Direct Measurements of the Forces Between Silver and Mica in Humic Substance-Rich Solution
Abstract
Nanosilver is one of the most broadly used engineered nanomaterials in consumer products, owing to its remarkably strong antimicrobial activity. Once nanosilver particles are released into the environment, deposition onto porous media will reduce their spreading, becoming an important process for assessing soil and groundwater quality. The deposition mechanism is controlled by the forces of interaction between particles and collectors, which are not well understood in solutions rich in humic substances. In this study, we investigated the origin and magnitude of opposing forces between silver and mica surfaces (representing nanosilver and sand grains) in solutions of variable concentrations of NaNO3, Ca(NO3)2, and dissolved organic matter in the form of humic acid (HA), using a surface force apparatus (SFA). The actual surface potentials, HA adsorbed layer thickness and compressibility, as well as total interaction forces were determined experimentally. The measured total force was separated into the individual contributions of electrostatic, steric, and van der Waals interactions. The force profiles obtained for different solution conditions were then translated into energy of interaction profiles for cases of nanosilver particles interacting with mica-like collectors. Each suspension's expected attachment efficiency was parameterized by precise measurements of surface and adsorbed layer properties. Our results indicate that HA forms adsorbed layers with significantly larger charge, thickness, compressibility, and mass onto mica than silver. Interactions with Ca+2 rendered the adsorbed HA layer onto mica more dense and promoted higher HA adsorption onto silver. Force-distance profiles indicate that when silver-mica systems were exposed to HA, osmotic and electrostatic repulsion govern the total interaction. Elastic-steric forces were negligible and soft particle theory was deemed inappropriate for modeling the system. Attachment efficiency estimates from measured surface properties, suggested high particle mobility when nanosilver is applied to HA-rich agricultural soils with modest ionic strength.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH043...07P
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1831 Groundwater quality;
- HYDROLOGY;
- 1832 Groundwater transport;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY