Classifications

• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M11/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising
  • D06M11/01—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with hydrogen, water or heavy water; with hydrides of metals or complexes thereof; with boranes, diboranes, silanes, disilanes, phosphines, diphosphines, stibines, distibines, arsines, or diarsines or complexes thereof
  • D06M11/05—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with hydrogen, water or heavy water; with hydrides of metals or complexes thereof; with boranes, diboranes, silanes, disilanes, phosphines, diphosphines, stibines, distibines, arsines, or diarsines or complexes thereof with water, e.g. steam; with heavy water
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
  • D01F11/10—Chemical after-treatment of artificial filaments or the like during manufacture of carbon
  • D01F11/16—Chemical after-treatment of artificial filaments or the like during manufacture of carbon by physicochemical methods
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M10/00—Physical treatment of fibres, threads, yarns, fabrics or fibrous goods made from such materials, e.g. by ultrasonic waves, corona discharge, irradiation, electric currents or magnetic fields; Physical treatment combined with treatment with chemical compounds or elements
  • D06M10/04—Physical treatment combined with treatment with chemical compounds or elements
  • D06M10/06—Inorganic compounds or elements
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M11/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising
  • D06M11/32—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with oxygen, ozone, ozonides, oxides, hydroxides or percompounds; Salts derived from anions with an amphoteric element-oxygen bond
  • D06M11/34—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with oxygen, ozone, ozonides, oxides, hydroxides or percompounds; Salts derived from anions with an amphoteric element-oxygen bond with oxygen, ozone or ozonides
• • 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
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
  • D06M2101/40—Fibres of carbon

