Alumina, A Good Accelerant for Cellulose

Jun 6, 2017 - Very recently, we developed a simple and facile in situ reduction and cross-linking strategy to fabricate a high strength integrated art...
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Reduced Graphene Oxide/Alumina, a Good Accelerant for Cellulose-Based Artificial Nacre with Excellent Mechanical, Barrier and Conductive Properties Kiran Shahzadi, Xueming Zhang, Imran Mohsin, Xuesong Ge, Yijun Jiang, Hui Peng, Huizhou Liu, Hui Li, and Xindong Mu ACS Nano, Just Accepted Manuscript • Publication Date (Web): 06 Jun 2017 Downloaded from http://pubs.acs.org on June 7, 2017

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Reduced Graphene Oxide/Alumina, A Good Accelerant for Cellulose-Based Artificial Nacre with Excellent Mechanical, Barrier and Conductive Properties Kiran Shahzadi,a Xueming Zhang, bImran Mohsin,c Xuesong Ge,a Yijun Jiang,a* Hui Peng, a Huizhou Liu, a Hui Li,a Xindong Mua* a. Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China. E-mail: [email protected]; [email protected]. Fax: +86-53280662724; Tel: +86-532-80662725. b. Beijing Forestry University, Beijing Key Lab Lignocellulos Chemistry, Beijing 100083, Peoples R China. c. Shenzhen Institute of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, China. ABSTRACT: In this paper, a simple strategy was employed to fabricate bio-inspired hybrid composite with carboxymethyl cellulose (CMC), graphene oxide and reduced graphene oxide/alumina (rGO/Al) by a facile solution casting method. The tensile strength and toughness of rGO/Al-CMC-GO can reach 586.6±12 MPa, 12.1±0.44 MJm-3, respectively, due to the interface strengthening of alumina, which is 1.43 and 12 times higher than steel and about 4.3 and 6.7 times that of nature nacre. The artificial nacre hybrid composite is conductive due to the introduction of rGO/Al on the surface. Interestingly this structure can also be coated on the surface of cotton thread to give the thread good mechanical performance and conductivity. Additionally, the artificial nacre has better fire shielding and gas barrier properties. The oxygen permeability (OP) for 1%rGO/Al- CMC decreased from 0.0265 to 0.003 mLµm m-2 day-1 kpa-1, the water vapour permeability (WVP) decreased from 0.363 to 0.205 gmmm-2 day-1 kpa-1 when the concentration increased from 1%rGO/Al to 6% rGO/Al. It is believed this work provided a simple and feasible strategy to fabricate ultra-strong and ultra-tough graphene based artificial nacre multi-functional materials. KEYWORDS: ultra-strong, ultra-tough, reduced graphene oxide and alumina, conductivity, barrier properties As conventional structural materials reach their performance limits, one of the major scientific challenges for the 21st century is the development of new high performance, multifunctional materials to support advances in diverse strategic fields, ranging from building and transportation to energy and biotechnology. 1 In the last decade, the structure of nacre has received enormous attention for its extraordinary combination of stiffness, toughness, and strength.2, 6 Natural nacre develops a hierarchical microstructure through a bio mineralized process to optimize its mechanical properties. The excellent mechanical performance of this biological material originates from a hierarchically ordered arrangement

of two-dimensional (2D) aragonite platelets and soft biopolymer layers, which is alternately stacked into a brick and-mortar structure.7, 8 Recently, great attempts have been made to fabricate artificial composites by mimicking the second level of hierarchy in nacre and built layered composites through a range of assembly techniques based on inorganic micro/nanoplatelets. The employed micro/nanoplatelets include clays, 9, 16 Al2O3, 17, 19and other artificial platelets.20, 21 Graphene, a twodimensional lattice of sp2-bonded carbon that is only one-atom thick, exhibits extraordinary properties as the strongest and stiffest material ever measured22 and is the best-known electrical conductor could have

