Synthesis, Characterization, and Electromagnetic Wave Absorption

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Synthesis, Characterization and Electromagnetic Wave Absorption Properties of Composites of Reduced Graphene Oxide with Porous LiFe5O8 Microspheres Ying Lin, Jingjing Dong, Hanwen Zong, Bo Wen, and Haibo Yang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b01307 • Publication Date (Web): 17 Jul 2018 Downloaded from http://pubs.acs.org on July 18, 2018

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ACS Sustainable Chemistry & Engineering

Synthesis, Characterization and Electromagnetic Wave Absorption Properties of Composites of Reduced Graphene Oxide with Porous LiFe5O8 Microspheres Ying Lin, Jingjing Dong, Hanwen Zong, Bo Wen, Haibo Yang  School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an, 710021, Weiyang District, Xi’an, China *Corresponding author, Email: [email protected]

*

Corresponding author. Tel: +86-29-86168688; Fax: +86-29-86168688; Email: [email protected]

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ABSTRACT: A novel three-dimensional composites of reduced graphene oxide sheets and porous LiFe5O8 microspheres was fabricated via a facile, green and highly tunable strategy, and its microstructure, composition and microwave absorbing performances of rGO/porous LiFe5O8 composite were characterized and investigated. The experimental results indicate that the porous LiFe5O8 microspheres are dispersed on the thin rGO sheets uniformly. Compared with the pure LiFe5O8 particles and porous LiFe5O8 microspheres, the as-prepared rGO/porous LiFe5O8 composites exhibit outstanding microwave absorbing performances including the efficient bandwidth and reflection loss. The rGO/porous LiFe5O8 composite (S-50) displays the maximum reflection loss of -53.4 dB at 12.2 GHz with a coating layer thickness of 2.2 mm, and a broad effective bandwidth of 3.5 GHz (from 10.4 GHz to 13.9 GHz). The outstanding microwave absorbing performances are assigned to employing magnetic micro-flowers with multi-interfaces to improve impedance matching, which is ascribed to strong relaxation loss, electrical loss, and magnetic loss. This further confirms that the rGO/porous LiFe5O8 composites could be potential candidates for lightweight microwave absorbing materials. KEYWORDS: Etching method, rGO/porous LiFe5O8 composites, Permittivity, Permeability, Electromagnetic wave absorption INTRODUCTION Recently, with the rapid advancement in communication technology, electromagnetic wave (EMW) pollution has become a serious problem, which is a threat to humans’ body and living system.1-4 Therefore, significant efforts have been devoted to the preparation of EMW absorbing materials in very diverse fields.5, 6 As an excellent EMW absorber, it should possess lightweight, small thickness, strong absorption characteristics, and wide absorption bandwidth.7-13 Compared with conventional EMW absorbing materials, reduced graphene oxide (rGO) has


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attracted much attention because of its high specific surface areas, residual defects and functional groups.14, 15 However, the high electrical conductivity of rGO displays weak microwave absorbing ability due to the poor impedance matching.16-18 One of the possible approach to solve the problem is to decorate rGO with magnetic materials or a semiconductor.19 Therefore, a great amount of efforts has been concentrated on the incorporation of rGO with magnetic constituents or a semiconductor to improve its EMW absorbing performances.20-25 Tian et al fabricated the rGO/α-Fe2O3 composite by a two-step method in a solution phase process. The composite exhibited a maximum reflection loss (RLmax) of -33.5 dB, and the absorption bandwidth was 6.4 GHz.26 NiFe2O4-rGO nanohybrids with absorption bandwidth of 4.2 GHz and RLmax of -50 dB reported by Ren et al.27 BiFeO3 nanowire-rGO nanocomposite with absorption bandwidth of 2.1 GHz and RLmax of -28.68 dB reported by Ghosh et al.28 It is found that the excellent EMW absorbing performances is attributed to impedance match and unique microstructure of EMW absorber. Over the previous decades, magnetic materials have been used as EMW absorbing materials in various forms.29 Lithium ferrites (LiFe5O8), as a typical magnetic material, with the merits of low cost, thermal stability, light weight,30,

