Polymeric nanocomposite films from functionalized vs suspended single-walled carbon nanotubes

The reported work was to demonstrate that the defect-derived photoluminescence in functionalized single-walled carbon nanotubes could be exploited in probing the dispersion of these nanotubes in polymeric nanocomposites because the luminescence emissions are sensitive to the degree of nanotube bundling and surface modification. The polyimide-SWNT nanocomposite thin films obtained from nanotubes with and without functionalization were compared. The spectroscopic results suggest that despite a similar visual appearance in the two kinds of films, the nanotube dispersion must be significantly better in the film with functionalized nanotubes, as reflected by the strong photoluminescence. In fact, the nanotubes embedded in polymer matrix that can be readily characterized by Raman spectroscopy are non-luminescent, while those that are difficult for Raman are strongly luminescent. Therefore, Raman and photoluminescence serve as complementary tools in the investigation of nanocomposites concerning the nanotube dispersion-related properties.     

Poly(N-vinyl carbazole)-functionalized single-walled carbon nanotubes: Synthesis, characterization, and nanocomposite thin films

A poly(N-vinyl carbazole) (PVK) copolymer containing pendant hydroxyl groups was synthesized for the functionalization of single-walled carbon nanotubes (SWNTs) under typical reaction conditions for the esterification of the nanotube-bound carboxylic acids. The functionalized nanotube samples, soluble in common organic solvents, were characterized by using optical absorption, Raman, and several microscopy techniques. The presence of ester linkages was supported by the results from chemical defunctionalization in hydrolysis that recovered insoluble SWNTs. The shared solubility of the functionalized nanotube samples with PVK enabled the wet-casting of high-quality PVK-SWNT nanocomposite thin films for an evaluation of their enhanced charge dissipation under illumination.     

Electrochemical properties of double wall carbon nanotube electrodes

Electrochemical properties of double wall carbon nanotubes (DWNT) were assessed and compared to their single wall (SWNT) counterparts. The double and single wall carbon nanotube materials were characterized by Raman spectroscopy, scanning and transmission electron microscopy and electrochemistry. The electrochemical behavior of DWNT film electrodes was characterized by using cyclic voltammetry of ferricyanide and NADH. It is shown that while both DWNT and SWNT were significantly functionalized with oxygen containing groups, double wall carbon nanotube film electrodes show a fast electron transfer and substantial decrease of overpotential of NADH when compared to the same way treated single wall carbon nanotubes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The study of thermodynamics and kinetics methyl orange and malachite green by SWCNTs,SWCNT-COOH and SWCNT-NH2 as adsorbents from aqueous solution

The effective removal of dyes from aqueous wastes is among the most important issues for many industrialized countries. Removal of methyl orange (MO) and malachite green (MG) from aqueous solutions were studied using single-walled carbon nanotubes (SWCNTs), carboxylate functionalized single-walled carbon nanotubes (SWCNT-COOH) and amide functionalized single-walled carbon nanotubes (SWCNT-NH₂). The adsorption process was found to be controlled by temperature, ionic strength, initial concentration, adsorbent dosage and contact time. The microstructure of carbon nanotubes was characterized using SEM and FTIR. The adsorbents studied exhibits high efficiency for MO and MG adsorption and the equilibrium states could be achieved in 20, 20, 15 (min) for SWCNTs, SWCNT-COOH, SWCNT-NH₂, respectively. Adsorption capacity of each adsorbent increased with increasing active groups on the surface of carbon nanotube, where SWCNT-NH₂ was the most effectively adsorbent.     

p-Hexafluoroisopropanol phenyl covalently functionalized single-walled carbon nanotubes for detection of nerve agents

Novel p-hexafluoroisopropanol phenyl (HFIPPH) covalently functionalized single-walled carbon nanotubes (SWCNTs) have been prepared through in situ diazonium reaction between SWCNTs and p-hexafluoroisopropanol aniline; moreover, the hybridized material can be characterized by ultraviolet vision near infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectrometry, field-emission scanning electron microscopy and high resolution transmission electron microscopy. The results reveal that the one-dimensional electronic structures of the functionalized tubes could be basically maintained without damaging their electronic properties. Considered that strong hydrogen-bonding can be formed between hexafluoroisopropanol groups and dimethyl methylphosphonate (DMMP) (simulant of nerve agent sarin), the SWCNT-HFIPPH sensing devices have been fabricated and employed to detect DMMP. Excellent sensitivity and selectivity of the hybridized SWCNT-HFIPPH devices suggest that it has great capability of detecting explosives and chemical warfare agents.     

