WO2011130507A1 - Highly functionalized reactive graphene nano-sheets and films thereof - Google Patents

Abstract

Provided are highly reactive graphene nanosheets and related methods for synthesizing these materials. Functional groups created on the materials are fully characterized using FTIR, Raman, and X-ray photoelectron spectroscopy, as well as by X-ray diffraction pattern. The thermal stability of the materials is characterized using thermogravimetric technique, and high resolution Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) are also used to demonstrate the level of exfoliation in the developed nanomaterials. Films and methods of making films from the graphene nanosheets are also provided.

Description

HIGHLY FUNCTIONALIZED REACTIVE GRAPHENE NANO-SHEETS AND FILMS

THEREOF

GOVERNMENT RIGHTS

[0001] This invention was made with the government support under Office of Naval Research (ONR) grant N00014-07-1-0889. The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the benefit of U.S. Provisional Application No. 61/323,999 filed April 14, 2010 and U.S. Provisional Application No. 61/425,612 filed

December 21, 2010. The entirety of each application is incorporated by reference herein for all purposes.

TECHNICAL FIELD

[0003] The present invention relates to the field of graphenic materials and methods of making graphenic materials.

BACKGROUND

[0004] 1. Introduction

[0005] Graphene is a two-dimensional sheet of carbon with carbon atoms attached to one another via sp² hybridized covalent bonds (which are the strongest bonds in nature), giving rise to a honeycomb structure. Graphene consists of two regimes: an aromatic region with unoxidized benzene rings and an aliphatic region with six member rings. The relative amount of two regions depends on the degree of oxidation.

[0006] Adjacent layers of graphene are cohesively bonded via Van der Waals interactions. Graphite oxide is an oxygen rich material (concentrations of about 30-40 wt. %) that is formed via oxidation of crystalline graphite. The exfoliated graphene material (from graphite oxide) is composed of stacks of nanosheets with sheet thicknesses in the range of 4 to 40 nm. Fully exfoliated graphene materials display good affinity for organic compounds and polymers. Graphenic materials are finding uses in composite materials, electronics, and photonics. Accordingly, there is a continuing need to invent new graphenic materials and processes for making graphenic materials.

SUMMARY [0007] Provided herein are methods of synthesizing reactive graphene nanosheets and related nanomaterials produced by mixing the graphene sheets made by three different techniques. The resulting nanomaterials exhibit properties that can be combined to achieve a particular overall characteristic for the nanomaterial. In addition, the reactivity of the disclosed nanomaterials is comparatively high relative to traditional carbon based nanomaterials.

Consequently, the disclosed materials are referred to as "Reactive Graphene Nano-Sheets" (RGNSs). The materials produced with each technique are fully characterized using various analytical and characterization techniques.

[0008] Also provided are methods of synthesizing a reactive graphenic material, comprising dispersing graphite oxide in water; and contacting the graphite oxide in water with hydrogen peroxide so as to produce a graphenic material. Methods for synthesizing graphenic materials are also provided, comprising dispersing graphite in water; filtering the dispersed graphite; drying the filtered graphite; and thermally shocking the dried graphite under an inert gas.

[0009] Methods of synthesizing functionalized graphene are also disclosed, the methods comprising: (a) forming an admixture of graphite and an acid; (b) adding an oxidizer to the admixture; (c) adding water to the admixture; and (d) adding hydrogen peroxide to the admixture.

[0010] Graphite oxide dispersed in water can also be prepared by dispersing graphite powder in an acid solution at a temperature in the range of from +10 degrees C to -78 degrees C to give rise to an acidic graphite dispersion, and treating the acidic graphite dispersion with an oxidizer to give rise to graphite oxide.

[0011] Additional methods of synthesizing functionalized graphene are described, the methods comprising: contacting graphite with water to form a first mixture; sonicating the first mixture; separating solid material from the sonicated first mixture; drying the solid material; and thermally shocking the dried solid material.

[0012] Also described are, inter alia, quasi-plastic films made from Reactive Graphene Nano Sheets (RGNSs). The materials produced with the synthesis techniques are characterized using various analytical techniques. Each nanomaterial displays a unique set of properties that can be combined to draw the overall effect of the nanomaterial.

[0013] Methods of forming graphenic films are also described, the methods comprising: coating a composition comprising graphene, water, and a polar organic compound to a substrate; and evaporating at least a portion of the water and a polar organic compound to give rise to a graphenic film adjacent to the substrate. [0014] In addition, methods of forming graphenic films are disclosed, the methods comprising: forming film comprising graphene, water, and a polar organic compound; and evaporating at least a portion of the water and polar organic compound to give rise to a graphenic film.

[0015] The reactivity of these nanomaterials is high compared to the traditional carbon based nanomaterials; the disclosed materials are hence referred to as "Reactive Graphene Nano- Sheets (RGNS)." Graphene quasi-plastic films (GQPF) can also be fabricated with practically any size and thickness using the disclosed methods.

[0016] Accordingly, there are also provided graphenic films, comprising a cohesive graphenic film, the film having an ultimate tensile strength of at least about 40 MPa; graphenic films, comprising a cohesive graphenic film, the film having an Young's modulus of at least about 300 MPa; and graphenic films, comprising a cohesive graphenic film, the film having a glass transition temperature (Tg) of at least about 25 degrees C.

[0017] And there are also provided methods of synthesizing graphene, comprising contacting graphite with water to form a first mixture; sonicating the first mixture; separating solid material from the sonicated first mixture; drying the solid material; and thermally shocking the dried solid material.

[0018] The general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims. Other aspects of the present invention will be apparent to those skilled in the art in view of the detailed description of the invention as provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The summary, as well as the following detailed description, is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings exemplary embodiments of the invention; however, the invention is not limited to the specific methods, compositions, and devices disclosed. In addition, the drawings are not necessarily drawn to scale. In the drawings:

[0020] Figure 1 illustrates a FTIR analysis of graphenes, showing the spectrum of (a) RGNS-I; (b) RGNS-II, (c) GNS-III suspended in ethanol and taken on KBr pellet; and (d) spectrum of solid dry GNS-III acquired in reflectance mode;

[0021] Figure 2 illustrates Raman analysis of RGNSs, showing the spectrum of solid and dry (a) RGNS-I; (b) solid RGNS-II, and (c) solid GNS-III; [0022] Figure 3 illustrates XPS analysis of RGNS-II; (a) surface survey scans displaying different elements, (b) deconvoluted carbon spectra displaying the signs of carboxyl and hydroxyl groups, and (c) deconvoluted oxygen spectra displaying signals from carbonyl and hydroxyl groups;

[0023] Figure 4 illustrates XPS analysis of GNS-III, showing (a) surface survey scans displaying different elements, (b) deconvoluted Cls spectra displaying the signs of carboxyl and hydroxyl groups, and (c) deconvoluted Ols spectra displaying signals from carbonyl and hydroxyl groups;

[0024] Figure 5 illustrates XRD analysis of graphite powder for RGNS-II and GNS-III; the peak position at approximately 2Θ = 26° represents (002) plane, while the peak at approximately 2Θ = 45° represents (100) plane;

[0025] Figure 6 illustrates inert atmosphere thermogravimetric analysis of RGNS; (a) weight loss as a function of temperature in case of RGNS-I; (b) weight loss as a function of temperature in case of RGNS-II; and (c) multiple step decomposition in case of GNS-III;

[0026] Figure 7 illustrates optical analysis of graphene; (a) RGNS-II powder was black and formed uniform suspension in water and ethanol, (b) GNS-III was grey and was challenging to suspend in liquid, (c) optical image of RGNS-I captured using Raman microscope camera, (d) optical image of RGNS-II captured using Raman microscope camera, (e) an optical image of GNS-III captured using Raman microscope camera, and (el) optical image of materials according to the claimed invention;

[0027] Figure 8 illustrates SEM images of graphene platelets (RGNS-I); (a) graphene platelets can be seen in the micrograph, (b) layers of graphene sheets are clearly visible, and (c) bundles of graphene;

[0028] Figure 9 illustrates TEM images obtained for RGNS-II; (a) multiple layers of graphene, (b) graphene sheet crumpled like a sheet of paper, (c) a few sheets of graphene, and (d) a likely single layer of graphene;

[0029] Figure 10 illustrates TEM images of GNS-III via direct thermal shock; (a-d) several layers of graphene sheets crumpled like sheets of paper;

[0030] Figure 11a illustrates a transmission FTIR spectral analysis of RGNS-I, RGNS- II, and GNS-III as solid and GNS-III sonicated in water;

[0031] Figure lib illustrates a deconvoluted FTIR spectrum of GQPF showing various functional groups;

