Heterogeneous Carbon Nanotube Research Articles

Microstructure evolution and strength-ductility improving mechanism change of heterogeneous CNT/2009Al composite after hot rolling

In this study, heterogeneous carbon nanotubes reinforced 2009Al (CNT/2009Al) composites composed of CNT-free ductile zones (DZs) and CNT-rich brittle zones were prepared by powder metallurgy, followed by hot extrusion and hot rolling. For the extruded heterogeneous composite (Hetero-C), its strength was increased by about 30 MPa with a more than 1/3 elongation increase, as compared with those of the uniform composite. After hot rolling, the two zones of the heterogeneous composite (R-Hetero-C) were much narrower than those of the Hetero-C, which was not beneficial to increase elongation. However, the texture analysis demonstrates that the Hetero-C had a< 111 > fiber texture, while the R-Hetero-C had strong plate textures including {011}< 111 > , {113}< 332 > and {215}< 342 > components. These plate textures with high Schmidt factor induced more matrix grains to participate in plastic deformation at relatively low stress, which could enhance the elongation but slightly reduce the strength. The synergy of these two different aspects led to the slightly reduced yield strength, similar ultimate tensile strength, and increased elongation for the rolled heterogeneous composite, as compared with those of the extruded heterogeneous composite.

Rotational and Gas Temperature Measurements for He-C Plasma: Application to Heterogeneous Carbon Nanotubes Synthesis

Plasmas containing carbon cover a wide range of application, either using graphite electrodes or carbon containing plasma gas. The study of the C2 molecule is an interesting way to get information on moderate temperature part of the discharge. In the case of heterogeneous carbon nanotubes (CNTs) synthesis by electric arc, reasonable yield can be achieved with substitution of boron and/or nitrogen atoms by optimizing synthesis parameters. This is based on the knowledge of the plasma and gas temperatures in the synthesis chamber. While electrodes material is vaporized through the arc, nanotubes formed in the growth zone a few centimeters away, when temperature decreases down to 1200 °C–1500 °C. Molecular temperature is particularly relevant since it corresponds to the outer part of the arc, in contact with the growth zone. In this article, Abel inversion is used on side-on integrated spectral profiles for C2(0,0) Swan band, in order to get radial rotational temperature profiles. In addition, gas temperature measurements are performed using thermocouples in the arc chamber. Results show that a strong plasma temperature gradient is associated with favorable synthesis conditions for carbon-bore-nitrogen nanotubes. Gas thermal homogeneity is reached in the chamber after about 30 s, mainly through convection processes.

Oil/water separation membranes with stable ultra-high flux based on the self-assembly of heterogeneous carbon nanotubes

Due to the problem of membrane fouling, the preparation of oil/water separation membranes with stable ultra-high flux is still a challenge. At present, ultra-hydrophilicity is the main antifouling strategy, which indeed renders ultra-high base flux and high flux recovery rate. However, the flux usually declines to a low level during the real oil/water separation. With the assist of low surface energy (LSE) strategy, the flux stability can be remarkably enhanced, but at the cost of the reduced base flux. In order to combine the advantages of hydrophilic and LSE strategies, and avoid the undesired side effects of the LSE strategy, the distribution of hydrophilic and LSE microdomains on membrane surfaces is rationally designed and accurately manipulated in this study. Membranes are prepared by the vacuum-assisted self-assembly of heterogeneous carbon nanotubes (HCNTs), which consist of fluorinated multi-walled carbon nanotubes (FMCNTs), amino multi-walled carbon nanotubes (AMCNTs) and carboxylic single-walled carbon nanotubes (CSCNTs). AMCNTs and CSCNTs form great-area continuous and high porous hydrophilic microdomains through membranes, providing high base flux. FMCNTs form discrete linear LSE microdomains, providing good flux stability via LSE antifouling strategy. Except for the ultra-hydrophilic strategy, this study provides a reasonably and accurately manipulated LSE strategy in the energy-efficient membrane water treatment.

Hyperspectral Counting of Multiplexed Nanoparticle Emitters in Single Cells and Organelles.

