Stability and Transport of Novel Engineered Nanomaterials in Aqueous and Subsurface Environments
The primary goal of this doctoral research was to investigate the environmental parameters that may influence the fate and transport of engineered nanomaterials (ENMs) in natural and engineered systems. Studies were conducted with emerging "boutique" ENMs (graphene oxide and molybdenum disulfide). The influence of environmentally relevant parameters (i.e., ionic strength, pH, presence of natural organic matter, water type (groundwater vs. surface water, and presence of divalent cations (i.e., Ca+2, Mg+2)) on the stability, and transport of graphene oxide was investigated. The presence of a pluronic surfactant was also studied to observe its influence on the stability, aggregate morphology, and transport in porous media for a popular transitional metal di-chalcogenide molybdenum disulfide. It was hypothesized that traditional colloid filtration theory developed for spherical colloids, would accurately predict the deposition of graphene and molybdenum disulfide in aquatic systems, regardless of their unique two-dimensional planar geometry. Results from this dissertation confirm this hypothesis and provide crucial information that should be used for sustainable nanoparticle development, utilization, and regulation of graphene oxide and molybdenum disulfide. Solution chemistry parameters played a critical role in determining the behavior and movement of graphene oxide and molybdenum disulfide during transport in macroscopic porous media. Mechanisms responsible for these results were investigated and the following was concluded. The physical geometry (two-dimensional-planar) for these ENMs will likely play an important role in their transport through subsurface porous media where "straining" and "wedging" are the most likely physical removal mechanisms during transport in sediment beds. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory also provided additional insight into the deposition mechanisms for molybdenum disulfide and graphene oxide. Finally, the results from this study provide critical information to help predict the fate and transport of ENMs in aquatic environments.