亜硝酸塩からのラジカルに対するカチオンの効果(Cation Effects on Radicals from Nitrite)

2024-04-03 パシフィック・ノースウェスト国立研究所(PNNL)

＜関連情報＞

• https://www.pnnl.gov/publications/cation-effects-radicals-nitrite
• https://pubs.aip.org/aip/jcp/article/158/22/224503/2895603/Cations-impact-radical-reaction-dynamics-in

カチオンが濃厚多成分水溶液中のラジカル反応ダイナミクスに影響 Cations impact radical reaction dynamics in concentrated multicomponent aqueous solutions

Emily T. Nienhuis;Trent R. Graham;Nicolas L. D’Annunzio;Malgorzata I. Kowalska;Jay A. LaVerne;Thomas M. Orlando;Jacob G. Reynolds;Donald M. Camaioni;Kevin M. Rosso;Carolyn I. Pearce;Eric D. Walter
The Journal of Chemical Physics  Published:June 12 2023
DOI:https://doi.org/10.1063/5.0153132

Abstract

Ultraviolet (UV) photolysis of nitrite ions (NO₂⁻) in aqueous solutions produces a suite of radicals, viz., NO^·, O⁻, ^·OH, and ^·NO₂. The O⁻ and NO^· radicals are initially formed from the dissociation of photoexcited NO₂⁻. The O⁻ radical undergoes reversible proton transfer with water to generate ^·OH. Both ^·OH and O⁻ oxidize the NO₂⁻ to ^·NO₂ 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 ^·NO₂ 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 NO₂⁻ solvation were determined to alter the initial yields of ^·NO and ^·OH radicals as well as alter the reactivity of NO₂⁻ toward ^·OH, impacting the production of ^·NO₂. The implications of these results for the retrieval and processing of low-water, highly alkaline solutions that comprise legacy radioactive waste are discussed.