Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemistry

Major Professor

Shengqian Ma, Ph.D.

Committee Member

Julie P. Harmon, Ph.D.

Committee Member

Xiaodong Shi, Ph.D.

Committee Member

Qiong Zhang, Ph.D.

Keywords

air purification, metal-organic frameworks, porous organic polymers, resource recovery, water treatment

Abstract

Resource depletion, clean water shortages, and global climate change have led to environmental sustainability being of primary concern for both governmental and industrial practices. Current methods to address these challenges typically come as a double-edged sword, fixing one problem while contributing to another. As introduced in chapter one of this dissertation, adsorbent materials are seen as a promising alternative remediation system due to their low energy consumption and minimal chemical waste production. However, many traditional adsorbents, such as activated carbon, metal oxides, and resins, are hindered in practice. This is because they lack the structural tunability to have long-term effectiveness and/or specificity in application. Advanced materials can move beyond traditional adsorbents and are recognized for the vast number of molecular arrangements available to form extended porous structures. Materials in this realm include metal-organic frameworks (MOFs) and porous organic polymers (POPs), which have been successful in a variety of applications, with the focus of this work on resource recovery, water treatment, and air purification.

Chapters two and three explore structural modifications to enhance POPs for the recovery of finite natural resources. Palladium and uranium were the analytes of choice due to their wide use in the industrial and energy sector, respectively. POPs were found to have high stability in aqueous solutions, rapid kinetic efficiency, and selective recovery of the targets even in solutions with diverse chemical compositions; all important metrics for moving these adsorbents into practice. It was experimentally determined that performance could be greatly enhanced through variations of the binding site, highlighting the potential of such advanced materials.

Chapters four and five detail work done to employ MOFs and POPs for water treatment applications with a focus on nuclear and industrial waste streams. The organic struts of a water-stable MOF, MIL-101, were functionalized with a high density of ionexchange sites for effective capture of the radionuclides, cesium and strontium. Isolation of such compounds is required to reduce the total volume of nuclear waste that must be stored permanently. More prevalent, however, are the numerous industrial processes that contribute to a large influx of toxic compounds in waste streams, which can seep into our water sources. Of these, mercury is a toxin of concern with environmental and human health implications. A stable POP functionalized with a thiol group (POP-SH) was found to have a high mercury uptake capacity with fast kinetics due to the strong interaction of multiple functional groups in close proximity. These results indicate the exceptional performance that can be achieved through a targeted approach to remove contaminants from water.

Chapters five and six concentrate on air purification via capture of volatile contaminants, as well as the utilization of gases as a reactant for organic transformations. Due to the stability of the POP platform, POP-SH was able to remove mercury in the vapor phase, thus demonstrating its applicability in multiple stages of the mercury cycle. Furthermore, of overwhelming concern is the excess carbon dioxide in the environment, contributing to global climate change. Rather than traditional carbon capture and storage methods, using carbon dioxide for organic reactions can not only reduce the concentration in air, but also upcycle it to produce industrially relevant compounds such as cyclic carbonates. Through the use of a MOF as a functional host, the cycloaddition of epoxides with carbon dioxide can be achieved with minimal energy input. This technique fully utilizes the structural components of a MOF with promising results. This work demonstrates the success of advanced adsorbent materials for a multitude of applications aimed at environmental sustainability, and how structural and chemical modifications contribute to their effectiveness. Through optimization of the material’s design for the proposed function, enhancements in performance can move such materials into large-scale applications. This strategy can not only ensure the prolonged health of our environment, but also be applied for further technological development of advanced materials.

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