UC Riverside

The overall goal of this research was to identify the mechanisms involved in the fate, transport, and removal of nanomaterials in both natural and engineered systems. The project was developed based upon the hypothesis that nanomaterial properties (type, size, shape) and environmental parameters including solution chemistry (pH, ionic strength, and ion valence), as well as the presence of natural organic matter (NOM) and bacteria will control the transport and removal of nanomaterials. Nine different nanomaterials were used including three metal oxides, three sizes of TiO₂ and three types of single walled carbon nanotubes(SWNTs). Wide variation in physicochemical properties among these nanomaterials allowed the comparison with respect to size, shape, type, and synthesis method. Complementary transport studies were conducted in both macroscopic (column) and microscopic (flow cells) systems.

This dissertation work has allowed for the following critical observations to be made. Sonication, nanoparticle concentration and solution chemistry can significantly alter physicochemical properties of metal oxide nanoparticles to ensure reproducible dispersion of metal oxide nanoparticles for transport and toxicity studies. Transport of TiO₂ nanoparticles (TNPs) through macroscopic porous media showed that a combination of mechanisms including straining, blocking, DLVO and hydrodynamic forces were involved. Additionally experiments in the parallel plate chamber indicated that deposition of TNPs was controlled by a combination of DLVO and non-DLVO-type forces, aggregation, shear and gravitational forces. Also, the presence of both NOM and bacteria resulted in much less deposition than NOM or bacteria alone, indicating a combination of factors involved in deposition including electrosteric, electrostatic effects, and aggregation state of TNPs and TNP-bacteria. Another study with three distinctly sized TNPs revealed that heterogeneity in the nanoparticle aggregate - due to its composition of primary nanoparticles - plays a significant role in the transport and aggregate breakup. Finally, SWNTs synthesized by different methods resulted in distinctive breakthrough curves due to catalysts used in synthesis, whereas metal content of SWNTs affects the relative elution of SWNTs through column. This collection of studies suggests that consideration of these mechanisms is necessary to improve our ability to predict fate, transport and removal nanomaterials in the aquatic environments as well as set-up environmental regulations.