WO2020229882A1

WO2020229882A1 - A method for the manufacture of reduced graphene oxide from expanded kish graphite

Info

Publication number: WO2020229882A1
Application number: PCT/IB2019/054058
Authority: WO
Inventors: Thi Tan VU; Roberto Suarez Sanchez
Original assignee: ArcelorMittal SA
Current assignee: ArcelorMittal SA
Priority date: 2019-05-16
Filing date: 2019-05-16
Publication date: 2020-11-19
Anticipated expiration: 2021-11-16
Also published as: CA3140168A1; US12404179B2; US20220234898A1; BR112021020502A2; JP7366154B2; KR20210149138A; CA3140168C; EP3969418A1; CN113748084A; WO2020230010A1; KR102712261B1; JP2022532240A; CN113748084B

Abstract

The present invention relates to a Method for the manufacture of reduced graphene oxide from kish graphite comprising: A. The provision of kish graphite, B. Optionally, a pre-treatment of kish graphite, C. The intercalation of kish graphite with a persulfate salt and an acid at room temperature to obtain intercalated kish graphite, D. The expansion of the intercalated kish graphite to obtain expanded kish graphite and E. An oxidation step of the expanded kish graphite to obtain graphene oxide and F. A reduction of graphene oxide into reduced graphene oxide.

Description

A method for the manufacture of reduced graphene oxide from expanded kish graphite

The present invention relates to a method for the manufacture of reduced graphene oxide from expanded Kish graphite. In particular, reduced graphene oxide will have applications in metal industries including steel, aluminum, stainless steel, copper, iron, copper alloys, titanium, cobalt, metal composite, nickel industries, for example as coating or as a cooling reagent.

Kish graphite is a byproduct generated in the steelmaking process, especially during the blast furnace process or iron making process. Indeed, Kish graphite is usually produced on the free surface of molten iron during its cooling. It comes from molten iron at 1300-1500°C, which is cooled at a cooling rate between 0.40°C/min and 25°C/h when transported in the torpedo car or at higher cooling rates during the ladle transfer. An extensive tonnage of Kish graphite is produced annually in a steel plant.

Since Kish graphite comprises a high amount of carbon, usually above 50% by weight, it is a good candidate to produce graphene based materials. Usually, Graphene based materials include: graphene, graphene oxide, reduced graphene oxide or nanographite.

It is known to produce reduced graphene oxide (rGO) by reducing graphene oxide (GO). Reduced graphene oxide is composed of one or a few layers of graphene sheets containing some oxygen functional groups. Thanks to its interesting properties such as a high thermal conductivity and a high electrical conductivity, reduced graphene oxide, being hydrophobic, has many applications.

For example, reduced Graphene Oxide can be produced by chemical process such as a reduction of graphene oxide using a reducing agent such as hydrazine, ascorbic acid, urea, NaOH or by mechanical process such as thermal reduction at high temperature in an inert atmosphere. However, rGO with low oxygen content, i.e lower than 10%, is very difficult to obtain. Indeed, chemical or mechanical processes usually provides rGO having more than 10% of oxygen groups. Some oxygens groups such as epoxy groups are very difficult to reduce with conventional methods. In addition, the obtained rGO contains lot of defects thus demonstrating very low electrical conductivity.

Usually, reduced graphene oxide is synthesized based on Hummer Method comprising the following steps:

- the oxidation of Kish graphite with sodium nitrate (NaNC>3), sulfuric acid (H2SO4) and sodium or potassium permanganate (KMnC ) and

- the reduction of graphene oxide to obtain the reduced graphene oxide.

The patent application WO2018178845 discloses a Method for the manufacture of reduced graphene oxide from kish graphite comprising:

A. The provision of kish graphite,

B. A pre-treatment step of said kish graphite comprising the following successive sub-steps:

i. A sieving step wherein the kish graphite is classified by size as follows: a) Kish graphite having a size below 50pm,

b) Kish graphite having a size above or equal to 50pm, the fraction a) of kish graphite having a size below 50 pm being removed, ii. A flotation step with the fraction b) of kish graphite having a size above or equal to 50pm,

iii. An acid leaching step wherein an acid is added so that the ratio in weight (acid amount)/(kish graphite amount) is between 0.25 and 1 .0,

iv. Optionally, the kish graphite is washed and dried,

C. An oxidation step of the pre-treated kish-graphite obtained after step B) in order to obtain graphene oxide with an acid, sodium nitrate and an oxidizing agent and

D. A reduction of graphene oxide into reduced graphene oxide.

Nevertheless, when the oxidation step is performed with sodium nitrate (NaN03), toxic gases are produced leading to a polluting method. Moreover, the oxidation time is very long using NaNC>3, i.e. around 3hours.

The patent application PCT/IB2019/052804 discloses a method for the manufacture of reduced graphene oxide from kish graphite comprising:

A. The provision of kish graphite,

b) Kish graphite having a size above or equal to 50pm, the fraction a) of kish graphite having a size below 50pm being removed, ii. A flotation step with the fraction b) of kish graphite having a size above or equal to 50pm,

iv. Optionally, the kish graphite is washed and dried,

C. An oxidation step of the pre-treated kish-graphite in order to obtain graphene oxide with an acid, ammonium nitrate (NH4NO3) and an oxidizing agent and

D. A reduction of graphene oxide into reduced graphene oxide.

However, although the method using NH4NO3 is less polluting than the method using NaN03, there is a need to further provide an even less polluting method and to reduce the energy consumption.

Additionally, although the oxidation time is shorter using NH4NO3, i.e. 1 hour and 30minutes, compared to the oxidation time of the method using NaNC>3, i.e. 3hours, there is still a need to reduce the oxidation time and therefore to improve the productivity of the synthesis of reduced graphene oxide.

However, although the method using NH4NO3 is less polluting than the method using NaNC>3, there is a need to further provide an even less polluting method and to reduce the energy consumption.

Therefore, the purpose of the invention is to provide a less polluting method for the manufacture of reduced graphene oxide from Kish graphite compared to the prior art methods. Additionally, the object is to provide an industrial method to obtain reduced graphene oxide having good quality in the shortest time possible.

This is achieved by providing a method according to claim 1 . The method can also comprise any characteristics of claims 2 to 19 taken alone or in combination.

The following terms are defined: - Graphene oxide means one or a few layer(s) of graphene comprising oxygen functional groups including ketone groups, carboxyl groups, epoxy groups and hydroxyl groups,

- Reduced graphene oxide means graphene oxide that has been reduced. The reduced graphene oxide comprises one or a few layer(s) of graphene having some oxygen functional groups including ketone groups, carboxyl groups, epoxy groups and hydroxyl groups,

- Pristine graphene means Graphene is in its original condition, i.e. ideal, and does not have any defect. Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention and

- room temperature means between 0 and 45°C at atmospheric pressure.

Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention.

To illustrate the invention, various embodiments and trials of non-limiting examples will be described, particularly with reference to the following Figures:

Figure 1 illustrates an example of one layer of reduced graphene oxide according to the present invention.

Figure 2 illustrates an example of a few layers of reduced graphene oxide according to the present invention.

The invention relates to a Method for the manufacture of reduced graphene oxide from kish graphite comprising:

A. The provision of kish graphite,

B. Optionally, a pre-treatment of kish graphite,

C. The intercalation of kish graphite with a persulfate salt and an acid at room temperature to obtain intercalated kish graphite,

D. The expansion of the intercalated kish graphite at room temperature to obtain expanded kish graphite,

E. An oxidation step of the expanded kish graphite to obtain graphene oxide and

F. A reduction of graphene oxide into reduced graphene oxide.

Without willing to be bound by any theory, it seems that the method according to the present invention allows for the production of reduced graphene oxide having good quality. Moreover, the method including notably the intercalation at room temperature, the expansion at room temperature and the oxidation into graphene oxide is easy to implement at industrial scale and is less polluting than methods of the prior art. Indeed, it is believed that during the expansion, the persulfate salt acts like an oxidant to oxidize the kish graphite. Since the persulfate salt is an important oxygen donor, the intercalation gap between two kish graphite layers is further improved allowing the acid to enter more easily between the kish graphite layers. It is believed that the persulfate salt will decompose and release O2 gas causing an instantaneous pressure in the kish graphite interlayers making an exponential expansion of graphite at room temperature. The energy consumption is thus reduced.

Moreover, it is believed that using expanded kish graphite according to the present invention significantly reduces the oxidation time compared to the prior art methods. Indeed, it is believed that since there is a higher expansion volume, it is easier to oxidize the kish graphite layers since the gap between two kish graphite layers is higher using the persulfate salt and the acid. Thus, the oxidation time is significantly reduced.

Preferably, in step A), the Kish graphite is a residue of the steelmaking process. For example, it can be found in a blast furnace plant, in an iron making plant, in the torpedo car and during ladle transfer.

Preferably, in step B), the pre-treatment of kish-graphite comprises the following successive sub-steps:

i. A sieving step wherein the kish graphite is classified by size as follows:

a) Kish graphite having a size below 50pm,

b) Kish graphite having a size above or equal to 50pm, the fraction a) of kish graphite having a size below 50 pm being removed,

ii. A flotation step with the fraction b) of kish graphite having a size above or equal to 50pm,

iv. Optionally, the kish graphite is washed and dried. Without willing to be bound by any theory, it seems that when the kish graphite is pre-treated with the method according to the present invention, it allows for the production of pristine graphene having improved quality since the pre-treated Kish graphite has a high purity. Indeed, the Kish graphite obtained after step B) has a purity of at least 90%. Moreover, the pre-treatment step B) is easy to implement at industrial scale and is more environmentally friendly than conventional methods.

In step B.i), the sieving step can be performed with a sieving machine.

After the sieving, the fraction a) of Kish graphite having a size below 50 pm is removed. Indeed, without willing to bound by any theory, it is believed that the kish graphite having a size below 50pm contains a very small quantity of graphite, for example less than 10%.

Preferably in step B.ii), the flotation step is performed with a flotation reagent in an aqueous solution. For example, the flotation reagent is a frother selected from among: methyl isobutyl carbinol (MIBC), pine oil, polyglycols, xylenol, S-benzyl-S'- n-butyl trithiocarbonate, S,S'-dimethyl trithiocarbonate and S-ethyl-S'-methyl trithiocarbonate. Advantageously, the flotation step is performed using a flotation device.

Preferably, in step B.i), the fraction a) of kish graphite having a size below 55 pm is removed and in step B.ii), the fraction b) of kish graphite has a size above or equal to 55pm. More preferably, in step B.i), the fraction a) of kish graphite having a size below 60 pm is removed and wherein in step B.ii), the fraction b) of kish graphite has a size above or equal to 60pm.

Preferably, in steps B.i) and B.ii), the fraction b) of kish graphite has a size below or equal to 300 pm, any fraction of kish graphite having a size above 300 pm being removed before step B.ii).

More preferably in steps B.i) and B.ii), the fraction b) of kish graphite has a size below or equal to 275 pm, any fraction of kish graphite having a size above 275 pm being removed before step B.ii).

Advantageously, in steps B.i) and B.ii), the fraction b) of kish graphite has a size below or equal to 250 pm, any fraction of kish graphite having a size above 250 pm being removed before step B.ii). In step B.iii), the (acid amount)/(kish graphite amount) ratio in weight is between 0.25 and 1 .0, advantageously between 0.25 and 0.9, more preferably between 0.25 and 0.8. For example, the (acid amount)/(kish graphite amount) ratio in weight is between 0.4 and 1 .0, between 0.4 and 0.9 or between 0.4 and 1 . Indeed, without willing to be bound by any theory, it seems that if the (acid amount)/(kish graphite amount) ratio is below the range of the present invention, there is a risk that the kish graphite comprises a lot of impurities. Moreover, it is believed that if the (acid amount)/(kish graphite amount) ratio is above the range of the present invention, there is a risk that a huge amount of chemical waste is generated.

Preferably, in step B.iii), the acid is selected among the following elements: chloride acid, phosphoric acid, sulfuric acid, nitric acid or a mixture thereof.

The pre-treated Kish graphite obtained after step B) of the method according to the present invention has a size above or equal to 50pm. The pre-treated Kish graphite has a high purity, i.e. at least of 90%. Moreover, the degree of crystallinity is improved compared to conventional methods allowing higher thermal and electrical conductivities and therefore higher quality.

Preferably, in step C), the ratio in weight of persulfate salt with respect to kish graphite is between 1 and 8, more preferably between 1 and 6 and advantageously between 1 and 5. Indeed, without willing to be bound by any theory, it seems that the intercalation is further improved.

Preferably, in step C), the ratio in weight of the acid with respect to kish graphite is between 2 and 8, more preferably between 4 and 8. Indeed, if the ratio of the acid with respect to kish graphite is below 2, there is a risk that only a part of kish graphite is expanded. If the ratio of the acid with respect to kish graphite is above 8, there is a risk that the expansion occurs very slowly and to decrease the volume expansion since the acid in excess cannot penetrate the kish graphite interlayer. Therefore, the intercalated kish graphite is surrounded by the acid, which prevent the release of oxygen from the decomposition of the persulfate salt.

Preferably, in step C), the persulfate salt is chosen from: Sodium persulfate (Na2S2C>8), Ammonium persulfate ((NH4)2S20s) and Potassium persulfate (K2S2O8) or a mixture thereof. Preferably, in step C), the acid is chosen from: H2SO4, HCI, HNO3, H3PO4, C2H2CI2O2 (dichloroacetic acid), HSO2OH (alkylsulfonic acid) or a mixture thereof. Preferably, in step D), the expansion is naturally performed by leaving the kish graphite, the persulfate salt and the acid at room temperature in an open vessel. For example, they are in an opened bowl, opened glassware, opened lab reactor or opened pilot reactor.

Preferably, in step E) comprises the following successive sub-steps:

i. The mixture of the expanded kish graphite, an acid, an oxidizing agent and optionally a salt,

ii. The addition of a chemical element to stop the oxidation reaction,

iii. the separation of graphite oxide from the mixture obtained in step E.ii),

iv. The exfoliation of graphite oxide into graphene oxide.

Without willing to be bound by any theory, it is believed that in step E.i), the oxidation time of the expanded kish graphite with an acid, an oxidizing agent and a salt is significantly reduced. Moreover, it seems that the oxidation of the expanded kish graphite with an acid and an oxidizing agent, i.e. without the salt, allows for an even shorter oxidation time.

Optionally, in step E.i), the salt is chosen from: NaN03, NH4NO3, KNO3, Ni(N03)2, CU(N03)2, Zn(N03)2, AI(N03)3 or a mixture thereof.

Preferably, in step E.i), the acid is chosen from: H2SO4, HCI, HNO3, H3PO4, C2H2CI2O2 (dichloroacetic acid), HSO₂OH (alkylsulfonic acid) or a mixture thereof.

Preferably, in step E.i), the oxidizing agent is chosen from: potassium permanganate, H2O2, O3, H2S2O8, H2SO5, KNO3, NaCIO or a mixture thereof.

Then, advantageously in step E.ii), the element used to stop the oxidation reaction is chosen from: an acid, non-deionized water, deionized water, H2C>2 or a mixture thereof.

In a preferred embodiment, when at least two elements are used to stop the reaction, they are used successively or simultaneously. Preferably, deionized water is used to stop the reaction and then H2O2 is used to eliminate the rest of the oxidizing agent. In another preferred embodiment, hydrochloric acid is used to stop the reaction and then H2O2 is used to eliminate the rest of the oxidizing agent. In another preferred embodiment, H2O2 is used to stop the reaction and eliminate the rest of the oxidizing agent by this following reaction:

2KMn04 + H2O2+ 3H SC>4 = 2MnS0₄ +O2 + K2SO4 + 4H 0.

Without willing to be bound by any theory, it seems that when the element to stop the reaction is added into the mixture, there is a risk that this addition is too exothermic resulting in explosion or splashing. Thus, preferably, the element used to stop the reaction is slowly added into the mixture obtained in step E.ii). More preferably, the mixture obtained in step E.ii) is gradually pumped into the element used to stop the oxidation reaction. For example, the mixture obtained in step E.ii) is gradually pumped into deionized water to stop the reaction.

In step E.iii), graphite oxide is separated from the mixture obtained in step E.ii). Preferably, the graphene oxide is separated by centrifugation, by decantation or filtration.

