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  • The initial submission of this article was received on August 7th, 2020 and was peer-reviewed by 2 reviewers and the Academic Editor.
  • The Academic Editor made their initial decision on August 27th, 2020.
  • The first revision was submitted on September 29th, 2020 and was reviewed by the Academic Editor.
  • The article was Accepted by the Academic Editor on October 6th, 2020.

Version 0.2 (accepted)

· Oct 6, 2020 · Academic Editor


Dear Prof. Machado,

Thank you for providing your revised manuscript. In my judgment, you have addressed the reviewers' scientific critiques satisfactorily and I am pleased to accept your work for publication in PeerJ Materials Chemistry.

Please note that my recommendation about section organization for your manuscript was just to ease your post-acceptance production work with our journal staff. It doesn't affect my decision, and it is not my own requirement. Staff may or may not require changes to figures or organization in future revisions.

I recommend a final check for minor English typos and style. As a courtesy, I have included a manuscript where I highlighted areas of grammatical/typographical concern.

Again, I appreciate the chance to field your work, and look forward to seeing it published.

Nicholas Marshall

[# PeerJ Staff Note: Although the Academic and Section Editors are happy to accept your article as being scientifically sound, a final check of the manuscript shows that it would benefit from further English editing. Therefore, if you can identify further edits, please work with our production group to address them while in proof stage #]

Version 0.1 (original submission)

· Aug 27, 2020 · Academic Editor

Major Revisions

Dear Prof. Machado,

Thank you for submitting your manuscript on TiO2 photocatalysis to PeerJ Materials Science. The reviewers found your work to be suitable for the journal, particularly praising the multiple-technique characterization of the material and its use in several different applications. I agree with this position. However, both reviewers raised concerns or constructive suggestions about the analysis of your data, including questions about UV-vis analysis and fitting, TEM, and PXRD results.

Because at least one reviewer has requested a revision that may require an experiment, I am deeming these reviews as requiring "major revisions." However, in my opinion, the reviews are constructive and favorable and the paper should be able to be made publication-ready with a quite reasonable amount of effort.

Reviewer 2 has asked for an analysis of X-ray data on the commercial catalyst which may require another sample to be sent for characterization, as well as further information about the reaction of some catalysts with the dye RR120. Also, please clarify your experimental approach in response to their question on dye concentration (concerning lines 141 and 142).

The reviewers have also pointed out a number of minor typos and graphical issues that should be fixed before resubmission. I have noticed some as well, and enclose a marked PDF. I would encourage you to carefully revise your manuscript to remove reference-manager errors and minor English typos.

Please note that PeerJ policy discourages the use of color alone to distinguish graphical features, as one reviewer mentioned graphs with traces that are difficult to distinguish. You may want to go ahead and prepare graphs with lines distinguished by line or marker style, or in some other way.

In general, if there are any re-analyses or new experiments requested by reviewers that you do not believe to be necessary, I ask that you provide a thorough explanation (with peer-reviewed sources if applicable) of this position in your response letter.

Again, thank you for choosing PeerJ Materials Science for your work.

Nicholas Marshall
Academic Editor, PeerJ Materials Science

[# PeerJ Staff Note: Please ensure that all review comments are addressed in a rebuttal letter and any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.  It is a common mistake to address reviewer questions in the rebuttal letter but not in the revised manuscript. If a reviewer raised a question then your readers will probably have the same question so you should ensure that the manuscript can stand alone without the rebuttal letter.  Directions on how to prepare a rebuttal letter can be found at: #]

Reviewer 1 ·

Basic reporting

no comment

Experimental design

no comment

Validity of the findings

no comment

Annotated reviews are not available for download in order to protect the identity of reviewers who chose to remain anonymous.

Reviewer 2 ·

Basic reporting

The authors presented a synthetic method based in co-precipitation of the titanium alkoxides in a mixture of water/acetone in different proportions. Then, the authors analyzed the microstructural properties of these samples and analyzed their respective performance on photocatalytic discoloration and mineralization of two different dyes, and in the H2 evolution.

Although the synthetic method is not novel and innovative, the authors managed to apply the synthesized samples in different applications. This fact makes the manuscript appropriate for publication after some improvement.
The introduction is well-written and provide enough context to understand the manuscript development. Some references I suppose could not be properly found by Editorial Office or Editor. I suppose the authors should try to address this issue as well.

Experimental design

The experimental design is properly described and performed throughout the research. There is a small concern about the accuracy of determining the concentration of the both dyes simultaneously by using absorption spectrum. This concern is explained in more detailed in the section 4 of this report.

Validity of the findings

Although the synthetic model is straightforward the findings obtained different applications, such as dyes mineralization, discoloration and H2 evolution are very useful and worth to be communicated in a peer-review article.

