Electrophoretic Deposition and Characteristics of Chitosan–Nanosilver Composite Coatings on a Nanotubular TiO₂ Layer

Round 1

Reviewer 1 Report

The authors described various characteristics of Chitosan/nanosilver coatings. However, their conclusion on the advantages of surface-active compound are not well understood from the experiments. The paper could be accepted with following revisions

1) From Figure 2B and 2C, we cannot conclude uniform dispersion of Ag nanoparticles. Rather, what’s observed here is the agglomeration of Ag. Repeat these experiments by modifying different parameters during electrophoretic deposition. 2) You can provide images from different areas in order to accurately support your conclusion from Figure 5 and 6. There is barely any improvement in the dispersion of Ag nanoparticles in specimens A and B. Both images reflect only agglomerations of Ag nanoparticles. Cannot conclude from the images whether Polysorbate 20 does indeed play a significant role.  3) a) Mention the (hkl) plane for individual spectrum in Fig 7. b) Both TiO₂ and Ag have bands at 38 deg. Hence, we cannot conclude nanosilver layer formations from Fig 7. The band at 44 deg is still barely visible in specimen A, but not in B and C. This particular region should be enlarged in order to conclude the presence of nanosilver. c) Provide description for the different peaks present above 50 deg. d) The description in lines 285-293 is confusing. Unable to compare relative intensities, as no scale is available in the spectra Fig 7. e) Typo at line 285: change ‘nit’ to ‘not’.  4) There are several conclusions drawn on the effectiveness of a surface-active agent, Polysorbate 20. However, the authors should compare the results with a minimum of two more surface-active agents to reach an agreeable conclusion. 5) The introduction is too long and often suffers extended sentences. Too many applications have been described and this can well be narrowed down. Suggestion is to be concise and use connective words like ‘for example’, ‘additionally’ etc.  Provide a small introduction on surface dispersing agents, since that’s the major highlight of this paper. 6) Line 122-123: Change the sentence “after oxidation,the..applied” to “After oxidation, the specimens were rinsed with distilled water and dried in air at ambient temperature for 24 h”.

Author Response

Response to Reviewer 1 Comments

On behalf of all the authors, I would like to thank you for the review.

All the comments and introduced changes are presented below.

 

1) From Figure 2B and 2C, we cannot conclude uniform dispersion of Ag nanoparticles. Rather, what’s observed here is the agglomeration of Ag. Repeat these experiments by modifying different parameters during electrophoretic deposition.

Authors' response: We agree with this point. New SEM measurements with different magnifications were made. The presented results clearly indicate the influence of the use of dispersant. New photos, also with higher magnifications, were included in the manuscript in place of older ones.

 

2) You can provide images from different areas to accurately support your conclusion from Figure 5 and 6. There is barely any improvement in the dispersion of Ag nanoparticles in specimens A and B. Both images reflect only agglomerations of Ag nanoparticles. Cannot conclude from the images whether Polysorbate 20 does indeed play a significant role.

Authors` response: We agree with this point. New SEM measurements were made with elements identification. The presented results indicate that the use of the dispersant, with the same value of electrophoretic deposition, results in the formation of much smaller nanoAg agglomerates. The new figure has been put into the manuscript.

 

3)

7. a) Mention the (hkl) plane for individual spectrum in Fig 7.

Authors` response: A description for both titanium and oxide phases has been added.

 

7. b) Both TiO2 and Ag have bands at 38 deg. Hence, we cannot conclude nanosilver layer formations from Fig 7. The band at 44 deg is still barely visible in specimen A, but not in B and C. This particular region should be enlarged in order to conclude the presence of nanosilver.

Authors` response: The authors agree that in the case of nanoparticles, it is hard to conclude about their presence solely based on XRD. In the case of nanostructures, the relative intensity is low, especially in this case, while we use a low concentration of Ag on crystalline support. The discussion was clarified.

 

1. c) Provide description for the different peaks present above 50 deg.

Authors response: The low-intensity peaks can be associated with metal support alloy. The appropriate explanation was introduced into the manuscript.

 

7. d) The description in lines 285-293 is confusing. Unable to compare relative intensities, as no scale is available in the spectra Fig 7.

Authors` response: All diffractograms are normalized. The description was added to the text, and the mentioned sentence was clarified.

 

1. e) Typo at line 285: change ‘nit’ to ‘not’.

Authors` response: Change has been made.

 

4) There are several conclusions drawn on the effectiveness of a surface-active agent, Polysorbate 20. However, the authors should compare the results with a minimum of two more surface-active agents to reach an agreeable conclusion.

Authors response: The authors thank you for your comment. We agree with this point. A comparison of Polysorbate 20 with other dispersants used was added to the manuscript. In the future, the authors plan to use other dispersants used in the research, but unfortunately, the short time for reviewing the manuscript does not allow further tests to be carried out, and only to place the comparison in the theoretical field based on literature studies.

 

5) The introduction is too long and often suffers extended sentences. Too many applications have been described and this can well be narrowed down. Suggestion is to be concise and use connective words like ‘for example’, ‘additionally’ etc. Provide a small introduction on surface dispersing agents, since that’s the major highlight of this paper.

Authors response: We agree with this point, and changes have been made. The introduction has been shortened, and a small introduction about surface dispersing agents has been provided.

 

6) Line 122-123: Change the sentence “after oxidation,the..applied” to “After oxidation, the specimens were rinsed with distilled water and dried in air at ambient temperature for 24 h”.

Authors response: We agree with this point, and change has been made.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors of the manuscript ‘Electrophoretic deposition and Characteristics of Chitosan/Nonosilver composite coating on the nanotubular TiO₂ Layer’ presents the deposition of chitosan/nanosilver onto a TiO₂ layer. They have characterized the composite coatings in terms of its microstructure, morphology, thickness, wettability, and its nanomechanical properties.

In my opinion, the presented manuscript could be considered for publication after some major revision according to the comments presented below:

The authors in the introduction present many examples of the different studies regarding Chitosan and silver composites. It would nice if they could shorten the introduction and present more clearly the novelty of their work.

In line 109 and 119 the authors should define what Sa and DC is respectively.

In figure 2 the authors present SEM images of the different coatings. Do the authors have higher magnification images that will enable the observation of the size of silver nanoparticles?

In figure 7 the authors present the XRD of the composite coatings.  They mention that a board peak at 15-25^o is observed for the specimens A, B, and C assigned to Chitosan. However, in the XRD diffractogram is not obvious the presence of this peak even for specimen C that contains a higher amount of CS. Can the authors identify the peaks in the XRD diffractogram? Where the XRD peaks of crystalline TiO₂ are expected to be observed? Are they overlapped with the peaks of Ti13Zr13Nb? The peak at 38^o assigned to silver nanoparticles is not very clearly observed while the peak at 44^o assigned to silver nanoparticles is overlapped with the peaks of Ti13Zr13Nb. Can the authors present the XRD diffractogram of CS, of silver nanoparticles and of CS/Ag composites for comparison?

In figure 8 the authors present the FTIR spectra of the specimens. It would be nice if the authors could add the FTIR spectrum of Chitosan for comparison. They could assign the main peaks of Chitosan to the spectrum of chitosan instead on the spectrum of specimen C.

 

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 2 Comments

 

 

On behalf of all the authors, I would like to thank you for the review.

All of the comments and introduced changes are presented below.

 

 

The authors in the introduction present many examples of the different studies regarding Chitosan and silver composites. It would nice if they could shorten the introduction and present more clearly the novelty of their work.

Authors` response: We agree with this point, and changes have been made. The introduction has been shortened, a small introduction about surface dispersing agents has been provided, and a more accurate description of the novelty of their work has been presented.

 

In line 109 and 119 the authors should define what Sa and DC is respectively.

Authors` response: We agree with this point. Sa and DC have been defined.

 

In figure 2 the authors present SEM images of the different coatings. Do the authors have higher magnification images that will enable the observation of the size of silver nanoparticles?

Authors` response: We agree with this point. New SEM measurements with different magnifications were made. The presented results clearly indicate the influence of the use of dispersant. New photos, also with higher magnifications, have been replaced and included in the manuscript.

 

In figure 7 the authors present the XRD of the composite coatings. They mention that a board peak at 15-25o is observed for the specimens A, B, and C assigned to Chitosan. However, in the XRD diffractogram is not obvious the presence of this peak even for specimen C that contains a higher amount of CS.

Authors` response: We agree that due to the small thickness of the layer, the peak is not so clearly visible for other samples than specimen A and even thou its intensity is very low. The discussion has been rephrased.

 

Can the authors identify the peaks in the XRD diffractogram?

Authors` response: The majority of the peaks can be assisted solely to the support. The other phases peaks (apart from chitosan) overlap with support phase peaks. The peak labeling has been added for the primary phase.

 

Where the XRD peaks of crystalline TiO2 are expected to be observed?

Authors` response: The TiO2 nanotube layer peaks probably could be assigned to both rutile and anatase; however, the presence of the layer is only indicated by the change in relative intensity of the peaks in the range of 35-42deg. Based on XRD, it’s not possible to conclude about the crystallinity or phase composition of the TiO2 layer. 

