Sidewalls Of Multiwalled Carbon Nanotubes Research Articles

Positive Charge-doping on Carbon Nanotube Walls and Anion-directed Tunable Dispersion of the Derivatives

An efficient and novel positive charge-doping on the sidewalls of multi-walled carbon nanotubes has been achieved in the presence of tetrahydrofuran as a dopant and Lewis acidic ionic liquids, [bmim]SbnF5n+1 (n >= 2; bmim = 1-butyl-3-methylimidazolium), as an activator, leaving air-stable derivatives having positively charged sidewalls and the counter anions, [MWCNTy+][SbF6-](y) (MWCNT = multi-walled carbon nanotube). The derivatization took place very fast in one-pot and under mild reaction conditions. The ionic structure enabled a tunable dissolution of the derivatives in various solvents through anion exchange.

Functionalization of Multiwalled Carbon Nanotubes with Thermotropic Liquid-Crystalline Polymer and Thermal Properties of Composites

A novel high-performance multiwalled carbon nanotube (MWCNT) nanocomposite (MWCNT-TLCP) was prepared using an in situ polycondensation approach by grafting a thermotropic liquid-crystalline polymer (TLCP) onto the sidewalls of MWCNTs functionalized with hydroxyphenyl groups. FTIR spectroscopy revealed that TLCP was covalently attached to the MWCNTs, and Raman signals corresponding to the D- and G-bands of MWCNTs were attenuated after functionalization. TEM and TGA results showed that the average thicknesses of grafted TLCP layers on the MWCNT surface were 5-7 nm, and the amount of grafted TLCP was about 56 wt %. The morphology of MWCNT-TLCP/TLCP composite containing 3 wt % liquid-crystalline polymer-modified MWCNTs was examined by SEM. SEM images of the composite fracture surfaces showed a homogeneous dispersion of the MWCNT-TLCP nanocomposite in the TLCP matrix. The mesophase temperature region of the composite was obviously increased because of the presence of functionalized MWCNTs.

Preparation, Characterization, and Properties of Polyurethane-Grafted Multiwalled Carbon Nanotubes and Derived Polyurethane Nanocomposites

We incorporated hydroxyl groups into the polyurethane backbone and then used the “grafting to” approach to functionalize the multiwalled carbon nanotubes (MWNTs) via the esterification reaction between MWNTs and segmented polyurethanes (PUs). X-ray photoelectron spectroscopy (XPS) spectra showed that the sidewalls of MWNTs had been functionalized with acid treatment, and the amount of COOH increased with increasing acid treatment time. FTIR spectra further confirmed that PU was covalently attached to the sidewalls of MWNTs. The functionalized acid amount and the grafted PU amount were determined by thermogravimetric analyses (TGAs). Comparative studies based on SEM images of the PU-functionalized and chemically defunctionalized MWNT samples also revealed the covalent coating character. Dynamic mechanical analysis (DMA) of nanocomposite films prepared from PU and PU-functionalized MWNTs showed enhanced mechanical properties and increased soft segment . Tensile properties indicated that PU-functionalized MWNTs were effective reinforcing fillers for the polyurethane matrix.

Covalent functionalization of carbon nanotubes for ultimate interfacial adhesion to liquid crystalline polymer

In this study, we have selectively introduced three types of chemical functional groups, namely nitrophenyl (C6H4NO2), aminophenyl (C6H4NH2) and benzoic acid (C6H4COOH), on the sidewalls of multiwalled carbon nanotubes (MWCNTs) with the aim to find the optimal functionalization of MWCNTs for the most desirable intermolecular interaction with a liquid crystalline polymer (LCP). We have investigated the effects of electron withdrawing (–NO2 and –COOH) and donating (–NH2) groups attached to the benzene rings of the functionalized MWCNTs on the dispersion of MWCNTs in the LCP matrix and the interaction with the LCP. FTIR analysis showed that the composite containing –C6H4NH2 functionalized MWCNTs exhibited the maximum intermolecular interactions (hydrogen bonding) between the –C6H4NH2 group of MWCNTs and –CO group of LCP. This strong intermolecular hydrogen bonding greatly improved the dispersion of p-C6H4NH2 functionalized MWCNTs in the polymer matrix as well as the interfacial adhesion. The highest complex viscosity, storage modulus and loss modulus were observed for the p-C6H4NH2-functionalized MWCNT/LCP composites among all the composites studied. The mechanical strength and electrical conductivity of this composite system were also the highest. Thus, these results testified that the extent of intermolecular interactions between the functionalized MWCNTs and the polymer matrix is key for an optimal improvement in the composite properties.

Field emission arrays fabricated utilizing conjugated ZnO quantum dot/carbon nanotube hybrid nanocomposite

In situ growth of ZnO quantum dots (QDs) on the surface of multiwalled carbon nanotube (MWCNTs) was realized via a mild solution-process method, and their application in field emission device was demonstrated. High resolution transmission electron microscopy observation revealed the conjugation between ZnO QDs and MWCNTs. Field emission arrays based on ZnO QD/MWCNT hybrid nanocomposite exhibited significantly improved luminance intensity and emitting dot density when compared with the MWCNT-only arrays. It is proposed that the introduction of the ZnO QDs on the sidewall of MWCNTs can enhance the tunnelling probability, and result in the improved field emission property for the hybrid emitters.

One-Pot Synthesis of Pt/Carbon Nanotubes by Self-Regulated Reduction for Electrocatalysis

This paper describes a method for size-controlled synthesis of Pt nanoparticles and their attachment to the sidewalls of multiwall carbon nanotubes (CNTs) by self-regulated reduction of sodium n-dodecyl sulfate (SDS), without surface pretreatment. The size of the Pt nanoparticles is controlled by adjusting the concentration of SDS. When Pt/CNTs are heated to 500 degrees C in N2 atmosphere, Pt nanochains are formed on the CNTs; some of these nanochains contain small islands. Electrochemical measurements confirm that the electroactivities of the Pt/CNT nanocatalysts increase with a decrease in the size of the Pt nanoparticles. Additionally, comparing with the heated Pt/CNT nanocatalysts containing smooth Pt nanochains, the heated Pt/CNT nanocatalysts containing Pt nanochains with small Pt islands show higher electrocatalysis activities and stability.

Selective enhanced electrochemical response of DNA bases on carbon nanotube–gold nanocomposites modified gold electrode

AbstractIn this study, multi‐walled carbon nanotube–gold (MWCNT–Au) nanocomposites have been synthesized by using one‐step method, where gold nanoparticles were deposited on the sidewall of multiwalled carbon nanotubes directly and orderly. By combination of these MWCNT–Au nanocomposites with electrochemical biosensing, our study indicates that the modification of gold electrode with these nanocomposites could remarkably enhance the electrochemical response of DNA bases and extends the application of relevant electrodes. It is noted that the selective enhancement effect of DNA bases was related to the special interaction of different bases with the nanointerface and the large effective surface area of this modified electrode. Especially, the pyrimidine bases' signal has been enhanced for several times at the MWCNT–Au nanocomposites modified electrodes than that of the carbon nanotube modified electrodes, suggesting that the MWCNT–Au nanocomposite modified gold electrodes could selectively and sensitively recognize the pyrimidine from other bases in DNA related determinations. magnified image Electrochemical detection of DNA bases based on MWCNT–Au nanocomposites modified gold electrode.

