Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Dr. J. Clara Wren

Abstract

This thesis presents work on the understanding of the effects of ionizing radiation on phosphonium-based ionic liquids (ILs). The capability of ILs to dissolve a wide range of molecules, and the potential of ILs to be highly resilient in energy-intensive environments makes them particularly promising media for the separation and sequestration of metal ion contaminants from radioactive waste effluents in nuclear fuel cycles. For this application, a water/IL system will be exposed to a continuous stream of ionizing radiation. The radiation environment will strongly influence the chemical state of the water phase in the system and the chemical parameters affecting the separation efficiency of the system. This work examines irradiation of gas/IL and water/IL biphasic systems containing phosphonium-based ionic liquids.

When exposed to ionizing radiation, ionic liquids undergo radiolysis, resulting in the formation of ionic liquid excited species and radiolytic fragments. As well, when exposed to ionizing radiation, water decomposes into a range of reducing (•eaq−, •O2−, •H) and oxidizing (O2, •OH, HO2•, H2O2) species. To develop a better understanding of the biphasic water/IL systems when exposed to radiation, small samples of the biphasic systems were exposed to continuous radiation in a gamma-cell for periods of time up to several days. A number of surface, spectroscopic, and electrochemical techniques were employed to follow the evolution of the systems. This combination of analytical techniques allowed for the study of changes in the ionic liquid phase, the water phase, and the gas phase in the systems.

Results indicate that even long-term continuous doses of gamma-radiation induce a negligible chemical change in phosphonium-based ILs when they are in contact with a gas phase. In the case of the water/IL system, ion transfer occurs across the water/IL interface, even with the most immiscible phosphonium-based ILs. Irradiation produces surfactants that can accumulate at the interface and accelerate mixing of the IL and water phases by emulsification and the formation of micelles. Despite the micelle formation and emulsification, studies concluded that the phosphonium-based ILs studied undergo very little radiolytic degradation in steady-state gamma-radiation fields.

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