Thin Multi-walled Carbon Nanotubes Research Articles

Thermally Stable, Thin, Ultralight, Reusable, and Flexible Multiwalled Carbon Nanotube Membranes for Removal of Heavy Metals, Polycyclic Aromatic Hydrocarbons, and Particulates from Coal Smoke

Thermally Stable, Thin, Ultralight, Reusable, and Flexible Multiwalled Carbon Nanotube Membranes for Removal of Heavy Metals, Polycyclic Aromatic Hydrocarbons, and Particulates from Coal Smoke

Needlelike, short and thin multi-walled carbon nanotubes: comparison of effects on wild type and p53+/− rat lungs

Carbon nanotubes (CNTs) are nanomaterials presenting an occupational inhalation risk during production or handling. The International Agency for Research on Cancer classified one CNT, Mitsui-7 (MWNT-7), as ‘possibly carcinogenic to humans’. In recognition of their similarities, a proposal has been submitted to the risk assessment committee of ECHA to classify all fibers with ‘Fibre Paradigm’ (FP)-compatible dimensions as carcinogenic. However, there is a lack of clarity surrounding the toxicity of fibers that do not fit the FP criteria. In this study, we compared the effects of the FP-compatible Mitsui-7, to those of NM-403, a CNT that is too short and thin to fit the paradigm. Female Sprague Dawley rats deficient for p53 (GMO) and wild type (WT) rats were exposed to the two CNTs (0.25 mg/rat/week) by intratracheal instillation. Animals (GMO and WT) were exposed weekly for four consecutive weeks and were sacrificed 3 days or 8 months after the last instillation. Exposure to both CNTs induced acute lung inflammation. However, persistent inflammation at 8 months was only observed in the lungs of rats exposed to NM-403. In addition to the persistent inflammation, NM-403 stimulated hyperplasic changes in rat lungs, and no adenomas or carcinomas were detected. The degree and extent of hyperplasia was significantly more pronounced in GMO rats. These results suggest that CNT not meeting the FP criteria can cause persistent inflammation and hyperplasia. Consequently, their health effects should be carefully assessed.

Using a Novel Approach to Estimate Packing Density and Related Electrical Resistance in Multiwall Carbon Nanotube Networks.

In this work, we use contrast image processing to estimate the concentration of multi-wall carbon nanotubes (MWCNT) in a given network. The fractal dimension factor (D) of the CNT network that provides an estimate of its geometrical complexity, is determined and correlated to network resistance. Six fabricated devices with different CNT concentrations exhibit D factors ranging from 1.82 to 1.98. The lower D-factor was associated with the highly complex network with a large number of CNTs in it. The less complex network, having the lower density of CNTs had the highest D factor of approximately 2, which is the characteristic value for a two-dimensional network. The electrical resistance of the thin MWCNT network was found to scale with the areal mass density of MWCNTs by a power law, with a percolation exponent of 1.42 and a percolation threshold of 0.12 g/cm. The sheet resistance of the films with a high concentration of MWCNTs was about six orders of magnitude lower than that of less dense networks; an effect attributed to an increase in the number of CNT–CNT contacts, enabling more efficient electron transfer. The dependence of the resistance on the areal density of CNTs in the network and on CNT network complexity was analyzed to validate a two-dimension percolation behavior.

Direct growth of carbon nanotubes forests on carbon fibers to replace microporous layers in proton exchange membrane fuel cells

A novel microporous layer structure for fuel cell application has been developed based on the direct growth of thin multiwall carbon nanotubes forests on the carbon fiber support of a commercial gas diffusion media free of hydrophobic treatment. The growth process is a hot filaments assisted chemical vapor deposition coupled with a specific catalyst dedicated to the growth of carbon nanotubes on carbon support. The so obtained carbon nanotube forests are perpendicularly aligned all along the carbon fibers and cover the surface of the gas diffusion media, providing a unique and new structure of microporous layer. The carbon nanotubes composing the forests are about 10 μm–20 μm long, with about 6 walls for an average diameter of 7.5–8 nm. Fuel cell testing demonstrated a performance improvement up to 30% compared to the best state of the art gas diffusion media, even in the presence of liquid water in the fuel cell, which is the main issue limiting performances.

Colloidal MoS2 van der Waals Template for Growing Highly Uniform Nanomaterials.

