Oxidative dissolution of silver nanoparticles by dioxygen: a kinetic and mechanistic study.

We have recently reported a kinetic and mechanistic study on oxidative dissolution of silver nanoparticles (AgNPs) by H(2)O(2). In the present study, the parameters that govern the dissolution of AgNPs by O(2) were revealed by using UV/Vis spectrophotometry. Under the same reaction conditions (Tris-HOAc, pH 8.5, I=0.1 M at 25 °C) the apparent dissolution rate (k(app)) of AgNPs (10±2.8 nm) by O(2) is about 100-fold slower than that of H(2)O(2). The reaction rate is first-order with respect to [Ag(0)], [O(2)], and [Tris](T), and inverse first-order with respect to [Ag(+)] (where [Ag(0)]=total concentration of Ag metal and [Tris](T)=total concentration of Tris). The rate constant is dependent on the size of AgNPs. No free superoxide (O(2)(-)) and hydroxyl radical (·OH) were detected by trapping experiments. On the basis of kinetic and trapping experiments, an amine-activated pathway for the oxidation of AgNPs by O(2) is proposed.

Oxidative dissolution of silver nanoparticles by biologically relevant oxidants: a kinetic and mechanistic study.

The oxidative dissolution of silver nanoparticles (AgNPs) plays an important role in the synthesis of well-defined nanostructured materials, and may be responsible for their activities in biological systems. In this study, we use stopped-flow spectrophotometry to investigate the kinetics and mechanism of the oxidative dissolution of AgNPs by H(2)O(2) in quasi-physiological conditions. Our results show that the reaction is first order with respect to both [Ag(0)] and [H(2)O(2)], and parallel pathways that involve the oxidation of H(2)O(2) and HO(2)(-) are proposed. The order of the reaction is independent of the size of the AgNPs (approximately 5-20 nm). The rate of dissolution increases with increasing pH from 6.0 to 8.5. At 298 K and I=0.1 M, the value of k(b) is five orders of magnitude higher than that of k(a) (where k(a) and k(b) are the rate constants for the oxidative dissolution of AgNPs by H(2)O(2) and HO(2)(-), respectively). In addition, the effects of surface coating and the presence of halide ions on the dissolution rates are investigated. A possible mechanism for the oxidative dissolution of AgNPs by H(2)O(2) is proposed. We further demonstrate that the toxicities of AgNPs in both bacteria and mammalian cells are enhanced in the presence of H(2)O(2), thereby highlighting the biological relevance of investigating the oxidative dissolution of AgNPs.