碳源对碳纳米管形态的影响

以苯和甲苯为碳源,二茂铁为催化剂,含硫化合物为助催化剂,采用浮游催化裂解法制备了碳纳米管,并采用TEM对不同条件下所得碳纳米管进行了形态分析。结果发现,碳源中苯和甲苯的配比对碳纳米管的形态有着重要的影响。以纯苯为碳源时,产物主要为直线型碳纳米管,并存在极少量短的弯曲型碳纳米管。随着碳源中甲苯比例的增加,产物中折线型碳纳米管增加。以纯甲苯为碳源,产物中仍有少量直线型碳纳米管,而不完全是折线型碳纳米管;此外,产物中还发现了极少量分支型碳纳米管。根据所得结果讨论分析了甲苯的加入对碳纳米管形态的影响以及各种碳纳米管的形成机理,认为可能是由于甲苯在催化热解过程中产生的碳种不同于苯催化热解所产生的碳种,造成碳在催化剂颗粒各处浓度不同,从而在碳纳米管的不同部位引入五元环和七元环而形成各种形态的碳纳米管。     

Preparation and investigation of multiwall carbon nanotube—polymer composites

In our research we focus on thermoplastic composites of multiwall carbon nanotubes. Different composition of carbon nanotubes and polymers were produced by a special mixing unit called Infinitely Variable Dynamic Shear Mixer (IDMX) using ABS and polycarbonate polymers as matrix materials. Polycarbonate/multiwall carbon nanotube masterbatch was used in the preparation of different compositions. Concentration series were manufactured and investigated. The nanotube composites were granulated and test pieces were injection moulded. The prepared materials were characterised by scanning electron microscopy. Mechanical, electrical properties of the materials were also determined. Correlation was found between the yield stress and the nanotube contents. Impact strength of the composites decreased with the nanotube content, showing more rigid structure than the original pure matrix material. Glass transition of the composites was determined by DSC method. It was found that the characteristic temperatures change by the ratio of the pure materials. Slight change also was found as the carbon nanotube content changes.     

THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

A high yield (∼32 wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800-1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

ABSTRACT

A high yield (～32?wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800–1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

Chemical functionalization of carbon nanotubes for the mechanical reinforcement of polystyrene composites

An organometallic approach was used to functionalize multiwalled carbon nanotubes with n-butyllithium. This procedure was repeated two more times to achieve a higher degree of multiwalled carbon nanotube functionalization. The functionalized nanotubes have been characterized by Fourier transform infrared and Raman spectroscopy, thermogravimetrical analysis, scanning electron microscopy and sedimentation studies. It was possible to form stable suspensions of the functionalized nanotubes in tetrahydrofuran and they were used to make nanotube polymer composites. The mechanical properties of these new nanotube polymer composites were tested and they were found to show an increase of up to 25% in their Young's moduli and up to 50% in their tensile strength over pure polystyrene.     

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles

This paper studies the mechanism of the formation of carbon nanostructures on carbon nanofibers with Pd nanoparticles by using different carbon sources. The carbon nanofibers with Pd nanoparticles were produced by carbonizing electrospun polyacrylonitrile (PAN) nanofibers including Pd(Ac)(2). Such PAN-based carbon nanofibers were then used as substrates to grow hierarchical carbon nanostructures. Toluene, pyridine and chlorobenzine were employed as carbon sources for the carbon nanostructures. With the Pd nanoparticles embedded in the carbonized PAN nanofibers acting as catalysts, molecules of toluene, pyridine or chlorobenzine were decomposed into carbon species which were dissolved into the Pd nanoparticles and consequently grew into straight carbon nanotubes, Y-shaped carbon nanotubes or carbon nano-ribbons on the carbon nanofiber substrates. X-ray diffraction analysis and transmission electron microscopy (TEM) were utilized to capture the mechanism of formation of Pd nanoparticles, regular carbon nanotubes, Y-shaped carbon nanotubes and carbon nano-ribbons. It was observed that the Y-shaped carbon nanotubes and carbon nano-ribbons were formed on carbonized PAN nanofibers containing Pd-nanoparticle catalyst, and the carbon sources played a crucial role in the formation of different hierarchical carbon nanostructures.     

Self-assembled interconnection by bamboo-like carbon nanotubes

Carbon nanotubes (CNTs) could be formed on Si substrate using nickel catalyst under microwave plasma-enhanced chemical vapor deposition system. Under the high, negative-bias voltage (−400 V) condition, we found the formation of the carbon nanotube islands and the bamboo-like carbon nanotube interconnection lines. Most of the bamboo-like carbon nanotubes connected with the carbon nanotubes themselves, which indicates the self-assembled characteristics of the carbon nanotube interconnection lines. The self-assembled characteristics of the bamboo-like carbon nanotube interconnection lines were evaluated using computer-aided image analysis.     

The effect of nanotube radius on the constitutive model for carbon nanotubes

We investigate the effect of nanotube radius on the constitutive model of single wall carbon nanotubes. We adopt a modified Cauchy–Born rule to incorporate the interatomic potential into the continuum analysis, and such an approach ensures the equilibrium of atoms. It is shown that the nanotube radius has little effect on the mechanical behavior of single wall carbon nanotubes subject to simple tension or pure torsion, while the nanotube orientation has somewhat larger influences.     

Effects of hydrogen on the formation of aligned carbon nanotubes by chemical vapor deposition

Well-aligned carbon nanotubes with controllable properties were grown on porous silicon substrates by thermal chemical vapor deposition. The morphologies of the carbon nanotubes were varied with the introduction of H2 during the catalyst activation and/or carbon nanotube growth processes. It was found that H2 promotes the growth of carbon nanotubes while preventing the formation of spherical amorphous carbon particles. Without the introduction of H2 during the C2H2 thermal decomposition, aligned carbon nanotubes mixed with spherical carbon particles were formed on the substrate. However, with the introduction of H2, pure carbon nanotubes were synthesized. These nanotubes also had uniform diameters of 10-20 nm, which is much smaller than nanotubes synthesized without H2. The average growth rate of nanotubes was also affected by the introduction of hydrogen into the reaction chamber during nanotube growth. With the addition of hydrogen, the average growth rate changed from 78 nm/s to 145 nm/s. A possible growth mechanism, including the effect of a high ratio of H2 to C2H2, is suggested for the growth of these well-aligned carbon nanotubes with uniform diameters.     

Chiral selectivity in the charge-transfer bleaching of single-walled carbon-nanotube spectra

Chiral selective reactivity and redox chemistry of carbon nanotubes are two emerging fields of nanoscience. These areas hold strong promise for producing methods for isolating nanotubes into pure samples of a single electronic type, and for reversible doping of nanotubes for electronics applications. Here, we study the selective reactivity of single-walled carbon nanotubes with organic acceptor molecules. We observe spectral bleaching of the nanotube electronic transitions consistent with an electron-transfer reaction occurring from the nanotubes to the organic acceptors. The reaction kinetics are found to have a strong chiral dependence, with rates being slowest for large-bandgap species and increasing for smaller-bandgap nanotubes. The chiral-dependent kinetics can be tuned to effectively freeze the reacted spectra at a fixed chiral distribution. Such tunable redox chemistry may be important for future applications in reversible non-covalent modification of nanotube electronic properties and in chiral selective separations.     

Mechanical Characteristics and Preparation of Carbon Nanotube Fiber‐Reinforced Ti Composite

Carbon nanotubes, a kind of high order fullerenes, offers remarkable electronic as well as mechanical properties, e.g., an extremely high Young’s modulus of TPa order has been reported. This suggests the suitability of carbon nanotubes as novel fiber materials for metal matrix composites. The authors demonstrate that Ti/ nanotube composites show a large increase in hardness and Young’s modulus as compared to pure Ti. This makes the composite an attractive advanced material for future applications.     