Additional comments

In this section there are the comments that I would like to see some improvements made by the authors, in order to make the manuscript more appropriate for publication before its acceptance. Please pay attention and try to address them:

On page 5, line 123:
The expression Transmission Electron Microscopy was wrongly abbreviated as MET. The correct acronym is TEM.

On page 5, lines 141 and 142, where it is written:
“Monitoring was done in the maximum absorbance wavelength in the visible of each dye – 507 nm for P4R and 512 nm for RR120 - using a UV-1201 (Shimadzu) spectrophotometer.”
I am concerned about if it is truly possible to determine the concentration of the two dyes simultaneously accurately. My concern is based on the fact that one of the dyes absorbs at 507 nm and the other absorbs at 512 nm. I suppose there is a huge peak overlap. So, the authors should add a section in the supporting information containing an actual absorption spectrum. There, they should explain a detailed way of how they manage to distinguish the two peaks. For instance, if they used some peak deconvolution software or not.
Another point that should be detailed in this explanation section is the calibration curves. For instance, when the authors were preparing the calibration curves. Did they make two separate calibration curves or only one with the two dyes mixed?

On page 5, lines 150 to 152, where it is written:
“For this, after each reaction the photocatalyst was separated from the supernatant by decanting, washed with distilled water, centrifuged and dried at 70°C for 24 hours, and then reused under the same described conditions using a new load of the same dye.”
When the authors were washing and drying the powder for recovering, how much of the initial powder were the authors able to recover?
I suppose, at least, a small amount of the catalyst is lost during the washing/drying process. And if so, in the second and subsequent cycles, did the authors decrease the dyes initial concentrations proportionally to the mass of TiO2 unable to be recovered?

About Figure 1:
In figure 1, there is no way to distinguish the standard patterns of anatase and brookite. One pattern is black and the other one is dark green. There is not enough color difference allowing to distinguish the two patterns.
If the authors want to keep the standard patterns this way, they should change the colors of the standard patterns, in such a way they are two clearly distinguishable colors.

Still about figure 1, there are the expressions: “Refletions de Bragg Anatase” and “Refletions de Bragg Brookite”
None of these expressions are written in standard English language. The authors should correct these two expressions.

Second, I recommend the authors to perform the Rietveld Refinement in the TiO2 P-25 sample. This way, they will be able to verify how the brookite-anatase-rutile proportion from P-25 compares with the ones of the samples prepared in the study.

About Table 2:
The caption of this table should be corrected, because it shows Table 1, instead of Table 2. Also, I do not think the morphological parameters would be the best expression. I think the expression “textural parameters” would be more appropriate.

About Table 3:
For each entry wherever the rate constants of discoloration or mineralization where presented, there are two values. It is not clear what these two values mean. Is it the result of two equal trials? If yes, I think it is more appropriate to present the data as an average and standard deviation.
Or are those two values related to the two-stages pseudo-first-order rate constant? If yes, I recommend the authors to present these values in different columns, and clearly label the columns as first-stage degradation and second-stage degradation, for instance.
Second, for the RR120 dye, why is there only one value for the discoloration rate constant? The reason why there is only one value should be clearly explained by the authors.
Third, why were the samples W1-25 and W1-75 not tested neither for mineralization nor discoloration for RR120? If the authors have the possibility to perform this analysis, they should timely do it for the revisions of this paper. If the authors are unable to do it, the reason why should be clearly explained in the manuscript text.
Fourth, to complement the data, I recommend the authors to present the R2 values obtained from the pseudo-first-order model fit to the experimental data.
Fifth, the caption should be checked, as it is showing Table 1 instead of Table 3.

About the Mineralization and Discoloration Kinetics:
As the mineralization and discoloration kinetics present two different linear regions, with different rate constants. It would be more interesting if the authors could calculate an apparent rate constant by doing a non-linear fitting to the data.
Explaining more in depth, the linear model used by the authors is represented by the equation:
ln⁡〖(A_t/A_0 )=-kt〗 Eq. 1

This Eq. 1 comes from the non-linear Eq. 2
A_t=A_0 e^(-kt) Eq. 2
So, by using some graphing software like Origin or the solver function in Excel is possible to obtain the rate constant from the non-linear model (Eq. 2). The rate constant values obtained from the non-linear model can be more representative of the process, and complement well the two-stage linear analysis done in the manuscript.
To help the authors, in case they are not familiar with non-linear curve fitting, the video below teaches how to setup a non-linear fitting using the software Origin:
Curve Fitting: Origin 8.6: Nonlinear Curve Fit Tool
Also, always present the R2 values for each fit (linear or non-linear) done in the paper.

Annotated reviews are not available for download in order to protect the identity of reviewers who chose to remain anonymous.

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