Functionalization Of Single-walled Carbon Nanotubes Research Articles

Vibrational properties of the electrochemically synthesized polyindole/single-walled carbon nanotubes composite

Electrochemical polymerization of indole in a LiClO 4/CH 3CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm −1 is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH 4OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect.

Preparation of carbon nanotube bioconjugates for biomedical applications

Biomedical applications of carbon nanotubes have attracted much attention in recent years. Here, we summarize our previously developed protocols for functionalization and bioconjugation of single-walled carbon nanotubes (SWNTs) for various biomedical applications including biological imaging; using nanotubes as Raman, photoluminescence and photoacoustic labels; sensing using nanotubes as Raman tags and drug delivery. Sonication of SWNTs in solutions of phospholipid-polyethylene glycol (PL-PEG) is our most commonly used protocol of SWNT functionalization. Compared with other frequently used covalent strategies, our non-covalent functionalization protocol largely retains the intrinsic optical properties of SWNTs, which are useful in various biological imaging and sensing applications. Functionalized SWNTs are conjugated with targeting ligands, including peptides and antibodies for specific cell labeling in vitro or tumor targeting in vivo. Radio labels are introduced for tracking and imaging of SWNTs in real time in vivo. Moreover, SWNTs can be conjugated with small interfering RNA (siRNA) or loaded with chemotherapy drugs for drug delivery. These procedures take various times ranging from 1 to 5 d.

Tilted-view transmission electron microscopy-access for chirality assignment to carbon nanotubes integrated in MEMS

Front side etching in combination with sample tilting – instead of wafer through etching – allows for transmission electron microscopy (TEM) investigations on nanostructures integrated in microelectromechanical systems (MEMS). We present electron diffraction (ED) of an individual single-walled carbon nanotube (SWNT) suspended between sharp polysilicon tips on the bulk of a MEMS chip. This novel approach for transmission beam characterization avoids complex wafer backside processing while allowing for chirality assignment to the integrated functional SWNT, as demonstrated here.

Lyotropic Liquid‐Crystalline Solutions of High‐Concentration Dispersions of Single‐Walled Carbon Nanotubes with Conjugated Polymers

The 1D structure of single-walled carbon nanotubes (SWNTs) leads to unique physical properties, which have been investigated extensively. Numerous applications and device prototypes have been demonstrated; however, most have used SWNTs grown in situ by chemical vapor deposition. This limits throughput and choice of substrate owing to the high growth temperatures involved. Solution-based postsynthesis device fabrication, typically involving purification, solubilization, chemical functionalization, cutting, and/ or controlled assembly of SWNTs, is more desirable because of low cost, scalability to large areas, and compatibility with flexible plastic substrates. Unfortunately, SWNTs are not readily soluble, and chemical functionalization strategies for their solubilization usually alter their electronic properties. Furthermore, to take full advantage of the anisotropic charge-transport properties of SWNTs and to enhance their performance in high-strength composite materials, it is necessary to align them over a large area. Noncovalent functionalization of SWNTs is a particularly attractive avenue for dispersion because it enables modification of material properties without altering the chemical structure of the nanotubes. To date, most high-concentration dispersions (>1mg mL ) have been obtained in aqueous solutions by mixing SWNTs with surfactants, doubleor

Functional single-walled carbon nanotubes based on an integrinαvβ3 monoclonal antibody for highly efficient cancer cell targeting

The application of single-walled carbon nanotubes (SWNTs) in the field of biomedicine is becomingan entirely new and exciting topic. In this study, a novel functional SWNT based on an integrinαvβ3 monoclonal antibody was developed and was used for cancer cell targeting in vitro. SWNTswere first modified by phospholipid-bearing polyethylene glycol (PL–PEG). The PL–PEGfunctionalized SWNTs were then conjugated with protein A. A SWNT–integrinαvβ3 monoclonal antibody system (SWNT–PEG–mAb) was thus constructedby conjugating protein A with the fluorescein labeled integrinαvβ3 monoclonal antibody. In vitro study revealed that SWNT–PEG–mAb presented a high targeting efficiency onintegrin αvβ3-positive U87MG cells with low cellular toxicity, while for integrinαvβ3-negative MCF-7 cells, the system had a low targeting efficiency, indicating that thehigh targeting to U87MG cells was due to the specific integrin targeting of themonoclonal antibody. In conclusion, SWNT–PEG–mAb developed in this research isa potential candidate for cancer imaging and drug delivery in cancer targetingtherapy.

