Three-Dimensional Ordered Arrays of Zeolite Nanocrystals with Uniform Size and Orientation by a Pseudomorphic Coupled Dissolution-Reprecipitation Replacement Route

We report a simple and facile hydrothermal pseudomorphic replacement route to synthesize three-dimensional (3D) ordered arrays of zeolite nanocrystals with uniform size and crystallographic orientation. We demonstrate this route by synthesizing analcime monoliths as an example using leucite crystals as precursors. The leucite crystals contain an inherent 3D ordered network of nanometer-sized lamellar twins. Such highly ordered 3D patterns were precisely preserved during hydrothermal pseudomorphic replacement reactions in pH buffered NaCl solutions, resulting in 3D ordered arrays of analcime nanocrystals. Moreover. these analcime nanocrystals have a uniform size and crystallographic orientation due to epitaxial nucleation and growth facilitated by the similarity of crystal lattice between leucite and analcime. The morphology of the nanocrystals is tunable by simply changing solution pH values. Mild acidic to mild alkaline conditions tend to produce cuboid-shaped nanocrystals, while strong alkaline conditions favor the formation of cylindrical-shaped nanocrystals. The replacement follows the coupled dissolution-reprecipitation mechanism that the rate of leucite dissolution equals the rate of analcime precipitation. This pseudomorphic replacement route has the potential to synthesize other ordered arrays of functional nanocrystals with controlled shape, size, and crystallographic orientation.