Civil Engineering ETDs

Publication Date

Fall 8-28-2019

Abstract

The aim of this dissertation was to investigate the interactions occurring at the organic – inorganic interface between solid media and aqueous contaminants for water treatment and sensor applications. The gaps in current literature on these interfacial organic-inorganic interactions must be bridged in order to develop advanced water treatment and monitoring technologies for improving water quality and thus, restore and protect the contaminated water resources. As a part of this dissertation, manganese oxides-based composites and electrospun polymer mats were developed and investigated for gaining mechanistic insights of organic (bisphenol A and acetaminophen) and inorganic (uranium) contaminants removal, respectively. These reactions were studied for (i) surficial changes on the solid media (ii) removal mechanism of aqueous contaminant and (iii) processes affecting the removal kinetics using multiple techniques such as spectroscopy, chromatography, electrochemistry and kinetic modelling.

The specific research objectives for the first study was to evaluate the removal of Bisphenol A by commercial MnOx and synthesized MnOx using spectroscopic and aqueous chemistry techniques. The removal of 99.7% BPA was observed by applying synthesized MnOx, while 71.2% BPA removal was observed by applying commercial MnOx after 44 hours of reaction of 10 mM MnOx(s) media with 1mM BPA at pH 5.5. The reduction of Mn was detected in the surface of both BPA reacted media, but a higher content of reduced Mn was observed in synthesized MnOx. The reaction of BPA with synthesized MnOx fit the electron transfer-limited model, while the reaction of BPA with Com-MnOx had a better fit for surface complex formation-limited model. These results suggest that BPA removal and the reactivity of MnOx(s) are affected by the differences in surface area and impurities present in these media. Thus, this study has relevant implications for the reaction of MnOx(s) with phenolic contaminants in natural systems and for water treatment applications.

The objective of the second study was to determine the binding mechanism of U with phosphonate functionalized groups in electrospun polymer to understand U uptake with different co-occurring ions such as calcium and carbonate. A HDPA (hexadecyl phosphonate) functionalized electrospun polymer was developed in order to study the U-surface association. The U uptake was similar in control solutions containing no Ca2+ and HCO3- (resulting in 19% U uptake), and in those containing only 5 mM Ca2+ (resulting in 20% U uptake). A decrease in U uptake (13% U uptake) was observed in experiments with HCO3-, indicating that UO2-CO3 complexes may increase uranium solubility. Almost negligible U uptake (3% U uptake) was observed in experiments with U, Ca, and HCO3 likely due to the formation of neutral and negatively charged U-Ca-CO3 ternary complexes as indicated by chemical equilibrium modelling. Results from shell-by-shell EXAFS fitting and aqueous extractions indicate that U is bound to phosphonate as a monodentate inner sphere surface complex to one of the hydroxyls in the phosphonate functional groups. The main finding from this study was that the aqueous speciation of U influenced the uptake on the phosphonate. This U binding information for in-situ sensor application by integrating spectroscopy microscopy and solution chemistry.

The third study involved development of electrochemically active MnOx/C media for application towards removal of acetaminophen in environmentally relevant conditions. The reaction mechanism of MnOx/C composites for treating phenolic micropollutants in water systems was investigated to obtain information on interfacial interactions occurring at organic-inorganic interface by integrating aqueous chemistry and electrochemistry measurements. Improved electrochemical activity was measured for the MnOx/C composite compared to pure undoped carbon and MnOx oxide media tested individually. The enhanced electrochemical activity of the MnOx/C composite resulted in the faster oxidation of acetaminophen when compared to individual effects of just oxidation with pure MnOx and adsorption on undoped carbon. The findings from this study are relevant as using a cost efficient and ubiquitous manganese oxide on carbon composites for acetaminophen oxidation is promising towards development of efficient water treatment technologies.

This Ph.D. research contributes to the body of knowledge by improving the understanding of processes at the solid – liquid interface which affect the organic-inorganic reactions, contaminant removal and reactive media performance. The goal of this dissertation was to provide essential insights on the effect of surface and structure of solid media on the reaction with aqueous contaminants by using advanced spectroscopy, microscopy and analytical chemistry tools. The scientific information obtained from this dissertation, such as the identification of the contaminant associated with the solid surface and contaminant removal rate limiting step, is crucial towards proposing appropriate detection and remediation strategies for contaminated sites with similar water chemistry especially in rural communities with non-centralized potable water treatment system.

Keywords

Interfacial interaction, surface chemistry, uranium chemistry, manganese oxides, fate of contaminants, spectroscopy

Document Type

Dissertation

Language

English

Degree Name

Civil Engineering

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

Jose M. Cerrato

Second Committee Member

Abdul-Mehdi S. Ali

Third Committee Member

Kerry J. Howe

Fourth Committee Member

Fernando H. Garzon

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