Synthesis of reduced graphene oxide - Mn₀.₈Zn₀.₂Fe₂O₄ - porous polyaniline nanocomposite materials for effective microwave absorption in X-band

 Journal of Science and Technique - N.211 (12-2020) - Le Quy Don Technical University 
SYNTHESIS OF REDUCED GRAPHENE OXIDE - Mn0.8Zn0.2Fe2O4 - 
 POROUS POLYANILINE NANOCOMPOSITE MATERIALS FOR 
 EFFECTIVE MICROWAVE ABSORPTION IN X-BAND 
Nguyen Vu Tung*, Tran Quang Dat, Nguyen Tran Ha, Nguyen Thanh Nam, Do Quoc Hung 
 Le Quy Don Technical University, Hanoi, Vietnam 
 Abstract 
 In this paper, a composite of reduced graphene oxide (RGO), manganese/zinc ferrite 
 (Mn0.8Zn0.2Fe2O4 - MZF) nanoparticles, and porous polyaniline (PANI) was successfully 
 synthesized to improve microwave absorption properties exclusively in X-band. The 
 experimental results demonstrate that the synthesized ternary composite had RGO 
 nanosheets decorated mostly with MZF nanoparticles, and porous PANI was uniformly 
 coated onto the surface of RGO-MZF. The strong reflection loss value of -60.4 dB at 
 10 GHz and wide effective bandwidth are effectively achieved with the sample which had 
 thicknesses of 2 mm and contained 33 weight % of product. The marked display of 
 the microwave absorption properties of this composite was associated with their 
 notable structure. 
 Keywords: Ferrite; graphene; polyaniline; absorber. 
1. Introduction 
 Recent years have witnessed significant development of microwave absorption 
materials (MAMS) because of the growing exploitation of electronics and 
communication in industry, commerce, and military. A hot research topic in the MAMS 
field is the design of efficient microwave absorber with thin thickness, lightweight, 
strong and wide band absorption and antioxidant properties [1]. The loss mechanism of 
the microwave absorber is primarily due to magnetic loss and dielectric loss. Largely, 
conventional microwave absorbing materials with a single loss (magnetic or dielectric 
loss) are unable to fulfill the specific application requirements [2]. Hence, the multiple-
component composites with multiple loss mechanism have been recently investigated 
for enhanced microwave absorption. The microwave absorption properties of 
magnetic/dielectric composites can be further improved by modifying the 
electromagnetic parameters, impedance matching, and microstructure with high 
interface and surface properties [2, 3, 4, 5, 6]. 
 Reduced graphene oxide (RGO), a thin and lightweight material with special 
surface properties, unique two-dimensional layers, and high dielectric, might probably 
* Email: tungnv1976@lqdtu.edu.vn 
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Journal of Science and Technique - N.211 (12-2020) - Le Quy Don Technical University 
be one of the best microwave absorbers [3]. However, RGO has weak magnetic loss 
property and high conductivity, therefore exhibiting limited microwave absorption 
performance [7]. The microwave absorption properties of RGO can be enhanced by 
incorporating magnetic ferrite nanoparticles onto the surface of RGO nanosheets as 
demonstrated in [3]. Among the popular magnetic ferrite, manganese/zinc ferrite spinel 
materials have been explored as microwave absorbent due to their high permeability, 
adequate mechanical, and low dielectric loss [8, 9]. Recently, polyaniline (PANI) has 
emerged as one of the most promising materials for microwave absorption applications. 
Compared to other microwave absorbers, PANI embodies several notable features, 
including unique electromagnetic parameters in ultrahigh radio-frequencies, low 
density, processability, complete resistance to corrosion, and excellent environmental 
stability. Indeed, PANI has been widely considered as a promising alternative to 
traditional MAMS for enhanced microwave absorption [10]. 
 In our previous reports, RGO - copper/nickel ferrite - PANI composites have been 
prepared and tested for microwave absorption enhancement [11]. In this work, ternary 
composites composed of RGO, manganese/zinc ferrite (Mn0.8Zn0.2Fe2O4 - MZF) and 
porous PANI are developed. The porous structure of PANI in the ternary composites is 
envisaged to offer new energy dissipation mechanisms, thus leading to significant 
enhancement in the microwave absorption performance of the ternary composites. 
