Graphene Nanofibrous Foam Designed as an Efficient Oil Absorbent

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Materials and Interfaces

Graphene Nanofibrous Foam Designed as an Efficient Oil Absorbent Zhangqi Feng, Fangfang Wu, Lin Jin, Ting Wang, Wei Dong, and Jie Zheng Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05646 • Publication Date (Web): 04 Feb 2019 Downloaded from http://pubs.acs.org on February 4, 2019

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Industrial & Engineering Chemistry Research

Graphene Nanofibrous Foam Designed as an Efficient Oil Absorbent Zhang-Qi Fenga,#,*, Fangfang Wub,#, Lin Jinc,*，Ting Wangd, Wei Donge, and Jie Zhengf a,b,e

School of Chemical Engineering, Nanjing University of Science and Technology, 200 Xiao Ling Wei, Nanjing, 210094, China.

cThe

Key Laboratory of Rare Earth Functional Materials and Applications, Zhoukou Normal University, Zhoukou 466001, PR China

dState

Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, China

f

Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA b

Nanjing Daniel New Mstar Technology Ltd, Nanjing, 211200, China

a e-mail:

[email protected]

b e-mail:

[email protected]

c e-mail:

[email protected]

d e-mail:

[email protected]

e e-mail:

[email protected]

f e-mail:

[email protected]

* Corresponding Author. [#] These authors contributed equally to this work.

Keywords: Graphene; 3D fluffy nanofibers; Liquid-assisted electrospinning; Oil absorbent.

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 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 Organic pollution is considered as a long-term, urgent global issue for energy, environmental and ecological applications. Carbon-based materials have shown great potential in addressing this global issue. However, development of low-cost and high-performance of carbon-based three-dimensional materials has also proved to challenging for removal of organic pollutants from water. Here, we developed a new technique combining a liquid-assisted electrospinning and interface self-assembly of graphene to successfully fabricate novel graphene fluffy nanofibrous scaffold (GFNs) as efficient organic pollution absorbent. The resultant GFNs with several advantages of distinctive 3D fluffy macro-structure, super porosity, low density, strong mechanical stability, and super hydrophobicity/oleophicity, demonstrated high adsorption capacity for organic solvents (201 times their own weight) and oils (119 times their own weight), as well as excellent recyclability by simple extrusion. Different from conventional graphene sponges that require a high content of graphene for complex fabrication, the preparation of GFNs only used a very small amount of graphene (1.0 mg/cm3) to achieve comparable or even better adsorption capacity and recyclability. Because of the viable synthesis method, GFNs with unique advantages and superior performance show great potential for industrial applications in environmental protections such as oil pollution cleanup and waste water treatment.


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1. Introduction Increasing pollution from crude oil, petroleum products, and toxic organic solvents has caused an urgent global issue on energy, environmental, and ecological applications1-6. Unlike chemically related pollutant process that may induce the secondary pollution, physical adsorption offers an efficient and green method to deal with oil and organic pollutants. Physical adsorption of pollutants on adsorbent generally involve different non-covalent interactions including hydrogen bonds, hydrophobic interactions, π-π interactions, ionic/electrostatic interactions, and van der Waals interactions. Delicate design of physical absorbents with novel structures and chemistry allows to achieve high absorption selectivity, high absorption capacity, proper recyclability, good mechanical properties, and low cost1, 3, 7, 8.

Carbon-based materials have been considered as one of the most efficient absorbents for separating and removing oil and organic liquid spills7,

9, 10.

Among different

carbon-based materials, graphene exhibits unique structural and functional properties, such as high specific surface area, high chemical and mechanical stability, strong hydrophobicity, and planar honeycomb lattice structure composed of sp2- hybrid-orbit carbon atom, all of which make it a promising potential for the advanced adsorption applications11-14. Significant efforts and progress have been made to fabricated different graphene-based porous materials for pollutant removal, including graphene foam, graphene sponge, and graphene aerogel2, 15-17. While these absorbents exhibit high adsorption capacity and good recyclability for pollutant removal, the preparation of these absorbents (graphene sponges, aerogels, or foams) is usually process-tedious,



involves harmful precursors, and requires complex equipment and unconventional skills, which greatly limit their practical applications in a large scale. Especially, these graphene materials always contain a relatively high content (>95 wt%), leading to fabrication process being more expensive and complex. And sometimes, these materials are mechanically weak and brittle even with high density. Therefore, it is critical for the development of an easy, economical, and environment-friendly approach for the massive fabrication of 3D graphene-based macroscopic materials for pollutant adsorption and removal.