31

and environmental benignity,32 has been used in many fields,

including microwave absorber,33 catalysis and photocatalysis,34 ferrite-core memory systems,35 and lithium battery.36-40 Up to now, there is few studies on rGO/porous LiFe5O8 composite for EMW absorber. Therefore, in order to further research the EMW absorbing performance of LiFe5O8, we prepared porous LiFe5O8 particles by a facile etching method, which anchored on rGO uniformly to form rGO/porous LiFe5O8 composite. And on the basis of our previous works,41 we utilized the complexing agent (methyl mercaptoacetate) and reducing agent (hydrazine) via a simultaneously etching method to



get a nanohybrid of numerous LiFe5O8 particles and GO nanosheets, forming the rGO/porous LiFe5O8 composite, as shown in Scheme 1. And the EMW absorbing performance of LiFe5O8 particles are significantly enhanced. The rGO/porous LiFe5O8 composite (S-50) with a small thickness of 2.2 mm showed an RLmax of -53.4 dB at 12.2 GHz and an effective absorption bandwidth of 3.5 GHz. The excellent EMW absorbing performance depend on the better impedance matching and the multiple interfacial polarizations of the rGO-LiFe5O8 composite. Thus, the rGO-LiFe5O8 composites are promising EMW absorbing materials. EXPERIMENTAL PROCEDURE Materials. GO was prepared by the improved Hummers method. 42 Lithium carbonate (Li2CO3), Iron oxide (Fe2O3), Sodium sulfate (Na2SO4), Lithium sulfate (Li2SO4), Methyl mercaptoacetate, DMF and Hydrazine (NH2NH2·H2O) were commercially purchased from Sinopharm Chemical Reagent, Co., Ltd (China). All the chemicals were of analytical grade. Ethanol and distilled water were used throughout the reactions. Synthesis of rGO/porous LiFe5O8 composites. LiFe5O8 particles were synthesized by molten salt method, as reported by our group previously. 41 The preparation process of rGO/porous LiFe5O8 composite is as follows: 0.1 g LiFe5O8 particles and a certain amount of freeze-dried GO were dissolved in DMF using ultrasonication for 60 min, and subsequently heated at 80 oC under the water-bath. Then 12.5 mL of hydrazine and 5 mL of methyl mercaptoacetate were added dropwisely while N2 protection keeping on. The chemical reactions were ended by cold ethanol after etching for 45 min. The obtained black powder was separated through centrifugation and washed by deionized water and ethanol. Subsequently the precipitation was freeze-dried for 12 h. The products of rGO/porous LiFe5O8 composites were named as S-20, S-50, and S-80 corresponding to adding different mass of GO


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nanosheets (20, 50, 80 mg). Materials characterization. The as-prepared samples were measured by X-ray diffraction (XRD, D/max-2200, Japan), raman spectra (Horiba Jobin Yvon, France), x-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250, USA), scanning electron microscope (SEM, Hitachi, S-4800, Japan), transmission electron microscope (TEM, JEOL-2010, Japan), energy dispersive X-ray analysis (EDX) and Brunner-Emmet-Teller (BET, ASAP 2020, Micromeritics). EMW absorption measurement. The EMW parameters of rGO/porous LiFe5O8 composites were tested on an vector network analyzer (VNA, HP8720ES, Agilent, USA) in the range of 2-18 GHz. The samples were made by mixing 70 wt% wax with rGO/porous LiFe5O8 composite uniformly and were pressed into cylindrical-shaped specimens (Φout = 7.00 mm and Φin = 3.04 mm). The EMW absorbing performance of rGO/porous LiFe5O8 composites can be evaluated by the reflection loss (RL), which is estimated by the following expression:43 𝑍𝑖𝑛 = 𝑍0

