bonded to the graphene

sheets. Electromagnetic wave absorption shows that the

material has a reflection loss exceeding -10 dB in

7.5–18 GHz for an absorber thickness of 1.48–3 mm,

accompanying a maximum reflection loss value of

-30.1 dB at a 1.48-mm matching thickness and 17.2-

GHz matching frequency. Theoretic analysis shows that

the electromagnetic wave absorption behavior obeys

quarter-wave principles. The results suggest that the

magnetic Fe3O4–graphene hybrids are good candidates

for the use as a light-weight electromagnetic wave-

absorbing material in X- and Ku-bands.

Keywords Fe3O4 � Graphene � Hybrids �Magnetic � Electromagnetic

Introduction

Graphene, as a novel carbon-based material (Geim and

Novoselov 2007), has attracted ever-increasing atten-

tion for both fundamental and experimental scientific

research due to its remarkable physical properties,

such as optical conductivity (Mak et al. 2008), thermal

conductivity (Balandin et al. 2008), room-temperature

quantum Hall effect (Novoselov et al. 2007), as well as

its mechanical stiffness (Lee et al. 2008). These

extraordinary properties make graphene an outstand-

ing candidate for various technological applications

(Alwarappan et al. 2009, 2010, 2012a, b, c; Huang

et al. 2012; Wan et al. 2011). Besides, graphene canElectronic supplementary material The online version ofthis article (doi:10.1007/s11051-013-1472-1) containssupplementary material, which is available to authorized users.

X. Li � H. Yi � J. Zhang � J. Feng � F. Li (&) �D. Xue � Y. Peng

Key Laboratory of Magnetism and Magnetic Materials

of Ministry of Education, School of Physical Science

and Technology, Lanzhou University, Lanzhou,

People’s Republic of China

e-mail: lifs@lzu.edu.cn

Y. Peng

e-mail: pengy@lzu.edu.cn

H. Zhang

State Key Laboratory of Applied Organic Chemistry,

College of Chemistry and Chemical Engineering,

Lanzhou University, Lanzhou, People’s Republic

of China

N. J. Mellors

Nano Materials Group, School of Computing, Science

and Engineering, University of Salford, Greater

Manchester, UK

123

J Nanopart Res (2013) 15:1472

DOI 10.1007/s11051-013-1472-1

also act as a nanoscale building block for novel hybrid

materials owning to its huge surface area and special

layered structure (Dutta and Pati 2010; Xu et al. 2012).

Decorating graphene sheets with polymer or inorganic

nanoparticles is an effective approach to form novel

graphene-based hybrids with tailored properties (Gao

et al. 2012; Huang et al. 2011; Liu et al. 2011; Xu et al.

2008; Zhu et al. 2012). For example, assembling

inorganic nanoparticles onto the graphene sheets not

only decreases the restacking of the graphene sheets to

provide a higher surface area but also immensely

enhances the properties of the graphene.

Electromagnetic wave-absorbing materials have

been universally applied in newly developed wireless

devices, advanced electronics, electromagnetic inter-

ference (EMI) shielding, and military electromagnetic

wave electronics. The material features achieved,

include thin matching thickness, light weight, wide

band adsorption, and high adsorption, which are the

principal properties for an ideal electromagnetic

wave-absorbing material (Zhu et al. 2010). Traditional

electromagnetic wave-absorbing materials such as

ferrites (Wang et al. 2011) and magnetic metals (Liu

et al. 2008; Liu et al. 2009) have strong EMI shielding

properties due to their high complex permeability.

However, these magnetodielectric absorbers have a

high density and can only be produced with large

thickness, which often restricts their universal appli-

cation. Therefore, the demand for the development of

lightweight and stable electromagnetic absorbing

materials is becoming increasing necessary with

rapidly growing number of potential applications.

According to the quarter-wavelength matching model

(Li et al. 2011), the enhancement of the complex

permeability (lr) and permittivity (er) are the main

factors dominating the electromagnetic wave-absorb-

ing properties of a material with a thin thickness (tm).

For this reason, carbon nanotube (CNT) filled with

magnetic materials has been widely studied as a

lightweight electromagnetic wave absorber (Che et al.

2004; Lv et al. 2008; Wen et al. 2011; Qing et al. 2010;

Che et al. 2006). But, the low decorating content of

magnetic nanoparticles and the complex fabrication

method of CNT, limit their practical applications.

Graphene which can be considered as an unrolled

CNT (Geim and Novoselov 2007) has similar mechan-

ical and physical properties to CNT, but with superior

thermal and electrical properties and larger surface

areas (Singh et al. 2011). Graphene has been used for

dispersing electrostatic charges (Xian et al. 2011) and

for shielding from EMI (Liang et al. 2009) due to its

excellent conductivity. The remarkable thermal con-

ductivity also enables it to perform across a wide

temperature range. Its very large surface areas close to

2,600 m2 g-1 make it easier decorate and form hybrid

materials, and its high aspect ratio is expected to be

able to support a highly effective network for potential

electromagnetic wave-absorbing applications. More-

over, the plate-like materials may exceed the Snoek’s

limit in the high frequency range and show more

effective absorption properties owing to the large

shape anisotropy in contrast to the rod-like or spherical

geometries in conventional systems. In addition, there

should be further advantage by using graphene as a

composite of electromagnetic wave-absorbing mate-

rial since it is lightweight, flexible, and anticorrosive.

