Izabela Janowska

Nitrogen-doped carbon nanotubes as a highly active metal-free catalyst for selective oxidation.

Catalytic reactions are generally carried out on supported metals or oxides, which act as an active phase and require impregnation and thermal treatment steps. During tests, the metal or oxide nanoparticles could be further sintered, which would induces deactivation. Direct incorporation of the active phase into the matrix of a support could be an elegant alternative to prevent catalyst deactivation. Here, we report that nitrogen-doped carbon nanotubes (N-CNTs) can be efficiently employed as a metal-free catalyst for oxidative reactions that allow the selective transformation of the harmful, gaseous H(2)S into solid sulfur. The catalyst exhibits a high stability during the test at high space velocity. The macroscopic shaping of the catalyst on the silicon carbide foam also increases its catalytic activity by improving the contact between the reactants and the catalyst. Such macroscopic shaping allows the avoidance of problems linked with transport and handling of nanoscopic materials and also reduces the pressure drop across the catalyst bed to a large extent.

Electrical Transport Measured in Atomic Carbon Chains

The first electrical-transport measurements of monatomic carbon chains are reported in this study. The chains were obtained by unraveling carbon atoms from graphene ribbons while an electrical current flowed through the ribbon and, successively, through the chain. The formation of the chains was accompanied by a characteristic drop in the electrical conductivity. The conductivity of the chains was much lower than previously predicted for ideal chains. First-principles calculations using both density functional and many-body perturbation theory show that strain in the chains has an increasing effect on the conductivity as the length of the chains increases. Indeed, carbon chains are always under varying nonzero strain that transforms their atomic structure from the cumulene to the polyyne configuration, thus inducing a tunable band gap. The modified electronic structure and the characteristics of the contact to the graphitic periphery explain the low conductivity of the locally constrained carbon chain.

3D analysis of the morphology and spatial distribution of nitrogen in nitrogen-doped carbon nanotubes by energy-filtered transmission electron microscopy tomography.

We present here the application of the energy-filtered transmission electron microscopy (EFTEM) in the tomographic mode to determine the precise 3D distribution of nitrogen within nitrogen-doped carbon nanotubes (N-CNTs). Several tilt series of energy-filtered images were acquired on the K ionization edges of carbon and nitrogen on a multiwalled N-CNT containing a high amount of nitrogen. Two tilt series of carbon and nitrogen 2D maps were then calculated from the corresponding energy-filtered images by using a proper extraction procedure of the chemical signals. Applying iterative reconstruction algorithms provided two spatially correlated C and N elemental-selective volumes, which were then simultaneously analyzed with the shape-sensitive reconstruction deduced from Zero-Loss recordings. With respect to the previous findings, crucial information obtained by analyzing the 3D chemical maps was that, among the two different kind of arches formed in these nanotubes (transversal or rounded ones depending on their morphology), the transversal arches contain more nitrogen than do the round ones. In addition, a detailed analysis of the shape-sensitive volume allowed the observation of an unexpected change in morphology along the tube axis: close to the round arches (with less N), the tube is roughly cylindrical, whereas near the transversal ones (with more N), its shape changes to a prism. This relatively new technique is very powerful in the material science because it combines the ability of the classical electron tomography to solve 3D structures and the chemical selectivity of the EFTEM imaging.

Microstructural investigation of magnetic CoFe2O4 nanowires inside carbon nanotubes by electron tomography.

Magnetic nanowires of CoFe 2O4 were casted inside the channel of multiwall carbon nanotubes by mild chemical synthesis. A detailed investigation of these nanowires was performed using mainly the electron tomography technique; this study provides a complete characterization of their microstructure in terms of the spatial organization and the size distribution of individual particles forming the nanowire as well as its residual porosity. In particular, we have shown that the size of the CoFe 2O4 monocrystalline particles is closely dependent on the location of the particle within the nanotube, i.e., small particles close to the tube tip (5 nm) and bigger particles inside the tube channel (15 nm). As the theoretical critical size for superparamagnetic relaxation in CoFe 2O4 is estimated within the range of 4-9 nm, the size distribution obtained by 3D-TEM agrees with the Mossbauer study that suggests the presence of two different magnetic components inside the nanowire. We have shown also that, by using this preparation method and for this internal diameter of nanotube, the CoFe 2O4 nanowire exhibits a continuous structure along the tube, has a residual porosity of 38%, and can fill the tube at only 50%, parameters which influence in a significant manner the magnetic behavior of this system.

A few-layer graphene–graphene oxide composite containing nanodiamonds as metal-free catalysts

We report a high yield exfoliation of few-layer-graphene (FLG) with up to 17% yield from expanded graphite, under 5 h sonication time in water, using graphene oxide (GO) as a surfactant. The aqueous dispersion of GO attached FLG (FLG–GO), with less than 5 layers, is used as a template for further decoration of nanodiamonds (NDs). The hybrid materials were self-organized into 3D-laminated nanostructures, where spherical NDs with a diameter of 4–8 nm are homogeneously distributed on the surface of the FLG–GO complex (referred to as FLG–GO@NDs). It was found that GO plays a dual role, it (1) mediated exfoliation of expanded graphite in aqueous solution resulting in a FLG–GO colloid system, and (2) incorporated ND particles for the formation of composites. A high catalytic performance in the dehydrogenation of ethyl-benzene on FLG–GO@ND metal-free catalyst is achieved; 35.1% of ethylbenzene conversion and 98.6% styrene selectivity after a 50 h reaction test are observed which correspond to an activity of 896 mmolST gcatalyst−1 h−1, which is 1.7 and 5 times higher than those of the unsupported NDs and traditional catalysts, respectively. The results demonstrate the potential of the FLG–GO@ND composite as a promising catalyst for steam-free industrial dehydrogenation applications.

Few layer graphene decorated with homogeneous magnetic Fe3O4 nanoparticles with tunable covering densities

Magnetic iron oxide nanoparticles (NPs) with narrow size distribution (8 ± 2 nm), well defined chemical composition and crystalline structure are synthesized and homogeneously dispersed onto the surface of few-layer graphene (FLG) via a solvothermal decomposition method. The iron oxide NPs are strongly anchored to the graphene surface and confer a magnetic character to the final composite. The metal oxide/support interaction is high enough to avoid the NPs coalescence and/or agglomeration and thus to preserve the NPs size and dispersion after thermal treatment up to 400 °C. The introduced iron oxide NPs on FLG also play a role of nano-spacers to prevent the re-stacking of the graphene sheets upon the drying process. It is expected that such a composite could find use in several application fields such as catalyst support for liquid-phase reactions with easy magnetic separation, in electrochemical energy storage and in waste water treatment. The ability of the synthesized iron oxide NP/FLG composite to adsorb foreign elements (organic pollutants) is demonstrated in the methylene blue (MB) adsorption and its catalytic properties are evaluated in the selective oxidation of H2S.

Synthesis of porous carbon nanotubes foam composites with a high accessible surface area and tunable porosity

The macroscopic shaping of carbon nanostructure materials with tunable porosity, morphologies, and functions, such as carbon nanotubes (CNT) or carbon nanofibers (CNF), into integrated structures is of great interest, as it allows the development of novel nanosystems with high performances in filter applications and catalysis. In the present work, we report on a low temperature chemical fusion (LTCF) method to synthesize a self-macronized carbon nanotubes foam (CNT-foam) with controlled size and shape by using CNT as a skeleton, dextrose as a carbon source, and citric acid as a carboxyl group donor reacting with the hydroxyl group present in dextrose. The obtained composite has a 3D pore structure with a high accessible surface area (>350 m2 g−1) and tunable meso- and macro-porosity formed by the addition of a variable amount of ammonium carbonate into the starting mixture followed by a direct thermal decomposition. The as-synthesized CNT-foam also exhibits a relatively high mechanical strength which facilitates its handling and transport, while the nanoscopic morphology of the CNT significantly reduces the problem of diffusion and contributes to an improvement of the effective surface area for subsequent applications. These CNT-foams are successfully employed as selective and recyclable organic absorbers with high efficiency in the field of waste water treatment.

Ferrocenyl D-π-A chromophores containing 3-dicyanomethylidene-1-indanone and 1,3-bis(dicyanomethylidene)indane acceptor groups

The nonlinear optical properties of ferrocenyl (Fc) D-π-A chromophores containing powerful 3-dicyanomethylidene-1-indanone ( 2 ) and 1,3-bis(dicyanomethylidene)indane-based acceptor group ( 3 ) have been measured by EFISH technique at 1.907 μm and compared with those reported for the Fc compound containing the 3-dicyanomethylidene-2,3-benzo[ b ]thiophen-1,1-dioxide group ( 1 ). The values of μβ ·(2 ω ) are 160 and 280×10 −48 esu for 2 and 3 , respectively, whereas 1 displays a value of 140×10 −48 esu [Inorg. Chim. Acta 242 (1996) 43]. The X-ray crystallographic study of 1 and 2 revealed significant distortions of the structure of the ferrocene moieties due to the contribution of a charge-separated η 6 -fulvene mesomeric form and important steric effects. The cyclic voltammetry data showed an anodic shift of the Fe(II)/Fe(III) oxidation potentials of 2 and 3 in comparison to those of ferrocenecarboxaldehyde ( 4 ) and 2-(ferrocenylmethylidene)-1,3-indandione ( 5 ), and an approximately additive effect of the substitution of one or two carbonyl oxygens in 5 by the C(CN) 2 group.

Hybrid Films of Graphene and Carbon Nanotubes for High Performance Chemical and Temperature Sensing Applications

A hybrid composite material of graphene and carbon nanotube (CNT) for high performance chemical and temperature sensors is reported. Integration of 1D and 2D carbon materials into hybrid carbon composites is achieved by coupling graphene and CNT through poly(ionic liquid) (PIL) mediated-hybridization. The resulting CNT/PIL/graphene hybrid materials are explored as active materials in chemical and temperature sensors. For chemical sensing application, the hybrid composite is integrated into a chemo-resistive sensor to detect a general class of volatile organic compounds. Compared with the graphene-only devices, the hybrid film device showed an improved performance with high sensitivity at ppm level, low detection limit, and fast signal response/recovery. To further demonstrate the potential of the hybrid films, a temperature sensor is fabricated. The CNT/PIL/graphene hybrid materials are highly responsive to small temperature gradient with fast response, high sensitivity, and stability, which may offer a new platform for the thermoelectric temperature sensors.

A 3D insight on the catalytic nanostructuration of few-layer graphene

The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting.