Preparation of Graphene Aerogel with High Mechanical Stability and

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The preparation of graphene aerogel with high mechanical stability and microwave absorption ability via combining surface support of metallic-CNTs and interfacial cross-linking by magnetic nanoparticles Yan Qin, Yan Zhang, Na Qi, Qiaozhi Wang, Xuejie Zhang, and Ying Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b22382 • Publication Date (Web): 19 Feb 2019 Downloaded from http://pubs.acs.org on February 20, 2019

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ACS Applied Materials & Interfaces

The preparation of graphene aerogel with high mechanical stability and microwave absorption ability via combining surface support of metallic-CNTs and interfacial cross-linking by magnetic nanoparticles

Yan Qin, Yan Zhang, Na Qi, Qiaozhi Wang, Xuejie Zhang, Ying Li* Key Lab. of Colloid and Interface Chemistry of State Education Ministry, Shandong University, Jinan 250100, China

Corresponding author: Ying Li Tel: +86-531-88362078 Fax: +86-531-88364464 Email: [email protected]

Keyword: graphene aerogel; metallic-oxide nanoparticles; surface support; interfacial cross-linking; mechanical stability; microwave absorption.

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Abstract

The preparation of graphene aerogel by hydrothermal reduction or chemical reduction has been one of the hot topics of research. But in the process of assembly, the random weak connection of GO flakes will lead to irreversible deformation under compression, the mechanical stability of aerogel based on graphene is one of its drawbacks hard to overcome. Here, a novel method to prepare graphene aerogel with high mechanical stability was proposed via combining surface support brought by metallic-CNTs network and interfacial cross-linking of GO sheets achieved by nanoparticle selective absorption. Thoroughly dispersed metallic-CNTs absorbed on the basal plane of GO flakes formed a continuous network structures, which not only improve the mechanical performance of flakes, but also provide steric effect to impel the adsorption of metallic oxide magnetic nanoparticles concentrated on the edge of GO flakes, thereby the interfacial connection of adjacent rGO flakes by nanoparticles cross-linking was guaranteed. Meanwhile, the surface and interface reinforce approach can greatly improve the electrical conductivity and mechanical stability of composites. Owing to the light-weight, abundant interface, high electrical conductivity, combining with the superparamagnetic properties brought by the magnetic nanoparticles, composite aerogel with high mechanical stability and excellent microwave absorption was achieved, of which the effective absorption bandwidth of the aerogel is 4.4-18 GHz, and the maximum value can reach -49 dB. This approach not only could be used to prepare microwave absorption materials with light weight and high performance, but also be meaningful to enlarge the construction and application of carbon-based materials.

1. Introduction

Aerogel, as the lightest solid materials in the world, has attracted wildly attention owing to the three-dimensional network structures, high porosity and the lower density.1-3 As one of the most important component of carbon-based materials, graphene has good thermal conductivity, large


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specific surface area and high electron mobility,4-6 which has been widely used to prepare three-dimensional aerogel by various preparation methods, such as electrochemical synthesis, chemical vapor deposition, hydrothermal or solvothermal reduction, chemical reduction.7-10 The graphene aerogel have high specific surface area, high porosity, good electrical and thermal conductivity, which can be used widely in many fields, including energy storage, environmental protection, supercapacitors, sensors and microwave absorption.11-13 Among the above mentioned preparation methods, self-assembly via chemical or hydrothermal reduction were often used.14-15 However, the assembly process relies on the random weak connection between GO flakes. The prepared graphene aerogel (GA) is too brittle to bear the relative high external force due to their disordered assembly.16-17 To overcome this problem, polymers and some small molecules were introduced into the process to act as cross-linkers or barriers.18-19 However, taking all the prospect performances and the mechanical stability into account at the same time is still a big challenge.

