Formation of Hexabranched GeO2 Nanoparticles via a Reverse Micelle System

We report the first synthesis of GeO2 nanoparticles with six symmetrically arranged branches running along the long axis of each particle. The nanoparticles have a shape resembling that of a star fruit. A reverse micelle system with Triton X-100 serving as the capping surfactant for the aqueous phase and n-hexanol as the cosurfactant was adopted. Ge(OEt)(4) was selected as the germanium source. Using the optimal synthesis procedure by reacting the mixture at room temperature for 3 h, hexabranched GeO2 particles with an average length of 185 nm were produced. The products have been examined by FE-SEM, TEM, X-ray diffraction, and FT-IR techniques. GeO2 nanoparticles with structually well-developed branches were gnereated only with solution pH values in the range of 0.9-1.1. At a low [H2O/[Ge(OEt)(4)] molar ratio of 45, particles having a hexagonal bipyramidal shape but without branch formation were observed. Increasing this ratio to 90, branches begin to appear from the six side edges of the particles. By simply varying the reaction time, the sizes of the branched GeO2 nanoparticles can be adjusted from around 100 nm in length to as large as 300 nm in length.