Synthesis of Zeolite Nanocrystals in Polymer Hydrogels
There has been considerable interest in the synthesis of zeolite nanocrystals because they are useful for study of zeolite nucleation and growth mechanisms, seeded growth of zeolite films and membranes, and construction of hierarchical zeolite structures and polymer-zeolite nanocomposites. The improved performance achieved by using zeolites in the form of nanocrystals has affected their traditional application in areas such as catalysis, ion exchange, adsorption, and separation. In addition, nanocrystals have allowed zeolites to find new applications as low-k dielectrics in microelectronics, and in fuel cells, etc..
Dispersible zeolite nanocrystals with small size are required for most of these applications. Synthesis of colloidal zeolite nanocrystals generally requires the use of a large amount of organic structure directing agent (SDA) to control the process of zeolite crystallization. In the synthetic system without involving SDA, controlling nanocrystal size becomes much more difficult. The synthetic strategies of using space-confining additives such as carbon black, starch, gelling polymer, and even carbon nanotubes have been developed to achieve such SDA-free synthesis. We have been particularly interested in developing the synthesis method using gelling polymers. Both physically crosslinked hydrogels and chemically crosslinked hydrogels have been used to control zeolite nucleation and growth, and thus zeolites A, X, Y, and SAPO nanocrystals have been successfully synthesized. In this presentation, we will focus on the effect of polymer hydrogel structures on the zeolite crystal size and morphology, and the understanding of self assembly of zeolite nanocrystals within polymer networks.