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.