Sidewalls Of Carbon Nanotubes Research Articles

High performance carbon nanotube spun yarns from a crosslinked network

We report a new method to create covalent crosslinks between carbon nanotubes (CNTs) with reduced intertube and interbundle spaces, for improving the mechanical properties of CNT spun yarns. This is achieved through the pretreatment of a CNT yarn with 4-carboxybenzenediazonium tetrafluoroborate to form reactive carboxyphenyl groups on the CNT sidewalls. These carboxyphenyl groups are then reacted with a multifunctional crosslinker hexa(methoxymethyl) melamine, leading to a highly crosslinked network within the yarn. The CNT yarns were characterized by X-ray photoelectron spectroscopy, focused ion beam scanning electron microscope, and also assessed for their mechanical properties. The results showed that the method developed effectively improved mechanical properties of CNT yarns: we are able to produce CNT yarns with a tensile strength up to 2.5GPa and Young’s modulus 121GPa.

Electrical detection of specific versus non-specific binding events in breast cancer cells.

Detection of circulating tumor cells (CTCs) from patient blood samples offers a desirable alternative to invasive tissue biopsies for screening of malignant carcinomas. A rigorous CTC detection method must identify CTCs from millions of other formed elements in blood and distinguish them from healthy tissue cells also present in the blood. CTCs are known to overexpress certain surface receptors, many of which aid them in invading other tissue, and these provide an avenue for their detection. We have developed carbon nanotube (CNT) thin film devices to specifically detect these receptors in intact cells. The CNT sidewalls are functionalized with antibodies specific to Epithelial Cell Adhesion Molecule (EpCAM), a marker overexpressed by breast and other carcinomas. Specific binding of EpCAM to anti-EpCAM causes a change in the local charge environment of the CNT surface which produces a characteristic electrical signal. Two cell lines are tested in the device: MCF7, a mammary adenocarcinoma line which overexpresses EpCAM, and MCF10A, a non-tumorigenic mammary epithelial line which does not. Introduction of MCF7s causes significant changes in the electrical conductance of the devices due to specific binding and associated charge environment change near the CNT sidewalls. Introduction of MCF10A displays a different profile due to purely nonspecific interactions. The profile of specific vs. nonspecific interaction signatures using carbon based devices will guide development of this diagnostic tool towards clinical sample volumes.

Theoretical study of chemisorption of hydrogen atoms on the sidewalls of armchair single-walled carbon nanotubes with Stone–Wales defect

The geometrical structures and electronic properties as well as thermal stabilities of hydrogenated armchair (n,n) (n=4–8) SWCNTs with Stone–Wales (SW) defect were investigated using density functional theory (DFT-B3LYP) in combination with the 6-31G* basis set. It is found that the chemisorptions of two hydrogen atoms inside and outside the SW defective SWCNTs are exothermic processes. As the nanotube diameter increases, the reaction energy of exohedral addition decreases, whereas that of endohedral addition increases. Exohedral nanotube adsorption is energetically more favorable than endohedral adsorption for smaller diameter (4,4)-SW, (5,5)-SW SWCNTs, but not for larger diameter (7,7)-SW and (8,8)-SW SWCNTs. The result is different from hydrogen on perfect nanotubes. Significantly, compared with the adsorption on the exterior sidewalls of perfect SWCNTs, the reaction energies of the endo-hydrogenated (7,7)-SW and (8,8)-SW SWCNTs are more exothermic, meaning that the central CC bond of SW defect inside the armchair (7,7)-SW and (8,8)-SW SWCNT sidewalls is more reactive than that in perfect sites. This is different from the result reported on the sidewall reactivity of SW defects outside the armchair SWCNTs. The calculated energy gaps indicate that the hydrogen-chemisorbed SW defective armchair tubes are always wide energy gap structures. The energy gaps of endohedral hydrogen-chemisorbed tubes are higher than those of the corresponding perfect tubes.

Nonionic, Water Self-Dispersible “Hairy-Rod” Poly(p-phenylene)-g-poly(ethylene glycol) Copolymer/Carbon Nanotube Conjugates for Targeted Cell Imaging

The generation and fabrication of nanoscopic structures are of critical technological importance for future implementations in areas such as nanodevices and nanotechnology, biosensing, bioimaging, cancer targeting, and drug delivery. Applications of carbon nanotubes (CNTs) in biological fields have been impeded by the incapability of their visualization using conventional methods. Therefore, fluorescence labeling of CNTs with various probes under physiological conditions has become a significant issue for their utilization in biological processes. Herein, we demonstrate a facile and additional fluorophore-free approach for cancer cell-imaging and diagnosis by combining multiwalled CNTs with a well-known conjugated polymer, namely, poly(p-phenylene) (PP). In this approach, PP decorated with poly(ethylene glycol) (PEG) was noncovalently (π-π stacking) linked to acid-treated CNTs. The obtained water self-dispersible, stable, and biocompatible f-CNT/PP-g-PEG conjugates were then bioconjugated to estrogen-specific antibody (anti-ER) via -COOH functionalities present on the side-walls of CNTs. The resulting conjugates were used as an efficient fluorescent probe for targeted imaging of estrogen receptor overexpressed cancer cells, such as MCF-7. In vitro studies and fluorescence microscopy data show that these conjugates can specifically bind to MCF-7 cells with high efficiency. The represented results imply that CNT-based materials could easily be fabricated by the described approach and used as an efficient "fluorescent probe" for targeting and imaging, thereby providing many new possibilities for various applications in biomedical sensing and diagnosis.

Solvothermal synthesis and optical limiting properties of carbon nanotube-based hybrids containing ternary chalcogenides

Two or three types of semiconductor nanoparticles (NPs) have been deposited on the sidewalls of multi-wall carbon nanotubes (MWCNTs) by a solvothermal treatment of a mixture containing poly(sodium 4-styrenesulfonate) (PSS) wrapped MWCNTs, metal chloride (CuCl2 and SnCl2), and thiourea. Changing the ratio of Cu2+ to Sn2+ alters the composition of the resultant MWCNT–PSS–NP hybrids. Under Cu/Sn ratios of 3:1 and 2:1, MWCNTs can be simultaneously decorated with Cu2S and Cu3SnS4 NPs. When the ratio is reduced to 1:1, Cu3SnS4, Cu2S and SnO2 NPs would be formed at the same time. Further decreasing the ratio results in the formation of Cu2SnS3 and SnO2 instead of Cu3SnS4 and Cu2S. Open-aperture z-scan measurements have been carried out on three typical MWCNT–PSS–NP samples to study their optical limiting (OL) properties. The addition of semiconductor NPs can improve the OL performance of MWCNTs, and the composition of the NPs has a significant effect on the OL behavior of the hybrids.

A new protocol for the carboxylic acid sidewall functionalization of single-walled carbon nanotubes

The carboxylic acid termination of the single-walled carbon nanotubes (SWNTs) provides a convenient link for covalent bonding between the SWNTs and polymer or biological systems. In this work, two approaches for covalent attachment of carboxylic acid groups to the side-walls of single walled carbon nanotubes are presented. Both protocols are based on chemical manipulation of benzonitrile residues, easily introduced onto the SWNTs by in situ diazonium salt formation of 4-aminobenzonitrile. In the first approach, benzonitrile groups on SWNTs were treated with aq. NaOH solution to form benzoic acid moieties. The second approach on benzonitrile groups is leaded to the formation of benzothiomorpholides via Willgerodt–Kindler reaction which is then converted to benzoic acid moieties on SWNTs. Moreover, a simple one-pot entry into the formation of benzoic acid moieties is presented. SWNTs were characterized by a set of methods including FT-IR, UV/vis, TGA, SEM and Raman techniques. The presence of thioamide groups on SWNT is also proved directly by XPS spectroscopy.

“Click” on Tubes: a Versatile Approach towards Multimodal Functionalization of SWCNTs

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. Here, an efficient and versatile approach for the organic/organometallic functionalization of single-walled carbon nanotubes (SWCNTs) capable of imparting multimodality to these fundamental nanostructures, is described. Our strategy takes advantage of well-established Cu-mediated acetylene-azide coupling (CuAAC) reactions applied to phenylazido-functionalized SWCNTs for their convenient homo-/heterodecoration with a number of organic/organometallic frameworks, or mixtures thereof, bearing terminal acetylene pendant arms. Phenylazido-decorated SWCNTs were prepared by chemoselective arylation of the CNT sidewalls with diazonium salts under mild conditions, and subsequently used for the copper-mediated cycloaddition protocol in the presence of terminal acetylenes. The latter reaction was performed in one step by using either single acetylene derivatives or equimolar mixtures of terminal alkynes bearing either similar functional groups (masked with orthogonally cleavable protecting groups) or easily distinguishable functionalities (on the basis of complementary analytical/spectroscopic techniques). All materials and intermediates were characterized with respect to their most relevant aspects/properties by TEM microscopy, thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), elemental analysis, cyclic voltammetry (CV), Raman and UV/Vis spectroscopy. The functional loading and related chemical grafting of both primary amino- and ferrocene-decorated SWCNTs were spectroscopically (UV/Vis, Kaiser test) and electrochemically (CV) determined, respectively.