𝜇𝑟 𝜀𝑟

𝑡𝑎𝑛 𝑕 𝑗

RL 𝑑𝐵 = 20 𝑙𝑔

2𝜋 𝑐

𝜇𝑟 𝜀𝑟 𝑓𝑑

𝑍 𝑖𝑛 −𝑍 0 𝑍 𝑖𝑛 +𝑍 0

(1) (2)

Where Zin is the impedance of rGO/porous LiFe5O8 composites. Z0≈377 Ω is the impedance of air. μr and Ɛr are the relative complex permeability and permittivity of the absorber. f is the EMW frequency. d is the thickness of the absorber and c is the velocity of light. RESULTS AND DISCUSSION



Scheme 1 Scheme for the fabrication of rGO/porous LiFe5O8 composites by the etching process. Characterization of rGO/porous LiFe5O8 composites. The morphologies of the LiFe5O8 particles, the porous LiFe5O8 microspheres and the rGO/porous LiFe5O8 composite are examined by SEM and TEM, as shown in Figure 1. In Figure 1a, the LiFe5O8 particles possess a lumpy shape with a size of 0.2-0.7 μm. After etching, lithium and iron ions were gradually dissolved in the mixture of DMF, and then plentiful LiFe5O8 nanosheets re-crystallize and gather on the surfaces of the remains of bulk LiFe5O8 particles to form porous microspheres with the remains as cores. Consequently, the LiFe5O8 microspheres present a bigger average size. And the as-prepared porous LiFe5O8 microspheres exhibit a more regular shape (Figure 1b). In addition, the microstructure of porous LiFe 5O8 microspheres has been changed after the addition of GO. And Figure 1c, d display the SEM and TEM images of rGO/porous LiFe5O8 composite. It is clearly observed that porous LiFe5O8 microspheres composed of numerous nanorods are uniformly anchored on GO sheets.


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Figure 1 SEM images of (a) LiFe5O8 particles, (b) porous LiFe5O8 microspheres and (c) rGO/porous LiFe5O8 composite (S-50); (d) TEM image of rGO/porous LiFe5O8 composite (S-50). The XRD patterns of rGO, LiFe5O8 particles, porous LiFe5O8 microspheres and the resulting composites of rGO/porous LiFe5O8 composite (S-50) are presented in Figure 2a. For LiFe5O8 particles and porous LiFe5O8 microspheres, all the diffraction peaks can be assigned to the typical orthorhombic structure of LiFe5O8 (JCPDS No. 38-0259). Owing to the porous structure which involves abundant nano-sized fragments, the intensities of characteristic peaks of the porous LiFe5O8 microspheres display a visible decrease contrast with LiFe5O8 particles. In addition, no noticeable diffraction peaks for rGO are detected in the rGO/porous LiFe5O8 composite (S-50), which may be covered by the strong diffraction peaks of LiFe5O8 in the rGO/porous LiFe5O8 composite (S-50). The Raman spectra of GO, as-prepared LiFe5O8 particles, porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite (S-50) are given in Figure 2b. From the Raman spectrum of GO, the D (~1352 cm-1) and G (~1588 cm-1) bands appear in GO and come from local defects and vibrations of



