US 20060104886 A1
A method of providing bulk products of pure-chirality single walled nanotubes having substantially one chirality, and bulk products of pure-chirality nanotubes having at least 50% one chirality. By providing bulk products of pure-chirality nanotubes, the electrical conductivity of the nanotubes can be predetermined and can be made more electrically conductive or more semi-conductive, as desired. Also provided are methods of purifying bulk products of multiple chirality nanotubes into pure-chirality nanotube bulk products, as well as methods of identifying chiralities of bulk product nanotubes. Moreover, fluorocarbon surfactant systems capable of solubilizing nanotubes in perfluorocarbon solvents and facilitating purification and processing are also provided.
1. A bulk product comprising at least 10,000 nanotubes, wherein the nanotubes comprise at least 50% nanotubes of one (n,m) chirality.
2. The bulk product of
3. The bulk product of
a liquid consisting of dispersant, solvent and/or solution; and
nanotubes comprising at least 90% of one (n,m) chirality.
4. The bulk product of
5. The bulk product of
6. The bulk product of
n−m=3×I, wherein I is zero or any positive integer.
7. The bulk product of
n−m=3×I, wherein I is not zero or any positive integer.
8. The bulk product of
9. The bulk product of
10. The bulk product of
11. The bulk product of
12. A method of reducing aggregation of pure-chirality single-walled carbon nanotubes (SWNTs) during storage, comprising:
mixing pure-chirality SWNTs with an inert perfluorocarbon-hydrocarbon hybrid surfactant additive.
13. A method for growing pure-chirality single-walled carbon nanotubes (PC-SWNTs) comprising:
cutting bulk sample/product of PC-SWNT into suitable lengths to provide PC-SWNT seeds for nanotube growth;
adding a metal catalyst to one or both ends of the PC-SWNT seeds;
exposing the PC-SWNT seeds and the metal catalyst to a carbon feedstock at a predetermined pressure and a predetermined temperature; and
growing PC-SWNTs to form bulk quantities of PC-SWNTs with substantially the same chirality as the PC-SWNT seeds.
14. The method of
15. The method of
16. Components for transistors, optical devices, coded-security tagging materials, and/or medical devices and/or applications comprising single-walled carbon nanotubes, wherein the single-walled carbon nanotubes comprise at least 50% nanotubes with the same (n,m) chirality.
17. The components of
18. The components of
19. The components of
20. The components of
This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 60/628,204 entitled PURE-CHIRALITY CARBON NANOTUBES AND METHODS and filed on Nov. 17, 2004, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to pure-chirality carbon nanotubes (PC-SWNT) in industrially relevant quantities, as well as their production and use in solutions and/or dispersions. Additionally, this invention relates to a new composition of carbon nanotubes consisting essentially of pure-chirality carbon nanotubes of substantially one chirality. Also, this invention relates to perfluorocarbon surfactants that can be used for dissolving and dispersing nanotubes in perfluorocarbon solvents.
2. Description of the Related Art
Fullerene nanotubes originated with studies of fullerenes (C60), also known as “buckyballs.” Tubular relatives of the buckyballs are so-called single-walled nanotubes (hereinafter “SWNT” or “nanotubes” generally), which can be formed in tubular or cylindrical form. Nanotubes, generally, can conduct electricity better than copper and can be 100 times stronger than steel at ⅙ the weight.
As conventional nanotubes are made in batch processes, nanotubes are conventionally formed as nanotube batches consisting of mixtures of different chiralities or different lattice orientations. For example, a milligram sized nanotube batch can include many different chirality nanotubes therein. The properties of each nanotube in the batch can have a different chirality than the other nanotubes in the batch, wherein the electrical conductivity and optical properties, as well as other properties of each nanotube would be based upon the particular chirality of the individual nanotube.
Typically, a bulk nanotube batch product contains a ratio of about two-thirds semi-conductive chirality nanotubes to about one-third metallically conductive (i.e., highly conductive) chirality nanotubes. However, as the electrical and mechanical properties of each nanotube depends directly on the chirality of each tube, the specific characterization of the chirality of each nanotube, as well as the separation and/or production of batches or bulk product nanotubes with predetermined chiralities are desired.
