Accumulation Of Carbon Nanotubes Research Articles

Assembly and Alignment of High Packing Density Carbon Nanotube Arrays Using Lithographically Defined Microscopic Water Features.

High packing density aligned arrays of semiconducting carbon nanotubes (CNTs) are required for many electronics applications. Past work has shown that the accumulation of CNTs at a water-solvent interface can drive array self-assembly. Previously, the confining interface was a large-area, macroscopic feature. Here, we report on the CNT assembly on microscopic water features. Water microdroplets are formed on 10-100 μm wide hydrophilic stripes patterned on a substrate. Exposure to CNTs dispersed in solvent accumulates CNTs at the microdroplet-solvent interface, driving their alignment and deposition at the microdroplet-solvent-substrate contact line. Compared with macroscopic methods in which the contact line uncontrollably moves across the substrate as it is pulled out of the liquids, the hydrophilic patterns and microdroplets allow pinning of the contact line. As CNTs deposit, the contact line self-translates, allowing for dense CNT packing. We realize monolayer CNT arrays aligned within ±3.9° at density of 250 μm-1 and field effect transistors with a high current density of 1.9 mA μm-1 and transconductance of 1.2 mS μm-1 at -0.6 V drain bias and 60 nm channel length.

Formation of a conductive network in urea−formaldehyde/carbon nanotube composite foams for electromagnetic shielding

AbstractDue to advantages of low cost and intrinsic flame retardancy, urea−formaldehyde (UF) foams with electromagnetic shielding function present a promising application prospect in the fields of construction, transportation and electronics. In this study, by using carbon nanotubes (CNTs) as conductive filler and thermo‐expandable microspheres (EMs) as physical foaming agent, a series of UF/CNT composite foams with perfect and polygonal closed cellular structure were prepared for electromagnetic shielding. By adding 6 wt% EMs, the composite foam exhibited a uniform cell wall thickness, while the local accumulation of CNTs was inhibited and CNTs were distributed evenly within the cell walls. With increasing CNT content the dispersion of CNTs transformed from a scattered and ‘island‐like’ structure to an interconnected structure, and for samples with CNT content higher than 1.34 vol% a continuous conductive network was constructed within the cell walls, thus significantly improving the electrical conductivity and electromagnetic shielding effectiveness for the foams, which reached 34.5 dB and satisfied the requirement of commercial applications. Moreover, the contribution of absorption to the electromagnetic shielding effectiveness was much larger than that of reflection for composite foams, indicating that absorption was the dominant shielding mechanism. © 2023 Society of Industrial Chemistry.

Influence of carbon nanotube on the mechanical and electrical characteristics of concrete – A review

Conventional concrete, which is composed of cement, coarse aggregate, fine aggregate, water, and superplasticizer, has the disadvantages of low maximum split tensile strength and low ductility, which can lead to sudden failure. However, the use of carbon nanotubes (CNT) can improve the binding to detect cracks in the structure before it collapses, as well as increase the maximum split tensile strength and ductility. The CNT is utilized to improve the mechanical characteristics of concrete, including its compressive strength, split tensile strength, and flexural strength. In addition to self-sensing, researchers examined the impact of carbon fiber and CNT particles on the mechanical characteristics of beam specimens with the suggested reinforcement arrangement. In this review, mechanical tests such as compressive strength, split tensile strength, and flexural strength are examined to determine the impact percentage of CNT that is beneficial for enhancing the strength of concrete. The study also further reviewed the resistivity of self-sensing CNT concrete. The review explored that CNT also improves electrical properties, such as resistivity and conductivity, and thermal conductivity of cement composites. To increase the electrical conductivity of beams, CNT and chopped carbon fibers (CF) were utilized. As a Nano-material, CNT may be widely distributed in the concrete through a proper mixing strategy. Due to their high modulus of elasticity, tensile strength, and yield strain, CNTs are an appealing material for concrete reinforcement. Using ultrasonication and a superplasticizer, a solution of dispersed CNTs with exceptional workability in concrete was made because the accumulation of CNTs significantly decreased the electrical resistance. The purpose of adding CNT to concrete for the Structure Health Monitoring technique is to detect building fractures using self-sensing concrete (SHM). The research finally concludes that CNT is highly beneficial to enhance compressive strength, flexure strength, and split tensile strength.

Light-induced thermal convection for collection and removal of carbon nanotubes

Carbon nanotubes (CNTs) have exhibited immense potential for applications in biology and medicine, and once their intended purpose is fulfilled, the elimination of residual CNTs is essential to avoid negative effects. In this study, we demonstrated the effective collection and simple removal of CNTs dispersed in a suspension via thermal convection. First, a tapered fiber tip with a cone angle and end diameter of 10° and 3 μm, respectively, was fabricated via a heating and pulling method. Further, a laser beam with a power and wavelength of 100 mW and 1.55 μm, respectively, was launched into the tapered fiber tip, which was placed in a CNT suspension, resulting in the formation of a microbubble on the fiber tip. The temperature gradient on the microbubble and suspension surface induced thermal convection in the suspension, which resulted in the accumulation of CNTs on the fiber tip. The experimentally formed CNT cluster possessed a circular top surface with a diameter of 87 μm and an arched cross-section with a height of 19 μm. Furthermore, this CNT cluster was firmly attached to the fiber tip. Therefore, the removal of CNT clusters can be realized by simply removing the fiber tip from the suspension. Moreover, we simulated the thermal convection that caused CNT aggregation. The obtained results indicate that convection near the fiber tip flows toward it, which pushes the CNTs toward the fiber tip and enables their attachment to it. Further, the flow velocity is symmetrically distributed as a Gaussian function, which results in the formation of a circular top surface and arched cross-sectional profile for the CNT cluster. Our method may be applied in biomedicine for the collection and removal of nano-drug residues.

A trophic transfer study: accumulation of multi-walled carbon nanotubes associated to green algae in water flea Daphnia magna

Carbon nanotubes (CNT) are promising nanomaterials in modern nanotechnology and their use in many different applications leads to an inevitable release into the aquatic environment. In this study, we quantified trophic transfer of weathered multi-walled carbon nanotubes (wMWCNT) from green algae to primary consumer Daphnia magna in a concentration of 100 μg L−1 using radioactive labeling of the carbon backbone (14C-wMWCNT). Trophic transfer of wMWCNT was compared to the uptake by daphnids exposed to nanomaterials in the water phase without algae. Due to the rather long observed CNT sedimentation times (DT) from the water phase (DT50: 3.9 days (d), DT90: 12.8 d) wMWCNT interact with aquatic organisms and associated to the green algae Chlamydomonas reinhardtii and Raphidocelis subcapitata. After the exposition of algae, the nanotubes accumulated to a maximum of 1.6 ± 0.4 μg 14C-wMWCNT mg−1 dry weight−1 (dw−1) and 0.7 ± 0.3 μg 14C-wMWCNT mg−1 dw−1 after 24 h and 48 h, respectively. To study trophic transfer, R. subcapitata was loaded with 14C-wMWCNT and subsequently fed to D. magna. A maximum body burden of 0.07 ± 0.01 μg 14C-wMWCNT mg−1 dw−1 and 7.1 ± 1.5 μg 14C-wMWCNT mg−1 dw−1 for D. magna after trophic transfer and waterborne exposure was measured, respectively, indicating no CNT accumulation after short-term exposure via trophic transfer. Additionally, the animals eliminated nanomaterials from their guts, while feeding algae facilitated their excretion. Further, accumulation of 14C-wMWCNT in a growing population of D. magna revealed a maximum uptake of 0.7 ± 0.2 μg mg−1 dw−1. Therefore, the calculated bioaccumulation factor (BAF) after 28 d of 6700 ± 2900 L kg−1 is above the limit that indicates a chemical is bioaccumulative in the European Union Regulation REACH. Although wMWCNT did not bioaccumulate in neonate D. magna after trophic transfer, wMWCNT enriched in a 28 d growing D. magna population regardless of daily feeding, which increases the risk of CNT accumulation along the aquatic food chain.

Unexpectedly High Salt Accumulation inside Carbon Nanotubes Soaked in Dilute Salt Solutions.

We experimentally demonstrate the formation of salt aggregations with unexpectedly high concentration inside multiwalled carbon nanotubes (CNTs) soaked only in dilute salt solution sand even in solutions containing only traces of salts. This finding suggests the blocking of fluid across CNTs by the salt aggregations when CNTs are soaked in a dilute salt solution with the concentration of seawater or even lower, which may open new avenues for the development of novel CNT-based desalination techniques. The high salt accumulation of CNTs also provides a new CNT-based strategy for the collection or extraction of noble metal salts in solutions containing traces of noble metal salts. Theoretical analyses reveal that this high salt accumulation inside CNTs can be mainly attributed to the strong hydrated cation-π interactions of hydrated cations and π electrons in the aromatic rings of CNTs.

Biodistribution of Carbon Nanotubes in Animal Models.

The many interesting physical and chemical properties of carbon nanotubes (CNT) make it one of the most commercially attractive materials in the era of nanotechnology. Here, we review the recent publications on in vivo biodistribution of pristine and functionalized forms of single-walled and multi-walled CNT. Pristine CNT remain in the lung for months or even years after pulmonary deposition. If cleared, the majority of CNT move to the gastrointestinal (GI) tract via the mucociliary escalator. However, there appears to be no uptake of CNT from the GI tract, with a possible exception of the smallest functionalized SWCNT. Importantly, a significant fraction of CNT translocate from the alveolar space to the near pulmonary region including lymph nodes, subpleura and pleura (<7% of the pulmonary deposited dose) and to distal organs including liver, spleen and bone marrow (~1%). These results clearly demonstrate the main sites of long-term CNT accumulation, which also includes pleura, a major site for fibre-induced pulmonary diseases. Studies on intravenous injection show that CNT in blood circulation are cleared relatively fast with a half-life of minutes or hours. The major target organs were the same as identified after pulmonary exposure with the exception of urine excretion of especially functionalized SWCNT and accumulation in lung tissue. Overall, there is evidence that CNT will primarily be distributed to the liver where they appear to be present at least one year after exposure.

Микроструктура и микротвердость металломатричных композитов с углеродными нанотрубками, полученные интенсивной пластической деформацией

Research of microstructure, X-ray diffraction and microhardness metall-matrix composites reinforced with carbon nanotubes (CNT) obtained by severe plastic deformation were carried out. As starting materials for the preparation of composites multi-walled CNT and powders of copper and aluminium were used. Composites in the form of discs with a diameter of 10 mm and a thickness of 0.15 mm were obtained by means of high pressure torsion about 5 GPa . Copper-CNT and aluminium-CNT with them 4% and 2% weight content of CNT respectively were investigated. Studies using scanning electron microscopy showed that in the center and on the edge of the disk microstructure is different. In particular, in the center of the disc the pores and cracks were observed. CNT are located predominantly in the form of cloth large extent. With increasing distance from the center to the edge of the disk, pores and cracks were absent, CNT accumulation were observed in the form of clusters. Microstructure analysis of composites using methods of transmission electron microscopy and X-ray diffraction showed that the introduction and increase concentration of CNT in the matrix of metal leads to decrease of the mean grain size up to 50 nm. Evaluation of the dislocation density and microhardness testing showed that with increasing concentration of CNT their values are increased. In particular, microhardness value of composite Cu-4%CNT and Al-2%CNT is 1.5 times higher compared to the metal without CNT. Rotating moments of composites depending on rotation number in the process of high pressure torsion were measured. Measurements have shown that the value of rotating moment for the sample with CNT exceeds that value for the sample without CNT.

Interactions of multiwalled carbon nanotubes with algal cells: Quantification of association, visualization of uptake, and measurement of alterations in the composition of cells

Carbon nanotubes (CNTs) are considered promising materials in nanotechnology. We quantified CNT accumulation by the alga Desmodesmus subspicatus. Cells were exposed to radiolabeled CNTs (14C-CNTs; 1 mg/L) to determine uptake and association, as well as elimination and dissociation in clear media. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to detect effects of CNTs on algae. CNT-cell interactions were visualized by electron microscopy and related to alterations in their cell composition. A concentration factor of 5000 L/kg dry weight was calculated. Most of the material agglomerated around the cells, but single tubes were detected in the cytoplasm. Computational analyses of the ATR-FTIR data showed that CNT treated algae differed from controls at all sampling times. CNT exposure changed the biochemical composition of cells. The fact that CNTs are bioavailable for algae and that they influence the cell composition is important with regard to environmental risk assessment of this nanomaterial.