[0032] Figure 12a illustrates a Raman spectral analysis of solid graphite powder, RGNS-I, RGNS-II, and GNS-III; [0033] Figure 12b illustrates a deconvoluted Raman spectrum of GQPF showing various functional groups;

[0034] Figure 12c provides Table 1, which illustrates assignments of the peaks obtained from the deconvolution of FTIR and Raman spectrums from GQPF;

[0035] Figure 13 illustrates solid state ¹³C NMR analysis of GQPF showing various functional groups in the material;

[0036] Figure 14a, 14b, and 14c illustrate XPS analysis of RGNS-II powder: (a) Surface survey scan; (b) Cls deconvolution; (c) Ols deconvolution showing the presence of various functional groups;

[0037] Figure 15a, 15b, and 15c illustrate XPS analysis of GNS-III powder: (a) Surface survey scan; (b) Cls deconvolution; (c) Ols deconvolution showing the presence of various functional groups;

[0038] Figure 16a and 16b illustrate XPS analysis of GQPF: (a) Cls deconvolution curves obtained after etching the film for different interval of time, (b) Ols deconvolution curves obtained after etching the film for different interval of time;

[0039] Figure 16c shows Table 2, which illustrates data obtained from the XPS analysis of GQPF;

[0040] Figure 17 illustrates XRD analysis in RGNS-II and GNS-III— the inset shows the XRD pattern in graphite powder;

[0041] Figure 18a, 18b, 18c and 18d illustrate an inert atmosphere thermogravimetric analysis of (a) RGNS-I, (b) RGNS-II, (c) GNS-III at three different heating rates, and (d) GQPF at 10°C/min heating rate;

[0042] Figure 19a, 19b, and 19c illustrate photographs of synthesized graphenes and graphene suspended in ethanol: (a) Gel stage of RGNS-I, (b) solidified RGNS-II after thermal shock, and (c) solidified GNS-III after thermal shock;

[0043] Figure 20a, 20b and 20c illustrate optical microscopic images of (a) RGNS-I, (b) RGNS-II, and (c) GNS-III;

[0044] Figure 21a, 21b and 21c illustrates a morphological analysis using electron microscopy: (a) FESEM image of RGNS-I, (b) FESEM image of RGNS-I, and (c) FESEM scanning tunneling image of RGNS-I;

[0045] Figure 22a, 22b, 22c and 22d illustrate a morphological analysis using electron microscopy: (a) TEM image of RGNS-II, (b) TEM image of RGNS-II, (c) TEM image of RGNS-II, and (d) TEM image of RGNS-II; [0046] Figure 23a, 23b, 23c and 23d illustrate a morphological analysis using electron microscopy: (a) TEM image of GNS-III, (b) TEM image of GNS-III, (c) TEM image of GNS-III, and (d) TEM image of GNS-III;

[0047] Figure 24 illustrates optical microscope and FESEM images of GQPF cross- section;

[0048] Figure 25 illustrates a TEM image of ultrasonically treated GQPF;

[0049] Figure 26a and 26b illustrate AFM images of GQPF showing the surface roughness at nanometer regime: (a) larger area of scan, and (b) magnified surface scan;

[0050] Figure 27a, 27b, 27c and 27d illustrate various stages of the development of the GQPF: (a) colloidal solution of the precursor to GQPF ready for spray, (b) drying the solvent by blowing the hot air or leaving the coated substrate overnight, (c) GQPF peeled off the substrate, and (d) GQPF cut into desired size and shape;

[0051] Figure 28 illustrates that GQPF can be ultrasonically treated in a solvent to convert into graphene nano-sheets;

[0052] Figure 29 illustrates the thin sheets (approximately 0.01 mm) of GQPF tested in tensile testing mode using a universal testing machine; and

[0053] Figure 30 illustrates results of dynamic mechanical thermal analysis performed on the thin sheets of GQPF in tensile mode to evaluate the Tg of the material.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0054] The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, applications, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention. Also, as used in the specification including the appended claims, the singular forms "a," "an," and "the" include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. The term "plurality", as used herein, means more than one. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable. [0055] It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, reference to values stated in ranges includes each and every value within that range.

[0056] In a first aspect, the present invention provides methods of synthesizing a reactive graphenic material. These methods suitably include dispersing graphite oxide in water; and contacting the graphite oxide in water with hydrogen peroxide so as to produce a graphenic material. Graphite oxide is suitably synthesized by a modified Hummers methods, as described elsewhere herein. Graphite oxide can also be prepared by dispersing graphite powder in icy cold acids, for example near 0 degrees C, with acid temperatures generally in the range of from +10 degrees C to -78 degrees C. This acid treated graphite dispersion is further reacted with a suitable oxidizer to give rise to graphite oxide. The user also suitably filters and washes the graphenic material, which washing may be performed by using as acid, such as 10% HC1. The resultant material may then be purified by centrifugation, after which the resulting material (which may be in semi-solid form), is dried and may be further sonicated. The sonication may be performed in ethanol.

[0057] The inventive methods also suitably include thermally shocking the graphenic material while contacting the material with an inert gas, such as argon. The thermal shocking suitably includes exposing the graphenic material to a temperature of at least about 500 °C, or even to a temperature of about 1000 °C. The shocking may take place for intervals lasting several seconds; intervals that last from about 5 to about 30 seconds, or even from about 15 to about 30 seconds are considered suitable.

[0058] The present invention also provides additional methods of synthesizing graphenic material. These methods suitably include dispersing graphite (e.g., graphite flakes) in water; filtering the dispersed graphite; drying the filtered graphite; and thermally shocking the dried graphite under an inert gas. The thermal shocking suitably occurs for periods lasting from a few to 30 or more seconds, and may include temperatures of about 500 °C to about 1000 °C.

[0059] The filtered graphene material is suitably dried such that it has an approximately 10% moisture content. While drying is not necessary, at higher moisture content levels, thermal shocking is less effective in exfoliating the layers, impairing performance of the inventive methods. [0060] The present invention also provides additional methods of synthesizing functionalized graphene, comprising forming an admixture of graphite and an acid; adding an oxidizer to the admixture; adding water to the admixture; and adding hydrogen peroxide to the admixture. Suitable oxidizers for use here and in other embodiments include potassium salts, nitric acid, nitrates, nitrous oxide, hypochlorites, chlorites, chlorates, perchlorates, silver oxide, persulphuric acids, ssulfoxides, a Tollen's reagent, osmium tetraoxide, or any combination thereof. A preferred potassium salt comprises potassium permanganate.

[0061] In certain preferred embodiments, the admixture of oxidizer, graphite, and acid are maintained at less than about 20 degrees C for at least about 30 minutes. Afterwards, it is desirable, but not required to filtering this admixture. Likewise, it is desirable, but not required to wash the filtered admixture with an acid. Any number of common acids and combinations of acids can be suitably used. A preferred acid for washing the filtered admixture comprising hydrochloric acid. Subsequent separation and purification steps known in the art can also be used to isolate solid material, such as centrifuging the washed admixture to give rise to a solid, or solid-like precipitate and decanting the liquid supernatant.

[0062] The isolated solid grapheme material isolated by centrifugation can be further dried. The process may be further carried out with an additional step of dispersing the dried solid material in a solvent, wherein the dried solid can be dispersed in the solvent using sonication, homogenization, mechanical mixing, or any combination thereof. Any suitable organic, or aqueous solvent can be used, such as an alcohol. A preferred solvent comprises ethanol.

[0063] Alternatively, the isolated solid grapheme material isolated by centrifugation can be further contacted with ethanol and water so as to form a film precursor mixture. This film precursor mixture may be further sonicated to ensure a degree of dispersion and homogeneity in the mixture. The precursor mixture can then be coated atop a substrate and dried so as to give rise to a grapheme film atop the substrate.

[0064] Grapheme material isolated from the liquid phase by a separation means, such as by centrifugation, often has residual liquid that is adsorbed in the interstices and surfaces of the material. This liquid may be further driven off by heating (e.g., dried), which heating may also effect a physical change, a chemical change, or both in the grapheme material. For example, after centrifugation, the isolated solid material may be heated to a temperature of at least about 250 degrees C, or even at least about 500 degrees C, or even at least about 1 100 degrees C.

Suitable heating time periods are in the range of from about 1 second to about 60 seconds, and preferably less than about 30 seconds. [0065] Another way of synthesizing graphene comprises contacting graphite with water to form a first mixture; sonicating the first mixture; separating solid grapheme material from the sonicated first mixture; drying the solid graphenic material; and thermally shocking the dried solid graphenic material. The dried solid graphenic material may be further contacted with an inert gas, such as a noble gas, so as to effect a chemical change in the graphenic material, to prevent the readsorption of water or oxygen from the environment, or both. Suitable methods for separating the solid material from the sonicated first mixture include centrifugation. After the solid graphenic material is dried, it is treated with a thermal shocking step, which step comprises exposing the separated solid graphenic material to a temperature in the range of from about 250 degrees C to about 1100 degrees C for a thermal shock time in the range of from about 1 sec to about 60 seconds. Preferred thermal shock temperatures are in the range of from about 400 degrees C to about 1100 degrees C. Preferred thermal shock times are in the range of from about 5 seconds to about 30 seconds.

[0066] Graphenic films can also be formed by coating a composition to a substrate, the composition comprising graphene and a precursor solution, the precursor solution comprising water and a polar organic compound; and removing at least a portion of the precursor solution to give rise to a graphenic film adjacent to the substrate. Suitable ways of coating the composition includes dipping, flowing, roll coating, and preferably spraying. Preferably, the precursor solution forms an azeotrope. Suitable ways of removing the precursor solution includes sublimation, freeze drying, and preferably evaporation.

[0067] Graphenic films can also be formed by forming a film comprising graphene, water, and a polar organic compound; and evaporating at least a portion of the water and polar organic compound to give rise to a graphenic film. Suitable graphenic films formed according to the methods described throughout this specification are capable of having any of one or more of a variety of useful properties. For example, the graphenic films may comprise a cohesive graphenic film, the film having an ultimate tensile strength of at least about 40 MPa, or even at least about 60 MPa, or even at least about 80 MPa . The graphenic films may also comprise a cohesive graphenic film, the film having an Young's modulus of at least about 300 MPa, or even at least about 400 MPa, or even at least about 500 MPa, as well as up to about 600 MPa, or even as high as 800 MPa. As well, the graphenic films may also comprise a cohesive graphenic film, the film having an Tg of at least about 25 degrees C, or even a Tg up to about 100 degrees C. EXAMPLES

[0068] 2. Experimental

[0069] 2.1. Materials [0070] Two different forms of graphite were provided by Asbury Carbon, USA. The product data sheet states that the graphite flakes (1721) were acid treated, while the graphite powder (3775) was manufactured with a proprietary technique. Concentrated sulfuric acid, potassium permanganate, hydrogen peroxide, and hydrogen chloride were purchased from Sigma- Aldrich. Chemicals were of analytical and characterization grades and were used without further purification. The water used during the synthesis process was ultrapure.

[0071] 2.2. Synthesis Method

[0072] RGNS- . Graphite oxide was prepared by adopting a modified Hummers method, known in the art. Sulfuric acid (46 ml) was pre-cooled to about 0 °C in an ice bath followed by the addition of 2 g of graphite powder. The mixture was stirred with a magnetic stirrer for 30 min, followed by gradual addition of 6 g KMn0₄. The temperature of the reaction mixture suitably remained below about 20 °C; the temperature is suitably controlled using an ice bath. The temperature of the reaction bath was increased to 35 °C (by increasing the temperature of the liquid) and the reaction mixture was stirred for 2 hours until a gray-colored semi-solid paste was obtained. The solution was brought to room temperature and left standing for 48 hours.

[0073] Ultrapure water (92 ml) was added slowly to the above-described paste, and the result was stirred slowly on the magnetic stirrer. The viscous liquid was then added to 280 ml of pure water followed by vigorous stirring (using a magnetic stirrer) for about 1 h. Hydrogen peroxide was added to this solution; the color of the solution turned from grey to yellow. The functionalized graphite solution was filtered through a sintered/fritted glass funnel and was washed several times with a 10% dilute HC1 solution.

[0074] The resultant composition was isolated using a high speed centrifuge. The semi-solid content was dried at 50 °C for 96 h in a constant temperature incubator and the residue was sonicated in ethanol (having twice the volume of the residue) for 48 h.

[0075] RGNS-II: Semi-solid content obtained after centrifugation was taken in a quartz round bottom flask and left at 50 °C for 72 h in a constant temperature incubator. Argon gas was passed into the flask for 30 min and the content was thermally shocked for about 15-30 seconds at approximately 1000 °C temperature in a horizontal preheated furnace. A dry solid black powder was obtained.

[0076] GNS-III: Two grams of graphite flakes (Asbury Carbons, 1721) of pH 4.93 were taken in a fritted funnel and added to 250 ml of distilled water. The mixture was sonicated for 2 h and filtered under vacuum using a Teflon™ coated filter paper (50 micron mesh); a high speed centrifuge is suitable for separating the solid when filtering was not feasible. The semisolid material was dried at 50 °C for 14 days in a constant temperature incubator. Dried material was transferred to a quartz glass round bottom flask and purged with argon gas for 30 min. The content of the flask was thermally shocked for 30 sec at approximately 1000 °C (as explained above).

[0077] 2.3. Characterization Methods

[0078] The following describes various analytical techniques used to characterize the different nanomaterials disclosed herein (i.e., RGNS-I, RGNS-II, and GNS-III).

[0079] 2.3.1. FTIR Spectroscopic Investigations

[0080] FTIR Analysis was conducted on a Bruker IFS 66/S FT-IR spectrometer. Solid powder or liquid suspensions of reactive nano graphene sheets (RGNSs) were taken on KBr pellet and analyzed directly under the spectroscope. Solid powder was also observed in absorbance mode under the FTIR microscope. A minimum of 60 scans were acquired at a resolution of 4 cm^"1.

[0081] 2.3.2. Raman Spectroscopic Investigations

[0082] Raman spectra shown were excited by an Invictus 785 nm NIR laser and measured with a fiber-coupled micro-Raman RXN system (Kaiser Optical Systems, Inc., Ann Arbor, MI) using a 50 μιη slit. The cosmic rays were removed by the software provided by the Kaiser optical system, which measured the spectra twice and delete the random peaks due to cosmic rays. All spectra were measured under identical conditions; the spectra shown here are smoothed and corrected for their baseline.

[0083] The spectra are vertically shifted for clarity of the presentation. Commercially available polished aluminum sheets with a thickness of 0.5 mm (purchased from Anomet, Inc., Ontario, Canada) were cleaned with methanol and used as substrates. Dry graphene powders were analyzed directly under the dispersive Raman spectrophotometer. A background spectrum was collected prior to collecting a spectrum of the sample.

[0084] 2.3.3. Wide Angle X-ray Diffraction Studies

[0085] The interlayer spacing in graphite and graphene samples were recorded using D8 XRD from Bruker instrument using a Cu-Κα source. The adopted X-ray scanning rate was 0.1 degrees per second.

[0086] 2.3.4. Microscopic Investigations

[0087] Field Emission Scanning Electron Microscope (FESEM) analysis was performed on a Hitachi S4800, and TEM analysis was performed on a LE0912 Energy-Filtering Transmission Electron Microscope. Samples were carbon coated to prevent charging during FESEM analyses.

[0088] 2.3.5. Thermogravimetric Analysis [0089] Thermogravimetric analysis (TGA) was performed on SDT2960 equipment from TA Instruments. Weight of the semi-solid samples were stabilized on the equipment's pan until constant weight was achieved. Variable heating rates were adopted for the solid samples.

[0090] 2.3.6. X-ray Photoelectron Spectroscopic Analysis

[0091] XPS analysis was performed on Kratos Axis Ultra equipment with system pressure of 10^~8 torr during the analysis. The X-ray source was monochromatic Al Ka (1486.6 eV) and X-ray power was 280 watts (14 keV, 20 mA). The takeoff angle was 90° with respect to the plane of the sample. All the peaks were referenced to Cls=285 eV peak.

[0092] 3. Results and Discussion

[0093] The development of RGNSs was affected after discovering processes that produce highly functionalized and fully exfoliated graphene nanosheets. These sheets have highly functionalized surfaces and are capable of reacting with other available functional materials. Extensive analyses were conducted on the materials that were developed employing three different techniques.

[0094] The first technique produces a material that can be used in the solution stage while the third technique generates a low quality material that can be produced in a bulk quantity. The second technique produced high quality reactive graphene nanosheets. In this section, we discuss the results obtained from different analytical and characterization techniques on the three types of produced nanomaterials (i.e., RGNSs).

[0095] 3.1. FTIR Spectroscopic Analysis of Synthesized Materials

[0096] Figures 1-3 show FTIR spectra acquired on RGNS-I, thermally shocked RGNS- II, and thermally exfoliated GNS-III. Acid (-COOH) functionality can be seen at 1714 cm^"1 while C=C aromatic stretching can be seen at 1515 and 1538 cm^"1, C-OH stretching at 1224 cm^"1, and C-0 stretching at 1056 cm^"1. Vibration present at 1628 cm^"1 may be due to unoxidized graphite domains.

[0097] 3.2. Raman Spectroscopic Analysis of Synthesized Materials

[0098] Figure 2 shows a Raman analysis of solid dried RGNS-I, II & GNS III films.

The ordered graphite shows two main bands at 1575 cm^"1 corresponding to G-band from the graphite lattice and a peak at 1355 cm^"1 representing D-band from the graphite edges. The

Raman spectrum shown in Figure 2a from RGNS-I shows shifts in G-band to 1602 cm^"1 and D- band to 1328 cm^"1, suggesting a substitution on the surface of the material.

[0099] In case of RGNS-II (Figure 2b), G-band was found at 1601 cm^"1 while D-band shifted to 1336 cm^"1, indicating that substituted sheets are exfoliated that show Raman signal at higher wavelength as compared to RGNS-I. [0100] The two Raman signals obtained from GNS-III (Figure 2c), were found at 1584 cm^"1 (G-band), i.e., a frequency closer to the graphite absorption and approximately at 1326 cm- 1, i.e., a frequency similar to graphene absorption.

[0101] 3.3. X-Ray Photoelectron Spectroscopy of Synthesized Materials

[0102] A surface survey scan of RGNS-II sown in Figure 3 a displayed sharp peaks for Cls and Ols, indicating successful oxidation in the material. The deconvo lution of carbon peak (Fig. 3b) displayed two peaks concentrated at 284.5 eV corresponding to aromatic or conjugated carbon, 285.8 eV for C-OH bonds and a "hump" concentrated at 289 eV representing C=0 and 0-C=0 bonds. The deconvolution of oxygen peak (Fig. 3c) also showed three major peaks. Peaks were found concentrating at 530.6 eV corresponding to C=0 and 0=C-OH bonding and 533.8 eV corresponding to C-OH bonding. The broad hump around 536 eV represents Auger peaks.

[0103] Figure 4a shows a surface survey scan on GNS-III. Three distinct peaks from S2p, Cls, and Ols are seen in the spectra. The deconvolution of these peaks suggests that the mechanism of reaction occurred over the surface of the carbon.

[0104] In deconvoluted Cls spectra (Fig. 4b), the peak at 254.8 eV is possibly due to conjugate C=C bond, while the peak appearing at 286 eV could be a shift of C-OH bond.

Without being bound to any particular theory, the broad hump appearing between 289 eV-292 eV may be due to 0-C=0 linking. The deconvoluted Ols spectra (Fig. 4c) displays two peaks at approximately 532 eV due to shifted C=0 and 533.8 eV due to C-OH bonding.

[0105] The peak position for different elements suggests that sufficient

functionalization has taken place on the graphene surface. The presence of sulfur on the surface of GNS-III suggested that sulfuric acid was present in the final GNS-III structure.

[0106] 3.4. X-ray Diffraction Studies of Synthesized Materials

[0107] The wide angle X-ray diffraction pattern of graphite powder (Fig. 5 inset), RGNS-II, and GNS-III are shown in Figure 5. In the case of pure graphite powder, peaks appearing at 2Θ = 26.50 with d-spacing of 3.36 A correspond to (002) crystal plane while peak appearing at 2Θ = 42.40 with d-spacing of 2.13 A corresponds to (100) crystal plane. The peak at 2Θ = 44.5 with d-spacing of 2.03 A appears due to (101) crystal plane, and peak at 2Θ = 54.67 with d-spacing 1.67 A corresponds to (004) crystal plane.

[0108] In case of RGNS-II (Fig. 5), instead of a sharp peak at 2Θ = 26.50, a broad peak appears at 2Θ = 24.58 with d-spacing of 3.62 A (002) corresponding to exfoliated graphene nanosheets or platelets. However, a peak at 2Θ = 43.17 representing (100) plane showed d- spacing of 2.09 A. Without being bound to any particular theory, the shift in 2Θ values may be due to different thicknesses of the powder sample under analysis.

[0109] The XRD peaks in case of GNS-III (Fig. 5) were similar to that in graphite powder, with similar d-spacing, suggesting GNS-III was not fully converted to graphene. The intensity of peak at 2Θ = 26.66 (002) was lower as compared with graphite powder.

[0110] 3.5. Thermogravimetric Analysis of Synthesized Materials

[0111] Figure 6 shows inert atmosphere thermograms for RGNS acquired at three different heating rates. The thermal degradation pattern of RGNS-I shown in Figure 6a suggests an approximately 10 wt% loss between 144 - 164 °C. This weight loss could be due to the associated volatile components including acids that were utilized during the functionalization. Approximately, 40 wt% of the material was lost up to 250 °C, possibly due to the decomposition of the smaller components. The residue obtained after the complete decomposition was in the range of 40-50 wt%.

[0112] Thermal stability of RGNS-II was determined by the TGA technique and is shown in Figure 6b. RGNS-II was thermally stable up to 500 °C, as the onset of decomposition was observed at 525 °C. Single step decomposition pattern is observed in this case, indicating the absence of any possible volatile components. The residue obtained beyond pyro lysis at 1000 °C was between 20-40 wt. %.

[0113] Degradation of GNS-II was not uniform as in the case of the other two materials (Figure 6c). The weight loss of 10 wt% was observed at approximately 300 °C. Decomposition pattern was random up to 460 °C, which after stabilization leads to residues of between 50-60 wt. %.

[0114] 3.6. Microscopic Analysis of Synthesized Materials

[0115] Figures 7a and 7b show optical micrographic images for graphenes prepared using three different methods. The RGNSs show uniform distribution in ethanol and water while the GNS is difficult to mix with the two liquids. The dry RGNS-II and GNS-III samples show different textures. The RGNS-II sample is black and sinks when added to water, while GNS-III is dark grey in color and floats on water.

[0116] Figures 7c, 7d, and 7e are optical microscopic images of three graphene samples. The appearances of RGNS-I and GNS-III are similar, while RGNS-II show a surface that was challenging to image using an optical microscope.

[0117] Figures 8a, 8b, and 8c show FESEM images of RGNS-I acquired after the removal of the solvent. Although the solution was sonicated for 72 hours, the graphite layers were still not fully exfoliated at this stage. The thickness estimation based on FESEM image suggests that graphite powder has been modified/oxidized to a certain extent.

[0118] Figure 9 shows TEM images acquired on the fully exfoliated RGNS-II. Several stages of the graphene exfoliation can be seen in the TEM study. A single sheet of graphene can be clearly seen on the equipment's grid. The estimated thickness of the reactive graphene nanosheets was approximately 4 to 7 nm suggesting that graphene sheets observed under the microscope were actually made of at least 3 to 10 layers.

[0119] Figure 10 shows TEM images acquired for GNS-III. Several layers of graphene nanosheets piled up to form platelets. The numbers of graphene layers found in GNS-III samples were higher than those found in RGNS-II.

[0120] Summary of Results Described in the Previous Sections

[0121] Three types of graphene sheets were synthesized employing three different techniques. Several spectroscopic techniques were utilized to determine the functional groups over the surface of the nanomaterial. Thermal stability of the nanomaterials was determined using thermogravimetric analysis. The RGNS-II samples showed the highest thermal stability as compared with the nanomaterials prepared by the other two techniques. Microscopic analyses suggest that the highest level of exfoliation is achieved in the case of RGNS-II. Graphene nanosheets prepared utilizing the technique that produces RGNS-II (as explained here) are thus suitable for preparing highly exfoliated and functionalized graphene. Finally, a mixture of graphene nanosheets can be prepared by mixing the nanomaterials obtained from the three different techniques.

[0122] 4. Description

[0123] Also provided first are methods of synthesizing functionalized graphene. These methods suitably include the steps of (a) forming an admixture of graphite and an acid; (b) adding an oxidizer to the admixture; (c) adding water to the admixture; (d) adding hydrogen peroxide to the admixture so as to give rise to graphene.

[0124] Graphite suitable for the claimed methods includes graphite that is commercially available. A variety of acids are also suitable; as discussed elsewhere herein, sulfuric acid is considered especially suitable for the disclosed methods.

[0125] The acid may be cooled (e.g., to 5 deg. C or even 0 deg. C.) before contact with the graphite. Once the acid and graphite are contacted, the mixture may be stirred, mixed, or otherwise agitated to combine the materials. [0126] The temperature of the acid/graphite reaction mixture is suitably kept below about 20 deg. C. This may be accomplished by a cooled jacket for the reaction vessel, by refrigeration, or by other methods of cooling.

