Wolfgang K. Maser

Sensitivity of single wall carbon nanotubes to oxidative processing: structural modification, intercalation and functionalisation

Abstract The effect of oxidation on modification of single wall carbon nanotubes (SWCNTs) through successive purification steps has been studied. The efficient elimination of metal impurities has been followed by induced coupled plasma spectroscopy. Upon acid treatment, Raman spectroscopy clearly proofed that HNO3 molecules were intercalated into the bundles of SWCNTs. At the same time, SWCNTs also have suffered a high degree of degradation and defects were introduced. The subsequent thermal processes led to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO3 molecules. Changes in the structure of the SWCNT bundles have been observed by transmission electron microscopy. While bundles tend to separate upon acid treatment, after the complete purification process, the remaining SWCNTs tend to form thick bundles again. The existence of functional groups in the raw single wall carbon nanotubes material and their modification and almost complete removal after the final annealing step has been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption. Nitrogen adsorption isotherms analysed according to Brunauer–Emmet–Teller showed important changes in the pore volume and surface area through the purification steps.

Production of high-density single-walled nanotube material by a simple laser-ablation method

Abstract A continuous-wave 250 W CO2-laser operating at 10.6 μm has been employed to evaporate graphite/bi-metal targets in a vertical evaporation chamber. Without the help of an additional furnace, web-like soot material has been easily produced. This contains high densities of bundles of single-walled nanotubes (SWNTs). Electron microscopy, Raman spectroscopy and neutron diffraction show the high quality of the SWNT material. The use of this simple laser-ablation system offers additional possibilities to study experimental parameters important for the formation of SWNTs leading to a better understanding of its growth mechanism.

Synthesis of a new polyaniline/nanotube composite: “in-situ” polymerisation and charge transfer through site-selective interaction

A new polyaniline/multi-wall carbon nanotube (PANI/MWNT) composite has been successfully synthesized by an “in-situ” polymerisation process; Raman studies indicate a site-selective interaction between the quinoid ring of the polymer and the MWNTs opening the way for charge transfer processes; transport measurements clearly reveal drastic changes in the electronic behaviour confirming the formation of a true composite material with enhanced electronic properties.

Single-Walled Carbon Nanotubes as Electrodes in Supercapacitors

7 pages.-- PACS: 82.47.Uv; 82.45.Fk; 85.35.Kt; 68.43.Mn; 82.45.Yz; 82.45.Gj; 81.40.Gh; 78.30.Na

Synthesis and characterization of new polyaniline/nanotube composites

Abstract New polyaniline/nanotube (PANI/NT) composites have been synthesized by “in situ” polymerization processes using both multi-wall carbon nanotubes (MWNTs) and single-wall carbon nanotubes (SWNTs) in concentrations ranging from 2 to 50 wt.%. Although no structural changes are observed using MWNTs above a concentration of 20 wt.%, the in situ synthesis results in electronic interactions between nanotubes and the quinoid ring of PANI leading to enhanced electronic properties and thus to the formation of a genuine PANI/MWNT composite material. On the other hand, using SWNTs favors the formation of inhomogeneous mixtures rather than of a homogeneous composite materials, independent of the SWNT concentration. X-ray diffraction, Raman and transport measurements show the different behavior of both classes of nanotubes in PANI/NT materials. The difficulties in the formation of a true PANI/SWNT composite are related to the far more complex structure of the SWNT material itself, i.e. to the presence of entangled bundles of SWNTs, amorphous carbon and even catalytic metal particles.

Modifications of single-wall carbon nanotubes upon oxidative purification treatments

A systematic characterization of single-wall carbon nanotube (SWCNT) material after successive purification steps, including reflux treatment with nitric acid, air oxidation, and annealing, has been performed. Inductively coupled plasma–optical emission spectroscopy shows that a considerable reduction of the metal impurities by up to 95% can be obtained by the nitric acid reflux treatment. During this process, Raman spectroscopy clearly proves that HNO3 molecules are intercalated into the bundles of SWCNTs. At the same time, SWCNTs have suffered a high degree of degradation and defects are being introduced. The subsequent thermal processes lead to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO3 molecules. Transmission electron microscopy reveals that the remaining SWCNT bundles tend to form thick bundles. Thus the applied purification process results in a high-purity SWCNT material with a drastically reduced content of metal nanoparticles and composed of large bundles of SWCNTs.

Raman studies on single walled carbon nanotubes produced by the electric arc technique

Carbon single walled nanotubes (SWNTs) have been produced in high yields using the electric arc technique. TEM studies show that the SWNTs have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we focus on the characterization of these samples by high resolution Raman spectroscopy (HRRS). The presence of large amounts of SWNTs in the samples induces a very rich structure in the Raman spectra, typical for this class of carbonaceous material. Armchair tubes with (8,8) to (12,12) geometry can be detected, in agreement with the narrow diameter distribution observed by TEM measurements. The ability of HRRS as a highly sensitive fingerprint technique in identifying SWNTs with different diameters and geometries is discussed.

A soluble and highly functional polyaniline–carbon nanotube composite

A completely soluble polyaniline-multi-wall carbon nanotube (CNT–PANI) composite with drastically enhanced conductivity, improved thermal stability, and luminescent behaviour, has been synthesized. The presence of straight multi-wall carbon nanotubes during the polymerization of aniline induces the formation of a more planar conformation of polyaniline which acts as coating layer for the carbon nanotubes and leads to favourable interaction between the constituents. The polyaniline-coated multi-wall carbon nanotubes align into bundles and form a three-dimensional network in the overall composite. A highly functional carbon nanotube composite completely soluble in n-methylpyrrolidinone (NMP) exhibiting all the favourable processing and transformation possibilities of PANI has been obtained. These findings have important consequences for practical technological applications, especially for the development of opto-electronic devices.

Graphene-based potentiometric biosensor for the immediate detection of living bacteria

In this communication we present a potentiometric aptasensor based on chemically modified graphene (transducer layer of the aptasensor) and aptamers (sensing layer). Graphene oxide (GO) and reduced graphene oxide (RGO) are the basis for the construction of two versions of the aptasensor for the detection of a challenging living organism such as Staphylococcus aureus. In these two versions, DNA aptamers are either covalently (in the GO case) or non-covalently (in the RGO case) attached to the transducer layer. In both cases we are able to selectively detect a single CFU/mL of S. aureus in an assay close to real time, although the noise level associated to the aptasensors made with RGO is lower than the ones made with GO. These new aptasensors, that show a high selectivity, are characterized by the simplicity of the technique and the materials used for their construction while offering ultra-low detection limits in very short time responses in the detection of microorganisms.

Raman characterization of singlewalled carbon nanotubes and PMMA-nanotubes composites

The Raman spectroscopy have allowed us to perform studies on singlewalled nanotubes (SWNTs) produced by following methods: electric arc, laser ablation and solar energy. As this characterization method provides a great deal of informations, we will present a comparison between the nanotubes produced by all these processes and the influence of some synthesis parameters. By using spin casting, we have produced thin films of PMMA-SWNTs for different concentrations. Then, we have characterized these new materials by Raman spectroscopy. The aim of these investigations is to get information on the possible interactions between these two materials. In particular, we have studied the evolution of the composites films spectra as a function of the nanotubes concentration in the polymer.