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

Abstract

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.

Bidimensional Engineered Amorphous a-SnO2 Interfaces: Synthesis and Gas Sensing Response to H2S and Humidity

“…To conclude, we also tried to investigate the recrystallization mechanism of amorphous a -SnO 2 into crystalline SnO 2 , as shown in Figure d,h. We found that by an extra week of annealing at 280 °C, crystalline domains are initially formed on step edges, as shown in Figure d with corresponding interatomic plane distances of 0.33 nm (Figure h), attributed to the (110) plane distances of tetragonal rutile SnO 2 . It turns out that the recrystallization of a -SnO 2 into crystalline SnO 2 proceeds from the outside to the inside of the flake, considering that no nucleating SnO 2 crystallites are visible inside the flakes as shown in Figure d,h.…”

“…We found that by an extra week of annealing at 280 °C, crystalline domains are initially formed on step edges, as shown in Figure 4 d with corresponding interatomic plane distances of 0.33 nm ( Figure 4 h), attributed to the (110) plane distances of tetragonal rutile SnO 2 . 44 It turns out that the recrystallization of a -SnO 2 into crystalline SnO 2 proceeds from the outside to the inside of the flake, considering that no nucleating SnO 2 crystallites are visible inside the flakes as shown in Figure 4 d,h. The limited extension of the crystalline domains with respect to the amorphous ones shown in Figure 4 d,h may also explain the lack of any diffraction peak attributed to crystalline SnO 2 in the GI-XRD pattern of Figure 3 .…”

“…We found that by an extra week of annealing at 280 °C, crystalline domains are initially formed on step edges, as shown in Figure 4d with corresponding interatomic plane distances of 0.33 nm (Figure 4h), attributed to the (110) plane distances of tetragonal rutile SnO 2 . 44 It turns out that the recrystallization of a-SnO 2 into crystalline SnO 2 proceeds from the outside to the inside of the flake, considering that no nucleating SnO 2 crystallites are In conclusion, the whole amorphization process here presented, comprising the recrystallization of a-SnO 2 to SnO 2 , possibly represents interesting evidence of a nearly topotactic transformation of a 2D SnSe 2 metal chalcogenide into a 2D a-SnO 2 metal oxide, which includes loss of selenium and oxygen gain so that the final a-2D structure, retains the same bidimensional feature of the original material. This process represents a matter worthy of further investigation, eventually constituting a promising route to synthesize new metal oxide a-2D interfaces for gas sensing applications.…”

Manufacturing a TiO2-Based Semiconductor Film with Nanofluid Pool Boiling and Sintering Processes toward Solar-Cell Applications

“…Hold times at these temperatures were 1 or 6 h. For comparison purposes, one sample was left entirely unsintered. For solar cells, the substrate was sintered at 500 °C as reported previously [ 15 ]. Three substrates for different solar cells (Devices 2–4 as mentioned in the following section) were prepared.…”

“…Both unsintered and sintered substrates were characterized using x -ray diffraction (XRD; Rigaku RINT Ultima/PC with monochromated Cu Kα radiation, Tokyo, Japan). Except for the perovskite layer, the solar cell was assembled using the method that has been previously reported in our group, where TiO 2 substrates were sintered in air at 500 °C [ 15 ]. In regards to the TiO 2 -based electron-transport layer (ETL) in perovskite solar cells, a TiO 2 /FTO substrate was prepared, using the spin-coating process and sintering at 500 °C for comparison (Device 1).…”