title: Silver nanoparticles coated with natural polysaccharides as models to study AgNP aggregation kinetics using UV-Visible spectrophotometry upon discharge in complex environments.
abstract: 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 aggregaton process. Alginate coating resulted in a moderate stabilization of AgNPs in terms of critical coagulation concentration (~82mM 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 77mM NaCl, but only when the silver ion content initially present in solution was low (<10% total Ag). The ALG and GA coated AgNPs showed a strongly enhanced stability in natural fjord waters (ca. 5h required to reduce the area of the surface plasmon resonance band (SPRB) by two fold) compared with NaCl at an equivalent ionic strength (1-2min period for a two fold SPRB reduction). This is ascribed to a stabilizing effect from dissolved organic matter present in natural fjord waters. Interestingly, for AgNP-GA solutions with 40% of total silver present as unreacted silver ions in the NP stock solution, fast aggregation kinetics were observed in NaCl solutions (SPRB area was reduced by ca. 50% within 40-150min), with even more rapid removal in fjord waters, attributed to the high amount of silver-chloride charged species, that interact with the NP coating and/or organic matter and reduce the NPs stabilization.
authors.affiliation: Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, SO14 3ZH Southampton, UK; GEOMAR, Helmholtz Centre for Ocean Research, 24148 Kiel, Germany. Electronic address: plodeiro@geomar.de.
authors.forename: Pablo
authors.initials: P
authors.lastname: Lodeiro
authors.affiliation: Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, SO14 3ZH Southampton, UK; GEOMAR, Helmholtz Centre for Ocean Research, 24148 Kiel, Germany.
authors.forename: Eric P
authors.initials: EP
authors.lastname: Achterberg
authors.affiliation: GEOMAR, Helmholtz Centre for Ocean Research, 24148 Kiel, Germany.
authors.forename: Joaquín
authors.initials: J
authors.lastname: Pampín
authors.affiliation: GEOMAR, Helmholtz Centre for Ocean Research, 24148 Kiel, Germany.
authors.forename: Alice
authors.initials: A
authors.lastname: Affatati
authors.affiliation: Department of Chemistry, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589, Saudi Arabia.
authors.forename: Mohammed S
authors.initials: MS
authors.lastname: El-Shahawi
mesh_terms: D004785:Environmental Pollutants / Q000737:chemistry*; D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D008956:Models, Chemical; D011134:Polysaccharides / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D013472:Sunlight; D014466:Ultraviolet Rays
chemical_list: D004785:Environmental Pollutants; D011134:Polysaccharides; D012834:Silver
keywords: Aggregation; Alginate; Fjord waters; Gum Arabic; Oxidation; Silver nanoparticles