Control of the single-wall carbon nanotube mean diameter in sulphur promoted aerosol-assisted chemical vapour deposition

The influence of gas flow on nanotube diameter during the synthesis of high-purity, very long single-wall carbon nanotubes (SWCNT) via aerosol-assisted chemical vapour deposition is reported. The sample morphology, nanotube yield, defect concentration and amount of carbonaceous impurities, as well as the mean diameter and the diameter distribution of the SWCNTs were analysed by combined scanning- and transmission electron microscopy, Fourier Transform Raman spectroscopy and optical absorption spectroscopy. The results show that by using a solution of ferrocene and sulphur in m-xylene the addition of sulphur as a promoter was found to enhance the SWCNT growth and to increase the yield. A reduction of the mean diameter and a change in the diameter distribution are observed when the total gas flow is increased.     

Growth of Cement Hydration Products on Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNT) were distributed on the surface of ordinary Portland cement (OPC) grains. The OPC/SWCNT composite was then hydrated at a 0.5 w/c ratio. The effects of the SWCNT on the early hydration process were studied using isothermal conduction calorimetry, high-resolution scanning electron microscopy and thermogravimetric analysis. The observed behavior of the composite samples was compared with both OPC sonicated without SWCNT and previously published data on as-delivered OPC. The SWCNT were found to accelerate the hydration reaction of the C₃S in the OPC. The morphology of both the initial C₃A and the C₃S hydration products were found to be affected by the presence of the SWCNT. In particular, the nanotubes appeared to act as nucleating sites for the C₃S hydration products, with the nanotubes becoming rapidly coated with C–S–H. The resulting structures remained on the surface of the cement grains while those in the sonicated and as-delivered OPC samples grew out from the grain surfaces to form typical C–S–H clusters. Classical evidence of reinforcing behavior, in the form of fiber pullout of the SWCNT bundles, was observed by 24 h of hydration.     

Electrical conductivity and transparency of polymer hybrid nanocomposites based on poly(trimethylene terephthalate) containing single walled carbon nanotubes and expanded graphite

Single‐walled carbon nanotubes (SWCNT)/expanded graphite (EG)/poly(trimethylene terephthalate) (PTT) hybrid nanocomposites were prepared via in situ polymerization. Raman spectroscopy and scanning electron microscopy (SEM) were employed to determine both, purity and morphology of the nanofillers and the dispersion of nanotubes and nanosheets. The electrical and optical properties of thin polymer films based on both “single” nanocomposites and hybrid nanocomposites were studied. For PTT/SWCNT nanocomposites, results confirmed that films optical transmittance decreases as the concentration of SWCNT increases, attaining almost no optical transmittance for 0.3 wt % of nanofiller. Conversely, the electrical conductivity of nanocomposites was found to increase by increasing the nanofiller amount and the σ_dc values indicate that percolation occurs at a very low SWCNT content (around 0.05 wt %). In the case of PTT/SWCNT + EG nanocomposites, when the content of SWCNT is 0.05%, the hybrid system presents lower conductivity than that corresponding to the “single” nanocomposite. The incorporation of additional EG to the PTT/SWCNT nanocomposite has a small effect on the electrical conductivity but inhibits the transparency of the system. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44370.     

Controlled cutting of single-walled carbon nanotubes and low temperature annealing

Many applications in nanotechnology require short and unentangled single-walled carbon nanotubes (SWCNT). Liquid-phase oxidative cutting gives nonuniform short tubes and causes significant material loss. Mechanical cutting is good for shortening SWCNT, but it leaves collapsed tube ends and might not be favorable for further manipulation. Solid-state reaction cutting is better for multi-walled carbon nanotubes than for SWCNT. Herein, we present a method combining mechanical and oxidative cutting. The SWCNT sample was first ground with a Wig-L-Bug grinding mill for 30 min, introducing structural defects into the side walls of SWCNT. The treated SWCNT were then soaked in a Piranha solution, in which the oxidants attack the existing side wall defects and give a complete cut. According to statistical analysis from transmission electron microscopy, most of the shortened SWCNT fall in the range of 50–200 nm. The material loss is 12.2 wt%. The functional groups on the tube surface introduced by shortening were removed by refluxing in a soda lime/water suspension. Then, the carbon nanotubes were further annealed by sonicating in ethanol. After annealing, the defect level of shortened carbon nanotubes was reduced significantly, as determined by Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis.     

