Developing Hydrophobic Graphene Foam for Oil Spill Cleanup

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Developing Hydrophobic Graphene Foam for Oil spill Cleanup Ahmed Subrati, Subrata Mondal, Mujtaba Ali, Ali Alhindi, Rakan Ghazi, Ahmed Abdala, Donald Reinalda, and Saeed M. Alhassan Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 23 May 2017 Downloaded from http://pubs.acs.org on May 24, 2017

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Industrial & Engineering Chemistry Research

Developing Hydrophobic Graphene Foam for Oil spill Cleanup Ahmed Subratia, Subrata Mondala,b, Mujtaba Alia, Ali Alhindia, Rakan Ghazia, Ahmed Abdalac,d, Donald Reinaldaa and Saeed Alhassana* a

Department of Chemical Engineering, The Petroleum Institute, Abu Dhabi, United Arab Emirates

b

National Institute of Technical Teachers’ Training and Research (An autonomous institute

under MHRD, Govt. of India), Sector III, Block FC, Salt Lake City, Kolkata, West Bengal, India c

Qatar Environmental and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar

d

College of Arts and Science, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar

*Corresponding author, email: [email protected], fax: +971 (2) 6075 200

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ABSTRACT Oil spills have been responsible for a number of environmental problems such as water pollution, subsequent danger to aquatic life along with massive oil losses. Such disasters have stimulated the need for development of novel materials with improved sorption capacity for oil-spill cleanup. Among various available methods, the use of adsorbents holds great promises to remove and recover oil from minor or major spills. In the present work, we report the development of hydrothermally-reduced graphene oxide foam (RGO) functionalized with, Fe3O4, magnetic nanoparticles (MNP) for sorption of oil. Magnetic nanoparticles were used to produce RGO-MNP hybrid foams which could be separated by a magnetic field. The synthesized RGO and RGO-MNP hybrid foams were characterized by using Fourier Transform Infrared spectroscopy (FTIR), Raman spectroscopy, X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA). Motor oil was used as the adsorbate to determine the sorption capacity of the produced foams. Experimental results revealed that graphene foam is an excellent candidate to be used as a sorbent for oil spill cleanup due to its high specific surface area and hydrophobicity. KEYWORDS: Graphene foam • Magnetic nanoparticles • Sorption • Oil-water separation


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1. INTRODUCTION An oil spill is a form of pollution due to release of liquid petroleum hydrocarbons, especially in the marine area. Catastrophes like the Mexico Gulf oil spill in 2010 is an unsettling reminder of the importance for the development of novel sorbents in oil spill cleanup1. Oil spills have resulted in various catastrophes which includes water pollution, danger to aquatic life (environmental pollution) along with massive oil loss. There is an emerging worldwide interest to prevent such incidents during the production, storage and transportation of oil. Generally, oil spills are treated either through containment with huge floating barricades (called oil fences) after which oil is either vacuumed off or soaked up by absorbents using specialized ships2. Hence, there is a growing interest to develop novel adsorbent materials and efficient methods which could cleanup oil from affected areas3. Broadly, oil spill cleaning methods can be classified into three groups, such as separation and collection of oil from water surface, mixing oil and water using dispersing agents to aid the natural decomposition, and in situ burning of the oil spill4. Sanaz et al. referred various materials used as adsorbents for the oil spill with distinct sorption capacities as tabulated in Table 12. Graphene is a single atomic layer of carbon atoms arranged in a two-dimensional honeycomb network. Graphene oxide (GO) sheets comprise of various oxygen-containing functional groups such as carboxyl, hydroxyl and epoxide groups. Hydroxyl groups and epoxides are located on the basal planes of a GO sheet, whereas carboxyl groups tend to be located on the edges1,3,10. Due to the presence of excessive oxygen functional groups, graphene oxide is hydrophilic and form stable aqueous colloids to facilitate the assembly of macroscopic structures. Reduced graphene oxide (RGO) is prepared from reduction of graphene oxide by thermal, chemical or electrical means, therefore, RGO is more hydrophobic as compared to GO. However, as the name 3 ACS Paragon Plus Environment


