Journal of Colloid and Interface Science 552 (2019) 196–203

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Journal of Colloid and Interface Science

journal homepage: www.elsevier.com/locate/jcis

Dependence of reduction degree on electromagnetic absorption

of graphene nanoribbon unzipped from carbon nanotube
Yujie Ding a, Jiaqi Zhu a,⇑, Shasha Wang a, Minglong Yang a, Shuang Yang a, Lei Yang b,
Xu Zhao a, Fan Xu a, Zhijiang Wang c,⇑, Yibin Li a,d,⇑
a
National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, Center for Composite Materials and Structures,
Harbin Institute of Technology, Harbin 150080, PR China
b
Center of Analysis and Measurement, Harbin Institute of Technology, Harbin 150001, PR China
c
School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, PR China
d
Shenzhen STRONG Advanced Materials Institute Ltd. Corp, Shenzhen 518000, PR China

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o a b s t r a c t

Article history: Carbon materials are very promising for electromagnetic wave absorption application due to their light
Received 26 February 2019 weight and low cost, where the reflection loss is used to evaluate the absorption efficiency. However, the
Revised 7 May 2019 reflection loss of carbon materials (carbon foam, graphene, and carbon nanotube) without loading mag-
Accepted 9 May 2019
netic particles is not as high as expected. Here, we propose to unzip carbon nanotubes into graphene
Available online 16 May 2019
oxide nanoribbons (GONRs), followed by controllable reduction treatment using hydrazine hydrate,
and the reduced GONRs were finalized (called as r-GONRs). The r-GONRs exhibit obvious dielectric relax-
Keywords:
ation behaviors compared to GONRs, and the dielectric loss is improved by increasing the reduction
Graphene oxide nanoribbons
Unzipping
degree. The optimized r-GONRs show ultrahigh electromagnetic absorption, up to
65.09 dB at a thick-
Controllable reduction ness of 2 mm, which is more advantageous than the reported values of other carbon materials. The effi-
Electromagnetic wave absorption cient absorption bandwidth (reflection loss 
10 dB) reaches 7.06 GHz. These are attributed to the large
dielectric loss of the unique graphene nanoribbon. Our controllable reduced graphene nanoribbon is
promising in the application of radar wave absorption and electromagnetic shielding.
Ó 2019 Elsevier Inc. All rights reserved.

1. Introduction

⇑ Corresponding authors at: National Key Laboratory of Science and Technology With the rapid development of electronic technology, electro-
on Advanced Composites in Special Environments, Center for Composite Materials magnetic (EM) pollution is becoming increasingly serious; it not
and Structures, Harbin Institute of Technology, Harbin 150080, PR China (Y. Li).
only causes EM interference on electronic devices, and leakage of
E-mail addresses: zhujq@hit.edu.cn (J. Zhu), wangzhijiang@hit.edu.cn (Z. Wang),
information, but also threatens human health [1–3]. One feasible
liyibin@hit.edu.cn (Y. Li).

https://doi.org/10.1016/j.jcis.2019.05.033
0021-9797/Ó 2019 Elsevier Inc. All rights reserved.
 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203 197

