Graphene, a 2D sheet of carbon atoms arranged in a chicken wire pattern, is a fascinating material that boasts many exciting properties like mechanical strength, thermal and electrical conductivity, intriguing optical properties and more. Graphene is the focus of vigorous R&D, but its relatively high price is a hindrance at the moment.
Graphene oxide is a form of graphene that includes oxygen functional groups, and has interesting properties that can be different than those of graphene. By reducing graphene oxide, these oxidized functional groups are removed, to obtain a graphene material. This graphene material is called reduced graphene oxide, often abbreviated to rGO. rGO can also be obtained from graphite oxide, a material made of many layers of graphene oxide, after a series of reduction to graphene oxide and then to rGO.
How is rGO produced?
Since effective yet inexpensive ways to make graphene (or closely related materials, such as rGO) are being intensively sought for, the reduction of graphene oxide (or graphite oxide) to rGO is popular and attractive. Several methods of reduction into rGO exist, and are rather cost-efficient and simple.
While rGO is indeed a form of graphene with properties similar to that of graphene (good conductive properties etc.), rGO usually contains more defects and is of lesser quality than graphene produced directly from graphite. Reduced graphene oxide (rGO) contains residual oxygen and other heteroatoms, as well as structural defects. Despite rGO’s less-than-perfect resemblance to pristine graphene, it is still an appealing material that can definitely be sufficient in quality for various applications, but for more attractive pricing and manufacturing processes. Reduced graphene oxide can be used (depending on the specific material’s quality) for the same various applications suitable for graphene use, like composite materials, conductive inks, sensors and more.
Reduced GO is often a natural and understandable choice for applications that call for large amounts of material due to the relative ease in creating sufficient quantities of graphene in a relatively low cost.
The process of reducing graphene oxide to produce reduced graphene oxide is extremely important as it has a large impact on the quality of the rGO produced, and therefore will determine how close rGO will come, in terms of structure and properties, to pristine graphene.
A number of processes exist for the reduction of GO, based on chemical, thermal or electrochemical approaches. Some of these techniques are able to produce very high quality rGO, similar to high-quality graphene, but can be complex, expensive or time consuming to carry out.
Once reduced graphene oxide has been produced, there are ways to functionalize the material for specific use in different applications. By treating rGO with various chemicals or by creating new compounds by combining rGO with other two-dimensional materials, it’s possible to enhance the properties of the compound to suit commercial applications.
In some applications, the reduction of the GO to rGO is performed as part of the device manufacturing process. For example, a process could start with GO, mix it with a material to create a composite, and reduce the GO into rGO as part of the composite creation process or afterwards.
In general, it can be said that rGO is suitable for the same sorts of applications as graphene, as the properties of these materials are similar, albeit normally less impressive at the rGO end. As was said before, the properties of rGO can vary depending on the method of preparation and the resulting morphology and chemistry of the specific rGO.
Reduced GO can be used for many applications, among these are: energy storage, composite materials, field effect transistors and more.
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The latest reduced graphene oxide news:
Global Graphene Group, and its subsidiary Angstron Energy (AEC) has developed a new graphene/silicon composite anode material (GCA-II-N) which can increase the capacity of Li-Ion batteries while reducing the battery's size and weight. AEC current market focus is on electronic bikes and consumer electronics, but is also working with Tier-1 electric cars and trucks makers.
AEC tells us that by wrapping single-layer graphene (or r-GO) around silicon nanoparticles, the volume expansion/contraction of the Silicon during the battery's charge/discharge cycle can be cushioned by the flexibility and mechanical strength of the graphene. The graphene sheets also form a 3D conductive network which ensures good electrical contacts between the Silicon particles and the current collector.
Researchers at Chalmers University of Technology, Sweden, have recently developed a promising breakthrough for lithium sulphur batteries, using a catholyte with a graphene sponge. Such batteries may offer a theoretical energy density more than five times that of lithium ion batteries.
The researchers' approach relies on a porous, sponge-like aerogel, made of reduced graphene oxide, that acts as a free-standing electrode in the battery cell and allows for better and higher utilization of sulphur.
Researchers from the Graphene Flagship have developed hybrids of graphene and molybdenum disulphide quantum dots to stabilize perovskite solar cells (PSCs). PSCs are a novel type of solar cells which are efficient, relatively easy to produce, made with cheaper materials and, due to their flexibility, can be used in locations where traditional silicon solar cells cannot be placed.
A collaboration between the Graphene Flagship Partners Istituto Italiano di Technologia, University of Rome Tor Vergata, and BeDimensional resulted in a novel approach based on graphene and related materials to stabilize PSCs, thus addressing the stability issue of PSCs, a major hurdle hindering their commercialization.
Researchers at Swinburne, the University of Sydney and Australian National University have collaborated to develop a solar absorbing, ultra-thin graphene-based film with unique properties that has great potential for use in solar thermal energy harvesting.
The 90 nanometre material is said to be a 1000 times finer than a human hair and is able to rapidly heat up to 160°C under natural sunlight in an open environment.
Researchers from Washington University have designed a novel membrane technology that purifies water while preventing biofouling, or buildup of bacteria and other harmful microorganisms that reduce the flow of water. And they used graphene and bacteria to build these filtering membranes.
The team developed an ultrafiltration membrane using graphene oxide and bacterial nanocellulose that they found to be highly efficient, long-lasting and environmentally friendly. If their technique were to be scaled up to a large size, it could benefit many developing countries where clean water is scarce.