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suggests, in RGO there are still some residual oxygen functionalities which could form stable dispersion as well as facilitate self-assembly. Self-assembled reduced graphene oxide foam of three-dimensional (3D) architecture possesses many interesting characteristics such as interconnected porous structure, light weight and high surface area. Moreover, excellent adsorption property of graphene 3-D porous material makes them ideal for many environmental applications including oil spill cleanup1,3. Graphene foam (GF) is essentially a three dimensional (3D) graphitic architecture built by selfassembly of graphene sheets. The GF and its derivatives can be synthesized via a hydrothermal method, chemical reduction method or a combination of both, as well as chemical vapor deposition method11,12. The pore size of GF ranges from sub-micrometer levels to several micrometers, which consequently results in ultralight, high compressibility, considerable mechanical strength, excellent thermal and electrical conductivity, and sorption capacity characteristics. The macroporous texture of GF helps to prevent pristine sheets, i.e. sp2 – hybridized graphitic carbon sheets, from the aggregation during the process of assembling. Xu et al. reported a hydrothermal method for GF preparation by using GO as a precursor (reagent). Self-assembled graphene foam with interconnected 3D porous network structure was prepared at 180˚C for 12 hr of hydrothermal process13. The structure was formed by partial overlapping and agglomeration of graphene sheets with physical cross-linking sites. Accumulating interactions − of graphene sheets is the major driving interaction for the foam structure. Morphology and structure of the GO precursor based foam were mainly dependent on the GO initial concentration and hydrothermal reduction time13. Synthesis of GF through the reduction of GO on a porous membrane using hydrazine monohydrate as a reducing agent was proposed by Niu et al.14. Oxygen-containing groups in the graphene oxide sheet form hydrogen bonding which is the 4 ACS Paragon Plus Environment

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driving force for the chemical reduction method. This method leads to rapid evolution of gaseous species (e.g. H2O and CO2). The evolved gases could get absorbed within layered films to expand the foam structure. The drawback for this method is that the gases evolved may induce the defects and ruptures in the graphene skeleton hence reduces its sorption capacity, as well as negatively affects its mechanical properties14. The GF prepared by using conventional methods would suffer from morphological instability due to severe structural defects in the graphene sheets. A free standing GF can be prepared by using porous nickel foam as a template for the deposition of graphene by CVD at 1000˚C under ambient pressure using methane as feed gas12. The resulting GF mimicked the interconnected, macroporous, 3D structure of the nickel foam template. The CVD graphene foam has a similar morphology to the nickel foam and the resulting graphene skeleton is uniform with the minimum number of ruptures and improved mechanical properties12. Li et al. reported a new method to synthesize graphene foams in which alkylsilanes were grafted on GO sheets in presence of pyrrole molecules by electrostatic interaction with the carboxyl groups located on the GO edges, afterwards, the material was reduced to form a three dimensional foam structure13. The alkylsilane is typically a 3-methlyacryloxypropyl-trimethoxy silane which is commercially known as KH570. The foam hydrophobicity as well as the affinity of the alkene units (C=C) to polymerize via free radical mechanism enhanced to form chemical bonding between the KH570 and the GO sheets to create cross-linked structure and increase the hydrophobicity of the GF15. Yang et al. prepared a freestanding porous film like graphene oxide foam by filtration of GO, magnetic nanoparticle (MNP) and carbon nanotube (CNT) suspension, afterwards, composite film was stabilized at moderate hydrothermal process. Introduction of CNT into the composite



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structure possibly provided free standing property of the film structure. The porous film shows excellent motor oil adsorption characteristics (~27 g oil/g film)3. In this study, we report a method to develop hydrothermally-reduced free standing graphene oxide foam (RGO) functionalized with magnetic nanoparticles (MNP) for oil spill cleanup. Magnetic nanoparticles were used to produce RGO-MNP hybrid foam which could be separated by a magnetic driven field. Foams were characterized by using various material characterization tools, whereas, motor oil was used to study the sorption capacity of prepared foams.

