Walls Of Multi-walled Carbon Nanotubes Research Articles

Effect of scale and surface chemistry on the mechanical properties of carbon nanotubes-based composites

In this article, Multi-Walled Carbon Nanotubes (MWCNTs) of varying diameters, both untreated and polycarboxylated, were dispersed at constant weight percentage in an epoxy matrix, and resulting fracture toughnesses (KIc) were measured in each case. We show that changing the MWCNT diameter has two effects on the composite fracture toughness: (i) a small MWCNT diameter enables larger interfacial surface for adhesion maximization, which increases toughness; (ii) at the same time, it limits the available pull-out energy and reduces the MWCNT ability to homogeneously disperse in the matrix due to this same large active surface: this decreases toughness. Most commercially available MWCNTs have a length range of several μm, thus an optimal diameter exists which depends on MWCNT wall thickness and surface treatment. Such optimal diameter maximizes pull-out energy and thus composite fracture toughness. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Multi-walled carbon nanotube/silver nanoparticles used for thermal transportation

A green method was applied to prepare composites of multi-walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (Ag-NPs). MWNTs were functionalized using ball milling technology in the presence of ammonium bicarbonate, and the traditional method of silver mirror was used to decorate MWNTs to obtain Ag/MWNT composite. The obtained Ag/MWNT composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transmission infrared spectroscopy, and Brunauer–Emmet–Teller (BET) surface area analysis. SEM characterization showed that Ag-NPs distributed uniformly on the walls of MWNTs. The content and size of Ag-NPs could be controlled by adjusting the redox time. XRD patterns demonstrated that the Ag-NPs are composed of pure Ag and crystallized well. BET analysis indicated that the specific surface areas of Ag/MWNT decrease with increasing the content of Ag-NPs, and this result is similar to that of the literature. The measurement results of the thermal property showed that the thermal conductivity of the nanofluid containing Ag/MWNT composites was higher than that of nanofluid containing pristine or functionalized MWNTs.

Multiwalled Carbon Nanotubes Decorated with Cobalt Oxide Nanoparticles

Multiwalled carbon nanotubes (MWCNTs) synthesized by spray pyrolysis were decorated with cobalt oxide nanoparticles using a simple synthesis route. This wet chemistry method yielded nanoparticles randomly anchored to the surface of the nanotubes by decomposition of cobalt nitrate hexahydrate diluted in acetone. Electron microscopy analysis indicated that dispersed particles were formed on the MWCNTs walls. The average size increased with the increasing concentration of cobalt nitrate in acetone in the precursor mixture. TEM images indicated that nanoparticles were strongly attached to the tube walls. The Raman spectroscopy results suggested that the MWCNT structure was slightly damaged after the nanoparticle growth.

Facile and green method for polystyrene grafted multi-walled carbon nanotubes and their electroresponse

Polystyrene (PS) microspheres with a mean diameter of 69nm were prepared by emulsion polymerization. The PS microspheres were successfully decorated to multi-walled carbon nanotubes (MWNTs) induced by benzoyl peroxide in water during a high temperature refluxing process under nitrogen atmosphere. The as-prepared multi-walled carbon nanotube/polystyrene (MWNT/PS) nanocomposites were characterized by FTIR spectroscopy, Raman spectroscopy, SEM, TEM, differential scanning calorimetry (DSC), and electrical resistance measurements. The results reveal that PS microspheres are mainly covalently grafted onto the walls of MWNTs. The PS-decorated MWNTs show high solubility in toluene and xylene without sedimentation after 24h. With MWNTs in the hybrids, PS achieved a considerable increase in electrical conductivity and glass-transition temperature (Tg). In particular, the obtained MWNT/PS composites were examined for electrorheological (ER) fluids, which showed thin and dense chains of particles after the application of an electric field. The facile and environmentally friendly technique presented in the present study could be an effective and promising method for the functionalization of MWNTs by other polymers.

Multiwalled carbon nanotubes functionalized with maleated poly(propylene) by a dry mechano-chemical process

Ball milling was used to graft maleated polypropylene (MAPP) on the surface of multiwalled carbon nanotubes (MWCNTs), with a view to preparing MWCNT/polypropylene composites with improved matrix/nanotube compatibility. The occurrence of the grafting reaction was evaluated by FTIR spectroscopy and the yield was quantified by thermogravimetric analysis, as a function of the milling time. Dispersion experiments confirmed the nanotube surface modification of the nanotubes since functionalized MWCNTs remained stably dispersed in an ethanol/xylene solution for more than 48 h after sonication. No evidences of significant structural damage after the mechano-chemical treatment were shown by Raman spectroscopy. Moreover, a layer attributable to the presence of grafted MAPP chains on MWCNT walls was clearly detected by transmission electron microscopy. The average thickness of this amorphous layer was evaluated and compared with quantitative TGA data.

Ultrasonic Approach for Formation of Erbium Oxide Nanoparticles with Variable Geometries

Ultrasound (20 kHz, 29 W·cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (μs) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.

Magnetic field-guided orientation of carbon nanotubes through their conjugation with magnetic nanoparticles

Low intensity magnetic fields (22mT) rendered by a pair of bar magnets have been used to achieve in situ precise orientation of multiwalled carbon nanotubes (MWCNTs) and their directional deposition on solid substrates. The nanotubes were imparted magnetic characteristics through Fe3O4 (magnetite) nanoparticles covalently attached to their surface. The side walls of nanotubes were first acid oxidized with H2SO4/HNO3 (3:1 v/v) mixture and amine-functionalized magnetic nanoparticles were then interfaced to ends and side walls of the nanotubes through covalent linkages in the presence of a zero length cross linker, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide. Fourier transformed infrared spectroscopic investigations affirmed the functionalization of nanostructures and formation of a magnetic nanohybrid. Transmission electron microscopy results revealed the attachment of nanoparticles along the side walls of MWCNTs. A flow cell was utilized to orient magnetic nanohybrid in the desired direction and also to create thin films of aligned MWCNTs. Further, directional assembly of magnetic MWCNTs at different orientation angles on solid substrates was studied by field emission scanning electron microscopy and optical microscopy. The procedure can be scaled to align CNTs on large surface areas for numerous applications, e.g., nanosensors, field emitters, and composites.

Dispersion Stability of Fluorinated Multi-Walled Carbon Nanotubes in FC-27 Refrigerant

In order to achieve the dispersion stability of multi-walled carbon nanotubes (MWCNT) in a fluorinated refrigerant (FC-72) used in various cooling purposes, fluorinated MWCNT (MWCNT-F) was prepared by a combined process of oxidation and fluorination. As a fluorine source, (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane was used to react with hydroxyl groups on MWCNT (MWCNT-OH) generated by chemical oxidation. Pristine MWCNT, MWCNT-OH, and MWCNT-F were dispersed in FC-72 and MWCNT-F was also dispersed in polar and nonpolar solvents. The MWCNT-F has excellent colloidal stability in FC-72 because of the chemical affinity between FC-72 and functional groups (-CFn) on the side walls of MWCNT. Through surface modifications, we could obtain the enhanced dispersion stability of MWCNT in a refrigerant. This homogenous MWCNT solution in FC-72 may be used to increase the heat transfer in FC-72 based nanofluids.

Microwave assisted fast fabrication of Fe 3O 4-MWCNTs nanocomposites and their application as MRI contrast agents

Uniform Fe 3O 4 nanoparticles with diameters of 3–5 nm are successfully decorated onto the external walls of multiwall carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of Fe(acac) 3 in polyol solution under the irradiation of microwave. With this method, reaction time of forming Fe 3O 4-MWCNTs nanocomposites has been significantly shortened to 15 min. The resulting Fe 3O 4-MWCNTs nanocomposites show superparamagnetic property at room temperature and can be remained as stable aqueous dispersion for 2 months. Longitudinal relaxivity (r 1) and transverse relaxivity (r 2) of the magnetic MWCNTs are 8.34 Fe mM −1 S −1 and 146 Fe mM −1 S −1 respectively. The much higher r 2 value and the obvious change in the gray scale of MR images confer the Fe 3O 4-MWCNTs nanocomposites as potential candidates for T 2-weighted MRI contrast agents.

