Tips Of Carbon Nanofibers Research Articles

Pseudo-topotactic growth of diamond nanofibers

We report pseudo-topotactic growth of single-crystal diamond fibers by nanosecond laser melting of amorphous carbon nanofibers (CNFs) and crystalline multi-wall carbon nanotubes (MWCNTs). A rapid laser melting in a super undercooled state and subsequent quenching convert the tips of CNFs and MWCNTs into phase-pure <110> nanodiamonds along the growth directions. Subsequent laser pluses melt regions below <110> nanodiamonds that provide seeds for epitaxial growth. By repeating this process, the length of <110> nanodiamond fibers can be increased, as each pulse results in ∼50 nm nanodiamond region, depending upon the initial size of CNFs and MWCTs. This conversion process can be carried at ambient temperature and pressure in air. The epitaxial nature of <110> nanodiamond fibers has been confirmed by systematic electron-back-scatter-diffraction studies along the fiber in high-resolution scanning electron microscopy, and high-resolution TEM imaging and diffraction. The nature of C–C bonding characteristics was studied by high-resolution electron-energy-loss spectroscopy to establish the formation of diamond phase by the characteristic peak at 292 eV for sp3 bonding (σ∗), and absence of 284 eV peak for sp2 (π∗) graphitic bonding. The characteristic diamond Raman peak at 1332 cm−1 is found to downshift to 1321 cm−1 because of phonon confinement in nanodiamonds associated with nanofibers. These nanodiamond structures can be doped with both n- and p-type dopants with concentrations far higher than thermodynamic solubility limit due to solute trapping during quenching from the liquid phase. Thus, these nanodiamond structures provide ideal platform for nanosensing, computing and communication, including efficient field emitting devices.

Direct conversion of carbon nanofibers into diamond nanofibers using nanosecond pulsed laser annealing.

Here, we show the direct conversion of carbon nanofibers (CNFs) into diamond nanofibers (DNFs) by irradiating CNFs with an ArF nanosecond laser at room temperature and atmospheric pressure. The nanosecond laser pulses melt the tips of CNFs into a highly undercooled state, and their subsequent quenching results in the formation of DNFs. This formation of DNFs is dependent on the degree of undercooling which is controlled by nanosecond laser energy density and one-dimensional heat flow characteristics in CNFs. The conversion process starts at the top and extends with the number of pulses. Therefore, our highly non-equilibrium nanosecond laser processing opens a new avenue for the synthesis of exciting pure and doped diamond structures at ambient temperatures and pressures for a variety of applications.

Ternary Platinum-Copper-Nickel Nanoparticles Anchored to Hierarchical Carbon Supports as Free-Standing Hydrogen Evolution Electrodes.

Developing cost-effective and efficient hydrogen evolution reaction (HER) electrocatalysts for hydrogen production is of paramount importance to attain a sustainable energy future. Reported herein is a novel three-dimensional hierarchical architectured electrocatalyst, consisting of platinum-copper-nickel nanoparticles-decorated carbon nanofiber arrays, which are conformally assembled on carbon felt fabrics (PtCuNi/CNF@CF) by an ambient-pressure chemical vapor deposition coupled with a spontaneous galvanic replacement reaction. The free-standing PtCuNi/CNF@CF monolith exhibits high porosities, a well-defined geometry shape, outstanding electron conductivity, and a unique characteristic of localizing platinum-copper-nickel nanoparticles in the tips of carbon nanofibers. Such features render PtCuNi/CNF@CF as an ideal binder-free HER electrode for hydrogen production. Electrochemical measurements demonstrate that the PtCuNi/CNF@CF possesses superior intrinsic activity as well as mass-specific activity in comparison with the state-of-the-art Pt/C catalysts, both in acidic and alkaline solutions. With well-tuned composition of active nanoparticles, Pt42Cu57Ni1/CNF@CF showed excellent durability. The synthesis strategy reported in this work is likely to pave a new route for fabricating free-standing hierarchical electrodes for electrochemical devices.

Method for Measuring the Distribution of Adhesion Forces on Continuous Nanoscale Protrusions Using Carbon Nanofiber Tip on a Scanning Probe Microscope Cantilever

The adhesion force on surfaces has received attention in numerous scientific and technological fields, including catalysis, thin-film growth, and tribology. Many applications require knowledge of the strength of these forces as a function of position in three dimensions, but until now such information has only been theoretically proposed. Here, we demonstrate an approach based on scanning probe microscopy that can obtain such data and be used to image the three-dimensional surface force field of continuous nanoscale protrusions. We present adhesion force maps with nanometer and nanonewton resolution that allow detailed characterization of the interaction between a surface and a thin carbon nanofiber (CNF) rod synthesized by plasma-enhanced chemical vapor deposition (PECVD) at the end of a tip on a scanning probe microscope cantilever in three dimensions. In these maps, the positions of all continuous nanoscale protrusions are identified and the differences in the adhesive forces among limited areas at inequivalent sites are quantified.

ChemInform Abstract: Recent Advances in Synthesis of Reshaped Fe and Ni Particles at the Tips of Carbon Nanofibers and Their Catalytic Applications

AbstractReview: 90 refs.

Lateral distribution of field-emitted electrons from a carbon nanofiber array: A theoretical calculation

The authors have calculated the lateral distribution of field emitted electrons from a carbon nanofiber (CNF) array—a quantity of importance in designing field emission displays—by calculating the electron distribution from an individual CNF and subsequently summing the contribution from all individual CNFs. The authors have not obtained the absolute value of the current but only its relative distribution in space. The full width at half maximum of the lateral distribution has been examined with respect to the following parameters: 1) the CNF tip radius, 2) the anode to cathode distance, and 3) the cathode to anode potential difference. Reasonable agreement with experimental results is obtained.

In Situ Production of Ni Catalysts at the Tips of Carbon Nanofibers and Application in Catalytic Ammonia Decomposition

Ni-carbon nanofibers (Ni-CNFs) catalysts were synthesized in situ by the decomposition of carbon-containing gases (i.e., CH4, CO, and C2H4) over Ni/Al2O3 catalyst and directly used to catalyze ammonia decomposition. The results showed that Ni nanoparticles were found to locate at the tips of CNFs when using CH4 and CO as carbon sources, while they located at the roots of CNFs when using C2H4 as a carbon source. For ammonia decomposition, Ni catalysts at the tips of CNFs showed higher activity, which could be due to the more accessible surfaces to the reactants. Interestingly, the Ni catalyst at the tips of CNFs with CH4 as a carbon source exhibited higher activity than that with CO as a carbon source, even though the former catalyst had a larger average particle size. The possible mechanism was given by combining characterization results with our previous simulation results. Finally, when using CH4 as a carbon source, the effect of the Ni-CNFs catalysts with different growth times on the activity was further studied.

Tuning the Acid/Metal Balance of Carbon Nanofiber‐Supported Nickel Catalysts for Hydrolytic Hydrogenation of Cellulose

Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/CNFs were characterized by various analytical methods. To prepare a selective Ni/CNF catalyst, the influences of the nature of oxidation agent, Ni activation, and Ni loading were investigated. Under the applied reaction conditions, the best result, that is, 76 % yield in hexitols with 69 % sorbitol selectivity at 93 % conversion of cellulose, was obtained on a 7.5 wt % Ni/CNF catalyst prepared by chemical vapor deposition of CH(4) on a Ni/γ-Al(2)O(3) catalyst, followed by oxidation in HNO(3) (twice for 1 h at 383 K), incipient wetness impregnation, and reduction at 773 K under H(2). This preparation method leads to a properly balanced Ni/CNF catalyst in terms of Ni dispersion and hydrogenation capacity on the one hand, and the number of acidic surface-oxygen groups responsible for the acid-catalyzed hydrolysis on the other.

High-Resolution Imaging of Plasmid DNA in Liquids in Dynamic Mode Atomic Force Microscopy Using a Carbon Nanofiber Tip

High-Resolution Imaging of Plasmid DNA in Liquids in Dynamic Mode Atomic Force Microscopy Using a Carbon Nanofiber Tip

High-Resolution Imaging of Plasmid DNA in Liquids in Dynamic Mode Atomic Force Microscopy Using a Carbon Nanofiber Tip

To understand the motion of DNA and DNA complexes, the real-time visualization of living DNA in liquids is quite important. Here, we report the high-resolution imaging of plasmid DNA in water using a rapid-scan atomic force microscopy (AFM) system equipped with a carbon nanofiber (CNF) probe. To achieve a rapid high-resolution scan, small SiN cantilevers with dimensions of 2 (width) × 0.1 (thickness) × 9 µm (length) and a bent end (tip view structure) were employed as base cantilevers onto which single CNFs were grown. The resonant frequencies of the cantilever were 1.5 MHz in air and 500 kHz in water, and the spring constant was calculated to be 0.1 N/m. Single CNFs, typically 88 nm in length, were formed on an array of the cantilevers in a batch process by the ion-irradiation method. An AFM image of a plasmid DNA taken in water at 0.2 fps (5 s/image) using a batch-fabricated CNF-tipped cantilever clearly showed the helix turns of the double strand DNA. The average helical pitch measured 3.4 nm (σ: 0.5 nm), which was in good agreement with that determined by the X-ray diffraction method, 3.4 nm. Thus, it is presumed that the combined use of the rapid-scan AFM system with the ion-induced CNF probe is promising for the dynamic analysis of biomolecules.

Selective Bifunctional Catalytic Conversion of Cellulose over Reshaped Ni Particles at the Tip of Carbon Nanofibers

Access to cellulose: Carbon nanofibers grown over Ni supported on γ-Al2O3 act as efficient catalysts for the one-pot conversion of cellulose to sugar alcohols, owing to the enhanced accessibility of the water-insoluble substrate towards the active catalytic sites. The new catalyst design concept yields unprecedented results for selective cellulose conversion using inexpensive Ni catalysts.

Catalytic synthesis of carbon nanofibers and nanotubes by the pyrolysis of acetylene with iron nanoparticles prepared using a hydrogen-arc plasma method

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were synthesized at different temperatures by the catalytic pyrolysis of acetylene with iron nanoparticles prepared using a hydrogen-arc plasma method. The obtained carbon nanomaterials were characterized by transmission electron microscopy and field-emission scanning electron microscopy. An iron nanoparticle was always located at the tip of CNFs or CNTs, whose diameter was approximately identical with the diameter of the iron nanoparticle. The structures of the products were closely related to the reaction temperature, and could be changed from fibers to tubes by simply increasing the temperature. CNFs were obtained at the reaction temperature of 550–650 °C. When the reaction temperature was increased to 710–800 °C, CNTs were obtained.

Field emission from a single carbon nanofiber at sub 100nm gap

The authors report the electron field emission from a single carbon nanofiber (CNF) over a range of anode to CNF tip separations of 20–5500nm. Our results show that the field enhancement factor γ is associated with the electrode separation (S). The modified Miller equation is a reasonable empirical model to describe the behavior of γ, which varies with S over a large range of values. The γ approaches to an asymptotic value of 415 or 1 when S is very large or very small as compared to the length of the CNF, respectively. The maximum field emission current sustained by the single CNF without causing damage was estimated to be as high as 15μA.

Carbon Nanofiber Electrodes and Controlled Nanogaps for Scanning Electrochemical Microscopy Experiments

The electrochemical behavior of electrodes made by sealing carbon nanofibers in glass or with electrophoretic paint has been studied by scanning electrochemical microscopy (SECM). Because of their small electroactive surface area, conical geometry with a low aspect ratio and high overpotential for proton and oxygen reduction, carbon nanofiber (CNF) electrodes are promising candidates for producing electrode nanogaps, imaging with high spatial resolution and for the electrodeposition of single metal nanoparticles (e.g., Pt, Pd) for studies as electrocatalysts. By using the feedback mode of the SECM, a CNF tip can produce a gap that is smaller than 20 nm from a platinum disk. Similarly, the SECM used in a tip-collection substrate-generation mode, which subsequently shows a feedback interaction at short distances, makes it possible to detect a single CNF by another CNF and then to form a nanometer gap between the two electrodes. This approach was used to image vertically aligned CNF arrays. This method is useful in the detection in a homogeneous solution of short-lifetime intermediates, which can be electrochemically generated at one electrode and collected at the second at distances that are equivalent to a nanosecond time scale.

Carbon coated monoliths as support material for a lactase from Aspergillus oryzae: Characterization and design of the carbon carriers

Tunable carbon-coated monoliths as carriers for enzyme adsorption are presented. Depending on enzyme properties and reaction conditions, the carrier can be adjusted to optimize enzyme loading. Carbon–ceramic composites were prepared by sucrose carbonization, polyfurfuryl alcohol (PFA) carbonization, and by growth of carbon nanofibers (CNFs) over deposited Ni. All carbons were treated in air and subsequently in 1 M HNO 3, and analyzed with respect to porosity, morphology and surface chemistry. The composites were applied as a carrier for a lactase from Aspergillus oryzae. The CNFs proved to be the best carrier, with respect to enzyme loading. Untreated fibers could adsorb 115 mg lactase/g carbon. After air/HNO 3 treatment this value increased to 360 mg/g. Porosity was not affected by air and air/HNO 3 treatment, implying that lactase adsorption mainly depends on surface chemistry. A clear trend was observed between oxygen content of different CNFs and lactase adsorption. Ni could be removed completely from the fiber tips of CNFs by different concentrated acids—nitric acid, hydrochloric acid, and oxalic acid. However, with HCl and HNO 3 the porosity and surface chemistry were affected. Treatment in oxalic acid removed Ni from the tips by complexation, without changing the porosity. For these samples, 30% of the Ni remained present in the sample as residual NiC 2O 4. This was confirmed by TGA-MS and XRD.