For nanotubes, as illustrated
For nanotubes of type (n,m), the conductivity of the nanotube can be determined by the equation:
As illustrated in
Nanotube electrical conductivity, as with any material, is a function of the “fundamental gap,” “gap” or “Egap.” The “gap” is defined as the difference between the HOMO (Highest Occupied Molecular Orbital), which is the highest-energy orbital with one or two electrons, and the LUMO (Lowest Unoccupied Molecular Orbital), which is the lowest-energy orbital with no electrons). For nanotubes, the size of the gap is determined by small variations of the diameter and bonding angle. For example, semi-conductive chirality (hereinafter “semi-conductive”) nanotubes can have a gap on the order of 0.5 eV. On the other hand, highly electrically conductive chirality (hereinafter “metallic”) nanotubes can have a gap on the order of 0.0 eV. The gap can be modeled by the function:
In general, based upon the results mentioned above, while not wishing to be bound by theory, the conductivity is believed to be a function of the wrapping angle and circumference (n,m). Therefore, since the conductivity can be predetermined based upon the chirality of a nanotube, the isolation of macroscopic quantities of a single (n,m) type or pure-chirality nanotubes can be useful for providing predetermined properties on an extremely small scale.
Challenges to pure-chirality nanotube production include: (1) large scale production, and (2) processing issues, such as purification and identification of batch mixed chirality nanotubes into single chirality, or pure chirality nanotubes.
A new composition of matter, single-walled carbon nanotubes of specific helical forms on bulk scale and a method for their identification based on their spectral and other properties is provided herein. The “pure composition of matter” is a single type of chirally oriented (n,m) or “pure-chirality” nanotube, wherein n=1 to 100 and m=1 to 100 and n and m are the same for each (n,m) nanotube in the “pure composition of matter” or “pure-chirality” nanotubes.
Also provided is a bulk product comprising at least 10,000 nanotubes, wherein the nanotubes comprise at least 50% nanotubes of one (n,m) chirality. Also provided is a bulk product comprising at least 1 milligram of at least 50% pure-chirality nanotubes, wherein the at least 1 milligram of nanotubes includes more than 10,000 nanotubes.
Also provided is a method of reducing aggregation of pure-chirality single-walled carbon nanotubes (SWNTs) during storage, comprising: mixing pure-chirality SWNTs with an inert perfluorocarbon-hydrocarbon hybrid surfactant additive.
Also provided is a method for growing pure-chirality single-walled carbon nanotubes (PC-SWNTs) comprising: cutting bulk sample/product of PC-SWNT into suitable lengths to provide PC-SWNT seeds for nanotube growth; adding a metal catalyst to one or both ends of the PC-SWNT seeds; exposing the PC-SWNT seeds and the metal catalyst to a carbon feedstock at a predetermined pressure and a predetermined temperature; and growing PC-SWNTs to form bulk quantities of PC-SWNTs with substantially the same chirality as the PC-SWNT seeds.
Also provided are components for transistors, optical devices, coded-security tagging materials, and/or medical devices and/or applications comprising single-walled carbon nanotubes, wherein the single-walled carbon nanotubes comprise at least 50% nanotubes with the same (n,m) chirality.
As discussed herein, methods for identifying, characterizing and/or forming nanotubes, for example separating and distinguishing between (4,5) SWNTs from (9,10) SWNTs, as well as selecting semi-conductive or metallic SWNTs are provided herein, including one or more of the following:
1. Generating SWNTs using catalytic chemical vapor deposition (CVD) by using a carbon source, wherein a pure-chirality nanotube can be used as a seed for self growth;
2. Using near IR fluorescence to decode the fingerprint of helical nanotubes in order to determine chiralities of a sample, and to establish the purity of a sample of a single type of (n,m) SWNT;
3. Using hybrid perfluorocarbon-hydrocarbon surfactants and using organic-fluorous phase liquid-liquid separations, such as counter-current chromatography; and
4. Using isolated single (n,m) type SWNT to prepare solutions and/or dispersions for production purposes.
Pure-chirality single-walled nanotubes (PC-SWNT) can be uniquely suited to many high-end applications, such as molecular electronics and computing, optical devices (photonic crystals and solar cell materials), electromagnetic interference (EMI) shielding, transistors, such as field effect transistors, coded-security tagging materials, medical devices and/or applications, etc.
As used herein, pure-chirality nanotubes include nanotubes with the same (n,m) chirality as primarily or substantially all of the other nanotubes in a bulk product of nanotubes or a plurality of at least 10,000 nanotubes. For example, in bulk products, nanotubes with at least 50%, 90%, or 98% of nanotubes with the same (n,m) chirality as the (n,m) chirality of the remainder of the bulk, as well as nanotubes which are substantially all one, single (n,m) chirality, are pure-chirality nanotubes and can be used to provide the high-end applications listed above. In addition, individual PC-SWNT molecules can be used as seeds to induce growth of additional PC-SWNT materials of the same chirality.
Methods for identifying, separating and/or characterizing different helical forms of single-walled carbon nanotubes (SWNTs) on a bulk scale are described herein. The methods can provide for identifying, separating, characterizing and/or forming of the different helical forms based on their spectral and other properties.
As identification of different helical forms of carbon nanotubes can be achieved, a pure composition of matter for a number of carbon nanotubes of type (n,m), wherein the helical wrapping angle is determined and the molecules can be made in substantially pure form. The pure (n,m) chirality nanotubes can preferentially have n=1 to 20 and m=1 to 20. It is noted, as mentioned above, that n relates generally to the size of the tube, while m relates generally to the inclination of twist. Larger diameter tubes can also be prepared, purified, and identified with n from 1 to 100 or m from 1 to 100.
An exemplary graphene sheet showing (n,m) numbering for SWNTs is illustrated in
An example of Pure-chirality SWNTs is illustrated in
SWNT can be tubes wrapped from graphite sheets and can be named (n,m), wherein a chiral vector is defined by n and m. The term in common use is chirality which refers to the angle of wrapping. This does not mean left or right handedness in the usual sense of chirality but would be better termed helicity that refers to the pitch or the helix angle of wrapping normal “as-produced” carbon nanotubes.
As illustrated in
In an exemplary embodiment, a bulk sample of HiPCO nanotubes, which contain a mixture of at least 26 different chiralities, can be purified to greater than 50% of a single pure-chirality. This bulk sample of HiPCO nanotubes can be purified to give bulk quantities of single pure-chirality nanotube bulk products. Exemplary pure-chirality nanotube bulk product compositions include those (n,m) chiralities illustrated in
It is noted that these molecular graphs of pure-chirality (n,m) angles of pure-chirality nanotube bulk product compositions are similar to polymeric monomers, wherein the actual nanotubes can be much longer but are composed of repeating units of these twisted pure-chirality (n,m) graphene sheets. It is further noted that the properties of the pure-chirality nanotube bulk product compositions are believed to be directly related to the pure-chirality (n,m) wrapping angles.
While SWNTs are discussed herein, it is noted that double walled or multi-walled tubes can also be subjected to the same methods of identifying, separating, characterizing and/or forming different helical forms. For example, SWNTs of different chiralities can be nested, i.e., a (5,5) SWNT can be nested within a (10,10) SWNT to form a double or nested tube.
Additionally, a chiral surface of known chirality such as crystals of tartaric acid, peptides or amino acids, sugars, etc. can be used to catalyze the formation of one helical form of nanotube. However, it is possible to use chiral surfaces crystals of tartaric acid, peptides or amino acids, sugars, etc to chromatographically separate one helical form of nanotube.
An improved chiral nanotube method can include creating a selective chiral surface in bulk by lithographic techniques. For example, this method could be done by imaging lines on an oriented graphite surface.
Other methods are reported for the purification, solubilization, and formation of pure-chirality single walled nanotubes (SWNT). These methods include the use of antibodies and phage display to create affinity purification methods for pure-chirality SWNT, the use of hybrid perfluorocarbon-hydrocarbon block copolymers, and the use of organic-fluorous phase liquid-liquid separations, such as counter-current chromatography.
1. Generating SWNTs using catalytic chemical vapor deposition (CVD) by using alcohol or other carbon source, wherein a pure-chirality nanotube can be used as a seed for self growth.
SWNTs can be generated by catalytic chemical vapor deposition (CVD) by using alcohol as the carbon source. For example, high-purity SWNTs can be generated at relatively low CVD temperatures from metal catalytic particles supported on zeolite or directly dispersed on flat substrates, such as mesoporous silica, quartz and silicon. In exemplary embodiments, a zeolite support can be provided for bulk generation of SWNTs, wherein direct growth of SWNTs on zeolites as a film on a substrate can be used for optical or semi-conductor applications. For example, low-temperature CVD preparation can be used to synthesize SWNTs near armchair nanotubes. It is believed that the near armchair nanotubes can be produced from low-temperature CVD because of the stability of nanotube cap structure for thin nanotubes. Additionally, the growth process of SWNTs simulated by molecular dynamics method also appears to suggest this chirality-selective generation of SWNTs.
Additionally, ethanol can be used as the alcohol carbon source. By using ethanol for the catalytic CVD, a CVD apparatus can be used to form a vertically aligned SWNTs mat with a couple of microns grown on quartz substrates by employing the activation of catalytic metals.
Approaches to forming SWNTs include CoMoCAT™, a method developed by SouthWest NanoTechnologies, Inc. (SWeNT™) of Norman, Okla. and High-Pressure CO Conversion (HiPCO). However, the SWNTs formed by CoMoCAT and HiPCO provide mixed chirality SWNTs rather than PC-SWNTs. By using these CoMoCAT™ and HiPCO for synthesizing SWNTs, comparisons of the resolved spectral intensities, and thus an example of the selectivity of different SWNT synthesis processes can be compared. Comparing the two approaches, the % of (n,m) chirality compounds are shown in Table 1, wherein the (n,m) map of HiPCO SWNTs is shown in
Individual PC-SWNT molecules can be used as seeds to induce growth of additional PC-SWNT materials of the same chirality, as illustrated in
2. Using near infrared (1R) fluorescence to decode the fingerprint of helical nanotubes in order to determine chiralities of a sample, and to establish the purity of a sample of a single type of (n,m) SWNT.
In addition to generating PC-SWNTs using the methods described above, the chirality distribution of bulk and individual SWNTs can be determined using near infrared (IR) fluorescence to decode the “fingerprint” and thus the chirality of individual nanotubes. Because individual chiralities have individual fluorescence signatures and because each of the individual fluorescence signatures for each type of (n,m) SWNT is known, near IR fluorescence can be utilized to identify individual nanotubes based upon their fingerprints. Thus, this method can be used to determine the exact (n,m) number of a one or more SWNTs, and thus the can be used to determine the precise chiral structure.
As illustrated in
Thus, by utilizing purification techniques, bulk quantities of PC-SWNTs can be attained, wherein the pure-chirality aspect can be confirmed using near IR fluorescence. Therefore, by utilizing the methods described herein, industrially relevant amounts of PC-SWNT compounds can be produced and confirmed.
3. Using hybrid perfluorocarbon-hydrocarbon surfactants and using organic-fluorous phase liquid-liquid separations.
A. Perfluorocarbon Molecules
Perfluorocarbon molecules resemble hydrocarbons but with all hydrogen atoms replaced by fluorine atoms. Despite such a structural resemblance, perfluorocarbons (liquids and gases) include a separate class of compounds due to their unique physical and chemical properties, such as high density, low viscosity, overall inertness, high gas dissolving capability, excellent electrical insulating characteristics and immiscibility with water and most of organic solvents. Several extremely interesting fields of application arise from such properties. In particular, surfactants can be used for dispersion of carbon nanotubes. For example, fluorocarbon solvents can be used, wherein one or more carbon nanotubes can be solubilized within the solvents.
B. Use of Perfluoroalkylated Solvents in Catalysis and Organic Chemistry
Liquid-liquid biphase systems can be used in synthetic, catalytic and separation processes. The formation of a liquid-liquid biphase system is due to significantly different intermolecular forces of two liquids, which can result in limited or negligible solubility of the two solvents in each other. For example, aqueous biphase systems, which employ water as one phase and a hydrocarbon (or organic or other low polarity solvent) as the other, can result in limited solubility of the two solvents in one another.
In an aqueous biphase system, the aqueous phase can be used to recover water-soluble reagents and catalysts, while the organic phase can be used to accumulate products of the reaction that are not water-soluble. Unfortunately, aqueous biphasic processes cannot employ water-sensitive reagents or catalysts. The low solubility of organic substrates in water is also a potential limitation of aqueous biphasic systems in catalysis.
A fluorous biphase system (FBS) can be used to mix otherwise immiscible perfluoroalkyl solvents with water and many common organic solvents (see Table 2 below). See also, Horvath, I. T.; Rabai, J. Science 1994, 266, 72-75, which is incorporated herein by reference in its entirety. These systems include perfluorinated or highly fluorinated fluorous solvent and a second organic or inorganic solvent that is insoluble or poorly soluble in former.
Perfluorocarbons (PFCs) are commercially available at modest cost and are nontoxic and biologically compatible, consistent with the extensive experience with fluorocarbon coatings in cookware and artificial organ implants.
C. Examples of Fluorous Separation
SWNTs can be solubilized in liquid phases for solubilization testing. While water and organic surfactants can be used for solubilization of SWNTs, the presence of water can adversely affect many potential electronic applications of carbon nanotubes and organic solvents can cause SWNTs to aggregate into ropes or bundles. Thus, the use of water and organic surfactants can yield undesirable results. However, dispersion of SWNTs can also be accomplished through the use of organic-fluorous surfactants. For example, organic-fluorous surfactants can be mixed with fluorous solvents, such as C6F14, and SWNTs to form micelles. By utilizing organic-fluorous surfactants to solubilize SWNTs in a fluorous phase and forming micelles, separation of pure-chirality nanotubes from one another can be achieved, as well as chiral separation, as desired. Exemplary organic-fluorous surfactants include hybrid perfluorocarbon-organic surfactants.
An exemplary a surfactant for water/organic dispersions is SDS (Sodium Dodecyl Sulfate), which is “A” as illustrated in
While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention.