Method for exfoliating carbonaceous materials containing graphite, assisted by a Diels-Alder reaction

Abstract

The present invention relates to a process for exfoliating graphite in carbonaceous materials facilitated by a Diels-Alder reaction, and the applications of same, in particular for producing electronic or microelectronic components such as transparent conductive electrodes. The inventive method comprises a Diels-Alder reaction between a material containing graphite and an anthrone compound represented by formula (I), wherein X, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined in the description, in an organic solvent, in the presence of a base, and subjected to sonication, ball-milling and/or high-shear mixing, at a temperature of between 15° C. and 65° C., to obtain the corresponding graphene Diels-Alder adduct.

Claims

1. A process for the exfoliation of graphite in a graphite-containing material, comprising subjecting the graphite-containing material to a Diels-Alder reaction with a compound of formula (I): ##STR00030## wherein: X represents O or S; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 independently represent a hydrogen atom, —NR.sup.AR.sup.B, —N.sup.+R.sup.AR.sup.BR.sup.C, —OR, —CO.sub.2M or —SO.sub.3M; or else R.sub.1 and R.sub.2, on the one hand, and R.sub.3 and R.sub.4, on the other hand, together form an optionally substituted unsaturated C.sub.6 cycloalkyl group to result in a pentacenone-type compound of formula (II) having the following structure: ##STR00031## wherein: X represents O or S; R′.sub.1, R′.sub.2, R′.sub.3 and R′.sub.4 independently represent a hydrogen atom, —NR.sup.AR.sup.B, —N.sup.+R.sup.AR.sup.BR.sup.C, —OR, —CO.sub.2M or —SO.sub.3M; where M represents a hydrogen atom or an alkali metal atom; and each occurrence of R, R.sup.A, R.sup.B and R.sup.C independently represents a hydrogen atom or a linear or branched C.sub.1 to C.sub.16 alkyl; wherein the R radical can also represent, independently for each occurrence of R, a polyethylene glycol radical of formula: ##STR00032##  wherein n represents an integer from 1 to 6; in an organic solvent, in the presence of a base, and under sonication, ball-milling and/or high-shear mixing, at a temperature of between 15° C. and 65° C., to obtain the corresponding graphene Diels-Alder adduct.

2. The process of claim 1, wherein the compound of formula (I) has one of the following structures: ##STR00033##

3. The process of claim 1, wherein the organic solvent is selected from the group consisting of a saturated or unsaturated aliphatic or alicyclic hydrocarbon, an aromatic hydrocarbon, an alcohol, a glycol, a halogenated hydrocarbon, a ketone, an ester, an ether, a glycol ether or another suitable organic solvent, and a mixture of two or more thereof.

4. The process of claim 1, wherein the organic solvent is selected from the group consisting of tetrahydrofuran (THF), acetonitrile, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), 2-propanol, toluene, benzene, chlorobenzene, and 1,2-dichlorobenzene.

5. The process of claim 1, wherein the base is di- or trialkylamine.

6. The process of claim 1, wherein the Diels-Alder reaction is carried out at a temperature of 20-65° C.

7. The process of claim 1, further comprising a centrifuging step.

8. The process of claim 7, further comprising a step of filtering the supernatant obtained from the centrifuging step, to isolate the Diels-Alder adduct of graphene sheets obtained by the process.

9. The process of claim 1, wherein the graphite-containing material is carbon black or graphite.

10. The process of claim 1, further comprising a step of annealing the Diels-Alder adduct of graphene sheets under vacuum, to obtain monolayer graphene, or multilayer graphene of 2 to 5 graphene sheets, or a mixture of these.

11. A Diels-Alder adduct of graphene sheets obtainable by a process according to claim 1.

12. The process of claim 3, wherein the organic solvent is an alcohol comprising at least 3 carbon atoms.

13. The process according to claim 1, wherein n represents an integer from 1 to 3.

14. The process according to claim 5, wherein the di- or trialkylamine is selected from the group consisting of diethylamine, dimethylamine, aza-crown ether, diisopropylamine, diisopropylethylamine, triethylamine, trimethylamine, tripropylamine, tributylamine, N-methylcyclohexylamine, N-ethylcyclohexylamine, N-methylcyclopentylamine, and N-ethylcyclopentylamine.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents a diagram of the keto-enol equilibrium of anthrone (left) and of 6,6-dihydropentacen-13-one (right), respectively giving anthracenol and pentacenol, and reaction of the latter with the dienophile sites of the graphene sheets.

