Controlled growth of microporous crystals nucleated in reverse micelles

Abstract

THE development of new methods for nucleating and growing microporous crystals has made available new framework structures and morphologies for these technologically important materials¹. These approaches have included solution-based synthesis² and the use of simple organic structure-directing agents³ and complex organic assemblies such as liquid-crystal phases^4,5. Here we show that the growth of microporous zincophosphate^6–8 with the sodalite structure can be controlled by preparing the crystals from reactants included within the interior aqueous phase of reverse micelles dispersed in an organic solvent. The growth of inorganic phases in reverse micelles has been exploited previously for the preparation of monodisperse oxide⁹, semiconductor¹⁰ and metal particles¹¹. In this study, we introduce the two inorganic components—zinc and phosphate ions—in separate micelles, so that crystallization is controlled by the collision and exchange kinetics of the surfactant structures. Moreover, the surfactant–water interface provides the site for crystal nucleation, favouring initial nucleation at the (111) and/or (110) crystal faces and subsequent growth of the zinco-phosphate crystals by deposition along the {100} faces. The growth process is ultimately interrupted by sedimentation when the crystals grow large enough, producing a precipitate of micro-crystals several hundred nanometres in size. Our results indicate that this approach can provide a means of controlling the morphology as well as the size of growing crystals.