WO2004016550A2 - Method for opening carbon nanotubes at the ends thereof and implementation - Google Patents

Method for opening carbon nanotubes at the ends thereof and implementation Download PDF

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Publication number
WO2004016550A2
WO2004016550A2 PCT/FR2003/002499 FR0302499W WO2004016550A2 WO 2004016550 A2 WO2004016550 A2 WO 2004016550A2 FR 0302499 W FR0302499 W FR 0302499W WO 2004016550 A2 WO2004016550 A2 WO 2004016550A2
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carbon nanotubes
nanotubes
oxidation
opening
carbon
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PCT/FR2003/002499
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French (fr)
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WO2004016550A3 (en
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François BEGUIN
Sandrine Delpeux
Katarzyna Szostak
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Centre National De La Recherche Scientifique (C.N.R.S.)
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Priority to AU2003274239A priority Critical patent/AU2003274239A1/en
Priority to CA002495094A priority patent/CA2495094A1/en
Priority to EP03758222A priority patent/EP1527014A2/en
Priority to US10/523,397 priority patent/US20050163697A1/en
Priority to JP2004528596A priority patent/JP2005535550A/en
Publication of WO2004016550A2 publication Critical patent/WO2004016550A2/en
Publication of WO2004016550A3 publication Critical patent/WO2004016550A3/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • C01B32/168—After-treatment
    • C01B32/178—Opening; Filling
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/06—Multi-walled nanotubes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/20—Nanotubes characterized by their properties
    • C01B2202/36—Diameter

Definitions

  • the present invention relates generally to the post-treatment of carbon nanotubes and their applications.
  • the present invention relates to a process for opening carbon nanotubes at their ends and more especially multi-wall carbon nanotubes.
  • hollow carbon nanotubes can prove to be excellent reservoirs of gases, such as hydrogen, natural gas ... It is now well known that the presence of topological defects is necessary to close the graphene planes at the ends of carbon nanotubes. According to Euler's law, six pentagons are necessary to ensure the closure of the carbon nanotubes at each end. These regions of tension are of course the most useful sites for addition reactions, in particular on the double bonds connecting a pair of pentagons.
  • Oxidation in air or in oxygen is not selective enough. These treatments lead to a significant loss of material and the external graphene planes are often seriously damaged due to the uncontrollable nature of the reaction.
  • Oxidation is much more homogeneous when the carbon nanotubes are dispersed in an oxidizing solution.
  • carbon nanotubes obtained by decomposition of acetylene at 600 ° C on cobalt particles supported by zeolites often contain carbon impurities and have closed ends. It is then possible to carry out an attack with potassium permanganate both to partially remove these impurities by oxidation and to open part of the ends of the carbon nanotubes.
  • the object of the invention is therefore to provide a method making it possible to quickly and efficiently obtain the opening of carbon nanotubes, while preserving their morphology, their quality, and with reduced losses.
  • the process for opening carbon nanotubes according to the invention is characterized in that it comprises two oxidation stages, the first in the liquid phase in a concentrated acid, the second in the gas phase.
  • the oxidation stage in the liquid phase then makes it possible to directly obtain open nanotubes.
  • this has the advantage of making the major part of the residual metallic impurities enclosed at the ends accessible, for example following the syntheses carried out in the presence of catalyst.
  • the disordered carbon appearing during the oxidation reaction in the liquid phase is eliminated during the second stage in the gas phase.
  • the carbon nanotubes are multi-wall carbon nanotubes.
  • the concentrated acid is nitric acid.
  • concentrated nitric acid is used in excess.
  • this oxidation step is carried out at reflux, with stirring.
  • the reflux heating will last from 30 to 50 minutes, in particular approximately 35 minutes.
  • an additional step of gas phase oxidation is carried out at low temperature.
  • a particular implementation of this step consists of a treatment of approximately 1 to 2 hours, in particular under C0 2 to 500 to 600 ° C, in particular from 500 to 550 ° C and in particular from 525 ° C, to 1 at 1:40 min.
  • the method according to the invention will be implemented with a linear speed of said carbon dioxide of 40 to 100 cm / min, in particular from 50 to 70 cm / min, in particular of the order of 60 cm / min .
