Separation Of Carbon Nanotubes Research Articles

High energy-capacity and multiresponsive phase change fibers via in situ polymer composition with expanded carbon nanotube networks

Phase change fibers with abilities to storage/release thermal energy and response to multiple stimuli are of high interest for wearable thermal management textiles. However, there are long-term challenges for carbon nanotube (CNT) network-directed phase change composites, such as the limited polymer loading, nonuniform composite structure, and weak connectivity between CNTs. Herein, an expansion-based in situ composition strategy is proposed to impregnate polyethylene glycol (PEG) into CNT network, leading to a high and homogeneous PEG loading (96 wt%) and robust PEG confinement inside the expanded CNT network. As the expansion induced CNT separation from aggregation, leading to the full utilization of CNT surfaces, the CNT/PEG composite fibers at the highest PEG loading exhibited superior high latent heat of 195–205 J g−1, and were electrically and thermally conductive. More importantly, owing to the confinement, these fibers showed remarkable cyclic thermal stability, without any liquid leakage. The composite fibers were also embroidered and woven into various fabrics, which showed excellent thermal managing capacity and rapid responses to electrical and optical stimuli.

Computational Investigation of Chirality-Based Separation of Carbon Nanotubes Using Tripeptide Library

Carbon nanotubes (CNT) have fascinating applications in flexible electronics, biosensors, and energy storage devices, and are classified as metallic or semiconducting based on their chirality. Semiconducting CNTs have been teased as a new material for building blocks in electronic devices, owing to their band gap resembling silicon. However, CNTs must be sorted into metallic and semiconducting for such applications. Formerly, gel chromatography, ultracentrifugation, size exclusion chromatography, and phage display libraries were utilized for sorting CNTs. Nevertheless, these techniques are either expensive or have poor efficiency. In this study, we utilize a novel technique of using a library of nine tripeptides with glycine as a central residue to study the effect of flanking residues for large-scale separation of CNTs. Through molecular dynamics, we found that the tripeptide combinations with threonine as one of the flanking residues have a high affinity for metallic CNTs, whereas those with flanking residues having uncharged and negatively charged polar groups show selectivity towards semiconducting CNTs. Furthermore, the role of interfacial water molecules and the ability of the tripeptides to form hydrogen bonds play a crucial role in sorting the CNTs. It is envisaged that CNTs can be sorted based on their chirality-selective interaction affinity to tripeptides.

Highly efficient and environmental-friendly separation and purification of carbon nanotubes from molten salt via ultrasound-assisted carbonation

Carbon dioxide (CO2) released by the carbon-intensive energy industry has caused heightened ecological and environment concerns globally. The electrochemical conversion of CO2 into high-valued carbon nanotubes (CNTs) in molten salt media offers a promising pathway to mitigate climate change and advance carbon neutrality goals. Pilot scale has been implemented, whereas, this cutting-edge technology is being impeded by separation and purification of the CNTs. The conventional method is to dissolve the crude cathode products with hydrochloric (HCl) acid, then rinse and dry the filtered carbon powder. Heavy dependence on HCl, undoubtedly, on the one hand increases the operating cost, on the other hand causes environment pollutions. From the perspective of industrial application, a green and sustainable purification method is urgently desired. Here, a simple but effective carbon product separation method, i.e. ultrasound-assisted carbonation, was firstly proposed and validated in this study, where CNTs and lithium carbonate (Li2CO3) can be thoroughly separated from each other with high efficiency and low resource consumption. Meanwhile, this study constructed a closed substance loop: with the CNTs separated, Li2CO3 can be employed to continue the next round of electrolysis, and water and CO2 that were used as feedstocks in the separation process could also be circulated. In this way, the work paved the way for CNTs separation from molten salts in a more sustainable and economic manner, thereby alleviating the environmental concerns and creating more economic benefits simultaneously.

