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DOE OSTI · 1988229

Cations impact radical reaction dynamics in concentrated multicomponent aqueous solutions

Nienhuis, Emily T.·Graham, Trent R.·D’Annunzio, Nicolas L.·Kowalska, Malgorzata I.·LaVerne, Jay A.·Orlando, Thomas M.·Reynolds, Jacob G.·Camaioni, Donald M.·Rosso, Kevin M.·Pearce, Carolyn I.·Walter, Eric D.
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Abstract

Ultraviolet (UV) photolysis of nitrite ions (NO 2 – ) in aqueous solutions produces a suite of radicals, viz., NO · , O – , · OH, and · NO 2 . The O – and NO · radicals are initially formed from the dissociation of photoexcited NO 2 – . The O – radical undergoes reversible proton transfer with water to generate · OH. Both · OH and O – oxidize the NO 2 – to · NO 2 radicals. The reactions of · OH occur at solution diffusion limits, which are influenced by the nature of the dissolved cations and anions. Here, we systematically varied the alkali metal cation, spanning the range from strongly to weakly hydrating ions, and measured the production of NO · , · OH, and · NO 2 radicals during UV photolysis of alkaline nitrite solutions using electron paramagnetic resonance spectroscopy with nitromethane spin trapping. Comparing the data for the different alkali cations revealed that the nature of the cation had a significant effect on production of all three radical species. Radical production was inhibited in solutions with high charge density cations, e.g., lithium, and promoted in solutions containing low charge density cations, e.g., cesium. Through complementary investigations with multinuclear single pulse direct excitation nuclear magnetic resonance (NMR) spectroscopy and pulsed field gradient NMR diffusometry, cation-controlled solution structures and extent of NO 2 – solvation were determined to alter the initial yields of · NO and · OH radicals as well as alter the reactivity of NO 2 – toward · OH, impacting the production of · NO 2 . The implications of these results for the retrieval and processing of low-water, highly alkaline solutions that comprise legacy radioactive waste are discussed.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYchemical solutionsdiffusion rateselectrolyteselectron paramagnetic resonance spectroscopynuclear magnetic resonance spectroscopynuclear wastephotodissociationraman spectroscopysolvation

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Nienhuis, Emily T., Graham, Trent R., D’Annunzio, Nicolas L., Kowalska, Malgorzata I., LaVerne, Jay A., Orlando, Thomas M., Reynolds, Jacob G., Camaioni, Donald M., Rosso, Kevin M., Pearce, Carolyn I., Walter, Eric D.. 2023-06-12. Cations impact radical reaction dynamics in concentrated multicomponent aqueous solutions. https://doi.org/10.1063/5.0153132

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