Here, a novel method was proposed to prepare composite graphene aerogel (CGA) with high mechanical stability via surface and interface reinforce approach. Firstly, adsorption behavior of metallic-CNTs on GO flakes was explored through molecular dynamics (MD) simulation. It was found that the metallic-CNTs tend to adsorb on the surface of GO flakes and form the network structure. The connected network not only improve strength and prevent the stacking of GO flakes, but also impel the absorption of magnetic Fe3O4 nanoparticles (NPs) concentrated on the edge of GO flakes via steric effect. Next, the tight connection of magnetic NPs on the edge of GO flakes further promote the interfacial strength. The made-up CGA was lightweight, has high mechanical stability, high conductivity and superparamagnetic properties, which thereby have high potential be used as microwave absorption (MA) materials. And it was proved that the CGA shows excellent MA performance over C, X, Ku band, and the maximum value can reach -49 dB, which confirms the potential being used as lightweight and efficient absorber.

2. Experimental Section ACS Paragon Plus Environment


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2.1 Materials: Graphite powder (325 mesh, 99.95%, metals basis) was bought from Macklin. The SWCNT

(produced

by

a

CoMoCAT

catalytic

CVD

process)

was

purchased

from

SIGMA-ALDRICH Co., used as received to process the splitting process according to Ref. [21], the details are as follows. The other materials KMnO4 (A.R.), NaNO3(A.R.), FeCl3·6H2O(A.R.), 98% H2SO4, 30% H2O2 aqueous solution, FeCl2·4H2O, NH3·H2O solution, anhydrous ethanol and ethylenediamine (EDA), were purchased from Sinopharm Chemical Reagent Co., Ltd. And the ultrapure water was produced by a Millipore system.

2.2 Dispersion of Fe3O4 NPs in water and ethanol mixture: Fe3O4 NPs were prepared by co-precipitation methods.20 The morphology and size of NPs are shown in Fig. S-1a, they are spherical and the size is uniform at around 10 nm in diameter. 40 mg of NPs were mixed with the mixture of ethanol-water with volume ratio is 3:1, and then sonicated for 30 min (KQ3200E ultra-sonic cleaning device: 40 kHz, 150 W).

2.3 Preparation and dispersion of metallic-CNTs: Metallic-CNTs with high purity were prepared according to our previous work.21 1 mg of SWCNT was added into the 20 mL of aqueous solution (10 mg/mL) of amino acid surfactant LGS, and sonicated for 2 h to obtained a homogeneous suspension. The mixture was centrifuged (60000 rpm) for 1 h, the bottom phase was extracted and mixed with 3 ml of ultrapure water for further experiment. The purity of the metallic-CNTs in the spilt carbon nanotubes is 95%.

2.4 Preparation of the CGA: The GO was prepared via modified Hummers method as reported previous.22-23The lateral size is about 8-12 μm and the thickness is about 1 nm, as shown in Fig. S-1b. Firstly, 5 ml of GO suspension (8 mg/ml), 1.5g of pre-dispersed Fe3O4 NPs suspension (5 mg/mL) were added into a certain amount of metallic-CNTs suspension and successively sonicated for 30 min. Next, the mixture which was uniformly blended with 60 μL of EDA poured into a 25 ml Teflon-lined stainless autoclave and hydrothermal treated at 140 °C for 2 h. The obtained black


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hydrogel was dialysis by ultrapure water and ethanol with a volume ratio of 20% for 1 day. Finally, the hydrogel was froze at -60°C for 6h and freeze-drying into CGA. By altering the amount of metallic-CNTs suspension as 2g, 4g, 6g, the resulted CGA was labeled CGA-1, CGA-2, CGA-3, respectively. In addition, the Fe3O4/graphene aerogel was prepared by the above method for comparison.

2.5 Structure characterizations: XRD were measured by Rigaku Dmax-rc X-ray diffractometer. XPS was performed on photoelectron spectrometer ESCALAB 250 XI. SEM and TEM image was performed on JEOLLTD JSM-6700F and HT-7700, respectively. Raman spectra was obtained by using Horbin PHS-3C, while FT-IR spectra is obtained on Bruker ALPHA-T instrument using KBr discs. The compression performance of CGA was measured by a texture analyzer (TA, TMS-PRO, FTC, USA).