Small organic molecules act as a trigger in an “unzippering” mechanism to facilitate carbon nanotube dispersion

In binary dispersing agents system, the contribution and roles of different sized molecules to carbon nanotubes (CNTs) dispersion remain unclear, which hinders the understanding of the environmental behaviour and risks of CNTs. This study compared the dispersion of CNTs by m-nitrobenzoic acid (NBA), trans-cinnamic acid (TCA), tannic acid (TA), and their mixtures. The dispersion efficiency of CNTs significantly reduced with the increased solid-phase concentration (Qe) of TA due to the adsorption of TA on newly exposed CNTs surfaces. However, the CNTs dispersion efficiency by NBA or TCA was independent of Qe because the dispersed CNTs surface was completely occupied by NBA or TCA without new exposed sites available for subsequent adsorption. The mixture of NBA or TCA with TA significantly enhanced the dispersion efficiency of CNTs, indicating a synergistic effect of CNTs dispersion. The addition of NBA or TCA decreased the hydrodynamic diameter of CNTs dispersed by TA, which indicated that NBA or TCA facilitated TA wedging into CNTs bundles for more complete separation of CNTs. This study highlighted the triggering effect of small molecules in the “unzippering” mechanism for improving the dispersing efficiency of CNTs by large molecules.

Extraction of carbon nanotubes with porphyrin- and pyrene-based nanotweezers and nanocalipers: Insight from the association constants

Strong interaction between porphyrin and nanocarbons including carbon nanotubes (CNTs) has been utilized to form stable complexes between them. We have applied the stable complex of CNTs with V- and U-shaped porphyrins and pyrenes, designated as nanotweezers and nanocalipers respectively, to separation of CNTs through their extraction to liquid phase. In order to know more about the CNT complex in liquid phase, we determined the association constants and the extraction ability of the host molecules, porphyrins, pyrenes, porphyrin- and pyrene-based nanotweezers and nanocalipers, to single-walled carbon nanotubes (SWNTs). As we expected, the order of the association constant is nanocalipers > nanotweezers > monoporphyrins > monopyrenes in the host molecules. The extraction ability of these host molecules is roughly proportional to the order of the association constants, but mismatching of the cavity size of the host and the diameter of CNTs is considered to become more apparant in liquid phase than in solid phase, destabilizing the complex in liquid phase and lowering the extraction ability.

Conductive CNT/nanofiber composite hollow fiber membranes with electrospun support layer for water purification

Hollow fiber membranes (HFMs) have been extensively used to alleviate the crisis of water resources because of their large contact area per unit volume. However, developing high permeability and mechanical strength HFMs remains a great challenge. In this study, we design a novel carbon nanotube (CNT)/nanofiber composite hollow fiber membrane (CNC-HFM) that possesses significant advantages of permeability and mechanical strength. Specifically, the pure water flux and Young's modulus of CNC-HFMs are 7.3 and 12.7 times higher than the commercial polyacrylonitrile HFMs with comparable pore size, respectively. The outstanding merits derive from the continuous interlaced nanofiber-scaffold structure of electrospun nanofiber support layer and crosslinked CNT separation layer, with low-tortuosity membrane pore, high porosity and mechanical strength. In addition, benefiting from the good electrical conductance of CNT separation layer, CNC-HFMs can exhibit a mitigation of membrane fouling and an improvement of separation performance during surface water treatment under electro-assistance. The approach of constructing asymmetrical HFMs with electrospun nanofibers as the support layer and CNTs as separation layer provides unique thoughts for the design and manufacture of efficient separation membranes.

Synthetic strategies for the enhancement of Mg(OH)2 thermochemical performances as heat storage material

This work deals with the study of influence of multi walled carbon nanotubes (CNTs) characteristics on thermochemical performance of hybrid materials based on Mg(OH)2 (M) as heat storage medium. Two different functionalized CNTs samples are investigated, separated curly tubes (SN) and bundles of straight nanotubes (BN). Hybrids were synthesized by reverse deposition precipitation method and their structure was characterized by X-ray analysis and scanning electron microscopy. The heat storage performance was studied through a thermogravimetric apparatus, simulating heat storage/release cycles. It is demonstrated that separated CNTs owning mainly carboxylic groups increase the interaction with precipitated magnesium hydroxide, improving the reacted fraction during dehydration/hydration cycle. In terms of dehydration/hydration conversion the samples’ rank is SN-M>Mg(OH)2>BN-M. SN-M exhibits higher heat storage/output capacity (~1250 kJ/kgMg(OH)2, ~350 MJ/m3).

Thermal conductivity of Ni-coated MWCNT reinforced 70Sn-30Bi alloy

Abstract The high thermal conductivity of thermal interface material (TIM) is essential since the heat dissipation of electronic chips in an integrated circuit is solely achieved through TIM, which forms the bottleneck of the heat conduction. In the current study, the efficiency of utilizing multi-walled carbon nanotubes (MWCNTs) to increase the thermal conductivity of a typical TIM 70Sn-30Bi alloy has been investigated. Encapsulation of carbon nanotubes (CNTs) with nickel by electroless deposition was used to prevent aggregation of CNTs and to enhance the interfacial bonding between CNTs and the metal matrix. The nickel encapsulation also allows avoiding the separation of CNTs from the molten metal due to the buoyancy effect. The dispersion of Ni-encapsulated CNTs was assisted by sonication. The thermal conductivity of 3 wt % Ni/MWCNTs reinforced 70Sn-30Bi alloy was found to be more than 170% greater than that of the base alloy.

