Graphene-like carbon nanoparticles with low polycyclic aromatic hydrocarbon concentrations and their preparation process

Abstract

Graphene nanosheets having reduced polycyclic aromatic hydrocarbon (PAH) content, processes for making graphene nanosheets, and processes for removing polycyclic aromatic hydrocarbons from graphene nanosheets are provided. The polycyclic aromatic hydrocarbon concentration is less than about 0.7% by weight, and less than about 0.08 g / cm as measured by ASTM B527-15. 3 Graphene nanosheets having a tap density of less than about 250 m are provided. 2 The graphene nano-sheets also have a specific surface area (BET) of greater than 1 / g. Also provided are processes for making graphene nano-sheets and for removing polycyclic aromatic hydrocarbons from graphene nano-sheets, comprising heating the graphene nano-sheets in an oxidizing atmosphere at a temperature of at least about 200°C.

Description

[Technical Field]

[0001] This application claims priority to US 62 / 457,472, filed February 10, 2017, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to the field of graphene-like carbon nanoparticles, and more specifically to graphene nanosheets with reduced polycyclic aromatic hydrocarbon (PAH) content and processes therefor. [Background technology]

[0003] Commercially available graphene can be divided into three categories: single-layer graphene by chemical vapor deposition (CVD) onto a substrate, multilayer graphene by exfoliation of graphite, and few-layer graphene nanosheets produced using a plasma torch. CVD graphene has the qualities of true single-layer graphene but likely would not be produced in the quantities required for bulk applications. Exfoliated multilayer graphene is available in bulk quantities suitable for energy storage, filler, and conductive ink applications, but does not possess the specifications or spectroscopic characteristics of single-layer graphene and cannot reach the electrical conductivity values ​​expected of single-layer graphene. Few-layer and multilayer graphene, also referred to herein as graphene nanosheets, are the subject of this disclosure.

[0004] Few-layer graphene nanosheets can be produced in bulk quantities with characteristics (Raman spectra and specific surface area) similar to those of single-layer graphene by the plasma torch process described in U.S. Patent Nos. 8,486,363, 8,486,364, and 9,221,688, U.S. Provisional Application No. US62 / 437,057, and PCT Application No. WO2015189643A1, all of which are incorporated herein by reference in their entireties. However, the production of graphene nanosheets by plasma processes results in the formation of polycyclic aromatic hydrocarbons (PAHs) as by-products, typically at concentrations ranging from about 0.1 to about 2 wt. %. In such processes, PAHs are formed on the surface of the few-layer graphene nanosheets.

[0005] PAHs are undesirable compounds present on carbon-based powders, produced from the pyrolysis of gaseous hydrocarbon precursors or when a mixture of hydrogen and carbon precursors is simultaneously present during the production of carbon-based powders. PAHs are primarily composed of carbon and hydrogen (C X H Y ) encompasses many compounds, with carbon being mostly sp 2 They are arranged in a hybrid, aromatic ring configuration. PAHs may also contain traces of oxygen, nitrogen, or other atoms. PAHs are toxic and carcinogenic, and can cause serious harm to humans who handle PAH-containing carbon nanoparticles and to consumers who use products containing PAHs (see Borm PJ, et al., Formation of PAH-DNA adducts after in vivo and vitro exposure of rats and lung cells to different commercial carbon blacks, Toxicology and Applied Pharmacology, 2005 Jun. 1;205(2):157-167). As a result, there are regulations limiting the proportion of PAHs present in manufactured carbon powders (for example, EU Directive 2007 / 19 / EC sets a maximum benzo(a)pyrene content in carbon black of 0.25 mg / kg). Furthermore, the presence of PAHs on the carbon surface can adversely affect performance in energy storage applications by blocking small pores and thus reducing the specific surface area.

[0006] Additionally, the Harmonized System (HS) established by the World Customs Organization (WCO) classifies many PAHs as carcinogenic, mutagenic or toxic to reproduction (CMR) substances in Category 1B. Accordingly, the new European REACH Regulation, Annex XVII, limits the concentration of PAHs in consumer products to 0.0001% by weight (or 1 mg / kg).

[0007] Wet chemical processes are known for cleaning or rinsing carbon particles to remove PAHs. Such processes, such as Soxhlet extraction, generally require the use of toxic nonpolar solvents such as toluene due to the very limited solubility of PAHs. However, such processes involving toxic solvents result in large amounts of waste formed by the PAH-contaminated solvent. Wet chemical PAH removal processes therefore have adverse environmental impacts and increase the cost of the PAH-free final product. Therefore, it is highly desirable to develop a simple gas-phase (dry) method for removing PAHs from carbon nanoparticles and graphene nanosheets, especially plasma-grown graphene nanosheets, that is both economical and does not involve solvent waste. The use of liquid-phase processes also results in significant densification of the carbon powder after drying. Such higher density can be a hindrance to further processing, such as dispersion.

[0008] Therefore, it is highly desirable to directly fabricate graphene nanoplatelets containing very low levels of PAHs using a plasma process without post-treatment. Indeed, it is possible to wash away PAHs using wet chemical processes such as Soxhlet extraction, but this increases the cost of the final PAH-free graphene material. Summary of the Invention

[0009] The present disclosure relates to graphene nanosheets having low amounts of polycyclic aromatic hydrocarbons. These graphene nanosheets do not require a liquid-phase or wet chemical process and therefore exhibit a lower tap density. The present disclosure further relates to a process for making the graphene nanosheets of the present disclosure.

[0010] In one embodiment, graphene nanosheets are provided having a polycyclic aromatic hydrocarbon concentration of less than about 0.7% by weight.

[0011] In another embodiment, the polycyclic aromatic hydrocarbon concentration is less than about 0.7% by weight, and less than about 0.08 g / cm as measured by ASTM B527-15 standard.3 Graphene nanosheets having a tap density of less than 1000 nm are provided.

[0012] In another aspect, there is also provided a process for removing volatile impurities from graphene nano-sheets, the process comprising heating the graphene nano-sheets in a reactive atmosphere at a temperature of at least about 200°C.

[0013] In another aspect, there is provided a process for increasing the specific surface area (BET) of graphene nanosheets, the process comprising heating the graphene nanosheets at a temperature of at least about 200° C. in an oxidizing atmosphere.

[0014] In another aspect, there is provided a process for dispersing graphene nano-sheets in a solvent, the process comprising heating graphene nano-sheets in an oxidizing atmosphere at a temperature of at least about 200° C. and dispersing the graphene nano-sheets in the solvent.

[0015] In another aspect, there is provided a process for improving the electrical conductivity of graphene nano-sheets, the process comprising heating the graphene nano-sheets at a temperature of at least about 200° C. in an oxidizing atmosphere.

[0016] In the present specification, in one aspect, injecting a carbon-containing material into a thermal region of the plasma at a velocity of at least 60 m / s at standard temperature and pressure (STP) to nucleate graphene nanosheets; and quenching the graphene nanosheets with a quench gas at a temperature of 1000°C or less. further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0017] As used herein, in another aspect, injecting a carbon-containing material into a thermal region of the plasma at a velocity of at least 60 m / s STP to nucleate graphene nanosheets; and quenching the graphene nanosheets with a quench gas at 1000°C or less, thereby producing graphene nanosheets having a Raman G / D ratio of 3 or greater and a Raman 2D / G ratio of 0.8 or greater, as measured using an incident laser wavelength of 514 nm; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0018] In a further aspect herein, injecting a carbon-containing material into the thermal region of the plasma at a velocity of at least 60 m / s STP and a quench gas to carbon ratio of at least 75 standard liters per minute (slpm) of quench gas per mole of carbon injected per minute, thereby producing graphene nanosheets; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0019] In a further aspect herein, injecting a carbon-containing material into the thermal region of the plasma at a velocity of at least 60 m / s STP and a quench gas to supplied plasma torch power ratio of at least 1.25 slpm of quench gas per kW of supplied plasma torch power, thereby producing graphene nanosheets; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0020] In yet another aspect herein, injecting a carbon-containing material into the thermal region of the plasma, the injection of the carbon-containing material being carried out using multiple jets at a speed of at least 60 m / s STP, and directing the injected carbon-containing material to distribute radially around the torch axis and be diluted before reaching a quench gas, thereby producing graphene nanosheets having a Raman G / D ratio of 3 or greater and a Raman 2D / G ratio of 0.8 or greater, as measured using an incident laser wavelength of 514 nm; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0021] Another aspect provided herein is a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: injecting a carbon-containing material into the thermal zone of the plasma at a velocity of at least 60 m / s STP and a quench gas to supplied plasma torch power ratio of at least 1.25 slpm of quench gas per kW of supplied plasma torch power, thereby producing graphene nanosheets at a rate of at least 120 g / h; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets, comprising:

[0022] Another aspect provided herein is a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: injecting a carbon-containing material into the thermal region of the plasma, the injection of the carbon-containing material being carried out using a plurality of jets at a speed of at least 60 m / s STP, and guiding the injected carbon-containing material to radially distribute around the torch axis and be diluted before reaching a quench gas, thereby producing graphene nano-sheets at a rate of at least 120 g / h; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets, comprising:

[0023] Further aspects provided herein include injecting a carbon-containing material into the thermal region of the plasma at a velocity of at least 60 m / s, thereby producing graphene nanosheets at a rate of at least 2 g / kWh of supplied plasma torch power; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets, comprising:

[0024] In a further aspect herein, injecting a carbon-containing material into the thermal region of the plasma at a velocity of at least 60 m / s and a supplied plasma torch power of more than 35 kW, thereby producing graphene nanosheets at a rate of at least 80 g / h; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0025] In a further aspect herein, injecting natural gas or methane into the thermal region of the plasma at a velocity of at least 60 m / s STP to nucleate graphene nanosheets; and quenching the graphene nanosheets with a quench gas; further heating the graphene nanosheets in a reactive atmosphere at a temperature of at least about 200°C; A plasma process for producing graphene nanosheets is provided, comprising:

[0026] The process described herein has been found to be effective in removing polycyclic aromatic hydrocarbons, thus enabling the economical, large-scale production of graphene nanosheets that have very low PAH content, are safe to handle, and are safe for incorporation into end-user applications. Furthermore, the process described herein is effective in cleaning the surface of graphene nanosheets, increasing their specific surface area and improving the ability of electrons to flow freely along their surfaces. Thus, the process is effective in improving the electrical conductivity of graphene nanosheets.

[0027] The products and processes described herein are effective in enhancing the ability of graphene nanosheets to disperse in solvents, thus enhancing their utility and performance in conductive applications where percolation at low loadings is advantageous.

[0028] The following drawings depict, by way of example only, various embodiments of the present disclosure. [Brief explanation of the drawings]

[0029] [Figure 1A] The heating enclosure (oven) used to perform the heat treatment is shown in FIG. 1A, which is a top view, and FIG. 1B, which is a cross-sectional view along line AA in FIG. 1A. [Figure 1B] The heating enclosure (oven) used to perform the heat treatment is shown in FIG. 1A, which is a top view, and FIG. 1B, which is a cross-sectional view along line AA in FIG. 1A. [Figure 2] FIG. 2A (bottom view) and FIG. 2B (cross-sectional view along line 1B-1B in FIG. 1A) show the five-hole showerhead nozzle used for injection of the carbon-containing material. [Figure 3] Plot of Raman spectra obtained at an incident wavelength of 514 nm from a sample prepared using a multi-hole injector. For each of these injector holes, the injection velocity was greater than 60 m / s STP (standard temperature and pressure), and the injection angle was 25 degrees with respect to the axis of symmetry of the plasma. [Figure 4]1 is a plot of a Raman spectrum obtained at an incident wavelength of 514 nm from a sample prepared using a single-hole injector and a lower injection velocity (less than 60 m / s STP). [Figure 5] 1 shows the plasma torch including the multi-hole injector used in Example 1, and the qualitative flow of carbon-free gas and gas containing carbon-containing material. [Figure 6] 1 shows the plasma torch including the single-hole injector used in Example 2, and the qualitative flow of carbon-free gas and gas containing carbon-containing material. DETAILED DESCRIPTION OF THE INVENTION

[0030] As used herein, the term "graphene nanosheet" refers to a single atom thick graphene nanosheet arranged in a honeycomb lattice. 2 This refers to crumpled graphene nanosheets, which have a structure comprising one or more stacks of sheets of bonded carbon atoms. At least some of these stacked sheets are curled, bent, or buckled, giving them a 3D morphology. Such particles are also known as graphene nanoplatelets (GNPs), graphene nanoflakes, wrinkled graphene, few-layer graphene, graphene-like carbon particles, or simply graphene. For example, graphene nanosheets are composed of 10 or fewer layers and have a high BET specific surface area (≥ 250 m²) as measured by ASTM D 3663-78 standard. 2 The particles may be referred to as particles that exhibit a 2D band (approximately 1350 cm-1 / g) (Brunauer et al.). The particles have a thickness in the range of 0.5-10 nm and a width typically greater than 50 nm, thus exhibiting a high aspect ratio of at least 5:1 but typically greater than 10:1. The particles, when analyzed using Raman spectroscopy with an incident laser wavelength of 514 nm, exhibit typical D, G, and 2D bands (approximately 1350 cm-1 / g) respectively. -1 , 1580cm -1 , 2690cm -1Graphene nanosheets exhibit a G / D ratio of 3 or greater (G / D≧3) and a 2D / G ratio of 0.8 or greater (2D / G≧0.8). As used herein, the G / D ratio and the 2D / G ratio refer to the ratio of the peak intensities of these bands. Graphene nanosheets can be produced from the plasma torch process described, for example, in U.S. Pat. Nos. 8,486,363, 8,486,364, and 9,221,688, and Provisional Application No. US62 / 437,057, which are incorporated herein by reference in their entireties.

[0031] As used herein, the phrase "aspect ratio" refers to the ratio of the longest dimension of a graphene particle to the shortest dimension of the graphene particle. For example, a graphene particle having an average width of 100 nm and an average thickness of 2 nm has an aspect ratio of 50:1.