Neutralized fluorine radical detection using single-walled carbon nanotube network

It is known that single-walled carbon nanotubes (SWCNTs) can be functionalized by fluorine gas. Here, we report neutralized fluorine radical detection using a matted sheet of SWCNTs, prepared by alternating current dielectrophoresis. Upon exposure to neutralized radicals containing fluorine atoms in a plasma, as model analytes, the conductance of the SWCNT matt showed fast modulation. The transduction mechanism was investigated by electrical transport measurements, X-ray photoelectron spectroscopy and Raman spectroscopy. Metallic nanotubes were shown to react covalently to the near exclusion of semiconducting species. The selectivity was promoted by the curvature-induced strain of the nanotubes. The results open new opportunities for the detection of fluorine radicals at specific locations inside the reaction zone using a simple, miniaturized carbon nanotube network.     

Buckling of functionalized single-walled nanotubes under axial compression

Buckling characteristics of functionalized single-walled carbon nanotubes under axial compression are investigated by molecular mechanics simulation. The influences of the content, the distribution density and the location of the sp³-hybridized carbon atoms as well as the chirality on the critical buckling strains of functionalized single-walled carbon nanotubes are carefully studied. The results indicate that the chirality and the distribution density have dominant effect on the critical buckling strains. The critical buckling strains of present armchair (5, 5) and zigzag (10, 0) carbon nanotube are degraded by about 43% and 70%, respectively, due to the dense distribution of the sp³-hybridized carbon atoms. The reduction amplitude of the critical strain increases with increasing the tubule radius of an armchair or zigzag single-wall carbon nanotube. The dramatic reduction of the critical strain could cause a great loss of reinforcing role of carbon nanotubes in composites.     

Single-walled carbon nanotube growth from liquid gallium and indium

We present the first demonstration of single-walled carbon nanotube growth from liquid gallium and indium catalysts. The nanotubes were grown via thermal chemical vapor deposition from 1 to 3 nm films of gallium and indium, which dissociate into liquid droplets on silicon substrates at high temperatures. The nanotubes were characterized by Raman spectroscopy and atomic force microscopy and are found to have diameters between 1 and 2 nm.     

Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/single-walled carbon nanotube composites

Electrochemical polymerization of 2,2′-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430-1450 cm⁻¹ indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600-800 cm⁻¹ resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH₄OH solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm⁻¹.     

Modifying the electronic properties of single-walled carbon nanotubes using designed surfactant peptides

The electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino acid sequence of X(Valine)(5)(Lysine)(2), where X indicates an aromatic amino acid containing either an electron-donating or electron-withdrawing functional group (i.e. p-amino-phenylalanine or p-cyano-phenylalanine). Circular dichroism spectra showed that the surfactant peptides primarily have random coil structures in an aqueous medium, both alone and in the presence of SWCNTs, simplifying analysis of the peptide/SWCNT interaction. The ability of the surfactant peptides to disperse individual SWCNTs in solution was verified using atomic force microscopy and ultraviolet-visible-near-infrared spectroscopy. The electronic properties of the surfactant peptide/SWCNT composites were examined using the observed nanotube Raman tangential band shifts and the observed additional features near the Fermi level in the scanning tunneling spectroscopy dI/dV spectra. The results revealed that SWCNTs functionalized with surfactant peptides containing electron-donor or electron-acceptor functional groups showed n-doped or p-doped altered electronic properties, respectively. This work unveils a facile and versatile approach to modify the intrinsic electronic properties of SWCNTs using a simple peptide structure, which is easily adaptable to obtain peptide/SWCNT composites for the design of tunable nanoscale electronic devices.     

Functionalization of single-walled carbon nanotubes by using alkyl-halides

In this paper we demonstrate the functionalization of single-walled carbon nanotubes prepared by chemical vapor deposition. The chosen functionalization agents were alkyl-halides such as trifluoromethane (TFM) and trichloromethane (TCM); or double bond containing alkyl-halides as tetrachloroethylene (TCE) and hexafluoropropene (HFP) that can easily form radicals. Functionalization of samples was carried out under mild conditions, by ball milling of nanotubes in an atmosphere of functionalization agent, at room temperature. For the sake of comparison, chlorination was also performed by chlorine gas. In this process the cleavage of nanotube C-C bonds results in active sites, which can activate molecules in gas phase or adsorbed on the surface of carbon nanotubes. Halogenated samples were characterized by means of particle induced γ-ray emission, transmission electron microscopy, thermogravimetry, and X-ray photoelectron spectroscopy. We concluded that this method gives functionalized single-walled carbon nanotubes in the range of 0.3-3.5 wt.% of fluorine and 5.5-17.5 wt.% of chlorine.     

Chemically immobilised carbon nanotubes on silicon: Stable surfaces for aqueous electrochemistry

Diazonium ion chemistry has been used to electrochemically graft aminophenyl layers onto p-type silicon (1 0 0) substrates. A condensation reaction was used to immobilise single-walled carbon nanotubes with high carboxylic acid functionality directly to this layer. Electrochemical monitoring of the aminophenyl groups confirmed the formation of an amide linkage between the single-walled carbon nanotubes and the aminophenyl layer. The carbon nanotube electrode showed high stability and good electrochemical performance in aqueous solution. At moderate scan rates the Ru(NH₃)₆^+3/+2 couple exhibited quasi-reversible electron transfer kinetics with a standard heterogenous rate constant of 1.2 × 10⁻³ cm s⁻¹ at the covalently-linked carbon nanotube surface. The electrode thus combines the advantages of a silicon substrate for easy integration into sophisticated electrical and electronic devices, carbon nanotubes for desirable electrochemical properties, and stability in aqueous medium for future applications in environmental sensing.     

Parametric analysis of sonication and centrifugation variables for dispersion of single walled carbon nanotubes in aqueous solutions of sodium dodecylbenzene sulfonate

Dispersion of single-walled carbon nanotubes with the aid of surfactants has become a common procedure for generating aqueous solutions containing a high fraction of individualized nanotubes, though methodologies vary greatly among the literature. A parametric study was performed in order to analyse the effect of ultracentrifugation temperature, duration and applied force on dispersions of arc-discharge nanotubes in sodium dodecylbenzene sulfonate. The amount of metallic impurities remaining after varying levels of centrifugation was investigated by electron microscopy and X-ray spectroscopy. The effect of intensity and duration of exposure to ultrasound was also examined. Solutions were characterized with UV–vis–NIR absorbance spectroscopy, Raman spectroscopy and atomic force microscopy in order to find optimal ranges of these parameters for this particular system. In general, optimal conditions were accomplished via tip sonication at a power below 0.6 W mL⁻¹ to deliver around 450 J mL⁻¹ to the solution, followed by centrifugation at ∼120 × 10³g for 1–2 h. The scission of nanotubes was found to follow a power law such that the average length of the ensemble decreased proportional to t^−0.38 under continuous tip sonication, while the relationship between mean nanotube length and the Raman D:G ratio was approximately linear for both 1.58 and 2.33 eV excitation.     

Influence of Single-Walled Carbon Nanotubes on the Performance of Poly(Azomethine-Ether) Composite Materials

The present work is aimed to fabricate a new set of composite materials containing conducting poly(azomethine-ether) reinforced with single-walled carbon nanotubes in the form of single-walled carbon nanotube/poly(azomethine-ether)_1–5 for excellent enhanced thermal as well as conducting behavior of poly(azomethine-ether). Single-walled carbon nanotubes of variable loading have been embedded into conducting poly(azomethine-ether) using in situ polymerization technique. Before attempting the polymerization, 1,3-thiazole established poly(azomethine-ether) and its conformable monomers have been prepared and their chemical structures have been correlated by spectral analyses. Furthermore, η_inh and M_w values for poly(azomethine-ether) were found 0.89?dL?g^?1 and 39723.6, respectively. The fabricated single-walled carbon nanotube/poly(azomethine-ether)_1–5 composites were specified and characterized by wide-angle X-ray diffraction patterns, Fourier transform infrared spectroscopy, thermal behavior, scanning electron microscopy, and transmission electron microscopy characterization techniques. A perfect indicative response for this composite material was estimated by Fourier transform infrared spectra and X-ray diffraction as well. Both techniques displayed all intensive characteristic peaks regarding single-walled carbon nanotubes and poly(azomethine-ether) in the spectra or diffraction pattern for single-walled carbon nanotube/poly(azomethine-ether)_1–5. The role of single-walled carbon nanotubes on the performance of poly(azomethine-ether) was considerably examined. Single-walled carbon nanotube/poly(azomethine-ether)_1–5 showed relatively higher thermal stability. Single-walled carbon nanotube/poly(azomethine-ether)₁ displayed the lowest final composite degradation temperature value (552°C), whereas single-walled carbon nanotube/poly(azomethine-ether)₅ displayed the highest value (621°C). T₁₀ and T₂₅ values showed a gradual temperature increased while single-walled carbon nanotubes increased. Single-walled carbon nanotube/poly(azomethine-ether)₁ showed the lowest thermal stability and single-walled carbon nanotube/poly(azomethine-ether)₅ showed the highest thermal stability between all fabricated products. Furthermore, transmission electron microscopy images showed a prominent increase in single-walled carbon nanotubes diameters (40–60?nm). The conductivity values were significantly increased while single-walled carbon nanotubes content was increased and reached to the semiconductors. ε′ values were also increased in both single-walled carbon nanotube/poly(azomethine-ether)_4,5 which have higher single-walled carbon nanotubes content.     

Linear carbon chains encapsulated in multiwall carbon nanotubes: Resonance Raman spectroscopy and transmission electron microscopy studies

In this paper we report the characterization of linear carbon chains encapsulated in multiwalled carbon nanotubes by using Raman spectroscopy and transmission electron microscopy. The chains are characterized by strong vibrational peaks around 1850 cm⁻¹ and both the frequency and intensity of these peaks were found to be dependent on laser excitation energy. Furthermore, resonance Raman spectroscopy was used for constructing the resonance window of the linear carbon chains. The Raman spectroscopy data showed that long chains have lower highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps and weaker carbon–carbon bonds. Besides the spectroscopy evidence for the linear carbon chain, we used scanning transmission electron microscopy/electron energy loss spectroscopy analysis of the nanotube cross section to unambiguously show the existence of a 1D structure present within the innermost carbon nanotube with an unprecedented clarity compared to previous reports on this kind of system.     

Hydrogen adsorption on single-walled carbon nanotubes studied by core-level photoelectron spectroscopy and Raman spectroscopy

We have investigated the adsorption of atomic hydrogen on vertically aligned carbon nanotube (CNT) films using in situ synchrotron-radiation-based core-level (CL) photoelectron spectroscopy and Raman spectroscopy. From C 1s CL spectra, we identified a CL peak component due to C-H bonds of carbon atoms in single-walled carbon nanotubes (SWCNTs). We also found the suppression of π-plasmon excitation, indicating that the hydrogen adsorption deforms the bonding structure. Raman spectra of the SWCNT film indicated that the radial-breathing-mode intensities of SWCNTs decreased due to the adsorption-induced bonding-structure deformation. Moreover, the decrease for small-diameter SWCNTs was more severe than that for large-diameter SWCNTs. Our results strongly suggest that the hydrogen adsorption, which induces the structure deformation from sp² to sp³-like bonding, depends on the diameter of SWCNTs.     