Hybrids of a Genetically Engineered Antibody and a Carbon Nanotube Transistor for Detection of Prostate Cancer Biomarkers

We developed a novel detection method for osteopontin (OPN), a new biomarker for prostate cancer, by attaching a genetically engineered single-chain variable fragment (scFv) protein with high binding affinity for OPN to a carbon nanotube field-effect transistor (NT-FET). Chemical functionalization using diazonium salts is used to covalently attach scFv to NT-FETs, as confirmed by atomic force microscopy, while preserving the activity of the biological binding site for OPN. Electron transport measurements indicate that functionalized NT-FET may be used to detect the binding of OPN to the complementary scFv protein. A concentration-dependent increase in the source-drain current is observed in the regime of clinical significance, with a detection limit of approximately 30 fM. The scFv-NT hybrid devices exhibit selectivity for OPN over other control proteins. These devices respond to the presence of OPN in a background of concentrated bovine serum albumin, without loss of signal. On the basis of these observations, the detection mechanism is attributed to changes in scattering at scFv protein-occupied defect sites on the carbon nanotube sidewall. The functionalization procedure described here is expected to be generalizable to any antibody containing an accessible amine group and to result in biosensors appropriate for detection of corresponding complementary proteins at fM concentrations.

Electrical Characteristics of Carbon Nanotube Devices Prepared with Single Oxidative Point Defects

A thorough understanding of how electrons pass through point defects in carbon nanotubes is crucial for building carbon nanotube devices. We have generated point defects in the sidewalls of pristine carbon nanotubes via voltage pulses from a conducting atomic force microscope probe and studied the resulting changes in electron transport properties. We find that the incorporation of an oxidative defect leads to a variety of possible electrical signatures including sudden switching events, resonant scattering, and breaking of the symmetry between electron and hole transport. We discuss the relationship between these different electronic signatures and the chemical structure/charge state of the defect. Tunneling through a defect-induced Coulomb barrier is modeled with numerical Verlet integration of Schrodinger’s equation and compared with experimental results.

Palladium nanoparticles decorated carbon nanotubes: facile synthesis and their applications as highly efficient catalysts for the reduction of 4-nitrophenol

Two completely green and facile strategies have been developed to decorate Pd nanoparticles onto carbon nanotubes (CNT) sidewalls via non-covalent interactions assisted with newly synthesized hyperbranched polymers (PiHPs). The resultant CNT/PiHP/Pd heterogeneous catalysts exhibit ultrahigh catalytic reactivity towards the reduction of 4-nitrophenol.

Graphenated carbon nanotubes for enhanced electrochemical double layer capacitor performance

This letter reports on nucleation and growth of graphene foliates protruding from the sidewalls of aligned carbon nanotubes (CNTs) and their impact on the electrochemical double-layer capacitance. Arrays of CNTs were grown for different time intervals, resulting in an increasing density of graphene foliates with deposition time. The samples were characterized using electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. Both low and high frequency capacitance increased with increasing foliate density. A microstructural classification is proposed to explain the role of graphene edges, three-dimensional organization, and other features of hybrid carbon systems on their electrochemical properties.

O] [H] functionalization on carbon nanotube using (O2–H2) gas mixture DC glow discharge