Multiwalled carbon nanotubes dispersed in carminic acid for the development of catalase based biosensor for selective amperometric determination of H2O2 and iodate

We report the preparation of stable dispersion of multiwalled carbon nanotubes (MWCNTs) using carminic acid (CA) as a dispersing agent. The transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) results confirmed that MWCNT is well dispersed in CA aqueous solution and CA has been well adsorbed at MWCNT walls. Fourier transform infrared (FTIR) and UV–vis absorption spectra results also confirmed the adsorption of CA at MWCNT. To develop a highly selective amperometric biosensor for H2O2 and iodate, the model enzyme catalase (CAT) was immobilized at CACNT modified glassy carbon electrode surface. The immobilized CAT exhibits well defined quasi reversible redox peaks at a formal potential (E°′) of −0.559V in 0.05M pH 7 phosphate buffer solution (PBS). The proposed CAT/CACNT biosensor exhibits excellent amperometric response towards H2O2 and iodate in the linear concentration range between 10μM to 3.2mM and 0.01–2.16mM. The sensitivity values are 287.98μAmM−1cm−2 and 0.253mAmM−1cm−2, respectively. Moreover, the developed CAT biosensor exhibits high affinity for H2O2 and iodate with good selectivity.

Ultrasound-Aided Formation of Gold Nanoparticles on Multi-Walled Carbon Nanotubes Functionalized with Mercaptobenzene Moieties

A hybrid of multi-walled carbon nanotube (MWCNT) and gold nanoparticle (Au NP) was prepared under ultrasound irradiation. The approach starts with the functionalization of the walls of MWCNTs with mercaptobenzene moieties for the subsequent immobilization of Au NPs. From the Raman spectra, mercaptobenzene was proven to exist on the MWCNTs. Gold ions were added to the aqueous dispersion of functionalized MWCNTs (f-MWCNTs), and were reduced with the aid of ultrasound and ammonium hydroxide. The reduced gold nanoparticles were examined from the TEM images. Au NPs adhered specifically on the thiol groups of mercaptobenzene to be deposited uniformly on the outer walls of the f-MWCNTs. The application of ultrasound led to a high yield of MWCNT-Au nanocomposites and to the dense distribution of the Au NPs. Moreover, the synthesis reaction rate of the hybrid was considerably enhanced relative to synthesis with mechanical agitation. Through an adsorption test using gold-binding-peptide-(GBP)-modified biomolecules, the hybrid's potential for biological diagnosis was verified.

Synthesis of Multi-walled Carbon Nanotubes/ZnO Nanocomposites using Absorbent Cotton

Abstract This letter focuses on the synthesis of multi-walled carbon nanotubes (MWNTs) and MWNTs/ZnO nanocomposites using absorbent cotton. The MWNTs have been synthesized by a rapid heating of absorbent cotton at different temperature (400°C, 550°C, 600°C). The MWNTs/ZnO nanocomposites have been synthesized by heating mixtures of Zn(OH)2/H2O/absorbent cotton at different temperature (at about 550°C and 600°C). The X-ray diffraction (XRD) pattern and energy dispersive spectrum (EDS) clearly show that the pure MWNTs and ZnO nanocomposites (with a mean size of 35.9 nm) were synthesized. The scanning electron microscopy (SEM) images demonstrate that the structure of synthesized MWNTs was middle-hollow, with inner and outer diameter of around 10 and 80 nm. The ZnO nanocomposites that had grown on the walls of MWNTs were nonuniform and agglomerated, with an outer diameter of around 110 nm. The selected area diffraction (SAD) patterns and Raman spectrum indicate that the MWNTs were well-crystallised, and there are a few defects in the walls. Infrared absorption spectroscopy (IR) spectra suggest that the surface of MWNTs has been covered by ZnO.

Nanoporous Silica Membranes Fabricated Using Multiwalled Carbon Nanotubes

Nanoporous silica membranes were fabricated using 3-aminopropyltriethoxysilane (APS) and acyl chloride-functionalized multiwalled carbon nanotubes (MWCNTs). The amine groups of silane reacted with the functional groups (e.g., acid chloride) that were attached to the sidewall of the MWCNTs. The APS that was grafted to the sidewall of the MWCNTs was polymerized in order to coat the MWCNTs wall through heating. The thickness of the silica layer on the surface of the MWCNTs was controlled by adjusting the growth time of the SiO2 layer. Approximately 20 nm-sized pores were formed through the removal of the MWCNTs using a simple thermal process, but some traces of the MWCNTs still remained. The porous properties of the nanoporous silica membrane were analyzed from the nitrogen adsorption-desorption isotherms that were obtained using a surface area and porosimetry analyzer. The structure and composition of the silane-modified MWCNTs were characterized using scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy.

Protein adsorption on functionalized multiwalled carbon nanotubes with amino‐cyclodextrin

AbstractA novel amino‐cyclodextrin was synthesized, and it was covalently attached to multiwalled carbon nanotubes (MWNTs). The functionalized MWNTs (f‐MWNTs) have very good aqueous dispersibility. Bovine serum albumin (BSA) was adsorbed onto f‐MWNTs through noncovalent interactions, including the hydrophobic interaction of the residues of BSA with the wall of MWNT and the guest–host interaction of the residues with the cyclodextrin (CD) moieties of f‐MWNTs. The ultraviolet–visible (UV–vis) absorption of the f‐MWNT‐BSA hybrid was measured with UV–vis spectrometer, and the absorbance can be described well with the Beer–Lambert law. The X‐ray diffraction patterns have indicated that the crystalline form of BSA has been changed after the adsorption of BSA on f‐MWNTs. The circular dichroism spectra have shown that a high percentage of α‐helical content can be retained for BSA adsorbed on f‐MWNTs. The results also indicate that the change of secondary structure of BSA is mainly due to the hydrophobic interaction of the residues of BSA with the wall of f‐MWNT, whereas the secondary structure is much less affected by the interaction of the CD moieties with BSA. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Dynamic characteristics of multi-walled carbon nanotubes under a transverse magnetic field

This paper reports the results of an investigation into the effect of transverse magnetic fields on dynamic characteristics of multi-walled carbon nanotubes (MWNTs). Couple dynamic equations of MWNTs subjected to a transverse magnetic field are derived and solved by considering the Lorentz magnetic forces induced by a transverse magnetic field exerted on MWCNTs. Results show that the transverse magnetic field exerted on MWNTs makes the lowest frequency of the MWNTs nonlinearly decrease and the highest frequency, changeless. When the strength of applied transverse magnetic fields is larger than a given value the two walls of MWNTs appear in the radial and axial coaxial vibration phenomena.

Shape-regulated high yield synthesis of electrocatalytically active branched Pt nanostructures for oxygen reduction and methanol oxidation reactions

We describe a shape regulated synthesis of branched Pt nanostructures (nPts) by a simple polyol method using 1,3-propanediol as solvent and poly(diallyldmethylammonium chloride) (PDDA) as stabilizing agent and their electrocatalytic activity in the oxygen reduction and methanol oxidation reactions. The transmission electron microscopic measurements show that the nanoparticles have multiple branches. The size of the branched nanostructures ranges from 10 to 15 nm and the branches have the width of 3–5 nm. The X-ray diffraction measurement indicates the existence of face centered cubic structure of Pt. UV-vis spectroscopic measurement suggests that the reduction of Pt(IV) proceeds through the formation of Pt(II) species. The solvent and the stabilizing agent plays vital role in the growth of nPts. Aggregated nanoparticles were obtained in the absence of PDDA. The traditional solvent ethylene glycol in the presence of PDDA yields only spherical nanoparticles. The nPts were loaded onto the walls of multiwall carbon nanotube (MWCNT) to examine their electrocatalytic activity. The nanoparticles on MWCNT retain their initial shape, size and morphology. The electrocatalytic activity of nPts toward oxygen reduction reaction (ORR) was evaluated in terms of kinetic current density using rotating-ring-disk electrode (RRDE) system. The nanostructured electrocatalyst favors the 4-electron pathway for the reduction of oxygen at a more positive potential with a kinetic current density of 11.97 mA cm−2. The electrocatalytic performance of the catalyst in the methanol oxidation reaction (MOR) was studied with chronoamperometry and potential dependent electrochemical impedance spectroscopy measurements. The nPts show high specific activity in the ORR and MOR. The electrocatalytic activity of nPts towards ORR and MOR is compared with the commercial catalyst and spherical nanoparticles.

Corrugation of the external surface of multiwall carbon nanotubes by catalytic oxidative etching and its effect on their decoration with metal nanoparticles

It was established that partial combustion of carbon constituting the walls of multiwall carbon nanotubes (MWCNTs) catalyzed by previously deposited CaCO3 nanoparticles converts parallel graphene layers in a multiwall structure to aggregates formed by nano-onions with a diameter of 5–12 nm. The areas with positive curvature of graphene layers on the external surface of air-etched MWCNTs played the role of docking stations for nickel nanoparticles inserted by sonochemical deposition after removal of the CaCO3. The nickel nanoparticles were located exclusively at the tops of the onions. Formation of nanoscale curvature at the MWCNT support surfaces decreased the average size of Ni nanocrystals at similar loading of 50–60 wt% from 8 to 2 nm. Partial catalytic combustion did not change the concentration of surface carbonyl groups measured by titration, which attributes the observed phenomena directly to the corrugation of the MWCNT surfaces. The catalytic tests revealed a significant increase of catalytic activity of supported Ni catalyst due to corrugating of the external surface of the MWCNT support. After oxidative etching of the MWCNTs, the rate of chloroacetophenone hydrogenation measured with a Ni–MWCNT catalyst increased by a factor of 2 without change in selectivity yielding chlorophenylethanol as the main product.

Unzipped Multiwalled Carbon Nanotubes for Mechanical Reinforcement of Polymer Composites

Multiwalled carbon nanotubes (MWNTs) have been widely used as mechanical reinforcement agents in the past few years. However, the enhancement of mechanical properties of composites has been greatly hampered by its limited available interface area in composites. Toward solving this intrinsic limitation of MWNTs, in this paper, we report the use of unzipped MWNTs (uCNTs) as nanofillers for reinforcement of polymer composites for the first time. The uCNTs were produced by an oxidative unzipping process, involving the lengthwise cutting and opening the walls of MWNTs, and yielded separated ribbonlike graphene layers, thus increasing the surface area of MWNTs. With different amounts of oxidant (KMnO4), uCNTs with different unzipping degrees were obtained. For the surface functional groups that were generated during oxidation treatment, the morphologies and structures of uCNTs with different unzipping degrees were well characterized by several measurements. The mechanical testing of the resultant poly(vinyl alc...

Optimizing load transfer in multiwall nanotubes through interwall coupling: Theory and simulation

An analytical model is developed to determine the length scales over which load is transferred from outer to inner walls of multiwall carbon nanotubes (MWCNTs) as a function of the amount of bonding between walls. The model predicts that the characteristic length for load transfer scales as ℓ∼tE/μ¯, where t is the CNT wall spacing, E is the effective wall Young’s modulus, and μ¯ is the average interwall shear modulus due to interwall coupling. Molecular dynamics simulations for MWCNTs with up to six walls, and with interwall coupling achieved by interwall sp3 bonding at various densities, provide data against which the model is tested. For interwall bonding having a uniform axial distribution, the analytic and simulation models agree well, showing that continuum mechanics concepts apply down to the atomic scale in this problem. The simulation models show, however, that load transfer is sensitive to natural statistical fluctuations in the spatial distribution of the interwall bonding between pairs of walls, and such fluctuations generally increase the net load transfer length needed to fully load an MWCNT. Optimal load transfer is achieved when bonding is uniformly distributed axially, and all interwall regions have the same shear stiffness, implying a linear decrease in the number of interwall bonds with distance from the outer wall. Optimal load transfer into an n-wall MWCNT is shown to occur over a length of ∼1.5nℓ. The model can be used to design MWCNTs for structural materials, and to interpret load transfer characteristics deduced from experiments on individual MWCNTs.

Load transfer between cross-linked walls of a carbon nanotube

Cross links between inner and outer walls of multiwalled carbon nanotubes are believed to increase nanotube modulus and therefore nanotube effectiveness for reinforcing composites. In order to investigate changes in the Young's modulus of individual double-walled nanotubes (DWNTs) as a function of cross-link density and type, molecular-dynamics simulations are employed to evaluate strain coupling and corresponding load transfer from outer to inner walls. Results show that interwall $s{p}^{3}$ bonds and interstitial carbon atoms can increase load transfer between DWNT walls and that interwall $s{p}^{3}$ bonds are most effective. However, the maximum size of the modulus increase is limited to about 25% for the investigated small-diameter, short DWNTs because the defects decrease the stiffnesses of the nanotube walls.