2. Experimental 
2.1. Synthesis of the composite 
 All chemicals used in this work are analytical grade. Solutions were prepared with 
deionized water (DI). RGO was synthesized from graphite powder using the modified 
Hummers method [11, 12, 13]. The RGO/MZF composite was synthesized by 
coprecipitation combined with hydrothermal treatment. Firstly, a mixture of 60 mL of 
ethylene glycol, 40 mL of DI water, 4.0 mmol of Fe(NO3)3, 1.6 mmol of MnCl2, and 
0.4 mmol of Zn(NO3)2 was prepared (i.e. with agitation at room temperature for 1 h). 
Then, RGO powder was slowly added to the mixture following with another 1 h of 
agitation. Subsequently, 4 mL of NH3 solution (25%) was dropped into the mixture. The 
coprecipitation reaction occurred in 4 h under continuous agitation. The suspension after 
the coprecip ... RGO. In Fig. 3b, the peak at 539 cm-1 could be 
recognized to the vibration of Fe-O bond. Besides, the peak at 1639 and 1430 cm-1 
corresponds to the C=C stretching vibration and O-H deformation. In Fig. 3c, the 
vibration of Fe-O bond is found at 575 cm-1. The peaks at 798 and 1045 cm-1 are 
associated with the stretching vibration mode of C-H bond and C-O bond, respectively. 
The vibrations of C-N bonds located at 1242 and 1296 cm-1. The peaks at 1496 and 
1590 cm-1 could be attributed to the vibration of C=C stretching of benzenoid and 
quinonoid rings [11, 13]. The XRD pattern and FTIR spectra demonstrate that RGO, 
MZF, and PANI exist in this composite. 
 The RGO/MZF/PANI magnetic hysteresis loop at room temperature is shown in 
Fig. 4. The hysteresis loop of composite displays that the remanence and coercive force 
are near zero. This result indicated that obtained composite was typically 
superparamagnetic-like. The maximum value of magnetizatio n of RGO/MZF/PANI 
composite is about 48 emu/g. The high saturation magnetization implies that the 
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Journal of Science and Technique - N.211 (12-2020) - Le Quy Don Technical University 
composite has the natural resonance loss and the eddy current loss which is responsible 
for increasing the magnetic loss [14]. 
 60
 40
 20
 0
 4
 2
 (emu/g) M -20 0
 -2
 M (emu/g) M
 -40 -4
 -40 -20 0 20 40
 H (Oe)
 -60
 -10000 -5000 0 5000 10000
 H (Oe)
 Fig. 4. Room temperature magnetic hysteresis loops of RGO/MZF/PANI. 
3.2. Microwave absorption properties of composites 
 The microwave absorption properties of absorbers are related closely with the real 
and imaginary parts of complex permittivity and complex permeability. Fig. 5 shows 
these frequency-dependent values of the sample with thickness of 2.0 mm. 
 It can be seen from this figure, the values of both the real part (µ’) and imaginary 
part (µ”) of relative complex permeability remain almost constant with slight variations. 
The gradual decrease of the real part (’) and imaginary part (”) of relative complex 
permitivity in 8-12 GHz band is observed. The high values of ’ is certified to the 
improvement of dipolar polarization and interfacial polarization. Furthermore, the high 
” value is correlated to the low resistivity which related to the efficient electronic 
transmission performance in the composite [15]. 
 16 1.2
 e' e'' m' m'' tande
 tand
 1.0 m
 12
 0.8
 8
 0.6
 0.4
 4
 0.2
 Permitivity,permeability 0
 0.0
 8 9 10 11 12 tangent loss Electromagetic 8 9 10 11 12
 Frequency (GHz) f (GHz) 
Fig. 5. The real, imaginary part of complex Fig. 6. The dielectric and magnetic loss 
 permittivity and complex permeability of tangent of RGO/MZF/PANI. 
 RGO/MZF/PANI. 
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 Journal of Science and Technique - N.211 (12-2020) - Le Quy Don Technical University 
 Generally, the dielectric loss (tan e = ’’/’) and magnetic loss (tan m = µ’’/µ’) 
are the major energy attenuation in microwave absorbers. The magnetic loss tangent and 
dielectric loss tangent were calculated and presented in Fig. 6. Here, the value of tan e 
is larger than that of tan m in the whole frequency range, which indicates that the 
dielectric loss has the significant contribution to electromagnetic loss of the composite. 
