Conductive Multi-walled Carbon Nanotubes Research Articles

MWCNTs/BaTiO3 metacomposite with negative permittivity behavior and electric percolation phenomenon in radio frequency

Negative permittivity has taken off as a research topic in percolative composites recent years. Comparing with the common conductive constituent element in the preparation of metamaterials such as metal, one-dimensional conductive carbon nanotubes (CNTs) provide another choice of functional phase. In this paper, barium titanate (BaTiO3) with multi-walled carbon nanotubes (MWCNTs) uniformly dispersed in the ceramic matrix were prepared by traditional ceramic sintering technology. Field emission scanning electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize microstructures and phase composition of the metacomposites. With the increasing of CNTs content, the percolation phenomenon of electrical conductivity (9.95 wt%) was found and the conductive mechanism changed because of the formation of conductive MWCNTs networks. Moreover, the negative permittivity behavior was observed when the MWCNTs content reached 7 wt% and the plasma-like negative permittivity behavior could be well explained by the low frequency plasmonic state generated from conductive nanotube networks using the Drude model.

Highly efficient defluoridation using a porous MWCNT@NiMn-LDH composites based on ion transport of EDL coupled with ligand exchange mechanism

Water defluoridation still remains challenge since most of currently applied fluoride adsorbents always have low adsorption capacity with difficulty in regeneration. Herein, NiMn-layered double hydroxide (NiMn-LDH) nanosheets coated conductive multiwalled carbon nanotubes (MWCNTs) were successfully fabricated on the electrode via a unipolar pulse electrodeposition (UPED) method for efficient water defluoridation. It is found that the NiMn-LDH nanosheets with large surface areas can be grafted uniformly on the skeleton of conductive MWCNTs to facilitate the electron transport. Compared to ion exchange (IX) process, faster and more efficient reversible uptake/release of fluoride ions (F−) was realized by modulating the positive and negative charges on the electrical double layer (EDL) of the composite, coupling with ligand exchange at the active sites of NiMn-LDH during the electrochemical redox process. Especially, in a broad pH range (4–10), the electroactive MWCNTs@NiMn-LDH can remove F− effectively. Moreover, the F− adsorption onto MWCNTs@NiMn-LDH followed the pseudo-second-order model, with the maximum F− adsorption quantity of 135.1 mg/g from the Langmuir model. After 5 uptake/release cycles, ion exchange quantity still retained 92.4% of its initial value. Furthermore, the EDL ion transport coupled with ligand exchange mechanism in MWCNTs@NiMn-LDH was verified by XPS analysis. The continuous F− separation runs implied that the flux of F− by MWCNTs@NiMn-LDH was twice over that of by MWCNTs only while the time of the concentration reached even below WHO standard was quarter of that of by MWCNTs only. It is concluded that the MWCNTs@NiMn-LDH is a promising electroactive material for defluoridation, especially combining it in electrochemically switched ion permselective (ESIP) system can realize a continuous F− separation.

Modification of Carbon Paste Electrode with Conductive Polyglycine-nafion Composite Membrane and Multi-wall Carbon Nanotubes for the Determination of Dopamine

Modification of Carbon Paste Electrode with Conductive Polyglycine-nafion Composite Membrane and Multi-wall Carbon Nanotubes for the Determination of Dopamine

Strain-sensitivity conductive MWCNTs composite hydrogel for wearable device and near-infrared photosensor

