WO2010138085A1

WO2010138085A1 - Polymethacrylates with pendant aromatic functional groups for enriching different species of carbon nanotubes

Info

Publication number: WO2010138085A1
Application number: PCT/SG2010/000202
Authority: WO
Inventors: Bee Eng Mary Chan; Xiaoyong Pan; Lain-Jong Li
Original assignee: Nanyang Technological University
Priority date: 2009-05-29
Filing date: 2010-05-31
Publication date: 2010-12-02

Abstract

The present invention is direct to a method of enriching specific species of single-walled carbon nanotubes by subjecting a composition of carbon nanotubes to one or more polymers according to Formula (I). The present invention is also directed to an electrode comprising single-walled carbon nanotube species separated using a method described herein and a field-effect transistor comprising a sem-single-walled carbon nanotube separated using a method described herein.

Description

POLYMETHACRYLATES WITH PENDANT AROMATIC FUNCTIONAL GROUPS FOR ENRICHING DIFFERENT SPECIES OF CARBON NANOTUBES

CROSS-REFERENCE TO RELATED APPLICATIONS [0001 ] This application makes reference to and claims the benefit of priority of an application for "Electronic Property and Diameter Selective Enrichment of Single- Walled Carbon Nanotubes using Polymethacrylates with Pendant Aromatic Functional Groups" filed on May 29, 2009 with the United States Patent and Trademark Office, and there duly assigned serial number 61/182,305. The content of said application filed on May 29, 2009 is incorporated herein by reference for all purposes, including an incorporation of any element or part of the description, claims or drawings not contained herein and referred to in Rule 20.5(a) of the PCT, pursuant to Rule 4.18 of the PCT.

FIELD OF THE INVENTION [0002] The present invention refers to the field of polymer chemistry, in particular chemical methods using polymers for enriching different species of carbon nanotubes.

BACKGROUND OF THE INVENTION

[0003] Since their discovery single-walled carbon nanotubes (SWNTs) have generated much interest as one of the best candidates for electronic devices owing to their exceptional conductivity and field-effect transistor (FET) behavior. However, an unsolved obstacle to the realization of their widespread applications is the control of nanotube electronic properties. [0004] During nanotube growth processes, the wrapping around and joining of a graphene sheet leads to many possible chiralities. With most growth processes, about a third of the nanotube species are metallic (met-SWNTs) and the rest semiconducting (sem-SWNTs).

[0005] For use as the FET active material, only sem-SWNTs are desired. The poor growth selectivity of sem-SWNTs and efficiency of destroying met-SWNTs make efficient post- synthesis separation schemes necessary. Although ac dielectrophoresis, anion exchange chromatography of DNA wrapped carbon nanotubes, and density gradient centrifugation method etc. have been successfully employed in separation of met- and sem- SWNTs, the difficulty of scaling up limits their application. [0006] Chemical methods, which can be classified into covalent and non-covalent functionalization, are more easily scalable and therefore more attractive separation techniques; non-covalent approaches are particularly interesting because they are able to preserve nearly all of the SWNTs' intrinsic properties. The selective precipitation of met- SWNTs by adhesion of small molecules such as octadecylamine and bromine, has been successfully reported but these methods still achieve only limited selectivity. In both cases, selective adsorption occurs when the molecules are adsorbed on SWNTs sidewall via weak linkage similar to hydrogen bonding. Recently, falvin mononucleotide, based on hydrogen bonding, has been demonstrated to be highly effective for chirality-selective enrichment. [0007] Alternatively, SWNTs, considered to be extended π electron systems, can associate strongly with other x electron systems, such as aromatic molecules, via x-x stacking interaction. Experimental results have proved the feasibility of pyrene derivatives or conjugated aromatic polymers to selectively suspend certain SWNTs species. However, the poor dispersion capability of the small neutral pyrene derivative molecules limits their efficiency and the strong 7T-7T interaction between SWNTs and the conjugated aromatic polymers associated with the quite large stacking areas hinders removal of the polymers from the SWNTs after enrichment. In addition, the strong π-π interaction may, to some extent, hinder the adjustment of the conformation of the polymers on the SWNTs sidewall so as to decrease separation efficiency. [0008] Thus it is an object of the present invention to provide alternative methods for enriching different species of SWNTs.

SUMMARY OF THE INVENTION

[0009] In the first aspect the present invention relates to a method of enriching specific species of carbon nanotubes by subjecting a composition of carbon nanotubes to one or more polymers according to Formula (I):

(i) wherein

R¹ is H or CH₃;

R² is selected from hydrogen, an optionally substituted C_1-6 aliphatic group, an optionally substituted C_5-2O aryl group and an optionally substituted C_5-20 heteroaryl group;

R³ is selected from an optionally substituted C_5-20 aryl group and an optionally substituted C_5-20 heteroaryl group;

X is a spacer molecule or a direct bond; n is an integer from 2 to 10000; m is an integer from 0 to 10000; with the proviso that R² is not hydrogen or an optionally substituted C_1-6 aliphatic group in case m = 0.

[0010] In a second aspect the present invention relates to an electrode comprising a carbon nanotube species separated using a polymer according to the invention or separated using a method of the invention.

[0011] In a third aspect the present invention relates to a field-effect transistor comprising a sem-single-walled carbon nanotube separated using a polymer according to the invention or separated using a method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

[0013] Fig. 1 shows chemically separated SWNTs characterized by UV-Vis-NIR absorbance spectra, (a), (c), (e) CoMoCAT produced SWNTs with PNMA, PMMAFA and

PAMMA respectively; (b), (d), (f) HiPco produced SWNTs with PNMA, PMMAFA and

PAMMA respectively. The black SWNT lines are spectra of the "as received" SWNTs dispersed in the D₂O/SDBS solution.

[0014] Fig. 2 shows PLE maps of unseparated SWNTs dispersed with SDBS solution (a, e) and of SWNT precipitates after chemical separation (b-d, f-h): (a) as-received CoMoCAT

SWNTs; (b-d) CoMoCAT SWNT precipitates after separation with (b) PNMA (c) PMMAFA and (d) PAMMA; (e) as-received HiPco SWNTs; (f-h) HiPco SWNT precipitates after separation with (f) PNMA (g) PMMAFA and (h) PAMMA.

[0015] Fig. 3 shows standing time dependence characterization by UV-Vis-NIR absorbance spectra of CoMoCAT produced SWNTs; (a) different standing periods of 0 day, 3 days, 1 week, 2 weeks for PNMA; (b) different standing periods of 0 day, 3 days, 1 week, 2 weeks for PMMAFA.

[0016] Fig. 4 shows electrical transport measurement and devices of chemically separated

CoMoCAT SWNTs; (a) a schematic drawing of electrode configuration; (b) transfer characteristics (/ds-Fgs) of the devices at Fds= 2 V; (c) Current- Voltage characteristics (/ds- Fds) of the device at different Fgs from -10 to 10 V with the step of 4 V from bottom to top.

