Date of Award
Doctor of Philosophy in Environmental Science - (Ph.D.)
Chemistry and Environmental Science
Sanjay V. Malhotra
A. J. Francis
Tamara M. Gund
Norman W. Loney
Ionic liquids (ILs) are new materials with unique properties such as non-measurable vapor pressure, low melting point below 100°C and tunable physical-chemical properties. These liquids demonstrate tremendous potential applications in many fields, including nuclear waste treatment.
In this study, new MOEMIM (methoxyethyl methyl imidazolium)-based ionic liquids were synthesized. Their properties were characterized by UV-Vis spectroscopy (UV-vis), Fourier transform infrared spectroscopy (ETIR), mass spectroscopy (MS) and NMR (Nuclear magnetic resonance). The interaction between ILs and uranium has been explored by various analysis techniques, including pH, potentiometric titration, UV-vis, MS and EXAFS (extended x-ray absorption fine structure). Among all the ILs studied here, MOEMIMBF4 demonstrated a strong complexation with uranium, while others showed weak interaction.
Next, the effect of ILs on the bioreduction of uranium by clostridium sp. was explored. The result revealed that, in presence of MOEMIMBF4, most of the U(VI) and reduced U(IV) can be maintained in the aqueous phase for long time, while most of uranium precipitates out very quickly in presence of other ILs. This could be explained by the formation of uranium complex associated with MOEMIMBF4. However, the complexation reduced bioavailability of uranium, resulting in the decreased bioreduction efficiency. The effect of different concentration of MOEMLMBF4 was also investigated in this study. The results disclosed that the elevated concentration could diminish the bioredution percentage, which may result from the raised toxicity.
In addition, toxicity of a variety of ILs on clostridium sp. was also examined here. Optical density (OD), pH and gas production were determined. The result revealed that the anion plays a very important role on toxicity. The more fluorine atoms the anion contains, the more toxic the IL is. Furthermore, the EC50-48hour of each IL on clostridium sp. was determined, and the partition coefficient (Kow) between octanol and water was measured, and also the ELUMO was calculated by Sparton'02. Based on these data, a series of QSAR models were developed to predict the toxicity of ILs.
Besides, the biodegradation of pyridium-based ILs by urealyticum bacteria in presence of low concentration uranium was explored in this study. The bacteria growth was monitored by GD, pH, UV-vis, and the biodegradation products were determined by HPLC (high performance liquid chromatography) and MS, and the concentration of uranium in the solution was measured by KPA ( kinetic phosphorescence analyzer). The result revealed that uranium under low concentration doesn't exert much inhibition on bacterium growth, but it formed complex with the biodegradation intermediate, leading to the elevated uranium concentration in the solution. After the intermediate was further consumed by bacterium, uranium was released again and precipitated out of the solution. Later, with the pH decrease because of the acids produced from biodegradation, uranium came back to solution again. The biodegradation pathway is similar to that in absence of uranium examined in previous work by Zhang (2006).
Wang, Hao, "Interaction of methoxyethyl methyl imidazolium-based ionic liquids with uranium and its effect on bioreduction of uranium" (2007). Dissertations. 836.