In situ Study of Au Nanoparticle Growth in a Mechanochemical-Aging-Based Synthesis

Abstract

As we strive to perform chemical transformations in a more sustainable fashion, inducing reactions through the absorption of mechanical energy has emerged as a highly successful approach. Due to the wide-ranging applications of gold nanoparticles (AuNPs), mechanochemical strategies have already been employed for their synthesis. However, we do not yet fully understand the underlying processes surrounding the gold salt reduction, nucleation and growth of AuNPs in the solid state. Herein, we present a mechanically activated aging synthesis of AuNPs, through a solid-state Turkevich reaction. Solid reactants are only briefly exposed to mechanical energy before being aged statically for a period of six weeks at different temperatures. The aging step grants a greater period of time to analyze the initial reduction and subsequent nanoparticle formation processes. During the aging period the reaction was monitored using a combination of X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) to gain meaningful insights into the solid-state formation of gold nanoparticles.

Direct observation by high resolution transmission electron microscopy of gold(iii) particle transformation during aging reduction reaction

“…Yet solvent dispersion can induce morphological and chemical changes in NPs. 38 Therefore, to monitor the changes to the HAuCl 4 particles during the solid-state process, we employed the solid-state grid preparation outlined in the Experimental section.…”

“…The AuNPs formed in this study were produced in a similar fashion to that of our previous work. 38 Typically, a 15 mL zirconia milling jar (Form-Tech Scientific), one 10 mM zirconia milling ball, 47.7 mg of HAuCl 4 ·3H 2 O (0.121 mmol), 163.2 mg of 1-octadecylamine (0.605 mmol), and 39.2 mg of trisodium citrate dihydrate (0.133 mmol) were chilled separately over dry ice for approximately one hour. Then, the milling ball and three solid reactants were added to the jar which was sealed and shaken on a Retsch MM400 mixer mill at 29.5 Hz for 60 s, upon which a free flowing yellow powder was obtained.…”

“…The samples were then aged for a period of six weeks at −18 °C, 21 °C and 32 °C. 38 Analysis of the resulting powders by X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), PXRD and TEM, allowed a deep mechanistic analysis of the reaction. We could track the growth of nanoparticles, track gold reduction and evaluate an activation energy for this reaction.…”