Edito of the special focus issue on Environmental Toxicity of Nanoparticles

“The main goal of this special focus issue is to introduce the main parameters that affect the potential ecotoxicity of nanoparticles and to describe the state of the art with a few selected examples of interaction of different nanoparticles...

Meta- and hybrid-CNTs: A clue for the future development of carbon nanotubes

A new generation of carbon nanotubes (CNTs), which may be named “meta-nanotubes”, is more and more the focus of the research worldwide. They result from the transformation of “regular” CNTs by various ways such as functionalisation, doping, substitution, etc. The new nanomaterials thereby created are likely to exhibit new behaviors, specifically regarding properties that pristine CNTs do not possess (reactivity, solubility, magnetism…). The paper includes the description of the various routes to synthesize hybrid CNTs and their related advantages and limitations, while providing examples of the resulting materials from both literature and author’s team work. Hybrid SWNTs (abbreviated as X@SWNTs) are one example of meta-nanotubes, and consist in SWNTs whose the hollow core is fully or partially filled with foreign atoms, molecules, or compounds. The inserted material may then exhibit a peculiar behavior with respect to the macroscopic state, for several non-exclusive reasons: 1D-dimension preventing electron scattering and enhancing the role of surface atoms, protection from surface adsorption of disturbing molecules by the carbon sheath, anisotropic lattice distortion or creation of new structures due to imposed dimensions, interactions/electron coupling with the surrounding carbon lattice. A wide field is thus open, possibly even wider than for pristine SWNTs

Comparative micro-Raman spectroscopy study of tellurium-filled double-walled carbon nanotubes

Tellurium-filled double-walled carbon nanotubes Te@DWNTs have been studied by Raman spectroscopy in the temperature interval from 300 to 700 K employing 785 nm excitation wavelength, and their spectra have been compared to those of pristine double-walled carbon nanotubes DWNTs. The DWNTs were synthesized by catalytic chemical vapor deposition. Assignment of the radial breathing modes and the tangential modes was done based on the one dimensional electronic energy band structure of carbon nanotubes. The tangential mode components of Te@DWNT are downshifted compared to those of pristine DWNT consistent with the proposed weakening of the carbon-carbon bond due to the introduced van der Waals interaction of the Te atoms with the DWNT. It was established that Te@DWNT can be unambiguously identified by the 30% temperature coefficient decrease of the G-band position

Raman spectroscopy of iodine-doped double-walled carbon nanotubes

We present a Raman spectroscopy study of iodine-intercalated (p-type-doped) double-walled carbon nanotubes. Double-walled carbon nanotubes (DWCNTs) are synthesized by catalytic chemical vapor deposition and characterized by Raman spectroscopy. The assignment of the radial breathing modes and the tangential modes of pristine DWCNTs is done in the framework of the bond polarization theory, using the spectral moment method. The changes in the Raman spectrum upon iodine doping are analyzed. Poly-iodine anions are identi- fied, and the Raman spectra reveal that the charge transfer between iodine and DWCNTs only involves the outer tubes

Application of homogeneously precipitated nanosized Fe-doped alumina powders to carbon nanotube growth.

Homogeneous precipitation of hydroxides was investigated as an alternative method to synthesize Fe-doped aluminum oxide (α-Al2−2xFe2xO3) particles over which carbon nanotubes (CNTs) were grown via a catalytic chemical vapor deposition (CCVD) method. Performance of the homogeneously precipitated particles for CNT growth was quantitatively compared with that of the combustion-synthesized particles. The main advantage of the homogeneous precipitation of hydroxides and subsequent calcination process against to the combustion synthesis and other commonly practiced chemical routes is the ability to tailor the Fe-doped Al2O3 precursor powder characteristics such as size and specific surface area (SSA) without requiring any milling step and also to control the phase composition of the oxide powder with high Fe content, and subsequently the quality and quantity of CNTs during CCVD process. The particle size of the precipitated and calcined α-Al2−2xFe2xO3 powders varies between ∼50 and 400 nm for 5–10 cat.% Fe-containing systems. The monodispersed particle size distribution and optimum phase composition of the homogeneously precipitated powders, particularly for a 10 cat.% Fe content in the starting oxide, and their much higher SSA than similar materials prepared by other chemical routes lead to production of high amounts of good quality CNTs

The weight and density of carbon nanotubes versus the number of walls and diameter

The weight and density of carbon nanotubes are calculated as a function of their characteristics (inner diameter, outer diameter, and number of walls). The results are reported in the form of diagrams which may be useful to other researchers, in particular in the fields of synthesis/production, materials and composites, health/toxicity studies

A simple and versatile method for statistical analysis of the electrical properties of individual double walled carbon nanotubes

Double-walled carbon nanotubes (DWNTs) are potential candidates for new generation of on chip interconnections due to their nearly metallic behaviour. For such large scale integration purpose it is mandatory to characterize their electrical properties in a statistical way. We thus propose a new methodology for characterizing in one step, the electrical properties of a large population of nanotubes. The method enables to obtain histograms of the conductance and maximum current density of individual nanoobjects

Micro-Raman scattering of selenium-filled double-walled carbon nanotubes: Temperature study

Selenium-filled double-walled carbon nanotubes Se@DWNT have been studied by high resolution transmission electron microscopy HRTEM and micro-Raman spectroscopy in the temperature interval from 80 to 600 K employing 785 nm excitation wavelength. The temperature dependences of the dominant bands G-band and G-band are analyzed in terms of the model developed by Klemens Phys. Rev. 148, 845 1966, Hart et al. Phys. Rev. B 1, 638 1970, Cowley J. Phys. France 26, 659 1965 and extended by Balkanski et al. Phys. Rev. B 26, 1928 1983 for anharmonic decay of optical phonons. The findings were compared to analogous study for empty double-walled carbon nanotubes DWNTs. The DWNT interatomic force constant modification as a result of the presence of the Se atoms inside the tubes is revealed through larger anharmonicity constants describing the temperature dependences of the G-band and the inner tube tangential modes G-ban

Temperature dependence of Raman scattering in filled double-walled carbon nanotubes

Four types of filled double-walled carbon nanotubes (DWNTs) (Se@DWNT; Te@DWNT; HgTe@DWNT; and PbI2@DWNT) have been studied by high-resolution transmission electron microscopy and micro-Raman spectroscopy in the temperature interval from 80 to 700 K employing 785 nm excitation wavelength. The temperature dependence of the dominant bands (D-band, G-band, and the (2D)-band) are analyzed in terms of the model developed by Klemens, Hart, Agraval, Lax, and Cowley and extended by Balkanski for anharmonic decay of optical phonons. The quasiharmonic frequencies and the anharmonicity constants were obtained from the temperature dependences of the analyzed Raman bands. The findings were compared to analogous study for empty DWNTs. The strength of the van der Waals interaction between the guest material and the carbon nanotube (CNT) estimated through the quasiharmonic frequencies was found to decrease in the following order: Se@DWNT; Te@DWNT; PbI2@DWNT, and HgTe@DWNT. In agreement with this, the anharmonicity due to the phonon–phonon interactions was found to decrease in the same order

Catalytic CVD Synthesis of Double and Triple-walled Carbon Nanotubes by the Control of the Catalyst Preparation

We report the influence of catalyst preparation conditions for the synthesis of carbon nanotubes (CNTs) by catalytic chemical vapour deposition (CCVD). Catalysts were prepared by the combustion route using either urea or citric acid as the fuel. We found that the milder combustion conditions obtained in the case of citric acid can either limit the formation of carbon nanofibres (defined as carbon structures not composed of perfectly co-axial walls or only partially tubular) or increase the selectivity of the CCVD synthesis towards CNTs with fewer walls, depending on the catalyst composition. It is thus for example possible in the same CCVD conditions to prepare (with a catalyst of identical chemical composition) either a sample containing more than 90% double- and triple-walled CNTs, or a sample containing almost 80% double-walled CNTs