Doctor of Philosophy (PhD)
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Advanced Oxidation Process, Organophosphorus Compounds, Organophosphate Ester, Photocatalysis, Sonolysis, Perfluoroalkyl substance, PFAS, GenX, Naled, TCEP, Ultrasonic degradation, Photocatalytic degradation
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The presence of persistent organic pollutants, including organophosphorus esters (OPEs) and perfluoroalkyl substances (PFASs) in drinking water sources, is a serious threat to the environment and human health. Advanced oxidation processes (AOPs), specifically TiO2 photocatalysis and sonolysis, were evaluated to degrade these pollutants in water.
The UV/TiO2 photocatalysis can effectively degrade tris (2-chloroethyl) phosphate (TCEP) to innocuous materials. The degradation follows pseudo-first-order kinetics and consistent with the Langmuir-Hinshelwood model. Intermediate products identified by 31P-NMR show sequential oxidation of alkyl chains, ultimately leading to phosphate. Scavenger studies indicate hydroxyl radical (•OH) is the primary species responsible for the degradation.
One of the primary drawbacks of TiO2 photocatalysis is the costly UV required for TiO2 activation. We, therefore, synthesized doped NFP-TiO2 photocatalysts and demonstrated visible light activation yields •OH, keys for the photocatalysis of organic toxins. Prepared TiO2 was characterized by X-ray and spectroscopic techniques, and •OH generation was quantitated using coumarin trap under UV and visible light.
Ultrasonic irradiation, an AOP, does not require any catalysts to treat organic pollutants in water. We demonstrated the ultrasonic degradation of TCEP at 640 kHz. Hydroxyl radical scavengers added into the reaction solution before treatment indicate the degradation of TCEP proceeds through both pyrolysis and hydroxyl-mediated oxidation. Ultrasonic treatment of TCEP leads to three primary products, including the diester and monoester of TCEP confirmed by UHPLC-Orbitrap-MS studies.
Naled, a highly toxic organophosphate pesticide, was sprayed extensively aerially to exterminate mosquitos harboring the Zika virus. Little is known about the fate and degradation of Naled. Our results demonstrated that Naled can persist in the environment significantly upon condition. Ultrasonic irradiation at 640 kHz dramatically enhances the degradation of Naled, leading to the byproducts, including dimethylphosphate identified by FT-ICR-MS.
Effective degradation of a variety of emerging PFAS has been demonstrated by ultrasonic irradiation. A detailed kinetic investigation on the problematic PFAS GenX revealed that the degradation proceeds primarily by pyrolysis, and hydroxyl radical-mediated degradation is insignificant. UHPLC-Orbitrap-MS was used to identify the PFAS primary intermediates. We proposed that PFAS partition to the gas-liquid interfacial region and undergo extensive pyrolysis, leading to the conversion of fluorides.
Abdullah, A M, "Advanced Oxidation Processes for the Remediation of Problematic Organophosphorus Compounds and Perfluoroalkyl Substances" (2020). FIU Electronic Theses and Dissertations. 4442.
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