Hydrothermal Growth of Tailored SnO₂ Nanocrystals

Abstract

We studied the growth of SnO2 nanocrystals with a tailored structure via surface capping assisted hydrothermal approach with tetramethyl ammonium hydroxide (N(CH3)4OH; TMAH). KOH and NaOH were also used instead of TMAH for comparison. The nanocrystals with a size ranging from 3.2 ± 0.9 to 74 ± 20 nm were grown at 150 °C for 24 h depending on the pH. N(CH3)4 + capped the surface of SnO2 and improved the dispersion of the nanocrystals in basic aqueous solutions. The capping provided nanocrystals finer than those grown with KOH and NaOH because of suppressed Ostwald ripening via a reduction in surface energy. High-resolution transmission electron microscopy revealed that the nanocrystals grown in strong basic solutions with TMAH had cubic morphology terminated by the (001) and (110) faces. This strongly suggests that N(CH3)4 + preferentially caps the (001) face with the highest surface energy and decreases its surface energy to be comparable to that of the (110) face with the lowest surface energy. Anisotropic capping promotes the formation of the cubic superstructure via the directed self-assembly of primary cubic nanocrystals in very strong basic solutions. Raman spectroscopy suggested that the SnO2 nanocubes grown in strong basic solutions with TMAH have less of a surface hydration layer as well as bulk combined water.

Surface Capping-Assisted Hydrothermal Growth of Gadolinium-Doped CeO2 Nanocrystals Dispersible in Aqueous Solutions

“…The prevention of Ostwald ripening through surface capping with N(CH 3 ) 4 + was also observed in the growth of SnO 2 nanocrystals via the hydrothermal treatment of Sn(OH) 6 2− in basic aqueous solutions. 18 Furthermore, the strong conjugation of the N(CH 3 ) 4 + on the GDC nanocrystals can be observed in Figure S-2; while the capping agent persisted on the nanocrystals during heating, it was removed by burning out, coupled with the evolution of CO 2 and H 2 O at approximately 240°C, which is higher than the evaporation temperature of TMAH and TMAHC under ambient pressure ( Figure S-4). Figure 8 shows the effect of the reaction conditions on the morphology of the GDC nanocrystals.…”

Hydrothermal Synthesis of Yttria-Stabilized Zirconia Nanocrystals with Controlled Yttria Content

“…Furthermore, the size of the nanocrystals is kept small due to the prevented dissolution of the nanocrystals by capping, which is the driving force of Ostwald ripening. 13 The average size of nanocrystals synthesized after 3 h is in the range of 13−18 nm with the exception of 3YSZ, suggesting that the nanocrystals are approximately 10 nm or less in size since hydrodynamic diameter overestimates the real size of particles by several nanometers and it involves the size of the inorganic core, surface capping agent, and solvation (hydration) layer. 14 The size of N(CH 3 ) 4 + is approximately 0.7 nm in diameter, and solvation layer is commonly a few nm.…”

Morphological Control of Metal Oxide for Semiconductor-Based Gas Sensor

“…Morphological control of metal oxide (MO) is important for enhancement of sensing properties such as sensor response and response-recovery characteristics. Our research group has been developed MO based gas sensors fabricated by WO3 and SnO2 nanocrystals synthesized by hydrothermal method for high sensor response to NO2 or H2 [1,2]. On the other hand, shuttle-shape SnO2 showed the sensor response to NO2 and H2S at room temperature.…”