Process for purifying semiconducting single-walled carbon nanotubes

Abstract

A process for purifying semi-conducting single-walled carbon nanotubes (sc-SWCNTs) provides electronic grade materials with sc-SWCNT purity in excess of 99.99%. An initial dispersion containing sc-SWCNTs and metallic SWCNTs (m-SWCNTs) dispersed in a non-polar organic liquid medium is exposed to a fiber-like adsorption medium. The fiber-like adsorption medium preferentially adsorbs m-SWCNTs over sc-SWCNTs from the initial dispersion. A purified dispersion is collected after exposure of the initial dispersion to the fiber-like adsorption medium. In the purified dispersion a weight ratio of m-SWCNTs to sc-SWCNTs is smaller than a weight ratio of m-SWCNTs to sc-SWCNTs in the initial dispersion.

Description

PROCESS FOR PURIFYING SEMICONDUCTING SINGLE-WALLED CARBON NANOTUBESFIELD

[0001] The present disclosure relates generally to carbon nanotubes, and more particularly to a process for purifying semiconducting single-walled carbon nanotubes (sc- SWCNTs).BACKGROUND

[0002] Single-walled carbon nanotubes (SWCNTs) are an important class of carbon nanotubes. These materials are normally produced as ensemble samples containing both metallic (m-SWCNT) and semiconducting carbon nanotubes (sc-SWCNT) with a distribution of chiralities centered at a mean diameter. Several methods have been used to produce SWCNTs, which yield different distributions of chiralities, diameter ranges, semiconducting / metallic (sc / m) contents and average lengths. For example, SWCNTs produced using the high-pressure carbon monoxide (HiPCO®) and cobalt-molybdenum catalyst (CoMoCat®) processes are relatively smaller in diameter (0.6-1.3 nm), while arc-discharge, laser (laser-ablation) and plasma SWCNTs are relatively larger in diameter (1.0-2.2 nm). Although materials having a sc- SWCNT content as high as 95% can be achieved using techniques such as CoMoCat®, most as- prepared SWCNT samples have less than 70% sc-SWCNT content.

[0003] Recently, particular interest has been focused on using sc-SWCNTs in the electronics industry to replace current silicon-based CMOS technology. However, to satisfy the low threshold for variation of each thin fdm transistor (TFT) device on a chip with multi-million TFT devices, the sc-SWCNT material is required to have a purity higher than one m-SWCNT per-million sc-SWCNT.

[0004] Recent device-engineering developments in Prof. M Shulaker’s lab have reduced the purity requirement to be tolerant to about 99.99% sc-SWCNT. Unfortunately, the best current production methods, which are based on a hybrid conjugated polymer extraction / inorganic particle adsorption (hybrid-CPE / IPA) technique can achieve only about 99.9% purity of sc-SWCNT. Thus, an order of magnitude improvement is still required to meet the purity target for applications in the electronics industry.

[0005] There remains a need for a process that overcomes at least some of the limitations of the known techniques.SUMMARY OF THE INVENTION

[0006] The following presents a simplified summary of various aspects of the present disclosure in order to provide a basic understanding of such aspects. This summary is not an extensive overview of the disclosure. It is intended to neither identify key or critical elements of the disclosure, nor delineate any scope of the particular embodiments of the disclosure or any scope of the claims. Its sole purpose is to present some concepts of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

[0007] In one aspect of the present disclosure, there is provided a process for purifying single-walled carbon nanotubes (SWCNTs), the process comprising: obtaining an initial dispersion containing SWCNTs dispersed in anon-polar organic liquid medium, the SWCNTs including semiconducting single-walled carbon nanotubes (sc-SWCNTs) and metallic singlewalled carbon nanotubes (m-SWCNTs); exposing the initial dispersion to a fiber-like adsorption medium to preferentially adsorb the m-SWCNTs over the sc-SWCNTs from said initial dispersion; and collecting a purified dispersion after exposure of the initial dispersion to the fiber-like adsorption medium, a weight ratio of m-SWCNTs to sc-SWCNTs in the purified dispersion being smaller than a weight ratio of m-SWCNTs to sc-SWCNTs in the initial dispersion.

[0008] In one aspect of the present disclosure, there is provided a process for selectively separating semiconducting single-walled carbon nanotubes (sc-SWCNTs) from metallic singlewalled carbon nanotubes (m-SWCNTs), comprising: obtaining a mixture of single- walled carbon nanotubes (SWCNTs) containing the sc-SWCNTs and the m-SWCNTs; using the conjugated polymer extraction (CPE) technique, extracting the mixture of sc-SWCNTs and m-SWCNTs with a conjugated polymer to produce a first material having a weight ratio of m-SWCNTs to sc- SWCNTs that is smaller than a weight ratio of m-SWCNTs to sc-SWCNTs in the mixture; dispersing the first material in a non-polar organic liquid medium to form an initial dispersion; and exposing the initial dispersion to a fiber-like adsorption medium to preferentially adsorb the m-SWCNTs in the initial dispersion, to thereby further separate the sc-SWCNTs from the m- SWCNTs.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Exemplary embodiments will be described in accordance with the drawings, which are not drawn to scale, and in which:

[0010] Fig. 1 is a flow diagram of a method according to an embodiment.

[0011] Fig. 2 is a flow diagram of a method according to an embodiment.

[0012] Fig. 3 shows purity “ ” and yield “77” results for laser sc-SWCNTs obtained by the conjugated polymer extraction process (Orig), after purification by the fibrous material adsorption (FMA) technique (K-F, al+K-F, CMC+K-F, Kw+K-F), and after purification by the inorganic particle adsorption (IP A) technique (Si+K-F, Si+Kw-Fa, Si+Kw-Fb).

[0013] Fig. 4 shows purity " " and yield “r results after glass fiber and cellulose fiber treatment of a supernatant containing plasma tubes obtained by the conjugated polymer extraction technique using PFDD, SI: original solution from CPE, Kw: Washed Kim wipe fiber adsorption, QI: qualitative filter paper fiber adsorption, a-C: a-cellulose fiber adsorption, Gx: glass fiber adsorption at a usage of 8 mg (G8), 4 mg (G4), 2 mg (G2) and 1 mg (Gl), G-Fa: filtration through a 2 mm glass fiber plug, and G-Fb: filtration through a 5 mm glass fiber plug.

[0014] Fig. 5 A shows the transfer curves of 100 devices from the 10k device test for purified laser sc-SWCNTs before FMA.

[0015] Fig. 5B shows the transfer curves of 100 devices from the 10k device test for purified laser sc-SWCNTs after FMA.

[0016] Fig. 6A shows the transfer curves of 100 devices from the 10k device test for the purified plasma sc-SWCNTs before FMA.

[0017] Fig. 6B shows the transfer curves of 100 devices from the 10k device test for the purified plasma sc-SWCNTs after FMA.

[0018] Fig. 7A shows SEM images of the micro glass fiber from the glass filter paper.

[0019] Fig. 7B shows SEM images of the silica gel particles for chromatography.DETAILED DESCRIPTION OF THE DRAWINGS

[0020] While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, areintended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

[0021] Definitions:

[0022] Throughout the disclosure and in the appended claims, the following terms shall be understood to have the following meanings.

[0023] The term “microfiber” is defined as a man-made or natural fiber with a diameter within the range between about 0.01 pm and about 100 pm.

[0024] The term “fiber-like adsorption material” is defined as a material comprised of a microfiber.

[0025] The term “particulate” is defined as a particle-like material with various shapes (including e.g., generally regular or irregular spherical, plate-like or fiber-like particles) and a size ranged from about 0.05 to about 500 pm.

