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Emerging contaminants (ECs) such as estrogen hormones, perfluoro compounds (PFCs), bisphenol-A (BPA), and 1,4-dioxane have been detected in natural water at many places. The existing conventional wastewater treatment systems are not designed for the removal of these contaminants. This critical issue leads to the need for the development of advanced and effective technologies.β-cyclodextrin (β-CD) is a glucose-based molecule which has high affinity for different organic contaminants by the formation of host/guest inclusion complexes. In this research, water soluble β-CD was reacted with certain crosslinking agents and copolymers to form water insoluble β-CD and to coat β-CD onto silica particles. The development of such novel hybrid adsorbents provides high binding capacity with organic contaminants along with high mechanical strength. Three different approaches were used to develop adsorbents by using two crosslinking agents (epichlorohydrin (EPI) and hexamethylene diisocyanate (HMDI), two copolymers (glycidoxypropyl trimethoxysilane and aminopropyl triethoxysilane) and three solvents (NaOH, dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The developed adsorbents were tested for the removal of ECs of interest (estrogens, PFCs, 1,4-dioxane, and BPA) under batch and column conditions from Milli-Q water. The adsorbent prepared by reacting β-CD with HMDI as crosslinking agent with the molar ratio of 1:8 showed best results in removing the target compounds. The adsorbent showed more than 95% removal of 17β-estradiol (in single component) and more than 90% of most of the estrogens (in multicomponent), more than 99% of PFOA, and a maximum of 90% removal in case of BPA. However, the developed adsorbent did not show any removal in case of 1,4-dioxane. The developed adsorbent showed a good regeneration capacity in removing PFOA over three successive cycles. The characterization of the adsorbents using FTIR, TGA, and TEM confirmed the coating of β-CD onto silica particles. The removal of ECs of interest was dependent on the nature of both adsorbents and adsorbates. The nature of adsorbent such as type of crossling agent, molar ratio between β-CD and crosslinking agents affect the removal of the contaminants. Similarly, the nature of adsorbates such as size, shape, and presence of functional groups affect the removal efficiency. / Civil Engineering

The nitrogen–oxygen single bond (>N–O–) is commonly found in organic contaminants ranging from aromatic N–oxides (ANOs), oximes, isoxazoles, to hydroxylamines. The introduction of N–O containing contaminants (NOCs) such as pesticides, pharmaceuticals, and reaction intermediates into aquatic environments is arguably an important emerging water issue. Soluble FeII and natural organic ligands, commonly co-existing in reducing environments, have been found to quickly reduce a number of organic contaminants in anoxic aqueous solution due to their low reduction potentials and high redox reactivity. The major objective of this research was to understand the reduction kinetics and mechanisms of various NOCs by FeII–tiron complex, a highly reactive, homogenous model environmental reductant. Experimental results show that various NOCs were reduced by FeII–tiron complex at different rates. The 1:2 FeII–tiron complex, FeL26-, is the dominant reactive species because its concentration highly correlated with the observed NOC reactivity. Depending on the structure, NOCs may undergo different reaction pathways, and the rate-limiting steps can be protonation, complexation, electron transfer or N–O bond cleavage. Specifically, for ANOs, three types of complexes can form between ANOs and FeII–tiron, leading to different reactivity and mechanisms: type I refers to those forming 5-membered ring complexes through the N and O atoms on the side chain; type II refers to those forming 6-membered ring complexes through the N-oxide O atom and the O atom on the side chain; and type III refers to complexation through the N-oxide O atom only. The density functional theory calculations suggested that the elementary reactions, including protonation, N–O bond cleavage, and the 2nd electron transfer processes, are barrierless, indicating that the first electron transfer is rate-limiting. Consistent with the theoretical results, the experimental solvent isotope effect, KIEH, for the reduction of quinoline N-oxide (a type III ANO) was obtained to be 1.072 ± 0.025, suggesting protonation was not involved in the rate-limiting step. The measured nitrogen kinetic isotope effect, KIEN, for the reduction of pyridine N-oxide (a type III ANO) (1.022 ± 0.006) is in good agreement with the calculated KIEN for its first electron transfer (1.011 ~ 1.028), confirming that the first electron transfer is rate-limiting. Electrochemical cell experiments demonstrated that the electron transfer process can be facilitated significantly by type I complexation with FeL26-, to some extent by type II complexation with free FeII, but not by weak type III complexation. Reduction products of several ANOs were identified by HPLC and LC-QToF-MS to be the deoxygenated analogs. Similar to ANOs, reduction products of various substituted isoxazoles (ISXs) were