  • the method according to the invention comprises, between said first step of oxidation in the liquid phase and said second step of oxidation in the gas phase, an intermediate step of filtration and washing of the open nanotubes, in particular with distilled water.
  • the method according to the invention may include an additional step of treatment with hydrochloric acid in order to eliminate any metal particles, initially trapped in the central channel, and released during the opening of the nanotubes.
  • Figure 1 represents an image obtained by scanning electron microscopy (SEM) of carbon nanotubes after an HN0 3 + C0 2 treatment according to the invention
  • - Figure 2 represents a picture obtained by transmission electron microscopy (TEM) of nanotubes carbon after HN0 3 + C0 2 treatment according to the invention
  • FIG. 3 represents a MET radiograph (mode of network fringes C0 2 ) of an open end of a carbon nanotube after a treatment according to the method of the invention
  • FIG. 4 represents isothermal adsorption-desorption of nitrogen at 77K of the carbon nanotubes before (solid extract curve) and after implementation of the process according to the invention (dashed curve).
  • the process of the invention has been optimized on multi-wall carbon nanotubes synthesized by decomposition of acetylene at 600 ° C. on solid solutions of Co x Mg ( ⁇ _ x) 0.
  • the carbon nanotubes are dispersed in concentrated nitric acid and oxidized at reflux (130 ° C) for 35 minutes with continuous stirring (1 g of nanotubes in 1 liter of 69% acid by weight). Then, the mixture is filtered, then the solid is washed with distilled water until a neutral pH of the filtrate is obtained.
  • This first oxidation step allows the opening of the tubes.
  • a gentle oxidation is then carried out using a CO 2 current at low temperature.
  • the carbon nanotubes powder is placed in a quartz crucible equipped with a porous sintered glass disk allowing an upward flow of C0 2 to be introduced , at a linear speed of 60 cm / min, at 525 ° C .
  • the reaction is carried out for about 60 to 100 min. Selective oxidation of the disordered carbon nanostructures which are produced during the first oxidation reaction is obtained.
  • the porous texture of carbon nanotubes is characterized by the adsorption of nitrogen at 77 ° K (Micrometrics, ASAP 2000). Before the adsorption experiments, the samples are degassed at 350 ° C (10 ⁇ 6 bar) for 12 h.
  • Another heat treatment can be carried out at high temperature, at 1600-2800 ° C, for several hours, under nitrogen, to graphitize the aromatic layers of the walls and allow the sublimation of metallic Co.
  • the carbon nanotubes used have a strong entanglement.
  • the nitrogen adsorption isotherm at 77K is type IV, characteristic of a swelling mesoporous solid
  • the above method is applied to nanotubes having outside diameters of approximately 7 to 25 mm, but can be applied to nanotubes of larger diameters by adjusting the treatment time with nitric acid and C0 2 .
  • This process can of course be used with carbon nanotubes other than those obtained by catalytic processes.
  • the opening of carbon nanotubes with a very high crystallinity, in particular those which are synthesized by vaporization of graphite, will require longer reaction times.
  • the method according to the invention will then be effective in the context of the opening of carbon nanotubes. More particularly, the method according to the invention will be applied to the opening of multi-wall carbon nanotubes.
  • the method according to the invention will be applied to multi-wall carbon nanotubes having an outside diameter of between 7 and 25 nm.

Abstract

The invention relates to an efficient and non-damaging method for opening carbon nanotubes which consists in carrying out two oxidation stages. The first stage is carried out in a liquid phase in concentrated acid, the second stage being carried out in a gaseous phase.

Description

« Procédé d' ouverture de nanotubes de carbone à leurs extrémités et applications » "Method of opening carbon nanotubes at their ends and applications"
La présente invention concerne d'une manière générale le post traitement des nanotubes de carbone et leurs applications. En particulier, la présente invention vise un procédé d'ouverture des nanotubes de carbone à leurs extrémités et plus spécialement de nanotubes de carbone multiparois .The present invention relates generally to the post-treatment of carbon nanotubes and their applications. In particular, the present invention relates to a process for opening carbon nanotubes at their ends and more especially multi-wall carbon nanotubes.