Electrospinning is a simple, efficient, and low-cost fabrication method for preparing ultrafine polymer nanofibers. Electrospun nanofibers can be used as adsorbent materials due to its large specific surface area and controllable cell morphology18, 19. So, electrospun nanofibers could serve as a basic scaffold for preparing graphene-coated absorbents by coating of tiny amounts of graphene on the surface of the nanofibers to reduce the cost and simplify the preparing process, while with excellent adsorption efficiency and mechanical properties. However, traditional electrospun nanofibers mats have very tiny interstices (< 1 µm) among the nanofibers, so that graphene sheets (normally with the size of > 3 µm) can only be deposited onto the surface of the nanofibers mat. Therefore, to improve adsorption capacity, it is necessary to obtain electrospun nanofibrous scaffolds with a large internal interstice (> 10 µm) that would permit graphene sheets to enter the inside of the scaffold, and adhered onto the surface of the nanofibers in the scaffold to form a novel graphene nanofibrous scaffold as absorbent material for organic pollutants.


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Figure 1. Schematic illustration of the setup for liquid-assisted electrospinning and the preparation process of GFNs Herein, we developed a liquid-assisted electrospinning to prepare fluffy nanofibrous scaffold (FNs), followed by NH3 plasma treatment to give -NR chemical groups on the surface of the nanofibers to drive the self-assembly of GO sheets in the FNs, and then chemical reduction to produce novel GFNs (Figure. 1 and Figure. S1). GFNs materials can absorb a variety of oils and organic solvents with a maximal adsorption capacity up to 119-201 times of their own weights. GFNs also exhibited excellent recyclability to maintain a high adsorption capacity even after 9 cycles repeated extrusion. This work provides GFNs as alternative carbon-based adsorbents for pollutant-related applications. 2. Experimental Materials and Methods 2.1 Materials PAN copolymer (91.4% acrylonitrile and 8.6% methyl acrylate, Mw=50,000 g/mol) was supplied by Suzhou Takino Polymer Co., Ltd. N, N-dimethylformamide (DMF, 99.5%) was purchased from Sinopharm Group Chemical Reagent Co., Ltd. Graphene oxide (GO, monolayer) was purchased from Nanjing Xianfeng NanoMaterials



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Technology Co., Ltd. Hydrazine hydrate (85%, AR) was purchased from Sinopharm Group Chemical Reagent Co., Ltd. 2.2 Preparation of FNs The

industrially

pure

polyacrylonitrile

(PAN)

was

dissolved

in

N,

N-dimethylformamide (DMF) to make a 10%(w/v) solution, followed by mechanical stirring and heating at 50℃ overnight to ensure complete dissolution. The experimental setup for electrospinning was illustrated in Figure. 1. The PAN/DMF solution was placed into a syringe capped with a 23-gauge blunt-tipped needle and then driven by a syringe pump (Silugao Co. Beijing, China) at a fixed flow rate of 1.0 mL/h. A voltage of 14 KV was supplied by a High DC power supply (Dongwen High Voltage, China) and the distance between the tip of the needle and the collector was 10 cm. Electrospinning nanofibers were collected by a mixture liquid of water/ethanol (2:8) in an insulating plastic container, where the ethanol was later gradually substituted by water. And then PAN nanofibers prepared by previous steps were freeze-dried for 8 h to obtain FNs. Subsequently, NH3 plasma treatment was performed under an optimized condition of input power at 20 W for 60 s to the FNs to modify -NR chemical group on the surface of the FNs. 2.3 Preparation of GFNs GO was dispersed in deionized water at concentrations of 0.25 mg/mL, 0.5 mg/mL, 1.0 mg/mL and 2.0 mg/mL respectively, then ultrasonicated for 30 mins. The following step was soaking the NH3 plasma treated FNs in these dispersions with shaking and freeze-dried for 8 h to obtain GOFNs. GFNs were gained through the reduction of GOFNs by hydrazine vapor at 80 ℃ overnight. Figure. 1 showed the schematic illustration of the setup for liquid-assisted electrospinning and the


