WO2014202740A1 - Systèmes et procédés de synthèse de nanotubes de carbone - Google Patents

Systèmes et procédés de synthèse de nanotubes de carbone Download PDF

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Publication number
WO2014202740A1
WO2014202740A1 PCT/EP2014/062978 EP2014062978W WO2014202740A1 WO 2014202740 A1 WO2014202740 A1 WO 2014202740A1 EP 2014062978 W EP2014062978 W EP 2014062978W WO 2014202740 A1 WO2014202740 A1 WO 2014202740A1
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WO
WIPO (PCT)
Prior art keywords
porous
substrate
parent
nanostructures
child
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PCT/EP2014/062978
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English (en)
Inventor
Jin Won Seo
Ignaas Verpoest
Luis GONZALEZ-URBINA
Roel LOCUS
Filip de Clippel
Bert Sels
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Katholieke Universiteit Leuven
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Priority claimed from GB201310929A external-priority patent/GB201310929D0/en
Priority claimed from GB201310927A external-priority patent/GB201310927D0/en
Priority claimed from GB201320172A external-priority patent/GB201320172D0/en
Application filed by Katholieke Universiteit Leuven filed Critical Katholieke Universiteit Leuven
Publication of WO2014202740A1 publication Critical patent/WO2014202740A1/fr

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    • 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
    • C01B32/158—Carbon nanotubes
    • C01B32/16—Preparation
    • C01B32/164—Preparation involving continuous processes
    • 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
    • C01B32/158—Carbon nanotubes
    • C01B32/16—Preparation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures

Definitions

  • the present invention relates to the synthesis of nanostructures, and more particularly, to the a method and system for synthesis of nanostructures, to the use of a membrane, (optionally a hierarchical membrane), for the synthesis of such nanostructures and to methods and systems for preparing a porous body.
  • Carbon nanotubes show extremely high stiffness (up to 1060 GPa) and high strength (up to 60 GPa has been reported) owing to their perfect and oriented structure of a tubular graphene sheet. Combined with the low density (1 .8 kg/lit) they have high potential to be used as reinforcing element.
  • CNTs The major problem of CNTs is currently that their handling is very difficult due to the fact that their diameter is only a few nanometer. Moreover, as-produced CNTs are mostly entangled, and randomly oriented, unless they are grown as aligned CNT forest. In the latter case, however, the density (number of CNTs/cm2) is very difficult to control.
  • a CNT forest is grown from a metal catalyst deposited as a thin film on a flat substrate. The film breaks up into small nanoparticles upon heating to CVD process temperatures (400-1000 °C). Hence, the location and the CNTs characteristics are rather randomly determined by the nanoparticles formed. For instance in WO2005098084 a CVD based process is described for the growth of CNTs.
  • the length of CNTs is also rather limited.
  • diffusion of feedstock gas to catalyst particles becomes more and more difficult with the dense CNT carpet thickness, and the growth finally stops because of the obstruction of the gas flow.
  • the growth strongly comes at the expense of increase in amorphous carbon for high thickness carpets, which limits the interaction between individual CNTs in a carpet.
  • the fibers spun from a gas phase suspension has shown so far the best mechanical properties with stiffness of up to 350GPa and strength up to 8GPa. These values are beyond any other strongest commercially available fibers.
  • the main drawback of that approach is however that small catalyst particles are present weakening the fibers, such as in WO2005098084.
  • the CNT length is rather limited to about 1 mm.
  • the pores may extend through the full thickness of the substrate.
  • the synthesis can then be based on a flow through mechanism. It is an advantage of embodiments of the present invention that an efficient method for synthesis is obtained.
  • the growth is performed directly in the pores, followed by a graphitizing process afterwards. It is an advantage of embodiments of the present invention that by growing directly in the pores the catalytic particles are not enclosed in the nanostructures. Avoiding enclosure of the catalytic particles in the nanostructures is advantageous as catalytic particles could destroy the walls of the nanostructures and may result in inferior mechanical properties.
  • nanostructures are to be decorated with metal particles, the latter can be performed in a simple process, by for instance coating CNTs with a solution containing metal particles and subsequent drying or using a metal particles containing aerosol.
  • Such structures can lead to hybrid structures able for hydrogen storage, chemical detection, catalysis etc.
  • nanostructures is not limited by gas obstruction caused by the densely growing nanostructures or by a strongly limited diffusion process of gas through the substrate.
  • a substrate which preferably comprises a porous body having an upstream surface and a downstream surface.
  • the substrate further may include a plurality of catalyst particles deposited inside the pores of the porous body, and from which nanostructures may be synthesized.
  • the porosity of the body provides pathways through which a reaction gas can travel across the upstream surface and out the downstream surface to initiate growth of nanostructures from the catalyst particles.
  • the substrate in one embodiment, may be provided with pore size ranging from about 0.5 nm to about 500 microns, and a void fraction of from about 10 percent to about 95 percent.
  • the catalyst particles in the pores or pore channels of the substrate may range from about 0.5 nm to about 50 nm.
  • the catalyst particles are deposited in the pores of the substrate in such a way that they advantageously enable a pathway through which a reaction gas can travel across the upstream surface and out the downstream surface, and thus the catalyst particles do not block the pathway of the reaction gas.
  • the catalyst particles in the pores or pore channels of the substrate may have a size from about 0.5 nm to about 50 nm but not exceeding 50 percent of the pore size.
  • the average number (i.e. averaged over all pathways) of catalyst particles positioned in the pathways is higher than 1 .0. It was found that advantageously, the number of particles in the pores can be larger than one, resulting in a higher growth efficiency, because the chance that a carbon precursor molecule flowing through a specific channel is "caught" is at least twice as high as compared to the case where there was only a single catalyst particle per pathway. In this way, a high efficiency for growing nanostructures can be obtained leading to high number of nanostructures per pore as well as highly efficient use of the process gases.
  • each of the pathways has a substantially gas-impermeable wall (unlike e.g. an array of needles). This offers the advantage that the growth will be more efficient. It also offers a higher implementation of the carbon atoms into the nanostructures because the movement of the precursor gas is confined by the pathways walls.
  • an AnoporeTM inorganic membrane (AnodiscTM) of Whatman, may be used.
  • a porous membrane advantageously has a precise, nondeformable honeycomb pore structure with no lateral crossovers between individual pores, that preferably may filter at precisely the stated cut-off, allowing no larger sized particles to pass through the membrane.
  • Embodiments of the invention provide the use of inorganic porous membranes, whereby said membranes may be composed of a high purity alumina matrix that is manufactured electrochemically.
  • porous substrate known in the art, has been used for capture of micro-organisms and particulate material on the surface of the membrane for subsequent analysis by light or electron microscopy, however embodiments of the present invention provide the novel use of such a porous membrane as a substrate for the synthesis of nanostructures, whereby catalyst particles are deposited inside the pores.
  • the term "in” or “inside” used herein may refer to that a catalyst particle is positioned at an inner or interior part of the pore or pore channel.
  • a substrate for the synthesis of nanostructures is a membrane which preferably is hydrophilic and is compatible with most solvents and aqueous material.
  • such membrane preferably used as a porous substrate, is preferably peripherally bonded to e.g. an annular polypropylene ring for ease of handling and is suitable for both vacuum and pressure filtration.
  • catalyst particles are provided in or inside the pores or pore channels of a porous substrate by modifying the surface of the substrate by e.g. chemical etching and bringing in the catalyst inside the pores by impregnation, e.g. dipping into a catalyst solution, e.g. a metal-salt catalyst solution, and preferably drying said substrate comprising the dipped catalyst, e.g. metal-salt, in order to obtain a substrate comprising the catalyst inside the pore channels.
  • a catalyst solution e.g. a metal-salt catalyst solution
  • the catalyst particles are distributed evenly along the pore channels driven by the wetting of the channel walls.
  • the catalyst deposition distribution will be inhomogeneous and difficult to control, especially the pores on the left- and righthand side will be deposited differently (unless the sample is rotated) because of the different angle of the directed beam of sputtered material or molecular beam as well as because of the shallow opening of the pores.
  • a substrate in order to enable the introduction of catalyst particles inside the pore channel of the substrate, one can use this method for substrates with different pore diameters.
  • a substrate comprising pores with large diameters may be used, because shallow pores will disadvantageously lead to a high shadowing effect.
  • the chemical etching may be performed by for instance NaOH/HCI etching, the latter advantageously provides a modification of the surface of a porous substrate, for instance by providing a cleaner surface. Moreover, said modification advantageously improves the adhesion qualities of the substrate surface. In addition, said modification, e.g. etching, increases the roughness of the walls of the pore channels of the membrane or substrate providing nucleation sizes for catalyst particles after dip-coating.
  • a membrane which in embodiments of the invention is used as a substrate, may be hardened or coated e.g. with a sol-gel of alumina in order to increase its mechanical stability.
  • the catalyst particles are preferably evenly distributed along the pore channel of the porous body, e.g. a substrate used for the synthesis of nanostructures.
  • the porous substrate may be a porous hierarchical substrate, said porous hierarchical substrate comprising a porous parent body, said parent body comprising a plurality of pores and whereby at least one pore of said parent body comprises at least one porous child body, whereby said porous child body comprises a plurality of pores, and wherein said plurality of catalyst particles are comprised in said child body.
  • the child body may comprise a thickness of at least 0.3% and up to 1 00% of the parent body thickness.
  • the pore diameter of the child body may be smaller than the pore diameter of the parent body.
  • a pore of the parent body may be defined by a channel and whereby said channel extends through the whole parent body.
  • a pore of the child body may be defined by a channel and whereby said channel extends through the child body.
  • the channel of the parent and/or child body may comprise a hexagonal or circular or cubic or lameral cross-section.
  • the porous parent body may comprise a first and second outer body surface.
  • the parent or child pores channels may be oriented perpendicularly with respect to the first and second outer body surface.
  • the channel may be straight or is inclined with respect to the surface with a degree of 0 to 90 °.
  • the channel may be straight or may be inclined with respect to the surface with a degree of 5 to 90 °.
  • the parent body may have a thickness ranging from 20 ⁇ up to 1 0 mm, for example from 60 ⁇ up to 1 mm or from 60 ⁇ to 200 ⁇ .
  • the channel length of the parent pore channel may range from 20 ⁇ up to 1 0 mm, for example from 60 ⁇ up to 1 mm or from 60 ⁇ to 200 ⁇ .
  • the child body may have a thickness ranging from 1 00 nm up to 1 0 mm, for example from 150 nm up to 1 mm or from 200 nm up to 1 ⁇ .
  • the parent body of the substrate may be made from a material provided with pore size ranging from about 20 nm to about 2 mm.
  • the child body of the substrate may be made from a material provided with pore diameter ranging from about 2nm to about 50 nm.
  • the parent and/or child porous body may comprise a void fraction of from about 1 0 percent to about 90%.
  • the catalyst particles may be substantially evenly distributed across the child body pores.
  • the invention provides holders for substrates used for the synthesis of nanostructures.
  • a holder advantageously enables that reactive gas may go through the membrane pores of a substrate according to embodiments of the invention in order to separate an inlet, which e.g. supplies reactive gasses, from an outlet, whereby the exhaust gasses might influence the growth process.
  • a holder according to embodiments of the invention enables that the gas flow fully or mainly goes through the pores of the substrates, whereby said pore channels of the substrate comprise catalyst particles, and thus generates CNTs inside of the pores of the substrate and limited on the surface of the substrate.
  • the holder is a passageway across the thickness of the holder, for instance a cylindrical tube, with a partially closed ending on one side and an open ending at the opposite side (see drawing).
  • the diameter of the holder preferentially corresponds to the inner diameter of the reactor tube and can be scaled from 1 mm to 1 m.
  • the closed ending is directed towards the inlet of the gases, preferably at the upstream side, and the open side towards the outlet of the reactor, preferably at the downstream side.
  • the partially closed side contains one or several apertures depending on the size of the reactor and the substrates.
  • the apertures preferably have the design of a truncated-cone forming pockets where the substrates are placed.
  • the smaller base of the truncated cone of the pockets and the substrates must be of the same size and shape.
  • an accessory in the shape of smaller cylinder with a conical ground join may be provided which ensures the fixation of the substrate in the pocket.
  • a holder may be provided which allows hosting of one or more membranes (e.g. 7 membranes such as in the drawing).
  • the basic principle of the holder can be adapted to include 1 membrane as well as numerous membranes.
  • the number of the pockets is limited by the holder diameter dh as well as by the membrane diameter dm.
  • the pockets are arranged in hexagonal packing.
  • the central pocket is surrounded by 6 other pockets. With increasing diameter of the holder multiples of 6 pockets come into addition, hence the number of the pockets goes from 1 to 6-( with n being an integer number (e.g. 7, 19, 37 etc.).
  • the holder material is chosen such that it withstands the high temperature of 400 °C up to 1400 °C and the exposure to the reactive gases.
  • the holder is therefore preferentially made of quartz.
  • Preferred embodiments of the invention provide the use of inorganic membranes, such as for instance an anodised aluminium oxide, as a growing substrate in a system for synthesis of nanostructures.
  • the invention provides methods of preparing a porous body, said method comprising:
  • the child body comprises a metal oxide or metal oxide gel.
  • providing the metal oxide gel may be performed by synthesis of the metal oxide in said empty part with or without precursors.
  • providing the metal oxide gel is performed by mechanical force, sonication, vibration, evaporation-intrusion or liquid filtration.
  • the porous child body comprises a thickness of at least 0.3% and up to 99.7% of the parent body thickness.
  • the method of preparing a porous body further comprises providing metal particles in said pores of the porous child body.
  • Preferably providing the metal particles may be performed by selective deposition of the metal particles in the porous child body.
  • the porous child body comprises channels extending throughout the child body, e.g. extends over its entire thickness.
  • the porous child body may fill the pores of the parent body over substantially their full width, i.e. over substantially the full cross-section of the channels.
  • the latter may be for example, over at least 95% of the cross-section of the pore the parent body, e.g. over at least 99% of the cross-section of the pore of the parent body
  • the average number (i.e. averaged over all pore channels) of catalyst particles positioned in the pore channels of the porous child body is 1 .0 or higher. This offers the advantage of a higher growth efficiency, because the chance that a carbon precursor molecule flowing through a specific channel is "caught" is higher (if more than one catalyst particle is used) compared to the case where there was only a single catalyst particle per channel.
  • the catalyst particles are primarily located inside the pore channels through which the reaction gas flows, rather than on the downstream surface of the substrate, in that a higher density of CNTs can be obtained because of the direct exposure of catalyst particles to the reaction gases, and because the carbon concentration of the gas is higher inside the pore channels than at the downstream surface location.
  • each of the pore channels has a substantially gas-impermeable wall (unlike e.g. an array of needles). This offers the advantage that the process gases will be more efficiently exploited. It also offers a higher growth efficiency because the diffusion of carbon through the pore channel walls is limited.
  • the body is a layer or a particle.
  • the particle is a silica particle. More preferably the body may be a porous membrane.
  • Embodiments of the method for providing a porous body according to the invention provide a porous body having a hierarchical structure, whereby the porous body is manufactured using a method according to embodiments of the invention.
  • the present invention provides porous bodies comprising a porous parent body, said porous parent body comprising a plurality of pores and whereby at least one pore of said parent body comprises at least one porous child body, whereby said porous child body comprises a plurality of pores, whereby said porous child body comprises a thickness of at least 0.3%.
  • said porous child body comprises a thickness of at least 0.3% and up to 99.7% of the parent body thickness.
  • the pore diameter of the porous child body is smaller than the pore diameter of the porous parent body.
  • a pore of the porous parent body is defined by a channel and whereby said channel extends through the whole porous parent body.
  • the pore of the child body is defined by a channel and whereby said channel extends through the porous child body.
  • the body is a layer or particle.
  • the channel of the parent and/or child body comprises a hexagonal or circular or cubic or lameral cross-section.
  • the child body pores may comprise metal particles.
  • the metal particles are positioned along and in the porous child body channel.
  • the porous parent body comprises a first and second outer body surface.
  • the parent or child pores channels may be oriented perpendicularly with respect to the first and second outer body surface.
  • the channel is straight or is inclined with respect to the surface with a degree of 0 to 90 °. In other preferred embodiments the channel is straight or is inclined with respect to the surface with a degree of 5 to 90 °.
  • the child porous body is positioned at the first outer body surface or at the second outer body surface or in-between the first and second outer body surface.
  • the parent body has a thickness ranging from 20 ⁇ up to 10 mm. In preferred embodiments of the porous body the parent body has a thickness ranging from 60 ⁇ up to 1 mm. In other preferred embodiments the parent body has a thickness ranging from 60 ⁇ to 200 ⁇ . In preferred embodiments the channel length of the parent pore channel ranges from 20 ⁇ up to 10 mm. In other preferred embodiments the channel length of the parent pore channel ranges from 60 ⁇ up to 1 mm. More preferably the channel length of the parent pore channel may range from 60 ⁇ to 200 ⁇ .
  • the child body has a thickness ranging from 1 00 nm up to 1 0 mm.
  • the child body may have a thickness ranging from 150 nm up to 1 mm. More preferably the child body may have a thickness ranging from 200 nm to 1 ⁇ .
  • the porous body is a membrane.
  • the invention provides a porous body, whereby said porous parent body comprises a pore diameter between 20 nm and up to 2mm.
  • the parent body may comprise a void fraction between 1 0 and 90%.
  • the porous child body comprises a pore diameter between 2nm and 50nm and a void fraction between 1 0 and 90%.
  • the porous child body is a catalytic active thin metal oxide layer.
  • Preferred embodiments of the invention provide a porous body, whereby the porous body is a hierarchical porous body.
  • a hierarchical porous body may link the parent and/or at least one child body either directly or indirectly, and either vertically or horizontally.
  • the porous parent body is made from a material including carbon foams, glassy carbon, silica, alumina, alumina coated with silica, zirconia, zeolites, sintered titanium, titania, magnesia, yttria, copper, iron, iron nickel, iron cobalt, cobalt, steel, iron carbide, nickel, or a combination thereof.
  • the invention provides the use of the porous membrane according to embodiments of the invention for synthesis of nanostructures.
  • the invention provides systems for producing a porous membrane body having a hierarchical structure, the system comprising at least means for providing a porous parent body, means for filling of at least one pore of the parent body along a pore channel, with a filling substance, resulting in a filled and in an empty part of the parent pore, means for providing a child body in the empty part of the parent pore and means for removing the filling substance in the filled part of the parent pore, for performing a method according to embodiments of the invention for provide a porous body.
  • the pore channel of a child porous body is parallel to the pore channel of a parent porous body.
  • a parent body, preferably a layer or a membrane, used in embodiments of the present invention may be commercial layers or membranes known in the art.
  • a layer or child particle such as metal oxides or a hexagonal COK-12 silica particle respectively
  • advantageously provide a child body, e.g. a membrane, in at least one pore of the parent body e.g. layer or membrane moreover embodiments of the present invention enable a hierarchical body e.g. a hierarchical membrane which can be used as a substrate for e.g. CNT growth.
  • a hierarchical membrane may be a parent crystalline mesoporous parent silica material, being obtained by an assembly of nanometer size building units having a zeolite framework, said crystalline mesoporous silica material having two or more children levels of porosity and structural order.
  • the crystalline mesoporous hierarchical materials, e.g. silica materials, according to embodiments of the invention are useful in a number of industrial applications, such as, but not limited to, the fixation of biologically active species, as well as an electro-optical or dielectric material or for catalysis, molecular separation or adsorption of metal ions.
  • the hierarchical bodies according to embodiments of the invention can be used for biosensing and for photo conversion or photo devices (e.g. fluorescent carbon dots or CNTs).
  • said oxide based material may comprise one or more oxides selected from the group consisting of silica, germanium oxide and metallic oxides.
  • a preferred non-metallic oxide is silica.
  • the metallic oxides may derive from any metal selected from groups 4 to 12 of the periodic table. Preferred metals are aluminum and transition metals.
  • Exemplary metallic oxides are preferably selected from the group consisting of alumina, titania, zirconia, ceria, manganese oxide, niobium oxide, tantalum oxide, tungsten oxide, tin oxide, gallium oxide, iron oxide, and hafnium oxide.
  • ternary or quaternary oxides can be used, which can be a combination of two or three of the named oxides.
  • the parent, e.g. mesoporous oxide, based material according to the invention may comprise silica in combination with one or more such metallic oxides, which will be selected according to the intended end use of the material.
  • silica, alumina, titania, zirconia and their mixtures in a wide range of proportions may be considered for use as acidic catalysts.
  • a mesoporous tungsten oxide material may be used as a carrier for a number of ruthenium based catalysts for diverse chemical reactions including polymerization, metathesis, epoxidation, hydro-amination, aziridination and the like.
  • a mesoporous semiconducting oxide material may be used for industrial applications such as the construction of fuel cells.
  • Embodiments of the present invention advantageously provide a novel hierarchical body or e.g. membrane as support or substrate for e.g. vertical CVD growth
  • the membrane according to embodiments of the invention comprises a parent layer e.g. membrane, whereby pores of the parent membrane comprise a porous metal oxide as a child membrane or e.g. a hexagonal COK-12 silica particle as a child porous particle, preferably within the channels of the parent layer e.g. membrane.
  • the orientation of the pores and/or pore channels in the layer, e.g. parent or child membrane is preferably perpendicular with respect to the surface of the layers.
  • the hierarchical nature of a porous body or membrane according to embodiments of the invention can be preferably obtained by e.g. filling a parent layer or membrane channel with silica for a limited part along its axial length or by partial filling along the full length of the membrane channel or by deposition of individual metal oxide particles along the membrane channel.
  • a method for providing a porous layer or particle e.g. membrane, preferably a catalytic active thin metal oxide layer in the parent membrane can comprise at least the steps of:
  • the metal oxide synthesis gel may be introduced in the open membrane channel of the parent membrane by mechanical force i.e. sonication, vibration, evaporation-intrusion and liquid filtration.
  • Preferred embodiments of the invention provide a method to control metal deposition at a thin top layer of a membrane by selective deposition of metal particles on the newly introduced metal oxide phase, preferably in the child membrane structure.
  • a continuous gas flow through the porous membrane is enabled by limiting the amount of growth nuclei in each pore of the child membrane and providing gas large transport channels in the hierarchical structure.
  • the membrane method according to embodiments of the invention can be used for growing fibrous carbon nanostructures using CVD synthesis conditions, like for example the one proposed in WO'084.
  • the carbon nanostructures are preferably grown after providing contact between the metal comprising hierarchical membranes with at least a carbon-containing gas and optionally a support or carrier gas at elevated temperature between 200 °C and 1400 °C, preferably between 400 °C and 1200 °C and more preferably between 600 °C and 1000 °C.
  • the metal catalyst particles can be provided on or preferably within the pores of the child body or membrane.
  • Embodiments of the present invention provide a method to align the produced fibrous carbon nanostructures under influence of gravimetric forces, gas flow and an increased density of growth nuclei and optionally further supported by a magnetic field.
  • Hierarchical membranes according to embodiments of the present invention can be used for the synthesis for any kinds of nanostructures by means of a CVD process, whenever catalyst particles, gas flow, formation of nanostructures are involved. This can be for instance the case for the growth of nanowires based on the catalytic VLS-growth.
  • hierarchical membranes can be used for carbon nanostructures as well and more specifically for CNTs.
  • the invention provides systems for synthesis of nanostructures, the system comprising:
  • -a housing having a first end, an opposite second end, and a passageway extending between the first and second ends;
  • said hierarchical porous substrate comprising a porous parent body, said parent body comprising a plurality of pores and whereby at least one pore of said parent body comprises at least one porous child body, whereby said porous child body comprises a plurality of pores and whereby said porous substrate is situated within the passageway of the housing;
  • -said child body comprising a plurality of catalyst particles, and from which nanostructures can be synthesized upon interaction with a reaction gas;
  • a heating mechanism circumferentially placed about the substrate for generating energy sufficient to maintain an environment within which nanostructures are synthesized within a specified temperature range
  • the body is a layer or particle, e.g. a silica particle.
  • the child body comprises a thickness of at least 0.3% and up to 100% of the parent body thickness.
  • the pore diameter of the child body is smaller than the pore diameter of the parent body.
  • the pore of the parent body is defined by a channel and whereby said channel extends through the whole parent body.
  • the pore of the child body is defined by a channel and whereby said channel extends through the child body.
  • the channel of the parent and/or child body comprises a hexagonal or circular or cubic or lameral cross-section.
  • the porous parent body may comprise a first and second outer body surface.
  • the parent or child pores channels may be oriented perpendicularly to the first and second outer body surface.
  • the channel may be straight or is inclined with respect to the surface with a degree of 0 to 90 °. More preferably the channel may be straight or is inclined with respect to the surface with a degree of 5 to 90 °.
  • the parent body has a thickness ranging from 20 ⁇ up to 10 mm. In other preferred embodiments the parent body may have a thickness ranging from 60 ⁇ up to 1 mm. In preferred embodiments the parent body has a thickness ranging from 60 ⁇ to 200 ⁇ . In preferred embodiments the channel length of the parent pore channel may range from 20 ⁇ up to 10 mm. In other preferred embodiments the channel length of the parent pore channel may range from 60 ⁇ up to 1 mm. In preferred embodiments the channel length of the parent pore channel ranges from 60 ⁇ to 200 ⁇ . In other preferred embodiments the child body may have a thickness ranging from 100 nm up to 10 mm.
  • the hierarchical substrate according to embodiments of the invention, whereby the child body has a thickness ranging from 150 nm up to 1 mm.
  • the child body may have a thickness ranging from 200 nm to 1 ⁇ .
  • Preferred embodiments of a system for synthesis of nanostructures further may include an exhaust port through which reaction waste product flowing from the substrate may be removed.
  • the housing may be made from a strong, substantially gas-impermeable material.
  • the material is substantially resistant to corrosion and/or high temperature.
  • the material may be quartz.
  • the substrate is sufficiently porous so that a pressure difference between both surfaces of the substrate can be substantially low, so as to permit the substrate to maintain its structural integrity.
  • the parent body of the substrate is made from a material provided with a pore size ranging from about 20 nm to about 2 mm.
  • the child body of the substrate is made from a material provided with pore diameter ranging from about 2nm to about 50 nm.
  • the parent and/or child porous body may comprise a void fraction of from about 1 0 percent to about 90%.
  • the substrate is made from a material including carbon foams, glassy carbon, silica, alumina, alumina coated with silica, zirconia, zeolites, sintered titanium, titania, magnesia, yttria, copper, iron, iron nickel, iron cobalt, cobalt, steel, iron carbide, nickel, or a combination thereof.
  • the substrate is one of foam, channel plate, felt, wool, fibers, cloth, or array of needles.
  • the catalyst particles may be substantially evenly distributed across the child body pores.
  • the catalyst particles are made from a material including iron, nickel, cobalt, iron oxides, nickel oxides, cobalt oxides, metal salts with sulfate, metal salts with sulfamates, acetate, citrate, oxalates, nitrites, nitrates, or a combination thereof.
  • the catalyst particles range from about 0.5 nm to about 50 nm in size.
  • the heating mechanism can maintain the temperature of the growth environment within a range of from about 200 °C to about 1400 °C.
  • the heating mechanism can maintain the temperature of the growth environment within a range of from 400 °C up to 1200 °C. More preferably the heating mechanism can maintain the temperature of the growth environment within a range of from 600 °C to 1 000 °C.
  • Preferred embodiments of a system for synthesis of nanostructures according to the invention provide that the energy generated from the heating mechanism may include thermal energy, frictional energy, visible light photons or other types of electromagnetic radiation, chemical, electrical, or electrochemical energy, microwave radiation, eddy currents, or ultrasound shock waves or compression.
  • the flanges are substantially gas- impermeable.
  • Preferred embodiments of a system for synthesis of nanostructures according to the invention further include a tube for accommodating the porous substrate, the tube being situated within the passageway of the housing for providing a pathway for the reaction gas from the inlet to the substrate.
  • the substrate may be situated within the tube.
  • the tube is made from a strong, substantially gas-impermeable material.
  • the material may be quartz.
  • Preferred embodiments of a system according to invention further may include: a first electrode situated within the pathway of the tube upstream of the porous substrate; and a second electrode situated within the pathway of the tube downstream of the porous substrate.
  • the upstream electrode and the downstream electrode may be designed to generate an electric field there between to provide physical support to the nanostructures growing from the substrate.
  • the upstream and downstream electrodes may be designed to generate an electric field there between to control and maintain direction of growth to the nanostructures growing from the substrate.
  • the electrodes permit flow of reaction gas within the tube there through.
  • the electrodes are made from an electrically conductive material that is non-reactive and resistant to nanostructure growth.
  • the material from which the electrodes are made includes graphite, copper, titanium, vitreous carbon, a combination thereof, or other conductive materials not catalytic to carbon nanostructure formation.
  • a porous substrate is positioned circumferentially about an exterior surface of the tube at one end of the tube, and the system further includes: a tubular electrode having an open end and sufficiently sized so as to concentrically accommodate the porous substrate through the open end; and a plurality of guides, positioned between the tubular electrode and the substrate, and over which growing nanostructures can be directed.
  • the porous substrate may be designed to be an electrode, such that along with the tubular electrode, an electric field can be generated there between to provide physical support to the nanostructures growing from the substrate.
  • the porous substrate and the tubular electrode designed to generate an electric field there between to control and maintain direction of growth to the nanostructures growing from the substrate.
  • the substrate may be made from an electrically conductive material including, glassy carbon, porous titania, porous zirconia, or sintered titanium powder.
  • the substrate is made from an inert material coated with an electrically conductive material including, copper, tin oxide, titania, titanium, tungsten or platinum.
  • tubular electrode is rotatable and retractable from its position over the substrate so as to pull growing nanostructures there along.
  • the guides may include a series of rings circumferentially placed about the substrate.
  • a system according to embodiments of the invention further may include a second inlet situated across the flange capping the first end of the housing and through which an evacuation gas can be directed into the passageway of the housing to displace and remove reaction waste product within the housing.
  • the invention provides substrates for synthesis of nanostructures, the substrate comprising: a porous parent body having an upstream surface and a downstream surface; the porous body further comprising at least a porous child body in said parent pore and a plurality of catalyst particles, deposited in said child body, whereby said child body is positioned or on the upstream or on the downstream surface or in-between the upstream and downstream surface of the substrate, and from which nanostructures can be synthesized; wherein the porous body provides pathways through which a reaction gas can travel across the upstream surface and out the downstream surface to initiate growth of nanostructures from the catalyst particles.
  • said porous substrate is hierarchical or ordered.
  • the porous substrate is sufficiently porous so that a pressure difference between the upstream surface and the downstream surface can be substantially low, so as to permit the body to maintain its structural integrity.
  • the invention provides methods for synthesizing nanostructures, the method comprising: -providing a porous hierarchical substrate;
  • the step of directing includes allowing the gas, after exiting the downstream surface of the substrate, to flow past growing nanostructures, so as to provide support to the growing nanostructures.
  • the step of directing includes adding a carbon-containing source to the reaction gas prior to directing the reaction gas to the substrate.
  • the carbon- containing source may include ethanol, methane, methanol, ethylene, acetylene, xylene, carbon monoxide, or toluene.
  • the method further may include introducing an evacuation gas to displace and remove reaction waste product.
  • the step of decomposing may include generating energy to temperatures ranging from about 200 °C to about 1400 °C.
  • the step of decomposing may include generating energy to temperatures ranging from about 400 °C to about 1400 °C.
  • the energy in the step of generating, may include thermal energy, frictional energy, visible light photons or other types of electromagnetic radiation, chemical, electrical, or electrochemical energy, microwave radiation, eddy currents, or ultrasound shock waves or compression.
  • the step of allowing includes growing the nanostructures in a direction substantially parallel to the flow of reaction gas.
  • the step of allowing may include growing the nanostructures in a direction substantially radially to the flow of reaction gas.
  • the step of allowing may include growing the nanostructures to a specified length.
  • the specified length may be at least 1 cm. In other preferred embodiments, in the step of growing, the specified length may be at least 1 m.
  • the method further may include generating an electrostatic field having a strength between about 5 kV/m and about 1000 kV/m to provide support the nanostructures as they grow from the substrate, so as to contribute to the straightness of the nanostructures.
  • the method further may include generating a magnetic field having a magnitude between about 0.1 T and about 50T to provide support the nanostructures as they grow from the substrate, so as to contribute to the straightness and/or alignment of the nanostructures. More preferably a magnetic field having a magnitude between about 0.1 T and about 30T may be generated.
  • the values of the magnetic field according to embodiments of the invention are chosen such to enable in situ orientation but also to enable a base growth mechanism.
  • One preferably uses a high magnetic field in order to orient CNTs after the growth (up to 50T, preferably up to 30T), for instance CNTs dispersed in a solution or CNTs powder etc.
  • the magnetic field applied is much lower because of the magnetic catalyst particles involved.
  • the magnetic field is preferably chosen such that the magnetic metal particle (e.g. all CNT growing particles such as Co, Ni, Fe, etc.) stay attached to the membrane surface according to embodiments of the invention.
  • the method further may include generating an electric field having a magnitude between about 5 kV/m and about 1000 kV/m to provide support to the nanostructures as they grow from the substrate, so as to contribute to the straightness and alignment of the nanostructures.
  • the method further may including collecting the nanostructures once the nanostructures have grown to a desired length.
  • the invention provides a fibrous material comprising a plurality of nanostructures according to embodiments of the invention.
  • a fibrous material may be used in thermal management applications.
  • the invention provides heat conductors comprising the fibrous material set obtained by using method according to the present invention.
  • Preferred embodiments of the invention provide a low eddy current, low resistance winding for an electric motor comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a low eddy current, low resistance winding for a high frequency solenoid comprising fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a winding for a high frequency transformer comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a fabric comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a protective armour or clothing comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a rope or cable comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a yarn comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a sheet comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a heat sink comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a high strength, low eddy current, low resistance electric power transmission line comprising the fibrous material according to embodiments of the invention.
  • Preferred embodiments of the invention provide a process for packing of carbon nanotubes comprising: generating the nanotubes according to embodiments of the invention; coating the nanotubes with one of furfuryl alcohol, epoxy resin, or Resol; and arranging the coated nanotubes in bundles for packing.
  • multi-walled nanoparticles e.g. carbon nanotubes
  • single-walled nanoparticles can be obtained using embodiments of the present invention.
  • large as well as small catalyst particles can be used.
  • the smallest pore diameter determines the lowest limit of the nanoparticles diameter and the upper limit of the nanoparticles diameter, e.g. carbon nanotube diameter, is determined by the metal catalyst particles formed on the pore side walls.
  • high density nanoparticle arrays e.g. high density carbon nanotube arrays
  • Such arrays can be densely packed but are still permeable for gasses.
  • the obtained arrays typically are highly efficient and highly sensitive.
  • catalyst particles are not in the nanoparticles grown and therefore do not weaken the materials. It is an advantage of embodiments of the present invention that the nanoparticles can be properly oriented, resulting in a good close packaging.
  • reaction gas flows through the pores, resulting in advantageous growth of nanoparticles as described.
  • a porous substrate may make use of a hierarchical structured substrate, i.e. a substrate comprising a porous parent body and comprising a child body in the pores of the porous parent body.
  • Fig. 1 illustrates, in correspondence with one embodiment of the present invention, an example (vertical) set-up of the chemical vapour deposition setup as used for the growth of fibrous carbon nanostructures.
  • Fig. 2 shows an exemplary strategy in order for the preparation of a hierarchical membrane applied as a substrate in the CVD set-up.
  • Fig. 3a shows the targeted localization of the catalytic active metal particles within the pores of the membrane substrate according to embodiments of the invention.
  • Fig. 3b shows the targeted localization of the catalytic active metal particles within the pores of the membrane substrate according to alternative embodiments of the invention
  • Fig. 4 summarizes the different steps involved in the synthesis of the fibrous carbon nanostructures according to embodiments of the invention.
  • Fig. 5 is a SEM image and illustrates a partial pore filling as intermediate step toward hierarchical membranes, according to embodiments of the invention.
  • Fig. 6a is a SEM image and shows the partial filling of the membrane channels with a mesoporous solid, according to embodiments of the invention.
  • Fig. 6b is a SEM image and shows the complete filling of the membrane channels with a mesoporous solid according to embodiments of the invention.
  • Fig. 7 illustrates the deposition of mesoporous particles inside the membrane channels according to embodiments of the invention.
  • Fig. 8 illustrates schematically a porous ordered membrane.
  • Fig. 9a schematically illustrates a porous anodised aluminim oxide (AAO) membrane known in the art, where said AAO membrane is a relatively inexpensive and commercially available membrane, such a membrane is for instance described by Sonny S. Mark et al., in Colloids and Surfaces B: Biointerfaces (2008) vol 65, pp. 230-238.
  • Fig 9b illustrates images showing an AAO membrane comprising catalyst particles inside the pore channels or columns of the AAO membrane, according to embodiments of the invention.
  • AAO anodised aluminim oxide
  • Figs. 10a and 10b illustrate a holder, according to embodiments of the invention, which may comprise a porous membrane or an porous ordered membrane, whereby the membranes both can be used as a substrate in systems for synthesis of nanostructures according to embodiments of the invention.
  • a holder preferably is used for CVD growth systems of nanostructures.
  • Fig. 10 illustrates an image of the membrane holder according to embodiments of the invention
  • Fig. 10b schematically illustrates a holder, according to embodiments of the invention, when used for a large CVD oven that allows inserting 7 membranes into the holder or a small CVD oven that allows mounting only 1 membrane.
  • Fig. 10a and 10b illustrate a holder, according to embodiments of the invention, which may comprise a porous membrane or an porous ordered membrane, whereby the membranes both can be used as a substrate in systems for synthesis of nanostructures according to embodiments of the invention.
  • Fig. 10 illustrates an image of the membrane holder according to
  • FIG. 1 1 1 illustrates a holder according to embodiments of the invention, whereby said holder is used for the synthesis of extended length carbon nanotubes with one or more pockets, whereby he amount of pockets in the holder depends on the size of of the reactor and the diameter of the membrane, which can be up to 100 or even more), more specifically in this figure 7 pockets are provided an example.
  • Figure 1 1 depicts the plane view (on the left) and the lateral view (on the right).
  • Fig. 12 illustrates how a holder, according to embodiments of the invention, and in addition illustrates how the diameter of such a holder (dh) depends on the size, e.g. diameter (dm), of the membrane.
  • membrane used in this text relates to a thin, film-like structure that separates two phases, for instance in fluids, like for instance liquid and/or gas environments It acts as a selective barrier, allowing some particles or chemicals to pass through, but not others.
  • Membranes can be of various thicknesses, with homogeneous or heterogeneous structure. Membrane can also be classified according to their pore diameter (dp). According to lUPAC, there are three different types of pore size classifications: microporous (dp ⁇ 2 nm), mesoporous (2 nm ⁇ dp ⁇ 50 nm) and macroporous (dp > 50 nm).
  • dp ⁇ 2 nm microporous
  • mesoporous 2 nm ⁇ dp ⁇ 50 nm
  • macroporous dp > 50 nm.
  • Membranes can be neutral or charged, and particles transport can be active or passive. The latter can be facilitated by pressure, concentration,
  • Hierarchical used in this text relates to a structure arranged in a graded order which as a result form a hierarchy.
  • a hierarchy is then preferably an arrangement of items, in this text of porous bodies or structures or substrates, in which the items can represented as being "above”, such as a parent, "below” such as a child, or "at the same level as” one another.
  • a hierarchy can be modeled mathematically as a rooted tree: the root of the tree forms the top level, and the children of a given vertex are at the same level, below their common parent.
