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Scientific Reports Volume 6, Article Number: 21858 (2016) Cite this article

Water purification and oil/water separation are the main motivations for the development of new methods for sustainable development. In this case, because of the scarcity of supply, providing clean water to the ecosystem is as important as restoring oil spills. Inspired by the design of an engineering material that can be used not only for this purpose, but also for other applications to protect natural resources, it is therefore recommended to use a simple template-free process to make super porous, super hydrophobic, super thin graphite sponge. In addition, the process is designed to be cheap and scalable. The made sponge can be used to clean up different types of oils, organic solvents, toxic and corrosive pollutants. This multifunctional microstructure can maintain its function even after crushing. Due to its ferromagnetic properties, sponges are suitable for targeted adsorption and collection. We hope that this cost-effective process can be widely accepted and implemented.

In the past few decades, the alarming consumption of the earth's resources and the ensuing environmental pollution have aroused people's attention. Frequent oil spills and tanker accidents have disastrous consequences for marine wildlife and ecosystems are clear examples and informers. In order to prevent further damage to the environment, the most favored are new materials and methods for immediately purifying and purifying water and maintaining scarce natural resources. Therefore, research has focused on the adoption and development of new oil-absorbing materials 1, 2, 3, 4, and 5. The most advanced materials used for such purposes should have low water absorption and high oil absorption6. In addition, it is expected to cause minimal harm to the environment and must be reusable6. Nevertheless, the proposed structure must be equally cheap and scalable in order to be widely adopted to achieve sustainability7,8. Different physical and chemical processes have been foreseen and implemented to design such materials with enhanced superhydrophobicity and super lipophilicity and high surface area in the form of membranes. It is reported that the hydrophobicity of the graphene foam obtained on the sacrificial nickel foam template is significantly increased by synthesizing carbon nanotubes (CNT) on the graphene foam, which physically changes the surface 9,10. Therefore, the contact angle between water and the structure has changed from 108.5° to 152.3°. However, the porosity of these structures is limited to macroscopic, almost no mesopores. Recently, it has been reported that CNT and carbon nanofiber (CNF) sponges have excellent oil absorption capacity and recyclability11, 12. Although these sponges may only be used for specific purposes, this may result in a costly and challenging transition to industry. Due to its high surface area to volume ratio, very low density and ideal electrical properties, as well as chemical and mechanical stability, three-dimensional (3-D) graphene-based structures, such as foams, sponges, and aerogels, have been considered versatile and feasible Candidate materials. Oil-absorbing material 10,13. In addition, it was found that this graphene-based structure is useful for gas sensing 14 and adsorption 15, biological applications 16, thermal management 17, radiation protection and shielding 18, energy conversion and storage 10, 15, 19, 20 and even structural reinforcement 21, 22 It is a very advantageous material. Although chemical activation must be used to improve the total surface area of ​​graphene-based sponges for certain specific applications, it is believed that it is more practical to utilize a multifunctional and scalable paradigm. According to reports, the most widely used manufacturing process for graphene-based sponges is the hydrothermal reduction and assembly of graphene oxide nanosheets10,23,24. Although the well-thought-out functionalization of these structures produces tailored components for specific environmental applications 25, 26, the hydrothermal process is very long and precedes the Hummer method 23, 24. Therefore, the properties and effectiveness of the sponge depend to a large extent on the well-developed Hummers method, which is as long as 27. Here, in order to propose a simple, relatively fast and scalable manufacturing process, we report the synthesis of a scalable, multi-functional, free-standing ultra-thin graphite sponge with super-hydrophobic, lipophilic and ferromagnetic properties. Sponge provides a special surface area and multi-modal porous structure, including macropores, mesopores and micropores. In this sense, the structure can be considered as self-activated, and it is mainly not necessary to perform a separate chemical activation to enhance the surface properties. The structure and synthesis process are considered to be effortless, cheap and scalable, and can be adapted to different applications with only minor modifications.