 

Are they overlapped with the peaks of Ti13Zr13Nb? The peak at 38o assigned to silver nanoparticles is not very clearly observed, while the peak at 44o assigned to silver nanoparticles is overlapped with the peaks of Ti13Zr13Nb.

Authors` response: The low relative intensity of both chitosan and suggested silver peaks can be associated with main factors: high crystallinity of metal alloy support, amorphicity of chitosan, and low concentration of nanosilver particles. It is, in fact, hard to determine the presence of the nanosilver phase due to the main peak overlapping with peaks associated with support. Therefore we agree with a reviewer that it is hard to determine the composition of the layers conclusively by diffraction patterns, but since it has been proved by other methods, e.g., FTIR and is observed via microscopy, we are sure of its presence. More the change in relative intensity between diffractograms of support and support with layers indicates the layer formation. The discussion has been clarified.

 

Can the authors present the XRD diffractogram of CS, of silver nanoparticles and of CS/Ag composites for comparison?

Authors' response: Since the work has been performed on layers on metal support is not possible to replicate the exact same stand-alone material.

 

In figure 8 the authors present the FTIR spectra of the specimens. It would be nice if the authors could add the FTIR spectrum of Chitosan for comparison. They could assign the main peaks of Chitosan to the spectrum of chitosan instead of the spectrum of specimen C.

Authors` response: The authors feel that presenting specimen C FTIR is necessary since it confirms the formation of the chitosan layer that couldn’t be concluded based on XRD.

 

Reviewer 3 Report

The manuscript presents the preparation testing and characterization of nanotubular Ti13Zr13Nb decorated with nano-silver. The presented results are interesting and feasible. The manuscript deserves publication after major revision. I suggest:

XPS should be carried out for the prepared materials. The surface atomic percentages and the oxidation states should be clearly deconvoluted.  The ions release should be quantified using ICP-MS.  Line 19: remove "of" A clear mechanism for the antibacterial activity should be drawn. This means active species intervening in the mechanism should be identified. I suggest reviewing: Colloids and Surfaces B: Biointerfaces 170 (2018) 92-98 and other relevant publications.  Bacterial inactivation at the interface of silver-based catalysts have been showed to happen through two different pathways, surface-contact effect and ions-diffusion effect. I suggest to clearly elucidate one (or possible both) of these mechanisms. I suggest reviewing : ACS Applied Materials and Interfaces 10 (2018) 12021-12030; Materials Today Chemistry 6 (2017) 62-74.

Author Response

Response to Reviewer 3 Comments

 

 

On behalf of all the authors, I would like to thank you for the review.

All of the comments and introduced changes are presented below.

 

XPS should be carried out for the prepared materials.

Authors` response: The XPS study needs a lot of time and is expensive, and we have not been able to do such experiments for 10 days. Besides, the XPS method gives fine details on chemical bonds, which here are not very necessary.

 

The surface atomic percentages and the oxidation states should be clearly deconvoluted.

Authors` response: The atomic percentages may very easily be calculated from weight percentages, and then the oxidation states can also be achieved. However, such values are not crucial for the aim of this research. Anyway, we will take into account the reviewer`s remark in future research. 

 

The ions release should be quantified using ICP-MS.

Authors` response: The authors thank you for your attention. In future research, it is planned to use the measuring technique proposed by the reviewer. The authors used the available ASA technique, which indicated the relationship between the rate of ion release into SBF solutions. Because the time for revision of the manuscript is short, it is not possible to conduct long-term tests using equipment to which the authors do not have free access.

 

Line 19: remove "of"

Authors` response: Change has been made.

 

A clear mechanism for the antibacterial activity should be drawn. This means active species intervening in the mechanism should be identified. I suggest reviewing: Colloids and Surfaces B: Biointerfaces 170 (2018) 92-98 and other relevant publications.  Bacterial inactivation at the interface of silver-based catalysts have been showed to happen through two different pathways, surface-contact effect and ions-diffusion effect. I suggest to clearly elucidate one (or possible both) of these mechanisms. I suggest reviewing : ACS Applied Materials and Interfaces 10 (2018) 12021-12030; Materials Today Chemistry 6 (2017) 62-74. 

Authors` response: Thank you very much for your helpful remark. The appropriate comment has been introduced to our manuscript.

 

Round 2

Reviewer 1 Report

Authors' answers to the reviews are satisfactory. I understand some of the experiments are not feasible in given timeframe.

Reviewer 2 Report

The authors made the appropriate changes thus the manuscript can be accepted in the present form.

Reviewer 3 Report

Authors answered the reviewer queries and I understand that some experiment were not possible.