Pathway from a Molecular Precursor to Silver Nanoparticles: The Prominent Role of Aggregative Growth

A mechanistic study of Ag-nanoparticle growth by reaction of [(PPh3)(2)Ag(O2CC13H27)] and AIBN is reported. The half-life for precursor disappearance at 130.0 +/- 0.1 degrees C under the reaction conditions is determined to be 3.65 +/- 0.42 min, which defines the time scale for classical (LaMer) nucleation and growth to be within the first 15 min (4 half-lives). The nanoparticle-growth kinetics are separately determined by TEM monitoring and UV-visible spectroscopy. Fits to the kinetic data establish that the active-growth regime extends to 58 min, and that Ostwald ripening ensues shortly thereafter. Evidence for an aggregative nucleation and growth process is obtained. The quantitative data indicate that classical nucleation and growth, aggregative nucleation and growth, and Ostwald ripening occur in consecutive time regimes with little overlap, and that nanoparticle growth is dominated by the aggregative regime. Aggregative growth should be considered a potential contributing mechanism in all nanoparticle-forming reactions.