Polypropylene Carbon Nanotubes Nanocomposites: Combined Influence of Block Copolymer Compatibilizer and Melt Annealing on Electrical Properties

We study the influence of melt annealing and the presence of a block copolymer compatibilizer on the electrical properties of polypropylene carbon nanotubes (CNT) nanocomposites from the DC limit to microwave frequencies and link it to the morphological details. We show that the compatibilizer concentration controls three types of morphologies: separate CNT agglomerates, a network of well dispersed but interconnected CNT, and individualized but separate nanotubes. This explains why conductivity reaches an optimum over the whole frequency range at a low compatibilizer concentration. We model the corresponding structures by a semiquantitative schematic equivalent electrical circuit. A key outcome of the work is the understanding and control of dispersion mechanisms in order to optimize the electrical performances for efficient EMI shielding depending on the targeted frequency range.

Highly efficient hyperbranched CNT surfactants: influence of molar mass and functionalization.

End-group-functionalized hyperbranched polymers were synthesized to act as a carbon nanotube (CNT) surfactant in aqueous solutions. Variation of the percentage of triphenylmethyl (trityl) functionalization and of the molar mass of the hyperbranched polyglycerol (PG) core resulted in the highest measured surfactant efficiency for a 5000 g/mol PG with 5.6% of the available hydroxyl end-groups replaced by trityl functions, as shown by UV-vis measurements. Semiempirical model calculations suggest an even higher efficiency for PG5000 with 2.5% functionalization and maximal molecule specific efficiency in general at low degrees of functionalization. Addition of trityl groups increases the surfactant-nanotube interactions in comparison to unfunctionalized PG because of π-π stacking interactions. However, at higher functionalization degrees mutual interactions between trityl groups come into play, decreasing the surfactant efficiency, while lack of water solubility becomes an issue at very high functionalization degrees. Low molar mass surfactants are less efficient compared to higher molar mass species most likely because the higher bulkiness of the latter allows for a better CNT separation and stabilization. The most efficient surfactant studied allowed dispersing 2.85 mg of CNT in 20 mL with as little as 1 mg of surfactant. These dispersions, remaining stable for at least 2 months, were mainly composed of individual CNTs as revealed by electron microscopy.

Separation of dispersed carbon nanotubes from water: Effect of pH and surfactants on the aggregation at oil/water interface

With the extensive use of carbon nanotubes (CNTs), the environmental health risk raised by this nanomaterial is concerned. Dispersed CNTs in aqueous suspension greatly increase the possibility of human and ecological exposures, but little attention has been paid to the decontamination/remediation of CNT pollution. In this study, an oil/water interface aggregation (OWIA) method was proposed for the decontamination of CNTs aqueous suspension. Tuning the water pH to suitable ranges (⩽1.8 or ⩾13.2) or adding cationic surfactant CTAB (0.075–1mM) can cause the aggregation of CNTs at the oil/water interface, which allows the subsequent separation of CNTs from the liquids. Through the OWIA process, more than 99% of the CNTs were removed from water, and the remnant CNTs in water were less than 1mg/L. Adding surfactant or extreme pHs may change the charged status of CNTs’ surface, and induced the aggregation of CNTs when the repulsion force between individual CNTs diminished. The cationic surfactant CTAB molecules have different interaction models with dispersed CNTs, depending on the concentrations of CTAB. This study provides a feasible approach for future decontamination of CNTs or other nanoparticles from aqueous environments.