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Promising applications in many fields.23, 24 All above exclusive characters makes it an excellent candidate as the “bricks” for fabricating nacre-like composites. In this perspective, many graphene-based artificial nacres (GBAN) have been reported. Very recently, the mechanical performance (tensile strength and toughness) for these GBAN were also well summarized by Cheng Qufeng.25 For example, An Zhi 26 demonstrated ultra-stiff artificial nacre (tensile strength of 160±18 MPa, toughness of 0.14 MJm-3) through borate orthoester covalent bonding between GO nanosheets (GO-borate), Tian and his co-workers also demonstrated high-strength artificial nacre (tensile strength of 209.9 MPa. toughness of 0.23 MJm3) through covalent bonding between polydopamine (PDA)-modified GO nanosheets and poly (ether imide) (PEI) polymers.27Similarly ， Zhang 28 fabricated reduced GO materials with ultrahigh strength and toughness with poly (acrylic acid-co-(4acrylamidophenyl) boronic acid) (PAPB), which interacts extremely well with GO nanosheets. The tensile strength (382 MPa) and toughness (7.5 MJ m-3) reach two and four times higher than those of natural nacre (tensile strength of 80-135MPa, toughness of 1.8 MJm-3), respectively. Very recently, we developed a simple and facile in-situ reduction and cross-linking strategy to fabricate a high strength integrated artificial nacre based on sodium carboxy methyl cellulose (CMC) and borate cross-linked graphene oxide (GO) sheets. The tensile strength and toughness of cellulose based hybrid material reached to 480.5±13.1 MPa and 11.8 ±0.4 MJm-3 which are 3.55 and 6.55 times that of nature nacre. 29 Although lots of

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achievements for the designing and fabricating of GBAN (Graphene based advance nanomaterial) have been made, GBAN is still in its early stages the mechanical of GBAN would be greatly enhanced by the synergistic effects of designing interface interactions and combining different building blocks.30 But, optimization of the tensile strength often comes at the expense of toughness. [30] So it is still a great challenge to develop some simple and facile methods to obtain integrated bio-inspired layered materials, which exhibit high tensile strength and toughness simultaneously. Additionally, it is also desirable to give the GBAN added-function. In this paper, a facile solution casting method was employed to fabricate bio-inspired hybrid composite with carboxymethyl cellulose, graphene oxide and reduced graphene oxide/alumina. The artificial nacre has the following advantages I. Ultra-strong and ultra-tough. The tensile strength and toughness of CMC-reduced GO/alumina can reach 586.6±12 MPa, 12.1±0.44 MJm3, respectively, due to the interface strengthening of alumina, which is 1.43 and 12 times higher than steel 31, 32 and about 4.3 and 6.7 times of that of nature nacre.32 II. Green and sustainable. Instead of commercial polymer, sustainable bio-based polymer CMC was employed to act as organic composition; III. Conductive. The artificial nacre hybrid composites are conductive due to the introduction of reduced graphene oxide/alumina on the surface. It is believed this research work provided a simple and feasible strategy to fabricate ultra-strong and ultra-tough graphene based artificial nacre functional materials.

Figure1: Schematic illustration for preparation process of rGO/Al-CMC-GO hybrid film RESULT AND DISCUSSION Figure.1 is showing the whole process for fabricating rGO/Al-CMC-GO hybrid film. Firstly, the Al nuclei are

continuously precipitated on the surface of GO as the water evaporated, and then all Al nuclei are

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transformed in to Al oxide material and GO is reduced by oxidation and calcination under high temperature.33, 35During this Process, agglomeration of GO is prevented because Ԉ-electron-stacking

between GO planes is weakened by coating Al material. Secondly, the rGO/Al was dispersed in CMCGO solution and then casting the solution to form the GBAN.

