Hydrothermal Growth of Tailored SnO₂ Nanocrystals

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

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

In this study, we demonstrate for the first time the hydrothermal synthesis of yttria-stabilized zirconia (YSZ) nanocrystals with controlled yttria content (<i>x</i> = 3–12 mol %; <i>x</i>YSZ) with negligible aggregation from aqueous solution. The nanocrystals were grown via the hydrothermal treatment of basic Zr­(IV) and Y­(III) carbonate complex aqueous solutions in the presence of a cationic ligand, N­(CH₃)₄⁺. The nanocrystals were characterized in detail by dynamic light scattering, ζ-potential measurement, X-ray diffraction, specific surface area measurement based on the Brunauer–Emmett–Teller theory, transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. Shorter reaction times and higher Y₂O₃ content produce aqueous solutions with higher transparencies containing nanocrystals with sizes of 10 nm or less. Nanocrystals with the target composition were obtained by hydrothermal reaction for longer than 3 h, regardless of the Y₂O₃ content. The main phase is tetragonal for (3–6)­YSZ and cubic with disordered oxygen vacancies for (8–12)­YSZ. The characteristics of the nanocrystalline material synthesized are consistent with those of bulk YSZ crystals, indicating the growth of high-quality nanocrystals