Graphene is a multidisciplinary material with applications in almost every science and engineering sector. This article aims to provide insight into the importance of green synthesis methods in graphene nanomaterials synthesis.
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Role of Sustainability in Graphene and Why is it Important?
Ever since its scientific breakthrough in 2004, graphene has shown a high promise for future electronic and optical devices attributed to its unique features. Graphene has a lot of promise for applications such as anti-corrosion coatings and paints, sensors, wearable, flexible displays, energy storage, healthcare, electronics and many more.
The chemical reduction method is widely used to synthesize graphene; however, this method mostly includes highly hazardous reducing agents that pose significant health and environmental risks. The presence of unwanted toxic contamination in reduced graphene oxide (rGO) can limit its applications, particularly in bio-related areas, if excessive amounts of reducing agents are used.
Moreover, the currently available commercial graphene materials are expensive, resulting in significantly slowing down their potential usage in these applications. Hence, the growing demand for sustainable mass production of graphene has triggered a worldwide focus on synthesizing graphene from natural and environmentally friendly sources.
Examples of Synthesizing Graphene from Natural Sources
Carbon is the primary source of graphene and is present abundantly in nature. A recent study suggested biomass as a highly appropriate alternative starting material for preparing valuable carbonaceous materials due to its eco-friendliness, global availability, sustainable production in large quantities, and low cost.
For example, agricultural and food waste biomass such as coconut shell, orange peel, and sugarcane bagasse progressively attracted global attention as a low-cost resource for synthesizing nanomaterials. Researchers have reported biochar from rice straw biomass, an agricultural waste generated in bulk, was used as the parent substrate for synthesizing high-quality graphene oxide nanoplatelets.
A different approach in which biomaterials have been used in the reduction of GO as these are non-hazardous, comparatively cheap, and easily available in the market. For example, it is reported that rGO is produced by reducing ascorbic acid, also known as vitamin C, in solutions for several days without affecting its electronic structure. Another approach reported Tulsi leaf as a green alternative for bio-reduction of GO with around 90% yield.
In addition, graphene synthesis from various raw materials and waste products such as honey, animal waste, essential oil, rice husk, vegetable waste, leaf waste, and so on has been reported as a low-cost, environmentally friendly alternative.
New Development: Flash Joule Technique
Prof. James Tour from Rice University introduced Flash Joule Heating in 2020 to produce gram-scale quantities of powder graphene from a variety of feedstocks such as natural wastes/municipal solid wastes, food waste, plastics and other sources of waste. The technique employs a "flash" of electricity to heat the carbon to approximately 3000 K, converting it into graphene flakes.
Flash Joule synthesis requires no solvent, reactive gases, or furnace and can generate yields of 80 to 90 %, with carbon purity exceeding 99 % without any purification process.
For example, very recently, Prof. James Tour's group, in collaboration with Ford Motors Company, turned waste plastic parts in vehicles into graphene using the flash joule heating technique.
To show the practical value of the synthesized graphene, they used 0.1 weight % graphene as an additive in polyurethane foam composite for cars, leading to improved tensile strength by 34% and 25% increase in low-frequency noise absorption.
Notably, they could upcycle the resulting foam composite back into equal-quality flash graphene, a great example of circular recycling.
Sustainable Manufacturers and Suppliers of Graphene
UK-based Levidian is the most significant green graphene company in the world with annual production about 5 tons. They have a patented LOOP reactor, a decarbonizing service to capture carbon from greenhouse gas methane in the form of pure graphene. Their LOOP device is modular and the most scalable graphene manufacturing alternative that exists today.
Bio Graphene Solutions (BGS), based in the USA is a sustainable manufacturer and supplier of graphene that uses organic, renewable resources rather than graphite. Their eco-friendly process relies on producing biochar from wood waste to manufacture graphene with a primary focus on solving real environmental issues within the concrete and asphalt industries.
GrapheneCR is another clean, renewable graphene company that produces high-quality graphene from biomass, a renewable, sustainable source. A pyrolysis process is used to produce a very high-quality biochar which is converted to the ProCNano®, a low-grade multi-layer graphene. This is followed by a very proprietary upgrade process to ProCene® a high-quality Graphene powder with 75% yield. Their monthly production capacity is 150 metric tons of ProCNano Nanoplatelets and 15 metric tons of high-quality Graphene powder.
US-based Avadain, France-based Blackleaf, Canada based HydroGraph Clean Power Inc., are some of the other companies that produce high-quality and affordable graphene with their green technology approach.
Commercial Applications of Green Graphene
The first commercial product with GrapheneCR ProCene® is for dental applications from Nanomex. Quantum Paint reported paint with 5% ProCene® dries 3.3 times faster and showed to be 100% effective in anti-fouling.
Graphene Manufacturing Group (GMG) is a clean-technology company that produces graphene from natural gas (methane) rather than mined graphite, with a primary focus on paints, coolants, and lubricants that demonstrate improved heat transfer in air-conditioning.
Their Graphene aluminum-ion batteries have demonstrated a very high cycling rate for over 3000 cycles with negligible performance reduction compared to Li-ion batteries, whose performance drops to 60% of original capacity after 1000 cycles.
Challenges for Commercial Production
The production of graphene from natural resources and waste products has the potential to be economically viable and scaled up. However, the widespread use of graphene could be hampered by a number of different factors. One of these factors is the restricted amount of output volume. Hence, reaching commercial level volume manufacturing will be one of the most difficult challenges for the sustainable graphene industry in the next 2–5 years.
Reproducibility of graphene's properties is an additional significant challenge; the quality of the biowaste materials used to produce graphene significantly impacts the final product's properties. Therefore, selecting the appropriate biowaste for each batch is of utmost significance.
Indeed, integrating sustainability into the synthesis of graphene has been regarded as one of the environmentally friendly options to deal with the challenges posed by global pollution. In this direction, green nanotechnology has emerged as a flexible platform capable of providing solutions to the global sustainability disputes that our society is currently facing that is simple, efficient, cost-effective, and environmentally tolerable.
References and Further Reading
Al-Ahmed, A., & Inamuddin, (2022). Graphene from Natural Sources: Synthesis, Characterization, and Applications (1st ed.). CRC Press. https://doi.org/10.1201/9781003169741
Pacchioni, G. (2022). Graphene from plastic waste makes cars greener. Nature Reviews Materials, 1-1. https://doi.org/10.1038/s41578-022-00452-x
Nanaografi (2020) What is Green Graphene. [online] nanografi.com Available at https://nanografi.com/blog/what-is-green-graphene/
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/
Levidian (2022) LOOP Reactor. [online] levidian.com Available at https://www.levidian.com/levidian-graphene
GrapheneCR (2021) Clean renewable graphene company. [online] graphenecr.com Available at https://graphenecr.com/our-vision