Multiple-walled Carbon Nanotubes Research Articles

Convective heat transfer in MHD slip flow over a stretching surface in the presence of carbon nanotubes

In the present study, thermal conductivity and viscosity of both single-wall and multiple-wall Carbon Nanotubes (CNT) within the base fluids (water, engine oil and ethylene glycol) of similar volume have been investigated when the fluid is flowing over a stretching surface. The magnetohydrodynamic (MHD) and viscous dissipation effects are also incorporated in the present phenomena. Experimental data consists of thermo-physical properties of each base fluid and CNT have been considered. The mathematical model has been constructed and by employing similarity transformation, system of partial differential equations is rehabilitated into the system of non-linear ordinary differential equations. The results of local skin friction and local Nusselt number are plotted for each base fluid by considering both Single Wall Carbon Nanotube (SWCNT) and Multiple-Wall Carbon Nanotubes (MWCNT). The behavior of fluid flow for water based-SWCNT and MWCNT are analyzed through streamlines. Concluding remarks have been developed on behalf of the whole analysis and it is found that engine oil-based CNT have higher skin friction and heat transfer rate as compared to water and ethylene glycol-based CNT.

Resistive Gas Sensors Based on MWCNTs-PVP Composite Films

In this paper, multiple-walled carbon nanotubes (MWCNTs) monolayer film and MWCNTs-polyvinylpyrrolidone (PVP) composite films were fabricated on interdigitated electrodes (IDEs) by airbrush technology, respectively. Response performance of all the sensors to various concentrations of vapors including methanol, ethanol, acetone, tetrahydrofuran, water and 1,2-dichloroethane were investigated. The results showed that a larger sensing response was obtained for the composite films compared with the MWCNTs monolayer film. Moreover, the MWCNTs-PVP composite films had a good selectivity for 1,2-dichloroethane vapor.

Q-switched erbium doped fiber laser based on single and multiple walled carbon nanotubes embedded in polyethylene oxide film as saturable absorber

Abstract A passive, stable and low cost Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), which are embedded in polyethylene oxide (PEO) film as a saturable absorber (SA). The film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation operating at wavelength of 1533.6 nm. With SWCNTs, the laser produces a stable pulse train with repetition rate and pulse width ranging from 9.52 to 33.33 kHz and 16.8 to 8.0 μs while varying the 980 nm pump power from 48.5 mW to 100.4 mW. On the other hand, with MWCNTs, the repetition rate and pulse width can be tuned in a wider range of 6.12–33.62 kHz and 9.5– 4.2 μs, respectively as the pump power increases from 37.9 to 120.6 mW. The MWCNTs produce the pulse train at a lower threshold and attain a higher repetition rate compared to the SWCNTs. This is due to thicker carbon nanotubes layer of the MWCNTs which provides more absorption and consequently higher damage threshold. The Q-switched EDFL produces the highest pulse energy of 531 nJ at pump power of 37.9 mW with the use of MWCNTs-PEO SA.

Dynamics of multiple viscoelastic carbon nanotube based nanocomposites with axial magnetic field

Nanocomposites and magnetic field effects on nanostructures have received great attention in recent years. A large amount of research work was focused on developing the proper theoretical framework for describing many physical effects appearing in structures on nanoscale level. Great step in this direction was successful application of nonlocal continuum field theory of Eringen. In the present paper, the free transverse vibration analysis is carried out for the system composed of multiple single walled carbon nanotubes (MSWCNT) embedded in a polymer matrix and under the influence of an axial magnetic field. Equivalent nonlocal model of MSWCNT is adopted as viscoelastically coupled multi-nanobeam system (MNBS) under the influence of longitudinal magnetic field. Governing equations of motion are derived using the Newton second low and nonlocal Rayleigh beam theory, which take into account small-scale effects, the effect of nanobeam angular acceleration, internal damping and Maxwell relation. Explicit expressions for complex natural frequency are derived based on the method of separation of variables and trigonometric method for the “Clamped-Chain” system. In addition, an analytical method is proposed in order to obtain asymptotic damped natural frequency and the critical damping ratio, which are independent of boundary conditions and a number of nanobeams in MNBS. The validity of obtained results is confirmed by comparing the results obtained for complex frequencies via trigonometric method with the results obtained by using numerical methods. The influence of the longitudinal magnetic field on the free vibration response of viscoelastically coupled MNBS is discussed in detail. In addition, numerical results are presented to point out the effects of the nonlocal parameter, internal damping, and parameters of viscoelastic medium on complex natural frequencies of the system. The results demonstrate the efficiency of the suggested methodology to find the closed form solutions for the free vibration response of multiple nanostructure systems under the influence of magnetic field.

