Enhanced electromagnetic wave absorption of hybrid-architectures Co? SiOxC

Article abstract of DOI:10.1016/j.jallcom.2020.154442

Rational design on the well wrapped core-shell microstructure of Co? SiO_xC composites was successfully conducted through reduction process of cobalt, efficient condensation reaction of KH-550 silane coupling agent as well as high temperature calcination. The SiO_xC shell possessed 3D cross-linked network structure consisting of dielectric carbon and silicon composition for optimal electromagnetic matching. The microstructure, morphology, elements distribution, electromagnetic property and microwave absorption performance were fully characterized, respectively. This SiO_xC shell effectively inhibited the agglomeration of cobalt particles, and regulated the complex electromagnetic parameters by decreasing permittivity and introducing polarization relaxation, all of which determined the efficient reflection loss with RL_min value of ?60.3 dB at 16.2 GHz and matching thickness of only 2.05 mm. Meanwhile, the effective absorption band is up to 7.1 GHz at 2.3 mm. By optimizing of core-shell structure and material components, the high-absorption performance was obtained through impedance matching, multi-interfacial polarizations, dipole (or defects) polarization and magnetic loss. Therefore, the Co? SiO_xC composites present a facile and promising route toward the design of large-scale-preparation and excellent microwave absorbing materials.

Full text of DOI:10.1016/j.jallcom.2020.154442

Journal of Alloys and Compounds 831 (2020) 154442
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Enhanced electromagnetic wave absorption of hybrid-architectures
Co@ SiOxC
Jianwen Ge 1, Yu Cui b 1, Li Liu a , Rui Li , Fandi Meng , Fuhui Wang
a
,
,
,
*
a
a
a
a
Shenyang National Laboratory for Materials Science, Northeastern University, Shenyang, 110819, China
Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110016, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 November 2019
Received in revised form
Rational design on the well wrapped core-shell microstructure of Co@ SiO C composites was successfully
conducted through reduction process of cobalt, efficient condensation reaction of KH-550 silane coupling
agent as well as high temperature calcination. The SiO C shell possessed 3D cross-linked network
x
structure consisting of dielectric carbon and silicon composition for optimal electromagnetic matching.
The microstructure, morphology, elements distribution, electromagnetic property and microwave ab-
x
5
February 2020
Accepted 20 February 2020
Available online 7 March 2020
x
sorption performance were fully characterized, respectively. This SiO C shell effectively inhibited the
agglomeration of cobalt particles, and regulated the complex electromagnetic parameters by decreasing
permittivity and introducing polarization relaxation, all of which determined the efficient reflection loss
with RLmin value of ꢀ60.3 dB at 16.2 GHz and matching thickness of only 2.05 mm. Meanwhile, the
effective absorption band is up to 7.1 GHz at 2.3 mm. By optimizing of core-shell structure and material
components, the high-absorption performance was obtained through impedance matching, multi-
Keywords:
Co@SiO C composites
x
KH-550
Carbon
Microwave absorption performance
x
interfacial polarizations, dipole (or defects) polarization and magnetic loss. Therefore, the Co@ SiO C
composites present a facile and promising route toward the design of large-scale-preparation and
excellent microwave absorbing materials.
©
2020 Elsevier B.V. All rights reserved.
1
. Introduction
Recent results show that, on the basis of synergetic or comple-
mentary behavior, enhanced microwave absorption performance
can be successfully achieved via a rational design of uniform core-
To further ensure the electronic stealth technology and defense
safety, tremendous effort has been devoted to fabricate highly
effective microwave absorber [1e4]. Core-shell structure as a
typical method in synthesizing materials is widely used in the
application of storage, catalyst and physics, providing excellent
carriers for designing outstanding absorbers [5e8]. Magnetic
powders (Fe, Co, Ni) and their derived core-shell structures are
concentrated on their high saturation magnetization, high perme-
ability and abundant reserves [9e11]. In general, excellent
absorbing performance can be hardly obtained since ferromagnetic
Fe, Co, Ni only possess magnetic loss mechanism. In order to further
broaden the effective absorption bandwidth and enhance the ab-
sorption intensity, a strategy of providing single or multi-layered
coating with many defects was proposed to combine magnetic
absorption components with dielectric loss components [12e14].
shell type absorbers, such as FeCo@SiO
Ni@SnO [17], Fe @C [18], Fe@ZnO [19], C@NiCo
Fe@Fe [21], Fe@C [22], Co@C [23], Ni@C [24], Fe
Ni@TiO
2
@PPy [15], Fe
3
O
4
@TiO
@Fe
@SiO
2
[16],
[20],
[25],
2
3
O
4
2
O
4
3
O
4
3
O
4
3
O
4
2
2
[26], which were endowed with magnetic loss, conduction
loss, polarization relaxation as well as impedance match
mechanisms.
Moreover, carbon composition is widely used as a successful or
facile coating onside the surfaces of strong magnetic cores for
further effective attenuation of electromagnetic wave (EMW) based
on electron migration [27e29]. For example, Li et al. fabricated
carbon-encapsulated Co nanoparticles (15 nm) through arc-
discharge method, with RLmin value of ꢀ30 dB, and the reflection
loss can be effectively tailored through the coating thickness by
controlling the cavity current [23]. Ding and his co-workers pre-
pared the core-shell Co@C microspheres via in-situ polymerization
and subsequent high-temperature carbonization, and the intro-
duction of amorphous carbon (with thickness of ~80 nm) enhanced
the attenuation of EMW with the RLmin value of ꢀ68.7 dB at
*
Corresponding author. Tel.: þ86 24 8108 3918.
E-mail address: liuli@mail.neu.edu.cn (L. Liu).
J. Ge and Y. Cui. contributed equally.
1
https://doi.org/10.1016/j.jallcom.2020.154442
925-8388/© 2020 Elsevier B.V. All rights reserved.
0

2
J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
10.6 GHz [27]. One of the essential causes accounting for the high-
2.2. Synthesis of cobalt micro-particles
absorption performance is the excellent dielectric loss properties
provided by high permittivity, but subsequent reflection and scat-
tering will also occur on the surface of carbon, due to the intrinsi-
Cobalt particles were prepared through the reducing process
using hydrazine hydrate as reducing agent described previously.
First, cobalt acetate (2 g, 0.023 mol) were dissolved in 30 ml
deionized water, stirring evenly for 5 min, and then 3 ml hydrazine
hydrate were added dropwise and stirred for another 5 min. After
that, the mixed solution was transformed in Teflon-lined stainless-
steel autoclave with a capacity of 50 ml, then the autoclave was
cally excellent electron migration [30]. Though SiO
wave-transmitting materials, it is able to adjust high permittivity
and realize optimal impedance matching. This characteristic of SiO
2
is one kind of
2
leads to the possibility of producing some outstanding absorbing-
performance materials by adding SieO bonds. Sergey S. Maklakov
ꢁ
prepared corrosion-resistive magnetic powder Fe@SiO
2
by using a
allowed to heat up to 100 C for 2 h and then cooled to room
modified St o€ ber process, with RLmin value of ꢀ40 dB and corre-
temperature. The black precipitation was washed by alcohol and
sponding thickness of 1.5 mm [31]. A ternary composite material
water with three times, and collected after filtration as well as the
ꢁ
FeCo@SiO
2
@PPy was successfully synthesized with the effective
oven dry at 40 C for 24 h, then grinded for 15 min.
absorption band (EAB) of 6.8 GHz, which was attributed to the
synergistic effect of magnetic loss (FeCo) and dielectric loss
2.3. Synthesis of Co@ SiO
x
C composites
C were originated from Co@OSR
(
SiO
makes up for the deficiency of low electron mobility compared with
single SiO composition, and SiO can regulate impedance match-
2
@PPy) [15]. Typically, the incorporation of dielectric carbon
The ant acupoints-like Co@SiO
x
2
2
composites, which were synthesized according to mechanical
agitation as well as high temperature pyrolysis process. First, 0.8 g
of the as-prepared cobalt microparticles were successively placed
into a mixed solution containing KH-550 silane coupling agent
solution (13 ml), deionized water (10 ml) and alcohol (8 ml). After
mechanical agitation for 10 min at 800 rpm, the obtained black
powder was collected via filtration and the oven dry again. Finally,
in order to obtain chemically stable product, the black powder was
ing for the composites, which provides a new strategy to design
strong-absorption materials by optimizing the composition and
structure.
KH-550 silane coupling agent can give rise to a large amount of
silicone alcohol (SieOH) by hydrolysis reaction. Moreover, these
hydrolysates can not only successfully combine with metal or metal
oxides to form a coating on the basis of hydroxyl groups, but also
can effectively generate lattice-like structures composites, orga-
ꢁ
subjected to high temperature calcination at 650 C for 70 min in
nosilicon resin (OSR), which is similar to SiO
2
by self-condensation
2
99.9% N atmosphere. With the decline of the temperature, the final
reaction [32e34]. Therefore, in this paper, author creatively used
the hydrolysate of KH-550 silane coupling agent as the preliminary
coating, followed by calcination process for a dielectric shell. And
products ant acupoints-like Co@SiO
fully obtained.
x
C composites were success-
then the roles of SiO
x
C (the shell of final product) containing a large
2.4. Characterization
number of SieO bonds and dielectric carbon components in EMW
attenuation have been further explored.
The characterization of the crystal structure was performed by
using an X-ray diffractometer (XRD, Rigaku SmartLab) via Cu-Ka as
the irradiation source. Thermogravimetric analysis (TGA) was
recorded on a TA SDT-Q700 thermal gravimetric analyzer in air
x
Herein, the Co@ SiO C composites were successfully synthesized
by a simple reduction process, subsequent in-situ condensation and
calcination process. To the best of our knowledge, this is the first
report on the use of silane coupling agent as the precursor shell to
design core-shell absorber with enhanced absorption performance.
The well-reduced Co particles were found to be uniformly wrapped
by transparent membranous SiO C matrix. Dielectric carbon
x
composition consumed the electromagnetic energy by intrinsic
electrical conductivity and relative defects originated from pyrol-
ꢁ
environment from room temperature to 780 C with a heating rate
ꢁ
of 10 C/min. The morphology of the sample was obtained using
field-emission scanning electron microscopy (FESEM, Hitachi SU-
70) with an accelerating voltage of 10 kV. The microstructure and
specific distribution of components were observed by a trans-
mission electron microscope (TEM, JEOL JMF-2100F) with an
accelerating voltage of 200 kV. The chemical states and surface
components of the samples were analyzed on an X-ray photo-
electron spectrometer (XPS, ESCALAB 250XI) operated at 15.0 kV.
The C 1s neutral carbon peak at 284.6 eV served as a reference peak
for all binding energies. The magnetic properties of the samples
were measured via a vibrating sample magnetometer (VSM, Lake-
Shore 7404) at room temperature. The parameters and perme-
ability were obtained by a vector network analyzer (VNA, Agilent
E5071C) on the basis of the coaxial-line method. Samples and
paraffin were evenly mixed at a weight ratio of 1:1, and then
extruded into concentric rings with an inner diameter of 3.04 mm
and an outer diameter of 7.0 mm.
x
ysis process. The results suggested that the Co@SiO C composites
could be functionalized with the various dipolar configurations by
intrinsic defects, so called lattice-like structures, existing in the
disordered arrangement of reticulated SieOeSi main chains. The
x
Co@SiO C composites showed an enhanced EMW absorbing per-
formance with a RLmin of ꢀ60.3 dB at 16.2 GHz with a matching
thickness of 2.05 mm, and a wide absorbing band is up to 7.1 GHz
(
RL < ꢀ10 dB). This high absorption performance can be due to the
optimized impedance matching, synergistic effects, dielectric loss
and magnetic loss. Experimental results evidenced that such a
configuration provides an easy-to-implement method for creating
excellent microwave absorption materials with large-scale
properties.
3. Results and discussion
2
. Experimental details
The detailed synthetic processes and formation mechanisms of
2.1. Materials
Co@SiO
typical preparation of Co@SiO
x
C composites were schematically illustrated in Fig. 1. The
C composites contains three primary
x
Cobalt acetate and silane coupling agent (KH-550) were ob-
steps: I. Reduction of cobalt ions with hydrazine hydrate as
reducing agent (Fig. 1a); II. KH-550 coating cobalt particles by hy-
drolysis and condensation reaction (Fig. 1b and c); III. High tem-
perature calcination reaction. Firstly, the hydrolysis reaction of KH-
550 gradually took place in a mixture of alcohol and deionized
tained from Sinapharm Chemical Reagent Co., Ltd. Ethanol, Hy-
drazine hydrate was purchased from Aladdin Corporation. All the
above chemicals were of analytical grade and used without further
purification.

J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
3
Fig. 1. Schematic diagrams of the fabrication processes of Co@SiO
x
C composites: (a) reduction of cobalt ions. (b and c) KH-550 coating cobalt particles via stirring process. (d)
formation mechanisms of Co@SiO C composites. (A color version of this figure can be viewed online.)
x
water, where the hydrolyzed monomer, high-reactive silanol
molecule, was successfully generated under the intense stirring
progress. Moreover, the activity of silanol molecular increases with
the number of SieOH bonds [35,36]. The surfaces of cobalt particles
containing a large amount of hydroxyl groups endow the attach-
ment of silanol molecule as a sharp condensation reaction or
hydrogen bond occurred between SieOH and hydroxyl groups on
cobalt surfaces [37,38]. Generally, it is believed that, among three
SieOH groups formed by hydrolysis of a single silane molecule,
only one SieOH base bonded with the hydroxyl groups on the
surfaces of the substrate at the interface, while the other two
SieOH groups could react with the SieOH of other silane molecules
or maintained in a free state [34]. Subsequently, organicsilicon resin
area effectively demonstrated the core-shell heterogeneous archi-
tecture with the shell thickness of approximately 90 nm. And the
rough-surface cobalt particles were wrapped effectively by the thin
films. Importantly, the transparent thin film revealed the relatively
uniform distribution of heterogeneous elements (C, O and Si)
within the shell after calcination (Fig. 3cee).
The crystal structure and phase purity of the as-prepared
products were identified by XRD. Fig. 4a shows the typical XRD
patterns of the Co particles and the calcined final products. As
ꢁ
ꢁ
ꢁ
shown, the detected diffraction peaks locating at 41.7 , 44.3 , 47.3 ,
ꢁ
ꢁ
51.5 and 75.8 are indexed to the (100), (002), (101), (102) and
(110) plans of cubic spinel structure of Co (JCPDS card no.15e0806).
After wrapping with multiple-element heterogeneous shell and
subsequent calcination, no obvious diffraction peaks can be found,
revealing the presence of amorphous nature of C and Si compo-
nents. The average grain size (D) of the Co particles was assessed on
(
2
OSR) composites, lattice-like structure similar to SiO , were
formed by mutual condensation reaction of numbers of silanol
molecules, adhering to the surfaces of cobalt particles [39,40].
k
l
COS
Finally, the Co@ organicsilicon resin (Co@OSR) precursor was sub-
the basis of Scherrer’s equation (D(hkl)
26.4 nm [12]. Fig. 4b illustrates the FTIR spectra of Co@OSR and the
final product Co@SiO C hybrids. As for the Co@OSR composites, the
main absorption peaks, eCH
¼
q) with approximately
b
ꢁ
jected to 650 C treatment in N
2
, leading to the break of CeC bond
C hybrids.
The morphology and microstructure of Co@SiO
and subsequently forming Co@SiO
x
x
ꢀ
1
ꢀ1
x
C hybrids were
2
(2970 cm ), SieC (767-690 cm ),
ꢀ
1
ꢀ1
characterized via SEM pictures (Fig. 2). Fig. 2a displays the irregular
cobalt particles. The big holes formed during the curing process of
SieOeSi (1112-1038 cm ), CeN (1386 cm ), eNH
3500 cm ) can be clearly observed. However, after calcination
process at 650 C, only the SieOeSi and SieC absorption peaks
2
(3400-
ꢀ1
ꢁ
KH-550, possess irregular shape with average size of 15
tiny sphere particles with the size of 1e2 m piled up together
Fig. 2b). The white cobalt particles were wrapped tightly by the
transparent film, which was fully exhibited because of different
conductivity, shown in Fig. 2d. STEM images of Co@SiO C hybrids
were illustrated in Fig. 3. The transparent thin films and inner black
mm. Many
m
appeared, revealing that the thorough pyrolysis process was con-
ducted. The presence of SieC absorption peak and disappearance of
eCH , CeN bonds occurred in the calcination process, manifest that
2
the pyrolysis process might mainly act on the CeC bond (shown in
(
x
Fig. 1).

4
J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
x
Fig. 2. SEM images of microstructures of prepared Co (a) and (bed) Co@SiO C composites with different amplification ratios. (A color version of this figure can be viewed online.)
Raman spectroscopy was employed to further characterize the
both of which are lower than that of Co (M
:154.6 Oe). This result can be ascribed to the nonmagnetic shell.
The detailed comparison of coercivity can be directly seen in the
inset. It’s also worth mentioning that M value of Co is not very high,
which is attributed to the larger H with the competitive relation-
ship. With the regard of higher H , investigation of the unique
s
: 112.0 emu/g and
degree of graphitization of the final composites (Fig. 4c). It is found
H
c
ꢀ
1
ꢀ1
that two distinguishable peaks at 1332 cm
and 1577 cm
correspond to G and D band, respectively, while the peak of 669 eV
is attributed to Co. Generally, G band is assigned to the first-order
scattering of the E2g model, representing the crystalline degree of
the hexagonal lattices of carbon materials, whereas D band is used
to characterize the lattice defects of carbon atoms [37]. Further-
more, the intensity ratio of D and G band is of 1.01, indicating the
appearance of a certain amount of structural defects existing in
Co@OSR composites and low graphitization degree in amorphous
carbon.
s
c
c
morphology and microstructures reveals that two main causes are
associated with this phenomenon, namely, shape anisotropy and
the presence of small size particles. Whereas the higher M
s
and H
-1)
c
are both conducive to magnetic attenuation, due to
(m
s
1
f
r
¼
g
ꢂM
s
(Snoek limit) and 2
p
f
r
¼
a s
gH , where m is the static
3
p
permeability, f
r
is the natural magnetic resonance frequency and g
XPS (Fig. 4def) was employed to analyze the elemental valence
states of the surface of heterogeneous core-shell hybrids. As shown
in Fig. 4d, the wide-scan spectrum indicates that Co, C, O, Si coexist
in core-shell hybrids, which is consistent with STEM. Moreover,
there is no significant N absorption peaks, suggesting that N con-
nected at the end of C chain may disappear along with the pyrolysis
process. The Si 2p (Fig. 4e) is fitted with two peaks locating at
is the gyromagnetic ratio. The thermogravimetric analysis (TGA)
ꢁ
curve recorded in N
2
atmosphere from room temperature to 780 C
is shown in Fig. 5b. The smooth curve exhibits two sharply down-
ꢁ
ꢁ
ꢁ
ꢁ
ward stages (①: 30 Ce100 C, ③: 300 Ce600 C). The first slight
weight loss approximately 2% occurred from room temperature to
ꢁ
100 C is attributed to volatilization of water in sample, while the
second corresponds to the thermal decomposition with weight loss
of approximately 7%, which may be due to the disappearance of
CeCeN in the form of volatile organic small molecules. Since one
silicon is connected to three oxygen atoms, it is assumed that all the
silicon hydroxyl groups in the sianol monomer were involved in the
condensation reaction, and the existence of defects is ignored.
Hence, the composition of the final product can be defined as
Co@SiO1.5C. At the same time, the content of cobalt in Co@OSR can
be effectively calculated by the following formula:
1
01 eV and 103.6 eV, corresponding to SieC and SieO, further
demonstrating the site of pyrolysis of C. The peaks at 788 eV and
05 eV (Fig. 4f) are assigned to the ionization of Co 2p 3/2 and Co 2p
/2. Above results testified that the shell of Co@OSR exhibits a cross-
8
1
linked semi-organic polymer characteristic, which results in
numbers of atomic-scale defects derived from lattice-like struc-
tures on the basis of condensation reaction of KH-550. For the final
ꢁ
product (under 650 C treatment), it is hard to determine the ratio
of Si to O, due to numbers of defects (from condensation and
calcination) as well as the existence of KH-550 monomer without
hydrolysis and SieOH without condensation. Therefore, the final
t
W %(SiO1.5C) ¼ M(SiO1.5C) ꢂ 7%/M(CeCeN)
(1)
product is confirmed to be Co@SiO
Co particles were favorably decorated with SiO
the formation mechanisms and above detection results.
Fig. 5a displays the hysteresis loops of Co and Co@SiO
x
C hybrids. Such well-reduction
C shell, based on
Where W % (SiO1.5C) is the weight percentage of SiO1.5C in
Co@OSR composites, and M reveals the molecular weights of
SiO1.5C and CeCeN. It is calculated that the relative content of
t
x
C com-
SiO1.5C is 10.5% in Co@OSR composites. Therefore, as for Co@SiO1.5C
x
posites. The Co@SiO
characteristic at room temperature with the saturation magneti-
zations (M ) of 81.4 emu/g and the coercive fields (H ) of 131.4 Oe,
x
C composites exhibit the typical ferromagnetic
composites, the relative content of SiO1.5C is approximately 11.3%
(10.5%/100%e7%).
The microwave absorption performances of the as-synthesized
s
c

J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
5
Fig. 3. Energy dispersive X-ray (EDS) analysis for elemental mapping. (a) STEM images of core-shell Co@SiO
images. (A color version of this figure can be viewed online.)
x
C composites. (bee) elemental Co, C, O, Si and their integrated mapping
Co and Co@SiO
x
C hybrids are shown in Fig. 6 with different thick-
RL¼20 log10|Zin-Z0/ ZinþZ0|
(4)
ness in the range of 2e18 GHz. Generally, the RL values determine
the capability of electromagnetic wave attenuation, while effective
absorption is defined as the RL values below ꢀ10 dB [41e44],
indicating that 90% of the incident wave is absorbed. The RL values
were calculated from the frequency-dependence complex permit-
tivity and permeability determined by a given layer thickness and
frequency, which can be shown by following formulas:
Where Zin is input impedance of the absorber, Z
impedance of free space. ε , m are the complex permittivity and
r r
complex permeability, respectively. f is the frequency of electro-
magnetic wave, and d is the thickness of absorber, c is velocity in
free space.
0
is the input
As shown in Fig. 6a, the reflection loss of well reduced Co par-
ticles differs with the thickness of layers, and the RLmin value
of ꢀ43.7 dB appearing at 9.8 GHz corresponds to the thickness of
Z
in ¼ Z
0
(
r
m /ε
r
)1/2tanh[j(2
pfd/c) $ (m
r
·ε
r
)1/2
]
(2)
(3)
2.42 mm. Compared with Co, Fig. 6b confirms that the core-shell
Z
0
¼(m
0
/ε
0
)1/2
x
Co@SiO C heterostructure is found to possess much lower RLmin
value (ꢀ60.3 dB) at 16.1 GHz with the matching thickness of only

6
J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
x x x
Fig. 4. (a) XRD diffraction spectra of Co and Co@SiO C composites. (b) FTIR spectra of Co@OSR and Co@SiO C composites. (c) Raman spectra of Co@SiO C composites. XPS spectra of
the Co@SiO C composites: (d) survey scan, (e) Si 2p region, (f) Co 2p region.
x
Fig. 5. (a) Hysteresis loops of Co and Co@SiO
x
C composites at room temperature, and the inset gives an enlarged view of the hysteresis loops. (b) TGA curve of Co@OSR composites
under air N . (A color version of this figure can be viewed online.)
2

J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
7
Fig. 6. Absorption performance of Co, Co@SiO
x
C composites and relevant absorbers. 3D representations of reflection loss (RL) values of Co (a) and Co@SiO
x
C composites (b). The
x
effective absorption bands (EAB) with different corresponding thicknesses of Co (c) and Co@SiO C composites (d). The EAB and RLmin values of relevant core-shell absorbers (e). (A
color version of this figure can be viewed online.)
2
.05 mm. The white line area represents the effective absorption,
thickness of 3 mm. Importantly, Ku band (12e18 GHz) used to
survey topography and dominate the guidance of missiles, satellites
and some other aircraft, is covered with the thickness of 2.3 mm.
Detailed EAB values and RLmin of relevant absorbers published in
recent years are also summarized in Fig. 6e. The comparison of
EMW absorption performance identifies that a superior combina-
tion of EAB (7.1 GHz) and RLmin (ꢀ60.3 dB) at thickness (2.05 mm)
can be obtained via the combination of magnetic core Co and
where the area of Co@SiO C hybrids is much larger than that of Co
x
in the whole frequency. To further investigate the accurate relation
between the effective absorption bands and different lay thickness,
the comparison was conducted in Fig. 6c and d. The largest EAB of
Co@SiO
ness of 2.30 mm, which is much larger than that of Co (4.6 GHz).
Moreover, stronger absorption performance of Co@SiO C compos-
ites (EABꢃ4 GHz) is assigned to the range of 2e3.5 mm. The
excellent absorbing performance of Co@SiO C composites with a
x
C hybrid is 7.1 GHz (10.9e18 GHz) at the matching thick-
x
x
dielectric material SiO C. At the same time, this result proves that
the core-shell structure can achieve more efficient electromagnetic
attenuation.
x
wide frequency bandwidth was fully manifested in 4e18 GHz, and
the whole X band (8e12 GHz) is completely covered with the
Dielectric loss and magnetic loss can account for the high

8
J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
efficiency attenuation [45e49]. In order to reveal the intrinsic
relation of the efficient absorption behavior, the frequency
interfacial polarization. Under an alternating EM fields, the electric
ꢀ2
ꢀ9
dipoles are able to take 10 -10 s to be oriented. If the external
field frequency is relatively low, the dipoles possess sufficient re-
action time to respond. But dipoles cannot fit with the variation
when frequency ascends to a certain extent [44,45]. Importantly,
different electrical conductivity was also employed to C and SiO ,
x
under alternating electric field, which resulted in the tendency of
0
dependent complex permittivity (ε
r
¼ ε -jε") and complex perme-
0
ability (m
r
¼
m
-jm
") are calculated by E5071C network analyzer. The
real parts of complex permittivity (ε ) and complex permeability
0
0
(m
) signify the storage of electric and magnetic energy, and the
") represent the attenuation or loss per-
formance of electric and magnetic energy [50e52]. Moreover, the
variations of complex permittivity in Co and Co@SiO C hybrids
correspond to different dielectric loss performances, shown in
Fig. 7a (ε ) and Fig. 7b (ε"). The ε values of Co and Co@SiO
posites are both approaching to a constant. The values of Co (8.5)
are larger than that of Co@SiO C (5.2), mainly because of excellent
conductivity. With the respect of Co@SiO C hybrids, Fig. 7b illus-
imaginary parts (ε" and
m
electron migration toward C (low resistivity). Therefore, many
x
micro interfaces would be formed between C and SiO
another interfacial polarization. The atomic-scale structural defects
(existing in SiO C shell) originated from calcination process and
x
, leading to
0
0
x
C com-
x
asymmetric arrangements of SieOeSi main chains, would accu-
mulate considerable space charge (dipoles) at the micro defects
sites, promoting the dielectric loss.
x
x
trates one high-intensity peak and three small relaxation peaks
associated with polarization loss in the range of 10e13.2 GHz,
Cole-Cole semicircle is introduced to demonstrate the presence
of diversified polarization processes, the curves of ε" versus ε are
0
1
3.4e14.8 GHz, 15e16.1 GHz and 16.3e17.8 GHz, respectively. It is
shown in Fig. 7c. According to the Debye theory, the relation be-
tween ε and ε" can be deduced as
0
known that the dielectric loss can be divided into conductivity loss
and polarization loss. The polarization loss includes electronic po-
larization, ionic polarization, dipole orientation polarization and
interfacial polarization (space charge polarization) [53e55]. Among
these, ionic polarization and electronic polarization can be negli-
gible because they usually occur at much higher frequency region
ꢀ
ꢁ
ꢀ
ꢁ
ε þ ε
∞
2
ε ꢀ ε
∞
2
S
2
S
ε’ ꢀ
þ ðε}Þ ¼
(5)
2
2
In general, one semicircle is assigned to one relaxation process
3
6
(
10 e10 GHz) [56,57]. Owning to the different dielectric properties
based on the Debye theory [58,59]. The curve of Co@SiO C com-
x
between Co core and SiO C shell as well as SiO C shell and paraffin
x
x
posites exhibits four distorted and distinguishable semicircles
wax, the movements of free electrons are impeded at the junctions,
which causes the uneven distribution of space charges at the
heterogenous interfaces, leading to the enhancement of the
(Fig. 7c), which fully proves the presence of multiple relaxation
processes. Consequently, the SiO C shell would effectively give rise
x
to dielectric loss. The dielectric loss tangents (tan dε) and magnetic
0
Fig. 7. Real parts (a) and imaginary parts (b) of the complex permittivity of Co and Co@SiO
x
C composites, and the corresponding plots of ε" versus ε for Co@SiO
x
C composites (c),
x
dielectric loss (tan dε) and magnetic loss (tan dm) of Co@SiO C composites (d).