solution for this problem, is to use EM absorbing materials to preparation method is shown in our previous work [33]. Then, the
attenuate unwanted energy. Consequently, EM absorption has cleaned graphene oxide nanoribbons were dispersed in DI water
become a research hotspot, and considerable efforts have been and dried by freeze-drying. Next, the dried GONRs were chemically
devoted to developing high-performance EM absorbers. Besides reduced by hydrazine hydrate vapor at 90 °C for 24 h. The weight
having strong absorption characteristics, ideal EM absorbers ratios of hydrazine hydrate to GONRs were set as 1:10, 1:1, 10:1
should be lightweight, chemically and thermally stable, and have and 20:1. In the following content, we also named the r-GONRs
a wide absorption bandwidth, especially for practical applications samples as 1:10, 1:1, 1 0:1 and 20:1. Finally, the r-GONRs were
in the areas of electronic equipment, aviation and aerospace [4– dried in vacuum at 100 °C for 24 h to remove the residual hydra-
6]. Among the EM absorption materials, carbon materials such as zine and water.
carbon fibers (CFs) [7,8], carbon nanotubes (CNTs) [5,9,10], and
graphene [1,6,11–15] have received attractive attention in the field 2.2. Characterization
of EM absorption owing to their lightweight, resistance to high
temperature and corrosion, and unique electrical properties. The morphology of GONRs and r-GONRs were characterized by
As the thinnest carbon material, graphene is lightweight, and SEM (ZEISS RIGMA, Germany) and TEM (Tecnai G2 F30, FEI, US).
possesses large specific surface area, high conductivity, and abun- Raman spectroscopy measurements were performed on InVia with
dant surface defects, which can meet the requirements of an ideal a 532 nm laser. The X-ray photoelectron spectroscopy (XPS) mea-
absorbers to the greatest extent [16–18]. However, graphene has surements were recorded on ESCALAB 250Xi spectrometer (Ther-
been proved to exhibit poor absorption performance due to the ter- mofisher Scientific Company, US) with Al Ka source and a pass
rible impedance matching [11]. According to the EM wave absorp- energy of 20 eV to investigate the chemical composition of r-
tion principle, good impedance matching requires similar GONRs.
permittivity and permeability between the material and air [19].
However, both the permittivity and conductivity of graphene are
2.3. EM parameters measurements
higher than those of air, resulting in poor impedance matching
[15,20]. In order to develop excellent EM absorbers based on gra-
For EM parameters measurements, the samples were prepared
phene, many efforts have been devoted to improving the impedance
by milling 10 wt% of r-GONRs or GONRs in a paraffin wax matrix
matching. Compositing or hybridizing graphene with magnetic
at 85 °C. The mixtures were then pressed into a toroidal shape with
materials is the most common method, and it has been proved to
an outer diameter of 7.0 mm, inner diameter of 3.0 mm, and height
be an effective strategy for improving the impedance matching by
of 3.0 mm (Fig. S1). The complex permittivity and complex perme-
introducing a magnetic property. These materials, such as
ability were measured by a network analyzer (Agilent Technolo-
Fe3O4/graphene nanohybrids [21], CoS2-reduced graphene oxide
gies N5230A) in the transmission-reflection coaxial line mode
(RGO) hybrids [22] and RGO/MnFe2O4 nanocomposites [23], present
within the frequency range of 2–18 GHz.
higher EM absorption property than single graphene. However, this
kind of absorbers shows low corrosion, oxidation resistance and
high density, which cannot satisfy the demands of ideal absorbers. 3. Results and discussion
