Simultaneous Electrochemical Generation of Ferrate and Oxygen Radicals to Blue BR Dye Degradation

Round 1

Reviewer 1 Report

In this article an innovative combination of electro-oxidation with ferrate ions [Fe(VI)] were tested to synthetic effluent.

The process is innovative but method is trivial and tested thousand times before.

Current density is high.

Line 39 to 46: improve more on your statement by adding more reference. As you use not real but synthetic effluent better to focus on process not effluent. Better to remove

Line 47 to 54: develop more on the process.

Line 78 to 81: remove the redundancy

As cell is so small, how did you do kinetics test.

Remove the equation 1

Why using HClO4 as it also oxidant

Better to combine figure 2, 3 and 4 into one figure (a), (b) and (c).

Separate the result of two electrode in figure 5, as it is difficult to understand. Or mention only rate of oxidation and put figure in supplementary files.

Mention the rate of oxidation.

Direct oxidation can be also occurred.

Remove figure 6 and instead show the oxidation rate in chart figure.

Show K1 value in 1/h

Be more critical not only explain your result use some references to compare your results.

Line 238 to 246: try to show the mechanism in a figure, especially for graphical abstract.

There are no error bar in figure 8 and 9.

Author Response

The process is innovative but method is trivial and tested thousand times before.

Current density is high.

The currents that were used for this work were based on preliminary studies and reports from the literature (https://doi.org/10.1002/cjce.23142).

 

Line 39 to 46: improve more on your statement by adding more reference. As you use not real but synthetic effluent better to focus on process not effluent. Better to remove

The following information was added:

An alternative known since the 1970s is Ferrate(VI) ion, formula FeO₄^2-, where the oxidation state +6 of iron makes it a very strong oxidizer chemically green (1–4)

Ferrate (VI) is one of the most stable oxidizing species in aqueous medium known, especially at alkaline and neutral pH. However, it is important to emphasize that its highest oxidizing power is in an acidic medium, and less oxidant in alkaline pH (reaction 1 and 2).(2,5)

             E° = +2.20 V vs. SHE             (1)

     E° = +0.72 V vs. SHE             (2)

Ferrate anions can exist in various oxidation states: [FeO₄]^2- with Fe (VI), [FeO₄]^3- with Fe (V) or [FeO₄]^4- with Fe (IV)(6). However, Fe(VI) is the most stable form in which it is used industrially. Ferrate (VI) has unique chemical properties such as:

1. High redox potential, with the ability to oxidize harmful organic and inorganic species such as nitrosamines, phenol, nitrilotriacetic acid, hydrazine, thiourea, sulfides, cyanide, thioacetamide, ammonia, thiocyanate, soluble oils, as well as viruses and bacteria.(3,6–9)
2. A bifunctional ability to act as an oxidizing and coagulating agent, due to the simultaneous release of ferric ions (Fe(III)), specifically under neutral or alkaline conditions.(10–12)
3. It has a higher redox potential than other oxidizing agents commonly used for the treatment of water such as chlorine (1.358 V SHE), hydrogen peroxide (1.776 V vs. SHE) and ozone (2.076 V vs. SHE)(13), its use prevents the formation of carcinogenic by-products (mainly trihalomethanes).
4. Generates non-toxic reduction by-products such as Fe (III) and Fe (II), which can even be used for other purposes.
5. Ferrate can also be used for biofouling control and for the removal of other contaminants such as metals, nonmetals, and radionuclides.(14–16)

 

