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.

Reference

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 Trapping. ACS Nano, 2013; 7 (8): 7062 DOI: 10.1021/nn402371c

Further Reading:

Allotropes Tutorial

Graphene and Fullerenes Tutorial

Nanotechnology Tutorial

Metallic Bonding Tutorial

Wetting Tutorial

Surface Tension Tutorial

Density Tutorial

Water as a Solvent (aqueous solutions) Tutorial

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.

Buckyballs and Nanotubes

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Borospherene

A molecule containing 60 carbon atoms in a cage-like spherical shape was first produced in 1985 and was called buckminsterfullerene, or bucky-ball. The structure is like a soccer ball, made up of 20 hexagons and 12 pentagons.
A bucky-ball is shown on the right. Each blue sphere represents a carbon atom, and each cream-coloured line represents a covalent bond between 2 carbon atoms.
One of the reasons that scientists are very interested in buckminsterfullerene is because of its ability to hold atoms of different elements inside the cage-like structure. This could enable bucky-balls to be used to deliver drugs in the body, or to store atoms such as hydrogen.

In 1991, scientists discovered that carbon atoms can also form nanotubes, and in 2004, sheets of carbon atoms just 1 atom thick known as graphene were discovered.

But can atoms other than carbon make these kinds of 3-dimensional networks at the nanometre level?

Researchers from Brown University, Shanxi University and Tsinghua University in China have shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball. It's the first experimental evidence that a boron cage structure does indeed exist.
This boron cage, called borospherene, isn't quite as spherical as its carbon cousin. Rather than a series of five- and six-membered rings formed by carbon, borospherene consists of 48 triangles, 4 seven-sided rings and 2 six-membered rings. Several atoms stick out a bit from the others, making the surface of borospherene somewhat less smooth than a buckyball.

Because of the electron deficiency of boron, borospherene is likely to bond well with hydrogen. So these tiny boron cages could serve as safe houses for hydrogen molecules.

Reference:
Brown University. "Researchers discover boron 'buckyball'." ScienceDaily. ScienceDaily, 13 July 2014. .

Further Reading:
Graphene
Molecular Formula
Allotropes

Suggested Study Questions:

1. Write the molecular formula for buckminsterfullerene given the information in the article above.
2. How many covalent bonds does each carbon atom in buckminsterfullerene make?
3. Do you expect buckminsterfullerene to be soluble or insoluble in water? Explain your answer.
4. Draw a representation of graphene.
5. How many covalent bonds does each carbon atom make in graphene?
6. Do you expect graphene to conduct electricity? Explain your answer.
7. Write the molecular formula for borospherene based on the information provided in the article.
8. In the pictorial representation of borospherene given above, what do each of the following represent:
   • red spheres
   • yellow lines
9. In what ways are the structures of bucky-balls and borospherene similar?
10. In what ways are the structures of bucky-balls and borospherene different?

Graphene Capillary

Graphene is made up of carbon atoms, it is an allotrope of carbon.
 Each carbon atoms bonds to 3 other carbon atoms forming hexagons. Each hexagon shares each side with another hexagon. So this lattice of hexagons extends indefinitely, but it is only 1 carbon atom high! For this reason graphene is referred to as a two-dimensioal lattice or array.

Graphene is strong, light, nearly transparent and an excellent conductor of heat and electricity. Graphene is also hydrophobic, it repels water. However, narrow capillaries made out of graphene actually suck in water, if the water layer is only one atom thick.

Two years ago, researchers at the University of Manchester found that graphene capillaries could be made by stacking layers of graphene oxide on top of each to form a laminate. One-atom wide graphene capillaries are produced between these layers. These laminates are impermeable to all gases and vapours, except for water. This means that no gas or vapour, except for water, can pass through the laminate. Even helium, the smallest of the Nobel Gases cannot pass through the laminate.

These results suggest that graphene capillaries could be used to filter water. Researchers at the University of Manchester having been studying the use of graphene for water filtration and have found that ions less than 9 angstroms can quickly flow through with the water, but larger ions are blocked. With further research it is hoped to control the graphene mesh size to reduce it below 9 angstroms so that even the smallest ions like those found in seawater could be filtered out of water.

Reference:
R. K. Joshi, P. Carbone, F. C. Wang, V. G. Kravets, Y. Su, I. V. Grigorieva, H. A. Wu, A. K. Geim, R. R. Nair. Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes. Science, February 14, 2014 DOI: 10.1126/science.1245711

Further Reading
Allotropes
Metric Conversions

Suggested Study Questions:

1. What is meant by the term "graphene is an allotrope of carbon?"
2. Name, and describe the structure of, two other allotropes of carbon.
3. Explain how the structure of graphene is different to the structure of graphite.
4. Why is graphene considered to be a good electrical conductor? 
5. Which other allotrope of carbon is considered to be good electrical conductor? Explain how this allotrope conducts electricity.
6. 1 angstrom = 1 Å = 10^-10 metres. Convert 9 Å to:
   • metres
   • millimetres
   • microns (micrometres)
   • nanometres
7. 1 picometre = 1 pm = 10^-12 metres. Convert 900 pm to :
   • metres
   • millimetres
   • microns (micrometres)
   • nanometres
   • angstroms
8. Consider the crystal ionic radius for each of the following ions commonly found in seawater:
   • Na⁺ : 116 pm
   • Mg²⁺: 86 pm
   • Cl^- : 167 pm
   • F^- : 119 pm
   • What is the diameter of each of these ions in angstroms?
   • Which, if any, of these ions would pass through a graphene capillary? Explain your answer.
9. A nitrate ion has a diameter of about 0.33nm and a sulfate ion has a diameter of about 0.49 nm. Which of these ions, if any, could pass through a graphene capillary? Explain your answer.

Graphene: AUS-e-NEWS December 2010

Excitement is growing in the scientific community about the possible uses for graphene.
This simple, naturally occurring allotrope of carbon could revolutionize our world.
The December 2010 issue of AUS-e-NEWS, AUS-e-TUTE's quarterly newsletter, takes a look at the chemistry of graphene, and at its possible future uses.

To subscribe to AUS-e-TUTE's free newsletter email:


and type subscribe as the subject.

Nobel Prize for Work on Graphene

The 2010 Nobel Prize in Physics has been awarded to Andre Geim and Konstantin Novoselov for their "groundbreaking experiments regarding the two-dimensional material graphene".

Graphene is an allotrope of carbon, it is the thinnest and strongest material known. It conducts electricity as well as copper and outperforms all other materials as a conductor of heat. It is almost completely transparent, yet it is so dense that not even helium, the smallest known gas atom, can pass through it.

Geim and Novoselov extracted graphene from a piece of graphite such as is found in "lead" pencils. Using a piece of adhesive tape they obtained a flake of carbon that was just one atom thick, which is the allotrope known as graphene.

Reference:
http://static.nobelprize.org/nobel_prizes/physics/laureates/2010/info_publ_phy_10_en.pdf

Further Reading
Allotropes
Elements

Study Questions:

1. What is meant by the term allotrope?
2. Name two other naturally occurring allotropes of carbon.
3. Draw a table listing the physical properties of both of these allotropes and graphene.
4. Discuss the similarities and differences between these allotropes.
5. Draw a possible structure for graphene.
6. Describe the similarities and differences between the structure for graphene that you have drawn and the structures for the other two allotropes in your table.
7. Using your structure for graphene, explain the similarities and differences between the physical properties of graphene and the other two allotropes.
   

Hexagonal Boron Nitride

Graphene, a single-atom thick allotrope of carbon and an electrical conductor, is considered to be a possible successor to silicon in microelectronics applications.
Hexagonal boron nitride (h-BN) is an insulator. It is highly elastic and nearly as strong as graphene. Rice University scientists have found a way to implant sheets of h-BN into sheets of graphene, which controls the sheet's electronic character.
They have also found a way to deposit sheets of pure h-BN, 1 to 5 atoms thick, onto a copper substrate using a chemical vapour deposition process at about 1,000^oC. The h-BN material can then be transferred to other substrates. The size of h-BN sheets is limited only be the size of the copper foil and furnace used to grow it.
It should be possible to draw microscopic patterns of graphene and h-BN, useful in creating nanoscale field-effect transistors, quantum capacitors or biosensors.

Reference:
Li Song, Lijie Ci, Hao Lu, Pavel B. Sorokin, Chuanhong Jin, Jie Ni, Alexander G. Kvashnin, Dmitry G. Kvashnin, Jun Lou, Boris I. Yakobson and Pulickel M. Ajayan. Large Scale Growth and Characterization of Atomic Hexagonal Boron Nitride Layers. Nano Letters, 2010; 100722142755098 DOI: 10.1021/nl1022139

Study Questions

1. What is meant by the term allotrope?
2. What are the naturally occurring allotropes of carbon?
3. In what ways are these allotropes of carbon the same?
4. In what ways are these allotropes of carbon different?
5. If the formula for boron nitride is BN, what is the oxidation state (number) of boron?
6. Given the name hexagonal boron nitride, draw a possible Lewis Structure (electron dot diagram) for hexagonal boron nitride.
7. In what ways are graphite and hexagonal boron nitride the same?
8. In what ways are graphite and hexagonal boron nitride different?
9. Why is graphite a conductor while hexagonal boron nitride is an insulator?