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    • 专利摘要:
    The present invention relates, principally, to a process for preparing multi-walled carbon nanotubes (NTC) doped (MWCNT) with sulfur by a CVD technique, implementing the thermal decomposition a gaseous flow, source of carbon and sulfur, in contact with the reduced form of a metal catalyst, characterized in that, prior to being brought into contact with said gaseous flow, source of carbon and sulfur, said catalyst is contacted with a gas stream which contains at least one hydrocarbon compound and is free of heteroatom source compound, under conditions conducive to the initiation of the growth of carbon nanotubes. It also aims sulfur-doped multi-wall carbon nanotubes (NTC) in accordance with the invention.
    公开号:FR3063721A1
    申请号:FR1751904
    申请日:2017-03-08
    公开日:2018-09-14
    发明作者:Stephane Louisia；Marie Heitzmann；Pierre-Andre JACQUES
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    Holder (s): COMMISSIONER OF ATOMIC ENERGY AND ALTERNATIVE ENERGIES Public establishment.
    Extension request (s)
    Agent (s): NONY CABINET.
    4) SULFUR-DOPED CARBON NANOTUBES AND THEIR PREPARATION PROCESS.
    FR 3 063 721 - A1 (5 / d The present invention relates, principally, to a process for preparing doped multi-walled carbon nanotubes (NTC) (MWCNT acronym for “Multi Wall Carbon Nano Tubes”) with sulfur. a CVD technique, implementing the thermal decomposition of a gas stream, source of carbon and sulfur, in contact with the reduced form of a metal catalyst, characterized in that, before it is brought into contact with said gas stream , source of carbon and sulfur, said catalyst is brought into contact with a gas stream which contains at least one hydrocarbon compound and is free of source compound in heteroatom, under conditions suitable for initiating the growth of carbon nanotubes.
    It further relates to multi-walled carbon nanotubes (CNT) doped with sulfur in accordance with the invention.
    i
    The present invention relates to a new type of multi-wall doped carbon nanotubes (NTC) (MWCNT, acronym for "Multi Wall Carbon Nano Tubes") with sulfur and offers an original process for this purpose.
    CNTs have been the subject of intensive research in recent years because they have good mechanical properties and are capable of providing improved electrical and / or thermal conduction properties to any composite material containing them.
    More specifically, the CNTs consist of one or more graphitic sheets arranged concentrically around a longitudinal axis. For nanotubes composed of a single sheet, we speak of SWNT (acronym of "Single Wall Nanotubes") and for nanotubes composed of several concentric sheets, we speak of MWNT (acronym of "Multi Wall Nanotubes").
    The invention relates more particularly to MWNTs.
    Generally, these CNTs are manufactured using the CVD process (acronym for "Chemical Vapor Deposition"). This process consists in injecting a source of gas rich in carbon, conventionally methane, ethane, ethylene, acetylene or benzene, in a reactor containing a metallic catalyst brought to high temperature, generally iron, cobalt or nickel, most often supported by a solid substrate, such as alumina, silica, magnesite or even carbon. This technology is described in particular in document WO 86/03455 of Hyperion Catalysis International Inc.
    It is known that the electrochemical performance of CNTs can be improved by intervening on the electronic properties of their sp 2 carbons and a large number of developments have been made in this direction in recent years. This improvement is in particular obtained by inserting heteroatoms, like nitrogen and sulfur, within the structure of CNTs. These CNTs comprising heteroatoms incorporated within their structures are proposed for various applications such as in the fields of biomass conversion, for the support of catalysts, in optoelectronics, solar panels, or even energy storage. .
    Thus, the publication Yingchun Zhu et al. “Synthesis of Sulfur-Doped Carbon Nanotubes by Liquid Precursor Materials Focus 2, 44-47 (2013) describes the preparation of sulfur doped MWCNT which is carried out according to a procedure involving the high temperature decomposition (1000 ° C) of methyl sulfide on a cobalt catalyst This process requires the use of a high flow of inert gas (argon at 700 ml / min) in order to bubble it up and vaporize it in the reaction chamber in a satisfactory manner. However, the exposed structures of the compounds formed according to this operating mode seem to be assemblies of nanotubes covered with sulfur sheaths and not nanotubes comprising within their structure sulfur atoms. The publication by Kun-Hong Lee et al. “Synthesis of high-quality carbon nanotube fibers by controlling the effects of sulfur on the catalyst agglomeration during the direct spinningprocess” RSC Adv. 5.41894 (2015) also reports a process using thiophene, in addition to an iron catalyst, to form CNTs at very high temperatures (1170 ° C). However, thiophene is in this case used for the purpose of activating the catalyst and not for doping the carbon nanotubes which are formed during this process. Thus, the EELS (English acronym for "Electron Energy Loss Spectroscopy") analysis carried out in this work makes it possible to observe the presence of encapsulated sulfur on the surface of the metal, and not in the walls of CNTs.
