Initial nucleation process in the synthesis of Platinum Nanoparticle from chloroplatinic acid. (April 2021)

• Record Type: Journal Article
• Authors: Ye, Qing; Xu, Wei; Chen, Shuangming; Wang, Zhebin; Duan, Xiaoxi; Liu, Hao; Zhang, Huan; Sun, Liang; Yang, Weiming; Zhang, Chen; Zhou, Jing
• Is Part Of: Nano today. Volume 37(2021)
• Publication Date: 2021-04
• Subjects: Nucleation -- Platinum Nano‐particle -- First principle calculation -- Molecular dynamic simulation; Nanotechnology -- Periodicals; Nanosciences -- Périodiques; 620.505
• DOI: 10.1016/j.nantod.2021.101093
• Languages: English
• ISSNs: 1748-0132

Abstract

Highlights: This work reveled the reduction-nucleation processes in the chloroplatinic acid/methanol/water system. The initial [PtCl6 ] 2- cluster is found to transform to the divalent [PtCl3 ] - and then to neutron [PtCl2 H] - . The initial nucleation process is different from the classical nucleation theory's prediction. The water molecule can reduce the activation energy and accelerate the reaction rate by the proton transport mechanism. Graphical Abstract: (a): Diagrammatic sketch to explain the water molecule's "acceleration mechanism" in the reduction of a tetravalent Pt cluster to the divalent Pt cluster. (right panel) the water molecule acts as a "bridge" to promote the proton transport process in the reaction: methanol gives a hydrogen atom to water and then another hydrogen atom in water transfers to bond to the Cl atom, this reaction path has a activation energy of 10.919 Kcal/mol; on the contrary, (left panel) in the absence of water the methanol group in the PtCl5 (CH3 OH) cluster needs to bend to a large extent to reach and bond to the Cl atom and the reaction energy barrier will increase to 18.031 Kcal/mol. (b): Snapshots from a typical trajectory of our Car-Parrinello (CP) molecular dynamics simulation, which exhibits the initial nucleation process. According to our thermodynamic analysis and kinetic simulation, the initial nucleus has been identified to be the [PtCl3 --PtClCH2 OHH2 O], its molecular weight and Pt‒Pt bond length are in highly consistent with our in-situ liquid chromatography mass spectrometry (LCMS) result and previous X-ray Absorption Spectroscopy (XAS) results, respectively. ga1 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 (H2 PtCl6 ) 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.