The Influence of Mechanochemical Activation on the Properties of a Double Complex Salt [Co(NH3)6][Fe(CN)6] and Its Thermolysis Products
, Alexander M. Kalinkin 1, Vladimir Vinogradov 1, Diana Manukovskaya 1,*, Viktor Nikolaev 2, Vasilii Semushin 3 and Maria Teplonogova 4Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper describes mechanochemical activation of a double metal salt complex and the role of the activation on the thermolysis products. I really do not know what the point of the work is. This is never clear in the paper
This seems to be an expensive way to make FeCo. Is this the goal of the work? It seems to be the result of what they are doing. If this is the goal, then compare other ways to make FeCo and discuss relative costs.
Make sure to define MCA in the text at first use besides in the abstract.
Line 133. Remove proposed.
Lines 133-145. This needs to be rewritten. Move the sections on hydrogenation to earlier and only focus from lines 125 to 145 on what is in the current paper. It was not clear to me that the goal was to make intermetallic compounds.
The IR section 3.1.2 is not really readable. The IT intensities should be in parentheses. Change 2112st to 2112 (st) as an example.
They state FeIII-CN. They mean the CN stretch in the FeIII complex. They need to write it this way. I have no idea what is meant by the intensity of the FeII vibrations. What do the mean? The CN vibrations in the FeII complex? This makes no sense as written.
What do they mean by degrading in terms of the IR frequencies. The term degrading deformation makes no sense and is not correct spectroscopic nomenclature. Just write out the descriptions each time as theway they use the abbreviations does not make any sense. I think the authors are talking about the NH3 bends in the regions they are describing. Just state this.
They have the same p[problem with NH3 atoms sym def. They mean the symmetric NH3 bend or inversion. Again, clean up this entire section and do not use abbreviations for describing the vibrational modes. also, give references to the mode assignments. This is not done for the NH3 bending modes.
Explain what is happening on lines 237-245 in terms of NH2 modes. Have they lost a hydrogen? I am sure that there are other Metal-NH2 references other than the complex of a of a metal with hydrazine (ref 53) as this not what is being formed here.
What about elemental analysis of the cation? They need to do that if they can do the anion. Note that for the anion, only %C is given. What about the other elements?
If additional Fe is introduced during the milling process, I do not understand the point of the work then as they are changing the stoichiometry. What happens if different types of metals for the balls are used? Do they also introduce impurity metals? This has been a problem with ball milling going back decades.
If impurities are added and defects introduced, how does heating lead to more perfect crystals? This makes no sense as described.
Make figures 5, 6, 7 a table and add in the error bars. The figures are not really showing anything that could not be better put in a table with less space occupied.
Section 3.2.3 is not just about IR as it has many other analytical techniques here. Rewrite this section and add in new title as it is not just IR. What is the point of this section?
Figures 9 and 10 need error bars.
Section 3.2.4.1 should be titled sorption isotherms
Table 5. are the numbers good to the number of significant figures. Also, add error bars.
Figures 14 and 15 are too hard to read. They all look like a single color in many of them as the contrast with black is very low. This is especially true in Figure 15.
The authors never discuss the redox of FeIII to FeII in the paper and why it is important.
Why do they want to make FeCo? Why not write it as FeCo instead of Fe0.5Co0.5? They should be the same.
What is the point of the intermetallic carbon?
The authors never make it clear what the point of the work is.
Comments on the Quality of English Language
see review
Author Response
Reviewer 1.
This paper describes mechanochemical activation of a double metal salt complex and the role of the activation on the thermolysis products. I really do not know what the point of the work is. This is never clear in the paper
Answer
Dear reviewer! Thank you for your comments. We have tried to answer them all. We hope that now our main goal is more clear.
Reviewer 1.
This seems to be an expensive way to make FeCo. Is this the goal of the work? It seems to be the result of what they are doing. If this is the goal, then compare other ways to make FeCo and discuss relative costs.
Answer
We've added a topic related to Fischer-Tropsch synthesis to the Introduction in the relevance part. The introduction now has the following logics: intermetallic compounds are required for Fischer-Tropsch synthesis, and obtaining them from DCS is advantageous due to the synergy effect and environmental considerations (fewer harmful gases are emitted).
Reviewer 1.
Make sure to define MCA in the text at first use besides in the abstract.
Answer
Thank you, we have done this
Reviewer 1.
Line 133. Remove proposed.
Answer
Thank you for your attention, we have done what you asked.
Reviewer 1.
Lines 133-145. This needs to be rewritten. Move the sections on hydrogenation to earlier and only focus from lines 125 to 145 on what is in the current paper. It was not clear to me that the goal was to make intermetallic compounds.
Answer
We added information about the catalytic properties of CoFe at the very beginning of the Introduction. The lines mentioned by the reviewer contain important details that we didn't want to move to the beginning and disrupt the logic of the introduction's relevance.
Reviewer 1.
The IR section 3.1.2 is not really readable. The IT intensities should be in parentheses. Change 2112st to 2112 (st) as an example.