Healable, flexible, near infrared sensitive and strain-sensitive for wearable device and healthcare monitoring are successfully formed from sensitive, conductive and biocompatible hydrogels. In this work, a sensitive, mechanically self-healing hydrogel was fabricated via the incorporation of multiwalled carbon nanotubes (MWCNTs) into the hydrophobically associated polyacrylamide hydrogels. As a result, the optimal tensile strength (0.91 MPa) and electrical conductivity (0.5 S m−1) were achieved for the PAM/MWCNTs composite hydrogels. Due to its various functions, the cross-linking hydrogel could be made as a strain sensor. The strain sensor achieved a gauge factor of 5.6, and its response time was 0.3 s. It could be stretched at least for 200 cycles, which was further applied to monitor human movement, including movement of the hands, elbow and even swallowing. With excellent mechanical properties, tensile sensitivity and biocompatibility, the prepared hydrogels could be used as a perfect material for electronic skin. At the same time, flexible and healable PAM/MWCNTs hydrogel had a sensitive near-infrared light response, and we create a new flexible and healable near-infrared light-sensitive photosensor because of the incorporation of MWCNTs, which is different from the traditional NIR photosensor. It could be used in NIR detector, medical instrument and health equipment.

Controlled assembly and alignment of CNTs in ferrofluid: Application in tunable heat transfer

Abstract Nanofluids are new generation of heat transfer fluids with enhanced thermal properties. When using nanofluids, one of the major problems is aggregation of nanoparticles. In this study, in order to benefit from controlled aggregation of nanoparticles by application of magnetic field, we used magnetic nanoparticles (MNPs) as one of the most useful nanoparticles in recent energy and biomedical researches. To achieve a more precise insight about behavior of MNPs under magnetic field, a water-based nanofluid of Fe3O4/MWNTs was studied. Due to the importance of thermal conductivity (TC) of nanofluids, it was investigated for the mentioned nanofluid. Taking advantage of magnetic properties of magnetite nanoparticles besides high thermal conductivity of multi-wall carbon nanotubes, a water-based nanofluid of 0.1 wt% Fe3O4/MWNT was prepared and its thermal conductivity was measured for the situations in which temperature gradient and magnetic field were either parallel or perpendicular. The findings suggested that TC was increased by 52% and 11.9% at H = 0.14 T for the two situations, respectively. This finding proved the anisotropic behavior of magnetic nanofluid. Formation of chain-like structures of MNPs was demonstrated through a novel approach. This phenomenon was found to be the reason of thermal conductivity enhancement. Our findings show that employing Fe3O4/MWNT is a promising approach for improving heat transfer efficiency of heat carriers.

Optimization of compression moulding parameters of multiwall carbon nanotube/synthetic graphite/epoxy nanocomposites with respect to electrical conductivity

This study aims to optimize the electrical conductivity of multiwall carbon nanotube (MWCNT)/synthetic graphite (SG)/epoxy nanocomposites through varying the compression moulding parameters. SG and MWCNTs were used as primary and secondary fillers, respectively. The moulding temperature, moulding pressure, and moulding time were the factors controlled in this research, using the orthogonal array (OA)-Taguchi method. Analysis of variance (ANOVA) and signal to noise ratio (SNR) were used to analyse the results. The optimum nanocomposite electrical conductivity obtained was 163 S/cm, exceeding the electrical conductivity required by the Department of Energy of the United States for bipolar plate applications.

Operating voltage diminution of field emission cathodes based on carbon nanotubes

The possibility of minimizing the operating voltages of the diode structure with a field emission cathode based on an array of carbon nanotubes is investigated. The numerical simulation method was used to perform theoretical calculations that showed the potential for an unlimited reduction in the operating voltage by reducing the diameter of the emitters, increasing the height of the emitters and reducing the value of the interelectrode gap. Established deviation of the experimental values of the operating voltage from theoretically calculated when approaching in the interelectrode gap near to values commensurate with the height of the emitters. It is shown that the observed effect is caused by low conductivity of multi-walled carbon nanotubes, high contact resistance with a substrate, as well as micro- and macroinhomogeneities of the structure of an array of carbon nanotubes.