[0017] Fig. 5 shows the absorption spectra of polymers in DMF.

[0018] Fig. 6 shows PAMMA separated SWNTs characterized by UV-Vis-NIR absorbance spectra.

[0019] Fig. 7 shows electrical transport measurement of as-received CoMoCAT SWNTs; (a) transfer characteristics (/ds-Fgs of the devices at Fds= 2 V); (b) Current- Voltage characteristics (Ids-Vds) of the device at different Fgs from -10 to 10 V with the step of 4 V from bottom to top.

DETAILED DESCRIPTION OF THE PRESENT INVENTION [0020] In a first aspect the present invention refers to a method of enriching specific species of carbon nanotubes by subjecting a composition of carbon nanotubes to one or more polymers according to Formula (I):

wherein

R¹ is H or CH_3; R² is selected from hydrogen, an optionally substituted C_1-6 aliphatic group, an optionally substituted C_5-2O aryl group and an optionally substituted C_5-20 heteroaryl group;

R³ is selected from an optionally substituted C_5-20 aryl group and an optionally substituted C_5-2O heteroaryl group; X is a spacer molecule or a direct bond; n is an integer from 2 to 10000; m is an integer from 0 to 10000; with the proviso that R² is not hydrogen or an optionally substituted C_1-6 aliphatic group in case m = 0. [0021] Generally, a nanostructured material, such as nanotubes, refers to a material with dimensions in the nanometer range. Nanostructured materials can be classified into the following dimensional types: Zero dimensional (OD): nanospherical particles (also called nanoparticles); one dimensional (ID): nanorods, nanowires (also called nano fibers) and nanotubes; and two dimensional (2D): nano flakes, nano flowers, nanodiscs and nanofilms. [0022] A carbon nanotube as used in the present invention is a cylinder of rolled up graphitic sheets. Single-, double- and multi-walled carbon nanotubes are known and can equally be used in the method of the present invention. The carbon nanotubes may be of any desired length, such as in the range from about 0.1 nm to about 10 μm, such as about 1 nm to about 5 μm or 10 nm to about 1 μm. In one embodiment the carbon nanotubes may be at least 1 μm or at least 2 μm or between about 0.5 μm and about 1.5 μm or between about 1 μm and about 5 μm. The conductivity of the carbon nanotubes used may be freely selected according to any specific requirements. Depending on the arrangement of the carbon hexagon rings along the surface of the nanotubes, carbon nanotubes can be metallic or semiconducting. Any such carbon nanotubes may be used in a method according to the present invention. [0023] Carbon nanotubes exist in different forms, such as single- walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), multi-walled carbon nanotubes (MWNT), or modified multi-walled carbon nanotubes.

[0024] A single-walled carbon nanotube (SWNT) is a seamless cylinder formed from one graphite layer. For example, carbon nanotubes can be described as a graphite plane (so called graphene) sheet rolled into a hollow cylindrical shape so that the structure is one-dimensional with axial symmetry, and in general exhibiting a spiral conformation, called chirality. A single-wall nanotube can be defined by a cylindrical sheet with a diameter of about 0.7 to about 20 nm, such as about 1 to about 20 run.

[0025] Double-walled carbon nanotubes (DWNT) consist of two layers of graphite sheets rolled in on to form a tube shape. The two layers of graphite sheets can form a concentric cylinder. The nanotubes are considered as a cross between SWNT and MWNT as they can have the electronic properties of the SWNT, and the mechanical strength of MWNT. [0026] Multi-walled carbon nanotubes (MWNT) consist of multiple layers of graphite rolled in on to form a tube shape. The nanotubes can also exist in forms in which they have hydrophilic groups such as hydroxyl group, pyrenes, esters, thiols, amines, a carboxyl group and mixtures thereof on their surface.

[0027] Carbon nanotubes may be prepared by several different methods known in the art. For example, SWNT may be grown by carbon monoxide (CO) disproportionation (decomposition into C and CO₂) at 700-950 ⁰C in flow of pure CO at a total pressure that typically ranges from 1 to 10 atm using a catalyst comprising cobalt (Co) and molybdenum (Mo) on a mesoporous silica support, leading to so-called CoMoCAT SWNTs. Using this method, diameter control of SWNTs can be achieved. Another possibility is the synthesis using high pressure carbon monoxide (HiPCo) leading to so-called HiPco SWNTs. Generally, in a HiPco method, metal catalyst is formed in situ when Fe(CO)₅ or Ni(CO)₄ is injected into a reactor along with a stream of CO gas at a temperature range of about 900- 1100 °C at a pressure of about 30 to 50 atm. The metal catalyst formed can be in the form of nanometer sized particles. HiPCo SWNTs are produced following the disproportionation of CO by the metal catalyst particles. In the present invention all types of SWNTs may be used for the enrichment process. In an exemplary embodiment CoMoCAT and HiPco SWNTs were used to demonstrate the usability of the polymers described herein. [0028] The polymers according to Formula (I) of the present invention belong to the general group of poly(meth)acrylates with pendant aromatic functional groups. This means that the polymer backbone is composed of methacrylate or methacrylate and acrylate monomers, wherein aromatic side-groups are attached to the polymer backbone. [0029] In the above Formula (I), R¹ may be H or CH₃. In one embodiment of the invention, R¹ is CH₃ constituting a polymethacrylate polymer.

[0030] R² may be an optionally substituted Cj_-6 aliphatic group. The term "aliphatic", alone or in combination, refers to a straight chain or branched chain hydrocarbon comprising at least one carbon atom. Aliphatics include alkyls, alkenyls, and alkynyls. Aliphatics include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert.-butyl, pentyl, hexyl, ethenyl, propenyl, butenyl, ethynyl, butynyl, propynyl, and the like, each of which may be optionally substituted. The term "alkyl", alone or in combination, refers to a fully saturated aliphatic hydrocarbon. In certain embodiments, an alkyl comprises 1 to 6 carbon atoms, for example 1 to 4 carbon atoms or 1 to 2 carbon atoms, wherein (whenever it appears herein in any of the definitions given below) a numerical range, such as "1 to 6" or "Cr₆", refers to each integer in the given range, e.g. "Cr₆ alkyl" means that an alkyl group comprises only 1 carbon atom, or 2 carbon atoms, 3 carbon atoms, 4 carbon atoms, 5 carbon atoms up to and including 6 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, tert- amyl, pentyl, hexyl and the like. In one embodiment of the present invention the aliphatic group is methyl. [0031] R² and R³ may independently be a Cs_-20 aryl group. The term "aryl" refers to an aromatic ring wherein each of the atoms forming the ring is a carbon atom. The term "aromatic" refers to a group comprising a covalently closed planar ring having a delocalized [TΓ] -electron system comprising 4n+2 [π] electrons, where n is an integer. Aryl rings may be formed by 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. Aryl groups may be optionally substituted. Examples of aryl groups include, but are not limited to phenyl, naphthalenyl, phenanthrenyl, anthracenyl, tetralinyl, fluorenyl, indenyl, and indanyl. In certain embodiments, an aryl group is substituted at one or more of the para, meta, and/or ortho positions. Examples of aryl groups comprising substitutions include, but are not limited to, 3-halophenyl, 4-halophenyl, 3-hydroxyphenyl, 4-hydroxyphenyl, 3-aminophenyl, 4- aminophenyl, 3-methylphenyl, 4-methylphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 4- trifluoromethoxyphenyl, 3-cyanophenyl, 4-cyanophenyl, dimethylphenyl, naphthyl, hydroxynaphthyl, hydroxymethylphenyl, (trifluoromethyl)phenyl, alkoxyphenyl, 4- morpholin-4-ylphenyl, 4-pyrrolidin-l-ylphenyl, 4-pyrazolylphenyl, 4-triazolylphenyl, and 4- (2-oxopyrrolidin-l- yl)phenyl. In one embodiment of the present invention the C_5-20 aryl group is phenyl, naphthalenyl, phenanthrenyl, anthracenyl, tetralinyl, fluorenyl, indenyl, or indanyl, for example napthalenyl, phenanthrenyl or anthracenyl.

[0032] R² and R³ may independently be a C_5-20 heteroaryl group. The term "heteroaryl" refers to an aromatic heterocycle. Heteroaryl rings may be formed by 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 atoms. Heteroaryls may be optionally substituted. Examples of heteroaryl groups include, but are not limited to, aromatic C_3-8 heterocyclic groups comprising one oxygen or sulfur atom or up to four nitrogen atoms, or a combination of one oxygen or sulfur atom and up to two nitrogen atoms. Examples of heteroaryl groups may include, but are not limited to, unsubstituted and mono- or di-substituted derivatives of furan, benzofuran, thiophene, benzothiophene, pyrrole, pyridine, indole, oxazole, benzoxazole, isoxazole, benzisoxazole, thiazole, benzothiazole, isothiazole, imidazole, benzimidazole, pyrazole, indazole, tetrazole, quinoline, isoquinoline, pyridazine, pyrimidine, purine and pyrazine, furazan, 1,2,3-oxadiazole, 1,2,3-thiadiazole, 1 ,2,4-thiadiazole, triazole, benzo triazole, pteridine, phenoxazole, oxadiazole, benzopyrazole, quinolizine, cinnoline, phthalazine, quinazoline, quinoxaline, and fluorescein.

[0033] In case m = 0, then R² is not hydrogen or an optionally substituted C_1-6 aliphatic group so that a polymethacrylate backbone is formed. [0034] In the above Formula (I), X is a spacer molecule or a direct bond. The term "spacer" refers to an atom or group of atoms that separate two or more groups from one another by a desired number of atoms. For example, in certain embodiments, it may be desirable to separate two or more groups by one, two, three, four, five, six, or more than six atoms. In such embodiments, any atom or group of atoms may be used to separate those groups by the desired number of atoms. In one embodiment of the present invention, the spacer group is a C_1-6 aliphatic group, for example -CH₂- or -CH₂CH₂-.

[0035] The term "optionally substituted" refers to a group in which none, one, or more than one of the hydrogen atoms has been replaced with one or more group(s) are independently selected from a C_1-6 aliphatic group, hydroxy, alkoxy, cyano, F, Cl, Br, I, carbonyl, thiocarbonyl, nitro, silyl, and amino, including mono- and di-substituted amino groups.

[0036] n and m are integers, n may be from about 2 to about 10000, such as about 10 to about 10000, about 25 to about 10000, about 100 to about 10000 or about 500 to about 10000. In one embodiment, n may be from about 10 to about 500 or about 10 to about 250 or about 10 to about 100 or about 10 to about 50. m may be from 0 to about 10000, such as about 10 to about 10000, about 25 to about 10000, about 100 to 10000 or about 500 to about 10000. In one embodiment, n may be from about 10 to about 500 or about 10 to about 250 or about 10 to about 100 or about 10 to about 50. In one embodiment m may be 0. [0037] In one embodiment of the present invention R¹ is methyl and R² is napthalenyl or anthracenyl. In one further embodiment of the present invention R¹ is methyl; R² is napthalenyl or anthracenyl and X is a direct bond or -CH₂-. In a still further embodiment of the present invention, R¹ is methyl; R² is napthalenyl or anthracenyl; X is a direct bond or

-CH₂- and m is 0, such as

(designated poly(2-naphthylmethacrylate; PNMA)

_or

(designated poly(9-anthracenylmethyl methacrylate; PAMMA).

[0038] In one embodiment, when PNMA is used, n may be from about 20 to about 80, or from about 30 to 50 or about 40, and m is 0. In another embodiment, when PAMMA is used, n may be from about 5 to about 50, or from 5 to 25, or about 15, and m is 0.

[0039] In a further embodiment of the present invention, R¹ is CH₃ and R² is an optionally substituted C_1-6 aliphatic group. In a further embodiment of the present invention, R¹ is CH₃;

R² is CH₃; X is a direct bond and R³ is napthalenyl, anthracenyl or fluorescein, such as

(designated poly(methylmethacrylate-co- fiuorescein-o-acrylate; PMMAFA). [0040] In one embodiment, when PMMAFA is used, n may be from about 20 to, about 90, or from about 30 to about 70, or about 45, and m may be from about 5 to about 50, or from about 5 to about 30, or about 15.

[0041] The method of the present invention is for enriching specific species of carbon nanotubes. "Enriching" in this respect means that the different nanotubes which may be present in the mixture are separated or purified down to a unique species with specific electrical properties from a given nanotube material. The method of the present invention enables the enrichment of nano tubes according to their electronic properties and/or diameter. In this respect, the term "a composition of carbon nanotubes" as used in the present invention means that at least one carbon nanotube or two or more different carbon nanotubes are present in the system. In one embodiment of the present invention single-walled carbon nanotubes (SWNT) are enriched.