  • a hierarchy can link entities either directly or indirectly, and either vertically or horizontally.
  • a substrate having a hierarchical structure thus may be a substrate comprising at least one porous parent body having pores and comprising at least one child body positioned in a pore of the porous parent body.
  • Embodiments of the present invention relate to a method for the synthesis of a hierarchical porous body, e.g. a layer or membrane.
  • the invention further relates to a method to form fibrous carbon nanostructures in high yields via a chemical vapour deposition approach from inside the body pores, e.g. membrane pores, which functions as the support.
  • Embodiments of the present invention relate to a novel method to deposit and control the amount of (transition) metal nanoparticles in a porous body, e.g. a membrane, the metal being crucial to initiate the growth of the carbon nanostructures.
  • a porous body e.g. a membrane
  • the metal nanoparticles are provided in a child body of the porous parent body.
  • the invention relates the maximization of the metal dispersion and density in order to increase the amount of carbon nanostructure nuclei exiting the membrane surface.
  • the final properties of the carbon nanostructure can be partially controlled.
  • More specifically hierarchical membranes according to embodiments of the invention guarantee a continuous growth by offering straight transport channels, connecting both surface ends of the porous body, e.g. membrane, and in the size range preferably of 10 nm to 0.9 mm, for the reaction gas and by preventing pore blocking during carbon growth due to selective metal deposition.
  • the invention implies a sustained gas flow without pressure built-up and continuous growth of the fibrous carbon nanostructures in order to increase their overall length.
  • the present invention is further related to the field of reinforcing materials and the use of fibrous carbon nanostructures in composite materials.
  • the invention is further related to the alignment and consequent bundling of the individual fibrous carbon nanostructures into larger scale threads.
  • Advantageously embodiments of the present invention provide a method to grow CNTs with a tunable density, whereby density refers to the number of CNTs per cm 2 , as well as with infinite or ultra-long (preferably greater than 10 cm) length by using a membrane, more specifically a hierarchical membrane, according to embodiments of the invention, as support for the growth of CNTs.
  • This membrane advantageously enables tuning of the CNT density by tuning the pore density of the membrane. It also enables that the gas obstruction does not occur because the catalyst preferably will remain accessible via CNTs growing along the downstream direction according to embodiments of the invention.
  • fibrous carbon nanostructures can be formed in the presence of metals, preferably transition metals (such as nickel, cobalt, iron) or combinations thereof in multimetallic clusters (bi- or trimetallic) in said porous child body.
  • Metal precursors are deposited into a hierarchical membrane, according to embodiments of the invention, as a metal salt or as present in a substance with ion exchange properties (e.g. hyperbranched polymer) using a standard procedure preferably ion exchange, wet/incipient wetness impregnation or electrodeposition.
  • the formation of metal nanoparticles can be preferably obtained after an optional oxidation step, performed e.g.
  • the temperature is chosen between 200 and 1200 °C, a heating rate preferably between 0.01 °C min 1 to 50 °C min 1 and a duration time preferably from 0 to 1200 min of the pretreatment/reaction control the final size of the metal particles, next to the confinement effect of the porous hierarchical membrane described below.
  • Embodiments of the present invention advantageously enable the synthesis and the use of CNTs with significantly longer, preferably greater than 1 cm or at least 1 mm of length. It is an object of the present invention to provide a method to incorporate ordered porous metal oxides in a meso/macroporous membrane.
  • the porous parent body e.g. membrane
  • the porous parent body comprises pores with a pore diameter between 20 nm and 2 mm and provides a void fraction between 1 0 and 90 %.
  • the child porous body e.g. metal oxide
  • the present invention enables a large increase, up to a factor of 1 x 1 01 1 , of the pore density with a maximum of 1 pore per 7.79 nm 2 , while controlling pore orientation and allows a dense and aligned growth of fibrous carbon nanostructures out from e.g. the child membrane pores.
  • Control of the porous child body whereby said porous child body comprises a pore diameter in the mesopore size between 2 and 50 nm, allows confinement of the deposition of the metal particles advantageously yielding better-controlled size-distribution and spatial distribution of catalyst particles (limits agglomeration).
  • the confinement provides that catalyst particles are well separated pore-wise and the residual gas originating from individual CNT growth will significantly less impact the neighboring growth.
  • the invention further provides an improved method for growing carbon nanostructures within the (hierarchical) membrane by improving the gas supply to the metal particle via large macro/meso-porous transport channels toward the mesoporous grown channels of the metal oxide.
  • selective deposition of metal particles on the metal oxide phase allows control of the amount of nuclei sites in each pore channel thus reducing interdependent pore blocking.
  • the improved growth method gives a significantly higher carbon density (yield) compared to state of the art techniques.
  • Embodiments of the invention solve the problem of state of the art techniques to combine high metal particle density (and dispersion) and carbon nanostructure yield and a continuous growth of aligned using a membranes support.
  • the problem is solved by the use of hierarchical porous bodies, such as for instance membranes, or the selective deposition of metal particles in the child body, e.g. a mesoporous oxide layer, with a thickness ranging from 200 nm up to 3 mm, preferably covering only a top part, e.g. stretching from the parent body outer surface, e.g. membrane surface, to a well-defined depth, of the full porous body, e.g. membrane cross section which can vary between 60 ⁇ and 3 mm.
  • a mesoporous oxide layer e.g. a mesoporous oxide layer
  • the porous child body can not only be positioned in the top part of the parent body, but also in the middle part of the parent body pore, in the bottom part of the parent body, or a combination thereof.
  • the porous child body can be a layer or a particle, according to embodiments of the invention.
  • the catalyst particles are preferably positioned inside the pores and/or pore channels of the membrane, rather than on the upstream and downstream surface of the membrane.
  • the number of catalyst particles positioned inside the membrane is higher than the number of catalyst particles positioned on the upstream surface resp. the downstream surface of the membrane.
  • the substrate may comprise at least one pore where more than one catalyst particle is present.
  • the substrate may comprise on average more than 1 .0 nanostructures per pore.
  • the substrate may comprise on average one or more than 1 nanostructures per pore. This offers the opportunity to provide more than one particle, and hence more than one nanostructure per pore or pore channel.
  • embodiments of the present invention provide the advantage that the predetermined size, between 2 and 50 nm of the child porous body, and cross-section geometry (e.g. either lamellar, cubic, hexagonal or disordered) of the mesopores within the pores of the parent porous body, e.g. meso/macroporous membrane, can be used to determine the diameter and hence properties of the synthesized carbon nanostructures (e.g. chirality and amount of wall in CNTs).
  • this is disadvantageously done by providing an additional design pattern as to form a designed pattern to synthesize specific CNT shapes, e.g. prismatic structures.
  • Embodiments of the method of the invention to provide carbon nanostructures within hierarchical (i.e. bi- or trimodal pore size distribution) membranes with pore channels perpendicular to the membrane surface have the advantage to grow easily carbon nanostructures in away from the substrate thus reducing pore blocking at the downstream side of the porous body or parent body, e.g. membrane.
  • the pore orientation is crucial in order to allow good contact of the carbon precursor gas to the metal particles, to sustain gas flow over the metal particles and to reduce pressure built-up endangering the integrity of the support membrane.
  • the vertical set-up and perpendicular growth allow for the aligned growth of bundles of fibrous carbon nanostructures.
  • the invention also provides a method to integrate membrane supported CVD growth of aligned bundles of carbon fibrous nanostructures to its further processing in weaving or incorporation in polymer matrices as reinforcing material.
  • a method for the synthesis of a porous child body e.g. mesoporous metal oxides with controlled pore size and orientation, within the channels of a porous parent body, e.g. membrane.
  • the method for providing mesoporous metal oxide into the porous membrane may comprise at least the steps of:
  • porous parent body e.g. membrane, comprising an open channel system
  • Embodiments of the invention include a method to use the novel membrane support to grow fibrous carbon nanostructures from within the hierarchical body pores, e.g. membrane pores. Its embodiment may comprise at least the steps of:
  • the gas supply consisting of a carrier, support and carbon precursor gas, preferably at a temperature between 350 °C and 950 °C. Heating the membrane and reaction gas at the metal particles between 400 and 1200 °C in order to initiate the growth of fibrous carbon nanostructures
  • an improved method is provided to obtain a continuous growth of fibrous carbon nanostructures (e.g. CNT) from within the pores of a hierarchical membrane.
