WO2015157280A1 - Production respectueuse de l'environnement de dispersions de graphène hautement conductrices et propres - Google Patents

Production respectueuse de l'environnement de dispersions de graphène hautement conductrices et propres Download PDF

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WO2015157280A1
WO2015157280A1 PCT/US2015/024710 US2015024710W WO2015157280A1 WO 2015157280 A1 WO2015157280 A1 WO 2015157280A1 US 2015024710 W US2015024710 W US 2015024710W WO 2015157280 A1 WO2015157280 A1 WO 2015157280A1
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graphene
graphene sheets
sheets
eco
solution
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Huixin He
Keerthi SAVARAM
Mehulkumar PATEL
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Rutgers, The State University Of New Jersey
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/194—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C01B32/19—Preparation by exfoliation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties

Definitions

  • the invention relates to a novel eco-friendly, rapid approach to directly produce highly-conductive and "clean" graphene sheets of different lateral sizes without involving any toxic regents or metal-containing compounds, and without generating toxic byproducts, thus enabling a broad spectrum of applications, by solution processing techniques of low cost.
  • the approach relies on the synergy of piranha solution, intercalated molecular oxygen, and microwave heating that enables controlled oxidation of graphite particles, leading to rapid and direct generation of highly-conductive, clean graphene sheets of different lateral sizes without releasing any toxic gases and/or any potentially toxic aromatic byproducts.
  • Graphene is a flat monolayer of carbon atoms tightly packed into a two- dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities. It can be wrapped up into 0D fullerenes, rolled into ID nanotubes or stacked into 3D graphite. Due to its excellent electronic, thermal and mechanical properties, and its large surface area and low mass, graphene holds great potential for a range of applications. Except for ultrahigh speed electronics, most of the proposed applications require large quantities of high-quality, low cost large graphene sheets (preferably solution-processable) for practical industrial scale applications. Examples include energy and hydrogen storage devices, inexpensive flexible macroelectronic devices, and mechanically reinforced conductive coatings including films for electromagnetic interference (EMI) shielding in aerospace applications.
  • EMI electromagnetic interference
  • graphene nanoplatelets mainly starts with expandable graphite flakes, which are essentially H 2 SO 4 -HNO 3 graphite intercalation compounds (GIC). Quick high temperature heating of these GIC leads to expansion and exfoliates these graphite flakes due to generation of large amount of gas, including toxic N0 2 .
  • GIC graphite intercalation compounds
  • the highly reduced GO sheets and graphene nanoplatelets cannot be directly dispersed into water, the most useful, clean and eco-friendly solvent. They can only be dispersed either in special organic solvents, such as N-methyl-pyrrolidinone (NMP), or in aqueous solutions with the help of surfactants for stabilization.
  • NMP N-methyl-pyrrolidinone
  • the mixture of H 2 S0 4 /HN0 3 which generates nitronium ions (N0 2+ ) could intercalate into the graphite layers, accompanying oxidation of the graphene sheets in graphite particles.
  • the unique process leads to a controllable oxidation of randomly positioned carbon atoms across an entire graphene sheet.
  • the oxidation is controlled by the concentration of nitronium ions and the microwave irradiation power, and/or time of microwave heating, such that only the minimum density of oxygen atoms is incorporated into graphene sheets to enable exfoliation of graphite powders.
  • the separated graphene sheets also known as microwave-enabled low oxygen graphene (ME-LOGr)
  • ME-LOGr microwave-enabled low oxygen graphene
  • high concentrations of clean and well separated ME-LOGr can be obtained in both aqueous and organic solvents.
  • toxic gas N0 2
  • N0 2 toxic gas
  • the present invention includes highly- conductive amphiphilic graphene sheets, which can be directly and rapidly fabricated from cheap and abundant graphite particles without post reduction processing, and can be dispersed in aqueous or organic solvents without stabilizers. Also, the present invention includes monodispersed graphene nanosheets that are directly and rapidly fabricated from cheap and abundant graphite particles without post- separation and reduction processes, and also can be dispersed in aqueous or organic solvents without stabilizers.
  • the disclosed methods offer many advantages for mass production of high quality graphene dispersions, such as (1) the process is eco-friendly - toxic agents are not used, toxic gas or potentially toxic aromatic byproducts are not generated or released; (2) the process is a rapid and low energy fabrication process; (3) production of graphene sheets with different lateral sizes is possible without a post-reduction; (4) fabricated sheets have lower level of oxygen-containing groups, which ensures outstanding electrical and optical properties; (5) high temperature annealing process is not required; (6) high-concentration dispersions both in aqueous and organic solvents (without requiring polymeric or surfactant stabilizers); (7) dramatically reduced waste from purification steps; and (8) byproducts can be reused to produce soil fertilizers. All these advantages ensure mass production of high quality graphene dispersions with low environmental footprints and at a much lower-cost.
  • piranha solution a mixture of H 2 SO 4 and H 2 O 2
  • these methods include production of reversible graphite intercalation compounds ("GIC"), oxygen purging, and the microwave irradiation of the oxygen-purged GICs in a piranha solution.
  • GIC reversible graphite intercalation compounds
  • one embodiment of this invention includes a method for making Eco-friendly Microwave Enabled Low Oxygen Graphene Sheets ("Eco-ME-LOGr”), which includes preparing reversible graphite intercalation compounds (“GIC”), followed by a short period of oxygen purging, and microwave irradiation in piranha solution until a finely dispersed suspension of Eco-ME-LOGr sheets is formed in said solution.
  • Eco-ME-LOGr sheets can be readily dispersed into various solvents, such as aqueous solvents, without surfactants, thus making a "clean" graphene surface achievable.
  • the term "clean" means that the graphene sheets or surfaces have a level of surface contamination, such as, for example, from residual reducing agents, metal ions or surfactants, which is below a level that produces un-wanted reactions or is detrimental to the desired applications, for example a level that reduces the conductivity unacceptably.
  • the distance between graphene sheets is increased, which provides enough space for 0 2 intercalation.
  • the positive charges on the graphene sheets formed within the HSO 4 -GIC also induces a strong attractive driving force for its intercalation.
  • the interaction between the positive charges and O 2 also helps stabilize the intercalated O 2 and/or HSO 4 " ions against de-intercalation upon introduction of piranha solution.
  • the existence of the intercalated O 2 not only maintains the inter-sheet distance for piranha to access and oxidize the inner parts of graphite particles, but also acts as a mild oxidant to generate more oxygen-containing groups on the graphene sheets, which facilitate graphene sheet dispersion into aqueous solutions.
  • the synergy of the piranha- generated oxygen radicals, the intercalated O 2 , and microwave heating enables rapid (60 seconds), direct and controllable fabrication of highly-conductive graphene sheets of different lateral sizes without requirement of post reduction procedure.
  • the intrinsic oxidation mechanism of the disclosed method determines that no small aromatic toxic molecules are generated, and no toxic gas is released.
  • the unique microwave heating not only dramatically speeds up the fabrication process, it also facilitates large graphene sheet fabrication, compared to those fabricated via traditional heating.
  • Another embodiment of this invention further includes the steps of controlling the microwave power and irradiation time, oxygen purging and the ratio of ⁇ 2 0 2 and H 2 S0 4 in the piranha solution to allow the fabrication control of graphene sheets from tens of micrometers down to several tens of nanometers.
  • One embodiment of this invention includes an Eco-ME-LOGr product produced according to the disclosed method.
  • Another embodiment of this invention includes graphene sheets with an average lateral size between about 0.5 micrometer and about 100 micrometers fabricated by oxidation of graphite particles.
  • Another embodiment of this invention includes graphene nanosheets with an average lateral size between about 3 nanometers and about 200 nanometers fabricated by oxidation of graphite particles.
  • the graphene sheets fabricated from graphite have a carbon-to-oxygen ratio between about 10: 1 and about 50: 1, and preferably between 20: 1 and 40: 1, more preferably 30: 1.
  • Yet another embodiment of this invention includes the as- synthesized graphene sheets fabricated from graphite can assemble to graphene films with a conductivity between 7,000 S/m and 50,000 S/m.
  • Low temperature annealing meaning without requirement of high temperature annealing, i.e., below 300 °C under argon
  • the conductivity is about 75,000 to about 200,000 S/m.
  • the conductivity is about 100,000 to about 200,000 S/m.
  • the electrical performance of the Eco-ME-LOGr films significantly outperforms the ME-LOGr films fabricated via nitronium microwave oxidation.
  • FIG. 1 is a schematic representation of the graphene production processes with the disclosed eco-friendly approach.
  • FIG. 2A-2C are representative STEM, SEM and AFM images of the Eco-ME-
  • FIG. 3A is a UV- Visible-Near Infrared spectrum of the Eco-ME-LOGr dispersion in water.
