Effects of aggregate structure on the dissolution kinetics of citrate-stabilized silver nanoparticles.

Aggregation and dissolution kinetics are important environmental properties of silver nanoparticles (AgNPs), and characterization of the interplay between these two processes is critical to understanding the environmental fate, transport, and biological impacts of AgNPs. Time-resolved dynamic light scattering was employed to measure the aggregation kinetics of AgNPs over a range of monovalent electrolyte (NaCl) concentrations. The fractal dimensions (Df) obtained from aggregation kinetics and static light scattering were found to be dependent on the aggregation mechanism and, in accord with expectation, varied from 1.7 for diffusion-limited cluster aggregation to 2.3 for reaction-limited cluster aggregation. An aggregation-dissolution model, in which the proportion of accessible reactive sites on primary particles as well as the aggregate size and Df are assumed to be key determinants of reactivity, is found to provide an excellent description of the decline of normalized rate of dissolution of AgNPs during aggregation for different NaCl concentrations. This model also provides fundamental insights into the factors accounting for the observed change in rate of dissolution of AgNPs on injection into seawater thereby facilitating improved prediction of the likely toxicity of AgNPs in the marine environment.