By: Akanksha Urade (Ph.D. Scholar at IIT Roorkee and Graphene & 2D Materials Science Writer)
Imagine a future where there are no controls on the sale of antibiotics, and anyone can manufacture them without regulations and sell them without any quality standards. Many people would be reluctant to use them for fear of adverse side effects or lack of confidence in their efficacy – both of which could (literally) be fatal. That’s the situation with graphene, where lack of quality and inconsistency is leading to a condition that, while not fatal, is nonetheless causing widespread confusion that is unacceptable.
Two-dimensional, high quality, pristine graphene, used as an additive material, has repeatedly demonstrated its amazing characteristics, including strength (200x stronger than steel), electrical conductivity (1,000,000x better current density than copper) and capacity to store tremendous amounts of energy (because of its extremely high surface area (2,600 m2/g) compared to traditionally used graphite (~10 m2/g). But to achieve all these fantastic qualities and more, graphene flakes must be large (30+ µm in lateral flake size) to achieve this tensile strength; thin (1-5 atomic layers) to achieve high surface area; and, nearly defect free for almost perfect electron mobility. But if quality is not rigorously managed and commercial use is inadvertently based on ‘fake’ graphene, we risk never achieving the promise and potential of pristine graphene. “The absence of standards has been a major obstacle to the commercialization of graphene and layered materials,” laments Prof. Jari Kinaret, Director of the Graphene Flagship.
Large Graphene Flakes
Although the science is clear that the amazing strength of graphene occurs at > 30 µm, there are many companies making the claim that their materials have high quality, pristine graphene’s tensile strength. Some are a little bit more clever, and simply state in their marketing material what high quality, pristine graphene’s tensile strength is and do not actually discuss their material’s strength. And there is more than one company which has tried to sell its material to be used in body armor, only to have expensive and time-consuming testing reveal that their material was brittle – absolutely the last thing you need in a bullet proof vest!
Thin Graphene Flakes
Another question is, how thin must the graphite flakes be to have graphene’s qualities? The International Organization for Standardization (ISO) defines graphene as ten or fewer atomic layers of hexagonal carbon. This is a clear-cut standard. More than ten atomic layers are nanoplatelets (11-2,999 layers) or graphite (3000+ layers). Unfortunately, there are companies which are marketing nanoplatelets under the name “graphene” or “graphene nanoplatelets”. There are also companies marketing graphite powder as “graphene”.
Graphene, nanoplatelets and graphite have different characteristics and can provide diverse product performance outcomes. Even within real graphene, the number of atomic layers can provide different outcomes. Electrodes for neurological applications, for instance, have been reported to perform best when they are made from defect-free monolayer flakes. In contrast, few layer graphene would provide the optimum performance in composite materials applications. For a product developer to make an informed decision about a material, however, accurate labelling and characterization are always necessary.
Nearly Defect Free Graphene Flakes
One of the most well-established processes for commercially manufacturing graphene is liquid-phase exfoliation. This involves oxidizing graphite with a mixture of sulfuric acid, sodium nitrate, potassium permanganate and water to exfoliate graphene sheets. In this process, oxygen atoms bind to the carbon framework in the form of hydroxy, carboxyl and epoxy groups, separating the layers from each other, producing a material called graphene oxide (GO). A reduction reaction can be used to partially eliminate some of the oxygen groups, resulting in another material called reduced graphene oxide (rGO). Even so, rGO is replete with random defects (though less than GO) and is also not pristine graphene. My fellow science journalist, Kerry Taylor-Smith, explains it this way: “Pristine graphene – that is graphene in its original, pure, unoxidized form – enjoys superior properties to its oxidized counterpart, but pristine graphene isn’t easy to come by and its lack of abundance has held back the development of graphene-based functional devices.” But in their marketing and bottle labels, many manufacturers offering GO and rGO conveniently call these materials graphene.