[0032] As used herein, the phrases "polycyclic aromatic hydrocarbon," "PAH," or "PAHs (plural)" refer to a group of chemicals formed during the incomplete combustion of coal, oil, gas, wood, trash, or other organic matter, such as tobacco and charcoal grills. There are over 100 different PAHs. PAHs generally occur as complex mixtures (e.g., as part of combustion products such as soot) rather than as single compounds. They can also be found in materials such as crude oil, coal, coal tar pitch, creosote, and roofing tar. The list of PAHs includes, but is not limited to, biphenylene, acenaphthylene, phenanthrene, anthracene, fluoranthene, pyrene, xylene, naphthalene, benzo(A)pyrene (BaP), benzo[E]pyrene (BeP), benz[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbFA), benzo[j]fluoranthene (BjFA), benzo[k]fluoranthene (BkFA), and dibenz[a,h]anthracene (DBAhA).

[0033] As used herein, the phrases "reactive atmosphere" or "reactive environment" refer to, for example, an oxidizing atmosphere or a reducing atmosphere.

[0034] As used herein, the term "oxidizing atmosphere" or "oxidizing environment" refers to an atmosphere containing at least one oxidizing agent as described herein.

[0035] As used herein, the phrase "oxidant" refers to a gas mixture, including, but not limited to, air, oxygen, ozone, peroxides (such as hydrogen peroxide), F, CO, HO, NO, Cl, or oxidizing acids such as alcohols, sulfuric acid, perchloric acid, persulfuric acid, hypohalite (such as sodium hypochlorite), and mixtures thereof. The gas mixture may also include a noble gas (such as Ar) or N.

[0036] As used herein, the phrase "reducing atmosphere" or "reducing environment" refers to an atmosphere containing at least one reducing agent as described herein.

[0037] As used herein, the term "reducing agent" refers to NH4, H2, H2S, CO, and mixtures thereof.

[0038] The concentration of polycyclic aromatic hydrocarbons in graphene samples can be quantitatively determined, for example, by Soxhlet extraction in toluene followed by analysis using gas chromatography-mass spectrometry (GC / MS), as is common for quantifying benzo-α-pyrene (BaP) in carbon black samples. The standard method for quantifying polycyclic aromatic hydrocarbons in carbon samples is described in standard ASTM D7771-17, "Standard Test Method for Determination of Benzo-α-pyrene (BaP) Content in Carbon Black." While this standard focuses on benzo-α-pyrene (BaP), the measurement method can be used for other compounds in the PAH family. The reported % PAH concentrations in this study are the sum of all detected PAHs. Our Soxhlet extractions typically took only about 4-6 hours, compared to the 16 hours required by the ASTM standard. The Soxhlet was configured for high-efficiency extraction with rapid fill / drain cycles. The eluent was colorless before the extraction was completed. The extract was analyzed directly by GC / MS without concentration and compared to a commercially available standard PAH mixture. The detection limit of this method is on the order of 35-90 ppm PAHs (0.0035-0.0090 wt% PAHs).

[0039] As used herein, the phrase "tapped density" refers to a measurement obtained by mechanically tapping a graduated cylinder containing a sample until no significant further volume change is observed, as described by ASTM standard B527-15, "Standard Test Method for Tapped Density of Metal Powders and Compounds." Tapped density is calculated as the mass divided by the final volume of the powder (e.g., g / cm). 3 ).

[0040] As used herein, the phrase "thermally produced" refers to graphene nanosheets produced by a plasma process. Examples are described in U.S. Patent Nos. 8,486,363, 8,486,364, and 9,221,688, and Provisional Application No. US 62 / 437,057, all of which are incorporated herein by reference in their entireties.

[0041] As used herein with respect to tap density, "substantially unchanged" means that the tap density of the treated graphene nano-sheets increases or decreases by less than about 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% after the thermal reactive treatment described herein.

[0042] As used herein, the phrase "carbon-containing material" refers to a compound or material that contains at least one carbon atom.

[0043] As used herein, the phrase "thermal field" refers to a thermal field that may be generated, for example, by a quasi-thermal plasma, e.g., a plasma near local thermal equilibrium (LTE), formed by, for example, an inductively coupled plasma torch (ICP), a direct current plasma torch (DC-plasma), an alternating current plasma (AC-plasma), or a microwave plasma torch, or any other suitable method of generating hot gases in a plasma state. Plasmas are high pressure (typically greater than 100 Torr) and near LTE, where collisions between electrons, ions, neutrals, and radicals are frequent.

[0044] As used herein, the term "plasma torch delivered power" refers to the power delivered to the plasma torch. Because the plasma torch is not 100% efficient in transferring the delivered power to the plasma gas, the delivered power is equal to or greater than the power output of the plasma.

[0045] As used herein, the term "quench gas to carbon ratio" refers to the volume of quench gas per unit time, e.g., standard liters per minute (slpm) of gas injected, relative to the volume per unit time (e.g., slpm) of carbon-containing material, e.g., carbon-containing gas, injected. As used herein, the term "quench gas to carbon ratio" also refers to the volume per unit time of quench gas relative to the number of moles of carbon injected (1 mole of carbon equals 12 grams of carbon). As used herein, the term "quench gas to carbon ratio" also refers to the mass per unit time (e.g., grams per second or grams per minute) of quench gas injected into a reactor relative to the mass per unit time (e.g., grams per second or grams per minute) of carbon-containing material.

[0046] As used herein, the term "quench gas" refers to and can include any carbon-free gas with a high thermal conductivity of 17.9 milliwatts per meter per degree Kelvin or greater at STP (the thermal conductivity of argon at STP; see E.W. Lemmon and R.T. Jacobsen). Quench gas may be composed of, for example, argon, helium, hydrogen, nitrogen, or any other gas with a thermal conductivity of 17.9 mW / m·K or greater, or any mixture of these gases. Those skilled in the art will appreciate that the thermal conductivity of a gas is a determining factor in the quench rate of reactants. Quench gas is typically injected near or within the plasma torch, but may be injected elsewhere in the reactor and in multiple layers or locations. As used herein, "quench gas" also refers to the sheath gas injected adjacent to the plasma gas in RF-plasma or DC-plasma torches and used to protect torch components from thermal shock and degradation (see FIGS. 5 and 6).

[0047] As used herein, all gas volumes and velocities are intended to represent amounts at standard temperature and pressure (STP) unless otherwise specified. Those skilled in the art will readily appreciate that these values ​​will vary at the elevated temperatures and pressures experienced within a plasma torch.

[0048] As used herein, terms of degree, such as "about" and "approximately," refer to a reasonable amount of deviation from the modified term that does not significantly alter the end result. These terms of degree should be considered to include a deviation of at least ±5% or at least ±10% of the modified term, provided that this deviation does not negate the meaning of the word it modifies.

[0049] The present disclosure relates to graphene nanosheets with a low content of polycyclic aromatic hydrocarbons that have not undergone a liquid-phase processing step such as Soxhlet extraction. These graphene nanosheets have a tapped density of about 0.06 g / cm, as described by ASTM standard B527-15, "Standard Test Method for Tapped Density of Metal Powders and Compounds." 3 The graphene nanosheets may exhibit a low tap density of less than about 0.3 wt.%, less than about 0.1 wt.%, less than about 0.01 wt.%, or below the detection limit of a gas chromatography mass spectrometry (GC / MS) instrument. The graphene nanosheets may exhibit a Raman G / D ratio of about 2 or greater, a Raman 2D / G ratio of about 0.8 or greater (measured using an incident laser with a wavelength of 514 nm), and a Raman 2D / G ratio of about 250 m 2 The tap density of graphene nanosheets is typically about 0.03 to about 0.05 g / cm. 3 According to embodiments of the present disclosure, thermally produced graphene nanosheets may be produced by, for example, the processes and methods disclosed in U.S. Patent Nos. 8,486,363, 8,486,364, and 9,221,688, which are incorporated herein by reference in their entireties.

[0050] A method for obtaining graphene nanosheets containing low PAH content involves exposing PAH-containing graphene nanosheets to heat treatment at temperatures above 200°C or above 300°C in an atmosphere containing reactive species, such as oxidizing species like oxygen. The duration of this heat treatment in an oxidizing environment can be one hour or longer. The temperature in an enclosure (e.g., an oven) containing carbon nanoparticles or graphene can be gradually increased, and the gas atmosphere can be a mixture of an inert gas and reactive species. For example, if the reactive species is an oxidizing species, the gas mixture can be a mixture of nitrogen and oxygen, a mixture of argon and oxygen, a mixture of air, argon, nitrogen, and oxygen, or any other mixture of oxidizing and inert species. The reactive species can also be a reducing species. The pressure in the enclosure can be below atmospheric pressure (partial vacuum), atmospheric pressure, or above atmospheric pressure. For example, the treatment can be carried out in a vacuum or at high pressure in an oxidizing atmosphere (e.g., air, a mixture of oxygen and argon, a mixture of oxygen and nitrogen, or any other gas mixture containing an oxidizing agent) so that the PAHs or a portion thereof are removed. The graphene nanosheets can be subjected to sufficient temperatures on the order of about 300°C to about 500°C (or higher, such as 500°C to 650°C). Heating can occur for any time sufficient to achieve PAH removal. Heating can occur in any type of furnace or other apparatus capable of heating particles in a reactive atmosphere, and preferably at atmospheric pressure. Temperatures can be between 200°C and 500°C, such as between 290°C and 500°C, or between 400°C and 500°C. Temperatures above 500°C can be used, such as between 500°C and 650°C, or even higher. Those skilled in the art will appreciate that at temperatures above 600°C in an oxidizing environment, graphene particles can be oxidized, combusted, and destroyed. Those skilled in the art will appreciate that exposing graphene particles to higher temperatures with lower oxygen concentrations can have a similar effect as exposing the particles to lower temperatures and higher oxygen concentrations.

[0051] The graphene nanosheets resulting from the disclosed process have a PAH concentration of less than 0.01 wt. %, a Raman G / D ratio of 2 or greater, a Raman 2D / G ratio of 0.8 or greater (measured using an incident laser with a wavelength of 514 nm), and a Raman 2D / G ratio of 250 m 2 It is characterized by a specific surface area (BET) of more than 1000 / g.

[0052] For example, graphene nanosheets have a mass of approximately 0.06 g / cm as measured according to the ASTM B527-15 standard. 3 has a tap density of less than

[0053] For example, graphene nanosheets have a mass of approximately 0.04 g / cm as measured according to the ASTM B527-15 standard. 3 has a tap density of less than

[0054] For example, graphene nanosheets have a density of about 0.03 to about 0.05 g / cm as measured according to the ASTM B527-15 standard. 3 The tap density is

[0055] For example, graphene nanosheets have a density of about 0.03 to about 0.04 g / cm when measured according to the ASTM B527-15 standard. 3 The tap density is

[0056] For example, graphene nanosheets have a mass of approximately 0.03 g / cm as measured according to the ASTM B527-15 standard. 3 The tap density is

[0057] For example, a graphene nanosheet is approximately 250 m 2 / g.

[0058] For example, a graphene nanosheet is approximately 300 m 2 / g.

[0059] For example, a graphene nanosheet is approximately 350 m 2 / g.

[0060] For example, graphene nanosheets are approximately 250 to 600 m 2 / g specific surface area (BET).

[0061] For example, graphene nanosheets are approximately 300 to 600 m 2 / g specific surface area (BET).

[0062] For example, a graphene nanosheet is approximately 400 to 600 m 2 / g specific surface area (BET).

[0063] For example, a graphene nanosheet is about 500 to 600 m 2 / g specific surface area (BET).

[0064] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 500 ppm.

[0065] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 400 ppm.

[0066] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 200 ppm.

[0067] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 100 ppm.

[0068] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 90 ppm.

[0069] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 80 ppm.

[0070] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 70 ppm.

[0071] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 60 ppm.

[0072] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 50 ppm.

[0073] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 40 ppm.

[0074] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than 35 ppm.

[0075] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.6% by weight.

[0076] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.5% by weight.

[0077] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.4% by weight.

[0078] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.3% by weight.

[0079] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.2% by weight.

[0080] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.1% by weight.

[0081] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.01% by weight.

[0082] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.01% to about 0.7%.

[0083] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.01% to about 0.5%.

[0084] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.01% to about 0.3%.

[0085] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.1% to less than about 0.3% by weight.

[0086] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.01% to about 0.1%.

[0087] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.15% to less than about 0.25% by weight.

[0088] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.1% by weight to about 0.6% by weight.

[0089] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.05% by weight to about 0.6% by weight.

[0090] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.05% by weight to about 0.5% by weight.

[0091] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.1% by weight to about 0.5% by weight.

[0092] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.01% by weight to about 0.4% by weight.

[0093] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.05% by weight to about 0.4% by weight.

[0094] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.1% by weight to about 0.4% by weight.

[0095] For example, the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of about 0.05% by weight to about 0.3% by weight.

[0096] For example, graphene nanosheets have a polycyclic aromatic hydrocarbon concentration below the detection limit as measured by gas chromatography mass spectrometry (GC / MS) or Soxhlet extraction according to ASTM D7771-11.

[0097] For example, the graphene nanosheets have a Raman G / D ratio of about 3 or greater and a Raman 2D / G ratio of about 0.8 or greater when measured using an incident laser wavelength of 514 nm. The graphene nanosheets have a Raman G / D ratio of about 2.5 or greater and a Raman 2D / G ratio of about 0.8 or greater when measured using an incident laser wavelength of 514 nm, and the graphene nanosheets have a polycyclic aromatic hydrocarbon concentration of less than about 0.7 wt%.

[0098] For example, graphene nanosheets have a mass of approximately 0.06 g / cm as measured according to the ASTM B527-15 standard. 3 has a tap density of less than

[0099] For example, graphene nanosheets are thermally produced.

[0100] For example, the volatile impurities are polycyclic aromatic hydrocarbons.

