title: H2O2-mediated oxidation of zero-valent silver and resultant interactions among silver nanoparticles, silver ions, and reactive oxygen species.
abstract: The H(2)O(2)-mediated oxidation of silver nanoparticles (AgNPs) over a range of pH (3.0-14.0) is investigated here, and an electron charging-discharging model capable of describing the experimental results obtained is developed. AgNPs initially react with H(2)O(2) to form Ag(+) and superoxide, with these products subsequently reacting to reform AgNPs (in-situ-formed AgNPs) via an electron charging-discharging mechanism. Our experimental results show that the AgNP reactivity toward H(2)O(2) varies significantly with pH, with the variation at high pH (>10) due particularly to the differences in the reactivity of H(2)O(2) and its conjugate base HO(2)(-) with AgNPs whereas at lower pH (3-10) the pH dependence of H(2)O(2) decay is accounted for, at least in part, by the pH dependence of the rate of superoxide disproportionation. Our results further demonstrate that the in-situ-formed AgNPs resulting from the superoxide-mediated reduction of Ag(+) have a different size and reactivity compared to those of the citrate-stabilized particles initially present. The turnover frequency for AgNPs varies significantly with pH and is as high as 1776.0 min(-1) at pH 11.0, reducing to 144.2 min(-1) at pH 10.0 and 3.2 min(-1) at pH 3.0.
authors.affiliation: School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW, Australia.
authors.forename: Di
authors.initials: D
authors.lastname: He
authors.forename: Shikha
authors.initials: S
authors.lastname: Garg
authors.forename: T David
authors.initials: TD
authors.lastname: Waite
mesh_terms: D002414:Cations, Monovalent; D002951:Citrates / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010316:Particle Size; D017382:Reactive Oxygen Species / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D013482:Superoxide Dismutase / Q000737:chemistry
chemical_list: D002414:Cations, Monovalent; D002951:Citrates; D017382:Reactive Oxygen Species; C514290:trisodium citrate; D012834:Silver; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase