Supercritical fluid process for producing nano graphene platelets

• US 20100044646A1
• Filed: 08/25/2008
• Published: 02/25/2010
• Est. Priority Date: 08/25/2008
• Status: Active Grant

• Current Assignee: Global Graphene Group, Inc.
• Original Assignee: Nanotek Instruments, Inc.
• Inventors: Zhamu, Aruna, Jang, Bor Z.
• Granted Patent: US 8,696,938 B2
• Time in Patent Office: Days
• US Class Current: 252/511
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: C01B 2204/02 Single layer graphene
• CPC Class Codes: C01B 2204/22 Electronic properties
• CPC Class Codes: C01B 32/19 by exfoliation
• CPC Class Codes: C01B 32/192 starting from graphitic oxides
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: Y02P 20/54 using solvents, e.g. supercritical solvents or ionic liquids

Abstract

The present invention provides a process for producing pristine or non-oxidized nano graphene platelets (NGPs) that are highly conductive. The process comprises: (i) subjecting a graphitic material to a supercritical fluid at a first temperature and a first pressure for a first period of time in a pressure vessel and then (ii) rapidly depressurizing the fluid at a fluid release rate sufficient for effecting exfoliation of the graphitic material to obtain the NGP material. Conductive NGPs can be used as a conductive additive in transparent electrodes for solar cells or flat panel displays (e.g., to replace expensive indium-tin oxide), battery and supercapacitor electrodes, and nanocomposite for electromagnetic wave interference (EMI) shielding and static charge dissipation, etc.

Claims

1. A process for producing a nano graphene platelet (NGP) material, said process comprising:

(i) subjecting a graphitic material to a supercritical fluid at a first temperature and a first pressure for a first period of time in a pressure vessel and then (ii) rapidly depressurizing said fluid at a fluid release rate sufficient for effecting exfoliation of said graphitic material to obtain said NGP material.

2. The process as set forth in claim 1 wherein said supercritical fluid comprises a fluid selected from carbon dioxide, water, water oxidation, hydrogen peroxide (H₂O₂), methane, ethane, ethylene, ozone, sulfonic group (SO₃), or a combination thereof.

3. The process as set forth in claim 1 wherein said graphitic material is selected from the group consisting of natural graphite, artificial graphite, graphite oxide, graphite fluoride, graphite fiber, carbon fiber, carbon nano-fiber, carbon nano-tube, mesophase carbon micro-bead (MCMB), soft carbon, hard carbon, and combinations thereof.

4. The process as set forth in claim 1 further comprising a procedure of essentially repeating step (i) and step (ii) that includes (a) subjecting said NGP material to a supercritical fluid at a second temperature and a second pressure for a second period of time in a pressure vessel and then (b) rapidly depressurizing said fluid at a fluid release rate sufficient for effecting further exfoliation of said NGP material.

5. The process as set forth in claim 4 wherein said second temperature differs from said first temperature or said second pressure differs from said first pressure.

6. The process as set forth in claim 1 wherein said supercritical fluid contains a surfactant or dispersing agent dissolved therein.

7. The process as set forth in claim 6 further comprising a procedure of repeating step (i) and step (ii) that includes (a) subjecting said NGP material to a supercritical fluid at a second temperature and a second pressure for a second period of time in a pressure vessel and then (b) rapidly depressurizing said fluid at a fluid release rate sufficient for effecting further exfoliation of said NGP material.

8. The process as set forth in claim 7 wherein said second temperature differs from said first temperature or said second pressure differs from said first pressure.

9. The process as set forth in claim 1 wherein said supercritical fluid contains a coating agent dissolved therein and said process further comprises a procedure of repeating step (i) and step (ii) that includes (a) subjecting said NGP material to a supercritical fluid at a second temperature and a second pressure for a second period of time in a pressure vessel and then (b) rapidly depressurizing said fluid at a fluid release rate sufficient for effecting further exfoliation of said NGP material.

10. The process as set forth in claim 9 wherein said coating agent comprises a monomer, a prepolymer or oligomer, a polymer, a resin, a curing agent, or a combination thereof.

11. The process as set forth in claim 1 wherein said supercritical fluid contains a curing agent dissolved therein and the process further comprises mixing said nano graphene material with a thermosetting resin.

12. The process as set forth in claim 1 wherein said supercritical fluid contains a curing agent dissolved therein and the process further comprises a procedure of repeating step (i) and step (ii) and a procedure of mixing said graphene material with a resin.

13. The process as set forth in claim 1 wherein said nano graphene platelet material, when formed into a thin film with a thickness no greater than 100 nm, exhibits an electrical conductivity of at least 100 S/cm.

14. The process as set forth in claim 1 wherein said nano graphene platelet material, when formed into a thin film with a thickness no greater than 100 nm, exhibits an electrical conductivity of at least 1,000 S/cm.

15. The process as set forth in claim 1 wherein said nano graphene material has a specific surface area of approximately from 300 m²/g to 2,600 m²/g.

16. The process as set forth in claim 1 wherein said nano graphene platelet material comprises single-layer graphene.

17. The process as set forth in claim 1, further comprising imparting a chemical group to said nano graphene material in said pressure vessel.

18. The process as set forth in claim 1, wherein said supercritical fluid comprises a reactive chemical group.

19. The process as set forth in claim 1, wherein said supercritical fluid comprises a reactive chemical group and a surfactant.