Optionally, graphite oxide is washed. For example, graphene oxide is washed with an element chosen from among: deionized water, non-deionized water, an acid or a mixture thereof. For example, the acid is selected among the following elements: chloride acid, phosphoric acid, sulfuric acid, nitride acid or a mixture thereof.

Optionally, the graphite oxide is dried, for example with air or at high temperature in the vacuum condition.

Preferably in step E.iv), the exfoliation is performed by using ultrasound, mechanical agitator, sieve shaker or thermal exfoliation. Preferably, the mixture obtained in step E.iii) is exfoliated into one or a few layers of graphene oxide.

By applying the method according to the present invention, Graphene oxide comprising at least 25% by weight of oxygen functional groups.

Then, in step F), graphene oxide is reduced into reduced graphene oxide.

Preferably, in step F.i), the reducing agent is chosen from: acid ascorbic; urea; hydrazine hydrate; alkaline solution such as NaOFI or KOFI; phenols such as gallic acid, tannin acid, dopamine or tea polyphenol; alcohols such as methyl alcohol, ethyl alcohol or isopropyl alcohol; glycine; sodium citrate or sodium borohydride. More preferably, the reducing agent is acid ascorbic since the ascorbic acid is more environmentally friendly.

After the reduction of GO into rGO, optionally rGO is washed. For example, rGO is washed with water. rGO can be dried, for example with air or by lyophilization.

Advantageously, in step F.i), the reduction is performed at a temperature between 50 and 120°C, more preferably between 90 and 100°C.

Preferably, in step F.i), the reduction is performed during less 24 hours, more preferably during less than 15 hours and advantageously during 1 to 10 hours.

By applying the method according to the present invention, reduced graphene oxide (rGO), comprising one or a few layer(s) of graphene having between 10 and 25% by weight of oxygen functional groups is obtained.

Optionally, in step F.ii), rGO is further reduced into microwave-reduced graphene oxide (MW-rGO).

Preferably, in step F.ii), the catalyst is chosen from: pristine graphene, graphene nanoplatelet(s), graphite or graphite nanoplatelets. More preferably, the catalyst is pristine graphene. Without willing to be bound by any theory, it is believed that pristine graphene can better absorb the electromagnetic field in the form of microwaves due to the nature, the form and the properties of pristine graphene. Indeed, pristine graphene, being conductive, is a single layer of Graphite consisting of carbons bonded together in a hexagonal honeycomb lattice. It is an allotrope of carbon in the structure of a plane of sp² bonded atoms with which microwaves are attracted and can easily be absorbed.

Preferably, in step F.ii), the ratio in weight of rGO with respect to the catalyst amount of rGO

is as follows: 50 < £ 150. Advantageously, the ratio in weight of amount of catalyst

amount of rGO

rGO with respect to the catalyst is as follows: 75 < < 125. Without amount of catalyst

willing to be bound by any theory, it is believed that when the ratio in weight of rGO with respect to the catalyst is as above, the reduction of rGO into MW- rGO is further improved. Indeed, this above ratio leads to MW-rGO having even less oxygen groups.

Preferably, in step F.ii), the microwave frequency is between 300MFIz and 100GFIZ, preferably between 1 and 5GFIz and for example, of 2.45GFIz. Preferably, step F.ii) is performed with a microwave frequency heating device. Preferably, it is a microwave oven.

Advantageously, the microwave has a power between 100W and 100KW, more preferably between 100 and 2000KW.

Preferably, in step F.ii), the microwaving is performed during at least 2 seconds. Indeed, without willing to be bound by any theory, it is believed that when the microwaving is performed during at least 2 seconds, the reduction into MW-rGO is further improved.

Optionally, Microwave-reduced graphene oxide (MW-rGO) comprising one or a few layer(s) of graphene having less than 10% by weight, more preferably less than 7%, by weight of oxygen functional groups is obtained.

Figure 1 illustrates an example of one layer of reduced graphene oxide according to the present invention. The lateral size means the highest length of the layer through the X axis, the thickness means the height of the layer through the Z axis and the width of the nanoplatelet is illustrated through the Y axis.

Figure 2 illustrates an example of a few layers of reduced graphene oxide according to the present invention. The lateral size means the highest length of the layer through the X axis, the thickness means the height of the layer through the Z axis and the width of the nanoplatelet is illustrated through the Y axis.

Preferably, reduced graphene oxide is deposited on metallic substrate steel to improve some properties such as corrosion resistance of a metallic substrate.

In another preferred embodiment, reduced graphene oxide is used as cooling reagent. Indeed, reduced graphene oxide can be added to a cooling fluid. Preferably, the cooling fluid can be chosen from among: water, ethylene glycol, ethanol, oil, methanol, silicone, propylene glycol, alkylated aromatics, liquid Ga, liquid In, liquid Sn, potassium formate and a mixture thereof. In this embodiment, the cooling fluid be used to cool down a metallic substrate.

For example, the metallic substrate is selected from among: aluminum, stainless steel, copper, iron, copper alloys, titanium, cobalt, metal composite, nickel.

The invention will now be explained in trials carried out for information only. They are not limiting.

Examples: T rials 1 to 4 were prepared by providing Kish graphite from steelmaking plant. Then, Kish graphite was sieved to be classified by size as follows:

a) Kish graphite having a size below < 63pm and

b) Kish graphite having a size above or equal to 63pm.

The fraction a) of Kish graphite having a size below 63 pm was removed.

A flotation step with the fraction b) of Kish graphite having a size above or equal to 63pm was performed. The flotation step was performed with a Humboldt Wedag flotation machine with MIBC as frother. The following conditions were applied: Cell volume (I): 2, Rotor speed (rpm): 2000, Solid concentration (%): 5-10, Frother, type: MIBC, Frother, addition (g/T): 40, Conditioning time (s): 10 and Water conditions: natural pH, room-temperature.

All Trials were then leached with the hydrochloric acid in aqueous solution. Trials were then washed with deionized water and dried in air at 90^Q C. the purity of the kish graphite was of 95%.

After, the kish graphite was expanded at 25 or 35°C with ammonium persulfate with sulfuric acid with different ratios. The obtained material is called expanded Kish Graphite.

Trials 1 to 4 were mixed at room temperature with optionally ammonium nitrate, sulfuric acid and KMnCP. After the oxidation, Trials were gradually pumped into deionized water. H2O2 in aqueous solution was added until there was no gas producing and mixtures were stirred to eliminate the rest of H2O2.

Then, for all Trials, Graphite oxide was separated from the mixture by decantation. They were exfoliated using ultrasound in order to obtain one or two layer(s) of graphene oxide. Finally, graphene oxide was separated from the mixture by centrifugation, washed with water and dried with air to obtain graphene oxide powder.

L-ascorbic acid were mixed with aqueous solutions of Trials 1 to 4. The reaction mixtures were agitated at 90°C to reduce the graphene oxide sheets. Trials were then washed and dried to obtain reduced graphene oxide powder.

Then, for Trials 1 and 4, rGO was disposed in a microwave oven (800W) under air atmosphere during 2 seconds. A catalyst being Pristine Graphene was added. rGO was reduced into MW-rGO by microwaving. Graphene oxide and reduced graphene oxide were analyzed by scanning electron microscopy (SEM), X ray diffraction spectroscopy (XRD), Transmission electron microscopy (TEM), LECO analysis and Raman spectroscopy.

Trials 5 and 6 correspond respectively to Trial 1 of WO2018178845 and Trial 1 of PCT/IB2019/052805. Table 1 shows the results obtained.

The method of Trials 1 to 4 is more environmentally friendly than comparative Trials. Moreover, the oxidation time with the method of Trials 1 to 4 is significantly improved.

Claims

CLAIMS 1. Method for the manufacture of graphene oxide from kish graphite comprising:

A. The provision of kish graphite,

B. Optionally, a pre-treatment of kish graphite,

C. The intercalation of kish graphite with a persulfate salt and an acid at room temperature to obtain intercalated kish graphite, D. The expansion of the intercalated kish graphite at room temperature to obtain expanded kish graphite,

E. An oxidation step of the expanded kish graphite to obtain graphene oxide and

F. A reduction of graphene oxide into reduced graphene oxide.

2. Method according to claim 1 , wherein in step B), the pre-treatment of kish- graphite comprises the following successive sub-steps:

i. A sieving step wherein the kish graphite is classified by size as follows:

a) Kish graphite having a size below 50pm,

iii. An acid leaching step wherein an acid is added so that the ratio in weight (acid amount)/(kish graphite amount) is between 0.25 and 1.0,

iv. Optionally, the kish graphite is washed and dried.

