Transport of Nanoparticles in Heterogeneous Systems: Methodology and Applications

Engineered nanoparticles are making their way into natural environment as a result of a growing nanochemical industry. However, processes that govern the deposition and transport of nanoparticles are yet to be understood and often complicated by technical difficulties in tracing these nanoparticles once they enter into and/or mixed with heterogeneous minerals in the natural environment. In this presentation, we discuss the transport of nanoparticles in heterogeneous systems such as in a mixed colloidal system of silica, ferrihydrite and natural organic matter in the light of new methodologies that may be used for such complicated systems. Transport of heterogeneously charged nanoparticles was investigated in column studies using quartz or iron-oxide-coated quartz as collector surfaces. Monodisperse SiO2 (~40 and ~80 nm) and ferrihydrite (~100 nm) particles and a natural humic acid was used. Results indicate that, even under favorable conditions, ferrihydrite nanoparticles show a conservative transport through oppositely charged quartz media when they coexist with the humic acid or with oppositely charged silica nanoparticles. The ratio of oppositely charged nanoparticles is critical in determining their mobility. Similarly, the transport and detachment of iron oxide nanoparticles from iron oxide- coated quartz were observed when humics were present in the feed solution. Our results imply that transport or co-transport of oppositely charged nanoparticles can occur simultaneously under conditions that are relevant to natural geochemical environment. Further studies are needed to understand detailed mechanisms and processes that govern the deposition and transport of engineered nanoparticles under realistic environmental conditions and in the presence of heterogeneous sediment collectors. New tools such as the used of various labeled nanoparticles (such as fluorescent-labeled nanoparticles) and neutron scattering techniques could be useful in studies of such complicated systems.