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Continuous dry dispersion of multi-walled carbon nanotubes to aerosols with high concentrations of individual fibers.

ABSTRACT: The assessment of the toxicity of airborne nanofibers is an important task. It relies on toxicological inhalation studies and validated exposure measurement techniques. Both require nanofiber-containing aerosols of known morphological composition and controlled fraction of individual fibers. Here, a dry powder dispersion method is presented that operates with mixtures of nanofibers and microscale beads. Aerosolization experiments of mixtures of multi-walled carbon nanotubes (MWCNTs) and glass beads that were continuously fed into a Venturi nozzle enabled high generation rates of aerosols composed of individual and agglomerate nanofiber structures. The aerosol process achieved good stability over more than 2 h with respect to concentration and aerodynamic size distribution. Its operation duration is limited only by the reservoir volume of the cyclone used to separate the beads from the aerosol. The aerosol concentration can be controlled by changing the mass ratio of MWCNTs and glass beads or by adapting the mass feed rate to the nozzle. For two agglomerated MWCNT materials, aerosol concentrations ranged from 1700 to 64,000 nano-objects per cm³. Comprehensive scanning electron microscope analysis of filter samples was performed to categorize and determine the morphological composition of the aerosol, its fiber content as well as fiber length and diameter distributions. High fractions of individual fibers of up to 34% were obtained, which shows the setup to be capable of dispersing also highly tangled MWCNT agglomerates effectively.

SUBMITTER: Simonow BK

PROVIDER: S-EPMC5984959 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Scanning electrochemical microscopy of individual single-walled carbon nanotubes.

Project description:Here we report on the novel application of scanning electrochemical microscopy (SECM) to enable spatially resolved electrochemical characterization of individual single-walled carbon nanotubes (SWNTs). The feedback imaging mode of SECM was employed to detect a pristine SWNT (approximately 1.6 nm in diameter and approximately 2 mm in length) grown horizontally on a SiO(2) surface by chemical vapor deposition. The resulting image demonstrates that the individual nanotube under an unbiased condition is highly active for the redox reaction of ferrocenylmethyltrimethylammonium used as a mediator. Micrometer-scale resolution of the image is determined by the diameter of a disk-shaped SECM probe rather than by the nanotube diameter as assessed using 1.5 and 10 microm diameter probes. Interestingly, the long SWNT is readily detectable using the larger probe although the active SWNT covers only approximately 0.05% of the insulating surface just under the tip. This high sensitivity of the SECM feedback method is ascribed to efficient mass transport and facile electron transfer at the individual SWNT.

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The Dispersion State of Tangled Multi-Walled Carbon Nanotubes Affects Their Cytotoxicity.

Project description:The medical applications of carbon nanotubes (CNTs) have garnered much attention. However, evaluating the safety of CNTs remains difficult, and no consensus has been reached. Moreover, assessing the biosafety of multi-walled CNTs (MWCNTs), which can become tangled during manufacturing, is challenging because they do not readily disperse. We studied how the dispersion state of tangled MWCNTs affects their cytotoxicity, using three sonicators. Flotube 9110 (FT9110), tangled MWCNTs, were dispersed in two dispersants (fetal bovine serum and polysorbate 80) using a new type of sonicator (PR-1) and two conventional sonicators. The size and cytotoxicity of the dispersed FT9110 were measured using the BEAS-2B human bronchial epithelial cell line. The PR-1 dispersed the FT9110 to agglomerates <200 nm in diameter; FT9110 dispersed with the PR-1 did not show cytotoxicity regardless of dispersant. The other sonicators dispersed the FT9110 to particles >1000 nm in diameter, and cytotoxicity depended on the dispersant. We found that excluding cells adhered to agglomerated FT9110 before evaluating cytotoxicity can lead to false-positive results. The PR-1 sonicator dispersed tangled FT9110 to many single fibers, which showed lower cytotoxicity than conventionally-sonicated MWCNTs. We suggest that dispersion state should be accounted for when evaluating the cytotoxicity of MWCNTs.

| S-EPMC5245756 | biostudies-literature

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Biocompatible nanoscale dispersion of single-walled carbon nanotubes minimizes in vivo pulmonary toxicity.

Project description:Excitement surrounding the attractive physical and chemical characteristics of single walled carbon nanotubes (SWCNTs) has been tempered by concerns regarding their potential health risks. Here we consider the lung toxicity of nanoscale dispersed SWCNTs (mean diameter approximately 1 nm). Because dispersion of the SWCNTs increases their aspect ratio relative to as-produced aggregates, we directly test the prevailing hypothesis that lung toxicity associated with SWCNTs compared with other carbon structures is attributable to the large aspect ratio of the individual particles. Thirty days after their intratracheal administration to mice, the granuloma-like structures with mild fibrosis in the large airways observed in mice treated with aggregated SWCNTs were absent in mice treated with nanoscale dispersed SWCNTs. Examination of lung sections from mice treated with nanoscale dispersed SWCNTs revealed uptake of the SWCNTs by macrophages and gradual clearance over time. We conclude that the toxicity of SWCNTs in vivo is attributable to aggregation of the nanomaterial rather than the large aspect ratio of the individual nanotubes. Biocompatible nanoscale dispersion provides a scalable method to generate purified preparations of SWCNTs with minimal toxicity, thus allowing them to be used safely in commercial and biomedical applications.