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 NH 4OH 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.

The incorporation of single-walled carbon nanotubes into polymerized high internal phase emulsions to create conductive foams with a low percolation threshold

New methods for the incorporation of single-walled carbon nanotubes (SWCNTs) into styrene-divinylbenzene-based high internal phase emulsions (HIPEs) are addressed with specific attention to minimizing the SWCNT loading while maintaining a high level of conductivity of the final polyHIPE–SWCNT composites. Stable HIPEs were achieved using sodium dodecyl sulfate-stabilized SWCNTs, thus eliminating the necessity of SWCNT functionalization. PolyHIPE–SWCNT composites were made with water: oil ratios (vol/vol) of 75:25 and of 84:16. The percolation threshold was determined to be 0.2 and 0.1 wt%, respectively. These threshold values are lower than that obtained for non-porous, polystyrene–SWCNT composites made by means of a latex-based route followed by melt-processing.

Scalable Functional Group Engineering of Carbon Nanotubes by Improved One-Step Nitrene Chemistry

A facile, green, low cost and efficient one-step technology to synthesize highly dispersible functional single-walled and multiwalled carbon nanotubes (f-SWNTs and f-MWNTs) up to supergrams is reported. Large-scale (up to hundreds of grams) synthesis of functional azides was developed at first, and various reactive groups (i.e., −OH, −NH2, −COOH, and −Br) were then introduced onto the convex surfaces of CNTs in merely one reaction of nitrene addition under a relatively mild condition without causing significant damage to nanotubes. The contents of the functional moieties can be easily controlled by adjusting the feed ratio of the azide compounds to CNTs. In order to demonstrate the reactivity and functions of the immobilized organic moieties, different chemical reactions, including surface-initiated polymerizations, amidation, and reduction of metal ions, were performed on the functional CNTs, affording various CNT-polymer and CNT-Pt nanohybrids. The resulting materials were characterized by various measurements, such as TGA, Raman, XPS, FTIR, NMR, XRD, SEM, TEM, and HRTEM. The presented one-step methodology opens the avenue for industrial production of functional CNTs.

First-principles study of the B- or N-doping effects on chemical bonding characteristics between magnesium and single-walled carbon nanotubes

We investigated theoretically the adsorption of individual Mg atoms on single-walled carbon nanotubes (SWCNTs) by first-principles method within density functional theory in order to clarify the binding energies and the electronic structures of Mg atoms contact with SWCNTs. Our results suggest that the interaction of Mg atom adsorbed on pristine SWCNTs, which is normally very weak, can be enhanced upon functionalization of SWCNTs by B- or N-doping. Especially, the B-doping increases dramatically the binding energies of Mg-adsorbed on both armchair and zigzag SWCNTs.

Molecular Dynamics Study of a Nanotube-Binding Amphiphilic Helical Peptide at Different Water/Hydrophobic Interfaces

Many potential applications of single-walled carbon nanotubes (SWNTs) require that they be isolated from one another. This may be accomplished through covalent or noncovalent SWNT functionalization. The noncovalent approach preserves the intrinsic electrical, optical, and mechanical properties of SWNTs and can be achieved by dispersing SWNTs in aqueous solution using surfactants, polymers, or biomacromolecules like DNA or polypeptides. The designed amphiphilic helical peptide nano-1, which contains hydrophobic valine and aromatic phenylalanine residues for interaction with SWNTs and glutamic acid and lysine residues for water solubility, has been shown to debundle and disperse SWNTs, although the details of the peptide-SWNT interactions await elucidation. Here we use fully atomistic molecular dynamics simulations to investigate the nano-1 peptide at three different water/hydrophobic interfaces: water/oil, water/graphite, and water/SWNT. The amphiphilic nature of the peptide is characterized by its secondary structure, peptide-water hydrogen bonding, and peptide-hydrophobic surface van der Waals energy. We show that nano-1 has reduced amphiphilic character at the water/oil interface because the peptide helix penetrates into the hydrophobic phase. The peptide alpha-helix cannot match its hydrophobic face to the rigid planar graphite surface without partially unfolding. In contrast, nano-1 can curve on the SWNT surface in an alpha-helical conformation to simultaneously maximize its hydrophobic contacts with the SWNT and its hydrogen bonds with water. The molecular insight into the peptide conformation at the various hydrophobic surfaces provides guidelines for future peptide design.

