WO2022160055A1 - Méthode de fabrication de nanocornets de carbone et nanocornets de carbone ainsi produits - Google Patents

Méthode de fabrication de nanocornets de carbone et nanocornets de carbone ainsi produits Download PDF

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WO2022160055A1
WO2022160055A1 PCT/CA2022/050120 CA2022050120W WO2022160055A1 WO 2022160055 A1 WO2022160055 A1 WO 2022160055A1 CA 2022050120 W CA2022050120 W CA 2022050120W WO 2022160055 A1 WO2022160055 A1 WO 2022160055A1
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carbon
plasma
reactor
nanohorns
gas
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PCT/CA2022/050120
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Nadi BRAIDY
Fanny CASTEIGNAU
Kossi Eyadéma BERÉ
Richard Martel
Charlotte Allard
Taki Eddine AISSOU
Jocelyn VEILLEUX
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Socpra Sciences Et Génie S.E.C.
Polyvalor, Limited Partnership
Université de Montréal
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Publication of WO2022160055A1 publication Critical patent/WO2022160055A1/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K9/00—Medicinal preparations characterised by special physical form
    • A61K9/48—Preparations in capsules, e.g. of gelatin, of chocolate
    • A61K9/50—Microcapsules having a gas, liquid or semi-solid filling; Solid microparticles or pellets surrounded by a distinct coating layer, e.g. coated microspheres, coated drug crystals
    • A61K9/51—Nanocapsules; Nanoparticles
    • A61K9/5107—Excipients; Inactive ingredients
    • A61K9/5115—Inorganic compounds
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K9/00—Medicinal preparations characterised by special physical form
    • A61K9/0087—Galenical forms not covered by A61K9/02 - A61K9/7023
    • A61K9/0092—Hollow drug-filled fibres, tubes of the core-shell type, coated fibres, coated rods, microtubules or nanotubes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/18—Nanoonions; Nanoscrolls; Nanohorns; Nanocones; Nanowalls
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite

Definitions

  • the present invention relates to a method of manufacturing carbon nanohorns. More specifically, the present invention is concerned with a method of manufacturing carbon nanohorns using a carbon precursor and promotor gas injected in a thermal plasma torch under a set of operation parameters allowing the nucleation and growth of the desired carbon nanohorns.
  • the present invention also relates to the carbon nanohorns produced, which are characterized by their small sizes compared to conventional carbon nanohorns.
  • carbon nanohorns are carbon allotropes with a structure close to carbon nanotubes (CNTs) except that they are closed on one end by a conical cap with an apex angle ranging from ⁇ 20° to - 113° due to the presence of five to one pentagons respectively.
  • Carbon nanohorns are produced as 3D aggregates.
  • the so-called ‘dahlia-like’ nanohorns are aggregates in which individual nanohorns are arranged in the flower-like pattern shown in Fig. 1a.
  • the diameter of the individual nanohorns is typically between 2 nm for the top and 5 nm for the base and their length is about 40-50 nm thus yielding 'dahlia-like' nanohorns aggregates with average diameter of about 80-100 nm - see Fig. 1b and 1c.
  • the CNHs hollow structure (like carbon nanotubes), high specific surface and inertness make them a good candidate for drug-delivery or nanomarkers; methane or hydrogen storage; supercapacitors; drug medical application (poor toxicity and good biocompatibility), and also, for composite matrix reinforcement.
  • Pentagon-heptagon defects present on the CNHs walls improve their surface reactivity for functionalization or oxidation, expanding further the range of properties required for specific applications.
  • One of the most obvious advantage of CNHs over carbon nanotubes is that their synthesis does not require a metallic catalyst. Such catalyst is typically used to produce carbon nanotubes and undesirably remains as an impurity in the nanotubes. This is a considerable advantage for medical applications as no post-synthesis treatment is required to remove any trace of metals or residues.
  • CNHs were first synthesized by Pr. Harris in 1994 and then highlighted by microscopy by S. lijima and his colleagues in 1999 by CO2 laser ablation. Following this discovery, other methods were developed to produce CNHs, such as direct current (DC) arc discharge and direct vaporization of graphite. All these methods produce CNHs on an industrial scale. However, these methods require solid carbon sources such as graphite with a purity of more than 99%, a high energy source to vaporize carbon, and also, a high quenching rate to form the nanostructures in an inert gas such as argon, helium or nitrogen. Typically, 5-15% of by-products are synthesized with CNHs such as amorphous carbon, nanoflakes or graphitic nanocapsules (GNCs), depending on the synthesis parameters.
  • DC direct current
  • GNCs graphitic nanocapsules
  • a method of manufacturing carbon nanohorns comprising the steps of: a) providing a carbon precursor and a promotor gas b) providing a plasma reactor comprising a thermal plasma torch generating a plasma, c) feeding the carbon precursor and the promotor gas into a section of the plasma that is at a temperature allowing decomposition of the carbon precursor, thereby decomposing the carbon precursor into reactive species, d) allowing said reactive species to migrate downstream in the plasma reactor, there causing nucleation and growth of the carbon nanohorns, and e) allowing the carbon nanohorns to migrate further downstream in the plasma reactor into a non-reactive zone of the plasma reactor, wherein the promotor gas is nitrogen, hydrogen, helium, argon, a molecular gas consisting of a combination of nitrogen and hydrogen atoms, or a mixture thereof, wherein, during step c) to e), the pressure in the reactor is between about 66 and about 94 kPa; wherein the carbon precursor and the promotor gas are fed into the plasma
  • a method of manufacturing carbon nanohorns comprising the steps of: a) providing a carbon precursor and a promotor gas b) providing a plasma reactor comprising a thermal plasma torch generating a plasma, c) feeding the carbon precursor and the promotor gas into a section of the plasma that is at a temperature allowing decomposition of the carbon precursor, thereby decomposing the carbon precursor into reactive species, d) allowing said reactive species to migrate downstream in the plasma reactor, there causing nucleation and growth of the carbon nanohorns, and e) allowing the carbon nanohorns to migrate further downstream in the plasma reactor into a non-reactive zone of the plasma reactor, wherein the promotor gas is nitrogen, hydrogen, helium, argon, a molecular gas consisting of a combination of nitrogen and hydrogen atoms, or a mixture thereof, wherein the carbon precursor and the promotor gas are fed into the plasma in a promotor atom: carbon atom ratio of about 4.6 to about 5.4, wherein, step c) to e) are
  • the pressure in the reactor is between about 66 and about 94 kPa.
  • the carbon precursor is fed into the plasma at a carbon feeding rate of about 0.068 mol of C/min to about 0.16 mol of C/min.
  • the promotor gas is nitrogen, hydrogen, helium, or argon, preferably nitrogen or helium, and more preferably nitrogen.
  • the pressure in the reactor is: about 66 kPa or more, about 69 kPa or more, about 72 kPa or more, about 75 kPa or more, about 77 kPa or more, about 80 kPa or more, and/or about 94 kPa or less, preferably about 91 kPa or less, more preferably about 88 kPa or less, and most preferably about 85 kPa or less.
  • the pressure in the reactor is about 83 kPa, preferably about 82.7 kPa.
  • the method of any one of embodiments 1 to 7, wherein the promotor atom: carbon atom ratio is from about 4.8 to about 5.2, preferably of about 5.0.
  • carbon precursor can comprise carbon in any of its forms, a hydrocarbon, an oxygenated hydrocarbon, a nitrogenated hydrocarbon, or a mixture thereof.
  • thermal plasma torch is an inductively coupled plasma (ICP) torch, preferably a radio frequency inductively coupled plasma (RF ICP) torch.
  • ICP inductively coupled plasma
  • RF ICP radio frequency inductively coupled plasma
  • the reactor comprises a refractory insert tube, preferably made of graphite, located at the top of the reactor just below the plasma torch to modify the thermal properties of the plasma jet or the reacting zone.
  • step g) comprises:
  • step iv) is carried out by removing the liquid from the supernatant, preferably by evaporating the liquid from the supernatant.
  • a catalyst such as a metal catalyst, for example Fe, Ni, Co, Y2O3, and/or CeO2-containing metal catalysts.
  • Carbon nanohorns of embodiment 30, wherein the superstructures with a toroid-like shape have a diameter between about 45 nm and about 105 nm (preferably an average diameter of 66 about nm) with a hole having a diameter between about 11 nm and about 35 nm (preferably an average diameter of 20 about nm).
  • Carbon nanohorns of any one of embodiments 29 to 32 being free of nitrogen.
  • Carbon nanohorns of any one of embodiments 29 to 33 being produced by the method of any one of embodiments 1 to 28.
  • Fig. 1 A is a cross-sectional scheme of ‘dahlia-like’ carbon nanohorns (left) with a close-up on the tip of an individual carbon nanohorn (right).
  • Fig. 1B is a microscopic image of numerous 'dahlia-like' carbon nanohorns.
  • Fig. 1C is a microscopic image of a single 'dahlia-like' carbon nanohorns.
  • Fig. 2A is a schematic of the inductively coupled thermal plasma reaction set-up.
  • Fig. 2B is a schematic of the inductively coupled thermal plasma reaction set-up with a refractory insert tube inside the main reactor.
  • Fig. 3A is a TEM image of the nanostructures synthesized at 46.7 kPa.
  • Fig. 3B is a TEM image of the nanostructures synthesized at 53.3 kPa.
  • Fig. 3C is a TEM image of the nanostructures synthesized at 66.7 kPa.
  • Fig. 3D is a TEM image of the nanostructures synthesized at 78.7 kPa.
  • Fig. 3E is a TEM image of the nanostructures synthesized at 82.7 kPa.
  • Fig. 3F is a TEM image of the nanostructures synthesized at 94.7 kPa.
  • Fig. 4A shows the Raman spectra of the nanostructures synthesized at different pressures.
  • Fig. 4B shows the intensity ratio of the G and D bands observed in the Raman spectra of the nanostructures synthesized at different pressures.
  • Fig. 5A is a TEM image of the nanostructures synthesized with a F ⁇ CF ratio equal to 0.
  • Fig. 5B is a TEM image of the nanostructures synthesized with a F ⁇ CFU ratio equal to 0.3.
  • Fig. 5C is a TEM image of the nanostructures synthesized with a F ⁇ CFU ratio equal to 0.5.
  • Fig. 5F is a TEM image of the nanostructures synthesized with a F ⁇ CFU ratio equal to 0.7.
  • Fig. 5E is a TEM image of the nanostructures synthesized with a FtCFU ratio equal to 1.0.
  • Fig. 5F is a TEM image of the nanostructures synthesized with a FtCFU ratio equal to 1.5.
  • Fig. 6A shows the Raman spectra of the nanostructures synthesized with different F ⁇ CFU ratio.
  • Fig. 6B shows the intensity ratio of the G and D bands observed in the Raman spectra of the nanostructures synthesized at different F ⁇ CFU ratios.
  • Fig. 7A is a TEM image of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa for a F ⁇ CFU ratio of 0.3.
  • Fig. 7B is a TEM image of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa for a F ⁇ CFU ratio of 0.5.
  • Fig. 7C is a TEM image of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa for a F ⁇ CFU ratio of 0.8.
  • Figure 7D is an overview of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa for a F ⁇ CFU ratio equal to 0.5.
  • Fig. 8A shows the Raman spectra of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa with different F ⁇ CFU ratio.
  • Fig. 8B shows the intensity ratio of the G and D bands observed in the Raman spectra of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa at different H2:CH4 ratios.
  • Fig. 10 shows a purification pathway by centrifugation in ethanol.
  • Fig. 11 A is a TEM image of the nanostructures synthesized with a N2:CH4 ratio of 0.3.
  • Fig. 11 B is a TEM image of the nanostructures synthesized with a N2:CH4 ratio of 0.5.
  • Fig. 11C is a TEM image of the nanostructures synthesized with a N2:CH4 ratio of 0.7.
  • Fig. 11 D is a TEM image of the nanostructures synthesized with a N2:CH4 ratio of 1 .
  • Fig. 12A shows the Raman spectra of the nanostructures synthesized with different N2:CH4 ratios.
  • Fig. 12B shows the intensity ratio of the G and D bands observed in the Raman spectra of the nanostructures synthesized at different N2:CH4 ratios.
  • Fig. 13 shows a high-resolution TEM image of carbon nanohorns synthesized with a N2:CH4 ratio of 0.5 at 82.7 kPa
  • Fig. 14 shows XPS spectrum of samples synthesized with nitrogen at different N2:CH4 ratios and global flow rates.
  • OES optical emission spectroscopy
  • Fig. 18A is a TEM image of the nanostructures synthesized at a global flow rate of 1.7 slpm at 82.7 kPa for a N2:CH4 ratio of 0.3.
  • Fig. 18B is a TEM image of the nanostructures synthesized at a global flow rate of 1.7 slpm at 82.7 kPa for a N2:CH4 ratio of 0.5.
  • Fig. 18C is a TEM image of the nanostructures synthesized at a global flow rate of 1.7 slpm at 82.7 kPa for a N2:CH4 ratio of 0.7.
  • Fig. 19A shows the Raman spectra of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa with different N2:CH4 ratios.
  • Fig. 19B shows the intensity ratio of the G and D bands observed in the Raman spectra of the nanostructures synthesized at a global flow rate of 1 .7 slpm at 82.7 kPa at different N2:CH4 ratios.
