Making Buckminsterfullerene

The Carbon-Arc Experiment

The following experiment describes the way to make buckminsterfullerene. The apparatus showed below is the original machine that was used to make the first quantities of C60 at Sussex University in 1989 - 90.( Document source is obtained from "University of Sussex, Fullerene Group Homepage")

Total experimental time - about 1 hour

• Setting up the bell-jar apparatus

Remove the glass bell-jar and if necessary fit some new carbon rods as described during the demonstration. Also arrange the KBr plates to within 6-7 cm from the rods.

• The carbon arc and using the power supply

Pump down the system (see the demonstrator) and introduce Helium gas into the chamber. Repeat (purge). Finally fill the bell-jar with about 100 Torr of Helium.

Connect up the welding kit power supply (NOTE: the welding kit power supply is a high current, low voltage supply and therefore there is little risk of electrical shock, however care should be taken as with any other 240 v mains operated device). Turn the on / off switch on the supply to the on position for 10 to 15 seconds. Afterwards there should be plenty of black soot like material produced inside the bell-jar.

• Collecting the material

After a 5-10 min cool down period fill the bell-jar to atmospheric pressure. Take the bell-jar off and scrape the glass surfaces clean, collect all the material. Believe it or not, 10 % of the soot should be made up of C60.

• Measuring the IR spectra

Take the soot covered KBr plate and measure the IR spectrum as directed by the demonstrator. You should be able to observe the tell-tale signs of C60, i.e. four weak absorptions on top of the larger absorption (see below).

• Background note - testing for Buckminsterfullerene - IR analysis

Most molecules absorb in the Infra-red (IR) and the number of absorptions is dependant on the number of atoms in the molecule and how symmetrical the structure of the molecule is. In general an N atom molecule will have about 3N absorptions in the IR. As the symmetry increases the number of IR absorptions falls. For a molecule having 60 atoms one would expect 3 x 60 = roughly 180 IR absorptions. However because of the unique symmetry of Buckminsterfullerene, C60 has just 4 IR absorptions. This incredibly simple spectral fingerprint for C60 made IR spectroscopy a particularly effective method by which to probe for C60 in the arc made materials. We are going to use this technique to check that the carbon arc materials have C60 present in them.

• Extracting the fullerenes from the soot

Place a lot of the collected soots into a small flask. Add 20-30 ml of toluene and stopper the flask. Shake gently. Is there any colour change ? Next filter the solution. What colour is it ?

The fullerenes was just extracted from the soot. The coloured solution is due to a mixture of C60, C70 and larger fullerene cage molecules.

The next step is to purify the mixture of the fullerenes into separate fractions. Chromatography,which is the basis of the next experiments is used. To do the chromatography properly quite a lot of soot extracted solution is needed.

Purifying the Fullerenes

- by Chromatography

The chromatographic separation and purification of the fullerenes was first achieved at Sussex University soon after the carbon arc technique was discovered. Separation of pure allotropes by chromatography is believed to be unique to fullerenes.

Total experimental time - about 1 hour

Stage 1

• Fill the column, to the level shown, with the carbon granules (using a funnel).

Stage 2

• Add some toluene (using a different funnel) and allow the solvent to drip out of the bottom of the column into a 100 ml flask. Continue until the level of the solvent falls to the height of the carbon granules.

Stage 3

• 1) Using one of the 100 ml flasks, add 30 - 40 mg of soot extracted fullerene mixture to about 50 ml of toluene

   

• 2) Stopper the flask and shake gently for about 20 seconds. You should get a deep red solution.

   

• 3) Pour the solution into the dropper flask (check that the tap is closed first !).

   

• 4) Connect the dropper flask to the top of the column. Open all the taps and collect the drops in a clean flask.

Stage 4

• 1) Collect the drops from the column and every couple of min pour the collected solvent into the waist bottle. When the colour of the solvent starts to change, collect all the solvent in the same flask.

   

• 2) The hand pump can speed up the process if necessary.

   

• 3) Eventually the level of the red fullerene mixture will fall below the carbon granules. Turn all the taps off. Refill the dropper funnel with fresh toluene. Open all the taps and continue collecting the fractions.

Stage 5

• 1) After 20 - 30 min the magenta colour of pure C60 will appear and should continue for a further 20 min or so.

   

• 2) When the colour disappears from the solvent allow the remaining toluene to fall to the carbon granule line. Then add dichlorobenzene to the dropper flask. Continue collecting fractions (use another flask).

   

• 3) After a while the red C70 fraction will appear. C60 and C70 are now successfully separated from the fullerene mixture.

   

• 4) Let the dichlorobenzene pass through the column and leave to drain.

The production of fullerenes can also be done in many other convenient ways. The example are the Solar Fullerene Production and the Pyrolytic Production of Fullerenes. The production of related fullerene is also done in the recent year. Example of this is the Fullerene Nanoprobes Production

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