Selective laser treatment and laser patterning of metallic and semiconducting nanotubes in single walled carbon nanotube films

Single wall carbon nanotubes (SWCNT) synthesized using mass production methods such as pulsed arc deposition consist of a mixture of metallic and semiconducting nanotubes. In this work, we report on an approach for the selective removal of either metallic or semiconducting SWCNT by a heat-treatment process with cw-lasers and pulsed lasers with specific wavelengths. The results show that using ultraviolet–visible radiation (with wavelengths between 473 nm and 632 nm) it is possible to remove predominantly metallic nanotubes. In contrast, near infrared lasers with 785 nm and 1064 nm wavelengths can be used to remove predominantly the semiconducting nanotubes. Finally, the fabrication of SWCNT films with an anisotropic distribution of metallic and semiconducting nanotubes is demonstrated using a direct laser interference pattering method.     

Ambient effects on the electrical conductivity of carbon nanotubes

We show that the electrical conductivity of single walled carbon nanotubes (SWCNT) networks is affected by oxygen and air humidity under ambient conditions by more than a magnitude. Later, we intentionally modified the electrical conductivity by functionalization with iodine and investigated the changes in the band structure by optical absorption spectroscopy.Measuring in parallel the tubes electrical conductivity and optical absorption spectra, we found that conduction mechanism in SWCNT is comparable to that of intrinsically conducting polymers. We identified, in analogy to conducting polymers, in the infrared spectra a new absorption band which is responsible for the increased conductivity, leading to a closing gap in semiconducting SWCNT.We could show that by different functionalizations of the same SWCNT starting material the properties like conductivity can be dramatically changed, leading to different imaginable applications. We investigated here, an ultraviolet sensor with weakly modified SWCNT.     

Characterization of melt flow instabilities in polyethylene/carbon nanotube composites

The effect of single (SWCNT) and multi- (MWCNT) walled carbon nanotubes on the melt flow instabilities of polyethylenes with different topologies was characterized by means of a novel capillary rheometer allowing in-situ measurements of the pressure fluctuations inside the die and by scanning electron microscopy (SEM) analysis. Our results show that carbon nanotubes modify the main characteristics of the spurt instability developed by the linear polyethylene. Furthermore, the sharkskin instability, developed in short chain branched polyethylene, is reduced at low amounts of MWCNT and SWCNT. Noteworthy, the critical shear rate for the on-set of the spurt and the sharkskin instabilities decreases in the nanocomposites due to the physical interactions between the polymer and the nanofiller.At high shear rates, the gross melt fracture instability is completely erased in the nanocomposites based on the linear polymer whereas in short chain branched polyethylene the amplitude of this bulk distortion is rather moderated. These changes were confirmed by on-line pressure measurements using the novel capillary rheometer set-up. Based on our results, it is concluded that carbon nanotubes drastically affect the non-linear molecular dynamic leading to polyethylene melt flow instabilities.     

Re-growth of single-walled carbon nanotube by hot-wall and cold-wall chemical vapor deposition

Single-walled carbon nanotube (SWCNT) was synthesized from short nanotubes using chemical vapor deposition (CVD) and the associated factors affecting the re-growth of the SWCNT were both investigated and optimized. Long, dense nanotubes were prepared from a mixture of acetylene and ethanol on air-annealed ST-cut quartz substrates by hot-wall CVD. Raman and photoluminescence analyses of the resulting material demonstrated that SWCNT was generated from the initial seeds since the chiralities of the seeds were maintained in the re-grown SWCNT. The re-growth of SWCNT was also achieved by cold-wall CVD. In both CVD systems, the efficiency of SWCNT re-growth was largely determined by the pretreatment conditions and growth parameters. By varying these factors, the growth of SWCNT from seeds was controlled. The re-growth mechanism is discussed based on experimental observations.     

GCMC simulation of hydrogen physisorption on carbon nanotubes and nanotube arrays

Properties of hydrogen physisorption in single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and SWCNT arrays are investigated in detail by grand canonical Monte Carlo simulation. The optimization of hydrogen storage capacity at 298 K and 10 MPa as a function of SWCNT diameter, MWCNT inter-tube spacing, and SWCNT array configuration is discussed.     

Formation of single-walled carbon nanotube thin films enriched with semiconducting nanotubes and their application in photoelectrochemical devices

Single-walled carbon nanotube (SWCNT) thin films, containing a high-density of semiconducting nanotubes, were obtained by a gel-centrifugation method. The agarose gel concentration and centrifugation force were optimized to achieve high semiconducting and metallic nanotube separation efficiency at 0.1 wt% agarose gel and 18,000g. The thickness of SWCNT films can be precisely controlled from 65 to 260 nm with adjustable transparency. These SWCNT films were applied in photoelectrochemical devices. Photocurrents generated by semiconducting SWCNT enriched films are 15-35% higher than those by unsorted SWCNT films. This is because of reducing exciton recombination channels as a result of the removal of metallic nanotubes. Thinner films generate higher photocurrents because charge carriers have less chances going in metallic nanotubes for recombination, before they can reach electrodes. Developing more scalable and selective methods for high purity semiconducting SWCNTs is important to further improve the photocurrent generation efficiency by using SWCNT-based photoelectrochemical devices.     

On-line detection of single-walled carbon nanotube formation during aerosol synthesis methods

Differential electrical mobility (DMA) method for the on-line detection of single-walled carbon nanotubes (SWCNTs) formation was used for the first time. Three different gas-phase synthesis processes were used to produce SWCNTs via CO disproportionation in the presence of catalyst nanoparticles formed either by a hot wire generator method or via thermal decomposition of ferrocene or iron pentacarbonyl. The typical product measured with the DMA method was bundles of SWCNTs, which further agglomerated prior to the measurement. Despite the different product morphology and concentration, the on-line measurement was able to distinguish SWCNT formation in each experimental set-up as an increase in the geometric mean particle diameter and as a decrease in the total particle number concentration. Furthermore, information regarding the relative SWCNT concentration can also be obtained from the DMA measurement. A theoretical approach to the mobility of nonspherical particles in the electric field was successfully developed in order to convert the electrical mobility size of the high aspect ratio SWCNTs measured with DMA to the physical size of the product. Size-selected SWCNTs were studied with transmission electron microscopy in order to find the correlation between the on-line DMA measurement data and the SWCNT morphology.     

Raman characterisation of single-walled carbon nanotubes produced by the catalytic pyrolysis of methane

Bundles of single-wall carbon nanotubes (SWCNT) were synthesised using a chemical vapour deposition technique. This basic process was optimised over a wide range of process parameters. For the optimal results, ethane was decomposed at 950 °C over a catalyst material consisting of 2% by wt Fe chemically deposited on an MgO support. The samples were characterised using scanning electron microscopy and transmission electron microscopy to show the presence of nanotubes and also to measure their diameters and the size of amorphous carbon deposits. Raman scattering was also used to probe the electronic properties and hence derive the distribution of diameters of the SWCNT. Samples were measured in both the radial breathing mode and tangential mode ranges using three different laser lines. For comparison purposes, similar data have been reported for a standard commercial SWCNT material (HiPCO). From the data, we can conclude that the tubes in our sample are significantly different to those in the HiPCO sample. In particular, we conclude that samples produced by our method contain a much narrower distribution of tube diameters than does the commercial sample.     

Adsorption of hydrogen on single-walled carbon nanotubes with defects

We present molecular dynamics (MD) simulations and density functional theory (DFT) calculations of hydrogen adsorption on single-walled carbon nanotubes (SWCNT) with various kinds of defects. The nature of defects, which is characterized here by the number of carbon atoms present in a ring on the surface of nanotube, plays a significant role in determining the hydrogen adsorption capacity of the SWCNT. Nanotubes containing the Stone–Wales defect with 5 and 8-member rings were found to have the largest hydrogen adsorption ability that increases further with the number of rings with such defects. Whereas, the presence of defects with 5, 3-5-8-member rings and the Stone–Wales defect with 5 and 7-member rings decreases the adsorption ability of the defective SWCNT significantly with respect to defect-free nanotubes. Our results indicate that the huge discrepancies in hydrogen storage capacities of SWCNT reported in the literature could be attributed to the nature of defects present in nanotubes. DFT calculations also reveal that the adsorption energy depends not only on the nature and number of defects present on the surface of nanotube but also on the equilibrium structure of rings.     

国外关于碳纳米管在火炸药中的应用研究

介绍了国外利用碳纳米管制造的含能材料,其中一种是碳纳米管上固定聚合氮的新型绿色高能炸药,通过电化学工艺将聚合氮固定在单壁碳纳米管的侧壁上,分析结果表明在纳米管壁上形成了原子簇N4和N8;另一种新型含能材料是金属化单壁碳纳米管,运用石墨和双组份催化剂激光烧蚀法制备金属化单壁碳纳米管,保证了金属化SWCNT的高质量和高产量,这是生产低感度高能纳米复合物的新途径。此外还介绍了碳纳米管在HTPB(羟基尾聚丁二烯Hydroxyl Termina-ted Polybuiadicne)基推进剂中的应用和用作点火材料的情况。     

Photonics based on carbon nanotubes

Among direct-bandgap semiconducting nanomaterials, single-walled carbon nanotubes (SWCNT) exhibit strong quasi-one-dimensional excitonic optical properties, which confer them a great potential for their integration in future photonics devices as an alternative solution to conventional inorganic semiconductors. In this paper, we will highlight SWCNT optical properties for passive as well as active applications in future optical networking. For passive applications, we directly compare the efficiency and power consumption of saturable absorbers (SAs) based on SWCNT with SA based on conventional multiple quantum wells. For active applications, exceptional photoluminescence properties of SWCNT, such as excellent light-emission stabilities with temperature and excitation power, hold these nanometer-scale materials as prime candidates for future active photonics devices with superior performances.     