Porous graphene materials, such as graphene foam [6,15,24],
graphene microflowers [25], and graphene micro-popcorns [26], The synthetic process of r-GONRs via chemical reduction
have been reported to be excellent EM absorbers due to the method using hydrazine hydrate as the reductant is schematically
increased surface area, strong dielectric loss and multi-reflection depicted in Fig. 1a. First, the multi-walled CNTs were oxidized and
of EM wave. Therefore, constructing porous graphene materials is longitudinally unzipped into GONRs by H2SO4/KMnO4 solution.
a valid means to obtain high EM absorption. Meanwhile, the chem- Then, the GONRs were dried by the freeze-drying method. The
ical doping of graphene can effectively change its electronic prop- freeze-dried GONRs powder were reduced with hydrazine hydrate
erties and increase the dielectric loss due to the defects introduced vapor at 90 °C for 24 h. In order to study the effect of reduction
by doping [27]. Therefore, doped-graphene with high EM absorp- degree on the EM parameter of r-GONRs, different amounts of
tion can be achieved by adjusting the doping concent. The reflec- hydrazine hydrate were added into the reduction container at this
tion loss of nitrogen doped graphene can achieve-24.6 dB at step. Finally, the r-GONRs were dried in vacuum to remove the
8.51 GHz and an absorption bandwidth of 4.89 GHz (7.55– residual hydrazine and water. During the oxidation and reduction
12.44 GHz, reflection loss <
10 dB) at a thickness of 3 mm [28]. process, the color of powder changed very obviously: the CNTs
Graphene nanoribbons (GNRs) have a narrow strip morphology show black, the GONRs show gray and the r-GONRs show black,
with a high aspect ratio similar to CNTs [29,30]. GNRs are more as shown in Fig. S2.
adjustable than graphene due to their special edge structure, size The morphology and microstructure of the MWCNTs, GONRs
effects, and confinement effects [31], which indicate that GNRs and r-GONRs are shown in Fig. 1b–g. The diameters of the
can also be as a promising candidate for EM absorber. As a result, MWCNTs were 30–80 nm (Fig. 1b). After longitudinal unzipping,
we can optimize the EM absorption performance of GNRs by regu- it can be clearly observed that the unzipped MWCNT demonstrates
lating the reduction degree. Here, we propose to unzip carbon nan- the nanoribbon-like structure instead of tube structure, as shown
otubes into graphene oxide nanoribbons (GONRs), followed by in Fig. 1c. It is also noted that partial tube-like structure in GONRs
controllable reduction treatment. The reduced graphene oxide remains. The SEM and TEM images show that the widths of the
nanoribbons (r-GONRs) show ultrastrong EM absorption, which is GONRs falls in the range of 100–200 nm, and the lengths are sev-
promising in the application of radar wave absorption and electro- eral micrometers, as shown in Fig. 1c–e. In Fig. 1f and g, the r-
magnetic shielding. GONRs present a large sheet structure because the nanoribbons
were squeezed into sheets as the ice crystals grew during the
2. Experimental methods freeze-drying process. These observations confirm that the
MWCNTs were successfully unzipped into GONRs using the chem-
2.1. Synthesis of graphene nanoribbons ical method.
The elemental composition and functional groups of our mate-
At first, graphene oxide nanoribbons were prepared by longitu- rials were identified by XPS. As shown in Fig. 2a, the carbon con-
dinal unzipping of multi-walled CNTs (MWCNTs) [32]. The specific tent continually increases with the enhanced addition of
198 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203

Fig. 1. (a) Schematic illustration for the fabrication process of the r-GONRs. (b) SEM image of the MWCNTs. (c) SEM image of the GONRs. (d) and (e) TEM images of the GONRs.
(f) and (g) SEM images of the r-GONRs.

hydrazine hydrate, while the oxygen content drops down. In addi- pyridinic N, pyrrolic N and graphitic N (as shown in Fig. 3b),
tion, the XPS spectra show the presence of nitrogen in the nanorib- respectively [26,40]. The pyridinic N refers to the N atoms bonding
bons after reduction with hydrazine hydrate, whose content also to two C atoms at the edge of graphene nanoribbons, and each of
increases with the enhanced addition of hydrazine hydrate. which contributes one p-electron to the aromatic p system. The
Fig. 2b presents the C1s XPS spectra of GONRs and r-GONRs as well pyrrolic N refers to the N atoms incorporation into other four C
as the N1s XPS spectrum of r-GONRs. The C1s XPS spectrum of atoms forming a five-membered heterocyclic, and each of which
GONRs clearly indicates a considerable degree of oxidation degree. contributes to the p system with two p-electrons. The graphitic
As seen in Fig. 2b, the C1s peak can be split into four components at N refers to the N atoms that substitute the C atoms in the graphitic
binding energies of 284.8 eV, 286.9 eV, 287.6 eV, skeleton [28,40–44]. Therefore, nitrogen doping can tune the elec-
and  288.9 eV, corresponding to CAC (in aromatic), CAO (epoxy tronic structure of graphene nanoribbon, thus affecting its electri-
and hydroxyl), C@O (carbonyl) and OAC@O (carboxyl), respec- cal properties.
tively [6,14,34,35]. Grafting of these hydrophilic groups onto the Raman spectroscopy is an effective tool to characterize the
nanoribbons is beneficial to the dispersion of GONRs in water. structure and quality of carbon materials. Fig. 2c shows the Raman
Obviously, the CAO is the main oxygen-containing group in the spectra of the as-prepared GONRs and r-GONRs. After reduction by
GONRs. hydrazine hydrate, the characteristics of the Raman spectra were
After being reduced with hydrazine hydrate, the C1s XPS spec- similar to those of GONRs, indicating that the r-GONRs preserve
tra of the r-GONRs also exhibit the same oxygen functionalities, the basic structural properties of the GONRs during the reduction
but their peak intensities are much smaller than those in GONRs. process. There are three main features in the spectra of the GONRs
The relative percentage of the CAC bonds in aromatic increases and r-GONRs in the 800–3000 cm
1 region: D band at about 1349–
from 60.40% (for GONRs) to 71.35% (for r-GONRs-20:1), and the 1352 cm
1, G band at 1589–1597 cm
1, and a weak and broadened
relative percentage of the oxygen containing groups shows a 2D band at about 2700 cm
1. The appearance of the D band can be
remarkable drop from 39.6% (for GONRs) to 12.5% of (for r- attributed to the presence of defects and edge effects in the GONRs
GONRs-20:1), indicating that the GONRs are effectively reduced and r-GONRs. Therefore, the D band can reflect the structural
by hydrazine hydrate (Table S1). At the same time, there is an addi- defects of the samples. The G band derives from the in-plane
tional component located at  285.8 eV, corresponding to the C stretching vibration of the graphite lattice i.e. E2g mode, which
bound to nitrogen after reduction with hydrazine hydrate [36], reflects the structural integrity of the material [39,40]. In general,
and the percentage of CAN bonds increases with the amount of the intensity ratio of D band to G band (ID/IG) is used to evaluate
hydrazine hydrate (Table S1). These observations indicate that the lattice-defect density of carbon materials [37]. As depicted in
there was considerable de-oxygenation by the reduction process Fig. 2c, the ID/IG increases from 0.935 (for GONRs) to 1.021 (for r-
as well as nitrogen doping, which are consistent with the observa- GONRs-20:1) with the addition of hydrazine hydrate, implying
tions of reduced graphene oxide by hydrazine hydrate [37–39]. the increase in defects during the reduction process [14,37,40].
From the N1s XPS spectra of the r-GONRs (as shown in Figs. 2b Combining the above analysis and the previous research on the
and S3), it can be seen that the N1s envelope contains three peaks defects in reduced graphene and graphene nanoribbons
at  399 eV, 400.1 eV, and  401.3 eV, which can be assigned to [14,34,38,39], the increased defects are probably caused from the
 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203 199

Fig. 2. (a) X-ray photoelectron spectra of GONRs and r-GONRs. (b) C1s spectrum of GONRs and r-GONRs and N1s spectrum of r-GONRs of 10:1. (c) Comparison of Raman
spectra at 532 nm for GONRs and r-GONRs.

(a) (b)
Reducing with
hydrazine hydrate

Vacancy

C O H pyridinic N pyrrolic N
graphic N
Fig. 3. The possible generation mechanism of the defects in r-GONR from GONR during the reduction process.

