Nanotube solutions with high concentration and low contamination and methods for purifiying nanotube solutions
View Patent ↗Solutions of carbon nanotubes and methods for purifying the solutions are provided. The methods include mixing, for example, at least one complexing agents, at least one ionic species, and/or at least one buffer oxide etch (BOE) with a liquid medium containing carbon nanotubes and different types of contaminants, such as metal impurities, amorphous carbon, and/or silica particles, and performing a filtration process to the liquid medium so as to remove or reduce the contaminants in the liquid medium. As a result, carbon nanotube solutions of low contaminants are produced. In some embodiments, the solutions of this disclosure include a high concentration of carbon nanotubes and are substantially free from metal, amorphous carbon, and/or silica impurities.
1. A method for producing a nanotube solution, comprising:
dispersing functionalized nanotube: materials in a liquid medium in a first operation, wherein at least a portion of said functionalized nanotube materials have surface carboxylic acid functional groups bound with binary metal counter ions;
mixing at least one complexing agent with the liquid medium to complex and remove said binary metal counter ions from said functional groups of said functionalized nanotube materials in a second operation; and
performing a filtration process to the liquid medium so as to remove the complexed binary metal ions in the liquid medium in a third operation;
wherein said second operation is performed subsequent to said first operation and prior to said third operation.
2. The method of claim 1 , further comprising sonicating the liquid medium after mixing the at least one complexing agent with the liquid medium.
3. The method of claim 2 , wherein sonicating the liquid medium comprises sonicating the liquid medium in a chilled sonication bath having a temperature of about 5-25° C.
4. The method of claim 1 , wherein the filtration process is a cross flow filtration process using a filtration membrane having a pore size of about 0.2 to 2 microns.
5. The method of claim 1 , further comprising repeating the cross flow filtration process until concentrations of individual metal impurities are below a predetermined concentration.
6. The method of claim 5 , wherein the predetermined concentration is 25 parts per billion (ppb).
7. The method of claim 1 , further comprising repeating the mixing step and the performing step until a concentration of individual metal impurities is below a predetermined concentration.
8. The method of claim 7 , wherein the predetermined concentration is 25 part per billion.
9. The method of claim 1 , further comprising performing a centrifugation process to the liquid medium so as to remove amorphous carbon and larger particles.
10. The method of claim 1 , wherein mixing the at least one complexing agent with the liquid medium includes adding a chelating agent in the liquid medium.
11. The method of claim 10 , wherein adding the chelating agent comprises adding in the liquid medium one or more of a first amount of ethylenediaminetetraacetic acid (EDTA), a second amount of diethylene triamine pentaacetic acid (DTPA), and a third amount of etidronic acid.
12. A solution, comprising:
a liquid medium; and
a plurality of functionalized nanotubes dispersed in the liquid medium, wherein at least a portion of said functionalized nanotubes have surface carboxylic acid functional groups, whereby binary metal counter ions on said functional groups have been complexed with a complexing agent and removed from the functional groups;
wherein the liquid medium comprises composite molecules of said complexed binary metals complexed with said complexing agent.
13. The solution of claim 12 , wherein the liquid medium is one selected from the group consisting of an aqueous solvent, a non-aqueous solvent, and a mixture of the aqueous solvent and the non-aqueous solvent.
14. The solution of claim 12 , wherein a first concentration of metal impurities is equal to or less than about 25 parts per billion.
15. The solution of claim 12 , wherein the metal ions comprise ionic iron or ionic calcium.
16. The solution of claim 15 , wherein a second concentration of residual complexing agent is equal to or less than 25 parts per billion.
17. The solution of claim 12 , wherein the solution has a nanotube concentration of about 333 mg/L or more.
18. A method for using a nanotube solution, comprising applying the solution of claim 12 on a substrate so as to form a nanotube fabric layer on the substrate.
19. The method of claim 18 , wherein applying the solution comprises spin coating the solution on the substrate.
20. The method of claim 18 , wherein applying the solution comprises spraying the solution on the substrate.