They state FeIII-CN. They mean the CN stretch in the FeIII complex. They need to write it this way. I have no idea what is meant by the intensity of the FeII vibrations. What do the mean? The CN vibrations in the FeII complex? This makes no sense as written.
Answer
Iron can have different oxidation states of +2 and +3. Depending on the oxidation state, the wave number shifts, and IR spectroscopy can unambiguously identify the oxidation state of iron in a complex with cyano groups [Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry, 6th ed.; John Wiley & Sons: Hoboken, New Jersey, USA, 2009; p. 484.]. FeIII-CN indicates that the spectrum contains a line with a wavelength of 2112 cm-1, which indicates Fe in the +3 oxidation state, bound to cyano groups. Similarly, FeII-CN: if the wavelength is 2043 cm-1, we assume that the compound contains Fe in the +2 oxidation state, bound to cyano groups. Since we realized from your comment that the designations were not the most appropriate, we decided to change them. In the text of the article, FeIII-CN has been replaced with Fe+3-CN and FeII-CN with Fe+2-CN.
In obtaining our results, we relied on well-known and long-standing data published in reliable sources.
|
DCS type |
Fe oxidation states |
Wavenumbers, cm-1 |
doi |
|
[Co(NH3)6]4[Fe(CN)6]3∙12H2O |
+2 |
2029s |
doi.org/10.1007/s10973-018-7647-3 |
|
[Co(dien)2]4[Fe(CN)6]3∙23H2O |
+2 |
2024s |
doi.org/10.1007/s10973-018-7647-3 |
|
[Co(NH3)6]4[Fe(CN)6]3∙12H2O |
+2 |
2029s |
doi.org/10.1007/s10973-018-7647-3 |
|
[Cо(Еn)3]4[Fe(CN)6]3 ⋅ 15H2O |
+2 |
2028 |
10.1134/S1070328412090060 |
|
[Co(NH3)6]4[Fe(CN)6]3 · 8 H2O |
+2 |
2050 |
doi.org/10.1007/s11173-005-0183-2 |
|
[Cо(Еn)3][Fe(CN)6] ⋅ 2H2O |
+3 |
2125, 2117, 2108 |
10.1134/S1070328412090060 |
|
[Ni(NH3)6]3[Fe(CN)6]2 |
+3 |
2169, 2095 |
doi:10.3390/nano10020389 |
|
[Cd(dien)2]3[Fe(CN)6]23H2O |
+3 |
2105 s |
doi.org/10.1016/j.poly.2021.115101 |
|
NH4[Bu4N][Cd(dien)2]2[Fe(CN)6]2 |
+3 |
2110 m 2102vs |
doi.org/10.1016/j.poly.2021.115101 |
|
[Co(en)3][Fe(CN)6]H2O |
+3 |
2116 |
doi:10.1186/1752-153X-7-28 |
|
[Rh(NH3)6][Fe(CN)6] |
+3 |
2114s |
doi.org/10.1134/S0036023624603684 |
Reviewer 1.
What do they mean by degrading in terms of the IR frequencies. The term degrading deformation makes no sense and is not correct spectroscopic nomenclature. Just write out the descriptions each time as theway they use the abbreviations does not make any sense. I think the authors are talking about the NH3 bends in the regions they are describing. Just state this.
Answer
The reviewer is correct; the term "def" has been replaced with "mode." The term "degrading deformation" has been removed from the article.
Reviewer 1.
They have the same problem with NH3 atoms sym def. They mean the symmetric NH3 bend or inversion. Again, clean up this entire section and do not use abbreviations for describing the vibrational modes. also, give references to the mode assignments. This is not done for the NH3 bending modes.
Answer
The term “inversion” was not used in the article at all. We discuss specifically symmetric and asymmetric vibrations. We attributed the lines according to [Nakagawa, I. Far infrared and Raman spectra of K3[Co(CN)6] and [Co(NH3)3][Co(CnN)6]. Bull. Chem. Soc. Jpn. 1973, 46(12), 3690–3693. https://doi.org/10.1246/bcsj.46.3690]. The reference is given in the text.
Reviewer 1.
Explain what is happening on lines 237-245 in terms of NH2 modes. Have they lost a hydrogen? I am sure that there are other Metal-NH2 references other than the complex of a of a metal with hydrazine (ref 53) as this not what is being formed here.
Answer
Thank you for your valuable comment. Since we cannot determine the precise state of coordinated ammonia within the scope of this study, and this was not the goal of the work, we have corrected the statement from "metal-NH2 complexes" to "NHx≤3." A detailed explanation with calculations is provided in the text of the article.
Reviewer 1.
What about elemental analysis of the cation? They need to do that if they can do the anion. Note that for the anion, only %C is given. What about the other elements?
Answer
We have updated the text of the article with a Table with additional elemental analysis data. These data confirm a decrease in nitrogen content in samples subjected to MCA.
Reviewer 1.
If additional Fe is introduced during the milling process, I do not understand the point of the work then as they are changing the stoichiometry. What happens if different types of metals for the balls are used? Do they also introduce impurity metals? This has been a problem with ball milling going back decades.
Answer
The rubbing concentration was less than 1 wt%. A smaller amount of the compound was also applied before the MCA. This detail is now reflected in the methodology.
Reviewer 1.
If impurities are added and defects introduced, how does heating lead to more perfect crystals? This makes no sense as described.
Answer
We don't monitor the internal mechanisms that occur when the temperature rises during MCA. Overall, the mill drum cools, but inserting a temperature probe inside the drum is not possible due to the mill's technical limitations.
Reviewer 1.
Make figures 5, 6, 7 a table and add in the error bars. The figures are not really showing anything that could not be better put in a table with less space occupied.
Answer
Figure 5-7 are made a table. The method error was general and it was 5%. The corresponding data was added to the Methods section.
Reviewer 1.
Section 3.2.3 is not just about IR as it has many other analytical techniques here. Rewrite this section and add in new title as it is not just IR. What is the point of this section?
Answer
The reviewer is correct, we mislabeled the section. It is now called 'Physical Analysis'.
Reviewer 1.
Figures 9 and 10 need error bars.
Answer
The figures contain such data that additional error bars would make the figure incomprehensible. However, the reviewer is correct; we've added instrumental error to the Methods section.
Reviewer 1.
Section 3.2.4.1 should be titled sorption isotherms
Answer
Indeed, this is a more precise heading.
Reviewer 1.
Table 5. are the numbers good to the number of significant figures. Also, add error bars.
Answer
We changed the incorrect value. The error in Table 5 corresponds to 5%, which we added to the Methods section in accordance with the previous comment.
Reviewer 1.
Figures 14 and 15 are too hard to read. They all look like a single color in many of them as the contrast with black is very low. This is especially true in Figure 15.
Answer
Unfortunately, this is a characteristic of the EDX method. Figure 14 shouldn't be any brighter. Perhaps the esteemed reviewer is confused by sections f and j in Figure 15. They should be dark; the absence of a signal (a distinct color) indicates the absence of these substances in the sample, and therefore the correct synthesis method.
Reviewer 1.
The authors never discuss the redox of FeIII to FeII in the paper and why it is important.
Answer
This is not the goal of our work; we still subsequently expose the iron to the oxidizing effects of atmospheric oxygen.
Reviewer 1.
Why do they want to make FeCo? Why not write it as FeCo instead of Fe0.5Co0.5? They should be the same.
Answer
We apologize; this point wasn't clearly highlighted in the article. At the very beginning of the introduction, we now demonstrate the difference between a solid solution and an intermetallic compound of Fe0.5Co0.5 composition. The reason for obtaining the intermetallic compound is also explained at the beginning of the introduction. Thank you for this comment.
Reviewer 1.
What is the point of the intermetallic carbon?
Answer
The purpose of this article is to find optimal conditions for intermetallic synthesis from DСS. To ensure the desired synthesis mechanism, annealing is performed in an oxygen-free atmosphere. In addition to FeCo, carbon nanotubes are synthesized. In this article, this is a byproduct of the intermetallic synthesis mechanism. The paper [S.I. Pechenyuk, D.P. Domonov, Yu.P. Semushina, N.S. Tsvetov, G.I. Kadyrova, A.T. Belyaevskii, Metal-carbon compositions as thermolysis products of complex compounds [Co(А)6]х[Fe(CN)6]у•nH2O (А = NH3, en/2), Thermochimica Acta,Volume 703,2021,179009, https://doi.org/10.1016/j.tca.2021.179009.] demonstrates that еhe specific surface area of the thermolysis products of DСS with nanotubes is 2-3 times greater than that of carbon-metal composites. The compositions are obtained by etching metals from the primary products of thermolysis. Therefore, it can be assumed that the presence of carbon nanotubes results in a higher specific surface area than without X-ray amorphous carbon. Specific surface area is highly important in catalysis.
Reviewer 1.
The authors never make it clear what the point of the work is.
Answer
We've updated our Introduction to more clearly demonstrate the relevance of producing intermetallic compounds using this method. We thank the reviewer for reading the article so carefully and spotting this shortcoming. We hope it has now been corrected.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis study investigated the effects of mechanical chemical activation (MCA) on the double complex salt precursor [Co(NH₃)₆][Fe(CN)₆] and its argon pyrolysis products using XRD, IR, STA, SEM-EDX, BET, and other techniques. Results indicate that MCA induces amorphization of the precursor structure, partial reduction of Fe(III) to Fe(II), altered ammonia coordination, and reduced thermal stability. After pyrolysis at 650°C, the intermetallic compound Co₀.₅Fe₀.₅ is formed, with MCA significantly regulating the product morphology: hollow carbon tubes without MCA, plate-like particles after 5 minutes of MCA, and whisker-covered agglomerates after 10 minutes of MCA.
- The introduction provides a broad overview of the research background on DCS. It is recommended to focus more specifically on why [Co(NH₃)₆][Fe(CN)₆] was selected as the subject of study and its specific application potential in CO/CO₂ hydrogenation.
- The abstract contains a duplicate instance of “mixed-valet species” and a suspected spelling error (should be “mixed-valence species”). Certain abbreviations (e.g., IIR) are not defined in the list of abbreviations. Reference formatting is inconsistent (e.g., some references lack page numbers or have non-standard DOI formats). These issues require unified correction.
- The article contains multiple instances of grammatical errors, awkward phrasing, and non-standard terminology. It is recommended that grammatical issues and expressions be thoroughly reviewed and revised.
- In the nitrogen adsorption-desorption experiments, the specific calculation method for the BJH pore size distribution and relevant parameters (e.g., the basis for selecting the desorption branch) were not provided. Furthermore, the correlation between the approximately 50 nm pore structure of sample MCA-10-650 and carbon nanotube spacing lacks direct characterization evidence (e.g., TEM images). Supplementary data supporting these claims is required.
- The catalytic performance of pyrolysis products was referenced solely from prior research data without validation using MCA-treated products from this study. It is recommended to supplement the study with catalytic activity testing of MCA-modified Co₀.₅Fe₀.₅ (e.g., CO/CO₂ hydrogenation reaction) to enhance the application-oriented focus of the research.
- In IR analysis, the reaction pathway for the reduction of Fe(III) to Fe(II) is only speculated to involve ammonia. This has not been further corroborated by elemental analysis or XPS data. Additional evidence regarding ammonia consumption or transformation is required to clarify the specific mechanism of the reduction reaction.
- Regarding the process by which MCA causes sample amorphization, the analysis is limited to describing changes in XRD peak intensity without quantifying the relationship between amorphization degree and MCA duration (e.g., through crystallinity calculations). It is recommended to supplement the study with relevant quantitative analyses to refine the understanding of structural evolution patterns.
- When discussing the reasons for the significant reduction in CSR size of pyrolysis products due to MCA, the analysis only mentions structural defects and energy accumulation without further elaboration based on literature or theoretical calculations. A deeper analysis of the underlying mechanism of this phenomenon is required.
- Some figures lack complete captions (e.g., Figures 11 and 12 do not clearly indicate corresponding captions), requiring standardized formatting to enhance readability.
Author Response
Reviewer 2
This study investigated the effects of mechanical chemical activation (MCA) on the double complex salt precursor [Co(NH₃)₆][Fe(CN)₆] and its argon pyrolysis products using XRD, IR, STA, SEM-EDX, BET, and other techniques. Results indicate that MCA induces amorphization of the precursor structure, partial reduction of Fe(III) to Fe(II), altered ammonia coordination, and reduced thermal stability. After pyrolysis at 650°C, the intermetallic compound Co₀.₅Fe₀.₅ is formed, with MCA significantly regulating the product morphology: hollow carbon tubes without MCA, plate-like particles after 5 minutes of MCA, and whisker-covered agglomerates after 10 minutes of MCA.
Answer
Dear reviewer, thank you for your kind words and comments. We have tried to answer all of them. Hope, now it looks better.
Reviewer 2
- The introduction provides a broad overview of the research background on DCS. It is recommended to focus more specifically on why [Co(NH₃)₆][Fe(CN)₆] was selected as the subject of study and its specific application potential in CO/CO₂ hydrogenation.
Answer
This compound has already been tested as a precursor for the production of catalysts for the CO/CO₂ hydrogenation reaction in [https://doi.org/10.3390/catal13121475 and https://doi.org/10.3390/molecules26133782]. To facilitate future scaling and progress to pilot-scale testing, the following requirements must be met. The synthesis of DCS and its precursors must be simple and high-yield. The precursors must be inexpensive and readily available. As previously emphasized, this article is largely exploratory. DCS has not previously been studied using MCA. Therefore, it is important to select a compound for which a large body of scientific research exists, allowing us to compare our results with published data. DCS [Co(NH₃)₆][Fe(CN)₆] satisfies all of the above requirements.
Reviewer 2
- The abstract contains a duplicate instance of “mixed-valet species” and a suspected spelling error (should be “mixed-valence species”). Certain abbreviations (e.g., IIR) are not defined in the list of abbreviations. Reference formatting is inconsistent (e.g., some references lack page numbers or have non-standard DOI formats). These issues require unified correction.
Answer
We have added additional information to refs. 15, 35,38,40,41.
Reviewer 2
- The article contains multiple instances of grammatical errors, awkward phrasing, and non-standard terminology. It is recommended that grammatical issues and expressions be thoroughly reviewed and revised.
Answer
We have made what is possible here.
Reviewer 2
- In the nitrogen adsorption-desorption experiments, the specific calculation method for the BJH pore size distribution and relevant parameters (e.g., the basis for selecting the desorption branch) were not provided. Furthermore, the correlation between the approximately 50 nm pore structure of sample MCA-10-650 and carbon nanotube spacing lacks direct characterization evidence (e.g., TEM images). Supplementary data supporting these claims is required.