Conceptual design of carbon nanotube processes

Carbon nanotubes, discovered in 1991, are a new form of pure carbon that is perfectly straight tubules with diameter in nanometers, length in microns. The conceptual designs of two processes are described for the industrial-scale production of carbon nanotubes that are based on available laboratory synthesis techniques and purification methods. Two laboratory-scale catalytic chemical vapor deposition reactors were selected for the conceptual design. One (CNT-PFR process) used the high-pressure carbon monoxide disproportionation reaction over iron catalytic particle clusters (HiPCO reactor), and the other (CNT-FBR process) used catalytic disproportionation of carbon monoxide over a silica supported cobalt–molybdenum catalyst (CoMoCAT reactor). Purification of the carbon nanotube product used a multi-step approach: oxidation, acid treatment, filtration and drying. Profitability analysis showed that both process designs were economically feasible. For the CNT-PFR process, the net present value, based on a minimum attractive rate of return of 25% and an economic life of 10 years, was $609 million, the rate of return was 37.4% and the economic price was $38 per kg of carbon nanotube. For the CNT-FBR process, the net present value was $753 million, rate of return was 48.2% and the economic price was $25 per kg of carbon nanotube. The economic price for these processes is an order of magnitude less than the prevalent market price of carbon nanotubes and is comparable to the price of carbon fibers.     

Encapsulation of a benzene molecule into a carbon nanotube

Aromatic hydrocarbon molecules encapsulated in carbon nanotubes have been proposed for applications as semiconductors. They can be formed by exploiting the van der Waals interaction as a simple method to incorporate molecules into carbon nanotubes. However, the existence of energy barriers near the open ends of carbon nanotubes may be an obstacle for molecules entering carbon nanotubes. In this paper, we investigate the encapsulation mechanism of a typical aromatic hydrocarbon, namely a benzene molecule, into a carbon nanotube in order to determine the dependence on radius of the tube. A continuous approach which assumes that the molecular interactions can be approximated using average atomic densities together with the semi-empirical Lennard–Jones potential function is adopted, and an analytical expression for the interaction energy is obtained which may be readily evaluated by algebraic computer packages. In particular, we determine the threshold radius of the carbon nanotube for which the benzene molecule will enter the carbon nanotube. The analytical approach adopted here provides a computationally rapid procedure for the determination of critical numerical values.     

Effect of filler geometry on interfacial friction damping in polymer nanocomposites

Single-walled carbon nanotube polycarbonate and C60 polycarbonate nanocomposites were fabricated using a solution mixing method. The composite loss modulus was characterized by application of dynamic (sinusoidal) load to the nanocomposite and the pure polymer samples. For a loading of 1 weight %, the single-walled nanotube fillers generated more than a 250% increase in loss modulus compared to the baseline (pure) polycarbonate. Even though the surface area to volume ratio and surface chemistry of C60 is similar to that for nanotubes, we report no significant increase in the energy dissipation for the 1% weight C60 nanoparticle composite compared to the pure polymer. We explain these observations by comparing qualitatively, the active sliding area (considering both normal and shear stresses) for a representative volume element of the nanotube and the nanoparticle composites. These results highlight the important role played by the filler geometry in controlling energy dissipation in nanocomposite materials.     

Conversion of toluene into carbon nanotubes using arc discharge plasmas in solution

In order to form nanocarbon materials, an arc discharge plasma method in hydrocarbon solvent is developed. In the case that the arc discharge is performed in toluene with nickel electrodes, tube-like nanocarbons were formed from toluene. The catalysis of the metal electrodes is found to be an important factor for the formation of the nanocarbons by the arc discharge in toluene. This method has a possibility of forming carbon nanotubes from liquid state solvents as a new carbon source by using catalyst ingredient as discharge electrodes.     