[0026] Hybrid CPE / IPA Technique:

[0027] Several methods have been proposed for enriching and isolating sc-SWCNTs with greater than 99% sc-SWCNT purity, as assessed by absorption spectroscopy. These methods include density gradient ultracentrifugation (DGU), gel chromatography (GC), dielectrophoresis, and selective conjugated polymer extraction (CPE). Of these methods, GC and CPE provide the clearest path to scalable enrichment of sc-SWCNTs. Additionally, the simplicity of the CPE process, which generally entails a dispersion step followed by a centrifugation step, further distinguishes it from the other methods as a particularly cost-effective method for the isolation of sc-SWCNTs with greater than 99% sc-SWCNT content by weight.

[0028] To date, many homopolymers and copolymers of phenylenevinylene, carbazole, thiophene and fluorene have been investigated for their potential for sc-SWCNT enrichment via the CPE technique. For example, poly (3 -dodecyl thiophene) (P3DDT) displayed a promising result in the separation of HiPCO® nanotubes, however P3DDT is not suitable for the separation of larger diameter SWCNTs, which are more desirable when trying to minimize contact resistance and to obtain a large electron mobility in thin film transistors (TFTs). Similarly, it has been observed that poly(9,9-dioctylfluorene) (PFO) has a high selectivity in dispersing small-diameter sc-SWCNTs with large chiral angles (2O°<0<3O°), but not large-diameter SWCNTs, which are believed to be difficult to disperse and enrich because of the strong interaction between the nanotubes associated with the low curvature of the nanotube walls. As a result, comonomer units have been introduced into the polyfluorene main chain in order to target specific tube chiralities / diameters, including: phenylene- 1,4-diyl, thiophen-2,5-diyl, anthracene-9,10- diyl, anthracene- 1,5-diyl, naphthalene-l,5-diyl, 2,2-bithiophene-5,5'-diyl, and benzo-2,1,3- thiadiazole-4,7-diyl.

[0029] It has also been observed that the length of the side alkyl chain of the polymers used in the CPE method has a significant impact on the enrichment effectiveness. Polymers with 12-carbon long side chains showed an improved selectivity to sc-SWCNTs with larger diameters. Recent work on the enrichment of large diameter SWCNTs using fluorene homopolymers with long alkyl side chains has been done, which achieved a device performance of 14.3 cm2 / Vs and on / off ratio over 105. However, the sc-SWCNT purity that can be achieved using the CPE process alone remains well below the target 99.99% threshold for use in the electronics industry.

[0030] More recently, a hybrid process has been developed which combines the CPE technique and an inorganic particle adsorption (IP A) technique, which has proved to be an efficient process for large scale sc-SWCNT enrichment at a purity higher than 99.9%. In general, the hybrid CPE / IPA process includes extracting a mixture of sc-SWCNTs and m- SWCNTs with a conjugated polymer to produce an enriched sc-SWCNT dispersion by the CPE process, and then exposing the enriched sc-SWCNT dispersion to an inorganic adsorptive medium in a non-polar liquid medium. The inorganic adsorptive medium selectively binds the m-SWCNTs to further separate the sc-SWCNTs from the m-SWCNTs and thereby enhance the sc-SWCNT purity to about 99.9%.

[0031] The mixture of sc-SWCNTs and m-SWCNTs that is to be purified may come from any convenient source of CNT preparation. Such starting material preferably comprises raw (about 0.6 to 2.2 nm average diameter) SWCNTs prepared from HiPCO®, CoMoCAT®, CVD, arc-discharge, laser-ablation (laser), or plasma processes. The amount of conjugated polymer used in the extraction in relation to the amount of SWCNTs in the mixture of sc- SWCNTs and m-SWCNTs (i.e. polymer: SWCNT mass ratio) is preferably about 0.5:1 or greater, for example 0.5: 1 to 10: 1.

[0032] The conjugated polymer may comprise any suitable polymer that will selectively fractionate sc-SWCNTs from the starting mixture. The polymer may be a homopolymer or a copolymer. Some examples of polymers include polyfluorenes, polythiophenes, polyphenylenevinylenes, and their copolymers with one or more co-monomer units (e.g., bithiophene, phenylene, bipyridine, anthracene, naphthalene and benzothiadiazole) or combinations thereof. The conjugated polymer preferably comprises a poly fluorene derivative, for example a 9,9-dialkyl-substituted polyfluorene, or a 9,9-diC10-36-alkyl-substituted polyfluorene, or a 9,9-diC10-18-alkyl-substituted polyfluorene. The alkyl substituent may be linear or branched. The conjugated polymer preferably has a number average molecular weight (Mn) greater than about 10,000 Da, for example from about 10,000 Da to about 500,000 Da, preferably from about 10,000 Da to about 30,000 Da. The combination of the TI-TI interaction between the conjugated polymer and the nanotubes, and the wrapping / coating of the conjugated polymer on the nanotubes affords a high selectivity based on the electronic properties and chiralities of the nanotubes. Furthermore, the selective polymer wrapping / coating enables the dispersion of individual SWCNTs to afford a good separation between m-Zsc-nanotubes. This feature provides a path towards high purity which is required for many electronic device applications. In addition, the composition and architecture of the polymer side chains can be adjusted to balance the dispersibility and the interaction with the nanotubes to optimize selectivity. Further, the molecular design of the polymer main chain provides the conjugated polymer a unique interaction with the nanotubes as well as some other desired properties.

[0033] In order to enhance the selectivity for sc-SWCNT enrichment, extracting with the conjugated polymer is preferably accomplished in a non-polar organic liquid medium, and is preferably the same organic liquid medium in which the enriched sc-SWCNT dispersion is exposed to an inorganic adsorptive medium in the IPA step of the process. The mixture of sc- SWCNTs and m-SWCNTs may be dispersed in the non-polar organic liquid medium in the presence of the conjugated polymer. The mixture of sc-SWCNTs and m-SWCNTs is preferably dispersed at a concentration of from about 0.1 mg / mL to about 10.0 mg / mL, preferably about 0.4 mg / mL to about 2.0 mg / mL, with a polymer / SWCNT ratio of 0.5:1 to 10:1. The polymer / SWCNT ratio will significantly impact the extraction yield and sc-SWCNT purity. A high ratio will produce a high yield but a low purity.

[0034] Formation of the dispersion may be assisted by known techniques in the art, for example, sonication, mechanical agitation and the like. Subsequent separation of the well- dispersed SWCNTs from the poorly dispersed SWCNTs collects polymer coated SWCNTs inthe dispersion, while undispersed non-coated SWCNTs are removed. The subsequent separation may be accomplished by any suitable method, for example centrifugation, fdtration and the like, or any combination thereof. Centrifugation is preferred. Such centrifugation typically yields sediment and supernatant, the sediment having gravitated to the bottom of a centrifuge tube and the supernatant being the liquid on top. The sediment is enriched in m-SWCNTs, and the supernatant is enriched in sc-SWCNTs, relative to the starting mixture. Because the conjugated polymer selectively interacts with the sc-SWCNTs to keep them dispersed, the SWCNTs remaining in the dispersion (e.g., in the supernatant) after separation are enriched in sc- SWCNTs, while the SWCNTs separated from the dispersion (e.g., in the sediment) are enriched in m-SWCNTs. Further extraction processes can be applied to the sediment, and the resulting combination dispersion will give a higher yield of sc-SWCNTs.

[0035] The dispersion from the CPE technique (i.e., the CPE dispersion), obtained as discussed supra, contains polymer-coated SWCNTs enriched in sc-SWCNTs and may be exposed directly to the inorganic adsorptive medium in the IPA step. Alternatively, further processing may be performed prior to performing the IPA step. The further processing may include, for example: separating the polymer-coated SWCNTs from the CPE dispersion by fdtration, washing, and then re-dispersing the washed polymer-coated SWCNTs to form an enriched sc-SWCNT dispersion (i.e., the redispersed CPE dispersion). Filtration and washing of the enriched sc-SWCNTs can cause the removal of some of the excess polymer that is not attached to SWCNTs. It may therefore be desirable to adjust the polymer: SWCNT stoichiometry of the redispersed CPE dispersion prior to performing the IPA step. This is because the polymer: SWCNT stoichiometry influences the effectiveness of the subsequent adsorption purification process, and also the device performance as well.

[0036] The CPE dispersion or the redispersed CPE dispersion, as defined supra, is then exposed to an inorganic adsorptive medium in a non-polar organic liquid medium, preferably in the same organic liquid medium that was used in the CPE step. The inorganic adsorptive medium selectively binds m-SWCNTs to further separate the sc-SWCNTs from the m-SWCNTs. The inorganic adsorptive medium and dispersed SWCNTs are preferably present in a mass ratio of inorganic adsorptive medium to SWCNT of between about 10:1 to 1000: 1, or more preferably between about 50:1 to 500:1. The inorganic adsorptive medium preferably comprises an inorganic oxide, for example silica (porous or non-porous), alumina, titania, a zeolite, a diatomaceous earth (e.g., Celite®) or mixtures thereof. The inorganic adsorptive medium may be functionalized to assist with specificity of reaction toward m-SWCNTs over sc-SWCNTs. Somesuitable functional groups include, for example, cyano, amino, hydroxyl, mercapto, halo (F, Cl or Br), alkyl and aromatic groups. The inorganic adsorptive medium should be dispersed in the non-polar organic liquid medium by agitation, such as for instance by shaking, stirring and / or sonication. The non-polar organic liquid medium is preferably an organic aromatic liquid medium. Some examples of suitable non-polar organic liquid mediums include, for example, toluene, benzene, ethyl benzene, xylenes, 1 -methylnaphthalene and mixtures thereof. Toluene is preferred. After mixing, the mixture is preferably allowed to sit for a period of time from 5 min to 5 h, preferably 10 to 60 min by using stirring, shaking and / or sonication. In some embodiments bath sonication is preferred.

[0037] After exposing the CPE dispersion or the redispersed CPE dispersion to the inorganic adsorptive medium, the sc-SWCNTs may be recovered by any suitable method, for example centrifugation, filtration and the like, or any combination thereof. Centrifugation is preferred. The adsorbent enriched in m-SWCNTs is a solid that is easily collected in the sediment of a centrifugation process while the sc-SWCNTs remain dispersed in the supernatant (i.e., the IPA dispersion). Further processing and isolation of the sc-SWCNTs may be include filtration to recover sc-SWCNT solid material, which may be washed to remove free polymer that is not attached to the SWCNTs. The washed sc-SWCNT solid material may then be redispersed in a non-poler organic liquid medium to form the redispersed IPA dispersion.

[0038] The hybrid CPE / IPA enrichment process discussed supra includes two-steps, the first step based on selective dispersion and extraction of semiconducting sc-SWCNTs using conjugated polymer (i.e., the CPE technique) followed by a second step based on an adsorptive process (i.e., the IPA technique), whereby a product of the CPE step is exposed to an inorganic absorptive medium to selectively bind predominantly metallic m-SWCNTs such that what remains dispersed in the dispersion is further enriched in semiconducting sc-SWCNTs. The hybrid CPE / IPA process is easily scalable for semi-conducting single-walled carbon nanotube (sc-SWCNT) enrichment with average diameters in a range, for example, of about 0.6 to 2.2 nm.

[0039] In addition, there are other advantages of this hybrid enrichment process compared to the extraction (i.e., CPE) process alone. For example, sc-SWCNT purity is promoted to a higher level than a single or multiple polymer extraction process is able to achieve, thereby resulting in improved device performance. Further, both high sc-SWCNT purity (for example greater than 99%) and a high yield (up to about 20% or higher) are obtainable together. This is in contradistinction to the CPE process, in which a high sc-SWCNT purity can only be achieved when a low polymer / SWCNT ratio such as 1:1 is used. However, atthis ratio, a low yield always results. It is therefore the case that there is a trade-off between the sc-SWCNT purity and yield in the CPE process. The hybrid CPE / IPA process overcomes this limitation by initially forming a product in high yield in the CPE step by using a high polymer / SWCNT ratio, for example 4: 1. The purity of this product is then enhanced in the IPA step at a yield of above 50%. The hybrid CPE / IPA process maintains the combined yield at a high level (for example >13.2x0.5=6.6%) while providing high sc-SWCNT purity with a <p value larger than 0.40. To obtain a similar yield by polymer extraction, a <p value of only about 0.37 can be obtained, where <p is the SWCNT peak ratio ( =ACNT / (ACNT+AB)), where ACNT is the enveloping area of the Mu and S22 bands enclosed by the linear baseline in the region from 8400 cm1to 16000 cm1(1190-625 nm) for laser and plasma SWCNTs, attributed to the nanotubes, and AB is the area covered by the linear baseline of the same region, attributed mostly to amorphous carbon.

[0040] Both CPE and IPA processes are based on the difference in the intrinsic electronic properties of the two types of nanotubes, i.e., polarizability. Metallic-SWCNTs (m-SWCNTs) have a polarizability ~104times higher than sc-SWCNTs, and thus they can generate much stronger interactions with a polar surface, charged species or particles. At the same time, due to their semiconducting property with a small energy gap (~1 eV), sc-SWCNTs are easily doped in ambient conditions and will become charged. This property causes m-SWCNTs to form a strong interaction with sc-SWCNTs to generate bundles in the liquid medium, driving the m-SWCNTs to precipitate out of the solution during an enrichment process, and thus m-SWCNTs are easily removed in a CPE enrichment by centrifugation to produce a product having a sc-SWCNT purity up to about 99%. The high polarizability is also the driving force in the IPA process to further promote the sc-SWCNT purity, where m-SWCNTs are preferentially adsorbed onto the silica gel due to the stronger interactions with the polar surface of S i O2 particles. This process can improve the sc-SWCNT purity up to about 99.9%.

[0041] As will be apparent, the hybrid CPE / IPA process represents an improvement over prior methods that have been used for obtaining purified sc-SWCNTs, but still does not achieve a purity higher than 99.99% while at the same time maintaining acceptable yield for commercial applications, such as for instance applications in the electronics industry.

[0042] Fibrous Medium Adsorption (FMA) Technique

[0043] The FMA technique has been found to enhance the sc-SWCNT purity of materials that are produced via either the CPE technique alone or the hybrid-CPE / IPA technique.Fig. 1 shows a simplified flow diagram of a method according to an embodiment. Step 100 is a step of obtaining an initial dispersion containing SWCNTs dispersed in a non-polar organic liquid medium, the SWCNTs including sc-SWCNTs and m-SWCNTs. Step 200 is a step of exposing the initial dispersion to a fiber-like adsorption medium to preferentially adsorb the m- SWCNTs over the sc-SWCNTs from said initial dispersion. In some embodiments, a CPE dispersion or a redispersed CPE solution is obtained at step 100 as discussed supra and then exposed to a fiber-like adsorption medium in a non-polar liquid medium at step 102 (i.e., the CPE / FMA technique). In some embodiments, the CPE dispersion or the redispersed CPE dispersion is exposed to an inorganic adsorptive medium to obtain an IPA dispersion or a redispersed IPA dispersion at step 100 as discussed supra, and the IPA dispersion or the redispersed IPA dispersion is then exposed to a fiber-like adsorption medium in a non-polar liquid medium at step 102 (i.e., the CPE / IPA / FMA technique). In some embodiments, exposing the m-SWCNT and sc-SWCNT containing dispersion to the fiber-like adsorption medium at step 102 includes adding an amount of the fiber-like adsorption medium to the dispersion and then using agitation etc. followed by a long sitting time to ensure good contact between the m- SWCNTs and the fiber-like adsorption medium. The added fiber-like adsorption medium, with adsorbed m-SWCNT impurity, can be removed at step 104 by centrifugation or by passing the dispersion through a column containing a plug of the fiber-like adsorption medium or another suitable fiber-like material.

