Elevated performances of SnS anodes with MWNTs as conductive agent for rechargeable lithium-ion batteries

SnS nanoparticles were mechanochemically synthesized and fabricated into electrodes with two kinds of conductive agents, acetylene black and multi-wall carbon nanotubes (MWNTs), respectively. The morphology and structure of as-synthesized SnS powder were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical properties of as-prepared electrodes were investigated by discharge–charge test, cyclic voltammogram, and electrochemical impedance spectrum. By comparing the variation of the charge-transfer impedance R _ct at different discharge states, it was found that the value of R _ct of the electrode with MWNTs as conductive agent was less than that of the electrode with acetylene black as conductive agent. The electrode with MWNTs as conductive agent had preferable cycling performances, which was believed to be attributed to the tenacity and good conductivity of MWNTs.     

Electrical properties of boron-doped MWNTs synthesized by hot-filament chemical vapor deposition

We have synthesized a large amount of boron-doped multiwalled carbon nanotubes (MWNTs) by hot-filament chemical vapor deposition. The synthesis was carried out in a flask using a methanol solution of boric acid as a source material. The scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy were performed to evaluate the structural properties of the obtained MWNTs. In order to evaluate the electrical properties, temperature dependence of resistivity was measured in an individual MWNTs with four metal electrodes. The Raman shifts suggest carrier injection into the boron-doped MWNTs, but the resistivity of the MWNTs was high and increased strongly with decreasing temperature. Defects induced by the plasma may cause this enhanced resistivity.     

Vertically aligned peapod formation of position-controlled multi-walled carbon nanotubes (MWNTs)

We have succeeded in making peapod structures with vertically aligned multi-walled carbon nanotubes (MWNTs), grown on a silicon substrate using hot filament chemical vapor deposition. Opening the tips of the MWNTs was performed at 600 C using oxygen and then C₆₀ molecules were deposited on them to fill their inner spaces. We confirmed that the MWNTs were open at the tips and filled with C₆₀ molecules using transmission electron microscopy. In addition, it has been determined that MWNTs can be filled with other materials, such as molybdenum oxide.     

Electrically Conductive Multiwall Carbon Nanotubes/Poly(vinyl alcohol) Composites with Aligned Porous Morphologies

Electrically conductive multiwall carbon nanotubes (MWNTs)/poly(vinyl alcohol) (PVA) composites with aligned porous structure were obtained by a directional freeze-drying process. The results show that the morphologies of the MWNTs/PVA composite can be tailored by adding different contents of MWNTs in the PVA matrix. Because of the aligned porous structure of the MWNTs/PVA composites, the conductivity property of MWNTs/PVA composite does not coincide absolutely with the universal percolation theory. In the aligned porous MWNTs/PVA composites, the existence of the micro-pores destroys the uniform distribution of the conductive network along the direction perpendicular to the aligned pores and results in a nonuniform distribution conductive network. When being used to monitor flowing vapors in pipes, compared with a film sensor with the thickness from several decades to hundreds of microns, the aligned porous conductive MWNTs/PVA composite with micron-sized pores should be a much better sensor.     

Studies on the Nonisothermal Crystallization Behavior of Polypropylene/Multiwalled Carbon Nanotubes Nanocomposites

Polypropylene/multiwalled carbon nanotubes (PP/MWNTs) nanocomposites were prepared by a melt compounding process. The morphology and nonisothermal crystallization of these nanocomposites were investigated by means of optical microscopy, scanning electron microscopy, and differential scanning calorimetry. Scanning electron microscope micrographs of PP/MWNTs composite showed that the MWNTs were well dispersed in the PP matrix and displayed a clear nucleating effect on PP crystallization. Avrami theory, modified by Jeziorny and Mo's method, was used to analyze the kinetics of the nonisothermal crystallization process. It was found that the addition of MWNTs improved the crystallization rate and increased the peak crystallization temperature of the PP/MWNTs nanocomposites as compared with PP. The results show that the Jeziorny theory and Mo's method successfully describe the nonisothermal crystallization process of PP and PP/MWNTs nanocomposites.     