Young’s moduli of functionalized single-wall carbon nanotubes under tensile loading

This paper quantitatively investigates the effect of chemical functionalization on the axial Young’s moduli of single-walled carbon nanotubes (SWCNTs) based on molecular mechanics (MM) simulation, in which the COMPASS force field is used to model the interatomic interactions in a nonfunctionalized nanotube or a functionalized nanotube grafted with vinyl groups. We obtain the axial Young’s moduli of both functionalized and nonfunctionalized SWCNTs. The influences of the number and distribution density of the sp3-hybridized carbon atoms and the radius and chirality of the SWCNTs on Young’s moduli are studied. The results indicate that Young’s moduli depend strongly on the chirality of the SWCNTs and the distribution density of the sp3-hybridized carbon atoms. A 37.50% content of sp3-hybridized carbon atoms may degrade Young’s modulus by up to 33.36%. In addition, MM simulations show that the functionalization of SWCNTs results in a decrease of Young’s moduli of the corresponding SWCNT/polyethylene composites.

Theoretical investigation of the stability, electronic and magnetic properties of thiolated single‐wall carbon nanotubes

AbstractThe addition of SH and OH groups to single‐wall carbon nanotubes (SWCNTs) was investigated employing first principles calculations. In the case of the semiconducting (10, 0) SWCNT the SWCNT‐SH binding energy is weak, 2–4 kcal/mol. However, for the metallic (5, 5) SWCNT it is larger, 7–9 kcal/mol. Thus metallic SWCNTs seem to be more reactive to SH than the semiconducting ones. Indeed, the (6, 6) SWCNT is more reactive to SH than the (10, 0) SWCNT, by 2–3 kcal/mol, something that can be explained only considering the electronic structure of the tube, because the (6, 6) has a larger diameter. The binding energies are larger for the addition of the OH group, 25 and 30 kcal/mol for the (10, 0) and (5, 5) SWCNTs, respectively. When a single OH or SH group is attached to the metallic SWCNTs, we observe important changes in the DOS at the Fermi level. However, when multiple SH groups are attached, the changes in the electronic and magnetic properties depend on the position of the SH groups. The small binding energy found for the SH addition indicates that the successful functionalization of SWCNTs with SH, SCH3, and S(CH2)nSH groups is mostly due to the presence of defects created after acid treatment and to a minor extent by the metallic tubes present in the samples. Perfect semiconducting SWCNTs showed very low reactivity against the SH group. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Single-Walled Carbon Nanotube as a Unique Scaffold for the Multivalent Display of Sugars

Single-walled carbon nanotube (SWNT) is a pseudo-one-dimensional nanostructure capable of carrying/displaying a large number of bioactive molecules and species in aqueous solution. In this work, a series of dendritic beta-D-galactopyranosides and alpha-D-mannopyranosides with a terminal amino group were synthesized and used for the functionalization of SWNTs, which targeted the defect-derived carboxylic acid moieties on the nanotube surface. The higher-order sugar dendrons were more effective in the solubilization of SWNTs, with the corresponding functionalized nanotube samples of improved aqueous solubility characteristics. Through the functionalization, the nanotube apparently serves as a unique scaffold for displaying multiple copies of the sugar molecules in pairs or quartets. Results on the synthesis and characterization of these sugar-functionalized SWNTs and their biological evaluations in binding assays with pathogenic Escherichia coli and with Bacillus subtilis (a nonvirulent simulant for Bacillus anthracis or anthrax) spores are presented and discussed.

Two-Phonon Combination Raman Modes in Covalently Functionalized Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes covalently functionalized with chloro-phenyl groups were investigated by Raman spectroscopy. We examine the features observed in the spectral ranges 350−1200, 1650−2000, and 2400−3200 cm−1. The Raman modes associated with the presence of defects, strongly enhanced by the functionalization are clearly distinguished from those defect independent. We indicate that some features highly enhanced by the electron−phonon coupling are very sensitive to charge transfers between the nanotubes and functional groups. A feature at ∼2900 cm−1 is observed in the spectra of functionalized nanotubes, and its origin is explained here as a combination of two disorder-induced modes.

Improved dispersion of carbon nanotubes in chitosan

Carbon nanotubes (CNT)/chitosan films and fibers can find use in specialized applications like the artificial muscles and other intelligent switching devices. The dispersion state of the single walled carbon nanotubes (SWCNTs) in chitosan matrix plays a major role in deciding the ultimate properties of composite. A suitable chemical treatment for purification and functionalization of SWCNTs is reported. Optimal conditions to prepare water soluble and stable, dispersion of SWCNT in chitosan are presented. The dispersion behavior of purified and functionalized SWCNT was characterized by visual observations, transmission electron microscopy (TEM), and Raman spectroscopy. The dispersion obtained using functionalized SWCNT was stable, while the purified SWCNT dispersion showed limited stability. The better stability of functionalized SWCNT dispersion in chitosan was evidenced by improved interaction between chitosan and carboxyl functional groups of SWCNT.

Facile Decoration of Functionalized Single-Wall Carbon Nanotubes with Phthalocyanines via “Click Chemistry”

We describe the functionalization of single-wall carbon nanotubes (SWNTs) with 4-(2-trimethylsilyl)ethynylaniline and the subsequent attachment of a zinc-phthalocyanine (ZnPc) derivative using the reliable Huisgen 1,3-dipolar cycloaddition. The motivation of this study was the preparation of a nanotube-based platform which allows the facile fabrication of more complex functional nanometer-scale structures, such as a SWNT-ZnPc hybrid. The nanotube derivatives described here were fully characterized by a combination of analytical techniques such as Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy (AFM and SEM), and thermogravimetric analysis (TGA). The SWNT-ZnPc nanoconjugate was also investigated with a series of steady-state and time-resolved spectroscopy experiments, and a photoinduced communication between the two photoactive components (i.e., SWNT and ZnPc) was identified. Such beneficial features lead to monochromatic internal photoconversion efficiencies of 17.3% when the SWNT-ZnPc hybrid material was tested as photoactive material in an ITO photoanode.

Bolometric detector on the basis of single-wall carbon nanotube/polymer composite

Infrared imaging sensors that operate without cryogenic cooling have the potential to provide the military or civilian users with infrared vision capabilities packaged in a camera of extremely small size, weight and power consumption. We present here the uncooled bolometric sensor on the basis of single-walled carbon nanotubes (SWNTs) polymer composite with enhanced sensitivity. The voltage responsivity of device working at room temperatures exceeds 150 V/W. The absorption coefficient of single-wall carbon nanotubes was increased by involving Forster type energy transfer from polymer film to dispersed SWNT. The temperature gradient of resistivity was substantially improved by chemical functionalization of SWNT.

Functionalization of Single-Walled Carbon Nanotubes with Azides Derived from Amino Acids Using Click Chemistry

Single-walled carbon nanotubes (SWCNTs) were chemically functionalized with amino acid-based moieties. The covalent functionalization of alkyne-derived SWCNTs with well defined azides derived from amino acids was accomplished through Cu(I)-catalyzed Huisgen [3+2] dipolar cycloaddition click chemistry. Transmission electron microscopy, Raman spectroscopy, and infrared spectroscopic measurements confirmed the functionalization of SWCNTs by organic molecules derived from amino acids, and the resulting material showed some good solubility in the organic solvents such as tetrahydrofuran, CH2Cl2, and CHCl3.

FUNCTIONALIZATION EFFECT ON THE ELECTRONIC PROPERTIES OF SINGLE WALLED CARBON NANOTUBES

OH-functionalized single-walled carbon nanotubes (SWNTs), i.e. SWNT–OH, were prepared through the ball-milling of purified SWNTs with KOH. The composition of the pristine SWNTs bulk sample was characterized by resonance Raman scattering. The OH-functionalization-induced shrinking of the energy gap, the charge transfer from C to –OH, the depletion of top valence band density, the modification of energy band structure and the significant reduction in the work function of SWNTs were experimentally studied by variable temperature FTIR, Raman scattering, ultra-violet photoelectron spectroscopy, X-ray photoelectron energy loss spectroscopy etc. Ab initio calculation was also performed to assist the discussion.

Effective electrical conductivity of functional single-wall carbon nanotubes in aqueous fluids

In this paper, for the first time, we have used a coaxial fixture to successfully obtain the relatively low and precise electrical conductivity values of nanofluids based on functional sulfonated carbon nanotubes. From 0 to 0.5 wt.% nanotube loading, the conductivity increased approximately 13 times. However, no percolation threshold phenomenon is observed. The linear conductivity increase versus the weight percentage indicates that the dominant conduction mechanism might be the ionic conduction, which is in agreement with the chemical structure of functional SWNT (anion SO 3 − group).