  • 3B is a Raman shift spectrum of the Eco-ME-LOGr films on an alumina anodic membrane.
  • FIG. 4 is a plot showing electronic percolation of the Eco-ME-LOGr films prepared by simple vacuum filtration.
  • FIG. 5A-5D are XPS spectra of Eco-ME-LOGr films (5 A, 5B) and ME-LOGr films (5C, 5D) on Au substrates. 5A and 5C show the C ls signal, and 5B and 5D show the 0 2p signal.
  • FIG. 6A-6D are AFM images of graphene sheets prepared from fresh GIC (6A) without 0 2 purging; (6B) GIC purged with 20 minutes 0 2 ; (6C) GIC with 5 minutes 0 2 purging, but longer microwave irradiation (75 second, instead of 60 seconds); and (6D) GIC with 5 minutes 0 2 purging with traditional heating instead of microwave heating.
  • the disclosed invention provides highly-conductive (the as- synthesized graphene sheets have a conductivity above 7000 S/m), low oxygen containing (C:0 ratio higher than 10: 1) amphiphilic graphene sheets which can be dispersed in aqueous or organic solvents without stabilizers and/or a reduction process, and simple and scalable methods for quickly and directly producing said highly-conductive amphiphilic graphene sheets in an ecologically friendly manner.
  • the method for producing highly-conductive graphene sheets includes at least three steps: (1) the production of reversible graphite intercalation compounds ("GICs"), (2) the 0 2 purge, and (3) the microware irradiation in a piranha solution.
  • GICs reversible graphite intercalation compounds
  • the present invention demonstrates that the piranha solution generates oxygen radicals (0 ⁇ ) having similar functions as the N0 2 + generated by the mixture of H 2 S0 4 /HN0 3 described in U.S. Pat. Publication No. 2013/0266501, yet without producing any toxic agents or byproducts.
  • the direct replacement of HN0 3 /H 2 S0 4 with piranha solution for the oxidation of graphite particles does not provide the desired graphene because piranha solution has limited capability to reach and oxidize the internal sites of the graphite particles.
  • the distance between graphene sheets is enlarged before microwave oxidation in piranha by exposing graphite powders to a mixture of ammonium persulfate ((NH 4 ) 2 S 2 08) and sulfuric acid (H 2 S0 4 ) to produce reversible graphite intercalation compounds ("GICs").
  • the distance between graphene sheets is enlarged by exposing graphite powders to a mixture of sulfuric acid (H 2 S0 4 , 98%) and ammonium persulfate ((NH 4 ) 2 S 2 0s) at a weight ratio beween 1: 1 and 100: 1, preferably between 10: 1 and 50: 1, and more preferably between 15: 1 and 30: 1.
  • the ratio for sulfuric acid and graphite is between 500: 1 and 10: 1, preferably between 300: 1 and 30: 1, more preferably between 150: 1 and 50: 1 to produce reversible sulfuric acid-based GICs.
  • the graphite powder is exposed to such a mixture at room- temperature for 2 to 48 hours (e.g. , about 24 hours in one embodiment).
  • the GICs prepared in such manner are subjected to microwave irradiation in a piranha solution.
  • the product is very similar to those obtained without any intercalation process.
  • the concentration is slightly increased (0.17 mg/ml), while the size of the sheets is still very small ( ⁇ 100 nm).
  • the formed GICs e.g., from (NH 4 ) 2 S 2 0 8
  • the formed GICs are reversible since there are no C-0 bonds formed and rapid de- intercalation occurs. For instance, with water washing the intercalated HS0 4 " and H 2 S0 4 in the GICs formed from (NH 4 ) 2 S 2 0 8 rapidly de-intercalate.
  • 0 2 gas is purged through the freshly prepared GICs.
  • the rate and/or the duration of the 0 2 purge can be varied to optimize stabilization of the GIC against deintercalation.
  • the GICs are 0 2 - purged at the rate of 50-500 ml/min, preferably 50-200 ml/min and more preferably 70-90 ml/min, for a duration sufficient to stabilize the GICs against deintercalation.
  • the GICs are 0 2 -purged at the rate of 79-84 ml/min for 1 to 120 minutes before putting them into the piranha solution. In another embodiment, the GICs are 0 2 -purged at the rate of 79-84 ml/min for about 5 minutes before putting them into the piranha solution.
  • Table 1 Weights of Graphite and GICs with and without 5-min 0 2 purge after wash.
  • the oxidation of graphite particles occurs on both internal and external graphene sheets upon addition of piranha solution followed by microwave irradiation.
  • the piranha solution as used herein, is a mixture of sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 0 2 ).
  • the amount of sulfuric acid and hydrogen peroxide mixed together is selected to provide oxygen radicals to controllably oxidize graphene sheets in graphite particles. Relative amounts of sulfuric acid and hydrogen peroxide should be mixed together for a given quantity of graphite to achieve the desired amount of oxygen radicals.
  • piranha solution is defined as a mixture of H 2 SO 4 and H 2 0 2 solutions in a volume ratio between about 20: 1 and about 1: 1, inclusive of water in the H 2 SO 4 (95 to 98% by weight) and H 2 0 2 (30 to 35%, by weight) solutions. According to one embodiment the ratio is between about 7: 1 and about 1: 1. In one exemplary embodiment, the ratio is about 3: 1.
  • the key to directly produce large, conductive graphene sheets by piranha solution treatment is to quickly produce the low concentration of oxygen moieties that is required for the separation of individual graphene sheets, and then quench the reaction before holes and/or vacancies formation.
  • microwave heating is exploited. Indeed, it was observed that the majority of the products prepared via conventional heating were nanosheets (heating for 7 hours at 100 °C) with lateral dimensions smaller than 100 nm (FIG. 6D), which is much smaller than the ones obtained via microwave irradiation (several ⁇ ).
  • the process used in accordance with the present invention heats a sample of 0 2 -purged GICs, sulfuric acid and hydrogen peroxide (i.e., piranha solution) by irradiating the sample with electromagnetic radiation in the microwave or radio frequency range.
  • the frequency of the electromagnetic radiation used ranges from 10 8 to 1011 Hertz (Hz).
  • the input power is selected to provide the desired heating rate.
  • the preferred output power is up to about 10 kilowatts.
  • the output power is between 200 W and 900 W. In another exemplary embodiment, the output power is about 300 W.
  • the electromagnetic radiation may be pulsed or continuous.
  • pulsed radiation any arrangement of pulse duration and pulse repetition frequency which allows for the dissipation of adverse heat buildup may be used in the present invention.
  • the pulse duration may be varied, from 1 to 100 microseconds and the pulse repetition frequency from 2 to 1000 pulses per second.
  • the sample may be irradiated for any period of time sufficient to oxide the graphite particles that allows dispersion of the graphene sheets with the desired lateral sizes into solvents. These conditions can be readily determined by one of ordinary skill in the art without undue experimentation. The time required to achieve the result will be shorter for higher power settings.
  • the sample When continuous radiation is utilized, the sample is heated for a time sufficient to oxidize the graphite particles that allows dispersion of the graphene sheets with desired lateral sizes into solvents.
  • the irradiation time is at least about 30 seconds.
  • the irradiation time ranges from about 30 seconds to 5 minutes in order to achieve the desired extent of oxidation.
  • the time, and power input can be routinely adjusted to achieve the desired result, which can be readily determined by one of ordinary skill in the art without undue experimentation.
  • continuous radiation is first employed to attain the desired reaction temperature, after which, pulsed radiation is employed to maintain the desired temperature. Accordingly, the duration of continuous radiation, pulse radiation duration, and radiation frequency can be readily adjusted by one having ordinary skill in the art to achieve the desired result based on simple calibration experiments. The extent of graphite oxidation may be confirmed, by conventional analytical techniques.
  • Irradiation of the sample may be conducted in any microwave and/or radio frequency heating device which is capable of continuous or pulsed radiation and has the power requirements necessary to thermally induce the conversion to graphene.
  • Suitable heating devices include microwave ovens, wave guides, resonant cavities, and the like. Suitable heating devices are well known in the art, and are commercially available.
  • One preferred device for performance of the present invention is a single-mode resonant cavity. Any available mode for heating in this device can be used in the present invention. However, the present invention is not to be limited to use of this device but can be performed in any microwave or radio frequency heating equipment.
  • the process of the present invention is carried out by placing the sample inside a microwave or radio frequency device and applying the appropriate input power.
  • the present invention may be applied as either a batch or continuous process.
  • the mixture of oxygen-purged GIC and piranha solution is heated using microware irradiation for 10 to 90 seconds, or longer.
  • the mixture is heated using microware irradiation for less than 90 seconds.
  • the mixture is heated using microware irradiation for about 60 seconds.
  • microwave heating is volumetric heating, the irradiation time and/or power increases as the amount of reactant increases, especially for large scale production.
  • those of ordinary skill in the art could readily adjust the power and duration to compensate for the increased amount of the reactant.
  • nitronium ions not only attack the existing defects on the graphene, but also randomly attack the relatively inert defect-free graphene basal planes, generating multiple oxygen-containing groups, such as -OH and epoxy, across the graphene sheets.
  • N0 2 + continues to attack the already oxidized carbon atoms (results in etching and generating vacancies and holes) and carbon atoms far away from those already oxidized (producing more oxygen-containing groups).
  • C0 2 and CO were released, and a large amount of small aromatic molecules were also generated as byproducts which were filtrated out during cleaning.
  • the route of piranha oxidation is the generation of atomic oxygen, which directly attacks a carbon in a graphene sheet to form a carbonyl group.
  • the formation of the carbonyl group simultaneously disrupts the bonds of the neighboring carbon atoms.
  • the initial carbonyl group can be converted into C0 2 (carbon lost) and at the same time, a new carbonyl group is created on the neighboring carbon atoms whose bonds are disrupted.
  • the intercalated molecular oxygen is involved in generation of epoxy groups on the graphene surfaces and etching (carbon lost as C0 2 ) upon microwave heating.
  • the intrinsically different oxidation mechanisms determines that the piranha/0 2 approach is eco-friendly, while all the nitronium oxidation related approaches were accompanied by releasing of toxic gases, such as, N0 2 , and generating small aromatic molecules as byproducts, which could cause potential contamination to the environment and ground water system if they are not treated properly.
  • a graphite intercalation compound with HS0 4 " was achieved by following the process described in Dimiev, A. M. et al. ACS Nano 2012, 6, 7842 (incorporated herein by reference in its entirety).
  • 1000 mg of ammonium per sulfate [(NH 4 ) 2 S 2 0 8 ] (reagent grade 98%; Sigma Aldrich) was dissolved in 10 ml of H 2 S0 4 (98%; Pharmaco Aaper).
  • the obtained mixture solution was stirred for 5-10 min and then 200 mg of synthetic graphite powder (size ⁇ 20 ⁇ ; Sigma Aldrich) was added.
  • the obtained mixture was stirred for 24 hrs, which led to the formation of Graphite intercalation Compound (reversible S0 4 -GIC).
  • oxygen was purged for 5 min at a rate of 79-84 ml/min using extra dry grade 0 2 .
  • the obtained slurry was washed via vacuum filtration through a polycarbonate membrane with a pore size of 0.8 ⁇ with 200 ml water each for four times.
  • the final product was dispersed in 40 ml deionized water by sonication in a bath sonicator for 30 min. With the aid of bath sonication, the cleaned filtration cake on the filter paper can be re-dispersed in a wide range of solvents to form colloidal solutions without the use of surfactants or stabilizers (see Table 2).
  • the solution was allowed to settle for 3-5 days; the supernatant solution obtained contains large graphene sheets.
  • the filtrate was collected and then extracted with THF to study the byproducts via gas chromatography-mass spectrometry (GC-MS).
  • GC-MS gas chromatography-mass spectrometry
  • graphene sheets can be dispersed in water, N-methyl-pyrrolidinone (NMP), and chloroform in similar concentrations.
  • NMP N-methyl-pyrrolidinone
  • the graphene sheets can be dispersed both in water (220 mg/L), which is commonly used to disperse graphene oxide (GO), and NMP (290 mg/L), ⁇ , ⁇ -dimethylformamide (DMF) (200 mg/L), which are well known solvents to disperse intrinsic graphene sheets and platelets.
  • a nonpolar solvent such as chloroform, in which neither GO, r-GO, nor graphene platelets can be dispersed
  • Eco-ME-LOGr can be dispersed with a concentration of 190 mg/L.
  • the lateral size and thickness of the dispersed Eco-ME-LOGr sheets were characterized by scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).
  • the AFM samples were prepared by dropping 1-2 ⁇ 1 of the dispersed graphene solution onto a freshly cleaved mica surface and then allowing it to dry. After drying, the sample was washed with water drop by drop to remove the dirt on the sample and was again dried. This sample was scanned using a Nanoscope Ilia multimode SPM (Digital Instruments) with a J scanner for small scan size and G scanner for larger scan size operated in "Tapping mode".
  • the AFM tips for imaging were 160 ⁇ long rectangular silicon cantilever/tip assembly from AppNano, which was used with a resonance frequency of 160 kHz and a spring constant of approximately 7.7N/m with a tip radius of less than 10 nm.