2.6 Molecular dynamics simulation: The results of MD calculation was obtained from Discover module of Materials Studio.24-25 The system consisted of a (6, 6) single-walled carbon nanotube and GO flakes. The COMPASS was selected as force field, and atom-based cutoff was used to calculated Van der Waals interaction. All the simulations were carried out with Nose-Hoover thermostat, and the temperature is constant at 298K.

2.7 Electromagnetic measurements: The parameters of MA abilities were obtained by network analyzer (Ceyear 3672B) in the frequency range of 2-18GHz. For MA measurement, 15% of the samples and paraffin were homogenous mixed and were pressed into cirque. The diameter of inner and outer is 7.00 mm and 3.04 mm, respectively.

3. Results and Discussion



Fig. 1. 1) a) The snapshots of (6, 6)metallic-CNT interact with GO flakes at time intervals from 0 to 500 ps; b) the evolution of the binding energy with distance between metallic-CNT and GO flakes; 2) TEM image of metallic-CNTs network structure on GO flakes; 3) Schematic diagram for the preparation procedure and mechanism of CGA; a) GO flakes, with defects and heteroatoms on the surface; b) metallic-CNTs network structures on GO flakes; c) Fe3O4 NPs mainly interacted with oxygen-containing functional groups on the edge of GO flakes; d) Fe3O4 NPs attract with each other; e) Fe3O4 NPs enhanced the interlaminar connectivity of flakes; f) the redundant NPs were encapsulated on the pore of CGA.; 4) SEM image of: a) Fe3O4 NPs bridged the adjacent GO flakes of CGA (the yellow circle); b) the surface of CGA have scarcely any NPs; c) the pore structure of CGA.

MD simulation was used to explore adsorption behavior of the (6, 6) metallic-CNT on GO flake, as shown in Fig. 1-1.A metallic-CNT was put into the simulation box randomly not too far from the GO flake, the average distance between the GO flake and metallic-CNT was 11.11 Å


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initially, while after ran the molecular dynamic simulation for 500 ps, the distance between GO flake and metallic-CNT changed to 2.98 Å. In Fig. 1-1 b, as the distance between GO flake and metallic-CNT decreased, the negative binding energy value increased, and drastically increase after the distance got nearer than about 4 Å, which means there are definitely affinity interaction existing between them,26and it would be the driving force for the adsorption of metallic-CNT on the GO flake.27The formula for calculating binding energy is shown in Equation S-1. As it was shown in Fig. 1-2, when enough amount of metallic-CNTs were mixed with GO, the continuous network structure formed by metallic-CNTs on GO flake could be observed, which greatly prevent the stacking of GO flakes.

Basing on the above discovery, a strategy preparing composite graphene aerogel (CGA) with high mechanical stability via surface and interface reinforce approach was designed, trying to achieve the mechanic stability and high MA performance simultaneously by combining the surface support through metallic-CNT network and the interfacial cross-linking achieved by metal oxide nanoparticles, as shown in Fig. 1-3. Owing to the formation of metallic-CNT network structures on the basal plane of GO flake, the generated steric effect impel Fe3O4 NPs interact with the oxygen-containing functional groups on the edge of GO flakes. As the adjacent GO flakes get closed, the magnetic NPs attracted and tightly linked to each other, thereby the interfacial connectivity of CGA via magnetic dipole interaction was strengthened,28meanwhile the redundant Fe3O4NPs were encapsulated on holes during the formation of CGA, which can be evidenced by SEM image, as shown in Fig.1-4.The absorption of Fe3O4 NPs concentrated on the interfacial intersection of CGA, and in Fig. 1-4 b, the wall of CGA is relatively smooth and there are only a small amount of NPs absorbed, which further confirmed our conjecture. The pore structure of CGA was relatively uniformity via the ordered assembly, as shown in Fig. 1-4 c, the average size of hole is about 6μm.



