From Carbon Dioxide to Few-Layer Graphene


High resolution image of a single graphene sheet (source: http://www.grapheneenergy.net)

In a recent paper published in the Journal of Material Chemistry entitled “Conversion of Carbon Dioxide to Few-Layer Graphene” researchers from Illinois and Texas propose a new, possibly more cost effective way to produce high yields of graphene. The researchers burned magnesium in dry ice.  This process led to the formation of magnesium oxide and carbon. While the principle reaction and process has been known for long, the group of researchers claims that it is the first time to demonstrate that the described processing results in the formation of few-layer nanosheets of graphene in high yields.

Graphene is a two-dimensional material comprised of a single layer of atoms which are arranged on a hexagonal lattice. In the past few years graphene has received much attention for its excellent mechanical and electronic properties. It is thought to possibly replace silicone as the material of the future. Applications of graphene are seen in sectors diverse such as the fields of sensors, nano-electronics, composites, hydrogen storage, lithium-ion batteries and health-care.  However, currently one of the limits is the rather challenging and cost-intensive production process. This is why research on graphene does not solely concentrate on the material’s properties, but also on possible production processes which in the future may provide industrial scale production.

Currently, the literature describes a list of varying graphene production processes such as mechanical exfoliation of graphite, epitaxial growth on silicon carbine, epitaxial growth on metal substrates, graphite oxide reduction, growth from metal substrates, graphite oxide reduction, growth from metal-carbon melts, pyrolysis of sodium ethoxide, from nanotubes, from sugar and from graphite by sonication. In addition, some of the described methods rely on strong oxidizing agents which one preferably would want to avoid.

The newly presented strategy by Hosmane and co-workers has actually already been explored within the quest of a metal–CO2 propulsion system for mars missions, but the process outcome has not yet been systematically investigated with respect to the formation of solid structured nanomaterials. As a first step  it is based on burning a strip of magnesium insight a dry ice bowl which again is covered up by another dry ice slab. After completing the burning process the outcome was given into a solution of high concentrated hydrochloric acid where it was kept for several hours. Due to the reaction of the remaining magnesium and the formed magnesium oxide with the hydrochloric acid to water soluble magnesium chloride it was possible to easily divide the carbon matter from the unwanted byproducts. After several washing and filtering processes the isolated solid carbon could be dried under high vacuum at 100 °C.  Relying on several methods such as Raman spectroscopy, energy-dispersive X-ray analysis, X-ray powder diffraction and transmission electron microscopy it could be established that a few-layer graphene nanosheet had formed.

Currently, the exact mechanism behind this process is not understood. However, the authors argue that the high temperature present during the burning of the magnesium may play a crucial role. They hypothesize that the combustion of magnesium in gaseous carbon dioxide possibly favors the rapid flee of the solid product from the reaction center. Hence, the sp2 orbital atoms of the carbon dioxide in the reaction center lack the time to form multi-layer graphene (graphite). Thus, the kinetics favors the formation of only a few-layer graphene.

Finally, the authors claim that “the synthetic process is cost effective and can be used to produce few-layer graphene in large quantities.”

Source:

Conversion of carbon dioxide to few-layer graphene

Amartya Chakrabarti,Jun Lu,  Jennifer C. Skrabutenas,  Tao Xu, Zhili Xiao, John A. Maguireb and Narayan S. Hosmane

J. Mater. Chem., 2011, 21, 9491

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