The Influence of SnO₂ and Noble Metals on the Properties of TiO₂ for Environmental Sustainability

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

see attachment

Comments for author File: Comments.pdf

Comments on the Quality of English Language

see attachment

Author Response

Response to Reviews

The manuscript has been modified as follows:

green  color - text added

strikethrough red color - text deleted

 

Reviewer #1:

• The abstract should be rewritten with a right English language

 

Response

The Abstract have been modified as you suggested.

 

• The introduction should better organized, shortened and improved from the English level point of view

 

Response

As you recommended, we've improved the Introduction section.

 

• The comments about the EDS results are only devoted to comment the origin of impurities. The authors must add comments about the determined amount of noble metals with respect to the stoichiometry values (3wt% was used, how these atom amounts compare with it?). I also want to know how these impurities could have an impact on the sample Another point is that the carbon amount determined from EDS is not reliable, as universally known, due to the low molecular weight of the element, so all the subsequent reasoning about it are questionable.

 

Response

Thank you for the comment, we added comments in the manuscript regarding the degree of loading with Au and Ag, as you very well suggested. The presence of carbon as well as all other impurities is proven by both EDS and XPS results, but their influence on the properties of nanomaterials can only be studied by comparing with the pure material, without impurities, which can be an objective for a future research. We mention that we not find in the specialized literature the influence of these impurities in the studied applications, in order to be sure.

 

 

• The XRD part is very confusing. It must be exposed with a logic. I think that Ag is not visible from XRD patterns…the equation for cry size determination is that of SCHERRER, NOT DEBYE SCHERRER!!! The Williamson Hall is a plot, not an approximation. I want to know which peak was used to determine the crystallite sizes for A and R It is also important to show the Williamson Hall plot because in many cases not reliable results are obtained. The crystallite sizes should be also determined for noble metals, to be compared with the values reported from TEM. In addition, when the authors refer to specific hkl indices they should be reported on the patterns or instead they should refer to the peak positions, because the readers maybe do not know the TiO2 structure. I also suggest to determine the lattice parameters of TiO2 because it seems to me that they could change with SnO2 and noble metals addition.

 

Response

Thank you very much for detailed comment, necessary modification have been made. Obtained Williamson-Hall plot are introduced in the supplementary part of the article. Crystallite size obtained from Williamson-Hall plot for TiO₂-SnO₂ and decorated samples are irrelevant and in that case Scherrer equation have been used on the most intense peak from respective phase and it is mentioned in the table. In case of the SnO₂ and decorated Nobel Metals, the values are written in the text. It should be mentioned that the grain size and crystallite size have different definition and the values could be also different.

 

 

• The authors should change the plot of Raman spectra because nothing can be understood, also the colours should be changed. I suggest to shift the spectra for a better visualization of the possible differences. The Raman section needs an English revision as well as a better explanation of the differences of the collected spectra with the expectations, the authors only propose hypotheses that are not however

 

Response

Thank you for the comment, Raman spectra have been modified and additional references have been added. At the same time, some of the proposed hypotheses have been mentioned in the XPS and photoluminescence part.

 

 

• The TEM images are not informative. The samples are agglomeration/overlapping of particles so the determination of sizes is biased. HR-TEM images are out focus, they should be repeated or the quality of the images improved because nothing can be seen. In line 427 the authors say that dislocations cannot be seen, but this is also due to the bad quality of the image. Line 440, how may we sure that the small particles are due to Ag in fig. 4e and f?

 

Response

 Thanks for your comments, we modified Figure 4 for better quality images and supplemented with EDX results.

 

• The explanation of BET results is difficult to be In fact, the Au amount is very low, so how this small amount of gold could produce a variation of density and a small surface area? Together with the area, the porosity should be also determined, to evidence possible differences.

 

Response

Thank you for the comment, the specific surface area is a ratio between surface area and mass. Theoretically, if the surface area remains constant, but the mass increase, than the specific surface area value will decrease. Taking into account that the grain size of the samples does not change by 2-3 times, then we should assume that the mass of the grain changes. From the point of view of the powder density and atomic weight, it is most probable explanation. Porosity could also explain that differences, but unfortunately for us, we do not have equipment for that kind of measurements.

 

 

• The physical-chemical characterization of the samples must be improved, as well as the English level 1

 

Response

Thank you for the recommendation, we have revised the manuscript taking into account this reviewer's observation.

Reviewer 2 Report

Comments and Suggestions for Authors

1)Generalization of Environmental Results:

How can the results obtained in the field of environmental applications, such as CH4 detection and MO pollutant degradation, be extrapolated to other environmental  ?

2)Mention of Increased Durability in Nanocomposites:

The conclusion mentions "increased durability" of nanocomposites. Could you provide details on the durability tests conducted and how these nanocomposites maintain their effectiveness over time in real-world conditions?

3)Comparison with Existing Technologies in Gas Detection and Photocatalysis:

How do these nanocomposites compare to existing technologies in terms of gas detection and photocatalysis, especially regarding their effectiveness, cost, and ease of implementation?

Discussion on Biocompatibility Evaluations and Compliance with Standards:

The conclusion refers to biocompatibility evaluations. What are the implications in terms of human and environmental safety, and how do these nanoparticles align with current standards and regulations?

4)Envisioning Practical and Large-scale Application of Nanocomposites:

 

How do you envision the practical and large-scale application of these nanocomposites in industries or real-world contexts? Are there potential challenges related to manufacturing, material availability, or other logistical aspects?

5)Update of References:

The mentioned references must be recent. Could you provide updated sources to enhance the validity and relevance of the presented information?

6)Inclusion of All Used Methods, e.g., BET and XPS:

The conclusion does not address all the methods used, such as BET and XPS. Could you include a discussion on all characterization methods employed and their contribution to the robustness of the results?

7)Preferably, Confirming Photocatalytic Tests with DCO Data:

Preferably, could you confirm the photocatalytic tests by including Demand Chemical Oxygen (DCO) data? This would strengthen the reliability of conclusions related to pollutant degradation.

Author Response

Reviewer #2:

1) Generalization of Environmental Results:

How can the results obtained in the field of environmental applications, such as CH4 detection and MO pollutant degradation, be extrapolated to other environmental ?

 

Response

Based on structural similarity, the results obtained for methane detection using our TiO₂-based NPs/PEI nanocomposite in SAW sensor, we can expect that this sensor to be responsive also to other light saturated hydrocarbons such as ethane, propane or butane, including thus LPG vapors (Liquefied Petroleum Gas).  The performant photodegradation of MO in the presence of our TiO₂-SnO₂ - Noble metals nanocomposite can be extrapolated for photodecomposition of other structurally related anionic azo dyes pollutants such as Acid Orange 7, Acid Red 88, Congo Red, Methyl Red, etc. Due to the photodegradation mechanism based on photogeneration of reactive oxygen species [Prakash, J.; Sun, S.; Swart, H.C.; Gupta, R.K.  Noble metals-TiO₂ nanocomposites: From fundamental mechanisms to photocatalysis, surface enhanced Raman scattering and antibacterial applications Appl. Materials Today 2018, 11, 82–135] we can also extrapolate that our NMs decorated nanocomposites may be used for catalytic degradation under UV/VIS light of other organic water-soluble pollutants (such as drugs, pesticides).

 

2) Mention of Increased Durability in Nanocomposites:

The conclusion mentions "increased durability" of nanocomposites. Could you provide details on the durability tests conducted and how these nanocomposites maintain their effectiveness overtime in real-world conditions?

Response

We use in Conclusions the expressions "remarkable sustainability features" and "enhanced sustainability" but not the "increased durability" for our nanocomposites. We targeted the environmental dimension of sustainability and proved enhanced results in photodegradation of persistent aqueous pollutants such as MO dye (when compared with reference commercial Degussa P25 TiO₂ photocatalyst) and also sensitivity to explosive and greenhouse gas methane when integrated in PEI matrix in SAW sensors with better response than pure polymer. Also related to environmental pollution and human health, their biocompatibility was high with human skin cells, even better than Degussa P25 for the highest particle concentrations tested.

 

 

3) a) Comparison with Existing Technologies in Gas Detection and Photocatalysis:

How do these nanocomposties compare to existing technologies in terms of gas detection and photocatalysis, especially regarding their effectiveness, cost, and ease of implementation?

Response

In term of gas detection, the commercial sensors for reductive gases such as methane are usually conductometric-type based on tin dioxide which requires heating at few hundred °C for gas detection. SAW sensors work at room temperature, and benefit by the high specific surface of oxidic NPs incorporated in the polymeric layer. They have low power consumption, fast response, a good sensing efectiveness at low gas concentration, can be tuned to enhance selectivity and are easy to implement due the facile deposition of polymer-NPs sensitive layer by spin-coating.

Regarding the photocatalityc applications of the TiO₂-SnO₂ noble metal decorated nanocomposites, even if their cost is higher than pure titania, they have the advantage of being active under visible light (TiO₂ pure acting only under UV light) which can be easily provided by the solar radiation. Moreover, under UV lamp irradiation those NMs decorated nanocomposites show higher effectiveness in dye photodegradation when compared with pure TiO₂ or TiO₂-SnO₂ and also with reference commercial Degussa P25 nanopowder.

 

1. b) Discussion on Biocompatibility Evaluations and Compliance with Standards:

The conclusion refers to biocompatibility evaluations. What are the implications in terms of human and environmental safety, and how do these nanoparticles align with current standards and regulations?

Response

TiO₂-SnO₂-based nanomaterials are commonly used in various applications, such as cosmetics, sunscreens, food packaging, and biomedical devices. Therefore, ensuring their biocompatibility is crucial for human safety. Our in vitro results showed a good biocompatibility of TiO₂-SnO₂@NMs compared to the high toxicity of bare TiO₂, being in alignment with the current European standards and regulations focused on human health and environmental safety implications of manufactured nanomaterials [Ramos, D.; Almeida, L. Overview of Standards Related to the Occupational Risk and Safety of Nanotechnologies. Standards 2022, 2, 83-89. https://doi.org/10.3390/standards2010007]. By demonstrating compliance with European Chemicals Agency (ECHA) guidelines and Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) requirements, our nanomaterials could be safety and successfully integrated into diverse applications.

 

4) Envisioning Practical and Large-scale Application of Nanocomposites

How do you envision the practical and large-scale application of these nanocomposites in industries or real-world contexts? Are there potential challenges related to manufacturing, material availability, or other logistical aspects?

Response

Our concerns regarding the applications of these nanocomposites in industry is the topic for a patent in progress to our national authority - OSIM.

 

5) Update of References:

The mentioned references must be recent. Could you provide updated sources to enhance the validity and relevance of the presented information?

Response

Thank you for the recommendation, we have replaced the references with recent ones if it was possible.

 

6) Inclusion of All Used Methods, e.g., BET and XPS:

The conclusion does not address all the methods used, such as BET and XPS. Could you include a discussion on all characterization methods employed and their contribution to the robustness of the results?

Response

Thank you for the recommendation, more information from all characterization methods were added to the Conclusions.

 

7) Preferably, Confirming Photocatalytic Tests with DCO Data:

Preferably, could you confirm the photocatalytic tests by including Demand Chemical Oxygen (DCO) data? This would strengthen the reliability of conclusions related to pollutant degradation.

Response

The reviewer is right, the photocatalytic tests can be confirmed by Demand Chemical Oxygen (DCO) results, and would strengthen the reliability of conclusions related to pollutant degradation. Our system/infrastructure (the photoreactor, the irradiation device, and all setup) do not allows such measurements at this moment. This is why our results are based on the photocatalytic tests. Exactly as the reviewer said, DCO is just for confirmation, and accordingly there are many other already published papers in important journals without DCO data (https://doi.org/10.1016/j.matchemphys.2008.06.059, http://dx.doi.org/10.1016/j.materresbull.2013.01.022, https://doi.org/10.3390/molecules29061190, https://doi.org/10.1038/s41598-023-40659-8).

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

see attachment

Comments for author File: Comments.pdf

Comments on the Quality of English Language

the english must be improved

Author Response

Response to Reviews

The manuscript has been modified as follows:

blue  color - text added

strikethrough brown color - text deleted

 

Reviewer #1:

1. I think that the English also needs to be improved, many sentences do not have sense.

Response

Thanks for your comments, we have made improvements to the manuscript's English.

 

2. The introduction was not reorganized, but only shortened.

Response

As you recommended, we've improved the Introduction section.

 

3. As I suspected, the Williamson Hall plots are very bad, it is difficult to see a linear trend. I think that the results obtained from them cannot be reliably used. The XRD part again needs to be improved

Response

Thank you for the comment, XRD modifications have been made.

 

4. I cannot find the citation of Fig. 4d and 4g in the text.

Response

 

We appreciate your comments and we revised the manuscript with citations for Fig.4d and 4g.

 

5. I think that 67 papers cited for a research paper are too much!!

Response

 

Thank you for the recommendation, we’ve reduced the number of citations to 48