Figure 2: Digital image of rGO/Al-CMC-GO hybrid film (a) SEM image for rGO/Al powder (b) SEM-EDS mapping for alumina in rGO/Al (c) SEM image for 1%rGO/Al-CMC-GO (d) EDS spectra for 1%rGO/Al-CMC-GO (e) and SEM-EDS mapping for alumina indicating uniform distribution in hybrid film (f) This rGO/Al can be well dispersed in CMC to form a homogenous solution (Figure S1 Supporting Information) which also indicated the agglomeration of rGO is prevented in our process. At last, in order to get a conductive GBAN, the rGO/Al sol was coated on the surface of GBAN. It can be clear observed that the cross-section of the blank CMC is smooth with SEM images (Figure S1, Supporting Information), after the introduction of GO, the bio-based hybrid materials showed typical nacre-like structure (Figure S1, Supporting Information). SEM images for rGO/Al clearly showing similar morphology like GO. Amorphous alumina deposited on rGO as shown in Figure 2b. SEM show that the alumina was coated on the surface of GO tightly and the average size of alumina ranged from 4 nm to 14 nm. The average value for particle size found 8nm with a standard deviation of 2 nm (Figure S2 Supporting Information). To get further information about the surface of rGO/Al, atomic force microscopy (AFM) was employed. It is found the height of rGO/Al found approx. 16nm with variation of 0.6nm, which is larger than the size of alumina particle due to the existence of GO layer. (Figure S3 Supporting Information) At last, the thermogravimetric analysis (TG) was conducted to calculate the amount of alumina in rGO/Al. The TG results showed that the amount of alumina and GO in the rGO/Al is 59.8 wt% and 40.2 wt% respectively (Figure S2 d).While X-ray photoelectron spectroscopy (XPS) in Figure 2c demonstrated the existence of alumina in rGO /Al. It should be noticed that the SEM images of rGO/Al-CMC-GO showing well-

ordered layered structure in Figure 2(d). In hybrid film with high concentration of rGO and alumina aligned sheet like arrangement took place with little aggregation as shown (Figure S1 Supporting Information). EDS spectra and SEM-EDS mapping further confirmed alumina presence and well distribution in resultant nanocomposite Figure 2(e-f). XRD and FTIR analysis of rGO/Al composite powder and rGO/Al-CMC-GO further confirmed the reduction of GO with alumina. XRD patterns of GO, rGO/Alcomposite powder and rGO/Al-CMC-GO are shown in (Figure S4, Supporting Information). In GO a sharp peak identified at 10.80o, corresponds to an interlayer distance of 7.6 Å (d 002) due to overlapping of GO sheets. While in rGO/Al a broad peak observed at 23.5o after removal of water molecules and oxide groups, which also indicated that the alumina coating prevented the overlapping of GO sheet.35From inset of Figure S4(Supporting Information) it is clear that XRD patterns for rGO /Al-CMC-GO hybrid films have almost have no difference due to well dispersion and small quantity. FTIR was employed to give the information about the structural changes of the assynthesized samples (Figure 3a). It can be seen that the GO shows two peaks at 1620 cm-1 and 1724 cm-1, which were attributed to C=C and C=O respectively. When GO was reduced with alumina (1% rGO /AlCMC-GO), the peaks at 1620 cm-1 and 1724 cm-1 were absent, indicating the reduction of GO with alumina. Due to removal of some oxygen containing groups these peaks also found absent in 1%GO-CMC hybrid films after partial reduction.28 Furthermore in pure

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Figure 3: FTIR spectrum for GO,CMC,rGO/Al ,1%rGO/Al-CMC-GO (a) Raman spectrum for GO, rGO/Al , 1%rGO/Al-CMC-GO (b) C1s XPS spectrum for GO (c) C1s XPS spectrum for rGO/Al (d) O1s XPS spectrum for rGO/Al (e) Al2p spectrum (1-3) for alumina , rGO/Al ,1% rGO/Al-CMC-GO respectively (f). CMC and 1%GO-CMC peak at 3370 cm-1 that can be assign to O-H group almost diminish in 1%rGO/AlCMC due to reduction of GO. For pure CMC, peaks at 1050 cm-1, 1600 cm-1 can be assigned to typical C-O stretching and symmetrical modes of carboxylate ions. [36] In rGO/Al and rGO/Al-CMC two peaks at 1400 cm-1 and 1595 cm-1 detected that can be attributed to alumina.37, 38 In which peaks at 1400cm-1 and 1595 cm-1 can be due to surface species of alumina and O-H bending respectively. Additionally, comparing with1%CMC-GO being sharper, there was a peak shift from 1050 cm-1 to 1080 cm-1 in 1% rGO /Al-CMC indicating some interaction between CMC and alumina. 39 Raman spectra of GO showed two peaks at 1340 cm-1 (D band) and 1598 cm-1 (G band) that can be assign to first order scattering of the E2g phonon of sp2 carbon atoms and size of in plane sp2 domains

