Amalgamated Titanium Oxide-Carbon Hollow Sphere/Nickel-Layered Double Hydroxide as an Efficient Photocatalyst for the Degradation of Methyl Orange

Round 1

Reviewer 1 Report

The manuscript titled “Amalgamated titanium oxide-carbon hollow sphere/nickel-layered double hydroxide as an efficient photocatalyst for the degradation of methyl orange"

In this manuscript, authors reported synthesis of Amalgamated titanium oxide-carbon hollow sphere/nickel-layered double hydroxide as efficient photocatalyst. The prepared catalyst was fully characterized by different characterization techniques such as X-ray diffraction (XRD), Scanning electron microscopy (SEM), High-resolution Transmission electron microscopy (HRTEM), FTIR spectroscopy, and X-ray photoelectron spectroscopy (XPS). The accomplished samples performance is impressive. Therefore, I would like to recommend published this work after addressing the following points:

1. The reusability test is very interesting. Any possible explanation about the degradation reason? This might add extra insight to this paper

2. The comparison on catalytic activity of as-prepared samples with some typical Titania-based catalysts ever reported should be added.

3. The authors are responsible for the English, which should be polished throughout the manuscript to clear some minor typo/grammar errors.

4. In the introduction part, Some publications on photocatalysis are suggested to refer to improve the quality of the manuscript, such as: https://doi.org/10.1007/s10904-022-02389-8 , https://doi.org/10.1016/j.heliyon.2022.e09652 , https://doi.org/10.1021/acsomega.1c03735, https://doi.org/10.1016/j.jmrt.2022.03.067.

5. The author should better improve the beauty and quality of the figures in the manuscript.

6. Some photoelectrochemical tests, such as EIS and LSV plots conducted under visible-light irradiation should be added.

7. More information on filter should be added. If it is not a commercial one, the authors should provide lamp spectra before and after the insertion of the filter to show UV photons are not present.

8. How about the effect of structure on the degradation of organic pollutants? Is the results from the degradation of MO is harmful?

 

Author Response

Reviewer #1

 

1. The reusability test is very interesting. Any possible explanation about the degradation reason? This might add extra insight to this paper.

 

Response 1

 

• We thank the reviewer for the remark. Based on the reviewers’ comment, we have added an explanation about the degradation reason in page 13 with the addition of the reference number 43 in the text and in the list of references.

 

 

2. The comparison on catalytic activity of as-prepared samples with some typical Titania-based catalysts ever reported should be added.

 

Response 2

 

• We thank the reviewer for the remark. Based on the reviewer comment, we have modified the text in pages 12&13 by adding some literature review on the comparison of the catalytic activity of as-prepared samples with some typical titania-based catalysts for degradation of MO

 

3. The authors are responsible for the English, which should be polished throughout the manuscript to clear some minor typo/grammar errors.

 

Response 3

 

• I would like to thank the reviewer for the remark. The manuscript was modified and the English mistakes were corrected

 

4. In the introduction part, Some publications on photocatalysis are suggested to refer to improve the quality of the manuscript, such as: https://doi.org/10.1007/s10904-022-02389-8, https://doi.org/10.1016/j.heliyon.2022.e09652 , https://doi.org/10.1021/acsomega.1c03735, https://doi.org/10.1016/j.jmrt.2022.03.067.

 

Response 4

 

• I thank the reviewer for the valuable comment. Suggested publications were added in the introduction (see page 2) with the addition of the references numbers 9,11, 12, and 13 in the text and in the list of references.

 

5. The author should better improve the beauty and quality of the figures in the manuscript.

 

Response 5

 

• We thank the reviewer for the remark. The quality of the figures was improved as we can.

 

6. Some photoelectrochemical tests, such as EIS and LSV plots conducted under visible-light irradiation should be added.

 

Response 6

 

• We appreciate the suggestion; we know the importance of performing tests that provide information about the electronic structure and the behavior of the charge carriers generated in the photocatalyst. However, we don`t have the apparatus for conduct these tests at this moment and these studies are contemplated shortly.

 

7. 7. More information on filter should be added. If it is not a commercial one, the authors should provide lamp spectra before and after the insertion of the filter to show UV photons are not present.

 

Response 7

 

• In fact, the lamp used emits UV/VIS radiation, there is no filter, only a quartz tube that prevents the lamp from contact with the effluent. The lamp spectra have been previously reported and the reference has been added to the manuscript (page 17- Ref.46).

 

8. How about the effect of structure on the degradation of organic pollutants? Is the results from the degradation of MO is harmful?

 

Response 8

 

• We acknowledge the reviewer for the good question. In the current version, we added the XRD for the catalysts after the test reaction. There was no change in the crystal structure as evidenced from the XRD pattern, however, a change in morphology was detected by changing the degree of crystallinity of the phase structures (Section 1.2.2 recycling test) page 13- Fig. S4

Author Response File: Author Response.pdf

Reviewer 2 Report

Referee report on manuscript “Amalgamated titanium oxide-carbon hollow sphere/nickel-layered double hydroxide as an efficient photocatalyst for the degradation of methyl orange “ by Auhood S. Al-Soihi et al.

 

1.  Word “amalgamated” at least once needs to be  in the Introduction. Moreover, everything related to the Title should be disclosed in one way or another in the Introduction.

2. Second paragraph, Nothing is said about theoretical efforts and their importance. Nevertheless, the theoretical contribution to the solution of the described problems cannot be overestimated.  See, one of the recent MDPI paper and references therein:

Kenmoe, S., Lisovski, O., Piskunov, S., Zhukovskii, Y. F., & Spohr, E. (2019). Electronic and optical properties of pristine, N-and S-doped water-covered TiO2 nanotube surfaces. The Journal of Chemical Physics, 150(4), 041714.

3. It is absolutely necessary to compare FTIP data (Fig.1) with those recently reported in:

 Serga, V.; Burve, R.; Krumina, A.; Romanova, M.; Kotomin, E.A.; Popov, A.I. Extraction–Pyrolytic Method for TiO₂ Polymorphs Production. Crystals 2021, 11, 431. https://doi.org/10.3390/cryst11040431

Why you do not see much of what should have been present ?

4.  Fig.S1.  What causes absorption in the region 250-350 nm?

5. Estimate the accuracy of determining Eg from Fig. S1A, taking into account the following remark of the Editors of Optical Materials:

 Brik, M. G., Srivastava, A. M.. (2022). A few common misconceptions in the interpretation of experimental spectroscopic data. Optical Materials, 127, 112276.

 

In principle, this is a rather interesting topic, which, of course, needs to be developed and promoted, the results obtained are interesting and can be recommended for publication after a detailed consideration and disclosure of the above-mentioned ambiguities.

Author Response

Reviewer #2

 

1. Word “amalgamated” at least once needs to be in the Introduction. Moreover, everything related to the Title should be disclosed in one way or another in the Introduction.

 

Response 1

 

• Based on the reviewers’ comment, we have modified the manuscript. The word Amalgamated was highlighted in green throughout the manuscript.

 

2. Second paragraph, nothing is said about theoretical efforts and their importance. Nevertheless, the theoretical contribution to the solution of the described problems cannot be overestimated.  See, one of the recent MDPI paper and references therein:

Kenmoe, S., Lisovski, O., Piskunov, S., Zhukovskii, Y. F., & Spohr, E. (2019). Electronic and optical properties of pristine, N-and S-doped water-covered TiO2 nanotube surfaces. The Journal of Chemical Physics, 150(4), 041714.

 

Response 2

 

• I do agree with the reviewer in saying for theoretical efforts and their importance which may help gaining more insights into the interpretation of the experimental data. However, we do not have an access to DFT calculations at our departments. It would mean that we need to seek for external collaboration which is not quite easy to achieve in KAU. Accordingly, we did not mention this paragraph in the introduction part to avoid the discrepancy that could be arrived as the manuscript does not devote to such a method.

 

3. It is absolutely necessary to compare FTIR data (Fig.1) with those recently reported in:

 Serga, V.; Burve, R.; Krumina, A.; Romanova, M.; Kotomin, E.A.; Popov, A.I. Extraction–Pyrolytic Method for TiO₂ Polymorphs Production. Crystals 2021, 11, 431. https://doi.org/10.3390/cryst11040431

Why you do not see much of what should have been present?

 

Response 3

 

• We appreciate the informative point of view of the reviewer and we agree with his valuable comment. The discussion on (page 3-Ref. 24) has been improved and highlighted in FTIR section.

 

 

4. Fig.S1. What causes absorption in the region 250-350 nm?

 

Response 4

 

• We thank the reviewer for the remark. The discussion on Page 12 has been added with the addition of reference number 40 in the text and in the list of references.

 

5. Estimate the accuracy of determining Eg from Fig. S1A, taking into account the following remark of the Editors of Optical Materials:

 Brik, M. G., Srivastava, A. M. (2022). A few common misconceptions in the interpretation of experimental spectroscopic data. Optical Materials, 127, 112276.

 

Response 5

 

• We appreciate the reviewer’s comment and we agree with him and other literature for using the PL as a more precise method for E_g calculation which provides more accurate information as it is capable to detect the mobility of electrons. However, UV−vis DRS was performed to investigate the light response property of the synthesized photocatalysts, since the photocatalytic activity is relevant to the optical absorption characteristics as mentioned in a hundred of publications every day. We are planning to fix a new technique for the upcoming work.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors prepared a TiO₂-C/NiAl-LDH photocatalyst, which has a significantly improved photocatalytic degradation activity compared to the single catalyst. The experimental design is attractive. However, some key issues should be addressed. So I think a significant revision is needed.

1、In the FT-IR spectrum, TiO₂ and TiO₂-C have apparent differences in the range of 500-1000 cm^-1. Why is that?

2、In Section 2.1.3, some sentences are difficult to understand, such as “While the NiAl-LDH band … (Fig. 3c, d and e)”. In addition, some descriptions of XPS binding energies are inconsistent with those shown in Fig. 3. The author is requested to check and correct them carefully. For ease of viewing, it is recommended that the author mark the corresponding element in each XPS spectrum or plot the same element of different materials in one graph.

3、In SEM, it is impossible to confirm that TiO₂ grows on the surface of the C sphere, and the morphology of NiAl-LDH cannot be seen. The authors should provide more explicit SEM images at higher magnifications to illustrate the morphology of the samples.

4、Why is the material called amalgamated TiO₂-C/NiAl-LDH? Is it any different from the composites constructed with TiO₂-C and NiAl-LDH?

5、It can be seen from Fig. 6 that the lattice spacing of TiO₂ and TiO₂-C is very different. Why? Besides, TiO₂-C/NiLDH disagrees with the HRTEM results of a single material. Why? The authors should explain the lattice spacing in Fig. 6 in detail.

6、In Section 2.1.7, the authors mentioned that NiAl-LDH was introduced into the TiO₂ lattice structure. However, it can be seen from the SEM and TEM images that the structure of NiAl-LDH is not smaller than that of TiO₂. How is it introduced into the TiO₂ lattice?

7、In Fig. S2, the removal efficiency (a and b) and the degradation rate (c and d) have the same meaning. Using two kinds of data is not necessary to describe the photocatalytic performance.

8、How the authors obtained the valence and conduction band potentials of TiO₂-C, TiO₂ and LDH need to be supplemented with experiments or necessary explanations in the manuscript. The authors need to supplement the electrochemical and PL properties of the materials to explain the reasons for the enhanced photocatalytic performance.

9、The author needs to supplement the XRD of the photocatalyst after the reaction.

10、The active species experiment is crucial for analyzing the photocatalytic degradation mechanism, and the authors should supplement the active species capture experiment to explain the degradation mechanism in detail.

11、 Suggestion: More recent papers involving photocatalytic environmental remediation can be referenced in the manuscript. (Liu C, Mao S, Wang H, et al. Chemical Engineering Journal, 2022, 430: 132806; Liu C, Mao S, Shi M, et al. Journal of Hazardous Materials, 2021, 420: 126613; Chemical Engineering Journal, 2022, 449: 137757).

Author Response

1. In the FT-IR spectrum, TiO₂and TiO₂-C have apparent differences in the range of 500-1000 cm^-1. Why is that?

 

Response 1

 

• We would like to thank the reviewer for the remark. The discussion on Page 3 has improved and highlighted in FT-IR section.

 

2. In Section 2.1.3, some sentences are difficult to understand, such as “While the NiAl-LDH band … (Fig. 3c, d and e)”. In addition, some descriptions of XPS binding energies are inconsistent with those shown in Fig. 3. The author is requested to check and correct them carefully. For ease of viewing, it is recommended that the author mark the corresponding element in each XPS spectrum or plot the same element of different materials in one graph.

 

Response 2

 

• We apologise to the misleading words and/or Figures arrangement. We agree with the reviewer's comment and a substantial change in XPS section was improved and added in page 6 in the current version.

 

 

3. In SEM, it is impossible to confirm that TiO₂grows on the surface of the C sphere, and the morphology of NiAl-LDH cannot be seen. The authors should provide more explicit SEM images at higher magnifications to illustrate the morphology of the samples.