3. Method according to claim 1 or 2, wherein in step C), the ratio in weight of persulfate salt with respect to kish graphite is between 1 and 8.

4. Method according to anyone of claims 1 to 3, wherein in step C), the ratio in weight of the acid with respect to kish graphite is between 2 and 8.

5. Method according to anyone of claims 1 to 4, wherein in step C), the persulfate salt is chosen from: Sodium persulfate (Na2S20s), Ammonium persulfate ((NH4)2S2C>8) and Potassium persulfate (K2S2O8) or a mixture thereof.

6. Method according to anyone of claims 1 to 5, wherein in step C), the acid is chosen from: H2SO4, HCI, HNO3, H3PO4, C2H2CI2O2 (dichloroacetic acid), HSO2OH (alkylsulfonic acid) or a mixture thereof.

7. Method according to anyone of claims 1 to 6, wherein in step D), the expansion is naturally performed by leaving the kish graphite, the persulfate salt and the acid at room temperature in an open vessel.

8. Method according to anyone of claims 1 to 7, wherein in step E) comprises the following successive sub-steps:

ii. The addition of a chemical element to stop the oxidation reaction,

iii. the separation of graphite oxide from the mixture obtained in step E.ii),

iv. The exfoliation of graphite oxide into graphene oxide.

9. Method according to claim 8, wherein in step E.i), the salt nitrate is chosen from: NaNOa, NH4NO3, KNOa, Ni(NOa)2, Cu(NOa)2, Zn(NOa)2, AI(NOa)a or a mixture thereof.

10. Method according to claim 8 or 9, wherein in step E.i), the acid is chosen from:

H2SO4, HCI, HNO3, H3PO4, C2H2CI2O2 (dichloroacetic acid), HSO2OH (alkylsulfonic acid) or a mixture thereof.

1 1 . Method according to anyone of claims 8 to 10, wherein in step E.i), the oxidizing agent is chosen from: potassium permanganate, H2O2, O3, H2S2O8, H2SO5, KNO3, NaCIO or a mixture thereof.

12. Method according to anyone of claims 8 to 1 1 , wherein in step E.ii), the chemical element used to stop the oxidation reaction is chosen from: an acid, non- deionized water, deionized water, FteC or a mixture thereof.

13. Method according to claim 12, wherein when at least two elements are chosen to stop the reaction, they are used successively or simultaneously.

14. Method according to anyone of claims 8 to 13, wherein in step E.ii), the mixture obtained in step E.i) is gradually pumped into the element used to stop the oxidation reaction.

15. Method according to anyone of claims 8 to 14, wherein in step E.iii), the graphite oxide is separated by centrifugation, decantation, distillation or filtration.

16. Method according to anyone of claims 8 to 15, wherein in step E.iv), the exfoliation is performed by using ultrasound, mechanical agitator, sieve shaker or thermal exfoliation.

17. Method according to anyone of claims 1 to 16, wherein step F) comprises the following sub-steps: i. The reduction of GO into reduced graphene oxide (rGO), comprising one or a few layer(s) of graphene having between 10 and 25% by weight of oxygen functional groups, using a reducing agent and

ii. Optionally, the reduction of rGO into microwave-reduced graphene oxide (MW-rGO), comprising one or a few layer(s) of graphene having less than 10% by weight of oxygen functional groups, by microwaving rGO under air atmosphere in presence of a catalyst.

18. A Method according to claim 17, wherein in step F.i), the reducing agent is chosen from: acid ascorbic; urea; hydrazine hydrate; alkaline solution such as NaOH or KOH; phenols such as gallic acid, tannin acid, dopamine or tea polyphenol; alcohols such as methyl alcohol, ethyl alcohol or isopropyl alcohol; glycine; sodium citrate or sodium borohydride.

19. A Method according to claim 17 or 18, wherein in step F.ii), the catalyst is chosen from: pristine graphene, graphene nanoplatelet(s), graphite or graphite nanoplatelets.