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

Abstract

A mechanistic study of Ag-nanoparticle growth by reaction of [(PPh 3 ) 2 Ag(O 2 CC 13 H 27 )] and AIBN is reported. The half-life for precursor disappearance at 130.0 ( 0.1 °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.

Kinetics and Mechanisms of Aggregative Nanocrystal Growth

“…For aggregative nucleation and growth from small primary nanocrystals, we have suggested that any additive that influences the colloidal stability of the nanocrystals may potentially vary the nucleationrate behavior. 92,94,95 Indeed, nucleation rates in protein crystallization have been controlled in this manner. 110−112 In contrast, nucleation control in classical nucleation will require factors that influence the stability of monomer species consisting of a single to a few atoms, which are similar to reactive intermediates.…”

“…36,45,46,49,50,55,57,63,92,94,95 By studying the growth of small, preformed primary nanoparticles, classical nucleation and growth are removed from the mechanistic scheme. Then the kinetics and other mechanistic observations only need to distinguish between aggregative growth and Ostwald ripening.…”

“…94 The rate of Agprecursor conversion was monitored by 31 P NMR, using the disappearance of the precursor PPh 3 and the appearance of the product Ph 3 PO resonances. The conversion kinetics were first order in precursor concentration, with a half-life of t 1/2 = 3.65 ± 0.42 min, establishing the time scale for classical LaMer nucleation and growth.…”

“…Aggregative growth also has induction periods and other characteristics that mimic classical nucleation (see Figure 3). 31,[45][46][47]49,50,60,92,94,95,171,199 This subsection will show that the induction of aggregative growth may either be a nonclassical nucleation, or modeled as one, although the underlying physics is different from that in classical nucleation.…”

Silver/poly(N -vinyl-2-pyrrolidone) hydrogel nanocomposites obtained by electrochemical synthesis of silver nanoparticles inside the polymer hydrogel aimed for biomedical applications

“…It is generally considered that the nanoparticles obtained from molecular (atom) precursors grow by classical nucleation and growth, while nanoparticles originated from smaller nanocrystals grow by Ostwald ripening. There are also reports that aggregative growth contributes in both growing processes . A previous study, concerning the synthesis of silver nanoparticles in alginate solutions, confirmed the growth of AgNPs for 3 days after the synthesis by aggregative mechanism and Ostwald ripening.…”