Sidewalls Of Single-walled Carbon Nanotubes Research Articles

Analysis of the Relationship between Reaction Energies of Electrophilic SWNT Additions and Sidewall Curvature: Chiral Nanotubes

The relationship of reaction energies for CH2/NH/O exo- and endo-[2 + 1] cycloadditions to chiral single-walled carbon nanotube (SWNT) sidewalls with the inverse tube diameter (1/d) was investigated using density functional theory (DFT) and density functional tight binding (DFTB) methods. We considered additions to the three nonequivalent C−C bond types t (bond most parallel to tube axis), d (“diagonal” bond, slightly skewed), and p (bond most perpendicular to tube axis), using hydrogen-terminated (2n,n) SWNT model systems with n = 2−8. Exoadditions are classified into two types, one where the original C−C bond is broken (exo(l)), and one where it remains intact (exo(s)) in the addition complex. Endoadditions are found to always belong to the latter (endo(s)) type. It is found that (a) exoadditions are more exothermic than endo additions, and (b) that exoadditions are more exothermic with larger bond-tube axis angle (p > d > t). A nearly perfect linear relationship between the total reaction energy ΔE and...

One-Pot Synthesis of Carbon Nanotube-Polyaniline-Gold Nanoparticle and Carbon Nanotube-Gold Nanoparticle Composites by Using Aromatic Amine Chemistry

Harsh oxidative treatment of single-walled carbon nanotubes (SWNTs) was used to generate carboxyl groups on SWNT sidewalls. The oxidized SWNTs can disperse well in ethanolic solutions containing aniline (or it derivative, 4-dodecylaniline), possibly due to the formation of proton-transfer complexes between carboxyl and amine groups. Addition of HAuCl 4 into the above-mentioned solutions can readily produce SWNT-polyaniline (PANI)-Au nanoparticle (NP) or SWNT-Au NP composites in an in situ one-pot fashion. Transmission electron microscopy, UV-vis spectroscopy and cyclic voltammetry have been employed to characterize the obtained composites. Our findings suggest that the obtained composites and electrodes modified with this material may find interesting applications in electrochemical sensors and conducting polymer coatings.

Demonstration of covalent sidewall functionalization of single wall carbon nanotubes by NMR spectroscopy: Side chain length dependence on the observation of the sidewall sp3 carbons

Carboxylic acid-functionalized single walled carbon nanotubes (SWNTs) prepared via the reaction of an amino acid, NH2(CH2) n CO2H where n = 1 (glycine, GLY), 5 (6-aminohexanoic acid, AHA), 10 (11-aminoundecanoic acid, AUDA), with fluorinated single walled carbon nanotubes (F-SWNTs) have been characterized by MAS 13C NMR spectroscopy. The ease of observing the aliphatic CH2 groups and the resolution of the signal are dependent on the length of the amino acid’s aliphatic chain. We have proposed that where substituent chains are short (making NMR data collection difficult) chemical modification to extend the chain length should alleviate analysis problems. In this regard, we have investigated the esterification of the carboxylic acid termini. The amino acid-functionalized SWNTs were esterified with an appropriate alcohol to ensure parity of the overall substituent length, i.e., GLY-SWNT (C1) + 1-dodecanol (C12) = DOD-GLY-SWNT (1), AHA-SWNT (C5) + 1-octanol (C8) = OCT-AHA-SWNT (2), and AUDA-SWNT (C10) + 1-propanol (C3) = PRO-AUDA-SWNT (3). The 13C NMR shift for the sp3 nitrogen-substituted carbon atoms of the SWNT sidewall is observed at δ ≈ 75 ppm. Increasing the length of SWNT sidewall functional groups enhances the ability to observe the sidewall sp3 carbon. The methylene carbon signal intensity is less attenuated in the dipolar dephasing spectrum of the ester-functionalized SWNTs than their associated amino acid derivatives, suggesting more motional freedom of the side chain in the solid state. The confirmation of the dipolar dephasing spectral effects was assisted by the characterization of the ester of AUDA-SWNT with 1,3-propanediol: PPD-AUDA-SWNT (4).

Electrochemical Opening of Single-Walled Carbon Nanotubes Filled with Metal Halides and with Closed Ends

