Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) in Montmorillonite/TiO₂ Composite for Photocatalytic Degradation of Phenol

Round 1

Reviewer 1 Report

The manuscript entitled “Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) 2 in Montmorillonite/ TiO2 Composite for Photocatalytic 3 Degradation of Phenol” is found to be interesting for the readers of Minerals. It has scientific value and recommended for publication. However, revision on the following points is required:

1. Introduction is less informative. Kindly discuss the key characteristics for choosing TiO2 as a photocatalyst other than its abundance. Why phenol is chosen as standard organic pollutant. What are its harmful effects on environment? Authors may consult recent relevant literature for better explanation to support their work.  

Catalysis Today Volume 380 (2021) Pages 93-104, Ceramics international Volume 46 (2020) Pages 1203-1210, Chemical engineering journal Volume 430 (2022) 132917, Ceramics international Volume 46 (2020) Pages 14195-14205, Journal of Alloys and compounds Volume 708  (2017) Pages 903-910, Ceramics international Volume 46 (2020) Pages 24194-24203, Synthetic metals Volume 259 (2020) 116228, Computational condensed matter Volume 28 (2021) e00576, Material science and Engineering Volume 271 (2021) 115311, Optik Volume 210 (2020) 164605.

2. What is the effect of Fe doing and Fe adsorption on the crystallite size of resultant materials? It should be mentioned and discussed in XRD section.
3. SEM and TEM images of two synthesized materials xFe-Mt/ (1-x) Fe-TiO2 and Fe/ 10 Mt/ TiO2 should be included in manuscript to understand morphological role towards photodegradation of phenol.
4. Values of kinetic parameters like rate constant, half-life, R2 should be mentioned for photodegradation of phenol in presence of synthesized photocatalysts. Also mention the value of rate constant for scavenging experiments.
5. Mention percentage degradation of phenol in photocatalysis section and abstract.
6. The whole manuscript required a language check. Remove improper terms used, like survey spectrum and light adsorption ability, etc.
7. Perform recycling experiments to see stability of synthesized photocatalysts.
8. Grammatical errors and typing mistakes must be carefully checked and removed.

Author Response

Reviewer #1:

The manuscript entitled “Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) 2 in Montmorillonite/ TiO2 Composite for Photocatalytic 3 Degradation of Phenol” is found to be interesting for the readers of Minerals. It has scientific value and recommended for publication. However, revision on the following points is required:

1. Introduction is less informative. Kindly discuss the key characteristics for choosing TiO2 as a photocatalyst other than its abundance. Why phenol is chosen as standard organic pollutant. What are its harmful effects on environment? Authors may consult recent relevant literature for better explanation to support their work.  

Catalysis Today Volume 380 (2021) Pages 93-104, Ceramics international Volume 46 (2020) Pages 1203-1210, Chemical engineering journal Volume 430 (2022) 132917, Ceramics international Volume 46 (2020) Pages 14195-14205, Journal of Alloys and compounds Volume 708  (2017) Pages 903-910, Ceramics international Volume 46 (2020) Pages 24194-24203, Synthetic metals Volume 259 (2020) 116228, Computational condensed matter Volume 28 (2021) e00576, Material science and Engineering Volume 271 (2021) 115311, Optik Volume 210 (2020) 164605.

Response: Thank you very much for the good suggestion and the provided references. All the references were read, and some were cited.

The reason for choosing TiO₂ as the main photocatalyst was explained (lines 34-35). TiO₂ is highly photocatalytic active, non-toxic, chemically stable to most conditions, and has a low cost. Moreover, abundant studies have been applied to this material. Thus, it will be much easier to distinguish how the Mt and Fe(Ⅲ) improved the photocatalytic performance of the main photocatalyst in the composite.

The Fe(Ⅲ) doping on montmorillonite was introduced, but the explanation about Fe(Ⅲ) doping on TiO₂ is missing. Therefore, the Fe((Ⅲ) doping effects on TiO₂ were also added in the introduction as the new paragraph 3 (line 62-67). since the Fe(Ⅲ) ion in TiO₂ can introduce a Femi level as an electron donor or acceptors narrowing the  of the TiO₂ and red shifting the irradiation adsorption on TiO₂ [1–3]. It was also intensively proposed that the transition metal doing on TiO₂ will generate oxygen vacancies which act as the charge trapping sites promoting the generation of active radicals [4, 5].

