Starlite.pdf

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Article

Multifunctional Stiff Carbon Foam Derived from Bread Ye Yuan, Yujie Ding, Chunhui Wang, Fan Xu, Zaishan Lin, Yuyang Qin, Ying Li, Minglong Yang, Xiaodong He, Qingyu Peng, and Yibin Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b03985 • Publication Date (Web): 13 Jun 2016 Downloaded from http://pubs.acs.org on June 14, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Multifunctional Stiff Carbon Foam Derived from Bread Ye Yuan,1 Yujie Ding,1 Chunhui Wang,1 Fan Xu,1 Zaishan Lin,1 Yuyang Qin,1Ying Li,1 Minglong Yang,1 Xiaodong He,1 Qingyu Peng1,2*, Yibin Li1,* 1

Center for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150080, P. R. China 2

Division of Aircraft Dynamics and Control, School of Astronautics, Harbin Institute of Technology, Harbin 150080, P. R. China

ABSTRACT The creation of stiff yet multifunctional three dimensional porous carbon architecture at very low cost is still challenging so far. In this work, lightweight and stiff carbon foam (CF) with adjustable pore structure was prepared by using flour as basic element via a simple fermentation and carbonization process. The compressive strength of CF exhibits a high value of 3.6 MPa while its density is 0.29 g/cm3 (compressive modulus can be 121 MPa). The electromagnetic interference (EMI) shielding effectiveness measurements (specific EMI shielding effectiveness can be 78.18 dB·cm3·g-1) indicate that CF can be used as lightweight, effective shielding material. Unlike ordinary foam structure materials, the low thermal conductivity (lowest is 0.06 W/m·K) with high resistance to fire makes CF a good candidate for commercial thermal insulation material. These results demonstrate a promising method to fabricate an economical, robust carbon material for applications in industry as well as topics regarding environmental protection and improvement of energy efficiency. KEYWORDS: Carbon foam, tunable pore structure, mechanically stiff, EMI

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

shielding, thermal insulating INTRODUCTION Carbon foams have an interconnected three-dimensional cellular network, which endows them with many attractive performances including lightweight, adjustable thermal and electrical conductivity, high temperature tolerance and impact damping properties. Therefore, carbon foams have been widely used in various applications such as thermal management, aerospace, energy storage and damping absorption1-8. Creating foam structures using bottom-up approach allow tailoring of properties by integrating specific elements in suitable proportions. Although graphene sheets have been attracted tremendous interests and have been widely used in making monolithic foams,1, 9-14 the prepared foams are associated with conspicuous problems of poor mechanical stability. Further, fabrication graphene foams requires various complex operations, long time, and relatively high costs, making largescale production of graphene foams quite difficult. Thus, developing an environmentally friendly and inexpensive approach to fabricate mechanically stiff foams is still a great scientific and engineering challenge unresolved. Biomass is a qualified carbon raw material for the preparation of valuable carbon materials because it is available in high quality and huge amount, and is an environmentally friendly renewable resource. Recently, carbon foams based on biomass (such as watermelon,15, 16 lignin,17 bagasse,18 pomelo peel,19 banana peel,20 bacterial fiber,21, 22 bacterial cellulose23, 24 et al) have been successfully fabricated by different methods, including freeze-drying,25 hydrothermal treatment,26 ionothermal

ACS Paragon Plus Environment

Page 2 of 34

Page 3 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

carbonization (ITC),27 and direct carbonization.28,

29

Among these methods, direct

carbonization is the most commonly used and low-cost route. As a sustainable material, biomass can be directly transformed into carbon foam under proper carbonization conditions. These carbon materials have shown great potential in fields such as energy storage, oil absorption, drug delivery and catalysis. For instance, Wu et al.30 fabricated ultralight and flexible carbon nanofiber aerogels from bacterial cellulose by pyrolysis at a high temperature, which shows high oil absorption performance and fire resistance. However, for biomass derived foam structure material, uncontrollable inner pore structures have a huge impact on its mechanical stability, thermal or electromagnetic performance. What’ s more, the inherent limits on diversity of raw materials, together with the lack of structural control of inner pore morphology, present main challenges in fabricating tunable pore structure foams. These features would seriously restrict biomass derived foam materials into actual engineering applications. Herein，a low-cost, green and template-free carbonization method was adopted to form a tunable hierarchical morphology carbon foam with good mechanical stability, high EMI shielding efficiency and thermal property. Different from previous reports on carbon foams or hierarchical porous structures, 31 our carbon foam is a self-assembled structure that uses flour as basic element and inherits the shape and original hierarchical network structure from the bread. The carbon foam is mechanically stiff and able to sustain a considerable load without deformation. We demonstrated potential applications of the carbon foams as high performance

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

electromagnetic interference shielding and thermal insulating porous carbon materials with high fire resistance.

EXPERIMENTAL SECTION Materials. The flour and yeast were purchased from local supermarket. All water used to dissolve dry yeast and mix with flour is deionized (DI) water (18.2 MΩ, Milli-Q, Millipore Co.). Preparation of Carbon Foam. In a typical process, 5g dry yeast was dissolved in 115mL water by stirring. After completely dissolved, the mixture was poured into 300g flour, which was placed in a dough mixer in advance. The dough mixer kneaded slowly for about 10 minutes until wet flour cohered to a paste. The paste fermented for about 60 minutes at 35℃ to form the porous structures. Then, the bread was baked in an oven at 180℃ for 40 minutes. After that, the bread was sent into an oven to dry for 18 hours at 80℃. Finally, the dry bread was put into a laboratory tube furnace under Argon gas conditions to carbonize at different temperature. Heating rate was set as 10 ℃/min and the holding time was set as 120 min. Lastly, the sample was natural cooled in Ar atmosphere till room temperature. Materials Characterization. The surface morphology of carbon foam was characterized by field-emission scanning electron microscope (FESEM) (Carel Zeiss, supra55), whereas transmission electron microscopy (TEM) images were acquired on a TecnaiG220 transmission electron microscope operating at 160 kV. Fourier transform infrared (FT-IR) spectroscopy was obtained with a TENSOR 27 from Bruker. X-ray powder diffraction was conducted using a Philips X' Pert PRO

