Metal-organic frameworks (MOFs) are an emerging class of porous materials that have been widely studied over the last three decades and have been proposed for numerous applications. Recently, the hybridization of MOFs and polymers has shown potential to combat some of the major drawbacks of this class of materials.Their structural modularity makes MOFs ideal for producing functional hybrids with enhanced properties and improved stability/processability. However, polymer intrusion into the internal pore space is often problematic in some cases for enabling optimal accessibility of the desired high surface area of the MOF.A core-shell approach is applied to produce MOF-polymer composites where the growth of polymer is restricted to the outer shell, leaving a pristine, high surface area internal core (chapter 2). The tethering of initiators by post-synthetic modification from amine groups on the IRMOF-3 shell enables the selective growth of polymer localized to the outer shell of an IRMOF-3@MOF-5 crystal. Spatial confinement of initiators leads to composites having high internal surface area. Although the hydrolytic stability is marginally increased, defects in the shell can allow for direct entry of guests.A second facile approach to MOF-polymer hybridization is explored wherein polymer is evenly distributed throughout the crystals of MOF-5, eliminating problems with shell defects (chapter 3). Simply heating neat styrene with MOF-5 initiates the grafting of polystyrene with polymer incorporation precisely controlled by varying reaction time. Polystyrene grafting alters the physiochemical properties of MOF-5, evident by examining the solvatochromic behavior of dye molecules adsorbed into the MOF-5-PS composites. Furthermore, the CO2 adsorption capacity is increased in certain composites relative to MOF-5. Polymer incorporation increases the hydrophobicity of these hybrids enabling them to maintain their high surface areas after 3 months in 53 % relative humidity. Chapter 4 introduces an emerging application of MOFs and coordination polymers (CPs) as energetic materials. These materials show promise as a new class of tunable energetics for applications from munitions to mining. Among the reported energetic MOFs and CPs, there are few examples of nitro-aromatic linkers, motifs consistent with more traditional energetics. The thermal decomposition pathways of extensively nitrated MOFs shows that deflagration transforms cubic MOFs into anisotropic carbon structures that contain highly dispersed metal. The mechanism of thermal decomposition is investigated through decomposition gas analysis, high-speed imaging, and chemical characterization of the decomposition product. The importance of intimate mixing for the efficient anisotropic decomposition of CuNbO-1 highlights the utility of the pore space and regularity in the MOF. A new method for the synthesis of energetic MOF composites using the same principle of intimate molecular mixing is described in chapter 5. This method for producing energetic MOFs enables the use of the vast library of highly fuel-rich non-energetic MOFs for the adsorption of oxidants resulting in a molecularly mixed fuel and oxidant. The adsorption of oxidants tetranitromethane (TNM) and hexanitroethane (HNE) into MOF-5 results in composites with high heat released upon decomposition, neutral oxygen balances, and suppressed vapor pressure of the volatile oxidant guest. Moreover, the prototype system (MOF-5-TNM and MOF-5-HNE) results in primary energetics, materials very sensitive to impact. This method enables the safe transportation of the individual components, which can be combined at the source generating the energetic composite.
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Fundamental Studies on Metal-Organic Framework Functionalization and Reactivity
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