Graphene’s negative environmental impacts
May 1, 2014
Researchers at the University of California, Riverside Bourns College of Engineering have found graphene oxide nanoparticles are very mobile in lakes or streams and likely to cause negative environmental impacts if released.
Graphene oxide* nanoparticles are an oxidized form of graphene, a single layer of carbon atoms prized for its strength, conductivity and flexibility. Applications for graphene include everything from cell phones and tablet computers to biomedical devices and solar panels.
The use of graphene and other carbon-based nanomaterials, such as carbon nanotubes, are growing rapidly. At the same time, recent studies have suggested graphene oxide may be toxic to humans.
As production of these nanomaterials increase, it is important for regulators, such as the Environmental Protection Agency, to understand their potential environmental impacts, said Jacob D. Lanphere, a UC Riverside graduate student who co-authored a just-published paper about the transport of graphene oxide nanoparticles in ground and surface water environments.
“To our knowledge, there is no current information regarding the concentration of graphene oxide nanoparticles present in the environment; however, as the research and development of graphene oxide nanoparticles increases, portions of these materials will inevitably end up in aqueous environments,” the researchers state in a paper published in a special issue of the journal Environmental Engineering Science.
“The situation today is similar to where we were with chemicals and pharmaceuticals 30 years ago,” Lanphere said. “We just don’t know much about what happens when these engineered nanomaterials get into the ground or water. So we have to be proactive so we have the data available to promote sustainable applications of this technology in the future.”
The research was performed in the lab of Sharon L. Walker, an associate professor and the John Babbage Chair in Environmental Engineering at UC Riverside. Walker’s lab is one of only a few in the country studying the environmental impact of graphene oxide. The research focused on understanding graphene oxide nanoparticles’ stability, or how well they hold together, and movement in groundwater versus surface water.
- In groundwater, which typically has a higher degree of hardness and a lower concentration of natural organic matter, the graphene oxide nanoparticles tended to become less stable and eventually settle out or be removed in subsurface environments.
- In surface waters, where there is more organic material and less hardness, the nanoparticles remained stable and moved farther, especially in the subsurface layers of the water bodies.
- Graphene oxide nanoparticles, despite being nearly flat, as opposed to spherical, like many other engineered nanoparticles, follow the same theories of stability and transport.
The research is supported by Lanphere’s National Science Foundation Graduate Research Fellowship; a NSF grant received by the UC Center for Environmental Implications for Nanotechnology, of which Walker is a member; and an NSF Career Award and U.S. Department of Agriculture Hispanic Serving Institution grant, both received by Walker.
* UPDATE May 1, 2014: According to Lanphere in an email to KurzweilAI:
Graphene oxide is the oxidized form of graphene that has undergone extreme conditions (e.g., exposure to highly concentrated sulfuric acid, high temperatures, ultra sonication) during its synthesis process. This results in oxygen functional (e.g., carbonyl, carboxyl, hydroxyl) groups being present on the surface and basal planes of the graphene oxide flakes. These oxygen functional groups result in the material being more stable than graphene and also more toxic. The main difference between GO and graphene is the functional groups on GO allow for the further derivitization of the surface of GO therefore allowing for additional chemical modification. GO can be deposited on additional substrates for thin conductive films where the surface can be tuned to facilitate other desired interactions to be used in sensors (e.g., heavy metal detecting sensors), electrodes, or even biomedical applications to name a few. Graphene on the other hand is not very stable and has many potential applications in the field of electrochemistry. In addition, GO has been proposed to be the precursor for bulk production of graphene based products. GO will therefore be used to synthesize graphene based hybrids or composite materials. Therefore their are two ways that GO can be introduced into the environment 1. Through primary applications (sensors, electrodes, etc) and 2. secondary applications (precursors material in graphene production and hybrid materials). For more information please read the following journal article: Chen, D.; Feng, H. B.; Li, J. H. Graphene Oxide: Preparation, Functionalization, and Electrochemical Applications. Chemical Reviews. 2012, 112 (11), 6027-6053.
Abstract of Environmental Engineering Science paper
The effects of groundwater and surface water constituents (i.e., natural organic matter [NOM] and the presence of a complex assortment of ions) on graphene oxide nanoparticles (GONPs) were investigated to provide additional insight into the factors contributing to fate and the mechanisms involved in their transport in soil, groundwater, and surface water environments. The stability and transport of GONPs was investigated using dynamic light scattering, electrokinetic characterization, and packed bed column experiments. Stability results showed that the hydrodynamic diameter of the GONPs at a similar ionic strength (2.1±1.1 mM) was 10 times greater in groundwater environments compared with surface water and NaCl and MgCl2 suspensions. Transport results confirmed that in groundwater, GONPs are less stable and are more likely to be removed during transport in porous media. In surface water and MgCl2 and NaCl suspensions, the relative recovery was 94%±3% indicating that GONPs will be very mobile in surface waters. Additional experiments were carried out in monovalent (KCl) and divalent (CaCl2) salts across an environmentally relevant concentration range (0.1–10 mg/L) of NOM using Suwannee River humic acid. Overall, the transport and stability of GONPs was increased in the presence of NOM. This study confirms that planar “carbonaceous-oxide” materials follow traditional theory for stability and transport, both due to their response to ionic strength, valence, and NOM presence and is the first to look at GONP transport across a wide range of representative conditions found in surface and groundwater environments.