Dissertation
The study of nanoscale water confinement in metal-organic nanotubes
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2024
DOI: 10.25820/etd.007378
Abstract
Water under confinement exhibits properties that differ significantly from bulk water due to frustration of the hydrogen-bond network induced by interactions with the pore wall. Much of the previous work has focused on water confined within carbon nanotubes, which possess hydrophobic environment, or in hydrophilic silica-based nanoporous materials. Complex materials often possess variability in the polarity of the surface and the exact arrangement of these hydrophobic and hydrophilic functional groups may control the structure and behavior of water in these systems. To evaluate this further, we are exploring the behavior of water within hybrid metal organic nanotubes, which possess 1D pore space.
In Forbes group, a uranium-based metal-organic nanotube (UMONT) was synthesized using zwitterionic ligands like iminodiacetic acid (IDA). IDA chelates to the U(VI) metal center in a tridentate fashion and doubly protonated IDA linker connects the neighboring uranyl moieties until it forms hexameric macrocycles. These macrocycles stack into a nanotubular array due to supramolecular interactions. Single crystal X-ray diffraction studies displayed there are two crystallographically unique water molecules that can be removed reversibly at 37 ˚C. In the current body of work, we are trying to understand the fundamentals of water behavior within this 1D nanoporous material by changing physicochemical properties such as temperature and pressure.
The single crystal XRD data for UMONT was collected at temperatures ranging from 100 to 270 K with a 10 K increment, and a method was developed to track the changes in electron density at confined water sites over the temperature series. This was done to understand the mobility of water with external temperature changes. The influence of internal polarity on the hydrogen bonding network within hybrid materials was investigated using two different MONT materials (copper-based MONT (Cu-LaMONT) and lanthanum-based MONT (LaMONT)) as model systems, and their hydrogen bonding networks were compared with that of UMONT. The changes in the hydrogen bonding network with temperature variation from 100 to 250 K were analyzed to gain a deeper understanding of the polarity effect and electron density mapping was used to observe the changes in confined water structure. This polarity effect on proton conductivity through the water network within UMONT and Cu-LaMONT was measured using electrochemical impedance spectroscopy, varying the external humidity and temperature. Another study, the effect of external pressure on the confined water structure within UMONT was studied by conducting in situ and ex situ pressurization using an environmental control cell (ECC) and a Parr vessel, respectively.
Details
- Title: Subtitle
- The study of nanoscale water confinement in metal-organic nanotubes
- Creators
- Tiron Hasitha Lakmal Jahinge
- Contributors
- Tori Z Forbes (Advisor)Scott R Daly (Committee Member)Edward G Gillan (Committee Member)Johna Leddy (Committee Member)Leonard R MacGillivray (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2024
- DOI
- 10.25820/etd.007378
- Publisher
- University of Iowa
- Number of pages
- xviii, 184 pages
- Copyright
- Copyright 2024 Tiron Hasitha Lakmal Jahinge
- Grant note
- The authors acknowledge NMR assistance from William H. Casey at the University of California at Davis. We acknowledge support from the National Science Foundation Division of Materials Research (NSF-DMR2004220) and William H. Casey acknowledges support from Office of Basic Energy Sciences in the Department of Energy through its Geoscience via grant DE-FG0205ER15693. In addition, used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. (47) We acknowledge support from the National Science Foundation Division of Materials Research (NSF-DMR15246700) (91) We acknowledge support from the National Science Foundation Division of Materials Research (NSF-DMR15246700). The authors acknowledge Benjamin S. Revis for his support to design of glass chamber used in the impedance measurements and Dr. Scott Shaw for insights into the circuit models. We also acknowledge the University of Iowa Materials, Analysis, Testing, and Fabrication facility for use of the powder X-ray diffractometer and scanning electron microscope. (125) We acknowledge support from the National Science Foundation Division of Materials Research (NSF-DMR15246700). The authors acknowledge Benjamin S. Revis for his support to design of Environment Control Cell used in the in-situ data collection. (156)
- Language
- English
- Date submitted
- 04/23/2024
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 161-184).
- Public Abstract (ETD)
Water is crucial for the existence of all living beings, and it covers 75% of Earth's surface. Despite this abundance, obtaining fresh water remains a challenge in certain regions because the majority of water is found in the oceans or trapped in ice. Due to the obstacles in securing clean drinking water, it's essential to grasp the fundamental principles of water chemistry to innovate new water purification techniques.
This body of work mainly focused on the fundamental understanding of water confined into nanometer sized (typically the thickness of human hair ~ 50,000 nanometers) porous materials. These materials are referred as a metal organic nanotube (MONT) and is formed by connecting metals nodes and organic linkers (carbon containing) into a tubular shape. In our group, we have developed a novel MONT that can trap pure water inside its one-dimensional pore space. The metal and the organic linker that was used in our material is uranium and iminodiacetic acid, respectively. This MONT shows a fondness for water rarely seen in materials. In fact, attempts to load any substance into its channels other than water result in failure. This type of water selectivity is seen in biology, specifically in a family of proteins called aquaporins. My graduate work mainly focusses on understanding water behavior within this material under different physical conditions such as high pressures and temperatures. In addition to this MONT system, several other MONT systems were used to get comprehensive understanding of water behavior under confined atmospheres. This dissertation tells that story and direct future usage of MONT materials in water treatment and many other applications.
- Academic Unit
- Chemistry
- Record Identifier
- 9984647149102771
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