• Carbon letters
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• v.12 no.3
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• pp.162-166
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• 2011

Conducting polymer-coated multiwalled carbon nanotubes (MWCNTs) were prepared by template polymerization in order to enhance their gas sensitivity. This investigation of the conducting polymer phases that formed on the surface of the MWCNTs is based on field-emission scanning electron microscopy images. The thermal stability of the conducting polymer-coated MWCNTs was significantly improved by the high thermal stability of MWCNTs. The synergistic effects of the conducting polymer-coated MWCNTs improve the gas-sensing properties. MWCNTs coated with polyaniline uniformly show outstanding improvement in gas sensitivity to $NH_3$ due to the synergistic combination of efficient adsorption of $NH_3$ gas and variation in the conduction of electrons.

• Carbon letters
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• v.13 no.2
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• pp.99-108
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• 2012

The sol-gel technique has been studied to fabricate a homogeneous Fe-Mo/MgO catalyst. Ambient effects (air, Ar, and $H_2$) on thermal decomposition of the citrate precursor have been systematically investigated to fabricate an Fe-Mo/MgO catalyst. Severe agglomeration of metal catalyst was observed under thermal decomposition of citrate precursor in air atmosphere. Ar/$H_2$ atmosphere effectively restricted agglomeration of bimetallic catalyst and formation of highly-dispersed Fe-Mo/MgO catalyst with high specific surface-area due to the formation of Fe-Mo nanoclusters within MgO support. High-quality thin-multiwalled carbon nanotubes (t-MWCNTs) with uniform diameters were achieved on a large scale by catalytic decomposition of methane over Fe-Mo/MgO catalyst prepared under Ar-atmosphere. The produced t-MWCNTs had outer diameters in the range of 4-8 nm (average diameter ~6.6 nm) and wall numbers in the range of 4-7 graphenes. The as-synthesized t-MWCNTs showed product yields over 450% relative to the utilized Fe-Mo/MgO catalyst, and indicated a purity of about 85%.

• Advanced Composite Materials
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• v.17 no.2
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• pp.157-166
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• 2008

In this study, multiwalled carbon nanotubes (MWCNTs) were compounded with the poly($\varepsilon$-caprolactone) (PCL) matrix at the solution state using chloroform. For homogeneous dispersion of MWCNTs in polymer matrix, oxygen-containing groups were introduced on the surface of MWCNTs. The mechanical properties of the PCL/MWCNTs composites were effectively increased due to the incorporation of MWCNTs. The composites were characterized using scanning electron microscopy in order to obtain information on the dispersion of MWCNT in the polymeric matrix. In case of 1.2 wt% of MWCNTs in the matrix, strength and modulus of the composite increased by 12.1% and 164.3%, respectively. In addition, the dispersion of MWCNTs in the PCL matrix resulted in substantial decrease of the electrical resistivity of the composites as the MWCNTs loading was increased from 0 to 2.0 wt%. Furthermore, thermal stability of the PCL and PCL/MWCNTs-COOH composites were investigated using the data acquired from the thermogravimetric analysis. The detailed kinetics of the thermal degradation of the composites was investigated by analyzing their thermal behavior at different heating rates in a nitrogen atmosphere. Activation energy of thermal degradation was determined by using the equations proposed by Kissinger and Flynn-Wall-Ozawa. The apparent activation energy of PCL/MWCNTs-COOH composite was considerably higher than that of neat PCL.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.238-243
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• 2018

A nanofiber was fabricated with carbon nanotubes for transparent electrodes. It was prepared with a composite solution of bio-molecules polycaprolactone (PCL) and multiwalled carbon nanotubes (MWCNTs) by electrospinning on a glass substrate, following which its electrical characteristics were investigated. The content of MWCNTs was varied during electrospinning, while that of PCL was fixed. Further, a nanometer-thick thin film of silver was deposited on the nanofiber layer using a thermal evaporator to improve the electrical characteristics; the sheet resistance significantly reduced after this deposition. The results showed that this carbon nanotube nanofiber has potential applications in biotechnology and as a flexible transparent display material.

• Carbon letters
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• v.12 no.4
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• pp.218-222
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• 2011

Well-aligned multi-walled carbon nanotubes (MWCNTs) were successfully synthesized by catalytic chemical vapor deposition using a hydrogen sulfide ($H_2S$) additive onto Al/Fe thin film deposited on Si wafers. Transmission electron microscopy images indicated that the as-grown carbon products were thin MWCNTs with small outer diameters of less than 10 nm. $H_2S$ plays a key role in synthesizing thin MWCNTs with a large inside hollow core. The well-aligned thin MWCNTs showed a low turn-on voltage of about 1.1 V/${\mu}m$ at a current density of 0.1 ${\mu}A/cm^2$ and a high emission current of about 1.0 mA/$cm^2$ at a bias field of 2.3 V/${\mu}m$. We suggest a possible growth mechanism for the well-aligned thin MWCNTs with a large inside hollow core.