Nanomaterials are the subject of a range of biomedical, commercial, and environmental investigations involving measurements in living cells and tissues. Accurate quantification of nanomaterials, at the tissue, cell, and organelle levels, is often difficult, however, in part due to their inhomogeneity. Here, we propose a method that uses the distinct optical properties of a heterogeneous nanomaterial preparation in order to improve quantification at the single-cell and organelle level. We developed "hyperspectral counting", which employs diffraction-limited imaging via hyperspectral microscopy of a diverse set of fluorescent nanomaterials to estimate particle number counts in live cells and subcellular structures. A mathematical model was developed, and Monte Carlo simulations were employed, to improve the accuracy of these estimates, enabling quantification with single-cell and single-endosome resolution. We applied this nanometrology technique with single-walled carbon nanotubes and identified an upper limit of the rate of uptake into cells─approximately 3,000 nanotubes endocytosed within 30 min. In contrast, conventional region-of-interest counting results in a 230% undercount. The method identified significant heterogeneity and a broad non-Gaussian distribution of carbon nanotube uptake within cells. For example, while a particular cell contained an average of 1 nanotube per endosome, the heterogeneous distribution resulted in over 7 nanotubes localizing within some endosomes, substantially changing the accounting of subcellular nanoparticle concentration distributions. This work presents a method to quantify the cellular and subcellular concentrations of a heterogeneous carbon nanotube reference material, with implications for the nanotoxicology, drug/gene delivery, and nanosensor fields.

Magnetically aligned CNT/magnetite heterogeneous composite membranes for electromagnetic wave shielding and heat dissipation

The miniaturization and integration of next-generation electronic devices are accompanied by a substantial increase in electromagnetic interference (EMI) and heat generation, which requires light and thin EMI shielding materials. Herein, we attempt to tackle this challenge by designing a heterogeneous membrane using carbon nanotubes (CNTs) and magnetite (Fe3O4) nanorods. The polymer-coated Fe3O4 uniformly adsorbs on the surface of the polyaniline (PANi) coated CNTs, forming a self-supporting composite membrane with vertical CNTs under a magnetic field. Due to the entanglement of the CNTs, the vertical alignment is more effective in the top region of the membrane than in the bottom, resulting in an asymmetric structure that is beneficial to EMI absorption. When electromagnetic waves are incident from the top surface, high-absorption electromagnetic shielding is obtained due to multiple attenuations and absorption-reflection losses. The vertical orientation and heterogeneous CNTs network structure of the membrane also enable stable heat dissipation.

Structure optimization for improving the strength and ductility of heterogeneous carbon nanotube/Al–Cu–Mg composites

Heterogeneous carbon nanotube (CNT)/Al–Cu–Mg composites, consisting of ductile zones (DZs) free of CNTs and brittle zones (BZs) rich of CNTs, were fabricated in powder metallurgy route. It was shown that the grain size and width of the DZs in the heterogeneous composites could be controlled by high energy ball milling (HEBM) on additional Al–Cu–Mg alloy powders. Appropriate grain refinement in the DZs and a medium DZ width were identified to be beneficial for improving the strength-ductility. Under the optimized condition, a heterogeneous CNT/Al–Cu–Mg composite exhibited 88% increase in the elongation and 2% increase in the tensile strength compared to the uniform composite. Although the yield strength of the heterogeneous composite was lower than that of the uniform composite, the appropriate grain refinement in the DZs was good for alleviating the low yield phenomenon. Furthermore, the abundant grain boundaries could reduce the local slip bands passing through the DZs, which could significantly relax the stress concentration of the BZs. As a result, the medium width DZs could contribute more to the plastic deformation, thereby further improving the strength-ductility. Finally, a model was proposed to assist the design of the heterogeneous structure parameters. The calculated optimized DZ size was in accordance with the DZ width of the heterogeneous composite with the best strength-ductility.

Multiple stable dynamic responses based on interlayer and edge coupling effect in carbon nanotube transmission system

The interlayer and edge coupling effect in carbon nanotube (CNT) based rotation transmission system (RTS) is one of the key issue for precise control. Taking the advantages of multiple edge layouts in armchair CNTs and interlayer rotating stability in zigzag CNTs, the dynamic responses of concentric heterogeneous CNT as rotating rotor is systematically studied using molecular dynamics (MD) simulation. Both the synchronous and asynchronous transmission results detected from heterogeneous rotor are extremely stable. The interlayer friction can continually change with speed or chirality distribution, which also determines whether rotor rotates synchronously with motor or not. There exist two kinds of edge layouts, i.e. Head-to-Head and Plug-In, that can provide constant frequency differences and constant output frequency respectively. The coupling effect from transmission edge can make an adjustment with interlayer friction for feasible equilibrium state of rotor.

Oil/Water Separation Membranes with Stable Ultra-High Flux Based on the Self-Assembly of Heterogeneous Carbon Nanotubes

Oil/Water Separation Membranes with Stable Ultra-High Flux Based on the Self-Assembly of Heterogeneous Carbon Nanotubes

Effect of Fe/N-doped carbon nanotube (CNT) wall thickness on CO2 conversion: A DFT study

Many researches on CO2 adsorption using carbon nanotubes (CNTs) have been actively studied, but experimental and theoretical studies on CO2 conversion are still in demand. In particular, the effect of CNT wall thickness on CO2 conversion is not yet established clearly. This study employed two different-walled CNT catalysts doped with iron and nitrogen, single-walled CNT (Fe-N-SWCNT) and double-walled CNT (Fe-N-DWCNT). The structural and electrical properties of these CNTs and their influences on CO2 conversion were characterized and compared using density functional theory (DFT) calculations. As a result, Fe-N-DWCNT was shown to improve catalyst stability with higher formation energy and adsorption energy for CO2 adsorption than Fe-N-SWCNT. Also, the CO2 molecules were found to be highly delocalized and strongly hybridized with Fe-N-DWCNT, leading to more active charge transfer in the catalyst. These findings demonstrate the potential of selective CO2 conversion, as wall thickness differences can lead to different electrical properties of CNTs by showing that the larger the thicknesses, the lower the energy barrier required for CO2 conversion. Specifically, Fe-N-DWCNT is easier to convert CO2 to HCOOH than Fe-N-SWCNT at lower overpotential (0.15 V) obtained with limiting potentials and free energies calculated by understanding the possible reaction pathways in the proton-electron transfer process. Therefore, these results support the hypothesis that the wall thickness of CNT influences CO2 conversion by showing that the double-walled heterogeneous CNT (Fe-N-DWCNT) is a potential catalyst to selectively produce HCOOH from CO2 conversion.

Growth and Mechanics of Heterogeneous, 3D Carbon Nanotube Forest Microstructures Formed by Sequential Selective-Area Synthesis.

Three-dimensional carbon nanotube (CNT) forest microstructures are synthesized using sequenced, site-specific synthesis techniques. Thin-film layers of Al2O3 and Al2O3/Fe are patterned to support film-catalyst and floating-catalyst chemical vapor deposition (CVD) in specific areas. Al2O3 regions support only floating-catalyst CVD, whereas regions of layered Al2O3/Fe support both film- and floating-catalyst CNT growth. Sequenced application of the two CVD methods produced heterogeneous 3D CNT forest microstructures, including regions of only film-catalyst CNTs, only floating-catalyst CNTs, and vertically stacked layers of each. The compressive mechanical behavior of the heterogeneous CNT forests was evaluated, with the stacked layers exhibiting two distinct buckling plateaus. Finite element simulation of the stacked layers demonstrated that the relatively soft film-catalyst CNT forests were nearly fully buckled prior to large-scale deformation of the bottom floating-catalyst CNT forests.

Multifunctional Heterogeneous Carbon Nanotube Nanocomposites Assembled by DNA-Binding Peptide Anchors.

Although carbon nanotubes (CNTs) are remarkable materials with many exceptional characteristics, their poor chemical functionality limits their potential applications. Herein, a strategy is proposed for functionalizing CNTs, which can be achieved with any functional group (FG) without degrading their intrinsic structure by using a deoxyribonucleic acid (DNA)-binding peptide (DBP) anchor. By employing a DBP tagged with a certain FG, such as thiol, biotin, and carboxyl acid, it is possible to introduce any FG with a controlled density on DNA-wrapped CNTs. Additionally, different types of FGs can be introduced on CNTs simultaneously, using DBPs tagged with different FGs. This method can be used to prepare CNT nanocomposites containing different types of nanoparticles (NPs), such as Au NPs, magnetic NPs, and quantum dots. The CNT nanocomposites decorated with these NPs can be used as reusable catalase-like nanocomposites with exceptional catalytic activities, owing to the synergistic effects of all the components. Additionally, the unique DBP-DNA interaction allows the on-demand detachment of the NPs attached to the CNT surface; further, it facilitates a CNT chirality-specific NP attachment and separation using the sequence-specific programmable characteristics of oligonucleotides. The proposed method provides a novel chemistry platform for constructing new functional CNTs suitable for diverse applications.

Improving the efficiency of GaAs solar cells using a double semi-transparent carbon nanotubes thin layer

To investigate the efficiency of a single-junction solar cell that was performed using a numerical analysis method, the effect of creating several different surface-enhancer layer structures on the efficiency of the solar cell was performed. In this study, several carbon nanotube structures adapted to the solar cell structure of the gallium arsenide (GaAs) substrate were used. These elements have two important features of transparency and conductivity. Here, the effect of various parameters such as structure type, dimensions, number of layers, usable impurities and their arrangement on the solar cell efficiency was investigated. In this research, the layer added on the surface of a solar cell can be modeled on a heterogeneous carbon nanotube network. Finally, an optimized single-junction solar cell was obtained by examining the performance of the solar cell using the final carbon nanotube layers. This work resulted, the solar cell with a combination of a double-layer carbon nanotube enhancer by about 30% of efficiency, due to the ability to absorb more photons in one layer of the nanotubes, and better electrical transferability in the other layer of the nanotubes. In this solar cell, two different layers of carbon nanotube with a surface ratio of 10% and 90% of the total surface enhancer layer were used, with a cellular efficiency of about 1% improvement in performance compared with the previous one.

Enhancement of the strength-ductility relationship for carbon nanotube/Al–Cu–Mg nanocomposites by material parameter optimisation

Abstract Heterogeneous carbon nanotube (CNT)/Al–Cu–Mg composites, consisting of CNT-free coarse grain (CG) bands and CNT-rich ultrafine grain (UFG) zones, were fabricated to significantly enhance their strength-ductility. Their mechanical behavior as well as extra-strengthening and elongation increase mechanisms were investigated in detail, with the help of high-resolution digital image correlation (DIC) and extended finite element method (XFEM). A narrow CG band and medium CG content were found to be beneficial in increasing the strength-ductility. Under optimized conditions, a heterogeneous 3 vol% CNT/Al composite exhibited more than 100% elongation increase with nearly no ultimate tensile strength loss as compared to the uniform composite. Geometrically necessary dislocations were induced between the CG and UFG zones, leading to extra-strengthening beyond the rule-of-mixtures. Local strain and micro-crack propagation analyses based on DIC and XFEM indicated that strain localization was greatly suppressed and micro-cracks were effectively blunted because of the existence of CG bands, leading to considerably enhanced elongation. Finally, a model was proposed to assist the selection of the heterogeneous structure parameters for the strength-ductility design of the nanocomposite. The calculated safety zones for CG parameter selection were in well agreement with the experimental results.