  • SEM samples were prepared by dropping 1-2 ⁇ 1 of the sample onto a cleaned silicon substrate.
  • the silicon substrate was cleaned initially with piranha solution and then water, and then dried with N 2 gas.
  • the sample solution was dropped onto silicon substrate and then allowed to dry for 2-3 min and then dried in N 2 gas to spread the sample throughout the substrate.
  • the SEM images were captured using a Hitachi S-4800 Field Emission Scanning Electron Microscope (FE-SEM, Hitachi Co. Ltd.) under an accelerating voltage of 1-2KV and a probe current of 10 ⁇ to obtain images with high contrast.
  • FE-SEM Field Emission Scanning Electron Microscope
  • SEM samples were prepared by dropping ⁇ of the sample on a Cu TEM grid. After the samples were dried in air, they were imaged with a Hitachi S-4800 FE SEM under high accelerating voltage of 30KV and a probe current of 10-15 ⁇ with a working distance of 15mm.
  • the Eco-ME-LOGr sheets have a lateral size of up to several tens of micrometers with an average of one to two ⁇ .
  • the thickness of the Eco-ME-LOGr sheets is between 0.7-3 nm, corresponding to one to a few layers as shown in FIG. 2.
  • the color of the Eco-ME-LOGr suspensions is grayish-black, which is very similar to the previously reported r-GO and ME- LOGr suspensions, but quite different from the typical brown GO solutions.
  • the optical properties of the graphene dispersions were measured by UV-VIS NIR spectroscopy.
  • the spectra were obtained on a Cary-5000 Ultraviolet- Visible-Near Infrared Spectroscopy operated in double beam mode with 200-1000 nm wavelength range.
  • the UV- Vis- near infrared (NIR) spectrum of the Eco-ME-LOGr solution displayed a plasmon band absorption maximum at 268 nm and strong absorption in the visible and NIR region, qualitatively suggesting that the as-prepared Eco-ME-LOGr sheets already contain a large amount of intact graphene domains without the requirement for a post-reduction procedure.
  • NIR UV- Vis- near infrared
  • Raman spectroscopy was utilized to characterize the size of the intact graphene domains.
  • Raman spectra of graphene sheets were collected with a Kaiser Optical Systems Raman Microprobe with a 785 nm solid state diode laser, the collection time is 60 sec for each spectrum and average three times.
  • the typical features of the G band, defect D band, and 2D band are shown in the Raman spectrum of Eco-ME-LOGr film prepared on an anodic filter membrane via vacuum filtration (see FIG. 3B).
  • the intensity ratio of D to G band (I D /I G ) is 0.75, and is much lower than those of GO and r-GO.
  • the size of the intact graphene domains was ca. 6.0 nm in Eco-ME-LOGr, slightly smaller than those in ME-LOGr, while much larger than those in GO(l-3.5 nm).
  • the graphene films were then transferred onto Si surfaces after etching the alumina anodic membrane in a strong base (NaOH, 4M), followed by washing with water until the pH of the solution became neutral. After transferring to Si surfaces, the samples were dried in vacuum and then the average thickness for each graphene film was measured with Rutherford Backscattering Spectroscopy (RBS) using a 2 MeV He 2+ ion beam produced in a tandem accelerator with an ionic current of 2-3 nA. Spectra were collected in the back scattering geometry and simulations were performed using the SIMNRA program. The conductivity of the films was calculated from the sheet resistance and thickness by the formula:
  • This formula can be used to measure the films with thickness not more than half of the probe spacing (the distance between two probes of the four point probe instrument). The error in this case is less than 1%.
  • the Eco-ME- LOGr films show percolation-type electronic behavior.
  • the sheet resistance of the Eco-ME- LOGr film decreases with increasing film thickness, as shown in FIG. 4.
  • the Eco-ME-LOGr sheets reached percolation at a thickness of 88 nm, which has a sheet resistance of 0.5 kQ/ square. This corresponds to a DC conductivity of 22,560 S/m.
  • the conductivity was further increased to 74,433 S/m.
  • These conductivity values dramatically outperformed our previous ME- LOGr films fabricated via nitronium microwave oxidation (6600 S/m for as-prepared films and 19,200 S/m after 2-hour annealing at 300°C). To the best of our knowledge, these films have achieved the highest conductivity values reached the highest conductivity compared to all the previous reported paper-like graphene films prepared by vacuum filtration from solution dispersed graphene sheets (see Table 3).
  • GC-MS Gas chromatography-mass spectroscopy
  • THF extract 1 ⁇ of the THF extract was injected into the same GC-MS system by sampling through the septum of one of four vials containing: (1) THF extract of the filtrate from the nitronium oxidation approach, (2) the filtrate from the present Eco-friendly approach, (3) the filtrate from a control experiment via the Eco- friendly approach without adding graphite particles, and (4) pure THF solvent.
  • a temperature program was performed, starting at 50 °C held for 1 min, followed by temperature ramping at a rate of 10 °C/min to a final temperature of 300 °C and held for an additional 1 min. The results show that the majority of the components are 0 2 with a small amount of C0 2 , while no toxic S0 2 or CO were detected.
  • the filtrate was mixed with a polar and low-melting organic solvent, such as tetrahydrofuran (THF), before injection.
  • a polar and low-melting organic solvent such as tetrahydrofuran (THF)
  • THF tetrahydrofuran
  • the filtrates from a nitronium oxidation and a blank solution obtained by microwave irradiation of the same amount of (NH 4 ) 2 S 2 0 8 and piranha solution but without graphite particles
  • the filtrate from nitronium oxidations shows several peaks at retention time of 1.5 min, 4.17 min, 7.49 min, and 11.78 min.
  • the mass spectrum (MS) for each of the peaks was determined.
  • the molecular structures were identified based on the score (max score is 1.00) of the MS spectrum compared to the spectra in a mass bank database.
  • a peak at 1.5 min is mainly from THF, and peaks at 4.17 min are most possibly from flavanol derivatives. While the peaks at 7.49 min, and 11.78 min were related to some relatively high molecular weight compounds like cyanine or 1,1'- dianthrimide.
  • Detailed molecular structures and their score compared to the mass spectra in the mass bank database are given in Table 4.
  • the GC spectrum of the filtrate obtained from the piranha oxidation approach is similar to the spectra of THF and the blank. No peak was observed in the GC spectra of the filtrate except the peaks from the solvent itself (THF alone), demonstrating this new piranha/0 2 oxidation approach is indeed eco-friendly without releasing any toxic gases and generating toxic aromatic byproducts.
  • Table 4 Detailed molecular structures and their score compared to the mass spectra in the mass bank database.
  • XPS X- Ray photoelectron spectroscopy
  • the spectrum of C ls of the Eco-ME-LOGr sheets shows a main peak of oxygen- free carbon and a shoulder of oxygen-containing carbon (see FIG. 5A).
  • the oxygen- free carbon makes up 76% of the spectrum, comparable to the spectrum of rGO and ME-LOGr obtained with nitronium oxidation.
  • the oxygen free carbon is mainly derived from the C ls peak of aromatic rings (284.2 eV, 61.8%), and that of the aliphatic rings and/or linear alkylinic carbon chains (284.7 eV, 13.9%).
  • the 0 2p spectra complement the information provided by the C ls spectra and the peak was deconvoluted into three peaks (see FIG.
  • the dispersed graphene was prepared under various conditions.
  • the duration of the microwave exposure should be optimized to maximum the extent of oxidation of graphite particles while avoiding over oxidation- induced gasification (as evidenced by carbon loss).

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Abstract

L'invention concerne une nouvelle approche rapide, respectueuse de l'environnement pour produire directement des feuilles de graphène hautement conductrices et "propres" sans utiliser de quelconque réactifs toxiques ou composés contenant un métal, et sans générer de sous-produits toxiques, ce qui permet d'obtenir un large spectre d'applications par des techniques de traitement de solution de faible coût. Selon un mode de réalisation, l'approche repose sur la synergie d'une solution piranha, d'oxygène moléculaire intercalé, et d'un chauffage par micro-ondes qui permet de réguler l'oxydation des particules de graphite, conduisant à une génération rapide et directe de feuilles de graphène hautement-conductrices, propres, sans dégagement de gaz toxiques et/ou de quelconque sous-produits aromatiques potentiellement toxiques.