  • Fig. 20A is a TEM image of the nanostructures synthesized with the addition of a graphite liner inside the main reactor at
  • Fig. 20B is a TEM image of the nanostructures synthesized with the addition of a graphite liner inside the main reactor at
  • Fig. 21 A is a TEM image of the nanostructures synthesized with a F ⁇ F ratio of 0.5.
  • Fig. 21 B is a TEM image of the nanostructures synthesized with a F ⁇ F ratio of 0.7.
  • Fig. 21C is a TEM image showing buds-like carbon nanohorns produced along with the short nanohorns synthesized in Example 4.
  • Fig. 21 D is a TEM image showing buds-like structures and graphitic structures.
  • Fig. 22A shows the Raman spectra of the nanostructures synthesized with different F ⁇ F ratios.
  • Fig. 22B shows the intensity ratio of the G and D bands observed in the Raman spectra of the nanostructures synthesized at different F ⁇ F ratios.
  • Fig. 23 is a TEM image of the nanohorns sold by NEC Corporation®, Japan.
  • Fig. 24 is a TEM image of the Single Wall Carbon Nanohorns (SWCNH) sold by Carbonium®, Italy.
  • Fig. 25 shows the Raman spectra of nanohorns according to an embodiment of the invention, NEC nanohorns, and Carbonium nanohorns alone (bottom spectra) and with encapsulated dye before (middle spectra) and after (top spectra) washing.
  • Fig. 26 is a graphical abstract summarizing the tests and results reported in Examples 1-2 above.
  • CNHs carbon nanohorns
  • the method of the invention is an advantageous way of producing CNHs.
  • a 50kW RF ICP torch, operated at 15 kW nanohorns yields of 15-20 g/h were achieved.
  • a higher production rate could easily be achieved simply by using a larger reactor with a plasma torch operated with a higher power and flow (industrial-sized 100, 200, 500, and even 1000 kW RF ICP apparatus are available).
  • the present plasma-based method is more easily scalable.
  • the use of a gaseous precursor in some embodiments of the method of the invention facilitates the implementation of a continuous process.
  • a method of manufacturing carbon nanohorns comprising the steps of: a) providing a carbon precursor and a promotor gas, b) providing a plasma reactor comprising a thermal plasma torch generating a plasma, c) feeding the carbon precursor and the promotor gas into a section of the plasma that is at a temperature allowing decomposition of the carbon precursor, thereby decomposing the carbon precursor into reactive species, d) allowing said reactive species to migrate downstream in the plasma reactor, there causing nucleation and growth of the carbon nanohorns, and e) allowing the carbon nanohorns to migrate further downstream in the plasma reactor into a non-reactive zone of the plasma reactor, wherein the promotor gas is nitrogen, hydrogen, helium, argon, a molecular gas consisting of a combination of nitrogen and hydrogen atoms, or a mixture thereof, wherein, during step c) to e), the pressure in the reactor is between about 66 and about 94 kPa; wherein the carbon precursor and the promotor gas
  • a method of manufacturing carbon nanohorns comprising the steps of: a) providing a carbon precursor and a promotor gas b) providing a plasma reactor comprising a thermal plasma torch generating a plasma, c) feeding the carbon precursor and the promotor gas into a section of the plasma that is at a temperature allowing decomposition of the carbon precursor, thereby decomposing the carbon precursor into reactive species, d) allowing said reactive species to migrate downstream in the plasma reactor, there causing nucleation and growth of the carbon nanohorns, and e) allowing the carbon nanohorns to migrate further downstream in the plasma reactor into a non-reactive zone of the plasma reactor, wherein the promotor gas is nitrogen, hydrogen, helium, argon, a molecular gas consisting of a combination of nitrogen and hydrogen atoms, or a mixture thereof, wherein the carbon precursor and the promotor gas are fed into the plasma in a promotor atom : carbon atom ratio of about 4.6 to about 5.4, wherein
  • the carbon precursor and the promotor gas are fed into the plasma generated by the thermal plasma torch using central gas (and the sheath gas) as is well known to the skilled person. They are thus brought into a section of the plasma that is at a temperature allowing decomposition of the carbon precursor. As is well- known to the skilled person, this would typically be the center of the induction coil.
  • the thermal plasma generated by the thermal plasma torch is typically "flame-shaped” (the flame being more or less elongated) with the plasma temperature being the highest at the plasma core and gradually decreasing as the plasma flows toward the torch exit. Temperatures of up to about 10000 K and even more can be reached in the hottest zone of a plasma generated by a thermal plasma torch.
  • the shape and dimension of the plasma jet can be modulated by several parameters, for example: the type of ionizing gas, the ratio between the central gas and sheath gas used, the shape of the reactor, the pressure in the reactor, and the power level.
  • the central gas is argon, preferably at a feed rate of 3 about slpm.
  • the sheath gas is argon, preferably at a feed rate of about 67 slpm.
  • Decomposition of the carbon precursors yields various reactive species such as electrons, ions, and radicals. These reactive species will be carried by the flow of species and other forces, such as gravity, electrophoresis, thermophoresis, and magnetic fields, through a temperature gradient toward colder parts of the jet and then colder parts of the reactor, which will allow nucleation and growth of these reactive species into the carbon nanohorns and eventually allow the produced carbon nanohorns to exit the reactive zone of the plasma reactor and migrate into a non-reactive zone of the plasma reactor, typically referred to as a "quench zone”.
  • reactive species such as electrons, ions, and radicals.
  • the set of parameters provided herein use of a carbon precursor, nature of the promotor, pressure, power, promotor atom : carbon atom ratio, and carbon feeding rate
  • create conditions in the reactor temperature, temperature gradients, plasma viscosity, plasma density, plasma enthalpy, plasma specific heat, plasma thermal conductivity, nature and concentration of the reactive species, as well as the residence time, etc.
  • the carbon nanohorns may be accompanied by other forms of carbon (e.g., nanoflakes, bud-like nanohorns, embryos of nanohorns, hybrid form of flakes and nanotubules, etc.).
  • other forms of carbon e.g., nanoflakes, bud-like nanohorns, embryos of nanohorns, hybrid form of flakes and nanotubules, etc.
  • PL-50 torch preferred equipment described hereinbelow
  • step c) to e) are carried out under operation parameters A and B when using the reference reactor and torch described above or under operation parameters equivalent to operation parameters A and B when using a different reactor and/or a different plasma torch.
  • operation parameters that are “equivalent to operation parameters A and B” are operation parameters that create conditions in said different reactor that are similar enough to those in the reference reactor to allow the nucleation and growth of carbon nanohorns.
  • CFD computational fluid dynamics
  • the conditions (e.g., the concentration profile and/or the temperature gradient) in said different reactor could be within +/- about 15%, preferably +/- about 10%, +/- about 5%, +/- about 1% of the conditions (e.g., the concentration profile and/or the temperature gradient) in the reference reactor.
  • the promotor gas is argon, nitrogen, hydrogen, helium, a molecular gas consisting of a combination of nitrogen and hydrogen, or a mixture thereof.
  • molecular gases consisting of a combination of nitrogen and hydrogen atoms include NH3 and N2H2.
  • the promotor gas is nitrogen, hydrogen, helium, or argon, preferably nitrogen, hydrogen, or helium, and more preferably nitrogen or helium. These last two promoters produce less by-product - such graphitic nanocomposites - than hydrogen and argon. Indeed, the Examples below show that products prepared with hydrogen contain in average about 40% nanocapsules, while those prepared with nitrogen and helium comprise in average about 14% and 11% nanocapsules, respectively.
  • the promotor gas is nitrogen.
  • the pressure in the reactor is between about 66 and about 94 kPa.
  • the pressure in the reactor is between about 66 and about 94 kPa.
  • the pressure is about 66 kPa or more, about 69 kPa or more, about 72 kPa or more, about 75 kPa or more, about 77 kPa or more, about 80 kPa or more, and/or
  • the pressure is about 94 kPa or less, preferably about 91 kPa or less, more preferably about 88 kPa or less, and most preferably about 85 kPa or less.
  • the pressure is about 83 kPa, and more preferably about 82.7 kPa.
  • the carbon precursor and the promotor gas are fed into the plasma in a promotor atom: carbon atom ratio of from about 4.6 to about 5.4.
  • the promotor atom: carbon atom ratio is from about 4.8 to about 5.2, and more preferably of about 5.0.
  • the promotor atom: carbon atom ratio is calculated using the number of atoms of the promotor provided in the reactor and the number of carbon atoms provided in the reactor in a given amount of time. For example, if H2 and CH4 are used at flow rate ratio of hydrogen to methane (F ⁇ CFU) of 0.5; 5 atoms of hydrogen and provided for each atom of carbon, thus yielding a promotor atom: carbon atom ratio of 5.0.
  • the carbon precursor is fed into the plasma at a carbon feeding rate of from about 0.068 mol of C/min to about 0.16 mol of C/min.
  • the carbon precursor is fed into the plasma at a carbon feeding rate of from about 0.071 mol of C/min to about 0.14 mol of C/min, more preferably from about 0.071 mol of C/min to about 0.10 mol of C/min, and most preferably at a carbon feeding rate of 0.071 mol of C/min.
  • the carbon precursor and the promotor gas can be fed coaxially or radially into the plasma torch.
  • a reactant is fed coaxially, it is fed in a direction that is more or less parallel to the longitudinal axis of the plasma jet (i.e., the axis going from the base to tip of the jet).
  • a reactant is fed radially, it is fed in a direction that is more or less normal to the longitudinal axis of the plasma jet. In both cases, the reactants are fed close toward the base of the plasma jet.
  • the carbon precursor and/or the promotor gas are fed coaxially to favour a uniform decomposition of the precursor.
  • the carbon precursor can be in powder form, in liquid form, in gaseous form, or can be any mixture of these forms. In preferred embodiments, the carbon precursor is in gaseous form.
  • Liquid forms of carbon precursors include, for example, solutions, suspensions, slurries etc., in liquids such as organic solvents.
  • the carbon precursor can be any source of carbon, which is free of elements deleterious to the reaction.
  • the carbon precursor can comprise carbon in any of its forms, hydrocarbons, oxygenated or nitrogenated hydrocarbon, or a mixture thereof.
  • the carbon precursor is a hydrocarbon.
  • Non-limiting examples of carbon precursors that are in powder form include ashes, carbon nanoparticles/nanospheres, carbon nanoflakes and carbon black.
  • hydrocarbons (C x H y ) are defined as an organic compound consisting entirely of hydrogen and carbon atoms.
  • Preferred hydrocarbons include CH4, C2H6 and C2H2, and most preferably CH4.
  • Oxygenated hydrocarbons (C x H y O z ) or nitrogenated hydrocarbons (C x H y N z ) are hydrocarbons that contain one or more atoms of oxygen or nitrogen, respectively.
  • Any suitable thermal plasma torch can be used in the method of the invention, including those generating plasma by direct current (DC) (including non-transferred and transferred type DC plasma torches), alternating current (AC), radio-frequency (RF), microwave discharge, dielectric-barrier discharge and other discharges, such as capaciti vely- or inductively-coupled RF discharge.
  • DC direct current
  • AC alternating current
  • RF radio-frequency
  • microwave discharge dielectric-barrier discharge
  • dielectric-barrier discharge dielectric-barrier discharge and other discharges, such as capaciti vely- or inductively-coupled RF discharge.
  • the thermal plasma torch is an inductively coupled plasma (ICP) torch, which is a type of plasma source in which the energy is supplied by electric currents produced by electromagnetic induction, that is, by time-varying magnetic fields.
  • ICP inductively coupled plasma
  • the thermal plasma torch is a radio frequency inductively coupled plasma (RF ICP) torch.
  • RF ICP radio frequency inductively coupled plasma
  • radio frequency AC currents in a coil generate an oscillating magnetic field that couples to a partially ionized gas flowing through the coil (the discharge cavity) generating thereby a stable plasma discharge.
  • the plasma torch is a PL-50 torch from Tekna Plasma System® (the number 50 referring to the internal diameter in mm of its ceramic confinement tube) equipped with a 60 kW plate power but preferably operated at 15 kW powered by a 3 MHz Lepel RF power supply.
  • Tekna Plasma System® the number 50 referring to the internal diameter in mm of its ceramic confinement tube
  • Lepel RF power supply the number 50 referring to the internal diameter in mm of its ceramic confinement tube
  • this torch including its structure and its plasma temperature profile, see Dolbec et al. NSTI-Nanotech 2008, vol.1 , 672-675, incorporated herein by reference.
  • the thermal plasma torch is housed into a reactor.
  • Any type of reactor equipped with a plasma torch can be used in the method of the invention.
  • Such reactors are typically cylindrical, but other configuration can be contemplated such as conical reactors.
  • the walls of the reactor are cooled to prevent premature damage. This has also the advantage to attract the produced nanohorns (via thermophoresis).
  • the plasma reactor can be connected to an auxiliary chamber.
  • the reactor comprises a refractory insert tube, preferably made of graphite, located at the top of the reactor just below the plasma torch.
  • a refractory insert tube preferably made of graphite, located at the top of the reactor just below the plasma torch.
  • Such tube allows modifying the thermal properties of the plasma jet or the reacting zone.
  • the examples below show that the use of such a tube promoted growth of the carbon nanohorns, by decreasing the gradient of temperature in the plasma jet
  • the produced carbon nanohorns after the produced carbon nanohorns have reached a non-reactive zone of the plasma reactor at step e), they can be allowed to settle (e.g., on the reactor walls, at the bottom of the reactor, etc.) where they can be collected, or they can be directed toward an auxiliary chamber (e.g., using a vacuum) for easier collection.
  • the produced carbon nanohorns can be allowed to settle in the auxiliary chamber or the auxiliary chamber may be equipped with any desired solid/gas separation equipment (for example filters) separating the nanohorns from their carrier gases (namely, the gas mixture exiting the plasma after the reaction).
  • the method of the invention further comprises the step f) of collecting the carbon nanohorns, e.g. from the plasma reactor or from the auxiliary chamber in which filters capture the carbon species, if such a chamber is used.
  • the carbon nanohorns produced by the method of the invention may comprise graphitic nanocapsules as an impurity.
  • Various methods can be used, together or separately, to eliminate these graphitic nanocapsules. These methods are described below.
  • the method of the invention further comprises the step g) of removing the graphitic nanocapsules from the carbon nanohorns after their manufacture.
  • step g) comprises: i. dispersing the carbon nanohorns as collected from the reactor in a liquid to obtain a solid/liquid mixture, ii. centrifuging the mixture to obtain a solid residue containing the graphitic nanocapsules and a supernatant containing the carbon nanohorns, ill. separating the supernatant from the solid residue, and iv. isolating the carbon nanohorns from the supernatant.
  • the liquid can be any liquid in which the carbon nanohorns are not soluble, but in which the nanohorns can be dispersed in a stable manner. Since the carbon nanohorns as produced by the above method are hydrophobic, organic non solvents are preferred. In embodiments, the liquid is ethanol.
  • Step iv) of isolating can be carried out, for example, by removing the liquid from the supernatant.
  • the liquid is evaporated from the supernatant yielding the carbon nanohorns.
  • a quench gas is often used to decrease abruptly and dramatically the temperature in the plasma reactor. This can be done after the nanostructures have exited the plasma or beforehand (the quench gas, in effect, abruptly "cutting” the plasma jet). In the method of the invention, this is not required. Thus, in embodiments, the method of the invention does not include a step of using a quench gas.
  • the method of the invention does not include the use of catalysts, such as metal catalysts, e.g. Fe, Ni, Co, Y2O3, and/or CeO2-containing catalysts.
  • metal catalysts e.g. Fe, Ni, Co, Y2O3, and/or CeO2-containing catalysts.
  • the carbon nanohorns of the invention are aggregated together into disorderly and roughly spherical or spheroidal aggregates and/or arranged into conventional ‘dahlia-like’ aggregates. Both types of aggregates can be present simultaneously or separately in the produced nanohorns.
  • These aggregates (both types) have an average diameter between about 15 nm and about 50 nm, preferably of about 25 nm (when produced using H2 as a promotor) or preferably of about 45 nm (when produced using N2 as a promotor). This is in contrast with 'dahlia-like' nanohorns aggregates of the prior art, which are typically 80-100 nm in diameter. See, for example, the TEM images of the conventional nanohorns aggregates used in Example 5, which have diameters of 89 nm and 94 nm.
  • these aggregates are themselves arranged into superstructures.
  • These superstructures can be disorderly or have a toroid-like (donut) shape - see for example Fig. 5g and 14b.
  • the toroid superstructures have a diameter between about 45 nm and about 105 nm (preferably an average diameter of about 66 nm) with a hole having a diameter between about 11 nm and about 35 nm (preferably an average diameter of about 20 nm).
  • the Examples below show that the carbon nanohorns produced do not contain nitrogen (even when they are produced with nitrogen). This also in contrast with conventional nanohorns, synthesized by other methods using nitrogen, which do contain nitrogen. Thus, in embodiments, the carbon nanohorns of the invention are free of nitrogen.
  • the carbon nanohorns of the invention are expected to find application in all the same fields as conventional nanohorns including drug-delivery or optical or radio nanomarkers; methane or hydrogen storage; lubricant; anode or cathodes in batteries; supercapacitors; for electronic or mechanical devices, for drug medical application, or for composite matrix reinforcement.
  • the term "about 1 has its ordinary meaning. In embodiments, it may mean plus or minus 10% or plus or minus 5% of the numerical value qualified.
  • the nanohorns of the invention are often referred to as "short carbon nanohorns''.
  • Example 1 Manufacturing carbon nanohorns using H2 as promotor gas
  • CNHs carbon nanohorns
  • ICP inductively coupled thermal plasma
  • CH4 gaseous carbon precursor
  • a promoter gas such as hydrogen
  • the global concentration of methane and hydrogen inside the plasma jet also has an impact to the reaction.
  • the RF ICP is a potentially continuous process allowing a high production rate, in excess of 20 g/h of CNHs with a plasma torch operated at 15 kW.
  • Graphitic nanocapsules were also produced during the CNHs synthesis but can be easily removed by centrifugation.
  • FIG. 2A A reactor comprising a refractory insert tube, used in some of the experiments, is shown in Fig. 2B.
  • the setup was composed of three main parts.
  • the plasma torch (PL-50 from Tekna Plasma System Inc. Canada) where reactive gases were mixed coaxially in a ceramic tube and ionized by an induction coil.
  • the torch was driven by a power set to 15 kW with an excitation frequency of 3 MHz.
  • the second part is the main reactor where the reaction occurred, and the third part is an auxiliary chamber with three porous filters connected to a vacuum pump to control the reaction pressure with a butterfly valve.
  • the reactor, the probe and the plasma torch were cooled by water flowing in a double-walled jacket and attracted the nanostructures by thermophoresis.
  • a thermocouple was placed in the middle of the main reactor, to monitor the reaction temperature just below the plasma jet. The pressure, water coolant temperature and reaction temperature were monitored during the reaction.
  • powder was collected separately on the main reactor (M), auxiliary chamber (Aux) and filters (F).
  • M main reactor
  • Aux auxiliary chamber
  • filters F
  • a blow-back system injected high-pressure gas flow at regular intervals to unclog the filters.
  • Central and sheath gas were injected inside the ceramic tube (central gas) to create and stabilize the plasma between the ceramic and the quartz tube (sheath gas) to protect this tube from high temperatures.
  • the central gas is injected tangentially into the quartz tube placed in the center of the ceramic tube in the upper part of the torch.
  • a CH4: H2 mixture was injected by the water-cooled probe inserted axially inside the center of the torch. The gas mixtures were ionized by the plasma jet and NPs nucleation occurred along the plasma jet and were quenched.
  • Ratio between the flow rate of hydrogen and methane (H2:CH4) 0, 0.3, 0.5, 0.7, 1 and 1 .5
  • Carbon nanostructures were first characterized by TEM (Hitachi, H-7500) at an acceleration voltage of 120 kV. Samples were prepared by sonicating ⁇ 1 mg of CNHs materials in ethanol during 10 min in ultrasonic bath. The suspension was then drop casted on a 200-mesh holey carbon-coated Cu TEM grid and left to dry. Care was taken to limit the dose of the electron beam, as amorphization occurred within seconds under normal observation.