Fig. 2. 1) The difference about the lamp with light and darkness of a) Fe3O4/graphene aerogel; b) CGA-2; c) CGA-3. 2) a) The stress-strain curve of CGA at the maximum strain of 30% for 1-200 cycles; b) the stress-strain curve of CGA at different maximum strain of 30%, 65%, 80% and 95%, respectively; c) the comparison of the maximum stress with other literature.

Benefited from the surface support by metallic-CNTs network structure and the interfacial cross-linking by NPs, the electrical conductivity and mechanical performance of CGA was greatly improved. In Fig. 2-1, comparison with the Fe3O4/graphene aerogel, the addition of metallic-CNT makes the lamp brighter, and the brightness of the lamp increased with the increasing of the amount of metallic-CNT added.29While the amount of magnetic NPs have no obvious effect on electrical conductivity, as shown in Fig. S-2. Owing to the small diameter and large aspect ratio, relatively small amount of metallic-CNTs is enough to form connected network structure on GO flakes.30 The cyclic strain-stress of CGA as shown in Fig. 2-2. In Fig. 2-2 a, the stress-strain curves almost unchanged even after 200 cycles at the maximum strain of 30%, which illustrated the nice structural stability of CGA.31-32Fig. 2-2 b shows the stress-strain curve of CGA at maximum strain of 30%, 65%, 80% and 95%, respectively. The aerogel shows reversibility even at the strain up to 95%, and the curve can recover to origin point implies the fully reversible elastic deformation of CGA.33-34 In Fig. 2-2c, the CGA has a larger maximum stress comparing with other literature, which attributed to ACS Paragon Plus Environment

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the surface and interface reinforce.35-39 As the large deformation occurred in CGA, there is no obvious destroy in microstructure owing to the protection of metallic-CNTs network structures and the tightly connected of NPs, which can be seen in Fig. S-3.The relationship of the amount of magnetic NPs with mechanical stress and density is shown in Fig. S-4. As the amount of magnetic NPs increased, the mechanical performance shows wavy variations, which owing to the increase of hardness caused by the redundant NPs adsorbed on graphene sheets. With the content of NPs added sequentially, brittleness of composites will occurred accordingly. The density of composites increases with the amount of the NPs increasing, and the minimum value is about 11.1 mg/cm3 (Fig. S-5).

It is worth to note that, we found that the mixture of ethanol and water can greatly reduce the gathering tendency of NPs, which might attribute to the hydrogen bond interaction and capillary force between Fe3O4 NPs and water molecules being weakened by ethanol. And the crystallographic structure of Fe3O4 NPs which was dispersed by the mixture has not changed, as shown in Fig. S-6. Moreover, the excellent dispersion is one of the key point to ensure the effective combination of all the components.



Fig. 3. 1) a) XRD patterns of the prepared GO (black line), Fe3O4 NPs (blue line) and CGA (red line); b) Raman spectra of rGO (black line) and CGA (red line); c) FT-IR spectra of GO (black line), CGA (red line) and Fe3O4 NPs (blue line).2) XPS spectra: a) wide scan of GO (black line), GA (red line) and CGA (blue line); b) Fe 2p spectra of CGA; c) the C 1s spectra of GO; d) the C 1s spectra of CGA; e) the O 1s spectra of GO; f) the O 1s spectra of CGA.

The crystallographic structure of GO, Fe3O4 NPs and CGA was measured by XRD in Fig. 3-1 a. The diffraction peak of GO is about 11.4 °, which belongs to (001) crystal plane and the interplanar spacing of 0.77nm. The enhanced interplanar space illustrated that the introduction of functional groups on flakes.40 For Fe3O4 NPs and CGA, the characteristic peaks vest in the inverse spinel structure of Fe3O4 (JCPDS card No. 74-0748),41 which means the Fe3O4 NPs are successfully assembled into CGA. ACS Paragon Plus Environment

