Graphene
Graphene is a one atom thick crystalline form of carbon. Graphene's structure is organized into a hexagonal (honeycomb) shape and can exist naturally in the stacked form of graphite or charcoal. Graphene also forms the fundamental structural units of graphene nanotubes. Graphene is best known for its excellent tensile strength, transparency to light, and high electrical and thermal conductivity[2]. It has an extremely high surface area-to-weight ratio, which is responsible for many of its properties.
Properties
The electrical and thermal conductivities of graphene are among the highest of any known element at room temperature. The thermal conductivity is the rate in which thermal energy can transfer across a material. The surface area is the total area of the objects faces. The electrical resistance of graphene is among the lowest of any known material at room temperature. It can be defined as the ease in which electrons can pass through the material. Graphene also has very high transparency to light, only absorbing 2.3% of the total white light passing through it. Currently, graphene is very expensive, but its price is predicted to drop by a factor of 4 by the year 2022(cite?).
Table 1. The surface area, resistance and thermal conductivity of graphene, copper and silver [3][4].
| Graphene | Copper | Silver | |
|---|---|---|---|
| Surface Area (meter2/gram) | 1520 | 4.11 | 2-6 |
| Resistance (Ohms/meter) | 1x10-8 | 1.68x10-8 | 1.59x10-8 |
| Thermal Conductivity (Watt/meter*Kelvin) | 4.84x103 | 401 | 429 |
Applications
Electronic: Graphene has a low electrical resistivity, allowing it to be used in LCD display screens, transistors, and electric circuits. Graphene is also applied to solar cells due to its high optical transparency.
Energy storage: Due to graphene's high surface area and low electrical conductivity, it can be applied as electrodes in supercapacitors and Lithium ion batteries [5].
Distillation: With a uniform pore size, graphene is used in ethanol distillation and the desalination of water [6].
Medical: Due to increasingly cheaper production methods, scientists have proposed graphene be used for microbial detection [7].
Production
Graphene can be produced by a variety of methods. Currently, the cheapest methods to produce graphene are laser scribed graphene, inkjet printing, thermal reduction of graphene oxide, as well as chemical deposition of graphene.
Laser scribed graphene
Laser scribed graphene is produced by pouring graphene oxide onto a plastic coated DVD disk and left to dry. Once dried, the graphene and the DVD disk are inserted into a LightScribe DVD burner. The DVD burner emits radiation on the graphene oxide, splitting the bonds between the carbon and oxygen groups. Graphene is the product of this reaction and can be seen by the change in colour from light brown to black on the DVD [8].
Inkjet printing and thermal reduction of graphene
Graphene, produced by the inkjet printing method utilizes graphene oxide dissolved in water as an “ink” for the printer. The particle size of commercially purchased graphene oxide is much larger than the size of the internal diameter of the nozzle. This results in clogging of the nozzle, preventing the particles from passing through. This is mitigated by filtering the graphene with a mylex syring and bombarding the graphene oxide molecules with sound waves to reduce the particle size. The graphene oxide solution is then loaded into a cartridge for jetting. Tiny droplets, produced by the nozzle, are printed onto a tin sheet and inserted into an oven. The oven adds thermal energy to the graphene oxide, splitting off an oxygen atom, producing graphene [9].
Chemical vapour deposition of graphene
Chemical vapor deposition is the process in which carbon atoms bond to an underlying layer (a metal substrate) in very high temperatures. When the carbon atom bonds to the material, it takes up a position in space on the surface of the material. The carbon atoms push each other aside when they bond to the underlying layer. Once every position on the underlying layer is filled, a one atom thick, continuos layer of carbon atoms is formed. The temperature is then reduced and the carbon atoms form bonds with each other creating a sheet of graphene [10].
Carbon nanotubes
Graphene is used to create carbon nanotubes, which are a small, hollow fiber with the highest tensile strength known to man. They are extremely expensive at this point, but future applications include lightweight body armour, ultra-strong carbon fiber, and even small and lightweight wires for carrying electricity.
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References
- ↑ H. Zhang et al., “Layer-by-layer inkjet printing of fabricating reduced graphene-polyoxometalate composite film for chemical sensors,” Phys. Chem. Chem. Phys., vol. 14, no. 37, pp. 12757–12763, Oct. 2012.
- ↑ Y. Song, H. Yang, Y. Wang, S. Chen, D. Li, S. Zhang, and X. Zhang, “Controlling the assembly of graphene oxide by an electrolyte-assisted approach.,” Nanoscale, vol. 5, no. 14, pp. 6458–63, Jul. 2013.
- ↑ G. C. Chinchen et al., “The measurement of copper surface areas by reactive frontal chromatography,” J. Catal., vol. 103, no. 1, pp. 79–86, Jan. 1987.
- ↑ J. E. Schroeder, D. Pouli, and H. J. Seim, “High Surface Area Silver Powder as as OxygenN Catalyst.”
- ↑ M. D. Stoller, S. Park, Y. Zhu, J. An, and R. S. Ruoff, “Graphene-based ultracapacitors.,” Nano Lett., vol. 8, no. 10, pp. 3498–502, Oct. 2008.
- ↑ D. Cohen-Tanugi and J. C. Grossman, “Water desalination across nanoporous graphene.,” Nano Lett., vol. 12, no. 7, pp. 3602–8, Jul. 2012.
- ↑ [1] N. Mohanty and V. Berry, “Graphene-based single-bacterium resolution biodevice and DNA transistor: interfacing graphene derivatives with nanoscale and microscale biocomponents.,” Nano Lett., vol. 8, no. 12, pp. 4469–76, Dec. 2008.
- ↑ 8.0 8.1 M. F. El-Kady et al., “Laser scribing of high-performance and flexible graphene-based electrochemical capacitors,” Science, vol. 335, no. 6074, pp. 1326–1330, Mar. 2012.
- ↑ X. Yang et al., “Liquid-mediated dense integration of graphene materials for compact capacitive energy storage,” Science, vol. 341, no. 6145, pp. 534–537, Aug. 2013.
- ↑ B. Pollard, “Growing Graphene via Chemical Vapor Deposition,” pp. 1–47, 2011.