ACS Paragon Plus Environment

Page 4 of 34

Page 5 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

diffractometer with nickel-filtered Cu Kα radiation. Raman spectra were obtained with a Lab RAM HR800 from JY Horiba. The nitrogen sorptions of samples were measured at Autosorb iQ from Quantachrome Instruments. The apparent surface area was calculated using the BET method, at 77 K. The pore size distribution plots were recorded

from

the

desorption

branch

of

the

isotherms

based

on

the

Barrett-Joyner-Halenda (BJH) model. The carbon (C), nitrogen (N) and oxygen (O) contents of materials were analyzed using an X-ray photoelectron spectroscopy (XPS) (VG Scientific ESCALAB Mark Ⅱspectrometer). Element analysis of samples was also measured by EDS, Oxford Instrument. Thermal and EMI Performance Test. The thermal conductivity was tested using TPS 2500S from Hot Disk at room temperature. The tested samples were prepared by cutting into cylinder with R=30 mm, h =10 mm. The electrical conductivity was tested using PARSTAT 4000, Princeton Applied Research. The sample was cut into 30 mm×5 mm ×5 mm strips. Two silver wires were stuck to both small area side of the strip by elargol to connect the instrument for test. Transmission coefficient S and electromagnetic interference shielding were measured by Vector Network Analyzer (Agilent TechnologiesN5227A, USA). Wax was used as binder and matrix material for preparing samples. Two kinds of wax composites samples with different carbon foam content (10% and 30%) were prepared to make a comparison of dielectric properties.

RESULTS AND DISCUSSION Formation of Tunable Pore Structure Carbon Foam. We prepared carbon foam

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 34

with various densities (0.08 ~ 0.3 g/cm3) simply by adjusting the concentrations of starting materials. The unique advantages of the hierarchical pore structure can be further demonstrated by following performance test. The preliminary fabrication step is based on bread making process, subsequent carbonization sketch is illustrated in Figure 1, in which flour-based (containing glucose and protein) bread was used as a carbon source. After simply carbonized in Argon gas atmosphere, the dry bread was transformed into carbon foam. The original shape of pore structure remains but their size reduces compared with dry bread. This process comprised of two reactions, involving dehydration and carbonization. During carbonizing in Argon gas atmosphere, the following reaction would take place: (C6H10O5)n (starch)→6n C+5n H2O

(1)

Pore size and distribution are important factors determining the properties of porous carbon materials.32 Carbon foams with larger and irregular pores usually have a low density. The hierarchical pore structures can be tuned by many factors. In this work, two extremely important factors, yeast and water content, were investigated to realize the control of hierarchical morphology during fermentation process. The assumed evolution of pore growth process during fermentation was shown in Figure 2a. The left SEM image in Fig 2b shows carbon foam fabricated with dry yeast content of 0.5 g per 100 g flour (where 55ml water was added per 100 g flour). Near-round pores a few hundred of micrometers in size can be visible to the naked eye. On closer inspection, a mass of round pores concentratively distribute in the cell walls between two large neighboring pores. The size of these smaller pores ranges

ACS Paragon Plus Environment

Page 7 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

from few to several ten microns. A high magnification image is shown in Figure 2d, it can be observed that some of these pores are open structure, but some are covered with transparent hemisphere carbon film. The TEM image of the foam is also shown in Figure 2d. A series of oval pore with size in hundred nanometers can be observed. These nano-pores may come from the remove of impurity during carbonization. The above images reveal a hierarchical pore structure ranges from millimeter to nanometer scale. The middle SEM image in Figure 2b shows carbon foam fabricated with dry yeast content of 1.0 g per 100 g flour. Obviously, pores turn to be irregular, and many small pores randomly distribute in the cell walls. On further increasing the dry yeast to 1.5 g per 100 g flour, carbon foam with larger and disordered pore structure can be obtained. Also, quantities of minor pores in cell walls increased. The diameter of large pores can be as large as 2~3 millimeter. Figure 2c shows the cross section morphologies of carbon foam containing with different water content (the yeast content keeps 1.0 g per 100 g flour). Familiar with changing yeast content, the pores tend to be larger and irregular while adding more water. On the contrary, quantities of minor pores in the cell walls do not increase synchronously. Instead, these pores tend to become larger and irregular. We also characterize the specific surface area by BET analyzer. The maximum BET specific surface area of obtained carbon foam measured is 988 m2/g (for large and irregular pore structure), and the minimum value is only 19 m2/g (for round and regular pore structure), as shown in Figure 3f. Pore distributions measured by BET analyzer are illustrated in the inset picture in Figure 3f. It can be observed that pores with a

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

diameter of 3 nm and 5 nm domain in the micro-pore range, which shows the same trend in both of these two materials. Above all, by changing the content of yeast and water, inner pore structure and morphology can be simply tuned without any template. We further analyzed the pore growth process in the bread. Yeast and water provide a vital role during formation of pore structure. After adding water, the starches can be gelatinized and proteins in the flour fully absorb water to form a gluten network structure. Meanwhile, the yeast will produce and release carbon dioxide gases to form pores when dispersing in the paste. According to the balance of pressure, the process of pore growth would be affected by hydrostatic pressure and additional surface pressure of the paste, which can be expressed as: Pc= Pstat +Psurf

(2)

where Pc is the pressure that the released gases can be afforded. Pstat is the sum of atmospheric pressure and whole hydrostatic pressure. Psurf relates to surface tension and gluten network of pores. It is obvious that the pore morphology is closely associated with the gas pressure and strength of gluten network. Gas pressure mainly depends on the amount of gas produced from yeast, and strength of gluten network is closely related to the proportion of water adding into flour. When adding more yeast in the paste, both gas amounts and active site will increase. At the same time, the strength of gluten network will decrease after adding excess water. Finally, pore structure was determined under the balance of above two factors. It is worth noting that the pore shape and size would

ACS Paragon Plus Environment

Page 8 of 34

Page 9 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

be out of control once excessive amounts of yeast and water added in the paste. The composition of carbon foam was analyzed by XPS, XRD pattern, Raman spectroscopy and FT-IR spectroscopy. X-ray photoelectron spectroscopy (XPS) analysis in Figure 3a reveals changes in the nitrogen N 1s band for samples carbonized at 500ºC and 2000ºC. The content of nitrogen was estimated to be 2.95% carbonized at 500 ℃, but this value decreased to 0% when carbonized at 2000 ℃. Also, the content of oxygen decreased from 8.87% to 4.41%. This indicates the removal process of organics when increasing the carbonized temperature. The C1s spectrum ranging from 280.5 to 289 eV is shown in Figure 3b. After carefully being fitted toward C1s, it can be divided into three obvious peaks centering at ca. 284.58, 285.48 and 286.18 eV. For B500, the binding energy at ca. 284.5 eV can be attributed to sp2 C–sp2 C bonds, ca. 285.48 eV corresponding to sp3-C bonds, while ca. 286.49 eV assignable to C–O bonds. Figure 3c shows powder X-ray diffraction (XRD) in the wide-angle region of the carbon foam. Peak at 22.3º and a weak peak at 43.8º can be attributed to typical reflections from the (002) and (100) planes of disordered carbon materials. These weak diffraction peaks indicate that no graphitization occurred under the present carbonization process. [33] Raman spectroscopy is a powerful analytical tool for quantifying the properties of carbon materials. Two major Raman signals can be indented, as shown in Figure 3d. The peaks located at around 1320 and 1590 cm-1 are assigned to the characteristic D (defects and disorder) and G (graphitic) bands of carbon materials, respectively. The D/G ratio of band intensities indicates the degree of structural order with respect to a

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

perfect graphitic structure. Here, the D/G intensity ratios of B500, B1000, B1500 and B2000 were determined to be 1.12, 0.99, 0.91 and 0.69 respectively. The relatively lower D/G intensity ratio for B2000 might indicate a reduced amount of heteroatom doping (such as N and O). The high temperature is revealed to be a key factor in obtaining a high degree of carbonization with few defects in the carbon structure. Fourier transform infrared (FT-IR) spectroscopy was used to identify the surface functional groups of samples, as shown in Figure 3(e). The band at 3420 cm-1 is attributed to the O-H stretching vibrations. The observed bands at 1629 cm-1 are attributed to the C=C stretching vibrations. The bands at about 1450 ~ 1380 cm-1 can be attributed to C-H bending vibration. The bands at 1100 and 880 cm-1 can be ascribed to the C-O-C stretching vibration and deformation vibration of vinyl C-H, respectively[15].The apparent change of C-H vibration band at 1450 ~ 1380 cm−1 in Figure 3e suggests micro structure changes of carbon foam at different carbonized temperature. Mechanical Strength Figure 4a shows the compressive strength of CF carbonized at 1000 ℃ with different bulk density. It is observed that the compressive strength strongly depends on its bulk density. The insert simplified pore structure evolution indicates the effect of density to the pore structure. The maximum compressive strength of tested carbon foam is about 3.6 MPa with a low density of 0.29 g/cm3 and its compressive modulus can be about 121 MPa, which is higher than the values for previously reported carbon foams with the same density. This relatively high strength and modulus is related to the high moduli of carbon particle, and the fact that the

ACS Paragon Plus Environment

Page 10 of 34

Page 11 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

carbon particle makes the cell walls stiffer by crosslinking. Also, micro and macro structure plays a significantly important role in its mechanical property.1 What’s more, the unique interconnected 3D network structure attributes to the strong mechanical properties, suggesting that the CF have a great potential for robust 3D functional materials. Actually, the compressive strength and modulus may have a little difference for samples with almost the same density. This mainly attributes to the tiny difference of microstructure, which cannot be controlled so precisely by our method. In order to obtain a more reliable result, number of tested samples with the same carbonized temperature or same density was at least three. Finally, the obtained result is the mean values of tested results. Also, error bars were added according to standard deviation calculation. In order to explain the effect of pore structure on mechanical performance, a finite element method (FEM) was employed to analyze the stress distribution in a 2D cross section just prior to its sudden collapse. The affecting variables to compressive strength, such as porosity, pore shape and distribution, are briefly discussed in Supporting Information Figure S7. Figure S7c, e and g are the simplified simulation geometry for compression analysis that own larger porosity, different pore shape and disordered pore distribution compared with Figure S7a. Figure S7d, f and h are the maps of Mises stress on the x-y plane of the carbon foam. When applied with equal compressive stress from top of the block, it can be clearly seen that the maximum stress on the pore edge node in Figure S7a, is much smaller than that in Figure S7d, f and h. It means for carbon foam with larger porosity, irregular pore size and disordered pore distribution, they are easy to cause cracks under the same

