Tailoring the Microstructure of 2D Molecular Sieve Materials for Thin Film Application

Zeolites and metal organic frameworks (MOFs) are microporous materials, with pores of molecular dimensions, that are of interest in a variety of applications including catalysis, adsorption, ion-exchange, separation membranes etc. With a global need of developing clean energy resources and reducing the carbon footprint of existing processes, they are being increasingly sought after as catalysts for the conversion of biomass to chemicals and fuels, in separation membranes to replace the existing energy intensive industrial separations with clean energy-efficient processes and for capture and storage of carbon dioxide. Their performance in these applications depends mainly on their pore size but also on our ability to tune their microstructure (crystal morphology and size, orientation, phase purity, defect densities etc.) as desired for an optimum performance. Recent advances in synthesis of molecular sieve materials have resulted in the development of advanced morphologies such as hierarchical materials, core-shell catalysts, two-dimensional nanosheets and thin films. However, a lot of the reports in the literature focus on conventional crystals and studies focusing on nanoscale crystal growth control are still in their infancy. This dissertation focuses on developing synthetic methods that will enable us to tailor the microstructure of 2D molecular sieve materials at a nanoscale approaching single-unit-cell dimensions with a goal of optimizing their performance in thin film applications. A novel coating technique was applied to isolate 2D MFI zeolite nanosheets and form monolayer coatings on versatile supports such as Si wafers. Using this as a prototype, growth conditions were developed that lead to unprecedented control of zeolite MFI growth at a scale approaching single-unit-cell dimensions. It was demonstrated that these growth conditions are robust enough and can be used to grow zeolite MFI crystals of varied sizes and morphology. It also enabled us to precisely control the microstructure of MFI thin films leading to the development of a material that had one of the lowest reported dielectric constant. Furthermore, the nanoscale growth control also allowed us to tailor the design of hierarchical catalysts by controllably thickening the zeolite domains in them and open opportunities to design multifunctional catalysts. A scalable and direct synthesis of Cu(BDC) MOF nanosheets was developed. Hybrid nanocomposites incorporating the MOF nanosheets in polymer matrices were fabricated which demonstrated significantly improved performance for CO2/CH4 separation.