Commercially available and laboratory-prepared multi-walled carbon nanotubes (MWCNTs) are systematically investigated by the use of micro-Raman spectroscopy (MRS), thermogravimetric analysis (TGA) and complementary techniques (scanning electron microscopy (SEM) and transmission electron microscopy (TEM)) with the aim of establishing a standardised postgrowth diagnostic protocol for the assessment of their overall crystalline quality. By studying a set of 'reference' samples, clear correlations are evidenced between the Raman graphitisation indexes (D/G, G /G and G /D intensity ratios) commonly adopted to describe the crystalline arrangement of nanotubes, and their reactivity towards oxygen, as measured by the apparent activation energy needed for their oxidation, inferred from the kinetic analysis in quasi-isothermal conditions. The higher the crystalline perfection degree, the higher the energy needed for oxidising them. The efficacy of the found correlations in indirectly assessing the reactivity of nanotubes prepared under different conditions is successfully demonstrated by the use of a second set of samples. The physical meaning and range of validity of the shown correlations are further discussed. Copyright

Oxygen quenching of the luminescence of mononuclear and dinuclear Ir(III) cyclometalated complexes immobilized in the pPEGMA matrixes has been studied. Linear Stern-Volmer plots, even when experiments at different emission wavelengths have been performed, were evidenced. Despite the different luminescence lifetimes of the chromophores in the absence of quencher, similar Stern-Volmer slopes have been calculated. This behavior was tentatively interpreted by taking into account the size and charge of the chromophores. Increased sizes and lower charges seem to enhance the sensitivity of the systems. Such findings could be of interest for the design of new solid-state luminescent oxygen sensors with improved performance.

A set of nanotubes with moderate contents of amorphous phases (0.4–5.1 wt %) are systematically investigated by Raman spectroscopy, kinetic thermal analysis, and complementary techniques. Results show that, in spite of their small amount, the presence of amorphous phases has a strong impact on the oxidation path of nanotubes. The apparent activation energy for oxidizing them, as inferred from thermal kinetic analysis, decreases linearly with increasing the content of amorphous species. The presence of non-sp2 defects causes the failure of the commonly adopted Raman graphitization indexes, with consequent breakdown of the correlations between crystalline quality and activation energy evidenced in the absence of the amorphous phases. This drawback is overcome by introducing a generalized Raman indicator of the crystalline quality, whose value increases with increasing energy needed for oxidizing nanotubes independently on the typology (sp2 or non-sp2) of defects present in their walls.

In luminescence‐based oxygen sensors the active luminescent species is usually a transition metal complex immobilized in a polymeric matrix—in most cases a ruthenium(II) polypyridine complex. In an attempt to overcome some of the disadvantages of these systems, a polymer‐immobilized iridium(III) complex has been prepared and used for the first time as the active species in such a sensor. The luminescence properties of this system are described and its drawbacks with regard to sensors technology discussed.

This work reports for the first time a straightforward solvent-free chemical procedure to gain access to Δ-1-pyrroline grafted onto multiwalled carbon nanotubes by the 1,3-dipolar cycloaddition of the mesoionic 4-methyl-2-phenyloxazol-5(4H)-one.

Catalytic activity of iron based catalysts in the production of multi-walled carbon nanotubes (MWCNTs) has been investigated. The effect of the carbon source (ethane or isobutane), catalyst support (Al2O3 or SiO2), iron loading, catalyst reduction temperature and reaction temperature on yield and quality of carbon products has been examined. The structural and morphological properties of catalyst and carbon products obtained have been analyzed by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). The iron-based catalysts supported on alumina seem to be efficient systems for the production of carbon nanotubes from chemical vapor deposition (CVD) of isobutane with very interesting yields. The opportune calibration of reaction parameters, such as iron loading and reaction temperature, can in fact drive the synthesis toward the formation of high quality CNTs.

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