Graphene nanomaterials have gained popularity within nanotechnology research due to their versatile carbon-based structure, which allows them to be used for various applications, advancing different fields from biomedical science to electronics.
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While graphene has innovated many fields, the release of graphene into the environment may have some concerns over its role in a sustainable future. The environmental impact of graphene nanomaterials will be explored further in this article.
What are Graphene Nanomaterials?
Graphene nanomaterials (GFNs) include a class of graphene-like materials that are structured similarly, with various variables, including size, layers, and surface chemistry.
Examples of these nanomaterials consist of graphene oxide (GO), reduced graphene oxide, graphene quantum dots, as well as structures made with these materials.
Graphene has risen in popularity due to its reputation as an extremely thin (one atom thick) 2D material that is many times stronger than steel. The application of graphene to a wide range of industrial and research sectors is expected to revolutionize many areas of modern technology.
The benefits of GNFs include having remarkable mechanical properties, thermal and chemical stability, as well as temperature and radiation resistance. Additionally, these nanomaterials are associated with a low cost of production, which further highlights its attraction for applications within various fields.
Currently, there are more than 26,000 graphene-based patents that have been filed and registered on a global scale. Additionally, the global market for this material was estimated to be $620 million in 2020, with predictions of growth to $1.48 billion in 2025. This has been calculated to have a compound annual growth rate of 19%.
Environmental Concern of Nanomaterials
While beneficial, the use of graphene nanomaterials on a large scale requires discussion and careful consideration of any environmental consequences.
These 2D carbon nanomaterials may be an environmental threat due to the release of particles into the environment, such as water, air, and soil. Additionally, subsequent environmental factors, including physical, chemical, and biotransformation, can occur on GFNs, resulting in changes to their structure and physical and chemical properties.
Such a development is a concern as it can also lead to changes in the level of toxicity of GFNs. Exploring any corresponding changes that may produce subsequent toxicity to the environment is very significant for a sustainable future.
A semi-quantitative tool called a life cycle assessment (LCA) can be used to analyze a cascade of causal effects, which may begin with economic activity and result in a negative side effect on public health that can cause the destruction of ecosystems and resources.
Environmental Systems: A Closer Look
Air, water, and soil are the three most important systems within the environment, and the effect of GFNs on these systems is significant for assessing the environmental impact of graphene based materials.
Nanomaterial particles can be released into the air and remain suspended within the environment for a long period of time. When these nanomaterials are airborne, they can agglomerate with each other as well as combine with substances within the air, including gas molecules, solid particles, and the ozone.
Research on this topic has included laser-induced graphene that has been treated with ultraviolet and ozone; the results have included alterations to the surface morphology of the laser-induced graphene as well as changes to the hydrophilicity. This demonstrates the significance of studying interactions of existing environmental substances and graphene released into the ecosystem.
Sunlight is another variable that can affect graphene, with previous literature illustrating the ability of natural light to degrade or reduce graphene oxide; this can occur when light energy exceeds the band gap of graphene oxide, enabling the compound to be transformed.
The release of GFNs within the soil may be more complex, as the nanomaterials can move through the soil, with migration and transformation within the soil reported in many studies within the literature.
Research on GFNs within the soil and potential mineralization has been undertaken using technology with radioisotopes, which has found the conversion of GO into CO2 to be very challenging, as well as difficult with being released by water. This may be due to graphene oxide or soil particles undergoing aggregation, further enabling GO retainment within the soil.
Additionally, the interaction between microorganisms and GFNs can be significant for the degradation and transformation of GFNs, with nitrogen-fixing bacteria having the ability to convert GO into reduced GO.
Interestingly, fungi are known to be an efficient decomposers, which can be helpful in this role; research into white rot fungus, Phanerochaetes chrysosporium, has demonstrated the ability of this fungus to add oxygen to reduced graphene oxide and reduce the carbon content within this graphene compound.
Within an aqueous environment, GFNs can react with inorganic ions, surfactant molecules, as well as biological colloids, which can impact the GFN behavior as well as its direction within water. It can also be affected by pH, with subsequent color changes.
Future Outlook
Environmentally transformed GFNs can still present a risk to humans and mammals; however, this risk may differ from that of pristine GFNs. With the increase of graphene-derived technology and products, an assessment of the impact these nanomaterials can have on the environment and public health is required.
Further research into the environmental impact of graphene and graphene-derived nanomaterials can enable environmentally friendly GFNs to be designed. It can also ensure that a demand increase for this unique nanomaterial does not correlate to a higher cost in environmental toxicity.
References and Further Reading
Baysal , A., et al. (2020) Risks of graphene nanomaterial contamination in the soil: evaluation of major ions. Environ Monit Assess, 192(10), https://doi.org/10.1007/s10661-020-08561-2
Ding, X., et al. (2022) Environmental and health effects of graphene-family nanomaterials: Potential release pathways, transformation, environmental fate and health risks. Nano Today, 42, p. 101379. https://doi.org/10.1016/j.nantod.2022.101379
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