Ultra-thin graphite sponge (hereinafter referred to as UtGS) is synthesized through a sol-gel process, then cured and annealed at high temperatures. The synthesis process is schematically shown in Figure 1(a). Prepare a clear, homogeneous aqueous solution of the precursor (sol) and add a few drops of nitric acid to the solution to adjust the pH to 3 and initiate the polymerization reaction. Under continuous stirring at 90 °C, a viscous resin (gel) forms after a few hours. The viscous resin is spread on a glass substrate and cured in a vacuum oven at 120 °C to form a sponge-like substance as an intermediate precursor. Cut the sponge-like precursor into the desired shape with a blade. The UtGS structure is achieved by heat-treating the intermediate precursor at high temperature (500-1000°C) under argon and hydrogen flows in a horizontal tube furnace.

(a) Synthesis diagram (b) UtGS on the right container is soaked in toluene dyed with n-blue. (c) No leakage of toluene from the sponge into the water was observed. (d) UtGS can still clean toluene overflowing from the water surface. (e) SEM image of sponge microstructure. (f) A high-magnification SEM image taken from the surface of the sponge, roughly at the position indicated by the white arrow.

As shown in Figure 1(bd), UtGS can be used to remove toluene from water, where toluene is dyed with n-blue dye. In this typical experiment, the UtGS sample floating on the water surface was first immersed in toluene droplets (Figure 1(b)). It seems that toluene is contained in the sponge (Figure 1(c)), and the soaked sponge can further absorb toluene (Figure 1(d)). In addition, Supplementary Figure 1 illustrates the chloroform highlighted with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4 H-pyran (DCM) Separation from the water. The sequence also shows the replacement of air with chloroform in the sponge structure. Compared with water, UtGS seems to be able to absorb organic pollutants of different densities and several dyes and stains in water, and it can also maintain its function underwater.

To test the recyclability of UtGS, the sample was soaked in toluene and then placed in a flame. Burn the sample containing the absorbed toluene until all the toluene is consumed. Since there is no fuel, the fire is self-extinguishing, and the UtGS sample remains intact and can be used again (Supplementary Figure 2(ac)). Similar studies have been conducted to demonstrate the fire resistance and recyclability of graphene-based sponges28, 29. However, recovery of absorbents such as oil and organic solvents from the adsorbent after absorption is still a priority. A simple process can be implemented to heat the UtGS containing the absorbent to evaporate the absorbed contaminants. The steam can then be condensed into liquid form and recycled 30. To further quantify cyclic recovery, the weight change of UtGS samples was evaluated (Supplementary Figure 3). In this case, the sample was saturated with ethanol, and the ethanol was evaporated by annealing at 500°C for 30 minutes. The UtGS dry weight was exactly the same within 10 cycles, and the measured value was 20.78 mg. The weight of UtGS after saturation was 469.8 to 471.2 mg, and no significant decrease in absorption capacity was observed.

Figure 1(e) reveals the microstructure of UtGS, which appears to be a maze of interconnected large holes. A higher magnification SEM (Figure 1(f)) shows that the surface of the sponge appears to be very porous, which can be considered as a possible connection between mesopores and channels. It is also possible to identify randomly oriented graphene flakes and thin stacks of layers on the surface. The TEM image shows that UtGS is composed of wrinkled and curled flakes (multi-layer graphene layers) and dispersed nanoparticles with an average diameter of about 20 nm (Figure 2(a)). Higher magnification TEM imaging shows that iron nanoparticles are wrapped in several layers of graphene in the structure (Figure 2(b)). The HRTEM image shows an interplanar spacing of 0.34 nm, which corresponds to the stacking of sp2 hybridized carbon layers (Figure 2(b) inset). As pointed out in Figure 2(c), the structure appears to include many tiny graphene domains and randomly oriented flakes, which have obtained a rough microstructure containing microchannels. The HRTEM image resolved from the sponge surface shows the presence of very small graphene-based domains with random orientation and complex stacking and sub-nano channels separating them (Figure 2(d)). In this sense, the width of the microchannel separating the graphene domains seems to be slightly different from the measured interplanar spacing of 0.34 nm. HRTEM characterization of UtGS shows that the interconnected porous structure is supported by graphite walls composed of approximately 10-15 graphene-based layers (Supplementary Figure 4). In addition, the measured interplanar spacing of the stacked layers seems to be consistent with the interplanar spacing of the graphite structure.

(a) Low magnification TEM image of UtGS (b) High magnification image of Fe nanoparticles encapsulated in a graphene substrate (Inset: HRTEM image shows the graphene layer, highlighting the interplanar spacing). (c) Low magnification image around UtGS surface. (d) HRTEM image showing the microstructure of UtGS surface.

Figure 3(a) shows the measured value of the contact angle of water on the sponge, which is estimated to be 154.72°. This special hydrophobicity is the result of a large number of micro- and nano-scale air voids and surface roughness at the interface with water, and the possible absence of hydrophilic groups on the surface of the sponge. In order to study the absorption behavior of the UtGS structure over time, the sample was exposed to compressor oil and its weight change was monitored within one minute (Figure 3(b)). The oil is absorbed into the sponge on contact and reaches maximum absorption in about 4 to 6 seconds. To enumerate the absorption capacity of UtGS (c = 15.57), the mass change after oil absorption (mf = 327 mg) is divided by the initial mass of the sponge (mi = 21 mg). Therefore, the maximum weight of compressor oil that UtGS can absorb is approximately 15.57 times its weight. At the same time, UtGS showed a similar ethanol adsorption trend (Supplementary Figure 5(a)), and the calculated absorption capacity was 22.69. The absorption capacity of different organic pollutants is compared in Supplementary Figure 5(b), which shows the complex influence of the density, viscosity and surface tension of the absorbent on the adsorption phenomenon9. Figure 3(c) shows a snapshot of the diffusion and absorption behavior of compressor oil in contact with the UtGS surface, taken at 60 millisecond intervals. This indicates that the sponge is lipophilic because the oil penetrates into the structure on contact and is completely absorbed by the sponge within about 300 milliseconds. Although the oil absorption capacity of UtGS is higher than that of modified polyurethane foam (about 13.25 gg-1)3, it is much lower than that of CNF aerogel (about 200 gg-1) 12 and CNT aerogel (about 125 gg-1) 31 Oil absorption capacity, graphene aerogel (about 85 gg-1) 32 and CVD-graphene/CNT mixed foam (about 90 gg-1) 9. The porosity of these foams and aerogels is the result of mesopores and macropores. These 3-D structures also exhibit considerable volume changes, which contribute to the adsorption kinetics. However, UtGS provides micropores, mesopores and macropores at the same time, and the high internal surface area of ​​UtGS is mainly attributed to mesopores and micropores. Due to the limitation of the surface tension of the oil, these pores and channels may not contribute to the oil absorption, which can explain the decrease in the oil absorption capacity of UtGS compared with CNF, CNT and graphene aerogel. Or, this setback can be made up for by UtGS' simple manufacturing process, versatility and scalability.

(a) The contact angle measurement of UtGS shows superhydrophobicity. (b) The graph shows the change in oil absorption of UtGS over time. (C) Snapshot showing the diffusion and absorption of oil of lipophilic UtGS.

