One-Pot Synthesis of TiO₂/Hectorite Composite and Its Photocatalytic Degradation of Methylene Blue

Round 1

Reviewer 1 Report

The article presents the synthesis of TiO2/hectorite composite by hydrothermal method. The synthesized material were studied for the photocatalytic degradation of methylene blue under UV light. The manuscript lacks the novelty and hence I recommend finding other suitable journal. Authors can consider below comments to improve the manuscript quality.

1. Several reports are available on TiO2 and their composites as photocatalysts till date and TiO2-hectorite is been well known for years as efficient photocatalytic material e.g. Applied Clay Science, 2010, 47, 3, 433-43, what are the significance of the present study.
2. Section 3.2, author should mention the exact amount of the chemicals or reagents used e.g LiF and MgSO4.
3. Authors should write the complete terms of all abbreviations e.g. TBOT
4. Author stated that some diffraction peaks of hectorite in the TiO2/hectorite samples disappeared, precisely which peak disappeared? Sample TH-4 and TH-5 shows many peaks between 35 to 60 degrees as compare to other sample, what are those.
5. Figure 5B, the scale on X-axis should be only till 10 nm to have clear understanding of pore size distribution.
6. Author mentioned that compared with hectorite, it can be obviously observed that TiO2 particles successfully entered into the interlayer of hectorite, however it is not possible to observe by SEM images.
7. Similar to that of Figure 3, author should include the TEM images for all samples.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The hydrothermal method is used to prepare TiO₂/hectorite Composite, which contains lithium, magnesium and silicon. The purpose is to improve photocatalytic performance in order to remove hazardous dyes like methylene blue from wastewater. The goal is to minimize the optical band gap of TiO₂-based composites by increasing their surface area.

 

The work is well-written, however, it requires some minor editing before it can be published in Catalysts. My thoughts are as follows:

 

1. In abstract,“The apparent rate constant of TH-2 was...” This part is not reflected in “2. Photocatalytic Study”and should be added.
2. Characterization: rewrite sentence“The amount of lithium ion and magnesium ion has some effect on TiO₂/hectorite in the hydrothermal systhesis.”
3. I think the SEM images show low magnification; if higher magnification is available, it will be better.
4. Conclusions:“In BET analysis”is inconsistent with Characterization，suggest rewriting the statement.
5. For high efficiency photocatalysts, the following work should be mentioned by the author, such as: J. Catal. 373 (2019)161-172; Bull. Korean Chem. Soc. 34 (2013) 3039–3045; Appl. Catal. A-Gen. 590 (2020) 117342; Appl. Catal. B-Environ. 248 (2019) 380-387; Org. Biomol. Chem., 2018,16, 2406-2410; Electrochimica Acta 216(2016) 517-527; Colloids and Surfaces A: Physicochemical and Engineering Aspects 633(2)(2022) 127918

 

Author Response

Point 1: In abstract,“The apparent rate constant of TH-2 was...”This part is not reflected in “2.2. Photocatalytic Study”and should be added.  

 

Response 1: This part has been added to“2.2. Photocatalytic Study”. The revisions are given in Line 275-276 of Page 9.

 

Point 2: Characterization: rewrite sentence“The amount of lithium ion and magnesium ion has some effect on TiO₂/hectorite in the hydrothermal systhesis.”

 

Response 2: We have rewritten the sentence. The revisions are given in Line 96 of Page 3.

 

Point 3: I think the SEM images show low magnification; if higher magnification is available, it will be better.

 

Response 3: First of all, thank you very much for your advice. We tried higher magnification, but due to limited equipment conditions, SEM images at high magnification are blurry and it is difficult to observe the morphology of the samples, so we chose a lower magnification.

 

Point 4: Conclusions:“In BET analysis”is inconsistent with Characterization，suggest rewriting the statement.

 

Response 4: We have rewritten the statement. The revisions are given in Line 421 of Page 14.

 

Point 5: For high efficiency photocatalysts, the following work should be mentioned by the author, such as: J. Catal. 373 (2019)161-172; Bull. Korean Chem. Soc. 34 (2013) 3039-3045; Appl. Catal. A-Gen. 590 (2020) 117342; Appl. Catal. B-Environ. 248 (2019) 380-387; Org. Biomol. Chem.,2018,16, 2406-2410; Electrochimica Acta 216(2016) 517-527; Colloids and Surfaces A: Physicochemical and Engineering Aspects 633(2)(2022) 127918.

Response 5: We have benefited from a careful reading of the articles you have provided. Thank you very much for your suggestions, we have cited these works in our manuscript, which can improve the quality of the manuscript.

Reviewer 3 Report

In this manuscript the authors show the synthesis of a catalyst based on TiO₂/ hectorite and its use for the degradation of methylene blue. The catalyst is characterized through numerous techniques including XRD, SEM, TEM, UV XPS. They prove that the resulting material is porous and measure the size of the pores on the surface.

Finally, this catalyst is used for the degradation of methylene blue, and the authors show through the use of blank tests, how its presence is fundamental to maximize this process.

I just have a couple of considerations. Page 5 line 5-6, the authors write that "Compared with hectorite, it can be obviously observed that TiO2 particles successfully entered into the interlayer of hectorite."

Is it that obvious? The image of titanium alone? Do these images give us precise indications on the structure?

To prove that this catalyst is indeed so effective in degrading organic dyes, why not test it on others besides MB?

For these reasons, I believe this manuscript may be accepted after minor revisions.

Author Response

Point 1: Page 5 line 5-6, the authors write that "Compared with hectorite, it can be obviously observed that TiO₂ particles successfully entered into the interlayer of hectorite."

Is it that obvious? The image of titanium alone? Do these images give us precise indications on the structure?

Response 1: The description of this sentence is indeed imprecise. This conclusion cannot be obviously drawn from the images. It can only be observed that the structure of hectorite was changed after the introduction of TiO₂. TEM analysis can prove that TiO₂ enters the interlayer of hectorite. Therefore, this sentence is inappropriate here and we decided to delete it. The revisions are given on page 4.

Point 2: To prove that this catalyst is indeed so effective in degrading organic dyes, why not test it on others besides MB?

Response 2: The hectorite layer is negatively charged because lithium ions replace some magnesium ions in the magnesia octahedron, so it is conducive to the adsorption of cationic dyes.

MB is a cationic dye commonly used in industry, choosing MB will be more representative, therefore, MB was used as the target pollutant to study the photocatalytic performance of the catalyst.  

In addition, your comments are very worthy of our consideration. We will also study the degradation of other organic dyes in the future.

Round 2

Reviewer 1 Report

The manuscript has been sufficiently improved now and can be accepted in present format.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

My comments and remarks are the following:

1. A significant part of the abstract is a list of the methods used, which I think is unnecessary.
2. Abstract: “The improvement of photocatalytic efficiency of the composite is mainly due to its high specific surface area, light trapping ability and effective separation of electrons (e− ) and holes (h+ )” - the author lists all possible causes but does not describe which one is the most important, which is less critical.
3. Introduction, line 35: “In addition, TiO2 exhibits low specific surface area, easy agglomeration and poor reutilization, which limit its application range” – agglomeration? I think it should be aggregation… I think the reutilization of TiO2 is extremely good. Would you please revise your statement?
4. The introduction is brief and does not provide relevant information on the advantages AND disadvantages of clay combined with TiO2.
5. Why did you compare the activity of the prepared material to the P25? I miss the characterization of the synthesized pure TiO2 (without hectorite), even though the manuscript aims to characterize the TiO2/hectorite composite. I consider it is essential to study the prepared TiO2 (structure and photocatalytic activity) and hectorite (structure and photocatalytic activity) separately, in pure form and not only as composites, especially if you want to demonstrate the beneficial properties of their composite.
6. I miss the investigation of the adsorption capacity of the synthesized materials (especially because authors interpret the better activity as the consequence of the higher specific surface area and beneficial adsorption). In the case of dyes, the surface charge has an important role. Did you investigate, or do you have information about it?
7. The author state that the best composite is TH2. But no significant difference between the activity of TH2 and TH3. At the same time, TH1 is practically only adsorbed the MB; the transformation is very slow, almost negligible. I miss the interpretation of these results.  I suggest revising the kinetic curves' evaluation and calculating the k values.  In the case of TH2 the last point does not fit the linear – this point changes the k value; however, the kinetic curves show no difference between TH2 and TH3.
8. The effect of radical scavengers (the 10% change) is not considered significant. Moreover, the authors did not investigate the effect of the added substances on the adsorption of MB. No correct conclusions can be drawn from these results.
9. How did you measure reusability? This would be important for evaluating the results. Did you wait for the MB to run out and then reuse the filtered catalyst, or did you add another dose of MB to the suspension?

Although the results are interesting and the characterization of the synthesized materials is detailed, the manuscript is not suitable for publication in the present form. The experiments' design and their evaluation and interpretation have many shortcomings and inaccuracies. I suggest a major revision.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The hydrothermal process is used to make TiO2/Hectorite Composite, which contains lithium, magnesium, and silicon. The goal is to improve photocatalytic effectiveness in order to remove hazardous colors like methylene blue from wastewater. The goal is to minimize the optical bandgap of TiO2-based composites by increasing their surface area.

The work is well-written, however, it requires some minor editing before it can be published in Catalysts. My thoughts are listed below:

• In abstract, what mean by (TH-1, TH-2, TH-3, TH-4, TH-5). I think k is better if removed these abbreviations because are not defined.
• Edit “Fourier transform infrared spectroscopy (FTIR)” to “Fourier transform infrared (FTIR) spectroscopy”.
• For the first appearance, the abbreviation BET should be defined.
• I believe the keywords should be enhanced, and the phrase "one-pot method" is inappropriate.
• In the introduction, the authors state that "TiO2 exhibits low specific surface area." Does this also apply to nanostructured TiO2, such as TiO2 nanotubes and nanoparticles? This sentence should be examined in more detail in the introduction.
• What does "low crystallinity" imply? Are you referring to partially crystalline?
• What is the crystal structure type, as well as other key factors such as strain, dislocation density, d-spacing, cell volume, and so on?
• The SEM photos show low magnification; if higher magnification is available, it will be better.
• The optical bandgap determined in Fig. 6b needs to be adjusted. The single hectorite has the smallest optical bandgap, according to the plot. Also, what is the mechanism of the optical transition, and are there any other conceivable transitions?
• Equation (4) states that the fitted lines in Figure 8b should pass through the origin point, but this does not occur. Is there a reason for this?
• Several mechanisms might be used to investigate the degradation in greater depth; for further information, check the published article:
  https://doi.org/10.3390/catal11101137; 
  https://doi.org/10.3390/ma14175030;
  https://doi.org/10.3390/catal11070855;

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear Authors,

Please read the attached file, which includes my reflections. I still think the manuscript reflects a lot of work and presents valuable results. However, the evaluation and interpretation of the kinetic measurements and effect of radical scavengers are, in my opinion, not adequate.
 which should be essential for a newspaper with such an impact factor.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Because the authors have addressed all of the comments, I recommend that the revised manuscript be published in Catalyst.

Author Response

Thank you for your recognition of our manuscript. We will continue to work harder in the filed of Catalyst.