Synthesis, postsynthetic modification, and investigation of metal-organic frameworks for environmental and biological applications
Date
2018
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Abstract
Metal-organic frameworks (MOFs) are unique porous coordination polymers having record-high surface areas, and tunability at both the organic linkers and metal ions. As such, MOFs are advantageous for various applications including electronics, gas adsorption, and separations amongst others. Despite the advantages associated with MOFs, there are several key challenges that must be addressed in order to broadly expand the practicality of these materials. Such challenges include synthetic pitfalls, structural instability, selectivity, and inefficient heterogeneous catalysis. For instance, most MOFs are not stable in moisture-rich environments, which leads to structural collapse even in the open atmosphere. This instability poses a serious limitation for useful applications. In addition, the synthesis of MOF-related ligands is underdeveloped, which can lead to costly or inaccessible materials. To overcome these challenges, one goal of this research is to develop a solution to enhance the kinetic stability of MOFs to water and another is to execute an efficient and cost-effective synthetic strategy to generate the MOFs used herein. CuBTC (copper benzene-1,3,5-tricarboxylate), a commercially available MOF that has been well-studied and designated as having great potential for many applications, undergoes rapid degradation in humid atmospheres. Therefore, a novel synthetic approach was developed to efficiently access NH2BTC on gram-scale. Postsynthetic modification to the amine of the MOF powder material enhances the kinetic stability of the MOF to water. A distinct linear relationship between the number of carbons in the modification and observed water contact angle is described for the first time. This facilitates the first report of reliable access to mixed-ligand frameworks with predictable, calculated wettability and tunable kinetic stability to water. This work is also the first report of functionalizing copper MOFs as well as MOFs containing a benzene-1,3,5-tricarboxylate ligand to alter hydrophobic characteristics. That initial work inspired further exploration of CuNH2BTC as an antibacterial surface when synthetically grown on the surface of carboxymethylated cotton. The resultant material is capable of tunable Cu2+ ion release (via postsynthetic modification) and exceeds current industry standards for antibacterial agents, exhibiting a log-3 or greater reduction in bacteria both on the surface and in solution. As the scientific community continues to explore and understand MOFs, the implementation of these materials for various applications is dramatically increasing. As such, the second part of this research was devoted to applying and manipulating MOFs to better understand the interactions of MOFs with small molecules and ions. The photophysical properties of CuNH2BTC were investigated and specific interactions between anions and metal ions with MOFs were identified, encouraging the strategic design of MOFs to detect target-analytes via changing fluorescence emission properties in dimethylformamide (quenching or enhancing emission intensity or changing emission wavelength). This work provides a prerequisite study towards the development of improved next-generation MOF chemosensors. In addition, the open coordination site of thermodynamically stable porphyrin-based MOFs was exploited for simultaneous heavy metal detection and metal ion removal from aqueous solutions. Lastly, to better understand heterogenous catalysis with MOFs in biologically relevant media water, a 1HNMR method with solvent suppression was implemented and allows for kinetic and mechanistic studies of biologically relevant MOF-catalyzed decomposition of GSNO with thermodynamically stable MOF CuBTTri in H2O and eventually in blood. As a whole this research provides valuable insights as to how MOFs may be strategically designed, manipulated, and utilized for sensing, catalysis, and antibacterial applications.
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Subject
ligand synthesis
postsynthetic modification
wettability
metal-organic framework
heterogeneous catalysis
surface chemistry