Cause for Concern
It is concerning that some manufacturers are mislabeling black powders as graphene and selling them for a premium price when they actually comprise primarily cheap graphite. Industry and researchers risk wasting time and money because of low-quality graphite powder sold as high-quality graphene. Also concerning are the growing number of companies manufacturing nanoplatelets and marketing these as graphene.
“We need [graphene] standards now, not in ten years,” warns Dr. Antonio Castro Neto, Director of the Centre for Advanced 2D Materials at the National University of Singapore (CA2DM). “Because if there are no standards now people will keep buying bad material. The properties of this material will not be the properties of graphene. There will be a feeling that graphene is not fulfilling its full potential, which is not true, because we know that in the lab graphene really delivers everything that it promises. The problem is that in the open market, without quality control, people are buying something that doesn’t really work.”
In a study published in Advanced Materials, researchers from the National University of Singapore generated a systematic test protocol based on well-known methodologies for evaluating graphene from 60 different manufacturers from the Americas, Asia and Europe. Surprisingly, the investigation indicated that the majority of these companies were selling graphite microplatelets. The investigation indicated that less than 10% of the material contained graphene, and none of the examined products had more than 50% graphene. The study also noted that the majority of graphene samples on the market are actually GO and rGO. In addition, carbon content analysis reveals that samples are frequently heavily contaminated and that a considerable number of companies make an inferior material with low carbon content. There are numerous potential causes of contamination, but the most likely are the chemicals utilized in the manufacturing process. An even more devastating conclusion is that “our extensive studies of graphene production worldwide indicate that there is almost no high quality graphene, as defined by ISO, in the market yet.”
A take-away from the NUS study is that many companies are crushing graphite into powder and setting up websites to sell it. As far as the current graphene market is concerned, it is guided by the doctrine caveat emptor – let the buyer beware.
“Dozens of emerging applications for graphene are closely linked to some of society’s grand challenges: health, climate, renewable energy and sustainability,” observes Dr. Peter Bøggild of the Center for Nanostructured Graphene, Technical University of Denmark. He warns that “some of these applications might never leave the starting block if the early development is based on ‘fake graphene’.”
The Graphene Council launched “The Verified Graphene Producer®” initiative to reassure customers that they are dealing with a reputable and competent graphene supplier. “Consumers want to know that the products they purchase are genuine and will perform as advertised,” said Terrance Barkan, executive director of The Graphene Council. “It is very hard for industrial companies that don’t understand the nuances of different graphene materials or which supplier is reputable. The Graphene Verified Producer program is designed to bring a measure of transparency to the market.”
To help combat fake graphene, the Verified Graphene Producer Program performs physical inspections of graphene production facilities to ascertain the raw materials used, the method of graphene production and the quality and safety of the final product. To ensure that graphene materials conform to ISO technical specifications, a random sample is taken from the manufacturing process and characterized using tests like SEM, TEM, Raman, XPS, and AFM at world class labs (like the UK’s National Physical Laboratory). The Graphene Council plays a pivotal role in this space by facilitating communication and trying to establish marketplace trust.
It is crucial to understand that these fake graphene materials can never confer the superlative properties of the Nobel Prize-winning two-dimensional material. It is more important than ever to educate end-user companies and the general public about how real graphene can power another Industrial Revolution, while fake graphene can only lead to disillusionment.
References
Bøggild, Peter. “The war on fake graphene.” (2018): 502-503.
Kauling, Alan P., et al. “The worldwide graphene flake production.” Advanced Materials 30.44 (2018): 1803784.
Wick, Peter, et al. “Classification framework for graphene-based materials.” Angewandte Chemie International Edition 53.30 (2014): pp-7714.
The Graphene Council Verified Graphene Producer Program (2023)
https://www.thegraphenecouncil.org/page/VerifiedProducer#:~:text=The%20Graphene%20Council%20Verification%20Program,end%2Dusers%20a%20degree%20of
