Photochemical reactions of polychlorobenzenes and polychlorobiphenyls in surfactant micelle and surfactant-extracted-soil solutions
Abstract
Photochemical reactions of polychlorobenzenes and polychlorobiphenyl congeners (PCBp) in aqueous solutions containing surfactant micelles have been investigated. All photolysis experiments were performed in a Rayonet$\sp{\rm TM}$ RPR-100 merry-go-round photoreactor utilizing 253.7 nm mercury monochromatic ultraviolet (UV) lamps. Photo-reduction through photo-dechlorination was shown to be the main decay pathway in which lesser chlorinated congeners, benzene, and phenol, were formed as measurable intermediates. Final non-carbon products included H$\sp+$ and Cl$\sp-$, produced in approximately stoichiometric amounts of each other from the starting materials. In addition, some minor pathways were observed, including photo-chlorination (the reverse reaction), photo-hydrolysis and photo-isomerization. The quantum yield for photodecay of hexachlorobenzene was found to be about an order of magnitude greater in several micellar solutions than in water alone. The hydrogen source sodium borohydride proved to be a promising photodechlorination rate enhancer at elevated concentrations. Photolytic destruction following surfactant-aided soil washing was examined also in this study. Hexachlorobenzene, 2,3,4,5-tetrachlorobiphenyl (2,3,4,5-TeCBp), and Arochlor 1254 were used as pollutant probes. In this process, the materials that co-extracted from the soil with the probe molecules played an important role. At low concentration, this (humic) material enhanced the quantum yields of pollutant transformation. Presumably, the co-extracted material may act as additional hydrogen source, act as sensitizers, and/or form free radicals upon illumination, triggering additional free radical chain reactions. At high humic concentration, however, the observed dechlorination reaction is slightly reduced. Through data analysis, it was shown that effect could be accounted for by competition for light. Limitation on reuse of the washing solution (micellar solution) are discussed.
Degree
Ph.D.
Advisors
Jafvert, Purdue University.
Subject Area
Civil engineering|Public health|Organic chemistry
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