Superelastic and multifunctional graphene-based aerogels by interfacial reinforcement with graphitized carbon at high temperatures

Accepted Manuscript Superelastic and multifunctional graphene based aerogels by interfacial reinforcement with graphitized carbon at high temperatures Ji Liu, Yafeng Liu, Hao-Bin Zhang, Yang Dai, Zhangshuo Liu, Zhong-Zhen Yu PII:

S0008-6223(18)30147-7

DOI:

10.1016/j.carbon.2018.02.026

Reference:

CARBON 12862

To appear in:

Carbon

Received Date: 19 December 2017 Revised Date:

28 January 2018

Accepted Date: 4 February 2018

Please cite this article as: J. Liu, Y. Liu, H.-B. Zhang, Y. Dai, Z. Liu, Z.-Z. Yu, Superelastic and multifunctional graphene based aerogels by interfacial reinforcement with graphitized carbon at high temperatures, Carbon (2018), doi: 10.1016/j.carbon.2018.02.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Graphical Abstract

ACCEPTED MANUSCRIPT

Superelastic and multifunctional graphene based aerogels by interfacial

RI PT

reinforcement with graphitized carbon at high temperatures

Ji Liu a, Yafeng Liu a, Hao-Bin Zhang a,*, Yang Dai b, Zhangshuo Liu b, Zhong-Zhen Yu a,b,c* a

Beijing Key Laboratory of Advanced Functional Polymer Composites, Beijing University of

b

SC

Chemical Technology, Beijing 100029, China

State Key Laboratory of Organic-Inorganic Composites, College of Materials Science and

c

M AN U

Engineering, Beijing University of Chemical Technology Beijing 100029, China Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing

University of Chemical Technology, Beijing 100029, China

ABSTRACT: Although lightweight and three-dimensional graphene aerogels and foams

TE D

combining ultrahigh electrical conductivity, superelasticity and fatigue resistance are highly desirable for widespread applications, it remains a large challenge to construct a multifunctional

EP

framework affording the rapid electron transport and efficient load transfer due to the weak interfaces between highly reduced graphene oxide sheets. Herein, we report an efficient approach

AC C

for fabricating an integrated graphene aerogel by bridging its reduced graphene oxide sheets with polyimide macromolecules followed by graphitization at 2800 oC. During the graphitization process, the reduced graphene oxide sheets are thermally reduced to graphene efficiently by removing their residual oxygen-containing groups and healing their defects, while the polyimide component is graphitized to turbostratic carbon to bridge the graphene sheets, resulting in an integrated graphene aerogel with satisfactory mechanical and functional performances, including _____________________________________________________

*Corresponding author: E-mail: [email protected] (H.-B. Zhang); [email protected] (Z.-Z. Yu)

ACCEPTED MANUSCRIPT

ultrahigh electrical conductivity (> 1000 S m-1) at a low density, unprecedented high electromagnetic interference shielding effectiveness of ~83 dB in X-band, 90% reversible compressibility, and reliable resistance to fatigue for 1000 compressive cycles at 50% strain. The

RI PT

integrated graphene aerogels with such multifunctional performances hold a great promise for applications as electromagnetic interference shielding materials, oil adsorbents, and conductive

SC

scaffolds for polymer nanocomposites.

1. Introduction

M AN U

Three-dimensional (3D) graphene architectures with outstanding electrical conductivity, superelasticity, high porosity, and low density are highly attractive in the fields of flexible electronics [1-4], energy damping [5-7], current collector of electrodes [8], electromagnetic wave absorption/shielding materials [1, 9], and absorbents of contaminates [7, 10, 11]. In general, the

TE D

overall performances of the cellular foams are determined by their geometric morphology, intrinsic properties of constituents, as well as sheet-to-sheet interfaces. Thus, to realize the outstanding attributes of graphene into monolithic architectures, various strategies have been

EP

exploited to optimize the specific properties required for practical applications. Superelastic graphene aerogels and foams can be readily constructed by hydrothermal or solvothermal

AC C

methods with partially reduced graphene oxide (RGO) as building blocks [2, 5-7, 12]. For example, Zhang et al. [12] prepared a 3D graphene metamaterial with large negative Poisson’s ratio and superelasticity by a modified hydrothermal approach followed by oriented freeze-casting process. Gao et al. [5] created a highly compressible lamellar multi-arch graphene monolith with excellent fatigue resistance using a bidirectional freezing process. Overall, the mechanical properties of graphene aerogels are mainly controlled by the strong and robust

2

ACCEPTED MANUSCRIPT

sheet-to-sheet interfaces, facilitating the efficient load transfer, impacted by van der Waals forces, hydrogen bonding, or even covalent bonding provided by insulating polymers or amorphous carbon with low conductivity [5, 6, 12-15].

RI PT

Unfortunately, most superelastic graphene aerogels show electrical conductivities less than 102 S m-1 [5-7, 13, 16], because the electrons cannot efficiently transport through the defective and oxygen-containing RGO network that may be favorable for load transfer by constructing highly

SC

interconnected and mechanically strong porous structures. To obtain high conductivity, the structural defects and oxygen functionalities of RGO sheets [17-22] should be completely

M AN U

eliminated by chemical or thermal reductions and the sheet-to-sheet interfaces should be enhanced with more conductive materials [23-25]. For instance, Xin et al. prepared ultrahigh conductive graphene fibers by annealing at extremely high temperature of 2850 °C to reduce the phonon and electron scattering centers, thus enhancing the conductive properties [17]. However,

TE D

paradoxically, the strong interactions including hydrogen bonding and covalent interconnections that afford desirable mechanical properties would inevitably be greatly weakened because of the removal of the functional groups and the decomposition of the polymeric materials by

EP

high-temperature annealing. After thermal reduction of RGO aerogels at temperatures higher than 2000 oC, there are no adequate interfacial interactions holding the resultant highly reduced

AC C

graphene oxide sheets together to resist external loading under large cyclic strains at low bulk densities because high crystallinity and low defect of graphene sheets inevitably leads to brittleness [22]. To fabricate graphene architectures with desirable conductive properties, some novel strategies were adopted. Lin et al. [26] fabricated a highly conductive graphene aerogel with a high conductivity of 900 S m-1 by assembling high-quality pristine graphene sheets using a room-temperature freezing gelation method, but its mechanical properties are not satisfactory.