ordered sp2 carbon atoms, respectively.44 The six prominent peaks at 197, 280, 350, 480, 703 and 1344 cm-1 can be observed in the Raman spectrum of LiFe5O8 particles. The peak positions of porous LiFe5O8 microspheres are still unchanged but the intensities display a decreasing trend, corresponding to the above XRD result. The spectrum of rGO/porous LiFe 5O8 composite (S-50) shows that the D and G bands of GO also exist, indicating that the coexistence of LiFe5O8 phase and GO phase in the composite. The intensity ratio of ID/IG of rGO/porous LiFe5O8 composite is 1.06, and is higher than 0.89 of GO, revealing that the degree of defects has been increased in the rGO/porous LiFe 5O8 composites45 and GO has been reduced into rGO in the composites during the etching course. The N2 adsorption/desorption isotherms and BJH pore-size distribution plots of the fabricated specimens are displayed in Figure 2c and Figure 2d. The surface area, pore volume and pore size calculated by using the BET equation are shown in Table S1. As shown in Figure 2c, the isotherm of the as-prepared samples displays a typical IV isotherm, demonstrating the presence of pores. The surface areas were 0.41, 44.06 and 59.67 m2 g-1 for LiFe5O8 particles, porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite, respectively. The pore size distributions exhibited in Figure 2d shows that the rGO/porous LiFe5O8 composite has macropores with a pore size distribution of about 14-107 nm, which is wider than those of LiFe5O8 particles and porous LiFe5O8 microspheres.


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Figure 2 (a) XRD patterns of rGO, LiFe 5O8 particles, porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite (S-50); (b) Raman spectra of GO, LiFe5O8 particles, porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite (S-50); (c) N2 adsorption-desorption isotherms and (d) pore size distribution of the prepared LiFe5O8 particles, porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite (S-50). The surface elemental composition and chemical valence state of elements in LiFe 5O8 particles and porous LiFe5O8 microspheres was further investigated by XPS (Figure S1). In Figure S1a, it is obvious that the elements of Li, Fe, and O are detected in the survey of the XPS spectra. As shown in Figure S1b, by comparison with LiFe 5O8 particles, Li 1s peaks of porous LiFe5O8 microspheres slightly move to much higher binding energy because of the presence of surface defects.46 And as shown in Figure S1c, the peaks at 710.6 eV (Fe 2p3/2) and 724.6 eV (Fe 2p1/2) corresponding to the ferric(III) in the unetched LiFe5O8 particles, migrate to the location of the ferric(II) for the porous LiFe 5O8



microspheres.47, 48 For Figure S1d, the O 1s correspond to three peaks. Two peaks at 530.1 and 531.7 eV are well matched with oxygen vacancy and ordered lattice oxygen ions in the LiFe 5O8, and the other at 533.4 eV is referred to the hydroxyl of the absorbed H 2O on the surfaces of the LiFe5O8 samples.49 After etching, the peak intensity of lattice oxygen ions is enhanced. All of the above results clearly reveal that the certain Fe3+ of LiFe5O8 particles are changed to the Fe2+ through the hydrazine reduction. In addition, the C 1s spectra of the porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite (S-50) are shown in Figure 3 in order to elucidate their surface compositions. In Figure 3a-b, the three peaks centered at 284.6, 285.7 and 288.6 eV are assigned to C-C/C＝C, C-O, and O-C＝O respectively, suggesting the reduction of GO to rGO in the as-prepared composites after etching treatment.50

Figure 3 C 1s spectra of (a) porous LiFe5O8 microspheres and (b) rGO/porous LiFe5O8 composite (S-50). The X-ray diffraction patterns of rGO/porous LiFe5O8 composites with various rGO contents are presented in Figure 4. It is clear that all the diffraction peaks can be assigned to the orthorhombic structure of LiFe5O8 phase (JCPDS No. 17-0115). Notably, no diffraction peak of rGO is obviously observed in the XRD patterns of composites, which maybe covered by the strong diffraction peaks of LiFe5O8 in rGO/porous LiFe5O8 composites. In addition, no other characteristic peaks of impurities can be seen, which confirms the high purity of the rGO/porous LiFe5O8 composites.