    The publication by D. Demendoza et al. Synthesis of carbon nanofibers and nanotubes using carbon disulfide as the precursor REVISTA MEXICANA DE FISICA S 53, 5, 9-12 (2007) reports on a process using an iron catalyst and decomposing carbon sulfide at 900 ° C . The nanofibers obtained have a diameter between 50 nm and 500 nm and contain little sulfur (0.25 atomic%, or 0.7% by weight).
    Consequently, and to the knowledge of the inventors, there is to date no effective method for doping satisfactorily and homogeneously MWCNT with sulfur.
    The object of the invention is precisely to meet this need.
    Thus, the invention relates, according to one of its aspects, to a process for preparing carbon nanotubes with multiple walls, (MWNT) and doped with sulfur, by a CVD technique, implementing the thermal decomposition of a flux. gaseous, source of carbon and sulfur, in contact with the reduced form of a metal catalyst, characterized in that, prior to being brought into contact with said gaseous flow, source of carbon and sulfur, said catalyst is brought into contact with a gas flow which contains at least one hydrocarbon-based compound and is free from a source compound as a heteroatom, under conditions suitable for initiating the growth of carbon nanotubes.
    Within the meaning of the invention, the priming operation or else the activation of the catalyst is an operation during which a gas carrying a hydrocarbon compound, only source of carbon because devoid of heteroatom and therefore devoid of sulfur element, will be contacted with the catalyst for a short time to promote thermal decomposition of the hydrocarbon compound to initiate the growth of carbon nanotubes. On contact with the catalyst, the carbon of the hydrocarbon derivative will begin to reorganize in the form of nanotubes.
    Against all expectations, the inventors have indeed found that the implementation of a priming / activation step of the catalyst by at least one gaseous flow, also called priming gaseous flow, containing a hydrocarbon gas and not sulfur, beforehand the interaction of this catalyst with a specific sulfur-containing hydrocarbon gas, and under adjusted operating conditions, is particularly decisive for accessing MWCNTs doped homogeneously and not only at the surface, in sulfur.
    Advantageously, the priming gas flow comprises and preferably consists of a single hydrocarbon compound which is devoid of heteroatom.
    According to a preferred embodiment, the hydrocarbon compound of said priming gas stream is chosen from ethylene, methane and ethane and preferably is ethylene gas.
    Advantageously, the priming gas flow is preferably implemented in conjunction with a hydrogen flow.
    As regards the gas flow source of carbon and sulfur, it is advantageously a gaseous mixture of hydrogen and inert gas carrying at least one sulfur hydrocarbon. Advantageously, the sulfur-containing hydrocarbon can be chosen from hydrocarbons containing sulfur, liquid at room temperature and having a low boiling temperature. As such, dimethyl disulfide, carbon sulfide and more preferably thiophene are suitable.
    Of course, all the gas flows considered according to the invention are controlled and optimized in order to reduce the degradation or saturation of the catalyst and the formation of reaction by-products, while maintaining the catalyst in its reduced active form.
    More specifically, the method according to the invention comprises at least the steps consisting in
    a) have, in a reactor-oven heated to a temperature varying from 600 ° C to 800 ° C preferably about 750 ° C and under a flow of an inert gas, of the form reduced by at least a metal catalyst suitable for the preparation of multi-walled carbon nanotubes (MWNT) by the CVD technique,
    b) exposing said catalyst of step a) in contact with a gas stream which contains at least one hydrocarbon compound and is free of source compound as a heteroatom, under conditions suitable for initiating the growth of carbon nanotubes , and
    c) exposing said activated catalyst at the end of step b) to a source gas stream of carbon and sulfur under conditions favorable to the formation of sulfur-doped multi-walled carbon nanotubes (MWNT).
    Advantageously, the reduced form of the catalyst of step a) is obtained beforehand, by exposure within the reactor, of said catalyst to hydrogen gas.
    According to another of its aspects, the present invention relates to a sulfur-doped multi-walled carbon nanotube (MWCNT) characterized in that it contains more than 2% by weight, and preferably more than 3% or even more than 5%. by weight of sulfur element distributed within its structure and has a decomposition temperature below 600 ° C.
    Within the meaning of the invention, the expression “distributed within the structure” means to mean that the sulfur element is present on the external surface of the walls of the nanotubes and also in depth of these walls, that is to say in their thickness.
    FIG. 2 makes it possible in particular to visualize this homogeneous distribution of the sulfur element on the surface and in the multiple walls constituting the doped carbon nanotubes according to the invention.
    More precisely, after purification of the doped multi-walled carbon nanotubes according to the invention, the sulfur element can be characterized therein in at least two forms, preferably three forms and more preferably four distinct chemical forms chosen from thiol, disulfide units , sulfide, thioester, sulfoxide, sulfite or sulfate and sulfonic acid entities and preferably thioester, sulfoxide and sulfite.
    This diversity of patterns is in particular characterized in Table 1 below.
    According to another of its aspects, the present invention relates to the use of sulfur-doped multi-walled carbon nanotubes according to the invention for the support of catalysts, in the fields of optoelectronics, solar panels and fuel cells .
    PROCESS ACCORDING TO THE INVENTION
    As specified above, the method according to the invention is based on the use of the CVD technique for the formation of carbon nanotubes doped with sulfur.
    This technique is based more particularly on the decomposition at high temperature of a carbon source in the gaseous state in contact with a metal catalyst generally supported and contained in a reactor. This CVD technique is in particular illustrated in the document WO 2011/020970 A2.
    An experimental device suitable for the invention is notably represented in FIG. 1.
    It is a fluidized bed reactor which consists of a quartz column equipped with a distributor plate (sintered) placed inside a vertical oven. The catalyst is placed in the enclosure and the latter is supplied in a controlled manner with the gas flows required according to the invention. The whole is heated to temperatures between 600 ° C and 800 ° C.
    More specifically, the process for preparing sulfur-doped multi-walled carbon nanotubes according to this technique can be detailed as follows:
    The catalyst is heated to a temperature below 800 ° C and preferably above 700 ° C under a flow of inert gas in the reactor-furnace.
    If necessary, the catalyst is reduced beforehand by contacting with hydrogen so that it is in an active form.
    A first synthesis step consisting in priming the catalyst with a hydrocarbon gas (s) devoid of a heteroatom is then carried out to initiate the growth of carbon nanotubes.
    A second synthesis step consisting in the growth of sulfur-doped MWCNTs is then carried out by introduction into the enclosure of a second gaseous flow source of carbon and sulfur. This gas flow is advantageously generated by bubbling, at a temperature preferably below ambient temperature, of an inert gas / Fh mixture at a controlled flow rate in a hydrocarbon solvent containing sulfur and which must be liquid at ambient temperature and have a low temperature. of boiling.
    Preferably, the sulfur doped MWCNTs thus obtained can then be purified in a heated water / sulfuric acid mixture.
    The main originality of the process therefore rests on the preliminary contacting of the catalyst with a gas flow which contains at least one hydrocarbon-based compound and is free of source compound as a heteroatom. In other words, this gas flow is only a source of the carbon element. This step is carried out according to the invention, prior to bringing the activated catalyst into contact with a gas flow, source of carbon and sulfur elements. The inventors have indeed found that bringing the catalyst into contact only with a gaseous flow source of carbon and sulfur, that is to say without this initiation / priming step with this first gaseous flow, does not allow access to sulfur doped carbon nanotubes according to the invention.
    a) priming gas flow
    The priming gas flow comprises as source of carbon element at least one hydrocarbon derivative chosen from alkanes in particular methane or Tethane, and alkenes, preferably ethylene, Tisopropylene, propylene, butene, butadiene , and mixtures thereof.
    As previously pointed out, this gas flow does not carry a heteroatom capable of interacting during the initiation of the growth of carbon nanotubes. It is thus devoid of any sulfur-containing hydrocarbon derivative but also of nitrogen-containing hydrocarbon derivative.
    Advantageously, this gaseous flow source of carbon and devoid of heteroatom and therefore sulfur, comprises at least and preferably consists of ethylene.
    The priming gas flow is implemented in the process of the invention with a speed varying from 2.3 mm / s to 7.0 mm / s and preferably from 4.6 mm / s to 5.75 mm / s and generally for a time less than 10 minutes.
    The speed unit, expressed in mm / s, translates the distance traveled by the priming gas flow within the reactor in one second.
    Advantageously and according to the invention, this priming gas flow, carbon source, and preferably consisting of ethylene, is implemented jointly in the presence of a hydrogen gas flow.
    The speed of the hydrogen gas flow is preferably chosen between 3 mm / s and
    7.0 mm / s.
    As specified above, the gas flows considered according to the invention are controlled and optimized in order to reduce the degradation or saturation of the catalyst and the formation of reaction by-products, while maintaining the catalyst in its reduced active form. Thus, advantageously, the priming step is implemented with a carbon source gas flow / hydrogen gas flow in a ratio of 3/2.
    Advantageously, the contacting of the catalyst with the priming gas flow is carried out at a temperature below 900 ° C, preferably ranging from 600 ° C to 800 ° C.
