Elucidation of the Crystal Growth Characteristics of SnO2 Nanoaggregates Formed by Sequential Low-Temperature Sol-Gel Reaction and Freeze Drying

• Published in: Nanomaterials (Basel, Switzerland) Vol. 11; no. 7; p. 1738
• Main Authors: Vafaei, Saeid, Wolosz, Alexander, Ethridge, Catlin, Schnupf, Udo, Hattori, Nagisa, Sugiura, Takashi, Manseki, Kazuhiro
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2021; MDPI
• Subjects: Crystal growth; Crystallization; Freeze drying; Functional materials; High resolution electron microscopy; Low temperature; low-temperature synthesis; Methods; Nanocrystals; Nanomaterials; Nanoparticles; Nanotechnology; oxygen vacancies; Photoelectron spectroscopy; Photoelectrons; Reaction time; SnO2; Sol-gel processes; Tin dioxide; Transmission electron microscopy; X ray photoelectron spectroscopy; United States > US; Japan
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano11071738

SnO2 nanoparticles are regarded as attractive, functional materials because of their versatile applications. SnO2 nanoaggregates with single-nanometer-scale lumpy surfaces provide opportunities to enhance hetero-material interfacial areas, leading to the performance improvement of materials and devices. For the first time, we demonstrate that SnO2 nanoaggregates with oxygen vacancies can be produced by a simple, low-temperature sol-gel approach combined with freeze-drying. We characterize the initiation of the low-temperature crystal growth of the obtained SnO2 nanoaggregates using high-resolution transmission electron microscopy (HRTEM). The results indicate that Sn (II) hydroxide precursors are converted into submicrometer-scale nanoaggregates consisting of uniform SnO2 spherical nanocrystals (2~5 nm in size). As the sol-gel reaction time increases, further crystallization is observed through the neighboring particles in a confined part of the aggregates, while the specific surface areas of the SnO2 samples increase concomitantly. In addition, X-ray photoelectron spectroscopy (XPS) measurements suggest that Sn (II) ions exist in the SnO2 samples when the reactions are stopped after a short time or when a relatively high concentration of Sn (II) is involved in the corresponding sol-gel reactions. Understanding this low-temperature growth of 3D SnO2 will provide new avenues for developing and producing high-performance, photofunctional nanomaterials via a cost-effective and scalable method.