| dc.description.abstract | Due to the rapidly growing population, industrial manufacturers and agricultural producers are seeking every opportunity to meet the booming demands, which have inevitably led to the aggravated water contamination by a variety of recalcitrant pollutants. Among the various water treatment technologies, advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) possess significant potentials owing to their capability of degrading recalcitrant pollutants via highly reactive species. This dissertation aims to further explore the potentials of homogeneous AOPs induced by persulfates and ARPs mediated by heterogeneous photocatalysts in the removal of persistent legacy and emerging pollutants.
Chapter I of this dissertation provides an overview of the urgent situation of water contamination and the basics of AOPs and ARPs.
Chapter II describes the first catalyst-free activation of peroxydisulfate (PDS) by visible light. Importantly, the formation of reactive species is distinctively different in the PDS visible light system with and without pollutant (e.g., atrazine (ATZ)). In addition to the sulfate radical (SO4●-) generated via S2O82- dissociation under visible light, O2●- and 1O2 are also produced in both systems. In the absence of ATZ, H2O2 and O2●- are key intermediates and precursors for 1O2, whereas in the presence of ATZ, oxidation of ATZ by SO4●- under oxic condition is critical for the formation of 1O2. Overall, both radical and nonradical processes contribute to the degradation of ATZ.
Chapter III discusses the direct activation of peroxymonosulfate (PMS) by co-existing phosphate and carbonate to produce SO4●-. Overall, SO4●--induced degradation was the major pathway for the degradation of atrazine, whereas direct oxidation by PMS served as a supporting pathway. Without any catalysts, PMS also displayed appreciable effectiveness in real lake and river waters.
In chapter IV, a zinc ferrite/zero-valent iron (ZFO/nZVI) nanocomposite with a unique core-shell-skin tertiary structure consisting of an nZVI core surrounded by ZnFe2O4 shell and further wrapped by wrinkled ZnFe2O4 skin layer is reported. The nanocomposite displayed an impressive 100% and 99.7% simultaneous removal for nitrate and arsenate at pH 7.0 under visible light. Reduction by photogenerated electrons was the dominant mechanism for nitrate removal, while adsorption is the primary process for arsenate removal.
Chapter V demonstrates the efficient photocatalytic degradation of perfluorooctanoic acid (PFOA) by a titanium-based metal-organic framework (MOF) MIL-125-NH2 with glucose as the sacrificial reductant. A 100% removal rate of PFOA and a 66.7% of total defluorination rate were achieved within 24 hours. Based on the untargeted analysis for degradation metabolites, H/F exchange and chain-shortening initiated by hydrated electron (eaq-) were proposed as the dominant degradation pathways for PFOA. In addition, the MOF almost completely removed PFOA after three cycles and maintained a high degree of structural integrity, illustrating excellent recyclability and stability.
In the last chapter, chapter VI, a summary of the dissertation is described along with my recommendations for future research. | |
