Transport of carbon nanoparticles in porous media and its effect on the transport of concurrent contaminants

The extensive use of carbon nanoparticles (CNPs) inevitably results in their introduction into soil and groundwater, which poses a significant risk to the safety of these natural resources. Therefore, it is crucial to understand the transport behavior of CNPs in the subsurface environment and how it affects the transport of co-contaminants such as heavy metals, organic compounds, nano-plastics, engineered metal and metal oxide nanoparticles. This review focuses on recent advancements in research on the transport behaviors of CNPs in porous media and its effect on the transport of co-contaminants, with respect to the mechanisms associated with CNPs transport and the mechanisms of action of CNPs on co-contaminant transport, as well as the factors that influence these processes. Results of the existing research indicate that aggregation, attachment, detachment, straining, blocking and ripening are the primary processes governing CNPs transport due to their unique physiochemistry. CNPs can either act as carriers, facilitating the transport of co-contaminants, or as competitors, hindering the deposition of co-contaminants. Additionally, they can serve as collectors for co-contaminant deposition or co-deposit with co-contaminants, inhibiting their transport. The interactions between CNPs, co-contaminants, and the medium determine the exact role played by CNPs in co-contaminant transport. The processes of CNPs transport and its effect on co-contaminant transport are affected by the physicochemical properties of CNPs and porous media, as well as the chemistry and hydrodynamics of groundwater. This review article is of great significance for risk assessment of CNPs in soil and groundwater.