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preparation of GNFs. Figure. 1S showed the practicality pictures of the setup for liquid-assisted electrospinning and the preparation of FNs, GOFNs, and GNFs. And the Figure. 2S showed the FNs in the mix of water and ethanol. 2.4 Characterizations The zeta potential of NH3 plasma treated FNs and GO sheets was measured by Nano-particle size potential analyzer (Nano zs90 zetasizer, England). XPS (PHI quantera II, Japan), XRD (X`pert Pro, Netherland) and Raman Spectrum (Lab Ram Aramis, France) measurement were used to demonstrate the successful reduction of GO in the preparation of GFNs. The SEM (Hitachi-s3000N, Japan) was applied to observe the morphological structure of GFNs. In order to observe the original micromorphology of the fluffy nanofibrous scaffold, the rhodamine was loaded into the FNs, and then detected by Laser Confocal Microscope.

2.5 Evaluation of oil adsorption capacity (Q) Blocks of GFNs or GOFNs (the weight is m0) were put into a beaker containing oils or organic liquids, in turn, allowing to absorb enough liquid, and then the GFNs or GOFNs was taken out from the beaker containing when the liquid didn’t drip down, the weight of the GFNs was measured again (the weight is me). Q = (me-m0) / m0 (1) The GFNs or GOFNs material, which have absorbed oils was squeezed with the tweezers until the weight of adsorbent is constant, recording the material mass ml, and then put it into the solution to be adsorbed to absorb oils again, the weight of the material weighing m2, the cycles of oil absorption capacity was calculated by the following formula: Q = (m2 -m1) / m0 (2)



3. Results and Discussion 3.1 Morphology characterization The successful preparation of GFNs requires a two-step fabrication process. First, FNs were produced using electrospinning with liquid receiving device as a collector (Figure. 1). Compared to traditional electrospun nanofibrous meshes (Figure. S2), most of nanofibers in FNs (Figure. 2a) were discrete, with only few nanofibers being occupied at the same level. SEM images showed that FNs have large interstice with a size distribution from 10-100 µm. FNs had a relatively narrow diameter distribution of fibers ranging from 200 nm to 1.2 µm with an average diameter of 0.77 µm. Fabricated FNs were very soft and felt like cotton. Such mechanical softness and uniform porous structure enabled GO sheets to be packed in the deep interior of FNs, which will further facilitate the self-assembly of GO sheets using the NH3 plasma treatment to modify the -NR chemical groups on the surface of FNs. To confirm the incorporated components, the zeta potential of the NH3 plasma treated FNs and GO sheets were examined. Results showed that zeta potential of the GO dispersion was -39.8 mV, indicating that the oxygen-containing functional groups (hydroxyl groups, carboxyl groups) on the GO layer were ionized by a negative charge20. Zeta potential of the NH3 plasma treated FNs was +7.2 mV under the condition of pH = 2.7, due to the presence of -NR chemical groups. The electrostatic attraction stemmed from oxygen-containing functional groups and -NR chemical groups is considered as major driving force for the self-assembling of GO sheets on the surface of the FNs21. Figure. 2b compared the macro- and micro-morphology of GOFNs and GFNs with different contents of graphene sheets, where GFNs are the reduction products of GOFNs by using steam of ammonia and hydrazine hydrate. It can be seen in SEM images that the reduction process did not significantly change the shape of these


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Figure. 2. (a) Light microscope and laser confocal microscope images of FNs in water (red fluorescence: rhodamine), and their SEM image on the surface of FNs. Diameter distribution of FNs in inset. (b) Photograph of GOFNs and GFNs fabricated from GO sheets dispersions with different concentrations and their SEM images. scaffold, but made their colors become darker as the increase of loading graphene sheets contents. Figure. 3a and b showed the SEM images of FNs and GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL). After coating and chemical reduction, graphene sheets were fully distributed onto the individual nanofibers to form flag-like micro-structure, indicating that (i) the three-dimensional nanofiber network is not disturbed, (ii) the electrostatic self-assembly indeed drives welldispersed GO sheets to firmly adsorb onto the surface of the FNs and (iii) GFNs is stable three-dimensional porous structure formed by graphene oxide sheets with a large surface area and extremely discrete FNs, so GFNs has a large specific surface



Figure. 3. SEM images of (a) FNs, (b) GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL), (c) the GFNs at higher magnification. area, approximately 900-1100 m2/g. A close-up SEM image of GFNs (Figure. 3c) showed that after chemical reduction some typical wrinkles of graphene sheets appeared on the attached points of FNs. Additional, the concentration of GO suspension significantly affected the distribution of graphene sheets and the morphology of GFNs. When the GO concentrations reached up to 2.0 mg/mL, these graphene sheets were aggregated together to form an entirety with the sizes of 80-260 µm. Then, the original spatial porous structure of FNs was filled with disconnected massive interstices and large graphene blocks (Figure. S3). Moreover, the density of GFNs (GO dispersion liquid of 1.0 mg/mL), as calculated by the volume and quality of GFNs in cylinder shape, was about ~0.003 g/cm3 (Figure. S4), which was much lower than that of graphene composites in literatures22-24.

3.2 Chemical characterization X-ray Photoelectron spectrum (XPS), Raman spectra, and X-Ray Diffraction (XRD) were performed to characterize the reduction degree of the GO in GOFNs (GO suspension is 1.0 mg/mL). XPS results in Figure. 4a showed that only the peaks indicator of the removal of most oxygen-containing groups after the GO reduction.


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Figure. 4. (a) XPS spectrum, (b) Raman spectra and (c) XRD diffraction of the GOFNs and the GFNs.

Raman spectra in Figure. 4b showed the two prominent peaks at ~1350 cm-1 for D (the symmetry A1g mode) and at ~1590 cm-1 for G (the E2g mode of sp2 carbon atoms), respectively. Compared with GOFNs, the D/G intensity ratio of GFNs was increased at the expense of a decrease in the average size of the sp2 domains of GO. XRD analysis further confirmed the successful reduction of GO in GOFNs as showed in Figure. 4c. A typical peak at 2θ=9.69° in the XRD pattern of the GOFNs clearly corresponded to the (002) reflection of GO. However, for GFNs, XRD pattern showed a typical peak disappeared and a new peak appeared at 2θ=24.09°. Again, a decrease of d-spacing in the XRD pattern indicates the elimination of the oxygen-containing



groups on the basal planes26, well consisted with the previous findings in literature that the reduction of GO in GOFNs indeed happen27, 28.

3.4 Mechanical performance Figure. 5 shows mechanical properties of the GFNs. A glass bottle was placed on top of the GFNs prepared at different concentrations of GO aqueous suspensions. All GFNs showed a nearly complete recovery after 5-65% compression. Even under extreme brute force to squeeze GFNs, the flattened GFNs can immediately recover back to its original shape upon force release (Figure. 5e). When given a compression amount of 11 mm by Universal Testing Machine, the compression modulus of GFNs(from GO sheets dispersions with concentrations of 1.0 mg/mL), with strong mechanical properties, can be higher than 90Pa in Figure. 5e. Such mechanical strength and recovery were due to synergistic interactions between FNs and graphene in GFNs. The fluffy macro- and micro-structure of FNs provides a sufficient space to accommodate GO sheets inside FNs, which serve as crosslinkers to connect most of nanofibers and to form a stable and strong network. Thus, introduction of graphene sheets into nanofibers allows to transfer the force from graphene sheets to polymer backbone of nanofibers, to dissipate energy effectively, thus to enhance mechanical properties of GFNs. In the absence of graphene sheets, FNs became very flexible, easy to be compressed (Figure. S5a). Differently, Figure. S5c showed that in the case of pure graphene foam, the graphene sheets were prone to slip in a particular direction and collapse immediately under a weak compression (Figure. S 5b). Side-by-side comparison of the mechanical properties between FNs and GFNs reveals that the synergistic interaction of FNs with graphene sheets in GFNs plays an important role in the mechanical improvement of GFNs, which is in turn beneficial to improve the stability of GFNs during the adsorption and recycle process of organic pollutants.


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Figure. 5. Photographs of compression mechanical examination of the GFNs fabricated from GO aqueous suspensions at different concentrations of (a) 0.25 mg/mL, (b) 0.5 mg/mL, (c) 1.0 mg/mL, (d) 2.0 mg/mL, respectively. 3.5 Hydrophobicity and lipophilicity Figure. 6 shows the hydrophobicity and lipophilicity of GFNs and FNs. As a control, it can be seen in Figure. 6a that FNs can absorb water quickly and immerse into the water due to their hydrophilicity and low density. Differently, GFNs floated on the water presumably due to the hydrophobicity of graphene sheets that wrap around the



surface of FNs (Figure. 6b). In Figure. 6c, by pushing GFNs into water, upon releasing GFNs immediately floated up to the surface of water and kept its dry state. In a sharp contrast, Figure. 6d showed that GFNs rapidly sank down into oil in 5s. This behavior clearly indicates the hydrophobicity and lipophilicity property of GFNs, which favor to stay in oil than in water. The water contact angle of GFNs was performed as showed, which was about 145°±3.2° (Figure. 6e). Thus, GFNs demonstrate its hydrophobic and oleophilic nature, which can be used for oil-water separation due to its high selectivity for oil against water.

Figure. 6. Photographs of (a) the FNs placed on the water surface, (b) the GFNs placed on the water surface, (c) the GFNs immersed on the water surface, (d) the GFNs placed on pump oil, (e) contact angle measurement of GFNs.


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3.6 Oil absorption At a first glance, when applying GFNs (8.6 mg) to contact with a mixture solution of 0.6 mL of toluene (stained by Sudan black B) and 10 mL water, GFNs can quickly and specifically adsorbed all oils from water in 5 s (Figure. 7a). To test and compare the pump oil adsorption capacity for GFNs, GOFNs, FNs, we immersed each adsorbent into pump oil for 2 mins and then taken them out. The absorption capacity (Q) was evaluated by mass difference before and after adsorption of pump oil. As shown in Figure. 7b, FNs had a fair absorption capability (69.35 g/g) due to its high porosity. However, FNs are too mechanically brittle to be used as absorbents for practical applications. In the case of GFNs, the absorption capacity of the GFNs showed a significant improvement as an optimal graphene contents. Specifically, GFNs prepared at 1.0 mg/mL GO suspension exhibited the highest absorption capacity of 119.26 g/g. However, an excess of graphene sheets in GFNs would block the interstice of the FNs (Figure. S3), leading to the decrease of Q. Among three adsorbents, GOFNs exhibited the smallest adsorption capacity for pump oil (45.31 g/g), which was almost independent of GO sheets concentrations. Such low oil adsorption capacity of GOFNs is likely attributed to the oleophobicity of oxygen-containing groups in the GO sheets that prevent pump oil from penetrating into GOFNs. Figure. 7c and Table 1 showed the adsorption capacity of GFNs for different oils and organic solvents including chloroform, soybean oil, n-heptane, DMSO, olive oil, pump oil, n-hexane, and ethanol. The absorption capacity of GFNs was in a range of 82 g/g for lubricate oil to 201 g/g for chloroform. In general, our GFNs exhibit ~25% higher adsorption capacity than other three-dimensional in literature (Table 2), and are far better than commercial absorbents (20~40 g/g).



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Figure. 7. (a) Absorption process of toluene (stained with Sudan Black B) on water by the GFNs within 5s, (b) comparison of the absorption capacities (Q) of the GFNs and GOFNs for pump oil, (c) the diagram of absorption capacities of the GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL) for several oils and organic liquids. Table 1. Absorption capacities of the GFNs for different kinds oils and organic liquids29-31. Sorbates

Q [g·g-1]

Q in literatures [g·g-1]

Chloroform

201.24

~148

Soybean oil

166.39

~78

n-Heptane

155.47

~26

DMSO

148.77

~16

Olive oil

121.56

~78

Pump oil

119.26

~10

n-Hexane

109.21

~70

Ethanol

80.61

~44


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Table 2. Absorption capacities of several absorbents for chloroform10, 15, 30-32. Absorbents Our GFNs

