UC San Diego

Metal-organic frameworks (MOFs) are crystalline, porous materials with unique properties valued for applications in chemical storage, separation, and catalysis. While MOFs have shown great potential for these applications, a major shortcoming of these materials is their inherently crystalline nature, which limits their processability into the form factors required for these applications. To overcome this issue, MOFs have been combined with polymers in order to form composites that incorporate the flexibility and processability of polymers while retaining the properties of the MOF material. However, incompatibilities between the MOF surface and the polymer matrix can result in defects and mechanical failure. Lowering the MOF loading to circumvent this greatly diminishes or negates the contribution of the MOF to the material properties. Therefore, a method is needed to formulate composites that allows for high MOF loading while retaining the desirable properties of the polymer.To develop a solution to this issue, Chapter 2 describes the preparation of polymer-coated MOFs using surface-initiated controlled radical polymerization (SI-CRP) from coordinating initiators. This method allows for the preparation of single nanoparticle composites, with the polymer directly attached to the MOF surface. The resulting particles were then self-assembled into monolayers at the air-water interface that were found to be free-standing when removed from the water surface. This method was found to be generalizable to several other MOFs, providing a platform for polymer-MOF composites with intrinsically high loadings of MOF particles. Chapter 3 systematically studies the different factors of polymer-grafted MOFs on both the particle self-assembly and the physical properties of the resulting monolayers. The effect of particle size, polymer length, and polymer composition were systematically varied. Monolayers of exceptional flexibility and toughness were found using poly(methyl acrylate). Additionally, the self-assembly of particles into ordered structures was studied both experimentally and computationally to be a result of particle size, polymer grafting density, and polymer hydrophobicity. Chapter 4 analyzes the coordination of different ligands to the surface of MOFs. Using a fluorescent dye containing a coordinating ligand, the amount of ligand present on the MOF surface can be determined using UV-visible spectroscopy. Furthermore, the stability of this coordination can be easily measured by analyzing the amount of dye that disassociates from the surface under various conditions. This feature was used as a diagnostic to determine the binding strength of several classes of ligands to different MOFs and provides a simple platform for the analysis of MOF surface coordination.