Single-wall Carbon Nanotubes In Air Research Articles

Arsenic removal from water by nanometer iron oxide coated single-wall carbon nanotubes

Single-wall carbon nanotubes (SWCNTs) were prepared by arc discharge evaporation of a carbon electrode containing Fe catalyst so that there are an amount of iron nanoparticles attached tightly on SWCNTs. The iron oxide nanoparticle coated SWCNT composite was prepared in situ by oxidizing the above as-grown SWCNTs in air at 350°C, which was used as an adsorbent for As5+ removal from water. It was found that the maximum As5+ adsorption capacity of the composite was 42.30mgg−1 at pH8 and 49.65mgg−1 at pH4, respectively. The kinetics data were best fitted with a pseudo-second order, thus suggesting chemical adsorption on the surface and pores of iron oxide nanoparticles. The adsorption isotherm obtained at pH8 was best fitted to the Freundlich model, therefore a non-ideal adsorption on heterogeneous surfaces for As5+ ions on iron oxide nanoparticles was proposed. The firm web structure with high adsorption capacity makes the composite a promising adsorbent for arsenic removal in contaminated water.

Atmospheric ions as the origin of photoinduced degrading of photoluminescence from a single-walled carbon nanotube

Air-suspended single-walled carbon nanotubes (SWCNTs) were exposed to atmospheric ions for identifying the origin of photoinduced degrading of photoluminescence from SWCNTs in air. Decreased intensity and a low energy shift of photoluminescence from the SWCNT were observed after the exposure, and the reaction was found to be accelerated by laser illumination. The amount of the decrease and shift had a weak correlation and were attributed to the chemisorption of hydronium ions along with water molecules.

Electrical and thermal transport in metallic single-wall carbon nanotubes on insulating substrates

We analyze transport in metallic single-wall carbon nanotubes (SWCNTs) on insulating substrates over the bias range up to electrical breakdown in air. To account for Joule self-heating, a temperature-dependent Landauer model for electrical transport is coupled with the heat conduction equation along the nanotube. The electrical breakdown voltage of SWCNTs in air is found to scale linearly with their length, approximately as 5V∕μm; we use this to deduce a thermal conductance between SWCNT and substrate g≈0.17±0.03WK−1m−1 per tube length, which appears limited by the SWCNT-substrate interface rather than the thermal properties of the substrate itself. We examine the phonon scattering mechanisms that limit electron transport, and find the strong temperature dependence of the optical phonon absorption rate to have a remarkable influence on the electrical resistance of micron-length nanotubes. Further analysis reveals that unlike in typical metals, electrons are responsible for less than 15% of the total thermal conductivity of metallic nanotubes around room temperature, and this contribution decreases at high bias or higher temperatures. For interconnect applications of metallic SWCNTs, significant self-heating may be avoided if power densities are limited below 5μW∕μm, or if the SWCNT-surrounding thermal interface is optimized.

Raman Spectroscopy of Individual Single-Walled Carbon Nanotubes from Various Sources

Resonance Raman spectroscopy/microscopy was used to study individualized single-walled carbon nanotubes (SWNTs) both in aqueous suspensions as well as after spin-coating onto Si/SiO2 surfaces. Four different SWNT materials containing nanotubes with diameters ranging from 0.7 to 1.6 nm were used. Comparison with Raman data obtained for suspensions shows that the surface does not dramatically affect the electronic properties of the deposited tubes. Raman features observed for deposited SWNTs are similar to what was measured for nanotubes directly fabricated on surfaces using chemical vapor deposition (CVD) methods. In particular, individual semiconducting tubes could be distinguished from metallic tubes by their different G-mode line shapes. It could also be shown that the high-power, short-time sonication used to generate individualized SWNT suspensions does not induce defects in great quantities. However, (additional) defects can be generated by laser irradiation of deposited SWNTs in air, thus giving rise to an increase of the D-mode intensity for even quite low power densities (approximately 10(4) W/cm2).

