Synthesis and assembly of molecular sieves for applications in advanced materials

Molecular sieves and zeolites are materials whose crystalline frameworks form nanometer or subnanometer pores. A variety of different crystal structures are known having a range of pore sizes. Because the pore sizes are usually smaller than 2 nm, they are classified as microporous materials. Although microporous materials have ordered structure over the nanometer scale, they do not typically have ordered structure at larger dimensions. Most commercially available microporous materials are in the form of powders with little control of crystal size, shape, and size distribution. Crystals with well-defined morphology and small size distribution can be used as building blocks for generating complex structures by particle assembly techniques. In this thesis, three microporous materials AlPO4-5, silicalite-1, and zeolite A were synthesized with novel morphologies by a microemulsion-directed synthesis technique. Confinement in the microemulsion was shown to reduce crystal size and surface active components adsorbing onto the growing crystals altered crystal shape. As a result, the microemulsion-based synthesis resulted in significantly altered crystal morphology. AlPO4-5 was synthesized in the form of various novel particles such as rods, tetrapods and truncated cones. Silicalite-1 was synthesized in the form of rods and nanoparticles and novel spherical zeolite A was also obtained by the technique. The rod-shaped AlPO4-5 particles were assembled into thin films with preferred orientation under an applied electric field. When the pores of the molecular sieve were filled with dye, the oriented film displayed polarization angle-dependent absorption due to the long range order in the pore direction. The oriented thin film was also used as seed layer for secondary growth of oriented AlPO 4-5 membranes with the pore direction perpendicular to the substrate. The electric field-driven process can be applied to align and assemble various types of particles to create advanced materials, such as microporous membranes, optical materials, and polymer/inorganic composites. The control of particle morphology and assembly offers a means to optimize transport through membranes used in solar cells, fuel cells, and chemical separations.