[0127] The added oxidizer is suitably a potassium salt, such as potassium

permanganate. Other oxidizers may be used; such oxidizers include nitric acid, a nitrate, nitrous oxide, a hypochlorite, a chlorite, a chlorate, a perchlorate, silver oxide, a persulphuric acid, a sulfoxide, Tollens' reagent, osmium tetraoxide, and the like. The user may add the oxidizer gradually, or in a bolus; gradual addition is considered suitable.

[0128] The mixture of oxidizer, graphite, and acid is suitably maintained at less than ambient temperature for a time. For example, the mixture may be kept at about 20 degrees C or even about 15 degrees C for 10, 20, 30, or even 45 minutes. The mixture may attain a paste or slurry form, after which the material may be allowed to reach room temperature.

[0129] The resultant admixture may be filtered, washed, or both. After cooling, the reaction mixture may be heated for a time, as explained in the accompanying examples.

[0130] After application of hydrogen peroxide, using an acid (e.g., hydrochloric acid) to wash the filtered admixture is useful. The washed admixture may be centrifuged or further filtered to as to isolate solid material that may be present. Excess moisture may also be removed by using an evaporator, a dessicator, or other methods of moisture removal.

[0131] Solid material that is isolated may be dried (e.g., via an incubator or other drying device). The material may be dispersed and sonicated in a fluid (e.g., ethanol) to effect further purification. The resultant material known as RGNS-I (reactive graphene nanosheets I).

[0132] In some embodiments, the isolated material is subjected to further heat processing, which process may be termed "thermal shocking." The material may be heated to a temperature in the range of from about 250 degrees up to about 1100 degrees C. As well, the material may be heated to at least about 250 degrees C, to at least about 350 degrees C, to at least about 450 degrees C, to at least about 500 degrees C, to at least about 600 degrees C, to at least about 1000 degrees C, or even to at least about 1100 degrees C. The material is suitably heated for a time in the range of from 1 second to about 60 seconds, although heating times of a few minutes are also suitable. The resultant material is known as RGNS-II (reactive graphene nanosheets II).

[0133] Processed material (including material that is isolated by centrifugation) may then be combined with ethanol (or some other polar solvent) and water so as to form a film precursor mixture. The graphene may be suspended in virtually any fluid that can evaporated.

This film precursor mixture may then be sonicated. [0134] Once processed, the precursor mixture may be applied to a substrate (e.g., glass, plastic, metal, PTFE) to give rise to a graphenic film atop the substrate by then permitting the liquid present in the precursor mixture to evaporate. The substrate may be heated to promote liquid evaporation.

[0135] Other methods of synthesizing graphene are also provided. In one embodiment, the user may contact graphite with water to form a first mixture. The weight ratio of graphite to water may suitably be from 10,000: 1 to 1 : 10,000, although other ratios are permissible. The first mixture is then suitably sonicated (e.g., in ethanol), after which solid material present in the mixture may be separated (e.g., via centrifugation) from the sonicated composition. The solid material is then suitably dried. The dried material may be contacted with an inert gas (e.g., a noble gas, or even nitrogen). The gas may be applied to remove excess, unwanted species from the solid material.

[0136] The dried, gas-treated material may also then be thermally shocked. The thermal shocking suitably includes exposing the separated solid material to a temperature in the range of from about 250 deg. C. up to about 1000 deg. C, 1 100 deg. C, or even up to about 1500 deg. C. The duration of the exposure is suitably for from about 1 second to about 60 seconds, although longer exposures are also suitable. The resultant graphene is of high quality and utility, and is termed GNS-III (graphene nanosheets III).

[0137] Methods of forming graphenic films (known as GQPF, graphene quasi plastic films) are also provided. These methods suitably include coating a composition comprising graphene, water, and a polar organic compound onto a substrate, and evaporating at least a portion of the water and a polar organic compound to give rise to a graphenic film adjacent to the substrate. The substrate may be prepared with a nonstick film, such as a mold release agent. Alternatively, the substrate may be made from a non-stick material, such as PTFE.

[0138] The user may apply the composition to the substrate by brushing, spraying, pouring, rolling, or even dripping. Spraying may be effected by a standard spraying device, such as one that propels liquid via air or via other gas, such as nitrogen. The precursor solution may be azeotropic (i.e., is not fractionated by distillation).

[0139] The film thickness may be controlled by the amount of solvent and duration of application at a particular location on the substrate. For example, spraying for a longer time on a particular location will lead to a thicker film. A more viscous solution will also lead to a thicker film. The solution may be thinned or have its viscosity reduced to form a thinner film.

[0140] The user may form several films atop one another by applying a film precursor and solidifying the precursor and then applying additional film precursor and solidifying that precursor material. Successive film layers may be from different film precursor materials. For example, a first layer may be of a grapheme precursor that contains 50% graphene by weight. The second layer may be of a precursor that contains 75% graphene by weight.

[0141] The disclosed films may be made using a precursor that includes (by weight) up to 50% graphene, 60% graphene, 75% graphene, and even up to 90% or 95% graphene by weight. Ethanol is considered an especially suitable polar solvent, although other solvents (e.g., other alcohols) are suitable.

[0142] A variety of techniques are used to evaporate the carrier solution from the graphene once the solution is applied to the substrate. Blown air, convective heating, conductive heating, radiative heating, and the like are all considered suitable techniques. The evaporation methods may be chosen to give rise to an uniform temperature along the fluid that has been applied to the substrate. Films that are a few millimeters in thickness may be achieved by these methods.

[0143] The substrate and film may be separated from one another. The separation may be effected by mechanical peeling. The substrate may also be etched or dissolved away to leave behind the film. The graphene film may itself be formed atop a flexible film substrate. The graphene film may also comprise an adhesive material in order that the graphene film may then be adhered to a substrate. The graphene film may be formed where needed (e.g., to strengthen a body) or may be applied where needed at a later time, e.g., to fix a damaged body.

[0144] Additional methods of forming graphenic films are also disclosed. These methods include forming a film precursor that includes graphene, water, and a polar organic compound, and then evaporating at least a portion of the water and polar organic compound to give rise to a graphenic film. The evaporation may be effected by way of an evaporator, an oven, a dehumidifier, and the like. The films may be formed as bubbles, e.g., via Langmuir- Blodgett techniques.

[0145] The provided graphenic films exhibit unique mechanical properties. The films may have an ultimate tensile strength of at least about 40 MPa, of at least about 50 MPa, or even of at least about 60 or 65 MPa. The films may have a Young's modulus of at least about 300 MPa, or even at least about 350 MPa. The graphenic films may also have a Tg (glass transition temperature) value of about 25 degrees C, or even about 30 degrees C. [0146] 5. Experimental

[0147] 5.1 Materials System

[0148] Two different forms of graphite were provided by Asbury Carbon, USA.

Product data sheet obtained from Asbury Carbon states that the graphite flakes (1721) were acid treated while graphite powder (3775) was manufactured adopting a proprietary technique.

[0149] Concentrated sulfuric acid (ACS grade, i.e., 99% strength), potassium permanganate (Reagent ACS grade, i.e., 99% strength), hydrogen peroxide (ACS grade, i.e., 99% strength, 30% solution in water) and hydrogen chloride (TraceMetal grade, i.e., 99% strength) were purchased from Sigma- Aldrich. The chemicals were of ACS grades and were used without further purification. Water used during the synthesis process was ultrapure with 18μ resistivity.

[0150] 5.2 Synthesis Methods

[0151] RGNS-I: Graphite oxide was prepared by adopting a modified Hummers method. ACS grade sulfuric acid (46 ml) was pre-cooled to 0 °C in ice bath for 30 min followed by the addition of 2 g graphite powder. The mixture was stirred (employing magnetic stirrer) for 30 min followed by gradual addition of 6 g KMn0₄. It was useful to insure that the temperature of the reaction mixture remains below 20 °C for 30 min (employing ice cold water jacket). The temperature of the reaction bath was increased to 35 °C (using a hot plate) and then kept constant while the reaction mixture was stirred (employing magnetic stirrer) for 2 h until a grey colored semi-solid paste was obtained. The reaction mixture was brought to room temperature and left undisturbed for 48 h. Water (92 ml) was then added slowly to the above paste and the content was stirred slowly for 30 min. The obtained viscous liquid was then added to 280 ml of pure waster followed by vigorous stirring (employing magnetic stirrer) for 1 h. Next, ten ml of 30% hydrogen peroxide was added (in 5 sec) to this solution that immediately turned the color of the solution from grey to yellow. The obtained functionalized graphite solution was then filtered through a sintered/fritted glass funnel (24 h) and washed three times (in separating funnel) with 10% dilute HC1 (total 30 ml, ACS grade) solution.

[0152] Finally, the content was isolated using high speed centrifuge (for 8 h). The obtained semi-solid content was dried at 50 °C for 72 h (employing a constant temperature incubator) and sonicated in ACS grade absolute ethanol for 48 h.

