Method and system for enhancing carbon conversion and selective synthesis of semiconducting single-walled carbon-nanotube fibers

Abstract

The present invention discloses a radial mixing system (100) and method (800) designed to enhance carbon conversion and selectively synthesize semiconducting single-walled carbon nanotube (SWCNT) fibers via floating catalyst chemical vapor deposition (FC-CVD). A mixed solution of a carbon source, catalyst precursor, and promotor in specified atomic ratios, is prepared. This solution is vaporized in a preheater (106) and the resulting vapors are introduced into a reactor (102) maintained at predefined temperatures. A fan (104), rotating at a defined RPM, facilitates mixing in the evaporation and re-nucleation zones. The process yields cylindrical SWCNT aerogels (108) in the re-nucleation zone, which exit the reactor via carrier gas flow. Subsequent condensation in a water bath unit (112) converts the aerogels into SWCNT fibers (114), collected efficiently on a rotating roller (120).

Description

METHOD AND SYSTEM FOR ENHANCING CARBON CONVERSION AND SELECTIVE SYNTHESIS OF SEMICONDUCTING SINGLE-WALLED CARBON-NANOTUBE FIBERS

[0001] FIELD OF THE INVENTION

[0002] The present invention relates to carbon nanotube fibers, and particularly, to a radial mixing method and system for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube fibers by floating catalyst chemical vapor deposition.

[0003] BACKGROUND OF THE INVENTION

[0004] Carbon nanotube (CNT) is an allotrope of carbon having properties several orders superior to conventional materials. Some attractive properties include high tensile strength (-100 GPa), high elastic modulus (-1 TPa), high thermal conductivity (-3000 W / mK), and high electrical conductivity (-107). Unfortunately, these exotic properties are not translated from individual CNT to macroscale. Significant translation of properties in the macroscale is achieved when CNT is produced in the form of fibers. The methods for producing CNTs in the form of fiber include forest spinning, spinning using surfactant, spinning using super acid, and floating catalyst chemical vapor deposition (FC-CVD).

[0005] In the forest spinning process, catalysts like Co / Fe are deposited on the substrate like Si / SiOi. CVD is carried out on this substrate. The CNT grows vertically from the catalyst to form a forest-like structure. The forest-like structure is pulled and twisted to form fiber.

[0006] In spinning using surfactants, surfactants like sodium dodecyl sulfate are used to disperse CNT in aqueous liquid. This liquid is passed through a solution having a polymer like PVA. The PVA displaces surfactant in the liquid and gets attached to CNT to form a fiber. The fiber produced in this method however is not neat and is in the form of a polymer-CNT composite.

[0007] In spinning using super acids, CNTs are dispersed in super acids like chlorosulfonic acid and this solution is injected into a coagulant which precipitates out CNT in the form of fibers.

[0008] The aerogel spinning in FC-CVD is the only continuous method that has the potential for scale-up. The fiber produced by FC-CVD methods has so far had the best mechanical properties having tensile strength above 9 GPa. In this method, CNT fibers are produced by carrying out CVD using a carbon source like methane, toluene, etc., a catalyst precursor like ferrocene, and a promoter precursor like thiophene. During FC-CVD the parameters are adjusted to ensure a high aspect ratio of CNT to ensure self-assembly. The high aspect ratios are ensured by using high temperatures (above 1100 °C) and thepresence of a promotor like sulfur (S). Depending on the synthesis conditions the CNTs can be single-walled CNT (SWCNT) or multi-walled CNT (MWCNT). The self-assembly of the CNTs result will result in the formation of CNT aerogel. The CNT aerogel can be converted into fiber when dipped or sprayed with aqueous or organic liquids. The major drawback of the FC-CVD is its low carbon conversion which is in the range of 4%. Several methods have been adopted to enhance the conversion.

[0009] SWCNT synthesized by FC-CVD and other processes is mostly a mixture of semiconducting single-walled CNT (SWCNT) and metallic SWCNT. Only semiconducting and metallic SWCNT is produced by post-processing by methods like chromatography. Some researchers have increased the selectivity of semiconducting SWCNT in FC-CVD by selective etching of metallic SWCNT using H2 gas and H2O.

[0010] The carbon nanotube fiber was first synthesized by Vigolo et al. by surfactantbased coagulation spinning as described in a document “Macroscopic Fibers and Ribbons of Oriented Carbon Nanotubes. Science 2000,290(5495): 1331-4. https: / / doi.org / 10.1126 / science.290.5495.1331” . The synthesized fiber was a composite fiber of PVA and CNT. The first neat CNT fiber was synthesized by Jiang et al. by forest spinning technique as described in a document titled “Spinning continuous carbon nanotube yarns. Nature 2002,419(6909):801-. https^ / d0i^g / lO:lO384J^^l,.

[0011] Neat CNT fiber can also be produced by spinning using superacids which was first reported by Ericson et al., as described in a document titled “Macroscopic, Neat, Single - Walled Carbon Nanotube Fibers. Science 2004,305(5689): 1447-50. https: / / doi.org / 10.1126 / science.1101398”. The above processes are two-step process that requires the synthesis of CNT separately before spinning into fiber. The first single-step process of spinning CNT was achieved by Li et al. through aerogel spinning in a floating catalyst chemical vapor deposition (FC-CVD) process, as described in a document titled “Direct Spinning of Carbon Nanotube Fibers from Chemical Vapor Deposition Synthesis. Science 2004, 304(5668):276-8. https: / / doi.org / 10.! 126 / science.1094982” .

[0012] The synthesis of CNT fibers in FC-CVD has been carried out using different hydrocarbons by different researchers. The synthesis of CNT fibers in FC-CVD has been carried out using different researchers. The first successful spinning of CNT fiber was carried out using methane as a carbon source, as described in the document titled “Direct Spinning of Carbon Nanotube Fibers from Chemical Vapor Deposition Synthesis. Science 2004, 304(5668):276-8. https: / / doi.org / 10.! 126 / science.1094982” , which was followed by many other researchers, as described in documents “Controlling the crystalline quality of carbon nanotubes with processing parameters from chemical vapor depositionSUBSTITUTE S?IEET (RULE 26)