Activation of ferrate by carbon nanotube for enhanced degradation of bromophenols: Kinetics, products, and involvement of Fe(V)/Fe(IV)

Very recently, several studies have found that homogeneous reducing agents (e.g., sodium thiosulfate (Na2S2O3), and sodium sulfite (Na2SO3)) can activate ferrate to enhance the degradation of selected contaminants. In this work, it was found that heterogeneous carbon nanotube (CNT) could accelerate ferrate (Fe(VI)) for the degradation of bromophenols (BrPs) of environmental concerns and alleviate the appearance of undesired by-products in effluent. Fe(VI) could react with BrPs over a wide pH range of 6–10 with apparent second-order rate constants of 1.8–1850 M−1 s−1. Electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQMS) analysis showed that dibrominated dihydroxylated biphenyls and dibrominated phenoxyphenols were possibly formed via coupling reaction of BrPs radicals generated from Fe(VI) oxidation through one-electron transfer. The presence of CNT could remarkably accelerate the degradation rates of BrPs by Fe(VI) in a wide pH range from 7 to 10. Moreover, the formed undesired polybrominated products during Fe(VI)/CNT oxidation were absorbed on CNT surface and thus removed from treated water. The Fe(VI)/CNT system was capable of selectively oxidizing electron-rich pollutants (e.g., BrPs, and sulfamethoxazole (SMX)), but reluctant to iopamidol (IPM) and nitrobenzene (NB). High-valent metal-oxo intermediates Fe(V)/Fe(IV) formed in situ from the reaction of CNT with Fe(VI) were likely responsible for this activation effect of CNT, which was further confirmed via using methyl phenyl sulfoxide (PMSO) as a probe compound. Comparatively, homogeneous reducing agent Na2S2O3 could enhance Fe(VI) degradation of BrPs at pH 7 and 8, while undesired polybrominated products were detected in effluent from Fe(VI)/Na2S2O3 system. These findings have crucial implications for the development of a promising oxidation process by combination of Fe(VI) and CNT for water and wastewater treatment.

Hybrid Architectures of Heterogeneous Carbon Nanotube Composite Microstructures Enable Multiaxial Strain Perception with High Sensitivity and Ultrabroad Sensing Range.

Low-dimensional nanomaterials are widely adopted as active sensing elements for electronic skins. When the nanomaterials are integrated with microscale architectures, the performance of the electronic skin is significantly altered. Here, it is shown that a high-performance flexible and stretchable electronic skin can be produced by incorporating a piezoresistive carbon nanotube composite into a hierarchical topography of micropillar-wrinkle hybrid architectures that mimic wrinkles and folds in human skin. Owing to the unique hierarchical topography of the hybrid architectures, the hybrid electronic skin exhibits versatile and superior sensing performance, which includes multiaxial force detection (normal, bending, and tensile stresses), remarkable sensitivity (20.9 kPa-1 , 17.7 mm-1 , and gauge factor of 707 each for normal, bending, and tensile stresses), ultrabroad sensing range (normal stress = 0-270 kPa, bending radius of curvature = 1-6.5 mm, and tensile strain = 0-50%), sensing tunability, fast response time (24 ms), and high durability (>10 000 cycles). Measurements of spatial distributions of diverse mechanical stimuli are also demonstrated with the multipixel electronic skin. The stress-strain behavior of the hybrid structure is investigated by finite element analysis to elucidate the underlying principle of the superior sensing performance of the electronic skin.

Heterogeneous carbon nano-tube window layer with higher sheet resistance improve the solar cell performance

The heterogeneous Carbon Nano-Tube (CNT) layers deposited on the window surface of solar cells that allow better charge carrier collection was numerically analyzed and studied in modern TCAD tools. The quantum efficiency(EQE) as well as power conversion efficiency (η) were found to be improved significantly based on the light transmission capabilities of the CNT layer. Two CNT network models using experimental sheet resistance values of 75 Ω/□ and 128 Ω/□ as a top conducting layer in a GaAs solar cell were compared. It is found that the CNT networks allow for a greater area of charge collection as well as serve as a lower resistance path for charge carriers with minimum voltage loss to travel to the top contact. This model thus significantly improve the η up to 30% under AM0 with more than 90% EQE. The effect of cell width varying starting from 200 μm to 4000 μm with CNT top layer on Jsc, Voc and Pmax parameters were studied and found that these parameters remain almost constant irrespective of cell width. This work thus shown that a thin CNT top layers of lower sheet resistance with a higher light transmission can greatly improve the efficiency of solar cells.

