Answers to questions on Nanotechnology

1. (a) Nanotechnology is the research and use of compounds whose size lies between one and one hundred nanometres (1 x 10⁻⁹ and 1 x 10⁻⁷ m).

(b) A nanotube contains walls made of graphene closed at one or both ends with a hemisphere of buckminsterfullerene.

(c) Small airborne particles may become lodged in the lungs and the potential health hazards associated with these small particles are still not fully known. It is possible that the immune system may not be effective at combatting problems caused by nanoscale compounds.

2. They have a large surface area to attract reactant molecules.
They are able to bind nanoparticles of good transition metal catalysts, such as rhodium and platinum, to their surface to enable the catalysis to occur.

3. The carbon atoms in carbon nanotubes contain delocalised electrons, which are able to flow with virtually no resistance and thus conduct both electricity and heat.

4. The high pressure carbon monoxide process, HIPCO, involves the decomposition of iron pentacarbonyl in a continuous flow of carbon monoxide at a pressure of 30-50 atmospheres and a temperature of 900-1100 ^oC. During this process the iron pentacarbonyl breaks down to form carbon monoxide and iron nanoparticles.
Fe(CO)₅(s) → Fe(s) + 5CO(g)
The iron nanoparticles provide the surface upon which the carbon monoxide can transform into single-walled nanotubes.
xCO(g) → CNT(s) + ½ xCO₂(g)
where x = about 6000 to produce a nanotube, CNT, containing about 3000 carbon atoms.

5. In arc discharge either the surface of the carbon electrode is vaporised or an arc is discharged through metal electrodes in a hydrocarbon solvent so that oxidation occurs on the anode to form nanoparticles. In CVD a carbon containing gas, such as ethene, in the plasma phase (caused by a strong electric field) is decomposed in the presence of an inert gas (e.g. N₂) over heated layers of metal particles. The gas decomposes at the surface of the catalyst particles, where the carbon is transported to the edge of the particles where it forms the naonotubes.

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