 

Response 3

- We do agree with the reviewer, and we apologise for the presented SEM images provided by the lab at KAU. We did not have better SEM images, but the TEM images suppots the new presentation of the imgae. However, we have changed this section in the text and the modified part was highlighted in yellow (page 7)

4.Why is the material called amalgamated TiO₂-C/NiAl-LDH? Is it any different from the composites constructed with TiO₂-C and NiAl-LDH?

 

Response 4

 

• A good and reasonable question, I would agree with the reviewer. The word amalgamated is usually used precisely to describe the composition of different materials combined together, while composite is more related to the metal oxides combined together. As we introduced carbon- hollow sphere in the structure of TiO₂ and NiLDH materials we preferred to use the term Amalgamated instead of composite.

 

5. It can be seen from Fig. 6 that the lattice spacing of TiO₂and TiO₂-C is very different. Why? Besides, TiO₂-C/NiLDH disagrees with the HRTEM results of a single material. Why? The authors should explain the lattice spacing in Fig. 6 in detail.

 

Response 5

 

• We appreciate this insight meaningful remark by the reviewer. After keen revision and doing fringes spacing analysis and in comparison, to the XRD data and magnified TEM images, we did substantial change in the text and the new paragraph after the necessary change was highlighted in the new version.

 

6. In Section 2.1.7, the authors mentioned that NiAl-LDH was introduced into the TiO2 lattice structure. However, it can be seen from the SEM and TEM images that the structure of NiAl-LDH is not smaller than that of TiO₂. How is it introduced into the TiO₂ lattice?

 

Response 6

 

- We did the necessary change to clarify the meaning, as the first sentence was misleading to what we are intended to address for. The new sentence was given in section 2.1.7 in the light of the requested corrections. Where synergistic effect between NiLDH nanosheets and TiO₂-C enable the absorb photons of longer wavelength.

 

7. 7. In Fig. S2, the removal efficiency (a and b) and the degradation rate (c and d) have the same meaning. Using two kinds of data is not necessary to describe the photocatalytic performance.

 

Response 7

 

• I agree with the Reviewer and the text has improved see Page 2 in Supporting Information.

 

 

8. How the authors obtained the valence and conduction band potentials of TiO2-C, TiO2 and LDH need to be supplemented with experiments or necessary explanations in the manuscript. The authors need to supplement the electrochemical and PL properties of the materials to explain the reasons for the enhanced photocatalytic performance.

 

Response 8

 

• It seems that the reviewer is kindly referring to the data mentioned in the photocatalytic mechanism section. The data presented in the tentative mechanism are in agreement with that mentioned in the literature. The necessary references were mentioned in the revised version.

 

9. The author needs to supplement the XRD of the photocatalyst after the reaction.

 

Response 9

 

• We do thank the reviewer for the valuable comment and suggestion. In the current version, we added the XRD for the catalysts after the test reaction. There was no change in the crystal structure as evidenced from the XRD pattern, however, a change in morphology was detected by changing the degree of crystallinity of the phase structures (Section 1.2.2 recycling test) page 13 -Fig. S4.

 

10. The active species experiment is crucial for analyzing the photocatalytic degradation mechanism, and the authors should supplement the active species capture experiment to explain the degradation mechanism in detail.

 

Response 10

 

• Subsequently, to response 8 , the tentative mechanism is hypothetical according to the well known previously published work and we did not have the facilities to carry out the requested calculations.

 

11. Suggestion: More recent papers involving photocatalytic environmental remediation can be referenced in the manuscript. (Liu C, Mao S, Wang H, et al. Chemical Engineering Journal, 2022, 430: 132806; Liu C, Mao S, Shi M, et al. Journal of Hazardous Materials, 2021, 420: 126613; Chemical Engineering Journal, 2022, 449: 137757).

 

Response 11

 

• We thank the reviewer for the remark. The suggestion papers have been referenced in the manuscript (Ref.3, 41, 42).

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Accepted in the present form

Author Response

I would like to express my sincere appreciation to the reviewers comments and I thank him for the acceptance of the manuscript in the present form.

Reviewer 2 Report

The authors have strongly improved their original version of the manuscript, which now can be recommended for publication.

Author Response

It is my great pleasure to send my sincere appreciation to the reviewer for his effort and valuable comments as well as his acceptance of the manuscript in the present form

Reviewer 3 Report

The author addressed most of my comments well. The paper can be considered for publication.

Author Response

I would like to express my great thanks to the reviewer. His valuable comments helped us to polish our work to appear in a suitable shape matching the esteemed Journal catalysts