Therefore, graphene-based magnetic hybrids, which

combine the excellent conductivity of graphene with

the highly complex permeability of the deposited

magnetic nanoparticles, are believed to be an ideal

combination as a lightweight electromagnetic wave-

absorbing material for the next generation of EMI

materials.

In this paper, Fe3O4–graphene hybrids were syn-

thesized through a simple polyol method. Combining

both the benefits of excellent complex permittivity

from Fe3O4 nanoparticles and permeability from the

light-weight graphene, the Fe3O4–graphene hybrids

show excellent electromagnetic wave absorption

properties which obey the quarter-wavelength match-

ing model. The results show that the magnetic

graphene-based hybrids could be ideal candidate

materials for the manufacture of light-weight electro-

magnetic wave-absorbing devices in X- and Ku-bands.

Experimental

Preparation of graphene oxide (GO)

All chemical materials are of analytical grade and

were used as received without further purification.

GO was prepared using natural graphite flake by a

modified Hummers method (Hummers and Offeman

1958), including graphite oxidation, exfoliation, and

chemical reduction. K2S2O8 (5.0 g) and P2O5 (5.0 g)

were dissolved in concentrated H2SO4 (30 ml) at

Page 2 of 11 J Nanopart Res (2013) 15:1472

123

90 �C. The mixture was cooled down to 80 �C, and

natural graphite flake (150 mg) was slowly added

into the mixture followed by stirring at 80 �C for

4.5 h. Then, the mixture was cooled down to room

temperature naturally, diluted with lots of deionized

water, and left to stand overnight. The mixture was

filtered by a 0.2-micron Nylon film and washed with

deionized water until the filtrate was neutral. The

product was dried at 50 �C in vacuum oven for

one day.

The pretreated graphite powder was added into

concentrated H2SO4 (12 ml) at 0 �C. KMnO4 (1.5 g)

was added slowly to the above mixture until com-

pletely dissolved, during which the reaction temper-

ature was kept by ice bath. Successively, the mixture

was heated to 35 �C and stirred for 2 h. Then, 25 ml

water was added, and the mixture was heated to reflux

at 90 �C for 0.5 h. When the solution was cold to room

temperature, the mixture was diluted by additional

water (75 ml) and then H2O2 (30 %) was added in

drops until the color of the mixture became brilliant

yellow. Then, the mixture was washed by performing

dialysis for one week to remove the residual ion. The

resulting yellow-brown solution was then centri-

fuged at 12,000 rpm for 20 min to obtain the graphene

oxide.

Preparation of Fe3O4–graphene hybrids

Fe3O4–graphene hybrids were fabricated by chemi-

cal thermolysis of iron ions attracted to GO through a

simple polyol method. In a typical process, 20 mg

GO was dissolved in 30 ml EG and ultrasound

applied for 3 h to produce GO with few layers, during

which a claybank solution was formed. FeCl3�6H2O

(3 mmol) was then added into this GO-containing

solution and further treated with ultrasound for an

additional 3 h to enhance the Fe3? attraction onto the

surface of the GO. Then, NaAc (15 mmol) was added

to the solution and heated to reflux for 10 h. In this

case, NaAc was not only used for electrostatic

stabilization to prevent the agglomeration of the

particles but also to assist in the reduction of Fe3? to

Fe3O4; EG was used as both a reducing agent and

solvent. The obtained Fe3O4–graphene hybrids were

centrifuged at 10,000 rpm and washed with water

and ethanol several times. The products were then

dried at 60 �C in air.

Characterizations

The morphology and microstructure of the Fe3O4–

graphene hybrids was characterized by high-resolution

transmission electron microscope (TEM) (Tecnai TM G2

F30, FEI) embedded with energy-dispersive X-Ray

analysis (EDAX, AMETEK Co., LTD), high angle

annular dark field (HAADF), and scanning transmission

electron microscopy (STEM). The scanning electron

microscopic (SEM) image was captured using a Hitachi

S-4800 field emission scanning electron microscope

(SEM). The crystal structure of the samples was

characterized by X-ray diffraction (XRD) using Cu Ka

radiation (k = 1.5418 A) (X’pert powder, Philips).

FTIR spectrums of the hybrids were obtained using a

170SX spectrometer in the range of 400–4,000 cm-1.

Raman spectra were observed by Reinishaw confocal

spectrometry incorporating a 633-nm wavelength laser.

Magnetic properties of the samples were studied using a

Lake Shore 7304 vibrating sample magnetometer (VSM)

at room temperature.

