Multi-walled Carbon Nanotubes Network Research Articles

Tailored Self-sensing of Failure Mechanisms in Glass Fiber/Carbon Nanotube/Vinyl Ester Multiscale Hierarchical Composites Loaded in Tension

The damage sensing capabilities of a glass fiber/carbon nanotube/vinyl ester multiscalecomposite containing a tailored electrically conductive network of multiwall carbonnanotubes (MWCNTs) is investigated. The tailored MWCNT network is achievedby manufacturing the composite into two architectures depending on the location ofthe MWCNTs within the composite: (1) randomly dispersed within the matrix, or (2)deposited onto the glass fibers. The former architecture was achieved by dispersingMWCNTs within the uncured vinyl ester resin, while the later architecture by depositingMWCNTs onto the glass fibers by using an ultrasonic-aided dipping deposition method.The damage sensing capabilities of the composite were investigated under quasi-statictension loading by using specimens with fibers oriented at 0° and 90° with respect tothe load direction for both composite architectures. In situ measurements of electricalresistance while loading the composite show distinctive features, which allow discerningbetween fiber breakage from matrix or fiber/matrix interfacial damage, dependingon the composite’s architecture and failure mode.

Highly Enhanced Vapor Sensing of Multiwalled Carbon Nanotube Network Sensors by n‐Butylamine Functionalization

The sensing of volatile organic compounds by multiwall carbon nanotube networks of randomly entangled pristine nanotubes or the nanotubes functionalized by n‐butylamine, which were deposited on polyurethane supporting electrospinned nonwoven membrane, has been investigated. The results show that the sensing of volatile organic compounds by functionalized nanotubes considerably increases with respect to pristine nanotubes. The increase is highly dependent on used vapor polarity. For the case of highly polar methanol, the functionalized MWCNT network exhibits even more than eightfold higher sensitivity in comparison to the network prepared from pristine nanotubes.

Low-power CMOS LC QVCO using zero-biased transistor coupling of MWCNT network-based VCO structure

This paper presents design, analysis and implementation of a 2.4GHz QVCO (Quadrature Voltage Controlled Oscillator), for low-power, low-voltage applications. Cross coupled LC VCO (Inductor–Capacitor Voltage Controlled Oscillator) topology realized using integration of a micro-scaled capacitor and a MWCNT (Multi-Wall Carbon Nano-Tube) network based inductor together with the CMOS circuits is utilized together with MOS transistors as coupling elements to realize QVCO. With the passive coupling achieved from the MOS transistors, power consumption is minimized while maintaining a small chip area. The variable capacitors and the inductors are designed using ANSYS and imported through DAC components in ADS (Advanced Design software). Accurate simulation of the QVCO is performed in the software environments and the results are provided. The measurement results show that the QVCO provides quadrature signals at 2.4GHz and achieves a phase noise of −130dBc/Hz 1MHz away from the carrier frequency. The VCO produces frequency tuning from 2.1GHz to 2.60GHz (20.83%) with a control voltage varying from 0 to 0.3V. It achieves a peak to peak voltage of 0.59V with an ultra low power consumption of 3.8mW from a 0.6V supply voltage. The output power level of the QVCO is −10dBm, with an improved quality factor of 45. The phase error of the QVCO is measured as 3.1°.

Transport and electrical properties of natural rubber/nitrile rubber blend composites reinforced with multiwalled carbon nanotube and modified nano zinc oxide

As a surface modified zinc oxide, stearic acid‐coated nano zinc oxide (ZOS) has been prepared by sol‐gel method and was used along with N‐benzylimine aminothioformamide‐N‐cyclohexyl benzthiazyl sulfonamide binary accelerator system, multiwalled carbon nanotube (MWCNT) and sulfur for vulcanizing 20/80 natural rubber/nitrile rubber (NR/NBR) blend. Different formulations have been prepared by using 1–7 phr of MWCNT. Solvent transport and electrical properties of the rubber compounds have been investigated. The equilibrium solvent uptake (Q∞) decreased with increase in concentration of the filler due to the decrease in the free volume and the increase in tortuousity. The conductivities of the vulcanizates increased with increase in the dosage of MWCNT from 1 phr in NBCNT1 to 7 phr in NBCNT4 indicating the formation of percolating network of MWCNTs in the NBR/NR matrix. POLYM. COMPOS., 35:956–963, 2014. © 2013 Society of Plastics Engineers

