Pure Multi-walled Carbon Nanotubes Research Articles

Effect of MWCNT filled epoxy adhesives on the quality of adhesively bonded joints

Most adhesively bonded joints exhibit adhesive or cohesive failure, i.e. failure at the adhesive/adherend interface or within the adhesive, respectively. The main objective of this study is to investigate the effect of surface modification of the metal substrate accompanied by modification of the adhesive properties on the strength and failure mechanism of bonded joints. A 5061 aluminium alloy has been used as the metal substrate onto which two types of surface treatments were applied; chemical surface modification and gritblasting. A standard epoxy resin was used as the adhesive medium, in which multi-wall carbon nanotubes (MWCNTs) were dispersed, with a range of weight fraction content (from 0.03% to 0.5%). The resin was fully characterised by mechanical testing in order to determine the optimum weight fraction to enhance its properties. Aluminium to aluminium and glass fibre reinforced polymer (GFRP) composite to aluminium single lap joints bonded with either pure epoxy resin or MWCNT reinforced epoxy resin were subsequently manufactured and tested. The tests show a moderate increase of the joint strength when MWCNTs are added into the adhesive with the failure mechanism changing from cohesive to adhesive. In addition, the comparison between different surface preparation methods shows that gritblasting results in considerably improved adhesive strength over chemical treatment.

Pulsed current field assisted surface modification of carbon nanotubes with nanocrystalline titanium carbide

Multiwalled carbon nanotubes (MWCNTs) were surface modified with titanium carbide (TiC) nanocrystalline particles by a novel pressureless spark plasma sintering method. The microstructure and properties of the nano-TiC modified MWCNTs were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, thermal gravity analysis and nanoindentation. Experimental results showed that the TiC nanoparticles were generated and grown epitaxially on the surface of MWCNTs by the pulsed current field assisted solid-state reaction between Ti and MWCNTs. The TiC nanoparticles were preferentially nucleated at defective sites of the nanotubes surfaces and grown along the [111] direction. Nano-TiC modified MWCNTs showed better oxidation resistance than that of the pure MWCNTs. Improvements of Young's modulus (31.18%) and nanohardness (62.74%) were achieved by doping of 1.0 wt.% TiC coated-MWCNTs into the aluminium matrix. The proposed modification strategy can be a versatile route for fabricating other nano-carbide coating on one dimensional nano-reinforcements.

Solvothermal synthesis of CdS QDs/MWCNTs nanocomposites with high efficient photocatalytic activity under visible light irradiation

Cadmium sulphide (CdS) quantum dots (QDs) deposited multi-walled carbon nanotubes (MWCNTs) photocatalysts were synthesized via a facile one-pot solvothermal process. The as-prepared samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), Fourier transform infrared spectra (FT-IR) and photoluminescence (PL). The CdS QDs with the size at range of 5–8 nm were immobilized on the surface of MWCNTs. The photocatalytic activity of the CdS QDs/MWCNTs nanocomposites were evaluated by the decomposition of malachite green (MG) under visible light irradiation. All CdS QDs/MWCNTs photocatalysts possessed higher photocatalytic activity than pure MWCNTs. It could be found that MG was photodegraded with the highest degradation efficiency of 94.5% by 2.5-CdS QDs/MWCNTs photocatalysts under visible light irradiation. This enhanced photocatalytic performance was attributed to an efficient electron–hole separation of photogenerated electron–hole pairs of CdS. Moreover, the photocatalytic mechanism of CdS QDs/MWCNTs nanocomposites was also discussed.

Hexagonal boron nitride (h-BN) nanoparticles decorated multi-walled carbon nanotubes (MWCNT) for hydrogen storage

Hydrogen is considered as the most promising clean energy carrier because of its abundance, environmental friendliness and high conversion efficiency. However, developing safe, compact, light weight and cost-effective hydrogen storage materials is one of the most technically challenging barriers to the widespread use of hydrogen as fuel. The present work reports the hydrogen storage performance of multi-walled carbon nanotubes (MWCNT)/hexagonal boron nitride (h-BN) nanocomposites (MWCNT/h-BN), where ultrasonication method is adopted for the synthesis of the MWCNT/h-BN nanocomposites. Hydrogenation process was carried out using Seiverts-like hydrogenation setup. Characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Nitrogen adsorption–desorption isothermal studies (BET), CHN-elemental analysis and Thermogravimetric Analysis (TGA) were used to analyze the samples at various stages of the experiment. A maximum of 2.3 wt% hydrogen storage is achieved in the case of acid treated MWCNTs (A-MWCNT) with 5 wt% of h-BN nanoparticles compared to pure MWCNTs that could store 0.15 wt% only. Moreover the calculated binding energy (0.42 eV) of stored hydrogen of A-MWCNT with 5 wt% of h-BN nanocomposite lies in the recommended range of binding energy (0.2–0.6 eV) for fuel cell applications. The TG study shows that 100% desorption is achieved at the temperature range of 120–410 °C and confirms that the prepared hydrogen storage medium will serve effectively in the realm of hydrogen fuel economy in near future.