respectively.33The D/G intensity ratio for GO, rGO/Al, rGO/Al-CMC-GO found 1.2 ,1.6 , 1.58 respectively. This increase in D/G intensity ratio that is actually due to increase in the number of sp2 domains further confirming GO reduction in CMC at high temperature and with alumina (Figure 3b).Similarly the D/G intensity for 1%GO-CMC found more than GO (Figure S4 Supporting Information)indicating partial reduction in hybrid, this result agreed well with our previous experiments .29Finally UV-Vis spectroscopy was employed to characterize, rGO/Al, rGO/Al-CMCGO film (Figure S4 Supporting Information). It is found the peak centred at 233 nm with GO (π→π* transitions of the aromatic C=C bonds) shifted to 270 nm for rGO/Al and rGO/Al-CMC-GO film. That is also further indication of reduction for rGO/Al-CMC-GO.

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Figure 4: Stress-strain curves for CMC, CMC-Al+3, CMC-Al , 1%GO-CMC, 1%GO-CMC+Al+3 ,1%rGO/Al-CMC-GO (a) Tensile strength and toughness for all hybrid films with different (%) rGO/Al ( b )Tensile strength comparison of present work with other reported hybrids and structural steel and (c) fracture morphology of modified film (d). XPS analysis were further conducted to explore the interaction of alumna with GO after reduction as shown in Figure 3c. The high resolution C1s XPS spectrum of GO showing diverse functional groups C=C (282.61 eV), C–O (284.6 eV) and C–O–C or C=O bonds (286.12 eV). 40, 41 While increased C=C peak at 284.8 eV and decreased signal intensity of C–O at

286.9 eV in C1s XPS spectrum of rGO-Al further indicates the reduction of GO (Figure 3d). A change in peak shift of C=C from 284.2eV to 284.8eV can be attributed to reduction of GO with alumina. 24, 30 UV vis-spectrum and XPS analysis collectively suggested that the Al on the surface of GO has some interaction with the rGO, and also reacted with CMC.

