THE BREN SCHOOL OF Environmental Science & Management Presents
Gregory V. Lowry Carnegie Mellon University
11:00 a.m. - 12:00 p.m. Bren Hall Pine Room (3526)
"Reactive Nanomaterials for In Situ Aquifer Remediation: Effect of Surface Coatings on Reactivity, Transport, and Emplacement"
Hosted by Bren Professor Arturo Keller
Summary Novel reactive nanomaterials, such as Fe0 nanoparticles (NZVI), offer the potential for highly efficient targeted delivery of remedial agents to subsurface contaminants. The primary challenge to application is selecting appropriate surface modifiers that enable emplacement in the contamination zone, but do not adversely impact the particle’s reactivity with the contaminant. Concomitant optimization of mobility and reactivity requires a fundamental molecular level understanding of the surface modifiers properties along with their effect on mobility and reactivity. Dynamic light scattering and electrophoretic mobility measurements, along with Ohshimas’s analysis, are used to characterize the layer conformation and properties of different types of common synthetic and natural polyelectrolytes adsorbed onto NZVI. I will discuss how then batch reactivity studies as well as column and two-dimensional flow cell studies under a variety of hydrogeochemical conditions and heterogeneities were conducted on polyelectrolyte-modified NZVI to determine the effect of the adsorbed layer properties on reactivity and mobility. Surface coatings decreased particle reactivity with trichloroethylene by up to a factor of 20. The magnitude of the effect depends on the adsorbed layer conformation of the polyelectrolyte as explained using the Scheutjens and Fleer train-loop-tail conceptual model for homopolymer sorption. In this study, it was shown that modifiers providing electrosteric repulsion, which are less sensitive to changes in ionic strength, were needed to provide good mobility in saturated sand columns under geochemical conditions representative of groundwater conditions. More polydisperse samples containing larger particles (several hundred nanometers) are less mobile than monodisperse samples containing only small particles (<100 nm). The higher deposition rate of the polydisperse samples and the lower degree of deposition reversibility are attributed to increased particle aggregation from the magnetic attractive forces between particles that increased with r6. This study emphasized the important role of aggregation on nanoparticle transport, and a systematic study of mobility enhancement by different polyelectrolytes yielded a new semi-empirical approach to predicting the transport of polyelectrolyte or natural organic matter–coated nanomaterials in porous media.
Biography Gregory V. Lowry is an associate professor in the department of Civil and Environmental Engineering at Carnegie Mellon University. He received his BS in chemical engineering from the University of California, Davis, an MS in civil environmental engineering from the University of Wisconsin, Madison, and a PhD in civil-environmental engineering from Stanford University. His research interest is broadly defined as transport and reaction in porous media, with a focus on the fundamental physical/geochemical processes affecting the fate of inorganic and synthetic organic contaminants and engineered nanomaterials in the environment. __________________________________________________________________________________
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