Towards practical metal-organic framework materials: Operando and in situ studies by leveraging synchrotron and neutron sources

Thesis

Metal-Organic Frameworks (MOFs) are a new class of porous materials with dozens of potential future practical applications. This thesis strives to bring that future nearer by leveraging synchrotron and neutron sources to study MOFs for next generation dielectrics, catalysts and sensors. A novel approach to measuring broadband dielectric functions of pelletised MOF powders using specular reflectance Fourier Transform Infrared (FTIR) spectroscopy is developed. MIL-53(Al) is investigated as a model system, and ab initio calculations for dielectric functions of its large pore and narrow pore phases show good agreement with experimental data. Rapidly synthesised Pd@MOF composites based on the OX-1 material are developed and investigated using a combination of FTIR, inelastic neutron scattering and x-ray absorption spectroscopy. The Pd@OX-1 structure is shown as a step towards next generation heterogenous single-metal-site catalysts, where Pd atoms reside selectively on benzene rings of the linkers and are recaptured during catalytic cycles. The ZnQ@OX-1 composite is studied using in situ transmission FTIR spectroscopy to identify key vibrational modes responsible for its photo-chemical sensing of acetone, and to probe the limits of its sensitivity. It is shown that ZnQ@OX-1 is a promising competitor for the currently best performing metal oxide-based sensors. Quantum tunnelling methyl rotors inside ZIF-8 pores are used as more exotic sensors for gas molecules adsorbed into its pores. The importance of chemical interactions of N₂ and Ar molecules are highlighted by shifts in neutron powder diffraction patterns, while the likely importance of specific adsorption sites is brought to bear by inelastic neutron scattering spectra, which reveal shifts in energies of the quantum tunnelling methyl rotors. The ‘gate opening’ phenomenon is reclassified as ‘gate blocking’ based on these operando experiments. Overall, this thesis develops practical MOFs and extends the toolbox for their further advancement.

Authors: Titov, K

• DOI: 10.5287/ora-o87e4pv1r
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford