Zoltán Kónya

Large-scale synthesis of single-wall carbon nanotubes by catalytic chemical vapor deposition (CCVD) method

The 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.

Production of short carbon nanotubes with open tips by ball milling

Short multi-wall carbon nanotubes can be obtained by ball milling. The average length of the ball milled carbon nanotubes, synthesised by decomposition of acetylene on different types of supported metal catalysts, is ca. 0.8 μm. The cleavage was caused by the collision between one agate ball and the nanotube powder contained in an agate mortar.

Control of the outer diameter of thin carbon nanotubes synthesized by catalytic decomposition of hydrocarbons

Abstract Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo, Co–V and Co–Fe mixtures supported either on zeolite or corundum alumina were used as catalysts. When Fe or V is added to Co, the carbon deposit increases. The nanotubes were characterized by both low and high resolution TEM. From histograms representing the outer diameter distributions, it is clear that the outer diameter of the nanotubes can be controlled by choosing the appropriate catalyst.

Bulk production of quasi-aligned carbon nanotube bundles by the / catalytic chemical vapour deposition CCVD method

Abstract The large-scale production of quasi-aligned carbon nanotube bundles is reported. The method includes catalytic decomposition of acetylene over well-dispersed metal particles embedded in commercially available zeolite at a lower temperature (700°C). In-depth studies of this nanotube through scanning electron microscopy and transmission electron microscopy reveal their homogeneity as well as perfect graphitization, along with inner (2.5–4 nm) and outer diameters (10–12 nm) of the tubes. Details of the optimum conditions for producing these nanotubes are also described.

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.