Comparison of carbon nanotube modified electrodes for photovoltaic devices

Substrates with four different nanotube modifications have been prepared and their electron transport properties measured. Two modification techniques were compared; covalent chemical attachment of both single and multi-walled carbon nanotubes to transparent conductive (fluorine doped tin oxide) glass surfaces and chemical vapour deposition (CVD) growth of both single and multi-walled carbon nanotubes on highly doped conductive silicon wafers. These carbon nanotube modified substrates were investigated using scanning electron microscopy and substrates with nanotubes grown via CVD have a much higher density of nanotubes than substrates prepared using chemical attachment. Raman spectroscopy was used to verify that nanotube growth or attachment was successful. The covalent chemical attachment of nanotubes was found to increase substrate electron transfer substantially compared to that observed for the bare substrate. Nanotube growth also enhanced substrate conductivity but the effect is smaller than that observed for covalent attachment, despite a lower nanotube density in the attachment case. In both modification techniques, attachment and growth, single-walled carbon nanotubes were found to have superior electron transfer properties. Finally, solar cells were constructed from the nanotube modified substrates and the photoresponse from the different substrates was compared showing that chemically attached single-walled nanotubes led to the highest power generation.     

Nucleobase-pairing triggers the self-assembly of uracil-ferrocene on adenine functionalized multi-walled carbon nanotubes

Shortened and oxidized multi-walled carbon nanotubes (MWCNTs) were functionalized with adenine using the amidation strategy. The adenine functionalized MWCNTs (Ad-MWCNTs) were complexed with a uracil substituted ferrocene and characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM), electron diffraction X-ray spectroscopy (EDX), and atomic force microscopy (AFM). The electrochemical properties of these novel nanohybrids were studied by cyclic voltammetry. The favorable supramolecular interaction of the electroactive species with the functionalized nanotubes through the efficient adenine–uracil base-pairing can be exploited for the design of new electronic devices.     

Formylation of single-walled carbon nanotubes

Formyl or aldehyde groups are transferred to the surface of single-walled carbon nanotubes (SWCNTs) by reaction of reduced carbon nanotubes with N-formylpiperidine. This could open the way for more versatile chemical modification reactions of carbon nanotubes than is currently possible using functionalization methods reported to date. The formylated SWCNTs were characterized by thermogravimetric analysis-mass spectrometry and Raman, UV-vis-NIR and FTIR spectroscopy. The location and distribution of the functional groups was determined by AFM using electrostatic interactions with gold nanoparticles. The formylated SWCNTs were further derivatized with a fluorescent dye and studied using fluorescence spectroscopy.     

Microwave-assisted poly(glycidyl methacrylate)-functionalized multiwall carbon nanotubes with a ‘tendrillar’ nanofibrous polyaniline wrapping and their interaction at bio-interface

Multiwall carbon nanotubes (MWCNTs) were activated by microwave irradiation and covalently functionalized with poly(glycidyl methacrylate) (PGMA) through free radical polymerization using ‘fishing process’ when the propagating polymer radicals were attached onto the graphitic surface of the nanotube. The PGMA-functionalized MWCNTs were then used as a precursor to non-covalently wrap polyaniline (PAni) nanofiber onto them. The functionalized nanotubes exhibited stable dispersion up to 180 days in tetrahydrofuran, dimethyl formamide and dimethyl sulfoxide. Fourier transform infrared analyses indicated the attachment of the epoxide and benzenoid–quinoid functional moieties onto the nanotube surface. The PGMA coating on the nanotube and surrounding PAni nanofiber on the MWCNT scaffold were confirmed by transmission electron microscopy. The Raman spectroscopy confirmed the phonon-assisted modification of the nanotube. The differential action of the pristine and functionalized MWCNTs against an opportunistic bacterium (Escherichia coli ) and its plasmid deoxyribonucleic acid was also investigated. Pristine nanotubes exhibited bacterial inhibitory action and no condensation with the pET-32α(+) plasmid. On the other hand, the anti-bacterial PAni nanofiber and functionalized nanotubes showed complex formation with the bacterial plasmid.