Comparison of Hydrogen Sulfide Sensing Properties between Multiple-Walled Carbon Nanotubes (MWNTs) and MWNTs-HAuCl<sub>4</sub> Materials

The rapid and precise detection of hydrogen sulfide (H2S) has great significance due to its high toxicity. In this work, the response properties of multiple-walled carbon nanotubes (MWNTs) and MWNTs-HAuCl4 to H2S at room temperature were compared. Scanning electron microscopy (SEM) technique was used to characterize MWNTs and MWNTs-HAuCl4 films. It was found that sensors with MWNTs-HAuCl4 exhibited much higher response value. On the other hand, sensors with MWNTs were observed to have faster response time and better recovery properties.

Rapid Multiplug Filtration Cleanup with Multiple-Walled Carbon Nanotubes and Gas Chromatography–Triple-Quadruple Mass Spectrometry Detection for 186 Pesticide Residues in Tomato and Tomato Products

This study reports the development and validation of a novel rapid cleanup method based on multiple-walled carbon nanotubes in a packed column filtration procedure for analysis of pesticide residues followed by gas chromatography-triple-quadruple tandem mass spectrometry detection. The cleanup method was carried out by applying the streamlined procedure on a multiplug filtration cleanup column with syringes. The sorbent used for removing the interferences in the matrices is multiple-walled carbon nanotubes mixed with anhydrous magnesium sulfate. The proposed cleanup method is convenient and time-saving as it does not require any solvent evaporation, vortex, or centrifugation procedures. It was validated on 186 pesticides and 3 tomato product matrices spiked at two concentration levels of 10 and 100 μg kg(-1). Satisfactory recoveries and relative standard deviations are shown for most pesticides using the multiplug filtration cleanup method in tomato product samples. The developed method was successfully applied to the determination of pesticide residues in market samples.

A miniature electronic nose system based on an MWNT–polymer microsensor array and a low-power signal-processing chip

This article introduces a power-efficient, miniature electronic nose (e-nose) system. The e-nose system primarily comprises two self-developed chips, a multiple-walled carbon nanotube (MWNT)-polymer based microsensor array, and a low-power signal-processing chip. The microsensor array was fabricated on a silicon wafer by using standard photolithography technology. The microsensor array comprised eight interdigitated electrodes surrounded by SU-8 "walls," which restrained the material-solvent liquid in a defined area of 650 × 760μm(2). To achieve a reliable sensor-manufacturing process, we used a two-layer deposition method, coating the MWNTs and polymer film as the first and second layers, respectively. The low-power signal-processing chip included array data acquisition circuits and a signal-processing core. The MWNT-polymer microsensor array can directly connect with array data acquisition circuits, which comprise sensor interface circuitry and an analog-to-digital converter; the signal-processing core consists of memory and a microprocessor. The core executes the program, classifying the odor data received from the array data acquisition circuits. The low-power signal-processing chip was designed and fabricated using the Taiwan Semiconductor Manufacturing Company 0.18-μm 1P6M standard complementary metal oxide semiconductor process. The chip consumes only 1.05mW of power at supply voltages of 1 and 1.8V for the array data acquisition circuits and the signal-processing core, respectively. The miniature e-nose system, which used a microsensor array, a low-power signal-processing chip, and an embedded k-nearest-neighbor-based pattern recognition algorithm, was developed as a prototype that successfully recognized the complex odors of tincture, sorghum wine, sake, whisky, and vodka.

