Graphene: It runs right through a river?

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  • Published: Apr 1, 2012
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Graphene: It runs right through a river?

Modern material made by microbes

Image of reduced graphene oxide sheets
on a SiO2/Si substrate.

A research team in Japan has synthesized the "wonder material" graphene by reducing graphene oxide using microorganisms extracted from a local river. Analysis by Raman spectroscopy verifies the chemistry of the graphene flakes.

A low-cost, highly efficient, and environmentally friendly method for the mass production of high quality graphene could help speed up our approach to a future generation of microelectronics devices based on this material, which looks set to complement silicon semiconductors initially and perhaps displace the standard model in years to come. Graphene is a unique allotrope of carbon, it can be viewed as a monolayer of graphite, resembling chickenwire fencing with an arrangement of carbon atoms at the vertices of the "chickenwire hexagons". It is tough, incredibly strong, thin, and has a wide range of unique optical and electronic properties that have become the focus of intense interest since the Nobel-winning work of Andre Geim and Konstantin Novoselov of the University of Manchester used sticky tape to tear a strip off. However, despite Geim and Novoselov's neat laboratory approach to making small quantities of graphene if there is to be an industrial revolution based on this material there is an overwhelming need to make industrial quantities cheaply.

The chemical reduction, or exfoliation, of graphene oxide (GO) flakes can be used to synthesise graphene. In this process, the critical stage of reducing the oxide flakes to the bare carbon sheeting requires the researchers to expose the oxide to the explosive and toxic organic nitrogen compound hydrazine, better known as rocket fuel. Obviously, the properties of hydrazine limits its use in large-scale or even preliminary pilot-scale production. An alternative reducing agent has now been found by the Graphene Research Group at Toyohashi University of Technology, in Aichin, in what might be one of the most unlikely of places - the team's nearby river.

Tales of the riverbank

Earlier research had demonstrated that graphene oxide can act as a terminal electron acceptor for the action of certain bacteria. The oxide is reduced by microbial action in this "respiratory" electron transport process. The Toyohashi Tech group has now exploited this behaviour in a hybrid approach to graphene production. They first use a conventional chemical process to generate graphene oxide flakes from graphite and then apply a biological reagent in the form of microbes from the riverbank near the University's Tempaku Campus to reduce the oxide to naked graphene. The proof of reduction lies with the Raman scattering measurements obtained by the team which prove the microbes do indeed reduce the graphene oxide to graphene. Indeed, the team reported recently that their procedure enabled the production of approximately 100 micrometre-sized reduced graphene sheets, which showed "excellent" Raman spectra associated with high quality reduced graphene. They have detailed the relationship between the specific species of microbe involved in the process and the properties of the resulting reduced graphene.

SpectroscopyNOW asked team leader Adarsh Sandhu about the nature of the microbes the team has found to be active in this process. "We cannot disclose the type of bacteria yet because we are preparing another paper based on this information," he told us. However, he did tell us that, "It should be relatively easy to industrialise this method. The last step of reducing graphene oxide would simply be carried out in a tank containing the bacteria. The byproducts would not be dangerous and would be easy to dispose without expensive equipment."

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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