[0044] Fig. 2 shows a simplified flow diagram of a method according to another embodiment. In general terms, an enhanced purification method includes obtaining a mixture of single-walled carbon nanotubes (SWCNTs) containing sc-SWCNTs and m-SWCNTs at step 200. The mixture of sc-SWCNTs and m-SWCNTs may come from any convenient source of CNT preparation. As discussed in the previous section, such starting material preferably comprises raw (about 0.6 to 2.2 nm average diameter) SWCNTs prepared from HiPCO®, CoMoCAT®, CVD, arc-discharge, laser-ablation (laser), or plasma processes. The amount of conjugated polymer used in the extraction relative to the amount of SWCNTs in the mixture of sc-SWCNTs and m-SWCNTs (i.e., the polymer:SWCNT mass ratio) is preferably about 0.5:1 or greater, for example 0.5: 1 to 10: 1.

[0045] At step 202, the mixture of sc-SWCNTs and m-SWCNTs is extracted with a conjugated polymer in a non-polar solvent to produce an enriched sc-SWCNT dispersion by the CPE process. Optionally, step 202 includes exposing the enriched sc-SWCNT dispersion to aninorganic adsorptive medium in a non-polar solvent to increase sc-SWCNT purity by the IPA process. The purified material is optionally washed and dried.

[0046] At step 204 the purified material obtained at step 202 is dispersed in a non-polar organic liquid medium to form an initial dispersion. The non-polar organic liquid medium is optionally the same as the non-polar solvent used in step 202.

[0047] At step 206 the initial dispersion containing the material obtained at step 202 is exposed to a fiber-like adsorption medium. The fiber-like adsorption medium selectively binds the m-SWCNTs that are present in the dispersion to further separate the sc-SWCNTs from the m-SWCNTs and thereby enhance the sc-SWCNT purity to about 99.99% or higher. The added fiber-like adsorption medium, with the adsorbed m-SWCNT impurity, can be removed from the resulting dispersion by centrifugation or by passing the dispersion through a column containing a plug of the fiber-like adsorption medium or another suitable fiber-like material.

[0048] The starting dispersion for the FMA process may be any suitable dispersion obtained by the CPE process or the hybrid-CPE / IPA process. The CPE process may be performed substantially as described in the previous section, using the same polymers, non-polar liquid medium, and other parameters that have already been discussed. The starting dispersion for the FMA process may be the supernatant obtained by the CPE process after centrifugation to remove the solids portion containing the m-SWCNT impurity. Optionally, multiple CPE extractions are performed. The starting dispersion for the FMA process may be the supernatant obtained by the IPA process, after centrifugation to remove the solids portion containing the m- SWCNT impurity. Alternatively, the starting dispersion for the FMA process may be the redispersed dispersion from CPE or IPA, where the CPE or IPA dispersion may be filtered using e.g., a Teflon® filter with 0.2-micron pore size to collect the sc-SWCNT, which is then redispersed in the non-polar liquid medium and the ratio of the conjugated polymer to sc- SWCNT is adjusted to a desired value.

[0049] In order to enhance the selectivity for sc-SWCNT enrichment, extracting with the conjugated polymer is preferably accomplished in a non-polar liquid medium, and preferably the same liquid medium that will be used in the optional IPA step of the process, and is further preferably also the same liquid medium that will be used in the optional FMA step of the process. The mixture of sc-SWCNTs and m-SWCNTs may be dispersed in the non-polar liquid medium in the presence of the conjugated polymer. The mixture of sc-SWCNTs and m- SWCNTs is preferably dispersed in the liquid medium at a concentration of from about 0.1mg / mL to about 10.0 mg / mL, preferably about 0.4 mg / mL to about 2.0 mg / mL, with a polymer / SWCNT ratio of 0.5:1 to 10:1. The polymer / SWCNT ratio used in the CPE process significantly impacts the extraction yield and sc-SWCNT purity. A high ratio will produce a high yield but a low purity.

[0050] The dispersion from the CPE technique (i.e., the CPE dispersion) or from the hybrid-CPE / IPA technique (i.e., the IPA dispersion), obtained as discussed supra, containing polymer-coated SWCNTs enriched in sc-SWCNTs, may be exposed directly to the fiber-like adsorption medium, or alternatively further processing may be performed prior to contacting the enriched sc-SWCNT dispersion with the fiber-like adsorption medium. The further processing may include, for example: isolating the polymer-coated SWCNTs from the dispersion (i.e., the CPE dispersion or the IPA dispersion) by filtration, washing, and then re-dispersing the polymer- coated enriched sc-SWCNTs to form an enriched sc-SWCNT dispersion (i.e., the redispersed CPE dispersion or the redispersed IPA dispersion). Filtration and washing of the enriched sc- SWCNTs can cause the removal of some of the excess polymer that is not attached to SWCNTs. It may therefore be desirable to adjust the polymer: SWCNT stoichiometry of the redispersed dispersion prior to performing the FMA step. This is because the polymer: SWCNT stoichiometry influences the effectiveness of the subsequent FMA adsorption purification process, and also the device performance as well.

[0051] The starting dispersion for FMA is then exposed to the fiber-like adsorption medium in a non-polar liquid medium, preferably in the same liquid medium that was used in the previous steps. The fiber-like adsorption medium selectively binds m-SWCNTs to further separate the sc-SWCNTs from the m-SWCNTs. Preferably, a weight-amount of the fiber-like adsorption medium is between about 0.1 and about 100 times a weight-amount of the dispersed SWCNTs, more preferably between about 0.5 and about 10 times. The fiber-like adsorption medium preferably comprises glass fiber, cellulose fiber, or asbestos fiber. The fiber-like adsorption medium preferably has surface OH or NH2 groups. The fiber-like adsorption medium should be stable in non-polar liquid media. The non-polar liquid medium preferably comprises an organic liquid medium, more preferably an organic aromatic liquid medium. Some examples of suitable, non-polar organic aromatic liquid media include, toluene, benzene, xylene, trimethyl benzene, ethyl benzene, chlorobenzene, di chlorobenzene, and methylnaphthalene. Toluene is preferred. After mixing, ultrasonic energy may be applied for a period of time of between about 10 minutes and about 120 minutes to ensure good dispersion of the fiber-like medium, and then the mixture may be allowed to sit at room temperature for a period of time of between about 1hour and about 60 hours, preferably between about 1 hour and about 24 hours. Finally, the added fiber-like adsorption medium with the adsorbed impurity is removed by centrifugation or by passing the mixture dispersion through a column containing a plug of the fiber-like adsorption medium.

[0052] After exposing the enriched sc-SWCNT dispersion to the fiber-like adsorption medium, the sc-SWCNTs may be recovered by any suitable method, for example centrifugation, filtration and the like, or any combination thereof. Centrifugation is preferred. The adsorbent enriched m-SWCNTs is a solid that is easily collected in the sediment of a centrifugation process while the sc-SWCNTs remain dispersed in the supernatant. The recovered sc-SWCNTs in the dispersion have a conjugated polymer wrapping / coating. This dispersion has an improved sc- purity and better stability with the polymer / SWCNT weight ratio proper for using as the ink for device fabrication. Optionally, the dispersion is filtered through a 0.2 pm Teflon® membrane to collect the polymer-wrapped sc-SWCNTs which are subsequently washed to remove excess polymer and redispersed.

[0053] Examples:

[0054] Example 1: Kim-wipe filtration of hybrid-CPE / IPA dispersion.

[0055] CPE step: Laser SWCNT raw material was extracted using the CPE technique. 200 mg of the laser SWCNTs were introduced into 200 ml of toluene with 200 mg of poly(9,9- di-n-dodecylfluorenyl-2,7-diyl) (PFDD). The mixture was homogenized for 30 min at 30°C using horn sonication (Branson Sonicator 250, maximum power, 200 W) with a 10 mm tip operated at a duty cycle of 60% and output of 70%. The resulting dispersion was then centrifuged at a relative centrifuge force (RCF) of 23,700 g (12,500 rpm on an SLA1500 rotor) for 30 min. This process was repeated three times by dispersing the sediment obtained in a previous extraction step using 200 mL of PFDD / toluene solution (1 mg mL '). and centrifuging as described supra. The supernatant was collected as the CPE dispersion.

[0056] IPA step: 15 mg of the CPE enriched laser sc-SWCNT material from the CPE step (collected e.g., by filtering the CPE dispersion using a 0.2 pm Teflon filter to collect the polymer wrapped SWCNTs, which were then washed and dried etc.) and 75 mg of PFDD was dispersed in 200 mL of toluene with 120 min bath sonication. 0.75 g of silica gel was added to the resulting dispersion, and the mixture was sonicated for 40 min and then stored at roomtemperature (RT) overnight. Solids were separated by a centrifugation at 12,500 rpm (SLA1500 rotor, RCF:23700g) for 30 min (200 mL bottle), and the supernatant was collected.

[0057] FMA step: The supernatant from the IPA step was used in the FMA step without any additional prior treatment. The IPA supernatant was passed through a 1 cm Kim-wipe plug, and then fdtered using a 0.2 pm Teflon® membrane to collect the purified solid and to remove excess polymer. The collected solid was washed and characterized. A low flow rate was used when passing the IPA supernatant through the Kim-wipe plug to provide a long contact time between the dispersion and the adsorption medium. The obtained sc-SWCNT product was high purity, with a <p value of about 0.43 compared to only about 0.39 for the CPE sample, as summarized in Table 1 below.

[0058] Table 1, UV sample characterization comparing the yield and purity of sc- SWCNT products obtained by CPE and CPE / ISA / FMA.

[0059] Example 2: Kim-wipe filtration of redispersed hybrid-CPE / IPA dispersion:

[0060] Laser SWCNTs were purified by CPE / IPA as described in Example 1. After centrifugation to remove the silica gel, the supernatant was filtered through a 0.2 pm Teflon® membrane to collect the suspended polymer-wrapped SWCNTs, which was rinsed (e.g., using a small amount of toluene) and then dried to obtain a solid. Next, 3.4 mg of the solid was added to 16 mL of toluene and bath sonicated for 40 min to form a stable dispersion.

[0061] The resulting dispersion was passed through a column containing a 0.5 cm long Kim-wipe plug and the liquid component exiting the column was collected. The obtained liquid component of the dispersion showed a high stability and the <p value determined by UV characterization was about 0.424 compared to only 0.418 prior to exposure to the Kim-wipe fibers, as summarized in Table 2, below.

[0062] A multi-TFT test performed using the sc-SWCNT obtained by CPE / IPA / FMA showed a very narrow variation of device performance with 99% of the devices having a threshold voltage variation of less than 0.5 V., corresponding to a sc-SWCNT purity higher than 99.99%.

[0063] Table 2, UV characterization of the samples before and after K-fdtration.

[0064] Examples 1 and 2 indicate that a high purity sc-SWCNT dispersion, suitable for CMOS type electronic applications, is obtained after performing an additional FMA step in which a dispersion or redispersed dispersion that has already been purified by the hybrid- CPE / IPA technique is passed through a plug of a fiber-like adsorption medium.

[0065] Example 3. Adsorbent treatment of a low purity laser sc-SWCNTs dispersion using different type of cellulose fibers:

[0066] A study was carried out to compare the purity and yield of the sc-SWCNTs obtained using different fiber-like adsorption media, including different combinations of some different types of cellulose fibers and silica gel. In each case, the original sc-SWCNT dispersion was the supernatant with a low <p value collected from the 4thextraction of a CPE process using PFDD to extract laser SWCNTs. In some cases, the original sc-SWCNT dispersion was contacted with the fiber-like adsorption medium either by flowing the original sc-SWCNT dispersion through a column containing a plug of the fiber-like adsorption medium or by adding the fiber-like adsorption medium to the original sc-SWCNT dispersion and then flowing the resulting dispersion through a column containing a plug of the fiber-like adsorption medium. In some cases, Si (Silica gel 60 A, 230-400 mesh) was added to the original sc-SWCNT dispersion, and the resulting mixture was contacted with the fiber-like adsorption medium either by flowing through a column containing a plug of the fiber-like adsorption medium or by adding the fiberlike adsorption medium to the mixture and then flowing the resulting dispersion through a column containing a plug of the fiber-like adsorption medium. The different fiber-like adsorption media used in the study were: 1) K: Kim- wipe without any treatment; 2) Kw: WashedKim-wipe fiber: Kim wipe was dispersed in water using a blender, filtered and washed with MeOH twice, and then dried in air and then under vacuum; 3) al, a-cellulose, (Aldrich C8002);4) CMC, Cellulose micro-crystalline, 20 micron, (Aldrich 316097).

[0067] Procedure:

[0068] Sample 1 “Orig”: Supernatant from the 4th extraction of a CPE using PFDD without exposure to any of the fiber-like adsorption media. This process is the same process used for Example 1 CPE step, where the CPE extraction was repeated for 4 times and the supernatant from the 4thextraction was used as “Orig” in this example.

[0069] Sample 2 “K-F”: 10 g of Orig was filtered through a Kim-wipe plug (5 mm long, Kim-wipe not washed) during 10 min.

[0070] Sample 3 “al+K-F”: 10 g of Orig was added with 5 mg of a-cellulose. The mixture was sonicated for 20 min and then sat overnight. The dispersion was filtered through a Kim-wipe plug (5 mm long, Kim-wipe not washed) during 10 min.

[0071] Sample 4 “CMC+K-F”: 10 g of Orig was added with 5 mg of CMC. The mixture was sonicated for 20 min and then sat overnight. The dispersion was filtered through a Kim- wipe plug (5 mm long, Kim-wipe not washed) during 10 min.

[0072] Sample 5 “Kw+K-F”: 10 g of Orig was added with 5 mg of washed Kim-wipe fiber (Kw). The mixture was sonicated for 20 min and then sat overnight. The dispersion was filtered through a Kim-wipe plug (5 mm long, Kim-wipe not washed) during 10 min.

[0073] Sample 6 “Si+K-F”: 10 g of Orig was added with 10 mg of silica gel. The mixture was sonicated for 20 min and then sat overnight. The resulting CPE / IPS dispersion was filtered through a Kim-wipe plug (5 mm long, Kim-wipe not washed) during 10 min.

[0074] Sample 7 “Si+Kw-Fa”: 10 g of Orig was added with 5 mg of silica gel. The mixture was sonicated for 20 min and then sat overnight. The resulting CPE / IPA dispersion was filtered through a washed Kim-wipe (Kw) plug (5 mm long) during 10 min.

[0075] Sample 8 “Si+Kw-Fb”: 10 g of Orig was added with 5 mg of silica gel. The mixture was sonicated for 20 min and then sat overnight. The resulting CPE / IPA dispersion was filtered through a washed Kim-wipe (Kw) plug (10 mm long) during 10 min.

[0076] Results:

[0077] Purity “ ” and yield “77” results for Samples 1-8 are presented in Fig. 3.Comparing the results of Sample 1 and Sample 2, the fdtration of the Orig dispersion through an untreated Kim- wipe plug was observed to improve the <p value from about 0.37 to about 0.38 but with about 10% loss in yield. This result indicates that the cellulose fiber of the untreated Kim- wipe strongly and rapidly adsorbed m-SWCNTs in the Orig dispersion.

[0078] The corresponding results obtained for Samples 3-5 demonstrate the effect of allowing the Orig dispersion to sit overnight after the addition of three different types of fiberlike adsorption media, which were dispersed using sonication, followed by sitting overnight and then filtration through an untreated Kim- wipe plug. In each case, the sc-SWCNT purity was enhanced compared to Sample 1 and Sample 2 and the sc-SWCNT yield was comparable to the yield that was observed for Sample 2. Sample 6 corresponds to the traditional hybrid CPE / IPA process followed by filtration through an untreated Kim-wipe plug of 5 cm length as measured along the fluid flow direction. As shown in Fig. 3, the results for Samples 4 and 5 are noticeably better than the results for sample 6 in terms of both sc-SWCNT purity and sc-SWCNT yield, and the results for Sample 3 are at least comparable to the results for sample 6. Similarly, Samples 7 and 8 correspond to the traditional hybrid CPE / IPA process followed by filtration through a washed Kim-wipe plug of 5 cm length and of 10 cm length, respectively, as measured along the fluid flow direction. Although the sc-SWCNT purity of Samples 7 and 8 are comparable or superior to the sc-SWCNT purity of Samples 3-5, the sc-SWCNT yields are much lower. This result may indicate that the washed fiber has a larger capacity for accommodating both m- SWCNTs and sc-SWCNTs on its surface.

[0079] Fig. 3 suggests that the cellulose fibers used in the FMA step possess the same or better capability to remove m-SWCNTs compared to the silica particle gel used in the traditional CPE / IPA hybrid technique. Separation processes in which the SWCNT dispersion is exposed to both the silica gel and fiber-like adsorption materials provide very high purity sc-SWCNT containing products in good yield overall.

[0080] Example 4. Comparison of different cellulose treatment conditions.

[0081] Materials:

[0082] A study was carried out to compare the purity ( ) and yield (p) of sc-SWCNT products obtained using different cellulose treatment conditions. In each case, the original sc- SWCNT dispersion (Orig) was the supernatant that was collected from the fourth extraction in a CPE process using PFDD to extract laser SWCNTs, which is the same as “Orig” used in Example 3. The cellulose fiber used was CMC, (cellulose micro-crystalline, 20 micron, Aldrich 316097). The different conditions used in this study are summarized in Table 3. In general, the indicated amount of CMC was added to 5 g of the original sc-SWCNT dispersion and the mixture was sonicated for (tsoni) min at a selected sonication temperature (Tsoni) and then allowed to sit for (tsit) h. After sitting, the mixture was filtered through a Kim-wipe plug (1cm long). In addition, moisture effects have been tested by adding water saturated toluene into the solvent.

[0083] Results:

[0084] Table 3. Cellulose treatment conditions and results

[0085] Table 3 shows that the temperature during dispersion of the CMC material by sonication has a significant influence on the sc-SWCNT purity in the final product that is obtained. Sonication at a temperature of about 40 °C achieves better purification compared to sonication with at a solution temperature of about 0 °C, as indicated by the higher <p value in the first two rows of Table 3 (i.e., <p = 0.389 and 0.378, respectively).

[0086] The effect of varying the weight of CMC used in the FMA step is summarized in rows 3 to 8 of Table 3, where the CMC values are expressed in mg of CMC added to 5.0 g of the original SWCNT dispersion (Orig). Table 3 shows that all samples purified using over 2 mg CMC per 5 g of Orig gave promising results, although the specific amount of CMC used in this test had little effect on the final sc-SWCNT purity.

[0087] Moisture content also has a significant effect on the CPE / IPA / FMA purification process, with a linear reduction in purity being observed as the moisture content of the non-polar liquid medium increased. The moisture test results show that lower moisture content is beneficial for obtaining a high purity material.

[0088] Sonication times of over 20 min all give promising results, indicating 20 min sonication can sufficiently disperse the added CMC in the solution.

[0089] The sc-SWCNT purity was observed to improve continuously as the sitting time after adding the CMC to the dispersion was increased.

[0090] Example 5. Comparison of the purification of plasma sc-SWCNT solutions using different types of fiber-like adsorption media.

[0091] Materials:

[0092] A study was carried out to compare the purity and yield of sc-SWCNTs final products obtained using different fiber-like adsorption media. In each case, the original sc- SWCNT dispersion was the supernatant from the 2ndextraction of a CPE using PFDD. Plasma SWCNT raw material was extracted using the CPE technique. 200 mg of the laser SWCNTs were introduced into 200 ml of toluene with 200 mg of poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFDD). The mixture was homogenized for 30 min at 30°C using hom sonication (Branson Sonicator 250, maximum power, 200 W) with a 10 mm tip operated at a duty cycle of 60% and output of 70%. The resulting dispersion was then centrifuged at a relative centrifuge force (RCF) of 23,700 g (12,500 rpm on an SLA1500 rotor) for 30 min. This process was repeated threetimes to the sediment obtained in a previous extraction step by adding 200 mL of PFDD / toluene solution (1 mg mL1), sonicating and centrifuging as described supra. The supernatant from the 2ndextraction was used in this test.

[0093] Into 5 g of the original solution, different fiber-like adsorption media used in the study were: 1) Gx: Glass microfiber from filter paper (Whatman glass microfiber filters, adhesive free, Cat#: 1821 047). The glass microfiber was dispersed in water using a blender, filtered and washed with water twice and MeOH twice, and then dried in air and then under vacuum, x represents x mg of the fiber. 2) Kw: Washed Kim wipe fiber. The Kim wipe was dispersed in water using a blender, filtered and washed with MeOH twice, and then dried in air and then under vacuum; 3) QI: Washed Whatman qualitative filter paper (#1). The filter paper was dispersed in water using a blender, filtered and washed with MeOH twice, and then dried in air and then under vacuum; 4) a-C: a-cellulose, (Aldrich C8002); 5) G-F, the original SWCNT- containing dispersion was passed through a column containing a short length plug of glass fiber (G-Fa, 2 mm long plug was used), or through a column containing a medium length plug of glass fiber (G-Fb, 5 mm long plug was used).

[0094] Results:

[0095] The results of this study are summarized in Table 4 below and also in Fig. 4, which shows purity “ ” and yield “77” for the various samples. Among the four types of fibers (i.e., glass, washed Kim-wipe, filter paper, and a-cellulose), the glass microfiber produced the best results with a <p value of up to 0.440 for purified sc-SWCNT material obtained from plasma tubes. In particular, the results that were obtained for G4 and G8, both of which used glass fibers, indicate that longer sitting times and larger amounts of fiber contribute to higher purity.

[0096] As noted above, samples G-Fa and G-Fb were not subjected to the same conditions of adding the fiber-like adsorption medium to the original sc-SWCNT solution, sonicating the mixture to disperse the adsorption medium, and then sitting for a period of time to allow m-SWCNTs to be adsorbed onto the medium. Rather, the results for G-Fa and G-Fb were obtained by passing the original sc-SWCNT dispersion through a column containing a 2mm long plug of the glass fiber material or through a column containing a 5mm length plug of the glass fiber material, respectively, as measured along the fluid flow direction. The yield and purity for the G-Fa sample are comparable to the results that were observed after the addition of between 1 mg and 4 mg of glass fibers to the original sc-SWCNT dispersion followed by 2 hours sitting time. The G-Fa sample purity was much lower than the G8 sample, albeit with a slightly betteryield. Increasing the length of the plug of glass fiber material from 2 mm to 5 mm resulted in a modest improvement in the sc-SWCNT purity (< > value increased from 0.406 to 0.427), but this improvement was achieved at the cost of a dramatic decrease in the yield of sc-SWCNTs. This is because more glass fiber (~20 mg and ~50 mg of glass fiber was used in the 2 mm and 5 mm plug) was used in G-F sample and thus it will adsorb more CNTs with less selectivity due to the short adsorption time.