3

ACCEPTED MANUSCRIPT

Chen et al. pioneered the synthesis of highly conductive lightweight 3D graphene foams using a chemical vapor deposition (CVD) method [4]. Recently, Bi et al. fabricated a 3D tubular graphene architecture with superelasticity and excellent electrical conductivity synthesized by

RI PT

conformal CVD method with SiO2 as the template [27]. Despite to the encouraging advances for graphene aerogels, however, it is still highly required to develop a scalable and efficient

lightweight porous graphene architecture.

SC

approach to integrate superb electrical/thermal conductivities and superelasticity into one

Herein, we demonstrate an efficient and scalable approach for constructing superelastic,

M AN U

fatigue resistant, highly conductive, and multifunctional integrated graphene aerogels (IGAs) by bridging the RGO sheets with polyimide (PI) macromolecules followed by graphitization at 2800 o

C. The purpose of the graphitization is to convert the RGO sheets and PI component to highly

conductive graphene sheets and graphitized carbon, respectively, forming high-quality graphene

TE D

aerogels with various remarkable electrical conductivity, ultrahigh EMI shielding performance,

recyclability.

2. Experimental

AC C

2.1. Materials

EP

outstanding mechanical properties, and strong adsorption capacity with excellent durability and

Pristine graphite flakes were supplied by Huatai Lubricant and Sealing (China). Sodium nitrate, sulphuric acid (98%), potassium permanganate (99.5%), hydrogen peroxide (30%), and hydrochloric acid (37%) were purchased from Beijing Chemical Works (China). Triethylamine (TEA, 99%), N,N-dimethylacetamide (DMAc, 99%), 4,4-diaminodiphenyl ether (ODA, 98%)

4

ACCEPTED MANUSCRIPT

were bought from Alfar Aesar Chemicals (China). 4,4'-Oxydiphthalic dianhydride (ODPA, 99%) was provided by Aladdin Industrial Co. (China). All the materials were used as received. 2.2. Preparation of graphene oxide (GO) and Water-Soluble PI Precursor

RI PT

GO was prepared by using a modified Hummers method and the water-soluble poly(amic acid) (PAA) with a weight molecular weight of ~ 4000 g mol-1 was synthesized according to a reported method [28, 29]. Typically, the homogenous PAA solution was obtained by dispersing

SC

ODA (1.95 g) in DMAc (30 mL) followed by adding a certain amount of ODPA (3.05 g) under vigorous mechanical stirring for 1 h. The resultant solution was then poured into deionized water

M AN U

and the precipitate was washed and dried at a low temperature to avoid the degradation of PAA. Aqueous solution of PAA was obtained by dissolving PAA of 0.054 g in water (1 mL) with 0.01 g TEA.

2.3. Fabrication of RGO/PI aerogel and IGA architectures

TE D

The PAA solution and the GO suspension (5 mg/mL) were mixed with different volume ratios. The uniform mixture was placed in an ultralow temperature chamber (-80 °C) for 24 h followed by lyophilizing in a freeze-dryer for 72 h. The resultant GO/PAA aerogel (GO/PAA) was

EP

thermally annealed at 300 °C in an argon atmosphere for 2 h, during which GO was partially reduced to RGO and PAA was converted to PI macromolecules. Finally, IGA was fabricated by

AC C

thermally treating the RGO/PI aerogel at high temperatures of 600, 1000, 1800, 2200 and 2800 °C, which were designated as IGA-600, IGA-1000, IGA-1800, IGA-2200, and IGA-2800, respectively. A series of IGAs with different initial GO/PAA ratios were prepared and designated as IGA0.08, IGA0.16, IGA0.22, and IGA0.27, where the numbers present the mass contents of GO in the prepared GO/PAA aerogels. IGAs with different densities were obtained by adjusting the concentration of initial GO/PAA aqueous suspensions with certain GO/PAA ratios.

5

ACCEPTED MANUSCRIPT

2.4. Preparation of paraffin/IGA composites Paraffin/IGA composites were prepared by vacuum-assisted impregnation of melted paraffin into IGAs. Typically, IGAs were immersed into the melted paraffin in a vacuum oven at 60 °C for 6

RI PT

h, and then the IGAs filled with melted paraffin were cooled in air to obtain paraffin/IGA composites. 2.5. Characterization

SC

Gel permeation chromatography (GPC) measurements were performed on a Shimadzu system using DMAc containing 2.1 g L−1 of lithium chloride (LiCl) as eluent with a flow rate of 1 mL

M AN U

min−1 at 80 °C. The morphology and structure of IGA and its precursors were observed with a Hitachi S4700 field-emission scanning electron microscope (SEM) and a Tecnai G2 F20 S-TWIN transmission electron microscope (TEM). X-ray diffraction (XRD) patterns were recorded with a Rigaku D/Max 2500 diffractometer (Cu Kα radiation, λ = 0.154 nm). The

TE D

composition variations from GO/PAA to RGO/PI and IGA aerogels were analyzed with a Thermo Fisher Escalab 250 X-ray photoelectron spectroscopy (XPS) and a Nicolet Nexus 670 Fourier-transform infrared (FT-IR). Contact angles were measured with a Data Physics TUB 90E

EP

goniometer. The compression properties were tested with an Instron E1000 universal testing machine. Because of the porous structure, the thermal conductivity of IGA was evaluated by

AC C

measuring the conductivity of its paraffin composites by eliminating the negative effect of insulating air. Thermal conductivity (κ) was calculated by κ = α × ρ × Cp, where Cp is the specific heat capacity, α is the thermal diffusivity and ρ is the density. Thermal diffusivities of IGA/paraffin composites were measured with a Netzsch LFA467 light flash apparatus at ~30 °C. Specific heat capacity of IGA/paraffin composites was characterized with a Perkin-Elmer Pyris 1 differential scanning calorimeter (DSC) at a scanning rate of ~10 oC min-1. Electrical

6

ACCEPTED MANUSCRIPT

conductivity was measured with 4-ProbeTech RTS-8 four-probe resistivity meter (China). To measure the electrical conductivity accurately, the aerogels were fabricated into regular shapes with small thicknesses. The sheet resistances (ρs) of the aerogels were measured from multiple

RI PT

sites to obtain an averaged value. In general, ρs = C×V/I, where C is the correction factor. The resistivity (ρ) was calculated by ρ = ρs × thickness, and the conductivity (σ) was calculated by σ = 1/ρ [30-32]. The EMI SE was measured with a Keysight N5247A PNA series vector network

SC

analyzer within 8.2-12.4 GHz. In the uptake studies of IGA, the IGA weights after and before absorption were recorded for calculating the weight gain. Note that the weight measurements

M AN U

were done quickly to avoid evaporation of absorbed organic liquids.