La plupart des méthodes de synthèse, produisent des nanotubes de carbone avec des extrémités fermées ce qui peut, par exemple, provoquer l'inclusion d'impuretés provenant du milieu réactionnel dans le canal central du nanotube. Ceci se produit, notamment, lors des synthèses catalytiques des nanotubes de carbone. De plus, lorsque les nanotubes sont initialement ouverts, ils peuvent aussi se refermer lors de post-traitements à haute température. L'intérêt d'avoir des nanotubes de carbone ouverts est d'abord la possibilité de remplir leur canal central par de nombreuses espèces notamment conductrices (métaux, polymères conducteurs,...) de manière à fabriquer des nanofils conducteurs pour des applications en nanoélectronique. Les nanotubes de carbone remplis se révèlent aussi d'un intérêt grandissant dans les applications catalytiques, et pour le stockage d'énergie. Par ailleurs, les nanotubes de carbone creux peuvent s'avérer être d'excellents réservoirs de gaz, comme l'hydrogène, le gaz naturel... II est maintenant bien connu que la présence de défauts topologiques est nécessaire pour fermer les plans de graphène aux extrémités des nanotubes de carbone. Selon la loi d'Euler, six pentagones sont nécessaires pour assurer la fermeture des nanotubes de carbone à chaque extrémité. Ces régions de tension sont bien entendu les sites les plus utiles pour les réactions d' addition, en particulier sur les doubles liaisons reliant une paire de pentagones.Most synthesis methods produce carbon nanotubes with closed ends which can, for example, cause the inclusion of impurities from the reaction medium in the central channel of the nanotube. This occurs, in particular, during catalytic syntheses of carbon nanotubes. In addition, when the nanotubes are initially opened, they can also close during post-treatments at high temperature. The advantage of having open carbon nanotubes is first of all the possibility of filling their central channel with numerous species, in particular conductive (metals, conductive polymers, etc.) so as to manufacture conductive nanowires for applications in nanoelectronics. . Filled carbon nanotubes are also proving to be of growing interest in catalytic applications, and for energy storage. Furthermore, hollow carbon nanotubes can prove to be excellent reservoirs of gases, such as hydrogen, natural gas ... It is now well known that the presence of topological defects is necessary to close the graphene planes at the ends of carbon nanotubes. According to Euler's law, six pentagons are necessary to ensure the closure of the carbon nanotubes at each end. These regions of tension are of course the most useful sites for addition reactions, in particular on the double bonds connecting a pair of pentagons.
Parmi les méthodes proposées pour ouvrir les nanotubes, on citera l'oxydation chimique par les oxydants forts en phase liquide (acide nitrique, acide sulfurique ou mélange de ces deux acides, permanganate de potassium...) , les réactions en phase gazeuse sous courant d'air à des températures variant de 500°C à 700°C et depuis peu, le broyage par choc en particulier pour couper et raccourcir les nanotubes ou encore la sonication.Among the methods proposed to open nanotubes, we will mention chemical oxidation by strong oxidants in the liquid phase (nitric acid, sulfuric acid or mixture of these two acids, potassium permanganate, etc.), gas phase reactions under current. air at temperatures varying from 500 ° C to 700 ° C and recently, impact grinding in particular to cut and shorten the nanotubes or even sonication.
L'oxydation sous air ou sous oxygène n'est pas assez sélective. Ces traitements conduisent à une perte importante de matière et les plans de graphène externes sont souvent sérieusement endommagés en raison du caractère incontrôlable de la réaction.Oxidation in air or in oxygen is not selective enough. These treatments lead to a significant loss of material and the external graphene planes are often seriously damaged due to the uncontrollable nature of the reaction.
D'autres travaux ont préconisé d'utiliser du C02 à 850 °C mais à de telles températures, qui sont proches des conditions généralement utilisées pour activer les matériaux carbonés, les rendements en nanotubes ouverts sont très faibles, la perte de masse est très importante et les couches externes de graphène sont fortement endommagées.Other work has recommended using C0 2 at 850 ° C but at such temperatures, which are close to the conditions generally used to activate carbonaceous materials, the yields of open nanotubes are very low, the loss of mass is very important and the outer layers of graphene are badly damaged.
L'oxydation est bien plus homogène lorsque les nanotubes de carbone sont dispersés dans une solution oxydante. Par exemple, les nanotubes de carbone obtenus par décomposition de l'acétylène à 600 °C sur des particules de cobalt supportés par des zéolithes contiennent souvent des impuretés carbonées et ont des extrémités fermées. Il est alors possible de procéder à une attaque par le permanganate de potassium à la fois pour éliminer partiellement ces impuretés par oxydation et pour ouvrir une partie des extrémités des nanotubes de carbone.Oxidation is much more homogeneous when the carbon nanotubes are dispersed in an oxidizing solution. For example, carbon nanotubes obtained by decomposition of acetylene at 600 ° C on cobalt particles supported by zeolites often contain carbon impurities and have closed ends. It is then possible to carry out an attack with potassium permanganate both to partially remove these impurities by oxidation and to open part of the ends of the carbon nanotubes.
Cependant, là encore, les résultats en matière d'efficacité et de sélectivité s'avèrent nettement insuffisants . Les inventeurs ont constaté que ces inconvénients pouvaient être surmontés en soumettant des nanotubes à deux étapes d'oxydation distinctes, réalisées dans des conditions déterminées . L'invention a ainsi pour but de fournir un procédé permettant d'obtenir rapidement et avec efficacité l'ouverture de nanotubes de carbone, tout en préservant leur morphologie, leur qualité, et avec des pertes réduites.Here again, however, the results in terms of efficiency and selectivity are clearly insufficient. The inventors have found that these drawbacks can be overcome by subjecting nanotubes to two distinct oxidation stages, carried out under determined conditions. The object of the invention is therefore to provide a method making it possible to quickly and efficiently obtain the opening of carbon nanotubes, while preserving their morphology, their quality, and with reduced losses.
Ainsi, le procédé d'ouverture de nanotubes de carbone selon l'invention, est caractérisé en ce qu'il comprend deux étapes d'oxydation, la première en phase liquide dans un acide concentré, la seconde en phase gazeuse.Thus, the process for opening carbon nanotubes according to the invention is characterized in that it comprises two oxidation stages, the first in the liquid phase in a concentrated acid, the second in the gas phase.
L'étape d'oxydation en phase liquide permet alors d'obtenir directement des nanotubes ouverts. De plus, cela offre l'avantage de rendre accessible la majeure partie des impuretés métalliques résiduelles enfermées aux extrémités, par exemple à la suite des synthèses effectuées en présence de catalyseur .The oxidation stage in the liquid phase then makes it possible to directly obtain open nanotubes. In addition, this has the advantage of making the major part of the residual metallic impurities enclosed at the ends accessible, for example following the syntheses carried out in the presence of catalyst.
Le carbone désordonné apparaissant lors de la réaction d' oxydation en phase liquide est éliminé au cours de la seconde étape en phase gazeuse.The disordered carbon appearing during the oxidation reaction in the liquid phase is eliminated during the second stage in the gas phase.
Avantageusement, les nanotubes de carbone sont des nanotubes de carbone multiparois.Advantageously, the carbon nanotubes are multi-wall carbon nanotubes.
Plus particulièrement, l'acide concentré est l'acide nitrique.More particularly, the concentrated acid is nitric acid.
Préférentielle ent, l'acide nitrique concentré est utilisé en excès.Preferably, concentrated nitric acid is used in excess.
Des résultats satisfaisants sont ainsi obtenus avec 1 g de nanotubes de carbone dans 0,5 litre à 2 litres de HN03 concentré, notamment de HN0 à 60%-75% en poids, en particulier 1 litre d'acide nitrique à une concentration de l'ordre de 68-70% en poids. Selon une mise en œuvre particulière de l'invention, cette étape d'oxydation est réalisée à reflux, sous agitation. De manière avantageuse, le chauffage à reflux durera de 30 à 50 minutes, notamment environ 35 minutes. Aux fins de purification, on procède à une étape complémentaire d'oxydation en phase gazeuse, à basse température .Satisfactory results are thus obtained with 1 g of carbon nanotubes in 0.5 liter to 2 liters of concentrated HN0 3 , in particular of HN0 at 60% -75% by weight, in particular 1 liter of nitric acid at a concentration of around 68-70% by weight. According to a particular implementation of the invention, this oxidation step is carried out at reflux, with stirring. Advantageously, the reflux heating will last from 30 to 50 minutes, in particular approximately 35 minutes. For the purpose of purification, an additional step of gas phase oxidation is carried out at low temperature.
C'est plus particulièrement cette étape qui permet d' éliminer par oxydation ménagée les structures carbonées désordonnées provenant de l'ouverture des extrémités des nanotubes de carbone lors de l'étape d'ouverture par oxydation en phase liquide.It is more particularly this stage which makes it possible to eliminate by controlled oxidation the disordered carbon structures originating from the opening of the ends of the carbon nanotubes during the stage of opening by oxidation in the liquid phase.
Avantageusement, une mise en œuvre particulière de cette étape consiste en un traitement d'environ 1 à 2 heures, notamment sous C02 à 500 à 600 °C, en particulier de 500 à 550°C et notamment de 525°C, de 1 à lh40 min.Advantageously, a particular implementation of this step consists of a treatment of approximately 1 to 2 hours, in particular under C0 2 to 500 to 600 ° C, in particular from 500 to 550 ° C and in particular from 525 ° C, to 1 at 1:40 min.
Plus particulièrement encore, le procédé selon l'invention sera mis en œuvre avec une vitesse linéaire dudit dioxyde de carbone de 40 à 100 cm/min, notamment de 50 à 70 cm/min, en particulier de l'ordre de 60 cm/min.More particularly still, the method according to the invention will be implemented with a linear speed of said carbon dioxide of 40 to 100 cm / min, in particular from 50 to 70 cm / min, in particular of the order of 60 cm / min .
Avantageusement, le procédé selon l'invention comprend entre ladite première étape d' oxydation en phase liquide et ladite seconde étape d'oxydation en phase gazeuse, une étape intermédiaire de filtration et de lavage des nanotubes ouverts, notamment par de l'eau distillée. Le procédé selon l'invention pourra comprendre une étape supplémentaire de traitement à l'acide chlorydrique afin d'éliminer les éventuelles particules métalliques, initialement piégées dans le canal central, et libérées lors de l'ouverture des nanotubes.Advantageously, the method according to the invention comprises, between said first step of oxidation in the liquid phase and said second step of oxidation in the gas phase, an intermediate step of filtration and washing of the open nanotubes, in particular with distilled water. The method according to the invention may include an additional step of treatment with hydrochloric acid in order to eliminate any metal particles, initially trapped in the central channel, and released during the opening of the nanotubes.
La mise en oeuvre des dispositions qui précèdent, combinant une réaction en phase liquide suivie d'une réaction en phase gazeuse, permet d'obtenir des rendements d'au moins 90% en nanotubes ouverts, sans détérioration de la surface des nanotubes et de la pureté qui reste à des taux supérieurs à 97%.The implementation of the above arrangements, combining a reaction in the liquid phase followed by a reaction in the gas phase, makes it possible to obtain yields of at least 90% in open nanotubes, without deterioration of the surface of the nanotubes and of the purity which remains at rates greater than 97%.
L'efficacité de l'invention sera mieux comprise à la lecture de l'exemple détaillé ci dessous en référence aux figures dans lesquelles :The effectiveness of the invention will be better understood on reading the example detailed below with reference to the figures in which:
La Figure 1 représente une image obtenue par microscopie électronique à balayage (MEB) de nanotubes de carbone après un traitement HN03 + C02 selon l'invention, - La Figure 2 représente un cliché obtenu par microscopie électronique à transmission (MET) de nanotubes de carbone après traitement HN03 + C02 selon l'invention,Figure 1 represents an image obtained by scanning electron microscopy (SEM) of carbon nanotubes after an HN0 3 + C0 2 treatment according to the invention, - Figure 2 represents a picture obtained by transmission electron microscopy (TEM) of nanotubes carbon after HN0 3 + C0 2 treatment according to the invention,
La Figure 3 représente un cliché MET (mode de franges de réseau C02) d'une extrémité ouverte d'un nanotube de carbone après un traitement selon le procédé de l'invention, etFIG. 3 represents a MET radiograph (mode of network fringes C0 2 ) of an open end of a carbon nanotube after a treatment according to the method of the invention, and
La Figure 4 représente des isothermes d' adsorption- désorption d'azote à 77K des nanotubes de carbone avant (courbe extrait plein) et après mise en œuvre du procédé selon l'invention (courbe en pointillés).FIG. 4 represents isothermal adsorption-desorption of nitrogen at 77K of the carbon nanotubes before (solid extract curve) and after implementation of the process according to the invention (dashed curve).
