Redox potential measurements and Mössbauer spectrometry of FeII adsorbed onto FeIII (oxyhydr)oxides
Redox potential measurements and Mössbauer spectrometry of FeII adsorbed onto FeIII (oxyhydr)oxides
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DOI：
10.1016/j.gca.2005.06.013
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发表时间：
2005-10
影响因子：
5
通讯作者：
E. Silvester;L. Charlet;C. Tournassat;A. Géhin;J. Greneche;E. Liger
中科院分区：
文献类型：
--
作者：
E. Silvester;L. Charlet;C. Tournassat;A. Géhin;J. Greneche;E. Liger
The redox properties of FeIIadsorbed onto a series of FeIII(oxyhydr)oxides (goethite, lepidocrocite, nano-sized ferric oxide hydrate (nano-FOH), and hydrous ferric oxide (HFO)) have been investigated by rest potential measurements at a platinum electrode, as a function of pH (−log10[H+]) and surface coverage. Using the constant capacitance surface complexation model to describe FeIIadsorption onto these substrates, theoretical values of the suspension redox potential (EH) have been computed, under the assumption that FeIIadsorption occurs at crystal growth sites of the substrate surface. Good agreement between calculated and experimental EHvalues is observed for nano-FOH and HFO, however the redox potentials measured for lepidocrocite and goethite are significantly more oxidizing than predicted. Mössbauer spectroscopic analysis of57FeIIadsorbed onto HFO and goethite shows that in both cases the adsorbed57FeIIis incorporated into the crystal structure of the substrate, in broad agreement with the thermodynamic model, but is almost completely oxidized to57FeIII. The mechanism by which the adsorbed57FeIIis oxidized is not resolved in this work, but is thought to be due to electron transfer to the substrate, rather than a net oxidation of the suspension. The disagreement between experimental and calculated rest potential measurements in the goethite and lepidocrocite systems is thought to be due to the poor electrochemical equilibration of these suspensions with the platinum electrode, rather than a failure of the thermodynamic model. The model developed for the redox potential of adsorbed FeIIallows direct assessment of the reactivity of this species towards oxidized pollutants.
