Photolytic fate of organo-selenium and -tin compounds in natural and engineered water systems
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Date
2020-01-01
Type of Work
Department
Chemical, Biochemical & Environmental Engineering
Program
Engineering, Civil and Environmental
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Distribution Rights granted to UMBC by the author.
This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
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Abstract
Organometallic chemicals contain at least one metal atom covalently bound to at least one carbon atom. Due to their sorption, redox, and catalysis properties, organometallics are commonly used as antibiotics, antioxidants, chemotherapy agents, pesticides, and semiconductors in the biomedical, agricultural, and electrical fields. While photochemical degradation is a significant abiotic process that governs the fate of organic pollutants in water, few studies have elucidated the photochemical transformation of organometallics in natural (i.e., 365 nm) and engineered (i.e., 254 nm) systems. This dissertations (i) assessed the suitability of conventional protocols, which are employed to study the photochemistry of organic contaminants, for organometallics, (ii) measured quantum yields for direct photolysis of organometallics, specifically organo-selenium and -tin, at 254 nm and 365 nm, (iii) determined the second-order rate constants for the reaction of organometallic chemicals with the singlet oxygen (1O2), hydroxyl radical (�OH), and triplet state dissolved organic matter (3DOM*) reactive species, (iv) the half-lives of organometallics in diverse water sources using the Aqueous Photochemistry of Environmentally occurring Xenobiotics (APEX) modeling tool, and (v) identified the primary photoproducts and toxicity of organometallics in the UV-254 and UV-H2O2 treatment systems. Atypical phototransformation kinetics were observed for ebselen in the presence of reactive species sensitizers, scavengers, and quenching agents due to ebselen reaction with active intermediates that are not kinetically relevant for most organic contaminants. These findings confirmed that the selenium atom leads to the high photoreactivity of ebselen and informed proper protocols for future study of organoselenium compounds.Triphenyltin hydroxide exhibited negligible direct photolysis at 365 nm, and indirect photolysis by 1O2, �OH, and 3DOM* were the dominant photodegradation mechanisms. The second-order rate constants for triphenyltin hydroxide reaction with 1O2, �OH, and 3DOM* were (3.9 � 0.5) � 106 M-1 s-1, (7.81 � 0.37) � 108 M-1 s-1, and (1.41 � 0.06) � 106 M-1 s-1, respectively. APEX model simulations indicated that the of triphenyltin hydroxide half-lives were as follows: 126-262 d in surface water; 77-178 d in wastewater effluent; 55-126 d in stormwater; 51-78 d in wetlands; and, 106-202 d in natural organic matter extracts. In summary, this dissertations reports critical knowledge on the complex photochemical behavior of ebselen and triphenyltins for UV-254, advanced oxidation systems, and the natural environment. The information reported in this dissertations will assist with (i) understanding the fate of organometallics in natural systems and current water/ wastewater treatment processes and (ii) selecting appropriate photochemical and photocatalytic treatment systems for legacy and emerging organometallic chemicals.