Initial nucleation process in the synthesis of Platinum Nanoparticle from chloroplatinic acid

Abstract

The size, morphology, and polymorphism of nano-materials, the key factors determining their physicochemical properties, are significantly affected by the nucleation processes from precursors. Understanding the nucleation kinetics at the atomic scale is fundamental to the designed synthesis of nano-materials with tailored composition, shape and size. Here we report our investigation on the nucleation process in synthesis Platinum nano-particles by chemical reduction of chloroplatinic acid in methanol and methanol/water mixed system. In synergy with the liquid chromatography mass spectrometry (LCMS) and first-principle transition-state calculations, specific reaction processes at the pre-nucleation stage are revealed in which the precursor chloroplatinic acid (H2PtCl6) undergoes a two-step reduction process to form divalent and non-valent Pt-contained clusters, respectively. It is found that in both steps, the presence of water molecular can lower the activation energy and accelerate the reaction rate through a proton transport mechanism. Moreover, through free energy analysis and ab-initio molecular dynamic simulation, we identified the initial nucleation process which is characterized by the formation of Pt-Pt bond between two divalent Pt (II)-contained clusters. The theoretical calculations explain the pre-nucleation reaction paths and the nucleation process, consistent with the LCMS measurements and previous XAFS results. This work indicates the nucleation processes in chloroplatinic acid/methanol/water system exhibit more complexities than that described by the classical nucleation theory as well as previous research results on the same system. The finding may shed light upon the size-and-shape-controlled synthesis of noble metal nanoparticles.