PhD Proposal Defense - Mamatha Hopanna

Photolytic fate of organo-selenium and -tin compounds in natural and engineered water systems

Friday, May 24th at 11:00 am

Organometallic compounds are broadly classified as chemicals that include a metal atom covalently bound to a carbon atom. Due to the presence of the organic moiety and the metal atom, these chemicals participate in unique sorption, redox, and catalysis reactions. As a result, organometallics are widely applied in the biomedical, agricultural, and electrical fields as antibiotics, chemotherapy agents, antioxidants, pesticides, and semiconductors. The growing demand for organometallic chemicals may proportionally increase the environmental loading of these contaminants. Unlike conventional organic compounds, the special properties of organometallics pose distinct environmental concerns and suggest interesting environmental chemistry. Some of these compounds are transformed in the environment through mechanisms that release the inorganic metal, which is often more toxic than the organometallic chemical. Photochemical oxidation is a major abiotic process that governs the fate of organic contaminants in natural water; however, few studies have elucidated the photochemical transformation of organometallics in natural and engineered (i.e., 254 nm) and systems. The factors that control the phototransformation kinetics of different organometallics are currently unknown. This dissertation will, therefore, identify (i) quantum yields for direct photolysis of organometallics, in particular, organo-selenium and -tin compounds, (ii) second-order rate constants for organometallic reaction with reactive species (e.g., singlet oxygen (¹O₂), hydroxyl radicals (^•OH), and triplet state dissolved organic matter (³DOM*)), (iii) the effects of water quality (e.g., pH, temperature, ionic strength, and DOM) on phototransformation, and (iv) the primary organometallic photoproducts formed through direct and indirect photolysis mechanisms.