Transport and retention of engineered silver nanoparticles in carbonate-rich sediments in the presence and absence of soil organic matter

Abstract

The transport and retention behavior of polymer-(PVP-AgNP) and surfactant-stabilized (AgPURE) silver nanoparticles in carbonate-dominated saturated and unconsolidated porous media was studied at the laboratory scale. Initial column experiments were conducted to investigate the influence of chemical heterogeneity (CH) and nano-scale surface roughness (NR) arising from mixtures of clean, positively charged calcium carbonate sand (CCS), and negatively charged quartz sands. Additional column experiments were performed to elucidate the impact of CH and NR arising from the presence and absence of soil organic matter (SOM) on a natural carbonate-dominated aquifer material. The role of the nanoparticle capping agent was examined under all conditions tested in the column experiments. Nanoparticle transport was well described using a numerical model that facilitated blocking on one or two retention sites. Results demonstrate that an increase in CCS content in the artificially mixed porous medium leads to delayed breakthrough of the AgNPs, although AgPURE was much less affected by the CCS content than PVP-AgNPs. Interestingly, only a small portion of the solid surface area contributed to AgNP retention, even on positively charged CCS, due to the presence of NR which weakened the adhesive interaction. The presence of SOM enhanced the retention of AgPURE on the natural carbonate-dominated aquifer material, which can be a result of hydrophobic or hydrophilic interactions or due to cation bridging. Surprisingly, SOM had no significant impact on PVP-AgNP retention, which suggests that a reduction in electrostatic repulsion due to the presence of SOM outweighs the relative importance of other binding mechanisms. Our findings are important for future studies related to AgNP transport in shallow unconsolidated calcareous and siliceous sands.

Colloid Interaction Energies for Surfaces with Steric Effects and Incompressible and/or Compressible Roughness

“…In contrast, the primary minima for compressible roughness occur at much larger values of h – h min than for incompressible roughness. The presence of shallow primary minima on compressible surfaces can explain why limited amounts of aggregation and retention have been commonly observed for NPs in the presence of compressible organic (polymers, surfactants, and humic material) coatings. ,− The presence of patchy or incomplete coverage of an adsorbed organic layer could also locally eliminate steric effects to create retention, but this hypothesis cannot explain observed differences in stability and retention with alterations of solution or solid-phase chemistry. − …”

“…Indeed, interaction energy calculations that have been extended to include steric interactions predict that the energy barrier dramatically increases, and the primary minimum is eliminated when organic layers overlap . However, NP suspensions that are stabilized by adsorbed organics frequently show various amounts of aggregation and retention that cannot be explained by steric effects. ,− One plausible explanation that will be investigated in this work is that the interaction energy profiles have been altered by compressible nanoscale roughness from adsorbed organic layers . However, previous research has not yet simultaneously considered the influence of both steric and incompressible and/or compressible roughness effects on interaction energies.…”

Evaluating the potential of capillary rise for the migration of Pt nanoparticles in Luvisols and Phaeozems (Western Siberia)

“…A significant limiting factor for the migration of highly dispersed matter is the presence of carbonates in the horizon. The results of various studies concerning the transport of metallic NPs in the saturated porous media showed that their mobility also decreases with the increase in the content of carbonates (Laumann et al, 2013;Adrian et al, 2019).…”

Microplastics and nanoplastics in agriculture—A potential source of soil and groundwater contamination?

“…Similar to soils, fine-grained unconsolidated aquifer material typically contains organic matter, which is an important parameter controlling transport of colloidal particles (Adrian et al 2019). Aquifer chemical properties such as pH or ionic strength can also significantly affect MnP transport and retention (Dong et al 2021b, Jiang et al 2021Wu et al 2020).…”