Method for purification of as-produced fullerene nanotubes
This invention relates generally to a fullerene nanotube purification process and more particularly to a purification process that comprises heating the fullerene nanotube-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, fullerene nanotube-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 fullerene nanotube material will be etched to a significant degree. When material having a high proportion of fullerene nanotubes is purified, the preparation produced will be enriched in fullerene nanotubes, so that the fullerene nanotubes are substantially free of other material.
1. A method for purifying a mixture comprising fullerene 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 fullerene 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 fullerene 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, wherein said oxidizing conditions comprise an aqueous solution of an inorganic oxidant;
(b) recovering a product comprising at least about 80% by weight of fullerene nanotubes; and
(c) subjecting the product of step (b) to a saponification treatment.
5. The method of claim 4 wherein said saponification treatment comprises contacting said product with a basic solution.
6. The method of claim 5 wherein said basic solution comprises sodium hydroxide.
7. The method of claim 5 additionally comprising the step of neutralizing the saponified product with an acid.
8. The method of claim 7 wherein said acid is hydrochloric acid.
9. The method of claim 7 additionally comprising the step of recovering a solid product from the saponified, neutralized product.
10. The method of claim 9 wherein said product is recovered by a method selected from the group consisting of filtration, settling by gravity, chemical flocculators, and liquid cycloning.
11. The method of claim 9 wherein said solid product is a paper-like two-dimensional product.
12. The method of claim 11 additionally comprising the step of drying the product.
13. The method of claim 12 wherein said product is dried at about 850° C. in a hydrogen gas atmosphere.