The van der Waals (vdW) structures of transition metal dichalcogenides (TMDCs) have been studied extensively owing to the excellent electronic, optoelectronic, and catalytic performance with the atomic-scale sharpness of the interfaces. In addition, the presence of substitution and redox reactions in the vdW gaps also provides huge potential to be employed as a nanoscale reactor. Herein, the vdW gap of colloidal MoS2 is reported as a natural template for the formation of CoMo bimetallic oxide nanoparticles (BMONPs) with highly uniform size (∼4 nm), which resulted in further synthesis of the thin multiwalled carbon nanotubes with extremely narrow diameter distribution. This study not only pioneers a new application of TMDCs but also provides an efficient means to control the size of nanomaterials, which directly affect material properties.

Cytotoxicity profiles of multi-walled carbon nanotubes with different physico-chemical properties

Multi-walled carbon nanotubes (MWCNTs) have industrial applications in the nanotechnology field. The physico-chemical properties of MWCNTs vary greatly depending on MWCNT manufacture and application. It has been pointed out that their needle shape and high durability are important factors that determine the biopersistence of fibers and can lead to inhalation toxicity or cytotoxicity. In this study, we prepared six suspensions of MWCNTs differing in diameter and length, and performed in vitro cell-based assays for 24 h using NR8383 rat alveolar macrophages. Rigid, needle-shaped MWCNTs with a large diameter (>50 µm) penetrated the cytoplasm and decreased cell survival without generating intracellular reactive oxygen species (ROS), significantly up-regulated many genes involved in inflammatory responses, response to oxidative stress and apoptosis, and extracellular matrix degradation. Bent MWCNTs with a small diameter (<20 µm) were phagocytosed in vacuole-like cellular compartments and decreased cell survival along with intracellular ROS generation. Straight, thin MWCNTs with a small diameter (<20 µm) caused a slight intracellular ROS generation but no decrease in cell viability. Some straight, long, and thin MWCNTs were found in the mitochondria and near the nuclei; however, no mutagenesis was observed. The in vitro cell-based assays showed high cytotoxicity of MWCNTs with a large diameter (>50 µm), moderate and low cytotoxicity of MWCNTs with a small diameter (<20 µm). These results suggested that the diameter of MWCNTs considerably contributes to their cytotoxicity.

Dynamic analysis of laminated composite sandwich beam containing carbon nanotubes reinforced magnetorheological elastomer

In this study, dynamic analysis of three-layered sandwich beam with thin orthotropic skins and multiwall carbon nanotubes reinforced magnetorheological elastomer (MWCNT-MRE) core have been investigated. The laminates are made of glass fiber/epoxy composites with ply orientation of [0/90] s and are prepared using vacuum-assisted hand layup process. Experiments are performed to investigate the vibration characteristics of MWCNT-MRE and MRE sandwich structures by applying the various magnetic field intensities under different end conditions. Further, the laminated composite MWCNT-MRE and MRE sandwich beams are modeled using ABAQUS finite element software and validated through experimental results in terms of natural frequencies. Also, the present finite element model is validated with available literature in terms of natural frequencies. A very good agreement is observed between the results of the experimental method and those extracted from numerical simulation. Also, the influence of applied magnetic field levels, core thickness ratio, ply orientation, and various boundary conditions on the vibration behavior of laminated composite MWCNT-MRE and MRE sandwich beams are analyzed.

The preparation and characterization of buckypaper made from carbon nanotubes impregnated with chitosan

AbstractBiopolymer chitosan was incorporated into a thin multiwalled carbon nanotube membrane (MWNT buckypaper) via filtration and soaking in 0.1% (w/v) of low‐molecular‐weight (MW) chitosan. The properties of the buckypaper membrane before and after annealing and after soaking were characterized by measurement of their electrical conductivities (19 ± 2 to 42 ± 2 S/cm), contact angles (31 ± 4° to 71 ± 4°), and mechanical properties (tensile strength, small‐ranging between 1.4 ± 0.1 and 4.2 ± 0.7 MPa; Young's modulus: 85 ± 4 to 443 ± 20 MPa). Moreover, the morphological properties, surface area, and permeability toward water of these buckypaper membranes were characterized and compared with corresponding carbon nanotube membranes prepared with Triton X‐100 (Trix) as the surfactant. Scanning electron microscopic (SEM) images and Brunauer, Emmett, and Teller (BET) data of MWNT‐annealing buckypaper membranes revealed that the diameters of their surface pores were significantly higher than that of the corresponding buckypaper membranes soaked in chitosan solution. The solution of chitosan incorporated inside the porous structure of the annealed MWNT membrane led to a significantly reduced surface area and pore size distribution of the composite membrane, revealing that this could be a useful method for desalination.

Toxicity studies of 1020 Long Multiwalled Carbon Nanotubes (L-MWNT-1020) administered by inhalation to Sprague Dawley (Hsd:Sprague Dawley SD) rats and B6C3F1/N mice.

Multiwalled carbon nanotubes (MWCNTs) are highly ordered hexagonal lattices of carbon atoms arranged into cylinders by hydrogen bonding, dipolar forces, hydrophilic or hydrophobic interactions, gravity, and other forces. MWCNTs are synthesized by applying energy to a carbon source, which produces individual or groups of carbon atoms that reassemble into tubes. One of the primary uses of MWCNTs is in nanotube-reinforced polymer composite materials that take advantage of their low-density and high load-bearing capacity. Nanoscale materials were nominated by the Rice University Center for Biological and Environmental Nanotechnology to the National Toxicology Program for toxicologic testing. Because long-term inhalation toxicity and carcinogenicity studies were being conducted on a relatively short, rigid MWCNT, a representative long and thin MWCNT was selected for these studies. Following an evaluation of 24 different long, thin MWCNTs, the 1020 Long Multiwalled Carbon Nanotube (L-MWNT-1020) (Sun Innovations, Fremont, CA) was selected for study based on availability, high purity (97%), and the low amount of residual nickel catalyst (0.52% by weight). The average L-MWNT-1020 nanotube length was 2,600 nm and the average width was 15.3 nm. Because nickel was shown to be tightly bound to L-MWNT-1020, tissue nickel content was measured to determine lung burden. (Abstract Abridged).

Controllable synthesis of N-doped aligned carbon nanotubes from melamine-based carbon by water-assisted chemical vapor deposition

N-doped well-aligned thin multiwall carbon nanotubes (CNTs) have been prepared by a facile water-assisted chemical vapor deposition (CVD) process using melamine as both the carbon precursor and N-dopant and ferrocene as both the catalyst and carbon precursor. It is shown that the synthetic temperature has strong effects on the growth of carbonaceous structure. Carbon films started to grow at reaction temperature of 700 °C, and the optimal temperature for the synthesis of aligned CNTs, based on the experiment results, was found to be 900 °C. The lengths of the CNTs can be tuned by changing the annealing time of the pyrolysis process, it could reach as long as 40.2 μm. The atomic percentage of nitrogen doping in aligned CNTs could be achieved to 1.71%. It was found that there were many joints and defects in the as-prepared CNTs which may offer more nucleation sites on the chemically inert CNT surface for various specialized applications such as supercapacitor.

Physicochemical predictors of Multi-Walled Carbon Nanotube-induced pulmonary histopathology and toxicity one year after pulmonary deposition of 11 different Multi-Walled Carbon Nanotubes in mice.

Multi‐walled carbon nanotubes (MWCNT) are widely used nanomaterials that cause pulmonary toxicity upon inhalation. The physicochemical properties of MWCNT vary greatly, which makes general safety evaluation challenging to conduct. Identification of the toxicity‐inducing physicochemical properties of MWCNT is therefore of great importance. We have evaluated histological changes in lung tissue 1 year after a single intratracheal instillation of 11 well‐characterized MWCNT in female C57BL/6N BomTac mice. Genotoxicity in liver and spleen was evaluated by the comet assay. The dose of 54 μg MWCNT corresponds to three times the estimated dose accumulated during a work life at a NIOSH recommended exposure limit (0.001 mg/m3). Short and thin MWCNT were observed as agglomerates in lung tissue 1 year after exposure, whereas thicker and longer MWCNT were detected as single fibres, suggesting biopersistence of both types of MWCNT. The thin and entangled MWCNT induced varying degree of pulmonary inflammation, in terms of lymphocytic aggregates, granulomas and macrophage infiltration, whereas two thick and straight MWCNT did not. By multiple regression analysis, larger diameter and higher content of iron predicted less histopathological changes, whereas higher cobalt content significantly predicted more histopathological changes. No MWCNT‐related fibrosis or tumours in the lungs or pleura was found. One thin and entangled MWCNT induced increased levels of DNA strand breaks in liver; however, no physicochemical properties could be related to genotoxicity. This study reveals physicochemical‐dependent difference in MWCNT‐induced long‐term, pulmonary histopathological changes. Identification of diameter size and cobalt content as important for MWCNT toxicity provides clues for designing MWCNT, which cause reduced human health effects following pulmonary exposure.

Antimicrobial properties of lignin-decorated thin multi-walled carbon nanotubes in poly(vinyl alcohol) nanocomposites

Lignin-decorated thin multi-walled carbon nanotubes (t-MWNTs) were prepared to obtain mechanically strong poly(vinyl alcohol) (PVA) nanofibers (NFs) with high antimicrobial properties. The t-MWNTs were well-dispersed in the aqueous lignin solution owing to their good interaction with lignin molecules, resulting in decoration of the lignin molecules on the surface of the t-MWNTs. The lignin-decorated t-MWNT/PVA NF webs were prepared by electrospinning lignin/t-MWNT/PVA solutions containing 1 wt% t-MWNTs. They displayed enhanced mechanical properties in terms of breaking stress and modulus, compared to lignin/PVA nanofibers. Superior antimicrobial activity was also exhibited by the lignin/t-MWNTs/PVA composites compared to lignin/PVA composites. The mechanical properties of the lignin/t-MWNT/PVA NFs could be preserved even after the heat treatment of PVA, which is a necessary process for medical applications such as wound healing on the skin’s dermal layer.

Influence of carbon nanotube on the tribological properties of vegetable-based oil

A pin-on-disk friction and wear tester was used to investigate the tribological properties of multi-walled carbon nanotubes with different sizes and volume fractions as LB2000 vegetable-based oil additive. The wear scar of disk was characterized using scanning electron microscopy and Raman spectroscopy. Furthermore, the lubrication mechanism of multi-walled carbon nanotubes as vegetable-based oil additive was also discussed. It was found that thin and short multi-walled carbon nanotubes could improve the friction-reducing and anti-wear properties of vegetable-based oil more effectively than thick and long multi-walled carbon nanotubes. The optimal volume fraction of thin and short multi-walled carbon nanotubes was found to be 0.05%.

Use of tapered Pyrex capillary tubes to increase the mechanical stability of multiwall carbon nanotubes field emitters

In this study, NanocylTM NC 7000 Thin Multiwall Carbon Nanotubes (MWCNTs) were used with a high aspect ratio (>150) made by the process of catalytic chemical vapor deposition (CCVD). The field emitter tips were prepared by inserting these MWCT into fine glass capillary tubes that were pulled at high temperatures and then cut. Measurements were carried out under ultra-high vacuum (UHV) conditions with a base pressure of 10−9 mbar. The data show the effects of initial conditioning of MWCNT and hysteresis. Compression of the MWCNT by the capillary tubes appears to provide adequate mechanical support without requiring the use of a low-melting point electrically-conductive binder as has been used previously. Emission currents in excess of 1 μA were obtained so this technique shows promise as a reliable, stable, powerful electron source.

Enhanced thermal conductivity and mechanical properties of polyurethane composites with the introduction of thermally annealed carbon nanotubes

Here we report a significant enhancement in the physical properties of polyurethane composites by incorporating thermally annealed carbon nanotubes. The highly pure and crystalline carbon nanotubes were prepared by thermally annealing the catalytically grown thin multi-walled carbon nanotubes (t- MWNTs) at 2,300 °C using a graphite furnace in argon. The results of thermally annealing the catalytically as-grown carbon nanotubes in argon at high temperature were the effective removal of metallic impurities, the decrease in both the interlayer spacing and R-value, and the development of straight, crystalline layers. Moreover, the observation of the strong optical signal from the thermally annealed carbon indicates the possibility of growing small diameter innermost tubes below 1 nm within the hollow core of t-MWNTs. Finally, the introduction of the thermally annealed carbon nanotubes allowed us to make more mechanically strong and more thermally conductive polyurethane nanocomposites.

Ultraviolet to far-infrared transmission properties of thin film multi-walled carbon nanotube random networks

Thin films of multi-walled carbon nanotubes forming random networks were produced by vacuum filtration method, and their broadband electromagnetic radiation transmittance spectra are presented. Thickness of the nanotube films was between 100 nm and 1 μm, and the transmission properties are demonstrated for the wavelength range from 300 nm to 400 μm. It is observed that transmittance is an increasing function of a radiation wavelength, and for the thickest films it almost saturates above 1 μm wavelength. To explain the experimental results in the ultraviolet–near infrared range, we employed effective medium theory (in the form of symmetric Bruggeman model) correlating properties of multi-walled carbon nanotubes with the effective dielectric function of a nanotube network. The optical properties of a single multi-walled carbon nanotube that were used for calculations were based on ordinary and extraordinary dielectric functions of bulk graphite. The proposed theoretical model has been successfully fitted to the experimental results. It has been also found that despite the fact that radiation undergoes multiple internal reflections at the film interfaces, the transmittance–thickness relation can be still described by exponential decay.

Flexible Transparent Conducting Films Composed of Photochemically Oxidized Thin Multi-Walled Carbon Nanotubes

Flexible Transparent Conducting Films Composed of Photochemically Oxidized Thin Multi-Walled Carbon Nanotubes

Thin film composite membranes combining carbon nanotube intermediate layer and microfiltration support for high nanofiltration performances

In this work, we report a novel thin film composite (TFC) nanofiltration membrane (NFM) by incorporating a thin hydrophilic multi-walled carbon nanotubes (MWCNTs) interlayer between the microfiltration membrane support and the dense skin layer from interfacial polymerization. The MWCNT interlayer can absorb and storage the aqueous amino solution to facilitate the following interfacial polymerization, as well as provide a robust mechanical support to enable the nanofiltration of thin skin layer on the microporous substrate. Compared to those TFC NFMs supported by the ultrafiltration membranes, our membranes exhibit increased water permeation flux as high as 105.4Lm−2h−1 at 0.6MPa (which doubles the flux of the conventional ones) with high rejection for Na2SO4 (~95%). Moreover, the TFC NFMs show good stability during a long-term nanofiltration operation. This research provides us a promising approach to fabricate the high-flux NFMs for low pressure operation.

Decoration of gold nanoparticles on thin multiwall carbon nanotubes and their use as a glucose sensor

Thin multiwall carbon nanotubes (MWCNTs) have been decorated with gold nanoparticles (Au NPs) with polyaniline (PANI) as an inter-linker by a simple wet chemical method. The synthesized AuNPs:MWCNT:PANI composite was studied with UV–vis, FTIR, Raman spectroscopy, x-ray diffractometer, transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting AFM (C-AFM) images of the composite reveal the role played by the two components in electrochemical reactions. The size of the Au NPs was found to be 13 ± 2 nm in the composite as observed from TEM. The synthesized AuNPs:MWCNT:PANI composite was further drop casted onto a glassy carbon electrode (GCE) for electrocatalytic study. The resulting composite exhibits good electrocatalytic activity towards reduction of H2O2 and O2. A glucose biosensor was developed by immobilizing glucose oxidase into AuNPs:MWCNT:PANI composite film on GCE. The fabricated sensor demonstrates good linear response to glucose (i.e. R = 0.9975) in the range of 2 to 12 mM.

Methane decomposition over Pd promoted Ni/MgAl2O4 catalysts for the production of COx free hydrogen and multiwalled carbon nanotubes

This article reports the synthesis, characterization and catalytic performance of Pd promoted Ni/MgAl2O4 spinel catalysts for the thermal decomposition of methane into hydrogen and carbon nanotubes. The as-synthesized catalysts were characterized for their structural, textural, morphological properties. The catalytic properties of the Ni/MgAl2O4 catalyst were found to be enhanced with Pd promoter. It effectively increased the surface area of the catalyst without affecting the pore parameters and improved the fine dispersion of NiO particles on the surface of the magnesium aluminate. The reduction temperature of Ni/MgAl2O4 was found to be lowered after Pd deposition. Moreover, the Pd promoted catalyst provided high catalytic activity and stability for methane decomposition. A maximum hydrogen yield of ∼57% was obtained over the Pd catalyst at a reaction temperature of 700°C without any deactivation for 420min of time on stream. Moreover highly uniform, interwoven and thin multi-walled carbon nanotubes with high graphitization degree were deposited over the catalysts.