| Summary: | Nanoporous metal-organic frameworks (MOFs) have attracted tremendous
interest due to their potential applications in gas-storage, gas separation, gas sensing, and
catalysis. MOFs consist of metal-oxygen polyhedera interconnected with a variety of
organic linker molecules, resulting in tailored nanoporous materials. With a judicious
choice of organic linker groups, it is possible to fine-tune size, shape, and chemical
functionality of the cavities and the internal surfaces. This unique structural feature
offers unprecedented opportunities in small-molecule separations as well as chiral
separations and catalysis.
Prototypical iso-reticular metal-organic frameworks (IRMOFs) have been
extensively studied among MOFs due to the simplicity of their synthesis and the variety
of their potential applications. IRMOFs are a specific series of metal-organic
frameworks developed by Yaghi and his coworkers. All IRMOFs are composed of
oxygen-centered Zn4O tetrahedra interconnected with dicarboxylate linkers, forming a
cubic type three dimensional (3D) porous network with high surface area.
Despite a great deal of research in the synthesis and characterization of MOFs,
there have been relatively few reports on the development of their applications, such as
the fabrication of MOF thin films and membranes for gas separations. This is mainly due
to the challenges associated with relatively difficult heterogeneous nucleation (seeding)
and growth of MOFs on supports, and crack formation compared to their counterparts.
Thin films and membranes of MOFs have great potentials for applications in membranebased
gas separations, reactors, chemical sensors, and nonlinear optical devices.
In this dissertation, the fabrication of IRMOF-1 membrane using a novel seeding
method and its gas diffusion properties has been demonstrated. Introduction of the new
seeding method for MOFs using microwaves resulted in well inter-grown IRMOF
membranes showing Knudsen type transport of small gases through its pore. The heteroepitaxial
growth of one IRMOF on another produced multi-layered IRMOF membranes.
In addition, postsynthetic modification (PSM) of IRMOFs created functionalized
membranes with enhanced stability against water as well as reduced crack formation
during membrane fabrication. Lastly, hierarchical IRMOFs with improved CO2
adsorption properties were synthesized via PSM with cyanuric chloride.
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