Carbon nanotube separation by reversible gelation

1. A method for separating carbon nanotubes comprising:

adding a gelling agent including an organic amine having two or more functional groups to a solution having a first type of carbon nanotubes and a second type of carbon nanotubes to form a gel;

compacting the gel to form a compacted gel and a liquid;

removing at least a portion of the liquid;

removing at least a portion of the first type of carbon nanotubes from the liquid;

dispersing the compacted gel to form a dispersed gel; and

removing at least a portion of the second type of carbon nanotubes from the dispersed gel.

2. The method of claim 1 , wherein the first type of carbon nanotubes comprise metallic carbon nanotubes and the second type of carbon nanotubes include semiconducting carbon nanotubes.

3. The method of claim 2 , wherein the gel is formed by substantial noncovalent cross-linking between the organic amine and at least a portion of the semiconducting nanotubes.

4. The method of claim 1 , wherein the organic amine comprises a bi-functional amine.

5. The method of claim 1 , wherein the organic amine comprises a poly-functional amine.

6. The method of claim 1 , wherein removing the first type of carbon nanotubes from the liquid comprises one or more of precipitating, washing, drying, heating, evaporation or dissolution by a co-solvent.

7. The method of claim 1 , wherein removing the first type of carbon nanotubes from the liquid comprises:

adding a second gelling agent to the liquid to form a second gel;

compacting the second gel to form a second compacted gel and a second liquid;

removing at least a portion of the second liquid; and

removing the first type of carbon nanotubes from the second liquid.

8. The method of claim 7 , wherein removing the first type of carbon nanotubes from the liquid further comprises:

determining whether the liquid has a desired purity.

9. The method of claim 1 , wherein removing the portion of the second type of carbon nanotubes from the dispersed gel comprises:

compacting the dispersed gel to form a second compacted gel and a second liquid;

removing at least a portion the second liquid;

dispersing the second compacted gel to form a second dispersed gel; and

removing the second type of carbon nanotubes from the second dispersed gel.

10. A method for separating carbon nanotubes comprising:

adding an organic amine having two or more functional groups to a solution having metallic carbon nanotubes and semiconducting carbon nanotubes to form a gel;

compacting the gel to form a compacted gel and a liquid;

removing at least a portion of the liquid;

removing at least a portion of the metallic carbon nanotubes from the liquid;

dispersing the compacted gel to form a dispersed gel; and

removing at least a portion of the semiconducting carbon nanotubes from the dispersed gel.

11. The method of claim 10 , wherein the organic amine comprises a bi-functional amine.

12. The method of claim 10 , wherein dispersing the compacted gel comprises one or more of heating, agitating, stirring or adding a solvent.

13. The method of claim 10 , wherein removing the semiconducting carbon nanotubes from the dispersed gel comprises:

compacting the dispersed gel to form a second compacted gel and a second liquid;

removing at least a portion the second liquid;

dispersing the second compacted gel to form a second dispersed gel; and

removing the semiconducting carbon nanotubes from the second dispersed gel.

14. A method for separating carbon nanotubes comprising:

adding a gel including an amine to a solution having a first type of carbon nanotubes and a second type of carbon nanotubes to form an expanded gel;

compacting the expanded gel to form a compacted gel and a liquid;

removing at least a portion of the liquid;

removing at least a portion of the first type of carbon nanotubes from the liquid;

dispersing the compacted gel to form a dispersed gel; and

removing at least a portion of the second type of carbon nanotubes from the dispersed gel.

15. The method of claim 14 , wherein the first type of carbon nanotubes comprise metallic carbon nanotubes and the second type of carbon nanotubes include semiconducting carbon nanotubes.

16. The method of claim 15 , wherein the gel comprises an inorganic amine.

17. The method of claim 14 , wherein removing the first type of carbon nanotubes from the liquid comprises:

adding a second gel to the liquid to form a second expanded gel;

compacting the second expanded gel to form a second compacted gel and a second liquid;

removing at least a portion of the second liquid; and

removing the first type of carbon nanotubes from the second liquid.

18. The method of claim 14 , wherein removing the first type of carbon nanotubes from the liquid comprises:

adding a gelling agent to the liquid to form a second gel;

compacting the second gel to form a second compacted gel and a second liquid;

removing at least a portion of the second liquid; and

removing the first type of carbon nanotubes from the second liquid.

19. The method of claim 14 , wherein removing the portion of the second type of carbon nanotubes from the dispersed gel comprises:

compacting the dispersed gel to form a second compacted gel and a second liquid;

removing at least a portion the second liquid;

dispersing the second compacted gel to form a second dispersed gel; and

removing the second type of carbon nanotubes from the second dispersed gel.

20. The method of claim 14 , wherein compacting the gel comprises one or more of centrifugation, cooling or adding a co-solvent.

21. A method for separating carbon nanotubes comprising:

adding an inorganic amine based gel to a solution having metallic carbon nanotubes and semiconducting carbon nanotubes to form an expanded inorganic amine based gel;

compacting the expanded inorganic amine based gel to form a compacted gel and a liquid;

removing at least a portion of the liquid;

removing at least a portion of metallic carbon nanotubes from the liquid;

dispersing the compacted gel to form a dispersed gel; and

removing at least a portion of the semiconducting carbon nanotubes from the dispersed gel.

22. The method of claim 21 , wherein removing the metallic carbon nanotubes from the liquid comprises:

adding a second gel to the liquid to form a second expanded gel;

compacting the second expanded gel to form a second compacted gel and a second liquid;

removing at least a portion of the second liquid; and

removing the metallic carbon nanotubes from the second liquid.

23. The method of claim 21 , wherein removing the metallic carbon nanotubes from the liquid comprises:

adding a gelling agent to the liquid to form a second gel;

compacting the second gel to form a second compacted gel and a second liquid;

removing at least a portion of the second liquid; and

removing the metallic carbon nanotubes from the second liquid.

24. The method of claim 21 , wherein removing the semiconducting carbon nanotubes from the dispersed gel comprises:

compacting the dispersed gel to form a second compacted gel and a second liquid;

removing at least a portion the second liquid;

dispersing the second compacted gel to form a second dispersed gel; and

removing the semiconducting carbon nanotubes from the second dispersed gel.