Abstract
Highly crystallized GeO2 nanosheets were synthesized by hydrolysis and condensation reactions of germanium alkoxide using 2-dimensional flat thin water phase of lamellar structure composed of surfactant molecules and water at the liquid-liquid interface as a confined reaction space. Lamellar phase was made by contacting water with mixed solution of surfactant (laurylamine (LA)) and germanium alkoxide (Ge(OEt)4). In situ small angle X-ray scattering (SAXS) measurements were carried out every second for several minutes using strong X-rays by synchrotron radiation in the SPring 8, and the formation processes of GeO2 nanosheet was examined. SAXS results showed that layered structure composed of GeO2 nanosheets and LA bilayer was formed at 2.5 sec after contact and increased with time when the mole ratio of Ge(OEt)4 to LA was 0.2. The produced GeO2 nanosheets were characterized by transmission electron microscope (TEM) images, X-ray diffraction (XRD), selected area electron diffraction (SAED) and SAXS. The square shape of GeO2 nanosheets was observed by TEM, and XRD and SAED results showed that GeO2 nanosheets had highly crystallized structure. The periodical distance of a layered structure was almost constant regardless of time, being 3.7 nm corresponding to the total thickness of LA bilayer and nanosheet. The analysis of the peak shape of the lamellar phase obtained by SAXS revealed that 84 % Gauss distribution at 2.5 sec changed to 100 % Lorentz distribution after 25 sec from contact of two liquids at [Ge(OEt)4]/[LA]=0.2, indicating increase in crystallinity with time. These findings clearly showed the formation of highly crystalized GeO2 nanosheets at extremely low temperature. This formation method of nanosheets is easily applicable for the formation of other ceramic nanosheets.
