Dissolution-Accompanied Aggregation Kinetics of Silver Nanoparticles

Bare silver nanoparticles with diameters of 82 +/- 1.3 nm were synthesized by the reduction of the Ag(NH3)(2)(+) complex with D-maltose, and their morphology, crystalline structure. UV-vis spectrum, and electrophoretic mobilities were determined. Dynamic light scattering was employed to assess early stage aggregation kinetics by measuring the change in the average hydrodynamic diameter of the nanoparticles with time over a range of electrolyte types (NaCl, NaNO3, and CaCl2) and concentrations. From this the critical coagulation concentration values were identified as 30, 40. and 2 mM for NaNO3, NaCl, and CaCl2, respectively. Although the silver nanoparticles were observed to dissolve in all three electrolyte solutions, the aggregation results were still consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dissolution or the silver nanoparticles, which were coated with a layer or Ag2O, was highly dependent on the electrolyte type and concentration. In systems with Cl- a secondary precipitate, likely AgCl, also formed and produced a coating layer that incorporated the silver nanoparticles. Aggregation of the silver nanoparticles was also examined in the presence of Nordic aquatic fulvic acid and was little changed compared to that evaluated under identical fulvic acid-Free conditions. These results provide a fundamental basis for further studies evaluating the environmental fate of silver nanoparticles in natural aquatic systems.