Characterization Of Multi-walled Carbon Nanotubes Research Articles

Multiwalled carbon nanotube thin films prepared by aerosol deposition process for use as highly efficient Pt-free counter electrodes of dye-sensitized solar cells

In this study, transparent and catalytic multiwalled carbon nanotube (MWCNT) thin films with controlled thickness were fabricated using a simple and conventional multiple nozzle-based aerosol deposition process (ADP). MWCNTs were homogeneously dispersed in deionized water via surfactant treatment, and the MWCNT-dispersed aqueous solution was then aerosolized and deposited on fluorine-doped tin oxide glass substrates to form MWCNT thin films. The characteristics of MWCNTs, degree of MWCNT dispersion stability in the aqueous solution, and morphology and light transmittance of the prepared MWCNT thin films were systematically examined. Finally, the prepared MWCNT thin films were used as the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). For comparison purposes, the photovoltaic performance of DSSCs composed of MWCNT thin-film CEs was compared to that of reference DSSCs composed of conventional Pt thin-film CEs. The results showed that the power conversion efficiency of DSSCs composed of critical amount of MWCNTs coated on CEs was almost equal or slightly higher than that of conventional Pt-based DSSCs. Thus, it can be concluded that the ADP-assisted precisely controlled accumulation of transparent and catalytic MWCNT thin films on the CEs of DSSCs is a very promising approach for replacing the expensive Pt metal that is currently used in DSSC industries.

Multi-walled carbon nanotube with multivacancy defects: porous structure and Pt decoration.

This study reports on the morphological characteristics of multi-walled carbon nanotube with multi-vacancy defects (MWCNT-MD) of carbon atoms and shows the potential of MWCNT-MD as a support for metal deposition by decorating Pt nanoparticles (NPs). Multi-carbon vacancies on MWCNT were introduced by oxidizing cobalt oxide-decorated MWCNT at 250 degrees C for 6 h in air by means of carbon gasification reaction, resulting in holes and thinned walls on MWCNT. It was revealed that creating multivacancy defects led to the increase of specific surface area from 107 to 152 m2/g and pore size in the range of 5-8 nm increased on MWCNT compared with that of pristine MWCNT. 30 wt.% Pt was decorated on MWCNT-MD by impregnation method to investigate the effect of carbon vacancies on the degree of Pt dispersion, and the presence of Pt metal was confirmed by X-ray diffraction. Transmission electron microscopy images clearly displayed that Pt NPs with average particle size of 2.8 nm were evenly dispersed on the defective site of holes and thinned walls. This study is clear evidence showing that defective sites of MWCNT are active and good anchor site for metal decoration.

Development and Characterization of Nanostructured Hybrid Materials for Oxidation of Ethanol in Fuel Cells and Biofuel Cells

Our research interests concern development of the direct alcohol fuel cells as alternative technology to hydrogen based electrochemical energy systems. For example, ethanol can be ideally oxidized to carbon dioxide thus delivering 12 electrons.But realistically the reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials. Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals (one or two), such as Ru, Sn, Mo, W or Rh, are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of polyoxometallates, particularly heteropolymolybdates. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts.We are going to describe a concept of utilization of functionalized titanium dioxide, tungsten oxide or zirconium oxide matrices (by admixing them with polyoxometallate-modified gold nanoparticles) for supporting and activating noble metal nanoparticles (Pt, Pt-Ru or Pt-Rh) during electrooxidation of ethanol. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account improvement of overall conductivity (due to the presence of nanostructured gold) at the electrocatalytic interface (formed by metal oxide support), as well as and possibility of specific Pt-metal oxide or Pt-Au electronic interactions and existence of active hydroxyl groups on transition metal oxo species.in the vicinity of catalytic Pt sites. Further, the capping layers of Keggin-type phosphomolybdates, which are known to undergo fast stepwise multi-electron redox processes as well as to activate Pt-based electrocatalysts during ethanol oxidation, may also contribute to the overall enhancement effect.Having in mind a wide spectrum of powerful catalytic activities of zeolites, it is reasonable to expect that application of certain protonically/electronically conducting zeolite-type matrices shall lead to enhancement of the overall reactivity of anode electrocatalysts. Among potential candidate materials for rigid and active matrices in electrocatalysis, there are cesium salts of Keggin-type heteropolyacids of molybdenum and tungsten. These salts are insoluble in water and organic solvents, and they posses micro and mesopores of high surface area (often exceeding 100 m2 g-1). Contrary to typical alkali-exchanged zeolites, the analogous heteropolyacid salts retain their strong acidity. In the present work, we describe preparation and physicochemical (including electrochemical) properties of cesium salts of selected Keggin-type heteropolyacids of molybdenum and tungsten, as well as address their influence on catalytic activity of Vuclcan-supported Pt, PtRu and PtSn nanoparticles (Pt40%/Vulcan XC-72) during electrooxidation of methanol and ethanol.Oxidation of ethanol can also be pursued under neutral conditions in so called biofuel cells. In our work, we have exploited unique characteristics of multi-walled carbon nanotubes (CNTs) to construct the efficient anodic bioelectrocatalytic system of potential utility for biofuel cells and biosensors. Some attention has been also paid to the choice of the modifying agent poly(diallyldimethylammonium chloride) (PDDA) used to stabilize CNTs. While PDDA seems to form stable ultra-thin layers on CNTs, it is not expected to serve as a good charge (electron) mediator but it is reasonable to expect that PDDA would interact or attract electrostatically with negatively charged sites of the enzyme (or combination of dehydrogenase enzymes). Our highly porous CNT-based films have presumably acted as three-dimensional network of nanowires around the enzyme molecules and have promoted the efficient electron transfer. On the whole, combination of PDDA-modifed MWCNTs and two distinct dehydrogenase enzymes within the film has produced a catalytic system capable of oxidation of ethanol at fairly low potentials (ca. 0.15 V versus Ag/AgCl). Among important issues are good stability and reproducibility of responses both under voltammetric and amperometric conditions.

