Ákos Kukovecz

Large scale production of short functionalized carbon nanotubes

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.

Low-temperature large-scale synthesis and electrical testing of ultralong copper nanowires.

Copper nanowires (NWs) with uniform diameters and lengths ranging from several hundreds of nanometers to several micrometers have been prepared with high yield by a simple hydrothermal procedure. The X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) analysis data indicate that the copper nanowires are free of any contamination, while the electron diffraction (ED) analysis has revealed the nanowires to be single crystals. The nanowire growth mechanism has also been discussed. Hexadecylamine is the surface stabilizing agent in our method, while glucose facilitates formation of single-crystalline seeds on which the copper nanowires grow. The electrical properties of the as-synthesized copper NWs have also been investigated.

Nitrogen-Doped Anatase Nanofibers Decorated with Noble Metal Nanoparticles for Photocatalytic Production of Hydrogen

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

Catalytic synthesis of carbon nanotubes over Co, Fe and Ni containing conventional and sol–gel silica–aluminas

An attempt has been made to synthesise multiwalled carbon nanotubes using cobalt, iron and nickel supported on different types of silica–aluminas to investigate the rules governing their nanotube producing activity. Acetylene was used as the source of carbon. Decomposition of acetylene has been carried out at atmospheric pressure. The effect of reaction temperature in the 770–970 K range and the flow rate of the hydrocarbon has been investigated. The catalysts were analysed by XRD, UV–VIS, surface area and porosity measurements. Formation of carbon nanotubes was followed by electron microscopy. The amount of deposited carbon increased with increasing reaction temperature and the flow rate of acetylene, but decreased with increasing concentration of alumina in the catalyst support. Each catalyst showed high production of carbon nanotubes at 970 K; however, they were inactive at 770 K. The yield of tube formation was very low at 870 K. The high-resolution transmission electron microscopic (HREM) analysis showed that the outer diameter of the tubes generated varied from 8 to 40 nm, the tubes were multiwalled, and the number of the layers was between 8 and 30. Sol–gel derived samples were also found to be working catalysts, indicating the existence of an optimal metal particle size.

Functionalized Low Defect Graphene Nanoribbons and Polyurethane Composite Film for Improved Gas Barrier and Mechanical Performances

A thermoplastic polyurethane (TPU) composite film containing hexadecyl-functionalized low-defect graphene nanoribbons (HD-GNRs) was produced by solution casting. The HD-GNRs were well distributed within the polyurethane matrix, leading to phase separation of the TPU. Nitrogen gas effective diffusivity of TPU was decreased by 3 orders of magnitude with only 0.5 wt % HD-GNRs. The incorporation of HD-GNRs also improved the mechanical properties of the composite films, as predicted by the phase separation and indicated by tensile tests and dynamic mechanical analyses. The improved properties of the composite film could lead to potential applications in food packaging and lightweight mobile gas storage containers.

Three-Dimensional Carbon Nanotube Scaffolds as Particulate Filters and Catalyst Support Membranes

Three-dimensional carbon nanotube scaffolds created using micromachined Si/SiO2 templates are used as nanoparticulate filters and support membranes for gas-phase heterogeneous catalysis. The filtering efficiency of better than 99% is shown for the scaffolds in filtering submicrometer particles from air. In the hydrogenation of propene to propane reaction low activation energy of E(a) approximately 27.8 +/- 0.6 kJ x mol(-1), a considerably high turnover rate of approximately 1.1 molecules x Pd site(-1) x s(-1) and durable activity for the reaction are observed with Pd decorated membranes. It is demonstrated that appropriate engineering of macroscopic-ordered nanotube architectures can lead to multifunctional applications.

Trace level voltammetric determination of lead and cadmium in sediment pore water by a bismuth-oxychloride particle-multiwalled carbon nanotube composite modified glassy carbon electrode

Two multiwalled carbon nanotubes-based composites modified with bismuth and bismuth-oxychloride particles were synthesized and attached to the glassy carbon electrode substrate. The resultant configurations, Bi/MWCNT-GCE and BiOCl/MWNT-GCE, were then characterized with respect to their physicochemical properties and electroanalytical performance in combination with square-wave anodic stripping voltammetry (SWASV). Further, some key experimental conditions and instrumental parameters were optimized; namely: the supporting electrolyte composition, accumulation potential and time, together with the parameters of the SWV-ramp. The respective method with both electrode configurations has then been examined for the trace level determination of Pb(2+) and Cd(2+) ions and the results compared to those obtained with classical bismuth-film modified GCE. The different intensities of analytical signals obtained at the three electrodes for Pb(2+) and Cd(2+) vs. the saturated calomel reference electrode had indicated that the nature of the modifiers and the choice of the supporting electrolyte influenced significantly the corresponding stripping signals. The most promising procedure involved the BiOCl/MWCNT-GCE and the acetate buffer (pH 4.0) offering limits of determination of 4.0 μg L(-1) Cd(2+) and 1.9 μg L(-1) Pb(2+) when accumulating for 120 s at a potential of -1.20 V vs. ref. The BiOCl/MWCNT electrode was tested for the determination of target ions in the pore water of a selected sediment sample and the results agreed well with those obtained by graphite furnace atomic absorption spectrometry.

Diameter selective reaction processes of single-wall carbon nanotubes

A method is presented which allows the study of diameter selective reactions in single-wall carbon nanotubes with an unprecedented accuracy. It is based on the transformation of fullerene peapods into double-wall carbon nanotubes and the study of the resulting diameter distribution of the inner nanotubes with Raman spectroscopy. This yields a spectral resolution increase of about 40 for the modes of different tubes. The method is demonstrated for the diameter selective healing of nanotube defects and yield from C70 peapod samples. The growth of very small diameter inner tubes from C70 peapods is demonstrated, which challenges the models of inner nanotube formation. An anomalous absence of middiameter inner tubes is explained by the suppressed amount of C70 peapods in the transition region between standing and lying C70 configurations.

Synthesis of tungsten carbide and tungsten disulfide on vertically aligned multi-walled carbon nanotube forests and their application as non-Pt electrocatalysts for the hydrogen evolution reaction

Direct growth of tungsten carbide and sulfide on vertically aligned carbon nanotubes (CNTs) is demonstrated for a facile construction of three-dimensional electrocatalyst nanostructures. A thin layer of tungsten was first deposited on free-standing CNT forests followed by annealing in an inert atmosphere or in the vapor of sulfur for obtaining tungsten carbide or disulfide, respectively. Besides structural characterization of the composites by means of scanning and transmission electron microscopy, Raman spectroscopy and X-ray diffraction, the produced CNT–catalyst composites are also evaluated in the hydrogen evolution reaction and compared to Pt as well as to the original and W coated CNT forests. The results indicate that the template growth of catalyst nanostructures on vertically aligned CNT forests is a suitable approach for catalytic electrode fabrication, which for example may find use in the hydrogen evolution reaction.

Mechanochemically assisted synthesis of pristine Ca(II)Sn(IV)-layered double hydroxides and their amino acid intercalated nanocomposites

Syntheses of Ca(II)Sn(IV)-layered double hydroxides (LDHs) are attempted by the traditional co-precipitation as well as mechanochemical methods. Both the co-precipitation method and the one-step milling operation proved to be unsuccessful; these methods only produced physical mixtures of hydroxides and carbonates of the two metal ions. However, a two-step milling operation (dry milling followed by milling in the presence of minute amount of water) led to successful synthesis, verified by a range of characterisation methods. Surprisingly, it was found that ball-milling was not even necessary; the reaction proceeded on manual grinding of the components in an agate mortar with a pestle. The preparation of nanocomposites through intercalation of the anions of cystine or valine into Ca(II)Sn(IV)-LDH could also be achieved by the two-step milling method verified again by a range of instrumental methods.