Structure of Guests in MOF and Their Applications
by
Ievgen Kapustin
Doctor of Philosophy in Chemistry
University of California, Berkeley
Professor Omar M. Yaghi, Chair
Chapter 1. Introduction to the fundamentals of reticular chemistry, metal-organic frameworks (MOFs), crystallographic studies of MOFs, and sorption studies of MOFs.
Chapter 2. MOF-520 is used to coordinatively bind and align molecules of varying size, complexity, and functionality. The reduced motional degrees of freedom obtained with this coordinative alignment method allow the structures of molecules to be determined by single-crystal x-ray diffraction techniques. The chirality of the MOF backbone also serves as a reference in the structure solution for an unambiguous assignment of the absolute configuration of bound molecules. Sixteen molecules representing four common functional groups (primary alcohol, phenol, vicinal diol, and carboxylic acid), ranging in complexity from methanol to plant hormones (gibberellins, containing eight stereocenters), are crystallized and have their precise structure determined. Single and double bonds in gibberellins can be distinguished crystallographically. A racemic mixture of jasmonic acid is crystallized enantioselectively and its absolute configuration is determined for the first time.
Chapter 3. Despite numerous studies on chemical and thermal stability of MOF, mechanical stability remains largely undeveloped. To date, no strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure. Here, we show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4′-biphenyldicarboxylate (BPDC) linker as a “girder” to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structure from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.
Chapter 4. Atmospheric water is a resource equivalent to ~10% of all fresh water in lakes on Earth. However, an efficient process for capturing and delivering water from air, especially at low humidity levels (down to 20%), has not been developed. We report the design and demonstration of a device based on a porous metal-organic framework {MOF-801, [Zr6O4(OH)4(fumarate)6]} that captures water from the atmosphere at ambient conditions by using low-grade heat from natural sunlight at a flux of less than 1 sun (1 kilowatt per square meter). This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20% and requires no additional input of energy.
Chapter 5. Water scarcity is a particularly severe challenge in arid and desert climates. While a substantial amount of water is present in the form of vapor in the atmosphere, harvesting this water by state-of-the-art dewing technology can be extremely energy intensive and impractical, particularly when the relative humidity (RH) is low (i.e., below ~40% RH). In contrast, atmospheric water generators that utilize sorbents enable capture of vapor at low RH conditions and can be driven by the abundant source of solar-thermal energy with higher efficiency. Here, we demonstrate an air-cooled sorbent-based atmospheric water harvesting device using the metal−organic framework (MOF)-801 operating in an exceptionally arid climate (10–40% RH) and sub-zero dew points (Tempe, Arizona, United States) with a thermal efficiency (solar input to water conversion) of ~14%. We predict that this device delivered over 0.25 L of water per kg of MOF for a single daily cycle.
Chapter 6. Energy-efficient production of water from desert air has not been developed. A proof-of-concept device for harvesting water at low relative humidity was reported; however, it only delivers droplets of water but not of sufficient quantity to be collected. Here, we report a laboratory-to-desert experiment where a prototype employing up to 1.2 kg of metal-organic framework-801 was tested in the laboratory and later in the desert of Arizona, United States. It produced 100 grams of water per kilogram of MOF-801 per day-and-night cycle, using only natural cooling and ambient sunlight as a source of energy. We also report an aluminum-based MOF-303, which delivers more than twice the amount of water. The desert experiment uncovered key parameters pertaining to the energy, material, and air requirements for efficient production of water from desert air, even at a sub-zero dew point.