Study of the Variables in the Synthesis of Carbon Nanotubes by the Spray Pyrolysis of Benzene–Ferrocene Mixtures

Pure multiwalled carbon nanotubes were synthesized by the spray pyrolysis of benzene–ferrocene mixtures at 1173–1273 K. Several variables were studied: temperature, ferrocene concentration in benzene, pump (feed) rate of benzene–ferrocene mixture, and flow rate of carrier gas (argon). Characterization of the CNTs and the effects of the variables were studied with the help of X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetry. The yield and morphology of CNT was found to be optimum at 1273 K. The effect of temperature on the yield of CNT is explained thermodynamically. Also, the standard Gibbs energy of formation of C6H6(s), which is a new thermodynamic data, is generated. Ferrocene concentration affected the yield inversely. The pump rate controlled the number of walls of the CNT produced and the control of argon flow rate helped to achieve proper alignment of the CNTs.

Experimental investigation on the ammonia adsorption and heat transfer characteristics of the packed multi-walled carbon nanotubes

Carbon nanotube (CNT) is considered as a kind of potential adsorbent because of its large surface area, uniform micropores and unique physicochemical properties. The adsorption performance of ammonia on the packed multi-walled carbon nanotubes (MWCNTs) were studied in this paper. Firstly, the packed MWCNTs were characterized by the scanning electron microscope (SEM) and transmission electron microscopy (TEM). Secondly, the effect of working pressure and adsorbent temperature on the adsorption capacity of ammonia by the packed MWCNTs was investigated. Thirdly, Langmuir and Freundlich models were used to analyze the equilibrium adsorption data and the adsorption kinetics was also discussed using a classical gas diffusion model. The Freundlich isotherm model could elucidate well the adsorption of ammonia on the MWCNTs when compared to the Langmuir equation. The research results showed that the equilibrium adsorption amount of ammonia by the MWCNTs varied between 22.69 and 90.05 mg/gCNT at the adsorbent temperature of 25–35 °C and working pressure of 0.368–0.744 MPa. It seems that the pure MWCNT is not appropriate to act as the adsorbent for the solid–gas adsorption refrigeration due to its low adsorption capacity. However, our research indicates that the MWCNTs can be used as additive to some other chemical adsorbents to improve their heat transfer characteristics.

Capabilities of asymmetric flow field-flow fractionation coupled to multi-angle light scattering to detect carbon nanotubes in soot and soil

Analytical detection and quantification of multi-walled carbon nanotubes (MWCNTs) in complex matrices such as soils is very challenging. In an initial approach to this task, we identify MWCNTs by making use of their different (e.g., rod-like) shape compared to other (native) soil particles and in particular soot, which is ubiquitously present in soils. A shape factor ρ, determined using asymmetric flow field-flow fractionation coupled to multi-angle light scattering (aF4-MALS), was used to discriminate MWCNTs of different aspect ratios, as well as mixtures of soot and MWCNTs, in pure suspensions. MALS results were additionally confirmed using automated electron microscopy image analysis. We then analyzed different soil types which consistently showed ρ-values that differed from pure MWCNTs. To test the performance of the method for MWCNT detection in such complex matrices, we conducted standard additions of a MWCNT as well as soot to an agricultural soil. Extracts from these MWCNT-spiked soils showed increased ρ-values compared to soot-spiked or native soil. The method detection limit for the MWCNT was 1.6 to 4.0 mg g−1 soil and lies within the range of commonly used black carbon quantification methods, but is much higher than any currently predicted environmental concentration. Additionally, the method is currently limited by a relatively narrow dynamic range of ρ. Despite these limitations, our results suggest that aF4-MALS provides specific shape information that may be linked to an actual MWCNT presence in soils. Further method improvement potential is outlined along different steps of the workflow.

Palladium-nanoparticle-coated carbon nanotube gas sensor

Flexible hydrogen gas sensors were fabricated using multi-walled carbon nanotubes (MWCNTs) decorated with Pd nanoparticles for the detection of H2 gas at room temperature. A comparative gas-sensing study was carried out on both the Pd-nanoparticles-decorated and undecorated MWCNT sheets in order to examine the effect of Pd nanoparticles on the gas-sensing performances at room temperature. Experimental results showed that the MWCNTs/Pd sensor exhibited fast response and recovery as well as high sensitivity compared with the pure MWCNT sensor. The improved sensing properties of this sensor were attributed to the spillover effect of Pd nanoparticles and the highly conductive MWCNT sheet.

L-Phenylalanine amino acid functionalized multi walled carbon nanotube (MWCNT) as a reinforced filler for improving mechanical and morphological properties of poly(vinyl alcohol)/MWCNT composite

Abstract Carbon nanotube dispersion in polymer matrix is one of the most crucially important aspects in carbon nanotube/polymer composites. This paper is aimed to discuss the considerable improvement in dispersion of multi walled carbon nanotubes (MWNTs) in poly(vinyl alcohol) (PVA) matrix that was attained through bio-functionalization of MWCNTs. Initially, for getting better dispersion in water, pure MWCNTs have been functionalized by l -phenylalanine amino acid. The functionalized MWCNTs (f-MWCNTs) show much enhanced solubility in water. So, effects of modified MWCNT on dispersion in PVA matrix and certain properties of the resulting composites, like; mechanical, thermal and morphological properties were studied. The prepared composites were examined by Fourier transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy. Also, the mechanical and thermal properties of composite films have been investigated and revealed that incorporation of just a few percent of f-MWCNTs can improve the PVA mechanical and thermal properties significantly.

Spectroscopic Studies on Pure and Histidine-Functionalized Multiwalled Carbon Nanotubes

ABSTRACT Electron paramagnetic resonance, Fourier transform infrared, and ultraviolet-visible studies were carried out for pure and histidine-functionalized multiwalled carbon nanotubes. Electron paramagnetic resonance absorption spectral data were found to be the best fit for the Gaussian lineshape. The g-values indicate the presence of magnetic impurities in the samples and the interaction between the localized electrons and delocalized electrons in the nanotubes trapped at defects or magnetic ion sites. The electron spin concentration decreases with increasing concentration of histidine, which implies that the unpaired electrons undergo a reduction process in the histidine-functionalized multiwalled carbon nanotubes. Fourier transform infrared study confirms the presence of functional groups in pure and histidine-functionalized multiwalled carbon nanotubes. Ultraviolet-visible study reveals the formation of a charge transfer complex in histidine-functionalized multiwalled carbon nanotubes.

Fabrication and consolidation behavior of Al 6061 nanocomposite powders reinforced by multi-walled carbon nanotubes

The composite behavior of an Al 6061 nanocrystalline matrix reinforced with different weight percentages (0, 0.5, 1.0, 1.5 and 2.0wt.%) of multi-walled carbon nanotubes (MWCNTs) produced by mechanical alloying (MA) with a milling time of 30h was investigated. MWCNTs were added during the last 2h of milling to avoid structural damage during MA. The milled powders were consolidated by cold uni-axial compaction followed by sintering at different temperatures (450°C, 525°C and 600°C) under a reducing atmosphere (N2) to evaluate the materials' sinterability. The structure of the MWCNTs was evaluated by Raman spectroscopy of as-received pure MWCNTs, Al 6061-2wt.% MWCNT nanocomposite powder after 30h MA and sintered samples of Al 6061-1wt.% MWCNTs & Al 6061-2wt.% MWCNTs. The crystallite size and lattice parameter of the composites were examined. The relative density, compressibility, green compressive strength, sinterability and Vickers hardness of the composites were also examined. The effects of MWCNTs as reinforcement on the consolidation behavior of the nanocrystalline matrix were studied using the Heckel, Panelli and Ambrosio Filho and Ge equations. The fabricated composites exhibited high Vickers hardness of 76HV (818MPa), which is approximately three times higher than that of microcrystalline Al 6061. However, because of MWCNTs that were added during the last 2h of milling, higher hardness values were obtained in this investigation.

Experimental study of the ammonia adsorption characteristics on the composite sorbent of CaCl2 and multi-walled carbon nanotubes

A new composite sorbent made of CaCl2 and multi-walled carbon nanotube (MWCNT) was prepared for solid–gas ammonia adsorption refrigeration systems in the paper. The composite sorbent was fabricated by impregnating MWCNTs matrix with CaCl2 to improve the adsorption performance of the chemical sorbent. The ammonia adsorption capacity of the composite sorbent and the MWCNTs matrix were measured using a Rubotherm magnetic suspension balance. Experimental results showed that the maximum adsorption amount of ammonia by the MWCNTs matrix and the composite sorbent are 90.05 mg gCNT−1 and 859.85 mg gsorbent−1 under the experimental conditions. Moreover, the chemical reaction plateaus and steps of the reaction between CaCl2 and NH3 were analyzed and the adsorption capacities of the composite sorbent at different working conditions were evaluated. The results indicated that although the adsorption capacity of ammonia on the pure MWCNTs is relatively low, the addition of MWCNTs into the chemical sorbent can avoid the agglomeration and prevent the adsorption performance attenuation of reactive salt.

Improving compression-after-impact performance of carbon–fiber composites by CNTs/thermoplastic hybrid film interlayer

Abstract Multi-walled carbon nanotubes (MWCNTs) have been effectively dispersed with polyetherketone cardo (PEK-C)/dichloromethane by ball milling technique. Pure PEK-C film and MWCNTs hybrid PEK-C (MWCNTs/PEK-C) films with different MWCNTs content were made employing an solvent casting technology. Transmission electron microscope (TEM) showed the MWCNTs shortened by ball milling. The neat and nano-hybrid films were used as interleaves for carbon fiber/bismaleimide (BMI) composite laminates. C-scan results showed that impact damage area decreased for PEK-C film interleaved laminates and further reduced by modification of MWCNTs. The compression after impact (CAI) strength was significantly improved for interleaved composite laminates when compared to baseline composite laminate. Maximum improvement (∼33%) of CAI value was achieved by interlayer of hybrid film with 10 wt% MWCNTs. The toughening micromechanism of enhanced resistance to low-energy impact with the incorporation of MWCNTs were investigated based on scanning electron microscopic (SEM) images of the fracture surfaces of the tested specimens. It is suggested that thermoplastics, BMI particles and MWCNTs had combined action to reduce interlaminar impact damage and thus to improve CAI strength.

Power generation using polyaniline/multi-walled carbon nanotubes as an alternative cathode catalyst in microbial fuel cells

SUMMARY Optimization of the cathode catalyst is critical to the study of microbial fuel cells (MFCs). By using the open circuit voltage and power density as evaluation standards, this study focused on the use of polyaniline (PANI)/multi-walled carbon nanotube (MWNT) composites as cathode catalysts for the replacement of platinum (Pt) in an air-cathode MFC, which was fed with synthetic wastewater. Scanning electron microscopy and linear scan voltammogram methods were used to evaluate the morphology and electrocatalytic activity of cathodes. A maximum power density of 476 mW/m2 was obtained with a 75% wt PANI/MWNT composite cathode, which was higher than the maximum power density of 367 mW/m2 obtained with a pure MWNT cathode but lower than the maximum power density of 541 mW/m2 obtained with a Pt/C cathode. Thus, the use of PANI/MWNT composites may be a suitable alternative to a Pt/C catalyst in MFCs. PANI/MWNT composites were initially used as cathodic catalysts to replace Pt/C catalysts, which enhanced the power generation of MFCs and substantially reduced their cost. Copyright © 2014 John Wiley & Sons, Ltd.

Enhanced dielectric and electro-optical properties of a newly synthesised ferroelectric liquid crystal material by doping gold nanoparticle-decorated multiwalled carbon nanotubes

In this article, a newly synthesised ferroelectric liquid crystal (FLC) material, namely LAHS 22, has been characterised. The characterisation of the FLC material has been performed using dielectric relaxation spectroscopy, differential scanning calorimetry and polarisation optical microscopy. We observed an enhancement in the dielectric and electro-optical properties of the FLC material by incorporating gold nanoparticles (GNPs)-decorated multiwalled carbon nanotubes (MWCNTs). The GNPs-decorated MWCNTs cause an increment in dielectric dispersion (up to kHz), absorption, spontaneous polarisation and rotational viscosity of the FLC material. The pure and GNPs-decorated MWCNTs doped FLC cells were analysed by means of various dielectric spectroscopic and optical measurements. The observed enhancement in the dielectric and electro-optical properties of the FLC material has also been studied with concentration of GNPs-decorated MWCNTs in FLC material. The GNPs-decorated MWCNTs/FLC composites are not only of fundamental importance, but also useful materials for device applications such as liquid crystal displays and memory devices.

A study of reaction kinetics in Al – 2% MWCNT composites

A composite obtained from pure aluminum and multiwall carbon nanotubes by mechanical milling in a high-power mill and ultrasonic mixing is studied. The apparent activation energy and the order of the reaction between carbon nanotubes and aluminum are determined using the Kissinger and Crane equations and differential scanning calorimetry under non-isothermal conditions.

Characteristics of graphite based composite electrodes containing carbon nanotubes for vanadium redox flow batteries

Graphite (GP) based composite electrodes containing multi-walled carbon nanotube (MWCNT) were prepared for vanadium redox flow batteries (VRFB) using polytetrafluoroethylene (PTFE) as binding agent. Electrochemical performance of the GP-MWCNT composite electrodes was characterized by chronoamperometry, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that both positive and negative electrode reactions of VRFB benefited from the use of more MWCNT in the composite electrode, and the best electrochemical performance was obtained with pure MWCNT electrode. A VRFB was therefore constructed using pure MWCNT electrodes as both the positive and negative electrodes. Preliminary charge/discharge tests at a current density of 30 mA/cm 2 demonstrated that the VRFB had a good stability and electrochemical performance. The current efficiency, voltage efficiency and energy efficiency were 96%, 87% and 84%, respectively.

Multiwalled carbon nanotubes bearing ‘terminal monomeric unit’ for the fabrication of epinephrine imprinted polymer-based electrochemical sensor

Carbon-nanotubes play a pivotal role in molecularly imprinted polymer technology for inculcating conducting property, high surface to volume ratio, and maximum porosity in the film texture. Contrary to the non-covalent heterogeneous dispersion of pure (unmodified) multiwalled carbon nanotubes in the imprinted polymer film, the homogeneous distribution of their functionalized derivative was found more effective to augment the sensitivity of the measurement. This could be made feasible using multiwalled carbon nanotubes bearing terminal monomeric unit (termed as “CNT-mer”) for the polymerization (one CNT-mer in each repeating unit). In this work, the CNT-mer entails a N-hydroxyphenyl maleimide functionality to be utilized in the chain propagation with simultaneous imprinting of epinephrine in the polymeric network. This system, when casted on the tip of a pencil graphite electrode, responded a highly sensitive and selective response for epinephrine, prevalent in aqueous and real samples at ultratrace level (linear range 0.09–5.90ngmL−1, limit of detection 0.02ngmL−1, S/N=3), without any cross-reactivity and matrix effects. The proposed sensor is advantageous in obtaining enhanced differential pulse anodic stripping voltammetric current vis-a-vis the corresponding imprinted sensor modified with randomly dispersed flocculated multiwalled carbon nanotubes bundles. While the latter might restrict the interlayer diffusion of analyte in the film, the former sensor facilitated high diffusivity with the channelized electron transport to respond higher current. The CNT-mer dispersed sensor was found to be stable and rugged against mechanical stress and can be used, after regeneration, for more than hundred consecutive experiments in clinical settings.

DIFFERENCES IN CYTOCOMPATIBILITY BETWEEN MWCNTs AND CARBOXYLIC FUNCTIONALIZED MWCNTs

Influence of carboxylic functionalization on the cytocompatibility of multiwalled carbon nanotubes (MWCNTs) was investigated in this work. Water contact angle assay showed that the surface of MWCNTs-containing carboxyl (MWCNTs-COOH) became much more hydrophilic compared with pure MWCNTs. In cell-adhesion assays, two cell lines, mouse fibroblast cells (L929) and human umbilical vein endothelial cells (EAHY926) were used to assess the cytocompatibility of materials. The MWCNTs-COOH displayed the improved cell proliferation, viability and adhesion due to the enhanced wettability, indicating their superior cytocompatibility over MWCNTs. The existence of carboxyl groups should be benefit to the adhesion and growth of both cells, which implied that MWCNTs-COOH were helpful for seeding both cells and could be used as the functional surface for the adhesion and growth of cells.

S125 Pro-Fibrotic Effects of Multi-Walled Carbon Nanotube Exposure on Primary Human Alveolar Type II Epithelial Cells and Fibroblasts

Multi-walled carbon nanotubes (MWCNTs) are hollow fibre-like nanomaterials which are being investigated for use in drug delivery and as biosensors. However, due to their structural similarity to asbestos fibres, inhaled...