The (O) (H) functionalization of carbon nano- tube (CNT) was studied using oxygen-hydrogen (O2-H2) gas mixture direct current (DC) glow discharge plasma technique for cathode/CNT-anode separation of 0.10 ± 0.01 cm. O2 and H2 were fixed at flowrate of 10.0 ml/min in order to obtain gas mixture ratio of 1:1. During the (O2-H2) gas mixture DC glow discharge, current-voltage (I-V) characteristic of gaseous species studied for various settings of gas pressures 1, 2, 3 and 4 mbar. The voltage at gap between cathode/CNT and anode, a breakdown voltage, was identified as ''functionalization voltage'' (Vfunc). Vfunc was noticed responsible for functionalization of functional groups on sidewall of CNT. The Vfunc were recorded as 796, 707, 594, and 663 V for gas pressures of 1, 2, 3 and 4 mbar, respectively. The co-relation between Vfunc and gas pressure was identified as linear relationship. But a voltage obtained due to the CNT/Cathode fall shows exponential relationship with the gas pressures. The possibility of (O) (H) functional- ization was proved using Fourier transmission infra-red (FTIR) spectroscopy. Hydroxyl (-OH), carboxyl (-COOH), and carbonyl (-C=O) functional groups were identical as identified in the FTIR spectra. The field emission scanning electron microscope images show significant changes in the morphology of CNT which proves that the DC gas discharge plasma is a possible technique for (O) (H) functionalization on the sidewall of CNT.

Functionalization of multi-walled carbon nanotubes by epoxide ring-opening polymerization

In this study, covalent functionalization of carbon nanotubes (CNTs) was accomplished by surface-initiated epoxide ring-opening polymerization. FT-IR spectra showed that polyether and epoxide group covalently attached to the sidewalls of CNTs. TGA results indicated that the polyether was successfully grown from the CNT surface, with the final products having a polymer weight percentage of ca. 14–74 wt%. The O/C ratio of CNTs increased significantly from 5.1% to 29.8% after surface functionalization of CNTs. SEM and TEM images of functionalized CNTs exhibited that the tubes were enwrapped by polymer chains with thickness of several nanometers, forming core–shell structures with CNTs at the center.

Catalytic activity toward oxygen reduction of transition metal porphyrins covalently linked to single-walled carbon nanotubes: A density functional study

The interaction of molecular oxygen with the metal center of transition metal porphyrins (MP, with M $=$ Mn, Fe, Co, and Ni) covalently linked to single-walled carbon nanotubes (CNTs) are addressed by density functional theory calculations. Two geometries for the CNT sidewall functionalization with porphyrin radicals are proposed, considering $s{p}^{2}$ and $s{p}^{3}$ chemical bonds. By computing the stability and electronic properties of the CNT-MP complexes, and the interaction of the O${}_{2}$ molecule with the metal center, we investigate their catalytic activity toward the oxygen reduction reaction (ORR). According to our results, CNT-MnP, CNT-CoP, and CNT-FeP linked by $s{p}^{2}$ covalent bonds are highly stable, preserving the CNT metallic character. We also find a significant O--O bond weakening after the oxygen adsorption on the porphyrin metal center, showing favorable conditions toward ORR. These results support experimental evidences of ORR activity in CNT-based transition metal-N${}_{4}$ centers.

Quantitative trace analysis of benzene using an array of plasma-treated metal-decorated carbon nanotubes and fuzzy adaptive resonant theory techniques

The functionalization of carbon nanotube sidewalls with metal nanoparticles is exploited here to improve the sensitivity and selectivity of gas sensors operated at room temperature. An array of sensors using oxygen plasma treated multiwalled carbon nanotubes (bare and decorated with Pt, Pd or Rh nanoparticles) is shown to selectively detect traces of benzene (i.e., 100 ppb) in the presence of carbon monoxide, hydrogen sulfide or nitrogen dioxide at different humidity levels. Employing a quantitative fuzzy adaptive resonant theory (ART) network whose inputs are the responses of the sensor array, it is possible to accurately estimate benzene concentration in a changing background. The quantitative fuzzy ART is especially suited for compensating the nonlinear effects in sensor response caused by changes in ambient humidity, which explains why this method clearly outperforms partial least squares calibration models at estimating benzene concentration. These results open the way to design new affordable, wearable, sensitive and selective detectors aimed at the personal protection of workers subject to occupational exposure to benzene, toluene, ethyl benzene and xylenes.

Improved electrical conductivity of a non-covalently dispersed graphene–carbon nanotube film by chemical p-type doping

Using a high-pressure air spray we developed a method to deposit electrically-conducting thin films consisting of non-covalently dispersed graphene and carbon nanotubes. The graphene–carbon nanotube film was immersed in a nitric acid and followed by exposure to fuming nitric acid. The acid treatment induced an increased concentration of atomic nitrogen on the graphene basal plane and carbon nanotube sidewall. This result indicates chemical p-type doping of the graphene oxide–carbon nanotube film. After the two acid treatments, the spray coated graphene oxide–carbon nanotube films on a glass substrate exhibit a low sheet resistance of 171 Ω/sq, and a high transmittance of 84% at a wavelength of 550 nm.