    This priming step is carried out the time required to initiate the growth of carbon nanotubes.
    Commonly, this initiation requires a processing time on a minute scale, at least 30 seconds to 10 minutes and preferably 1 to 4 minutes.
    The initiation of carbon nanotube growth can be monitored by transmission electron microscopy (TEM).
    b) gaseous flow source of carbon and sulfur
    Following the priming gas flow, the catalyst is brought into contact with a second gas flow source of carbon and sulfur.
    This second gaseous flow source of carbon and sulfur preferably consists of a gaseous mixture of hydrogen and inert gas carrying at least one sulfur hydrocarbon.
    The inert gas is preferably chosen from argon (Ar) or nitrogen.
    The speed of this inert gas is preferably chosen between 2.3 mm / s and 7.0 mm / s.
    The hydrogen speed is preferably chosen between 2.3 mm / s and 7.0 mm / s.
    The sulfur-containing hydrocarbon is advantageously chosen from hydrocarbons containing sulfur, liquid at room temperature and having a low boiling temperature, such as dimethyl disulfide, carbon sulfide and preferably is thiophene.
    This second gas flow is advantageously generated by bubbling a gaseous mixture of hydrogen and inert gas in a container containing the hydrocarbon containing sulfur, liquid at room temperature and having a low boiling temperature, chosen according to the invention .
    The temperature of the sulfur-containing hydrocarbon-based solvent is advantageously adjusted as a function of the gas flow rates in order to entrain enough of it to allow growth but not in excess to avoid poisoning of the catalyst and the excess of this solvent at the outlet. . Thus, in the specific case of thiophene, this is implemented at a temperature between 5 ° C and 17 ° C, preferably at 17 ° C.
    Preferably, the inert gas and hydrogen flow rates are also adjusted to obtain the growth of sulfur-doped MWCNTs by limiting the amount of amorphous carbon and of catalyst encapsulated around them at the end of the reaction.
    Thus, this second gaseous flow source of carbon and sulfur is advantageously implemented with a speed varying from 4.3 mm / s to 13.8 mm / s and preferably from 7.0 mm / s to 9.3 mm / s.
    This second gas stream enriched in carbon and sulfur is kept in contact with the catalyst until the desired end of the growth of sulfur doped MWCNTs.
    Generally, this sulfur doping step of the MWCNTs is completed after a period of 30 minutes. Beyond this period, inactivation of the catalyst occurs due to its prolonged exposure to the sulfur element.
    All of the priming and growth steps for carbon nanotubes can be carried out at a temperature between 600 ° C and 800 ° C, preferably around 700 ° C. In other words, bringing the catalyst into contact with said gas stream, a source of carbon and sulfur, is advantageously carried out at a temperature between 600 ° C. and 800 ° C., preferably 700 ° C.
    The catalytic yield of a synthesis of sulfur-doped carbon nanotubes according to the invention is at least 25% by weight of nanotubes expressed relative to the weight of catalyst.
    c) Catalyst
    According to an advantageous embodiment, the catalyst can be chosen from iron (Fe), nickel (Ni), cobalt (Co), molybdenum (Mo) or mixtures of these like AlFeCo or FeMo in proportions ranging from 5% to 20%. Advantageously, the catalyst is chosen from iron (Fe), nickel (Ni) or cobalt (Co) and preferably is an iron-based catalyst preferably supported on alumina.
    Adjusting the amount of catalyst is clearly within the skill of the skilled artisan. It is generally suitable for obtaining a good yield of MWCNT doped with sulfur while taking care not to form too much amorphous carbon at the end of the reaction. An amount of less than 5 g of catalyst can in particular be considered for a catalyst of the Fe (5%) / Al2O3 type.
    As is apparent from the above, the catalyst is used in its reduced form. This is generally obtained by exposing the catalyst considered according to the invention to hydrogen. In this way, the catalyst material is reduced in situ in said reactor, and its catalytic layer is not oxidized when it is used for the synthesis of carbon nanotubes.
    This catalyst is advantageously supported on a porous substrate which is of course chosen for its chemical inertness during the operating conditions of the CNT synthesis process by the CVD technique.
    This substrate can represent from 30% to 70% by total mass of the catalyst.
    Advantageously, this substrate can be inorganic. It is especially chosen from alumina, activated carbon, silica, silicate, magnesia, titanium oxide, zirconia, a zeolite or even carbon fibers. According to an advantageous embodiment, the substrate is alumina.
    Advantageously, the catalyst supported on porous substrate is, after its introduction into the reactor firstly heated under a flow of inert gas, then reduced with the introduction of hydrogen at a controlled rate, while maintaining the flow of inert gas.
    d) Purification.