[0042] The arrangement of the carbon hexagon rings can be characterized by the chiral vector of the carbon nanotubes. Chiral vector is a two dimensional vector (p, q) that is commonly used to describe the geometry of carbon nanotubes (see for example, Wildoer J.W.G. et al, Nature 391, 6662, 59-62 (1998)). The values of p and q determine the chirality, or "twist" of the nanotube. The chirality in turn affects properties such as conductance, density, and lattice structure of the carbon nanotubes. Depending on the arrangement of the carbon hexagon rings along the surface of the nanotube as characterized by its chiral vector, carbon nanotubes can be metallic or semiconducting. For example, SWNTs can be metallic when p - q = 3r, where r is an integer, and can be semiconducting otherwise. Metallic SWNTs refer to carbon nanotubes with non-zero density of states (DOS) at its Fermi level. The term "density of states" refers to the number of states at an energy level that are available to be occupied, and the term "Fermi level" refers to an energy level with a probability of 50 percent for existence of an electron. Therefore, a SWNT can be metallic when the DOS value at its Fermi level is not zero. Semiconducting SWNTs refer to carbon nanotubes with varying band gaps, wherein the term "band gap" refers to difference in energy between the valance band and the conduction band of a material. Such carbon nanotubes can be separated or enriched by a method according to the present invention. Thus, the method of the present invention allows the enrichment according to electronic properties in order to separate met- SWNT (metallic) from sem-SWNT (semiconducting). [0043] The enrichment of the carbon nanotubes or SWNT according to the inventive method may also be carried out by diameter. This means, that the respective nanotubes are enriched or separated depending on their particular diameter. For example, it is possible with the method of the present invention to enrich SWNT having a diameter below about 1 nm from SWNT having a diameter above 1 nm. In one embodiment SWNT above and below about 2 nm, above and below about 3 nm, above and below about 4 nm, above and below about 5 nm, above and below about 6 ran, above and below about 7 ran, above and below about 8 ran, above and below about 9 nm, above and below about 10 ran, above and below about 12 nm, above and below about 14 nm, above and below about 16 nm, above and below about 18 nm, or above and below about 20 nm may be enriched In one embodiment, SWNT having a diameter ranging from about 0.7 nm to about 1 nm is enriched. [0044] In order to achieve the desired enrichment the composition with the carbon nanotubes is mixed with a liquid composition of a polymer according to the invention. The resulting mixture is subsequently incubated. During incubation a supernatant and a precipitate is formed which may be separated subsequently.

[0045] The mixing can be carried out by standard mixing methods known in the art. Any suitable mixing device may be used, wherein the invention is not limited to a particular device. In one embodiment of the invention the mixing may be carried out, but is not limited to, by sonicating or stirring or shaking the mixture. The mixing time may be chosen according to the used nanotube mixture and/or the used polymer. In one embodiment of the present invention the mixing is carried out for about 1 to about 60 minutes, such as about 1 to about 30 minutes or about 1 to about 10 minutes. For example, the mixing time may be, but is not limited to, about 1 min, about 2 min, about 3 min, about 4 min, about 5 min, about 6 min, about 7 min, about 8 min, about 9 min, about 10 min, about 15 min, about 20 min, about 25 min, about 30 min, about 35 min, about 40 min, about 45 min, about 50 min, about 55 min, or about 60 min. AU mentioned time specifications may be the lower or upper limit of a respective time range. In embodiments where sonication is used as the mixing method, wattage on the sonicator can additionally be varied to achieve a specific level of mixing. A person skilled in the art is able to choose and determine the appropriate mixing time and settings based on the mixing method used to derive a specific weight enrichment of the carbon nanotubes or SWNT. [0046] The liquid composition of the polymer is made by dissolving the respective polymer in a solvent. Any solvent suitable for dissolving the polymer or a mixture thereof is encompassed by the present invention. Any desired liquid can be employed, whether an aqueous or non aqueous liquid, an organic liquid (solvent), or a nonpolar aprotic, nonpolar protic, dipolar protic, dipolar aprotic, or an ionic liquid. Examples of nonpolar aprotic liquids include, but are not limited to, hexane, heptane, cyclohexane, benzene, toluene, pyridine, dichloromethane, chloroform (CHCl₃), carbon tetrachloride, carbon disulfide, tetrahydrofuran (THF), dioxane, diethyl ether, diisopropylether, ethylene glycol monobutyl ether or tetrahydrofuran. Examples of dipolar aprotic liquids are methyl ethyl ketone, methyl isobutyl ketone, acetone, cyclohexanone, ethyl acetate, isobutyl isobutyrate, ethylene glycol diacetate, dimethylformamide (DMF), acetonitrile (CH₃CN), N,N-dimethyl acetamide, nitromethane, acetonitrile, N-methylpyrrolidone, and dimethylsulfoxide. Examples of polar protic liquids are water, methanol, ethanol, butyl alcohol, formic acid, dimethylarsinic acid [(CH₃)₂AsO(OH)], N,N-dimethyl-formamide, N,N-diisopropylethylamine, or chlorophenol. Examples of nonpolar protic liquids are acetic acid, tert.-butyl alcohol, phenol, cyclohexanol, or aniline. Two illustrative examples of ionic liquids are 1,3-dialkylimidazolium-tetrafluoro- borates and 1,3-dialkylimidazolium-hexafluoroborates. In some embodiments the liquid is a polar ionic liquid. Examples of a polar ionic liquid include, but are not limited to, l-ethyl-3- methylimidazolium tetrafluoroborate, N-butyl-4-methylpyridinium tetrafluoroborate, 1,3- dialkylimidazolium-tetrafluoroborate, 1 ,3-dialkylimidazolium-hexafluoroborate, 1 -ethyl-3- methylimidazolium bis(pentafluoroethyl)phosphinate, l-butyl-3 -methylimidazolium tetra- kis(3,5-bis(trifluoromethylphenyl)borate, tetrabutyl-ammonium bis(trifluoromethyl)imide, ethyl-3-methylimidazolium trifluoromethanesulfonate, l-butyl-3 -methylimidazolium methyl- sulfate, l-n-butyl-3 -methylimidazolium ([bmim]) octylsulfate, and l-n-butyl-3- methylimidazolium tetrafluoroborate. Examples of a non-polar liquid include, but are not limited to mineral oil, hexane, heptane, cyclohexane, benzene, toluene, dichloromethane, chloroform, carbon tetrachloride, carbon disulfide, dioxane, diethyl ether, diisopropylether, methyl propyl ketone, methyl isoamyl ketone, methyl isobutyl ketone, cyclohexanone, isobutyl isobutyrate, ethylene glycol diacetate, and a non-polar ionic liquid. Examples of a non-polar ionic liquid include, but are not limited to, 1 -ethyl-3-methylimidazolium bis[(tri- fluoromethyl)sulfonyl] amide bis(triflyl)amide, 1 -ethyl-3-methylimidazolium bis[(trifiuoro- methyl)sulfonyl] amide trifluoroacetate, l-butyl-3 -methylimidazolium hexafluorophosphate, 1 -hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1 -butyl-3-methylimidazol- ium bis(trifluoromethylsulfonyl)imide, trihexyl(tetradecyl)phosphonium bis[oxalato(2- )]borate, 1-hexy 1-3 -methyl imidazolium tris(pentafiuoroethyl)trifluorophosphate, l-butyl-3- methyl-imidazolium hexafluorophosphate, tris(pentafluoroethyl)trifluorophosphate, trihexyl- (tetradecyl)phosphonium, N"-ethyl-N,N,N',N'-tetramethylguanidinium, 1 -butyl- 1 -methyl pyrrolidinium tris(pentafluoroethyl) trifluorophosphate, 1 -butyl- 1 -methyl pyrrolidinium bis- (trifluoromethylsulfonyl) imide, l-butyl-3 -methyl imidazolium hexafluorophosphate, 1 -ethyl- 3-methylimidazolium bis(trifluoromethylsulfonyl)imide and l-n-butyl-3 -methylimidazolium. In one embodiment of the present invention the solvent may be selected from DMF, CHCl₃, CH₃CN, THF and toluene.