(2) FIG. 2 illustrates photographs of the samples obtained in examples 1 to 3 after centrifuging.

(3) FIG. 3 represents additional experiments without base (3A), without anthrone (3C) and without anthrone or base (3B) in THF: 4 h of sonication and 30 min of centrifuging at 3000 rpm.

(4) FIG. 4 represents TEM (Transmission Electron Microscopy) images of sheets of Graphene Diels-Alder adduct obtained by the use of anthrone (4A and 4C) or pentacenone (4B and 4D), as shown in examples 1 and 2 respectively.

(5) FIG. 5: A: Raman spectrum of a sample of graphite exfoliated according to the process of the invention using anthrone of formula I (R.sub.1-R.sub.4═H, solvent=THF, base=diisopropylethylamine) deposited on a glass slide and dried in the air. B: Raman spectrum of a sample of graphite exfoliated according to the process of the invention using anthrone of formula I (R.sub.1-R.sub.4═H, solvent=THF, base=diisopropylethylamine) deposited on a glass slide and dried in the air after annealing at 200° C. under vacuum for 60 min. The intensity of the D band is proportional to the presence of defects (sp.sup.3 C atoms). The I.sub.D/I.sub.G ratio can thus be used to deduce therefrom the content of defects (borders of the sheets, DA adducts, or other). It is seen that I.sub.D/I.sub.G is high (approximately 1) after exfoliation and that it substantially decreases (I.sub.D/I.sub.G=0.14) if heating is carried out. The defects decrease because the Diels-Alder reaction is reversible and the graphene is reformed. A film of graphene sheets with few defects is thus obtained. The residual defects can be due to the edge effects or to the presence of minor defects produced during sonication.

(6) FIG. 6: A Table compiling the graphene concentrations obtained in THF in example 3. B Corresponding photographs of the various samples obtained.

(7) FIG. 7: Solutions obtained in example 6 (X═S) after filtration and redispersion in THF (on the left, C=0.0335 mg/ml) and in toluene (on the right, C=0.0495 mg/ml).

(8) FIG. 8: A Mapping carried out over regions of approximately 10 μm.sup.2, in 2 μm steps, of a solution of graphene in THF obtained in example 9. B DIC (Differential Interference Contrast)/Raman spectrum at λ=568 nm, corresponding to the sample of FIG. 8A. C Mapping carried out over regions of approximately 10 μm.sup.2, in 6 μm steps, of a solution of graphene in THF obtained in example 9. D DIC (Differential Interference Contrast)/Raman spectrum at λ=568 nm, corresponding to the sample of FIG. 8B. In FIGS. 8A and 8C, the difference in color represents the differences in intensity of the G band, at 1578 cm.sup.−1. The wavelength used is 568 nm.

(9) FIG. 9: Diagram of the system used in example 10 for the measurement of the conductivity of the graphene layers by the four-point probe method.

(10) FIG. 10: Photographs of the different solutions of carbon black which are obtained in example 12 after sonication and separation by settling for 20 days (3 months for the DMSO).

EXAMPLES

Example 1: Preparation of Compounds of Formula (I)

1) 2,6-Diaminoanthracen-9(10H)-one

(11) ##STR00021##

(12) 2,6-Diaminoanthracen-9(10H)-one is synthesized from commercial 2,6-diaminoanthracene-9,10-dione using a method of reduction with tin (Sn) (Tetrahedron Letters, 2011, 52, 5083). The yield is 80% after purification.

(13) .sup.1H NMR (300 MHz, DMSO) δ (ppm)=7.86 (d, J=8.4 Hz, 1H), 7.31 (d, J=2.5 Hz, 1H), 7.15 (d, J=8.3 Hz, 1H), 6.83 (dd, J=8.5 Hz; 2.6 Hz, 1H), 6.61 (dd, J=8.5 Hz; 2.2 Hz, 1H), 6.52 (d, J=2.1 Hz, 1H), 6.04 (s, 2H), 5.19 (s, 2H), 4.04 (s, 2H).

(14) .sup.13C NMR (75 MHz, DMSO) δ (ppm)=181.684, 152.93, 147.195, 143.639, 132.454, 128.898, 127.694, 120.658, 119.052, 113.26, 110.545, 109.761, 30.974

(15) HRMS (+TOF MS). Found: [M+Na] 247.0841. Calculated: 247.0841

2) 2,6-Dihydroxyanthracen-9(10H)-one

(16) ##STR00022##

(17) 2,6-Dihydroxyanthracen-9(10H)-one is synthesized from commercial 2,6-dihydroxyanthracene-9,10-dione by using a method of reduction with tin chloride in an acid medium (Tetrahedron Letters, 2003, 44, 945-948). The yield is 65% after purification.

(18) .sup.1H NMR (300 MHz, DMSO) δ (ppm)=8.35 (d, J=8.1 Hz, 1H), 8.30 (d, J=8.6 Hz, 1H), 7.58 (td, J=7.4 Hz; 1.9 Hz, 1H), 7.46 (m, 2H), 6.94 (dd, J=8.7 Hz; 2.4 Hz, 1H), 6.90 (d, J=2.1 Hz, 1H), 4.315 (s, 2H).

(19) .sup.13C NMR (75 MHz, DMSO) δ (ppm)=182.086, 161.629, 156.104, 143.983, 132.493, 131.307, 129.969, 129.319, 123.641, 120.926, 115.382, 113.891, 111.271, 31.031.

(20) HRMS (CI-DEP). Found: [M-H].sup.+=227.07065. Calculated: 227.07082.

3) 2,6-Bis(octyloxy)anthracen-9(10H)-one

(21) ##STR00023##

(22) 2,6-Bis(octyloxy)anthracen-9(10H)-one is synthesized from 2,6-bis(octyloxy)anthracene-9,10-dione by the use of activated zinc in a basic medium (Helvetica Chimica Acta, 2006, 89, 333). The yield is 99%.

(23) .sup.1H NMR (300 MHz, CDCl.sub.3) δ (ppm)=8.34 (d, J=8.8 Hz, 1H), 7.8 (d, J=2.8 Hz, 1H), 7.33 (d, J=8.5 Hz, 1H), 7.15 (dd, J=8.5 Hz; 2.8 Hz, 1H), 6.98 (dd, J=8.8 Hz; 2.5 Hz, 1H), 6.88 (d, J=2.6 Hz, 1H), 4.23 (s, 2H), 4.06 (q, J=6.1 Hz, 4H), 1.82 (m, 4H), 1.48 (m, 4H), 1.30 (m, 16H), 0.89 (m, 6H).

(24) .sup.13C NMR (75 MHz, CDCl.sub.3) δ (ppm)=183.382, 162.887, 158.318, 133.177, 132.737, 130.061, 129.564, 125.510, 121.840, 114.689, 112.548, 109.776, 68.480, 32.155, 31.964, 29.479, 29.364, 29.307, 26.152, 22.802, 14.241.

(25) HRMS (FD+). Found: [M+] 450.31151. Calculated: 450.31339

4) 2-Hydroxyanthracen-9(10H)-one

(26) ##STR00024##

(27) 2-Hydroxyanthracen-9(10H)-one is synthesized from 2-hydroxyanthracene-9,10-dione by the method of reduction with tin chloride in an acid medium (Tetrahedron Letters, 2003, 44, 945-948).

(28) .sup.1H NMR (300 MHz, DMSO) δ (ppm)=8.35 (d, J=8.1 Hz, 1H), 8.30 (d, J=8.6 Hz, 1H), 7.58 (td, J=7.4 Hz; 1.9 Hz, 1H), 7.46 (m, 2H), 6.94 (dd, J=8.7 Hz; 2.4 Hz, 1H), 6.90 (d, J=2.1 Hz, 1H), 4.315 (s, 2H).

(29) .sup.13C NMR (150 MHz, DMSO) δ (ppm)=181.976, 161.816, 143.582, 140.637, 132.340, 131.494, 129.343, 128.709, 123.642, 115.447, 113.850, 31.675.

(30) HRMS (FD+). Found: [M+] 210.06762. Calculated: 210.06808

5) 2,6-Bis(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)anthracen-9(10H)-one

(31) ##STR00025##

(32) 2,6-Bis(2-(2-(2-hydroxyethoxy)ethoxy)-ethoxy)anthracen-9(10H)-one is synthesized by reduction of 2,6-bis(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)anthracene-9,10-dione (Eur. J. Org. Chem., 2000, 591), with sodium borohydride, followed by dehydration in an acid medium. At the end of the reaction, a mixture of anthrone, anthraquinone and anthracene is obtained. Separation was not possible and the product is used directly.

(33) LRMS (+TOF MS): [M+Na]=513.2

6) Thioanthrone

(34) 1) Starting from 9-bromoanthracene in diethyl ether, the corresponding lithium derivative is formed by addition of n-BuLi at 0° C. and then addition of inorganic sulfur makes it possible to form 9-anthracenethiol (Asian Journal of Organic Chemistry, 2012, 1, 274).
2) Starting from anthrone, by reaction with Lawessons reagent in toluene at 80° C. After treatment, the compound recovered is 9-anthracenethiol (in “keto-enol” equilibrium with the thioanthrone compound).

(35) ##STR00026##

(36) According to the NMR of the crystalline product, the two entities are present in solution. The predominant product in solution is the anthracenethiol:

(37) .sup.1H NMR (400 MHz, CDCl.sub.3) δ (ppm)=8.63 (dd, J=8.9 Hz; 1.4 Hz, 2H), 8.38 (s, 1H), 8.00 (dd, J=8.4 Hz; 1.4 Hz, 2H), 7.59 (ddd, J=8.9 Hz; 6.6 Hz; 1.4 Hz, 2H), 7.50 (ddd, J=8.4 Hz; 6.6 Hz; 1.4 Hz, 2H), 3.68 (s, 1H).

(38) .sup.13C NMR (100 MHz, CDCl.sub.3) δ (ppm)=129.122, 127.132, 126.484, 126.255, 125.449.

(39) LRMS: [M+]=210.0

(40) HRMS (CI-DEP). Found: [M-H]+=211.05785. Calculated: 211. 05815.

Example 2: Exfoliation of Graphite by Virtue of a Diels-Alder Reaction Using Anthrone

(41) Anthrone of Formula I:

(42) ##STR00027##

(43) (200 mg, 1.03 mmol), graphite powder (100 mg), N,N-diisopropylethylamine (30 mg, 0.23 mmol) and THF (50 ml) are introduced into a 100 ml centrifuge tube. The mixture is subjected to ultrasound in an ultrasonic bath (30 kHz, 150 W) for 4 hours and then centrifuged at a speed of 3000 revolutions per minute for 30 minutes in order to separate the unexfoliated graphite. The supernatant is then withdrawn using a pipette and then filtered through a nylon filter (diameter of the pores of 0.22 μm), which had been dried and weighed beforehand. The whole (filter and residue) is then dried and then weighed. A weight of Graphene Diels-Alder adduct of 1.0 mg is thus obtained, i.e. a concentration of 0.02 mg.Math.ml.sup.−1 of Graphene Diels-Alder adduct in suspension in the supernatant.

Example 3: Exfoliation of Graphite by Virtue of a Diels-Alder Reaction Using Anthrone Derivatives

(44) Method: 100 mg of graphite, 50 mg of anthrone derivative product and 25 mg of DIPEA (diisopropylethylamine) are dissolved in 50 ml of THF (C.sub.graphite=2 mg/ml) and subjected to ultrasound at 60-65° C. for 4 h (180 W, 37 kHz) in an ultrasonic bath. The mixture is then centrifuged at 3000 rpm for 30 minutes and then left to separate by settling for 24 h. The supernatant is subsequently withdrawn and then filtered through nylon filters (size of the pores 0.22 μm). The solid obtained is thus redispersed in 10 ml of THF.

(45) The results are listed in FIGS. 6A and 6B.

Example 4: Exfoliation of Graphite by Virtue of a Diels-Alder Reaction Using 6,6-dihydropentacen-13-one

(46) 6,6-Dihydropentacen-13-one of formula II:

(47) ##STR00028##

(48) (10 mg, 0.034 mmol), graphite powder (100 mg), N,N-diisopropylethylamine (1 mg, 0.0077 mmol) and THF (50 ml) are introduced into a 100 ml centrifuge tube. The mixture is subjected to ultrasound in an ultrasonic bath (37 kHz, 150 W) for 4 hours and then centrifuged at a speed of 3000 revolutions per minute for 30 minutes in order to separate the unexfoliated graphite. The supernatant is then withdrawn with a pipette and then filtered through a nylon filter (diameter of the pores 0.22 μm) dried and weighed beforehand. The combination (filter and filtrate) is then dried and then weighed. A weight of Graphene Diels-Alder adduct of 0.7 mg is thus obtained, i.e. a concentration of 0.014 mg.Math.ml.sup.−1 of Graphene Diels-Alder adduct in suspension in the supernatant.

Example 5

(49) The experimental protocol of example 2 was repeated with different solvents. The results obtained with anthrone are listed in table 1, including the results of example 2 with THF.

(50) TABLE-US-00001 TABLE 1 Weight and concentration of Graphene Diels-Alder adduct which are obtained as a function of solvent used during the exfoliation of graphite with anthrone (200 mg) in the presence of DIPEA (20 mol %) 2- THF Acetonitrile NMP DMF Propanol Toluene Weight of 1.0 0.75 1.5 2.2 0.5 1.4 Graphene Diels-Alder adduct (mg) Concentration 0.02 0.015 0.03 0.044 0.01 0.028 of Graphene Diels-Alder adduct (mg .Math. ml.sup.−1)

Example 6: Exfoliation of Graphite by Virtue of a Diels-Alder Reaction Using Thioanthracenone

(51) By analogy with anthrone, the use of sulfur-comprising derivatives for carrying out the exfoliation of graphite by a Diels-Alder reaction proves to be advantageous for the subsequent functionalization of the exfoliated graphene.

(52) ##STR00029##

(53) Method:

(54) 100 mg of graphite, 100 mg of anthracenethiol and 20 mg of DIPEA are dissolved in 50 ml of solvent (C.sub.graphite=2 mg/ml) and subjected to ultrasound at 60-65° C. (180 W, 37 kHz) in an ultrasonic bath for 4 h. The mixture is then centrifuged at 3000 rpm for 30 minutes and then left to separate by settling for 24 h. The supernatant is subsequently withdrawn and then filtered through nylon filters (size of the pores 0.22 μm). The solid obtained is thus redispersed in 10 ml of solvent.

(55) TABLE-US-00002 X = S X = O THF Toluene THF Toluene Weight (mg) 1.34 1.98 1.0 1.4 Concentration 0.268 0.0396 0.02 0.028 (mg .Math. ml.sup.−1)

Example 7: Exfoliation of Graphite by Virtue of a Diels-Alder Reaction Using 2,6-bis(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)anthracen-9(10H)-one

(56) In order to improve the process for the exfoliation of the graphite via the Diels-Alder reaction with an anthrone-type compound, use was made of 2,6-bis(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)anthracen-9(10H)-one. The latter exhibits two (PEG).sub.3 chains with an end hydroxyl functional group, which is targeted at improving the exfoliation in alcoholic and/or aqueous media.

(57) Method:

(58) 100 mg of graphite, 50 mg of anthrone-derived product (crude) and 25 mg of DIPEA are dissolved in 50 ml of solvent (C.sub.graphite=2 mg/ml) and subjected to ultrasound at 60-65° C. (180 W, 37 kHz) in an ultrasonic bath for 4 h. The mixture is then centrifuged at 3000 rpm for 30 minutes and then left to separate by settling for 24 h. The supernatant is subsequently withdrawn and then filtered through nylon filters (size of the pores 0.22 μm). The solid obtained is thus redispersed in 10 ml of solvent.

