Design and Characterization of Functional Metal-Organic Frameworks for CO2/CH4 and C2H2/CH4 Separation

Metal Organic Frameworks (MOFs) compared to traditional porous materials, such as zeolites, and active carbons, are the recent class of crystalline porous materials with many special properties, including high surface areas and large internal pore volumes which result in maximum gas-adsorption capacity at high pressure.

MOFs can be assembled from a diverse set of organic linkers and metal ions, which can expose selectivity for particular gases and other analytes. The coordination obtained from organic linkers can provide more flexibility in the final framework structure compared to other robust materials based on pure inorganic composition such as zeolites. This flexibility enables a dynamic behavior in porous coordination network and thus facilitates structural modification without loss of structural integrity.

The development of MOFs for gas separation, several factors (porosity and rigidity of the framework and controlling pore size, and thermal stability) play roles. This dissertation work deals with the development of new strategies towards interpenetration control and tunability of pores to enhance the selectivity of both CO₂ and C₂H₂ impurity removal from CH₄, and other hydrocarbon mixtures resulting from industrial processes. In this study, critical to the design process, polyhedron-based metal-organic frameworks were used to direct self-assembly of unique MOF structures. Furthermore, mixed ligand tactics along with hetero-functional and multi-carboxylate ligands were applied as a different source of MOF versatility. The investigation of these materials reveals different crystal sutures having a unique selectivity for CO₂ and C₂H₂ over CH₄ during the gas separation, particularly at room temperature.