The use of nanoscale SnO2 hollow spheres as a redox-active sensor is investigated. The underlying hollow spheres are prepared via a microemulsion approach and exhibit an outer diameter of about 15−25 nm, a highly crystalline shell with a thickness of 3−5 nm and an inner cavity of 10−20 nm in diameter. Subsequent to materials characterization based on SEM, STEM, TEM, IR, TG, BET, and XRD the applicability of as-prepared hollow spheres as highly porous layers in sensor operation is tested. Accordingly, SnO2 hollow spheres deposited on common sensor substrates show a good response to CO in a concentration range of 50 to 300 ppm. Moreover, the material turned out to be useful as a model system to study the conduction model of a porous layer with small grains.

KSCN and phenylalanine are encapsulated with nanoscale hollow spheres acting as containers. These hollow spheres, composed of Au, CuS, AlO(OH), or SnO2, and can be prepared using a microemulsion technique, and yield particles with outer diameters of 15–30 nm and wall thicknesses of 2–10 nm.

We studied the local structural disorder and relaxation in different nanostructures of SnO2 by using 119Sn MAS NMR in combination with 119Sn Mössbauer spectroscopy. We investigated nanocrystalline powders with an average crystallite size of 8 nm as well as hollow spheres with a wall thickness of 3 nm and a diameter of 14 nm, and compared the results to coarse-grained materials. Whereas the uniform SnO6 octahedra in the coarse-grained material show a well-known distortion and thus large electric field gradients, the nanocrystalline SnO2 exhibits a structural relaxation leading to a distribution of local environments and more symmetric octahedra. The SnO2 hollow spheres show strong local disorder in combination with highly asymmetric environments around the Sn atoms.

Liquid ammonia on the nanoscale: Ammonia-in-oil microemulsions are used to synthesize Bi, Re, CoN, and GaN nanoparticles, which can be obtained without further thermal treatment. These microemulsions are as reproducible and simple as their water-in-oil conterparts, with the exception of the required low temperature of -40 °C.

GaN nanoparticles, 3-4 nm in size, are synthesized in a microemulsion using liquid ammonia as the polar droplet phase. Surprisingly, GaN is readily crystalline although prepared at -40 °C. The nanoparticles show a band gap of 4.4 eV as well as light emission with its maximum at 336 nm. Both confirm the expected quantum-confinement effect.