Currently, a number of techniques are used to produce graphene and these include epitaxial growth, chemical vapour deposition (CVD), and thermal or mechanical exfoliation. Large scale production of graphene can also be effectively realized through chemical reduction of graphene oxide.
Since graphene was first reported in 2004, made using mechanical exfoliation from graphite, graphite oxide has attracted a great deal of interest, as researchers have explored simpler, more efficient, cheaper and better yielding methods of synthesizing graphene, which can be scaled up easily and retain commercially viable properties for industrial applications.
From Graphite Oxide to Graphene Oxide
Graphite is a 3D-carbon based material, which can be thought of as being made from many layers of graphene. Graphite oxide is slightly different from graphite.
When strong oxidizing agents are used to oxidize graphite, oxygenated functionalities are introduced in the structure of the graphite, which makes the material hydrophilic, and also expands the layer separation.
This feature makes it possible to exfoliate the graphite oxide in water through sonication and this eventually produces monolayer or few-layer oxygen-functionalized graphene, called graphene oxide or GO.
The number of layers is the major difference between graphene oxide and graphite oxide. Although graphite oxide is a multilayer system, monolayer flakes and few-layer flakes can be found in a graphene oxide dispersion.
Properties and Applications of Graphene Oxide
Due to the presence of oxygen functionalities, graphene oxide can easily disperse in organic solvents, water, and different matrixes. This is a major benefit when combining the material with polymer or ceramic matrixes to enhance their mechanical and electrical properties.
With respect to electrical conductivity, graphene oxide functions as an electrical insulator, because of the disturbance of its sp2 bonding networks. It is important to reduce the graphene oxide so as to recover the honeycomb hexagonal lattice of graphene, in order to restore electrical conductivity.
After a large number of oxygen groups have been removed, it is not easy to disperse the reduced graphene oxide (rGO), because this material tends to produce aggregates.
The properties of graphene can be changed by the functionalization of graphene oxide. The chemically-altered graphenes obtained by this method could possibly be used in several applications. Depending on the intended application, the graphene oxide can be functionalized in a number of ways.
One way to ensure that the chemically-altered graphenes disperse easily in organic solvents is to use amines through organic covalent functionalization, for instance. This makes the material better suited to production of biodevices and optoelectronics, and for use in drug delivery.
Also, it has been shown that it is possible to attach fullerene-functionalized secondary amines and porphyrin-functionalized primary amines to graphene oxide platelets, to enhance the nonlinear optical performance of the material.
Graphene oxide could potentially be used as an intermediary in the production of single layer or few-layer graphene sheets. To achieve this, an oxidization and reduction process should be developed that can isolate carbon layers and separate then without changing their structure.
In terms of mass production of graphene, the chemical reduction of graphene oxide is considered to be one of the most viable methods. However, scientists have found it challenging to create graphene sheets that have the same quality as those made by mechanical exfoliation on a large scale.
Graphene Oxide Film from Graphenea
Graphenea produce a graphene oxide film (Figure 1), by filtering a monolayer graphene oxide dispersion. The film is non-conductive, has a thickness of 12 to 15µm, and measures 4cm in diameter.
Figure 1. Graphene oxide film
Millipore Filter Specifications
- Thickness: 105µm
- Porosity: 70%
- Pore size: 0.025µm
- Material: Biologically inert mixtures of cellulose nitrate and cellulose acetate s
- Oxygen: 41 – 50%
- Hydrogen: 0 – 1%
- Nitrogen: 0 – 1%
- Sulfur: 0 – 2%
- Carbon: 49 – 56%
Graphene oxide films are used in the following applications:
- Graphene research
- Solar cells
- Graphene/polymer composite materials
- Support for metallic catalysts
- Low permeability materials
- Multifunctional materials
Graphenea supplies graphene oxide filters that go through stringent quality check process so as to ensure that the products produced are of high quality and have good reproducibility. The company also provides customized solutions for application requiring more specific quality control.
This information has been sourced, reviewed and adapted from materials provided by Graphenea.
For more information on this source, please visit Graphenea.