Le procédé de l'invention a été optimisé sur des nanotubes de carbone multiparois synthétisés par décomposition de l'acétylène à 600°C sur des solutions solides de CoxMg(ι_x)0.The process of the invention has been optimized on multi-wall carbon nanotubes synthesized by decomposition of acetylene at 600 ° C. on solid solutions of Co x Mg ( ι_ x) 0.
Au cours d'une première étape, les nanotubes de carbone sont dispersés dans 1 ' acide nitrique concentré et oxydés à reflux (130°C) pendant 35 minutes sous agitation continue (1 g de nanotubes dans 1 litre d'acide à 69% en poids). Ensuite, le mélange est filtré, puis le solide est lavé avec de l'eau distillée jusqu'à l'obtention d'un pH neutre de filtrat. Cette première étape d'oxydation permet l'ouverture des tubes.During a first step, the carbon nanotubes are dispersed in concentrated nitric acid and oxidized at reflux (130 ° C) for 35 minutes with continuous stirring (1 g of nanotubes in 1 liter of 69% acid by weight). Then, the mixture is filtered, then the solid is washed with distilled water until a neutral pH of the filtrate is obtained. This first oxidation step allows the opening of the tubes.
On procède ensuite à une oxydation douce à l'aide d'un courant de C02 à faible température. Cette réaction est basée sur la réaction de Boudouard (C+C02 → 2CO(ΔH = +159 kJ/mole) . La poudre de nanotubes de carbone est placée dans un creuset en quartz équipé d'un disque en verre fritte poreux permettant d'introduire un flux ascendant de C02, à raison d'une vitesse linéaire de 60 cm/min, à 525°C. La réaction est effectuée pendant environ 60 à 100 min. On obtient une oxydation sélective des nanostructures de carbone désordonnées qui sont produites durant la première réaction d'oxydation.A gentle oxidation is then carried out using a CO 2 current at low temperature. This reaction is based on the Boudouard reaction (C + C0 2 → 2CO (ΔH = +159 kJ / mole). The carbon nanotubes powder is placed in a quartz crucible equipped with a porous sintered glass disk allowing an upward flow of C0 2 to be introduced , at a linear speed of 60 cm / min, at 525 ° C . The reaction is carried out for about 60 to 100 min. Selective oxidation of the disordered carbon nanostructures which are produced during the first oxidation reaction is obtained.
La perte de masse cumulée reste inférieure à 50%. L'utilisation d'un microscope électronique à balayage (Hitachi S 4200) permet d'évaluer la qualité des échantillons de nanotubes (Figure 1) .The cumulative loss of mass remains below 50%. The use of a scanning electron microscope (Hitachi S 4200) makes it possible to assess the quality of the nanotube samples (Figure 1).
L'observation par MET à 200 kV (Philips CM20) montre l'efficacité de ce procédé quant à l'ouverture des nanotubes aux extrémités (Figures 2 et 3) . Pour cette observation, les échantillons sont soumis à une sonication dans de l'éthanol anhydre et une gouttelette est déposée sur une grille en cuivre recouverte d'un film de carbone.Observation by TEM at 200 kV (Philips CM20) shows the efficiency of this process with regard to the opening of the nanotubes at the ends (Figures 2 and 3). For this observation, the samples are subjected to sonication in anhydrous ethanol and a droplet is placed on a copper grid covered with a carbon film.
La texture poreuse des nanotubes de carbone est caractérisée par l'adsorption d'azote à 77 °K (Micrometrics, ASAP 2000). Avant les expériences d' adsorption, les échantillons sont dégazés à 350°C (10~6 bar) durant 12 h.The porous texture of carbon nanotubes is characterized by the adsorption of nitrogen at 77 ° K (Micrometrics, ASAP 2000). Before the adsorption experiments, the samples are degassed at 350 ° C (10 ~ 6 bar) for 12 h.
Après l'ouverture, on peut procéder à un autre traitement thermique à haute température, à 1600 - 2800°C, pendant plusieurs heures, sous azote, pour graphitiser les couches aromatiques des parois et permettre la sublimation du Co métallique.After opening, another heat treatment can be carried out at high temperature, at 1600-2800 ° C, for several hours, under nitrogen, to graphitize the aromatic layers of the walls and allow the sublimation of metallic Co.
