Low-temperature synthesis of amorphous carbon nanocoils via acetylene coupling on copper nanocrystal surfaces at 468 K: a reaction mechanism analysis

A new type of amorphous helical carbon nanofibers has been synthesized using copper nanocatalysts and an acetylene gas source at atmospheric pressure. The nanofibers are grown at 468 K, which is the lowest temperature by ordinary metal-catalyzed thermal chemical vapor deposition of hydrocarbon, and exhibit a symmetric growth mode in the form of twin helices. IR, XRD, Raman, and C/H molar ratio analyses reveal a polymer-like structure with a weak trans-polyacetylene feature. The nanofibers are a mixture of solid polymers and a small amount of carbon. A reaction mechanism has been proposed on the basis of the previous studies of acetylene adsorption, desorption properties, and surface reactions on copper (111), (110), and (001) planes under ultrahigh-vacuum (UHV) conditions as well as the results obtained in our study. The reaction mechanism of acetylene on copper single-crystal surfaces under UHV conditions indeed reflects the reaction mechanism under practical catalytic conditions at atmospheric pressure. The nanofibers grow mainly via acetylene coupling to solid polymers on copper nanocrystal surfaces. Acetylene also couples to yield small amounts of liquid oligomers and gaseous products, and undergoes slight carbon deposition during the fiber growth.     

Enhancement of conductivity by diameter control of polyimide-based electrospun carbon nanofibers

Oxydianiline-pyromellitic dianhydride poly(amic acid) (ODA-PMDA PAA) was polymerized with a catalyst support of triethyl amine for controlling molecular weight. This polymer was used for electrospinning in the preparation of PAA nanofibers, a precursor of carbon nanofibers. Here the amount of catalyst and concentration of PAA solution were optimized to produce polyimide-based carbon nanofibers approximately 80 nm in diameter. The effects of molecular weight of PAA, bias voltage, and spinning rate on the morphology of electrospun PAA and polyimide nanofibers have been evaluated. We showed that the conductivity of the carbon nanofiber mat decreased with increasing nanofiber diameter, where the conductivity of polyimide-based carbon nanofiber mat was much higher than those of other types of carbon nanofiber mat. The key ingredient to increase conductivity in a carbon nanofiber mat was found to be the number of cross junctions between nanofibers.     

一步法溶剂热催化合成纳米碳纤维

利用四氢呋喃为溶剂和碳源,通过溶剂热催化方法在500 ℃一步合成了纳米碳纤维,X-射线衍射（XRD）分析显示此法合成的碳纤维晶型为碳的六方石墨相,场发射电镜(FESEM)和透射电镜(TEM)照片进一步表明碳纤维平均直径为100 nm,长度达几百纳米至几微米,高分辨电镜照片揭示产品中碳的晶间距为0.34 nm;产品纯度通过热重法（TGA）分析;同时,拉曼光谱图显示在1 347和1 584 cm^-1处有2个强峰,这与石墨相碳的典型拉曼光谱图是一致的。     

Deposition precipitation for the preparation of carbon nanofiber supported nickel catalysts

Deposition precipitation of nickel hydroxide onto modified carbon nanofibers has been studied and compared to deposition onto silica. The carbon nanofiber support materials consisted of graphite-like material of the fishbone-type with a diameter of 20-50 nm and a specific surface area of 150 m2/g. Modification involved surface oxidation (CNF-O) optionally followed by partial reduction (CNF-OR) or thermal treatment (CNF-OT). Titration of the support materials showed the presence of 0.17 and 0.03 mmol/g carboxylic acid groups for CNF-O and CNF-OR, respectively. For the CNF-OT only basic groups were present. The deposition precipitation of 20 wt % nickel onto these supports has been studied by time dependent pH and nickel loading studies. With silica, nickel ion adsorption did not occur prior to nucleation of the nickel hydroxide phase at pH = 5.6. With CNF-O, nickel ion adsorption took place right from the start of the deposition process at pH = 3.5, and at pH = 5.6 already 4 wt % nickel was adsorbed. Nucleation of nickel hydroxide onto adsorbed nickel ion clusters proceeded subsequently. Characterization of the dried Ni/CNF-O samples with TEM and XRD showed well dispersed and thin (5 nm) platelets of nickel hydroxide adhering to the carbon nanofibers. After reduction at 773 K in hydrogen the Ni/CNF-O contained metallic nickel particles of 8 nm homogeneously distributed over the fibers. With CNF-OR and CNF-OT, precipitation of large platelets (> 500 nm) separate from the support took place. Clearly, the presence of carboxylic acid groups is essential to successfully deposit nickel hydroxide onto modified carbon nanofibers.     

New carbon nanofiber/graphite felt composite for use as a catalyst support for hydrazine catalytic decomposition

Graphite felt supporting 40 nm diameter carbon nanofibers was synthesized and successfully used as a support for a high loaded iridium catalyst (30 wt%) in the decomposition of hydrazine; a strong mechanical resistance and a high thermal conductivity led to a very efficient and stable catalyst as compared to that used industrially, iridium supported on a high surface area alumina.     

Long-term and thermally stable superhydrophobic surfaces of carbon nanofibers

Carbon nanofibers were prepared from polyvinyl alcohol (PVA) by a simple wetting-compatible method. The surfaces of the aligned carbon nanofibers show excellent thermal- and time-stable superhydrophobicity. The average water contact angle (CA) values are about 153.1+/-2.2 degrees at room temperature, with little difference coming from experimental error. In addition, the CA of the aligned carbon nanofibers surface maintains 139.1+/-3.2 degrees after 10 months of exposure to the ambient environment. Nanostructure on the surface of carbon nanofibers and the intrinsic thermal resistance of carbon contribute to this unique surface property.     

TGA analysis of polypropylene-carbon nanofibers composites

TGA investigations on the thermal degradation of isotactic polypropylene-vapor grown carbon nanofibers composites in nitrogen are reported. The mass evolution as a function of temperature is a single sigmoid for both polypropylene and polypropylene loaded with carbon nanofibers. The inflection temperature of these sigmoids increases as the concentration of carbon nanofibers is increased. The width of the degradation process narrows as the concentration of carbon nanofibers is increased due to a better homogenization of the local temperature provided by the high thermal conductivity of carbon nanofibers. Thermogravimetric analysis data indicate the formation of polymer-carbon nanofiber interface. Based on TGA data, a two-layer structure is proposed for carbon nanofibers-polypropylene interface. The external layer is soft and has a thickness of about 10² nm that confines most polymer molecules in interaction with nanofibers. The core layer is rigid and has a thickness of the order of few nanometers.     

丙烯腈-衣康酸基纳米纤维纱线的热稳定及碳化研究

碳纳米纤维主要以聚丙烯腈(PAN)作为前驱体,通过纺丝、热稳定、碳化等后处理工艺制备而得.但是,PAN基纳米纤维取向度低、致密性差,热稳定后环化度低,碳化后导电性差等缺点阻碍其在高性能碳纳米纤维领域的发展.因此,在PAN分子链中引入衣康酸(IA),通过溶液聚合法合成了P(AN-co-IA)共聚物并通过静电纺丝法制备了P...     

Biocompatible Crosslinked Nanofibers of Poly(Vinyl Alcohol)/Carboxymethyl‐Kappa‐Carrageenan Produced by a Green Process

This study presents a new type of biocompatible nanofiber based on poly(vinyl alcohol) (PVA) and carboxymethyl‐kappa‐carrageenan (CMKC) blends, produced with no generation of hazardous waste. The nanofibers are produced by electrospinning using PVA:CMKC blends with ratios of 1:0, 1:0.25, 1:0.4, 1:0.5, and 1:0.75 (w/w PVA:CMKC) in aqueous solution, followed by thermal crosslinking. The diameter of the fibers is in the nanometer scale and below 300 nm. Fourier transform infrared spectroscopy shows the presence of the carboxyl and sulfate groups in all the fibers with CMKC. The nanofibers from water‐soluble polymers are stabilized by thermal crosslinking. The incorporation of CMKC improves cytocompatibility, biodegradability, cell growth, and cell adhesion, compared to PVA nanofibers. Furthermore, the incorporation of CMKC modulates phenotype of human adipose‐derived stem cells (ADSCs). PVA/CMKC nanofibers enhance ADSC response to osteogenic differentiation signals and are therefore good candidates for application in tissue engineering to support stem cells.     

Polymer‐nanofiber composites: Enhancing composite properties by nanofiber oxidation

Nanocomposites of styrene and vinyl phenol copolymers, which contain varying (10, 20, and 40 mol %) vinyl phenol content, were prepared with 1 wt % unoxidized, 1 wt % oxidized, and 5 wt % oxidized carbon nanofibers. Dynamic mechanical analysis and differential scanning calorimetry indicate that the composites prepared from oxidized nanofibers exhibit improved thermal and structural properties relative to those prepared from unoxidized nanofibers. The optimum enhancement in the mechanical and thermal properties was observed for the composite containing oxidized nanofibers and the 20% vinyl phenol copolymer. These results are in excellent agreement with our previous work on carbon nanotube–polymer composites and suggest that the presence of intermolecular interactions between the copolymer matrix and nanofibers are responsible for the observed property enhancement. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3053–3061, 2006     

Design,Preparation and Properties of Bio-inspired Hierarchical Structure Yarns with Enhanced Thermal Insulation and Water Transfer Ability

Encouraged by the porous and stable structure of cold-resist animals' hair or feather, bio-inspired hierarchical structure yarns combining polyacrylonitrile(PAN) nanofibers and polypropylene(PP) hollow microfibers have been developed by a modified conjugate electrospinning technology. Physical cross-linking has been built to increase fibers adhesion and construct interlayer support for nanofibrous assembly. The nanofibers and hollow microfibers construct a stable porous structure with porosity of 62%, providing excellent thermal insulating ability[temperature diffe-rence(|ΔT|) between skin and yarn surface is 4.9℃] as well as good mechanical property. More interestingly, the water transfer ability (infiltrate the yarn in 10 s) of synthetic fibers has been improved greatly by the combination of thin diameter nanofibers to the yarn. It is believed that the research lays the foundation for bio-inspired engineering technology in the manufacture of thermal comfort.     

碳纳米纤维负载Pd-Pt催化剂的萘加氢耐硫性能

Catalytically-grown carbon nanofibers of two different conformations,fishbone and parallel types of the arrangement of carbon layers,were employed as the support of Pd-Pt metal catalysts for the hydrogenation of naphthalene to tetralin. The sulfur tolerance of the catalyst system was investigated with the addition of 0. 05% thiophene to the reactant of naphthalene in the process. The dispersion of Pd-Pt metal particles on the support was observed with a HREM and a pulsed hydrogen chemisorption method. The hydrogenation reaction of naphthalene was carried out in a CSTR at 250℃ and with the hydrogen pressure of 6 MPa. The results showed that the Pd-Pt catalyst supported on the carbon nanofibers was active in the process. The Pd-Pt metal catalyst supported on the parallel carbon nanofibers showed a higher sulfur tolerance than that on the fishbone carbon nanofibers. The reason may be attributed to their different conformations of the carbon layers,which leads to the different interaction of carbon layers with the supported metal particles.     

Novel multilamellar mesostructured molybdenum oxide nanofibers and nanobelts: synthesis and characterization

One-dimensional molybdenum oxide nanostructures with layered mesostructures were prepared directly from commercial bulk MoO3 crystals by a surfactant-templated hydrothermal process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectra, and thermal analyses have been used to characterize the obtained molybdenum oxide nanomaterials. By use of cetyltrimethylammonium bromide as the structure-directing template, novel molybdenum oxide nanofibers with triple interlayer distances of 2.84, 2.66, and 2.46 nm have been obtained. The nanofibers have diameters of 20-100 nm and length up to 20 microm. The growth of multilamellar molybdenum oxide nanofibers can be interpreted by the combination of surfactant/inorganic self-assembly process and host/guest intercalation chemistry. On the basis of the X-ray diffraction and infrared results, a possible arrangement of surfactant in the interlayer space of molybdenum oxide by bilayer micelles with different tilt angles has been proposed. In addition, the thermal stability of surfactant has been improved by intercalation. Moreover, molybdenum oxide nanobelts with two kinds of interlayered structures were also produced in the presence of n-alkylamines (n = 12, 14, 16, and 18) following a similar method, these nanobelts show length up to more than 10 microm, width ranging between 200 and 600 microm, and width-to-thickness ratios of about 3-12. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains.     

Study of the thermal properties of polyester composites loaded with oriented carbon nanofibers using the front-face flash method

In this work, we have prepared polyester resin based composites, loaded with carbon nanofibers decorated with magnetite nanoparticles (m-CNF) in several volumetric concentrations covering from 0 to 3.25% and oriented applying a constant magnetic field before polymerization. A study of the heat transfer along the direction of the alignment of the fibers was performed by measuring the in-depth thermal diffusivity and thermal effusivity using the laser flash method in the front-face configuration. For the maximum volumetric concentration of aligned nanofibers along the thickness of the sample, an improvement of 80% of the thermal conductivity above the thermal conductivity of the polyester resin was observed. In contrast, the increment of the thermal conductivity was only of 20% above the value of the matrix for samples with non-oriented carbon nanofibers. The effects of the m-CNF and their orientation on the effective thermal conductivity of the composites were analyzed using a simple theoretical model, which takes into account the thermal mismatch between the matrix and the fillers, as well as the aspect ratio of the embedded fibers.     

Strongly Veined Carbon Nanoleaves as a Highly Efficient Metal‐Free Electrocatalyst

Effective integration of one‐dimensional carbon nanofibers (CNF) and two‐dimensional carbon sheets into three‐dimensional (3D) conductive frameworks is essential for their practical applications as electrode materials. Herein, a novel “vein‐leaf”‐type 3D complex of carbon nanofibers with nitrogen‐doped graphene (NG) was prepared through a simple thermal condensation of urea and bacterial cellulose. During the formation of the 3D complex CNF@NG, the graphene species was tethered to CNF via carbon–carbon bonds. Such an interconnected 3D network facilitates both the electron transfer and mass diffusion for electrochemical reactions.     

Electrospun fibers from poly(methyl methacrylate)/vapor grown carbon nanofibers

Electrospinning has been used to obtain poly(methyl methacrylate) (PMMA) microfibers and nanofibers and PMMA/vapor grown carbon nanofibers (VGCNFs or CNFs) composite fibers with micrometer and nanometer size diameters. Thermogravimetric analysis (TGA) indicated that addition of CNFs caused a decrease in the thermal stability of the composite fibers. Scanning electron microscopy (SEM) was used to confirm the micro‐ and nano‐ nature of the fibers and transmission electron microscopy (TEM) was utilized to confirm the presence of CNFs embedded within the polymer matrix and along the surface. Copyright © 2006 John Wiley & Sons, Ltd.     

Carbon nanofibers grown on sodalime glass at 500°C using thermal chemical vapor deposition

Carbon nanofibers are grown homogeneously on a large area of nickel-deposited sodalime glass substrate by thermal chemical vapor deposition of acetylene at 500°C. The diameters of carbon nanofibers are uniformly distributed in the range between 50 and 60 nm. Most of the carbon nanofibers are curved or bent in shape, but some fractions are twisted. They consist of defective graphitic sheets with a herringbone morphology. The maximum emission current density from the carbon nanofibers is 0.075 mA/cm² at 16 V/μm, which is sufficient for commercializing the carbon-nanofibers-based field emission displays.     

Cyclization and carbonization of anionic polyacrylonitrile in the presence of carbon nanofibers

Composites based on anionic polyacrylonitrile and carbon nanofibers were studied by X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, and electron microscopy. The effect of carbon nanofibers on the specific features of cyclization and carbonization of anionic polyacrylonitrile at temperatures of to 550°C was studied.     

Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: electrospun composite nanofiber sheets

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.     

Spectroscopic investigations on polypropylene‐carbon nanofiber composites. I. Raman and electron spin resonance spectroscopy

Isotactic polypropylene‐vapor grown carbon nanofiber composites containing various fractions of carbon nanofibers, ranging from 0 to 20 wt %, have been prepared. Raman spectroscopy was used to analyze the effect of the dispersion of carbon nanofibers within polypropylene and the interactions between carbon nanofibers and macromolecular chains. The as‐recorded Raman spectra have been successfully fitted by a linear convolution of Lorentzian lines. Changes of the Raman lines parameters (position, intensity, width, and area) of polypropylene and carbon nanofibers were analyzed in detail. The Raman spectra of the polymeric matrix—at low concentrations of nanofibers—show important modifications that indicate strong interactions between carbon nanofibers and the polymeric matrix reflecting by vibrational dephasing of macromolecular chains. The Raman spectrum of carbon nanofibers is sensitive to the loading with carbon nanofibers, showing changes of the resonance frequencies, amplitudes, and width for both D‐ and G‐bands. Raman data reveals the increase of the disorder, as the concentration of carbon nanofibers is increased. The presence of the typical ESR line assigned to conducting electrons delocalized over carbon nanofibers is confirmed and the presence of a spurious magnetic line due to catalyst's residues is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1644–1652, 2009