introduced nitrogen and the vacancies resulting from deoxygena- complex permeability is taken as 1 [46]. The real part of complex
0
tion in the reduction process with hydrazine hydrate, as shown permittivity (e ) represents the ability to store electric energy
in Fig. 3. The 2D band is usually used to determine the thickness within the medium, and the imaginary part of complex permittiv-
of graphene sheets [43]. The presence of the weak and broadened ity (e}) corresponds to the dissipation (or loss) of electric energy.
2D band illustrates that the GONRs and r-GONRs are multi-layered, Thus, a high e} indicates strong dielectric loss to EM energy
which is in good accordance with the SEM results (Fig. 1f and g). [45–47]. Fig. 4a and b show the frequency dependent complex
According to the EM energy conversion principle, the permittivity of the wax composites containing 10 wt% GONRs or
0 0
complex permittivity (er ¼ e
je}) and complex permeability r-GONRs. The e of all samples decreases gradually with increasing
0
(lr ¼ l
jl}) are very important parameters that can determine frequency in the measured region with several fluctuations, and
and adjust the reflection and attenuation characteristics of EM the decreasing trend weakens with increasing frequency. The e}
absorbents [6,45]. Here, we just focus on the complex permittivity of GONRs/wax, r-GONRs-1:10,
1:1, and
20:1/wax composites
0
because of the weak magnetic property of our materials, and the are similar to the e , and decreases as the frequency increases with
200 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203

Fig. 4. The real part (a) and imaginary part (b) of permittivity of r-GONRs/wax and GONRs/wax composites over 2–18 GHz. (c) Modulus of Zin
1 of r-GONRs/wax and
GONRs/wax with a thickness of 3 mm in the frequency range of 2–18 GHz. (d) The dielectric loss tangent of r-GONRs/wax and GONRs/wax composites over 2–18 GHz. (e–i)
0
The Cole-Cole semicircles (e vs. e}) of r-GONRs/wax and GONRs/wax composites over 2–18 GHz.

several fluctuations. The e} of r-GONRs-10:1/wax composites has are important to evaluate the EM absorption performance. Impe-
slight fluctuations in the 2–8.6 GHz range, then slightly increases dance matching can determine the transmission behavior of EM
in the 8.6–9.9 GHz range, and finally the volatility decreases in wave at the interface between material and air [19]. The modulus
0
the remaining measured frequency range. Both e and e} exhibit of Zin
1can be used to investigate the impedance matching [48].
typical dielectric resonances at 9–18 GHz, and the higher the
1=2 h
1=2 i
reduction degree, the more obvious the resonance effect, which Zin ¼ Z 0 lr =er tanh jð2pfd=cÞ lr er ð1Þ
should come from the electron polarization due to the defects gen-
erated from the vacancies and the nitrogen introduced into the lat- Here, Zin is the input impedance of the material, Z 0 is the impe-
tice of nanoribbons in the reduction process. dance of air, lr and er are the relative permittivity and permeabil-
Overall, increasing the reduction degree of r-GONRs results in ity of the material respectively, f is the microwave frequency, d is
0
the increase in e and e} of r-GONRs/wax, as shown in Fig. 4a and the thickness of the material, and c is the velocity of light in vac-
b. According to the free-electron theory, e} ¼ r=x (here, rrepre- uum. In our case, the complex permeability is considered as 1
sents conductivity of materials and x is the frequency of the EM (lr ¼ 1) [6,14,46]. When the modulus of Zin
1 is approaching to
wave), e} and rare positively correlated. Meanwhile, the electrical zero, the impedance matching is desirable. Fig. 4c shows the mod-
conductivity of our materials increases with the reduction degree, ulus of Zin
1of r-GONRs/wax and GONRs/wax with a thickness of
and it increases from 1.2  10
7 S/m to 5.5  10
2 S/m (Fig. S4). 3 mm in the range of 2–18 GHz. For GONRs, r-GONRs-1:10 and
Consequently, the above-mentioned situation attributes to the
1:1, the modulus of Zin
1are much larger than zero, indicating
improvement of conductivity and reinstitution of electrically con- their impedance are mismatched. For r-GONRs-10:1, the modulus
ductive paths for hopping electrons by removing the oxygen- of Zin
1within the frequency range of 10–18 GHz are closest to
containing groups from GONRs and introducing nitrogen through zero than others, which indicates the impedance matching is most
the reduction process [14]. excellent.
For non-magnetic or weakly magnetic dielectric materials, both The tangential dielectric loss represents the capability of dissi-
impedance matching and tangential dielectric loss (tan de ¼ e}=e0 ) pating EM wave energy [9]. Fig. 4d shows the frequency depen-
 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203 201

