LCN team develops cheaper way of separating nanotubes

Engineerblogger
Jan 12, 2012

Researchers in London have said they have developed a cheaper way of producing high-quality carbon nanotubes in larger quantities than existing methods.

A team from the London Centre for Nanotechnology (LCN) has licensed the process, which separates nanotubes into usable quantities without damaging them, to German-based industrial gases company the Linde Group.

Carbon nanotubes are one-atom-thick cylinders of carbon that have a wide range of applications — from strengthening material structures to improving the efficiency of solar panels — but are currently difficult to produce in large quantities.

‘It needs to be cheaper because at the moment it’s £1bn per kilo, which is not very plausible,’ LCN’s co-director Milo Shaffer told The Engineer.

‘But it doesn’t need to be incredibly cheap, because a lot of applications use quite a small amount of material.

‘We’ve done a gram at a time, but, in principle, you can do much more. Alternatives tend to work on a milligram scale.’

Nanotubes are difficult to manufacture because they come in many different types and, once they have been synthesised, tend to bind together and are difficult to separate.

‘A lot of the solutions are quite aggressive,’ said Shaffer, who is a professor of materials chemistry at Imperial College London. ‘You either use ultrasound to tear everything up or you use a lot of aggressive chemistry to oxidise the surface.

‘The trouble with that is that it damages the intrinsic properties you’re interested in and particularly reduces the length of the tubes — they get chopped up in the process.’

These methods can also require the nanotubes to be placed in a centrifuge, to force them to separate by spinning them at high speeds. This typically makes the process costly and limits the amount of material that can be manufactured at a time.

LCN’s solution was to charge the nanotubes with electrons so that they naturally repel each other, by reacting them with an alkali metal such as sodium in a solution of ammonia.

This solution of separated nanotubes can then be used for manufacturing things such as composites, or the nanotubes can be precipitated out of the solution.

‘In principle, you can get back to the material you started from,’ said Shaffer. ‘So you’ve managed to dissolve it, process it and separate it without any kind of damage, which is very appealing compared to the alternatives.’

Graham McFarlane, head of Linde nanomaterials, said in a statement: ‘We have already scaled the technology at our research and development centre in San Marcos, California. Products based on the technology will be available soon.’

Shaffer said that LCN, which is a joint venture between Imperial and University College London (UCL), decided to license the technology rather than form a spin-out firm due to the expertise and equipment needed to handle the ammonia.

Source: The Engineer