Definitions

• the present invention relates to a method for etching carbon fibers, in particular carbon nanofibers, and to the carbon nanofibers obtainable by this method and their use.
• Nanofibres in a polymer matrix and the resulting strong interactions between fiber and matrix are advantageous in composites (Calvert, P., Nature 399: 210-21 (1999)) .
• As catalyst supports, impurities must be deposited on the nanofibers, and anchor sites are like functional groups
• the inert surface of the as-grown nanofibers must be modified (Xia, W. et al., Ch Em. Mater. 17: 5737-5742 (2005)).
• nanofibers are cleaved into smaller fibrous units (Liu, J. et al., Science 280: 1253-1256 (1998)).
• the identification of surface defects remains challenging due to the small dimensions and surface curvature of carbon nanofibers (Ishigami, M. et al., Phys. Rev. Lett., 93: 196803/4 (2001)).
• Scanning tunneling microscopy (STM) is a very powerful tool (Osväth, Z. et al., Phys. Rev. B 72: 045429 / 1-045429 / 6 (2005)).
• Fan and co-workers identified chemical surface defects with atomic force microscopy (AFM) by defect-sensitive oxidation with H 2 Se (Fan, Y. et al., Adv. Mater. 14: 130-133 (2002)).
• AFM atomic force microscopy
• the change in surface area of carbon nanofibers is obtained by deposition of cyclohexane on iron-loaded carbon nanofibers.
• secondary carbon nanofibers (tree-like structures of trunk and branches) are not functional, the surface modifications obtained can not be used for loading with functional molecules.
• MWNT multi-walled carbon nanotubes
• etching occurs at the interface and is limited to the locations of the carbon fibers where iron particles are present.
• the etching can be easily controlled by suitable choice of parameters for pretreatment (loading of iron, annealing time, etc.) and process parameters (reaction time, temperature, partial pressure of the water, etc.).
• pretreatment loading of iron, annealing time, etc.
• process parameters reaction time, temperature, partial pressure of the water, etc.
• the carbon fibers according to the present invention include, but are not limited to, carbon nanofibers and carbon microfibers.
• Figure 1 Two-dimensional schematic illustration of the four main steps in the etching process.
• the nanofibers were functionalized with concentrated nitric acid to increase the number of oxygen atoms on the surface. Iron from ferrocene as a precursor was then deposited from the vapor phase. The following etching was carried out with 1 vol.% Water vapor in helium. The metal particles were finally removed by washing with 1 M nitric acid at room temperature.
• Figure 2 Schematic image of the apparatus for the iron deposition (a) and for the water vapor etching of carbon nanofibers (b).
• Figure 3 Consumption of water and release of carbon monoxide during water vapor etching, recorded by on-line mass spectrometry.
• FIG. 4 SEM images of the nanofiber after the etching: (a) untreated, with the iron nanoparticles; (b) after removal of the iron nanoparticles by 1 M nitric acid.
• FIG. 5 shows TEM images of the nanofiber after etching with water at 670 0 C.
• FIG. 6 Powder diffractograms of the untreated and the etched nanofibers.
• FIG. 7 Isotherms of the nitrogen physisorption measurements for untreated and etched nanofibers.
• the inserted graph shows the pore radius distribution of the etched nanofibers.
• the carbon fibers in the context of the present invention are structures obtainable by polymerization of unsaturated hydrocarbon compounds.
• the carbon fibers are carbon nanofibers. These consist of carbon, z. B. from Kohlenwassertoffen be prepared by catalytic pyrolysis and z. Available from Applied Sciences Inc. (Cedarville, Ohio, USA) or from Bayer MaterialScience.
• Such carbon nanofibers usually have an outer diameter of 50 to 500 nm, preferably about 100 nm, an inner diameter of 10 to 100 nm, preferably about 50 nm and a surface area of 10 to 60 m 2 / g, preferably from 20 to 40 m 2 / g on.
• the etching process according to the invention increases the specific surface area of the carbon nanofibers to 90 to 100 m 2 / g.
• the carbon fibers are microfibers.
• microfibers consist for. B. carbon, z. B. prepared by pyrolysis of polyacrylonitrile and z. From Zoltek Companies Inc. (St. Louis, USA) or Toho Tenax Europe GmbH.
• These microfibers have an outer diameter of 3 to 10 microns, preferably about 6 microns and a surface area of less than 1 m 2 / g.
• the etching process according to the invention increases the specific surface area of the microfibers to 5 to 50 m 2 / g.
• the surface of the carbon fibers is functionalized by an oxidative treatment of the fibers.
• This can preferably be done by heating with oxidizing acids or oxygen plasma treatment.
• Particular preference is given to heating with nitric acid, eg. As with concentrated nitric acid.
• metal particles are applied to or deposited on the fiber treated in step (a).
• These metal particles are preferably selected from iron (Fe), cobalt (Co) and nickel (Ni), with Fe particles being particularly preferred.
• the loading of 1 to 20, preferably 5 to 10 wt .-% metal, based on the total weight of the loaded carbon nanofibers, are applied.
• the deposition / deposition of the metal particles is preferably carried out by contacting with dissolved metal salts or metallocenes (preferably ferrocenes), in particular at a temperature of 100 to 600 0 C and subsequent reduction with hydrogen at a temperature of 300 to 800 0 C preferably at about 500 ° C.