Surface modification and dispersion of ceramic particles using liquid-liquid extraction method for application in supercapacitor electrodes

Particle extraction through liquid-liquid interface (PELLI) was used for the extraction of MnO2, Mn3O4, FeOOH and ZnO particles from an aqueous synthesis medium to the n-butanol phase. The benefits of PELLI were demonstrated by the fabrication of supercapacitor electrodes, which showed good electrochemical performance at high active mass loadings. Octyl gallate (OG) was found to be an efficient and versatile extractor for the ceramic particles. The phase transfer of the particles resulted in reduced agglomeration, which allowed for improved electrolyte access to the particle surface and facilitated their mixing with conductive multiwalled carbon nanotube (MWCNT) additives. It was shown that OG is a promising extractor material for the fabrication of ceramic-ceramic, ceramic-metal and ceramic-MWCNT nanocomposites. The strong adsorption of OG on the particle surface involved bridging or chelating bidentate bonding of the catechol group to the metal atoms. The capacitive properties of FeOOH-MWCNT electrodes were tested in the negative potential window. MnO2-MWCNT and Mn3O4-MWCNT electrodes were investigated for charge storage in the positive potential window. The highest capacitance of 5.7 F cm−2 for positive electrodes was achieved using MnO2-MWCNT composites with active mass loading of 36 mg cm−2. The Mn3O4-MWCNT electrodes exhibited improved capacitance retention at high charge-discharge rates.

Effect of nanofiller on fibre laser drilling quality of carbon fibre reinforced polymer composite laminates

Laser machining of carbon fibre reinforced polymer composites is a challenging task due to a significant difference between physical and thermal properties of the constituent materials, i.e. polymer matrix and carbon fibres. This results in extended heat-affected zone (HAZ), taper kerf and poor surface finishing. This paper focuses on an investigation, attempting to minimise the divergence in the decomposition temperature of carbon fibres and epoxy resin by adding multi-walled carbon nanotubes in polymer matrix as a secondary reinforcement. High thermal conductivity of multi-walled carbon nanotubes increases the thermal diffusivity of polymer matrix, which in turn reduces the matrix recession. In addition, laser power and scan speed was also considered as an input parameter and their influence on output responses such as HAZ, taper angle and surface roughness has been studied. To analyse the effect of multi-walled carbon nanotubes on the resultant thermal damage, an innovative technique, i.e. scanning acoustic microscopy was used. This technique provides a ply-by-ply damage analysis. C-scans of the top and bottom surface of the machined holes in the composite were also carried out. Further, micrographs of the holes were taken to analyse the quality of the holes using field-emission scanning electron microscope. The obtained results indicated that HAZ, taper angle and surface roughness of holes decreased by ∼30%, ∼47% and ∼43%, respectively, with 1.5 wt% multi-walled carbon nanotubes doped carbon fibre reinforced polymer laminates, when compared with the results obtained from experiments with neat carbon fibre reinforced polymer composite laminates.

Direct implementation of K3Fe(CN)6 as cathode materials of sodium-ion batteries

Transition metal cyanides are considered as a promising cathode candidate of sodium-ion batteries. Herein, we reported a direct implementation of commercial K3Fe(CN)6 (KFC) as active cathode material of SIBs by a simple recrystallization method. Our results suggest that by integrating conductive carbons (SuperP, abbreviated as SP) and multi-walled carbon nanotubes (CNTs) with KFC, an efficient conducting network could be well established for the utilization of KFC active components, thereby endows excellent cyclic and rate performances. Specifically, the KFC/SP/CNTs composite delivers its theoretical capacity of 81 mAh g−1 at 0.1C, and a reversible capacity of 75.6 mAh g−1 at 1C which maintains 62.6 mAh g−1 after 500 cycles. At ultrahigh rate of 12C, the capacity retention can reach 68% of initial. Our effort suggests that direct implementing industrial KFC as cathode materials for SIBs is highly feasible, which may provide a low-cost cathode candidate of sodium-ion batteries for large-scale energy storage.

