A two-site filtration model for 14C-labeled few-layer graphene mobility in saturated porous media: Effect of ionic strength

Graphene-based nanoparticles (GNPs) have been widely used in various applications such as energy, medical, and electronic, however, the environmental risks associated with these nanomaterials are not well understood due to a limited number of studies. Understanding their transport characteristics in soil-groundwater system, as an important exposure medium is imperative to accurate assessment of the environmental risk posed by GNPs.

A mathematical modeling study was conducted to examine the effect of ionic strength (IS) on the mobility of ¹⁴C-labeled few-layer graphene (FLG) in saturated porous media. Several colloid transport models including clean-bed filtration (CFT), maximum retention capacity (MRC), and multi-attachment-site (2S) model classes were implemented to simulate particle-collector surface interactions. Simulation results based on the inverse analyses of experimental FLG elution data show a superior performance of 2S and MRC in regard to sum of squared residuals over CFT model. Two subclasses of 2S that consider a mix of favorable and unfavorable attachment sites with irreversible attachment to favorable sites were most consistent with the filtration theory predictions. In all simulations, increasing solution IS resulted in greater particle-collector attachment efficiency which represents greater retention of FLG in the sand columns, nonetheless, the decrease of detachment rate coefficient occurred under the same circumstance.