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Electronic Raman scattering on individual semiconducting single walled carbon nanotubes.

Project description:We report experimental measurements of electronic Raman scattering by electrons (holes) in individual single-walled carbon nanotubes (SWNTs) under resonant conditions. The Raman scattering at low frequency range reveals a single particle excitation feature. And the dispersion of electronic structure around the center of Brillouin zone of a semiconducting SWNT (14, 13) is extracted.

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Quantum dot-like excitonic behavior in individual single walled-carbon nanotubes.

Project description:Semiconducting single-walled carbon nanotubes are one-dimensional materials with great prospects for applications such as optoelectronic and quantum information devices. Yet, their optical performance is hindered by low fluorescent yield. Highly mobile excitons interacting with quenching sites are attributed to be one of the main non-radiative decay mechanisms that shortens the exciton lifetime. In this paper we report on time-integrated photoluminescence measurements on individual polymer wrapped semiconducting carbon nanotubes. An ultra narrow linewidth we observed demonstrates intrinsic exciton dynamics. Furthermore, we identify a state filling effect in individual carbon nanotubes at cryogenic temperatures as previously observed in quantum dots. We propose that each of the CNTs is segmented into a chain of zero-dimensional states confined by a varying local potential along the CNT, determined by local environmental factors such as the amount of polymer wrapping. Spectral diffusion is also observed, which is consistent with the tunneling of excitons between these confined states.

| S-EPMC5111057 | biostudies-literature

Dispersion of Single-Walled Carbon Nanotubes by Aromatic Cyclic Schiff Bases via Non-Covalent Interactions

Project description: Not available

| S-EPMC11243016 | biostudies-literature

Pressure dependent conduction of individual multi-walled carbon nanotubes: the effect of mechanical distortions.

Project description:Multi-walled carbon nanotubes (MWCNTs) show an oscillation in electrical resistance (from I-V measurements) during mechanical distortion in which peak separation is inversely correlated with the diameter of the MWCNTs. These results provide the first experimental support of the theoretical prediction that distortion causes Van Hove singularities and Dirac cones in MWCNTs to misalign and cause the opening of the band gap, and suggest that when fabricating contacts for CNTs for device applications, the pressure caused by the contact deposition method must be taken into account for manufacturing devices with consistent properties.

| S-EPMC9418891 | biostudies-literature

Dispersion, sedimentation and aggregation of multi-walled carbon nanotubes as affected by single and binary mixed surfactants.

Project description:Two commonly used dispersants, octyl phenol ethoxylate (Triton X-100) and sodium dodecyl sulfate (SDS), were employed to explore the effects of single or mixed surfactants on the dispersion, sedimentation and aggregation of multi-walled carbon nanotubes (MWCNTs). Non-ionic surfactant TX100 showed much superior capability to anionic surfactant SDS in dispersing MWCNTs due to the benzene ring structure in its tail group. The addition of SDS reduced the adsorption of TX100 on the surface of MWCNTs and the consequent suspension of MWCNTs. The dispersing ability of TX100-SDS binary mixture was between those of individual SDS and TX100. The introduction of SDS greatly retarded the sedimentation and aggregation of suspended MWCNTs. The critical coagulation concentration (CCC) values of suspended MWCNTs dispersed by TX100 (2000 mg l-1), SDS (2000 mg l-1) and TX100-SDS (2000 mg l-1 of each component) were 48.6, 398 and 324 mM, respectively, for Na+ treatments. The CCC values were much lower for Ca2+ treatments, which were 30.4 and 32.1 mM, respectively, for MWCNTs dispersed by TX100 and TX100-SDS mixture. Overall, these results demonstrated that although the introduction of SDS did not improve the ability of TX100 in suspending MWCNTs, the suspensions exhibited more stable properties than those dispersed by TX100 alone. Our findings have important implications for the design of surfactant mixtures and the prediction of the behaviour and fate of MWCNTs in the water environment.

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Polymethyl(1-Butyric acidyl)silane-Assisted Dispersion and Density Gradient Ultracentrifugation Separation of Single-Walled Carbon Nanotubes.

Project description:Individual single-walled carbon nanotubes (SWNTs) with distinct electronic types are crucial for the fabrication of SWNTs-based electronic and magnetic devices. Herein, the water-soluble polymethyl(1-butyric acidyl)silane (BA-PMS) was synthesized via the hydrosilylation reaction between 3-butenoic acid and polymethylsilane catalyzed by 2,2'-azodibutyronitrile. As a new dispersant, BA-PMS displayed a quite good dispersing capacity to arc-discharged SWNTs and moderate selectivity for metallic species. The application of sucrose-DGU, the density gradient ultracentrifugation with sucrose as the gradient medium, to the co-surfactants (BA-PMS and sodium dodecyl sulfonate) individually dispersed SWNTs yielded metallic SWNTs of 85.6% purity and semiconducting SWNTs of 99% purity, respectively. This work paves a path to the DGU separation of the SWNTs dispersed by polymer-based dispersants with hydrophobic alkyl chains.

| S-EPMC9227055 | biostudies-literature

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