A hierarchical approach for creating electrically conductive network structure in polyurethane nanocomposites using a hybrid of graphene nanoplatelets, carbon black and multi-walled carbon nanotubes

Hierarchical organization of carbon nanomaterials is the best strategy to combine desirable factors and synergistically impart mechanical and electrical properties to polymers. Here, we investigate the relaxation behavior of carbon nanofillers filled polyurethane (PU) with special reference to particle size and aspect ratio, filler morphology, filler loading to understand the conductive network formation of fillers in the PU matrix. Typically, an addition of 2 wt% hybrid fillers of graphene nanoplatelets (GNPs), conductive carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) in PU at 1:1:2 mass ratio (GCM112-PU2) showed lowest surface resistivity ∼106.8 Ω/sq along with highest improved mechanical properties. Our results demonstrate how hierarchical compositions may function in polymer configurations that are useful for thermal and electrical systems.

Influence of CdS Morphology on the Efficiency of Dye-Sensitized Solar Cells.

Cadmium sulfide (CdS) used in dye-sensitized solar cells (DSSCs) is currently mainly synthesized by chemical bath deposition, vacuum evaporation, spray deposition, chemical vapor deposition, electrochemical deposition, sol–gel, solvothermal, radio frequency sputtering, and hydrothermal process. In this paper, CdS was synthesized by hydrothermal process and used with a mixture of titanium dioxide anatase and rutile (TiO2(A+R)) to build the photoanode, whereas the counter electrode was made of nanocomposites of conductive polymer polyaniline (PANI) and multiwalled carbon nanotubes (MWCNTs) deposited on a fluorine-doped tin oxide substrate. Two morphologies of CdS have been obtained by using hydrothermal process: branched nanorods (CdSBR) and straight nanorods (CdSNR). The present work indicates that controlling the morphology of CdS is crucial to enhance the efficiency of DSSCs device. Indeed, the higher power conversion energy of 1.71% was achieved for a cell CdSBR–TiO2(A+R)/PANI–MWCNTs under 100 mW/cm2, whereas the power conversion energy of 0.97 and 0.83% for CdSNR–TiO2(A+R)/PANI–MWCNTs and TiO2(A+R)/PANI–MWCNTs, respectively. Therefore, by increasing the surface to volume ratio of CdS nanostructures and the crystallite size into those structures opens the way to low-cost chemical production of solar cells.

Two-Dimensional Metal-Organic Layers on Carbon Nanotubes to Overcome Conductivity Constraint in Electrocatalysis.

Application of metal-organic frameworks (MOFs) in electrocatalysis is of great interest, but is limited by low electrical conductivities of most MOFs. To overcome this limitation, we constructed a two-dimensional version of MOF-metal-organic layer (MOL) on conductive multiwalled carbon nanotubes (CNTs) via facile solvothermal synthesis. The redox-active MOLs supported on the CNT efficiently catalyze the electrochemical oxidation of alcohols to aldehydes and ketones. Interestingly, this CNT/MOL assembly also endowed the selectivity for primary versus secondary alcohols via well-designed interfacial interactions. This work opens doors toward a variety of designer electrocatalysts built from functional MOFs.

Flexible and Thermally Stable Optical Polarizers Based on Highly Aligned Carbon Nanotube Sheets for the Visible Spectral Range

AbstractDevelopment of new types of optical components applicable to flexible and stretched substrates is essential for designing innovative display platforms for wearable and outdoor applications. Here, a novel polarizer based on highly aligned macroscopic carbon nanotube (CNT) sheets with flexibility, thermal stability, high polarization efficiency, and high transmittance is introduced. Since the conductive multiwalled CNTs are essentially held together by van der Waals forces, wire‐grid‐type polarizers of well‐aligned conductive CNTs in one direction can be developed without complex and difficult manufacturing processes. The CNT sheet exhibits uniform polarization efficiency in the visible light region and maintains its polarization characteristics without physical deformation even at temperatures greater than 100 °C. Moreover, the transmission according to the angle formed by two CNT sheets follows the Malus law, similar to a typical polarizer. Finally, the applicability of the CNT sheet polarizer on a commercial liquid crystal displays monitor is demonstrated.

Large-scale preparation of segregated PLA/carbon nanotube composite with high efficient electromagnetic interference shielding and favourable mechanical properties

Environment friendly conductive polymer composites (CPCs) with high electromagnetic interference (EMI) shielding performance and favourable mechanical properties were successfully produced on large scale from poly (l-lactid acid) (PLLA), poly (lactic acid) stereocomplex crystallite (PLASC) and multi-wall carbon nanotube (MWCNT). The morphology results indicated that the perfect segregated structure was easily manipulated by controlling the injection temperature. The prepared composite exhibits good conductivity and high EMI shielding effectiveness (EMI SE) under low MWCNT content due to the selective dispersion of the conductive MWCNT in the continuous PLLA phase. With the addition of only 3 wt% MWCNT, the composite exhibits high electrical conductivity of 6.42 S/m and outstanding EMI shielding performance of 31.02 dB at 8.2 GHz. Moreover, similar molecular structure between PLLA and PLAsc endowed excellent interfacial adhesion, thus results in favourable mechanical properties of composites. The work provides a novel idea for manufacting high EMI shielding materials with both toughness and degradation.

Thermal annealing induced enhancement of electrical properties of a co-continuous polymer blend filled with carbon nanotubes

In the current study, it is found that the electrical properties of a co-continuous polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend containing with conductive multi-wall carbon nanotubes (MWCNTs) can be remarkably improved via the thermal annealing treatment. Utilizing the on-line (rheometer and optical microscope) and off-line (transmission electron microscopy) instruments, the evolution of the morphology and microstructure of PS/PMMA/MWCNTs composites are visualized. It is observed that thermal annealing can induce the coalescence of small phases into the more perfect co-continuous phase structure, which can significantly improve the electrical properties of the composites. Moreover, the re-aggregation of MWCNTs under thermal annealing also helps to improve the electrical properties of the composites. Furthermore, it is worth to note that parts of MWCNTs can be enriched at the interface of a co-continuous PS/PMMA blend to build up the conductive network during the thermal annealing, which further enhances the electrical properties of the composites.

Metal-organic framework/carbon nanotube-coated polyethylene separator for improving the cycling performance of lithium-sulfur cells

Since the so-called ‘shuttle effect’ is the key obstacle for the practical development of lithium-sulfur batteries, the present attempt is to make the separator less permeable for polysulfides. For this purpose, we synthesized Ni-based metal-organic framework (Ni-MOF) particles and coated them with multi-walled carbon nanotubes (MWCNTs) onto the polyethylene (PE) separator. The Ni-MOF particles on separator effectively blocked the migration of lithium polysulfides toward the anode side owing to the strong interaction between Ni-MOFs and lithium polysulfides. The highly conductive MWCNTs in the coating layer allowed reutilization of the trapped reaction intermediates during the subsequent cycles. Due to these beneficial effects of coating materials, the lithium-sulfur cell assembled with Ni-MOF/MWCNT-coated PE separator initially delivered a high discharge capacity of 1358 mAh g−1 with good cycling stability and high-rate performance.

A lightweight scalable agarose-gel-synthesized thermoelectric composite

Electronic devices are now advancing beyond classical, rigid systems and moving into lighweight flexible regimes, enabling new applications such as body-wearables and ‘e-textiles’. To support this new electronic platform, composite materials that are highly conductive yet scalable, flexible, and wearable are needed. Materials with high electrical conductivity often have poor thermoelectric properties because their thermal transport is made greater by the same factors as their electronic conductivity. We demonstrate, in proof-of-principle experiments, that a novel binary composite can disrupt thermal (phononic) transport, while maintaining high electrical conductivity, thus yielding promising thermoelectric properties. Highly conductive Multi-Wall Carbon Nanotube (MWCNT) composites are combined with a low-band gap semiconductor, PbS. The work functions of the two materials are closely matched, minimizing the electrical contact resistance within the composite. Disparities in the speed of sound in MWCNTs and PbS help to inhibit phonon propagation, and boundary layer scattering at interfaces between these two materials lead to large Seebeck coefficient (> 150 μV/K) (Mott N F and Davis E A 1971 Electronic Processes in Non-crystalline Materials (Oxford: Clarendon), p 47) and a power factor as high as 10 μW/(K2 m). The overall fabrication process is not only scalable but also conformal and compatible with large-area flexible hosts including metal sheets, films, coatings, possibly arrays of fibers, textiles and fabrics. We explain the behavior of this novel thermoelectric material platform in terms of differing length scales for electrical conductivity and phononic heat transfer, and explore new material configurations for potentially lightweight and flexible thermoelectric devices that could be networked in a textile.

3D printing nano conductive multi-walled carbon nanotube scaffolds for nerve regeneration

Objective. Nanomaterials, such as carbon nanotubes (CNTs), have been introduced to modify the surface properties of scaffolds, thus enhancing the interaction between the neural cells and biomaterials. In addition to superior electrical conductivity, CNTs can provide nanoscale structures similar to those present in the natural neural environment. The primary objective of this study is to investigate the proliferative capability and differential potential of neural stem cells (NSCs) seeded on a CNT incorporated scaffold. Approach. Amine functionalized multi-walled carbon nanotubes (MWCNTs) were incorporated with a PEGDA polymer to provide enhanced electrical properties as well as nanofeatures on the surface of the scaffold. A stereolithography 3D printer was employed to fabricate a well-dispersed MWCNT-hydrogel composite neural scaffold with a tunable porous structure. 3D printing allows easy fabrication of complex 3D scaffolds with extremely intricate microarchitectures and controlled porosity. Main results. Our results showed that MWCNT-incorporated scaffolds promoted neural stem cell proliferation and early neuronal differentiation when compared to those scaffolds without the MWCNTs. Furthermore, biphasic pulse stimulation with 500 µA current promoted neuronal maturity quantified through protein expression analysis by quantitative polymerase chain reaction. Significance. Results of this study demonstrated that an electroconductive MWCNT scaffold, coupled with electrical stimulation, may have a synergistic effect on promoting neurite outgrowth for therapeutic application in nerve regeneration.

Thermoelectric and mechanical properties of PLA/Bi0·5Sb1·5Te3 composite wires used for 3D printing

Thermoelectric (TE) composite wires with polylactic acid (PLA) as the matrix and Bi0·5Sb1·5Te3 (BST) as the filler are synthesized by extruding. The effects of silane coupling agent KH570, plasticizer ATBC, and conductive additive multi-walled carbon nanotubes (MWCNTs) on the composition, TE, and mechanical properties of the composite wires are systematically studied. It is necessary to add KH570 into the composite wires to make the actual BST loading the same as the designed value. The addition of ATBC greatly increases the flexibility of the composite wires and improves the wires' mechanical properties. When the BST loading increases from 35.8 to 87.5 wt%, the flexural modulus increases from 1684.0 to 4379.8 MPa and the flexural strength monotonically decreases from 50.1 to 13.4 MPa. In aspect of TE properties, the power factor PF of the composite wires increases with the increase of the BST loading, and the maximum Seebeck coefficient reaches 200 μV K−1. When MWCNTs are added into the composite wires, the electrical conductivity is significantly enhanced and thus the PF of the wires is raised. The highest PF of 11.3 μW m−1 K−2 is obtained for the wire containing 81.3 wt% BST and 4 wt% MWCNTs. A TE figure of merit ZT of 0.011 is obtained at room temperature. The excellent TE properties and satisfactory mechanical properties of the BST/PLA composite wires make them a promising candidate used for 3D printing of TE devices.