Browsing by Subject "Metal-organic frameworks"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Design, Synthesis, and Characterization of Porous Metal-Organic Materials(2013-04-19) Park, JinheePorous metal-organic materials (MOMs) are assembled through coordination between two types of building units, metal or metal-containing nodes and organic linkers. Metal-organic frameworks (MOFs) have 3-D infinite structures and are especially known for high porosity and enormous surface area, leading to diverse applications such as selective gas separation, gas storage and catalysis. In contrast, metal-organic polygons/polyhedra (MOPs) as discrete molecular coordination assemblies are soluble in certain solvents, allowing us to study their solution-chemistry. In the first project, a microporous MOF with 1-dimensional (1D) bridging helical chain secondary building units (SBUs) shows facile transition from micro- to mesoporosity upon activation conditions. The quickly activated MOF shows permanent microporosity while the slow removal of coordinated aqua ligand results in formation of the mesopores in the microporous MOF. Second, a strategy to introduce not only the functional groups but also functionalized meso-cavities into microporous MOFs through metal-ligand-fragment coassembly has been studied. With this functionalization, the interior of the MOFs can be tuned by a wide range of functional groups on the ligand fragments, including polar and ionic ones. Depending on the functional groups on the ligand fragments, the introduced cavities can be extended to mesopores in a controllable manner. Third, a MOF constructed from dicopper paddlewheels and a predesigned ligand bearing carboxylate, pyridine, and amide groups enables selective adsorption of CO2 over CH4 and high H2 adsorption. The cooperative catalytic activity in a tandem one-pot deacetalization-Knoevenagel condensation was demonstrated. In the fourth and fifth section, an optically and thermally switchable azobenzene was introduced into a MOF and MOPs, respectively. The freshly synthesized MOF adsorbed a significant amount of CO2. Upon light irradiation, the adsorbed gas molecules were squeezed out of the MOF due to the change of conformation of the azobenzene groups inside the pores. The adsorbent returned to its original state when allowed to stay with gentle heating. In addition, solubility of srMOPs was optically controlled by trans-cis isomerization of the azobenzene moieties. Interestingly, guest molecules were trapped during cis to trans isomerization and released in the trans to cis conversion. This srMOP can be applied to uses requiring stimuli responsive capture and release of guest molecules, such as in controlled drug delivery systems. Finally, an organic linker with multiple conformations was used to synthesize both single and core-shell molecular squares, whose formations were controlled by reaction temperatures. Intriguingly the core-shell structure assembly was successfully employed as a template to prepare a heterobimetallic assembly, in which the metal substitution occurred exclusively in the core. This work might pave the way for the exploration of enzyme-mimicking molecular catalysts.Item Porous Metal-Organic Frameworks for Energy Storage Applications: Design, Synthesis and Mechanism Studies(2014-05-05) Liu, YangyangThe self-assembly of metal ions and organic linkers could afford 3-dimensional (3D) porous metal-organic frameworks (MOFs). They are promising materials for clean energy applications including carbon capture, hydrogen storage and methane storage. The primary goal of this research is the synthesis and characterization of new MOFs for these applications, and their structure-property relationship studies based on both experiments and simulations. Firstly, a stable magnesium MOF with 1-dimensional (1D) channel structure was synthesized. In-situ powder X-ray diffraction studies reveal its interesting phase transitions properties. After removing coordinated solvent at magnesium chains, this MOF can selectively adsorb CO_(2) over N_(2). Secondly, by varying the conditions in the solvothermal reaction, five MOFs with diverse structures were synthesized from a tetratopic ligand. Hydrogen storage properties were studied for these MOFs. A list of factors including catenation, metal nodes, charge, topology and pore size are evaluated for hydrogen storage application. In addition, four isostructural MOFs with various functionalized pore surfaces were synthesized from a series of di-isophthalate ligands. These MOFs exhibit a new network-topology and very high hydrogen uptake. They also showed reasonable adsorption selectivity of CO_(2) over CH_(4) and N_(2). Finally, high pressure methane uptake properties have been studied both experimentally and computationally for the series of isostructural MOFs with varying functional groups. All showed very high methane storage capacity at 298 K, 65 bar. Structure-property relationships were established for these MOFs, and simulations were employed to understand the mechanism of methane storage in MOFs. The role of copper paddlewheels and other adsorption sites for methane was evaluated. By thorough studies and careful analyses of simulation and experimental data, we proposed three novel mechanisms for methane storage in MOFs. Significantly, with the help of the mechanism studies, another two MOFs were designed, synthesized and discovered to have even higher methane storage capacities. Ligand design has been a powerful tool in synthesizing new MOFs. Besides surface area, pore size has been discovered to be a key factor for gas storage capacities of MOFs. These findings could serve as guidance for rational design of better performing materials for clean energy applications.