Formation of FeS and its effect on the electrode reactions of the Fe(II)/Fe system in thiocyanate solutions at mercury electrodes

Winkler, Krzysztof; Krogulec, Tadeusz; Galus, Zb́igniew

doi:10.1016/0013-4686(85)80172-9

Cited by 18 publications

(8 citation statements)

References 15 publications

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“…while in accordance with the literature the C3/A3 peak pair can be assigned to the reversible electrochemical exchange reaction with Hg [14][15][16][17][18]:…”

Section: Resultssupporting

confidence: 86%

Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Ciglenečki

Bura-Nakić

Marguš

2011

J Solid State Electrochem

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Cyclic voltammetry on the Hg electrode was used to investigate the electrochemical behavior of NaCl/NaHCO 3 electrolyte solutions supersaturated with respect to Zn sulfide phases. The voltammetric results clearly show how an Hg electrode, due to exchange between Hg 2+ from an HgS adlayer and Zn 2+ from solution, becomes the site for surface ZnS adlayer formation in the potential range −0.45 to −0.6 V. The exchange reaction is reversible, and the surface-formed ZnS adlayer persists at the Hg electrode surface until −1.3 V during cathodic scans. Near −1.3 V, it is reduced. In the same solution, evidence for reduction of bulk Zn sulfide species including nanoparticles was not obtained. The approach emphasized here can be readily extended to any other system consisting of metal electrode and chalcogenide anions, pointing to the importance of choosing experimental conditions (i.e., deposition potential, stirring, and accumulation times) to avoid artifacts and wrong interpretation of data due to surface formation of metal sulfide species.

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“…while in accordance with the literature the C3/A3 peak pair can be assigned to the reversible electrochemical exchange reaction with Hg [14][15][16][17][18]:…”

Section: Resultssupporting

confidence: 86%

Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Ciglenečki

Bura-Nakić

Marguš

2011

J Solid State Electrochem

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“…It would be likely that the energies of Fe(II) reduction on FeS and Fe(0) would be different, so there should be a shift in reduction potential. This possibility is consistent with Winklers statement [19] that peaks A1 1 and A1 2 in Figure 1 are due to the oxidation of iron deposited on the surface that was completely and partly covered by FeS, pointing at a similar cathodic process. We believe that both peaks represent oxidation of Fe(II) deposited on the FeS surface since the sum of A1 1 and A1 2 charges (not shown) is proportional to the concentration of free Fe(II).…”

Section: C1 Doubletssupporting

confidence: 91%

“…The peaks A1 1 and A1 2 are due to the oxidation of iron deposited on the surface that was completely and partly covered by FeS [19].…”

Section: Resultsmentioning

confidence: 99%

Characterization of Iron Sulfide Species in Model Solutions by Cyclic Voltammetry. Revisiting an Old Problem

Bura-Nakić¹,

Krznarić²,

Helz³

et al. 2011

Electroanalysis

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A long-standing problem associated with voltammetric determination of iron and sulfide in reduced natural waters has been the nature of the presumed analyte responsible for a reduction peak at À1.1 V vs. Ag/AgCl. Cyclic voltammetry at the Hg electrode is used here to study solutions with different Fe(II) to sulfide ratios in chloride and acetate electrolytes (pH 6-7). The results indicate that the À1.1 V peak can be assigned to reduction of Fe 2 + or its labile complexes on FeS layers that partially cover the Hg electrode. Hg electrodes covered with FeS act like FeS solid electrodes over a very wide potential range (À0.35 to À1.9 V). Two mechanisms for forming FeS layers on Hg are described. Over the broadest deposition potential range, the dominant mechanism involves attachment at the Hg surface of FeS nanoparticles, which are generated quickly in initially supersaturated mixtures of Fe(II) and S(-II). In a narrow deposition potential range, roughly À0.56 to À0.70, FeS layers are produced additionally by replacement of preformed HgS. Because Fe 2 + is reduced at À1.1 V on FeS layers and at À1.4 V on bare Hg, it may be underdetermined when only the À1.4 V peak is measured.

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“…Here, we offer a completely new interpretation of the peak at −1.1 V, ,, which has some similarities to that of Davison et al who attributed the peak at −1.1 V (our C1) to surface species. Although we have discussed FeS electrochemical behavior in the previous papers, ,, the explanation of the most important reactions presented in Table is stated here in brief: The C1 peak arises from the reduction of Fe(II) or its labile complexes on the Hg electrode modified by a FeS layer. ,− Fe(0) deposited at the C1 peak potential is oxidized in reverse scan at the A1 peak. ,− The C3/A3 peak couple corresponds to the electrochemical transformation of FeS to HgS. ,− It is important to notice that the A3 peak can only be recorded in solutions of Fe(II) and S(-II), which are initially supersaturated with respect to mackinawite (FeS mw ) (i.e. at concentrations of iron and sulfide that satisfied K s for mackinawite). ,,,, Therefore, the A3 peak shown here was used as an indication (ultimately measure) of the presence of FeS NPs. , We already showed that experimental conditions (i.e.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical and Colorimetric Measurements Show the Dominant Role of FeS in a Permanently Anoxic Lake

Bura-Nakić

Viollier

Ciglenečki

2012

Environ. Sci. Technol.

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Recent publications have shown that the anodic reaction between FeS and Hg can be used for electrochemical detection of colloidal and particulate FeS in natural waters. Anodic waves that were recorded around -0.45 V (vs Ag/AgCl) in model solutions correspond to the electrochemical transformation of nanoparticulate FeS to HgS. Here, as a further step, the proposed approach is tested on anoxic, sulfidic, and iron-rich samples of a meromictic freshwater lake (Lake Pavin, France). Based on new and more comprehensive work on FeS electrochemistry in model and anoxic Lake Pavin samples, a new interpretation is given for previously recorded voltammetric signals in sulfide and iron rich environment, usually designated FeS(aq), and its role in controlling solubility of different FeS phases. A comparison of the depth profiles of S(-II) measured by voltammetry and the methylene blue method showed that the majority of S(-II) is in the form of FeS. In the monimolimnion layer, thermodynamic calculations based on total Fe(II) and S(-II) concentration, measured by ferrozine and the methylene blue method, predict precipitation of FeS with log K(s) values between -3.6 and -3.8, very close to mackinawite's K(s) value. In the upper part of the same layer, precipitation of greigite is predicted. It is shown that modification of a Hg electrode by surface-formed FeS has a significant influence on voltammetric Fe(II) determination, since reduction of Fe(II) under such conditions occurs both on bare (-1.4 V) and on FeS modified Hg surfaces (-1.1 V); Fe(II) may be underdetermined when only the -1.4 V peak is measured.

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Formation of FeS and its effect on the electrode reactions of the Fe(II)/Fe system in thiocyanate solutions at mercury electrodes

Cited by 18 publications

References 15 publications

Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Characterization of Iron Sulfide Species in Model Solutions by Cyclic Voltammetry. Revisiting an Old Problem

Electrochemical and Colorimetric Measurements Show the Dominant Role of FeS in a Permanently Anoxic Lake

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