3. Results and discussion

Fig. 1a illustrates the fabrication process of the lightweight, highly conductive and superelastic

TE D

IGAs. The detailed procedure was described in the experimental section. Typically, a suspension of GO sheets and a solution of PAA (Fig. S1) were mixed, and the mixture was frozen in a freezer (-80 °C) followed by freeze-drying to form a 3D and porous GO/PAA aerogel. The

EP

strong interactions between the hydrosoluble PAA chains and the hydrophilic GO sheets, evidenced by the large thickness of the PAA coated GO (Fig. S2), are crucial for constructing the

AC C

PAA-reinforced GO aerogel and its derivatives by interfacial reinforcement design. The thermal treatment at 300 °C in an argon atmosphere converts the GO/PAA to RGO/PI by thermally initiating the polymerization of PAA to form PI and thermally reducing GO to RGO. The in situ polymerized PI bridge adjacent RGO sheets to reinforce the 3D porous architecture [3, 33]. However, it is rather challenging for graphene aerogels to simultaneously possess both superb

7

ACCEPTED MANUSCRIPT

electrical conductivity and strong interactions between the graphene sheets especially after

AC C

EP

TE D

M AN U

SC

RI PT

high-temperature annealing.

Fig. 1. (a) Schematic illustration for fabricating IGA from GO/PAA and RGO/PI aerogels. The lightweight and porous IGA can rest on the tip of dandelion. (b) Images showing the

8

ACCEPTED MANUSCRIPT

compressibility of IGA. (c) SEM image of the lamella surface in IGA. Surface morphology of the internal cellular structures of (d) GA and (e) IGA. (f, g) SEM images highlighting the graphitized carbon reinforced junctions in IGA. (h) TEM and (i) HRTEM images of the IGA

RI PT

cellular walls.

Further thermal annealing of RGO/PI at 2800 °C leads to a high-quality graphene monolith by ultimately removing the residual oxygen-containing groups and defects in RGO component and

SC

graphitizing the insulating polymer of PI into graphitized carbon. Moreover, the scalable and efficient approach provides a great flexibility for tuning the shape and size of IGA (Fig. S3), as

M AN U

well as its density by simply controlling the PAA/GO ratio and the concentration of GO/PAA solution. For comparison, graphene aerogel (GA) and graphitized PI aerogel (GPA) are prepared with the same conditions as IGA. Interestingly, after thermal annealing at 2800 °C, IGAs completely recover to its original shape even after large-strain manual compression, far superior

TE D

to the easily crushed rigid GPA and the inelastic GA (Fig. 1b, S4).

The microstructures of graphene aerogels greatly depend on the fabrication routes and conditions. IGA exhibits ordered, hierarchical, and hyperbolic-like structures due to the modified

EP

freeze-casting process [12, 34]. The oblate pores are radially arrayed from inside to outside along the graphene sheets, with the synchronous growth of ice crystals inward from different directions

AC C

for GO/PAA suspension in a glass vial during the freezing process (Fig. S5). After the high-temperature annealing at 2800 oC, the resultant graphitic carbon leads to distinct internal microstructure of IGA as compared to its counterpart (GA). It is believed that the ultrathin and smooth graphene sheets in GA are loosely packed with weak physical contacts mainly by π-π interaction (Fig. 1d). In striking contrast, the wrinkled graphene sheets of IGA are compactly interconnected with the graphitized carbon to form a seamless graphene framework with

9

ACCEPTED MANUSCRIPT

integrated structure (Fig. 1c,e). The integrated graphene networks are expected to withstand cyclic compression. Note that the perfect bridging nodes between graphene sheets and the ‘Y’ shape sheets compactly stacked together on one end and bifurcated on the other end could

RI PT

effectively improve the continuity and integrity of the interfused network structure in IGA (Fig. 1f-h). High-resolution transmission electron microscopy (TEM) image further confirms the presence of graphitic carbon with turbostratic structure that is closely attached on graphene

SC

sheets and their junctions (Fig. 1i). Therefore, the seamlessly integrated continuous graphene network is well constructed by interfacial welding with the sandwiched multilayer structure. The

M AN U

amount of the graphitic carbon attached on the graphene skeleton and its thickness are tuned by varying the mass ratio of GO/PAA components (Fig. S6). Higher initial amounts of PAA results in higher amounts of the graphitic carbon and thicker carbon layers in IGAs. Therefore, the formation of numerous junctions in IGA indeed reinforces the 3D graphene framework by

TE D

enhancing the connections between constituent sheets, offering highway for efficient transport of electrons and phonons, and external load transfer. XRD, XPS, and FT-IR are used to analyze the structures and compositions of GO/PAA,

EP

RGO/PI, and IGA with an initial GO content of 0.22. In the XRD patterns, the characteristic (002) peak shifts from 12.0° of GO to 8.6° of GO/PAA, implying the enlarged interlayer spacing

AC C

upon the intercalation of PAA into the GO galleries (Fig. 2a). Different from the broad weak peaks of RGO/PI and GPA, IGA exhibits a sharp and strong graphitic characteristic peak at 26.6°, verifying high crystallinity of the highly graphitized IGA (Fig. 2a,S7) [35]. Compared to GO (2.51) and GO/PAA (3.82), RGO/PI has a larger C/O ratio (5.22) due to the partial reduction of GO by thermal treatment at 300 °C (Fig. 2b). Simultaneously, the successful synthesis of PI from PAA is proved by the characteristic peaks of imide C=O (1718 and 1775 cm-1), C-N (1371

10

ACCEPTED MANUSCRIPT

cm-1), and C=C (1501 cm-1) groups in the FT-IR spectrum (Fig. S8) [3]. Further thermal treatment at 2800 °C converts PI to graphitic carbon and eliminates the oxygen functionalities and defects of RGO completely, evidenced by both the ultrahigh C/O ratio of 80.3 and the almost

AC C

EP

TE D

M AN U

SC

RI PT

disappeared O1s peak (Fig. 2b,S9).

Fig. 2. (a) XRD patterns, (b) XPS spectra, and (c) Raman spectra of GO, GO/PAA, RGO/PI, and IGA. (d) Raman spectra showing variation of ID/IG in different samples. The structural evolution is further confirmed by Raman results (Fig. 2c). Clearly, compared to GO (0.88) and GO/PAA (0.93), RGO/PI even has a slightly higher ID/IG ratio (0.99) because of the increased defect content. Interestingly, IGA exhibits an ultralow ID/IG ratio (0.07),

11

ACCEPTED MANUSCRIPT

comparable to those of natural graphite and high-quality graphene aerogels prepared by CVD or thermal annealing at 3000 °C [8, 36]. Consistent with the TEM results (Fig. 1i), IGA exhibits a 2D peak indicating the features of turbostratic and Bernal stacked carbons, again confirming the

RI PT

coexistence of the pyrolytic PI-derived graphitic carbon and the highly crystallized multilayer graphene sheets (Fig. 2d,S10) [37-41]. It is thus reasonable that the lightweight and porous graphitized IGA reinforced with graphitic carbon is able to integrate many intriguing attributes

SC

including remarkable electrical and thermal conductivities, high EMI shielding performance, and outstanding mechanical properties.

M AN U

The high quality graphene framework is highly beneficial for the exceptional electrical, thermal, and EMI shielding properties of IGAs (Fig. 3a,b). Importantly, the higher-temperature annealing endows IGA with superior electrical and thermal conductions due to the improved graphitization and structural integrity (Fig. 3a,S11,S12). By comparison, RGO/PI exhibits a low

TE D

electrical conductivity of 2×10-2 S m-1 due to the presence of electrically insulating PI component. With increasing the temperature, PI is first converted to amorphous carbon and then to graphitic carbon, bridging the simultaneously thermally reduced graphene sheets and thus

EP

benefiting electrical and thermal conductions of the graphitized aerogel. As expected, superb electrical conductivities of 1000, 1144, 1200, 1335 S m-1 are achieved for IGAs-2800 with

AC C

respective low densities of 7.6, 12.2, 18.0, 24.5 mg cm-3, which are comparable to or even higher than the best results for CNT- or graphene-based aerogels with similar densities [4, 23, 26, 27, 37]. Moreover, the superb thermal conductivity of IGA is manifested by the high values of ~2.55 (1.33 wt%) and 4.56 W m-1 K-1 (2.20 wt%) for paraffin/IGA composites at ultralow loadings, which are far superior to the reported composites at much higher loadings of graphene or other thermally conductive fillers due to the continuity of the prebuilt conductive networks (Fig. S13,

12

ACCEPTED MANUSCRIPT

S14) [42-45]. In addition to the highly reduced graphene framework, the strong graphitic carbon junctions between individual graphene sheets are also considered to greatly contribute to the

AC C

EP

TE D

M AN U

SC

RI PT

outstanding performances of IGA by reducing the interfacial contact resistance (Fig. 1f-h).

Fig. 3. (a) Plots of electrical conductivity of IGA0.22 and thermal conductivity of paraffin/IGA composites versus annealing temperature. (b) Effect of IGA0.22 annealing temperature on EMI shielding performance of IGAs. (c) Comparison of electrical conductivity of various graphene

13

ACCEPTED MANUSCRIPT

aerogels versus bulk density. Our lightweight IGA uniquely combines superb electrical conductivity and superelasticity. (d) The stress-strain curves of IGA0.22-2800 with different set strains. (e) stress-strain curves of IGA0.27-2800 under different strain rates. (f) Cycling stability

RI PT

measurements of IGA0.22-2800 under applied strain of 50% for 1000 cycles.

The supreme electrical conductivity implies the great promise of the lightweight and robust

SC

IGAs for EMI shielding application. Fig. 3b shows the improved EMI shielding performances of IGAs as a function of annealing temperature. Compared to the nearly microwave transparent

M AN U

RGO/PI, IGA0.22-600, IGA0.22-1000, IGA0.22-1800 and IGA0.22-2200 show higher EMI shielding performances of 23.6, 40.8, 56.7, and 66.4 dB in X-band, respectively. Surprisingly, IGA0.22-2800 with a density of 18 mg cm-3 and an electrical conductivity of 1200 S m-1 presents an unprecedented high EMI shielding value of ∼83 dB over the whole X-band frequency range and gives an ultrahigh specific EMI SE (SSE) of 4703 dB·cm3 g-1, which is comparable to the

TE D

best reported values of carbon-based shielding materials [24, 46]. The excellent EMI shielding performance hints promising applications of the lightweight and robust IGA in aircraft and portable electronics. To analyze the shielding mechanism for the IGA, the absorption (SEA) and

EP

reflection (SER) in the shielding are calculated using the following equations: SER = -10log10

AC C

(1-R) and SEA = -10log10 [T/(1-R)], where R is reflection coefficient, A is absorption coefficient, and T is transmission coefficient, and A, T and R can be obtained based on the measured S parameters [47-50]. The shielding mechanism analysis for the porous IGA reveals that the SEA contributes larger than SER in attenuating the electromagnetic wave (Fig. S15), and most of the incident electromagnetic wave is dissipated by absorption, giving an absorption-dominant EMI shielding mechanism [1, 51]. As previously reported [1, 9, 46, 52, 53], the unique shielding mechanism is attributed to the highly conductive network with abundant interfaces, which

14

ACCEPTED MANUSCRIPT

facilitates the incident radiations to be repeatedly scattered and reflected on the air-graphene interfaces, and finally to be dissipated as heat. Note that SEA represents the ability of a material

incident plane before absorption [24, 54, 55].

RI PT

to attenuate microwave that only penetrates the material except for the reflection occurred at the

More importantly, the highly reduced, seamless graphene framework reinforced with the graphitized carbon uniquely combines the superb electrical conductivity and superelasticity,

SC

superior to most previously reported graphene aerogels with only single excellent performance (Fig. 3c). To assess the mechanical properties of IGA, Fig. 3d shows the compressive stress (σ)

M AN U

as a function of strain (ε) under loading-unloading cycles from 10 to 90%. It is interesting that the lightweight cylindrical IGA-2800 shows elasticity and reversibility even at large compressive strain of up to 90%. The strain returns to its original point (ε=0) after unloading, implying the fully reversible elastic deformation of IGA. The compressive stress is highly dependent on the

TE D

compositions of the aerogels (Fig. S16). At the compression stain of 70%, the compressive stress is ~11.2 kPa for IGA0.27-2800, 22.4 kPa for IGA0.22-2800, 118.0 kPa for IGA0.16-2800, and ~189.6 kPa for IGA0.08-2800 (Fig. S17). Generally, the hysteresis loops are thought to arise

EP

from the dissipation of mechanical energy resulted from the sliding friction between cellular walls during the cycling compression. More importantly, the stable and robust architecture

AC C

enables IGA-2800 to maintain its superelasticity during extremely fast deformation at loading speeds from 100% to 500% strain min-1 (Fig. 3e). To explore the fatigue resistance under dynamic deformation, IGA0.22-2800 with a density of ~12 mg cm-3 is repeatedly compressed for loading-unloading cycles at 2 Hz with a strain of 50% for 1000 times (Fig. 3f). Note that IGA is pre-stabilized by applying a few loading/unloading cycles before testing to eliminate the effect of the first cycle [23]. Surprisingly, IGA shows a

15

ACCEPTED MANUSCRIPT

negligible plastic volume deformation (~ 2%) and retains 90% of the maximal stress after 1000 cycles of fast compression (Fig. 3f). Thus, IGA could tolerate large and repeated elastic deformation without obvious damage or structural collapse, suggesting its reliable fatigue

RI PT

resistance and long-term service life as a multifunctional material. The minor structural damage under the cyclic compression also leads to small changes in the energy loss coefficient with cycling (Fig. S18). For comparison, after thermal annealing at 2800 °C, the compressible

SC

graphene aerogels, prepared according to the same protocols proposed by previously reported works [6, 12], lose their original high compressibility (Fig. S19). In addition, to eliminate the

M AN U

effect of microstructures on compressibility of the graphitic carbon-reinforced aerogels, IGAs with different cellular structures, such as disordered porous structure and aligned porous structure, are also fabricated using directional freezing method and modified freezing method (Fig. S20) [56]. Surprisingly, these aerogels all show high compressibility even after thermal

TE D

annealing at 2800 °C (Fig. S20). These results further confirm the unique superiorities and universality of our interfacial reinforcement approach for fabricating lightweight graphene aerogels combining excellent mechanical performances and superb electrical conductivities

EP

(Table S1).

The successful combination of good conductivity and superelasticity of IGA makes it an ideal

AC C

variable linear electrical resistor. The resistance of IGA0.22-2800 rapidly decreases with increasing the compressive strain, causing the connected bulb much brighter at the same time (Fig. S21a). The repeatability of the electronic resistance and the negligible resistance loss even after 10 loading-unloading cycles (Fig. S21b) further confirm the structural robustness. Additionally, the IGA with hierarchical honeycomb-like microstructures exhibits a negative Poisson’s ratio response when compressed. As shown in Fig. S22, the cylindrical IGA

16

ACCEPTED MANUSCRIPT

demonstrates hyperboloid shaped shrinkage in the macroscopic configuration and obvious contraction along the transverse direction under longitudinal compression. Thus, our IGA also shows a great potential for protective objects, such as body armors, shock absorbers, and packing

RI PT

materials [12].

Except for the above intriguing properties, the robust and porous IGA also exhibits strong adsorption capability for organic solvents with excellent recyclability. This originates from the

SC

typical hydrophobic nature of IGA, as evidenced by its much larger contact angle of 128.5° than that of RGO/PI (86.6°) (Fig. S23). IGA0.27-2800 with a density of ~8 mg cm-3 shows strong

M AN U

adsorption capability toward various organic solvents and a maximum capacity of 167 times its own weight for the collection of chloroform (Fig. 4a). The sorption capacity of our IGA is higher than those of previously reported adsorbents, such as ~1 time of activated carbons [57], 14 times of wool-based nonwoven [58], and 140 times of superoleophilic graphene modified foam [59].

TE D

Additionally, the robust, porous and integrated graphene framework presents excellent durability and recyclability in liquids and during high-temperature treatment, which is rarely reported for 3D aerogels with high adsorption capacities (Fig. 4b, Movie S1, S2) [60-62]. More importantly,

EP

the unique porous structure and wetting behavior of IGA afford the fast adsorption process that is crucial for practical applications. For example, IGA rapidly adsorbs the pump oil floating on the

AC C

water surface (Fig. 4c). The fast adsorption of ethanol can be completed within 3 seconds by a piece of IGA after its bottom touches the liquid surface (Fig. S24) and the adsorbed flammable ethanol can be removed by direct combustion to regenerate the IGA and its adsorption capacity remains almost unchanged even after 10 cycles of adsorbing-burning process (Fig. 4d,e). Microstructure observation reveals that the structural integrity and continuity of IGA are well retained as compared to its original counterpart (Fig. 1e and 4f,g). Therefore, the unique porous,

17

ACCEPTED MANUSCRIPT

hydrophobic structure of IGA enables it capable of strong and fast adsorption properties, and its graphitic carbon-reinforced robust structure imparts remarkable durability and stable recyclability. All these attributes lend our lightweight IGA great promise as an ideal adsorbent

AC C

EP

TE D

M AN U

SC

RI PT

for organic pollutant removal.

Fig. 4. Oil uptake behavior of IGA. (a) Adsorption capacities of IGA for various organic liquids. (b) Photographs showing structural stability of IGA against vigorous stirring in water. (c) IGA adsorbing pump oil colored with Sudan III dye. (d) Recyclability of IGA adsorbing sponge. (e)

18

ACCEPTED MANUSCRIPT

Digital images and (f, g) SEM images showing the intact structure of IGA after 10 adsorbing-burning cycles.