[0013] Acetylene and Many liquid carbon precursor like toluene, as described in documents “High thermal conductivities of carbon nanotube films and micro-fibres and their dependence on morphology. Carbon 2017,114:160-8. https: / / doi.Org / htlps: / / doi.org / 10.1016 / j.carbon.2016.12.006” and “The influence of carbon source and catalyst nanoparticles on CVD synthesis of CNT aerogel. Chemical Engineering Journal 2017,314:388-95. https: / / doi.Org / https: / / doi.org / 10.1016 / j.cej.2016.ll.157” , acetone, n-hexane, as described in documents “The effect of a convection vortex on sock formation in the floatinghttps: / / doi.Org / https: / / doi.org / 10.1016 / j.matdes.2017.06.070”, ethanol, as described in documents “Carbon nanotube and graphene multiple -thread yarns. NanoscaleCommunications 2014,5(1 ):3848. https: / / doi.org / 10.1038 / ncomms4848” , methanol, as described in document “One-step floating conversion of biomass into highly graphitized and continuous carbon nanotube yarns. Green Energy & Environment 2022. https: / / doi.Org / https: / / doi.org / 10.1016 / j.gee.2022.04.002” , butanol, as described in document “Controlling Carbon Nanotube Type in Macroscopic Fibers Synthesized by the Direct Spinning Process. Chemistry of Materials 2014,26(ll):3550-7. https: / / doi.org / 10.1021 / cm501187x”, ethylene glycol, as described in documentSUBSTITUTE S?IEET (RULE 26)“ Mechanical Properties of Continuously Spun Fibers of Carbon Nanotubes. Nano Letters 2005,5(8):1529-33. https: / / doi.org / 10.1021 / nl050634V .

[0014] The most widely utilized promotor for the synthesis of CNT fiber is Sulphur, as described in a document titled “Synthesis of high-quality carbon nanotube fibers by controlling the effects of sulfur on the catalyst agglomeration during the direct spinning process. RSC Advances 2015,5(52):41894-900. https: / / doi.org / 10.1039 / C5RA04691B” . Mas et al. A document “Group 16 elements control the synthesis of continuous fibers of carbon nanotubes. Carbon 2016,101:458-64. https: / / doi.Org / https: / / doi.org / 10.1016 / j.carbon.2016.02.005” has shown Selenium and Tellurium can also be utilized for spinning CNT fiber. The CNT fiber synthesis has been carried out in 3 reactor configuration namely (a) vertical top-down configuration where a vertical reactor with precursor are fed from top and CNT fiber is collected at bottom, as described in documents “Direct Spinning of Carbon Nanotube Fibers from Chemical Vapor Deposition Synthesis. Science 2004,304(5668):276-8. https: / / doi.org / 10.1126 / science.1094982” and “Controlling Carbon Nanotube Type in Macroscopic Fibers Synthesized by the Direct Spinning Process. Chemistry of Materials 2014,26(ll):3550-7. https: / / doi.org / 10.1021 / cm501187x”, (b) vertical bottom-up configuration where vertical reactor with precursor are fed at bottom and CNT fiber is collected at top, as described in document “Synthesis, Structure and Electrical Resistivity of Carbon Nanotubes Synthesized over Group VIII Metallocenes. Nanomaterials. 10. 2020”, and (c) horizontal reactor configuration, as described in documents “The effect of a convection vortex on sock formation in the floating catalyst method for carbon nanotube synthesis. Carbon 2016,102:513-9. https: / / doi.Org / https: / / doi.org / 10.1016 / j.carbon.2016.02.087\ “Gas phase pyrolysis synthesis of carbon nanotubes at high temperature. Materials & Design 2017,132:112-8. https: / / doi.Org / https: / / doi.org / 10.1016 / j.matdes.2017.06.070”, and “Bi-directional catalyst injection in floating catalyst chemical vapor deposition for enhanced carbon nanotube fiber yield. Carbon Trends 2022,9:100211. https: / / d0i.0rg / htps: / / d0i.0rg / l 0.1016 / j.cartre.2O22.100211”.

[0015] Researchers have utilized different approaches in FC-CVD process for enhancing the carbon conversion. Roddies et al., as described in a document titled “Carbon nanotube synthesis and spinning as macroscopic fibers assisted by the ceramic reactor tube. Scientific Reports 2019,9(1 ):9239. https: / / doi.org / 10.1038 / s41598-019-45638-6” , utilized mullite reactor tube to enhance the carbon conversion. Zhang et al., as described in a document titled “Carbon nanotube fibers prepared by activating deactivated iron particlesin floating catalyst chemical vapor deposition tail gas. Materials Science / Medziagotyra 2017,23(3 ):260-5”, used tail gas from one reactor as a precursor to another. Lee et al., as described in a document titled “ Deep-injection floating-catalyst chemical vapor deposition to continuously synthesize carbon nanotubes with high aspect ratio and high crystallinity. Carbon 2021,173:901 -9. https: / / doi. org / https: / / doi. org / 10.1016 / j. carbon.2020.11.065”, Utilized deep injection method of the precursor to enhance carbon conversion.

[0016] In the deep injection method, the precursor is injected away from the vortex formed in the inlet region. Zhang et al., as described in a document titled “Transparent and Freestanding Single-Walled Carbon Nanotube Films Synthesized Directly and Continuously via a Blown Aerosol Technique. Advanced Materials 2020,32(39):2004277. https: / / doi.Org / https: / / doi.org / 10.1002 / adma.202004277” , utilized blown FC-CVD to produce transparent CNT film with high conversion. Moon et al., as described in a document titled “The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality. Chemistry - A European Journal 2019, 25( 59 ): 13635 -9. https: / / doi. org / https: / / doi.org / l 0.1002 / chem.201903273”, reported enhanced yield by using Fe-Ni bi-metallic catalyst. Kuraeva et al., as described in a document titled “Synthesis, Structure and Electrical Resistivity of Carbon Nanotubes Synthesized over Group VIII Metallocenes. Nanomaterials 2020,10(11). https: / / doi.org / 10.3390 / nanol0112279”, reported enhanced yield by using Fe-Ni-Co tri- metallic catalyst.

[0017] Single-walled carbon nanotube in FC-CVD is achieved by maintaining a low Fe / S ratio. Weller et al. has shown that at low S / Fe CNT causes CNT to only nucleate from a small region in the catalyst where S deposits in a catalyst. High S causes CNT to nucleate from the entire catalyst as S coats the entire catalyst causing the nucleation of multi-walled CNT. Enhancement of semiconducting CNT content in the FC-CVD process has been carried selective etching of the metallic CNT. Li et al., as described in a document titled “High-Quality, Highly Concentrated Semiconducting Single-Wall Carbon Nanotubes for Use in Field Effect Transistors and Biosensors. ACS Nano 2013,7(8):6831-9. https: / / doi.org / 10.1021 / nn401998r”, have used hydrogen carrier gas to etch metallic CNT. Li et al., as described in a document titled “Preparation of isolated semiconducting singlewall carbon nanotubes by oxygen-assisted floating catalyst chemical vapor deposition. Chemical Engineering Journal 2022,450:137861. https: / / doi.Org / https: / / doi.org / 10.1016 / j.cej.2022.137861” , has also utilized O2 gas to etch metallic CNT.

[0018] Patent no. US7323157B2 titled "PRODUCTION OF AGGLOMERATES FROMSUBSTITUTE S&EET (RULE 26)GAS PHASE " describes a process for the production of an agglomerate by passing gaseous reactants into a reactor. The gaseous reactants react in the reactor forming agglomerates of the product particles which are continuously removed from the reactor by applying a force. The major claim recites the usage of a mechanical force either in the form of a spindle or rod rotating either in a clockwise or anticlockwise direction. In addition to mechanical force, the agglomerated products are removed out of the reactor via electrostatic or magnetic force.

[0019] Patent no. US9567220B2 titled "APPARATUS FOR MANUFACTURING CARBON NANOTUBE FIBERS" describes the design of a sub-synthesis furnace that is in the shape of a pipe in which raw material flows through the inner walls of the subsynthesis furnace which is equipped with heating arrangement.

[0020] Patent no. US20170044689A1 titled "CARBON NANOTUBE FIBER AND METHOD FOR PRODUCING THE SAME" describes the synthesis of carbon nanotube fibers with tensile strength of more than 5 GPa. The high tensile strength of carbon nanotube fibers is achieved with the usage of cross linkers.

[0021] Patent no US20170327378 titled "METHOD FOR THE PRODUCTION OF CARBON NANOTUBE STRUCTURES " describes a method for the production of carbon nanostructures. The major claim includes the exact position of the release of carbon source i.e. beginning of the first temperature zone and at the end of the second temperature zone. In addition, the inventors also claimed that the release of sulfur must be after the release of the carbon source.

[0022] Patent no US9969619B2 titled " CARBON MATERIALS COMPRISING CARBON NANOTUBES AND METHODS OF MAKING CARBON NANOTUBES" describes the formation of carbon nanotubes having conductivity typically in the range of 0.7 x 106S nT i

[0023] Patent no US20130196156A1 titled "CHEMICAE TREATMENT OF CARBON NANOTUBE FIBRES" describes that the carbon nanotube fibers synthesized were treated with a polymer which acts as a crosslinker. 1,5 hexadiene is used as a crosslinker and crosslinking is done by exposing the carbon nanotube fiber with 254 nm ultraviolet radiation.

[0024] Patent no US 20090282802 Al titled "CARBON NANOTUBEYARN, THREAD, ROPE, FABRIC AND COMPOSITE AND METHODS OF MAKING THE SAME" describes a process for making CNT yam / thread using CNT arrays using dry and wet process. In the dry spin process, CNT was pulled out from the CNT array and subsequently heat-treated. In the wet spun process the CNT fibers pulled from CNT arrays were treatedSUBSTITUTE S^EET (RULE 26)with PEG - 2000 and subsequently transformed into a film. The major claims by authors are that CNTs in CNT yam / thread possess lengths in the range of mm. The chemical treatment given to the CNT yam leads to the formation of ionic bonds, covalent bonds, metallic bonds, and combinations of such bonds.

[0025] Patent no US 7354877B2 titled "CARBON NANOTUBE FABRICS " describes the making of fabrics possessing unique chemical, electrical, and thermal properties. The major claim of the inventors is the CNT fibers in fabric consist of CNT with insulating, semiconducting, conducting, or superconducting properties.

[0026] Patent no US 20040109815 / A1 titled "CARBON NANOTUBE ARRAY AND METHOD FOR MAKING SAME'1describes a method for making CNT-based device. The CNT -based device consists of a substrate, nano-sized particles as a catalyst, and a CNT array grown over it. The major claim of inventors is a type of nanoparticle tuning the growth of the CNT array.

[0027] Patent no US 9656246B2 titled "VERTICAEEY ALIGNED ARRAYS OF CARBON NANOTUBES FORMED ON MULTILAYER SUBSTRATES" describes a method for making CNT arrays using multilayer substrates. Here, aluminum or copper surface was used as a substrate over which the iron layer was deposited. On top of the iron layer, aluminum hydroxide particle with iron nanoparticles. The major claim of the inventor is adhesion layer of iron over the aluminum or copper substrate helps in the migration of the catalytic layer into the interlayer during the synthesis of CNT arrays.

[0028] Patent no. US 20180305211A1 titled "CARBON MATERIALS COMPRISING CARBON NANOTUBES AND METHODS OF MAKING CARBON NANOTUBES" describes the method for making CNT using vertical CVD reactor using methane as carbon source. The major claim recites a product consisting of armchair chirality typically possessing metallic properties.

[0029] Patent no. CN115403032A titled "By using CO2 Method for continuously preparing carbon nano tube fiber" describes the production of carbon nanotube fiber by floating catalyst chemical vapour deposition using CO2 as a carbon source.

[0030] Patent no. US10246333B1 titled "Method for continuous manufacture of cntf having high strength and high conductivity" describes the production of high strength and high conductivity carbon nanotube fiber continuously by treating the fibers with strong acid.

[0031] Patent no. US20050006801A1 titled "Production of agglomerates from gas phase" describes the production of agglomerates of CNT in a reactor by gas phase reaction which can be converted into fibers.SUBSTITUTE S?IEET (RULE 26)

[0032] Patent no. US10273599B2 titled " Apparatus for manufacturing carbon nanotube fiber” describes an application of current to the carbon nanotube fiber for joule heating to remove amorphous carbon.

[0033] Patent no. CN109311673B titled "Method for preparing single-walled carbon nanotube fiber aggregate" describes a methodology for the production of single-walled carbon nanotube by controlling the carbon source to reduce gas.

[0034] Patent no. JP2013011039A titled "Device for producing carbon nanotube continuous fiber and producing method thereof' describes the production of carbon nano tube fiber continuously in a tubular reactor.

[0035] Patent no. CN 109537110A titled "A kind of preparation method of carbon nanotubefibre" describes the production of carbon nanotube fiber with twisting.

[0036] Although, each of the above documents refers to some improvement over the known solutions, however, as discussed above, in the conventional solutions of synthesis of CNT fiber by FC-CVD, the conversion is low, ranging at around 4%. Further, the end product also contains a significantly high amount of impurities, such as amorphous carbon and iron from the catalyst utilized.

[0037] Thus, there is a need for improved techniques to enhance the conversion of CNT fiber synthesis in the FC-CVD process with high selectivity of semi-conducting SWCNT, and to make the end product with low impurities.

[0038] OBJECTS OF THE INVENTION:

[0039] Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are listed herein below.

[0040] The main objective of the present invention is to enhance the conversion of CNT fiber synthesis in the FC-CVD process with high selectivity of semi-conducting SWCNT.

[0041] Another objective of the present invention is to make the product with low impurities.

[0042] These and other objects and advantages will become more apparent when reference is made to the following description and accompanying drawings.