Effect of multiwalled carbon nanotube and temperature on dielectric and impedance spectroscopy of chlorobutyl elastomer nanocomposites

Dielectric relaxation characteristics of multiwalled carbon nanotube (MWCNT)-reinforced chlorobutyl (CIIR) nanocomposites have been studied as a function of frequency (100–106 Hz) at different filler loadings (0, 2, 4, 6 and 8 phr) over a wide range of temperatures (30–120°C). The effect of MWCNT loadings and temperature on the dielectric permittivity ( ∊′), dielectric loss tangent (tan δ), complex impedance ( Z*) and electrical conductivity ( σ) was studied. The variation of ∊′ with MWCNT loading has been explained based on the interfacial polarization of the fillers within a heterogeneous system. A significant effect of MWCNT loading on the real ( Z′) and imaginary ( Z′′) part of Z* was observed due to the relaxation dynamics of polymer chains at the CIIR-MWCNT interface. The non-linearity of CIIR nanocomposites has been studied from Nyquist plots. The dielectric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The permittivity and conductivity of the nanocomposites have been analyzed based on scaling theory at increasing temperatures. The frequency dependency and percolation phenomenon in the composites have been discussed in terms of σ. The percolation threshold ( Φcrit) occurred at around 6 phr of MWCNT loading irrespective of temperature. The dispersion of MWCNT in the CIIR matrix and agglomeration of the filler at higher loading have been studied using scanning electron microscopic photomicrographs.

Preparation and characterization of multi-walled carbon nanotubes grown on transition metal catalysts

Abstract Transition metal catalysts (mainly: iron, cobalt and nickel) on various supports are successfully used in a largescale production of carbon nanotubes (CNTs), but after the synthesis it is necessary to perform very aggressive purification treatments that cause damages of CNTs and are not always effective. In this work a preparation of unsupported catalysts and their application to the multi-walled carbon nanotubes synthesis is presented. Iron, cobalt and bimetallic iron-cobalt catalysts were obtained by co-precipitation of iron and cobalt ions followed by solid state reactions. Although metal particles were not supported on the hard-to-reduce oxides, these catalysts showed nanometric dimensions. The catalysts were used for the growth of multi-walled carbon nanotubes by the chemical vapor deposition method. The syntheses were conducted under ethylene - argon atmosphere at 700°C. The obtained catalysts and carbon materials after the synthesis were characterized using transmission electron microscopy (TEM), X-ray diffraction method (XRD), Raman spectroscopy and thermogravimetric analysis (TG). The effect of the kind of catalyst on the properties of the obtained carbon material has been described.

Evaluation of Adsorption Characteristics of Multiwalled Carbon Nanotubes Modified by a Poly(propylene imine) Dendrimer in Single and Multiple Dye Solutions: Isotherms, Kinetics, and Thermodynamics

This research investigates the isotherm, kinetics, and thermodynamic parameters of the adsorption of two direct dyes in single and multiple dye solutions onto the modified multiwalled carbon nanotubes using poly(propylene imine) dendrimer (CNT-Den). The surface morphology and functional groups of the prepared CNT-Den were studied using field emission scanning electron microscopy (FESEM) images and Fourier transform infrared (FTIR) spectra, respectively. The Langmuir, Freundlich, and Tempkin isotherms were studied, and the results indicated that the data followed the Langmuir isotherm. The kinetic studies revealed that the pseudo-second order model was best fitted to our results rather than pseudo-first and intraparticle diffusion model. The calculated thermodynamic parameters showed the endothermic and spontaneous nature of the adsorption process. The overall results illustrated that CNT-Den can be effectively used as an adsorbent for the removal of dyes from colored wastewaters especially textile effluents.