Single-walled carbon nanotube incorporated novel three phase carbon/epoxy composite with enhanced properties

In the present work, single-walled carbon nanotubes were dispersed within the matrix of carbon fabric reinforced epoxy composites in order to develop novel three phase carbon/epoxy/single-walled carbon nanotube composites. A combination of ultrasonication and high speed mechanical stirring at 2000 rpm was used to uniformly disperse carbon nanotubes in the epoxy resin. The state of carbon nanotube dispersion in the epoxy resin and within the nanocomposites was characterized with the help of optical microscopy and atomic force microscopy. Pure carbon/epoxy and three phase composites were characterized for mechanical properties (tensile and compressive) as well as for thermal and electrical conductivity. Fracture surfaces of composites after tensile test were also studied in order to investigate the effect of dispersed carbon nanotubes on the failure behavior of composites. Dispersion of only 0.1 wt% nanotubes in the matrix led to improvements of 95% in Young's modulus, 31% in tensile strength, 76% in compressive modulus and 41% in compressive strength of carbon/epoxy composites. In addition to that, electrical and thermal conductivity also improved significantly with addition of carbon nanotubes.     

The influence of carbon nanotube functionalization route on the efficiency of dispersion in polypropylene by twin-screw extrusion

The joint effect of chemical functionalization and polymer melt blending conditions on carbon nanotube dispersion in polypropylene, as well as its influence on the electrical and mechanical properties of the resulting composites were investigated. Melt blending was performed using a prototype twin screw extruder enabling sampling along the barrel. The carbon nanotube dispersion was assessed by optical and scanning electron microscopy. The functionalization reaction was tailored for compatibility with the polymer, and characterized by X-ray photoelectron spectroscopy. In particular, nanotubes covalently bonded to polypropylene showed distinctive dispersion ability, while the carbon nanotube dispersion remained stable even after re-melting. However, the polypropylene-functionalized nanotubes produced composites with higher electrical resistivity, possibly due to the insulating effect of the polymer bonded to the nanotubes surface.     

Molecular dynamic simulations on tensile mechanical properties of single-walled carbon nanotubes with and without hydrogen storage

Using a bond order potential, molecular dynamics (MD) simulations have been performed to study the mechanical properties of single-walled carbon nanotubes (SWNTs) under tensile loading with and without hydrogen storage. (10,10) armchair and (17,0) zigzag carbon nanotubes have been studied. Up to the necking point of the armchair carbon nanotube, two deformation stages were identified. In the first stage, the elongation of the nanotube was primarily due to the altering of angles between two neighbor carbon bonds. Young's Modulus observed in this stage was comparable with experiments. In the second stage, the lengths of carbon bonds are extended up to the point of fracture. The tensile strength in this stage was higher than that observed in the first stage. Similar results were also found for the zigzag carbon nanotube with a lower tensile strength. Hydrogen molecules stored in the nanotubes reduced the maximum tensile strength of the carbon nanotubes, especially for the armchair type. The effect may be attributed to the competitive formation between the hydrogen–carbon and the carbon–carbon bonds.     

碳纳米管传感器的研究进展

综述了不同功能碳纳米管传感器(微型碳纳米管气体离子传感器、无线被动碳纳米管气体传感器、碳纳米管化学和力学传感器、碳纳米管阵列生物传感器、碳纳米管温度和风速传感器、碳纳米管神经毒气传感器)的制备、结构特点、性能和发展方向.     

Nitrogen doping in carbon nanotubes

Nitrogen doping of single and multi-walled carbon nanotubes is of great interest both fundamentally, to explore the effect of dopants on quasi-1D electrical conductors, and for applications such as field emission tips, lithium storage, composites and nanoelectronic devices. We present an extensive review of the current state of the art in nitrogen doping of carbon nanotubes, including synthesis techniques, and comparison with nitrogen doped carbon thin films and azofullerenes. Nitrogen doping significantly alters nanotube morphology, leading to compartmentalised 'bamboo' nanotube structures. We review spectroscopic studies of nitrogen dopants using techniques such as X-ray photoemission spectroscopy, electron energy loss spectroscopy and Raman studies, and associated theoretical models. We discuss the role of nanotube curvature and chirality (notably whether the nanotubes are metallic or semiconducting), and the effect of doping on nanotube surface chemistry. Finally we review the effect of nitrogen on the transport properties of carbon nanotubes, notably its ability to induce negative differential resistance in semiconducting tubes.