[0043] SUMMARY OF THE INVENTION

[0044] This summary is provided to introduce concepts related to a radial mixing method and system for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalystSUBSTITUTE S^IEET (RULE 26)chemical vapor deposition, FC-CVD. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0045] In an aspect of the present disclosure, a radial mixing method for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, is described. The method includes the step of providing a mixed solution of a carbon source, a catalyst precursor, and a promotor taken in a predefined atomic ratio, into a reactor maintained at a predefined reactor temperature, through a preheater maintained at a predefined preheater temperature. At the preheater temperature, the mixed solution is converted into vapours. The vapours are carried into a heating zone of the reactor with carrier gases. A fan rotating at a predefined rotation per minute, RPM, is placed in an evaporation zone of the reactor, and close to a re-nucleation zone of the reactor.

[0046] The method further includes the step of receiving at least one CNT aerogel having a cylindrical structure, formed in the re-nucleation zone of the reactor, coming out from an outlet of the reactor, by a flow of the carrier gases.

[0047] The method further includes the step of passing the at least one CNT aerogel through a water bath for condensing the at least one CNT aerogel into at least one CNT fiber.

[0048] The method further includes the step of collecting the at least one CNT fiber on a rotating roller.

[0049] In an embodiment of the present invention, the method further includes the step of determining the re-nucleation and the evaporation zones of the reactor for placing the fan in the reactor.

[0050] In another embodiment of the present invention, the reactor is made of a quartz tube having an inner diameter of 45mm and a length of 1200 mm and includes a heating length of 800 mm.

[0051] In another embodiment of the present invention, the mixed solution is provided, at a flow rate of 0.06 ml / min, by a syringe pump, to the reactor.

[0052] In another embodiment of the present invention, the predefined preheater temperature of the preheater is 140 °C.

[0053] In another embodiment of the present invention, the predefined atomic ratio of the carbon source, the catalyst precursor, and the promotor in the mixed solution is 100: 1:0.2, wherein the mixed solution is obtained by mixing together the carbon source, the catalyst precursor, and the promotor for at least 10 minutes by ultrasonication, and wherein theSUBSTITUTE SfdEET (RULE 26)carbon source, the catalyst precursor, and the promoter are toluene, ferrocene, and thiophene, respectively.

[0054] In another embodiment of the present invention, the carrier gases are argon and hydrogen, with a flow rate of 0.25 SLPM and 1.75 SLPM, respectively.

[0055] In another embodiment of the present invention, the predefined reactor temperature is 1200 °C through SiC heating rod resistance heating.

[0056] In another embodiment of the present invention, the fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the at least one CNT aerogel sticking on the fan, and wherein the fan is rotated with a rotation axis parallel to the reactor and one or more blades of the fan at 120° apart are parallel to an axial direction of the reactor.

[0057] In another embodiment of the present invention, the reactor outlet is connected to a glove box maintained in an inert condition by purging argon or nitrogen.

[0058] In another embodiment of the present invention, the method further includes the step of verifying, by scanning electron microscopy (SEM) and / or Raman spectroscopy, if the formed at least one CNT fiber contains SWCNT.

[0059] In another aspect of the present disclosure, a radial mixing-based system for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC- CVD, is described. The system includes a reactor, a water bath unit, and a rotating roller. The reactor is maintained at a predefined reactor temperature and includes a fan of a predefined geometry, rotating at a predefined rotation per minute, RPM, placed in an evaporation zone of the reactor, and close to a re-nucleation zone of the reactor. A mixed solution of a carbon source, a catalyst precursor, and a promotor taken in a predefined atomic ratio is provided into the reactor through a preheater maintained at a predefined preheater temperature and coupled to the reactor. At the preheater temperature, the mixed solution is converted into vapours. The vapours are carried into a heating zone of the reactor with carrier gases. At least one CNT aerogel having a cylindrical structure, are formed in the re-nucleation zone of the reactor.

[0060] The water bath unit is coupled with an outlet of the reactor. The at least one CNT aerogel, coming out from the outlet of the reactor, by a flow of the carrier gases, is passed through the water bath for condensing the at least one CNT aerogel into at least one CNT fiber. The rotating roller coupled to the water bath unit collects the at least one CNT fiber.

[0061] In an embodiment of the present invention, the re-nucleation and the evaporation zones of the reactor are determined for placing the fan in the reactor.SUBSTITUTE SWEET (RULE 26)

[0062] In another embodiment of the present invention, the reactor is made of a quartz tube having an inner diameter of 45mm and a length of 1200 mm and includes a heating length of 800 mm.

[0063] In another embodiment of the present invention, the mixed solution is provided, at a flow rate of 0.06 ml / min, by a syringe pump, to the reactor.

[0064] In another embodiment of the present invention, the predefined preheater temperature of the preheater is 140 °C.

[0065] In another embodiment of the present invention, the predefined atomic ratio of the carbon source, the catalyst precursor, and the promotor in the mixed solution is 100: 1:0.2, wherein the mixed solution is obtained by mixing together the carbon source, the catalyst precursor, and the promotor for at least 10 minutes by ultrasonication, and wherein the carbon source, the catalyst precursor, and the promotor are toluene, ferrocene, and thiophene, respectively.

[0066] In another embodiment of the present invention, the carrier gases are argon and hydrogen, with a flow rate of 0.25 SLPM and 1.75 SLPM, respectively.

[0067] In another embodiment of the present invention, the predefined reactor temperature is 1200 °C through SiC heating rod resistance heating.

[0068] In another embodiment of the present invention, the fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the at least one CNT aerogel sticking on the fan, and wherein the fan is rotated with a rotation axis parallel to the reactor and the predefined geometry of the fan includes one or more blades of the fan at 120° apart parallel to an axial direction of the reactor.

[0069] In another embodiment of the present invention, the reactor outlet is connected to a glove box maintained in an inert condition by purging argon or nitrogen.

[0070] In another embodiment of the present invention, the formed at least one CNT fiber is verified, by scanning electron microscopy (SEM) and / or Raman spectroscopy, for if the formed at least one CNT fiber contains SWCNT.

[0071] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0072] BRIEF DESCRIPTION OF DRAWINGS:

[0073] The illustrated embodiments of the subject matter will be understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:

[0074] FIG. 1 illustrates an assembly of an AC motor, a preheater, a fan, a reactor, a water bath unit, and a roller, for CNT fiber synthesis, in accordance with an exemplary embodiment of the present disclosure;

[0075] FIG. 2 illustrates a fan having a plurality of blades used for radial mixing in a reactor, in accordance with an exemplary embodiment of the present disclosure;

[0076] FIG. 3 illustrates at least one CNT fiber collected on a rotating roller, in accordance with an exemplary embodiment of the present disclosure;

[0077] FIG. 4 illustrates SEM micrographs of carbon nanotube fiber, in accordance with an exemplary embodiment of the present disclosure;

[0078] FIG. 5 illustrates a typical Raman spectra of semiconducting CNT fiber, in accordance with an exemplary embodiment of the present disclosure;

[0079] FIG. 6 illustrates (a) the Raman spectrum of the RBM peaks region of CNT fiber (S- semiconducting region, M- metallic region), and (b) the UV-Vis-NIR spectrum of CNT fiber, in accordance with an exemplary embodiment of the present disclosure;

[0080] FIG. 7 illustrates (a) thermogravimetry (TG) of CNT fiber in the O2 atmosphere, and (b) differential TG (DTG) of CNT fiber, in accordance with an exemplary embodiment of the present disclosure; and

[0081] FIG. 8 illustrates a radial mixing method for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, in accordance with an exemplary embodiment of the present disclosure.