Carbon nanotubes‐filled thermoplastic polyurethane–urea and carboxylated acrylonitrile butadiene rubber blend nanocomposites

ABSTRACTThis article reports the preparation and characterization of multiwalled carbon nanotubes (MWCNTs)‐filled thermoplastic polyurethane–urea (TPUU) and carboxylated acrylonitrile butadiene rubber (XNBR) blend nanocomposites. The dispersion of the MWCNTs was carried out using a laboratory two roll mill. Three different loadings, that is, 1, 3, and 5 wt % of the MWCNTs were used. The electron microscopy image analysis proves that the MWCNTs are evenly dispersed along the shear flow direction. Through incorporation of the nanotubes in the blend, the tensile modulus was increased from 9.90 ± 0.5 to 45.30 ± 0.3 MPa, and the tensile strength at break was increased from 25.4 ± 2.5 to 33.0 ± 1.5 MPa. The wide angle X‐ray scattering result showed that the TPUU:XNBR blends were arranged in layered structures. These structures are formed through chemical reactions of NH group from urethane and urea with the carboxylic group on XNBR. Furthermore, even at a very low loading, the high degree of nanotubes dispersion results in a significant increase in the electrical percolation threshold. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40341.

Dynamic stability of carbon nanotubes reinforced composites

Based on an effective model of multi-walled carbon nanotubes and Donnell-shell theory, an analytical method is presented to study dynamic stability characteristics of multi-walled carbon nanotubes reinforced composites considering the surface effect of carbon nanotubes. From obtained results it is seen that carbon nanotubes composites, under combined static and periodic axial loads, may occur in a parametric resonance, the parametric resonance frequency of dynamic instability regions of CNTs reinforced composites under axially oscillation loading enhances as the stiffness of matrix surrounding CNTs increases, and the surface effective modulus and residue stress of carbon nanotubes make the parametric resonance frequency and the region breadth of dynamic instability of carbon nanotubes reinforced composites increase.

Preparation and characterization of multi-walled carbon nanotubes (MWCNTs), functionalized with phosphonic acid (MWCNTs–C–PO3H2) and its application as a novel, efficient, heterogeneous, highly selective and reusable catalyst for acetylation of alcohols, phenols, aromatic amines, and thiols

A novel, efficient, heterogeneous, and reusable multi-walled carbon nanotubes (MWCNTs), functionalized with phosphonic acid (MWCNTs–C–PO3H2) has been synthesized. The synthesized CNTs were characterized using some electron microscopic techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), Energy dispersive X-ray spectroscopy (EDAX), and also some thermal and spectroscopic methods such as thermogravimetry (TG). The nitrogen adsorption behavior of the MWCNTs–C–PO3H2 catalyst was evaluated using the TG instrumentation system at 25 °C. The catalyst was applied successfully for highly efficient and selective acetylation of alcohols, phenols, thiols and aromatic amines with acetic anhydride at room temperature under solvent-free conditions. The reusability of the catalyst was checked and the recovered catalyst was reused for five runs without significant loss in activity.

Impedance characteristics and conductivity of CNT/ABS nanocomposites

Electrical impedance characteristics of multi-walled carbon nanotube (MWCNT)/acrylonitril–butadiene–styrene nanocomposite was studied as a function of MWCNT concentration in the frequency range of 100–106 Hz. The nanocomposites were prepared by solution processing and characterized to have good dispersion of the nanofiller within the polymer matrix as observed by the transmission electron microscopy. In the frequency range of 1–104 Hz, the alternating current (ac) conductivity versus frequency plot of the 0.25 wt% MWCNT nanocomposite exhibited a direct current (dc) plateau indicating that there is a segregated network within this nanocomposite. In the low-frequency region, the bode diagram of the real part of impedance and ac conductivity of the nanocomposites filled with 0.25 wt% up to 4 wt% MWCNT showed a frequency independent plateau followed by an increase obeying the universal dynamic response indicating that conduction in this MWCNT concentration range might be due to tunnelling in addition to the direct contact between filler nanoparticles. For nanocomposites filled with at least 7 wt% MWCNT, the ac conductivity was frequency independent over the entire frequency range (up to 106 Hz) revealing that conduction is due to direct contact between nanoparticles.