Answer
Automated determination of the specific surface area of thermolysis products using the BET method was performed on a TriStar 3020 automated sorption unit manufactured by Micromeritics (USA). The volumetric version of the sorption method was used. The specific surface area is calculated using the low-temperature sorption isotherm of nitrogen vapor along the desorption branch, since desorption occurs at a higher temperature than adsorption. Therefore, the desorption peak is more symmetrical than the adsorption peak. Furthermore, the adsorption value at any relative pressure is always greater for the desorption branch than for the adsorption branch.
We are unable to provide TEM images since this is a rare and expensive analysis.
Reviewer 2
- The catalytic performance of pyrolysis products was referenced solely from prior research data without validation using MCA-treated products from this study. It is recommended to supplement the study with catalytic activity testing of MCA-modified Co₀.₅Fe₀.₅ (e.g., CO/CO₂ hydrogenation reaction) to enhance the application-oriented focus of the research.
Answer
We thank the esteemed reviewer for the valuable contribution to our work. Conducting just one of the catalytic experiments you recommended takes a week. Additional time is required for repeats to check reproducibility, to study the effect of catalyst activation in a flow of H2, and to calculate the chromatographic data. Therefore, unfortunately, it is not possible to supplement this article with catalytic experiments. We will definitely conduct these measurements later.
Reviewer 2
- In IR analysis, the reaction pathway for the reduction of Fe(III) to Fe(II) is only speculated to involve ammonia. This has not been further corroborated by elemental analysis or XPS data. Additional evidence regarding ammonia consumption or transformation is required to clarify the specific mechanism of the reduction reaction.
Answer
We've updated the text of the article with a table containing additional elemental analysis data. This data confirms a reduction in nitrogen levels in samples subjected to MCA.
Reviewer 2
- Regarding the process by which MCA causes sample amorphization, the analysis is limited to describing changes in XRD peak intensity without quantifying the relationship between amorphization degree and MCA duration (e.g., through crystallinity calculations). It is recommended to supplement the study with relevant quantitative analyses to refine the understanding of structural evolution patterns.
Answer
We used Segal's peak height determination method [https://doi.org/10.1039/D2CS00569G] and determined the degree of crystallinity (see table). The data confirm that amorphization occurs due to MCA.
|
MCA time, min |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
Degree of crystallinity, % 16° 2theta |
88,07 |
65,47 |
31,85 |
28,32 |
14,61 |
13,57 |
14,88 |
10,84 |
3,67 |
3,25 |
2,96 |
|
30° 2theta |
85,21 |
69,59 |
39,74 |
38,16 |
15,07 |
15,35 |
13,33 |
7,89 |
4,08 |
3,62 |
3,13 |
|
Average |
86,64 |
67,53 |
35,79 |
33,24 |
14,84 |
14,46 |
14,01 |
9,36 |
3,87 |
3,43 |
3,04 |
Reviewer 2
- When discussing the reasons for the significant reduction in CSR size of pyrolysis products due to MCA, the analysis only mentions structural defects and energy accumulation without further elaboration based on literature or theoretical calculations. A deeper analysis of the underlying mechanism of this phenomenon is required.
Answer
Structural defects and energy accumulation are the predominant factors. This work does not intend to provide a step-by-step study of the mechanism; rather, it is exploratory and exploratory in nature.
Reviewer 2
- Some figures lack complete captions (e.g., Figures 11 and 12 do not clearly indicate corresponding captions), requiring standardized formatting to enhance readability.
Answer
Thank you for your attention, the caption to Fig. 11 has been expanded.
Reviewer 3 Report
Comments and Suggestions for AuthorsThis work is a comprehensive investigation comparing the stability and decomposition properties of Co-Fe double salts with NH3 and CN ligands that are subjected to ball milling with different times (so varying input energies) to change precursor structure/composition/morphology that results in changes in decomposition properties and final metal alloy morphology. This work looks appropriate for the Thermo audience after some clarifications and data.
line 40 - typo mixed-valet
line 102 - MCA not defined so it is confusing to interpret how the method has advantages over DCS pyrolysis.
line 133 - this paper is not a "proposed study" as it is an actually performed or described study.
line 150 - how was the byproduct KCl removed from the synthesized DCS product?
line 155 - was air removed from the MCA experiment or could water and O2 be present during grinding? Is their an rpm value for the milling motion? How much heating is expected from the milling process (between the steel balls/walls and DCS powder)?
line 207 - I can see a new crystalline set of XRD peaks is present after 10 minutes (broad peaks but not amorphous (at ~17, 24, 35 degrees). Could this be an intermediate of nanoparticles of Fe/Co elements or oxides? A full view of the 10 minute product (XRD added to supporting info?) would be helpful.
line 219 - it is unclear what is meant by Fe(II) vs. Fe(III) vibrations - what are these ions connected to - are they Fe-CN vibrations? Can all peaks for the MCA-0 sample be assigned to DCS bonded atoms?
line 252 - the data for CHN would have been more informative than just the C analysis value.
From Figure 4 it is hard to see any peak shifts, especially ones where the 10 min one would have its peaks shift to lower angles (so higher lattice parameter). Of course, the shift is very small (<0.001 Angstrom). Also label each peak in one pattern in Fig. 4 with the (hkl) values for the standard pattern and identify that Co0.5Fe0.5 result in the figure caption.
line 323, 327 - typo = of the of
Figure 14, 15 - in addition to the qualitative elemental maps, is there any quantitative Co:Fe atomic ratio data for the 0, 5, 10 min samples?
Is there any know catalytic uses for the Co/Fe alloy (any literature on its uses) that could be described in the introduction?
Author Response
Reviewer 3
This work is a comprehensive investigation comparing the stability and decomposition properties of Co-Fe double salts with NH3 and CN ligands that are subjected to ball milling with different times (so varying input energies) to change precursor structure/composition/morphology that results in changes in decomposition properties and final metal alloy morphology. This work looks appropriate for the Thermo audience after some clarifications and data.
Answer
Dear Reviewer, We deeply appreciate your kindness and valuable comments. We have done our best to answer all your questions.
Reviewer 3
line 40 - typo mixed-valet
Answer
We have fixed the mistake, thank you for the comment
Reviewer 3
line 102 - MCA not defined so it is confusing to interpret how the method has advantages over DCS pyrolysis.
Answer
This article is exploratory and more detailed description of MCA simply will not add information essential to the essence of the article.
Reviewer 3
line 133 - this paper is not a "proposed study" as it is an actually performed or described study.
Answer
We have fixed the mistake, thank you for the comment
Reviewer 3
line 150 - how was the byproduct KCl removed from the synthesized DCS product?
Answer
After merging the cationic [Co(NH3)6]Cl3 and anionic K3[Fe(CN)6] complexes, the target [Co(NH3)6][Fe(CN)6] DCS precipitates, while KCl remains in the mother liquor. The DCS is filtered off under vacuum, and the wet residue is washed with ice-cold water until the silver nitrate reacts negatively with chloride ion. The DCS is then washed with ethanol. Thus, the presence of KCl in the DCS used for mechanochemical analysis and subsequent thermolysis is excluded. This is precisely what is confirmed by the uncolored figures 15 f and 15 j.
The corresponding methodological data are added to the Methods section.
Reviewer 3
line 155 - was air removed from the MCA experiment or could water and O2 be present during grinding? Is their an rpm value for the milling motion? How much heating is expected from the milling process (between the steel balls/walls and DCS powder)?
Answer
MCA is performed in air. Air removal is not included in the technical specifications. The rotation speed is 2220 rpm. We did not measure the temperature during the mechanical grinding process. However, in theory, due to water cooling of the outer part of the drums during MCA, the temperature inside the drums should not exceed 50-60°C [Milyukova I.V., Sobyanin S.V. THE SINTERING PROCESS LIMITS GRINDING QUARTZ POWDER IN A PLANETARY MILL AGO-2 WITH OPTIMAL ENERGOTENSION. Yugra State University Bulletin 2018, 14(4), 41-48. https://doi.org/10.17816/byusu20180441-48 (In Russian)].
Reviewer 3
line 207 - I can see a new crystalline set of XRD peaks is present after 10 minutes (broad peaks but not amorphous (at ~17, 24, 35 degrees). Could this be an intermediate of nanoparticles of Fe/Co elements or oxides? A full view of the 10 minute product (XRD added to supporting info?) would be helpful.
Answer
Even if some additional set of phases does form, this is unimportant to us. We are interested in the tendency toward amorphization due to MCA. We have added another calculation method and an additional table that describes the dependence of the degree of crystallinity of the samples on the MA time.
Reviewer 3
line 219 - it is unclear what is meant by Fe(II) vs. Fe(III) vibrations - what are these ions connected to - are they Fe-CN vibrations?
Answer
Iron can have different oxidation states of +2 and +3. Depending on the oxidation state, the wavenumber shifts, and IR spectroscopy can unambiguously identify the oxidation state of iron in a complex with cyano groups [Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry, 6th ed.; John Wiley & Sons: Hoboken, New Jersey, USA, 2009; p. 484.]. I.e. FeIII-CN means that the spectrum contains a line with a wavelength of 2112 cm-1, which indicates Fe with an oxidation state of +3, associated with cyano groups. Similarly, FeII-CN: if the wavelength is 2043 cm-1, then we consider that the compound contains Fe with an oxidation state of +2, associated with cyano groups. Since we realized from your comment that the designations chosen were not the most appropriate, we decided to change them. In the text of the article, we have replaced FeIII-CN with Fe+3-CN and FeII-CN with Fe+2-CN.
Reviewer 3
Can all peaks for the MCA-0 sample be assigned to DCS bonded atoms?
Answer
Yes, it's certainly possible. A full IR attribution of the original DCS has been added to the article.
Reviewer 3
line 252 - the data for CHN would have been more informative than just the C analysis value.
Answer
We fully agree with the esteemed reviewer. We conducted additional analyses and added a Table with the CHN results.
Reviewer 3
From Figure 4 it is hard to see any peak shifts, especially ones where the 10 min one would have its peaks shift to lower angles (so higher lattice parameter). Of course, the shift is very small (<0.001 Angstrom). Also label each peak in one pattern in Fig. 4 with the (hkl) values for the standard pattern and identify that Co0.5Fe0.5 result in the figure caption.
Answer
We have redrawn the Figure. The figure caption is widened.
Reviewer 3
line 323, 327 - typo = of the of
Answer
Since the figures with such caption are turned into the table, the comment is no more applicable.
Reviewer 3
Figure 14, 15 - in addition to the qualitative elemental maps, is there any quantitative Co:Fe atomic ratio data for the 0, 5, 10 min samples?
Answer
The presence of the Co0.5Fe0.5 phase is strictly determined by XRD data in accordance with PDF card 01-071-5029
Reviewer 3
Is there any know catalytic uses for the Co/Fe alloy (any literature on its uses) that could be described in the introduction?
Answer
Yes, there is. We apologize for not clearly stating that the primary goal of this work was to obtain a compound with promising catalytic properties, Co0.5Fe0.5. The introduction has been slightly expanded to address this shortcoming.
Reviewer 4 Report
Comments and Suggestions for AuthorsPlease check the attachment.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 4
For authors.
The paper is interesting, it deals about mechanochemical activation on the properties 2 of a double complex salt [Co(NH₃)₆][Fe(CN)₆]. The paper is mainly experimental and it is necessary to provide more interpretation of the figures.
Answer
Dear reviewer! We appreciate the time and effort dedicated to our work. We feel that the reviewer has paid a deep attention to our work and tried to answer all of the reviewers comment.
Reviewer 4
Page3,line 107.-“The MCA effectiveness of is due to both the acceleration”….please correct….””The MCA effectiveness is due to both the acceleration”
Answer
Thank you for the comment. We have fixed the mistake.
Reviewer 4
Page 4, line 145.-“products of its therolysis”. …..please correct….”products of its thermolysis.”
Answer
Thank you for the comment. We have fixed the mistake.
Reviewer 4
Page7, line 237.-“a band at 590w cm-1 appears, its intensity increases”…please correct….”a band at 590 cm-1 appears, its intensity increases”
Answer
w = weak, the designation ‘590w cm-1’ is correct.
Reviewer 4
Page8,In Table 3, please expain what is the meaning of T-extremum.
Answer
Mass loss is accompanied by thermal effects. For greater data clarity and ease of comparison, we processed Figure 3 and divided thermolysis into stages. Experiments have shown that the response on the DCS curve is somewhat delayed compared to the mass loss on the TG curve. Thus, the T-extremum is the temperature of the maximum or minimum thermal effect corresponding to each stage of mass loss. The corresponding explanation is added to the text.
Reviewer 4
Page 11, line In Legend of figure 7.-“CSR of the of thermolysis products in argon”…please correct….”CSR of the thermolysis products in argon”
Answer
The data from the Figure has turned into the Table.
Reviewer 4
Please provide more discussión about figures 5, 6and 7.Certainly there are texts explaining these figures, but some of them without justificationor references and it is not possible to relate the texts with the figures. For example “(Page 9, line 305) Intensive mechanical processing of precursors in a planetary mill leads not only to the chemical changes described above but also to the accumulation of excess energy in the form of various structural defects”. In which figure can we see this statement?
Answer
The data from these Figures has turned into the Table. This probably will make the data uinderstanding easier.
Reviewer 4
Page 12, What type of isoterms are reported in Figure 9?, type IV?, type II?
Answer
We believe that the pronounced hysteresis loops give us the right to classify the isotherms as type IV according to the Brunauer classification. The corresponding explanation is added to the text.
Reviewer 4
Page13,line367.-“confirming the results obtained when obtaining the hysteresis loop”….Please correct….”confirming the results obtained with the hysteresis loop”
Answer
Thank you for the comment. We have fixed the mistake.
Reviewer 4
Page14,line401.-“The SEM data confirm the data on the pore distribution “…please correct….”The SEM results confirm the data on the pore distribution”
Answer
Thank you for the comment. We have fixed the mistake.
Reviewer 4
Page 14, please provide more interpretation of figures 11 and 12.
Answer
The feel that data is not described enough could be caused by a difference in figure captions. We have changed this, maybe this way the data will be clearer.
Reviewer 4
Page 17, line450.-“We determined that 10 minutes of MCA is sufficient to obtain tubes of the same size as those obtained without MCA, but smaller. “….Please re-work this text, it is not clear….”tubes of the same size”….”but smaller”.
Answer
Thank you for the comment. We have fixed the mistake.
Reviewer 4
Please indicate what is new in this paper and what is the main contribution.
Answer
DCS of such a composition was subjected to the MCA first time ever. At least, we did not find any mention of such a pre-treatment. We have stated this in the Introduction part quite clearly.
Reviewer 4
What is the difference of the results obtained in this work, related with those obtained by other authors?
Answer
As long as we are the first to pre-treat DCS of such a composition with MCA, total comparison is impossible.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is improved. The authors need to provide a better comparison to other ways to make FeCo and how their material differs from other formulations. This will put their work into better context.
Author Response
Reviewer 1
The manuscript is improved. The authors need to provide a better comparison to other ways to make FeCo and how their material differs from other formulations. This will put their work into better context.
Answer:
Dear reviewer!
We are deeply grateful for your attention in reading our Manuscript. We have added a review of existing FeCo material studies to the Introduction section.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have revised their paper to address prior concerns, but a few minor clarifications remain.
line 51: do the authors mean to say "the study of DCS decomposition is a rapidly developing area"?
line 84: The Table 1 title is confusing as it says "Characteristics of carbon" but the products are presumably composites of carbon with CoFe? Or did the acid treatment remove most metal and so structures are mainly carbon?
line 179: I cannot figure out what the new added statement refers to "lining was carried out with a smaller amount of composition". What lining and what is composition? Sounds like some coating or pre-treatment was applied to the interior of the milling jars?
line 238: systematically instead of symbatically?
line 252: units for numbers in this table? Are these crystallite size measurements using XRD peak widths? If they are nanometers, one decimal place is sufficient.
It looks like the new Table 2 and later Table 5 are the same data?
line 387: in Table 8, the accuracy of the cubic lattice parameter values seems much too high for powder XRD. (errors in the 10,000ths of an Angstrom? - your data acquisition step size would be limiting here).
Author Response
Reviewer 3
The authors have revised their paper to address prior concerns, but a few minor clarifications remain.
Answer:
Dear reviewer!
You effort while reading our paper have helped us to improve the Manuscript text a lot, thank you for that. We have tried to answer all the questions.
Reviewer 3
line 51: do the authors mean to say "the study of DCS decomposition is a rapidly developing area"?
Answer:
We believe that the study of all the properties of DCS is a rapidly developing area of coordination chemistry. We present several such properties and support this with literature references: structures [4], magnetic properties [5, 6], biological activity, especially DCS with urea [7, 8], mixed-valence species [9], metal-to-metal charge transfer [10], and other interesting and useful properties [11-13].
Therefore, we are not only discussing the decomposition of DCS, but rather the study of DCS in the full diversity of their properties. Therefore, we believe that this proposal does not require modification.
Reviewer 3
line 84: The Table 1 title is confusing as it says "Characteristics of carbon" but the products are presumably composites of carbon with CoFe? Or did the acid treatment remove most metal and so structures are mainly carbon?
Answer:
We thank the reviewer for their valuable feedback. We have made changes to the text of the article and the table.
Reviewer 3
line 179: I cannot figure out what the new added statement refers to "lining was carried out with a smaller amount of composition". What lining and what is composition? Sounds like some coating or pre-treatment was applied to the interior of the milling jars?
Answer:
Lining here is the application of a thin layer of DCS to the grinding media and drum walls to prevent contamination of the DCS due to the self-abrasion of the drum and ball material during MCA. Lining was accomplished by grinding a small amount of DCS for 1 minute at 45-50 g.
Reviewer 3
line 238: systematically instead of symbatically?
Answer:
Dear reviewer, we meant the term "symbate." "Symbate change" is a phenomenon in which a change in parameter A leads to a corresponding change in parameter B. For example, an increase in the concentration of components leads to an increase in the reaction rate. In the case of our article, the decrease in nitrogen content with increasing mechanochemical activation time in samples MСA-0 (44.3 wt%) and MСA-5 (35.5 wt%) did not lead to a decrease in hydrogen content in MСA-0 (4.60 wt%) and MСA-5 (4.09 wt%). Therefore, the decrease in N and H content does not occur symbately.
Reviewer 3
line 252: units for numbers in this table? Are these crystallite size measurements using XRD peak widths? If they are nanometers, one decimal place is sufficient.
Answer:
Thank you for your comment. The degree of crystallinity is measured as a percentage. The corresponding notation has been added to the table. X-ray fluorescence data was used for these calculations, so the data in Table 4 has been rounded to one decimal place.
Reviewer 3
It looks like the new Table 2 and later Table 5 are the same data?
Answer:
We have removed section 3.1.4 because it is a copy of section 3.1.1. Tables have been renumbered.
Reviewer 3
line 387: in Table 8, the accuracy of the cubic lattice parameter values seems much too high for powder XRD. (errors in the 10,000ths of an Angstrom? - your data acquisition step size would be limiting here).
Answer:
We have removed the errors.
