Surfactant-free synthesis of size controlled platinum nanoparticles: Insights from in situ studies
Jonathan Quinson, Alexandra Dworzak, So̷ren Bredmose Simonsen, Luise Theil Kuhn, Kirsten M. Ø. Jensen, Alessandro Zana, Mehtap Oezaslan, Jacob J. K. Kirkensgaard, Matthias Arenz
Abstract
The controlled synthesis of surfactant-free nanoparticles (NPs) remains a challenge. To develop improved and reproducible syntheses, a deeper understanding of the formation mechanism of surfactant-free NP is key. Pt NPs in particular are important catalysts for a wide range of applications. In situ X-ray absorption near edge structure (XANES) spectroscopy, in situ small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) are used to study the formation of surfactant-free Pt NPs in alkaline ethylene glycol. For the first time, different concentrations of H2PtCl6 (4 mM or 10 mM), different NaOH/Pt molar ratios between 0 and 20 and a wide temperature range from 30 to 140 °C are investigated. It is shown that the NaOH/Pt molar ratio influences the kinetics of the NP formation and is a key parameter to tune in order to achieve size control. At higher NaOH/Pt molar ratio the formation of Pt NPs is slower and smaller NPs are formed in a reproducible manner across various experimental conditions. This is related to the surface properties of the NPs. NPs with a diameter ca. 1 nm are easily obtained with a NaOH/Pt molar ratio of 10–20 and their formation takes place faster at higher temperatures.