Dissertation
From adsorption to stability: water behavior in metal organic nanotubes
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
DOI: 10.25820/etd.008473
Abstract
Water exhibits unique physical and chemical properties when confined within nanoporous environments that differ significantly from its bulk phase. Understanding how nanoconfinement, surface chemistry, and environmental conditions such as radiation influence water structure and transport is critical for the development of advanced materials for separations, water purification, and energy-related applications. My thesis investigates water uptake, structural organization, and chemical reactivity within metal organic nanotubes (MONTs), a class of hybrid crystalline materials composed of inorganic metal nodes connected by organic linkers to form one-dimensional porous channels.
Initial adsorption studies focused on a uranium-based metal organic nanotube (UMONT) synthesized by the Forbes group, which previously demonstrated complete selectivity for H₂O over other solvents and isotopologues. Vapor sorption experiments combined with thermogravimetric and spectroscopic analyses confirm that water uptake occurs through a two-step mechanism consisting of surface adsorption via hydrogen bonding followed by pore filling into nanochannels. Adsorption isotherms consistent with a Type IV BET profile and Langmuir modeling of surface interactions demonstrate that adsorption behavior is governed by relative humidity of the environment.
The role of surface chemistry was further examined through controlled surface modifications using hydrophobic coatings. Chemisorbed ammonium trifluoroacetate (ATFA) significantly disrupted water uptake and selectivity by blocking surface adsorption sites, while polymer coatings such as polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) produced more subtle effects. These results confirm that surface interactions play a dominant role in controlling water transport within nanotubular materials.
Structural investigations across multiple MONT systems, including UMONT, LaMONT, and Cu-LaMONT, revealed that confined water molecules form highly ordered hydrogen-bonded networks within the nanochannels. Several other techniques including electron density mapping, kinetic modeling, interaction enthalpy analysis, and Hirshfeld surface visualization were used to correlate water network topology with adsorption kinetic and thermodynamics.
Finally, the impact of confined and surface waters on the nanotube stability was examined by exposing the UMONT to thermal treatment and ionizing radiation. Electron paramagnetic resonance spectroscopy revealed the formation of defect sites generated during dehydration. Despite defect formation, structural characterization confirmed that the crystalline framework and confined water channels remain intact even after ultraviolet and γ irradiation up to 20 kGy, demonstrating the exceptional robustness of these materials.
Details
- Title: Subtitle
- From adsorption to stability: water behavior in metal organic nanotubes
- Creators
- Vidumini Suchintha Samarasiri
- Contributors
- Tori Forbes (Advisor)Johna Leddy (Committee Member)Korey Carter (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 2026
- DOI
- 10.25820/etd.008473
- Publisher
- University of Iowa
- Number of pages
- xvi, 200 pages
- Copyright
- Copyright 2026 Vidumini Suchintha Samarasiri
- Language
- English
- Date submitted
- 04/08/2026
- Description illustrations
- Illustrations, graphs, charts, tables
- Description bibliographic
- Includes bibliographical references (pages 136-158).
- Public Abstract (ETD)
Water behaves very differently when confined within extremely small spaces compared to its behavior in bulk. This thesis investigates how water molecules organize, interact, and move when trapped inside the narrow channels of MONTs, crystalline materials composed of metal nodes connected by organic linkers. These nanotubes contain well-defined channels capable of trapping and releasing water in controlled ways.
Water exhibits complex behavior inside MONTs, forming ordered, chain-like or ice-like structures depending on how it interacts with the channel walls. This work explored design principles for building MONTs with tunable water behavior by systematically modifying surface chemistry, pore wall structure, and the chemical environment within the nanochannels. Using structural and spectroscopic techniques, I examined how water molecules assemble, hydrogen bond, and transport under nanoscale confinement.
The results show that subtle changes in pore polarity and surface functionality strongly influence how water is captured, arranged, and released. Hydrophilic and hydrophobic regions within the channels play a critical role in shaping water structure and mobility. These findings demonstrate that surface chemistry and channel design can be strategically engineered to create MONT materials with desirable water selectivity and transport properties. In addition, I have seen that MONTS such as the UMONT remain structurally stable even after exposure to radiation, maintaining both its crystalline framework and the tiny water channels inside the nanotubes.
Overall, this research provides fundamental insight into how nanoconfined water behaves and offers guidance for designing smarter porous materials to support clean water technologies, advanced separations, and sustainable energy solutions.
- Academic Unit
- Chemistry
- Record Identifier
- 9985177376902771
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