J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
9
0
2 ꢀ1
) f (c) for Co and Co@SiO
Fig. 8. Real parts (a) and imaginary parts (b) of the complex permeability of Co and Co@SiO
x
C composites, the corresponding curves of
m
"/(
m
x
C
composites. (A color version of this figure can be viewed online.)
ꢀ1
loss tangents (tan dm) as the major concept for characterization of
loss abilities are shown in Fig. 7d. By contrast, the value of tan dm is
where
m
0
(Hꢂmꢀ1) is the permeability in vacuum and
s
(Sꢂm ) is
electrical conductivity [63,64]. Suppose the eddy current loss is the
0
2
closer to the constant (0.18), while the value of tan
the range of 10e18 GHz. The values of tan ε fluctuate around 0.12
in 2e10 GHz, and then introduce a short band between 10 and
3.2 GHz with a sharp peak value of 0.35 at 11.8 GHz, then followed
by three small peaks. On the whole, magnetic loss occupies the
major loss mechanism, but the values of tan ε are much larger than
dε fluctuates in
sole resource of the magnetic loss, the values of
m
"/(
d /3 should be constant along with the whole frequency
[65,66]. As can be seen in Fig. 8c, there is a downward trend in the
m ) f
ꢀ1
2
d
¼ 2
0
pm s
0
2 ꢀ1
1
m"/(m ) f values of Co and Co@SiO C composites in the range of
x
2e14 GHz and a relatively horizontal stage in 14e18 GHz, sug-
gesting the multiple magnetic loss mechanisms (eddy current loss
and ferromagnetic resonance) in 2e14 GHz and only eddy current
loss in 14e18 GHz. The eddy current loss has not reduced greatly,
which is mainly because of the relatively low ε’ (only 8.5), so that
the shell is failure to play a decisive role toward reducing conduc-
tivity greatly, though a certain reduction conducted. Another
reason can also not be ignored, that is, Co possesses its own
conductive networks, which is not hampered seriously by the shell.
Finally, ferromagnetic resonance and eddy current are contributing
to magnetic loss.
d
that of tan dm from 10.6 to 12.9 GHz, suggesting the essential role
played by dielectric loss.
0
To investigate the magnetic loss mechanisms, the
m
and
m’’
values of Co and Co@SiO
x
C hybrids are displayed in Fig. 8a and
0
Fig. 8b. The tendency of
m
and
m
’’ values of the Co@SiO
x
C com-
posites along with whole frequency is basically the same to that of
Co, and the values of Co@SiO C become a little smaller. Generally,
x
the magnetic loss mainly derived from domain-wall resonance,
hysteresis loss, eddy current effect, natural ferromagnetic reso-
nance and exchange resonance [60e62]. It is mentioned that
domain-wall resonance tends to happen at megahertz, and hys-
teresis loss should be negligible in the weak electromagnetic field
In general, larger attenuation constant (
impedance matching (Z) are regarded as two important parameters
for evaluating reflection loss. The attenuation constant ( ) can be
expressed by following equation based on transmission line theory:
a) and reasonable
a
[
63,64]. Furthermore, the major mechanisms of magnetic loss
should be related to eddy current effect, natural ferromagnetic
resonance and exchange resonance. The eddy current loss is usually
characterized by following equation:
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
pffiffiffi
2
c
pf
2
’
’ 2
a
¼
ꢄ
ð
m
} ε} ꢀ
m
’ ε’Þ þ
m
} ε} ꢀ
m
’ ε’ þ ð
m
ε} þ }ε Þ
m
(
7)
0
)2
2
m
" ¼ 2pm
0
(
m
s
ꢂ d f/3
(6)

10
J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
Fig. 9. The attenuation constants (a) and impedance matching ratio for Co and Co@SiO
x
C composites. (A color version of this figure can be viewed online.)
where f is the frequency and c is the velocity of light [67e69]. Fig. 9a
exhibits that the attenuation constants of Co@SiO C are always
higher than that of Co in the range of 2e18 GHz, suggesting that
Co@SiO C composites possess stronger attenuation capabilities for
2.0 GHz, 1.8 GHz and 1.9 GHz at the thickness of 2.05 mm, 2.3 mm
and 2.8 mm, respectively. Whereas the counterparts of Co@SiO C
x
composites correspond to 4.4 GHz, 4.3 GHz and 4 GHz, respectively.
In addition to more EMWs inside the absorbers, remarkable
x
x
electromagnetic wave. Impedance matching determines the extent
to which EMW enters the absorbers, which can be expressed by
following equation:
x
attenuation capability is also assigned to Co@SiO C composites.
Therefore, the coexistence of strong attenuation capability and
optimized impedance matching leads to the excellent absorption
performance.
Z ¼ Zin /Z
0
r
¼ (m /ε
r
)1/2tanh[j(2
p
fd/c) $ (
r
m ·ε
r
)1/2
]
(8)
x
It suggests that the SiO C as a shell can greatly contribute to the
microwave attenuation. The mechanisms of high-performance
microwave absorption can be divided into various mechanisms
(Fig. 10). Firstly, ferromagnetic resonance (deriving from the uni-
form precession modes of magnetization vector) and eddy current
loss, as two major magnetic loss mechanisms, contribute to the
attenuation of electromagnetic wave. Second, two kinds of inter-
The optimal impedance matching can be achieved on the con-
dition that ε equals to , which suggests that all the incident EMW
can enter into the inner of the absorbers. According to the above
equation, lower ε tends to result in the optimized impedance
r
m
r
r
matching. In order to permit more microwaves to propagate into
the samples and then absorb or attenuate, the values of Z are
supposed to be equal to 1, so as to guarantee less reflection of EMW
at the air-absorber interfaces. The calculated Z values of Co and
face polarizations can be rooted in SiO C shell and Co cores as well
x
as C and SiO existing in shell. Third, numbers of atomic-scale de-
x
fects derived from condensation and calcination processes coexist
Co@SiO
.05 mm, 2.3 mm and 2.8 mm, respectively. In contrast, the dis-
tance closer to 1 is assigned to Co@SiO C composites at the same
thickness, suggesting less reflection on the absorber surfaces.
Specifically, for Co particles, the bands of Z curves over 0.6 are
x
C are illustrated in Fig. 9b with the matching thickness of
in amorphous SiO C shell, which break the balance of charges
distribution and can generate lots of dipole polarizations. Fourth,
carbon composition and Co can lead to conduction loss by certain
electronic transmission characteristics. Finally, optimal impedance
x
2
x
matching is achieved in Co@ SiO C composites.
x
x
Fig. 10. Schematic illustration of the attenuation mechanisms in Co@SiO C hybrids.

J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
11
4
. Conclusion
high-performance microwave absorption, Phys. Chem. Chem. Phys. 15 (2013)
6104e16110.
10] C.Y. Liang, C.Y. Liu, H. Wang, L.N. Wu, Z.H. Jiang, Y.J. Xu, B.Z. Shen, Z.J. Wang,
SiC-Fe dielectric-magnetic hybrid nanowires: controllable fabrication,
characterization and electromagnetic wave absorption, J. Mater. Chem. A 2
2014) 16397e16402.
11] J. Deng, X. Zhang, B. Zhao, Z. Bai, S. Wen, S. Li, S. Li, J. Yang, R. Zhang, Fluffy
microrods to heighten the microwave absorption properties through tuning
the electronic state of Co/CoO, J. Mater. Chem. C 6 (2018) 7128e7140.
1
[
The construction of a well wrapped core-shell structure
3 4
O
x
Co@SiO C hybrids originated from Co@OSR composites, which was
demonstrated by in-situ polymerization of KH-550 silane coupling
agent on the surface of well-reduced cobalt particles. The absorp-
(
[
[
x
tion performance of hybrid-architectures Co@SiO C can be realized
12] W.Y. Yang, Y.F. Zhang, G.Y. Qiao, J.B. Yang, Tunable magnetic and microwave
by reflection loss with RLmin of ꢀ60.3 dB locating at 16.2 GHz and
matching thickness of only 2.05 mm, and the effective absorption
band is up to 7.1 GHz (10.9e18 GHz). This 3D multicomponent hi-
erarchical core-shell structure combined the excellent magnetic
loss from Co core with certain dielectric loss by SiO C shell, and the
x
high-absorption performance mechanisms can be further sub-
divided into conductivity loss, interfacial polarizations, dipole (or
absorption properties of Sm1.5
45 (2018) 331e336.
[13] M. Zhang, Z. Li, T. Wang, S. Ding, G. Song, J. Zhao, A. Meng, H. Yu, Q. Li,
Preparation and electromagnetic wave absorption performance of Fe Si/SiC@
SiO nanocomposites, Chem. Eng. J. 362 (2019) 619e627.
x
Y0.5Fe17-xSi and their composites, Acta Mater.
1
3
2
[
14] T. Wang, H.D. Wang, X. Chi, R. Li, J.B. Wang, Synthesis and microwave ab-
sorption properties of Fe-C nanofibers by electrospinning with disperse Fe
nanoparticles parceled by carbon, Carbon 7 (2014) 312e318.
[
15] S. Li, Y. Huang, N. Zhang, M. Zong, P. Liu, Synthesis of polypyrrole decorated
x
defects) polarization and magnetic loss. Due to the dielectric SiO C
FeCo@SiO
J. Alloys Compd. 774 (2019) 532e539.
[16] J. Liu, J. Xu, R. Che, H. Chen, M. Liu, Z. Liu, Hierarchical Fe
microspheres with enhanced microwave-absorption properties, Chemistry 19
2013) 6746e6752.
17] B. Zhao, X. Guo, W. Zhao, J. Deng, G. Shao, B. Fan, Z. Bai, R. Zhang, Yolk-Shell
Ni@SnO Composites with a designable interspace to improve the electro-
magnetic wave absorption properties, ACS Appl. Mater. Interfaces 8 (2016)
8917e28925.
18] C. Fu, D. He, Y. Wang, X. Zhao, Facile synthesis and microwave absorption
2
as a high-performance electromagnetic absorption material,
layer, it is suggested that this result may provide insights into
construction of new core-shell structure for easy-to-implement,
large-scale-preparation and high-absorption absorbers.
3 4 2
O @TiO yolk-shell
(
[
Declaration of competing interest
2
2
This part of work has no conflict of interest.
[
[
[
[
3 4
performance of coated carbon nanotubes by porous Fe O @C nanorods, Synth.
Met. 248 (2019) 76e80.
19] J. Wang, Z. Wang, R. Liu, Y. Li, X. Zhao, X. Zhang, Heterogeneous interfacial
polarization in Fe@ZnO nanocomposites induces high-frequency microwave
absorption, Mater. Lett. 209 (2017) 276e279.
CRediT authorship contribution statement
Jianwen Ge: Conceptualization, Software, Investigation, Writing
original draft, Writing - review & editing. Yu Cui: Validation,
20] S. Wei, X. Wang, B. Zhang, M. Yu, Y. Zheng, Y. Wang, J. Liu, Preparation of
-
2 4 3 4
hierarchical core-shell C@NiCo O @Fe O composites for enhanced micro-
wave absorption performance, Chem. Eng. J. 314 (2017) 477e487.
21] C. Chen, S. Bao, B. Zhang, Y. Chen, W. Chen, C. Wang, Coupling Fe@Fe O
3 4
Formal analysis, Resources, Software, Methodology. Li Liu: Valida-
tion, Formal analysis, Visualization, Writing - review & editing. Rui
Li: Resources, Writing - review & editing, Supervision, Data cura-
tion. Fandi Meng: Writing - review & editing, Supervision, Data
curation, Writing - review & editing.
nanoparticles with multiple-walled carbon nanotubes with width band
electromagnetic absorption performance, Appl. Surf. Sci. 467e468 (2019)
836e843.
[22] F. Wang, Y. Sun, D. Li, B. Zhong, Z. Wu, S. Zuo, D. Yan, R. Zhuo, J. Feng, P. Yan,
Microwave absorption properties of 3D cross-linked Fe/C porous nanofibers
prepared by electrospinning, Carbon 134 (2018) 264e273.
Acknowledgements
[23] Y. Li, J. Wang, R. Liu, X. Zhao, X. Wang, X. Zhang, G. Qin, Dependence of
gigahertz microwave absorption on the mass fraction of Co@C nanocapsules
in composite, J. Alloys Compd. 724 (2017) 1023e1029.