Recognition behavior of chiral nanocomposites toward biomolecules and its application in electrochemical immunoassay

The novel nanocomposites were obtained by covalently linking arginine enantiomers with the sidewall of multi-walled carbon nanotubes, and utilized as sensing materials for biomolecular recognition in electrochemical immunoassay. They were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and circular dichroism spectroscopy (CD). Nano-gold and Prussian Blue were employed to amplify the analytical signal responses. Prostate specific antibody/antigen and carcinoembryonic antibody/antigen were used as model systems. The results showed that the different configurations of nanocomposites could readily facilitate chiral recognition of antibodies, and D-nanocomposites displayed a larger signal.

Quenching of Photoluminescence in ZnO QDs Decorating Multiwalled Carbon Nanotubes

We report the controlled growth of ZnO quantum dots (QDs) on the sidewalls of multiwalled carbon nanotubes (MWCNTs) by a one-step process and study the effect on the photoluminescence (PL) properties of the ZnO QDs-MWCNT composite. The PL intensity of the composite is quenched and the lifetime is reduced compared to the only ZnO QDs. The origin of the PL quenching is discussed in terms of energy transfer, which is examined by varying the density and size of ZnO QDs by changing the molar concentration of the precursor solution for ZnO and the amount of MWCNT.

Thermal conductance and phonon transmissivity of metal–graphite interfaces

The thermal boundary conductances between c-axis oriented highly ordered pyrolytic graphite and several metals have been measured in the temperature range 87–300 K and are found to be similar to those of metal–diamond interfaces. The values obtained are indicative of the thermal interface conductance between metals and the sidewalls of multiwall carbon nanotubes (CNTs) and, therefore, have relevance for the accurate characterization of the thermal properties of CNTs, graphene, and the design and performance of composite materials and electronic devices based on these structures. A modified diffuse mismatch model is used to interpret the data and extract the phonon transmissivity at the interface. The results indicate that metal–graphite adhesion forces and interfacial mixing effects play important roles in determining the boundary conductance.

UV-assisted grafting of polymers: A method towards biocompatible carbon nanotubes

A strategy for covalent grafting of biocompatible polymers onto sidewalls of multi-walled carbon nanotubes (MWNTs) via UV-initiated free-radical polymerization is presented. The effects of the irradiation doze(time) and monomer/MWNTs ratio on the stability of the corresponding aqueous dispersions were investigated. It was found that stable dispersions of MWNTs modified with polyacrylamide, poly(N-isopropylacrylamide), poly[poly(ethylene glycol) methacrylate] and poly(sodium methacrylate) can be obtained by irradiation with UV light for at least 5 min at an irradiation dose rate of 5.7 J/cm2 min at a minimum monomer/CNTs ratio of 200:1. Biocompatibility of polymer-modified MWNTs was assessed using the standard MTT-dye reduction assay and compared to pristine MWNTs. As a rule, all polymer-functionalized nanotubes examined in this study were non-cytotoxic up to concentration 150 μg/mL and, remarkably, MWNTs-g-PNIPAAm did not exhibit cytotoxicity even at the highest concentration studied (300 μg/mL). MWNTs modified with stimuli-sensitive polymers underwent a reversible transition from well-dispersed nanotubes in water to precipitate triggered by changes in temperature or pH.

Preparation and characterization of CdS–TiO2 nanoparticles supported on multi-walled carbon nanotubes

Abstract Nanoscopic CdS–TiO 2 particles supported on multi-walled carbon nanotubes (MWCNTs) are prepared via a sol–gel method. TEM, BET, XPS and UV–vis absorption results confirm that TiO 2 and CdS nanoparticles having relatively small particle size and homogeneous structure are coated on the sidewall of MWCNTs. The results of the toluene degradation show that the presence of MWCNTs and CdS nanoparticles plays a significant role in improving the photocatalytic performance. Under the irradiation UV light at the wavelength of 254 nm, the removal efficiency of toluene decomposition on CdS–TiO2/MWCNT catalysts reached 55.3%.

In situ growth of copper nanoparticles on multiwalled carbon nanotubes and their application as non-enzymatic glucose sensor materials

Cu-nanoparticles were coated on the sidewall of multiwalled carbon nanotubes (MWCNTs) by a facile and effective in situ approach via the template of a polyelectrolyte (polyethylenimine or poly(sodium 4-styrene sulfonate)) noncovalently functionalized on MWCNTs. Extensive characterizations of the fabricated nanocomposites have been studied using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, thermal gravimetric analysis and inductively coupled plasma. The results demonstrate that Cu-nanoparticles were well distributed on the surface of MWCNTs. The nanocomposites can be easily modified on the glassy carbon electrodes due to the presence of polyelectrolyte. The electrocatalytic activity of the modified electrodes towards glucose oxidation was investigated by cyclic voltammetry and chronoamperometry. The nanocomposites showed good non-enzymatic electrocatalytic responses to glucose in alkaline media, and can be used for the development of enzyme-free glucose sensors.

Sonochemical hybridization of carbon nanotubes with gold nanoparticles for the production of flexible transparent conducing films

We have demonstrated the fabrication of flexible, transparent, conducting multiwalled carbon nanotube (MWCNT)/gold nanoparticle hybrid films with improved optoelectronic properties by combining the ionic liquid-assisted sonochemical method (ILASM) for hybrid synthesis with the vacuum filtration (VF) method for thin film preparation. Au nanoparticles (NPs) with diameters of 10.3±1.5nm were uniformly distributed onto the sidewalls of MWCNTs through ILASM, and flexible, transparent, conducting films of Au/MWCNT hybrids (HBs) were reproducibly fabricated by the VF method. In particular, the sheet resistance of Au-MWCNT-HB films was more than 2-fold lower than the sheet resistance of pristine MWCNT films due to the well-interconnected three-dimensional nanotube network structure and the synergistic effect of hybridization of MWCNTs with Au-NPs.

Decoration of carbon nanotubes with CdS nanoparticles by polythiophene interlinking for optical limiting enhancement

The sidewalls of multiwalled carbon nanotubes (MWCNTs) were decorated with CdS nanoparticles using a mild two-step approach, with in situ polymerized thiophene (PTh) acting as an interlinker. Extensive characterization of the materials has been carried out using transmission electron microscopy, selected area electron diffraction, X-ray diffraction, thermal gravimetric analysis, ultraviolet–visible absorption spectroscopy and photoluminescence spectroscopy. Optical limiting (OL) studies have been performed using the open Z-scan technique at the laser wavelengths of 532 and 1064 nm. The MWCNT–PTh–CdS system shows an enhanced OL effect in comparison to the pristine MWCNTs, particularly at 1064 nm. Possible underlying mechanisms are proposed based on the results of nonlinear scattering measurements.

Metal sulfide coated multiwalled carbon nanotubes synthesized by an in situ method andtheir optical limiting properties

A metal sulfide such as ZnS, CdS,Ag2S or PbS was coated on the sidewall of multiwalled carbon nanotubes (MWCNTs) by an insitu wet chemical synthesis approach via noncovalent functionalization of MWCNTs with apolyelectrolyte (polyethylenimine or poly(diallyldimethylammonium chloride)) withoutcausing significant electronic and structural modification of the carbon nanotubes.Extensive characterizations of the fabricated nanocomposites have been performed usingx-ray diffraction, transmission electron microscopy (TEM), high resolution TEM, energydispersive x-ray spectroscopy, selected area electron diffraction, thermal gravimetricanalysis, Fourier transform IR spectra, UV–vis spectra and x-ray photoelectronspectroscopy. The coating layers were composed of metal sulfide nanoparticleswith a mean size of less than 10 nm. The optical limiting property measurementsfor some metal sulfide coated MWCNTs were carried out by the open-aperturez-scan technique. The results demonstrate that the samples suspended in water showedoptical limiting behavior better than that of purified MWCNTs.