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Figure 4 XRD patterns of rGO/porous LiFe5O8 composite with different rGO contents. The morphology and EDS mapping of the rGO/porous LiFe 5O8 composite (S-50) are presented in Figure 5. As shown in Figure 5a, b, the porous LiFe5O8 microspheres with the average diameter of about 0.5-1 μm are anchored on the multi-graphene sheets. From the magnified SEM image of rGO/porous LiFe5O8 composite (Figure 5c), it can be found that the LiFe5O8 nanorods are successfully synthesized with a average length of 200-500 nm. In order to detect the distribution of porous LiFe 5O8 microspheres on the graphene sheets, the EDS mapping analysis of the rGO/porous LiFe 5O8 composite is employed, as shown in Figure 5e. It can be found that the three elements of C, O and Fe can be observed in rGO/porous LiFe5O8 composite, implying the presence of the rGO and LiFe5O8.



Figure 5 (a-d) SEM images with different magnifications, (e) EDS mapping of C, O, and Fe elements of rGO/porous LiFe5O8 composite (S-50) and Cu element of copper foil substrate (the scale bar of (e) is 1 μm). EMW absorbing performances of rGO/porous LiFe5O8 composites. The real (ε′) and imaginary (ε″) parts of the complex permittivity, the real (μ′) and imaginary (μ″) parts of the permeability and RL values of the LiFe5O8 particles and porous LiFe5O8 microspheres are shown in Figure S2. It is obviously found that the ε′ and ε″ of porous LiFe5O8 microspheres are significantly higher than those of LiFe5O8 particles, demonstrating that the porous LiFe5O8 microspheres possess higher dielectric loss compared with LiFe5O8 particles. It could be attributed to the presence of many vacancies in porous LiFe5O8 microspheres, which causes multiple reflections, dipole polarizations and interfacial polarizations produced by the formation of defects.51, 52 The µ′ and µ″ of LiFe5O8 particles and porous LiFe5O8 microspheres are relatively stable with increasing the frequency. The RL values of LiFe5O8 particles and porous LiFe5O8 microspheres over 2-18 GHz with various thicknesses can be obtained using Equation (1) and (2). The LiFe5O8 particles display a RLmax value of -8.4 dB at the thickness of 2.5 mm, while the RLmax value of porous LiFe5O8 microspheres with a thickness of 2 mm


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can reach -15.2 dB at 11.4 GHz. Figures 6 shows the electromagnetic parameters of rGO/porous LiFe5O8 composites with different mass ratios of rGO. In Figure 6a, b, the value of ε′ and ε″ tend to decrease with increasing the frequency, except a slight rising at ~15 GHz for S-50 and S-80. And with increasing the content of rGO, both ε′ and ε″ are enhanced owing to the high electrical conductivity of rGO. Generally, ε′ stands for the polarizability of a material and ε″ is on behalf of the dielectric loss, which is correlated with the electrical conductivity of a material.53 According to Debye theory, these results suggest that the rGO/porous LiFe5O8 composites possess the multiple polarizations including interfacial and dipole polarizations that result from the complicated porous structure of LiFe5O8 with many interfaces between the two media and unsaturated coordination bonds, along with the residual defects and groups of rGO surface (Figure 7).54 The ε’-ε” curves of the rGO/porous LiFe5O8 composites in Figure 8 show several semicircles, demonstrating that several Debye relaxation processes exist.55 In Figure 8a, c, three small semicircles are discovered for S-20 and S-80. However, for S-50 three small semicircles and a large semicircle can be discovered (Figure 8b), demonstrating the existence of four dielectric relaxation processes for S-50. It demonstrates that the interfaces of LiFe5O8-rGO would cause dielectric loss.56 In addition, the defects and groups in rGO also cause self-doping, which brings extra relaxation processes. 57 Figure 6c-d show the complex permeability of rGO/porous LiFe 5O8 composites. As for the values of μ′, it presents a slow rise in the range of 2 to 14 GHz, then an abrupt decrease occurs from 14 to 18 GHz, except S-20. In addition, the μ″ of rGO/porous LiFe5O8 composites show the same tendency as that of μ′ in the 2-14.5 GHz range. And the µ″ of S-50 displays a broad peak at 13.7-16.8 GHz. It can be concluded that LiFe5O8 has relatively poor dielectric properties and brilliant hysteresis performance,



which is related to the magnetic properties of absorber. Meanwhile, the rGO composites have better dielectric properties than the pure nanocrystals. We can conclude that the improved EMW absorbing performance of the rGO composites may be attributed to the efficient complementarities between the excellent electrical properties of rGO nanosheets and special magnetic properties of LiFe5O8.58

Figure 6 Frequency dependence of (a) real part, (b) imaginary part of complex permittivity and (c) real part, (d) imaginary part of complex permeability for rGO/porous LiFe5O8 composite with different mass ratios of rGO.


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Figure 7 Schematic illustration of EMW absorption mechanism for rGO/porous LiFe5O8 composite.

Figure 8 (a-c) Typical Cole-Cole semicircles of the rGO/porous LiFe5O8 composites (S-20, S-50 and S-80). Figure 9 presents the calculated RL curves of the samples with various thicknesses over 2-18 GHz. In the investigated region, S-50 displays obviously superior absorption performance compared with S-20 and S-80. The RLmax of S-20 reaches 45.2 dB at an optimal sample thickness of 2.1 mm and the bandwidth of RL≤10 dB is 3.4 GHz (from 14.6 GHz to 18 GHz)(Figure 9a). When increasing the loading mass of GO to 50 mg, the RLmax of S-50 is superior to that of S-20 and reaches -53.4 dB at 12.2 GHz with the thickness of 2.2 mm, and the bandwidth of RL values below -10 dB is as well as 3.5 GHz located over 10.4-13.9 GHz (Figure 9b). As the GO content increases to 80 mg, the RLmax values are reduced (Figure 9c), demonstrating that high conductance does influence the impedance match and



lead to poor microwave absorbing performance.59,

60

It is clear that the appropriate rGO mass is

beneficial to the improvement of EMW absorption. The thickness (tm) of absorber and frequency (fm) meet the equation: 𝑡m = 𝑛𝑐 (4𝑓m

𝜇r Ɛr ) (n=1, 3, 5, …).61 The curves of the tm versus fm of

rGO/porous LiFe5O8 composites are shown in Figure 9d-f, respectively. Obviously, the RLmax frequencies fit well with the λ/4 matching model of all the samples. The three-dimensional representations of RLs of the rGO/porous LiFe5O8 composites at different thicknesses (1.6-3 mm) in the frequency range of 2-18 GHz are displayed in the Figure 10. This suggests that the EMW absorbing performance of the rGO/porous LiFe5O8 composites at various frequencies can be modulated by adjusting the thickness of absorber.

Figure 9 (a-c) Dependence of reflection loss (RL) of rGO/porous LiFe5O8 composites with different rGO contents (S-20, S-50 and S-80); (d-f) RL curves dependence of matching thickness (t m) on matching frequency of rGO/porous LiFe 5O8 composites at the wavelengths of λ/4, 3λ/4, and 5λ/4.


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Figure 10 (a-c) Three-dimensional presentations of the reflection loss of rGO/porous LiFe 5O8 composites with different rGO contents (S-20, S-50 and S-80).



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Impedance matching is an important factor in determining the EMW absorbing performance of rGO/porous LiFe5O8 composites. According to Equation (2), the RLmax can be obtained when imaginary input impedance approaches zero while the corresponding real input impedance equals to 377 Ω. Figure 11 diaplays the complex impedance of rGO/porous LiFe5O8 composites at the layer thickness of 2.4 mm. It can be seen that S-50 has the best impedance match. Z″in for S-50 is -475 Ω with the corresponding Z′in of 413 Ω at 14.4 GHz.

Figure 11 Complex impedance of the composites: (a) imaginary impedance and (b) real impedance. EMW absorbing performances of rGO/porous LiFe5O8 hybrid absorber and other rGO-based materials are displayed in Table S2. Compared with most of them,55,

58, 62-69

rGO/porous LiFe5O8

composite (S-50) exhibits prominent performance at a thin thickness, which meet the requirement of high efficient and light weight. It is more intuitive to observe from the Figure 11. Thus, the rGO/porous LiFe5O8 composites can be potentially used as a high-efficient and tunable microwave absorbers.


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Figure 12 Reflection loss versus bandwidth for the typical EMW absorbing materials reported in recent literatures. CONCLUSIONS In summary, a new-type rGO/porous LiFe5O8 composites with a strikingly enhanced EMW absorbing performances have been successfully synthesized by a facile etching approach. Structure, morphology and EMW absorbing performances of the samples were investigated in detail. And the rGO/porous LiFe5O8 composite (S-50) has an outstanding EMW absorbing performances due to the combination of the advantages of LiFe5O8 nanoparticles (magnetic materials) and grapheme (dielectric materials), resulting in strong relaxation loss, electrical loss, and magnetic loss. The RLmax reaches -53.4 dB at 12.2 GHz and the effective absorption bandwidth is 3.5 GHz with the sample thickness of only 2.2 mm. It can be concluded that the rGO/porous LiFe5O8 composites are advantageous candidate materials for EMW absorption for electromagnetic interference shielding application. Supporting Information XPS spectra of LiFe5O8 particles and porous LiFe5O8 microspheres; frequency dependence of



relative complex permittivity and permeability for LiFe5O8 particles and porous LiFe5O8 microspheres; reflection loss curves for the LiFe5O8 particles and porous LiFe5O8 microspheres; porous characteristics of LiFe5O8 particles, porous LiFe5O8 microspheres and rGO/porous LiFe5O8 composite (S-30); the microwave absorption performance of rGO-based composites in recent literatures. ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (Grant No. 51772177), the Science Fund for Distinguished Young Scholars of Shaanxi Province (Grant No. 2018JC-029), the Shaanxi Science & Technology Co-ordination & Innovation Project of China (2017TSCXL-GY-08-05) and the Industrialization Foundation of Education Department of Shaanxi Provincial Government (Grant No. 16JF002). REFERENCES (1) Jian, X.; Wu, B.; Wei, Y.; Dou, S. X.; Wang, X.; He, W.; Mahmood, N. Facile synthesis of Fe3O4/GCs composites and their enhanced microwave absorption properties. ACS Appl. Mater. Inter. 2016, 8 (9), 6101-6109, DOI 10.1021/acsami.6b00388. (2) He, J. Z.; Wang, X. X.; Zhang, Y. L.; Cao, M. S. Small magnetic nanoparticles decorating reduced graphene oxides to tune the electromagnetic attenuation capacity. J. Mater. Chem. C 2016, 4 (29), 7130-7140, DOI 10.1039/c6tc02020h. (3) Liu, P.; Yao, Z.; Zhou, J.; Yang, Z.; Kong, L. B. Small magnetic Co-doped NiZn ferrite/graphene nanocomposites and their dual-region microwave absorption performance. J. Mater. Chem. C 2016, 4 (41), 9738-9749, DOI 10.1039/c6tc03518c. (4) Yang, Z.; Wan, Y.; Xiong, G.; Li, D.; Li, Q.; Ma, C.; Guo, R.; Luo, H. Facile synthesis of ZnFe2O4/reduced graphene oxide nanohybrids for enhanced microwave absorption properties. Mater.


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For Table of Contents Only

In this work, a new-type rGO/porous LiFe5O8 composites with a strikingly enhanced EMW absorption properties has been successfully synthesized by a facile etching method. The rGO/porous LiFe5O8 composite (S-50) exhibits the minimum reflection loss of -53.4 dB at 12.2 GHz with a thickness of only 2.2 mm, and its effective absorption bandwidth less than -10 dB is 3.5 GHz (from 10.4 GHz to 13.9 GHz).


Synthesis, Characterization, and Electromagnetic Wave Absorption

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