Transport of Single-Layered Graphene Oxide Nanosheets through Quartz and Iron Oxide-Coated Sand Columns

Single-layered graphene oxide (SLGO) nanosheets are distinguished from other colloids by their extreme anisotropy, which likely exerts a strong control on their transport behavior. Hence, this study investigates the influence of both environmentally relevant pH and ionic strength on the transport of SLGO nanosheets through saturated quartz or iron oxide-coated sands. Both the nanosheets and quartz sands are negatively charged throughout the experimental conditions, resulting in very little nanosheet deposition onto the quartz sands. However, increasing ionic strength and decreasing pH did cause measurable increases in nanosheet deposition, likely due to decreases in the magnitude of negative charges near the respective surfaces. Conversely, nanosheets and iron oxide-coated sands are oppositely charged throughout the experimental conditions, resulting in significant nanosheet deposition onto the iron oxide-coated sands. These trends suggest that nanosheet deposition is largely controlled by electrostatic forces, although the deposition rate of the high ionic strength iron oxide-coated sand treatment could not be explained by electrostatic interactions alone and instead may be influenced by nanosheet aggregation. Collectively, these measurements enable prediction of SLGO transport throughout a range of realistic environmental and geologic conditions.