Hollow inorganic capsules via colloid-templated layer-by-layer electrostatic assembly

The preparation of hollow inorganic capsules of defined shape, composition and with tailored properties is of immense scientific and technological interest. This chapter highlights a recently developed layer-by-layer (LbL) assembly process for the creation-of coated colloid particles (core-shell colloids), which are subsequently converted into hollow inorganic capsules. Sacrificial core template particles are coated with multiple layers of preformed inorganic nanoparticles, or inorganic molecular precursors, and oppositely charged polyelectrolyte, utilizing electrostatic attraction for construction of the layers on the particles. Calcination of the core-shell nanocomposite colloids yields hollow inorganic capsules of defined size and composition, determined by the template diameter and the nature of the charged inorganic species deposited, respectively. The capsule wall thickness can be controlled with nanoscale precision through the number of layers formed on the particles. The flexibility of the LbL strategy is demonstrated by a number of examples of nanoengineered hollow ' capsules. The creation of macroporous materials from the hollow capsules is also described. Additionally, the potential applications of the hollow colloid particles prepared are briefly discussed.