  • the improved method gives rise to a significantly improved density as well as tuning of the density of the carbon product in comparison to non-modified and non-hierarchical meso/macroporous membranes known in the art.
  • these known membranes are for instance used for biosensing means, however there are not used in systems which are adapted for synthesis of nanostructures.
  • a hierarchical membrane comprising a parent and child porous body, whereby the child porous body has a thickness of at least 0.3% of the parent body thickness.
  • Embodiments of the method of the present invention advantageously achieves metal deposition either preferably directly via the synthesis gel or via a post synthesis introduction (e.g. impregnation or ion-exchange) of the required metals.
  • a post synthesis introduction e.g. impregnation or ion-exchange
  • control of the metal deposition can be either controlled via controlling the degree of ion exchange site via isomorphous substitution either by modifying the concentration of the metal salt during impregnation.
  • sintering of the metals can be reduced via the optimization of the thermal treatment or by the use of polymers with a fixed amount of exchange sites (e.g. hyper branched polymers or dendrimers).
  • Embodiments of the present invention provide methods to grow a porous child body, e.g. a mesoporous porous metal oxide, in at least one pore of a parent body, in order to create new hierarchical membranes as described above which are preferably compatible with an improved method to grow aligned fibrous carbon nanostructures (e.g. CNT) from within the pores of the membrane.
  • the improved method may comprise at least the steps of:
  • Preheating the gas supply consisting of a carrier, support and carbon precursor gas.
  • the macro pore membrane e.g. the parent layer
  • the membrane may be any suitable membrane which is chosen in function of further applications.
  • the membrane is preferably highly thermally stable as well as chemically stable against the reactive gasses used, therefor the membrane is preferably made from an inorganic material e.g. aluminum oxide, silica or titania.
  • the meso/macroporous parent membrane has preferentially one- dimensional pores perpendicular to the surface of the membrane and a diameter in the range of 20 nm up to 1 ⁇ .
  • porosity should be maximal while sustaining a high thermal stability.
  • Porosity should be preferably in the range of 1 0 to 90%, and more preferably in the range between 20 and 70%.
  • a porous parent body e.g. a meso/macroporous membrane
  • a porous parent body e.g. a meso/macroporous membrane
  • a hierarchical porous body, e.g. membrane, according to embodiments of the invention can reduce the pressure built up, caused by hampered gas flow, by limiting the thickness of the layer of the porous child body, with small mesopores, which is deposited inside the meso/macroporous membrane according to embodiments of the invention.
  • Reduction of the thickness of the layer wherein the metal catalyst particles are located, preferably in the porous child body can ensure a reduction of the amount of fibrous structures in one pore thus providing continuous gas flow and reduction of pore blocking inside the porous oxide channels.
  • metal oxide synthesis solution which is used to create a child body, may comprise a metal oxide precursor, a surfactant, and a source of acidity/basicity and optionally hetero- elements such as Al, P, etc. for the execution of an isomorphous substitution in order to create ion exchange sites in the final porous metal oxide solid.
  • the metal oxide used in embodiments of the invention is preferably produced via the soft templating methodology using a bi-constituent synthesis mixture.
  • Si is preferred but others metals (group I I, IV and V) and transition metal are included in the invention.
  • An ordered mesoporous silica with 1 D-pores and a high width-to-thickness ratio such as COK-12 is preferred.
  • members of the following families of ordered mesoporous silica materials can be used: TUD, SBA, COK, MCM, FSM, KIT, MSU, HMS and HMM.
  • the synthesis gel can be introduced into the pores via mechanical forces out from the following selection: sonication, vibration and liquid filtration.
  • the typical bi-constituent mixture can be mixed inside the membrane pores by a two-step intrusion method. First the surfactant and (co)solvent are introduced into the membrane pores via aforementioned method after which the membrane is put into a solution of the metal oxide precursor and the proper pH controlling agent.
  • Excess of synthesis gel from the membrane is preferably removed via spin-coating condition, washing for limited time, or mechanically e.g. by whipping.
  • the hydrothermal treatment is used modify the silica pore size and hydrothermal stability.
  • Suitable hydrothermal conditions comprise the heating of the substrate under autogeneous pressure for 2-48h at 40 to 1 00 °C.
  • washing and drying step to remove excess synthesis solution is performed using doubly-distilled water.
  • Partial filling of the parent body may be achieved by the use of a temporarily filling substance.
  • the filling substance can be introduced into the porous parent body, e.g. meso/macroporous membrane, by for instance a top-down or bottom up approach and is removed chemically or by thermal treatment after the deposition and growth of the metal oxide in the remainder parent body, e.g. membrane, channel voids.
  • the top-down approach for partial filling of the membrane channels is preferably achieved by an in situ polymerization or intrusion of a polymer (e.g. melting) into the parent body, e.g. membrane, channels.
  • a polymer e.g. melting
  • polymerization selective etching of the polymer is achieved by chemical treatment, laser, etc.
  • a bottom-up approach for partial filling of the parent body, e.g. membrane, channels may be achieved by the use of thermo hardening chemicals and its subsequent local heating under influence of a laser equipment.
  • the step of growing the carbon nanostructures may be achieved using high temperature CVD conditions.
  • the reaction gas is a carbon containing gas, e.g. acetylene, ethylene and methane (possibly in high pressure conditions), or liquid precursor (ethanol, methanol etc.).
  • an additional carrier e.g. He, N2, Ar
  • support gas e.g. slightly oxidative to remove amorphous carbon i.e. CO2, H2O or reducing H2, NH3
  • nitrogen containing carbon sources can be used in order to prepare N-doped CNTs, as these functionalized CNTs can interesting for catalysis, gas sensors, batteries, nanoelectronics etc....
  • the growth of the fibrous carbon nanostructures may be performed with a, preferentially vertical, CVD setup.
  • the gas reactor preferably is capable of optionally preheating the gas flow and heating the membrane support up to 1200 °C.
  • Gas flow is then preferably controlled with a combined flow rate between 10 ml/min "1 to 10 l/min -1 , and more preferably between 10 ml/min -1 to 5 ml/min -1 , as the membrane and tube diameter may vary between 1 to 500 cm, preferably between 1 to 100 cm, and more preferably between 1 to 10 cm. Its relation is of upmost importance in order to carefully control the contact time between carbon precursor gas and the metal catalyst particle.
  • Figure 1 illustrates a set-up, as used in embodiments of the invention, for the growth of the fibrous carbon nanostructures 1 .
  • the orientation of the set-up, here illustrated, is vertical although other positions are also possible.
  • the substrate 2, provided using methods of the present invention, is hierarchical and preferably is hold into position by a substrate e.g. membrane support 3 and as such positioned along the full cross section of reaction tube 8.
  • the gas inlet which is connected to the reaction tube provides a gas mixture according to prior art consisting of either a pure carbon source gas 5 or its mixture with a support gas 6 such as e.g. CO2, CO, H2, O2 and H2O or a carrier gas 7 such as He, Ar and N2 or combination thereof.
  • a support gas 6 such as e.g. CO2, CO, H2, O2 and H2O
  • carrier gas 7 such as He, Ar and N2 or combination thereof.
  • the reaction tube 9 is preferably made from quartz or metal (if non-atmospheric pressures are applied).
  • a pre-heating element 10 preferably ensures the attainment of the required temperature of the reaction gas when contacted with the metal catalyst particles and can be installed in the first part of the reaction tube 6 or at the tubing of the gas inlet 4.
  • the preheating element 10 commonly operates at slightly lower temperature (100 to 1200 °C) then the chosen reaction temperature according to embodiments of the invention e.g. 400-1200 °C.
  • the heating element 1 1 is preferably positioned at the location of the substrate, e.g. membrane, and extending along both sides of the membrane for preferably 0,1 cm to 1 m.
