Graphene / Graphene Oxide Core / Shell Particles, Methods of Making Same, and Methods of Using Same

Abstract

A method for producing graphene / graphene oxide particles under mild conditions includes reacting pristine graphene with hydrogen peroxide and an iron source to oxidize the outer surface of the pristine graphene particles in solution to yield graphene / graphene oxide particles, as well as methods and articles incorporating the same.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application Nos. 62 / 862,251, filed June 17, 2019, 62 / 935,438, filed November 14, 2019, and 63 / 016,637, filed April 28, 2020, each entitled "GRAPHENE TO GRAPHENE / GRAPHENE OXIDE CORE / SHELL PARTICULATES AND METHODS OF MAKING AND USING THE SAME," each of which is incorporated herein by reference in its entirety.

[0002] Technical Field The present invention relates to particulate graphene-based materials with oxidized surfaces that can be further functionalized to produce a variety of derivative compounds. [Background technology]

[0003] Description of Related Art Graphene has a hexagonal crystal structure and is sp 2Graphene is a two-dimensional monolayer of bonded carbon atoms. Stacking of graphene sheets forms graphite with a 0.335 nm interplanar spacing. Graphene has attracted considerable interest due to its unique physical properties, including excellent mechanical strength, high intrinsic carrier mobility at room temperature, and electrical and thermal conductivities comparable to those of graphite. These properties pave the way for graphene's applications in technological areas such as nanoelectronics, sensors, nanocomposites, batteries, supercapacitors, hydrogen storage, solar cells, light-emitting diodes (LEDs), touchscreens, and smart glasses for devices such as windows and phones. Medical and biological applications of graphene are also contemplated. However, the use of graphene has been hindered by its poor solubility and dispersibility due to the material's hydrophobic nature and its strong van der Waals forces. Therefore, graphene is only suitable for obtaining physical mixtures, not chemical conjugates. Functionalized derivatives of graphene, such as graphene oxide (GO), have been explored as an improvement.

[0004] The traditional approach to GO starts with graphite (G) and uses strong oxidizing agents and unfriendly chemical reaction conditions. Three basic approaches were developed by Brodie (KClO3 in HNO3) (On the atomic weight of graphite. Philosophical Transactions of the Royal Society of London, 1859 (Vol. 149), pp. 249-259), Staudenmaier (KClO3 in H2SO4 or H2SO4 / HNO3) (Verfahren zur Darstellung der Graphitsaure. Ber Dtsch Chem Ges, Vol. 31: pp. 1481-1487, 1898), and Hummers and Offeman (NaNO3 and KMnO4 in H2SO4) (Preparation of graphitic oxide. Journal of the American Chemical Society, 1958, Vol. 80(6), pp. 1339-1339). Numerous variations on these methods exist in the literature. All of these methods have in common the starting point of graphite, which must be reacted to form graphite oxide, followed by exfoliation and subsequent oxidation to graphene oxide (Figure 1). The exfoliation process is driven by unfavorable chemical conditions and subsequent heating. Sulfuric acid acts as an intercalator between the graphite layers, expanding the interlayer spacing from 0.335 nm to over 0.6 nm. The literature agrees that all conventional methods for synthesizing GO from graphite are somewhat unreproducible, making them less than ideally suited for GO applications in materials science and electronics. Furthermore, conventional GO production generates significant amounts of chemical waste and releases harmful gases such as ClO3, NO2, or N2O4. Furthermore, sodium and potassium cations are difficult to remove from graphene oxide after the oxidation process is complete, resulting in impurities. GO, produced by chemical oxidation of graphite followed by exfoliation and further oxidation, is characterized by carbonyl and carboxylic acid groups at the edges and epoxy and hydroxyl groups within the basal plane (Figure 2).

[0005] Alternative GO synthesis approaches have been reported. These involve the hydrothermal polymerization of glucose onto a quartz wafer to synthesize graphene oxide nanosheets (GONs) on the surface, followed by thermal annealing at 1300 K. This method allows for the tunable synthesis of single-layer and few-layer (fewer than five) GONs with lateral dimensions of approximately 20 μm and 100 μm, respectively. While this method appears to be an environmentally friendly approach to graphene oxide, it is energy-intensive and therefore unable to produce large quantities of GO. Furthermore, the chemical structure of GONs on quartz has not been fully characterized.

[0006] Another approach involves oxidizing epitaxial graphene on SiC(0001) using atomic oxygen in ultrahigh vacuum. The chemisorption of oxygen atoms onto graphene was verified using scanning tunneling microscopy (STM), high-resolution core-level X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet photoelectron spectroscopy (UPS). Thermal reversibility occurred at 533 K. Again, this approach, while interesting for the semiconductor industry, does not allow for the mass production of chemically stable GO. Summary of the Invention

[0007] The present invention broadly relates to a method for producing graphene / graphene oxide particles. The method typically involves reacting pristine graphene particles with hydrogen peroxide in an aqueous reaction solution at a low pH (5.0 or less) in the presence of an iron source. The reaction solution is stirred or agitated for a period of time, during which hydroperoxyl radicals generated in the reaction solution react with the graphene particles, oxidizing the outer surfaces of the pristine graphene particles in solution to yield graphene / graphene oxide particles, which can then be recovered from the solution.

[0008] Also described herein are graphene / graphene oxide particles comprising a graphene core and a thin graphene oxide surface coating or shell, comprising at least 85% carbon and up to about 15% oxygen.

[0009] Also described herein are compositions comprising, consisting essentially of, or consisting of a plurality of graphene / graphene oxide particles according to various embodiments of the present invention. The compositions can be visually characterized as fluffy or fuzzy black powders or particles. In one or more embodiments, the compositions are free-flowing powders.

[0010] Also described herein is an article comprising a substrate having a surface and a layer comprising a G / GO composition according to various embodiments of the present invention deposited on the substrate surface. In one or more embodiments, the composition is dispersed in a solvent system and wet-applied to the surface. In one or more embodiments, the composition is mixed with a polymer system and printed onto the surface (e.g., including printing as a three-dimensional form). In one or more embodiments, graphene / graphene oxide particles are reacted with multiple monomers to provide a composite polymer having the graphene / graphene oxide particles embedded therein and deposited on the substrate surface. In one or more embodiments, the layer is a thin film having a thickness of less than 1 mm. In one or more embodiments, the layer is a thin film having a thickness of less than 0.5 mm. In one or more embodiments, the composition is sintered onto the substrate surface.

[0011] Also described herein are composite articles. In one or more embodiments, these composite articles comprise a composition according to various embodiments of the present invention dispersed in a polymer, resin, or cement matrix. Also described herein are composite polymers comprising a plurality of graphene / graphene oxide particles according to various embodiments of the present invention reacted with a polymer matrix. In one or more embodiments, the polymer is selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyacrylate, polyacrylamide, polymethyl methacrylate, polytetrafluoroethylene, polyester, polyamide, polyurethane, and copolymers thereof.

[0012] Also described herein are solid articles comprising compositions according to various embodiments of the present invention formed into porous bodies, which bodies are optionally sintered. [Brief explanation of the drawings]

[0013] The patent or application file contains at least one color drawing. Copies of this patent or patent application publication containing color drawing(s) will be provided by the U.S. Patent and Trademark Office upon request and payment of the necessary fee.

[0014] [Figure 1] Figure 1 illustrates the conventional synthesis of graphene oxide via oxidation and exfoliation of graphite. [Figure 2] Figure 2 illustrates the structure of GO produced by conventional chemical oxidation of graphite. [Figure 3] FIG. 3 is an illustration of a multilayer fractal aggregate of Fenton oxidized graphene. [Figure 4] FIG. 4 is a close-up view of a multilayered graphene core containing graphene oxide, illustrating a graphene / graphene oxide core / shell particle containing a chemically intact graphene core and an amorphous shell of graphene oxidation products (carboxylic acid and ketone groups, and possibly hydroxyl groups) on the surface of the intact layered graphene sheets. [Figure 5] FIG. 5 shows an enlarged side view of a multilayered graphene core with a graphene oxide surface. [Figure 6A] Figure 6A shows a cross-sectional illustration of a core / shell structure consisting of three layers (core) of graphene and each outer layer (shell) of graphene oxide, showing that -OH groups are present on the surface and -COOH groups are present at the edges. From FTIR and titration, -COOH appears to be the predominant functional group (>90%), although it is understood that some -OH groups may also be present at the edges. [Figure 6B] Figure 6B shows the Fenton oxidation of graphene to graphene oxide. [Figure 7] FIG. 7 is a transmission electron microscope (TEM) image of the fractal aggregates of pristine graphene synthesized by the detonation method, which were used as starting materials. [Figure 8] Figure 8 shows enlarged TEM images from Figure 8 at (A) 20 nm scale and (B) 10 nm scale, showing the coexistence of ordered and disordered layered graphene regions. This particular structure shows at least 10 graphene layers stacked together. [Figure 9] Figure 9 shows a TEM image of a fractal aggregate of Fenton-oxidized graphene. After Fenton oxidation, the overall structure of the material remains essentially unchanged. The oxidized material exhibits a very similar structure, consisting of ordered and disordered layered graphene domains. [Figure 10] Figure 10 shows enlarged TEM images at (A) 50 nm scale and (B) 10 nm scale, which show the coexistence of ordered and disordered layered graphene regions, similar to the starting material. [Figure 11] FIG. 11 shows the general graphene oxide and graphene oxide methyl ester reactions, where R represents a variable based on the primary amine used in the reaction. [Figure 12] Figure 12 shows a comparison of the XRD spectra of detonation-synthesized graphene (GN, 99.2% C, 0.1% H, 0.7% O, Table 1) and Fenton-oxidized graphene (GO, 90.1% C, 1.7% H, 8.2% O, Table 1). [Figure 13] Figure 13 shows a graph comparing the FTIR transmission spectra of pristine graphene synthesized by the detonation method (99.2% C, 0.1% H, 0.7% O, Table 1, upper spectrum) and Fenton oxidized graphene (90.1% C, 1.7% H, 8.2% O, Table 1, lower spectrum). [Figure 14]Figure 14 shows a graph comparing the thermogravimetric behavior of graphene (G: 99.2% C, 0.1% H, 0.7% O, Table 1) and Fenton-oxidized graphene oxide (GO: 90.1% C, 1.7% H, 8.2% O, Table 1). [Figure 15] Figure 15 shows graphs for (A) the reaction surface of Doehlert Matrix 1 (catalyst change: 50–150 mg FeSO4·7H2O; temperature change: 40–60 °C); and (B) the reaction surface of Doehlert Matrix 2 (catalyst change: 50–150 mg FeSO4·7H2O; temperature change: 50–70 °C). [Figure 16] FIG. 16 is a graph of the thermogravimetric behavior of Fenton-oxidized graphene oxide (GO: 90.1% C, 1.7% H, 8.2% O) after conversion of the carboxylic acid groups to methyl esters. [Figure 17] FIG. 17 is a graph showing that all graphene derivatives have high optical extinction E. [Figure 18] FIG. 18 is a graph showing the dispersibility of G, GO, mGO, GON, and GONB in HO at 20° C. [Figure 19] Figure 19 is a graph showing cell viability of mouse neural progenitor cells after 24 hours of incubation with graphene (G), graphene oxide (GO) compared to the control group, as measured by MTT assay (MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). The relative error is less than 3 percent. [Figure 20] Figure 20 shows the differential thermogravimetric analysis (DTA) of graphene (under N2). Significant weight loss occurs below 50 °C (water desorption) and above 500 °C, indicating superior thermal stability of core / shell graphene / graphene oxide compared to conventionally prepared graphene oxide (Hummers process). [Figure 21] Figure 21 shows a graph showing differential thermogravimetric analysis (TGA) of graphene (under N2), showing significant weight loss (water desorption) at temperatures below 60°C. [Figure 22] Figure 22 shows the FTIR of graphene oxide (large batch), where the presence of carboxylic acid groups can be clearly identified. [Figure 23] Figure 23 shows the Fischer ester synthesis reaction from GO to mGO. [Figure 24] Figure 24 shows the ester synthesis reaction from GO to mGO via thionyl chloride. [Figure 25] FIG. 25 shows (A) differential thermogravimetric analysis (TGA) and (B) FTIR graphs of graphene oxide methyl ester (mGO) prepared according to Method B (thionyl chloride-mediated ester synthesis reaction). [Figure 26] Figure 26 shows the high-pressure mediated ester synthesis reaction from GO to mGO. [Figure 27] Figure 27 shows the ester synthesis reaction from graphene oxide (GO) to graphene oxide diethylene glycol ester (degGO) via thionyl chloride. [Figure 28] FIG. 28 is a graph of the differential thermogravimetric analysis (TGA) of degGO prepared by thionyl chloride-mediated ester synthesis reaction. [Figure 29] Figure 29 shows the synthesis of graphene amide oxide (aGO) from mGO. [Figure 30] FIG. 30 shows (A) FTIR and (B) differential thermogravimetric analysis (TGA) graphs of aGO. [Figure 31] Figure 31 shows the synthesis of graphene oxide diethylamide (deaGO) from mGO. [Figure 32] FIG. 32 shows the synthesis of graphene oxide 1-aminohexan-6-amide (dahmGO) from mGO. [Figure 33] Figure 33 illustrates the hydrogen ion-catalyzed polymerization of GO derivatives, where the R groups represent various monomer moieties (e.g., carbon / alkyl groups, hydrogen, oxygen, etc.) in the main and / or side chains of the polymer, and n represents the monomer repeat unit. [Figure 34] Figure 34 illustrates the radical-mediated polymerization of GO derivatives, where the R groups represent various monomer moieties (e.g., carbon / alkyl groups, hydrogen, oxygen, etc.) in the main and / or side chains of the polymer, and n represents the monomer repeat unit. [Figure 35] Figure 35 illustrates metal-catalyzed polymerization. Zr(cp)2Cl2+-[O-Al(CH3)3]n- (cp: cyclopentadienyl ligand) is an example of a metal organic polymerization catalyst (developed after the Ziegler-Natta type), where the R groups represent various monomer moieties (e.g., carbon / alkyl groups, hydrogen, oxygen, etc.) in the polymer backbone and / or side chains, and n represents the monomer repeat unit. [Figure 36] Figure 36 illustrates anionic (living) polymerization, where mGO is initiated by reacting with a metal hydride, where the R groups represent various monomer moieties (e.g., carbon, hydrogen, oxygen, etc.) in the polymer backbone and / or side chains, and n represents the monomer repeat unit. [Figure 37] FIG. 37 shows the incorporation of graphene / graphene oxide (nano)particles into nylon-type polymers, where m and n indicate the monomer repeat units. [Figure 38] FIG. 38 shows the incorporation of graphene / graphene oxide (nano)particles into polyester-type polymers, where m and n indicate the monomer repeat units. [Figure 39] Figure 39 is a graph of the titration curve (pH vs. volume of 0.100 M HCl) starting from adding 20 mL of 0.100 M NaOH to 100 mg of GO. Black squares: titration of GO; gray diamonds: reference curve (no added GO). DETAILED DESCRIPTION OF THE INVENTION

[0015] This disclosure relates to a novel method for producing tailored graphene / graphene oxide (G / GO) particles, preferably using detonation-synthesized graphene as a starting material (Nepal et al., One-step synthesis of graphene via catalyst-free gas-phase hydrocarbon detonation. Nanotechnology, 2013, Vol. 24(24), 245602). Consequently, improved graphene oxide particle materials, functionalized derivatives of these materials, composites thereof, and applications thereof are described. Pristine graphene starting materials are preferably used in embodiments of the present invention. In other words, the method of the present invention preferably does not involve exfoliation or graphite starting materials, as are involved in conventional approaches.

[0016] Detonation-synthesized graphene is a preferred pristine graphene material, and its preparation is described in detail in U.S. Patent No. 9,440,857, incorporated herein by reference. The method involves a single-step process involving the controlled detonation of a carbon-containing material, whether solid, liquid, or gaseous, with an oxidizer or oxygen source (e.g., O , NO , NO ), in a relatively high-temperature reactor, to produce pristine graphene nanosheets and branched fractal aggregates of these nanosheets without the use of a catalytic material. Typically, a desired amount of reactants is added to the reactor, and detonation of the material is achieved using a spark. An aerosol gel containing graphene particles is produced. In a scaled-up approach, the apparatus includes a reaction chamber, a vacuum source operatively connected to the reaction chamber, and an ignition assembly. The reaction chamber is operatively connected to a source of carbon-containing material and a source of oxidizer. The vacuum source is operable to selectively evacuate at least a portion of the contents of the reaction chamber, particularly after production of the particulate material. An ignition assembly is also operatively connected to the reaction chamber and configured to initiate combustion of the content of carbon-containing material and the content of oxidizer delivered to the reaction chamber from the respective sources. The ignition assembly includes a pair of electrodes operative to generate an ionized arc therebetween, each electrode housed in a respective cassette removably mounted within the ignition assembly.

[0017] Exemplary carbon-containing materials for use in the reaction include injectable materials such as carbon-rich precursors, gases, gas mixtures, powders, and aerosols. The starting material can include any hydrocarbon compound, particularly saturated or unsaturated C1-C12 hydrocarbon compounds. In some embodiments, acetylene is a particularly preferred hydrocarbon material. The carbon-containing material can include a single material or compound or a mixture of carbon-containing compounds.

[0018] In one or more embodiments, the combustion reaction occurs at a temperature of at least 3000 K, at least 3500 K, or at least 4000 K. In particular embodiments, the combustion reaction occurs at a temperature between about 3000 K and about 5000 K, between about 3500 K and about 4500 K, or about 4000 K. It has been found that combustion of a carbon-containing material and an oxidizer at these temperatures favors the formation of highly oriented graphene particles rather than graphitic soot. If necessary, an inert gas, such as helium, neon, argon, or nitrogen, can be included in the reaction mixture introduced into the reactor to aid in temperature control during combustion. Additionally, in some embodiments, particularly those in which the combustion reaction is a detonation, combustion of the reaction mixture proceeds very rapidly. Detonation typically involves a supersonic exothermic front accelerating through a medium, ultimately generating a shock front that propagates directly in front of it. In some embodiments, the combustion has a duration of about 5 to about 100 milliseconds, about 10 to about 75 milliseconds, or about 20 to about 50 milliseconds.

[0019] The ratio of oxidant to carbon-containing material present in the reactor prior to detonation can contribute to the characteristics of the graphene particles formed after detonation of the reaction mixture. In some embodiments, the molar ratio of oxidant to carbon-containing material is 1.5 or less. In particular embodiments, the ratio of oxidant to carbon-containing material is about 0.1 to about 1.5, about 0.2 to about 1.2, about 0.2 to about 1.0, or about 0.3 to about 0.8. This process allows for the synthesis of bulk or large quantities of graphene with excellent purity.

[0020] Another approach to synthesizing pristine graphene is flash graphene (Luong et al., Gram-scale bottom-up flash graphene synthesis, Nature, 2020, incorporated herein by reference), which utilizes flash Joule heating of inexpensive carbonaceous materials or other carbon sources, such as coal, petroleum coke, biochar, carbon black, food waste, rubber tires, and mixed plastic waste, to convert the material into graphene. The carbon source is lightly compressed between two electrodes in a reactor, and a high-voltage discharge from a capacitor bank heats the carbon source material in the reactor to at least 3000 K in less than 100 milliseconds. This process converts the amorphous carbon in the carbon source into flash graphene. The yield of this process is highly dependent on the carbon content of the starting material. In some embodiments, the carbon source material may be mixed with carbon black or another similar conductive material to improve the conductivity of the material. In some embodiments, flash graphene has an average particle size of less than 20 nm. In some embodiments, flash graphene is produced in the form of larger but thinner sheets with an average size of 0.5-1.2 μm.

[0021] The graphene starting material may take a variety of forms, but is preferably in the form of branched fractal aggregates, nanosheets, crystalline flakes, nanoplatelets, and platelet chains as single-layer or multi-layer graphene, and can typically be characterized macroscopically as a high-purity (greater than 98.5% carbon), fluffy or fuzzy, black powder or particulate material. In other words, the graphene starting material is preferably essentially free of graphite or graphite oxide. The particles are preferably nano-sized particles, typically having a maximum surface-to-surface dimension of about 350 nm, preferably about 20 nm to about 100 nm. The particles can be observed under an electron microscope as thin monolayers with overlapping edges and entangled with one another, or as more ordered nanosheet stacks containing or consisting of 2-3 layers, possibly up to 15 layers, preferably 1-10 layers, more preferably 1-5 layers, and even more preferably 1-2 or 3 layers, up to 5 layers. That is, the graphene used in the present invention is highly pure, also known as pristine, essentially free of foreign matter and impurities (i.e., less than 0.5%, preferably less than 0.1%) and has a carbon content of at least about 98.5%, preferably at least 99% (conversely, an oxygen content of less than 1%).

[0022] Pristine graphene particles were oxidized under mild Fenton oxidation conditions at temperatures below 100°C (preferably below 80°C, more preferably below 75°C) to yield G / GO particles, each particle comprising (consisting essentially of, or consisting of) a substantially pure and intact graphene core and a thin graphene oxide surface coating or shell. Figure 3 shows multiple G / GO particles in the form of fractal aggregates. Figures 4 and 5 show exaggerated views of a particle 10 having oxidized surfaces 12a, 12b and a substantially intact graphene core 14. See also Figure 6A.

[0023] This oxidation method typically involves preparing a reaction solution containing an aqueous solvent system with a low pH (preferably less than 5.0, preferably about 2.5 to about 4.0, more preferably about 2.8 to about 3.2, and even more preferably about 3.0). The reaction solution contains about 2.5 w / w% to about 25 w / w% (preferably 2.5 w / w% to about 15 w / w%) hydrogen peroxide as an oxidizing agent and about 0.1 w / w% to about 10 w / w% (preferably about 1 w / w% to about 8 w / w%) pristine graphene particles. The reaction solution is stirred or agitated for a period of time to disperse the graphene particles in the solvent system and obtain a substantially uniform dispersion of the particles. If necessary, the pH of the solution can be lowered using a suitable acid system. After the graphene particles are dispersed, an iron source, such as ferrous iron (usually iron(II) sulfate, FeSO4) hydrate, ferric iron, or ferrate, is added to the reaction solution as a catalyst in an amount of about 0.005 w / w% to about 5 w / w% (preferably about 0.05 w / w% to about 2.5 w / w%). The reaction solution is stirred or agitated for a period of time to generate hydroperoxyl radicals, which react with the graphene carbon to oxidize the particle surfaces in the solution. The reaction solution is typically stirred for about 1 hour to about 24 hours, preferably for at least about 1 hour, preferably for at least about 10 hours, and more preferably for about 24 hours. During this process, the reaction solution is preferably maintained at a temperature below 100°C, preferably between about 0°C and about 100°C, preferably between about 25°C and about 85°C, and more preferably between about 40°C and about 75°C. The reaction process is shown in Figure 6B.

[0024] The resulting oxidation product (G / GO particles) is then removed from the reaction solution, for example, by filtration and / or centrifugation. The recovered G / GO particles are preferably washed in an aqueous solvent system to neutralize the reaction product until a neutral pH of greater than 6 is obtained in the supernatant. The G / GO particles can be dried, such as under vacuum, or lyophilized and stored for further use. The resulting G / GO particles can be considered to be composed of a substantially intact graphene core with an oxidized surface that can be considered a thin GO shell (Figure 6A). This means that there is little change in the spacing, such as the interplanar spacing and lattice spacing, of the graphene within the core compared to the starting material. The resulting G / GO particles also contain at least 85% carbon, preferably at least 90% carbon, more preferably at least 92% carbon, and even more preferably about 92-98% carbon. Similarly, the G / GO particles contain up to 15% oxygen (about 0.5% to 15%), preferably up to 10% oxygen (about 0.5% to 10%), more preferably about 1% to about 8% oxygen, and preferably about 3 to about 4% oxygen. In other words, the starting graphene material has been functionalized with a thin oxide layer on the surface and has undergone "just enough" oxidation to impart the desired characteristics of a functionalized water-dispersible material (e.g., carboxylic acid, ketone, and / or alcohol surface groups), but otherwise retains the various advantageous characteristics of graphene throughout the body / core of each particle.

[0025] In one or more embodiments, the process conditions can be adjusted to achieve various properties in the resulting GO / GO particles, such as varying the surface oxygen content and / or the surface charge (zeta potential) of the graphene oxide. For example, an increase in surface oxygen content (greater than 8%) can be achieved by increasing the amount of iron source and raising the reaction temperature (e.g., 3 wt% HO and 0.125 wt% FeSO 7HO at 60°C). Similarly, a decrease in surface oxygen content (less than 3%) can be achieved by decreasing the amount of iron source and lowering the reaction temperature (e.g., 3 wt% HO and 0.05 wt% FeSO 7HO at 50°C). An increase in the zeta potential (greater than +14 mV) can be achieved by using a lower temperature and a reduced amount of iron source (e.g., 3 w / w% HO and 0.15 w / w% FeSO 7HO at 50 °C). On the other hand, a decrease in the zeta potential (less than -5 mV) can be achieved by using a higher temperature and a slightly higher amount of iron source (e.g., 3 w / w% HO and 0.125 w / w% FeSO 7HO at 60 °C). It should be understood that the total zeta potential is also affected by the initial zeta potential of the starting pristine graphene material. By mixing the materials used in the synthesis of the detonation graphene starting material in different stoichiometric ratios, graphenes with different zeta potentials can be obtained.

[0026] Advantageously, the morphology of the starting graphene particles is substantially preserved in the G / GO particles, i.e., the G / GO particles are in the form of branched fractal aggregates, nanosheets, crystalline flakes, nanoplatelets, and platelet chains as single-layer or multilayer graphene. They can typically be macroscopically characterized as high-purity, fluffy, black, powdery, or particulate G / GO material. This is illustrated in the TEM images in Figures 7-10. Figures 7-8 show TEM images of pristine graphene obtained by detonation. As can be seen from the TEM images in Figures 9 and 10, the morphology of the starting graphene particles is substantially preserved in the G / GO particles produced by the present invention. The particle size of individual G / GO particles typically ranges from about 20 nm to about 100 nm (where "size" refers to the largest surface-to-surface dimension in a cross-sectional view of the particle, e.g., diameter).

[0027] The G / GO particles thus prepared have good water dispersibility of at least about 5 mg / mL, preferably about 5 mg / mL to about 20 mg / mL, and more preferably about 10 mg / mL to about 20 mg / mL. The G / GO particles thus prepared also have high thermal stability up to about 550°C, exhibiting only a small weight loss (about 3.5%) at temperatures below 600°C. In other words, the particles are thermally stable and do not exhibit thermal decomposition at temperatures above 100°C, preferably above 200°C, more preferably above 300°C, more preferably above 400°C, and even more preferably above 500°C (up to about 550°C). The G / GO particles also have a broad absorption spectrum ranging from 200 nm to about 1400 nm, making them particularly useful in hyperthermia applications, such as therapeutic and / or theranostic techniques.

[0028] It should be appreciated that the above method and resulting product avoid the undesirable chemicals and waste products required in the prior art. For example, because the graphene is not exfoliated in the above method, the G / GO particles are essentially free of intercalants such as sulfuric acid. Furthermore, the G / GO particles are essentially free of other contaminants or impurities, such as sodium and / or potassium ions. As used herein, "essentially free" means less than 0.1 wt. % of the total weight of the particles, taken as 100 wt. %, preferably less than 0.05 wt. %, and more preferably less than 0.01 wt. %.

[0029] Various applications of the G / GO particles and resulting products are also contemplated herein. For example, G / GO particles can be layered or deposited as thin films to create conductive films for flexible electronics, solar cells, chemical sensors, battery electrodes, capacitors, and the like. G / GO particles can also be dispersed with various polymers and fillers to create a wide variety of reinforced composites. Furthermore, G / GO particles can serve as filtration media or be formed into filtration membranes. G / GO particles can be formed and sintered to create graphene foams. It should be understood that the oxide layer can be removed, if desired. In one or more embodiments, the oxide layer of the G / GO particles can be removed by heating, allowing for the synthesis of layered graphene aggregates, and the like.

[0030] Alternatively, the surface groups of the oxide layer can be further reacted, modified, or functionalized to create a wide variety of novel materials (e.g., GO derivatives) depending on the desired application. For example, the carboxylic acid groups on the oxidized surface can be reacted with a wide variety of organic or inorganic materials. In one or more embodiments, the graphene oxide surface layer is reacted with methanol under various conditions, including in the presence of thionyl chloride, to produce GO methyl ester (mGO). The methyl groups can be converted to GO methyl esters (mGO) by heating in organic solvents (e.g., THF, hexane, DMF, ammonium hydroxide) with ammonia (NH3) or primary amines (R-NH2, R = C1-C8 alkyl, e.g., CH3-C8H). 20 ), yielding, for example, graphene oxide amide, graphene oxide diethylamide, graphene oxide carboxylamide, and graphene oxide carboxylbutylamide. Similarly, mGO can be reacted with ethylene glycol to form graphene oxide diethylene glycol ester (degGO). Exemplary reaction schemes are provided in the examples. Additional mGO derivatives can be made as described in more detail below. Surface-modified or functionalized G / GO particles can be used to prepare composite compositions, such as by dispersing the surface-modified or functionalized G / GO particles in a matrix resin or resin cement, either alone or in combination with reinforcing fibers (e.g., glass fibers) and / or aggregates such as sand, stone, gravel, or rock. Surface-modified or functionalized G / GO particles can also be reacted with various monomers to yield composite polymers with enhanced properties due to the incorporation of G / GO particles.

[0031] Surface-modified or functionalized G / GO particles can also be further functionalized with various moieties, including but not limited to antibodies, aptamers, peptides, etc. These novel materials are utilized in a variety of techniques for biochemical and biosensing applications, including through the use of electrical impedance measurements.

[0032] Advantageously, after reducing, removing, or chemically reacting the graphene oxide shell, the remaining graphite core possesses the mechanical and electrical properties of graphene. Further advantages of various embodiments of the present invention will be apparent to those skilled in the art upon review of the disclosure herein and the examples below. It is understood that the various embodiments described herein are not necessarily mutually exclusive, unless specifically stated otherwise herein. For example, features described or depicted in one embodiment may be included in other embodiments, but are not necessarily included therein. That is, the present invention encompasses various combinations and / or integrations of the specific embodiments described herein.

[0033] As used herein, the term "and / or," when used in connection with a list of two or more items, means that any one of the listed items may be employed alone, or any combination of two or more of the listed items may be employed. For example, if a composition is described as containing or not containing components A, B, and / or C, the composition may contain or not contain A alone; B alone; C alone; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0034] Additionally, numerical ranges are used herein to quantify certain parameters in connection with various embodiments of the present invention. It should be understood that when a numerical range is provided, such range should be construed as providing literal support for claim limitations reciting only the lower value of the range and for claim limitations reciting only the upper value of the range. For example, if a numerical range of about 10 to about 100 is disclosed, literal support is provided for claims reciting "greater than about 10" (without an upper limit) and claims reciting "less than about 100" (without a lower limit). [Example]

[0035] The following examples describe methods according to the present invention, however, it should be understood that these examples are provided by way of illustration and that nothing therein should be considered a limitation on the overall scope of the invention.

[0036] Example 1 Fenton-type reaction as an advanced oxidation method The key reaction in the thermal Fenton-type reaction is the reaction between iron(II) and hydrogen peroxide in aqueous solution. The observed reaction kinetics of H2O2 consumption show an exponential dependence on temperature. Depending on the substrate and the chelation potential of iron(II), there are two competing main reactions:

[0037] [ka]

[0038] In reaction (1), a hydroxyl radical is formed via electron transfer from iron(II) to H2O2. In reaction (2), an oxoiron(IV) species is formed. Note that the water molecules participating in these reactions are not shown for clarity. Hydroxyl radicals can react via (a) hydrogen abstraction (which is unlikely in detonation-synthesized graphene due to its low hydrogen content), (b) electron transfer from graphene to the hydroxyl radical, or (c) addition to a carbon-carbon double bond.

[0039] [ka]

[0040] All of these reactions form organic radicals, which then react with oxygen in the formation of peroxyl radicals (d), which react further to ultimately form ketones or carboxylic acids.

[0041] [ka]

[0042] Oxoiron(IV) species can remain in aqueous solution for up to a few seconds. They react with organic compounds by electron transfer (e).

[0043] [ka]

[0044] This reaction is followed by the addition of oxygen (d), leading to the formation of oxidation products such as carboxylic acids and ketones via chemical reactions of the peroxo radicals.

[0045] In conclusion, both major reaction pathways lead to the oxidation of graphene, with oxoiron(IV) being more effective than hydroxyl radicals because the latter can recombine to hydrogen peroxide.

[0046] [ka]

[0047] In addition to reacting with graphene, both reaction intermediates in the Fenton-type reaction are capable of reacting with H2O2.

[0048] [ka]

[0049] As shown in Table 1, hydroperoxyl radicals (HO2 · ) is a strong oxidizing agent. Hydroperoxyl radicals react with organic materials, such as graphene, through hydrogen abstraction, electron transfer, and addition to previously formed radicals.

[0050] Iron(III) reacts with the hydroperoxyl radical (HO2 · ) conjugate base, superoxide (O2 ·- ) and recycled via reaction with (pKa (HO2 · / O2 ·- )=4.88 22 ) (Haber-Weiss reaction). This step completes the catalytic cycle of the Fenton-type reaction.

[0051] [ka]

[0052] An inherent problem with complex reaction networks is that the kinetics of graphene to graphene / graphene oxide are virtually impossible to predict, so optimal experimental design methodology was applied to optimize the reaction conditions.

[0053] Fenton-type oxidation of graphene The oxidation and optimization experiments reported herein were carried out in a 250 mL flask equipped with a motorized overhead stirrer and an electronic thermometer with a stainless steel probe. The flask was immersed in a water bath maintained at the appropriate temperature (see Table 1). 90.0 mL of an aqueous solution (sulfuric acid, Fisher Chemical) with a pH of 3.0 was added to the flask and stirred until the temperature inside the flask reached that of the outer water bath (allowed ΔT = 2 K).

[0054] Next, 10.0 mL of 30% H2O2 (Across Organics) was added to the flask. The mixture was stirred for 5 minutes, and then 1.0 g of pristine graphene, in the form of branched fractal aggregates, nanosheets, and nanoplatelets (fluffy graphene powder, sometimes called an aerosol gel), was added. This graphene is synthesized by detonation, providing a high-purity starting material. Each of these experiments used 0.3% graphene, which refers to the mole fraction of oxygen relative to carbon in the O2 / H2C2 mixture used for synthesis. (A 30% oxygen stoichiometry during detonation results in graphene with a zeta potential of +60.0 mV.)

[0055] The resulting suspension was stirred until a dispersion formed (approximately 10 min). At this point, the required amount of FeSO 7H O (Table 1) was added as a solid in one portion. The Fenton oxidation reaction mixture was allowed to stir at the selected bath temperature for 24 h.

[0056] [Table 1]

[0057] The oxidation product (graphene / graphene oxide (G / GO) core / shell particles) was then filtered using either a Corning 3606060M glass filter (pore size: 10-15 μm) or a GE Healthcare 1001030 (medium pore size) filter paper. Alternatively, the formed G / GO particles could be centrifuged at 7000 RPM for 5 minutes. The resulting G / GO particles were resuspended in 100 mL of double-distilled water and filtered (or centrifuged) again. This process was repeated five times until the pH of the supernatant exceeded 6.0. The resulting G / GO particles were dried over PO in a vacuum desiccator for 24 hours and then stored at room temperature in a polyethylene or polypropylene container.

[0058] Typical yields ranged from 75–80% (filtration) and 82–85% (centrifugation). The zeta potentials of the graphene / graphene oxide obtained by filtration and centrifugation were virtually identical (±0.1 mV).

[0059] Characterization of reaction products Elemental (CHO) analysis CHO analysis was performed as an indicator of the oxidation of the graphene starting material. The degree of oxidation depends on the process conditions selected (Table 1). While other reports have described C / O ratios as low as 1:1 when synthesizing graphene oxide using the traditional Hummers method, the C / O ratio reported here does not exceed 10:1. This finding can be taken as experimental evidence that the outer shell around the graphene particles is oxidized, resulting in graphene / graphene oxide core / shell nanoparticles.

[0060] Powder X-ray diffraction (XRD) As shown in Figure 12, the position of the most intense line is essentially the same for graphene and Fenton-oxidized graphene oxide. Consequently, there is no significant change in the interplanar spacing between graphene layers (less than 0.05%) between graphene and graphene oxide. In contrast, graphene oxide synthesized by graphite oxidation, i.e., the Hummers process, is known to be characterized by an increase in interplanar spacing due to the intercalation of sulfuric acid between the graphene layers followed by oxidation, resulting in a discernible leftward shift in the position of the most intense peak. The absence of this effect leads to the conclusion that no intercalation occurred during synthesis. Based on a comparison of the XRD spectra of graphene and graphene oxide, this new material possesses a substantially intact graphene core surrounded by an amorphous graphene oxide shell.

[0061] Fourier transform infrared spectroscopy (FTIR) FTIR is ideal for detecting the presence of functional groups with permanent dipole moments in materials. As shown in Figure 13, there is a significant difference between the powder FTIR spectrum of detonation-synthesized graphene (99.2% C, 0.1% H, 0.7% O) and that of Fenton-oxidized graphene (90.1% C, 1.7% H, 8.2% O). The high-energy FTIR window of Fenton-oxidized graphene is dominated by signals from -COOH groups (3500–2500 cm). -1 ), which is completely absent in graphene. In the low-energy FTIR window, a broad C=O absorption band (1800–1680 cm -1 ) and 1330 cm indicating the presence of COH functional groups -1 "A shoulder around the center is observed in the Fenton-oxidized graphene but not in the unoxidized graphene. From the FTIR data, it was concluded that the Fenton oxidation generates carboxylic acid groups on the exterior of the graphene particles and potentially other oxidation products (e.g., ketones and alcohols). This finding substantiates the paradigm of the formation of graphene / graphene oxide core / shell particles during the Fenton oxidation of graphene."

[0062] Zeta potential measurement This data clearly demonstrates chemical changes at the surface of Fenton graphene oxide. While the zeta potential of pristine graphene synthesized by the detonation method in HO (pH = 7.0) is +60 mV (Table 1), in the case of Fenton graphene oxide, it decreases to +17.7–−8.2 mV depending on the actual oxidation conditions. Compared to graphene oxide synthesized using the Hummers method, which has a zeta potential of approximately −40 mV in water (pH = 7.0), the data obtained for the oxidation methods discussed herein are clearly different, indicating that the oxidized structure obtained by the Fenton oxidation of graphene is different. The lack of negative zeta potential observed for graphene oxide is consistent with the explanation that graphene does not undergo exfoliation during oxidation. Therefore, the content of carboxylic acids in graphene oxide is low because single graphene sheets in multilayer graphene cannot be oxidized from both sides. The graphene / graphene oxide core-shell particle paradigm best fits this experimental finding.

[0063] thermogravimetry The thermal (and mechanical) stability of graphene derivatives is of paramount importance for their use in novel materials. The higher the thermal (and mechanical) stability of graphene oxides, the more suitable they are for composite applications. Graphene is known to exhibit excellent thermal stability up to 900 °C, whereas conventionally synthesized graphene oxides decompose between 200 and 400 °C, depending on the degree of oxidation. The mass of graphene oxide synthesized by Fenton oxidation decreases by 3.5 wt% (Figure 14) to 5 wt% (other oxidation conditions, not shown) when heated to 600 °C. Most importantly, this process begins at 550 °C, which is significantly higher than that observed for other graphene oxides. Note that below 100 °C, variable mass loss (up to 7 wt%) was observed for Fenton-oxidized graphene oxide, which was attributed to physisorbed water and low-molecular-weight oxidation products. As shown in Figure 14, although slight weight gain is observed for graphene due to slight oxidation at high temperatures, Fenton-oxidized graphene oxide exhibits thermal stability up to 550 °C. At 600 °C, a weight loss of 3.5% is observed. These results confirm that the graphene core is preserved during the formation of graphene / graphene oxide core / shell particles.

[0064] Example 2 Optimization of Fenton-type oxidation of detonation-synthesized graphene to graphene / graphene oxide core / shell particles Optimal Experimental Design Method (OEDM) To optimize the Fenton oxidation conditions of graphene, two key process variables (U iThe effect of the ferrous sulfate concentration (U1, milligrams per 100 ml of H2O2 aqueous solution (pH = 3.0)) and the zeta potential of the resulting graphene / graphene oxide core / shell nanoparticles (experimental reactions R1 and R2) was determined: (I) the iron(II) sulfate concentration (U1, milligrams per 100 ml of H2O2 aqueous solution (pH = 3.0)) and (II) the reaction temperature (U2, °C). OEDM was used to design an experimental matrix that would yield meaningful results with a minimum number of experiments. OEDM is based on a multivariate model in which the experimental settings for each independent variable are simultaneously varied to form an experimental matrix that allows statistically significant modeling and prediction of the optimized variables. The so-called Doehlert matrix was chosen because it offers a very simple approach to process parameter optimization. In this design, the independent variables U i is normalized. The central variable x i is defined as follows:

[0065]

number

[0066] In the formula, U i,0 =(max U i +Min U i ) / 2 is the U at the center of the experimental domain (Doehlert hexagon) i The value of ΔU i is (maximum U i -Min U i ) / 2. In the case of the Doehlert matrix, the dependent variable Y=f(x i ) is expressed as the following second-order polynomial model:

[0067]

number

[0068] When there are two independent variables, the Doehlert matrix contains seven uniformly distributed experiments, forming a hexagon containing the center variable. The center experiment should be repeated at least three times to ensure statistical reproducibility of the results. The coefficients of the polynomial model were calculated using the DESIGN Expert2 program package. The least squares method was applied to obtain a surface response, and an F-test was used to confirm the validity of the second-order polynomial model. An ANOVA analysis of the model shown in Figure 15(A) yielded a significant p-value of less than 0.0001. The final response equation for this model is:

[0069]

number

[0070] ANOVA analysis was performed on the model shown in Figure 15(B) and the result was significant with a p-value of less than 0.0001. The final response equation for this model is:

[0071]

number

[0072] The second Doehlert optimization clearly shows that the maximum approaches 60 °C and 125 mg FeSO4·7H2O.

[0073] XPS measurements of Fenton oxidized detonation graphene (0.3) The graphene oxide particles were characterized in an ultra-high vacuum (1 × 10) chamber equipped with a monochromatic Alkα X-ray source. -9X-ray photoelectron spectroscopy (PHI 5000 VersaProbe II, Physical Electronics Inc.) was performed on a 100 μm XPS instrument. Survey spectra were recorded at a pass energy (PE) of 117 eV, a step size of 1 eV, and a dwell time of 20 ms. High-energy resolution spectra were recorded at a PE of 23 eV, a step size of 0.05 eV, and a dwell time of 20 ms. Auto-z (i.e., automatic height adjustment for highest intensity) was performed before each measurement to focus the analyzer. The average number of sweeps for each component was adjusted (5–25 sweeps) to obtain an optimal signal-to-noise ratio. Data collected from the XPS acquisition were analyzed using the Multipak software tool. Three peaks corresponding to O1s, C1s, and Fe2p3 were identified in the survey spectrum of GO (not shown). The atomic composition of the elements was determined to be 96.3 percent, 3.2 percent, and 0.5 percent C, O, and Fe, respectively (not shown).

[0074] To analyze other forms of carbon and acid groups, the C1s peak of GO was deconvoluted. Deconvolution revealed peaks at 286.2 eV (CO), 284.67 eV (CC), and 284.38 eV (sp 2 C) showed three carbon and oxygen group components (data not shown). Comparative XPS literature data (1) O1s 531.50 keV OC=O (2) O1s 532.34 keV C=O (3)O1s 533.10keV C-OH (4) O1s 534.07keV COC Comparison with XPS literature data indicated the presence of carboxylic acids on the surface of the graphene / graphene oxide core / shell particles.

[0075] Chemical surface modification of detonation-derived graphene (G)-derived graphene oxide (GO) The reaction of graphene oxide derived from detonation graphene (Fenton process, GO) with methanol in the presence of thionyl chloride yields GO methyl ester (mGO, the carboxymethyl ester of detonation graphene-derived graphene oxide). The resulting material still has a negative zeta potential (-20 ± 5 mV). The presence of methyl groups and the disappearance of -COOH groups can be confirmed by Fourier transfer infrared spectroscopy. By heating in organic solvents (THF, hexane), ammonia (NH3) or primary amines (R-NH2, R = CH3 to CH8H) can be obtained. 20 The methyl group can be substituted by either

[0076] mGO synthesis: 500 mg of detonation-derived graphene (0.3)-derived GO was dispersed in 25 mL of anhydrous methanol by sonication for 5 minutes. After cooling on ice for 15 minutes, 4 mL of thionyl chloride (SOCl2) was added dropwise. The solution was stirred for 2 hours and then heated to reflux for 1 hour. After cooling to room temperature, the mGO was collected by centrifugation (7,000 RPM, 15 minutes), resuspended in methanol, and collected again. This procedure was repeated two more times. The mGO was then freeze-dried to remove any remaining traces of methanol. (Yield: essentially quantitative). The thermal stability of the material is excellent. The mass loss of graphene oxide was approximately 3.5% between 550 and 600 °C, while the mass loss of GO methyl ester was less than 1.0%. Furthermore, no loss of adsorbed water was observed between room temperature and 100 °C.

[0077] GON synthesis: 100 mg of mGO was dispersed in concentrated aqueous ammonia (33% NH3 in H2O) by sonication for 5 minutes, followed by heating at reflux for 1 hour to synthesize carboxylamides of detonation-derived graphene oxide. After cooling to room temperature, the GON was collected by centrifugation (7,000 RPM, 15 minutes), resuspended in methanol, and collected again. This procedure was repeated two more times. The mGO was then freeze-dried to remove any remaining traces of methanol. (Yield: essentially quantitative)

[0078] GONB synthesis: 100 mg of mGO was dispersed in 10 ml of DMF containing 5 wt% 1-butylamine by sonication for 5 minutes, followed by heating at 120 °C for 1 hour to synthesize carboxyl butyramide detonation-derived graphene oxide. After cooling to room temperature, the GONB was collected by centrifugation (7,000 RPM, 15 minutes), resuspended in methanol, and collected again. This procedure was repeated two more times. The mGO was then freeze-dried to remove any remaining traces of methanol. (Yield: essentially quantitative)

[0079] Chemical stability of chemical graphene oxide derivatives All of the chemical graphene oxide derivatives discussed here exhibit very similar thermogravimetric behavior. Thermal stability is increased compared to GO. As shown in Figure 16, the observed mass loss at 600 °C is less than 2.5%.

[0080] Ultraviolet-visible (UV / Vis) absorption studies of graphene, graphene oxide, and graphene carboxylamide As shown in Figure 17, all graphene derivatives have high absorbance, E, which allows photothermal applications in tissue at virtually all wavelengths. However, for in vivo applications, wavelengths of 700-800 nm (and above) are preferred (the optical window region of biological tissues).

[0081] Dispersibility of G, GO, mGO, GON, and GONB in water The dispersibility of G, GO, mGO, GON, and GONB in HO was investigated by sonicating appropriate masses in double-distilled water for 15 minutes, allowing the material to settle for 1 hour, and then decanting the solution and graphene derivative precipitate by centrifugation (7000 RPM, 30 minutes). The results are shown in Figure 18. It is noteworthy that the approximate dispersibility of mGO was 4.6 mg / mL, which allows mGO to undergo chemical reactions in water. This finding allows for the attachment of any type of amine derivative to mGO, including therapeutic peptide sequences and proteins (including antibodies and antibody fragments), via exchange of methanol for the amine derivative. R-CO-OCH3+R-NH2→R-CO-NH2+CH3OH

[0082] Cytotoxicity in neural progenitor cells The potential biochemical and biosensing applications of detonation graphene and graphene oxide were evaluated by incubation with mouse neural progenitor cells. As shown in Figure 19, cell viability decreased from 100% to approximately 60% after 24 hours of incubation with graphene and graphene oxide at 0.25 mg / ml of G and GO. Cell viability plateaued after 24 hours of incubation at 0.25–1.0 mg / ml of G and GO. These initial experiments suggest that both materials are highly suitable for biochemical and biosensing applications.

[0083] Example 3 Scaling up the synthesis—increasing the batch size and synthesizing further GO derivatives Further work was carried out to scale up the synthesis conditions to produce larger batches of GO, and procedures were carried out to synthesize various functionalized derivatives of GO to tailor the material properties.

[0084] Graphene oxide synthesis from detonation graphene by Fenton-type oxidation In this experiment, we used GO detonation graphene (40% oxygen stoichiometry during detonation) with a zeta potential of ζ = 16.26 mV. To prepare the reaction solution, 1.0 g of GO graphene was added to 100 ml of aqueous reactant solution (10 vol% H2O2 / water (pH = 3, sulfuric acid)) in a 500 ml flask. The sample was sonicated until the graphene was dispersed in the aqueous reactant solution and then heated to 333 K. Slight bubbling was observed. Next, 125 mg of solid FeSO4·7H2O was added in one portion. The mixture was stirred at 60 °C for 24 h. The GO was recovered by centrifugation (7000 rpm for 10 min) and washed 5–7 times with water. Finally, the GO was freeze-dried overnight and characterized. Yield: 0.90 g (90%), zeta potential: ζ = -8.2 mV. As shown in Figure 20, differential thermogravimetric analysis showed significant weight loss at temperatures below 50 °C (water desorption) and above 500 °C, indicating the superior thermal stability of core / shell graphene / graphene oxide compared to conventionally prepared graphene oxide (Hummers method).

[0085] Scaling up the synthesis of graphene oxide from detonation graphene In this experiment, 98 g of graphene oxide was obtained by oxidizing 100 g of 0.4% graphene as follows: 100 g of graphene was added to 1000 ml of aqueous reactant solution (10 vol% H2O2 / water (pH = 3, sulfuric acid)) in a 5000 ml flask. The sample was stirred using a mechanical stirrer for 1 hour. During this time, the graphene dispersed in the aqueous reactant solution and the reaction began. After 30 minutes, the temperature reached 80 ± 5 °C. Significant foaming was observed. The reactor was stirred continuously until the temperature dropped to 60 °C. 1.25 g of solid FeSO4·7H2O was then added in one portion. The temperature rose to 95 ± 5 °C within 15 minutes and then slowly decreased. The mixture was stirred for 24 hours. The GO was recovered by centrifugation (7000 rpm for 10 minutes) and washed 5–7 times with water. Finally, the GO was freeze-dried overnight and characterized. Yield: 98 g (98%), Zeta potential: ζ = -16.7 mV. As shown in Figure 21, the graphene oxide remained stable up to T = 600 °C, demonstrating the superior thermal stability of the scaled-up core / shell graphene / graphene oxide compared to both small-scale GO and conventionally prepared GO (Hummers process). FTIR confirmed the successful oxidation of the scaled-up batch, as shown in Figure 22.

[0086] Graphene Oxide Methyl Ester (mGO) - Three Synthesis Protocols Fischer ester synthesis reaction 64.5 mg of graphene oxide (GO) was suspended in 100 mL of anhydrous methanol in a 150 mL round-bottom flask equipped with a magnetic stirrer and a reflux condenser by sonication. Next, 1 mL of concentrated sulfuric acid was added to the GO suspension, followed by reflux for 24 h (Figure 23). After 24 h, mGO was collected by centrifugation (7,000 rpm for 10 min) and washed five times with distilled water. Finally, the mGO was freeze-dried overnight. Yield: 59.3 g (65%), Zeta potential: ζ = -11.3 mV.

[0087] Carboxylic Acid Chloride Reaction 500 mg of GO was sonicated and suspended in 25 mL of methanol in a 150 mL round-bottom flask equipped with a magnetic stir bar and a reflux condenser. The GO suspension was then cooled to 0 °C in an ice bath, and 1.25 mL of thionyl chloride was slowly added (1.25 mL of SOCl2 was 5% by volume of the methanol). After the addition of SOCl2 was complete, the reaction mixture was stirred at room temperature for 24 h (Figure 24). After 24 h, the reaction mixture was refluxed for 1 h and then allowed to cool to room temperature. Finally, the mGO was recovered by centrifugation (7,000 rpm for 10 min), washed five times with distilled water, and then freeze-dried overnight. Yield: 472 mg (94%), zeta potential: ζ = -15.34 mV. Figure 25 shows (A) the thermal stability and (B) FTIR analysis of the above product.

[0088] High-Pressure Reactor 500 mg of GO was suspended in 5 mL of methanol in a Pyrex vial designed for a PARR4560 pressurized reactor (Figure 26). The pressurized reactor was then heated to 200 °C / 250 psi under argon for 1 h. It was then allowed to cool to room temperature for another 1 h. Finally, the mGO was recovered by centrifugation (7,000 rpm for 10 min), washed five times with distilled water, and then freeze-dried overnight. Yield: 457 mg (91%), zeta potential: ζ = -16.4 mV.

[0089] Graphene oxide diethylene glycol ester (degGO) 200 mg of mGO was suspended in 20 mL of ethylene glycol using sonication in a 150 mL round-bottom flask equipped with a magnetic stir bar and a reflux condenser (Figure 27). The suspension was stirred at room temperature for 24 h and then refluxed at 197–198 °C for 1 h. The degGO suspension was then cooled to room temperature, collected by centrifugation (7,000 rpm for 10 min), washed five times with distilled water, and lyophilized overnight. Yield: 188 mg (94%), zeta potential: ζ = −12.9 mV. The thermal stability is shown in Figure 28.

[0090] Graphene amide oxide (aGO) 50 mg of mGO was suspended in 25 mL of ammonium hydroxide (30 wt% NH in H2O) with sonication in a 150 mL round-bottom flask equipped with a magnetic stirrer and reflux condenser (Figure 29). The suspension was refluxed for 1 h and then allowed to cool to room temperature. The amidated GO was then recovered by centrifugation (7,000 rpm for 10 min), washed five times with distilled water, and then freeze-dried overnight. Yield: 34 mg (68%), zeta potential: ζ = -27.6 mV. Figure 30 shows (A) FTIR analysis and (B) thermal stability of aGO.

[0091] Graphene oxide diethylamide (deaGO) 50 mg of mGO was suspended in 20 mL of dimethylformamide (DMF) containing 1 weight percent (0.19 g) of dimethylamine using sonication in a 150 mL round-bottom flask equipped with a magnetic stirrer and a reflux condenser (Figure 31). The suspension was refluxed at 154–155 °C for 1 h and then allowed to cool to room temperature. The amidated GO was then recovered by centrifugation (7,000 rpm for 10 min), washed five times with anhydrous diethyl ether, and then freeze-dried overnight. Yield: 31 mg (64%), zeta potential: ζ = −24.8 mV.

[0092] Graphene oxide 1-aminohexan-6-amide (dahmGO) 50 mg of mGO was suspended in 20 mL of DMF containing 1 weight percent (0.19 g) of 1,6-diaminohexane using sonication in a 150 mL round-bottom flask equipped with a magnetic stirrer and reflux condenser (Figure 32). The suspension was refluxed at 154–155 °C for 1 h and then allowed to cool to room temperature. The amidated GO was then recovered by centrifugation (7,000 rpm for 10 min), washed five times with anhydrous diethyl ether, and then freeze-dried overnight. Yield: 33 mg (66%), zeta potential: ζ = −22.7 mV.

[0093] From the above reactions, it can be seen that GO or mGO particles can be reacted with virtually any type of dipolar, aprotic, and monopolar solvent, as well as sterically hindered alcohols such as isopropanol and tert-butanol, to produce new compound derivatives.

[0094] Attachment of peptides to graphene oxide (GKK-GO synthesis) 10 mg of GO was suspended in 5 mL of DMF in a 5-dram clear glass vial by sonication. Next, 20 mg of oligopeptide GKK, 5 mg of EDC, and 5 mg of DMAP were suspended and sonicated for 5 minutes. The suspension was then stirred overnight at room temperature. Finally, the GKK-modified GO was recovered by centrifugation (7,000 rpm for 10 minutes), washed five times with DMF and five times with anhydrous diethyl ether, and then lyophilized. Yield: 15 mg (75%), zeta potential: ζ = +1.51 mV.

[0095] Binding of peptides to graphene oxide methyl ester (GKK-mGO) 10 mg of mGO was suspended in 5 mL of DMF containing 10 mg of a short oligopeptide (GKK) in a Pyrex vial designed for a PARR4560 pressurized reactor. The pressurized reactor was then heated to 200 °C / 170 psi under argon for 1 h. It was then allowed to cool to room temperature for another 1 h. Finally, the GKK-mGO was recovered by centrifugation (7,000 rpm for 10 min), washed five times with DMF and five times with anhydrous diethyl ether, and then lyophilized overnight. Yield: 17 mg (85%), zeta potential: ζ = +4.8 mV.

[0096] Incorporation of GO derivatives into polymers Because mGO contains polymerizable double bonds, it can be integrated with a variety of polyaddition polymers, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyacrylate (PA), and polyacrylamide (PAM), polymethyl methacrylate (PMMA), and polytetrafluoroethylene (TEFLON®), via ionic, cationic, or metal-catalyzed polymerization syntheses (Figures 33-35).

[0097] In this study, 100 mg of mGO was dispersed in 5 mL of anhydrous diethyl ether or tetrahydrofuran (THF) by sonication. Under argon, 20 mg of LiAlH4 (or a metal hydride such as NaH) was added as a solid. Vigorous dihydrogen evolution occurred after this. The reactive mixture was stirred at room temperature until no further H2 evolution was observed (1 h) and then evaporated to dryness under reduced pressure at room temperature. Anionic mGO can be used as a starter in living polymerization reactions.

[0098] As shown in Figure 36, a typical anionic (living) polymerization consists of incubating LiAlH4 and mGO with a monomer containing at least one double bond at 60-150 °C under argon (or after at least three freeze-degassing cycles) for 1-24 hours.

[0099] The GO derivative dahmGO reacts with all nylon-type polymers (polyamides) during polycondensation. It can be mixed with the starting mixture in virtually any mass ratio (Figure 37). If the polycondensation reaction is carried out at temperatures above 80°C, mGO can also be used. Methyl ester exchange to amide then occurs during the reaction. mGO also reacts with all polyesters during polycondensation (Figure 38). It can be mixed with the starting mixture in virtually any mass ratio. In the case of polyethylene terephthalate, degGO can also be used.

[0100] Both dahmGO or similar compounds and degGO or similar compounds (e.g., glycerol esters) react with isocyanates, allowing them to be incorporated into thermoplastic and duroplastic polyurethanes, the latter characterized by a higher degree of cross-linking and a higher weight-based amount of graphene / graphene oxide derivative core / shell particles.

[0101] Titration of graphene oxide 100 mg of Fenton-oxidized graphene oxide was suspended in 20 mL of 0.100 M NaOH. After stirring the suspension at 300 K for 5 min, a 0.100 M HCl solution was added stepwise. After ensuring equilibrium was reached at each step (1–5 min), the pH of the solution was recorded using a pH meter, followed by the addition of the next amount of HCl. A similar procedure was used using the same volume of NaOH, but without the addition of GO. The difference in the volume of HCl in the two titration curves at the same pH value of approximately 7.00 gives the concentration of ionized groups (hydroxyl and carboxyl groups) per weight increment of GO. The results are shown in Figure 39. The volume difference at approximately pH 7 is 170 μL. This corresponds to 1.7 × 10 per 100 mg of GO. -5 moles of acidic groups, i.e., 1.7 × 10 per gram of GO -4 moles of acidic groups. Furthermore, from the shape of the titration curve, it can be concluded that the acidic groups are mainly (more than 95%) -COOH, since at high pH, the -OH are (re)protonated, where the titration curves of both GO and the standard are nearly identical. This suggests that on each side, each -COOH molecule is approximately 10 -18 m 2 It can be calculated that the area occupied by the 2 is equal to.

Claims

1. 1. A method of making graphene / graphene oxide particles comprising a multilayered graphene core and a graphene oxide surface, comprising: preparing a reaction solution comprising an aqueous solvent system having a pH of 5.0 or less, hydrogen peroxide, and pristine multilayer graphene particles having an outer surface; adding an iron source to the reaction solution; stirring or agitating the reaction solution for a period of time to allow hydroperoxyl radicals to react with and oxidize the multilayered graphene particles to form carboxylic acid groups on the outer surfaces of the pristine multilayered graphene particles in solution, thereby obtaining the graphene / graphene oxide particles comprising a multilayered graphene core and a graphene oxide surface; and recovering the graphene / graphene oxide particles from the solution; A method comprising:

2. 10. The method of claim 1, wherein forming the reaction solution comprises dispersing hydrogen peroxide in an aqueous solvent system having a pH of 5.0 or less, adding the pristine multilayer graphene particles to the solvent system, and stirring the solution for a period of time to obtain a substantially uniform dispersion of the particles in the reaction solution.

3. 2. The method of claim 1, wherein the iron source is selected from the group consisting of ferrous ion, ferric ion, and ferrate, and is preferably iron (II) sulfate hexahydrate.

4. 10. The method of claim 1, wherein the reaction mixture is maintained at a temperature of 100°C or less during the creating, adding, and stirring steps.

5. 5. The method of claim 4, wherein the reaction mixture is maintained at a temperature of from 40°C to 75°C during the steps of making, adding, and stirring.

6. 10. The method of claim 1, wherein the graphene / graphene oxide particles are recovered by filtration and / or centrifugation.

7. 10. The method of claim 1, further comprising washing the recovered graphene / graphene oxide particles in an aqueous solvent system to neutralize reaction products.

8. 10. The method of claim 1, further comprising drying the recovered graphene / graphene oxide particles under vacuum to obtain powdered graphene / graphene oxide particles.

9. 10. The method of claim 1, wherein the pristine multilayer graphene particles are fractal aggregates of graphene synthesized by detonation.

10. 10. The method of claim 1, wherein each of the recovered graphene / graphene oxide particles comprises a graphene core and a thin graphene oxide surface coating or shell.

11. 11. The method of claim 10, further comprising reacting the graphene oxide surface with methanol to obtain GO methyl ester (mGO).

12. 12. The method of claim 11, comprising reacting the graphene oxide surface with the methanol in the presence of thionyl chloride or sulfuric acid, or under high pressure and high temperature, to obtain the mGO.

13. 12. The method of claim 11, further comprising substituting the methyl groups by heating the mGO in a solvent system.

14. 14. The method of claim 13, wherein the solvent is selected from the group consisting of hexane, ammonium hydroxide, concentrated ammonium, THF, DMF, ethylene glycol, and alcohol.

15. 14. The method of claim 13, wherein the methyl group is substituted with a primary amine group, an ester group, or an amide group.

16. 14. The method of claim 13, wherein the substitution results in an mGO derivative selected from the group consisting of graphene oxide carboxylamide, graphene oxide carboxylbutyramide, graphene oxide, graphene oxide diethylene glycol ester (degGO), graphene oxide amide (aGO), graphene oxide diethylamide (deaGO), and graphene oxide 1-aminohexan-6-amide (dahmGO).

17. 12. The method of claim 11, further comprising functionalizing the graphene oxide surface layer with a moiety.

18. 18. The method of claim 17, wherein the moiety is selected from the group consisting of an aptamer, a peptide, an antibody, a receptor protein, and combinations thereof.

19. 12. The method of claim 11, further comprising reacting the mGO or derivative thereof with a plurality of monomers to obtain a composite polymer having the graphene / graphene oxide particles incorporated therein.

20. 11. The method of claim 10, further comprising removing the graphene oxide surface coating or shell.

21. 10. Graphene / graphene oxide particles formed according to the method of claim 1, comprising a multilayered graphene core and a thin graphene oxide surface coating or shell comprising carboxylic acid groups, and comprising at least 85% carbon and up to 15% oxygen.

22. 22. The graphene / graphene oxide particle of claim 21 comprising at least 90% carbon and 3% to 4% oxygen.

23. 22. The graphene / graphene oxide particle of claim 21 , wherein the graphene oxide surface coating or shell further comprises one or more of ketone and / or alcohol surface groups.

24. 22. The graphene / graphene oxide particle of claim 21 having thermal stability up to 550°C.

25. 22. The graphene / graphene oxide particle of claim 21, essentially free of intercalants, contaminants and impurities.

26. 22. The graphene / graphene oxide particle of claim 21 , wherein the granular graphene core has a spacing at least 99.5% identical to the spacing of a control graphene material that is not oxidized.

27. 22. The graphene / graphene oxide particle of claim 21 , wherein the thin graphene oxide surface coating or shell is functionalized.

28. 22. The graphene / graphene oxide particle of claim 21 , wherein the thin graphene oxide surface coating or shell comprises a methyl ester, a primary amine, an amide, an alcohol ester, a hydroxide, a carboxylic acid, or a combination thereof.

29. 22. The graphene / graphene oxide particle of claim 21 , wherein the thin graphene oxide surface coating or shell comprises a targeting moiety selected from the group consisting of an aptamer, a peptide, an antibody, a receptor protein, and combinations thereof.

30. 22. The graphene / graphene oxide particle of claim 21 made by the method of any one of claims 1 to 20.

31. 22. The graphene / graphene oxide particle of claim 21, produced by oxidizing the surface of fractal aggregates of graphene synthesized by detonation.

32. 22. The graphene / graphene oxide particle of claim 21 , wherein the oxidation is carried out at a temperature below 100° C. using hydrogen peroxide as an oxidizing agent.

33. 22. The graphene / graphene oxide particle of claim 21, wherein the graphene core comprises 1 to 15 graphene layers.

34. 22. The graphene / graphene oxide particle of claim 21, wherein the graphene core comprises 1 to 10 graphene layers.

35. 22. The graphene / graphene oxide particle of claim 21, wherein the graphene core comprises 1 to 5 graphene layers.

36. 22. The graphene / graphene oxide particle of claim 21, wherein the graphene core comprises 1 to 2 graphene layers.

37. 37. A composition comprising a plurality of the graphene / graphene oxide particles of any one of claims 21 to 36, characterized in that the particles appear macroscopically as fluffy or fuzzy black powders or particles.

38. 38. The composition of claim 37, which is a free-flowing powder.

39. 38. An article comprising: a substrate having a surface; and a layer comprising the composition of claim 37 deposited on the substrate surface.

40. 40. The article of claim 39, wherein the composition is dispersed in a solvent system and wet applied to the surface.

41. 40. The article of claim 39, wherein the composition is mixed with a polymer system and printed onto the surface.

42. 40. The article of claim 39, wherein the graphene / graphene oxide particles are reacted with a plurality of monomers to provide a composite polymer having the graphene / graphene oxide particles incorporated therein and deposited on the substrate surface.

43. 40. The article of claim 39, wherein the layer is a thin film having a thickness of less than 1 mm.

44. 40. The article of claim 39, wherein the layer is a thin film having a thickness of less than 0.5 mm.

45. 40. The article of claim 39, wherein the composition is sintered onto the surface.

46. 38. A composite article comprising the composition of claim 37 dispersed in a polymer, resin, or cement matrix.

47. 37. A composite polymer comprising a plurality of graphene / graphene oxide particles according to any one of claims 21 to 36 reacted with a polymer matrix.

48. 48. The composite polymer of claim 47, wherein the polymer matrix is selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyacrylate, polyacrylamide, polymethyl methacrylate, polytetrafluoroethylene, polyester, polyamide, polyurethane, and copolymers thereof.

49. 38. A solid article comprising the composition of claim 37 formed into a porous body.

50. 50. The solid article of claim 49, wherein the porous body is sintered.

51. 26. The graphene / graphene oxide particle of claim 25, wherein the intercalant is sulfuric acid and / or the contaminants and impurities are sodium ions and / or potassium ions.

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