Cross-linked graphene oxide membrane functionalized with self-cross

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Cross-linked graphene oxide membrane functionalized with selfcross-linkable and bactericidal cardanol for oil/water separation Min-Young Lim, Yong-Seok Choi, Huiseob Shin, Kihyun Kim, Dong Myung Shin, and Jong-Chan Lee ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00241 • Publication Date (Web): 30 May 2018 Downloaded from http://pubs.acs.org on May 30, 2018

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ACS Applied Nano Materials

Cross-linked graphene oxide membrane functionalized with self-cross-linkable and bactericidal cardanol for oil/water separation

Min-Young Lim†,1, Yong-Seok Choi†,1, Huiseob Shin1, Kihyun Kim1, Dong Myung Shin2, and Jong-Chan Lee*,1

1

School of Chemical and Biological Engineering and Institute of Chemical Processes, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea

2

IT&E Materials R&D, LG Chemical Research Park, 188 Moonji-ro, Yuseong-gu, Daejeon 34122, Republic of Korea

*Corresponding author. Tel: +82-02-880-7070. E-mail: [email protected] (J.-C. Lee)

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ACS Applied Nano Materials 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

Abstract Cross-linked graphene oxide (GO) membrane was fabricated by a simple vacuum filtration which precedes to a thermal treatment on GO functionalized with renewable cardanol (cardanol-GO). The cardanol-GO was fabricated through the reactions between epoxy groups on GO surface and phenolic moiety of cardanol with the participation of catalyst. The prepared cardanol-GO membrane was then heated to form the cross-linked structure by the reactions between the double bonds of cardanol. The cross-linked GO membrane exhibited outstanding dimensional stability and oil/water separation efficiency. Furthermore, the crosslinked cardanol-GO membrane proved to contain marked antibacterial property against Escherichia coli (E. coli) which originates from cardanol moieties. Keywords: graphene oxide membranes, cardanol, ring opening, cross-linking, oil/water separation, antibacterial property


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1. Introduction Recently, graphene-based nanomaterials have attracted much attention as a novel membrane material for scientific research and industrial utilization as a consequence of exceptional mechanical strength, physiochemical stability, and unique two-dimensional structures.1-9 Especially, separation technologies such as water purification and gas separation have been the most promising field for GO membranes, because GO can be produced in large quantity by the oxidative exfoliation of graphite. Moreover, GO can be fabricated into membranes which have layered structure forming two-dimensional nanochannels by the simple processes such as drop-casting, vacuum filtration, layer-by-layer assembly, and spin coating.3-5,7-11 Since the unique planar nano size channels between the stacked GO layers that function like selective pathway for molecules and ions owing to the size sieving effect, the GO membranes have demonstrated excellent performance in the field of gas and liquid separations.4,5,7-9,12 Nevertheless, the practical application of GO as water treatment membrane has been finite due to its inherent hydrophilicity and electrostatically repulsive force between negatively charged GO layers in aqueous environment, leading to the disintegration of the membrane structure in the practical water purification process.10,13 In order to use the GO membranes as the high-performance separation membranes in an aqueous environment, the membrane structure and interlayer spacing should be maintained under the aqueous conditions. Since the oxygen functional groups in GO, for instance, carboxylic acid, hydroxy, and epoxy groups, can react with various organic molecules, chemical bonds such as covalent bond connecting the GO layers can be introduced to improve the physical or the chemical stability of the membranes. For example, the covalently cross-linked GO membranes having stability under aqueous condition could be prepared by the reaction of the oxygen functional groups in GO with the cross-linkers such as diamines, dicarboxylic acids, acyl chloride, and 1



