Silver nanoparticles coated with natural polysaccharides as models to study AgNP aggregation kinetics using UV-Visible spectrophotometry upon discharge in complex environments

This study provides quantitative information on the aggregation and dissolution behaviour of silver nanoparticles (AgNPs) upon discharge in fresh and sea waters, represented here as NaCl solutions of increasing ionic strength (up to 1M) and natural fjord waters. Natural polysaccharides, sodium alginate (ALG) and gum arabic (GA), were used as coatings to stabilize the AgNPs and the compounds acted as models to study AgNP aggregation kinetics. The DLVO theory was used to quantitatively describe the interactions between the AgNPs. The stability of AgNPs was established using UV-Visible spectrophotometry, including unique information collected during the first seconds of the aggregation process. Alginate coating resulted in a moderate stabilization of AgNPs in terms of critical coagulation concentration (∼82 mM NaCl) and a low dissolution of <10% total Ag in NaCl solutions up to 1M. Gum arabic coated AgNPs were more strongly stabilized, with ∼7-30% size increase up to 77 mM NaCl, but only when the silver ion content initially present in solution was low (