A Modified Preparation Procedure for Carbon Nanotube-Confined Nd/Na Heterobimetallic Catalyst for anti-Selective Catalytic Asymmetric Nitroaldol Reactions

A recyclable asymmetric metal-based catalyst is a rare entity among the vast collection of asymmetric catalysts developed so far. Recently we found that the combination of a self-assembling metal-based asymmetric catalyst and multiwalled carbon nanotubes (MWNTs) produced a highly active and recyclable catalyst in which the catalytically active metal complex was dispersed in the MWNT network. Herein we describe an improved preparation procedure and full details of a Nd/Na heterobimetallic complex confined in MWNTs. Facilitated self-assembly of the catalyst with MWNTs avoided the sacrificial use of excess chiral ligand for the formation of the heterobimetallic complex, improving the loading ratio of the catalyst components. Eighty-five percent of the catalyst components were incorporated onto MWNTs to produce the confined catalyst, which was a highly efficient and recyclable catalyst for the anti-selective asymmetric nitroaldol reaction. The requisite precautions for the catalyst preparation to elicit reproducible catalytic performance are summarized. Superior catalytic profiles over the prototype catalyst without MWNTs were revealed in the synthesis of optically active 1,2-nitroalkanols, which are key intermediates for the synthesis of therapeutics.

Temperature-dependent charge transport in TiO2–multiwalled carbon nanotube composites

Charge transport properties of TiO2–multiwalled carbon nanotube (MWCNT) composites were investigated. The TiO2–MWCNT composites were fabricated by spark plasma sintering of a mixture of TiO2 nanoparticles and MWCNTs. Temperature-dependent electrical conductivities of the composites reveal that the percolation threshold for the MWCNT network is affected by temperature, and that the activation process for electron hopping is also influenced by the percolation. Based on this interdependence, an integrated charge transport model, including both the effects of the percolation and the electron hopping, is proposed for this system.

Compressibility of highly porous network of carbon nanotubes

A simple analytical model for predicting the compressibility of highly porous network of carbon nanotubes (CNTs) has been proposed based on the theory of compression behavior of textile materials. The compression model of CNT network has accounted for their physical, geometrical, and mechanical properties. The compression behavior of multi-walled carbon nanotubes (MWCNTs) has been predicted and compared with the experimental data pertaining to the compressibility of highly porous nanotube sponges. It has been demonstrated that the compressibility of network of MWCNTs can be tailored depending upon the material parameters and the level of compressive stresses.

Ultraviolet Photodetector Fabricated From Multiwalled Carbon Nanotubes/Zinc-Oxide Nanowires/p-GaN Composite Structure

An ultraviolet (UV) heterojunction photodetector was fabricated from multiwalled carbon nanotubes (MWCNTs)/zinc-oxide nanowires (NWs)/p-GaN composite structure. The photodetector demonstrated significant rectifying characteristics and relative fast transient response with response time on the order of milliseconds. Under back illumination, the photodetector exhibited a narrow bandpass photoresponse spectrum (13-nm full-width at half-maximum) centered at 375 nm with a maximum responsivity of 6 mA/W. The good performance of this heterojunction photodetector is attributed to improved carrier transport and collection efficiency through the MWCNTs network deposited on top of the ZnO NWs.

Wideband nonlinear characteristics of random multiwalled carbon nanotubes network

ABSTRACTIn this work, multiwalled carbon nanotubes (MWCNTs) were randomly deposited in gaps of microstrip interdigitated capacitive (IDC) structure. Measured I‐V characteristics show nonlinear behavior of MWCNTs. Supported by an analytical Schottky‐based model, the nonlinear mechanism is attributed to semiconductor/metallic (S/M) junction properties. Measuring the IDC over a wide frequency band, from 1 kHz up to 3 GHz, we demonstrate there is a maximum frequency (∼10 MHz) beyond which the nonlinear behavior of the MWCNTs network vanishes. An equivalent lumped element circuit for MWCNTs‐based IDC describes well the measured behavior up to 3 GHz. Thanks to the extracted equivalent circuit, we demonstrate that the capacitive couplings between MWCNTs dominate over nonlinear effects above 10 MHz. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2648–2652, 2013

Polyetherimide/Bucky Gels Nanocomposites with Superior Conductivity and Thermal Stability

Polyetherimide (PEI) nanocomposites comprising bucky gels of industrial-grade multiwalled carbon nanotubes (MWCNTs) and ionic liquid (IL, 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIM][PF6])) were prepared. The processing framework for this nanocomposite is simple, reproducible, and easily scalable. The strong interaction between IL and MWCNTs caused the latter to uniformly disperse in the PEI matrix while IL flowed into the gaps between the nanotubes' walls. The nanocomposite exhibited an enhanced conductivity of 2.01 × 10(4) Ω·cm volume resistivity at room temperature; the value decreased dramatically by 12 orders of magnitude, compared to pristine PEI. The IL free ions and MWCNTs networks provided excellent channels for electron transfer. PEI/bucky gels nanocomposites also showed improved thermal stability and high tensile strength. Other than having antiwear properties, this material can have numerous applications in the aerospace and electronics industries. Moreover, our work presents a "green" method toward modified nanocomposites industrial production as IL is environmentally safe and is easily recyclable.

Silver Phosphate/Carbon Nanotube-Stabilized Pickering Emulsion for Highly Efficient Photocatalysis

This study demonstrates a first exploitation of the unique properties inherent in Pickering emulsions to develop a new kind of photocatalytic system. We engineered the system by using silver phosphate (Ag3PO4) as a photocatalytic active metal oxide semiconductor and multiwalled carbon nanotubes (MWNTs) as a hydrophobic conducting nanostructure to form the Pickering emulsions. The photocatalytic activity of the as-formed Ag3PO4/MWNT-stabilized Pickering emulsion-based system is studied toward dye decomposition and oxygen evolution. Results imply that the Pickering emulsion-based photocatalytic system exhibits a much higher efficiency, as compared with traditional solution-dispersed photocatalytic system. This high efficiency is elucidated in terms of the unique properties inherent in Pickering emulsions including (i) the self-assembled Ag3PO4/MWNT nanohybrid at water/oil interface, well ensuring a large surface area of the photocatalyst, (ii) the use of MWNTs to facilitate the formation of amphiphilic nanostructures self-assembled at water/oil interface, promoting the charge separation of the semiconductor through the π–π network of MWNTs by shuttling and storing photogenerated electrons from the visible light irradiated Ag3PO4, and (iii) the separation of the product (e.g., O2 evolved from water oxidation) from the reactants during the photocatalytic process, well accelerating the photocatalytic reactions. In addition to the high efficiency, the fast and simple procedures employed for demulsifying (e.g., sonication or centrifugation) and re-emulsifying (e.g., shaking) essentially make our Pickering emulsion-based photocatalytic system technically simple and thus practically applicable. This study opens a new way to developing novel photocatalytic systems with high efficiency and good practical applicability based on Pickering emulsion science and technology.

Photocatalysis-assisted water filtration: Using TiO2-coated vertically aligned multi-walled carbon nanotube array for removal of Escherichia coli O157:H7

A porous ceramic was coated with vertically aligned multi-walled carbon nanotubes (MWCNTs) by spray pyrolysis. Titanium dioxide (TiO2) nanoparticles were then coated onto this densely aligned MWCNT. The presence of TiO2/MWCNT interfacial arrays was confirmed by X-ray diffraction (XRD), scanning electron microscope–energy dispersive analysis of X-ray (SEM–EDAX) and transmission electron microscope (TEM). This is a novel report in which water loaded with a most dreadful enterohemorrhagic pathogenic strain of Escherichia coli O157:H7 was filtered through TiO2/MWCNT coated porous ceramic filter and then analysed. Bacterial removal performance was found to be significantly lower in control i.e. plain porous ceramic (P<0.05) as compared to TiO2/MWCNT coated ceramic. The photocatalytic killing rate constant for TiO2-ceramic and MWCNT/TiO2-ceramic under fluorescent light was found be 1.45×10−2min−1 and 2.23×10−2min−1 respectively. Further, when I–V characteristics were performed for TiO2/MWCNT composite, it was corroborated that the current under light irradiation is comparatively higher than that in dark, thus proving it to be photocatalytically efficient system. The enhanced photocatalysis may be a contribution of increased surface area and charge transfer rate as a consequence of aligned MWCNT network.

Microstructure and Performance of Multiwalled Carbon Nanotube/m-Aramid Composite Films as Electric Heating Elements

We report microstructure of thermomechanically stable multiwalled carbon nanotube (MWCNT)/poly(m-phenylene isophthalamide) (m-aramid) composite films containing 0.0-10.0 wt % MWCNTs and their performance as electric heating elements. FE-SEM images show that the MWCNTs are well dispersed in the composite films and are wrapped with m-aramid chains and that the interfacial thickness of m-aramid wrapped MWCNTs decreases with the MWCNT content. The electrical resistivity of films varies from ∼10(13) Ω cm for the neat m-aramid to ∼10(0) Ω cm of the film with 10.0 wt % MWCNT owing to the formation of a conductive three-dimensional network of MWCNTs. Accordingly, the performance of MWCNT/m-aramid films as electric heating elements is strongly dependent on MWCNT content as well as applied voltage. For the composite film with 10.0 wt % MWCNT, a maximum temperature of ∼176 °C is attained even at a low applied voltage of 10 V. The excellent performance such as rapid temperature response and high electric power efficiency at given applied voltages is found to be related with the microstructural features of the MWCNT/m-aramid films.

Coupling of titania with multiwall carbon nanotubes for decomposition of gas-phase pollutants under simulated indoor conditions

This study synthesized multiwall carbon nanotube (MWNT)–titania (TiO2) composites and examined their characteristics and photocatalytic performance for the cleaning of gas-phase benzene, toluene, ethyl benzene, and o-xylene (BTEX) under simulated indoor conditions. Optical and spectral surveys of the as-synthesized composite confirmed that the TiO2 nanoparticles were bound intimately to the MWNT networks. The photocatalytic performance was evaluated using an annular-type reactor inner-coated with MWNT–TiO2 or Degussa P25 TiO2. The composite revealed gas removal ability superior to that of stand-alone TiO2. This composite was also less affected by humidity during toluene decomposition compared to the previous result obtained from a stand-alone TiO2. Unlike another previous result obtained from the TiO2, the performance of the composite was not affected by changes in input concentration (IC) within a simulated indoor air quality range (0.1–1.0 ppm) but it decreased significantly when the IC was increased to 5 and 10 ppm. As the flow rate was decreased from 4.0 to 1.0 L min−1, the average efficiency for the target compounds increased to 95% or ∼100%. The MWNT–TiO2 composite could be applied effectively to the decomposition for BTEX under certain simulated indoor conditions. Implications: Unlike water applications, there are few reports of gas-phase applications of multiwall carbon nanotubes (MWCNT)–TiO2 composites. This study found that MWCNT–TiO2 composites showed performance in the removal of toxic gaseous aromatic superior to that of stand-alone TiO2. In addition, the pollutant degradation efficiency of the composite was less affected by humidity than for a stand-alone TiO2 unit within a simulated indoor relative humidity range. Moreover, unlike the TiO2 unit, the composite's performance was not affected by variations in the input concentrations within the simulated indoor air quality (IAQ) range. In addition, the decomposition efficiencies increased to 100% with decreasing flow rate.

Label-Free Detection of Hemoglobin Using MWNT-Embedded Screen-Printed Electrode

The synthesis of a network of cross-linked multiwalled carbon nanotubes (MWNTs) on a cysteamine-functionalized screen-printed gold electrode (MWNT/Au-SPE) and its use as a sensor for hemoglobin (Hb) determination is reported. It is proved to be a ready-to-use platform for routine clinical analysis in the blood after the separation of red blood cells. The study shows direct electron transfer between Hb-FeIII and Hb-FeII on applying a potential difference which is beneficial in detecting the presence of Hb in solution. The characterization of MWNT-embedded electrode was accomplished through Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy (EIS), Raman spectroscopy, optical profiling, and cyclic voltammetry. EIS studies show a reduction in the value of surface charge transfer resistance (Rct) from MWNT/Au-SPE (−2.72 kΩ) to bare Au-SPE (−24.38 kΩ), respectively. MWNT/Au-SPE showed better electrochemical characteristics, and kinetic studies revealed the heterogeneous rate transfer constant (ks) of 1.26 s−1. The electrochemically active surface area was also increased 100 times from bare Au-SPE (2.41 × 10−6 cm2) to MWNT/Au-SPE (2.052 × 10−4 cm2). The sensitivity of the sensor for Hb determination was found to be 20.50 μA g−1 dl in the linear range of 9–15 g dl−1 for lyophilized Hb. It is also found to be extremely sensitive for Hb determination in blood samples with 38.75 μA g−1 dl sensitivity in the same linear range.

Self‐Assembling Neodymium/Sodium Heterobimetallic Asymmetric Catalyst Confined in a Carbon Nanotube Network

Confined cat works better: A self-assembling heterobimetallic catalyst, comprised of a Nd/Na/amide ligand confined in an entangled multiwalled carbon nanotube (MWNT) network, outperforms the unconfined catalyst in anti-selective catalytic asymmetric nitroaldol reactions. The confined catalyst could be used repeatedly through simple filtration, and was applied to a concise enantioselective synthesis of anacetrapib.

Perfect High‐Temperature Plasticity Realized in Multiwalled Carbon Nanotube‐Concentrated α‐Al2O3 Hybrid

We investigate the high‐temperature compressive deformation behavior of a novel, fully dense and structurally uniform, 20 vol% multiwalled carbon nanotube (MWCNT)–α‐Al2O3 matrix hybrid, which has a strong room‐temperature interfacial shear resistance (ISR) and a unique MWCNT‐concentrated grain‐boundary (GB) structure. We realized a perfect plastic deformation at 1400°C and a rather high initial strain rate of 10−4 s−1 by a low ~30 MPa flow stress, which is contrary to the strain hardening response of fine‐grain monolithic Al2O3. This unique performance in CNT–ceramic system in compression is explained as follows: the concentrated network of individual MWCNTs perfectly withstands the high‐temperature and shear/compressive forces, and strongly preserves the nanostructure of Al2O3 matrix by preventing the dynamic grain growth, even during a large ~44% deformation. Furthermore, the presence of large amount of radially soft/elastic, highly energy‐absorbing MWCNTs in the GB and specially multiple junction areas, and a potentially weak 1400°C‐ISR, could greatly facilitate the GB sliding process (despite the hybrid's strong room‐temperature ISR), as evidenced by the formation of some submicrometer‐scale MWCNT aggregates in GB area, the equiaxed grains and dislocation‐free nanostructure of the deformed hybrid. The results presented here could be attractive for the ceramic forming industry and could be regarded as a reference for oxide systems in which, the GB areas are occupied with soft/elastic, highly energy‐absorbing nanostructures.

Decoration of Spongelike Ni(OH)2 Nanoparticles onto MWCNTs Using an Easily Manipulated Chemical Protocol for Supercapacitors

This study uses a "bottom-up" approach chemical method to coat nanocrystalline Ni(OH)2 onto multiwalled carbon nanotubes (MWCNTs) for flexible supercapacitor electrodes, where the higher electronic conductivity of MWCNTs permits their use as the supporting backbone onto which Ni(OH)2 can be deposited. The paper portrays the advantages of the facile successive ionic layer adsorption and reaction (SILAR) method for depositing Ni(OH)2/MWCNT thin films onto large area flexible substrates. We demonstrate that these Ni(OH)2/MWCNT films consist of a uniform coating of sponge-like Ni(OH)2 on the MWCNT network structure using scanning electron micrographs and transmission electron micrographs; this structure is promising for supercapacitor applications. Ni(OH)2/MWCNT films exhibit a specific capacitance of 1487 F g(-1) at a scan rate of 5 mV s(-1) in a 2 M KOH aqueous solution. The electrodes are generated using a simple three-beaker SILAR system at ambient conditions, thus providing an easy approach to fabricate high-power and high-energy flexible supercapacitors. Ni(OH)2/MWCNTs demonstrate a good rate capability and excellent long-term cyclic stability (96% capacity retention after 1000 cycles). Such high-performance capacitive behavior indicates that Ni(OH)2/MWCNT composites are promising electrode materials for the fabrication of supercapacitors. Thus, the method described in this paper provides a generalized route for the production of a wide range of Ni(OH)2/MWCNT-based materials for applications beyond electrochemical energy storage. These encouraging results promote interest in developing such devices, including nontoxic and greener components, compared with current organic-based devices.

Comparison of filler percolation and mechanical properties in graphene and carbon nanotubes filled epoxy nanocomposites

This paper compares the filler percolation network of multi-walled carbon nanotubes (MWCNTs) grown by chemical vapor deposition and thermally reduced functionalized graphene sheets (FGSs) in an epoxy resin. The filler network was evaluated by the plate–plate rheological response of un-cured dispersions and the electrical properties of cured materials. We found that FGS did not raise the viscosity of the system as much as MWCNT, maintaining the Newtonian behavior even at 1.5wt.% FGS. MWCNT readily formed a filler network compared to FGS, evidenced by lower electrical and rheological percolation thresholds, presence of yield stress and higher storage modulus of the dispersions. On the other hand, the mechanical performance of the cured FGS nanocomposites outperformed the MWCNT, with enhancements of 50% and 15% of Young’s modulus and strength, respectively. This combination of good processing properties with low viscosity and enhanced mechanical properties makes FGS great candidates to develop multifunctional polymer materials.

Reduction of percolation threshold through double percolation in melt‐blended polycarbonate/acrylonitrile butadiene styrene/multiwall carbon nanotubes elastomer nanocomposites

AbstractWe demonstrate a method that involves melt blending of polycarbonate (PC) and melt‐blended acrylonitrile butadiene styrene (ABS) with multiwall carbon nanotubes (MWCNTs) to prepare electrically conducting PC/MWCNT nanocomposites at significantly low MWCNT loading. The partial solubility of ABS in PC led to a selective dispersion of the MWCNTs in the ABS phase after melt‐blending PC and ABS. Thus, a sudden rise in electrical conductivity (∼108 orders of magnitude) of the nanocomposites was found at 0.328 vol% of MWCNT, which was explained in terms of double percolation phenomena. By optimizing the ratio of PC and the ABS–MWCNT mixture, an electrical conductivity of 5.58 × 10−5 and 7.23 × 10−3 S cm−1 was achieved in the nanocomposites with MWCNT loading as low as 0.458 and 1.188 vol%, respectively. Transmission electron microscopy revealed a good dispersion and distribution of the MWCNTs in the ABS phase, leading to the formation of continuous MWCNT network structure throughout the matrix even at very low MWCNT loading. Storage modulus and thermal stability of the PC were also increased by the presence of a small amount of MWCNTs in the nanocomposites.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers