Magic or Malice? Assessing the Environmental Impacts of Graphene-Based Materials
By Bryan Kim
From the Stone Age to the contemporary Silicon Age, materials have defined and transformed human civilization. But, every new material must have its side effects well-understood in order to avoid environmental disasters. Environmental mismanagement of promising materials has happened before. Plastic, a material deemed the “discovery of the century” in the early 1900s, witnessed a rapid fall from grace as its technological applications gave way to immense waste buildup due to its slow rate of decomposition.
Fast forward to 2010, when the discovery of a new “magic material” became the subject of the 2010 Nobel Prize in Physics: graphene. First isolated in 2004, graphene is a single layer of carbon atoms, a type of “2D material.” Despite its simple structure, graphene exhibits properties akin to science fiction: it is 200 times stronger than steel, lighter than paper, and both electrically and thermally conductive. These properties quickly inspired ideas of graphene’s potential applications ranging from flexible electronics to space elevator technology.
However, to this day, graphene still remains in its infancy. Scientists seek to discover a way to mass-produce high quality graphene in a cost-effective way. Although graphene may not have been as immediately impactful as popular science anticipated it to be, this has allowed the discussion and assessment of graphene’s environmental impacts. In order to mitigate environmental disasters, graphene’s effects on ecosystems and organisms require deep understanding in order to minimize ecological risks.
Not all graphene-based materials (GBMs) are the same. Besides pure graphene, some examples of different types of GBMs include graphene oxide (“GO” – graphene with oxygen-containing groups) and reduced graphene oxide (“rGO” – GO that is processed to reduce oxygen content). A visual classification guide for various GBMs is linked below:
While the large-scale production of pure graphene remains in progress, GOs provide an alternative, chemical route to mass-produce graphene in a relatively inexpensive and easy way. However, the environmental impacts of GO production include chemical leakage, since GO powders are usually transported in liquid solvents as an input for production. Additionally, essential manufacturing steps transform the liquid solution into a dry-mass state. Other GBMs demand high amounts of electricity due to thermal and electrochemical treatment steps. Scientists thus summarize that in order to pursue sustainable, eco-friendly GBM production, two goals should be kept in mind: (1) reduce the use of chemical substances for GO production, and (2) pursue energy efficiency across all GBM production processes.
As production of GBMs continues to scale, GBMs will inevitably leak into the environment during their life cycle. Soil environments particularly remain at high risk as GBMs have applications in agricultural production and soil contaminant removal. Through water-based transport such as surface runoff and precipitation, GBMs can assimilate into the soil and affect the microbiome—specifically, GOs threaten plants and microorganisms. Scientists from the Graphene Flagship Project, one of the European Commission’s “Future and Emerging Technology Flagship Projects,” used a model plant called Arabidopsis thaliana to demonstrate GOs’ damage upon seed plants such as nuclear fragmentation, membrane damage, and hindrance of seed germination. Nankai University scientists have also explored how GOs in soil can move through soil via water. Upon addition of reduced GO nanosheets labeled with palladium (“rGO-Pd”) in the soil, scientists have found that the microbial diversity significantly increased. A metric called the chao1 index estimates the number of microbial species in a given community. The soil with rGO-Pd yielded a chao1 index between 1100-1200, much higher than that of soil without rGO-Pd (chao1 index of 500). This increase in microbial species can disturb the stability of the soil’s microbial environment.
Ecotoxicity studies of GBMs, much like graphene itself, are still in development. While efforts such as the European Graphene Flagship initiative evaluate the life cycle and potential side effects of GBMs, further research needs to be done to fully understand GBMs’ environmental impact. It is imperative for scientists to continue characterizing GBMs as their production processes advance into large-scale, manufacturable levels.
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