The Chemistry of Metal Oxyhydroxides and their 3D Porous Hybrid Materials for the Capture, Transport and Degradation of Toxic Chemicals

Abstract

Growing concerns regarding chemical weapons and toxic chemicals require the development and testing of robust materials and methods to capture and destroy these harmful chemicals. This dissertation discusses the fundamental properties (e.g., structure, stability and activity) of metal oxyhydroxide based 3-dimensional porous materials, such as metal organic frameworks (MOFs), and covalent organic frameworks (COFs), and their applications for gas capture and degradation, especially for toxic gases and chemical warfare agent simulants. We report and verify that the active sites in UiO-67 MOFs are the metal nodes (oxyhydroxides) and developed a paradigm which correlates the activities of the MOFs, the metal oxyhydroxides and their precursors. This new understanding can help researchers choose the optimum metal for the intended applications by avoiding the tedious and time-consuming procedures of MOF synthesis and purification. In addition, to characterize and understand the structures of active sites in UiO-67 MOFs, temperature programmed desorption mass spectrometry (TPD-MS) and in situ Fourier-transform infrared (FTIR) spectroscopy were performed under ultra-high vacuum (UHV) and revealed unconventional binding sites and assisted in the successful characterization of missing linker defects. Here, our research helped in identification of a new class of binding sites, via NH-π interactions, in UiO-67 MOFs will assist researchers working in the areas of gas storage/release in developing better materials. This study should facilitate the structural understanding of MOFs, their important attributes such as defects and their chemistry in the presence of toxic gases. After successful identification of active species in MOFs, with the ultimate goal of isolating andii depositing the active sites on porous carbonaceous materials, e.g., COFs, we have engineered a facile technique to synthesize robust nanoparticle-COF and evaluated the reasons for its improved catalytic properties over other materials. The discoveries and their implications discussed in this thesis address fundamental knowledge gaps and should aid the rational design of superior materials for in operando applications.