    The sulfur doped MWCNTs are preferably isolated at the end of the reaction, then purified.
    ίο
    This purification step is in particular carried out in order to remove the amorphous carbon which may have formed during the reaction, as well as the catalyst remaining around the sulfur doped MWCNTs formed.
    This purification can be carried out by heating in a water / acid mixture the supported catalyst as well as the dark matter which has formed around it.
    Preferably, according to the process of the invention, the nanotubes obtained at the end of step c) are purified and recovered in an H2SO4 / H2O mixture for 3 h at 140 ° C., as illustrated in example 1 below.
    MWNCT DOPES TO SULFUR ACCORDING TO THE INVENTION
    The invention also relates to sulfur-doped multi-walled carbon nanotubes (MWCNT) which can be obtained by the process described and detailed above.
    Advantageously, these are multi-walled carbon nanotubes, comprising for example from 5 to 15, and preferably from 7 to 10, graphene sheets wound concentrically.
    The nanotubes obtained according to the invention usually have an average diameter ranging from 0.1 to 50 nm, more preferably from 0.4 to 50 nm and, better still, from 1 to 30 nm and advantageously a length of more than 0.1 μm. and advantageously from 0.1 to 20 μm, for example around 6 μm. Their length / diameter ratio is advantageously greater than 10 and most often greater than 100. Their specific surface area is for example between 100 and 600 m 2 / g and their apparent density can in particular be between 0.01 and 0.5 g / cm 3 and more preferably between 0.07 and 0.2 g / cm 3 .
    As previously explained, the carbon nanotubes doped with sulfur according to the invention have the specificity of having a distribution of the sulfur element which is not only localized on the surface of the walls of nanotubes. This element is integrated into the structure of these compounds, as illustrated in FIG. 2.
    The sulfur-doped multi-walled carbon nanotubes in accordance with the invention are also characterized in that the sulfur element is present therein in at least two forms, preferably three forms and more preferably four distinct chemical forms chosen from thiol units , disulfide, sulfide, thioester, sulfoxide, sulfite or sulfate and sulfonic acid entities.
    This can be characterized in particular by XPS analysis (acronym for "Xray photoelectron spectroscopy"). An example of this type of analysis is detailed in particular in Example 1 below.
    The sulfur-doped multi-walled carbon nanotubes according to the invention are also characterized by elementary analysis in that they contain more than 2%, preferably more than 3%, or even more than 5% by weight of sulfur element distributed. within their structures. In particular, the sulfur-doped multi-walled carbon nanotubes produced contain at least 6%, preferably at least 7% by weight of sulfur element relative to their total weight.
    Furthermore, the Raman analysis of the carbon nanotubes doped with sulfur according to the invention makes it possible to highlight two bands Id and Ig, (Id for the disordered carbon and Ig for the graphitized carbon) respectively present at 1330 cm 1 and 1575 cm ' 1 . The ratio of the intensities of these bands (Id / Ig) is characteristic of the material synthesized but also of the method of synthesis. Thus, the Id / Ig ratio is equal to 1.7 for undoped MWCNT and less than 1.7 or even less than 1.5 and in particular equal to approximately 1 for the sulfur doped MWCNT according to the invention.
    The carbon nanotubes doped with sulfur according to the invention also have a decomposition temperature of less than 600 ° C, preferably less than 570 ° C, ie less than that of nanotubes composed solely of carbon. This is in particular illustrated in FIG. 3 which reports on the thermogravimetric analysis of carbon nanotubes doped with sulfur obtained according to example 1.
    Thus, advantageously, a sulfur-doped multi-walled carbon nanotube prepared according to the method of the invention contains more than 5% by weight of sulfur distributed within its structure and has a decomposition temperature below 600 ° C.
    USE OF MWCNT DOPED WITH SULFUR ACCORDING TO
    THE INVENTION
    The invention also relates to the use of the sulfur-doped MWCNTs according to the invention in the fields of optoelectronics, solar panels and fuel cells, metallic nanoparticles and also in the form of support for catalysts in various fields of chemistry.
    Thus, the invention also relates to the use of MWCNTs doped with sulfur according to the invention in composite materials to give them improved electrical conduction properties and / or mechanical properties, in particular resistance to elongation.
    In particular, the sulfur-doped MWCNTs according to the invention can be used in macromolecular compositions intended for the packaging of electronic components or for the manufacture of petrol lines (fuel line) or of antistatic coatings or paints, or in thermistors or electrodes for supercapacitors or for the manufacture of structural parts for the aeronautical, nautical or automotive fields, or as a catalyst support.