[0047] After mixing the resulting mixture is incubated for a specific period of time. Incubation in this respect means letting the mixture stand for a particular period of time. Standing time is a factor influencing the efficiency of enrichment. It has been shown that longer standing times result in higher selectivity. In one embodiment of the present invention the standing time may be between about 0 days and about 4 weeks, such as between about 1 day and about 3 weeks or between about 2 days and about 2 weeks. In one embodiment the standing time is at least about 1 day, at least about 2 days, at least about 3 days, at least about 4 days, at least about 5 days, at least about 6 days, at least about 1 week, at least about 2 weeks, at least about 3 weeks, or at least about 4 weeks. AU the afore-mentioned time specification may constitute the lower or upper limit of possible time ranges. Without to be bound by any theory, it is assumed that the adjustment of the polymer conformation after mixing is necessary for the mixture to form some stable wrapping states. [0048] After incubation the resulting mixture is present in the form of a supernatant and a precipitated solid. Both the supernatant and the precipitate contain the polymer-nanotube complex which has been formed during the preceding procedure. In the following about 50% of the supernatant are separated from the mixture, such as about 60%, about 70%, about 80% or about 90%. Also, in the following about 50% of the precipitate are separated from the mixture, such as about 60%, about 70%, about 80% or about 90%.

[0049] In one embodiment of the invention the mixture is centrifugated before separating the supernatant and the precipitate formed during incubation. The centrifugation may be carried out with generally used conditions. For example, the centrifugation may be carried out, but is not limited to, at least about 5 minutes, at least about 10 minutes, at least about 15 minutes, at least about 20 minutes, at least about 25 minutes, at least about 30 minutes, at least about 35 minutes, at least about 40 minutes, at least about 45 minutes, at least about 50 minutes, or at least about 55 minutes. In one embodiment the centrifugation is carried out for 1 hour. The centrifugation speed may be, but is not limited to, about 10 Kg, about 20 Kg, about 30 Kg or more. [0050] In one embodiment both the supernatant and the precipitate are thoroughly washed with an organic solvent. The organic solvent may be any solvent already mentioned above and which may be suitable for the respective nanotube. In one embodiment the solvent may be toluene.

[0051] The method of the present invention enables the enrichment or separation of specific species of carbon nano tubes. Depending on the polymer used in the inventive process, different carbon nanotubes can be enriched. Thus, modification, in particular of the aromatic moiety of the polymer may be used to adapt the enrichment as suitable for the respective nanotubes. In one embodiment of the present invention, the polymers referred to herein, such as the three polymethacrylates (specifically PNMA, PAMMA and PMMAFA) with pendant aromatic functional groups have been successfully employed in the separation of SWNTs according to their electronic properties (met-lsem-) and diameters and highly effective enrichment has been achieved. Optical absorbance spectra and photoluminescence excitation maps indicate that this family of polymers has strong selectivity towards certain SWNTs species with specific electronic properties and diameters and the species selectivity is highly sensitive to the polymer structures. For example, PMMAFA and PAMMA preferentially disperse semiconducting CoMoCAT SWNTs but they disperse metallic HiP co SWNTs. PNMA preferentially disperses metallic CoMoCAT and HiPCo SWNTs. All three polymers preferentially disperse small diameter CoMoCAT and HiPCo SWNTs. [0052] The carbon nanotube species, such as SWNTs enriched according to the present invention may be used as electrode material for forming an electrode. For example, the electrodes manufactured using those enriched SWNTs can be used for batteries, such as metal-air batteries. Examples for metal-air batteries include a lithium, aluminium, carbon, zinc-air battery in which at least one electrode is made of carbon. They can also be used for fuel cells. In case they are used in fuel cells catalytic noble metal materials in particulate form can be added to the electrode. [0053] The single-walled carbon nanotube of the invention may also be used as field- effect transistor (FET). Basically, the FET structure involves two metal electrodes designated as "source" and "drain" connected by a semiconducting channel. In conventional devices, the channel is made of Si. In the FET of the present invention the channel is replaced by a sem- single-walled carbon nanotube according to the invention. [0054] The single-walled carbon nanotube of the invention may also be used as an optical or an optoelectronic device, such as transistors, memory devices and optoelectronic couplers. [0055] The invention illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms "comprising", "including", "containing", etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied therein herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

[0056] The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0057] Other embodiments are within the following claims and non- limiting examples. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

EXPERIMENTAL SECTION

[0058] Materials

[0059] CoMoCAT and HiPco SWNTs were purchased from SouthWest Nanotechnologies, Inc. and Carbon Nanotechnologies Inc. respectively, and were used as received. The polymers, poly(2-naphthylmethacrylate) (PNMA), poly(9- anthracenylmethylmethacrylate) (PAMMA) and poly(methylmethacrylate-co-fluorescein-o- acrylate) (PMMAFA) as well as sodium dodecylbenzenesulfonic acid (SDBS) were obtained from Aldrich and were used as received. The solvents, N,N-dimethylformamide (DMF), toluene and deuterium oxide (D₂O), were purchased from Sino Chemical Company Pte. Ltd and were used without further purification except as specified elsewhere. [0060] SWNTs separation with polymers

[0061] Separation was carried out by suspending 2 mg of as-received SWNTs in 10 ml solution of polymer in DMF. After sonication for 10 minutes at 175 W, standing for 2 weeks followed by centrifugation at 20 Kg for 1 hour, both the upper 90% of the supernatant and the precipitate were collected for further experiments. The standing periods between the sonication and centrifugation were set to be 2 weeks for all separations to remove standing time as a variable affecting the measured enrichment. UV-Vis-NIR absorbance spectra of SWNTs separated in the supernatant solutions were obtained directly from the supernatant except for PAMMA in which absorbance bands of polymer and SWNTs badly overlap (Fig. 5). Polymer-wrapped precipitated SWNTs were thoroughly washed with toluene. The clean SWNTs powders were redispersed in 1% SDBS solution and then centrifuged (at 57 Kg) prior to UV-VIS-NIR and photo luminescence spectroscopic scans. Polymer-dispersed supernatant SWNTs were thoroughly washed with toluene to remove polymer before application to device fabrication. [0062] Characterization Techniques

[0063] UV-Vis-NIR spectra of SWNTs solutions were recorded on a Cary 5000 UV-Vis- NIR spectrophotometer. 0.1% polymer in DMF was used as reference for background subtraction for PNMA- and PMMAFA- suspended supernatant SWNTs; 1% SBDS in D₂O was used for other supernatant SWNTs scans. No background subtraction of polymer absorptions was applied for the UV- Vis spectra of the precipitates because the toluene washing strongly suppressed these polymers' absorption features (Fig. 6). Some spectra have been magnified for comparison but it will not change the content ratio of different species. (In the spectra, the sharp edge at almost exactly 800 nm is due to the change of the laser source during data collection.)

[0064] Photoluminescence excitation (PLE) measurements of the SDBS re-suspended precipitates were performed on a Jobin-Yvon Nanolog-3 spectra fluorometer with an InGaAs detector. [0065] Back-gated SWNT-FETs were fabricated on heavily doped p-type silicon wafers capped with 300nm thermally grown silicon dioxide layers. The source and drain electrodes were made of IOnm thick Ti and 60nm thick Au by photolithography. Heavily doped p-type silicon was used as the back gate. The channel width and length were lOOμm and 20μm respectively. AU electrical measurements were carried out in ambient conditions using a Keithley semiconductor parameter analyzer Model 4200-SCS. [0066] Example 1: UV-Vis-NIR spectra [0067] UV-Vis-NIR absorption spectra of post-separation suspended and precipitated SWNTs for all polymer/SWNTs combinations are shown in Figure 1. Also shown are the absorbance spectra of the SWNTs dispersed in D₂O solution using the ionic SDBS surfactant, which is assumed to disperse SWNTs without any preferentiality. [0068] The optical absorbance spectra can be used to estimate the contents of different SWNTs species since the peak intensity is proportional to the species concentration, irregardless whether the SWNTs are individually dispersed or bundled. The optical absorption spectra in this work consist of spectroscopic signature of the interband electronic transitions corresponding to M₁₁ band of /net-SWNTs as well as Eu and E₂₂ bands of sem- SWNTs. [0069] All separations were performed with the same process parameters, including sonication power and time, concentration of polymer solution, and centrifugation conditions. Figure 5 shows the absorption spectra of the neat polymers and only PAMMA has absorbance in the region that will overlap with absorbance of SWNTs. With non- overlapping PNMA and PMMAFA, SWNTs suspended in the supernatant solution were wrapped with polymer but the polymers were not removed prior to spectroscopy (Fig Ia, b, c, d). For the separation agent PAMMA, SWNTs in the supernatant solutions (Fig Ie, f) were thoroughly washed with toluene to remove polymer before resuspension for characterization. [0070] Figure la,c,e show the absorbance spectra of CoMoCAT SWNTs (supernatant suspended, resuspended precipitate, and reference unseparated in surfactant solution) for each of the tested polymers. The CoMoCAT SWNTs have pronounced characteristic absorption bands from 350 to 510nm for metallic species and from 510 to 1350nm for semiconducting species. The bands at 800-1350nm and 51O-8OOnm can be assigned to S₁₁ and S₂₂, respectively. The sharp absorbances at about 576nm and lOOOnm are the fingerprints of the E₂₂ and En interband transitions of the (6,5) nanotube species. The Mπ/S₂₂ peak intensity ratio is used as the criterion to estimate the relative content of the met-SWNTs and the se/w-SWNTs since S₂₂ is less susceptible to environmental doping effects.

[0071 ] Figure 1 a shows that PNMA preferentially suspends met-SWNTs; the supernatant spectrum has a large M₁₁ peak while the S₂₂ band is dramatically suppressed with respect to the reference spectrum (as-received CoMoCAT SWNTs in SDBS solution). Correspondingly, the wet-SWNTs feature is more suppressed in the PNMA precipitate spectrum than are the sem-SWNTs features. Similar qualitative analysis of the spectra in Figures Ic and Ie indicates that PMMAFA and PAMMA preferentially suspend sem- SWNTs [0072] Another obvious feature of the enriched supernatant solution, especially for PNMA and PMMAFA (Fig. Ia, c), in contrast to the as-received CoMoCAT, is the red shift of the peal wavelengths, especially for the E₁₁ peak at -lOOOnm. For PAMMA (Fig. Ie), with removal of polymer, the tendency is reversed and substantially blue shift of the peaks of supernatant can be observed; before PAMMA removal, red shift of peak wavelengths in the supernatant solution (Fig. 6) can also clearly be seen. The red shift can be indicative of large diameter selectivity or the influence of dispersion media environments. From the photo luminescence results discussed below, the larger diameter selectivity factor can be eliminated. [0073] Figure lb,d,f show the absorbance spectra of polymer-suspended, precipitated, and unseparated HiPco SWNTs. Again, with PNMA and PMMAFA, UV-Vis-NIR absorbance spectrum of SWNTs suspended in the supernatant solutions (in Fig 1 f) was obtained without removal of polymer but PAMMA with thorough washing with plenty of toluene to eliminate the presence of polymer absorption features. The diagnostic features in these spectra are the first interband transitions for /wet-SWNTs, M₁₁, which appear between 400 and 550nm and the first and second interband transitions for sem-SWNTs, S₁₁ and S₂₂, which show characteristic absorption peaks from 900 to 1 800nm and from 550 to 900nm, respectively.

[0074] The M₁₁ features are superposed on a background that increases rapidly at shorter wavelength, but it is apparent from inspection of Figures Ib, Id and If that the amplitude of the Mn "wiggles" is substantially larger in the spectra of the supernatant solutions than in the spectra of the precipitates or the unseparated HiPCo SWNTs. The S₂₂ features are not enhanced as much, indicating (in this qualitative analysis) an increase in Mπ/S₂₂ which is a signal of enrichment in met-SWNTs. AU features are suppressed in the precipitates and it is hard to qualitatively assess the band ratios, but it follows that the precipitates should be enriched in sem-SWNTs since the supernatant is enriched in met-SWNTs. [0075] Again, there is evidence of a red- ward shift in peak wavelength, especially for the S₁₁ and S₂₂ peaks, in the precipitate spectra. This may be due to the change of the relative contents of the different diameter semiconducting species since different diameter species show their characteristic absorbance bands at different wavelengths; such a change is confirmed in the photo luminescence excitation maps, which are discussed below. [0076] Example 2: Photoluminescence-Excitation (PLE) [0077] Photo luminescence excitation maps (Figure 2) were used to characterize the (n,m) distributions of semiconducting chiral species of SWNTs in the washed precipitates. As-received SWNTs dispersed in 1% SDBS solution in D₂O were also studied as a reference. No photoluminescence map of the supernatant solution was employed in the comparison in order to avoid the effects of the change of the microenvironment (i.e., due to interaction with the polymer dispersants) on the photoluminescence wavelengths and quantum yields, which influence the determination of the contents of semiconducting species.

[0078] As-received CoMoCAT SWNTs (Fig 2a) are dominated by the (6,5) and (8,4) species. Also present with reasonably strong signals are the (8,3), (7,5) and (7,6) species. The polymer-separated precipitates (Fig 2b,c,d) exhibit similar modifications in their chiral distributions; the (6,5), (7,5) and (8,3) species PLE peaks are suppressed by all three polymers, indicating preferential suspension of these (with respect to (7,6) and (8,4)) in the supernatant solution. The preferentially suspended species (8,3), (7,5), (6,5) are somewhat smaller (with cftube = 0.782nm, 0.829 nm and 0.757nm respectively) than the precipitate species (7,6) and (8,4) (dtube = 0.895 nm and 0.840 nm), which suggests a smaller size preference for dispersion by the polymers. However, the band gap Ei₁ correlates closely (inversely) with the tube diameter, so preferential interaction between the polymers and SWNTs that is produced by a process related to the SWNTs' electronic structure is also compatible with our data. The redshift observed with PNMA- and PMMAF A-suspended CoMoCAT SWNTs UV-Vis-NIR spectra (Fig. 1 a, c - supernatant) should then be attributed to the presence of unwashed polymer in the supernatant. [0079] The inconspicuous factor which will possibly lead us to the misinterpretation of the PLE maps is the energy transfer from smaller tubes (high energy peak) to larger tubes (low energy peaks), the involvement of which we have tentatively eliminated in the estimation of the relative contents of different species since the dispersion media and the solution preparation conditions, especially the concentration of SWNTs solutions and centrifugation g forces, were kept approximately the same for all PLE solutions. [0080] Figure 2e,f,g,h show the photoluminescence spectra of the as-received HiPco SWNTs and the semiconductor enriched precipitates which were obtained via centrifugation following dispersion in solutions of different polymers. The labeled chiralities in Figure 2e for the SDBS solution in D₂O represent a typical species distribution of HiPco SWNTs. The PLE maps of the SWNTs precipitates made with the polymers of the present invention are manifestly radically different, with obvious substantial reduction of emission shortward of about 1150nm. The suppressed species (such as (6,5), (7,5), (7,6), (8,3), (8,4), (9,4), (10,2)), which have been preferentially suspended in the supernatant solution, all have diameters on the order of or smaller than about 0.916nm, while the species which persist in the precipitate have larger diameters. The diameter effect is strong; with the suppression factors for the λ_em< 1150nm peaks (relative to the (11,1) peak) ranging from ~3 to -10 times higher than those for the λ_em^> 1150 within individual maps. Preferential enrichment of the precipitates with larger diameter/smaller band-gap SWNTs can explain the observed red- ward shift in the S₁₁ and S₂₂ peaks in the UV-Vis-NIR spectra (Fig. Ib, d, f — precipitate curves). The mechanism of the size selectivity is, however, unclear from this data and calls for further study.

[0081] It is evident from both the UV-Vis-NIR absorbance spectra and the PLE maps that the species selectivity differs noticeably for the different polymers and nanotubes of different synthetic origins (HiPco versus CoMoCAT). Specifically, PMMAFA and PAMMA preferentially disperse semiconducting CoMoCAT SWNTs but metallic HiPco SWNTs. PNMA preferentially disperse metallic CoMoCAT and HiPCo SWNTs. AU three polymers preferentially disperse smaller diameter CoMoCAT and HiPCo SWNTs. [0082] Without to be bound by any theory, it is suggested that at least two factors, i.e., electronic interaction and diameter selectivity, are involved in the SWNTs wrapping with the employed polymers since single factor cannot explain the diversity of the selectivity. Theoretical and experimental investigations have suggested the discrimination between met- and sent- SWNTs using large aromatic molecules. On the other hand, both the effect of SWNTs' curvatures on the adsorption of polycyclic aromatic hydrocarbon and the influence of radius and chirality of SWNTs on the conformation of polyethylene (with similar flexible backbone as our employed polymers) on SWNTs surface have been successfully reported. Moreover, the influence of SWNTs' diameter and metallicity on the separation of SWNTs has been found to be quite critical in polar aprotic media. The selectivity of PMMAFA and PAMMA may be dominated by two factors together, electronic interaction and also diameter selectivity. Therefore we can possibly see different behavior for different nanotubes (CoMoCAT vs. HiPco) and resolve the contradiction between our conclusion and other reported results. Diameter selectivity is possibly resulted from the different polymer conformation, which is also believed to be influenced by the size of the pendant functional groups. Systematic study, which is needed to explore the detailed mechanism responsible for the diversity of the species selectivity, is needed. [0083] Besides chemical structures of the polymers and SWNTs sources, the standing time of the dispersed SWNTs solution after sonication was also found to be a critical factor which will affect the performance of the polymer with regard to the SWNTs separation. UV-Vis-NIR spectra were employed to characterize different batches of separated SWNTs at different standing times after sonication. CoMoCAT SWNTs were studied in these tests. Only the polymers PNMA and PMMAFA were tested as PAMMA has too much absorption at short wavelength.

[0084] According to the absorption spectra (Figure 3), standing time is obviously one critical factor for high efficiency enrichment. Different extent of enrichment was resulted with different standing periods of 0 day, 3 days, 1 week, and 2 weeks respectively. The longer the standing time, the higher the selectivity is. If centrifugation was carried out immediately (0 day) after sonication, no enrichment of any species can be observed for both polymers. For PNMA, if the dispersed solution was kept at for a longer time (e.g. 2 weeks) before centrifugation, the content of met-S WNTs will increase dramatically. The longer the standing time, the higher the content of met-SWNTs is in the supernatant solution. For PMMAFA, which is selective to semiconducting CoMoCAT SWNTs as contrast to the met- SWNTs selectivity of PNMA, the same tendency can be observed: the longer the standing time, the higher the content of the sem-SWNTs is in the supernatant solution. [0085] The same tendency of the improvement of the selectivity with increasing standing time for these two polymers may possibly suggest that the adjustment of the polymer conformation after sonication is necessary for the mixture to form some stable wrapping states. It is reasonable for them to show similar time dependent characteristics since adjustment of the polymer conformation is anticipated to be necessary for all selective wrapping. Theoretical investigation has confirmed the selective conformation of polyethylene on SWNTs surface, induced by the interaction with the SWNTs lattice. Polymer domains have been predicted to merge to further lower the interaction energy at boundaries of polymer backbones and slow dynamics is expected, which is possibly responsible for the relatively long standing time for high efficiency enrichment suggested by the above results.

