Editorial Feature

A Top-Down Approach To Graphene Synthesis

Graphene is a two-dimensional material composed of carbon atoms organized in a honeycomb pattern. Because of its extraordinary and unique features, it has piqued the curiosity of experts from all fields of engineering and research. This article aims to provide insights into the synthesis of this nanomaterial via a top-down approach.

A Top-Down Approach To Graphene Synthesis

Image Credit: Forance/Shutterstock.com

Graphene: Wonder Material of 21st Century

Following its discovery in 2004 by researchers from the University of Manchester, single-layer graphene has shown a high promise for future electronic and optical devices. Its unique properties such as high surface area (~2600 m2/g), high electron mobility (200000 cm2/Vs), high thermal conductivity (3000 Wm/K), high optical transparency (97.4%), and high mechanical strength with Young's modulus of 1 TPa evidence its applicability for a wide range of industries.

Recently, properties such as superconductivity, quantum tunneling, and magnetism have been demonstrated by tuning graphene's structure. By increasing the number of layers, this nanomaterial exhibits different properties.

Graphene exhibits different properties with an increase in the number of layers. Hence, every individual multilayer sequence is a new nanomaterial in its own right.

Approaches for Graphene Synthesis

Single layer graphene was first successfully synthesized using the scotch tape method. Here, layers were separated from graphite flakes using adhesive tape. Following exfoliation, these layers were deposited using dry deposition on a silicon wafer. Synthesis techniques can be broadly classified as top-down and bottom-up approaches.

Bottom-up fabrication utilizes carbon molecules as the primary building block, converting carbon precursors such as hydrocarbon gases, aromatic hydrocarbons, and polymers to graphene via chemical vapor deposition, thermal pyrolysis, and epitaxial growth. However, these processes are complicated because they frequently necessitate sophisticated infrastructure and operating conditions. In comparison, top-down production methods are easier to scale up and are less expensive.

A Top-Down Approach to Graphene Synthesis

The top-down method breaks down precursors like graphite into layers that are atom thick. This method simply converts graphite to graphene via mechanical exfoliation, liquid-phase exfoliation (LPE), electrochemical exfoliation, and chemical oxidation-reduction.

Scotch tape is a mechanical exfoliation technique that produces a high-quality nanomaterial product. In LPE at first, the interlayer spacing of graphite is increased via a reduction reaction, and then the graphite is exfoliated via rapid heating, sonication, or high shear forces to yield graphene.

Electrochemical exfoliation involves applying an electric voltage to induce ionic species to intercalate into graphite rods, where they form gaseous molecules capable of exfoliating distinct layers.

Finally, the most widely used method to produce graphene layers is the chemical oxidation-reduction of graphite. The process begins with converting graphite into graphene oxide (GO) using the hummer's method, then reducing it into reduced GO using chemical (such as hydrazine), thermal, or electrochemical methods.

Mass Synthesis of Graphene by Top-down Approach

Mechanical exfoliation yields graphene that is only a few hundred micrometers in size and it is a time-consuming process. As a result, this method appears limited to laboratory research and unlikely to be scaled up for industrial production. LPE methods, on the other hand, result in average quality graphene production. This method, however, causes defects in the graphene structure.

Similarly, hydrazine-mediated chemical reduction of GO is by far the most common method for producing large quantities of powder graphene-like materials. However, the by-products released during processing are extremely toxic, and the rGO produced is generally of lower quality, as the strong oxidation and reduction processes cause defects and oxygen functionalities to remain, lowering the product's conductivity and tensile strength.

For the reduction of GO, researchers have begun investigating non-toxic and environmentally friendly green reductants such as sugar, lemon extract, green tea, and ascorbic acid.

Using electrochemically assisted exfoliation, a team from Xi'an Jiaotong University has reported production rates as high as 25 g/h for few-layer graphene (70% being 1–3 layer) with high conductivities and very low defect densities.

Scientists from IIT Patna have developed a new method for solvent-free graphite exfoliation using plasma spraying. Most notably, production rates of up to 48 g/h have been reported without the use of solvent, and a material cost of $1.12 g-1 has been estimated with batch-to-batch reproducibility.

Manufacturers and Suppliers

First Graphene Limited, based in Australia, is a leading supplier of high-performance bulk graphene products with an annual production capacity of 100 tons. Another Australian-based company, Graphene Manufacturing Group Ltd, produces high-quality, low-cost graphene powder from cheap feedstock.

US-based NeoGraf Solutions announced that it has started to produce graphene (GNP) materials, branded as Graf-X whose annual capacity is estimated to be over 750 metric tons and over 1,300 tons of its graphene precursors. The company mainly targets thermoset and thermoset and thermoplastic applications.

Some companies such as Bio Graphene Solutions (BGS) are utilizing organic, renewable resources to synthesize graphene instead of conventional graphite. Graphene Star is a manufacturer and developer of graphene powder and graphene water slurry at a competitive price. Their patented manufacturing processes are reportedly both environmentally friendly and scalable.

UK-based Applied Graphene Materials is the world leader in the production of graphene dispersion, and the Italian firm Directa Plus has developed its own exfoliation process (dubbed G+) for producing pristine GNPs, water-dispersed GNPs, and fine nanographite powder.

Commercial Applications of Graphene Nanomaterials

Graphene nanomaterials have been intensely investigated as active materials in electrodes for energy storage. For example, Graphene Manufacturing Group is currently developing coin cell prototypes of aluminum graphene batteries. Testing reportedly confirmed a very high cycling rate for over 3000 cycles with negligible reduction in performance in comparison to Li-ion batteries, whose performance reduces to 60% of original capacity after 1000 cycles.

Applied Graphene Materials is a leading supplier of graphene-based anticorrosion coatings. They recently announced the successful use of their anti-corrosion primer by England's environment agency for flood defense. 

Future Perspective

Graphene has taken a while to mature, but now its commercial production is moving quite rapidly. Total annual production is estimated to reach 3800 tons per year in 2026. Furthermore, industrial-scale graphene synthesis might accelerate with the development of highly efficient Flash Joule heating (FJH).

With the advancement of graphene production capabilities, commercial applications in materials composites, lubricants, concrete, energy-storage materials, coatings, and other applications will be possible in the coming years.

Continue reading: Large-Scale, Available Graphene Supercapacitors; How Close are We?

References and Further Reading

Kumar, N., (2021). Top-down synthesis of graphene: A comprehensive review. FlatChem, 27, 100224. https://www.sciencedirect.com/science/article/pii/S2452262721000039

Wyss, K. M., (2022). Large‐Scale Syntheses of 2D Materials: Flash Joule Heating and Other Methods. Advanced Materials, 2106970. https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202106970

First Graphene Limited (2019) PureGRAPH product line. [online] firstgraphene.net. Available at: https://firstgraphene.net/puregraph-50-added-to-product-line/

NeoGraf (2021) Graf-X Graphene Additives. [online] neograf.com. Available at: https://neograf.com/products/powders-and-additives/graf-x

Graphene Manufacturing Group (2021) Aluminum ion battery [online]. graphenemg.com. Available at: https://graphenemg.com/energy-storage-solutions/aluminum-ion-battery/

Bio Graphene Solutions (2020). Clean tech alternative to traditional graphene [online]. biographenesolutions.com. Available at: https://biographenesolutions.com/technology/

Graphene Star (2021). Graphene products [online]. graphene-star.com.Available at: https://graphene-star.com/

Graphenea (2010). Graphene products [online]. graphenea.com Available at: https://www.graphenea.com

Applied Graphene Materials (2010) Graphene dispersions. [online]. appliedgraphenematerials.com Available at: https://www.appliedgraphenematerials.com/products/genable-graphene-dispersions/

Directa Plus (2014) Graphene nanoplatelets. [online]. directa-plus.com. Available at: https://www.directa-plus.com/g-technology

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Akanksha Urade

Written by

Akanksha Urade

Akanksha is a Ph.D. research scholar at the Indian Institute of Technology, Roorkee, India. Her research area broadly includes Graphene synthesis by the chemical vapor deposition technique. Akanksha also likes to write science articles regarding the latest research in 2D materials, especially Graphene, and reads relevant papers to understand what is being claimed and try to present it in a simplified way. Her goal is to help every reader understand Graphene Technology, regardless of whether their background is scientific or non-scientific. She believes that everyone can learn - provided it's taught well.

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Comments

  1. ephraim Tapfumaneyi ephraim Tapfumaneyi Zimbabwe says:

    a very informative article

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