Synthesis of a Modified Metal Organic Framework as a Gas Storage and Sensing Material

Friday, February 12, 2016
Megha Vyakaranam, Independence High School, Frisco, TX
Around the world, fossil fuels are burned in substantial amounts to fuel human activities resulting in an over-consumption with serious environmental and health impacts. Increased greenhouse gas emissions due to fossil fuel usage can be significantly reduced through the adoption of alternative fuels. One of the most promising developments in the field of alternative fuels has been hydrogen usage, especially in gas vehicles due to its various eco-friendly advantages over diesel fueled vehicles. However, the factor that has prevented the widespread adoption of these vehicles is the inability to effectively store this gas. Since gases have a tendency to concentrate around surfaces, materials with high surface areas have the capacity to store gases without high compression. These materials include Metal Organic Frameworks (MOFs), materials consisting of bonds between transition metal cations and an organic linker. Although MOFs have been tested for high porosity and surface areas, MOFs with rich electron density, quenching, and chemical sensors are yet to be discovered. In this study, a process of MOF synthesis was explored to create a novel MOF that had better quenching and chemical sensing properties when compared to existing MOFs. The synthesizing process, a reductive amination, acted as a chemical functionalization to create the organic ligand, 2-(dimethylamino)terephthalic acid. Different concentrations of ligand were dissolved in DMF and trace amounts of zinc nitrate hexahydrate were added to the existing solution. MOF-5, the parent structure, was also synthesized to compare and highlight the benefits of the newly synthesized MOF (DMA-MOF) over MOF-5. Mechanisms used to indicate these differences included nuclear magnetic resonance (NMR) testing and fluorescence testing. An NMR was obtained to aid in the process of determining the purity of the organic linker which proved to be 92% pure with trace amounts of acetic acid and water. Through fluorescence results, the novel MOF proved to be a better quencher in comparison to MOF-5 with reduced electron density due to its interaction with the electron-deficient, Tetracyanoquinodimethane (TCNQ). Total integrated fluorescence intensity and the barycentric mean fluorescence were calculated for both the DMA-MOF and MOF-5 to determine surface area and chemical sensing properties. Since fluorescence intensity directly correlates with the ability to quench, the high fluorescence intensity in the DMA-MOF proved the MOF to be a better quencher than MOF-5. More external quenching also confirmed that the DMA-MOF had a higher surface area. The barycentric mean fluorescence determined whether the DMA-MOF had potential applications in chemical sensing. The greater difference in barycentric mean between 20mL and 40mL of TCNQ demonstrated a higher chemical sensitivity in the DMA-MOF when compared to MOF-5. Although it will take more experimentation to optimize this crystalline structure, this study is an imperative initial step to effective storage of the fuel.