RI PT

4. Conclusions

We demonstrate an efficient and facile interfacial reinforcement approach for fabricating lightweight, porous and integrated graphene architectures by using the graphitic carbon derived

SC

from PI precursor to interconnect graphene sheets. Thermal annealing of RGO/PI aerogel at 2800 °C plays critical roles in both improving the quality of graphene by ultimately removing the

M AN U

residual oxygen-containing groups and defects of the RGO component and converting the insulating PI component to graphitic carbon by graphitization. The porous and robust IGA versatilely integrates various intriguing attributes, including remarkable electrical conductivity of more than 1000 S m-1, superb EMI shielding performance of larger than 83 dB over the X-band

TE D

frequency range, reversible compressibility even under 90% strain, excellent resistance to fatigue for 1000 cycles at 50% of strain, and strong adsorption capacity with recyclability, which makes it appealing to the field of flexible electronics, acoustic/energy damping, current collector in

EP

electrodes, microwave pollution control, and contaminates absorbents.

AC C

Acknowledgments

Financial support from the National Natural Science Foundation of China (51673015, 51373011, 51533001) and the Fundamental Research Funds for the Central Universities (BHYC1707B, YS201402) is gratefully acknowledged. Appendix A. Supplementary data References

19

ACCEPTED MANUSCRIPT

[1] Z. Chen, C. Xu, C. Ma, W. Ren, H.M. Cheng, Lightweight and Flexible Graphene Foam Composites for High-Performance Electromagnetic Interference Shielding, Adv. Mater. 25(9) (2013) 1296-1300.

RI PT

[2] L. Lv, P. Zhang, H. Cheng, Y. Zhao, Z. Zhang, G. Shi, et al., Solution-Processed Ultraelastic and Strong Air-Bubbled Graphene Foams, Small 12(24) (2016) 3229-3234.

[3] Y. Qin, Q. Peng, Y. Ding, Z. Lin, C. Wang, Y. Li, et al., Lightweight, Superelastic, and

SC

Mechanically Flexible Graphene/Polyimide Nanocomposite Foam for Strain Sensor Application, ACS Nano 9(9) (2015) 8933-8941.

M AN U

[4] Z. Chen, W. Ren, L. Gao, B. Liu, S. Pei, H.M. Cheng, Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition, Nat. Mater. 10(6) (2011) 424-428.

[5] H.L. Gao, Y.B. Zhu, L.B. Mao, F.C. Wang, X.S. Luo, Y.Y. Liu, et al., Super-elastic and

TE D

fatigue resistant carbon material with lamellar multi-arch microstructure, Nat. Commun. 7 (2016) 12920.

[6] L. Qiu, J.Z. Liu, S.L.Y. Chang, Y. Wu, D. Li, Biomimetic superelastic graphene-based

EP

cellular monoliths, Nat. Commun. 3 (2012) 1241. [7] Y. Wu, N. Yi, L. Huang, T. Zhang, S. Fang, H. Chang, et al., Three-dimensionally bonded

AC C

spongy graphene material with super compressive elasticity and near-zero Poisson’s ratio, Nat. Commun. 6 (2015) 6141.

[8] H. Chen, F. Guo, Y. Liu, T. Huang, B. Zheng, N. Ananth, et al., A Defect-Free Principle for Advanced Graphene Cathode of Aluminum-Ion Battery, Adv. Mater. 29(12) (2017) 1605958.

20

ACCEPTED MANUSCRIPT

[9] Y. Zhang, Y. Huang, T. Zhang, H. Chang, P. Xiao, H. Chen, et al., Broadband and Tunable High-Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam, Adv. Mater. 27(12) (2015) 2049-2053.

Aerogels, Adv. Mater. 25(18) (2013) 2554-2560.

RI PT

[10] H. Sun, Z. Xu, C. Gao, Multifunctional, Ultra-Flyweight, Synergistically Assembled Carbon

[11] T. Liu, M. Huang, X. Li, C. Wang, C.X. Gui, Z.Z. Yu, Highly Compressible Anisotropic

SC

Graphene Aerogels Fabricated by Directional Freezing for Efficient Absorption of Organic Liquids, Carbon 100 (2016) 456-464.

M AN U

[12] Q. Zhang, X. Xu, D. Lin, W. Chen, G. Xiong, Y. Yu, et al., Hyperbolically Patterned 3D Graphene Metamaterial with Negative Poisson's Ratio and Superelasticity, Adv. Mater. 28(11) (2016) 2229-2237.

[13] H. Hu, Z. Zhao, W. Wan, Y. Gogotsi, J. Qiu, Ultralight and Highly Compressible Graphene

TE D

Aerogels, Adv. Mater. 25(15) (2013) 2219-2223.

[14] Y. Xu, K. Sheng, C. Li, G. Shi, Self-Assembled Graphene Hydrogel via a One-Step Hydrothermal Process, ACS Nano 4(7) (2010) 4324-4330.

EP

[15] M. Yang, N. Zhao, Y. Cui, W. Gao, Q. Zhao, C. Gao, et al., Biomimetic Architectured Graphene Aerogel with Exceptional Strength and Resilience, ACS Nano 11(7) (2017)

AC C

6817-6824.

[16] B. Yao, J. Chen, L. Huang, Q. Zhou, G. Shi, Base-Induced Liquid Crystals of Graphene Oxide for Preparing Elastic Graphene Foams with Long-Range Ordered Microstructures, Adv. Mater. 28(8) (2016) 1623-1629. [17] G. Xin, T. Yao, H. Sun, S.M. Scott, D. Shao, G. Wang, et al., Highly thermally conductive and mechanically strong graphene fibers, Science 349(6252) (2015) 1083-1087.

21

ACCEPTED MANUSCRIPT

[18] Z. Li, Z. Xu, Y. Liu, R. Wang, C. Gao, Multifunctional non-woven fabrics of interfused graphene fibres, Nat. Commun. 7 (2016) 13684. [19] B. Shen, W. Zhai, W. Zheng, Ultrathin Flexible Graphene Film: An Excellent Thermal

RI PT

Conducting Material with Efficient EMI Shielding, Adv. Funct. Mater. 24(28) (2014) 4542-4548. [20] G. Xin, H. Sun, T. Hu, H.R. Fard, X. Sun, N. Koratkar, et al., Large-Area Freestanding Graphene Paper for Superior Thermal Management, Adv. Mater. 26(26) (2014) 4521-4526.

SC

[21] J. Chen, T. Shi, T. Cai, T. Xu, L. Sun, X. Wu, et al., Self healing of defected graphene, Appl. Phys. Lett. 102(10) (2013) 103107.

M AN U

[22] L. Peng, Z. Xu, Z. Liu, Y. Guo, P. Li, C. Gao, Ultrahigh Thermal Conductive yet Superflexible Graphene Films, Adv. Mater. 29(27) (2017) 1700589.

[23] H. Wang, W. Lu, J. Di, D. Li, X. Zhang, M. Li, et al., Ultra-Lightweight and Highly Adaptive All-Carbon Elastic Conductors with Stable Electrical Resistance, Adv. Funct. Mater.

TE D

27(13) (2017) 1606220.

[24] Q. Song, F. Ye, X. Yin, W. Li, H. Li, Y. Liu, et al., Carbon Nanotube–Multilayered Graphene

Edge

Plane

Core–Shell

Hybrid

Foams

for

Ultrahigh-Performance

EP

Electromagnetic-Interference Shielding, Adv. Mater. 29(31) (2017) 1606220. [25] Y. Chen, H.B. Zhang, M. Wang, Q. Xin, A. Dasari, Z.Z. Yu. Phenolic Resin-Enhanced

AC C

Three-Dimensional Graphene Aerogels and Their Epoxy Nanocomposites with High Mechanical and Electromagnetic Interference Shielding Performances. Compos. Sci. Technol. 152 (2017) 254-262.

[26] Y. Lin, F. Liu, G. Casano, R. Bhavsar, I.A. Kinloch, B. Derby, Pristine Graphene Aerogels by Room-Temperature Freeze Gelation, Adv. Mater. 28(36) (2016) 7993-8000.

22

ACCEPTED MANUSCRIPT

[27] H. Bi, I.W. Chen, T. Lin, F. Huang, A New Tubular Graphene Form of a Tetrahedrally Connected Cellular Structure, Adv. Mater. 27(39) (2015) 5943-5949. [28] G.M. Bower, L.W. Frost, Aromatic polyimides, J. Polym. Sci., Part A: Gen. Pap. 1(10)

RI PT

(1963) 3135-3150.

[29] N.C. Stoffel, C.A. Dai, E.J. Kramer, T.P. Russell, V. Deline, W. Volksen, et al., High-Resolution Profiling of the Polyimide−Polyimide Interface, Macromolecules 29(21) (1996)

SC

6880-6891.

[30] M.A. Worsley, P.J. Pauzauskie, T.Y. Olson, J. Biener, J.H. Satcher, T.F. Baumann,

M AN U

Synthesis of Graphene Aerogel with High Electrical Conductivity, J. Am. Chem. Soc. 132(40) (2010) 14067-14069.

[31] F. Qian, P.C. Lan, M.C. Freyman, W. Chen, T. Kou, T.Y. Olson, et al., Ultralight Conductive Silver Nanowire Aerogels, Nano Lett. 17(12) (2017) 7171-7176.

37(3) (1958) 711-718.

TE D

[32] F.M. Smits, Measurement of sheet resistivities with the four-point probe, Bel. Syst. Tech. J.

[33] M. Wang, X. Duan, Y. Xu, X. Duan, Functional Three-Dimensional Graphene/Polymer

EP

Composites, ACS Nano 10(8) (2016) 7231-7247. [34] X. Xu, Q. Zhang, Y. Yu, W. Chen, H. Hu, H. Li, Naturally Dried Graphene Aerogels with

AC C

Superelasticity and Tunable Poisson's Ratio, Adv. Mater. 28(41) (2016) 9223-9230. [35] R. Rozada, J.I. Paredes, S. Villar-Rodil, A. Martínez-Alonso, J.M.D. Tascón, Towards full repair of defects in reduced graphene oxide films by two-step graphitization, Nano Res. 6(3) (2013) 216-233.

[36] D.L. Duong, G.H. Han, S.M. Lee, F. Gunes, E.S. Kim, S.T. Kim, et al., Probing graphene grain boundaries with optical microscopy, Nature 490(7419) (2012) 235-239.

23

ACCEPTED MANUSCRIPT

[37] K.H. Kim, Y. Oh, M.F. Islam, Graphene coating makes carbon nanotube aerogels superelastic and resistant to fatigue, Nat. Nanotechnol. 7(9) (2012) 562-566. [38] O. Frank, M. Mohr, J. Maultzsch, C. Thomsen, I. Riaz, R. Jalil, et al., Raman 2D-Band

RI PT

Splitting in Graphene: Theory and Experiment, ACS Nano 5(3) (2011) 2231-2239.

[39] C. Faugeras, A. Nerrière, M. Potemski, A. Mahmood, E. Dujardin, C. Berger, et al., Few-layer graphene on SiC, pyrolitic graphite, and graphene: A Raman scattering study, Appl.

SC

Phys. Lett. 92(1) (2008) 011914.

[40] J.A. Robinson, M. Wetherington, J.L. Tedesco, P.M. Campbell, X. Weng, J. Stitt, et al.,

M AN U

Correlating Raman Spectral Signatures with Carrier Mobility in Epitaxial Graphene: A Guide to Achieving High Mobility on the Wafer Scale, Nano Lett. 9(8) (2009) 2873-2876. [41] M.S. Dresselhaus, A. Jorio, M. Hofmann, G. Dresselhaus, R. Saito, Perspectives on Carbon Nanotubes and Graphene Raman Spectroscopy, Nano Lett. 10(3) (2010) 751-758.

TE D

[42] J. Yang, X. Li, S. Han, Y. Zhang, P. Min, N. Koratkar, et al., Air-dried, high-density graphene hybrid aerogels for phase change composites with exceptional thermal conductivity and shape stability, J. Mater. Chem. A 4(46) (2016) 18067-18074.

EP

[43] S.H. Song, K.H. Park, B.H. Kim, Y.W. Choi, G.H. Jun, D.J. Lee, et al., Enhanced Thermal Conductivity of Epoxy–Graphene Composites by Using Non-Oxidized Graphene Flakes with

AC C

Non-Covalent Functionalization, Adv. Mater. 25(5) (2013) 732-737. [44] N. Song, X. Hou, L. Chen, S. Cui, L. Shi, P. Ding, A Green Plastic Constructed from Cellulose and Functionalized Graphene with High Thermal Conductivity, ACS Appl. Mater. Interfaces 9(21) (2017) 17914-17922.

24

ACCEPTED MANUSCRIPT

[45] X. Zeng, J. Sun, Y. Yao, R. Sun, J.B. Xu, C.P. Wong, A Combination of Boron Nitride Nanotubes and Cellulose Nanofibers for the Preparation of a Nanocomposite with High Thermal Conductivity, ACS Nano 11(5) (2017) 5167-5178.

RI PT

[46] Z. Zeng, H. Jin, M. Chen, W. Li, L. Zhou, Z. Zhang, Lightweight and Anisotropic Porous MWCNT/WPU Composites for Ultrahigh Performance Electromagnetic Interference Shielding, Adv. Funct. Mater. 26(2) (2016) 303-310.

SC

[47] Y. Yang, M.C. Gupta, K.L. Dudley, R.W. Lawrence, Novel Carbon Nanotube−Polystyrene Foam Composites for Electromagnetic Interference Shielding, Nano Lett. 5(11) (2005)

M AN U

2131-2134.

[48] M.H. Al-Saleh, W.H. Saadeh, U. Sundararaj, EMI shielding effectiveness of carbon based nanostructured polymeric materials: A comparative study, Carbon 60 (2013) 146-156. [49] N. Li, Y. Huang, F. Du, X. He, X. Lin, H. Gao, et al., Electromagnetic Interference (EMI)

1141-1145.

TE D

Shielding of Single-Walled Carbon Nanotube Epoxy Composites, Nano Lett. 6(6) (2006)

[50] E.J. Takahashi, Y. Nabekawa, K. Midorikawa, Low-divergence coherent soft x-ray source

EP

at 13 nm by high-order harmonics, Appl. Phys. Lett. 84(1) (2004) 4-6. [51] W.L. Song, X.T. Guan, L.Z. Fan, W.Q. Cao, C.Y. Wang, M.S. Cao, Tuning

AC C

three-dimensional textures with graphene aerogels for ultra-light flexible graphene/texture composites of effective electromagnetic shielding, Carbon 93 (2015) 151-160. [52] J. Liu, H.B. Zhang, R. Sun, Y. Liu, Z. Liu, A. Zhou, et al., Hydrophobic, Flexible, and Lightweight MXene Foams for High-Performance Electromagnetic-Interference Shielding, Adv. Mater. 29(38) (2017) 1702367.

25

ACCEPTED MANUSCRIPT

[53] R. Sun, H.B. Zhang, J. Liu, X. Xie, R. Yang, Y. Li, et al., Highly Conductive Transition Metal Carbide/Carbonitride(MXene)@polystyrene Nanocomposites Fabricated by Electrostatic Assembly for Highly Efficient Electromagnetic Interference Shielding, Adv. Funct. Mater.

RI PT

27(45) (2017) 1702807.

[54] G. Gradoni, D. Micheli, V. Mariani Primiani, F. Moglie, M. Marchetti, Determination of the electrical conductivity of carbon/carbon at high microwave frequencies, Carbon 54 (2013)

SC

76-85.

[55] F. Moglie, D. Micheli, S. Laurenzi, M. Marchetti, V. Mariani Primiani, Electromagnetic

M AN U

shielding performance of carbon foams, Carbon 50(5) (2012) 1972-1980.

[56] H. Bai, Y. Chen, B. Delattre, A.P. Tomsia, R.O. Ritchie, Bioinspired large-scale aligned porous materials assembled with dual temperature gradients, Sci. Adv. 1(11) (2015). [57] M.A. Lillo-Ródenas, D. Cazorla-Amorós, A. Linares-Solano, Behaviour of activated

TE D

carbons with different pore size distributions and surface oxygen groups for benzene and toluene adsorption at low concentrations, Carbon 43(8) (2005) 1758-1767. [58] M.M. Radetić, D.M. Jocić, P.M. Jovančić, Z.L. Petrović, H.F. Thomas, Recycled

1008-1012.

EP

Wool-Based Nonwoven Material as an Oil Sorbent, Environ. Sci. Technol. 37(5) (2003)

AC C

[59] H. Zhu, D. Chen, W. An, N. Li, Q. Xu, H. Li, et al., A Robust and Cost-Effective Superhydrophobic Graphene Foam for Efficient Oil and Organic Solvent Recovery, Small 11(39) (2015) 5222-5229.

[60] H. Bi, X. Xie, K. Yin, Y. Zhou, S. Wan, L. He, et al., Spongy Graphene as a Highly Efficient and Recyclable Sorbent for Oils and Organic Solvents, Adv. Funct. Mater. 22(21) (2012) 4421-4425.

26

ACCEPTED MANUSCRIPT

[61] H. Bi, X. Huang, X. Wu, X. Cao, C. Tan, Z. Yin, et al., Carbon Microbelt Aerogel Prepared by Waste Paper: An Efficient and Recyclable Sorbent for Oils and Organic Solvents, Small 10(17) (2014) 3544-3550.

RI PT

[62] H. Bi, Z. Yin, X. Cao, X. Xie, C. Tan, X. Huang, et al., Carbon Fiber Aerogel Made from Raw Cotton: A Novel, Efficient and Recyclable Sorbent for Oils and Organic Solvents, Adv.

AC C

EP

TE D

M AN U

SC

Mater. 25(41) (2013) 5916-5921.

27

ACCEPTED MANUSCRIPT

Highlights Lightweight, highly conductive and superelastic graphene aerogels are fabricated

RI PT

An interfacial reinforcement approach is proposed to reinforce graphene networks Highly reduced graphene sheets are well interconnected with graphitized polyimide carbon The aerogel shows satisfactory conductivity and EMI shielding performance (83 dB)

AC C

EP

TE D

M AN U

SC

It shows excellent resistance to fatigue and reversible compressibility

28