PCT/US2015/024710 2014-04-07 2015-04-07 Production respectueuse de l'environnement de dispersions de graphène hautement conductrices et propres WO2015157280A1 (fr)

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CN106276874A (zh) * 2016-08-10 2017-01-04 安徽省宁国天成电工有限公司 一种加热器用石墨烯的制备方法
CN107937029A (zh) * 2017-12-22 2018-04-20 中国科学院上海高等研究院 一种煤基电石制乙炔的方法和系统
US9997334B1 (en) 2017-02-09 2018-06-12 Lyten, Inc. Seedless particles with carbon allotropes
WO2018232109A1 (fr) 2017-06-14 2018-12-20 Rutgers, The State University Of New Jersey Fabrication évolutive de nanoplaquettes de graphène pur trouées par irradiation par micro-ondes sèche
US10428197B2 (en) 2017-03-16 2019-10-01 Lyten, Inc. Carbon and elastomer integration
US10502705B2 (en) 2018-01-04 2019-12-10 Lyten, Inc. Resonant gas sensor
US10756334B2 (en) 2017-12-22 2020-08-25 Lyten, Inc. Structured composite materials
US10920035B2 (en) 2017-03-16 2021-02-16 Lyten, Inc. Tuning deformation hysteresis in tires using graphene
CN113735103A (zh) * 2021-09-30 2021-12-03 昆明理工大学 一种快速规模制备大片石墨烯的方法
US11304304B2 (en) 2019-11-11 2022-04-12 International Business Machines Corporation Ionic contaminant cleaning
US11309545B2 (en) 2019-10-25 2022-04-19 Lyten, Inc. Carbonaceous materials for lithium-sulfur batteries
US11489161B2 (en) 2019-10-25 2022-11-01 Lyten, Inc. Powdered materials including carbonaceous structures for lithium-sulfur battery cathodes

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Cited By (20)

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Publication number Priority date Publication date Assignee Title
CN106082180A (zh) * 2016-06-06 2016-11-09 南通伟德动力电池研究所（普通合伙） 一种用酸插层石墨和过硫酸铵为原料制造石墨烯的方法
CN106276874A (zh) * 2016-08-10 2017-01-04 安徽省宁国天成电工有限公司 一种加热器用石墨烯的制备方法
US10373808B2 (en) 2017-02-09 2019-08-06 Lyten, Inc. Seedless particles with carbon allotropes
US11380521B2 (en) 2017-02-09 2022-07-05 Lyten, Inc. Spherical carbon allotropes for lubricants
US9997334B1 (en) 2017-02-09 2018-06-12 Lyten, Inc. Seedless particles with carbon allotropes
US10920035B2 (en) 2017-03-16 2021-02-16 Lyten, Inc. Tuning deformation hysteresis in tires using graphene
US11008436B2 (en) 2017-03-16 2021-05-18 Lyten, Inc. Carbon and elastomer integration
US10428197B2 (en) 2017-03-16 2019-10-01 Lyten, Inc. Carbon and elastomer integration
US11377356B2 (en) 2017-06-14 2022-07-05 Rutgers, The State University Of New Jersey Scalable fabrication of pristine holey graphene nanoplatelets via dry microwave irradiation
CN111247096A (zh) * 2017-06-14 2020-06-05 新泽西鲁特格斯州立大学 通过干微波辐射的原始多孔石墨烯纳米片的可规模化制备
WO2018232109A1 (fr) 2017-06-14 2018-12-20 Rutgers, The State University Of New Jersey Fabrication évolutive de nanoplaquettes de graphène pur trouées par irradiation par micro-ondes sèche
EP3642155A4 (fr) * 2017-06-14 2021-05-05 Rutgers, the State University of New Jersey Fabrication évolutive de nanoplaquettes de graphène pur trouées par irradiation par micro-ondes sèche
US10756334B2 (en) 2017-12-22 2020-08-25 Lyten, Inc. Structured composite materials
CN107937029A (zh) * 2017-12-22 2018-04-20 中国科学院上海高等研究院 一种煤基电石制乙炔的方法和系统
US10502705B2 (en) 2018-01-04 2019-12-10 Lyten, Inc. Resonant gas sensor
US11309545B2 (en) 2019-10-25 2022-04-19 Lyten, Inc. Carbonaceous materials for lithium-sulfur batteries
US11489161B2 (en) 2019-10-25 2022-11-01 Lyten, Inc. Powdered materials including carbonaceous structures for lithium-sulfur battery cathodes
US11304304B2 (en) 2019-11-11 2022-04-12 International Business Machines Corporation Ionic contaminant cleaning
CN113735103A (zh) * 2021-09-30 2021-12-03 昆明理工大学 一种快速规模制备大片石墨烯的方法
CN113735103B (zh) * 2021-09-30 2022-09-16 昆明理工大学 一种快速规模制备大片石墨烯的方法

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