Morphology control of porous materials and molecular sieve membrane applications.

Abstract

For advanced applications of porous materials, morphology control of porous materials is desired. Simultaneous dissolution and surfactant-induced re-assembly via micelle formation with dissolved species were performed to introduce mesoporosity in the amorphous silica spheres and zeolite crystals. Textural features of mesoporous silica spheres were controlled from corrugated to smooth. Mesoporous zeolite catalysts were synthesized via surfactant-induced re-assembly with dissolved crystal fragments of zeolite crystals. In addition, the concept of confined synthesis was used for control of morphologies of zeolite crystals. Using 3-D ordered macroporous (3DOM) carbon as a template, growth patterns and shape development of zeolite crystals were studied. Various shaped zeolite crystals, e.g., hollow interior (geode-like structure), corrugated/smooth surface of polycrystalline crystals, needle-shaped crystals and 3DOM imprinted single crystals, were produced by careful choice of reaction parameters during the confined synthesis. Polycrystalline aggregates produced by the confined synthesis were used as seed particles for zeolite membrane fabrication. Novel seeding techniques, rubbing and leveling methods, were applied to deposit the confinement product directly on the surface of porous alumina supports, and zeolite membranes were grown by secondary hydrothermal growth. Moreover, rapid thermal processing and conventional calcination were used to investigate the effect of thermal treatments on the overall membrane quality. To evaluate the membrane quality, permeation measurements to separate p-/o-xylene isomers based on the zeolite's intrinsic capability of size-selective molecular separations were conducted. A high separation factor and high permeance were observed.