The reasons for choosing phenol as the target and its harmful effects were revised in paragraph 4 in the introduction (lines 71-77). Phenolic compounds are ubiquitous and toxic with low concentrations [6]. More importantly, phenol kept neutrally charged under pH 10 [7], the adsorption or repulsion from Mt can be prevented in neutral pH.

2. What is the effect of Fe doing and Fe adsorption on the crystallite size of resultant materials? It should be mentioned and discussed in XRD section.

Response: Thank you very much for your valuable suggestion. The XRD pattern of original montmorillonite and the Fe(Ⅲ) cation doped montmorillonite (Fe-Mt) (wt. % of Fe(Ⅲ) in Fe-Mt is the same in the composites) was added in figure 1 for comparison. (the synthesis of Fe-Mt was added in lines 103-106. Then, the discussion about the effects of Fe(Ⅲ) on the XRD results was added in paragraph 2 in the 3.1 section (line 186-197). The expansion of Mt interlayer in the composites was only caused by Fe(Ⅲ) ion. The TiO₂ should only distribute on the surface of Mt.

3. SEM and TEM images of two synthesized materials xFe-Mt/ (1-x) Fe-TiO2 and Fe/ 10 Mt/ TiO₂ should be included in manuscript to understand morphological role towards photodegradation of phenol.

Response: Thank you very much for your valuable suggestion. The SEM-EDX and TEM-EDX for the samples were added and the morphology was discussed in line227-239. The significant reduction of the TiO₂ particles on both the composites was investigated.

4. Values of kinetic parameters like rate constant, half-life, R2 should be mentioned for photodegradation of phenol in presence of synthesized photocatalysts. Also mention the value of rate constant for scavenging experiments.

Response: Thanks for the reviewer’s suggestion. The parameters for kinetics were newly listed in Table S2. The rate constant for photodegradation of phenol in presence of synthesized photocatalysts was discussed in line 327. The rate constant for scavenging experiments was added in lines 392-394.

5. Mention percentage degradation of phenol in photocatalysis section and abstract.

Response: Thank you very much for pointing out it. The percentage degradation of phenol was added in the photocatalysis section in line 317 and abstract in line 15.

6. The whole manuscript required a language check. Remove improper terms used, like survey spectrum and light adsorption ability, etc.

Response: Thank you very much for pointing out it. The terms were carefully checked including survey spectrum and light adsorption ability etc. And the language was also corrected.

7. Perform recycling experiments to see stability of synthesized photocatalysts.

Response: Thanks for the reviewer’s suggestion. The reusability test was added from line 335 to line 339. High efficiency of Fe/ Mt/ TiO₂ for phenol photocatalytic degradation was achieved. The Fe/ Mt/ TiO₂ is chemically stable during the photocatalytic reaction.

8. Grammatical errors and typing mistakes must be carefully checked and removed.

Response: Thanks for the reviewer’s suggestion. Grammatical errors and typing mistakes were carefully checked.

References:

[1]      X. Zheng et al., “Construction of Fe-doped TiO2− x ultrathin nanosheets with rich oxygen vacancies for highly efficient oxidation of H2S,” Chem. Eng. J., vol. 430, p. 132917, 2022.

[2]      N. Kanjana, W. Maiaugree, P. Poolcharuansin, and P. Laokul, “Synthesis and characterization of Fe-doped TiO2 hollow spheres for dye-sensitized solar cell applications,” Mater. Sci. Eng. B, vol. 271, p. 115311, 2021.

[3]      A. Mancuso et al., “Visible light active Fe-Pr co-doped TiO2 for water pollutants degradation,” Catal. Today, 2021.

[4]      F. Kara, M. Kurban, and B. Coşkun, “Evaluation of electronic transport and optical response of two-dimensional Fe-doped TiO2 thin films for photodetector applications,” Optik (Stuttg)., vol. 210, p. 164605, 2020.

[5]      W. Pezeshkian and S. J. Marrink, “Simulating realistic membrane shapes,” Curr. Opin. Cell Biol., vol. 71, pp. 103–111, 2021.

[6]      S. Mohammadi, A. Kargari, H. Sanaeepur, K. Abbassian, A. Najafi, and E. Mofarrah, “Phenol removal from industrial wastewaters: a short review,” Desalin. Water Treat., vol. 53, no. 8, pp. 2215–2234, 2015.

[7]      J. Jover, R. Bosque, and J. Sales, “Neural network based QSPR study for predicting pKa of phenols in different solvents,” Qsar Comb. Sci., vol. 26, no. 3, pp. 385–397, 2007.