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 34

mechanical compression. The trend of FEM analysis is in line with our experimental results. Figure 4b shows the corresponding compressive modulus of CF (all of the bulk densities range from 0.21 to 0.22 g/cm3) carbonized from 500 ℃ to 2000 ℃. It can be observed that the carbon foam carbonized at 1000 ℃ obtained the largest modulus. The compressive modulus of samples increased from 62.64 MPa to 121 MPa, when carbonized temperature rose from 500 ℃ to 1000 ℃. But, after that, modulus decreased when carbonized at higher temperature. For example, when the carbonized temperature reaches 2000℃, the modulus was down to 57.73 MPa. It can be concluded that 1000 ℃ is the best carbonized temperature if a stiff foam is required. The comparison of load state between real bread and carbon foam is shown in Figure 4c. It can be observed that the bread was squashed after a 100 g weight standing on it. Contrarily, the carbon foam is stiff enough to carry the same weight without deformation. The carbon foam can also stand on a bamboo leaf, which shows its light weight. EMI Shielding Efficiency Electromagnetic interference (EMI) shielding is currently in high demand for both commercial and defense purposes.11,

34-38

Conventional EMI shielding materials are usually heavy or unable to sustain a considerable load, especially in spaceship and aircraft. Thus, the CF provides a competitive candidate for the application in aerospace engineering. Figure 5a and b shows the electromagnetic parameters of wax composites, containing weight of 30% and 10% carbon foam (carbonized at 1000℃). As shown in Figure 5a, the ε′ and ε″

ACS Paragon Plus Environment

Page 13 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

values of ε′10% and ε″10% tend to keep steady at 3.30 and 0 with increasing frequency. However, the ε′ values of ε′30% decreases continuously from 11.51 to 8.72 until at 14.9 GHz and then increases to 9.53. The opposite situation occurs at the value of ε″30%, the ε″ values of ε″30% increases at first and then gradually decreases from its peak at 4.23 at 12.00 GHz to 2.16 at 18 GHz, with increasing frequency. It is also clearly observed that the value of ε′30% and are ε″30% significantly larger than those of ε′10% and are ε″10%. Likewise, tan δE of C30% is greater than that of C10% (Figure 5b). This indicates that C30%, as compared to C10%, exhibits higher storage and loss capabilities for electric energy. Permittivity behavior mainly attributes to the increase of electric conductivity. Usually, the permittivity values of carbon/resin composites increase with increasing loading of carbon particles, which is called percolation theory. The EMI shielding effectiveness of a material is defined as the ratio between the incoming power (Pin) and outgoing power (Pout) of an electromagnetic wave. In general, SE is expressed in decibels (dB). In this study, the EMI shielding effectiveness of CF was measured using an Agilent N5234A vector network analyzer. An electromagnetic wave was injected directly into the foam using a waveguide setup. Details on the EMI shielding effectiveness measurement of CF are provided in the Supporting Information. The measured CF was carbonized at 1000℃ with an electric conductivity of 0.26 S/cm. Because of the limit of the measurement equipment, we only analyzed the effectiveness scanned from 6.0 to 12.4 GHz range. It is observed in Figure 5d that the shielding effectiveness of CF is almost independent of the frequency in the measured frequency region. The shielding effectiveness of CF with

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

thickness 3 mm is measured to be about 15.7 dB over a frequency range of 6.0-12.4 GHz. This increment of the EMI shielding effectiveness is attributed mainly to the interconnected hierarchical carbon pore networks. The increased pores could attenuate the incident electromagnetic microwaves by reflecting and scattering between cell walls, and the microwaves were hard to escape from the CF before being absorbed and transferred to heat, as is shown in Figure 5c. The results also show that the EMI shielding effectiveness increases with increasing CF thickness. The EMI shielding effectiveness for CF with thickness of 4 mm and 5 mm is about 16.3 dB and 17.2 dB. For aircraft or aerospace applications, density has to be taken into consideration. The specific EMI shielding effectiveness (EMI shielding effectiveness divided by the density) is more appropriate for use in comparing the shielding performance between typical metals and CF. In this work, the specific EMI shielding effectiveness of measured CF (thickness is 3 mm) is calculated to be 71.36 dB·cm3·g-1, which is much higher than that of shielding metals (compared to 10 dB·cm3·g-1 for solid copper). We further analyzed the EMI shielding mechanism of CF. When an electromagnetic wave is incident on a shielding material, the incident power is divided into reflected power, absorbed power and transmitted power. The total EMI shielding effectiveness (SE) is the sum of the effectiveness of all attenuating mechanisms, including absorption (LA), reflection (LR), and can be expressed in the following equation: SE = 20log(1/|S12|)= LA (dB)+LR (dB), where LA=(1-|S11|2)/(|S12|2), and LR=1/(1-|S11|2). Figure 5e displays the electrical conductivity of CF as a function of carbonized temperature measured at room temperature. It can be seen that, the

ACS Paragon Plus Environment

Page 14 of 34

Page 15 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

conductivity sharply increases when increase the carbonized temperature from 500℃ (σ500= 1.94 × 10-8 S/cm) to 1000 ℃ (σ1000=0.263 S/cm). After enhancing the carbonized temperature to 1500℃ or 2000℃, the conductivity has a less increase. Figure 5f shows SE, LA and LR of CF as a function of electrical conductivity at the frequency of 9 GHz. Obviously, SE, LA and LR increase with increasing electrical conductivity. What’s more, the contribution of LA to the EMI shielding effectiveness is much larger than that of LR. It is observed that CF with a conductivity of 0.357 S/cm, SE, LA and LR are 18.37 dB, 3.40 dB and 16.97 dB, respectively. Through the above results, it is suggested that contributes more to the EMI SE of CF in this frequency region. This mainly attributes to the hierarchical pores which increase the reflection and scattering of microwave in the body of CF. The introduction of pores in CF body not only decreases its density but also increases the EMI efficiency. Thermal Performance Thermal insulation plays a major role in controlling the energy efficiency. Commercial organic thermal insulating materials often show poor fire resistance, along with toxicity problems. Therefore, developing new inorganic thermal insulating materials with high security to substitute for original flammable organic thermal insulation materials is significantly important. Figure 6a shows the thermal conductivity of carbon foam (bulk density ranges from 0.17~0.18 g/cm3) derived from different carbonization temperature. It is observed that the thermal conductivity of CF carbonized at 500℃ is as low as 0.06 W/m·K. When

raising

carbonized temperature to 2000℃, the thermal conductivity increased to 0.28 W/m·K. Actually, thermal conductivity of samples with the same treated condition has a tiny

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

difference. This is mainly attributed to the control of inner pore morphology of porous materials cannot be as precise as ensuring each sample the same. Thus, we prepared the measured samples as the same way with mechanical performance test. The thermal conductivity of each sample was measured for four times. Number of tested samples with the same carbonized temperature or same density was at least three. Finally, the obtained thermal conductivity is the mean values of tested results. Also, error bars were added according to standard deviation calculation. The low thermal conductivity of carbon foam can be related to the thermal properties of nano-sized components and the microstructure in the cell wall. Heat conduction in carbon materials is usually dominated by phonons, which can be explained by strong sp2 bonding resulting in efficient heat transfer by lattice vibrations.39, 40 When carbonizing at 500℃, the organics existed in the bread cannot be removed clearly. Also, the CF has a lower degree of intralayer condensation and disordered micro carbon structure with many defects. Those defects and impurity may reduce mean free path of phonon and impart an interfacial thermal resistance which reduce the conductivity.35 After raising the carbonizing temperature, the CF base would remain fewer and fewer impurity. At the same time, the micro carbon structure turns to be aligned with each other, which has been proved in above XPS and XRD analysis. Thus, less defects and rough edges in the sample contribute a high heat transfer. In order to investigate the effect of microstructure to heat transfer, thermal conductivity of carbon foam with different bulk densities (e.g. carbonized at 1000 ℃) was measured. Figure 6b shows the bulk density changes from 0.09 to 0.23 g/cm3 while thermal conductivity varying

ACS Paragon Plus Environment

Page 16 of 34

Page 17 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

from 0.08 to 0.17 W/m·K. Actually, thermal conductivity will increase for higher density samples. The relationship between thermal conductivity and porosity can be estimated according to K = (1-kε) K0

(3)

K is the thermal conductivity; K0 is the thermal conductivity when porosity is zero. k is the correction factor and ε is the actual porosity. For CF samples, bulk density is related to its porosity. Figure 6c illustrates the contribution of conduction, convection and radiation to thermal conductivity of carbon foam. Conduction includes solid conduction and gas conduction, and it is known that thermal conductivity of gas is much smaller than solid. Thus, the hierarchical pores shown in Figure 6c will all significantly contribute to thermal resistance. In order to show the contribution of hierarchical structure to the thermal resistance, one-dimensional temperature distribution models were analyzed by finite element method (FEM) in Figure S8. Figure S8a and b represent two hypothetically ideal structures, large round pores and hierarchical pores. Temperature field of 300 ℃ and 25 ℃ is applied at the top and bottom boundaries of two models, respectively. After a steady state heat transfer process, the temperature distributions are shown in Figure S8. It is clearly observed that heat transfers slower at hierarchical pore structure than common single pore structure under the same condition. Further FEM thermal analysis on CF with different bulk density is shown in Figure S9. According to the experimental observation, irregular hierarchical pore

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

structure (IHPS) represents low density microstructure，and therefore porosity of IHPS is designed to be larger than that of uniform hierarchical pore structure (UHPS). Temperature field of 300 ℃ and 25 ℃ is applied at the top and bottom boundaries in Figure S9, respectively. After a steady state heat transfer process, the temperature distribution for UHPS and IHPS are shown in Figure S9c and 9d. Obviously, heat transfers faster at UHPS than that of IHPS under the same condition. The FEM analysis is consistent with our experimental results. Additionally, thermal conductivities of carbon foams keep a relatively low value. A challenge for general thermal insulating materials is their poor resistance to fire. The burning experiment in Figure 6d indicates our carbon foam has a high fire-resistance performance. These results show that the carbon foam is a good candidate for thermal insulation materials.

CONCLUSIONS We present a facile and green strategy for fabrication of lightweight yet stiff carbon foam with tunable pore structure. Key factors for making tunable pore structure carbon foam include control of yeast and water content. The carbon foam exhibited low thermal conductivity, favorable EMI shielding efficiency with high compressive modulus. Finally, this fabrication scheme could be broadly applied to other composite material structures for the myriad of technologies that require lightweight, low thermal conductivity, and high EMI shielding efficiency materials.

ASSOCIATED CONTENT Supporting Information

ACS Paragon Plus Environment

Page 18 of 34

Page 19 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Carbon yields at different carbonized temperature, EDS elemental analysis of samples carbonized at different temperature, EMI shielding measurement process, schematic of thermal transport measurement, finite element method for brief mechanical and thermal analysis, and the tested data statistic. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], Tel & Fax: +86-451-86402326 *E-mail: [email protected], Tel & Fax: +86-451-86402326 Author Contributions All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation in China (NSFC 11272109, 51503052), the Ph. D. Programs Foundation of Ministry of Education of China (20122302110065), the Fundamental Research Funds for the Central Universities (Grant No. HIT. BRETIII.201507) and China Postdoctoral Science Foundation funded project (Grant No. 2015M580259).

