Isabelle Willems

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.

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.

Purification of catalytically produced multi-wall nanotubes

Carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co incorporated zeolite NaY support. Purification of multi-wall nanotubes was required in order to eliminate catalyst and amorphous carbon produced by thermal decomposition of hydrocarbon. First, separation of nanotubes and catalyst particles was carried out by hydrofluoric acid treatment. Then, two ways of removing amorphous carbon were studied: permanganate oxidation and air oxidation. The quality of nanotubes was characterized by means of transmission electron microscopy and the yield of pure nanotubes was quantitatively determined. Changes caused by treatment of the nanotubes were investigated by high resolution electron microscopy and a comparison was made between the nanotubes produced by this method and those synthesized by an arc discharge process after oxidation treatment.

Synthesis of single-wall carbon nanotubes by catalytic decomposition of hydrocarbons

Individual single-wall carbon nanotubes (SWNTs) and bundles can be obtained over different types of supported metal catalysts by decomposition of ethylene, similar to the synthesis of multi-wall carbon nanotubes.

Functional groups generated by mechanical and chemical breaking of multiwall carbon nanotubes

Since the discovery of carbon nanotubes several attempts were made to modify them by various physical and chemical methods. Applying a ball-milling system mechanical cutting of nanotubes can be achieved. TEM, surface area and porosity measurements are used to follow these changes on the nanotubes. Using different reagents and methods functional groups can be generated on the nanotubes. To prove the existence of these groups infrared spectroscopy is used. Finally, it will be shown that the physical and chemical breaking processes complete each other very well.

Large scale synthesis of carbon nanotubes and their composite materials

MgO supported transition metals are very interesting systems for possible large scale synthesis of carbon nanotubes. Indeed, the catalytic decomposition of acetylene at high temperature leads to the formation of very thin multi-wall carbon nanotubes (inner and outer diameters are in the range of 2–4 nm and 5–9 nm, respectively). The decomposition of methane, on the other hand, produces bundles and isolated single-wall nanotubes (SWNTs) of high purity. Typically, the diameters of isolated SWNTs are 1–5 nm. For the SWNTs aligned in the bundles, the diameter values vary between 0.8 and 2 nm. The samples are characterized by TEM, and HREM. The purity of the nanotubes is evaluated by PIXE (proton induced X-ray emission) and by thermal analysis. The nanotubes are cut mechanically in a ball-mill and the introduction of various functional groups is determined by XPS. Finally, homogeneous mixture of carbon nanotubes and polyacrylonitrile will be shown.

Synthesis, characterization and catalytic application of inorganic nanotubes

Abstract Nanotubes of inorganic compositions have been prepared and characterized by various techniques. Two main additives were used for the preparation. As template material carbon nanotubes were used for preparation of silica and alumino-silica tubes with diameter of nanometer scale. Optically active organic acids were used as additives for synthesis of silica nanotubes. In this case the structure of the tube showed that its geometry was angular rather then circular. For removal of organic material from the as prepared nanotubes two different methods were applied. Besides the conventional burning with oxygen, a novel method, applying ozone as oxidant, was also used. The inorganic nanotubes were suitable support for heteropoly acids as catalytically active components.