Oxidation mechanism of Ce(III) to Ce(IV) by δ-MnO2: Insights from EXAFS spectroscopy and density functional theory
Abstract
The oxidation of cerium (Ce) from the soluble trivalent state (Ce(III)) to the insoluble tetravalent state (Ce(IV)) on manganese (Mn) oxides critically influences its environmental fate and geochemical cycle, and is also of interest in water treatment. However, a comprehensive mechanistic understanding of the process by which Ce is immobilized upon interaction with Mn oxides in soils and marine sediments is still lacking. The bonding structure of Ce on δ-MnO2, the most abundant Mn oxide, was investigated by X-ray absorption spectroscopy at environmentally relevant pH and Ce concentration, and the oxidation reaction was modeled by atomistic calculation. Ce(III) is adsorbed as a six-coordinate complex at particle edges and a nine-coordinate complex at Mn(IV) vacancy sites of the MnO2 phyllomanganate layer. Ce(III) oxidation is non-spontaneous and requires hydrolysis of the sorption complexes to proceed. Gibbs free energy calculations of possible oxidation pathways show that electron transfers from Ce(III) to Mn(IV) at edge sites, and from Ce(III) to interlayer Mn(III) at vacancy sites, are thermodynamically favorable. Thus, the redox reactivity of δ-MnO2 depends on its crystallographic structure and the Mn valence. Our findings show that Mn(IV) and Mn(III) are better oxidants of Ce(III) than dissolved oxygen, and therefore, that cerium can be immobilized by Mn oxides even under suboxic conditions. The new mechanistic insights from this study contribute to an improved understanding of the oxidative uptake of Ce by Mn oxides and its relevance in natural and engineered systems.
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BibTeX
@article{manceau2026oxidation,
title = {{Oxidation mechanism of Ce(III) to Ce(IV) by δ-MnO2: Insights from EXAFS spectroscopy and density functional theory}},
author = {Alain Manceau and Yan Li and Jianlin Liao and Andrea Giacomelli and Lorenzo Spadini and Stephan N. Steinmann and Olivier Mathon},
journal = {Environmental Science and Technology},
year = {2026},
month = aug,
doi = {10.1021/acs.est.6c06467},
url = {https://hal.science/hal-05762909v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Oxidation mechanism of Ce(III) to Ce(IV) by δ-MnO2: Insights from EXAFS spectroscopy and density functional theory
AU - Alain Manceau
AU - Yan Li
AU - Jianlin Liao
AU - Andrea Giacomelli
AU - Lorenzo Spadini
AU - Stephan N. Steinmann
AU - Olivier Mathon
PY - 2026
DA - 2026/08/21
JO - Environmental Science and Technology
DO - 10.1021/acs.est.6c06467
UR - https://hal.science/hal-05762909v1
AB - The oxidation of cerium (Ce) from the soluble trivalent state (Ce(III)) to the insoluble tetravalent state (Ce(IV)) on manganese (Mn) oxides critically influences its environmental fate and geochemical cycle, and is also of interest in water treatment. However, a comprehensive mechanistic understanding of the process by which Ce is immobilized upon interaction with Mn oxides in soils and marine sediments is still lacking. The bonding structure of Ce on δ-MnO2, the most abundant Mn oxide, was investigated by X-ray absorption spectroscopy at environmentally relevant pH and Ce concentration, and the oxidation reaction was modeled by atomistic calculation. Ce(III) is adsorbed as a six-coordinate complex at particle edges and a nine-coordinate complex at Mn(IV) vacancy sites of the MnO2 phyllomanganate layer. Ce(III) oxidation is non-spontaneous and requires hydrolysis of the sorption complexes to proceed. Gibbs free energy calculations of possible oxidation pathways show that electron transfers from Ce(III) to Mn(IV) at edge sites, and from Ce(III) to interlayer Mn(III) at vacancy sites, are thermodynamically favorable. Thus, the redox reactivity of δ-MnO2 depends on its crystallographic structure and the Mn valence. Our findings show that Mn(IV) and Mn(III) are better oxidants of Ce(III) than dissolved oxygen, and therefore, that cerium can be immobilized by Mn oxides even under suboxic conditions. The new mechanistic insights from this study contribute to an improved understanding of the oxidative uptake of Ce by Mn oxides and its relevance in natural and engineered systems.
SN - 0013-936X
SN - 1520-5851
ER -