Life Cycle Aspects of Nanoproducts, Nanostructured Materials, and Nanomanufacturing: Problem Definitions, Data Gaps, and Research Needs
Chicago, Illinois: November 5-6, 2009
Thomas L. Theis
Institute for Environmental Science and Policy
University of Illinois at Chicago
Research on Life Cycle and Nanotechnology
The pace of exploration and product development in the nanotechnology area has grown exponentially during the past decade. Figure 1 summarizes the total number of published scientific articles related to nanotechnology during the 18 year interval from 1990-2007, which is now approaching one hundred thousand annually. In comparison research publications on the general topic of environment, health, and safety (EHS) are much smaller, but also show an increasing trend. The large majority of EHS research at present focuses on the fate, transport, transformation, and toxicity of nanostructured materials, particularly nanoparticles. Understanding exposure and effects of the nanoproducts themselves is critically important information and hence such an emphasis is warranted. However, among EHS publications, those focusing on life cycle studies are considerably smaller, perhaps one percent, with an inconsistent publication trend.
The lack of a concerted research effort on the life cycle aspects of nanotechnology means that a number of critical issues that impact environmental quality are not being adequately addressed. These include resource availability and allocation, energy requirements, manufacturing efficiency, supply chain management, environmental properties of nanomaterials, waste generation, and end-of-life management (which includes disposal, containment, and recycling/reuse). For example, Figure 2 illustrates the energy demands for the manufacture of several nanoproducts in comparison with common materials (steel and aluminum). Of course the demands for materials such as aluminum and steel, by weight, far exceed those for nanomaterials (and will continue to exceed them into the distant future), however using the Royal Society (2004) near term estimate (105 MT by 2020) for total manufactured quantity of nanomaterials, it is clear that the near term energy requirements for nanomaterials will approach, and may exceed, current requirements for aluminum and steel. Figure 2 also suggests that the energy requirement for a given nanomaterial is related to the complexity of its molecular structure (i.e. nanotubes and quantum dots having more sophisticated structures and shapes than carbon fibers or crystalline Si), however further data is needed before such a trend can be confirmed. Sengul and Theis (2008) have provided an overview of all nanomanufacturing methods along with the sources of waste materials attributable to each.
Among the life cycle stages that has been especially poorly studied is stability of nanostructured materials under environmental conditions. These materials are composed of an increasing variety of raw components, with approximately 80 elements, and many organic substances, in use or under development today. Within the semiconductor class of materials alone, over 600 inorganic substances, the large majority of which do not occur naturally, have been synthesized (Orton, 2004). Most nanostructured materials are manufactured under highly specialized and environmentally stringent conditions in which their formation is thermodynamically favored. However examination of the environmental literature shows relatively little information on the environmental behavior of such materials under natural environmental conditions, for example the solubility of synthetic substances in aquatic systems—a critical need for establishing both end-of-life properties in typical disposal environments as well as human tissues. An example is shown in Figure 3 for the stability of cadmium selenide, a common semiconductor used in a variety of nanostructures.
Although CdSe(s) is quite insoluble in water, its field of stability is limited to chemically reducing environments. Under typical environmental conditions CdSe(s) is not thermodynamically favored and dissolution to Cd+2 and one or more selenium oxyanions is to be expected. Although this information has been developed for a single compound, there is reason to believe that the results might be generally true for several classes of nanomaterials, which are composed of metal cations and reduced group 5 and group 6 anions. Of course the rate at which such reactions proceed is not known. Information such as this is critical for understanding the chemical behavior of nanostructured materials in the natural environment.
References
Gutowski,T., J. Dahmus, A. Thiriez, M. Branham,and A. Jones (2007). “A Thermodynamic Characterization of Manufacturing Processes” Proceedings IEEE.
Orton, J. (2004). The Story of Semiconductors, Oxford University Press, Oxford, UK.
The Royal Society and the Royal Academy of Engineering, (2004) Nanoscience and Nanotechnologies.
Sengul, H., T.L. Theis, and S. Ghosh (2008). “Towards Sustainable Nanoproducts: An Overview of Nanomanufacturing Methods” Journal of Industrial Ecology 12(3):329-359.