Composite MoS 2 /carbon nanotube material has been produced by hydrothermal decomposition of a mixture of multiwall carbon nanotubes (CNTs) and a water solution of ammonium molybdate and thiourea. Transmission electron microscopy and Raman spectroscopy showed formation of MoS 2 layers on the CNT surface and MoS 2 flakes. X-ray photoelectron spectroscopy revealed a downshift of C 1s peak of the composite as compared to the pristine CNT sample that was related to charge transfer between the components. This fact was confirmed by near-edge X-ray absorption fine structure spectroscopy which detected a decrease of intensity of π* resonance in the C K-edge spectrum after the MoS 2 deposition. Quantum-chemical calculations of a CNT@MoS 2 model showed a positive charging of the CNT surface. Comparison of field emission characteristics of CNTs and the composite indicated lowering of the voltage threshold in the latter sample.

Multi‐walled carbon nanotubes (CNTs) and nitrogen‐doped carbon (CNx) nanotubes have been synthesized by the aerosol‐assisted chemical vapour deposition (CVD) method. The samples were prepared from toluene and acetonitrile taken in different proportion. The structure of CNTs and CNx nanotubes was compared using first‐ and second‐order Raman spectra. The disorder‐induced D band was found to up‐shift with increase of the acetonitrile fraction. The ID/IG and IG′/IG ratios showed the opposite dependence on the doping level of CNTs. Both kinds of the substitute nitrogen: graphitic‐like and pyridinic‐like contribute to the disorder in CNx nanotube layers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

Highly oriented pyrolytic graphite characterized by a low misorientation of crystallites is fluorinated using a gaseous mixture of BrF(3) with Br(2) at room temperature. The golden-colored product, easily delaminating into micrometer-size transparent flakes, is an intercalation compound where Br(2) molecules are hosted between fluorinated graphene layers of approximate C(2)F composition. To unravel the chemical bonding in semifluorinated graphite, we apply angle-resolved near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and quantum-chemical modeling. The strong angular dependence of the CK and FK edge NEXAFS spectra on the incident radiation indicates that room-temperature-produced graphite fluoride is a highly anisotropic material, where half of the carbon atoms are covalently bonded with fluorine, while the rest of the carbon atoms preserve π electrons. Comparison of the experimental CK edge spectrum with theoretical spectra plotted for C(2)F models reveals that fluorine atoms are more likely to form chains. This conclusion agrees with the atomic force microscopy observation of a chain-like pattern on the surface of graphite fluoride layers.

The applicability of Cu/C catalysts is limited by sintering of Cu leading to deactivation in catalytic reactions.We show that the problem of sintering could be resolved by N-doping of the carbon support. Cu nanocatalysts with 1 at% of metal were synthesized by Cu acetate decomposition on N-free and Ndoped (5.7 at% N) mesoporous carbon supports as well as on thermally expanded graphite oxide.Catalytic properties of these samples were compared in hydrogen production from formic acid decomposition. The N-doping leads to a strong interaction of the Cu species with the support providing stabilization of Cu in the form of clusters of less than 5 nm in size and single Cu atoms, which were observed in a significant ratio by atomic resolution HAADF/STEM even after testing the catalyst under harsh conditions of the reaction at 600 K. The mean size of the obtained Cu clusters was by a factor of 7 smaller than that of the particles in the N-free catalyst. The N-doped Cu catalyst possessed good stability in the formic acid decomposition at 478 K for at least 7 h on-stream and a significantly higher catalytic activity than the N-free Cu catalysts. The nature of the strongly interacting Cu species was studied by XPS, XRD and other methods as well as by DFT calculations. The presence of single Cu atoms in the N-doped catalysts should be attributed to their strong coordination by pyridinic nitrogen atoms at the edge of the graphene sheets of the support. We believe that the N-doping of the carbon support will allow expanding the use of Cu/C materials for different applications avoiding sintering and deactivation.

TOULOUSE Archive Ouverte (OATAO)OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.

Nitrogen-containing carbon nanotubes were obtained by pyrolysis of acetonitrile (CH 3 CN) at 850 °C over catalytic nanoparticles formed by the thermal decomposition of Co and Ni bimaleates or their mutual solutions. Structure and composition of synthesized samples were studied by electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that the yield of the nanotubes, the quality of the layer packing, and nitrogen content in the CN x nanotubes depend on the catalyst composition. XPS of the N 1s spectra show that nitrogen atoms are in two different electronic states in the carbon nanotubes. According to quantum chemical calculations these states can be ascribed to nitrogen atoms substituting for carbon atoms in the graphite network and pyridine-like atoms. It was shown that the nanotubes synthesized using catalyst with the ratio Ni/Co 1:1 contain the greatest proportion of pyridine-like nitrogen.

No abstract