The electrochemical opening of closed-ended, pristine single-walled carbon nanotubes (SWCNTs) upon the application of either a sufficiently oxidizing or reducing electrode potential is reported. Hitherto, it has been unclear whether the side walls of SWCNTs are electrochemically active, or whether, like their multiwalled counterparts (MWCNTs), the electroactive sites on SWCNTs also reside at the edge-plane-like defects at the open ends of the tubes. Evidence is presented herein that suggests the latter case is true, i.e., that SWCNTs require edge-plane sites to be electroactive. Comparisons of the voltammetric response of end-closed SWCNTs (EC-SWCNTs), end-open (EO-SWCNTs), and SWCNTs encapsulating a metal halide filling (MX@SWCNTs, where MX represents either NaI or CuI) in aqueous electrolytes indicate that SWCNTs undergo electrochemical opening if the applied electrode potential is greater than +1.2 V vs SCE or less than −1.5 V vs SCE. This was further confirmed using ex situ X-ray photoelectron spectroscopy. The nonaqueous voltammetry of NaCl@SWCNTs, NaI@SWCNTs, CuI@SWCNTs, and ZnCl2@SWCNTs in dimethyl formamide (DMF) containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) all exhibited voltammetric responses identical to that of EC-SWCNTs unless the potential was cycled beyond ca. +1.6 V vs Ag (+2.129 V vs the cobaltocene/cobaltocenium redox couple) whereupon voltammetry corresponding to the filling material was observed, again indicating that the SWCNTs had become open-ended. Evidence for quantized charging of the EC-SWCNTs is presented in terms of the unusual “bow-tie” shape of the background charging current in DMF is also presented.

Scaffolding carbon nanotubes into single-molecule circuitry

While nanowires and nanotubes have been shown to be electrically sensitive to various chemicals, not enough is known about the underlying mechanisms to control or tailor this sensitivity. By limiting the chemically sensitive region of a nanostructure to a single binding site, single molecule precision can be obtained to study the chemoresistive response. We have developed techniques using single-walled- carbon-nanotube (SWCNT) circuits that enable single-site experimentation and illuminate the dynamics of chemical interactions. Discrete changes in the circuit conductance reveal chemical processes happening in real-time and allow SWCNT sidewalls to be deterministically broken, reformed, and conjugated to target species.

Nanoassembly of meso-Tetraphenylporphines on Surfaces of Carbon Materials: Initial Steps as Studied by Molecular Mechanics and Scanning Tunneling Microscopy

We employed MM+ molecular mechanical modeling and scanning tunneling microscopy (STM) in order to analyze the initial steps of nanoassembly of meso-tetraphenylporphine H2TPP and its cobalt(II) complex CoTPP on the surface of highly-oriented pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs). According to the MM+ results, monolayer H2TPP adsorption is more favorable energetically than the formation of porphyrin stacks on both graphite and nanotube sidewall; the formation of parallel interacting chains of H2TPP on graphite is more preferable than the growth of long single chains; and the assembly into a long-period helix is favored versus the formation of a short-period helix on SWNT sidewall. STM observations of CoTPP complex deposited onto bare HOPG and onto the graphite with deposited SWNTs are consistent with theoretical results. At the same time, both CoTPP single chains and ribbons were observed on HOPG. The formation of short-period helices on the nanotube sidewalls was concluded to be more likely than the long-period helical nanoassembly.

Photoinduced Self‐Assembly of TiO2 and SiO2 Nanoparticles on Sidewalls of Single‐Walled Carbon Nanotubes

Titanium oxide and silicon oxide nanoparticles (TiO2 and SiO2 NPs) are selectively self-assembled on the sidewalls of single-walled carbon nanotubes (SWNTs) grown on a p-type Si substrate by using a simple UV irradiation in an aqueous media. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2007/c2660_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Density functional theory calculations of ozone adsorption on sidewall single-wall carbon nanotubes with Stone-Wales defects

In this study, we employed density functional theory to investigate the adsorption mechanisms of O 3 on the sidewalls of C(5,5), C(8,8), and C(10,0) single-wall carbon nanotubes (SWCNTs), also having Stone-Wales (SW) defects with different orientations. An understanding of the adsorption of O 3 on SWCNT sidewalls with SW defects was obtained by examining local structural changes, described by the pyramidalization angle, while in investigating the electronic structure of ozonized SWCNT, the results were found to be consistent with experimental observations in some cases.

Radical functionalization of single-walled carbon nanotubes with azo(bisisobutyronitrile)

The isobutyronitryl groups from thermal decomposition of azobisisobutyronitrile in a 1,2-dichlorobenzene solution were successfully attached to the sidewalls of single-walled carbon nanotubes; thermogravimetic analysis shows a weight loss of 20% (compared to raw SWNTs), which was calculated to be ca. 1 isobutyronitryl group in 23 carbon atoms.

Synthesis and electroactivity of carbon-nanomaterials-supported Pd nanoparticles from self-regulated reduction of sodium n-dodecyl sulfate

This report describes that the Pd nanoparticles are prepared and decorated successfully at the sidewalls of single-walled carbon nanotubes, multiwall carbon nanotubes, and graphite nanofibers without any surface pretreatments by self-regulated reduction of sodium n-dodecyl sulfate. As supported by electrochemical measurements, the newly prepared Pd-nanoparticles-decorated carbon nanomaterials are found to have the high activity for oxygen reduction.

