Commercial Multi-walled Carbon Nanotubes Research Articles

Antioxidative Activity of Carbon Nanotube and Nanofiber

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have electron affinities similar to those of fullerenes C60 and C70 and they are therefore capable of acting as radical scavengers in free radical chain reactions, including polym- erisation and the thermo-oxidative degradation of polymers. It is assumed that the CNTs and CNFs used as integral part of polymer composites are able to exhibit an antioxidant effect in these materials because of their radical accepting capacity. To examine this presumption the antioxidative activity of original and purified commercial multiwall carbon nanotube MWCNT and carbon nanofibre of platelet structure CNF-PL has been studied by means of a model oxidation reaction of cumene initiated (2,2'-azobisisobutyronitrile, AIBN) in liquid phase. This model reaction was designed to simulate the thermo-oxidative processes in carbon-chain polymers and allows comparison and transfer of obtained results to a polymer system. Kinetic measurements of oxidation rates showed that the effect of inhibition for the model oxidative reaction in the pres- ence of the original and purified MWCNT and CNF-PL strongly depends on the presence of metals (Co, Fe) in the nanoparticles. Rates of oxidation Wo2 (CNT;CNF) observed for the unrefined samples are result of the two competing rates - rate of inhibition Winh.(CNT; CNF) caused by structures of the CNT or CNF and the rates of initiation Wi(M) due to the follow- ing interaction: ROOH + M (Co;Fe) i.e, Wo2 ~ W inh (CNT;CNF) + Wi(M). The effective rate constants for the addition of cumyl radicals (R� ) to MWCNT and CNF-PL have been determined. These constants reduced to the same concentration (0.5wt.%) and temperature (60 o C) units have magnitudes: k1(MWCNT) (MWCNT) = (2.8 ± 0.3) � 10 4 s -1 and k1(CNF) (CNF) = (6.0 ± 1.0) � 10 3 s -1 . Thus, the effective rate constant, reflecting the antioxidative activity for the CNT, is five times higher than that for the CNF, is about equal to the rate constant for HAS Chimassorb 2020: k1(Chim.2020)(Chim. 2020) = (2.2 ± 0.3) � 10 4 s -1 , is ten times less than that for the HAS Chimassorb 119FL: k1(Chim.119FL)(Chim. 119FL) = (2.8 ± 0.3) � 10 5 s -1 and is about forty times less than that for the case of fullerene C60: k1(C60)(C60)(353K) = (1.2 ± 0.2) � 10 6 s -1 .

Rubber-toughened epoxy loaded with carbon nanotubes: structure–property relationships

The paper reports on the preparation, structure and properties of ternary thermosetting blends, based on DGEBA epoxy, cured with 3,3′-DDS and modified by the addition of CTBN reactive liquid rubber and/or 0.3 wt% of commercial multi-walled carbon nanotubes. The toughening effect of the phase-separated rubber particles is enhanced by the presence of the nanotubes, through a change in the morphology. In the absence of the rubber, the nanotubes alone produce a minimal effect upon the thermo-mechanical characteristics of the resin. However, the electrical conductivity of the cured resin samples is found to increase by five orders of magnitude, up to 3.6 × 10−3 S/m in the ternary blend.

Improvement of dehydrogenation kinetics ofLiBH4 dispersed on modified multi-walled carbon nanotubes

The dehydrogenation kinetics ofLiBH4 dispersed on multi-walled carbon nanotubes (MWCNTs) by the solvent infiltrationtechnique has been studied. Commercial MWCNTs were ball-milled for different millingtimes in order to increase the specific surface area (SSA) as measured by the BETtechnique. Thermal programmed desorption measurements have been performed using aSievert’s apparatus on samples with different SSA of MWCNTs and differentLiBH4 to MWCNT ratio. Pressure composition isotherms (PCI) havebeen obtained at different temperatures in order to estimate theΔH andΔS of dehydrogenation. It has been observed that the dispersion ofLiBH4 on MWCNTs leads to a lower dehydrogenation temperature compared to pureLiBH4. Moreover, the dehydrogenation temperature further decreases with increasing MWCNTsurface area. An interpretation of the kinetic effect is proposed.

The electrochemical properties of carbon nanotubes and carbon XC-72R and their application as Pt supports§

The results of an investigation of two samples of commercial multi-walled carbon nanotubes and a sample of carbon black, in the raw and activated state, were presented in the lecture. The activation of the carbon materials led to the formation of an abundance of oxygencontaining functional groups on the surface, an increased electrochemically active surface area, an enhanced charge storage ability and a promotion of the electron-transfer kinetics. It was presented that the morphology of the carbon nanotubes is important for the electrochemical properties, because nanotubes with a higher proportion of edge and defect sites showed faster electron transfer and pseudocapacitive redox kinetics. Modification of oxidized nanotubes by ethylenediamine and wrapping by poly(diallyldimethylammonium) chloride led to a decrease in the electrochemically active surface area and to reduced electron-transfer kinetics. Pt nanoparticles prepared by the microwave-assisted polyol method were deposited at the investigated carbon materials. A much higher efficiency of Pt deposition was observed on the modified CNTs than on the activated CNTs. The activity of the synthesized catalyst toward electrochemical oxygen reduction was almost the same as the activity of the commercial Pt/XC-72 catalyst.

Physiological effect of multi-walled carbon nanotubes (MWCNTs) on conidia of the entomopathogenic fungus, Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes)

The aim of the investigation was to assess the influence of commercial and carboxylated multi-walled carbon nanotubes (MWCNTs) on conidia of the entomopathogenic fungus Paecilomyces fumosoroseus. The commercial MWCNTs had an external diameter of about 40–60 nm, a length of 300–600 nm, a specific density of 140 to 300 g/dm3 and a carbon content of above 80%. Carboxylated MWCNTs were obtained by oxidizing commercial MWCNT by heating in HNO3, filtering, washing with water and drying. Conidia after different times of contact (from 1 to 865 hours) with nanomaterials in aqueous solutions were cultured for linear and biomass growth. Growth and sporification of mycelium after culture were evaluated. MWCNTs are not greatly cytotoxic for P. fumosoroseus conidia in the applied concentrations. The linear growth of mycelium obtained from conidia after contact with nanotubes was inhibited only in 2 (out of 18) cases (ones for both kinds of nanotubes). Carboxylated nanotubes did not inhibit biomass growth at all, but commercial nanotubes inhibited biomass growth in 2 cases. Sporification was the feature most strongly modified by carbon nanotubes. The commercial nanotubes again more strongly limited sporification of mycelium than carboxylated nanotubes did. The relatively greater influence of commercial versus carboxylated nanotubes was observed in the experiments.

Size response of an SMPS–APS system to commercial multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are representative-engineered nanomaterials with unique properties. The safe production of CNTs urgently requires reliable tools to assess inhalation exposure. In this study, on-line aerosol instruments were employed to detect the release of multi-walled CNTs (MWCNTs) in workplace environments. The size responses of aerosol instruments consisting of both a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS) were examined using five types of commercial MWCNTs. A MWCNT solution and powder were aerosolized using atomizing and shaking methods, respectively. Regardless of the phase and purity, the aerosolized MWCNTs showed consistent size distributions with both SMPS and APS. The SMPS and APS measurements revealed a dominant broad peak at approximately 200–400 nm and a distinct narrow peak at approximately 2 μm, respectively. Comparing with field application of the two aerosol instruments, the APS response could be a fingerprint of the MWCNTs in a real workplace environment. A modification of the atomizing method is recommended for the long-term inhalation toxicity studies.

