Reductive-expansion synthesis of graphene
Exemplary embodiments provide materials and methods for forming graphene-based exfoliated products with low oxygen contents by a reductive-expansion reaction from a physical mixture containing graphite-based precursor(s) and a chemical agent. Exemplary embodiments also provide materials and methods for forming graphene-based exfoliated products with controllable amounts of nitrogen and/or other impurities incorporated in the material structure as a result of a reductive-expansion reaction from a physical mixture containing graphite-based precursor(s) and a chemical agent.
1. A method of forming a graphene-based product comprising:
forming a solid phase, physical mixture comprising one or more graphite-based precursors and one or more solid phase reduction-expansion chemical agents selected from the group consisting of urea [(NH 2 ) 2 CO] and thiourea [SC(NH 2 ) 2 ], wherein each of the one or more graphite-based precursors comprises one or more of a graphite oxide, an expandable graphite, and a combination thereof; and
heating the physical mixture in an inert atmosphere at a temperature sufficient to thermally decompose the solid phase reduction-expansion chemical agent to produce a reducing gas and form a graphene-based product comprising one or more of a single graphene sheet, a stack of two or more single graphene sheets, entangled single graphene sheets, and combinations thereof.
2. The method of claim 1 , wherein the physical mixture comprises a molar ratio of the one or more graphite-based precursors to the chemical agent, wherein the molar ratio ranges from about 1:100 to about 100:1.
3. The method of claim 1 , wherein the step of forming a physical mixture comprises:
mixing the one or more graphite-based precursors with the solid phase reduction-expansion chemical agent as a solid mixture.
4. The method of claim 1 , wherein the step of forming a physical mixture comprises:
forming a chemical agent-containing solution by dissolving the solid phase reduction-expansion chemical agent in a solvent,
mixing the chemical agent-containing solution with the one or more graphite-based precursors, and
drying the mixture containing the chemical agent and the one or more graphite-based precursors during or prior to the heating step.
5. The method of claim 1 , wherein the temperature ranges from about 300° C. to about 800° C., the temperature being sufficient to result in a reductive-expansion process of the one or more graphite-based precursors.
6. The method of claim 1 , wherein the step of heating the physical mixture comprises placing the physical mixture in a pre-heated device at a heating temperature.
7. The method of claim 1 , wherein the step of heating the physical mixture comprises placing the physical mixture in an oven, wherein the oven is then heated from room temperature to a heating temperature.
8. The method of claim 1 , wherein the inert atmosphere is provided by a chemically inert gas comprising N 2 , Ar, He, or a combination thereof
9. The method of claim 1 , further comprising:
cooling the graphene-based product under an inert atmosphere following the heating step, and
collecting the graphene-based product.
10. The method of claim 1 , wherein the graphene-based product comprises a nano-sheet.
11. The method of claim 1 , wherein the graphene-based product has a carbon content of at least about 90% by weight.
12. The method of claim 1 , wherein the graphene-based product is formed with more than about 0.1% nitrogen by weight of the total graphene-based product.
13. The method of claim 1 , wherein the graphene-based product comprises about 30% or less impurity atomic species by weight of the total graphene-based product.
14. A method of forming a graphene-based product comprising:
forming a physical mixture by physically mixing graphite oxide with a reductive-expansion agent comprising urea;
heating the physical mixture in an inert atmosphere at a heating temperature to form a free-standing graphene-based product, wherein the heating temperature is at or above a decomposition temperature of the reductive-expansion agent; and
cooling the free-standing graphene-based product, wherein the graphene-based product comprises one or more of a single graphene sheet, a stack of two or more single graphene sheets, and entangled single graphene sheets.
15. The method of claim 14 , wherein the step of heating the physical mixture comprises placing the physical mixture in a device pre-heated at a heating temperature of about 600° C. or higher.
16. The method of claim 14 , wherein the step of heating the physical mixture comprises placing the physical mixture in a device, wherein the device is then heated from room temperature to the heating temperature of about 600° C. or higher for about 30 minutes or less.
17. The method of claim 14 , wherein the reduction-expansion agent is a solid, and the heating temperature ranges from about 300° C. to about 800° C.
18. A method of forming free standing graphene comprising:
forming a physical mixture by physically mixing graphite oxide with a reductive-expansion agent comprising urea;
heating the physical mixture in an inert atmosphere at a heating temperature to form free standing graphene, wherein the heating temperature is at or above a decomposition temperature of the reductive-expansion agent; and
cooling the free-standing graphene, wherein the free standing graphene comprises graphene sheets.
19. The method of claim 18 , wherein heating the physical mixture comprises heating at a temperature of 600° C. or higher.
20. The method of claim 14 , wherein the physical mixture comprises a molar ratio of the graphite oxide to the urea, wherein the molar ratio ranges from 1:2 to 1:10.