Probing the Structure-Property Relationship of Porous Sorbents for Atmospheric Water Adsorption
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Salinger, Jamie Lynn
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Abstract
This dissertation investigates the structure-property relationship of porous sorbents and their water adsorption behavior to develop materials for atmospheric water harvesting. Currently, the global water crisis is the biggest threat to mankind, with over half of the world’s population experiencing water scarcity at some time in the year. This issue is exacerbated by climate change, rapid population growth, and inadequate water infrastructure, and it is only expected to become more dire without proper scientific intervention. Common solutions, such as desalination, are often difficult to implement in remote or inland regions, arid regions, or areas where infrastructure is not abundant. Because of this, the development of adsorption based atmospheric water harvesting (AWH) technologies is becoming increasingly appealing.
Adsorption-based AWH technologies are explored in depth in Chapter 1. These technologies are attractive due to their ability to generate water from all environmental conditions, including arid air, and their continual renewability. An ideal water harvesting material must have high water capacity, have fast kinetics and mass transfer, be cyclically stable, and be able to be regenerated easily. To that end, this dissertation focuses on two classes of porous sorbents, hierarchical silicas and metal-organic frameworks (MOFs), for water adsorption applications, which are discussed in Chapter 2.
One of the biggest limitations of porous sorbents is their difficulty adsorbing significant quantities of water vapor from arid air. Materials that can adsorb water vapor from arid air typically possess small pore volumes which limit their maximum water capacity. On the other hand, materials that have large pore volumes and can capture large quantities of water require exposure to humid air. To that end, Chapter 3 focuses on developing a hierarchical silica-salt composite with record-setting water capacities across the full relative humidity regime. Through the incorporation of a hygroscopic salt into the pores of the silica matrix, there is a synergistic effect between the pore structure and hydrophilicity, harnessing the benefits of both the salt and silica sorbent. Similarly, this composite also exhibits cyclical stability, which suggests that the salt is stable within the pores of the silica and can continually be exposed to water adsorption and desorption.
Next, to understand how specific structural properties can be synthetically introduced to tune the water adsorption behavior, defects were engineered into MOF structures via soft templating. In Chapter 4, robust, water stable MOFs are synthesized in the presence of CTAB surfactants to introduce structural defects to modify pore size and volume. Large macropores and interparticle voids were generated with smaller MOF crystals, resulting in changes to the water adsorption behavior. Lastly, in Chapter 5, a MOF was post-synthetically modified through cation exchange allowing for the tailoring of the water adsorption behavior in a singular framework, resulting in increased water capacity, better performance in arid conditions, and increased hydrolytic stability.
In summary, by exploring three distinct methods of material engineering, namely hygroscopic salt impregnation, synthetic defect engineering, and post-synthetic cation exchange, this dissertation explores the intricacies of specific material properties on water adsorption behavior to develop a better understanding of how adsorption-based atmospheric water harvesting can be used to mitigate the global water crisis.
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2025-04-07
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Dissertation