The devil is in the details (or the surface): impact of surface structure and surface energetics on understanding the behavior of nanomaterials in the environment

Metal and metal oxide nanomaterials are found in many consumer products for use in a wide range of applications including catalysis, sensors and contaminant remediation. Because of the extensive use of metal-based nanomaterials, there are concerns that these materials have the potential to get into the environment sometime during production, distribution, use and/or disposal. In particular, there exists the potential that they will make their way into water systems, e.g. drinking water systems, ground water systems, estuaries and lakes. In this review, some of the uncertainties in understanding nanoparticle behavior, which is often due to a lack of fundamental knowledge of the surface structure and surface energetics for very small particles, are discussed. Although classical models may provide guidance for understanding dissolution and aggregation of nanoparticles in water, it is the detailed surface structure and surface chemistry that are needed to accurately describe the surface free energy, a large component of the total free energy, in order to fully understand these processes. Without this information, it is difficult to develop a conceptual framework for understanding the fate, transport and potential toxicity of nanomaterials. Needed research areas to fill this void are discussed.