Author Response File: Author Response.pdf

Reviewer 2 Report

The topic is interesting, the data presented are applicable and the experiments were properly performed and adequately presented / discussed. This manuscript is suitable for publication in Minerals. However, there are some corrections needed throughout the manuscript.

The introduction must be discussed along with the novelty of the present approach over the earlier one. Please be sure that your manuscript thoroughly establishes how this work is fundamentally novel. The novelty of this study (the last paragraph of the introduction section) is not well described. The authors need to explain the fundamental difference between their work and all previous studies.

The first time when the authors use an abbreviation in the text, the authors should present both the spelled-out version and the short form. After the definition of an abbreviation, they should use only the abbreviation. Example: iron – Fe, LDH, DFT, etc.

The manuscript doesn’t follow completely the guidelines (example: references in the introduction section (In the text, reference numbers should be placed in square brackets [ ], and placed before the punctuation; for example [1], [1–3] or [1,3]), lines 136-149). Please apply.

The conclusion section should have the main results in a more quantitative statement.

English of the paper is rather good – in my opinion the language of the paper should be a little improved. I am asking for corrections by a native speaker.

I consider that the article can be accepted for publication only after a major revision.

Author Response

Reviewer #2:

The topic is interesting, the data presented are applicable and the experiments were properly performed and adequately presented / discussed. This manuscript is suitable for publication in Minerals. However, there are some corrections needed throughout the manuscript.

1. The introduction must be discussed along with the novelty of the present approach over the earlier one. Please be sure that your manuscript thoroughly establishes how this work is fundamentally novel. The novelty of this study (the last paragraph of the introduction section) is not well described. The authors need to explain the fundamental difference between their work and all previous studies.

Response: Thank you very much for noticing us a very good point. A more detailed explanation about the novelty of this paper was added in the last paragraph in the introduction (lines 80-84). And the lacked information about Fe(Ⅲ) in previous studies was mentioned in lines 59-61. In this paper, the distribution of Fe(Ⅲ) on the Mt/ TiO₂ composites was controlled using the strategy to change the timing of adding Fe(Ⅲ) on the composites. Thus, the role of Fe(Ⅲ) can be revealed based on its location on the composites. The whole synthesizing procedure was strictly controlled under pH 2 to inhibit any form of iron oxides or iron hydroxides. The Fe(Ⅲ) should be always in the form of the cation. Compared with the previous study, our work controlled the pH to keep the Fe(Ⅲ) as cation and changed the location of Fe(Ⅲ) to detect the role of Fe(Ⅲ) in the composites.

2. The first time when the authors use an abbreviation in the text, the authors should present both the spelled-out version and the short form. After the definition of an abbreviation, they should use only the abbreviation. Example: iron – Fe, LDH, DFT, etc.

Response: Thank you very much for pointing out this mistake. All the abbreviations were carefully checked.

3. The manuscript doesn’t follow completely the guidelines (example: references in the introduction section (In the text, reference numbers should be placed in square brackets [ ], and placed before the punctuation; for example [1], [1–3] or [1,3]), lines 136-149). Please apply.

Response: We apologies for the mistakes. The format of all the citations was revised.

4. The conclusion section should have the main results in a more quantitative statement.

Response: Thanks for the reviewer’s suggestion. The conclusion was revised to be more quantitative.

5. English of the paper is rather good – in my opinion the language of the paper should be a little improved. I am asking for corrections by a native speaker.

Response: Thanks for the reviewer’s suggestion. Languages were revised with the help of a native speaker.

I consider that the article can be accepted for publication only after a major revision.

Author Response File: Author Response.pdf

Reviewer 3 Report

Minor Revision

minerals-1476707-peer-review-v1

The submitted article “minerals-1476707-peer-review-v1” describes the Fe(Ⅲ)-doped montmorillonite (Mt)/ TiO₂ composites were fabricated by adding Fe(Ⅲ) during or after aging of TiO₂/Ti(OH)⁴ sol-gel on Mt, named as xFe-Mt/ (1-x)Fe-TiO₂ and Fe/Mt/ TiO₂ respectively. In the xFe-Mt/ (1-x) Fe-TiO₂, Fe(Ⅲ) ions are expected to locate in the structure of TiO₂ and on the surfaces of Mt, while Fe(Ⅲ) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO₂. The narrower energy bandgap (Eg) and lower photo-luminescence intensity was observed for the composites compared with TiO₂

But still, there are a few points that need to be addressed carefully before final acceptance in minerals.