    Other advantages and characteristics of the invention will emerge more clearly on reading the detailed description of examples of implementation of the invention submitted by way of illustration and not limitation of the invention and with reference to the following figures:
    - Figure 1 is a diagram of the furnace / reactor suitable for the invention.
    FIG. 2 is an image obtained by TEM micrography of the sulfur-doped carbon nanotubes prepared according to Example 1.
    - Figure 3 shows the result of the ATG analyzes obtained for the sulfur doped MWCNTs according to the invention (dotted patterns) and for conventional CNTs (black line).
    FIG. 4 presents the plots of the spectra obtained by Raman spectroscopy for the MWCNTs doped with sulfur prepared in example 1 (dotted patterns) as well as those obtained for conventional CNTs (black trace).
    FIG. 5 presents the XPS analysis of the sulfur doped MWCNTs prepared in example 1.
    FIG. 6 presents the images obtained by TEM micrography of Co / Pt nanoparticles deposited on carbon nanotubes doped with sulfur according to the invention.
    FIG. 7 presents a comparison of the catalytic activity of PtCo catalysts grafted on Vulcan system (full histogram) and grafted on sulfur doped MWCNT prepared in Example 1 (TIRETS histogram) measured by RRDE (English acronym for "Rotating Ring-Disk" Electrode ”) at 100pgPt / cm 2 at a speed of 5 mV / s.
    EXAMPLE 1
    Preparation of MWCNT doped with sulfur according to the invention
    a) Synthesis of the Fe / AhCh catalyst
    In an 11 ml Erlenmeyer flask, 72.1 mg of Fe (NO3) 3.9H2O (98%, Strem Chemicals) are dissolved in 500 ml of distilled water. 5 g of AI2O3 alumina (Pural NW from Sasol and supplied by Arkema) are added to the reaction mixture. The metal salt and the support are brought into contact with stirring for 2 hours at ambient temperature. The solvent is then evaporated on a rotary evaporator and the powder is allowed to dry under vacuum for 2 hours. This powder is then studied at 110 ° C for 15h. The final catalyst is obtained by calcination in air at 450 ° C for 8h.
    b) Preparation
    4.64 g of the iron alumina catalyst Fe (5%) / ALO3 prepared above are heated to 750 ° C. under a flow of argon (at a speed of 7.0 mm / s) in a vertical reactor-oven of a diameter of 3 cm and reduced by hydrogen mixed with argon (Ar at a speed of 5.3 mm / s and H2 at a speed of 3.5 mm / s). This catalyst is then primed in the presence of IL (at a speed of 3.5 mm / s) by contact with ethylene gas (C2H4 at a speed of 5.3 mm / s) for 3 minutes. MWCNT growth is continued by oiling an Ar / FL mixture (Ar at a speed of 3.5 mm / s and LL at a speed of 5.3 mm / s) in thiophene at 17 ° C for 27 min. A step of purifying the 1.08 g of MWCNT doped with sulfur, thus obtained, is carried out by immersion of these in a sulfuric acid / water mixture (H2SO4 / H2O) for 3 h at 140 ° C.
    c) Physicochemical characterization of sulfur doped MWCNTs
    The sulfur-doped multi-walled carbon nanotubes obtained according to this method contain 7.7% of sulfur according to an elementary analysis, (CHN Perkin Elmer elem entai analyzer).
    They have a decomposition temperature of 570 ° C characterized by thermogravimetric analysis (Figure 3), (Thermobalance Perkin Elmer Diamond TG / TDA 25 ° C up to 1000 ° C at 10 ° C / min in air).
    These nanotubes were also characterized by TEM analysis (Figure 2), by 5 Raman spectrometry (Figure 4), (JEOL JEM-1011 at 100 kV for TEM).
    XPS analysis (Figure 5), (K-alpha ThermoScientific apparatus with a non-chromatic source Mg K source (1253.6 eV, 300 W) with a passage energy of 20 eV) of the doped nanotubes formed reveals the presence of the different sulfur groups.
    Table 1 below gives an account of the various characterized sulfur patterns.
    XPS ANALYSIS Sample from Example 1 % thiol and / or bisulfide units % sulfide and / or thioether units % sulfoxide and / or sulfite units % Sulfate, and / or sulfonate units S: CNT 5.0 64.9 7.2 22.9
    In parallel, these nanotubes were characterized in terms of composition as follows.