[0153] RGNS-II: The semi-solid content obtained after the centrifugation step for the RGNS-I was taken in a quartz round bottom flask and left at 50°C in incubator for 72 h. Argon gas (analytical grade) was passed in the flask for 30 min (approximately 30 ml) and the content was thermally shocked by keeping the flask in the preheated high-temperature furnace for 15-30 sec at approximately 1100°C temperature. The dry solid black powder (RGNS-II) obtained using this technique can be used as nanofiller, as one application example.

[0154] GNS-III: Two grams graphite flakes (Asbury Carbons-1721) of pH 4.93 were taken in a fritted funnel and added with 250 ml of distilled water. The mixture was sonicated for 2 h and filtered under vacuum (24 h). High speed centrifuge was used for 16 h to separate the solid during the instances when it was not feasible to filter the content. The semi-solid material was dried in incubator at 50 °C for 14 days. The obtained dried material was transferred to a quartz glass round bottom flask and purged with argon gas (analytical grade) for 15 min. The content of the flask was then thermally shocked by keeping the flask in a preheated high- temperature furnace for 30 sec at approximately 1 100 °C temperature.

[0155] GQPF-IV: The semi-solid content, that was obtained after the high speed centrifugation step employing the RGNS-I technique introduced here, was mixed with 50 wt% of ethanol (absolute, 99.5%) and sonicated for 72 h in ultrasonic water bath. The water present in the RGNS-I mixes well with the added ethanol to form a homogenous solution. The

homogeneous solution was left over night in ambient conditions. The surface of a borosilicate glass plate was prepared by polishing it with a silicone based mold release agent. The graphene solution was taken in a spray can and sprayed on the glass substrate. Ultrapure nitrogen

(analytical grade) was used as a propellant for the spray gun. The coated surface was left overnight in ambient conditions and finally peeled off the substrate. The thickness of the GQPF film can be controlled by controlling the amount of solvent (i.e., ethanol & water) in the solution.

[0156] 5.3 Characterization Methods

[0157] This section describes the various analytical techniques employed to

characterize a number of different nanomaterials.

[0158] 5.3.1 FTIR Spectroscopic Investigations

[0159] FTIR Analysis was conducted on Bruker IFS 66/S FT-IR spectrometer. Solid powder or liquid suspension of reactive nano graphene sheets were taken on KBr pellet and analyzed directly under the spectroscope. Solid powder was also observed in absorbance mode under the FTIR microscope. A minimum of 60 scans were acquired at a resolution of 4 cm^"1.

[0160] 5.3.2 Raman Spectroscopic Investigations

[0161] All the Raman spectra shown here were excited by an Invictus 785 nm NIR laser and measured with a fiber-coupled micro-Raman RXN system (Kaiser Optical Systems, Inc., Ann Arbor, MI) using a 50 μηι slit. The cosmic rays were removed by the software provided by the Kaiser optical system, which measures the spectra twice and deletes the random peaks due to cosmic rays. All spectra were measured under identical conditions. All spectra shown here were smoothened and corrected for their baseline. Commercially available polished aluminum sheets with a thickness of 0.5 mm were purchased from Anomet, Inc., Ontario, Canada, and cleaned with methanol and used as substrates. Dry graphene powders were analyzed directly under the dispersive Raman spectrophotometer. A background spectrum was collected prior to collecting a spectrum of the sample.

[0162] 5.3.3 Nuclear Magnetic Resonance Investigations

[0163] The solid state spectrum of ¹³C-labeled GQPF was recorded at a ¾ frequency of 399.97 MHz with a Varian Innova 400 instrument. The d20 was used as solvent and acquisition time was 0.01 sec with total of 2368 repetitions.

[0164] 5.3.4 Wide Angle X-ray Diffraction Studies

[0165] The interlayer spacing in graphite and graphene samples were recorded using D8 XRD from Bruker instrument using Cu-Κα source. The adopted X-ray scanning rate was 0.1 degrees per second.

[0166] 5.3.5 Microscopic Investigations

[0167] The FESEM analysis was performed on Hitachi S4800 and TEM analysis was performed on LE0912 Energy-Filtering Transmission Electron Microscope. The samples were carbon coated to prevent the charging during FESEM analyses.

[0168] 5.3.6 Thermogravimetric Analysis

[0169] The thermogravimetric analysis (TGA) was performed on SDT2960 equipment from TA instruments. Weight of the semi-solid samples were stabilized on the equipment's pan until constant weight was achieved. Variable heating rates were adopted for the solid samples while the liquid precursor to GQPF was heated at the rate of 10 °C/min in 2 atmosphere.

[0170] 5.3.7 X-ray Photoelectron Spectroscopic Analysis

[0171] The XPS analysis was performed on Kratos Axis Ultra equipment with system pressure of 10^"8 torr during the analysis. The X-ray source was monochromatic Al Ka (1486.6 eV) and X-ray power was 280 watts (14 keV, 20 mA). The takeoff angle was 90° with respect to sample plane. All the peaks were referenced to Cls=285 eV peak. [0172] 5.3.8 Dynamic Mechanical Thermal Analysis

[0173] The samples were tested employing a Perkin Elmer DMA8000 dynamic mechanical thermal analyzer. The specimens were placed in the DMTA instrument and oscillated at frequencies of 1.0 Hz in a tensile testing mode. The specimens were heated from - 150 °C to 200 °C at a rate of 5°C/min. The strain amplitude was maintained at 0.01%. The rectangular sheet geometry was chosen for this study.

[0174] 5.3.9 Mechanical Performance Evaluation

[0175] The mechanical properties of the thin films were studies using the Insight 2 Material Testing System universal testing machine. They were run with 200N Advantage pneumatic grips with flat rubber grip faces and a 100N load cell. For tensile testing, the samples were cut as rectangular sheet and tested according to ASTM D882. A span length of 50 mm was employed with a crosshead speed of 1 mm/min.

[0176] 6. Results and Discussion of Sections 4-5

[0177] The development of RGNS has been accomplished after going through the vast available literature and optimizing the conditions that are absolutely necessary for the production of highly functionalized and fully exfoliated nano graphene sheets. These sheets have highly functionalized surfaces and tend to react with other available functional materials. Extensive analyses were conducted on the graphene sheets materials that were developed employing the three different techniques. The first technique produces a material that can be used in the solution stage while the third technique generates a relatively low quality material that can be produced in a bulk quantity. The second technique was useful and produced a high quality reactive graphene nano sheets. To produce GQPF, the homogeneous solution of the RGNS-I was prepared in an azeotropic mixture of water and alcohol that can be sprayed or coated on glass substrate to form a smooth film. In this section we will discuss the results obtained from different analytical techniques on four types of nano-materials.

[0178] 6.1 FTIR Spectroscopic Analysis of Synthesized Materials

[0179] Figure 11a shows FTIR spectra acquired on RGNS-I, thermally shocked RGNS- II, and thermally exfoliated GNS-III. The acid (-COOH) functionality can be seen at 1714 cm^"1 while C=C aromatic stretching can be seen at 1515 and 1538 cm^"1. C-OH stretching at 1224 cm^"1 and C-0 stretching at 1056 cm^"1. Vibration at 1628 cm^"1 may be due to unoxidized graphite domains . [0180] The deconvolution of FTIR peaks (Fig. 1 lb) obtained in the case of dry graphene quasi-plastic film (GQPF) displayed various functional groups in the material. The peak assignments are shown in Table 1.

[0181] 6.2 Raman Spectroscopic Analysis of Synthesized Materials

[0182] Figure 12 shows Raman analysis of solid dried RGNS-I, II, & III film. The ordered graphite shows two main bands at 1575 cm^_1corresponding to G-band from graphite lattice and a peak at 1355 cm^"1 representing D-band from the graphite edges. The Raman spectrum shown in Figure 12a from RGNS-I shows shift in G-band to 1602 cm^"1 and D-band to 1328 cm^"1 suggesting a substitution on the surface of the material.

[0183] In case of RGNS-II (Figure 12a), G-band was found at 1601 cm^"1 while D-band sifted to 1336 cm^"1 indicating that substituted sheets are exfoliated that show Raman signal at higher wavelength compared to RGNS-I.

[0184] The two Raman signals obtained in GNS-II (Figure 12a), were found at 1584 cm^"1 (G-band), a frequency closer to the graphite absorption and approximately at 1326 cm^"1 a frequency similar to graphene absorption.

[0185] Figure 12b shows deconvoluted peaks obtained from the Raman spectrum of dry GQPF. The peak assignment is shown in Table 1.