polyethyleneimines.10,14,15 In addition to the cross-linking of the GO layers to improve the membrane stability, surface modification of the GO-based membranes can be also very advantageous for the practical filtration applications, such as liquid separation, because the selectivity of the membrane for the liquid separation is closely related to both the interlayer spacing and the surface properties of the membrane.16-20 In this work, GO membranes were constructed by a simple vacuum filtration process with GO functionalized with self-cross-linkable and bactericidal cardanol. Cardanol, extracted from cashew nut shell liquid, has been known to be one of the significant renewable resources, containing a phenolic moiety with an unsaturated C15 hydrocarbon chain that can be used to form the cross-linked structures by thermal curing and/or UV light irradiation.21,22 Therefore, this time it was possible to fabricate steady cross-linked cardanol-GO membrane by thermal curing of the cardanol-GOs and the resulting cross-linked cardanol-GO membrane also demonstrated antibacterial properties in addition to the superb dimensional stability and oil/water separation performance. We believe that this is the first report of the bactericidal properties of surface-modified GO membranes with a unique functional moiety, cardanol. The preparation and characterization of GO membranes functionalized with cardanol are fully researched in this paper.

2. Experimental 2.1 Materials All information related to the materials can be found in the Supporting Information. 2.2 Preparation of cardanol-functionalized GO (cardanol-GO) 2


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Graphene oxide (GO) was fabricated in observance of the modified Hummers method.23,24 GO (0.1 g) was put into 50 mL of DMSO and sonicated for a half hour. Cardanol (0.5 g, 1.7 mmol) and DMAP (0.2 g, 1.7 mmol) were added to the GO dispersion and the mixture was stirred under nitrogen (N2) atmosphere at 100 ºC for 3 days. The product was collected by vacuum filtration with an anodic aluminum oxide (AAO) membrane filter of 0.2 µm sized pores. The residue on the AAO membrane was washed with DMSO several times. After redissolved in DMSO and filtrated again, the residue was eventually washed using THF to remove any remaining reagents, including cardanol. The resulting solid (cardanol-GO) was dried in vacuo at 35 ºC overnight. 2.3 Preparation of cardanol-GO membrane First, a cardanol-GO suspension (0.1 mg mL-1) was prepared by adding 5 mg of cardanolGO to 50 mL of DMSO, followed by ultrasonication for 1 h. Then, the cardanol-GO dispersion was vacuum-filtered through a 0.45-µm-pore-size-PA membrane to form a cardanol-GO membrane on the PA support. The cardanol-GO layer was heated on a hot plate at 180 ºC for 5 h to produce a cross-linked membrane. The resulting membrane was referred to as a cardanol-GO membrane. To clarify the effect of cardanol moiety, a GO membrane was fabricated following the same vacuum filtration process as a control. 2.4 Characterization All instruments and detailed measurement methods are described in the Supporting Information. 2.6. Antibacterial tests

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Detailed procedures of two antibacterial tests, airborne test and shake flask test, are described in the Supporting Information.

3. Results and discussion 3.1 Preparation and characterization of cardanol-GO Cardanol-functionalized GO, named as cardanol-GO, was prepared from the reaction of GO with cardanol, catalyzed by DMAP, a base catalyst, as described in Figure 1; a base-catalyzed ring opening reaction between the phenolic group in cardanol and epoxy groups in GO proceeded.

Figure 1. Schematic diagram of the preparation of cardanol-GO

Figure S2a shows the FT-IR results of GO, cardanol, and cardanol-GO. In the spectrum of GO, a broad O-H stretching peak from the hydroxyl groups and the water adsorbed in GO at 3450 cm-1, a C=O peak from the ketone and carboxyl acid groups at 1740 cm-1, aromatic C=C and O-H bending peaks from phenolic groups at 1620 cm-1, a C-O peak from the epoxy 4


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groups at 1240 cm-1, and a C-O peak in the alkoxy groups at 1050 cm-1 are observed.24,30 On the contrary, the IR spectrum of cardanol-GO shows characteristic absorption peaks at 2926 and 2851 cm-1 corresponding to sp3 C-H stretching from the long alkyl chains in cardanol and a weak absorption peak at 3010 cm-1 corresponding to the C-H stretching from the unsaturated hydrocarbon in cardanol, indicating the incorporation of the cardanol moieties in GO.21,22 The C1s XPS spectrum of cardanol-GO also indicates the incorporation of the cardanol moieties in GO to form cardanol-GO (Figure S2b). The C1s XPS spectrum of GO was deconvoluted into four peaks C-C at 284.5 eV, C-O at 286.5 eV, C=O at 287.5 eV, and OC=O at 288.5 eV.14,26,27 The peak integration of the C-C groups in the C1s XPS spectrum of cardanol-GO is relatively larger than that of GO since the long alkyl chains in cardanol moieties are attached to the surface of GO. The amount of the grafted cardanol moiety on GO was estimated from the TGA curves for GO and cardanol-GO as demonstrated in Figure S2c. It is well-known that the weight loss below 300 ºC is due to the thermal reduction of the oxygen functional groups in GO, and that between 300-500 ºC is due to the thermal degradation of other moieties in GO.24,30 Therefore, 12 wt% weight loss between 300-500 ºC for cardanol-GO indicates the approximate amount of the cardanol moiety grafted on GO. The slightly smaller weight loss of cardanol-GO below 300 ºC than that of GO indicates that cardanol-GO contains less oxygen functional groups than GO. Since cardanol-GO was prepared at high temperature for a long reaction time (100 ºC for 3 day, the reduction of oxygen functional groups in GO could have occurred. The reduction was further confirmed by the red shift of 6 cm-1 in Raman spectra from 1603 cm-1 of the G band for GO to 1597 cm-1 for cardanol-GO (Figure S2d), as reported previously.28,29

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3.2 Fabrication and characterization of the cardanol-GO membrane

Figure 2. Schematic illustrations of (a) the fabrication process of the cardanol-GO membrane and (b) the formation of the covalently-bonded interlayer bridges between the cardanol-GO sheets

As synoptically depicted in Figure 2a, the procedure to prepare the cardanol-GO membrane is composed of two principal steps. In the first step, the cardanol-GO suspension (0.1 mg mL-1) was vacuum-filtrated onto the polyamide (PA) membrane with 0.45 µm pores. The GO sheets accumulate on the PA support, resulting to the formulation of planar nano size pathways between the stacked GO layers.7,9 In the second step, the prepared cardanol-GO layer on PA support was heated to cross-link the unsaturated C=C bonds in cardanol moiety 6


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on GO (Figure 2b). It is already reported that drying oils containing unsaturated bonds such as cardanol can be cross-linked under air through an autoxidation process which proceeds in several steps, for example, formation and decomposition of peroxides and polymerization. These oxidation processes can be promoted by heat or UV light.21,30 Therefore, the unsaturated bonds in cardanol-GO could be oxidized under air in the presence of heat to form cross-linked networks between the GO sheets. In particular, we could prepare the cardanol-GO membrane with a only small amount of cardanol-GO such as 5 mg in 50 mL of DMSO. This was found to the optimum amount to show the best membrane performance for the oil/water separation, as discussed in the later part of this paper. It was possible to monitor the development of cross-linked structure between the double bonds in cardanol-GO with FT-IR. Since the cross-linking reaction proceeds between the unsaturated bonds, the reaction state could be tracked by measuring the intensity fluctuation of the C-H stretching vibration peak at 3010 cm-1 from the unsaturated hydrocarbon in cardanol-GO. After the heating process, the decrease of the peak intensity was clearly observed, meaning that the double bonds in cardanol-GO had reacted, as indicated in Figure 3. As the cross-linked structure formulates, the dimensional stability of membrane should increase. In this context, by examining the stability of GO and cardanol-GO membrane in water by water-dipping test, the presence of cross-linked structure can be proved. After dipping the membranes, the GO membrane was readily destroyed and detached from the PA support with no physical stimuli, whereas the cardanol-GO membrane was not damaged in water, indicating that the introduction of covalently cross-linked structure into GO could increase the dimensional stability of GO-based membranes in the aqueous environments (Figure S4). In addition, after the heat treatment, the cardanol-GO layer remained intact in water without any detachment from the PA support, indicating that cardanol is the very 7



effective cross-linker between the GO sheet and PA support as well as between cardanolGOs.14

Figure 3. FT-IR spectra of cardanol and the cardanol-GO layer on the PA support and the cardanol-GO membrane

The microscale structural characteristics of the cardanol-GO membrane were observed by SEM. As demonstrated in Figure 4, the cardanol-GO membrane has typical wrinkled surface and lamellar structure of the GO-based membranes.15,31 In particular, the surface pattern of the cardanol-GO membrane did not change markedly even after the heating procedure, and the surface of the membrane remained continuous and crack-free. In addition, it can be inferred from the cross-section SEM images of the cardanol-GO membrane that GO sheets stacked on the PA support construct ordered layer-by-layer structure and adhere well to the PA support which can be explained by the effective cross-linking of cardanol moieties. The 8


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thickness values of the cardanol-GO layer on the PA support before and after the heat treatment were found to be about 2.3 µm and 1.6 µm, respectively. The thinner layer of the GO moieties in the cardanol-GO membrane than those in the cardanol-GO layer could be ascribed to the closer stacking of the cardanol-GO sheets resulting from the formation of covalently cross-linked structure through the heat treatment.32

Figure 4. SEM images of (a) the PA support, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane

The surface morphology of the cardanol-GO membrane was investigated by AFM (Figure 5). The PA support exhibited relatively rough surface (root-mean-square (RMS) of surface roughness = 0.378 µm) compared to the cardanol-GO membrane which showed less rugged surface with smaller RMS value of surface roughness (RMS = 0.210 µm) due to the uniform coating of cardanol-GO on the PA support. Especially, the RMS value of surface roughness 9



for the cardanol-GO membrane was found to be slightly smaller than that of the cardanol-GO layer on the PA support (before the heat treatment), indicating that the cardanol-GO sheets

stacked more compactly and uniformly through the heat treatment. Figure 5. AFM images of (a) the PA support, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane

To confirm the effect of formation of cross-linked structure numerically, the inter lamellar distance of the cardanol-GO membrane was examined by analyzing the XRD patterns. In Figure 6, the XRD patterns of GO membrane, cardanol-GO layer on the PA support and the cardanol-GO membrane are compared. The number with largest two theta value, 10.8°, is the cardanol-GO membrane which means that the cardanol-GO membrane has the smallest inter layer distance of 8.58 Å. The two-theta value of GO membrane is 10.3° which corresponds to the inter layer distance of 8.73 Å and it is similar to the previously reported results.7,14,15,33 10


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The wider inter layer distance between the cardanol-GO layer could be ascribed to the bulky cardanol moiety on GO expanding the distance between the GO layers. The heat treatment process forming the cross-linked structures of the cardanol-GO membrane results in the narrower inter layer distance, which is consistent with the SEM result in Figure 4.

Figure 6. XRD patterns of the GO membrane, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane

3.3 Oil/water separation performance The hydrophilic and/or hydrophobic characteristics of the membrane surface have been known to be one of the most significant properties to impart the oil/water selectivity of the membranes and they can be normally evaluated by water contact angle (WCA) measurement.21 In Figure 7, the water contact angle of the GO and the cardanol-GO membrane are compared. The GO membrane shows a hydrophilic nature with a water contact 11



angle of 35.8°, as reported previously8,12-14, while the cardanol-GO membrane was quite hydrophobic (water contact angle of 108.1°), indicating that the hydrophobic cardanol moieties on the surface of the cardanol-GO membrane can make the surface of the GO-based membrane quite hydrophobic. Interestingly, we also observed that the water contact angle of the cardanol-GO membrane is dependent on the thickness of the cardanol-GO layer on the PA support.

