Materials and methods for atomistic characterization of emergent nanoporous adsorbents
Camp, Jeffrey S.
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Metal organic frameworks (MOFs) are an emerging class of nanoporous materials that have shown promise in applications including gas storage, separations, and catalysis. The complexity and diversity of MOF chemical space frustrates experimental efforts to examine even a representative subset of the thousands of known MOFs. High-throughput computational screening can guide experimental efforts by identifying top candidate structures for applications of interest. These screening efforts require a database of crystallographic structural information that has been prepared for molecular simulations by removal of solvent molecules, partially occupied atoms, and disordered atoms. In this thesis, we describe algorithms to automatically prepare MOF structures for molecular simulations. The outcome of this work was a publicly available database of over 5,000 computation-ready MOF structures. As an example of using our database, we perform simulations of CH4 adsorption in each material and identify key thermodynamic parameters influencing adsorbed natural gas storage. In additional, we assign framework charges to nearly 3,000 structures using periodic density functional theory calculations. These DFT derived point charges were used to identify materials potentially useful in the adsorptive removal of a corrosive sulfurous odorant (tert-butyl mercaptan) from methane. Detailed atomistic simulation can be used to understand the properties of the most promising materials identified by computational screening. Of particular interest are adsorbate diffusivities, which are an important predictor of material performance in both equilibrium and kinetic separation applications. We describe methods to measure adsorbate diffusion in flexible nanoporous materials at timescales inaccessible to conventional molecular dynamics. These methods are applied to a novel class of porous molecular cage compounds that crystallize in the solid state without intermolecular covalent or coordination bonds. Our results show that cage crystal 3 has promise in the diffusive separation of rare gases and aromatics.