[0101] For example, the reactive atmosphere is an oxidizing atmosphere.

[0102] For example, the oxidizing atmosphere comprises an oxidizing agent selected from air, water vapor, oxygen, ozone, peroxide, F2, CO2, H2O, NO2, Cl2, alcohol, sulfuric acid, perchloric acid, persulfuric acid, hypohalite, halogens, oxyhalides, nitrous oxide, and mixtures thereof.

[0103] For example, an oxidizing atmosphere includes an inert gas and an oxidizing agent.

[0104] For example, the inert gas is nitrogen, argon, helium, neon, krypton, xenon or a mixture thereof.

[0105] For example, the gas mixture includes oxygen and argon.

[0106] For example, the process involves injecting a gas mixture that includes oxygen into an enclosure containing graphene nanosheets.

[0107] For example, the gas mixture is injected at a constant flow rate.

[0108] For example, the gas mixture is injected at a constant flow rate of about 1 to 10 slpm.

[0109] For example, the reactive atmosphere is a reducing atmosphere.

[0110] For example, the reducing atmosphere includes NH4, H2, H2S, CO, and mixtures thereof.

[0111] For example, the reducing atmosphere includes an inert gas and a reducing agent.

[0112] For example, the process is effective in reducing the concentration of polycyclic aromatic hydrocarbons in graphene nanosheets to less than about 2%.

[0113] For example, the process is effective in reducing the concentration of polycyclic aromatic hydrocarbons in graphene nanosheets to less than about 1%.

[0114] For example, the graphene nanosheets are heated to a temperature of at least about 300°C.

[0115] For example, the graphene nanosheets are heated to a temperature of at least about 400°C.

[0116] For example, the graphene nanosheets are heated to a temperature of at least about 500°C.

[0117] For example, the graphene nanosheets are heated to a temperature of at least about 600°C.

[0118] For example, the graphene nanosheets are heated at a temperature of about 200°C to about 1000°C.

[0119] For example, the graphene nanosheets are heated at a temperature of about 200°C to about 750°C.

[0120] For example, the graphene nanosheets are heated at a temperature of about 300°C to about 550°C.

[0121] For example, the process is carried out at atmospheric pressure.

[0122] For example, the process is carried out at sub-atmospheric pressure or under partial vacuum.

[0123] For example, the process is carried out at superatmospheric pressure.

[0124] For example, the specific surface area (BET) increases by at least 20%.

[0125] For example, the specific surface area (BET) increases by at least 30%.

[0126] For example, the specific surface area (BET) increases by at least 40%.

[0127] For example, the specific surface area (BET) increases by at least 50%.

[0128] For example, the specific surface area (BET) increases by at least 60%.

[0129] For example, the specific surface area (BET) increases by at least 70%.

[0130] For example, the specific surface area (BET) increases by at least 80%.

[0131] For example, the specific surface area (BET) increases by at least 90%.

[0132] For example, the specific surface area (BET) increases by at least 100%.

[0133] For example, the process is carried out in the absence of a liquid or solvent.

[0134] For example, the process is a dry process.

[0135] For example, the process is a continuous process.

[0136] For example, the process is carried out in a fluidized bed reactor.

[0137] For example, the process is carried out in a rotary oven.

[0138] For example, the process is a batch process.

[0139] For example, the tap density of the graphene nanosheets remains substantially unchanged as measured by the ASTM B527-15 standard.

[0140] For example, the tap density of the graphene nanosheets increases or decreases by less than 5% as measured according to the ASTM B527-15 standard.

[0141] For example, the tap density of the graphene nanosheets increases or decreases by less than 10% as measured according to the ASTM B527-15 standard.

[0142] For example, the polycyclic aromatic hydrocarbon is selected from biphenylene, acenaphthylene, phenanthrene, anthracene, fluoranthene, pyrene, xylene, naphthalene, benzo(A)pyrene (BaP), benzo[E]pyrene (BeP), benzo[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbFA), benzo[j]fluoranthene (BjFA), benzo[k]fluoranthene (BkFA), dibenz[a,h]anthracene (DBAhA), and mixtures thereof.

[0143] For example, the polycyclic aromatic hydrocarbon is selected from biphenylene, acenaphthylene, phenanthrene, anthracene, fluoranthene, pyrene, xylene, naphthalene, benzo(A)pyrene (BaP), benzo[E]pyrene (BeP), benzo[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbFA), benzo[j]fluoranthene (BjFA), benzo[k]fluoranthene (BkFA), dibenz[a,h]anthracene (DBAhA), and mixtures thereof.

[0144] For example, the graphene nanosheets are quenched with a quench gas having a temperature below 1300°C.

[0145] For example, the graphene nanosheets are quenched with a quench gas having a temperature of less than 900°C.

[0146] For example, the graphene nanosheets are quenched with a quench gas having a temperature of less than 600°C.

[0147] For example, the graphene nanosheets are quenched with a quench gas having a temperature of less than 300°C.

[0148] For example, the graphene nanosheets are quenched with a quench gas having a temperature below 100°C.

[0149] For example, the carbon-containing material is injected at a quench gas to carbon ratio of at least 50 slpm of quench gas per mole of carbon per minute.

[0150] For example, the carbon-containing material is injected at a quench gas to carbon ratio of at least 160 slpm of quench gas per mole of carbon per minute.

[0151] For example, the carbon-containing material is injected at a quench gas to carbon ratio of at least 250 slpm of quench gas per mole of carbon per minute.

[0152] For example, the carbon-containing material is injected at a quench gas to carbon ratio of about 50 slpm to about 125 slpm of quench gas per mole of carbon per minute.

[0153] For example, the carbon-containing material is injected at a quench gas to carbon ratio of about 100 slpm to about 250 slpm of quench gas per mole of carbon per minute.

[0154] For example, injection of carbon-containing materials carried out using multiple jets.

[0155] For example, injection of carbon-containing materials carried out using at least three jets.

[0156] For example, injection of carbon-containing materials carried out using at least four jets.

[0157] For example, injection of carbon-containing substances carried out using at least five jets.

[0158] For example, injection of carbon-containing materials carried out using more than five jets.

[0159] For example, graphene nanosheets are produced at a rate of at least 120 g / h.

[0160] For example, graphene nanosheets are produced at a rate of at least 150 g / h.

[0161] For example, graphene nanosheets are produced at a rate of at least 200 g / h.

[0162] For example, graphene nanosheets are produced at a rate of at least 250 g / h.

[0163] For example, graphene nanosheets are produced at a rate of about 120 to about 150 g / h.

[0164] For example, graphene nanosheets are produced at a rate of about 150 to about 250 g / h.

[0165] For example, the graphene nanosheets are quenched with a quench gas delivered at a rate of at least 3 slpm of quench gas per kW of delivered torch power.

[0166] For example, the graphene nanosheets are quenched with a quench gas delivered at a rate of at least 1 slpm of quench gas per kW of delivered torch power.

[0167] For example, the graphene nanosheets are quenched with a quench gas delivered at a rate of at least 0.5 slpm of quench gas per kW of delivered torch power.

[0168] For example, the graphene nanosheets are quenched with a quench gas delivered at a rate of about 0.5 slpm to about 1.5 slpm of quench gas per kW of supplied torch power.

[0169] For example, graphene nanosheets are quenched with a quench gas delivered at a rate of about 1.5 slpm to about 4 slpm of quench gas per kW of supplied torch power.

[0170] For example, graphene nanosheets are produced at a rate of at least 1 g / kWh of supplied plasma torch power.

[0171] For example, graphene nanosheets are produced at a rate of at least 2.5 g / kWh of supplied plasma torch power.

[0172] For example, graphene nanosheets are produced at a rate of at least 3 g / kWh of supplied plasma torch power.

[0173] For example, graphene nanosheets are produced at a rate of at least 5 g / kWh of supplied plasma torch power.

[0174] For example, graphene nanosheets are produced at a rate of about 2 to about 3 g / kWh of supplied plasma torch power.

[0175] For example, graphene nanosheets are produced at a rate of about 3 to about 5 g / kWh of supplied plasma torch power.

[0176] For example, the carbon-containing substance is a carbon-containing gas.

[0177] For example, the carbon-containing gas is a C1-C4 hydrocarbon.

[0178] For example, the carbon-containing gas is selected from methane, ethane, ethylene, acetylene, vinyl chloride, propane, propene, cyclopropane, allene, propyne, butane, 2-methylpropane, 1-butene, 2-butene, 2-methylpropene, cyclobutane, methylcyclopropane, 1-butyne, 2-butyne, cyclobutene, 1,2-butadiene, 1,3-butadiene, or 1-buten-3-yne, or mixtures thereof.

[0179] For example, the carbon-containing substance is a carbon-containing liquid.

[0180] For example, carbon-containing liquids are C5 to C 10 It is a hydrocarbon.

[0181] For example, the carbon-containing liquid is selected from n-propanol, 1,2-dichloroethane, allyl alcohol, propionaldehyde, vinyl bromide, pentane, hexane, cyclohexane, heptane, benzene, toluene, xylene, or styrene, or mixtures thereof.

[0182] For example, the carbon-containing material is methane or natural gas.

[0183] For example, the carbon-containing material is a carbon-containing solid.

[0184] For example, the carbon-containing solid is selected from graphite, carbon black, norbornylene, naphthalene, anthracene, phenanthrene, polyethylene, polypropylene, or polystyrene, or mixtures thereof.

[0185] For example, a carbon-containing gas, a carbon-containing liquid, or a carbon-containing solid may be in admixture with a carrier gas.

[0186] For example, the carrier gas comprises an inert gas.

[0187] For example, the inert gas is selected from argon, helium, nitrogen, hydrogen, or mixtures thereof.

[0188] For example, the quench gas is selected from argon, helium, nitrogen, hydrogen, or mixtures thereof.

[0189] For example, the quench gas comprises an inert gas.

[0190] For example, the quench gas comprises hydrogen.

[0191] For example, the quench gas comprises argon.

[0192] For example, the quench gas is delivered at a rate of 1 to 10 slpm of gas per kW of supplied plasma torch power.

[0193] For example, the thermal zone has a temperature of about 4000°C to about 11000°C.

[0194] For example, the thermal zone has a temperature of about 3000°C to about 8000°C.

[0195] For example, the thermal zone has a temperature of about 2600°C to about 5000°C.

[0196] For example, the carbon-containing material is injected at a velocity of at least 70 m / s STP.

[0197] For example, the carbon-containing material is injected at a velocity of at least 90 m / s STP.

[0198] For example, the carbon-containing material is injected at a velocity of at least 100 m / s STP.

[0199] For example, the carbon-containing material is injected at a velocity of about 60 to about 100 m / s STP.

[0200] For example, the carbon-containing material is injected at a velocity of about 70 to about 90 m / s STP.

[0201] For example, the carbon-containing material is injected at a velocity of about 75 to about 85 m / s STP.

[0202] For example, the process can be carried out at an injection angle of the carbon-containing material of about 10 to about 40 degrees, about 20 to about 30 degrees, or about 25 degrees with respect to the axis of symmetry of the plasma.

[0203] For example, the process can be carried out at an injection angle of the carbon-containing material of about 15 to about 35 degrees, about 20 to about 30 degrees, or about 25 degrees with respect to the axis of symmetry of the plasma.

[0204] For example, the process can be carried out using a plasma torch including a multi-hole injector for injecting the carbon-containing material, where for each of the injector holes, the injection velocity is at least 60 m / s STP and the injection angle is about 15 to about 35 degrees with respect to the axis of symmetry of the plasma.

[0205] For example, the process can be carried out using a plasma torch including a multi-hole injector for injecting the carbon-containing material, where for each of the injector holes, the injection velocity is at least 60 m / s STP and the injection angle is about 20 to about 30 degrees with respect to the axis of symmetry of the plasma.

[0206] For example, the process can be carried out using a plasma torch including a multi-hole injector for injecting the carbon-containing material, where for each of the injector holes, the injection velocity is at least 60 m / s STP and the injection angle is about 25 degrees with respect to the axis of symmetry of the plasma.

[0207] For example, the quench gas is injected around the hot zone.

[0208] For example, the process further includes recovering the produced graphene nano-sheets.

[0209] For example, the produced graphene nanosheets are collected in a bag filter, on a filter cartridge, or in a cyclone.

[0210] For example, graphene nanosheets have a maximum strength of 250 m as measured by ASTM D 3663-78. 2 / g or more.

[0211] For example, graphene nanosheets have an aspect ratio of at least 5:1.

[0212] For example, graphene nanosheets have an aspect ratio of at least 10:1.

[0213] For example, graphene nanosheets have a Raman G / D ratio of at least 3 when measured using an incident laser wavelength of 514 nm.

[0214] For example, graphene nanosheets have a Raman 2D / G ratio of at least 0.8 when measured using an incident laser wavelength of 514 nm.

[0215] For example, the plasma torch power supplied is over 35 kW.

[0216] For example, the plasma torch power supplied is over 100 kW.

[0217] For example, the plasma torch power supplied is over 200 kW.

[0218] For example, the plasma torch power supplied is over 1000 kW.

[0219] The following examples are non-limiting and are used to better illustrate the materials and processes of the present disclosure. The scope of the claims should not be limited by the specific embodiments and examples provided in this disclosure, but should be accorded the broadest interpretation consistent with the entire disclosure.

[0220] Example Example 1: Heat treatment to reduce the polycyclic aromatic hydrocarbon content of graphene nanosheets In one exemplary embodiment, wrinkled graphene nanosheet powder produced using an ICP plasma torch with methane as a precursor (as described in U.S. Provisional Application No. 62 / 437,057) is treated with a dry process to remove PAHs. Prior to the gas-phase (dry) process, the produced wrinkled graphene powder contained 0.16 wt. % PAHs (as measured by Soxhlet extraction with toluene) and 302 m 2 / g BET specific surface area.

[0221] Referring now to Figure 1A, the enclosure (oven) includes a port (11) for the inlet of the gas mixture and a port (12) for the outlet of the gas mixture containing decomposed PAHs. Referring now to Figure 1B, the enclosure includes a flange (13) for receiving both ports (12) and (13). Another port (14) is provided in the enclosure for inserting a shaft that mixes the powder during the thermal oxidation process. The enclosure is housed in a wall (15) and includes a groove (16) for an O-ring that seals the enclosure, as well as bottom (17) and side (18) heating elements. Those skilled in the art will understand that any other suitable enclosure may be used to carry out the processes disclosed herein.

[0222] The as-prepared graphene nanosheet powder contained 0.16 wt. % PAHs (as determined by Soxhlet extraction with toluene) and 302 m 2The powder has a BET specific surface area of ​​1 / g. The gas-phase (dry) process for removing PAHs involves thermal oxidation under a constant, high-volume gas flow (3 slpm) consisting of a mixture of Ar and O2 (9% by volume O2). The temperature inside the heated enclosure is approximately 400°C, and the enclosure is maintained at atmospheric pressure. The gas flow is used to ensure that volatile components are removed and expelled from the powder. A 1-hour ramp is used to reach 400°C, followed by a 40-minute plateau and approximately 2 hours of cooling. 10 g to 400 g were processed per run. The batch process can be easily converted to a continuous process, for example, by using a fluidized-bed thermal reactor, without loss of generality, or by passing the material to be processed through a rotary oven or another heating zone, such as a conveyor belt. The amount processed can be easily scaled up by increasing the size of the oven and therefore the heating zone.

[0223] The thermal oxidation treatment evaporates and / or decomposes the PAHs present on the graphene nanosheets. The graphene nanosheets have a highly graphitized state (high level of crystallinity) and do not undergo significant mass loss during this thermal treatment. The weight loss during the treatment is related to the removal and destruction of PAHs (and therefore related to the initial concentration of PAHs). The following oxidizing agents can be used instead of oxygen, for example: air, water vapor, carbon dioxide, etc. It will be readily apparent to those skilled in the art that the atmosphere (gas composition and pressure) used and the amount of material treated will determine the temperature and time used.

[0224] Disordered carbon has an etching rate an order of magnitude higher than graphitized carbon. The tap density of the powder (measured by ASTM standard B527-15) is not altered by the thermal oxidation treatment, but a significant increase in the BET specific surface area is measured (due to the removal of pore-blocking PAHs). A slight increase in the concentration of oxygen functional groups on the graphene surface can be observed (approximately 1-2 atomic % O / C as measured by XPS). After treatment, the resulting graphene nanosheets contain no measurable PAHs (less than the detection limit of 90 ppm by Soxhlet extraction). After the treatment described in this example, the BET specific surface area is reduced from 302 m to 102 m before treatment. 2 / g to 567m after treatment 2 / g. Graphene with a higher Raman G / D ratio exhibited a mass loss of 300 to 450 m / g without significant mass loss. 2 The change in BET specific surface area to / g was measured.

[0225] After thermal oxidation treatment, there is no measurable weight loss (apart from the percentage of PAHs removed) and no change in tap density, but there is a clear increase in BET surface area. The increase in clear BET surface area is typically about 20 to about 100%.

[0226] There is no significant change in the relative ratios of the three major Raman bands (D, G, and 2D bands) in the Raman spectrum of as-prepared graphene compared to the heat-treated material.

[0227] Example 2 In a second exemplary embodiment, a second type of oven is used to remove PAHs. The second oven used is a Paragon natural convection kiln furnace; the air flow (O2 / N2, 21 / 79% by volume) is not forced internally but comes from natural convection due to the high and low temperatures inside and outside the oven, respectively. Two circular openings (with a diameter of approximately one-half inch) are located on the sides of the oven to allow natural convection to circulate and refresh the air in the oven. In this example, graphene nanosheets produced using an ICP plasma torch with methane as a precursor gas (described in Provisional Application No. 62 / 437,057) are treated in a gas-phase process to remove PAHs. In this example, the as-produced graphene nanosheets contained 0.50 wt. % PAHs (as measured by Soxhlet extraction with toluene) and were analyzed by a 288 m 2 / g. The treatment is carried out at atmospheric pressure.

[0228] The temperature-time profile for this oven is as follows: 40 minutes from room temperature to 290°C, then 20 minutes from 290°C to 440°C, followed by a 2-hour plateau at 440°C, and a slow cool to room temperature (lasting approximately 2 hours). The material to be processed is placed on the oven's multi-tiered plates, each containing 40-80 grams of flat-layered graphene powder (160-320 grams are processed per batch). Again, this batch process can be easily converted to a continuous process.

[0229] After treatment, the resulting graphene nanosheets contained no measurable PAHs (below the detection limit of the Soxhlet extraction method) and had a BET specific surface area of ​​430 m 2 / g. The tap density of the powder (measured according to ASTM standard B527-15) remains unchanged, but an important increase in the BET specific surface area is measured, again without significant mass loss. A slight increase in the concentration of oxygen functional groups on the graphene surface can be observed (approximately 1%-2% as measured by XPS).

[0230] There is no significant change in the relative ratios of the three major Raman bands (D, G, and 2D bands) in the Raman spectrum of as-prepared graphene compared to the heat-treated material.

[0231] Example 3: Counterexample Using the same wrinkled graphene powder (PAH concentration of 0.16 wt. % PAH, BET surface area of ​​302 m / g) produced in Example 1, and directly (without thermal oxidation treatment) performing Soxhlet extraction with toluene, the final BET surface area was 329 m. 2 / g. Knowing that the accuracy of the specific surface area measurement is approximately ±10%, no significant changes were observed.

[0232] After the Soxhlet extraction step (wet process), a change in the tap density of the wrinkled graphene powder was observed. The tap density was 0.04 g / cm. 3 to 0.11 g / cm 3 This supports the idea that the wet process results in an increase in tap density.

[0233] This Soxhlet extraction sample (329m 2 / g) followed by a heat treatment step in pure argon atmosphere (approximately 300 °C for 1.5 h) did not further increase the BET specific surface area. 2 This heat treatment in the absence of oxygen resulted in a final BET specific surface area of ​​1 / g. , Gu We conclude that it is not effective in increasing the specific surface area of ​​laphene.

[0234] Example 4: Preparation of graphene nanosheets The starting material (graphene nanosheets) for some of the processes disclosed in this disclosure can be prepared in a variety of different ways. For example, graphene nanosheets can be prepared by using the thermal plasma process disclosed below.

[0235] In one exemplary embodiment, the hydrocarbon precursor is methane and is injected into an inductively coupled plasma torch (ICP) at a maximum plate power of 60 kW. Figure 5 shows the ICP torch 100 and the qualitative flow of gases including non-carbon-containing gases and carbon-containing materials.

