Influence of the Physical Properties on the Antibacterial and Photocatalytic Behavior of Ag-Doped Indium Sulfide Film Deposited by Spray Pyrolysis

Round 1

Reviewer 1 Report

The paper deals with the peparation of Indium sulphide/Ag composite materials by spray pyrolysis and with the evaluation of their antibacterial and photocatalytic properties.

The paper is well written and organized, but the real advantage due to the Ag doping on indium sufide, in terms of photocatalytic and antibacterial properties, is not so clear. I recommended the authors to take into account the following observations and comments:

- Materials and methods: the authors should give more details about the prepration of Indium sulphide/Ag composites, as for example the Ag wt%. In ref [40] the authors reported the preparation of compounds with different Ag loadings, up to 8 wt%: are all these compounds used in the present paper? Otherwise, what compounds was used?

- XRD patterns and analysis: the authors compared the microstrain and the cristallite size of In₂S₃, taken from ref [40] and In₂S₃:Ag compound. Were the parameters of In₂S₃ and In₂S₃:Ag acquired in the same conditions and using the same models?

- Electrical properties: the authors should underlie the relationship between electrical properties of In₂S₃:Ag and its antibacterial and photocatalytic properties.

-Photocatalytic activity: the authors should report a kinetic study (absorbance of MB and relative concentration of MB, as a function of time), as generally done to evaluate the catalytic properties of a certain compound. The catalytic data reported are non sufficient to evaluate the photocatalytic properties of the two compounds. Moreover,  they reported that In₂S₃:Ag exhibited higher efficiency than undoped In₂S₃ (85.5 % vs. 80.0 %): this difference is not so high to talk about a significant improvement of the catalytic properties due to the presence of Ag.

-Antibacterial activity: what about the activity of undoped In₂S₃? The authors should report this information.

Author Response

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Reviewer 2 Report

The manuscript reports the characterization studies of an Ag doped indium sulphide film deposited by spray pyrolysis. The study is of practical significance and the data have been well performed and presented. The manuscript could be accepted for publication after revision, with the following concerns addressed:

• In my opinion the term “film” should be inserted in the title (an example of suggested title: “Influence of physical properties on antibacterial and photo-catalytic behavior of Ag doped indium sulphide film deposited by spray pyrolysis”).
• Abstract should contain some quantitative information also.
• To homogenize the text, in line 92, it would be more correct to write " In₂S₃:Ag and In₂S₃ un-doped films" instead of “In₂S₃:Ag samples”. It is suggested to correct also in the lines 296 and 297.
• AFM images of In₂S₃ un-doped film have been not shown. Roughness, morphology and surface area of both films should be compared. Please clarify this aspect.
• As reported in the paper “Effect of silver doping on structural and optical properties of In₂S₃ thin films fabricated by chemical pyrolysis” [REF: 40], the films have been prepared spraying 50 mL of solutions with opportune amount of indium chloride, thiourea and silver nitrate (0 or 0.0014 g). It is possible to hypothesize that the amount of In₂S₃ deposited respectively on the In₂S₃:Ag and In₂S₃ un-doped films could be different due to the presence of the silver. In order to estimate the role played by silver, it would be more appropriate to study the photocatalytic activity keeping constant the In₂S₃ amount.
• The antibacterial test have been performed on In₂S₃:Ag film. However, to demonstrate the antibacterial properties of silver, measurements on In₂S₃ un-doped film should also achieved. In additions, measurements in dark and under light irradiation should be compared to prove the ROS production.

Author Response

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Reviewer 3 Report

The authors present, “Influence of the physical properties on antibacterial and photo3 catalytic behavior of Ag doped indium sulphide deposited by spray pyrolysis”. The manuscript presents fair amount of electrochemical and photocatalytic data and explained well. However, there are lacking physiochemical proof of the materials. following revision should be made before acceptance.

1. Write the novelty of the work in detail.
2. The authors should explain the rational uses of spray pyrolysis techniques used for photocatalysis.
3. In the introduction part, the authors should include the detail of the effect of metal doping on the host materials. Following articles may help to understand in detail.

https://doi.org/10.1016/j.matlet.2020.127363 ,

4. The formula equation should be cited.
5. Update the Figure 1 a, providing the PDF card number.
6. The author should provide the sufficient morphology of the materials.
7. Surface area and porosity has significant impact on the performance of the materials. “The photocatalytic effect and the antibacterial activities are significantly reinforced by larger surface areas……………….”. what is the surface area of materials? the revised manuscript should be updated with the BET, BJH information.
8. Compare the photocatalytic and electric performance of the In₂S₃ based materials.
9. The influence of Ag nanoparticles on Transition metal oxide/sulfide should be integrate with the following manuscript.

https://doi.org/10.1016/j.est.2020.101693

10. What is the charge transfer resistance of materials?
11. Some similarities has been detected, check and correct before submission.