磁场辅助热处理金属化碳纳米管场发射性能

利用化学镀方法对多壁碳纳米管(multi-walled carbon nanotubes,MWNTs)表面金属化镀镍(MWNTs/Ni),采用丝网印刷制备MWNTs/Ni场发射阴极,并在磁场辅助下热处理所得阴极,研究磁场辅助热处理对MWNTs/Ni阴极的场发射性能的影响,经300mT磁场辅助热处理的MWNTs/Ni的场发射阴极开启场强约为0.80V·μm~(-1),场增强因子β约为16068,对单根MWNTs/Ni在磁场中的受力情况进行建模分析,实验结果表明:磁场辅助热处理有助于提高MWNTs/Ni在阴极表面的直立分布,提高了MWNTs/Ni的场发射性能。     

Properties and Morphology of Poly(Lactic Acid)/Calcium Carbonate Whiskers Composites Prepared by a Vane Mixer based on an Extensional Flow Field

Binary composites of poly(lactic acid) (PLA)/calcium carbonate whiskers (CCW) with different weight fractions were prepared with a vane mixer based on extensional rheology. The mechanical properties, thermostability, crystallization behavior, rheology behaviors and micromorphology of the composites were analysed to study the effect of the CCW fibers on the composite's properties; a pure PLA sample was also prepared for comparison. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed that the CCW fibers had excellent compatibility with the PLA matrix and the CCW fibers were dispersed and distributed evenly in the PLA matrix under the action of the extensional flow field produced by the vane mixer. Differential scanning calorimetric (DSC) analysis showed that introducing a vane mixer into the PLA processing could increase the degree of crystallization (χ_c) of the composites significantly, and moderate CCW fibers adding could further increase its χ_c value. Thermogravimetric analysis (TGA) revealed that adding the CCW fibers reduced the thermostability of the composites. The G′, G″, η* and the torque, T_N, of the composites, obtained from rheology analyses, declined obviously, because of the hydrolysis and chains scission induced by residual water and fatty acid when the CCW content less than 4%. Tensile tests proved that filling moderate amounts of CCW fibers into PLA could increase its tensile strength and strain at break, increasing by 5% and 29.6%, respectively.     

Fabrication of high-performance supercapacitors based on transversely oriented carbon nanotubes

High-performance supercapacitors with organic electrolyte 1 M TEABF₄ (tetraethyl ammonium tetrafluoroborate) in PC (propylene carbonate) were fabricated and tested, based on multiwall carbon nanotubes (MWNTs) deposited by electrophoresis on three types of alternative substrates: aluminium foil, ITO (indium tin oxide) coated PET (polyethylene terephthalate) film and PET film. In all cases, SEM (scanning electron microscopy) and STEM (scanning transmission electron microscopy) micrographs demonstrated that protruding, transversely oriented MWNT structures were formed, which should increase the transverse conductivity of these MWNT electrodes. The best supercapacitor cell of MWNT electrodes deposited on aluminium foil displayed good transverse orientation of the MWNT structures as well as an in-plane MWNT network at the feet of the protruding structures, which ensured good in-plane conductivity. Capacitor cells with MWNT electrodes deposited either on ITO-coated PET film or on PET film demonstrated lower but still very good performance due to the high density of transversely oriented MWNT structures (good transverse conductivity) but some in-plane inhomogeneities. Capacitor cells with drop-printed MWNTs on aluminium foil, without any transverse orientation, had 16–30 times lower specific capacitance and 5–40 times lower power density than the capacitor cells with the electrophoretically deposited MWNT electrodes.     

Multi-walled carbon nanotubes supported Cu-doped ZnO nanoparticles and their optical property

Multi-walled carbon nanotubes (MWNTs)/Cu-doped ZnO composite powders were prepared by co-precipitation method, and were characterized by X-ray diffraction, electron microscopy, fluorescence spectrum, and ultraviolet spectrum. Experimental results show that the MWNTs can be modified by Cu-doped ZnO nanoparticles with hexagonal wurtzite structure after annealed at 450?°C, and the nanoparticle size is about 15?nm. Two ultraviolet (UV) peaks and a green band centered at about 510?nm are observed in the fluorescence spectrum of MWNTs/Cu-doped ZnO composite powder annealed at 450?°C. Furthermore, MWNTs and Cu doping significantly improve the UV absorption ability of ZnO.     

Multiwalled carbon nanotubes mass-produced by dc arc discharge in He–H2 gas mixture

Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H₂ gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼ ∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm², indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source.     

Synthesis of multiwall carbon nanotubes by chemical vapor deposition of ferrocene alone

Multiwall carbon nanotubes (MWNTs) filled with Fe nanoparticles (NPs) have been synthesized by thermal chemical vapor deposition of ferrocene alone as the precursor. The MWNTs were grown at different temperatures: 980 and 800 ^°C. Characterization of as-prepared MWNTs was done by scanning and transmission electron microscopy, and X-ray diffraction. The transmission electron microscopy study revealed that Fe NPs encapsulated in MWNTs grown at 980 and 800 ^°C are spherical and rod shaped, respectively. Room-temperature vibrating sample magnetometer studies were done on the two samples up to a field of 1 T. The magnetization versus magnetic field loop reveals that the saturation magnetization for the two samples varies considerably, almost by a factor of 4.6. This indicates that Fe is present in different amounts in the MWNTs grown at the two different temperatures.     

Synthesis, field emission and glucose-sensing characteristics of nanostructural ZnO on free-standing carbon nanotubes films

Free-standing multiwall carbon nanotubes (MWNTs) films were coated, using chemical vapor deposition method, with a thin layer of nanostructural ZnO. The morphology and crystal structure of the as-grown products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman scattering analyses. Field emission (FE) results demonstrated that the needle-like and spherical ZnO-MWNTs composite structure films possessed good performance with a turn-on field of 1.3, 2.2 V μm⁻¹ and a threshold field of 2.6, 4.5 V μm⁻¹, respectively. The glucose-sensing characteristic has also been studied. The multi-layer electrode (PDDA/GOx/ZnO/MWNTs) exhibited significant electrocatalysis to the oxidation and reduction of H₂O₂ than the PDDA/GOx/MWNTs electrode, which provided wide potential applications in clinical, environmental, and food analysis.     

High-Speed Melt Spinning of Polylactide/Poly(Butyleneterephthalate) Bicomponent Fibers: Mechanism of Fiber Structure Development and Dyeing Behavior

Bicomponent fibers consisting of polylactide (PLA) as the sheath and poly(butylene terephthalate) (PBT) as the core were produced by high-speed spinning to obtain materials suitable for medical clothing. The higher-order structure of the PLA fiber component appeared to exhibit simple, alternately stacked, uniaxially oriented amorphous and crystalline regions. Therefore, fairly large tanδ peaks were observed for single-component PLA fibers, even when the orientation-induced crystallization was achieved by high-speed spinning. By conjugating PLA with PBT, although limited mutual interference with the crystallization of each component occurred, both the PLA (Mw?=?170,000, L-lactide content?=?98.7%) and PBT (intrinsic viscosity?=?0.835-0.865 dL/g) could crystallize on a high-speed spinning line, and the proposed formation of a shish-kebab-like structure in the PBT component enhanced the thermal stability of the bicomponent fibers, particularly resulting in shrink-proof properties. The bicomponent fibers developed herein could be deeply dyed at 98?°C, with results comparable to those of industrial polyester, and peeling of the PLA skin layer was rarely observed, even when the dyed fibers were flattened by a rubbing force.     

Effect of Coagulation Bath DMSO Concentration on the Structure and Properties of Polyacrylonitrile (PAN) Nascent Fibers during Wet-Spinning

Polyacrylonitrile nascent fibers, as spun into the coagulation bath, were prepared by solution polymerization and wet-spinning, and a dimethyl sulphoxide (DMSO)/H ₂ O coagulation bath system was adopted. The effect of coagulation bath DMSO concentration on the structure and properties of the nascent fibers was studied in detail, and the diffusion coefficients of DMSO and H₂O for different bath DMSO concentrations were calculated by Crank's equation to explain the structural changes of the nascent fibers, including cross-section, core/shell structure, and surface morphology. The surface morphology of nascent fibers was observed by field emission scanning electron microscopy (FESEM). The results showed that as the coagulation bath DMSO concentration increased, the diffusion coefficients gradually decreased. More circular cross-section, less core/shell structure, higher degree of crystallinity, larger crystal size, larger bulk density, and higher sound velocity of the nascent fibers were obtained when thecoagulation bath DMSO concentration was 70 wt% compared to lower or higher bath DMSO concentration. Moreover, compared with the nascent fibers spun in other bath DMSO concentrations, smoother surfaces of the nascent fibers were obtained at the bath DMSO concentration of 70 wt%.     

Lateral growth of aligned mutilwalled carbon nanotubes under electric field

In this work we report laterally aligned multi-walled carbon nanotube (MWNT) by an electric field during growth. The MWNTs were selectively grown between lateral sides of the catalytic metals on predefined electrodes by chemical-vapor deposition. The electric field distribution for various geometries was simulated using Maxwell 2D simulation in order to realize better alignment of laterally grown carbon nanotubes (CNTs). The experimental results show that the electric field direction at the vicinity of catalyst and nanotubes-substrate interactions are principal factor in aligning CNTs laterally.     

High-performance electric double-layer capacitors using mass-produced multi-walled carbon nanotubes

Mass-produced multi-walled carbon nanotubes (MWNTs, which have the trademark VGNF®) have been investigated for their potential for use in electric double-layer capacitors (EDLCs). The variation aspects of these MWNTs by KOH activation showed quite interesting features. The gravimetric capacitance enhancement and specific surface area on KOH activation increased linearly. However, the capacitance per unit surface area has a maximum at 200 wt.?% of KOH addition. The VGNF-KOH 500 sample exhibits a capacitance enhancement as much as 13 times greater (28.3 F/g) than that of the as-grown materials (2.2 F/g), under the conditions of charging up to 3.5 V and discharging at a current density of 10 mA/cm². Interestingly, for this MWNT (VGNF®), selective attack on its amorphous carbon impurity has also been observed, as demonstrated from both scanning electron microscopy observations and Raman spectra. Consequently, the results of this study will provide insight into the potentiality of using MWNTs for EDLC electrodes, which would enable the cheapest production cost among the various types of carbon nanotubes.     

Correlation between diamagnetic susceptibility and electron spin resonance feature for various multiwalled carbon nanotubes

Determination of the structural features is a fundamental subject in nanotube research. A simple method is proposed to evaluate the structure of multiwalled carbon nanotubes (MWNTs) having either the concentric or the scrolled structure. Although transmission electron microscopy and Raman scattering did not indicate a distinct difference in the structural features of the MWNTs, the temperature dependence of the diamagnetic susceptibility showed a clear difference; one was temperature-independent constant diamagnetism and the others indicated temperature-dependent diamagnetic susceptibilities with different magnitudes. The former phenomenon can be explained by applying the nested concentric nature to the MWNTs, and the latter by the scrolled nature. The difference in the magnitude of the temperature dependence is evidence for the mixed nature of the concentric and scrolled structures. PACS 61.46.Fg; 75.75.+a; 76.30.Pk; 78.67.Ch; 81.07.De     

Comparative study on modification of multi-walled carbon nanotubes by a hydrophilic polymer with different approaches

The multi-walled carbon nanotubes (MWNTs) modified by a hydrophilic polymer were prepared with polymerization and blending approaches. The differences of both modified MWNTs were compared by Fourier transform infrared and Raman spectroscopies, thermogravimetric analysis and transmission electron microscopy. Chemical grafting reaction had occurred between MWNTs and polyvinyl pyrrolidone (PVP) after modification with polymerization and blending approaches. Polymerization modification can graft more PVP on the surface of MWNTs compared with blending modification. Polymerization modification of MWNTs belongs to the “grafting from” mechanism, while blending modification belongs to the “grafting to” mechanism. Modified MWNTs exhibit remarkable solubility in water, ethanol and dimethyl formamide.     

Preparation and Properties of Polylactide/Poly(ethylene-co-octene)/nano-SiO2 Ternary Composites

Polylactide (PLA)/poly(ethylene-co-octene)(POE) blends with various contents of nano-SiO₂ were prepared via melt mixing. The structure and properties of the PLA/POE/nano-SiO₂ ternary composites were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), rheometry, and tensile testing. The particle size of the dispersed POE phase first decreased with increasing nano-SiO₂ content and then remained constant. Nano-SiO₂ played an important role in the heterogeneous nucleation of PLA, which resulted in an increase of the crystallinity of PLA. The synergistic effect of both POE and nano-SiO₂ can significantly improve the toughness, strength, and modulus of PLA. When the ratio of PLA/POE/nano-SiO₂ was 90/10/0.5, PLA/POE/nano-SiO₂ composite had the best comprehensive properties.     

A novel route to aligned nanotubes and nanofibres using laser-patterned catalytic substrates

We describe the generation of aligned carbon nanotube bundles and films by pyrolysis of solid organic precursors (for example 2-amino-4,6-dichloro-s-triazine, s-triaminotriazine) at 950-1050 °C over laser-patterned thin metal (Fe, Co, Ni) films, deposited on silica substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies reveal that surface roughness of the laser-etched catalytic substrates plays a key role in achieving control of nanotube growth. We believe that, during the etching process, the energised (ablated) metal clusters condense and recrystallise evenly, possibly as the metal oxide, within the edges or surface of the eroded regions. During pyrolysis these catalytic particles, embedded in the silica substrates, are responsible for carbon agglomeration and subsequent tube axial growth, suggesting that nanotube alignment strongly depends upon the etching conditions (for example laser power, pulse duration, and focal distance). The pyrolysed products (usually nanotubes or nanofibres) were characterised by SEM, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX). Samples containing only small amounts of amorphous carbon and other carbonaceous particles are notably absent. We observe that the degree of graphitisation is dependent upon the catalyst and the organic precursor. Interestingly, a nitrogen content З% was detected within the nanofibres, which exhibit corrugated graphite-like morphologies. This pyrolytic method may be used to advantage in generating aligned heteroatomic nanostructures such as B_xC_yN_z systems.