Interaction Of Single-walled Carbon Nanotubes Research Articles

PHOTOLUMINESCENCE AND PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY OF SEMICONDUCTING SINGLE WALL CARBON NANOTUBES

Since the discovery of single wall carbon nanotubes (SWNT) in 1991, this nanomaterial has received an enormous attention from the nanoscience and nanotechnology community, not only due to the clear prospects for applications such as novel nanoelectronic and nano-optoelectronic devices, but also because this unique one dimensional (1D) system offered a new possibility for the investigation of novel physical phenomena in low dimensions. In 2002 it was demonstrated that photoluminescence (PL) could be observed in suspensions of isolated SWNTs and, later on, that PL could also be observed from individual, suspended SWNTs. Since then, there has been an increasing amount of work directed towards the investigation of the optical properties of semiconducting SWNTs by PL and photoluminescence excitation spectroscopy (PLE), and the use of PL and PLE for the qualitative and quantitative identification of SWNTs species within and ensemble of carbon nanotubes. In 2005 it was shown that the observed optical transitions are associated to 1D excitons and, from the point of view of optical properties, the rich physics of excitons in SWNTs has received much attention. For instance, it is now clear that excitons and exciton-phonon interactions play a major role in the mechanisms responsible for the emission and the absorption of light in SWNTs. Also, the interaction of SWNTs with their vicinity, which includes the interaction with organic and inorganic molecules, and the modifications in the excitonic system caused by changes in the dielectric constant, can be readily investigated by PL and PLE. In this talk we presented an overview of our recent work in the optical spectroscopy of SWNTs.1–3 In particular, we showed some of our results on the investigation of the exciton-phonon interaction in semiconducting SWNTs and on the modifications in the PL and PLE spectra associated to the interactions with its surrounding environment. Note from Publisher: This article contains the abstract only.

Spectroscopic Evidence for Interaction of Poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] Conformers and Single-Walled Carbon Nanotubes in Solvent Dispersions

Organic photovoltaic devices promise low-cost, flexible options for future renewable energy that will reduce reliance on oil. Single-wall carbon nanotubes (SWCNTs) provide possibilities for increasing the efficiency of organic solar cells through increasing conductivity of composites used in such devices or through use as a charge acceptor in a bulk heterojunction device. We present data to indicate the physical interaction of SWCNTs with a conjugated polymer, poly[2'-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), on the basis of the spectroscopic assignments of various conformational species of different optical signature in N,N-dimethylacetamide (DMA) dispersions. We go on to show that energy transfer from nonaggregated MEH-PPV leads to enhanced SWCNT fluorescence in solutions of poorer solvent quality. Energy transfer from polymer chain lengths that are torsionally restricted is not observed. This would suggest that any electron transfer taking place is occurring through a concerted Dexter mechanism and that use of SWCNTs as an electron acceptor will likely have associated drawbacks.

A Comparative Study of Poly(3-octylthiophene) and Poly(3-hexylthiophene) Solar Cells Blended with Single Walled Carbon Nanotubes

Poly(3-hexylthiophene) (P3HT):single walled carbon nanotube (SWNT) and poly(3-octylthiophene) (P3OT):SWNT thin films and bulk heterojunction solar cells were fabricated with 0, 1, and 2 wt % of SWNTs. The current density in P3HT is found to be higher than that of P3OT by an order of magnitude at 5 V. Hole mobility in P3HT is found to be higher than in P3OT. Photoluminescence measurements show that the nature of electronic interaction of SWNTs with P3OT and P3HT is not same. For P3OT:SWNT (1 wt %) devices, a ∼3 times increase in the short circuit current density Jsc was obtained compared to pristine P3OT device. For P3HT:SWNT devices, no such improvement was found. The open circuit voltage Voc of P3HT:SWNT (1 wt %) solar cell was found to be 0.82 V while 1.2 V was obtained for P3OT:SWNT (1 wt %) solar cell. This is higher than 0.98 V previously reported for similar solar cells. It is found that the Voc decreases with increase in SWNT content due to the SWNTs acting as shunt paths between anode and cathode.

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.

Noncovalent Assembly of Carbon Nanotubes and Single-Stranded DNA: An Effective Sensing Platform for Probing Biomolecular Interactions

In this paper, we report the assembly of single-walled carbon nanotubes (SWNTs) and single-stranded DNA to develop a new class of fluorescent biosensors which are able to probe and recognize biomolecular interactions in a homogeneous format. This novel sensing platform consists of a structure formed by the interaction of SWNTs and dye-labeled DNA oligonucleotides such that the proximity of the nanotube to the dye effectively quenches the fluorescence in the absence of a target. Conversely, and very importantly, the competitive binding of a target DNA or protein with SWNTs for the oligonucleotide results in the restoration of fluorescence signal in increments relative to the fluorescence without a target. This signaling mechanism makes it possible to detect the target by fluorescence spectroscopy. In the present study, the schemes for such fluorescence changes were examined by fluorescence anisotropy and fluorescence intensity measurements for DNA hybridization and aptamer-protein interaction studies.

Interaction of SWCNT and PPTA with sulfuric acid—Compatibilization of two materials in a common solvent

AbstractThe results of a calorimetric study on the melting and crystallization behavior of concentrated sulfuric acid containing dispersed single wall carbon nanotubes (SWCNT), dissolved water, and dissolved poly‐p‐phenyleneterphthalate (PPTA) polymer are presented. The measured reduction of the heat of crystallization is caused by the build‐up of an associated layer of structured acid molecules around SWCNT and PPTA. The freezing point depression is related to the number of dissolved species such as ions. It is shown that this theory accurately describes the experimental data for dissolved water and sulfur trioxide, but not for large molecules such as SWCNT. A mechanism for the interaction between sulfuric acid and SWCNT is proposed, based on preferred adsorption of sulfur trioxide and dissociation of sulfuric acid, leading to an increased number of dissolved low‐molecular‐weight species. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1914–1922, 2008

Intracellular uptake, trafficking and subcellular distribution of folate conjugated singlewalled carbon nanotubes within living cells

Herein we studied the uptake, trafficking and distribution of folate conjugated single walledcarbon nanotubes (SWNTs) within living cells. SWNTs were noncovalently functionalizedwith chitosan and then linked with folate acid and fluorescence dye Alexa Fluor 488(denoted FA-SWNTs). Hep G2 cells were cultured in vitro and incubated with FA-SWNTsat different levels. The FA-SWNTs exhibited a concentration-dependent uptake withinHep G2 cells, and Hep G2 cells were able to internalize FA-SWNTs via a folatereceptor-mediated pathway. The distribution of nanotubes inside cells demonstratedthat the FA-SWNTs only locate in the cytoplasm and not in nuclei, indicatingthe failure of transporting through the nuclear envelope. Transmission electronmicroscope (TEM) results showed the presence of FA-SWNTs in lysosomes and thedischarge to extracellular space after incubation with nanotubes for 5 h. No obviouscellular death rate was observed when the concentration of nanotubes was below50 µg ml−1. However, cells with FA-SWNT uptake showed a concentration-dependent apoptosis.These discoveries might be helpful for understanding the interaction of SWNTs and livingcells.

Charge transfer composites of bis(cyclopentadienyl) and bis(benzene) transition metal complexes encapsulated in single-walled carbon nanotubes

The interaction of two organometallic $\ensuremath{\pi}$-aryl $(M{L}_{2})$ complexes, cobaltocene $[\mathrm{Co}{({\ensuremath{\eta}}^{5}\text{\ensuremath{-}}{\mathrm{C}}_{5}{\mathrm{H}}_{5})}_{2}]$ and bis(benzene) chromium $[\mathrm{Cr}{({\ensuremath{\eta}}^{6}\text{\ensuremath{-}}{\mathrm{C}}_{6}{\mathrm{H}}_{6})}_{2}]$, with a series of semiconducting $(n,0)$ $(n=11--18)$ single-walled carbon nanotubes (SWNT) has been investigated using density-functional theory calculations. Dependence of the $M{L}_{2}$-SWNT interaction on the diameter and band structure of the nanotube was studied. We find that both cobaltocene and bis(benzene) chromium act as electron donors to form composites ${[M{L}_{2}]}^{q+}{[\mathrm{SWNT}]}^{q\ensuremath{-}}$ in which the extent of the charge transfer, and hence the binding energy, is modulated by the diameter and band structure of the nanotube. The relative influence of the ionization energy of the $M{L}_{2}$ complexes and the electron attachment energy of the SWNT on the binding energy for these composites is described.

Mechanico‐chemical interaction of SWNTs with different host matrices evidenced by SERS spectroscopy

AbstractSurface enhanced Raman scattering (SERS) performed with 676.4 and 1064 nm excitations were used to investigate single‐walled carbon nanotubes (SWNTs) thin films prepared from platelets obtained by non‐hydrostatic compression at 0.58 GPa. SWNTs were compressed alone or dispersed into chemical reactive and non‐reactive host matrices. SERS spectra indicate that by compression, SWNTs break into fragments of different sizes, which in turn can react or not with the host matrix. In inorganic hosts (KI, Ag) donor‐acceptor complexes are formed. The appearance of short fragments of SWNTs with a closed‐shell fullerenes behaviour is revealed in SERS spectra. This typical signature appears in the Raman spectrum as a line at ca. 1460 cm–1 associated with a pentagonal pinch mode. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Controlling the shape, orientation, and linkage of carbon nanotube features with nano affinity templates.

Directed assembly of nanoscale building blocks such as single-walled carbon nanotubes (SWNTs) into desired architectures is a major hurdle for a broad range of basic research and technological applications (e.g., electronic devices and sensors). Here we demonstrate a parallel assembly process that allows one to simultaneously position, shape, and link SWNTs with sub-100-nm resolution. Our method is based on the observation that SWNTs are strongly attracted to COOH-terminated self-assembled monolayers (COOH-SAMs) and that SWNTs with lengths greater than the dimensions of a COOH-SAM feature will align along the boundary between the COOH-SAM feature and a passivating CH3-terminated SAM. By using nanopatterned affinity templates of 16-mercaptohexadecanonic acid, passivated with 1-octadecanethiol, we have formed SWNT dot, ring, arc, letter, and even more sophisticated structured thin films and continuous ropes. Experiment and theory (Monte Carlo simulations) suggest that the COOH-SAMs localize the solvent carrying the nanotubes on the SAM features, and that van der Waals interactions between the tubes and the COOH-rich feature drive the assembly process. A mathematical relationship describing the geometrically weighted interactions between SWNTs and the two different SAMs required to overcome solvent-SWNT interactions and effect assembly is provided.

Adsorption of Organic Vapors on Single-Walled Carbon Nanotubes

Adsorption properties of single-walled carbon nanotubes (SWNTs) were investigated using standard gravimetric techniques. Equilibrium vapor-phase adsorption isotherms were measured for three fundamentally different molecules on SWNTs of two different diameters (12 and 16.8 Å). SWNT interactions with aromatic (benzene), aromatic and heterocyclic (thiophene), and nonaromatic (cyclohexane) molecules were investigated, as well as the effects of diameter on adsorption. Stronger adsorption was observed for the smaller SWNTs. Isosteric heats of adsorption were calculated from the adsorption isotherms and followed the order thiophene > benzene> cyclohexane. Furthermore, batch adsorption experiments were performed to investigate the feasibility of desulfurization of fuels using SWNTs. Batch experiments were performed to verify preferential adsorption of thiophene over benzene using a model fuel. Selectivity for thiophene over benzene was demonstrated, and a test with a commercial diesel sample was performed. Heat treatments were found to increase the sulfur capacity. Removal of sulfur species was comparable to that of BPL activated carbon.

Photoexcited electron relaxation processes in single-wall carbon nanotubes

The relaxation processes for photoexcited electrons in single-wall carbon nanotubes (SWNTs) are discussed in connection with recent photoluminescence excitation (PLE) spectroscopy experiments. The electron-phonon $(e\text{\ensuremath{-}}\mathrm{ph})$ interaction of SWNTs is calculated for each phonon mode as a function of photoexcited electron energy. Because of the cylindrical surface of a SWNT, the twisting and radial breathing phonon modes are responsible for the $e\text{\ensuremath{-}}\mathrm{ph}$ interaction in the lower phonon energy region. Optic phonon modes are also responsible for the relaxation of photoexcited electrons. Compared with graphite, the relaxation of electrons is much faster in SWNTs because of their cylindrical shape. We identify and explain some aspects of both photoluminescent and Raman processes appearing in PLE plots for SWNTs.

Ordering and interaction of molecules encapsulated in carbon nanotubes

A clear understanding of the interactions between the building blocks of self-assembled molecular materials is essential for rational design of functional nanostructures. Intermolecular interactions have been investigated for three different classes of fullerenes in single-walled carbon nanotubes (SWNTs); van der Waals molecule – molecule and molecule – SWNT interactions control the geometry of the molecular arrays inside nanotubes; electrostatic intermolecular forces influence the alignment of polar endohedral fullerenes M@C82; and hydrogen bonding between functionalised fullerenes has a significant effect on the selectivity of insertion of functionalised fullerenes into SWNTs.

Solubilization of single-wall carbon nanotubes by supramolecular encapsulation of helical amylose.

We have developed a simple, efficient process for solubilization of single-wall carbon nanotubes (SWNTs) with amylose in aqueous DMSO. This process requires two important conditions, presonication of SWNTs and subsequent amylose treatment in an optimum mixture of DMSO/H2O. The former step separates SWNT bundles, and the latter step provides a maximum cooperative interaction of SWNTs with amylose, leading to the immediate and complete solubilization. The best solvent condition for this is around 10-20% DMSO, in which amylose assumes a random conformation or an interrupted helix. This indicates that the amylose helix is not the prerequisite for encapsulation of SWNTs. The SEM and AFM images of the encapsulated SWNTs manifest loosely twisted ribbons wrapping around SWNTs, which are locally intertwined as a multiple twist, but no clumps of the host amylose are seen on SWNT capsules.

Single-walled carbon nanotube–amylopectin complexes

Single-walled carbon nanotubes (SWCNTs) are wetted in aqueous solution of pure potato and waxy corn amylopectins. Formation of weak sorption complexes of amylopectins on carbon nanotubes is postulated based on the micro-Raman spectra, differential scanning calorimetric and thermogravimetric studies as well as scanning electron micrographs and atomic force microscope images. Under an influence of ultrasounds bundles of SWCNTs disintegrated much more readily in aqueous solution of waxy corn amylopectin. In the solid state resulting from evaporation of suspensions to dryness interactions of SWCNTs with waxy corn amylopectin were also stronger than with potato amylopectin.