Poly(vinyl chloride)/single wall carbon nanotubes composites: Investigation of mechanical and thermal characteristics

Composites of polyvinylchloride (PVC) with single wall carbon nanotubes (SWCNTs) were prepared by plastisol curing. Scanning electron microscopy (SEM) observations revealed that appropriate dispersion of the nanotubes was achieved. The mechanical properties showed that SWCNT improved the Young's modulus and tensile strength of the PVC. The composites have higher elongation at break and toughness as well. By comparing the mechanical properties of the composites, it is found that there is a critical SWCNT loading (about 1 wt%) below which the tensile properties increase with increasing nanofiller concentration. For the composites containing 0.25–0.75 wt% of SWCNT, this situation was observed, whereas for a sample with 1 wt% SWCNT, the mechanical properties decreased due to the agglomeration of the nanotubes. Thermogravimetric analysis indicated that the SWCNT increased T_5%, T_10%, T_50%, T_onset, and T_max and decreased weight loss in the degradation process of the PVC. In addition, by adding SWCNT to the polymer, residual mass at 600°C increased significantly. These results are advantages for the applications of the polymer in which high mechanical properties, including high tensile modulus and toughness, and good thermal properties are needed. J. VINYL ADDIT. TECHNOL., 22:128–133, 2016. © 2014 Society of Plastics Engineers     

Preparation of transparent and conductive thin films of carbon nanotubes using a spreading/coating technique

This study demonstrates large-scale purification of single-walled carbon nanotubes (SWCNTs) and preparation of transparent and conductive thin films of carbon nanotubes using a spreading/coating technique. Wire-bar, which wraps a stainless steel wire around a shaft, is useful equipment to spread inks on flexible materials. Coating of purified SWCNT film thickness was tunable depending not only on the wire-bar thickness but also on the SWCNT concentration in dispersion. The SWCNT concentration in the dispersion increased concomitantly with the increase of the C₆₀(OH)_n concentration. These two factors, wire-bar thickness and SWCNT concentration in dispersion, control the film’s conductivity and transparency.     

Carbon Nanotube Reinforced Alumina-Based Ceramics with Novel Mechanical, Electrical, and Thermal Properties

The extraordinary mechanical, thermal, and electrical properties of single-wall carbon nanotubes (SWCNT) have prompted the development of advanced engineering materials with improved properties through the incorporation of carbon nanotubes in selected matrices. Dense SWCNT reinforced alumina nanocomposites have been fabricated by novel spark-plasma-sintering (SPS) technique. SWCNT were also successfully used to convert insulating nanoceramics to metallically conductive composites. Additionally, novel anisotropic thermal properties have been observed in the carbon nanotube composites. Such multifunctional carbon nanotube/ceramic composites with improved mechanical and electrical properties along with anisotropic thermal properties are envisaged for a wide range of applications.     

Chirality fingerprinting and geometrical determination of single-walled carbon nanotubes: Analysis of fine structure of X-ray diffraction pattern

Single-walled carbon nanotubes (SWCNTs) are seamless cylindrical tubes consisting of carbon atoms with diameters ranging from less than one nanometer to a few nanometers. The arrangement of carbon atoms in a SWCNT is uniquely specified by using a pair of integers (n, m) referred to as the chiral indices. While the detailed structures, such as a carbon–carbon bond length, should be important, they have not been fully clarified yet. In this work, we examine the possibility of powder X-ray diffraction (XRD) method to characterize structures of SWCNTs. It is found that the XRD is a useful tool to “fingerprint” the chiral indices of bulk SWCNT samples. Besides, we find that information on the detailed structure within a SWCNT can be obtained from the XRD pattern. The application to a highly concentrated SWCNTs clarifies that the (6,5) SWCNT is expanded along the radial direction compared to that of ideal rolling up structure of graphene, with a negligible change along the tube axis.     

Selective deposition of semiconducting single-walled carbon nanotubes onto amino-silane modified indium tin-oxide surface for the development of poly(3-hexylthiophene)/carbon-nanotube photovoltaic heterojunctions

A method is described to obtain separation of single-walled carbon nanotubes (SWCNTs) on an indium tin-oxide (ITO) substrate by modifying the conducting surface of ITO with amino-silane functional groups. Scanning electron microscopy confirmed that the amino-silane functionalization of the substrate is a critical parameter for the immobilization of separated nanotubes. In particular spin coating the SWCNT solution onto the amino-silane modified ITO surface results in a lower nanotube density with respect to the reference sample obtained on pure ITO together with the immobilization of semiconducting carbon nanotubes onto the substrate. The possibility of using these SWCNT thin films to obtain polymer/nanotube heterojunctions for the development of organic solar cells is considered.