Le diamètre des tubes diminue légèrement à la suite du traitement d'oxydation et le taux d'ouverture est supérieur à 90% (Figure 2 ; les flèches montrent des tubes ouverts) . La qualité des échantillons n'est pas affectée par le traitement d'ouverture et les teneurs en nanotubes sont supérieures à 97%. Les observations de TEM en mode de franges de réseau 002 montrent que les parois ne sont pas endommagées (Figure 3) .The diameter of the tubes decreases slightly following the oxidation treatment and the opening rate is greater than 90% (Figure 2; the arrows show open tubes). The quality of the samples is not affected by the opening treatment and the nanotube contents are greater than 97%. TEM observations in 002 network fringe mode show that the walls are not damaged (Figure 3).
Les nanotubes de carbone utilisés présentent un fort enchevêtrement. L'isotherme d'adsorption d'azote à 77K est de type IV, caractéristique d'un solide mésoporeux gonflantThe carbon nanotubes used have a strong entanglement. The nitrogen adsorption isotherm at 77K is type IV, characteristic of a swelling mesoporous solid
(Figure 4) . Leur surface BET est de 220 m2/g et le volume mésoporeux est très important (environ 1 cm3/g) , avec un diamètre BJH de l'ordre de 15 nm qui correspond aux ménisques définis par l'enchevêtrement des nanotubes. Après ouverture des extrémités selon l'invention, le volume mésoporeux augmente jusqu'à environ 1,6 cm3/g. La surface BET est alors de l'ordre de 300 m2/g, ce qui démontre l'intérêt de ces nanotubes pour le stockage de l\énergie ou de gaz.(Figure 4). Their BET surface area is 220 m 2 / g and the mesoporous volume is very large (approximately 1 cm 3 / g), with a BJH diameter of the order of 15 nm which corresponds to the menisci defined by the entanglement of nanotubes. After opening the ends according to the invention, the mesoporous volume increases up to approximately 1.6 cm 3 / g. The BET surface is then of the order of 300 m 2 / g, which demonstrates the advantage of these nanotubes for the storage of energy or gas.
Le procédé ci-dessus est appliqué à des nanotubes présentant des diamètres extérieurs de 7 à 25 mm environ, mais peut être appliqué à des nanotubes de plus gros diamètres en ajustant le temps de traitement à l'acide nitrique et au C02.The above method is applied to nanotubes having outside diameters of approximately 7 to 25 mm, but can be applied to nanotubes of larger diameters by adjusting the treatment time with nitric acid and C0 2 .
Ce procédé est bien entendu utilisable avec des nanotubes de carbone autres que ceux obtenus par des procédés catalytiques.This process can of course be used with carbon nanotubes other than those obtained by catalytic processes.
L' ouverture de nanotubes de carbone avec une très forte cristallinité, notamment ceux qui sont synthétisés par vaporisation du graphite, nécessitera des temps de réaction plus longs. Le procédé selon l'invention sera alors efficace dans le cadre de l'ouverture de nanotubes de carbone. Plus particulièrement, on appliquera le procédé selon l'invention à l'ouverture de nanotubes de carbone multiparois.The opening of carbon nanotubes with a very high crystallinity, in particular those which are synthesized by vaporization of graphite, will require longer reaction times. The method according to the invention will then be effective in the context of the opening of carbon nanotubes. More particularly, the method according to the invention will be applied to the opening of multi-wall carbon nanotubes.
Plus particulièrement, on appliquera le procédé selon 1' invention à des nanotubes de carbone multiparois ayant un diamètre extérieur compris entre 7 et 25 nm.More particularly, the method according to the invention will be applied to multi-wall carbon nanotubes having an outside diameter of between 7 and 25 nm.
Plus particulièrement encore, les nanotubes de carbone multiparois sur lesquels on appliquera le procédé selon l'invention seront obtenus par décomposition de l'acétylène à 600°C sur une solution solide CoxMg(ι-X)0.More particularly still, the multi-wall carbon nanotubes on which the method according to the invention will be obtained by decomposition of acetylene at 600 ° C on a solid solution Co x Mg ( ι- X ) 0.