Current-induced energy barrier suppression for electromigration from first principles

We present an efficient method for evaluating current-induced forces in nanoscale junctions, which naturally integrates into the nonequilibrium Green's function formalism implemented within density functional theory. This allows us to perform dynamic atomic relaxation in the presence of an electric current while evaluating the current--voltage characteristics. The central idea consists of expressing the system energy density matrix in terms of Green's functions. To validate our implementation, we perform a series of benchmark calculations, both at zero and at finite bias. First we evaluate the current-induced forces acting over an Al nanowire and compare them with previously published results for fixed geometries. Then we perform structural relaxation of the same wires under bias and determine the critical voltage at which they break. We find that although a perfectly straight wire does not break at any of the voltages considered, a zigzag wire is more fragile and snaps at 1.4 V, with the Al atoms moving against the electron flow. The critical current density for the rupture is estimated to be 9.6 \ifmmode\times\else\texttimes\fi{} 10${}^{10}$ A/cm${}^{2}$, in good agreement with the experimentally measured value of 5 \ifmmode\times\else\texttimes\fi{} 10${}^{10}$ A/cm${}^{2}$. Finally, we demonstrate the capability of our scheme to tackle the electromigration problem by studying the current-induced motion of a single Si atom covalently attached to the sidewall of a (4,4) armchair single-walled carbon nanotube. Our calculations indicate that if Si is attached along the current path, then current-induced forces can induce migration. In contrast, if the bonding site is away from the current path, then the adatom remains stable regardless of the voltage. An analysis based on decomposing the total force into a wind and an electrostatic component, as well as on a detailed evaluation of the bond currents, shows that this remarkable electromigration phenomenon is due solely to the position-dependent wind force.

The adsorption of DNA bases on neutral and charged (8, 8) carbon-nanotubes

We report the molecular dynamics simulations of the adsorption of DNA bases on (8, 8) carbon nanotubes (CNTs) in solvent environment. The adsorption processes of bases on neutral and charged CNTs have been observed. Results show that bases can rapidly adsorb on the sidewall of neutral CNTs due to the van der Walls interaction. But the binding geometries of the bases–CNT change with the charge density of CNT, bases no longer stack on highly charged nanotube surfaces. The competition between polarized water and bases results in the instability of the adsorption of DNA based on charged CNTs.

Facile functionalization by π-stacking of macroscopic substrates made of vertically aligned carbon nanotubes: Tracing reactive groups by electrochemiluminescence

We report a simple, fast and reliable non-covalent route of functionalization of macroscopic carbon nanotubes (CNTs) surfaces based on the π-stacking of CNTs sidewall with fluorescein derivatives (i.e., amino- and isothiocyanate-). The electrochemiluminescent emission of Ru(bpy) 3 2+ labels bearing –COOH and –NH 2 side groups coupled with colorimetric and XPS measurements allowed to estimate the quantity of –NH 2 and –N C S functions obtained. The evaluation of reactivity suggests that functionalized CNTs substrates, in particular those carrying –N C S groups, are suitable to covalently bind probe molecules such as proteins and oligonucleotides, thus opening up the possibility of future application in genomics and proteomics fields.

Adsorption of the insensitive explosive TATB on single-walled carbon nanotubes

The non-covalent adsorption of the insensitive explosive TATB (1,3,5-triamino-2,4,6-trinitrobenzene) on the sidewalls of single-walled carbon nanotubes (CNTs) has been calculated using an ONIOM approach. It was found that TATB deformed remarkably when attached non-covalently on the surface of CNTs, especially on the inner wall of the nanotubes. The diameter of the nanotube determined the degree of distortion of the inner-adsorbed TATB, but had little effect on the deformation of the outer-attached TATB. The non-covalent combination of TATB with the nanotube is an exothermic process due to the negative adsorption energy. TATB adsorption on the inner wall of nanotubes was energetically more favorable than that on the outer wall of the nanotubes. In both cases, the adsorption became more stable with increasing diameter of the nanotube. Our theoretical results can be used as a guideline for the design of energetic nanocomposites based on CNTs and aromatic nitro-explosives.