(59) IPA: Isopropanol (2-Propanol)

(60) TABLE-US-00003 IPA IPA/H.sub.2O (100%) (75/25) Weight (mg) 2.21 1.87 Concentration 0.0442 0.0374 (mg/ml)

Comparative Example 8

(61) The quality and the characteristics of the graphene sheets obtained by the process of the invention (for example in examples 1 to 7) can be compared with those of known processes, such as: powerful sonication (much more powerful than that recommended for the process of the present invention). This method typically gives damaged graphene multilayer sheets; or to proceed for oxidation/reduction of the graphite.

(62) For example, use may be made of the experimental protocol described in reference 11 (Tagmatarchis et al., 2012).

(63) Reference may also be made to the following protocol:

(64) High intensity sonication (tipsonication) is carried out with a Bandelin Sonoplus HD 3200 ultrasonic homogenizer equipped with a flat head probe (VS70T), operating at 10% of the maximum power (250 W). In a typical experiment, 50 mg of graphite flakes are added per 100 ml of solvent [N,N-dimethylformamide (DMF), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), pyridine, o-dichlorobenzene (O-DCB) or N-methyl-1,2-pyrrolidone (NMP)]. The mixture is subjected to ultrasound for different periods of time (5, 15, 30 and 60 minutes). The graphene dispersion ink obtained is centrifuged for 15 min and the supernatant is collected and analyzed. On the basis of these measurements and calculations, the concentration of exfoliated graphene after high intensity sonication in O-DCB for 60 min was judged to be 17.8 mg.Math.ml.sup.−1, whereas the concentration of the dispersion of exfoliated graphene in NMP was measured at 3.8 mg.Math.ml.sup.−1.

(65) The graphene obtained by the process of the invention (exfoliation of graphite assisted by a Diels-Alder reaction+ annealing under vacuum) and by the abovementioned known methods can be characterized by Raman spectroscopy and TEM. The graphene obtained by the process of the invention should contain fewer defects and thus be characterized by the usual spectroscopic (UV/vis absorption, Raman) and microscopic (AFM, SEM, TEM) techniques.

Example 9: Characterization by Raman Spectroscopy of the Graphene Exfoliated by the Diels-Alder Reaction with Anthrone Derivatives

(66) DIC (Differential Interference Contrast)/Raman study at λ=568 nm (60× lens)

(67) This method consists in deriving the contrast of the refractive index differences of the components of the sample. This converts the phase difference of the light, induced by the refractive index of the sample, by detectable differences in amplitude. The advantage of this experiment is that an object would appear bright on a dark background but without the diffraction halo associated with a phase contrast. This process uses the differences in optical path length in the sample to generate the contrast; thus, the three-dimensional appearance of the samples on the image may not represent reality.

(68) Samples were prepared by spin coating on glass slides starting from a solution of graphene in THF. The solution used is a solution resulting from the redispersion of the graphene after filtration.

(69) Mappings were carried out over regions of approximately 10 μm.sup.2, in steps of 2 μm for the first spectrum and of 0.6 μm for the second (FIGS. 8A and 8C). On the map, the difference in color represents the differences in intensity on the G band, at 1578 cm.sup.−1. The wavelength used is 568 nm.

(70) In the spectra obtained, at 1335 cm.sup.−1, an intense D band is observed, synonymous with the presence of defects in the sample. This is due to the functionalization of the material by the anthrone, which creates sp.sup.3 centers and thus structural deformations. Subsequently, at 2678 cm.sup.−1, the shape of the 2D band indicates the number of layers of the sample. In this instance, the completely Lorentzien shape of this band makes it possible to demonstrate the presence of functionalized graphene monolayer sheets (FIG. 8).

Example 10: Examples of the Preparation of Transparent Electrodes Using Graphene Exfoliated by Diels-Alder Reaction

(71) One of the major applications of graphene is the manufacture of transparent conducting electrodes using conducting inks. The graphene obtained by exfoliation of graphite using the process described here can be used directly in the manufacture of such electrodes. The graphene films can be obtained by various methods which have been tested, such as spin coating, spray coating or vacuum filtration. In view of the graphene concentrations used, the most effective method for the preparation of graphene films is vacuum filtration.

(72) The four-point probe method was used to measure the conductivity of the graphene layers: the current is sent by a generator between points 1 and 4, while the voltage is measured between points 2 and 3. The ratio of the voltage measured to the current which passes through the sample gives the resistance of the length between the points 2 and 3 (FIG. 9).

(73) To obtain the resistivity of this section, the infinitesimal resistances between point 1 and points 2 and 3 are integrated.

(74) Graphene films were obtained by vacuum filtration of solutions (50 ml) of different concentrations (calculated using the Beer-Lambert law and a calibration curve) through Anodisc aluminum membranes (47 mm, size of pores of 0.02 μm). The results are presented in table 2.

(75) TABLE-US-00004 TABLE 2 Conductivity of graphene layers obtained by filtration of 50 ml of graphene dispersion as described in the experimental part Concentration Resistance Conductance Filter Graphite Solvent (mg/ml) (Ω) (S) 1 Normal THF 0.01  1.1 × 10.sup.5 3.8 × 10.sup.−5 3 Nano THF 5.55 × 10.sup.−4 2.25 × 10.sup.5   2 × 10.sup.−5 4 100 μm THF 2.17 × 10.sup.−3 9.37 × 10.sup.4 4.8 × 10.sup.−5 5 Normal Toluene 2.48 × 10.sup.−3 1.36 × 10.sup.5 3.3 × 10.sup.−5 7 Normal Toluene + 2.31 × 10.sup.−3 1.05 × 10.sup.5 4.3 × 10.sup.−5 THF

(76) The points used are 1.6 mm apart with a radius of 40.6 μm. They are equidistant; thus, the formula=4.532 U/I (π=3.14159) is used to calculate the resistance Rs.

Example 11: Use of Alternative Techniques to Sonication: Ball-Milling

(77) The use of sonication to accelerate the process for exfoliation by a Diels-Alder reaction can be replaced by any other technique which makes it possible to promote heterogeneous reactions. Thus, it is possible to use alternative methods to sonication, such as ball-milling or high-shear mixing (Nature Materials, 2014, 13, 624-630 [ref. 18]).

(78) On consulting recent studies on high-shear mixing making possible the exfoliation of graphite (Nature Materials, 2014, 13, 624-630), it was demonstrated by us that this method makes it possible to considerably reduce the use of sonication. A first experiment was carried out with an initial concentration of graphite of 2 mg/ml, i.e. 100 mg of graphite, 200 mg of anthrone and 30 mg of DIPEA in 50 ml of THF. The high-shear mixing time is 25 minutes, using a rotor/stator system with a diameter of 22 mm, at a speed of 4500 rpm. Subsequently, the mixture is subjected to sonication for 2 h (180 W, 37 kHz) and then purified by centrifuging (30 minutes at 3000 rpm). The graphene concentration, determined by the Beer-Lambert law using a calibration curve (ε=26.2), is 0.0234 mg/ml (in comparison, C=0.02 mg/ml for sonication for 4 h without high-shear mixing). In another experiment on a larger scale, an initial graphite concentration of 30 mg/ml, i.e. 1.0 g of graphite, 1.5 g of anthrone and 180 mg of DIPEA in 50 ml of THF, was used. Under the same reaction conditions as above, the graphene concentration obtained is 0.0765 mg/ml.

Example 12: Stabilization of Carbon Black Suspensions

(79) The process consists in subjecting graphitic carbon black (100 mg) to ultrasound in an ultrasonic bath (4 h, 180 W, 60° C.) in the presence of anthrone (200 mg) and N,N-diisopropylethylamine (30 mg, 20 mol %) in an organic solvent (50 ml). Stable suspensions in different organic solvents are obtained (FIG. 10).

(80) On reading the present patent application and the illustrative examples above, a person skilled in the art will observe that the present process is general and that it is applicable with all the graphites known to a person skilled in the art.