AlO(OH) hollow spheres are realized via a water-in-oil (w/o) microemulsion, applying the liquid-to-liquid-phase boundary of the micellar system as a template. Scanning electron microscopy, transmission electron microscopy (TEM), and dynamic light scattering analyses show the presence of nonagglomerated hollow spheres exhibiting an outer diameter of about 30 nm and a wall thickness of 5-6 nm. High-resolution TEM images show highly ordered lattice fringes, indicating the crystallinity of the sphere wall and identifying the wall to consist of gamma-AlO(OH) (boehmite). The container functionality of as-prepared AlO(OH) hollow spheres is validated as a proof of concept by encapsulating the fluorescent dye rhodamine (R6G) inside the alumina shell. Subsequent to centrifugation and careful purification, R6G is evidenced via photoluminescence to be still present. Finally, release of R6G is initiated by acidic dissolution of the sphere wall.

A wide variety of different nanomaterials, including ZnO, (NH4)Y(C2O4)2·H2O, Y(OH)3, Y2O3, In2O3:Sn, CePO4:Tb, CaCO3, CuS, Co3[Co(CN)6]2, and K3[Co(NO2)6] are realized by a microemulsion approach. While heating the micellar system to reflux (200 to 215 °C), highly crystalline materials can be realized, which are still nanosized and do not agglomerate afterwards. Furthermore, a phase separation is initiated by the addition of diethylene glycol, which allows a facile removal of the nanomaterials by the application of low solvent quantitities, and again excludes agglomeration. Both aspects—the realization of highly crystalline materials and the facile separation of non‐agglomerated particles—represent a useful extension of microemulsion techniques. Besides the number and quality of the nanomaterials, the success of the experimental approach is further proven by the realization of physical properties that are restricted to crystalline materials. Namely, these are the bright colors of Co3[Co(CN)6]2 and K3[Co(NO2)6] as pigments, the electrical conductivity of In2O3:Sn (ITO), and the luminescence of CePO4:Tb.

The aim of this study is the synthesis of nanoscale, nonagglomerated, and redispersible Co 3 [Co(CN) 6 ] 2 nanoparticles via a microemulsion approach. Furthermore, the micellar system is heated to reflux to enhance materials crystallinity. Crystallinity, chemical composition, and optical and thermal properties of the title compound are investigated in detail. SEM, XRD, and DLS measurements evidence an average diameter of 25-30 nm of the as-prepared nanocrystals as well as of powder samples subsequent to centrifugation, washing, drying, and resuspension. Based on IR and UV-vis spectra, the anhydrous character of Co 3 [Co(CN) 6 ] 2 is validated. The thermal decomposition of Co 3 [Co(CN) 6 ] 2 results in the formation of Co 3 O 4 , which is still nanoscaled.

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