Carbon Nanocoils Research Articles

A molecular dynamics study of the mechanical properties of a double-walled carbon nanocoil

Molecular dynamics simulation was used to investigate the mechanical properties of (5,5), and (10,10) single-walled nanocoils, as well as (5,5)@(10,10) double-walled carbon nanocoils (CNCS). The second reactive empirical bond order potential was employed to model the interaction between carbon atoms. The atomic slip vector and sequential slip vector were used to investigate the structural variations at different strains during the tension process. The yield stress, maximum tensile strength, and Young’s modulus were determined from the tensile stress–strain profiles. The results show that the nanocoils have superelastic characteristics and have a high strength similar to that of carbon nanotube with same chirality.

Laser Driven Paraffin Microsphere Transportation on a Single Carbon Nanocoil

Laser driven mass transportation on a single carbon nanocoil (CNC) has been investigated, by regulating the controlling current and the laser focus position. It is found that a paraffin microsphere on a single CNC can be removed by the irradiation of an infrared laser beam on the CNC body near themicrosphere. This phenomenon is explained by a thermal driven forceresulted by a temperature gradient along the CNC around the irradiation spot wherethe laser energy is transformed into thermal energy.

Investigation on Fe-Sn-O Catalyst Activity for the Growth of Carbon Nanocoils

We have investigated the relationship between the catalyst and the growth of CNCs. It is found that with the increase of deposition time the yield of CNCs gradually increased, while their growth rate decreased exponentially. The short reaction time would lead to the growth of CNCs with smaller coil diameters, however, CNCs with larger coil diameters are increased gradually after a long-time reaction. The Fe-Sn-O catalyst particles are not uniform in sizes. It is considered that CNCs with smaller/larger coil diameters can be synthesized from the smaller/larger catalyst particles. A further fitting of the growth curve indicates that the as-prepared catalyst particles have different activities. It can be inferred that catalyst particles with different sizes have different catalytic activities. The smaller catalyst particles have a higher activity but a shorter lifetime, and the coil diameter of CNCs synthetized from it is smaller.

Nanostructured Carbon Materials as Supports in the Preparation of Direct Methanol Fuel Cell Electrocatalysts

Different advanced nanostructured carbon materials, such as carbon nanocoils, carbon nanofibers, graphitized ordered mesoporous carbons and carbon xerogels, presenting interesting features such as high electrical conductivity and extensively developed porous structure were synthesized and used as supports in the preparation of electrocatalysts for direct methanol fuel cells (DMFCs). The main advantage of these supports is that their physical properties and surface chemistry can be tailored to adapt the carbonaceous material to the catalytic requirements. Moreover, all of them present a highly mesoporous structure, diminishing diffusion problems, and both graphitic character and surface area can be conveniently modified. In the present work, the influence of the particular features of each material on the catalytic activity and stability was analyzed. Results have been compared with those obtained for commercial catalysts supported on Vulcan XC-72R, Pt/C and PtRu/C (ETEK). Both a highly ordered graphitic and mesopore-enriched structure of these advanced nanostructured materials resulted in an improved electrochemical performance in comparison to the commercial catalysts assayed, both towards CO and alcohol oxidation.

Water molecular flow control with a (5,5) nanocoil switch

Molecular dynamics simulation was employed to investigate the diffusion behaviors of water molecules within a (5,5) carbon nanocoil (CNC) at different tensile strains, the length and coil diameter of CNC are 22 and 6.83 Ǻ, respectively. Condensed-phase, optimized molecular potentials for atomistic simulation studies were employed to model the interaction between atoms. The results show that the diffusion in the axial direction can be enhanced by the tensile strain and the water molecule flow can be blocked at a higher strain once the deformed areas appear at the higher strain. Moreover, the deformed (5,5) CNC at strain of 2.8 can recover its original structure at strain of 0, indicating that the adjustment of diffusion coefficient is repeatable by applying different strains in the axial direction.

An active surface enhanced Raman scattering substrate using carbon nanocoils

Abstract

Growth of multiwall carbon nanocoils using Fe catalyst films prepared by ion sputtering – ERRATUM

In Li et al.1, Figs. 2–5 are incorrectly ordered and labeled.

Controllable synthesis of carbon coils and growth mechanism for twinning double-helix catalyzed by Ni nanoparticle

A simple approach using ∼90nm Ni nanoparticles to tune the growth of carbon fibers is developed basing on the bottom-up regulation in this study. By adjusting the preparing temperature and atmospheric composition, the nickel-containing catalysts with specific sizes and shapes are alternately prepared from 90nm to 500nm. The straight carbon nanofibers and three kinds of carbon coils (single-helix carbon nanocoils, single-helix carbon microcoils and twinning double-helix carbon microcoils) with the coil diameter ranging from 150nm to 3μm are achieved by using the as-prepared catalyst. The relationship between the carbon coil and catalyst particle, and the growth mechanism for different kinds of helices are discussed in details. The results suggest that catalytic anisotropy come from growing tendency and rate of carbon deposition on the facets, edges and vertices of catalyst grain. The twinning structure exists in each fiber of the double-helix carbon microcoils regardless of circular or flat fiber, which is separated by the tip of the catalyst particle due to the different rate of carbon deposition at edge and vertex.

Growth of multiwall carbon nanocoils using Fe catalyst films prepared by ion sputtering

Abstract

Supporting PtRu catalysts on various types of carbon nanomaterials for fuel cell applications

PtRu catalysts were supported on five types of carbon nanomaterials of various shapes, sizes, and graphitic properties and the catalyst supports evaluated. The carbon nanomaterial used included three types of nanoparticles: Arc Black (AcB), Vulcan XC-72 (Vulcan) and graphene oxide (GO), and two types of nanofibers: carbon nanocoil (CNC) and carbon nanotube (CNT). Pt and Ru were supported by the reduction method using sodium borohydride. The metal catalyst loading was confirmed by thermo-gravimetric analysis (TGA), electron microscopy, and X-ray diffraction (XRD). Transmission electron microscopy (TEM) and XRD revealed that the diameter of PtRu catalyst nanoparticles loaded on reduced GO (rGO) and AcB were ~2 nm and was the smallest among all the samples. Shifts in Pt (111) XRD peaks of CNC and CNT were larger than those of AcB, Vulcan, and rGO. These results suggest that the diameters of catalyst nanoparticles became smaller by loading on the carbon nanoparticles with a large surface area including rGO, AcB, and Vulcan. Loading onto the carbon nanofibers enhanced the degree of PtRu alloying.

Comparative study of Pt catalysts supported on different high conductive carbon materials for methanol and ethanol oxidation

Different carbon materials with high electrical conductivity have been studied as electrocatalyst support for direct alcohol fuel cells (DAFCs). The aim of the work was to establish the influence of the support on the catalyst properties and to improve their efficiency in the fuel cell. Carbon nanofibers (CNFs), carbon nanocoils (CNCs) and ordered mesoporous carbons (gCMK-3) have been used for synthesizing platinum catalysts by the polyol method. Results have been compared with those obtained for a platinum catalyst supported on Vulcan XC-72R, prepared by the same method, and for the commercial Pt/C catalyst from E-TEK. It has been demonstrated that novel carbon supports could help to oxidize CO adsorbed on platinum particles more easily than the commercial carbon support and improve the alcohol oxidation reaction, both in terms of onset potential and current density. The catalyst supported on gCMK-3 carbon resulted to be the most effective in both the methanol and ethanol oxidation, which can be attributed to its ordered structure and high electrical conductivity.

Carbon nanocoils as catalysts support for methanol electrooxidation: A Differential Electrochemical Mass Spectrometry (DEMS) study

Carbon nanocoils (CNCs) were used to prepare Pt and Pt–Ru catalysts by the sodium borohydride (BM), methanol (MM) and polyol (EGM) solution reduction methods. Their physicochemical properties were studied by means of energy dispersive X-ray analysis, X-ray diffraction and transmission electron microscopy, whereas the electrochemical activity towards carbon monoxide and methanol oxidations was studied using cyclic voltammetry and chronoamperometry. Furthermore, differential electrochemical mass spectrometry experiments were carried out to study the reaction mechanisms. Results were compared with those obtained for the commercial Pt/C and PtRu/C catalysts from E-TEK. It is shown that choosing an adequate synthesis procedure, better electrocatalytic behaviours towards CO and methanol oxidation can be obtained by using carbon nanocoils as support material.

Synthesis of carbon nanocoil forests on BaSrTiO3 substrates with the aid of a Sn catalyst

A simple route for the Sn-assisted synthesis of carbon nanocoils (CNCs) by chemical vapor deposition of acetylene on polycrystalline BaSrTiO3 (BST) substrates is reported. In this study, high-quality CNC forests have been synthesized on BST substrates with the presence of Sn. The morphologies and qualities of the CNCs were characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy, while the structures and compositions of catalysts were investigated by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Structural control over the CNCs was achieved by simply altering the Sn concentration or acetylene flow rates. This study demonstrates that Sn can act as an efficient catalyst for CNC synthesis in conjunction with either perovskite oxides (BST) or transition metals (Fe).

The effect of a tin oxide buffer layer for the high yield synthesis of carbon nanocoils

In this paper, we show that the efficiency in the growth of carbon nanocoils is significantly improved by introducing a SnO2 buffer layer. Carbon nanocoils were synthesized by chemical vapor deposition using an Fe–Mg–Co or Fe–Mg–Co–Sn catalyst supported on an Al2O3 substrate coated with a 30nm SnO2 buffer layer. The carbon nanocoil growth rate improved by more than 200% compared with the non-coated substrate when using Fe–Mg–Co–Sn or Fe–Mg–Co catalyst layers 600 or 300nm thick, respectively. The byproduct layer was also reduced significantly, which results in more than 50% gain in the consumption of carbon source gas during the synthetic process. The role for an external Sn supply from the buffer layer is discussed based on the experimental results.

Manufacturing of Electric Double-layer Capacitors using Carbon Nanocoils and Evaluation of their Specific Capacitance at a High Scan Rate

Electric double-layer capacitors (EDLCs) have problems that the specific capacitance decreases by increasing scan rate. In this study, activated carbon (AC) and various carbon nanomaterials are compared by their specific capacitances. Carbon nanomaterials used were arc-black (AcB) which was prepared by an arc discharge and carbon nanocoil (CNC) which was prepared by a chemical vapor deposition. CNC and AcB showed lower charge transfer resistance than AC in the measurement of electrochemical impedance spectroscopy (EIS). This explains that the EDLCs composed of CNC and AcB kept their specific capacitance at a high scan rate.

Microwave Absorption Properties of Carbon Nanocoils Coated with Highly Controlled Magnetic Materials by Atomic Layer Deposition

In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

K and Au Bicatalyst Assisted Growth of Carbon Nanocoils from Acetylene: Effect of Deposition Parameters on Field Emission Properties

We demonstrated the growth of carbon nanocoils (CNCs) via chemical vapor deposition (CVD) using Au and K metals as the catalysts to assist the thermal decomposition of C(2)H(2). Typical CNCs (wire diameter: 50-80 nm, coil diameter: 110-140 nm, pitch: 100-200 nm, tens of micrometers), identified as amorphous coiled carbon fibers by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were grown at proper combinations of reaction parameters. Au nanoparticles (NPs), identified by energy dispersion X-ray spectroscopy (EDX) and electron diffraction (ED), were located at the tips of the CNCs. The observations suggested that a tip-growth mechanism involving the Au NPs as the nucleation sites was in operation. In the reaction, the liquid-phase K metal assisted the decomposition of C(2)H(2) by lowering the reaction temperature. We propose that acetylide and hydride intermediates were formed in the reaction. Further decomposition of the acetylide intermediates generated solid-phase carbon to grow the CNCs. Effects of varying the reaction conditions on the CNC growth were investigated. On the basis of the results, a Au and K bicatalyst enhanced tip-growth vapor-liquid-solid (VLS) mechanism was proposed to rationalize the CNC formation process. Electron field emission (EFE) characteristics of the CNCs were studied. The best EFE result showed a turn-on field (E(to)) of 3.78 V/μm and a field enhancement factor (β) of 1852. In addition, the current density (J) was as high as 43 mA/cm(2) at 6.87 V/μm. The data suggest that the CNCs could be employed for field emission device applications.

Near-infrared response of a single carbon nanocoil

The near-infrared photoresponse of a single suspended carbon nanocoil (CNC) is investigated. Under the irradiation of a 785 nm laser beam, the photoresponse is generated in the voltage-biased CNC. At a voltage of 50 mV, the ratio of the conductance change to the initial conductance, which is defined as the sensitivity in this paper, can reach 22% and the typical response time is 5 ms. It is found from the changes of photoresponse with pressure and with the laser power that the photoresponse of the CNC is mainly attributed to the bolometric effect. Because of the increase of Joule heating, the sensitivity reduces with the elevation of the bias voltage. However, the responsivity increases with the increase of the bias voltage, which is opposite to the change of the sensitivity. The maximum responsivity of the single CNC IR sensor is 0.22 A W(-1).

Versatile Bottom‐up Approach to Stapled π‐Conjugated Helical Scaffolds: Synthesis and Chiroptical Properties of Cyclic o‐Phenylene Ethynylene Oligomers

Spring loaded: the smallest members of a family of carbon nanocoils (CNCs), adopting a fixed helical structure, have been synthesized by introduction of one or two staples in o-phenylene ethynylene oligomers. The chiroptical responses of the systems having enantiopure L-tartrate-derived staples confirmed the induced helicity. Theoretical studies suggest that these CNCs are pseudoelastic.

Bulb-Shaped Field Emission Lamps Using Carbon Nano-Coil Cathodes

Bulb-shaped field emission lamps (FELs) using carbon nano-coil (CNC) cathodes were fabricated and their performances were characterized. A straight steel wire grown with CNCs was placed on the symmetry axis in the bulb as the cathode. The anode was defined by a Ni film deposited on the bottom hemisphere of a 60-mm-diameter glass bulb. And a phosphor layer was coated on the Ni film for light generation via cathodoluminescence. A numerical simulation model for this geometry also was constructed. The simulated current-voltage curves agree well with the experimental results and reproduce the trends observed in the experiment. The effects of varying the length and diameter of the cathode were studied. Both experiment and simulation showed that the total field emission current increases with the cathode length and decreases with the cathode diameter. Although the design is simple and inherently low-cost, good uniformity of light emission over the entire anode was demonstrated.