At a glance
Isolated for the first time in 2004 by Nobel Prize laureates, Andre Geim and Konstantin Novoselov, the allotrope of carbon known as graphene has gathered an steadily increasing attention by scientists and industries alike. A bidimensional crystal stable at standard conditions, its structure confers it a number of unusual mechanical, thermal, and electric properties that has placed it over traditional materials such as silicon.
Some of graphene's intersting properties are:
- Graphene is one of the hardest material known. A single layer of this carbon structure can achieve a Young's modulus of 1.0 TPa (Lee et al, 2008). This elastic modulus, which works as a measure of a material's stiffness, overmatches steel's by 5 (Halliday, Resnick and Walker, 2001).
- Graphene is regarded as a 2D material because it is made up of a single layer of carbon atoms. This means it has an effective thickness around 3 Å (Cooper et al, 2012), that is about 300,000 times thinner than an average piece of paper (Sherlis, 2001).
- Graphene's exceptional thermal conductivity (up to 5000 W⁄mK for a single sheet of graphene) could improve performance and reliability of electronic devices (Singh et al, 2011).
- Thin graphene samples can fully adhere and follow the topography of an elastic substrate. This means that these kind of samples are highly sensitive to tension, thus they are easier to deform (Cooper et al, 2002).
- Graphene only absorbs 2.3% of incident light, indicating that it is a good candidate to build transparent electronic components such as electrodes, polarizers, and ultrafast lasers (Tsakmakidis, 2013).
Graphene´s quality is important since any deformations produced by impurities, structural disorders or wrinkles can directly impact in its properties, resulting in a material with poor electronic and optical applicability.
Nowadays, there are two major bottlenecks when talking about production of high quality graphene:
- First, its mass production, since it is very difficult to produce large amounts of graphene with needed qualities for electrical sectors given that it must have a high conductivity and optical transparency.
- Secondly, actual methods to synthesize graphene involve the usage of hazardous chemicals, like hydrazine, that generate toxic gases and waste.
To address these issues, it is imperative to develop a greener process with an eco-friendly approach, since the demand of this material will increase, and as such, its pollutants if the process is not modified.
Some of the currents methods for graphene are summarized next:
|Liquid Phase Exfoliaton||Nanosheets (nm to a few μm)||
|Chemical Reduction of Graphite Oxide||Nanoflakes or powder (nm to a few μm)||
|Micromechanical Exfoliation||Flakes (5 to 100 μm)||
|Epitaxial Growth||Thin films (>50 μm)||
|Carbon Nanotube Unzipping||Nanoribbons (few microns)||
|Chemical Vapour Deposition (on Ni, Cu, Co)||Thin films (≤75 cm)||
From all these methods, the chemical reduction is the most likely to be used in mass production given that its disadvantages vary according to the reducing agent Actually, hydrazine is the reducing agent of choice, but its toxicity has pushed researchers to look for other alternatives.
Over the years, several reducing agents have been reported in the literature as replacements of hydrazine. The use of these substances and compounds has an impact on the final properties of the reduced material. In the table below, the electrical conductivity of rGO is shown as a function of the chemical involved in its synthesis.
|Reducing agent||Electrical conductivity (S⁄m)||Reference|
|Hydrazine||9960||(Wang et al, 2008)|
|Ascorbic acid||7700||(Fernández-Merino et al, 2010)|
|Benzyl alcohol||4600||(Dreyer et al, 2011)|
|Isopropanol||1019||(Dreyer et al, 2011)|
|Pyrogallol||488||(Fernández-Merino et al, 2010)|
|Tea polyphenols||53||(Wang, Shi and Yin, 2011)|
|Yeast biomass||43||(Khanra et al, 2012)|
|Ethanol||1.8 × 10−4||(Dreyer et al, 2011)|
|Methanol||3.2 × 10−4||(Dreyer et al, 2011)|
- Cooper, D., D’Anjou, B., Ghattamaneni, N., Harack, B., Hilke, M., Horth, A., Majlis, N., Massicotte, M., Vandsburger, L., Whiteway, E. and Yu, V. (2012). Experimental Review of Graphene. ISRN Condensed Matter Physics, 2012, pp.1-56.
- Dreyer, D., Murali, S., Zhu, Y., Ruoff, R. and Bielawski, C. (2011). Reduction of graphite oxide using alcohols. J. Mater. Chem., 21(10), pp.3443-3447.
- Fernández-Merino, M., Guardia, L., Paredes, J., Villar-Rodil, S., Solís-Fernández, P., Martínez-Alonso, A. and Tascón, J. (2010). Vitamin C is an ideal substitute for hydrazine in the reduction of graphene oxide suspensions. J. Phys. Chem. C, 114(14), pp.6426-6432.
- Halliday, D., Resnick, R. and Walker, J. (2001). Fundamentals of physics, extended. New York: Wiley.
- Khanra, P., Kuila, T., Kim, N., Bae, S., Yu, D. and Lee, J. (2012). Simultaneous bio-functionalization and reduction of graphene oxide by baker's yeast. Chemical Engineering Journal, 183, pp.526-533.
- Lee, C., Wei, X., Kysar, J. and Hone, J. (2008). Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science, 321(5887), pp.385-388.
- Sherlis, J. (2001). Thickness of a piece of paper. [online] The Physics Factbook. Available at http://hypertextbook.com/facts/2001/JuliaSherlis.shtml
- Singh, V., Joung, D., Zhai, L., Das, S., Khondaker, S. and Seal, S. (2011). Graphene based materials: Past, present and future. Progress in Materials Science, 56(8), pp.1178-1271.
- Tsakmakidis, K. (2013). Coherent absorption in graphene. Nature Materials, 12(8), pp.688-688.
- Wang, G., Yang, J., Park, J., Gou, X., Wang, B., Liu, H. and Yao, J. (2008). Facile synthesis and characterization of graphene nanosheets. J. Phys. Chem. C, 112(22), pp.8192-8195.
- Wang, Y., Shi, Z. and Yin, J. (2011). Facile synthesis of soluble graphene via a green reduction of graphene oxide in tea solution and its biocomposites. >ACS Appl. Mater. Interfaces, 3(4), pp.1127-1133.