  • Insulation 12 is preferably provided in the reactor embodiment around 6 and 1 1 , to control the temperature and out of safety/economic motives.
  • a magnetic field and/or an electric field 13 can be created to govern the orientation and alignment of the fibrous carbon nanostructures which are then governed toward a collector.
  • the waste gas is preferably collected at the end of the reaction tube 9 and governed toward the exhaust.
  • FIG. 2 schematically illustrates the steps involved in the methodology to prepare a hierarchical porous body 20, e.g. membrane, according to embodiments of the invention.
  • This substance can be a polymer or monomer solution.
  • Hardening of the polymer is then performed preferably by cross-linking or polymerisation in situ.
  • a partial pore filling can be obtained via a top down or bottom up approach.
  • the bottom up approach preferably comprises the local hardening of the filling substance under influence of chemicals, e.g. cross-linker, initiator, etc.
  • the top down approach preferably embodies a first complete filling of the membrane pore followed by the partial removal by locally heating or one side chemical treatment (e.g. salt, acid or base solution). Consequently a metal oxide synthesis solution is loaded into the free pore voids 1 6 of the modified parent body, e.g. membrane.
  • a mesoporous metal oxide 1 8 with pores between 2 and 50 nm, is formed by a hydrothermal gel synthesis method or via e.g. EISA synthesis methods known in the art, which provides at least a child body in said parent pore channel.
  • the remainder of the filling substance 1 7 is preferably finally removed to ensure the accessibility of the pore system of the final hierarchical membrane 20 by e.g. heat treatment or chemical etching.
  • Figures 3a show the selective deposition of the metal particles 21 , which preferably can function as a catalyst in the synthesis of fibrous carbon nanostructures.
  • Selective positioning in the porous child body e.g. a thin mesoporous metal oxide top layer of the hierarchical porous body e.g. membrane, is preferably obtained by introducing metal particles prior to removal of the filling substance 1 7 or by isomorphous substitution in the metal oxide layer 1 8 thus creating exchange sites for the catalyst metal precursor solution.
  • Figure 3b shows different embodiments of the hierarchical porous body used as a substrate to synthesize fibrous carbon nanostructures.
  • the left figure schematically illustrates a porous body according to embodiments of the invention, whereby the porous body comprises a particle as porous child body.
  • the particle can be a hexagonal prism and be made of COK-12 silica particle which is preferably placed in a AAO parent pore.
  • the silica child particle is positioned in on top or bottom of the parent pore.
  • the silica child particle can be positioned in the middle of the parent pore.
  • the middle figure illustrates a porous body according to embodiments of the invention, whereby the channels defining the pores of the porous child body extend through the thickness of the parent porous body.
  • the right figure of Fig. 3b schematically illustrates a hierarchical porous body according to embodiments of the invention, whereby the channel of the child body partially extends over the channel of the parent porous body.
  • FIG. 4 shows a flowchart 23 showing a preferred embodiment of the processing steps to synthesize fibrous carbon nanostructures using a hierarchical porous body, e.g. membrane, according to preferred embodiments of the invention.
  • the first step 24 comprises a preheating of the reaction gas.
  • the reaction gas is brought to the hierarchical membrane 22, which is positioned in a tubular flow reactor which is positioned at a fixed angle, e.g. vertically as illustrated in Fig. 1 or horizontally (not shown), and covering the complete cross section of the reactor tube, and decorated with active metal particles 21 .
  • the metal particles deposited 21 inside the pores of the hierarchical membrane 22 gas are brought in contact with the gas flow.
  • step 27 the gas is decomposed by action of the metal particles 21 . Consequently, carbon is dissolved into the metal particles 28 and after oversatu ration growth of fibrous carbon nanostructures occurs.
  • the specific design of the hierarchical membrane ensures a continuous flow through the porous membrane in step 29, in order to have a controlled and non-variable contact time (during carbon growth) between gas and metal particle to sustain the prolonged growth of the carbon nanostructures.
  • Alignment of the fibrous carbon nanostructures is obtained in the final step 30 as a direct result of the high density of the carbon product or by the usage of either one of the following techniques or a combination thereof: gravimetric (via positioning of the membrane, e.g. vertical), magnetic fields, electric fields and gas flow.
  • gravimetric via positioning of the membrane, e.g. vertical
  • magnetic fields e.g. magnetic fields
  • electric fields e.g. gas flow
  • FIG. 5 is a SEM photograph of a parent porous body, e.g. a meso/macroporous membrane, filled with a polymeric filling substance 17 which was later partially removed by a top down approach using chemical etching according to embodiments of the invention. Consequently a partially filled membrane is obtained.
  • a parent porous body e.g. a meso/macroporous membrane
  • Such membrane can be used for further processing toward the deposition of a thin mesoporous metal oxide layer, which can act as a child body, inside the remaining open voids 16 of the parent porous body.
  • the picture in Fig. 5 thus illustrates step 2 in the formation of a hierarchical porous body, e.g. membrane, according to a methodology depicted in Figure 2.
  • Figure 6 illustrates the growth of mesoporous metal oxide inside the parent meso-macroporous membrane 14 according to embodiments of the invention.
  • the variation in morphology of the final metal oxide layer is shown in Figure 6 and Figures 7 (a) and (b). Hollow 31 and full 32 cylinders of a metal oxide can be formed inside the parent membrane channels according to embodiments of the invention.
  • Figure 7 shows the deposition of individual metal oxide particles 33, size controlled by their confinement, along the membrane channel.
  • embodiments of the invention advantageously provide continuous fabrication of carbon nanotubes using chemical vapour deposition (CVD).
  • Embodiments of the invention furthermore employ a carbon source in the form of a gas and high temperatures to dissociate its molecules into atoms.
  • the gas is preferably brought in contact with catalyst nanoparticles that are distributed inside of a porous substrate and helps to direct the continuously growing carbon nanotubes towards the exhaust of the CVD system.
  • a holder 1 1 according to embodiments of the invention, to support the porous substrate is provided.
  • the holder 1 1 is preferably a cylindrical tube with a partially closed ending 1 1 1 on one side and an open ending 1 12 in the opposite side.
  • the closed ending 1 1 1 is preferably directed towards the inlet of the gases and the open side 1 12 preferably towards the outlet of the reactor.
  • the partially closed side 1 1 1 contains one or several apertures 12, for instance from 1 to 15 depending on the size of the reactor and the substrates.
  • the apertures preferably have the design of a truncated-cone forming pockets 12, where one places a substrate 14 according to embodiments of the invention.
  • the smaller base of the truncated cone of the pockets 12 and the substrates 14 are preferably of the same size and shape.
  • an accessory 13 in the shape of smaller cylinder with a conical ground glass join preferably is provided which can ensure the fixation of the substrate 14 in the pocket 12.
  • the gas is then forced to go through the pores of the substrate where the catalyst particles are located in.
  • the material of the holder 1 1 and the accessories 13 might be the same or different, and able to stand high temperatures, from 400 to 1000 e C, without reacting with the gases (eg. Quartz).

Abstract

La présente invention concerne des systèmes, des procédés et des substrats poreux (hiérarchiques ou non) pour la synthèse de nanotubes de carbone. Une matière fibreuse comprenant de tels nanofils, l'utilisation de tels nanofils et un support pour un tel substrat sont également décrits.
PCT/EP2014/062978 2013-06-19 2014-06-19 Systèmes et procédés de synthèse de nanotubes de carbone WO2014202740A1 (fr)

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GB201310929A GB201310929D0 (en) 2013-06-19 2013-06-19 Systems and methods for synthesis of nanostructures
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GB201310927A GB201310927D0 (en) 2013-06-19 2013-06-19 Systems and methods for synthesis of nanostructures
GB1310929.3 2013-06-19
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GB201320172A GB201320172D0 (en) 2013-11-15 2013-11-15 Systems and methods for synthesis of nanostructures

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CN111996825A (zh) * 2020-08-24 2020-11-27 山东大学 一种氧化锆连续纤维编织绳及其制备方法
CN112041266A (zh) * 2018-04-25 2020-12-04 格亚诺马特有限公司 由含碳材料与金属氧化物组成的纳米材料的获得方法
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