[0086] Example 3: Electrical measurement

[0087] To confirm the species enrichment, short channel thin film FETs devices using semiconductor enriched SWNTs have been fabricated and the electrical properties of the nano electronics have been characterized. The solution employed for the devices fabrication was obtained by dispersing with SDBS the semiconductor enriched CoMoCAT SWNTs from the supernatant solution with separation agent PMMAFA. For the preparation of electronics devices, prefer supernatant is used because precipitate normally contains lots of bundles which cannot be dispersed well into individual tubes. The thin film FETs were fabricated by the drop-casting method. A gate bias was applied to the underlying Si substrate, which served as the gate electrode, to modulate the carrier concentration in the SWNTs network. The electrode configuration and a typical device performance are schemed in Figure 4. [0088] At least 90% of the devices (9 out of 10) exhibited good FET performance with on/off ratio of about 10³; this confirms the enrichment of sem-SWNTs as compared to the performance of the devices made from the as-received CoMoCAT SWNTs (1 out of 10 devices shows on/off ratio of -10 and the rest <10). The relatively low on-state current is possibly limited by the low SWNTs density in the channel, the lower on-current carrying capacity of small diameter SWNTs (preferentially selected by PMMAFA) compared with larger diameter SWNTs and possibly due to the higher Schottky barriers and non-ohmic contacts. The high (about 10³) FET on/off ratio corroborates with other evidences of electronic-property-specific selective enrichment. Further improvement of the devices performance can be anticipated by using larger diameter SWNTs or higher work function electrodes since on-state current can be substantially increased by the decrease of the Schottky barriers. The optimization of the electrode geometry and conditions for devices fabrication will further improve the device performance. [0089] The species selectivity is confirmed to be quite sensitive to the polymer structures. Different aromatic functional groups show different discrimination between various SWNTs species, depending on their chiralities and diameters. Use of multiple highly selective polymers in combination may provide higher purity and even single species enrichment. The selectivity has also been observed to be influenced by the SWNTs synthesis method and the standing time of the SWNTs solution has been observed to be highly essential for the enrichment.

[0090] This method is scalable, nondestructive, compatible with SWNTs of different sources, iteratively repeatable and affordable, thus makes widespread application possible according to Mark C. Hersam's criteria. Further improvement of the devices performance is anticipated with using larger diameter SWNTs or higher work function electrodes as well as with the optimization of electrode geometry and the conditions for devices fabrication.

Claims

Claims:

1. A method of enriching specific species of carbon nanotubes by subjecting a composition of carbon nanotubes to one or more polymers according to Formula (I):

wherein

R¹ is H or CH_3, R² is selected from hydrogen, an optionally substituted C_1-6 aliphatic group, an optionally substituted C_5-20 aryl group and an optionally substituted C_5-20 heteroaryl group;

2. The method of claim 1, wherein the C_1-6 aliphatic group is selected from methyl, ethyl, propyl, butyl, pentyl and hexyl.

3. The method of claim 1, wherein the C_5-20 aryl group is selected from phenyl, naphthalenyl, phenanthrenyl, anthracenyl, tetralinyl, fluorenyl, indenyl, and indanyl.

4. The method of claim 1, wherein the C_5-20 heteroaryl group is selected from furan, benzofuran, thiophene, benzothiophene, pyrrole, pyridine, indole and fluorescein.

5. The method of any of the preceding claims, wherein R¹ is CH₃.

6. The method of claim 5, wherein R² is napthalenyl or anthracenyl.

7. The method of claim 6, wherein X is a direct bond or -CH₂-.

8. The method of claim 5, wherein n is an integer from 10 to 500, and m is 0.

9. The method of claim 5, wherein R² is CH₃.

10. The method of claim 9, wherein R³ is napthalenyl, anthracenyl or fluorescein.

11. The method of any of the preceding claims, wherein the polymer is

12. The method of any one of the preceding claims, wherein the carbon nanotubes are single-walled carbon nanotubes.

13. The method of any of the preceding claims, wherein the method is to enrich single- walled carbon nanotubes according to their electronic properties and/or diameter of single- walled carbon nanotubes.

14. The method of claim 13, wherein enrichment according to electronic properties allows to separate /wet-single-walled carbon nanotubes from se/w-single-walled carbon nanotubes.

15. The method of claim 13 or 14, wherein the method is to enrich single-walled carbon nano tubes having a diameter of equal or below 1 run from single- walled carbon nanotubes having a diameter of above 1 nm.

16. The method of any of the preceding claims, wherein the method comprises:

^■ mixing the composition of carbon nanotubes with a liquid composition of a polymer according to claim 1 dissolved in an organic solvent to form a mixture,

^■ incubating the mixture; and

^■ separating a supernatant and a precipitate formed in the mixture.

17. The method of claim 16, wherein mixing the composition of single walled carbon nanotubes is carried out by sonicating or stirring or shaking the mixture.

18. The method of any of the preceding claims, wherein the organic solvent is selected from the group consisting of hexane, heptane, cyclohexane, benzene, toluene, pyridine, dichloromethane, chloroform, carbon tetrachloride, carbon disulfide, tetrahydrofuran, dioxane, diethyl ether, diisopropylether, ethylene glycol monobutyl ether, methyl ethyl ketone, methyl isobutyl ketone, acetone, cyclohexanone, ethyl acetate, isobutyl isobutyrate, ethylene glycol diacetate, dimethylformamide, acetonitrile, N,N-dimethyl acetamide, nitromethane, acetonitrile, N-methylpyrrolidone, dimethylsulfoxide water, methanol, ethanol, butyl alcohol and. formic acid

19. The method of any one of claims 16 to 18, wherein the mixture is left to stand during incubation.

20. The method of any one of claims 16 to 19, wherein incubation is carried out for a period of time for between about 1 day to about 4 weeks.

21. The method of claim 20, wherein incubation is carried out for a period of time of at least about one day.

22. The method of claim 19, wherein incubation is carried out for a period of time of about 2 weeks.

23. The method of any one of claims 16 to 22, wherein the mixture is centrifugated before separating of the supernatant and the precipitate formed in the mixture.

24. The method of any one of claims 16 to 23, wherein only about 90 % of the supernatant are separated from the mixture after incubation.

25. The method of any one of claims 16 to 24, wherein single-walled carbon nanotubes comprised in the precipitate and the supernatant are washed with an organic solvent after separation.

26. An electrode comprising a single-walled carbon nanotube species separated using a method of any one of claims 1 to 25.

27. A field-effect transistor comprising a se/n-single-walled carbon nanotube separated using a method of any one of claims 1 to 25.