The latest and possibly greenest of graphene production methods has emerged from work conducted at Toyohashi University in Japan. Research conducted by a team lead by Yuji Tanizawa has shown that microorganisms can be usefully employed to reduce grahene oxide flakes by means of respiration and electron transport. The new method vastly improves the current hydrazine vapour and high temperature techniques which are toxic and uneconomical.
Working from an educated hunch informed by recent research into Macromolecular rapid communications the team designed an experiment that would test the ability of the graphene oxide to act as a terminal electron acceptor with respect to microorganisms. The lucky specimens, taken from a river bank near the Tempaku Campus of Toyohashi University of Technology, were applied to graphene oxide on a silicon substrate and allowed to incubate for three days at 28° centigrade. The samples were then cleaned and raman spectroscopy conducted to determine the results.
The production method first requires the synthesis of graphene oxide from graphite powder, and is described in detail in the paper.
GO was synthesized by the modified Hummer’s method [5, 6] using natural graphite powder (Ito
Kokuen Co., Ltd, Japan) cleaned using K2S2O8, P2O5 and H2SO4, and oxidized in KMnO4 and H2SO4.
After overnight sedimentation and washing with 3wt% HCl aq. and MilliQ water… The resulting graphite oxide was then exfoliated into GO using centrifugation (10000rpm, 45min) instead of ultra-sonication,
because if we use ultra-sonication, the size of GO sheets become smaller and smaller. Finally,
a GO aqueous dispersion was purified by dialysis for one week to remove residual metal ions, acids
and to adjust pH to neutral
Yuri Tanizawa then goes on to describe the mechanism of production thus,
The GO was reduced when electrons from a sodium acetate solution were passed to the GO by
anaerobic breathing of the environmental microorganisms. These microbes have the ability to use a
large array of organic and inorganic compounds as terminal electron acceptors in their respiratory
Although the new production method needs much further investigation before it can be commercialised it does propose a solution to the problems arising from current production techniques. With these issues in mind it is hoped that bacterial cultivation will result in a low-cost, efficient, and environmentally friendly method for the mass production of high quality graphene.
As with all new developments in this fast moving field the repercussions may well be felt quickly. Companies that utilize the hydrazine and high temperature methods of reducing graphene oxide flakes will be watching closely to determine whether their particular mode of operation will be forced to change. With environmental concerns at the forefront of business and consumer decisions the potential this technique has to disrupt the current graphene investment choices of businesses is huge.
Original Paper can be read here.