Date of Award
Fall 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemical and Environmental Engineering (ENAS)
First Advisor
Zimmerman, Julie
Abstract
Provision of safe drinking water is of global importance, as evidenced by the United Nations Sustainable Development Goals, and yet significant inequities still exist in its access. Particularly, people that are geographically and/or economically limited bear the greatest burden. Within the United States, high costs of treatment for small communities or individual households pose significant barriers to the removal of contaminants below regulatory limits, let alone to health protective concentrations. Of particular concern are inorganic oxoanions (e.g., arsenic (As) and selenium (Se)), which pose serious risks to human and environmental health and are simultaneously challenging to remove because of their high aqueous mobility, various redox states, and abundance of anthropogenic and geogenic sources of release. Removing these contaminants becomes even more challenging because they often occur in orders of magnitude lower concentrations than competitive ions (e.g., nitrate, sulfate, phosphate). The objective of this dissertation is to elucidate the mechanisms governing effective and selective removal of target contaminants through an adsorption process. With strategic design, adsorbents can be low cost and easily implemented, making them attractive options for small-scale, point-of-use water treatment technologies. By exploring the fundamental interfacial reactions between sorbent and sorbate, this dissertation aims to establish a foundation by which environmentally abundant materials can be engineered to be high-performing sorbents for widescale implementation. This work will begin by highlighting the complexity of environmental injustices and draw attention to the inequities that persist in safe drinking water access. Next, the literature on faceted nanoscale metal oxides will be comprehensively reviewed to draw conclusions on how their structure governs their performance in a variety of sorption-driven environmental applications (i.e., catalysis, gas-sensing, aqueous contaminant removal). Key areas where further experimental and computational research is needed to develop a more robust structure-property-function understanding of performance will be highlighted. Next, the influence of persistent surface capping agents on observed facet-dependent Se(IV) adsorption by faceted hematite nanostructures will be explored. Through the development of a facile ligand-exchange procedure, the nanohematite samples will be capped with the same organic surfactant (poly(N-vinyl-2-pyrrolidone)) to equivalently compare facet-dependent sorption performance. The resulting impacts of capping agent and exposed crystal facet will be statistically analyzed to draw robust conclusions on both of their contributions to observed sorption behavior. Next, the faceted hematite nanostructures will be assessed for their selective removal of Se(IV), Se(VI), As(III), and As(V) target contaminants in the presence of a P competitor. Facet-dependent differences deriving from different orientations and densities of surface Fe and O atoms (e.g., complexation mechanisms and surface water networks as assessed by XAS spectroscopy and DFT calculations), will be emphasized as key factors contributing to observed selective adsorption. This selectivity will be assessed at different pH values to demonstrate the feasibility of developing selective faceted sorbents for environmentally relevant conditions. Lastly, transition metal crosslinked chitosan beads will be evaluated as a platform in which to embed the faceted nanohematite for the removal of As(V). Using a flow-through column setup, the mechanical stability and removal performance of the beads will be assessed over several weeks. The impact of freeze-drying the beads on the kinetics of removal are also examined. The crosslinked beads are also assessed for effective removal of other oxoanion contaminants (As, Se, V, Cr), and the selective removal of Se(IV) in the presence of P. Overall, this dissertation supports the rational design of environmentally abundant materials for effective and selective removal of toxic oxoanion contaminants by elucidating the factors that contribute to their sorption performance. It highlights opportunities for further development in synthetic design so as to exploit interfacial interactions to great effect. Towards the goal of enabling equitable, sustainable, and secure access to safe drinking water in the short- and long-term, this dissertation combines a fundamental chemical understanding with engineering design to inform future strategic development of high-performing sorbent materials.
Recommended Citation
Rudel, Holly Elizabeth, "Informing Design of Sustainable Sorbents for Drinking Water Treatment: Faceted Nanohematite for Oxoanion Removal" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1225.
https://elischolar.library.yale.edu/gsas_dissertations/1225
