Method for purification of as-produced single-wall carbon nanotubes
This invention relates generally to a single-wall carbon nanotube (SWNT) purification process and more particularly to a purification process that comprises heating the SWNT-containing felt under oxidizing conditions to remove the amorphous carbon deposits and other contaminating materials. In a preferred mode of this purification procedure, the felt is heated in an aqueous solution of an inorganic oxidant, such as nitric acid, a mixture of hydrogen peroxide and sulfuric acid, or a potassium permanganate. Preferably, SWNT-containing felts are refluxed in an aqueous solution of an oxidizing acid at a concentration high enough to etch away amorphous carbon deposits within a practical time frame, but not so high that the single-wall carbon nanotube material will be etched to a significant degree. When material having a high proportion of SWNT is purified, the preparation produced will be enriched in single-wall nanotubes, so that the SWNT are substantially free of other material.
1. A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate, said method comprising the steps of:
(a) heating said mixture under oxidizing conditions sufficient to remove the said amorphous carbon; and
(b) recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes, wherein the product is washed with a solution comprising a surfactant.
2. The method of claim 1 wherein the surfactant is sodium dodecyl sulfate.
3. The method of claim 1 wherein the surfactant is a non-ionic surfactant.
4. A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate, said method comprising the steps of:
(a) heating said mixture under oxidizing conditions sufficient to remove the said amorphous carbon; and
(b) recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes.
5. The method of claim 4 wherein said oxidizing conditions comprise an aqueous solution of an inorganic oxidant.
6. The method of claim 5 wherein said inorganic oxidant is selected from the group consisting of nitric acid, a mixture of sulfuric acid and hydrogen peroxide, potassium permanganate and mixtures thereof.
7. The method of claim 5 wherein said aqueous solution is heated to reflux.
8. The method of claim 5 additionally comprising the step of subjecting the oxidized product of step (b) to a saponification treatment.
9. The method of claim 8 wherein said saponification treatment comprises contacting said product with a basic solution.
10. The method of a claim 9 wherein said basic solution comprises sodium hydroxide.
11. The method of claim 9 additionally comprising the step of neutralizing the saponified product with an acid.
12. The method of claim 11 wherein said acid is hydrochloric acid.
13. The method of claim 11 additionally comprising the step of recovering a solid product from the saponified, neutralized product.
14. The method of claim 13 wherein said product is recovered by a method selected from the group consisting of filtration, settling by gravity, chemical flocculators, and liquid cycloning.
15. The method of claim 13 wherein said solid product is a paper-like two-dimensional product.
16. The method of claim 15 additionally comprising the step of drying the product.
17. The method of claim 16 wherein said product is dried at about 850° C. in a hydrogen gas atmosphere.
18. The method of claim 4 wherein said product comprises at least about 90% by weight of single-wall carbon nanotubes.
19. The method of claim 4 wherein said product comprises at least about 95% by weight of single-wall carbon nanotubes.
20. The method of claim 4 wherein said product comprises at least about 99% by weight of single-wall carbon nanotubes.
21. A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate, said method comprising the steps of:
(a) heating said mixture under oxidizing conditions; and
(b) recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes, wherein the product comprises fullerene torroids.