Reviewer comments

1. In the introduction section, the authors need to include more information related to properties and the particle size role of the prepared nanocomposite. For more information, the author needs to read and cite the related articles.

 doi.org/10.1016/j.ceramint.2021.02.065

doi.org/10.1038/s41598-018-19617-2

 doi.org/10.1016/j.apsusc.2021.150337

2. In the introduction section, as the author mentioned “Phenol is a representative organic substance and a significant group of organics with an aromatic ring on the structure. Therefore, detecting the photocatalytic degradation of the materials on phenol can give a hint about their photocatalytic capacity towards other organics”. The authors need to write the reason with appropriate citation.
3. In XRD, is there any shifting of 2 Theta angle in the prepared nanocomposite? If so, please write the reason with proper citation.
4. After completion of all the suggested comments, the author needs to check the complete manuscript to avoid typographical errors.
5. References must follow the journal guidelines, please check and revise them accordingly.

Overall, the writing and included information seem reasonable except for the above-mentioned comments, the author needs to include all the suggestions and cite the given articles before acceptance.

Comments for author File: Comments.pdf

Author Response

Reviewer #3:

The submitted article “minerals-1476707-peer-review-v1” describes the Fe(Ⅲ)-doped montmorillonite (Mt)/ TiO₂ composites were fabricated by adding Fe(Ⅲ) during or after aging of TiO₂/Ti(OH)⁴ sol-gel on Mt, named as xFe-Mt/ (1-x)Fe-TiO₂ and Fe/Mt/ TiO₂ respectively. In the xFe-Mt/ (1-x) Fe-TiO₂, Fe(Ⅲ) ions are expected to locate in the structure of TiO₂ and on the surfaces of Mt, while Fe(Ⅲ) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO₂. The narrower energy bandgap (Eg) and lower photo-luminescence intensity was observed for the composites compared with TiO₂

But still, there are a few points that need to be addressed carefully before final acceptance in minerals.

1. In the introduction section, the authors need to include more information related to properties and the particle size role of the prepared nanocomposite. For more information, the author needs to read and cite the related articles.

 doi.org/10.1016/j.ceramint.2021.02.065

doi.org/10.1038/s41598-018-19617-2

 doi.org/10.1016/j.apsusc.2021.150337

Response: Thank you very much for the useful references. All the papers were cited in lines 42-44. The TiO₂ has a smaller particle size on the composite than only TiO₂, which was also proved by the newly added SEM images.

2. In the introduction section, as the author mentioned “Phenol is a representative organic substance and a significant group of organics with an aromatic ring on the structure. Therefore, detecting the photocatalytic degradation of the materials on phenol can give a hint about their photocatalytic capacity towards other organics”. The authors need to write the reason with appropriate citation.

Response: Thanks for the reviewer’s suggestion. The reasons for choosing phenol as the target and its harmful effects were revised in paragraph 4 in the introduction (line71-77). Phenolic compounds are ubiquitous and toxic with low concentrations [6]. More importantly, phenol kept neutrally charged under pH 10 [7], the adsorption or repulsion from Mt can be prevented in neutral pH.

3. In XRD, is there any shifting of 2 Theta angle in the prepared nanocomposite? If so, please write the reason with proper citation.

Response: Thank you very much for your valuable suggestion. The XRD pattern of original montmorillonite and the Fe(Ⅲ) cation doped montmorillonite (Fe-Mt) (wt. % of Fe(Ⅲ) in Fe-Mt is the same in the composites) was added in figure 1 for comparison. (the synthesis of Fe-Mt was added in lines 103-105. Then, the discussion about the effects of Fe(Ⅲ) on the XRD results was added in paragraph 2 in the 3.1 section (line 186-197). The expansion of Mt interlayer in the composites was only caused by Fe(Ⅲ) ion. The TiO₂ should only distribute on the surface of Mt.

4. After completion of all the suggested comments, the author needs to check the complete manuscript to avoid typographical errors.

Response: Thanks for the reviewer’s suggestion. Languages were carefully checked.

5. References must follow the journal guidelines, please check and revise them accordingly.

Response: We apologies for the mistakes. The format of all the citations was revised.

Overall, the writing and included information seem reasonable except for the above-mentioned comments, the author needs to include all the suggestions and cite the given articles before acceptance.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Revised paper is recommended for publishing.

Reviewer 2 Report

The manuscript can be accepted for publication.