Figure 7. Water contact angle images of (a) the GO membrane and (b) the cardanol-GO membrane

For example, the water contact angle values of the cardanol-GO membranes prepared using 1.0, 5.0, and 10 mg of cardanol-GO in 50 mL of DMSO were found to be 97.7°, 108.1°, and 93.9°, respectively (Figure S6). It is still clear that the functionalization of GO with hydrophobic cardanol can reduce the hydrophilicity of the GO-based membrane surface because the water contact angle values of the cardanol-GO membranes prepared using different amounts of cardanol-GO are always larger than that of the GO membrane. The cardanol-GO membrane prepared using 5 mg of cardanol-GO exhibited a larger water contact angle value than the other cardanol-GO membranes. This may result from both of the 12


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hydrophobicity of the cardanol-GO membrane surface and the optimized dual-scale roughness of the membrane surface originating from the nanoscale roughness of GO and microscale roughness of the PA support.31,34 The microscale roughness of the PA support can be easily observed from the SEM and AFM images in Figure 4a and Figure 5a, respectively. The surface structure of the cardanol-GO membrane with the nanoscale roughness is shown in Figure S7, and similar nanoscale structures of the GO-based membranes have been reported previously.31,35 It is well-known that the hydrophobicity of the membrane can be improved using the hydrophobic coating materials and it can be further improved by formation of a micro/nanoscale hierarchically rough membrane surface, as reported by others. 31,34

It was found that the microscale rough surface structure of the PA support gradually

disappeared with increasing the amount of cardanol-GO shown in Figure S8. This could be further quantitatively proved by the RMS values of the membrane surfaces; they are 0.378, 0.354, 0.210, and 0.160 µm for the PA support, the cardanol-GO membranes prepared using 1.0, 5.0, and 10 mg of cardanol-GO, respectively. Still the cardanol-GO membrane prepared with 5 mg of cardanol-GO has the largest water contact angle value or the most hydrophobic surface, possibly because the microscale roughness of the PA support remains to some degree and the nanoscale roughness of the self-corrugated cardanol-GO sheets is also welldeveloped.31,34,35 For the cardanol-GO membrane prepared using very small amount of cardanol-GO (1 mg), the less hydrophobic PA support cannot be fully covered by the hydrophobic cardanol-GO, which makes the membrane surface less hydrophobic than that prepared with 5 mg of cardanol-GO loading.31 For the cardanol-GO membrane prepared using larger amount of cardanol-GO (10 mg), the microscale surface structure of PA support is not well-observed, and this in-turn lead to the decrease of water contact angle and the membrane hydrophobicity. Besides, because of the synergetic effect of the hydrophobic surface of the cardanol-GO membrane and the planar nano-size channels between cardanol13



GO layers in the membrane which could function as “oil favored” stoma, the planar nano-size channels between the cardanol-GO layers could enhance the selectivity of the membrane in oil/water process.36

Figure 8. Photographs of the oil/water separation tests using (a) a mixture of methylene chloride and water containing CuSO4 (1:1, v/v) and (b) a mixture of petroleum ether and water containing CuSO4 (1:1, v/v)

The membranes with a hydrophobic surface have been used to segregate oil from oil/water mixtures by the simple filtration process using gravity only.34,37 Therefore, the oil/water 14


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separation by the most hydrophobic cardanol-GO membrane prepared using 5 mg of cardanol-GO loading was tested. As shown in Figure 8, the membrane was sandwiched with the upper cylinder and the bottom filter flask of the filter apparatus and the separation process was conducted by gravity only. Methylene chloride readily spreads across the surface of the cardanol-GO membrane, while water (stained with CuSO4 to aid the observation) forms a bead, indicating that the membrane can allow oil to pass through, while block the water permeation (Figure S9). Therefore, when a mixture of methylene chloride and water containing CuSO4 (1:1, v/v) was poured into the upper cylinder, methylene chloride located in the bottom layer due to its higher density subsequently permeated through the hydrophobic membrane, while water remained on the membrane (Figure 8a). In addition, the collected methylene chloride in the bottom flask was found to be one phase without any separated phase, indicating that the oil/water separation was successfully achieved without any leakage of water through the cardanol-GO membrane. The water content in the collected methylene chloride after separation was found to be less than 1000 ppm, suggesting the high separation efficiency of the cardanol-GO membrane. However, when a mixture of petroleum ether and water was used, petroleum ether could not be separated from the mixture because lower and denser water layer could not pass through the hydrophobic membrane and it worked as a physical barrier to petroleum ether (Figure 8b). Therefore, the cardanol-GO membrane with a hydrophobic surface can be utilized in oil/water separation field of various oil species and/or organic reagents mixed with water.34 3.4 Antibacterial properties The antibacterial activity of the cardanol-GO membrane was examined using model bacteria (E. coli, ATCC 8739) by airborne bacteria tests. When the bacterial population on the membrane is denser than a specific concentration, bacteria attached on membrane can 15