Fig. 5. Contour maps and theoretical curves of the calculated EM wave reflection loss values of (a,b) GONRs/wax and r-GONRs/wax (c,d) 1:10, (e,f) 1:1, (g,h) 10:1, (i, j) 20:1.

dence of the tan de ¼ e}=e0 . Compared to GONRs/wax, the of GONRs/wax composite is below 0.1 in the whole measured fre-
tan de ¼ e}=e0 of r-GONRs/wax composites are significantly quency range; for r-GONRs-1:10/wax, the tan de ¼ e}=e0 is more
increased by increasing the reduction degree. The tan de ¼ e}=e0 than 0.15 in the whole frequency range; for r-GONRs-1:1/wax,
202 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203

the tan de ¼ e}=e0 is above 0.4 in the range of 1–10.5 GHz; for r- wax composites exhibit weak EM absorption, with the RLm of
GONRs-10:1/wax, the tan de ¼ e}=e0 is above 0.4 in the frequency
1.27 dB occurring at 10.3 GHz with a thickness of 5 mm. How-
range of 2.4–18 GHz with a maximum value of 0.73 at 12.3 GHz; ever, in the case of r-GONRs (the GONRs were reduced with hydra-
for r-GONRs-20:1/wax, the tan de ¼ e}=e0 is above 0.44 over the zine hydrate), the reflection loss properties of the incident EM
entire measured frequency range with a maximum value of 0.61 wave were dramatically enhanced. It can be seen that the mini-
at 9.7 GHz. Meanwhile, at 8.3–18 GHz, the tan de ¼ e}=e0 of 10 wt mum reflection loss of r-GONRs is becoming larger and larger as
% r-GONRs-10:1 in wax is higher than that of the other composite the reduction degree increases, peaking at
65.09 dB when the
samples, which illustrates that r-GONRs-10:1/wax composites thickness is 2.12 mm.
exhibit higher loss capacity for EM wave energy. These permittivity The r-GONRs-10:1 and
20:1 present good EM absorption. The
behaviors can be attributed to the variation of electric conductivity RLm of 20:1 is
36.5 dB at 15.05 GHz with a thickness of 2 mm.
and space-charge polarization among nanoribbons dispersed in the The effective bandwidth (EAB) (the bandwidth of RL below
wax. Comparing Fig. 4a with b, it can be seen that the variation ten-
10 dB) at this thickness is 5.35 GHz (12.65–18 GHz). For the r-
0
dency of e is out-of-sync with that of e}, and some peaks are GONRs-10:1, the RLm at 2.5 mm thickness is
19.6 dB with a
observed in Fig. 4d, which indicates that the r-GONRs/wax and broad EAB of 7.06 GHz (10.75–17.81 GHz). The broad bandwidth
GONRs/wax exhibit obvious dielectric relaxation behavior [49]. of r-GONRs-10:1 is attributed to the better impedance matching
Debye dipolar relaxation is an important mechanism of dielec- (as shown in Fig. 4c) and the larger dielectric loss (as shown in
tric absorbing materials. According to the Debye theory, the rela- Fig. 4d). Fig. 4c indicates that the impedance Zin of r-GONRs-
tive complex permittivity can be expressed as follows [6]: 10:1 is the most matchable with air (1) in the range of 10–
18 GHz, which means that more electromagnetic wave enters into
es
e1
er ¼ e1 þ ð2Þ the material. At the same time, the dielectric loss is larger than
1 þ jxs other ratios during this frequency range, which means that the
where e1 is the relative dielectric permittivity at infinite frequency, strong absorption occurs.
es is the static dielectric permittivity, x is the angular frequency All the RL values of r-GONRs are lower than that of
0
(x ¼ 2pf ), and s is the polarization relaxation time. e and e} can GONRs, demonstrating that EM absorption can be greatly
be described as enhanced by reduction. In addition, compared to the other carbon
absorbing materials (Table S2), the r-GONRs exhibit comparable or
es
e1 more advantageous EM absorption performance. Moreover, the RL
e0 ¼ e1 þ ð3Þ
1 þ x2 s2 values of these materials tend to increase with the increasing
reduction degree. This is ascribed to the enhanced dielectric
xsðes
e1 Þ loss (natural resonance, electron polarization relaxation and
e} ¼ ð4Þ
1 þ x2 s2 Debye dipolar relaxation), which was induced by the increased
0 defects and conductivity during reduction. Based on the above
Based on Eqs. (3) and (4), the relationship between e and e} can
analysis, it can be confirmed that the EM absorption of r-GONRs
be written as
can be effectively regulated by adjusting the reduction degree of
 es þ e1 2 e
e 2 r-GONRs.
0 s 1
e
þ ðe}Þ2 ¼ ð5Þ
2 2
0
Thus, the curve of e versus e} would be a single semicircle,
4. Conclusion
which is generally defined as the Cole-Cole semicircle, and each
semicircle corresponds to a Debye relaxation process. Fig. 4e-i
0 In conclusion, the graphene oxide nanoribbons were success-
show the e
e} curves of the r-GONRs/wax and GONRs/wax com-
fully unzipped using chemical method. The post reduction degree
posites over the 2–18 GHz frequency range. There are several semi-
by hydrazine hydrate has great effect on the chemical groups of
circles in each curve of the GONRs/wax and r-GONRs/wax
graphene oxide nanoribbons, which dramatically affects the elec-
composites, which demonstrates that the GONRs/wax and r-
tromagnetic absorption. As the reduction degree increases, the
GONRs/wax composites have multiple dielectric polarization
reflection loss becomes larger reflecting that electromagnetic
relaxation processes. At the same time, the r-GONRs-10:1/wax
absorption is stronger. In the optimized reduction condition, the
composites exhibit the most obvious dielectric polarization relax-
0
reflection loss is up to
65 dB. Moreover, the efficient absorption
ation behavior by contrasting thesee
e}curves. Consequently, bandwidth (reflection loss 
10 dB) reaches 7.06 GHz, showing
the dielectric loss of r-GONRs can be attributed to the natural res- more advantageous than the reported carbon materials. The strong
onance, electron polarization relaxation and Debye dipolar relax- absorption with broad bandwidth of optimized r-GONR is attribu-
ation. The reduction with hydrazine hydrate can adjust the ted to the excellent impedance matching and large dielectric loss.
defects and conductivity of r-GONRs, resulting in the regulation Our reduced graphene oxide nanoribbons are very promising to
of the dielectric loss. avoid electromagnetic pollution. Our unzipped carbon nanotube
To further investigate the EM absorption performance of the is very promising in the application of electromagnetic pollution
r-GONRs/wax composites, we calculated the reflection loss (RL) or radar detection.
values at various thicknesses from 2 to 18 GHz according to the
following relation based on the transmission line theory [4]:
  Acknowledgements
Z in
Z 0 
RLðdBÞ ¼ 20 log  ð6Þ
Z in þ Z 0 
This work was financially supported by the National Science
Fig. 5 shows the RL values of the GONRs/wax and r-GONRs/wax Fund for Distinguished Young Scholars (Grant No. 51625201);
(10 wt% in wax) composites with various thicknesses of 0.5–5 mm The National Key Research and Development Program of China
within the frequency range of 2–18 GHz. All the samples exhibit (Grant No. YFE0201600), National Key Laboratory Funds (Grant
typical quarter-wavelength attenuation, that is, with increasing No. 914C490106150C49001); The Fundamental Research Funds
thickness of the sample, the minimum reflection loss (RLm) moves for the Central Universities (Grant No. HIT. NSRIF. 2017002); The
to a lower frequency [50]. As shown in Fig. 5a and b, the GONRs/ Nanjing Institute of Technology (Grant No. YKJ201312).
 Y. Ding et al. / Journal of Colloid and Interface Science 552 (2019) 196–203 203

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