Formed through self-assembly of polynuclear node clusters and multitopic organic linkers, metal–organic frameworks (MOFs) are a class of three-dimensional crystalline materials. Due to their exceptional porosity, high surface areas, amenability to construction, chemical diversity, uniformly arrayed metal-containing nodes, and highly modular nature, MOFs are an ideal class of materials for use in a wide range of applications, including gas storage and separation, catalysis, biological and chemical sensing, and drug delivery. In today’s quickly evolving world, the complex challenges that humanity faces require advanced material solutions to reduce energy consumption and to provide safety against chemical warfare weapons. Due to the large potential benefits MOFs may provide, it is imperative to study, understand, and characterize the fundamental behavior of MOFs in order to help combat these difficult, and potentially existential, threats to us and to the environment. In this thesis, factors affecting the structural and chemical features of MOFs are scrutinized. First, to determine the effects of varying metal composition in the nodes, a systematic study with ethylene uptakes of a series of analogues of the same MOF was conducted and showed that the host-guest interactions of different metals to ethylene can be utilized towards different applications. The analogue offering a metal with labile binding to ethylene due to Jahn-Teller distortion (d9 pseudo-octahedral geometry upon interaction with gas molecules) is advantageous for higher deliverable storage, while the analogue with a metal that binds the strongest is useful in ethylene related separation or abatement applications. Second, to tailor the structural features of MOF channels for ethylene/ethane separations, as a proof of concept, a sterically demanding ligand was incorporated on to a MOF node via post-synthetic modification to occupy the void space at the center of a hexagonal channel, forcing gas molecules to pack near where binding sites are, and thus achieve better ethylene/ethane selectivity especially at higher pressures, by minimizing physisorption of gases. Next, products from hydrolytic degradation of a nerve agent and a simulant were verified to bind to the active aqua sites on MOF nodes and inhibit the catalytic performance of the MOF after thousands of turnovers. The developed mathematical model using binding coefficients from these hydrolysis reactions matched well with original experimental data, further confirming the inhibition effect from products. This product inhibition effect was found to have weak dependence on the configuration of MOF nodes. Further, proton configurations on MOF nodes and their effect on hydrolysis rate were investigated, especially of the aqua sites protons (Zr-OH2). The increase in aqua sites in active protonated form (by decreasing pH of reaction solution) resulted in a slight increase in hydrolysis rate, while the decrease of OH– in the solution caused a larger decrease in the rate, leading to an overall decrease of catalyzed hydrolysis of nerve agent simulant. Last, to expand the potential of MOFs in hydrolysis applications, hierarchical MOF/fiber composites simultaneously possessing macro-, meso-, and micro pores were synthesized. The flexible composites displayed good processability, hydrolytic activity, and recyclability, showing new possibilities for MOFs in heterogeneous catalysis.

Creator

• Liao, Yijun

DOI

• https://doi.org/10.21985/n2-kh4y-kk74

Subject

• Chemistry

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:15116
• etdadmin_upload_743673

Keyword

• Chemical Separation
• Gas Storage and Delivery
• Metal–Organic Frameworks
• Heterogeneous Catalysis Mechanism
• Porous Materials
• Degradation of Nerve Agent and Simulant

Date created

• 2020-01-01

Resource type

• Dissertation

Rights statement

• In Copyright