Spontaneous Partition of Carbon Nanotubes in Polymer-Modified Aqueous Phases

The distribution of nanoparticles in different aqueous environments is a fundamental problem underlying a number of processes, ranging from biomedical applications of nanoparticles to their effects on the environment, health, and safety. Here, we study distribution of carbon nanotubes (CNTs) in two immiscible aqueous phases formed by the addition of polyethylene glycol (PEG) and dextran. This well-defined model system exhibits a strikingly robust phenomenon: CNTs spontaneously partition between the PEG- and the dextran-rich phases according to nanotube's diameter and metallicity. Thermodynamic analysis suggests that this chirality-dependent partition is determined by nanotube's intrinsic hydrophobicity and reveals two distinct regimes in hydrophobicity-chirality relation: a small diameter (<1 nm) regime, where curvature effect makes larger diameter tubes more hydrophobic than small diameter ones, and a large diameter (>1.2 nm) regime, where nanotube's polarizability renders semiconducting tubes more hydrophobic than metallic ones. These findings reveal a general rule governing CNT behaviors in aqueous phase and provide an extremely simple way to achieve spatial separation of CNTs by their electronic structures.

Atomistic Modeling of Charge Transport across a Carbon Nanotube–Polyethylene Junction

The conduction mechanism in carbon nanotube (CNT) polymer nanocomposites is complex, and there has been a considerable amount of work invested in understanding the role of the distribution of the CNTs in the composite and how it influences the conductivity. However, less interest has been devoted to the electron transport across a single CNT–polymer–CNT junction. We present a first atomistic study of the electron transmission through a CNT–polyethylene–CNT junction. The morphology of the junction is described using classical molecular dynamics simulations, and transport properties are calculated within density functional tight binding method. The electron transmission depends noticeably on the CNT–CNT separation and on the consequent polymer wrapping. At CNT–CNT distances shorter than 6 Å, the polyethylene molecules do not penetrate in the space between the CNTs. In this near contact regime, the electron transmission proceeds via direct tunneling between the two CNTs across a vacuum region without relevant contribution from the surrounding polymer. For distances larger than 6 Å, the PE molecules enter into the junction region. The frontier orbitals of the PE molecules in the junction provide localized states, which can couple to the CNT metallic states. This resonance tail increases the electron transmission probability between the CNTs across the junction by several orders of magnitude, thus lowering the effective barrier. The gradual interpenetration of the polymer is resembled in transmission fluctuations. An averaging of the transmission in energy and time along MD trajectories allows a quantitative estimation of the junction resistance and tunneling barrier.

Carbon Nanotube Flocculation as a Green Nanoseparation

Abstract A facile technique is described here that can separate carbon nanotubes (CNTs) from corrosive CNTs/acid mixtures. The total time by flocculation method is ca. 0.5 h, which is only 5%, 20%, and 50% of that for dialysis, membrane filtration, and high-speed centrifugation. This strategy is a “green” process because our approach can recycle the “wasted acids.” Transmission electron microscopy (TEM) and contact angle measurement also show that the transition of surface properties of nanotubes plays a significant role in the separation of CNTs.

Interaction of nucleic acids with carbon nanotubes and dendrimers

Nucleic acid interaction with nanoscale objects like carbon nanotubes (CNTs) and dendrimers is of fundamental interest because of their potential application in CNT separation, gene therapy and antisense therapy. Combining nucleic acids with CNTs and dendrimers also opens the door towards controllable self-assembly to generate various supra-molecular and nano-structures with desired morphologies. The interaction between these nanoscale objects also serve as a model system for studying DNA compaction, which is a fundamental process in chromatin organization. By using fully atomistic simulations, here we report various aspects of the interactions and binding modes of DNA and small interfering RNA (siRNA) with CNTs, graphene and dendrimers. Our results give a microscopic picture and mechanism of the adsorption of single- and double-strand DNA (ssDNA and dsDNA) on CNT and graphene. The nucleic acid-CNT interaction is dominated by the dispersive van der Waals (vdW) interaction. In contrast, the complexation of DNA (both ssDNA and dsDNA) and siRNA with various generations of poly-amido-amine (PAMAM) dendrimers is governed by electrostatic interactions. Our results reveal that both the DNA and siRNA form stable complex with the PAMAM dendrimer at a physiological pH when the dendrimer is positively charged due to the protonation of the primary amines. The size and binding energy of the complex increase with increase in dendrimer generation. We also give a summary of the current status in these fields and discuss future prospects.