    XPS ANALYSIS Sampleofexample 1 %VS B.E Carbon (eV) % O B.E.Oxygen (eV) % S B.ESulfide (eV) S: CNT 92.7 284.1 3.6 533.9 3.7 164.1
    d) characterization of sulfur doped MWCNTs in terms of activity
    i) Preparation of Pt / Co nanoparticles on MWCNT 20 200 mg of sulfur-doped nanotubes according to the invention are introduced into a schlenk type reactor and placed under vacuum for 30 minutes, then under argon. 0.48 mmol of [bmim] [Tf2N] (99% Solvionic) are added to the reactor. The reaction takes place under an inert atmosphere. 2.04 mmol of COCI2.6H2O (98% Strem Chemicals) are dissolved in 60 ml of ethanol and added to the reaction medium. The reaction medium is placed under ultrasound for 20 min. 60 ml of a 0.15 mol.l 1 solution of NaBLL (99.99% Sigma Aldrich) in ethanol are added to the reaction medium. After 30 minutes, 100 ml of distilled water is added to the mixture. 3 h later, 1.27 mmol of fUPtCL (99.9% Strem Chemicals) are dissolved in 60 ml of distilled water and added to the reaction mixture. After stirring overnight, the solution is filtered and washed with a mixture of distilled water and ethanol, then dried for 24 hours at 80 ° C. The particles obtained at the end of the reaction were studied by TEM micrography and the images obtained are shown in Figure 6.
    ii) Comparison of activity in RRDE
    The catalyst thus prepared is compared to a commercial reference by RRDE. 10 10 mg of catalyst prepared in step i) are dispersed in 4 ml of a mixture
    Isopropanol / Distilled water / Nafion® (D-2020 Dupont Fluoroproduct, 90 / 19.5 / 0.5) and placed under ultrasound for 30 min. 30 μl of the ink thus prepared is deposited in three times on a disk-type electrode of vitreous carbon, previously polished. A fine deposit of catalyst loaded with 100 pg Pt / cm 2 is obtained after evaporation of the solvent in air at room temperature.
    The mass activity of the catalyst is measured 0.9 V / RHE by cyclic voltammetry made in a 0.5 M H2SO4 solution saturated with N2 at 5 mV / s between 0.04 and 1.2 V / RHE at 900 rpm / min. The same procedure is carried out for the commercial reference Pt 3 Co / Vulcan XC-72.
    It can be noted that the catalyst prepared with the sulfur-doped nanotubes has a greater activity for the reduction of oxygen (FIG. 7).
    权利要求:
    Claims (20)
    [1" id="c-fr-0001]
    1. Process for the preparation of carbon nanotubes with multiple walls (MWNT) and doped with sulfur, by a CVD technique, implementing the thermal decomposition of a gas flow, source of carbon and sulfur, in contact with the form reduced by a metal catalyst, characterized in that, prior to being brought into contact with said gaseous flow source of carbon and sulfur, said catalyst is brought into contact with a gaseous flow which contains at least one hydrocarbon compound and is free of source compound heteroatom, under conditions conducive to the initiation of the growth of carbon nanotubes.
    [2" id="c-fr-0002]
    2. Method according to the preceding claim comprising at least the steps consisting in:
    a) have, in a reactor-oven heated to a temperature varying from 600 ° C to 800 ° C preferably about 750 ° C and under a flow of an inert gas, of the form reduced by at least a metal catalyst suitable for the preparation of multi-walled carbon nanotubes (MWNT) by the CVD technique,
    b) exposing said catalyst of step a) in contact with a gas stream which contains at least one hydrocarbon compound and is free of source compound as a heteroatom, under conditions suitable for initiating the growth of carbon nanotubes , and
    c) exposing said activated catalyst at the end of step b) to a source gas stream of carbon and sulfur under conditions favorable to the formation of sulfur-doped multi-walled carbon nanotubes (MWNT).
    [3" id="c-fr-0003]
    3. Method according to the preceding claim wherein the reduced form of the catalyst of step a) is obtained beforehand, by exposure within the reactor, of said catalyst to hydrogen gas.
    [4" id="c-fr-0004]
    4. Method according to any one of claims 2 or 3 in which the nanotubes obtained in step c) are purified and recovered in an H2SO4 / H2O mixture for 3 h at 140 ° C.
    [5" id="c-fr-0005]
    5. Method according to any one of the preceding claims, in which said priming gas flow comprises and preferably consists of a single hydrocarbon compound which is devoid of heteroatom.
    [6" id="c-fr-0006]
    6. Method according to any one of the preceding claims, in which the hydrocarbon compound of said priming gas flow is chosen from ethylene, methane and ethane and preferably is ethylene gas.
    [7" id="c-fr-0007]
    7. Method according to any one of the preceding claims, in which the contacting of said catalyst with said priming gas flow is carried out at a temperature below 900 ° C, preferably varying from 600 ° C to 800 ° C.
    [8" id="c-fr-0008]
    8. Method according to any one of the preceding claims, in which said priming gas flow is implemented with a speed varying from 2.3 mm / s to 7.0 mm / s and preferably 4.6 mm / s at 5.75 mm / s for a time of less than 10 minutes.