Q [g·g-1] 201.24

3D Graphene coated Superwetting Mesh Film

148

Carbon-Coated Sponges

78

3D conjugated microporous polymers

16

Commercial oil absorbent material

21

Carbonized rice husks

7.5

Activated carbon

3

In real-world applications, it is particularly important to reuse oil adsorbents and recycle the adsorbed oils. Compared to heat- or flame-treatment for adsorbent recycling in literatures2, 9, our recycle method is very simple and straightforward. By simply squeezing the oils from the adsorbents, GFNs and GOFNs can be easily reused for multiple times (Figure. 8a). Figure. 8b shows recycling tests for GFNs and GOFNs. Both GFNs and GOFNs decreased their absorption capacity after the first cycle, due to the inevitable residue of oil in the absorbents. But after the first cycle, the absorption capacity unchanged for the rest of 9 cycles, with the final adsorption capacity was 70.98 g/g for GFNs and 27.36 g/g for GOFNs, where GFNs had much higher adsorption capacity than GOFNs for each cycle (Figure. 8b). In addition, the recyclability of GFNs was not largely improved with the increasing of graphene sheets. For each cycle, visual inspection also showed that after immersing the flattened GFNs and GOFNs into pump oil for up to 10 minutes, GFNs exhibited both high elasticity and oil absorbency and expanded to a sponge-like state, while GOFNs still kept its flat appearance. These data indicate that the GNFs have excellent stability and repeatability for organic pollutants adsorption.



Figure. 8. (a) The recycling process of GFNs via squeezing, (b) recyclability study of GFNs and GOFNs using pump oil as the sorbat

4. Conclusions In this work, we fabricated robust and recyclable GFNs via green route for highly efficient oil and organic pollutants cleanup using a combined technique of liquid-assisted electrospinning and self-assembly of graphene sheets. The graphene was creatively introduced into the framework of FNs to achieve a 3D fluffy nanofibrous network with a low density of 1.0 mg/cm3 of graphene, and excellent mechanical elasticity and strength. The as-prepared GFNs can absorb a variety of oils


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and organic solvents with a maximal sorption capacity up to 201 times the weight of the pristine GFNs. GFNs also exhibited excellent recyclability and maintained 60% sorption capacity after 9 cycles simply through the squeezing recycles. In addition, our GFNs only contained very tiny of graphene as compared to other graphene-based adsorbents, making a easy and low-cost fabrication. These results demonstrated that GFNs can be employed as promising reusable absorbents for different pollution removal applications.

Acknowledgements The authors acknowledge financial support from the A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the National Natural Science Foundation of China (51773093, 11204033), and Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX17_0167), and the Fundamental Research Funds for the Central Universities (30916011313), and the Open Research Fund of State Key Laboratory of Bioelectronics, Southeast University. J.Z. thanks financial supports from NSF (1806138 and 1825122). References 1. Pham, V. H.; Dickerson, J. H., Superhydrophobic Silanized Melamine Sponges as High Efficiency Oil Absorbent Materials. Acs Applied Materials & Interfaces 2014, 6, (16), 14181-14188. 2. Bi, H. C.; Xie, X.; Yin, K. B.; Zhou, Y. L.; Wan, S.; He, L. B.; Xu, F.; Banhart, F.; Sun, L. T.; Ruoff, R. S., Spongy Graphene as a Highly Efficient and Recyclable Sorbent for Oils and Organic Solvents. Adv Funct Mater 2012, 22, (21), 4421-4425. 3. Zhu, Q.; Chu, Y.; Wang, Z. K.; Chen, N.; Lin, L.; Liu, F. T.; Pan, Q. M., Robust superhydrophobic polyurethane sponge as a highly reusable oil-absorption material. Journal Of Materials Chemistry A 2013, 1, (17), 5386-5393. 4. Gros, J.; Socolofsky, S. A.; Dissanayake, A. L.; Jun, I.; Zhao, L.; Boufadel, M. C.; Reddy, C. M.; Arey, J. S., Petroleum dynamics in the sea and influence of subsea dispersant injection during Deepwater Horizon. Proc Natl Acad Sci U S A 2017, 114, (38), 10065-10070.



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For Table of Contents Only



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Table Captions. Table 1. Absorption capacities of the GFNs for different kinds oils and organic liquids. Table 2. Absorption capacities of several absorbents for pump oil.