A comparative study of the electrochemical properties of carbon nanotubes and carbon black

Two samples of commercial multi-walled carbon nanotubes (Sigma–Aldrich and Sun Nanotech) and a sample of carbon black (Vulcan XC-72R) were investigated in raw state and after the activation in nitric and sulfuric acid by ultrasound agitation. Atomic force microscopy revealed that activated Sigma–Aldrich nanotubes are straight with corrugated walls (bamboo-like structure), while Sun Nanotech nanotubes are tortuous with smooth walls. Fourier transform infrared spectroscopy showed that abundance of oxygen-containing functional groups was formed on both Sigma–Aldrich and Sun Nanotech carbon nanotubes, as well as on carbon black surfaces. Electrochemical properties were studied by cyclic voltammetry and electrochemical impedance spectroscopy. It was found that the electrochemically active surface area of all carbon samples is expanded, charge storage ability is enhanced and the electron-transfer kinetics, probed by Fe ( CN ) 6 3 - / Fe ( CN ) 6 4 - redox couple, is promoted upon activation. The characteristics of carbon nanotubes were superior to carbon black. Morphology of the carbon nanotubes was found to be important; nanotubes with corrugated walls showed faster electron-transfer and pseudocapacitive redox kinetics than nanotubes with smooth walls. This was explained by the higher proportion of edge and defect sites, which are known as more electrochemically active than the walls of uniform graphene structure.

Effect of activation/purification of multiwalled carbon nanotubes (MWCNTs) on the activity of non-platinum based hypo-hyper d-electrocatalysts for hydrogen evolution

Commercial multiwalled carbon nanotubes (MWCNTs) were used as a catalyst support for non-platinum hypo-hyper d-electrocatalysts. In order to improve the performance of these catalysts, activation/purification of MWCNTs in acid medium (HNO 3) was carried out. The physical and surface changes of MWCNTs were investigated by DTA/TGA analysis, Raman spectroscopy, and cyclic voltammetry. Structural changes of the electrocatalysts were observed by infrared spectroscopy and SEM. Their use as a support for electrocatalysts for hydrogen evolution was demonstrated, and shown to be more suitable compared to the traditional carbon support material − carbon black (Vulcan XC-72). The electrocatalysts consisted of 10% Co + 18% TiO 2 + MWCNTs. Activation/purification removes the amorphous carbon phase in the MWCNTs. As a result of both shortening and opening of carbon nanotubes, better dispersion of metallic particles (the active catalytic centers) was achieved. Thus, trans-particle and inter-particle porosity of the electrocatalytic material was improved, implying increase of catalytic activity for hydrogen evolution.

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.

Microstructures and Nanostructures for Environmental Carbon Nanotubes and Nanoparticulate Soots

This paper examines the microstructures and nanostructures for natural (mined) chrysotile asbestos nanotubes (Mg3 Si2O5 (OH)4) in comparison with commercial multiwall carbon nanotubes (MWCNTs), utilizing scanning and transmission electron microscopy (SEM and TEM). Black carbon (BC) and a variety of specific soot particulate (aggregate) microstructures and nanostructures are also examined comparatively by SEM and TEM. A range of MWCNTs collected in the environment (both indoor and outdoor) are also examined and shown to be similar to some commercial MWCNTs but to exhibit a diversity of microstructures and nanostructures, including aggregation with other multiconcentric fullerenic nanoparticles. MWCNTs formed in the environment nucleate from special hemispherical graphene "caps" and there is evidence for preferential or energetically favorable chiralities, tube growth, and closing. The multiconcentric graphene tubes ( approximately 5 to 50 nm diameter) differentiate themselves from multiconcentric fullerenic nanoparticles and especially turbostratic BC and carbonaceous soot nanospherules ( approximately 8 to 80 nm diameter) because the latter are composed of curved graphene fragments intermixed or intercalated with polycyclic aromatic hydrocarbon (PAH) isomers of varying molecular weights and mass concentrations; depending upon combustion conditions and sources. The functionalizing of these nanostructures and photoxidation and related photothermal phenomena, as these may influence the cytotoxicities of these nanoparticulate aggregates, will also be discussed in the context of nanostructures and nanostructure phenomena, and implications for respiratory health.