2. EXPERIMENTAL SECTION 2.1. Materials GO powder was obtained from Graphene Supermarket®, USA. Magnetic Nanoparticles were obtained from Sigma Aldrich®. VOYAGER Silver, motor Oil (obtained from Abu Dhabi National Oil Distribution Company (ADNOC Distribution)) was used as the adsorbate. 2.2. Synthesis Procedure GO powder was dispersed in deionized (DI) water (100 mg GO/25 mL DI water) and the GO water suspension was sonicated for 2 hr prior to the hydrothermal process. While mixing, the magnetic nanoparticles were added into the mixture. Then the solution was transferred to a 50 mL Teflon-lined autoclave, sealed and placed in a convection oven at 180 °C. After 20 hr of the hydrothermal reaction, the autoclave was left to cool down to room temperature. The prepared foams were kept in DI water prior to the freeze drying step. The foam was freezedried at -70 °C, and subsequently vacuum-dried at 60 °C for 24 hr. The whole process of foam 6 ACS Paragon Plus Environment

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preparation is schematically illustrated in Figure 1. The magnetic nanoparticles loading in the foam was 10 wt % of GO powder. 2.3. Characterizations The FTIR spectra were obtained using PerkinElmer Spectrum Two FTIR spectrometer. Potassium Bromide (KBr) was grounded with the sample to prepare the pellet for better resolution of the peaks. All samples were scanned in the wave number range of 400 – 4000 cm-1. The surface morphology of the samples was studied using a scanning electron microscope (SEM) (Philips, Holland) at an accelerating voltage of 20-30 kV. The elemental composition in terms of oxygen and carbon content were measured by energy dispersive X-ray (EDX) attached to the SEM. All samples were analyzed without sputter coatings. The Raman spectra were obtained using a Jobin Yvon Horiba LabRAM spectrometer with backscattered confocal configuration using a 514 nm air cooled ionized Argon laser (Ar+) to excite the samples. A long working distance objective with magnification of 50x was used both to collect the scattered light and to focus the laser beam on the sample surface. Raman shifts were calibrated using Si wafer at 520.7 ± 1 cm-1. Samples were scanned from Raman shift of 700 to 2000 cm-1. The XRD spectra were obtained using an analytical X’Pert PRO powder diffractometer. The samples were mounted on a zero-background holder and scanned by using Cu-Kα radiation (λ = 1.5406 Å) with the following experimental conditions: applied voltage of 40 kV, intensity of 30 mA, angular range (2θ) 5 – 80 ° and 0.05 steps/s.



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The well grinded powder sample was dispersed in isopropanol to study the morphology using transmission electron microscope (TEM) in an FEI Tecnai 20 ST electron microscope (1.1 Å point resolution and operated at 200 kV), equipped with an EDAX microanalysis system for Xray energy dispersive spectroscopy (EDS) and a GIF for electron energy loss spectroscopy (EELS) experiments. Thermo gravimetric analyses (TGA) of the samples were carried out using thermo-gravimetric analyzer (Discovery TGA, TA Instrument). 5 mg of each sample were tested from room temperature to 500 °C at a heating rate of 10 °C/min in a nitrogen atmosphere (with a corresponding flow of 25 mL/min). 2.4. Oil Sorption and Foam Regeneration The initial sorption capacity (Q) of produced graphene foams (RGO/RGO-MNPs) for motor oil was calculated according to the following equation:

=

The sorption capacity for the consecutive cycles deteriorates over time due to the presence of entrapped oil within the bulk of foam samples after regeneration. Therefore, the amounts of oil entrapped and adsorbed were calculated as follows: = − = − − There are two regeneration techniques implemented in this work. The first one is the thermal regeneration technique by using an oven operated at 110 ˚C in which the oil adsorbed foam was 8 ACS Paragon Plus Environment

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put on a funnel for one hour and oil was collected in a beaker on which the funnel was mounted. In the second method, ethanol bath was heated up to 60 ˚C and the foam that adsorbed oil was soaked in the bath for fifteen minutes in order to replace the motor oil by ethanol from the foam.

