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Title: Mechanisms of neptunium redox reactions in nitric acid solutions

Abstract

First transuranium element neptunium (Np) exhibits complicated behavior in acidic solutions because it can adopt wide range of oxidation states typically from +3 to +6 and coordinate large variety of ligands. In particular, accurate determination of Np redox potentials in nitric acid solutions is challenging due to overlapping chemical and electrochemical reactions leading to significant experimental uncertainties. Furthermore, over past decades spectrophotometry has been extensively applied to identify and characterize Np solution species in different oxidation states. However, relevant spectral database of Np in nitric acid solutions that can serve for the reference purposes has yet to be established due to the experimental difficulty to isolate and stabilize Np species in pure oxidation states without compromising solution optical properties. This work demonstrates that combination of voltammetry and controlled-potential in situ thin-layer spectropotentiometry overcomes these challenges so that Np species in pure +3, +4, +5, or +6 oxidation states were electrochemically generated in the systematically varied 0.1 – 5 M nitric acid solutions, and corresponding vis-NIR spectral signatures were obtained. In situ optical monitoring of the interconversion between adjacent Np oxidation states resulted in elucidation of the mechanisms of the involved redox reactions, in-depth understanding of the relative stability of themore » Np oxidation states, and allowed benchmarking of the redox potentials of the NpO22+/NpO2+, NpO2+/Np4+ and Np4+/Np3+ couples. Notably, the NpO2+/Np4+ couple was distinguished from the proximal Np4+/Np3+ process overcoming previous concerns and challenges encountered in accurate determination of the respective potentials.« less

Authors:
ORCiD logo; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1378005
Report Number(s):
PNNL-SA-122161
Journal ID: ISSN 2052-1553; ICFNAW
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Inorganic Chemistry Frontiers (Online)
Additional Journal Information:
Journal Volume: 4; Journal Issue: 4; Journal ID: ISSN 2052-1553
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Chatterjee, Sayandev, Bryan, Samuel A., Casella, Amanda J., Peterson, James M., and Levitskaia, Tatiana G. Mechanisms of neptunium redox reactions in nitric acid solutions. United States: N. p., 2017. Web. doi:10.1039/c6qi00550k.
Chatterjee, Sayandev, Bryan, Samuel A., Casella, Amanda J., Peterson, James M., & Levitskaia, Tatiana G. Mechanisms of neptunium redox reactions in nitric acid solutions. United States. doi:10.1039/c6qi00550k.
Chatterjee, Sayandev, Bryan, Samuel A., Casella, Amanda J., Peterson, James M., and Levitskaia, Tatiana G. Sun . "Mechanisms of neptunium redox reactions in nitric acid solutions". United States. doi:10.1039/c6qi00550k.
@article{osti_1378005,
title = {Mechanisms of neptunium redox reactions in nitric acid solutions},
author = {Chatterjee, Sayandev and Bryan, Samuel A. and Casella, Amanda J. and Peterson, James M. and Levitskaia, Tatiana G.},
abstractNote = {First transuranium element neptunium (Np) exhibits complicated behavior in acidic solutions because it can adopt wide range of oxidation states typically from +3 to +6 and coordinate large variety of ligands. In particular, accurate determination of Np redox potentials in nitric acid solutions is challenging due to overlapping chemical and electrochemical reactions leading to significant experimental uncertainties. Furthermore, over past decades spectrophotometry has been extensively applied to identify and characterize Np solution species in different oxidation states. However, relevant spectral database of Np in nitric acid solutions that can serve for the reference purposes has yet to be established due to the experimental difficulty to isolate and stabilize Np species in pure oxidation states without compromising solution optical properties. This work demonstrates that combination of voltammetry and controlled-potential in situ thin-layer spectropotentiometry overcomes these challenges so that Np species in pure +3, +4, +5, or +6 oxidation states were electrochemically generated in the systematically varied 0.1 – 5 M nitric acid solutions, and corresponding vis-NIR spectral signatures were obtained. In situ optical monitoring of the interconversion between adjacent Np oxidation states resulted in elucidation of the mechanisms of the involved redox reactions, in-depth understanding of the relative stability of the Np oxidation states, and allowed benchmarking of the redox potentials of the NpO22+/NpO2+, NpO2+/Np4+ and Np4+/Np3+ couples. Notably, the NpO2+/Np4+ couple was distinguished from the proximal Np4+/Np3+ process overcoming previous concerns and challenges encountered in accurate determination of the respective potentials.},
doi = {10.1039/c6qi00550k},
journal = {Inorganic Chemistry Frontiers (Online)},
issn = {2052-1553},
number = 4,
volume = 4,
place = {United States},
year = {2017},
month = {1}
}

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