In order to characterize the details of the microstructure and ignore the structural changes and phase evolution, X-ray diffraction (XRD) and Raman spectroscopy were performed on UtGS samples prepared at different temperatures. Figure 4(a) shows and compares the XRD patterns of UtGS samples heat-treated at 500, 600, 700, 800, 900, and 1000 °C. According to the characteristic diffraction angle, the sp2 hybrid layer in the form of graphene and α-Fe33 and Fe3O433,34 can be identified at different temperatures (Figure 4(a)). The peak at 24° may correspond to the (002) reflection, and the peak at 43° may be related to the superposition of the (101) and (100) reflections in the sp2 hybrid graphite lattice structure. According to other researchers, these two peaks may be related to graphene sheets and flakes 36, 37, 38, 39. In addition, synthesis at higher temperatures will produce higher structural crystallinity, because the XRD peaks appear sharper at higher relative intensities. As shown in Figure 2(a,b), the dispersed nanoparticles in the microstructure are probably α-Fe nanoparticles with a diameter of about 20 nm. Although some of the nanoparticles are wrapped in several layers of graphene, some nanoparticles can be found on the surface of the sponge that are not protected. It should be noted that the final heat treatment of the sponge precursor is performed under an argon and hydrogen atmosphere, which can prevent the oxidation of Fe nanoparticles. However, once the sponge is taken out of the reducing environment of the furnace and exposed to the air, the nanoparticles are prone to surface oxidation. Therefore, trace amounts of Fe3O4 can be observed in the XRD pattern at 700 °C (Figure 4(a)). Supplementary Figure 6(a) and (b) show the energy dispersive X-ray spectroscopy (EDS) spectra of the untreated UtGS sample and the sample treated with hydrochloric acid (HCl), respectively. As a result of the acid treatment, by dissolving the unprotected Fe nanoparticles, the amount of Fe in the structure was reduced from 12.69% by weight to 5.55% by weight. Therefore, approximately 5.55 wt% of the structure is considered to be graphene-encapsulated α-Fe nanoparticles. To supplement this assessment, untreated UtGS samples have been affected by a mixture of C2H4:H2 to use iron nanoparticles as a catalyst to synthesize carbon nanotubes (CNT). Supplementary Figures 6(c) and (d) show that multi-walled carbon nanotubes of various diameters containing iron nanoparticles at their tips can originate from the sponge surface. As a demonstration of its versatility and versatility, UtGS can be used to easily manufacture an independent 3-D graphene-CNT hybrid architecture.

(a) Multiple XRD patterns of UtGS heat treatment at different temperatures. (b) Raman spectra of UtGS heat-treated at different temperatures.

Figure 4(b) shows the Raman spectra of UtGS heat-treated at different temperatures. Three characteristic Raman peaks D, G and G'of graphene can be observed in the spectrum, which are located at 1335, 1580 and 2680 cm-1, respectively. Since the G'peak of graphite is considered asymmetric and split into four peaks 41, 42, the peak centered at about 2680 cm-1 can be related to the G'peak of graphene. The broad D peaks in the spectrum indicate a high degree of disorder in the structure. In order to study the change of UtGS structure, the peak intensity ratios from D to G (ID/IG) and G'to G (IG'/IG) at different heat treatment temperatures are plotted in Supplementary Figure 7. As the temperature increases, ID/IG refers to the disorder in the graphene layer, which follows an overall upward trend except for a decrease from 600 to 700 °C. Similarly, IG'/IG, which is a measure of the number of stacked graphene layers, increases with temperature. It seems that the formation of the graphene substrate starts at about 700 °C, because the G'peak appears at this temperature. The evolution of the system from 600 to 700 °C can be explained by the incubation of the amorphous to crystalline transition. As the graphene substrate begins to nucleate and grow, the degree of disorder seems to temporarily decrease. Later, the formation of spatially intricate graphene sheets produces a higher degree of disorder. The rising trend of IG'/IG means that the growing graphene layers are not stacked or may form a turbulent layer structure, where the stacked layers slide sideways relative to each other to create microchannels 43. The presence of the D'peak at 1608 cm-1 exacerbates the highly disordered graphene domains, and also indicates that the graphene substrate may be doped with nitrogen 44.

