Mixed Metal Oxide Derived from Polyoxometalate-Based Metal–Organic Framework as a Bi-Functional Heterogeneous Catalyst for Wastewater Treatment
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe present work deals with Mixed metal oxide derived from polyoxometalate-based metal-organic framework as a bi-functional heterogeneous catalyst for wastewater treatment. Although the current work contains some interesting results, there are some points that must be noted before it is accepted for publication in this prestigious journal.
1. From the reviewer's point of view, it is better to start before section (2. Results and discussion) with the experiment part (3. Experimental).
2. There is mention to Fig. S2 in the manuscript. The authors stated, “the measured and simulated XRD patterns of CuMoV were compared to confirm the successful synthesis of CuMoV”, the Rietveld refinement figures should be added with all fitting parameters to confirm the singularity of the crystal phase. How can a compound be judged to be a single phase when it contains six other different compounds? Please explain more. Both XRD of CuMoV and CuMoV(450) must also be added so that the comparison is clear.
3. The unit of transmittance of FTIR should be added to the graph.
4. Also, Fig. S2, Fig. S3, Fig. S4, Table S1 were missing from the manuscript. (There may be a supplementary file missing that contains these shapes and table).
5. Absorbance should not have [a.u.] unit because it is dimensionless. Why were the MB degradation rates of CuMoV less than CuMoV(450)?
6. In figure (5-b), the logarithmic dependence does not correspond to a linear fit. This aspect needs further analysis, discussion, and explanation.
7. The authors mentioned in the experimental section that the BET measurement and fluorescence analysis were used, but there were no specific results related to them within the manuscript.
8.
Comments on the Quality of English LanguageThe English could be improved to more clearly express the research.
Author Response
Reviewer #1
The present work deals with Mixed metal oxide derived from polyoxometalate-based metal-organic framework as a bi-functional heterogeneous catalyst for wastewater treatment. Although the current work contains some interesting results, there are some points that must be noted before it is accepted for publication in this prestigious journal.
Comment 1: From the reviewer's point of view, it is better to start before section (2. Results and discussion) with the experiment part (3. Experimental).
Response: I agree with your opinion, but “Results and discussion” coming before “Experimental” is the format requirement of the journal.
Comment 2: There is mention to Fig. S2 in the manuscript. The authors stated, “the measured and simulated XRD patterns of CuMoV were compared to confirm the successful synthesis of CuMoV”, the Rietveld refinement figures should be added with all fitting parameters to confirm the singularity of the crystal phase. How can a compound be judged to be a single phase when it contains six other different compounds? Please explain more. Both XRD of CuMoV and CuMoV(450) must also be added so that the comparison is clear.
Response: Fig. S2 was provided in the supporting information while not in the manuscript.
CuMoV was synthesized as single crystals and was the parent compound of CuMoV(450), and CuMoV(450) was a mixed oxide with six compositions.
The XRD spectrum of the synthesized CuMoV was highly consistent with the spectrum fitted based on single crystal data, proving CuMoV was single crystal.
We have added both the XRD of CuMoV and CuMoV(450) according to your suggestion.
Comment 3: The unit of transmittance of FTIR should be added to the graph.
Response: The unit was added at the moment.
Comment 4: Also, Fig. S2, Fig. S3, Fig. S4, Table S1 were missing from the manuscript. (There may be a supplementary file missing that contains these shapes and table).
Response: They are in the supporting information.
Comment 5: Absorbance should not have [a.u.] unit because it is dimensionless. Why were the MB degradation rates of CuMoV less than CuMoV(450)?
Response: We have deleted the absorbance unit.
The structural difference caused the different MB degradation rates. Mo existed as Mo6+ in CuMoV, and as Mo6+ and Mo5+ in CuMoV(450). Mo5+ could enhance the production of •O2- which could degrade MB.
Comment 6: In figure (5-b), the logarithmic dependence does not correspond to a linear fit. This aspect needs further analysis, discussion, and explanation.
Response: The final fitting correlation coefficient R2 reached 0.955, indicating the linear fit was acceptable. Such result was mainly caused by the different sampling intervals. We explained this in the text.
Comment 7: The authors mentioned in the experimental section that the BET measurement and fluorescence analysis were used, but there were no specific results related to them within the manuscript.
Response: We are sorry for the mistake and have corrected it.
Comment 8: The English could be improved to more clearly express the research.
Response: We have tried our best to improve the English expressions.
Reviewer 2 Report
Comments and Suggestions for AuthorsA very complicate metal oxide catalyst described in this manuscript is found to be extremely effective for the wastewater purification from both methylene blue (MB) and Cr IV. Idea of this study is justified well. The catalyst preparation and investigation is described in detail. Mechanism of MB degradation on this catalyst is studied and corresponding kinetic scheme is introduced. The authors applied the fruitful idea of adding various radical sources in order to check the mechanism of MB degradation and to use HPLC-MS method in order to found an order of MB structure transformation under degradation conditions.
However, there are several comments:
- The catalyst is very complicate. In reality, CuMoV(450) consists of number of oxides, molybdates, vanadates and phosphates. Thus, interpretation of XRD and FT-IR data is under discussion. The only one fact is clear that only inorganic part of the sample exists after 450 oC of treatment (see Fig. 2).
- Fig. 3. As follows from SEM micrograph, the catalyst consists of microblocks due to MOF structure used as support. What means the appearance of dark spots on the block surface? If the authors use the porous starting material, it is important to clearly show the morphological changes of support after 450 oC of treatment. The specific surface area and porosity both are likely to be important for the wastewater purification.
- From Line 233. Reaction scheme. The catalyst contains many elements with variable valence. What is the role of these elements?
- Fig. 9b. Why the authors choose the FT-IR to prove the catalyst stability?
- Line 299. To give the name of reagent company.
- References: DOI is necessary to introduce to each of reference.
7. Reference [26]: Year 2017. https://doi.org/10.1016/j.jallcom.2016.08.118
Author Response
Reviewer #2
A very complicate metal oxide catalyst described in this manuscript is found to be extremely effective for the wastewater purification from both methylene blue (MB) and Cr IV. Idea of this study is justified well. The catalyst preparation and investigation is described in detail. Mechanism of MB degradation on this catalyst is studied and corresponding kinetic scheme is introduced. The authors applied the fruitful idea of adding various radical sources in order to check the mechanism of MB degradation and to use HPLC-MS method in order to found an order of MB structure transformation under degradation conditions. However, there are several comments:
Comment 1: The catalyst is very complicate. In reality, CuMoV(450) consists of number of oxides, molybdates, vanadates and phosphates. Thus, interpretation of XRD and FT-IR data is under discussion. The only one fact is clear that only inorganic part of the sample exists after 450 oC of treatment (see Fig. 2).
Response: The XRD results confirmed that the Keggin sub-unit was disappeared and CuMoV(450) was composed of six components. The combination of XRD and FT-IR data could confirm the composition of CuMoV(450).
Comment 2: Fig. 3. As follows from SEM micrograph, the catalyst consists of microblocks due to MOF structure used as support. What means the appearance of dark spots on the block surface? If the authors use the porous starting material, it is important to clearly show the morphological changes of support after 450 oC of treatment. The specific surface area and porosity both are likely to be important for the wastewater purification.
Response: The dark spots on the block surface of CuMoV(450) was caused by the loss of organic ligands of CuMoV. The parent CuMoV was a pure compound, there was no support for the synthesis of CuMoV(450). The purpose of calcination was only to remove the organic composition and obtain mixed oxides.
Comment 3: From Line 233. Reaction scheme. The catalyst contains many elements with variable valence. What is the role of these elements?
Response: The variable valences of Mo and V elements were useful to initiate the redox cycles and generate free radicals •O2- to degrade MB.
Comment 4: Fig. 9b. Why the authors choose the FT-IR to prove the catalyst stability?
Response: FT-IR can be used for fingerprint detection and is also one of the commonly used characterization methods for catalyst stability.