Inter-allotropic transformations in the heterogeneous carbon nanotube networks.

The allotropic transformations of carbon provide an immense technological interest for tailoring the desired molecular structures in the scalable nanoelectronic devices. Herein, we explore the effects of morphology and geometric alignment of the nanotubes for the re-engineering of carbon bonds in the heterogeneous carbon nanotube (CNT) networks. By applying alternating voltage pulses and electrical forces, the single-walled CNTs in networks were predominantly transformed into other predetermined sp2 carbon structures (multi-walled CNTs and multi-layered graphitic nanoribbons), showing a larger intensity in a coalescence-induced mode of Raman spectra with the increasing channel width. Moreover, the transformed networks have a newly discovered sp2-sp3 hybrid nanostructures in accordance with the alignment. The sp3 carbon structures at the small channel are controlled, such that they contain up to about 29.4% networks. This study provides a controllable method for specific types of inter-allotropic transformations/hybridizations, which opens up the further possibility for the engineering of nanocarbon allotropes in the robust large-scale network-based devices.

A settling curve modeling method for quantitative description of the dispersion stability of carbon nanotubes in aquatic environments.

Understanding the aggregation and deposition behavior of carbon nanotubes (CNTs) is of great significance in terms of their fate and transport in the environment. Attachment efficiency is a widely used index for well-dispersed CNT solutions. However, in natural waters, CNTs are usually heterogeneous in particle size. The attachment efficiency method is not applicable to such systems. Describing the dispersion stability of CNTs in natural aquatic systems is still a challenge. In this work, a settling curve modeling (SCM) method was developed for the description of the aggregation and deposition behavior of CNTs in aqueous solutions. The effects of water chemistry (natural organic matter, pH, and ionic strength) on the aggregation and deposition behavior of pristine and surface-functionalized multi-walled carbon nanotubes (MWCNTs) were systematically studied to evaluate the reliability of the SCM method. The results showed that, as compared to particle size and optical density, the centrifugal sedimentation rate constant (ks) from the settling curve profile is a practical, useful and reliable index for the description of heterogeneous CNT suspensions. The SCM method was successfully applied to MWCNT in three natural waters. The constituents in water, especially organic matter, determine the dispersion stability of MWCNTs in natural water bodies.

Determination of association constants towards carbon nanotubes.

Single-walled carbon nanotubes (SWNTs) are one of the most promising nanomaterials and their supramolecular chemistry has attracted a lot of attention. However, despite well over a decade of research, there is no standard method for the quantification of their noncovalent chemistry in solution/suspension. Here, we describe a simple procedure for the determination of association constants (Ka) between soluble molecules and insoluble and heterogeneous carbon nanotube samples. To test the scope of the method, we report binding constants between five different hosts and two types of SWNTs in four solvents. We have determined numeric values of Ka in the range of 1-104 M-1. Solvent effects as well as structural changes in both the host and guest result in noticeable changes of Ka. The results obtained experimentally were validated through state-of-the-art DFT calculations. The generalization of quantitative and comparable association constants data should significantly help advance the supramolecular chemistry of carbon nanotubes.

Adhesion Between Thin Cylindrical Shells With Parallel Axes

Energy principles are used to investigate the adhesion of two parallel thin cylindrical shells under external compressive and tensile loads. The total energy of the system is found by adding the strain energy of the deformed cylinder, the potential energy of the external load, and the surface energy of the adhesion interface. The elastic solution is obtained by linear elastic plate theory and a thermodynamic energy balance, and is capable of portraying the measurable quantities of external load, stack height, contact arc length, and deformed profile in the reversible process of loading-adhesion and unloading-delamination. Several worked examples are given as illustrations. A limiting case of adhering identical cylinders is shown to be consistent with recent model constructed by Tang et al. Such results are of particular importance in modeling the aggregation of heterogeneous carbon nanotubes or cylindrical cells, where the contacting microstructures have a different radius and/or bending stiffness.