produce biofilm layer through the quorum sensing effect, which can significantly decrease the flux of the membrane.38-41 Therefore, the bactericidal ability is one of the significant properties of membranes to maintain filtration efficiency for practical use. From Figure 9, it can be identified that no cell grew on both GO and cardanol-GO membrane, in contrast to the control study which shows plenty of cell colonies in the absence of either GO or cardanol-GO membrane.42

Figure 9. Photographs of E. coli growth on (a) the GO membrane and (b) the cardanol-GO membrane (incubation for 18 h at 37 ºC)

It is well-known that the antimicrobial property of GO originates from the unique sheetlike structure of GO. The basal planes in GO interact with bacteria causing oxidative stress and the edge of GO also cause cell damage by orthogonal contact.43,44 Since the GO membrane consists of flat stacking of GOs, the orthogonal cell contact with the edges of GO is not much expected, while the oxidative stress on bacterial cells mediated by the interactions with basal planes of GO is possible.44 Since the cardanol-GO membrane is quite hydrophobic, it is expected that the surface of the cardanol-GO planes in the membranes are 16


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mostly covered by hydrophobic cardanol. Therefore, the bactericidal property of the cardanol-GO membrane result from the cardanol moiety which has intrinsic bactericidal activity, not the basal planes in GO. Still the bactericidal activity of the cardanol-GO membrane is quite close to that of the GO membrane likely due to the excellent bactericidal activity of cardanol. For more detailed understand on the bactericidal effect of cardanol, the bactericidal property of GO and cardanol-GO was examined in suspension was by a shaking flask method under dynamic contact conditions. Figure 10 is a set of optical images that show the antibacterial test results and the bacterial inhibition rates computed from equation (1), respectively. In comparison with GO, cardanol-GO demonstrated bactericidal property; the bacterial inhibition rates of cardanol-GO samples were 84.7 and 85.0% for 400 and 800 ppm of cardanol-GO, respectively, while that of GO was found to be almost 0 %. Ruiz, et al. also reported that GO suspension does not have any bactericidal activity because the oxidative stress which is the significant factor that affect the antimicrobial property of GO diminished under the dynamic contact condition.45 Although the antimicrobial activity of GO in suspension state is still controversial and further investigation is required42,43,45,46, it is still very clear that cardanol-GO fabricated in this work is a very effective bactericidal materials because of the cardanol moiety on GO surface, according with our recent study of the bactericidal activities of cardanol-containing polymers.21

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Figure 10. Results of antibacterial tests against E. coli. (a) Photographs and (b) bactericidal activity of GO and cardanol-GO

4. Conclusion Graphene oxide functionalized with renewable cardanol (cardanol-GO) was synthesized by the reaction of cardanol with graphene oxide using a base catalyst, and then cross-linked GO membrane was fabricated by simple filtration and heating process. The cross-linked GO membrane demonstrated dimensional stability in aqueous condition because of the covalently-connected network present in cardanol-GO sheets. It also showed good oil/water 18


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separation performance owing to its water-repellent surface that could be understood with the hydrophobic nature of the cardanol moiety and the hierarchical micro/nanoscale rough structure of the membrane surface. In addition, the cross-linked GO membrane showed considerable antibacterial property due to the bactericidal cardanol moieties on the surface. Therefore, we believe that the functionalization of GO with self-cross-linkable and bactericidal cardanol is a propitious approach to the development of unprecedented GO-based membrane systems for practical applications in oil/water separations.

ASSOCIATED CONTENT Supporting Information Materials, characterization, airborne bacteria tests of the cardanol-GO membrane, shake flask method for cardanol-GO, TEM image of GO (Figure S1), FT-IR spectra, XPS spectra, TGA curves, Raman spectra of GO and cardanol-GO (Figure S2), optical photographs of the GO membrane and the cardanol-GO membrane after 7days of water dipping test (Figure S4), water contact angles of the cardanol-GO layer and the cardanol-GO membrane (Figure S5), water contact angles of the PA support and the cardanol-GO membranes with different amounts of cardanol-GO (Figure S6), SEM images of the surface of the cardanol-GO membrane (Figure S7), AFM images of the PA support and the cardanol-GO membranes (Figure S8), optical photographs of droplets of DI water and methylene chloride on the surface of the cardanol-GO membrane (Figure S9), optical photographs of the cardanol-GO membrane after dipping test in organic solvents (Figure S10)

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AUTHOR INFORMATION Corresponding Author * Tel: +82-02-880-7070. E-mail: [email protected]. ORCID J.-C. Lee: 0000-0002-5587-1183 Author Contributions †

These authors contributed equally.

Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This research was supported by Basic Science Research Program through the National Research Foundation of Korea (Grant No.: NRF-2016R1D1A1A02937104) and Jeollannamdo (2017 R&D supporting program operated by Jeonnam Technopark).

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Table of Contents Graphic

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Figures Figure 1. Schematic diagram of the preparation of cardanol-GO Figure 2. Schematic illustrations of (a) the fabrication process of the cardanol-GO membrane and (b) the formation of the covalently-bonded interlayer bridges between the cardanol-GO sheets Figure 3. FT-IR spectra of cardanol and the cardanol-GO layer on the PA support and the cardanol-GO membrane Figure 4. SEM images of (a) the PA support, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane Figure 5. AFM images of (a) the PA support, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane Figure 6. XRD patterns of the GO membrane, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane Figure 7. Water contact angle images of (a) the GO membrane and (b) the cardanol-GO membrane Figure 8. Photographs of the oil/water separation tests using (a) a mixture of methylene chloride and water containing CuSO4 (1:1, v/v) and (b) a mixture of petroleum ether and water containing CuSO4 (1:1, v/v) Figure 9. Photographs of E. coli growth on (a) the GO membrane and (b) the cardanol-GO membrane (incubation for 18 h at 37 ºC)

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Figure 1. Schematic diagram of the preparation of cardanol-GO

3



Figure 2. Schematic illustrations of (a) the fabrication process of the cardanol-GO membrane and (b) the formation of the covalently-bonded interlayer bridges between the cardanol-GO sheets

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Figure 3. FT-IR spectra of cardanol and the cardanol-GO layer on the PA support and the cardanol-GO membrane

5



Figure 4. SEM images of (a) the PA support, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane

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Figure 5. AFM images of (a) the PA support, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane

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Figure 6. XRD patterns of the GO membrane, (b) the cardanol-GO layer on the PA support, and (c) the cardanol-GO membrane

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Figure 7. Water contact angle images of (a) the GO membrane and (b) the cardanol-GO membrane

9



Figure 8. Photographs of the oil/water separation tests using (a) a mixture of methylene chloride and water containing CuSO4 (1:1, v/v) and (b) a mixture of petroleum ether and water containing CuSO4 (1:1, v/v)

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Figure 9. Photographs of E. coli growth on (a) the GO membrane and (b) the cardanol-GO membrane (incubation for 18 h at 37 ºC)

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Cross-linked graphene oxide membrane functionalized with self-cross

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