    [9" id="c-fr-0009]
    9. Method according to any one of the preceding claims, in which said priming gas stream is implemented in the presence of a hydrogen gas stream.
    [10" id="c-fr-0010]
    10. Method according to any one of the preceding claims, in which said carbon and sulfur source gas flow consists of a gaseous mixture of hydrogen and inert gas carrying at least one sulfur hydrocarbon.
    [11" id="c-fr-0011]
    11. Method according to the preceding claim wherein the sulfur-containing hydrocarbon is chosen from hydrocarbons containing sulfur, liquid at room temperature and having a low boiling temperature, such as dimethyl disulfide, carbon sulfide and preferably is thiophene .
    [12" id="c-fr-0012]
    12. Method according to any one of the preceding claims, in which the gas flow source of carbon and sulfur is implemented with a speed varying from
    4.3 mm / s to 13.8 mm / s and preferably from 7.0 mm / s to 9.3 mm / s.
    [13" id="c-fr-0013]
    13. Method according to any one of the preceding claims, in which the contacting of said catalyst with said source gas stream of carbon and sulfur is carried out at a temperature between 600 ° C and 800 ° C, preferably 700 ° vs.
    [14" id="c-fr-0014]
    14. Method according to any one of the preceding claims, in which the catalyst is chosen from iron (Fe), nickel (Ni) or cobalt (Co) and preferably is an iron-based catalyst preferably supported on alumina .
    [15" id="c-fr-0015]
    15. Sulfur doped multi-walled carbon nanotube (MWCNT) obtained according to the method according to any one of the preceding claims.
    [16" id="c-fr-0016]
    16. Sulfur doped multi-walled carbon nanotube characterized in that it contains more than 5% by weight of sulfur distributed within its structure and has a decomposition temperature below 600 ° C.
    [17" id="c-fr-0017]
    17. A sulfur-doped multi-walled carbon nanotube according to claim 5, characterized in that the sulfur element is present therein in at least two forms, preferably three forms and more preferably four distinct chemical forms chosen from thiol units, disulfide, sulfide, thioester, sulfoxide, sulfite or sulfate and sulfonic acid entities.
    [18" id="c-fr-0018]
    18. A sulfur-doped multi-walled carbon nanotube according to any one of claims 16 or 17 containing at least 6%, preferably at least 7% by weight of sulfur element relative to its total weight.
    [19" id="c-fr-0019]
    19. A sulfur-doped multi-walled carbon nanotube according to any one of claims 16, 17 or 18, the Raman analysis of which has two bands Id and Ig, respectively present at 1330 cm 1 and 1575 cm ^ -and whose Id / Ig ratio is lower
    15 to 1.7 or even less than 1.5 and in particular equal to approximately 1.
    [20" id="c-fr-0020]
    20. Use of sulfur-doped multi-walled carbon nanotubes obtained according to any one of claims 1 to 14 or according to any one of claims 16 to 19, in the fields of optoelectronics, solar panels and batteries with fuel and in particular for the support of catalysts.
    1/4
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    同族专利:
    公开号 | 公开日
    FR3063721B1|2021-05-21|
    WO2018162378A1|2018-09-13|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    CN112110438A|2020-09-18|2020-12-22|深圳市德方纳米科技股份有限公司|Doped multiwalled carbon nanotubes and electrode materials|US4663230A|1984-12-06|1987-05-05|Hyperion Catalysis International, Inc.|Carbon fibrils, method for producing same and compositions containing same|
    FR2949075B1|2009-08-17|2013-02-01|Arkema France|FE / MO SUPPORTED CATALYST, PROCESS FOR PREPARING THE SAME, AND USE IN THE MANUFACTURE OF NANOTUBES|CN110040720A|2019-04-22|2019-07-23|中国科学院金属研究所|High-purity, narrow diameter distribution, minor diameter double-walled carbon nano-tube preparation method|
    CN110775958A|2019-11-06|2020-02-11|渤海大学|Carbon nano tube derived from thienyl nickel complex and synthetic method and application thereof|
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1751904A|FR3063721B1|2017-03-08|2017-03-08|SULFUR-DOPED CARBON NANOTUBES AND THEIR PREPARATION PROCESS|
    FR1751904|2017-03-08|FR1751904A| FR3063721B1|2017-03-08|2017-03-08|SULFUR-DOPED CARBON NANOTUBES AND THEIR PREPARATION PROCESS|
    PCT/EP2018/055280| WO2018162378A1|2017-03-08|2018-03-05|Sulphur-doped carbon nanotubes and method for preparing same|
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