  • Raman spectroscopy provided additional information about the general structure present in the sample but not on the precise structure of the CNHs.
  • the samples were analyzed by SP2500 Acton Raman spectrometer with a 514 nm laser at 30 mW to evaluate the overall carbon nature.
  • Raman G, D and D' bands present in the spectra were fitted with 3 Lorentzians and the maximum (height) of the fitting curves was used to determine the ratio I G /I D .
  • Fig. 3a-f shows the TEM micrographs of carbon nanostructures synthesized at different pressures with the mixture H2:CH4.
  • Symbols F, E, H, G and sC designate nanoflakes, embryos of carbon nanohorns, hybrid forms of tubules and flakes, graphitic nanocapsules, and short carbon nanohorns, respectively.
  • FIG. 3a shows a second structure, which appears to be embryos of aggregates of carbon nanohorns (E).
  • E carbon nanohorns
  • Fig. 3c shows another carbon nanostructure in the form of a graphitic nanocapsule, indicated by a “G” in Fig. 3c (GNC).
  • GNCs walls are composed of 20-25 graphene layers.
  • Fig. 4a shows a series of Raman spectra in the range from 1200 to 1900 cm 1 recorded from samples produced at different pressures. Two main peaks are assigned to the G band (1580-1595 cm 1 ) and the D band (1340- 1355 cm 1 ).
  • the D band is due to the presence of (i) sp 3 -type of defects, such as punctual defects, edges or lattice disorder and (ii) the presence of pentagons on the cap.
  • the D band is mostly assigned to a loss of basal symmetry due to the presence pentagons on the cone region.
  • the D-band shape is characterized by a single Lorentzian, indicating that the cone structure is well-ordered.
  • the G band is the result of E2 g vibrations of the sp 2 hybridized carbon atoms.
  • the G band can present a shoulder peak, which is called the D' band, located above 1600 cm 1 .
  • the D' band is sometimes observed at 1615 cm 1 and this feature is known to be induced by defects on the graphene.
  • the D' band is more prominent for experiments at 66.7, 78.7 and 82.7 kPa, where horns grow in the vicinity of nanoflakes or as aggregates.
  • the relative intensity ratio, I G /I D (Fig. 4b) is used to correlate the Raman spectra with each nanostructure and this ratio is estimated using the maxima of the Lorentzian deconvolution peaks (not shown).
  • I G /I D A decrease of I G /I D is indicative of the presence of defects. Indeed, the CNHs I G /I D is lower than carbon nanoflakes or graphitic nanocapsules due to the disorder caused by the presence of pentagon-heptagon defects and their aggregation. This is consistent with the TEM observations indicating that embryos of horns stabilize at 66.7 kPa. At higher pressures, short carbon nanohorns dominate in the collected samples.
  • Hydrogen is known to reduce the electrons density and, more generally, the plasma density resulting in a decrease of dehydrogenation reaction.
  • Fig. 5a-f shows TEM micrographs of nanostructures synthesized at 82.7 kPa with different H2:CH4 ratios.
  • the sample synthesized without H2 (Fig. 5a) exhibited spherical aggregates of amorphous structures referred to as 'seed-like' carbon nanohorns.
  • Increasing the H2:CH4 to 0.3 (Fig. 5b) allows the nucleation of embryos of carbon nanohorns (E) and the hybrid form of nanotubules and flakes (H).
  • H2:CH4 ratio of 0.5 and 0.7
  • the nanohorns are better defined and the main structure is comprised of short carbon nanohorns with a few carbon nanoflakes and of the hybrid form H.
  • a ratio of H2:CH4 > 0.7 promotes the formation of carbon nanoflakes and large by-product graphitic nanocapsules (Fig. 5e and f).
  • Graphitic nanocapsules are present for all samples, as described below. We note that aggregates of short CNHs tend to assemble into a toroid-like shape (see Fig. 5c and Fig. 5g, for instance). To our knowledge, this morphology has never been reported before.
  • Fig. 5h is a high-resolution TEM image of a carbon nanohorn.
  • Fig. 6a shows the Raman spectra for different H2:CH4 ratios and a graph of the I G /I D ratio as a function of H2:CH4 ratio (Fig. 6b).
  • the shoulder at 1615 cm 1 is present in all spectra, but it significantly widens the G band at low H2:CH4 ratios.
  • the I G /I D is comprised between 1 and 1 .8, which is consistent with the dahlia-like or buds-like CNHs.
  • I G /1 D increases, however, with the ratio H2:CH4, which is ascribed to the presence of graphene flakes and graphitic nanocapsules (Fig. 5e). Effect of the overall gases flow rate (F H2 + F CH )
  • Fig. 7 shows TEM images of CNHs synthesized using a total flow rate of 1 .7 slpm for different H2:CH4 ratio (0.3, 0.5 and 0.7).
  • the nanostructures formed with a low ratio are mainly CNHs with some horns embryos (E) and carbon nanoflakes (F).
  • E horns embryos
  • F carbon nanoflakes
  • a ratio of 0.5 CNHs and few flakes are still predominant in the sample, but the embryos are no longer present.
  • Graphitic nanocapsules are present in every condition explored.
  • a ratio of H2:CH4 0.8 produces short carbon nanohorns (Fig.
  • Fig. 8 shows Raman spectra (Fig. 8a) and the corresponding graph of the ratios I G /I D vs. H2:CH4 (Fig. 8b).
  • I G /1 D increases with the H2:CH4 ratio and remains between 1 .5 and 2.8.
  • the G band shoulder is still present and it is more visible for samples grown at a H2:CH4 ratio of 0.3.
  • Methane decomposition is favored by low pressure, high power and low total gas flow rate. Longer residence time in the plasma achieved by a smaller flow rate was also found to be beneficial to the occurrence and crystallinity of CNHs. Indeed, a longer residence time helps the assembly of carbon atoms into graphitic structures. In addition, a smaller flow rate improved the conversion of CH4 into carbon. Preliminary results indicate that the CH4 conversion almost doubles with a flow rate cut by half.
  • H2 act as a promotor rather than a catalyst and plays a role in the growth of CNHs, probably by having an impact (among others) on temperature and temperature gradient of the growth environment.
  • This synthesis is easily scalable and can be made continuous, which is clearly an interesting alternative compared to previous methods based on laser-, arc- or induction-based vaporization of graphite rods.
  • Our method also allows the production of additional carbon allotropes, such as carbon nanoflakes, hybrids, embryos, bud-like CNHs and graphitic nanocapsules depending on the synthesis conditions.
  • Example 1 Purification of the product of Example 1 by centrifugation
  • the second pathway to separate residual by-products from the products obtained in Example 1 is to perform a centrifugation of the collected materials in ethanol. This method is easy to implement and is summarized in Fig. 10. The centrifugal force used depends on the GNCs structures (and mass) found in the samples.
  • Example 2 Manufacturing carbon nanohorn using different promotor gases (H2, N2, Ar, and He)
  • hydrogen may have two possible roles in the CNHs synthesis: (i) it is a promotor of ionized species or (ii) it is a catalyst of the growth of carbon sp 2 materials.
  • H2 we replaced hydrogen by nitrogen, helium or argon. This substitution is motivated by similar physical properties between hydrogen and nitrogen or between helium and argon in the plasma, such as electrical conductivity (proportional to the electron number density).
  • electrical conductivity proportional to the electron number density
  • nitrogen is not known to be a catalyst for CNH formation.
  • CNHs can be produced by RF ICP using methane mixed with various promotor gases (argon, hydrogen, helium and nitrogen).
  • the main role of the promotor gas is to modulate the properties of the plasma jet (specific heat, thermal conductivity, viscosity, and C2 local concentration), but it could also participate to catalytic activities promoting nucleation and growth of various nanocarbon species.
  • H2 and Ar promoters the growth generates unstructured CNHs with a large fraction of GNCs (40% vol. for H2 and 22% vol. for Ar).
  • the aspect ratio of the CNHs and their purity are, however, improved using nitrogen or helium. Since no incorporation of N atoms is seen into the CNH structures after growth, we think that the role of the precursor gases is mostly on the plasma properties.
  • Example 1 we propose a novel method to produce CNHs using RF ICP by injecting CH4 with H2 at a ratio of 2:1 .
  • CH4 with H2 was identified the growth conditions that favor the growth of CNHs by optimizing the ratio of precursors (CH4 with H2) and their respective flow rate and total pressure.
  • Measurements of the plasma were acquired with the IsoPlane SCT 320 spectrograph from Princeton Instruments connected to a PIXI S:256E CCD camera. The light was collected through seven optical fibers spaced vertically from each other with a distance of 1 .5 cm, and with a scan every 0.2 cm (left and right) giving a map of 20x90 cm.
  • the OES measurement was performed with an IsoPlane SCT-320 spectrometer (Princeton Instruments) connected to a PIXIS: 256E CCD camera.
  • the 1800 g/mm grating allowed a resolution of 0.037 nm and covered a spectral range of 38 nm.
  • the fibers were moved horizontally during the experiment to map the plasma
  • the temperature and density measurements were based on C2 species acquired in the wavelength range from 410 nm to 667 nm. All data were processed by a home-made code.
  • Example 1 The reactor used in this second study is described in the Example 1 .
  • the promotor H2 is replaced successively by nitrogen, helium and argon before to be mixed with methane. Those precursors are then injected inside the water- cooled probe inserted axially inside the center of the torch. The gas mixtures were ionized by the plasma jet and NPs nucleation occurred along the plasma jet and were quenched.
  • Table 2 summarizes the parameters studied. Nitrogen, helium or argon was injected in the probe in replacement of hydrogen.
  • Fig. 11 a-d shows TEM micrographs of carbon nanostructures synthesized at 82.7 kPa with the mixture N2:CH4 with ratio between 0.3 and 1.
  • the samples synthesized with a ratio N2:CH4 of 0.3 and 0.5 show short
  • N2:CH4 s 0.7 promotes the formation of carbon nanoflakes, hybrid form of flakes and horns with embryos (Fig. 11c and d).
  • Symbols F, E, H and sC represent respectively nanoflakes, embryos of carbon nanohorns, hybrid form of flakes and tubules and short carbon nanohorns.
  • N2:CH4 ratio 0.3
  • E embryos of carbon nanohorns
  • E embryos of carbon nanohorns
  • sC short carbon nanohorns
  • N2:CH4 0.7
  • N2:CH4 1
  • carbon nanohorns are mainly replaced by carbon nanoflakes mixed with fewer CNHs embryos.
  • graphitic nanocapsules are present in every sample and for all the conditions.
  • the Raman spectra shown in Fig. 12a for the different conditions explored are similar between each other, and indicates the existence of highly disordered sp 2 carbon typical of the carbonaceous species observed by TEM.
  • a I G /ID ratio increases to ⁇ 1 .2, 1 .6 and 2.3 when the N2:CH4 changes to 0.3, 0.7 and 1 , respectively.
  • Nitrogen was thus successfully used as a promotor for the synthesis of CNHs by thermal plasma. Even if H2 is not introduced as a reactant, the decomposition of the hydrocarbon precursor is observed and the plasma conditions in the presence of methane induce the formation of CNHs.
  • a promotor gas such as N2 or H2 is essential to the formation of CNHs.
  • CHNs aggregates produced with N2 are larger than those obtained using H2 (diameter of about 45 nm, in average, Fig. 13).
  • Carbon nanohorns are only made of carbon.
  • X-ray photoelectron spectroscopy shown in Fig. 14 that these carbon nanostructures, when synthesized with nitrogen, mainly contain carbon and some trace of oxygen due to exposure to ambient air.
  • the quantitative analysis of the XPS peak intensity reveals an amount of 0.19 % atomic of nitrogen, which is within the error of the method.
  • the carbon content in the sample exceeds 97% atomic.
  • Fig. 15 shows TEM micrographs of CNHs synthesized at 82.7 kPa with He:CH4 of 0.5. Short carbon nanohorns are produced with hybrid forms of flakes and horns.
  • Fig. 16 shows TEM micrographs of CNHs synthesized at 82.7 kPa with Ar:CH4 of 0.5. Embryos and short carbon nanohorns were produced with argon.
  • Fig. 17a and b show respectively C2 temperature mapping (Fig. 17a) and C2 density mapping (Fig. 17b) obtained by Emission optical spectroscopy of the plasma jet at the probe exit with different promotor (Ar, He, H2, N2).
  • Sample synthesized by mixing nitrogen and methane contains mainly carbon nanohorns (-93%) with -7% of GNCs, as estimated by analyzing multiple TEM micrographs of the sample. GNCs are co-produced, but can be easily removed by centrifugation as demonstrated in the Example T.
  • the co-precursors such as nitrogen, hydrogen, helium or argon influence mainly properties of the plasma jet, especially the temperature gradient and the C2 density, as shown in in Fig. 17a and b. These parameters change the conditions of nucleation and growth of carbon nanohorns inside the plasma reactor.
  • Fig. 18 shows TEM images of CNHs synthesized using a total flow rate of 1.7 slpm for different N2:CH4 ratio (0.3, 0.5 and 0.7).
  • the nanostructures synthesized with a low ratio are mainly short carbon nanohorns with hybrid forms of flakes and horns while at a ratio N2:CH4 of 0.5, CNHs are mainly formed (Fig. 18b).
  • At higher ratio 0.7, Fig. 18b
  • short carbon nanohorns are formed with hybrid forms and a large quantity of graphitic nanocapsules.
  • Fig. 19 shows Raman spectra (Fig. 19a) and the corresponding graph of the ratios I G /I D vs. N2:CH4 (Fig. 19b). I G /I D increases with the N2:CH4 ratio and remains between 1 and 1.5.
  • the promotor has a predominant role on the properties of the plasma jet as demonstrated by Fig. 17a-b. Nitrogen and helium confine the C2 density near the exit of the probe that promotes nucleation and growth of CNHs, while argon and hydrogen extend the C2 density through the plasma jet increasing the production of graphitic nanocapsules.
  • a quantification of GNCs using a thresholding method of a dozen of TEM micrographs for each sample reveals that mixing methane with a promotor such as hydrogen, argon, nitrogen or helium respectively produces respectively 40%, 22%, 14% and 11% of GNCs.
  • Fig. 2B shows a schematic set-up of the addition of a refractory insert tube made in graphite inside the top of the main reactor.
  • a refractory insert tube is added inside the main reactor to promote the CNHs growth by decreasing the gradient of temperature in the plasma jet. All other operating conditions were previously optimized and were fixed to the values summarized by Table 4.
  • the refractory insert tube made in graphite should be pre-heated following parameters detailed in the Table 5 for 15 minutes.
  • Sheath gas (Q2) 90 slpm Ar + 8 slpm H2
  • Fig20-b show TEM micrographs of CNHs synthesized with a graphite liner pre-heated at 600°C and a mixture of CH4:H2 (Fig. 20a) and CH4:N2 (Fig. 20b) following parameters detailed in the Table 5.
  • the refractory insert tube also allows the production of CNHs by decomposing a stream of methane with either hydrogen or nitrogen.
  • Fig. 20a shows TEM micrographs of CNHs synthesized with a graphite liner pre-heated at 600°C and a mixture of CH4:H2 (Fig. 20a) and CH4:N2 (Fig. 20b) following parameters detailed in the Table 5.
  • the refractory insert tube also allows the production of CNHs by decomposing a stream of methane with either hydrogen or nitrogen.
  • Ratio between the flow rate of hydrogen and methane H2:C2H2 0.5 0.5 0.7 Total flow rate of reactive gases (F W2 (Q1) 3.4 slpm 2.5 slpm 2 slpm
  • Sheath gas (Q2) 67 slpm Ar 59 slpm Ar 67 slpm Ar
  • FIG. 22a The Raman signatures with I G /I D ⁇ 1 (Fig. 22b) indicate that the sample is made of disordered graphitic carbons, typical of carbon nanohorns, bud-like NCCs and distorted graphitic nanocapsules.
  • I G /I D ranges from 0.8 and 0.9. This value is slightly below 1-1.5, and therefore consistent with reported I G /I D values for carbon nanohorns.
  • This Example has shown how short carbon nanohorns can be produced by thermal plasma with a mixture of acetylene and hydrogen precursors. Bud-like NCCs and distorted graphitic nanocapsules were also found as byproducts. unlike the example using CH4 precursor, there was no trace of carbon nanoflakes in the collected samples. According to the TEM analyses, the NCCs produced with C2H2 in the plasma reactor are almost twice as long as those produced using H2 and CH4 mixture. The reason for this is still under investigation.
  • the present nanohorns were characterized using an encapsulation procedure with organic dyes. As is well- known from the prior art, the encapsulation of an organic dye in a nanostructure like carbon nanotubes and nanohorns increases the Raman signal of this compound. We have tested the CNHs structures produced in the plasma reactor and found after encapsulating an organic dye with a better loading than conventional nanohorns.
  • nanohorns of the invention used for this experiment were manufactured as described in Example 1 with a pressure of 82.7 kPa, a global flow rate of 1 .7 slpm and H2:CH4 ratio of 0.5.
  • the conventional (commercial) nanohorns were:
  • NEC The nanohorns sold by NEC Corporation®, Japan as described in “Carbon Nanohorns'' Tech Sheet, by NEC Corporation, dated February 2017, 2 pages. These nanohorns feature Dalhia-like nanohorns aggregates of about 94 nm in diameter and bud-like nanohorns of about 73 nm in diameter (see Fig 23).
  • Carbonium The Single Wall Carbon Nanohorns (SWCNH) sold by Carbonium®, Italy, which are described in the product brochure entitled “Single Wall Carbon NanoHorns/Graphene Nanostars published by Carbonium si. These nanohorns feature Dalhia-like nanohorns aggregates of about 89 nm in diameter and bud-like nanohorns of about 58 nm in diameter (see Fig 24).
  • the encapsulated dye was o-sexithiophene (6T) and this dye served as a reference because of many available results from the literature.
  • the experiment involved exposing the nanohorns to a solution of the dye in N,N- dimethylformamide (DMF) and then filtering and washing with DMF to remove the excess of o-sexithiophene located outside the nanohorns. This procedure ensured that the measured Raman signal comes only from the encapsulated (therefore protected) molecules.
  • the Raman spectra of these nanohorns is shown in Fig. 25, middle spectra. We can see that both the nanohorns of this invention and the NEC nanohorns provide a stronger Raman signal than that of the Carbonium nanohorns.
  • the nanohorns were subsequently exposed to piranha solution (F SO ⁇ F O?) 5:1 for 5 minutes.
  • the piranha solution eliminated all traces of organic molecules located outside the CNHs. If a dye molecule had not been encapsulated in a stable manner inside a nanohorn, it would have been eliminated by the piranha solution.
  • the Raman spectra of these nanohorns is shown in Fig. 25, top spectra. As can be seen, the Raman signal of the nanohorns of the invention is about twice as intense as the signal for the NEC and Carbonium nanohorns. This early result shows that the nanohorns of the invention are better adapted than conventional nanohorns for encapsulating dyes for Raman detection.
  • Fig. 26 is a figure summarizing the tests and results reported in Examples 1-2 above.

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Abstract

L'invention concerne des nanocornets de carbone et leur méthode de fabrication. La méthode comprend la génération du nanocornet à partir d'un précurseur de carbone et d'un gaz promoteur dans une certaine plage de rapport atome de promoteur : atome de carbone, à l'aide d'une torche à plasma thermique. Le gaz promoteur est de l'azote, de l'hydrogène, de l'hélium, de l'argon, un gaz moléculaire constitué d'une combinaison d'atomes d'azote et d'hydrogène, ou un mélange de ceux-ci. De plus, les nanocornets sont fabriqués dans un paramètre de fonctionnement A (plage de pression) et un paramètre de fonctionnement B (plage de taux d'alimentation en carbone) lors de l'utilisation d'un réacteur de référence et d'une torche à plasma de référence ou dans des paramètres de fonctionnement équivalents aux paramètres de fonctionnement A et B lors de l'utilisation d'un réacteur différent du réacteur de référence et/ou d'une torche à plasma différente de la torche à plasma de référence.
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