Crystal growth of zincophosphates from conventional media and reverse micelles: mechanistic implications

Zincophosphates can be synthesized with frameworks analogous to aluminosilicate zeolites. Previous studies have shown that reverse micelles, which are microdroplets of water dispersed in an oil-like medium, can serve as nucleation and growth centers for microporous materials. Zincophosphates with the sodalite framework can be readily made from reverse micelles, whereas the more open structure resembling the faujasite framework (ZnPO-X) could not be made. The concentration of sodium ions is found to play an important role in the nucleation of both sodalite and ZnPO-X. At increased sodium ion concentrations under conventional synthesis conditions, sodalite growth is favored. On the other hand, the addition of crown ethers and cryptands which complex sodium ions leads to growth of ZnPO-X, Based on these studies, we propose that the high sodium ion concentrations in reverse micelles cause the formation of sodalite. Infrared spectroscopic studies indicate that zinc- and phosphate-containing reverse micelles also contain significant amounts of disordered water, which can inhibit the nucleation of open-pore frameworks, such as ZnPO-X. (C) 1998 Elsevier Science B.V.