International audienceThe large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities of SWNTs can be synthesised by catalytic decomposition of methane over well-dispersed metal particles supported on MgO at 1000°C. The thus produced SWNTs can be separated easily from the support by a simple acidic treatment to obtain a product with high yields (70-80%) of SWNTs. Because the typical synthesis time is 10 min, 1 g of SWNTs can be synthesised per day by this method. The SWNTs are characterized by high-resolution transmission electron microscopy and by Raman spectroscopy, showing the quality and the quantity of products

Catalytic synthesis and some characterization of multi-and single-wall carbon nanotubes are presented. Supported transition-metal catalysts were prepared by different methods and were tested in the production of nanotubes by decomposition of hydrocarbons at 700 • C, using a fixed-bed flow reactor.The quantities of deposited carbon were measured and the quality of the nanotubes was characterized by means of transmission electron microscopy and scanning tunneling microscopy. The inner and outer diameters of the nanotubes were also measured and the diameter distribution histograms were established. The multi-wall straight and coiled nanotubes were found to be quite regular with an average inner (outer) diameter of 4-7 nm (15-25 nm) and with lengths up to 50 µm. The walls contain concentric cylindrical graphene sheets separated by the graphitic interlayer distance. The single-wall nanotubes were found as bundles of hundreds of aligned straight 1-nm-diameter nanotubes with lengths up to 1-µm.The influence of various parameters such as the method of catalyst preparation, the nature and the pore size of the support, the nature of the metal, the quantity of catalyst active particles, and the reaction conditions on the nanotubes formation were studied. The numbers and dimensions of the catalyst active particles dispersed on the support were found to be of importance in regulating the shape of the produced nanotubes. Following these results, a model of growth mechanism was suggested for the nanotubes obtained by this method.The recent discovery of fullerenes [1], fullerenic onions [2], and hollow turbostratic carbon tubes of nanometer diameter [3] opened a new chapter in carbon chemistry. Because of their calculated chemical and physical properties [4][5][6][7], speculations about the possible applications of carbon nanotubes have been reported [8][9][10]. For the synthesis of carbon nanotubes several methods have been reported. The arc-discharge method developed for C 60 synthesis supplied a very surprising result, namely the growth of fullerene tubes on the carbon cathode [3,[11][12][13][14]. Other nanotube synthesis methods were also used such as plasma decomposition of hydrocarbons [15,16] and co-evaporating a catalyst during a carbon arc-discharge [17][18][19][20][21]. Single-wall nanotubes could be produced by the catalytic method evaporating cobalt or iron in the system. Recently, another catalytic process involving decomposition of hydrocarbons over supported catalysts and working under relatively mild conditions has been reported for carbon nanotube production [22,23]. Compared with other synthesis methods, the selectivity of this process to carbon nanotubes is significantly higher [24]. The advantages of the latter method increase if applying zeolites as catalyst supports [25]. Single-and multi-shell nanotubes of regular dimensions are produced by catalytic decomposition of hydrocarbons over Co/Y-zeolite catalysts. ExperimentalDifferent silica-and zeolite-supported transition-metal (Co, Cu, and Fe) catalysts have...

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Here, we report on the synthesis of MoS2 nanosheets using a simple two-step additive-free growth technique. The as-synthesized nanosheets were characterized to determine their structure and composition, as well as their optical properties. The MoS2 nanosheets were analyzed by scanning electron microscopy, transmission electron microscopy (TEM), including high-resolution scanning TEM imaging and energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL). The as-produced MoS2 nanosheets are vertically aligned with curved edges and are densely populated. The TEM measurements confirmed that the nanosheets have the 2H-MoS2 crystal structure in agreement with the Raman results. The XPS results revealed the presence of high purity MoS2. Moreover, a prominent PL similar to mechanically exfoliated few and mono-layer MoS2 was observed for the as-grown nanosheets. For the thin (≤50 nm) nanosheets, the PL feature was observed at the same energy as that for a direct band-gap monolayer MoS2 (1.83 eV). Thus, the as-produced high-quality, large-area, MoS2 nanosheets could be potentially useful for various optoelectronic and catalysis applications.

Hexagonal‐shaped nanoplates (HNPs) of MoS2 on vertically aligned carbon nanotubes (CNTs) over a patterned area (a circular area of 1 cm2 diameter) are produced by chemical vapor deposition technique. With an optimized initial Mo film thickness, a uniform coverage of MoS2 HNPs with a thickness around 20 nm is achieved. The results confirm that the CNT template plays an important role in the MoS2 HNPs growth. Each MoS2 HNP consists of abundant exposed edges, interesting for sensing and catalysis applications. High crystallinity and quality of the as‐produced material are revealed by X‐ray photoelectron and Raman spectroscopies. Furthermore, NO2 gas‐sensing studies show better sensitivity and recovery for MoS2/CNT samples as compared to pristine CNTs. The detection of NO2 gas in a few tens of parts per million to a few hundreds of parts per billion range, at room temperature, is achieved. Density‐functional theory calculation indicates that the exposed edges of MoS2 play a significant role in the NO2 sensing as compared to horizontally aligned MoS2 layers. The present report can promote the research toward the fabrication of efficient and reliable MoS2‐based hybrid materials for toxic gas‐sensing applications for air quality monitoring in various environments.

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The ability to functionalize carbon nanotubes (CNTs) through controlled structural modifications is an essential prerequisite for application purposes, as it may lead to increased solubility and processability(1-3) as well as opportunities for fine-tuning the physical and chemical properties,(4, 5) thereby enabling the exploitation of the mechanical, thermal, and optical properties of CNTs(6) in a wide range of applications in both material(7) and biomedical sciences.(5, 8, 9) A major challenge in this field, therefore, is to develop a range of reliable and effective functionalization methodologies that allow the construction of CNTs-based macromolecular species of highly versatility and usefulness, to be further modified by coupling them to a variety of organic functionalities and in the mean time do not extensively disrupt the graphitic π-conjugated surface (consequently altering their electronic(10) and thus optical properties(11-13)). In this respect, halogenated CNTs-based materials can represent a useful class of intermediates as they could act as precursors to a number of organometallic species and suitable substrates for metal-catalyzed cross coupling reactions. Halogenation of CNTs has mainly been performed with highly oxidizing F2 gas,(14-16) with electrochemically generated Cl2 and Br2(17) and with I2 through a modified Hunsdiecker-type reaction.(18) The low-susceptibility of CNTs to weak oxidizing species, such as Br2, was instead utilized as a means of purification for MWCNTs containing carbon nanoparticles(19) and to the best of our knowledge, no definitive reports about the C−Br bond formation on single- or double-walled CNTs have been reported at time. We thus report the synthesis and characterization of double-walled carbon nanotubes (DWCNTs) functionalized with Br2 (Br-DWCNTs) under microwave-assisted (MiW) conditions,(20-22) to link covalently the Br atoms to DWCNTs with a percentage of functionalization of ca. 5−8 % in weight