Investigating gas adsorption, PSM and molecular-level structure in MOFs

Metal-organic frameworks are hybrid organic-inorganic solids that have many important applications including gas storage, separations, heterogeneous catalysis, drug delivery, electrochemical storage and conversion. Although they have various applications, the gas adsorption mechanism, local structures and molecular-level features (which are important to understanding and improving the specific performance of MOFs) are often ambiguous. In this work, a combination of multiple techniques including solid-state NMR (SSNMR), single crystal XRD (SCXRD) and computational methods is employed to investigate gas adsorption mechanism and molecular-level structure in several MOFs. Equally important is the designing of functionalized MOFs with a variety of functional groups, since the modified MOFs can gain enhanced performance in many exiting and lead to new applications. Therefore, this thesis is also focused on modifying MOFs by introducing various non-framework metal ions and organic functional groups via post-synthetic modification (PSM). Chapter 1 is a brief introduction of MOFs and SSNMR. In Chapters 2 and 3, gas adsorption mechanism in MOFs Pb-, Cd-SDB (SDB: 4,4′-sulfonyldibenzoate) and Cu(INAIP) (5-(isonicotinamido) isophthalate) were investigated by a combination of SSNMR and SCXRD. In addition, based on the SCXRD of gas loaded Cu(INAIP), computational methods were used to elucidate the host-guest interaction. In Chapter 4, 14 different non-framework metal ions have been loaded into MOF MIL-121 via its free carboxylic acid groups. The materials have been extensively characterized. Several metal loaded MIL-121 variants show enhanced gas adsorption and excellent catalytic performance. In Chapter 5, we found that hierarchical pores can be created in the microporous MIL-121 via controlled linker thermolysis. The MOFs with both micropores and mesopores were characterized by a combination of gas adsorption test, scanning electron microscope (SEM) and multinuclear SSNMR. In Chapter 6, the hierarchical MIL-121 obtained in Chapter 5 has been used for grafting several organic molecules and Pt salts by PSM. In chapter 7, 43Ca SSNMR and quantum chemical calculations are used to probe the local structure of calcium metal centers within several Ca-MOFs