Thursday, September 7, 2017

Graphene from Graphite

In 2004, University of Manchester researchers isolated graphene by applying sticky tape to a piece of graphite and peeling off a layer, then repeating the sticking and peeling process on this and subsequent layers until they had a layer that was just one carbon atom thick. The final 2-dimensional layer of carbon atoms is graphene. The structure of graphene is shown below:

The researchers, Professors Andre Geim and Kostya Novoselov were awarded the 2010 Nobel Prize in Physics.

Graphene is a highly sought after material. It is stronger than steel, yet it is a million times thinner a strand of hair. It is also a better conductor than the copper commonly used for electrical wiring. In order to use graphene in consumer products it needs to be produced on a large scale and in commercial quantities. It is not commercially viable to spend large amounts of time peeling off layers from graphite using sticky tape to produce small quantities of graphene. So the race has been on to find a process that could be used commercially.

One method is to oxidize graphite using hazardous oxidizing agents like anhydrous sulfuric acid and potassium peroxide. A representation of a layer of this oxidized graphene from the stacked layers making up graphite is shown below:

Layers of oxidized graphene can then be separated chemically from the bulk graphite, but these processes take a long time, and, the product is not graphene but oxidized graphene which is not as conductive as pure graphene.

University of Connecticut (UConn) Professor Doug Adamson has found a new way to produce graphene based on its solubility. Graphene is insoluble in liquids like oil, hexane and water.
Imagine you have a jug containing some oil and some water. If you wait, the two liquids will separate out, forming two distinct layers as represented below:

The less dense oil will float on top of the more dense water. If you add graphite to the area where these two liquids meet (the interface), then the stacked layers of graphene sheets in the graphite spontaneously "unstack" and spread out to cover this interface. These trapped graphene sheets can be locked into place using a cross-linked polymer.

The researchers are now investigating how this graphene composite material could be used to desalinate brackish water.

  1. Steven J. Woltornist, Andrew J. Oyer, Jan-Michael Y. Carrillo, Andrey V. Dobrynin, Douglas H. Adamson. Conductive Thin Films of Pristine Graphene by Solvent Interface TrappingACS Nano, 2013; 7 (8): 7062 DOI: 10.1021/nn402371c

Further Reading:

Suggested Study Questions
  1. Explain why graphite is a good conductor of electricity.
  2. Explain how the structure of graphene and graphite are:
    • similar
    • different
  3. Explain why graphene is considered to be a 2-dimensional material but graphite is considered to be a 3-dimensional material.
  4. Explain why graphene is a much better conductor of electricity than graphite.
  5. What characteristics of graphene allow it to be peeled off in layers from bulk graphite. Explain your answer.
  6. Explain why a mixture of oil and water will separate out into 2 distinct layers rather than forming a homogeneous mixture.
  7. Consider the structure of graphene to explain the insolubility of graphene in:
    • water
    • oil
  8. Explain why copper is a good conductor of electricity.
  9. Discuss how the structures of copper and graphene are:
    • similar 
    • different
  10. Explain why graphene is a much better conductor of electricity than copper.

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