Deposition of carbon nanotubes by a marine suspension feeder revealed by chemical and isotopic tracers

Carbon nanotubes (CNTs) are one of the few truly novel nanomaterials and are being incorporated into a wide range of products, which will lead to environmental release and potential ecological impacts. We examined the toxicity of CNTs to marine mussels and the effect of mussels on CNT fate and transport by exposing mussels to 1, 2, or 3mg CNTsl−1 for four weeks and measuring mussel clearance rate, shell growth, and CNT accumulation in tissues and deposition in biodeposits. We used metal impurities and carbon stable isotope ratios of the CNTs as tracers of CNT accumulation. Mussels decreased clearance rate of phytoplankton by 24% compared with control animals when exposed to CNTs. However, mussel growth rate was unaffected by CNT concentrations up to 3mgl−1. Based on metal concentrations and carbon stable isotope values, mussels deposited most CNTs in biodeposits, which contained >110mg CNTsg−1 dry weight, and accumulated about 1mg CNTsg−1 dry weight of tissue. We conclude that extremely high concentrations of CNTs are needed to illicit a toxic response in mussels but the ability of mussels to concentrate and deposit CNTs in feces and pseudofeces may impact infaunal organisms living in and around mussel beds.

Effects of Subchronic Exposure to Multi-Walled Carbon Nanotubes on Mice

Carbon nanotubes have attracted attention not only due to electrical, optical, and mechanical applications but also due to their presence in biological and pharmaceutical products. In this study, modified multi-walled carbon nanotubes (MWCNT) were used as a model to evaluate potential subchronic effects of carbon nanotubes on mice. ICR mice were treated with phosphorylcholine-grafted multi-walled carbon nanotubes (MWCNT-PC) daily for 28 d at 10, 50, or 250 mg/kg by the intraperitoneal (ip) route. Subchronic exposure to MWCNT-PC did not produce any apparent systemic effects in mice. The body weight of the high-dose group was significantly lower than control in male mice, whereas tissue to body weight ratios of liver, spleen, and lung rose significantly with increase of dose of MWCNT-PC. There were significant differences between high-dose exposure and control groups. Accumulation of carbon nanotubes and inflammation response in liver, spleen, and lung were observed in the high-dose exposure group. No systemic toxicity and histopathological changes were found in 10-mg/kg exposure groups. Data in the present study support the view that MWCNT in vivo do not exert apparent marked effects in mice and that MWCNT products are relatively safe for human consumption.

THERMAL DECOMPOSITION AND FLAMMABILITY OF ACRYLONITRILE-BUTADIENE-STYRENE/MULTI-WALLED CARBON NANOTUBES COMPOSITES

Thermal and flammability properties of acrylonitrile-butadiene-styrene copolymer (ABS) with the addition of multi-walled carbon nanotubes (MWNTs) were studied. ABS/MWNTs composites were prepared via melt blending with the MWNTs content varied from 0.2% to 4.0% by mass. Thermogravimetry results showed that the addition of MWNTs accelerated the degradation of ABS during the whole process under air atmosphere, and both onset and maximum degradation temperature were lower than those of pure ABS. The destabilization effect of MWNTs on the thermal stability of the composites became unobvious under nitrogen, and the addition of MWNTs could improve the maximum degradation temperature. The heat release rate and time of ignition (tign) for the composites reduced greatly with the addition of MWNTs especially when the concentration of nanotubes was higher than 1.0%. The accumulation of carbon nanotubes with a network structure was observed and the char layer became thicker with increasing nanotubes concentration. Results from Raman spectra showed a higher degree of graphitization for the residues of ABS/MWNTs composites.