Researchers Make Carbon Nanotubes Without Metal Catalyst

14 August 2009

Scientists at MIT have discovered that nanotubes can grow without a metal catalyst. The researchers have demonstrated that zirconium oxide can be used to grow nanotubes without the unwanted side effects of metal.

Researchers found that if they just used zirconium oxide nanoparticles on the substrate, when growing nanotubes in the traditional method, they could coax carbon into nanotubes. According to the team responsible, this resulted in growth which appeared completely different from that of metal nanoparticle-grown tubes; instead of dissolving into the nanoparticle and precipitating out, zirconia-grown nanotubes appeared to assemble directly on the surface.

In collaboration with Professor Stephan Hofmann at the University of Cambridge in England, the MIT researchers took images of the oxide-based nanotubes using X-ray photoelectron spectroscopy during growth. This allowed them to see that when nanotubes formed, zirconium oxide persisted, and didn't form into a metal.

Historically, nanotubes have been grown using elements unsuitable for clean room environments, but using this alternative catalyst could provide a solution to this problem. The new development also allows researchers to view the formation process using infrared spectroscopy, something which is difficult to accomplish when using metals.

""I think this fundamentally changes the discussion about how we understand carbon nanotubes synthesis,"" says Brian Wardle, professor of aeronautics and astronautics.

Wardle suspects that more oxide-based catalysts will be found in the coming years. He and his team will focus on trying to understand the fundamental mechanisms of this type of nanotube growth and continue in their attempts to discover further non-metal catalysts. While the researchers don't have a timeline, they suspect that it would be easy to commercialize the process as it's simple, adaptable and, in many ways, more flexible than growth with metal catalysts.

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