[0097] Table 4 the cellulose treatment condition and results are summarized

[0098] Example 6: Optimized Purification Process Using FMA Technique AfterCPE / IPA Purification

[0099] The results from Examples 1 to 5 discussed above indicate that glass microfibers (GMF) have a better capability for removing m-SWCNTs from dispersion compared to the other types of fiber materials that were examined. In particular, glass fiber sample G8 produced the highest <p value when equal weights of the different fibers were used. However, as shown in Table 4, the yield that was obtained using 8.0 mg of GMF was only 60% compared to 80-88% when using 8.0 mg of the other fiber-like adsorption media. Better yields were observed using smaller amounts of GMF and a longer adsorption time. It was also observed that an anhydrous dispersion provided better purification results.

[0100] A test was performed using optimized conditions for a large quantity dispersion. More specifically, adsorption treatment was performed to purify a CPE enriched laser sc- SWCNT film sample with a polymer / SWCNT (P / SWCNT) weight ratio of 1 / 1. 6.0 mg of the film sample from CPE / IPA and 9.0 mg of PFDD was added to and dispersed in 100 mL of anhydrous toluene using 2 h bath sonication at 30 °C to obtain a dispersion. 5.0 mg of GMF wasadded to the dispersion, which was then subjected to sonication at 30°C for 30 min to thoroughly disperse the fiber. 1.0 g of dried molecular sieves (8-12 mesh) were added to the dispersion, followed by agitation overnight on a shaker (Junior Oribitor shaker, Lab-line Instrument Inc). The dispersion was subsequently filtered through a short column containing a 1 cm long plug of washed Kim-wipe (Kw). The liquid portion was collected and characterized. Good purity was indicated by the determined <p value, which was over 0.44. A Raman mapping test showed that a purity better than 1 ppm was achieved.

[0101] The purity of the product that was obtained using this method was confirmed by MIT multiprobe device test, where 10,000 FET devices were tested. Based on the results that were obtained, the purity of the product was estimated to be 99.995%. It should be noted that all the devices with on / off ratio lower than 50 are defined as metal containing devices in this test. As such, the actual sc-SWCNT purity value should be higher than the estimated value because some of on / off<50 devices could be ascribed to semi-metal or bundles.

[0102] In addition to producing materials with improved sc-SWCNT purity, the disclosed CPE / IPA / FMA technique also produces SWCNT dispersions with improved stability. The final IPA dispersion obtained from the hybrid CPE / IPA process has been observed to be stable for about 2 weeks. After this time, small amount of precipitate form in the dispersion, which depends on the size of tubes, with large tubes usually having a higher stability. In contradistinction, after purification using the disclosed CPE / IPA / FMA technique there was no precipitate observed after 6 months.

[0103] Example 7: sc-SWCNT-based FET device performance

[0104] The effects of improved purity of laser sc-SWCTs, which were purified using the disclosed CPE / IPA / FMA technique, on FET device performance has been investigated in 10k device tests. The results that are presented in Figs. 5A and 3B compare the transfer curves of 100 devices from the 10k device test for laser sc-SWCNTs purified without using FMA (Fig. 5A) and for laser sc-SWCNTs obtained by CPE / IPA / FMA treatment (Fig. 5B).

[0105] Fig. 5B indicates a one order of magnitude increase of the on / off ratio for the sample obtained using the CPE / IPA / FMA technique relative to the sample obtained without FMA treatment. In addition, Fig. 5B shows the improved reproducibility of on / off ratio and threshold voltage of the 10k devices. More particularly, Fig. 5B shows that the threshold voltage of the laser sc-SWCNTs purified using the disclosed CPE / IPA / FMA technique varied in a verynarrow range, while Fig. 5 A shows that the threshold voltage of the laser sc-SWCNTs purified without using FMA treatment varied in a relatively broader range.

[0106] Similarly, the effect of improved purity of plasma sc-SWCTs, which were purified using the disclosed CPE / IPA / FMA technique, on FET device performance has also been investigated in 10k device tests. The results that are presented in Figs. 6A and 6B compare the transfer curves of 100 devices from the 10k device test for plasma sc-SWCNTs purified without using FMA (Fig. 6A) and for the plasma sc-SWCNTs obtained by CPE / IPA / FMA treatment (Fig. 6B). The results shown in Figs. 6A and 6B for the plasma SWCNTs are similar to the results shown in Figs. 5 A and 5B for the laser SWCNTs.

[0107] The above-mentioned improvements are important for expanding the use of sc- SWCNT materials to CMOS-type electronic applications. Further, the very high ink stability and high reproducibility of devices fabricated from this ink are unique and very important properties for CMOS type device application.

[0108] Without wishing to be bound by any particular theory, it is believed that the improved sc-SWCNT purification that is observed when the disclosed FMA technique is used in combination with one or more other purification technique results from one or more of the following:1) Use of microfibers with a diameter in a range between tens of nm to about 10 pm, to provide sufficient surface area for an efficient m-SWCNT adsorption.2) Use of microfibers with a polar surface, covered with polar groups such as OH, NH2 etc. to generate strong interaction with m-tubes.3) Use of high aspect ratio microfibers with a smooth surface and uniform cylindrical structure along the fiber length, to facilitate nanotube packing.

[0109] Many different types of microfiber materials having the above-mentioned characteristics are expected to be suitable for use in the FMA technique, such as for instance glass microfibers, cellulose microfibers, and some types of asbestos microfibers. As discussed above, the use of glass microfibers resulted in a sc-SWCNT product with the highest purity among all of the fiber-like absorbents that were tested, as determined based on the psi ratio calculation of the sc-SWCNT products. One structural difference between cellulose microfibers and glass microfibers, which is believed to contribute to the improved purity results that areobserved with glass microfibers, is that the glass microfibers have a straight and substantially cylindrical surface structure, with a diameter between about 0.1 gm and about 10 gm. It is believed that a long, straight, and substantially cylindrical fiber surface is important for m-tube adsorption.

[0110] This observation may be explained by comparing the surface and topological structure of the glass fibers to that of silica gel particles. Both the glass fibers and the silica gel particles have a highly polar surface structure covered with hydroxyl groups, and accordingly the surfaces of both types of adsorbents have a high affinity to interact with m-tubes and produce a tight adsorption interaction. However, silica gel particles are 200 to 400 mesh, the individual particles being about 40-70 pm in size with a high surface roughness, while glass fibers are about 0.1-10 pm in diameter and a few gm to a few mm in length. Due to differences in particle morphology, the glass fibers have a much larger surface area for accommodating the adsorbed SWCNTs. Furthermore, as illustrated in Fig. 7A, the straight and long cylindrical structure of the glass fibers is better able to facilitate packing of the straight carbon nanotubes on the surface thereof with more tight adhesion compared to the spherical structure of the silica gel particles shown in Fig. 7B. This characteristic makes the glass fibers, as well as the cellulose fibers for the same reason, a better adsorbent than the silica gel particles, enabling m-SWCNTs to stick more tightly on their surface and thereby improve the purity of sc-SWCNTs that remain in the dispersion.

[0111] Numerous other embodiments may be envisaged without departing from the scope of the invention.

Claims

CLAIMSWhat is claimed is:

1. A process for purifying single-walled carbon nanotubes (SWCNTs), the process comprising: obtaining an initial dispersion containing SWCNTs dispersed in a non-polar organic liquid medium, the SWCNTs including semiconducting single-walled carbon nanotubes (sc- SWCNTs) and metallic single-walled carbon nanotubes (m-SWCNTs); exposing the initial dispersion to a fiber-like adsorption medium to preferentially adsorb the m-SWCNTs over the sc-SWCNTs from said initial dispersion; and collecting a purified dispersion after exposure of the initial dispersion to the fiber-like adsorption medium, a weight ratio of m-SWCNTs to sc-SWCNTs in the purified dispersion being smaller than a weight ratio of m-SWCNTs to sc-SWCNTs in the initial dispersion.

2. The process of claim 1, further comprising obtaining the initial dispersion using a conjugated polymer extraction (CPE) technique.