In order to study the chemical reaction and changes of the precursor during the synthesis process, Fourier transform infrared (FTIR) spectroscopy was performed on the cured resin. Due to the stretching vibration of the OH bond, the FTIR result (Figure 5(a)) shows a broad peak at 3398 cm-1. The weak bands at 2920 and 2879 cm-1 correspond to the symmetric and asymmetric vibrations of the CH bond 46, and the bands at 1718 and 1622 cm-1 are due to the stretching vibrations of the C=O and C=C bonds 45, 47, respectively. The narrow band at about 1405 cm-1 is related to the bending vibration of the OH bond45 and the peak at about 1350 cm-1 is the result of the stretching vibration of the C-OH bond48. The stretching vibration of the CN bond and the breathing vibration of the epoxy group can be attributed to the peak at about 1200 cm-1 49. The vibration at about 1050-1070 cm-1 may be related to the stretching vibration of the CO bond45,46. A further trace of the CH bond can be seen at 932 cm-1 as an out-of-plane vibration band 49. The frequency band between 480 and 730 cm-1 is considered to be related to the Fe-O stretching vibration 47,49. The chemical principle of the sol-gel process is schematically illustrated in Supplementary Figure 8. It seems that in the sol-gel process, the addition of nitric acid after the hydrolysis of sucrose results in the formation of sugar acids50,51. PVA monomers and iron cations react with saccharinic acid at 90 °C at the same time to first produce long chains of polymer resins, and then produce chain cross-links, transforming the sol into a gel50,51. These long chains in the gel contain iron cations, and they seem to contain all the aforementioned bonds, which have been determined in FTIR measurements. Heat treatment at high temperature is likely to separate the bonds between carbon and hydrogen, oxygen and nitrogen, and cause them to leave the structure in the form of gas molecules. This may also contribute to the formation of microchannels and the possible chaotic layer structure of the graphene substrate. The heat treatment also causes the decomposition of hydrophilic groups on the sponge surface, which contributes to hydrophobicity in its terminology. When the structure is carbonized at high temperature in a reducing atmosphere, adjacent iron cations will aggregate and form iron nanoparticles. As an example of the adaptability of UtGS, a similar improved sol-gel process has been reported for the synthesis of metal oxides, which means that other metal nanoparticles can be added to the structure for designated applications 50,51.

(a) FTIR spectrum of UtGS precursor after curing and before final heat treatment. (b) BET surface area measurement of UtGS, combined with type I and type IV N2 adsorption. (c) The pore size distribution of UtGS (calculated based on the DFT model). (d) The hysteresis loop curve obtained from UtGS.

Brunauer-Emmett-Teller (BET) surface area measurement has been used to quantify the surface area and porosity of UtGS structures. Figure 5(b,c) summarizes the results of adsorption-desorption isotherms and BET pore size distribution, respectively. The structure appears to exhibit a combination of type I and type IV N2 adsorption-desorption isotherms52,53. Adsorption at a relative pressure of less than about 0.1 means that micropores or microchannels can be found in the sample, and the hysteresis loop of the relative pressure from about 0.5 to 1.0 is related to mesopores. The DFT model is used to calculate the average pore size to be about 1.4 nm. The Langmuir and BET surface areas of UtGS samples were measured to be 1356.30 and 823.77 m2.g-1, respectively, which means that chemical activation is not the main concern to improve porosity and surface area. In addition, the density of UtGS is calculated to be 0.017 gr.cm-3. It can be inferred that most of the surface area is due to micropores and microchannels. Nevertheless, this cannot contradict the reality and contribution of mesopores that can be identified in high-magnification SEM images (Figure 1(e)). Although the mesopores may contain part of the total volume of condensate, the number of micropores and microchannels is clearly dominant. Therefore, the mesopores will not contribute to the pore distribution as expected. Supplementary Figures 9(a) to (e) represent snapshots taken during an experiment aimed at qualitatively evaluating the effectiveness of powdered UtGS. Pour the crushed sample into a water container contaminated with ethanol stained with rhodamine b. Place the magnet in the container to collect the sponge powder. The collected samples seemed to effectively absorb the contaminants because there was no trace of rhodamine b (pink dye dissolved in ethanol). Supplementary Figure 9(f,g) gives the concept of particle size; and shows a high-magnification SEM image of the fracture cross section to depict the porosity in the UtGS body separately. In this sense, the absorption of pollutants may be attributed to mesopores and micropores. The aggregated graphene-based layer and exposed iron nanoparticles as well as mesopores and pores can be envisaged within the cross-section of the powdered sponge particles (Supplementary Fig. 9(g)).

In order to further prove the versatility of G-sponge, the viscous resin was cured, and at the same time, a constant nitrogen flow was used to generate bubbles in the resin, and the microstructure was affected, as shown in the different magnifications in Supplementary Figure 10 (a) and (b) It seems that this process promotes the formation of macropores rather than mesopores, because the surface does not seem to be too porous (Supplementary Figure 10(b)). On the contrary, when cured under nitrogen pressure, a conformal layered structure is formed after annealing at high temperature (Supplementary Figure 10(c), (d)), as if the crosslinking of resin chains is suppressed under pressure.

The hysteresis loop of UtGS is shown in Figure 5(d), which is consistent with the hysteresis loop of ferromagnetic materials. At room temperature, the saturation magnetic force (MS) and coercive force (HC) have been measured to be 8.49 emu.g-1 and 336 Oe. Therefore, α-Fe nanoparticles can accommodate a single magnetic domain due to the high measurement of HC and the average diameter of the particles (20 nm)56. Compared with the reported value of α-Fe nanoparticles of similar size, the measured MS is relatively small because it only accounts for 12.69% of the total weight. Returning to the XRD multi-pattern shown in Figure 4(a), at 500 and 600°C, no traces of α-Fe or tiny traces are observed, which indicates that there may be no traces of α-Fe in the samples heat-treated below 600°C Ferromagnetism is observed. Ferromagnetic properties can provide selectivity for the targeted delivery and collection of sponges.

In conclusion, we have successfully demonstrated the synthesis of a scalable, multifunctional ultra-thin graphite sponge with excellent porosity and surface area, as well as superhydrophobic and lipophilic properties through an improved sol-gel assisted process. The structure and synthesis process are designed to be effortlessly inexpensive and highly scalable for widespread adoption and use. Since the average diameter of graphene-encapsulated α-Fe nanoparticles is about 20 nm, the synthesized sponge is ferromagnetic. We also demonstrated the versatility of the architecture, enabling the required modifications, such as direct CNT growth or adding other metal nanoparticles to the structure, thereby expanding its application areas. The obtained sponge has a contact angle of 154.72° with water and has lipophilicity. It provides a significant surface area of ​​823.77 m2.g-1 and an average pore diameter of 1.4 nm without chemical activation. This surface area is due to the presence of macropores, mesopores and micropores and channels in the structure. Sponge is effectively suitable for underwater use, even after crushing. Because of the embedded ferromagnetic α-Fe nanoparticles, the sponge can also be transported and collected to contaminated coordinates selectively and targeted. The implemented architecture provides a promising capability for environmental cleaning applications, such as oil-water separation and water purification. Due to its multifunctional microstructure, it can also be used for gas filtration and sensing and energy storage.

UtGS is prepared by an improved sol-gel process, then cured in vacuum and annealed at high temperature. In short, 2.82 g sucrose (Sigma-Aldrich, >99.5%), 0.12 g polyvinyl alcohol (Sigma-Aldrich, 98-99%), and 0.84 g ferric nitrate nonahydrate (Sigma-Aldrich, >98%) Dissolve in 17 ml of deionized solution (DI) water and stir to form a homogeneous solution. Add 0.1 ml of nitric acid (HNO3) to the final solution (sol), then raise the temperature to 90 °C and keep it for 1 hour. As a result of a series of chemical reactions and polymerizations, a thick dark brown resin (gel) is formed. The resin is cured under vacuum at 120°C for 2 hours. The cured resin is then cut into the desired shape with a blade and transferred to a horizontal tube furnace. The temperature rises to the final temperature (500, 600, 700, 800, 900, and 1000 °C) at a rate of 10 °C.min-1. The samples were annealed in Ar and H2 atmospheres at a flow rate of 100 and 50 sccm at 5 Torr for 30 minutes to form the final sponge structure.

