Mechanistic Details of the Organizer-Assisted Nucleation of Gold Nanoparticles by the Turkevich Method

RP Pothukuchi and S Kumar and SN Punnathanam, JOURNAL OF PHYSICAL CHEMISTRY C, 128, 17642-17650 (2024).

DOI: 10.1021/acs.jpcc.4c03537

Turkevich's method for synthesizing citrate-stabilized AuNPs is the most popular method because of its straightforward methodology and reliability in producing highly stabilized AuNPs ranging from 5 to 150 nm. The mechanism involves the reduction of auric Au3+ species to aurous Au+ species using trisodium citrate and disproportionation of the aurous Au+ species to metallic gold (Au) atoms. Several studies have been conducted in the last 20 years to understand the mechanism of the Turkevich method. It has been hypothesized that the disproportionation of aurous Au+ species is aided by the formation of a complex between aurous Au+ species and dicarboxy acetone (DCA), which is a byproduct of the first reaction involving the reduction of auric Au3+ species. However, there has been no direct evidence through experiments or molecular simulation of the existence of such a complex. In this work, we use molecular simulations to study the nucleation of AuNPs from the aurous Au+ species with a specific focus on the role of DCA as an organizer. The simulations are able to give detailed insights into the mechanism of AuNP formation, including the structure of the complex between Au+ and DCA. The simulations reveal a probable two-step nucleation mechanism consisting of (i) nucleation of the DCA-Au+ complex into a cluster and (ii) nucleation of metallic gold within this cluster. The nucleation mechanism proposed in this work can serve as a prototype in other organizer-assisted nucleation of metallic nanoparticles.

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