Focal Amplification of HOXD-Harboring Chromosome Region Is Implicated in Multiple-Walled Carbon Nanotubes-Induced Carcinogenicity

Multiple-walled carbon nanotubes (MWCNTs) may cause carcinogenesis. We found that long-term exposure to MWCNTs can induce irreversible oncogenic transformation of human bronchial epithelial cells and tumorigenicity in vivo. A genome-wide array-comparative genomic hybridization (aCGH) analysis revealed global chromosomal aberration in MWCNTs-treated clones, predominantly at chromosome 2q31-32, where the potential oncogenes HOXD9 and HOXD13 are located. Functional assays confirmed that this variation can modulate oncogenic signaling and plays a part in MWCNTs-induced tumorigenesis, suggesting that MWCNTs are carcinogens that act by altering genomic stability and oncogenic copy numbers.

Improved the electrochemical property of multiwall carbon nanotubes by mesophase pitch fluoride coating

The surfaces of two types of multiple wall carbon nanotubes (MWCNTs), namely, straight and distorted tubes, were modified by mesophase pitch fluoride coating (PFC). Brunauer–Emmett–Teller analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to compare the specific surface area (SSA), functional groups, and micrograph of the MWCNTs with and without modified coating. Results show that PFC can improve the SSA of the straight tube (55 %) more significantly than that of the distorted tube (7.27 %). However, surface coating is more easily implemented on the latter (F/C = 0.48) than on the former (F/C = 0.44) because of self-structure features. Electrochemical measurements indicate that PFC may enhance the specific surface capacitance and energy density of the two MWCNTs because of the effect of functional groups on the modified surface.

The electrocatalytic behaviour of Pt and Cu nanoparticles supported on carbon nanotubes for the nitrobenzene reduction in ethanol

In view of investigating the possibility of cogeneration of chemicals and electricity in a fuel cell type reactor, a suitable electrocatalyst and optimal reaction conditions have to be found. The nitrobenzene reduction was taken as the case study reaction for this investigation. In literature no suitable electrocatalyst has been found for this reaction. Pt and Cu nanoparticles, supported by multiple wall carbon nanotubes, were taken as electrocatalysts and ethanolic and acidic ethanolic environments were studied as possible reaction media. The Cu nanoparticle catalyst displayed superior electrocatalytic behaviour since less overpotential is needed for the nitrobenzene reduction in both ethanolic and acidic ethanolic environment. The acidic ethanolic conditions were superior to the ethanolic conditions as less overpotential was required for the nitrobenzene reduction reaction and a higher conversion of nitrobenzene is obtained. In acidic ethanolic environment, a four-electron reduction is taking place, which was assigned to the reduction of nitrobenzene into phenylhydroxylamine. This compound is re-oxidised into nitrosobenzene when the solution comes into contact with oxygen, and the formed nitrosobenzene selectively reacts with another phenylhydroxylamine molecule, yielding azoxybenzene. The latter is an important compound in organic synthesis.

Caffeine monitoring in biological fluids by solid surface fluorescence using membranes modified with nanotubes

BackgroundIn this work, a new methodology based upon enhancement of rhodamine B fluorescent signal is proposed for the quantification of caffeine traces. MethodsMembrane filters treated with multiple wall carbon nanotubes were employed as solid support for determination step by solid surface fluorescence. ResultsExperimental variables that influence the preconcentration step and fluorimetric sensitivity have been optimized using uni-variation assays, presenting linearity from 1.1 to 9.7×103μg/l, with a correlation coefficient of 0.99. At optimal conditions, a limit of detection of 0.3μg/l and a limit of quantification of 1.1μg/l were obtained. The method showed good sensitivity and adequate selectivity and was satisfactorily applied to the determination of trace amounts of caffeine in urine, plasma and serum belonging to subjects with different sex, ages and habit of caffeine intake. ConclusionsChemofiltration step eliminated the highly fluorescent matrix, thus enabling and allowing CF quantification, in the presence of other methylxanthines. The proposed methodology represents an innovative application of the solid surface fluorescence using membrane filters modified with MWCNTs.

Low-cost multiple-walled carbon nanotubes absorber for passively Q-switched and mode-locked Nd:YVO4 laser

A low-cost multiple-walled carbon nanotubes/polyvinyl alcohol (MWCNTs/PVA) absorber was fabricated by the characteristics of high viscosity in large molecule PVA aqueous solution and vertical evaporation technique. Sandwich structured MWCNT/PVA absorber was constructed by a piece of MWCNT absorber, a piece of round quartz and a piece of reflective mirror. We exploited it to realize Q-switched mode locking operation in a diode-pumped Nd:YVO4 laser. The maximum average output power is about 630mW.

Preparation of bilayer/three-layer PEO-carbon nanotube composite thin films and their toluene-sensing application

The bilayer poly (ethylene oxide)/multiple-walled carbon nanotubes (PEO/MWCNTs) and three-layer PEO/MWCNTs/PEO composite thin films were fabricated with the spraying process on the interdigitated transducers (IDTs) as gas sensors for toluene-sensing application. Compared with the bilayer thin film sensor, the sensor with three-layer thin films exhibited higher response values and better recovery property. The microstructures of sensing films were characterized by scanning electron microscopy (SEM) to indicate that the better sensing response of three-layer thin films might be ascribed to the sufficient adsorption of toluene molecules on the surfaces of upper and bottom PEO films. The selectivity of the three-layer film sensor was further investigated by comparing responses upon exposure to different interference vapors with the response to toluene exposure, and much higher response was observed in the case of toluene. Good repeatability of the three-layer film sensor was also observed.

Enhanced conductivity of Y-doped ZnO thin films by incorporation of multiple walled carbon nanotubes

Multiple walled carbon nanotubes have been incorporated into yttrium-doped zinc oxide (YZO) films through sol–gel method. Sol–gel process is used since it is an inexpensive means of thin film deposition when compared to the more expensive and time consuming techniques like RF sputtering. The structural, electrical and optical properties of the YZO films with and without multiple walled carbon nanotubes (MWCNT) are investigated. The carrier concentration of YZO/MWCNT composite films (2.95×1019cm−3) is found to be twice that of the YZO films (1.49×1019cm−3) achieving lower electrical resistivity of 4.36×10−2Ω-cm and an optical transparency over 85% making it suitable for application as channel injection layer in transparent organic thin film transistors. The spin coating or printable procedure of the solution processed YZO/MWCNT for incorporating a channel injection layer can replace expensive vacuum processes techniques.

Preparation and properties of the polyimide thin films reinforced by acylchloride-functionalized multiple-walled carbon nanotubes

A series of polyimide composites with various mass fractions of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization. To increase the chemical compatibility of carbon nanotubes with the polyimide matrix, MWNTs were treated with an acid mixture and sulfoxide chloride in turn. The modified MWNTs are dispersed homogeneously in the matrix while the structure of the PI and MWNTs are stable in the preparation process. The composite films hold preferable thermal stability the same as the pure PI. The composite films exhibited good thermomechanical properties. The storage modulus increased significantly by increasing MWNT content and decreasing the enhancement of temperature. The films’ glass transition temperature increased with enhancing of MWNTs frictions. The dielectric constants of the composites decrease with increasing frequency and increase sharply with the adding of MWNTs, which is favorable for practical use in anti-static materials and embedded capacitors.

Combination of laccase and catalase in construction of H2O2–O2 based biocathode for applications in glucose biofuel cells

In this study, we propose a new strategy to boost the power density of glucose biofuel cells (GBFCs) biocathodes. By combining laccase with catalase enzymes electrophoretically deposited by means of AC electric fields on multiple walled carbon nanotubes modified platinum black and, then stabilized by an outer layer of polypyrrole in the construction of GC/MWCNTs/Ptb/LAc-CAt/PPy biocathode, we can take advantage of the H2O2 present in the solution or body tissue to increase the level of the dissolved O2. The results from cyclic voltammetry, amperometry and electrochemical impedance spectroscopy demonstrate that the deposited enzymes laccase and catalase by means of AC-EPD did not inhibit each other and carry out ∼90% of the catalytic reduction process of O2–H2O2. The power density of the non-compartmentalized GBFC constructed from GC/MWCNTs/Ptb/LAc-CAt/PPy biocathode and GC/MWCNTs/GOx/PPy bioanode in phosphate buffer containing 10mM glucose and equal amounts of dissolved O2 and H2O2 (0.3mM) is almost doubled because of the presence of catalase enzyme in the constructed biocathode. The latter might be of great interest for in vivo studies of GBFCs where the concentration of dissolved O2 in the body tissues or biological fluids is very low compared to in vitro conditions (buffers under air).

Copper oxide nanoleaves decorated multi-walled carbon nanotube as platform for glucose sensing

Nanoleave-shaped copper oxide (CuONL) decorated multiple-walled carbon nanotubes (MWCNTs) composites have been prepared by a facile chemical precipitation method. The as-prepared nanocomposites show remarkable properties as a platform for glucose sensing.

Photodegradation of perfluorooctanoic acid by synthesized TiO2–MWCNT composites under 365 nm UV irradiation

Degradation of perfluorooctanoic acid (PFOA) is of great importance due to its global distribution, persistence and toxicity to bioorganisms. In present study, a composite TiO2 with multiple wall carbon nano-tubes (MWCNTs) was synthesized using sol–gel method and it was used as photocatalyst to degrade PFOA in water. The prepared composite catalyst displayed significant absorption in UV to visible light region. The loading content of TiO2 on MWCNTs could be adjusted by changing the ratio of precursor to MWCNTs. Due to the combined effect of the adsorption ability and e− transport capacity of MWCNT, the composites displayed much higher photocatalytic ability to PFOA as compared to pure TiO2 under UV irradiation. The photocatalyst prepared with 10:1 of tetrabutyl titanate/MWCNT was the most effective. With the optimal dosage at 1.6gL−1, almost 100% of PFOA was degraded in acid medium after irradiation for 8h. It was proposed that PFOA were mainly degraded by stepwise losing a moiety of CF2.

Radiation effects on styrene–butadiene–ethylene–propylene diene monomer‐multiple walled carbon nanotube nanocomposites: vulcanization and characterization

AbstractVarying compositions of styrene–butadiene rubber (SBR) and ethylene–propylene diene monomer (EPDM) 50:50 blend containing multiple walled carbon nanotube (MWNT) as nanoparticulate filler (0.5–5%) were prepared and their efficacy for radiation vulcanization was analyzed by gel‐content, Charlesby‐Pinner parameter, and crosslinking density measurements. Radiation sensitivity of the nanocomposites increased with increase in the MWNT fraction and radiation dose in the dose range studied. The elastic modulus, tensile strength increased with the radiation dose, while elongation at break exhibited downward trend. The extent of reinforcement as assessed using Kraus equation suggested high reinforcement of blend on MWNT addition. The reinforcing mechanism of nanocomposites was studied by various micromechanics models which predicted higher modulus than the experimentally observed results, indicating agglomeration in the nanocomposites. The thermal stability of the composites increased with increase in MWNT loading has been attributed to the antioxidancy induced by nanotubes and higher crosslinking extent of the nanocomposites. Copyright © 2010 John Wiley & Sons, Ltd.

Radiation Processed Styrene-Butadiene Rubber/Ethylene-Propylene Diene Rubber/Multiple-Walled Carbon Nanotubes Nanocomposites: Effect of MWNT Addition on Solvent Permeability Behavior

Different compositions of SBR/EPDM 50:50 blends containing multiple-walled carbon nanotubes (MWNT) as nanoparticulate fillers (0.5%–10%) were evaluated for radiation sensitivity and solvent permeability. The efficiency of radiation ***cross-linking was analyzed by gel-content and Charlesby–Pinner parameter measurements. ***Gamma-radiation-induced cross-linking extent was found to increase with radiation dose and MWNT concentration, which was reflected in different extents of swelling. Rigorous analysis of swelling and diffusion data, on the basis of the transport exponent (n) values and diffusion/relaxation rate indicated anomalous diffusion behavior for most of the nanocomposites. The swelling extent in different solvents was found to be a function of polymer-solvent interaction as well as stearic hindrance due to the structure/size of the solvent molecules. Polymer-filler interaction investigated by a Kraus plot indicated high reinforcement of the SBR/EPDM matrix on MWNT addition. There was no significant change in surface energy or hydrophilicity of the SBR/EPDM matrix on introduction of MWNT into it.