Ethanol-sensing properties of potassium bromide/multi-walled carbon nanotube composites

The work reported in this paper is related to the fabrication and electrical characterization of multi-walled carbon nanotubes (MWNT)-based solid composites pellets with potential application as gas sensor at room temperature, using potassium bromide as supporting material. Results show an electrical conductivity of the composites as a function of the MWNT loading following a power law associated with a percolation phenomenon. A variation of the electrical resistance of the composites as a function of ethanol concentration in a nitrogen atmosphere has also been observed, allowing detection of ethanol from about hundred of ppm. It is also shown the existence of an optimal MWNT loading for which the composite reaches its best ethanol-sensing performances.

Functionalization and Characterization of Multi-Walled Carbon Nanotubes Using Chemical Oxidation Method

Functionalization and Characterization of Multi-Walled Carbon Nanotubes Using Chemical Oxidation Method

Synthesis and characterization of pressureless sintered carbon nanotube reinforced alumina nanocomposites

This paper presents sintering and characterization of multiwalled carbon nanotube reinforced alumina nanocomposites and their comparison with the sintering behavior of pure alumina. Two types of composites were prepared by different techniques and both contained 1, 2 and 3wt% of as-received and functionalized carbon nanotubes which were synthesized by pressureless sintering. The mixing and dispersion of carbon nanotubes in alumina were done by a novel technique of gas purging sonication. Varying percentages of carbon nanotubes in the composites were compacted using a uniaxial press followed by sintering at 1600°C in flowing argon. Nanocomposites with 1wt% carbon nanotubes gave 98.5% relative density with no degradation of carbon nanotubes. Moreover, it also resulted in an increase in fracture toughness from 8.1% and 9.4% and Young's modulus by 5% and 7% when compared to as-received and functionalized carbon nanotube nanocomposites respectively with respect to pure alumina. This investigation has shown that the densification can be achieved without degradation of carbon nanotubes at elevated temperatures in the carbon nanotube–alumina nanocomposites sintered by the conventional route.

Electrochemical Characterization of Multi-walled Carbon Nanotubes/ Polyvinyl Alcohol Coated Electrodes for Biological Applications

Electrochemical Characterization of Multi-walled Carbon Nanotubes/ Polyvinyl Alcohol Coated Electrodes for Biological Applications

Investigation of Low‐Pressure Bimetallic Cobalt‐Iron Catalyst‐Grown Multiwalled Carbon Nanotubes and Their Electrical Properties

A bimetallic cobalt‐iron catalyst was utilized to demonstrate the growth of multiwalled carbon nanotubes (CNTs) at low gas pressure through thermal chemical vapor deposition. The characteristics of multiwalled CNTs were investigated based on the effects of catalyst thickness and gas pressure variation. The results revealed that the average diameter of nanotubes increased with increasing catalyst thickness, which can be correlated to the increase in particle size. The growth rate of the nanotubes also increased significantly by ~2.5 times with further increment of gas pressure from 0.5 Torr to 1.0 Torr. Rapid growth rate of nanotubes was observed at a catalyst thickness of 6 nm, but it decreased with the increase in catalyst thickness. The higher composition of 50% cobalt in the cobalt‐iron catalyst showed improvement in the growth rate of nanotubes and the quality of nanotube structures compared with that of 20% cobalt. For the electrical properties, the measured sheet resistance decreased with the increase in the height of nanotubes because of higher growth rate. This behavior is likely due to the larger contact area of nanotubes, which improved electron hopping from one localized tube to another.

6PM1-A-4 MEMSデバイスによる多層カーボンナノチューブの層間すべり変形機構の解明(6PM1-A マイクロナノプロセス技術II(センサシンポジウムとの合同セッション))

We have developed the in-situ scanning electron microscopy (SEM) nanomaterial manipulation system including newly designed Electrostatically Actuated NAnotensile Testing devices (EANATs), in order to investigate mechanical characteristics of multi-walled carbon nanotubes (MWCNTs) synthesized by an atmosphere pressure-chemical vapor deposition (APCVD). The new EANATs can measure uniaxial tensile displacement of nanomaterials with the capacitive displacement sensor incorporated to the cantilever motion amplification system. The nanomaterial manipulation system functions to pick up an individual MWCNT from a substrate and to fix it on EANATs. Stress-strain relations of MWCNTs were successfully obtained from the nanotensile tests, and Young's moduli were estimated to be 243 to 623 GPa. The shear strength at stick-slip event during interlayer sliding of MWCNTs under tensile loading was directly derived from the shear interaction force in tensile force-displacement curves and SEM observations.

Synthesis and characterization of multi-walled carbon nanotubes modified with octadecylamine and polyethylene glycol

Chemical modification of MWCNTs via oxidation followed by side wall functionalization using polyethylene glycol (PEG) and octadecylamine (ODA); separately, was studied. Different characterization techniques such as FTIR spectrometry, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and solubility in different solvents were performed for the oxidized MWCNTs, MWCNTs–PEG and MWCNTs–ODA. The characterization techniques proved the presence of the functional groups on the MWCNT surface. Thermal gravimetric analysis revealed that nearly 16% (by weight) of the MWCNTs were functionalized with PEG and 39% (by weight) was functionalized with ODA.

Mathematical models for the oxidative functionalization of multiwalled carbon nanotubes

A systematic, quantitative study has been conducted to elucidate the effect of oxidation protocol and time on the size, integrity and surface characteristics of multiwalled carbon nanotubes (MWCNTs). Pristine MWCNTs with initial lengths ranging between (i) 2–5μm and (ii) 1–2μm were selected for the study. Two oxidation protocols, sonication at 40°C and reflux at 80°C in a mixture of concentrated H2SO4 and HNO3 (3:1 v/v) were examined with each variety of MWCNTs. Time dependence of oxidative shortening could be correlated by two empirical, exponential relationships: (i) √L0−√Lt=k log t (Eq. (1)) and (ii) Lt/L0=c×exp (kt) (Eq. (2)), where L0 and Lt represented the initial and final length of the nanotubes oxidized separately for t hours under ultrasonication and reflux conditions respectively. Time and length dependence of surface carboxyl density was modeled using the following equations: (iii) COOH density (mmol/g, ultrasonication)=3.088+[0.353×t(h)]–[1.185×Lt (μm)] (Eq. (3)) (iv) COOH density (mmol/g, reflux)=2.412+[0.604×t(h)]–[0.662×Lt (μm)] (Eq. (4)), which suggest that oxidative shortening and carboxyl enrichment of MWCNTs is not only time-dependent but equally influenced by the oxidation protocol.

Effect of fluorination of multiwalled carbon nanotubes (MWCNTs) on the surface properties of fouling-release silicone/MWCNTs coatings

The characterisation of poly(dimethylsiloxane) (PDMS)-based fouling-release coatings filled with pristine and fluorinated multiwalled carbon nanotubes (MWCNTs) are reported. The fluorination of MWCNTs was performed via a three-step procedure, which consisted of oxidation in an acid mixture, reduction by diisobutylaluminium hydride and silanisation by (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane. Characterisation of MWCNTs by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and thermogravimetric analyses showed the formation of functional groups in each step of the modification process. The coatings were prepared by filling the PDMS with pristine and fluorinated MWCNTs in three weight percentages (0.05, 0.1 and 0.2wt.%). The surface chemistry and structure of the coatings were studied using critical surface energy determination and atomic force microscopy. The results showed that both types of nanotubes led to changes in some surface properties of the coatings, even when present in low amounts. However, the measurements of mechanical properties via tensile tests showed that the modulus and tensile strength of the coatings did not change in the presence of either pristine or fluorinated MWCNTs. The effect of the presence of the fluorinated MWCNTs on the surface of the coatings improved the fouling-release properties by reducing the pseudobarnacle adhesion strength by 67% compared to that of the unfilled sample. The results also revealed a 47% decrease in the adhesion strength of pseudobarnacles on the coatings filled with the pristine MWCNTs.

Fabrication and characterization of multi-walled carbon nanotube incorporated ferromagnetic nanowires with self-formed anti-oxidation layers

Ferromagnetic FeCoNi alloy nanowires (NWs) with self-formed anti-oxidation (Si/Al) layers were prepared via electrospinning a sol–gel precursor solution containing Si and Al element and multi-walled carbon nanotubes (MWNTs), and their structures and magnetic properties were investigated. The uniform and narrow-sized MWNTs-magnetic alloy NWs with a well-crystallized bcc (110) texture of FeCo along the easy axis were formed by introduction of MWNTs acted as a sintering inhibitor during annealing. The coercive field at room temperature increased two times higher than that of MWNT-free magnetic NWs due to the well-developed texture and the small grain size, which is slightly larger than the single domain size within the 10–15nm range for most magnetic metals. As a result, the highly enhanced ferromagnetic NW mats with a MWNT-incorporated nanowire structure have shown great promise for providing a wide range of potential applications, including magnetic recording and ultrahigh-density magnetic storage devices operating room temperature.