Turning diesel soot into useful carbon nanomaterials

A group of environmentally-conscious Japanese scientists have come up with a way of producing something useful from the noxious emissions of diesel engines.

Could the exhaust from diesel electric generators and ship engines be used to produce useful carbon nanomaterials?

Masaru Tachibana at Yokohama City University, together with university colleagues and researchers working for carmaker Nissan and environmental technologists Juon, has taken green nanotechnology to a new level.

In a technique developed by Juon’s Tetsuro Nishimoto, particulate matter from diesel engines is trapped on ceramic filters in the exhaust pipes of diesel engines. Composed of soot, soluble organic fractions and sulphates, the particulates are separated from the filters by ultrasonic washing with water or ethanol. The diesel soot is then collected using a technique known as Soxhlet extraction, and subjected to laser vaporisation to synthesize single-walled carbon nanotubes.

Whether it will ever prove economically viable to implement this technology in the real world depends on a number of factors, and fitting diesel soot extractors to domestic cars will most likely never be feasible. Tachibana argues that it would be better to focus on large diesel electric generators and seagoing vessels.

But it all depends on the seriousness of the pollution problem. “Practical application would be accelerated if political control [of diesel pollution] becomes severe,” says Tachibana. “Taking into account current activity surrounding environmental pollution, our process might be implemented earlier than expected.”

On a technical level, the usefulness of the nanotubes produced in this way is limited by the relatively low purity levels achievable. Applications such as electrodes and car tyres are a distinct possibility, however, and the Japanese researchers are currently looking into this in collaboration with a number of companies.

Eiji Osawa, President of the NanoCarbon Research Institute, is fascinated by the research results. Although he has serious doubts about the economic feasibility of producing nanotubes, Osawa believes that the technique could be extended to produce multishell fullerenes, the precursor to nano-diamonds.

Figure: Could the exhaust from diesel electric generators and ship engines be used to produce useful carbon nanomaterials? (© Japanese Journal of Applied Physics).

Further reading: Synthesis of Single-Wall Carbon Nanotubes from Diesel Soot, Uchida et al., Japanese J. App. Phys. 45, 8027 (2006).

Article first published in Nanomaterials News.