References

1. Sharma VK. Potassium ferrate(VI): Properties and applications. ACS Div Environ Chem Prepr [Internet]. 2000;40(1):131–2. Available from: https://www.scopus.com/inward/record.uri?eid=2-s2.0-0347014037&partnerID=40&md5=c048377e018bf00ac50e473b478f1452
2. H. Wood R. The Heat, Free Energy and Entropy of the Ferrate(VI) Ion. J Am Chem Soc. 2002 May 1;80(9):2038–41.
3. Denvir A, Pletcher D. Electrochemical generation of ferrate Part I: Dissolution of an iron wool bed anode. J Appl Electrochem [Internet]. 1996;26(8):815–22. Available from: https://doi.org/10.1007/BF00683743
4. Mácová Z, Bouzek K, Híveš J, Sharma VK, Terryn RJ, Baum JC. Research progress in the electrochemical synthesis of ferrate(VI). Electrochim Acta [Internet]. 2009;54(10):2673–83. Available from: http://www.sciencedirect.com/science/article/pii/S0013468608013182
5. Ibanez JG, Tellez-Giron M, Alvarez D, Garcia-Pintor E. Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 6: Microscale Production of Ferrate. J Chem Educ [Internet]. 2004 Feb 1;81(2):251. Available from: https://doi.org/10.1021/ed081p251
6. Sharma VK, Kazama F, Jiangyong H, Ray AK. Ferrates (iron(VI) and iron(V)): Environmentally friendly oxidants and disinfectants. J Water Health [Internet]. 2005 Mar 1;3(1):45–58. Available from: https://doi.org/10.2166/wh.2005.0005
7. Sharma VK, Burnett CR, O’Connor DB. Ferrate(VI) and ferrate(V) oxidation of thiocyanate. In: ACS Division of Environmental Chemistry, Preprints [Internet]. 2000. p. 600–1. Available from: https://www.scopus.com/inward/record.uri?eid=2-s2.0-0347645686&partnerID=40&md5=2b16aad210caaf15f48deeb32a81396a
8. Sharma VK, Rivera W, Joshi VN, Millero FJ, O’Connor D. Ferrate(VI) Oxidation of Thiourea. Environ Sci Technol [Internet]. 1999 Aug 1;33(15):2645–50. Available from: https://doi.org/10.1021/es981083a
9. Lescuras-Darrou V, Lapicque F, Valentin G. Electrochemical ferrate generation for waste water treatment using cast irons with high silicon contents. J Appl Electrochem [Internet]. 2002;32(1):57–63. Available from: https://doi.org/10.1023/A:1014269523898
10. Jiang JQ. Advances in the development and application of ferrate(VI) for water and wastewater treatment. J Chem Technol Biotechnol. 2014;89(2):165–77.
11. Alsheyab M, Jiang J-Q, Stanford C. On-line production of ferrate with an electrochemical method and its potential application for wastewater treatment – A review. J Environ Manage [Internet]. 2009;90(3):1350–6. Available from: http://www.sciencedirect.com/science/article/pii/S0301479708002831
12. Sharma VK. Potassium ferrate(VI): an environmentally friendly oxidant. Adv Environ Res [Internet]. 2002;6(2):143–56. Available from: http://www.sciencedirect.com/science/article/pii/S1093019101001198
13. Jiang J-Q, Lloyd B. Progress in the development and use of ferrate(VI) salt as an oxidant and coagulant for water and wastewater treatment. Water Res [Internet]. 2002;36(6):1397–408. Available from: http://www.sciencedirect.com/science/article/pii/S004313540100358X
14. Talaiekhozani A, Talaei MR, Rezania S. An overview on production and application of ferrate (VI) for chemical oxidation, coagulation and disinfection of water and wastewater. J Environ Chem Eng [Internet]. 2017;5(2):1828–42. Available from: http://www.sciencedirect.com/science/article/pii/S2213343717301161
15. Potts ME, Churchwell DR. Removal of Radionuclides in Wastewaters Utilizing Potassium ferrate(VI). Water Environ Res [Internet]. 1994;66(2):107–9. Available from: www.jstor.org/stable/25164670
16. Liu J, Zhang Z, Liu Z, Zhang X. Integration of ferrate (VI) pretreatment and ceramic membrane reactor for membrane fouling mitigation in reclaimed water treatment. J Memb Sci [Internet]. 2018;552:315–25. Available from: http://www.sciencedirect.com/science/article/pii/S0376738817335251

 

Line 47 to 54: develop more on the process.

The answer is above

Line 78 to 81: remove the redundancy

It was removed.

As cell is so small, how did you do kinetics test.

 

Remove the equation 1

It was removed

Why using HClO4 as it also oxidant

 

Better to combine figure 2, 3 and 4 into one figure (a), (b) and (c).

For a better comprehension just figure 3 and 4 were combined

Separate the result of two electrode in figure 5, as it is difficult to understand. Or mention only rate of oxidation and put figure in supplementary files.

The figure was separated

Mention the rate of oxidation.

it was included in manuscript

Direct oxidation can be also occurred.

Yes, it was included in manuscript

Remove figure 6 and instead show the oxidation rate in chart figure.

The oxidation rate was included

Show K1 value in 1/h

Be more critical not only explain your result use some references to compare your results.

it was included suggestion in manuscript

Line 238 to 246: try to show the mechanism in a figure, especially for graphical abstract.

it was included graphical abstract for both cases in manuscript

There are no error bar in figure 8 and 9.

The error was amended

Author Response File: Author Response.pdf

Reviewer 2 Report

The subject is interesting, although improvements are needed. Please see specific comments below:

1) Introduction is poor and should be expanded.

2) The novelty of this work should be given in details

3) Fig. 2, 3 and 4 should be combined.

4) Figs 5, 6 and 7.

5) Figs 8 and 9 should be combined.

6) Discussion is limited and should be expanded.

7) Conclusion should not only repeat the results

Author Response

1) Introduction is poor and should be expanded.

The introduction has been expanded

2) The novelty of this work should be given in details

The novelty was included in the manuscript

3) Fig. 2, 3 and 4 should be combined.

For a better comprehension just figure 3 and 4 were combined

The recommendation has been included

4) Figs 5, 6 and 7.

The recommendation has been included

5) Figs 8 and 9 should be combined.

The recommendation has been included

6) Discussion is limited and should be expanded.

The discussion was expanded

7) Conclusion should not only repeat the

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

 

 This study combines electro-oxidation by BDD and in situ generation of ferrate ions for removal of color in conventional BBR dye (BBR) effluent, which seems interesting and innovative. The processes are well optimized.

• Introduction is well developed.
• Analysis should be better explained in a separate part
• Explain the procedure of synthetic solution
• Combine figure 1, 2, 3 and 4
• Compare your results with literature in part 3.1
• In Figure 5, you have to report concentration of dye by figuring out the relation between adsorption and dye concentration; furthermore, kinetic constant of dye should be reported.
• Discussion is very weak
• Should not report the same thing in figure inside the text

Author Response

Processes 756069

Simultaneous Electrochemical Generation of Ferrate and Oxygen Radicals and their application for Blue BR Dye Degradation.

Dear reviewer, thank you for the time that you spend reviewing our manuscript, we appreciate all your comments and observations.

This study combines electro-oxidation by BDD and in situ generation of ferrate ions for removal of color in conventional BBR dye (BBR) effluent, which seems interesting and innovative. The processes are well optimized.

• Introduction is well developed.

Thank you for your comment, we really work hard to improve it.

• Analysis should be better explained in a separate part

Thanks for your recommendation, however we consider that in the current form the manuscript is divided into the appropriate sections to explain each of the procedures analyzed, so no changes will be made.

• Explain the procedure of synthetic solution

We add the follow paragraph Line 110-113: The BBR dye (chemical formula = C32H28N2Na2O8S2, molecular weight = 678.68 g/mol, and max = 695 nm), was used in this study. An accurately weighed quantity of the dye was dissolved in distilled water to prepare the stock solution (100 mg L-1). Experimental solutions of desired concentration (50 mg L-1) were obtained by successive dilution.

Combine figure 1, 2, 3 and 4

Thanks for your comment, the reason why it is not feasible to combine Figures 1 to 4 is because there are deep differences, Figures 1 and 2 correspond to the study of VC in an HCLO4 medium and Figures 3 and 4 in a solution From Na2SO4, as you know, the potentials of each medium are very different, so, the scales change drastically, so, it is not possible to carry out a combination of figures.

• Compare your results with literature in part 3.1

References 33 and 34 are works related to this research, so a comparison is not necessary.

• In Figure 5, you have to report concentration of dye by figuring out the relation between adsorption and dye concentration; furthermore, kinetic constant of dye should be reported.
• Discussion is very weak
• Should not report the same thing in figure inside the text

To improve the discussion on this figure, the following information was added:

Lines 121.123: For the different parameters tested, the kinetics approach of the combined electrochemical degradation of BBR dye was determined by a pseudo-first order model, Ln(A₀/A_t)=kt, where A₀ is the initial absorbance, A_t is the absorbance after degradation time t, and k is the apparent rate constant.

 

Lines 199-205: From this study, pseudo-first-order kinetics was calculated as described above. In the case of HClO₄ medium the following results were obtained, (▲) 0.0038, (▲) 0.0045, (▲) 0.0086 min^-1, respectively. For Na₂SO₄ supporting electrolyte, the following values were obtained, (¿) 0.0043, (¿) 0.0161, (¿) 0.0293 min^-1, respectively. For all the experimental fittings using the pseudo-first order kinetics model, the minimum R² value obtained was 0.99, suggesting that kinetics model describes the chemical process fairly good. As shown, the k-values found for Na₂SO₄ were about 3.5 times higher than those observed when HClO₄ was used as supporting electrolyte.

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript has been improved

Author Response

Dear reviewer, thank you very much for considering that the improvements to our work were sufficient to consider its publication. We appreciate the time you spent on the review.