Tous les nanotubes de carbone ainsi traités et ouverts se révéleront d' un intérêt économique et industriel fort en particulier dans leur utilisation pour la fabrication de nanofils conducteurs, pour le stockage de l'énergie, pour le stockage ou la filtration des gaz et/ou pour la réalisation de support de catalyseur. All the carbon nanotubes thus treated and opened will prove to be of great economic and industrial interest in particular in their use for the manufacture of conductive nanowires, for the storage of energy, for the storage or filtration of gases and / or for the production of catalyst support.

Claims

REVE ND I C AT I O N S DREAM ND IC AT IONS
1. Procédé d'ouverture de nanotubes de carbone, caractérisé en ce qu'il comprend deux étapes d'oxydation, la première en phase liquide dans un acide concentré, la seconde en phase gazeuse. 1. A method of opening carbon nanotubes, characterized in that it comprises two oxidation stages, the first in the liquid phase in a concentrated acid, the second in the gas phase.
2. Procédé selon la revendication 1, caractérisé en ce que les nanotubes de carbone sont des nanotubes de carbone multiparois .2. Method according to claim 1, characterized in that the carbon nanotubes are multi-wall carbon nanotubes.
3. Procédé selon la revendication 2, caractérisé en ce que l'acide concentré est de l'acide nitrique, de préférence utilisé en excès.3. Method according to claim 2, characterized in that the concentrated acid is nitric acid, preferably used in excess.
4. Procédé selon l'une des revendications 2 ou 3, caractérisé en ce qu'on utilise 1 g de nanotubes de carbone dans 0,5 litres à 2 litres d'acide nitrique concentré à 60-75% en poids, en particulier, 1 litre d'acide nitrique à une concentration de l'ordre de 68-70% en poids.4. Method according to one of claims 2 or 3, characterized in that 1 g of carbon nanotubes is used in 0.5 liters to 2 liters of concentrated nitric acid at 60-75% by weight, in particular, 1 liter of nitric acid at a concentration of about 68-70% by weight.
5. Procédé selon l'une quelconque des revendications 2 à5. Method according to any one of claims 2 to
4, caractérisé par un chauffage à reflux, sous agitation.4, characterized by reflux heating, with stirring.
6. Procédé selon l'une quelconque des revendications 1 à6. Method according to any one of claims 1 to
5, caractérisé en ce que ladite seconde étape d'oxydation en phase gazeuse est une oxydation desdits nanotubes par du dioxyde de carbone à basse température.5, characterized in that said second oxidation step in the gas phase is an oxidation of said nanotubes with carbon dioxide at low temperature.
7. Procédé selon la revendication 6, caractérisé par le traitement des nanotubes de carbone avec ledit dioxyde de carbone de 500 à 600°C, pendant 1 à 2h, en particulier de 500 à 550 °C, pendant lh à lh40 min.7. Method according to claim 6, characterized by the treatment of carbon nanotubes with said carbon dioxide from 500 to 600 ° C, for 1 to 2 hours, in particular from 500 to 550 ° C, for 1 hour to 1 hour 40 minutes.
8. Procédé selon l'une quelconque des revendications 1 à 7, caractérisé en ce qu'il comprend, entre ladite première étape d' oxydation en phase liquide et ladite seconde étape d'oxydation en phase gazeuse, une étape intermédiaire de filtration et de lavage desdits nanotubes ouverts, notamment par de l'eau distillée. 8. Method according to any one of claims 1 to 7, characterized in that it comprises, between said first step of oxidation in the liquid phase and said second step of oxidation in the gas phase, an intermediate step of filtration and washing said open nanotubes, in particular with distilled water.
9. Utilisation des nanotubes obtenus par la mise en œuvre du procédé selon l'une quelconque des revendications 1 à 8, pour le stockage de l'énergie, pour le stockage ou la filtration des gaz et/ou pour la réalisation de support de catalyseur. 9. Use of nanotubes obtained by implementing the method according to any one of claims 1 to 8, for energy storage, for gas storage or filtration and / or for the production of catalyst support .
PCT/FR2003/002499 2002-08-08 2003-08-08 Method for opening carbon nanotubes at the ends thereof and implementation WO2004016550A2 (en)

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