Redox Properties of Structural Fe in Clay Minerals: 5. The Role of Fe in the Tetrahedral Sheets of Synthetic Smectites.
6 affiliations
- 1School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL) , 1015Lausanne, Switzerland.
- 2Université de Poitiers, CNRS, IC2MP , 86073Poitiers, France.
- 3PSI Center for Nuclear Engineering and Sciences , 5232Villigen PSI, Switzerland.
- 4School of Engineering, Newcastle University, Newcastle Upon TyneNE1 7RU, United Kingdom.
- 5Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600Dübendorf, Switzerland.
- 6Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich , 8092Zürich, Switzerland.
Abstract
Iron-bearing smectite clay minerals are important redox-active phases in soils and sediments. Yet, the influence of iron substitution in the tetrahedral sheets (TetFe) of smectites on their redox properties remains poorly understood. Here, we investigated the repeated reduction and re-oxidation of synthetic Fe-rich smectites, known as synthetic nontronites (SyN), with constant content of Fe in the octahedral sheet (OctFe) but variable initial content of TetFe. The redox properties of redox-cycled smectites were characterized using mediated electrochemical analysis. The resulting Fe2+/FeTotal ratios determined over a wide range of reduction potentials were analyzed using a process-based model to extract thermodynamic and kinetic descriptors of the interfacial electron transfer and subsequent charge redistribution processes that occur during the redox reaction. The fitted standard reduction potentials and apparent diffusion coefficients for charge redistribution were insensitive to TetFe content, indicating that thermodynamics and bulk charge transport within the smectite crystal are predominantly governed by the Fe-O-Fe networks in the octahedral sheet. Conversely, samples containing TetFe exhibited fitted interfacial electron-transfer rate constants approximately an order of magnitude higher than the TetFe-free sample. Comparison of these thermodynamic and kinetic descriptors between synthetic nontronites and natural reference smectites showed that parameter values converge within a narrow range across iron-rich dioctahedral smectites. These model-based results highlight the distinct roles of OctFe and TetFe in controlling smectite redox reactivity in subsurface environments, with OctFe governing the thermodynamics and TetFe primarily influencing interfacial electron-transfer kinetics.
Related
- The Effect of Redox Cycling on the Fate of Tetrahedral Iron in Smectites
- NH₄‐Smectites as Potential Precursors of Nitrogen Compounds Evolved During Analyses by the Sample Analysis at Mars (SAM) Instrument on the Curiosity Rover
- Structural and dynamical properties of hydrous magmatic liquids at high pressure: insights from Raman spectroscopy observations during diamond anvil cell experiments
- An accurate and efficient framework for modeling multimetal competitive adsorption on clay minerals
- Impact of S-metolachlor, atrazine and their metabolites on the morphological, structural and functional properties of the intestinal barrier
BibTeX
@article{pothanamkandathil2026redox,
title = {{Redox Properties of Structural Fe in Clay Minerals: 5. The Role of Fe in the Tetrahedral Sheets of Synthetic Smectites.}},
author = {Vineeth Pothanamkandathil and Fabien Baron and Anke Neumann and Jagannath Biswakarma and Michael Sander and Thomas B Hofstetter and Meret Aeppli},
journal = {Environmental science \& technology},
year = {2026},
month = oct,
doi = {10.1021/acs.est.6c07316},
url = {https://europepmc.org/article/MED/42916014},
note = {CC BY},
}
RIS
TY - JOUR
TI - Redox Properties of Structural Fe in Clay Minerals: 5. The Role of Fe in the Tetrahedral Sheets of Synthetic Smectites.
AU - Vineeth Pothanamkandathil
AU - Fabien Baron
AU - Anke Neumann
AU - Jagannath Biswakarma
AU - Michael Sander
AU - Thomas B Hofstetter
AU - Meret Aeppli
PY - 2026
DA - 2026/10/01
JO - Environmental science & technology
DO - 10.1021/acs.est.6c07316
UR - https://europepmc.org/article/MED/42916014
AB - Iron-bearing smectite clay minerals are important redox-active phases in soils and sediments. Yet, the influence of iron substitution in the tetrahedral sheets (TetFe) of smectites on their redox properties remains poorly understood. Here, we investigated the repeated reduction and re-oxidation of synthetic Fe-rich smectites, known as synthetic nontronites (SyN), with constant content of Fe in the octahedral sheet (OctFe) but variable initial content of TetFe. The redox properties of redox-cycled smectites were characterized using mediated electrochemical analysis. The resulting Fe2+/FeTotal ratios determined over a wide range of reduction potentials were analyzed using a process-based model to extract thermodynamic and kinetic descriptors of the interfacial electron transfer and subsequent charge redistribution processes that occur during the redox reaction. The fitted standard reduction potentials and apparent diffusion coefficients for charge redistribution were insensitive to TetFe content, indicating that thermodynamics and bulk charge transport within the smectite crystal are predominantly governed by the Fe-O-Fe networks in the octahedral sheet. Conversely, samples containing TetFe exhibited fitted interfacial electron-transfer rate constants approximately an order of magnitude higher than the TetFe-free sample. Comparison of these thermodynamic and kinetic descriptors between synthetic nontronites and natural reference smectites showed that parameter values converge within a narrow range across iron-rich dioctahedral smectites. These model-based results highlight the distinct roles of OctFe and TetFe in controlling smectite redox reactivity in subsurface environments, with OctFe governing the thermodynamics and TetFe primarily influencing interfacial electron-transfer kinetics.
SN - 0013-936X
SN - 1520-5851
ER -