Changes In Single-walled Carbon Nanotubes Research Articles

An efficient method to quantitatively detect competitive adsorption of DNA on single-walled carbon nanotube surfaces

In this study, we quantitatively detected adsorption and desorption of DNA molecules that competed with sodium cholate (SC) molecules on single-walled carbon nanotubes (SWNTs) by fluorescence spectroscopy. In previous studies, competitive adsorption and/or replacement were studied based on techniques such as near-infrared (NIR) absorbance and photoluminescence (PL) spectroscopy of SWNTs. In those studies, adsorption of organic molecules was detected as spectral changes in SWNTs, but not in organic molecules. In this study, we employed fluorescent-labeled DNA (Fc-DNA) to detect competitive adsorption through quenching of fluorescent dyes that were attached to DNA molecules. Through this approach, the adsorption behaviors of DNA molecules could be directly determined. Hence, we found that Fc-DNA molecules adsorbed on SWNT surfaces that were pre-wrapped with SC when the SC concentration was reduced. However, when SC concentrations recovered after three days of incubation, detachment of Fc-DNA molecules was observed. In addition, our method could be applied to evaluate the adsorption of fluorescent dyes on SWNT surfaces instead of DNA molecules. Hence, our method is effective in studying competitive adsorption of organic molecules on SWNT surfaces. The obtained information is complementary to that obtained from NIR spectroscopy of SWNTs.

Peptide secondary structure modulates single-walled carbon nanotube fluorescence as a chaperone sensor for nitroaromatics

A class of peptides from the bombolitin family, not previously identified for nitroaromatic recognition, allows near-infrared fluorescent single-walled carbon nanotubes to transduce specific changes in their conformation. In response to the binding of specific nitroaromatic species, such peptide-nanotube complexes form a virtual "chaperone sensor," which reports modulation of the peptide secondary structure via changes in single-walled carbon nanotubes, near-infrared photoluminescence. A split-channel microscope constructed to image quantized spectral wavelength shifts in real time, in response to nitroaromatic adsorption, results in the first single-nanotube imaging of solvatochromic events. The described indirect detection mechanism, as well as an additional exciton quenching-based optical nitroaromatic detection method, illustrate that functionalization of the carbon nanotube surface can result in completely unique sites for recognition, resolvable at the single-molecule level.

Theoretical investigation of [5,5], [9,0] and [10,10] closed SWCNTs

Hartree–Fock and density functional theory calculations were performed on closed single-walled carbon nanotubes (SWCNTs) with the number of atoms up to 400. The calculated results demonstrate that the HOMO–LUMO gaps of [5,5]- and [9,0]-SWCNTs change with a different manner from those of [10,10]-SWCNTs and they are all dependent on their diameters and lengths. The calculated total energies per carbon and energy gaps of these SWCNTs demonstrate that the stability order is [10,10]>[9,0]≈[5,5]-SWCNTs with the same number of atoms. The calculated average bond lengths (ABLs) decrease with the number of atoms and the ABLs of SWCNTs with smaller diameters are larger than those of SWCNTs with larger diameters.

Bending buckling of single-walled carbon nanotubes by atomic-scale finite element

This paper employs the atomic-scale finite element method to study bending buckling of single-walled carbon nanotubes (SWNTs). As the bending angle increases, kinks will appear and the morphology of the SWNT will change abruptly. The (15, 0) SWNT changes into a one-kinked structure, and finally contains two kinks; while the (10, 0) SWNT changes into a one-kinked structure, then into a two-kinked one, and finally contains three kinks. Strain energy grows initially as a quadratic function of bending angle, then increases gradually slowly, and finally changes approximately linearly. The energy releases suddenly at morphology bifurcations and the amount depends on degree of morphology change. The simulation shows that the appearance of kinks associated with the large deformation nearby reduces the slope of the strain energy curve in the post-buckling stages and hence increases the flexibility of the SWNTs.

Structural properties of carbon peapods under extreme conditions studied usingin situx-ray diffraction

Structural properties of carbon peapods, ${\mathrm{C}}_{60}$, trapped into single-walled carbon nanotubes (SWNT), have been studied under high-pressure/high-temperature conditions (HPHT) by in situ x-ray diffraction. The ${\mathrm{C}}_{60}$ chain structure together with the influence of the filling on the SWNT change under HPHT treatment is investigated. Synthesis of a one-dimensional polymer chain of ${\mathrm{C}}_{60}$ inside the single-walled carbon nanotubes is evidenced. At $4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, increasing the temperature up to $1023\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ leads to a progressive ${\mathrm{C}}_{60}$ polymerization that is associated to a shortening of ${\mathrm{C}}_{60}\text{\ensuremath{-}}{\mathrm{C}}_{60}$ distance down to $8.7\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Back to ambient conditions, the ${\mathrm{C}}_{60}$ chain remains polymerized, emphasizing the high stability of this material. In addition, our data strongly suggest a symmetry change of the two-dimensional bunde lattice under pressure.

The first-principles calcultion of the electronic structure of finite length carbon nanotubes grafted by carboxyl

We report the first-principles calculation of the electronic distribution and the density of states (DOS) of the armchair(5,5) and zigzag (9,0) single-walled carbon nanotubes (SCNTs) grafted by carboxyl within the framework of density-functional-theory(DFT). It was found that the electronic structure of the SCNTs changes significantly due to the graft, namely, the electron density of states near Fermi level and the delocalized degree of the highly occupied molecular orbital decline greatly with increase of the number of carboxylic functional groups grafted. This suggests that the graft weakens the electronic transport properties of SCNTs.

Structural changes in single-walled carbon nanotubes under non-hydrostatic pressures:x-ray and Raman studies

Using in situ x-ray diffraction and Raman scattering techniques, we have investigatedthe behaviour of single-walled carbon nanotubes bundles under non-hydrostaticpressures. It is seen that the diffraction line corresponding to the two-dimensionaltriangular lattice in the bundles is not reversible for pressures beyond 5 GPa,in sharp contrast to earlier results under hydrostatic pressure conditions. Mostinterestingly, radial breathing and tangential Raman modes of the pressure-cycledsamples from 21 and 30 GPa match very well with those of the starting sample.Raman and x-ray results put together clearly suggest that the ordering of tubes inthe bundles is only marginally regained with a very short coherence length ondecompression.

Irradiation of Single-Walled Carbon Nanotubes with High-Energy Protons

Morphological changes in single-walled carbon nanotubes (SWNTs) upon bombardment with 3MeV protons were monitored by transmission electron microscopy in a wide range of irradiation doses. Evident morphological alterations were observed at >0.1 mC, such as curving of the nanotubes, a loss of their straight shape, and formation of short pieces. During further irradiation (doses approaching 1 mC) SWNTs degraded into an amorphous material, although a significant fraction of them were present as pieces of different lengths.

Surface Reconstructions and Dimensional Changes in Single-Walled Carbon Nanotubes

Dimensional stability is crucial to possible applications of single-walled nanotubes, as their properties are linked to size and topology. We observe nanotubes responding to uniform atom loss, through surface reconstruction and drastic dimensional changes. Experiments using electron irradiation evidence nanotube diameters shrinking from $\ensuremath{\sim}1.4$ to 0.4 nm. Molecular dynamics simulations show that surface reconstruction and size reduction occur through dangling bond saturation, forming nonhexagonal rings and 5-7 defects in the lattice. Nonuniform atom removal results in inhomogeneous tube deformations and local necking, and formation of linear atomic carbon chains in the nanotube body.