[0236] In a power generation system delivering 56 kW to an induction-coupled plasma torch (PN-50 model, Tekna, Sherbrooke, Quebec, Canada), 20 slpm of argon was used as the central vortex gas 128, surrounded by a layer of quench gas (sheath gas) 124 consisting of 174 slpm of argon and 30 slpm of hydrogen gas, as shown in Figure 5. 33.6 slpm of natural gas (carbon feed gas) 120 was injected through an injector probe 110 with a designed nozzle. A coil 122 conducting high-frequency alternating current generates the plasma. A qualitative isotherm 126 is shown inside the plasma torch. The pressure in the reactor was 500 Torr. The injection velocity was 80.6 m / s at standard temperature and pressure (STP). It should be understood that for plasma conditions at extreme temperatures and pressures, these gas injection velocities will be higher and values ​​must be corrected to account for different temperature and pressure values. Those skilled in the art will appreciate that this injection rate value will increase if the process is scaled up, for example, to a larger plasma volume or larger plasma torch size.

[0237] The process lasted for 45 minutes and resulted in a graphene production rate of 225 g / h, measured by dividing the weight of powder collected downstream of the high-temperature plasma region by the operating time required to synthesize this powder.

[0238] The injected carbon is 33.6 slpm / 22.4 l=1.5 moles / min or 18 g / min of carbon.

[0239] The quench gas to carbon ratio is at least 120 liters STP of carbon-free gas for 1 mole of carbon (also at least 180 slpm of carbon-free gas for 18 g / min of carbon; 10.0 liters of carbon-free gas for 1 g of carbon in gaseous form).

[0240] The injected carbon per watt is typically 33.6 slpm for a delivered torch power of 56 kW, equivalent to 0.6 slpm C / kW of torch power.

[0241] 2A and 2B, the injector used was a multi-hole nozzle 10 containing five injection holes 12, each hole having a diameter of 0.052 inches. The nozzle 10 contained a channel 16 for hydrocarbon delivery, with the nozzle surface 14 perpendicular to the injection holes 12. This configuration provided an injection velocity of 80.6 m / s STP. The carbon gas injection angle was 25 degrees with respect to the axis of symmetry of the plasma. Those skilled in the art will appreciate that a water-cooled injection nozzle would provide longer wear resistance and allow for longer production runs under stable operating conditions.

[0242] The resulting product was high-quality graphene nanosheets, as seen from the Raman spectrum (shown in Figure 3). The specific surface area of ​​the material (using the BET method) was 431 m after the PAHs were removed. 2 The Raman spectrum of the product is characterized by a 2D / G ratio of 1.3 and a G / D ratio of 4.7, measured using an incident wavelength of 514 nm.

[0243] To limit residence time in the high temperature region, the carbon precursor is injected at a high velocity of at least 60 m / s STP, typically 80 m / s STP, and even 100 m / s STP. This may be achieved by injecting the gaseous material, such as natural gas, through a small-hole showerhead nozzle at an injection velocity equal to or greater than the velocity of the plasma gas. The high delivery velocity combined with the small holes results in a high injection velocity and a short residence time in the high temperature region.

[0244] Example 5: Counterexample Conversely, using parameters similar to those described above in Example 4, but injecting methane with a single-hole nozzle at an injection velocity less than 60 m / s STP, produced a significant proportion of carbon nodules and spherical carbon particles, resulting in a typical Raman spectrum of acetylene black (shown in Figure 4). Figure 6 shows the ICP torch 200 used in this counterexample, as well as the qualitative flow of carbon-free gas and gas containing carbon-containing material.

[0245] In this example, an injection velocity of 28.6 m / s STP was used, as shown in Figure 6. The carbon precursor gas feed rate was 34.7 slpm CH4, and the achieved production rate was 142 g / h. 20 slpm of argon was used as the central vortex gas 228, surrounded by a layer of quench gas (sheath gas) 224 consisting of 125 slpm argon and 8 slpm hydrogen gas. Otherwise, the same method and apparatus as in Example 4 were used. The carbon precursor gas 220 was injected through a designed nozzleless injector probe 210 (e.g., with a single-hole nozzle). A coil 222 conducting high-frequency alternating current generated the plasma. Qualitative isotherms 226 are shown inside the plasma torch.

[0246] The resulting material was 150 m 2 The resulting particles exhibit a low specific surface area (BET) of 0.1 / g and a Raman spectrum (Figure 4) characteristic of thick graphitic nodules instead of thin graphene-like particles. The resulting particles exhibit a Raman G / D ratio of 1.1 and a Raman 2D / G ratio of 0.5, measured using an incident wavelength of 514 nm. As shown in Figure 6, the carbon precursor is injected into the high-temperature region through a single-hole probe without a nozzle, resulting in a longer residence time in the high-temperature region, poor quenching efficiency, and the resulting formation of acetylene-type carbon black (e.g., not graphene). The carbon precursor gas is injected at a 0° angle with respect to the symmetry axis of the plasma.

[0247] The embodiments of paragraphs

[0029] to

[0246] of the present disclosure are presented in a manner that demonstrates that, where applicable, all combinations of embodiments may be made. These embodiments are therefore presented in the specification in a manner that is equivalent to creating dependent claims for all embodiments that depend on any preceding claim (including previously presented embodiments), thereby demonstrating that they may be combined in all possible ways. For example, all possible combinations between the embodiments of paragraphs

[0029] to

[0246] and the processes and graphene nanosheets of paragraphs

[0009] to

[0025] , where applicable, are hereby encompassed by the present disclosure.

[0248] The scope of the claims should not be limited by the specific embodiments and examples provided in this disclosure, but should be accorded the broadest interpretation consistent with the entire disclosure.

[0249] References 1. Borm PJ, et al., Formation of PAH-DNA adducts after in vivo and vitro exposure of rats and lung cells to different commercial carbon blacks, Toxicology and Applied Pharmacology, 2005 Jun. 1; 205(2): 157-167. 2. Jeongmin Lim et al., A study of TiO2 / carbon black composition as counter electrode materials for dye-sensitized solar cells. Nanoscale Research Letters 2013; 8(1): 227. 3. Stephen Brunauer, PH Emmett, Edward Teller, The Journal of the American Chemical Society 60 (1938) 309. 4.E. W. Lemmon and R. T Jacobsen, International Journal of Thermophysics, Vol. 25 (2004) 21-68.

Claims

Claim 1: A process for removing volatile impurities from graphene nano-sheets, comprising heating the graphene nano-sheets in a reactive atmosphere at a temperature of at least 200°C; the process is for reducing the polycyclic aromatic hydrocarbon concentration in the graphene nanosheets to less than 2 wt. %; The reactive atmosphere is a reducing atmosphere. process.

2. A plasma process for producing graphene nanosheets, comprising: injecting a carbon-containing material into a thermal region of the plasma at a velocity of at least 60 m / s STP to nucleate the graphene nano-sheets; quenching the graphene nano-sheets with a quench gas at or below 1000°C, thereby producing the graphene nano-sheets having a Raman G / D ratio of 3 or greater and a Raman 2D / G ratio of 0.8 or greater, as measured using an incident laser wavelength of 514 nm; and further heating the graphene nano-sheets at a temperature of at least 200°C in a reactive atmosphere. Plasma processes, including

3. 3. The process of claim 2, wherein the graphene nano-sheets are heated at a temperature between 200°C and 1000°C.

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