Silver Nanoparticle Formation: Predictions and Verification of the Aggregative Growth Model

Abstract

The mechanisms of growth of 5−30 nm silver particles produced from the reduction of silver perchlorate by sodium borohydride are explored. Evidence is provided that, within 5 s of mixing of silver perchlorate with borohydride, the concentration of ionic silver has dropped 2 orders of magnitude, initially resulting in the formation of ∼2.5 nm silver particles. We hypothesize that growth takes place over the next 20−50 min by an aggregative growth mechanism. This hypothesis is tested by comparing model predictions with experimental results of particle growth rates over a range of ionic strengths and reaction temperatures. The model assumes particles interact via electrostatic and van der Waals forces, and comparison of numerical solutions to population balance models for aggregation and coalescence demonstrates that particle growth rates and final sizes can be predicted with surface potentials within 20% of those previously reported under reaction conditions.