Revealing the Mechanisms behind SnO₂ Nanoparticle Formation and Growth during Hydrothermal Synthesis: An In Situ Total Scattering Study

Abstract

The formation and growth mechanisms in the hydrothermal synthesis of SnO(2) nanoparticles from aqueous solutions of SnCl(4)·5H(2)O have been elucidated by means of in situ X-ray total scattering (PDF) measurements. The analysis of the data reveals that when the tin(IV) chloride precursor is dissolved, chloride ions and water coordinate octahedrally to tin(IV), forming aquachlorotin(IV) complexes of the form [SnCl(x)(H(2)O)(6-x)]((4-x)+) as well as hexaaquatin(IV) complexes [Sn(H(2)O)(6-y)(OH)(y)]((4-y)+). Upon heating, ellipsoidal SnO(2) nanoparticles are formed uniquely from hexaaquatin(IV). The nanoparticle size and morphology (aspect ratio) are dependent on both the reaction temperature and the precursor concentration, and particles as small as ~2 nm can be synthesized. Analysis of the growth curves shows that Ostwald ripening only takes place above 200 °C, and in general the growth is limited by diffusion of precursor species to the growing particle. The c-parameter in the tetragonal lattice is observed to expand up to 0.5% for particle sizes down to 2-3 nm as compared to the bulk value. SnO(2) nanoparticles below 3-4 nm do not form in the bulk rutile structure, but as an orthorhombic structural modification, which previously has only been reported at pressures above 5 GPa. Thus, adjustment of the synthesis temperature and precursor concentration not only allows control over nanoparticle size and morphology but also the structure.

Development of a Dual-Stage Continuous Flow Reactor for Hydrothermal Synthesis of Hybrid Nanoparticles

“…This was observed in situ at temperatures above 250°C by Jensen et al 29 However, because of the lower concentration and shorter reaction time scale in our experiment, Ostwald ripening is likely not a major contributor to particle growth inside the dual-stage reactor.…”

Three-Dimensional Mesoporous Graphene Aerogel-Supported SnO2 Nanocrystals for High-Performance NO2 Gas Sensing at Low Temperature

“…However, the Sn 4+ -contained precursor was first hydrolyzed to form [Sn-(H 2 O) 6−x (OH) x ] (4−x)+ and then reacted with functional groups on the surfaces and edges of graphene oxide sheets, such as hydroxyl, carboxyl, and epoxy, and subsequently dehydrated and crystallized into SnO 2 nanocrystals. 24,25 It should be pointed out that during these two reaction procedures, urea , which can promote the nucleation of Sn M+ (M = 2, 4) and the formation of nanocrystals. The main reactions from Sn 2+ and Sn 4+ could be described as follows: …”

DNA-modulated photo-transformation of AgCl to silver nanoparticles: visiting the formation mechanism

“…Once silver nucleus evolves on AgCl, the growth of silver nanostructures can be controlled through its interaction with an appropriate ligand [12][13][14]. Owing to DNA's programmable nature and rich chemical functionality [45][46][47][48][49], a tremendous research efforts have been devoted to utilizing DNA as a template for and a controller of nanoparticle growth [50][51][52][53].…”

“…Recent research efforts have further revolutionized the colloidal synthesis methods, and have pushed forward a wide spectrum of related research fields. The mechanism of nanoparticle formation has been widely explored using many analytical techniques [6][7][8][9][10][11][12]. The shape-controlled synthesis of metal nanoparticles toward tailored optical properties has been well established by chemists and material scientists [4,13,14].…”