Surface functionalization of multi-walled carbon nanotubes via electron reduction of benzophenone by potassium metal

The covalent sidewall functionalization of multi-walled carbon nanotubes (MWCNTs) via the electron reduction of benzophenone by potassium metal is reported. Fourier transform infrared spectroscopy (FTIR) results show that diphenylcarbinol (DPC) groups were successfully grafted to the MWCNTs sidewalls after 10 days of reaction time. Raman and UV–vis spectroscopies reveal the presence of covalent sidewall functionalization. The percentage of residues for DPC-MWCNTs was found to be lower than that for pristine MWCNTs, which indicates the existence of functional groups on the sidewalls of DPC-MWCNTs. It is shown that the sidewall of the DPC-MWCNTs was covered by non-uniform layer of DPC, as observed by transmission electron microscopy (TEM). Results from Raman spectroscopy, FTIR, TGA, UV–vis spectroscopy and TEM confirm that the functionalization of the covalent sidewalls of MWCNTs was successfully performed by this method.

The formation of magnetite nanoparticles on the sidewalls of multi-walled carbon nanotubes

Linear polyethyleneimine (PEI) was used as a non-covalent functionalizing agent to modify multi-walled carbon nanotubes (MWCNTs). Fe 3O 4 nanoparticles were then formed along the sidewalls of the as-modified MWCNTs through a simple solvothermal method. X-ray diffraction, Fourier transform infrared spectrometry, transmission electron microscopy, and vibrating sample magnetometry were used to characterize the MWCNT/Fe 3O 4 nanocomposites. Results indicated that Fe 3O 4 nanoparticles with diameters ranging from 50 to 200 nm were attached to the surface of the MWCNTs by electrostatic interaction. PEI was found to improve the electrical conductivity of the MWCNT/Fe 3O 4 nanocomposites. The magnetic saturation value of these magnetic nanocomposites was 61.8 emu g −1. These magnetic MWCNT/Fe 3O 4 nanocomposites are expected to have wide applications in bionanoscience and technology.

Comparison of some gold/carbon nanotube composites prepared by control of electrostatic interaction

Nanocomposites of gold and multi-walled carbon nanotubes (MWNTs) were prepared with gold nanoparticles and MWNTs stabilized by 4-(dimethylamino)pyridine (DMAP) and dispersion agents, respectively, and studied in detail with UV/vis spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). UV/vis spectra of Au-MWNT nanocomposites showed the characteristic surface plasmon bands at ∼525 nm. There was only slight change on the band shape with change of dispersion agent for MWNTs. Through TEM images and XPS analysis, the distribution of gold nanoparticles on the sidewalls of MWNTs was deliberately investigated on three species of Au-MWNT nanocomposites treated with different dispersion agents and compared with one another.

Functionalization of multiwalled carbon nanotube via surface reversible addition fragmentation chain transfer polymerization and as lubricant additives

AbstractPolymer‐grafted multiwalled carbon nanotube (MWCNT) hybrid composite which possess a hard backbone of MWCNT and a soft shell of brush‐like polystyrene (PSt) were synthesized. The reversible addition fragmentation chain transfer (RAFT) agents were successfully immobilized onto the surface of MWCNT first, and PSt chains were subsequently grafted from sidewall of MWCNT via RAFT polymerization. Chemical structure of resulting product and the quantities of grafted polymer were determined by Fourier transform infrared, thermal gravimetric analysis, nuclear magnetic resonance, and X‐ray photoelectron spectra. Transmission electron microscopy and field emission scanning electron microscopy images clearly indicate that the nanotubes were coated with a polymer layer. Furthermore, the functionalized MWCNT as additives was added to base lubricant and the tribological property of resultant MWCNT lubricant was investigated with four‐ball machines. The results indicate that the functionalization led to an improvement in the dispersion of MWCNT and as additives it amended the tribological property of base lubricant. The mechanism of the significant improvements on the tribological properties of the functionalized MWCNT as additives was discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3014–3023, 2008