'Anionic surfactant-assisted the transport of carbon dots through saturated soil and its variation with aqueous chemistry

There is little understanding of how anionic surfactants affect the transport of carbon dots (CDs) nanoparticles in soil. In this study, the mobility characteristics of CDs in soil columns with sodium dodecyl sulfate (SDS, a model anionic surfactant) under various conditions were investigated. The results showed that the presence of SDS enhanced CDs mobility at pH 7.0 when Na+ was the main background electrolyte. The increased electrostatic repulsion, the competitive deposition between SDS and nanoparticles for the sites on soil particle surfaces, the decreased straining effect, and the steric hindrance were all attributed to trend. Interestingly, in the presence of divalent metal cation (i.e., Ca2+ or Cu2+), SDS suppressed the mobility of CDs. This phenomenon was most likely stemmed from the precipitation of scum (i.e., SDS-Cu2+/Ca2+ complexes) and adsorbed SDS-metal-CDs complexes. Furthermore, the extent of the enhanced effects of SDS on CDs mobility decreased with increasing solution pH from 5.0 to 9.0, which was primarily due to a decrease in the steric effect and deposition site competition. A two-site transport model was also applied to fit the observed mobility data of CDs in soil media. Overall, findings from this work provide meaningful insights into the fate of co-existing carbon-based nanoparticles and anionic surfactants in the subsurface systems.

Automated summary

This study investigates the effects of anionic surfactants on the transport of carbon dots nanoparticles in soil. The presence of the surfactant enhances the mobility of the nanoparticles under certain conditions, but it suppresses their mobility in the presence of divalent metal cations. Additionally, the effects of the surfactant on nanoparticle mobility decrease with increasing solution pH.