Transport of TiO2 and CeO2 nanoparticles in saturated porous media in the presence of surfactants with environmentally relevant concentrations

Nanomaterials are threatening the environment and human health, but there has been little discussion about the stability and mobility of nanoparticles (NPs) in saturated porous media at environmentally relevant concentrations of surfactants, which is a knowledge gap in exploring the fate of engineered NPs in groundwater. Therefore, the influences of the anionic surfactant (sodium dodecylbenzene sulfonate, SDBS), the cationic surfactant (cetyltrimethylammonium bromide, CTAB), and the nonionic surfactant (Tween-80) with environmentally relevant concentrations of 0, 5, 10, and 20 mg/L on nano-TiO2 (nTiO(2), negatively charged) and nano-CeO2 (nCeO(2), positively charged) transport through saturated porous media were examined by column experiments. On the whole, with increasing SDBS concentration from 0 to 20 mg/L, the concentration peak of nTiO(2) and nCeO(2) in effluents increased by approximately 0.2 and 0.3 (dimensionless concentration, C/C-0), respectively, because of enhanced stability and reduced aggregate size resulting from enhanced electrostatic and steric repulsions. By contrast, the transportability of NPs significantly decreased with increasing CTAB concentration due to the attachment of positive charges, which was opposite to the charge on the medium surface and facilitated the NP deposition. On the other hand, the addition of Tween-80 had no significant influence on the stability and mobility of nTiO(2) and nCeO(2). The results were also demonstrated by the colloid filtration theory (CFT) modeling and the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction calculations; it might promote the assessment and remediation of NP pollution in subsurface environments.

Automated summary

The study found that the presence of anionic surfactant SDBS increased the stability and reduced aggregate size of nTiO(2) and nCeO(2), resulting in higher concentrations in effluents. Conversely, the cationic surfactant CTAB decreased the transportability of NPs due to positive charge attachment, causing NP deposition. Tween-80 had no significant impact on the stability and mobility of the nanoparticles. The results have implications for assessing and remediating NP pollution in subsurface environments.