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Modeling Spontaneous Formation of Precursor Nanoparticles in Clear-Solution Zeolite Synthesis

Summary: Modeling Spontaneous Formation of Precursor Nanoparticles
in Clear-Solution Zeolite Synthesis
M. Jorge, Scott M. Auerbach,*,, and P. A. Monson*,
Contribution from the Department of Chemical Engineering and Department of Chemistry,
UniVersity of Massachusetts, Amherst, Massachusetts 01003
Received April 13, 2005; E-mail: auerbach@chem.umass.edu; monson@ecs.umass.edu
Abstract: We present a lattice model describing the formation of silica nanoparticles in the early stages of
the clear-solution templated synthesis of silicalite-1 zeolite. Silica condensation/hydrolysis is modeled by
a nearest-neighbor attraction, while the electrostatics are represented by an orientation-dependent, short-
range interaction. Using this simplified model, we show excellent qualitative agreement with published
experimental observations. The nanoparticles are identified as a metastable state, stabilized by electrostatic
interactions between the negatively charged silica surface and a layer of organic cations. Nanoparticle
size is controlled mainly by the solution pH, through nanoparticle surface charge. The size and concentration
of the charge-balancing cation are found to have a negligible effect on nanoparticle size. Increasing the
temperature allows for further particle growth by Ostwald ripening. We suggest that this mechanism may
play a role in the growth of zeolite crystals.
I. Introduction
Zeolites are nanoporous alumino-silicates used in industrial
applications such as catalysis and separations.1 Understanding
how zeolites nucleate and grow is of fundamental scientific and


Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst


Collections: Chemistry