To evaluate the kinetic adsorption behavior, a 1:1 ratio of deionized (DI) water and pollutants was used. Place the UtGS sample on the water surface and weigh it at different times after absorption. The measurement continues until the plateau period of weight change is reached. Each set of measurements is repeated eight times.

To measure the absolute absorption capacity, the UtGS sample was immersed in a contaminant container and sonicated for 10 minutes. Each group of measurements were repeated 8 times.

Using Fe nanoparticles on the surface of UtGS as a catalyst, CNTs were grown on UtGS by chemical vapor deposition (CVD) in a horizontal tube furnace. The mixture of Ar, H2 and ethylene (as a carbon precursor) flows at a rate of 150, 100, and 50 sccm, respectively. The temperature rises to 750 °C at a rate of 10 °C.min-1 and grows for 30 minutes at 700 Torr.

UtGS samples were sonicated overnight in a 1:1 mixture of ethanol and HCl by volume. The acid-treated sample was sonicated and washed several times with absolute ethanol until it reached a neutral pH value, and then dried under vacuum at 90°C overnight.

A scanning electron microscope (SEM; FIB NNS450) equipped with X-ray energy dispersive spectroscopy (EDS) and a transmission electron microscope (TEM; Philips, CM300) with a LaB6 cathode operating at 300 KV were used for morphological studies and imaging analysis. For TEM imaging, ultrasonically disperse the crushed sponge in ethanol for 1 hour, and then drop the diluted sample onto a carbon-coated TEM grid. The crystal structure and phase were identified by X-ray diffraction analysis (XRD, Philips X'Pert) using Cu Kα radiation. A Horiba LabRAM HR spectrometer and an excitation source with a wavelength of 532 nm were used to collect Raman spectra. Use Bruker Equinox 55 FTIR for Fourier transform infrared spectroscopy. The surface area and pore size distribution analysis is done by Brunauer-Emmett-Teller (BET) measurement using Micromeritics ASAP 2020 and nitrogen. A vibrating sample magnetometer (VSM) is used to measure the magnetic properties.

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Department of Mechanical Engineering, University of California, Riverside, California 92521

Hamed Hosseini Bay and Cengiz S. Ozkan

Materials Science and Engineering Project, University of California, Riverside, 92521, California, USA

Daisy Patino, Zafer Mutlu, Paige Romero and Cengiz S. Ozkan

Department of Electrical and Computer Engineering, University of California, Riverside, California 92521

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HHB, MO and CSO designed experiments. HHB and DP have carried out material synthesis. HHB designed and supervised all characterization. Material characterization is completed by HHB, DP, ZM and PRHHB analysis data. HHB, MO and CSO wrote the manuscript. The CSO and MO manage the research team. All authors reviewed the manuscript.

The author declares that there are no competing economic interests.

This work is licensed under the Creative Commons Attribution-Non-Commercial Use-Prohibited Derivation 4.0 International License Agreement. The images or other third-party materials in this article are included in the Creative Commons license of the article, unless otherwise stated in the credit line; if the material is not included under the Creative Commons license, the user will need permission from the license holder to copy The material. To view a copy of this license, please visit http://creativecommons.org/licenses/by-nc-nd/4.0/

Bay, H., Patino, D., Mutlu, Z. etc. Scalable multi-functional ultra-thin graphite sponge: freestanding, super porous, super hydrophobic, lipophilic structure, with ferromagnetic properties for environmental cleaning. Scientific Report 6, 21858 (2016). https://doi.org/10.1038/srep21858

DOI: https://doi.org/10.1038/srep21858

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