3. RESULTS AND DISCUSSION 3.1. Chemical Structure and Composition Figure 2(a) shows the FTIR spectrum of pure GO, which reveals the existence of some oxygencontaining functionalities. The peak at 3369 cm-1 corresponds to the O-H (hydroxyl) stretching vibrations. The peak at 1713 cm-1 is attributed to the C=O (carboxyl) stretching vibrations in the carboxylic edges of the GO basal planes. The sample also exhibits two intense absorption bands at 1207 cm-1 and 1048 cm-1, that correspond to the C-O (alcohol) and C-O (epoxide) stretching vibrations, respectively16. Figure 2(b) shows the FTIR spectrum of RGO, which reveals the existence of some residual oxygen-containing functionality. The peak at 1727 cm-1 is attributed to the C=O (aldehydes) stretching vibrations. The peak at 1564 cm-1 is attributed to the C=C stretching vibrations in the isolated aromatic domains in the basal planes of RGO. The absorption band at 1192 cm-1, may be attributed to the C-O stretching vibration of epoxide group. Figure 2(c) shows the FTIR spectrum of RGO that has entrapped magnetic nanoparticles (MNP). The first obvious difference from the pure RGO is the lower degree of reduction exhibited by RGO-MNP, can be verified by the peak at 3288 cm-1 that corresponds to O-H stretching vibrations. However, it is important to note that the O-H peak is less intense than that of GO. The peaks at 2845 and 2912 cm-1 correspond to the symmetric and asymmetric C-H stretching vibrations in ethylene (-CH2-) in RGO-MNP, respectively. The small peak at 1715 cm-1 is 9 ACS Paragon Plus Environment


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attributed to the C=O (carboxylic group) stretching vibrations in the edges of the basal planes. The peaks at 1536 and 1057 cm-1 correspond to the C=C and C-O (epoxide) stretching vibrations, respectively. The peak at 462 cm-1 is attributed to absorption by the Fe–O bond of the iron oxide16,17. Possibly, Fe-O-C bond is formed between Fe3O4 and graphene18. Elemental composition in terms of carbon (C) and oxygen (O) was determined by Energy Dispersive X-ray spectroscopy by SEM (Table 2). GO has clearly the lowest carbon to oxygen ratio (C/O = 4.43) due to the presence of many oxygen-containing functionalities (confirmed by FTIR and XRD). The EDX spectra of RGO and RGO-MNPs foam samples have C/O ratios of 9.42 and 9.14, respectively. EDX results confirmed the loss of oxygen-containing groups upon hydrothermal reduction. The MNPs have roughly equal oxygen to iron content. The RGO-MNPs have lower C/O ratio (when relatively compared to RGO) due to the presence of MNPs that hold significant oxygen content within its molecular structure. 3.2. Morphology Raman Spectroscopy provides an overview about the morphology of carbon containing materials. There are two dominant bands for such materials such as the D and G bands (Figure 3). For GO, the G band at 1599 cm-1 is attributed to the in-plane vibrations of the sp2 carbon atoms present in the isolated aromatic domains in the basal planes of GO. The D band at 1360 cm-1 is attributed to the structural defects caused by the sp3 carbon atoms that are covalently bonded to the hydroxyl and epoxide functional groups. The peak intensity ratio of D to G bands (ID/IG) is used as a measure of disorder in the sample (e.g. edges, defects, or ripples). The G band results from the in-plane vibrations of sp2 bonded carbon atoms within the basal plane of a graphene sheet whereas the D band is due to out of plane vibrations, such as the ones located on


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the edges of a sheet, which is attributed to the presence of structural defects. Based on the peak intensity ratio (ID/IG), we could calculate the degree of reduction and defects. The ratio for both RGO (ID/IG = 1.09) and RGO-MNPs (ID/IG = 1.1) increased compared to GO (ID/IG = 1.07), indicating the reduction of GO in the hydrothermal process. Furthermore, the fractional increase in the ratio suggests that the reinforcement of MNPs took place in the remaining epoxide sites and carboxylic edges of RGO; hence, not disturbing the defective sp3-hybridized sites in the basal planes of GO. Figure 4 shows the XRD patterns of GO, RGO and RGO-MNPs. These patterns exhibited strong peaks at 11.42°, 24.60° and 24.50°, corresponding to the interlayer spacing of 7.74 Å, 3.62 Å and 3.63 Å. The GO peak corresponds to an interlayer spacing of about 7.74 Å, which is very close to the value reported in the literature (7.6 Å)19, confirming and indicating the presence of functional groups containing oxygen18. Upon hydrothermal reduction, the typical diffraction peak of 2θ shifted from 11.42° for GO to around 24.5° for RGO foams. This could be attributed to the GO is partial reduction to graphene and supported the literature3. The lower interlayer spacing values for RGO and RGO-MNPs can be justified by the reduction of GO and enhancing the spatial alignment of the RGO basal planes. The spacing for RGO is also consistent with the value reported in literature (3.4 Å)20. As compared with RGO foam, XRD results did not show any apparent shifts in the diffraction peaks for RGO-MNP foam, therefore, these results indicated that Fe3O4 particles are attached on the surface of graphene foam3. The small hump around 2θ = 35.8˚ in the RGO-MNPs spectrum (see the dashed violet circle in Figure 4) confirmed the MNP in the hybrid foam. Figure 5 illustrates representative SEM image of isopropanol dispersed magnetic nanoparticles (MNPs, Fe3O4), magnetic particles reduced graphene oxide foam (RGO-MNPs) and RGO foam. 11 ACS Paragon Plus Environment


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Figure 5 (a) presents the high degree of agglomeration for pure MNPs. The agglomeration is attributed to the Van der Waals attractive forces between the particles, as well as the influence of isopropanol which was used to disperse the sample prior to SEM imaging. Figures 5 (b) and (c) reveal a degree of high-porosity and non-uniformity in the RGO-MNPs skeleton as a result of deformation upon hydrothermal reduction. It is worth mentioning that the oxygen-containing groups provide active sites for nucleation of nanoparticles. Whereas, pure RGO foam samples exhibited a slightly higher degree of skeleton uniformity and porosity (see Figures 5 (d) and (e)). This difference can be attributed to the MNPs grafting on the RGO sheets causing ripples. The TEM image in Figure 6 (a) shows the surface morphology of pure MNPs. A transparent GO sheet with small ripples appearing in Figure 6 (b); which are composed of few multilayers as revealed by the high resolution TEM image. These ripples are focused near the sheets edges. Figure 6 (c) shows the TEM image of RGO and as expected, it holds a higher number of ripples due to the hydrothermal reduction. MNPs can be clearly identified in Figure 6 (d) as dim spots ranging in size due to agglomeration via Van der Waals forces. RGO-MNPs sheet reveals a slightly higher degree of ripples formation that might be attributed to the hindering effect exhibited by the grafted MNPs. 3.3. Thermal Stability The TGA thermogram of RGO exhibits an initial drop in mass below 100 °C (Figure 7, red curve). This drop is attributed to the moisture (water) loss from the samples. In the interval of 100-500 °C, there exists a persistent drop in mass. The latter drop is attributed to the gradual loss of epoxide, carboxyl and the least abundant hydroxyl functional groups where they are hydrothermally decomposed into H2O, CO, and CO2. TGA thermogram of hydrothermally


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reduced graphene oxide functionalized with magnetic nano-particles (RGO-MNPs) (Figure 7, blue curve) does not differ significantly from the pattern exhibited by pure RGO due to the small fraction of MNPs (10 wt.% of the GO present in the foam). Both samples are thermally quite stable as 10 wt.% loss was observed for both samples over the temperature range of 25˚C to 500˚C. 3.4. Motor Oil Sorption Figure 8 summarizes the sorption results of two different types of foam, RGO foams and RGOMNPs foams. The MNPs had negligible effect on the sorption capacity. Slight decrease of oil sorption capacity for the MNP containing graphene foam was observed possibly due to the increase of hydrophilicity (due to the existence of oxygen molecules in MNP) of composite foam. Another reason could be that the MNP loading onto the RGO foam slightly reduced the surface area and the pore volume. The morphology of the foam, defects and edges, were mostly responsible for deviations in the oil sorption capacities. For the RGO foam, two different regeneration techniques such as ethanol and thermal regeneration were employed, whereas, for the RGO-MNP hybrid foam, thermal regeneration technique was employed. Sample for thermal regeneration of RGO was synthesized with GO concentration of 2 mg/mL of DI water, whereas, rest of two samples were synthesized by using the GO concentration of 4 mg/mL of DI water. The thermal regeneration method was inefficient in recovering sufficient amount of the adsorbed oil, as the sorption capacity deteriorated drastically. Warm ethanol exhibited effective removal of the motor oil. It can be justified by the fact that the saturation sorption time of low-viscosity organic solvents (ethanol) is much shorter than that of high-viscosity oils (motor oil). The saturation sorption time of ethanol is less than 30 seconds21, while it takes more than 10 minutes



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to reach saturation for motor oil. This difference could be due to the fact that the low-viscosity organic solvents penetrate the three-dimensional network structure of the RGO foam much more easily when compared to motor oil, hence, replaces the motor oil by ethanol in the foam. Figure 9 shows the sorption process for one of the RGO-MNP samples for 8 minutes. For hydrocarbon, like motor oil, the σ electron in the adsorbed molecules can interact with the π electron on the graphene foam to enhance the motor oil sorption. Further, 3 D porous large surface area, super hydrophobic and oleophilic surface of the graphene foam are highly desirable for the motor oil sorption. Mainly, large pores can influence the motor oil sorption. Hence, the sorption is fast and equilibrium was reached within 8 min22-25. The ethanol regeneration technique is illustrated in Figure 10.

4. CONCLUSION We have successfully prepared 3D self-assembled graphene foam by simple hydrothermal reduction method. Magnetic nanoparticles were successfully incorporated in the foam by in situ hydrothermal process. The prepared foam (with/out magnetic nanoparticles) with porous and hierarchical structures showed excellent capability to adsorb motor oil. The foam achieved a maximum sorption capacity of 40 goil/gfoam at ambient conditions. The foam demonstrated good reusability and durability when applied under cyclic operations. In this approach, we have demonstrated that RGO/MNP-RGO hybrid foam works very well for the oil adsorption and recovery. However, there are few significant challenges such as foams’ brittleness, high cost, and moreover, the weak attraction of the functionalized foam (i.e. RGO-MNP) to magnet. In our future study, we will focus on these challenges.


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15. Li, H.; Liu, L.; Yang, F., Covalent assembly of 3D graphene/polypyrrole foams for oil spill cleanup. J. Mater. Chem. A. 2013, 1, 3446. 16. Diagboya, P. N.; Olu-Owolabi, B. I.; Adebowale, K. O., Synthesis of covalently bonded graphene oxide–iron magnetic nanoparticles and the kinetics of mercury removal. Rsc Advan. 2015, 5, 2536. 17. Yoon, T.; Kim, J.; Kim, J.; Lee, J. K., Electrostatic self-assembly of Fe3O4 nanoparticles on graphene oxides for high capacity lithium-ion battery anodes. Energies 2013, 6, 4830. 18. Fu, C.; Zhao, G.; Zhang, H.; Li, S., A facile route to controllable synthesis of Fe3O4/graphene composites and their application in lithium-ion batteries. Int. J. Electrochem. Sci. 2014, 9, 46. 19. Wang, Y.; He, Q.; Qu, H.; Zhang, X.; Guo, J.; Zhu, J.; Zhao, G.; Colorado, H. A.; Yu, J.; Sun, L., Magnetic graphene oxide nanocomposites: nanoparticles growth mechanism and property analysis. J. Mater. Chem. C. 2014, 2, 9478. 20. WooáLee, J.; BináKim, S., Enhanced Cr (VI) removal using iron nanoparticle decorated graphene. Nanoscale 2011, 3, 3583. 21. Wu, Z.-Y.; Li, C.; Liang, H.-W.; Zhang, Y.-N.; Wang, X.; Chen, J.-F.; Yu, S.-H., Carbon nanofiber aerogels for emergent cleanup of oil spillage and chemical leakage under harsh conditions. Sci. Reports 2014, 4, 4079. 22. He, Y. Q.; Liu, Y.; Wu, T.; Ma, J. K.; Wang, X. R.; Gong, Q. J.; Kong, W. N.; Xing, F. B.; Liu, Y.; Gao, J. P., An environmentally friendly method for the fabrication of reduced graphene oxide foam with a super oil absorption capacity. J. Hazard. Mater. 2013, 260, 796805. 23. Zhu, H. G.; Chen, D. Y.; Li, N. J.; Xu, Q. F.; Li, H.; He, J. H.; Lu, J. M., Graphene Foam with Switchable Oil Wettability for Oil and Organic Solvents Recovery. Adv. Funct. Mater. 2015, 25, 597-605. 24. Dong, X. C.; Chen, J.; Ma, Y. W.; Wang, J.; Chan-Park, M. B.; Liu, X. M.; Wang, L. H.; Huang, W.; Chen, P., Superhydrophobic and superoleophilic hybrid foam of graphene and carbon nanotube for selective removal of oils or organic solvents from the surface of water. Chem. Commun. 2012, 48, 10660-10662. 25. Zhai, P.; Jia, H. M.; Zheng, Z. Y.; Lee, C. C.; Su, H. J.; Wei, T. C.; Feng, S. P., Tuning Surface Wettability and Adhesivity of a Nitrogen-Doped Graphene Foam after Water Vapor Treatment for Efficient Oil Removal. Adv. Mater. Interfaces 2015, 2, 8.