[0186] 6.3 Nuclear Magnetic Resonance Analysis of GQPF

[0187] The solid state ¹³C NMR analysis was conducted on the GQPF and a typical spectrum is shown in Figure 13. The peak obtained at 176 ppm corresponds to the carbon from acid functionality (RCOOH). Three peaks between 109 to 160 ppm corresponded to the double bonded carbon (0=Ο¾), i.e., the ring structure. The peak obtained at 71 ppm corresponds to the carbon attached to the oxygen (possibly -C-OH) while the peak at 43 ppm corresponded to the carbon attached to the alkyl carbon (=C-CHR₂) as in epoxide linkage.

[0188] 6.4 X-Ray Photoelectron Spectroscopy of Synthesized Materials

[0189] The surface survey scan of RGNS-II shown in Figure 14a displayed sharp peaks for C Is and Ols indicating the successful oxidation process in the material. The deconvolution of carbon peak (see Fig. 4b) displayed two peaks concentrated at 284.5 eV corresponding to aromatic or conjugated carbon, 285.8 eV for C-OH bonds and a hump concentrated at 289 eV representing C=0 and 0-C=0 bonds. The deconvolution of oxygen peak (see Fig. 14c) also showed three major peaks. Peaks were found concentrating at 530.6 eV corresponding to C=0 & 0=C-OH bonding and 533.8 eV corresponding to C-OH bonding. A broad hump around 536 eV represents Auger peaks . [0190] Figure 15a shows surface survey scan on GNS-III. Three distinct peaks from S2p, Cls and Ols can be clearly seen from the spectra. The deconvolution of these peaks suggests the mechanism of reaction occurred over the surface of the carbon. In deconvo luted Cls spectra (see Fig. 15b), the peak appeared at 254.8 eV is possibly due to conjugate C=C bond while peak appearing at 286 eV could be a shift of C-OH bond. The broad hump appearing between 289 eV-292 eV is possibly due to 0-C=0 linking. The deconvoluted Ols spectra (see Fig. 15c) displayed two peaks at approximately 532 eV due to shifted C=0 and 533.8 eV due to C-OH bonding.

[0191] The peak position for different elements suggests that sufficient fictionalization has taken place on the graphene surface. However, small amount of sulfur was found of the surface of GNS-III suggesting that sulfuric acid was still present in the final GNS-III structure.

[0192] Figure 6a shows deconvolution of Cls peak and Figure 16b shows

deconvolution of Ols peaks from the different layers of graphene. The atomic concentration of carbon and oxygen in different layers is shown Table 2. It should be noted that, in most cases, Cls and Ols peak displayed three peaks corresponding to possible carboxyl, epoxy, and hydroxyl groups in the material as suggested by FTIR and Raman spectroscopy. It was interesting to note that the peaks position on the surface layer was different than the bulk of the material suggesting that chemical bonding on the surface layer was different compared to the succeeding layers. The surface survey scan displayed traces of sulfur (approximately 1.0 at %) on the surface layer.

[0193] 6.5 X-ray Diffraction Studies of Synthesized Materials

[0194] The wide angle X-ray diffraction pattern of graphite powder (see Fig. 17, inset), RGNS-II and GNS-III are shown in Figure 17. In case of pure graphite powder, peaks appearing at 29=26.50 with d-spacing 3.36 A corresponding to (002) crystal plane while peak appearing at 29=42.40 with d-spacing 2.13 A corresponds to (100) crystal plane. The peak appearing at 29=44.5 with d-spacing 2.03 A appears due to (101) crystal plane and peak at 29=54.67 with d- spacing 1.67 A corresponds to (004) crystal plane.

[0195] In case of RGNS-II (see Fig. 17), instead of sharp peak at 29=26.50, a broad peak appears at 29=24.58 with d-spacing of 3.62 A (002) corresponding to exfoliated graphene sheets or platelets. However, peak at 29=43.17 representing (100) plane showed d-spacing of 2.09 A. A little shift in 29 values could be due to different thickness of the powder sample under analysis. [0196] The XRD peaks in case of GNS-III (see Fig. 17) were similar to that in graphite powder with exactly similar d-spacing suggesting that GNS-III was not fully converted to graphene. The intensity of peak at 29=26.66 (002) was however lower compare to graphite powder.

[0197] 6.6 Thermogravimetric Analysis of Synthesized Materials

[0198] Figure 8 shows inert atmosphere thermograms for RGNS acquired at three different heating rates . The thermal degradation pattern of RGNS-I shown in Figure 18a suggest that approximately 10 wt% losses occurred between 144 - 164 °C. This weight loss could be due to the associated volatile components including acids that were utilized during the

functionalization. Approximately, 40 wt% of the material was lost up to 250 °C temperature possibly due to the decomposition of the smaller components. Residue obtained after the complete decomposition was in the range of 40-50 wt%.

[0199] The thermal stability of RGNS-II was determined by TGA technique and is shown in Figure 18b. It was found that RGNS-II was thermally stable until 500 °C as onset of decomposition was observed at 525 °C temperature. A single step decomposition pattern was observed in this case indicating the absence of any possible volatile components. The residue obtained after 1000 °C pyro lysis was between 20-40 wt. %.

[0200] The degradation of GNS-III was not uniform as in the case of other two above- mentioned materials (see Fig. 18c). The weight loss of 10 wt% was observed at approximately 300 °C temperature. Decomposition pattern was random until 460 °C which after stabilization leads to residue between 50-60 wt. %.

[0201] The liquid precursor to GQPF was studied in thermogravimetric analyzer under inert (N₂) gas atmosphere. Figure 8d shows a typical thermogram obtained on the liquid precursor to GQPF along with its first derivative as a function of temperature. It can be seen that approximately 10 % weight loss was observed until 100 °C temperature suggesting that the precursor solution contained 10 wt% solvent. The derivatogram suggested that decomposition of GQPF was a multiple step process that initiated with the evaporation of volatile components followed by the degradation of carbon network. There was a continuous weight loss between 125 °C and 210 °C suggesting that the decomposing material have lower thermal stability. The lower thermal stability is also an indication that graphene existed as single layered material. The residue obtained after 225 °C was approximately 1% that corresponded to the graphitized structure in the material. [0202] 6.7 Morphological Analysis of Synthesized Materials

[0203] Figures 19a to 19c show optical images for graphene prepared using the three different methods. The RGNS showed uniform distribution in ethanol and water while GNS was difficult to mix with the two liquids. The dry samples of RGNS-II and GNS-III showed different textures. The RGNS-I sample was a thick paste that formed a homogeneous grey suspension in water or ethanol. The RGNS-II sample was black that form homogeneous solution in water or ethanol while GNS-III was dark grey in color and floats on the surface of the water or ethanol.

[0204] Figures 20a to 20c are optical microscopic images of three graphene samples. The appearance of RGNS-I and GNS-III were similar, while RGNS-II showed a surface that was hard to capture using optical microscope.

[0205] Figures 21 a to 2 lc show FESEM images of RGNS-I acquired after the removal of solvent. It can be found the figure that these graphite layers were still not fully exfoliated at this stage, though the solution was sonicated for 72 hours. The thickness estimation based on FESEM image suggests that graphite powder has been modified/oxidized to a certain extent.

Figures 22a to 22d show TEM images acquired on the fully exfoliated RGNS-II. Several stages of the graphene exfoliation can be demonstrated from the TEM study. A single sheet of graphene can be seen clearly seen on the equipment's grid. The estimated thickness of the reactive graphene nano sheets was approximately 4 to 7 nm suggesting that graphene sheets observed under the microscope were actually made of at least 3 to 10 layers.

[0206] Figures 23a to 23d show TEM images acquired on GNS-III. Several layers of graphene sheets piled up to form platelets. The numbers of layers of the graphenes were found to be much higher in GNS-III samples as compared with those in RGNS-II.

[0207] Figure 24 shows optical and scanning electron microscopic images of the GQPF. The optical microscopic image was acquired on the deliberately creased film so as to produce the desired contrast. The cross section of the thick portion of the film showed the stacking of multiple layers of the graphene sheets. The average thickness of the graphene quasi- plastic film was approximately 2.35 micron. However, the film of practically any thickness and dimension can be fabricated by adopting this technique. In few sites, the corner and edges of the film were found exfoliated while the surface was relatively rough.

[0208] The GQPF was dissolved in absolute ethanol by ultrasonic treatment for 30 min. The solution contained homogeneously dispersed graphene was taken on the TEM grid and solvent was evaporated at room temperature. The remains of graphene over TEM grid were observed under TEM to check the quality of graphene. Figure 25 shows a single layer of graphene suggesting that ultrasonic treatment of GQPF in a solvent can dissociate the GQPF and restore the single layer structure of functionalized graphene.

[0209] The AFM image was acquired on the 25 μιη thin GQPF as shown in Figures 26a & 26b. The surface topography can be clearly seen in the nanograph. The surface roughness was in the order of approximately 0.5 μιη. However, there were no signs of pin hole, cavities or any other surface defects.

[0210] Figures 27a to 27d shows various stages of the development of the GQPF. The colloidal solution of the material can be sprayed on the glass plate that results into a film of uniform thickness. The solvent present in the film can be dried by blowing the hot air or leaving the coated substrate overnight. The dried film can be peeled off the substrate and cut into desired shape. The GQPF can be re-dissolved into solvents (such as water, ethanol, or other volatile solvents) with the help of ultrasonic technique. The solution of graphene was stable and homogeneous as shown in Figure 28.

[0211] 6.8 Mechanical Performance of Thin Sheets

[0212] The thin sheets (approximately 0.01 mm) of GQPF were tested in tensile testing mode using universal testing machine. The typical stress-strain curves obtained on the GQPF are shown in Figure 29. The ultimate tensile strength was approximately 40 MPa, while the maximum elongation was approximately 1.22 mm. The Young's modulus value was approximately 298 MPa.

[0213] The thin (approximately 0.01 mm) were also tested for the glass transition temperature (Tg). The dynamic mechanical thermal analysis was performed on the thin sheets in tensile mode to evaluate the Tg of the material. The dynamic mechanical response of the thin sheets was studied at wide range of temperature from -150 °C to 100 °C. A typical storage modulus (Ε') and phase angle (Tan δ) plot is shown in Figure 30. It was discovered that Tg of the material exists at room temperature (i.e. approximately 25 °C).

[0214] 7. Conclusions

[0215] The generations of graphene nano-sheets are synthesized employing three different techniques. The spectroscopic techniques were utilized to determine the functional groups over the surface of the nano-materials. Thermal stability of the nano-materials was determined using thermogravimetric analysis. The RGNS-II samples showed highest thermal stability compared to the nano-materials prepared by the other two techniques. Microscopic analysis suggested that the highest level of exfoliation was achieved in case of RGNS-II. It was therefore concluded that the graphene sheets prepared by utilizing the technique that produces RGNS-II was the best to prepare highly exfoliated and functionalized graphene nanosheets. The GQPF was developed employing RGNS-I and an azeotropic mixture of alcohol and water. Thin plastic-like films of practically any size can be fabricated employing the spray and drying technique. The GQPF so obtained displayed high level of functionality that can be utilized in various applications such as nanofillers for polymer composites, liquid crystal display, super capacitors, batteries, etc.

[0216] When ranges are used herein for physical properties, such as molecular weight, or chemical properties, such as chemical formulae, all combinations, and subcombinations of ranges for specific embodiments therein are intended to be included.

[0217] The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in its entirety.

[0218] Those skilled in the art will appreciate that numerous changes and modifications can be made to the preferred embodiments of the invention and that such changes and modifications can be made without departing from the spirit of the invention. It is, therefore, intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the invention.

Claims

What is Claimed:

1. A method of synthesizing a reactive grapheme material, comprising: dispersing graphite oxide in water; and contacting the graphite oxide in water with hydrogen peroxide so as to produce a reactive grapheme material.

2. The method of claim 1, further comprising washing the reactive grapheme material.

3. The method of claim 1, further comprising purifying the reactive graphenic material by centrifugation.

4. The method of claim 3, further comprising thermally shocking the reactive graphenic material while contacting the material with an inert gas.

5. The method of claim 4, wherein the thermal shocking comprises exposing the reactive graphenic material to a temperature of at least about 500 °C.

6. The method of claim 5, wherein the thermal shocking comprises exposing the reactive graphenic material to a temperature of at about 1000 °C.

7. The method of claim 4, wherein the thermal shocking occurs for periods of from about 5 seconds to about 30 seconds.

8. A method of synthesizing a graphenic material, comprising: dispersing graphite in water; filtering the dispersed graphite; drying the filtered graphite; and thermally shocking the dried graphite under an inert gas to give rise to graphenic material.

9. The method of claim 8, wherein the thermal shocking occurs for periods of from about 5 seconds to about 30 seconds.

10. The method of claim 9, wherein the thermal shocking comprises exposing the graphenic material to a temperature of at least about 500 °C.

11. The method of claim 5, wherein the thermal shocking comprises exposing the graphenic material to a temperature of at about 1000 °C.

12. A method of synthesizing functionalized graphene, comprising:

forming an admixture of graphite and an acid;

adding an oxidizer to the admixture;

adding water to the admixture;

adding hydrogen peroxide to the admixture.

13. The method of claim 12, wherein the oxidizer comprises a potassium salt, nitric acid, a nitrate, nitrous oxide, a hypochlorite, a chlorite, a chlorate, a perchlorate, silver oxide, a persulphuric acid, a sulfoxide, a Tollen's reagent, osmium tetraoxide, or any combination thereof.

14. The method of claim 13, therein the potassium salt comprises potassium permanganate.

15. The method of claim 12, further comprising maintaining the admixture of oxidizer, graphite, and acid at less than about 20 degrees C for at least about 30 minutes.

16. The method of claim 12, further comprising filtering the admixture produced in step (d).

17. The method of claim 16, further comprising washing the filtered admixture with an acid.

18. The method of claim 17, wherein the acid comprises hydrochloric acid.

19. The method of claim 17, further comprising centrifuging the washed admixture so as to isolate solid material.

20. The method of claim 19, further comprising drying the isolated solid material.

21. The method of claim 20, further comprising dispersing the dried solid material in a

solvent.

22. The method of claim 21, wherein the dried solid is dispersed in the solvent using sonication, homogenization, mechanical mixing, or any combination thereof.

23. The method of claim 21, wherein the solvent comprises ethanol.

24. The method of claim 19, further comprising contacting material isolated by centrifugation with ethanol and water so as to form a film precursor mixture.

25. The method of claim 24, further comprising sonicating the film precursor mixture.

26. The method of claim 25, further comprising applying the precursor mixture to a substrate so as to give rise to a graphenic film atop the substrate.

27. The method of claim 19, further comprising heating material isolated by centrifugation to at least about 250 degrees C.

28. The method of claim 27, further comprising heating material isolated by centrifugation to at least about 500 degrees C.

29. The method of claim 28, further comprising heating material isolated by centrifugation to at least about 1100 degrees C.

30. The method of claim 27, wherein the material is heated for a time period in the range of from about 1 second to about 60 seconds.

31. The method of claim 30, wherein the heating time period is less than about 30 seconds.

32. A method of synthesizing graphene, comprising:

contacting graphite with water to form a first mixture;

sonicating the first mixture;

separating solid material from the sonicated first mixture;

drying the solid material; and

thermally shocking the dried solid material.

33. The method of claim 32, wherein the separating is effected by centrifugation.

34. The method of claim 32, further comprising contacting the dried solid material with an inert gas.

35. The method of claim 34, wherein the inert gas comprises a noble gas.

36. The method of claim 32, wherein the thermal shocking comprises exposing the separated solid material to a temperature in the range of from about 250 °C to about 1100 °C for from 1 sec to about 60 seconds.

37. A method of forming a grapheme film, comprising:

coating a composition to a substrate, the composition comprising graphene and a precursor solution, the precursor solution comprising water and a polar organic compound; and

removing at least a portion of the precursor solution to give rise to a graphenic film adjacent to the substrate.

38. The method of claim 37, wherein the coating is effected by spraying.

39. The method of claim 37, wherein the precursor solution is azeotropic.

40. A method of forming a graphenic film, comprising:

forming a film comprising graphene, water, and a polar organic compound;

evaporating at least a portion of the water and polar organic compound to give rise to a graphenic film.

41. A graphenic film, comprising:

a cohesive graphenic film, the film having an ultimate tensile strength of at least about 40 MPa.

42. A graphenic film, comprising:

a cohesive graphenic film, the film having an Young's modulus of at least about 300 MPa.

43. A graphenic film, comprising:

a cohesive graphenic film, the film having an Tg of at least about 25 degrees C.

44. The method of claim 1, wherein the graphite oxide in water is prepared by dispersing graphite powder in an acid solution at a temperature in the range of from +10 degrees C to -78 degrees C to give rise to an acidic graphite dispersion, and treating the acidic graphite dispersion with an oxidizer to give rise to graphite oxide.

45. The method of claim 8, wherein the graphite oxide in water is prepared by dispersing graphite powder in an acid solution at a temperature in the range of from +10 degrees C to -78 degrees C to give rise to an acidic graphite dispersion, and treating the acidic graphite dispersion with an oxidizer to give rise to graphite oxide.