Early-late intermetallic phases have garnered increased attention recently for their catalytic properties. To achieve the high surface areas needed for industrially relevant applications, these phases must be synthesized as nanoparticles in a scalable fashion. Herein, Pt 3 Y-targeted as a prototypical example of an early-late intermetallic-has been synthesized as nanoparticles approximately 5-20 nm in diameter in a solution process and characterized by XRD, TEM, EDS and XPS. The key development is the use of a molten borohydride (MEt 3 BH, M= Na, K) as both the reducing agent and reaction medium. Readily available halide precursors of each metal are used. Accordingly, no organic ligands/surfactants are necessary as the resulting halide salt byproduct prevents sintering, which further permits dispersion of the nanoscale intermetallic onto a support. The versatility of this approach was validated by synthesis of other intermetallic phases such as Pt

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.

Covellite (CuS), digenite (Cu(1.8)S) and chalcocite (Cu(2)S) are prepared as nanoscaled hollow spheres by reaction at the liquid-to-liquid phase boundary of a w/o-microemulsion. According to electron microscopy (SEM, STEM, TEM, HRTEM) the hollow spheres exhibit an outer diameter of 32-36 nm, a wall thickness of 8-12 nm and an inner cavity of 8-16 nm in diameter. The phase composition is determined based on HRTEM, electron-energy loss spectroscopy, X-ray powder diffraction and thermal analysis. In face of the advanced morphology of the hollow spheres, precise control of its phase composition is nevertheless possible by adjusting the experimental conditions (i.e. type and concentration of the copper precursor, concentration of ammonia inside of the micelle). Such phase-engineering of nanoscale hollow spheres is firstly observed and might allow adjusting even further compositions/structures as well as tailoring of phase-specific properties in the future.

Size control in advance: water‐in‐oil microemulsions exhibiting micelles of precisely adjusted size can be used to prepare La(OH)3 hollow spheres with fine‐tuned diameter and cavity size. Namely La(OH)3 hollow spheres are obtained with outer diameters ranging from 11 to 30 nm and an inner cavity from 2 to 17 nm.

A wide variety of nanoscale hollow spheres can be obtained via a microemulsion approach. This includes oxides (e.g., ZnO, TiO2, SnO2, AlO(OH), La(OH)3), sulfides (e.g., Cu2S, CuS) as well as elemental metals (e.g., Ag, Au). All hollow spheres are realized with outer diameters of 10−60 nm, an inner cavity size of 2−30 nm and a wall thickness of 2−15 nm. The microemulsion approach allows modification of the composition of the hollow spheres, fine-tuning their diameter and encapsulation of various ingredients inside the resulting “nanocontainers”. This review summarizes the experimental conditions of synthesis and compares them to other methods of preparing hollow spheres. Moreover, the structural characterization and selected properties of the as-prepared hollow spheres are discussed. The latter is especially focused on container-functionalities with the encapsulation of inorganic salts (e.g., KSCN, K2S2O8, KF), biomolecules/bioactive molecules (e.g., phenylalanine, quercetin, nicotinic acid) and fluorescent dyes (e.g., rhodamine, riboflavin) as representative examples.