| SEM-EDS structural formula | Na₀.₃₈[Fe³⁺₁.₉₁Al₀.₀₉][Si₃.₆₂Al₀.₃₈]O₁₀(OH)₂; octahedral Fe 25 wt. %; tetrahedral Fe 0 wt. %; total Fe 25 wt. % |
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| ICP-OES, 20 g L⁻¹ clay | Al 8.42 × 10⁻⁴ mol L⁻¹; Fe 3.40 × 10⁻³ mol L⁻¹; Na 3.19 × 10⁻³ mol L⁻¹; Si 7.34 × 10⁻³ mol L⁻¹ |
| Mediated electrochemical reduction, as synthesized, Nernst–Frumkin fit | Tetrahedral Fe 0.00 mol per half-unit cell; E∅H −0.198 V vs. SHE; σ(E∅H) 0.095 V; g∅ 5.69; g∅ range 5.32 to 9.69; r² 0.89 |
| Mediated electrochemical reduction and oxidation, redox manipulated, process-based fit | Residual tetrahedral Fe 0.00 atoms per half-unit cell; initial Fe²⁺s/FeTotal 2 % for the reduction curve and 93 % for the oxidation curve; E⁰H 0.171 ± 0.046 V vs. SHE at pH 7.5; log(k⁰/cm s⁻¹) −10.09 ± 0.10; log(D/cm² s⁻¹) −11.61 ± 0.05; α 0.57 ± 0.08; g 12.12 ± 1.97; r² 0.98 |
Vineeth Pothanamkandathil, Fabien Baron, Anke Neumann, Jagannath Biswakarma, Michael Sander, Thomas B. Hofstetter, Meret Aeppli. “Redox properties of structural Fe in clay minerals: 5. the role of Fe in the tetrahedral sheet of synthetic smectites.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15003018/v2
Values presented only in mediated-electrochemical, SEM-EDS, or ICP-OES plots or images were not transcribed
| Mediated electrochemical reduction, as synthesized, Nernst–Frumkin fit | Tetrahedral Fe 0.38 mol per half-unit cell; E∅H −0.197 V vs. SHE; σ(E∅H) 0.075 V; g∅ 4.75; g∅ range 0.75 to 6.16; r² 0.97 |
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| SEM-EDS structural formula | Na₀.₆₄[Fe³⁺₂][Si₃.₃₆Fe³⁺₀.₆₄]O₁₀(OH)₂; octahedral Fe 25 wt. %; tetrahedral Fe 8 wt. %; total Fe 33 wt. % |
|---|---|
| ICP-OES, 20 g L⁻¹ clay | Fe 6.85 × 10⁻³ mol L⁻¹; Na 6.28 × 10⁻³ mol L⁻¹; Si 1.37 × 10⁻² mol L⁻¹; Fe content 12.6 at. % |
| Mediated electrochemical reduction, as synthesized, Nernst–Frumkin fit | Tetrahedral Fe 0.60 mol per half-unit cell; E∅H −0.197 V vs. SHE; σ(E∅H) 0.073 V; g∅ 3.35; g∅ range 3.15 to 7.35; r² 0.88 |
| Mediated electrochemical reduction and oxidation, redox manipulated, process-based fit | Residual tetrahedral Fe 0.07 ± 0.01 atoms per half-unit cell; initial Fe²⁺s/FeTotal 1 % for the reduction curve and 98 % for the oxidation curve; E⁰H 0.054 ± 0.020 V vs. SHE at pH 7.5; log(k⁰/cm s⁻¹) −9.49 ± 0.05; log(D/cm² s⁻¹) −11.47 ± 0.02; α 0.65 ± 0.04; g 11.69 ± 0.88; r² 0.98 |
| SEM-EDS structural formula | Na₁.₀₃[Fe³⁺₂][Si₂.₉₇Fe³⁺₁.₀₃]O₁₀(OH)₂; octahedral Fe 24 wt. %; tetrahedral Fe 12 wt. %; total Fe 36 wt. % |
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| ICP-OES, 20 g L⁻¹ clay | Fe 6.94 × 10⁻³ mol L⁻¹; Na 3.93 × 10⁻³ mol L⁻¹; Si 8.37 × 10⁻³ mol L⁻¹; Fe content 13.5 at. % |
| Mediated electrochemical reduction, as synthesized, Nernst–Frumkin fit | Tetrahedral Fe 1.04 mol per half-unit cell; E∅H −0.173 V vs. SHE; σ(E∅H) 0.078 V; g∅ 3.11; g∅ range −0.89 to 4.20; r² 0.99 |
| Mediated electrochemical reduction and oxidation, redox manipulated, process-based fit | Residual tetrahedral Fe 0.24 ± 0.03 atoms per half-unit cell; initial Fe²⁺s/FeTotal 1 % for the reduction curve and 97 % for the oxidation curve; E⁰H 0.110 ± 0.022 V vs. SHE at pH 7.5; log(k⁰/cm s⁻¹) −9.12 ± 0.12; log(D/cm² s⁻¹) −11.63 ± 0.04; α 0.47 ± 0.05; g 6.23 ± 1.18; r² 0.99 |
| SEM-EDS structural formula | Na₁.₀₆[Fe³⁺₂][Si₂.₉₄Fe³⁺₁.₀₆]O₁₀(OH)₂; octahedral Fe 24 wt. %; tetrahedral Fe 13 wt. %; total Fe 37 wt. % |
|---|---|
| ICP-OES, 20 g L⁻¹ clay | Fe 8.00 × 10⁻³ mol L⁻¹; Na 3.90 × 10⁻³ mol L⁻¹; Si 1.17 × 10⁻² mol L⁻¹; Fe content 14.3 at. % |
| Mediated electrochemical reduction, as synthesized, Nernst–Frumkin fit | Tetrahedral Fe 1.09 mol per half-unit cell; E∅H −0.169 V vs. SHE; σ(E∅H) 0.078 V; g∅ 2.81; g∅ range −1.19 to 3.74; r² 0.98 |
| Mediated electrochemical reduction and oxidation, redox manipulated, process-based fit | Residual tetrahedral Fe 0.12 ± 0.06 atoms per half-unit cell; initial Fe²⁺s/FeTotal 1 % for the reduction curve and 99 % for the oxidation curve; E⁰H 0.086 ± 0.016 V vs. SHE at pH 7.5; log(k⁰/cm s⁻¹) −9.28 ± 0.07; log(D/cm² s⁻¹) −11.67 ± 0.05; α 0.56 ± 0.04; g 8.05 ± 0.74; r² 0.99 |