[0082] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize fromthe following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

[0083] DESCRIPTION OF THE INVENTION:

[0084] The following is a detailed description of embodiments of the disclosure depictedSUBSTITUTE s'fTEET (RULE 26)in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0085] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[0086] The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a device, system, or assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.

[0087] The present invention is directed to a radial mixing method and system for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube (SWCNT) fibers by floating catalyst chemical vapor deposition (FC- CVD).

[0088] The present invention describes a process to synthesize carbon nanotube (CNT) fiber by radial mixing inside a reactor with a rotating fan of a predefined geometry at a particular zone, whereby (1) the carbon conversion of 15% is achieved, (2) selectivity towards semiconducting SWCNT is 95%, and (3) the obtained CNT fiber is almost free of amorphous carbon and low iron without any purification step.

[0089] The radial mixing in the range of 80-150 rpm using a fan with three radial blades parallel to the reactor tube at 120° apart placed at the junction of evaporation and renucleation zone was able to enhance the carbon conversion upto 15% from 4% obtained while not using the fan.

[0090] The radial mixing enhances the selectivity of the semiconducting SWCNT up to 95% in the CNT fiber produced by the FC-CVD method, which is otherwise a mixture of metallic and semiconducting (31:69) SWCNT.

[0091] The CNT fiber has less than 0.1% amorphous carbon and less than 2 % iron residueSUBSTITUTE S^EET (RULE 26)using the radial mixing method of the present invention.

[0092] The present invention provides a method of enhancing the carbon conversion from 4% to 15% (enhancement by 275% w.r.t. conventional solutions) in the FC-CVD reactor for the production of CNT fiber continuously. The produced CNTs are predominantly (95%) semiconducting and have low impurity and are semiconducting which can be used in many applications such as composite reinforcement, thermoelectric generators, and sensors.

[0093] The present invention is carried out as per the following:

[0094] At the outset, determination of the re-nucleation and evaporation zones are made for the placement of a rotating fan in a reactor. The reactor made of a quartz tube having an inner diameter of 45mm and a length of 1200 mm is used for carrying out the present invention. Further, the reactor includes a heating length of 800 mm for carrying out the present invention. The schematic of the reactor is illustrated in Figure 1.

[0095] The synthesis of carbon nanotube (CNT) fiber with toluene as carbon source, ferrocene as catalyst precursor, and thiophene as promotor is taken with 100: 1:0.2 (C: Fe:S) atomic ratio. They are mixed together for 15 min by ultrasonication.

[0096] The mixed solution is pumped into the reactor by a syringe pump through a preheater maintained at 140 °C where it is converted into vapour. The vapour is carried into a heating zone of the reactor with argon (0.25 SLPM) and hydrogen (1.75 SLPM) as the carrier gases. The reactor is maintained at 1200 °C through resistance heating by SiC heating rod.

[0097] A CNT aerogel starts forming in two locations, one near an inlet of the reactor called a nucleation zone, and another near an outlet of the reactor called a re-nucleation zone. The CNT aerogel formation required for the CNT fiber production takes place in the re-nucleation zone. A region or zone where the CNT aerogel does not form is called an evaporation zone.

[0098] A region where the CNT aerogel formation is taking place can be seen as a black region on the reactor tube as a transparent quartz tube is utilized. A temperature in different zones of the reactor is recorded using a thermocouple.

[0099] A three-blade fan with its blade parallel to the tube axis has been utilized for mixing in the reactor. The fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the CNT aerogel sticking on the fan. The fan and its shaft are made of Inconel 725 to sustain the high temperature with a minimum creep. The geometry of the fan is illustrated in Figure 2.

[0100] The fan is rotated with a rotation axis parallel to the reactor tube and the fan blades are parallel to the reactor tube axial direction. This is done to increase only the radial velocity of the carrier gases without increasing the axial velocity which helps in maintaining the residence time. The long-duration synthesis is carried out on an alumina tube.

[0101] Now, a conversion of the CNT aerogel to a CNT fiber starts taking place as the following:

[0102] The CNT aerogel that is formed in the reactor comes out through an outlet of the reactor by a flow of the carrier gases. The reactor outlet is connected to a glove box (111 as shown in Fig. 1) which is maintained in an inert condition by purging argon or nitrogen. The glove box (111) may include an inlet (116 as shown in Fig. 1) for providing the argon / nitrogen gases and an outlet (118 as shown in Fig. 1). The CNT aerogel is passed through a water bath where it condenses into the CNT fiber. The CNT fiber is collected on a rotating roller.

[0103] Finally, scanning electron microscopy (SEM) and Raman spectroscopy are taken to verify if the formed CNT fiber contains SWCNT.

[0104] Now, for better understanding, one or more embodiments of the present invention shall be described with respect to the earlier-mentioned drawings.

[0105] FIG. 1 illustrates an assembly of an AC motor, a preheater, a fan, a reactor, a water bath unit, and a roller, for CNT fiber synthesis, in accordance with an exemplary embodiment of the present disclosure. FIG. 2 illustrates a fan having a plurality of blades used for radial mixing in a reactor, in accordance with an exemplary embodiment of the present disclosure. FIG. 3 illustrates at least one CNT fiber collected on a rotating roller, in accordance with an exemplary embodiment of the present disclosure.

[0106] As illustrated, a radial mixing-based system (100) for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, is described. The system (100) includes a reactor (102) having a fan (104), a preheater (106), a water bath unit (112), and a rotating roller (120).

[0107] The reactor (102) is maintained at a predefined reactor temperature. The fan (104) is of a predefined geometry, rotating at a predefined rotation per minute, RPM, and is placed in an evaporation zone of the reactor, and close to a re-nucleation zone of the reactor. The fan (104) may be rotated by a motor (107).

[0108] A mixed solution of a carbon source, a catalyst precursor, and a promotor taken in a predefined atomic ratio is provided into the reactor through the preheater (106)SUBSTITUTE S^EET (RULE 26)maintained at a predefined preheater temperature and coupled to the reactor.

[0109] At the preheater temperature, the mixed solution is converted into vapours. The vapours are carried into a heating zone of the reactor with carrier gases. At least one carbon nanotube, CNT, aerogel (108) having a cylindrical structure, is formed in the renucleation zone of the reactor. The water bath unit (112) coupled with an outlet (110) of the reactor (102). The at least one CNT aerogel (108), by a flow of the carrier gases, comes out from the outlet of the reactor. The at least one CNT aerogel is passed through the water bath unit (112) for condensing the at least one CNT aerogel into at least one CNT fiber (114). A rotating roller (120) coupled to the water bath unit (112) is adapted for collecting the at least one CNT fiber (114). The typical CNT fiber collected on the rotating roller is illustrated in Figure 3.

[0110] In an embodiment of the present invention, the re-nucleation and the evaporation zones of the reactor (102) are determined for placing the fan (104) in the reactor (102).

[0111] In another embodiment of the present invention, the reactor (102) is made of a quartz tube having an inner diameter of 45 mm and a length of 1200 mm and includes a heating length of 800 mm.

[0112] In another embodiment of the present invention, the mixed solution is provided, at a flow rate of 0.06 ml / min, by a syringe pump, to the reactor.

[0113] In another embodiment of the present invention, the predefined preheater temperature of the preheater is 140 °C.

[0114] In another embodiment of the present invention, the predefined atomic ratio of the carbon source, the catalyst precursor, and the promotor in the mixed solution is 100: 1:0.2. The mixed solution is obtained by mixing together the carbon source, the catalyst precursor, and the promotor for at least 10 minutes by ultrasonication. Further, the carbon source, the catalyst precursor, and the promotor are toluene, ferrocene, and thiophene, respectively.

[0115] In another embodiment of the present invention, the carrier gases are argon and hydrogen, with a flow rate of 0.25 SLPM and 1.75 SLPM, respectively.

[0116] In another embodiment of the present invention, the predefined reactor temperature is 1200 °C through resistance heating of SiC heating rod.

[0117] In another embodiment of the present invention, the fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the at least one CNT aerogel sticking on the fan, and wherein the fan is rotated with a rotation axis parallel to the reactor and theSUBSTITUTE S^EET (RULE 26)predefined geometry of the fan includes a plurality of blades (202, 204, 206) at 120° apart, parallel to an axial direction of the reactor.

[0118] In another embodiment of the present invention, the reactor outlet is connected to a glove box maintained in an inert condition by purging argon or nitrogen.

[0119] FIG. 4 illustrates SEM micrographs of carbon nanotube fiber, in accordance with an exemplary embodiment of the present disclosure.

[0120] FIG. 5 illustrates a typical Raman spectra of semiconducting CNT fiber, in accordance with an exemplary embodiment of the present disclosure.

[0121] FIG. 6 illustrates (a) the Raman spectrum of the RBM peaks region of CNT fiber (S- semiconducting region, M- metallic region), and (b) the UV-Vis-NIR spectrum of CNT fiber, in accordance with an exemplary embodiment of the present disclosure.

[0122] FIG. 7 illustrates (a) thermogravimetry (TG) of CNT fiber in O2 atmosphere, and (b) differential TG (DTG) of CNT fiber, in accordance with an exemplary embodiment of the present disclosure.

[0123] In another embodiment of the present invention, the formed at least one CNT fiber is verified, by scanning electron microscopy (SEM) and / or Raman spectroscopy, for if the formed at least one CNT fiber contains SWCNT.

[0124] FIG. 8 illustrates a radial mixing method for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, in accordance with an exemplary embodiment of the present disclosure.

[0125] As illustrated, a radial mixing method (800) for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, is described. The method includes the step of providing (802) a mixed solution of a carbon source, a catalyst precursor, and a promotor taken in a predefined atomic ratio, into a reactor maintained at a predefined reactor temperature, through a preheater maintained at a predefined preheater temperature.

[0126] At the preheater temperature, the mixed solution is converted into vapours. The vapours are carried into a heating zone of the reactor (102) with the carrier gases. A fan (104) of a predefined geometry, rotating at a predefined rotation per minute, RPM, is placed in an evaporation zone of the reactor, and close to a re-nucleation zone of the reactor.

[0127] The method further includes the step of receiving (804) at least one CNT aerogel having a cylindrical structure, formed in the re-nucleation zone of the reactor,coming out from an outlet of the reactor, by a flow of the carrier gases.

[0128] The method further includes the step of passing (806) the at least one CNT aerogel through a water bath unit for condensing the at least one CNT aerogel into at least one CNT fiber. The method further includes the step of collecting (808) the at least one CNT fiber on a rotating roller.

[0129] In an embodiment of the present invention, the method further includes the step of determining the re-nucleation and the evaporation zones of the reactor for placing the fan in the reactor.

[0130] In another embodiment of the present invention, the reactor is made of a quartz tube having an inner diameter of 45mm and a length of 1200 mm, and includes a heating length of 800 mm.

[0131] In another embodiment of the present invention, the mixed solution is provided, at a flow rate of 0.06 ml / min, by a syringe pump, to the reactor.

[0132] In another embodiment of the present invention, the predefined preheater temperature of the preheater is 140 °C.

[0133] In another embodiment of the present invention, the predefined atomic ratio of the carbon source, the catalyst precursor, and the promotor in the mixed solution is 100: 1:0.2. The mixed solution is obtained by mixing together the carbon source, the catalyst precursor, and the promotor for at least 10 minutes by ultrasonication. Further, the carbon source, the catalyst precursor, and the promotor are toluene, ferrocene, and thiophene, respectively.

[0134] In another embodiment of the present invention, the carrier gases are argon and hydrogen, with a flow rate of 0.25 SLPM and 1.75 SLPM, respectively.

[0135] In another embodiment of the present invention, the predefined reactor temperature is 1200 °C through resistance heating of SiC heating rod.

[0136] In another embodiment of the present invention, the fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the at least one CNT aerogel sticking on the fan. The fan is rotated with a rotation axis parallel to the reactor and the predefined geometry of the fan includes a plurality of blades (202, 204, 206) at 120° apart, parallel to an axial direction of the reactor.

[0137] In another embodiment of the present invention, the reactor outlet is connected to a glove box maintained in an inert condition by purging argon or nitrogen.

[0138] In another embodiment of the present invention, the method further includes the step of verifying, by scanning electron microscopy (SEM) and / or RamanSUBSTITUTE S? EET (RULE 26)spectroscopy, if the formed at least one CNT fiber contains SWCNT. A typical SEM and Raman spectra of the CNT fiber are illustrated in Figures 4 and 5, respectively

[0139] Now, a few typical examples have been presented to illustrate how the present invention is carried out in actual practice:

[0140] Example 1 (15% Carbon Conversion and 95% semiconducting)

[0141] Step 7: Toluene, Ferrocene, and Thiophene are taken with a 100: 1:0.2 (C: Fe:S) atomic ratio. All three chemicals are mixed for 10 minutes by ultrasonication.

[0142] Step 2 The mixed solution is pumped into the preheater maintained at 140°C with a flow rate of 0.06 ml / min.

[0143] Step 3: Hydrogen flow was maintained at 1.75 SLPM and argon flow was maintained at 0.25 SLPM.

[0144] Step 4: A fan which is kept in the evaporation zone and close to the renucleation zone is rotated with an rpm of 150.

[0145] Step 5: The reactor is maintained at a temperature of 1200 °C.

[0146] Step 6: A CNT aerogel comes out of the reactor outlet as a cylindrical structure and it is converted into a CNT fiber by passing it through a water bath unit and continuously collecting on a rotating roller.

[0147] Step 7: The purity of the CNT fiber is determined by thermogravimetry and the semiconducting percentage of the CNT fiber is determined by UV- visible spectroscopy.

[0148] Step 8: An additional characterization of the CNT fiber using SEM, TEM, and Raman spectroscopy is carried out.

[0149] Example 2 (10% Carbon Conversion and 80% semiconducting)

[0150] Step 1 Toluene, Ferrocene, and Thiophene are taken with a 100:1:0.2 (C: Fe:S) atomic ratio. All three chemicals are mixed for 10 minutes by ultrasonication.

[0151] Step 2: The mixed solution is pumped into the preheater maintained at 140°C with a flow rate of 0.06 ml / min.

[0152] Step 3: A hydrogen flow was maintained at 1.75 SLPM and an argon flow was maintained at 0.25 SLPM.

[0153] Step 4: A fan which is kept in the evaporation zone and close to the renucleation zone is rotated with an rpm of 80.

[0154] Step 5: The reactor is maintained at a temperature of 1200 °C.

[0155] Step 6: A CNT aerogel comes out of the reactor outlet as a cylindrical structure and it is converted into a CNT fiber by passing it through a water bath unit and continuously collecting on a rotating roller.SUBSTITUTE s'tlEET (RULE 26)

[0156] Step 7: The purity of the CNT fiber is determined by thermogravimetry and the semiconducting percentage of the CNT fiber is determined by UV-Vis-NIR spectroscopy.

[0157] Step 8: An additional characterization of the CNT fiber using SEM, TEM, and Raman spectroscopy is carried out.

[0158] Example 3 (4% Carbon Conversion and 69% semiconducting)

[0159] Step 1 Toluene, Ferrocene, and Thiophene are taken with a 100: 1:0.2 (C: Fe:S) atomic ratio. All three chemicals are mixed for 10 minutes by ultrasonication.

[0160] Step 2: The mixed solution is pumped into the preheater maintained at 140°C with a flow rate of 0.06 ml / min.

[0161] Step 3: A hydrogen flow was maintained at 1.75 SLPM and an argon flow was maintained at 0.25 SLPM.

[0162] Step 4: A synthesis is carried out without using a fan inside the reactor.

[0163] Step 5: The reactor is maintained at a temperature of 1200 °C

[0164] Step 6: A CNT aerogel comes out of the reactor outlet as a cylindrical structure and it is converted into a CNT fiber by passing it through a water bath unit and continuously collecting on a rotating roller.

[0165] Step 7: The purity of the CNT fiber is determined by thermogravimetry and the semiconducting percentage of the CNT fiber is determined by UV-Vis-NIR spectroscopy.

[0166] Step 8: An additional characterization of the CNT fiber using SEM, TEM, and Raman spectroscopy is carried out.

[0167] Determining if a CNT fiber is metallic or semiconducting, and quantifying it

[0168] The Raman spectrum of a CNT fiber can be used to determine whether the CNT fibers are semiconducting or metallic based on the radial breathing mode (RBM) peaks that occur between approximately 150 to 250 cm1. The RBM peak is exclusive to SWCNT and arises due to the radial contraction and expansion of the CNT fibers in the radial direction. The peak position can be utilized to identify whether the CNTs are metallic or semiconducting using the Katura plot. The Katura plot is described in the documents “Strano, M. S. (2003). Probing chiral selective reactions using a revised Kataura plot for the interpretation of single-walled carbon nanotube spectroscopy. Journal of the American Chemical Society, 125(51), 16148-16153” and “Tian, Y., Jiang, H., Laiho, P., & Kauppinen, E. I. (2018). Validity of measuring metallic and semiconducting single-walled carbon nanotube fractions by quantitative Raman spectroscopy. AnalyticalSUBSTITUTE ^?EET (RULE 26)chemistry, 90(4), 2517-”. The Raman spectrum showing the semiconducting and metallic peak regions is shown in Figure 6 (a).

[0169] The quantification of the semiconducting / metallic CNT percentage can be performed using the UV-Vis-NIR spectrum (Figure 6 (b)). The ratio of the peak areas was calculated using Eq(l and 2). 100(1) rs= 100 — rs(2)Where, rM = Percentage of metallic CNT r$= Percentage of semiconducting CNTAM = Area fraction of Mu peakAs = Area fraction of S22 peak

[0170] Purity calculation

[0171] The purity of the CNT fiber was determined using thermograviometry (TG). The TG of a CNT fiber is shown in Figure 7(a). The CNT fiber is heated up to 1000 °C in an O2 atmosphere and weight loss is monitored. The weight loss of CNT fiber below 400 °C is due to an amorphous carbon and weight loss above 400 °C is due to the CNT. The mass that does not oxidize is due to iron. The quantification of the weight loss can be done by taking the differential TG (DTG) (Figure 7(b)) and the area of the peak below 400 °C is proportional to the mass fraction of amorphous carbon, area of peaks above 400 °C corresponds to the mass fraction of CNT and mass which has not oxidized corresponds to iron.

[0172] A few of the major advantages of the present invention over the conventional solutions:• The conversion of carbon was enhanced to 15 % from 4% (an increase of 275%) in the CNT fiber by radial mixing inside the reactor by rotation of the fan in radial direction with blades parallel to the reactor tube axial direction at 150 rpm.• The process / method was able to provide 95% selectivity of semiconducting SWCNT in the CNT fiber.SUBSTITUTE ^EET (RULE 26)• The end product i.e. CNT fiber is almost free of amorphous carbon and low iron without any purification step.• The CNT fiber synthesized by the FC-CVD is generally a mixture of metallic and semiconducting SWCNTs. The radial mixing by rotating a fan of a predefined specific geometry at a particular location increases the selectivity of semiconducting SWCNT to 95%.• The carbon conversion of spinnable CNT is generally low in the order of 4%, however, the radial mixing enhances carbon conversion to 15 %• The radial mixing also ensures the CNT fibers have low impurities. The amorphous carbon is not detectable by thermogravimetry (<0.1%) and residual iron is low (2%).• A high selectivity of semiconducting SWCNT and low impurities will enable the material to be utilized without any post-processing and purification.