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The Raman and IR spectra of the CGA and GO/rGO were measured, through which the charge transfer between GO-Fe3O4 and the S-S interaction between GO-metallic-CNTs of CGA were verified. In Fig. 3-1 b, the band at about 1340 cm-1 and 1590 cm-1 corresponding to the D-band and G-band of rGO, respectively.42 For CGA, the position of D band and G band were all shifted. The shift of D band means that the S-S interaction between GO and metallic-CNTs, while the shift of G band means the charge transfer between GO and Fe3O4 NPs.43-44 The IR spectrum of GO, Fe3O4 NPs and CGA were shown in Fig. 3-1 c. For GO, the peaks of 1625 cm-1, 1394 cm-1, 1258 cm-1 and 1056 cm-1 are associated to the stretch of C=O of carboxylic groups, C-OH deformation vibration, stretching of C–OH and C-O, respectively.45 For Fe3O4 NPs, the peak at about 3441 cm-1 is associated to O-H stretching vibration, and owing to the existence of –OH groups on the surface of NP, the position of Fe-O peak shifted to 600 cm-1.46 In comparison with GO and Fe3O4 NPs, the peaks of C=O and C-OH of CGA are shifted, which attributed to the hydrogen bond interaction between them.

The chemical composition of GO, GA and CGA were obtained by XPS, as shown in Fig. 3-2. Fig. 3-2 a shows the wide-scan XPS profiles of GO, GA and CGA. In Fig. 3-2 b, there is an obvious Fe peak in CGA which can be divided into Fe 2p3/2 and Fe 2p1/2 at about 710.4 eV and 724.2 eV.47 and the value of the binding energy is close to the other literature. Meanwhile, there are no peak at about 719 eV, which means there is no existence of γ-Fe2O3.48-49 The C 1s spectrum of GO and CGA is shown in Fig. 3-2 c-d. For GO, the binding energy at 284.8eV, 286.3eV, 287.3eV, 288.2eV is corresponded to the C-C/C=C, C-OH, C-O-C, C=O groups, respectively.50 And for CGA, the intensity of oxygen-containing functional groups are greatly reduced, which ascribed to EDA-dominant hydrothermal reduction reaction. In Fig. 3-2 e, the O 1s spectrum of GO can be divided at 531.7 eV, 532.4 eV and 533.1eV, corresponding to C=O, C-OH and C-O-C groups, respectively.51-52 Comparing GO with CGA, the position of O 1s peak transferred from 532.5 eV to 530.9 eV, and there is a new peak appeared at about 531.5 eV, which all means that the bond formation between GO and Fe3O4 NPs.53-54 ACS Paragon Plus Environment


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Fig. 4. The magnetic hysteresis loops of CGA and Fe3O4 NPs.

The magnetic properties of Fe3O4 NPs and CGA were investigated via magnetic hysteresis loops, as shown in Fig. 4. Both of the magnetic hysteresis loop show typically S-like shape and have negligible coercivity and remanence, which implies the superparamagnetic characteristic of the NPs and CGA (Fig. S-7).55-56 Compared to pure Fe3O4 NPs (64 emu/g), the decreased saturation magnetization value of CGA (8.5 emu/g) is caused by the addition of carbon-based materials and small amount of magnetic NPs.57

Recently, the preparation methods of 3D graphene composites have been developed. The abundant interface and pore structure can increase multiple reflection of microwave and eventually enhance MA ability by the impedance mismatching of graphene sheets and air.58 Thus, owing to the lightweight, high electrical conductivity, good mechanical properties of CGA, associated with the superparamagnetic characteristic, the material can be used for microwave absorption.59-60 The excellent mechanical stability can not only provide abundant hole, but also improve the electrical conductivity of the composites via interface connectivity, thereby enhance the microwave absorption performance. Meanwhile, the mechanical stability is also favourable for applications.

The MA ability can be evaluated by reflection loss (RL) value.61 The equations are as follows.

୞୧୬ିଵ

RL=20logቚ

ቚ

୞୧୬ାଵ


(1)

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Zin=ሺߤ௥ Ȁߝ௥ ሻଵȀଶ tanhൣ݆ሺʹߨȀܿሻሺߤ௥ Ȁߝ௥ ሻଵȀଶ ݂݀൧

(2)

Where Zin is the input impedance of microwave absorber; ሺߤ௥ Ȁߝ௥ ሻଵȀଶ is the impedance of free space. μr (μr=μ′-jμ″) is the complex permeability and εr (εr=ε′-jε″) is the complex permittivity of the composites. f is the frequency of measured and the d is the thickness of microwave absorber. Ordinarily, the bandwidth at RL value İ -10 dB is usually uesd as a criterion for qualified microwave absorbers.62

Fig. 5. Frequency dependence of 1) a) real part and b) imaginary parts of complex permittivity, c) real part and d) imaginary parts of complex permeability of Fe3O4 NPs (black line), CGA-1 (red line), CGA-2 (blue line) and CGA-3 (green line); 2) attenuation constants of Fe3O4 NPs (black line), CGA-1 (red line), CGA-2 (blue line); 3) a) dielectric loss tangent and b) magnetic loss tangent of Fe3O4 NPs (black line), CGA-1 (red line), CGA-2 (blue line) and CGA-3 (green line); c) μ″(μ′)-2f-1 of CGA-1 (black line), CGA-2 (red line) and CGA-3 (blue line).

The complex permittivity and permeability is one of the index for evaluating microwave absorption abilities.63 The value of the real part (ε′, μ′) and the imaginary part (ε″, μ″) is represented the abilities of store or dissipate electric energy and magnetic energy, respectively.64 Fig. 5-1 a-b shows the trendency of complex permittivity versus frequency. It shows that the ε′ and ε″ of the CGA are much higher than Fe3O4 NPs in the whole frequency band, and the value of ε′ and ε″ rises ACS Paragon Plus Environment


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with metallic-CNTs increasing, which mainly attributed to the formation of metallic-CNTs conductive network structures and the polarization relaxation of the residual groups and defect of rGO.65 The variation of μ′ and μ″ of Fe3O4 NPs and CGA was illustrated in Fig. 5-1 c-d. The value of μ′ and μ″ of CGA is slightly decreased comparison with Fe3O4 NPs, which ascribed to the addition of non-magnetic carbon-based materials.66

Attenuation constant (α) is another coefficient to decide the MA abilities of the materials, and the equation is expressed as follows:67

α=

ξଶగ௙ ටሺɊǳɂǳ ௖

െ Ɋǯɂǯሻ ൅ ඥሺɊǳɂǳ െ Ɋǯɂǯሻଶ ൅ ሺɊǳɂǯ ൅ Ɋǯɂǳሻଶ

(3)

Where ε′, ε″, μ′, μ″ is represented the real part and the imaginary part of the complex permittivity and complex permeability, and f is the frequency of measured. The variation of α with frequency was illustrated in Fig. 5-2. It shows that the attenuation constant of CGA are much higher than Fe3O4 NPs and shows a rising tendency in the whole frequency band, which implies CGA have a great microwave attenuation abilities.68

The variety of dielectric loss tangent (tan δε=ε″/ε′) and magnetic loss tangent (tan δμ=μ″/μ′) of CGA as shown in Fig. 5-3 a-b, which can be used for identifying the MA performance. The value of δε for CGA is almost constant over 2-18 GHz at around 0.4-0.5. And the CGA shows enhanced dielectric loss than Fe3O4 nanoparticles, and the dielectric loss increases with the increase of metallic-CNTs, which indicated that the continuous metallic-CNTs network structure and frame of graphene aerogel plays an important role in it. Besides, the abundant multistage-interface of CGA also significant for improving the dielectric loss.69-70 For δμ, the value of tan δμ is sharply decreased from 2-8 GHz and then maintained at around 0.004 over 8-18 GHz. In comparison with Fe3O4 nanoparticles, the introduction of metallic-CNT and graphene have little influence on magnetic loss. And the value of dielectric loss is much higher than magnetic loss over 2-18 GHz, which means the


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dielectric loss plays a major role in microwave absorption. The variety of μ″(μ′)-2f-1 is also measured to investigated the mechanism of magnetic loss, as shown in Fig. 5-3 c.71 The value of μ″(μ′)-2f-1 is sharply decreased in the frequency of 2-8 GHz and constant in 8-18 GHz afterward. Therefore, the magnetic loss at 2-8 GHz is affected by natural ferromagnetic resonance, while exchange resonance occurred at 8-18 GHz. Besides, the eddy current effect also acting in the whole frequency.72-73

Fig. 6. 1) 3D image of RL value for a) Fe3O4 NPs; b-d) CGA 1-3, respectively; 2) a)microwave absorption performance of CGA-2; b) schematic representation of microwave absorption mechanism.

The 3D image of RL value for Fe3O4 NPs and CGA 1-3 as shown in Fig. 6-1. The RL values of Fe3O4 NPs is lower than -10 dB in the whole frequency range, while the magnetic NPs crosslinked graphene aerogel with metallic-CNTs network structures, the resulting CGA shows enhanced MA abilities under different proportioning (Fig. S-8). The maximum RL value of composites first increases and then decreases with the amount of metallic-CNTs increasing, which might due to the



impedance mismatch. In Fig. 6-2 a, the qualified frequency bandwidth of CGA-2 covers C (4-8 GHz), X (8-12 GHz) and Ku (12-18 GHz) band, and the maximum value can reach -49 dB, which satisfied the demand of satellite communications and military radar. The comparison of microwave absorption performance with composites prepared by other methods is shown in Fig. S-9. And the mechanism of excellent MA performance as shown schematically in Fig. 6-2 b. After the incident electromagnetic microwave entering the material, a part of it might be attenuated by the multi-stage pore and the metallic-CNTs reticulated structure induced current in CGA.74 The induced current decayed quickly, and gradually convert into heat energy. Meanwhile, the residual functional groups and defects of rGO lead to polarization relaxation, which resulted in energy loss. And the magnetic loss comes from eddy current effect, exchange and natural resonance of Fe3O4 nanoparticles also take a vital role in microwave absorption.

4. Conclusion

In this paper, surface and interface reinforced graphene aerogel was prepared via combining surface support brought by metallic-CNTs network and interfacial cross-linking of magnetic nanoparticles. Molecular dynamics simulation explored the adsorption behavior of metallic-CNT on GO flake, and the formed metallic-CNT network structure was verified by TEM image. Owing to the steric effect caused by metallic-CNTs network structure, the magnetic nanoparticles concentrated absorption on the edge of GO flake. And the CGA shows enhanced electrical conductivity and mechanical performance by the surface and interface reinforce approach. Meanwhile, the CGA shows great MA performance. The effective absorption bandwidth (RL ≤ -10 dB) can cover C, X, Ku band, and the maximum value can reach -49 dB. All in all, this work can provide a new strategy to achieve mechanical performance and functionality of graphene aerogel simultaneously, and also advanced the development of functional carbon-based/metallic oxide nanocomposites.


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ASSOCIATED CONTENT

Supporting information

The size of GO flakes and Fe3O4 nanoparticles was determined by TEM image; the formula for calculating binding energy of GO and metallic-CNTs was provided; the effect of the amount of Fe3O4 nanoparticles on electrical conductivity, compressive stress and density was supplied; the crystallographic structure of Fe3O4 nanoparticles which dispersed by ethanol and water was performed by XRD; the preparation process, compressibility, magnetic and fire-resistant property, and the comparison of RL value with other literature were supplied in Supporting Information.

AUTHOR INFORMATION

Corresponding Author E-mail: [email protected]. Fax: +86-531-88364464. Tel: +86-531-88362078. ORCID Ying Li: 0000-0002-2862-083X Yan Qin : 0000-0001-8282-8394 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS

The funding from the National Science Fund of China (No. 21872084, 61575109, and 21473103) and the Key Research and Development Project of Shandong Province (No. 2018GSF117025) is gratefully acknowledged. We thank Professor Dechun Li, Jia Zhao and Liuge Du for the help of providing electromagnetic measurements.

REFERENCES ACS Paragon Plus Environment


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Preparation of Graphene Aerogel with High Mechanical Stability and

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