The investigation was supported by the National Natural Science
Foundation of China under the contract No. 51622106, the Funda-
mental Research Funds for the Central Universities under the
contract No.2017YFB0702303, and Liao Ning Revitalization Talents
Program under the contract No. XLYC1807076.
[
[
[
[
24] G.M. Shi, S.-H. Lv, X.B. Cheng, X.-L. Wang, S.T. Li, Enhanced microwave ab-
sorption properties of modified Ni@C nanocapsules with accreted N doped C
shell on surface, J. Mater. Sci. Mater. Electron. 29 (2018) 17483e17492.
3 4 2
25] X. Sun, X. Lv, X. Li, X. Yuan, L. Li, G. Gu, Fe O @SiO nanoparticles wrapped
with polypyrrole (PPy) aerogel: a highly performance material as excellent
electromagnetic absorber, Mater. Lett. 221 (2018) 93e96.
26] B. Zhao, G. Shao, B. Fan, W. Zhao, R. Zhang, Investigation of the electromag-
2 2
netic absorption properties of Ni@TiO and Ni@SiO composite microspheres
References
with core-shell structure, Phys. Chem. Chem. Phys. 17 (2015) 2531e2539.
27] D. Ding, Y. Wang, X. Li, R. Qiang, P. Xu, W. Chu, X. Han, Y. Du, Rational design
of core-shell Co@C microspheres for high-performance microwave absorp-
tion, Carbon 111 (2017) 722e732.
[
[
[
[
1] T. Wang, H.D. Wang, X. Chi, R. Li, J.B. Wang, Synthesis and microwave ab-
sorption properties of Fe-C nanofibers by electrospinning with disperse Fe
nanoparticles parceled by carbon, Carbon 7 (2014) 312e318.
2] J. Yan, Y. Huang, C. Chen, X. Liu, H. Liu, The 3D CoNi alloy particles embedded
in N-doped porous carbon foams for high-performance microwave absorbers,
Carbon 152 (2019) 545e555.
[28] H. Zhao, Y. Cheng, H. Lv, G. Ji, Y. Du, A novel hierarchically porous magnetic
carbon derived from biomass for strong lightweight microwave absorption,
Carbon 142 (2019) 245e253.
[29] G.L. Wu, Y.H. Cheng, Z.H. Yang, H.L. Li, P.Z. Guo, H.L. Lv, Design of carbon
sphere/magnetic quantum dots with tunable phase compositions and boost
dielectric loss behavior, Chem. Eng. J. 333 (2018) 519e528.
[30] C. Chen, J. Xi, Y. Han, L. Peng, W. Gao, Z. Xu, C. Gao, Ultralight graphene micro-
popcorns for multifunctional composite applications, Carbon 139 (2018)
545e555.
[31] S.S. Maklakov, A.N. Lagarkov, S.A. Maklakov, Y.A. Adamovich, D.A. Petrov,
K.N. Rozanov, I.A. Ryzhikov, A.Y. Zarubina, K.V. Pokholok, D.S. Filimonov,
Corrosion-resistive magnetic powder Fe@SiO for microwave applications,
2
J. Alloys Compd. 706 (2017) 267e273.
[32] D. Hua, J. Tang, J. Jiang, Z. Gu, L. Dai, X. Zhu, Controlled grafting modification of
silica gel via RAFT polymerization under ultrasonic irradiation, Mater. Chem.
Phys. 114 (2009) 402e406.
3] Q. Zeng, X.H. Xiong, P. Chen, Q. Yu, Q. Wang, R.C. Wang, H.R. Chu, Air@rGO@
3 4
Fe O microspheres with spongy shells: self-assembly and microwave ab-
sorption performance, J. Mater. Chem. C 4 (2016) 10518e10528.
4] R. Bin Yang, P.M. Reddy, C.J. Chang, P.A. Chen, J.K. Chen, C.C. Chang, Synthesis
3 4
and characterization of Fe O /polypyrrole/carbon nanotube composites with
tunable microwave absorption properties: role of carbon nanotube and pol-
ypyrrole content, Chem. Eng. J. 285 (2016) 497e507.
[
[
[
5] X. Xue, H.Y. Yan, Y.Q. Fu, Preparation of pure and metal-doped Li
4
Ti
5
O
12
composites and their lithium-storage performances for lithium-ion batteries,
Solid State Ionics 335 (2019) 1e6.
6] H.Y. Yan, Y.Q. Fu, X.M. Wu, X.X. Xue, C. Li, L. Zhang, Core-shell structured
NaTi (PO ) @polyaniline as an efficient electrode material for electrochemical
2 4 3
energy storage, Solid State Ionics 336 (2019) 95e101.
7] J. Tang, N. Liang, L. Wang, J. Ge, T. Dong, S.H. Feng, Three-dimensional
nitrogen-doped reduced graphene oxide aerogel decorated with Ni nano-
particles with tunable and unique microwave absorption, Carbon 152 (2019)
[33] X.W. Li, R.G. Song, Y. Jiang, C. Wang, D. Jiang, Surface modification of TiO
2
nanoparticles and its effect on the properties of fluoropolymer/TiO
composite coatings, Appl. Surf. Sci. 276 (2013) 761e768.
2
nano-
[34] C. Pan, K. Kou, Q. Jia, Y. Zhang, G. Wu, T. Ji, Improved thermal conductivity and
dielectric properties of hBN/PTFE composites via surface treatment by silane
coupling agent, Compos. B Eng. 111 (2017) 83e90.
5
75e586.
8] M.L. Ma, Y.Y. Yang, D.L. Liao, P.L. Yu, J.W. Zhang, L.Z. Zhang, Synthesis, char-
acterization and catalytic performance of core-shell structure magnetic Fe
P(GMA-EGDMA)-NH /HPG-COOH-Pd catalyst, Appl. Organomet. Chem.
2019) 67e72.
9] S. Xie, X.N. Guo, G.Q. Jin, X.Y. Guo, Carbon coated Co-SiC nanocomposite with
[
3
O
4
/
[35] H. Shi, Y. He, Y. Pan, H. Di, G. Zeng, L. Zhang, C. Zhang, A modified mussel-
2
inspired method to fabricate TiO decorated superhydrophilic PVDF mem-
brane for oil/water separation, J. Membr. Sci. 506 (2016) 60e70.
[36] D. Su, C. Huang, Y. Hu, Q. Jiang, L. Zhang, Y. Zhu, Preparation of
2
2
(
[

12
J. Ge et al. / Journal of Alloys and Compounds 831 (2020) 154442
superhydrophobic surface with a novel solegel system, Appl. Surf. Sci. 258
2011) 928e934.
37] X. Wan, Y. Zhan, Z. Long, G. Zeng, Y. He, Core@double-shell structured mag-
netic halloysite nanotube nano-hybrid as efficient recyclable adsorbent for
methylene blue removal, Chem. Eng. J. 330 (2017) 491e504.
38] B. Wei, Q. Chang, C. Bao, L. Dai, G. Zhang, F. Wu, Surface modification of filter
medium particles with silane coupling agent KH550, Colloid. Surface. 434
[53] S. Dai, Y. Cheng, B. Quan, X. Liang, W. Liu, Z. Yang, G. Ji, Y. Du, Porous-car-
bonbased Mo C nanocomposites as excellent microwave absorber: a new
(
2
[
[
[
exploration, Nanoscale 10 (2018) 6945e6953.
[54] W. Liu, J. Pan, G. Ji, X. Liang, Y. Cheng, B. Quan, Y. Du, Switching the electro-
magnetic properties of multicomponent porous carbon materials derived
from bimetallic metaleorganic frameworks: effect of composition, Dalton
Trans. 46 (2017) 3700e3709.
[55] S. Wang, X. Ke, S. Zhong, Y. Lai, D. Qian, Y. Wang, Q. Wang, W. Jiang, Bimetallic
zeolitic imidazolate frameworks-derived porous carbon-based materials with
efficient synergistic microwave absorption properties: the role of calcining
temperature, RSC Adv. 7 (2017) 46436e46444.
(
2013) 276e280.
39] Q. Zhang, F. Gao, C. Zhang, L. Wang, M. Wang, M. Qin, G. Hu, J. Kong, Enhanced
dielectric tunability of Ba0.6Sr0.4TiO /Poly(vinylidene fluoride) composites via
interface modification by silane coupling agent, Compos. Sci. Technol. 129
2016) 93e100.
40] Y. Zhan, J. Zhang, S. He, S. Zhao, Y. Bai, X. Liu, Thermally stable and dielectric
nanocomposite based on poly(arylene ether nitrile) and BaTiO functionalized
3
(
[56] Z. Yang, H. Lv, R. Wu, Rational construction of graphene oxide with MOF-
derived porous NiFe@C nanocubes for high-performance microwave attenu-
ation, Nano Res. 9 (2016) 3671e3682.
[
[
[
3
by modified mussel-inspired route, J. Polym. Res. 26 (2019) 253e266.
41] N. Li, G.W. Huang, H.M. Xiao, Q.P. Feng, S.Y. Fu, Investigations on structure-
[57] Javida, Y.L. Zhou, D.X. Wang, Strong microwave absorption of Fe@SiO
2
nanocapsules fabricated by one-step high energy plasma, J. Phys. Chem. Solid.
129 (2019) 242e251.
[58] H.L. Xu, X.W. Yin, X.M. Fan, Z.M. Tang, Z.X. Hou, Constructing a tunable het-
erogeneous interface in bimetallic metal-organic frameworks derived porous
carbon for excellent microwave absorption performance, Carbon 148 (2019)
421e429.
[59] S.P. Li, Y. Huang, D. Ling, N. Zhang, M. Zong, X.L. Qin, P.B. Liu, Enhanced
microwave-absorption with carbon-encapsulated Fe-Co particles on reduced
graphene oxide nanosheets with nanoscale-holes in the basal plane, J. Colloid
Interface Sci. 544 (2019) 188e197.
dependent microwave absorption performance of nano-Fe
3
O
4
coated
carbon-based absorbers, Carbon 144 (2019) 216e227.
42] Z. Jia, B.B. Wang, A.L. Feng, J.J. Liu, M. Zhang, Z.Y. Huang, G.L. Wu, Development
of spindle-cone shaped of Fe/a-Fe hybrids and their superior wideband
electromagnetic absorption performance, J. Alloys Compd. 799 (2019)
16e223.
2 3
O
2
[
43] T.Q. Hou, B.B. Wang, Z.R. Jia, H.J. Wu, D. Lan, Z.Y. Huang, A.L. Feng, M.L. Ma,
G.L. Wu, A review of metal oxide-related microwave absorbing materials from
the dimension and morphology perspective, J. Mater. Sci. 30 (2019)
1
0961e10984.
44] G.L. Wu, H.X. Zhang, X.X. Luo, L.J. Yang, H.L. Lv, Investigation and optimization
of Fe/ZnFe as a Wide-band electromagnetic absorber, J. Colloid Interface
[60] P.B. Liu, Y.Q. Zhang, J. Yan, Y. Huang, L. Xia, Z.X. Guang, Synthesis of light-
weight N-doped graphene foams with open reticularstructure for high-
efficiency electromagnetic wave absorption, Chem. Eng. J. 368 (2019)
285e298.
[
2 4
O
Sci. 536 (2019) 548e555.
[
45] W. Feng, Y. Wang, J. Chen, B. Li, L. Guo, J. Ouyang, D. Jia, Y. Zhou, Metal organic
framework-derived CoZn alloy/N-doped porous carbon nanocomposites:
tunable surface area and electromagnetic wave absorption properties,
J. Mater. Chem. C 6 (2018) 10e18.
[61] J. Zhan, H. Zhang, G. Zhu, Magnetic photocatalysts of cenospheres coated with
3 4 2
Fe O /TiO core/shell nanoparticles decorated with Ag nanopartilces, Ceram.
Int. 40 (2014) 8547e8559.
[62] Y. Wang, W. Wang, J. Sun, C. Sun, Y. Feng, Z. Li, Microwave-based preparation
and characterization of Fe-cored carbon nanocapsules with novel stability and
super electromagnetic wave absorption performance, Carbon 135 (2018)
1e11.
[
46] Q. Liao, M. He, Y. Zhou, S. Nie, Y. Wang, S. Hu, H. Yang, H. Li, Y. Tong, Highly
cuboid-shaped heterobimetallic metal-organic frameworks derived from
porous Co/ZnO/C microrods with improved electromagnetic wave absorption
capabilities, ACS Appl. Mater. Interfaces 10 (2018) 29136e29144.
47] Q. Liu, X. Liu, H. Feng, H. Shui, R. Yu, Metal organic framework-derived Fe/
carbon porous composite with low Fe content for lightweight and highly
efficient electromagnetic wave absorber, Chem. Eng. J. 314 (2017) 320e327.
48] X. Zhang, G. Ji, W. Liu, B. Quan, X. Liang, C. Shang, Y. Cheng, Y. Du, Thermal
[63] Z.C. Mo, R.L. Yang, D.W. Lu, L.L. Yang, Q.M. Hua, Lightweight, three-
[
[
2
dimensional carbon Nanotube@TiO sponge with enhanced microwave ab-
sorption performance, Carbon 144 (2019) 433e439.
[64] Z. Yang, H. Lv, R. Wu, Rational construction of graphene oxide with MOF-
derived porous NiFe@C nanocubes for high-performance microwave attenu-
ation, Nano Res. 9 (2016) 3671e3682.
[65] H.L. Xua, X.W. Yin, M. Zhu, M.H. Li, H. Zhang, H.J. Wei, Constructing hollow
graphene nano-spheres confined in porous amorphous carbon particles for
achieving full X band microwave absorption, Carbon 142 (2019) 346e353.
conversion of an Fe
efficient FeeCo/nanoporous carbon microwave absorbing material, Nanoscale
(2015) 12932e12942.
3 4
O @metaleorganic framework: a new method for an
7
[
[
[
49] R. Qiang, Y. Du, H. Zhao, Y. Wang, C. Tian, Z. Li, X. Han, P. Xu, Metal organic
framework-derived Fe/C nanocubes toward efficient microwave absorption,
J. Mater. Chem. A 3 (2015) 13426e13434.
50] Y.Y. Lü, Y. Wang, H. Li, Y. Lin, Z. Jiang, Z. Xie, Q. Kuang, L. Zheng, MOF-derived
porous Co/C nanocomposites with excellent electromagnetic wave absorption
properties, ACS Appl. Mater. Interfaces 7 (2015) 13604e13611.
51] W. Liu, Q. Shao, G. Ji, X. Liang, Y. Cheng, B. Quan, Y. Du, Metaleorganic-
frameworks derived porous carbon-wrapped Ni composites with optimized
impedance matching as excellent lightweight electromagnetic wave absorber,
Chem. Eng. J. 313 (2017) 734e744.
2 4
[66] F. Yan, D. Guo, S. Zhang, C. Li, C. Zhu, X. Zhang, Y. Chen, An ultra-small NiFe O
hollow particle/graphene hybrid: fabrication and electromagnetic wave ab-
sorption property, Nanoscale 10 (2018) 2697e2703.
[67] G. Sun, H. Wu, Q. Liao, Y. Zhang, Enhanced microwave absorption perfor-
mance of highly dispersed CoNi nanostructures arrayed on graphene, Nano
Res. 11 (2018) 2689e2704.
3 4
[68] P.B. Liu, Y. Huang, X. Zhang, Superparamagnetic Fe O nanoparticles on gra-
pheneepolyaniline:Synthesis, characterization and their excellent electro-
magnetic absorption properties, J. Alloys Compd. 596 (2014) 25e31.
[69] X.P. Li, Z.M. Deng, Y. Li, H.B. Zhang, Controllable synthesis of hollow micro-
spheres with Fe@Carbon dual-shells for broad bandwidth microwave ab-
sorption, Carbon 147 (2019) 172e181.
[
52] X. Xiao, W. Zhu, Z. Tan, W. Tian, Y. Guo, H. Wang, J. Fu, X. Jian, Ultra-small Co/
CNTs nanohybrid from metal organic framework with highly efficient mi-
crowave absorption, Composites Part B 152 (2018) 316e323.