Formation of zincophosphates from zinc and phosphate containing
reverse micelles (water droplets in hexane)
has been examined. The frameworks formed resemble those made by
conventional hydrothermal synthesis.
Dynamics of crystal growth are however quite different and form
the main focus of this study. In particular,
the formation of zincophosphate with the sodalite framework was
examined in detail. The intramicellar pH
was found to have a strong influence on crystal growth. Crystals
with a cubic morphology were formed
directly from the micelles, without an apparent intermediate amorphous
phase over a period of 4 days by a
layer-by-layer growth at the intramicellar pH of 7.6. At a pH of
6.8, an amorphous precipitate rapidly sediments
in hours. Sodalite was eventually formed from this settled phase
via surface diffusion and reconstruction
within 4 days. With a rotating cell, it was possible to minimize
sedimentation and crystals were found to
grow epitaxially from the spherical, amorphous particles.
Intermediate pH's of 7.2 led to formation of
aggregated sodalite crystals prior to settling, again without any
indication of an intermediate amorphous phase.
These diverse pathways were possible due to changes in
intramicellar supersaturation conditions by minor
changes in pH. In contrast, conventional syntheses in this pH
range all proceeded by similar crystallization
pathways through an amorphous gel. This study establishes that
synthesis of microporous frameworks is not
only possible in reverse micellar systems, but they also allow
examination of possible crystallization pathways.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.