Synthesis of submicrometer crystals of aluminum oxide by aqueous intravesicular precipitation

Abstract

Single compartment unilamellar vesicles were used as microreactors for controlled precipitation of crystals in the nanometer size range within their internal cavity. The model explored was the aqueous phase reaction of aluminum and hydroxyl ions. The method relies on the fact that the vesicle wall is selectively permeable to the anions only. An aluminum salt solution was first encapsulated within the intravesicular space. The extravesicular aluminum ions were replaced with sodium ions by ion exchange. A sodium hydroxide solution was then added to the extravesicular phase. When hydroxyl ions permeated through the vesicle wall and reacted with the encapsulated aluminum ions, the product was found to be spherical crystals of alumina. The specific polymorph appeared to depend on the aluminum salt anion. Under similar conditions, in the absence of vesicles, a gelatinous precipitate of aluminum hydroxide comprising of plate-like particles was formed.