3. The process of claim 1, wherein exposing the initial dispersion to the fiber-like adsorption medium comprises adding an amount of the fiber-like adsorption medium to the initial dispersion.

4. The process of claim 3, wherein exposing the initial dispersion to the fiber-like adsorption medium further comprises 1) applying ultrasonic energy for a period of time of between about 10 minutes and about 120 minutes to form a second dispersion, and 2) allowing the second dispersion to rest at room temperature for a period of time of between about 1 hour and about 24 hours.

5. The process of claim 4, wherein collecting the purified dispersion after exposure to the fiberlike adsorption medium comprises separating the fiber-like adsorption medium from the second dispersion and collecting the remainder as the purified dispersion.

6. The process of claim 5, wherein separating the fiber-like adsorption medium from the second dispersion comprises at least one of:centrifuging the second dispersion and collecting a supernatant from above a sediment layer, the sediment layer including the fiber-like adsorption medium, and passing the second dispersion through a plug of fiber-like material, the plug having a length that is between about 0.2 cm and about 5 cm measured along a direction of fluid flow.

7. The process of claim 6, wherein the fiber-like material and the fiber-like adsorption medium have a same composition.

8. The process of claim 6, wherein the fiber-like material and the fiber-like adsorption medium have a different composition.

9. The process of claim 1, wherein the initial dispersion is obtained using a conjugated polymer extraction / inorganic particle adsorption hybrid technique (hybrid-CPE / IPA), in which the inorganic particle adsorption (IP A) technique is performed after the conjugated polymer extraction (CPE) technique to produce the initial dispersion, the IPA technique comprising exposing a dispersion obtained from the CPE technique to an inorganic adsorption medium.

10. The process of claim 2, wherein the initial dispersion is a re-dispersed solution containing enriched sc-SWCNTs from the CPE technique and having a conjugated polymer: SWCNT weight ratio within a range between about 1 : 1 and about 20: 1.

11. The process of claim 10, wherein the conjugated polymerSWCNT weight ratio is within a range between about 2: 1 and about 6:1.

12. The process of claim 10, wherein the conjugated polymerSWCNT weight ratio is about 4:1.

13. The process of claim 1, wherein the fiber-like adsorption medium comprises a microfiber having a diameter within the range between about 0.01 pm and about 100 pm.

14. The process of claim 1, wherein a surface of the fiber-like adsorption medium comprises polar groups selected from OH and NH2.

15. The process of claim 1, wherein the fiber-like adsorption medium comprises a microfiber selected from a glass microfiber, a cellulose microfiber, and an asbestos microfiber.

16. The process of claim 1, wherein a weight-amount of the fiber-like adsorption medium is within a range between about 0.1 and about 100 times a weight-amount of the dispersed SWCNTs.

17. The process of claim 16, wherein a weight-amount of the fiber-like adsorption medium is within a range between about 0.5 time and about 10 times a weight-amount of the dispersed SWCNTs.

18. The process of claim 1, wherein the SWCNTs in the collected purified dispersion are at least 99.99 % sc-SWCNTs by weight.

19. The process of claim 1, wherein the non-polar organic liquid medium is selected from toluene, benzene, xylene, trimethyl benzene, ethyl benzene, chlorobenzene, dichlorobenzene, and methylnaphthalene.

20. The process of claim 1, wherein the non-polar organic liquid medium is toluene.

21. A process for selectively separating semiconducting single- walled carbon nanotubes (sc- SWCNTs) from metallic single-walled carbon nanotubes (m-SWCNTs), comprising: obtaining a mixture of single-walled carbon nanotubes (SWCNTs) containing the sc- SWCNTs and the m-SWCNTs; using the conjugated polymer extraction (CPE) technique, extracting the mixture of sc- SWCNTs and m-SWCNTs with a conjugated polymer to produce a first material having a weight ratio of m-SWCNTs to sc-SWCNTs that is smaller than a weight ratio of m-SWCNTs to sc-SWCNTs in the mixture; dispersing the first material in a non-polar organic liquid medium to form an initial dispersion; and exposing the initial dispersion to a fiber-like adsorption medium to preferentially adsorb the m-SWCNTs in the initial dispersion, to thereby further separate the sc-SWCNTs from the m- SWCNTs.

22. The process of claim 21, wherein exposing the initial dispersion to the fiber-like adsorption medium comprises flowing the initial dispersion through a plug of the fiber-like adsorptionmedium, wherein the plug is between about 0.2 cm and about 5 cm in length, measured along a direction of fluid flow.

23. The process of claim 21, wherein exposing the initial dispersion to the fiber-like adsorption medium comprises adding an amount of the fiber-like adsorption medium to the initial dispersion.

24. The process of claim 23, wherein exposing the initial dispersion to the fiber-like adsorption medium further comprises 1) applying ultrasonic energy for a period of time of between about 10 minutes and about 120 minutes to form a second dispersion, and 2) allowing the second dispersion to rest at room temperature for a period of time of between about 1 hour and about 24 hours.

25. The process of claim 24, further comprising collecting a purified dispersion after exposure to the fiber-like adsorption medium, comprising separating the fiber-like adsorption medium from the second dispersion and collecting the remainder as the purified dispersion.

26. The process of claim 25, wherein separating the fiber-like adsorption medium from the second dispersion comprises at least one of: centrifuging the second dispersion and collecting a supernatant from above a sediment layer including the fiber-like adsorption medium, and passing the second dispersion through a plug of fiber-like material, the plug having a length that is between about 1 cm and about 5 cm measured along a direction of fluid flow.

27. The process of claim 26, wherein the fiber-like material and the fiber-like adsorption medium have a same composition.

28. The process of claim 26, wherein the fiber-like material and the fiber-like adsorption medium have a different composition.

29. The process of claim 21, wherein extracting the mixture of sc-SWCNTs and m-SWCNTs with the conjugated polymer produces a semi-enriched sc-SWCNT dispersion, and furthercomprising exposing the semi-enriched sc-SWCNT dispersion to a particulate inorganic adsorption medium, for selectively binding the m-SWCNTs to further separate the sc-SWCNTs from the m-SWCNT and thereby produce the first material.

30. The process according to claim 21, wherein the dispersion formed by dispersing the first material in the non-polar organic liquid medium has an initial conjugated polymer: SWCNT weight ratio of about 1:1, and comprising adding the conjugated polymer to the dispersion to adjust the polymer: SWCNT weight ratio to between about 1 : 1 and about 20: 1.

31. The process of claim 30, wherein the conjugated polymer: SWCNT weight ratio is adjusted to between about 2: 1 and about 6: 1.

32. The process of claim 30, wherein the conjugated polymer: SWCNT weight ratio is adjusted to about 4:1.

33. The process of claim 21, wherein the fiber-like adsorption medium comprises a microfiber having a diameter in the range 0.01 pm to 100 pm.

34. The process of claim 21, wherein a surface of the fiber-like adsorption medium comprises polar groups selected from OH and NH2.

35. The process of claim 21, wherein the fiber-like adsorption medium comprises a microfiber selected from a glass microfiber, a cellulose microfiber and an asbestos microfiber.

36. The process of claim 21, wherein the initial dispersion is exposed to a weight-amount of the fiber-like adsorption medium that is between about 0.1 time and about 100 times a weightamount of the dispersed SWCNTs.

37. The process of claim 21, comprising collecting a purified dispersion after the exposing the initial dispersion to the fiber-like adsorption medium, wherein the SWCNTs in the collected purified dispersion are at least 99.99% sc-SWCNTs by weight.

38. The process of claim 21, wherein the non-polar liquid medium is selected from toluene, benzene, xylene, trimethyl benzene, ethyl benzene, chlorobenzene, dichlorobenzene, and methylnaphthalene.

39. The process of claim 21, wherein the non-polar organic liquid medium is toluene.

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