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Furthermore, the GO can also be reduced by CMC, then has some interaction with CMC as our previous report. 29So, these bindings between Al-rGO, Al-CMC, and CMC-rGO would really help to improve film final strength. The mechanical performance of all the films was evaluated. It is found the strength and toughness of the pure CMC film are 98.8±4.8 MPa and 3.8±0.8 MJm-3 respectively (Figure 4 a). Addition of Al+3 ions in to CMC could increase the strength and toughness to reach 112 ± 3.5 MPa, and 3.85 ±0.6 MJm-3. Comparing with Al+3 same concentration of alumina can also increase the strength and toughness of CMC film to get 127.8± 5.5 MPa and 3.9±0.4 MJm-3, indicating the alumina can increase the strength of the CMC film more due to the interaction between the alumina and CMC. Compared with alumina, when GO was added to the CMC film, the strength and toughness can be improve very much due to the m reduction as our previous reported 29 strength and toughness of GOCMC film can reach to 293.5±4.5 MPa and 8.6±0.5 MJm-3 when 0.4% GO was added and found maximum 376.7±5.6 MPa and 9.8±0.4 with 1% GO. Increasing concentration of GO more than 1% can reduce film strength as shown in (Figure S5, Supporting information).Which can be attributed to the agglomeration of GO layers. Interestingly introduction of Al+3 in 1%CMC-GO media can improve strength and toughness up to 478.6 ± 4.5 MPa and 10.2 ± 0.3 MJm-3 respectively. Crosslinking of Al+3 with GO and CMC can be possible reason for such kind of improvement in mechanical strength.43 For comparison we also prepared rGO/Al-CMC hybrid films. Like GO increasing concentration of rGO/Al strength and toughness increased gradually and found maximum 495.2±2.3 MPa and 10.3±0.3MJm-3 respectively for 1%rGO/Al-CMC. While increasing concentration of rGO/Al more than 1% resulted in reduction of strength like GO (Figure S5c and 4a). To improve the mechanical performance of the bio hybrid film further, the rGO/Al was employed utilizing two step method. In which initially in-situ reduction of 1%GO in CMC media, improve the strength to certain extent while introduction of rGO/Al improve the strength further. Surprisingly, introduction of rGO/Al can significantly improve the mechanical properties for hybrid film. That can be due to strong covalent bonding between the alumina and rGO. The tensile strength and toughness for bio hybrid film of 1%rGO/Al-CMC-GO is 586.6 ± 12 MPa,12.1± 0.44MJm -3, respectively, which is about 2 and 1.4 times of GO-CMC film, 6 and 3.3 times of that of pure CMC. It should be noticed that this data of strength for rGO-CMC hybrid film is higher than that of structure steel (400Mpa) 31, 4.3 times that of natural nacre (80-135MPa).32 To the best of our knowledge, this rGO-CMC showed the highest strength among the reported GO-CMC films. Comparing with some GO-hybrid i.e. GO/Gelatin and GO/Cellulose 44, 45most of hybrids showed less strength than 1%rGO/Al-CMC-GO. For example, 2.85 times that of

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rGO-PDA (204.9MPa) 33, 1.11 times that of rGO-CS (526 MPa) 46, 2.14 times that of rGO-CNC (273MPa) 47, 1.89 times that of rGO-PAA (309MPa) 48, 1.53 times of rGO-PAPB (382MPa). 28 For the toughness, this hybrid film is 6.7 times higher than that of natural nacre (1.8MJm-3) 32and 12 times than that of steel(1.0 MJm3)31. At the same time, the mechanical property for the hybrid film is superior to other previous reported artificial nanocomposites such as (MTM-PVA12, GOPMMA49,rGO-PAPB 28 ,rGO-PDA 33,GO-PCDO 52, (GOSL ,rGO-SL)51, GO-Borate 26, GO-PEI 27, GO-GA 50, rGODWNT-PCDO)53, (GO-MoS2-TPU, rGO-MoS2TPU)54,(GO-Mg2+,GO-Ca2+)55,(GO-PVA, rGO –PVA )56 shown in Figure 4(c).This high strength of hybrid film can be illustrated by strengthen mechanism of material interface (Figure 4d). For pure CMC, the strength is derived from the interaction of CMC molecules by hydrogen and ionic bonding. When the GO was introduced into the film, except the interaction among CMC molecules, the interaction between CMC and GO play an important role to increase the strength of the film. The energy to destroy the interface energy of GO-CMC must be much higher than that of CMC-CMC. When the GO was reduced by alumina, then there will exist a strong interaction between rGO and alumina due to the introduction of some covalent bond.35 When the rGO/Al was introduced into the CMC film, there are more interface (CMC-CMC, CMC-rGO, CMC-Al, rGO-Al) to be broken during pulling or external force in the film. It can be expected that the energy to break CMCAl, rGO-Al much higher than that of CMC-GO. It is well known that water content has great effect on mechanical properties of GO-based biofilm. For this a series of relative humidity’s (RHs) such as 25%, 50%, 75%, and 100% were tuned by environmental conditions. The mechanical properties of pure CMC, 1%GO-CMC, 1%rGO/Al-CMC-GO under different RHs were tested that contained tensile strength, toughness and tensile strain. From Figure 5(a-c) it is clear there was prominent decrease in tensile strength and toughness at high RHs. The tensile strength for rGO/Al-CMC was reduced from 586.6±12.1MPa to 510.5±4.5MPa, when the humidity is changed from 25% to 100%. In the same condition, for GO-CMC, the tensile strength was reduce form 376.7±5.6 MPa to 302.5± 2.5 MPa. Obviously, the tensile strength of GOCMC is more sensitive than rGO/Al-CMC-GO due to the hydrophilic character of GO. While the toughness of GO-CMC are not sensitive to RH due to better extensibility under high RH. To further prove the water stability of rGO/Al-CMC-GO, the film of CMC, GO-CMC and rGO/Al-CMC-GO was immerged in water. It is found the pure CMC film dissolved within 30 min, the film of GO-CMC dissolved within 90 min, while the film of rGO/Al-CMC-GO could not be dissolved even after 24 h. This result strongly suggested the rGO/Al probably produced some bonding net in the film, which was also proved by the FTIR, Raman, XPS.