identified by HPLC/QToF-MS to be the ring-cleavage analogs. The density functional theory calculations suggested that the elementary protonation processes are barrierless, while the N–O bond cleavage processes have small energy barriers, suggesting they are not the rate-limiting step. The experimental iron kinetic isotope effects, KIEFe, for the reduction of 3-amino-5-methylisoxazole (AMX) and 3,5-dimethylisoxazole (DMX) were obtained to be 1.0076 ± 0.0049 and 1.0075 ± 0.0018. Both numbers revealed that FeII participated in the rate-limiting step, demonstrating that the electron transfer step is rate-limiting. Meanwhile, KIEH for the reduction of AMX was obtained to be 1.992 ± 0.068, indicating that proton is involved in the rate-limiting step, while that for DMX was 1.209 ± 0.079, suggesting no protonation is involved in the rate-limiting step. Thus, the reduction of AMX and DMX undergoes different pathways. Ring complexes formed between ISXs and FeII–tiron species can be categorized into three types: type I complex forms through 3-N and ring-O; type II complex forms through 5-N/O and ring-N; and type III complex forms through 6-O and ring-N. However, complexation only occured after ring cleavage due to the lower energies calculated for the ring-opened complexes. Electrochemical cell experiments revealed that the electron transfer process can be facilitated by various types of complexation at different levels. The kobs of type I or II ISXs increased a few times as [FeII] increased significantly in the cathodic cell, suggesting that the reduction can be accelerated by either type I or II complexation with free FeII to some extent. Meanwhile, the significantly higher kobs of ISXs in the batch experiments than that in the cell experiments indicated that type I and type II-N complexation with FeL26- can strongly facilitate ISX degradation. Based on these findings, future work will rely on both experimental and computational approaches to examine the reduction kinetics and mechanisms of other categories of NOCs. Upon successfully elucidating the rate-limiting step for each group of NOC, various molecular descriptors will be examined to develop QSARs as predictive tools for reducing activity of other structurally-related NOCs. Overall, this project has provided a wealth of new mechanistic information on the transformation of NOCs in model aquatic environments, which will enable researchers and regulatory agencies to develop environmental fate simulators to accurately assess their fate in and possible risks to water supply and environmental systems. / Environmental Engineering

Polychlorinated biphenyls (PCBs) are a class of persistent organic contaminants that are ubiquitous and persistent in the environment. In the environment, PCBs have been shown to undergo various degradation processes and generate hydroxylated metabolites known as hydroxylated polychlorinated biphenyls (OH-PCBs). There is a growing scientific interest in studying OH-PCBs as they are being increasingly detected in biotic and abiotic samples. Due to their widespread presence in the air, water, and soil, as well as their ability to bioaccumulate in living organisms, they pose a high danger to human beings and thus need to be remediated. Though phytoremediation has been proposed as a useful technology for the environmental management of PCBs, there is a lack of information about potential phytoremediation of OH-PCBs The hypothesis underlying this study is that hydroxylation of PCBs to OH-PCBs results in different toxicity and physiological effects on plants. In order to test this hypothesis, we conducted experiments aimed at understanding the toxicity and metabolism of PCBs and OH-PCBs by A. thaliana plants at physiological and transcriptomic levels. The applicability of FTIR to analyze lignin and cellulose content in the cell wall was tested for the purpose of biofuel production. More precisely, the specific aims of this study are as follows: 1. To determine the toxicity of selected PCBs and their hydroxylated metabolites (OH-PCBs) toward the model plant A. thaliana. 2. To understand the regulation of the response to and metabolism of PCBs and OH-PCBs in exposed A. thaliana at the transcriptomic level. 3. To determine the change in the biomass composition of A. thaliana upon exposure to different PCBs and OH-PCBs. Toxicity results indicated no observable toxicity of the parent PCBs toward the plants. However, lower chlorinated OH-PCBs resulted in a significant reduction in the growth and germination rate of the plants. Genome wide expression microarrays were used to investigate the transcriptional response of A. thaliana plants to 2,5-DCB and three of its OH-metabolites. Exposure to 2,5-DCB caused up-regulation of genes that are involved in toxic stress response and detoxification functions, and induction of multiple xenobiotic response genes. FTIR analysis was used to determine the effects of different PCBs and their hydroxylated metabolites on the composition of the plant biomass. Significant changes in the lignin and cellulose content were observed between different treatments, which indicated an overall effect on the cell wall components upon exposure to PCBs and its OH metabolites. / Environmental Engineering