Table 1. Absorption capacities of the GFNs for different kinds oils and organic liquids. Sorbates

Q [g·g-1]

Q in literatures [g·g-1]

Chloroform

201.24

~160

Soybean oil

166.39

~110

n-Heptane

155.47

~16

DMSO

148.77

~95

Olive oil

121.56

~96

Pump oil

119.26

~97

n-Hexane

109.21

~8

Lubricate oil

80.61

~110


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Table 2. Absorption capacities of several absorbents for pump oil. Absorbents

Q [g·g-1]

Our GFNs

119.26

GPU sponge

98

Graphene sponge

68

Expanded graphite

47

Polyurethane sponge

41

Paper towel

21

Commercial oil absorbent material

16

Activated carbon

3

Carbonized rice husks

7.5



Figure Captions. Figure 1. Schematic illustration of the setup for liquid-assisted electrospinning and the preparation process of GFNs. Figure 2. (a) Light microscope and laser confocal microscope images of FNs in water (red fluorescence: rhodamine), and their SEM image on the surface of FNs. Diameter distribution of FNs in inset. (b) Photograph of GOFNs and GFNs fabricated from GO sheets dispersions with different concentrations and their SEM images. Figure 3. SEM images of (a) FNs, (b) GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL), (c) the GFNs at higher magnification. Figure 4. (a) XPS spectrum, (b) Raman spectra and (c) XRD diffraction of the GOFNs and the GFNs. Figure 5. Photographs of compression mechanical examination of the GFNs fabricated from GO aqueous suspensions at different concentrations of (a) 0.25 mg/mL, (b) 0.5 mg/mL, (c) 1.0 mg/mL, (d) 2.0 mg/mL, respectively. Figure 6. Photographs of (a) the FNs placed on the water surface, (b) the GFNs placed on the water surface, (c) the GFNs immersed on the water surface, (d) the GFNs placed on pump oil, (e) a water droplet on the GFNs

for contact angle measurement.

Figure 7. (a) Absorption process of toluene (stained with Sudan Black B) on water by the GFNs within 5s, (b) comparison of the absorption capacities (Q) of the GFNs and GOFNs for pump oil, (c) the diagram of absorption capacities of the GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL) for several oils and organic


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liquids. Figure 8. (a) The recycling process of GFNs via squeezing, (b) recyclability study of GFNs and GOFNs using pump oil as the sorbat



Figure 1. Schematic illustration of the setup for liquid-assisted electrospinning and the preparation process of GFNs.

Figure. 3. SEM images of (a) FNs, (b) GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL), (c) the GFNs at higher magnification.


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Figure. 4. (a) XPS spectrum, (b) Raman spectra and (c) XRD diffraction of the GOFNs and the GFNs.



Figure. 2. (a) Light microscope and laser confocal microscope images of FNs in water (red fluorescence: rhodamine), and their SEM image on the surface of FNs. Diameter distribution of FNs in inset. (b) Photograph of GOFNs and GFNs fabricated from GO sheets dispersions with different concentrations and their SEM images.


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Figure. 5. Photographs of compression mechanical examination of the GFNs fabricated from GO aqueous suspensions at different concentrations of (a) 0.25 mg/mL, (b) 0.5 mg/mL, (c) 1.0 mg/mL, (d) 2.0 mg/mL, respectively.



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Figure. 6. Photographs of (a) the FNs placed on the water surface, (b) the GFNs placed on the water surface, (c) the GFNs immersed on the water surface, (d) the GFNs placed on pump oil, (e) a water droplet on the GFNs measurement.


for contact angle

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Figure. 7. (a) Absorption process of toluene (stained with Sudan Black B) on water by the GFNs within 5s, (b) comparison of the absorption capacities (Q) of the GFNs and GOFNs for pump oil, (c) the diagram of absorption capacities of the GFNs (from GO sheets dispersions with concentrations of 1.0 mg/mL) for several oils and organic liquids.



Figure. 8. (a) The recycling process of GFNs via squeezing, (b) recyclability study of GFNs and GOFNs using pump oil as the sorbat


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Graphene Nanofibrous Foam Designed as an Efficient Oil Absorbent

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