Removal of cationic dyes from aqueous solution using magnetic multi-wall carbon nanotube nanocomposite as adsorbent

A magnetic multi-wall carbon nanotube (MMWCNT) nanocomposite was synthesized and was used as an adsorbent for removal of cationic dyes from aqueous solutions. The MMWCNT nanocomposite was composed of commercial multi-wall carbon nanotubes and iron oxide nanoparticles. The properties of this magnetic adsorbent were characterized by scanning electron microscopy, X-ray diffraction and BET surface area measurements. Adsorption characteristics of the MMWCNT nanocomposite adsorbent were examined using methylene blue, neutral red and brilliant cresyl blue as adsorbates. Experiments were carried out to investigate adsorption kinetics, adsorption capacity of the adsorbent and the effect of adsorption dosage and solution pH values on the removal of cationic dyes. Kinetic data were well fitted by a pseudo second-order model. Freundlich model was used to study the adsorption isotherms. The prepared MMWCNT adsorbent displayed the main advantage of separation convenience compared to the present adsorption treatment.

Conductive Property of Carbon-Nanotube Dispersed Nanocomposite Coatings for Steel

Nanostructured modification of polymers has opened up new perspective for multifunctional materials. Carbon-nanotubes have the potential to increase the conductivity of their composite, with improved or retaining mechanical performance. This study focuses on the evaluation of the thermal and electrical conductivities of carbonnanotube filled alkyd resins for steel coatings. Polymer/Carbon-nanotube nanocomposites have been prepared by mixing commercial multiwall carbon-nanotubes with alkyd resins and by curing. The thermal and electrical conductivities of carbon-nanotubes filled nanocomposite was found to be increased comparing with the original resin without any fillers or with the resin with carbon-black or carbon-nanofiber.

Direct contact cytotoxicity assays for filter-collected, carbonaceous (soot) nanoparticulate material and observations of lung cell response

A simple, direct contact, cytotoxicity (in vitro) assay has been developed where particulate matter (PM) collected on glass fiber filters was exposed to human epithelial (lung) cells. Carbonaceous (soot) PM included tire, wood, diesel, candle, and variously combusted natural gas PM from a kitchen stove range. Black carbon PM and a commercial multiwall carbon nanotube aggregate PM was also examined in vitro as surrogate materials, and all experimental PM was characterized by field emission scanning electron microscopy and transmission electron microscopy. Assay results for 48 h cultures showed toxicity for all carbonaceous PM with various natural gas PM being the most toxic; this was comparable to the toxicity induced by the surrogate PM. Light microscopy examination of affected epithelial cells confirmed the semi-quantitative results. Comparison of polycyclic aromatic hydrocarbon (PAH) content and concentration for the carbonaceous PM showed no PAH correlation with relative cell viability (cell death) after 48 h.

High-sensitivity matrix-assisted laser desorption/ionization Fourier transform mass spectrometry analyses of small carbohydrates and amino acids using oxidized carbon nanotubes prepared by chemical vapor deposition as matrix

In matrix-assisted laser desorption/ionization (MALDI) Fourier transform mass spectrometry (FTMS) analyses of small oligosaccharides and amino acids, high sensitivities for oligosaccharides (10 fmol) were obtained by introducing oxidized carbon nanotubes (CNTs) with short and open-end structure as valuable matrix. The CNTs were deposited in porous anodic alumina (PAA) templates by chemical vapor deposition. Transmission electron microscopy (TEM) images show that those CNTs include low levels of amorphous carbon. Thus, the background interference signals generally caused by amorphous carbon powder in CNTs can be reduced effectively. Experiments also confirmed that the FTMS signal intensity of CNTs prepared in PAA template is much lower than that of commercial multi-wall carbon nanotubes (MCNTs). Moreover, the purified process for CNTs with mixed acid (H 2SO 4 and HNO 3) also contributed to the minimization of background. Intense signals corresponding to alkali cation adduct of neutral carbohydrates and amino acids have been acquired. In addition, reliable quantitative analyses for urine and corn root were also achieved successfully. The present work will open a new way to the application of oxidized CNTs as an effective matrix in MALDI MS research.

Combustion-Generated Nanoparticulates in the El Paso, TX, USA / Juarez, Mexico Metroplex: Their Comparative Characterization and Potential for Adverse Health Effects

In this paper we report on the collection of fine (PM1) and ultrafine (PM0.1), or nanoparticulate, carbonaceous materials using thermophoretic precipitation onto silicon monoxide/formvar-coated 3 mm grids which were examined in the transmission electron microscope (TEM). We characterize and compare diesel particulate matter (DPM), tire particulate matter (TPM), wood burning particulate matter, and other soot (or black carbons (BC)) along with carbon nanotube and related fullerene nanoparticle aggregates in the outdoor air, as well as carbon nanotube aggregates in the indoor air; and with reference to specific gas combustion sources. These TEM investigations include detailed microstructural and microdiffraction observations and comparisons as they relate to the aggregate morphologies as well as their component (primary) nanoparticles. We have also conducted both clinical surveys regarding asthma incidence and the use of gas cooking stoves as well as random surveys by zip code throughout the city of El Paso. In addition, we report on short term (2 day) and longer term (2 week) in vitro assays for black carbon and a commercial multiwall carbon nanotube aggregate sample using a murine macrophage cell line, which demonstrate significant cytotoxicity; comparable to a chrysotile asbestos nanoparticulate reference. The multi-wall carbon nanotube aggregate material is identical to those collected in the indoor and outdoor air, and may serve as a surrogate. Taken together with the plethora of toxic responses reported for DPM, these findings prompt concerns for airborne carbonaceous nanoparticulates in general. The implications of these preliminary findings and their potential health effects, as well as directions for related studies addressing these complex issues, will also be examined.

Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment.

Nanotechnology and nanomaterials have become the new frontier world-wide over the past few years and prospects for the production and novel uses of large quantities of carbon nanotubes in particular are becoming an increasing reality. Correspondingly, the potential health risks for these and other nanoparticulate materials have been of considerable concern. Toxicological studies, while sparse, have been concerned with virtually uncharacterized, single wall carbon nanotubes, and the conclusions have been conflicting and uncertain. In this research we performed viability assays on a murine lung macrophage cell line to assess the comparative cytotoxicity of commercial, single wall carbon nanotubes (ropes) and two different multiwall carbon nanotube samples; utilizing chrysotile asbestos nanotubes and black carbon nanoaggregates as toxicity standards. These nanotube materials were completely characterized by transmission electron microscopy and observed to be aggregates ranging from 1 to 2 microm in mean diameter, with closed ends. The cytotoxicity data indicated a strong concentration relationship and toxicity for all the carbon nanotube materials relative to the asbestos nanotubes and black carbon. A commercial multiwall carbon nanotube aggregate exhibiting this significant cell response was observed to be identical in structure to multiwall carbon nanotube aggregates demonstrated to be ubiquitous in the environment, and especially in indoor environments, where natural gas or propane cooking stoves exist. Correspondingly, preliminary epidemiological data, although sparse, indicate a correlation between asthma incidence or classification, and exposure to gas stoves. These results suggest a number of novel epidemiological and etiological avenues for asthma triggers and related respiratory or other environmental health effects, especially since indoor number concentrations for multiwall carbon nanotube aggregates is at least 10 times the outdoor concentration, and virtually all gas combustion processes are variously effective sources. These results also raise concerns for manufactured carbon nanotube aggregates, and related fullerene nanoparticles.