Reactivity of oxygen species in homogeneous and heterogeneous aqueous environments

Three different topics related to the reactivity of oxygen species in homogenous and heterogeneous aqueous environments were studied. An introduction that covers theory and motivation for the research is presented in the first chapter. The second and third chapters examine superoxide reactivity in water-aprotic solvent and water-solid mixtures, respectively. Superoxide species are of interest in environmental chemistry because they have potential to destroy highly oxidized organic chemicals such as chlorinated solvents, pesticides, dioxins and other chemicals that are carcinogenic in majority cases. Superoxide is a strong nucleophile in organic solvents; however, it shows a significantly lower reactivity in aqueous systems. The results of the first phase of research revealed that increasing amounts of water added to nonaqueous systems decreased the activity of superoxide in the nonaqueous media, but enough activity remained for effective treatment. Superoxide was then generated in the aqueous phase of two-phase water organic media systems, and significant superoxide activity was achieved in the organic media with the addition of phase transfer catalysts (crown ether and polyethylene glycol) to transfer superoxide into the nonaqueous phase. The results of this research demonstrate that superoxide that is generated in water photochemically, electrochemically, or through the catalytic decomposition of peroxygens has the potential to be transferred to oils, sludges, and other less toxic nonaqueous media to destroy highly refractory contaminants such as PCDDs. The results of the second phase of study on superoxide reactivity in water-solid matrices showed that similar to the addition of solvents, the presence of solid surfaces also enhances the reactivity of superoxide in water, possibly by altering the superoxide solvation shell. Linear relations were found between superoxide reactivity and surface area of the solids in aqueous solutions. The third phase of research elucidates the mechanism of base activated persulfate system, which has important implications for groundwater and soil treatment processes. A mechanism for base activated persulfate was proposed in which 1) persulfate decomposes to hydroperoxide through alkaline hydrolysis, and 2) hydroperoxide reduce another persulfate molecule resulting in the formation of sulfate radical and sulfate; the hydroperoxide is then oxidized to superoxide