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These results found consistent with theoretical prediction by simulation. 57 As is known that the rGO can show excellent conductivity due to its different structure. So, in our hybrid film the alumina coated rGO sheets was coated on the surface of hybrid film to improve film conductivity. Resistivity measurements confirmed successful reduction of GO with alumina and conductivity of rGO/Al-CMC-GO film. While pure CMC and GO-CMC were not conductive as shown in Figure 6a.This can be due to electrical insulating properties of CMC and GO. 56 So bio-hybrid films with

varying concentration of rGO/Al were analysed for conductivity. Film resistivity values reduced with increasing the concentration of rGO/Al content in CMC. When concentration of rGO/Al increased from 1 to 6% film resistivity values decreased gradually and found minimum 0.5KΩ/Sq. This was further demonstrated in Figure S6 (Supporting Information) in which 1%GO-CMC did not flash the LED lamp while for hybrid films with different contents of rGO/Al lightened the LED lamp and its intensity increased with more concentration of

Figure 5: The effect of relative humidity on (a) tensile strength (b) Young’s modulus (c) tensile strain for pure CMC and 1%GO-CMC, 1% rGO/Al-CMC hybrid films (d) water stability (1) for pure CMC after 30 minutes and (2)1%GO-CMC after 90 min (3) 1%GO+CMC after 2 hours (4) and (5) rGO/Al-CMC-GO after 2 and 24 hours respectively.

rGO /Al. This increase in conductivity can be attributed to the uniformly dispersed rGO/Al sheets which make conductive networks in insulating matrix. While in case of GO more oxygen containing groups destroy its conductivity. Interestingly all modified films had flexibility. Even film with 3%rGO/Al content could be twisted and folded without any damage and LED lamp flashed well under this condition as shown in Figure S6, (Supporting Information). The thermogravimetric (TGA) and differential thermogravimetric (DTG) analysis were used to characterize the thermal properties of CMC, 1%GOCMC and 1% rGO/Al-CMC-GO composite films. It is clear from the Figure 6(c) that residual weight percent of 1% rGO/Al-CMC found higher than pure CMC and 1%GO-CMC which can be attributed to excellent thermal stability of rGO.41 From (DTG) curves as shown in inset of Figure 6(c) the initial,

maximum and final decomposition temperatures for CMC were 290 °C, 332 °C 370 °C. While for 1%GOCMC and 1%r GO/Al-CMC-GO hybrid film were 331 °C, 390 °C and 422 °C and 391 °C, 445°C and 495°C respectively. Thus rGO/Al in CMC with excellent mechanical properties also make it thermally stable, the initial decomposition temperature can be increased about 100 °C due to the introduction of alumina. Alumina coated rGO sheets homogenously dispersed in CMC provide extra thermal stability. To improve the applicability of our methods, the method was also employed to coat cotton thread to give the thread good mechanical performance and conductivity. Intersestingly, the successfully coated cottoton thread not only exibited improved strength (Figure S7 Supporting Information), but also show good conductivity as shown in (Figure S8 Supporting Information). It should be noticed that coating of

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rGO/Al-CMC-GO do not not effect on fibers flexibility as shown in (Figure S9 Supporting Information). So this method can be easily applied in large scale by simple coating. This thermally stable hybrid films also showed improved barrier properties which can be due to coating of alumina on rGO sheets. These rGO/Al composites can be excellent filler for improving barrier properties of polymer matrix, which protect CMC film from absorption of water and oxygen molecules from surroundings.58 Figure S10 Supporting Information) demonstrated the effect of rGO/Al loading on barrier properties on modified films. In our case extremely low oxygen permeability (OP) was observed with increasing concentration of

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rGO/Al in resultant component. The oxygen permeability (OP) for 1%rGO/Al-CMC-GO decreased from 0.0265 to 0.003 mLµm m-2 day-1 kpa-1 when the concentration increased from 1%rGO/Al to 6% rGO/Al (Figure S8 Supporting Information). The hybrid film also showed good water vapour permeability (WVP) Figure S10 Supporting Information). WVP values decreased from 0.363 to 0.205 gmmm-2 day-1 kpa-1 for 1%rGO/Al-CMC and with 6% rGO/Al-CMC-GO it reduced to 0.150 gmmm-2 day-1 kpa-1. In this work bio hybrid film also showed good fire retardant behaviour with alumina and rGO. Such kind of rGO/Al-CMC-GO films can be used to protect flammable biological materials from burning

Figure 6 : Resistivity graph with different rGO/Al content and inset showing (1) pure CMC and (2) GO-CMC are nonconductor while (3) hybrid film of rGO/Al –CMC is conductive (a) Circuit scheme with Lightening of LED with 6%rGO/Al-CMC (b) DTG curves with inset of TG curves for (1) for pure CMC (2)1%GO-CMC(3)1%rGO/Al-CMC (c) Fire shielding behaviour of 1%rGO/Al-CMC which can protect cotton wool more than one minute (d).

in short time. A piece of cotton took few seconds to burn, while placed behind the modified film did not catch the fire even after two minutes as shown in Figure S11 and movie provided in Supplementary Information. From SEM image of Fig S11, Supporting Information) it is clear that our multifunctional biofilm did not change its shape even after one minute when exposed to fire, owing to the alumina coating and rGO sheets with strong interaction of CMC. The limit oxygen index (LOI) values of CMC and other modified films with different concentration of GO and rGO /Al contents are shown in (Fig S11 Supporting Information). The LOI value for pure CMC found 23.8% indicating it is flammable polymeric material. It can be seen clearly that introduction of rGO /Al in the CMC improved its LOI value from 23.8 to 30.4%. The

alumina introduction can increased the carbon forming of the film and reduce the permeability of the oxygen. Considering this extra property in modified film, such an effort could contribute to finding variable, environmentally friendly alternatives for future fire-barrier materials CONCLUSION In summary, bio-inspired artificial nacre was fabricated with Carboxy methyl cellulose and reduced graphene oxide/alumina by a facile solution casting method. The artificial nacre is ultra-strong and ultratough. The tensile strength and toughness of CMCreduced GO/alumina can reach 586.6±12 MPa , 12.1±0.44 MJm-3, respectively, due to the interface strengthening of alumina, which about 4.3 and 6.7 times of that of nature nacre. The artificial nacre

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hybrid composite is flexible and conductive due to the introduction of reduced graphene oxide/alumina on surface. This artificial nacre structure can also be coated on the surface of cotton thread to give good mechanical performance. Additionally, the artificial nacre has better fire shielding and gas barrier properties which give the material multi-functions for application. It is believed this work provided a simple and feasible strategy to fabricate ultra-strong and ultra-tough graphene based artificial nacre multifunctional material. METHOD/EXPERIMENTAL Materials Graphite powder (