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

REFERENCES (1) Vinod, S.; Tiwary, C. S.; da Silva Autreto, P. A.; Taha-Tijerina, J.; Ozden, S.; Chipara, A. C.; Vajtai, R.; Galvao, D. S.; Narayanan, T. N.; Ajayan, P. M. Low-density Three-dimensional Foam Using Self-reinforced Hybrid Two-dimensional Atomic Layers. Nat. Commun 2014, 5,4541 (2) Xu, Y.; Sheng, K.; Li, C.; Shi, G. Self-Assembled Graphene Hydrogel via a One-Step Hydrothermal Process. ACS Nano 2010, 4, 4324-4330. (3) Yan, Z.; Ma, L.; Zhu, Y.; Lahiri, I.; Hahm, M. G.; Liu, Z.; Yang, S.; Xiang, C.; Lu, W.; Peng, Z.; Sun, Z.; Kittrell, C.; Lou, J.; Choi, W.; Ajayan, P. M.; Tour, J. M. Three-Dimensional Metal-Graphene-Nanotube Multifunctional Hybrid Materials. ACS Nano 2013, 7, 58-64. (4) Sudeep, P. M.; Narayanan, T. N.; Ganesan, A.; Shaijumon, M. M.; Yang, H.; Ozden, S.; Patra, P. K.; Pasquali, M.; Vajtai, R.; Ganguli, S.; Roy, A. K.; Anantharaman, M. R.; Ajayan, P. M. Covalently Interconnected Three-Dimensional Graphene Oxide Solids. ACS Nano 2013, 7, 7034-7040. (5) Geim, A. K.; Novoselov, K. S. The Rise of Graphene. Nat. Mater 2007, 6, 183-191. (6) Chen, Z.; Ren, W.; Gao, L.; Liu, B.; Pei, S.; Cheng, H. M. Three-dimensional Flexible and Conductive Interconnected Graphene Networks Grown by Chemical Vapour Deposition. Nat. Mater 2011, 10, 424-428. (7) Zhou, G.; Yin, L.C.; Wang, D. W.; Li, L.; Pei, S.; Gentle, I. R.; Li, F.; Cheng, H.M. Fibrous Hybrid of Graphene and Sulfur Nanocrystals for High-Performance

ACS Paragon Plus Environment

Page 20 of 34

Page 21 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Lithium-Sulfur Batteries. ACS Nano 2013, 7, 5367-5375. (8) You, B.; Jiang, J.; Fan, S., Three-Dimensional Hierarchically Porous All-Carbon Foams for Supercapacitor. ACS Appl. Mater. Interfaces 2014, 6, 15302-15308. (9) Hu, C.; Xue, J.; Dong, L.; Jiang, Y.; Wang, X.; Qu, L.; Dai, L. Scalable Preparation of Multifunctional Fire-Retardant Ultralight Graphene Foams. ACS Nano 2016, 10, 1325-1332. (10) Du, X.; Liu, H. Y.; Mai, Y. W. Ultrafast Synthesis of Multifunctional N-Doped Graphene Foam in an Ethanol Flame. ACS Nano 2016, 10, 453-462. (11) Nardecchia, S.; Carriazo, D.; Ferrer, M. L.; Gutierrez, M. C.; del Monte, F. Three Dimensional Macroporous Architectures and Aerogels Built of Carbon Nanotubes and/or Graphene: Synthesis and Applications. Chem. Soc. Rev 2013, 42, 794-830. (12) Chen, Z.; Xu, C.; Ma, C.; Ren, W.; Cheng, H. M. Lightweight and Flexible Graphene Foam Composites for High-Performance Electromagnetic Interference Shielding. Adv. Mater. 2013, 25, 1296-1300. (13) Sun, H.; Xu, Z.; Gao, C. Multifunctional, Ultra-Flyweight, Synergistically Assembled Carbon Aerogels. Adv. Mater. 2013, 25, 2554-2560. (14) Chen, W.; Li, S.; Chen, C.; Yan, L. Self-Assembly and Embedding of Nanoparticles

by In

Situ Reduced

Graphene

for Preparation

of a

3D

Graphene/Nanoparticle Aerogel. Adv. Mater. 2011, 23, 5679-5683. (15) Wu, X. L.; Wen, T.; Guo, H. L.; Yang, S.; Wang, X.; Xu, A. W. Biomass-Derived

Sponge-like

Carbonaceous

Hydrogels

ACS Paragon Plus Environment

and

Aerogels

for

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Supercapacitors. ACS Nano 2013, 7, 3589-3597. (16) Ren, Y. M.; Xu, Q.; Zhang, J. M.; Yang, H. X.; Wang, B.; Yang, D. Y.; Hu, J. H.; Liu, Z. M. Functionalization of Biomass Carbonaceous Aerogels: Selective Preparation of MnO2@CA Composites for Supercapacitors. ACS Appl. Mater. Interfaces 2014, 6, 9689-9697. (17) Yang, Y.; Tong, Z.; Ngai, T.; Wang, C. Nitrogen-Rich and Fire-Resistant Carbon Aerogels for the Removal of Oil Contaminants from Water. ACS Appl. Mater. Interfaces 2014, 6, 6351-6360. (18) Hao, P.; Zhao, Z.; Tian, J.; Li, H.; Sang, Y.; Yu, G.; Cai, H.; Liu, H.; Wong, C. P.; Umar, A. Hierarchical Porous Carbon Aerogel Derived from Bagasse for High Performance Supercapacitor Electrode. Nanoscale 2014, 6, 12120-12129. (19) Liang, Q.; Ye, L.; Huang, Z. H.; Xu, Q.; Bai, Y.; Kang, F.; Yang, Q. H. A Honeycomb-like Porous Carbon Derived from Pomelo Peel for Use in High-performance Supercapacitors. Nanoscale 2014, 6, 13831-13837. (20) Liu, R. L.; Yin, F. Y.; Zhang, J. F.; Zhang, J.; Zhang, Z. Q. Intestine-like Micro/mesoporous Carbon Built of Chemically Modified Banana Peel for Size-selective Separation of Proteins. RSC Adv. 2014, 4, 21465-21470. (21) Rojo, E.; Alonso, M. V.; Oliet, M.; Del Saz-Orozco, B.; Rodriguez, F. Effect of Fiber Loading on the Properties of Treated Cellulose Fiber-reinforced Phenolic Composites. Compos. Pt. B-Eng. 2015, 68, 185-192. (22) Zhang, Z.; Sebe, G.; Rentsch, D.; Zimmermann, T.; Tingaut, P. Ultralightweight and Flexible Silylated Nanocellulose Sponges for the Selective Removal of Oil from

ACS Paragon Plus Environment

Page 22 of 34

Page 23 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Water. Chem. Mater. 2014, 26, 2659-2668. (23) Svagan, A. J.; Samir, M. A. S. A.; Berglund, L. A. Biomimetic Foams of High Mechanical Performance Based on Nanostructured Cell Walls Reinforced by Native Cellulose Nanofibrils. Adv. Mater. 2008, 20, 1263-1269. (24) Wu, Z. Y.; Li, C.; Liang, H. W.; Chen, J. F.; Yu, S. H. Ultralight, Flexible, and Fire-Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose. Angew. Chem., Int. Ed. 2013, 52, 2925-2929. (25) Ren, Y.; Zhang, J.; Xu, Q.; Chen, Z.; Yang, D.; Wang, B.; Jiang, Z. Biomass-derived Three-dimensional Porous N-doped Carbonaceous Aerogel for Efficient Supercapacitor Electrodes. RSC Adv. 2014, 4, 23412-23419. (26) Sevilla, M.; Gu, W.; Falco, C.; Titirici, M. M.; Fuertes, A. B.; Yushin, G. Hydrothermal

Synthesis

of

Microalgae-derived

Microporous

Carbons

for

Electrochemical Capacitors. J. Power Sources 2014, 267, 26-32. (27) Zhang, P.; Gong, Y.; Wei, Z.; Wang, J.; Zhang, Z.; Li, H.; Dai, S.; Wang, Y. Updating Biomass into Functional Carbon Material in Ionothermal Manner. ACS Appl. Mater. Interfaces 2014, 6, 12515-12522. (28) Tao, X. Y.; Zhang, J. T.; Xia, Y.; Huang, H.; Du, J.; Xiao, H.; Zhang, W. K.; Gan, Y. P. Bio-inspired Fabrication of Carbon Nanotiles for High Performance Cathode of Li-S Batteries. J. Mater. Chem. A 2014, 2, 2290-2296. (29) Qian, W. J.; Sun, F. X.; Xu, Y. H.; Qiu, L. H.; Liu, C. H.; Wang, S. D.; Yan, F. Human Hair-derived Carbon Flakes for Electrochemical Supercapacitors. Energy Environ. Sci. 2014, 7, 379-386.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(30) Wu, Z. Y.; Li, C.; Liang, H. W.; Chen, J. F.; Yu, S. H. Ultralight, Flexible, and Fire-Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose. Angew. Chem., Int. Ed. 2013, 125, 2997-3001. (31) Chen, B.; Zhang, S.; Zhang, Q.; Mu, Q.; Deng, L.; Chen, L.; Wei, Y.; Tao, L.; Zhang, X.; Wang, K., Microorganism Inspired Hydrogels: Fermentation Capacity, Gelation Process and Pore-forming Mechanism Under Temperature Stimulus. RSC Adv. 2015, 5, 91937-91945. (32)

Barg, S.; Perez, F. M.; Ni, N.; do Vale Pereira, P.; Maher, R. C.;

Garcia-Tuñon, E.; Eslava, S.; Agnoli, S.; Mattevi, C.; Saiz, E., Mesoscale Assembly of Chemically Modified Graphene into Complex Cellular Networks. Nat. Commun 2014, 5,4328 (33) Pradhan, B. K.; Sandle, N. K., Effect of Different Oxidizing Agent Treatments on the Surface Properties of Activated Carbons. Carbon 1999, 37, 1323-1332. (34) Ma, J.; Zhan, M.; Wang, K. Ultralightweight Silver Nanowires Hybrid Polyimide Composite Foams for High-Performance Electromagnetic Interference Shielding. ACS Appl. Mater. Interfaces 2015, 7, 563-576. (35) Wen, B.; Cao, M.; Lu, M.; Cao, W.; Shi, H.; Liu, J.; Wang, X.; Jin, H.; Fang, X.; Wang, W.; Yuan, J. Reduced Graphene Oxides: Light-Weight and High-Efficiency Electromagnetic Interference Shielding at Elevated Temperatures. Adv. Mater. 2014, 26, 3484-3489. (36) Kumar, A.; Alegaonkar, P. S., Impressive Transmission Mode Electromagnetic Interference Shielding Parameters of Graphene-like Nanocarbon/Polyurethane

ACS Paragon Plus Environment

Page 24 of 34

Page 25 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Nanocomposites for Short Range Tracking Countermeasures. ACS Appl. Mater. Interfaces 2015, 7, 14833-14842. (37) Zhang, H. B.; Yan, Q.; Zheng, W. G.; He, Z.; Yu, Z. Z., Tough Graphene-Polymer Microcellular Foams for Electromagnetic Interference Shielding. ACS Appl. Mater. Interfaces 2011, 3, 918-924. (38) Cao, M. S.; Yang, J.; Song, W. L.; Zhang, D. Q.; Wen, B.; Jin, H. B.; Hou, Z. L.; Yuan, J., Ferroferric Oxide/Multiwalled Carbon Nanotube vs Polyaniline/Ferroferric Oxide/Multiwalled Carbon Nanotube Multiheterostructures for Highly Effective Microwave Absorption. ACS Appl. Mater. Interfaces 2012, 4, 6949-6956. (39) Balandin, A. A. Thermal Properties of Graphene and Nanostructured Carbon Materials. Nat. Mater 2011, 10, 569-581. (40) Mir Mohammad Sadeghi, I. J., and Li Shi. Phonon-interface Scattering in Multilayer Graphene on An Amorphous Support. PNAS 2013, 110, 16321-16326.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FIGURES AND CAPTIONS

Figure 1. Raw diagram for the fabrication of carbon foam derived from bread

Figure 2. (a) Micro structure evolution of bread by changing the content of yeast and water, SEM cross-section images of microscopic structures evolution of carbon foam: (b) water content keeps as 55 ml per 100 g flour, and the dry yeast content is 0.5 g, 1.0 g, 1.5 g per 100 g flour from left to right, (c) dry yeast content keeps as 1.0 g per 100 g flour, and water content is 50 ml, 55ml and 65 ml per 100 g flour from left to right, (d) Hierarchical pore structures, (e) Length scale of hierarchical pores.

