Nanoscale Hollow Spheres: Microemulsion-Based Synthesis, Structural Characterization and Container-Type Functionality

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

Sorption and separation of CO2via nanoscale AlO(OH) hollow spheres

The CO2 uptake on nanoscale AlO(OH) hollow spheres (260 mg g−1) as a new material is comparable to that on many metal–organic frameworks although their specific surface area is much lower (530 m2 g¬1versus 1500–6000 m2g¬1). Suited temperature–pressure cycles allow for reversible storage and separation of CO2 while the CO2 uptake is 4.3-times higher as compared to N2