Comment 5: Line 299. To give the name of reagent company.
Response: We have given the name of reagent company.
Comment 6: References: DOI is necessary to introduce to each of reference.
Response: We have added the DOI of each reference.
Comment 7: Reference [26]: Year 2017. https://doi.org/10.1016/j.jallcom.2016.08.118
Response: It has been corrected.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe presented paper is interesting and well organized. There is some points that have to be clarified before publishing. Please, see the comments below:
1. Bearing in mind the presented results, Fig. 2 has to be focused in the Finger print region, only, as the authors did not comment the vibrations in above 1600 cm-1.
2. Why the authors have commented the TG results but they did not show these results in a separate figure?
3. More details concerning the used conditions for the XRD analysis have to be provided.
4. What is the particles size measured by XRD? It has to be pointed out.
5. The particles size estimated by XRD and SEM analyses must be compared in the paper.
6. On p. 11, section 3.3 Chemical analyses, the authors stated usage of UV-Vis analysis. Such Figure and results were not presented in all over the paper. It has to be removed if such analysis is not performed. This part has to be revised.
7. The same section, it has been mentioned BET measurements - the same problem, such data were not provided.
8. The manuscript text must be improved, there are repetition of words and many typos, which have to be corrected.
Comments on the Quality of English LanguageEnglish is satisfied.
Author Response
Reviewer #3
The presented paper is interesting and well organized. There is some points that have to be clarified before publishing. Please, see the comments below:
Comment 1: Bearing in mind the presented results, Fig. 2 has to be focused in the Finger print region, only, as the authors did not comment the vibrations in above 1600 cm-1.
Response: The paper was focused on the study of CuMoV(450) which did not contain the Keggin unit as CuMoV did, and the peaks of the Keggin unit were appeared in finger print region.
Comment 2: Why the authors have commented the TG results but they did not show these results in a separate figure?
Response: The TG results were given in the supporting information.
Comment 3: More details concerning the used conditions for the XRD analysis have to be provided.
Response: The used conditions for the XRD analysis was provided in the revised version.
Comment 4 : What is the particles size measured by XRD? It has to be pointed out.
Response: We calculated the particles size using the Scherrer formula based on the XRD data, and the result obtained (23 nm) was 23 times of the SEM result (1 nm). CuMoV (450) was a block shaped material with a size around 1 mm, while the Scherrer formula is applicable to spherical samples with a size range below 100 nm, so it is not suitable to accurately calculate the particle size of CuMoV (450) using the Scherrer formula. The photo of CuMoV (450) was shown below.
The photo of CuMoV (450).
Comment 5: The particles size estimated by XRD and SEM analyses must be compared in the paper.
Response: In our case, the particle size estimated by XRD was unreasonable, and the SEM results were relatively accurate. So, it is not necessary to compare the two data.
Comment 6: On p. 11, section 3.3 Chemical analyses, the authors stated usage of UV-Vis analysis. Such Figure and results were not presented in all over the paper. It has to be removed if such analysis is not performed. This part has to be revised.
Response: UV-Vis analysis was used to monitor the MB degradation and Cr(VI) reduction processes. We have revised.
Comment 7: The same section, it has been mentioned BET measurements - the same problem, such data were not provided.
Response: We are sorry for the error and have corrected it.
Comment 8: The manuscript text must be improved, there are repetition of words and many typos, which have to be corrected.
Response: We have tried our best to improve the manuscript text.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have modified and changed everything that was required to make the research acceptable for publication in this prestigious journal.
Comments on the Quality of English LanguageEnglish is acceptable in its current state.
Author Response
Reviewer #1
Comment 1: The authors have modified and changed everything that was required to make the research acceptable for publication in this prestigious journal.
Response: Thanks for your attention.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe Figures are not well resolved. They have to be improved.
Comments on the Quality of English LanguageEnglish is OK.
Author Response
Reviewer #3
Comment 1: The Figures are not well resolved. They have to be improved.
Response: We have revised the Figures for the improvement.