• step (c) of the method according to the invention the etching of the metal particles doped fibers takes place.
• This is done according to the invention by treatment with steam in a helium atmosphere, wherein preferably the water vapor content of the helium atmosphere is 0.1 to 10, particularly preferably about 1% by volume.
• the helium atmosphere contains 1 to 20, preferably about 10 vol .-% H 2 to keep the metal catalyst active.
• the etching is preferably carried out at a temperature of 500 to 800 ° C., more preferably above 600 ° C.
• step (d) of the process according to the invention the removal of the metal particles takes place. This is preferably done by treatment with an acid, in particular aqueous hydrochloric acid or a mixture of HNO 3 / H 2 SO 4 . Depending on the desired application, the resulting carbon fiber may be loaded with functional ligands at the etched positions in a subsequent step (e). So requires z. As an application as a catalyst loading with the required metal atoms / - particles.
• FIG. 1 A typical etching process is illustrated in FIG.
• the MWNTs (inner diameter: several tens of nm, outer diameter: about 100 nm, Applied Sciences Inc., Ohio, USA) were first refluxed in concentrated nitric acid for 2 hours, and then iron was precipitated from ferrocene.
• the deposition and sintering of iron nanoparticles is described in Xia, W. et al., Chem. Mater. 17: 5737-5742 (2005).
• the iron loading in the present work varies in the range of 5 to 10 wt .-% and can be changed by varying the amount of ferrocene precursor.
• the iron-loaded nanofibers were reduced and annealed at 500 ° C. in hydrogen for 1 h.
• the removal of the iron particles from the surface of the carbon nanofibers can, as in Wue, P. et al., Surf. Interface Anal. 36: 497-500 (2004), by aqueous hydrochloric acid, mixture of HNO 3 and H 2 SO 4 .
• FIG. 4a shows the nanofibers in the untreated state.
• the existence of nanoscale iron oxide particles embedded in the surface of the nanofibers in the etched samples can be observed ( Figure 4b).
• the spherical etch pits are clearly visible after the iron particles have been removed by washing with acid ( Figure 4c).
• the TEM image shown in FIG. 5a demonstrates the embedding of the iron nanoparticles due to the etching process.
• the surface roughness was significantly increased by the etching, as shown by the TEM images after washing out the iron nanoparticles ( Figure 5b-c).
• the damage to the wall of the nanofiber can be observed.
• a spherical hole was etched into the nanofiber, apparently by removing the outer walls one at a time.
• FIG. 6 shows the result of X-ray diffraction (XRD) on nanofibers etched for more than one hour. Compared to the untreated nanofibers, the signal intensity decreases the etching is significantly reduced. While it does not make sense to correlate intensity directly with crystallinity, there is no doubt that a significant increase in disorder after etching can be deduced from highly reproducible XRD results. Smaller mesopores were produced by the etch, as can be demonstrated by the nitrogen physisorption measurements (Figure 7).
• mesoporous MWNTs with spherical etch pits can be produced in a targeted, local etching process that is both environmentally friendly and based on cheap raw materials (iron and water).
• the etching takes place on the surface of the nanofibers and is limited to the boundary layer between the iron particles and the nanofiber. All parts of the nanofiber surface without iron particles are not changed by the etching.
• the simple control and variation of the process parameters make the etching extremely flexible.
• the applications are in the field of polymer composites, catalysis and biosensors. We assume that the etch pits can effectively reduce the surface mobility of deposited nanoscale catalyst particles, thus avoiding the aggregation (sintering) leading to deactivation of the catalysts.
• the increased surface roughness will be useful for immobilizing functional proteins in biosensors and result in significantly improved oxygen functionalization.
• the iron-loaded nanofibers (10% by weight, available from Applied Sciences Inc., Cedarville, Ohio, USA) were heated at 500 ° C. in a mixture of hydrogen and helium (1: 1, 100 ml min -1 STP) Reduced and tempered for an hour pert.
• a total gas flow of 100 ml min -1 STP with a hydrogen concentration of 10% by volume and a water concentration of 1% by volume was produced as follows: Helium (32.3 ml min -1 STP) was passed through a saturator which was flushed with water (Room temperature) was filled.
• Hydrogen (10 ml min "1 STP) and additional helium (57.7 ml min " 1 STP) were combined in the reactor before the fixed bed with the hydrous helium stream.
• the hydrogen used (10 vol.%) was used to keep the iron catalyst active.
• the control of all gas streams was ensured by online mass spectrometry (MS).
• MS mass spectrometry
• the reactor was heated from 500 ° C. to 670 ° C. with a ramp of 20 K min -1 .
• the reactor under helium 100 ml min "1 , STP cooled at 10 K min -1 to 450 ° C.
• the reaction time is 1.5 h.
• the reaction time is 1 h.

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• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Carbon And Carbon Compounds (AREA)
• Inorganic Fibers (AREA)
• Catalysts (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)

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