Electromagnetic measurements

The electromagnetic wave absorption of the Fe3O4–

graphene hybrids was investigated using an Agilent

Technologies E8363B network analyzer in the range of

0.1–18 GHz. Electromagnetic wave measurement sam-

ples were prepared by mixing paraffin with 15 vol.%

Fe3O4–graphene hybrids and pressed into toroidal

(wout: 7.00 mm, win: 3.04 mm).

Results and discussion

Fe3O4–graphene hybrids were prepared by a simple

polyol method as schematically illustrated in Fig. 1.

Typically, GO (Fig. 2) and FeCl3�6H2O were dis-

solved in EG by ultrasound, followed by reflux for

10 h to obtain the Fe3O4–graphene hybrids. The

morphology and structure of GO sheets have been

characterized before the iron oxide nanoparticles were

assembled. Figure 2a–c presents the TEM images of

GO at different magnifications. A crumpled structure

with scrolling on the edge of the GO sheets is

obviously existed, revealing the deformation due to

the exfoliation and restacking process. The selected

area electron diffraction (SAED) pattern indicates

the high crystalline characterization of the GO, as

J Nanopart Res (2013) 15:1472 Page 3 of 11

123

displayed in Fig. 2d. Furthermore, the reciprocal

space of the GO shows a set of six rods with a weak

and monotonous intensity variation normal to the

plane, suggesting that the GO is few-layer (Meyer

et al. 2007). These results show that individual GO

sheets are molecularly thin and have an hcp structure

(Fig. 2d). The interplanar spacing of (001) planes were

measured at approximately 0.78 nm, which is larger

than that of graphite.

Figure 3 shows the SEM images of original GO and

Fe3O4–graphene hybrids. It is clear that Fe3O4 nano-

particles highly covered on the surface of the two-

dimensional GO nanosheets (Fig. 3b), indicating a

possibly electrostatic attraction mechanism between

graphene and Fe3O4 nanoparticles.

A representative TEM image of the Fe3O4–graph-

ene hybrids is shown in Fig. 4a. The result shows that

this piece of translucent graphene sheet is homoge-

neously decorated by iron oxide nanoparticles and that

there are no nanoparticles attached to the holey carbon

film of the TEM grid. This observation is accordant

with the SEM analysis (Fig. 3b). This result suggests

that there could be covalent bonding between the

graphene sheets and the iron oxide nanoparticles. A

detailed investigation of the chemical bonding will be

given latter in this work.

A single Fe3O4 nanoparticle which sticks onto the

graphene sheet is shown in Fig. 4b, revealing that each

nanoparticle is not a single crystal, but consists of a

cluster of tiny Fe3O4 particles with a diameter of about

10 nm. Diffraction analysis of the single Fe3O4

nanoparticle by a SAED technique, for example the

170 nm particle in Fig. 4b, further confirms that each

Fe3O4 nanoparticle is polycrystalline with an fcc

spinel structure as shown in the bottom-left inset of

Fig. 4b. HRTEM analysis (Fig. 4c) shows that the

lattice spacing of the Fe3O4 particles is approximate

0.253 nm, corresponding to the (311) crystallographic

plane of Fe3O4 with a spinel structure.

The structural analysis of GO and Fe3O4–graphene

hybrids were further confirmed by XRD, which is

shown in Fig. 4d. The XRD spectrum of GO displayed

by the black curve in Fig. 4d can be indexed to (001)

and (002) planes. By means of Bragg’s law, the

interplanar spacing of the strong diffraction (001) peak

located at 10.5� is calculated to be 0.78 nm, which is

larger than that of bulk graphite (0.31 nm). It can be

deduced that this originates from an introduction of

oxygen-containing functional groups intercalated onto

the graphite sheets. The XRD spectrum of Fe3O4–

graphene hybrids marked by the red curve (Fig. 4d)

can be indexed to (111), (220), (311), (222), (400),

(422), (511), (440), and (533) planes. This proves that

the spinel structure of bulk Fe3O4 (JCPDS No.

65-3107) is preserved in the Fe3O4–graphene hybrids,

and is consistent with the above crystal characteriza-

tion by SAED. It is also seen that the typical diffraction

peaks of GO (001) and (002) are not observed in this

curve, suggesting that the GO was reduced to graphene

by EG during the polyol procedure.

In order to understand the chemical bonding and

structural changes of the carbon framework in Fe3O4–

graphene hybrids and GO, Raman and FT-IR spec-

troscopy techniques were adopted. Figure 4e shows

two representative Raman spectra of the GO and

Fe3O4–graphene hybrids. It is seen that the G- and

D-band on the red curve shift to lower frequency

and 2D band at 2,644 cm-1 appears on the Fe3O4–

graphene hybrids spectrum in comparison with the

black curve of the GO, which reveals that the GO has

been reduced to graphene. This confirms the results of

earlier publications (Lambert et al. 2009; Stankovich

Fig. 1 Scheme of the fabrication process of Fe3O4–graphene hybrids

Page 4 of 11 J Nanopart Res (2013) 15:1472

123

et al. 2007). In addition, the D/G band ratio of the

Fe3O4–graphene hybrids is clearly larger than that of

GO. It is suggested that this increase derives from a

greater number of smaller sized sp2 domains in the

carbon frame due to a reduction of the exfoliated GO.

In comparison, the Raman spectra of graphene

reduced by the same route without iron salt are

displayed in Fig. S2, which is accordant with that of

Fe3O4–graphene hybrids. The appearance of 2D band

further suggests that GO was reduced to graphene.

Fig. 2 a–c Different resolution TEM images and d SAED pattern of GO

Fig. 3 SEM images of a original GO and b Fe3O4–graphene hybrids

J Nanopart Res (2013) 15:1472 Page 5 of 11

123

Figure 4f shows a comparison of the FT-IR spectra

obtained from the ionic interactions of GO, Fe3O4–

graphene hybrids and pure Fe3O4. The peaks on the GO

spectrum (black curve in Fig. 4f) match the character-

istic bonds of O-H (mO-H at 3,400 cm-1), C = O (mC=O

at 1,726 cm-1), C = C (mC=C at 1,625 cm-1), and

C–O–C (mC–O at 1,230 and 1,060 cm-1). There is also a

broad peak located at 3,432 cm-1, which can be

ascribed to the superposition of O-H deformation

vibrations of the COOH groups and the stretching

vibration of adsorbed water molecules. In comparison

with GO, the characteristic bonds of oxygen-based

functionalities including mO-H, mC=O, mC=C, and mC–O on

the spectra of Fe3O4–graphene hybrids (red curve in

Fig. 4f) and pure Fe3O4 (green curve in Fig. 4f) have

disappeared, and the intensities of all peaks are weaker.

This result proves that the GO has been chemically

reduced into graphene after the preparation of Fe3O4–

graphene hybrids, consistent with the observation from

the XRD and Raman spectra of the Fe3O4–graphene

hybrids and Fe3O4. The peak at 596 cm-1 on both

Fe3O4–graphene hybrids and Fe3O4 spectra corre-

sponds to the stretching vibration of Fe–O bonds in

Fe3O4. The 2,935 and 2,873 cm-1 peaks on the Fe3O4–

graphene hybrids spectrum are assigned to the asym-

metric and symmetric stretching vibration of –CH2

groups, respectively, which do not appear in the pure

Fe3O4 spectrum. X-ray photoelectron spectroscopy

spectra (see Fig. S3 in the supporting information for

detail) further confirm the observation of chemi-

cal bonding and structural changes of the carbon

framework in Fe3O4–graphene hybrids and GO through

the electron-state change of Fe, O, and C elements.

On the basis of these experiments and observations,

a formation mechanism of the Fe3O4–graphene

hybrids is proposed. The Fe3? ions are first inserted

and absorbed on the surface of GO (the middle

schematic diagram of Fig. 1), followed by primary

nucleations of nanocrystals in a supersaturated solu-

tion and then secondary growth of larger Fe3O4

nanoclusters (the last schematic diagram of Fig. 1),

which leads to an exfoliation of GO sheets. In the

polyol procedure, EG serves as both solvent and

reducing agent. GO is reduced and the Fe3? partially

reduced by EG, forming the Fe3O4–graphene hybrids.

TGA data (see Fig. S4 in the supporting information

for detail) indicate that there is approximately 88 wt%

of Fe3O4 nanoparticles attached to the surface of

graphene.

The morphology and chemistry of the Fe3O4–

graphene hybrids were further studied by HAADF-

STEM and EDX elemental mapping analysis. Fig-

ure 5a shows a representative HAADF-STEM image of

Fe3O4 nanoparticles anchored on graphene sheets. The

contrast of incoherent high-resolution HAADF-STEM

images depends directly on the sample atomic number

Z and thickness for the materials (Gonzalez et al. 2009).

In the Fe3O4–graphene hybrids image, a pure chemical

phase is revealed and the individual Fe3O4 nanoparti-

cles are about 170 nm in diameter and composed of

small Fe3O4 particles. This is the same as the above

HRTEM observations. Figure 5b–d displays the

Fig. 4 Morphological,

structural, and chemical

bonding analysis of the

Fe3O4–graphene hybrids:

a TEM image of a section of

Fe3O4–graphene hybrids;

b a single Fe3O4

nanoparticle anchored onto

the graphene sheet. Inset

shows the SAED pattern of a

complete Fe3O4

nanoparticle in b; c lattice-

resolution HRTEM of the

area marked by yellow

square in b; d–f XRD

patterns, FTIR spectra, and

Raman spectra of GO and

Fe3O4–graphene hybrids,

respectively

Page 6 of 11 J Nanopart Res (2013) 15:1472

123

corresponding EDX mappings of carbon (Ka, 0.28 keV),

iron (Ka, 6.4 keV), and oxygen (Ka, 0.52 keV) elements,

respectively. It is clear that the C element is evenly

distributed throughout the whole graphene sheet, while

the elements Fe and O only appear in the particle

positions perturbed by a thickness contrast.