[0173] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art by devising various systems that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to further the art and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.

[0174] Although embodiments for the present subject matter have been described in language specific to package features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system / device of the present invention willbe apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

Claims

CLAIMS:

1. A radial mixing method (800) for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, the method comprising: i) providing (802) a mixed solution of a carbon source, a catalyst precursor, and a promotor taken in a predefined atomic ratio, into a reactor (102) maintained at a predefined reactor temperature, through a preheater maintained at a predefined preheater temperature, wherein, at the preheater temperature, the mixed solution is converted into vapours, wherein the vapours are carried into a heating zone of the reactor with carrier gases, and wherein a fan (104) of a predefined geometry, rotating at a predefined rotation per minute, RPM, is placed in an evaporation zone of the reactor, and close to a re-nucleation zone of the reactor; ii) receiving (804) at least one CNT aerogel having a cylindrical structure, formed in the re-nucleation zone of the reactor, coming out from an outlet of the reactor, by a flow of the carrier gases; iii) passing (806) the at least one CNT aerogel through a water bath unit (112) for condensing the at least one CNT aerogel into at least one CNT fiber; and iv) collecting (808) the at least one CNT fiber on a rotating roller.

2. The method (800) as claimed in claim 1, comprises determining the re-nucleation and the evaporation zones of the reactor for placing the fan in the reactor.

3. The method (800) as claimed in claim 1, wherein the reactor is made of a quartz tube having an inner diameter of 45mm and a length of 1200 mm, and includes a heating length of 800 mm.

4. The method (800) as claimed in claim 1, wherein the mixed solution is provided, at a flow rate of 0.06 ml / min, by a syringe pump, to the reactor.

5. The method (800) as claimed in claim 1, wherein the predefined preheater temperature of the preheater is 140 °C.

6. The method (800) as claimed in claim 1, wherein the predefined atomic ratio of the carbon source, the catalyst precursor, and the promotor in the mixed solution is 100: 1:0.2, wherein the mixed solution is obtained by mixing together the carbon source, the catalyst precursor, and the promotor for at least 10 minutes by ultrasonication, and wherein the carbon source, the catalyst precursor, and the promotor are toluene, ferrocene, and thiophene, respectively.SUBSTITUTE ^EET (RULE 26)7. The method (800) as claimed in claim 1, wherein the carrier gases are argon and hydrogen, with a flow rate of 0.25 SLPM and 1.75 SLPM, respectively.

8. The method (800) as claimed in claim 1, wherein the predefined reactor temperature is 1200 °C through resistance heating of SiC heating rod.

9. The method (800) as claimed in claim 1, wherein the fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the at least one CNT aerogel sticking on the fan, and wherein the fan is rotated with a rotation axis parallel to the reactor and the predefined geometry of the fan includes a plurality of blades (202, 204, 206) at 120° apart, parallel to an axial direction of the reactor.

10. The method (800) as claimed in claim 1, wherein the reactor outlet is connected to a glove box (111) maintained in an inert condition by purging argon or nitrogen.

11. The method (800) as claimed in claim 1, comprises verifying, by scanning electron microscopy (SEM) and / or Raman spectroscopy, if the formed at least one CNT fiber contains SWCNT.

12. A radial mixing-based system (100) for enhancing the carbon conversion and selective synthesis of semiconducting single-walled carbon nanotube, SWCNT, fibers by floating catalyst chemical vapor deposition, FC-CVD, the system comprising: i) a reactor (102) maintained at a predefined reactor temperature comprising a fan (104) of a predefined geometry, rotating at a predefined rotation per minute, RPM, placed in an evaporation zone of the reactor, and close to a renucleation zone of the reactor, wherein a mixed solution of a carbon source, a catalyst precursor, and a promotor taken in a predefined atomic ratio, is provided into the reactor through a preheater (106) maintained at a predefined preheater temperature and coupled to the reactor, wherein, at the preheater temperature, the mixed solution is converted into vapours, wherein the vapours are carried into a heating zone of the reactor with carrier gases, and wherein at least one CNT aerogel (108) having a cylindrical structure, are formed in the re-nucleation zone of the reactor;ii) a water bath unit (112) coupled with an outlet (110) of the reactor (102), wherein the at least one CNT aerogel (108), coming out from the outlet of the reactor, by a flow of the carrier gases, are passed through the water bath unit (112) for condensing the at least one CNT aerogel into at least one CNT fiber (114); and iii) a rotating roller (120) coupled to the water bath unit (112) and adapted for collecting the at least one CNT fiber (114).

13. The system (100) as claimed in claim 12, wherein the re-nucleation and the evaporation zones of the reactor are determined for placing the fan (104) in the reactor (102).

14. The system (100) as claimed in claim 12, wherein the reactor (102) is made of a quartz tube having an inner diameter of 45 mm and a length of 1200 mm, and includes a heating length of 800 mm.

15. The system (100) as claimed in claim 12, wherein the mixed solution is provided, at a flow rate of 0.06 ml / min, by a syringe pump, to the reactor.

16. The system (100) as claimed in claim 12, wherein the predefined preheater temperature of the preheater is 140 °C.

17. The system (100) as claimed in claim 12, wherein the predefined atomic ratio of the carbon source, the catalyst precursor, and the promotor in the mixed solution is 100: 1:0.2, wherein the mixed solution is obtained by mixing together the carbon source, the catalyst precursor, and the promotor for at least 10 minutes by ultrasonication, and wherein the carbon source, the catalyst precursor, and the promotor are toluene, ferrocene, and thiophene, respectively.

18. The system (100) as claimed in claim 12, wherein the carrier gases are argon and hydrogen, with a flow rate of 0.25 SLPM and 1.75 SLPM, respectively.

19. The system (100) as claimed in claim 12, wherein the predefined reactor temperature is 1200 °C through resistance heating of SiC heating rod.

20. The system (100) as claimed in claim 12, wherein the fan is placed in the evaporation zone as close to the re-nucleation zone as possible in order to maximize its influence on the re-nucleation zone without the at least one CNT aerogel sticking on the fan, and wherein the fan is rotated with a rotation axis parallel to the reactor and the predefined geometry of the fan includes a plurality of blades (202, 204, 206) at 120° apart, parallel to an axial direction of the reactor.SUBSTITUTE ^EET (RULE 26)21. The system (100) as claimed in claim 12, wherein the reactor outlet is connected to a glove box (111) maintained in an inert condition by purging argon or nitrogen.

22. The system (100) as claimed in claim 12, wherein the formed at least one CNT fiber is verified, by scanning electron microscopy (SEM) and / or Raman spectroscopy, for if the formed at least one CNT fiber contains SWCNT.SUBSTITUTE ^?EET (RULE 26)

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