Mechanisms of graphene oxide aggregation, retention, and release in quartz sand

Authors: LIANG, YAN - Guangxi University; Bradford, Scott; SIMUNEK, JIRI - University Of California; KLUMPP, ERWIN - Agrosphere Institute

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2018
Publication Date: 11/22/2018
Citation: Liang, Y., Bradford, S.A., Simunek, J., Klumpp, E. 2018. Mechanisms of graphene oxide aggregation, retention, and release in quartz sand. Science of the Total Environment. 656:70-79. https://doi.org/10.1016/j.scitotenv.2018.11.258.
DOI: https://doi.org/10.1016/j.scitotenv.2018.11.258

Interpretive Summary: Graphene oxide (GO) has found widespread use in industrial and environmental applications, but there is concern about the adverse influence of GO on organisms, cells, and ecosystems. The objective of this study was to investigate the influence of various physical (grain size and input concentration) and chemical (solution ionic strength and cation type) factors on the mobility of GO in groundwater environments. Theory was extended to quantity interactions of GO, and clays, on natural surfaces. The critical role of surface roughness and adsorbed ions on GO interfaces was demonstrated, and used to explain experimental observations. These results improve our understanding of mechanisms that control GO interactions with surfaces and its environmental fate. This information will be of special interest to scientists and engineers concerned with assessing the risk of GO in the environment.

Technical Abstract: The roles of graphene oxide (GO) particle geometry, GO surface orientation, surface roughness, and nanoscale chemical heterogeneity on interaction energies, aggregation, retention, and release of GO in porous media were not fully considered in previous studies. Consequently, mechanisms controlling the environmental fate of GO were incompletely or inaccurately quantified. To overcome this limitation, plate-plate interaction energies were modified to account for these factors and used in conjunction with a mathematical model to interpret the results of GO aggregation, retention, and release studies. Calculations revealed that these factors had a large influence on the predicted interaction energy parameters. Similar to previous literature, the secondary minimum was predicted to dominate on smooth, chemically homogeneous surfaces that were oriented parallel to each other, especially at higher IS. Conversely, shallow primary minimum interactions were sometimes predicted to occur on surfaces with nanoscale roughness and chemical heterogeneity due to adsorbed Ca2+ ions, especially when the GO particles were oriented perpendicular to the interacting surface. Experimental results were generally consistent with these predictions and indicated that the primary minimum played a major role in GO retention and the secondary minimum contributed to GO release with IS reduction. Cation exchange (Na+ replacing Ca2+) enhanced GO release with IS reduction when particles were initially deposited in the presence of Ca2+ ions. However, retained GO were always completely recovered into the excess deionized water when the sand pore structure was destroyed during excavation, and this indicates that primary minima were shallow and that the pore structure also played an important role in GO retention. Further evidence for the role of pore structure on GO retention was obtained by conducting experiments in finer textured sand and at higher input concentrations that induced greater aggregation. In both cases, greater GO retention occurred, and retention profiles became more hyperexponential in shape.