• Advances in nano research
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• v.11 no.6
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• pp.667-678
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• 2021

Multiwalled carbon nanotubes (MWCNTs) were first oxidized (O-CNTs) to introduce carboxylic group and then further functionalized (F-CNTs) with m-phenylenediamine, which was confirmed by FTIR and SEM. It was used as an effective adsorbent for the adsorptive removal of diclofenac drug from water. Under optimum conditions of pH 6, stirring speed 600 rpm, the maximum adsorption capacity obtained was 532 mg g^-1 which is superior to the values reported in literature. The adsorption was quite rapid as 25 mg L^-1 drug solution was adsorbed in only 3 minutes of contact time with 10 mg of adsorbent dose. The adsorption kinetics and isotherms were studied using various models to evaluate the adsorption process. The results showed that the data best fit in kinetics pseudo-second order and Langmuir isotherm model. Furthermore, the oxidized and functionalized MWCNTs were applied on gram-negative Escherichia coli and gram-positive Staphylococcus aureus using agar disc diffusion assay to validate their anti-microbial activity. Results were unique as both oxidized and functionalized MWCNTs were equally active against both E. coli and S. aureus. The newly synthesized F-CNTs have great potential in water treatment, with their dual action of removing drug and pathogens from water, makes it potential applicant to save environment.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1443-1446
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• 2005

We have synthesized thin multi-walled carbon nanotubes (t-MWCNTs) using a catalytic chemical vapor deposition (CCVD) method with FeMoMgO catalyst. The number of tube walls were 2 ${\sim}$ 6 with the corresponding diameters of 3 ${\sim}$ 6 nm. We obtained high production yield of over 3000 wt% compared to the weight of the supplied catalyst. These t-MWCNTs revealed the intermediate structural characteristics between single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs). We have also characterized the field emission properties such as turn-on field and emission current, and current degradation from these t-MWCNTs together with SWCNTs and MWCNTs.

• Carbon letters
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• v.11 no.3
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• pp.184-191
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• 2010

Carbon nanotubes are unique tubular structures of nanometer diameter and large length/diameter ratio. The nanotubes may consist of one up to tens and hundreds of concentric shells of carbons with adjacent shells separation of ~0.34 nm. Multiwalled carbon nanotubes were synthesized by arc-discharge technique. MWCNTs were formed at the cathode deposit along with other carbonaceous materials like amorphous carbon, graphite etc. However, to get the best advantage of carbon nanotubes in various advanced applications, these undesired carbonaceous materials to be removed which is a challenging task. In the present study, various techniques were tried out for purifying MWCNTs such as physical filtration, chemical treatment and thermal annealing. SEM, FTIR, TGA and BET techniques were used to characterize the CNTs at various stages. Results shows that suitable chemical treatment followed by thermal annealing under controlled flow of oxygen gives the better route for purification of carbon nanotubes.

• Carbon letters
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• v.8 no.4
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• pp.292-298
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• 2007

In order to investigate functional groups on the surface of Multi-walled Carbon Nanotubes (MWCNTs) induced by oxyfluorination, XPS (X-ray photoelectron spectroscopy) analysis was carried out. All core level spectra of MWCNTs were deconvoluted to several Pseudo-Voigt functions (sum of Gaussian-Lorentzian functions). Both O1s and F1s binding energy of oxyfluorinated MWCNTs shifted high value as increment of fluorine mixing ratio. The carbon-fluorine covalent bonding concentration increased as increment of fluorine mixing ratio. The shape and intensity of OF10-MWCNTs are similar with those of as-received MWCNTs. However, the intensity and binding energies of main peak position of OF20-MWCNTs and OF30-MWCNTs were dramatically increased by oxyfluorination.

• Steel and Composite Structures
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• v.25 no.3
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• pp.347-360
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• 2017

The goal of this study is to fill this apparent gap in the area about vibration analysis of multiwalled carbon nanotubes (MWCNTs) curved panels by providing 3-D vibration analysis results for functionally graded multiwalled carbon nanotubes (FG-MWCNTs) sandwich structure with power-law distribution of nanotube. The effective material properties of the FG-MWCNT structures are estimated using a modified Halpin-Tsai equation. Modified Halpin-Tsai equation was used to evaluate the Young's modulus of MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the MWCNTs wt% range considered. Also, the mass density and Poisson's ratio of the MWCNT/phenolic composite are considered based on the rule of mixtures. Parametric studies are carried out to highlight the influence of MWCNT volume fraction in the thickness, different types of CNT distribution, boundary conditions and geometrical parameters on vibrational behavior of FG-MWCNT thick curved panels. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary conditions including Free, Simply supported and Clamped at the curved edges. For an overall comprehension on 3-D vibration analysis of sandwich panel, some mode shape contour plots are reported in this research work.