The magnetic properties of Fe3O4–graphene hybrids

and pure Fe3O4 nanoparticles were recorded by VSM

measurement at room temperature (Fig. 6). The mag-

netic hysteresis loop of the Fe3O4–graphene hybrids

shows an S-like shape to the curve and are ferromagnetic

at room temperature (Hc = 31 Oe, Mr = 3.9 emu/g).

The saturation magnetization of the Fe3O4–graphene

hybrids (Ms = 65 emu/g) was smaller than that of pure

Fe3O4 nanoparticles, which was mainly due to the

existence of grapheme.

The electromagnetic wave absorption properties of

the Fe3O4–graphene/paraffin hybrids are determined by

its complex permeability (lr = l’–jl’’) and complex

permittivity (er = e’–je’’). The frequency dependence

of complex permittivity and complex permeability

recorded from the Fe3O4–graphene/paraffin hybrids

(15 vol.%) are shown in Fig. 7. The frequency corre-

sponding to the maximum imaginary permeability

(l00

max), is defined as the resonance frequency (fr).

The imaginary permeability (l’’) shows a wide band

ranging from 0.4 to 7 GHz (Fig. 7a). The real part of

complex permittivity (e’) decreases from 35.7 to 8.9

with the increase of frequency from 0.1 to 18 GHz,

while the imaginary part of complex permittivity (e’)decreases from 16.1 to 3.5 (Fig. 7b). Compared with

the pure Fe3O4 nanoparticles (see Fig. S5b in the

supporting information for detail), it is clear that the

complex permittivity of the Fe3O4–graphene hybrids

is improved efficiently, which is believed to be of great

interest for the electromagnetic wave absorption

Fig. 5 Elemental mappings of Fe3O4–graphene hybrids: a Representative HAADF-STEM image of Fe3O4–graphene hybrids;

b carbon mapping; c oxygen mapping; d iron mapping

J Nanopart Res (2013) 15:1472 Page 7 of 11

123

properties according to the quarter-wavelength match-

ing model (Li et al. 2011).

Figure 8a presents a schematic of a physical model

which shows the interaction of an electromagnetic

(EM) wave and the absorption properties of the

Fe3O4–graphene hybrids with a metal back plate.

When the EM wave is incident on the absorber, the

dominant loss of the incident EM wave is absorbed by

the absorber through absorption mechanism, of which

energy consumption is mainly attributed to magnetic

loss and dielectric loss. The magnetic loss has

originated from a natural resonance and eddy current

loss of the Fe3O4 nanoparticles. The graphene nano-

sheets with its high aspect ratio could constitute a

network for dispersing electrostatic charges, resulting

in a high dielectric loss. The magnetic loss and

dielectric loss are depleted as heat, which will spread

rapidly due to the excellent thermal conductivity of

graphene. A small part of the incident EM wave will

be reflected from the front (reflected beam � in

Fig. 8a) and (reflected beam ` in Fig. 8a) back

interfaces of the absorber layer. When the thickness

of the Fe3O4–graphene hybrids absorber generates two

waves out of phase by 180�, wave cancelation occurs

at the air-absorber interface.

To better understand the electromagnetic wave

absorption behavior of the Fe3O4–graphene hybrids, a

transmission line theory has been adapted. The

reflection loss (RL) curve of a single layer absorber

backed by a metal plate is calculated based on the

above measured complex permittivity and permeabil-

ity in Fig. 7 by the equation (Liu et al. 2003):

RL ¼ 20 logZin � Z0

Zin þ Z0

����

����

ð1Þ

Zin ¼ Z0

lr

er

� �1=2

tanh j2pfd

c

� �

lrerð Þ1=2

� �

ð2Þ

where f is the frequency of electromagnetic wave, d is

the thickness of an absorber, c is the speed of light in

vacuum, Z0 is the air impedance, and Zin is the input

impendence of absorber. The variations of the RL

values versus frequency of the Fe3O4–graphene/

paraffin hybrids with eight thicknesses are shown in

Fig. 8b. No absorption peak appears in the frequency

range of 0.1–18 GHz when the thickness of the

Fe3O4–graphene/paraffin is 1 mm. A minimum RL

value of -30.1 dB is obtained at 17.2 GHz when the

thickness of the Fe3O4–graphene/paraffin is 1.48 mm.

Typically, RL level of -10 dB (90 % of absorption)

is used to evaluate the material quality of electro-

magnetic wave absorption. Therefore, this result

indicates that the sample with an absorber thickness

of 3–1.48 mm has good absorbing characteristic in

X-band (8–12 GHz) and Ku-band (12–18 GHz),

which is of great interest for the military radar and

Fig. 6 Magnetic hysteresis loops of a pure Fe3O4 nanoparticles

and b Fe3O4–graphene at room temperature

Fig. 7 Frequency

dependence of a complex

permeability and b complex

permittivity recorded from

the Fe3O4–graphene/

paraffin hybrids with

15 vol.% concentration

Page 8 of 11 J Nanopart Res (2013) 15:1472

123

direct broadcast satellite (DBS) due to its high-

resolution imaging and precision target identification.

The absorption peak shifts to lower frequency range

with the increase of absorber thickness. When

the absorber thickness is larger than 5 mm, two

absorption peaks simultaneously appear. It is obvious

that the Fe3O4–graphene hybrids perform enhanced

electromagnetic wave absorption properties in com-

parison with the pure Fe3O4 nanoparticles (see Fig. S6

in the supporting information for detail).

The physical phenomenon for the electromagnetic

wave absorption of Fe3O4–graphene hybrids can be

explained by the quarter-wave principle [16]. The

relationship between the absorber thickness, tm, and

the peak frequency, fm, can be described by the

quarter-wavelength (k/4) condition (Li et al. 2011):

tm ¼nc

4fmffiffiffiffiffiffiffiffiffiffiffiffiffi

lrj j erj jp ð3Þ

where |er| and |lr| are the moduli of the measured er and

lr (Fig. 7) at fm, respectively, and c is the speed of light

in a vacuum. When the thickness of the Fe3O4–

graphene/paraffin satisfies the Eq. (3), the incident

electromagnetic wave and its partially reflected wave

are out of phase by 1808, which results in an extinction

of each other at the air-absorber interface. Figure 8c

displays a simulation of the absorber thickness, tm,

versus peak frequency, fm, in the case of our Fe3O4–

graphene/paraffin. The black solid curve is under k/4

condition, and red dashed curve is for 3k/4 condition.

The red stars and blue dots on two curves are matching

thicknesses calculated by the Eq. (1) (the transmission

line theory) using twelve thicknesses (tmsim), including

the seven thicknesses of which matching thicknesses

were directly read from the curves in Fig. 8b. The blue

dots correspond to the matching thicknesses at the

high frequency when the curves of RL verse frequency

appear as two peaks. It is seen that the simulations

using the quarter-wave principle is in good agreement

with the calculations by the transmission line theory

for Fe3O4–graphene hybrids.

The frequency dependence of Z = |Zin/Z0| for

Fe3O4–graphene hybrids (black dashed curve) was

further calculated by the Eq. (2) as shown in Fig. 8d,

of which relevant relationship between RL at the

matching thickness (RLrm) and frequency is displayed

by the blue solid curve. When the matching frequency

is 17.2 GHz, there is the smallest RL on the blue solid

curve in Fig. 8d with a reading of -30 dB, of which

relevant Z (on the black dashed curve in Fig. 8d) is

close to 1 and matching thickness is 1.48 mm (on the

black solid curve in Fig. 8b). This result shows that the

combinations of the quarter-wave principle with

the transmission line theory is a good way to quickly

Fig. 8 a Schematic representation of a physical model which

shows the interaction of electromagnetic (EM) waves and the

absorption properties of the Fe3O4–graphene hybrids with a

metal plate backing; b the variations of RL values versus

frequency for Fe3O4–graphene/paraffin hybrids with eight

thicknesses; c Simulations of the absorber thickness tm versus

peak frequency fm in the case of Fe3O4–graphene/paraffin, of

which black solid curve is under k/4 condition, and red dashed

curve is for 3k/4 condition; (d) the modulus of normalized input

impedance |Zin/Z0| generated from the Fe3O4–graphene hybrids

J Nanopart Res (2013) 15:1472 Page 9 of 11

123

achieve the optimal parameters for electromagnetic

wave absorption and provide an effective guide as to

the thickness design required for the electromagnetic

wave absorber for a particular absorbing material after

its complex permittivity er and complex permeability

lr have been experimentally measured.

Conclusion

We have demonstrated a preparative method for

fabricating magnetic Fe3O4–graphene hybrids by a

simple polyol method. The experimental results sug-

gest that individual Fe3O4 nanoparticles with a uniform

chemical phase and a spinel structure are chemically

bonded onto graphene sheets. Taking advantage of the

combined benefits of excellent complex permittivity

from Fe3O4 nanoparticles and permeability from the

light-weight graphene, the Fe3O4–graphene hybrids

show excellent electromagnetic wave absorption prop-

erties, which obey the quarter-wavelength matching

model. For the electromagnetic wave absorption

properties in X- and Ku-bands, the RL exceeds

-10 dB in 7.5–18 GHz with the absorber thickness

of 3–1.48 mm. This work suggests that the magnetic

graphene-based hybrids could be ideal candidate

materials for the manufacture of light-weight electro-

magnetic wave-absorbing devices in X- and Ku-bands.

Acknowledgments This work was supported by the National

Basic Research Program of China (973 Program) (Grant No.:

2012CB933104), the National Natural Science Foundation of

China (Grant No. 11274145), and the Fundamental Research

Funds for Central Universities from the Ministry of Education of

the People’s Republic of China (Grant No. 860521).

References

Alwarappan S, Erdem A, Liu C, Li CZ (2009) Probing the elec-

trochemical properties of graphene nanosheets for biosen-

sing applications. J Phys Chem C 113(20):8853–8857. doi:

10.1021/jp9010313

Alwarappan S, Liu C, Kumar A, Li CZ (2010) Enzyme-doped

graphene nanosheets for enhanced glucose biosensing. J Phys

Chem C 114(30):12920–12924. doi:10.1021/jp103273z

Alwarappan S, Boyapalle S, Kumar A, Li CZ, Mohapatra S

(2012a) Comparative study of single-, few-, and multilayered

graphene toward enzyme conjugation and electrochemical

response. J Phys Chem C 116(11):6556–6559. doi:10.1021/

jp211201b

Alwarappan S, Cissell K, Dixit S, Li CZ, Mohapatra S (2012b)

Chitosan-modified graphene electrode for DNA mutation

analysis. J Electroanal Chem 686(11):69–72. doi:10.1016/

j.jelechem.2012.09.026

Alwarappan S, Singh SR, Pillai S, Kumar A, Mohapatra S

(2012c) Direct electrochemistry of glucose oxidase at a

gold electrode modified with graphene nanosheets. Anal

Lett 45(7):746–753. doi:10.1080/00032719.2011.653900

Balandin AA, Ghosh S, Bao WZ, Calizo I, Teweldebrhan D,

Miao F, Lau CN (2008) Superior thermal conductivity of

single-layer graphene. Nano Lett 8(3):902–907. doi:

10.1021/nl0731872

Che RC, Peng LM, Duan XF, Chen Q, Liang XL (2004)

Microwave absorption enhancement and complex permit-

tivity and permeability of Fe encapsulated within carbon

nanotubes. Adv Mater 16(5):401–405. doi:10.1002/adma.

200306460

Che RC, Zhi CY, Liang CY, Zhou XG (2006) Fabrication and

microwave absorption of carbon nanotubes/CoFe2O4 spi-

nel nanocomposite. Appl Phys Lett 88(3):033105. doi:

10.1063/1.2165276

Dutta S, Pati SK (2010) Novel properties of graphene nanorib-

bons: a review. J Mater Chem 20(38):8207–8223. doi:

10.1039/C0JM00261E

Gao YY, Pu XP, Zhang DF, Ding GQ, Shao X, Ma J (2012)

Combustion synthesis of graphene oxide-TiO2 hybrid

materials for photodegradation of methyl orange. Carbon

50(11):4093–4101. doi:10.1016/j.carbon.2012.04.057

Geim AK, Novoselov KS (2007) The rise of graphene. Nat

Mater 6(3):183–191. doi:10.1038/nmat1849

Gonzalez JC, Hernandez JC, Lopez-Haro M, Rıo ED, Delgado

JJ, Hungrıa AB, Trasobares S, Bernal S, Midgley PA,

Calvino JJ (2009) 3D characterization of gold nanoparti-

cles supported on heavy metal oxide catalysts by HAADF-

STEM electron tomography. Angew Chem Int Ed

48(29):5313–5315. doi:10.1002/anie.200901308

Huang X, Yin ZY, Wu SX, Qi XY, He QY, Zhang QC, Yan QY,

Boey F, Zhang H (2011) Graphene-based materials: syn-

thesis, characterization, properties, and applications. Small

7(14):1876–1902. doi:10.1002/smll.201002009

Huang X, Qi XY, Boey F, Zhang H (2012) Graphene-based

composites. Chem Soc Rev 41(2):666–686. doi:10.1039/

C1CS15078B

Hummers WS, Offeman RE (1958) Preparation of graphitic oxide.

J Am Chem Soc 80(6):1339. doi:10.1021/ja01539a017

Lambert TN, Chavez CA, Sanchez BH, Lu P, Bell NS,

Ambrosini A, Friedman T, Boyle TJ, Wheeler DR, Huber

DL (2009) Synthesis and characterization of titania-

graphene nanocomposites. J Phys Chem C 113(46):19812–

19823. doi:10.1021/jp905456f

Lee CG, Wei XD, Kysar JW, Hone J (2008) Measurement of the

elastic properties and intrinsic strength of monolayer graphene.

Science 321(5887):385–388. doi:10.1126/science.1157996

Li ZW, Yang ZH, Kong LB (2011) Enhanced microwave

magnetic and attenuation properties for Z-type barium

ferrite composites with flaky fillers. J Appl Phys 110(6):

063907. doi:10.1063/1.3638448

Liang JJ, Wang Y, Huang Y, Ma YF, Liu ZF, Cai JM, Zhang

CD, Gao HJ, Chen YS (2009) Electromagnetic interference

shielding of graphene/epoxy composites. Carbon 47(3):

922–925. doi:10.1016/j.carbon.2008.12.038

Page 10 of 11 J Nanopart Res (2013) 15:1472

123

Liu JR, Itoh M, Machida KI (2003) Electromagnetic wave

absorption properties of a-Fe/Fe3B/Y2O3 nanocomposites

in gigahertz range. Appl Phys Lett 83(19):4017–4019. doi:

10.1063/1.1623934

Liu XG, Geng DY, Zhang ZD (2008) Microwave-absorption

properties of FeCo microspheres self-assembled by Al2O3-

coated FeCo nanocapsules. Appl Phys Lett 92(24):243110.

doi:10.1063/1.2945639

Liu XG, Geng DY, Choi CJ, Kim JC, Zhang ZD (2009) Magnetic

properties, complex permittivity and permeability of FeNi

nanoparticles and FeNi/AlOx nanoparticles. J Nanopart Res

11(8):2097–2104. doi:10.1007/s11051-008-9575-9

Liu S, Wang L, Tian JQ, Lu WB, Zhang YW, Wang XD, Sun XP

(2011) Microwave-assisted rapid synthesis of Pt/graphene

nanosheet composites and their application for methanol

oxidation. J Nanopart Res 13(10):4731–4737. doi:10.1007/

s11051-011-0440-x

Lv RT, Kang FY, Gu JL, Gui XC, Wei JQ, Wang KL, Wu DH

(2008) Carbon nanotubes filled with ferromagnetic alloy

nanowires: lightweight and wide-band microwave absor-

ber. Appl Phys Lett 93(22):223105. doi:10.1063/1.304

2099

Mak KF, Sfeir MY, Wu Y, Lui CH, Misewich JA, Heinz TF

(2008) Measurement of the optical conductivity of graph-

ene. Phys Rev Lett 101(19):196405. doi:10.1103/PhysRev

Lett.101.196405

Meyer JC, Geim AK, Katsnelson MI, Novoselov KS, Obergfell D,

Roth S, Girit C, Zettl A (2007) On the roughness of single-

and bi-layer graphene membranes. Solid State Commun

143(1–2):101–109. doi:10.1016/j.ssc.2007.02.047

Novoselov KS, Jiang Z, Zhang Y, Morozov SV, Stormer HL,

Zeitler U, Maan JC, Boebinger GS, Kim P, Geim AK

(2007) Room-temperature quantum hall effect in graphene.

Science 315(5817):1379. doi:10.1126/science.1137201

Qing YC, Zhou WC, Luo F, Zhu DM (2010) Epoxy-silicone filled

with multi-walled carbon nanotubes and carbonyl iron par-

ticles as a microwave absorber. Carbon 48(14):4074–4080.

doi:10.1016/j.carbon.2010.07.014

Singh V, Joung D, Zhai L, Das S, Khondaker SI, Seal S (2011)

Graphene based materials: past, present and future. Prog

Mater Sci 56(8):1178–1271. doi:10.1016/j.pmatsci.2011.

03.003

Stankovich S, Dikin DA, Piner RD, Kohlhaas KA, Kleinham-

mes A, Jia YY, Wu Y, Nguyen ST, Ruoff RS (2007)

Synthesis of graphene-based nanosheets via chemical

reduction of exfoliated graphite oxide. Carbon 45(7):1558–

1565. doi:10.1016/j.carbon.2007.02.034

Wan XJ, Long GK, Huang L, Chen YS (2011) Graphene—a

promising material for organic photovoltaic cells. Adv

Mater 23(45):5342–5358. doi:10.1002/adma.201102735

Wang FL, Liu JR, Kong J, Zhang ZJ, Wang XZ, Itoh M,

Machida K (2011) Template free synthesis and electro-

magnetic wave absorption properties of monodisperse

hollow magnetite nano-spheres. J Mater Chem 21(12):

4314–4320. doi:10.1039/C0JM02894K

Wen FS, Zhang F, Liu ZY (2011) Investigation on microwave

absorption properties for multiwalled carbon nanotubes/

Fe/Co/Ni nanopowders as lightweight absorbers. J Phys

Chem C 115(29):14025–14030. doi:10.1021/jp202078p

Xian L, Lopez SB, Chou MY (2011) Effects of electrostatic field

and charge doping on the linear bands in twisted graphene

bilayers. Phys Rev B 84(7):075425. doi:10.1103/PhysRevB.

84.075425

Xu C, Wang X, Zhu JW (2008) Graphene-metal particle nano-

composites. J Phys Chem C 112(50):19841–19845. doi:

10.1021/jp807989b

Xu WG, Ling X, Xiao JQ, Dresselhaus MS, Kong J, Xu HX, Liu

ZF, Zhang J (2012) Surface enhanced raman spectroscopy

on a flat graphene surface. Proc Natl Acad Sci USA

109(24):9281–9286. doi:10.1073/pnas.1205478109

Zhu CL, Zhang ML, Qiao YJ, Xiao G, Zhang F, Chen YJ (2010)

Fe3O4/TiO2 core/shell nanotubes: synthesis and magnetic

and electromagnetic wave absorption characteristics. J Phys

Chem C 114(39):16229–16235. doi:10.1021/jp104445m

Zhu J, Xue H, Zhang L, Yu JH, Hu HQ (2012) Decoration of

ultrafine platinum-ruthenium particles on functionalized

graphene sheets in supercritical fluid and their electrocat-

alytic property. J Nanopart Res 14(9):935. doi:10.1007/

s11051-012-0935-0

J Nanopart Res (2013) 15:1472 Page 11 of 11

123