 It is known that the heterogeneous interfaces among RGO, porous PANI and MZF 
ferrite could create more polarization centers under the external electromagnetic field, 
which would increase interfacial polarization and improve related relaxation. According 
to Debye theory [11], one relaxation process can express as following equation: 
 2 2
 s  2  s  
 '  '' (3) 
 2 2 
where s,  are the static permittivity and the relative permittivity at the high-frequency limit. 
 10 0.010
 9 0.005
 0
 C
 ''
 e
 8 0.000
 7 -0.005
 9 10 11 12 13 8 9 10 11 12
 e' f (GHz) 
 Fig. 7. The typical Cole-semicircle curve Fig. 8. The C0 - f values of RGO/MZF/PANI. 
 of RGO/MZF/PANI. 
 The curve of ε’’ versus ε’ is called the Cole-Cole semicircle. In Fig. 7, multiple 
distinct semicircles can be observed, which indicates that the multi-dielectric relaxation 
process occurs in the RGO/MZF/PANI composite. Furthermore, the distorted Cole-Cole 
semicircles could be related to other factors, such as the electron polarization, Maxwell-
Wagner relaxation and dipole polarization, which will also generate other mechanisms 
to enhance the dielectric loss [2]. 
 The magnetic loss due to eddy currents can be estimated by the coefficient C0 
 2
defined as C0 = ’’/(’ .f), where f is frequency. It can be seen from Fig. 8, the value of 
C0 changes slightly with frequency. This result suggests that the magnetic loss of the 
composite is mainly caused by the eddy current effect in X-band. 
 To study the physical mechanism of the microwave absorption, the impedance 
 1/2
matching ratio is conducted. It is defined as  = (µr/r) . The best impedance matching 
ratio is equal to 1. From Fig. 9, the value of  cannot reach 1 and its maximum is 0.324 
at 10 GHz in X-band. 
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Journal of Science and Technique - N.211 (12-2020) - Le Quy Don Technical University 
 Fig. 10 displays the microwave reflection loss (RL) as function of frequency for 
the RGO/MZF/PANI samples with thicknesses of 1.5, 2.0, 2.5 and 3.0 mm, 
respectively. It can be seen from this figure that the effective absorption bandwidth of 
these samples covered wholly the X-band. In addition, as the thickness of the sample 
increases, the shift of the absorption peaks which move towards the lower frequency, 
will be also observed. The best minimum RL is -60.4 dB at a frequency of 10 GHz. 
 0.4
 0
 -10
 (dB) 
 -20
 -30
 0.3 
 -40
 -50 d = 1.5 mm
 d = 2.0 mm
 Reflection Loss Reflection -60 d = 2.5 mm
 Impedance matching ratio d = 3.0 mm
 0.2 -70
 8 9 10 11 12 8 9 10 11 12
 f (GHz) 
 f (GHz) 
 Fig. 9. The impedance matching ratio of Fig. 10. Reflection loss of RGO/MZF/PANI. 
 RGO/MZF/PANI. 
 Table 1 presents the comparison of microwave absorption properties of 
RGO/MZF/PANI composite with other reported binary and ternary ferrite-based 
composites. You et al. [9] synthesized MnZn particles which had the absorption 
bandwidth of 3.5 GHz with the best RL value of -18 dB (in X-band). Shen et al. [3] 
prepared RGO/Co0.8Fe2.2O4 composite and reported that the RL could reach -33 dB with 
the sample 2.5 mm. The ternary composite RGO/CoFe2O4/MWCNT reported by Zhang 
et al. [19] had the minimum RL at 11.6 GHz of -46.8 dB and narrow absorption 
bandwidth of 1.9 GHz. The RGO/CNF/PANI composite [11] had the optimal RL value 
can reach -40.7 dB at 9.8 GHz with a thickness of 3 mm and the effective wideband in 
X-band. By comparing these results, the RGO/MZF/PANI composite exhibits excellent 
microwave absorption performance with high reflection loss, wide effective absorption 
bandwidth and thin thickness. 
 The excellent microwave absorption performance of the RGO/MZF/PANI 
composite is associated to its structure original and composition. RGO and PANI are 
well known as impressive dielectric loss materials [11]. Second, the MZF nanoparticles 
in composite are combined to RGO and PANI to form substantial interfaces, centers 
polarization [3, 10]. Third, the 2-D structure of RGO can lead to other mechanisms of 
energy dissipation, such as multiple reflection plane, the oscillations of magnetic 
nanoparticles in electromagnetic field and the electron hopping in the conductive 
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 Journal of Science and Technique - N.211 (12-2020) - Le Quy Don Technical University 
network [7, 19]. In addition, the porous structure of PANI nano fiber is also attributed to 
the improvement of the microwave attenuation due to the large specific area and 3-D 
network structure. 
