Method for the manufacture of reduced graphene oxide from Kish graphite

1. A method for the manufacture of reduced graphene oxide from kish graphite comprising:

A. providing kish graphite;

B. pre-treating the 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 50 μm,

b) Kish graphite having a size greater than or equal to 50 μm,

 the fraction a) of kish graphite having a size below 50 μm being removed,

ii. a flotation step with the fraction b) of kish graphite having a size greater than or equal to 50 μm,

iii. an acid leaching step wherein an acid is added so that a ratio in weight (acid amount)/(kish graphite amount) is from 0.25 to 1.0,

iv. optionally, washing and drying the kish graphite;

C. oxidizing the pre-treated kish-graphite obtained after step B) in order to obtain graphene oxide; and

D. reducing the graphene oxide into reduced graphene oxide.

2. The method according to claim 1 , wherein in step B.i), the fraction a) of kish graphite having a size less than 55 μm is removed and in step B.ii), the fraction b) of kish graphite has a size greater than or equal to 55 μm.

3. The method according to claim 2 , wherein in step B.i), the fraction a) of kish graphite having a size below 60 μm is removed and wherein in step B.ii), the fraction b) of kish graphite has a size greater than or equal to 60 μm.

4. The method according to claim 3 , wherein in steps B.i) and B.ii), the fraction b) of kish graphite has a size less than or equal to 300 μm, any fraction of kish graphite having a size greater than 300 μm is removed before step B.ii).

5. The method according to claim 4 , wherein in steps B.i) and B.ii), the fraction b) of kish graphite has a size less than or equal to 275 μm, any fraction of kish graphite having a size greater than 275 μm is removed before step B.ii).

6. The method according to claim 5 , wherein in steps in steps B.i) and B.ii), the fraction b) of kish graphite has a size less than or equal to 250 μm, any fraction of kish graphite having a size greater than 250 μm is removed before step B.ii).

7. The method according to claim 1 , wherein in step B.iii), the acid amount/kish graphite amount ratio in weight is from 0.25 to 0.9.

8. The method according to claim 7 , wherein in step B.iii), the acid amount/kish graphite amount ratio in weight is from 0.25 to 0.8.

9. The method according to claim 1 , wherein in step B.iii), the acid is selected from the following elements: chloride acid, phosphoric acid, sulfuric acid, nitric acid or a mixture thereof.

10. The method according to claim 1 , wherein step C) comprises the following sub-steps:

i. preparing a mixture comprising the pre-treated kish-graphite, an acid and optionally sodium nitrate, the mixture being kept at a temperature below 5° C.,

ii. adding an oxidizing agent into the mixture obtained in step C.i),

iii. After the targeted level of oxidation is reached, adding an element to stop the oxidation reaction,

iv. optionally, separating graphite oxide from the mixture obtained in step C.iii),

v. optionally, washing the graphite oxide,

vi. optionally, drying the graphite oxide and

vii. exfoliating into graphene oxide.

11. The method according to claim 10 , wherein in step C.ii), the oxidizing agent is chosen from: sodium permanganate, H 2 O 2 , O 3 , H 2 S 2 O 8 , H 2 SO 5 , KNO 3 , NaClO or a mixture thereof.

12. The method according to claim 10 , wherein in step C.iii), the element used to stop the oxidation reaction is chosen from: an acid, non-deionized water, deionized water, H 2 O 2 or a mixture thereof.

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

14. The method according to claim 10 , wherein in step C.iii), the mixture obtained in step C.ii) is gradually pumped into the element used to stop the oxidation reaction.

15. The method according to claim 10 , wherein in step C.vii), the exfoliating is performed by using ultrasound or thermal exfoliation.

16. The method according to claim 10 , wherein in step C.iv), the graphene oxide is separated by centrifugation, by decantation or by filtration.

17. The method according to claim 10 , wherein steps C.iv) and C.v) are performed at least two times independently of each other.

18. The method according to claim 10 , wherein in step C.i), the acid is selected from the following elements: chloride acid, phosphoric acid, sulfuric acid, nitric acid or a mixture thereof.

19. The method according to claim 1 , wherein step D) comprises the following sub-steps:

i. reducing graphene oxide to reduced graphene oxide with a reducing agent by obtaining a mixture comprising the graphene oxide and the reducing agent,

ii. agitating the mixture obtained in step D.i),

iii. optionally, washing the reduced graphene oxide, and

iv. optionally, drying the reduced graphene oxide.

20. The method according to claim 19 , wherein in step D.i), an acid is used, and the acid is chosen from: acid ascorbic, urea or hydrazine hydrate.

21. The method according to claim 19 , wherein in step D.ii), the mixture is kept at a temperature from 50 to 120° C.

22. The method according to claim 19 , wherein in step D.ii), the agitation is performed during less than 24 hours.

23. The method according to claim 1 , wherein the fraction a) contains less than 10% graphite.

24. The method according to claim 1 , wherein the Kish graphite obtained after step B) has a purity of at least 90%.

25. The method according to claim 1 , wherein the reduced graphene oxide has from 0.4% to 25% by weight of oxygen groups.

26. The method of claim 1 , wherein the acid is hydrochloric acid.