Author Response

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Reviewer 4 Report

This is a very interesting work that suits the Coatings journal. It is very extensive and comprehensive work as it applies different techniques, from structural, electrical to antibacterial investigations. Nowadays, the application of metal-oxides in photocatalysis is a hot-topic; and thus, this study is especially relevant. However, there are several major and minor issues within the manuscript that hinder my reading process. These issues prevent me from fully understanding the paper. Therefore, my major concerns are listed in the continuation of this text, and please use them during the revision process.

Major Issues:

First, the authors should show an AFM image of the pure In2S3 film (if possible). Second, Fig. 2b implies two size distributions with positions of maxima at 17 and 25  nm however, the authors used only one “Gaussian fit”? Third, please explain on which grounds did you apply the proposed EEC. Also, why did you put inductor (L1) in parallel with R1 and  CPE1? So please explain. On the other hand, If you had applied  L1(R1Cpe1)(R2Cpe2) EEC then, L1 could be easily assigned to the noise from the cables, contacts, etc. So, please elaborate. Fourth, please check Fig. 8 as it appears that O2 (instead of .O2-) is involved in the degradation of organic dye? Also, please denote oxide radical with .O2- (. means electron). Hydroxyl radical should be denoted by .OH (. means electron). Why did you show H20 to OH conversion (via h+) if you stated in the text that holes cannot convert H2O into .OH? Fig. 8 should clearly “illustrate” findings presented in lines 339-400! Fifth, the antibacterial section (3.4) is not entirely clear and the impact of Ag dopant on the antibacterial property is not completely explained. Can authors add additional results obtained with In2S3:Ag obtained in dark (Fig.9)? The experiment in the dark would show only the impact of the “antibacterial property of silver” (see line 370). Then these new data can be compared with data obtained with light. By comparing data obtained in the dark and light, the impact of Ag in In2S3:Ag can be easily deduced.

Minor Issues:

Line 15: The abbreviation In2S3:Ag is not clear. According to XRD pattern (Fig. 1), the doped sample is a solid solution; and thus, the abbreviation should be something like AgxIn2-xS3. Please clarify!  

Line 21: Can you write “Nyquist diagrams” instead of “the Nyquist diagrams”?

Lines 41-43: The authors should also list some of the composites that are frequently used in photocatalysis.

Lines 48-49: Instead of “varieties” use “forms”.

Line 50: Instead of “the most stable structure” write “the most stable form”. The same situation occurs in line 51.

Line 51: Use plural “performances”.

Line 55-57: Please support this statement with reference.

Line 61: For clarity can you rephrase to: “..electrical resistivity that has to be reduced for certain applications [32]”

Line 65:  Consider this: “leading to decrease of the electrical resistivity due to increase in the concentration of electric charge carriers”.

Line 68: Is the “concentration of Ag doping” determined in this work? If not, rephrase this sentence.

Line 80: Check typo: see unit for step size?

Line 91: Typo “10-5 M”?

Line 92: Clearly explain in which form were the samples.

Line 97: Typo “C_final”? See, Eq. (1).

Line 101: Typo in units  “126 oC”.

Line 129: Please consider this: The obtained data (Fig.1b) show a linear trend; and thus, they can be fitted by the Williamson-Hall equation…

Line 138: Can you show data for pure In2S3 in Fig.1b?

Line 156: This is redundant “for different frequencies”.

Line 203: Typo “τ_0”?

Line 220: Can you write “...Z’ values shift to small values...”?

Line 236: Provide the value of “characteristic relaxation time”.

Line 277: CPE is a capacitor for beta = 1, is  a resistor for beta = 0, and is an inductor for beta = -1. So, please clarify this in the text.

Line 305:  “=” is missing.

Line 331: Explanation of Fig. 8 is not clear. You mean “Photocatalytic mechanism of In2S3:Ag”?

Lines 345-346: Consider this :”Both the color and the spectra of the solutions reveal that the incubation period induced different changes in the three solutions”.

If the aforementioned issues are clarified,  I will read the revised manuscript's version again.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors fulfilled the reviewers' requests and I consider the manuscript suitable for publication. I consider this paper the starting point for a more exhaustive evaluation of the real potentialities of this compound from an applicative point of view. I recommend the authors to submit in the future these information.

Reviewer 3 Report

The authors has revised the manuscript properly. It can now be published in MDPI coating.