Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article "Development of Magnetically Recoverable Multifunctional Hybrid Spheres Integrating Adsorption, Photocatalysis and Antimicrobial Activity for Water Sanitization" describes the obtaining, characterization, antibacterial and photocatalytic activities of a novel magnetic composite that can be used in water depollution. While the article shows promise, it requires major revisions before it can be considered for publication in this journal.

One generally cannot expect the same hypochlorite load to provide repeated antimicrobial action indefinitely. The system needs either replenishment/dosing or regeneration! This contradicts the reusability of this composite.

Explain why clean water has 0.16 A.U. and why was not used as a blank reference to have all spectra corrected. How clean is a “clean water” with such optical absorption? Why in section 3.6 authors use “corrected” data and in section 3.7 they use the experimental ones?

Some recent literature can be useful for comparison of results (doi: 10.3390/molecules30132879).

Authors should indicate which component is responsible for which action. As such the use of controls should be implemented to observe the individual activity and synergism (e.g. which is the improvement introduced by carbon particles? magnetite can also have some photocatalytic activity; hypochlorite + copper act synergic? Zeolite, carbon and alginate can adsorb cations from water etc)

The English language needs some polishing for style and typos (e.g. instead of “The spheres can be observed to exhibit an approximately spherical” use “The particles can be observed to exhibit an approximately spherical”; “transmission spectrum” is in fact UV-Vis spectrum recorded in transmission; “(0. 0.16 A. U.)” etc).

As authors used solar irradiation, they should indicate the exact day and time interval, as well as the geographical coordinates so any interested scientist be able to assess the conditions in follow up studies. On the other hand, the figures depict irradiation with an over-head lamp (in this case authors should correct the information and give the source power, distance from the baker etc). The methylene blue is a solid substance (row 173)! Therefore, the 0.05 mL most likely represent a solution of unknown concentration. Authors should indicate the exact concentration of the MB at the start of the experiment in the glass baker to allow comparison with previous literature results.

Authors should indicate how they assess the hardness of the water (content of calcium and magnesium ions). How was the reduction of iron ions determined?

Reusability tests have not been performed.

All Latin names should be italicized across the manuscript (e.g. bacterial strains row 293).

Author Response

Dear Editor and Reviewers.

 

We sincerely thank the reviewers for their constructive comments on our manuscript entitled “Development of Magnetically Recoverable Multifunctional Hybrid Spheres Integrating Adsorption, Photocatalysis and Antimicrobial Activity for Water Sanitization.” These comments were very valuable and helped us improve the quality of the paper. We have carefully considered each comment and revised the manuscript accordingly. All changes are highlighted in yellow in the revised version. The main revisions and our point-by-point responses to the reviewers’ comments are provided below:

 

Reviewer # 1

The article "Development of Magnetically Recoverable Multifunctional Hybrid Spheres Integrating Adsorption, Photocatalysis and Antimicrobial Activity for Water Sanitization" describes the obtaining, characterization, antibacterial and photocatalytic activities of a novel magnetic composite that can be used in water depollution. While the article shows promise, it requires major revisions before it can be considered for publication in this journal.

 

1. One generally cannot expect the same hypochlorite load to provide repeated antimicrobial action indefinitely. The system needs either replenishment/dosing or regeneration! This contradicts the reusability of this composite.

Answer: The reviewer is certainly correct; the section stating that the hypochlorite has a lifespan of up to 5 loads has been corrected—after that, the spheres must be re-impregnated.

 

2. Explain why clean water has 0.16 A.U. and why was not used as a blank reference to have all spectra corrected. How clean is a “clean water” with such optical absorption? Why in section 3.6 authors use “corrected” data and in section 3.7 they use the experimental ones?

Answer: Distilled water was used in the experiment, and its absorbance was measured, yielding a value of 0.16 A.U.; therefore, a correction was made in the calculation so that this initial value for the water would not affect the final results. Figure 9 was corrected using the corrected absorbance data (the same as in Section 6); although there is a change in the kinetic equation and in the R-squared value at this minimum, the kinetic behavior continues to follow that of a pseudo-first-order model.

 

3. Some recent literature can be useful for comparison of results (doi: 10.3390/molecules30132879).

Answer: Thank you very much for the recommendation; it was mentioned in the discussion section, and the manuscript was added to the references.

 

4. Authors should indicate which component is responsible for which action. As such the use of controls should be implemented to observe the individual activity and synergism (e.g. which is the improvement introduced by carbon particles? magnetite can also have some photocatalytic activity; hypochlorite + copper act synergic? Zeolite, carbon and alginate can adsorb cations from water etc)

Answer: We thank the reviewer for this valuable comment. We agree that identifying the individual contribution of each component and any synergistic effects would provide deeper mechanistic insight. However, the objective of this study was to develop and demonstrate the feasibility of an integrated multifunctional system in which all components are encapsulated within a single alginate matrix, rather than to isolate the contribution of each one. For this reason, control experiments with individual components were not performed. Actually, the description of Figure 2 and the figure itself explain the function of each of the components on the dial.

 

 

5. The English language needs some polishing for style and typos (e.g. instead of “The spheres can be observed to exhibit an approximately spherical” use “The particles can be observed to exhibit an approximately spherical”; “transmission spectrum” is in fact UV-Vis spectrum recorded in transmission; “(0. 0.16 A. U.)” etc).

Answer: The wording of the document was revised to make what was written clearer.

 

6. As authors used solar irradiation, they should indicate the exact day and time interval, as well as the geographical coordinates so any interested scientist be able to assess the conditions in follow up studies. On the other hand, the figures depict irradiation with an over-head lamp (in this case authors should correct the information and give the source power, distance from the baker etc). The methylene blue is a solid substance (row 173)! Therefore, the 0.05 mL most likely represent a solution of unknown concentration. Authors should indicate the exact concentration of the MB at the start of the experiment in the glass baker to allow comparison with previous literature results.

Answer: The dates and times of the tests, as well as the geographic location where they were conducted, were recorded in the experimental section. Methylene blue is a liquid, not a solid; however, the concentration used in each experiment was noted.

 

7. Authors should indicate how they assess the hardness of the water (content of calcium and magnesium ions). How was the reduction of iron ions determined?

Answer: The standard used to conduct these tests was recorded in the experimental section, and the references for the standards were added.

 

8. Reusability tests have not been performed.

Answer: Tests were conducted to evaluate the reusability of the spheres, yielding satisfactory results for up to 5 cycles of use; this is mentioned in the caption for Figure 2a.

 

9. All Latin names should be italicized across the manuscript (e.g. bacterial strains row 293).

Answer: All the Latin names were reviewed and corrected.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript reports the preparation and characterization of multifunctional hydrogel beads for water remediation.

It provides a contribution in the sector of water treatment, corroborating previous results reported in recent literature. In this regard, in order to take related previous works into proper account, I would suggest the authors to include the following references, which are papers that utilize very similar systems (alginate/chitosan magnetic or catalytic beads) for analogous applications:

-Environ. Sci.: Water Res. Technol. (2024) 10 (2): 551–564. https://doi.org/10.1039/d3ew00490b

-Water 2026, 18(17), 2078; https://doi.org/10.3390/w18172078

About the results, I would suggest addressing the following  major points:

-The experiments of the photocatalytic degradation of MB are not clear.  First, it is pretty strange to observe any absorbance of water in the visible range.

1. a) Is it possible that this signal is an effect of a residual contamination of MB? Otherwise, the origin of this absorbance should be explained, even though, looking at figure 8, it seems identical to that of MB.
2. b) What reference has been utilized to subtract the background of pure water?
3. c) What is the detection limit of the spectrophotometer?
4. d) Prior to proceed with photocatalysis, the adsorption of MB in dark should be evaluated, in order to precisely distinguish between pure adsorption and photocatalysis.
5. e) Details about the solar simulator setup and conditions of the photocatalytic experiments are missing.
6. f) Decolorization does not necessarily means degradation, or complete mineralization of MB. The process of degradation passes through the generation of several by-products, most of them are not coloured. I would suggest extending the range of acquisition to the UV range, in order to detect the presence of any possible byproducts.
7. g) One thing is not fully clear to me: Is MB added also to the solutions containing coliforms? If so, the role of MB in disinfection process should be considered, otherwise this part should be better clarified.

 

Author Response

Dear Editor and Reviewers.

 

We sincerely thank the reviewers for their constructive comments on our manuscript entitled “Development of Magnetically Recoverable Multifunctional Hybrid Spheres Integrating Adsorption, Photocatalysis and Antimicrobial Activity for Water Sanitization.” These comments were very valuable and helped us improve the quality of the paper. We have carefully considered each comment and revised the manuscript accordingly. All changes are highlighted in yellow in the revised version. The main revisions and our point-by-point responses to the reviewers’ comments are provided below:

 

Reviewer # 2

This manuscript reports the preparation and characterization of multifunctional hydrogel beads for water remediation.

It provides a contribution in the sector of water treatment, corroborating previous results reported in recent literature. In this regard, in order to take related previous works into proper account, I would suggest the authors to include the following references, which are papers that utilize very similar systems (alginate/chitosan magnetic or catalytic beads) for analogous applications:

 

-Environ. Sci.: Water Res. Technol. (2024) 10 (2): 551–564. https://doi.org/10.1039/d3ew00490b

 

-Water 2026, 18(17), 2078; https://doi.org/10.3390/w18172078

 

Thank you for the suggestion; both articles were included in the introduction section of the document.

 

About the results, I would suggest addressing the following major points:

 

1. -The experiments of the photocatalytic degradation of MB are not clear. First, it is pretty strange to observe any absorbance of water in the visible range.

Answer: Distilled water was used in the experiment, and its absorbance was measured, yielding a value of 0.16 A.U.; therefore, a correction was made in the calculation so that this initial value for the water would not affect the final results.

 

2. Is it possible that this signal is an effect of a residual contamination of MB? Otherwise, the origin of this absorbance should be explained, even though, looking at figure 8, it seems identical to that of MB.

Answer: We believe that this signal does not correspond to that of MB because, as previously mentioned, distilled water was used, and since its absorbance was measured as is, it likely corresponds to some other species present in the water. And it is precisely because of that initial value of 0.16 that the correction described in section 3.6 was made in order to rule out that initial absorbance value.

3. What reference has been utilized to subtract the background of pure water?

Answer: The initial absorbance value of pure water was used and corrected according to the procedure in Section 3.6 in order to compare the actual absorbance results.

 

4. What is the detection limit of the spectrophotometer?

Answer: The resolution data reported by the spectrophotometer manufacturer ranges from <0.5 nm to <9.0 nm and concentrations from <0.5 ppm to 10 000 ppm.

 

5. Prior to proceed with photocatalysis, the adsorption of MB in dark should be evaluated, in order to precisely distinguish between pure adsorption and photocatalysis.

Answer: We thank the reviewer for this important remark. A separate dark-adsorption experiment was not performed. However, prior to irradiation, the spheres were kept in contact with the MB solution in the dark for 1 h to allow the adsorption–desorption equilibrium to be established. Therefore, the removal attributed to photocatalysis excludes the MB uptake that occurred during this dark period. We have clarified this procedure in the Experimental section and acknowledged that quantifying dark adsorption separately would be valuable in future work.

 

6. Details about the solar simulator setup and conditions of the photocatalytic experiments are missing.

Answer: The experiments were performed under solar irradiation; in the experimental section major details of these experiments are included.

 

7. Decolorization does not necessarily means degradation, or complete mineralization of MB. The process of degradation passes through the generation of several by-products, most of them are not coloured. I would suggest extending the range of acquisition to the UV range, in order to detect the presence of any possible byproducts.

Answer: We greatly appreciate the suggestion and will implement it in future work. However, to test the effectiveness of the spheres, physicochemical tests were conducted, and the results are reported in Table 1.

 

8. One thing is not fully clear to me: Is MB added also to the solutions containing coliforms? If so, the role of MB in disinfection process should be considered, otherwise this part should be better clarified.

Answer: MB was not added to the solutions containing coliforms precisely in order to determine the effect of the spheres exclusively on coliforms. In any case, this clarification is provided in the experimental section and in section 3.7.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The article "Development of Magnetically Recoverable Multifunctional Hybrid Spheres Integrating Adsorption, Photocatalysis and Antimicrobial Activity for Water Sanitization" seems well-revised and now can be recommended for publication.

Author Response

Dear Editor and Reviewers.
We sincerely thank the reviewers for their careful evaluation of the manuscript and for their
valuable suggestions, which helped improve the quality of the article.

Reviewer # 1
The article "Development of Magnetically Recoverable Multifunctional Hybrid Spheres
Integrating Adsorption, Photocatalysis and Antimicrobial Activity for Water Sanitization"
seems well-revised and now can be recommended for publication.

Thanks you very much!

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed some of the key limitations, thus the manuscript can be published, even though the absorbance of distilled water would deserve further investigation. Please, let's highlight this point in the final version of the manuscript and specify that the products of degradation of MB have not been identified.

Author Response

Dear Editor and Reviewers.
We sincerely thank the reviewers for their careful evaluation of the manuscript and for their
valuable suggestions, which helped improve the quality of the article.

Reviewer # 2
Comments and Suggestions for Authors
The authors have addressed some of the key limitations, thus the manuscript can be
published, even though the absorbance of distilled water would deserve further investigation.
Please, let's highlight this point in the final version of the manuscript and specify that the
products of degradation of MB have not been identified.

Answer: We thank the reviewer for this valuable comment. We have addressed these points in the
revised manuscript by highlighting the need for further investigation into the absorbance of
distilled water and clarifying that the degradation products of methylene blue (MB) have not
been identified. All corresponding changes have been highlighted in yellow in the revised
manuscript for ease of reference.