 Tab. 1. Comparison of the microwave absorption properties with other absorbers. 
 RLmin Bandwidth Thickness 
 Absorber Ref. 
 (dB@frequency) in X-band (GHz) (mm) 
 RGO/SmFe5O12/CoFe2O4 -63.3 @ 11.1 GHz 3.0 3.0 [2] 
 RGO/Co0.8Fe2.2O4 -33 @ 9.0 GHz 4.0 2.5 [3] 
 CoFe2O4/MoS2 -35 @ 9.0 GHz 2.3 2.5 [4] 
 BaSmCoFe/Co/Carbon -28 @ 10.2 GHz 2.8 2.0 [4] 
 RGO/CoFe2O4/PVP -25 @ 9.0 GHz 3.5 3.0 [6] 
 -Fe2O3 NR/PNG -35 @ 10.0 GHz 2.3 2.0 [7] 
 MnZn ferrite -18 @ 9.5 GHz 3.5 2.4 [9] 
 MnZnNi ferrite/PANI -39 @ 9.25 GHz 2.8 3.5 [10] 
 RGO/CNF/PANI -40.7 @ 9.8 GHz 4.0 3.0 [11] 
 3D Ni0.33Co0.67Fe2O4@RGO -47.5 @ 9.0 GHz 3.0 3.0 [14] 
 FeO/ZnO -26 @ 10.5 GHz 3.0 2.0 [16] 
 Mn-Zn-Cu ferrite/PVDF thin film -33.5 @ 11.5 GHz 4.0 - [17] 
 CIP@SiO2@Mn0.6Zn0.4Fe2O4 -44.24 @ 11.57 GHz 3.0 2.0 [18] 
 RGO/CoFe2O4/MWCNT -46.8 @ 11.6 GHz 1.9 1.6 [19] 
 PANI/ZnO/CoFe2O4 -41.9 @ 10.3 GHz 3.3 3.0 [20] 
 This 
 RGO/MZF/porous PANI -60.4 @10.0 GHz 4.0 2.0 
 work 
4. Conclusion 
 In this work, the reduced graphene oxide-manganese/zinc ferrite-porous 
polyaniline composites have been successfully synthesized by a three-step method. The 
structural and morphology analyses (e.g. SEM, XRD, FTIR, and VSM technique) 
demonstrated that fine synthesized RGO and MZF particles and porous PANI were 
uniformly distributed. Moreover, the synthesized composites exhibited strong 
absorption and a wide absorption bandwidth. The minimum RL value was -60.4 dB at 
10 GHz with a thickness of 2.0 mm and the effective absorption bandwidth wholly 
covered the X-band. Therefore, the nanocomposite of RGO/MZF/PANI would be 
highly suitable for the promising microwave absorbers. 
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 CHẾ TẠO VẬT LIỆU NANOCOMPOSITE RGO - Mn0.8Zn0.2Fe2O4 - 
 POLYANILIN XỐP HẤP THỤ HIỆU QUẢ VI SÓNG BĂNG TẦN X 
 Tóm tắt: Trong bài báo này, composite bao gồm reduced graphene oxide (RGO), hạt 
nano mangan/kẽm ferrite (Mn0.8Zn0.2Fe2O4 - MZF) và polyanilin xốp (PANI) đã được tổng hợp 
nhằm cải thiện các đặc tính hấp thụ vi sóng trong dải băng X. Kết quả cho thấy các tấm nano 
RGO đã được phủ bởi các hạt nano MZF và các sợi PANI được phủ đồng đều lên trên bề mặt 
của cấu trúc RGO-MZF. Giá trị tổn hao phản xạ đạt được là -60,4 dB tại tần số 10 GHz và dải 
băng hấp thụ rộng ứng với mẫu có bề dày 2 mm và chứa 33% khối lượng của composite. 
Các đặc tính cải thiện về khả năng hấp thụ sóng có tương quan với thành phần, cấu trúc của vật 
liệu composite. 
 Từ khóa: Ferrite; graphene; polyanilin; vật liệu hấp thụ. 
 Received: 04/6/2020; Revised: 20/11/2020; Accepted for publication: 26/11/2020 
  
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