Visualization of graphene oxide transport in two-dimensional homogeneous and heterogeneous porous media

Highlights: • LTV technology was effective in visualizing GO transport in the 2-D porous media. • Preferential flow affected GO transport in 2-D heterogeneous porous media. • GO spread vertically through dispersion in 2-D porous media. • Double Monod model described GO transport and retention very well. -- Abstract: Graphene oxide (GO) has been indicated to be biotoxic and risky in environment, its environmental behavior thus has received increasing attention in recent. In this study, homogeneous and heterogeneous sand tanks were used to examine the transport behaviors of GO nanoparticles in two-dimensional (2-D) porous media under various conditions. Light transmission visualization (LTV) technology was applied to visualize the real-time transport, retention, and release of GO. GO transport in 2-D porous media was simulated with a simplified Double Monod model. GO mobility decreased with the increasing solution ionic strength (IS) and decreasing media grain size. Preferential flow played an important role in GO transport in 2-D heterogeneous porous media. Even without vertical flow in the sand tanks, GO still spread vertically through dispersion, suggesting the importance of the dispersion process to nanoparticle fate and transport in 2-D porous media. LTV images and breakthrough curves showed that some of the previous retained GO particles were instantaneously remobilized with IS decreasing. With the consideration of the vertical dispersion, simulations of the Double Monod model matched the experimental data well. Findings from this work contribute to expand current knowledge of environmental fate and transport of GO, leading to better assessment and prediction of its environmental risks.