Figure 3. (a) XPS spectra of B500 and B2000 samples, (b) C1s XPS spectra of B500 and B2000 samples, (c) XRD pattern, (d) Raman spectrum and (e) Infrared spectra of samples carbonized at 500℃(B500), 1000℃(B1000), 1500℃(B1500) and 2000℃(B2000) respectively, (f) The 77 K N2 sorption isotherms and corresponding pore size distributions for large pores (BL, with low bulk density) and small pores (BS, with high bulk density) samples.

Figure 4. (a) Stress–strain measurements of carbon foam with different bulk density carbonized at 1000℃, (b) Compressive moduli E of carbon foam carbonized at different temperature, bulk densities of measured sample are all between 0.21~0.22 g/cm3, (c) left: a 100g weight standing on a piece of bread, middle: a 100g weight standing on a carbon foam; right: the carbon foam standing on a bamboo leaf.

Figure 5. (a) Permittivity and (b) dielectric loss tangent characterization of the samples (C30% and C10%) in the 2~18 GHz range, (c) schematic representation of microwave transfer across the hierarchical pore structure of CF, (d) EMI shielding efficiency of carbon foam (carbonized at

ACS Paragon Plus Environment

Page 26 of 34

Page 27 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

1000℃, density is 0.22g/cm3): the thickness is 3 mm, 4 mm and 5 mm respectively, (e) electrical conductivity of CF carbonized at 500℃, 1000℃, 1500℃ and 2000℃, (f) the comparison of SE, microwave absorption (LA), and microwave reflection (LR) at f =9 GHz (the thickness of the samples is 3 mm)

Figure 6. Thermal conductivity of carbon foam (a) at different carbonized temperature of 500℃, 1000℃, 1500℃ and 2000℃, insert picture is alcohol lamp flame burning a flower standing on a thin carbon foam plate, (b) thermal conductivity carbonized at 1000℃ with different bulk density, (c) Schematic illustration of contributions to thermal conductivity in the foam with hierarchical pore structure, (d) burning an ethanol-soaked carbon foam results in a residue with a similar shape as the original shape，showing its fine fire resistance.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Raw diagram for the fabrication of carbon foam derived from bread

ACS Paragon Plus Environment

Page 28 of 34

Page 29 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Figure 2. (a) Micro structure evolution of bread by changing the content of yeast and water, SEM cross-section images of microscopic structures evolution of carbon foam: (b) Water content keeps as 55 ml per 100 g flour, and the dry yeast content is 0.5 g, 1.0 g, 1.5 g per 100 g flour from left to right, (c) Dry yeast content keeps as 1.0 g per 100 g flour, and water content is 50 ml, 55ml and 65 ml per 100 g flour from left to right, (d) Hierarchical pore structures, (e) Length scale of hierarchical pores.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. (a) XPS spectra of B500 and B2000 samples, (b) C1s XPS spectra of B500 and B2000 samples, (c) XRD pattern, (d) Raman spectrum and (e) Infrared spectra of samples carbonized at 500℃(B500), 1000℃(B1000), 1500℃(B1500) and 2000℃(B2000) respectively, (f) The 77 K N2 sorption isotherms and corresponding pore size distributions for large pores (BL, with low bulk density) and small pores (BS, with high bulk density) samples.

ACS Paragon Plus Environment

Page 30 of 34

Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Figure 4. (a) Stress–strain measurements of carbon foam with different bulk density carbonized at 1000℃, (b) Compressive moduli E of carbon foam carbonized at different temperature, bulk densities of measured samples are all between 0.21~ 0.22 g/cm3, (c) Left: a 100g weight standing on a piece of bread, middle: a 100g weight standing on a carbon foam; right: the carbon foam standing on a bamboo leaf.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5. (a) Permittivity and (b) dielectric loss tangent characterization of the samples (C30% and C10%) in the 2–18 GHz range, (c) Schematic representation of microwave transfer across the hierarchical pore structure of CF, (d) EMI shielding efficiency of carbon foam (carbonized at 1000℃, density is 0.22g/cm3): the thickness is 3mm, 4mm and 5mm respectively, (e) Electrical conductivity of CF carbonized at 500℃,1000℃,1500℃ and 2000℃, (f) The comparison of SE, microwave absorption (LA), and microwave reflection (LR) at f =9 GHz (the thickness of the samples is 3 mm)

ACS Paragon Plus Environment

Page 32 of 34

Page 33 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Figure 6. Thermal conductivity of carbon foam (a) at different carbonized temperature of 500℃, 1000℃, 1500℃ and 2000℃, insert picture is alcohol lamp flame burning a flower standing on a thin carbon foam plate, (b) Thermal conductivity carbonized at 1000℃ with different bulk density, (c) Schematic illustration of contributions to thermal conductivity in the foam with hierarchical pore structure, (d) Burning an ethanol-soaked carbon foam results in a residue with a similar shape as the original shape，showing its fine fire resistance.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents Graphic

A facile and green strategy for fabrication of lightweight yet stiff carbon foam with tunable pore structure is proposed.

ACS Paragon Plus Environment

Page 34 of 34