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List of Tables Table 1: Comparison of the maximum sorption capacities (g of oil/g of adsorbent) for crude oil by different sorbents Table 2: Summary of elemental compositions of sample determined by SEM-EDX



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List of Figures Figure 1: Schematic of reduced graphene foam synthesis by hydrothermal process Figure 2: FTIR spectra of (a) GO, (b) RGO and (c) RGO-MNP Figure 3: Raman spectra of GO, RGO and RGO-MNPs recorded using 514 nm laser excitation Figure 4: XRD spectra of GO, RGO, RGO-MNPs and MNPs (1.54 Å as wavelength) Figure 5: SEM images showing the morphology of (a) magnetic nanoparticles, MNPs (Fe3O4), (b) magnetic graphene foam (RGO-MNPs), (c) RGO-MNPs, (d) pure graphene foam (RGO) and (e) RGO (higher resolution) Figure 6: TEM images showing the morphology of (a) MNPs, (b) GO, (c) RGO, (d) RGO-MNPs and (e) RGO-MNPs (higher resolution) Figure 7: TGA thermograms of RGO and RGO-MNPs Figure 8: Sorption capacity of RGO & RGO-MNPs foams Figure 9: Illustration of the oil sorption by magnetic nanoparticle reinforced graphene foam Figure 10: Schematic of the warm ethanol bath regeneration technique


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Table 1 Maximum sorption Sorbent

Reference capacity [g oil/g adsorbent]

Thermally reduced graphene

131

5

105.4

2

Spongy graphene

86

6

Activated carbon

10

7

Carbon fiber

17

7

Polyurethane foam

69

8

Exfoliated graphene

83

9

Nanoporous graphene



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Table 2 Atom (%) Samples

C/O C

GO

O

Fe

81.6 18.4 -

MNPs (Fe3O4) -

4.43

46.5 53.5 -

RGO

90.4 9.6

-

9.42

RGO-MNPs

89.6 9.8

0.6

9.14


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Figure 1



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Figure 2


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Figure 3 23 ACS Paragon Plus Environment


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Figure 4


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GO

Pure RGO

RGO-MNPs

MNPs

11.42˚ ≡ 7.74 Å 24.60˚≡ 3.61Å 24.50˚≡ 3.63 Å

Intensity (a.u)

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35.87˚≡ 2.50 Å

5

10

15

20

25

30

35

40

2ϴ (deg)

Figure 5


45


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(a)

(c)

(b)

(d)

(e)

Figure 6


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(a)

(c)

(b)

(d)

(e)

Figure 7



Pure RGO

RGO-MNPs

100 90 80

Mass (%)

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70

100

60

99

50

98 97

40

96

30

95

20

94 25

50

75

100

125

150

175

200

225

10 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500

Temperature (°C)

Figure 8


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RGO - Thermal Regeneration RGO - Ethanol Regeneration RGO-MNP - Thermal Regeneration

40 35 30 Capacity (goil/gfoam)

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25 20 15 10 5 0 1

2

3

Cycle number

Figure 9



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t = 0 min

t = 8 min

Figure 10 30 ACS Paragon Plus Environment

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Table of Content (TOC):



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Developing Hydrophobic Graphene Foam for Oil Spill Cleanup

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