A model for carbon nanotube–DNA hybrid using one-dimensional density of states

A model for a carbon nanotube (CNT)–DNA hybrid embedded in an electrolyte solution is developed. The DNA charges are smeared out uniformly onto a cylindrical surface covering the CNT and the response of the CNT to the DNA charges is captured using the one-dimensional density of states (1D DOS) proposed by Mintmire et al. Coupled with the Debye–Hückel equation for the electrolyte, the expressions for the electric potential of the hybrid are obtained for both metallic and semiconducting CNT cores. For the surface charge density of the cylinder corresponding to the physically measured wrapping angles of a single-stranded DNA around a CNT, the developed model predicts that the induced charges on a semiconducting CNT are about one order of magnitude smaller than the DNA charges, while the induced charges on a metallic CNT can be comparable in magnitude to the DNA charges. Because of this, the magnitude of the electric potential for a metallic CNT–DNA hybrid can be as much as ≃30% smaller than that for a semiconducting one. This result can be used to explain the experiments on DNA-assisted CNT separation using ion exchange chromatography.

Purification and Separation of Single-Walled Carbon Nanotubes (SWCNTs)

Purification or separation of single-walled carbon nanotubes (SWCNTs) is one of the most fundamental steps before they are used for research and technological applications. Based on the difference of their physical and chemical properties, separation of carbon nanotubes (CNTs) can be categorized into three groups: length separation, metallic and semiconducting tubes separation and chirality separation. In this review, we first briefly review the purification of CNTs and then focus on the different methods for the separation of CNTs.

Perpendicularly aligned carbon nanotube/olefin composite films for the preparation of graphene nanomaterials

There remains a common and critical challenge in the preparation of carbon nanotube (CNT) composite materials, i.e., random dispersion of CNTs in the second phase. Here we have reported a general method to prepare perpendicularly aligned CNT/olefin composite films through a conventional slicing technique. The thickness of a composite film can be accurately controlled from about fifty nanometers to fifty micrometers, and the diameter and density of CNTs may be varied in a wide range as required. In particular, due to the generated defect at the end during the slicing process, the separated CNTs from the composite film have been easily unzipped to produce graphenes in the forms of nanoribbons and nanosheets with a yield of almost 100% under ultrasonic treatment.

A Universal Ultracentrifuge Spectrometer Visualizes CNT–Intercalant–Surfactant Complexes

Interacting solutes form mUltiple associates and usually mask each other in ensemble characterization. They are susceptible to preparation artefacts in the single-molecule techniques commonly applied. To overcome the problem of bulk characterization of a single-walled carbon nanotube (CNT) dispersion with a novel surfactant-intercalant mixture, we obtain color movies of fractionation under extreme gravity, such that each colloidal component is characterized independently. We combine the unique fractionation power of ultracentrifugationl!) with full absorption spectra etA) at each radial position r at each time step t during the sedimentation process.[2,3) In ref. [8], ligand attachment CNTs was studied with the Beckman model XLA centrifuge, which tracks only e(r,t) at a single wavelength, requiring extended modeling for analysis. Our spectrometer/CCD opticsI2.3) adds a third dimension and generates wavelength-resolved movies of the centrifuge fractionation e(r,t,},). This allows independent ligand and CNT tracking without hydrodynamic modeling. We identify the interactions in unpurified intercalant-surfactant-CNT dispersions and obtain the unexpected proof of four coexisting heteroassociates by a novel model-free evaluation. Solubilization of carbon nanotubes is of primary importance to increase the processability of this unique class of materials. Despite the progress in separating and sorting SWCNTs by electrophoresis, density gradient ultracentrifugation or chromatography, CNT-based technology has not yet been realized on a commercial scale, as the CNT separation is limited to individualized nanotubes.14,S) It has previously been shown that designed water-soluble perylene bisimide derivatives such as 1 are excellent CNT surfactants, yielding CNT dispersions with up to 73 % of the CNTs stably dispersed and containing 60% of in-

Automated Nanomanufacturing System to Assemble Carbon Nanotube Based Devices

In this paper we report the design and implementation of a novel automated manufacturing system for carbon nanotube (CNT)-based nanodevices, which integrates a new dielectrophoretic (DEP) microchamber into a robotic-based deposition workstation. The microchamber has been fabricated to separate and select CNTs with the desired electronic property by using DEP force. Moreover, a series of tools for mass-producing consistent nanodevices has been developed with the CNT deposition workstation, such as computer-controllable micromanipulators and a micro-active nozzle. Detailed experimental studies of the CNT separation and deposition processes have been performed on both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Preliminary results show that CNTs could be manipulated to multiple pairs of microelectrodes repeatedly. Consistent I—V characteristics and CNT formations of the fabricated devices were obtained. The yield of semi-conducting CNTs was also increased by using our system. Therefore, by using the proposed CNT separation and deposition system, CNT-based nanodevices with specific and consistent electronic properties can be manufactured automatically and effectively.