Noncovalent Functionalization of Carbon Nanotubes by Fluorescein−Polyethylene Glycol: Supramolecular Conjugates with pH-Dependent Absorbance and Fluorescence

We report the use of fluorescein−polyethylene glycol (Fluor-PEG) to noncovalently functionalize single-walled carbon nanotubes (SWNTs) for obtaining water-soluble nanotube conjugates (Fluor-PEG/SWNT) and simultaneously affording fluorescence labels to nanotubes. We find serendipitously that fluorescein, a widely used fluorophore, can strongly adsorb onto the sidewall of the SWNTs, likely via π-stacking, and the hydrophilic PEG chain imparts high aqueous solubility. Interaction between fluorescein and SWNT is pH dependent; it weakens as the pH is increased, causing the Fluor-PEG/SWNT conjugate to be less stable at high pHs. Fluorescein molecules bound to SWNTs exhibit interesting pH-dependent optical absorbance and fluorescence properties that are distinct from free molecules, as a result of pH-dependent interactions with SWNT sidewalls. Fluorescence emission from fluorescein adsorbed on SWNT is quenched by ∼67%, but remains sufficient and useful as a fluorescent label. The utility of Fluor-PEG/SWNT as a s...

Conductance-Controlled Point Functionalization of Single-Walled Carbon Nanotubes

We used covalent attachments to single-walled carbon nanotubes (SWNTs) to fabricate single-molecule electronic devices. The technique does not rely on submicrometer lithography or precision mechanical manipulation, but instead uses circuit conductance to monitor and control covalent attachment to an electrically connected SWNT. Discrete changes in the circuit conductance revealed chemical processes happening in real time and allowed the SWNT sidewalls to be deterministically broken, reformed, and conjugated to target species. By controlling the chemistry through electronically controlled electrochemical potentials, we were able to achieve single chemical attachments. We routinely functionalized pristine, defect-free SWNTs at one, two, or more sites and demonstrated three-terminal devices in which a single attachment controls the electronic response.

Synthesis and characterization of polyethylene chains grafted onto the sidewalls of single-walled carbon nanotubes via copolymerization

Polyethylene (PE) chains grafted onto the sidewalls of SWCNTs (SWCNT-g-PE) were successfully synthesized via ethylene copolymerization with functionalized single-walled carbon nanotubes (f-SWCNTs) catalyzed by rac-(en)(THInd)(2)ZrCl2/ MAO. Here f-SWCNTs, in which alpha-alkene groups were chemically linked on the sidewalls of SWCNTs, were synthesized by Prato reaction. The composition and microstructure of SWCNT-g-PE were characterized by means of H-1 NMR, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analyses (TGA), field-emission scanning electron microscope (FESEM), and transmission electron microscope (TEM). Nanosized cable-like structure was formed in the SWCNT-g-PE, in which the PE formed a tubular shell and several SWCNTs bundles existed as core. The formation of the above morphology in the SWCNT-g-PE resulted from successfully grafting of PE chains onto the surface of SWCNTs via copolymerization. The grown PE chains grafted onto the sidewall of the f-SWCNTs promoted the exfoliation of the mass nanotubes. Comparing with pure PE, the physical mixture of PE/f-SWCNTs and in situ PE/SWCNTs mixture, thermal stability, and mechanical properties of SWCNT-g-PE were higher because of the chemical bonding between the f-SWCNTs and PE chains.

Scaffolding Carbon Nanotubes into Single-Molecule Circuitry

AbstractWhile nanowires and nanotubes have been shown to be electrically sensitive to various chemicals, not enough is known about the underlying mechanisms to control or tailor this sensitivity. By limiting the chemically sensitive region of a nanostructure to a single binding site, single molecule precision can be obtained in order to study the chemoresistive response. We have developed techniques using single-walled-carbon-nanotube (SWCNT) circuits that enable single-site experimentation and illuminate the dynamics of chemical interactions. Discrete changes in the circuit conductance reveal chemical processes happening in real-time and allow SWCNT sidewalls to be deterministically broken, reformed, and conjugated to target species.

Origin of the Linear Relationship between CH2/NH/O−SWNT Reaction Energies and Sidewall Curvature: Armchair Nanotubes

The origin of the linear relationship between the reaction energy of the CH2/NH/O exo and endo additions to armchair (n, n) single-walled carbon nanotubes (SWNTs) and the inverse tube diameter (1/d) measuring sidewall curvature was elucidated using density functional theory and density functional tight binding methods for finite-size SWNT models with n = 3, 4, ..., 13. A nearly perfect linear relationship between DeltaE and 1/d all through exohedral (positive curvature) and endohedral (negative curvature) additions is due to cancellation between the quadratic contributions of the SWNT deformation energy and the interaction energy (INT) between the deformed SWNT and CH2/NH/O adducts. Energy decomposition analysis shows that the quadratic contributions in electrostatic, exchange, and orbital terms mostly cancel each other, making INT weakly quadratic, and that the linear 1/d dependence of INT, and therefore of DeltaE, is a reflection of the 1/d dependence of the back-donative orbital interaction of b1 symmetry from the occupied CH2/NH/O p pi orbital to the vacant C=C pi* LUMO of the SWNT. We also discuss the origin of the two isomers (open and three-membered ring) of the exohedral addition product and explain the behavior of their associated minima on the C-C potential energy surfaces with changing d.

Functionalization of single‐walled carbon nanotubes by aromatic molecules studied by scanning tunneling microscopy

AbstractA functionalization of single‐walled carbon nanotubes (SWCNTs) without the necessity to introduce defects to the atomic structure of the graphitic lattice can be achieved via π‐stacking interaction of the SWCNTs sidewalls with aromatic molecules. In our work we study the functionalization of SWCNTs with two different aromatic molecules by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Functionalization was performed in solution and the SWCNTs so obtained were transfered to a sputter‐annealed Au(111) substrate using dry transfer techniques in vacuum to avoid surface contamination. Differential conductance imaging of the atomically resolved functionalized SWCNT reveals a substructure which can be attributed to the molecular orbitals of aminoanthracene. These findings are compared to the STM images obtained from the bare molecule prepared by thermal evaporation on a clean Au(111) surface which are interpreted with the help of quantum chemical calculations of the molecular orbital structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An integrated route for purification, cutting and dispersion of single-walled carbon nanotubes

We have developed purification and cutting process of single-walled carbon nanotubes (SWNTs) by integrating (1) an acid reflux treatment to eliminate metal particles, (2) an ultrasonication in the H 2SO 4/HNO 3 and H 2SO 4/H 2O 2 to cut and polish the SWNTs, respectively, and (3) an ammonia gas treatment to remove residual carbon impurities and to repair the sidewalls of SWNTs. The final products with a higher purity than 98% are well dispersed in aqueous solution using Pluronic P123 dispersant, which has been rarely used for the SWNTs dispersion. The dispersed SNWTs solution can exist stably for over two months.

On SOCl 2 hydrolysis at carbon nanotubes

The experimentally observed oxygen content increase in SOCl 2 treated single-wall carbon nanotubes (SWCNTs) may be explained by the air moisture hydrolysis of the acid-chloride groups created at the structure defects as well as of SOCl 2 molecules adsorbed at SWCNT sidewalls. The adsorption of SOCl 2, and its hydrolysis products ( HOSO 2 - , HSO 3 - and SO 2 ) on coronene C 24H 12 as the simple SWCNT model has been studied at B3LYP/6-31+G ∗∗ level of theory (with relevant hydrogen atoms augmented by diffusion functions as well). Whereas the adducts with neutral molecules exhibit weak interactions of sulphur (SOCl 2 and SO 2) or oxygen (SOCl 2) atoms with π electron system of coronene, these interactions with cations are mediated via hydrogen bonds only. The optimal geometries indicate high affinity of all the adsorbed species to the structure defects (edges). The physisorption (especially of SOCl 2 and SO 2) produces a small gap, i.e. a tendency towards metallic character as seen in graphene sheets.

Specific Vectorial Immobilization of Oligonucleotide‐Modified Yeast Cytochrome c on Carbon Nanotubes

Iso-1-cytochrome c from the yeast Saccharomyces cerevisiae (YCC) contains a surface cysteine residue, Cys102, that is located opposite to the lysine-rich side containing the exposed heme edge, which is the docking site for enzymes. Site-specific vectorial immobilization of YCC via Cys102 on single-walled carbon nanotubes (SWNT) thus provides a selective interface between nanoscopic electronic devices and complex enzymes. We have achieved this by modification of Cys102 with an oligonucleotide (dT(18)). Atomic force microscopy, fluorescence imaging, and cyclic voltammetry show the specific adsorption of YCC, modified with dT(18), on the SWNT sidewall with retention of its native properties. Pretreatment of the SWNT with Triton-X405 blocks the nonspecific binding of untreated YCC but does not interfere with binding of the oligonucleotide-modified YCC.

Carbon Nanotube DNA Sensor and Sensing Mechanism

We report the fabrication of single-walled carbon nanotube (SWNT) DNA sensors and the sensing mechanism. The simple and generic protocol for label-free detection of DNA hybridization is demonstrated with random sequence 15mer and 30mer oligonucleotides. DNA hybridization on gold electrodes, instead of on SWNT sidewalls, is mainly responsible for the acute electrical conductance change due to the modulation of energy level alignment between SWNT and gold contact. This work provides concrete experimental evidence on the effect of SWNT-DNA binding on DNA functionality, which will help to pave the way for future designing of SWNT biocomplexes for applications in biotechnology in general and also DNA-assisted nanotube manipulation techniques.