Interfacial interactions of bare and functionalized nanoparticles with quartz sand: Role of humic acid and coexisting divalent cations

Abstract

Effective application of nanoparticles for in situ groundwater remediation strongly depends on their transportability across a sandy media. Retainment of the nanoparticles within the media is undesired as it will limit their reachability to the treatment zone. Henceforth, the interfacial interactions between the nanoparticles and the sand need to be fully understood. Present work aims to elucidate the retention of iron oxide nanoparticles by quartz sand in solution that are relevant to the typical environmental condition using batch mode mixing study. Results showed that the presence of humic acid and Ca2+ notably alters the nanoparticle-sand interaction in different manners. Bare nanoparticles (BNPs) was found to favourably retained by the sand under acidic medium (94%); while the counterpart that was functionalized with poly(sodium 4-styrenesulfonate), i.e. PSS-NPs, exhibited better rejection from the sand. The addition of humic acid further shield the attraction between PSS-NPs and sand, resulted in 0% retention. Interestingly, in the presence of 1–10 mM Ca2+ ions, the amount of PSS-NPs that was retained by the sand increased to 55%. Such observation may ascribe to the role of Ca2+ in bridging the PSS-NPs and the sand and in screening the repulsion force between both entities. Nevertheless, the retention percentage was successfully reduced to 11.8% when humic acid coexists. Outcome of this work provides an overview on the fate of the bare and surface functionalized nanoparticles upon released into the environmental system.