Single-Walled Carbon Nanotubes as Electrodes in Supercapacitors

As-grown and modified single-walled carbon nanotubes (SWCNTs) have been used as electrochemical active materials of electrode for electrochemical capacitors (supercapacitors). A series of modified SWCNTs has been obtained by oxidation of the as-grown SWCNTs in air at increasing temperatures in the range 300-550°C. The as-grown and modified samples have been characterized by Raman spectroscopy, adsorption, and transmission electron microscopy (TEM). Raman spectra of the modified samples show that heating at increasing temperature produces a decrease in the intensity of radial and tangential breathing modes of SWCNTs and an alteration of the structure of SWCNTs up to complete destruction at 550°C. Heat-treatment at 350°C leads to the highest specific surface area (644 m2 g−1) and the highest micropore volume (0.288 cm3 g−1). TEM images of the as-grown and 350°C-oxidized samples show a multicomponent structure with bundles of SWCNTs that are thinner in the oxidized sample compared to the as-grown one. The as-grown and 350°C-oxidized SWCNTs were mixed with polyvinylidenefluoride and compacted to get electrodes. 6 M KOH and 2 M aqueous solutions were utilized as electrolytes. The specific capacitances (30-140 F g−1) are discussed on the basis of the electrode material and the electrolyte chosen. The specific capacitance is higher for the 350°C-oxidized SWCNTs and when KOH is used as electrolyte. Typical values of the equivalent series resistance (ESR) are in the range 1-5 Ω, except for the oxidized sample when KOH is used as electrolyte; in this case, ESR is higher. The thermal treatment improves the energy density but does not affect the power density, this last being higher when is used. © 2004 The Electrochemical Society. All rights reserved.

Photoluminescence from an individual single-walled carbon nanotube

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are obtained from individual single-walled carbon nanotubes (SWNTs). Individual SWNT spectra are compared with spectra from ensembles. The PL spectrum of an individual SWNT in air at room temperature has a single asymmetric peak of width typically 10 to 15 meV, with no detected background. Both absorption and emission are strongly polarized along the tube axis. Photoluminescence excitation spectroscopy on single SWNTs clearly confirms the unique, one-to-one association of optical absorption resonances with individual emission peaks. Resonances in the PLE spectra are typically $\ensuremath{\approx}30\mathrm{meV}$ wide, with the PL intensity enhanced tenfold over nonresonant excitation. Whether for emission or absorption, the peak shape and peak width are almost the same for a single nanotube as they are for the corresponding species in a large ensemble. That is, there is no significant inhomogeneous broadening. While ensemble measurements are complicated by the superposition of many PL peaks from many different species, single nanotube spectra clearly isolate a single peak and are thus simpler to interpret.

Selective Coating of Single Wall Carbon Nanotubes with Thin SiO2 Layer

Single walled carbon nanotubes (SWNTs) have been shown to be highly sensitive gas sensors. However, attaching functional groups with selective sensing functions on nanotubes without destroying the intrinsic electronic property of the nanotubes is still challenging. Here, we report a new method of coating SWNTs with a thin layer of SiO2 using 3-aminopropyltriethoxyysilane as coupling layers. The thickness of the SiO2 could be controlled at about 1 nm. The coating of SiO2 on SWNTs was confirmed by burning the SWNTs in air. The effect of 3-aminopropyltriethoxyysilane was also discussed.

Purification of single-wall carbon nanotubes

With Y–Ni alloy and CaC 2–Ni as catalyst, large-scale single-wall carbon nanotubes (SWCNTs) were produced by d.c. arc-discharge method. The yield of SWCNTs and the composition of the raw-soot was quantified with thermogravimetric analysis (TGA). The burning temperature of SWCNTs in air was also determined. On these bases, 350°C was chosen for the first step purification of SWCNTs. Combining with the micro-filtration method, larger than 90% purity of SWCNTs and high purity of carbon nanoparticles were obtained.